Different expression of hepatic and renal cytochrome P450s between the streptozotocin-induced diabetic mouse and rat

Cytochrome P450 2E1 should not be neglected for acetaminophen-induced liver injury in metabolic diseases with altered insulin levels or glucose homeostasis

Acetaminophen (APAP) hepatotoxicity is mediated by N-acetyl-p-benzoquinone imine (NAPQI), a highly toxic metabolite generated by cytochrome P450 2E1 (CYP2E1). Thus, pathological conditions increasing CYP2E1 activity can favour APAP-induced liver injury, which is characterized by massive hepatocellular necrosis and secondary sterile inflammation. In a recent work, Wang et al. showed that APAP-induced hepatotoxicity was exacerbated in a murine model of type 1 diabetes induced by the administration of streptozotocin (STZ). Higher hepatotoxicity was in particular associated with a stronger proinflammatory response of the resident macrophages. Although the authors carried out numerous investigations, they did not study hepatic CYP2E1, nor discussed the possible role of this enzyme in the exacerbation of APAP hepatotoxicity. However, numerous investigations reported hepatic CYP2E1 induction in STZ-treated rodents, which could be secondary to insulinopenia and ketosis. This commentary also discusses the role of insulin resistance in CYP2E1 induction observed in obesity and nonalcoholic fatty liver disease. Investigators studying APAP-induced liver injury in the context of insulinopenia or hyperinsulinemia are thus encouraged to consider CYP2E1 as a significant player in the observed phenotypic changes.

Evaluation of hepatic CYP2D1 activity and hepatic clearance in type I and type II diabetic rat models, before and after treatment with insulin and metformin

INTRODUCTION

Conversion in the metabolism of drugs occurs in diabetes mellitus. Considering the importance of metabolic enzymes' activities on the efficacy and safety of medicines, the changes in liver enzymatic activity of CYP2D1 and its related hepatic clearance, by using Dextromethorphan as probe in the animal model of type I and type II diabetes, before and after treatment, was assessed in this study.

METHODS

Male Wistar rats were randomly divided into 6 groups. Seven days after induction of diabetes type I and type II, treatment groups were received insulin and metformin daily for 14 days, respectively. In day 21, rats were subjected to liver perfusion by Krebs-Henseleit buffer containing Dextromethorphan as CYP2D1 probe. Perfusate samples were analyzed by HPLC fluorescence method in order to evaluate any changes in CYP2D1 activity.

RESULTS

The average metabolic ratio of dextromethorphan and hepatic clearance were changed from 0.012 ± 0.004 and 6.3 ± 0.1 in the control group to 0.006 ± 0.0008 and 5.2 ± 0.2 in the untreated type I diabetic group, and 0.008 ± 0.003 and 5.0 ± 0.6 in the untreated type II diabetic rats. Finally, the mean metabolic ratio and hepatic clearance were changed to 0.008 ± 0.001 and 5.4 ± 0.1, and 0.013 ± 0.003 and 6.1 ± 0.4 in the treated groups with insulin and metformin, respectively.

CONCLUSION

In type I diabetic rats, corresponding treatment could slightly improve enzyme activity, whereas the hepatic clearance and enzyme activity reached to the normal level in type II group. Graphical abstract .

Dietary-Induced Obesity, Hepatic Cytochrome P450, and Lidocaine Metabolism: Comparative Effects of High-Fat Diets in Mice and Rats and Reversibility of Effects With Normalization of Diet

The effects of a high-fat diet on mRNA and protein of cytochrome P450 (CYP) enzymes in rats and mice and its impact on lidocaine deethylation to its main active metabolite, monoethylglycinexylidide (MEGX), in rats were investigated. The effect of a change in diet from high-fat to standard diet was also evaluated. Plasma biochemistry, mRNA, protein expression for selected CYP, and the activity of lidocaine deethylation were determined. The high-fat diet curtailed the activity and the expression of the majority of CYPs (CYP1A2, CYP3A1, CYP2C11, CYP2C12, and CYP2D1), mRNA levels (Cyp1a2 and Cyp3a2), and MEGX maximal formation rate (Vmax). Mice showed complementary results in their protein expressions of cyp3a and 1a2. Switching the diet back to standard chow in rats for 4 weeks reverted the expression levels of mRNA and protein back to normal levels as well as the maximum formation rates of MEGX. Female and male rodents showed similar patterns in CYP expression and lidocaine metabolism in response to the diets, although MEGX formation was faster in male rats. In conclusion, diet-induced obesity caused general decreases in CYP isoforms not only in rats but also in mice. The effects were shown to be reversible in rats by normalizing the diet.

A Pilot Study towards the Impact of Type 2 Diabetes on the Expression and Activities of Drug Metabolizing Enzymes and Transporters in Human Duodenum

To characterize effects of type 2 diabetes (T2D) on mRNA expression levels for 10 Cytochromes P450 (CYP450s), two carboxylesterases, and three drug transporters (ABCB1, ABCG2, SLCO2B1) in human duodenal biopsies. To compare drug metabolizing enzyme activities of four CYP450 isoenzymes in duodenal biopsies from patients with or without T2D. mRNA levels were quantified (RT-qPCR) in human duodenal biopsies obtained from patients with (n = 20) or without (n = 16) T2D undergoing a scheduled gastro-intestinal endoscopy. CYP450 activities were determined following incubation of biopsy homogenates with probe substrates for CYP2B6 (bupropion), CYP2C9 (tolbutamide), CYP2J2 (ebastine), and CYP3A4/5 (midazolam). Covariables related to inflammation, T2D, demographic, and genetics were investigated. T2D had no major effects on mRNA levels of all enzymes and transporters assessed. Formation rates of metabolites (pmoles mg protein⁻¹ min⁻¹) determined by LC-MS/MS for CYP2C9 (0.48 ± 0.26 vs. 0.41 ± 0.12), CYP2J2 (2.16 ± 1.70 vs. 1.69 ± 0.93), and CYP3A (5.25 ± 3.72 vs. 5.02 ± 4.76) were not different between biopsies obtained from individuals with or without T2D (p > 0.05). No CYP2B6 specific activity was measured. TNF-α levels were higher in T2D patients but did not correlate with any changes in mRNA expression levels for drug metabolizing enzymes or transporters in the duodenum. T2D did not modulate expression or activity of tested drug metabolizing enzymes and transporters in the human duodenum. Previously reported changes in drug oral clearances in patients with T2D could be due to a tissue-specific disease modulation occurring in the liver and/or in other parts of the intestines.

Novel differences in renal gene expression in a diet-induced obesity model

Obesity is a significant risk factor for both chronic kidney disease and end-stage renal disease. To better understand disease development, we sought to identify novel genes differentially expressed early in disease progression. We first confirmed that mice fed a high-fat (HF) diet exhibit early signs of renal injury including hyperfiltration. We then performed RNA-Seq using renal cortex RNA from C57BL6/J male mice fed either HF or control (Ctrl) diet. We identified 1,134 genes differentially expressed in the cortex on HF vs. Ctrl, of which 31 genes were selected for follow-up analysis. This included the 9 most upregulated, the 11 most downregulated, and 11 genes of interest (primarily sensory receptors and G proteins). Quantitative (q)RT-PCR for these 31 genes was performed on additional male renal cortex and medulla samples, and 11 genes (including all 9 upregulated genes) were selected for further study based on qRT-PCR. We then examined expression of these 11 genes in Ctrl and HF male heart and liver samples, which demonstrated that these changes are relatively specific to the renal cortex. These 11 genes were also examined in female renal cortex, where we found that the expression changes seen in males on a HF diet are not replicated in females, even when the females are started on the diet sooner to match weight gain of the males. In sum, these data demonstrate that in a HF-diet model of early disease, novel transcriptional changes occur that are both sex specific and specific to the renal cortex.

