Obacunone Retards Renal Cyst Development In Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease(ADPKD)is a common inherited disease that seriously threatens human health,which has become the fourth leading cause of end-stage renal diseases(ESRD).Unfortunately,the therapies for ADPKD are still limited.Tolvaptan is the only drug approved by Food and Drug Administration(FDA)for ADPKD treatment at present,but the hepatotoxicity limits its application.Dialysis therapy and replacement therapy remain the effective principles to maintain the lives of patients,which brings huge economic burden to patients and society.Therefore,it is of great significance to develop drugs with potent therapeutical effects and few adverse effects for ADPKD treatment.Oxidative stress is an important factor that promotes epithelial cell proliferation and fluid secretion of renal cysts in ADPKD.Inhibiting oxidative stress has been proven to effectively suppress renal cyst formation and expansion.Therefore,antioxidants exhibit great potential in ADPKD treatment.Lots of natural compounds possess antioxidative activities,which makes them ideal choices for drug development for ADPKD.The purposes of this study were to hunt for compound with therapeutic effect on ADPKD from natural antioxidant library and investigate the underlying pharmacological mechanisms of it.With connectivity map analysis,Madin-Darby canine kidney(MDCK)cyst model,embryonic kidney cyst model and kidney-specific Pkd1 knockout mouse(PKD)model,we identified obacunone as a candidate compound for ADPKD treatment from a natural antioxidant library.CCK-8 assay showed that obacunone had no significant cytotoxicity to MDCK cells at concentration of 50 μmol/L and below.At cellular level,obacunone significantly inhibited the formation and expansion of MDCK cysts in a dose-dependent manner at the concentration range of 3.12～50 μmol/L.At organic level,3.12～50 μmol/L obacunone dose-dependently inhibited the cyst formation and expansion in embryonic kidneys.In vivo study showed that intraperitoneal injection of 100 mg/(kg·d)obacunone in PKD mice from postnatal day 1 to day 4 significantly reduced the kidney index and cyst index without affecting the growth of mice.Immunofluorescence staining results showed that obacunone significantly promoted the nuclear translocation and activation of nuclear factor-E2 related factor 2(NRF2)in mouse inner-medullary collecting duct cells(m IMCD-3)and epithelial cells of MDCK cysts,which were consistent with the findings in PKD mice kidneys by Western blot.The activation of NRF2 not only inhibited oxidative stress,but also promoted the expression of glutathione peroxidase 4(GPX4)and activity of glutathione peroxidase(GSH-Px).These processes significantly inhibited lipid peroxidation and reduced the content of malondialdehyde(MDA)and 4-hydroxynonenal(4-HNE)in PKD mouse kidneys.Decrease of MDA and 4-HNE reversed abnormally activated mitogen-activated protein kinase(MAPK)and mammalian target of rapamycin(m TOR)signaling pathways,which inhibited the proliferation of cyst epithelial cells in the kidneys of PKD mice.This study firstly reported the therapeutic effect of obacunone on ADPKD.As a NRF2 agonist,obacunone significantly inhibited abnormal proliferation of cyst epithelial cells by suppressing lipid peroxidation.The advantages of low cytotoxicity,easy availability and potent efficacy make obacunone ideal to be developed as a therapeutic drug for ADPKD.