Quinine 3-hydroxylation as a biomarker reaction for the activity of CYP3A4 in man

Enzymatic Activities of CYP3A4 Allelic Variants on Quinine 3-Hydroxylation In Vitro

Cytochrome P450 3A4 (CYP3A4) enzyme activity is known to show considerable ethnic heterogeneity and inter-individual differences, affecting the outcome of drug treatment. CYP3A4 genetic polymorphisms are believed to be one of the important causes, leading to inter-individual variability in drug metabolism. Quinine is an antipyretic drug with antimalarial properties that is metabolized primarily by CYP3A4. Quinine 3-hydroxylation has been proven as a biomarker reaction for evaluating CYP3A4 ability. Quinine has frequent adverse effects and there are distinct inter-individual differences in quinine sensitivity. The open reading frame for 30 CYP3A4 allelic variants were constructed from wild-type CYP3A4*1A by an overlap extension polymerase chain reaction. Recombinant CYP3A4 variants were expressed using baculovirus-insect cell expression system, and their catalytic activities towards quinine hydroxylation were determined and evaluated. Of the 30 CYP3A4 allelic variants, 23 variants exhibited significantly reduced intrinsic clearance towards quinine, 2 variants showed increased intrinsic clearance for quinine, 2 variants possessed no significant differences towards quinine, compared with CYP3A4*1A, and 3 variants had no detected expression and enzyme activity. Our assessment on the enzymatic activities of CYP3A4 variants towards quinine may contribute to laying an experimental foundation for further clinical studies so as to accelerate the process of determining the associations between genetic variations and clinical phenotypes.

Erlotinib treatment induces cytochrome P450 3A activity in non-small cell lung cancer patients

AIMS

Erlotinib is a tyrosine kinase inhibitor used in the treatment of non-small cell lung cancer highly metabolized by the cytochrome P450 (CYP) 3A. Hence, CYP3A4 activity might be a useful predictor of erlotinib pharmacokinetics in personalized medicine. The effect of erlotinib on CYP3A activity was therefore studied in non-small cell lung cancer patients.

METHODS

The study included 32 patients scheduled for erlotinib monotherapy. CYP3A activity was assessed using quinine as a probe before and during erlotinib treatment. Plasma from blood samples drawn 16 hours post quinine administration were analysed using HPLC with fluorescence detection to determine the quinine/3-OH-quinine ratio.

RESULTS

Matched samples, available from 13 patients, showed an induction of CYP3A activity (P = 0.003, Wilcoxon's signed rank test) after 2 months of treatment. The quinine/3-OH-quinine ratio decreased from 20.2 (± 13.4) at baseline to 11.0 (± 4.34). Single-point samples, available from 19 patients, supported the decrease in ratio (P = 0.007, Mann-Whitney U-test). Generally, females had a higher CYP3A activity both at baseline and after two months of treatment. Statistical analysis by gender also showed significant increase in CYP3A activity (males, n = 10, P = 0.001, and females, n = 22, P = 0.001).

CONCLUSIONS

An induction of CYP3A activity was observed after 2 months of erlotinib treatment which was also seen when subdividing based on gender. It could be important to take this into consideration for patients co-administering other CYP3A-metabolizing drugs during erlotinib treatment and also makes it difficult to use baseline CYP3A activity to predict erlotinib pharmacokinetics.

Functional characterization of a unique cytochrome P450 in Toxoplasma gondii

The basic metabolic cytochrome P450 (CYP) proteins are essential for the biotransformation of sterols and xenobiotics. By contrast, the Toxoplasma gondii genome contains only one CYP gene, and the role of this enzyme in the physiology and biochemistry of apicomplexan parasites is unknown. Because it is a potential resistance gene, identifying the functionality of P450 in T. gondii is particularly important. Knocking out Tg-P450 had no significant effect on T. gondii survival, but mice infected with parasites overexpressing Tg-P450 exhibited significantly enhanced pathogenicity. Enzyme activity analyses demonstrated that this protein has mammalian CYP2B and CYP3A enzymatic activity. In addition, T. gondii lacking the P450 gene exhibited reduced resistance to quinine, mefloquine and clarithromycin compared with parasites overexpressing Tg-P450. These results suggest that P450 functions in T. gondii metabolism and detoxification is involved in vitally important processes in parasitic organisms, making this enzyme a potential drug target.

