Hepatic CYP3A Expression is Attenuated in Obese Mice Fed a High-Fat Diet

Potential impact of underlying diseases influencing ADME in nonclinical safety assessment

Nonclinical studies involve in vitro, in silico, and in vivo experiments to assess the toxicokinetics, toxicology, and safety pharmacology of drugs according to regulatory requirements by a national or international authority. In this review, we summarize the potential effects of various underlying diseases governing the absorption, distribution, metabolism, and excretion (ADME) of drugs to consider the use of animal models of diseases in nonclinical trials. Obesity models showed alterations in hepatic metabolizing enzymes, transporters, and renal pathophysiology, which increase the risk of drug-induced toxicity. Diabetes models displayed changes in hepatic metabolizing enzymes, transporters, and glomerular filtration rates (GFR), leading to variability in drug responses and susceptibility to toxicity. Animal models of advanced age exhibited impairment of drug metabolism and kidney function, thereby reducing the drug-metabolizing capacity and clearance. Along with changes in hepatic metabolic enzymes, animal models of metabolic syndrome-related hypertension showed renal dysfunction, resulting in a reduced GFR and urinary excretion of drugs. Taken together, underlying diseases can induce dysfunction of organs involved in the ADME of drugs, ultimately affecting toxicity. Therefore, the use of animal models of representative underlying diseases in nonclinical toxicity studies can be considered to improve the predictability of drug side effects before clinical trials.

A Prediction Model for Tacrolimus Daily Dose in Kidney Transplant Recipients With Machine Learning and Deep Learning Techniques

Tacrolimus is a major immunosuppressor against post-transplant rejection in kidney transplant recipients. However, the narrow therapeutic index of tacrolimus and considerable variability among individuals are challenges for therapeutic outcomes. The aim of this study was to compare different machine learning and deep learning algorithms and establish individualized dose prediction models by using the best performing algorithm. Therefore, among the 10 commonly used algorithms we compared, the TabNet algorithm outperformed other algorithms with the highest R² (0.824), the lowest prediction error [mean absolute error (MAE) 0.468, mean square error (MSE) 0.558, and root mean square error (RMSE) 0.745], and good performance of overestimated (5.29%) or underestimated dose percentage (8.52%). In the final prediction model, the last tacrolimus daily dose, the last tacrolimus therapeutic drug monitoring value, time after transplantation, hematocrit, serum creatinine, aspartate aminotransferase, weight, CYP3A5, body mass index, and uric acid were the most influential variables on tacrolimus daily dose. Our study provides a reference for the application of deep learning technique in tacrolimus dose estimation, and the TabNet model with desirable predictive performance is expected to be expanded and applied in future clinical practice.

Effect of laparoscopic sleeve gastrectomy on drug pharmacokinetics

INTRODUCTION

Given its feasibility and efficacy, laparoscopic sleeve gastrectomy (LSG) has become a widely accepted bariatric surgery for patients with clinically diagnosed severe obesity. LSG induces anatomical changes and subsequent weight loss which may affect drug pharmacokinetics (PK) and consequently impact dosing regimens. This review aims to examine the effect of LSG on drug PK and identify relevant gastrointestinal physiological alterations.

AREAS COVERED

PubMed, Embase, Scopus, and the Cochrane Library were searched for articles related to drug PK and LSG from inception to July 2021. Moreover, literature concerning postoperative physiological conditions in the gastrointestinal tract, such as gastric pH, gastric emptying, and small bowel transit time, etc., which may affect the PK profile of drug products was also reviewed.

EXPERT OPINION

Although LSG is classified as having restrictive property without malabsorptive bypass, postoperative changes in gastrointestinal physiology and subsequent weight loss may also lead to increased, decreased or unaltered drug exposure levels. General monitoring on drug efficacy or safety using biomarkers is proposed. In addition, therapeutic drug monitoring for those drugs when it is applicable and available is recommended to ensure efficient drug dosing and avoid adverse effects. Further research into many individual drugs are warranted.

Effects of Lingonberry (Vaccinium vitis-idaea L.) Supplementation on Hepatic Gene Expression in High-Fat Diet Fed Mice

The prevalence of nonalcoholic fatty liver disease (NAFLD) is growing worldwide in association with Western-style diet and increasing obesity. Lingonberry (Vaccinium vitis-idaea L.) is rich in polyphenols and has been shown to attenuate adverse metabolic changes in obese liver. This paper investigated the effects of lingonberry supplementation on hepatic gene expression in high-fat diet induced obesity in a mouse model. C57BL/6N male mice were fed for six weeks with either a high-fat (HF) or low-fat (LF) diet (46% and 10% energy from fat, respectively) or HF diet supplemented with air-dried lingonberry powder (HF + LGB). HF diet induced a major phenotypic change in the liver, predominantly affecting genes involved in inflammation and in glucose and lipid metabolism. Lingonberry supplementation prevented the effect of HF diet on an array of genes (in total on 263 genes) associated particularly with lipid or glucose metabolic process (such as Mogat1, Plin4, Igfbp2), inflammatory/immune response or cell migration (such as Lcn2, Saa1, Saa2, Cxcl14, Gcp1, S100a10) and cell cycle regulation (such as Cdkn1a, Tubb2a, Tubb6). The present results suggest that lingonberry supplementation prevents HF diet-induced adverse changes in the liver that are known to predispose the development of NAFLD and its comorbidities. The findings encourage carrying out human intervention trials to confirm the results, with the aim of recommending the use of lingonberries as a part of healthy diet against obesity and its hepatic and metabolic comorbidities.

