Implementing long-acting injectable antiretroviral treatments in Senegal: issues, challenges and conditions for introducing them. Qualitative study with healthcare providers and patients

Long-acting injectable antiretroviral therapy (LAI-ART) can offer people living with HIV (PLWH) a promising alternative to daily oral therapy. This article highlights the issues, challenges and conditions related to introducing LAI-ART into the social lives of PLWH and HIV-care practices in Senegal. Semi-structured interviews were conducted with 42 PLWH in two hospital care units in Dakar and with 13 healthcare providers and 6 peer educators. Interviews were transcribed, thematically coded and analysed using a cross-sectional approach. We found three key issues. First, simplifying living with HIV: PLWH respondents perceive LAI-ART as an opportunity to ease the burden associated with taking tablets. This enthusiasm may however be qualified by an ambivalent relationship with injections and is subject to certain conditions. Second, certain constraints linked to the medicalisation of care are to be anticipated, including the obligation to go to the hospital every two months for injections. These findings foreshadow the new management work for medical follow-up expected to fall on PLWH and caregivers. Third, the challenges of introducing LAI-ART in Senegal are to ensure adequate organisation of care and supply and sustainability of the program. These results clarify how to implement programs to introduce LAI-ART into real life in the West African context.

Injectable long acting antiretroviral for HIV treatment and prevention: perspectives of potential users

BACKGROUND

The use of long acting injectable (LAA) antiretroviral drugs may be an alternative option for HIV treatment and prevention. Our study focused on patient perspectives to understand which individuals, among people with HIV (PWH) and pre-exposure prophylaxis (PrEP) users, would constitute the preferential target for such treatments in terms of expectations, tolerability, adherence and quality of life.

METHODS

The study consisted in one self-administrated questionnaire. Data collected included lifestyle issues, medical history, perceived benefits and inconveniences of LAA. Groups were compared using Wilcoxon rank tests or Fisher's exact test.

RESULTS

In 2018, 100 PWH and 100 PrEP users were enrolled. Overall, 74% of PWH and 89% of PrEP users expressed interest for LAA with a significantly higher rate for PrEP users (p = 0.001). No characteristics were associated with acceptance of LAA in both groups in term of demographics, lifestyle or comorbidities.

CONCLUSION

PWH and PrEP users expressed a high level of interest in LAA, since a large majority seems to be in favor of this new approach. Further studies should be conducted to better characterize targeted individuals.

Knowledge of HIV prevention biomedical tools among African immigrants in France: the Makasi project

Background

In France, post-exposure prophylaxis (PEP) and pre-exposure prophylaxis (PrEP) have been available for several years. However, there is still no evidence on the level of knowledge of these HIV prevention tools among immigrants from sub-Saharan Africa living in precarious situations, a population particularly affected by HIV. The aim of this study is to describe the knowledge of these tools in this population and analyse the factors associated with this knowledge.

Methods

The data mobilized are from the Makasi interventional research that was conducted between 2018 and 2020 among immigrants from sub-Saharan Africa in precarious situations in the greater Paris area. Using data collected from 601 participants, we described levels of knowledge of HIV treatment effectiveness, treatment as prevention (TasP), post-exposure prophylaxis (PEP), and pre-exposure prophylaxis (PrEP), by sex with a chi2 test. We investigated factors associated with their knowledge with logistic regressions adjusted for sociodemographic characteristics, living conditions and sexual behaviors (p ≤ 0.2).

Results

The population surveyed was predominantly men (76%), from West Africa (61%) and in a precarious situation: 69% were unemployed, 74% were undocumented, 46% had no health coverage and 13% were homeless. In this population, knowledge of antiretroviral treatments for HIV prevention was heterogeneous: the effectiveness of HIV treatment was well known (84%), but only half of the respondents (46%) were aware of TasP and very few knew about PEP and PrEP: 6% and 5% respectively. Multivariable-adjusted models showed that these tools was better known by educated people, those who had a social network in France, those who have had access to the health system and those who were exposed to sexual risks.

