Repeated pulmonary exposures to zinc ions enhance inflammatory responses to subsequent metal exposures

Abstract

Aim of study: Metal contaminants contribute to adverse human health effects via acute and chronic exposures. Acute metal exposures followed by prolonged secondary metal exposures may elicit exaggerated inflammatory responses in certain individuals. The aim of this study is to determine whether repeated pulmonary exposures to zinc chloride (ZnCl2) alters subsequent responses to zinc or cerium exposures. Materials and Methods: Rats were intratracheally (IT) instilled with physiologic saline (n=24) or 0.05 mg/kg ZnCl2 (n=16) twice weekly for 4 weeks. Four days after last dosing, the saline group was divided into 3 subgroups, each IT-instilled with either saline, ZnCl2 or CeCl3 (both at 0.1 mg/kg). The ZnCl2 pre-instilled rats were divided into 2 subgroups, each instilled with 0.1 mg/kg ZnCl2 or CeCl3. Biomarkers of lung injury/inflammation were assessed in bronchoalveolar lavage (BAL) fluid collected 24 hours later. Oxidative stress was evaluated as total and reduced glutathione in BAL. Results: Increases in inflammatory cells, LDH, albumin, leptin, MCP-1, IP-10, fractalkine, TNFα and RANTES were observed in rats instilled with multiple PBS and then with 0.1 mg/kg ZnCl2 and CeCl3. However, rats pre-exposed repeatedly to 0.05 mg/kg ZnCl2 and then challenged with 0.1 mg/kg ZnCl2 or CeCl3 showed even more eosinophils, lymphocytes, and increased concentrations of hemoglobin and MIP-1α. Significant reduction in GSH/GSSG ratios in BAL in response to all ZnCl2 or CeCl3 exposures indicated oxidative stress. Conclusion: Previous exposure to zinc ions increases responsiveness to subsequent exposures to zinc and cerium ions. These findings suggest enhanced sensitization possibly due to a reduction in antioxidant defenses.