Effect of soy products on methotrexate toxicity in rats.

Several experiments were conducted to determine the effect of various soy products on methotrexate (MTX) toxicity. Products tested included soybean meal, soybean concentrate, soybean isolate and soybean fiber, which were provided as replacements for casein or cornstarch in a semipurified diet. Soybean meal and soybean concentrate offered the greatest protection, completely alleviating MTX-induced anorexia and diarrhea when included as the sole protein source and fed 14 d prior to and 7 d following intraperitoneal MTX injection at 20 mg/kg body weight. Positive responses also were observed with soybean isolate and soybean fiber. Histological examination of the small intestine of MTX-injected animals revealed that soybean concentrate and soybean isolate prevented the necrosis observed in animals fed the casein-based semipurified diet. Methotrexate levels in plasma were similar for animals fed semipurified diets in which protein was supplied by casein, soybean concentrate or soybean isolate. Thus, altered plasma MTX levels did not explain the differences among protein sources in ameliorating MTX-induced anorexia and gut toxicity. White blood cell counts were depressed by MTX in animals fed all diets.