Pimonidazole binding in C6 rat brain glioma: relation with lipid droplet detection

Abstract

In C6 rat brain glioma, we have investigated the relation between hypoxia and the presence of lipid droplets in the cytoplasm of viable cells adjacent to necrosis. For this purpose, rats were stereotaxically implanted with C6 cells. Experiments were carried out by the end of the tumour development. A multifluorescence staining protocol combined with digital image analysis was used to quantitatively study the spatial distribution of hypoxic cells (pimonidazole), blood perfusion (Hoechst 33342), total vascular bed (collagen type IV) and lipid droplets (Red Oil) in single frozen sections. All tumours (n ¼ 6) showed necrosis, pimonidazole binding and lipid droplets. Pimonidazole binding occurred at a mean distance of 114 mm from perfused vessels mainly around necrosis. Lipid droplets were principally located in the necrotic tissue. Some smaller droplets were also observed in part of the pimonidazole-binding cells surrounding necrosis. Hence, lipid droplets appeared only in hypoxic cells adjacent to necrosis, at an approximate distance of 181 mm from perfused vessels. In conclusion, our results show that severe hypoxic cells accumulated small lipid droplets. However, a 100% colocalisation of hypoxia and lipid droplets does not exist. Thus, lipid droplets cannot be considered as a surrogate marker of hypoxia, but rather of severe, prenecrotic hypoxia.

An investigation of human brain tumour lipids by high‐resolution magic angle spinning 1H MRS and histological analysis

“…A study on endothelial cells exposed to hypoxia showed an increase in lipid body formation to be dependent on O 2 concentration (26). It has also been shown in C6 rodent brain tumours that the presence of mobile lipids in viable cells is primarily associated with the highly hypoxic regions adjacent to necrotic areas (27). Hence, in non-necrotic biopsy samples, the positive correlation of total lipid droplets with cell density (Fig.…”

“…The wider range of droplet sizes that we observed compared with the C6 cell studies can be explained by tumour heterogeneity in vivo compared with cultured cells that are all in the same phase. It has also been observed in rodent C6 brain tumours that there is an increase in the number and size of droplets on going from the tumour periphery towards the central necrotic core (27).…”

Fatty Acid Uptake and Lipid Storage Induced by HIF-1α Contribute to Cell Growth and Survival after Hypoxia-Reoxygenation

“…LDs have long been recognized, based on light microscopy, to accumulate in hypoxic cells (Zoula et al, 2003), and studies have shown increased lipid metabolism in hypoxia (Laurenti et al, 2011;Mylonis et al, 2012;Shen et al, 2012). TGs contained in LDs are degraded to generate free FAs when cells need to produce ATP via b-oxidation, or to synthesize membranes.…”

Lipid Droplets: Their Role in Nanoparticle-Induced Oxidative Stress

“…Oxidative stress-induced LD accumulation is well studied and has been demonstrated under hypoxic conditions, irradiation and treatments with chemotherapeutic agents. [43][44][45][46] Recently, Gubern et al demonstrated that triglyceride synthesis and LD biogenesis during stress mainly takes place from pre-existing fatty acids and is dependent on group VI phospholipase A 2 (PLA 2 -VIA). 40 One possible explanation for LD accumulation is the impairment in mitochondrial fatty acid -oxidation, resulting from mitochondrial membrane damage, and leading to an increase in triglyceride storage.…”