Can the tea tree oil (Australian native plant: Melaleuca alternifolia Cheel) be an alternative treatment for human demodicosis on skin?

Australian tea tree oil (TTO) and its extract terpinen-4-ol (T4O) are found to be effective in moderating demodex-related diseases. Their possible effects are lowering the mite counts, relieving the demodex-related symptoms and modulating the immune system especially the inflammatory response. This review summarizes the topical treatments of TTO and T4O in human demodicosis, their possible mechanism of actions, side-effects and potential resistance in treating this condition. Although current treatments other than TTO and T4O are relatively effective in controlling the demodex mite population and the related symptoms, more research on the efficacy and drug delivery technology is needed in order to assess its potential as an alternative treatment with minimal side-effect profile, low toxicity and low risk of demodex resistance.

The dynamics and mechanism of the antimicrobial activity of tea tree oil against bacteria and fungi.

Tea tree oil (TTO) is a yellow liquid extracted from Melaleuca alternifolia. Although the antimicrobial activity of TTO has been known for a long time, its specific antimicrobial effects and mechanism underlying these remain poorly characterized. The present study investigated the chemical composition of TTO and the dynamics and mechanism of its antimicrobial activities in two bacterial and two fungal strains. Gas chromatography-mass spectrometry analysis identified alkenes and alcohols as the main constituents of TTO. Terpinen-4-ol was the most abundant individual component, accounting for approximately 23 % of the TTO. Poisoned food technique assessment showed that the minimum inhibitory concentrations of TTO for bacterial strains (Escherichia coli and Staphylococcus aureus) and fungal strains (Candida albicans and Aspergillus niger) were 1.08 and 2.17 mg/mL, respectively. Antimicrobial dynamic curves showed that with increasing concentrations of TTO, the rate of cell killing and the duration of growth lag phase increased correspondingly. These data indicated that TTO produced concentration and time-dependent antimicrobial effects. The minimum bactericidal and fungicidal concentrations of TTO were 2.17, 4.34, and 4.34 against E. coli, S. aureus, and C. albicans, respectively. However, A. niger conidia were not completely eradicated, even after 3 days in the presence of 17.34 mg/mL TTO. Transmission electron microscopy images indicated that TTO penetrated the cell wall and cytoplasmic membrane of all the tested bacterial and fungal strains. TTO may also penetrate fungal organelle membrane. These findings indicated that TTO maybe exerts its antimicrobial effects by compromising the cell membrane, resulting in loss of the cytoplasm and organelle damage, which ultimate leads to cell death.

In vitro activity of Melaleuca alternifolia (tea tree) oil on filamentous fungi and toxicity to human cells.

Invasive fungal wound infections (IFIs) are increasingly reported in trauma patients and cause considerable morbidity and mortality despite standard of care treatment in trauma centers by experienced medical personnel. Topical agents such as oil of melaleuca, also known as tea tree oil (TTO), have been proposed for adjunctive treatment of IFIs. We evaluated the activity of TTO against filamentous fungi associated with IFIs by testing 13 clinical isolates representing nine species via time-kill assay with seven concentrations of TTO (100%, 75%, 50%, 25%, 10%, 5%, and 1%). To ascertain the safety of topical application to wounds, cell viability assays were performed in vitro using human fibroblasts, keratinocytes, osteoblasts, and umbilical vein endothelial cells with 10 concentrations of TTO (75%, 50%, 25%, 10%, 5%, and 10-fold serial dilutions from 1 to 0.0001%) at five time points (5, 15, 30, 60, and 180 min). Compatibility of TTO with explanted porcine tissues was also assessed with eight concentrations of TTO (100%, 75%, 50%, 25%, 10%, 5%, 1%, and 0.1%) at the time points used for cellular assays and at 24 h. The time-kill studies showed that fungicidal activity was variable between isolates. The effect of TTO on cell viability was primarily concentration dependent with significant cytotoxicity at concentrations of ≥ 10% and ≥ 50% for cells lines and whole tissue, respectively. Our findings demonstrate that TTO possesses antifungal activity against filamentous fungi associated with IFIs; furthermore that negligible effects on whole tissues, in contrast to individual cells, were observed following exposure to TTO. Collectively, these findings indicate a potential use of TTO as topical treatment of IFIs.

Adaptation to NaCl Reduces the Susceptibility of Enterococcus faecalis to Melaleuca alternifolia (Tea Tree) Oil.

This study investigated the hypothesis that the salt adaptation response of Enterococcus faecalis alters susceptibility to tea tree oil (TTO). Six E. faecalis isolates were adapted to 6.5 % NaCl, and then exposed to TTO in phosphate-buffered saline (PBS). One isolate was also exposed to TTO in Brain Heart Infusion Broth (BHIB). The viability of salt-adapted and non-adapted control cells was determined at 0, 45 and 90 min and compared. MICs for several antibiotics and TTO were also determined by E test and broth microdilution, respectively. Results showed that susceptibility to TTO in PBS was significantly reduced after salt adaptation for five isolates (83 %) (P < 0.05). Mean differences between salt-adapted and non-adapted cell counts were 2.51 log at 45 min and 2.13 log at 90 min. However, when E. faecalis ATCC 19433 was exposed to TTO in BHIB, no significant differences were seen. In conclusion, salt adaptation resulted in reduced susceptibility to TTO in PBS for the majority of isolates, indicating that cross protection had occurred. This effect was absent in BHIB, suggesting that the uptake of compatible solutes from the growth medium protected non-adapted cells from TTO. Whether this has implications for the clinical effectiveness of TTO remains to be determined.

