Bioactive Secondary Metabolites from Orchids (Orchidaceae)

The Orchidaceae family is the largest group of flowering plants in the Angiosperm monocotyledons spread on our planet. Its members, called orchids, are herbs or epiphytes with showy flowers distributed mainly in tropical regions. Several classes of phytoconstituents have been so far isolated from therapeutically-used orchids showing a great chemical diversity. Among them, phenolic derivatives have been studied for their biological activities, especially in the field of cancer, inflammation, and neurodegeneration. On the other hand, limited information has been so far obtained on the numerous alkaloids and terpenoids isolated from several orchid species. Recent articles revealed pronounced effects of some alkaloids on the CNS. Published literature on orchids that are used in traditional medicine has been reviewed in this work indicating a great potential of such organisms as source of chemical entities for the development of new drugs.

Denbinobin upregulates miR-146a expression and attenuates IL-1β-induced upregulation of ICAM-1 and VCAM-1 expressions in osteoarthritis fibroblast-like synoviocytes

Interleukin-1β (IL-1β) upregulates intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expressions in osteoarthritis fibroblast-like synoviocytes (OA-FLS) via nuclear factor (NF)-κB-mediated mechanism; enhancement of leukocyte infiltration and upregulation of proinflammatory mediators play a crucial role in OA pathophysiology. MicroRNA (miR)-146a suppresses inflammatory responses by inhibiting NF-κB activity and target gene expression, and epigenetic mechanisms are reportedly involved in miR expression regulation. Here, we aimed to verify the inhibition of ICAM-1/VCAM-1 expression in OA-FLS on denbinobin treatment and to determine whether this inhibition was due to the miR-146a-dependent pathway. We also assessed the epigenetic regulation caused by histone acetyltransferases involved in denbinobin action. Denbinobin attenuated the upregulation of IL-1β-induced ICAM-1/VCAM-1 expression and monocyte adhesion to OA-FLS. The mechanism underlying the inhibitory effects of denbinobin involved miR-146a induction, which in turn inhibited NF-κB signaling. This is because miR-146a inhibitor abrogated the inhibitory effects of denbinobin. Furthermore, histone acetyltransferase inhibitor attenuated the denbinobin-induced upregulation of miR-146a expression and inhibited the acetylation of NF-κB-binding sites located within the miR-146a promoter region. These data suggest that an epigenetic mechanism plays a crucial role in the upregulation of miR-146a expression in response to denbinobin treatment. Our overall findings suggest that denbinobin can be used as a potent anti-inflammatory agent.

KEY MESSAGE

Denbinobin inhibited IL-1β-induced ICAM-1/VCAM-1 expression and monocyte adhesion to OA-FLS. It was due to denbinobin increased miR-146a level, which in turn inhibited NF-κB signaling. Our overall findings suggest that denbinobin can be used as a potent anti-inflammatory agent.

Denbinobin, a phenanthrene from Dendrobium nobile, impairs prostate cancer migration by inhibiting Rac1 activity

Prostate cancer is the most prevalent type of cancer in the United States. The most common site of prostate cancer metastasis is bone. CXCL12 is preferentially expressed in bone and is targeted by prostate cancer cells, which over-express the receptor for CXCL12, CXCR4. In response to CXCL12 stimulation, Rac1, a GTPase, along with its effectors, regulates actin polymerization to form lamellipodia, which is a critical event for cell migration. Cortactin, an actin-binding protein, is recruited to the lamellipodia and is phosphorylated at tyrosine residues. The phosphorylated cortactin is also involved in cell migration. The inhibition of Rac1 activity using a dominant negative Rac1 impairs lamellipodial protrusion as well as cortactin translocation and cortactin phosphorylation. Denbinobin, a substance extracted from Dendrobium nobile, has anticancer effects in many cancer cell lines. Whether denbinobin can inhibit prostate cancer cell migration is not clear. Here, we report that denbinobin inhibited Rac1 activity. The inhibition of Rac1 activity prevented lamellipodial formation. Cortactin phosphorylation and translocation to the lamellipodia were also impaired, and PC3 cells were unable to migrate. These results indicate that denbinobin prevents CXCL12-induced PC3 cell migration by inhibiting Rac1 activity.

Molecular mechanisms of denbinobin-induced anti-tumorigenesis effect in colon cancer cells

AIM: To explore both the in vitro and in vivo effects of denbinobin against colon cancer cells and clarify its underlying signal pathways.

METHODS: We used COLO 205 cancer cell lines and nude mice xenograft model to study the in vitro and in vivo anti-cancer effects of denbinobin.

RESULTS: Denbinobin at concentration of 10-20 μmol/L dose-dependently suppressed COLO 205 cell proliferation by MTT test. Flow cytometry analysis and DNA fragmentation assay revealed that 10-20 μmol/L denbinobin treatment induced COLO 205 cells apoptosis. Western blot analysis showed that caspases 3, 8, 9 and Bid protein were activated by denbinobin treatment to COLO 205 cells accompanied with cytochrome c and apoptosis-inducing factor (AIF) translocation. Pretreatment of MEK 1 inhibitor (U10126), but not p38 inhibitor (SB203580) and JNK inhibitor (SP600125), reversed denbinobin-induced caspase 8, 9 and Bid activation in COLO 205 cells suggesting that extracellular signal-regulated kinase were involved in the denbinobin-induced apoptosis in COLO 205 cells. Significant regression of tumor up to 68% was further demonstrated in vivo by treating nude mice bearing COLO 205 tumor xenografts with denbinobin 50 mg/kg intraperitoneally.

CONCLUSION: Our findings suggest that denbinobin could inhibit colon cancer growth both in vitro and in vivo. Activation of extrinsic and intrinsic apoptotic pathways and AIF were involved in the denbinobin-induced COLO 205 cell apoptosis.