Impact of obese levels on the hepatic expression of nuclear receptors and drug-metabolizing enzymes in adult and offspring mice

The prevalence of obesity-associated conditions raises new challenges in clinical medication. Although altered expression of drug-metabolizing enzymes (DMEs) has been shown in obesity, the impacts of obese levels (overweight, obesity, and severe obesity) on the expression of DMEs have not been elucidated. Especially, limited information is available on whether parental obese levels affect ontogenic expression of DMEs in children. Here, a high-fat diet (HFD) and three feeding durations were used to mimic different obese levels in C57BL/6 mice. The hepatic expression of five nuclear receptors (NRs) and nine DMEs was examined. In general, a trend of induced expression of NRs and DMEs (except for Cyp2c29 and 3a11) was observed in HFD groups compared to low-fat diet (LFD) groups. Differential effects of HFD on the hepatic expression of DMEs were found in adult mice at different obese levels. Family-based dietary style of an HFD altered the ontogenic expression of DMEs in the offspring older than 15 days. Furthermore, obese levels of parental mice affected the hepatic expression of DMEs in offspring. Overall, the results indicate that obese levels affected expression of the DMEs in adult individuals and that of their children. Drug dosage might need to be optimized based on the obese levels.

The influence of bariatric surgery on oral drug bioavailability in patients with obesity: A systematic review

Anatomical changes in the gastrointestinal tract and subsequent weight loss may influence drug disposition and thus drug dosing following bariatric surgery. This review systematically examines the effects of bariatric surgery on drug pharmacokinetics, focusing especially on the mechanisms involved in restricting oral bioavailability. Studies with a longitudinal before-after design investigating the pharmacokinetics of at least one drug were reviewed. The need for dose adjustment following bariatric surgery was examined, as well as the potential for extrapolation to other drugs subjected to coinciding pharmacokinetic mechanisms. A total of 22 original articles and 32 different drugs were assessed. The majority of available data is based on Roux-en-Y gastric bypass (RYGBP) (18 of 22 studies), and hence, the overall interpretation is more or less limited to RYGBP. In the case of the majority of studied drugs, an increased absorption rate was observed early after RYGBP. The effect on systemic exposure allows for a low degree of extrapolation, including between drugs subjected to the same major metabolic and transporter pathways. On the basis of current understanding, predicting the pharmacokinetic change for a specific drug following RYGBP is challenging. Close monitoring of each individual drug is therefore recommended in the early postsurgical phase. Future studies should focus on the long-term effects of bariatric surgery on drug disposition, and they should also aim to disentangle the effects of the surgery itself and the subsequent weight loss.

Transcriptional Repression of CYP3A4 by Increased miR-200a-3p and miR-150-5p Promotes Steatosis in vitro

Hepatic cytochrome P450 enzyme activities correlate with non-alcoholic fatty liver disease (NAFLD) and hepatic steatosis. The decreased activity of CYP3A4, an important drug-metabolizing enzyme, is associated with the progression of NAFLD. CYP3A4 is predicted as a target gene of miR-200a-3p and miR-150-5p by MicroInspector and TargetScan algorithms analyses. Here, we found decreased CYP3A4 and increased miR-200a-3p and miR-150-5p in LO2 cells with free fatty acid (FFA)-induced steatosis. Dual-luciferase assay confirmed that both miR-200a-3p and miR-150-5p targeted the 3'-untranslated region (3'-UTR) of CYP3A4 and that such interaction was abolished by miRNA binding site mutations in 3'-UTR of CYP3A4. Using miR-200a-3p and miR-150-5p mimics and inhibitors, we further confirmed that endogenous CYP3A4 was regulated posttranscriptionally by miR-200a-3p or miR-150-5p. Moreover, miR-200a-3p and miR-150-5p inhibitors attenuated FFA-induced steatosis in LO2 cells, and such effect was dependent on CYP3Y4 expression. These results suggest that miR-200a-3p and miR-150-5p, through directly targeting 3'-UTR of CYP3A4, contribute to the development of FFA-induced steatosis.

Skeletal Muscle Interleukin-6 Regulates Hepatic Cytochrome P450 Expression: Effects of 16-Week High-Fat Diet and Exercise

High-fat diet (HFD) induces several changes to the pathways regulating energy homeostasis and changes the expression of the hepatic cytochrome p450 (Cyp) enzyme-system. Despite these pervious findings, it is still unclear how the effects of HFD and especially HFD in combination with treadmill running affect hepatic Cyp expression. In this study, we investigated the mRNA and protein expression of selected Cyp's in mice subjected to 16 weeks of HFD and treadmill running. To understand the regulatory mechanisms behind the exercise-induced reversion of the HFD-induced changes in Cyp expression, we used a model in which the exercise-induced myokine and known regulator of hepatic Cyp's, interleukin-6 (IL-6), were knocked out specifically in skeletal muscle. We found that HFD increased the mRNA expression of Cyp1a1 and Cyp4a10, and decreased the expression of Cyp2a4, Cyp2b10, Cyp2e1, and Cyp3a11. HFD in combination with treadmill running reversed the HFD increase in Cyp4a10 mRNA expression. In addition, we observed increased Cyp1a and Cyp3a protein expression as an effect of exercise, whereas Cyp2b expression was lowered as an effect of HFD. IL-6 effected the response in Cyp3a11 and Cyp1a expression. We observed no changes in the content of the aryl hydrocarbon receptor, constitutive androstane receptor, pregnane X receptor, or peroxisome proliferation activator receptor alpha. In conclusion, we show that both HFD and exercise in HFD-fed animals can regulate hepatic Cyp expression and that changes in Cyp3a in response to HFD and exercise are dependent on skeletal muscular IL-6.

Higher Midazolam Clearance in Obese Adolescents Compared with Morbidly Obese Adults

BACKGROUND

The clearance of cytochrome P450 (CYP) 3A substrates is reported to be reduced with lower age, inflammation and obesity. As it is unknown what the overall influence is of these factors in the case of obese adolescents vs. morbidly obese adults, we studied covariates influencing the clearance of the CYP3A substrate midazolam in a combined analysis of data from obese adolescents and morbidly obese adults.

METHODS

Data from 19 obese adolescents [102.7 kg (62-149.5 kg)] and 20 morbidly obese adults [144 kg (112-186 kg)] receiving intravenous midazolam were analysed, using population pharmacokinetic modelling (NONMEM 7.2). In the covariate analysis, the influence of study group, age, total body weight (TBW), developmental weight (WTfor age and length) and excess body weight (WTexcess = TBW - WTfor age and length) was evaluated.

