Nanoemulsions (O/W) prepared from essential oil extracted from Melaleuca alternifolia: synthesis, characterization, stability and evaluation of anticancerous, anti-oxidant, anti-inflammatory and antidiabetic activities

Essential oil from Melaleuca alternifolia (also known as Tea tree essential oil, TTO) is used as traditional medicine and used as therapeutic in medicine, food and cosmetic sectors. However, this oil is highly unstable, volatile and prone to oxidation which limits its practical use. The objective of this study was synthesis of tea tree oil based O/W (oil/water) nanoemulsions (tea tree essential oil nanoemulsions, TNE) and evaluation of its biological potential. Physiological characterization was carried out using UV, fluorescent, and FT-IR techniques. Various biological activities such as anticancerous, antidiabetic and anti-inflammatory were also estimated. Pharmacokinetics study on TNE was carried out. Encapsulation efficiency of nanoemulsions was found to be 83%. Nanoemulsions were spherical in shape with globule size 308 nm, zeta potential -9.42 and polydispersity index was 0.31. Nanoemulsions were stable even after 50 days of storage at different temperatures. Anti-oxidant potential of TNE was conducted by various assays and IC50 were: Nitric oxide radical scavenging activity:225.1, DPPH radical scavenging activity:30.66, Iron chelating assay:38.73, and Iron reducing assay:39.36. Notable anticancer activity was observed with the percent cell viability of HeLa cells after treatment with 1, 2 and 5 µl of TNE was 82%, 41% and 24%, respectively. Antidiabetic study revealed that TNE inhibited -amylase in a dose-dependent manner, with 88% inhibition at its higher volume of 250 µl. Drug kinetic study revealed that nanoemulsions exhibited first-order model. Based on this, the possible role of M. alternifolia oil-based nanoemulsions in cosmetic, food, and pharma sectors has been discussed.

Comparison of chitosan and SLN nano-delivery systems for antibacterial effect of tea tree (Melaleuca alternifolia) oil against P. aeruginosa and S. aureus

Treatment of wounds is challenging due to bacterial infections, including Staphylococcus aureus and Pseudomonas aeruginosa. Using the merits of alternative antimicrobials like tea tree oil (TTO) and nanotechnology, they can be helpful in combatting bacterial infections. Solid lipid nanoparticle (SLN) and chitosan (CS) nanoparticles show great potential as carriers for enhancing the stability and therapeutic benefits of oils. The aim of this study is to compare the influence of nanocarriers in enhancing the antibacterial effects of TTO. The study evaluates the physicochemical and antibacterial properties of TTO-SLN and TTO-CS against P. aeruginosa and S. aureus. The TTO-SLN nanoparticles showed a clear round shape with the average diameter size of 477 nm, while the TTO-CS nanoparticles illustrated very homogeneous morphology with 144 nm size. The encapsulation efficiency for TTO-CS and TTO-SLN was ∼88.3% and 73.5%, respectively. Minimum inhibitory concentration against S. aureus and P. aeruginosa for TTO-CS, TTO-SLN, and pure TTO were 35 and 45 µg ml-1, 130 and 170 µg ml-1, and 380 and 410 µg ml-1, respectively. Since TTO-CS revealed an impressively higher antimicrobial effects in comparison with TTO-SLN and TTO alone, it can be considered as a nanocarrier that produces the same antimicrobial effects with lower required amounts of the active substance.

Fabrication and Biological Activities of All-in-One Composite Nanoemulsion Based on Blumea balsamifera Oil-Tea Tree Oil

Nanoemulsion is a new multi-component drug delivery system; the selection of different oil phases can give it special physiological activity, and play the role of "medicine and pharmaceutical excipients all-in-one". In this paper, we used glycyrrhizic acid as the natural surfactant, and Blumea balsamifera oil (BB) and tea tree oil (TTO) as the mixed oil phase, to obtain a new green functional composite nanoemulsion. Using the average particle size and polydispersion index (PDI) as the evaluation criteria, the effects of the oil ratio, oil content, glycyrrhizic acid concentration, and ultrasonic time on the nanoemulsion were systematically investigated. The stability and physicochemical properties and biological activities of BB-TTO NEs prepared via the optimum formulation were characterized. The optimal prescription was BB: TTO = 1:1, 5% oil phase, 0.7% glycyrrhizic acid, and 5 min ultrasonication time. The mean particle size, PDI, and zeta potential were 160.01 nm, 0.125, and -50.94 mV, respectively. The nanoemulsion showed non-significant changes in stability after centrifugation, dilution, and 120 days storage. These nanoemulsions were found to exhibit potential antibacterial and anti-inflammatory activities. The minimal inhibitory concentration (MIC) of BB-TTO NEs against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa is 2975 μg/mL, 2975 μg/mL, and 5950 μg/mL, respectively. A lower level of inflammatory cell infiltration and proportion of fibrosis were found in the synovial tissue of AIA rats treated with BB-TTO NEs. These findings demonstrate that the BB-TTO NEs produced in this study have significant potential for usage in antibacterial and anti-inflammatory areas.

Mid-infrared spectroscopy for the rapid quantification of eucalyptus oil adulteration in Australian tea tree oil (Melaleuca alternifolia)

Essential oil distilled from Melaleuca alternifolialeaves, commonly known as tea tree oil, is well known for its biological activity, principally its antimicrobial properties. However, many samples are adulterated with other, cheaper essential oils such as eucalyptus oil. Current methods of detecting such adulteration are costly and time-consuming, making them unsuitable for rapid authentication screening. This study investigated the use of mid-infrared (MIR) spectroscopy for detecting and quantifying the level of eucalyptus oil adulteration in spiked samples of pure Australian tea tree oil. To confirm the authenticity of the tea tree oil samples, GC-MS analysis was used to profile 37 of the main volatile constituents present, demonstrating that the samples conformed to ISO specifications. Three chemometric regression techniques (PLSR, PCR and SVR) were trialled on the MIR spectra, along with a variety of pre-processing techniques. The best-performing full-wavelength PLSR model showed excellent prediction of eucalyptus oil content, with an R²_CV of 0.999 and RMSECV of 1.08 % v/v. The RMSECV could be further improved to 0.82 % v/v through a moving window wavenumber optimisation process. The results suggest that MIR spectroscopy combined with PLSR can be used to predict eucalyptus oil adulteration in Australian tea tree oil samples with a high level of accuracy.

Nanolipogel Loaded with Tea Tree Oil for the Management of Burn: GC-MS Analysis, In Vitro and In Vivo Evaluation

The GC-MS analysis of tea tree oil (TTO) revealed 38 volatile components with sesquiterpene hydrocarbons (43.56%) and alcohols (41.03%) as major detected classes. TTO efficacy is masked by its hydrophobicity; nanoencapsulation can address this drawback. The results showed that TTO-loaded solid lipid nanoparticles (SLN1), composed of glyceryl monostearate (2% w/w) and Poloxamer188 (5% w/w), was spherical in shape with a core-shell microstructure. TTO-SLN1 showed a high entrapment efficiency (96.26 ± 2.3%), small particle size (235.0 ± 20.4 nm), low polydispersity index (0.31 ± 0.01), and high negative Zeta potential (−32 mV). Moreover, it exhibited a faster active agent release (almost complete within 4 h) compared to other formulated TTO-SLNs as well as the plain oil. TTO-SLN1 was then incorporated into cellulose nanofibers gel, isolated from sugarcane bagasse, to form the ‘TTO-loaded nanolipogel’ which had a shear-thinning behavior. Second-degree thermal injuries were induced in Wistar rats, then the burned skin areas were treated daily for 7 days with the TTO-loaded nanolipogel compared to the unmedicated nanolipogel, the TTO-loaded conventional gel, and the normal saline (control). The measurement of burn contraction proved that TTO-loaded nanolipogel exhibited a significantly accelerated skin healing, this was confirmed by histopathological examination as well as quantitative assessment of inflammatory infiltrate. This study highlighted the success of the proposed nanotechnology approach in improving the efficacy of TTO used for the repair of skin damage induced by burns.

