POLYAMINES ATTENUATE JEJUNAL MUCOSAL INJURY INDUCED BY OLEIC-ACID

Effects of putrescine, spermidine, and spermine on lipid-induced injury to jejunal mucosa were assessed in anesthetized rats. Mucosal epithelial integrity was continuously monitored by measuring blood-to-lumen clearance of Cr-51-labeled EDTA. Perfusion of jejunal lumen with emulsified lipid (20 mM sodium taurocholate and 40 mM oleic acid) increased Cr-51-EDTA clearance. Addition of spermidine (0.5 mM), but not putrescine (2.0 mM) or spermine (0.25 mM), to the lipid perfusate reduced the increment in Cr-51-EDTA clearance. Histological evaluation of jejunal mucosa indicated that the epithelial lining of the villous tips was damaged by emulsified oleic acid and that this injury was ameliorated by spermidine. Pretreatment of jejunal mucosa with spermidine did not prevent disruption of mucosal integrity induced by a subsequent perfusion with emulsified lipids. Intravenous infusion of spermidine to achieve an extracellular concentration of 0.5 mM did not prevent the lipid-induced increase in Cr-51-EDTA. Spermidine also ameliorated lipid-induced disruption of Caco-2 cell monolayers in culture; this protective effect was dose dependent and was observed only when spermidine was applied to the apical aspect of the monolayers. These findings indicate that spermidine must be present on the apical portion of the epithelial cell during lipid insult. Substitution of lysine or arginine for spermidine did not reduce the extent of lipid-induced injury to jejunal mucosa, indicating that spermidine's protective effects cannot simply be attributed to its cationic nature. Spermidine did not alter the turbidity of a micellar oleic acid solution, indicating that spermidine was not removing oleic acid from the soluble phase. These findings suggest that the protective effects of spermidine are not due to an interaction with oleic acid, which precipitates the fatty acid and thereby reduces its effective concentration at the epithelial cell surface. Because the concentration of spermidine used in the present study is similar to that measured in postprandial chyme, the findings of the present study suggest a physiologically relevant role for spermidine in modulating postprandial mucosal injury.