Effect of homocysteine on polymorphonuclear leukocyte activity and luminol-dependent chemiluminescence

Homocysteine is a non-protein-forming sulphur amino acid that plays an impo rtant role in remethylation and trans-sulphuration processes. In recent yea rs, a high plasma homocysteine concentration has been implied as a possible pathophysiological factor in atherosclerosis and artery and deep vein thro mbosis, probably through generation of H2O2, enhanced platelet activity and increased production of macrophage-derived tissue factor. Furthermore, an increase of polymorphonuclear leukocyte (PMN) activity mediated by homocyst eine-generated H2O2 has also been reported. Because some preliminary experi mental results in our laboratory did not confirm this effect of homocystein e on PMNs, we investigated the effect of homocysteine on the activity of PM Ns, measured by their luminol-dependent chemiluminescence. Moreover, we als o studied the effect of homocysteine in a luminol-hypochlorite chemilumines cent system. Our results clearly, indicate that homocysteine at mu mol/L co ncentrations (10-100 mu mol/L) slightly inhibits neutrophil chemiluminescen ce, while it strongly inhibits the luminescence of the luminol-hypochlorite system. Therefore, the hypothesis that homocysteine induces an increase of H2O2-mediated neutrophil activity is not supported and, probably, the comm on opinion that views the H2O2 generated by homocysteine as a possible mech anism for cardiovascular damage should be reconsidered. Copyright (C) 2000 John Wiley & Sons, Ltd.