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WHO Monographs on Selected Medicinal Plants - Volume 1
(1999; 295 pages) View the PDF document
Table of Contents
View the documentAcknowledgements
View the documentIntroduction
View the documentBulbus Allii Cepae
View the documentBulbus Allii Sativi
View the documentAloe
View the documentAloe Vera Gel
View the documentRadix Astragali
View the documentFructus Bruceae
View the documentRadix Bupleuri
View the documentHerba Centellae
View the documentFlos Chamomillae
View the documentCortex Cinnamomi
View the documentRhizoma Coptidis
View the documentRhizoma Curcumae Longae
View the documentRadix Echinaceae
View the documentHerba Echinaceae Purpureae
View the documentHerba Ephedrae
View the documentFolium Ginkgo
View the documentRadix Ginseng
View the documentRadix Glycyrrhizae
View the documentRadix Paeoniae
View the documentSemen Plantaginis
View the documentRadix Platycodi
View the documentRadix Rauwolfiae
View the documentRhizoma Rhei
View the documentFolium Sennae
View the documentFructus Sennae
View the documentHerba Thymi
View the documentRadix Valerianae
View the documentRhizoma Zingiberis
View the documentAnnex. Participants in the WHO Consultation on Selected Medicinal Plants
 

Aloe Vera Gel

Definition

Aloe Vera Gel is the colourless mucilaginous gel obtained from the parenchymatous cells in the fresh leaves of Aloe vera (L) Burm. f. (Liliaceae) (1, 2).

Synonyms

Aloe barbadensis Mill., Aloe chinensis Bak., A. elongata Murray, A. indica Royle, A. officinalis Forsk., A. perfoliata L., A. rubescens DC, A. vera L. var. littoralis König ex Bak., A. vera L. var. chinensis Berger, A. vulgaris Lam. (25). Most formularies and reference books regard Aloe barbadensis Mill. as the correct species name, and Aloe vera (L.) Burm. f. as a synonym. However, according to the International Rules of Botanical Nomenclature, Aloe vera (L.) Burm. f. is the legitimate name for this species (2–4). The genus Aloe has also been placed taxonomically in a family called Aloeaceae.

Selected vernacular names

Aloe vera gel, aloe gel.

Description

Succulent, almost sessile perennial herb; leaves 30–50 cm long and 10cm broad at the base; colour pea-green (when young spotted with white); bright yellow tubular flowers 25–35 cm in length arranged in a slender loose spike; stamens frequently project beyond the perianth tube (6).

Plant material of interest: liquid gel from the fresh leaf

Aloe Vera Gel is not to be confused with the juice, which is the bitter yellow exudate originating from the bundle sheath cells of the leaf. The drug Aloe consists of the dried juice.

General appearance

The gel is a viscous, colourless, transparent liquid.

Organoleptic properties

Viscous, colourless, odourless, taste slightly bitter.

Microscopic characteristics

Not applicable.

Geographical distribution

Probably native to north Africa along the upper Nile in the Sudan, and subsequently introduced and naturalized in the Mediterranean region, most of the tropics and warmer areas of the world, including Asia, the Bahamas, Central America, Mexico, the southern United States of America, south-east Asia, and the West Indies (2).

General identity tests

To be established in accordance with national requirements.

Purity tests

Microbiology

The test for Salmonella spp. in Aloe Vera Gel should be negative. Acceptable maximum limits of other microorganisms are as follows (7–9). For external use: aerobic bacteria-not more than 102/ml; fungi-not more than 102/ml; enterobacteria and certain Gram-negative bacteria-not more than 101/ml; Staphylococcus spp.-0/ml. (Not used internally.)

Moisture

Contains 98.5% water (10).

Pesticide residues

To be established in accordance with national requirements. For guidance, see WHO guidelines on quality control methods for medicinal plants (7) and guidelines on predicting dietary intake of pesticide residues (11).

Heavy metals

Recommended lead and cadmium levels are not more than 10 and 0.3mg/kg, respectively, in the final dosage form (7).

Radioactive residues

For analysis of strontium-90, iodine-131, caesium-134, caesium-137, and plutonium-239, see WHO guidelines on quality control methods for medicinal plants (7).