Conclusions

While sub-Saharan African immigrants know the effectiveness of HIV treatment and use certain prevention tools such as HIV testing, they are not aware of PEP and PrEP.

Key messages

Is empowerment in sexual health measurable? A scoping review of definitions and measurement indicators

The concept of empowerment in sexual health is widely used in health promotion. This scoping review aims to identify how it is defined and measured. PubMed, Sage Journals, PsycInfo and the Web of Science are data sources. The inclusion criteria for studies were as follows: (1) an analysis of empowerment in sexual health, (2) quantitative evaluation and (3) publication in a peer-reviewed journal in French or English since January 1996. Data were extracted using a summary table of the definitions and indicators of empowerment in sexual health. Of the 2181 articles found, 29 met the inclusion criteria. Only 4 studies on 29 clearly defined empowerment in sexual health. Five dimensions emerged from the indicators used in the 29 studies in relation to sexual empowerment (social participation, participation in decision making, power to act, sexual health knowledge and gender norms), with two types of indicators: indicators unspecific to sexual health, which can be viewed as empowerment basic skills, and indicators specific to sexual health. Most studies concerned women and focused on individual empowerment, with a lack of measure of collective and structural levels of empowerment. Despite great heterogeneity in the definitions and indicators used, a set of core indicators emerged: participation in decision making, sexual negotiation power and sexual communication skills, knowledge and use of contraceptive methods, and HIV and sexually transmitted infections risk perception. This set could be systematically used in each study based on sexual empowerment concept, completed by supplementary indicators considering the specific context.

Analyzing implementation of public health interventions : a need for rigor, and the challenges of stakeholder involvement

OBJECTIVES

This article shows how conceptual models can help to develop and evaluate public health interventions. It also reports on the challenges of getting stakeholders involved.

METHOD

The analysis is based on the reflexive approach applied by the authors during their participation in two public health intervention research (PHIR) projects, in France and in Burkina Faso.

RESULTS

In Paris, PHIR aimed to enable sub-Saharan immigrants to appropriate the existing means of prevention and sexual health care and to strengthen their empowerment in view of preserving their health. Evaluation was carried out using mixed methods. The intervention process theory is based on Ninacs' conceptual model of individual empowerment. The Consolidated Framework For Implementation Research (CFIR) was mobilized a posteriori to analyze the process. PHIR stemmed from collaboration between a research team and two associations. The different stakeholders were involved in the evaluation process, as were, at certain times, persons in highly precarious situations. In Ouagadougou, a community-based dengue vector control intervention was deployed to address an essential but neglected need. As regards evaluation, we opted for a holistic, mixed method approach (effectiveness and process). The contents of the intervention were determined based on tacit knowledge, a community preference survey and solid evidence. The theoretical framework of the intervention consisted in an eco-biological model of vector control. The implementation analysis combined an internal assessment of implementation fidelity with an external CFIR process analysis. All stakeholders were involved in the evaluation process.

DISCUSSION

Analysis confirmed not only the value of process evaluations in PHIR, but also the primordial importance of a rigorous approach. Stakeholder involvement is a major challenge to be addressed early in the planning of RISPs; with this in mind, effective and ethically sound assessment mechanisms need to be drawn up. Interdisciplinary evaluative approaches should be preferred, and the use of justified, relevant, and flexible frameworks is highly recommended.

CONCLUSION

Lessons learned for those wishing to engage in the process evaluation of a public health intervention are hereby presented.

Deterioration of mental health and insufficient Covid-19 information among disadvantaged immigrants in the greater Paris area

OBJECTIVES

The aim of this study is to provide information on changes in mental health among disadvantaged immigrants from Sub-Saharan Africa in the Greater Paris area and their level of information about Covid-19.

