Family

Aloaceae (formerly in Liliaceae).

Related Species

Aloe ferox Mill., A. africana Mill., A. spicata Baker., A. perryi Baker.; the Aloe genus has more than 300 species. Aloe vera has been widely hybridized in commerce, and cultivars are the primary source of the gel.

Habitat and Cultivation

Native to Africa, widespread in cultivation throughout subtropical regions in North and South America, West Indies, and East Asia; the cactuslike aloe is also a popular houseplant.

Parts Used

Aloe gel is a mucilaginous, colorless liquid derived from the central parenchymatous cells of the fresh leaves of aloe.

Note: Aloe gel and aloe latex are completely distinct remedies. The anthraquinone-containing dried juice, a yellow-orange latex, or sap exuded from the outer or pericycle (vascular bundles) area of the leaf, is often known as “Cape aloe” or “Curacao aloe.” Some traditional cultures have used the root as a medicine, but this is not a current Western usage. Aloe latex can be considered with the Rhamnacae species such as cascara ( Rhamnus purshiana DC), the buckthorns ( R. frangula L. and R. cathartica L.), as well as senna leaf and fruits ( Cassia senna L.) and rhubarb root ( Rheum palmatum L.). All these species contain closely related anthraquinone glycosides that dominate their pharmacology, particularly the pronounced laxative and purgative activity associated with these herbs.

Common Forms

100% Fresh gel and freeze-dried concentrates, typically 4.5:1 concentrate, equivalent to 11.25 mg/mL of acemannan.

• Standardized Extracts:   Preparations based on acemannan (acetylated mannose polysaccharide) obtained by hydroethanolic extraction from the inner leaf gel. Multiple proprietary products are available, including Carrysyn (73% acemannan, Carrington Laboratories).

Note: “Aloe juice” is not a pharmacopoeial term; it describes varied products sold commercially that contain diluted gel. These products may contain only small amounts of the active gel constituents and may incorporate added thickeners such as pectins and starch. These juice products are usually anthraquinone free.

Overview

Aloe vera gel, the clear, colorless mucilage from the central parenchyma of the leaf, is primarily known for promoting topical healing of burns, wounds, incisions, frostbite, ulcers, and related inflammatory problems. The gel is also widely incorporated into natural cosmetic and skin care products. Modern research interest has focused on identifying the active polysaccharide components of the gel and investigating their potential immunomodulatory properties as biological response modifiers. ¹ Internal applications are also of interest, such as for inflammatory bowel disease, and a positive trial in active ulcerative colitis patients is available. ^2,3

Proprietary aloe extracts based on hydrogel are available in professional and consumer markets. These are either stabilized by means of rapid pasteurization or freeze-dried as a soluble powder; both forms contain standardized amounts of the main active polysaccharide (acemannan). Professional products are available in a variety of applications for wound care, burn treatment, diabetic care, general first-aid dressings, and management of radiation and chemotherapy adverse effects. Limited clinical evidence supports these applications, although promotion of wound healing appears to be better supported by the available data than burn treatment.

In the United States, popular dietary supplement products combining freeze-dried acemannan with other ingredients are “network marketed” as “glyconutritionals.” These are promoted as nonspecific immunostimulants, often with wide-ranging therapeutic claims, including for the treatment of cancer and human immunodeficiency virus (HIV). Evidence for such claims is not substantial at this time and is partly extrapolated from non–peer-reviewed data supplied to the U.S. Patent Office based on in vitro or uncontrolled animal studies using parenteral routes of administration. ⁴

Aloe gel and its derivative products are not officially approved for internal medical use, although some proprietary topical hydrogel products have been approved by the U.S. Food and Drug Administration (FDA). The botanical literature emphasizes the anthraquinone herb rather than the gel. The World Health Organization (WHO) monograph series includes both remedies separately, but this is the exception. ⁵ Comprehensive literature reviews relating to recent immunological research on the gel are unavailable, although there are surveys of the data up to the late 1990s. ⁶ The available clinical trial evidence on aloe gel extracts was systematically reviewed in 1999 by Vogler and Ernst. ⁷

Historical/Ethnomedicine Precedent

Aloe leaf has been in recorded use for centuries, with documentation by Dioscorides, Pliny, and Galen, as well as in traditional Ayurvedic and Chinese medicine. The gel was allegedly used by Cleopatra for cosmetic skin enhancement, but Europeans became more familiar with uses of the gel from African tribes and subsequently planted specimens of Aloe spp. throughout their colonies, which became rapidly naturalized in subtropical zones. Aloe spread in the United States, especially Florida, where it was used by the Seminole people for healing burns and stings. The gel remains in widespread popular folk use; currently it is often kept as a houseplant, with a leaf cut to obtain fresh gel as treatment for sunburn, thermal burns, insect bite, and other first-aid needs.