Tissue Specific Modulation of cyp2c and cyp3a mRNA Levels and Activities by Diet-Induced Obesity in Mice: The Impact of Type 2 Diabetes on Drug Metabolizing Enzymes in Liver and Extra-Hepatic Tissues

Various diseases such as type 2 diabetes (T2D) may alter drug clearance. The objective of this study was to evaluate the effects of T2D on CYP450 expressions and activities using high-fat diet (HFD) as a model of obesity-dependent diabetes in C57BL6 mice. The cyp450 mRNA expression levels for 15 different isoforms were determined in the liver and extra-hepatic tissues (kidneys, lungs and heart) of HFD-treated animals (n = 45). Modulation of cyp450 metabolic activities by HFD was assessed using eight known substrates for specific human ortholog CYP450 isoforms: in vitro incubations were conducted with liver and extra-hepatic microsomes. Expression levels of cyp3a11 and cyp3a25 mRNA were decreased in the liver (>2-14-fold) and kidneys (>2-fold) of HFD groups which correlated with a significant reduction in midazolam metabolism (by 21- and 5-fold in hepatic and kidney microsomes, respectively, p < 0.001). HFD was associated with decreased activities of cyp2b and cyp2c subfamilies in all organs tested except in the kidneys (for tolbutamide). Other cyp450 hepatic activities were minimally or not affected by HFD. Taken together, our data suggest that substrate-dependent and tissue-dependent modulation of cyp450 metabolic capacities by early phases of T2D are observed, which could modulate drug disposition and pharmacological effects in various tissues.

Glucose-dependent regulation of pregnane X receptor is modulated by AMP-activated protein kinase

Pregnane X receptor (PXR) is a xenobiotic receptor that regulates the detoxification and clearance of drugs and foreign compounds from the liver. There has been mounting evidence of crosstalk between the drug metabolism pathway and the energy metabolism pathway, but little is known about this cross-regulation. To further delineate the energy metabolism and drug metabolism crosstalk in this study, we exposed HepG2 cells to varying glucose concentrations. We observed that PXR activity was induced under high-glucose conditions. This finding is consistent with previous clinical reports of increased drug clearance in patients with untreated diabetes. We demonstrated that AMP-activated protein kinase (AMPK) modulates PXR transcriptional activity and that pharmacologically manipulated AMPK activation exhibits an inverse relation to PXR activity. Activation of AMPK was shown to downregulate PXR activity and, consistent with that, potentiate the response of cells to the drug. Taken together, our results delineate a hitherto unreported axis of regulation that involves the energy status of the cell, PXR regulation, and drug sensitivity.

Inhibition of CYP4A reduces hepatic endoplasmic reticulum stress and features of diabetes in mice

BACKGROUND & AIMS

Endoplasmic reticulum (ER) stress is implicated in the development of type 2 diabetes mellitus. ER stress activates the unfolded protein response pathway, which contributes to apoptosis and insulin resistance. We investigated the roles of cytochrome P450 4A (CYP4A) in the regulation of hepatic ER stress, insulin resistance, and the development of diabetes in mice.

METHODS

We used mass spectrometry to compare levels of CYP450 proteins in livers from C57BL/6J and C57BL/KsJ-db/db (db/db) mice; findings were confirmed by immunoblot and real-time PCR analyses. To create a model of diet-induced diabetes, C57BL/6J mice were placed on high-fat diets. Mice were given intraperitoneal injections of an inhibitor (HET0016) or an inducer (clofibrate) of CYP4A, or tail injections of small hairpin RNAs against CYP4A messenger RNA; liver tissues were collected and analyzed for ER stress, insulin resistance, and apoptosis. The effect of HET0016 and CYP4A knockdown also were analyzed in HepG2 cells.

RESULTS

Levels of the CYP4A isoforms were highly up-regulated in livers of db/db mice compared with C57BL/6J mice. Inhibition of CYP4A in db/db and mice on high-fat diets reduced features of diabetes such as insulin hypersecretion, hepatic steatosis, and increased glucose tolerance. CYP4A inhibition reduced levels of ER stress, insulin resistance, and apoptosis in the livers of diabetic mice; it also restored hepatic functions. Inversely, induction of CYP4A accelerated ER stress, insulin resistance, and apoptosis in livers of db/db mice.

CONCLUSIONS

CYP4A proteins are up-regulated in livers of mice with genetically induced and diet-induced diabetes. Inhibition of CYP4A in mice reduces hepatic ER stress, apoptosis, insulin resistance, and steatosis. Strategies to reduce levels or activity of CYP4A proteins in liver might be developed for treatment of patients with type 2 diabetes.

Modulation of CYP3a expression and activity in mice models of type 1 and type 2 diabetes

CYP3A4, the most abundant cytochrome P450 enzyme in the human liver and small intestine, is responsible for the metabolism of about 50% of all marketed drugs. Numerous pathophysiological factors, such as diabetes and obesity, were shown to affect CYP3A activity. Evidences suggest that drug disposition is altered in type 1 (T1D) and type 2 diabetes (T2D). The objective was to evaluate the effect of T1D and T2D on hepatic and intestinal CYP3a drug-metabolizing activity/expression in mice. Hepatic and intestinal microsomes were prepared from streptozotocin-induced T1D, db/db T2D and control mice. Domperidone was selected as a probe substrate for CYP3a and formation of five of its metabolites was evaluated using high performance liquid chromatography. Hepatic CYP3a protein and mRNA expression were assessed by Western blot and reverse-transcription quantitative polymerase chain reaction respectively. Hepatic microsomal CYP3a activity was significantly increased in both T1D and T2D groups versus control group. Intestinal CYP3a activity was also significantly increased in both T1D and T2D groups. Moreover, significant increases of both hepatic CYP3a mRNAs and protein expression were observed in both T1D and T2D groups versus control group. Additional experiments with testosterone further validated the increased activity of CYP3a under the effect of both T1D and T2D. Although differences exist in the pathophysiological insults associated with T1D and T2D, our results suggest that these two distinct diseases may have the same modulating effect on the regulation of CYP3a, ultimately leading to variability in drug response, ranging from lack of effect to life-threatening toxicity.

Improvement of superoxide dismutase and catalase in streptozotocin-nicotinamide-induced type 2-diabetes in mice by berberine and glibenclamide

Abstract Context: Diabetes mellitus (DM) type 2 is a chronic disease characterized by hyperglycemia and insulin resistance. Oxidative stress participates in development and progression of DM, in which changes of superoxide dismutase (SOD) and catalase (CAT) were noted in DM mice. Berberine has been widely used as an alternative medicine and proved to be effective for the treatment of DM and dyslipidemia. Objective: Impacts of berberine on transcriptional regulation of SOD and CAT and their enzyme activities, including the level of malondialdehyde (MDA) formation, were examined in the DM type 2-induced mice to clarify its antioxidation potential, compared with a common hypoglycemic drug, glibenclamide. Materials and methods: Noninsulin-dependent diabetes was induced in mice by a single intraperitoneal streptozotocin-nicotinamide injection. Diabetic mice were treated daily with glibenclamide (10 mg/kg/d) and/or berberine (100 mg/kg/d) for 2 weeks. The fasting blood glucose and the MDA levels in the mouse liver, brain and kidneys were monitored using Glucometer® (Accu-Check® Advantage II Performa kits, Roche Diagnostics, Germany) and thiobarbituric acid substance assay, respectively. The expression of SOD and CAT mRNA were determined in the mouse liver and the activities of SOD and CAT enzymes were determined in mouse liver, brain and kidneys, respectively. Results: Berberine exhibited similar hypoglycemic potential as glibenclamide to lower area under the curve of the fasting blood glucose. In DM type 2 mice, berberine increased the hepatic CuZn-SOD mRNA expression and the kidney SOD and CAT activities to normal levels. Moreover, DM-induced lipid peroxidation by increasing of MDA levels in both the liver and brain and lipid peroxidation status was restored by berberine. Conclusion: Berberine possessed hypoglycemic properties and strong potential to improve the oxidant-antioxidant balance, though the combination treatment of berberine and glibenclamide did not show additional benefit over the treatment with berberine alone.