Extraction of essential oils from tea tree (Melaleuca alternifolia) and lemon grass (Cymbopogon citratus) using betaine-based deep eutectic solvent (DES)

INTRODUCTION

The essential oils of tea tree (Melaleuca alternifolia) leaves mainly contain eucalyptol, α-terpinene, γ -terpinene, and terpinen-4-ol and have anti-bacterial, anti-fungal, anti-infective, and anti-inflammatory actions. The essential oils of lemon grass (Cymbopogon citratus) leaves mainly contain neral, geranial, and geraniol and have anti-microbial and anti-fungal activities and hypocholesterolemic effect.

OBJECTIVES

The present study describes the use of low-toxicity solvents called betaine-based deep eutectic solvents (DESs) for efficient extraction of essential oils from tea tree and lemon grass. H₂ O and EtOH were used for extraction as control methods.

METHODOLOGY

Quantitative analysis was performed using gas chromatography-mass spectrometry (GC-MS) in selected ion monitoring mode. Scanning electron micrography (SEM) and antioxidant assays for extracted samples were also conducted.

RESULTS

The results indicated that extraction for tea tree using betaine/sucrose (molar ratio 2:1) improved the yields of terpinolene and eucalyptol 2.5- and 1.9-fold, respectively, compared with the control method. In lemon grass, extraction using betaine/sucrose (molar ratio 2:1) improved the yields of neral and geranial 1.9- and 1.7-fold, respectively, compared with the control method.

CONCLUSION

These results demonstrated the effective extraction of essential oils from plant leaves under milder conditions than those needed for the conventional methods. The environmentally benign DESs for the extraction would be applicable to the food and cosmetic industries.

Adulteration of Essential Oils: A Multitask Issue for Quality Control. Three Case Studies: Lavandula angustifolia Mill., Citrus limon (L.) Osbeck and Melaleuca alternifolia (Maiden & Betche) Cheel

The quality control of essential oils (EO) principally aims at revealing the presence of adulterations and at quantifying compounds that are limited by law by evaluating EO chemical compositions, usually in terms of the normalised relative abundance of selected markers, for comparison to reference values reported in pharmacopoeias and/or international norms. Common adulterations of EO consist of the addition of cheaper EO or synthetic materials. This adulteration can be detected by calculating the percent normalised areas of selected markers or the enantiomeric composition of chiral components. The dilution of the EO with vegetable oils is another type of adulteration. This adulteration is quite devious, as it modifies neither the qualitative composition of the resulting EO nor the marker's normalised percentage abundance, which is no longer diagnostic, and an absolute quantitative analysis is required. This study aims at verifying the application of the two above approaches (i.e., normalised relative abundance and absolute quantitation) to detect EO adulterations, with examples involving selected commercial EO (lavender, bergamot and tea tree) adulterated with synthetic components, EO of different origin and lower economical values and heavy vegetable oils. The results show that absolute quantitation is necessary to highlight adulteration with heavy vegetable oils, providing that a reference quantitative profile is available.

Characterization of tea tree essential oil and large-ring cyclodextrins (CD9 -CD22 ) inclusion complex and evaluation of its thermal stability and volatility

BACKGROUND

Although the structure and physicochemical properties of large ring cyclodextrins (LR-CDs) exhibit unique characteristics, and also possess very strong water solubility and high safety, little is known about the embedding performance of macrocyclodextrin. Encapsulation refers to a complex of tea tree oil (TTO) with the wall material, protecting the core material or changing its properties from adverse external factors, controlling its release rate against the evaporation and degradation of essential oils. In the present study, LR-CDs complexed with TTO were prepared by co-precipitation methods.

RESULTS

The mass ratio of LR-CDs-TTO was six and the maximum complexation efficiency was 86.23%. Fourier-transform infrared spectroscopy analysis presented the loss of characteristic peaks related to TTO in the complex and no other additional peaks were observed. X-ray diffraction examination demonstrated several sharp peaks and intensity peaks at the diffraction angle of the TTO-LR-CDs complex. ¹ H-NMR indicated a chemical shift as a result of the interaction between the molecules in the inclusion complex. Moreover, the thermal stability and aqueous solubility of TTO were enhanced after synergy with LR-CDs; particularly, the solubility of the complex was increased by 329-fold. The volatile characteristics of the encapsulated and original TTO were identical.

CONCLUSION

The results of the present study show that TTO was efficaciously complexed with LR-CDs and exhibited enhanced solubility and thermal stability. © 2020 Society of Chemical Industry.

Rosin modified aminated mesoporous silica adsorbed tea tree oil sustained-release system for improve synergistic antibacterial and long-term antibacterial effects

Tea tree oil, a natural antibacterial compound, cannot be used effectively because of its volatile nature. In this work, a biocompatible carrier was prepared and loaded with tea tree essential oil. The carrier was prepared via the electrostatic or chemical action of aminated mesoporous silica and sodium rosin for achieving a low volatilization rate of tea tree essential oil. A synergistic antibacterial effect was observed between sodium rosin and tea tree essential oil. This method utilized the positive charge of the amino group and the condensation reaction with the carboxyl group to achieve physical and chemical interactions with sodium rosin. Fourier Transform Infrared, Brunauer-Emmet-Teller, Zeta potential, SEM, TEM, and TG were performed to characterize the structure and properties of the samples. Compared to the electrostatic effect, the chemically modified system exhibited a longer sustained release, and the sustained release curve followed the Korsmeyer-Peppas release model. Also, the antibacterial properties of the chemically modified system exhibited better minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) respectively, the MIC and MBC forE. coliwere 0.3 mg ml^-1and 0.6 mg ml^-1respectively, forS. aureuswere 0.15 mg ml^-1and 0.3 mg ml^-1respectively. More strikingly, the sample also demonstrated long-term antibacterial performance. Therefore, this work provides a new way for the delivery of volatile antibacterial drugs to achieve sustained-release and long-lasting antibacterial effects.

Antifungal Activity of Melaleuca alternifolia Essential Oil (TTO) and Its Synergy with Itraconazole or Ketoconazole against Trichophyton rubrum

Over the past 20–30 years, Trichophyton rubrum represented the most widespread dermatophyte with a prevalence accounting for 70% of dermatophytosis. The treatment for cutaneous infections caused by Trichophyton spp. are imidazoles (ketoconazole (KTZ)) and triazoles (itraconazole (ITZ)). T. rubrum can develop resistance to azoles after prolonged exposure to subinhibitory concentrations resulting in therapeutic failures and chronic infections. These problems have stimulated the search for therapeutic alternatives, including essential oils, and their potential use in combination with conventional antifungals. The purpose of this study was to evaluate the antifungal activity of tea tree oil (TTO) (Melaleuca alternifolia essential oil) and the main components against T. rubrum and to assess whether TTO in association with KTZ/ITZ as reference drugs improves the antifungal activity of these drugs. We used a terpinen-4-ol chemotype (35.88%) TTO, and its antifungal properties were evaluated by minimum inhibitory and minimum fungicidal concentrations in accordance with the CLSI guidelines. The interaction between TTO and azoles was evaluated through the checkerboard and isobologram methods. The results demonstrated both the fungicide activity of TTO on T. rubrum and the synergism when it was used in combination with azoles. Therefore, this mixture may reduce the minimum effective dose of azole required and minimize the side effects of the therapy. Synergy activity offered a promise for combination topical treatment for superficial mycoses.

