Coumarin glycosides from Hydrangea paniculata slow down the progression of diabetic nephropathy by targeting Nrf2 anti-oxidation and smad2/3-mediated profibrosis.

BACKGROUND: Water extract of Hydrangea paniculata (HP) stem, rich in coumarin glycosides, has been demonstrated to have renal protective effect in several experimental kidney injury animal models. Currently, it is under pre-clinical development as a class 5 herbal drug against membranous nephropathy. However, whether it also benefits diabetic nephropathy (DN) is not clear. PURPOSE: This study was performed to investigate the protective effect of HP on streptozotocin-induced experimental DN, and further understand its molecular mechanisms. METHODS: In the present study, type 1 diabetes rat model was established by the intraperitoneal injection of streptozotocin. HP was orally administered every day for three months. Biochemical analysis and histopathological staining were conducted to evaluate the renal functions. In vivo pharmacokinetic study was conducted to analyse the metabolites of HP with high blood drug concentration. In vitro assay using these metabolites was performed to analyse their ability to reduce reactive oxygen species (ROS) production induced under high glucose (HG) condition by flow cytometry. Reverse transcription-polymerase chain reaction was conducted to analyse the mRNA level of nuclear factor (erythroid-derived 2)-like 2 (Nrf2) and IL6 and western blot was performed to analyse the phosphorylation status of smad 2/3 in HK2 cells under TGFß1 stimulation. RESULTS: The treatment with HP significantly reduced the blood urea nitrogen and serum creatinine content, and urine albumin excretion in diabetic rats, and increased the creatinine clearance rate. Periodic acid-schiff and methenamine staining and immunohistochemistry revealed that HP also ameliorated glomerulosclerosis and tubular vacuolar degeneration, as well as the deposition of fibronectin and collagen IV in the glomeruli. Pharmacokinetic study results revealed that the major coumarin compounds from HP were metabolised into umbelliferone and esculetin. By in vitro assay, umbelliferone and esculetin were found to significantly decrease ROS production induced by HG content, as well as increase the mRNA level of Nrf2. HP and its metabolites also can down-regulate fibronectin secretion in HK2 cells stimulated by TGFß1 and inhibit smad2/3 phosphorylation. CONCLUSION: HP has beneficial effect on DN by increasing Nrf2 expression and inhibiting TGF-smad signal activation. Further, it can be a novel herbal drug against DN.

Nicousamide attenuates renal dysfunction and glomerular injury in remnant kidneys by inhibiting TGF-ß1 internalisation and renin activity.

Nicousamide has been shown to exert renal protective effects against diabetic nephropathy and has moved to a phase II clinical trial in China for diabetic nephropathy indication. To expand its clinical indications, 5/6-nephrectomised rats were used to mimic glomerular and vascular sclerosis and tubulointerstitial scarring, with subsequent progression towards end-stage renal disease. Adult Wistar rats underwent 5/6 nephrectomy to induce the development of chronic kidney disease, with a sham operation performed as a control. The nephrectomised animals were treated orally with either saline, nicousamide (7.5,15, or 45 mg/kg), benazepril (4 mg/kg), or losartan (10 mg/kg) daily for 20 weeks. At 8, 16, and 20 weeks of treatment, blood pressure was measured in each animal, and blood and urine samples were collected for biochemical analysis, while kidney remnants were collected for histological examination. Levels of fibronectin and transforming growth factor beta 1 (TGF-ß1) were measured in kidneys by immunohistochemistry. Renin activity in the plasma was measured by an enzyme-linked immunosorbent assay. The results showed that nicousamide treatment significantly reduced systemic hypertension, proteinuria, and blood urea nitrogen (P < 0.05), effectively alleviated glomerular sclerosis scores and tubulointerstitial injuries in a dose-dependent manner (P < 0.01), and markedly decreased fibronectin and TGF-ß1 levels in kidney tissues of the 5/6-nephrectomised animals. In vitro studies suggested that nicousamide could moderately inhibit the renin activity and strongly block the TGF-ß1 internalisation into fibroblast cells. In summary, nicousamide may protect from renal failure through dual targeting, which involves a TGF-ß1-dependent mechanism and inhibition of renin activity.