BackgroundStudies in cell cultures and rodents suggest that TLR4 is involved in the pathogenesis of insulin resistance, but direct data in humans are limited. We tested the hypothesis that pharmacologic blockade of TLR4 with the competitive inhibitor eritoran would improve insulin resistance in humans.MethodsIn protocol I, 10 lean, healthy individuals received the following 72-hour i.v. infusions in a randomized crossover design: saline (30 mL/h) plus vehicle; Intralipid (30 mL/h) plus vehicle; or Intralipid (30 mL/h) plus eritoran (12 mg i.v. every 12 hours). In protocol II, also a randomized crossover design, 9 nondiabetic individuals with obesity received eritoran or vehicle for 72 hours. The effect of eritoran was assessed with euglycemic hyperinsulinemic clamps.ResultsIn protocol I, lipid infusion significantly decreased peripheral insulin sensitivity (M value) by 14% and increased fasting plasma glucose (FPG) concentrations, fasting plasma insulin (FPI) concentrations, and the homeostatic model assessment of insulin resistance (HOMA-IR) index by 7%, 22%, and 26%, respectively. Eritoran did not prevent lipid-induced alterations of these metabolic parameters. Eritoran also failed to improve any baseline metabolic parameters (M, FPG, FPI, HOMA-IR) in individuals with obesity and insulin resistance (protocol II).ConclusionsAcute TLR4 inhibition with eritoran did not protect against lipid-induced insulin resistance. Short-term eritoran administration also failed to improve obesity-associated insulin resistance. These data do not support a role for TLR4 in insulin resistance. Future studies with a different class of TLR4 inhibitors, longer drug exposure, and/or lipid-enhancing interventions richer in saturated fats may be needed to further clarify the role of TLR4 in metabolic dysfunction in humans.Trial registrationClinicalTrials.gov NCT02321111 and NCT02267317.FundingNIH grants R01DK080157, P30AG044271, P30AG013319, and UL1TR002645.