RESULTS

The population mean midazolam clearance was significantly higher in obese adolescents than in morbidly obese adults [0.71 (7%) vs. 0.44 (11%) L/min; p < 0.01]. Moreover, clearance in obese adolescents increased with TBW (p < 0.01), which seemed mainly explained by WTexcess, and for which a so-called 'excess weight' model scaling WTfor age and length to the power of 0.75 and a separate function for WTexcess was proposed.

DISCUSSION

We hypothesise that higher midazolam clearance in obese adolescents is explained by less obesity-induced suppression of CYP3A activity, while the increase with WTexcess is explained by increased liver blood flow. The approach characterising the influence of obesity in the paediatric population we propose here may be of value for use in future studies in obese adolescents.

Obesity and drug pharmacology: a review of the influence of obesity on pharmacokinetic and pharmacodynamic parameters

INTRODUCTION

The rising prevalence of obesity confronts clinicians with dosing problems in the (extreme) overweight population. Obesity has a great impact on key organs that play a role in the pharmacokinetics (PK) and pharmacodynamics (PD) of drugs, however the ultimate impact of these changes on how to adapt the dose may not always be known. Areas covered: In this review, physiological changes associated with obesity are discussed. An overview is provided on the alterations in absorption, distribution, drug metabolism and clearance in (morbid) obesity focusing on general principles that can be extracted from pharmacokinetic studies. Also, relevant pharmacodynamic considerations in obesity are discussed. Expert opinion: Over the last two decades, increased knowledge is generated on PK and PD in obesity. Future research should focus on filling in the knowledge gaps that remain, especially in connecting obesity-related physiological changes with changes in PK and/or PD and vice versa. Ultimately, this knowledge can be used to develop physiologically based PK and PD models on the basis of quantitative systems pharmacology principles. Moreover, efforts should focus on thorough prospective evaluation of developed model-based doses with subsequent implementation of these dosing recommendations in clinical practice.

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.

High-Fat Diet Feeding Alters Expression of Hepatic Drug-Metabolizing Enzymes in Mice

Medical conditions accompanying obesity often require drug therapy, but whether and how obesity alters the expression of drug-metabolizing enzymes and thus drug pharmacokinetics is poorly defined. Previous studies have shown that high-fat diet (HFD) feeding and subsequent obesity in mice lead to altered expression of transcriptional regulators for cytochrome P450 CYP2D6, including hepatocyte nuclear factor 4α (HNF4α, a transcriptional activator of CYP2D6) and small heterodimer partner (SHP, a transcriptional repressor of CYP2D6). The objective of this study was to examine whether diet-induced obesity alters CYP2D6 expression by modulating HNF4α and SHP expression. Male CYP2D6-humanized transgenic (Tg-CYP2D6) mice were fed with HFD or matching control diet for 18 weeks. Hepatic mRNA expression of CYP2D6 decreased to a small extent in the HFD group (by 31%), but the differences in CYP2D6 protein and activity levels in hepatic S9 fractions were found insignificant between the groups. Although hepatic SHP expression did not differ between the groups, HNF4α mRNA and protein levels decreased by ∼30% in the HFD group. Among major mouse endogenous cytochrome P450 genes, Cyp1a2 and Cyp2c37 showed significant decreases in the HFD group, whereas Cyp2e1 expression did not differ between groups. Cyp2b10 and Cyp3a11 expression was higher in the HFD group, with corresponding 2.9-fold increases in hepatic CYP3A activities in HFD-fed mice. Together, these results suggest that obesity has minimal effects on CYP2D6-mediated drug metabolism, although it modulates the expression of mouse endogenous P450s in a gene-specific manner.

Comparison of tacrolimus and cyclosporin A in CYP3A5 expressing Chinese de novo kidney transplant recipients: a 2-year prospective study

AIMS

To assess the efficacy and safety of tacrolimus and cyclosporin A (CsA)-based immunosuppressive regimens in Chinese de novo kidney transplant recipients who are CYP3A5 expressers.

METHODS

The CYP3A5 (6986 A>G, rs776746) polymorphism of eligible patients was determined before transplantation. De novo kidney transplant recipients enrolled in this study were assigned to tacrolimus (Tac group) or CsA (CsA group) based therapy. The follow-up period was 2 years. The incidence of acute rejection, patient and graft survival rates, renal allograft function and post-transplant complications were compared. The intra-individual variability (IIV) of Tac and CsA blood concentrations was analysed. Medication costs were also compared. The analysis was conducted on the intention-to-treat principle.

RESULTS

A total of 72 CYP3A5 expressers were enrolled, with 36 patients in each group. AR incidence was higher in the Tac group (11.1% vs. 5.6%), but there was no significant difference (p > 0.05). The 2-year patient and graft survival was comparable, and renal function was comparable in the two groups. Notably, the Tac group presented a significantly higher incidence of BK viremia (22.2% vs. 5.6%, p < 0.05) and BK viruria (38.9% vs. 16.7%, p < 0.05) than the CsA group. The CsA IIV at 1 and 3 months post-transplant was significantly lower than the Tac IIV (p < 0.05). The medical costs of both immunosuppressive drugs and management of complications was significantly lower in the CsA group.

CONCLUSIONS

Cyclosporin A-based maintenance therapy is safe for Chinese de novo kidney transplant recipients who are CYP3A5 expressers. CsA significantly reduced medication costs and decreased BKV infection, suggesting that it is more beneficial for this specific population.

Impact of obesity on accumulation of the toxic irinotecan metabolite, SN-38, in mice

AIM

Our aim is to investigate the impact of high fat diet-induced obesity on plasma concentrations of the toxic irinotecan metabolite, SN-38, in mice.

MAIN METHODS

Diet-induced obese (DIO, 60% kcal fed) and lean mice (10% kcal fed) were treated orally with a single dose of 10mg/kg irinotecan to determine pharmacokinetic (PK) parameters. Feces and livers were collected for quantification of irinotecan and its metabolites (SN-38 & SN-38G). SN-38G formation by Ugt1a1 enzyme was analyzed in liver S9 fractions. Expression of the pro-inflammatory cytokine, TNF-α was determined in liver and plasma. Hepatic β-glucuronidase and carboxylesterase enzymes (CES) were also determined.