Drug disposition in pathophysiological conditions

Expression and activity of several key drug metabolizing enzymes (DMEs) and transporters are altered in various pathophysiological conditions, leading to altered drug metabolism and disposition. This can have profound impact on the pharmacotherapy of widely used clinically relevant medications in terms of safety and efficacy by causing inter-individual variabilities in drug responses. This review article highlights altered drug disposition in inflammation and infectious diseases, and commonly encountered disorders such as cancer, obesity/diabetes, fatty liver diseases, cardiovascular diseases and rheumatoid arthritis. Many of the clinically relevant drugs have a narrow therapeutic index. Thus any changes in the disposition of these drugs may lead to reduced efficacy and increased toxicity. The implications of changes in DMEs and transporters on the pharmacokinetics/pharmacodynamics of clinically-relevant medications are also discussed. Inflammation-mediated release of pro-inflammatory cytokines and activation of toll-like receptors (TLRs) are known to play a major role in down-regulation of DMEs and transporters. Although the mechanism by which this occurs is unclear, several studies have shown that inflammation-associated cell-signaling pathway and its interaction with basal transcription factors and nuclear receptors in regulation of DMEs and transporters play a significant role in altered drug metabolism. Altered regulation of DMEs and transporters in a multitude of disease states will contribute towards future development of powerful in vitro and in vivo tools in predicting the drug response and opt for better drug design and development. The goal is to facilitate a better understanding of the mechanistic details underlying the regulation of DMEs and transporters in pathophysiological conditions.

Alteration of hepatic glutathione peroxidase and superoxide dismutase expression in streptozotocin-induced diabetic mice by berberine

CONTEXT

Diabetes mellitus (DM), a chronic disease, has been increasing and subsequently devastates the quality of life and economic status of the patients. Oxidative stress participates in development and progression of diabetes, in which levels of glutathione peroxidase (GPx) and superoxide dismutase (SOD) were changed in diabetic mice. Berberine has been widely used as an alternative medicine and proved to be effective for treatment of DM and dyslipidemia.

OBJECTIVE

Impacts of berberine on regulation of GPx and SOD messenger RNAs (mRNAs), and glutathione (GSH) content were examined in diabetic mice to clarify its antioxidative stress potential.

MATERIALS AND METHODS

Noninsulin-dependent diabetes was induced in mice by a single intraperitoneal streptozotocin injection. Diabetic mice were daily treated with metformin (100 mg/kg/d) or berberine (200 mg/kg/d) for 2 weeks. The fasting blood glucose and GSH content were monitored. GPx and SOD mRNA expression were semi-quantified by reverse transcription-polymerase chain reaction.

RESULTS

Berberine showed the same hypoglycemic potential as metformin, a hypoglycemic drug. Interestingly, berberine did not change levels of GPx, copper-zinc SOD (CuZn-SOD), and manganese SOD (Mn-SOD) mRNA in the normal mice but significantly recovered these levels in the diabetic mice to nearly the same levels as the normal. The GSH contents, including total GSH and reduced/oxidized GSH contents, were restored to the normal level by berberine, corresponded to GPx levels.

DISCUSSION AND CONCLUSION

Berberine conveyed antioxidative effect via down- and up-regulation of GPx and CuZn-SOD expression, respectively. Therefore, use of berberine as a hypoglycemic compound for alternative treatment of DM could bring extra-beneficent consequence according to its antioxidative stress.

Effects of brown rice and white rice on expression of xenobiotic metabolism genes in type 2 diabetic rats

Xenobiotics constantly influence biological systems through several means of interaction. These interactions are disturbed in type 2 diabetes, with implications for disease outcome. We aimed to study the implications of such disturbances on type 2 diabetes and rice consumption, the results of which could affect management of the disease in developing countries. In a type 2 diabetic rat model induced through a combination of high fat diet and low dose streptozotocin injection, up-regulation of xenobiotic metabolism genes in the diabetic untreated group was observed. Xenobiotic metabolism genes were upregulated more in the white rice (WR) group than the diabetic untreated group while the brown rice (BR) group showed significantly lower expression values, though not as effective as metformin, which gave values closer to the normal non-diabetic group. The fold changes in expression in the WR group compared to the BR group for Cyp2D4, Cyp3A1, Cyp4A1, Cyp2B1, Cyp2E1, Cyp2C11, UGT2B1, ALDH1A1 and Cyp2C6 were 2.6, 2, 1.5, 4, 2.8, 1.5, 1.8, 3 and 5, respectively. Our results suggest that WR may upregulate these genes in type 2 diabetes more than BR, potentially causing faster drug metabolism, less drug efficacy and more toxicity. These results may have profound implications for rice eating populations, constituting half the world’s population.

Modulations of cytochrome P450 expression in diabetic mice by berberine

Berberine, an isoquinoline alkaloid isolated from medicinal plants such as Berberis aristata, Coptis chinesis, Coptis japonica, Coscinium fenestatun, and Hydrastis Canadensis, is widely used in Asian countries for the treatment of diabetes, hypertension, and hypercholesterolemia. Interaction between berberine and the cytochrome P450 enzymes (CYPs) has been extensively reported, but there are only a few reports of this interaction in the diabetic state. In this study, the effect of berberine on the mRNA of the CYPs in primary mouse hepatocytes and in streptozotocin (STZ)-induced diabetic mice was investigated. In primary mouse hepatocytes, berberine suppressed the induction of Cyp1a1, Cyp1a2, Cyp2e1, Cyp3a11, Cyp4a10, and Cyp4a14 mRNA expression by their prototypical inducers in a concentration-dependent fashion. However, berberine treatment alone increased the expression of Cyp2b9 and Cyp2b10 mRNA. In vivo, berberine showed the same hypoglycemic activity as metformin, an established hypoglycemic drug. The hepatic mRNA levels of Cyp1a1, Cyp2b9, Cyp2b10, Cyp3a11, Cyp4a10, and Cyp4a14 were increased in STZ-induced diabetic mice. Interestingly, berberine itself suppressed the expression of Cyp2e1, an adverse hepatic event-associated enzyme, while the expression of Cyp3a11, Cyp4a10, and Cyp4a14 were restored to normal levels by berberine. In conclusion, berberine has the potential to modify the expression of CYPs by either suppression or enhancement of CYPs' levels. Consumption of berberine as an anti-hyperglycemic compound by diabetic patients might provide an extra benefit due to its potential to restore the expression of Cyp2e1, Cyp3a, and Cyp4a to normal levels. However, an herb-drug interaction might be of concern since any berberine-containing product would definitely cause pronounced interactions based on CYP3A4 inhibition.

Network analysis of hepatic genes responded to high-fat diet in C57BL/6J mice: nutrigenomics data mining from recent research findings

Obesity and its associated complications, including diabetes, dyslipidemia, atherosclerosis, and some cancers, have been a global health problem with a rapid increase of the obese population. In this study, we selected 31 obesity candidate genes in the liver of high-fat-induced obese C57BL/6J mice through investigation of literature search and analyzed functional protein-protein interaction of the genes using the STRING database. Most of the obesity candidate genes were closely connected through lipid metabolism, and in particular acyl-coenzyme A oxidase 1 appeared to be a core obesity gene. Overall, genes involved in fatty acid beta-oxidation, fatty acid synthesis, and gluconeogenesis were up-regulated, and genes involved in sterol biosynthesis, insulin signaling, and oxidative stress defense system were down-regulated with a high-fat diet. Future identification of core obesity genes and their functional targets is expected to provide a new way to prevent obesity by phytochemicals or functional foods on the basis of food and nutritional genomics.

