Design and selection of drug properties to increase the public health impact of next-generation seasonal malaria chemoprevention: a modelling study

BACKGROUND

Seasonal malaria chemoprevention (SMC) is recommended for disease control in settings with moderate to high Plasmodium falciparum transmission and currently depends on the administration of sulfadoxine-pyrimethamine plus amodiaquine. However, poor regimen adherence and the increased frequency of parasite mutations conferring sulfadoxine-pyrimethamine resistance might threaten the effectiveness of SMC. Guidance is needed to de-risk the development of drug compounds for malaria prevention. We aimed to provide guidance for the early prioritisation of new and alternative SMC drugs and their target product profiles.

METHODS

In this modelling study, we combined an individual-based malaria transmission model that has explicit parasite growth with drug pharmacokinetic and pharmacodynamic models. We modelled SMC drug attributes for several possible modes of action, linked to their potential public health impact. Global sensitivity analyses identified trade-offs between drug elimination half-life, maximum parasite killing effect, and SMC coverage, and optimisation identified minimum requirements to maximise malaria burden reductions.

FINDINGS

Model predictions show that preventing infection for the entire period between SMC cycles is more important than drug curative efficacy for clinical disease effectiveness outcomes, but similarly important for impact on prevalence. When children younger than 5 years receive four SMC cycles with high levels of coverage (ie, 69% of children receiving all cycles), drug candidates require a duration of protection half-life higher than 23 days (elimination half-life >10 days) to achieve reductions higher than 75% in clinical incidence and severe disease (measured over the intervention period in the target population, compared with no intervention across a range of modelled scenarios). High coverage is crucial to achieve these targets, requiring more than 60% of children to receive all SMC cycles and more than 90% of children to receive at least one cycle regardless of the protection duration of the drug.

INTERPRETATION

Although efficacy is crucial for malaria prevalence reductions, chemoprevention development should select drug candidates for their duration of protection to maximise burden reductions, with the duration half-life determining cycle timing. Explicitly designing or selecting drug properties to increase community uptake is paramount.

FUNDING

Bill & Melinda Gates Foundation and the Swiss National Science Foundation.

Measuring HIV Acquisitions Among Partners of Key Populations: Estimates From HIV Transmission Dynamic Models

BACKGROUND

Key populations (KPs), including female sex workers (FSWs), gay men and other men who have sex with men (MSM), people who inject drugs (PWID), and transgender women (TGW) experience disproportionate risks of HIV acquisition. The UNAIDS Global AIDS 2022 Update reported that one-quarter of all new HIV infections occurred among their non-KP sexual partners. However, this fraction relied on heuristics regarding the ratio of new infections that KPs transmitted to their non-KP partners to the new infections acquired among KPs (herein referred to as "infection ratios"). We recalculated these ratios using dynamic transmission models.

SETTING

One hundred seventy-eight settings (106 countries).

METHODS

Infection ratios for FSW, MSM, PWID, TGW, and clients of FSW were estimated from 12 models for 2020.

RESULTS

Median model estimates of infection ratios were 0.7 (interquartile range: 0.5-1.0; n = 172 estimates) and 1.2 (0.8-1.8; n = 127) for acquisitions from FSW clients and transmissions from FSW to all their non-KP partners, respectively, which were comparable with the previous UNAIDS assumptions (0.2-1.5 across regions). Model estimates for female partners of MSM were 0.5 (0.2-0.8; n = 20) and 0.3 (0.2-0.4; n = 10) for partners of PWID across settings in Eastern and Southern Africa, lower than the corresponding UNAIDS assumptions (0.9 and 0.8, respectively). The few available model estimates for TGW were higher [5.1 (1.2-7.0; n = 8)] than the UNAIDS assumptions (0.1-0.3). Model estimates for non-FSW partners of FSW clients in Western and Central Africa were high (1.7; 1.0-2.3; n = 29).

CONCLUSIONS

Ratios of new infections among non-KP partners relative to KP were high, confirming the importance of better addressing prevention and treatment needs among KP as central to reducing overall HIV incidence.

Public health benefits of shifting from hospital-focused to ambulatory TB care in Eastern Europe: Optimising TB investments in Belarus, the Republic of Moldova, and Romania

High rates of drug-resistant tuberculosis (DR-TB) continue to threaten public health, especially in Eastern Europe. Costs for treating DR-TB are substantially higher than treating drug-susceptible TB, and higher yet if DR-TB services are delivered in hospital. The WHO recommends that multidrug-resistant (MDR) TB be treated using mainly ambulatory care, shown to have non-inferior health outcomes, however, there has been a delay to transition away from hospital-focused MDR-TB care in certain Eastern European countries. Allocative efficiency analyses were conducted for three countries in Eastern Europe, Belarus, the Republic of Moldova, and Romania, to minimise a combination of TB incidence, prevalence, and mortality by 2035. A primary focus of these studies was to determine the health benefits and financial savings that could be realised if DR-TB service delivery shifted from hospital-focused to ambulatory care. Here we provide a comprehensive assessment of findings from these studies to demonstrate the collective benefit of transitioning from hospital-focused to ambulatory TB care, and to address common regional considerations. We highlight that transitioning from hospital-focused to ambulatory TB care could reduce treatment costs by 20% in Romania, 24% in Moldova, and by as much as 40% in Belarus or almost 35 million US dollars across these three countries by 2035 without affecting quality of care. Improved TB outcomes could be achieved, however, without additional spending by reinvesting these savings in higher-impact TB diagnosis and more efficacious DR-TB treatment regimens. We found commonalities in the large portion of TB cases treated in hospital across these three regional countries, and similar obstacles to transitioning to ambulatory care. National governments in the Eastern European region should examine barriers delaying adoption of ambulatory DR-TB care and consider lost opportunities caused by delays in switching to more efficient treatment modes.

Modelling to inform next-generation medical interventions for malaria prevention and treatment

Global progress against malaria has stagnated and novel medical interventions to prevent malaria are needed to fill gaps in existing tools and improve protection against infection and disease. Candidate selection for next-generation interventions should be supported by the best available evidence. Target product profiles and preferred product characteristics play a key role in setting selection criteria requirements and early endorsement by health authorities. While clinical evidence and expert opinion often inform product development decisions, integrating modelling evidence early and iteratively into this process provides an opportunity to link product characteristics with expected public health outcomes. Population models of malaria transmission can provide a better understanding of which, and at what magnitude, key intervention characteristics drive public health impact, and provide quantitative evidence to support selection of use-cases, transmission settings, and deployment strategies. We describe how modelling evidence can guide and accelerate development of new malaria vaccines, monoclonal antibodies, and chemoprevention.

Health and economic benefits of achieving contraceptive and maternal health targets in Small Island Developing States in the Pacific and Caribbean

INTRODUCTION

Reducing unmet need for modern contraception and expanding access to quality maternal health (MH) services are priorities for improving women's health and economic empowerment. To support investment decisions, we estimated the additional cost and expected health and economic benefits of achieving the United Nations targets of zero unmet need for modern contraceptive choices and 95% coverage of MH services by 2030 in select Small Island Developing States.

METHODS

Five Pacific (Kiribati, Samoa, Solomon Islands, Tonga and Vanuatu) and four Caribbean (Barbados, Guyana, Jamaica and Saint Lucia) countries were considered based on population survey data availability. For each country, the Lives Saved Tool was used to model costs, health outcomes and economic benefits for two scenarios: business-as-usual (BAU) (coverage maintained) and coverage-targets-achieved, which scaled linearly from 2022 (following COVID-19 disruptions) coverage of evidence-based family planning and MH interventions to reach United Nations targets, including modern contraceptive methods and access to complete antenatal, delivery and emergency care. Unintended pregnancies, maternal deaths, stillbirths and newborn deaths averted by the coverage-targets-achieved scenario were converted to workforce, education and social economic benefits; and benefit-cost ratios were calculated.

RESULTS

The coverage-targets-achieved scenario required an additional US$12.6M (US$10.8M-US$15.9M) over 2020-2030 for the five Pacific countries (15% more than US$82.4M to maintain BAU). This additional investment was estimated to avert 126 000 (40%) unintended pregnancies, 2200 (28%) stillbirths and 121 (29%) maternal deaths and lead to a 15-fold economic benefit of US$190.6M (US$67.0M-US$304.5M) by 2050. For the four Caribbean countries, an additional US$17.8M (US$15.3M-US$22.4M) was needed to reach the targets (4% more than US$405.4M to maintain BAU). This was estimated to avert 127 000 (23%) unintended pregnancies, 3600 (23%) stillbirths and 221 (25%) maternal deaths and lead to a 24-fold economic benefit of US$426.2M (US$138.6M-US$745.7M) by 2050.

CONCLUSION

Achieving full coverage of contraceptive and MH services in the Pacific and Caribbean is likely to have a high return on investment.

Cost-effectiveness of voluntary medical male circumcision for HIV prevention across sub-Saharan Africa: results from five independent models

BACKGROUND

Voluntary medical male circumcision (VMMC) has been a recommended HIV prevention strategy in sub-Saharan Africa since 2007, particularly in countries with high HIV prevalence. However, given the scale-up of antiretroviral therapy programmes, it is not clear whether VMMC still represents a cost-effective use of scarce HIV programme resources.

METHODS

Using five existing well described HIV mathematical models, we compared continuation of VMMC for 5 years in men aged 15 years and older to no further VMMC in South Africa, Malawi, and Zimbabwe and across a range of setting scenarios in sub-Saharan Africa. Outputs were based on a 50-year time horizon, VMMC cost was assumed to be US$90, and a cost-effectiveness threshold of US$500 was used.

