Molly Jacob

Indomethacin-induced mitochondrial dysfunction and oxidative stress in villus enterocytes

Nonsteroidal anti-inflammatory drugs (NSAIDs) are known to cause small intestinal damage but the pathogenesis of this toxicity is not well established. Intestinal epithelial cells are thought to be affected by these drugs in the course of their absorption. These cells are of different types, viz. villus, middle and crypt cells. There is little information on which of these cells, if any, are particularly vulnerable to the effects of NSAIDs. This paper aimed to study the effects of indomethacin, an NSAID commonly used in toxicity studies, on different populations of enterocytes. Effects of the drug were assessed in terms of oxidative damage, mitotic activity, mitochondrial function and lipid composition in enterocytes isolated from the small intestine of rats that had been orally administered indomethacin. In addition, the effects of arginine and zinc in protecting against such changes were assessed. Cell viability, tetrazolium dye (MTT) reduction and oxygen uptake were significantly reduced in villus tip cells from rats dosed with the drug. Thymidine uptake was higher in the crypt cell fraction from these rats. Similarly, products of lipid peroxidation were elevated in the villus tip cells with a corresponding decrease in the level of the anti-oxidant, alpha-tocopherol. In isolated mitochondrial preparations from various enterocyte fractions, significant functional impairment and altered lipid composition were seen mainly in mitochondria from villus cells. Arginine and zinc pre-treatment were found to protect against these effects. These results suggest for the first time that the villus tip cells are more vulnerable to the damaging effects of indomethacin and that oxidative stress is possibly involved in this damage.

Indomethacin-induced free radical-mediated changes in the intestinal brush border membranes.

Nonsteroidal anti-inflammatory drugs (NSAIDs) cause small intestinal damage but the pathogenesis of this toxicity is not well established. Our earlier work has shown that villus enterocytes are most susceptible to the effects of indomethacin, a commonly used NSAID. This study looked at the acute effect of indomethacin on brush border membranes (BBM), which are present mainly in the villus cells and are in immediate contact with the contents of the small intestinal lumen. Evidence of oxidative stress was found in the mucosa of the small intestine of rats dosed with indomethacin, as indicated by increased activity of xanthine oxidase with corresponding decrease in the levels of several free radical scavenging enzymes. These changes were associated with an increase in peroxidation parameters in the BBM and a fall in the level of alpha-tocopherol. These BBM also exhibited impairment in glucose transport. Significant changes were seen in the lipid composition of these membranes, with upregulation of an 85kDa isoform of phospholipase A(2). Pretreatment of animals with allopurinol, arginine or zinc protected against these effects of indomethacin. Thus this study suggests that in an acute model of indomethacin dosing there is impairment in structure and function of the BBM in enterocytes, with the effects possibly mediated by free radicals and phospholipases.

How reliable an indicator of inflammation is myeloperoxidase activity

BACKGROUND Myeloperoxidase (MPO) and interleukin-6 (IL-6) are often used as markers of inflammation. The aim of this study was to ascertain whether MPO activity is as reliable as IL-6 as an indicator of inflammation. METHODS Inflammation was induced in mice, using either turpentine or indomethacin. Duodenal tissue was removed from these animals at various time periods ranging from 6 h to 7 days later. Concentrations of IL-6 and MPO activity were estimated in the tissue. Histopathological examination was also carried out at some of the time periods to determine the presence of neutrophil infiltration in turpentine-treated mice. RESULTS Concentrations of IL-6 and MPO activity were significantly higher in tissue that had been treated with the agents used, at all the time periods studied, when compared with corresponding control tissue. Fold-increases in MPO activity were higher than fold-increases in IL-6. Concentrations of the 2 parameters showed significant positive correlation. Histopathological examination did not show significantly higher numbers of neutrophils infiltrating the tissue in response to turpentine, at the time periods studied. CONCLUSIONS Estimation of MPO activity is a reliable indicator of inflammation, being more sensitive than histopathological examination of tissue and as good as measurement of IL-6 concentrations.

