No Inhibition of Cytochrome P450 Activities in Human Liver Microsomes by Sulpiride, an Antipsychotic Drug

Mechanism-based inhibition of CYP3A subfamilies by macrolide antibiotics and piperine

OBJECTIVE

The mechanism-based inhibition of macrolide antibiotics, such as erythromycin and clarithromycin, and piperine on testosterone 6β-hydroxylation activities by cytochrome P450 (CYP) 3A4, polymorphically expressed CYP3A5, and fetal CYP3A7 were compared.

METHODS

6β-Hydroxy testosterone was determined by high-performance liquid chromatography.

RESULTS

Although preincubation with erythromycin and clarithromycin decreased CYP3A4-meditaed testosterone 6β- hydroxylation in a time-dependent manner, and the estimated maximum inactivation rate constant (k inact ) and the inactivation rate constant reaching half of k inact (K i ) for erythromycin were approximately 1/2 and 1/5, respectively, of those for clarithromycin. Obvious preincubation time-dependent inhibition of erythromycin against CYP3A5 and CYP3A7 was not observed. Piperine exhibited preincubation time- dependent inhibition, and the calculated K i and k inact values for CYP3A4 were approximately 1/7 and 1/2, respectively, of those for CYP3A5.

CONCLUSION

It is speculated that the preincubation-dependent inhibition by piperine would be more potent in CYP3A5 non-expressors than CYP3A5-expressors.

HLM-beads: Rapid Assessment of Nonspecific Binding to Human Liver Microsomes Using Magnetizable Beads

In early drug development, drug-drug interaction risk is routinely assessed using human liver microsomes (HLMs). Nonspecific binding of drugs to HLMs can affect the determination of accurate enzyme parameters (K_m, K_i, K_I). Previously, we described a novel in vitro model consisting of HLMs bound to magnetizable beads [HLM-magnetizable-beads system (HLM-beads)]. The HLM-beads enable rapid separation of HLMs from incubation media by applying a magnetic field. Here, HLM-beads were further characterized and evaluated as a tool to assess HLM nonspecific binding of small molecules. The free fractions (f_u,mic) of 13 compounds (chosen based on their pKa values) were determined using HLM-beads under three HLM concentrations (0.025, 0.50, and 1.0 mg/ml) and compared with those determined by equilibrium dialysis. Most f_u,mic values obtained using HLM-beads were within 0.5- to 2-fold of the values determined using equilibrium dialysis. The highest fold difference were observed for high binders itraconazole and BIRT2584 (1.9- to 2.9-fold), as the pronounced adsorption of these compounds to the equilibrium dialysis apparatus interfered with their f_u,mic determination. Correlation and linear regression analysis of the f_u,mic values generated using HLM-beads and equilibrium dialysis was conducted. Overall, a good correlation of f_u,mic values obtained by the two methods were observed, as the r and R² values from correlational analysis and linear regression analysis were >0.9 and >0.89, respectively. These studies demonstrate that HLM-beads can produce comparable f_u,mic values as determined by equilibrium dialysis while reducing the time required for this type of study from hours to only 10 minutes and compound apparatus adsorption. SIGNIFICANCE STATEMENT: This work introduces a new method of rapidly assessing nonspecific microsomal binding using human liver microsomes bound to magnetizable beads.

Comparison of the Stimulatory and Inhibitory Effects of Steroid Hormones and α-Naphthoflavone on Steroid Hormone Hydroxylation Catalyzed by Human Cytochrome P450 3A Subfamilies

