ABCG2 polymorphism markedly affects the pharmacokinetics of atorvastatin and rosuvastatin.

The ABCG2 c.421C>A single-nucleotide polymorphism (SNP) was determined in 660 healthy Finnish volunteers, of whom 32 participated in a pharmacokinetic crossover study involving the administration of 20 mg atorvastatin and rosuvastatin. The frequency of the c.421A variant allele was 9.5% (95% confidence interval 8.1-11.3%). Subjects with the c.421AA genotype (n = 4) had a 72% larger mean area under the plasma atorvastatin concentration-time curve from time 0 to infinity (AUC(0-infinity)) than individuals with the c.421CC genotype had (n = 16; P = 0.049). In participants with the c.421AA genotype, the rosuvastatin AUC(0-infinity) was 100% greater than in those with c.421CA (n = 12) and 144% greater than in those with the c.421CC genotype. Also, those with the c.421AA genotype showed peak plasma rosuvastatin concentrations 108% higher than those in the c.421CA genotype group and 131% higher than those in the c.421CC genotype group (P < or = 0.01). In MDCKII-ABCG2 cells, atorvastatin transport was increased in the apical direction as compared with vector control cells (transport ratio 1.9 +/- 0.1 vs. 1.1 +/- 0.1). These results indicate that the ABCG2 polymorphism markedly affects the pharmacokinetics of atorvastatin and, even more so, of rosuvastatin-potentially affecting the efficacy and toxicity of statin therapy.

Voriconazole increases while itraconazole decreases plasma meloxicam concentrations.

This study investigated the effect of voriconazole, an inhibitor of cytochrome P450 2C9 (CYP2C9) and CYP3A4, and itraconazole, an inhibitor of CYP3A4, on the pharmacokinetics and pharmacodynamics of meloxicam. Twelve healthy volunteers in a crossover study ingested 15 mg of meloxicam without pretreatment (control), after voriconazole pretreatment, and after itraconazole pretreatment. The plasma concentrations of meloxicam, voriconazole, itraconazole, and thromboxane B(2) (TxB(2)) generation were monitored. Compared to the control phase, voriconazole increased the mean area under the plasma concentration-time curve from 0 to 72 h (AUC(0-72)) of meloxicam by 47% (P < 0.001) and prolonged its mean half-life (t(1/2)) by 51% (P < 0.01), without affecting its mean peak concentration (C(max)). In contrast, itraconazole decreased the mean AUC(0-72) and C(max) of meloxicam by 37% (P < 0.001) and by 64% (P < 0.001), respectively, and prolonged its t(1/2) and time to C(max). The plasma protein unbound fraction of meloxicam was unchanged by voriconazole and itraconazole. Lowered plasma meloxicam concentrations during the itraconazole phase were associated with decreased pharmacodymic effects of meloxicam, as observed by weaker inhibition of TxB(2) synthesis compared to the control and voriconazole phases. Voriconazole increases plasma concentrations of meloxicam, whereas itraconazole, unexpectedly, decreases plasma meloxicam concentrations, possibly by impairing its absorption.

ABCB1 haplotypes differentially affect the pharmacokinetics of the acid and lactone forms of simvastatin and atorvastatin.

ABCB1 haplotypes were determined in 534 healthy Finnish volunteers, of whom 24 participated in a pharmacokinetic study on simvastatin and atorvastatin. The frequencies of occurrence of haplotypes c.1236T-c.2677T-c.3435T and c.1236C-c.2677G-c.3435C were 42.7 and 34.4%, respectively. The simvastatin acid AUC(0-12h) was 60% larger, the atorvastatin AUC(0-infinity) 55% larger, and the atorvastatin half-life 24% longer in subjects with the ABCB1 TTT/TTT genotype (n = 12) than in those with the CGC/CGC genotype (n = 12) (P < 0.05), but there were no differences between the two genotypes with respect to the pharmacokinetics of the lactones of these drugs.

Effects of gemfibrozil and atorvastatin on the pharmacokinetics of repaglinide in relation to SLCO1B1 polymorphism.

In a randomized crossover study, 24 SLCO181-genotyped healthy volunteers were given daily doses of 1,200 mg gemfibrozil, 40 mg atorvastatin, or placebo, followed by 0.25 mg of repaglinide on day 3. The mean increase in the repaglinide area under the plasma concentration-time curve from 0 h to infinity (AUC(0-infinity)) produced by gemfibrozil was larger in individuals with the SLCO1B1 c.521CC genotype (n = 6) than in those with the c.521TC (n = 6) and c.521TT (n = 12) genotypes, by factors of 1.56 (P = 0.004) and 1.54 (P = 0.002), respectively. Gemfibrozil prolonged the repaglinide elimination half-life 1.43 times more in the c.521 CC group than in the c.521TT group (P = 0.047), but no differences were seen in the effects on peak plasma concentration (C(max)). While on gemfibrozil, the minimum blood glucose concentration after repaglinide intake was 19% lower in the c.521CC participants than in the c.521TT participants (P = 0.009). In the c.521TT group, atorvastatin intake had the effect of increasing repaglinide Cmax and AUC(0-infinity) by41% (P = 0.001) and 18% (P = 0.033), respectively. In conclusion, the extent of gemfibrozil-repaglinide interaction depends on SLCO1B1 genotype. Atorvastatin raises plasma repaglinide concentrations, probably by inhibiting organic anion transporting polypeptide 1B1 (OATP1B1).

Effect of terbinafine and voriconazole on the pharmacokinetics of the antidepressant venlafaxine.

