The leaf is composed of three distinct layers: an outer layer of tough tissue; a corrugated lining just beneath the outer layer; and the major portion of the leaf, the inner layer consisting of parenchymal cells containing large vacuoles of a semisolid, gelatinous transparent gel. The bitter latex of the corrugated layer protects the plants from predators. Should an animal bite the leaf, the sap causes irritation. The dried latex (juice) derived from the corrugated layer is the source of the laxative properties of Aloe. The parenchymal tissue, or gel, is the portion of the Aloe used in other applications.

Aloe Vera contains numerous compounds possessing biological activity. The most important appear to be anthraquinones, polysaccharides (including glycoprotein and mucopolysaccharides), and prostaglandins.

Chemical Composition: Aloin, barbaloin, isobarbaloin, anthranol, aletic acid, anthracene, ester of cinnamic acid, Aloe-emodin, emodin, chrysophanoic acid, etheraeal oil, resistannol. In 1851, it was discovered that the cathartic action of Aloe was due to aloin, a lemon-yellow powder formed from drying of the bitter latex. From this material seVeral compounds known as Anthraquinones have been isolated, the major anthraquinones

being barbaloin. Barbaloin and aloin are often referred to synonymously. Although Aloe contains other Anthraquinone derivatives including Aloe-emodin, barbaloin is considered the most potent cathartic. As a whole, the Anthraquinone compounds are water-soluble glycosides easily separated from the water-insoluble resinous material.

Chemical composition: Cellulose, glucose, mannose, L-rhamnose, aldopentose. Recent research on Aloe Vera has focused on the glycoprotein, mucopolysaccharides, and polysaccharide constituents. Aloe contains the polysaccharides galactose, xylose, arabinose, and acetylated mannose. This latter polysaccharide, which is similar to guar and locust bean gums, has received considerable clinical research attention as an antiviral and immunopotentiating agent, especially in the treatment of AIDS. Acemannan, another water-soluble polysaccharide constituent, is discussed below.

Recently, seVeral prostaglandin (pros’–ta-GLAN-dins) and fatty acid compounds have been discovered in Aloe Vera extracts. Prostaglandins have a wide variety of functions. They modify responses to hormones, contribute to the inflammatory response, prevent stomach ulcers, dilate airways to the lungs, regulate body temperature, and influence formation of blood clots, to name just a few effects. They also alter smooth muscle contraction, glandular respiration, nerve impulse transmission, lipid metabolism, and immune responses. They also have roles in inflammation, in promoting fever, and in intensifying pain. The conversion of essential fatty acids to prostaglandins in a plant such as Aloe Vera is quite rare. The major unsaturated fatty acid in the plant is gamma-linoleic acid, which can be converted to prostaglandins of the 1 series. The 1-series prostaglandins are known to exert more favorable effects on inflammation, allergy, platelet aggregation, and wound healing. The presence of gamma-linoleic acid and / or prostaglandins in a stable medium, along with inhibitors of thromboxane syntheses, may be another of the important chemical characteristics of Aloe responsible for its wound healing effects.

Other biologically active compounds found in Aloe Vera include a serine carboxypeptidase (enzyme in pancreatic juice which breaks the peptide bond that attaches the terminal amino acid to the carboxyl acid end of the peptide, salicylates, minerals, vitamins, sterols, and amino acids.

Enzymes: Oxidase (adds oxygen), amylase (digestive enzyme), catalase (converts free radicals to less reactive substances), lipase (enzymes that split triglycerides and phospholipids/found in the stomach and pancreas), alkaline phosphatase (the enzyme that converts glucose 6-phosphate into glucose).

Amino Acids: Lysine, threonine, valine, methionine, leucine, isoleucine, phenylalanine

Vitamins: Vitamins B1, B2, B6, C, and E, folic acid, choline, beta-carotene

Minerals: Calcium, sodium, manganese, magnesium, zinc, copper, chromium

Miscellaneous: Cholesterol, triglycerides, steroids, uric acid, lignins, betasitosterol, gibberellin, salicylic acid.

