ABSTRACT
Xanthohumol (XH), the principal prenylflavonoid of the hop plant (Humulus lupulus L.), dose-dependently inhibited isobutylmethylxanthine (IBMX)-induced melanogenesis in B16 melanoma cells, with little cytotoxicity at the effective concentrations. Decreased melanin content was accompanied by reduced tyrosinase enzyme activity, protein and mRNA expression. The levels of tyrosinase-related protein 1 and 2 mRNAs were decreased by XH. XH also inhibited alpha-melanocyte stimulating hormone- or forskolin-induced increases in melanogenesis, suggesting an action on the cAMP-dependent melanogenic pathway. XH downregulated the protein and mRNA expression of microphthalmia-associated transcription factor (MITF), a master transcriptional regulator of key melanogenic enzymes. These results suggest that XH might act as a hypo-pigmenting agent through the downregulation of MITF in the cAMP-dependent melanogenic pathway.
Subject(s)
Animals , Mice , 1-Methyl-3-isobutylxanthine/pharmacology , Cell Line , Cell Survival/drug effects , Dose-Response Relationship, Drug , Down-Regulation , Drug Antagonism , Colforsin/pharmacology , Humulus , Intramolecular Oxidoreductases/antagonists & inhibitors , Melanins/antagonists & inhibitors , Melanocytes/drug effects , Melanoma, Experimental , Membrane Glycoproteins/antagonists & inhibitors , Microphthalmia-Associated Transcription Factor/antagonists & inhibitors , Monophenol Monooxygenase/antagonists & inhibitors , Oxidoreductases/antagonists & inhibitors , Propiophenones/pharmacology , Signal Transduction/drug effects , alpha-MSH/metabolismABSTRACT
Trifluoperazine (TFP) is a phenothiazine capable of inhibiting lymphocyte proliferation as well as natural killer cells (NK) and lymphokine-activated killer cells (LAK) cytotoxic activity. CD69 is a surface molecule induced by various mechanisms of cellular activation. In the present work the modulation of CD69 expression by TFP was investigated on PHA-stimulated peripheral blood mononuclear cells and compared to that of CD25 (IL-2 receptor) expression. Determination of surface molecules was performed in an indirect immunofluorescence assay using anti-CD69 or anti-CD25 monoclonal antibodies, and analyzed by flow cytometry. The time course of the expression of these two molecules differed: CD69 expression was already declining at 48 h, whereas CD25 was still increasing at 72 h after stimulation. TFP (10 muM) reduced CD69 expression by 71.8 per cent at 24 h, 68.4 per cent at 48 h and 24 per cent at 72 h following activation. In contrast, the same dose of TFP did not significantly affect CD25 expression at 24 h but showed an inhibitory effect at later times. These results suggest that different activation pathways are involved in the expression of CD25 and CD69.