New biological function of bovine alpha-lactalbumin: Protective effect against ethanol- and stress-induced gastric mucosal injury in rats

Although several studies have shown that milk protein components have a wid e range of biological activities, the potential role of these proteins in t he gastrointestinal mucosal defense system is less,well elucidated. In this study, we investigated the effect of the major proteins in cow's milk on g astric mucosal injury by using two acute ulcer models in Wistar rats. Gastr ic mucosal injury was induced by either intragastric 60% ethanol-HCl or wat er-immersion restraint stress (23 degreesC, 7h), Each test milk protein was orally administered 30 min before the induction of gastric injury. Among t he major milk proteins, alpha -lactalbumin (alpha -LA) is demonstrated to h ave a marked protective effect against ethanol-induced gastric injury, with the same potency as that of the typical antiulcer agent, Selbex, Whey prot ein isolate (WPI), which contained 25% alpha -LA, also protected against ga stric injury, while casein showed no effect, Comparative studies on the pro tective effect of the four major components of WPI, beta -lactoglobulin, al pha -LA, bovine serum albumin and alpha -globulins (immunoglobulins), on th e basis of their contents in WPI revealed that alpha -LA was responsible fo r the protective effect of WPI, being about 4-fold more effective than WPI itself, alpha -LA showed dose-dependent protection against gastric injury i nduced by stress as well as ethanol, Pretreatment with indomethacin (10 mg/ kg body weight, s.c.), which is a potent inhibitor of endogenous prostaglan din synthesis, resulted in a significant reduction in the protective effect of alpha -LA, These results indicate that alpha -LA has marked antiulcer a ctivity as an active component of cow's milk protein, and suggest that alph a -LA intake may serve to protect against gastric mucosal injury, in part t hrough endogenous prostaglandin synthesis.