FINDINGS

In South Africa and Malawi, the continuation of VMMC for 5 years resulted in cost savings and health benefits (infections and disability-adjusted life-years averted) according to all models. Of the two models modelling Zimbabwe, the continuation of VMMC for 5 years resulted in cost savings and health benefits by one model but was not as cost-effective according to the other model. Continuation of VMMC was cost-effective in 68% of setting scenarios across sub-Saharan Africa. VMMC was more likely to be cost-effective in modelled settings with higher HIV incidence; VMMC was cost-effective in 62% of settings with HIV incidence of less than 0·1 per 100 person-years in men aged 15-49 years, increasing to 95% with HIV incidence greater than 1·0 per 100 person-years.

INTERPRETATION

VMMC remains a cost-effective, often cost-saving, prevention intervention in sub-Saharan Africa for at least the next 5 years.

FUNDING

Bill & Melinda Gates Foundation for the HIV Modelling Consortium.

COVID-19 Vaccine Booster Strategies in Light of Emerging Viral Variants: Frequency, Timing, and Target Groups

Background

Vaccinations have reduced severe burden of COVID-19 and allowed for lifting of non-pharmaceutical interventions. However, with immunity waning alongside emergence of more transmissible variants of concern, vaccination strategies must be examined.

Methods

Here we apply a SARS-CoV-2 transmission model to identify preferred frequency, timing, and target groups for vaccine boosters to reduce public health burden and health systems risk. We estimated new infections and hospital admissions averted over 2 years through annual or biannual boosting of those eligible (those who received doses one and two) who are (1) most vulnerable (60+ or living with comorbidities) or (2) those 5+, at universal (98% of eligible) or lower coverage (85% of those 50+ or with comorbidities and 50% of 5–49 year olds) representing moderate vaccine fatigue and/or hesitancy. We simulated three emerging variant scenarios: (1) no new variants; (2) 25% more infectious and immune-evading Omicron-level severity variants emerge annually and become dominant; (3) emerge biannually. We further explored the impact of varying seasonality, variant immune-evading capacity, infectivity, severity, timing, and vaccine infection blocking assumptions.

Results

To reduce COVID-19-related hospitalisations over the next 2 years, boosters should be provided for all those eligible annually 3–4 months ahead of peak winter whether or not new variants of concern emerge. Only boosting those most vulnerable is unlikely to ensure reduced stress on health systems. Moreover, boosting all eligible better protects those most vulnerable than only boosting the vulnerable group. Conversely, while this strategy may not ensure reduced stress on health systems, as an indication of cost-effectiveness, per booster dose more hospitalisations could be averted through annual boosting of those most vulnerable versus all eligible, since those most vulnerable are more likely to seek hospital care once infected, whereas increasing to biannual boosting showed diminishing returns. Results were robust when key model parameters were varied. However, we found that the more frequently variants emerge, the less the effect boosters will have, regardless of whether administered annually or biannually.

Conclusions

Delivering well-timed annual COVID-19 vaccine boosters to all those eligible, prioritising those most vulnerable, can reduce infections and hospital admissions. Findings provide model-based evidence for decision-makers to plan for administering COVID-19 boosters ahead of winter 2022–2023 to help mitigate the health burden and health system stress.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40121-022-00683-z.

Transmission reduction, health benefits, and upper-bound costs of interventions to improve retention on antiretroviral therapy: a combined analysis of three mathematical models

BACKGROUND

In this so-called treat-all era, antiretroviral therapy (ART) interruptions contribute to an increasing proportion of HIV infections and deaths. Many strategies to improve retention on ART cost more than standard of care. In this study, we aimed to estimate the upper-bound costs at which such interventions should be adopted.

METHODS

In this combined analysis, we compared the infections averted, disability-adjusted life-years (DALYs) averted, and upper-bound costs of interventions that improve ART retention in three HIV models with diverse structures, assumptions, and baseline settings: EMOD in South Africa, Optima in Malawi, and Synthesis in sub-Saharan African low-income and middle-income countries (LMICs). We modelled estimates over a 40-year time horizon, from a baseline of Jan 1, 2022, when interventions would be implemented, to Jan 1, 2062. We varied increment of ART retention (25%, 50%, 75%, and 100% retention), the extent to which interventions could be targeted towards individuals at risk of interrupting ART, and cost-effectiveness thresholds in each setting.

FINDINGS

Despite simulating different settings and epidemic trends, all three models produced consistent estimates of health benefit (ie, DALYs averted) and transmission reduction per increment in retention. The range of estimates was 1·35-3·55 DALYs and 0·12-0·20 infections averted over the 40-year time horizon per additional person-year retained on ART. Upper-bound costs varied by setting and intervention effectiveness. Improving retention by 25% among all people receiving ART, regardless of risk of ART interruption, gave an upper-bound cost per person-year of US$2-6 in Optima (Malawi), $43-68 in Synthesis (LMICs in sub-Saharan Africa), and $28-180 in EMOD (South Africa). A maximally targeted and effective retention intervention had an upper-bound cost per person-year of US$93-223 in Optima (Malawi), $871-1389 in Synthesis (LMICs in sub-Saharan Africa), and $1013-6518 in EMOD (South Africa).

INTERPRETATION

Upper-bound costs that could improve ART retention vary across sub-Saharan African settings and are likely to be similar to or higher than was estimated before the start of the treat-all era. Upper-bound costs could be increased by targeting interventions to those most at risk of interrupting ART.

FUNDING

Bill & Melinda Gates Foundation.

The influence of biological, epidemiological, and treatment factors on the establishment and spread of drug-resistant Plasmodium falciparum

The effectiveness of artemisinin-based combination therapies (ACTs) to treat Plasmodium falciparum malaria is threatened by resistance. The complex interplay between sources of selective pressure-treatment properties, biological factors, transmission intensity, and access to treatment-obscures understanding how, when, and why resistance establishes and spreads across different locations. We developed a disease modelling approach with emulator-based global sensitivity analysis to systematically quantify which of these factors drive establishment and spread of drug resistance. Drug resistance was more likely to evolve in low transmission settings due to the lower levels of (i) immunity and (ii) within-host competition between genotypes. Spread of parasites resistant to artemisinin partner drugs depended on the period of low drug concentration (known as the selection window). Spread of partial artemisinin resistance was slowed with prolonged parasite exposure to artemisinin derivatives and accelerated when the parasite was also resistant to the partner drug. Thus, to slow the spread of partial artemisinin resistance, molecular surveillance should be supported to detect resistance to partner drugs and to change ACTs accordingly. Furthermore, implementing more sustainable artemisinin-based therapies will require extending parasite exposure to artemisinin derivatives, and mitigating the selection windows of partner drugs, which could be achieved by including an additional long-acting drug.

Cost-effectiveness and impact of pre-exposure prophylaxis to prevent HIV among men who have sex with men in Asia: A modelling study

INTRODUCTION

More than 70% of new HIV infections in Asia occurred in eight countries in 2020: Cambodia, China, India, Indonesia, Myanmar, Nepal, Thailand, and Vietnam-with a rising incidence among men who have sex with men (MSM). The World Health Organization (WHO) recommends pre-exposure prophylaxis (PrEP) for those at risk of acquiring HIV, yet wide-scale implementation of PrEP, on a daily or event-driven basis, has been limited in Asia.

METHODS

The Optima HIV model was applied to examine the impact of scaling-up PrEP over five-years to cover an additional 15% of MSM compared with baseline coverage, a target deemed feasible by regional experts. Based on behavioral survey data, we assume that covering 15% of higher-risk MSM will cover 30% of all sexual acts in this group. Scenarios to compare the impact of generic-brand daily dosing of PrEP with generic event-driven dosing (15 days a month) were modelled from the start of 2022 to the end of 2026. Cost-effectiveness of generic versus branded PrEP was also assessed for China, the only country with an active patent for branded, higher cost PrEP. The impact on new HIV infections among the entire population and cost per HIV-related disability-adjusted life year (DALY) averted were estimated from the beginning of 2022 to the end of 2031 and from 2022 to 2051.

RESULTS

If PrEP were scaled-up to cover an additional 15% of MSM engaging in higher-risk behavior from the beginning of 2022 to the end of 2026 in the eight Asian countries considered, an additional 100,000 (66,000-130,000) HIV infections (17%) and 300,000 (198,000-390,000) HIV-related DALYs (3%) could be averted over the 2022 to 2031 period. The estimated cost per HIV-related DALY averted from 2022 to 2031 ranged from US$600 for event-driven generic PrEP in Indonesia to US$34,400 for daily branded PrEP in Thailand. Over a longer timeframe from 2022 to 2051, the cost per HIV-related DALY averted could be reduced to US$100-US$12,700.

CONCLUSION

PrEP is a critical tool to further reduce HIV incidence in highly concentrated epidemics. Implementing PrEP in Asia may be cost-effective in settings with increasing HIV prevalence among MSM and if PrEP drug costs can be reduced, PrEP could be more cost-effective over longer timeframes.

Cost-effectiveness of easy-access, risk-informed oral pre-exposure prophylaxis in HIV epidemics in sub-Saharan Africa: a modelling study

BACKGROUND

Approaches that allow easy access to pre-exposure prophylaxis (PrEP), such as over-the-counter provision at pharmacies, could facilitate risk-informed PrEP use and lead to lower HIV incidence, but their cost-effectiveness is unknown. We aimed to evaluate conditions under which risk-informed PrEP use is cost-effective.

