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 dis eases, activate phospholipases A(2), a family of enzymes central to ph ospholipid metabolism and signal transduction. Little is known about i sozyme specificity with respect to this activation process. Accordingl y, a dietary:deficiency model known to induce oxidative stress was use d to investigate phospholipase A(2) isozyme activity in rat tissues. L ong-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. P hospholipase A(2) activity was assessed in lung, liver, kidney and hea rt 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 sampl es from rats deficient in both nutrients showed two- to tenfold higher calcium-independent phospholipase A(2) activity in lung cytosol and m icrosomes, and in liver cytosol compared with samples from control and single nutrient-deficient rats. In contrast, the calcium-dependent ac tivity was affected only slightly, The malondialdehyde concentration o f the organs was measured and the pattern obtained mirrored that of en hanced phospholipase A(2)-activity for lung but not for liver. The enh anced phospholipase A(2) activity in the lung cytosol and microsomes f rom rats deficient in both nutrients was partially blocked by p-bromop henacylbromide, further enhanced by dithiothreitol and unaffected by t reatment with diisopropylfluorophosphate. These results suggest that d eficiency of both vitamin E and selenium activates and/or induces uniq ue calcium-independent forms of phospholipase A(2) markedly in rat lun g, and to a lesser extent in liver.