Accumulation of 3-hydroxytetradecenoic acid: Cause or corollary of glucolipotoxic impairment of pancreatic β-cell bioenergetics?

• We found low capacity of islets to generate ATP after glucolipotoxic treatment.
• Found biphasic (up/down) respiratory time course as expression of glucolipotoxicity.
• We found β-Hydroxylated long FA metabolites as new glucolipotoxicity mediators.
• β-Hydroxylated long FAs are known to uncouple Ox/Phos.
• We propose defective bioenergetics as main cause of glucolipotoxicity.

ObjectivesHyperglycemia and elevated blood lipids are the presumed precipitating causes of β-cell damage in T2DM as the result of a process termed “glucolipotoxicity”. Here, we tested whether glucolipotoxic pathophysiology is caused by defective bioenergetics using islets in culture.MethodsInsulin secretion, respiration, ATP generation, fatty acid (FA) metabolite profiles and gene expression were determined in isolated islets treated under glucolipotoxic culture conditions.ResultsOver time, chronic exposure of mouse islets to FAs with glucose leads to bioenergetic failure and reduced insulin secretion upon stimulation with glucose or amino acids. Islets exposed to glucolipotoxic conditions displayed biphasic changes of the oxygen consumption rate (OCR): an initial increase in baseline and Vmax of OCR after 3 days, followed by decreased baseline and glucose stimulated OCR after 5 days. These changes were associated with lower islet ATP levels, impaired glucose-induced ATP generation, a trend for reduced mitochondrial DNA content and reduced expression of mitochondrial transcription factor A (Tfam). We discovered the accumulation of carnitine esters of hydroxylated long chain FAs, in particular 3-hydroxytetradecenoyl-carnitine.ConclusionsAs long chain 3-hydroxylated FA metabolites are known to uncouple heart and brain mitochondria [53], [54] and [55], we propose that under glucolipotoxic condition, unsaturated hydroxylated long-chain FAs accumulate, uncouple and ultimately inhibit β-cell respiration. This leads to the slow deterioration of mitochondrial function progressing to bioenergetics β-cell failure.