METHODS

We applied a mathematical model of HIV transmission to simulate 3000 setting-scenarios reflecting a range of epidemiological characteristics of communities in sub-Saharan Africa. The prevalence of HIV viral load greater than 1000 copies per mL among all adults (HIV positive and negative) varied from 1·1% to 7·4% (90% range). We hypothesised that if PrEP was made easily available without restriction and with education regarding its use, women and men would use PrEP, with sufficient daily adherence, during so-called seasons of risk (ie, periods in which individuals are at risk of acquiring infection). We refer to this as risk-informed PrEP. For each setting-scenario, we considered the situation in mid-2021 and performed a pairwise comparison of the outcomes of two policies: immediate PrEP scale-up and then continuation for 50 years, and no PrEP. We estimated the relationship between epidemic and programme characteristics and cost-effectiveness of PrEP availability to all during seasons of risk. For our base-case analysis, we assumed a 3-monthly PrEP cost of US$29 (drug $11, HIV test $4, and $14 for additional costs necessary to facilitate education and access), a cost-effectiveness threshold of $500 per disability-adjusted life-year (DALY) averted, an annual discount rate of 3%, and a time horizon of 50 years. In sensitivity analyses, we considered a cost-effectiveness threshold of $100 per DALY averted, a discount rate of 7% per annum, the use of PrEP outside of seasons of risk, and reduced uptake of risk-informed PrEP.

FINDINGS

In the context of PrEP scale-up such that 66% (90% range across setting-scenarios 46-81) of HIV-negative people with at least one non-primary condomless sex partner take PrEP in any given period, resulting in 2·6% (0·9-6·0) of all HIV negative adults taking PrEP at any given time, risk-informed PrEP was predicted to reduce HIV incidence by 49% (23-78) over 50 years compared with no PrEP. PrEP was cost-effective in 71% of all setting-scenarios, and cost-effective in 76% of setting-scenarios with prevalence of HIV viral load greater than 1000 copies per mL among all adults higher than 2%. In sensitivity analyses with a $100 per DALY averted cost-effectiveness threshold, a 7% per year discount rate, or with PrEP use that was less well risk-informed than in our base case, PrEP was less likely to be cost-effective, but generally remained cost-effective if the prevalence of HIV viral load greater than 1000 copies per mL among all adults was higher than 3%. In sensitivity analyses based on additional setting-scenarios in which risk-informed PrEP was less extensively used, the HIV incidence reduction was smaller, but the cost-effectiveness of risk-informed PrEP was undiminished.

INTERPRETATION

Under the assumption that making PrEP easily accessible for all adults in sub-Saharan Africa in the context of community education leads to risk-informed use, PrEP is likely to be cost-effective in settings with prevalence of HIV viral load greater than 1000 copies per mL among all adults higher than 2%, suggesting the need for implementation of such approaches, with ongoing evaluation.

FUNDING

US Agency for International Development, US President's Emergency Plan for AIDS Relief, and Bill & Melinda Gates Foundation.

Impacts of COVID-19-related service disruptions on TB incidence and deaths in Indonesia, Kyrgyzstan, Malawi, Mozambique, and Peru: Implications for national TB responses

Initial global-level estimates reported in June 2020 by the World Health Organization suggested that levels of disruption to TB service delivery could be as high as 25%-50% and result in an additional 6·3 million cases of tuberculosis (TB) and an additional 1·4 million TB-related deaths attributable to COVID-19 between 2020 and 2025. Quarterly epidemiological estimates and programmatic TB data capturing disruption levels to each TB service were collected by National TB Programmes in Indonesia, Kyrgyzstan, Malawi, Mozambique, and Peru. Data from 2019, for a pre-COVID-19 baseline, and throughout 2020, together with the NTP's COVID-19 response plans, were used within Optima TB models to project TB incidence and deaths over five years because of COVID-19-related disruptions, and the extent to which those impacts may be mitigated through proposed catch-up strategies in each country. Countries reported disruptions of up to 64% to demand-driven TB diagnosis. However, TB service availability disruptions were shorter and less severe, with TB treatment experiencing levels of disruption of up to 21%. We predicted that under the worse-case scenario cumulative new latent TB infections, new active TB infections, and TB-related deaths could increase by up to 23%, 11%, and 20%, respectively, by 2024. However, three of the five countries were on track to mitigate these increases to 3% or less by maintaining TB services in 2021 and 2022 and by implementing proposed catch-up strategies. Indonesia was already experiencing the worse-case scenario, which could lead to 270,000 additional active TB infections and 36,000 additional TB-related deaths by the end of 2024. The COVID-19 pandemic is projected to negatively affect progress towards 2035 End TB targets, especially in countries already off-track. Findings highlight both successful TB service delivery adaptions in 2020 and the need to proactively maintain TB service availability despite potential future waves of more transmissible COVID-19 variants.

Costs and impact on HIV transmission of a switch from a criminalisation to a public health approach to injecting drug use in eastern Europe and central Asia: a modelling analysis

BACKGROUND

HIV incidence is increasing in eastern Europe and central Asia, primarily driven by injecting drug use. Coverage of antiretroviral therapy (ART) and opioid agonist therapy are suboptimal, with many people who inject drugs (PWID) being incarcerated. We aimed to assess whether use of monies saved as a result of decriminalisation of drug use or possession to scale up ART and opioid agonist therapy could control HIV transmission among PWID in eastern Europe and central Asia.

METHODS

A dynamic HIV transmission model among PWID incorporating incarceration, ART, and opioid agonist therapy was calibrated to Belarus, Kazakhstan, Kyrgyzstan, and St Petersburg (Russia). Country-specific costs for opioid agonist therapy, ART, and incarceration were collated or estimated. Compared with baseline, the model prospectively projected the life-years gained, incremental costs (2018 euros), and infections prevented over 2020-40 for three scenarios. The decriminalisation scenario removed incarceration resulting from drug use or possession for personal use, reducing incarceration among PWID by 24·8% in Belarus, Kazakhstan, and Kyrgyzstan and 46·4% in St Petersburg; the public health approach scenario used savings from decriminalisation to scale up ART and opioid agonist therapy; and the full scale-up scenario included the decriminalisation scenario plus investment of additional resources to scale up ART to the UNAIDS 90-90-90 target of 81% coverage and opioid agonist therapy to the WHO target of 40% coverage. The incremental cost-effectiveness ratios per life-year gained for each scenario were calculated and compared with country-specific gross domestic product per-capita willingness-to-pay thresholds. Costs and life-years gained were discounted 3% annually.

FINDINGS

Current levels of incarceration, opioid agonist therapy, and ART were estimated to cost from €198 million (95% credibility interval 173-224) in Kyrgyzstan to €4129 million (3897-4358) in Kazakhstan over 2020-40; 74·8-95·8% of these total costs were incarceration costs. Decriminalisation resulted in cost savings (€38-773 million due to reduced prison costs; 16·9-26·1% reduction in overall costs) but modest life-years gained (745-1694). The public health approach was cost saving, allowing each setting to reach 81% ART coverage and 29·7-41·8% coverage of opioid agonist therapy, resulting in 17 768-148 464 life-years gained and 58·9-83·7% of infections prevented. Results were similar for the full scale-up scenario.

INTERPRETATION

Cost savings from decriminalisation of drug use could greatly reduce HIV transmission through increased coverage of opioid agonist therapy and ART among PWID in eastern Europe and central Asia.

FUNDING

Alliance for Public Health, US National Institute of Allergy and Infectious Diseases and National Institute for Drug Abuse, and Economist Intelligence Unit.

The risks and benefits of providing HIV services during the COVID-19 pandemic

INTRODUCTION

The COVID-19 pandemic has caused widespread disruptions including to health services. In the early response to the pandemic many countries restricted population movements and some health services were suspended or limited. In late 2020 and early 2021 some countries re-imposed restrictions. Health authorities need to balance the potential harms of additional SARS-CoV-2 transmission due to contacts associated with health services against the benefits of those services, including fewer new HIV infections and deaths. This paper examines these trade-offs for select HIV services.

METHODS

We used four HIV simulation models (Goals, HIV Synthesis, Optima HIV and EMOD) to estimate the benefits of continuing HIV services in terms of fewer new HIV infections and deaths. We used three COVID-19 transmission models (Covasim, Cooper/Smith and a simple contact model) to estimate the additional deaths due to SARS-CoV-2 transmission among health workers and clients. We examined four HIV services: voluntary medical male circumcision, HIV diagnostic testing, viral load testing and programs to prevent mother-to-child transmission. We compared COVID-19 deaths in 2020 and 2021 with HIV deaths occurring now and over the next 50 years discounted to present value. The models were applied to countries with a range of HIV and COVID-19 epidemics.

RESULTS

Maintaining these HIV services could lead to additional COVID-19 deaths of 0.002 to 0.15 per 10,000 clients. HIV-related deaths averted are estimated to be much larger, 19-146 discounted deaths per 10,000 clients.

DISCUSSION

While there is some additional short-term risk of SARS-CoV-2 transmission associated with providing HIV services, the risk of additional COVID-19 deaths is at least 100 times less than the HIV deaths averted by those services. Ministries of Health need to take into account many factors in deciding when and how to offer essential health services during the COVID-19 pandemic. This work shows that the benefits of continuing key HIV services are far larger than the risks of additional SARS-CoV-2 transmission.

Impact of vaccination and non-pharmaceutical interventions on SARS-CoV-2 dynamics in Switzerland

Background

As vaccination coverage against SARS-CoV-2 increases amidst the emergence and spread of more infectious and potentially more deadly viral variants, decisions on timing and extent of relaxing effective, but unsustainable, non-pharmaceutical interventions (NPIs) need to be made.

Methods

An individual-based transmission model of SARS-CoV-2 dynamics, OpenCOVID, was developed to compare the impact of various vaccination and NPI strategies on the COVID-19 epidemic in Switzerland. OpenCOVID uses the Oxford Containment Health Index (OCHI) to quantify the stringency of NPIs.

