In-vivo and in-vitro metabolic clearance of midazolam, a cytochrome P450 3A substrate, by the liver under normal and increased enzyme activity in rats

Pharmacokinetic alterations in poloxamer 407-induced hyperlipidemic rats

1. Plasma lipid profile abnormalities in hyperlipidemia can potentially alter the pharmacokinetics of a drug in a complex manner. To evaluate these pharmacokinetic alterations in hyperlipidemia and to determine the underlying mechanism(s), poloxamer 407-induced hyperlipidemic rats (HL rats), a well-established animal model of hyperlipidemia have been used. 2. In this review, we summarize findings on the pathophysiological and gene expression changes in drug-metabolizing enzymes and transporters in HL rats. We discuss pharmacokinetic changes in drugs metabolized primarily via hepatic cytochrome P450 (CYPs) in terms of alterations in hepatic intrinsic clearance (CL^'_int), free fraction in plasma (f_u) and hepatic blood flow rate (Q_H), depending on the hepatic excretion ratio, as well as drugs eliminated primarily by mechanisms other than hepatic CYPs. 3. For lipoprotein-bound drugs, increased binding to lipoproteins resulted in lower f_u values and volumes of distribution, with some exceptions. Generally, slower non-renal clearance (or total body clearance) of drugs that are substrates of hepatic CYP3A and CYP2C is well explained by the following factors: alterations in CL^'_int (due to down-regulation of hepatic CYPs), decreased f_u and/or possible decreased Q_H. 4. These consistent findings across studies in HL rats suggest more studies are needed at the clinical level for optimal pharmacotherapies for hyperlipidemia.

Probe ADME and test hypotheses: a PATH beyond clearance in vitro-in vivo correlations in early drug discovery

INTRODUCTION

In vitro cytochrome P450 (CYP450) metabolic profiling is pursued extensively to optimize drug properties. Still, the in vivo clearance of half of all new chemical entities (NCEs) remains poorly predicted by CYP450 metabolism, based on Novartis rat pharmacokinetic data. The conventional route to illuminating key drivers of in vivo clearance beyond hepatic metabolism is, frequently, the process of elimination, a time-consuming and sometimes resource-intensive practice. A more nimble and efficient diagnosis of drug clearance is imperative to support today's chemistry optimization.

AREAS COVERED

This article reviews in vitro-in vivo clearance correlation (IVIVC) analysis of drugs and NCEs including in silico advances, in vitro opportunities for clearance characterization and guidance for proper interpretation of clearance data. Potential mechanisms for under- and overestimation of in vivo clearance obtained from in vitro approaches are reviewed. The article offers insight into a practical PATH (Probe ADME and Test Hypotheses) for discovery data analysis that can enrich IVIVC development and guide more efficient use of the ADME-PK toolbox.

EXPERT OPINION

In vitro hepatic CYP450 stability measurements remain the most practical way to triage for high metabolic liabilities. Clearance is a complex process involving multiple mechanisms and many factors tend to be overlooked in routine correlation analyses. Equilibrium protein binding, intrinsic permeability and ionization may yield insight into distribution-limited clearance. In addition, hydrophobic character and transporter interaction can be valuable in diagnosing dominant clearance pathways. An integrated ADME approach to clearance interrogation is expected to help refine the in vitro-in silico strategies that guide medicinal chemistry.

Mild hypothermia decreases fentanyl and midazolam steady-state clearance in a rat model of cardiac arrest

OBJECTIVES

Therapeutic hypothermia is widely employed for neuroprotection after cardiac arrest. However, concern regarding elevated drug concentrations during hypothermia and increased adverse drug reaction risk complicates concurrent pharmacotherapy. Many commonly used medications in critically ill patients rely on the cytochrome P450 3A isoform for their elimination. Therefore, our study objectives were to determine the effect of mild hypothermia on the in vivo pharmacokinetics of fentanyl and midazolam, two clinically relevant cytochrome P450 3A substrates, after cardiac arrest and to investigate the mechanisms of these alterations.

DESIGN

Prospective, randomized, controlled study.

SETTING

University research laboratory.

SUBJECTS

Thirty-two adult male Sprague-Dawley rats.

