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Avenanthramides

Nonnutritive, History of Oats

Cultivated oats have been part of the human diet since the Bronze Age, but the topical application of oatmeal preparations for skin care rather than nutrition was first described by the ancient Romans.1,2 Medical texts by Pliny and other notables promoted the use of oatmeal flour for a variety of dermatologic conditions.2 More recent centuries have found health benefits for both topically applied and orally ingested oat preparations. For example, in the early 1800’s Henry Potter, a London pharmacist, produced a tincture of oats known as Potter’s Compound of Avena with Helionas Mixture No. 108A and Tonic No. 1.3 For the next hundred years, oats were regarded as so powerfully healthful that they were almost exclusively available at pharmacies.4

Oatmeal’s ability to relieve dry itch and function as a skin protectant when formulated in facial masks and bath oils was first documented in the 1930’s.4 Initially, topical oatmeal preparations were homemade affairs that were soothing, but posed the unusual risk of clogging drains with the hydrated oat flour. In the 50’s, Ready-to-use formulations simplified preparation and made it possible to conduct studies that showed colloidal oatmeal baths provided soothing treatment and nonirritating cleansing for inflamed skin associated with xerotic dermatoses.5-9

Another application of oats that sparked extensive investigation decades later was their use as a commercial antioxidant in food and beverage products.13,14 During the 1930’s, foods that were sensitive to oxidation, such as milk, butter, and ice cream, were protected from spoilage by finely ground oats.4

Active Oat Fractions: Phenolics and Avenanthramides

The recognized clinical benefits of finely ground oats are due to their remarkable chemical composition, and the fortunate coincidence that compounds essential for the natural development of oats may have beneficial effects on humans. Oats are generally regarded as having the highest protein and lipid content of any cereal grain, as well as a high fatty acid content.4,14 Oat flour (prepared from finely ground oats) is predominantly composed of starches (65% to 85%), proteins (15% to 20%, including enzymes), fiber and beta glucans (5% each), small amounts of vitamins, and lipids (3% to 11%). The lipids are protected from oxidation by a variety of natural antioxidant compounds, most important of which is a group of phenolic compounds usually present at concentrations below 300 ppm.14,15

These phenolic compounds are part of a group of more than 5000 naturally occurring structurally and functionally related molecules. Oat phenolics may serve as potent antioxidants by scavenging reactive oxygen and nitrogen species and/or by chelating transition minerals.13

As a group, phenolics are the strongest antioxidants found in nature, yet within the group, individual compounds have characteristic and antioxidant activity.16 Oat phenolic compounds include simple forms with a single phenol ring, such as ferulic acid, caffeic acid, and vanillic acid; complex compounds with 2 or more rings such as coumarin; and the avenanthramides, a class of more than 40 phenolic compounds found only in oats (Figure 1).15

Complex mixtures of phenolics can be isolated from oats by an ethanol-water extraction and have been further separated, identified, concentrated, standardized, and evaluated by in vitro and in vivo biologic models. They have been shown to inhibit oxidation of low-density lipoprotein; inhibit the autoxidation of linoleic acid and beta carotene; inhibit oxygen consumption following hemin-induced oxidation of linoleic acid; inhibit collagen oxidation by peroxinitrite; and inhibit oat oil oxidation with activity comparable to commercial antioxidants like butylated hydroxytoluene and propyl gallate.13-15,17,18

Some of the many biologically active phenolic compounds in oats.

Avenanthramide Anti-oxidant Activity

Avenanthramides have 10 to 30 times the antioxidant activity of other oat phenolic compounds and are currently being studied to further characterize their effects on the skin and chemical properties.14

Recently, separated oat fractions were tested in a skin erythema model to further explore the functional properties of various oat components. When compared to saponins, flavonoids, sugars and amino acids, ash, proteins, and lipids, the avenanthramide fraction was found to most effectively reduce UV-induced erythema 24 hours after skin application.19 A follow-up dose-response study of highly purified avenanthramides showed significant reduction in redness at concentrations from 45 ppm to below 2 ppm.19

Oat fraction redness reduction.

Avenanthramides were the most potent of 7 oat fractions at reducing skin redness 24 hours after application. In this trial, test sites were irradiated with 1.5 times the minimal erythema dose (MED) of ultraviolet light followed at 24 hours by application of 7 oat fractions. The change in skin color was measured 24 hours after samples were applied. The change in erythema was expressed relative to the dry weight of the applied sample.

Avenanthramide Standardization

The key role of avenanthramides in the overall activity of natural oats provides an opportunity to standardize oat preparations to known concentrations of ingredients. This is important because the chemical composition of oats varies with each species and subspecies and is further affected by soil type, growing conditions, and processing.14,15,17 Although whole oat flour provides effective topical relief, the use of standardized oat extracts will help achieve predictable clinical benefit. Laboratory synthesis of individual avenanthramides is underway and will enable further characterization of each unique compound.