Pregnane X receptor and constitutive androstane receptor at the crossroads of drug metabolism and energy metabolism

The pregnane X receptor (PXR) and the constitutive androstane receptor (CAR) are two closely related and liver-enriched nuclear hormone receptors originally defined as xenobiotic receptors. PXR and CAR regulate the transcription of drug-metabolizing enzymes and transporters, which are essential in protecting our bodies from the accumulation of harmful chemicals. An increasing body of evidence suggests that PXR and CAR also have an endobiotic function that impacts energy homeostasis through the regulation of glucose and lipids metabolism. Of note and in contrast, disruptions of energy homeostasis, such as those observed in obesity and diabetes, also have a major impact on drug metabolism. This review will focus on recent progress in our understanding of the integral role of PXR and CAR in drug metabolism and energy homeostasis.

Differences in the pharmacokinetics of Cyp3a substrates in TSOD and streptozotocin-induced diabetic mice

The pharmacokinetics of drugs can change in diabetes mellitus and even among diabetics. They may differ between type I diabetes (T1DM) and type 2 diabetes (T2DM). As triazolam was administered orally to Tsumura, Suzuki, obese, diabetes (TSOD) mice and streptozotocin (STZ) mice, clearance per body (CL/F) in TSOD mice did not differ compared with Tsumura, Suzuki, non-obesity (TSNO) mice. In STZ mice, CL/F was greater than in control mice. Small intestinal cytochrome P450 (Cyp) 3a expression in TSOD mice was significantly lower than in TSNO mice. No significant difference existed in small intestinal Cyp3a expression between STZ mice and control mice. In insulin-treated mice, small intestinal Cyp3a expression was significantly lower than in control mice. These results suggested that the differences in changes in small intestinal Cyp3a expression between T1DM and T2DM may be due to differences in plasma insulin concentrations. This may be a factor in the difference in the drug pharmacokinetics between T2DM and T1DM patients.

Pharmacokinetics of drugs in rats with diabetes mellitus induced by alloxan or streptozocin: comparison with those in patients with type I diabetes mellitus

Objectives

In rats with diabetes mellitus induced by alloxan (DMIA) or streptozocin (DMIS), changes in the cytochrome P450 (CYP) isozymes in the liver, lung, kidney, intestine, brain, and testis have been reported based on Western blot analysis, Northern blot analysis, and various enzyme activities. Changes in phase II enzyme activities have been reported also. Hence, in this review, changes in the pharmacokinetics of drugs that were mainly conjugated and metabolized via CYPs or phase II isozymes in rats with DMIA or DMIS, as reported in various literature, have been explained. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized in the kidney, and that were excreted mainly via the kidney or bile in DMIA or DMIS rats were reviewed also. For drugs mainly metabolized via hepatic CYP isozymes, the changes in the total area under the plasma concentration–time curve from time zero to time infinity (AUC) of metabolites, AUCmetabolite/AUCparent drug ratios, or the time-averaged nonrenal and total body clearances (CLNR and CL, respectively) of parent drugs as reported in the literature have been compared.

Key findings

After intravenous administration of drugs that were mainly metabolized via hepatic CYP isozymes, their hepatic clearances were found to be dependent on the in-vitro hepatic intrinsic clearance (CLint) for the disappearance of the parent drug (or in the formation of the metabolite), the free fractions of the drugs in the plasma, or the hepatic blood flow rate depending on their hepatic extraction ratios. The changes in the pharmacokinetics of drugs that were mainly conjugated and mainly metabolized via the kidney in DMIA or DMIS rats were dependent on the drugs. However, the biliary or renal CL values of drugs that were mainly excreted via the kidney or bile in DMIA or DMIS rats were faster.

Summary

Pharmacokinetic studies of drugs in patients with type I diabetes mellitus were scarce. Moreover, similar and different results for drug pharmacokinetics were obtained between diabetic rats and patients with type I diabetes mellitus. Thus, present experimental rat data should be extrapolated carefully in humans.

Constitutive androstane receptor mediates the induction of drug metabolism in mouse models of type 1 diabetes

Untreated type 1 diabetes increases hepatic drug metabolism in both human patients and rodent models. We used knockout mice to test the role of the nuclear xenobiotic receptors constitutive androstane receptor (CAR) and pregnane and xenobiotic receptor (PXR) in this process. Streptozotocin-induced diabetes resulted in increased expression of drug metabolizing cytochrome P450s and also increased the clearance of the cytochrome P450 substrate zoxazolamine. This induction was completely absent in Car(-/-) mice, but was not affected by the loss of PXR. Among the many effects of diabetes on the liver, we identified bile acid elevation and activated adenosine monophosphate-activated protein kinase as potential CAR-activating stimuli. Expression of the CAR coactivator peroxisome proliferator-activated receptor gamma coactivator (PGC)-1alpha was also increased in mouse models of type 1 diabetes.

CONCLUSION

The CAR-dependent induction of drug metabolism in newly diagnosed or poorly managed type 1 diabetes has the potential for significant impact on the efficacy or toxicity of therapeutic agents.

Pharmacokinetics of oltipraz in diabetic rats with liver cirrhosis

BACKGROUND AND PURPOSE

The incidence of diabetes mellitus is increased in patients with liver cirrhosis. Oltipraz is currently in trials to treat patients with liver fibrosis and cirrhosis induced by chronic hepatitis types B and C and is primarily metabolized via hepatic cytochrome P450 isozymes CYP1A1/2, 2B1/2, 2C11, 2D1 and 3A1/2 in rats. We have studied the influence of diabetes mellitus on pharmacokinetics of oltipraz and on expression of hepatic, CYP1A, 2B1/2, 2C11, 2D and 3A in rats with experimental liver cirrhosis.

EXPERIMENTAL APPROACH

Oltipraz was given intravenously (10 mg x kg(-1)) or orally (30 mg x kg(-1)) to rats with liver cirrhosis induced by N-dimethylnitrosamine (LC rats) or with diabetes, induced by streptozotocin (DM rats) or to rats with both liver cirrhosis and diabetes (LCD rats) and to control rats, and pharmacokinetic variables measured. Protein expression of hepatic CYP1A, 2B1/2, 2C11, 2D and 3A was measured using Western blot analysis.

KEY RESULTS

After i.v. or p.o. administration of oltipraz to LC and DM rats, the AUC was significantly greater and smaller, respectively, than that in control rats. In LCD rats, the AUC was that of LC and DM rats (partially restored towards control rats). Compared with control rats, the protein expression of hepatic CYP1A increased, that of CYP2C11 and 3A decreased, but that of CYP2B1/2 and 2D was not altered in LCD rats.

CONCLUSIONS AND IMPLICATIONS

In rats with diabetes and liver cirrhosis, the AUC of oltipraz was partially restored towards that of control rats.

Dietary phloridzin reduces blood glucose levels and reverses Sglt1 expression in the small intestine in streptozotocin-induced diabetic mice

Phloridzin is a dihydrochalcone typically contained in apples. In this study, it is shown that a diet containing 0.5% phloridzin significantly reduced the blood glucose levels in streptozotocin (STZ)-induced diabetic mice after 14 days. We detected phloridzin in the plasma of STZ-induced diabetic mice fed the phloridzin diet for 14 days, although its concentration was much lower than that of the phloridzin metabolites. A quantitative RT-PCR analysis showed a reversal of STZ induction of the sodium/glucose cotransporter gene Sglt1 and the drug-metabolizing enzyme genes Cyp2b10 and Ephx1 in the small intestine of mice fed a 0.5% phloridzin diet. These mice also showed a reversal of the STZ-mediated renal induction of the glucose-regulated facilitated glucose transporter gene Glut2. Dietary phloridzin improved the abnormal elevations in blood glucose levels and the overexpression of Sglt1, Cyp2b10, and Ephx1 in the small intestine of STZ-induced diabetic mice.

