Microbial adhesion of Cryptosporidium parvum: Identification of a colostrum-derived inhibitory lipid

We previously described an unidentified lipid purified from calf small intestine that inhibits the in vitro adhesion of Cryptosporidium parvum sporozoites to host cells [Johnson JK, Schmidt J, Gelberg HB, Kuhlenschmidt MS. Microbial adhesion of Cryptosporidium parvum sporozoites: purification of an inhibitory lipid from bovine mucosa. J Parasitol 2004;90:980–90]. Intestinal mucosa from some calves, however, failed to yield this bioactive lipid. Accordingly, we examined other potential sources, especially dietary sources, of the inhibitory lipid and discovered it was principally derived from bovine colostrum. Interestingly, fresh colostrum yielded little or no inhibitory lipid, however, the lipid was found in relatively large quantities following incubation of colostrum with the aqueous fraction of calf intestinal contents. Using FAB-MS and NMR analysis, the sporozoite inhibitory lipid (SIL) was identified as oleic acid, a monounsaturated fatty acid likely released from colostrum triglycerides and phospholipids by digestion in the lumen of the calf small intestine. Oleic acid dose-dependently inhibited in vitro sporozoite–host cell adhesion with an inhibitory constant (IC50) of approximately 5 μM. Comparison of oleic acid with other C-18 fatty acids revealed linolenic, but not stearic acid, also displayed potent inhibitory activity. Neither linolenic nor oleic acid, however, affect either sporozoite or host cell viability at concentrations that inhibit sporozoite adhesion. These results suggest certain colostrum-derived long-chain fatty acids may serve as natural inhibitors of the early steps in C. parvum sporozoite–host cell interactions.