Linear mixed models to handle missing at random data in trial-based economic evaluations

Trial-based cost-effectiveness analyses (CEAs) are an important source of evidence in the assessment of health interventions. In these studies, cost and effectiveness outcomes are commonly measured at multiple time points, but some observations may be missing. Restricting the analysis to the participants with complete data can lead to biased and inefficient estimates. Methods, such as multiple imputation, have been recommended as they make better use of the data available and are valid under less restrictive Missing At Random (MAR) assumption. Linear mixed effects models (LMMs) offer a simple alternative to handle missing data under MAR without requiring imputations, and have not been very well explored in the CEA context. In this manuscript, we aim to familiarize readers with LMMs and demonstrate their implementation in CEA. We illustrate the approach on a randomized trial of antidepressants, and provide the implementation code in R and Stata. We hope that the more familiar statistical framework associated with LMMs, compared to other missing data approaches, will encourage their implementation and move practitioners away from inadequate methods.

Supporting People With Type 2 Diabetes in the Effective Use of Their Medicine Through Mobile Health Technology Integrated With Clinical Care to Reduce Cardiovascular Risk: Protocol for an Effectiveness and Cost-effectiveness Randomized Controlled Trial

BACKGROUND

Type 2 diabetes is a common lifelong condition that affects over 400 million people worldwide. The use of effective medications and active self-management can reduce the risk of serious complications. However, people often have concerns when starting new medications and face difficulties in taking their medications regularly. Support provided by brief messages delivered through mobile phone-based SMS text messages can be effective in some long-term conditions. We have identified promising behavior change techniques (BCTs) to promote medication adherence in this population via a systematic review and developed SMS text messages that target these BCTs. Feasibility work has shown that these messages have fidelity to intended BCTs, are acceptable to patients, and are successful in changing the intended determinants of medication adherence. We now plan to test this intervention on a larger scale in a clinical trial.

OBJECTIVE

The aim of this trial is to determine the effectiveness and cost-effectiveness of this intervention for reducing cardiovascular risk in people with type 2 diabetes by comparing it with usual care.

METHODS

The trial will be a 12-month, multicenter, individually randomized controlled trial in primary care and will recruit adults (aged ≥35 years) with type 2 diabetes in England. Consenting participants will be randomized to receive short SMS text messages intended to affect a change in medication adherence 3 to 4 times per week in addition to usual care. The aim is to test the effectiveness and cost-effectiveness of the intervention when it is added to usual care. The primary clinical outcome will be a composite cardiovascular risk measure. Data including patient-reported measures will be collected at baseline, at 13 and 26 weeks, and at the end of the 12-month follow-up period. With 958 participants (479 in each group), the trial is powered at 92.5% to detect a 4-percentage point difference in cardiovascular risk. The analysis will follow a prespecified plan. A nested quantitative and qualitative process analysis will be used to examine the putative mechanisms of behavior change and wider contextual influences. A health economic analysis will be used to assess the cost-effectiveness of the intervention.

RESULTS

The trial has completed the recruitment phase and is in the follow-up phase. The publication of results is anticipated in 2024.

CONCLUSIONS

This trial will provide evidence regarding the effectiveness and cost-effectiveness of this intervention for people with type 2 diabetes.

TRIAL REGISTRATION

ISRCTN Registry ISRCTN15952379; https://www.isrctn.com/ISRCTN15952379.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/32918.

The SANAD II study of the effectiveness and cost-effectiveness of levetiracetam, zonisamide, or lamotrigine for newly diagnosed focal epilepsy: an open-label, non-inferiority, multicentre, phase 4, randomised controlled trial

BACKGROUND

Levetiracetam and zonisamide are licensed as monotherapy for patients with focal epilepsy, but there is uncertainty as to whether they should be recommended as first-line treatments because of insufficient evidence of clinical effectiveness and cost-effectiveness. We aimed to assess the long-term clinical effectiveness and cost-effectiveness of levetiracetam and zonisamide compared with lamotrigine in people with newly diagnosed focal epilepsy.

METHODS

This randomised, open-label, controlled trial compared levetiracetam and zonisamide with lamotrigine as first-line treatment for patients with newly diagnosed focal epilepsy. Adult and paediatric neurology services across the UK recruited participants aged 5 years or older (with no upper age limit) with two or more unprovoked focal seizures. Participants were randomly allocated (1:1:1) using a minimisation programme with a random element utilising factor to receive lamotrigine, levetiracetam, or zonisamide. Participants and investigators were not masked and were aware of treatment allocation. SANAD II was designed to assess non-inferiority of both levetiracetam and zonisamide to lamotrigine for the primary outcome of time to 12-month remission. Anti-seizure medications were taken orally and for participants aged 12 years or older the initial advised maintenance doses were lamotrigine 50 mg (morning) and 100 mg (evening), levetiracetam 500 mg twice per day, and zonisamide 100 mg twice per day. For children aged between 5 and 12 years the initial daily maintenance doses advised were lamotrigine 1·5 mg/kg twice per day, levetiracetam 20 mg/kg twice per day, and zonisamide 2·5 mg/kg twice per day. All participants were included in the intention-to-treat (ITT) analysis. The per-protocol (PP) analysis excluded participants with major protocol deviations and those who were subsequently diagnosed as not having epilepsy. Safety analysis included all participants who received one dose of any study drug. The non-inferiority limit was a hazard ratio (HR) of 1·329, which equates to an absolute difference of 10%. A HR greater than 1 indicated that an event was more likely on lamotrigine. The trial is registered with the ISRCTN registry, 30294119 (EudraCt number: 2012-001884-64).

FINDINGS

990 participants were recruited between May 2, 2013, and June 20, 2017, and followed up for a further 2 years. Patients were randomly assigned to receive lamotrigine (n=330), levetiracetam (n=332), or zonisamide (n=328). The ITT analysis included all participants and the PP analysis included 324 participants randomly assigned to lamotrigine, 320 participants randomly assigned to levetiracetam, and 315 participants randomly assigned to zonisamide. Levetiracetam did not meet the criteria for non-inferiority in the ITT analysis of time to 12-month remission versus lamotrigine (HR 1·18; 97·5% CI 0·95-1·47) but zonisamide did meet the criteria for non-inferiority in the ITT analysis versus lamotrigine (1·03; 0·83-1·28). The PP analysis showed that 12-month remission was superior with lamotrigine than both levetiracetam (HR 1·32 [97·5% CI 1·05 to 1·66]) and zonisamide (HR 1·37 [1·08-1·73]). There were 37 deaths during the trial. Adverse reactions were reported by 108 (33%) participants who started lamotrigine, 144 (44%) participants who started levetiracetam, and 146 (45%) participants who started zonisamide. Lamotrigine was superior in the cost-utility analysis, with a higher net health benefit of 1·403 QALYs (97·5% central range 1·319-1·458) compared with 1·222 (1·110-1·283) for levetiracetam and 1·232 (1·112, 1·307) for zonisamide at a cost-effectiveness threshold of £20 000 per QALY. Cost-effectiveness was based on differences between treatment groups in costs and QALYs.

INTERPRETATION

These findings do not support the use of levetiracetam or zonisamide as first-line treatments for patients with focal epilepsy. Lamotrigine should remain a first-line treatment for patients with focal epilepsy and should be the standard treatment in future trials.

FUNDING

National Institute for Health Research Health Technology Assessment programme.

The SANAD II study of the effectiveness and cost-effectiveness of valproate versus levetiracetam for newly diagnosed generalised and unclassifiable epilepsy: an open-label, non-inferiority, multicentre, phase 4, randomised controlled trial

BACKGROUND

Valproate is a first-line treatment for patients with newly diagnosed idiopathic generalised or difficult to classify epilepsy, but not for women of child-bearing potential because of teratogenicity. Levetiracetam is increasingly prescribed for these patient populations despite scarcity of evidence of clinical effectiveness or cost-effectiveness. We aimed to compare the long-term clinical effectiveness and cost-effectiveness of levetiracetam compared with valproate in participants with newly diagnosed generalised or unclassifiable epilepsy.