METHODS

Prior to the Covid-19 epidemic, the Makasi community-based cohort followed 850 immigrants from sub-Saharan Africa in the Greater Paris area. Between the 1st of April and the 7th of June 2020, all participants scheduled for a follow-up survey were systematically included into an additional COVID-19-related wave of data collection (N = 100). We compared participants' type of housing, level of food insecurity, work and mental health (PHQ9) before and during the first COVID-19-related lockdown, using paired-Mc Nemar chi-2 tests. We next described their level of information on Covid-19 and policy measures, broken down by sex.

RESULTS

Among the 100 participants, 68% had no legal residence permit. Food insecurity was more often reported during lockdown than before (62% vs 52%). 9% of participants had a score indicative of severe depression (PHQ9) before lockdown and 17% afterwards (p = 0.17). Only 51% knew about the possibility of asymptomatic transmission of the COVID-19 virus.

CONCLUSIONS

This study brings original information on a hard-to-reach population group. Our results suggest that the lockdown had a detrimental impact on various economic and mental health aspects among disadvantaged migrants residing in the Greater Paris area.

Telephone peer recruitment and interviewing during a respondent-driven sampling (RDS) survey: feasibility and field experience from the first phone-based RDS survey among men who have sex with men in Côte d'Ivoire

Background

Many respondent-driven sampling (RDS) methodologies have been employed to investigate hard-to-reach populations; however, these methodologies present some limits. We describe a minimally investigated RDS methodology in which peer recruitment and interviewing are phone-based. The feasibility of the methodology, field experiences, validity of RDS assumptions and characteristics of the sample obtained are discussed.

Methods

We conducted a phone-based RDS survey among men who have sex with men (MSM) aged 18 or above and living in Côte d’Ivoire. Eight initial MSM across Côte d’Ivoire were selected. Participants were asked to call a hotline to be registered and interviewed by phone. After the participants completed the questionnaire, they were asked to recruit a maximum of 3 MSM from their acquaintances.

Results

During the 9 months of the survey, 576 individuals called the hotline, and 518 MSM completed the questionnaire. The median delay between the invitation to participate and the completion of the questionnaire by peer-recruited MSM was 4 days [IQR: 1–12]. The recruitment process was not constant, with high variation in the number of people who called the hotline during the survey period.

RDS chain convergence to equilibrium was reached within 6 waves for most of the selected variables. For the network size estimation assumption, participants who incorrectly estimated their network size were observed.

Regarding the sample obtained, MSM were recruited from all the regions of Côte d’Ivoire with frequent interregional recruitment; 23.5% of MSM were recruited by someone who does not live in the same region. Compared to the MSM who participated in two other surveys in Côte d’Ivoire, the MSM in our sample were less likely to know about an MSM non-governmental organisation. However, MSM aged 30 years old and above and those with a low level of education were underrepresented in our sample.

Conclusion

We show that phone-based RDS surveys among MSM are feasible in the context of sub-Saharan Africa. Compared to other classical RDS survey methodologies, the phone-based RDS methodology seems to reduce selection bias based on geography and proximity with the MSM community. However, similar to other methodologies, phone-based RDS fails to reach older and less-educated MSM.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12874-021-01208-x.

Immigrants facing Covid 19 containment in France : An ordinary hardship of disaffiliation

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The precarious immigrant population is often invisible because it is at the interstices of care devices and, in the current epidemic context, isolation facilities.

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Confinement affects individuals' abilities to act, and generates a "disaffiliation process" to placing this precarious immigrant population even more on the margins of society.

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Covid-19 crisis exacerbates pre-existing difficulties, generating not so new situations for these precarious immigrant population.

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Need to formulate specifics interventions : targeted outreach intervention, participatory approach and deliberative spaces ; promote health promotion intervention; right based intervention.

In order to limit the spread of the SARS-CoV-2 virus, the majority of governments have introduced population containment. Certain population groups, including immigrants in precarious situations, are experiencing the impact of this measure in a brutal manner. This article is based on accounts of containment experiences collected by telephone within the framework of a pre-existing intervention research carried out among immigrants to France from Sub-Saharan Africa who are in a precarious situation. It highlights certain social effects of containment and the logics at work in the precarious situations. This research shows how this a priori unprecedented situation affects individual capacities to act and generates a ‘disaffiliation process’ causing individuals to shift towards ‘social non-existence’, repeating lived experiences and exacerbating pre-existing logics. The ordeal of containment proves to be an ordinary experience for these individuals.