INTERVENTIONS

An asphyxial cardiac arrest rat model was used and mild hypothermia (33°C) was induced 1 hr post injury by surface cooling and continued for 10 hrs to mimic the prolonged clinical application of hypothermia accompanied by intensive care interventions. Fentanyl and midazolam were independently administered by intravenous infusion and plasma and brain concentrations were analyzed using ultraperformance liquid chromatography tandem mass spectrometry. Cytochrome P450 3a2 protein expression was measured and a Michaelis-Menten enzyme kinetic analysis was performed at 37°C and 33°C using control rat microsomes.

MEASUREMENTS AND MAIN RESULTS

Mild hypothermia decreased the systemic clearance of both fentanyl (61.5 ± 11.5 to 48.9 ± 8.95 mL/min/kg; p < .05) and midazolam (89.2 ± 12.5 to 73.6 ± 12.1 mL/min/kg; p < .05) after cardiac arrest. The elevated systemic concentrations did not lead to parallel increased brain exposures of either drug. Mechanistically, no differences in cytochrome P450 3a2 expression was observed, but the in vitro metabolism of both drugs was decreased at 33°C vs. 37°C through reductions in enzyme metabolic capacity rather than substrate affinity.

CONCLUSIONS

Mild hypothermia reduces the systemic clearances of fentanyl and midazolam in rats after cardiac arrest through alterations in cytochrome P450 3a2 metabolic capacity rather than enzyme affinity as observed with other cytochrome P450s. Contrasting effects on blood and brain levels further complicates drug dosing. Consideration of the impact of hypothermia on medications whose clearance is dependent on P450 3A metabolism is warranted.

Mechanism-based inhibition of human cytochrome P4503A4 by domperidone

Domperidone was evaluated in direct and time-dependent cytochrome P450 (CYP) 3A inhibition assays in human liver microsomes with midazolam and testosterone as probe substrates. Domperidone was found to be a modest mechanism-based inhibitor of human and rat CYP3A. For human CYP3A, the inactivation constant (K(I)) is 12 microM, and the maximum inactivation rate (k(inact)) is 0.037 min(-1). A rat interaction study was conducted between midazolam and either a single dose or five daily doses of domperidone. Although a single oral dose of 10 mg kg(-1) domperidone did not affect the pharmacokinetics of 10 mg kg(-1) oral midazolam, five daily oral doses of domperidone almost doubled the area under the plasma concentration versus time curve (AUC) of midazolam, and increased the maximum plasma concentration (C(max)) of midazolam by 72%. Based on the simulation and rat in vitro-in vivo extrapolation, it is predicted that co-administration of domperidone in humans could modestly increase (approximately 50%) the exposure of drugs that are primarily cleared by CYP3A.

Changes of midazolam pharmacokinetics in Wistar rats treated with lipopolysaccharide: relationship between total CYP and CYP3A2

It has been reported that infection interferes with drug metabolism, resulting in changes in pharmacokinetics. In this study, we investigated the effects of lipopolysaccharide (LPS) on hepatic total cytochrome P450 (CYP), CYP3A2, and CYP2C11 contents in a transient, LPS-induced, endotoxemia model of rats. In addition, to assess the effects on CYP3A2 activities, the pharmacokinetics of midazolam (CYP3A2 substrate) and 1-OH-midazolam (metabolite of midazolam) were investigated. Hepatic total CYP contents were significantly low until day 3 ( P < 0.05) but returned to the control level on day 5. Hepatic CYP3A2 contents were significantly decreased on day 1 until day 5 ( P < 0.05) but returned to the control level on day 7. Hepatic CYP2C11 contents were continuously low until day 7, and lowest on day 3. The AUC of 1-OH-midazolam was significantly decreased on day 1 after LPS administration ( P < 0.01). In conclusion, LPS (5 mg/kg) challenge decreased hepatic total CYP, CYP3A2, and CYP2C11 contents and also decreased the activities of hepatic CYP3A2. It took at least 7 days for hepatic total CYP and CYP3A2 to recover to control levels, and it was suggested that the changes of hepatic total CYP contents might correlate with those of hepatic CYP3A2 contents and activities. Additionally, it is shown that their changes might reflect the recovery process from inflammation.

