Dietary soybean protein compared with casein retards senescence in the senescence accelerated mouse

The effects of replacing dietary casein with soybean protein on mean life span, mean life span of the last one-tenth of a group, grading scores of senescence and deposition of senile amyloid were investigated in senescence accelerated mice (SAM-P/1) compared with a control strain (SAM-R/1). SAM-R/1 mice fed the soybean protein-containing diet had mean life spans of 618 +/- 42 d (males) and 578 +/- 62 d (females), 58% (males) and 44% (females) longer than those of corresponding casein fed mice (P < 0.01). Similarly, in SAM-P/1 mean life-spans were 265 +/- 16 d (males) and 307 +/- 23 d (females) in the soybean diet group, 27% (males) and 30% (females) longer than in the casein diet groups (P < 0.01). The mean life span of the last one-tenth of each group fed soybean protein was significantly longer than the corresponding group fed casein. In SAM-R/1 mice, pathological studies revealed that severe secondary amyloid deposition (amyloid A protein) in the kidneys, spleen, stomach and liver was significantly suppressed, in males only, by replacing casein with soybean protein (P < 0.01). The occurrence of contracted kidneys caused by the infiltration of amyloid A protein was suppressed in SAM-R/1 mice fed the soybean protein-containing diet (P < 0.05). The deposition of senile amyloid in SAM-P/1 mice with aging was retarded by replacing casein with soybean protein (P < 0.01). These results indicate that dietary protein source is important in modulating the advance of senescence in SAM mice.