Vitamin A is essential for healthy growth and development, good vision, a strong immune system, and a healthy skin barrier. In the 1960s, dermatologists commonly used vitamin A for treating acne until it was later identified as an effective vitamin for the repair of aging skin.1 It is currently one of the most popular ingredients used in skin care formulations for skin revision. However, little information is presented concerning the importance and necessity of retinol binding proteins, which are required for the cells’ ability to utilize retinol.2 This article will focus on identifying the different forms of vitamin A, the metabolism, and the necessity of binding proteins to use retinols. First, it is important to identify the various types of vitamin A.
TYPES OF VITAMIN A
Vitamin A has three active forms: retinal, retinol, and retinoic acid.2 Retinyl ester is the storage form of vitamin A. The two forms of vitamin A most frequently used in skin care are retinyl palmitate and retinol. The alcohol form, retinol, is regarded by many as the true vitamin A or the complete molecule of vitamin A.1 It is this belief that has ignited the usage of synthetic forms of retinol in skin care formulations. But, it is not without its limitations, the most relevant being a short shelf life. Retinol absorbs quickly into the skin from surface application. However, the conversion to retinyl palmitate in the extracellular space and to enter the cell requires special receptors or retinol binding proteins and will be discussed later.1
Retinoic acid is the acid form of vitamin A and has also gained in popularity among cosmeceutical companies. Physicians prescribe this form of vitamin A as Tretinoin or Renova, but it is known to produce the most irritation to the skin. The side effects of topically applied retinoic acid can include redness, irritation, and flaking. While results may be achieved using this form of vitamin A, it is not without contraindications.1
Retinyl palmitate is found in large quantities in the extracellular space, which accounts for 80% of the total vitamin A found in human skin.4 Retinyl palmitate is converted into retinoic acid to sustain the DNA and cellular structures. This conversion occurs in a very complex cellular process. Because of the skin’s ability to use this form of vitamin A, it is primarily found in topical application formulas.
Vitamin A esters in the skin undergo a number of transitional stages before finally being used by the cells, with the conversion of retinol back to retinyl palmitate in the extracellular spaces as an example. The ester form of vitamin A plays a pivotal role in metabolism, even though it is not used directly by the cells until its conversion. The biological and metabolic functions that regulate the use of vitamin A by the cells indicate that rushing the process will not always provide the best results.4
UNDERSTANDING RETINOLS AND RETINOL BINDING PROTEINS
The retinol form of vitamin A is stored in the liver. In order to travel from the liver to the dermis, it has to be attached to a protein, most commonly referred to as retinol binding protein.2 When retinol or retinoic acid are circulating within the cells, it must be attached to a retinol binding protein. These proteins assist in the recycling process of retinol as it enters and exits the liver several times a day. Because retinoids are insoluble in water, they must bind to retinol binding protein to enter the cell and perform its task. When retinol or retinoic acid are circulating within cells, damaging or miscommunication to cells occurs.2
Another important vitamin A receptor is stimulated by retinoic acid 6 (STRA6). This receptor is a transmembrane cell receptor for retinol binding. It functions specifically as a cytokine signaling transporter.6 The primary responsibility of STRA6 is to transport retinol to the eye. STRA6 is also responsible for homeostasis and metabolism of cell signaling; therefore, this receptor is also necessary for retinol uptake.
Embryos are extremely sensitive to retinol concentration and malformations of the embryo may occur during development. If retinol or retinoic acid are out of balance, early embryo mortality or developmental malformations may occur.5 It is important to recognize that retinol is crucial to the growth of various tissues, most specifically in embryo formation. Subsequently, retinol binding protein binds to retinol and plays a critical role in regulating the transport and metabolism of retinol in embryos.
Vitamin A, in its many forms, is proclaimed to be the superior ingredient for skin revision, especially for the aging market and acne. However, important components to the success of retinols are retinol binding protein and specialized receptors like STRA6. As continuous and increased usage of retinols are available in cosmeceutical products, one must be cognizant of the cells’ ability to utilize them without becoming harmful and detrimental to the skin.
1 Anderson, Allie. “Special Feature: Using Vitamin A.” Aesthetics.
2 “Carotenoid Oxygenase.” InterPro. https://www.ebi.ac.uk/interpro/potm/2005_6/Page2.htm.
3 Berardi, John and Ryan Andrews. “The Essentials of Sport and Exercise Nutrition.” 2nd
Edition. Precision Nutrition, 2015.
4 D’Ambrosio, Diana N., Robin D. Clugston, and William S. Blaner. “Vitamin A Metabolism:
An Update.” Nutrients 3, no. 1 (2011): 63-103.
5 Wikepedia, s.v. “retinol-binding protein.”
6 Wikipedia, s.v. “Vitamin A receptor.”
Susan Wade is a licensed aesthetician joining Viktoria De’Ann in 2015 as the director of education and sales after being in the health and education industry for over 18 years. She has a master’s in higher education administration and enjoys sharing her wealth of knowledge with physicians, clinicians, and students nationwide. Wade has a diverse background beyond aesthetics as a college instructor in kinesiology and business and is an owner of a successful sports conditioning business’ and a nutrition coach. Her passion lies in understanding the complexities of physiology, nutrition, and biology and in educating practitioners on how to incorporate these areas to reach better solutions and successful results with their clients.