Other tests

Chemical tests for Aloe Vera Gel and tests for total ash, acid-insoluble ash, alcohol-soluble residue, foreign organic matter, and water-soluble extracts to be established in accordance with national requirements.

Chemical assays

Carbohydrates (0.3%) (12), water (98.5%) (10). Polysaccharide composition analysis by gas–liquid chromatography (13).

Major chemical constituents

Aloe Vera Gel consists primarily of water and polysaccharides (pectins, hemicelluloses, glucomannan, acemannan, and mannose derivatives). It also contains amino acids, lipids, sterols (lupeol, campesterol, and β-sitosterol), tannins, and enzymes (1). Mannose 6-phosphate is a major sugar component (14).

Dosage forms

The clear mucilaginous gel. At present no commercial preparation has been proved to be stable. Because many of the active ingredients in the gel appear to deteriorate on storage, the use of fresh gel is recommended. Preparation of fresh gel: harvest leaves and wash them with water and a mild chlorine solution. Remove the outer layers of the leaf including the pericyclic cells, leaving a "fillet" of gel. Care should be taken not to tear the green rind which can contaminate the fillet with leaf exudate. The gel may be stabilized by pasteurization at 75–80°C for less than 3 minutes. Higher temperatures held for longer times may alter the chemical composition of the gel (2).

Medicinal uses

Uses supported by clinical data

None.

Uses described in pharmacopoeias and in traditional systems of medicine

Aloe Vera Gel is widely used for the external treatment of minor wounds and inflammatory skin disorders (1, 14–17). The gel is used in the treatment of minor skin irritations, including burns, bruises, and abrasions (1, 14, 18). The gel is further used in the cosmetics industry as a hydrating ingredient in liquids, creams, sun lotions, shaving creams, lip balms, healing ointments, and face packs (1).

Aloe Vera Gel has been traditionally used as a natural remedy for burns (18, 19). Aloe Vera Gel has been effectively used in the treatment of first- and second-degree thermal burns and radiation burns. Both thermal and radiation burns healed faster with less necrosis when treated with preparations containing Aloe Vera Gel (18, 19). In most cases the gel must be freshly prepared because of its sensitivity to enzymatic, oxidative, or microbial degradation. Aloe Vera Gel is not approved as an internal medication, and internal administration of the gel has not been shown to exert any consistent therapeutic effect.

Uses described in folk medicine, not supported by experimental or clinical data

The treatment of acne, haemorrhoids, psoriasis, anaemia, glaucoma, petit ulcer, tuberculosis, blindness, seborrhoeic dermatitis, and fungal infections (2, 6, 19).

Pharmacology

Wound healing

Clinical investigations suggest that Aloe Vera Gel preparations accelerate wound healing (14, 18). In vivo studies have demonstrated that Aloe Vera Gel promotes wound healing by directly stimulating the activity of macrophages and fibroblasts (14). Fibroblast activation by Aloe Vera Gel has been reported to increase both collagen and proteoglycan synthesis, thereby promoting tissue repair (14). Some of the active principles appear to be polysaccharides composed of several monosaccharides, predominantly mannose. It has been suggested that mannose 6-phosphate, the principal sugar component of Aloe Vera Gel, may be partly responsible for the wound healing properties of the gel (14). Mannose 6-phosphate can bind to the growth factor receptors on the surface of the fibroblasts and thereby enhance their activity (14, 15).

Furthermore, acemannan, a complex carbohydrate isolated from Aloe leaves, has been shown to accelerate wound healing and reduce radiationinduced skin reactions (20, 21). The mechanism of action of acemannan appears to be twofold. First, acemannan is a potent macrophage-activating agent and therefore may stimulate the release of fibrogenic cytokines (21, 22). Second, growth factors may directly bind to acemannan, promoting their stability and prolonging their stimulation of granulation tissue (20).

The therapeutic effects of Aloe Vera Gel also include prevention of progressive dermal ischaemia caused by burns, frostbite, electrical injury and intraarterial drug abuse. In vivo analysis of these injuries demonstrates that Aloe Vera Gel acts as an inhibitor of thromboxane A2, a mediator of progressive tissue damage (14, 17). Several other mechanisms have been proposed to explain the activity of Aloe Vera Gel, including stimulation of the complement linked to polysaccharides, as well as the hydrating, insulating, and protective properties of the gel (1).

