Role of temperature on protein and mRNA cytochrome P450 3A (CYP3A) isozymes expression and midazolam oxidation by cultured rat precision-cut liver slices

An in vitro comparative study with furyl-1,4-quinones endowed with anticancer activities

We describe the biological activity of some furylbenzo- and naphthoquinones (furylquinones) on hepatocarcinoma cells and healthy rat liver slices. The effects of furylquinones on cancer cells (Transplantable Liver Tumor, TLT) were assessed by measuring cell death (membrane cell lysis); intracellular contents of ATP and GSH and the activity of caspase-3 were used to determine the type of cell death. Most of the furylquinones tested (at a concentration of 25 μg/ml) induced caspase-independent cell death but compound 4 had no cytotoxic effects. The levels of both ATP and GSH were severely affected by quinones 1, 2 and 5, while no effect was observed with compound 4. These cytotoxic properties of quinones are associated with physico-chemical properties as shown by the LUMO energies and lipophilicity. Interestingly, no cytotoxic effects of furylquinones were detected when the in vitro model of precision-cut liver slices (PCLS) was used. Indeed, although CYP2E1 activity was slightly affected, ATP and GSH levels as well as protein synthesis were not modified by furylquinones. Paracetamol, a well-known hepatotoxicant, reduced these parameters by more than 80% compared to control conditions. Taking into account the considerable incidence of adverse-effects induced by most current anticancer drugs, the selective cytotoxicity shown by compounds 1, 2 and 5, in particular that of 1, represents a safety factor that encourages the further development of these quinones as new drugs in cancer therapy.

Male-specific induction of CYP3A2 in rats by zolmitriptan

We report here a novel observation that zolmitriptan induced CYP3A2 in male but not female rats. As part of our research programme to evaluate sex differences in the response to zolmitriptan, we studied the effects of zolmitriptan on CYP3A activity, protein and gene expression in male and female rats. Zolmitriptan was found to induce CYP3A activity, measured as testosterone and diazepam metabolism in-vitro, as well as midazolam pharmacokinetics in-vivo, in male but not female rats. The sex difference in response to zolmitriptan was further evaluated by analysis of CYP3A1/2 mRNA levels using real-time PCR, and CYP3A1/2 protein levels using immunoblotting. Zolmitriptan preferentially induced CYP3A2 in male but not female rats. No obvious effects on CYP3A1 were observed at any dose in either sex. Thus, we concluded that the observed sex-dependent induction of CYP3A by zolmitriptan was largely due to induction of CYP3A2 in male rats.

Acetaminophen induces xenobiotic-metabolizing enzymes in rat: Impact of a uranium chronic exposure

The extensive use of uranium in civilian and military applications increases the risk of human chronic exposure. Uranium is a slightly radioactive heavy metal with a predominantly chemical toxicity, especially in kidney but also in liver. Few studies have previously shown some effects of uranium on xenobiotic-metabolizing enzymes (XME) that might disturb drug pharmacokinetic. The aim of this study was to determine whether a chronic (9 months) non-nephrotoxic low dose exposure to depleted uranium (DU, 1mg/rat/day) could modify the liver XME, using a single non-hepatotoxic acetaminophen (APAP) treatment (50mg/kg). Most of XME analysed were induced by APAP treatment at the gene expression level but at the protein level only CYP3A2 was significantly increased 3h after APAP treatment in DU-exposed rats whereas it remained at a basal level in unexposed rats. In conclusion, these results showed that a chronic non-nephrotoxic DU exposure specially modify CYP3A2 after a single therapeutic APAP treatment.

Change in pharmacokinetics of model compounds with different elimination processes in rats during hypothermia

