New small molecules that regulate the step-wise differentiation of human pluripotent stem cells into dopaminergic neurons have been identified. The steroid, guggulsterone, was found to be the most effective inducer of neural stem cells into dopaminergic neurons. These neurons are extensively characterized and shown to be functional. We believe this new approach offers a practical route to creating neurons of sufficient quality to be used to treat Parkinson's disease patients.

Signal transducers and activator of transcription 3 (STAT3) is a transcription factor that has been associated with survival, proliferation, chemoresistance, and angiogenesis of tumor cells. Whether the apoptotic, antiproliferative, and antimetastatic effects of guggulsterone (GS), a farnesoid X receptor antagonist, are linked to its ability to suppress STAT3 activation was investigated. We found that the Z but not the E stereoisomer of GS inhibited both constitutive and interleukin-6-induced STAT3 activation in human multiple myeloma cells. The suppression of STAT3 was mediated through the inhibition of activation of protein tyrosine kinases Janus-activated kinase 2 and c-Src. Vanadate treatment reversed the GS-induced down-regulation of STAT3, suggesting the involvement of a protein tyrosine phosphatase. Indeed, we found that GS induced the expression of both the protein and mRNA for tyrosine protein phosphatase SHP-1 that was not due to demethylation of the SHP-1 promoter previously implicated in the epigenetic silencing of SHP-1. Moreover, knockdown of SHP-1 by small interfering RNA suppressed the effect of GS on induction of SHP-1 and on the inhibition of STAT3 activation, thereby implicating SHP-1 in the action of GS. Finally, GS down-regulated the expression of STAT3-regulated antiapoptotic (Bcl-2, Bcl-xL, and Mcl-1), proliferative (cyclin D1), and angiogenic (VEGF) gene products; and this correlated with suppression of proliferation, the accumulation of cells in sub-G(1) phase of cell cycle, and induction of apoptosis. Overall, these results suggest that GS is a novel blocker of STAT3 activation and thus may have a potential in regulation of growth and metastasis of tumor cells.

Our previous studies have shown that z-guggulsterone, a constituent of Indian Ayurvedic medicinal plant Commiphora mukul, inhibits the growth of human prostate cancer cells by causing apoptosis. We now report a novel response to z-guggulsterone involving the inhibition of angiogenesis in vitro and in vivo. The z-guggulsterone treatment inhibited capillary-like tube formation (in vitro neovascularization) by human umbilical vein endothelial cells (HUVEC) and migration by HUVEC and DU145 human prostate cancer cells in a concentration- and time-dependent manner. The z- and E-isomers of guggulsterone seemed equipotent as inhibitors of HUVEC tube formation. The z-guggulsterone-mediated inhibition of angiogenesis in vitro correlated with the suppression of secretion of proangiogenic growth factors [e.g., vascular endothelial growth factor (VEGF) and granulocyte colony-stimulating factor], down-regulation of VEGF receptor 2 (VEGF-R2) protein level, and inactivation of Akt. The z-guggulsterone-mediated suppression of DU145 cell migration was increased by knockdown of VEGF-R2 protein level. Ectopic expression of constitutively active Akt in DU145 cells conferred protection against z-guggulsterone-mediated inhibition of cell migration. Oral gavage of 1 mg z-guggulsterone/d (five times/wk) to male nude mice inhibited in vivo angiogenesis in DU145-Matrigel plug assay as evidenced by a statistically significant decrease in tumor burden, microvessel area (staining for angiogenic markers factor VIII and CD31), and VEGF-R2 protein expression. In conclusion, the present study reveals that z-guggulsterone inhibits angiogenesis by suppressing the VEGF-VEGF-R2-Akt signaling axis. Together, our results provide compelling rationale for further preclinical and clinical investigation of z-guggulsterone for its efficacy against prostate cancer.

Guggulipid is an extract of the guggul tree Commiphora mukul and has been widely used to treat hyperlipidemia in humans. The plant sterol guggulsterone (GS) is the active agent in this extract. Recent studies have shown that GS can act as an antagonist ligand for farnesoid X receptor (FXR) and decrease expression of bile acid-activated genes. Here we show that GS, although an FXR antagonist in coactivator association assays, enhances FXR agonist-induced transcription of bile salt export pump (BSEP), a major hepatic bile acid transporter. In HepG2 cells, in the presence of an FXR agonist such as chenodeoxycholate or GW4064, GS enhanced endogenous BSEP expression with a maximum induction of 400-500{\%} that induced by an FXR agonist alone. This enhancement was also readily observed in FXR-dependent BSEP promoter activation using a luciferase reporter construct. In addition, GS alone slightly increased BSEP promoter activation in the absence of an FXR agonist. Consistent with the results in HepG2, guggulipid treatment in Fisher rats increased BSEP mRNA. Interestingly, in these animals expression of the orphan nuclear receptor SHP (small heterodimer partner), a known FXR target, was also significantly increased, whereas expression of other FXR targets including cholesterol 7alpha-hydroxylase (Cyp 7a1), sterol 12alpha-hydroxylase (Cyp 8b1), and the intestinal bile acid-binding protein (I-BABP), remained unchanged. Thus, we propose that GS is a selective bile acid receptor modulator that regulates expression of a subset of FXR targets. Guggulipid treatment in rats lowered serum triglyceride and raised serum high density lipoprotein levels. Taken together, these data suggest that guggulsterone defines a novel class of FXR ligands characterized by antagonist activities in coactivator association assays but with the ability to enhance the action of agonists on BSEP expression in vivo.

Extracts of the resin of the guggul tree (Commiphora mukul) lower LDL (low-density lipoprotein) cholesterol levels in humans. The plant sterol guggulsterone [4,17(20)-pregnadiene-3,16-dione] is the active agent in this extract. We show that guggulsterone is a highly efficacious antagonist of the farnesoid X receptor (FXR), a nuclear hormone receptor that is activated by bile acids. Guggulsterone treatment decreases hepatic cholesterol in wild-type mice fed a high-cholesterol diet but is not effective in FXR-null mice. Thus, we propose that inhibition of FXR activation is the basis for the cholesterol-lowering activity of guggulsterone. Other natural products with specific biologic effects may modulate the activity of FXR or other relatively promiscuous nuclear hormone receptors.