Omeprazole and CYP2C19 polymorphism: effects of long-term treatment on gastrin, pepsinogen I, and chromogranin A in patients with acid related disorders

BACKGROUND: The polymorphic enzyme CYP2C19 is of importance for the metabolism and effects of omeprazole during short-term treatment. AIM: To investigate the relationship between CYP2C19 genotype and the effects of long-term omeprazole treatment. MATERIAL AND METHODS: A total of 180 patients with acid related disorders were genotyped for wild type and mutated CYP2C19 alleles by allele-specific PCR amplification. Gastrin and chromogranin A were assessed by radioimmunoassays, and pepsinogen I and H. pylori serology were assessed by ELISA methods. RESULTS: In 108 of the patients, who received a single dose of 20 mg omeprazole, there was no difference in gastrin and chromogranin A concentrations between the three CYP2C19 genotypes. In 72 patients on long-term treatment (> 1 year) with 20 mg omeprazole daily, serum gastrin as well as plasma chromogranin A concentrations (mean +/- s.e.) were both about threefold higher in the wild type/mutated (52.1 +/- 7.6 pM and 7.3 +/- 1.3 nM (n=19), respectively) compared to wild type/wild type (14. 7 +/- 0.9 pM and 2.5 +/- 0.1 nM (n=52), respectively; both comparisons P=0.0001). In a single mutated/mutated patient on long-term treatment, both gastrin and chromogranin A were high (88 pM and 13.7 nM, respectively). Serum pepsinogen I concentration was significantly lower in wild type/mutated (n=19) patients on long-term treatment, compared with the corresponding wild type/wild type (n=49) group (147 +/- 19 microg/L vs. 193 +/- 12 microg/L, P=0. 04). CONCLUSION: Patients with one (and probably also with two) mutated CYP2C19 allele(s) on long-term treatment with omeprazole had significantly affected serum gastrin and pepsinogen I and plasma chromogranin A concentrations compared with patients with two normal alleles. This indicates that changes in gastric mucosal morphology during omeprazole treatment might be dependent upon the degree of the individual's capacity to metabolize omeprazole.     

Omeprazole treatment of Korean patients: effects on gastric pH and gastrin release in relation to CYP2C19 geno- and phenotypes

This study aimed to investigate the effect of omeprazole on intragastric pH and gastrin release as well as the plasma concentration of omeprazole in relation to CYP2C19 genotypes after repeated doses in Korean patients. Twenty-six Korean patients with acid related disease were genotyped for CYP2C19 by allele specific PCR (wt/wt, CYP2C19*1/*1; wt/mut, CYP2C19*1/*2 or *1/*3; mut/mut, CYP2C19*2/*2, *2/*3 or *3/*3). Intragastric pH was monitored during 24 hr, and the plasma concentrations of omeprazole, hydroxyomeprazole, omeprazole sulfone and meal-stimulated gastrin were measured during 4 hr before and after 8 consecutive daily doses of 20 mg omeprazole. Unexpectedly the AUCs of omeprazole in the three genotypes were similarly high on Day 8. The mean 24 hr pH increased significantly in all three genotypes (paired t-test; P<0.0001), and the AUCs (4 hr) of gastrin in all patients increased markedly from 129+/-73 to 298+/-142 pMhr (P<0.0001). However, there was no statistically significant difference between the three genotypes in the mean pH and gastrin AUCs on Day 8. After 8 consecutive doses of 20 mg omeprazole, the gastric pH and the plasma gastrin were increased significantly in all three CYP2C19 genotypes, which were confirmed by high plasma concentrations of omeprazole in all three genotype groups. We suggest that the reason why the wt/wt had high concentrations of omeprazole similar to those in the other two genotype groups is that some of them were old with low CYP2C19 activity. In these patients omeprazole accumulated from the first to the eighth dose similar to that in the heterozygotes.     

In vivo metabolic activity of CYP2C19 and CYP3A in relation to CYP2C19 genetic polymorphism in chronic liver disease

To study whether chronic liver disease (CLD) and genetic polymorphism affect the hepatic activity of cytochrome P450 (CYP) isoforms, we compared in vivo CYP2C19 and CYP3A activities using 3-hour omeprazole hydroxylation index (plasma concentration ratio of omeprazole to its 5-hydroxylated metabolite; a higher index indicates lower CYP2C19 activity) and partial formation clearance of cortisol to 6beta-hydroxycortisol (CL(cortisol-->6beta-HC)) in 31 CLD patients (9 with chronic hepatitis; 22 with cirrhosis comprising 20 Child-Pugh type A, 1 type B, and 1 type C) and 30 healthy subjects with different CYP2C19 genotypes. The mean (+/-SEM) omeprazole hydroxylation index in CLD patients with homozygous extensive metabolizer (EM) genotype (*1/*1, n = 8), heterozyous EM (*1/*2, n = 11; *1/*3, n = 6) genotypes and poor metabolizer (PM) genotypes (*2/*2, n = 3; *3/*3, n = 3) were 17.15 +/- 2.12, 20.02 +/- 2.63, and 26.04 +/- 3.15, respectively, which were significantly higher compared with control subjects with the corresponding CYP2C19 genotypes (0.81 +/- 0.09, 1.55 +/- 0.20, and 15.5 +/- 1.52). CLD patients with PM genotype had significantly (P < .05) higher omeprazole hydroxylation indexes than did those with homozygous EM genotype, and those with heterozygous EM genotypes had intermediate values. The mean CL(cortisol-->6beta-HC) decreased significantly (P < .001) in CLD patients compared with control subjects (1.19 +/- 0.12 versus 2.26 +/- 0.24 mL/min). Multiple regression analysis showed that CLD, serum albumin level, and CYP2C19 genotype correlated significantly (P < .05) with the omeprazole hydroxylation index, whereas no significant correlation was observed between CL(cortisol-->6beta-HC) and other variables, except CLD. Because CLD and genetic polymorphism of CYP2C19 act additively to reduce CYP2C19 activity, genotyping these patients may be of value in averting adverse reactions of drugs that depend on CYP2C19 for elimination.     

