Lipoprotein lipase expression, serum lipid and tissue lipid deposition in orally-administered glycyrrhizic acid-treated rats.
BACKGROUND
The metabolic syndrome (MetS) is a cluster of metabolic abnormalities comprising visceral obesity, dyslipidaemia and insulin resistance (IR). With the onset of IR, the expression of lipoprotein lipase (LPL), a key regulator of lipoprotein metabolism, is reduced. Increased activation of glucocorticoid receptors results in MetS symptoms and is thus speculated to have a role in the pathophysiology of the MetS. Glycyrrhizic acid (GA), the bioactive constituent of licorice roots (Glycyrrhiza glabra) inhibits 11beta-hydroxysteroid dehydrogenase type 1 that catalyzes the activation of glucocorticoids. Thus, oral administration of GA is postulated to ameliorate the MetS.


RESULTS
In this study, daily oral administration of 50 mg/kg of GA for one week led to significant increase in LPL expression in the quadriceps femoris (p < 0.05) but non-significant increase in the abdominal muscle, kidney, liver, heart and the subcutaneous and visceral adipose tissues (p > 0.05) of the GA-treated rats compared to the control. Decrease in adipocyte size (p > 0.05) in both the visceral and subcutaneous adipose tissue depots accompanies such selective induction of LPL expression. Consistent improvement in serum lipid parameters was also observed, with decrease in serum free fatty acid, triacylglycerol, total cholesterol and LDL-cholesterol but elevated HDL-cholesterol (p > 0.05). Histological analysis using tissue lipid staining with Oil Red O showed significant decrease in lipid deposition in the abdominal muscle and quadriceps femoris (p < 0.05) but non-significant decrease in the heart, kidney and liver (p > 0.05).


CONCLUSIONS
Results from this study may imply that GA could counteract the development of visceral obesity and improve dyslipidaemia via selective induction of tissue LPL expression and a positive shift in serum lipid parameters respectively, and retard the development of IR associated with tissue steatosis.
Lim
Wai Yen Alfred
WY
School of Science, Monash University Sunway Campus, Jalan Lagoon Selatan, Bandar Sunway 46150, Selangor Darul Ehsan, Malaysia. wylim3@student.monash.edu
Chia
Yoke Yin
YY
Liong
Shih Yeen
SY
Ton
So Ha
SH
Kadir
Khalid Abdul
KA
Husain
Sharifah Noor Akmal Syed
SN
D042842:11-beta-Hydroxysteroid Dehydrogenases / Q000037:antagonists & inhibitors; D052436:Adipose Tissue, White / Q000166:cytology / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D019695:Glycyrrhizic Acid / Q000008:administration & dosage / Q000494:pharmacology*; D007668:Kidney / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D050356:Lipid Metabolism / Q000187:drug effects*; D008055:Lipids / Q000097:blood*; D008071:Lipoprotein Lipase / Q000235:genetics* / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology / Q000473:pathology; D024821:Metabolic Syndrome / Q000517:prevention & control; D018482:Muscle, Skeletal / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D009206:Myocardium / Q000201:enzymology / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018709:Statistics, Nonparametric
D004791:Enzyme Inhibitors; D008055:Lipids; D019695:Glycyrrhizic Acid; D042842:11-beta-Hydroxysteroid Dehydrogenases; D008071:Lipoprotein Lipase