595 ALKALINE PHOSPHATASE IS A PROTECTIVE ENZYME DURING LIVER FIBROGENESIS

Abstract

Background and Aim: Serum alkaline phosphatase (AP) levels serve as a marker for many liver diseases. Recent studies indicate that AP may act as a protective enzyme by dephosphorylation of LPS because dephosphorylation blocks toxicity of this product. Gut-derived LPS is known to aggravate liver damage and fibrosis and we hypothesized that higher levels of AP may represent a physiological response upon higher levels of this toxin during fibrosis. We therefore studied hepatic expression levels and effects of intestinal AP during fibrogenesis. Methods: Intestinal AP knock-out C57BL/6 mice (iAP KO) were examined at 6 weeks of age and compared to age-matched wildtype. Liver fibrogenesis was induced by CCl4 administration to Balb/c mice for 1 day (acute studies) or 8 weeks (chronic studies). The latter group received saline or calf-intestinal AP (5 units, i.v.), from week 6 to 8 (3x/week, n = 6/group). Results: iAP KO mice displayed higher intrahepatic expression levels of fibrogenic markers (PAR-1, Collagen I) paralleled by an increase in macrophages of the pro-fibrotic M2 phenotype relative to WT. So, lack of intestinal AP stimulates fibrogenesis within the liver. We subsequently examined intrahepatic AP expression in normal mice, after CCl4-induced acute liver damage and after chronic CCL4 administration, characterized by liver fibrosis. Results show a gradual increase in intrahepatic AP-activity from normal to fibrotic animals. Histochemical analysis revealed that this APactivity is able to dephosphorylate the lipid A moiety of LPS. We further explored the role of AP by injecting iAP to mice with CCL4-induced fibrosis. Data show a reduced hepatic AP activity, paralleled by significant lower expression levels of desmin and significant lower accumulation of M2 macrophages in iAP-treated mice compared to control. Conclusions: Based on the increased hepatic fibrogenic activity in intestinal AP-KO mice, and the attenuated fibrogenesis in fibrotic mice receiving intestinal AP, we conclude that iAP attenuates fibrosis. The enhanced expression of AP in fibrotic livers and the demonstration that this AP activity is able to dephosphorylate LPS, suggests that endogenous AP serves as a protective enzyme after liver damage. Enhanced AP activity during disease may therefore reflect a physiological response to LPS.