Aparajita Dey

Alcohol and oxidative liver injury

Acute and chronic ethanol treatment has been shown to increase the production of reactive oxygen species, lower cellular antioxidant levels, and enhance oxidative stress in many tissues, especially the liver. Ethanol‐induced oxidative stress plays a major role in the mechanisms by which ethanol produces liver injury. Many pathways play a key role in how ethanol induces oxidative stress. This review summarizes some of the leading pathways and discusses the evidence for their contribution to alcohol‐induced liver injury. Many of the seminal reports in this topic have been published in Hepatology , and it is fitting to review this research area for the 25th Anniversary Issue of the Journal. (Hepatology 2006;43:S63–S74.)

Induction of cytochrome promotes liver injury in ob/ob mice

Cytochrome P450 2E1 (CYP2E1) activates several hepatotoxins and contributes to alcoholic liver damage. Obesity is a growing health problem in the United States. The aim of the present study was to evaluate whether acetone‐ or pyrazole‐mediated induction of CYP2E1 can potentiate liver injury in obesity. CYP2E1 protein and activity were elevated in acetone‐ or pyrazole‐treated obese and lean mice. Acetone or pyrazole induced distinct histological changes in liver and significantly higher aminotransferase enzymes in obese mice compared to obese controls or acetone‐ or pyrazole‐treated lean mice. Higher caspase‐3 activity and numerous apoptotic hepatocytes were observed in the acetone‐ or pyrazole‐treated obese mice. Increased protein carbonyls, malondialdehyde, 4‐hydroxynonenal‐protein adducts, elevated levels of inducible nitric oxide synthase, and higher 3‐nitrotyrosine protein adducts were found in livers of acetone‐ or pyrazole‐treated obese animals, suggesting elevated oxidative and nitrosative stress. Liver tumor necrosis factor α levels were higher in pyrazole‐treated animals. The CYP2E1 inhibitor chlormethiazole and iNOS inhibitor N‐(3‐(aminomethyl)‐benzyl) acetamidine abrogated the toxicity and the oxidative/nitrosative stress elicited by the induction of CYP2E1. Conclusion: These results show that obesity contributes to oxidative stress and liver injury and that induction of CYP2E1 enhances these effects. (HEPATOLOGY 2007;45:1355–1365.)

Rofecoxib decreases renal injury in obese Zucker rats

The present study tested the hypothesis that altered vascular regulation of arachidonic acid enzymes in obese Zucker rats contributes to renal damage. Protein expression of CYP450 (cytochrome P450) and COX (cyclo-oxygenase) enzymes in renal microvessels was studied in obese and lean Zucker rats at 20-21 weeks of age. Body weight and blood glucose averaged 649+/-13 g and 142+/-10 mg/dl in obese Zucker rats compared with 437+/-10 g and 111+/-5 mg/dl in age-matched lean Zucker rats. Renal microvascular CYP4A and COX-2 protein levels were increased and CYP2C protein levels decreased in obese Zucker rats. TX (thromboxane) B2 excretion was 2-fold higher and PG (prostaglandin) E2 excretion significantly lower in obese Zucker rats. Additional studies investigated the ability of the COX-2 inhibitor, rofecoxib, to slow the progression of renal injury in obese Zucker rats. Rofecoxib treatment decreased urinary PGF2alpha and 8-isoprostane levels in obese Zucker rats. Renal microvessel mRNA expression of pro-inflammatory chemokines was decreased in COX-2-inhibitor-treated obese Zucker rats. Urinary albumin excretion, an index of kidney damage, averaged 95+/-11 mg/day in vehicle-treated and 9+/-1 mg/day in rofecoxib-treated obese Zucker rats. Glomerulosclerosis, characterized by mesangial expansion, tubulo-interstitial fibrosis and extracellular matrix accumulation, was prominent in obese Zucker rats compared with a lack of damage in age-matched lean Zucker rats and rofecoxib-treated obese Zucker rats. These results suggest that altered vascular arachidonic acid enzymes contribute to the renal damage, and that COX-2 inhibition decreases glomerular injury in obese Zucker rats.

Geldanamycin, an Inhibitor of Hsp90, Potentiates Cytochrome P4502E1-Mediated Toxicity in HepG2 Cells

Cytochrome P450 2E1 (CYP2E1) potentiates oxidative stress-mediated cell death. Heat shock proteins (Hsps) modulate the stability and function of numerous proteins. We examined the effect of geldanamycin (GA), an inhibitor of Hsp90, on CYP2E1-mediated toxicity in transfected HepG2 cells overexpressing CYP2E1 (E47 cells). Basal expression of CYP2E1 and Hsp90 was higher in E47 cells compared with control C34 cells, which do not express CYP2E1. Treatment with GA resulted in significant toxicity to E47 cells compared with C34 cells. An enhanced loss of E47 cell viability was also observed using two different inhibitors of Hsp90, herbimycin A and radicicol. Treatment of E47 cells with GA caused depletion of glutathione coupled to an increase in reactive oxygen species level and lipid peroxidation. These effects of GA were more pronounced in the E47 than the C34 cells. The antioxidants trolox and N-acetylcysteine prevented the increased reactive oxygen species accumulation and resultant loss of viability. GA caused increased caspase 3 activity and Annexin V staining in E47 cells, suggesting an apoptotic mode of cell death. A decrease in mitochondrial membrane potential was observed in GA-treated HepG2 cells, and mitochondrial permeability transition inhibitors prevented the cytotoxicity of GA. These results suggest that Hsp90 is protective against CYP2E1-dependent oxidant stress and loss of cell viability in HepG2 cells.

CYP450, COX-2 and Obesity Related Renal Damage

Abstract The number of obese people in the world is growing rapidly worldwide and has reached epidemic status. Obesity is often associated with the clustering of metabolic and cardiovascular risk factors that contribute to metabolic syndrome or syndrome X. Likewise, metabolic syndrome and its associated traits are major contributing factors to the increase in nephropathy and end stage renal disease. The specific factors that link the metabolic syndrome traits to the progression of nephropathy remain largely unexplored. Recent studies have demonstrated that an imbalance between cyclooxygenase-2 (COX-2) and cytochrome P450 (CYP450) arachidonic acid metabolizing enzymes in the kidney may contribute to the renal damage associated with obesity. Along these lines, COX-2 inhibition decreases renal cytokine levels and glomerular injury in obese rats. Peroxisome proliferators-activated receptors (PPARs) are transcription factors that also contribute to chronic kidney disease in obesity and metabolic syndrome. Intriguingly, interactions between PPARs and arachidonic acid metabolites could be key determinants of renal damage in metabolic syndrome patients. Therefore, there is a promising future for pharmacological agents that manipulate COX-2 and CYP450 metabolites and PPARs to treat obesity related nephropathy.