Nitric oxide effect on colonocyte metabolism: co-action of sulfides and peroxide

Luminal levels of nitric oxide/nitrite are high in colitis. Whether nitric oxide is injurious or protective to human colonocytes is unknown and the role of nitric oxide in the genesis of colitis unclear. The aims were to establish whether nitric oxide was injurious to oxidation of substrates (n-butyrate and D-glucose) in isolated human and rat colonocytes both alone and in the presence of hydrogen sulfide and hydrogen peroxide, agents implicated in cell damage of colitis. Nitric oxide generation from S-nitrosoglutathione was measured by nitrite appearance. Colonocytes were isolated and incubated with [1-14C] butyrate or [6-14C] glucose and 2.6 microM nitric oxide, 1.5 mM sodium hydrogen sulfide or 2.5 mM hydrogen peroxide. Acyl-CoA esters were measured by high performance liquid chromatography, 14CO2 radiochemically and lactate/ketones by enzymic methods. Results indicate that nitric oxide very significantly (p < .001) reduced acyl-CoA formation but did not impair 14CO2 generation. Peroxide and sulfide with nitric oxide resulted in significant reduction (p < 0.01) of substrate oxidation to CO2. Sulfide significantly stimulated release of nitric oxide from S-nitrosoglutathione. The principal conclusion is that nitric oxide diminishes CoA metabolism in colonocytes. CoA depletion has been observed in chronic human colitis for which a biochemical explanation has been lacking. For acute injurious action in human colonocytes nitric oxide requires co-action of peroxide and sulfide to impair oxidation of substrates in cells. From current observations treatment of colitis should aim to reduce simultaneously nitric oxide, peroxide and sulfide generation in the colon.