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

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 (ZnCl) alter 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 ZnCl (n = 16) twice weekly for 4 weeks. Four days after last dosing, the saline group was divided into three subgroups, each IT-instilled with either saline, ZnCl or CeCl (both at 0.1 mg/kg). The ZnCl pre-instilled rats were divided into two subgroups, each instilled with 0.1 mg/kg ZnCl or CeCl. 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 ZnCl and CeCl. However, rats pre-exposed repeatedly to 0.05 mg/kg ZnCl and then challenged with 0.1 mg/kg ZnCl or CeCl 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 ZnCl or CeCl 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.