Biological effects of essential oils - A review

Saponins are steroid or triterpenoid glycosides, common in a large number of plants and plant products that are important in human and animal nutrition. Several biological effects have been ascribed to saponins. Extensive research has been carried out into the membrane-permeabilising, immunostimulant, hypocholesterolaemic and anticarcinogenic properties of saponins and they have also been found to significantly affect growth, feed intake and reproduction in animals. These structurally diverse compounds have also been observed to kill protozoans and molluscs, to be antioxidants, to impair the digestion of protein and the uptake of vitamins and minerals in the gut, to cause hypoglycaemia, and to act as antifungal and antiviral agents. These compounds can thus affect animals in a host of different ways both positive and negative.

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The biological action of saponins in animal systems: a review

Complementary and alternative medicines such as tea tree (melaleuca) oil have become increasingly popular in recent decades. This essential oil has been used for almost 100 years in Australia but is now available worldwide both as neat oil and as an active component in an array of products. The primary uses of tea tree oil have historically capitalized on the antiseptic and anti-inflammatory actions of the oil. This review summarizes recent developments in our understanding of the antimicrobial and anti-inflammatory activities of the oil and its components, as well as clinical efficacy. Specific mechanisms of antimicrobial and anti-inflammatory action are reviewed, and the toxicity of the oil is briefly discussed.

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Melaleuca alternifolia (Tea Tree) Oil: a Review of Antimicrobial and Other Medicinal Properties

Epidemiological studies have revealed that a diet rich in plant-derived foods has a protective effect on human health. Identifying bioactive dietary constituents is an active area of scientific investigation that may lead to new drug discovery. Kaempferol (3,5,7-trihydroxy-2-(4-hydroxyphenyl)-4H-1-benzopyran-4-one) is a flavonoid found in many edible plants (e.g. tea, broccoli, cabbage, kale, beans, endive, leek, tomato, strawberries and grapes) and in plants or botanical products commonly used in traditional medicine (e.g. Ginkgo biloba, Tilia spp, Equisetum spp, Moringa oleifera, Sophora japonica and propolis). Some epidemiological studies have found a positive association between the consumption of foods containing kaempferol and a reduced risk of developing several disorders such as cancer and cardiovascular diseases. Numerous preclinical studies have shown that kaempferol and some glycosides of kaempferol have a wide range of pharmacological activities, including antioxidant, anti-inflammatory, antimicrobial, anticancer, cardioprotective, neuroprotective, antidiabetic, anti-osteoporotic, estrogenic/antiestrogenic, anxiolytic, analgesic and antiallergic activities. In this article, the distribution of kaempferol in the plant kingdom and its pharmacological properties are reviewed. The pharmacokinetics (e.g. oral bioavailability, metabolism, plasma levels) and safety of kaempferol are also analyzed. This information may help understand the health benefits of kaempferol-containing plants and may contribute to develop this flavonoid as a possible agent for the prevention and treatment of some diseases.

A review on the dietary flavonoid kaempferol.

A status review on the medicinal properties of essential oils

The antimutagenic activity of Lavandula angustifolia (lavender) essential oil in the bacterial reverse mutation assay.

The antifungal activity of the essential oil of Lavandula angustifolia Mill. (lavender oil) and its main components, linalool and linalyl acetate, was investigated against 50 clinical isolates of Candida albicans (28 oropharyngeal strains, 22 vaginal strains) and C. albicans ATCC 3153. Growth inhibition, killing time and inhibition of germ tube formation were evaluated. The chemical composition of the essential oil was determined by gas chromatography and mass spectrometry. Lavender oil inhibited C. albicans growth: mean minimum inhibitory concentration (MIC) of 0.69% (vol./vol.) (vaginal strains) and 1.04% (oropharyngeal strains); mean MFC of 1.1% (vaginal strains) and 1.8% (oropharyngeal strains). Linalool was more effective than essential oil: mean MIC of 0.09% (vaginal strains) and 0.29% (oropharyngeal strains); mean MFC of 0.1% (vaginal strains) and 0.3% (oropharyngeal strains). Linalyl acetate was almost ineffective. Lavender oil (2%) killed 100% of the C. albicans ATCC 3153 cells within 15 min; linalool (0.5%) killed 100% of the cells within 30 s. The essential oil inhibited germ tube formation (mean MIC of 0.09%), as did the main components (MIC of 0.11% for linalool and 0.08% for linalyl acetate). Both the essential oil and its main components inhibited hyphal elongation of C. albicans ATCC 3153 (about 50% inhibition at 0.016% with each substance). Lavender oil shows both fungistatic and fungicidal activity against C. albicans strains. At lower concentrations, it inhibits germ tube formation and hyphal elongation, indicating that it is effective against C. albicans dimorphism and may thus reduce fungal progression and the spread of infection in host tissues.