METHODS

We did an open-label, randomised controlled trial to compare levetiracetam with valproate as first-line treatment for patients with generalised or unclassified epilepsy. Adult and paediatric neurology services (69 centres overall) across the UK recruited participants aged 5 years or older (with no upper age limit) with two or more unprovoked generalised or unclassifiable seizures. Participants were randomly allocated (1:1) to receive either levetiracetam or valproate, using a minimisation programme with a random element utilising factors. Participants and investigators were aware of treatment allocation. For participants aged 12 years or older, the initial advised maintenance doses were 500 mg twice per day for levetiracetam and valproate, and for children aged 5-12 years, the initial daily maintenance doses advised were 25 mg/kg for valproate and 40 mg/kg for levetiracetam. All drugs were administered orally. SANAD II was designed to assess the non-inferiority of levetiracetam compared with valproate for the primary outcome time to 12-month remission. The non-inferiority limit was a hazard ratio (HR) of 1·314, which equates to an absolute difference of 10%. A HR greater than 1 indicated that an event was more likely on valproate. All participants were included in the intention-to-treat (ITT) analysis. Per-protocol (PP) analyses excluded participants with major protocol deviations and those who were subsequently diagnosed as not having epilepsy. Safety analyses included all participants who received one dose of any study drug. This trial is registered with the ISRCTN registry, 30294119 (EudraCt number: 2012-001884-64).

FINDINGS

520 participants were recruited between April 30, 2013, and Aug 2, 2016, and followed up for a further 2 years. 260 participants were randomly allocated to receive levetiracetam and 260 participants to receive valproate. The ITT analysis included all participants and the PP analysis included 255 participants randomly allocated to valproate and 254 randomly allocated to levetiracetam. Median age of participants was 13·9 years (range 5·0-94·4), 65% were male and 35% were female, 397 participants had generalised epilepsy, and 123 unclassified epilepsy. Levetiracetam did not meet the criteria for non-inferiority in the ITT analysis of time to 12-month remission (HR 1·19 [95% CI 0·96-1·47]); non-inferiority margin 1·314. The PP analysis showed that the 12-month remission was superior with valproate than with levetiracetam. There were two deaths, one in each group, that were unrelated to trial treatments. Adverse reactions were reported by 96 (37%) participants randomly assigned to valproate and 107 (42%) participants randomly assigned to levetiracetam. Levetiracetam was dominated by valproate in the cost-utility analysis, with a negative incremental net health benefit of -0·040 (95% central range -0·175 to 0·037) and a probability of 0·17 of being cost-effectiveness at a threshold of £20 000 per quality-adjusted life-year. Cost-effectiveness was based on differences between treatment groups in costs and quality-adjusted life-years.

INTERPRETATION

Compared with valproate, levetiracetam was found to be neither clinically effective nor cost-effective. For girls and women of child-bearing potential, these results inform discussions about benefit and harm of avoiding valproate.

FUNDING

National Institute for Health Research Health Technology Assessment Programme.

Adalimumab in combination with methotrexate for refractory uveitis associated with juvenile idiopathic arthritis: a RCT

BACKGROUND

Children with juvenile idiopathic arthritis (JIA) are at risk of uveitis. The role of adalimumab (Humira^®; AbbVie Inc., Ludwigshafen, Germany) in the management of uveitis in children needs to be determined.

OBJECTIVE

To compare the efficacy, safety and cost-effectiveness of adalimumab in combination with methotrexate (MTX) versus placebo with MTX alone, with regard to controlling disease activity in refractory uveitis associated with JIA.

DESIGN

This was a randomised (applying a ratio of 2 : 1 in favour of adalimumab), double-blind, placebo-controlled, multicentre parallel-group trial with an integrated economic evaluation. A central web-based system used computer-generated tables to allocate treatments. A cost-utility analysis based on visual acuity was conducted and a 10-year extrapolation by Markov modelling was also carried out.

SETTING

The setting was tertiary care centres throughout the UK.

PARTICIPANTS

Patients aged 2-18 years inclusive, with persistently active JIA-associated uveitis (despite optimised MTX treatment for at least 12 weeks).

INTERVENTIONS

All participants received a stable dose of MTX and either adalimumab (20 mg/0.8 ml for patients weighing < 30 kg or 40 mg/0.8 ml for patients weighing ≥ 30 kg by subcutaneous injection every 2 weeks based on body weight) or a placebo (0.8 ml as appropriate according to body weight by subcutaneous injection every 2 weeks) for up to 18 months. A follow-up appointment was arranged at 6 months.

MAIN OUTCOME MEASURES

Primary outcome - time to treatment failure [multicomponent score as defined by set criteria based on the Standardisation of Uveitis Nomenclature (SUN) criteria]. Economic outcome - incremental cost per quality-adjusted life-year (QALY) gained from the perspective of the NHS in England and Personal Social Services providers. Full details of secondary outcomes are provided in the study protocol.

RESULTS

A total of 90 participants were randomised (adalimumab, n = 60; placebo, n = 30). There were 14 (23%) treatment failures in the adalimumab group and 17 (57%) in the placebo group. The analysis of the data from the double-blind phase of the trial showed that the hazard risk (HR) of treatment failure was significantly reduced, by 75%, for participants in the adalimumab group (HR 0.25, 95% confidence interval 0.12 to 0.51; p < 0.0001 from log-rank test). The cost-effectiveness of adalimumab plus MTX was £129,025 per QALY gained. Adalimumab-treated participants had a much higher incidence of adverse and serious adverse events.

CONCLUSIONS

Adalimumab in combination with MTX is safe and effective in the management of JIA-associated uveitis. However, the likelihood of cost-effectiveness is < 1% at the £30,000-per-QALY threshold.

FUTURE WORK

A clinical trial is required to define the most effective time to stop therapy. Prognostic biomarkers of early and complete response should also be identified.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN10065623 and European Clinical Trials Database number 2010-021141-41.

FUNDING

This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in Health Technology Assessment; Vol. 23, No. 15. See the NIHR Journals Library website for further project information. This trial was also funded by Arthritis Research UK (grant reference number 19612). Two strengths of adalimumab (20 mg/0.8 ml and 40 mg/0.8 ml) and a matching placebo were manufactured by AbbVie Inc. (the Marketing Authorisation holder) and supplied in bulk to the contracted distributor (Sharp Clinical Services, Crickhowell, UK) for distribution to trial centres.

Study protocol for a pragmatic randomised controlled trial comparing the effectiveness and cost-effectiveness of levetiracetam and zonisamide versus standard treatments for epilepsy: a comparison of standard and new antiepileptic drugs (SANAD-II)

INTRODUCTION

Antiepileptic drugs (AEDs) are the mainstay of epilepsy treatment. Over the past 20 years, a number of new drugs have been approved for National Health Service (NHS) use on the basis of information from short-term trials that demonstrate efficacy. These trials do not provide information about the longer term outcomes, which inform treatment policy. This trial will assess the long-term clinical and cost-effectiveness of the newer treatment levetiracetam and zonisamide.

METHODS AND ANALYSIS

This is a phase IV, multicentre, open-label, randomised, controlled clinical trial comparing new and standard treatments for patients with newly diagnosed epilepsy. Arm A of the trial randomised 990 patients with focal epilepsy to standard AED lamotrigine or new AED levetiracetam or zonisamide. Arm B randomised 520 patients with generalised epilepsy to standard AED sodium valproate or new AED levetiracetam. Patients are recruited from UK NHS outpatient epilepsy, general neurology and paediatric clinics. Included patients are aged 5 years or older with two or more spontaneous seizures requiring AED monotherapy, who are not previously treated with AEDs. Patients are followed up for a minimum of 2 years. The primary outcome is time to 12-month remission from seizures. Secondary outcomes include time to treatment failure (including due to inadequate seizure control or unacceptable adverse reactions); time to first seizure; time to 24-month remission; adverse reactions and quality of life. All primary analyses will be on an intention to treat basis. Separate analyses will be undertaken for each arm. Health economic analysis will be conducted from the perspective of the NHS to assess the cost-effectiveness of each AED.

ETHICS AND DISSEMINATION

This trial has been approved by the North West-Liverpool East REC (Ref. 12/NW/0361). The trial team will disseminate the results through scientific meetings, peer-reviewed publications and patient and public involvement.

TRIAL REGISTRATION NUMBERS

EudraCT 2012-001884-64; ISRCTN30294119.