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 indomethacin-induced small intestinal damage

The use of NSAIDs (non-steroidal anti-inflammatory drugs), although of great therapeutic value clinically, is limited by their tendency to cause mucosal damage in the gastrointestinal tract. In the small intestine, the effects these drugs have been shown to produce include inhibition of cyclo-oxygenase, mitochondrial dysfunction and free radical-induced oxidative changes, all of which contribute to the mucosal damage seen. Glutamine is a fuel preferentially used by enterocytes and is known to contribute to maintaining the integrity of these cells. In the present study, we investigated the effect of glutamine on indomethacin-induced changes in the small intestinal mucosa. Rats were given 2% glutamine or glutamic acid or isonitrogenous amino acids, glycine or alanine, in the diet for 7 days. Indomethacin was then administered orally at a dose of 40 mg/kg of body weight. After 1 h, the small intestine was removed and used for the measurement of parameters of oxidative stress and mitochondrial and BBM (brush border membrane) function. Evidence of oxidative stress was found in the mucosa of the small intestine of drug-treated rats, as indicated by significantly increased activity of xanthine oxidase (P < 0.001) and myeloperoxidase (P < 0.001), with corresponding decreases in the levels of several free radical scavenging enzymes and alpha-tocopherol (P < 0.001 in all cases). Levels of products of peroxidation were also significantly elevated (P < 0.001 for all the parameters measured). In addition, oxidative stress was evident in isolated intestinal mitochondria and BBMs (P < 0.001 for all the parameters measured), with associated alterations in function of these organelles (P < 0.001 for all the parameters measured). Supplementation of the diet with glutamine or glutamic acid prior to treatment with indomethacin produced significant amelioration in all the effects produced by the drug in the small intestine (P < 0.001 for all the parameters measured). Glycine and alanine were found to be much less effective in these respects.

BMPER Protein Is a Negative Regulator of Hepcidin and Is Up-regulated in Hypotransferrinemic Mice

Background: The mechanism by which anemia results in lowered hepcidin levels is not clear. Results: Bone morphogenetic protein (BMP)-binding endothelial cell precursor-derived regulator (BMPER), a known BMP antagonist, was found to be up-regulated in anemic Trfhpx/hpx mice and to suppress hepcidin transcription both in vivo and in vitro. Conclusion: BMPER is involved in suppressing hepcidin levels in Trfhpx/hpx mice. Significance: BMPER is a novel regulator of hepcidin and iron metabolism. The BMP/SMAD4 pathway has major effects on liver hepcidin levels. Bone morphogenetic protein-binding endothelial cell precursor-derived regulator (Bmper), a known regulator of BMP signaling, was found to be overexpressed at the mRNA and protein levels in liver of genetically hypotransferrinemic mice (Trfhpx/hpx). Soluble BMPER peptide inhibited BMP2- and BMP6-dependent hepcidin promoter activity in both HepG2 and HuH7 cells. These effects correlated with reduced cellular levels of pSMAD1/5/8. Addition of BMPER peptide to primary human hepatocytes abolished the BMP2-dependent increase in hepcidin mRNA, whereas injection of Bmper peptide into mice resulted in reduced liver hepcidin and increased serum iron levels. Thus Bmper may play an important role in suppressing hepcidin production in hypotransferrinemic mice.

Zinc prevents indomethacin-induced renal damage in rats by ameliorating oxidative stress and mitochondrial dysfunction

The clinical utility of non-steroidal anti-inflammatory drugs (NSAIDs) is limited by their gastrointestinal and renal toxicities. Indomethacin (an NSAID commonly used in toxicity studies) has been shown to induce significant oxidative stress and mitochondrial dysfunction in the rat kidney. The current study was designed to assess the potential of zinc, a known antioxidant, to protect the kidney against these drug-induced effects. Male Wistar rats were pre-treated with zinc sulphate (50 mg/kg) and dosed with indomethacin (20 mg/kg) by oral gavage. Rats were sacrificed 24 h after the dose of indomethacin. Parameters of oxidative stress, mitochondrial function and lipid content of the mitochondrial membranes were measured in the kidneys of these animals. It was found that zinc significantly attenuated indomethacin-induced oxidative stress, mitochondrial dysfunction and changes in the lipids in mitochondrial membranes in the kidney. The content of metallothionein, a cysteine-rich zinc-binding protein, was also determined in the tissue. There was no significant induction of metallothionein in the kidney in zinc-treated animals. Estimation of serum creatinine showed that zinc seemed to hasten functional recovery of the kidney following indomethacin administration. We conclude that pretreatment with zinc is effective in protecting against indomethacin-induced changes in the rat kidney. This protective effect does not appear to be mediated by metallothionein.

