HEATING UNSATURATED FATTY-ACIDS IN AIR PRODUCES HEMAGGLUTININS

When mono-unsaturated fatty acids are heated in air, they form hemaggl utinins. When the double bond is Delta-6,7 or Delta-9,10, the titer is higher than for Delta-11,12. Stearic acid does not become a hemagglut inin on heating. Hydroxy-monounsaturated fatty acids, ricinoleic (cis- 12-OH-Delta-9) and ricinelaidic (trans-12-OH-Delta-9) are not hemagglu tinins unless they are heated. Oleic acid (Delta-9-octadecenoic acid, OA) has a very low agglutination titer but lyses red cells at higher c oncentrations. Rabbit and rat erythrocytes (RBC) give the highest tite rs but RBCs of other species are also agglutinated. OA was chosen for further study. Its specific titer against rat RBCs increases with time of heating in air. Thin-layer chromatography (TLC) and mass spectrosc opy (MS) show that higher molecular weight compounds are formed and th at activity is associated with these materials. Synthetic (oxidation o f oleic acid with tert-butyl peroxide) and commercial preparations of oleic acid dimers (Emery and Unichema) and a commercial preparation of oleic trimer mixed with polymer (Emery) have high hemagglutination ti ters against rat erythrocytes. A cyclic, long-chain dicarboxylic acid, 5(6)-carboxy-4-hexyl-2-cyclohexene-1-oct acid (Westvaco) gives a very low titer unless heated and no lysis. Sialidase treatment of the red cells increases the titer. Removal of cations does not alter the titer but addition of Ca2+ or Mg2+ lowers the titer. Light microscopy was u sed to characterize and visualize the agglutination process with rat R BCs. Agglutination without lysis or fusion is observed for low concent rations of heated oleic acid and C-18 dimers and trimer-polymer prepar ations, and no large vesicles are seen. We conclude that the oligomeri c fatty acids with two or more hydrophobic chains of seven or more car bons are agglutinins at physiological pH. Agglutination by dimer may b e the result of the its two hydrophobic side chains inserting into adj acent RBC membranes or the result of dimer inserting completely into R BC membranes and altering their properties. The carboxyl groups may al so play a role in the process by interacting with polar headgroups in the RBC membrane.