Ameliorated hepatic insulin resistance is associated with normalization of microsomal triglyceride transfer protein expression and reduction in very low density lipoprotein assembly and secretion in the fructose-fed hamster.
To determine whether reduction of insulin resistance could ameliorate fructose-induced very low density lipoprotein (VLDL) oversecretion and to explore the mechanism of this effect, fructose-fed hamsters received placebo or rosiglitazone for 3 weeks. Rosiglitazone treatment led to normalization of the blunted insulin-mediated suppression of the glucose production rate and to a approximately 2-fold increase in whole body insulin-mediated glucose disappearance rate (p < 0.001). Rosiglitazone ameliorated the defect in hepatocyte insulin-stimulated tyrosine phosphorylation of the insulin receptor, IRS-1, and IRS-2 and the reduced protein mass of IRS-1 and IRS-2 induced by fructose feeding. Protein-tyrosine phosphatase 1B levels were increased with fructose feeding and were markedly reduced by rosiglitazone. Rosiglitazone treatment led to a approximately 50% reduction of VLDL secretion rates (p < 0.05) in vivo and ex vivo. VLDL clearance assessed directly in vivo was not significantly different in the FR (fructose-fed + rosiglitazone-treated) versus F (fructose-fed + placebo-treated) hamsters, although there was a trend toward a lower clearance with rosiglitazone. Enhanced stability of nascent apolipoprotein B (apoB) in fructose-fed hepatocytes was evident, and rosiglitazone treatment resulted in a significant reduction in apoB stability. The increase in intracellular mass of microsomal triglyceride transfer protein seen with fructose feeding was reduced by treatment with rosiglitazone. In conclusion, improvement of hepatic insulin signaling with rosiglitazone, a peroxisome proliferator-activated receptor gamma agonist, is associated with reduced hepatic VLDL assembly and secretion due to reduced intracellular apoB stability.
Carpentier
Andre
A
Department of Medicine, Division of Endocrinology and Metabolism, University Health Network, Hospital for Sick Children, University of Toronto, Toronto, Ontario M5G 2C4, Canada.
Taghibiglou
Changiz
C
Leung
Nathalie
N
Szeto
Linda
L
Van Iderstine
Stephen C
SC
Uffelman
Kristine D
KD
Buckingham
Robin
R
Adeli
Khosrow
K
Lewis
Gary F
GF
D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001055:Apolipoproteins B / Q000378:metabolism; D006224:Cricetinae; D005632:Fructose / Q000378:metabolism / Q000494:pharmacology*; D022781:Hepatocytes / Q000378:metabolism; D007004:Hypoglycemic Agents / Q000494:pharmacology; D015151:Immunoblotting; D007328:Insulin / Q000378:metabolism; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance; D047908:Intracellular Signaling Peptides and Proteins; D008079:Lipoproteins, VLDL / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D008297:Male; D008647:Mesocricetus; D008862:Microsomes, Liver / Q000378:metabolism*; D010477:Perfusion; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D000077154:Rosiglitazone; D015398:Signal Transduction; D013844:Thiazoles / Q000494:pharmacology; D045162:Thiazolidinediones; D013997:Time Factors; D014280:Triglycerides / Q000378:metabolism*
D001055:Apolipoproteins B; D007004:Hypoglycemic Agents; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008079:Lipoproteins, VLDL; D010750:Phosphoproteins; D013844:Thiazoles; D045162:Thiazolidinediones; D014280:Triglycerides; D000077154:Rosiglitazone; D005632:Fructose