K.A. Balasubramanian

Enterocyte viability and mitochondrial function after graded intestinal ischemia and reperfusion in rats

Ischemia/reperfusion of the small intestine can lead to metabolic and structural alterations in the mucosa. Cellular dysfunction occurs when mitochondrial metabolism is compromised, which may ultimately lead to impaired organ function. The aims of this study were to assess the suppression of cellular and mitochondrial oxidative metabolism and involvement of mitochondria in the ischemia/reperfusion injury. The mitochondria were prepared from isolated enterocytes obtained from the small intestine of anesthetized adult rats following different time periods of ischemia and ischemia followed by 5 min reperfusion. Cellular and mitochondrial function were assessed using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) reduction assay. Ischemia of increasing time periods caused a progressive decrease in cellular and mitochondrial MTT reduction in enterocytes and reperfusion showed further decrease of MTT formazan formation. Inclusion of 1 mM succinate, as respiratory subs trate, showed reversal of suppression of mitochondrial function in 30-60 min ischemia whereas 90 min ischemia or short time period ischemia followed by 5 min reperfusion indicated an irreversible damage to mitochondria. This study indicated that mitochondria are a sensitive target of damage due to oxygen deficiency and possibly due to sudden burst of oxygen free radicals. Mitochondria can withstand short periods of ischemia whereas long duration ischemia or reperfusion results in irreversible damage to mitochondrial function. (Mol Cell Biochem 167: 81-87, 1997)

Colonic mucosal antioxidant enzymes and lipid peroxide levels in normal subjects and patients with ulcerative colitis

Abstract Oxygen‐derived free radicals have been implicated in the pathogenesis of ulcerative colitis. Mammalian tissues contain antioxidant systems that offer protection from the damaging effect of these active species. In the present study, the activity of the antioxidant enzymes catalase, glutathione peroxidase, glutathione transferase and glutathione reductase were measured in rectal biopsies from patients with ulcerative colitis and compared with that obtained from normal subjects. A significant decrease in the activity of glutathione transferase was observed in ulcerative colitis (48.32 ± 6.73 units/mg protein, mean ± s.e.) compared to normal (68.20 ± 6.83; P= 0.015). There was no difference in the activity of other antioxidant enzymes between controls and ulcerative colitis. Myeloperoxidase, a marker for neutrophil infiltration, was considerably increased in ulcerative colitis while malonaldehyde, the end product of lipid peroxidation, was not increased. The reduced activity of glutathione transferase in ulcerative colitis may be an additional factor in the pathogenesis of mucosal damage in this disease.

Circulating antioxidants in ulcerative colitis and their relationship to disease severity and activity

Oxygen free radicals produced by neutrophils are important in the pathogenesis of mucosal damage in ulcerative colitis. Vitamin A, vitamin E and cysteine in the plasma can scavenge free radicals. In the present study, plasma levels of vitamin A, vitamin E, cysteine, cystine and protein‐bound cysteine were measured in active ulcerative colitis before and immediately after treatment of the active disease, and correlated with disease severity, extent and activity. Plasma vitamin A and cysteine were significantly reduced in active ulcerative colitis compared with controls. Levels of vitamin E, cystine and protein‐bound cysteine were not significantly altered in active ulcerative colitis. Vitamin A and cysteine concentrations returned to normal levels (P< 0.05) within 2 weeks of treating active colitis. There were significant negative correlations between clinical severity and the plasma concentrations of vitamin A and cysteine. Plasma cysteine levels also correlated inversely to disease extent. Depletion of the circulating antioxidants, vitamin A and cysteine, in active ulcerative colitis is likely to be important in the pathophysiology of the disease.

Liver injury in acute fatty liver of pregnancy: Possible link to placental mitochondrial dysfunction and oxidative stress

Acute fatty liver of pregnancy (AFLP) is a rare disorder which is fatal if not recognized and treated early. Delivery of the feto‐placental unit results in dramatic improvement in maternal liver function, suggesting a role for the placenta. However, the mechanisms by which defects in the fetus or placenta lead to maternal liver damage are not well understood and form the focus of this study. Placenta and serum were obtained at delivery from patients with AFLP, and placental mitochondria and peroxisomes were isolated. Placental mitochondrial function, oxidative stress, and fatty acid composition as well as serum antioxidants, oxidative and nitrosative stress markers, and fatty acid analysis were carried out. Hepatocytes in culture were used to evaluate cell death, mitochondrial function, and lipid accumulation on exposure to fatty acids. Oxidative stress was evident in placental mitochondria and peroxisomes of patients with AFLP, accompanied by compromised mitochondrial function. Increased levels of arachidonic acid were also seen in AFLP placenta when compared to control. Patients with AFLP also had a significant increase in oxidative and nitrosative stress markers in serum, along with decreased antioxidant levels and elevated levels of arachidonic acid. These levels of arachidonic acid were capable of inducing oxidative stress in hepatocyte mitochondria accompanied by induction of apoptosis. Exposure to arachidonic acid also resulted in increased lipid deposition in hepatocytes. Conclusion: Oxidative stress in placental mitochondria and peroxisomes is accompanied by accumulation of toxic mediators such as arachidonic acid, which may play a causative role in maternal liver damage seen in AFLP. (HEPATOLOGY 2010;51:191–200.)