Patient-Focused Drug Development Methods for Benefit-Risk Assessments: A Case Study Using a Discrete Choice Experiment for Antiepileptic Drugs

Regulatory decisions may be enhanced by incorporating patient preferences for drug benefit and harms. This study demonstrates a method of weighting clinical evidence by patients’ benefit–risk preferences. Preference weights, derived from discrete choice experiments, were applied to clinical trial data to estimate the expected utility of alternative drugs. In a case study, the rank ordering of antiepileptic drugs (AEDs), as indicated from clinical studies, was compared with ordering based on weighting clinical evidence by patients’ preferences. A statistically significant change in rank ordering of AEDs was observed for women of childbearing potential who were prescribed monotherapy for generalized or unclassified epilepsy. Rank ordering inferred from trial data, valproate > topiramate > lamotrigine, was reversed. Modeling the expected utility of drugs might address the need to use more systematic, methodologically sound approaches to collect patient input that can further inform regulatory decision making.

PET-PANC: multicentre prospective diagnostic accuracy and health economic analysis study of the impact of combined modality 18fluorine-2-fluoro-2-deoxy-d-glucose positron emission tomography with computed tomography scanning in the diagnosis and management of pancreatic cancer

BACKGROUND

Pancreatic cancer diagnosis and staging can be difficult in 10-20% of patients. Positron emission tomography (PET)/computed tomography (CT) adds precise anatomical localisation to functional data. The use of PET/CT may add further value to the diagnosis and staging of pancreatic cancer.

OBJECTIVE

To determine the incremental diagnostic accuracy and impact of PET/CT in addition to standard diagnostic work-up in patients with suspected pancreatic cancer.

DESIGN

A multicentre prospective diagnostic accuracy and clinical value study of PET/CT in suspected pancreatic malignancy.

PARTICIPANTS

Patients with suspected pancreatic malignancy.

INTERVENTIONS

All patients to undergo PET/CT following standard diagnostic work-up.

MAIN OUTCOME MEASURES

The primary outcome was the incremental diagnostic value of PET/CT in addition to standard diagnostic work-up with multidetector computed tomography (MDCT). Secondary outcomes were (1) changes in patients' diagnosis, staging and management as a result of PET/CT; (2) changes in the costs and effectiveness of patient management as a result of PET/CT; (3) the incremental diagnostic value of PET/CT in chronic pancreatitis; (4) the identification of groups of patients who would benefit most from PET/CT; and (5) the incremental diagnostic value of PET/CT in other pancreatic tumours.

RESULTS

Between 2011 and 2013, 589 patients with suspected pancreatic cancer underwent MDCT and PET/CT, with 550 patients having complete data and in-range PET/CT. Sensitivity and specificity for the diagnosis of pancreatic cancer were 88.5% and 70.6%, respectively, for MDCT and 92.7% and 75.8%, respectively, for PET/CT. The maximum standardised uptake value (SUVmax.) for a pancreatic cancer diagnosis was 7.5. PET/CT demonstrated a significant improvement in relative sensitivity (p = 0.01) and specificity (p = 0.023) compared with MDCT. Incremental likelihood ratios demonstrated that PET/CT significantly improved diagnostic accuracy in all scenarios (p < 0.0002). PET/CT correctly changed the staging of pancreatic cancer in 56 patients (p = 0.001). PET/CT influenced management in 250 (45%) patients. PET/CT stopped resection in 58 (20%) patients who were due to have surgery. The benefit of PET/CT was limited in patients with chronic pancreatitis or other pancreatic tumours. PET/CT was associated with a gain in quality-adjusted life-years of 0.0157 (95% confidence interval -0.0101 to 0.0430). In the base-case model PET/CT was seen to dominate MDCT alone and is thus highly likely to be cost-effective for the UK NHS. PET/CT was seen to be most cost-effective for the subgroup of patients with suspected pancreatic cancer who were thought to be resectable.

CONCLUSION

PET/CT provided a significant incremental diagnostic benefit in the diagnosis of pancreatic cancer and significantly influenced the staging and management of patients. PET/CT had limited utility in chronic pancreatitis and other pancreatic tumours. PET/CT is likely to be cost-effective at current reimbursement rates for PET/CT to the UK NHS. This was not a randomised controlled trial and therefore we do not have any information from patients who would have undergone MDCT only for comparison. In addition, there were issues in estimating costs for PET/CT. Future work should evaluate the role of PET/CT in intraductal papillary mucinous neoplasm and prognosis and response to therapy in patients with pancreatic cancer.

STUDY REGISTRATION

Current Controlled Trials ISRCTN73852054 and UKCRN 8166.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Renal transplant patients' preference for the supply and delivery of immunosuppressants in Wales: a discrete choice experiment

BACKGROUND

Prescribing policy recommendations aimed at moving immunosuppressant prescribing for renal transplant patients from primary to secondary care may result in benefits of increased safety and reduced cost. However, there is little evidence of patients' preferences for receiving their immunosuppressant therapy from hospitals compared to community dispensing. The aim of this study was to elicit patient preferences for different service configurations focusing in particular on home delivery versus collection of medication from hospital.

METHODS

A discrete choice experiment was administered to 265 renal transplant patients in North Wales. Respondents were presented 18 pairwise choices, labelled as either home delivery or hospital collection, and described by the attributes: frequency of supply, waiting time (for delivery or collection) and method of ordering (provider contact, patient contact via phone, patient contact electronically). Data were analysed using a random-effects logit model and marginal rates of substitution calculated based on the waiting time attribute.

RESULTS

A response rate of 63% was achieved, with 5332 usable observations from 150 respondents. Method of delivery (β coefficient 1.21; 95% confidence interval 1.05 to 1.38), frequency of supply (0.05; 0.03 to 0.08) waiting time (-0.00, -0.00 to -0.00), provider contact (desirable) (0.20; 0.12 to 0.27), patient contact by telephone (desirable) (0.09; 0.01 to 0.17) and patient contact electronically (undesirable) (-0.292; -0.37 to -0.21) were statistically significant (p < 0.05). Results indicate that patients are willing to increase waiting time by nearly 10 h to have a home delivery service.

CONCLUSION

Patients indicate a clear preference for a home delivery service. They prefer providers to make contact when new immunosuppressant supplies are required and show preference against ordering medication electronically. A policy for secondary care prescribing and hospital collection of medicines does not align with this preference.

Conducting Economic Evaluations Alongside Randomised Trials: Current Methodological Issues and Novel Approaches

Trial-based economic evaluations are an important aspect of health technology assessment. The availability of patient-level data coupled with unbiased estimates of clinical outcomes means that randomised controlled trials are effective vehicles for the generation of economic data. However there are methodological challenges to trial-based evaluations, including the collection of reliable data on resource use and cost, choice of health outcome measure, calculating minimally important differences, dealing with missing data, extrapolating outcomes and costs over time and the analysis of multinational trials. This review focuses on the state of the art of selective elements regarding the design, conduct, analysis and reporting of trial-based economic evaluations. The limitations of existing approaches are detailed and novel methods introduced. The review is internationally relevant but with a focus towards practice in the UK.

Adherence of patients to long-term medication: a cross-sectional study of antihypertensive regimens in Austria

OBJECTIVE

The objective of this study was to evaluate adherence and causes for non-adherence to antihypertensive therapy in Austrian patients. A special focus was placed on social parameters and behavioural theories.

METHODS

Patients were invited via advertisements in community pharmacies in Austria to complete an online survey. Inclusion criteria were an age of 18 years or older, a diagnosis of arterial hypertension and a current prescription of antihypertensive medication. Adherence was measured by the four-item Morisky scale. Non-adherence was defined by at least one point in the Morisky scale. Several demographic, social and behavioural parameters were analysed as potential co-variables associated with adherence.

RESULTS

A total of 323 patients completed the online survey, of which 109 (33.7%) met the criteria for non-adherence. In a multivariable model, self-efficacy and age were associated with adherence, whereas intention and barriers were linked to non-adherence; 56 patients (17.3%) were classified as intentionally non-adherent.

CONCLUSION

This study demonstrates that non-adherence affects an important proportion of patients in the treatment of arterial hypertension. Young age was a particularly important risk factor for non-adherence, and this patient population is, therefore, in need of special attention. Modifiable risk factors were identified that could help improving the treatment of arterial hypertension and potentially other chronic conditions.

Investigating preferences for support with life after stroke: a discrete choice experiment

Background

There is little evidence of service user preferences to guide the commissioning and improvement of services that support life after stroke. We report the first investigation of patients’ and family carers’ preferences for community services after stroke using a discrete choice experiment (DCE).