In vivo use of the P450 inactivator 1-aminobenzotriazole in the rat: varied dosing route to elucidate gut and liver contributions to first-pass and systemic clearance

The small intestine is regarded as an absorptive organ in the uptake of orally administered drugs, but also has the ability to metabolize drugs by both phase 1 and phase 2 reactions. The amount of drug that reaches the systemic circulation can be reduced by both intestinal and hepatic metabolism. 1-Aminobenzotriazole (ABT) is an irreversible inhibitor of cytochrome P450s. Through in vivo and in vitro studies, ABT has been evaluated for its utility in studying intestinal metabolism in rats. Rats have been exposed to ABT through varied routes of administration followed by p.o. and i.v. administration of midazolam (MDZ), a CYP3A substrate. The MDZ bioavailablity in rats dosed orally and in rats dosed intravenously with ABT is 58.5% and 0.7%, respectively (%F = 2.3% w/o ABT). The approximately 80-fold difference between the two groups suggests the majority of the extraction occurs in the intestine following an oral dose. To further study the utility of ABT, the antihistamine fexofenadine (Fex), which is not significantly metabolized and is a substrate for the uptake and efflux transporters, OATP and P-gp, was tested in rat. There was no change in oral or systemic exposure of Fex when animals were predosed with ABT, suggesting that ABT does not affect these transporters. These findings may lead to a better understanding of the interdependent role of absorption and metabolism and the specificity of ABT. This method should have utility in drug discovery for the identification of factors limiting oral bioavailability.

Synthesis and 5-HT(1A), 5-HT(2A) receptor activity of new beta-tetralonohydantoins

A series of new 3-[4-(4-arylpiperazinyl)-butyl]-beta-tetralonohydantoins (8a-13a) were synthesized. The compounds exhibited high affinity for 5-HT(1A) receptors (K(i)=6 to 55 nM) combined with moderate-to-high 5-HT(2A) receptor affinities (K(i)=45 to 213 nM). The results of in vivo studies indicated that of the compounds tested, 3-[4-(4-phenylpiperazinyl)-butyl-beta-tetralonohydantoin (8a) showed features of full (pre- and postsynaptic) 5-HT(1A) receptor agonists, whereas compounds 9a-13a behaved like antagonists of postsynaptic 5-HT(1A) receptors; additionally, compound 13a produced an effect characteristic of presynaptic 5-HT(1A) receptor agonists. Moreover, compounds 8a and 10a-13a exhibited properties of 5-HT(2A) receptor antagonists. Due to the most interesting 5-HT(1A)/5-HT(2A) functional profile compounds 8a and 13a were further tested for their potential psychotropic activity. In fact, compound 8a (but not 13a) showed diazepam-like anxiolytic activity and behaved like a weak antidepressant.

Cerebral and plasma kinetics of a high dose of midazolam and correlations with its respiratory effects in rats

Benzodiazepine poisoning causes coma and respiratory depression. Our objective was to determine whether, and to what extent, arterial blood gas disturbances correlated with blood or cerebral kinetics of midazolam. A 160 mgkg(-1) single dose of midazolam was infused intravenously over 20 min in catheterized male Sprague-Dawley rats. Midazolam kinetics was simultaneously determined in plasma and brain using striatal microdialysis. Midazolam concentrations were measured using a high-performance liquid chromatographic assay with ultraviolet detection. Midazolam (160 mgkg(-1)) reproducibly induced deep coma with respiratory acidosis. Plasma midazolam kinetics was well described by a bi-exponential model, with an elimination half-life of 6.4+/-1.8 h. The striatal dialysate concentration peaked at 50.0+/-8.9 min after the end of infusion, with a significant delay to peak concentration compared to plasma. Respiratory depression, assessed by the elevation in PaCO2, was more closely correlated with midazolam striatal dialysate rather than plasma kinetics. These results suggest a central mechanism for midazolam respiratory effects at toxic doses in rats. In conclusion, our study showed a delayed onset in peak PaCO2 and pH effects after the slow infusion of a toxic dose of midazolam in rats. The effects on arterial blood gases were better correlated with midazolam striatal concentrations than with plasma concentrations. This study may contribute to better understanding of benzodiazepine-induced respiratory depression in poisonings.

