Renoprotective mechanisms of celastrol in high glucose-mediated HK-2 cell injury through inhibition of the PI3K/Akt/NF-κB signalling pathway

Hyperglycemia-induced inflammation and fibrosis in renal tubular epithelial cells are critical factors driving the progression of diabetic nephropathy (DN). Celastrol, a bioactive compound derived from Tripterygium wilfordii Hook.F, is recognized for its anti-inflammatory and anti-fibrotic properties. This study aimed to investigate the renoprotective effects of celastrol against high glucose (HG)-induced damage in human kidney 2 (HK-2) cells. Briefly, HK-2 cells were exposed to high glucose and treated with celastrol. Cell viability and apoptosis were evaluated using CCK-8 assay kit and flow cytometry, respectively. The pro-inflammatory cytokines, oxidative stress markers, and fibrotic-related proteins were measured using ELISA and immunoblotting. To further confirm the mechanistic actions of celastrol, the PI3K/Akt/NF-κB pathway was examined, and HG-treated cells were co-incubated with the NF-κB inhibitor bortezomib. Our result revealed that celastrol at the moderate concentration of 50 nM mitigated HG-induced toxicity, suggesting an optimal therapeutic window. Celastrol improved cell viability and reduced apoptosis in HG-treated HK-2 cells. It significantly decreased levels of inflammatory cytokines such as IL-6, TNF-α, IL-1β, and MCP-1, while enhancing antioxidant activities of GSH-Px and SOD, and lowering MDA levels, indicating diminished oxidative stress. Mechanistically, these renoprotective effects of celastrol partly attributed via inhibition of the PI3K/Akt/NF-κB signalling pathway, as blocking NF-κB signalling by bortezomib resulted in similar inhibitory effects against inflammation and fibrosis. Collectively, celastrol acts as a renoprotective agent against renal inflammation, oxidative stress, and fibrosis, partly through the inhibition of the PI3K/Akt/NF-κB pathway, offering potential therapeutic benefits against hyperglycemia-induced renal injury in DN.