Resolvin D1 Protects Lipopolysaccharide-induced Acute Kidney Injury by Down-regulating Nuclear Factor-kappa B Signal and Inhibiting Apoptosis.

Background: Resolvin D1 (RvD1) is a newly found anti-inflammatory bioactive compound derived from polyunsaturated fatty acids. The current study aimed to explore the protective effect of RvD1 on lipopolysaccharide (LPS)-induced acute kidney injury (AKI) and its possible mechanism.

Methods: Both in vivo and in vitro studies were conducted. Male BALB/c mice were randomly divided into control group (saline), LPS group (LPS 5 mg/kg), RvD1 group (RvD1 5 μg/kg + LPS 5 mg/kg), and blockage group (Boc-MLP 5 μg/kg + RvD1 5 μg/kg + LPS 5 mg/kg). Boc-MLP is a RvD1 receptor blocker. The mice were intraperitoneally injected with these drugs and recorded for general condition for 48 h, while the blood and kidneys were harvested at 2, 6, 12, 24, and 48 h time points, respectively (n = 6 in each group at each time point). Human proximal tubule epithelial cells (HK-2) were randomly divided into control group (medium only), LPS group (LPS 5 μg/ml), RvD1 group (RvD1 10 ng/ml + LPS 5 μg/ml), and blockage group (Boc-MLP 10 ng/ml + RvD1 10 ng/ml + LPS 5 μg/ml). The cells were harvested for RNA at 2, 4, 6, 12, and 24 h time points, respectively (n = 6 in each group at each time point). Blood creatinine was tested by using an Abbott i-STAT portable blood gas analyzer. Tumor necrosis factor-α (TNF-α) level was detected by ELISA. Kidney pathology was observed under hematoxylin and eosin (HE) staining and transmission electron microscope (TEM). We hired immune-histological staining, Western blotting, and fluorescence quantitative polymerase chain reaction to detect the expression of RvD1 receptor ALX, nuclear factor-kappa B (NF-κB) signaling pathway as well as caspase-3. Kidney apoptosis was evaluated by TUNEL staining.

Results: RvD1 receptor ALX was detected on renal tubular epithelials. Kaplan-Meier analysis indicated that RvD1 improved 48 h animal survival (80%) compared with LPS group (40%) and RvD1 blockage group (60%), while RvD1 also ameliorated kidney pathological injury in HE staining and TEM scan. After LPS stimulation, the mRNA expression of toll-like receptor 4, myeloid differentiation factor 88, and TNF-α in both mice kidneys and HK-2 cells were all up-regulated, while RvD1 substantially inhibited the up-regulation of these genes. Western blotting showed that the phosphorylated-IκB/IκB ratio in LPS group was significantly higher than that in the control group, which was inhibited in the RvD1 group. RvD1 could inhibit the up-regulation of cleaved-caspase-3 protein stimulated by LPS, which was prohibited in RvD1 blockage group. RvD1 group also had a lower proportion of apoptotic nuclei in mice kidney by TUNEL staining compared with LPS group.

Conclusion: In LPS-induced AKI, RvD1 could decrease TNF-α level, ameliorate kidney pathological injury, protect kidney function, and improve animal survival by down-regulating NF-κB inflammatory signal as well as inhibiting renal cell apoptosis.