Relationship between pulmonary surfactant protein and lipid peroxidation in lung injury due to paraquat intoxication in rats

Abstract

Background: Pulmonary damage resulting from lipid peroxidation is a principal effect of paraquat intoxication. The host-defense functions of surfactant are known to be mediated by the surfactant proteins A and D (SP-A and SP-D, respectively). The primary objective of this study was to evaluate the variations over time in levels of surfactant protein and lipid peroxidation (LPO) in lung tissue following free-radical-induced injury.

Methods: 42 adult, male, Sprague-Dawley rats were administered intraperitoneal injections of paraquat (35 mg/kg body weight). SP-A and SP-D levels were determined via Western blot. LPO in the left lung homogenate was measured via analyses of the levels of thiobarbituric acid-reactive substances.

Results: LPO levels peaked at 6 hours, with no associated histological changes. SP-D levels increased until hour 12 and declined until hour 48; SP-D levels subsequently began to increase again, peaking at hour 72. SP-A levels peaked at hour 6, declining thereafter.

Conclusions: We suggest that in the early phase of paraquat injury, SP-D levels reflect alveolar damage and that de novo synthesis of SP-D takes 72 hours. Levels of SP-A, on the other hand, reflect abnormalities in the surfactant system in the late stage of paraquat intoxication. Surfactant proteins may play a role in protecting the lungs from reactive oxygen injury. A time-dependent variation has been observed in the levels of surfactant proteins A and D following paraquat injury, and it has been suggested that these proteins play a role in the protection of lung tissue against ROS-induced injuries.

Figure 1

Variations in the levels of surfactant protein D (SP-D) over time in rats treated with paraquat. SP-D was quantified via Western blot analysis and data were expressed as a fraction of that measured in the control group. Data are expressed as the meanSD values. No significant differences were detected in the initial SP-D levels among the groups (as assessed by ANOVA). The SP-D level in the 72-hour postinjection group was significantly higher than those of the control, and the 24-hour and 48-hour postinjection groups (^* ; p<0.05) (Student's t-test).

Figure 2

Variations in the levels of surfactant protein A (SP-A) over time in rats treated with paraquat. SP-A was quantified via Western blot analysis and data are expressed as a fraction of that measured in the control group. Data are presented as the meanSD values. Differences between groups were statistically significant (as assessed by ANOVA): SP-A levels in the control, and 6-hour and 12-hour postinjection groups were significantly different from those of the 24-hour, 48-hour, and 72-hour groups (^* ; p<0.05) (Tukey's test)

Figure 3

Variations in the levels of lipid peroxidation over time in rats treated with paraquat. Concentrations of thiobarbituric acid-reactive substances (TBA-RS) in left lung tissue, expressed as a fraction of that measured in the control group. Data are expressed as meanSD values. Differences between groups were statistically significant (as assessed by ANOVA): levels of lipid peroxidation in the control group differed significantly from those measured in the 6-hour postinjection group (^* ; p<0.05) (Tukey's test)

Figure 4

Light micrograph showing the inflammatory cell infiltration occurring after paraquat injection (hematoxylin and eosin, 100). The control (A) and 6-hour postinjection groups (B) evidence normal cytoarchitecture. The 12-hour postinjection group (C) exhibits inflammatory cell infiltration around the bronchiole. The 72-hour postinjection group (D) exhibits diffuse lung damage on the parenchyma and peribronchiole.