Practices and Obstacles to Provider-Initiated HIV Testing and Counseling (PITC) Among Healthcare Providers in Côte d'Ivoire

Practices of Provider-Initiated HIV Testing and Counseling (PITC) remains suboptimal in Côte d’Ivoire. The aim of this survey was to identify the practices and obstacles to PITC among healthcare professionals in Côte d'Ivoire. A nationally representative cross-sectional survey was conducted in 2018 by telephone among three separate samples of midwives, nurses and physicians practicing in Côte d'Ivoire. The number of HIV tests proposed during consultation in the month preceding the survey was collected for each professional. Factors associated with the number of proposed tests were identified through ordinal logistic regression models. A total of 298 midwives, 308 nurses and 289 physicians were interviewed. Midwives proposed the test more frequently, followed by nurses and physicians. Among midwives, a higher number of proposed tests was associated with the perception that HIV testing does not require specific consent compared to other diseases (aOR 4.00 [95% CI 1.37–14.29]). Among nurses, having received HIV training and the presence of community HIV counselors were associated with a higher number of proposed tests (aOR 2.01 [1.31–3.09] and aOR 1.75 [1.14–2.70], respectively). For physicians, the presence of a voluntary testing center was associated with a higher number of proposed tests (aOR 1.69 [1.01–2.86]). PITC practices and barriers differed across professions. Beyond improving environmental opportunities such as dedicated staff or services, strengthening the motivations and capabilities of healthcare professionals to propose testing could improve PITC coverage.

[Outreach strategies of HIV testing in Côte d’Ivoire: community providers under pressure]

BACKGROUND

Outreach HIV testing strategies have significantly contributed to the increase in the number of people knowing their HIV status in sub-Saharan Africa. This article analyzes the articulation of donor and field constraints on the implementation of outreach HIV testing strategies in Côte d’Ivoire.

METHODS

Qualitative research was conducted in three health districts (Man, Cocody-Bingerville and Aboisso) in Côte d’Ivoire in 2015-2016, through in-depth interviews with community providers, local leaders and people tested and through observation of outreach HIV testing activities.

RESULTS

Implementing organizations feel “under pressure” to meet donors’ objectives that are deemed unattainable, as well as the lack of training and funding. As a result, providers do not observe systematically the rules of the “three Cs” (counselling, informed consent, confidentiality), and propose testing to individuals who are “off-target” (in terms of locations and populations).

DISCUSSION

Implementing NGOs experience two types of constraints those resulting from the functioning of international aid (inadequate funding compared to actual costs, objectives too high, the important chain of intermediaries) and those related to the local context (spaces not adapted to guarantee confidentiality and the professional activity of target populations).

CONCLUSION

The pressure that is exerted at different levels on implementing NGOs is detrimental to the quality of HIV testing. It is now essential to develop a more qualitative approach in defining strategies and evaluation criteria.

Finding the missing link: when community-based outreach in public space is key to engage migrants in health prevention programmes in Paris, France

BACKGROUND

One of the classic challenges for prevention programmes is reaching the populations they serve. In France, a substantial number of African migrants living with HIV acquired their infection after migrating. The aim of this paper is to better understand the characteristics of the population reached by a community-based outreach approach.

METHODS

We compared sociodemographic characteristics across three different groups in the Paris greater area: (1) the general African migrant population (Population census), (2) the African migrant population using either the regular healthcare system or the system for vulnerable populations (PARCOURS Survey) and (3) the African migrant population reached through a community-based mobile unit (Afrique Avenir). Comparisons were conducted according to sex, age, region of origin, duration of residence and occupational and legal statuses using χ² tests.

