Mapping the Associations of the Plasma Lipidome With Insulin Resistance and Response to an Oral Glucose Tolerance Test.

CONTEXT: Insulin resistance (IR) remains a global health challenge. Lipidomics offers an opportunity to identify biomarkers and better understand mechanisms of IR associated with abnormal lipid metabolism. OBJECTIVE: The objective of this article is to determine plasma lipid species associated with indices of IR and evaluate the lipidome response to an oral glucose tolerance test (OGTT). DESIGN AND SETTING: This study was community based and cross-sectional. PARTICIPANTS AND SAMPLE: Plasma samples (collected at 0 and 120 min during an OGTT) from nonobese, young adults age 18 to 34 years (n = 246) were analyzed using liquid chromatography-tandem mass spectrometry. MAIN OUTCOME MEASURES: The associations between indices of IR and lipid classes and species (with a sex interaction term), or changes in lipid levels during an OGTT, were tested using linear models (adjusted for age, sex, body mass index, total cholesterol, high-density lipoprotein cholesterol, and triglycerides). RESULTS: Some (213) and (199) lipid species were associated with the homeostatic model assessment of insulin resistance and insulin area under curve (AUC), respectively. Alkylphosphatidylcholine (10), alkenylphosphatidylcholine (23), and alkylphosphatidylethanolamine (6) species were associated with insulin AUC in men only. Species of phosphatidylcholine (7) and sphingomyelin (5) were associated in women only. In response to an OGTT, a perturbation in the plasma lipidome, particularly in acylcarnitine species, was observed; and the changes in many lipid species were associated with insulin AUC. CONCLUSIONS: The plasma lipidome and changes in lipid levels during an OGTT were associated with indices of IR. These findings underlie the involvement of molecular lipid species in the pathogenesis of IR and possibly crosstalk between IR and sex-specific regulation of lipid metabolism.

Mechanisms of hyperinsulinaemia in apparently healthy non-obese young adults: role of insulin secretion, clearance and action and associations with plasma amino acids.

AIMS/HYPOTHESIS: This study aimed to examine the metabolic health of young apparently healthy non-obese adults to better understand mechanisms of hyperinsulinaemia. METHODS: Non-obese (BMI < 30 kg/m2) adults aged 18-35 years (N = 254) underwent a stable isotope-labelled OGTT. Insulin sensitivity, glucose effectiveness and beta cell function were determined using oral minimal models. Individuals were stratified into quartiles based on their insulin response during the OGTT, with quartile 1 having the lowest and quartile 4 the highest responses. RESULTS: Thirteen per cent of individuals had impaired fasting glucose (IFG; n = 14) or impaired glucose tolerance (IGT; n = 19), allowing comparisons across the continuum of insulin responses within the spectrum of normoglycaemia and prediabetes. BMI (~24 kg/m2) was similar across insulin quartiles and in those with IFG and IGT. Despite similar glycaemic excursions, fasting insulin, triacylglycerols and cholesterol were elevated in quartile 4. Insulin sensitivity was lowest in quartile 4, and accompanied by increased insulin secretion and reduced insulin clearance. Individuals with IFG had similar insulin sensitivity and beta cell function to those in quartiles 2 and 3, but were more insulin sensitive than individuals in quartile 4. While individuals with IGT had a similar degree of insulin resistance to quartile 4, they exhibited a more severe defect in beta cell function. Plasma branched-chain amino acids were not elevated in quartile 4, IFG or IGT. CONCLUSIONS/INTERPRETATION: Hyperinsulinaemia within normoglycaemic young, non-obese adults manifests due to increased insulin secretion and reduced insulin clearance. Individual phenotypic characterisation revealed that the most hyperinsulinaemic were more similar to individuals with IGT than IFG, suggesting that hyperinsulinaemic individuals may be on the continuum toward IGT. Furthermore, plasma branched-chain amino acids may not be an effective biomarker in identifying hyperinsulinaemia and insulin resistance in young non-obese adults.