In Vivo Cytochrome P450 3A Isoenzyme Activity and Pharmacokinetics of Imatinib in Relation to Therapeutic Outcome in Patients With Chronic Myeloid Leukemia

BACKGROUND

Cytochrome P450 3A (CYP3A) isoenzyme metabolic activity varies between individuals and is therefore a possible candidate of influence on the therapeutic outcome of the tyrosine kinase inhibitor imatinib in patients with chronic myeloid leukemia (CML). The aim of this study was to investigate the influence of CYP3A metabolic activity on the plasma concentration and outcome of imatinib in patients with CML.

METHODS

Forty-three patients with CML were phenotyped for CYP3A activity using quinine as a probe drug and evaluated for clinical response parameters. Plasma concentrations of imatinib and its main metabolite, CGP74588, were determined using liquid chromatography-mass spectrometry.

RESULTS

Patients with optimal response to imatinib after 12 months of therapy did not differ in CYP3A activity compared to nonoptimal responders (quinine metabolic ratio of 14.69 and 14.70, respectively; P = 0.966). Neither the imatinib plasma concentration nor the CGP74588/imatinib ratio was significantly associated with CYP3A activity.

CONCLUSIONS

The CYP3A activity does not influence imatinib plasma concentrations or the therapeutic outcome. These results indicate that although imatinib is metabolized by CYP3A enzymes, this activity is not the rate-limiting step in imatinib metabolism and excretion. Future studies should focus on other pharmacokinetic processes so as to identify the major contributor to patient variability in imatinib plasma concentrations.

Pharmacokinetic drug interactions in liver disease: An update

Inhibition and induction of drug-metabolizing enzymes are the most frequent and dangerous drug-drug interactions. They are an important cause of serious adverse events that have often resulted in early termination of drug development or withdrawal of drugs from the market. Management of such interactions by dose adjustment in clinical practice is extremely difficult because of the wide interindividual variability in their magnitude. This review examines the genetic, physiological, and environmental factors responsible for this variability, focusing on an important but so far neglected cause of variability, liver functional status. Clinical studies have shown that liver disease causes a reduction in the magnitude of interactions due to enzyme inhibition, which is proportional to the degree of liver function impairment. The effect of liver dysfunction varies quantitatively according to the nature, reversible or irreversible, of the inhibitory interaction. The magnitude of reversible inhibition is more drastically reduced and virtually vanishes in patients with advanced hepatocellular insufficiency. Two mechanisms, in order of importance, are responsible for this reduction: decreased hepatic uptake of the inhibitory drug and reduced enzyme expression. The extent of irreversible inhibitory interactions is only partially reduced, as it is only influenced by the decreased expression of the inhibited enzyme. Thus, for appropriate clinical management of inhibitory drug interactions, both the liver functional status and the mechanism of inhibition must be taken into consideration. Although the inducibility of drug-metabolizing enzymes in liver disease has long been studied, very conflicting results have been obtained, mainly because of methodological differences. Taken together, the results of early animal and human studies indicated that enzyme induction is substantially preserved in compensated liver cirrhosis, whereas no definitive conclusion as to whether it is significantly reduced in the decompensated state of cirrhosis was provided. Since ethical constraints virtually preclude the possibility of performing methodologically rigorous investigations in patients with severe liver dysfunction, studies have recently been performed in animals rigorously stratified according to the severity of liver insufficiency. The results of these studies confirmed that enzyme induction is virtually unaffected in compensated cirrhosis and indicated that the susceptibility of enzyme induction to severe liver dysfunction depends on the type of nuclear receptor involved and also varies among enzyme isoforms under the transcriptional control of the same nuclear receptor. These findings make it clear that no general conclusion can be reached from the study of any particular enzyme and partly explain the conflicting results obtained by previous studies. Since no general guidelines can be provided for the management of drug interactions resulting from enzyme induction, both the effects and the plasma concentration of the induced drug should be strictly monitored. The findings discussed in this review have important methodological implications as they indicate that, contrary to current guidelines, the magnitude of metabolic drug-drug interactions in patients with liver disease cannot be inferred from studies in healthy subjects.

