Allergic rhinitis (AR) affects 20-50% of the global population. Available treatments are limited by their adverse effects. We investigated the
anti-allergic effects of
catechin alone and combined with
cetirizine against
ovalbumin-induced AR. Rats were sensitized with
ovalbumin and received
catechin (14 days) and then challenged with aerosolized
ovalbumin (1%) to determine AR clinical scores.
Histamine, histamine release, and
histidine decarboxylase (HDC) activity were determined in blood, peritoneal mast cells, and stomachs, respectively. Vascular permeability and safety were assessed using
Evans blue leakage and
barbiturate-induced sleeping-time assays, respectively.
Catechin and
cetirizine binding with HDC was investigated by docking and binding energy analyses. The clinical scores of the combination regimen were superior to either drug alone. All treatments reduced vascular leakage, with no effect on
barbiturate-induced sleeping time. Only the
catechin-treated rats showed reduced
histamine levels and HDC activity. Docking studies revealed that
catechin has a 1.34-fold higher extra-precision docking score than
L-histidine. The binding energy scores for
catechin-HDC,
L-histidine-HDC, and
histamine-HDC were -50.86, -37.64, and -32.27 kcal/mol, respectively. The binding pattern of
catechin was comparable to the standard HDC inhibitor,
histidine methyl ester, but with higher binding free energy.
Catechin binds the catalytic residue S354, unlike
cetirizine. The
anti-allergic effects of
catechin can be explained by HDC inhibition and possible antihistaminic activity.