Oxidative stress and inflammatory responses involved in dietary nickel chloride (NiCl2)-induced pulmonary toxicity in broiler chickens

Abstract

The respiratory system is the primary target of nickel or nickel compound toxicity after inhalation exposure. There are no reports on the effects of nickel or nickel compounds on the lung via dietary administration at present. This study aimed to investigate pulmonary toxicity induced by dietary NiCl₂ in broiler chickens by using histopathology, qRT-PCR, and ELISA. In comparison with the control group, NiCl₂ intake induced oxidative damage to DNA (upregulation of 8-OHdG) and lipid peroxidation (upregulation of MDA), which was associated with the upregulation of NO and the downregulation of the expression levels and activities of pulmonary CuZn-SOD, Mn-SOD, CAT, GSH-Px, GR and GST mRNA. Also, the T-AOC activity, GSH content, ability to inhibit the generation of hydroxyl radicals, and ratio of GSH/GSSG were decreased in the groups treated with NiCl₂. Concurrently, the mRNA expression levels of iNOS, TNF-α, COX-2, IL-1β, IL-6, IL-8, IL-18 and IFN-γ were increased via the activation of NF-κB, and the mRNA expression levels of anti-inflammatory mediators including IL-2, IL-4 and IL-13 were decreased in the groups treated with NiCl₂. The above-mentioned results were the first to demonstrate that NiCl₂ intake induced pulmonary oxidative stress and inflammatory responses via the dietary pathway, which subsequently contributed to histopathological lesions and dysfunction.

Fig. 1. Histopathological changes in the lung at 42 days of age. Control group: no changes are observed; 300 mg kg^–1 group: the alveolar epithelial cells are swollen; 600 mg kg^–1 group: the alveolar epithelial cells are swollen. The alveolar walls are thickened with the infiltration of inflammatory cells and congestion; 900 mg kg^–1 group: the normal alveolar architecture has disappeared. Many exfoliated and necrotic alveolar epithelial cells, alveolar macrophages and inflammatory cells are observed (H&E).

Fig. 2. Changes in 8-OHdG, MDA and NO contents in the lung. The contents of NO (free radical), 8-OHdG (marker of oxidative damage to DNA), and MDA (LPO marker) are significantly increased in the NiCl₂-treated groups. The letters A, B, C, and D represent a significant difference (p < 0.01) among the four groups; the letters a, b, c, and d represent a difference (p < 0.05) among the four groups.

Fig. 3. Changes in mRNA expression levels of CuZn-SOD, Mn-SOD, CAT, GPx, GR, and GST in the lung. The mRNA expression levels of the antioxidant enzymes CuZn-SOD, Mn-SOD, CAT, GPx, GR, and GST are decreased in the lung. The letters A, B, C, and D represent a significant difference (p < 0.01) among the four groups; the letters a, b, c, and d represent a difference (p < 0.05) among the four groups.

Fig. 4. Changes in activities of T-AOC, CuZn-SOD, Mn-SOD, CAT, GPx, GR, GST, and ability to inhibit hydroxyl radicals in the lung. The activities of T-AOC, CuZn-SOD, Mn-SOD, CAT, GPx, GR, and GST, and the ability to inhibit hydroxyl radicals are decreased in the lung. The letters A, B, C, and D represent a significant difference (p < 0.01) among the four groups; the letters a, b, c, and d represent a difference (p < 0.05) among the four groups.

Fig. 5. Changes in contents of GSH and GSSG and the ratio of GSH/GSSG in the lung. The content of the non-enzymatic antioxidant molecule GSH and the ratio of GSH to GSSG are significantly decreased and the GSSG content is increased in the lung. The letters A, B, C, and D represent a significant difference (p < 0.01) among the four groups; the letters a, b, c, and d represent a difference (p < 0.05) among the four groups.

Fig. 6. Changes in the mRNA expression levels of inflammatory mediators in the lung. The mRNA expression levels of the pulmonary pro-inflammatory mediators NF-κB, TNF-α, IFN-γ, COX-2, iNOS, IL-1β, IL-6, IL-8 and IL-18 are increased, and the mRNA expression levels of the anti-inflammatory mediators IL-2, IL-4, and IL-13 are decreased in the lung. The letters A, B, C, and D represent a significant difference (p < 0.01) among the four groups; the letters a, b, c, and d represent a difference (p < 0.05) among the four groups.

Fig. 7. Changes in Ni content in the lung at 42 days. The pulmonary Ni content has significantly increased. Data are presented as the mean ± standard deviation (n = 5). The letters A, B, C, and D represent a significant difference (p < 0.01) among the four groups; the letters a, b, c, and d represent a difference (p < 0.05) among the four groups.