Quinine as a potential tracer for medication adherence: A pharmacokinetic and pharmacodynamic assessment of quinine alone and in combination with oxycodone in humans

Effective strategies to monitor pharmacotherapy adherence are necessary, and sensitive biological markers are lacking. This study examined a subtherapeutic dose of quinine as a potential adherence tracer. Primary aims included examination of the plasma and urinary pharmacokinetic profile of once-daily quinine; secondary aims assessed pharmacokinetic/pharmacodynamic interactions with oxycodone (a CYP3A and CYP2D substrate). Healthy, nondependent opioid users (n = 9) were enrolled in this within-subject, double-blind, placebo-controlled inpatient study. Participants received the following oral doses: day 1, oxycodone (30 mg); days 2-4, quinine (80 mg); day 5, quinine and oxycodone (2 hours postquinine). Blood and 24-hour urine samples were collected throughout the study, and pharmacodynamic outcomes were assessed during experimental sessions (days 1, 4, 5). Quinine displayed a plasma Tmax ∼2 hours and t1/2 ∼10 hours. Oxycodone and noroxycodone parameters (Tmax , Cmax , t1/2 ) were similar with or without quinine present, although drug exposure (AUC) was slightly greater when combined with quinine. No pharmacodynamic interactions were detected, and doses were safely tolerated. During washout, quinine urinary concentrations steadily declined (elimination t1/2 ∼16 hours), with a 94% decrease observed 72 hours postdose. Overall, low-dose quinine appears to be a good candidate for a medication additive to monitor adherence for detection of missed medication.

Influence of a Nigerian honey on CYP3A4 biotransformation of quinine in healthy volunteers

WHAT IS KNOWN AND OBJECTIVES

Some studies, howbeit with conflicting reports, have suggested that consumption of honey has a potential to modulate drug metabolizing enzymes which may result in a honey-drug interaction. Numerous studies have established that honey varies in composition, influenced by the dominant floral, processing and environmental factors. Thus, variation in honey composition may be a contributing factor to the controversial results obtained. No previous drug interaction study has been carried out with any honey from Africa. CYP 3A4 is an important enzyme in drug metabolism studies as it is involved in the metabolism of over 50% of drugs in clinical use and quinine remains very relevant in malaria treatment in the tropics, and we therefore determined whether there is potential drug interaction between a Nigerian honey and quinine, a drug whose metabolism to 3-hydroxyquinine is mediated majorly by CYP3A4.

METHODS

In a three-phase randomized crossover study with a washout period of 2 weeks between each treatment phase, ten (10) healthy volunteers received quinine sulphate tablet (600 mg single dose) alone (phase 1) or after administration of 10 ml of honey (Phase 2) and 20 mL of honey (Phase 3) twice daily for seven (7) days. Blood samples were collected at the 16th hour post-quinine administration in each phase, and quinine and its major metabolite, 3-hydroxyquinine, were analysed using a validated HPLC method.

RESULTS

After scheduled doses of honey, the mean metabolic ratios of quinine (3-hydroxyquinine/quinine) increased by 24·4% (with 10 mL of honey) and reduced by 23·9% (with 20 mL of honey) when compared to baseline. These magnitudes of alteration in the mean metabolic ratios were not significant (P > 0·05; Friedman test). The geometric mean (95% CI) for the metabolic ratio of quinine before and after honey intake at the two dose levels studied was 0·82 (0·54, 1·23) and 1·29 (0·96, 1·72), respectively, and were also not significant (P = 0·296 and 0·081 respectively; Student's t-test).

