Review on the Therapeutic Effects of Aloe spp.

Aloe species’ (Xanthorrhoeaceae) leaf pulp has been used in Iranian traditional medicine (ITM) dating back to the eighth century CE. The genus has 446 species, with aloe vera (Aloe vera, Xanthorrhoeaceae) the most commonly used and studied. Aloe spp. grow wild in tropical regions of the world but only a few species have been commercially cultivated. Aloe spp. are grown for health foods, medicines, cosmetics, and decoration. Products include inner leaf gel and a bitter yellow latex (also called aloe juice) from peripheral bundle sheath cells just under the leaf surface.* Aloe leaf pulp is about 98.5% water but also contains at least 75 other compounds. The majority of these are mannose-based polysaccharides, and to a lesser extent, anthraquinones/anthrones, carbohydrates, chromones, phenolics, enzymes, and water- and fat-soluble vitamins, minerals, proteins, and organic acids. Aloe-emodin, an anthraquinone in Aloe latex, has been well studied. Aloin, aloesin, aloenin, and aloeresin are also unique Aloe compounds. The authors explored ITM texts for references to Aloe spp. and compared uses found there with modern pharmacological studies. They do not describe their literature search.

In the 17 ITM texts reviewed, Aloe spp. are described as hot and dry in temperament; and in most, as strong laxatives (for bile, yellow bile, and phlegm), and drying, fattening, soporific, warming, relaxing, resolving, cleansing, and bitter agents. ITM uses are categorized by the organs or physical systems involved. These include liver- and kidney-protective effects, supported for both aloe vera and candelabra aloe (A. arborescens) by pharmacological studies, with most attention paid to the species’ anti-inflammatory, antioxidative, antifibrotic, and lipid-modifying effects. A review of candelabra aloe reported it most active in treating liver diseases, especially cancers. Aloe‘s uses for gastrointestinal (GI) problems are among the most reported in the traditional literature, with preparations prescribed for many stomach ailments and loss of appetite. Powdered Aloe leaf pulp also was mentioned for GI problems. Hemorrhoids, constipation, helminthic infestations, flatulence, and anal fissures were treated with Aloespp. However, Aloe treatment was contraindicated in some cases of hemorrhoids or anal fissures and could cause hemorrhage by relaxing the rectal veins. ITM often used Aloe spp. with other herbs for intestinal diseases to prevent excess dryness. Preclinical studies support the use of aloe vera and its compounds for colitis, intestinal polyps, irritable bowel syndrome, and stomach ulcers, among others. An aqueous extract of bitter aloe (A. ferox) was a potent laxative in vivo.

In the upper respiratory tract, ITM used Aloe spp. especially for asthma, via inhalation of burned leaf smoke. They were also used for mouth, nose, tongue, and gum diseases. Polysaccharides and glycoprotein fractions of Aloe are reported to improve peripheral phagocytosis, supporting the traditional use for asthma. Bioaron C® (Phytopharm Klęka S.A.; Nowe Miasto nad Wartą, Poland), an herbal medicine made with an aqueous extract of candelabra aloe, was effective against influenzas A and B and other viruses in vitro. This product also showed significant antimicrobial and antifungal activity in vitro in another study. It is the only commercial product among the many studies of Aloe spp. these authors cite. In mice, an aloe vera gel extract showed promise in modulating tobacco (Nicotiana tabacum, Solanaceae) smoking-induced changes in pulmonary tissue. Extracts of aloe vera and bitter aloe are reported to act against herpes simplex viruses 1 and/or 2 in vitro, supporting ITM use of Aloe spp. for many genitourinary diseases, particularly genital ulcers and lesions.

Most ITM books investigated report Aloe‘s uses in cleansing the brain of waste humors (yellow bile and phlegm) and warming the brain. It was used for depression, schizophrenia, obsession, and headache; to strengthen mental acuity and for insomnia. Pharmacological studies of Aloe spp. and their extracts report hypnotic, peripheral analgesic, and neuroprotective effects. Improvements in memory, learning, cognitive function, and a potential anti-Parkinson’s disease effect also have been reported. A candelabra aloe extract was “a potent agent” in vitro in an Alzheimer’s disease model. Anticonvulsant activity, mitochondrial protection, and a protective effect against cerebral ischemia have all been reported in vitro or in vivo.

Preparations of Aloe spp. are used in ITM for skin problems from infections to allergies, wounds, malignant lesions, ulcers, bruises, and parasitic skin infestations. Aloe is a moisturizing agent, despite its dry nature, slowing evaporation of the skin’s moisture from sun and wind exposure. Skin protective activity seen in vitro and in vivo includes benefits in healing burn wounds (perhaps the best-known folk use for Aloe species globally); anti-infective and anti-allergic effects; and a significant increase in collagen. Raw mucilaginous gel of A. littoralis was reported to be a potential wound-healing and anti-inflammatory agent. Eyes and hair benefited from ITM applications of Aloespp. and extracts, borne out at least in part by preclinical studies. Socotrine aloe (A. perryi) and aloe vera were used in other in vitro and in vivo studies. ITM used Aloe spp. for arthralgia, gout, and other problems of the joints, muscles, and bones; no modern studies have explored these uses. Oddly, 35 clinical studies of Aloe spp. in conditions affecting several organ systems are relegated to a table and not discussed.

While Aloe spp. are generally considered safe, ITM scientists reported that they could harm the liver if overused, a toxicity reflected in a few modern case reports. These effects could be due to preparations and/or dosages used. Some species have toxic compounds, e.g., Yemen tree aloe (A. sabaea). Additional studies are certainly warranted to explore efficacy and dosage for a range of relevant conditions.

* However, beverages containing “aloe juice” contain only the liquefied gel, sometimes mixed with water or some citrus (Citrus spp., Rutaceae) juice, with the latex removed. Apparent differences in the chemical composition of aloe gel and latex are barely touched upon in this review.

Resource:

Akaberi M, Sobhani Z, Javadi B, Sahebkar A, Emami SA. Therapeutic effects of Aloe spp. in traditional and modern medicine: a review. Biomed Pharmacother. December 2016;84:759-772.