Ivar Roots

Pharmacokinetic interaction of digoxin with an herbal extract from St John's wort (Hypericum perforatum).

Extracts of St Johns wort (Hypericum perforatum) are widely used in the treatment of depression, often as an over‐the‐counter drug. In contrast to its frequent use, knowledge about the pharmacokinetics of ingredients and drug interactions of St Johns wort is poor. We studied the interaction between hypericum extract LI160 and digoxin.

Effect of genetic polymorphisms in cytochrome p450 (CYP) 2C9 and CYP2C8 on the pharmacokinetics of oral antidiabetic drugs: clinical relevance.

Type 2 diabetes mellitus affects up to 8% of the adult population in Western countries. Treatment of this disease with oral antidiabetic drugs is characterised by considerable interindividual variability in pharmacokinetics, clinical efficacy and adverse effects. Genetic factors are known to contribute to individual differences in bioavailability, drug transport, metabolism and drug action. Only scarce data exist on the clinical implications of this genetic variability on adverse drug effects or clinical outcomes in patients taking oral antidiabetics.The polymorphic enzyme cytochrome P450 (CYP) 2C9 is the main enzyme catalysing the biotransformation of sulphonylureas. Total oral clearance of all studied sulphonylureas (tolbutamide, glibenclamide [glyburide], glimepiride, glipizide) was only about 20% in persons with the CYP2C9*3/*3 genotype compared with carriers of the wild-type genotype CYP2C9*1/*1, and clearance in the heterozygous carriers was between 50% and 80% of that of the wild-type genotypes. For reasons not completely known, the resulting differences in drug effects were much less pronounced. Nevertheless, CYP2C9 genotype-based dose adjustments may reduce the incidence of adverse effects. The magnitude of how doses might be adjusted can be derived from pharmacokinetic studies.The meglitinide-class drug nateglinide is metabolised by CYP2C9. According to the pharmacokinetic data, moderate dose adjustments based on CYP2C9 genotypes may help in reducing interindividual variability in the antihyperglycaemic effects of nateglinide. Repaglinide is metabolised by CYP2C8 and, according to clinical studies, CYP2C8*3 carriers had higher clearance than carriers of the wild-type genotypes; however, this was not consistent with in vitro data and therefore further studies are needed. CYP2C8*3 is closely linked with CYP2C9*2.CYP2C8 and CYP3A4 are the main enzymes catalysing biotransformation of the thiazolidinediones troglitazone and pioglitazone, whereas rosiglitazone is metabolised by CYP2C9 and CYP2C8. The biguanide metformin is not significantly metabolised but polymorphisms in the organic cation transporter (OCT) 1 and OCT2 may determine its pharmacokinetic variability.In conclusion, pharmacogenetic variability plays an important role in the pharmacokinetics of oral antidiabetic drugs; however, to date, the impact of this variability on clinical outcomes in patients is mostly unknown and prospective studies on the medical benefit of CYP genotyping are required.

MDR1 polymorphisms G2677T in exon 21 and C3435T in exon 26 fail to affect rhodamine 123 efflux in peripheral blood lymphocytes.

P‐glycoprotein (Pgp) is a member of the ABC‐transporter family, and in humans, is encoded by the MDR1 gene. Recently, several single‐nucleotide polymorphisms in the MDR1 gene were identified. The aim of the present study was to evaluate the effect of the MDR1 genetic polymorphisms G2677T and C3435T on Pgp activity in CD56+ and CD4+ peripheral blood cells. Using flow cytometry, rhodamine 123 (Rh123) efflux was determined in 46 male healthy volunteers. Median Rh123 fluorescence in control sample, after baseline dye uptake, was set as 100%. Rh123 fluorescence in efflux samples, exposed to different efflux periods, was used to calculate the percentage of Rh123 retained in the cells in comparison with control. There was no significant difference in Rh123 efflux in CD56+ cells after 5, 10, 15, and 30 min efflux between individuals with different MDR1 genotypes. Also, in CD4+ cells after 15, 30, 60, and 90 min, Rh123 efflux did not reveal statistically different results for the three genotypes at 2677 and 3435. Rh123 efflux was not enhanced by a 10‐day rifampin administration, as determined in 15 individuals before and after rifampin treatment. In conclusion, we found no impact of the MDR1 G2677T and C3435T polymorphisms on Pgp activity in CD56+ and CD4+ peripheral blood lymphocytes.