WHAT IS NEW AND CONCLUSION

This is a pioneer study on the effect of Nigerian/African honey on quinine metabolism. The findings indicated that low and high doses of honey did not significantly affect metabolism of quinine to 3-hydroxyquinine. This suggests that CYP3A4 activity is not significantly altered following low or high dose of honey, as CYP3A4 has been reported to be responsible for the conversion of quinine to 3-hydroxyquinine. In conclusion, the outcome of this study suggests that there may be no potential significant metabolic interaction between Nigerian honey and quinine administration.

Effect of dehusked Garcinia kola seeds on the overall pharmacokinetics of quinine in healthy Nigerian volunteers

We investigated the effect of concurrent ingestion of Garcinia kola seed on the pharmacokinetics of quinine. In a randomized crossover study, 24 healthy Nigerian volunteers were assigned into 2 groups (A and B; n = 12 per group) on the basis of G. kola dose orally ingested. Each subject received 600 mg quinine sulfate before and after ingesting 12.5 g of G. kola once daily for 7 days (group A) or 12.5 g twice daily for 6 days and once on the seventh day (group B). Blood samples were collected and analyzed for plasma quinine and its metabolite (3-hydroxyquinine) using a validated high performance liquid chromatography method. Concurrent administration of quinine with G. kola reduced quinine tmax by 48% (group A), mean Cmax by 19% and 26% in groups A and B, respectively, and slight reduction in mean AUC0- ∞ of quinine in both groups. 3-hydroxyquinine Cmax also reduced by 29% and 32%; AUC0-∞ by 13% and 9%, respectively. The point estimates of the T/R ratio of the geometric means for all Cmax obtained and only the AUC0-∞ at a higher dose of G. kola were outside the 80%-125% bioequivalence range. In conclusion, an herb-drug interaction was noted with concurrent quinine and G. kola administration.

Genome-wide association study reveals a complex genetic architecture underpinning-induced CYP3A4 enzyme activity

Atypical cytochrome P450 3A4 (CYP3A4) enzyme activity-induced and inhibited-is thought to be the driver of numerous poor or adverse therapeutic responses to up to 50 % of all commonly prescribed drugs. We carried out a genome-wide association study to identify common genetic variants associated with variation in induced CYP3A4 activity. A total of 310 twins were included in this study. Each participant had already completed a 14 days course of St John's Wort to induce CYP3A4, which was quantified through the metabolic ratio of exogenous 3-hydroxyquinine to quinine. We failed to detect any genome-wide significant associations (P < 1 × 10(-8)) with variation in induced CYP3A4 activity although several genomic regions were highlighted which may play minor roles. We report the first GWAS of variation in induced CYP3A4 activity and our preliminary results indicate a complex genetic architecture underpinning induced CYP3A4 enzyme activity.

4β-Hydroxycholesterol, an endogenous marker of CYP3A4/5 activity in humans

We have proposed that 4β-hydroxycholesterol (4β-OHC) may be used as an endogenous marker of CYP3A activity. The cholesterol metabolite 4β-OHC is formed by CYP3A4. Treatment of patients with strong inducers of CYP3A enzymes, e.g. anti-epileptic drugs, resulted in 10-fold increased concentrations of plasma 4β-OHC, while treatment with CYP3A inhibitors such as ritonavir or itraconazole resulted in decreased plasma concentrations. There was a relationship between the 4β-OHC concentration and the number of active CYP3A5*1 alleles showing that 4β-OHC was not only formed by CYP3A4, but also by CYP3A5. The concentration of 4β-OHC was higher in women than in men, confirming previous studies indicating a gender difference in CYP3A4/5-activity. The rate of elimination of 4β-OHC is slow (half-life 17 days) which results in stable plasma concentrations within individuals, but limits its use to study rapid changes in CYP3A activity. In short-term studies exogenous markers such as midazolam or quinine may be superior, but in long-term studies 4β-OHC is a sensitive marker of CYP3A activity, especially to assess induction but also inhibition. Under conditions where the cholesterol concentration is changing, the ratio of 4β-OHC:cholesterol may be used as an alternative to 4β-OHC itself. The use of an endogenous CYP3A marker has obvious advantages and may be of value both during drug development and for monitoring CYP3A activity in patients.

