Xenobiotic metabolism, cancer chemoprevention and cancer biomarkers

Division Of Basic Sciences - Nci

Investigators

Linked publications, trials & patents

Abstract

Project 1:Nonalcoholic fatty liver disease (NAFLD), characterized by massive ectopic lipid accumulation in the liver in the absence of significant alcohol consumption, is becoming the most common chronic and progressive liver disease, paralleling a worldwide increase in obesity fueled by the dramatic changes in lifestyle and diet during the past century. The global prevalence of NAFLD is currently estimated to be 24%. In the United States, NAFLD cases are predicted to expand from 83.1 million in 2015 to 100.9 million in 2030. NAFLD, particularly its more advanced stage nonalcoholic steatohepatitis (NASH), can progress to end-stage liver diseases such as cirrhosis and hepatocellular carcinoma (HCC), and is set to replace viral hepatitis as the leading cause for liver transplantation over the next decade or so, with the disease affecting both adults and. Despite the rising incidence, no drug has yet been approved for the treatment of NAFLD. MYC, encoded by proto-oncogene Myc, is a highly pleiotropic transcription factor with broad effects on cell proliferation, metabolism, angiogenesis, apoptosis, adhesion, and differentiation. Upon binding DNA with its partner MAX, MYC recruits factors that release paused RNA polymerases to drive transcription and amplify gene expression. Dysregulation of MYC is commonly found in various human cancers. Experimentally, MYC overexpression prompts and MYC inactivation represses tumor development. In addition to its role in cancer, MYC is also involved in the regulation of metabolic diseases including diabetes and fatty liver diseases. Accumulating studies demonstrate that MYC coordinates glucose homeostasis by regulating glucose transporters, key enzymes in the glycolytic pathway and mitochondrial function, the central feature implicated in insulin resistance and diabetes. Transgenic expression of MYC in hepatocytes promoted the progression of alcoholic liver disease (ALD) via induction of ER stress and inhibition of p53 signaling. Conversely, MYC inactivation in the liver suppressed ER stress and prevented diet-induced NAFLD. A recent study revealed that MYC cooperated with sterol-regulated element-binding protein 1 (Srebp1) to promote lipogenesis in hepatic, renal and lung tumor cells, studies with heterozygous Myc+/- mice showed that reduced expression of MYC increased longevity and enhanced healthspan, partially through elevated metabolic activity and decreased cholesterol synthesis in the liver (Hofmann et al., 2015). In recent years, the intestine has emerged as a central organ participating in lipid and glucose metabolism. However, the effects of intestinal MYC on metabolic diseases have not been investigated. Intestine-specific Myc disrupted mice were generated and used to clarify the role and dissect the mechanism of intestinal MYC in NAFLD development. Intestinal MYC was induced during obesity and intestine-specific Myc disruption ameliorated high-fat diet (HFD)-induced obesity and hepatic steatosis by inducing GLP-1 and suppressing the production and secretion of ceramides. Cers4, encoding a key enzyme in the de novo pathway of ceramide synthesis, was identified as a novel target of MYC in the intestine. Notably, pharmacological inhibition of MYC by 10058-F4 exhibited therapeutic effects on HFD-induced metabolic disorders. This study suggests that intestinal MYC could be a potential target for the treatment of NAFLD. Project 2: Triptolide is the most active component extracted from Triptergium wilfordii Hook. F, which has been used for the treatment of rheumatoid arthritis and systemic lupus erythematosus in China, and has other possible effects on immunosuppression, anti-inflammatory, anti-cancer and antifertility activities10. However, triptolide has a narrow therapeutic window and some patents exhibit liver toxicity. A serum metabolomics study revealed that triptolide alters levels of taurine, creatinine, free fatty acids, beta-hydroxybutyrate, citric acid cycle intermediates and amino acids, which indicated impaired mitochondria function and beta-oxidation of free fatty acid (FFA). Treatment with triptolide leads to more severe hepatoxicity and nephrotoxicity in cytochrome P450 oxidoreductase knockout mice than in wild-type mice, revealing the molecular mechanisms of triptolide-induced toxicity under conditions of hepatic CYP inactivation. Earlier studies revealed that lipid alterations and inflammation were associated with liver injury and urine metabolomics found several biomarkers associated with tryptophan, pantothenic acid and porphyrin associated with triptolide toxicity. However, endogenous metabolites are highly polar molecular, and thus we applied UPLC-ESI-QTOFMS using hydrophilic HILIC chromatography to improve the retention of polar metabolites and provide a relatively comprehensive separation method for the analysis of biological samples. Mice were administered triptolide orally to induced hepatic toxicity as revealed histologically and by quantitation of liver enzymes in serum. A total of 32 metabolites were observed that were significantly changed by triptolide treatment and most correlated with the severity of toxicity. These studies revealed that the triptolide-induced liver toxicity was related to alterations in multiple metabolic pathways, including glutathione metabolism, citric acid cycle, purine metabolism, glycerophospholipid metabolism, taurine and hypotaurine metabolism and amino acids metabolism. Project 3: Saururus chinensis (S chinensis) has been used as an herb to treat edema, jaundice, and gonorrhea. Manassantin B (MNSB), a dineolignan isolated from S chinensis, was identified as a potent adipogenesis/lipogenesis inhibitor (IC50 = 9.3 nM). To explore the underlying mechanism, both adipogenesis and lipogenesis were measured in differentiated 3T3-L1 preadipocytes, murine primary preadipocytes and adipose tissue explants upon MNSB treatment. Key regulators of adipogenesis/lipogenesis were downregulated by MNSB treatment, mainly resulting from increased phosphorylation of AMPK which was identified as a vital regulator of adipogenesis and lipogenesis. Moreover, MNSB did not increase AMPK phosphorylation in 3T3-L1 cells transfected with Prkaa1 (encoding protein kinase AMP-activated catalytic subunit alpha 1) siRNA or adipose tissue explants isolated from adipose-specific Prkaa1-disrupted mice (Prkaa1deltaad ). In diet-induced obese C57BL/6N mice, MNSB displayed preventive and therapeutic effects on obesity accompanied by decreased adipocyte size. MNSB was also found to increase AMPK phosphorylation both in subcutaneous white adipose tissue and brown adipose tissue in vivo. These findings suggest that MNSB can be a new therapeutic agent for the prevention and treatment of obesity and other related metabolic disorders.