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Eucalyptus globulus Labill

Eucalyptus globulus Labill

English: Blue gum tree, Australian fever tree

Hindi: Nilgiri

Sanskrit: Tailpama

The eucalyptus was first brought to Indla by the Sultan of Tippu in around 1790. It was grown initially in the Nandi hills of Karnataka and then extended to the Nilgiri hills of southern India. The species Eucalyptus iereticomis, popularly known as eucalyptus hybrid or Mysore gum, was then the most widely cultivated plantation species. Now, ?. globulus and E. citriodora are grown in the Nilgiris for their essential oil, distilled from the leaves, for use in the fragrance industry. E. globulus trees are coppiced once in every ten years and the timber used for the production of viscose fibre. The eucalyptus was only introduced to the west from Australia in the 19th century. Commercial production of the oil began in about 1860 in Victoria, Australia.


Habitat

Native to Australia and Tasmania, eucalyptus species are cultivated in many tropical, subtropical and temperate areas of the world. Planting can cause ecological problems because the trees absorb large amounts of water, which can inhibit the growth of native plants. Eucalyptus are among the world's fastest growing and tallest trees, the largest recorded at 99 m (326 ft).


Botanical description

A deciduous tree, usually reaching up to 40 m, with a twisted trunk and silver-grey bark (Plate 26). The juvenile leaves differ from the mature leaves, being ovate, cordate; or broadly lanceolate, up to 16 em long by 9 em wide, and glaucus. The mature leaves are narrower, lanceolate, acuminate or asymmetrical rounded, up to 13 em long by 4 em, and glossy green. The flowers are solitary on short pedicles. There are no sepals but numerous long, split stamens, turned inwards. The fruit is globose, up to 3 em long, somewhat tapering toward the base, with i four main ribs. Eucalyptus oil is obtained by steam distillation, followed by reetifieation,of the fresh leaves and bcanch tops.


Parts used

Oil, leaves, bark.


Traditional and modern use

Eucalyptus, a traditional Aboriginal remedy, is a powerful antiseptic still used all over the world for relieving coughs and colds, sore throats and other infections, including bronchitis. The diluted essential oil may be applied to the skin as a chest rub and has a decongestant and warming effect, which helps to relieve respiratory congestion. The diluted oil is also used to relieve aching pain and stiffness of rheumatic joints. The leaves and oil have been used as a febrifuge, expectorant and stimulant and for wounds, burns, ulcers and cancers. In Chinese medicine it is used for similar purposes and an aqueous extract ofthe leaves is used to treat aching joints, bacterial dysentery, ringworm and pulmonary tuberculosis. The steam produced by pouring boiling water on eucalyptus leaves has been used as a simple and useful disinfectant, for puritying the air of the sick room in cases of diphtheria, for example. The extract of the fresh leaves, suitably diluted, can also be employed as a disinfectant lotion in skin diseases, ulcers and offensive discharges of all kinds and as a gargle in mouth infections and bleeding gums.


Ethnoveterinary usage

The flowers, leaves and roots are used in the treatment of peeling of skin in ruminants, and the leaves in ruminants and poultry for the ",,,Imen' of fever, 'prnins end wound" The whole plant is insect repellent.


Major chemical constituents
Essential oil

1,S-Cineole, a-pinene, l3-pinene, limonene, p-cymene, globulol, aromadendrene,' a-terpineol, y-terpinene, terpinen-4-ol, terpinolene,6 allo-aromadendrene,7 l3-caryophyllene, citronellal, ocimene, fenchone, geraniol and many others in the volatile oil of the leaf and fruit.


Flavonoids

Rutin, quercitrin and many other quercetin glycosides are present in the leaf:,10 and rhamnetin, quercetin, taxifolin, engeletin, naringenin and eriodictoyol in the stem bark.


Tannins and polyphenols

Macrocarpals H, I, and], euglobals I-VII, tellimagrandin I, eucalbanin C, gallic acid glucosides, and (+)-catechin have been isolated from the leaf,12.13 and ellagic acid, with a number of rhamnosides, from the stem bark.8.14 Rutin is present in the root15 and gallic, vanillic and ellagic acids in the wood.


Triterpenoids

Oleanolic, acetyloleanolic, betulinic, acetylbetulinic, ursolic, acetylursolic, 23-hydroxyursolic and trans-p-methoxycinnamoyloxy-ursolic acids are present in the wood, as well as their derivatives such as methyl cis-p-ethoxycinnamoyloxyoleanolate and methyl cis-p-methoxycinnamoyloxyursolate, 13-amyrin, uvaol and l3-sitosteroI.


Others

(2-0-a- D-galactopyranosyl-4-0- methy l-a-D-glucurono)-D-xylan19 is present in the stem bark and pinoresinol in the wood.


Medicinal and pharmacological activities

Antioxidant activity: The antioxidant activity of eucalyptus oil was investigated using iron or EDTA-mediated oxidation of linoleic acid and compared with that of butylated hydroxytoluene and a-tocopherol. Eucalyptus oil showed antioxidant activity against linoleic acid autoxidation and did not show any prooxidant activity. The antioxidant activities of the ellagic acid rhamnosides were demonstrated by measuring the inhibition of lipid peroxidation using rat liver microsomes, with IC50 values of 10.0-14.0 llg/ml. Phenolic compounds including pinoresinol, methyl gallate, rhamnazin, rhamnetin, eriodictyol, quercetin, taxifolin, engelitin and catechin extracted from the wood and stem bark also showed antioxidant activity.