RESULTS

The migrants reached by the mobile unit were mostly men (69%), 52% of whom were younger than 35 years old. They more often lived in precarious situations than did the general sub-Saharan population (49% vs 35% were unemployed, respectively, p<0.001) and the ones accessing the regular healthcare system. Fewer of them lived in precarious situations than did migrants seeking healthcare consultations for vulnerable populations (42% in the mobile unit vs 54% in healthcare consultations were undocumented, p<0.028).

CONCLUSION

Our study shows that the outreach approach can constitute a missing link in the prevention chain among sub-Saharan African migrants, reaching a group that differs from the general migrant population and from the migrant population in healthcare services-not only the newly arrived migrants who live in more precarious situations but also those who have been in France for several years and are still affected by social hardship.

Perspectives of injectable long acting antiretroviral therapies for HIV treatment or prevention: understanding potential users' ambivalences

Recent clinical trial data showed that injectable long-acting antiretroviral treatment (LA-ART) every four or eight weeks could become an alternative option for HIV treatment or prevention. The purpose of our study was to explore perceptions and potential users' points of views of this new mode of administration through individuals' therapeutic itinerary and their singular history with ART. Between 2018 and 2019, a qualitative study was conducted in two University Hospitals in Paris, France. In-depth interviews were conducted with 15 virologically controlled People Living with HIV (PLWH) and 13 men on pre-exposure prophylaxis (PrEP) for at least six months. Interviews, focused on the daily experience with ART, were recorded, transcribed, and analyzed using thematic content analysis. Collected discourses were organized around three emergent concerns: social, material and experimental. Each of these concerns was perceived as ambivalent, balanced by skepticism and hope. It revealed the complexity of each individual's relationship to their HIV treatment or PrEP, leading to balance the injectable LA-ART popularity reported within clinical trials. This new mode of administration may be a suitable alternative for some PLWH and PrEP users, a "simplification" compared to the oral route. It opens a window for "customizable" ART-treatment according to individuals' lives.

[Practices and Factors Associated with Recent HIV Testing in the General Population, Côte d'Ivoire: Results of the ANRS Study 12323 DOD-CI]

With 2.9% of HIV prevalence in the general population, Côte d'Ivoire is one of the countries most affected by the HIV epidemic in West Africa. In this country, only 63% of people infected with HIV are aware of their status. A cross-sectional phone survey was conducted with a representative sample of 3,867 individuals to describe the practices and factors associated with a recent HIV testing (≤ 1 year) in Côte d'Ivoire. Data relative to the last done HIV test as well as the socio-demographic characteristics, sexual behavior, access to information, perceptions, capacities and autonomy as well as social and geographical environment of the participants were collected. Logistical regression models were used to identify the associated factors with a recent HIV test (≤ 1 year). Lack of information is one of the main barriers to HIV testing (only 60% of individuals know a place to get tested). For men, despite the fact that HIV testing is free of charge, poor economic conditions seem to be a barrier to testing. The social environment, including peer influence, also appears to have an effect on testing among men. For women, testing is associated with their perceptions of HIV exposure. There is a need to rethink the current HIV testing communication in Côte d'Ivoire and to identify economic or social incentives to remove access barriers to HIV testing.

Participatory development and pilot testing of the Makasi intervention: a community-based outreach intervention to improve sub-Saharan and Caribbean immigrants' empowerment in sexual health

Background

Sub-Saharan and Caribbean immigrants are particularly affected by HIV in Europe, and recent evidence shows that a large portion of them acquired HIV after arrival. There is a need for efficient interventions that can reduce immigrants’ exposure to HIV. We describe the pilot phase of a community-based empowerment outreach intervention among sub-Saharan and Caribbean immigrants in the greater Paris area aimed at 1) constructing the intervention, 2) assessing its feasibility, and 3) assessing the feasibility of its evaluation based on a stepped-wedge approach.

