Hepatic oxidant and antioxidant systems in portacaval-shunted rats

The effect of portacaval anastomosis on the expression of glutamine synthetase and ornithine aminotransferase in perivenous hepatocytes

There is functional zonation of metabolism across the liver acinus, with glutamine synthetase restricted to a narrow band of cells around the terminal hepatic venules. Portacaval anastomosis, where there is a major rerouting of portal blood flow from the portal vein directly to the vena cava bypassing the liver, has been reported to result in a marked decrease in the activity of glutamine synthetase. It is not known whether this represents a loss of perivenous hepatocytes or whether there is a specific loss of glutamine synthetase. To answer this question, we have determined the activity of glutamine synthetase and another enzyme from the perivenous compartment, ornithine aminotransferase, as well as the immunochemical localization of both glutamine synthetase and ornithine aminotransferase in rats with a portacaval shunt. The portacaval shunt caused a marked decrease in glutamine synthetase activity and an increase in ornithine aminotransferase activity. Immunohistochemical analysis showed that the glutamine synthetase and ornithine aminotransferase proteins maintained their location in the perivenous cells. These results indicate that there is no generalized loss of perivenous hepatocytes, but rather, there is a significant alteration in the expression of these proteins and hence metabolism in this cell population.

Liver impairment after portacaval shunt in the rat: the loss of protective role of mast cells?

Mast cells are involved in various liver diseases and appear to play a broader pathogenic role than originally thought. They may participate in the splanchnic alterations related to a porto-systemic shunt. To verify this hypothesis we studied the serum and hepatic histological changes in rats four weeks after an end-to-side portacaval shunt. In this experimental model of chronic liver insufficiency we also assessed the mucosal mast cells (MMC) and connective tissue mast cells (CTMC) in the liver, mesenteric lymph nodes and small intestine, as well as the serum levels of rat mast cell protease-II (RMCP-II). The results show liver and testes atrophy, with hypoalbuminemia (p=0.0001), hyperbilirubinemia (p=0.0001) and increase in aspartate aminotransferase (p=0.004) and alanine aminotransferase (p=0.0001). Hepatic histopathology demonstrates hepatocytic necrosis and apoptosis, portal inflammation, biliary proliferation, steatosis and fibrosis. There is a decrease of MMCs and CTMCs in the liver, while in the ileum CTMCs increase and MMCs decrease. These results suggest the involvement of mast cells in the pathophysiological splanchnic impairments in this experimental model. In particular, the decreased number of liver mast cells may be associated with the hepatic atrophy. If this is the case, we propose that the disruption of the hepato-intestinal axis after a portocaval shunt in the rat could inhibit the ability of the liver to developing an appropriate repair response mediated by mast cells.

The value of microsurgery in liver research

The use of an operating microscope in rat liver surgery makes it possible to obtain new experimental models and improve the already existing macrosurgical models. Thus, microsurgery could be a very valuable technique to improve experimental models of hepatic insufficiency. In the current review, we present the microsurgical techniques most frequently used in the rat, such as the portacaval shunt, the extrahepatic biliary tract resection, partial and total hepatectomies and heterotopic and orthotopic liver transplantation. Hence, reducing surgical complications allows for perfecting the resulting experimental models. Thus, liver atrophy related to portacaval shunt, prehepatic portal hypertension secondary to partial portal vein ligation, cholestasis by resection of the extrahepatic biliary tract, hepatic regeneration after partial hepatectomies, acute liver failure associated with subtotal or total hepatectomy and finally complications derived from preservation or rejection in orthotopic and heterotopic liver transplantation can be studied in more standardized experimental models. The results obtained are therefore more reliable and facilitates the flow of knowledge from the bench to the bedside. Some of these microsurgical techniques, because of their simplicity, can be performed by researchers without any prior surgical training. Other more complex microsurgical techniques require in-depth surgical training. These techniques are ideal for achieving a complete surgical training and more select microsurgical models for hepatology research.

Plasma redox status is impaired in the portacaval shunted rat--the risk of the reduced antioxidant ability

Background

Portacaval shunting in rats produces a reduction of hepatic oxidant scavenging ability. Since this imbalance in hepatic oxidant/antioxidant homeostasis could coexist with systemic changes of oxidant stress/antioxidant status, plasma oxidants and antioxidant redox status in plasma of portacaval shunted-rats were determined.

Results

Male Wistar male: Control (n = 11) and with portacaval shunt (PCS; n = 11) were used. Plasma levels of the oxidant serum advanced oxidation protein products (AOPP), lipid hydroperoxides (LOOH), the antioxidant total thiol (GSH) and total antioxidant status (TAX) were measured. Albumin, ammonia, Aspartate-aminotransferase (AST), Alanine-aminotransferase (ALT), thiostatin and alpha-1-acid glycoprotein (α₁-AGP) were also assayed 4 weeks after the operation. AOPPs were significantly higher (50.51 ± 17.87 vs. 36.25 ± 7.21 μM; p = 0.02) and TAX was significantly lower (0.65 ± 0.03 vs. 0.73 ± 0.06 mM; p = 0.007) in PCS compared to control rats. Also, there was hypoalbuminemia (2.54 ± 0.08 vs. 2.89 ± 0.18 g/dl; p = 0.0001) and hyperammonemia (274.00 ± 92.25 vs. 104.00 ± 48.05 μM; p = 0.0001) and an increase of thiostatin (0.23 ± 0.04 vs. 0.09 ± 0.01 mg/ml; p = 0.001) in rats with a portacaval shunt. The serum concentration of ammonia is correlated with albumin levels (r = 0.624; p = 0.04) and TAX correlates with liver weight (r = 0.729; p = 0.017) and albumin levels (r = 0.79; p = 0.007)

Conclusion

These findings suggest that in rats with a portacaval shunt a systemic reduction of oxidant scavenging ability, correlated with hyperammonemia, is principally produced. It could be hypothesized, therefore, that the reduced antioxidant defences would mediate a systemic inflammation.

