The human cytochrome P450 3A (CYP3A) enzymes, which metabolize 50% of currently used therapeutic drugs, exhibit great interindividual differences in activity that have a major impact on drug ...treatment outcome, but hitherto no genetic background importantly contributing to this variation has been identified. In this study we show that
CYP3A4 mRNA and hnRNA contents with a few exceptions vary in parallel in human liver, suggesting that mechanisms affecting
CYP3A4 transcription, such as promoter polymorphisms, are relevant for interindividual differences in CYP3A4 expression. Tanzanian (
n
=
143) healthy volunteers were phenotyped using quinine as a CYP3A probe and the results were used for association studies with
CYP3A4 genotypes. Carriers of
CYP3A4*
1B had a significantly lower activity than those with
CYP3A4*
1 whereas no differences were seen for five other SNPs investigated. Nuclear proteins from the B16A2 hepatoma cells were found to bind with less affinity to the
CYP3A4*
1B element around −392
bp as compared to
CYP3A4*
1. The data indicate the existence of a genetic
CYP3A4 polymorphism with functional importance for interindividual differences in enzyme expression.
OBJECTIVESTo 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.
METHODSTanzanian (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.
RESULTSTanzanians 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).
CONCLUSIONSClear 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.
The study was carried out to investigate the distribution of cytochrome P450 2D6 (CYP2D6) and CYP2C19 genotype frequencies in three African populations and to compare these frequencies between ...healthy individuals and psychiatric patients.
Three hundred and eighty-four subjects from South Africa (Venda), Tanzania, and Zimbabwe who consented to the study were genotyped for CYP2D6 (CYP2D6*1, *2, *3, *4, *5, and *17) and CYP2C19 (CYP2C19*1, *2, and *3) by PCR-RFLP (polymerase chain reaction restriction fragment length polymorphism) techniques.
The genotypes for CYP2D6 predicted a poor metabolizer frequency of 2.3% (2/88) in Tanzanian psychiatric patients, 1.9% (2/106) in Tanzanian healthy controls and 2.6% (2/76) in the South African Venda. The low-activity CYP2D6*17 allele frequency was higher in psychiatric patients (30%, 53/176) than in healthy individuals (20%, 43/212) in Tanzanians. The frequencies for CYP2C19*2 genotypes were predictive of a low prevalence of poor metabolizers (PMs). The CYP2C19*3 allele was absent in the three populations studied. There was no difference in CYP2D6 or CYP2C19 PM genotype frequencies between psychiatric patients and healthy subjects.
The genotype results predict a low prevalence of people with deficient CYP2D6 and CYP2C19 activity among linguistically (Bantu) related populations of East and Southern Africa. The high frequency of the low-activity CYP2D6*17 allele predicts that the Bantu people have a reduced capacity to metabolise drugs that are CYP2D6 substrates.
OBJECTIVESTo study the potential endogenous marker of CYP3A activity, 4β-hydroxycholesterol, and its relation to sex and the CYP3A5 geno/haplotypes and compare with CYP3A4/5 catalyzed 3-hydroxylation ...of quinine in the three major races.
METHODSThe plasma concentration of 4β-hydroxycholesterol was measured in healthy Tanzanians (n=138), Swedes (n=161) and Koreans (n=149) by gas chromatography–mass spectrometry. The metabolic ratio of quinine/3-hydroxyquinine in plasma 16-h post dose was determined by high performance liquid chromatography, previously reported in Tanzanians and Swedes, and now also in Koreans. The participants were genotyped for relevant alleles of CYP3A5.
RESULTSThe mean plasma concentrations of 4β-hydroxycholesterol in Koreans, Swedes and Tanzanians were 29.3, 26.8 and 21.9 ng/ml, respectively (P<0.01 between all three populations). Within all three populations there were significant differences in 4β-hydroxycholesterol levels between the CYP3A5 genotypes. Women had higher concentrations than men, but the difference was only significant in Tanzanians (P<0.001) and Koreans (P<0.00001). The quinine/3-hydroxyquinine metabolic ratio was significantly different in all three populations with the highest CYP3A activity in Koreans and the lowest in Tanzanians. Korean women had a lower metabolic ratio than men (P<0.00001). Significant correlations between 4β-hydroxycholesterol and quinine 3-hydroxylation were found in Tanzanians and Koreans.
CONCLUSIONClear differences in the activity of both CYP3A4 and CYP3A5 were shown in the three major human races. Both 4β-hydroxycholesterol and quinine/3-hydroxyquinine metabolic ratio showed a higher CYP3A activity in women than in men. The results give strong evidence that the plasma concentration of 4β-hydroxycholesterol may be used as an endogenous marker of CYP3A activity (CYP3A4+5).
Objective
The effects of the CYP2D6*17 and *29 alleles on substrate specificity and enzyme activity were studied by correlating CYP2D6 genotype to phenotype with 4 probe drugs (codeine, debrisoquine, ...dextromethorphan, metoprolol) in black Tanzanians and white Swedes.
