Tracheal relaxant effects of flavone derivatives and their structure-activity relationships

• Main Authors: Leu, Yi-Rong, 呂宜蓉
• Other Authors: Ko Wun-Chang
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/77050973243363611383

碩士 === 台北醫學院 === 醫學研究所 === 85 === The tracheal relaxant activities and action mechanisms of flavone derivatives, including 6-hydroxyflavone, 7-hydroxyflavone, chrysin, baicalein, luteolin, 5-methoxyflavone, 6-methoxyflavone, diosmetin, diosmin, acacetin, tangeretin and luteolin-7-glucoside were analyzed to understand their structure-activity relationships (SAR). The above tweleve flavones concentration-dependently relaxed the histamine (30 μM)-, carbachol (0.2 μM)-, and KCl (30 mM)- induced precontractions of isolated guinea-pig trachea. Roughly, according to their IC50 values, the order of their relaxant potency was 6-hydroxyflavone, 7-hydroxyflavone, luteolin, tangeretin > chrysin, 5-methoxyflavone, > baicalein, acacetin, luteolin-7-glucoside > 6-methoxyflavone, diosmetin, diosmin. The SAR was concluded as follows: (a) The substitution of sugar group at position 7, such as luteolin to luteolin-7-glucoside and diosmetin to diosmin, reduced their relaxant activities ; (b) The substitution of OH group at position 6 or 3', such as flavone to 6-hydroxyflavone or apigenin to luteolin, respectively, increased their relaxant activity, but at position 7 , such as flavone to 7-hydroxyflavone, and even at both positions 5 and 7, such as flavone to chrysin did not change its relaxant activity. On the contrary, substitution of OH group at positions 5, 6, and 7, such as flavone to baicalein, or at position 6 of 5, 7-dihydroxyflavone compound, such as chrysin to baicalein decreased their relaxant activities. (c) The substitution of OCH3 group at position 5, such as flavone to 5-methoxyflavone, or further substitution at many other positions, such as 5-methoxyflavone to tangeretin, did not change its relaxant activity, whereas at position 6, such as flavone to 6-methoxyflavone attenuate its relaxant activity. (d) The substitution of OCH3 to OH group at position 6, such as 6-hydroxyflavone to 6-methoxyflavone or at position 4', such as luteolin and apigenine to diosmetin and acacetin, respectively, markedly decreased their relaxant activity. The preincubation of the six more potent flavones, 6-hydroxyflavone, 7-hydroxyflavone, chrysin, luteolin, 5-methoxyflavone or tangeretin among the above twelve compounds, non-competitively inhibited contraction induced by cumulatively adding histamine, carbachol or KCl in isolated guinea-pig trachea. In general, their pD2' values were significantly less than their -logIC50 values. Therefore, their abilities of inhibition on calcium release from intracellular calcium stores may be less potent than those of suppression on calcium influx from extracellular fluid. They also non-competitively inhibited contractions of the trachealis induced by cumulatively adding calcium into high potassium (60 mM)-Ca2+ free medium in the trachealis. After maximal relaxation on histamine (30 μM)-induced precontraction by nifedipine (10 μM), they caused further relaxation of the trachealis. The result suggests that they may have other relaxing mechanisms in addition to inhibiting voltage (VOC) and/ or receptor operated calcium channels (ROC) in the trachealis. With exception of the following three flavones, their relaxant responses were not affected by the removal of epithelial cells or by the preincubation of propranolol (1 μM), glibenclamide (10 μM), methylene blue (25 μM) or 2',5'-dideoxyadenosine (10 μM), suggesting their relaxing effects may not be related to epithelium derived relaxing factor(s), activation of β- adrenoreceptor, opening of ATP-sensitive potassium channels, or activation of guanylate cyclase or adenylate cyclase. First, 2',5'-dideoxyadenosine (10 μM) parallelly rightward shifted the log concentration-response curve of 6-hydroxyflavone, suggesting that 6-hydroxyflavone may activate adenylate cyclase. Secondary, methylene blue (25 μM) parallelly to the rightward shifted the log concentration-response curve of luteolin, suggesting that luteolin may activate guanylate cyclase. Third, glibenclamide (10 μM) parallelly leftward shifted the log concentration- response curve of 5-methoxyflavone with unknown mechanism. 6-hydroxyflavone (20 μM) and luteolin (20 μM) parallelly leftward shifted the log concentration-response curve of forskolin, and enhance the pD2 value of forskolin. 6-hydroxyflavone (10, 20 μM), luteolin (20 μM), 5-methoxyflavone (20 μM) and tangeretin (20 μM) also parallelly leftward shifted the log concentration-response curve of nitroprusside and enhanced the pD2 value of nitroprusside. It seems that 6-hydroxyflavone, luteolin, 5-methoxyflavone, and tangeretin may inhibit phosphodiesterase (PDE) activity. From determination of PDE activity, we found that luteolin (100 and 300 μM) markedly inhibited cAMP-PDE and cGMP-PDE activity and that the inhibition on cGMP-PDE activity was significantly larger than on that of cAMP-PDE. Other flavone derivatives, such as 6-hydroxyflavone, 7-hydroxyflavone, chrysin, 5-methoxyflavone, and tangeretin partially inhibited cAMP-PDE and cGMP-PDE activities. Even at a high concentration such as 300 μM the inhibition was less than 70%. However, the inhibition on cAMP-PDE activity by 6-hydroxyflavone (100 μM) was significantly larger than that on cGMP-PDE, but the inhibition on cGMP-PDE activity by tangeretin (300 μM) was significantly larger than that on cAMP-PDE. These results suggest that the relaxant mechanism of luteolin is mainly the inhibition on PDE activity, especially on cGMP-PDE activity. 6-Hydroxyflavone may activate adenylate cyclase and slightly inhibit PDE activity. 7-Hydroxyflavone, chrysin, 5-methoxyflavone and tangeretin only slightly inhibit the activity of PDE. The above six flavones inhibit both calcium influx and calcium release from calcium store. In addition to luteolin, these six flavones may inhibit calcium influx more markedly than that on calcium release.