The inhibitory and stimulatory effects of steroid hormones and related compounds on the hydroxylation activity at the 6β-position of two steroid hormones, progesterone and testosterone, by CYP3A4, polymorphically expressed CYP3A5, and fetal CYP3A7 were compared to clarify the catalytic properties of the predominant forms of the human CYP3A subfamily. Hydroxylation activities of progesterone and testosterone by CYP3A4, CYP3A5, and CYP3A7 were estimated using HPLC. The Michaelis constants (K_m) for progesterone 6β-hydroxylation by CYP3A5 were markedly decreased in the presence of dehydroepiandrosterone (DHEA) and α-naphthoflavone (ANF), whereas progesterone and DHEA competitively inhibited testosterone 6β-hydroxylation mediated by CYP3A4, and progesterone competitively inhibited CYP3A5-mediated activity, which was weaker than that for CYP3A4. ANF noncompetitively inhibited testosterone 6β-hydroxylation mediated by both CYP3A4 and CYP3A5. Progesterone and testosterone 6β-hydroxylation mediated by CYP3A7 was inhibited or unaffected by DHEA, pregnenolone, and ANF. These results suggested that DHEA and ANF stimulated progesterone 6β-hydroxylation by CYP3A5 but not by CYP3A4 and CYP3A7; however, progesterone, DHEA, and ANF inhibited testosterone 6β-hydroxylation mediated by all CYP3A subfamily members. The inhibitory/stimulatory pattern of steroid-steroid interactions is different among CYP3A subfamily members and CYP3A5 is the most sensitive in terms of activation among the CYP3A subfamily members investigated.

The role of sulpiride in attenuating the cardiac, renal, and immune disruptions in rats receiving clozapine: mRNA expression pattern of the genes encoding Kim-1, TIMP-1, and CYP isoforms

The present study was aimed to explore the cardio-, immuno-, and nephrotoxic effects of the antipsychotic agent clozapine (CLZ) and the alleviative potency of sulpiride (SPD) on these impairments in rats. For this purpose, 40 male rats were divided into four groups and were orally treated with saline (control), CLZ (0.5 mg/kg bw), SPD (28 mg/kg bw), or a combination of CLZ and SPD (CLZ+SPD), daily for 30 consecutive days. At necropsy, blood samples and specimens from the heart, kidneys, and spleen were collected for biochemical, molecular, and histopathological investigations. The results showed that CLZ administration was associated with significantly lower immune status indices and increased serum levels of pro-inflammatory cytokines, lactate dehydrogenase, malondialdehyde, cardiac, and renal tissues injury markers. Moreover, the mRNA expression levels of Kidney Injury Molecule-1 (Kim-1), tissue inhibitor of metalloproteinase-1 (TIMP-1), and cytochrome P450 (CYP) isoforms were markedly upregulated in CLZ-treated rats, compared to the control group. On the other hand, rats treated with SPD alone showed non-significant differences in terms of immune response indices, tissue injury markers, and mRNA expression levels of Kim-1, TIMP-1, and CYP isoforms. Finally, CLZ+SPD co-treatment significantly modulated almost all biochemical indices. Besides, Kim-1, TIMP-1, and CYP2C19 mRNA expression levels were significantly downregulated, while other CYP isoforms showed no modulation, compared with CLZ-treated group. Histopathologically, CLZ-treated rats showed severe lesions in renal, splenic, and cardiac tissues, compared with control rats, which were restored in CLZ+SPD-co-treated rats. Overall, these findings demonstrate that CLZ treatment induces significant cardiac, immune, and nephropathic alterations, which were reduced with CLZ+SPD co-treatment.

Comparison of steroid hormone hydroxylation mediated by cytochrome P450 3A subfamilies

Hydroxylation activity at the 6β-position of steroid hormones (testosterone, progesterone, and cortisol) by human cytochromes P450 (CYP) 3A4, polymorphic CYP3A5, and fetal CYP3A7 were compared to understand the catalytic properties of the major forms of human CYP3A subfamily. Testosterone, progesterone, and cortisol 6β-hydroxylation activities of recombinant CYP3A4, CYP3A5, and CYP3A7 were determined by liquid chromatography. Michaelis constants (K_m) for CYP3A7-mediated 6β-hydroxylation of testosterone, progesterone, and cortisol were similar to those of CYP3A4 and CYP3A5. The maximal velocity (k_cat) and k_cat/K_m values for CYP3A4 were the highest, followed by CYP3A5 and those for CYP3A7 were the lowest among three CYP3A subfamily members. A decrease in K_m values for progesterone 6β-hydroxylation by CYP3A4, CYP3A5, and CYP3A7 in the presence of testosterone was observed, and the k_cat values for CYP3A5 gradually increased with increasing testosterone. This indicated that testosterone stimulated progesterone 6β-hydroxylation by all three CYP3A subfamily members. However, progesterone inhibited testosterone 6β-hydroxylation mediated by CYP3A4, CYP3A5, and CYP3A7. In conclusion, the k_cat values, rather than K_m values, for 6β-hydroxylation of three steroid hormones mediated by CYP3A7 were different from those for CYP3A4 and CYP3A5. In addition, the inhibitory/stimulatory pattern of steroid-steroid interactions would be different among CYP3A subfamily members.

