The ethanol extract of Osmanthus fragrans attenuates Porphyromonas gingivalis lipopolysaccharide-stimulated inflammatory effect through the nuclear factor erythroid 2-related factor-mediated antioxidant signalling pathway

Abstract

Background: In the present study, we explored the effect of the ethanol extract of Osmanthus fragrans (EOF) on the growth and collagenase activity of Porphyromonas gingivalis (P. gingivalis). We also investigated the capacity of EOF to attenuate P. gingivalis lipopolysaccharide (LPS)-induced inflammatory responses and the possible signalling pathway.

Methods: EOF was obtained by soaking the O. fragrans powder in the ethanol and concentrating the extracts under reduced pressure. Microplate dilution assays were used to determine the effect of EOF on P. gingivalis growth. Collagenase inhibition was detected using fluorometric and colorimetric assays. The effects of EOF on the production of the cytokines interleukin-6 (IL-6) and IL-8 were assessed using enzyme-linked immunosorbent assays (ELISAs). The oxidative stress biomarkers were assayed using commercial kits. The effects of EOF on the expression of cytoprotective enzymes and nucleoprotein nuclear factor erythroid 2-related factor (Nrf2) were tested by Western blot analysis.

Results: EOF significantly inhibited the growth of P. gingivalis, especially in the iron-limited culture medium. The inhibitory effect of EOF on P. gingivalis collagenase activity was time- and concentration-dependent. The P. gingivalis LPS-stimulated production of IL-6 and IL-8 was attenuated by EOF. LPS significantly induced the production of nitric oxide (NO) and malondialdehyde (MDA), and decreased the expression of superoxide dismutase (SOD) while pretreatment with EOF alleviated these effects. The presence of EOF markedly upregulated the expression levels of the cytoprotective enzymes and nucleoprotein Nrf2.

Conclusion: This study suggests that the potent Nrf2 activation capacity of O. fragrans may be useful in the adjunctive treatment of periodontal disease.

Keywords: Inflammation; Lipopolysaccharide; Nuclear factor erythroid 2-related factor; Osmanthus fragrans; Porphyromonas gingivalis.