Screening the effects of phytoestrogens on lipid metabolism in primary cultured adipocytes from rainbow trout (Oncorhynchus mykiss) and gilthead sea bream (Sparus aurata)

Aquafeed formulation has progressively reduced its dependence on fish-derived ingredients over the past decades. Plant-based substitutes have been a major focus, with soybean meal and its derivatives leading the way. However, many plants contain phytoestrogens, which may affect fish physiology. This study aimed to assess in vitro the effects of genistein (GE), daidzein (DZN), glycitein (GLY), and coumestrol (COU) on the lipid metabolism of rainbow trout (Oncorhynchus mykiss) and gilthead sea bream (Sparus aurata). Primary cultured adipocytes were incubated with these phytoestrogens, along with 17β-estradiol, at two doses each (1, 10, or 100 μM). The 100 μM dose of GE and DZN decreased adipocyte viability, and mainly enhanced lipid accumulation in both species, suggesting a hypertrophic condition. However, the reduction in adipocyte number and lipid content with 100 μM DZN in rainbow trout indicated a limiting effect on adipose tissue growth in this species. Interestingly, COU significantly increased cell viability in gilthead sea bream, potentially leading to hyperplastic growth, a more favorable metabolic state. In that species, which proved to be more phytoestrogens-sensitive, lipoprotein lipase was generally downregulated upon treatments. Moreover, 10 µM GE significantly decreased the mRNA levels of fatty acid transport protein 1 and fatty acid synthase, and increased those of fatty acid binding protein 1, suggesting an acceleration of the differentiation process compared to the control cells. This work provides new insights into how dietary phytoestrogens modulate fish lipid metabolism and supports that their presence in plant protein feedstuffs can potentially affect fish health and production performance.