Methods
The black Tanzanian subjects represented the following 6 genotypic groups: A, (CYP2D6*1 or *2)/(*1 or *2) (n = 13); B, CYP2D6*17/*17 (n = 5); C, CYP2D6*29/*29 (n = 4); D, CYP2D6*1/*17 (n = 5); E, CYP2D6*5/*17 (n = 4); and F, various genotypes (n = 4). The white subjects were from 4 groups, as follows: A, (CYP2D6*1 or *2)/(*1 or *2) (n = 7); B, (CYP2D6*1 or *2)/(*3, *4, or *5) (n = 7); C, homozygous for defect alleles (n = 7); and D, duplicated CYP2D6 gene (n = 2).
Results
The metabolic ratios of the 4 probe drugs correlated significantly (rs = 0.69–0.92; P < .001) in both populations. Tanzanian subjects homozygous for the CYP2D6*17 allele were slower metabolizers when debrisoquine or dextromethorphan was used as the probe drug than when codeine or metoprolol was used, showing a different substrate specificity of CYP2D6.17 than of CYP2D6.1 and CYP2D6.2. This was confirmed with analysis of covariance of the different metabolic ratios for a subgroup of subjects carrying only the CYP2D6*17 mutated allele (n = 9) compared with all other subjects (n = 44). The metabolic ratios of dextromethorphan and metoprolol differed significantly among Tanzanian subjects homozygous for the CYP2D6*29 allele compared with those with CYP2D6*1 or *2 alleles.
Conclusion
We found differences in the disposition of 4 CYP2D6 probe drugs in black Tanzanians compared with Swedes. The differences were caused by the presence of CYP2D6.17 and CYP2D6.29. The results show that CYP2D6.17 exhibits altered substrate specificity compared with CYP2D6.1 and CYP2D6.2.
Clinical Pharmacology & Therapeutics (2002) 71, 77–88; doi: 10.1067/mcp.2002.120239
To investigate the likelihood of artemisinin and thiabendazole causing pharmacokinetic interactions involving cytochrome P450 (CYP1A2) in humans given their potent inhibitory effects on the isoform ...in vitro.
Ten healthy volunteers received caffeine (136.5 mg), and after a washout period of 48 h, the volunteers were given a caffeine tablet (136.5 mg) together with thiabendazole (500 mg). After an additional 14 days, the volunteers received caffeine together with artemisinin (500 mg). After each treatment, plasma was obtained up to 24 h post-dose. The plasma concentrations of the drugs were measured by HPLC with UV and MS detection.
Using the ratio of paraxanthine to caffeine after 4 h as an indicator of CYP1A2 activity, thiabendazole and artemisinin inhibited 92 and 66%, respectively, of the enzyme activity in vivo. In addition, the pharmacokinetics of caffeine were altered in the presence of the drugs; increases in AUC(0-24) of 1.6-fold (P < 0.01) and 1.3-fold of caffeine in the presence of thiabendazole and artemisinin respectively were measured. The use of in vitro data to predict the effects of thiabendazole on the formation of paraxanthine yielded good results and underestimated the effects of artemisinin when total plasma concentrations were used. Corrections for protein binding resulted in underestimation of inhibitory effects on CYP1A2.
Co-administration of thiabendazole or artemisinin with CYP1A2 substrates could result in clinically significant effects. Our results highlight the validity of in vitro data in predicting in vivo CYP inhibition. The formation of paraxanthine seems to be a better indicator of in vivo CYP1A2 activity than caffeine levels.
CYP2C9 is a polymorphic gene with at least six known allelic variants (CYP2C9*1 to *6). CYP2C9*5 has been recently described in African-Americans. The lower activity of CYP2C9*5 encoded enzyme than ...*1 has been reported for the S-warfarin 7-hydroxylation in vitro. The aim of the present study was to develop an assay for the analysis of this variant and to determine the frequency of this polymorphism in different ethnic populations.
A PCR-based endonuclease digestion method, using a mismatched forward primer that introduced a recognition site for AvaII in all the CYP2C9 genotypes except CYP2C9*5, is described. DNA samples from 150 Ethiopians, 183 Tanzanians, 200 Caucasians from Sweden and 150 Orientals from Korea were screened for this variant allele.
The CYP2C9*5 allele was analysed using a polymerase chain reaction-based endonuclease method, and it was found in three Tanzanians (allele frequency, 0.0082) but not in Ethiopians, Caucasians or Orientals.
The human cytochrome P450 3A (CYP3A) enzymes, which metabolize 50% of currently used therapeutic drugs, exhibit great interindividual differences in activity that have a major impact on drug ...treatment outcome, but hitherto no genetic background importantly contributing to this variation has been identified. In this study we show that CYP3A4 mRNA and hnRNA contents with a few exceptions vary in parallel in human liver, suggesting that mechanisms affecting CYP3A4 transcription, such as promoter polymorphisms, are relevant for interindividual differences in CYP3A4 expression. Tanzanian (n = 143) healthy volunteers were phenotyped using quinine as a CYP3A probe and the results were used for association studies with CYP3A4 genotypes. Carriers of CYP3A4*1B had a significantly lower activity than those with CYP3A4*1 whereas no differences were seen for five other SNPs investigated. Nuclear proteins from the B16A2 hepatoma cells were found to bind with less affinity to the CYP3A4*1B element around -392 bp as compared to CYP3A4*1. The data indicate the existence of a genetic CYP3A4 polymorphism with functional importance for interindividual differences in enzyme expression.
PDF
