Background: Gum of Chios mastic (Pistacia lentiscus var. chia) is a
natural antimicrobial agent that has found extensive use in
pharmaceutical products and as a nutritional supplement. The molecular
mechanisms of its anti-inflammatory activity, however, are not clear. In
this work, the potential role of antioxidant activity of Chios mastic
gum has been evaluated.
Methods: Scavenging of superoxide radical was investigated by electron
spin resonance and spin trapping technique using EMPO spin trap in
xanthine oxidase system. Superoxide production in endothelial and smooth
muscle cells stimulated with TNF-alpha or angiotensin II and treated
with vehicle (DMSO) or mastic gum (0.1-10 mu g/ml) was measured by DHE
and HPLC. Cellular H2O2 was measured by Amplex Red. Inhibition of
protein kinase C (PKC) with mastic gum was determined by the decrease of
purified PKC activity, by inhibition of PKC activity in cellular
homogenate and by attenuation of superoxide production in cells treated
with PKC activator phorbol 12-myristate 13-acetate (PMA).
Results: Spin trapping study did not show significant scavenging of
superoxide by mastic gum itself. However, mastic gum inhibited cellular
production of superoxide and H2O2 in dose dependent manner in TNF-alpha
treated rat aortic smooth muscle cells but did not affect unstimulated
cells. TNF-alpha significantly increased the cellular superoxide
production by NADPH oxidase, while mastic gum completely abolished this
stimulation. Mastic gum inhibited the activity of purified PKC,
decreased PKC activity in cell homogenate, and attenuated superoxide
production in cells stimulated with PKC activator PMA and PKC-dependent
angiotensin II in endothelial cells.
Conclusion: We suggest that mastic gum inhibits PKC which attenuates
production of superoxide and H2O2 by NADPH oxidases. This antioxidant
property may have direct implication to the anti-inflammatory activity
of the Chios mastic gum