We compared the pharmacokinetics of model compounds with different elimination processes between hypothermic and normothermic rats, to obtain basic information concerning drug therapy during hypothermia. Male Wistar rats were anesthetized with sodium pentobarbital and kept at temperatures of 37 degrees C (normothermic group) by heat lamp, and 32 degrees C or 28 degrees C (hypothermic group) by external cooling. We chose phenolsulfonphthalein (PSP), indocyanine green (ICG) and fluorescein isothiocyanate (FITC)-dextran (FD-4, Mw 4400) as model compounds to determine changes in clearance pathways during hypothermia therapy. The plasma concentrations of PSP as biliary, urinary and metabolic elimination type were increased significantly in the hypothermic group (32 degrees C, 28 degrees C) after i.v. administration at a dose of 1 mg, compared to the normothermic group (37 degrees C). Each PSP clearance (bile, urine and metabolites) in the hypothermic group was decreased, suggesting an influence of hypothermia on the active elimination process. The decreasing tendency was marked at a temperature of 28 degrees C. Moreover, the plasma concentrations of ICG as the biliary excretion type after i.v. administration to the hypothermic rats at a dose of 1 mg were higher with more than 50% decrease in the total body clearance compared to normothermic rats. On the other hand, there was almost no difference in the i.v. pharmacokinetics of FD-4 as the urinary excretion type between 37 degrees C and 32 degrees C. However, renal clearance of FD-4 was significantly decreased at a temperature of 28 degrees C. Accordingly, the change in pharmacokinetics of a drug in the hypothermic group could differ with the elimination processes.

Effect of acetaminophen administration to rats chronically exposed to depleted uranium

The extensive use of depleted uranium (DU) in both civilian and military applications results in the increase of the number of human beings exposed to this compound. We previously found that DU chronic exposure induces the expression of CYP enzymes involved in the metabolism of xenobiotics (drugs). In order to evaluate the consequences of these changes on the metabolism of a drug, rats chronically exposed to DU (40mg/l) were treated by acetaminophen (APAP, 400mg/kg) at the end of the 9-month contamination. Acetaminophen is considered as a safe drug within the therapeutic range but in the case of overdose or in sensitive animals, hepatotoxicity and nephrotoxicity could occur. In the present work, plasma concentration of APAP was higher in the DU group compared to the non-contaminated group. In addition, administration of APAP to the DU-exposed rats increased plasma ALT (p<0.01) and AST (p<0.05) more rapidly than in the control group. Nevertheless, no histological alteration of the liver was observed but renal injury characterized by incomplete proximal tubular cell necrosis was higher for the DU-exposed rats. Moreover, in the kidney, CYP2E1 gene expression, an important CYP responsible for APAP bioactivation and toxicity, is increased (p<0.01) in the DU-exposed group compared to the control group. In the liver, CYP's activities were decreased between control and DU-exposed rats. These results could explain the worse elimination of APAP in the plasma and confirm our hypothesis of a modification of the drug metabolism following a DU chronic contamination.

In vivo effects of chronic contamination with depleted uranium on CYP3A and associated nuclear receptors PXR and CAR in the rat

In addition to its natural presence at high concentrations in some areas, uranium has several civilian and military applications that could cause contamination of human populations, mainly through chronic ingestion. Reports describe the accumulation of this radionuclide in some organs (including the bone, kidney, and liver) after acute or chronic contamination and show that it produces chemical or radiological toxicity or both. The literature is essentially devoid of information about uranium-related cellular and molecular effects on metabolic functions such as xenobiotic detoxification. The present study thus evaluated rats chronically exposed to depleted uranium in their drinking water (1mg/(ratday)) for 9 months. Our specific aim was to evaluate the hepatic and extrahepatic mRNA expression of CYP3A1/A2, CYP2B1, and CYP1A1 as well as of the nuclear receptors PXR, CAR, and RXR in these rats. CYP3A1 mRNA expression was significantly higher in the brain (200%), liver (300%), and kidneys (900%) of exposed rats compared with control rats, while CYP3A2 mRNA levels were higher in the lungs (300%) and liver (200%), and CYP2B1 mRNA expression in the kidneys (300%). Expression of CYP1A1 mRNA did not change significantly during this study. PXR mRNA levels increased in the brain (200%), liver (150%), and kidneys (200%). Uranium caused CAR mRNA expression in the lungs to double. Expression of RXR mRNA did not change significantly in the course of this study, nor did the hepatic activity of CYP2C, CYP3A, CYP2A, or CYP2B. Uranium probably affects the expression of drug-metabolizing CYP enzymes through the PXR and CAR nuclear receptors. These results suggest that the stimulating effect of uranium on these enzymes might lead to hepatic or extrahepatic toxicity (or both) during drug treatment and then affect the entire organism.