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.

Melaleuca alternifolia Induces Heme Oxygenase-1 Expression in Murine RAW264.7 Cells through Activation of the Nrf2-ARE Pathway.

Melaleuca alternifolia concentrate (MAC) is the refined essential oil of the Australian native plant Melaleuca alternifolia. MAC has been reported to suppress the production of pro-inflammatory cytokines in both murine RAW264.7 macrophages and human monocytes stimulated with lipopolysaccharide (LPS). However, the mechanisms involved in this effect remain unclear. This study aims to delineate the molecular mechanisms that drive the anti-inflammatory activity of MAC and its active component, terpinen-4-ol, in macrophages. The effects of MAC on RAW264.7 cells were studied using western blotting, real-time PCR, an electrophoretic mobility shift assay (EMSA), and NF-[Formula: see text]B luciferase reporter assays. Our results showed that MAC significantly increased both the mRNA and protein levels of heme oxygenase-1 (HO-1) via p38 and JNK MAPK activation. In addition, we showed that MAC significantly increased the activation and nuclear translocation of NF-E2-related factor 2 (Nrf2), a key transcription factor regulating HO-1 induction. MAC was also associated with significant inhibition of iNOS expression, NO production, and NF-[Formula: see text]B activation. HO-1 was required for these anti-inflammatory effects as tin protoporphyrin IX (SnPPIX), an HO-1 inhibitor, abolished the effects of MAC on LPS-induced iNOS, NO, and NF-[Formula: see text]B activation. Our results indicate that MAC induces HO-1 expression in murine macrophages via the p38 MAPK and JNK pathways and that this induction is required for its anti-inflammatory activity.

Green tea epigallocatechin-3-gallate attenuates Porphyromonas gingivalis-induced atherosclerosis.

The purpose of this study was to determine whether epigallocatechin-3-gallate (EGCG) ameliorates Porphyromonas gingivalis-induced atherosclerosis. EGCG is a polyphenol extract from green tea with health benefits and P. gingivalis is shown here to accelerate atheroma formation in a murine model. Apolipoprotein E knockout mice were administered EGCG or vehicle in drinking water; they were then fed high-fat diets and injected with P. gingivalis three times a week for 3 weeks. Mice were then killed at 15 weeks. Atherosclerotic plaques in the proximal aorta were determined by Oil Red O staining. Atherosclerosis risk factors in serum, liver or aorta were analysed using cytokine antibody arrays, enzyme-linked immunosorbent assay and real-time PCR. Atherosclerotic lesion areas of the aortic sinus caused by P. gingivalis infection decreased in EGCG-treated groups, wherein EGCG reduced the production of C-reactive protein, monocyte chemoattractant protein-1, and oxidized low-density lipoprotein (LDL), and slightly lowered LDL/very LDL cholesterol in P. gingivalis-challenged mice serum. Furthermore, the increase in CCL2, MMP-9, ICAM-1, HSP60, CD44, LOX-1, NOX-4, p22phox and iNOS gene expression levels in the aorta of P. gingivalis-challenged mice were reduced in EGCG-treated mice. However, HO-1 mRNA levels were elevated by EGCG treatment, suggesting that EGCG, as a natural substance, inhibits P. gingivalis-induced atherosclerosis through anti-inflammatory and antioxidative effects.

Activity of Melaleuca alternifolia (tea tree) oil on Influenza virus A/PR/8: study on the mechanism of action.

Our previous study demonstrated that Melaleuca alternifolia (tea tree) oil (TTO) had an interesting antiviral activity against Influenza A in MDCK cells. In fact, when we tested TTO and some of its components, we found that TTO had an inhibitory effect on influenza virus replication at doses below the cytotoxic dose; terpinen-4-ol, terpinolene, and alfa-terpineol were the main active components. The aim of this study was to investigate the mechanism of action of TTO and its active components against Influenza A/PR/8 virus subtype H1N1 in MDCK cells. None of the test compounds showed virucidal activity nor any protective action for the MDCK cells. Thus, the effect of TTO and its active components on different steps of the replicative cycle of influenza virus was studied by adding the test compounds at various times after infection. These experiments revealed that viral replication was significantly inhibited if TTO was added within 2h of infection, indicating an interference with an early step of the viral replicative cycle of influenza virus. The influence of the compound on the virus adsorption step, studied by the infective center assay, indicated that TTO did not interfere with cellular attachment of the virus. TTO did not inhibit influenza virus neuraminidase activity, as shown by the experiment measuring the amount of 4-methylumbelliferone, cleaved by the influenza virus neuraminidase from the fluorogenic substrate 2'-O-(4-methylumbelliferyl)-N-acetylneuraminic acid. The effect of TTO on acidification of cellular lysosomes was studied by vital staining with acridine orange using bafilomycin A1 as positive control. The treatment of cells with 0.01% (v/v) of TTO at 37°C for 4h before staining inhibited the acridine orange accumulation in acid cytoplasmic vesicles, indicating that TTO could inhibit viral uncoating by an interference with acidification of intralysosomal compartment.