Methods

Two workshops with patients and family carers (n = 8) explored stroke experiences, identifying attributes important in shaping views about service design, and piloted data collection strategies. Attributes were group versus individual support; service provider; additional support for social and leisure activities; and the total time required to access services. Patients and family carers were recruited six months post stroke-onset (mean 331 days) from four stroke services, and invited to participate in the DCE. Patients’ general health (EQ5D) and functional dependence (Barthel Index) were also assessed. Of 474 eligible patients, 144 (30%) expressed an interest in the study, and 80 (56%) of these completed the survey questionnaire. 34 of 74 (46%) family carers recruited through patients completed the DCE.

Results

All four attributes were significant in shaping patients preferences for stroke support service delivery (p < 0.05), confirming the interpretation of workshop findings. Patients prefer help and support for emotional needs, communication problems and physical difficulties to be provided on an individual basis; and to be offered additional social and leisure activities that they are able to attend on their own. Patients would appear to prefer that voluntary organisations do not provide these services, although this may be linked to lack of experience of these services. Family carers would prefer help and support in their caring role on a one-to-one basis. Whilst health related quality of life is associated with preference for format of service, results were relatively consistent across sub-groups, with the exception of time since stroke, where social and leisure activities had a greater impact on preferences of established service users.

Conclusions

The data provide unique insights into how preferences for community services that support life after stroke are shaped. This information can be used to inform both service re-design, and barriers to implementation that will need to be accounted for in policy shifts towards a more mixed economy of service provision.

Sodium channel Nav1.8 immunoreactivity in painful human dental pulp

BACKGROUND

The tetrodotoxin-resistant voltage-gated sodium channel Nav1.8 (SNS1/PN3) is expressed by nociceptors and may play a role in pain states.

METHODS

Using specific antibodies for immunohistochemistry, we studied Nav1.8 immunoreactivity in human dental pulp in relation to the neuronal marker neurofilament. Human tooth pulp was extracted from teeth harvested from a total of twenty-two patients (fourteen without dental pain, eight patients with dental pain).

RESULTS

Fibres immunoreactive for Nav1.8, were significantly increased on image analysis in the painful group: median (range) Nav1.8 to Neurofilament % area ratio, non-painful 0.059 (0.006-0.24), painful 0.265 (0.13-0.5), P = 0.0019.

CONCLUSION

Nav1.8 sodium channels may thus represent a therapeutic target in trigeminal nerve pain states.

Calcium-activated potassium channel SK1- and IK1-like immunoreactivity in injured human sensory neurones and its regulation by neurotrophic factors

Calcium-activated potassium ion channels SK and IK (small and intermediate conductance, respectively) may be important in the pathophysiology of pain following nerve injury, as SK channels are known to impose a period of reduced excitability after each action potential by afterhyperpolarization. We studied the presence and changes of human SK1 (hSK1)- and hIK1-like immunoreactivity in control and injured human dorsal root ganglia (DRG) and peripheral nerves and their regulation by key neurotrophic factors in cultured rat sensory neurones. Using specific antibodies, hSK-1 and hIK-1-like immunoreactivity was detected in a majority of large and small/medium-sized cell bodies of human DRG. hSK1 immunoreactivity was decreased significantly in cell bodies of avulsed human DRG (n = 8, surgery delay 8 h to 12 months). There was a decrease in hIK1-like immunoreactivity predominantly in large cells acutely (<3 weeks after injury), but also in small/medium cells of chronic cases. Twenty-three injured peripheral nerves were studied (surgery delay 8 h to 12 months); in five of these, hIK1-like immunoreactivity was detected proximally but not distally to injury, whereas neurofilament staining confirmed the presence of nerve fibres in both regions. These five nerves, unlike the others, had all undergone Wallerian degeneration previously and the loss of hIK1-like immunoreactivity may therefore reflect reduced axonal transport of this ion channel across the injury site in regenerated fibres, as well as decreased expression in the cell body. In vitro studies of neonatal rat DRG neurones showed that nerve growth factor (NGF) significantly increased the percentage of hSK1-positive cells, whereas neurotrophin 3 (NT-3) and glial cell line-derived neurotrophic factor (GDNF) failed to show a significant effect. NT-3 stimulated hIK1 expression, while NGF and GDNF were ineffective. As expected, NGF increased expression of the voltage-gated sodium channel SNS1/PN3 in this system. Decreased retrograde transport of these neurotrophic factors in injured sensory neurones may thus reduce expression of these ion channels and increase excitability. Blockade of IK1-like and other potassium channels by aminopyridines (4-AP and 3,4-DAP) may also explain the paraesthesiae induced by these medications. Selective potassium channel openers are likely to represent novel therapies for pain following nerve injury.

Distribution of the messenger RNA for the small conductance calcium-activated potassium channel SK3 in the adult rat brain and correlation with immunoreactivity

Small conductance calcium-activated potassium channels are voltage independent potassium channels which modulate the firing patterns of neurons by activating the slow component of the afterhyperpolarization. The genes encoding a family of small conductance calcium-activated potassium channels have been cloned and up to now three known members have been described and named small conductance calcium-activated potassium channel type 1, small conductance calcium-activated potassium channel type 2 and small conductance calcium-activated potassium channel type 3; the distribution of their messenger RNA in the rat CNS has already been performed but only in a limited detail. The present study represents the first detailed analysis of small conductance calcium-activated potassium channel type 3 mRNA distribution in the adult rat brain and resulted in a strong to moderate expression of signal in medial habenular nucleus, substantia nigra compact part, suprachiasmatic nucleus, ventral tegmental area, lateral septum, dorsal raphe and locus coeruleus. Immunohistological experiments were also performed and confirmed the presence of small conductance calcium-activated potassium channel type 3 protein in medial habenular nucleus, locus coeruleus and dorsal raphe. Given the importance of dorsal raphe, locus coeruleus and substantia nigra/ventral tegmental area for serotonergic, noradrenergic and dopaminergic transmission respectively, our results pose the morphological basis for further studies on the action of small conductance calcium-activated potassium channel type 3 in serotonergic, noradrenergic and dopaminergic transmission.

Sodium channel beta1 and beta2 subunits parallel SNS/PN3 alpha-subunit changes in injured human sensory neurons

Voltage-gated sodium channels consist of a pore-containing alpha-subunit and one or more auxiliary beta-subunits, which may modulate channel function. We previously demonstrated that sodium channel SNS/PN3 alpha-subunits were decreased in human sensory cell bodies after spinal root avulsion injury, and accumulated at injured nerve terminals in pain states. Using specific antibodies for immunohistochemistry, we have now detected sodium channel beta1 and beta2 subunits in sensory cell bodies within control human postmortem sensory ganglia (78% of small/medium (< or = 50 microm) and 68% of large (> or = 50 microm) cells); their changes in cervical sensory ganglia after avulsion injury paralleled those described for SNS/PN3 alpha-subunits. Our results suggest that alpha- and beta-subunits share common regulatory mechanisms, but present distinct targets for novel analgesics.

Plasticity of TTX-sensitive sodium channels PN1 and brain III in injured human nerves

Sensory neurones co-express voltage-gated sodium channels that mediate TTX-sensitive (TTX-S) and TTX-resistant (TTX-R) currents, which may contribute to chronic pain after nerve injury. We previously demonstrated that TTX-R channels were decreased acutely in human sensory cell bodies after central axotomy, but accumulated in nerve terminals after peripheral axotomy. We have now studied the TTX-S channels PN1 and Brain III, using specific antibodies for immunohistochemistry, in dorsal root ganglia (DRG) from 10 patients with traumatic central axotomy, nerves from 16 patients with peripheral axotomy, and controls. PN1 showed temporal changes similar to the TTX-R channels in sensory cell bodies of injured DRG. In contrast, Brain III was found only in injured nerves (not control nerves, or control/central axotomy DRG). PNI and Brain III are distinct targets for novel analgesics.

Identification and characterization of a novel human vanilloid receptor-like protein, VRL-2

Remarkable progress has been made recently in identifying a new gene family related to the capsaicin (vanilloid) receptor, VR1. Using a combination of in silico analysis of expressed sequence tag (EST) databases and conventional molecular cloning, we have isolated a novel vanilloid-like receptor, which we call VRL-2, from human kidney. The translated gene shares 46% and 43% identity with VR1 and VRL-1, respectively, and maps to chromosome 12q23-24.1, a locus associated with bipolar affective disorder. VRL-2 mRNA was most strongly expressed in the trachea, kidney, and salivary gland. An affinity-purified antibody against a peptide incorporating the COOH terminal of the receptor localized VRL-2 immunolabel in the distal tubules of the kidney, the epithelial linings of both trachea and lung airways, serous cells of submucosal glands, and mononuclear cells. Unlike VR1 and VRL-1, VRL-2 was not detected in cell bodies of dorsal root ganglia (DRG) or sensory nerve fibers. However, VRL-2 was found on sympathetic and parasympathetic nerve fibers, such as those innervating the arrector pili smooth muscle in skin, sweat glands, intestine, and blood vessels. At least four vanilloid receptor-like genes exist, the newest member, VRL-2 is found in airway and kidney epithelia and in the autonomic nervous system.