The use of precision-cut liver slices from male Wistar rats as a tool to study age related changes in CYP3A induction and in formation of paracetamol conjugates

Precision-cut liver slices (PCLS) offer a lot of advantages because all heterogeneity and cell-cell interactions within the original tissue matrix are maintained. This in vitro model was used to study the effect of ageing on certain aspects of drug metabolism and liver function in young (3 months), adult (9 months) and old (24 months) Wistar male rats. Protein synthesis, an important liver function, was not modified in young, adult and old rats, suggesting that ageing does not impair liver functionality but it affects some specific targets. Among them, a decrease in total P450 in liver microsomes and the loss of CYP3A23 inducibility in PCLS were clearly observed in old rats as compared to adult rats. Finally, the amount of total paracetamol conjugates was not modified between 9 and 24 months but in old rats, sulfoconjugation of paracetamol, its major route of elimination, was decreased.

Biphasic concentration change during continuous midazolam administration in brain-injured patients undergoing therapeutic moderate hypothermia

OBJECTIVE

To define the pharmacokinetics of midazolam, a probe for monitoring cytochrome (CYP) 3A 4 activity, during moderate hypothermic therapy.

DESIGN

A prospective randomized study.

SETTING

The intensive care unit of a medical university hospital.

PATIENTS AND INTERVENTIONS

In 15 consecutive brain-injured patients, midazolam concentrations were measured serially using high-performance liquid chromatography (HPLC). Under continuous administration of the agent, eight patients underwent moderate hypothermia of 32-34 degrees C (hypothermia group) and seven received normothermic therapy (normothermia group). A one-compartment model was selected for pharmacokinetic analyses for the continuous administration. Data represent +/-S.D. Statistical analysis was performed using ANOVA followed by Scheffe's F-test or the Mann-Whitney U-test ( P<0.05 ).

MEASUREMENT AND MAIN RESULTS

Serum midazolam concentrations in the hypothermia group increased linearly until the body temperature (BT) reached 35 degrees C without plateauing, even during continuous administration, after which the levels decreased remarkably when BT rose to 36 degrees C. However, the concentrations in the normothermia group remained on a plateau, which lasted until the end of the study. In the hypothermia group, elimination rate constant (k(e)) and clearance (CL) in the phase below 35 degrees C BT were much lesser than those above 35 degrees C BT, whereas distribution volume (V(d)) during the hypothermic phase was greater than that during the period above 35 degrees C BT.

CONCLUSION

This study has demonstrated for the first time that midazolum concentration changes biphasically even during continuous infusion in hypothermic therapy. The mechanisms for the change are unclear. Thus, further studies including confirmation of cytochrome 3A 4 activity are required, while monitoring for the development of undesirable effects from over-dosing is also needed.

Uranium induces TNFα secretion and MAPK activation in a rat alveolar macrophage cell line

Uranium is a toxic heavy metal found mainly in the nuclear industry, but it is also used in the manufacturing of military munitions. Inhalation studies using animal models have demonstrated that long-term exposure to uranium can lead to the development of neoplasia and fibrosis at the pulmonary level. Because it has been demonstrated that such effects are often associated with inflammation, the effect of uranium on TNFalpha, IL-1beta, and IL-10 synthesis by macrophages was assessed in vitro using the NR8383 cell line. Our results show that a significant TNFalpha secretion was induced by uranium but not by other metals such as gadolinium. However, IL-1beta and IL-10 secretions were unaffected by uranium treatment. TNFalpha secretion was detectable since 50 microM of uranium and was maximal after 24 h of exposure. Determination of the mechanisms of uranium-induced TNFalpha production was assessed through the evaluation of protein kinases activation. Our results showed that uranium treatment induced c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (p38 MAPK) activation. The use of pharmacological inhibitors suggested that both p38 MAPK and protein kinase C (PKC) participate in the signal transduction of uranium-induced TNFalpha secretion. The regulation of TNFalpha secretion involves TNFalpha mRNA accumulation at least through the stabilization of TNFalpha mRNA, but p38 MAPK did not appear to be involved in this stabilization. However, this observation does not exclude regulation of TNFalpha synthesis at the transcriptional level, which remains to be demonstrated. Taking together, these results suggest that uranium can induce TNFalpha secretion by macrophages, thus contributing to a better understanding of the pathological effect of uranium on the lung.