Identification of six methylenetetrahydrofolate reductase (MTHFR) genotypes resulting from common polymorphisms: impact on plasma homocysteine levels and development of coronary artery disease

Although three common MTHFR polymorphisms (C677T, A1298C, T1317C) have been reported, only polymorphism C677T has been investigated intensively as a risk factor for coronary artery disease (CAD). We investigated polymorphism frequencies, allelic associations and the effect of the resulting MTHFR genotypes on total plasma homocysteine (tHcy) levels and on coronary risk in a case-control study with 1000 angiographically confirmed Middle-European CAD patients and 1000 matched controls. Three out of four theoretically possible MTHFR haplotypes were detected: *1 (677C, 1298A), *2 (677T, 1298A), and *3 (677C, 1298C). The frequencies were *1: 36.4 and 34.4%; *2: 30.8 and 32.3%; and *3: 32.8 and 33.3%, in cases and controls, respectively. Only one patient was heterozygous for 1317C. None of the six resulting genotypes showed significant influence on tHcy levels. Moreover, there was no significant association with CAD risk or with disease severity or early disease manifestation. In the subgroup presenting with acute coronary syndromes, MTHFR genotypes *2/*3 and *3/*3 were surprisingly underrepresented (relative risk of *3/*3, 0.40; 95% confidence interval 0.20-0.79, P=0.009). We conclude from our genotype-based analysis that, in this well-fed Middle-European population, the observed common allelic variants of the MTHFR gene have no significant influence on tHcy levels or on the chronic process of CAD development.

Frequency of MRP1 genetic polymorphisms and their functional significance in Caucasians: detection of a novel mutation G816A in the human MRP1 gene

ObjectiveThe aim of the present study was to determine the frequency of the G816A, T825C, T1684C, and G4002A genetic polymorphisms of the human MRP1 gene in 230 healthy Caucasians. The functional assessment of these mutations was performed in fluorescence-activated cell sorting (FACS)-sorted peripheral blood CD4+ cells in a further 61 healthy volunteers by determining MRP1 mRNA expression.MethodsGenotyping of the MRP1 was carried out using real-time polymerase chain reaction (PCR) assays. Quantitative determination of the MRP1 mRNA expression was performed with real-time reverse-transcription-PCR.ResultsA novel silent mutation G816A in exon 8 was found in this study. Allele frequencies of the 816A, 825C, 1684C, and 4002A were 4.1, 30.0, 80.0, and 28.3%, respectively. The frequency of the T825C polymorphism was comparable with that found in a previous Japanese study. In contrast, the frequency of the T1684C (OR 0.06, 95% CI 0.03–0.11, P<0.0001, vs Japanese) and the G4002A (OR 0.47, 95% CI 0.24–0.86, P=0.01, vs Japanese) was significantly rarer. The mean MRP1 mRNA expression in peripheral blood CD4+ cells was 1.03×104±3.8×103 molecules/ng of total RNA with an eightfold variation among individuals. However, MRP1 mRNA expression in CD4+ cells was not found to correlate with genetic polymorphisms investigated in this study.ConclusionsThe genotypic results observed show an ethnic difference in the frequencies of the MRP1 genetic polymorphisms between Japanese and Caucasians. Further studies are required to better understand the clinical consequences of the MRP1 genetic variants.

Beta 2-adrenergic receptor polymorphism and susceptibility to primary congenital and primary open angle glaucoma

ObjectiveIt has been shown that arginine to glycine (Arg16Gly), glutamine to glutamic acid (Gln27Glu) and threonine to isoleucine (Thr164Ile) exchanges in codons 16, 27 and 164, respectively, of the beta 2-adrenergic receptor (B2AR) gene significantly alter receptor function. As B2ARs are located on the afferent blood vessels supplying the ciliary body and trabecular meshwork cells, which control aqueous humour dynamics, polymorphisms of B2AR may be involved in the pathophysiology of certain eye diseases, such as glaucoma. Therefore, the aim of the present study was to investigate the distribution of B2AR polymorphisms in patients with primary congenital and primary open angle glaucoma.MethodsA group of 30 patients with primary congenital glaucoma, 105 with primary open angle glaucoma and 92 control patients were analysed for the Arg16Gly, Gln27Glu, and Thr164IIe polymorphisms of the B2AR by polymerase chain reaction–restriction fragment length polymorphism.ResultsThe allelic frequencies of Gly16, Glu27 and IIe164 variant alleles were 66.7, 38.3 and 3.3% in patients with congenital glaucoma, 59.5, 31.0 and 1.0% with glaucoma, and 54.9, 26.6 and 0.5% in controls, respectively. Although statistically non-significant, the frequencies of variant alleles were slightly higher in both groups of the glaucoma patients.ConclusionsThese results suggest no evidence of an association between the Arg16Gly, Glu27Gln and Thr164Ile polymorphisms of the B2AR gene and risk of developing primary open angle glaucoma or primary congenital glaucoma. However, further studies are needed to understand the role of B2AR polymorphisms in patients with eye disease.

Hyperhomocysteinaemia and adverse events complicating coronary catheter interventions.

