Introduction & History

Figure 1. Components of Aloe.
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Aloe vera belongs to the Liliaceal family and is one of the few Aloe species important for its medicinal use (Vogler & Ernst, 1999).  It is postulated that aloe originated from South and East Africa, and then was brought over to areas such as North Africa, China and Spain (Haller, 1990).  Aloe has a history of use since the ancient Egyptians, Biblical times and Mediterranean civilizations (Grindlay & Reynolds, 1986).  The two parts of the aloe plant that are used medicinally are the aloe latex and the aloe gel.  The aloe latex is a bitter yellow juice collected from the pericyclic cells beneath the plant skin.  The aloe gel is colourless and obtained from the mucilaginous cells of the inner leaf (Klein & Penneys, 1988).  Traditionally, the entire aloe vera leaf could be used, or the aloe latex dried and the gel collected to be used separately (Grindlay & Reynolds, 1986).  Aloe was used in folk medicine as a laxative and for dermatological issues such as burns and wounds.  It was not until the 19th century was evidence found to support aloe use through the discovery of aloin.  Aloin is an active ingredient in aloe latex that can relieve constipation by increasing activity in the intestine and bowel.  By the 20th century, it became very popular in the United States and there were numerous formulations of aloe laxatives taken in the form of pills.  At this time, the use of aloe was not yet regulated.  Later it was discovered that ingestion of aloe induced painful griping, and so the use of aloe as a laxative has decreased (Haller, 1990). On the countrary, more recently, the use of aloe gel for dermatological wounds has increased in popularity (Grindlay & Reynolds, 1986).

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Active Components & Preparation


Figure 2. Chemical structure of acemannan.
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The two main components of the aloe plant used is the aloe latex and aloe gel.  There are many active constituents in aloe, including carboxypeptidase that inactivates bradykinin and reduces pain, salicylate that is an anti-inflammatory, and magnesium lactate that has anti-itching properties (Reynolds & Dweck, 1999).  The more widely researched components are anthraquinones and acemannan.  Anthraquinones are active phenolic compounds found in aloe latex with strong laxative properties, an example being aloin (Vogler & Ernst, 1999).  Acemannan is a long chain β-(1,4)-linked galactomananan polymer found in the aloe gel (Zhang & Tizard, 1996).  It has been found to enhance phagocytic activity in macrophages, thus having an effect on the immune system (Yates et al., 1992).  

Aloe vera is administered as ointments, medicated creams, lotions, capsules or even as a tonic depending on its desired effects.  Aloe gel preparation must now be FDA approved.  Aloe is harvested manually, cleaned by hand or with a mild chlorine solution and filleted to remove the central gel.  The gel is then filtered and put through a stabilization process to denature browning enzymes and preservatives may be added.  After this process, the gel is often modified in different ways to serve different purposes (Grindlay & Reynolds, 1986).

Source: (Vogler & Ernst, 1999) Box 1. Constituents of aloe.

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Current Research

Currently the most popular use for aloe is topically for dermatological conditions, but some do still ingest aloe to relieve constipation.  There has been a lot of current research on the efficacy of aloe and its potential side effects.  Aloe gel seems to be harmless, but ingestion of aloe is not recommended (Haller, 1990).  Two current studies by Choonhakarn, Busaracome, Sripanidkulchai and Sarakarn (2009) and Eshghi and collegues (2010) got positive results with the use of aloe vera gel topically for skin conditions. 
Choonhakarn et al. (2009) studied the efficacy of aloe vera gel compared to 0.1% triamcinolone acetonide (TA) on cases of mild to moderate plaque psoriasis (an autoimmune skin cell disease).  It was a randomized, double-blind, control trial with 75 adult patients with this condition with two conditions; aloe or 0.1% TA for 8 weeks.  Efficacy was measured using a Psoriasis Area Severity Index (PASI) and Dermatology Life Quality Index (DLQI) at week 0 and week 8.  Results showed that the aloe group had significantly better results with 1.1 points higher than the 0.1% TA group on the PASI scale.  There was not a significant difference between the DLQI scores.  There were 6 reported cases of itching but it was reversed with antihistamines, thus no serious adverse effects were elicited.  Choonhakarn et al. concluded that aloe is more clinically effective than 0.1% TA.
The importance of this study is that psoriasis is a chronic disease and topical corticosteroids is often administered for it, but it has many adverse effects. The authors sought a more natural remedy.  However, there are several points to address in this study.  Firstly, the authors made reference to other studies with a placebo control group, but did not include one themselves.  Therefore, the effect strength is unclear.  Also, there was not a clear description of how the aloe cream was prepared.  The participants were well controlled with no significant differences in baseline measures.  An important point is the authors suggested from the results that the 0.1% TA and aloe equally improved the quality of life for the patients.  However, the results showed that the DLQI score decreased about 6 points for both groups between week 0 and week 8.  This suggests that perhaps aloe as treatment by itself is perhaps not as promising as suggested, as it significantly decreased quality of life.  Lastly, only measures were taken at baseline and week 8, so long term effects were not studied.
The Eshghi et al. (2010) studied the effects of aloe on posthemorrhoidectomy pain, postdefection pain, and wound healing.  It was a randomized, double-blind controlled trial with two conditions - placebo or aloe applied to 3 times daily for 4 weeks to the surgical area.  There were 49 postoperative patients recruited and assessment was done in 12, 24 and 48 hours and 2, 4 weeks post surgery.  The results are summarized in the table below.  Pain was measured using a Visual Analog Scale (VAS), an expert surgeon assessed wound healing, and narcotics consumption was documented.