Associating chitosan and microemulsion as a topical vehicle for the administration of herbal medicines

A viscous solution of low molecular weight chitosan (CH) at 5% w/v (10.2 kDa, 75 % deacetylated, 1451 cP at 25 °C) was associated with a microemulsion (ME) that undergoes a phase transition after water absorption in situ (≈28 % w/w), forming a more viscous liquid crystal, which was potentially evaluated as a topical vehicle. The ME was selected from a phase diagram, selecting a composition based on Tween® 80 (52 %), myristate isopropyl (28 %), and the aqueous phase (water and polyethylene glycol 400, 60:40 w/w) (20 %), which was after replaced by CH and herbal medicines (HM). HM are alternatives to treat candidiasis, and Stryphnodendron adstringens shell extract, characterized by molecular networking, and Melaleuca alternifolia Chell essential oil (46 % of terpinen-4-ol), showed in vitro activity against Candida albicans. Associating CH in ME improved the mechanical properties of the topical formulation, as adhesiveness, which is an advantageous feature for the topical treatment of vulvovaginal candidiasis.

Appraisal on the wound healing potential of Melaleuca alternifolia and Rosmarinus officinalis L. essential oil-loaded chitosan topical preparations

The present study investigates the wound healing potential of three chitosan-based topical preparations loaded with either tea tree essential oil, rosemary essential oil or a mixture of both oils in vivo. Essential oils of M. alternifolia and R. officinalis were analyzed using GC/MS. Essential oil-loaded chitosan topical preparations were formulated. Wound healing potential was evaluated in vivo using an excision wound model in rats. GC/MS analysis of M. alternifolia and R. officinalis essential oils revealed richness in oxygenated monoterpenes, representing 51.06% and 69.61% of the total oil composition, respectively. Topical application of chitosan-based formulation loaded with a mixture of tea tree and rosemary oils resulted in a significant increase in wound contraction percentage compared to either group treated with individual essential oils and the untreated group. Histopathological examination revealed that topical application of tea tree and rosemary oil combination demonstrated complete re-epithelialization associated with activated hair follicles. The high percentage of oxygenated monoterpenes in both essential oils play an important role in the antioxidant and wound healing potential observed herein. Incorporation of tea tree and rosemary essential oils in chitosan-based preparations in appropriate combination could efficiently promote different stages of wound healing.

Antimicrobial effects of terpinen-4-ol against oral pathogens and its capacity for the modulation of gene expression

This study evaluated the antibacterial activity of terpinen-4-ol against Streptococcus mutans and Lactobacillus acidophilus and its influence on gbpA (S. mutans) and slpA (L. acidophilus) gene expression. As measured by XTT assay, the concentrations of terpinen-4-ol that effectively inhibited the biofilm were 0.24% and 0.95% for S. mutans and L. acidophilus, respectively. Confocal microscopy revealed the presence of a biofilm attached to the enamel and dentin block surfaces with significant terpinen-4-ol effects against these microorganisms. The expression of the gbpA and slpA genes involved in adherence and biofilm formation was investigated using RT-PCR. Expression of these genes decreased after 15 min with 0.24% and 0.95% terpinen-4-ol in S. mutans and L. acidophilus, respectively. These findings demonstrate the antimicrobial activity of terpinen-4-ol and its ability to modulate the expression of gbpA and slpA genes, emphasizing the therapeutic capacity of terpinen-4-ol as an alternative to inhibit adherence in biofilm.

Hypolipidemic effect of Youcha in hyperlipidemia rats induced by high-fat diet

Youcha is a novel tea drink from the northeast of Guangxi. This study aimed to investigate the hypolipidemic properties of Youcha in high-fat induced hyperlipidemic Sprague-Dawley (SD) rats. After designing the model, rats were randomly divided into six groups (n = 10): normal diet (NMD) group, high-fat diet (HFD) group, Xuezhikang (120 mg kg-1 d-1) (HFD+P) group and Youcha (150, 750 or 1500 mg kg-1 d-1) (HFD+L, HFD+M or HFD+H) groups. Youcha comprises tea polyphenols (1.51 g per 100 g), caffeine (34.80 mg per 100 g) and other functional compounds. To evaluate the lipid-lowering effects of Youcha, weight of the body, liver and fat, fat index, lipid metabolism, antioxidant properties and liver damage indices were examined. In addition, the activities of some enzymes in serum and liver tissue were examined to preliminarily study their possible mechanism. The results reveal that Youcha tends to reduce body weight, liver weight, fat index, total cholesterol (TC) and triglyceride (TG) contents, low-density lipoprotein cholesterol (LDL-C), atherogenic index (AI), malondialdehyde (MDA), aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and increase high-density lipoprotein cholesterol (HDL-C), superoxide dismutase (SOD) and glutathione peroxidase (GPx) relative to the HFD group. The hypolipidemic effect was partly due to the regulation of fatty acid synthetase (FAS) and lipase (LPS) rather than lipoprotein lipase (LPL) to decrease TG markedly. These findings suggest that Youcha could be potentially used to remedy hyperlipidemia and is hence worthy of promotion as a tea drink.

Determination of Enantiomeric Distribution of Terpenes for Quality Assessment of Australian Tea Tree Oil

A number of papers have appeared in recent years proposing the use of enantiomeric ratios of key monoterpenes in Australian tea tree oil (TTO) for detection of adulterated oils. There are however a range of reported values, even from exactly the same suite of authentic oils, and we address here probable reasons for these differences and stress the importance of establishing reference ratios within each laboratory based on oils of known provenance. Any biological variation in the ratio for the key terpene terpinen-4-ol has been demonstrated to be effectively unmeasurable, because the standard deviation on multiple measurements of the same oil is of the same order as that of multiple authentic oils.

Terpinen-4-ol: A Novel and Promising Therapeutic Agent for Human Gastrointestinal Cancers

Background

Terpinen-4-ol, a naturally occurring monoterpene is the main bioactive component of tea-tree oil and has been shown to have many biological activities.

Aim

To study the antitumor effects of terpinen-4-ol and its mechanism of action in prostate and GI malignancies, alone and in combination with chemotherapeutic and biological agents.

Methods

Terpinen-4-ol was administrated alone or combined with standard chemotherapy (Oxaliplatin, Fluorouracil, Gemcitabine, Tarceva) and biological agent (Cetuximab). It was also combined with humanized anti-CD24 mAbs (was developed by us). Killing effects were measured qualitatively by light microscopy and quantitatively using the MTT and FACS analysis, following treatment of colorectal, pancreatic, gastric and prostate cancer cells. Terpinen-4-ol effect on tumor development was evaluated in xenograft model.

Results

Terpinen-4-ol induces a significant growth inhibition of colorectal, pancreatic, prostate and gastric cancer cells in a dose-dependent manner (10–90% in 0.005–0.1%). Terpinen-4-ol and various anti-cancer agents (0.2μM oxaliplatin and 0.5μM fluorouracil) demonstrated a synergistic inhibitory effect (83% and 91%, respectively) on cancer cell proliferation. In KRAS mutated colorectal cancer cells, which are resistant to anti-EGFR therapy, combining of terpinen-4-ol with cetuximab (1 μM) resulted in impressive efficacy of 80–90% growth inhibition. Sub-toxic concentrations of terpinen-4-ol potentiate anti-CD24 mAb (150μg/ml)-induced growth inhibition (90%). Considerable reduction in tumor volume was seen following terpinen-4-ol (0.2%) treatment alone and with cetuximab (10mg/kg) (40% and 63%, respectively) as compare to the control group.

Conclusion

Terpinen-4-ol significantly enhances the effect of several chemotherapeutic and biological agents. The possible molecular mechanism for its activity involves induction of cell-death rendering this compound as a potential anti-cancer drug alone and in combination in the treatment of numerous malignancies. Terpinen-4-ol restores the activity of cetuximab in cancers with mutated KRAS.