Results

Even if NPIs in place in March 2021 were to be maintained and the vaccine campaigns rollout rapidly scaled-up, a ‘third wave’ was predicted. However, we find a cautious phased relaxation can substantially reduce population-level morbidity and mortality. We find that a faster vaccination campaign can offset the size of such a wave, allowing more flexibility for NPIs to be relaxed sooner. Model outcomes were most sensitive to the level of infectiousness of variants of concern observed in Switzerland.

Conclusion

A rapid vaccination rollout can allow the sooner relaxation of NPIs, however ongoing surveillance of - and swift responses to - emerging viral variants is of utmost importance for epidemic control.

Optima TB: A tool to help optimally allocate tuberculosis spending

Approximately 85% of tuberculosis (TB) related deaths occur in low- and middle-income countries where health resources are scarce. Effective priority setting is required to maximise the impact of limited budgets. The Optima TB tool has been developed to support analytical capacity and inform evidence-based priority setting processes for TB health benefits package design. This paper outlines the Optima TB framework and how it was applied in Belarus, an upper-middle income country in Eastern Europe with a relatively high burden of TB. Optima TB is a population-based disease transmission model, with programmatic cost functions and an optimisation algorithm. Modelled populations include age-differentiated general populations and higher-risk populations such as people living with HIV. Populations and prospective interventions are defined in consultation with local stakeholders. In partnership with the latter, demographic, epidemiological, programmatic, as well as cost and spending data for these populations and interventions are then collated. An optimisation analysis of TB spending was conducted in Belarus, using program objectives and constraints defined in collaboration with local stakeholders, which included experts, decision makers, funders and organisations involved in service delivery, support and technical assistance. These analyses show that it is possible to improve health impact by redistributing current TB spending in Belarus. Specifically, shifting funding from inpatient- to outpatient-focused care models, and from mass screening to active case finding strategies, could reduce TB prevalence and mortality by up to 45% and 50%, respectively, by 2035. In addition, an optimised allocation of TB spending could lead to a reduction in drug-resistant TB infections by 40% over this period. This would support progress towards national TB targets without additional financial resources. The case study in Belarus demonstrates how reallocations of spending across existing and new interventions could have a substantial impact on TB outcomes. This highlights the potential for Optima TB and similar modelling tools to support evidence-based priority setting.

Tuberculosis (TB) remains a leading global cause of death and morbidity, and 85% of deaths occur in countries where resources for TB care and control are limited. Many countries cannot finance all TB interventions or technologies, which means difficult decisions on what to prioritise and publically finance. Modelling tools can help decision-makers set priorities based on evidence, in a systematic and transparent way. This study presents Optima TB, a tool that estimates which allocations of spending across interventions will most likely maximise specified objectives—such as minimising TB deaths, prevalence and incidence. In partnership with local decision-makers and stakeholders, Optima TB was applied in Belarus. Recommendations from the model findings include focussing investment on outpatient rather than inpatient care and actively finding people with TB (e.g. through contact tracing) rather than mass testing of the population. The recommended reallocations of spending could reduce TB prevalence and deaths by up to 45% and 50%, respectively, by 2035 for the same amount of spending. Key stakeholders were engaged throughout the analysis and findings and uncertainty around the results were clearly communicated with decision-makers. The timeliness of the results helped inform national dialogue on TB care reform, among other key policy discussions.

Covasim: An agent-based model of COVID-19 dynamics and interventions

The COVID-19 pandemic has created an urgent need for models that can project epidemic trends, explore intervention scenarios, and estimate resource needs. Here we describe the methodology of Covasim (COVID-19 Agent-based Simulator), an open-source model developed to help address these questions. Covasim includes country-specific demographic information on age structure and population size; realistic transmission networks in different social layers, including households, schools, workplaces, long-term care facilities, and communities; age-specific disease outcomes; and intrahost viral dynamics, including viral-load-based transmissibility. Covasim also supports an extensive set of interventions, including non-pharmaceutical interventions, such as physical distancing and protective equipment; pharmaceutical interventions, including vaccination; and testing interventions, such as symptomatic and asymptomatic testing, isolation, contact tracing, and quarantine. These interventions can incorporate the effects of delays, loss-to-follow-up, micro-targeting, and other factors. Implemented in pure Python, Covasim has been designed with equal emphasis on performance, ease of use, and flexibility: realistic and highly customized scenarios can be run on a standard laptop in under a minute. In collaboration with local health agencies and policymakers, Covasim has already been applied to examine epidemic dynamics and inform policy decisions in more than a dozen countries in Africa, Asia-Pacific, Europe, and North America.

Covasim: An agent-based model of COVID-19 dynamics and interventions

The COVID-19 pandemic has created an urgent need for models that can project epidemic trends, explore intervention scenarios, and estimate resource needs. Here we describe the methodology of Covasim (COVID-19 Agent-based Simulator), an open-source model developed to help address these questions. Covasim includes country-specific demographic information on age structure and population size; realistic transmission networks in different social layers, including households, schools, workplaces, long-term care facilities, and communities; age-specific disease outcomes; and intrahost viral dynamics, including viral-load-based transmissibility. Covasim also supports an extensive set of interventions, including non-pharmaceutical interventions, such as physical distancing and protective equipment; pharmaceutical interventions, including vaccination; and testing interventions, such as symptomatic and asymptomatic testing, isolation, contact tracing, and quarantine. These interventions can incorporate the effects of delays, loss-to-follow-up, micro-targeting, and other factors. Implemented in pure Python, Covasim has been designed with equal emphasis on performance, ease of use, and flexibility: realistic and highly customized scenarios can be run on a standard laptop in under a minute. In collaboration with local health agencies and policymakers, Covasim has already been applied to examine epidemic dynamics and inform policy decisions in more than a dozen countries in Africa, Asia-Pacific, Europe, and North America.

Potential effects of disruption to HIV programmes in sub-Saharan Africa caused by COVID-19: results from multiple mathematical models

Background

The COVID-19 pandemic could lead to disruptions to provision of HIV services for people living with HIV and those at risk of acquiring HIV in sub-Saharan Africa, where UNAIDS estimated that more than two-thirds of the approximately 38 million people living with HIV resided in 2018. We aimed to predict the potential effects of such disruptions on HIV-related deaths and new infections in sub-Saharan Africa.

Methods

In this modelling study, we used five well described models of HIV epidemics (Goals, Optima HIV, HIV Synthesis, an Imperial College London model, and Epidemiological MODeling software [EMOD]) to estimate the effect of various potential disruptions to HIV prevention, testing, and treatment services on HIV-related deaths and new infections in sub-Saharan Africa lasting 6 months over 1 year from April 1, 2020. We considered scenarios in which disruptions affected 20%, 50%, and 100% of the population.

Findings

A 6-month interruption of supply of antiretroviral therapy (ART) drugs across 50% of the population of people living with HIV who are on treatment would be expected to lead to a 1·63 times (median across models; range 1·39–1·87) increase in HIV-related deaths over a 1-year period compared with no disruption. In sub-Saharan Africa, this increase amounts to a median excess of HIV deaths, across all model estimates, of 296 000 (range 229 023–420 000) if such a high level of disruption occurred. Interruption of ART would increase mother-to-child transmission of HIV by approximately 1·6 times. Although an interruption in the supply of ART drugs would have the largest impact of any potential disruptions, effects of poorer clinical care due to overstretched health facilities, interruptions of supply of other drugs such as co-trimoxazole, and suspension of HIV testing would all have a substantial effect on population-level mortality (up to a 1·06 times increase in HIV-related deaths over a 1-year period due to disruptions affecting 50% of the population compared with no disruption). Interruption to condom supplies and peer education would make populations more susceptible to increases in HIV incidence, although physical distancing measures could lead to reductions in risky sexual behaviour (up to 1·19 times increase in new HIV infections over a 1-year period if 50% of people are affected).

Interpretation

During the COVID-19 pandemic, the primary priority for governments, donors, suppliers, and communities should focus on maintaining uninterrupted supply of ART drugs for people with HIV to avoid additional HIV-related deaths. The provision of other HIV prevention measures is also important to prevent any increase in HIV incidence.

Funding

Bill & Melinda Gates Foundation.

Opportunities for improved HIV prevention and treatment through budget optimization in Eswatini

INTRODUCTION

Eswatini achieved a 44% decrease in new HIV infections from 2014 to 2019 through substantial scale-up of testing and treatment. However, it still has one of the highest rates of HIV incidence in the world, with 14 infections per 1,000 adults 15-49 years estimated for 2017. The Government of Eswatini has called for an 85% reduction in new infections by 2023 over 2017 levels. To make further progress towards this target and to achieve maximum health gains, this study aims to model optimized investments of available HIV resources.

METHODS

The Optima HIV model was applied to estimate the impact of efficiency strategies to accelerate prevention of HIV infections and HIV-related deaths. We estimated the number of infections and deaths that could be prevented by optimizing HIV investments. We optimize across HIV programs, then across service delivery modalities for voluntary medical male circumcision (VMMC), HIV testing, and antiretroviral refill, as well as switching to a lower cost antiretroviral regimen.

FINDINGS

Under an optimized budget, prioritising HIV testing for the general population followed by key preventative interventions may result in approximately 1,000 more new infections (2% more) being averted by 2023. More infections could be averted with further optimization between service delivery modalities across the HIV cascade. Scaling-up index and self-testing could lead to 100,000 more people getting tested for HIV (25% more tests) with the same budget. By prioritizing Fast-Track, community-based, and facility-based antiretroviral refill options, an estimated 30,000 more people could receive treatment, 17% more than baseline or US$5.5 million could be saved, 4% of the total budget. Finally, switching non-pregnant HIV-positive adults to a Dolutegravir-based antiretroviral therapy regimen and concentrating delivery of VMMC to existing fixed facilities over mobile clinics, US$4.5 million (7% of total budget) and US$6.6 million (10% of total budget) could be saved, respectively.

