Effect of exposure of various oxidants on rat liver and intestinal microsomes--a comparative study

Intestinal motility disorder induced by free radicals: a new model mimicking oxidative stress in gut

Literature data suggest that the inflamed intestine may be subjected to a considerable oxidative stress. Therefore, the aim of the present study was to simulate the oxidative stress in the gastrointestinal tract and to explore its effect on intestinal motility. This was attained by treating isolated segments from the rabbit jejunum and from the guinea pig ileum with 2,2'-Azobis (2-amidinopropane) dihydrochloride (ABAP), which generates peroxyl radicals by thermal decomposition. Treatment of intestinal segments with ABAP reduced the muscarinic cholinergic response to acetylcholine in both preparations and induced a dose-dependent inhibition of the spontaneous contractions in the jejunum, also in the presence of tetrodotoxin. ABAP was found to inhibit the contractile response induced by BaCl(2) in guinea pig ileum preparations. This effect was not dose-dependent and it was reversed by Bay-K 8644, which activates voltage operated L-type calcium channels. The rapid and reversible effects of ABAP suggest that it might directly affect L-type calcium channels before lipoperoxidation induction. In conclusion, the results of the present study show that ABAP could be a useful tool to simulate early contractility dysfunctions mediated by oxidative stress.

Palm versus soybean oil on intestinal recovery from malnutrition in Guinea pigs

Recent recommendations on feeding malnourished children do not provide indication on the nature of dietary lipids. Our aim was to compare the effect of palm oil (mainly saturated and monounsaturated fatty acids) and soybean oil (mainly polyunsaturated fatty acids) on the recovery from malnutrition in guinea pigs. In a first experiment, guinea pigs received a balanced (control group) or a maize (malnourished group) diet for 7, 12, and 21 d. In a second experiment, after 12 d of malnutrition, guinea pigs received a rehabilitation diet containing palm or soybean oil. Both rehabilitation diets allowed a partial recovery from the severe weight loss induced by malnutrition. Thiobarbituric acid reactive substances content, measured in intestinal homogenates, increased in malnourished guinea pigs compared with control animals (40%, p < 0.05) and returned to near control values after rehabilitation with palm (10%) but not soybean (43%) oil diet. Intestinal short-circuit current, assessed in jejunal segments mounted in Ussing chambers, increased progressively during malnutrition (p < 0.001) and returned to near control values with both rehabilitation diets. Compared with control animals, the cell turnover (Ki-67 index assessed by immunohistochemistry detection of the Ki-67 antigen) decreased after soybean (-60%, p < 0.01) but not after palm oil. These results confirm that experimental polydeficient malnutrition induces oxidative stress and dysfunction in the intestine. They show a differential effect of palm and soybean oil on these intestinal measurements, suggesting that the composition of dietary lipids may be important in the treatment of malnutrition.

Metal ion stimulation of phospholipase D-like activity of isolated rat intestinal mitochondria

Presence of phospholipase D-like (PLD) activity in the intestinal mitochondria was identified using endogenous phospholipids as substrate. The enzyme had a pH optimum of 6.5, did not show trans-phosphatidylation activity in the presence of ethanol or butanol, and the product formed was phosphatidic acid (PA). This was confirmed by separation of reaction products by high-performance liquid chromatography and analysis of composition of the PA formed which gave phosphate/fatty acid ratio of 1:2 PLD-like activity was further confirmed by the formation of ethanolamine and choline as products of enzyme action. This activity was stimulated by various metal ions; when stimulated by Mg2+ and Ba2+, it hydrolyzed both phosphatidylcholine and phosphatidylethanolamine, and when stimulated by Ca2+, it preferentially hydrolyzed phosphatidylethanolamine. There was no requirement for sodium oleate for the PLD-like activity in mitochondria. These results suggest that intestinal mitochondria have an active PLD-like enzyme which differs in certain properties from phospholipase D from other tissues.

Phospholipase D activity in the intestinal mitochondria: activation by oxygen free radicals

A prominent feature of cell damage caused by oxidative stress is morphological and functional changes in the mitochondria. The present study looked at the effect of free radical exposure on intestinal mitochondrial lipids. Free radical exposure did not alter neutral lipids, but among the phospholipids, phosphatidylethanolamine (PE) content was decreased on exposure to superoxide anion, generated by xanthine-xanthine oxidase or menadione with a concomitant increase in the level of phosphatidic acid (PA), suggesting activation of phospholipase D (PLD). This enzyme did not show transphosphatidylation activity in the presence of ethanol or butanol, and the product formed was phosphatidic acid (PA). This was confirmed by separation of reaction products by HPLC. This alteration in mitochondrial phospholipid was abolished by the presence of superoxide dismutase. Exposure to H2O2 did not have any significant effect. Activation of PLD by free radicals was further confirmed by quantitation of ethanolamine released from PE. Absence of any change in the content of lysophospholipid or diglyceride following exposure of mitochondria to superoxide ruled out the involvement of phospholipase A2 or C in the altered lipid composition. Moreover, inclusion of phospholipase A2 inhibitors, chlorpromazine, or p-bromophenacyl bromide did not prevent the generation of PA on exposure to free radicals. These findings suggest that superoxide anion stimulates intestinal mitochondrial PLD resulting in PE degradation and PA formation. These alterations in mitochondrial lipids may play a role in causing the functional alteration seen in oxidative stress.

Effect of luminal exposure of oxidants on intestinal mucosal lipid peroxidation and absorptive function

The lumen of the gastrointestinal tract is likely to have free iron and prooxidants that might generate free radicals, resulting in structural and functional damage to the absorptive cells. In the present study the effect of luminal exposure of different oxidants on intestinal mucosal lipid peroxidation and absorptive function in anaesthetized animals has been studied. Oxidants that require iron for free radical generation did not have any effect on the mucosa, whereas free radicals generated by using 2,2'azobis (2-amidino propane) dihydrochloride or menadione, which do not require iron, resulted in lipid peroxidation as assessed by malonaldehyde and conjugated diene formation and depletion of the antioxidant alpha-tocopherol. These oxidants also induced water and electrolyte secretion as studied by luminal perfusion. This observation is physiologically significant since the presence of prooxidants along with iron in the lumen may not have a damaging effect on the mucosa.