title: Dairy proteins protect against dimethylhydrazine-induced intestinal cancers in rats.
abstract: The impact of different dietary protein sources (whey, casein, soybean, red meat) on the incidence, burden and mass index of intestinal tumors induced by dimethylhydrazine in male Sprague-Dawley rats was assessed. A purified diet (based on AIN-76A) with a fat concentration of 20 g/100 g and other proteins substituted for casein (20 g/100 g) was used. Whey and casein diets were more protective against the development of intestinal tumors than were the red meat or soybean diets, as evidenced by a reduced incidence of rats affected (P = 0.15), fewer tumors per treatment group (burden, P < 0.005), and a reduced pooled area of tumors (tumor mass index) that formed (P = 0.39). Intracellular concentration of glutathione, an antioxidant and anticarcinogenic tripeptide, measured in liver, was greatest in whey protein- and casein-fed rats and lowest in soybean-fed animals (P < 0.001). For other tissues (spleen, colon, tumor) the differences were not significant, although the whey-fed animals had the highest concentrations of glutathione (P = 0.8). Whey is a source of precursors (cysteine-rich proteins) for glutathione synthesis and may be important in providing protection to the host by stimulating glutathione synthesis. A positive correlation was observed between mean fecal fat concentrations for rats in each treatment group and large intestinal tumor burden (r2 = 0.898, P = 0.05). Fecal fat could be involved in aiding initiation and/or promotion of carcinogenesis. Whatever the mechanism(s), dairy proteins, and whey proteins in particular, offer considerable protection to the host against dimethylhydrazine-induced tumors relative to the other protein sources examined.
authors.affiliation: CSIRO Division of Human Nutrition, Adelaide, South Australia.
authors.forename: G H
authors.initials: GH
authors.lastname: McIntosh
authors.forename: G O
authors.initials: GO
authors.lastname: Regester
authors.forename: R K
authors.initials: RK
authors.lastname: Le Leu
authors.forename: P J
authors.initials: PJ
authors.lastname: Royle
authors.forename: G W
authors.initials: GW
authors.lastname: Smithers
mesh_terms: D000818:Animals; D001823:Body Composition; D001835:Body Weight; D002364:Caseins / Q000592:standards / Q000627:therapeutic use; D004044:Dietary Proteins / Q000592:standards / Q000627:therapeutic use; D004127:Dimethylhydrazines / Q000009:adverse effects*; D005978:Glutathione / Q000032:analysis / Q000378:metabolism; D007414:Intestinal Neoplasms / Q000139:chemically induced* / Q000517:prevention & control*; D008099:Liver / Q000737:chemistry; D008297:Male; D008460:Meat / Q000592:standards; D008894:Milk Proteins / Q000592:standards* / Q000627:therapeutic use; D051381:Rats; D017207:Rats, Sprague-Dawley; D013025:Glycine max / Q000592:standards; D000067816:Whey Proteins
chemical_list: D002364:Caseins; D004044:Dietary Proteins; D004127:Dimethylhydrazines; D008894:Milk Proteins; D000067816:Whey Proteins; D005978:Glutathione