Surfactant protein-D (SP-D) gene polymorphisms and serum level as predictors of susceptibility and prognosis of acute kidney injury in the Chinese population

Background: Injury to the kidney epithelial barrier is a characteristic feature of acute kidney injury (AKI). Serum surfactant protein-D (SP-D), a known biomarker of damaged alveolar epithelium, is also secreted by renal tubular epithelial cells. Therefore, the aim of this study was to examine the possible association of SP-D with AKI susceptibility and prognosis. Methods: In this study, 159 AKI patients and 120 healthy individuals were included. SP-D polymorphisms Thr11Met and Thr160Ala, AKI patient serum SP-D levels at days 1, 3 and 7 and urine KIM-1 levels in both AKI patients and controls were examined. The obtained results were correlated with the AKI stage, duration of renal replacement therapy (RRT) and prognosis. Results: Serum SP-D level in AKI patients was higher than controls (p < 0.01). SP-D 11Thr/Thr genotype was more frequent in AKI patients than in controls (p < 0.01). Furthermore, AKI patients with SP-D 11Thr/Thr genotype had significantly higher serum SP-D levels (p < 0.05) compared to other genotypes. Serum SP-D levels corrected to the progression of AKI with a peak at day 3. Furthermore, the SP-D 11Thr/Thr genotype frequency and baseline serum SP-D level were higher in patients who subsequently died. Baseline serum SP-D levels positively correlated with the urine KIM-1 levels, AKI stage and RRT duration. Conclusion: In our study, elevated serum SP-D was associated with worse AKI clinical outcomes and patients with SP-D 11Thr/Thr genotype were more susceptible to AKI. Collectively, these findings suggest that SP-D may be useful as a biomarker of AKI susceptibility and prognosis.