Pharmacogenetic study of efavirenz in hiv patients: cyp 2b6 516g>t and 983t>c polymorphisms implication in the neurological side effects in cameroon

Abstract

The introduction of antiretroviral therapy (ART) as standard of care has considerably enhanced the life span and quality of life among people living with HIV/AIDS. Unfortunately, these drugs are associated with some adverse drug reactions (ADRs) that have been identified as a serious barrier to adherence which is the most important factor for success of therapy. As a consequence of this, there is an increased risk of viral resistance and treatment failure. The first line treatment recommended by WHO in resource limited countries, including Cameroon, consists of two Nucleoside Reverse Transcriptase Inhibitors (NRTI) plus one Non-Nucleoside Reverse Transcriptase Inhibitor (NNTIs) where Efavirenz (EFV) is the most commonly used. EFV was shown to be associated with many Central nervous system (CNS) side effects. Drug treatment in HIV disease is characterized by a great variability in response, in terms of both efficacy and toxicity that is why amongst individuals taking the same drug at the same doses, some will develop ADRs and others will not. Several factors may affect this variability among which, host genetic factors are by far the most important. EFV is principally metabolized by cytochrome P450 2B6 enzyme (CYP2B6). The gene that encodes for CYP2B6 is highly polymorphic. Up to date, about 60 allelic variants have been reported. Of these, CYP2B6 516G>T and 983T>C single nucleotide polymorphisms (SNPs) have been reported to be of clinical relevance. These polymorphisms were shown to be associated with increased plasma levels of EFV and the increased likelihood of developing central adverse effects. The general aim of this study was to obtain pharmacovigilance and pharmacogenetic data in a Cameroonian population on CYP2B6 gene coding for an enzyme involved in the metabolism of EFV and propose a procedure manual for the better management of HIV patients in Cameroon. To assess the general profile of ADRs and the prevalence of those associated with EFV, a retrospective study was carried out at the day care unit in the Central Hospital of Yaoundé in Cameroon. The patients recruited into this study were enrolled in the ART programme between January 2013 and December 2013. Data were obtained from clinical records of HIV/AIDS patients and gathered using a structured questionnaire. The collected data were entered in an excel sheet and statistical analyses were done using the Statistical Package for the Social Sciences software (SPSS) version 25. The pharmacogenetic study was conducted on the Outpatients enrolled at the day care unit of the Yaoundé Central Hospital (YCH) and the Bertoua Regional Hospital (BRH). HIV-infected individuals already under ART, with or without ADRs, were selected retrospectively, participants were prospectively recruited after contacting them through phone calls. Five (5) mL of venous blood were collected from participants who gave their consent. Blood was spotted on filter paper for further analysis by PCR. DNA was extracted using the Chelex method. The two polymorphisms under study were detected by the Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP). For CYP2B6 516 G>T and CYP2B6 983 T>C, the restriction enzymes used were BsrI and BsmAI respectively. The respective genotypes were determined according to a specific fragment pattern on agarose gel electrophoresis. Results were compared between patients with and without EFV-related side effects. A total of 1254 individuals were included in the retrospective study. The spectrum of adverse events in the study was wide and varied. The overall prevalence of adverse drug reactions was 24.40% (306/1254). The most common systems affected by adverse reactions were hematological, systemic, gastro-intestinal, dermatological and the central nervous system with 37.58%, 12.75%, 12.75%, 12.60 and 10.78% respectively. A total number of 425 participants among which 174 from Yaoundé Central Hospital and 251 from the Bertoua regional Hospital were included in the pharmacogenetic study. This study demonstrated that the CYP2B6 516G>T SNP was strongly associated with susceptibility to develop Central Nervous System (CNS) adverse events induced by Efavirenz in HIV/AIDS-infected Cameroonians. The 516GG genotype (extensive or normal metabolizers) was protective (OR=0.865, p=0.000) while the TT (slow metabolizers) was about seven times at risk of developing ADRs (OR=6.723, p=0.002). Individuals homozygous for the wild-type allele (983TT) appeared to be less likely to develop EFV associated ADRs compared to other genotypes although with no significant difference. Slow metabolizers (983CC) were shown to be more susceptible to develop hallucinations (OR=7.3, p=0.057), vision reduction (OR=22.700, p=0.011) and memory loss (OR=27.522, p=0.004). Additionally we showed that haplotypes were also associated with the susceptibility of developing CNS adverse effects. Individuals harboring the wild type genotype for the two polymorphisms (516GG/983TT) were shown to be protected against neurotoxicity (OR=0.356, p=0.011). CYP2B6 genotyping should be introduced in clinical practice because it would help to determine patients at high risk to develop adverse drug reactions and guide to choose a better therapeutic option thereby preventing or decreasing the adverse neuropsychiatric events after the initiation of EFV-based antiretroviral regimen.