Table 1. Avenanthramide dose response for erythema reduction. A purified avenanthramide fraction was prepared at concentrations of 45, 15, 5, 1.5, and 0.5 ppm and applied to skin 24 hours after exposure to 1.5 x MED; the change in skin color was measured 24 hours after avenanthramide application. Redness reduction was calculated relative to baseline skin color.

Avenanthramide Concentration, ppm

Erythema Reduction at 24 Hours, %

45.0 18.7*
15.0 18.4*
5.0 19.4*
1.5 14.0*
0.5 7.1
Untreated 5
*P<.05, t-test

Avenanthramide Potential in Skin Care

The avenanthramide fraction of oats has been shown to be a highly effective antioxidant in a number of test systems. It has been demonstrated to perform as a skin protectant both in vitro and in vivo. The dermatologic applications of this activity have potential use in skin care for infants, people with sensitive skin, and for caring for sun-exposed skin. Patients with itchy, dry skin may benefit from these topical soothing effects.

References

  1. Gibson L, Benson G. Origin, history, and use of oat (Avena sativa) and wheat (Triticum aestivum). Iowa State University. Department of Agronomy.
    http://www.agron.iastate.edu/courses/agron212/readings/oat_wheat_history.htm.
    Accessed June 4, 2007.
  2. Melardi MG. Avena. http://www.lapelle.it/alimentazione/avena.htm. Accessed June 4, 2007.
  3. Wren RC. Potter’s New Cyclopedia of Botanicals Drugs and Preparations. Saffron Waldon: England; 1907.
  4. Webster FH. Oat utilization: past, present and future. In: Webster FH, ed.Oats: Chemistry and Technology. St Paul, MN: American Association of Cereal Chemists, Inc; 1986:413-430.
  5. Smith GC. The treatment of various dermatoses associated with dry skin. JSC Med Assoc. 1958;54:282-283.
  6. Dick LA. Colloidal emollient baths in pediatric dermatoses. Arch Pediatr. 1958; 75:506-508.
  7. Dick LA. Colloidal emollient baths in geriatric dermatoses. Skin. 1962;1:89-91.
  8. Grais ML. Role of colloidal oatmeal in dermatologic treatment of the aged. AMA Arch Derm Syphilol. 1953;68:402-407.
  9. O’Brasky L. Management of extensive dry skin conditions. Conn Med. 1959; 23:20-21.
  10. Franks AG. Dermatologic use of baths. Am Pract Dig Treat. 1958;9:1998-2000.
  11. Varicella treatment. Centers for Disease Control and Prevention. http://www.cdc.gov/nip/diseases/varicella/faqs-gen-treatment.htm#1-treatments. Accessed June 5, 2007.
  12. Cercarial dermatitis. Centers for Disease Control and Prevention.
    http://www.cdc.gov./ncidod/dpd/parasites/cercarialdermatitis/factsht_cercarialdermatitis.htm. Accessed June 5, 2007.
  13. Chen C-Y, Milbury PE, Kwak HK, Collins FW, Samuel P, Blumberg JB. Avenanthramides and phenolic acids from oats are bioavailable and act synergistically with vitamin C to enhance hamster and human LDL resistance to oxidation. J Nutr. 2004;134:1459-1466.
  14. Dimberg LH, Theander O, Lingert H. Avenanthramides – a group of phenolic antioxidants in oats. Cereal Chemistry. 1993;70:637-641.
  15. Emmons CL, Peterson DM. Crop breeding, genetics & cytology; antioxidant activity and phenolic content of oats as affected by cultivar and location. Crop Science. 2001;41:1676-1681.
  16. Tsao R, Akhtar MH. Neutraceuticals and functional foods: I. Current trend in phytochemical antioxidant research. Journal of Food, Agriculture & Environment. 2005;3:10-17.
  17. Emmons CL, Peterson DM. Antioxidant activity and phenolic contents of oat groats and hulls.Cereal Chemistry. 1999;76:902-906.
  18. Kato Y, Ogino Y, Aoki T, Uchida K, Kawakishi S, Osawa T. Phenolic antioxidants prevent peroxynitrite-dervived collagen modification in vitro. J Agric Food Chem. 1997;45:3004-3009.
  19. Vollhardt J, Fielder DA, Redmont MJ. Identification and cosmetic application of powerful anti-irritant constituents of oat grain. XXI IFSCC International Congress 2000, Berlin. Proceedings; 395-402.
Avenanthramides
 
 
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