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 culture. The cells were suspended in a physiological medium added with arachidonic acid (AA) in a concentration range from 0.01 to 0.5 mM. The concentration profiles of the fatty acid and AA-metabolites were subsequently followed for 90 min. AA was measured by gas chromatography, whereas the AA-metabolites PGF2 alpha and LTB4 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, when 0.5 mM were added, AA concentrations of 0.36 +/- 0.055 mM were found 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 its concentration, although the decrease was markedly delayed as compared to the clearance in the presence of glial cells. AA was subjected to dose-dependent metabolisation in the cell suspension as demonstrated by the production of PGF2 alpha and LTB4. Following addition of 0.01 or 0.5 mM, concentrations of PGF2 alpha increased to a 1.9- or 4.9-fold level within 10 min, whereas those of LTB4 rose to a 1.3- or 33.7-fold level. This was attenuated or completely blocked, respectively, by the cyclo- and lipoxygenase inhibitor BW 755C. Formation of both metabolites from AA was also observed when studying astrocytes from primary culture. The current findings demonstrate an impressive efficacy of C6 glioma cells and astrocytes to clear arachidonic acid from the suspension medium and to convert the lipid compound into prostaglandins and leukotrienes. Uptake and metabolisation of AA by the glial elements may play an important role in vivo, for example in cerebral ischemia.