• Melissa K Thomas, Amir Nikooienejad, Ross Bray, Xuewei Cui, Jonathan Wilson, Kevin Duffin, Zvonko Milicevic, Axel Haupt, and Deborah A Robins.
• Eli Lilly and Company, Indianapolis, IN, USA.
• J. Clin. Endocrinol. Metab. 2021 Jan 23; 106 (2): 388-396.

ContextNovel dual glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptor agonist (RA) tirzepatide demonstrated substantially greater glucose control and weight loss (WL) compared with selective GLP-1RA dulaglutide.ObjectiveExplore mechanisms of glucose control by tirzepatide.DesignPost hoc analyses of fasting biomarkers and multiple linear regression analysis.SettingForty-seven sites in 4 countries.Patients Or Other ParticipantsThree hundred and sixteen subjects with type 2 diabetes.InterventionsTirzepatide (1, 5, 10, 15 mg), dulaglutide (1.5 mg), placebo.Main Outcome MeasuresAnalyze biomarkers of beta-cell function and insulin resistance (IR) and evaluate WL contributions to IR improvements at 26 weeks.ResultsHomeostatic model assessment (HOMA) 2-B significantly increased with dulaglutide and tirzepatide 5, 10, and 15 mg compared with placebo (P ≤ .02). Proinsulin/insulin and proinsulin/C-peptide ratios significantly decreased with tirzepatide 10 and 15 mg compared with placebo and dulaglutide (P ≤ .007). Tirzepatide 10 and 15 mg significantly decreased fasting insulin (P ≤ .033) and tirzepatide 10 mg significantly decreased HOMA2-IR (P = .004) compared with placebo and dulaglutide. Markers of improved insulin sensitivity (IS) adiponectin, IGFBP-1, and IGFBP-2 significantly increased by 1 or more doses of tirzepatide (P < .05). To determine whether improvements in IR were directly attributable to WL, multiple linear regression analysis with potential confounding variables age, sex, metformin, triglycerides, and glycated hemoglobin A1c was conducted. WL significantly (P ≤ .028) explained only 13% and 21% of improvement in HOMA2-IR with tirzepatide 10 and 15 mg, respectively.ConclusionsTirzepatide improved markers of IS and beta-cell function to a greater extent than dulaglutide. IS effects of tirzepatide were only partly attributable to WL, suggesting dual receptor agonism confers distinct mechanisms of glycemic control.© The Author(s) 2020. Published by Oxford University Press on behalf of the Endocrine Society.

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