Gamma-mangostin(31271-07-5), is a component of mangosteen, and is apparently a good, natural anti-estrogen, purified from the fruit hull of the medicinal plant Garcinia mangostana caused a parallel rightwards shift of the concentration/response curve for the contraction elicited by 5-hydroxytryptamine (5-HT) in the rabbit aorta (pA2 = 8.2) without affecting the contractile responses to KCl, phenylephrine (alpha1) or histamine (H1). The perfusion pressure response of rat coronary artery to 5-HT (5-HT2A) was reduced concentration dependently by gamma-mangostin (IC50 = 0.32 microM). 5-HT amplified, ADP-induced aggregation of rabbit platelets (5-HT2A) was inhibited by gamma-mangostin (IC50 = 0.29 microM), whereas that induced by thrombin was not affected, nor did gamma-mangostin affect 5-HT-induced contraction of the guinea-pig ileum (5-HT3)in the presence of 5-HT1, 5-HT2 and 5-HT4 receptor antagonists. Furthermore, 5-HT-induced contraction of the rat fundus (5-HT2B) and 5-HT-induced relaxation of the rabbit aorta in the presence of ketanserin (5-HT1) and carbachol-induced contraction of the guinea-pig ileum (muscarinic M3) were not affected by gamma-mangostin (5 microM). Gamma-mangostin inhibited [3H]spiperone binding to cultured rat aortic myocytes (IC50 = 3.5 nM). The Kd for [3H]spiperone binding was increased by gamma-mangostin (3 nM) from 11.7 to 27.4 nM without affecting Bmax. These results suggest that gamma-mangostin is a novel competitive antagonist, free from a nitrogen atom, for the 5-HT2A receptors in vascular smooth muscles and platelets.
In another research, Aberrant activation of Wnt/β-catenin signalling via genetic errors within β-catenin or APC has a crucial role in carcinogenesis. Here, we studied two xanthones, α- and γ-mangostin, as inhibitors of Wnt/β-catenin signalling. The mangostins inhibited TCF/β-catenin transcriptional activity. The mangostins also inhibited protein expression of β-catenin in colon cancer cells, but the inhibition was independent of the phosphorylation and degradation of β-catenin. Instead, the mangostins increased the levels of cGMP and cGMP-dependent kinase, indicating that the inhibition of β-catenin resulted from β-catenin gene regulation. Our results indicate that mangostins could be potential candidates for preventing colon cancer through a novel mechanism of inhibiting Wnt/β-catenin signalling.
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