Isoeucommin A attenuates kidney injury in diabetic nephropathy through the Nrf2/HO-1 pathway

Diabetic nephropathy (DN) is a common complication in patients with diabetes and a leading cause of mortality. The management of DN in the clinic still remains a challenge. Therefore, the identification of novel compounds for DN treatment and their characterization in preclinical DN models are crucial. Isoeucommin A is a lignan compound isolated from Eucommia ulmoides Oliv, which has not been studied in detail. Our aim was to investigate the effect of Isoeucommin A in DN and to elucidate the molecular mechanisms though which Isoeucommin A acts in vitro and in vivo. We first isolated and purified Isoeucommin A by microporous resin column chromatography and studied the mass spectrogram, as well as the structure of Isoeucommin A, by high-resolution electrospray ionization mass spectroscopy and NMR, respectively. We further established an in vivo rat DN model and measured the changes of blood glucose, body weight, kidney index (KI), blood urea nitrogen, creatinine (CRE), glutathione, malondialdehyde (MDA), SOD, albumin (ALB) and urinary ALB to CRE ratios on treatment with Isoeucommin A. In addition, we measured SOD, MDA, glycogen synthase kinase-3 beta (GSK-3 beta), phosphorylated (p)-GSK-3 beta, nuclear factor erythroid-derived 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) levels by quantitative real-time PCR and western blot, and estimated cell viability by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide assay. After Isoeucommin A treatment, body weight, as well as SOD, glutathione, HO-1 and Nrf2 expression levels, in DN rats increased in a dose-dependent manner. In contrast, the levels of blood glucose, KI, blood urea nitrogen, CRE, urinary ALB to CRE ratio, tumor necrosis factor-alpha, interleukin-1 beta, interleukin-6 and MDA decreased significantly. In addition, Isoeucommin A protected H2O2-stimulated renal tubular epithelial cells from oxidative stress and activated the Nrf2/HO-1 signaling pathway in high-glucose-stimulated human renal mesangial cells. In conclusion, Isoeucommin A could alleviate inflammation and oxidative stress in in vitro and in vivo DN models and thus attenuate kidney injury by activating the Nrf2/HO-1 signaling pathway. Isoeucommin A could have the potential to be used as an effective drug for the treatment of DN.