mRNA and protein expression of dog liver cytochromes P450 in relation to the metabolism of human CYP2C substrates

1. Interpretation of novel drug exposure and toxicology data from the dog is tempered by our limited molecular and functional knowledge of dog cytochromes P450 (CYPs). The aim was to study the mRNA and protein expression of hepatic dog CYPs in relation to the metabolism of substrates of human CYP, particularly those of the CYP2C subfamily. 2. The rate of 7-hydroxylation of S-warfarin (CYP2C9 in humans) by dog liver microsomes (mean +/- SD from 12 (six male and six female) dogs = 10.8 +/- 1.9 fmol mg(-1) protein min(-1)) was 1.5-2 orders of magnitude lower than that in humans. 3. The rate of 4'-hydroxylation of S-mephenytoin, catalysed in humans by CYP2C19, was also low in dog liver (4.6 +/-1.5 pmol mg(-1) protein min(-1)) compared with human liver. In contrast, the rate of 4'-hydroxylation of the R-enantiomer of mephenytoin by dog liver was much higher. The kinetics of this reaction (range of K(m) or K(0.5) 15-22 micro M, V(max) 35-59 pmol mg(-1) protein min(-1), n = 4 livers) were consistent with the involvement of a single enzyme. 4. In contrast to our findings for S-mephenytoin, dog liver microsomes 5'-hydroxylated omeprazole (also catalysed by CYP2C19 in humans) at considerably higher rates (range of K(m) 42-64 micro M, V(max) 22-46 pmol mg(-1) protein min(-1), n = 4 livers). 5. For all the substrates except omeprazole, a sex difference in their metabolism was observed in the dog (dextromethorphan N-demethylation: female range = 0.7-0.9, male = 0.4-0.8 nmol mg(-1) protein min(-1) (p < 0.02); S-warfarin 7-hydroxylation: female = 9-15.5, male = 8-12 fmol mg(-1) protein min(-1) (p < 0.02); R-mephenytoin 4'-hydroxylation: female = 16-35, male = 11.5-19 pmol mg(-1) protein min(-1) (p < 0.01); omeprazole 5'-hydroxylation: female = 15-20, male 13-22 pmol mg(-1) protein min(-1) (p < 0.2)). 6. All dog livers expressed mRNA and CYP3A12, CYP2B11, CYP2C21 proteins, with no sex differences being found. Expression of CYP2C41 mRNA was undetectable in the livers of six of 11 dogs. 7. Correlation analysis suggested that CYP2B11 catalyses the N-demethylation of dextromethorphan (mediated in humans by CYP3A) and the 4'-hydroxylation of mephenytoin (mediated in humans by CYP2C19) in the dog, and that this enzyme and CYP3A12 contribute to S-warfarin 7-hydroxylation (mediated in humans by CYP2C9). 8. In conclusion, we have identified a distinct pattern of hepatic expression of the CYP2C41 gene in the Alderley Park beagle dog. Furthermore, marked differences in the metabolism of human CYP2C substrates were observed in this dog strain compared with humans with respect to rate of reaction, stereoselectivity and CYP enzyme selectivity.     

Omeprazole disposition in children following single-dose administration

Omeprazole is frequently used to treat gastroesophageal reflux in infants and children despite the lack of age-specific pharmacokinetic and dosing information in the approved product labeling. To address this challenge, the authors examined the potential influence of development and cytochrome P450 2C19 (CYP2C19) genotype on omeprazole disposition by conducting two pharmacokinetic (PK) studies in children and adolescents (ages 2-16 years) after a single oral 10- or 20-mg dose of the drug. Plasma omeprazole concentrations were determined by HPLC-MS from seven plasma samples obtained over a 6-hour postdose period. Pharmacokinetic parameters were determined by noncompartmental methods. Subjects were genotyped for CYP2C19 by PCR-RFLP. Data were available from 37 patients (19 female), 10 of whom were < or = 5 years of age. No drug-associated adverse events were observed. The numbers of functional CYP2C19 alleles per subject in the cohort were 2 (n = 25), 1 (n = 11), and 0 (n = 1). Pharmacokinetic parameters (mean +/- SD, range) were as follows: tmax (2.1 +/- 1.2, 1-6 h), Cmax (331.1 +/- 333.6, 20.8-885.8 ng/mL), AUC0-->infinity (809.5 +/- 893.8, 236.9-1330.9 ng/mL.h), t1/2 (0.98 +/- 0.22, 0.7-1.4 h), and CL/F (1.8 +/- 1.4, 0.3-5.8 L/h/kg). Comparison of mean AUC0-->infinity values normalized for dose (i.e., per 1 mg/kg) between subjects with one versus two functional CYP2C19 alleles revealed no statistically significant difference. In addition, the CL/F and apparent elimination rate constant (lambda z) for omeprazole were not significantly different for subjects with one versus two functional CYP2C19 alleles. No association between age and CL/F, t1/2, or lambda z was observed. The range of t1/2 values for omeprazole was similar to those reported in adults (1-1.5 h). CONCLUSIONS: (1) in children ages 2 to 16 years receiving 10 or 20 mg of omeprazole as a single oral dose, the PK are quite comparable to values reported for adults, and (2) in pediatric patients who are CYP2C19 extensive metabolizers, there was no association between genotype and the pharmacokinetics of omeprazole.     

