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The liver enzymes aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lactate dehydrogenase (LDH) are commonly used but not specific markers to quantify hepatic injury. In this in vivo study it was determined whether hepatic expression and serum levels of the microRNAs (miRNA) miR-122, -21 and -223 are altered and correlated with the release of liver enzymes after warm hepatic ischaemia and reperfusion (IR). Male Wistar rats were subjected to either 45 min of partial (70%) hepatic ischaemia and 240 min of reperfusion (n=7) or sham operation (n=5). Expression levels of miR-122, -21 and -223 were analysed in serum and liver tissue by quantitative polymerase chain reaction and tested for correlation with serum activities of AST, ALT and LDH. The relative expression levels of circulating miR-122 increased after IR and correlated with the serum activity of AST, ALT and LDH. Neither increased serum level of miR-21 nor elevated relative hepatic expression of miR-223 correlated with the serum activity of liver enzymes. The hepatic expression of miR-122 was unaffected by IR. The correlation between circulating miR-122 expression levels and liver enzyme activity qualifies miR-122 as a potential biomarker of warm hepatic IR injury.

Background: Heparanase modulates the level of heparan sulfate proteoglycans (HSPGs) which have an important role in multiple cellular processes. Recent studies indicate that HSPGs have an important function in hepatic lipoprotein handling and processes involving removal of lipoprotein particles., Principal Findings: To determine the effects of decreased HSPGs chain length on lipoprotein metabolism and atherosclerosis, transgenic mice over-expressing the human heparanase gene were studied. Hepatic lipid uptake in hpa-Tg mice were evaluated by giving transgenic mice oral fat loads and labeled retinol. Sections of aorta from mice over-expressing heparanase (hpa-Tg) and controls (C57/BL6) fed an atherogenic diet were examined for evidence of atherosclerosis. Heparanase over-expression results in reduced hepatic clearance of postprandial lipoproteins and higher levels of fasting and postprandial serum triglycerides. Heparanase over-expression also induces formation of fatty streaks in the aorta. The mean lesion cross-sectional area in heparanase over-expressing mice was almost 6 times higher when compared to control mice (23,984 µm(2)±5,922 vs. 4,189 µm(2)±1,130, p<0.001)., Conclusions: Over-expression of heparanase demonstrates the importance of HSPGs for the uptake of intestinal derived lipoproteins and its role in the formation of fatty streaks.

Glutamine synthetase (GS) in the liver is restricted to a small perivenous hepatocyte population and plays an important role in the scavenging of ammonia that has escaped the periportal urea-synthesizing compartment. We examined the effect of a single intraperitoneal injection of lipopolysaccharide (LPS) in vivo on glutamine synthesis in rat liver. LPS injection induced expression of inducible nitric oxide synthase, which was maximal after 6 to 12 hours but returned toward control levels within 24 hours. Twenty-four hours after LPS injection, an approximately fivefold increase in tyrosine-nitrated proteins in liver was found, and GS protein expression was decreased by approximately 20%, whereas GS activity was lowered by 40% to 50%. GS was found to be tyrosine-nitrated in response to LPS, and immunodepletion of tyrosine-nitrated proteins decreased GS protein by approximately 50% but had no effect on GS activity. Together with the finding via mass spectrometry that peroxynitrite-induced inactivation of purified GS is associated with nitration of the active site tyrosine residue, our data suggest that tyrosine nitration critically contributes to inactivation of the enzyme. In line with GS inactivation, glutamine synthesis from ammonia (0.3 mmol/L) in perfused livers from 24-hour LPS-treated rats was decreased by approximately 50%, whereas urea synthesis was not significantly affected. In conclusion, LPS impairs hepatic ammonia detoxification by both downregulation of GS and its inactivation because of tyrosine nitration. The resulting defect of perivenous scavenger cell function with regard to ammonia elimination may contribute to sepsis-induced development of hyperammonemia in patients who have cirrhosis.

Mice bearing IL-1beta-secreting tumor were used to study the chronic effect of IL-1beta on glucose metabolism. Mice were injected with syngeneic tumor cells transduced with the human IL-1beta gene. Serum IL-1beta levels increased exponentially with time. Secretion of IL-1beta from the developed tumors was associated with decreased food consumption, reduced body weight, and reduced blood glucose levels. Body composition analysis revealed that IL-1beta caused a significant loss in fat tissue without affecting lean body mass and water content. Hepatic phosphoenolpyruvate carboxykinase and glucose-6-phosphatase activities and mRNA levels of these enzymes were reduced, and 2-deoxy-glucose uptake by peripheral tissues was enhanced. mRNA levels of glucose transporters (Gluts) in the liver were determined by real-time PCR analysis. Glut-3 mRNA levels were up-regulated by IL-1beta. Glut-1 and Glut-4 mRNA levels in IL-1beta mice were similar to mRNA levels in pair-fed mice bearing nonsecreting tumor. mRNA level of Glut-2, the major Glut of the liver, was down-regulated by IL-1beta. We concluded that both decreased glucose production by the liver and enhanced glucose disposal lead to the development of hypoglycemia in mice bearing IL-1beta-secreting tumor. The observed changes in expression of hepatic Gluts that are not dependent on insulin may contribute to the increased glucose uptake.

Chronic secretion of interleukin-6 (IL-6) in mice causes metabolic alteration in the liver, leading to increased synthesis of hepatic cholesterol and fatty acids (FA). Mice were injected with allogeneic tumor cells transduced with the murine IL-6 gene. During the 3 wk after tumor inoculation, elevated serum IL-6 levels were associated with increased spleen and liver weight. Histological examination of sections from the liver showed increased hepatocyte proliferation, resulting in liver enlargement. Body composition analysis revealed that IL-6 caused a significant loss in fat tissue without affecting lean body mass and water content. Hepatic de novo synthesis of FA and cholesterol, as measured by (3)H(2)O incorporation, was three to five times as high in mice secreting IL-6 (IL-6 mice) as in pair-fed mice bearing nonsecreting tumors. This increase in FA and cholesterol synthesis is sufficient to maintain hepatic triglyceride secretion at levels comparable with those of pair-fed mice bearing nonsecreting tumors and, presumably, is the main source of cholesterol and FA-phospholipids necessary for hepatocyte proliferation.

Mice bearing interleukin-6 (IL-6)-secreting tumor were used to study the chronic effect of IL-6 on carbohydrate metabolism. Mice were injected with allogeneic tumor cells transduced with the murine IL-6 gene. Serum IL-6 levels were correlated exponentially with tumor weight. Secretion of IL-6 from the developed tumors was associated with decreased food consumption, reduced body weight, and reduced blood glucose levels. Insulin levels did not change, and 2-deoxyglucose uptake was not affected in most tissues examined. A significant increase of 2-deoxyglucose uptake was measured in the liver. Glycogen content in the liver determined 0, 6, 12, and 18 days after tumor inoculation was 42, 23, 12, and 3 mg/g, respectively. The activity of phosphoenolpyruvate carboxykinase was not affected. The activity of glucose-6-phosphatase (G-6-Phase) determined 6, 12, and 18 days after tumor injection was 84, 70, and 50% of G-6-Pase activity in pair-fed mice bearing nonsecreting tumors, respectively. G-6-Pase mRNA levels were markedly reduced due to inhibition of G-6-Pase gene transcriptional rate.