Endothelin receptor antagonism in patients with chronic heart failure

OBJECTIVE

The relative importance of ETA and ETB receptors in mediating the constrictor effects of endogenous endothelin-1 in patients with chronic heart failure is not known. The primary purpose of this study was to compare the acute effects of selective ETA and ETB receptor antagonists in vivo in healthy subjects and patients with chronic heart failure. Our secondary aim was to examine more closely the effect of chronic heart failure on endothelin biosynthesis.

METHODS

We studied the effects of BQ-123 (a selective ETA antagonist) and BQ-788 (a selective ETB antagonist) in ten healthy subjects and ten patients with chronic heart failure. Locally active doses of each antagonist were infused into the non-dominant brachial artery for 90 min on separate days at least 1 week apart. Changes in forearm blood flow were measured by venous occlusion plethysmography. Venous blood samples were obtained prior to antagonist infusion for assay of total endothelin, big endothelin-1 and C-terminal fragment immunoreactivity.

RESULTS

BQ-123 (100 nmol/min) increased blood flow by 54+/-10% (P<0.001) and 30+/-5% (P<0.001) in controls and heart failure patients, respectively. BQ-788 (1 nmol/min) reduced blood flow by 15+/-5% (P=0. 036) and 9+/-4% (P=0.001) in controls and heart failure patients, respectively. Total endothelin immunoreactivity was non significantly greater in heart failure patients than controls (6. 8+/-1.4 vs. 4.6+/-0.5 pM; P=0.13). Big endothelin-1 (2.6+/-0.4 vs. 1. 7+/-0.1 pM; P=0.04) and C-terminal fragment immunoreactivity (2. 1+/-0.3 vs. 0.6+/-0.1 pM; P<0.0001) were each significantly greater in heart failure patients than controls.

CONCLUSIONS

Selective ETA receptor antagonism caused vasodilatation in the peripheral circulation of healthy subjects and patients with chronic heart failure while selective ETB receptor antagonism caused vasoconstriction in each group. ETB receptor antagonism may therefore cause potentially deleterious vasoconstriction in chronic heart failure. Chronic heart failure is associated with a significant increase in plasma big endothelin-1 and C-terminal fragment immunoreactivity.

Tollip, a new component of the IL-1RI pathway, links IRAK to the IL-1 receptor

Interleukin-1 (IL-1) is a proinflammatory cytokine that elicits its pleiotropic effects through activation of the transcription factors NF-kappaB and AP-1. Binding of IL-1 to its receptor results in rapid assembly of a membrane-proximal signalling complex that consists of two different receptor chains (IL-1Rs), IL-1RI and IL-1RAcP, the adaptor protein MyD88, the serine/threonine kinase IRAK and a new protein, which we have named Tollip. Here we show that, before IL-1beta treatment, Tollip is present in a complex with IRAK, and that recruitment of Tollip-IRAK complexes to the activated receptor complex occurs through association of Tollip with IL-1RAcP. Co-recruited MyD88 then triggers IRAK autophosphorylation, which in turn leads to rapid dissociation of IRAK from Tollip (and IL-1Rs). As overexpression of Tollip results in impaired NF-kappaB activation, we conclude that Tollip is an important constituent of the IL-1R signalling pathway.

Diversity of expression of the sensory neuron-specific TTX-resistant voltage-gated sodium ion channels SNS and SNS2

The differential distribution of two tetrodotoxin resistant (TTXr) voltage-gated sodium channels SNS (PN3) and SNS2 (NaN) in rat primary sensory neurons has been investigated. Both channels are sensory neuron specific with SNS2 restricted entirely to those small dorsal root ganglion (DRG) cells with unmyelinated axons (C-fibers). SNS, in contrast, is expressed both in small C-fiber DRG cells and in 10% of cells with myelinated axons (A-fibers). All SNS expressing A-fiber cells are Trk-A positive and many express the vanilloid-like receptor VRL1. About half of C-fiber DRG neurons express either SNS or SNS2, and in most, the channels are colocalized. SNS and SNS2 are found both in NGF-responsive and GDNF-responsive C-fibers and many of these cells also express the capsaicin receptor VR1. A very small proportion of small DRG cells express either only SNS or only SNS2. At least four different classes of A- and C-fiber DRG neurons exist, therefore, with respect to expression of these sodium channels.

Immunolocalization of SNS/PN3 and NaN/SNS2 sodium channels in human pain states

The tetrodotoxin-resistant (TTX-R) voltage-gated sodium channel SNS/PN3 and the newly discovered NaN/SNS2 are expressed in sensory neurones, particularly in nociceptors. Using specific antibodies, we have studied, for the first time in humans, the presence of SNS/PN3 and NaN/SNS2 in peripheral nerves, including tissues from patients with chronic neurogenic pain. In brachial plexus injury patients, there was an acute decrease of SNS/PN3- and NaN/SNS2-like immunoreactivity in sensory cell bodies of cervical dorsal root ganglia (DRG) whose central axons had been avulsed from spinal cord, with gradual return of the immunoreactivity to control levels over months. In contrast, there was increased intensity of immunoreactivity to both channels in some peripheral nerve fibers just proximal to the site of injury in brachial plexus trunks, and in neuromas. These findings suggest that the expression of these sodium channels in neuronal cell bodies is reduced after spinal cord root avulsion injury in man, but that pre-synthesized channel proteins may undergo translocation with accumulation at sites of nerve injury, as in animal models of peripheral axotomy. The latter may contribute to positive symptoms, as our patients all showed a positive Tinel's sign. Nerve terminals in distal limb neuromas and skin from patients with chronic local hyperalgesia and allodynia all showed marked increases of SNS/PN3-immunoreactive fibers, but little or no NaN/SNS2-immunoreactivity, suggesting that the former may be related to the persistent hypersensitive state. Axonal immunoreactivity to both channels was similar to control nerves in sural nerve biopsies in a selection of neuropathies, irrespective of nerve inflammation, demyelination or spontaneous pain, including a patient with congenital insensitivity to pain. Our studies suggest that the best target for SNS/PN3 blocking agents is likely to be chronic local hypersensitivity.

Localization of the type VI voltage-gated sodium channel protein in human CNS

The cellular distribution of the type VI human voltage-gated sodium channel (Type VI) was examined in selected human brain regions. Antibodies designed to be specific to rat and human Type VI were raised against a synthetic peptide from the predicted NH2-terminal of the protein, and used for an immunohistochemical investigation. Immunoblot experiments showed that purified antibodies specifically detected the presence of Type VI in transfected cells and human brain membrane preparations. Immunohistochemistry on perfusion fixed human tissue revealed a predominantly somato-dendritic distribution of Type VI in major output neurons of the cerebellum, cerebral cortex and hippocampus. The observed localisation of this channel may reflect an important role in the integration of synaptic input in the human CNS.

Upregulation of a silent sodium channel after peripheral, but not central, nerve injury in DRG neurons

After transection of their axons within the sciatic nerve, DRG neurons become hyperexcitable. Recent studies have demonstrated the emergence of a rapidly repriming tetrodotoxin (TTX)-sensitive sodium current that may account for this hyperexcitability in axotomized small (<27 microm diam) DRG neurons, but its molecular basis has remained unexplained. It has been shown previously that sciatic nerve transection leads to an upregulation of sodium channel III transcripts, which normally are present at very low levels in DRG neurons, in adult rats. We show here that TTX-sensitive currents in small DRG neurons, after transection of their peripheral axonal projections, reprime more rapidly than those in control neurons throughout a voltage range of -140 to -60 mV, a finding that suggests that these currents are produced by a different sodium channel. After transection of the central axonal projections (dorsal rhizotomy) of these small DRG neurons, in contrast, the repriming kinetics of TTX-sensitive sodium currents remain similar to those of control (uninjured) neurons. We also demonstrate, with two distinct antibodies directed against different regions of the type III sodium channel, that small DRG neurons display increased brain type III immunostaining when studied 7-12 days after transection of their peripheral, but not central, projections. Type III sodium channel immunoreactivity is present within somata and neurites of peripherally axotomized, but not centrally axotomized, neurons studied after <24 h in vitro. Peripherally axotomized DRG neurons in situ also exhibit enhanced type III staining compared with control neurons, including an accumulation of type III sodium channels in the distal portion of the ligated and transected sciatic nerve, but these changes are not seen in centrally axotomized neurons. These observations are consistent with a contribution of type III sodium channels to the rapidly repriming sodium currents observed in peripherally axotomized DRG neurons and suggest that type III channels may at least partially account for the hyperexcitibility of these neurons after injury.