Reliability of the omeprazole hydroxylation index for CYP2C19 phenotyping: possible effect of age, liver disease and length of therapy

AIMS: To evaluate the reliability of the omeprazole hydroxylation index as a marker for polymorphic CYP2C19 activity in a Japanese population of healthy young subjects (n = 78) and patients with peptic ulcer (n = 72). METHODS: Healthy subjects were administered a single dose of omeprazole (20 mg), whereas patients received 20 mg daily for at least 1 week. The ratio of the serum concentration of omeprazole to hydroxyomeprazole at 3 h postdose was determined and used as a measure of CYP2C19 activity. The CYP2C19 wild type (wt) gene and four mutant alleles associated with the poor metaboliser phenotype of (S)-mephenytoin, CYP2C19*2 in exon 5, CYP2C19*3 in exon 4, CYP2C19m4 in exon 9, and CYP2C19m3 in the initial codon were analysed. RESULTS: In the healthy volunteer study there was complete concordance between genotype and phenotype. However, eight of the patients who had the EM genotype had a high value for their hydroxylation index, and were classified as phenotypic PMs. No CYP2C19m4 and CYP2C19m3 mutations were detected in the eight mismatched patients. They were all genotypic heterozygous EMs, elderly (> or = 65 years) and/or had hepatic disease. Therefore, impaired CYP2C19 activity combined with partial saturation of omeprazole metabolism during multiple dosing may have contributed to the discrepancy between CYP2C19 genotyping and phenotyping. CONCLUSION: Although omeprazole has been used instead of mephenytoin as a probe for polymorphic CYP2C19, it does not appear to be reliable enough for clinical application in Japanese patients.     

Herbal medicine yin zhi huang induces CYP3A4-mediated sulfoxidation and CYP2C19-dependent hydroxylation of omeprazole

Aim： To explore the potential interactions between Y/n Zhi Huang （YZH） and omeprazole, a substrate of CYP3A4 and CYP2C19. Methods： Eighteen healthy volunteers, including 6 CYP2C19＊ 1/＊ 1, 6 CYP2C19＊1/＊2 or ＊3 and 6 CYP2C19＊2/ ＊2 were enrolled in a 2-phase, randomized, crossover clinical trial. In each phase, the volunteers received either placebo or 10 mL YZH oral liquid, 3 times daily for 14 d. Then all the patients took a 20 mg omeprazole capsule orally. Blood samples were collected up to 12 h after omeprazole administration. Plasma concentrations of omeprazole and its metabolites were quantified by HPLC with UV detection. Results： After 14 d of treatment of YZH, plasma omeprazole significantly decreased and those of omeprazole sulfone and 5-hydroxyomeprazole significantly increased. The ratios of the area under the plasma concentration-time curves from time 0 to infinity （AUC（0-∞） of omeprazole to 5-hydroxyomprazole and those of omeprazole to omeprazole sulfone decreased by 64.80%＋ 12.51% （P= 0.001） and 63.31%＋ 18.45 % （P=0.004） in CYP2C 19＊ 1/＊ 1, 57.98 %± 14.80% （P=0.002） and 54.87%±18.42% （P=0.003） in CYP2C19＊1/＊2 or ＊3, and 37.74%±16.07% （P= 0.004） and 45.16%±15.54% （P=0.003） in CYP2C19＊2/＊2, respectively. The decrease of the AUC（0-∞） ratio of omeprazole to 5-hydroxyomprazole in CYP2C19＊ 1/＊ 1 and CYP2C19＊1/＊2 or ＊3 was greater than those in CYP2C19＊2/＊2 （P=0.047 and P=0.009）. Conclusion： YZH induces both CYP3A4-catalyzed sulfoxidation and CYP2C19-dependent hydroxylation of omeprazole leading to decreases in plasma omeprazole concentrations.     

