Role of cytoplasmic lipids in altering diphenylhexatriene fluorescence polarization in malignant cells

Prior studies of fluorescence anisotropy (polarization) with diphenylhexatriene in normal and malignant cell populations have shown differences which have been attributed to an altered membrane lipid composition in cancer. We studied fresh tumor cells from patients with diverse lymphoid neoplasms and found a discrete range of whole-cell fluorescence polarization values (P values) for each type of neoplasm. Following cell fractionation, however, the P values of isolated plasma membranes from malignant cells did not differ significantly from the values obtained with normal donor lymphocytes. Therefore, the altered whole-cell fluorescence polarization measurements in malignant cells are not likely to be due to gross lipid changes in the plasma membrane. Histochemical staining and cell fractionation revealed the presence of cytoplasmic lipid accumulations, and these had extremely low P values, which could account for the low P values of malignant cells. Complementary studies of lymphoid cell lines showed whole-cell fluorescence polarization measurements to be extremely sensitive to exogenous lipid supplements, but membrane values remained stable. We conclude that alterations in membrane lipid fluidity, as measured by the diphenylhexatriene probe, are not consistently found in lymphoid neoplasms and hence cannot presently be invoked to account for the malignant behavior of these cells. However, intracellular neutral lipid accumulation appears to be a common feature of the lymphoid neoplasm. The lipid alterations described could be characteristic of cell immaturity or proliferation rather than malignancy; nevertheless, they may convey unappreciated biological consequences.