Dietary protein, immune function and colon carcinogenesis in the mouse

Abstract

Immune stimulation and colon cancer development were studied in A/J mice injected with azoxymethane (AOM) which were maintained on undenatured whey protein concentrate (WPC), Immunocal™ (IM), soy protein isolate (SPI) and a commercial casein (CC) as the only source of dietary protein for 32 weeks. No difference in growth rate and body weight was found for the different treatments. Immune stimulation, after challenge by subcutaneous injection of 5 × 106 sheep red blood cells, was evaluated by PFC (Plaque-Forming Cells) in the spleen. Response was equal and significantly higher for WPC- and IM-fed mice, the lowest response was found for the SPI group and an intermediate response for CC. A parallel increase was observed between PFC in the spleen and glutathione concentration in the liver. Aberrant crypt foci (ACF) were confirmed as reliable markers for colon carcinogenesis and were detected by fixation in formaldehyde solution and staining with methylene blue. A high linear correlation was found between ACF and actual number of colon tumors. The most important result of this work was the significant effect of the cysteine-rich proteins in the immunological response to SRBC antigen and tumor formation. These findings confirm and extend the works reported by other investigators. © INRA, EDP Sciences, 2006.