Influence of CYP2C19*18 and CYP2C19*19 alleles on omeprazole 5-hydroxylation: in vitro functional analysis of recombinant enzymes expressed in Saccharomyces cerevisiae

Omeprazole is one of the most widely used proton pump inhibitors for the treatment of gastric acid-related disorders. The major metabolic pathway of omeprazole is 5-hydroxylation, which is catalysed by CYP2C19. In this study, the effect of CYP2C19*18 and CYP2C19*19 alleles on omeprazole 5-hydroxylation was studied using recombinant CYP2C19 enzymes of wild-type (CYP2C19.1B having Ile331Val) and variants (CYP2C19.18 having Arg329His/Ile331Val and CYP2C19.19 Ser51Gly/Ile331Val) expressed in yeast cells. The K(m) value for omeprazole 5-hydroxylation of CYP2C19.1B was 1.46 microM. The K(m) value of CYP2C19.19 was significantly higher (1.5-fold) than that of CYP2C19.1B. V(max) and V(max)/K(m) values for omeprazole 5-hydroxylation of CYP2C19.1B on the basis of cytochrome P450 protein level were 8.09 pmol/min./pmol CYP and 5.45 microl/min./pmol CYP, respectively. The V(max) value of CYP2C19.19 was significantly higher (1.8-fold) than that of CYP2C19.1B, whereas the V(max)/K(m) value was comparable to that of CYP2C19.1B. In contrast, K(m), V(max) and V(max)/K(m) values of CYP2C19.18 were similar to those of CYP2C19.1B. These results suggest that CYP2C19*19 allele decreases the affinity between CYP2C19 enzyme and the substrate in omeprazole metabolism.     

Determinants of steady-state torasemide pharmacokinetics: impact of pharmacogenetic factors, gender and angiotensin II receptor blockers

BACKGROUND: Torasemide is frequently used for the treatment of hypertension and heart failure. However, the determinants of torasemide pharmacokinetics in patients during steady-state conditions are largely unknown. We therefore explored the impact of genetic polymorphisms of cytochrome P450 (CYP) 2C9 (CYP2C9) and organic anion transporting polypeptide (OATP) 1B1 (SLCO1B1), gender, and the effects of losartan and irbesartan comedication on the interindividual variability of steady-state pharmacokinetics of torasemide. PATIENTS AND METHODS: Twenty-four patients receiving stable medication with torasemide 10 mg once daily and with an indication for additional angiotensin II receptor blocker (ARB) treatment to control hypertension or to treat heart failure were selected. Blood samples were taken before torasemide administration and 0.5, 1, 2, 4, 8, 12 and 24 hours after administration. After this first study period, patients received either irbesartan 150 mg (five female and seven male patients aged 69+/-8 years) or losartan 100 mg (two female and ten male patients aged 61+/-8 years) once daily. After 3 days of ARB medication, eight blood samples were again collected at the timepoints indicated above. The patients' long-term medications, which did not include known CYP2C9 inhibitors, were maintained at a constant dose during the study. All patients were genotyped for CYP2C9 (*1/*1 [n=15]; *1/*2 [n = 4]; *1/*3 [n=5]) as well as for SLCO1B1 (c.521TT [n=13]; c.521TC [n=11]). RESULTS: Factorial ANOVA revealed an independent impact of the CYP2C9 genotype (dose-normalized area under the plasma concentration-time curve during the 24-hour dosing interval at steady state [AUC(24,ss)/D]: *1/*1 375.5+/-151.4 microg x h/L/mg vs *1/*3 548.5+/-271.6 microg x h/L/mg, p=0.001), the SLCO1B1 genotype (AUC(24,ss)/D: TT 352.3+/-114 microg x h/L/mg vs TC 487.6+/-218.4 microg x h/L/mg, p<0.05) and gender (AUC(24,ss)/D: males 359.5+/-72.2 microg x h/L/mg vs females 547.3+/-284 microg x h/L/mg, p<0.01) on disposition of torasemide. Coadministration of irbesartan caused a 13% increase in the AUC(24,ss)/D of torasemide (p=0.002), whereas losartan had no effect. CONCLUSION: This study shows that the CYP2C9*3 and SLCO1B1 c.521TC genotype and female gender are significant and independent predictors of the pharmacokinetics of torasemide. Coadministration of irbesartan yields moderate but significant increases in the torasemide plasma concentration and elimination half-life.     

Omeprazole as a CYP2C19 marker in Chinese subjects: assessment of its gene-dose effect and intrasubject variability

The objective of this study was to determine the reliability of omeprazole as a marker for CYP2C19 activity in Chinese subjects. In 27 healthy male Chinese subjects, the CYP2C19 phenotype was first determined with the standard mephenytoin hydroxylation index (HI) method. Subsequently, the subjects were randomized in a three-way crossover manner to receive an oral 40-mg dose from each of three omeprazole formulations (as part of a bioequivalence study). Multiple blood samples were obtained over 12 hours, and plasma concentrations of omeprazole, 5-hydroxyomeprazole, and omeprazole sulfone were determined by a high-performance liquid chromatography (HPLC) method. Individual CYP2C19 genotype was determined by the polymerase chain reaction/restriction fragment length polymorphism method. To assess the specificity for CYP2C19 activity, the hydroxylation metabolic ratio (MR) of omeprazole (AUC(omeprazole)/AUC(5-hydroxyomeprazole)) was compared to mephenytoin HI and related to CYP2C19 genotype status. The inter- and intrasubject variabilities of MR were also calculated, and their magnitudes were compared. The intersubject MR varied more than 20 fold. Among the subjects, there was a gene-dose effect, and the mean MR was 1.76, 3.45, and 33.08, respectively, in the homozygous extensive metabolizers (wt/wt, n = 9), heterozygous extensive metabolizers (wt/m1 or wt/m2, n = 10), and poor metabolizers (m1/m1 or m1/m2, n = 7). However, the coefficients of variation for intrasubject MR only ranged from 4.5% to 33.7% over the three periods with the three formulations. The phenotype based on MR was concordant with HI. In view of the clear gene-dose effect, concordance with mephenytoin HI, and low intrasubject variability, omeprazole MR following a 40-mg oral dose can be considered as a specific and sensitive marker for CYP2C19 activity in Chinese subjects.     

