Aloe vera is plant that contains a lot of substances including minerals, vitamins, amino acids, organic acids, phospholipids, enzymes, lignins, saponins but the most important components are two: glucomannans, that are complex sugars and especially the acemannans, and the anthraquinones.
The acemannan is a polymer constituted by 3-O-acetyl-β-D-mannopyranose (acetyl-mannose) unities united by β- 1→4 glycosidic bonds. It is a hydrophilic molecule and it has 49 acceptor groups and 16 hydrogen bond donors. Its biodisponibility is 1 according to principle of Lipinski.
We can found acemannan in the internal transparent gel of Aloe vera plant and has got immunomodulatory properties. It was demonstrated that acemannan stimulates the production of interferon, tumor necrosis factor and different interleukins by the macrophages and this prevents the formation of viral infections.
With regard to this, studies made on mice demonstrate that oral administration of Aloe vera gel has an immunomodulatory activity.
Chungbuk National University, Korea, In vivo evidence of the immunomodulatory activity of orally administered Aloe vera gel, 2010 Mar;33(3):451-6
Other studies demonstrate that acemannan administration makes possible an extension of animal life by inducing an increase of tumor necrosis and the fact that acemannan molecule is absorbed by the lymphatic system of animals. Nowadays acemannan is used to treat fibrosarcoma in cats and dogs and its use in the therapy of leukemia in animals has given positive results.
There were also made interesting studies concerning dentistry: with regard to that, acemannan stimulates dental pulp cell proliferation, differentiation, mineralization, and dentin formation;it also has pulpal bio compatibility and promotes soft tissue organization.
Bangkok, Thailand, Acemannan, an extracted product from Aloe vera, stimulates dental pulp cell proliferation, differentiation, mineralization, and dentin formation, 2010 Jun;16(6):1997-2006
In vitro experiments have shown that acemannan inhibits the replication of HIV virus, but in vivo experiments did not prove these results.
Anthraquinones are in the the green coriacea part of Aloe plant and they have a high laxative property.
Anthraquinones are a group of chemicals based upon the tricyclic anthracene nucleus. These rings can be substituted with hydroxyl, methyl or carboxyl groups to create monoanthrones, such as aloe-emodin, rhein, and frangula. Monoanthrones are coupled together to form dianthrones and can be conjugated with sugars to yield glycosides; and in plants anthraquinones are more likely to be present as glycosides.
The searches demonstrate that they arrive to large intestine where are transformed in aglycone ( anthrone), that are really active principle. However to see laxative action it’s necessary that they are swallowed like glycosides ( so preparations with aglycones are active only in high doses), that there is bile in intestine and an active intestinal flora.
The action mechanism is this:
- a percentage of swallowed glycosides is polymerized at gastric level, so it is inactivated;
- remaining glycosides travel undisturbed and not digested to large intestine where are transformed by bacterial micro flora in free aglycones ( anthrones);
- anthrones work in two ways: 1. fluid accumulation in intestinal lumen, since anthrones operate at topic level through chloride release stimulation by intestinal wall, that implies for osmosis phenomenon, a flow of water and sodium, that accumulate in intestinal lumen and increase stool fluidity and modify intestinal motility; 2. modification of intestinal motility, since anthrones increase intestinal muscle cell irritability, thus increasing muscle contractions and peristalsis;
- a large part of anthrones are eliminated with stool, but a small number is reabsorbed in caecum intestine and at hepatic level is glucose conjugated. 3-6% of conjugated are eliminated through kidneys, while remaining molecules are excreted to colon where are transformed in anthrones again. It’s possible that a share of anthrones pass to hematic circle and reach target cells, where anthrones act on protein biosynthesis bringing prostaglandins release that increase smooth intestinal muscle cells irritability.
The final effects of anthraquinones ingestion are: contractions and peristalsis increase, transit time reduction and stool volume increase.
Anthraquinones typically induce defecation 6–8 h after oral dosing.
Cures containing anthraquinones present many problems, as small doses act particularly on intestinal motility, while higher doses (chronic use) cause different problems:
- act on electrolytic secretions, with excessive electrolytes loss; this causes an aldosterone hyperproduction that reduces effect of laxative;
- almost complete emptying of the colon and in this way a natural lack of stimulus in next day (or also in the following two days) bring patients to use again laxative and so begin a vicious circle;
- tone loss in stimulated tissue;
- allergic reactions in some cases.
For these reasons, one of the phytotherapy rules provides that laxatives based on anthraquinones must be used only for short therapies.
Besides, not all constipations are caused by the atony of the bowel muscles: bowel problems can also arise owing to undue tension of the bowel muscles, for example irritable colon syndromes, or to dyskinesia.
Also when a person suffers from stress or anxiety, the nervousness may be spread to the colon or ‘mucous colitis’ results to loose motions or constipations. In all these cases anthraquinones are contraindicated.
There has been some concern that anthraquinones may predispose to colon cancer, but epidemiologic and animal studies do not support this concern.
Moreover, also anthraquinones, like acemannans, seem to have anti-tumor properties.
Department of Experimental Pharmacology, Naple, Italy, Anti-proliferative effect of rhein, an anthraquinone isolated from Cassia species, on Caco-2 human adenocarcinoma cells, 2010 Jul;14(7):2006-14
This study demonstrates the anti-proliferative effect of rhein, an anthraquinone isolated from Cassia species, on Caco-2 human adenocarcinoma cells.
Another study shows the anti-proliferative and anti-metastatic activity on murine B16-F10 melanoma cells of anthraquinones danthron and quinizarin.
Department of Biology, University Tor Vergata, Rome, Italy, Anthraquinones Danthron and Quinizarin Exert Antiproliferative and Antimetastatic Activity on Murine B16-F10 Melanoma Cells, 2009
Aloe vera has also some contraindications. For example a research about pregnant women shows as herbal products, including Aloe vera, in pregnancy is potentially harmful in some cases, and it is not always appropriate, also because the decision to use these products was based on personal judgments, without a medical prescription, and on the conviction that they are safer than other medical treatments. Among the users was found rash and itching as side-effects after local application of Aloe vera.
University of Verona, Italy, Use of herbal products among 392 Italian pregnant women: focus on pregnancy outcome, 2010 Nov;19(11):1151-8
Moreover, Aloe vera is considered as an agent that causes hepatotoxicity in some cases that are reported in the following study.
Department of Internal Medicine, Chuncheon, Korea, Aloe-induced toxic hepatitis, 2010 Mar;25(3):492-5
Aloe vera contains aloin, based on anthraquinones, that has an laxative and irritative effect on colon and it is considered abortive in pregnancy; for this reason aloe vera compounds prepared in a craft way, are not recommended.