BACKGROUND Since hyperhomocysteinaemia is an independent risk factor for development of atherosclerosis as well as for arterial and venous thrombosis we investigated whether elevated homocysteine levels are associated with procedural excess risk which complicates coronary interventions including coronary angioplasty (PTCA), stenting, or directional coronary atherectomy (DCA). DESIGN Consecutive cases receiving coronary catheter interventions. SETTING Tertiary referral centre in Germany. METHODS Fasting total plasma homocysteine levels (tHcy) were determined in 648 consecutive coronary artery disease patients who underwent catheter interventions (272 PTCA, 102 DCA, and 274 stenting). Hyperhomocysteinaemia was defined as tHcy >/=15 micromol/l. The patients were investigated for a 30-day composite endpoint, including need for target-vessel revascularization, myocardial infarction, and death. RESULTS Among the 648 patients, 78 (12%) demonstrated elevated tHcy levels. The composite endpoint occurred in 41 patients (6.3%). For the entire intervention group there was no evidence that hyperhomocysteinaemia was associated with excess procedural risk (odds ratio [OR]: 1.27; 95% confidence interval [CI]=0.52 to -3.13; P=0.62). In further analyses according to device, hyperhomocysteinaemia also failed to predict complications in the device related subgroups. CONCLUSION The results indicate that hyperhomocysteinaemia is not a major risk factor for 30-day adverse events complicating PTCA, DCA, or stenting.

Association of C3435T and G2677T/A polymorphisms of multidrug resistance (MDR1) gene with colorectal cancer risk

The human multidrug‐resistance (MDR1) gene encodes an integral cell membrane protein, P‐glycoprotein (PGP), which generates the ATP‐dependent cellular transport of substances. The activation of responsive elements in MDR1 gene promoter occurs in earlier colorectal carcinogenesis. In combination with cell proliferative activities of c‐myc and cyclin D1, MDR1 may initiate colorectal tumorogenesis by suppressing cell death pathways. The failure of correct cell death mechanisms disturbs the epithelium homeostasis and may induce tumorogenesis. We have studied if the hereditarily determined activity of MDR1 could modulate the risk of developing of colorectal cancer and have investigated genetic variant 3435C>T in exon 26 and triple polymorphism 2677G>T/A in exon 21 in a group of 289 colorectal cancer patients and sex‐ and age‐matched controls. Genotyping was performed by PCR/RFLP and Real‐Time PCR assays. Homozygous carriers of 3435C allele had 1.65 (95% C. I., 1.1‐2.5) higher risk (p=0.01) than carriers of 3435T allele. Presence of at least one 3435T protects significantly against colorectal cancer. Similar effect was shown for the mutation in exon 21. Carries of one 2677T allele had a lower risk of colorectal cancer (OR=0.65, 95% C. I., 0.45–0.94, p=0.02). The 2677G>T/A polymorphism and the 3435C>T polymorphism displayed tight allelic association (p<0.001). Our data suggest that carries of active MDR1 alleles are at the higher risk to develop the colorectal cancer.

Single-dose pharmacokinetics of temocapril and temocapril diacid in subjects with varying degrees of renal impairment.

AbstractObjective: The aim of this study was to determine the influence of renal impairment on the single-dose pharmacokinetics of temocapril and its pharmacologically active metabolite, temocapril diacid. Methods: A single oral dose of 20 mg temocapril hydrochloride was given after an overnight fast to eight healthy (control) subjects (group A, n=8) with a mean baseline creatinine clearance (CLCR) of 115.2 ml · min−1 and to three groups of patients with decreased renal function (mean CLCR 56.9 ml in group B, n=8, 30.0 ml · min−1 in group C, n=8 and 15.4 ml · min−1 in group D, n=5). Results: The mean peak concentration and median time to peak concentration for both temocapril and its diacid metabolite as well as the mean area under the curve (AUC0∞) for temocapril did not differ significantly between groups. The mean AUC0∞ for temocapril diacid increased only two- to threefold from group A to D. The mean terminal elimination half-life (t½) for temocapril diacid was prolonged in subjects with impaired renal function. However, prolongation of mean t½ and increase in AUC0−∞ did not parallel the decrease of mean renal clearance for temocapril diacid. Conclusion: The results suggest the existence of an alternative pathway in addition to the renal excretion of temocapril, e.g. via the bile. This pathway substantially contributes to the elimination of the active metabolite, temocapril diacid, in patients with decreased renal function. Nonetheless, to avoid any risks, the dose of temocapril hydrochloride in patients with moderate to severe renal impairment should be reduced.

Impact of CYP3A haplotypes on alprazolam kinetics with and without rifampicin induction

Human P‐450 Cytochromes (CYP) of the 3A class are involved in metabolism of most commonly used drugs. Several genetic variations within the CYP3A gene locus have been described but intergenic haplotype structures of the adjacent genes have never been determined. Further more, poor data on clinical relevance of genetic variations is available.