Aloe vera is traditionally used to treat injured or irritated skin (burns, cuts, insect bites and eczema) and digestive problems, as it has anti-inflammatory, anti-microbial and wound-healing properties.
The most studied active ingredients of aloe vera are aloe-emodin, aloin, aloesin, emodin and acemannan. Further mechanisms of action of aloe vera and its components have also been researched. The underlying study provides an overview of current pharmacological studies (in vitro studies, in vivo studies and clinical trials).
Skin-protecting properties
Most of the in vitro studies on the skin-protecting effect of aloe vera and its active ingredients investigated their wound-healing properties. In most cases, a human keratinocyte cell line (HaCaT) or an epidermal keratinocyte cell line (HEKa) or fibroblast cell lines were used for this purpose. These studies have shown that the skin-protecting effect of aloe vera and its main active ingredients (aloesin, aloin and emodin) occurs via their anti-oxidative and anti-inflammatory mechanisms of action.
Aloe vera upregulated the expression of TFGβ1, bFGF and Vegf-A in fibroblasts and increased the proliferation and differentiation of keratinocytes via lysosomal membrane stability. Furthermore, in the cellular model of primary cultures of corneal epithelial cells, aloe vera solution was able to accelerate wound closure even at low concentrations (≤175 µg/mL) by increasing the degradation of type IV collagen.
Furthermore, aloin protected the skin by reducing the production of IL-8, DNA damage, lipid peroxidation and ROS generation and by increasing the level of GSH and the activity of SOD. The compound aloesin, in turn, induced wound healing effects by increasing cell migration via phosphorylation of Cdc42, Rak1, cytokines and growth factors. In addition to the wound healing effects, studies have reported that aloe polysaccharide (20, 40 and 80 µg/mL for 24 hours) is useful as an agent in the treatment of psoriasis as it caused inhibition of TNF-a levels as well as protein expression of IL-8 and IL-12 in the human keratinocyte cell line.
Studies have also reported that aloe vera protects against X-rays due to its anti-oxidative properties by increasing the activity of anti-oxidative enzymes and GSH content and reducing the production of ROS and lipid peroxidation. Studies of the isolated active ingredients aloe-emodin and aloesin showed that their healing effect can be attributed to their angiogenic properties.
In the 6 years prior to the publication of the study on which this summary is based, various clinical studies were conducted, some of which investigated the efficacy of the use of aloe vera for the treatment of ulcers. It was found that twice daily application of an aloe vera gel over a period of 3 months improved and accelerated wound healing and also reduced hospitalization time.
In addition, clinical studies have shown that aloe vera causes rapid tissue epithelialization and granulation in burns, promotes the healing of caesarean section wounds and accelerates the healing of donor sites for split-thickness skin grafts.
Anti-inflammatory effect
In a study conducted by Thunyakitpisal et al. it was shown that the aloe vera ingredient acemannan increased the expression of IL-6 and IL-8 as well as NF-κB/DNA binding in gingival fibroblasts via the Toll-like receptor signaling pathway.
As there is a correlation between high levels of IL-1β and periodontal disease, Na et al. investigated the anti-inflammatory properties of aloin in oral Kb epithelial cells stimulated with saliva from healthy study participants in a further study. The study showed that the saliva samples with high levels of IL-1β-stimulated IL-8 production in KB cells and with pretreatment with aloin inhibited the production of IL-8 by decreasing p38 and extracellular signal-regulated kinase pathways.
In a study conducted by Ahluwalia et al., the effect of a standardized aloe vera extract containing alin and acemannan on the activation, proliferation and cytokine secretion of T blood cells of healthy male study participants was investigated. It was shown that the expression of CD25 and CD3 was reduced in CD3(+) T cells. Furthermore, the standardized aloe vera extract caused a concentration-dependent suppression of T cell proliferation as well as a reduction of IL-2, IFN-γ and IL-17A.
Anti-oxidative properties
In another study, an ethanol extract of Aloe vera was shown to protect microvascular endothelial cells against hydrogen peroxide and 4-hydroxynonenal-induced toxicity by reducing the production of ROS and HNE protein adducts. The anti-oxidant activity of Aloe vera is partly due to the anthraquinones and related compounds (10 µM) it contains, which have peroxyl radical scavenging properties and reduce capacity.
A clinical trial with 53 healthy participants showed that the intake of aloe vera extract over a period of 14 days increased the anti-oxidative capacity of the plasma of the trial participants.
Conclusion
The underlying study comes to the conclusion that aloe vera and various of its components (such as aloe-emodin and aloin) are active ingredients with various anti-oxidative, anti-inflammatory, anti-microbial and skin-protecting properties, which have been proven in various studies and whose mechanisms of action have been described there.
Underlying study:
Sánchez, M. et al: Pharmacological Update Properties of Aloe Vera and its Major Active Constituents; in: Molecules 2020, 25, 1324; doi:10.3390/molecules25061324