Much of the information about the curative properties of aloe vera is anecdotal and so far, few studies have been reported in the literature. This article will feature the chemical and the remedial qualities of aloe vera and the recent research studies about its potential uses in medicine and cosmetology.
History
In Mesopotamia around 1750 B.C.E., aloe vera was used for medical purposes. Egyptian books (550 B.C.E.) reported skin infections treated with aloe vera, and Discordes, a Greek doctor, wrote in his book (De Materia Medica, 74 C.E.) that aloe vera enhanced the healing of wounds, cured skin infections, treated hair loss, and hemorrhoids, Table 1. Many ailments have been reported to be alleviated by aloe vera such as peptic ulcers, colds, tuberculosis, cystic acne, amputation stump ulcers, gonorrhea, asthma, lacerations, headaches, and dysentery[1]. As well, often have been claims that aloe vera gel has anti-inflammatory, anti-fungal, anti-bacterial, anti-viral properties, and anti-oxidant effects. These therapeutic benefits derive from the chemical ingredients of aloe vera, Table 2 [2,3]. Nowadays, aloe vera is commercially relevant as a result of its remedial attributes, with a global market worth of 1.6 billion USD[3].
Table 1. History of aloe vera curative properties[1].
1750 B.C.E. In Mesopotamian clay tablets, aloe vera is described in curative treatments.
550 B.C.E. Egyptian books depicted skin infections treated with aloe vera.
74 C.E. Greek doctors reported aloe vera curative effect in hair loss, hemorrhoids, and wound healings.
700 C.E. In the Orient, aloe vera was employed to cure sinusitis and eczema.
1200 C.E. Used as a cathartic medicine.
1935 C.E. Studies started applying aloe vera with radiation-induced ulcerations.
The Aloe Vera Plant
Aloe vera is a succulent and drought-resistant plant belonging to the Liliaceae family. There are more than 400 species known in the genus Aloe and four of them with medicinal properties. Aloe barbadensis is called by the taxonomists as aloe vera. Aloe vera has yellow flowers and its leaves are arranged in a rosette configuration. The leaf of aloe vera is filled with a gel located in the central mucilaginous pulp along with a yellow bitter liquid that exudes from the peripheral bundle sheath cells. Aloe vera (Aloe barbadensis) contains a polysaccharide widely used in cosmetic products. The polysaccharide in aloe vera is responsible for the moisturizing property of this succulent plant[2]. Presently, aloe vera is the most extensively approved and employed for a variety of cosmetic, medical, and nutraceutical uses[1,3,4].
Chemical Ingredients of Aloe Vera
Aloe vera contains two components, a mucilaginous pulp, and a yellow, bitter liquid portion. The bitter liquid is mostly phenolic in nature with a considerable concentration of 1,8-dihydroxianthraquinone derivative (Aloe-emodin) and glycosides (aloins) which has cathartic or laxative property, Fig. 1. The aloe vera pulp consists of carbohydrate polymers (glucomannans or pectic acid) among other inorganics and organic ingredients, Table 2. This succulent plant encloses mono- and polysaccharides, sterols, organic acids, saponins, tannins, enzymes, minerals, and vitamins[2,4,5].
Fig. 1 Chemical structure of aloe vera[1].
Table 2. Chemical composition of aloe vera [1, 6]
Anthraquinones Aloin, barbaloin, isobarbaloin, anthranol, aloetic acid, anthracene, ester of cinnamic acid, aloe-emodin, emodin, chrysophanic acid, ethereal oil, resistannol.
Lipids Triterpenoid, arachidonic acid, γ-linolenic acid, steroids (campesterol, cholesterol, β-sitosterol), triglicerides.
Inorganic Calcium, sodium, chlorine, manganese, magnesium, zinc, copper, chromium, potassium sorbate.
Saccharides Cellulose, glucose, mannose, L-rhamnose, aldopentose.
Proteins Lectins, lectin-like substance.