Differential distribution of endothelin peptides and receptors in human adrenal gland

Sub-type selective ligands revealed a differential distribution of endothelin (ET) receptors within human adrenal glands. High densities of ETA receptors were localized, using [125I]-PD151242, to the smooth muscle layer of the arteries, smaller vessels within the capsular plexus and to the secretory cells of zona glomerulosa (KD = 139.8 +/- 39.7, Bmax = 69.7 +/- 9.1 fmol mg-1 protein, mean of 3 individuals+/-sem). ETB receptors were present in the medulla (KD = 145.2 +/- 16.4, Bmax = 75.5 +/- 12.3), zona glomerulosa (KD = 100.6 +/- 35.1, Bmax = 63.1 +/- 10.0), fasiculata (KD 145.1 +/- 16.2, Bmax = 67.9 +/- 6.9) and reticularis (KD = 118.2 +/- 18.6, Bmax = 71.9 +/- 6.5). ETB receptors were not detected within the smooth muscle of the vasculature. Messenger RNA encoding both sub-types was present in adrenals. ET-like immunoreactivity was localized to the cytoplasm of the endothelial cells from arteries supplying the gland and resistance vessels within the capsular plexus. Staining was also detected in these cells using anti-big ET-1 and less intensely with anti-big ET-2 antisera but not within cells within the cortex or medulla. Big ET-3-like immunoreactivity was localized to secretory cells of the medulla. Staining was not found using antiserum that could detect ET-3, suggesting further processing of big ET-3 may occur within the plasma, and that the adrenals could be a source of ET-3. The presence of ET-1 was confirmed by high performance liquid chromatography and radioimmunoassay although ET-3 was not detected. The results suggest that ET-1 is the predominant mature isoform, which is localized mainly to adrenal vasculature, particularly the capsular plexus, and may contribute to blood flow regulation in the gland.

The increase in human plasma immunoreactive endothelin but not big endothelin-1 or its C-terminal fragment induced by systemic administration of the endothelin antagonist TAK-044

1. We examined the effects of systemic infusion, in healthy human volunteers, of the endothelin antagonist TAK-044 on the plasma concentrations of mature endothelin, big endothelin-1 and the C-terminal fragment of big endothelin-1, by selective solid-phase extraction and specific radioimmunoassays. 2. Unlabelled TAK-044 competed with specific [125I]-endothelin-1 binding to human left ventricle tissue in a biphasic manner giving KD values of 0.11 nM and 26.8 nM at the ETA and ETB receptor subtypes, respectively, indicating a 244 fold selectivity for the ETA receptor subtype. 3. A 15 min intravenous infusion of placebo or 30 mg TAK-044 (giving a serum concentration of 2 nM, calculated to block > 95% of ETA but < 5% ETB receptors) had no effect on the immunoreactive plasma concentrations of the three peptides. 4. At the higher dose of 750 mg TAK-044 (giving a serum concentration of 80 nM, calculated to block > 99% of ETA and > 75% ETB receptors), the immunoreactive plasma endothelin concentrations were increased 3.3 fold over basal levels (P < 0.01). The concentrations of big endothelin-1 or C-terminal fragment of big endothelin-1 were unchanged. 5. At both doses of TAK-044, there were significant decreases in diastolic blood pressure, and peripheral vascular resistance, with corresponding increases in cardiac index and stroke index. There were no changes in systolic or mean arterial blood pressures or heart rate. 6. Since only the concentrations of the mature peptide were increased, we conclude that the most likely sources of endothelin contributing to the observed rise were displacement of receptor-bound peptide and reduction in plasma clearance rather than peptide synthesis.

Expression of endothelin peptides and mRNA in the human heart

1. We have examined the expression of endothelin isoforms and their precursors in the human heart using RIA, HPLC, immunocytochemistry and reverse transcriptase-polymerase chain reaction assays. 2. Highly specific RIAs were used to measure the levels of mature endothelin and big endothelin-1 immunoreactivity in extracts of human right ventricle. There was no significant difference between samples from patients with ischaemic heart disease and idiopathic dilated cardiomyopathy. 3. HPLC coupled with RIAs allowed the separation and identification of the three mature isoforms of endothelin, big endothelin-1 and the C-terminal fragment of big endothelin-1. In extracts of human endocardial endothelial cells, peaks of immunoreactivity that co-eluted with authentic endothelin-1, big endothelin-1 and C-terminal fragment were found. 4. Intense immunocytochemical staining of mature endothelin immunoreactivity was detected in the cytoplasm of endothelial cells of all regions of the heart tested. Big endothelin-1 immunoreactivity mirrored that of the mature peptide and, in two of three individuals tested, big endothelin-2 immunoreactivity was also detected. No big endothelin-3 immunoreactivity was detected in any of the tissues examined. 5. Reverse transcriptase-polymerase chain reaction assays demonstrated endothelin-1 and endothelin-2 mRNA in all three samples of human left ventricle tested. In two of the individuals, additional bands were also detected with the endothelin-2 primers which corresponded to splice variants. There was no evidence for the expression of endothelin-3 mRNA. 6. These data suggest that endothelin-1 is the predominant isoform of endothelin in the human heart and is probably largely synthesized by the endothelial cells within the heart. If released from the endothelial cells in vivo, this potent cardiotonic peptide may play an important paracrine role in human cardiovascular function.

Development of an enzyme-linked immunosorbent assay to measure total TIMP-1 (free TIMP-1 and TIMP-1 in combination with matrix-metalloproteinases) and measurement of TIMP 1 and CRP in serum

A panel of six monoclonal antibodies (MAbs) was raised against purified human fibroblast tissue inhibitor of metalloproteinase-1 (TIMP-1) and characterised. All possible antibody pairs were tested for their suitability as capture and revealing antibodies in a two-site enzyme-linked immunosorbent assay (ELISA) to measure total TIMP-1 (both free TIMP-1 and TIMP-1 together with matrix metalloproteinases (MMPs)). Using the best combination of MAbs the assay was optimised. The sensitivity of detection of the assay was 1.4 ng/ml, and inter- and intra-assay coefficients of variation were between 10.4-13.7% and 8.8-9.7%, respectively. Dilution series of human cerebrospinal and synovial fluids, plasma and sera paralleled those of the TIMP-1 standard curve indicating that the immunoreactivity detected in these samples was authentic TIMP-1. TIMP-2 shows no detectable cross reactivity in this assay confirming that this ELISA is specific for TIMP-1. The levels of total TIMP-1 and collagenase were measured in conditioned medium from A2058 human melanoma cells cultured in the absence or presence of human recombinant interleukin-1 alpha (hrIL-1 alpha). Total TIMP-1 was also measured in serum samples with known C-reactive protein (CRP) (n = 100) and alpha 1 antichymotrypsin (ACT) (n = 52) concentrations; no correlation was found between TIMP-1 levels and either of these acute phase reactants although the levels of TIMP-1 were raised when compared to normal sera. This ELISA provides a rapid and convenient procedure for the quantitation of total TIMP-1 in human biological fluids and supernatants from cultured cell lines.

