Avenanthramides (anthranilic acid amides, formerly called "avenalumins") are a group of phenolic alkaloids found mainly in oats (Avena sativa), but also present in white cabbage butterfly eggs (Pieris brassicae and P. rapae), and in fungus-infected carnation (Dianthus caryophyllus). A number of studies demonstrate that these natural products have anti-inflammatory, antioxidant, anti-itch, anti-irritant, and antiatherogenic activities. Oat kernel extracts with standardized levels of avenanthramides are used for skin, hair, baby, and sun care products. The name avenanthramides was coined by Collins when he reported the presence of these compounds in oat kernels. It was later found that three avenanthramides were the open-ring amides of avenalumins I, II, and III, which were previously reported as oat phytoalexins by Mayama and co-workers.
History
Oat has been used for personal care purposes since antiquity. Indeed, wild oats (Avena sativa) was used in skin care in Egypt and the Arabian peninsula 2000 BC. Oat baths were a common treatment of insomnia, anxiety, and skin diseases such as eczema and burns. In Roman times, its use as a medication for dermatological issues was reported by Pliny, Columella, and Theophrastus. In the 19th century, oatmeal baths were often used to treat many cutaneous conditions, especially pruritic inflammatory eruptions. In the 1930s, the literature provided further evidence about the cleansing action of oat along with its ability to relieve itching and protect skin.
Colloidal oatmeal
In 2003, colloidal oatmeal was officially approved as a skin protectant by the FDA. However, little thought had been given to the active ingredient in oats responsible for the anti-inflammatory effect until more attention was paid to avenanthramides, which were first isolated and characterized in the 1980s by Collins.
Since then, many congeners have been characterized and purified, and it is known that avenanthramides have antioxidant, anti-inflammatory, and anti-atherosclerotic properties, and may be used as a treatment for people with inflammatory, allergy, or cardiovascular diseases. In 1999 studies made by Tufts University showed that avenanthramides are bioavailable and remain bioactive in humans after consumption. More recent studies made by the University of Minnesota showed that the antioxidant and anti-inflammatory activities can be increased through the consumption of 0.4 to 9.2 mg/day of avenanthramides over eight weeks. The International Nomenclature of Cosmetic Ingredients (INCI) originally referred to an oat extract with a standardized level of avenanthramides as "Avena sativa kernel extract," but recently they have also accepted the INCI name "avenanthramides" to describe an extract containing 80% of these oat phenolic alkaloids.
Function in Avena sativa
A. sativa produces avenanthramides as defensive phytoalexins against infiltration by fungal plant pathogens. They were discovered as defensive chemicals especially concentrated in lesions of Puccinia coronata var. avenae f. sp. avenae (and at that time named "avenalumins").
Medical and personal care uses
Anti-inflammatory and anti-itch activity
Studies made by Sur (2008) provide evidence that avenanthramides significantly reduce the inflammatory response. Inflammation is a complex and self-protection reaction that occurs in the body against foreign substance, cell damage, infections, and pathogens. The inflammatory responses are controlled through a group called cytokines that is produced by the inflammatory cells. Furthermore, the expression of cytokines are regulated through inhibition of nuclear transcription factor kappa B (NF-κB). Many studies have demonstrated that avenanthramides can reduce the production of pro-inflammatory cytokines such as IL-6, IL-8, and MCP-1 by inhibiting NF-κB activation that is responsible for activating the genes of inflammatory response. Thus, these oat polyphenols mediate the decrease of inflammation by inhibiting the cytokine release. In addition, it was found that avenanthramides inhibit neurogenic inflammation, which is defined as an inflammation triggered by the nervous system that causes vasodilation, edema, warmth, and hypersensitivity. Also, avenanthramides significantly reduce the itching response, and its efficiency is comparable to the anti-itch effect produced by hydrocortisone.
Redness reduction
Avenanthramides have effective antihistaminic activity; they significantly reduce itch and redness compared with untreated areas.