Prediction of differences in in vivo oral clearance of N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl] ethylamine monohydrochloride (NE-100) between extensive and poor metabolizers from in vitro metabolic data in human liver microsomes lacking CYP2D6 activity and recombinant CYPs

1. It has previously been reported that N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE-100) was predominantly metabolized by cytochrome P450 (CYP) 2D6 in human liver microsomes (HLM). In the present study, the contribution of CYP forms involved in the formation of the major metabolites of NE-100 in human liver lacking CYP2D6 activity (PM-HLM) has been predicted by use of in vitro kinetic data on recombinant CYPs microsomes (rCYPs). 2. In PM-HLM, NE-100 is predicted to be metabolized to N-despropyl-NE-100 (NE-098), p-hydroxy-NE-100 (NE-152) and m-hydroxyl-NE-100 (NE-163), but not to O-demethy-NE-100 (NE-125), which is a major metabolite in pooled human liver microsomes (EM-HLM). The relative activity factor approach assumed that NE-098 formation is predominantly catalysed by CYP3A4 and CYP2C9 and the NE-152+163mix (a mixture of two hydroxylated metabolites, NE-152 and NE-163) formation is only catalysed by CYP3A4. 3. The predicted contribution rates of CYP3A4 and CYP2C9 for NE-098 formation were 58.1 and 34.6%, respectively, in PM-HLM. These predicted results were strongly supported by kinetic and inhibition studies using PM-HLM. The intrinsic clearance of NE-100 predicted from rCYPs (the predicted CLint-HLM-total) corresponded to those observed from EM- and PM-HLM (the observed CLint-HLM). 4. The in vivo oral clearance (CLoral) of NE-100 in extensive metabolizers and poor metabolizers of CYP2D6 was predicted to be 50times higher in extensive metabolizers than poor metabolizers using in vitro-in vivo scaling method based on the dispersion model. These data suggest that polymorphism of CYP2D6 might greatly affect NE-100 metabolism in vivo.

Pharmacokinetic Interactions between Japanese Traditional Kampo Medicine and Modern Medicine (IV). Effect of Kamisyoyosan and Tokisyakuyakusan on the Pharmacokinetics of Etizolam in Rats

Kamisyoyosan (KSS) and Tokisyakuyakusan (TSS) are widely used herbal formulas in Japanese traditional kampo medicine to relieve the symptoms occurred in climacteric disturbance. Since Japanese physicians frequently prescribe these formulas combined with etizolam, one of benzodiazepine anxiolytics, we evaluated the pharmacokinetic interaction between KSS or TSS and etizolam, and in vitro inhibitory effect of KSS and TSS on rat cytochrome P450 (CYP) 3A activity in rat microsomes, to obtain drug information to prevent from disadvantage or adverse effects by their combined therapy. In in vitro experiment, KSS and TSS inhibited CYP3A activity comparable to grapefruit juice. However in in vivo experiments, oral administration of KSS did not influence the plasma concentration profile of etizolam. The maximum concentration (Cmax) of etizolam was significantly reduced when TSS was co-administered at 20 times amount of human daily dosage. Since the double of human daily dose of TSS did not suppress the absorption of etizolam, TSS would not influence the pharmacokinetics of etizolam at the usual clinical dosage. Since both KSS and TSS did not influence the metabolism of etizolam, the result of in vitro experiment would not reflect to that of in vivo experiment or in clinic. The combination of etizolam with KSS or TSS at usual dosage would not cause drug interaction.

Effect of Neonatal Exposure of 17β-Estradiol Tamoxifen on Hepatic CYP3A Activity at Developmental Periods in Rats

We evaluated hepatic CYP3A activity during development in male and female rats and the effect of neonatal exposure of 17beta-estradiol and tamoxifen. In untreated and olive oil-treated (control) rats, hepatic CYP3A activities evaluated by erythromycin metabolism in vitro increased several-fold from age 2 to 9 weeks in males. In contrast, activity in females remained at a low and constant level from 2 to 15 weeks. Exposure of 17beta-estradiol to neonates at a dose of 10 micromol/kg daily for 3 days on day 1-3 (approximately) or 4-6 (approximately) after birth significantly increased hepatic CYP3A activity during the developmental period in both males and females, and a greater influence was observed in females exposed during days 4-6 (approximately). Pubertal exposure of 17beta-estradiol (7-weeks old, 10 micromol/kg daily for 3 days) also increased hepatic CYP3A activity, but only in females. Neonatal exposure to tamoxifen (10 micromol/kg daily for 3 days) showed no appreciable effect in either males or females. In conclusion, a marked sex-difference was observed in hepatic CYP3A activity, and exposure of 17beta-estradiol to neonates increased hepatic CYP3A activity during the developmental period, especially in female rats.