KEY FINDINGS

AUC0-8 and Cmax of SN-38 increased by 2-fold in DIO mice compared to their lean controls. This was accompanied by a~2-fold reduction in AUC0-8 and Cmax of SN-38G in DIO mice. There were no differences in the PK parameters of irinotecan in DIO or lean mice. Conversion of SN-38 to SN-38G by Ugt1a1 enzyme was reduced by ~2-fold in liver S9 fractions in DIO mice. Furthermore, in DIO mice, β-glucuronidase activity increased by 2-fold, whereas there was no change in CES activity. TNF-α mRNA expression was 3 fold higher in DIO mice.

SIGNIFICANCE

Our study demonstrates that reduced hepatic Ugt1a activity during obesity likely contributes to reduced glucuronidation, and results in higher levels of the toxic metabolite, SN-38. Thus, irinotecan dosage should be closely monitored for effective and safe chemotherapy in obese cancer patients who are at a higher risk of developing liver toxicity.

Midazolam pharmacokinetics in morbidly obese patients following semi-simultaneous oral and intravenous administration: a comparison with healthy volunteers

BACKGROUND

While in vitro and animal studies have shown reduced cytochrome P450 (CYP) 3A activity due to obesity, clinical studies in (morbidly) obese patients are scarce. As CYP3A activity may influence both clearance and oral bioavailability in a distinct manner, in this study the pharmacokinetics of the CYP3A substrate midazolam were evaluated after semi-simultaneous oral and intravenous administration in morbidly obese patients, and compared with healthy volunteers.

METHODS

Twenty morbidly obese patients [mean body weight 144 kg (range 112-186 kg) and mean body mass index 47 kg/m(2) (range 40-68 kg/m(2))] participated in the study. All patients received a midazolam 7.5 mg oral and 5 mg intravenous dose (separated by 159 ± 67 min) and per patient 22 samples over 11 h were collected. Data from 12 healthy volunteers were available for a population pharmacokinetic analysis using NONMEM(®).

RESULTS

In the three-compartment model in which oral absorption was characterized by a transit absorption model, population mean clearance (relative standard error %) was similar [0.36 (4 %) L/min], while oral bioavailability was 60 % (13 %) in morbidly obese patients versus 28 % (7 %) in healthy volunteers (P < 0.001). Central and peripheral volumes of distribution increased substantially with body weight (both P < 0.001) and absorption rate (transit rate constant) was lower in morbidly obese patients [0.057 (5 %) vs. 0.130 (14 %) min(-1), P < 0.001].

CONCLUSIONS

In morbidly obese patients, systemic clearance of midazolam is unchanged, while oral bioavailability is increased. Given the large increase in volumes of distribution, dose adaptations for intravenous midazolam should be considered. Further research should elucidate the exact physiological changes at intestinal and hepatic level contributing to these findings.

Acetaminophen-induced liver injury in obesity and nonalcoholic fatty liver disease

Although acetaminophen (APAP) is usually considered as a safe drug, this painkiller can lead to acute liver failure after overdoses. Moreover, there is evidence that the maximum recommended dosage can induce hepatic cytolysis in some individuals. Several predisposing factors appear to enhance the risk and severity of APAP-induced liver injury including chronic alcoholic liver disease and nonalcoholic fatty liver disease (NAFLD), which refers to a large spectrum of hepatic lesions linked to obesity. In contrast, obesity by itself does not seem to be associated with a higher risk of APAP-induced liver injury. Since 1987, seven studies dealt with APAP-induced hepatotoxicity in rodent models of NAFLD and five of them found that this liver disease was associated with higher APAP toxicity. Unfortunately, these studies did not unequivocally established the mechanism(s) whereby NAFLD could favour APAP hepatotoxicity, although some investigations suggested that pre-existent induction of hepatic cytochrome P450 2E1 (CYP2E1) could play a significant role by increasing the generation of N-acetyl-p-benzoquinone imine (NAPQI), the toxic metabolite of APAP. Moreover, pre-existent mitochondrial dysfunction associated with NAFLD could also be involved. In contrast, some investigations suggested that factors that could reduce the risk and severity of APAP hepatotoxicity in obesity and NAFLD include higher hepatic APAP glucuronidation, reduced CYP3A4 activity and increased volume of body distribution. Thus, the occurrence and the outcome of APAP-induced liver injury in an obese individual with NAFLD might depend on a delicate balance between metabolic factors that can be protective and others that favour large hepatic levels of NAPQI.

The use of transcriptomics to unveil the role of nutrients in Mammalian liver

Liver is the organ primarily responding to diet, and it is crucial in determining plasma carbohydrate, protein, and lipid levels. In addition, it is mainly responsible for transformation of xenobiotics. For these reasons, it has been a target of transcriptomic analyses. In this review, we have covered the works dealing with the response of mammalian liver to different nutritional stimuli such as fasting/feeding, caloric restriction, dietary carbohydrate, cholesterol, fat, protein, bile acid, salt, vitamin, and oligoelement contents. Quality of fats or proteins has been equally addressed, and has the influence of minor dietary components. Other compounds, not purely nutritional as those represented by alcohol and food additives, have been included due to their relevance in processed food. The influence has been studied not only on mRNA but also on miRNA. The wide scope of the technology clearly reflects that any simple intervention has profound changes in many metabolic parameters and that there is a synergy in response when more compounds are included in the intervention. Standardized arrays to systematically test the same genes in all studies and analyzing data to establish patterns of response are required, particularly for RNA sequencing. Moreover, RNA is a valuable, easy-screening ally but always requires further confirmation.

Hepatic CYP3A expression and activity in low birth weight developing female rats

BACKGROUND

We aimed to investigate the effects of low birth weight (LBW) on the hepatic expression of cytochrome P-450 3A (CYP3A) in developing female rats.

