Roles of peroxiredoxin 6 in the regulation of oxidative stress to lipopolysaccharide-induced acute lung injury

Abstract

To investigate the roles of peroxiredoxin (Prdx) 6 in the regulation of oxidative stress to lipopolysaccharide (LPS)-induced acute lung injury (ALI) in mice. Prdx6 knockout mice were tested for their genotype by PCR and Prdx6 protein expression was measured in lungs by immunohistochemistry. Eighteen male Prdx6 knockout mice were randomised to the Prdx6 knockout control group and the Prdx6 knockout LPS 24 h group, with 9 mice in each group. Eighteen male wild-type C57BL/6J mice were randomised to the wild-type control group and the wild-type LPS 24 h group, with 9 mice in each group. ALI was induced by intratracheal administration of 5mg/kg LPS. Twenty-four hours after stimulation, lung tissue slides were stained with hematoxylin and eosin for histological evaluation. The concentration of protein in the bronchial alveolar lavage fluid (BALF) was measured by using the Micro BCA Protein Assay Kit. Levels of reactive oxygen species (ROS) in the lungs were quantified by measurement of hydrogen peroxide (H(2)O(2)). Lipid and protein peroxidation were measured as levels of malondialdehyde (MDA) and protein carbonylation. H(2)O(2), MDA, protein carbonyl, total superoxide dismutase (SOD) activity, and total antioxidative capacity (TAOC) in lungs were measured by using assay kits from the manufacture. Prdx6 knockout mice presented their genotype and there was no Prdx6 protein expression in the lung. Increased polymorphonuclear cells in alveoli and bronchial wall thickening were observed in the lungs of LPS groups, which were more severe in Prdx6 knockout LPS 24 h group compared with wild-type LPS 24 h group. LPS instillation induced a significant elevated protein concentration in BALF in wild-type LPS 24 h group (441 ± 54) mg/L compared with wild-type control group (168 ± 20) mg/L (t = -4.71, P < 0.01). Significantly increased protein level in BALF was observed in Prdx6 knockout LPS 24 h group (770 ± 66) mg/L compared with wild-type LPS 24 h group (t = -3.69, P < 0.01). LPS instillation induced a significantly decreased SOD activity in wild-type LPS 24 h group (16.0 ± 1.2) U/mg protein compared with wild-type control group (26.5 ± 3.9) U/mg protein (t = 6.22, P < 0.01). SOD activity in Prdx6 knockout LPS 24 h group (14.5 ± 5.3) U/mg protein was not statistical different from wild-type LPS 24 h group (t = 0.56, P = 0.60). LPS instillation induced a significantly increased H(2)O(2) and MDA in wild-type LPS 24 h group [H(2)O(2)(52.3 ± 7.8) nmol/g protein; MDA (3.3 ± 0.5) nmol/mg protein] compared with wild-type control group [H(2)O(2)(29.5 ± 3.2) nmol/g protein, (t = -4.25, P < 0.01); MDA (1.6 ± 0.8) nmol/mg protein, (t = -5.94, P < 0.01)]. Significantly increased H(2)O(2) and MDA [H(2)O(2)(73.5 ± 12.4) nmol/g protein, (t = -3.01, P = 0.02); MDA (5.9 ± 0.9) nmol/mg protein, (t = -6.01, P < 0.01)] were observed in Prdx6 knockout LPS 24 h group compared with wild-type LPS 24 h group. No significant difference of protein carbonylation was observed in wild-type LPS 24 h group (6.9 ± 1.2) nmol/mg protein compared with wild-type control group (6.1 ± 0.9) nmol/mg protein (t = -1.62, P = 0.15). Significantly increased protein carbonylation (8.9 ± 0.9) nmol/g protein was observed in Prdx6 knockout LPS 24 h group compared with wild-type LPS 24 h group (t = -2.76, P = 0.03). LPS instillation induced a significantly decreased TAOC in wild-type LPS 24 h group (4.7 ± 0.6) U/mg protein compared with wild-type control group (6.5 ± 0.4) U/mg protein (t = 3.35, P < 0.01). Significantly decreased TAOC was observed in Prdx6 knockout LPS 24 h group (3.9 ± 0.4)U/mg protein compared with wild-type LPS 24 h group (t = 2.44, P = 0.04). The above parameters were not statistically different between Prdx6 knockout control group and wild-type control group. Deletion of peroxiredoxin 6 exaggerated LPS-induced acute lung injury with increased oxidative stress.