Melatonin exerts a therapeutic effect on cholestatic liver injury in rats with bile duct ligation

The Effect of Melatonin on Plasma Oxidant-Antioxidant Skeletal Muscle Reperfusion Injury in Rats

We investigated the effects of melatonin administration on skeletal muscle ischaemia-reperfusion injury (IRI) by assessing plasma malondialdehyde (MDA), superoxide dismutase (SOD), total glutathione (GSSH), glutathione peroxidase (GPX) and myeloperoxidase (MPO) concentrations. Male Sprague-Dawley rats ( n = 32) were randomized into four groups: group 1 served as time controls; group 2 were the test animals; group 3 received melatonin (30 mg/kg) intraperitoneally prior to the induction of ischaemia; and group 4 received melatonin (30 mg/kg) intraperitoneally prior to the reperfusion period. Administration of melatonin prior to reperfusion significantly decreased the elevated MDA concentration caused by IRI, and significantly elevated GSSH concentrations, which had been reduced by IRI. Ischaemia-reperfusion injury significantly increased activities of GPX, SOD and MPO, and melatonin administration reversed this effect. In conclusion, a pharmacological dose of melatonin showed significant protective effects against IRI by decreasing lipid peroxidation, MPO, SOD and GPX enzyme activities and regulating glutathione content.

Cholestatic syndromes

PURPOSE OF REVIEW

This review highlights recent developments in the molecular pathogenesis of cholestasis as well new aspects of pathogenesis and management of clinical cholestatic disorders.

RECENT FINDINGS

Highlights include the role of nuclear receptors including FXR ligands as potential therapeutic agents, new genetic defects for pediatric cholestasis and sclerosing cholangitis, and novel infections and environmental agents as etiologies for primary biliary cirrhosis. Important clinical studies have been published in the area of pediatric cholestatic syndromes, intrahepatic cholestasis of pregnancy, primary biliary cirrhosis, primary and secondary sclerosing cholangitis, cholestasis of sepsis, viral cholestatic syndromes, and drug-induced cholestasis.

SUMMARY

These advances continue to improve understanding of the pathophysiology, diagnosis, and management of cholestatic liver disease.

Melatonin and its precursor, L-tryptophan: influence on pancreatic amylase secretion in vivo and in vitro

Melatonin, considered as a main pineal product, may be also synthetized in the gastrointestinal tract from L-tryptophan. Melatonin has been recently shown to affect insulin release and its receptors have been characterized in the pancreas however, the effects of melatonin on the pancreatic enzyme secretion have not been examined. The aim of this study was to investigate the effects of melatonin or L-tryptophan on amylase secretion in vivo in anaesthetized rats with pancreato-biliary fistulas, and in vitro using isolated pancreatic acini. Melatonin (1, 5 or 25 mg/kg) or L-tryptophan (10, 50 or 250 mg/kg) given to the rats as a intraperitoneal (i.p.) bolus injection produced significant and dose-dependent increases in pancreatic amylase secretion under basal conditions or following stimulation of enzyme secretion by diversion of bile-pancreatic juice. This was accompanied by a dose-dependent rise in melatonin plasma level. Stimulation of pancreatic enzyme secretion caused by melatonin or L-tryptophan was completely abolished by vagotomy, deactivation of sensory nerves with capsaicin or pretreatment with CCK1 receptor antagonists (tarazepide or L-364,718). Pretreatment with luzindole, an antagonist of melatonin MT(2) receptor failed to affect melatonin- or L-tryptophan-induced amylase secretion. Administration of melatonin (1, 5 or 25 mg/kg i.p.) or L-tryptophan (10, 50 or 250 mg/kg i.p.) to the rats resulted in the dose-dependent increase of cholecystokinin (CCK) plasma immunoreactivity. Enzyme secretion from isolated pancreatic acini was not significantly affected by melatonin or L-tryptophan used at doses of 10(-8) -10(-5) M. We conclude that exogenous melatonin, as well as that produced endogenously from L-tryptophan, stimulates pancreatic enzyme secretion in vivo while increasing CCK release. Stimulatory effect of melatonin or L-tryptophan on the exocrine pancreas involves vagal sensory nerves and the CCK release by these substances.

Bile salt-induced hepatocyte apoptosis involves epidermal growth factor receptor-dependent CD95 tyrosine phosphorylation

BACKGROUND & AIMS

Hydrophobic bile acids induce CD95-dependent hepatocyte apoptosis.

METHODS

The mechanisms of bile acid-induced CD95 activation were studied in 24-hour cultured rat hepatocytes, in situ-perfused rat livers, and livers from bile duct-ligated rats.

RESULTS

Within 1 minute, the proapoptotic bile salts taurolithocholate-3-sulfate and glycochenodeoxycholate induced oxidative stress and EGF receptor (EGF-R) tyrosine phosphorylation followed by rapid c-Jun-N-terminal kinase (JNK) activation. Thereafter, EGF-R associated with CD95 with subsequent CD95 tyrosine phosphorylation, CD95 membrane targeting, and death-inducing signal complex (DISC) formation. All of these responses were also triggered by taurochenodeoxycholate except that DISC formation only occurred in the presence of phosphatidylinositol 3-kinase inhibitors. No activation of EGF-R or CD95 was observed with tauroursodeoxycholate or taurocholate. Taurolithocholate-3-sulfate-induced EGF-R phosphorylation was sensitive to N-acetylcysteine (NAC) and genistein, whereas CD95/EGF-R association was inhibited by NAC, JNK, or protein kinase C inhibition but not by AG1478. However, the latter compound as well as NAC, genistein, inhibition of JNK, or protein kinase C inhibited CD95 tyrosine phosphorylation, membrane trafficking, and DISC formation.

CONCLUSIONS

Induction of apoptosis by hydrophobic bile salts involves EGF-R activation and EGF-R-dependent CD95 tyrosine phosphorylation, which triggers CD95 membrane targeting and Fas-associated death domain/caspase-8 recruitment. The latter step is apparently also controlled by phosphatidylinositol 3-kinase.