Potential Application of Gambogic Acid for Retarding Renal Cyst Progression in Polycystic Kidney Disease

Abnormal cell proliferation and accumulation of fluid-filled cysts along the nephrons in polycystic kidney disease (PKD) could lead to a decline in renal function and eventual end-stage renal disease (ESRD). Gambogic acid (GA), a xanthone compound extracted from the brownish resin of the Garcinia hanburyi tree, exhibits various pharmacological properties, including anti-inflammation, antioxidant, anti-proliferation, and anti-cancer activity. However, its effect on inhibiting cell proliferation in PKD is still unknown. This study aimed to determine the pharmacological effects and detailed mechanisms of GA in slowing an in vitro cyst growth model of PKD. The results showed that GA (0.25–2.5 μM) significantly retarded MDCK cyst growth and cyst formation in a dose-dependent manner, without cytotoxicity. Using the BrdU cell proliferation assay, it was found that GA (0.5–2.5 μM) suppressed MDCK and Pkd1 mutant cell proliferation. In addition, GA (0.5–2.5 μM) strongly inhibited phosphorylation of ERK1/2 and S6K expression and upregulated the activation of phosphorylation of AMPK, both in MDCK cells and Pkd1 mutant cells. Taken together, these findings suggested that GA could retard MDCK cyst enlargement, at least in part by inhibiting the cell proliferation pathway. GA could be a natural plant-based drug candidate for ADPKD intervention

Potential Application of Gambogic Acid for Retarding Renal Cyst Progression in Polycystic Kidney Disease

Abnormal cell proliferation and accumulation of fluid-filled cysts along the nephrons in polycystic kidney disease (PKD) could lead to a decline in renal function and eventual end-stage renal disease (ESRD). Gambogic acid (GA), a xanthone compound extracted from the brownish resin of the Garcinia hanburyi tree, exhibits various pharmacological properties, including anti-inflammation, antioxidant, anti-proliferation, and anti-cancer activity. However, its effect on inhibiting cell proliferation in PKD is still unknown. This study aimed to determine the pharmacological effects and detailed mechanisms of GA in slowing an in vitro cyst growth model of PKD. The results showed that GA (0.25–2.5 μM) significantly retarded MDCK cyst growth and cyst formation in a dose-dependent manner, without cytotoxicity. Using the BrdU cell proliferation assay, it was found that GA (0.5–2.5 μM) suppressed MDCK and Pkd1 mutant cell proliferation. In addition, GA (0.5–2.5 μM) strongly inhibited phosphorylation of ERK1/2 and S6K expression and upregulated the activation of phosphorylation of AMPK, both in MDCK cells and Pkd1 mutant cells. Taken together, these findings suggested that GA could retard MDCK cyst enlargement, at least in part by inhibiting the cell proliferation pathway. GA could be a natural plant-based drug candidate for ADPKD intervention.</jats:p

Steviol reduces MDCK Cyst formation and growth by inhibiting CFTR channel activity and promoting proteasome-mediated CFTR degradation.

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

Effect of steviol and its derivatives on cyst progression in MDCK cyst model.

<p>(<b>A</b>) Inhibitory effect of steviol and its derivatives on MDCK cyst formation. MDCK cysts were incubated with 100 µM of steviol and its derivatives in media containing forskolin (10 µM) after cell seeding on day 0 onward. The graph represents percent of cyst colonies at day 6 after MDCK cell seeding in the absence (control) and presence of all compounds (mean±SE; <i>n</i> = 4 wells/condition; <i>**P</i><0.01 compared with control). (<b>B</b>) Inhibitory effect of steviol and its derivatives on MDCK cyst growth. The graph shows the outer cyst diameter at day 12 (mean±SE; <i>n</i> = 32−77 cysts; <i>**P</i><0.01 compared with control). (<b>C</b>) Dose-response of effect of steviol on MDCK cyst growth. After cell seeding in 3D collagen gel for 6 days, media containing forskolin and steviol at doses of 50, 100, and 200 µM were added to the MDCK cells from day 6 onward. Results were shown as mean value of cyst diameter at days 6, 8, 10, and 12 (<i>n</i> = 43−77 cysts; <i>**P</i><0.01 compared with control). (<b>D</b>) Representative light micrographs show MDCK cyst growth in 3D collagen gel after seeding of MDCK cells for 6 days. Three independent experiments were performed. Forskolin (10 µM) without (<b>2D, top</b>) or with steviol (100 µM) (<b>2D, middle, bottom</b>) was added to the culture medium at day 6. To test for reversibility, steviol was removed at day 9 (<b>2D, bottom</b>). Scale bar = 100 µm; magnification = ×10.</p