Genotype???phenotype associations for common CYP3A4 and CYP3A5 variants in the basal and induced metabolism of midazolam in European- and African-American men and women

CYP3A activity in adults varies between individuals and it has been suggested that this has a genetic basis, possibly related to variant alleles in CYP3A4 and CYP3A5 genes. Accordingly, genotype-phenotype associations were investigated under constitutive and induced conditions. Midazolam's systemic and oral clearances, and the erythromycin breath test (ERBT) were determined in 57 healthy subjects: 23 (11 men, 12 women) European- and 34 (14 men, 20 women) African-Americans. Studies were undertaken in the basal state and after 14-15 days pretreatment with rifampin. DNA was characterized for the common polymorphisms CYP3A4*1B, CYP3A5*3, CYP3A5*6 and CYP3A5*7 by direct sequencing, and for exon 21 and exon 26 variants of MDR1 by allele-specific, real-time polymerase chain reaction. In 95% of subjects, the basal systemic clearance of midazolam was unimodally distributed and variability was less than four-fold whereas, in 98% of the study population, oral clearance varied five-fold. No population or sex-related differences were apparent. Similar findings were observed with the ERBT. Rifampin pretreatment markedly increased the systemic (two-fold) and oral clearance (16-fold) of midazolam, and the ERBT (two-fold) but the variabilities were unchanged. No associations were noted between these phenotypic measures and any of the studied genotypes, except for oral clearance and its fold-increase after rifampin. These were related to the presence of CYP3A4*1B and the inversely linked CYP3A5*3 polymorphism, with the extent of induction being approximately 50% greater in CYP3A5*3 homozygotes compared to wild-type subjects. In most healthy subjects, variability in intestinal and hepatic CYP3A activity, using midazolam as an in-vivo probe, is modest and common polymorphisms in CYP3A4 and CYP3A5 do not appear to have important functional significance.

Effects of glucose on the pharmacokinetics of intravenous chlorzoxazone in rats with acute renal failure induced by uranyl nitrate

The effects of glucose on CYP2E1 expression in rats with acute renal failure induced by uranyl nitrate (U-ARF) have been reported. CYP2E1 was significantly induced (2.3-fold) in rats with U-ARF compared with that in control rats. In contrast, CYP2E1 expression was significantly decreased in rats with U-ARF supplied with glucose (dissolved in tap water to make 10%, w/v) in their drinking water for 5 days (U-ARFG) compared with that in rats with U-ARF. However, CYP2E1 in rats with U-ARFG was significantly greater than that in control rats. Chlorzoxazone (CZX) primarily undergoes hydroxylation, catalyzed mainly by CYP2E1, to form 6-hydroxychlorzoxazone (OH-CZX) rats. Hence, it could be expected that in rats with U-ARFG, formation of OH-CZX could significantly decrease and increase compared with those in rats with U-ARF and control rats, respectively. This expectation is proven by the following results of a study of intravenous administration of CZX at a dose 20 mg/kg to control rats and rats with U-ARF and U-ARFG. First, the total area under the plasma concentration-time curve from time zero to 8 h (AUC(0-8 h)) of OH-CZX in rats with U-ARFG (8730 microg x min/mL) was significantly greater than that in control rats (414 microg x min/mL) and significantly smaller than that in rats with U-ARF (11500 microg x min/mL). Second, the AUC(0-8 h, OH-CZX)/AUC(CZX) ratio in rats with U-ARFG (10.0) was significantly greater than that in control rats (0.252) and significantly smaller than that in rats with U-ARF (17.5). Finally, the in vitro intrinsic OH-CZX formation clearance (CL(int)) in rats with U-ARFG (27.9 mL/min/mg protein) was significantly slower than that in rats with U-ARF (36.7 mL/min/mg protein) and significantly faster than that in control rats (17.7 mL/min/mg protein).

