Catechin synergistically potentiates mast cell-stabilizing property of caffeine

Caffeine and catechin, contained in coffee and tea, are commonly consumed substances worldwide. Studies revealed their health promoting functions, such as anti-oxidant, anti-cancer and anti-bacterial properties. Additionally, studies also revealed their roles in ameliorating the symptoms of allergic disorders, indicating their anti-allergic properties. In the present study, using the differential-interference contrast (DIC) microscopy, we examined the effects of caffeine and catechin on the degranulation from rat peritoneal mast cells. Both caffeine and catechin dose-dependently decreased the numbers of degranulating mast cells. At concentrations equal to or higher than 25 mM, caffeine and catechin markedly suppressed the numbers of degranulating mast cells. In contrast, at relatively lower concentrations, both substances did not significantly affect the numbers of degranulating mast cells. However, surprisingly enough, low concentrations of catechin (1, 2.5 mM) synergistically enhanced the suppressive effect of 10 mM caffeine on mast cell degranulation. These results provided direct evidence for the first time that caffeine and catechin dose-dependently inhibited the process of exocytosis. At relatively lower concentrations, caffeine or catechin alone did not stabilize mast cells. However, low concentrations of catechin synergistically potentiated the mast cell-stabilizing property of caffeine.


To the editor,
Caffeine, a psychoactive alkaloid contained in coffee, and catechin, a polyphenolic flavonoid in tea, are commonly consumed substances worldwide [1,2]. Previous studies revealed their health promoting functions, including anti-oxidant, anti-cancer and anti-bacterial properties [3,4]. Additionally, both in humans or experimental animal models, recent studies also revealed their roles in ameliorating the symptoms of allergic disorders, such as bronchial asthma and anaphylaxis [5][6][7][8]. These studies indicated anti-allergic properties of caffeine and catechin, showing their additional pharmacological potency. In our previous studies, by continuously monitoring the process of exocytosis in mast cells, we provided in vitro evidence that anti-allergic drugs, anti-microbial drugs and corticosteroids exert mast cell-stabilizing properties [9][10][11][12][13]. In the present study, to elucidate the mechanisms underlying the anti-allergic properties of caffeine and catechin, we directly examined their effects on the degranulation from rat peritoneal mast cells.
Previous studies indirectly determined the mast cellstabilizing properties of caffeine or catechin by measuring the amount of chemical mediators released from mast cells [5,6,15]. However, besides their exocytotic release  of chemical mediators, including histamine, leukotrienes or β-hexosaminidase, mast cells generate various types of inflammatory cytokines or growth factors [16]. In this regard, to accurately define the ability of caffeine or catechin on the stabilization of mast cells, the release of all these substances have to be evaluated. Otherwise, the exocytotic process itself has to be monitored directly in mast cells. In the present study, we carefully observed the whole process of exocytosis under the microscope and actually counted the numbers of degranulating mast cells. Thus, we provided direct evidence for the first time that both caffeine and catechin dose-dependently inhibited the process of exocytosis and thereby exerted mast cellstabilizing properties. From our results, despite the lack of statistical significance, relatively lower concentrations of catechin (1, 2.5 mM) tended to decrease the numbers of degranulating mast cells (Fig. 2B). In our recently study, low dose prazosin, an α 1 -adrenergic receptor blocker, potentiated the ability of adrenaline, the first choice medication for anaphylaxis, to stabilize mast cells [13]. Therefore, expecting the similar additive therapeutic efficacy by low dose substances, we examined the effects of 1 or 2.5 mM catechin on the caffeine-induced inhibition of exocytosis (Fig. 3). Consistent with our results shown in Fig. 1B, 10 mM caffeine significantly but not markedly reduced the number of degranulating mast cells (control, 97.4 ± 1.80% vs. 10 mM caffeine, 46.2 ± 26.1%; n = 10, P < 0.05; Fig. 3B). However, surprisingly enough, in the presence of 1 or 2.5 mM catechin, the exocytotic process of mast cells was almost completely halted (Fig. 3Ac, d vs. b). Regarding the numbers of degranulating mast cells, they were more markedly decreased than those with 10 mM caffeine alone (10 mM caffeine + 1 mM catechin, 22.4 ± 10.9%, n = 34, P < 0.05; 10 mM caffeine + 2.5 mM catechin, 24.9 ± 8.38%, n = 10, P < 0.05; Fig. 3B), showing that the inhibitory effect of caffeine on exocytosis was augmented. These results suggested that lower concentrations of catechin can synergistically potentiate the mast cell-stabilizing property of caffeine.
In mast cells, as we demonstrated in patch-clamp studies [10], an increase in the intracellular Ca 2+ concentration ( [Ca 2+ ] i ) is the primary trigger of exocytosis [17]. According to several in vitro studies, caffeine and catechin suppress the elevation of [Ca 2+ ] i either directly or through the activation of adenylate cyclase and the subsequent increase in the intracellular cyclic adenosine monophosphate (cAMP) [5,6]. Recently, Nishikawa et al. additionally revealed the involvement of reactive oxygen species (ROS) in the effect of catechin on mast cell degranulation [15]. In their study, catechin exerted dual effects depending on the levels of intracellular ROS. When intracellular ROS level was low, catechin paradoxically suppressed the degranulation of mast cells. In the present study, 1 or 2.5 mM catechin alone was not enough to decrease the numbers of degranulating mast cells (Fig. 2B). However, in the presence of 10 mM caffeine, a potent scavenger of ROS [18], these concentrations of catechin remarkably reduced the numbers of degranulating mast cells (Fig. 3B). From these findings, caffeine-induced decrease in the intracellular ROS level was thought to elicit the ability of low concentrations of catechin to stabilize mast cells, which in turn synergistically potentiated the mast cell-stabilizing property of caffeine itself.
In our series of patch-clamp studies, by detecting the changes in whole-cell membrane capacitance (Cm) in mast cells, we provided electrophysiological evidence that anti-allergic drugs, anti-microbial drugs and corticosteroids inhibit the process of exocytosis, and thus exert mast cell-stabilizing properties [9][10][11][12][13]. Using the same approach in the future, we could more elaborately determine the mast cell-stabilizing property of caffeine or catechin.
In summary, this study provided direct evidence for the first time that caffeine and catechin dosedependently inhibit the process of exocytosis. At relatively lower concentrations, caffeine or catechin alone did not stabilize mast cells. However, low concentrations of catechin synergistically potentiated the mast cell-stabilizing property of caffeine.