Ayorinde Adehin

Polymorphisms of CYP1A2 and CYP2A6 activity: phenotypes and the effect of age and sex in a Nigerian population

Abstract Background: CYP1A2 and CYP2A6 are polymorphic enzymes that metabolise several compounds of clinical importance. This study investigated the prevalent phenotypes of these enzymes and the influence of age and sex on enzyme activity in a Nigerian population. Methods: Caffeine (110 mg) was administered to each of 129 healthy, unrelated subjects (85 males and 44 females) who were non-smokers. Urine voided within 7 h after caffeine administration was collected for a high performance liquid chromatographic assay of caffeine (137X), 1,7-dimethyluric acid (17U) and 1,7-dimethylxanthine (17X). CYP1A2 activity was measured as a ratio of (17U+17X) to 137X, while 17U/17X served as marker for CYP2A6. Transformed data were analysed and the influences of age and sex on activity were also determined. Results: Distribution of CYP1A2 activity in the population was bimodal with a mean±SD of 0.82±0.41, while that of CYP2A6 was trimodal with a mean±SD activity of 0.27±0.42 of the log-transformed urinary molar ratio of metabolites. The influences of age and sex on enzyme activity for both CYP1A2 and CYP2A6 were not significant (p>0.05). Conclusions: The study established the prevalence of polymorphism in phenotypes of CYP1A2 and CYP2A6 activity in the Nigerian population, but no influence of age and sex on enzyme activity was observed in this population.

Simultaneous determination of amodiaquine and pioglitazone on dried blood spots (DBS) by HPLC–DAD and its usefulness in pharmacokinetic studies

ABSTRACT A simple and rapid method for simultaneous determination of amodiaquine and pioglitazone in dried blood spots (DBS) was developed and validated. Blood samples were spotted on protein saver cards and dried and a 4-mm punch was extracted with methanol first and later with 1% acetic acid and dichloromethane. The separation was achieved on a C8 Zorbax Eclipse XDB analytical column (4 µm, 150 × 4.6 mm2 i.d.) at 27°C with a mobile phase of methanol/0.2% acetic acid (60:40) at a flow rate of 0.8 mL/min and detected at 230 nm. The method was linear over the range 2–80 ng/mL for amodiaquine and 10–1500 ng/mL for pioglitazone with correlation coefficients greater than 0.9995. The limits of detection were 1.12 and 10.93 µg/L and the limits of quantification were 3.39 and 33.11 µg/L for amodiaquine and pioglitazone, respectively. The inter- and intra-day precision were <6.7 and <7% for amodiaquine and <6.3 and <3% for pioglitazone. The method was applied to estimate the pharmacokinetic (PK) parameters in four healthy volunteers and it was found to yield identical PK profiles with other earlier methods supporting the use of DBS as an alternative for PK study. GRAPHICAL ABSTRACT

Polymorphisms in CYP2C8 and CYP3A5 genes in the Nigerian population

Polymorphisms in CYP2C8 and CYP3A5 genes have implications for responses elicited by the ingestion of some xenobiotics, the metabolism of which are mediated by these enzymes. CYP2C8*2, CYP2C8*3, CYP3A5*3, CYP3A5*6 and CYP3A5*7 are a few functionally-relevant variants of these genes which this study provides data for, in the Nigerian population. Blood samples were processed for genomic DNA from 178 unrelated subjects spread across Nigerian ethnicities and screened for these polymorphism through the Sequenom iPLEX MassARRAY platform. Results obtained were further validated with Sanger sequencing of a few samples and thereafter, the genotype data were statistically processed. All alleles were in Hardy-Weinberg equilibrium and CYP2C8*2 occurred at a frequency (95% CI) of 0.194 (0.154, 0.239), while CYP3A5*3, CYP3A5*6 and CYP3A5*7 were found at frequencies (95% CI) of 0.160 (0.124, 0.202), 0.096 (0.067, 0.131) and 0.126 (0.094, 0.166), respectively. However, CYP2C8*3 was not detected in the population. The study observed a 60% prevalence of carriers of at least a CYP3A5 polymorphism in the population, suggesting the probable existence of huge variability in CYP3A5 activity which may prove significant in the administration of drugs with narrow therapeutic windows and whose metabolism is largely mediated by CYP3A5.

