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The role of nitric oxide (NO) in the intestinal basal ion transport and under conditions of enterotoxin-induced ion secretion is controversial. Namely it is not clear whether NO enhances or counteracts intestinal ion secretion and whether the effects on transport result from a direct interaction with the enterocyte. The cell origin of NO is also unclear. We have tested the hypothesis that NO produced by the enterocyte directly regulates ion transport processes either in basal condition or in response to cholera toxin-induced secretion. Electrical variables reflecting transepithelial ion transport were measured in Caco-2 cell monolayers mounted in Ussing chambers exposed to the NO synthase inhibitor Nomega-nitro-l-arginine methyl ester, in the presence or absence of cholera toxin. cAMP concentrations were also measured. NO release was determined by nitrite-nitrate concentration. NO synthase activities were assayed by Western blot analysis. Nomega-nitro-l-arginine methyl ester had a secretory effect, as judged by increased basal short-circuit current and cAMP concentration. It also increased cholera toxin-induced electrical response and cAMP production. Either cholera toxin or the cAMP analog 8-bromo-cAMP induced a rapidly progressive and Ca2+-dependent increase in NO concentration, suggesting a homeostatic up-regulation of the constitutive form of NO synthase. Western blot analysis showed an increase in constitutive NO synthase enzyme isoform. These results indicate that the enterocyte regulates its own ion transport processes, either in basal condition or in the presence of active secretion, through the activation of a constitutive NO synthase-NO pathway, functioning as a braking force of cAMP-induced ion secretion.

Background & Aims: Severe diarrhea and enteropathy of unknown origin are frequent in patients infected with human immunodeficiency type 1 virus (HIV-1). The HIV-1 transactivating factor protein (Tat) is a key factor in the pathogenesis of acquired immunodeficiency syndrome. We investigated whether Tat could directly induce ion secretion and cell damage in enterocytes., Methods: Electrical parameters (ion transport studies) were measured in Caco-2 cell monolayers and in human colonic mucosa specimens mounted in Ussing chambers. The effect of Tat on intestinal mucosa integrity was determined by monitoring the transepithelial electrical resistance of Caco-2 cell monolayers. (3)H-thymidine incorporation and cell count were used to evaluate the effect of Tat on cell growth. Intracellular calcium concentrations were measured at the single-cell level using microfluorometry technique., Results: Tat protein induced ion secretion in Caco-2 cells and in human colonic mucosa similar to that induced by bacterial enterotoxins. It also significantly prevented enterocyte proliferation. In both instances, the effect of Tat was maximum at concentrations within the range detected in the sera of HIV-1-infected patients. Anti-Tat antibodies inhibited both effects. Ion secretion and the antiproliferative effects were mediated by L-type Ca(2+) channels. An increase in intracellular calcium concentration in Caco-2 cells was found after addition of Tat., Conclusions: These results indicate that Tat may be involved in HIV-1-related intestinal disease through direct interaction with enterocytes.

Background: A complex interplay of malnutrition, intestinal dysfunction, and immune impairment increases the progression of human immunodeficiency virus (HIV) disease in children. The authors tested the hypothesis that nutritional support improves intestinal and immune functions in children infected with human immunodeficiency virus (HIV)., Methods: A questionnaire was circulated through reference centers for pediatric HIV infection to evaluate the effects of nutritional rehabilitation, total parenteral nutrition (TPN) and enteral nutrition (EN), in children. Information included changes in body weight, CD4 cell numbers, and intestinal absorption-as judged by the xylose load-before and after clinical nutritional support and the outcome of children., Results: Sixty-two children underwent nutritional support: 46 received TPN and 16 received EN. All but three had full-blown acquired immunodeficiency syndrome, and all were severely malnourished. Baseline clinical conditions were worse in children receiving TPN than in those receiving EN. Intestinal dysfunction was detected in all children who received xylose oral load. A significant increase in CD4 cell count, xylose levels, and body weight followed EN. A similar pattern was observed after TPN, but none of the parameters significantly changed. Twenty-seven children who received TPN and three who received EN eventually died. Fourteen who received TPN and eight who received EN were shifted to oral feeding, and five who received TPN and five who received EN continued with clinical nutritional support at the end of the observation period., Conclusions: Nutritional intervention may restore intestinal absorption and increase CD4 cell numbers. The efficacy of nutritional intervention is enhanced if provided before a terminal stage of HIV infection. These data provide evidence of a close association among nutritional condition, intestinal absorption, and immune impairment.