Activation of CAR and PXR by Dietary, Environmental and Occupational Chemicals Alters Drug Metabolism, Intermediary Metabolism, and Cell Proliferation

The constitutive androstane receptor (CAR) and the pregnane × receptor (PXR) are activated by a variety of endogenous and exogenous ligands, such as steroid hormones, bile acids, pharmaceuticals, and environmental, dietary, and occupational chemicals. In turn, they induce phase I-III detoxification enzymes and transporters that help eliminate these chemicals. Because many of the chemicals that activate CAR and PXR are environmentally-relevant (dietary and anthropogenic), studies need to address whether these chemicals or mixtures of these chemicals may increase the susceptibility to adverse drug interactions. In addition, CAR and PXR are involved in hepatic proliferation, intermediary metabolism, and protection from cholestasis. Therefore, activation of CAR and PXR may have a wide variety of implications for personalized medicine through physiological effects on metabolism and cell proliferation; some beneficial and others adverse. Identifying the chemicals that activate these promiscuous nuclear receptors and understanding how these chemicals may act in concert will help us predict adverse drug reactions (ADRs), predict cholestasis and steatosis, and regulate intermediary metabolism. This review summarizes the available data on CAR and PXR, including the environmental chemicals that activate these receptors, the genes they control, and the physiological processes that are perturbed or depend on CAR and PXR action. This knowledge contributes to a foundation that will be necessary to discern interindividual differences in the downstream biological pathways regulated by these key nuclear receptors.

Diabetes and hypertriglyceridemia modify the mode of acetaminophen-induced hepatotoxicity and nephrotoxicity in rats and mice

Certain disease conditions can modify drug-induced toxicities, which, in turn, may cause a medication-related health crisis. Therefore, preclinical investigations into the alterations in drug-induced toxicities using appropriate disease animal models are very important. This paper reviews the reported data related to the effects of diabetes and hypertriglyceridemia, common lifestyle-related diseases in a modern society, on acetaminophen (APAP)-induced hepatotoxicity and nephrotoxicity in rats and mice. It has generally been reported that diabetes protects rats and mice from APAP-induced hepatotoxicity and there are several reports that help to speculate on the effects of diabetes on APAP-induced nephrotoxicity. In fructose-induced hypertriglyceridemic rats, hepatotoxicity of APAP becomes apparently less severe, whereas nephrotoxicity of APAP becomes significantly more severe. The mechanisms of alteration of APAP-induced hepatorenal toxicity under diabetic and hypertriglyceridemic conditions are also discussed in this paper.

The nuclear receptor CAR (NR1I3) regulates serum triglyceride levels under conditions of metabolic stress

The nuclear receptor constitutive androstane receptor (CAR) (NR1I3) regulates hepatic genes involved in xenobiotic detoxification as well as genes involved in energy homeostasis. We provide data that extend the role of CAR to regulation of serum triglyceride levels under conditions of metabolic/nutritional stress. The typically high serum triglyceride levels of ob/ob mice were completely normalized when crossed onto a Car(-/-) (mice deficient for the Car gene) genetic background. Moreover, increases in serum triglycerides observed after a high-fat diet (HFD) regime were not observed in Car(-/-) animals. Conversely, pharmacological induction of CAR activity using the selective mouse CAR agonist TCPOBOP during HFD feeding resulted in a CAR-dependent increase in serum triglyceride levels. A major regulator of hepatic fatty oxidation is the nuclear receptor PPARalpha (NR1C1). The expression of peroxisome proliferator-activated receptor alpha (PPARalpha) target genes was inversely related to the activity of CAR. Consistent with these observations, Car(-/-) animals exhibited increased hepatic fatty acid oxidation. Treatment of mice with 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) significantly decreased expression of PPARalpha mRNA as well as Cyp4a14, CPT1alpha, and cytosolic Acyl-CoA thioesterase (CTE) in the liver. These data have implications in disease therapy such as for diabetes and nonalcoholic steatohepatitis (NASH).

Phenobarbital Confers its Diverse Effects by Activating the Orphan Nuclear Receptor Car

In the early 1960s, phenobarbital (PB) was shown to induce hepatic drug metabolism and the induction was implicated in the molecular mechanism of drug tolerance development. Since then, it has become evident that PB not only induces drug metabolism, but also triggers pleiotropic effects on liver function, such as cell growth and communication, proliferation of the endoplasmic reticulum, tumor promotion, glucose metabolism, steroid/thyroid hormone metabolism, and bile acid synthesis. Upon activation by PB and numerous PB-type inducers, the nuclear receptor CAR mediates those pleiotropic actions by regulating various hepatic genes, utilizing multiple regulatory mechanisms.

Forkhead box A2-mediated regulation of female-predominant expression of the mouse Cyp2b9 gene

The regulation mechanism of female-predominant expression of the mouse Cyp2b9 gene was investigated in vivo and in vitro. Luciferase reporter assay revealed that the -234/-194 region of the Cyp2b9 gene may be responsible for sexually dimorphic expression. There is a predicted forkhead box A2 (FoxA2) (hepatic nuclear factor 3beta)-binding site in this region. Chromatin immunoprecipitation assay indicated that the binding protein to the site was FoxA2 in 5-week-old female mice, whereas this protein was found in both sexes at age 3 weeks, in accordance with our previous observation on the developmental expression of this gene. Mutation of the predicted FoxA2 site in the reporter construct containing the -234/+18 fragment led to complete elimination of luciferase activity, but deletion of the -234/-194 region resulted in considerable transcriptional activity, suggesting that by mutating the FoxA2-binding site a potent suppressor might bind to eliminate activity, whereas by deleting this region it could not. Sexually dimorphic secretion of growth hormone is involved in female-predominant expression of the gene, and the -234/-194 region was also responsible for suppressing the expression by male-type secretion.

Mechanisms and outcomes of drug- and toxicant-induced liver toxicity in diabetes

Increase dincidences of hepatotoxicity have been observed in diabetic patients receiving drug therapies. Neither the mechanisms nor the predisposing factors underlying hepatotoxicity in diabetics are clearly understood. Animal studies designed to examine the mechanisms of diabetes-modulated hepatotoxicity have traditionally focused only on bioactivation/detoxification of drugs and toxicants. It is becoming clear that once injury is initiated, additional events determine the final outcome of liver injury. Foremost among them are two leading mechanisms: first, biochemical mechanisms that lead to progression or regression of injury; and second, whether or not timely and adequate liver tissue repair occurs to mitigate injury and restore liver function. The liver has a remarkable ability to repair and restore its structure and function after physical or chemical-induced damage. The dynamic interaction between biotransformation-based liver injury and compensatory tissue repair plays a pivotal role in determining the ultimate outcome of hepatotoxicity initiated by drugs or toxicants. In this review, mechanisms underlying altered hepatotoxicity in diabetes with emphasis on both altered bioactivation and liver tissue repair are discussed. Animal models of both marked sensitivity (diabetic rats) and equally marked protection (diabetic mice) from drug-induced hepatotoxicity are described. These examples represent a remarkable species difference. Availability of the rodent diabetic models offers a unique opportunity to uncover mechanisms of clinical interest in averting human diabetic sensitivity to drug-induced hepatotoxicities. While the rat diabetic models appear to be suitable, the diabetic mouse models might not be suitable in preclinical testing for potential hepatotoxic effects of drugs or toxicants, because regardless of type 1 or type2 diabetes, mice are resistant to acute drug-or toxicant-induced toxicities.

