An unidentified inhibitor of lipid peroxidation in intestinal mucosa.

Lipid peroxidation in vitro was tested by malonaldehyde production in gastrointestinal mucosa and compared with other tissues. It was observed that gastrointestinal mucosa was resistant to both non-enzymatic and enzymatic lipid peroxidation. This was due to the presence of an inhibitor of lipid peroxidation in the membranous fractions of intestinal mucosa. This inhibitor was capable of inhibiting other recognised peroxidation systems, such as liver mitochondria. This effect was confirmed by measurement of diene conjugation and utilisation of arachidonic acid as other markers of peroxidation, in addition to malonaldehyde production. Preliminary characterisation of this inhibitor revealed that it is resistant to proteolysis, non-diffusable and extractable from membranes by organic solvents. It was partially purified by methanol extraction of the mucosa and by three successive preparative thin-layer chromatography steps. The purified material gave a single spot on thin-layer chromatography, using a number of different solvent systems. Mobility of the inhibitor on thin-layer chromatography was different from that of authentic tocopherol, and it was present in the intestine of vitamin-E-deficient animals. These results suggest that the resistance of intestinal mucosa to lipid peroxidation is due to the presence of a novel inhibitor which is lipidic in nature.