Leptin therapy in insulin-deficient type I diabetes

Abstract

In nonobese diabetic mice with uncontrolled type 1 diabetes, leptin therapy alone or combined with low-dose insulin reverses the catabolic state through suppression of hyperglucagonemia. Additionally, it mimics the anabolic actions of insulin monotherapy and normalizes hemoglobin A1c with far less glucose variability. We show that leptin therapy, like insulin, normalizes the levels of a wide array of hepatic intermediary metabolites in multiple chemical classes, including acylcarnitines, organic acids (tricarboxylic acid cycle intermediates), amino acids, and acyl CoAs. In contrast to insulin monotherapy, however, leptin lowers both lipogenic and cholesterologenic transcription factors and enzymes and reduces plasma and tissue lipids. The results imply that leptin administration may have multiple short- and long-term advantages over insulin monotherapy for type 1 diabetes.

Fig. 1.

Comparisons of various parameters in plasma of type 1 diabetic NOD mice. Mice were either untreated or treated with s.c.-infused leptin (•; n = 14) through an Alzet pump or with insulin delivered from a s.c. pellet (▲; n = 6). Untreated mice were either fed ad libitum (○; n = 4) or pair-fed with the leptin-treated group (△; n = 4), and all received an infusion of PBS through an Alzet pump. (A) Plasma leptin levels. (B) Blood glucose levels. (C) Plasma FFA levels. (D) Hemoglobin A1c (day 0 =■ day 12 = □). The dotted lines mark the normal values.

Fig. 2.

TG concentrations in plasma and liver and expression levels of transcription factors and enzymes involved in lipogenesis and cholesterologenesis in livers of type 1 diabetic NOD mice treated either with s.c.-infused leptin () or insulin delivered from an s.c. pellet (■). Untreated controls infused with PBS were either fed ad libitum (□) or pair-fed (PF) to the leptin-treated group (). (A) Plasma TG concentration. (B) Liver TG content. (C) Hepatic expression of a lipogenic transcription factor, LXRα and SREBP-1c, and lipogenic enzymes, FAS and GPAT. (D) Hepatic expression of transcription factors, SREBP-1a and -2, and enzyme, HMG CoA reductase, involved in cholesterologenesis. Relative expression signifies the ratio of the mRNA of interest to the mRNA of 36B4, the invariant control. The broken horizontal lines indicate the relative expression level of the mRNA in nondiabetic control mice. [*P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001 vs. ad libitum–fed untreated (PBF) controls; †P ≤ 0.05; ††P ≤ 0.01; †††P ≤ 0.001 leptin treatment vs. insulin.]

Fig. 3.

Plasma glucagon levels and activation of its transcription factor, CREB, and a target enzyme in livers of type 1 diabetic NOD mice treated with s.c.-infused leptin () or PEPCK insulin delivered from an s.c. pellet (■); untreated controls were infused with PBS and fed ad libitum (□) or PF to the leptin-treated group (). (A) Ratio of phosphorylated to total AMPK. (B) Plasma glucagon. (C) Ratio of phosphorylated to total CREB. (D) mRNA of phosphoenol pyruvate carboxykinase. (E) Ratio of phosphorylated to total STAT-3. ND, nondiabetic. (*P ≤ 0.05; **P ≤ 0.01; ***P ≤ 0.001 vs. ad libitum fed untreated PBF controls.)

Fig. 4.

(A) Comparison of blood glucose levels in glucagon receptor null (Gcgr^−/−) mice (□) and wild-type (Gcgr^+/+) controls (•) after treatment with double-dose alloxan. (B) Comparison of severity of insulin deficiency in the alloxan-treated Gcgr^−/− and Gcgr^+/+ and nondiabetic Gcgr^−/− and Gcgr^+/+ controls based on plasma insulin levels and morphometric values for insulin-immunostained β-cells in pancreata. The results indicate no significant difference in residual insulin that could explain the absence of hyperglycemia in the alloxan-treated Gcgr^−/− group. Nondiabetic, □; alloxan diabetic, ■.

Fig. 5.

Examples of metabolomic patterns of four classes of metabolites in livers of nondiabetic (), untreated diabetic (□), diabetic treated with insulin pellets (■), and diabetic leptin-treated mice (). (A) Acyl carnitines reflecting branch-chain amino acid metabolism and ketone production. (B) Long-chain acyl Co As and acyl carnitines (Inset). (C) Branch-chain amino acids. (D) Organic acids. Of 121 metabolites measured, 67 were abnormal in untreated diabetes. Of these, 55 were corrected or improved by both hormones. Three were corrected by leptin but not insulin. Three were corrected by insulin but not leptin. The remainder were not corrected.

Fig. 6.

(A) Comparison of plasma glucose levels in type 1 diabetic NOD mice treated with twice daily injection of insulin alone at a total dose of 0.2 U/day (▲), twice daily insulin alone at a total dose of 0.02 U/day fed ad libitum (○), twice daily insulin PF to the leptin-treated group (□), or a total daily dose of insulin of 0.02 U/day plus leptin injected at the doses and times indicated by arrows (•). (B) Evidence that much lower doses of infused leptin without insulin are also effective in reducing the hyperglycemia of T1DM. Blood glucose levels of diabetic NOD mice treated for 20 days with leptin monotherapy by osmotic infusion pump are shown. Priming doses during the first 7 days ranged from 1/500 to 1/2,000 of the doses injected with low-dose insulin, and maintenance doses of infused leptin thereafter ranged from 1/500 to 1/2,500 of the doses of injected leptin employed.