SIGNIFICANCE

With a relatively short five-year timeframe, even under a substantially increased and optimized budget, Eswatini is unlikely to reach their ambitious national prevention target by 2023. However, by optimizing investment of the same budget towards highly cost-effective VMMC, testing, and treatment modalities, further reductions in HIV incidence and cost savings could be realized.

Potential health gains in West and Central Africa through savings from lower cost HIV treatment

OBJECTIVE

Prices of antiretroviral (ARV) drugs in lower income countries have decreased substantially over the past two decades, helping to facilitate greatly expanded access to antiretroviral therapy (ART). However, ART coverage in many parts of the world remains low. We investigate the extent of epidemiological benefits that might be expected if ARV drug prices decline further.

DESIGN

A modeling study using data from seven countries in West and Central Africa (Cameroon, Democratic Republic of the Congo, Côte d'Ivoire, Niger, Nigeria, Senegal, and Togo).

METHODS

We investigated how the timing of ARV cost reductions could affect the impact and compared three different possible investment strategies: reinvesting in ART, reinvesting in the HIV response according to historical allocations, and reinvesting with the aim of minimizing HIV incidence and mortality.

RESULTS

If ARV drug prices fell by 37% relative to 2018 levels (i.e. following continued trend declines), we calculate ART unit costs could decrease by ∼20% (holding other cost components constant). If this could be achieved by 2020 and the savings were reinvested into ART, we estimate that an additional 8% of HIV infections and 11% of HIV-related deaths could be averted over 2020-2030 across the seven countries. Slightly greater gains could be attained if funds were reinvested in ART in combination with primary prevention. Delays in the year of introduction of ARV price reductions would reduce the impact by about 1% per year.

CONCLUSION

ARV price reductions could free up funds that - if strategically invested - would help countries move closer toward the elimination of HIV.

Modelling the impact of migrants on the success of the HIV care and treatment program in Botswana

Introduction

Botswana offers publicly financed HIV treatment to citizens, but not migrants, who comprised about 7% of the population in 2016. However, HIV incidence is not declining in proportion to Botswana’s HIV response. In 2018, Botswana had 86% of citizens living with HIV diagnosed, 95% of people diagnosed on treatment, and 95% viral suppression among those on treatment. We hypothesised that continued exclusion of migrants is hampering reduction of HIV incidence in Botswana. Hence, we modelled the impact of including migrants in Botswana’s HIV response on achieving 90-90-90 and 95-95-95 Fast-Track targets by 2020 and 2030, respectively.

Methods

The Optima HIV model, with demographic, epidemiological, and behavioural inputs, was applied to citizens of and migrants to Botswana. Projections of new HIV infections and HIV-related deaths were compared for three scenarios to the end of 2030: (1) continued status quo for HIV testing and treatment coverage, and maintenance of levels of linkage to care, loss to follow-up, and viral suppression among citizens and migrants (baseline); (2) with scaled-up budget, optimised to achieve 90-90-90 and 95-95-95 Fast-Track targets by 2020 and 2030, respectively, for citizens only; and (3) scaled-up optimised budget to achieve these targets for both citizens and migrants.

Results

A baseline of 172,000 new HIV infections and 8,400 HIV-related deaths was projected over 2020–2030. Scaling up to achieve targets among citizens only averted an estimated 48,000 infections and 1,700 deaths. Achieving targets for both citizens and migrants averted 16,000 (34%) more infections and 442 (26%) more deaths. Scaling up for both populations reduced numbers of new HIV infections and deaths by 44% and 39% respectively compared with 2010 levels. Treating migrants when scaling up in both populations was estimated to cost USD 74 million over 2020–2030.

Conclusions

Providing HIV services to migrants in Botswana could lead to further reductions in HIV incidence and deaths. However, even with an increased, optimised budget that achieves 95-95-95 targets for both citizens and migrants by 2030, the 90% incidence reduction target for 2020 will be missed. Further efficiencies and innovations will be needed to meet HIV targets in Botswana.

NanoRefinery of carbonaceous nanomaterials: Complementing dairy manure gasification and their applications in cellular imaging and heavy metal sensing

This article describes an efficient method, combining chemical oxidation and acetone extraction, to produce carbonaceous nanomaterials from dairy manure biochar. The optical and mechanical properties are similar to methods previously reported carbonaceous nanomaterials from biomass. Our novel process cuts the processing time in half and drastically reduces the energy input required. The acetone extraction produced 10 fractions with dairy manure biochar-derived carbonaceous nanomaterials (DMB-CNs). The fraction with the carbonaceous nanomaterials, DMB-CN-E1, with highest fluorescence was selected for in-depth characterisation and for initial testing across a range of applications. DMB-CN-E1 was characterised using atomic force microscope, electrophoresis, and spectrophotometric methods. DMB-CN-E1 exhibited a lateral dimension between 11 and 28 nm, a negative charge, and excitation/emission maxima at 337/410 nm, respectively. The bioimaging potential of DMB-CN-E1 evidenced different locations and different interactions with the cellular models evaluated. DMB-CN-E1 was quenched by several heavy metal ions showing a future application of these materials in heavy metal ion detection and/or removal. The demonstrated capabilities in bioimaging and environmental sensing create the opportunity for generating added-value nanomaterials (NanoRefinery) from dairy manure biochar gasification and, thus, increasing the economic viability of gasification plants.

Achieving 90-90-90 Human Immunodeficiency Virus (HIV) Targets Will Not Be Enough to Achieve the HIV Incidence Reduction Target in Australia

Background

We estimated the human immunodeficiency virus (HIV) incidence reduction in Australia that would correspond to achieving the United Nations Program on HIV and AIDS (UNAIDS) 90-90-90 targets by 2020 and extended targets of 95-95-95 by 2030. This was done in combination with various scale-ups of HIV testing, primary prevention, and preexposure prophylaxis (PrEP) among high-risk men who have sex with men (MSM). These projections were evaluated against the target of achieving a 90% reduction in HIV incidence by 2030 compared with 2010 levels.

Methods

A mathematical model.

Results

Achieving 90-90-90 by 2020 was estimated to reduce incidence by 10% from 2010 levels. Achieving 95-95-95 by 2030 was estimated to reduce incidence by 17% from 2010 levels, with the first "95" being achievable by testing low- and high-risk MSM 2 and 4 times per year, respectively. This was improved to a 34% reduction by including a 5-year scale-up of PrEP to 30% coverage among high-risk MSM and to 45% by also increasing MSM condom use from 42% to 60%. However, even with 95-95-95, 2 and 4 tests per year for low- and high-risk MSM, 100% high-risk MSM PrEP coverage, and 100% MSM condom use, only an 80% reduction in incidence was possible by 2030.

Conclusions

Many countries, particularly those with low HIV prevalence, will struggle to achieve a 90% reduction in HIV incidence by 2030, even if UNAIDS targets are met. Most will require substantially higher levels of prevention coverage and higher testing frequencies to reach this target.

Multivariate analysis of biochar-derived carbonaceous nanomaterials for detection of heavy metal ions in aqueous systems

This article focuses on implementing multivariate analysis to evaluate biochar-derived carbonaceous nanomaterials (BCN) from three different feedstocks for the detection and differentiation of heavy metal ions in aqueous systems. The BCN were produced from dairy manure, rice straw and sorghum straw biochar using our NanoRefinery process. The NanoRefinery process transforms biochar into advanced nanomaterials using depolymerisation/chemical oxidation and purification of nanomaterials using solvent extraction. Dairy manure biochar-derived carbonaceous nanomaterials (DMB-CN), rice straw biochar-derived carbonaceous nanomaterials (RSB-CN) and sorghum straw biochar-derived carbonaceous nanomaterials (SSB-CN) were utilised as probes for the evaluation of their fluorescent properties and the detection of heavy metal ions. The BCN fluorescence quenching and fluorescence recovery was tested with lead (Pb²⁺), nickel (Ni²⁺), copper (Cu²⁺) and mercury (Hg²⁺). Principal component analysis (PCA) and discriminant analysis were used to differentiate among heavy metal ions in water samples. The BCN from different feedstocks had different characteristics and produced different interactions with heavy metal ions. DMB-CN had the highest quenching for Hg²⁺ and Ni²⁺ while SSB-CN and RSB-CN responded best to Cu²⁺ and Pb²⁺, respectively. The fluorescence quenching was modelled using linear and empirical functions. PCA and discriminant analysis used the quenching measurements to differentiate heavy metal ions in aqueous system. A key result was that the discriminant analysis had a 100% accuracy to detect Pb²⁺, 66% for Ni²⁺ and Cu²⁺, and 33% for Hg²⁺. This study has shown that biochar-derived carbonaceous nanomaterials could be used in heavy metal ions sensing applications. This is the first step in the development of a fast and accurate method for the detection of heavy metal ions in waters using environmentally friendly BCN.

How should HIV resources be allocated? Lessons learnt from applying Optima HIV in 23 countries

Introduction

With limited funds available, meeting global health targets requires countries to both mobilize and prioritize their health spending. Within this context, countries have recognized the importance of allocating funds for HIV as efficiently as possible to maximize impact. Over the past six years, the governments of 23 countries in Africa, Asia, Eastern Europe and Latin America have used the Optima HIV tool to estimate the optimal allocation of HIV resources.