mRNA and protein expression of dog liver cytochromes P450 in relation to the metabolism of human CYP2C substrates

1. Interpretation of novel drug exposure and toxicology data from the dog is tempered by our limited molecular and functional knowledge of dog cytochromes P450 (CYPs). The aim was to study the mRNA and protein expression of hepatic dog CYPs in relation to the metabolism of substrates of human CYP, particularly those of the CYP2C subfamily. 2. The rate of 7-hydroxylation of S -warfarin (CYP2C9 in humans) by dog liver microsomes (mean ± SD from 12 (six male and six female) dogs = 10.8 ± 1.9 fmol?mg ? 1 protein?min ? 1) was 1.5-2 orders of magnitude lower than that in humans. 3. The rate of 4'-hydroxylation of S -mephenytoin, catalysed in humans by CYP2C19, was also low in dog liver (4.6 ± 1.5 pmol?mg ? 1 protein?min ? 1) compared with human liver. In contrast, the rate of 4'-hydroxylation of the R -enantiomer of mephenytoin by dog liver was much higher. The kinetics of this reaction (range of K m or K 0.5 15-22 µM, V max 35-59 pmol?mg ? 1 protein?min ? 1, n = 4 livers) were consistent with the involvement of a single enzyme. 4. In contrast to our findings for S -mephenytoin, dog liver microsomes 5'-hydroxylated omeprazole (also catalysed by CYP2C19 in humans) at considerably higher rates (range of K m 42-64 µM, V max 22-46 pmol?mg ? 1 protein?min ? 1, n = 4 livers). 5. For all the substrates except omeprazole, a sex difference in their metabolism was observed in the dog (dextromethorphan N-demethylation: female range = 0.7-0.9, male = 0.4-0.8 nmol?mg ? 1 protein?min ? 1 (p < 0.02); S -warfarin 7-hydroxylation: female = 9-15.5, male = 8-12 fmol?mg ? 1 protein?min ? 1 (p < 0.02); R -mephenytoin 4'-hydroxylation: female = 16-35, male = 11.5-19 pmol?mg ? 1 protein?min ? 1 (p < 0.01); omeprazole 5'-hydroxylation: female = 15-20, male 13-22 pmol?mg ? 1 protein?min ? 1 (p < 0.2)). 6. All dog livers expressed mRNA and CYP3A12, CYP2B11, CYP2C21 proteins, with no sex differences being found. Expression of CYP2C41 mRNA was undetectable in the livers of six of 11 dogs. 7. Correlation analysis suggested that CYP2B11 catalyses the N-demethylation of dextromethorphan (mediated in humans by CYP3A) and the 4'-hydroxylation of mephenytoin (mediated in humans by CYP2C19) in the dog, and that this enzyme and CYP3A12 contribute to S -warfarin 7-hydroxylation (mediated in humans by CYP2C9). 8. In conclusion, we have identified a distinct pattern of hepatic expression of the CYP2C41 gene in the Alderley Park beagle dog. Furthermore, marked differences in the metabolism of human CYP2C substrates were observed in this dog strain compared with humans with respect to rate of reaction, stereoselectivity and CYP enzyme selectivity.     

Effect of enprostil on serum gastrin and pepsinogen A and C levels in patients on long-term treatment with omeprazole

Background: Treatment of omeprazole induces profound inhibition of gastric acid secretion, resulting in hypergastrinaemia. In rats hypergastrinaemia induced by chronic administration of high doses of omeprazole resulted in ECL-cell hyperplasia and subsequent carcinoid formation. This finding may limit long-term therapy in man. The synthetic prostaglandin E₂ analogue enprostil not only inhibits gastric acid secretion but also reduces serum gastrin in normal subjects and in peptic ulcer patients. The present study was undertaken to determine whether enprostil reduces serum gastrin in patients on long-term treatment with omeprazole. Methods: Eight patients with reflux oesophagitis treated with 40 mg omeprazole once daily for at least 3 months received 3 5 μg enprostil t.d.s. during a 5-day treatment course. Basal and postprandial serum gastrin concentrations and pepsinogen A and C levels were measured on the day before, the first and the final day, and on the day after cessation of treatment. Results: Enprostil significantly (P < 0.05) reduced basal serum gastrin from 65±15 pmol/L to 51 ± 13 pmol/L on the first treatment day, and to 41 ± 9 pmol/L on the final day. Enprostil also significantly (P < 0.05) reduced postprandial integrated serum gastrin from 6173 ± 849 pmol.h/L to 4516 ± 906 pmol.h/L and to 3532 ± 706 pmol.h/L on the first and final treatment days, respectively. On the day after cessation of treatment basal (57± 11 pmol/L) and postprandial integrated serum gastrin concentrations (5766 ± 864 pmol.h/L) were not significantly different when compared to pretreatment values. Enprostil had no significant influence on serum pepsinogens A and C. Conclusion: Short-term co-administration of enprostil lowers the serum gastrin levels in patients on long-term treatment with omeprazole.     

