¹⁹F NMR studies of changes in membrane potential and intracellular volume during dexamethasone‐induced apoptosis in human leukemic cell lines

Abstract

The induction of apoptosis in leukemic cells by dexamethasone is well known, but the mechanism of this type of cell death and of dexamethasone resistance by some variants is still poorly understood. Apoptotic cell death is preceded by many changes in cellular properties, such as glucose metabolism, cell size, cell density, and others. In this study, 19F-NMR has been used to characterize changes in cell membrane potential and intracellular accessible volume during dexamethasone induced apoptosis. One dex-sensitive (CEM-C7) and three dex-resistant variants (CEM-C1, CEM-ICR27, and CEM-4R4) were examined. We have observed separate intracellular and extracellular resonances for trifluoroacetate and trifluoroacetamide added to suspended leukemic cells. From the equilibrium distribution of these fluoro-compounds between intra and extracellular spaces, the changes in membrane potential and intracellular accessible volume were calculated. The membrane potential for CEM-C7 cells was found to significantly decrease in the presence of dexamethasone (9-mV decrease within 18 h of dexamethasone treatment), while that of CEM-ICR27 was found in some samples to increase on dexamethasone incubation. The membrane potential for CEM-C1 decreased slightly, while that of CEM-4R4 was not appreciably affected by dexamethasone. The reduction of membrane potential seems to be an early step in the mechanism of dexamethasone induced apoptosis. Although the intracellular volume varied with cell type and dexamethasone incubation (for CEM-C7), the fractional intracellular volume (alpha = Vin/Vcell) was found to be the same (0.82 +/- 0.06) for all the cell lines in the presence and absence of dexamethasone.

31P NMR characterization of cellular metabolism during dexamethasone induced apoptosis in human leukemic cell lines

“…We have indeed observed that after 24 h the reduction in PME level for CEM-C1 cells is essentially independent of dex incubation time. Another observation that suggests the arrest of apoptosis in CEM-C1 cells in the early stages, the Effects of Dex on Rote of C h a n g e of Pi for C E M p C early arrest of dex-induced change in membrane potential, has recently been reported (Adebodun and Post, 1993). That dexamethasone induced an alkaline shift in CEM-C7, CEM-C1, and CEM-4R4, but not in CEM-ICR27 cells, suggests that the alkaline shift is a receptor-mediated phenomenon.…”

“…Aspects of glucocorticoid-induced apoptosis that have been reported include the elevation of cytosolic Ca(I1) concentration, protein kinase C activation, altered level of protein and RNA biosynthesis, induction of specific endonuclease, increase in cell density, and the cleavage of nuclear chromatin at internucleosomal sites (Arends and Wyllie, 1991;Raff, 1992;Fesus et al, 1991;Williams, 1991;Gerschenson and Rotello, 1992;Kerr et al, 1972;Golstein et al, 1991;Zawydiwski et al, 1983;Wyllie, 1980;Cohen and Duke, 1984). Studies in our laboratory have reported differences in glucose metabolism between CEM-C1 and CEM-C7 cells (Post et al, 1992) and the alteration of membrane potential (Adebodun and Post, 1993) during dex-induced apoptosis in human leukemic cell lines.…”

13C-NMR investigation of protein synthesis during apoptosis in human leukemic cell lines

“…Cell cultures were stored and defrosted as previously reported (Adebodun and Post, 1993a). Cells were grown in Iscove's medium containing 5% heat-inactivated fetal calf serum (FCS) and antibiotics (100 units/mL penicillin ϩ 100 g/mL streptomycin).…”

“…The sensitivity of human leukemic cells to dex is mediated by the presence of functional glucocorticoid receptors, although some variants with functional glucocorticoid receptors (e.g., the CEM-C1 cell line) are known to exhibit resistance to dex (Post and Baum, 1990;Zawydiwski et al, 1983;Post et al, 1992). Some key features of apoptosis identified by various studies include the alteration in protein kinase C activity, alteration in glucose metabolism, increase in cell density (i.e., cell size shrinkage), alteration in cell membrane potential, elevation of cytosolic Ca (II) concentration, induction of specific endonucleases, alteration in phospholipid metabolism, reduction in the intracellular ATP level, altered level of protein and RNA biosynthesis, and the cleavage of nuclear chromatin at internucleosomal sites (Arends and Wyllie, 1991;Raff, 1992;Fesus et al, 1991;Williams, 1991;Kerr et al, 1972;Wyllie, 1980;Goldstein et al, 1991;Cohen and Duke, 1984;Post et al, 1992;Gerschenson and Rotello, 1992;Adebodun and Post, 1993a, 1995.…”

Estimation of transmembrane potential of thymic lymphocytes during dexamethasone-induced apoptosis

“…On the contrary, FI of cyanic and merocyanic stains and anionic probes (ANS and oxolon stains) decreases with an increase in potentials. TMPs of various cells were intensely studied by using PFPs [7,12,14]. Values of Aqb of the mitochondrial and plasma membranes in lymphocytes, macrophages, hepatocytes, and adipocytes were determined.…”