Abstract:
BACKGROUND : Plants from the genus Ocimum are used as folk medicine for treating various diseases including
inflammatory and immune-related diseases. Numerous reports have suggested plant extracts and their constituents
as possible anti-inflammatory agents. Here, in vitro evidence of Ocimum labiatum’s immune-enhancing and antioxidant
properties is presented for the first time.
METHODS : The anti-inflammatory effect of O. labiatum ethanolic extract and an isolated diterpenoid was determined
using a cytometric bead array (CBA) technique. The effect on phytohemagglutinin (PHA)-induced nitric oxide (NO)
production in peripheral blood mononuclear cells (PBMCs) was also assessed. A battery of antioxidant assays were used
for detecting antioxidant activity while the anti-inflammatory mechanism was evaluated using an ELISA-based activator
protein (AP-1) (c-Jun) assay. Cytotoxicity was determined on TZM-bl and PBMCs using a tetrazolium dye and confirmed
by a novel label-free real-time assay.
RESULTS : A 25 μg/mL non-cytotoxic concentration of O. labiatum extract significantly (p < 0.05) inhibited the production
of pro-inflammatory cytokines; IL-2, IL-4, IL-6 and IL-17A. Except for the dual acting pro- or anti-inflammatory cytokine,
IL-6, which was upregulated, a non-cytotoxic 50 μM concentration of the isolated labdane diterpenoid compound
significantly (p < 0.05) decreased the production of all the pro-inflammatory cytokines. In the anti-inflammatory pathway
studies, the compound also inhibited AP-1 significantly (p < 0.05) at 50 μM. The extract demonstrated strong, dose
dependent antioxidant activity with IC50 values ranging from 13 ± 0.8 to 54.86 ± 1.28 μg/mL while the terpene had no
antioxidant property. The extract and diterpenoid decreased the production of the inflammatory mediator NO, at
non-cytotoxic concentrations. The CC50 of the extract in TZM-bl and PBMCs was 62.6 ± 0.6 and 30.1 ± 0.4 μg/mL while
that of the compound was 112.6 ± 0.2 and 70 ± 0.4 μM respectively. The real time studies confirmed tetrazolium dye
assessed viability and also detected a unique growth pattern for the plant materials compared to untreated cells.
CONCLUSIONS : O. labiatum extract demonstrated promising anti-inflammatory and antioxidant properties while the
terpenoid showed anti-inflammatory but no antioxidant activity. The anti-inflammatory mechanism of the terpene was
a result of inhibition of AP-1. These data represents promising first steps towards the development of naturally derived
anti-inflammation drugs.
