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Excess glucagon levels contribute to the hyperglycemia associated with type 2 diabetes. Reducing glucagon receptor expression may thus ameliorate the consequences of hyperglucagonemia and improve blood glucose control in diabetic patients. This study describes the antidiabetic effects of a specific glucagon receptor antisense oligonucleotide (GR-ASO) in db/db mice. The ability of GR-ASOs to inhibit glucagon receptor mRNA expression was demonstrated in primary mouse hepatocytes by quantitative real-time RT-PCR. Intraperitoneal administration of GR-ASO at a dosage of 25 mg/kg twice a week in db/db mice for 3 weeks resulted in 1) decreased glucagon receptor mRNA expression in liver; 2) decreased glucagon-stimulated cAMP production in hepatocytes isolated from GR-ASO-treated db/db mice; 3) significantly reduced blood levels of glucose, triglyceride, and free fatty acids; 4) improved glucose tolerance; and 5) a diminished hyperglycemic response to glucagon challenge. Neither lean nor db/db mice treated with GR-ASO exhibited hypoglycemia. Suppression of GR expression was also associated with increased ( approximately 10-fold) levels of plasma glucagon. No changes were observed in pancreatic islet cytoarchitecture, islet size, or alpha-cell number. However, alpha-cell glucagon levels were increased significantly. Our studies support the concept that antagonism of glucagon receptors could be an effective approach for controlling blood glucose in diabetes.

Signaling through the phosphatidylinositol 3'-kinase (PI3K) pathway is crucial for metabolic responses to insulin, and defects in PI3K signaling have been demonstrated in type 2 diabetes. PTEN (MMAC1) is a lipid/protein phosphatase that can negatively regulate the PI3K pathway by dephosphorylating phosphatidylinositol (3,4,5)-triphosphate, but it is unclear whether PTEN is physiologically relevant to insulin signaling in vivo. We employed an antisense oligonucleotide (ASO) strategy in an effort to specifically inhibit the expression of PTEN. Transfection of cells in culture with ASO targeting PTEN reduced PTEN mRNA and protein levels and increased insulin-stimulated Akt phosphorylation in alpha-mouse liver-12 (AML12) cells. Systemic administration of PTEN ASO once a week in mice suppressed PTEN mRNA and protein expression in liver and fat by up to 90 and 75%, respectively, and normalized blood glucose concentrations in db/db and ob/ob mice. Inhibition of PTEN expression also dramatically reduced insulin concentrations in ob/ob mice, improved the performance of db/db mice during insulin tolerance tests, and increased Akt phosphorylation in liver in response to insulin. These results suggest that PTEN plays a significant role in regulating glucose metabolism in vivo by negatively regulating insulin signaling.