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.


METHODS
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.


CONCLUSIONS
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.
Jeyakumar
Shanmugam M
SM
Department of Biochemistry, National Institute of Nutrition, Hyderabad, India.
Vajreswari
Ayyalasomayajula
A
Giridharan
Nappan V
NV
D000818:Animals; D008076:Cholesterol, HDL / Q000097:blood / Q000378:metabolism*; D004032:Diet; D008055:Lipids / Q000032:analysis / Q000097:blood; D008099:Liver / Q000737:chemistry / Q000187:drug effects; D008297:Male; D009765:Obesity / Q000097:blood / Q000378:metabolism* / Q000473:pathology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D051122:Scavenger Receptors, Class B / Q000097:blood / Q000378:metabolism*; D014801:Vitamin A / Q000494:pharmacology*
D008076:Cholesterol, HDL; D008055:Lipids; D012333:RNA, Messenger; C495125:Scarb1 protein, rat; D051122:Scavenger Receptors, Class B; D014801:Vitamin A