Effect of dibutyryl cyclic AMP and isoproterenol on 7β-hydroxycholesterol cytotoxicity and esterification in spontaneous transformed cell lines derived from astrocyte primary cultures

Incubation of spontaneous transformed cells derived from astrocyte primary cultures with 30 μM 7β-hydroxycholesterol (7β-OH-CH) which is lethal to the cells or with 150 μM isoproterenol reduces the intracellular level of cAMP (4- and 2-fold respectively). Treatment of the cultures with 0.5 mM dibutyryl (db)-cAMP and 7β-OH-CH increases 3-fold the intracellular level of cAMP and both, db-cAMP and isoproterenol, raise the lethal effect of 7β-OH-CH and its esterification on C-3-OH by naturally occurring fatty acids (metabolite). Kinetics studies of net steryl-3-esters hydrolysis revealed that db-cAMP and isoproterenol lower that of cholesteryl-3-esters (2-fold) whereas the opposite is found for the metabolite. These data demonstrate that (i) high cAMP intracellular levels modulate differently the net hydrolysis of cholesteryl-3-esters and metabolite, (ii) isoproterenol acts otherwise than cAMP on 7β-OH-CH esterification, (iii) the cytotoxicity of 7β-OH-CH is linked to its own esterification. The accumulation of metabolite subsequent to db-cAMP or isoproterenol treatment as a result of acyl-CoA:cholesterol acyl transferase activation is discussed.