EVALUATION OF THE TEA TREE OIL ACTIVITY TO ANAEROBIC BACTERIA--IN VITRO STUDY

The study of the sensitivity to tea tree oil (Australian Company TTD International Pty. Ltd. Sydney) was carried out on 193 strains of anaerobic bacteria isolated from patients with various infections within the oral cavity and respiratory tracts. The susceptibility (MIC) of anaerobes was determined by means of plate dilution technique in Brucella agar supplemented with 5% defibrinated sheep blood, menadione and hemin. Inoculum contained 10(5) CFU per spot was cultured with Steers replicator upon the surface of agar with various tea tree oil concentrations or without oil (anaerobes growth control). Incubation the plates was performed in anaerobic jars under anaerobic conditions at 37 degrees C for 48 h. MIC was defined as the lowest concentrations of the essential oil completely inhibiting growth of anaerobic bacteria. Test results indicate, that among Gram-negative bacteria the most sensitive to essential oil were strains of Veillonella and Porphyromonas species. Essential oil in low concentrations (MIC in the range of = 0.12 - 0.5 mg/mL) inhibited growth of accordingly 80% and 68% strains. The least sensitive were strains of the genus Tannerella, Parabacteroides and Dialister (MIC 1.0 - 2.0 mg/mL). In the case of Gram-positive anaerobic bacteria the tea tree oil was the most active to strains of cocci of the genus Anaerococcus and Ruminococcus (MIC in range = 0.12 - 0.5 mg/mL) or strains of rods of the genus Eubacterium and Eggerthella (MIC = 0.25 mg/mL). Among Gram-positive rods the least sensitive were the strains of the genus Bifidobacterium ( MIC = 2.0 mg/mL). The tea tree oil was more active to Gram-positive than to Gram-negative anaerobic bacteria.

The impact of biopreservatives and storage temperature in the quality and safety of minimally processed mixed vegetables for soup

BACKGROUND

The combined effects of bioactive agents (tea tree essential oil, propolis extract and gallic acid) and storage temperature on the microbiological and sensory quality of fresh-cut mixed vegetables for soup (celery, leek and butternut squash) were studied with the objective of preserving its quality and safety.

RESULTS

Refrigeration temperature was confirmed as the main factor to limit the growth of spoilage and pathogenic microorganisms. Biopreservatives applied on mixed vegetables were effective only when combined with optimal refrigeration temperature (5 °C). Bioactive compounds showed slight effectiveness in controlling the microbiota present in mixed vegetables, although coliforms were greatly reduced by gallic acid and propolis treatments, achieving 0.5-2 log unit reductions during storage. Also, these agents showed antimicrobial activity against endogenous Escherichia coli and inoculated E. coli O157:H7, exerting a bacteriostatic effect and reducing population counts by 0.9-1.2 log CFU g(-1) at 10 days of refrigerated storage. The combination of propolis treatment with refrigerated storage conditions effectively preserved the sensory quality and prolonged the sensory shelf life of fresh-cut mixed vegetables by 3 days.

CONCLUSION

The use of natural agents such as propolis extract to preserve the quality and safety of mixed vegetables for soup might be an interesting option to address the concerns of the consumer about the use of synthetic chemical antimicrobials potentially harmful to health.

Quality evaluation of terpinen-4-ol-type Australian tea tree oils and commercial products: an integrated approach using conventional and chiral GC/MS combined with chemometrics

GC/MS, chiral GC/MS, and chemometric techniques were used to evaluate a large set (n=104) of tea tree oils (TTO) and commercial products purported to contain TTO. Twenty terpenoids were determined in each sample and compared with the standards specified by ISO-4730-2004. Several of the oil samples that were ISO compliant when distilled did not meet the ISO standards in this study primarily due to the presence of excessive p-cymene and/or depletion of terpinenes. Forty-nine percent of the commercial products did not meet the ISO specifications. Four terpenes, viz., α-pinene, limonene, terpinen-4-ol, and α-terpineol, present in TTOs with the (+)-isomer predominant were measured by chiral GC/MS. The results clearly indicated that 28 commercial products contained excessive (+)-isomer or contained the (+)-isomer in concentrations below the norm. Of the 28 outliers, 7 met the ISO standards. There was a substantial subset of commercial products that met ISO standards but displayed unusual enantiomeric+/-ratios. A class predictive model based on the oils that met ISO standards was constructed. The outliers identified by the class predictive model coincided with the samples that displayed an abnormal chiral ratio. Thus, chiral and chemometric analyses could be used to confirm the identification of abnormal commercial products including those that met all of the ISO standards.

Hydrogels Containing Nanocapsules and Nanoemulsions of Tea Tree Oil Provide Antiedematogenic Effect and Improved Skin Wound Healing

In previous works, we developed nanocapsules and nanoemulsions containing the tea tree oil. The aim of this work was to prepare and characterize hydrogels containing these nanocarriers, and to evaluate their in vivo efficacy in protecting skin damage induced by UVB and cutaneous wound healing. Hydrogels were prepared using Carbopol Ultrez and their physicochemical characteristics were evaluated: macroscopic analysis, pH, spreadability and rheological properties. The in vivo antiedematogenic effect was evaluated by ear thickness measurement after UVB-irradiation. In order to evaluate healing action of hydrogels, we investigated the regression of the cutaneous lesion in rats. Hydrogels showed homogeneous aspect and pH values between 5.6-5.8 and a non-Newtonian behavior. The presence of nanocapsules and nanoemulsions in hydrogels did not change their spreadability profile. The inclusion of tea tree oil in the nanocapsules and nanoemulsions allowed reducing the edema induced by UVB exposure. Hydrogel containing nanocapsules presented a higher reduction of the wound area compared to the hydrogel containing nanoemulsions and hydrogel containing allantoin. This study shows the feasibility of obtained dermatological formulations containing the tea tree oil associated in nanostructured systems. These formulations represent a promising approach to topical treatment of inflammatory disorders and wound healing.

In vitro genotoxicity of Melaleuca alternifolia essential oil in human lymphocytes

ETHNOPHARMACOLOGICAL RELEVANCE

The volatile essential oil derived from the plant Melaleuca alternifolia, also called tea tree oil (TTO), is largely employed for its antimicrobial properties against several human pathogens. It is used in many topical formulations to treat cutaneous infections.

AIM OF THE STUDY

Since very few studies have been done on the safety and toxicity of the crude Melaleuca alternifolia essential oil, current investigation evaluates the possible genotoxic effects of TTO in human lymphocyte cultures.

MATERIAL AND METHODS

The composition of current TTO sample was determined by GC/MS and NMR. The level of cytotoxicity in TTO treated cultures was determined by decrease of mitotic index when compared to that in negative control. The genotoxic potential of TTO was assessed by the in vitro mammalian cell micronucleus and the chromosome aberrations (CA) tests.

RESULTS

Twenty-seven compounds were identified, accounting for 98.9% of the constituents. Terpinen-4-ol (42.8%), γ-terpinene (20.4%), p-cymene (9.6%), α-terpinene (7.9%), 1,8-cineole (3%), α-terpineol (2.8%) and α-pinene (2.4%) were the major compounds of the oil sample. None of the tested TTO concentrations (95μg/ml, 182μg/ml and 365μg/ml) caused a significant increase in the observed frequencies of micronuclei when compared to those in the untreated cultures (negative control). Additionally, no significant differences regarding the frequencies of CA were observed among the tested TTO concentrations and the negative control.

CONCLUSIONS

Results demonstrate that TTO, in the tested concentrations, is not genotoxic in in vitro mammalian cells.