METHODS

Pregnant rats were divided into two groups, a nourished group and an under-nourished group. The offspring of the nourished rats were defined as a normal weight, normal diet group (NN group). The offspring of the under-nourished rats were designated as a LBW, normal diet group (LN group). CYP3A mRNA expression, protein expression, protein localization and activity were determined.

RESULTS

The CYP3A1 mRNA expression levels of the LN group on days 3, 21, and 56 were significantly higher than those of the same age in the NN group (P≤0.01). The mRNA expression of CYP3A2 in the LN group on day 21 was higher than in rats of the same age in the NN group (P<0.01). The staining intensity and frequency of CYP3A1-positive hepatocytes were significantly lower on days 7 and 21 in the LN group than those of rats of the same age in the NN group (P<0.05). The staining intensity and frequency of CYP3A2-positive hepatocytes on days 14 and 21 were higher in the LN group than those on the same days in the NN group (P<0.05). The mean CYP3A activity of the LN group on day 3 was significantly higher than that of the NN group (P<0.001).

CONCLUSIONS

We found the effect of LBW on CYP3A activity was most prominent during the early days of life in rats. Investigators and clinicians should consider the effect of LBW on CYP3A in both pharmacokinetic study design and data interpretation, when prescribing drugs to LBW infants.

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.

Protective effect of Tuscan black cabbage sprout extract against serum lipid increase and perturbations of liver antioxidant and detoxifying enzymes in rats fed a high-fat diet

A diet rich in fat is considered a primary risk factor for CVD, cancer and failures in metabolism and endocrine functions. Hyperlipidaemia generates oxidative stress and weakens antioxidant defences as well as metabolic detoxification systems. Brassicaceae are vegetables rich in glucosinolates and isothiocyanates, affecting enzymatic antioxidant as well as phase II enzymes and conceivably counteracting high-fat diet (HFD)-associated pathologies. The protective role of Tuscan black cabbage (a variety of kale) sprout extract (TBCSE) intake against HFD alterations was here studied. The effects on rat hepatic antioxidant as well as detoxifying enzymes, and serum lipid- and body weightlowering properties of TBCSE, were investigated. Feeding the animals with a HFD for 21 d increased body as well as liver weights, and induced hyperlipidaemia, as confirmed by a higher serum lipid profile v. control diet. Daily intragastric administration of TBCSE to HFD-fed rats lowered serum total cholesterol, TAG and NEFA. Body and liver weight gains were also reduced. Antioxidant (catalase, NAD(P)H:quinone reductase, oxidised glutathione reductase and superoxide dismutase) and phase II (glutathione S-transferase and uridine diphosphate glucuronosyl transferase) enzymes were down-regulated by the HFD, while the extract restored normal levels in most groups. Generation of toxic intermediates, and membrane fatty acid composition changes by the HFD, might account for the altered hepatic antioxidant and detoxifying enzyme functions. The recovering effects of TBCSE could be attributed to high flavonoid, phenolic and organosulphur compound content, which possess free-radical-scavenging properties, enhance the antioxidant status and stimulate lipid catabolism. TBCSE intake emerges to be an effective alimentary strategy to counteract the perturbations associated with a diet rich in fat.

Pharmacokinetics of verapamil and its metabolite norverapamil in rats with hyperlipidaemia induced by poloxamer 407

In this study, the pharmacokinetics of verapamil and its active metabolite norverapamil were evaluated following intravenous and oral administration of 10 mg/kg verapamil to rats with hyperlipidaemia (HL) induced by poloxamer 407 (HL rats). The total area under the plasma concentration time curve (AUC) of verapamil in HL rats following intravenous administration was significantly greater (by 11.2%) than in control rats due to their slower (by 11%) non-renal clearance. The oral AUC of verapamil in HL rats was also significantly greater (by 116%) compared with controls, with a larger magnitude than the data observed following intravenous administration. This may have been a result of the decreased intestinal metabolism of verapamil in HL rats. The AUC of norverapamil and AUC(norverapamil)/AUC(verapamil) ratios following intravenous and oral administration of verapamil were unchanged in HL rats. Assuming that the HL rat model qualitatively reflects similar changes in patients with HL, the findings of this study have potential therapeutic implications. Further studies in humans are required to determine whether modification of the oral verapamil dosage regimen in HL states is necessary.

Pharmacokinetics of Antimicrobials in Obese Children

INTRODUCTION

Childhood obesity is common and results in substantial morbidity. The most commonly prescribed drugs in obese children are antibiotics. However, physiologic changes associated with childhood obesity can alter antibiotic pharmacokinetics and optimal body size measures to guide dosing in his population are ill defined. This combination can result in therapeutic failures or drug-related toxicities. This review summarizes pharmacokinetic information for antibiotics in obese children and implications for dosing.

METHODS

We conducted a comprehensive literature search of PubMed, EMBASE, and International Pharmaceutical Abstracts to identify pharmacokinetic studies of antimicrobial agents in obese children. We included the following search terms: obesity, pharmacokinetics, pharmacodynamics, drug toxicity, dosing, anti-infective agents, antiviral agents, and antifungal agents.

RESULTS

We identified four pharmacokinetic studies of antibiotics in obese children: one for cefazolin and tobramycin, one for gentamicin, and two for vancomycin. Only the cefazolin/tobramycin trial was prospective. The drugs studied differ in their tissue and body water distribution characteristics. Two of the studies (tobramycin and gentamicin) reported pharmacokinetic differences and required dosing modifications in obese children.

DISCUSSION

The lack of pharmacokinetic studies in obese children is pronounced. The scarcity of pharmacokinetic data limits the ability to predict drug disposition using drug physicochemical properties and impedes a rational approach to selection of appropriate body size measures for dosing. Given this knowledge gap, additional trials in obese children are urgently needed and is a public health concern.

CONCLUSION

Pharmacokinetic studies of antimicrobials in obese children are desperately needed to guide dosing and avoid therapeutic failures or unwanted toxicities.