Genetic variations in ABCB1 and CYP3A5 as well as sex influence quinine disposition among Ugandans

Quinine is one of the most effective antimalarial drugs, although its clinical use is limited as a result of its narrow safety margin. Quinine is a substrate of the polymorphic p-glycoprotein and CYP3A4/3A5. This study aimed to examine the effects of genetic variations in ABCB1 and CYP3A5 genes, sex, demographic, and biochemical variables (serum albumin, creatinine, alanine aminotransferase and albumin) on quinine disposition among Ugandans. Quinine (600 mg) was orally administered to 140 healthy volunteers. Quinine and its metabolite 3-hydroxyquinine concentrations were determined from 16-hour postdose plasma by high-performance liquid chromatography. CYP3A5 activity was measured using quinine/3-hydroxyquinine ratio (metabolic ratio). Genotyping for a total of 20 single nucleotide polymorphisms in ABCB1 (n = 13) and CYP3A5 (n = 7) was done using Taqman and minisequencing on microarray. There were 20.5- and 13-fold variations in body weight-adjusted plasma quinine concentrations (mean +/- standard deviation, 5.26 +/- 2.5 mumol/L; range, 0.88-18.10 mumol/L) and quinine-to-3-hydroxyquinine metabolic ratio (mean +/- standard deviation, 7.68 +/- 3.3 mumol/L; range, 1.66-22.3 mumol/L), respectively. Weight-adjusted plasma quinine concentration was significantly influenced by sex and ABCB1 haplotype. There was a significant sex difference in quinine metabolic ratio, women being faster metabolizers than men (P = 0.01). CYP3A5 genotype/haplotype significantly (P = 0.03) influenced quinine disposition with a clear CYP3A5*1 gene dose effect. The result confirms that quinine disposition is influenced mainly by sex as well as by ABCB1 and CYP3A5 genotypes. Despite being fast metabolizers, women display higher quinine bioavailability than men in Uganda. This may have clinical significance in determining an individual's susceptibility to quinine-associated adverse reactions such as cinchonism.

Pharmacogenetic studies of Paclitaxel in the treatment of ovarian cancer

The purpose of this study was to evaluate the role of sequence variants in the CYP2C8, ABCB1 and CYP3A4 genes and the CYP3A4 phenotype for the pharmacokinetics and toxicity of paclitaxel in ovarian cancer patients. Thirty-eight patients were treated with paclitaxel and carboplatin. The genotypes of CYP2C8*1B, *1C, *2, *3, *4, *5, *6, *7, *8 and P404A, ABCB1 G2677T/A and C3435T, as well as CYP3A4*1B, were determined by pyrosequencing. Phenotyping of CYP3A4 was performed in vivo with quinine as a probe. The patients were monitored for toxicity and 23 patients underwent a more extensive neurotoxicity evaluation. Patients heterozygous for G/A in position 2677 in ABCB1 had a significantly higher clearance of paclitaxel than most other ABCB1 variants. A lower clearance of paclitaxel was found for patients heterozygous for CYP2C8*3 when stratified according to the ABCB1 G2677T/A genotype. In addition, the CYP3A4 enzyme activity in vivo affected which metabolic pathway was dominant in each patient, but not the total clearance of paclitaxel. The exposure to paclitaxel correlated to the degree of neurotoxicity. Our findings suggest that interindividual variability in paclitaxel pharmacokinetics might be predicted by ABCB1 and CYP2C8 genotypes and provide useful information for individualized chemotherapy.

Time course of the increase in 4beta-hydroxycholesterol concentration during carbamazepine treatment of paediatric patients with epilepsy

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

CYP3A4 converts cholesterol into 4beta-hydroxycholesterol. We have suggested that 4beta-hydroxycholesterol could be used as a clinical marker for CYP3A4 activity aiding in dose adjustments. The kinetics of 4beta-hydroxycholesterol formation is not known, however, and must be determined in order to establish under what conditions 4beta-hydroxycholesterol can be used as a CYP3A marker.