Fatty acids influence binding of cobalt to serum albumin in patients with fatty liver

Human serum albumin binds ligands such as fatty acids and metals in circulation. Oxidative stress can modify albumin and affect ligand binding. This study examines the role of oxidative stress and fatty acids in modulating cobalt binding to albumin in patients with fatty liver. Elevated levels of malondialdehyde and protein carbonyls, indicative of oxidative stress were evident in serum of patients with fatty liver. A significant decrease in albumin-cobalt binding was also observed. Albumin isolated from patient serum also showed an increase in bound fatty acids. In vitro experiments indicated that while oxidant exposure or removal of fatty acids independently decreased cobalt binding to albumin, removal of fatty acids from the protein prior to oxidant exposure did not influence the oxidant effect on albumin-cobalt binding. These results suggest that oxidative stress and fatty acids on albumin can influence albumin-cobalt binding in patients with fatty liver by independent mechanisms.

Early activation of mucosal dendritic cells and macrophages in acute Campylobacter colitis and cholera: An in vivo study

Background and Aim:u2002 Macrophages and dendritic cells are closely related mononuclear phagocytic cells. Little is known about their in vivo role in acute intestinal bacterial infections in humans. We undertook to evaluate these cells in rectal mucosal biopsies of patients with acute colitis.

Luminal exposure of oxidamts alter colonic absorptive function

The colonic lumen is likely to contain oxidants derived from unabsorbed dietary materials including transition metals, rancid fat, drugs and bacterial metabolites. The present study looks at the effect of luminal exposure of different oxidants on colonic mucosal lipid peroxidation and absorptive function. All the oxidants tested induced fluid and electrolyte secretion and indomethacin, a prostaglandin synthesis inhibitor reversed this effect. Oxidants did not induce mucosal lipid peroxidation. This study suggests that oxidants induce functional alterations in colon possibly through stimulation of prostaglandin generation without influencing mucosal lipid peroxidation.

Acute fatty liver of pregnancy: an update on mechanisms

Acute fatty liver of pregnancy (AFLP), characterized by hepatic microvesicular steatosis, is a sudden catastrophic illness occurring almost exclusively in the third trimester of pregnancy. Defective fatty acid oxidation in the fetus has been shown to be associated with this disease. Since the placenta has the same genetic makeup as the fetus and as AFLP patients generally recover following delivery, we hypothesized that the placenta might be involved in pathogenesis of this disease. In an animal model of hepatic microvesicular steatosis (using sodium valproate), we found that microvesicular steatosis results in mitochondrial structural alterations and oxidative stress in subcellular organelles of the liver. In placentas from patients with AFLP, we observed placental mitochondrial dysfunction and oxidative stress in subcellular organelles. In addition, defective placental fatty acid oxidation results in accumulation of toxic mediators such as arachidonic acid. Escape of these mediators into the maternal circulation might affect the maternal liver resulting in microvesicular steatosis.

Isolation of Human Small Intestinal Brush Border Membranes Using Polyethylene Glycol and Effect of Exposure to Various Oxidants In Vitro

This study presents a method of brush border membrane (BBM) preparation from the human small intestine using polyethylene glycol (PEG) precipitation and also looks at the effect of in vitro oxidant exposure on structural and functional alterations in the membrane. Isolated BBM were relatively pure as judged by 10- to 14-fold enrichment of marker enzymes with less than 1% contamination by other subcellular organelles. These membranes showed uphill transport of glucose and lipid analysis showed a cholesterol–phospholipid (C/P) ratio of 1.19. Isolated BBM were found to be susceptible to superoxide generated by xanthine oxidase (XO), resulting in lipid and protein oxidation along with altered glucose uptake. Superoxide exposure also resulted in phospholipid alterations, especially generation of lyso phospholipids. These changes were prevented by inhibiting XO by allopurinol or scavenging superoxide by superoxide dismutase (SOD). Other oxidants studied did not have significant affect on these membranes. These studies suggest that PEG can be used for preparation of BBM from the human small intestine and these membranes undergo structural and functional alterations on exposure to superoxide.

The Hibernating Bear—A Good Analogy to Explain Why Acute Fatty Liver of Pregnancy Manifests in Late Pregnancy

The Hibernating Bear—A Good Analogy to Explain Why Acute Fatty Liver of Pregnancy Manifests in Late Pregnancy