Analysis Methods and Recent Advances in Nonlinear Pharmacokinetics from In Vitro through In Loci to In Vivo

An attempt has been made to review the nonlinearities in the disposition in vitro, in situ, in loci and in vivo mainly from a theoretical point of view. Parallel Michaelis-Menten and linear (first-order) eliminations are often observed in the cellular uptake, metabolism and efflux of drugs. The well-stirred and parallel-tube models are mainly adopted under steady-state conditions in perfusion experiments, whereas distribution, tank-in-series and dispersion models are often used under nonsteady-state conditions with a pulse input. The analysis of the nonlinear local disposition in loci is reviewed from two points of view, namely an indirect method involving physiologically based pharmacokinetics (PBPK) and a direct (two or three samplings) method using live animals. The nonlinear global pharmacokinetics in vivo is reviewed with regard to absorption, elimination (metabolism and excretion) and distribution.

Differential induction of midazolam metabolism in the small intestine and liver by oral and intravenous dexamethasone pretreatment in rat

1. Midazolam is metabolized in the rat by CYP3A enzymes to 4-OH-midazolam (4-OH-MDZ) and 1'-OH-midazolam (1'-OH-MDZ). The induction of midazolam metabolism was studied in male Wistar rats treated with dexamethasone (50 mg kg(-1) day(-1)) during 4 days via the oral or intravenous routes. Microsomes were prepared from the liver and the proximal small intestine and in vitro metabolism of midazolam was determined. In addition, CYP3A1- and CYP3A2-like protein levels were measured by gel electrophoresis and immunoblotting. 2. The V(max)'s (mean SEM) for 4-OH-MDZ and 1'-OH-MDZ formation were much lower in intestinal (0.078 +/- 0.002 and 0.074 +/- 0.002 microM min(-1) mg(-1) protein, respectively) compared with hepatic microsomes prepared from the uninduced rat (0.870 +/- 0.007 and 0.310 +/- 0.020 microM min(-1) mg(-1) protein, respectively). Induction by oral or intravenous dexamethasone pretreatment led to significant increases in V(max) for 4-OH-MDZ and 1'-OH-MDZ by both intestinal and hepatic microsomes. Oral dexamethasone pretreatment via the oral route resulted in a more pronounced increase in V(max) compared with intravenous administration of the inducer. 3. CYP3A1 and CYP3A2 protein levels in liver microsomes were significantly increased following oral (3.7- and 3.2-fold, respectively) or intravenous (2.6- and 2.1-fold, respectively) pretreatment with dexamethasone. On the contrary, only oral dexamethasone pretreatment resulted in a significant change in intestinal CYP3A2-like protein (7.3-fold). A slight difference in the migration distance of the immunoreactive band for CYP3A2 was also observed for intestinal microsomes. 4. These results suggest that intestinal CYP3A enzymes in the rat differ from hepatic CYP3A1 and CYP3A2. They also demonstrate that systemic dexamethasone administration can induce intestinal microsome activity.