Mesocaval shunt inhibits primary and metastatic hepatoma growth and enhances apoptosis

BACKGROUND

Previous reports indicate that hepatocyte growth factor and other hepatic trophic factors reach the liver presumably by portal venous inflow and stimulate experimental hepatic tumor growth, invasion, and metastasis. This study tests this hypothesis by evaluating whether a mesocaval shunt (MCS) alters hepatic tumor growth, the mitotic rate, apoptosis, and incidence and growth of lung metastasis in rats with implanted hepatoma.

METHODS

Morris hepatoma (1 x 10(5)) cells were implanted intrahepatically in 19 ACI rats. One week after implantation, 10 rats underwent MCS operation and nine controls a sham operation. Rats were killed 21 days after the operation to assess tumor volume, tumor cell mitosis, apoptosis, area of tumor necrosis, pulmonary metastases and percentage of lung tumor area.

RESULTS

Mesocaval shunt induced a significant increase in the rate of tumor apoptosis (25 +/- 5 v 14 +/- 6, P < .01) and the percentage of area of tumor necrosis (29% +/- 17% v 13% +/- 8%, P < .05), a decreased tumor volume (839 +/- 1,195 v 2,909 +/- 2,572, P < .05), a reduction in tumor mitosis (70 +/- 28 v 93 +/- 11, P < .05) and decreased percentage area of pulmonary metastatic tumor (9.8 +/- 6.8 v 18.8 +/- 14, P < .05).

CONCLUSION

These observations show that growth of intrahepatic tumor is influenced by portal venous inflow and suggest that MCS or other methods of regulating portal vein flow may be useful as adjunctive therapy in the treatment of advanced hepatoma.

Lysosomal exocytosis induced by hyperthermia: a new model of cancer death. III. Effect on liver metastasis

The purpose of the present study was to evaluate by morphological approaches (light and electron microscopy), the effect of hyperthermic treatment in one case of human liver metastasis. The results demonstrate that hyperthermia causes a significant reduction of the metastatic cells circulating into sinusoids and the "normalization" of the hepatocytes substructure. The data are consistent with a direct and/or indirect action of the temperature on the presence of infiltrating tumor cells. Particular importance is attributed to a general activation of lysosomes present in neoplastic cells, Kupffer cells and hepatocytes.

The potential of the hydrocarbon breath test as a measure of lipid peroxidation

The straight chain aliphatic hydrocarbons ethane and pentane have been advocated as noninvasive markers of free-radical induced lipid peroxidation in humans. In in vitro studies, the evolution of ethane and pentane as end products of n-3 and n-6 polyunsaturated fatty acids, respectively, correlates very well with other markers of lipid peroxidation and even seems to be the most sensitive test available. In laboratory animals the use of both hydrocarbons as in vivo markers of lipid peroxidation has been validated extensively. Although there are other possible sources of hydrocarbons in the body, such as protein oxidation and colonic bacterial metabolism, these apparently are of limited importance and do not interfere with the interpretation of the hydrocarbon breath test. The production of hydrocarbons relative to that of other end products of lipid peroxidation depends on variables that are difficult to control, such as the local availability of iron(II) ions and dioxygen. In addition, hydrocarbons are metabolized in the body, which especially influences the excretion of pentane. Because of the extremely low concentrations of ethane and pentane in human breath, which often are not significantly higher than those in ambient air, the hydrocarbon breath test requires a flawless technique regarding such factors as: (1) the preparation of the subject with hydrocarbon-free air to wash out ambient air hydrocarbons from the lungs, (2) the avoidance of ambient air contamination of the breath sample by using appropriate materials for sampling and storing, and (3) the procedures used to concentrate and filter the samples prior to gas chromatographic determination. For the gas chromatographic separation of hydrocarbons, open tubular capillary columns are preferred because of their high resolution capacity. Only in those settings where expired hydrocarbon levels are substantially higher than ambient air levels might washout prove to be unnecessary, at least in adults. Although many investigators have concentrated on one marker, it seems preferable to measure both ethane and pentane concurrently. The results of the hydrocarbon breath test are not influenced by prior food consumption, but both vitamin E and beta-carotene supplementation decrease hydrocarbon excretion. Nevertheless, the long-term use of a diet high in polyunsaturated fatty acids, such as in parenteral nutrition regimens, may result in increased hydrocarbon exhalation. Hydrocarbon excretion slightly increases with increasing age. Short-term increases follow physical and intellectual stress and exposure to hyperbaric dioxygen.(ABSTRACT TRUNCATED AT 400 WORDS)