| Summary: | 博士 === 國立臺灣大學 === 生物化學暨分子生物學研究所 === 92 === part 1
Propolis designates a series of gums, resins, and balms of viscous consistency which are gathered by honeybees from certain parts of plants, mainly the buds and barks. Bees bring propolis back to the hive, where it is modified and mixed with other substances like wax and salivary secretions. Crude extracts of propolis have very complicated compositions, resulting from variation in geographical and botanical origin. Propolis has been used in folk medicine all over the world. It has been shown to possess antitumor, antioxidant, antiinflammatory, immunomodulatory, antiviral, and antibacterial activities. The pharmacological properties of propolis can be mainly attributed to the large amount of flavonoids. In addition to flavonoids, propolis contains cinnamic derivatives such as caffeic, ferulic, cinnamic, and chlorogenic acids and their esters. Recently, it was reported that a component of Brazilian propolis, caffeic acid phenethyl ester (CAPE), exerts potent antiinflammatory, antioxidant, and antitumor activities.
Much in the literature has demonstrated that natural products used in cancer chemotherapy including taxol, adriamycin, VP16, camptothecin, and carnosol have apoptosis-inducing activity. We are interested in the composition and biological properties of Taiwanese propolis. We recently demonstrated that six compounds isolated and characterized from Taiwanese propolis by NMR displayed absorptions characteristic of the prenylflavanones-type. The six flavonoid compounds included four novel ones: propolin A, propolin B, propolin E, and propolin F. Both propolin C and propolin D were identical to the reported prenylflavanone compounds nymphaeol-A and nymphaeol-B. However, no biological activities of these two compounds have yet been reported.
In the report, we evaluate Taiwanese propolis for anticancer activities. Our results indicated that both propolin C and propolin D were markedly more active than CAPE in induction of apoptosis on the human melanoma cells. The IC50 values of propolin C and propolin D on the human melanoma cells was 8.5 μM. However, the six compounds may trigger apoptosis of human melanoma cells through similar pathways. Propolin C-induced apoptosis may be via the activation of caspase-8, Bid, and the induction of cytochrome c release from mitochondria to the cytosol, activating caspase-9, and caspase-3, and leading to cleavage of PARP, causing DNA fragmentation, and ultimately apoptosis. The activation process is called“mitochondrial-dependent pathway.”We evaluated the six flavonoid compounds on their ability to inhibit Xanthine Oxidase activity. Our data indicated that propolin C, propolin E and propolin D were more active inhibitors than CAPE. The IC50 values of propolin C, propolin E, propolin D and CAPE were 17.0μM, 17.0μM, 22.0μM, and 45.0μM, respectively. On free radical scavenging abilities, our data indicated that propolin C, propolin A, and propolin B were more active than CAPE to scavengers of free radicals.
Taiwanese propolis was found to be richer in prenylflavanones, effective at inducing apoptosis in many cancer cell lines, and strong in antioxidant properties. Furthermore, we evaluated Taiwanese propolis and Brazilian propolis for free radical scavenging activity, phenolic concentrations; apoptosis trigger activity, and propolis composition analysis. Our results indicated that Taiwanese propolis contained a higher level of phenolic compounds and showed more capability to scavenge free radicals than Brazilian propolis. Our results indicated that the anticancer activity of Taiwanese propolis was much stronger, about ten fold that of Brazilian propolis. Finally, seven kinds of Taiwanese propolis and four kinds of Brazilian propolis were used for HPLC analysis. Our results demonstrated that Taiwanese propolis contained a higher level of propolin C, propolin D, and propolin F. However, Brazilian propolis was found to be richer in CAPE. The findings suggest that Taiwanese propolis is more active at inducing apoptosis or antioxidant activity than Brazilian propolis, perhaps due to its higher level of propolins.
part 2
Rescue of damaged neurons and stimulation of neurogenesis are theoretically attractive strategies for the treatment of neurogenerative diseases. Neural stem cells exist not only in the developing mammalian nervous system but also in the adult nervous system of all mammalian organisms, including humans. Neural stem cells can be derived from embryonic stem cells. The mechanisms that regulate endogenous neural stem cells are poorly understood. Potential uses of neural stem cells in repair include transplantation to repair missing cells and the activation of endogenous neural stem cells to provide “self-renewal”. Neural stem cells can be realized; however, we must control their proliferation or differentiation available to their daughter cells. Many reports have demonstrated that neural stem cells are present in the mammalian CNS during development and throughout adulthood. These cells can be isolated and expanded in culture in the presence of mitogens such as basic fibroblast growth factor (bFGF) and epidermal growth factor (EGF). Upon removal of the mitogens and provision of appropriate substance and growth factors, or neurotrophic factors, neural stem cells differentiate into neurons, astrocytes, and oligodendrocytes. Several neurotrophic factors have been reported. Glial cell line-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), neurotrophic factor 3 and 4 (NT3 and NT4), and platelet-derived growth factor (PDGF) were the most potent and acted by increasing neuronal survival. However, their clinical use is limited by their inability to reach the brain after systemic administration. However, small molecules (natural products) with the ability to activate endogenous neural stem cells to promote proliferation or differentiation, or enhance neurotrophic signaling might provide another means of preventing neurogenerative diseases or a therapeutic approach.
In this report, we evaluated the possibility that propolin A, propolin B, and propolin C could promote cortical neuron survival and influence neural stem cell formation and differentiation fates. Our results indicated that both propolin A and propolin B treatment significantly reduced cell loss, increased cell viability, and inhibited apoptosis in low cell density cultured conditions. On neural stem cell formation, our data also indicated that propolin A markedly promoted neural stem cell (neurospheres) formation and maintained neural stem cell properties, more than either bFGF or EGF. Signaling study indicated that both propolin A and propolin B promoted neural stem cell formation due to the phosphorylation of both AKT and ERK and up-regulated Trk-B expression. Additionally, we investigated whether propolin A can influence the generation of neuronal progenitors from neural stem cells. Our results demonstrated that the propolin A is more potent in the regard than bFGF or EGF. On neuroprotective study, propolin A significantly prevented cell death induced by rotenone- or H2O2-treatment. All these results suggest that propolin A has neurotrophic-like effects and is a good neuroprotective agent.
Tea is one of the most popular beverages in the world because of its taste, aroma, and lately, its reported health benefits. We used capillary electrophoresis (CE) to determine of theanine, caffeine, and catechins in fresh tea leaves and Oolong tea. We evaluated the effect of fresh tea leaves or Oolong tea extract liquors on neural stem cells by migration assay. Our results indicated an untreated group can attach to the bottom of the plate and induce neural stem cell migration and neurite outgrowth. However, fresh tea leaves or Oolong tea extract liquors markedly inhibited neural stem cell attachment to the bottom of the plate and did not induce cell migration or neurite outgrowth. We remain interested in what kind of tea compositions can inhibit neural stem cells adhesion or migration. Treatment of neural stem cell with 0 to 50μg/mL of EGCg for 24 h resulted in dramatic inhibition of cell adhesion at a concentration of 20μg/mL. However, caffeine and theanine did not influence neural stem cell adhesion or migration at the high concentration of 50μg/mL (caffeine) or 348μg/mL (theanine). The results obtained in the experiments suggest that EGCg might influence neural stem cell differentiation fates and have a partial cytotoxicity effect at the level of 20-30μg/mL.
We conclude that Taiwaneses propolis polyphenols (especially in propolin A) have potential promote neural stem cell survival and differentiation into neurons, but tea polyphenols (especially in EGCg) are potentially cytotoxic to neural stem cell and influence stem cell differentiation fates.
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