Lipid-induced glucose intolerance is driven by impaired glucose kinetics and insulin metabolism in healthy individuals.

Hypertriglyceridemia is associated with an increased risk of type 2 diabetes. We aimed to comprehensively examine the effects of hypertriglyceridemia on major glucose homeostatic mechanisms involved in diabetes progression. In this randomized, cross-over, single-blinded study, two dual-labeled, 3-hour oral glucose tolerance tests were performed during 5-hour intravenous infusions of either 20 % Intralipid or saline in 12 healthy subjects (age 27.9 ± 2.6 years, 11 men, BMI 22.6 ± 1.4 kg/m²) to evaluate lipid-induced changes in insulin metabolism and glucose kinetics. Insulin sensitivity, β cell secretory function, and insulin clearance were assessed by modeling glucose, insulin and C-peptide data. Intestinal glucose absorption, endogenous glucose production, and glucose clearance were assessed from glucose tracers. The effect of triglycerides on β-cell secretory function was examined in perifusion experiments in murine pseudoislets and human pancreatic islets. Mild acute hypertriglyceridemia impaired oral glucose tolerance (mean glucose: +0.9 [0.3, 1.5] mmol/L, p = 0.008) and whole-body insulin sensitivity (Matsuda index: −1.67 [−0.50, −2.84], p = 0.009). Post-glucose hyperinsulinemia (mean insulin: +99 [17, 182] pmol/L, p = 0.009) resulted from reduced insulin clearance (−0.16 [−0.32, −0.01] L min⁻¹ m⁻², p = 0.04) and enhanced hyperglycemia-induced total insulin secretion (+11.9 [1.1, 22.8] nmol/m², p = 0.02), which occurred despite a decline in model-derived β cell glucose sensitivity (−41 [−74, −7] pmol min⁻¹ m⁻² mmol⁻¹ L, p = 0.04). The analysis of tracer-derived glucose metabolic fluxes during lipid infusion revealed lower glucose clearance (−96 [−152, −41] mL/kg FFM , p = 0.005), increased 2-hour oral glucose absorption (+380 [42, 718] μmol/kg FFM , p = 0.04) and suppressed endogenous glucose production (−448 [−573, −123] μmol/kg FFM , p = 0.005). High-physiologic triglyceride levels increased acute basal insulin secretion in murine pseudoislets (+11 [3, 19] pg/aliquot, p = 0.02) and human pancreatic islets (+286 [59, 512] pg/islet, p = 0.02). Our findings support a critical role for hypertriglyceridemia in the pathogenesis of type 2 diabetes in otherwise healthy individuals and dissect the glucose homeostatic mechanisms involved, encompassing insulin sensitivity, β cell function and oral glucose absorption. [Display omitted] • Mild acute hypertriglyceridemia has marked negative effects on oral glucose tolerance. • Mechanisms include whole body insulin resistance and faster glucose absorption. • These effects are attenuated by lipid-induced hyperinsulinemia. [ABSTRACT FROM AUTHOR]