Simmy Thomas

Oxidative stress in the development of liver cirrhosis: a comparison of two different experimental models.

Background/Aims:  Oxidative stress has been implicated in liver cirrhosis. Carbon tetrachloride and thioacetamide are the most widely used models to develop cirrhosis in rats and the present study compares oxidative stress in the liver induced by these compounds at different stages of cirrhosis development.

Intestinal mucosal alterations in rats with carbon tetrachloride-induced cirrhosis: changes in glycosylation and luminal bacteria.

Spontaneous bacterial peritonitis is a major cause of mortality after liver cirrhosis. Altered permeability of the mucosa and deficiencies in host immune defenses through bacterial translocation from the intestine due to intestinal bacterial overgrowth have been implicated in the development of this complication. Molecular mechanisms underlying the process are not well known. In order to understand mechanisms involved in translocation of bacteria, this study explored the role of oxidative stress in mediating changes in intestinal mucosal glycosylation and luminal bacterial content during cirrhosis. CCl4‐induced cirrhosis in rats led to prolonged oxidative stress in the intestine, accompanied by increased sugar content of both intestinal brush border and surfactant layers. This was accompanied by changes in bacterial flora in the gut, which showed increased hydrophobicity and adherence to the mucosa. Inhibition of xanthine oxidase using sodium tungstate or antioxidant supplementation using vitamin E reversed the oxidative stress, changes in brush border membrane sugar content, and bacterial adherence. In conclusion, oxidative stress in the intestine during cirrhosis alters mucosal glycosylation, accompanied by an increased hydrophobicity of luminal bacteria, enabling increased bacterial adherence onto epithelial cells. This might facilitate translocation across the mucosa, resulting in complications such as spontaneous bacterial peritonitis. (HEPATOLOGY 2006;43:837–846.)

Renal damage in experimentally‐induced cirrhosis in rats: Role of oxygen free radicals

Cirrhosis with ascites is associated with impaired renal function accompanied by sodium and water retention. Although it has been suggested that mediators such as nitric oxide play a role in the development of renal failure in this situation, other mechanisms underlying the process are not well understood. This study examined the role of oxidative stress in mediating renal damage during the development of cirrhosis in order to understand mechanisms involved in the process. It was shown that carbon tetrachloride– or thioacetamide‐induced cirrhosis in rats results in oxidative stress in the kidney as seen by increased lipid peroxidation and protein oxidation, accompanied by altered antioxidant status. Cirrhosis was also found to affect renal mitochondrial function, as assessed by measurement of the respiratory control ratio, the swelling of mitochondria, and calcium flux across mitochondrial membranes. Increased lipid peroxidation and changes in lipid composition were evident in the renal brush border membranes, with compromised transport of 14C glucose across these membranes. In conclusion, renal alterations produced as a result of cirrhosis in the rat are possibly mediated by oxidative stress. (HEPATOLOGY 2006;43: 1248–1256.)

Oral glutamine attenuates surgical manipulation-induced alterations in the intestinal brush border membrane.

BACKGROUND Our earlier work has shown that surgical manipulation of the intestine results in oxidative stress and mucosal damage along with alterations in the brush border membrane (BBM). Glutamine feeding is known to offer protection against damage to mucosa under various conditions and this study looked at the effect of oral supplementation of glutamine or glutamic acid in the intestinal BBM alterations after surgical manipulation. MATERIALS AND METHODS Control and rats pretreated for 7 days with 2% glutamine or glutamic acid or isonitrogenous amino acids, glycine, or alanine were subjected to surgical manipulation of the intestine. BBMs were isolated from the intestine and functional and structural alterations to these membranes were assessed and compared. RESULTS Surgical manipulation resulted in oxidative stress in the enterocyte BBM and these changes included a decrease in alkaline phosphatase activity and alpha-tocopherol content along with an increase in lipid peroxidation parameters. A decrease in glucose transport by the isolated BBM vesicles suggested functional impairment. Surgical manipulation also resulted in phospholipid degradation possibly mediated by PLA(2) and membrane protease activation. Glutamine or glutamic acid supplementation prevented these changes but not by glycine or alanine. CONCLUSION This study suggests that oral glutamine or glutamic acid supplementation prior to surgery can offer protection to the intestine and this might prevent postsurgical complications.

