Vitamin E. deficiency increases the synthesis of platelet-activating factor (PAF) in rat polymorphonuclear leucocytes

Vitamin E deficiency was found to stimulate FMLP (N-formyl-L-methionyl-L-leucyl-L-phenylalanine)-induced biosynthesis of PAF (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) in polymorphonuclear leucocytes (PMN) from rat peritoneum. In three separate experiments each, the amounts of PAF synthesized during 6 min and 12 min incubation of PMN cells from control, vitamin E-supplemented, and vitamin E-deficient rats were 129-240, 131-227 and 248-354 pmol/10(6) cells, respectively. The activity of the acetyl-transferase, which transfers the acetyl moiety of [3H]acetyl-CoA to 2-lysoPAF (1-O-alkyl-sn-glycero-3-phosphocholine) to form [3H]PAF, was higher in PMN homogenates from vitamin E-deficient rats (2.28 +/- 0.07 nmol/min/mg protein) than in those from E-supplemented rats (1.06 +/- 0.10 nmol/min/mg protein). However, there was no difference between the two groups in the activity of acetylhydrolase (4.26 +/- 0.71 and 4.26 +/- 0.06 nmol/min/mg protein, respectively), measured as degradation of [3H]PAF to [3H]lysoPAF. In vitro addition of alpha-tocopherol did not inhibit the increased activity of acetyl-transferase in vitamin E-deficient rats, indicating that the enzyme in vitamin E-supplemented rats was not directly inhibited by alpha-tocopherol. The acetyl-transferases of the two groups showed similar Km values for acetyl-CoA, but different Vmax values (225 microM and 6.4 nmol/min/mg protein in vitamin E-deficient rats, and 216 microM and 3.6 nmol/min/mg protein in vitamin E-supplemented rats), suggesting that the enzyme was not activated but increased in amount in vitamin E deficiency.