Soy milk suppresses cholesterol-induced inflammatory gene expression and improves the fatty acid profile in the skin of SD rats

Recently, an elevation in skin cholesterol level has been implicated in skin inflammation. Given the potential therapeutic effects of soy on low grade inflammatory diseases, we hypothesized that a CHOL diet could promote an inflammatory response in skin and that soy milk (SM) or fermented soy milk (F.SM) could prevent this cholesterol-induced skin inflammation. To test this hypothesis, freeze-dried SM or F.SM was provided as a protein replacement for 20% of the casein in the diets of Sprague–Dawley (SD) rats. The animals were divided into the following groups: (1) control group (CTRL), AIN76A diet without cholesterol, (2) high cholesterol (CHOL) group, AIN76A with 1% (w/w) cholesterol, (3) SM group, CHOL diet with freeze-dried SM, and (4) F.SM group, CHOL diet with F.SM. In the CHOL group, the expression levels of pro-inflammatory genes, including IL-1β, IL-1α, iNOS, and COX-2, were elevated. In comparison, the SM and F.SM groups displayed the lowered expression of IL-1β, COX-2, F4/80, and Cd68, an increase of a n-3/n-6 ratio, and a reduction in the estimated desaturase activities of delta 5 desaturase (D5D) and steaoryl CoA desaturase (SCD-1). In particular, F.SM significantly increased the proportion of dihomo-γ-linolenic acid (DGLA) in skin fatty acid (FA) composition compared with the CHOL group. Here we present evidence that SM or F.SM could alleviate the inflammatory response in the skin that is triggered by excess dietary cholesterol by reducing the expression of pro-inflammatory genes. This response could be partly associated with a decreased in macrophages in skin and/or by modulation of the skin’s FA composition.