EFFECTS OF SPHINGOSINE AND SPHINGOSINE ANALOGS ON THE FREE-RADICAL PRODUCTION BY STIMULATED NEUTROPHILS - ESR AND CHEMILUMINESCENCE STUDIES

Sphingolipids inhibit the activation of the neutrophil (PMN) NADPH oxi dase by protein kinase C pathway. By electron spin resonance spectrosc opy (ESR), we studied the effects of sphingosine (SPN) and chemilumine scence ceramide analogues on phorbol 12-myristate 13-acetate (PMA, 5 X 10(-7) M) stimulated PMN (6X10(6) cells), By ESR with spin trapping ( 100 mM DMPO: 5,5-dimethyl-1-pyrroline-N-oxide), we showed that SPN (5 to 8 X 10(-6) M), C-2-ceramide (N-acetyl SPN) and C-6-ceramide (N-hexa noyl SPN) at the final concentration of 2 X 10(-5) and 2x10(-4) M inhi bit the production of free radicals by stimulated PMN, The ESR spectru m of stimulated PMN was that of DMPO-superoxide anion spin adduct, Inh ibition by 5 x 10(-6) M SPN was equivalent to that of 30 U/ml SOD. SPN (5 to 8 X 10(-6) M) has no effect on in vitro systems generating supe roxide anion (xanthine 50 mM/ xanthine oxidase 110 mU/ml) or hydroxyl radical (Fenton reaction: 88 mM H2O2, 0.01 mM Fe2+ and 0.01 mM EDTA), SPN and N-acetyl SPN also inhibited the CL of PMA stimulated PMN in a dose dependent manner (from 2 X 10(-6) to 10(-5) M), but N-hexanoyl SP N was less active (from 2 X 10(-5) to 2 X 10(-4) M), These effects wer e compared with those of known PMN inhibitors, superoxide dismutase, c atalase and azide, SPN was a better inhibitor compared with these agen ts. The complete inhibition by SPN of ESR signal and CL of stimulated PMN confirms that this compound or one of its metabolites act at the l evel of NADPH-oxidase, the key enzyme responsible for production of ox ygen-derived free radicals.