WHAT THIS STUDY ADDS

The concentration of 4beta-hydroxycholesterol increases very slowly during CYP3A4/5 induction in paediatric patients. Whereas induction of CYP3A4/5 was apparently complete within 1-2 weeks of carbamazepine treatment, plasma 4beta-hydroxycholesterol levels continued to increase until at least 8 weeks of treatment. AIMS To investigate the time course of the increase in 4beta-hydroxycholesterol and carbamazepine plasma concentrations during treatment of paediatric patients with epilepsy.

METHODS

Eight paediatric patients with newly diagnosed epilepsy were studied. Blood samples were drawn before and after about 1, 2, 4, 8 and 16 weeks of carbamazepine treatment. The plasma concentrations of 4beta-hydroxycholesterol were determined by gas chromatography-mass spectrometry and carbamazepine and its epoxide metabolite by high-performance liquid chromatography.

RESULTS

The basal plasma concentrations of 4beta-hydroxycholesterol showed a large range of observed values between 18 and 99 ng ml(-1). Carbamazepine treatment increased mean plasma 4beta-hydroxycholesterol significantly already after 1 week of treatment (from 43 to 80 ng ml(-1), P < 0.001). 4beta-Hydroxycholesterol concentrations continued to increase until at least 8 weeks of treatment and the concentrations in the final samples (8-23 weeks of treatment) varied between 122 and 494 ng ml(-1). Plasma concentrations of carbamazepine and its epoxide metabolite reached steady state at 1-2 weeks after last dose change.

CONCLUSIONS

Carbamazepine treatment of paediatric patients with epilepsy resulted in an induction of CYP3A4/5 and a concomitant increase in plasma 4beta-hydroxycholesterol. Whereas the induction of CYP3A4/5 was apparently complete after 1-2 weeks, the increase in 4beta-hydroxycholesterol continued for several weeks. Thus CYP3A4 activity is not the only determinant of the circulating level of 4beta-hydroxycholesterol. Additional factors such as transport and storage or presence of another enzyme may thus be of importance.

Appropriate phenotyping procedures for drug metabolizing enzymes and transporters in humans and their simultaneous use in the "cocktail" approach

Phenotyping for drug metabolizing enzymes and transporters is used to assess quantitatively the effect of an intervention (e.g., drug therapy, diet) or a condition (e.g., genetic polymorphism, disease) on their activity. Appropriate selection of test drug and metric is essential to obtain results applicable for other substrates of the respective enzyme/transporter. The following phenotyping metrics are recommended based on the level of validation and on practicability: CYP1A2, paraxanthine/caffeine in plasma 6 h after 150 mg caffeine; CYP2C9, tolbutamide plasma concentration 24 h after 125 mg tolbutamide; CYP2C19, urinary excretion of 4'-OH-mephenytoin 0-12 h after 50 mg mephenytoin; CYP2D6, urinary molar ratio debrisoquine/4-OH-debrisoquine 0-8 h after 10 mg debrisoquine; and CYP3A4, plasma clearance of midazolam after 2 mg midazolam (all drugs given orally).

Inhibition of CYP3A4 and CYP3A5 catalyzed metabolism of alprazolam and quinine by ketoconazole as racemate and four different enantiomers

OBJECTIVE

The antifungal drug ketoconazole (KTZ) is known as an inhibitor of, especially, the CYP3A subfamily, which catalyzes the metabolism of a large variety of drugs. Interactions between KTZ and CYP3A substrates have been reported both in vivo and in vitro. Most of them, however, involved the KTZ racemate. KTZ racemate and the separate enantiomers, 2R,4R; 2R,4S; 2S,4S, and 2S,4R, were evaluated for their selectivity in inhibiting alprazolam and quinine metabolism.

