¹H MRS of high grade astrocytomas: Mobile lipid accumulation in necrotic tissue

Abstract

Sixty-four samples from six grade 4 astrocytomas were investigated ex vivo by 1H MRS at 360 MHz and subsequently by histopathology to obtain percentages of viable and necrotic tumour and grey and white matter. MR-visible lipids were detected in 87% of tumour samples. Necrotic foci were < 3 x 3 x 6 mm3. The means of the intensities/unit weight tissue of the lipid resonances at 5.33, 2.80, 1.29 and 0.89 ppm were significantly higher (p < 0.05) for three sets of comparisons: samples with 85-100% vs 50-75%; with 50-75% vs 10-40% and with 10-40% vs 0-5% necrosis. For the lipid resonance at 2.04 ppm the difference in the means was significant only for samples with 50-75% compared to those with 85-100% necrosis, because for samples with < 50% necrosis resonances from glutamine and possibly small amounts of glutamate, gamma-aminobutyrate and N-acetylaspartate anions contribute significantly to the spectral area at 2.0 ppm. We conclude that necrotic foci below MRI resolution yield the resonances at 1.3 and 0.9 ppm, and contribute to the intense resonance at 2.0 ppm observed in in vivo 1H spectra of some high grade astrocytomas.

Noninvasive estimation of tumour viability in a xenograft model of human neuroblastoma with proton magnetic resonance spectroscopy (1H MRS)

“…Consequently, events other than apoptosis or necrosis may also be responsible for the lipid resonances at 0.7 -1.5 ppm. This is in accordance with previous reports demonstrating the presence of MLs in viable tumour areas (Kuesel et al, 1994;. Recently, we performed 1 H spectroscopic investigations of a panel of human neuroblastoma cell lines in culture and found prominent ML signals in viable cells (Lindskog et al, unpublished observation).…”

“…These signals principally correspond to fatty acyl chains with methylene (CH 2 ) and methyl (CH 3 ) groups, and are commonly designated mobile lipids (MLs). Several reports indicate a possible correlation between the amount of MLs and tumour cell death (Kuesel et al, 1994(Kuesel et al, , 1996. Choline-(Cho) containing compounds (chemical shift ¼ 3.2 ppm) are abundant during the synthesis and degradation of cellular membranes.…”

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

“…In 1993, Callies et al (1993) demonstrated a correlation between the appearance of mobile lipids in proton magnetic resonance (MR) spectra of myeloma cells, and the formation of cytoplasmic droplets (1 mm in diameter). A relation between the amount of mobile lipids and the percentage of necrosis was also evidenced in proton spectra of human brain tumour biopsies (Kuesel et al, 1994b). All these results encouraged Rémy et al (1997) to make a new estimate of the size of the compartment in which mobile lipids were confined.…”

“…It has been suggested that the presence of lipid droplets in viable cells surrounding necrosis could be related to hypoxia Kuesel et al, 1994b). The aim of this study was to determine whether these cells were indeed hypoxic and if lipid droplets could be considered as a surrogate marker of hypoxia.…”

“…The harmful effects of the increase in the cell concentration of free fatty acids would be avoided by sequestering them in the form of triglycerides in lipid droplets. Thus, the accumulation of lipid droplets in viable tumoral cells located at the periphery of necrosis would result from a stress induced by the hypoxic state of these cells (Freitas et al, , 1996Kuesel et al, 1994b). This lipid accumulation would accelerate with the necrotic process (Kuesel et al, 1994b).…”