Critical Evaluation of Melaleuca alternifolia : A Review of the Phytochemical Profile, Pharmacological Attributes and Medicinal Properties in the Botanical, Human and Global Perspectives

Abstract

Melaleuca (tea tree) oil has become increasingly commonly used in recent decades. The essential oil in Australia for the past 120 years is now available globally as an active component in various products. Historically, Melaleuca oil is known for its antiseptic and anti-inflammatory actions. Currently, microwave technology is applied to extract Melaleuca oil, but this extraction technology is not commercially under practice. Traditionally, Melaleuca oil extraction is possible through steam distillation of the Melaleuca alternifolia terminal branches and leaves, and the resultant extract is always either clear or pale yellowish. Melaleuca oil has been promoted as a therapeutic agent because scientific studies indicate that the Rideal-Walker (RW) coefficients of its extract composition include 8 for cymene, 16 for terpineol, 13.5 for tepinen-4-ol and 3.5 for cineole. The mode of action against bacteria is now partially elucidated, and assumptions exist. Hydrocarbons partition into biological membranes to disrupt the vital functions of Melaleuca oil, and also its components behave in the same manner. Therefore, the inhibition of respiration and the leakage of ions or loss of intracellular material and the inability to maintain homeostasis reflect the loss of membrane integrity and lysis in Melaleuca oil products containing lower than usual terpenes concentrations. Melaleuca oil possesses antifungal properties and is known exclusively for the treatment of Candida albicans. This essential oil strongly changes the permeability of Candida albican cells. C. albicans treatment with 0.25% tea tree oil leads to propidium iodide uptake. However, a significant loss of 260-nmlight-absorbing materials after staining with methylene blue occurs after 6 hours. Melaleuca extracts alter the permeability of Candida glabrata that occurs when the membrane is treated with 0.25% Melaleuca oil. Melaleuca oils possess antiviral properties but most findings evidence that this oil fights against both non-enveloped and enveloped viruses, although the range of viruses tested to date is minimal. Melaleuca oil is known for its antiprotozoal activity because it causes a 50% reduction in the growth of protozoa Leishmania major and Trypanosoma brucei at concentrations of 403 mg/ml and 0.5 mg/ml, respectively, based on the studies done (in comparison to controls). An investigation has shown that terpinen-4-ol also contributes significantly to antiprotozoal activity. Tea tree oils at 300 mg/ml killed all cells of Trichomonas vaginalis, and also anecdotal in-vivo studies evidence that Melaleuca oil may be effective in treating infections caused by Trichomonas vaginalis. This review article summarizes the developments in our understanding of the phytochemistry, bioactivity, metabolism and the economic aspects of Melaleuca alternifolia, and it details how Melaleuca alternifolia species have evolved in the ecosystem.