Antioxidant and pro-oxidant capacity of catecholamines and related compounds. Effects of hydrogen peroxide on glutathione and sphingomyelinase activity in pheochromocytoma PC12 cells: potential relevance to age-related diseases

The antioxidant and pro-oxidant capacity of catecholamines (CA) and related compounds were analyzed using the oxygen radical absorbance capacity (ORAC ) assay. In the assay 2,2 ' -azobis (2-amidino-propane) dihydrochloride (AA PH), a peroxyl radical generator, ROOo; H2O2-Cu2+, mainly a hydroxyl radica l generator, (OH)-O-o; and Cu2+ a transition metal were used. The antioxida nt effect of CA and its related compounds were in the order: neurotransmitt ers: dopamine (DA), norepinephrine (NE) > metabolites > amino acid precurso rs as measured by using AAPH. The antioxidant effect of CA and related comp ounds as measured by using AAPH were linearly correlated with concentration , while the antioxidant effect of CA in scavenging (OH)-O-o produced by H2O 2-Cu2+ increased proportionally to concentration at low concentration, but after reaching a maximum declined with increasing concentration. In the pre sence of Cu2+, CA acted as pro-oxidant. Glutathione (GSH) acted as a pro-ox idant when H2O2-Cu2+ or when CU2+ alone was used as an oxidant and showed m uch higher pro-oxidant effect than DA, which could have relevance in the vu lnerability of dopaminergic neurons to oxidative stress in the aging and ag ing related diseases. The antioxidant capacity of CA and many related compo unds seems to be correlated with the numbers of hydroxyl groups and their p osition on the benzoic ring. The 0-methylation and sulfate conjugation of t he hydroxyl substitution inactivates both the antioxidant and pro-oxidant a ctivities of CA. Our results show that oxidative stress induced by low (5 m uM) or high (300 muM) doses H2O2 in pheochromocytoma PC12 cells significant ly up-regulate the activity of Mg-dependent neutral sphingomyelinase (Sase) , and significantly decreased GSH.