A simplified procedure to trace triglyceride‐rich lipoprotein metabolism in vivo

Glycerol tri[(3)H]oleate and [(14)C]cholesteryl oleate double‐labeled triglyceride‐rich lipoprotein (TRL)‐like particles are a well‐established tool to trace the effect of lipid‐modulating interventions on TRL metabolism. The routine generation of these particles involves sonication of a lipid mixture and subsequent fractionation of resulting particles into populations of different average size through density gradient ultracentrifugation. Here, we describe a simplified and more time‐efficient procedure for preparing TRL‐like particles without the need of fractionation. The simplified procedure shortened the preparation of particles from over 4 h to less than 2 h and generated particles with a higher yield, although with a smaller average size and more heterogeneous size distribution. In C57Bl/6J mice housed at thermoneutrality (30°C), the two preparations showed highly comparable plasma clearance and organ distribution of glycerol tri[(3)H]oleate‐derived [(3)H]oleate and [(14)C]cholesteryl oleate, as measures of lipolysis and core remnant uptake, respectively. Upon a cold challenge (14°C), plasma clearance was accelerated due to enhanced uptake of glycerol tri[(3)H]oleate‐derived [(3)H]oleate by brown adipose tissue. The simplified procedure resulted in a modestly increased particle uptake by the spleen, while uptake by other organs was comparable between the two preparations. In conclusion, the simplified procedure accelerates the preparation of TRL‐like particles for tracing in vivo TRL metabolism. We anticipate that this time‐efficient procedure will be useful for incorporation of PET‐traceable lipids to obtain more insight into human lipoprotein metabolism.