Concentrations of insulin glargine and its metabolites during long-term insulin therapy in type 2 diabetic patients and comparison of effects of insulin glargine, its metabolites, IGF-I, and human insulin on insulin and igf-I receptor signaling

Abstract

We investigated 1) the ability of purified glargine (GLA), metabolites 1 (M1) and 2 (M2), IGF-I, and NPH insulin to activate the insulin receptor (IR)-A and IR-B and IGF-I receptor (IGF-IR) in vitro; 2) plasma concentrations of GLA, M1, and M2 during long-term insulin therapy in type 2 diabetic patients; and 3) IR-A and IR-B activation in vitro induced by serum from patients treated with GLA or NPH insulin. A total of 104 patients (age 56.3 ± 0.8 years, BMI 31.4 ± 0.5 kg/m(2), and A1C 9.1 ± 0.1% [mean ± SE]) were randomized to GLA or NPH insulin therapy for 36 weeks. Plasma concentrations of GLA, M1, and M2 were determined by liquid chromatography-tandem mass spectrometry assay. IR-A, IR-B, and IGF-IR autophosphorylation was induced by purified hormones or serum by kinase receptor activation assays. In vitro, M1 induced comparable IR-A, IR-B, and IGF-IR autophosphorylation (activation) as NPH insulin. After 36 weeks, M1 increased from undetectable (<0.2 ng/mL) to 1.5 ng/mL (0.9-2.1), while GLA and M2 remained undetectable. GLA dose correlated with M1 (r = 0.84; P < 0.001). Serum from patients treated with GLA or NPH insulin induced similar IR-A and IR-B activation. These data suggest that M1 rather than GLA mediates GLA effects and that compared with NPH insulin, GLA does not increase IGF-IR signaling during long-term insulin therapy in type 2 diabetes.

FIG. 1.

Activation of the IGF-IR (A), IR-A (B), and IR-B (C) in vitro: comparing equimolar concentrations of NPH insulin, human IGF-I, insulin GLA, and M1 and M2. Dose-response profiles ranged from 0.1 to 100 nmol/L. Points represent the mean value (+ SEM) of three independent experiments. *P < 0.05 compared with NPH insulin.

FIG. 2.

Plasma concentrations of insulin GLA and its metabolites M1 and M2 at baseline and at 36 weeks of insulin GLA therapy determined by LCMS. Results are shown as median with interquartile ranges. The broken line shows the detection limit for all three substances (0.20 ng/mL).

FIG. 3.

Correlation between insulin GLA dose per kilogram per day at 36 weeks of insulin therapy and concentrations of its metabolite M1.

FIG. 4.

A: Correlation between NPH insulin dose per kilogram per day and serum-induced IR-A and IR-B activation at 36 weeks of insulin therapy. NPH dose per kilogram per day was positively related to IR-A activation. B: Correlation between concentrations of metabolite M1 and serum-induced IR-A and IR-B activation at 36 weeks of GLA therapy. M1 concentrations were positively correlated to IR-A activation.