Anti-inflammatory activity of thymol: inhibitory effect on the release of human neutrophil elastase

Elastase, a serine proteinase released by activated human neutrophils, can degrade a wide variety of biomacromolecules including elastin, and is considered a marker of inflammatory diseases. As the logical strategy to protect tissue is to inhibit excessive elastase activity, experimental and clinical researches have concentrated on trying to find efficient elastase inhibitors. As thymol, one of the major components of thyme oil with a phenolic structure, has been credited with a series of pharmacological properties, that include antimicrobial and antioxidant effects, the aim of this study was to explore whether it can also interfere with the release of elastase by human neutrophils stimulated with the synthetic chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP). After the neutrophils were incubated with increasing amounts of thymol (2.5, 5, 10, 20 microg/ml), elastase release was initiated by fMLP and measured using MeO-Suc-Ala-Ala-Pro-Val-MCA. The results showed that thymol inhibited fMLP-induced elastase release in a concentration-dependent manner, with the effects of 10 and 20 microg/ml being statistically significant. The behavior of cytosolic calcium mobilization revealed by fura-2 closely resembled that of elastase, thus suggesting that they may be related. The hydrophobic nature of thymol means that it can approach ion channel proteins through the lipid phase of the membrane, alter the local environment of calcium channels and thus inhibit capacitative calcium entry. In brief, thymol inactivates calcium channels machinery, thus triggering a corresponding reduction in elastase. The antibacterial and antimycotic activity of thymol is already well known, but our findings that it inhibits elastase extend our knowledge of the anti-inflammatory activity of this interesting molecule that is already credited with antioxidant activity. These two latter characteristics make thymol a molecule that can have helpful effects in controlling the inflammatory processes present in many infections.