Phosphoramidon inhibition of the in vivo conversion of big endothelin-1 to endothelin-1 in the human forearm

1. The vasoconstrictor peptide, endothelin-1 (ET-1) and a biologically inactive C-terminal fragment (CTF) are generated from an intermediate big ET-1 by a putative ET converting enzyme, sensitive to phosphoramidon. We have developed a procedure using selective solid-phase extraction and specific radioimmunoassays to measure the levels of immunoreactive (IR) big ET-1 and the products of conversion (ET-1 and CTF) in human plasma. These techniques have been used to determine the levels of the three peptides in venous plasma following local infusions of ET-1 and big ET-1, both alone and together with phosphoramidon. 2. Infusion of ET-1 into the brachial artery (5 pmol min-1) significantly increased (P < 0.05) IR ET levels from a basal level of 2.3 pM to 55.2 pM in plasma from the infused arm after 60 min of infusion. This corresponded with a marked decrease in forearm blood flow from a basal level of 2.6 ml dl-1 min-1 to 1.7 ml dl-1 min-1. The levels of IR big ET-1 and CTF were unchanged. Co-infusion of phosphoramidon (30 nmol min-1) with ET-1 had no significant effect on the plasma IR levels of ET, big ET-1, CTF, or blood flow. 3. Big ET-1 (50 pmol min-1) significantly increased (P < 0.05) venous concentrations of all three IR peptides after 60 min compared to basal (ET: from 2.2 to 7.7 pM, big ET-1; from 0 to 386.0 pM, CTF: from 0.2 to 37.0 pM). Forearm blood flow decreased significantly (P<0.05) from a basal level of 3.0 ml dl-1 min-1 to 1.6 ml dl-1 min-1.4. When phosphoramidon was co-infused with big ET-1, both the rise in IR ET and associated vasoconstriction were abolished. However, IR CTF was still detected, suggesting that either some conversion by phosphoramidon-insensitive enzyme(s) was occurring, and/or that CTF was being protected from further degradation by phosphoramidon.5. These data show that in the human forearm the activity of a phosphoramidon-sensitive ET converting enzyme is at least in part responsible for the vasoconstrictor properties of exogenous big ET-1. Furthermore, because measurable levels of newly synthesized ET-1 are likely to be rapidly reduced in the blood/plasma through receptor binding, assay of IR big ET-1 and CTF may be a more sensitive measure of ET-1 generation in disease.

Effects of phosphoramidon and pepstatin A on the secretion of endothelin-1 and big endothelin-1 by human umbilical vein endothelial cells: measurement by two-site enzyme-linked immunosorbent assays

1. Two-site enzyme-linked immunosorbent assays have been developed for the rapid, sensitive and non-isotopic measurement of endothelin-1 and big endothelin-1. The sensitivities of detection were 0.5 and 0.3 fmol/well, with ED50 values of 13 and 12 fmol/well for the endothelin-1 and big endothelin-1 assays, respectively. Each assay is highly selective for its corresponding antigen. The ET-1 assay showed no detectable cross-reactivity with ET-1-(1-20), indicating that the assay only recognizes the 21-amino acid biologically active peptide. 2. The two assays were used to measure the effects of two classes of protease inhibitor on the basal release of enothelin-1 and big endothelin-1 from cultured first-passage human umbilical vein endothelial cells. 3. The secretion of both peptides was time-dependent over 12 h. The metalloprotease inhibitor phosphoramidon (1 x 10(-4) mol/l) significantly reduced the amount of endothelin-1 secreted into the medium (P < 0.05), with a concomitant increase in the secreted levels of big endothelin-1 (P < 0.01). The aspartyl protease inhibitor, pepstatin A, also caused a significant decrease in the secretion of endothelin (P < 0.05). However, unlike phosphoramidon, there was no increase in the levels of big ET-1 compared with the controls. At these concentrations, neither inhibitor affected the viability of the cells as indicated by Trypan Blue exclusion. 4. The two assays permit the direct measurement of endothelin-1 and its precursor, and will be of use in the elucidation of the putative human endothelin-converting enzyme(s).(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro expression of calcitonin gene-related peptide in human endothelial cells transfected with plasmid and retroviral vectors

Introduction of cDNA encoding human alpha-calcitonin gene-related peptide (CGRP), a potent vasodilator, into cultured human umbilical vein endothelial cells (HUVEC) was undertaken by using plasmids and retroviral vectors. In order to improve expression, modification of context coding sequence for the initiation of CGRP translation and deletion of nontranslated regions of CGRP cDNA in the transfection vectors were tested. Stable transfer of neo in the HUVEC was achieved with both plasmid and retroviral vectors. Integration rates obtained by using retrovirus (approximately 1%), where higher than those achieved with plasmid-mediated transfection (< 1/1000). CGRP expressed in the transfected HUVEC was secreted into culture medium when a leading sequence was included in the expression vectors. CGRP was detected by enzyme-linked immunosorbent assay (ELISA) in the supernatants of both transiently transfected and stably transfected/infected HUVEC. Higher levels of expression were achieved by using plasmid (giving a maximum CGRP concentration of 6.5 +/- 0.5 pM in the supernatant) than retroviruses. Lipofectin-mediated transfer of CGRP cDNA also resulted in transient expression of CGRP in the HUVEC.

Demonstration of the neurotransmitter role of calcitonin gene-related peptides (CGRP) by immunoblockade with anti-CGRP monoclonal antibodies

1. Monoclonal antibodies (MAbs) against rat alpha-calcitonin gene-related peptide (alpha CGRP) were produced. Those which bound CGRP in a radioimmunoassay and inhibited the binding of 2-[125I]-iodohistidyl10-CGRP in a receptor binding assay were selected for immunoblockade experiments. 2. The effect of MAbs on CGRP inhibition of electrically stimulated contractions of the rat isolated vas deferens was characterized. Four out of 11 MAbs tested shifted the concentration-response curve of CGRP to the right compared with vehicle or irrelevant MAb control. MAb C4.19 produced equipotent blockade of rat alpha CGRP and rat beta CGRP and was chosen for further studies. MAb C4.19 had no pharmacologically significant effect on the concentration-response relationship of isoprenaline, rat beta-endorphin or somatostatin. 3. We demonstrated that the pharmacological response to CGRP in the presence of MAb C4.19 could be predicted when the dissociation constant and concentration of binding sites of the antibody were known. Comparison of experimental and computer simulated data showed good agreement for EC50 and maximum effect of CGRP in the presence of MAb C4.19. 4. Capsaicin at 1 microM inhibited the electrically stimulated contractions by 60.8% (95% confidence interval 51.8% to 69.9%). This effect was significantly attenuated by MAb C4.19 to 26.0% (95% confidence interval 15.2% to 36.8%; P < 0.003). 5. The immunoblockade of exogenous and endogenous CGRP described here, together with complementary evidence from other studies, strongly suggest that CGRP has a major neurotransmitter role at the neuroeffector junction of the rat vas deferens.

Is receptor cross-regulation in human heart caused by alterations in cardiac guanine nucleotide-binding proteins?

1. Guanine nucleotide-binding proteins (G-proteins) play a central role in signal transduction between a wide variety of cell-surface receptors and intracellular second messenger systems. Recently, we and others have demonstrated that cross-regulation can occur between a variety of G-protein-linked receptors in human heart. Chronic beta 1-adrenoceptor blockade gives rise to sensitization of beta 2-adrenoceptor and of 5HT 4-receptor responses, both of which are mediated via stimulation of adenylate cyclase through stimulatory G-proteins (Gs), and also gives rise to desensitization of muscarinic M2-receptor responses, which inhibit adenylate cyclase through inhibitory G-proteins (Gi). 2. In order to investigate whether these effects are due to quantitative changes in cardiac G-protein isoforms, we measured their abundance in right atrial appendage from patients taking or not taking beta 1-adrenoceptor antagonists, by immunoblotting. 3. Samples of right atrial appendage homogenate were subjected to SDS/PAGE, and proteins were electroblotted on to nitrocellulose membranes. These were then probed with specific anti-G protein anti-sera, and binding was revealed by means of a secondary antibody labelled with alkaline phosphatase and using a chromogenic substrate. The resulting bands were quantified by laser densitometry. 4. No quantitative differences were detected, between these two groups of patients, in the amounts of alpha-subunit of 'long' or 'short' Gs isoforms (Gs alpha L and Gs alpha S), or in the amounts of Gi 1 + 2 alpha-subunit (Gi alpha 1 + 2). Nor was any difference found in the abundance of the beta-subunit of G-proteins.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation of human cardiac endothelin receptors by a peptide-receptor mobility shift assay

1. A peptide-protein mobility shift assay has been developed, using native polyacrylamide-gel electrophoresis, that enables the isolation of de-natured receptor proteins from small amounts of human cardiac tissue. 2. Radiolabelled endothelin-1 and related peptides were used to identify and isolate endothelin receptors from partially purified membrane extracts of human atrial tissue. 3. Binding analysis using radiolabelled endothelin-1 gave an equilibrium dissociation constant (Kd) of 2 nmol/l, similar to results from binding experiments conducted directly on tissue. 4. Peptide-receptor complexes were electroeluted from native gels and dissociated. Receptor material was characterized by dot-immunobinding analysis of eluates using an antibody raised against a predicted human endothelin receptor sequence.