Vibrational spectroscopy as a rapid quality control method for Melaleuca alternifolia cheel (tea tree oil)

INTRODUCTION

Tea tree oil (TTO) is an important commercial oil which has found application in the flavour, fragrance and cosmetic industries. The quality is determined by the relative concentration of its major constituents: 1,8-cineole, terpinen-4-ol, α-terpineol, α-terpinene, terpinolene, γ-terpinene and limonene. Gas chromatography coupled to mass spectrometry (GC-MS) is traditionally used for qualitative and quantitative analyses but is expensive and time consuming.

OBJECTIVE

To evaluate the use of vibrational spectroscopy in tandem with chemometric data analysis as a fast and low-cost alternative method for the quality control of TTO.

METHODS

Spectral data were acquired in both the mid-infrared (MIR) and near infrared (NIR) wavelength regions and reference data obtained using GC-MS with flame ionisation detection (FID). Principal component analysis (PCA) was used to investigate the data by observing clustering and identifying outliers. Partial least squares (PLS) multivariate calibration models were constructed for the quantification of the seven major constituents.

RESULTS

High correlation coefficients (R(2) ) of ≥ 0.75 were obtained for the seven major compounds and 1,8-cineole showed the best correlation coefficients for both MIR and NIR data (R(2)  = 0.97 and 0.95, respectively). Low values were obtained for the root mean square error of estimation (RMSEE) and root mean square error of prediction (RMSEP) values thereby confirming accuracy.

CONCLUSION

The accurate prediction of the external dataset after introduction into the models confirmed that both MIR and NIR spectroscopy are valuable methods for quantification of the major compounds of TTO when compared with the reference data obtained using GC-MS. Copyright © 2013 John Wiley & Sons, Ltd.

Control of the chewing louse Bovicola (Werneckiella) ocellatus in donkeys, using essential oils

Infestations by lice can be a significant clinical and welfare issue in the management of large animals. The limited range of commercial pediculicides available and the development of resistance have led to the need to explore alternative louse management approaches. The results of in vitro and in vivo trials undertaken to control populations of the donkey chewing louse, Bovicola ocellatus (Piaget) (Phthiraptera: Trichodectidae) using the essential oils of tea tree (Melaleuca alternifolia) and lavender (Lavandula angustifolia) are reported here. Results of contact and vapour bioassays showed that 5% (v/v) tea tree and lavender oils resulted in > 80% louse mortality after 2 h of exposure. On farms, separate groups of 10 donkeys sprayed with 5% (v/v) tea tree and lavender oil as part of their usual grooming regime showed significant reductions in louse numbers compared with a control group (0.2% polysorbate 80 in water). These findings indicate that tea tree and lavender essential oils can provide clinically useful levels of control of B. ocellatus when used as part of a grooming routine and suggest that with further development could form the basis of an easy to apply and valuable component of a louse management programme for donkeys.

Characterization, antibiofilm, and mechanism of action of novel PEG-stabilized lipid nanoparticles loaded with terpinen-4-ol

Terpinen-4-ol, an active component of tea tree oil, exhibits broad-spectrum antimicrobial activity. However, the high volatilization of terpinen-4-ol and its nonwettability property have limited its application. Our objective was to synthesize novel nanocarriers to deliver and protect terpinen-4-ol. The polyethylene glycol (PEG)-stabilized lipid nanoparticles were prepared and characterized by scanning electron microscope, Zetasizer, and differential scanning calorimetry. These nanoparticles had an average diameter of 397 nm and a Ζ-potential of 10 mV after being modified by glycine. Results showed that homogeneous particle size, high drug loading, stability, and targeting were obtained by the nanoparticles. Liquid chromatography/mass spectrometry showed a sustained release trend from nanoparticles for terpinen-4-ol. Minimum inhibitory concentration and minimum biofilm eradication concentration were tested against Candida albicans ATCC 11231. Studies on isolated mitochondria showed the blockage of biofilm respiration and inhibition of enzyme activity. The effects can be ascribed to localization of terpinen-4-ol on the membrane of mitochondria.

Antimicrobial activity of two essential oils

The aim of the study was to evaluate the antimicrobial activity of essential oils in vitro for possible application to reduce the content of microorganisms in the air of animal houses. The essential oils of Cymbopogon citrarus L. and Malaleuca alternifolia L. were screened against bacteria Staphylococcus aureus, Enterococcus faecium, Pseudomonas aeruginosa, Escherichia coli, Proteus mirabilis and yeast Candida albicans. The minimal inhibitory concentration of the active essential oils was tested using broth dilution assay. The essential oils concentrations ranged from 0.1-50.0%. The combined effects of essential oils were tested for Malaleuca alternifolia L. and Cymbopogon citrarus L. concentrations ranged from 0.005-50.0%. The oils showed a wide spectrum of antibacterial activity. Concentrations of 0.1-0.5% of Cymbopogon citrarus L. and Malaleuca alternifolia L. reduced total microorganisms count of Proteus mirabilis and Candida albicans. High antibacterial activity was also revealed for Cymbopogon citrarus L. with bactericidal concentrations of 0.8% for Escherichia coli, 5.0% for Enterococcus faecium, 5.0% for Pseudomonas aeruginosa and 8.0% for Staphylococcus aureus. Bactericidal concentrations of Malaleuca alternifolia L. were 5.0% for Pseudomonas aeruginosa and Enterococcus faecium, and 8.0% for Staphylococcus aureus. The essential oils of Cymbopogon citrarus and Malaleuca alternifolia may be a promising alternative of air disinfection in animal houses.

Tea tree oil might combat melanoma

In this study we present new data from experiments focused on the antitumor activity of tea tree oil (TTO), an essential oil distilled from Melaleuca alternifolia. TTO proved to be capable of inhibiting the growth of melanoma cells and of overcoming multidrug resistance (MDR), as we reported in our previous study. Moreover, the survival role of the MDR-marker P-glycoprotein appears to be involved in the mechanism of invasion of melanoma cells. The results reported herein indicate that TTO and its main active component, terpinen-4-ol, can also interfere with the migration and invasion processes of drug-sensitive and drug-resistant melanoma cells.

Formulation study of tea tree oil patches

The antimicrobial, antifungal and anti-inflammatory properties of tea tree oil (TTO), the essential oil of Melaleuca alternifolia are well documented. In order to optimize its therapeutic activity, TTO patches were designed. The aim of this work was the formulation of monolayer patches containing TTO. Moreover, the performance of oleic acid (OA) as a skin penetration enhancer in patches was evaluated. Terpinen-4-ol (T4OL), the main component of TTO, was the marker used to evaluate TTO skin permeability. The permeation study was performed through human epidermis by using Franz diffusion cells. Patches were prepared by using methacrylic copolymers, Eudragit E100 (EuE100) or Eudragit NE (EuNE), and a silicone resin, BioPSA7-4602 (Bio-PSA). TTO and OA contents were fixed at 10% w/w and 3% w/w, respectively. The patches were prepared by a casting method and characterised in terms of T4OL content and skin permeability. All the selected polymers were suitable as the main component of the patch matrix. Since the main critical issue in the use of TTO is related to its toxicity after absorption, the local administration of TTO can take advantage of the use of patches based on EuE100 because of the high retained amount and the low permeation of T4OL. In this matrix, OA slightly increased the T4OL retained amount, improving the efficacy and safety of TTO patches.

The inhibition of Candida species by selected essential oils and their synergism with amphotericin B

In this work we highlight a possible synergistic anti-Candida effect between Melaleuca alternifolia, Origanum vulgare and Pelargonium graveolens essential oils and the antifungal compound Amphotericin B. The antifungal activity was assessed using the agar dilution method in eleven Candida strains. The results obtained indicate the occurrence of a synergistic interaction between the essential oils under study and Amphotericin B. P. graveolens essential oil appeared to be the most effective, inhibiting all the Candida species evaluated by this study.

In vitro antifungal activity of the tea tree (Melaleuca alternifolia) essential oil and its major components against plant pathogens

AIMS

The aim of this study was to examine the effect of Melaleuca alternifolia essential oil (TTO) and its principal components on four cereal-pathogenic fungi.

