CLEARANCE AND METABOLISM OF ARACHIDONIC-ACID BY C6 GLIOMA-CELLS AND ASTROCYTES

Effects of increased levels of arachidonic acid (AA) were analyzed in vitro by employment of C6 glioma cells and astrocytes from primary cul ture. The cells were suspended in a physiological medium added with ar achidonic acid (AA) in a concentration range from 0.01 to 0.5 mM. The concentration profiles of the fatty acid and AA-metabolites were subse quently followed for 90 min. AA was measured by gas chromatography, wh ereas the AA-metabolites PGF(2 alpha) and LTB(4) by radioimmunoassay ( RIA). Following administration of AA at 0.05 or 0.1 mM the medium was completely cleared from the fatty acid within 10 to 15 min. However, w hen 0.5 mM were added, AA concentrations of 0.36 +/- 0.055 mM were fou nd at 20 min, while 0.275 +/- 0.045 mM at 90 min. Addition of AA (0.1 mM) to cell-free medium was also associated with a steady decline of i ts concentration, although the decrease was markedly delayed as compar ed to the clearance in the presence of glial cells. AA was subjected t o dose-dependent metabolisation in the cell suspension as demonstrated by the production of PGF(2 alpha) and LTB(4). Following addition of 0 .01 or 0.5 mM, concentrations of PGF(2 alpha) increased to a 1.9- or 4 .9-fold level within 10 min, whereas those of LTB(4) rose to a 1.3- or 33.7-fold level. This was attenuated or completely blocked, respectiv ely, by the cyclo- and lipoxygenase inhibitor BW 755C. Formation of bo th metabolites from AA was also observed when studying astrocytes from primary culture. The current findings demonstrate an impressive effic acy of C6 glioma cells and astrocytes to clear arachidonic acid from t he suspension medium and to convert the lipid compound into prostaglan dins and leukotrienes. Uptake and metabolisation of AA by the glial el ements may play an important role in vivo, for example in cerebral isc hemia.