Enzymes Oxidase, amylase, catalase, lipase, alkaline phosphatase, alkaline phosphatase, carboxypeptidase, cyclooxidase, cyclooxygenase, phosphoenol, pyruvate carboxylase, superoxide dismutase.
Vitamins B1, B2, B6, C, choline, folic acid, alpha-tocopherol, beta carotene, choline.
Essential amino
acids Lysine, threonine, valine, methionine, leucine, isoleucine, phenylalanine.
Nonessential
amino acids Histidine, arginine, hydroxyproline, aspartic acid, glutamic acid, proline, glycerine, alanine, tyrosine.
Anthraquino-
nes/anthrones Ester of cinnamic acid, emodin, Aloe-emodin, aloetic-acid, anthranol, aloin A and B (or collectively known as barbaloin), isobarbaloin.
Polysaccharide Pure mannan, acetylated mannan, acetylated glucomannan, glucogalactomannan, galactan, galactogalacturan, arabinogalactan, galactoglucoarabinomannan, pectic substance, xylan, cellulose, hyaluronic acid. phenylalanine, threonine, tyrosine.
Minerals Zinc, iron, calcium, chlorine, chromium, sodium, copper, magnesium, manganese, potassium, phosphorous.
Chromones Auxins, gibberellins, 8-C-glucosyl-(2′ -O-cinnamoyl)-7-O-methylaloediol A, 8-Cglucosyl- (S)-aloesol, 8-C-glucosyl-7-O-methyl-(S)-aloesol, 8-C- glucosyl-7-Omethylaloediol, 8-C-glucosyl-noreugenin, isoaloeresin D, isorabaichromone, neoaloesin A hormones.
Other organic
compounds Uric acid, lignins, potassium sorbate, salicylic acid.
Miscellaneous Cholesterol, triglycerides, steroids, beta-sitosterol, lignins, uric acid, gibberellin, lectin-like substance, salicylic acid.
In Vivo and in vitro Studies of the Healing Capability of Aloe Vera
The first medicinal case of aloe vera was reported in 1935, a woman self-treated a radiodermatitis on her scalp with the gelatinous part of the fresh aloe vera. After 24 hours, she claimed the itching and burning ceased and in 5 weeks the dermatitis was cured[1]. Subsequently, a plethora of in vivo and in vitro studies of the healing properties of aloe vera have been carried off. For instance, an in vitro research demonstrated that aloe vera inhibited the proliferation of pathogenic fungi such as the species of genus Alternaria viz., A. alternata, A. citri, and A. tenuissima[4]. In another study, the wound healing capability of aloe vera was tested. Mice model induced wounds were treated with aloe vera orally and topically. The results showed a 62.5% reduction in wound diameter in mice treated with 100 mg/kg/day (aloe vera) oral, as well as a reduction in the wound of 50.8% in the mice treated topically with 25% (aloe vera). This study implied that aloe vera is efficient both topically and orally ways[7]. A research work compared the commercial estrogen vaginal cream to treat vaginal atrophy in menopause women with the aloe vera vaginal cream. After six weeks of the vaginal cream treatment on menopause females, the study concluded that aloe vera is beneficial to treat vaginal atrophy in menopause women[8]. A delivery mechanism was designed to deliver aloe vera extract use in cancer therapy, this research method demonstrated that the particles of phytosomes gel carriers improve the oral delivery of aloe vera in this cancer treatment[9]. A study prepared an edible alginate, aloe vera, and ferulic acid coat to be used on fresh-cut apples to delay quality changes, this work demonstrated that the edible coating may promote the safety and quality of fresh-cut produce[10]. The outermost layer of the epidermis or stratum corneum (SC) plays an important part in the regulation of the loss of water from the skin. The SC defends against environmental challenges, also retains and losses a small amount of water to hydrate and keep the skin flexible and functional[11]. For instance, a study demonstrated that after applying a single aloe vera extract (0.25% and 0.50% w/w) formulation, the water content of the SC increased. Thus, this study stated that freeze-dried aloe vera enhances skin hydration, and it can be applied as a moisturizing cosmetic formulation to try dry skin[11,12].
