ИСТИНА

Effect of homocysteine (HC) on functional activity of intact and activated rat neutrophils was studied. Intact neutrophils isolated from blood of healthy animals and neutrophils activated in vivo by administration of zymozan 4 hr before cell preparation were compared. HC effect on zymozan-induced respiratory burst in vitro measured by chemiluminescence procedure, intensity of degranulation process, intracellular cAMP content and participation of adenosine and NMDA receptors in neutrophils activation were tested. HC has been found to suppress the levels of reactive oxygen species (ROS) produced by myeloperoxidase in intact neutrophils. Moreover, HC (10 – 100 mkM) inhibits purified human myeloperoxidase. This effect is supposed to be caused by homocysteinylation of the enzyme. HC can also perform as a trap for hypochlorite anion similar to carnosine or taurine in the same concentration range. Milk xantine oxidase (0,5 – 10 mkM) is also inhibited by HC. These data suggest an antioxidative property of HC. Opposite effect of HC has been described when in vivo activated neutrophils were used in the experiments: high concentrations of HC (corresponded to toxic levels of HC in blood of human beings under neurodegenerative and cardiac diseases) strongly activated ROS production. Similar stimulation of ROS production by activated neutrophils was shown in the presence of NMDA. Moreover, effect of both HC and NMDA has been prevented by antagonist of NMDA receptors, MK-801. Activation of neutrophils is accompanied by de novo mRNA expression of NR1 subunit of NMDA receptors and internalization of NR1 and NR2B subunits on neutrophil membranes. Additionally, we have demonstrated that incubation of activated neutrophils with HC results in stimulation of degranulation process and increase of intracellular cAMP levels, the latter being suppressed by ZM 241385, antagonist of А2а adenosine receptors (Ki = 0.125 nM). This suggests an influence of HC on adenosine receptors mediated processes and therefore a regulation of neutrophils cytotoxic activity. We conclude that HC possesses both anti-oxidant and pro-oxidant effect on rat neutrophils depending on their functional state. Participation of adenosine receptors and glutamate receptors of NMDA class in its effect is discussed.