Measure
Significant Difference?
Overall Postoperative Pain
Yes; Aloe group had less pain at 12, 24 and 48 hours and at 2 weeks.
Defecation Pain
Yes; Aloe group had less pain at 24 and 48 hours.
No; there was no significant difference at 2 and 4 weeks.
Wound Healing
Yes; Aloe group had faster wound healing at week 2.
No; there was no significant difference at week 4.
Narcotics
Yes; Aloe group took less narcotics at 12 hours and 2 weeks.
Table 1: Summarized results from Eshghi et al. (2010) study on postoperative pain, defecation pain, wound healing and narcotics consumption. 

No adverse effects were observed.  The authors concluded that aloe was an effective treatment in reducing posthemorrhoidectomy pain and promoting wound healing.
Again, there are some strengths and weaknesses to this study.  There was not a description of the aloe vera powder used, but a list of all the ingredients that went into the aloe cream was included.  Measurement of pain using the VAS may be somewhat subjective, but the authors took care in standardizing the VAS scores, and a more objective measure of narcotics consumption was included.  More than half the participants in this study were females, but they were equally distributed amongst the conditions.  However, this may have had an effect on the results.

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Adverse Effects & Drug Interactions

5:48 PM by Winnie Ly 3 comments

In terms of adverse effects, aloe gel is used in research experiments more often, and is generally regarded as safe with minimal side effects.  In some rare cases, aloe has been found to cause allergic reactions when applied topically (Klein & Penneys, 1988).  On the other hand, caution must be taken when administering aloe orally.  Aloe latex as a laxative can cause diarrhea, abdominal pain and heart disturbances (Haller, 1990).  It can be fatal if taken in large doses over several days. Also, as a laxative it may decrease the efficacy of other oral drugs.  Aloe may lower blood sugar, so combined effects with other medications that also lower blood sugar such as antidiabetic drugs may be harmful.  Aloe may also decrease blood clotting and increase the chances of bleeding, so it is advised to be cautious if blood thinners are being taken or before a surgical procedure.  In regards to other herbs, as aloe is a laxative and when used with other herbs such as black root, jalap root and rhubarb root that also have laxative properties may be harmful.  Also, herbs such as horsetail, liquorice and figwort that lower blood sugar levels in combination with aloe may be unsafe (MedlinePlus, 2010).

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References


Choonhakarn, C., Busaracome, P., Sripanidkulchai, B., & Sarakarn, P. (2010). A prospective, randomized
clinical trial comparing topical aloe vera with 0.1% triamcinolone acetonide in mild to moderate plaque psoriasis. Journal of the European Academy of Dermatology and Venereology, 24(2), 168-172. doi: 10.1111/j.1468-3083.2009.03377.x

Eshghi, F., Hosseinimehr, S., Rahmani, N., Khademloo, M., Norozi, M., & Hojati, O. Effects of Aloe
vera Cream on Posthemorrhoidectomy Pain and Wound Healing: Results of a Randomized, Blind, Placebo-Control Study. The Journal of Alternative and Complementary Medicine, 16(6), 647-650. doi:10.1089/acm.2009.0428.

Grindlay, D., & Reynolds, T. (1986). The Aloe vera phenomenon: A review of the properties and modern
uses of the leaf parenchyma gel. Journal of Ethnopharmacology, 16(2-3),117-151. Retrieved from http://journals2.scholarsportal.info.myaccess.library.utoronto.ca/details-sfx.xqy?uri=/03788741/v16i2-3/117_tavparuotlpg.xml.

Haller, J. (1990). A drug for all seasons. Medical and pharmacological history of aloe. Bull N Y Acad
Med, 66(6), 647–659. Retrieved from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1809794/.

Klein, A., & Penneys, N. (1988). Aloe vera. Journal of the American Academy of Dermatology, 18(4),
714-720. Retrieved from http://www.aloe-vera.ma/presse/Therapy.pdf.

Reynolds, T., & Dweck, A. (1999). Aloe vera leaf gel: a review update. Journal of Ethnopharmacology,
68(1-3), 3-37. doi:10.1016/S0378-8741(99)00085-9

Vogler, B., & Ernst, E. (1999). Aloe vera: a systematic review of its clinical effectiveness. Br J Gen
Pract, 49(447), 823–828. Retrieved from http://www.ncbi.nlm.nih.gov.myaccess.library.utoronto.ca/pmc/articles/PMC1313538/?tool=pubmed.

Yates, K., Rosenberga, J., Harrisb, C., Bronstadb, D., King, G., Biehled, G., Walkerd, B., Forde, C.,
Halla, J., & Tizard, I. (1992). Pilot study of the effect of acemannan in cats infected with feline immunodeficiency virus. Veterinary Immunology and Immunopathology, 35(1-2), 177-189. doi:10.1016/0165-2427(92)90130

Zhang, L., & Tizard, I. (1996). Activation of a mouse macrophage cell line by acemannan: The major
carbohydrate fraction from Aloe vera gel. Immunopharmacology, 35(2), 119-128. doi:10.1016/S0162-3109(96)00135-X

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