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Deficiency of Vitamin E and Selenium Enhances Calcium-Independent Phospholipase A₂ Activity in Rat Lung and Liver^1,2,3,4,

Department of Foods and Nutrition, Purdue University, West Lafayette, IN 47907-1264

Conditions promoting oxidative stress, which is implicated in many diseases, activate phospholipases A₂, 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 A₂ 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 A₂ 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 A₂ 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 A₂ 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 A₂ activity for lung but not for liver. The enhanced phospholipase A₂ 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 A₂ markedly in rat lung, and to a lesser extent in liver.

KEY WORDS: • selenium • lung • vitamin E • phospholipase A₂ • rats

¹ A preliminary report of this data was presented by Chia-Feng Kuo in the Graduate Student Research Award Abstract Competition at Experimental Biology 94, April 24–28, 1994, Anaheim, CA [Kuo, C. F. & Burgess, J. R. (1994) Deficiency of vitamin E and selenium induces a low molecular weight, calcium-independent form of phospholipase A₂ in rat lung. FASEB J. 8: A925 (abs.)].

² Supported in part by the American Cancer Society, IRG 17-31, the Purdue Agricultural Experiment Station, and by the Showalter Trust. C.-F.K. is the recipient of a Purdue Research Foundation Research Grant.

³ Paper number 14315 of the Purdue University Agricultural Experiment Station, West Lafayette, IN 47907.

⁴ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

⁵ To whom correspondence and reprint requests should be addressed.

Manuscript received 14 July 1994. Revision accepted 1 December 1994.