Olive-Derived Hydroxytyrosol Shows Anti-inflammatory Effect without Gastric Damage in Rats

Hydroxytyrosol (HT) is a simple phenol compound present in olive oil. In a previous in vitro study, we showed that HT downregulated lipopolysaccharide-mediated expression of inducible nitric oxide synthase, cyclooxygenase-2 (COX-2), tumor necrosis factor alpha, and interleukin-1β, resulting in reduced nitric oxide and prostaglandin E₂ production. In the present study, we aimed to determine whether HT suppresses COX-2-induced inflammation in a carrageenan-induced rat paw edema model. Additionally, we compared its activity with those of the selective COX-2 inhibitor, celecoxib for a comparative control, and a representative nonsteroidal anti-inflammatory drug (NSAID), indomethacin for a positive control. HT, celecoxib, and indomethacin significantly suppressed swelling in carrageenan-injected rat paws. Although HT was less effective than celecoxib and indomethacin, it had a delayed onset of action. Moreover, we evaluated whether HT aggravates gastric damage, which is a typical adverse effect associated with NSAIDs and COX-2 inhibitors under low dose aspirin (LDA) treatment, in an aspirin-induced gastric damage rat model. Unlike celecoxib and indomethacin, HT did not cause gastric damage when co-administered with aspirin. Our results indicate that HT exerts a delayed but sustained anti-inflammatory effect against COX-2-mediated inflammation. Finally, the combination of short-acting conventional anti-inflammatory drugs and long-acting HT can be considered a new, safe, and effective anti-inflammatory treatment modality even when continuously administered for a long period under LDA treatment.