Identification of endothelin-1, endothelin-2 and endothelin-3 in human endometrium

This study determined the presence of specific endothelin isoforms in human endometrium using high performance liquid chromatography (HPLC) combined with radioimmunoassay, and immunocytochemistry to detect the endothelin precursors (proendothelin-1, proendothelin-2 and proendothelin-3). Endothelin-like immunoreactivity was measured in HPLC eluates using antisera raised in rabbits against the carboxy-terminal heptapeptide of endothelin-1, which is common to the three endothelin isoforms. Of eight endometrial samples analysed by HPLC, three were in the proliferative phase of the cycle, and five in the secretory phase. Endothelin-1 was detected in seven samples, whereas endothelin-2 and endothelin-3 were seen in four and five specimens, respectively. No relationship was seen between endothelin isoforms and the stage of the cycle. Immunocytochemistry was performed on five proliferative and three secretory phase tissues. When present, staining for the precursor proendothelins was localized to endometrial glandular and luminal epithelium (proendothelin-1, 5 of 8; proendothelin-2, 5 of 8; proendothelin-3, 6 of 8). In two sections, staining was also seen in vascular endothelium using antibody raised against proendothelin-1 (n = 1) and proendothelin-3 (n = 1). These data provide evidence that the three endothelin isoforms are present in human endometrium, and suggest that these potent vasoactive agents may play a role in the paracrine control of the uterine vascular bed.

Characterization and localization of endothelin receptor subtypes in the human atrioventricular conducting system and myocardium

The characterization and localization of endothelin A (ETA) and endothelin B (ETB) receptors have been determined in tissue sections of the human atrioventricular conducting system, surrounding regions of atrial and ventricular myocardium, and the left ventricular free wall by use of radioligand binding, polymerase chain reaction, and in situ hybridization. Selective ETA (BQ123) and ETB (BQ3020) compounds in conjunction with [125I]endothelin-1 revealed the presence of ETA and ETB receptors in the left ventricular free wall (BQ123: 57 +/- 5% ETA, 43 +/- 2% ETB, n = 3; BQ3020: 67 +/- 3% ETA, 33 +/- 3% ETB, n = 3). Autoradiography using [125I]endothelin-1 in the absence or presence of BQ3020, BQ123, or endothelin-1 showed ETA and ETB receptors localized to atrial and ventricular myocardium, the atrioventricular conducting system, and endocardial cells. There was a higher proportion of ETB receptors in the atrioventricular node and the penetrating and branching bundles of His than in the surrounding interventricular and interatrial septa (p < 0.0001). There was a lower density of ETB receptors in the interventricular septum compared with the interatrial septum and the atrioventricular conducting system (p = 0.009) and a lower density of ETA receptors in the atrioventricular conducting system compared with interatrial and interventricular septa (p = 0.008). Isolated right atrial myocytes showed a higher proportion of ETA receptors (91 +/- 12%, n = 3). Amplification of left ventricular free wall cDNA by polymerase chain reaction revealed the presence of ETA and ETB receptor mRNA. mRNA for both subtypes was detected in isolated atrial myocytes. In situ hybridization showed ETA and ETB receptor mRNA localization to atrial and ventricular myocardium, the atrioventricular conducting system, and endocardial cells. These studies demonstrate the presence of ETA and ETB receptors in human myocardium and the atrioventricular conducting system.

Characterization of endothelin isoforms in human heart: endothelin-2 demonstrated

In humans, three endothelin (ET) isoforms are predicted to exist by analysis of genomic DNA. However, evidence for the presence of all three mature ET peptides and their precursors remains unclear. Our aim was to identify the ET isoforms present in human heart, using radioimmunoassay (RIA) and reverse-phase high-performance liquid chromatography (RP-HPLC). Antisera raised against the ET-1[15-21] terminal sequence were specific for mature ETs, showing no cross-reactivity with their precursor pro-ETs. Antisera raised against the pro-ET-1[31-38] terminal sequence was specific for pro-ET-1, showing no cross-reactivity with other ET peptides. In extracts of human cardiac tissues, the concentrations of immunoreactive (IR) mature ET and pro-ET-1 were found to be as follows: left atrium (n = 3): 282.3 +/- 113.0, 21.9 +/- 11.0, respectively; right atrium (n = 5): 308.3 +/- 95.4, 43.1 +/- 12.8, respectively; left ventricle (n = 6): 218.5 +/- 64.6, 47.9 +/- 11.9, respectively; right ventricle (n = 4): 215.1 +/- 79.8, 53.9 +/- 13.0, respectively (fmol/g wet weight, mean +/- SEM, for total IR mature ET and pro-ET-1, respectively). RP-HPLC showed peaks of immunoreactivity that coeluted with authentic ET-1 in all extracts of human left atria and ventricle tested. In addition, peaks were also present corresponding to ET-2, ET-3, and pro-ET-1. These results suggest that in addition to ET-1 and pro-ET-1, ET-2 and ET-3 are present in the human heart.

Anatomical localization and pharmacological activity of mature endothelins and their precursors in human vascular tissue

OBJECTIVES

We developed four selective rabbit antisera in order to compare the distribution of immunoreactive mature endothelins and their precursors, proendothelin-1, proendothelin-2 and proendothelin-3, in the endothelium from human vascular tissue. Our second aim was to use in vitro pharmacological assays to test the vasoconstrictor actions of the mature endothelin and proendothelin peptides.

METHODS

The antisera were shown to be selective by enzyme-linked immunosorbent assays. With these antisera, we detected immunoreactivity in serial cryostat sections from saphenous and mesenteric veins, and mesenteric and internal mammary arteries, using a peroxidase-antiperoxidase technique. In pharmacological experiments, segments of human coronary and mesenteric arteries were exposed to cumulative (0.06-60 nmol/l) concentrations of the endothelins and their precursors.

RESULTS

Antisera directed against mature endothelin stained the cytoplasm of endothelial cells in all vessels tested. Immunoreactive proendothelin-1 and proendothelin-2 were also detected, but not proendothelin-3. Endothelin-1 and endothelin-2 were strongly vasoactive, with similar molar potencies, and caused a dose-related increase in contractile force in human coronary arteries (0.06-60 nmol/l). However, proendothelin-1 and proendothelin-2 were 100-fold and 1000-fold less vasoactive than their respective mature peptides. No contractile effect was seen with proendothelin-3 or endothelin-3 at the concentrations tested in human coronary arteries, and similar results were obtained with human mesenteric arteries.

CONCLUSIONS

These results suggest that proendothelin-1 and proendothelin-2 must be converted to their corresponding mature peptides to produce vasoconstrictor activity in human vessels. Immunoreactive mature endothelin is widely distributed in human vascular endothelial cells and, if released, may produce endothelin-mediated vasoconstriction.

Localization of immunoreactive endothelin and proendothelin in the human lung

The endothelins are a family of three 21-amino-acid peptides: endothelin-1, endothelin-2 and endothelin-3. They are powerfully vasoactive, causing both contraction and relaxation of blood vessels. They are also active in the lung causing long lasting bronchoconstriction. Antibodies were raised in rabbits against the C-terminal heptapeptide of endothelin-1 (endothelin-1(15-21)) and to portions of the C-terminus of the human proendothelin-1(31-38), proendothelin-2(31-37) and proendothelin-3(31-41 amide) and tested by enzyme-linked immunosorbent assay to determine their titre and cross-reactivity. We used these antibodies to determine the localization of mature endothelin in the adult human lung and to determine the distribution of each of the three proendothelins. Mature endothelin immunoreactivity was present in airway epithelia and submucosal glands throughout the lung. In the airway epithelia immunoreactive proendothelin-1 and proendothelin-3 were detected, while immunoreactivity of all three isoforms was present in submucosal glands. Quantitative in vitro receptor autoradiography was used to locate specific endothelin binding sites. The rank order for density of endothelin binding site occurrence was: lung parenchyma greater than airway smooth muscle greater than airway epithelia. If immunoreactive endothelin is released onto these sites in vivo, endothelin may act as a paracrine mediator in the human lung.