EVIDENCE THAT MOBILE LIPIDS DETECTED IN RAT-BRAIN GLIOMA BY H-1 NUCLEAR-MAGNETIC-RESONANCE CORRESPOND TO LIPID DROPLETS

Mobile lipids have been detected by proton nuclear magnetic resonance (NMR) in animal and human tumors (cultured cells, biopsies, and in viv o), but their origin and subcellular location are still unclear, They have been associated with malignancy, metastatic ability, drug resista nce, and necrosis, We wanted to determine whether these lipids are loc ated within plasma membrane microdomains or in lipid droplets for a C6 cell-induced rat glioma, NMR-visible mobile lipids were found in all subcellular fractions isolated from the rat tumor, except in the cytos olic supernatants. Transmission electron microscopy showed that lipid droplets were present in all subcellular fractions containing NMR-visi ble lipids and in the necrotic and perinecrotic areas of the tumor, Th e mean diameter of droplets isolated by flotation in the subcellular f ractionation protocol was 0.97 mu m (n = 682; droplet profile diameter range between 0.2 and 5.0 mu m). The apparent diffusion coefficient f or these lipids (46 +/- 17 mu m(2)s(-1)) measured in vivo by proton sp ectroscopy was four orders of magnitude higher than would be expected if mobile lipids were inside plasma membrane microdomains. The combine d results demonstrated that mobile lipids detected in vivo by proton N MR in the C6 rat glioma are located in large lipid droplets, associate d with the necrotic process.