In vitro and in vivo effects of phytoestrogens on protein turnover in rainbow trout (Oncorhynchus mykiss) white muscle

Authors: Cleveland, Beth

Submitted to: Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2014
Publication Date: 5/27/2014
Publication URL: http://handle.nal.usda.gov/10113/59403
Citation: Cleveland, B.M. 2014. In vitro and in vivo effects of phytoestrogens on protein turnover in rainbow trout (Oncorhynchus mykiss) white muscle. Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology. 165: 9-16. DOI: 10.1016/j.cbpc.2014.05.003.

Interpretive Summary: Concerns about long-term sustainability of fishmeal have promoted the search for alternative sources of protein for fish feeds. Soybean meal has performed well in early studies as a fishmeal replacement, however soy contains compounds called phytoestrogens, which can activate estrogen receptors. In rainbow trout estrogen has negative effects on growth performance, therefore the concern is that soy-derived phytoestrogens present in fish feeds prevent optimal growth performance due to their ability to mimic estrogen. We demonstrated that at high concentrations phytoestrogens, especially genistein, affect protein metabolism in a similar manner to estrogen. However, at low concentrations genistein may actually promote protein retention in muscle for positive effects on growth. Therefore, effects of dietary phytoestrogens on growth may depend on the amount of soybean meal in the diet. These results warrant additional studies to determine the extent to which dietary phytoestrogens, especially genistein, affect physiological processes that impact growth and nutrient retention.

Technical Abstract: Soybeans and other legumes investigated as fishmeal replacements in aquafeeds contain phytoestrogens capable of binding to and activating estrogen receptors. Estradiol has catabolic effects in salmonid white muscle, partially through increases in protein turnover. The current study determines whether phytoestrogens promote similar effects. In primary myocyte cultures, phytoestrogens reduced rates of protein synthesis and genistein, the phytoestrogen of greatest abundance in soy, also increased rates of protein degradation. Increased expression of the ubiquitin ligase fbxo32 and autophagy-related genes was observed with high concentrations of genistein (100 uM). In contrast, low genistein concentrations (0.01-0.10 uM) decreased fbxo32 expression. Phytoestrogens reduced cell proliferation, indicating effects of phytoestrogens extend from metabolic to mitogenic processes. Co-incubation of genistein with the estrogen receptor (ER) antagonist, ICI 182,780, ameliorated effects of genistein on protein degradation, but not protein synthesis or cell proliferation, indicating effects of genistein are mediated through ER-dependent and ER-independent mechanisms.