Retinoid metabolism in the rat small intestine.

Vitamin A (retinol) is essential for epithelial cell growth, differentiation and proliferation. The absorption of retinol occurs in the small intestine, and the metabolism of this vitamin is not well studied in this organ. The intestinal epithelium has a high rate of cell proliferation and differentiation, and the present study looked at the level of retinoids and metabolizing enzymes involved in their interconversion along the villus-crypt axis under normal conditions. Intestine was removed from control rats, and enterocytes at various stages of maturation and differentiation were quantified by the metal chelation method. Using HPLC, various retinoid concentrations in the cell homogenate and the metabolizing enzymes in the cytosol were quantified. The proliferating crypt cells were found to have a higher level of retinoic acid as well as of the enzymes involved in its formation, such as retinaldehyde oxidase and retinol dehydrogenase, compared with the villus cells, suggesting a possible role for this compound in intestinal epithelial cell proliferation and differentiation. The high level of retinol and high retinaldehyde reductase activity in the villus cells suggest the important role played by this enzyme in the conversion of dietary beta-carotene to retinol via retinaldehyde. In summary, this study has given for the first time a detailed analysis of the retinoid levels and metabolizing enzymes in different cell populations in the rat small intestinal epithelium.

Heat preconditioning prevents oxidative stress-induced damage in the intestine and lung following surgical manipulation

The intestine is increasingly recognized as a primary effector of distant organ damage, such as lung, following abdominal surgery. Surgical manipulation of the intestine generates oxygen free radicals resulting in mucosal damage. Heat preconditioning has been proposed to prevent various stress‐induced alterations in cells and tissues, including oxidative stress. This study examined the effect of heat preconditioning on oxidative stress‐induced damage to the intestine and lung, following surgical manipulation.

Surgical manipulation of the intestine results in quantitative and qualitative alterations in luminal Escherichia coli.

Objectives:To look at the qualitative and quantitative changes in the luminal bacterial flora in response to surgical manipulation of the small intestine. Summary Background Data:The barrier function of the intestine is compromised in pathologic conditions, such as shock, trauma, or surgical stress. Our earlier work has shown that surgical manipulation results in oxidative stress in the intestinal mucosa leading to permeability alterations. Methods:Studies were done on rats, which were randomly divided into four groups (n = 8): group I, control, group II, III, IV different time periods, such as 8, 12, and 24 hours after surgical manipulation, which was simulated by opening the abdominal wall and handling the intestine. The cecal wall and cecal luminal contents were harvested under sterile conditions and processed for quantitation for aerobes and anaerobes. Adherence assays using Hep-2 cells were carried out on Escherichia coli isolated under different experimental conditions. In addition, control E. coli were exposed to superoxide or hydrogen peroxide, followed by subculture and adherence studies. Results:Surgical manipulation of the intestine resulted in qualitative and quantitative alterations in the aerobic bacteria. There was an increase in the number and relative proportion of E. coli in the cecal flora, and there was also an increase in adherence of E. coli to cecal mucosa, which was confirmed by in vitro bacterial adherence studies with HEp-2 cells. These changes were maximum at 12 hours following surgical manipulation and by 24 hours, this came back to control pattern. Control E. coli after in vitro exposure to oxidants also showed increased adherence. Conclusion:These studies suggest that oxidative stress in the mucosa following surgical manipulation results in alterations in the luminal bacteria leading to increased bacterial adherence onto mucosal epithelium, which may contribute to postsurgical complications.

Mild Whole-Body Heat Stress Alters Retinoid Metabolism in the Rat Small Intestine

Mild heat treatment can modulate metabolism and prevent stress-induced alterations in cells and tissues. Retinoids are known to influence cellular metabolism and are essential for growth and differentiation, particularlepithelial tissue. This study examines the effect of mild heat treatment on retinoid alterations in enterocytes in the rat small intestine. Heat treatment changed the differentiation pattern of enterocytes along the villus-crypt axis, accompanied by increases in retinol, retinaldehyde, and retinoic acid in proliferating crypt cells. Activities of retinoid metabolizing enzymes such as retinaldehyde oxidase and retinaldehyde reductase were also increased. These results suggest that mild heat treatment can alter retinoid metabolism in the small intestine, which might influence epithelial cell proliferation and differentiation.