EVIDENCE FOR FREE RADICAL-MEDIATED REDUCTION OF LYMPHOCYTIC 5'-ECTONUCLEOTIDASE DURING STRESS

Previously we showed that stress and depression could result in a 50% lowering of lymphocytic 5'-ectonucleotidase (NT) which could be resolv ed by a diet high in antioxidants. This study suggested that high leve ls of free radicals mediated by stress/depression may be involved in l owering NT activities. The aim of the present study was to assess whet her oxygen radicals could directly affect NT and whether excess free r adicals generated in stress/depression may affect tissue ascorbate sto res. Exam-stressed students and depressed patients were compared respe ctively to these students at low stress and depressed patients on high antioxidant intakes. In this study, NT correlated positively with tis sue ascorbate stores. A range of antioxidants were tested as possible inhibitors of oxy radical interaction with NT using nitroblue tetrazol ium reduction to formazan with superoxide anion. At physiological plas ma concentrations ascorbate inhibited this reduction but dehydroascorb ate, tocopherol, retinol, selenium, urate, and reduced glutathione wer e ineffective. Superoxide anion directly reduced lymphocytic NT activi ty and this effect was reversed by either 100 mu molar ascorbate in vi tro or a high antioxidant intake in vivo. In conclusion, the low NT ac tivities and ascorbate stores found in stressed/depressed people appea r to be mediated by higher levels of free radicals reported in these s ubjects. These conclusions are consistent with published reports of (1 ) normal NT levels in melancholic patients on high antioxidant diets; (2) heightened inflammatory reponses during stress/depression; (3) low serum levels of zinc in depressed patients.