steviol and Polycystic-Kidney-Diseases

Overexpression of aquaporin 2 (AQP2) was observed and suggested to be involved in fluid secretion leading to cyst enlargement in polycystic kidney disease (PKD). The cyst expansion deteriorates the renal function and, therefore, therapies targeting cyst enlargement are of clinical interest. Of note, inhibition of vasopressin function using vasopressin 2 receptor (V2R) antagonist which decreased cAMP production along with AQP2 production and function can slow cyst growth in ADPKD. This finding supports the role of AQP2 in cyst enlargement. Steviol, a major metabolite of the sweetening compound stevioside, was reported to retard MDCK cyst growth and enlargement by inhibiting CFTR activity. Interestingly, its efficacy was found to be higher than that of CFTR

Topics: Animals; Aquaporin 2; Cysts; Diterpenes, Kaurane; Dogs; Dose-Response Relationship, Drug; Gene Expression; Madin Darby Canine Kidney Cells; Polycystic Kidney Diseases; TRPP Cation Channels

Malfunction of polycystin 1 (PC1) is linked to abnormally high epithelial cell proliferation and fluid secretion, eventually leading to renal cyst development and declined renal function as found in autosomal dominant polycystic kidney disease (ADPKD). Currently, there is no effective therapy for ADPKD. Recent studies report PC1 regulates CFTR chloride channels and β-catenin levels in normal renal epithelial cells. Concurrently, our previous study found steviol retarded renal cyst enlargement in an in vitro and in an in vivo models by reducing CFTR expression and activity. Therefore, a potential relationship between steviol and PC1 is worthy of exploration. The present study was aimed to determine the effect of steviol on PC1, CFTR, and β-catenin levels in renal epithelial cells with defective PC1 biogenesis and expression (Prkcsh

Topics: Animals; beta Catenin; Blotting, Western; Cell Proliferation; Cystic Fibrosis Transmembrane Conductance Regulator; Diterpenes, Kaurane; Epithelial Cells; Gene Expression Regulation; Gene Knockout Techniques; Kidney; Lysosomal-Associated Membrane Protein 2; Lysosomes; Mice; Polycystic Kidney Diseases; TRPP Cation Channels

Cyst enlargement in autosomal dominant polycystic kidney disease (ADPKD) is associated with cAMP-activated proliferation of cyst-lining epithelial cells and transepithelial fluid secretion into the cyst lumen via cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel leading to renal failure for which no effective treatment is currently available. We previously reported that steviol retards Madin-Darby canine kidney (MDCK) cyst enlargement by inhibiting CFTR channel activity and promoting proteasomal-mediated CFTR degradation. It is imperative to examine the effect of steviol in animal models of ADPKD. Therefore, we examined the effect of steviol on renal cyst growth in an orthologous mouse model of human ADPKD (Pkd1(flox/flox):Pkhd1-Cre). The results showed that daily treatment with both 200mg/kg BW of steviol and 1000mg/kg BW of stevioside for 14 days markedly decreased kidney weight and cystic index in these mice. However, only steviol markedly reduced blood urea nitrogen and creatinine values. Steviol also reduced cell proliferation but had no effect on cell apoptosis. In addition, steviol suppressed CFTR and mTOR/S6K expression in renal cyst-lining epithelial cells. Interestingly, steviol was found to stimulate AMP-activated protein kinase (AMPK). Our findings indicate that steviol slows cyst progression in ADPKD mouse model, in part, through the activation of AMPK which subsequently inhibits CFTR chloride channel expression and inhibits renal epithelial cell proliferation via mTOR/S6K pathway. Most importantly, steviol could markedly improve kidney function in a mouse model of ADPKD. Steviol thus has potential application for further development as a therapeutic compound for the treatment of polycystic kidney disease.

Topics: AMP-Activated Protein Kinases; Animals; Apoptosis; Cell Proliferation; Cystic Fibrosis Transmembrane Conductance Regulator; Diterpenes, Kaurane; Enzyme Activation; Epithelial Cells; Glucosides; Humans; Mice; Mice, Mutant Strains; Polycystic Kidney Diseases

Cyst enlargement in polycystic kidney disease (PKD) involves cAMP-activated proliferation of cyst-lining epithelial cells and transepithelial fluid secretion into the cyst lumen via cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. This study aimed to investigate an inhibitory effect and detailed mechanisms of steviol and its derivatives on cyst growth using a cyst model in Madin-Darby canine kidney (MDCK) cells. Among 4 steviol-related compounds tested, steviol was found to be the most potent at inhibiting MDCK cyst growth. Steviol inhibition of cyst growth was dose-dependent; steviol (100 microM) reversibly inhibited cyst formation and cyst growth by 72.53.6% and 38.2±8.5%, respectively. Steviol at doses up to 200 microM had no effect on MDCK cell viability, proliferation and apoptosis. However, steviol acutely inhibited forskolin-stimulated apical chloride current in MDCK epithelia, measured with the Ussing chamber technique, in a dose-dependent manner. Prolonged treatment (24 h) with steviol (100 microM) also strongly inhibited forskolin-stimulated apical chloride current, in part by reducing CFTR protein expression in MDCK cells. Interestingly, proteasome inhibitor, MG-132, abolished the effect of steviol on CFTR protein expression. Immunofluorescence studies demonstrated that prolonged treatment (24 h) with steviol (100 microM) markedly reduced CFTR expression at the plasma membrane. Taken together, the data suggest that steviol retards MDCK cyst progression in two ways: first by directly inhibiting CFTR chloride channel activity and second by reducing CFTR expression, in part, by promoting proteasomal degradation of CFTR. Steviol and related compounds therefore represent drug candidates for treatment of polycystic kidney disease.

Topics: Animals; Apoptosis; Biological Transport; Cell Line; Cell Proliferation; Chlorides; Cystic Fibrosis Transmembrane Conductance Regulator; Cysts; Diterpenes, Kaurane; Dogs; Dose-Response Relationship, Drug; Polycystic Kidney Diseases; Proteasome Endopeptidase Complex; Proteolysis; Time Factors