Clinical predictors of serum clozapine levels in patients with treatment-resistant schizophrenia

Fixed oral doses of clozapine produce up to 45-fold interindividual variability among its serum levels in patients with treatment-resistant schizophrenia. Although the relationship between serum clozapine level and its therapeutic response is uncertain, the presence of a therapeutic window and level-dependent adverse effects require the estimation of serum clozapine levels. As routine therapeutic drug monitoring of clozapine is not feasible in many clinical settings, identification of clinical predictors of serum clozapine levels is desirable. Hence, we aimed to evaluate the clinical variables associated with serum clozapine levels. We assessed the sociodemographic and clinical profiles, cognition, disability and psychopathology of 101 consecutive patients with treatment-resistant schizophrenia on a stable dose of clozapine, using standard assessment schedules. We determined their serum clozapine levels using high-performance liquid chromatography with ultraviolet detection. While employing multivariate robust regression models, oral clozapine dose (P<0.001), caffeine intake (P=0.04) and Valproate comedication (P=0.005) were associated with serum clozapine levels. Serum clozapine levels above 750 ng/ml increased the risk of seizures (odds ratio 5.15; P=0.03). Clinical variables are useful to model a dosing nomogram for serum clozapine levels. The importance of caffeine consumption and Valproate comedication should be considered during clozapine dose adjustments to enhance its therapeutic response and safety profile.

Effects of indomethacin on energy metabolism in rat and human jejunal tissue in vitro.

Non-steroidal anti-inflammatory drugs (NSAIDs) are known to cause enteropathy, but the mechanism by which this toxicity occurs is less well established. This paper sets out to test the hypothesis that these drugs affect oxidative phosphorylation in jejunal tissue, thereby interfering with energy metabolism and rendering the tissue vulnerable to damage. Jejunal tissue obtained from rats and humans was used for in vitro determinations of oxygen uptake, lactate production and energy charge levels in the presence of indomethacin, a commonly used NSAID. In the rat jejunal tissue, drug concentrations of 0.5 mM and 2.5 mM produced significant decreases in oxygen uptake (P<0.01) and energy charge levels in the tissue (P<0.05). There was a corresponding increase in lactate production by the tissue at these indomethacin concentrations (P<0.05). Rat jejunum examined by electron microscopy after incubation with various concentrations of indomethacin showed ultrastructural effects of the drug on mitochondrial morphology. In human tissue, an inhibitory effect of indomethacin on oxygen uptake was seen, but the effects on lactate production and energy charge were less conclusive. These findings suggest that indomethacin affects mitochondria and thereby impairs energy metabolism in jejunal tissue.

Zinc protects against indomethacin-induced damage in the rat small intestine.

The clinical utility of nonsteroidal anti-inflammatory drugs (NSAIDs) is often limited by the adverse effects that they produce in the small intestine. Alterations in the composition and functions of the glycocalyx and brush border membranes of the rat small intestine have been shown to occur in response to indomethacin, an NSAID often used in the study of adverse effects of these drugs. The micronutrient, zinc, has been documented to have cytoprotective effects in the gastrointestinal tract. The aim of this study was to evaluate the potential of zinc to reduce indomethacin-induced small intestinal damage. We pre-treated rats with zinc sulphate (50 mg/kg body weight) 2h before administration of indomethacin (20 mg/kg body weight) and sacrificed the rats 1, 12 or 24h after indomethacin. The extent of small intestinal mucosal damage and the content of lipids and sugars in the mucosa were determined. Bacterial counts in the intestinal lumen and the mucosa were ascertained. Activities of matrix metalloproteinases (MMPs) and levels of metallothionein in the mucosa were also measured. Pre-treatment with zinc sulphate was found to reduce the extent of indomethacin-induced mucosal damage. It also prevented drug-induced changes in the content of lipids and sugars in the mucosa. Drug-induced increases in activities of the MMPs and bacterial counts in the intestine were also attenuated by zinc. Metallothionein levels were significantly higher in animals pre-treated with zinc. We conclude that zinc was effective in protecting against indomethacin-induced small intestinal damage and suggest that it may do so by induction of metallothionein.