Antibacterial activity: The activity of the ethyl acetate extract obtained from acid hydrolysates of the wood was demonstrated against a selection of bacteria and yeasts. Minimum inhibitory concentrations (MIC) in the range of 102-105 llglml were obtained. The macrocarpals, which are phloroglucinol-sesquiterpene coupled constituents isolated from the leaves, demonstrated antibacterial activity against oral pathogens with MIC values ranging from 0.20 to 6.25 llglml. Inhibition of glucosyltransferase activity by these compounds was also noted. Callus cultures initiated from E. gwbulus produced intracellular activity against the Gram-negative bacteria Proteus vulgaris and Pseudomonas aeruginosa, but the extract did not show activity against the yeasts Candida albicans or C. tropicalis. Extracts of eucalyptus leaves were found to be as effective against Trichophyton mentagrophytes, Propionibacterium acnes and methicillin-resistant Staphylococcus aureus (MRSA) and, together with chitosan, showed synergistic antimicrobial activity
against Staph. aureus, Bacillus subtilis, Escherichia coli, Aspergillus niger and Penicillium citrinum. Application of the microbicides to chicken eggs, beef, wet tissues and disposable diapers was also described. The macrocarpals were active against oral bacteria and had an inhibitory effect on glucosyltransferase (GTase). 60% ethanol extracts, containing mostly macro carpals, were evaluated for their cariostatic effects in vitro and were found to significantly inhibit the growth of cariogenic bacteria, although their activity against intestinal bacteria was relatively low. The anticariogenic effect is enhanced by the strong inhibition of glucan synthesis (especially adhesive insoluble glucan) by GTase. The essential oil from eight species of eucalyptus leaves was investigated and the most active compounds found to be 1 ,8-cineole, caryophyllene, citronella! and cryptone. The antimicrobial activity was evaluated against five species of Gram-positive bacteria, four species of Gram-negative bacteria and seven species of fungi. Clarithromycin (antibacterial) and nystatin (antifungal) were used as standard reference compounds. The oil was effective against all the microorganisms used except! Penicillium digitatum and 1 ,8-cineole appeared to be more potent against both bacteria and fungi than the other components of the oil. The methanolic extract showed strong in vitro antimicrobial activity against Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans.


Hypoglycaemic activity: Eucalyptus is used as a traditional treatment for diabetes. Incorporation of leaves of eucalyptus into the diet (62.5 g/kg) and drinking water (2.5 g/l) reduced the hyperglycaemia of streptozotocin-treated mice. This was associated with reduced polydipsia, development of hyperphagia and hypoinsulinaemia and a reduced rate of body weight loss. An aqueous extract of eucalyptus (AEE) (0.5 g/l) enhanced 2-deoxy-glucose transport by 50%, glucose oxidation by 60% and incorporation of glucose into glycogen by 90% in mouse abdominal muscle and evoked a stepwise enhancement of insulin secretion from the clonal pancreatic ?-cellline (BRIN-BOll). The stimulatory effect was unaltered by the presence of 400 pmol diazoxide and prior exposure to AEE did not alter subsequent insulin secretory response to L-alanine, thereby negating a detrimental effect on cell viability. The effect of AEE was not potentiated by glucose or demonstrable in cells exposed to a depolarising concentration of KCl. The active principle was heat stable, acetone insoluble, stable to acid but abolished by exposure to alkali. Sequential extraction with solvents revealed activity in both the methanol and water fractions and indicated the presence of more than one biological active extract constituent.


Antiinflammatory activity: The seed reduced oedematous swelling of the ear, inhibited the proliferation of granuloma and reduced blood capillary permeability in mice and inhibited cotton pellet granuloma and carrageenan-induced oedema in rats.


Collagenase inhibition: 50% ethanol extract inhibited collagenase activity which was attributed to the polyphenol compounds present.


Antihypertensive and diuretic activity: The hydroalcoholic extract containing phloroglucinols produced 94.9% inhibition of angiotensin-converting enzyme (ACE)34 and a decoction of the dried leaf, administered nasogastrically to rats at a dose of 1.0 g/kg, showed diuretic activity.


Insect repellant and insecticidal activity: The oil has insect repellant, acaricidal and pediculicidal effects.


Larvicidal activity: The crude aqueous extract derived from fresh leaves demonstrated lethal activity against Aedes aegypti and Culex quinquefasciatus larvae, with a maximum effect after 48 hours exposure.


Antitumour activity: The euglobals and related compounds demonstrated strong inhibitory effects on Epstein-Barr virus activation by a short-term in vitro assay.


Safety profile

Eucalyptus globulus is listed as a Class 2d herb by the American Herbal Products Association. It is contraindicated in inflammatory diseases of the bile ducts and gastrointestinal tract and in severe liver diseases. Overdose leads in rare cases to nausea, vomiting and dia?rhoea. Eucalyptus oil induces liver enzymes, so may affect other drugs administered concurrently:o and can be dangerous if taken internally. Likewise, infants and children should not have preparations containing the oil applied directly to the face, as it can lead to glottal or bronchial spasms and asthma-like attacks. Mice treated subcutaneously with eucalyptus oil at a dose of 135 mg/kg body weight during the period of organogenesis (days 6-15 of gestation) showed no evidence of embryotoxicity or foetotoxicity. The oral LDsoof eucalyptus oil in the rat is 4.44 g/kg body weighe2 and 3.32 glkg in mice.


Dosage

  • Internal, average daily dose: leaf 4-6 g, oil
  • 0.3-0.6 g
  • External: 5-20% in oil and semi-solid preparations, 5-10% in aqueous alcoholic preparations

Ayurvedic properties

  • Rasa: Katu (pungent), tikta (bitter)
  • Guna: Laghu (light), snighda (unctuous) Veerya: Ushna (hot)
  • Vipaka: Katu (pungent)
  • Dosha: Pacifies kapha and vata