Effects of poloxamer 407-induced hyperlipidemia on the pharmacokinetics of carbamazepine and its 10,11-epoxide metabolite in rats: Impact of decreased expression of both CYP3A1/2 and microsomal epoxide hydrolase

The pharmacokinetics of carbamazepine (CBZ) and its active 10,11-epoxide metabolite (CBZ-E) were evaluated after intravenous and oral administration of 5 mg/kg CBZ to rats with hyperlipidemia induced by poloxamer 407 (HL rats) and controls. The total area under the plasma concentration-time curve (AUC) of CBZ in HL rats after intravenous administration was significantly greater than that in controls due to their slower non-renal clearance (CL(NR)). This was due to slower hepatic CL(int) for metabolism of CBZ to CBZ-E in HL rats via CYP3A1/2. This result was consistent with a previous study indicating reduced hepatic CYP3A1/2 expression in HL rats. Interestingly, the AUC of CBZ-E was also increased in HL rats, while AUC(CBZ-E)/AUC(CBZ) ratios remained unchanged. These results suggested that further metabolism of CBZ-E to the inactive metabolite trans-10,11-dihydoxyl-10,11-dihydro-CBZ (CBZ-D) via microsomal epoxide hydrolase (mEH) was also slowed in HL rats. The significantly reduced hepatic mRNA level and expression of mEH protein in HL rats compared to controls confirmed the above hypothesis. Similar pharmacokinetic changes were observed in HL rats after oral administration of CBZ. These findings have potential therapeutic implications assuming that the HL rat model qualitatively reflects similar changes in patients with hyperlipidemia. Caution is required regarding pharmacotherapy in the hyperlipidemic state in cases where drugs that are metabolized principally by CYP3A1/2 or mEH and have a narrow therapeutic range are in use.

Enalapril reverses high-fat diet-induced alterations in cytochrome P450-mediated eicosanoid metabolism

Metabolism of arachidonic acid by cytochrome P450 (CYP) to biologically active eicosanoids has been recognized increasingly as an integral mediator in the pathogenesis of cardiovascular and metabolic disease. CYP epoxygenase-derived epoxyeicosatrienoic and dihydroxyeicosatrienoic acids (EET + DHET) and CYP ω-hydroxylase-derived 20-hydroxyeicosatetraenoic acid (20-HETE) exhibit divergent effects in the regulation of vascular tone and inflammation; thus, alterations in the functional balance between these parallel pathways in liver and kidney may contribute to the pathogenesis and progression of metabolic syndrome. However, the impact of metabolic dysfunction on CYP-mediated formation of endogenous eicosanoids has not been well characterized. Therefore, we evaluated CYP epoxygenase (EET + DHET) and ω-hydroxylase (20-HETE) metabolic activity in liver and kidney in apoE(-/-) and wild-type mice fed a high-fat diet, which promoted weight gain and increased plasma insulin levels significantly. Hepatic CYP epoxygenase metabolic activity was significantly suppressed, whereas renal CYP ω-hydroxylase metabolic activity was induced significantly in high-fat diet-fed mice regardless of genotype, resulting in a significantly higher 20-HETE/EET + DHET formation rate ratio in both tissues. Treatment with enalapril, but not metformin or losartan, reversed the suppression of hepatic CYP epoxygenase metabolic activity and induction of renal CYP ω-hydroxylase metabolic activity, thereby restoring the functional balance between the pathways. Collectively, these findings suggest that the kinin-kallikrein system and angiotensin II type 2 receptor are key regulators of hepatic and renal CYP-mediated eicosanoid metabolism in the presence of metabolic syndrome. Future studies delineating the underlying mechanisms and evaluating the therapeutic potential of modulating CYP-derived EETs and 20-HETE in metabolic diseases are warranted.

The effects of a high-fat and high-energy diet on the hepatic expression of CYP3A in developing female rats

We aimed to investigate the effects of high-fat and high-energy (HFHE) diets on the hepatic expression of cytochrome P-450 3A (CYP3A) in developing female rats. The pups of the dams fed with the standard diet were defined as the NN group and those fed the HFHE diet were defined as the NH group. The mRNA and protein expression, the protein localization and activity was determined. The mRNA expression of CYP3A1 on day 3 in the NH group were higher versus NN groups (p < 0.05) and the expression of the NH group on days 28 and 56 were lower versus the NN group (p < 0.01). CYP3A1 immunolabeling had a zonal-restricted expressions pattern on day 28 and after in the NN groups, while the obvious zonal expression pattern was observed in the NH group on day 84. The mean activity for the NH groups on days 3, 7, 14 and 28 was higher versus the NN groups (p < 0.05). On day 84, the activity was lower for the NH group versus the NN group (p < 0.05). Our findings provide a basis for further studies on appropriate medication regimen in obese children.

Constitutive androstane receptor transactivates the hepatic expression of mouse Dhcr24 and human DHCR24 encoding a cholesterogenic enzyme 24-dehydrocholesterol reductase

Phenobarbital treatment has long been known to influence serum and hepatic cholesterol levels in rodents and humans. Constitutive androstane receptor (CAR), a member of the nuclear receptor superfamily, mediates various biological actions of phenobarbital. We have thus investigated whether CAR transactivates cholesterogenic genes in livers. Activation of CAR in mouse livers and cultured human hepatocytes increased mRNA levels of mouse Dhcr24 and human DHCR24, both of which encode 24-dehydrocholesterol reductase (DHCR24) catalyzing the last step of cholesterol biosynthesis. CAR transactivated the expression of these genes in reporter assays with cultured hepatoma cells. Furthermore, we have identified a DR4 (direct repeat separated by 4 nucleotides) motif in the human DHCR24 distal promoter as a binding site of CAR/retinoid X receptor α (RXRα) heterodimer. We have also demonstrated that the heterodimer of pregnane X receptor (PXR)/ RXRα binds to the DR4 motif and that human DHCR24 reporter gene is transactivated by the ligand-activated PXR. These results suggest a role of xenobiotic-responsive nuclear receptor CAR, and also possibly PXR, in cholesterol biosynthesis in the liver of mice and humans.

