Objectives: Ellagic acid (EA) has shown antinociceptive and anti-inflammatory effects. Inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2) enzymes and also cytokines play a key role in many inflammatory conditions. This study was aimed to investigate the mechanisms involved in the anti-inflammatory effect of EA.
Materials and methods: Carrageenan-induced mouse paw edema model was used for induction of inflammation.
Results: The results showed that intraplantar injection of carrageenan led to time-dependent development of peripheral inflammation, which resulted in a significant increase in the levels of tumor necrosis factor α (TNF-α) and interleukin 1 (IL-1) β, nitric oxide (NO) and prostaglandin E2 (PGE2) and also iNOS and COX-2 protein expression in inflamed paw. However, systemic administration of EA (1-30 mg/kg, intraperitoneal [i.p.]) could reduce edema in a dose-dependent fashion in inflamed rat paws with ED50 value 8.41 (5.26-14.76) mg/kg. It decreased the serum concentration of NO, PGE2, aspartate aminotransferase and alanine aminotransferase, and suppress the protein expression of iNOS, COX-2 enzymes, and attenuated the formation of PGE2, TNF-α and IL-1 β in inflamed paw tissue. We also demonstrated that EA significantly decreased the malondialdehyde (MDA) level in liver at 5 h after carrageenan injection. Moreover, histopathological studies indicated that EA significantly diminished migration of polymorphonuclear leukocytes into site of inflammation, as did indomethacin.
Conclusions: Collectively, the anti-inflammatory mechanisms of EA might be related to the decrease in the level of MDA, iNOS, and COX-2 in the edema paw via the suppression of pro-inflammatory cytokines (TNFα, IL1 β), NO and PGE2 overproduction.
Keywords: Carrageenan; Rat; ellagic acid; inducible nitric oxide synthase; prostaglandin E2.