Cold exposure induces dynamic changes in circulating triacylglycerol species, which is dependent on intracellular lipolysis: a randomized cross-over trial
Authors: Straat Maaike E. , Jurado-Fasoli Lucas , Ying Zhixiong , Nahon Kimberly J. , Janssen Laura G.M. , Boon Mariëtte R. , Grabner Gernot F. , Kooijman Sander , Zimmermann Robert , Giera Martin , Rensen Patrick C.N. , Martinez-Tellez Borja 
Published: September 2022

ABSTRACTBackgroundThe application of cold exposure has emerged as an approach to enhance whole-body lipid catabolism. The global effect of cold exposure on the lipidome in humans has been reported with mixed results depending on intensity and duration of cold.MethodsThis secondary study was based on data from a previous randomized cross-over trial (ClinicalTrials.govID:NCT03012113). We performed sequential lipidomic profiling in serum during 120 min cold exposure of human volunteers. Next, the intracellular lipolysis was blocked in mice using a small-molecule inhibitor of adipose triglyceride lipase (ATGL; Atglistatin), and were exposed to cold for a similar duration. The quantitative lipidomic profiling was assessed in-depth using the Lipidyzer platform.FindingsCold exposure gradually increased circulating free fatty acids reaching a maximum at 60 min, and transiently decreased total triacylglycerols (TAGs) only at 30 min. A broad range of TAG species was initially decreased, in particular unsaturated and polyunsaturated TAG species with ≤5 double bonds, while after 120 min a significant increase was observed for polyunsaturated TAG species with ≥6 double bonds. The mechanistic study in mice revealed that the cold-induced increase in polyunsaturated TAGs was largely prevented by blocking adipose triglyceride lipase.InterpretationWe interpret these findings as that cold exposure feeds thermogenic tissues with TAG-derived fatty acids for combustion, resulting in a decrease of circulating TAG species, followed by increased hepatic production of polyunsaturated TAG species induced by liberation of free fatty acids stemming from adipose tissue.Research in ContextEvidence before this studyCold exposure has emerged as a novel non-pharmacological strategy to enhance whole-body lipid catabolism, to improve lipid homeostasis and ultimately cardiometabolic health. In mice, cold exposure accelerates the clearance of triacylglycerol (TAG)-rich lipoproteins from the circulation, reducing circulating TAGs. In humans however, the effect of cold exposure on whole-body TAG metabolism remained thus far controversial, as mixed results are reported depending on intensity and duration of cold.Added value of this studyHere, we performed sequential lipidomic profiling in serum during 120 min cold exposure of human volunteers. We show that cold exposure gradually increases circulating free fatty acids and transiently decreases total TAGs after 30 min, accompanied with a dynamic change in circulating TAGs as dependent on their saturation status and length. Specifically, cold exposure decreases a broad range of more saturated and shorter TAG species, while after 90-120 min polyunsaturated TAG species with≥6 double bonds start to increase. Subsequently, we performed a mechanistic study in mice, in which we show that the cold-induced increase in polyunsaturated TAGs is largely prevented when blocking intracellular lipolysis.Implications of all the available evidenceOur findings describe a mechanism by which cold exposure provides thermogenic tissues with TAG-derived fatty acids for combustion. At the same time, cold exposure increases lipolysis in white fat to drive hepatic TAG production to further feed thermogenic tissues. For the first time, these results show that the TAG lowering effect of cold exposure as observed in mice can be recapitulated in humans, which warrants further studies on the beneficial effects of cold exposure on accelerating lipid metabolism to improve cardiometabolic health.