Efficacy-directed discrimination of the essential oils of three Juniperus species based on their in-vitro antimicrobial and anti-inflammatory activities

Ethnopharmacological relevance: Juniperus plants are considered important sources of cedar-wood oil which is used widely in folk medicine as antiseptic and in treatment of inflammatory disorders such as, rheumatoid arthritis but there is not enough scientific evidence to support the claimed uses and there is no specification of a certain Juniperus species as the most active.

Aim of the study: The aim of this study is volatiles profiling of three Juniperus species; J. communis, J. horizontalis and J. chinensis in addition to efficacy-directed discrimination of the three studied essential oils based on their antimicrobial, and anti-inflammatory activities in LPS (lipopolysaccharide)-stimulated WBCs (White blood cells) to investigate the inter-specific variability effect on the biological activities of each oil.

Materials and methods: Volatile components profiling of the three studied plants volatile oils was achieved using GC-FID (Gas chromatography - flame ionization detector) and GC-MS (Gas chromatography - mass spectrometry). The antimicrobial activity of the studied essential oils was investigated and the minimum inhibitory concentration (MIC) was determined for oils. The production of the pro-inflammatory cytokines was evaluated by ELISA (Enzyme linked immunosorbent assay). Identification of the biomarkers responsible for each activity was attempted through construction of orthogonal projection to latent structures model using multivariate statistical analysis.

Results: Forty five components were identified in the volatile oils of the three studied plants. J. horizontalis oil displayed the highest activity against E. coli while J. communis showed the highest activity against S. aureus. OPLS model biplot showed the in-between class discrimination of J. chinensis oil sample from J. communis and J. horizontalis. The three oils were found to significantly decrease the production of the pro-inflammatory cytokines tumour necrosis factor (TNF)- α, interleukin (IL)-1β, and gamma interferon (INF- γ) in lipopolysaccharide-activated white blood cells. All studied oils were similar in reduction of TNF-α, and INF-γ, while J. chinensis oil possessed the highest potency against IL-1β. The coefficient plots of TNF-α and INF-γ pro-inflammatory mediators showed that 1-terpineol, 4-terpineol, bornyl acetate, dl-limonene and α-pinene positive contributors to both activities while β-thujone, 3-carene and γ-muurolene were the positive contributors to IL-1β inhibitory activity.

Conclusion: The differences observed in the volatile profiles among the three studied oils demonstrate the effect of inter-specific variability on the biological activities of the tested oils. It was shown that the tested oils possessed good antibacterial activities against E.coli and S. aureus justifying its folk use as an a topical antiseptic while the observed anti-inflammatory effects in human WBCs is due at least in part to their inhibitory effect on the production of pro-inflammatory cytokines.

Keywords: Antibacterial; J. chinensis; J. horizontalis; Juniperus communis; LPS-Stimulated WBCs.