Impact of Vitamin D intake and high-fat diets on liver and muscle: a rat model of Western and Mediterranean Diets

Background: The metabolic syndrome is associated with sarcopenia. Decreased serum levels of Vitamin D (VitD) and insulin-like growth factor (IGF)-1 and their mutual relationship were also reported. We aimed to evaluate whether different dietary profiles, containing or not VitD, may exert different effects on muscle and liver. Methods: Twenty-eight male rats were fed for 10 weeks in order to detect early defects induced by different dietary regimens: regular diet (R); regular diet with vitamin D supplementation (R-DS) and regular diet with vitamin D restriction (R-DR); high-fat butter-based diets (HFB-DS and HFB-DR) with 41% energy from fat; high-fat extra-virgin olive oil-based diets (HFEVO-DS and HFEVO-DR) with 41% energy from fat. IL-1beta, insulin-like growth factor (IGF)1, Dickkopf-1 (DKK-1), and VitD-receptor (VDR) expressions were evaluated by immunohistochemistry in both muscle and liver, Collagen type I expression was evaluated in the liver. Muscle fiber perimeter was measured by histology and morphometric analysis. Severity of NAFLD was assessed by NAFLD Activity Score (NAS). Results: Muscle fibers of HEVO-DS rats were hypertrophic, comparable to those of the R-DS rats. An inverse correlation existed between the dietary fat content and the perimeter of the muscle fibers (p < 0.01). In HFB-DR rats, muscle fibers appeared hypotrophic with an increase of IL-1beta and a dramatic decrease of IGF-1 expression. All liver samples showed a NAS between 0 and 2 considered not diagnostic of steatohepatitis. Collagen I, although weakly expressed, was statistically greater in HFB-DS and HFB-DR groups. IL-1beta was mostly expressed in rats fed by HFBs and HFEVOs and R-DR, and almost absent in R and R-DS diets. IGF-1 and DKK-1 were reduced in HFBs and HFEVOs diets and in particular in DR groups. Conclusions: High-fat western diet could impair muscle and damage liver tissue in terms of inflammation and collagen I deposition, putting the basis for the subsequent steatohepatitis, still not identifiable histopathologically. VitD associated with a Mediterranean diet showed trophic action on the muscle fibers. Vitamin D restriction increases inflammation and reduces the expression of IGF-1 in the liver, worsening the fat-induced changing. EVO seems be protective against liver collagen I production.