Because many of the active ingredients appear to deteriorate on storage, the use of fresh gel is recommended. Studies of the growth of normal human cells in vitro demonstrated that cell growth and attachment were promoted by exposure to fresh Aloe vera leaves, whereas a stabilized Aloe Vera Gel preparation was shown to be cytotoxic to both normal and tumour cells. The cytotoxic effects of the stabilized gel were thought to be due to the addition of other substances to the gel during processing (23).

Anti-inflammatory

The anti-inflammatory activity of Aloe Vera Gel has been revealed by a number of in vitro and in vivo studies (14, 17, 24, 25). Fresh Aloe Vera Gel significantly reduced acute inflammation in rats (carrageenin-induced paw oedema), although no effect on chronic inflammation was observed (25). Aloe Vera Gel appears to exert its anti-inflammatory activity through bradykinase activity (24) and thromboxane B2 and prostaglandin F2 inhibition (18, 26). Furthermore, three plant sterols in Aloe Vera Gel reduced inflammation by up to 37% in croton oil-induced oedema in mice (15). Lupeol, one of the sterol compounds found in Aloe vera, was the most active and reduced inflammation in a dosedependent manner (15). These data suggest that specific plant sterols may also contribute to the anti-inflammatory activity of Aloe Vera Gel.

Burn treatment

Aloe Vera Gel has been used for the treatment of radiation burns (27–30). Healing of radiation ulcers was observed in two patients treated with Aloe vera cream (27), although the fresh gel was more effective than the cream (29, 30). Complete healing was observed, after treatment with fresh Aloe Vera Gel, in two patients with radiation burns (30). Twenty-seven patients with partialthickness burns were treated with Aloe Vera Gel in a placebo-controlled study (31). The Aloe Vera Gel-treated lesions healed faster (11.8 days) than the burns treated with petroleum jelly gauze (18.2 days), a difference that is statistically significant (t-test, P < 0.002).

Contraindications

Aloe Vera Gel is contraindicated in cases of known allergy to plants in the Liliaceae.

Warnings

No information available.

Precautions

No information available concerning general precautions, or precautions dealing with carcinogenesis, mutagenesis, impairment of fertility; drug and laboratory test interactions; drug interactions; nursing mothers; paediatric use; or teratogenic or non-teratogenic effects on pregnancy.

Adverse reactions

There have been a few reports of contact dermatitis and burning skin sensations following topical applications of Aloe Vera Gel to dermabraded skin (18, 32). These reactions appeared to be associated with anthraquinone contaminants in this preparation (33). A case of disseminated dermatitis has been reported following application of Aloe Vera Gel to a patient with stasis dermatitis (34). An acute bullous allergic reaction and contact urticaria have also been reported to result from the use of Aloe Vera Gel (35).

Posology

Fresh gel or preparations containing 10–70% fresh gel.

References

1. Bruneton J. Pharmacognosy, phytochemistry, medicinal plants. Paris, Lavoisier, 1995.

2. Grindlay D, Reynolds T. The Aloe vera phenomenon: a review of the properties and modern uses of the leaf parenchyma gel. Journal of ethnopharmacology, 1986, 16:117– 151.

3. Newton LE. In defence of the name Aloe vera. The cactus and succulent journal of Great Britain, 1979, 41:29–30.

4. Tucker AO, Duke JA, Foster S. Botanical nomenclature of medicinal plants. In: Cracker LE, Simon JE, eds. Herbs, spices and medicinal plants, Vol. 4. Phoenix, AR, Oryx Press, 1989:169–242.

5. Hänsel R et al., eds. Hagers Handbuch der Pharmazeutischen Praxis, Vol. 6, 5th ed. Berlin, Springer, 1994.

6. Youngken HW. Textbook of pharmacognosy, 6th ed. Philadelphia, Blakiston, 1950.

7. Quality control methods for medicinal plant materials. Geneva, World Health Organization, 1998.

8. Deutsches Arzneibuch 1996. Vol. 2. Methoden der Biologie. Stuttgart, Deutscher Apotheker Verlag, 1996.

9. European pharmacopoeia, 3rd ed. Strasbourg, Council of Europe, 1997.

10. Rowe TD, Park LM. Phytochemical study of Aloe vera leaf. Journal of the American Pharmaceutical Association, 1941, 30:262–266.