Role of high-fat diet in regulation of gene expression of drug metabolizing enzymes and transporters

AIM

Our aim is to investigate the molecular mechanism of regulation of gene expression of drug metabolizing enzymes (DMEs) and transporters in diet-induced obesity.

MAIN METHODS

Adult male CD1 mice were fed diets containing 60% kcal fat (HFD) or 10% kcal fat (LFD) for 14 weeks. RNA levels of hepatic DMEs, transporters and their regulatory nuclear receptors (NRs) were analyzed by real-time PCR. Activation of cell-signaling components (JNK and NF-κΒ) and pro-inflammatory cytokines (IL-1β, IL-6 and TNFα) were measured in the liver. Finally, the pharmacodynamics of drugs metabolized by DMEs was measured to determine the clinical relevance of our findings.

KEY FINDINGS

RNA levels of the hepatic phase I (Cyp3a11, Cyp2b10, Cyp2a4) and phase II (Ugt1a1, Sult1a1, Sultn) enzymes were reduced ~30-60% in HFD compared to LFD mice. RNA levels of Cyp2e1, Cyp1a2 and the drug transporters, multidrug resistance proteins, (Mrp)2, Mrp3 and multidrug resistant gene (Mdr)1b were unaltered in HFD mice. Gene expression of the NRs, PXR and CAR and nuclear protein levels of RXRα was reduced in HFD mice. Cytokines, JNK and NF-κΒ were induced in HFD mice. Thus reduction in hepatic gene expression in obesity may be modulated by cross-talk between NRs and inflammation-induced cell-signaling. Sleep time of Midazolam (Cyp3a substrate) was prolonged in HFD mice, while Zoxazolamine (Cyp1a2 and Cyp2e1 substrate)-induced sleep time was unaltered.

SIGNIFICANCE

This study demonstrates that gene-specific reductions in DMEs can affect specific drugs metabolized by these enzymes, thus providing a rationale to monitor the effectiveness of drug therapy in obese individuals.

The effect of bamboo extract on hepatic biotransforming enzymes--findings from an obese-diabetic mouse model

AIM OF THE STUDY

Bamboo leaves are used as a component in traditional Chinese medicine for the anti-inflammatory function. Our previous studies have demonstrated that an ethanol/water extract from Phyllostachys edulis ameliorated obesity-associated chronic systemic inflammation in mice, and therefore relieving the symptoms of type 2 diabetes. The aim of this project was to further investigate the effects of this bamboo extract on hepatic biotransformation enzymes in both lean and obese mice, as an initial step in the toxicological evaluation of using this traditional medicine in obese/diabetic population.

MATERIALS AND METHODS

Male C57BL/6J mice were randomized to 4 groups and fed standard (10% kcal from fat) diet with or without bamboo extract supplementation at a dose of 10 gram per kilogram diet (n=10 and n=9, respectively), or high fat (45% kcal from fat) diet with or without bamboo extract (n=8 and N=7, respectively). The dietary treatment lasted for 6 months. Subsequently, the activities and expression of the major Phase I and II hepatic biotransformation enzymes were assessed in subcellular fractions from murine livers.

RESULTS

Three groups of mice, lean bamboo extract-supplemented, obese/diabetic, and bamboo extract-supplemented obese/diabetic, showed greater activities of cytochromes P450 1a2 and 3a11 compared to control but no changes in the expression level of these proteins. For Phase II enzymes, bamboo extract supplementation in lean mice caused decreased glutathione-S-transferase activity (-12%) and greater uridine diphosphate glucuronosyltransferase activity (+46%), but had no effect on sulfotransferase activity. Conversely, the obese/diabetic condition itself increased glutathione-S-transferase and uridine diphosphate glucuronosyltransferase activities, but decreased total sulfotransferase activity and sulfotransferase 2a1 expression.

CONCLUSIONS

Bamboo extract and obesity/diabetes show significant independent effects on hepatic biotransformation as well as interaction effects in mice. These changes may alter the clearance of endo- and xenobiotics, including bamboo extract itself, hence this effect should be carefully considered in the medicinal application of bamboo extract as it has potential to alter its own metabolism and that of other medications concurrently administered to obese diabetic patients.

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.

Chronic treatment with epoxyeicosatrienoic acids modulates insulin signaling and prevents insulin resistance in hepatocytes

Epoxyeicosatrienoic acids (EETs) are arachidonic acid metabolites produced by cytochrome P450 epoxygenases which are highly expressed in hepatocytes. The functions of EETs in hepatocytes are not well understood. In this study, we investigated the effects of 14,15-EETs treatment on the insulin signal transduction pathway in hepatocytes. We report that chronic treatment, not acute treatment, with 30 μM 14,15-EETs prevents palmitate induced insulin resistance and potentiates insulin action in cultured HepG2 hepatocytes. 14,15-EETs increase Akt phosphorylation at S473, activating Akt, in an insulin dependent manner in HepG2 cells. Under insulin resistant conditions induced by palmitate, 14,15-EETs restore the insulin response by increasing S473-phosphorylated Akt. 8,9-EETs and 11,12-EETs demonstrated similar effects to 14,15-EETs. Furthermore, 14,15-EETs potentiate insulin-suppression of gluconeogenesis in cultured H4IIE hepatocytes. To elucidate the mechanism of EETs function, we analyzed the insulin signaling factors upstream of Akt. Inhibition of phosphatidylinositol 3-kinase (PI3K) with LY294002 attenuated the 14,15-EETs-induced activating phosphorylation of Akt. 14,15-EETs reduced palmitate-stimulated phosphorylation of IRS-1 on S312 and phosphorylation of c-Jun N-terminal kinase (JNK) at threonine 183 and tyrosine 185 residues. The regulation of insulin sensitivity in cultured hepatocytes by chronic 14,15-EETs treatment appears to involve the JNK-IRS-PI3K pathway. The requirement of chronic treatment with EETs suggests that the effects of EETs on insulin response may be indirect.

