Comparison of glutathione peroxidase-3 protein expression and enzyme bioactivity in normal subjects and patients with sepsis

Background: Serum glutathione peroxidase-3 (GPx-3) is known as a key selenoprotein with antioxidant properties. GPx-3 deficiency has been associated with sepsis. The objectives of this study are (1) to compare the GPx-3 protein concentrations and GPx-3 bioactivity in normal healthy subjects and septic patients, and (2) to evaluate the relationship between GPx-3 bioactivity and its protein concentration. Methods: Serum samples were collected from 50 normal healthy subjects and 70 septic patients. The reliable bioanalytical methods for GPx-3 protein concentration and bioactivity in human serum were developed and validated. Analyses of GPx-3 bioactivity and GPx-3 protein concentration were then performed. Results: Geometric mean GPx-3 bioactivity was 78.13. U/l for patients with sepsis, significantly lower than normal subjects with 108.21. U/l (p <. 0.0001). Similarly, the GPx-3 protein concentration was significantly lower in patients with sepsis than in normal subjects, with the mean GPx-3 value of 0.78 vs 3.10. μg/ml, respectively (p <. 0.0001). A positive correlation was observed between the GPx-3 bioactivity and its corresponding protein concentration in septic serum samples (R = 0.74, p <. 0.0001), regardless of gender or age difference. Conclusion: These findings suggest that the decrease in GPx-3 bioactivity observed in the septic patients was resulted from the significant sepsis-related decline of GPx-3 protein concentrations.