Accumulating evidence has implicated that liraglutide, one of the human glucagon‑like peptide‑1 (GLP‑1) analogues, elicits protective effects on diabetic nephropathy; however, the mechanism has yet to be fully elucidated. The present study aimed to assess the effect and underlying mechanisms of liraglutide in diabetic nephropathy. Wistar rats with streptozotocin‑induced diabetes mellitus were subcutaneously injected with liraglutide or phosphate buffer for 12 weeks at a dose of 0.3 mg/kg/12 h. The biochemical parameters were determined, renal histological examination was performed by hematoxylin and eosin and periodic acid Schiff base staining, and the mRNA levels of nuclear factor κB (NF‑κB) and endothelial nitric oxide synthase (eNOS) were assessed by quantitative polymerase chain reaction. Furthermore, the protein expression of NF‑κB and eNOS as well as eNOS phosphorylation were examined by western blot analysis and the levels of inflammatory cytokines downstream of NF‑κB were evaluated by fluorescence-assisted cell sorting and finally, the eNOS activity and nitric oxide (NO) production were evaluated by ELISA. Liraglutide decreased the levels of total cholesterol, urine, 24-h urinary albumin, blood urea nitrogen, serum creatinine and histological damage. Liraglutide also reduced the expression of NF‑κB at mRNA and protein levels; the expression of tumor necrosis factor‑α, interferon‑γ, interleukin‑6 and monocyte chemoattractant protein‑1 were also reduced. By contrast, eNOS phosphorylation, eNOS activity and NO production appeared to have increased. Liraglutide may have a direct beneficial effect on diabetic nephropathy by improving eNOS activity by inhibiting the NF‑κB pathway without eliciting a glucose lowering effect.

Toll-like receptor 4 (TLR4)-mediated immune and inflammatory signaling serves a pivotal role in the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Our previous study demonstrated that celastrol treatment was able to improve hepatic steatosis and inhibit the TLR4 signaling cascade pathway in type 2 diabetic rats. The present study aimed to investigate the effects of celastrol on triglyceride accumulation and inflammation in steatotic HepG2 cells, and the possible mechanisms responsible for the regulation of cellular responses following TLR4 gene knockdown by small interfering RNA (siRNA) in vitro. A cell model of hepatic steatosis was prepared by exposing the HepG2 cells to free fatty acid (FFA) in the absence or presence of celastrol. Intracellular triglycerides were visualized by Oil red O staining, and the TLR4/myeloid differentiation primary response 88 (MyD88)/nuclear factor-κB (NF-κB) signaling cascade pathway were investigated. To directly elucidate whether TLR4 was the blocking target of celastrol upon FFA exposure, the cellular response to inflammation was determined upon transfection with TLR4 siRNA. The results revealed that celastrol significantly reduced triglyceride accumulation in the steatotic HepG2 cells, and downregulated the expression levels of TLR4, MyD88 and phospho-NF-κBp65, as well as of the downstream inflammatory cytokines interleukin-1β and tumor necrosis factor α. Knockdown of TLR4 also alleviated FFA-induced inflammatory response. In addition, co-treatment with TLR4 siRNA and celastrol further attenuated the expression of inflammatory mediators. These results suggest that celastrol exerts its protective effect partly via inhibiting the TLR4-mediated immune and inflammatory response in steatotic HepG2 cells.

Reduced β2 glycoprotein I (β2GPI) has been demonstrated to exhibit a beneficial effect in diabetic atherosclerosis and retinal neovascularization. However, the effect of reduced β2GPI on vascular disorders in diabetic mellitus (DM) remains to be elucidated. The present study established a high glucose‑induced injury model using human umbilical cords veins (HUVECs) and evaluated the protective effects of reduced β2GPI against the injury. The data demonstrated that a low concentration of reduced β2GPI (0.5 µM) mitigated high glucose‑induced cell loss, decreased nitric oxide (NO) production and resulted in calcium overloading. Mechanically, reduced β2GPI additionally reversed high glucose‑induced phosphatase and tensin homolog (PTEN) accumulation, decrease of protein kinase B phosphorylation and nitric oxide synthase activity, and increase of cyclooxygenase‑2 activity. It was further confirmed that PTEN inhibitor‑bpV (1 µM) exhibited similar effects to those resulting from reduced β2GPI. Overall, the data revealed that reduced β2GPI exerts protective effects from glucose‑induced injury in HUVECs, potentially via decreasing PTEN levels. The present study suggests reduced β2GPI may act as a novel therapeutic strategy for the treatment of vascular disorders in DM.