Enhancing engraftment of islets using perioperative sodium 4-phenylbutyrate

Primary nonfunction (PNF) adversely impacts islet transplantation. In addition to determining whether sodium 4-phenylbutyrate (4-SPB), an anti-inflammatory agent, reduces PNF, this study investigates how 4-SPB affects PNF. Streptozotocin-induced diabetic C57BL/6 mice, that received 75 syngeneic islets underneath left subrenal space, were fed twice daily of either 4-SPB at 500 mg/kg body weight or isotonic saline (NaCl) from 2 days before through 7 days after transplantation. The graft was removed at days 3, 10 and 84 following transplantation. At 68 h following transplantation, serum levels of interleukin-1beta (IL-1beta) were 2.2+/-0.4 and 0.4+/-0.2 pmol/L (n=6, p<0.005) for NaCl and 4-SPB groups, respectively. Graft genetic expression of IL-1beta was significantly suppressed in 4-SPB group (p<0.01). At day 10, the blood glucose levels were 22.7+/-1.0 and 17.1+/-1.7 mmol/L (n=12, p<0.05) and graft insulin contents (IC) were 35.0+/-8.3 and 107.6+/-29.7 pmol (n=12, p<0.05) for NaCl and 4-SPB groups, respectively. Moreover, the 4-SPB group had a shorter temporary hyperglycemia (15+/-2, n=21 vs. 25+/-2 days, n=19, p=0.001) and a higher cumulative cure rate of diabetes (p<0.001) than the NaCl group. In-vitro studies indicated that 4-SPB did not impact the islets function. These experimental results demonstrated that perioperative administration of 4-SPB decreased serum level and graft genetic expression of IL-1beta and attenuated PNF, which enhanced islet engraftment in a syngeneic transplantation mouse model.     

中国健康志愿者的奥美拉唑及其代谢产物的药代动力学

目的　观察中国人CYP2C19基因型与奥美拉唑羟化代谢的关系。方法　采用高效液相 二极管阵列色谱法测定 2 5名po 2 0mg奥美拉唑胶囊后 2 4h内的奥美拉唑及其主要代谢产物的血药浓度 ,计算药代动力学参数。结果　在 2 5名奥美拉唑药物代谢的志愿受试者中 ,7名是CYP2C19强代谢者〔homoEMS(wt/wt,G1组 )〕 ;12名是CYP2C19中强代谢者〔heteroEMS(wt/m1orwt/m2 ,G2组 )〕 ;6名是CYP2C19弱代谢者〔PMS(m1/m1,G3组 )〕。奥美拉唑在G1,G2和G3组平均清除率分别为 2 2 .9,12 .7和 4 .9mL·h- 1,曲线下面积分别为 1.0 9,1.4 7和4 .87mg·L- 1·h ;G1,G2组的奥美拉唑的代谢动力学与G3组存在显著差别 ,表明奥美拉唑的代谢速率与CYP2C19的基因型有关系。结论　奥美拉唑羟化代谢存在着多态性。基因型为m1/m1的受试者的奥美拉唑羟化代谢明显低于基因型为wt/wt,wt/m1和wt/m2两组受试者     

Investigation of the in vivo activity of CYP3A in Brazilian volunteers: comparison of midazolam and omeprazole as drug markers

OBJECTIVE: This study compares midazolam with omeprazole as marker drugs for the evaluation of CYP3A activity in nine healthy self-reported white Brazilian volunteers. METHODS: Omeprazole was also used to evaluate the CYP2C19 phenotype. The volunteers received p.o. 20 mg omeprazole, and blood samples were collected 3.5 h after drug administration. After a washout period of 10 days, the volunteers received p.o. 15 mg midazolam maleate, and serial blood samples were collected up to 6 h after administration of the drug. CYP2C19 was genotyped for the allelic variants CYP2C19*1, CYP2C19*2, CYP2C19*3, and CYP2C19*17. Analysis of omeprazole, hydroxyomeprazole, omeprazole sulfone, and midazolam in plasma was carried out by LC-MS/MS. RESULTS: The volunteers genotyped as CYP2C19*1*17, CYP2C19*17*17, CYP2C19*1*1 (n = 8), or CYP2C19*17*2 (n = 1) presented a median hydroxylation index (omeprazole/hydroxyomeprazole) of 1.35, indicating that all of them were extensive metabolizers of CYP2C19. The volunteers (n = 9) presented a 0.12 log of the omeprazole/sulfone ratio and a median oral clearance of midazolam of 17.89 ml min(-1) kg(-1), suggesting normal CYP3A activity. CONCLUSIONS: Orthogonal regression analysis between midazolam clearance and log of the plasma concentrations of the omeprazole/omeprazole sulfone ratio (R = -0.7544, P < 0.05) suggests that both midazolam and omeprazole can be used as markers of CYP3A activity in the population investigated.     

