DEFICIENCY OF VITAMIN-E AND SELENIUM ENHANCES CALCIUM-INDEPENDENT PHOSPHOLIPASE A(2) ACTIVITY IN RAT LUNG AND LIVER

Conditions promoting oxidative stress, which is implicated in many diseases, activate phospholipases A(2), a family of enzymes central to phospholipid metabolism and signal transduction. Little is known about isozyme specificity with respect to this activation process. Accordingly, a dietary:deficiency model known to induce oxidative stress was used to investigate phospholipase A(2) isozyme activity in rat tissues. Long-Evans hooded rats were fed purified diets for 6 wk with or without;the addition of vitamin E and selenium in a 2 x 2 factorial design. Phospholipase A(2) activity was assessed in lung, liver, kidney and heart cytosol and microsomes in the presence (5 mmol/L CaCl2) or absence (5 mmol/L EGTA) of calcium with dipalmitoylphosphatidylcholine at pH 6.5. Lung phospholipase A(2) activity was also assessed with 1-stearoyl-2-arachidonoylphosphatidylcholine as substrate at pH 8.5. Organ samples from rats deficient in both nutrients showed two- to tenfold higher calcium-independent phospholipase A(2) activity in lung cytosol and microsomes, and in liver cytosol compared with samples from control and single nutrient-deficient rats. In contrast, the calcium-dependent activity was affected only slightly, The malondialdehyde concentration of the organs was measured and the pattern obtained mirrored that of enhanced phospholipase A(2)-activity for lung but not for liver. The enhanced phospholipase A(2) activity in the lung cytosol and microsomes from rats deficient in both nutrients was partially blocked by p-bromophenacylbromide, further enhanced by dithiothreitol and unaffected by treatment with diisopropylfluorophosphate. These results suggest that deficiency of both vitamin E and selenium activates and/or induces unique calcium-independent forms of phospholipase A(2) markedly in rat lung, and to a lesser extent in liver.