Effects of intestinal constituents and lipids on intestinal formation and pharmacokinetics of desethylamiodarone formed from amiodarone

To model the impact of intestinal components associated with a high fat meal on metabolism of amiodarone, rat everted intestinal sacs were evaluated for their ability to metabolize the drug to its active metabolite (desethylamiodarone) under a variety of conditions. The preparations were obtained from fasted rats or rats pretreated with 1% cholesterol in peanut oil. After isolation of the tissues, the intestinal segments were immersed in oxygenated Krebs Henseleit buffer containing varying concentrations of bile salts, cholesterol, lecithin and lipase with or without soybean oil emulsion as a source of triglycerides. Amiodarone uptake was similar between the five 10-cm segments isolated distally from the stomach. Desethylamiodarone was measurable in all segments. Based on the metabolite-to-drug concentration ratio within the tissues, there was little difference in metabolic efficiency between segments for any of the treatments. Between treatments, however, it appeared that the lowest level of metabolism was noted in rats pretreated with 1% cholesterol in peanut oil. This reduction in metabolic efficiency was not observed in gut sacs from the fasted rats to which soybean oil emulsion was directly added to the incubation media. Despite the apparent reduction in intestinal metabolism, there was no apparent change in the ratio of metabolite-to-drug area under the plasma concentration versus time ratios of fasted rats and those given 1% cholesterol in peanut oil, suggesting that the intestinal presystemic formation of desethylamiodarone is not substantial.

Diet-induced obesity alters vincristine pharmacokinetics in blood and tissues of mice

Obesity is associated with poorer outcome from many cancers, including leukemia. One possible contributor to this could be suboptimal chemotherapy dosing in obese patients. We have previously found that vincristine (VCR) is less effective in obese compared to non-obese mice with leukemia, despite weight-based dosing. In the present study, we administered (3)H-VCR to obese and control mice to determine whether obesity would cause suboptimal VCR exposure. Blood VCR concentrations were fitted with a three-compartment model using pharmacokinetic analysis (two-stage PK) in three subsets of VCR concentrations vs. time method. Tissue and blood VCR concentrations were also analyzed using non-compartmental modeling. Blood VCR concentrations showed a triexponential decay and tended to be slightly higher in the obese mice at all time-points. However, the t(1/2,beta) and t(1/2,gamma) were shorter in the obese mice (9.7 min vs. 44.5 min and 60.3h vs. 85.6h, respectively), resulting in a lower AUC(0-infinity) (13,099 ng/m Lh vs. 15,384 ng/mL h). Had the dose of VCR been "capped", as is done in clinical practice, the AUC(0-infinity) would have been 36% lower in the obese mice than the controls. Tissue disposition of VCR revealed a biexponential decay from spleen, liver, and adipose. Interestingly, VCR slowly accumulated in the bone marrow of control mice, but had a slow decay from the marrow in the obese mice. Thus, obesity alters VCR PK, causing a lower overall exposure in circulation and bone marrow. Given the high prevalence of obesity, additional PK studies should be performed in obese subjects to optimize chemotherapy dosing regimens.

Impact of obesity on oral contraceptive pharmacokinetics and hypothalamic-pituitary-ovarian activity

BACKGROUND

This study was conducted to determine whether increased body mass index (BMI) affects oral contraceptive (OC) pharmacokinetics and suppression of hypothalamic-pituitary-ovarian (HPO) axis activity.

STUDY DESIGN

Ovulatory reproductive-age women with normal weight (BMI <25 kg/m(2); n=10) and with obesity (BMI >30 kg/m(2); n=10) received OCs for two cycles (prospective cohort). Subjects were admitted for two 48-h inpatient stays at the beginning and end of the hormone-free interval. Ethinyl estradiol and levonorgestrel (LNG) levels were evaluated during both inpatient stays. Gonadotropin pulsatility (follicle-stimulating hormone and luteinizing hormone) was measured during the second inpatient stay. Estradiol (E(2)) and progesterone (P) were measured daily during inpatient stays and twice per week in Cycle 2.

RESULTS

BMI was greater in the obese compared to the normal-BMI group [37.3 kg/m(2) (SD, 6.0) vs. 21.9 kg/m(2) (SD, 1.6); p<.05]. The LNG half-life was significantly longer in the obese group (52.1+/-29.4 vs. 25.6+/-9.3 h, p<.05), which correlated with a lower maximum LNG concentration on Cycle 2, Day 1 [1.9 ng/mL (SD, 0.5) vs. 2.5 ng/mL (SD, 0.7)] and a longer time to reach steady state (10 vs. 5 days) in obese women. There were no significant differences in volume of distribution between groups. LH pulse parameters did not differ statistically between groups but trended toward greater HPO activity in the obese group. Additionally, more obese (6/10 vs. 3/10 normal BMI, p>.05) women exhibited E(2) levels consistent with development of a dominant follicle and P levels consistent with ovulation (2/10 vs. 1/10) during Cycle 2.

CONCLUSIONS

Compared to women with normal BMI, obese women exhibit differences in OC pharmacokinetics that are associated with greater HPO activity.

Unsaturated fatty acid regulation of cytochrome P450 expression via a CAR-dependent pathway

The liver is responsible for key metabolic functions, including control of normal homoeostasis in response to diet and xenobiotic metabolism/detoxification. We have shown previously that inactivation of the hepatic cytochrome P450 system through conditional deletion of POR (P450 oxidoreductase) induces hepatic steatosis, liver growth and P450 expression. We have exploited a new conditional model of POR deletion to investigate the mechanism underlying these changes. We demonstrate that P450 induction, liver growth and hepatic triacylglycerol (triglyceride) homoeostasis are intimately linked and provide evidence that the observed phenotypes result from hepatic accumulation of unsaturated fatty acids, which mediate these phenotypes by activation of the nuclear receptor CAR (constitutive androstane receptor) and, to a lesser degree, PXR (pregnane X receptor). To our knowledge this is the first direct evidence that P450s play a major role in controlling unsaturated fatty acid homoeostasis via CAR. The regulation of P450s involved in xenobiotic metabolism by this mechanism has potentially significant implications for individual responses to drugs and environmental chemicals.