Re-evaluation of anti-inflammatory activity of mastic using activated macrophages

Mastic is a resinous exudate obtained from the stem and the main leaves of Pistacia lentiscus. Mastic has shown several beneficial pharmaceutical properties such as antibacterial and apoptosis-modulating activities. The aim of this study was to investigate whether mastic affects the function of activated macrophages. Both solid and liquid types of mastic inhibited the production of pro-inflammatory substances such as nitric oxide (NO) and prostaglandin (PG)E(2) by lipopolysaccharide (LPS)-activated mouse macrophage-like RAW264.7 cells. This was accompanied by the decline of viable cell number. Western blot and RT-PCR analyses showed that mastic inhibited the expression of inducible NO synthase (iNOS) and cyclooxygenase (COX)-2 at both protein and mRNA levels. ESR spectroscopy revealed that mastic scavenged NO and superoxide radicals very poorly, in contrast to its potent hydroxyl radical scavenging activity. These data demonstrate that mastic inhibits the production of both NO and PGE(2) by activated macrophages mostly via its cytotoxic action. The narrow range of effective concentration of mastic due to its cytotoxicity may limit its potential application as an anti-inflammatory agent.