CTOLYTIC ACTION OF STORED HUMAN MILK AND ITS INHIBITION BY HUMAN SERUM ALBUMIN

In a recent experiment, we found a new cytolytic action of stored human milk that was exerted on Molt-4 and Raji cells, human leukocytes, red blood cells, and mononuclear cells found in human milk. This action was observed in about 90% of the human milk samples we examined, even those kept frozen at -20°C for 48h. Cytolysis was not seen in stored human milk heated at 56°C for 30 min or in milk treated with eserine. It was also noted that enhanced hemolysis was seen in those samples to which bile salts had been added. This suggests that the cytolytic action was induced by the action of lipoprotein lipase (LPL) and bile-salt-stimulated lipase (BSSL), both of which are found in human skims in cream (fat globules).Both fractions obtained from Pseudomonas aerginosa LPL and human milk, at the same retention time on HPLC, had hemolytic factor-producing activity. Furthermore, silica gel thin-layer chromatography revealed that the hemolytic action was due to oleic acid produced by hydrolysis of cream by LPL and BSSL during the storage period.We also observed that human serum albumin inhibited the hemolytic action of oleic acid contained in stored human milk.