Organelle movement in melanophores: Effects of Panax ginseng, ginsenosides and quercetin
Abstract: Panax ginseng is a traditional herb that has been used for over 2000 years to promote health and longevity. Active components of ginseng include ginsenosides, polysaccharides, flavonoids, polyacetylenes, peptides, vitamins, phenols and enzymes, of which the ginsenosides are considered to be the major bioactive constituents. Although widely used, the exact mechanisms of ginseng and its compounds remain unclear. In this thesis we use melanophores from Xenopus laevis to investigate the effects of Panax ginseng extract G115 and its constituents on organelle transport and signalling. Due to coordinated bidirectional movement of their pigmented granules (melanosomes), in response to defined chemical signals, melanophores are capable of fast colour changes and provide a great model for the study of intracellular transport. The movement is regulated by alterations in cyclic adenosine 3’:5’-monophosphate (cAMP) concentration, where a high or low level induce anterograde (dispersion) or retrograde (aggregation) transport respectively, resulting in a dark or light cell. Here we demonstrate that Panax ginseng and its constituents ginsenoside Rc and Rd and flavonoid quercetin induce a concentration-dependent anterograde transport of melanosomes. The effect of ginseng is shown to be independent of cAMP changes and protein kinase A activation. Upon incubation of melanophores with a combination of Rc or Rd and quercetin, a synergistic increase in anterograde movement was seen, indicating cooperation between the ginsenoside and flavonoid parts of ginseng. Protein kinase C (PKC) inhibitor Myristoylated EGF-R Fragment 651-658 decreased the anterograde movement stimulated by ginseng and ginsenoside Rc and Rd. Moreover, ginseng, but not ginsenosides or quercetin, stimulated an activation of 44/42-mitogen activated protein kinase (MAPK), previously shown to be involved in both aggregation and dispersion of melanosomes. PKC-inhibition did not affect the MAPK-activation, suggesting a role for PKC in the ginseng- and ginsenoside-induced dispersion but not as an upstream activator of MAPK.
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