Importance of PPAR alpha for the effects of growth hormone on hepatic lipid and lipoprotein metabolism

OBJECTIVE

Growth hormone (GH) enhances lipolysis in adipose tissue, thereby increasing the flux of fatty acids to other tissues. Moreover, GH increases hepatic triglyceride synthesis and secretion in rats and decreases the action of peroxisome proliferator-activated receptor (PPAR)alpha. PPARalpha is activated by fatty acids and regulates hepatic lipid metabolism in rodents. The aim of this study was to investigate the importance of PPARalpha for the effects of GH on hepatic gene expression and lipoprotein metabolism.

DESIGN

Bovine GH was given as a continuous infusion (5mg/kg/day) for 7 days to PPARalpha-null and wild-type (wt) mice. Plasma and liver lipids and hepatic gene expression were measured. In separate experiments, hepatic triglyceride secretion was measured.

RESULTS

GH treatment decreased hepatic triglyceride content and increased hepatic triglyceride secretion rate and serum cholesterol levels. Furthermore, GH increased hepatic acylCoA:diacylglycerol acyltransferase (DGAT)2 mRNA levels, but decreased the hepatic mRNA expression of acyl-CoA oxidase, medium-chain acyl-CoA dehydrogenase and PPARgamma1. All these GH effects were independent of PPARalpha. However, the effect of GH on Cyp4a10, PPARgamma2, and DGAT1 was different between the genotypes. GH treatment decreased Cyp4a10 mRNA expression in wt mice, but increased the expression in PPARalpha-null mice. In contrast, GH decreased the expression of DGAT1 and PPARgamma2 in PPARalpha-null mice, but not in wt mice.

CONCLUSIONS

Most of the effects of GH on lipid and lipoprotein metabolism were independent of PPARalpha. However, GH had unique effects on Cyp4a10, DGAT1, and PPARgamma2 gene expression in PPARalpha-null mice showing cross-talk between GH and PPARalpha signalling in vivo.

Gene expression profiles of drug-metabolizing enzymes and transporters with an overexpression of hepatocyte growth factor

BACKGROUND

It is important to elucidate the precise mechanism of drug metabolism during hepatic regeneration. Although cytochromes P450 (CYPs) are well known to be down-regulated in growth-stimulated cells, the overall gene expression profile of drug metabolizing enzymes are still not fully understood during hepatic regeneration. In this study, we investigated the gene expression profiles of such enzymes with an overexpression of hepatocyte growth factor (HGF).

METHODS

Gene expression profiles were obtained using the Affymetrix MOE430A GeneChip oligonucleotide microarray by comparing HGF transgenic mice and wild-type mice.

RESULTS

HGF produced a general decrease in mice with the expression of CYP isoforms such as Cyp1a2, Cyp2b10, Cyp2c, Cyp2d9, Cyp3a11, Cyp4a10, and Cyp7a1. Some isoforms of alcohol dehydrogenase, aldehyde dehydrogenase, and carboxylesterase also decreased. In the phase II enzymes, some isoforms of glutathione S-transferase and UDP-glucuronosyl transferase showed a reduced expression, although the sulfotransferase did not. In phase III transporters, some organic anion transporter and organic cation transporters were down-regulated. Among the nuclear receptors that are known to regulate the drug-metabolizing enzymes, small heterodimer partner and constitutive androstane receptor were down-regulated with an HGF overexpression. The protein level and enzymatic activity of Cyp2c decreased with an HGF overexpression. We furthermore investigated the inducibility of Cyp2b10 with xenobiotic inducers. Although the basal expression of Cyp2b10 was repressed, the inducibility was not abolished with the HGF overexpression.

CONCLUSIONS

HGF down-regulated not only CYPs but also some drug-metabolizing enzymes, transporters, and nuclear receptors. We thus have to take in our mind the low basal expression of drug metabolizing enzymes, when treating patients with a regenerative liver state.

In the regulation of cytochrome P450 genes, phenobarbital targets LKB1 for necessary activation of AMP-activated protein kinase

Transcriptional activation of cytochrome P450 (CYP) genes and various drug metabolizing enzymes by the prototypical inducer phenobarbital (PB) and many other drugs and chemicals is an adaptive response of the organism to exposure to xenobiotics. The response to PB is mediated by the nuclear receptor constitutive androstane receptor (CAR), whereas the chicken xenobiotic receptor (CXR) has been characterized as the PB mediator in chicken hepatocytes. Our previous results suggested an involvement of AMP-activated protein kinase (AMPK) in the molecular mechanism of PB induction. Here, we show that the mechanism of AMPK activation is related to an effect of PB-type inducers on mitochondrial function with consequent formation of reactive oxygen species (ROS) and phosphorylation of AMPK by the upstream kinase LKB1. Gain- and loss-of-function experiments demonstrate that LKB1-activated AMPK is necessary in the mechanism of drug induction and that this is an evolutionary conserved pathway for detoxification of exogenous and endogenous chemicals. The activation of LKB1 adds a proximal target to the so far elusive sequence of events by which PB and other drugs induce the transcription of multiple genes.

Effects of diabetes on rabbit kidney and lung CYP2E1 and CYP2B4 expression and drug metabolism and potentiation of carcinogenic activity of N-nitrosodimethylamine in kidney and lung

There are limited number of studies regarding the influence of diabetes on the regulation of cytochrome P450s and associated drug metabolizing enzyme activities especially in extrahepatic tissues such as kidney. However, there is almost no such study in lung. Alloxan-induced diabetes did not change CYP2B4 expression as measured with immunoblot analysis and associated enzyme, benzphetamine N-demethylase, activity in rabbit kidney and lung. Induction of cytochrome P4502E1 by diabetes was identified by immunochemical detection on Western blots in the lung and kidney microsomes of rabbits. In parallel to CYP2E1 induction, aniline 4-hydroxylase and p-nitrophenol hydroxylase activities were markedly increased in diabetic rabbit lung and kidney. CYP2B4 and CYP2E1 dependent drug metabolism did not show any tissue variation in diabetic rabbit. These findings are in contrast to those of rats, mice and hamster. The results of the present work, in combination with those of the previous work [Arinç, E., Arslan, S., Adali, O., 2005. Differential effects of diabetes on CYP2E1 and CYP2B4 proteins and associated drug metabolizing enzyme activities in rabbit liver. Arch. Toxicol. 79, 427-433], indicate the existence of species-dependent response of CYP-dependent drug metabolizing enzymes to diabetes. A procarcinogen and food contaminant, N-nitrosodimethylamine (NDMA), is converted to its carcinogenic form after it is activated with NDMA N-demethylase. In the current study, a statistically significant increase of liver, kidney and lung NDMA N-demethylase activity associated with CYP2E1 was shown in diabetic rabbit. Thus, it is expected that, the risk of nitrosamine induced carcinogenesis will be greater in liver, kidney and lung of the diabetic subjects.

Protective effect of type 2 diabetes on acetaminophen-induced hepatotoxicity in male Swiss-Webster mice

Type 2 diabetic (DB) mice exposed to CCl(4) (LD(50) = 1.25 ml/kg), acetaminophen (LD(80) = 600 mg/kg; APAP), and bromobenzene (LD(80) = 0.5 ml/kg) i.p. yielded 30, 20, and 20% mortality, respectively, indicating hepatotoxic resistance. Male Swiss-Webster mice were made diabetic by feeding high fat and administrating streptozotocin (120 mg/kg i.p.) on day 60. On day 71, time-course studies after APAP (600 mg/kg) treatment revealed identical initial liver injury in non-DB and DB mice, which progressed only in non-DB mice, resulting in 80% mortality. The hypothesis that decreased APAP bioactivation, altered toxicokinetics, and/or increased tissue repair are the underlying mechanisms was investigated. High-performance liquid chromatography analysis revealed no difference in plasma and urinary APAP or detoxification of APAP via glucuronidation between DB and non-DB mice. Hepatic CYP2E1 protein and activity, glutathione, and [(14)C]APAP covalent binding did not differ between DB and non-DB mice, suggesting that lower bioactivation-based injury is not the mechanism of decreased hepatotoxicity in DB mice. Diabetes increased cells in S phase by 8-fold in normally quiescent liver of these mice. Immunohistochemistry revealed overexpression of calpastatin in the newly dividing/divided cells, explaining inhibition of hydrolytic enzyme calpain in perinecrotic areas and lower progression of APAP-initiated injury in the DB mice. Antimitotic intervention of diabetes-associated cell division with colchicine before APAP administration resulted in 70% mortality in APAP-treated colchicine-intervened DB mice. These studies suggest that advancement of cells in the cell division cycle and higher tissue repair protect DB mice by preventing progression of APAP-initiated liver injury that normally leads to mortality.

