Dietary Soybean Isolate and Methionine Supplementation Affect Mammary Tumor Progression in Rats

Abstract

The effect of feeding soybean protein isolate (SBP) diet or soybean protein isolate diet supplemented with 0.7% DL-methionine (SBP + Met) on mammary tumor progression was investigated. Sprague-Dawley female rats were fed from weaning a 20% casein (CAS) diet supplemented with 0.3% DL-methionine (AIN-76) and injected via jugular vein with N-nitrosomethylurea (NMU, 40 mg/kg body weight) at 7 wk of age. Five weeks after NMU treatment, animals were divided into the three isoenergetic, isoprotein diet groups: CAS (25 rats); SBP (26 rats) and SBP + Met (25 rats). First palpable mammary tumors were evident 8, 9 and 13 wk and the mean latency period was 13.30 +/- 1.23, 16.70 +/- 1.32 and 17.82 +/- 1.28 wk after NMU treatment in the CAS, SBP + Met and SBP diet groups, respectively. Tumor incidence was 80% in the CAS group compared with 42.3% in the SBP group (P = 0.01). Methionine supplementation increased tumor incidence to 64%. Total number and total weight of tumors was greater in the CAS group compared with either SBP + Met or SBP groups: 41 vs. 28 or 21 tumors and 97.28 g vs. 27.87 or 32.46 g, respectively. These data indicate that SBP diet, low in methionine content, fed 5 wk after carcinogen exposure significantly repressed mammary tumor progression. Methionine supplementation increased the number of animals with tumors but not the mean tumor weight.

Lignans and isoflavonoids in plasma and prostatic fluid in men: Samples from Portugal, Hong Kong, and the United Kingdom

“…Both weak estrogenic [32] and antiestrogenic [33] properties have been reported for lignans and isoflavonoids; they are also inhibitors of aromatase [34] and 5␣-reductase [35] and stimulate sex hormone binding globulin synthesis in the liver [36]. In addition, soya and flaxseed inhibit tumorigenesis in experimental animals [37,38]. Genistein is an inhibitor of tyrosine kinases [39], topoisomerases [40], and angiogenesis [41].…”

Genistein, a Dietary Isoflavone, Down-Regulates the MDM2 Oncogene at Both Transcriptional and Posttranslational Levels

“…Genistein is now considered to be the primary anticancer component of soybeans; its in vitro and/or in vivo activities include the antagonism of estrogen, inhibition of protein tyrosine phosphorylation, suppression of angiogenesis, inhibition of hydrogen peroxide formation induced by tumor promoters, inhibition of topoisomerases, induction of apoptosis and cell differentiation, scavenging of free radicals, and inhibition of carcinogenesis and tumor promotion (2,(9)(10)(11)(12)(13).…”

Prepubertal exposure to zearalenone or genistein reduces mammary tumorigenesis

“…In three of a total of eight studies, a statistically significant association between high soy intake and low breast cancer risk has been found (Nomura et al, 1978;Hirohata et al, 1985;Lee et al, 1991;Yuan et al, 1995;Wu et al, 1996;Witte et al, 1997;Zheng et al, 1999). While most animal studies are supportive of the hypothesis that genistein inhibits mammary tumour promotion (Hawrylewicz et al, 1991;Messina et al, 1994;Barnes, 1997;Gotoh et al, 1998), some studies show an ability of genistein to increase mammary tumorigenesis (Hsieh et al, 1998). Prepubertal exposure via injections to a pharmacological dose of genistein (500 mg kg -1 ) on days 16, 18 and 20 is reported to dramatically reduce subsequent risk to develop mammary tumours (Murrill et al, 1996).…”