Effects of acute renal failure on the pharmacokinetics of chlorzoxazone in rats

The purpose of this study is to report the changes of CYP2E1, CYP1A2, CYP2B1/2, CYP2C11, CYP3A23, and CYP3A2 expression and pharmacokinetics and tissue distribution of chlorzoxazone (CZX) and 6-hydroxychlorzoxazone (OH-CZX) in rats with acute renal failure induced by uranyl nitrate (U-ARF), and the role of CYP3A23 and CYP3A2 in the formation of OH-CZX in rats with U-ARF. In rats with U-ARF, CYP2C11 decreased to 20% of control, whereas CYP2E1 and CYP3A23 increased 2.3 and 4 times, respectively, compared with control. But expression of CYP1A2 and CYP2B1/2 was not changed by U-ARF. After i.v. administration of CZX at a dose of 20 mg/kg to rats with U-ARF, the areas under the plasma concentration-time curve from time 0 to time infinity (AUCs) of CZX and OH-CZX were significantly smaller and greater, respectively, than those in control rats. In rats with U-ARF, CZX was below the detection limit at 120 min in all rat tissues studied, whereas it was detected in all tissues of control rats at both 30 and 120 min. However, in control rats, OH-CZX was below the detection limit at both 30 and 120 min in all rat tissues except kidney, whereas it was detected in all tissues of rats with U-ARF at both 30 and 120 min. Based on results from supporting experiments with DDT and 2,2-bis(4-chlorophenyl)1,1-dichloroethylene treatment of rats, the contribution of CYP3A23 and CYP3A2 to the enhanced formation of OH-CZX in rats with U-ARF is likely to be negligible.

New hepatocyte in vitro systems for drug metabolism: metabolic capacity and recommendations for application in basic research and drug development, standard operation procedures

Primary hepatocytes represent a well-accepted in vitro cell culture system for studies of drug metabolism, enzyme induction, transplantation, viral hepatitis, and hepatocyte regeneration. Recently, a multicentric research program has been initiated to optimize and standardize new in vitro systems with hepatocytes. In this article, we discuss five of these in vitro systems: hepatocytes in suspension, perifusion culture systems, liver slices, co-culture systems of hepatocytes with intestinal bacteria, and 96-well plate bioreactors. From a technical point of view, freshly isolated or cryopreserved hepatocytes in suspension represent a readily available and easy-to-handle in vitro system that can be used to characterize the metabolism of test substances. Hepatocytes in suspension correctly predict interspecies differences in drug metabolism, which is demonstrated with pantoprazole and propafenone. A limitation of the hepatocyte suspensions is the length of the incubation period, which should not exceed 4hr. This incubation period is sufficiently long to determine the metabolic stability and to allow identification of the main metabolites of a test substance, but may be too short to allow generation of some minor, particularly phase II metabolites, that contribute less than 3% to total metabolism. To achieve longer incubation periods, hepatocyte culture systems or bioreactors are used. In this research program, two bioreactor systems have been optimized: the perifusion culture system and 96-well plate bioreactors. The perifusion culture system consists of collagen-coated slides allowing the continuous superfusion of a hepatocyte monolayer with culture medium as well as establishment of a constant atmosphere of 13% oxygen, 82% nitrogen, and 5% CO2. This system is stable for at least 2 weeks and guarantees a remarkable sensitivity to enzyme induction, even if weak inducers are tested. A particular advantage of this systemis that the same bioreactor can be perfused with different concentrations of a test substance in a sequential manner. The 96-well plate bioreactor runs 96 modules in parallel for pharmacokinetic testing under aerobic culture conditions. This system combines the advantages of a three-dimensional culture system in collagen gel, controlled oxygen supply, and constant culture medium conditions, with the possibility of high throughput and automatization. A newly developed co-culture system of hepatocytes with intestinal bacteria offers the possibility to study the metabolic interaction between liver and intestinal microflora. It consists of two chambers separated by a permeable polycarbonate membrane, where hepatocytes are cultured under aerobic and intestinal bacteria in anaerobic conditions. Test substances are added to the aerobic side to allow their initial metabolism by the hepatocytes, followed by the metabolism by intestinal bacteria at the anaerobic side. Precision-cut slices represent an alternative to isolated hepatocytes and have been used fo the investigation of hepatic metabolism, hepatotoxicity, and enzyme induction. A specific advantage of liver slices is the possibility to study toxic effects on hepatocytes that are mediated or modified by nonparenchymal cells (e.g., by cytokine release from Kupffer cells) because the physiological liver microarchitecture is maintained in cultured slices. For all these in vitro systems, a prevalidation has been performed using standard assays for phase I and II enzymes. Representative results with test substances and recommendations for application of these in vitro systems, as well as standard operation procedures are given.