RELEVANCE OF ENDOGENOUS ASCORBATE AND TOCOPHEROL FOR BRAIN-CELL VITALITY INDICATED BY PHOTON-EMISSION

In vitro lipid peroxidation of brain cell membranes was recorded direc tly by monitoring the concomitant photon emission. Chemiluminescence a ppeared spontaneously after disintegration of vital brain cells (pig b rain cell homogenate, isolated oligodendrocytes), decreasing the high intracellular ascorbate concentration in the vital glial cell (1 mmol/ L) to a lower overall concentration (<100 mu mol/L). This had a prooxi dant effect in the homogenate. Intracellular high antioxidant ascorbat e concentrations were also efficient at protecting membrane lipids of vital oligodendrocytes against extracellular low prooxidant ascorbate concentrations (50 mu mol/L). The intramembranous cu-tocopherol conten t limited the antioxidant efficiency of ascorbate. With physiological concentrations (0.4 nmol of iron to 0.1 nmol of tocopherol per millili ter of membrane suspension), a 50% inhibition of lipid peroxidation wa s obtained with 410 nmol/ml ascorbate; this was reduced to 90 nmol/ml in the case of fivefold increased tocopherol content. So in vivo ascor bate concentrations were sufficient to protect against lipid peroxidat ion. Only when endogenous tocopherol was decreased to 20% was the in v ivo intracellular ascorbate concentration too small for antioxidative protection of lipids. The product of tocopherol concentration and asco rbate concentration, effective for 50% inhibition of lipid peroxidatio n, remained constant. When iron concentrations were increased 10(4)-fo ld, maximal chemiluminescence and malondialdehyde formation were incre ased twofold and less than 50%, respectively. This quantitative descri ption of the interactions between vitamin E, vitamin C, and iron are r elevant to the modification of interpretations of pathological conditi ons in parkinsonian brains. The chemiluminescent indicator reaction wa s characterized as a separate step following lipid peroxidation and ma londialdehyde formation. Its relevance as a new tool for sensitive mon itoring of changing cell vitality, e.g., by virus infection of cells o r by endogenous metabolites, is discussed.