leukotriene-b4 and Fatty-Liver

Insulin resistance results from several pathophysiologic mechanisms, including chronic tissue inflammation and defective insulin signaling. We found that liver, muscle and adipose tissue exhibit higher levels of the chemotactic eicosanoid LTB4 in obese high-fat diet (HFD)-fed mice. Inhibition of the LTB4 receptor Ltb4r1, through either genetic or pharmacologic loss of function, led to an anti-inflammatory phenotype with protection from insulin resistance and hepatic steatosis. In vitro treatment with LTB4 directly enhanced macrophage chemotaxis, stimulated inflammatory pathways, reduced insulin-stimulated glucose uptake in L6 myocytes, and impaired insulin-mediated suppression of hepatic glucose output in primary mouse hepatocytes. This was accompanied by lower insulin-stimulated Akt phosphorylation and higher Irs-1/2 serine phosphorylation, and all of these events were dependent on Gαi and Jnk1, two downstream mediators of Ltb4r1 signaling. These observations elucidate a novel role of the LTB4-Ltb4r1 signaling pathway in hepatocyte and myocyte insulin resistance, and they show that in vivo inhibition of Ltb4r1 leads to robust insulin-sensitizing effects.

Topics: Animals; Blood Glucose; Diet, High-Fat; Fatty Liver; Hepatocytes; Inflammation; Insulin; Insulin Receptor Substrate Proteins; Insulin Resistance; Leukotriene B4; Macrophages; Mice; Mice, Obese; Muscle Fibers, Skeletal; Obesity; Phosphorylation; Proto-Oncogene Proteins c-akt; Receptors, Leukotriene B4; Signal Transduction

To ascertain whether constitutive androstane receptor (CAR) activation by 1,4-bis-[2-(3,5,-dichloropyridyloxy)] benzene (TCPOBOP) modulates steatohepatitis in the methionine choline-deficient (MCD) diet-fed animal.. C57/BL6 wild-type mice were fed the MCD or standard diet for 2 wk and were treated with either the CAR agonist, TCPOBOP, or the CAR inverse agonist, androstanol.. Expression of CYP2B10 and CYP3A11, known CAR target genes, increased 30-fold and 45-fold, respectively, in TCPOBOP-treated mice fed the MCD diet. TCPOBOP treatment reduced hepatic steatosis (44.6 +/- 5.4% vs 30.4 +/- 4.5%, P < 0.05) and serum triglyceride levels (48 +/- 8 vs 20 +/- 1 mg/dL, P < 0.05) in MCD diet-fed mice as compared with the standard diet-fed mice. This reduction in hepatic steatosis was accompanied by an increase in enzymes involved in fatty acid microsomal omega-oxidation and peroxisomal beta-oxidation, namely CYP4A10, LPBE, and 3-ketoacyl-CoA thiolase. The reduction in steatosis was also accompanied by a reduction in liver cell apoptosis and inflammation. In contrast, androstanol was without effect on any of the above parameters.. CAR activation stimulates induction of genes involved in fatty acid oxidation, and ameliorates hepatic steatosis, apoptosis and inflammation.

Topics: Animals; Apoptosis; Choline Deficiency; Constitutive Androstane Receptor; Fatty Acids; Fatty Liver; Inflammation; Leukotriene B4; Methionine; Mice; Mice, Inbred C57BL; PPAR alpha; Pyridines; Receptors, Cytoplasmic and Nuclear; Transcription Factors