This study investigated the effect of terbinafine and voriconazole on the pharmacokinetics of venlafaxine in healthy volunteers. Plasma concentrations of venlafaxine and O-desmethylvenlafaxine (ODV) were measured after ingestion of 75 mg venlafaxine without pretreatment (control), after terbinafine pretreatment, or after voriconazole pretreatment. During the terbinafine phase, the area under the plasma concentration-time curve (AUC(0-infinity)) of venlafaxine was on average 490% (P<0.001) and that of ODV 57% (P<0.001) of the corresponding control value. Terbinafine decreased the AUC(0-infinity) ratio of ODV over venlafaxine by 82% (P<0.001). Voriconazole slightly increased the sum of AUC(0-infinity) of venlafaxine plus AUC(0-infinity) of ODV (active moiety) by 31% (P<0.001). The most likely mechanism for the interaction between terbinafine and venlafaxine is the inhibition of CYP2D6-mediated O-demethylation of venlafaxine, whereas the minor effects of voriconazole are probably due to the inhibition of CYP3A4-, CYP2C9-, or CYP2C19-mediated metabolism of venlafaxine.

Isoform-specific membrane translocation of protein kinase C after ischemic preconditioning.

Mild cerebral anoxic/ischemic/stress insults promote 'tolerance' and thereby protect the brain from subsequent 'lethal' anoxic/ischemic insults. We examined whether specific activation of PKC alpha, delta, epsilon, or zeta isoforms is associated with ischemic preconditioning (IPC) in rat brain. IPC was produced by a 2-minute global cerebral ischemia. Membrane and cytosolic fractions of the hippocampi were immunoblotted using specific antibodies for PKCalpha, delta, epsilon, and zeta. PKCalpha showed a significant translocation to the membrane fraction from 30 min to 4 h and PKCdelta at 4 h following IPC. In contrast, the membrane/cytosol ratio of PKCepsilon showed a tendency to decrease at 30 min and 8 h, and the membrane/cytosol ratio of PKCzeta was significantly decreased from 30 min to 24 h following IPC. These findings indicate PKC isoform-specific membrane translocations in the hippocampus after brief global brain ischemia and suggest that activation of PKCalpha and PKCdelta may be associated with IPC-induced tolerance in the rat hippocampus.

Preconditioning with spreading depression activates specifically protein kinase Cdelta.

Preconditioning with brief ischemia or spreading depression (SD) confers tolerance in cortical neurons to subsequent episode of ischemia. In myocardium a similar preconditioning is achieved by mechanisms, which are mediated by protein kinase C (PKC) alpha, delta, epsilon or zeta isoform. We induced SD by cortical application of KCl in the rat and analyzed cortical tissues after recovery of 30 min, 4 h and 12 h. While no changes at protein levels or activity of PKCalpha, epsilon or zeta were detected, a considerable increase in membrane translocation of PKCdelta was seen at 30 min and 12 h. A significant increase at mRNA level, protein amount and autophosphorylation at 12 h confirmed the late activation of PKCdelta, which may be involved in neuronal protection by preconditioning.

Genomic structure and chromosomal localization of the rat protein kinase Cdelta-gene.

Protein kinase Cdelta (PKCdelta) is a widely expressed calcium-independent PKC isozyme that is induced at mRNA and protein levels upon stimulation of different cellular pathways. We found the rat PKCdelta gene to consist of 19 exons and to span approximately 29 kb. The exon-intron junctions follow the GT/AG rule. The 5' untranslated region is nearly 12 kb in length, and the transcription initiation site is surrounded by CG-rich sequences. The 5' flanking region contains putative binding sites for activator protein 1 (AP-1), nuclear factor kappa B (NFkappaB), stimulatory protein-1 (Sp-1) and nerve growth factor induced-C (NGFI-C) transcription factors. The PKCdelta gene is localized at the rat chromosome 19p14. The cloned gene will help to elucidate the role of PKCdelta in growth, differentiation and death of mammalian cells.

[Gamma-35S]GTP autoradiography allows region-specific detection of muscarinic receptor-dependent G-protein activation in the chick optic tectum.

A recently introduced technique of [gamma-35S]GTP autoradiography was used to localize and characterize muscarinic receptor-dependent activation of G-proteins in tissue sections of the chick optic tectum, a brain region with relatively high expression of G-protein-coupled receptors for the neurotransmitter acetylcholine. Within the highly stratified tectal structure, the bulk of muscarinic receptor-mediated [gamma-35S]GTP signal was localized to the stratum griseum et fibrosum superficiale with considerably lower binding responses in other tectal layers. Quantitative comparison of [gamma-35S]GTP binding responses in tectal sections and membranes revealed a close match between the two tissue preparations for the response elicited by the cholinergic agonist carbachol, its dose-dependent reversal with the non-selective muscarinic antagonist atropine, its approximately 100-fold sensitivity towards blockade with M1-type (pirenzepine) over M2-type (gallamine) muscarinic antagonists, as well as absolute requirement for micromolar concentrations of GDP (EC50 approximately 10 microM) for the receptor-mediated [gamma-35S]GTP response. The pharmacological profile is consistent with that of cm4, a recently cloned chicken homolog of the mammalian m4 muscarinic acetylcholine receptor. Moreover, the strict GDP-dependence of the binding response suggest activation of Gi/o, the inhibitory class of G-proteins. These data provide the first functional characterization of the chick tectal muscarinic receptors. A close match between [gamma-35S]GTP responses in membranes and tissue sections strongly suggest that [gamma-35S]GTP autoradiography offers great potential for studies on G-protein-mediated signaling, with particular use within anatomically restricted regions that are not readily approached with more conventional techniques. It is anticipated that [gamma-35S]GTP autoradiography should greatly facilitate studies on signaling capacity of an individual receptor subtype whilst in its native cellular environment.