The Wizard of Oz, or the intriguing tale of the tea tree

Bioassay-Guided Isolation and Identification of Cytotoxic Compounds from Melaleuca quinquenervia Fruits

The fruit extract of Melaleuca quinquenervia yielded a total of 19 compounds, including two novel spiro-biflavonoid enantiomers (1a and 1b) and a chalcone derivative (3). Their structures were determined through spectroscopic analysis. The enantiomers of the racemic mixture of compound 1 were successfully resolved into (+)-1 and (-)-1 using chiral-phase HPLC. Single-crystal X-ray diffraction analysis was also used to confirm the structure of 1. The enantiomeric configurations of 1 and 2 were determined through a comparison of the calculated and experimental electronic circular dichroism spectra. Compounds 2 (melanervin), 14 (methyl betulinate), 15 (3-O-acetylbetulinic acid), and 16 (pyracrenic acid) were found to be highly cytotoxic, with compound 16 showing superior growth inhibition of nonsmall cell lung cancer cells (A549 cells) (IC50 2.8 ± 0.1 μM) compared to cisplatin (IC50 3.3 ± 0.0 μM), a positive control chemotherapeutic drug. Both compound 16 and cisplatin were significantly more cytotoxic toward A549 lung cancer cells compared to nontumorigenic Vero E6 cells.

Antimicrobial activity of essential oils against multidrug-resistant clinical isolates of the Burkholderia cepacia complex

Members of the Burkholderia cepacia complex (Bcc) are an important cause of opportunistic or nosocomial infections that may be hard to treat due to a high incidence of multidrug resistance. We characterised a collection of 51 clinical isolates from this complex, assigning them to 18 sequence types using multi-locus sequence type analysis. Resistance to eight commonly used antibiotics was assessed using by using agar-dilution assays to calculate MICs and widespread and heterogeneous multidrug resistance was confirmed, with eight strains proving resistant to all antibiotics tested. Disc diffusion screening of antimicrobial activity of a range of plant essential oils against these Bcc isolates identified six oils with significant activity (lavender, lemongrass, marjoram, peppermint, tea tree and rosewood) and broth microdilution assays indicated that of these lemongrass and rosewood oils had the highest activity, with MIC50 values of 0.5% and MIC90 values of 1%. Comparison of MIC and MBC values showed that four of these six oils, including lemongrass and rosewood, were bacteriocidal rather than bacteriostatic in their effects. Qualitative analysis of the four bacteriocidal essential oils via GC/MS indicated the presence of 55 different component compounds, mostly monoterpenes. We assessed selected essential oil components as anti-Bcc agents and demonstrated that terpinen-4-ol and geraniol were effective with MICs of 0.125-0.5% (v/v) and 0.125-1% (v/v), respectively. Time-kill studies indicate that these two alcohols are effective against non-growing cells in an efflux-dependent manner. Analysis of bacterial leakage of potassium ions and 260 nm UV-absorbing material on treatment with terpinen-4-ol and geraniol suggested that the observed anti-Bcc activity was a consequence of membrane disruption. This finding was supported by a gas chromatography analysis of bacterial fatty acid methyl esters, which indicated changes in membrane fatty acid composition caused by terpinen-4-ol and geraniol. These essential oils or oil components may ultimately prove useful as therapeutic drugs, for example to treat Bcc infections in CF patients.

Plants of the Melaleuca Genus as Antimicrobial Agents: From Farm to Pharmacy

Plants belonging to Melaleuca genus (Myrtaceae family) are native to Oceania, where they have been used for ages by Aborigine people in Australian traditional medicine, mainly because of their broad-spectrum antimicrobial activity. Although, M. linariifolia, M. dissitiflora, and other species of Melaleuca can also be used, the tea tree oil, an essential oil obtained from M. alternifolia shows the longest history of medicinal uses. Tea tree oil contains for the 80-90% several monoterpenes (terpinen-4-ol, α-terpinene, 1,8-cineol, p-cymene, α-terpineol, α-pinene, terpinolene, limonene, and sabinene). Sesquiterpenes and aromatic compounds further compose this oil. The essential oil of Melaleuca spp. has been reported to possess effective antibacterial and antifungal properties in vitro. In particular, data show that 1,8-cineol, terpinen-4-ol and methyl eugenol play the key role in mediating this oil's antimicrobial activity. Copyright © 2017 John Wiley & Sons, Ltd.

Plant Essential Oils and Mastitis Disease: Their Potential Inhibitory Effects on Pro-inflammatory Cytokine Production in Response to Bacteria Related Inflammation

This paper highlights the role of plant volatile organic compounds, found in essential oils, for the treatment of bacteria related inflammation. This report is focused on tea tree oil, particularly its main compound terpinen-4-ol. Analysis of the published literature shows that many essential oils have significant antibacterial, antifungal and anti-inflammatory effects. Some of their major components, such as terpinen-4-ol, act by inhibiting pro-inflammatory cytokine expression while stimulating production of anti-inflammatory cytokines. Such observations may be exploited to encourage biotherapy against mastitis. The use of synthetic antibiotics is being increasingly discouraged because their presence in dairy milk may have potential downstream effects on population health and the agri-food chain. In the context of inflammation and related mammalian responses, understanding the interplay between volatile organic compounds, especially terpinen-4-ol, and cytokines during bacteria related inflammation should clarify their mode of action to control mastitis.

Aqueous Solubility of Liquid Monoterpenes at 293 K and Relationship with Calculated Log P Value

Aqueous solubility is often a limiting factor in any concentration-dependent process and n-octanol/water partition coefficient, usually expressed as log P, is equilibrium between surrogate of nonaqueous biophases and water phase. The aqueous solubility of seven liquid monoterpenes: (+/-)-beta-citronellol, (+/-)-linalool, linalyl acetate, (-)-alpha-pinene, (-)-beta-pinene, eucalyptol and terpinen-4-ol were experimentally determined at 293 K. The obtained aqueous solubility data correlate well with log P values calculated by ACD/Log P software.