Conclusion
Several of the medical properties of aloe vera still in scrutiny, and there is a need for exhaustive research on this subject to eliminate inconsistencies. Aloe vera studies so far have found divergencies between its in vivo and in vitro results. Certainly, aloe vera research work should be performed in the same plant species and standardized for its preparation. Fortunately, aloe vera is gaining more and more attention from the scientific community. Evidently, the chemical components of aloe vera with most of the medical benefits need to be identified to obtain a clear panoramic of the pharmaceutic assets of the aloe vera plant.
References
1. Shelton Ronald M.. Aloe Vera Its Chemical and Therapeutic Properties.
2. Reynolds, T.; Dweck, A.C. Aloe Vera Leaf Gel: A Review Update. Journal of Ethnopharmacology 1999, 68, 3–37, doi:10.1016/S0378-8741(99)00085-9.
3. Jaiswal, S.K.; Mahajan, S.; Chakraborty, A.; Kumar, S.; Sharma, V.K. The Genome Sequence of Aloe Vera Reveals Adaptive Evolution of Drought Tolerance Mechanisms. iScience2021, 24, 102079, doi:10.1016/j.isci.2021.102079.
4. Bajwa, R.; Shafique, S.; Shafique, S. Appraisal of Antifungal Activity of Aloe Vera. 2007, 5.
5. Kuhn, M.A. Herbal Remedies: Drug-Herb Interactions. Critical Care Nurse 2002, 22, 22–32, doi:10.4037/ccn2002.22.2.22.
6. Nicolau-Lapeña, I.; Colàs-Medà, P.; Alegre, I.; Aguiló-Aguayo, I.; Muranyi, P.; Viñas, I. Aloe Vera Gel: An Update on Its Use as a Functional Edible Coating to Preserve Fruits and Vegetables. Progress in Organic Coatings 2021, 151, 106007, doi:10.1016/j.porgcoat.2020.106007.
7. Rh, D.; Mg, L.; Jm, R.; Me, B. Wound Healing, Oral & Topical Activity Of Aloe Vera. 9.
8. Poordast, T.; Ghaedian, L.; Ghaedian, L.; Najib, F.S.; Alipour, S.; Hosseinzadeh, M.; Vardanjani, H.M.; Salehi, A.; Hosseinimehr, S.J. Aloe Vera; A New Treatment for Atrophic Vaginitis, A Randomized Double-Blinded Controlled Trial. Journal of Ethnopharmacology 2021, 270, 113760, doi:10.1016/j.jep.2020.113760.
9. Murugesan, M.P.; Venkata Ratnam, M.; Mengitsu, Y.; Kandasamy, K. Evaluation of Anti-Cancer Activity of Phytosomes Formulated from Aloe Vera Extract. Materials Today: Proceedings 2020, S221478532038648X, doi:10.1016/j.matpr.2020.11.047.
10. Nicolau-Lapeña, I.; Aguiló-Aguayo, I.; Kramer, B.; Abadias, M.; Viñas, I.; Muranyi, P. Combination of Ferulic Acid with Aloe Vera Gel or Alginate Coatings for Shelf-Life Prolongation of Fresh-Cut Apples. Food Packaging and Shelf Life2021, 27, 100620, doi:10.1016/j.fpsl.2020.100620.
11. Rawlings, A.V.; Harding, C.R. Moisturization and Skin Barrier Function. Dermatologic Therapy 2004, 17, 43–48, doi:10.1111/j.1396-0296.2004.04S1005.x.
12. Dal’Belo, S.E.; Rigo Gaspar, L.; Berardo Gonçalves Maia Campos, P.M. Moisturizing Effect of Cosmetic Formulations Containing Aloe Vera Extract in Different Concentrations Assessed by Skin Bioengineering Techniques. Skin Research and Technology 2006, 12, 241–246, doi:10.1111/j.0909-752X.2006.00155.x.
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