Effect of penicillin-based antibiotics, amoxicillin, ampicillin, and piperacillin, on drug-metabolizing activities of human hepatic cytochromes P450

The effects of three kinds of penicillin-based antibiotics, amoxicillin, ampicillin, and piperacillin, on drug-metabolizing activity of human hepatic cytochrome P450 (P450 or CYP) were investigated. Metabolic activities of P450s expressed in recombinant Escherichia coli at substrate concentrations around the Michaelis constant were compared in the presence or absence of the antibiotics. Amoxicillin, ampicillin, and piperacillin at 0.5 or 1 mM concentrations neither inhibited nor stimulated CYP2C9-mediated tolbutamide methylhydroxylation, CYP2D6-mediated dopamine formation from p-tyramine, or CYP3A4- or CYP3A5-mediated testosterone 6β-hydroxylation. However, amoxicillin and piperacillin inhibited CYP2C8-mediated aminopyrine N-demethylation at 50% inhibitory concentration of 0.83 and 1.14 mM, respectively. These results suggest that piperacillin might inhibit CYP2C8 clinically, although the interactions between these three penicillin-based antibiotics and other drugs that are metabolized by P450s investigated would not be clinically significant.

The Effect of Genetic Polymorphism on the Inhibition of Azole Antifungal Agents Against CYP2C9-Mediated Metabolism

We investigated the effect of cytochrome P450 (CYP) 2C9 polymorphism on the inhibition of methylhydroxylation activity of tolbutamide, a typical CYP2C9 substrate, by triazole antifungal agents, fluconazole and voriconazole. Although the Michaelis constants (Km), maximal velocities (Vmax), and Vmax/Km values for CYP2C9.1 (wild type) and CYP2C9.2 (Arg144Cys) were similar and CYP2C9.3 (Ile359Leu) had a higher Km and a lower Vmax than CYP2C9.1 and CYP2C9.2, the inhibition constants of fluconazole and voriconazole against CYP2C9.2 were lower than that against CYP2C9.1 and CYP2C9.3. These results suggest that more careful administration of azole antifungals to patients with the CYP2C9*2 allele might be required because of the strong inhibitory effects.

Therapeutic drug monitoring and pharmacokinetic compartmental analysis of sulpiride double-peak absorption profile after oral administration to human volunteers

BACKGROUND

The pharmacokinetics of oral drugs that exhibit double peaks cannot be described adequately by using conventional compartmental models.

OBJECTIVE

The aim of this study was to describe the double-peak plasma pharmacokinetic profile of sulpiride after oral administration to healthy volunteers based on physiological and biopharmaceutical considerations.

METHODS

A single 100 mg dose of sulpiride was given to 16 healthy volunteers. Blood samples were drawn at different times and analysed by a validated HPLC assay method. Plasma profiles were evaluated by non-compartmental and compartmental approaches.

RESULTS

The non-compartmental parameters determined were k (0.079±0.008 h(-1)), t1/2 (9.0±2.9 h), Vd /F (330.5±87.3 L), Cl/F (38.2±9.8 L/h) and AUC0→∞ (1402.5±404.7 ng.h/mL). The compartmental analysis was described appropriately using a two-compartment body model, with first order absorption from two different sites in the gut. The parameters determined were k21 (0.68±0.2 h(-1)), ka1 (0.7±0.27 h(-1)), ka2 (2.7±1.8 h(-1)) Vc/F (45.1±15.7 L), α (33.3±1.5 h(-1)), β (0.11±0.03 h(-1)) and time for the beginning of the absorption from the second site (4.4±2.1 h).

CONCLUSION

The developed analytical method was suitable for use in pharmacokinetic studies and therapeutic drug monitoring implementation. Sulpiride was well tolerated by the patients without any serious adverse events being observed. The double peaks in the serum concentration-time profiles could be due to differential rates of absorption along the gastrointestinal tract. The discontinuous absorption model with two sites of absorption was adequate to describe the double-peak of the sulpiride plasma profile. ClinicalTrials. gov identifiers: NCT01777685.