Methods

1) To develop the intervention, a literature review was conducted on existing interventions and participatory approaches developed, including the constitution of peer groups. 2) To assess the intervention’s feasibility, a pilot was conducted between April 2018 and December 2018. A daily register was used to collect data on sociodemographic characteristics of all persons who visited the mobile team to assess eligibility and acceptability. 3) To assess the feasibility of performing a stepped-wedge trial to evaluate the intervention, we compared eligibility, enrolment and retention at 3 months in two arms (immediate vs deferred). Chi-squared tests were used to compare reach and retention between the two arms.

Results

Intervention development. The Makasi intervention was designed as an outreach intervention that starts with the persons’ capacities and helps them appropriate existing resources and information and obtain knowledge about sexual health, based upon motivational interviewing techniques.

Intervention Feasibility. Between April 2018 and December 2018, a total of 485 persons were identified as eligible. Participation in the intervention was proposed to 79% of eligible persons. When proposed, the persons enrolled in the intervention with a response rate of 69%. Some were lost to follow-up, and 188 persons were finally included.

Evaluation Feasibility. The proportions of eligible (45 and 42%) individuals and of enrolled individuals (65 and 74%) were similar and not significantly different in the immediate and deferred arms, respectively.

Conclusions

A community-based outreach intervention aimed at improving sub-Saharan and Caribbean immigrants’ empowerment in sexual health is feasible. The pilot phase was key to identifying challenges, designing a relevant intervention and validating the stepped-wedge protocol for evaluation.

Mieux comprendre les défis de la médicalisation de la prévention du VIH en France : la prophylaxie préexposition au prisme des sciences sociales

Résumé : Le recours aux traitements antirétroviraux pour la prévention du VIH transforme en profondeur le contexte des interventions dans ce domaine. La prophylaxie pré-exposition (Prep) en constitue l'une des facettes les plus visibles. Pour autant, l'utilisation de la Prep en France s'avère limitée. L'outil peine à trouver son public parmi les populations ciblées. Comment expliquer la sous-utilisation d'une approche de prévention dont la haute efficacité est pourtant démontrée ? Les réponses à cette question gagneraient à s'enrichir des sciences humaines et sociales tant pour penser les conditions de l'appropriation de l'outil par les publics ciblés que pour identifier les impensés et les logiques qui sous-tendent son déploiement. Loin de se limiter au VIH, la réflexion critique sur le recours aux médicaments comme outils de prévention ouvre des questions pertinentes pour le champ de la promotion de la santé.

Effect of organizational models of provider-initiated testing and counseling (PITC) in health facilities on adult HIV testing coverage in sub-Saharan Africa

The purpose of this paper is to identify which Provider-Initiated HIV Testing and Counseling (PITC) organizational models are the most efficient to maximize testing coverage. We conducted a systematic literature review to identify published articles that evaluated routine PITC programs implemented in adult health facilities in Sub-Saharan Africa. We considered only articles measuring PITC offer, PITC acceptability and PITC coverage. Adjusted meta-regression models were performed to measure the association between PITC offer, acceptability and coverage with PITC organizational model. A total of 30 articles were included in the meta-analysis. Overall, 85.4% [95%CI: 77.2-93.5] of patients were offered a test, and 87.1% [82.4-91.7] accepted the test resulting in a PITC coverage of 74.3% [66-82.6]. Four types of PITC organizational models were identified: PITC initiated and performed during the consultation (model A), PITC initiated before consultation (model B), PITC referred on-site (model C) and PITC referred off-site (model D). Compared to model A, model B had a similar coverage (aOR: 1.02 [0.82-1.26]). However, coverage was lower for model C (aOR: 0.81 [0.68-0.97]) and model D (aOR: 0.58 [0.44-0.77]). Initiating the testing process before or during medical consultation is recommended for maximizing testing coverage among patients.