Methods

Each study commenced with a request by the national government for technical assistance in conducting an HIV allocative efficiency study using Optima HIV. Each study team validated the required data, calibrated the Optima HIV epidemic model to produce HIV epidemic projections, agreed on cost functions for interventions, and used the model to calculate the optimal allocation of available funds to best address national strategic plan targets. From a review and analysis of these 23 country studies, we extract common themes around the optimal allocation of HIV funding in different epidemiological contexts.

Results and discussion

The optimal distribution of HIV resources depends on the amount of funding available and the characteristics of each country's epidemic, response and targets. Universally, the modelling results indicated that scaling up treatment coverage is an efficient use of resources. There is scope for efficiency gains by targeting the HIV response towards the populations and geographical regions where HIV incidence is highest. Across a range of countries, the model results indicate that a more efficient allocation of HIV resources could reduce cumulative new HIV infections by an average of 18% over the years to 2020 and 25% over the years to 2030, along with an approximately 25% reduction in deaths for both timelines. However, in most countries this would still not be sufficient to meet the targets of the national strategic plan, with modelling results indicating that budget increases of up to 185% would be required.

Conclusions

Greater epidemiological impact would be possible through better targeting of existing resources, but additional resources would still be required to meet targets. Allocative efficiency models have proven valuable in improving the HIV planning and budgeting process.

Microalgae biochar-derived carbon dots and their application in heavy metal sensing in aqueous systems

This research seeks a coupled solution for managing the large amounts of biochar produced by microalgae biofuel production, and the necessity for novel, economic and accurate heavy metal sensing methods. Therefore, this study evaluated the transformation of microalgae biochar (MAB) into carbon dots (Cdots) and their subsequent application as heavy metal ion sensors in aqueous systems. The experimental phase included the transformation of MAB into microalgae biochar-derived carbon dots (MAB-Cdots), MAB-Cdot characterisation and the evaluation of the MAB-Cdots as transducers for the detection of four heavy metal ions (Pb²⁺, Cu²⁺, Cd²⁺, and Ni²⁺). MAB-Cdot fluorescence was stable over a wide range of pH and resistant to photo-bleaching, making them suitable as fluorescence probes. The MAB-Cdot fluorescence was quenched by all of the metal ions and displayed different quenching levels. Depending upon the ions involved, MAB-Cdots were used to detect the presence of heavy metal ions from concentrations of 0.012 μM up to 2 mM by measuring the reduction in fluorescence intensity. Neutral and slightly alkaline pHs were optimal for Cu²⁺ Ni²⁺ and Pb²⁺ heavy metal quenching. To quantify the concentration of the heavy metal ions, linear and logarithmic functions were used to model the MAB-Cdot fluorescence quenching. The sensing mechanism was determined to be reversible and purely collisional with some fluorophores less accessible than the others. This work demonstrated the ability to produce Cdots from microalgae biochar, examined their application as a transducer for detecting heavy metal ions in aqueous systems and paves the way for novel sensing systems using MAB-Cdots.

The global Optima HIV allocative efficiency model: targeting resources in efforts to end AIDS

BACKGROUND

To move towards ending AIDS by 2030, HIV resources should be allocated cost-effectively. We used the Optima HIV model to estimate how global HIV resources could be retargeted for greatest epidemiological effect and how many additional new infections could be averted by 2030.

METHODS

We collated standard data used in country modelling exercises (including demographic, epidemiological, behavioural, programmatic, and expenditure data) from Jan 1, 2000, to Dec 31, 2015 for 44 countries, capturing 80% of people living with HIV worldwide. These data were used to parameterise separate subnational and national models within the Optima HIV framework. To estimate optimal resource allocation at subnational, national, regional, and global levels, we used an adaptive stochastic descent optimisation algorithm in combination with the epidemic models and cost functions for each programme in each country. Optimal allocation analyses were done with international HIV funds remaining the same to each country and by redistributing these funds between countries.

FINDINGS

Without additional funding, if countries were to optimally allocate their HIV resources from 2016 to 2030, we estimate that an additional 7·4 million (uncertainty range 3·9 million-14·0 million) new infections could be averted, representing a 26% (uncertainty range 13-50%) incidence reduction. Redistribution of international funds between countries could avert a further 1·9 million infections, which represents a 33% (uncertainty range 20-58%) incidence reduction overall. To reduce HIV incidence by 90% relative to 2010, we estimate that more than a three-fold increase of current annual funds will be necessary until 2030. The most common priorities for optimal resource reallocation are to scale up treatment and prevention programmes targeting key populations at greatest risk in each setting. Prioritisation of other HIV programmes depends on the epidemiology and cost-effectiveness of service delivery in each setting as well as resource availability.

INTERPRETATION

Further reductions in global HIV incidence are possible through improved targeting of international and national HIV resources.

FUNDING

World Bank and Australian NHMRC.

A tale of two countries: progress towards UNAIDS 90-90-90 targets in Botswana and Australia

UNAIDS 90-90-90 targets and Fast-Track commitments are presented as precursors to ending the AIDS epidemic by 2030, through effecting a 90% reduction in new HIV infections and AIDS-related deaths from 2010 levels (HIV epidemic control). Botswana, a low to middle-income country with the third-highest HIV prevalence, and Australia, a low-prevalence high-income country with an epidemic concentrated among men who have sex with men (MSM), have made significant strides towards achieving the UNAIDS 90-90-90 targets. These two countries provide lessons for different epidemic settings. This paper discusses the lessons that can be drawn from Botswana and Australia with respect to their success in HIV testing, treatment, viral suppression and other HIV prevention strategies for HIV epidemic control. Botswana and Australia are on target to achieving the 90-90-90 targets for HIV epidemic control, made possible by comprehensive HIV testing and treatment programmes in the two countries. As of 2015, 70% of all people assumed to be living with HIV had viral suppression in Botswana and Australia. However, HIV incidence remains above one per cent in the general population in Botswana and in MSM in Australia. The two countries have demonstrated that rapid HIV testing that is accessible and targeted at key and vulnerable populations is required in order to continue identifying new HIV infections. All citizens living with HIV in both countries are eligible for antiretroviral therapy (ART) and viral load monitoring through government-funded programmes. Notwithstanding their success in reducing HIV transmission to date, programmes in both countries must continue to be supported at current levels to maintain epidemic suppression. Scaled HIV testing, linkage to care, universal ART, monitoring patients on treatment over and above strengthened HIV prevention strategies (e.g. male circumcision and pre-exposure prophylaxis) will all continue to require funding. The progress that Botswana and Australia have made towards meeting the 90-90-90 targets is commendable. However, in order to reduce HIV incidence significantly towards 2030, there is a need for sustained HIV testing, linkage to care and high treatment coverage. Botswana and Australia provide useful lessons for developing countries with generalized epidemics and high-income countries with concentrated epidemics.

Kazakhstan can achieve ambitious HIV targets despite expected donor withdrawal by combining improved ART procurement mechanisms with allocative and implementation efficiencies

BACKGROUND

Despite a non-decreasing HIV epidemic, international donors are soon expected to withdraw funding from Kazakhstan. Here we analyze how allocative, implementation, and technical efficiencies could strengthen the national HIV response under assumptions of future budget levels.

METHODOLOGY

We used the Optima model to project future scenarios of the HIV epidemic in Kazakhstan that varied in future antiretroviral treatment unit costs and management expenditure-two areas identified for potential cost-reductions. We determined optimal allocations across HIV programs to satisfy either national targets or ambitious targets. For each scenario, we considered two cases of future HIV financing: the 2014 national budget maintained into the future and the 2014 budget without current international investment.

FINDINGS

Kazakhstan can achieve its national HIV targets with the current budget by (1) optimally re-allocating resources across programs and (2) either securing a 35% [30%-39%] reduction in antiretroviral treatment drug costs or reducing management costs by 44% [36%-58%] of 2014 levels. Alternatively, a combination of antiretroviral treatment and management cost-reductions could be sufficient. Furthermore, Kazakhstan can achieve ambitious targets of halving new infections and AIDS-related deaths by 2020 compared to 2014 levels by attaining a 67% reduction in antiretroviral treatment costs, a 19% [14%-27%] reduction in management costs, and allocating resources optimally.

SIGNIFICANCE

With Kazakhstan facing impending donor withdrawal, it is important for the HIV response to achieve more with available resources. This analysis can help to guide HIV response planners in directing available funding to achieve the greatest yield from investments. The key changes recommended were considered realistic by Kazakhstan country representatives.

Allocative and implementation efficiency in HIV prevention and treatment for people who inject drugs

BACKGROUND

Estimated global new HIV infections among people who inject drugs (PWID) remained stable over the 2010-2015 period and the target of a 50% reduction over this period was missed. To achieve the 2020 UNAIDS target of reducing adult HIV infections by 75% compared to 2010, accelerated action in scaling up HIV programs for PWID is required. In a context of diminishing external support to HIV programs in countries where most HIV-affected PWID live, it is essential that available resources are allocated and used as efficiently as possible.

METHODS

Allocative and implementation efficiency analysis methods were applied. Optima, a dynamic, population-based HIV model with an integrated program and economic analysis framework was applied in eight countries in Eastern Europe and Central Asia (EECA). Mathematical analyses established optimized allocations of resources. An implementation efficiency analysis focused on examining technical efficiency, unit costs, and heterogeneity of service delivery models and practices.

