[Effect and related mechanism of acetate in alleviating acute kidney injury in septic rats through G-protein coupled receptor 43].

OBJECTIVE

To explore the protective effect and mechanism of acetate on sepsis-induced acute kidney injury (AKI) in rats.

METHODS

Male Sprague-Dawley (SD) rats were divided into sham operation group (Sham group), sepsis group caused by cecal ligation and puncture (CLP group), and acetate pretreatment group [NaA group, gavage sodium acetate (NaA) 300 mg/kg twice a day for 7 consecutive days before CLP] using a random number table method, with 7 rats in each group. The blood was taken from the main abdominal artery 24 hours after modeling, and renal tissue was collected from the rats. Enzyme linked immunosorbent assay (ELISA) was used to detect the serum levels of interleukin-6 (IL-6), tumor necrosis factor-α(TNF-α), and kidney injury molecule-1 (KIM-1). The concentration of serum acetate was determined by high performance liquid chromatography. The level of malondialdehyde (MDA) in renal tissue was detected by thiobarbituric acid method. Myeloperoxidase (MPO) in renal tissue was detected by colorimetric method. Hematoxylin-eosin (HE) staining was used to observe histopathological changes and assess renal tubule injury score. Western blotting was used to detect the protein expressions of G-protein coupled receptor 43 (GPR43) and adenosine monophosphate-activated protein kinase/silence infor-mation regulator 1/peroxlsome proliferator-activated receptor-γ coactlvator-1α (AMPK/SIRT1/PGC-1α) pathway. The positive expressions of GPR43, phosphorylation-AMPK (p-AMPK), SIRT1, PGC-1α were detected by immunohistochemistry.

RESULTS

Compared with Sham group, the serum levels of IL-6, TNF-α and KIM-1 were significantly increased in CLP group, the contents of MDA and MPO in renal tissue were increased, and the content of acetate was significantly decreased. HE staining results showed that most of the tubular epithelial cells were denaturated with local necrosis, a large number of brush border injuries and shedding, tubular structure destruction and fragmentation, and more inflammatory cells infiltrated the renal interstitium, the renal tubular injury score significantly increased. The expressions of GPR43, p-AMPK/AMPK, SIRT1, and PGC-1α in renal tissue were significantly reduced, indicating renal injury and increased levels of oxidative stress and inflammation in septic rats. Compared with the CLP group, the serum levels of IL-6, TNF-α and KIM-1 in the NaA group were decreased [IL-6 (ng/L): 126.20±6.23 vs. 161.00±17.37, TNF-α (ng/L): 85.59±7.70 vs. 123.50±17.78, KIM-1 (μg/L): 2.92±0.38 vs. 4.73±0.36, all P < 0.05]. The contents of MDA and MPO in renal tissue were significantly decreased [MDA (μmol/g): 6.56±0.18 vs. 8.53±0.34, MPO (U/g): 2.99±0.20 vs. 3.72±0.29, both P < 0.05]. HE staining showed that kidney injury had been alleviated, with a decrease in renal tubular injury score [1 (1, 2) vs. 3 (2, 3), P < 0.05]. Western blotting showed that the expressions of GPR43 and AMPK/SIRT1/PGC-1α pathway related proteins were significantly increased in renal tissue (GPR43/β-actin: 0.62±0.09 vs. 0.41±0.09, p-AMPK/AMPK: 0.58±0.07 vs. 0.44±0.06, SIRT1/β-actin: 0.85±0.06 vs. 0.73±0.03, PGC-1α/β-actin: 0.79±0.07 vs. 0.62±0.05, all P < 0.05). Immunohistochemistry showed that the positive expressions of GPR43, p-AMPK, SIRT1 and PGC-1α were significantly increased in renal tissue [GPR43 positive area: (33.66±2.62)% vs. (16.21±1.66)%, p-AMPK positive area: (16.64±2.11)% vs. (5.04±1.28)%, SIRT1 positive area: (14.61±2.86)% vs. (7.34±1.00)%, PGC-1α positive area: (15.30±2.39)% vs. (4.84±1.67)%, all P < 0.05], the serum acetate concentration significantly increased (μg/L: 32 479±14 683 vs. 12 935±3 197, P < 0.05).

CONCLUSIONS

Acetate can ameliorate sepsis-induced AKI, the mechanism may be related to the activation of AMPK/SIRT1/PGC-1α pathway by GPR43.