Insight into the involvement of Kupffer cell-derived mediators in the hepatoprotective effect of glycine upon inflammation: study on rat precision-cut liver slices

Objective and design: To investigate the role of inflammatory mediators in the hepatoprotective effect of glycine against lipopolysaccharide (LPS)-induced liver injury in rats. Material or subjects: Male Wistar rats were used (N = 4 or 5 per group). Precision-cut liver slices (PCLS) were prepared for in vitro studies. Treatment: Glycine (10 mM) and LPS (10 mu g/ml) were added to the incubation medium of PCLS obtained 3 h after LPS intraperitoneal (i.p.) administration (10 mg/kg) or saline injection to rats. Glycine effects were also investigated in vivo by treating rats with a diet containing glycine (5%) during 3 days. Methods: Tissue injury was assessed by measuring adenosine triphosphate (ATP) and glycogen contents of liver tissue as well as by measuring aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) activity in the medium (in vitro) or in the serum (in vivo). Tumor necrosis factor-alpha (TNF-alpha), prostaglandin E-2 (PGE(2)) and NOx (reflecting nitric oxide production) were measured in the incubation medium or in the serum. Histological detection of both ED-2 and peroxidase activity were used as Kupffer cell markers. Student t test or two-way ANOVA were used for statistic analysis. Results: Glycine added to the culture medium increased both ATP and glycogen contents of PCLS from LPS-treated rats, reduced the production of TNF-alpha and NOx whereas PGE(2) secretion by PCLS increased. In contrast to the in vitro effect of glycine, we observed that a glycine-enriched diet decreased PGE(2) secretion in the serum after LPS challenge. Conclusion: The effect of glycine on LPS-induced mediator secretion is different considering in vitro or in vivo situations. Interestingly, glycine in vitro is able to prevent energy status depletion of PCLS occurring upon inflammation, a phenomenon probably linked to change in inflammatory mediator secretion pattern by hepatic immune cells, namely Kupffer cells.