Mitsuo Mori

Effect of tea polyphenols on histamine release from rat basophilic leukemia (RBL-2H3) cells: The structure-inhibitory activity relationship

We studied the effect of tea polyphenols on histamine release from rat basophilic leukemia (RBL‐2H3) cells. Among tea polyphenols, (‐)‐epigallocatechin gallate (EGCG) most strongly and dose‐dependently inhibited histamine release from cells stimulated with a calcium ionophore, A23187. (‐)‐Epigallocatechin (EGC) and (‐)‐epicatechin gallate (ECG) with a triphenol residue moderately inhibited histamine release, whereas diphenolic (+)‐catechin (C) and (‐)‐epicatechin (EC) did not. The magnitude of the inhibitory effect was in the order EGCG > ECG > EGC. Among simple polyphenols, the triphenol compounds, pyrogallol (PG) and gallic acid (GA) exerted inhibitory activity, but the diphenols, pyrocatechol, hydroquinone, and resorcinol did not. In addition, the mixture of PG and GA inhibited histamine release as strongly as EGCG with two triphenol residues. Similarly, they inhibited histamine release induced by IgE‐antigen complex stimulation more efficiently than that induced by A23187 stimulation. EGCG did not inhibit the increase of intracellular Ca2+ in RBL‐2H3 cells stimulated with A23187 or IgE antigen. These results indicate that the triphenol structure plays an important role in the inhibitory activity of tea polyphenols. Their activity seemed to be exerted through the metabolic events occurring after the elevation of intracellular Ca2+ concentration.

Inhibitory effect of tea polyphenols on histamine and leukotriene B4 release from rat peritoneal exudate cells.

SummaryThe effect of tea polyphenols on the release of chemical mediators, histamine and leukotriene B4 (LTB4), from rat peritoneal exudate cells (PEC) was studied. Among polyphenols, (−)-epigallocatechin gallate (EGCG) most strongly inhibited the histamine release from the cells stimulated with a calcium ionophore, A23187 or compound 48/80. Though (+)-catechin (C) and (−)-epicatechin (EC) had no effect, (−)-epigallocatechin (EGC) and (−)-epicatechin gallate (ECG) moderately inhibited the histamine release. Similarly, EGCG, ECG, and EGC inhibited LTB4 release from PEC, whereas C and EC were not effective. The magnitude of the inhibitory effect on the release of these mediators of tea polyphenols was in the order of EGCG>ECG>EGC. These results indicated an important role of the triphenol structure in the inhibitory activity. Therefore, the possible antiallergic effect of tea polyphenols can be expected.

STRUCTURE-ACTIVITY RELATIONSHIP OF POLYPHENOLS ON INHIBITION OF CHEMICAL MEDIATOR RELEASE FROM RAT PERITONEAL EXUDATE CELLS

SummaryThe effect of phenolic compounds in foodstuffs on histamine and leukotriene B4 (LTB4) release from rat peritoneal exudate cells and their antioxidative activity were examined to assess their antiallergenic activities. Among them, triphenols such as pyrogallol and gallic acid inhibited histamine release from the cells, but diphenols did not. On the other hand, o- and p-diphenols such as catechol and hydroquinone with strong antioxidative activity inhibited LTB4 release as strongly as pyrogallol, but an m-derivative resorcinol with weak antioxidative activity did not. Though carboxylated compounds and their noncarboxylated counterparts were antioxidative, the former exerted a much weaker inhibitory effect on the LTB4 release than the latter. In flavonols, only myricetin with a triphenolic B ring strongly inhibited histamine release, but all flavonols strongly suppressed LTB4 release irrespective of the number of OH groups in the B ring. Among flavonoids with an o-diphenolic B ring, flavonol and flavone with a C4-carbonyl group strongly inhibited LTB4 release, whereas the activity of anthocyan without C4-carbonyl was much weaker than the above compounds. These results suggest that triphenolic structure is essential for the inhibition of histamine release. On the other hand, antioxidative activity and membrane permeability of phenolic compounds seemed to be essential for the inhibition of LTB4 release. In addition, the C4-carbonyl group seemed to be important for strongly inhibiting LTB4 release.

Inhibition by dietary tea polyphenols of chemical mediator release from rat peritoneal exudate cells

Male Wistar rats were given purified diets containing safflower (SAF), perilla (PER), or palm (PAL) oils with or without 1% tea polyphenols (TP) for 3 weeks, and chemical mediator releasing activity from rat peritoneal exudate cells (PEC) was measured. Histamine releasing activity was not influenced by TP, while histamine release and intracellular histamine content were significantly increased in the PAL-fed group. On the contrary, leukotriene B4 (LTB4) release was significantly lower in rats fed PER than in those fed SAF and PAL, and TP significantly decreased the release in all fat groups. TP also significantly inhibited the release of LTB5, which was generated only in rats fed PER. TP significantly decreased the proportion of arachidonic acid (AA) in PEC in the SAF-fed group and that of eicosapentaenoic acid (EPA), the precursor of LTB5 in the PER-fed group, but did not influence that of AA in the PAL- and PER-fed group. These results suggest that ingestion of TP improves type I allergic symptom through the inhibition of LT release though the inhibition by TP could not be totally explained by the reduction of substrate fatty acid.