Impact of Vitamin A on High-Density Lipoprotein-Cholesterol and Scavenger Receptor Class BI in the Obese Rat

Objective: Scavenger receptor class BI (SR‐BI), authentic high‐density lipoprotein (HDL) receptors expressed in liver, are known to play an important role in HDL‐cholesterol (C) metabolism and reverse cholesterol transport. Interestingly, obese rats of WNIN/Ob strain have abnormally elevated levels of serum HDL‐C compared with their lean counterparts. Based on the well‐established role of SR‐B1 in HDL‐C metabolism, it was hypothesized that these obese rats may have an underexpression of hepatic SR‐B1 receptors. In view of the significant role of vitamin A in energy expenditure and obesity, we also tested whether vitamin A supplementation can correct abnormal HDL‐C metabolism. Research Methods and Procedures: To test this hypothesis, 7‐month‐old male lean and obese rats of WNIN/Ob strain were divided into two groups; each group was subdivided into two subgroups consisting of six lean and six obese rats and received diets containing either 2.6 or 129 mg vitamin A/kg diet for 2 months. Results: At the end, obese rats receiving normal levels of vitamin A diet showed high serum HDL‐C and lower hepatic SR‐BI expression levels compared with lean counterparts. Furthermore, chronic dietary vitamin A supplementation resulted in overexpression of hepatic SR‐BI receptors (protein and gene) with concomitant reduction in serum HDL‐C levels in obese rats. Discussion: Thus, our observations highlight the role of vitamin A in reverse cholesterol transport through up‐regulation of hepatic SR‐BI receptors and, thereby, HDL‐C homeostasis in obese rats of WNIN/Ob strain.