Silibinin inhibitis progesterone induced RANKL expression in human uterine leiomyoma cells

Abstract

Silibinin is a natural compound that was reported to inhibit the effects of RANKL; the underlying mechanism however is unclear. We previously demonstrated that progesterone stimulates receptor activator of nuclear factor kappa-B ligand (RANKL) expression in leiomyoma. Here we investigate whether silibinin inhibits progesterone induced RANKL expression, cell cycle proteins and extracellular matrix deposition. Molecular analysis in freshly isolated leiomyoma tissue and cells. Fresh leiomyoma tissue explants (n= 3 patients) were treated with vehicle or silibinin alone, as well as in the presence or absence of synthetic progesterone agonist R5020. Total RNA was extracted and quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR) was performed to asses fold change of RANKL mRNA levels. Next, we isolated leiomyoma smooth muscle cells from fresh fibroid tissues and maintained them in primary culture (n=3). The cells were treated with vehicle or varying doses of silibinin (30, 60, or 90 mM) for 24, 48, or 72 hours (h) respectively. Total RNA was extracted and RT-PCR was used to measure mRNA levels of RANKL, Cyclin D1 (a downstream target of RANKL and a cell cycle protein increased with cell proliferation) and Col1A2 and Col3A1 (markers of extracellular matrix deposition). Treatment of tissue explants with R5020 led to a significant increase in RANKL expression (p<0.001), which was significantly decreased by treatment with silibinin (p<0.01). In primary cells, silibinin reduced RANKL expression in a dose-dependent manner with the most significant change observed at 60 mM (up to 60% decrease, p<0.05). Silibinin significantly decreased cyclin D1, Col1A2 and Col3A1 mRNA levels in a dose-dependent manner by up to 80% change (p<0.05). Inhibition of RANKL, Cyclin D1, Col1A2 and Col3A1 expression by silibinin was observed as early as 24 h, peaked at 48 h and persisted till 72 h of treatment. Silibinin is an effective inhibitor of RANKL expression. Silibinin also decreased proliferative activity and extracellular matrix deposition in leiomyoma smooth muscle cells. Thus, silibinin may serve as a novel medical treatment option with no known side effects for uterine leiomyoma.