Bidirectional Pharmacokinetic Interaction Between Amodiaquine and Pioglitazone in Healthy Subjects

Amodiaquine (AQ) and pioglitazone (PGZ) are both metabolized by CYP2C8, an enzyme also inhibited by PGZ. These drugs are likely to be administered in instances of comorbidity of malaria with type 2 diabetes. This study, hence, evaluated the possibility of a drug interaction resulting from the concurrent use of both drugs. A 3‐period crossover design in 10 healthy subjects, that assessed the disposition of AQ and PGZ alone and when coadministered, was implemented with the administration of single oral doses of AQ and PGZ. Whole‐blood samples collected between 0 and 24 hours on protein saver cards across the study periods were processed and analyzed for AQ and PGZ contents. Pharmacokinetic parameters were derived by a noncompartmental analysis. Geometric mean ratios for the Cmax, area under the concentration‐time curve for 24 hours (AUC0‐24h), and AUC0‐∞, alongside their corresponding 90%CIs, were compared across the study periods to infer clinically significant changes in disposition. The coadministration of AQ and PGZ resulted in decreases of about 38% and 54% in the Cmax and AUC0‐24h of AQ, respectively. For PGZ, the Cmax increased by about 50%, and AUC0‐24 rose by 48%. The 90%CIs of geometric mean ratios for the Cmax, AUC0‐24h, and AUC0‐∞ were all outside the expected bioequivalence interval of 80% to 125% for both drugs, implying significant interactions. These findings suggest that a bidirectional interaction between AQ and PGZ, with likely implications for the therapy and toxicity of both drugs, may occur in the event of their coadministration.

Inter-individual variation in imatinib disposition: any role for prevalent variants of CYP1A2, CYP2C8, CYP2C9, and CYP3A5 in Nigerian CML patients?

Abstract Imatinib has been successful in the management of chronic myeloid leukemia (CML) but some patients experience adverse reactions or develop resistance to its use. The roles of some polymorphisms in genes encoding enzymes critical for the biotransformation of imatinib have been previously examined. This study, hence, evaluated some other unstudied functionally significant polymorphisms in CYP1A2, CYP2C8, CYP2C9, and CYP3A5. Trough imatinib blood levels and genotypes were determined in 42 CML patients by an HPLC-UV technique and a Sequenom iPLEX assay, respectively. Statistical analysis of the influence of genetic polymorphisms on standardized trough level detected no significant relationship. However, higher trough levels were observed in two homozygous carriers of CYP2C8*2 while diminished imatinib levels were seen in two homozygous carriers of CYP3A5*7. The study findings suggest that polymorphisms in drug metabolizing enzymes may be significant for imatinib therapy only in instances where all copies of the relevant studied genes are functionally impaired.

Relationship between metabolic phenotypes and genotypes of CYP1A2 and CYP2A6 in the Nigerian population

Abstract Background: CYP1A2 and CYP2A6 are polymorphic drug-metabolising enzymes that are also implicated in the activation of procarcinogens in humans. Some of their alleles and haplotypes, often varied in prevalence across populations, are thought to influence activity despite the known contribution of environmental factors. This study assessed the potential influence of some genetic variants of CYP1A2 and CYP2A6 on metabolic phenotypes in Nigerians. Methods: Genomic DNA was extracted from blood samples of 100 healthy, unrelated subjects for whom CYP1A2 and CYP2A6 phenotypes had previously been determined, alongside an additional 80 other individuals for whom phenotype data were unavailable. The samples were screened for CYP1A2 (*1C,*1D,*1E,*1F, *3,*4,*6,*7) and CYP2A6 (*9,*11,*17) alleles using the Sequenom MassARRAY platform for some alleles and direct Sanger sequencing for others. The genetic data acquired were subsequently analysed for haplotypes and assessed for concordance with phenotypes. Results: All five CYP1A2 haplotypes (CYP1A2*1F, 1J, 1N, 1L, 1W) identified in the Nigerian population were not significantly predictive of metabolic phenotypes. Heterozygous CYP1A2*1J carriers and homozygous CYP1A2*1W carriers showed statistically insignificant decrease in CYP1A2 activity. The CYP2A6*9/*17 genotype was, however, significantly associated with the CYP2A6-poor metabolic phenotype, whereas CYP2A6*9 or CYP2A6*17 alone did not show any such association. CYP2A6*11 was not detected in the population. Conclusions: Our findings suggest that CYP1A2 alleles or haplotypes were not predictive of metabolic phenotypes in the Nigerian population. Carriers of CYP2A6*9/*17 genotype are likely to be poor metabolisers of CYP2A6 substrates and may experience adverse reactions or poor efficacy while using drugs metabolised mainly by CYP2A6.