BACKGROUND: Studies have reported the antioxidant effects of lead and cadmium in the central nervous system, but very few have addressed the combined toxicity of lead and cadmium. The mechanisms by which these combined heavy metals are toxic, as well as how to protect cells from these agents, remains poorly understood.OBJECTIVE: Primary cultured rat cortical neurons were used to determine the effects of combined lead and cadmium on levels of glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), catalase (CAT), and acetylcholinesterase (AChE), as well as malondialdehyde (MDA), and to evaluate the neuroprotective effects of N-acetylcysteine (NAC).DESIGN, TIME AND SETTING: An in vitro toxicological observation was performed at the Comparative Medicine Center of Yangzhou University from August 2007 to April 2008.MATERIALS: Lead acetate, cadmium acetate, and NAC were purchased from Sigma-Aldrich (St. Louis, USA). Commercial kits of GSH-Px, SOD, CAT, AChE, and MDA were purchased from Nanjing Jiancheng Bioengineering Institute, Nanjing, China.METHODS: The cerebral cortical neurons were isolated from newb Sprague dawley rats at 24 hours after birth and primary cultured for 6 days. Thereafter, the cells were treated with a range of cadmium doses (0, 5.0, and 10.0 μmol/L), lead doses (0, 1.0, and 2.0 μmol/L), or a combination of the two for 12 hours at 37 °C in a 5% CO_2 incubator, respectively. In addition, the cells were incubated with different doses of cadmium and/or lead and (0 and 50 μmol/L) NAC for 12 hours to assess the protective effects on cell survival.MAIN OUTCOME MEASURES: The activity of SOD, GSH-Px, CAT, and AChE, as well as MDA content, in the cell lysates was detected using commercial kits.RESULTS: At 12 hours after treatment, compared to the control group, activity of GSH-Px, SOD, and AChE in the lead, cadmium, or combined treated cells was significantly decreased with increasing doses of cadmium/or lead (P < 0.05), but CAT activity and MDA levels were significantly increased (P < 0.05). The combination of cadmium and lead led to higher levels of toxicity than individual exposure.CONCLUSION: The degree of oxidative damage increased when the two heavy metals were combined. NAC protected neonatal cortical neurons by increasing activity of anti-oxidative enzymes, and reducing lipid peroxidation, but the reduction was not statistically significant.