Comparative effects of atorvastatin,simvastatin, and fenofibrate on serum homocysteine levels in patients with primary hyperlipidemia

Hyperhomocysteinemia is regarded as an independent risk factor for cardiovascular disease. Lipid-lowering agents, such as fibrates, can modify homocysteine levels. However, less is known about the effect of statin therapy on homocysteine. The authors compared the effects of atorvastatin (40 mg/day), simvastatin (40 mg/day), and micronized fenofibrate (200 mg/day) on the serum concentrations of total homocysteine, vitamin B12, and folic acid in patients with primary hyperlipidemia. A total of 128 patients with primary hyperlipidemia (total cholesterol > 240 mg/dL and triglycerides < 350 mg/dL) were assigned to atorvastatin, simvastatin, or fenofibrate. Serum lipid and metabolic parameters were measured at baseline and at 6 and 12 weeks of treatment. Homocysteine correlated positively with serum creatinine and uric acid levels and inversely with serum folic acid levels. All treatment modalities reduced total, low-density lipoprotein (LDL) cholesterol, and triglyceride concentrations. High-density lipoprotein (HDL) cholesterol levels significantly increased only in the fenofibrate-treated patients (47.9 +/- 12.5 vs. 50.7 +/- 12.6 vs. 51.2 +/- 12.8 mg/dL, p < 0.01). Atorvastatin and fenofibrate treatment resulted in a significant reduction of serum uric acid levels (5.3 +/- 1.6 vs. 4.9 +/- 1.4 vs. 4.8 +/- 1.4 mg/dL, p < 0.0001 for atorvastatin; 5.6 +/- 1.6 vs. 4.3 +/- 1.4 vs. 4.4 +/- 1.4 mg/dL, p < 0.0001 for fenofibrate). Homocysteine levels were significantly increased only by fenofibrate (10.3 +/- 3.3 vs. 14.1 +/- 3.8 vs. 14.2 +/- 3.6 microU/L, p < 0.001) but did not change from baseline following statin treatment. Neither statins nor fenofibrate had any effect on serum vitamin B12 and folic acid levels. In contrast to fenofibrate, therapeutic dosages of atorvastatin and simvastatin have a neutral effect on serum homocysteine levels, which is in favor of their "cardioprotective" properties.     

Different effects of proton pump inhibitors and famotidine on the clopidogrel metabolic activation by recombinant CYP2B6, CYP2C19 and CYP3A4

Inhibitory potential of proton pump inhibitors (PPIs) and famotidine, an H(2) receptor antagonist, on the metabolic activation of clopidogrel was evaluated using recombinant CYP2B6, CYP2C19 and CYP3A4. Formation of the active metabolite from an intermediate metabolite, 2-oxo-clopidogrel, was investigated by liquid chromatography-tandem mass spectrometry and three peaks corresponding to the pharmacologically active metabolite and its stereoisomers were detected. Omeprazole potently inhibited clopidogrel activation by CYP2C19 with an IC(50) of 12.8 μmol/L and more weakly inhibited that by CYP2B6 and CYP3A4. IC(50) of omeprazole for CYP2C19 and CYP3A4 was decreased about two- and three-fold, respectively, by 30-min preincubation with NADPH. Lansoprazole, esomeprazole, pantoprazole, rabeprazole and rabeprazole thioether, a major metabolite, also inhibited metabolic activation by CYP2C19, with an IC(50) of 4.3, 8.9, 48.3, 36.2 and 30.5 μmol/L, respectively. In contrast, famotidine showed no more than 20% inhibition of clopidogrel activation by CYP2B6, CYP2C19 and CYP3A4 at up to 100 μmol/L and had no time-dependent CYP2C19 and CYP3A4 inhibition. These results provide direct evidence that PPIs inhibit clopidogrel metabolic activation and suggest that CYP2C19 inhibition is the main cause of drug-drug interaction between clopidogrel and omeprazole. Famotidine is considered as a safe anti-acid agent for patients taking clopidogrel.     

Influence of age and cytochrome P450 2C9 genotype on the steady-state disposition of diclofenac and celecoxib

OBJECTIVE: To analyse the influence of age and cytochrome P450 (CYP) 2C9 genotype on the steady-state disposition of the standard NSAID diclofenac and the new COX-2 selective inhibitor celecoxib, both of which are metabolised by the polymorphically expressed CYP2C9. DESIGN: Double-blind randomised crossover study under steady-state conditions. SUBJECTS: 12 young (age 32 +/- 5 years, bodyweight 71 +/- 12kg; mean +/- SD) and 12 elderly (68 +/- 2 years, 82 +/- 15kg) healthy, drug-free, nonsmoking Caucasians of both sexes. METHODS: All subjects received oral celecoxib (200mg twice daily) and diclofenac (75mg twice daily) for 15 days separated by a drug-free interval of at least 3 weeks. Following the last morning dose, multiple blood samples were taken for 25 hours. Concentrations of celecoxib and diclofenac were measured by specific and sensitive high performance liquid chromatography. Identification of CYP2C9 genotype was performed by genomic DNA sequencing. Pharmacokinetic parameters for total and unbound drugs were individually analysed by noncompartmental techniques. RESULTS: For diclofenac, area under the concentration-time curve over the dosage interval (AUC(tau)) was larger in young subjects (3.2 +/- 1.0 mg * h/L) than in older individuals (2.4 +/- 0.4 mg * h/L; p < 0.05). As the terminal half-life (t((1/2)Z)) was very similar in both groups (3.9 +/- 4.4 vs 3.5 +/- 3.3 hours), either less complete absorption in the elderly or their higher bodyweight could account for the difference. For celecoxib, AUC(tau) (5.8 +/- 1.7 vs 5.6 +/- 2.3 mg * h/L) and t((1/2)z) (11.8 +/- 8.7 vs 11.2 +/- 2.9 hours) were almost identical in young and older subjects. Plasma protein binding of both NSAIDs was unaffected by age, and apparent oral clearances for unbound drugs were not different between the two groups of healthy subjects. When considering the genotype of all individuals (CYP2C9*1/*1, n = 10; CYP2C9*1/*2, n = 6; CYP2C9*2/*2, n = 2; CYP2C9*1/*3, n = 4; CYP2C9*3/*3, n = 1), no association with any pharmacokinetic parameter of either drug was apparent. Moreover, there was no significant correlation between the AUC values of celecoxib and diclofenac. CONCLUSIONS: Age and CYP2C9 genotype do not significantly affect the steady-state disposition of celecoxib and diclofenac. This would indicate that both drugs need no dosage reduction in the elderly (at least up to 75 years) and that, besides CYP2C9, additional CYP species contribute to the elimination of both agents.     

The impact of CYP2C19 and CYP2D6 genotypes on metabolism of amitriptyline in Japanese psychiatric patients

We investigated the effect of the CYP2C19 and CYP2D6 genotypes on the metabolism of amitriptyline (AT) in Japanese psychiatric patients. Steady-state concentrations of AT and its metabolites (nortriptyline [NT], trans-10-hydroxy-nortriptyline [EHNT], cis-10-hydroxy-nortriptyline [ZHNT], trans-10-hydroxy-amitriptyline [EHAT], and cis-10-hydroxy-amitriptyline [ZHAT]) in 50 patients were determined by high-performance liquid chromatography. Significantly higher plasma concentrations of AT corrected for dose and body weight in the subjects with two mutated alleles of CYP2C19 than in those with no mutated alleles of CYP2C19 were observed (no mutated alleles vs. two mutated alleles: 36.0 +/- 18.2 vs. 64.0 +/- 25.2 ng/mL/mg/kg, p = 0.025). A significantly higher AT/NT ratio was seen in the subjects with two mutated alleles of CYP2C19 than in those with no mutated alleles of CYP2C19 (no mutated alleles vs. two mutated alleles: 1.27 +/- 0.59 vs. 3.40 +/- 1.02, p = 0.001). A trend for higher NT/EHNT ratio in the subjects with two mutated alleles of CYP2D6 than in those with no mutated alleles of CYP2D6 was observed (no mutated alleles vs. two mutated alleles: 0.73 +/- 0.39 vs. 1.31 +/- 0.81, p = 0.068). A trend for higher plasma concentrations of total hydroxylated metabolites of AT (EHAT + ZHAT) corrected for dose and body weight in the subjects with two mutated alleles of CYP2C19 than in those with no mutated alleles of CYP2C19 was found (no mutated alleles vs. two mutated alleles: 9.5 +/- 5.8 vs. 17.8 +/- 8.9, p = 0.051). Therefore, the genotype of CYP2C19 is one of the important determinants of the plasma concentrations of AT and the capacity to desmethylate AT. Mother compound AT is shunted via hydroxylation pathways from AT to EHAT and ZHAT in the subjects with homozygotes of mutated alleles of CYP2C19 in order to compensate for the decreased capacity to desmethylate AT.     

Atrophic gastritis during long-term omeprazole therapy affects serum vitamin B12 levels

BACKGROUND: Omeprazole maintenance therapy for gastro-oesophageal reflux disease (GERD) has been associated with an increased incidence of atrophic gastritis in H. pylori-infected patients and with a decreased absorption of protein-bound, but not of unbound cobalamin. AIM: : To test the hypothesis that the combination of decreased cobalamin absorption and atrophic gastritis decreases serum cobalamin levels during omeprazole therapy. METHODS: Forty-nine H. pylori-positive GERD patients were treated with omeprazole for a mean (+/- s.d.) period of 61 (25) months. At the start of omeprazole treatment (T0) and at the latest follow-up visit (T1), serum was obtained for measurement of cobalamin. Corpus biopsy specimens were obtained at entry and follow-up for histopathological scoring according to the updated Sydney classification. RESULTS: At inclusion, none of the 49 patients had signs of atrophic gastritis. During follow-up, 15 patients (33%) developed atrophic gastritis, nine of whom had moderate to severe atrophy. These 15 patients did not differ from the other 34 patients with respect to age, serum cobalamin at T0 or the duration of follow-up. During follow-up, no change was observed in the median serum cobalamin level in the 34 patients without atrophy; (T0) 312 (136-716) vs. (T1) 341 (136-839) pmol/L (P=0.1). In the 15 patients who developed atrophy, a decrease in cobalamin was seen from 340 (171 to 787) at baseline to 285 (156-716) at latest follow-up (P < 0.01). CONCLUSIONS: The development of atrophic gastritis during omeprazole treatment in H. pylori-positive GERD patients is associated with a decrease of serum vitamin B12 levels.