11. Guidelines for predicting dietary intake of pesticide residues, 2nd rev. ed. Geneva, World Health Organization, 1997 (unpublished document WHO/FSF/FOS/97.7; available from Food Safety, WHO, 1211 Geneva 27, Switzerland).

12. Pierce RF. Comparison between the nutritional contents of the aloe gel from conventional and hydroponically grown plants. Erde international, 1983, 1:37–38.

13. Hart LA et al. An anti-complementary polysaccharide with immunological adjuvant activity from the leaf of Aloe vera. Planta medica, 1989, 55:509–511.

14. Davis RH et al. Anti-inflammatory and wound healing of growth substance in Aloe vera. Journal of the American Pediatric Medical Association, 1994, 84:77–81.

15. Davis RH et al. Aloe vera, hydrocortisone, and sterol influence on wound tensile strength and anti-inflammation. Journal of the American Pediatric Medical Association, 1994, 84:614–621.

16. Heggers JP, Pelley RP, Robson MC. Beneficial effects of Aloe in wound healing. Phytotherapy research, 1993, 7:S48–S52.

17. McCauley R. Frostbite-methods to minimize tissue loss. Postgraduate medicine, 1990, 88:67–70.

18. Shelton RM. Aloe vera, its chemical and therapeutic properties. International journal of dermatology, 1991, 30:679–683.

19. Haller JS. A drug for all seasons, medical and pharmacological history of aloe. Bulletin of New York Academy of Medicine, 1990, 66:647–659.

20. Tizard AU et al. Effects of acemannan, a complex carbohydrate, on wound healing in young and aged rats. Wounds, a compendium of clinical research and practice, 1995, 6:201–209.

21. Roberts DB, Travis EL. Acemannan-containing wound dressing gels reduce radiation-induced skin reactions in C3H mice. International journal of radiation oncology, biology and physiology, 1995, 15:1047–1052.

22. Karaca K, Sharma JM, Norgren R. Nitric oxide production by chicken macrophages activated by acemannan, a complex carbohydrate extracted from Aloe vera. International journal of immunopharmacology, 1995, 17:183–188.

23. Winters WD, Benavides R, Clouse WJ. Effects of aloe extracts on human normal and tumor cells in vitro. Economic botany, 1981, 35:89–95.

24. Fujita K, Teradaira R. Bradykininase activity of aloe extract. Biochemical pharmacology, 1976, 25:205.

25. Udupa SI, Udupa AL, Kulkarni DR. Anti-inflammatory and wound healing properties of Aloe vera. Fitoterapia, 1994, 65:141–145.

26. Robson MC, Heggers J, Hagstrom WJ. Myth, magic, witchcraft or fact? Aloe vera revisited. Journal of burn care and rehabilitation, 1982, 3:157–162.

27. Collin C. Roentgen dermatitis treated with fresh whole leaf of Aloe vera. American journal of roentgen, 1935, 33:396–397.

28. Wright CS. Aloe vera in the treatment of roentgen ulcers and telangiectasis. Journal of the American Medical Association, 1936, 106:1363–1364.

29. Rattner H. Roentgen ray dermatitis with ulcers. Archives of dermatology and syphilogy, 1936, 33:593–594.

30. Loveman AB. Leaf of Aloe vera in treatment of roentgen ray ulcers. Archives of dermatology and syphilogy, 1937, 36:838–843.

31. Visuthikosol V et al. Effect of Aloe vera gel on healing of burn wounds: a clinical and histological study. Journal of the Medical Association of Thailand, 1995, 78:403–409.

32. Hormann HP, Korting HC. Evidence for the efficacy and safety of topical herbal drugs in dermatology: Part 1: Anti-inflammatory agents. Phytomedicine, 1994, 1:161– 171.

33. Hunter D, Frumkin A. Adverse reactions to vitamin E and Aloe vera preparations after dermabrasion and chemical peel. Cutis, 1991, 47:193–194.

34. Horgan DJ. Widespread dermatitis after topical treatment of chronic leg ulcers and stasis dermatitis. Canadian Medical Association Journal, 1988, 138:336–338.

35. Morrow DM, Rappaport MJ, Strick RA. Hypersensitivity to aloe. Archives of dermatology, 1980, 116:1064–1065.

 

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