METHODS AND RESULTS

The antimycotic properties of TTO and of terpinen-4-ol, gamma-terpinen and 1,8-cineole (eucalyptol) were evaluated in vitro on Fusarium graminearum, Fusarium culmorum and Pyrenophora graminea. Moreover, barley leaves infected with Blumeria graminis were treated with whole TTO. All the tested fungi were susceptible to TTO and its components.

CONCLUSIONS

TTO exerted a wide spectrum of antimycotic activity. Single TTO purified components were more active than the whole oil in reducing in vitro growth of fungal mycelium and, among the tested compounds, terpinen-4-ol was the most effective.

SIGNIFICANCE AND IMPACT OF THE STUDY

TTO and its components can be considered potential alternative natural fungicides.

The effect of tea tree oil and antifungal agents on a reporter for yeast cell integrity signalling

Cell integrity in Saccharomyces cerevisiae is ensured by a rigid cell wall whose synthesis is controlled by a highly conserved MAP kinase signal transduction cascade. Stress at the cell surface is detected by a set of sensors and ultimately transmitted through this cascade to the transcription factor Rlm1, which governs expression of many genes encoding enzymes of cell wall biosynthesis. We here report on a number of versatile reporter constructs which link activation of a hybrid, Rlm1-lexA, by the MAP kinase Mpk1/Slt2 to the expression of the bacterial lacZ gene. This system was adapted to automated microwell screening and shown to be activated by a number of compounds inhibiting cell wall biosynthesis or interfering with plasma membrane function. In addition, we tested tea tree oil and two of its purified constituents (alpha-terpineol, terpinen-4-ol) for their effects on growth and on cell integrity signalling using such reporter strains. Tea tree oil was found to inhibit growth of wild-type and slg1/wsc1 mutant cells at a threshold of approximately 0.1% v/v, with the purified compounds acting already at half these concentrations. A mid2 deletion displayed hyper-resistance. Tea tree oil also induces the signalling pathway in a dose-dependent manner.

In vivo activity of terpinen-4-ol, the main bioactive component of Melaleuca alternifolia Cheel (tea tree) oil against azole-susceptible and -resistant human pathogenic Candida species

BACKGROUND

Recent investigations on the antifungal properties of essential oil of Melaleuca alternifolia Cheel (Tea Tree Oil, TTO) have been performed with reference to the treatment of vaginal candidiasis. However, there is a lack of in vivo data supporting in vitro results, especially regarding the antifungal properties of TTO constituents. Thus, the aim of our study was to investigate the in vitro and the in vivo anti-Candida activity of two critical bioactive constituents of TTO, terpinen-4-ol and 1,8-cineole.

METHODS

Oophorectomized, pseudoestrus rats under estrogen treatment were used for experimental vaginal infection with azole (fluconazole, itraconazole) -susceptible or -resistant strains of C. albicans. All these strains were preliminarily tested for in vitro susceptibility to TTO, terpinen-4-ol and 1,8-cineole for their antifungal properties, using a modification of the CLSI (formerly NCCLS) reference M27-A2 broth micro-dilution method.

RESULTS

In vitro minimal inhibitory concentrations (MIC90) values were 0.06% (volume/volume) for terpinen-4-ol and 4% (volume/volume) for 1,8-cineole, regardless of susceptibility or resistance of the strains to fluconazole and itraconazole. Fungicidal concentrations of terpinen-4-ol were equivalent to the candidastatic activity. In the rat vaginal infection model, terpinen-4-ol was as active as TTO in accelerating clearance from the vagina of all Candida strains examined.

CONCLUSION

Our data suggest that terpinen-4-ol is a likely mediator of the in vitro and in vivo activity of TTO. This is the first in vivo demonstration that terpinen-4-ol could control C. albicans vaginal infections. The purified compound holds promise for the treatment of vaginal candidiasis, and particularly the azole-resistant forms.

In vitro studies on release and human skin permeation of Australian tea tree oil (TTO) from topical formulations

Essential oils are widely used in pharmaceutical and cosmetic preparations e.g. as fragrance, active ingredient or penetration enhancer. However, reports on skin absorption are rare. Therefore, the aim of our study was to investigate the capability of terpinen-4-ol, the main compound of Australian tea tree oil (TTO), to permeate human skin. In static Franz diffusion cells permeation experiments with heat separated human epidermis were carried out using infinite dosing conditions and compared to liberation experiments. The flux values of three different semisolid preparations with 5% TTO showed the rank order semisolid O/W emulsion (0.067 microl/cm2 h) > white petrolatum (0.051 microl/cm2 h) > ambiphilic cream (0.022 microl/cm2 h). In comparison to the flux value obtained with the native TTO (0.26 microl/cm2 h), the flux values are remarkably reduced due to the lower amount of terpinen-4-ol. P(app) values for cream (2.74+/-0.06 x 10(-7) cm/s) and native TTO (1.62+/-0.12 x 10(-7) cm/s) are comparable whereas white petrolatum (6.36+/-0.21 x 10(-7) cm/s) and semisolid O/W emulsion (8.41+/-0.15 x 10(-7) cm/s) demonstrated higher values indicating a penetration enhancement. No relationship between permeation and liberation was found.

Interaction of tea tree oil with model and cellular membranes

Tea tree oil (TTO) is the essential oil steam-distilled from Melaleuca alternifolia, a species of northern New South Wales, Australia. It exhibits a broad-spectrum antimicrobial activity and an antifungal activity. Only recently has TTO been shown to inhibit the in vitro growth of multidrug resistant (MDR) human melanoma cells. It has been suggested that the effect of TTO on tumor cells could be mediated by its interaction with the plasma membrane, most likely by inducing a reorganization of lipid architecture. In this paper we report biophysical and structural results obtained using simplified planar model membranes (Langmuir films) mimicking lipid "rafts". We also used flow cytometry analysis (FCA) and freeze-fracturing transmission electron microscopy to investigate the effects of TTO on actual MDR melanoma cell membranes. Thermodynamic (compression isotherms and adsorption kinetics) and structural (Brewster angle microscopy) investigation of the lipid monolayers clearly indicates that TTO interacts preferentially with the less ordered DPPC "sea" and that it does not alter the more ordered lipid "rafts". Structural observations, performed by freeze fracturing, confirm that TTO interacts with the MDR melanoma cell plasma membrane. Moreover, experiments performed by FCA demonstrate that TTO does not interfere with the function of the MDR drug transporter P-gp. We therefore propose that the effect exerted on MDR melanoma cells is mediated by the interaction with the fluid DPPC phase, rather than with the more organized "rafts" and that this interaction preferentially influences the ATP-independent antiapoptotic activity of P-gp likely localized outside "rafts".

Natural Oils Affect the Human Skin Integrity and the Percutaneous Penetration of Benzoic Acid Dose-Dependently

Natural oils are extensively used in cosmetics and as treatment for a growing number of more or less specific ailments. Skin irritation and cases of allergy have repeatedly been described in the literature following exposure to these oils. The present study evaluated the extent to which three natural oils (eucalyptus oil, tea tree oil, peppermint oil) would affect the skin integrity and the percutaneous penetration of benzoic acid when applied topically in relevant concentrations. An experimental in vitro model using static diffusion cells mounted with human breast or abdominal skin was applied. The three natural oils decreased the skin integrity dose-dependently. Concomitant dermal exposure to low concentrations of peppermint oil reduced the percutaneous penetration of benzoic acid. The present study lends support to the notion that low concentrations of peppermint oil may act protective against percutaneous penetration of some chemicals, whereas higher concentrations may decrease the integrity of the dermal barrier.