Effect of insulin-mimetic vanadyl sulfate on cytochrome P450 2E1-dependent p-nitrophenol hydroxylation in the liver microsomes of streptozotocin-induced type 1 diabetic rats

CYP2E1 is known to be induced in streptozotocin (STZ)-treated diabetic rats (STZ rats), and its induction is improved by insulin. We have examined the age-dependent changes of CYP2E1 in the liver microsomes of type 1 diabetic STZ rats, the effects of VOSO4 on the contents of total P450 and CYP2E1, and the activities of CYP2E1 in terms of p-nitrophenol hydroxylation. The contents of P450 and CYP2E1 and CYP2E1 activity were enhanced with the development of diabetes. When the hyperglycemia of STZ rats was improved by daily intraperitoneal injections of VOSO4 for 10 days at the doses of 7 mg/kg body weight for 5 days, 5 mg/kg for the following 3 days, and then 2.5 mg/kg for 2 days, the P450 and CYP2E1 levels and CYP2E1 activity were lowered than those in the untreated STZ rats. To understand the mechanism underlying CYP2E1-dependent hydroxylation activity, the production of reactive oxygen species was examined in the NADPH-liver microsomal systems by ESR spin-trapping. Singlet oxygen (1O2) was detected in all microsomal systems, while superoxide anion radical(*O2-) and hydroxyl radical (*OH) were not. On the basis of these results, we conclude that (1) CYP2E1 level and activity are enhanced in the diabetic state, however, they are improved by VOSO4 treatment, and (2) 1O2 is generated during CYP2E1-dependent substrate oxygenation.

Differential effects of diabetes on CYP2E1 and CYP2B4 proteins and associated drug metabolizing enzyme activities in rabbit liver

The effects of diabetes on cytochrome P450 (CYP)-dependent drug metabolizing enzymes are yet to be clarified. The most widely used animals in these studies have been rats, and information on the effects of diabetes on rabbit liver drug metabolizing enzymes have been unavailable until now. In this study, for the first time, a significant induction of liver CYP2E1 is demonstrated via immunoblot analysis in alloxan-induced rabbits. The CYP2E1 content of diabetic microsomes was highly correlated with the activities of liver aniline 4-hydroxylase (r=0.82, p<0.05), and p-nitrophenol hydroxylase (r=0.86, p<0.01), and diabetes increased the activities of the enzymes associated with CYP2E1. The activities of aniline 4-hydroxylase and p-nitrophenol hydroxylase were significantly increased by 1.7 and 1.8-fold, respectively compared to those of control rabbits. In marked contrast, diabetes had no effect on the protein levels of CYP2B4 as determined by immunoblotting and on benzphetamine N-demethylase activity, which is known to be specifically metabolized by CYP2B4 in rabbit liver. The present study demonstrates that diabetes increases the activities of CYP2E1 and associated enzymes but does not change the activity levels of CYP2B4 and associated enzymes in diabetic rabbits. These findings are in contrast to those of mice, hamsters and rats, and that suggest the presence of species-dependent responses of CYP-dependent drug metabolizing enzymes to diabetes.

Effects of renal diseases on the regulation and expression of renal and hepatic drug-metabolizing enzymes: a review

1. The activity of drug-metabolizing enzymes (DMEs) in extrahepatic organs is highest in the kidneys. Generally, the kidneys contain most, if not all, of the DMEs found in the liver. Surprisingly, some of these DMEs show higher activity in the kidneys than in the liver. 2. Most of the renal DMEs are localized in the cortex of the kidneys, especially in the proximal tubules. DMEs are also found in the distal tubules and collecting ducts. 3. Renal diseases such as acute and chronic renal failure and renal cell carcinoma alter the regulation of both hepatic and extrahepatic phase I and II DMEs. Changes in the expression of these DMEs seem to be tissue and species specific. 4. Generally, there is significant down-regulation of most of the phase I and a few of phase II DMEs at the protein, mRNA and activity levels. Unfortunately, the mechanisms leading to the alteration in DMEs in renal diseases remain unclear, although many theories have been made. 5. The presence of some circulating factors such as cytokines, nitric oxide, parathyroid hormones and increased intracellular calcium play a role in the regulation of DMEs in renal diseases.

Diabetes inhibits the DOI-induced head-twitch response in mice

RATIONALE

Clinical studies suggest that the prevalence of psychiatric disorders is higher in diabetic patients than in the general population. It has been reported that central serotonin(2A) (5-HT(2A)) receptors may be involved in the pathogenesis and treatment of psychiatric disorders.

OBJECTIVES

We examined the effect of streptozotocin-induced diabetes on the function of central 5-HT(2A) receptors in mice.

METHODS

Male ICR mice were rendered diabetic by an injection of streptozotocin (200 mg/kg, i.v.). The experiments were conducted 2 weeks after the injection of streptozotocin. To evaluate the central 5-HT(2A) receptor function, head-twitch responses were measured for 15 min immediately after the treatment with (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI) (0.1-1 mg/kg, s.c.), a selective 5-HT(2) receptor agonist.

RESULTS

Significantly fewer head-twitch responses were induced by DOI in diabetic mice than in non-diabetic mice. The number and affinity of 5-HT(2A) receptors in the mouse frontal cortex were not affected by diabetes. The corticosterone response to DOI (1 mg/kg and 3 mg/kg, s.c.) was not different between non-diabetic and diabetic mice, although the baseline of plasma corticosterone levels was significantly higher in diabetic than in non-diabetic mice.

CONCLUSIONS

Our results suggest that a neuronal network that causes head-twitch responses by triggering by the activation of 5-HT(2A) receptors may be altered by type-1 diabetes in mice.

Nuclear receptors CAR and PXR cross talk with FOXO1 to regulate genes that encode drug-metabolizing and gluconeogenic enzymes

The nuclear receptors CAR and PXR activate hepatic genes in response to therapeutic drugs and xenobiotics, leading to the induction of drug-metabolizing enzymes, such as cytochrome P450. Insulin inhibits the ability of FOXO1 to express genes encoding gluconeogenic enzymes. Induction by drugs is known to be decreased by insulin, whereas gluconeogenic activity is often repressed by treatment with certain drugs, such as phenobarbital (PB). Performing cell-based transfection assays with drug-responsive and insulin-responsive enhancers, glutathione S-transferase pull down, RNA interference (RNAi), and mouse primary hepatocytes, we examined the molecular mechanism by which nuclear receptors and FOXO1 could coordinately regulate both enzyme pathways. FOXO1 was found to be a coactivator to CAR- and PXR-mediated transcription. In contrast, CAR and PXR, acting as corepressors, downregulated FOXO1-mediated transcription in the presence of their activators, such as 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) and pregnenolone 16alpha-carbonitrile, respectively. A constitutively active mutant of the insulin-responsive protein kinase Akt, but not the kinase-negative mutant, effectively blocked FOXO1 activity in cell-based assays. Thus, insulin could repress the receptors by activating the Akt-FOXO1 signal, whereas drugs could interfere with FOXO1-mediated transcription by activating CAR and/or PXR. Treatment with TCPOBOP or PB decreased the levels of phosphoenolpyruvate carboxykinase 1 mRNA in mice but not in Car(-/-) mice. We conclude that FOXO1 and the nuclear receptors reciprocally coregulate their target genes, modulating both drug metabolism and gluconeogenesis.