RESULTS

Findings from the latest reported data revealed that countries allocated between 4% (Bulgaria) and 40% (Georgia) of total HIV resources to programs targeting PWID - with a median of 13% for the eight countries. When distributing the same amount of HIV funding optimally, between 9% and 25% of available HIV resources would be allocated to PWID programs with a median allocation of 16% and, in addition, antiretroviral therapy would be scaled up including for PWID. As a result of optimized allocations, new HIV infections are projected to decline by 3-28% and AIDS-related deaths by 7-53% in the eight countries. Implementation efficiencies identified involve potential reductions in drug procurement costs, service delivery models, and practices and scale of service delivery influencing cost and outcome. A high level of implementation efficiency was associated with high volumes of PWID clients accessing a drug harm reduction facility.

CONCLUSION

A combination of optimized allocation of resources, improved implementation efficiency and increased investment of non-HIV resources is required to enhance coverage and improve outcomes of programs for PWID. Increasing efficiency of HIV programs for PWID is a key step towards avoiding implicit rationing and ensuring transparent allocation of resources where and how they would have the largest impact on the health of PWID, and thereby ensuring that funding spent on PWID becomes a global best buy in public health.

Does percutaneous tibial nerve stimulation improve global pelvic function in women with faecal incontinence?

AIM

Percutaneous tibial nerve stimulation (PTNS) is a minimally invasive treatment for faecal incontinence. Many patients with faecal incontinence have coexisting pelvic floor disorders such as urinary incontinence and vaginal symptoms. We utilized a pelvic floor assessment tool to analyse any effect of PTNS on global pelvic floor function.

METHODS

Patients with faecal incontinence attending our institution who had failed to respond sufficiently to biofeedback were offered a course of PTNS. Patients underwent pre- and post-stimulation assessment with a validated electronic Personal Assessment Questionnaire - Pelvic Floor (ePAQ-PF) for pelvic floor disorders. Scores were compared to assess the effect of treatment on global pelvic floor function.

RESULTS

During the study period pre- and post-stimulation ePAQ-PF data were available for 60 patients (55% of all patients starting PTNS). In this cohort there was a significant improvement in bowel continence, bowel related quality of life, irritable bowel syndrome and bowel evacuation with a large effect size for continence and bowel related quality of life. There was also a significant improvement in non-bowel related symptoms, including urinary pain and stress incontinence, urinary related quality of life and bowel related sexual function. Sixty-five per cent of those who answered the question reported improvement in global health after stimulation.

CONCLUSION

For patients presenting with faecal incontinence, PTNS appears to have a positive effect on bowel related function in approximately two-thirds of patients. However, for treatment responders, improvement appears to relate mainly to improvement in bowel related function rather than a global pelvic floor effect.

Triclosan antagonizes fluconazole activity against Candida albicans

Triclosan is a broad-spectrum antimicrobial compound commonly used in oral hygiene products. Investigation of its activity against Candida albicans showed that triclosan was fungicidal at concentrations of 16 mg/L. However, at subinhibitory concentrations (0.5-2 mg/L), triclosan antagonized the activity of fluconazole. Although triclosan induced CDR1 expression in C. albicans, antagonism was still observed in cdr1Δ and cdr2Δ strains. Triclosan did not affect fluconazole uptake or alter total membrane sterol content, but did induce the expression of FAS1 and FAS2, indicating that its mode of action may involve inhibition of fatty acid synthesis, as it does in prokaryotes. However, FAS2 mutants did not exhibit increased susceptibility to triclosan, and overexpression of both FAS1 and FAS2 alleles did not alter triclosan susceptibility. Unexpectedly, the antagonistic effect was specific for C. albicans under hypha-inducing conditions and was absent in the non-filamentous efg1Δ strain. This antagonism may be due to the membranotropic activity of triclosan and the unique composition of hyphal membranes.

Expression of bacterial levanase in yeast enables simultaneous saccharification and fermentation of grass juice to bioethanol

This study demonstrates use of recombinant yeast to simultaneously saccharify and ferment grass juice (GJ) to bioethanol. A modified Bacillus subtilis levanase gene (sacC) in which the native bacterial signal sequence was replaced with a yeast α-factor domain, was synthesised with yeast codon preferences and transformed into Saccharomyces cerevisiae (strain AH22) using the expression vector pMA91. AH22:psacC transformants secreted sacCp as an active, hyper-glycosylated (>180 kDa) protein allowing them to utilise inulin (β[2-1] linked fructose) and levan (β[2-6] linkages) as growth substrates. The control (AH22:pMA91) strain, transformed with empty plasmid DNA was not able to utilise inulin or levan. When cultured on untreated GJ levels of growth and bioethanol production were significantly higher in experiments with AH22:psacC than with AH22:pMA91. Bioethanol yields from AH22:psacC grown on GJ (32.7[±4] mg mL(-1)) compared closely to those recently achieved (Martel et al., 2010) using enzymatically pre-hydrolysed GJ (36.8[±4] mg mL(-1)).

Genome-wide generation of yeast gene deletion strains

In the year 2001 a collection of yeast strains will be completed that are deleted in the 6000 open reading frames selected as putative genes by the initial bioinformatic analysis of the Saccharomyces cerevisiae genome. The collection was produced by the transatlantic yeast gene deletion project, a collaboration involving researchers in the USA, Canada and Europe. The European effort was part of EUROFAN (European Functional Analysis Network) where some of the strains could feed into various functional analysis nodes dealing with specific areas of cell biology. With approximately 40% of human genes involved in heritable disease having a homologue in yeast and with the use of yeast in various drug discovery strategies, not least due to the dramatic increase in fungal infections, these strains will be valuable in trans-genomic studies and in specialised interest studies in individual laboratories. A detailed analysis of the project by the consortium is in preparation, here we discuss the yeast strains, reported findings and approaches to using this resource.

Expression, purification and use of the soluble domain of Lactobacillus paracasei beta-fructosidase to optimise production of bioethanol from grass fructans

Microbial inulinases find application in food, pharmaceutical and biofuel industries. Here, a novel Lactobacillus paracasei beta-fructosidase was overexpressed as truncated cytosolic protein ((t)fosEp) in Escherichia coli. Purified (t)fosEp was thermostable (10-50 degrees C) with a pH optimum of 5; it showed highest affinity for bacterial levan (beta[2-6] linked fructose) followed by nystose, chicory inulin, 1-kestose (beta[2-1] linkages) and sucrose (K(m) values of 0.5, 15, 15.6, 49 and 398 mM, respectively). Hydrolysis of polyfructose moieties in agriculturally-sourced grass juice (GJ) with (t)fosEp resulted in the release of >13 mg/ml more bioavailable fructose than was measured in untreated GJ. Bioethanol yields from fermentation experiments with Brewer's yeast and GJ+(t)fosEp were >25% higher than those achieved using untreated GJ feedstock (36.5[+/-4.3] and 28.2[+/-2.7]mg ethanol/ml, respectively). This constitutes the first specific study of the potential to ferment ethanol from grass juice and the utility of a novel core domain of beta-fructosidase from L. paracasei.

Differential azole antifungal efficacies contrasted using a Saccharomyces cerevisiae strain humanized for sterol 14 alpha-demethylase at the homologous locus

Inhibition of sterol-14 alpha-demethylase, a cytochrome P450 (CYP51, Erg11p), is the mode of action of azole antifungal drugs, and with high frequencies of fungal infections new agents are required. New drugs that target fungal CYP51 should not inhibit human CYP51, although selective inhibitors of the human target are also of interest as anticholesterol agents. A strain of Saccharomyces cerevisiae that was humanized with respect to the amino acids encoded at the CYP51 (ERG11) yeast locus (BY4741:huCYP51) was produced. The strain was validated with respect to gene expression, protein localization, growth characteristics, and sterol content. The MIC was determined and compared to that for the wild-type parental strain (BY4741), using clotrimazole, econazole, fluconazole, itraconazole, ketoconazole, miconazole, and voriconazole. The humanized strain showed up to >1,000-fold-reduced susceptibility to the orally active azole drugs, while the topical agents showed no difference. Data from growth kinetic measurements substantiated this finding but also revealed reduced effectiveness against the humanized strain for the topical drugs. Cellular sterol profiles reflected the decreased susceptibility of BY4741:huCYP51 and showed a smaller depletion of ergosterol and accumulation of 14 alpha-methyl-ergosta-8, 24(28)-dien-3beta-6 alpha-diol than the parental strain under the same treatment conditions. This strain provides a useful tool for initial specificity testing for new drugs targeting CYP51 and clearly differentiates azole antifungals in a side-by-side comparison.

Cytochrome P450 biodiversity and biotechnology

CYP (cytochrome P450) biodiversity and biotechnology is of importance given the industrial applications and potential for the huge array of genes and proteins that can constitute up to 1% of a coding genome. Historical biotechnological roles for CYPs in mutant fungi diverting the flux of metabolites towards penicillin production, in biotransformations allowing the production of corticosteroids and CYPs as drug targets contribute to interest in the roles of orphan CYPs in the emerging genomes. This area includes studies related to biotransformations and bioremediation, natural product synthesis and its manipulation, tools for exploiting CYPs and using CYPs as biomarkers and drug targets. Fundamental studies on diverse structure and function, on the ecological and evolution of CYPs through geological time and in drug/pesticide resistance also contribute distinctively to this field of CYP research.

Towards engineered topogenesis of cytochrome b5 and P450 for in vivo transformation of xenobiotics

Nature is endowed with catalysts capable of an unprecedented diversity of biotransformations, beyond the capabilities of synthetic chemistries. In a biotechnological context, there is a growing and emerging need to tap this catalytic potential. CYP (cytochrome P450) represents a superfamily of enzymes capable of a diverse array of catalytic activities. Distinct members are engaged in biosynthetic reactions within many organisms, while others have a role in the detoxification of foreign compounds. The latter substrates include medicines, pollutants, pesticides, carcinogens, perfumes and herbicides, representing considerable applied importance for pharmacology and toxicology. CYPs show a high degree of stereo- and regio-specificity for their reactions, which have wide industrial applications. Recombinant CYPs are commonly expressed as active recombinant cytosolic forms in Escherichia coli. However, selective permeability of E. coli to many substrates and products can cause problems with product recovery when using whole-cell systems. To overcome these problems, we have been developing approaches to facilitate export of functional recombinant haemoproteins to the inner membrane, periplasm and the outer membrane of E. coli. Here, we describe the progress in relation to cytochrome b5 and CYPs.

