Leukocyte ascorbate and glutathione: potential capacity for inactivating oxidants and free radicals.
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Biomedical subjects
Publications and source records attributed to L Stankova.
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Oxygen consumption, phagocytosis, and activity of hexosomonophosphate shunt (HMS) of dog and human polystyrene latex-activated polymorphonuclear leukocytes were inhibited by normal and infected human prostatic fluid (PF) and prostate extract; resting cells were not affected. Granulocytes incubated in 7 per cent PF increased five times their zinc content. Inorganic zinc added to synthetic medium which contained activated granulocytes also inhibited O2 consumption and phagocytosis of yeast particles in a concentration-dependent manner; resting cells were not affected. Incubation of PF with CaNa2 ethylenediamine tetraacetic acid (EDTA) abolished the inhibitory effect of PF; extensive dialysis of PF against this chelating agent reduced the inhibition by half. After the PF was dialyzed against saline, the low molecular weight dialysate retained inhibitory effects. Extracts from dog liver, spleen, and human saliva were not inhibitory. Polyamines, which next to zinc are also present in PF in high concentrations, had no effect on granulocytes, O2 consumption, and HMS activity. Human as well as dog PF were inhibitory to human or dog granulocytes, respectively. Besides granulocytes, rat peritoneal macrophages were inhibited by PF as well. It is concluded that PF and extract from prostate inhibit various functions of phagocytes mainly because of high concentration of zinc. The existence of other, large molecular weight, heat-resistant substances in PF which contribute to zinc effect cannot be ruled out.
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Scorbutic guinea pig neutrophils (PMN) were found to produce H2O2 and kill Staphylococcus aureus as well as control PMN, suggesting that ascorbate does not contribute significantly to phagocyte H2O2 production or bacterial killing. Total and reduced ascorbate contents of human PMN was observed to fall upon phagocytosis, whereas dehydroascorbate increased to a lesser extent. These observations are consistent with the view that ascorbate constitutes a functional part of the PMN's redox-active components and may thus function to protect cell constituents from denaturation by the oxidants produced during phagocytosis.
Incubation of human leukocytes with dehydroascorbate (DHA) results in an increase in their reduced ascorbate (AA) content and hexose monophosphate shunt (HMS) activity, independent of oxygen supply. Incubation with AA induces these changes only in the presence of oxygen. The increase in HMS activity observed as cell AA increases by 1 micromol is the same during incubation with either DHA or AA. We propose that human leukocytes take up ascorbate as DHA (AA after oxidation to DHA) and reduce it promptly to AA, and that HMS stimulation upon incubation with either AA or DHA is a result of DHA reduction.
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