Subtoxic concentration of manganese synergistically potentiates 1-methyl-4-phenylpyridinium-induced neurotoxicity in PC12 cells

Abstract

Endogenous or exogenous substances that are toxic to dopaminergic cells have been proposed as possible cause of idiopathic Parkinson’s disease (PD). 1-Methyl-4-phenylpyridinium (MPP +) and manganese are dopaminergic neurotoxins causing a parkinsonism-like syndrome. Here, we studied the possible synergistic reaction between these two neurotoxins using rat PC12 pheochromocytoma cells. MPP + induced a delayed neurotoxicity in PC12 cells. Although low concentration of manganese did not cause cell damage, it markedly enhanced MPP +-induced neurotoxicity with characteristics of apoptosis, such as DNA laddering and activation of caspase-3. To understand the mechanism of enhancement of subtoxic concentration of manganese on MPP +-induced neurotoxicity, we investigated the reactive oxygen species (ROS) generation using a molecular probe, 2′,7′-dichlorofluorescein diacetate. Although subtoxic concentration of manganese alone did not induce ROS increase, it significantly enhanced the ROS generation induced by MPP +. We also determined the intracellular MPP + content. A time- and concentration-dependent increase of MPP + levels was found in PC12 cells treated with MPP +. The accumulation of MPP + by PC12 cells was not affected by manganese. Taken together, these studies suggest that co-treatment with MPP + and manganese may induce synergistic neurotoxicity in PC12 cells and that subtoxic concentration of manganese may potentiate the effect of MPP + by an ROS-dependent pathway.