Pouvoir entre enseignante et doctorante : utilisation de données de recherche et signature scientifique

Enchâssée dans un rapport de pouvoir, cette étude de cas fictive met en évidence différentes pratiques d’utilisation de données de recherche dans le cadre d’une collaboration entre enseignante-chercheure et doctorante. Elle vise à mettre au jour les difficultés et enjeux éthiques d’une telle collaboration et particulièrement les défis liés à la signature scientifique et à l’utilisation des données à l’issue de la recherche.

[Barriers to tuberculosis awareness and screening: a qualitative study in a French department]

The incidence of tuberculosis in Seine-Saint-Denis is considerably higher than the national average. The north-west part of the department is particularly concerned. Screening teams encounter difficulties communicating on the disease, reaching the populations concerned and obtaining their adhesion to the screening proposal. The objective of this study was to identify and elucidate the obstacles to tuberculosis prevention and screening. A qualitative study was conducted based on observation of screening actions in Seine-Saint-Denis and semi-directive interviews with health professionals in charge of screening, community representatives and associations, and individuals from the population concerned. Obstacles to tuberculosis awareness and screening appear to be linked to the way in which screening is organized and implemented, and communication difficulties in relation to this disease. Three major obstacles were identified: the gap between the little attention paid to this disease and the sanitary crisis it can trigger in the event of an epidemic; the unsuitability of communication tools for the target population and their lack of attractiveness; maladjustment of screening actions to the local context. The study highlights the individual and social marginalization of the tuberculosis issue and the mechanisms producing this marginalization. It encourages the development of more interactive communication tools and modes, and increased awareness of the professionals involved in screening about field realities.

Slow-binding and competitive inhibition of 8-amino-7-oxopelargonate synthase, a pyridoxal-5'-phosphate-dependent enzyme involved in biotin biosynthesis, by substrate and intermediate analogs. Kinetic and binding studies

8-Amino-7-oxopelargonate synthase catalyzes the first committed step of biotin biosynthesis in micro-organisms and plants. Because inhibitors of this pathway might lead to antibacterials or herbicides, we have undertaken an inhibition study on 8-amino-7-oxopelargonate synthase using six different compounds. d-Alanine, the enantiomer of the substrate of this pyridoxal-5'-phosphate-dependent enzyme was found to be a competitive inhibitor with respect to l-alanine with a Ki of 0.59 mm. The fact that this inhibition constant was four times lower than the Km for l-alanine was interpreted as the consequence of the inversion-retention stereochemistry of the catalyzed reaction. Schiff base formation between l or d-alanine and pyridoxal-5'-phosphate, in the active site of the enzyme, was studied using ultraviolet/visible spectroscopy. It was found that l and d-alanine form an external aldimine with equilibrium constants K = 4.1 mm and K = 37.8 mm, respectively. However, the equilibrium constant for d-alanine aldimine formation dramatically decreased to 1.3 mm in the presence of saturating concentration of pimeloyl-CoA, the second substrate. This result strongly suggests that the binding of pimeloyl-CoA induces a conformational change in the active site, and we propose that this new topology is complementary to d-alanine and to the putative reaction intermediate since they both have the same configuration. (+/-)-8-Amino-7-oxo-8-phosphonononaoic acid (1), the phosphonate derivative of the intermediate formed during the reaction, was our most potent inhibitor with a Ki of 7 microm. This compound behaved as a reversible slow-binding inhibitor, competitive with respect to l-alanine. Kinetic investigation showed that this slow process was best described by a one-step mechanism (mechanism A) with the following rate constants: k1 = 0.27 x 103 m-1.s-1, k2 = 1.8 s-1 and half-life for dissociation t1/2 = 6.3 min. The binding of compound 1 to the enzyme was also studied using ultraviolet/visible spectroscopy, and the data were consistent with the kinetic data (K = 4.2 microm). Among the other compounds tested, two potential transition state analogs, 4-carboxybutyl(1-amino-1-carboxyethyl)phosphonate (4) and 2-amino-3-hydroxy-2-methylnonadioic acid (5) were found to be competitive inhibitors with respect to l-alanine with Ki of 68 microm and 80 microm, respectively.