In vitro, pharmacokinetic, and pharmacodynamic interactions of ketoconazole and midazolam in the rat

Interactions of midazolam and ketoconazole were studied in vivo and in vitro in rats. Ketoconazole (total dose of 15 mg/kg intraperitoneally) reduced clearance of intravenous midazolam (5 mg/kg) from 79 to 55 ml/min/kg (p < 0.05) and clearance of intragastric midazolam (15 mg/kg) from 1051 to 237 ml/min/kg (p < 0.05), increasing absolute bioavailability from 0.11 to 0.36 (p < 0.05). Presystemic extraction occurred mainly across the liver as opposed to the gastrointestinal tract mucosa. Midazolam increased electroencephalographic (EEG) amplitude in the beta-frequency range. Ketoconazole shifted the concentration-EEG effect relationship rightward (increase in EC(50)), probably because ketoconazole is a neutral benzodiazepine receptor ligand. Ketoconazole competitively inhibited midazolam hydroxylation by rat liver and intestinal microsomes in vitro, with nanomolar K(i) values. At a total serum ketoconazole of 2 microg/ml (3.76 microM) in vivo, the predicted reduction in clearance of intragastric midazolam by ketoconazole (to 6% of control) was slightly greater than the observed reduction in vivo (to 15% of control). However, unbound serum ketoconazole greatly underpredicted the observed clearance reduction. Although the in vitro and in vivo characteristics of midazolam in rats incompletely parallel those in humans, the experimental model can be used to assess aspects of drug interactions having potential clinical importance.

The influence of L-glutamine on the depression of hepatic cytochrome P450 activity in male rats caused by total parenteral nutrition

Total parenteral nutrition (TPN) bypasses the gut leading to intestinal and hepatic dysfunction, including decreased hepatic cytochrome P450 (P450) activity. Glutamine prevents the TPN-associated changes in gut function and morphology. This study examined the effect of glutamine supplementation on hepatic P450 activities in male Sprague-Dawley rats receiving continuous TPN. Animals received continuous lipid-free TPN for 7 days with 0, 0.1, or 4.5% glutamine. Surgical controls were allowed free access to rat chow. The V(max)/K(m) ratios (intrinsic clearance) for the formation of 4-hydroxymidazolam (CYP3A) were 12.8, 14.6, and 27.7 microl/min/mg for TPN treatment with 0, 0.1%, or 4.5% glutamine, respectively, compared with a chow-fed control (37.1 microl/min/mg). The corresponding values for 1'-hydroxymidazolam formation (CYP3A) were 3.7, 6.1, 11.7, and 15.2 microl/min/mg, respectively. The addition of glutamine to TPN similarly affected the formation rates for 2beta- and 6beta-hydroxytestosterone (CYP3A), and these metabolite formation rates were highly correlated (r = 0.865; p < 0.001). The formation rates for 2alpha- and 16alpha-hydroxytestosterone (CYP2C) were also highly correlated (r = 0.892; p < 0.001). Parenteral glutamine modified the TPN-associated suppression of CYP3A and CYP2C activities in adult male rats receiving TPN.

Effects of Single and Repeated Treatment with Itraconazole on the Pharmacokinetics of Midazolam in Rats

To estimate the influence of repeated administration of drug metabolism inhibitors on the extent of drug interaction, we investigated the effects of single intravenous or repeated oral administration of itraconazole on the pharmacokinetics of midazolam in rats. In the single administration study, the plasma concentration of itraconazole was maintained by intravenous infusion, and midazolam was administered into the portal vein to investigate its kinetics. In the repeated administration study, the kinetics of midazolam was investigated after seven-day oral treatment with itraconazole. The in vitro metabolism of midazolam and the contents of cytochrome P450 were investigated using liver microsomes from the itraconazole-treated rats. The area under the curve (AUC) of midazolam was increased by 1.45- or 1.44-fold after single or repeated itraconazole treatment, respectively. Meanwhile, the liver concentrations of itraconazole after single administration and repeated administration were 38.2 and 20.3 (nmol/g), respectively. In vitro maximum metabolic reaction velocity (V(max)) and Michaelis-Menten constant (K(m)) of midazolam were increased from 2.26 to 3.84 (nmol/min/mg protein) and from 8.28 to 13.0 (microM) by single itraconazole treatment, respectively, and decreased from 2.23 to 1.17 (nmol/min/mg protein) and from 7.86 to 4.47 (microM) by repeated treatment, respectively. Correspondingly, the content of CYP3A2 was significantly altered by single or repeated itraconazole administration. The increases in AUC could be predicted only when the changes in V(max) and K(m) were taken into consideration, in addition to the hepatic unbound concentration of itraconazole. In conclusion, changes in enzyme kinetics should be taken into account to predict the extent of drug interaction after repeated treatment with inhibitors.