Antifungal activity of Lavandula angustifolia essential oil against Candida albicans yeast and mycelial form

The antimicrobial activity of essential oil of Hyssopus officinalis L. var decumbens (Jordan & Fourr.) Briq. from France (Banon) and Hyssopus officinalis L. from Italy (Piedmont) was studied taking account of their chemical composition determined by GC and GC–MS. Pinocamphone and isopinocamphone are present in H. officinalis (4.4% and 43.3%, respectively), according to the ISO 9841 Standard (1991 E) but they are lacking in var. decumbens, where linalol (51.7%), 1,8-cineole (12.3%) and limonene (5.1%) instead are predominant. The disc diffusion tests carried out on Gram-positive (Staphylococcus aureus and Enterococcus spp.) and Gram-negative bacteria (Klebsiella oxytoca, Escherichia coli, Proteus mirabilis, Pseudomonas spp. and two strains of Salmonella spp.) showed an antimicrobial activity generally negligible for H. officinalis, but broader, and in a few cases more evident (Enterococcus spp. and E. coli), for var. decumbens. All yeasts (seven strains of Candida albicans, C. krusei and C. tropicalis) were strongly inhibited by both species. In liquid medium the MIC of H. officialis was always >1.2% v/v for bacteria and between 0.6 and 1.2% v/v for yeasts, while the MIC of var. decumbens was between 0.15 and 0.6% v/v for the Gram-positive bacteria, 0.3 and 1.2% v/v for the Gram-negative bacteria and 0.15 and 0.3% v/v for the yeasts. The effect of var. decumbens was generally bactericidal. Linalol, and in a lesser way, 1,8-cineole, may contribute to the greater antimicrobial activity of var. decumbens in comparison with H. officinalis, while limonene may be responsible for the antimycotic action observed in both oils, as suggested by results of the disc diffusion tests carried out on the pure reference substances. © 1998 John Wiley & Sons, Ltd.

Antimicrobial properties of the linalol‐rich essential oil of Hyssopus officinalis L. var decumbens (Lamiaceae)

Oleanolic acid is a triterpenoid which is quite common in nature in the form either of free acid or in triterpenoid saponin glycosides. This study describes the effect of oleanolic acid on the growth of human immunodeficiency virus-1 (HIV-1) in cultures of human peripheral mononuclear cells (PBMC) and of monocyte/macrophages (M/M). Its inhibitory activity was also evaluated on PBMC obtained from HIV-1 infected patients. Results obtained show that oleanolic acid inhibits the HIV-1 replication in all the cellular systems used (EC50 values: 22.7 microM, 24.6 microM and 57.4 microM for in vitro infected PBMC, naturally infected PBMC and M/M, respectively). As regards the mechanism of action, oleanolic acid inhibits in vitro the HIV-1 protease activity.

In vitro anti-HIV activity of oleanolic acid on infected human mononuclear cells.

In the last years several plant-derived natural compounds have been screened for their anti-HIV activity in order to find lead compounds with novel structures or mechanisms of action. Among these, several triterpenoids have been found to exhibit an antiretroviral activity with different mechanisms of action. In this study the effect of two limonoids, limonin and nomilin, on the growth of human immunodeficiency virus-1 (HIV-1) in culture of human peripheral blood mononuclear cells (PBMC) and on monocytes/macrophages (M/M) is described. Limonin and nomilin were found to inhibit the HIV-1 replication in all cellular systems used. A dose-dependent inhibition of viral replication was observed in PBMC isolated from healthy donors and infected with HIV-1 strain after incubation with limonin and nomilin (EC (50) values: 60.0 microM and 52.2 microM, respectively). The two terpenoids inhibited at all concentrations studied the production of HIV-p24 antigen even when the PBMC employed were chronically infected (EC (50) values of 61.0 microM for limonin and 76.2 microM for nomilin). Moreover, these compounds inhibited the HIV-1 replication even in infected M/M. In this cellular system the inhibitory effect was significant at the concentrations of 20 microM, 40 microM and 80 microM starting from day 14 and reached the maximum effect after 18 days of incubation. As regards the mechanism of action, limonin and nomilin inhibit in vitro HIV-1 protease activity. In general, the results obtained point out a similar anti-HIV activity of limonin and nomilin indicating that this activity is not drastically influenced by the structural difference between the two compounds.

Lucia Battinelli

Papers

The antimutagenic activity of Lavandula angustifolia (lavender) essential oil in the bacterial reverse mutation assay.

Antifungal activity of Lavandula angustifolia essential oil against Candida albicans yeast and mycelial form

Antimicrobial properties of the linalol‐rich essential oil of Hyssopus officinalis L. var decumbens (Lamiaceae)

In vitro anti-HIV activity of oleanolic acid on infected human mononuclear cells.

Effect of limonin and nomilin on HIV-1 replication on infected human mononuclear cells.