Susceptibility of pseudomonads to Melaleuca alternifolia (tea tree) oil and components

OBJECTIVES

Thirty isolates of Pseudomonas aeruginosa, 15 isolates of Pseudomonas putida and 11 isolates of Pseudomonas fluorescens were tested for susceptibility to tea tree oil (TTO), the essential oil of Melaleuca alternifolia, and the components terpinen-4-ol, alpha-terpineol, cineole, gamma-terpinene and rho-cymene.

METHODS

MICs were determined by broth microdilution in Mueller-Hinton medium supplemented with 0.002% (v/v) Tween 80.

RESULTS

The MIC90 of TTO for all isolates tested was 4% (v/v) or less. Susceptibility to components tested varied between species.

CONCLUSIONS

Pseudomonas spp. are susceptible to TTO and some of its components although they are less susceptible than many other bacteria tested previously.

A review of the toxicity of Melaleuca alternifolia (tea tree) oil

The essential oil of Melaleuca alternifolia, also known as tea tree or melaleuca oil, is widely available and has been investigated as an alternative antimicrobial, anti-inflammatory and anti-cancer agent. While these properties are increasingly well characterised, relatively limited data are available on the safety and toxicity of the oil. Anecdotal evidence from almost 80 years of use suggests that the topical use of the oil is relatively safe, and that adverse events are minor, self-limiting and occasional. Published data indicate that TTO is toxic if ingested in higher doses and can also cause skin irritation at higher concentrations. Allergic reactions to TTO occur in predisposed individuals and may be due to the various oxidation products that are formed by exposure of the oil to light and/or air. Adverse reactions may be minimised by avoiding ingestion, applying only diluted oil topically and using oil that has been stored correctly. Data from individual components suggest that TTO has the potential to be developmentally toxic if ingested at higher doses, however, TTO and its components are not genotoxic. The limited ecotoxicity data available indicate that TTO is toxic to some insect species but more studies are required.

Formulation and evaluation of an effective pH balanced topical antimicrobial product containing tea tree oil

The effect of pH on the antimicrobial activity of Melaleuca alternifolia essential oil formulations was studied. Microemulsions, liposomal dispersions, multiple emulsions and a colloidal bed of sterile clay were formulated using 5% w/w of tea tree oil. A number of formulations were prepared at various pH values (5.0, 5.5, 6.0, 6.5, and 7.0). Thermal stability studies showed that the formulations were stable for more than eight months. Agar dilution tests showed MICs of 1.0% v/v S. aureus and S. epidermidis. In the broth dilution test, MBC of the oil for P. acnes was 0.5% v/v. MIC and MBC values were comparable to those of non-formulated tea tree oil, indicating that tea tree oil retained its activity in the above-mentioned formulations. The microbiological evaluation showed that the formulations containing 5% w/w tea tree oil had a maximum effect at pH 5.5.

Anti-inflammatory effects of Melaleuca alternifolia essential oil on human polymorphonuclear neutrophils and monocytes

OBJECTIVE AND DESIGN

The fungicidal and bactericidal actions of the essential oil (EO) of Melaleuca alternifolia seem well established, but their anti-inflammatory and anti-oxidative effects remain unclear. In this study, we investigated in vitro the possible role of whole M. alternifolia EO as a modulator of the oxidative response, i.e. reactive oxygen species (ROS) production, of leukocytes (monocytes and polymorphonuclear neutrophils (PMNs)) in humans.

METHODS

Whole blood leukocytes from healthy human volunteers (n = 7), isolated from erythrocytes by haemolytic shock, were incubated for 30 min with M. alternifolia EO (0-0.1%) to determine their ROS production by flow cytometry with or without stimulation of cells. We compared the effects of 3 different stimulating agents acting differently on transductional pathways to stimulate the ROS production: a phorbol ester (PMA), formyl-methionyl-leucyl-phenylalanine (fMLP) and opsonised zymosan (OZ).

RESULTS

As attested by the Krüskall-Wallis test, M. alternifolia EO at 0.1% directly stimulated ROS production by PMNs (x 8.7 vs. 0% EO, p < 0.05) and increased the intracellular ROS produced by monocytes. Whichever the stimulating agent used (PMA, fMLP or OZ), M. alternifolia EO decreased the intracellular ROS production at the dilution of 0.1% by PMNs and monocytes, more so with PMNs.

CONCLUSION

M. alternifolia EO may be both a direct active mediator of the bactericidal action of the circulating leukocytes and may be efficient in protecting the organism from an excess of ROS, through an anti-oxidant and radical scavenging activity.

Inhibition of acetylcholinesterase by Tea Tree oil

Pediculosis is a widespread condition reported in schoolchildren. Treatment most commonly involves the physical removal of nits using fine-toothcombs and the chemical treatment of adult lice and eggs with topical preparations. The active constituents of these preparations frequently exert their effects through inhibition of acetylcholinesterase (AChE, EC 3.1.1.7). Increasing resistance to many preparations has led to the search for more effective treatments. Tea Tree oil, otherwise known as Melaleuca oil, has been added to several preparations as an alternative treatment of head lice infestations. In this study two major constituents of Tea Tree oil, 1,8-cineole and terpinen-4-ol, were shown to inhibit acetylcholinesterase at IC50 values (inhibitor concentrations required to give 50% inhibition) of 0.04 and 10.30 mM, respectively. Four samples of Tea Tree oil tested (Tisserand, Body Treats, Main Camp and Irish Health Culture Association Pure Undiluted) showed anticholinesterase activity at IC50 values of 0.05, 0.10, 0.08 and 0.11 microL mL(-1), respectively. The results supported the hypothesis that the insecticidal activity of Tea Tree oil was attributable, in part, to the anticholinesterase activity of Tea Tree oil.

Evaluation of antioxidant activity of Australian tea tree (Melaleuca alternifolia) oil and its components

Antioxidant activity of Australian tea tree (Melaleuca alternifolia) oil (TTO) was determined using two different assays. In the 2,2-diphenyl-1-picrylhydrazyl assay, 10 microL/mL crude TTO in methanol had approximately 80% free radical scavenging activity, and in the hexanal/hexanoic acid assay, 200 microL/mL crude TTO exhibited 60% inhibitory activity against the oxidation of hexanal to hexanoic acid over 30 days. These results were equivalent to the antioxidant activities of 30 mM butylated hydroxytoluene in both tests at the same experimental conditions. This indicated that the TTO could be a good alternative antioxidant. Inherent antioxidants, i.e., alpha-terpinene, alpha-terpinolene, and gamma-terpinene, in the crude TTO were separated and identified chromatographically using silica gel open chromatography, C(18)-high-pressure liquid chromatography, and gas chromatography-mass spectrometry. Their antioxidant activities decreased in the following order in both assays: alpha-terpinene > alpha-terpinolene > gamma-terpinene.

Antifungal activity of the components of Melaleuca alternifolia (tea tree) oil

AIMS

To investigate the in vitro antifungal activity of the components of Melaleuca alternifolia (tea tree) oil.

METHODS AND RESULTS

Activity was investigated by broth microdilution and macrodilution, and time kill methods. Components showing the most activity, with minimum inhibitory concentrations and minimum fungicidal concentrations of < or =0.25%, were terpinen-4-ol, alpha-terpineol, linalool, alpha-pinene and beta-pinene, followed by 1,8-cineole. The remaining components showed slightly less activity and had values ranging from 0.5 to 2%, with the exception of beta-myrcene which showed no detectable activity. Susceptibility data generated for several of the least water-soluble components were two or more dilutions lower by macrodilution, compared with microdilution.

CONCLUSIONS

All tea tree oil components, except beta-myrcene, had antifungal activity. The lack of activity reported for some components by microdilution may be due to these components becoming absorbed into the polystyrene of the microtitre tray. This indicates that plastics are unsuitable as assay vessels for tests with these or similar components.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has identified that most components of tea tree oil have activity against a range of fungi. However, the measurement of antifungal activity may be significantly influenced by the test method.