Cytochrome b(5) modulation of 17{alpha} hydroxylase and 17-20 lyase (CYP17) activities in steroidogenesis

CYP17 is a steroidogenic enzyme located in the zona fasciculata and zona reticularis of the adrenal cortex and gonad tissues and which has dual functions - hydroxylation and as a lyase. The first activity gives hydroxylation of pregnenolone and progesterone at the C(17) position to generate 17alpha-hydroxypregnenolone and 17alpha-hydroxyprogesterone, while the second enzymic activity cleaves the C(17)-C(20) bond of 17alpha-hydroxypregnenolone and 17alpha-hydroxyprogesterone to form dehydroepiandro-sterone and androstenedione respectively. The modulation of these two activities occurs through cytochrome b(5). Association of cytochrome b(5) and CYP17 is thought to be based primarily on electrostatic interactions in which the negatively charged residues pair up with positively charged residues on the proximal surface of the CYP17 molecule. Non-specific interactions of the hydrophobic membrane regions of cytochrome b(5) and CYP17 are also thought to play a crucial role in the association of these two haemoproteins. Although cytochrome b(5) is known to stimulate CYP activity by contributing the second electron in the catalytic cycle, in the case of CYP17, the mechanism of cleavage stimulation proceeds via an allosteric mode. It is hypothesised that cytochrome b(5) promotes the cleavage by aligning the iron-oxygen complex attack onto the C(20) rather than the C(17) atom of the steroid substrate molecule. Thus, further understanding of the mechanism of modulation by cytochrome b(5) of the hydroxylase and lyase activities should shed new insights on developing therapeutic targets in CYP17-linked biochemical processes such as adrenarche, polycystic ovary syndrome and prostate cancer.

Cloning and characterization of the lanosterol 14alpha-demethylase (ERG11) gene in Cryptococcus neoformans

The ergosterol pathway in fungal pathogens is an attractive antimicrobial target because it is unique from the major sterol (cholesterol) producing pathway in humans. Lanosterol 14alpha-demethylase is the target for a major class of antifungals, the azoles. In this study we have isolated the gene for this enzyme from Cryptococcus neoformans. The gene, ERG11, was recovered using degenerate PCR with primers designed with a novel algorithm called CODEHOP. Sequence analysis of Erg11p identified a highly conserved region typical of the cytochrome P450 class of mono-oxygenases. The gene was present in single copy in the genome and mapped to one end of the largest chromosome. Comparison of the protein sequence to a number of major human fungal pathogen Erg11p homologs revealed that the C. neoformans protein was highly conserved, and most closely related to the Erg11p homologs from other basidiomycetes. Functional studies demonstrated that the gene could complement a Saccharomyces cerevisiae erg11 mutant, which confirmed the identity of the C. neoformans gene.

Analysis of Acanthamoeba polyphaga surface carbohydrate exposure by FITC-lectin binding and fluorescence evaluation

AIMS

Characterization of the representative protozoan Acanthamoeba polyphaga surface carbohydrate exposure by a novel combination of flow cytometry and ligand-receptor analysis.

METHODS AND RESULTS

Trophozoite and cyst morphological forms were exposed to a panel of FITC-lectins. Population fluorescence associated with FITC-lectin binding to acanthamoebal surface moieties was ascertained by flow cytometry. Increasing concentrations of representative FITC-lectins, saturation binding and determination of K(d) and relative B(max) values were employed to characterize carbohydrate residue exposure. FITC-lectins specific for N-acetylglucosamine, N-acetylgalactosamine and mannose/glucose were readily bound by trophozoite and cyst surfaces. Minor incremental increases in FITC-lectin concentration resulted in significant differences in surface fluorescence intensity and supported the calculation of ligand-binding determinants, K(d) and relative B(max), which gave a trophozoite and cyst rank order of lectin affinity and surface receptor presence.

CONCLUSIONS

Trophozoites and cysts expose similar surface carbohydrate residues, foremost amongst which is N-acetylglucosamine, in varying orientation and availability.

SIGNIFICANCE AND IMPACT OF THE STUDY

The outlined versatile combination of flow cytometry and ligand-receptor analysis allowed the characterization of surface carbohydrate exposure by protozoan morphological forms and in turn will support a valid comparison of carbohydrate exposure by other single-cell protozoa and eucaryotic microbes analysed in the same manner.

HNF-1alpha G319S, a transactivation-deficient mutant, is associated with altered dynamics of diabetes onset in an Oji-Cree community

The prevalence of type 2 diabetes mellitus in the Oji-Cree of northwestern Ontario is the third highest in the world. A private mutation, G319S, in HNF1A, which encodes hepatic nuclear factor-1alpha (HNF-1alpha), was associated with Oji-Cree type 2 diabetes and was found in approximately 40% of affected subjects. The G319S mutation reduced the in vitro ability of HNF-1alpha to activate transcription by approximately 50%, with no effect on DNA binding or protein stability. There was no evidence of a dominant negative effect of the mutant protein. The impact of the G319S mutation at the population level was assessed by classifying subjects with type 2 diabetes according to HNF1A genotype and plotting the cumulative age of onset of diabetes. Disease onset was modeled satisfactorily by two-parameter sigmoidal functions for all diabetic subjects and all three HNF1A genotypes. Pairwise statistical comparisons showed significant between-genotype differences in t50 (all P < 0.00001), corresponding to the age at which half the subjects had become diabetic. Each dose of G319S accelerated median disease onset by approximately 7 years. Thus, the transactivation-deficient HNF1A G319S mutation affects the dynamics of disease onset. The demonstration of a functional consequence for HNF1A G319S provides a mechanistic basis for its strong association with Oji-Cree type 2 diabetes and its unparalleled specificity for diabetes prediction in these people, in whom diabetes presents a significant public health dilemma. The findings also show that HNF1A mutations can be associated with typical adult-onset insulin-resistant obesity-related diabetes in addition to maturity-onset diabetes of the young.

Human sterol 14alpha-demethylase activity is enhanced by the membrane-bound state of cytochrome b(5)

Human sterol 14alpha-demethylase (P45051; CYP51) catalyzes the oxidative removal of the C32 methyl group of dihydrolanosterol, an essential step in the cholesterol biosynthetic pathway. The reaction is dependent upon NADPH cytochrome P450 reductase (CPR) that donates the electrons for the catalytic cycle. Here we used a recombinant yeast CPR to investigate the abilities of four different forms of cytochrome b(5) to support sterol demethylation activity of CYP51. The cytochrome b(5) derivatives were genetically engineered forms of the native rat cytochrome b(5) core-tail: the soluble globular b(5) core (core), the core linked at its N-terminus with the secretory signal sequence of alkaline phosphatase (signal-core), and the signal sequence linked to the native b(5) (signal-core-tail). The rat core-tail enzyme greatly stimulated sterol demethylation, whereas the signal-core-tail was only marginally active. In contrast, the core and signal-core constructs were completely inactive in stimulating the demethylation reaction. Additionally, cytochrome b(5) enhanced sterol demethylation by more than threefold by accepting electrons from soluble yeast CPR and in its ability to reduce P450. We show that the nature of transient linkage between the hemoproteins and the redox partners is most likely brought about electrostatically, although productive interaction between cytochrome b(5) and CYP51 is governed by the membrane-insertable hydrophobic region in the cytochrome b(5) which in turn determines the correct spatial orientation of the core. This is the first report showing the stimulation of CYP51 by cytochrome b(5).

An old activity in the cytochrome P450 superfamily (CYP51) and a new story of drugs and resistance

Cytochrome P450 51 (CYP51) is sterol 14alpha-demethylase, known also as Erg11p in yeast. First studied in yeast, where it is one of three CYPs in the genome, it has subsequently gained attention as the only CYP found so far in different kingdoms of life. As such it is central to considerations of CYP evolution. Recent use of CYP51-inhibiting antifungal drugs, such as fluconazole, has also been associated with dramatic CYP51 evolution to numerous resistant forms in fungal pathogens. CYP51 has also been discovered in mycobacteria where antifungal azoles have effect and might be of value against tuberculosis. Evolutionary and therapeutic aspects of CYP51 studies are discussed.

Activities and kinetic mechanisms of native and soluble NADPH-cytochrome P450 reductase

Native yeast NADPH-cytochrome P450 oxidoreductase (CPR; EC 1.6.2.4) and a soluble derivative lacking 33 amino acids of the NH(2)-terminus have been overexpressed as recombinant proteins in Escherichia coli. The presence of a hexahistidine sequence at the N-terminus allowed protein purification in a single step using nickel-chelating affinity chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis confirmed the predicted molecular weights of the proteins and indicated a purity of >95%. Protein functionality was demonstrated by cytochrome c reduction and reconstitution of CYP61-mediated sterol Delta(22)-desaturation. Steady-state kinetics of cytochrome c reductase activity revealed a random Bi-Bi mechanism with NADPH donating electrons directly to CPR to produce a reduced intermediary form of the enzyme. The kinetic mechanism studies showed no difference between the two yeast CPRs in mechanism or after reconstitution with CYP61-mediated 22-desaturation, confirming that the retention of the NH(2)-terminable membrane anchor is functionally dispensable.