Tannic acid exhibits anti-inflammatory effects on formalin-induced paw edema model of inflammation in rats

The aim of the study was to determine the relationship between anti-inflammatory effects of the natural polyphenolic compound tannic acid (CAS number: 1401-55-4) and myeloperoxidase (MPO) enzyme activity in paw edema model. Thirty-five female rats were divided into five groups. The paws of rats were injected subcutaneously in the plantar surface with formalin except for the control group. Indomethacin and tannic acid were intraperitoneally administered 1 h after formalin injection. The paws volume was measured by using vernier caliper. MPO enzyme activity was determined using 4-aminoantipyrine-phenol solution as the substrate for MPO-mediated oxidation by H₂O₂. About 17% and 13% edema inhibition has detected in the indomethacin-applied group, at the measurements run every other hour right after the treatment. An inhibition of 16% was found at the group treated with 25 mg/kg tannic acid. However, in the group treated with 50 mg/kg tannic acid, 15% and 7% of the edema inhibition was observed. Serum and paw tissue MPO activities were decreased in treated groups with indomethacin and tannic acid according to formalin control group. Our study results suggest that tannic acid may contribute to the treatment of inflammation by decreasing MPO enzyme activity, but the molecular mechanism is still not clear.