Antimycotic activity of Melaleuca alternifolia essential oil and its major components

AIMS

The aim of this study was to analyse the antimycotic properties of Melaleuca alternifolia essential oil (tea tree oil, TTO) and its principal components and to compare them with the activity of 5-fluorocytosine and amphotericin B.

METHODS AND RESULTS

The screening for the antimycotic activity was performed by serial twofold dilutions in Roswell Park Memorial Institute medium with the inclusion of Tween-80 (0.5%). TTO and terpinen-4-olo were the most active compounds.

CONCLUSIONS

The majority of the organisms were sensitive to the essential oil, with TTO and terpinen-4-olo being the most active oils showing antifungal activity at minimum inhibitory concentration values lower than other drugs.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides a sample large enough to determine the antifungal properties of TTO and terpinen-4-olo and suggests further studies for a possible therapeutic use.

In vitro and in vivo activity of tea tree oil against azole-susceptible and -resistant human pathogenic yeasts

A tea tree oil (TTO) preparation of defined chemical composition was studied, using a microbroth method, for its in vitro activity against 115 isolates of Candida albicans, other Candida species and Cryptococcus neoformans. The fungal strains were from HIV-seropositive subjects, or from an established type collection, including reference and quality control strains. Fourteen strains of C. albicans resistant to fluconazole and/or itraconazole were also assessed. The same preparation was also tested in an experimental vaginal infection using fluconazole-itraconazole-susceptible or -resistant strains of C. albicans. TTO was shown to be active in vitro against all tested strains, with MICs ranging from 0.03% (for C. neoformans) to 0.25% (for some strains of C. albicans and other Candida species). Fluconazole- and/or itraconazole-resistant C. albicans isolates had TTO MIC50s and MIC90s of 0.25% and 0.5%, respectively. TTO was highly efficacious in accelerating C. albicans clearance from experimentally infected rat vagina. Three post-challenge doses of TTO (5%) brought about resolution of infection regardless of whether the infecting C. albicans strain was susceptible or resistant to fluconazole. Overall, the use of a reliable animal model of infection has confirmed and extended our data on the therapeutic effectiveness of TTO against fungi, in particular against C. albicans.

Monoterpenoid accumulation in 1,8-cineole, terpinolene and terpinen-4-ol chemotypes of Melaleuca alternifolia seedlings

Individual leaves of the three most common chemotypes of Melaleuca alternifolia were examined both quantitatively and qualitatively for volatile constituents from the emergence of the first true leaves, through to 6-week-old tenth leaf set material. The 1,8-cineole and terpinolene chemotypes were investigated and compared with the recently reported commercial terpinen-4-ol chemotype. The 1,8-cineole chemotype was found to accumulate 1,8-cineole and associated p-menthanes limonene, terpinen-4-ol and alpha-terpineol gradually with increasing leaf set number. As with the terpinen-4-ol variety, higher than expected concentrations of the pinenes and terpinolene were found only in the early leaf sets. The terpinolene variety showed two stages of terpinolene accumulation, the first at leaf sets 2-3 similar to the unexpected biosynthesis of terpinolene in the terpinen-4-ol chemotype and the second at leaf sets 8-9 which is characteristic of the terpinolene variety.

Gas chromatography: an investigative tool in multiple allergies to essential oils

Essential or fragrant oils are volatile odourous mixtures of organic chemical compounds that are widely used in aromatherapy and in the perfume industry. Because of their frequent use, allergy to essential oils is being increasingly recognized. We report 2 cases of multiple allergies to essential oils in professional aromatherapists. Gas chromatography/mass spectrometry was used to analyse the oils in order to identify a common allergen responsible for the contact dermatitis. In both the cases, alpha- and beta-pinene were found to be the most common constituent in the oils and thus appeared to be key allergens. alpha-pinene was confirmed as an allergen on repeat patch testing with pure alpha-pinene in both cases. 12 controls tested were negative for the same. Gas chromatography-mass spectrometry was found to be an extremely useful tool that could be utilized in investigating multiple allergies to essential oils.

Tea tree oil reduces the swelling associated with the efferent phase of a contact hypersensitivity response

OBJECTIVE

To examine the anti-inflammatory activities of tea tree oil (TTO) in vivo.

METHODS

Mice were sensitized to a chemical hapten, trinitrochlorobenzene, on their ventral skin and 7 days later challenged (or re-exposed) on their dorsal skin with the same hapten.

RESULTS

TTO applied 30 min before or up to 7 h after to the same dorsal site as hapten challenge caused a significant reduction in skin swelling after 24 h. TTO reduced oedema but not the influx of inflammatory cells. This finding was supported by the inability of TTO to suppress TNFalpha-induced E-selectin expression by human umbilical vein endothelial cells. TTO did not suppress irritant- or ultraviolet B-induced oedema.

CONCLUSION

Topical TTO, specifically the TTO components, terpinen-4-ol and alpha-terpineol can regulate the oedema associated with the efferent phase of a contact hypersensitivity response.

Monoterpenoid accumulation in Melaleuca alternifolia seedlings

Individual leaves of the commercial terpinen-4-ol type of Melaleuca alternifolia were examined both quantitatively and qualitatively for volatile constituents from the emergence of the first true leaves, through to 6-week-old tenth leaf set material. A GC internal standard addition method was used to measure changes in oil composition and the accumulation of volatile constituents expressed on a dry weight, unit leaf area and whole leaf basis. In the early stages of seedling growth, leaves contained higher concentrations of terpinolene, alpha-pinene and beta-pinene and lower concentrations of terpinen-4-ol, sabinene and cis-sabinene hydrate than mature leaf. Concentrations of the former constituents fell and the latter rose by the time leaf set 10 was 6 weeks old. Key constituent, 1,8-cineole remained in similar concentration throughout ontogeny. The variation in concentration of other key constituents during early stages of seedling development suggests that caution is required in extrapolating seedling leaf data to mature tree oil quality.

[Quality evaluation of essential oils]

Essential oils on the market were analyzed using GC-MS and the main ingredients of each essential oil were quantified. Analysis of the essential oil of Lavandula officinalis (lavender oil) showed that each sample had a different ratio of the contents of main ingredients, such as linalool, linalyl acetate, and camphor. In addition, some commercial lavender oils were analyzed by GC-MS for comparison with the Lavandula flagrans (lavandin oil) and the reference standard. As a result of this analysis, although the components of almost all commercial lavender oils were approximately the same as those of the reference standard, there were a few products that contained more than 0.5% of the amount of camphor in lavandin oil. This suggests that some lavender oil samples are mixed with lavandin oil to lower the price. Commercial essential oils of Melaleuca alternifolia (teatree oil) and Mentha piperita (peppermint oil) were also analyzed by GC-MS. Each of the peppermint oil samples had a different ratio in the content of its main ingredient. With respect to teatree oils, the amount of terpinens in each sample differed. These results led to concern about the efficacy of essential oils. For achieve the expected efficacy of essential oils, correct information on their ingredients should be available and quality control using instrumental analysis should be introduced.

In vitro evaluation of the antibacterial activity of beta-triketones admixed to Melaleuca oils

The in vitro antibacterial properties of mixtures of Australian tea tree oil and niaouli oil after adding the beta-triketone complex isolated from manuka oil were tested. MIC and MBC values for four different bacteria were determined applying the broth dilution method. Both Melaleuca oil mixtures showed good antimicrobial effects against Staphylococcus aureus and Moraxella catarrhalis, exceeding the effectiveness of myrtol, which is well established in the treatment of acute and chronic bronchitis and sinusitis. The death kinetics of S. aureus were determined to draw subtle comparisons between the mixtures. The kill rate data indicated that both Melaleuca oil mixtures achieved a complete kill within 240 min.