title: 1H MRS-visible lipids accumulate during apoptosis of lymphoma cells in vitro and in vivo.
abstract: Proton MRS detection of cellular lipid accumulation has been suggested as a noninvasive method for detecting apoptosis or programmed cell death (PCD) in vivo. The spectral changes that have been observed in apoptotic cells include a general increase in lipid signals and a specific increase in the ratio of the lipid methylene-to-methyl peak intensities. These changes were investigated here following drug-induced apoptosis, both in vitro with a murine lymphoma cell line (EL-4) and in vivo following implantation of these cells to form subcutaneous tumors. Fluorescence microscopy and flow cytometric measurements with a lipophilic dye revealed an accumulation of cytoplasmic lipid droplets in isolated EL-4 cells undergoing etoposide-induced apoptosis. (1)H MR spectra (both diffusion-weighted (DW) and unweighted) showed an increase in lipid signals. However, the methylene/methyl peak ratio showed only minimal changes. Localized in vivo spectroscopy of EL-4 tumors also showed an increase in lipid signals, including a signal from polyunsaturated lipid at 2.8 ppm, after 16-24 h of drug treatment. Again there was no significant change in the methylene/methyl peak ratio. This study confirms that MRS-detectable lipids accumulate in tumor cells undergoing apoptosis, and therefore may be usable as a marker for the noninvasive detection of tumor cell apoptosis in the clinic.
authors.affiliation: Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Schmitz
authors.forename: Mikko I
authors.initials: MI
authors.lastname: Kettunen
authors.forename: De-En
authors.initials: DE
authors.lastname: Hu
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Brindle
mesh_terms: D000818:Animals; D017209:Apoptosis; D014408:Biomarkers, Tumor / Q000378:metabolism*; D002452:Cell Count / Q000379:methods*; D045744:Cell Line, Tumor; D005047:Etoposide / Q000494:pharmacology; D005260:Female; D050356:Lipid Metabolism; D008223:Lymphoma / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D051379:Mice; D008810:Mice, Inbred C57BL; D011522:Protons; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013223:Statistics as Topic
chemical_list: D014408:Biomarkers, Tumor; D011522:Protons; D005047:Etoposide