METHODS

The inhibition of alprazolam and quinine metabolism was studied in an in vitro system of human liver microsomes (HLM), recombinant of CYP3A4 and CYP3A5. The concentrations of formed 3-hydroxyquinine and 4- and alpha-hydroxyalprazolam were measured by HPLC and LC-MS, respectively.

RESULTS

Quinine 3-hydroxylation was catalyzed to a similar extent by CYP3A4 and CYP3A5. The formation rate of 4-hydroxyalprazolam was higher than that of alpha-hydroxyalprazolam for each HLM, CYP3A4 and CYP3A5. KTZ racemate and enantiomers showed differential inhibitory effects of quinine and alprazolam metabolism. Quinine metabolism catalyzed by HLM, CYP3A4 and CYP3A5 was potently inhibited by the trans-enantiomer KTZ 2S,4S, with IC(50) value of 0.16 microM for HLM, 0.04 microM for CYP3A4 and 0.11 microM for CYP3A5. The same enantiomer showed the lowest IC(50) values of 0.11 microM for HLM and 0.04 microM for CYP3A5 with respect to alprazoalm 4-hydroxylation and also the same pattern for alprazolamalpha-hydroxylation, 0.13 microM for HLM and 0.05 microM for CYP3A5. Alprazolam metabolism (both alpha- and 4- hydroxylations) catalyzed by CYP3A4 was inhibited potently by the cis-enantiomer KTZ 2S,4R, with IC(50) values of 0.03 microM.

CONCLUSIONS

Alprazolam and quinine metabolism is catalyzed by both CYP3A4 and CYP3A5. The present study showed that different KTZ enantiomers inhibit CYP3A4 and CYP3A5 to different degrees, indicating that structural differences among the enantiomers would be related to their inhibitory potency on these two enzymes.

CYP3A5 genotype has significant effect on quinine 3-hydroxylation in Tanzanians, who have lower total CYP3A activity than a Swedish population

OBJECTIVES

To study the correlation between CYP3A5 genotype and quinine 3-hydroxylation in black Tanzanian and Swedish Caucasians as well as to investigate the interethnic differences in CYP3A activity between the two populations.

METHODS

Tanzanian (n=144) and Swedish (n=136) healthy study participants were given a single oral 250 mg dose of quinine hydrochloride and a 16-h post-dose blood sample was collected. The metabolic ratio of quinine/3-hydroxyquinine was determined in plasma by high-performance liquid chromatography. All the participants were genotyped for the known mutations of CYP3A5, which are relevant for the respective population. Correlation between quinine metabolic ratio and CYP3A5 genotype as well as the interethnic difference in CYP3A activity between the two populations was studied.

RESULTS

Tanzanians had significantly higher (P<0.0001) mean quinine metabolic ratio (9.5+/-3.5) than Swedes (7.6+/-3.1). As expected, the frequency of high CYP3A5 expression alleles was higher in Tanzanians (51%) than in Swedes (7%). The mean+/-SD quinine metabolic ratio (10.7+/-3.9) in Tanzanians homozygous for low CYP3A5 expression gene was significantly higher than the corresponding mean metabolic ratio in participants heterozygous (9.5+/-3.3; P=0.02) or homozygous (8.1+/-3.1; P=0.002) for high expression CYP3A5 alleles, respectively. A tendency to higher quinine metabolic ratio in Swedes with low expression alleles compared with those with one or two high expression alleles was observed. Tanzanians homozygous for low CYP3A5 expression gene (i.e. only CYP3A4 is expressed) had significantly (P<0.0001) higher quinine metabolic ratio (10.7+/-3.9) than corresponding Swedes (7.7+/-3.1).

CONCLUSIONS

Clear interethnic differences were observed in the activity of CYP3A between Tanzanians and Swedes. A significant association is noted between CYP3A5 genotype and quinine 3-hydroxylation in Tanzanians, indicating a significant contribution of CYP3A5 to total 3A activity. The CYP3A4 catalyzed hydroxylation of quinine (two low CYP3A5 expression alleles) was lower in Tanzanians than in Swedes.