Aloe has demonstrated activity against many common bacteria and fungi in seVeral studies. The antimicrobial effects of Aloe Vera compare quite favorably to those of silver sulfadiazine, a potent antiseptic used in the treatment of extensive burns. A 60 percent Aloe Vera extract was found to be bactericidal against Pseudomonas aeruginosa, Klebsiella pneumoniae, Serratia marcescens, Citrobacter species, Enterobacter cloacae, Streptococcus pyogenes, and Streptococus agalactiae. Seventy-percent concentrations of Aloe were bactericidal for Staphylococcus aureus, 80 percent for Escherichia coli, and 90 percent for Streptococcus faecalis and Candida albicans. Organisms inhibited in other studies include Mycobacterium tuberculosis, Trichophyton species, and Bacillus subtilis.

Acemannan (acetylated mannose) in injectable form has been approved for veterinary use in fibrosarcomas and feline leukemia. Its action in feline leukemia is quite impressive. Feline leukemia, like AIDS, is caused by a retrovirus (feline leukemia virus) the virus is so lethal that once cats develop clinical symptoms they are usually euthanized. Typically more than 70 percent of cats die within 8 weeks of the onset of clinical signs. In a study of 44 cats with clinically confirmed feline leukemia, acemannan was injected weekly for 6 weeks and reexamined 6 weeks after termination of treatment. At the end of the 12 week study, 71 percent of the cats were alive and in good health.

Acemannan has demonstrated significant antiviral activity against seVeral viruses, including human immunodeficiency virus type 1 (HIV-I), influenza virus, and measles virus. Although acemannan has demonstrated some direct antiviral activity against HIV-1 by inhibiting glycosylation of viral glycoproteins, its main promise in treating AIDS and HIV may be to enhance the action of azidothymidine (AZT), the antiviral drug used to combat AIDS. In vitro studies have shown that acemannan, combined with suboptimal noncytotoxic concentrations of AZT or acyclovir, acts synergistaically to inhibit the replication of HIV and herpes simplex type 1. On the basis of these studies, as well as preliminary human studies, researchers believe that the use of acemannan may reduce the amount of AZT required by as much as 90 percent. This is quite significant. In addition to AZT being extremely expensive, AZT’s use is often associated with severe side effects, including anemia and depression of white blood cell production.

Acemannan is a potent immune system stimulant. Prominent among the effects noted are the enhancement of macrophage activity as well as the release of immune system potentiators. Acemannan also enhances the function of T cells and interferon production, although these actions may also be due to enhanced macrophage function. Clinical animal research has shown promising results in sarcomas and spontaneous tumors.

Aloe Vera exerts a number of anti-inflammatory actions (including blocking of the generation of inflammatory mediators such as thromboxanes and bradykinin), thereby reducing swelling. SeVeral compounds in Aloe are responsible for these actions. The most important are glycoprotein, which inhibit and actually break down bradykinin, a major mediator of pain and inflammation; various anthraquinones; and salicylates. These anti-inflammatory substances may be of significance in both topical and oral applications.

Aloe Vera contains a number of compounds necessary for wound healing, including vitamin C, vitamin E, and zinc. Unlike many other anti-inflammatory substances, Aloe Vera has been shown to stimulate fibroblast and connective tissue formation, thereby promoting wound repair. In addition, Aloe appears to stimulate the epidermal growth and repair process, presumably due to its polysaccharides.

The results of experimental studies in rats and mice suggest that Aloe Vera may be effective, both topically and internally, in the treatment of diabetic leg ulcers. In addition to exerting positive effects on wound healing. Aloe Vera also exhibits a blood sugar-lowering effect in both normal and chemical induced diabetic mice.

Although physicians have prescribed the whole Aloe leaf as a cathartic for more than 2,000 years, it was not until 1851 that the active principle, aloin, was discovered. In small doses, aloin acts as a tonic to the digestive system, giving tone to the intestinal muscle. At higher dosages, it becomes a strong purgative. Its most obvious actions are on the large intestine, where it increases colonic secretions and peristaltic contractions. In combination with strychnine and belladonna, aloin became one of the most popular laxatives for chronic constipation for many years.

The use of Aloe Vera gel internally to treat peptic ulcers was studied in 1963. Twelve patients with X-ray confirmed duodenal ulcers were given a tablespoon of an emulsion of Aloe Vera gel in mineral oil once daily. At the end of 1 year, all patients demonstrated complete recovery and no recurrence. On the basis of experimental evidence, the following factors were though to be responsible for the effectiveness: