Influence Of CYP2C19 Pharmacogentic Polymorphism On The Metabolic Disposition Of Pantoprazole In Chinese Healthy Volunteers

Pantoprazole (PAN) is one of a new member of proton pump inhibitors after omeprazole and lansoprazole. It was manufactured by ALTANA PharmaAG in Germany. With the similar effects of other PPIs, PAN inhibits the enzyme hydrogenpotassium adenosine triphosphatase (H⁺, K⁺-ATPase, or gastric proton pump), the final step of gastric acid secretion. The metabolic of PAN by cytochrome P450 (CYP450) 2C19 is the main metabolic route, while the activity of CYP2C19 depends significantly on the CYP2C19 genotype status. This makes the different metabolic kinetics of PAN, and then has a different clinical effect. Therefore, we studied the kinetic characteristics of PAN in healthy subjects who had different genotype status and intended to set the basis of Pharmacokinetics for the clinical therapy regimen of PAN. Furthermore, we want to clinical therapy protocol is more safe, effective, reasonable and economy.Methods1. The CYP2C19 genotypes: A hundred unrelated healthy Chinese Han subjects took part in this study after being given written informed consent. The proportion of men and women was 70/30. Their age range was 23.18±1.26. Venous blood (2 ml) was obtained and the genome DNA was extracted by classic SDS-proteinase K-hydroxybenzene-chloroform methods from blood. Though regular polymerase chain reaction (PCR) amplification, electrophoresis on 2% agarose gel and Goldview Gene-Finder, we observed and analyzed the specific segments of CYP2C19m1 in exon 5 and CYP2C19m2 in exon 4, associated with the poor metabolizer phenotype. The 50bp DNA Ladder was used as DNA marker in ultraviolet transilluminator. From these performances, the chosen good samples went on being digested with restriction endonuclear enzyme BamHI SmaI separately. After electrophoresis on 4% agarose gel, took pictures using numeric camera and saved it in computer.2. The Pharmacokinetics of PAN based on identification of genotypes: Twenty-four unrelated healthy subjects were enrolled from a total of 100 subjects. Eight subjects were homozygous for the wild-type (wt) allele in both exon 5 and exon 4 (wt/wt) and classified as the homozygous extensive metabolizers (homoEMs) group. Eight subjects were classified as heterozygous extensive metabolizers (heteEMs), who have only one mutation allele in either exon4 or exon5 (wt/m1 or wt/m2). Eight subjects were classified as poor metabolizers (PMs), however, have two mutation alleles in both exon4 or 5 (ml/ml, ml/m2 or m2/m2). None of subjects had a history of significant medical illness or hypersensitivity to any drugs. They did not consume extensive amounts of alcohol and were non-smokes. None of them had taken any other drugs for at least 2 weeks before the study and did not take any other drugs during the study. The normal health status of the volunteers was judged on the basis of a physical examination with screening blood chemistries, urinalysis, a complete blood count, liver function test and electrocardiogram before the study. The protocol was approved by the ethics Committee of Zhengzhou University in advance. Written informed consent was obtained from each subject before participation in the study. After an overnight fast, each of them received an oral dose of 40 mg pantoprazole as the enteric-coated formulation with 200 ml water. Standard meals were prepared. Serial venous blood samples (3.5 ml each) were collected before the drug administration and at 1.5 2 2.5 3 3.5 4 4.5 5 6 7, 9 12 and 15h after the dosing. After collection, the blood samples were immediately centrifuged at 4000 r·min^-1 for 10 min. All samples were stored at -20°C until assayed. Plasma concentrations of pantoprazole were determined using an improved high performance liquid chromatography. The software used for the pharmacokinetic analysis was 3P97, which was edited by Mathematical Board of the Chinese Pharmacological Society. The peak concentration (C_max) and the time of the peak concentration (T_max) were obtained directly from the original data. The areas under the curve (AUC) were calculated by the linear trapezoidal method. The data are expressed as mean values±SEM throughout the paper. The main pharmacokinetic parameters of different genotype groups were analyzed independent-sample t test, and Student-Newman-Keuls test revealed that the differences between different groups. P values of <0.05 was considered to be statistically significant.Results1. Genotyping for CYP2C19: A hundred healthy volunteers were analyzed, forty volunteers were homozygous for the wt allele in both exon 5 and exon 4 (wt/wt; 40%), forty volunteers were heterozygous for the CYP2C19 m1 mutation (wt/m1) without the CYP2C19 m2 mutation (40%), six volunteers were heterozygous for the CYP2C19 m2 (wt/m2) mutation without CYP2C19 m1 mutation (6%), nine volunteers were homozygous for the CYP2C19 m1 mutation (m1/m1) without the CYP2C19 m2 mutation (9%), two volunteers were homozygous for the CYP2C19 m2 mutation (m2/m2) without the CYP2C19 m2 mutation (2%), there volunteers were heterozygous for the CYP2C19 ml and the CYP2C19 m2 mutation (m1/m2, 3%). Homozygous extensive metabolisms ratio in female (46.67%) was higher than that of male (37.14%).2. Kinetic disposition of pantoprazole: The mean plasma concentration-time profiles of pantoprazole in the homoEMs, heteEMs and PMs were both fitted to a one-compartment model. The values of C_max was (2551.8±1035.2) , (3316.63±1237.27) and (4256.04±573.47) ng·ml^-1 , T_max was (3.38±0.92) , (3.25±1.54) and (3.50±0.96) h, T_1.2Ke was (1.82±1.71), (1.34±0.22) and (5.83±3.28) h, AUC₀^t was (5616.37±1878), (8132.22±3549.4) and (24882.71±7051.33) ng·ml^-1-h. The mean C_max in the heteEM and PM groups were higher than that in the homoEMs (.P<0.01). The T_1/2Ke in PMs was about 3.2 times longer than that in homoEMs (P<0.01). The mean AUC₀^∞and mean AUC₀^t values for PAN were significantly different between the homoEM and PM groups and between the heteEM and PM groups (P<0.01) ; all of these parameters did not have significant differences between the homoEM and heteEM groups.Conclusions1. The difference of CYP2C19 genotype status is one of the major factor to influence the interindividual kinetic variability of pantoprazole.2. There were significant differences in the metabolic disposition of pantoprazole in three groups. The poor metabolizers had a significantly greater C_max and AUC, and longer T_1/2Ke.