Supressive effect of maslinic acid from pomace olive oil on oxidative stress and cytokine production in stimulated murine macrophages

The pentacyclic triterpene maslinic acid (MA) is a natural compound present in the non glyceride fraction of pomace olive oil, also called orujo olive oil. This compound has previously demonstrated antioxidant properties against lipid peroxidation in vitro, but its effects on reactive oxygen and nitrogen-derived species and pro-inflammatory cytokines generated by a cell system have not yet been investigated. In this study, we have tested the effect of MA upon oxidative stress and cytokine production using peritoneal murine macrophages. MA significantly inhibited the enhanced production of nitric oxide (NO) induced by lypopolysaccharide (LPS) when it was measured by the nitrite production with an inhibitory concentration 50% value (IC50) of 25.4 mu M. This inhibiting effect seems to be consequence of an action at the level of the LPS-induction of the inducible nitric oxide synthethase (NOS) gene enzyme expression rather than to a direct inhibitory action on enzyme activity. The secretion of the inflammatory cytokines interleukine-6 and TNF-alpha from LPS-stimulated murine macrophages was also significantly reduced (p < 0.05 and 0.01) by 50 and 100 mu M of MA. In addition, reactive oxygen species were measured after stimulation with phorbol-12-myristate-13-acetate (PMA). Thus, pre-treatment with MA reduced the generation of hydrogen peroxide from stimulated macrophages in a dose-dependent manner (IC50: 43.6 mu M) as assayed by the oxidation of the peroxidase enzyme. However, no inhibitory effect on superoxide release, measured by the reduction of ferricytochrome c, was observed after the pretreatment with MA in the culture medium. These results suggest a potential biopharmaceutical use of this hydroxy-pentacyclic triterpene derivative, present in orujo olive oil, on preventing oxidative stress and pro-inflammatory cytokine generation.