The effect of phospholipids and fatty acids on tight-junction permeabilityand bacterial translocation

The activity of phospholipase A(2) (PLA(2)) is elevated in the intestinal e pithelia of patients with inflammatory bowel disease (IBD). We recently rep orted that PLA(2) mediates hydrolysis of phosphatidylcholine (PC) to lysoph osphatidylcholine (L-PC) when both are applied to the apical surface of cul tured EC monolayers, resulting in increased bacterial translocation (BT) an d decreased transepithelial electrical resistance (TEER). Free fatty acids (FFA) are the other products of this reaction, however, their effect on Cac o-2 cell permeability has not been reported. In addition to PC, other lumin al phospholipids are present at the surface of the enterocyte. PLA(2) may a lso mediate the hydrolysis of luminal phospholipids other than PC. The aim of this study was to examine the effects of phospholipids other than PC and common FFA on intestinal epithelial permeability and BT. Human Caco-2 ente rocytes were grown to confluence on porous filters in the apical chamber of a two-chamber cell-culture system. Monolayer integrity and tight-junction permeability were measured as TEER. First, common FFA released by PC hydrol ysis were determined using thin-layer chromatography (TLC). In separate exp eriments, monolayers were treated with phosphatidylethanolamine (PE), lysop hosphatidylethanolamine (L-PE), or palmitoleic acid, oleic acids, linoleic acids, and arachidonic acid solubilized in solution with PC. The magnitude of BT was determined 2 h after treatment by adding Escherichia coli C25 to the apical chamber followed by quantitatively culturing basal-chamber sampl es. Statistical analysis was by the Kurosaki-Wallis test. TLC of PC samples incubated with PLA(2) on the apical surface of Caco-2 monolayers demonstra ted the production of palmitoleic acid, oleic acids, linoleic acids, and ar achidonic acid. L-PE significantly decreased TEER compared to controls, but to a lesser degree than L-PC alone. L-PE had no effects on BT. Palmitoleic acid and oleic acid likewise significantly decreased TEER compared to cont rols, however, less than L-PC. All FFA tested had no effect on BT. Phosphol ipids applied to the apical surface of enterocytes, such as those found in vivo in mucus, can be hydrolyzed by the enzyme PLA(2) resulting in lysophos pholipid and FFA species that can alter enterocyte monolayer permeability. However, FFA and L-PL, other than L-PC, appear to have no effect to stimula te BT. This observation may have clinical implications in the pathogenesis and treatment strategies for IBD patients in whom enterocyte PLA(2) activit y has been shown to be elevated.