Known or Potential Therapeutic Uses

• External/Topical:   Treatment of abscesses, burns, surgical incisions, wounds, ulcers (oral, leg), dermatitis, and psoriasis.

• Internal:   Antiviral (HIV/herpes simplex virus [HSV]), dysglycemia, inflammatory bowel disease, immunomodulation, peptic ulcer preventive, ulcerative colitis.

Key Constituents

The gel is more than 97% water by weight. The solid matter is approximately 65% carbohydrate, predominantly in the form of a long-chained, polydispersed, beta-(1,4)-acetylated mannan (acemannan). ^8,9Sterols, organic acids (especially oxalate), and various amino acids make up the remainder. Novel dihydrocoumarins have recently been described. ¹⁰ Naturally occurring enzymes are present in the fresh gel, and pasteurization is necessary to stabilize the gel to prevent enzymatic degradation.

Therapeutic Dosing Range

• Fresh Juice Concentrate:   25 mL up to four times daily.

• Standardized Extracts:   500 to 800 mg-equivalent acemannan daily.

Strategic Considerations

The WHO monograph on aloe gel does not ascribe any interactions involving the herb. ⁵ The anthraquinone-containing Aloe latex is not considered here, but the reader should refer to the Cascara monograph for some interactions typical of the anthraquinone-containing botanicals.

In the setting of externally applied medications, aloe interactions are limited to various combination preparations, using the hydrogel as a vehicle with related materials (e.g., algal gums, synthetic hydrogels) or as an ingredient of creams and ointments in combination with anti-inflammatory agents.

The topical effects of the gel are thought to be the result of several mechanisms. ^11,12Anti-inflammatory effects have been established experimentally in the treatment of adjuvant arthritis, paw edema, frostbite, and diabetic ulceration in animal models, ^11,13-15as well as in human mucosal CaCO2cells in vitro. ² The mechanisms involved are probably multifactorial and include inhibition of prostaglandin synthesis, antioxidant quenching of free radicals, and bradykinin inhibition, as well as promotion of connective tissue development, inhibition of collagenase (and metalloproteinase) activity, and stimulation of cell-mediated immunity. ^14,16-21Research at Carrington Laboratories has established that the pectins present in aloe vera gel are efficient stabilizers of peptides, which constitute a large class of tissue growth factors and immunomodulators, and may explain some of the observed activities of the plant gel (by increasing the half-life of peptide cytokines and growth factors). ²²

Since the 1930s, when aloe gel was first investigated for the topical treatment of “roentgen dermatitis,” there have been persistent attempts to establish its efficacy for topical treatment of ultraviolet B (UVB) and x-ray radiation burns, although with consistently mixed results. ²³ Recent animal tests have been positive, ²⁴ but the only randomized controlled clinical trial available failed to show any benefit of the gel against placebo on chest wall and breast irradiation in 108 breast cancer patients. ²⁵ Another oncological use is in chemotherapy-induced mucositis, although only oral (aphthous stomatitis) treatment has received substantial evidential support, and a proprietary aloe hydrogel product has been FDA approved for aphthous ulcer treatment. ²⁶

Internal use of the gel has been examined in relation to potential antiviral and immunostimulating effects for HIV patients, as well as for glycemic regulation in diabetic patients. Neither of these indications is well supported, nor are they in current general use clinically by practitioners of natural or botanical medicine. Suggestions of potential synergistic interactions with antivirals and antidiabetic agents are discussed later (see Theoretical, Speculative, and Preliminary Interactions Research). A recent United Kingdom trial established positive support for the use of aloe gel internally for ulcerative colitis. ^2,3Wide variation in commercial and proprietary processing methods, leading to products with differing activities, may underlie much of the conflicting results in clinical trials in various applications of “stabilized” Aloe vera products. The only relatively uniform activity would be from fresh gel obtained from freshly harvested aloe leaves, which are, however, logistically difficult to use in studies.

One recent, small, crossover-design human trial found a significant effect of aloe on the pharmacokinetics of vitamin C and vitamin E absorption. When single doses of the vitamins were consumed orally with 2 oz of aloe gel or whole-leaf extract, absorption of both the water-soluble and fat-soluble vitamins were significantly slowed, leading to longer half-life in plasma. The authors suggested that aloe could be used to complement the absorption of these nutrients. ²⁷

Data on the effects of aloe gel on drug-metabolizing enzymes and transporters are not available.

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