Plasma exposure to insulin glargine and its metabolites M1 and M2 after subcutaneous injection of therapeutic and supratherapeutic doses of glargine in subjects with type 1 diabetes

Abstract

OBJECTIVE - In vivo, after subcutaneous injection, insulin glargine (21A-Gly-31B-Arg-32B-Arg-human insulin) is enzymatically processed into 21A-Gly-human insulin (metabolite 1 [M1]). 21A-Gly-des-30B-Thr-human insulin (metabolite 2 [M2]) is also found. In vitro, glargine exhibits slightly higher affinity, whereas M1 and M2 exhibit lower affinity for IGF-1 receptor, as well as mitogenic properties, versus human insulin. The aim of the study was to quantitate plasma concentrations of glargine, M1, and M2 after subcutaneous injection of glargine in male type 1 diabetic subjects. RESEARCH DESIGN AND METHODS - Glargine, M1, and M2 were determined in blood samples obtained from 12, 11, and 11 type 1 diabetic subjects who received single subcutaneous doses of 0.3, 0.6, or 1.2 units · kg-1 glargine in a euglycemic clamp study. Glargine, M1, and M2 were extracted using immunoaffinity columns and quantified by a specific liquid chromatography-tandem mass spectrometry assay. Lower limit of quantification was 0.2 ng · mL-1(33 pmol · L-1) per analyte. RESULTS - Plasma M1 concentration increased with increasing dose; geometric mean (percent coefficient of variation) M1-area under the curve between time of dosing and 30 h after dosing (AUC0-30h)was 1,261 (66), 2,867 (35), and 4,693 (22) pmol · h · L-1 at doses of 0.3, 0.6, and 1.2 units · kg -1, respectively, and correlated with metabolic effect assessed as pharmacodynamics-AUC0-30h of the glucose infusion rate following glargine administration (r = 0.74; P < 0.01). Glargine and M2 were detectable in only one-third of subjects and at a few time points. CONCLUSIONS - After subcutaneous injection of glargine in male subjects with type 1 diabetes, exposure to glargine ismarginal, if any, even at supratherapeutic doses. Glargine is rapidly and nearly completely processed to M1 (21 A-Gly-human insulin), which mediates the metabolic effect of injected glargine. © 2012 by the American Diabetes Association.