CYP3A5 genotype has an impact on the metabolism of the HIV protease inhibitor saquinavir.

CYP3A is the main enzyme subfamily involved in the metabolism of the HIV protease-inhibitor saquinavir. We hypothesized that individuals homozygous for CYP3A5*1 might have a higher oral clearance of saquinavir, compared with subjects lacking functional CYP3A5 alleles. A single-dose pharmacokinetic trial of saquinavir soft gel capsules, 1,200 mg, was performed in 16 black Tanzanian healthy volunteers with two functional CYP3A5 alleles (*1/*1) and in 18 volunteers without functional CYP3A5 alleles (both alleles being either *3, *6, or *7). The median area under the plasma concentration-time curve (AUC)0-24 reached among subjects with two functional alleles was 1,410 ng h/ml (interquartile range (IQR) 826-1,929), whereas it was 2,138 ng h/ml (IQR 1,380-3,331) in subjects without (P=0.0533, Mann-Whitney U-test). The median ratio of saquinavir over its M2 plus M3 hydroxy metabolites in urine was 64 (IQR 52-73) in subjects with two functional alleles, whereas it was 145 (IQR 89-181) in those without (P=0.000078, Mann-Whitney U-test). In conclusion, saquinavir is metabolized by CYP3A5. The median AUC0-24 for saquinavir among individuals with two functional CYP3A5 alleles was 34% lower than among those with no functional alleles. To clarify the clinical importance of the CYP3A5 polymorphism, further studies should be conducted on saquinavir, dosed to steady state, in the presence of ritonavir boosting.

Bantu Tanzanians have a decreased capacity to metabolize omeprazole and mephenytoin in relation to their CYP2C19 genotype.

OBJECTIVE: To investigate the CYP2C19 polymorphism in Tanzanians because this enzyme shows large interindividual differences in activity and metabolizes several drugs of importance in Africa, especially the antimalarial agent chloroguanide (INN, proguanil). METHODS: Two hundred fifty-one Tanzanian healthy volunteers were phenotyped with respect to CYP2C19 with use of a single oral dose of mephenytoin (n = 106), a single oral dose of omeprazole (n = 207), or both. Sixty-two were phenotyped with both probe drugs. The urinary 0- to 8-hour S/R-mephenytoin ratio and the plasma omeprazole metabolic ratio (MR) (omeprazole/hydroxyomeprazole) 3 hours after drug intake were determined. The genotype was determined by analysis for CYP2C19*1 (wt), CYP2C19*2 (m1), and CYP2C19*3 (m2). Ten subjects with high omeprazole MR were screened for new mutations in the CYP2C19 gene by searching for single-strand conformation polymorphisms (SSCP). RESULTS: Eight subjects were classified as mephenytoin poor metabolizers (7.5%). Only 5 of these were homozygous for mutated alleles. The S/R ratio was skewed to the right (lower CYP2C19 activity) compared with other ethnic groups studied previously. No new mutations were found with polymerase chain reaction (PCR)-SSCP. We found 30 volunteers (14.5%) with an MR > 7, which is the antimode found previously in white subjects and Asian subjects. Of the 251 volunteers genotyped, 3.2% were homozygous for mutated alleles and 66.1% were homozygous for the wild-type allele. The allele frequencies of CYP2C19*1, *2, and *3 were 81.5%, 17.9%, and 0.6%, respectively. The correlation between the S/R-mephenytoin ratio and the omeprazole MR was significant (Spearman r = 0.59; P < .01). CONCLUSION: Tanzanians have a decreased capacity to metabolize both omeprazole and mephenytoin when their genotype is compared with metabolic capacity and genotype in other previously studied populations. We identified a low frequency of the Asian allele (CYP2C19*3). Although we did not find any new mutations, our results may be consistent with the presence of yet-unidentified mutations of CYP2C19 that causes decreased CYP2C19 activity in the Tanzanian population.

Inhibition of mast cell histamine release by copper.

Peritoneal mast cells collected from Wistar rats were pooled and purified by differential centrifugation in Ficoll. They were suspended at approximately 10(6) cells/ml in a buffered salt solution, divided into 300 microliters aliquots and incubated at 37 degrees C with or without copper (CuSO45H2O). Histamine release was induced by compound 48/80 or concanavalin-A and estimated from the supernatant following extraction and by fluorimetric techniques. These techniques completely eliminated copper from the final extract. Copper produced a dose-dependent inhibition of histamine release induced by the two agents. The inhibitory effect was present even in cells incubated with copper but washed free of copper before their challenge with the inducing agent. The presence of 10 mM EDTA in the incubating medium almost completely abolished the effect of copper but glucose concentrations up to 25 mM failed to reverse the action of copper.