20-HETE and circulating insulin in essential hypertension with obesity

Analogous to observations in Dahl salt-sensitive (SS) rats, we have shown that 20-hydroxyeicosatetraenoic acid (20-HETE) is involved in the pathogenesis of SS essential hypertension. A strong negative correlation between urine 20-HETE and body mass index (BMI) remains unexplained. We measured BP, urine sodium (UNaV), and 20-HETE in obese hypertensive subjects during a 24-hour salt load (160 mmol NaCl diet+2 L intravenous saline). We classified them into insulin-resistant (IR) (n=14) and insulin-sensitive (IS) (n=12), with the average insulin sensitivity index (SI=22.5x[fasting glucose x insulin](-1)) of 3 days (cutoff for IR, SI <0.161 mL x L/microU x mmol). IR were older (50+/-1 versus 44+/-2, P<0.03), more obese (BMI 38.2+/-1.4 versus 32.0+/-1.5 kg/m2, P<0.01), and had higher insulin (39.2+/-2.3 versus 22.0+/-1.1 microU/mL, P<0.0001) and lower SI (0.084+/-0.009 versus 0.222+/-0.013, P<0.0001) than IS. Blood pressure, UNaV, and sodium balance did not differ between groups. SI correlated negatively with age (r=-0.39, P<0.05) and BMI (r=-0.53, P<0.01). Urine 20-HETE was less in IR than in IS when normalized by serum insulin (0.91+/-0.25 versus 2.24+/-0.46 microg. 24 hours(-1)/microU x mL(-1), P<0.02), but not if uncorrected. Urinary 20-HETE excretion correlated negatively with insulin (r=-0.40, P<0.04), whereas the relationship between 20-HETE and SI was not statistically significant. Our data suggest that increased circulating insulin, not the state of insulin resistance, suppresses urine 20-HETE excretion in obese hypertensive subjects. Findings in experimental models suggest that an inhibitory effect of insulin on cytochrome P4504A, rather than effects of insulin on membrane-bound arachidonic acid or on its release to the cytosol, may explain our observation.

Hepatic expression of cytochrome P450s in hepatocyte nuclear factor 1-alpha (HNF1alpha)-deficient mice

Hepatocyte nuclear factor 1 alpha (HNF1alpha) is a liver enriched homeodomain-containing transcription factor that has been shown to transactivate the promoters of several cytochrome P450 (CYP) genes, including CYP2E1, CYP1A2, CYP7A1, and CYP27, in vitro. In humans, mutations in HNF1alpha are linked to the occurrence of maturity onset diabetes of the young type 3, an autosomal dominant form of non-insulin-dependent diabetes mellitus in which afflicted subjects generally develop hyperglycemia before 25 years of age. Mice lacking HNF1alpha also develop similar phenotypes reminiscent of non-insulin-dependent diabetes mellitus. To investigate a potential role for HNF1alpha in the regulation of CYPs in vivo, the expression of major CYP genes from each family was examined in the livers of mice lacking HNF1alpha. Analysis of CYP gene expression revealed marked reductions in expression of Cyp1a2, Cyp2c29 and Cyp2e1, and a moderate reduction of Cyp3a11. In contrast Cyp2a5, Cyp2b10 and Cyp2d9 expression were elevated. There are also significant changes in the expression of genes encoding CYPs involved in fatty acid and bile acid metabolism characterized by a reduction in the expression of Cyp7b1, and Cyp27 as well as elevations in Cyp4a1/3, Cyp7a1, Cyp8b1, and Cyp39a1 expression. These results point to a critical role for HNF1alpha in the regulation of CYPs in vivo and suggest that this transcription factor may have an important influence on drug metabolism as well as lipid and bile acid homeostasis in maturity onset diabetes of the young type 3 diabetics.

Regulation of P450 genes by liver-enriched transcription factors and nuclear receptors

Cytochrome P450s (P450s) constitute a superfamily of heme-proteins that play an important role in the activation of chemical carcinogens, detoxification of numerous xenobiotics as well as in the oxidative metabolism of endogenous compounds such as steroids, fatty acids, prostaglandins, and leukotrienes. In addition, some P450s have important roles in physiological processes, such as steroidogenesis and the maintenance of bile acid and cholesterol homeostasis. Given their importance, the molecular mechanisms of P450 gene regulation have been intensely studied. Direct interactions between transcription factors, including nuclear receptors, with the promoters of P450 genes represent one of the primary means by which the expression of these genes is controlled. In this review, several liver-enriched transcription factors that play a role in the tissue-specific, developmental, and temporal regulation of P450s are discussed. In addition, the nuclear receptors that play a role in the fine control of cholesterol and bile acid homeostasis, in part, through their modulation of specific P450s, are discussed.

Novel roles of liver X receptors exposed by gene expression profiling in liver and adipose tissue

Liver X receptor (LXR) alpha and LXRbeta are nuclear oxysterol receptors whose biological function has so far been elucidated only with respect to cholesterol and lipid metabolism. To expose novel biological roles for LXRs, we performed genome-wide gene expression profiling studies in liver and white and brown adipose tissue from wild-type (LXRalpha(+/+)beta(+/+)) and knockout mice (LXRalpha(-/-)beta(-/-)) treated with a synthetic LXR agonist. By an adapted statistical analysis, we detected 319 genes significantly regulated by LXR agonist treatment in wild-type but not in knockout mice, fulfilling most stringent criteria with an overall confidence of 94%. Down-regulation of essential enzymes of gluconeogenesis in liver could point to possible beneficial effects of LXR agonists in diabetes mellitus. LXR agonist treatment also altered expression of genes involved in steroid hormone synthesis and growth hormone receptor signaling, emphasizing a potential impact on endocrine function. Notably, LXR agonist treatment up-regulated CYP4A10 and CYP4A14 together with cytochrome P450 reductase, indicating a possible enhancement of microsomal lipid peroxidation. In conclusion, these gene expression profiling data identify novel areas of regulation by LXRs and provide a highly valuable basis for further research on the biological functions of these nuclear receptors and the pharmacological characteristics of their ligands.

Effect of hyperinsulinemia and type 2 diabetes-like hyperglycemia on expression of hepatic cytochrome p450 and glutathione s-transferase isoforms in a New Zealand obese-derived mouse backcross population

In subgroups of a New Zealand obese mouse-derived backcross population with defined aberrations of glucose homeostasis, a comprehensive study of the hepatic expression of cytochrome P450 and glutathione S-transferase was performed. Three patterns of alterations in response to insulin resistance (normoglycemia/hyperinsulinemia) or diabetes (hyperglycemia/hypoinsulinemia) were observed: mRNA levels of Cyp2b9, Cyp3a16, Cyp4a14, and Gstt2 as assessed by Northern- and dot-blot analysis were increased markedly in liver from diabetic mice with no or only a slight increase in insulin resistant mice. Western-blot analysis detected the corresponding changes of the CYP2B and CYP4A proteins. In contrast, expression of Cyp2c22, Cyp2c29, and Cyp2c40 was reduced in diabetic, but normal in insulin resistant mice. These alterations were correlated with changes in serum free fatty acid levels and, therefore, seem to be mediated by the peroxisome proliferator activated receptor-alpha. Furthermore, expression of Cyp1a2, Cyp7b1, Gstm3, and Gstm6 was reduced in both diabetic and insulin resistant mice. Because this third pattern was not correlated with the alterations of serum free fatty acid levels, it seems to reflect an early alteration in the course of the disease, and may be related to the progression of the syndrome from insulin resistance to the type 2-like diabetes.