Pulmonary embolism from persistent dilatation of the bladder secondary to anticholinergic side effects

OBJECTIVE

To discuss the risk that bladder distention resulting from anticholinergic side effects of antipsychotics can cause iliac vein compression syndrome (IVCS) and subsequent pulmonary embolism (PE).

METHOD

Case report, review of the literature and discussion.

RESULTS

We report the case of a 65-year-old man with depression who experienced PE associated with IVCS due to a distended urinary bladder resulting from anticholinergic side effects. PE disappeared after conservative therapy with heparin followed by warfarin.

CONCLUSION

When drugs with anticholinergic effects are given to immobilized patients such as those with severe depression, close observation including monitoring of urine volume is needed to prevent IVCS caused by drug-induced urinary retention, and subsequent PE.

Effect of cyclosporine and tacrolimus on cytochrome p450 activities in human liver microsomes

The effects of cyclosporine and tacrolimus on cytochrome P450 (CYP) 1A2-mediated 7-ethoxyresorufin O-deethylation, CYP2C9-mediated tolbutamide hydroxylation, CYP2C19-mediated S-mephenytoin 4'-hydroxylation, CYP2D6-mediated debrisoquine 4-hydroxylation, CYP2E1-mediated chlorzoxazone 6-hydroxylation, CYP3A4-mediated nifedipine oxidation, and CYP3A4-mediated testosterone 6beta-hydroxylation activities in human liver microsomes were compared. Cyclosporine and tacrolimus, at concentrations of 0.2 or 2 muM, neither inhibited nor stimulated any of the metabolic activities except for those of CYP3A4. On the other hand, cyclosporine and tacrolimus competitively inhibited CYP3A4-mediated nifedipine oxidation activity, with inhibition constants (K(i)) of 1.42 and 0.36 muM, respectively. In addition, 20 muM cyclosporine inhibited CYP2C19 and CYP2D6 activities by 29% and 30%, respectively. These results suggest that tacrolimus would not cause clinically significant interactions with other drugs, which are metabolized by CYPs, via the inhibition of hepatic metabolism and that the reason why cyclosporine, but not tacrolimus, has a pharmacokinetic inhibitory effect might be that the dosage and/or the unbound concentrations around its metabolic enzymes are higher than those of tacrolimus, rather than the differences in the inhibition potential. Obvious substrate-dependent effects on CYP3A4-inhibition potential were not observed.

Effects of serotonin-3 receptor antagonists on cytochrome P450 activities in human liver microsomes

The effects of three serotonin-3 (5-HT(3)) receptor antagonists, azasetron, ondansetron, and ramosetron, on cytochrome P450 (CYP) 1A2-mediated 7-ethoxyresorufin O-deethylation, CYP2C9-mediated tolbutamide hydroxylation, CYP2C19-mediated S-mephenytoin 4'-hydroxylation, CYP2D6-mediated debrisoquine 4-hydroxylation, CYP2E1-mediated chlorzoxazone 6-hydroxylation, CYP3A4-mediated nifedipine oxidation, and CYP3A4-mediated testosterone 6beta-hydroxylation activities in human liver microsomes were compared. Azasetron and ramosetron at a concentration of 1 or 10 muM neither inhibited nor stimulated any of the metabolic activities. On the other hand, ondansetron competitively inhibited CYP1A2 and CYP2D6 activities, and the inhibition constants (K(i)) were 3.2 and 21.0 muM, respectively, which are much higher than the reported plasma concentrations after clinical intravenous or oral dosing. The free fractions of the three 5-HT(3) receptor antagonists in the incubation mixture estimated by ultracentrifugation were more than 68.6%. These results suggest that azasetron, ondansetron, and ramosetron do not cause clinically significant interactions with other drugs that are metabolized by CYPs via the inhibition of metabolism.

Drug-Drug Interaction of Antifungal Drugs

This article reviews the in vitro metabolic and the in vivo pharmacokinetic drug-drug interactions with antifungal drugs, including fluconazole, itraconazole, micafungin, miconazole, and voriconazole. In the in vitro interaction studies, the effects of antifungal drugs on specific activities of cytochrome P450s (CYPs), including CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4, in human liver microsomes are compared to predict the possibility of drug interactions in vivo. Fluconazole, micafungin, and voriconazole have lower inhibitory effects on CYP3A4 activities than itraconazole and miconazole, and IC(50) and/or K(i) values against CYP2C9 and CYP2C19 activities are the lowest for miconazole, followed by voriconazole and fluconazole. In in vivo pharmacokinetic studies, it is well known that itraconazole is a potent clinically important inhibitor of the clearance of CYP3A4 substrates, and fluconazole and voriconazole are reported to increase the blood or plasma concentrations of not only midazolam and cyclosporine (CYP3A4 substrates) but also of phenytoin (CYP2C9 substrate) and/or omeprazole (CYP2C19/CYP3A4 substrate). On the other hand, no inhibition of CYP activities except for CYP3A4 activity by micafungin is observed in vitro, and the blood concentrations of cyclosporine and tacrolimus are not affected by coadministration of micafungin in vivo, suggesting that micafungin would not cause clinically significant interactions with drugs that are metabolized by CYPs via the inhibition of metabolism. Miconazole is a potent inhibitor of all CYPs investigated in vitro, although there are few detailed studies on the clinical significance of this except for CYP2C9. Therefore the differential effects of these antifungal drugs on CYP activities must be considered in the choice of antifungal drugs in patients receiving other drugs.

Effect of Antifungal Drugs on Cytochrome P450 (CYP) 2C9, CYP2C19, and CYP3A4 Activities in Human Liver Microsomes

The effects of five antifungal drugs, fluconazole, itraconazole, micafungin, miconazole, and voriconazole, on cytochrome P450 (CYP) 2C9-mediated tolbutamide hydroxylation, CYP2C19-mediated S-mephenytoin 4'-hydroxylation, and CYP3A4-mediated nifedipine oxidation activities in human liver microsomes were compared. In addition, the effects of preincubation were estimated to investigate the mechanism-based inhibition. The IC50 value against tolbutamide hydroxylation was the lowest for miconazole (2.0 microM), followed by voriconazole (8.4 microM) and fluconazole (30.3 microM). Similarly, the IC50 value against S-mephenytoin 4'-hydroxylation was the lowest for miconazole (0.33 microM), followed by voriconazole (8.7 microM) and fluconazole (12.3 microM). On the other hand, micafungin at a concentration of 10 or 25 microM neither inhibited nor stimulated tolbutamide hydroxylation and S-mephenytoin 4'-hydroxylation, and the IC50 values for itraconazole against these were greater than 10 microM. These results suggest that miconazole is the strongest inhibitor of CYP2C9 and CYP2C19, followed by voriconazole and fluconazole, whereas micafungin would not cause clinically significant interactions with other drugs that are metabolized by CYP2C9 or CYP2C19 via the inhibition of metabolism. The IC50 value of voriconazole against nifedipine oxidation was comparable with that of fluconazole and micafungin and higher than that of itraconazole and miconazole. The stimulation of the inhibition of CYP2C9-, CYP2C19-, or CYP3A4-mediated reactions by 15-min preincubation was not observed for any of the antifungal drugs, suggesting that these drugs are not mechanism-based inhibitors.

Effect of Antifungal Drugs on Cytochrome P450 (CYP) 1A2, CYP2D6, and CYP2E1 Activities in Human Liver Microsomes

The effects of five antifungal drugs, fluconazole, itraconazole, micafungin, miconazole, and voriconazole, on cytochrome P450 (CYP) 1A2-mediated 7-ethoxyresorufin O-deethylation, CYP2D6-mediated debrisoquine 4-hydroxylation, and CYP2E1-mediated chlorzoxazone 6-hydroxylation activities in human liver microsomes were compared. In addition, the effect of preincubation was estimated in order to investigate the mechanism-based inhibition. IC50 values of miconazole against CYP1A2 and CYP2D6 activities were 2.90 and 6.46 microM, respectively, and miconazole at 10 microM concentration slightly inhibited CYP2E1 activity. On the other hand, other antifungal drugs neither inhibited nor stimulated all of the metabolic activities. The stimulation of the inhibition of the metabolic activities mediated by CYP1A2, CYP2D6, or CYP2E1 by 15-min preincubation was not observed for any of the antifungal drugs, suggesting that these antifungal drugs are not mechanism-based inhibitors. These results suggest that miconazole is the strongest inhibitor against CYP1A2, CYP2D6, and CYP2E1 among the antifungal drugs investigated.