In past issues, we have considered in detail biopolymers – high molecular weight ingredients. In the new year, we propose to start getting acquainted with low molecular cosmetic raw materials. We will refer to it substances that are not biopolymers – vitamins, amino acids, trace elements, etc. Due to their high bioavailability, these ingredients are found in topical cosmetics and injectable formulas. We begin a new series of reviews with the most famous of the vitamins, studied from and to, – ascorbic acid, or vitamin C. We will analyze the features of its structure, mechanisms of action and methods of application.
General information
As usual, let us start with chemistry. Vitamin C, or ascorbic acid (AA), or gamma-lactone 2, 3-dehydrogulonic acid, is water-soluble crystals with a sour taste, odorless. The optimal pH level of the aqueous solution is 3.5 pH. Due to their high photosensitivity, vitamin C and its solutions prefer storage in dark or opaque containers. Ascorbic acid is easily and quickly oxidized by atmospheric oxygen, acquiring a dark orange hue.
The molecular structure of vitamin C determines its optical activity, which leads to the existence of two stereoisomers: L – ascorbic and D – ascorbic acids. The mammalian organism is built in such a way that most molecules with a similar structure enter into metabolic processes only in the L-form, and vitamin C is no exception. Therefore, L-ascorbic acid is highly reactive.
The uniqueness of ascorbic acid is manifested even from the classification. As you know, vitamins include organic substances that can be converted into coenzymes and affect metabolic processes. Vitamin C, in turn, is itself a reducing coenzyme, which determines its high antioxidant activity.
Vitamin C is not produced in the human body, so it is necessary to carefully monitor the level of its intake. Hypovitaminosis of ascorbic acid is dangerous by a decrease in immunity, and hypervitaminosis can lead to less absorption of vitamin B12 and the development of urolithiasis. Therefore, vitamin C should be taken in moderate amount, not exceeding the daily dose.
Interesting fact: the only disease that can be treated with vitamin C is scurvy. Only one thing can be said about the therapeutic effect of ascorbic acid in relation to all known diseases: it is not a panacea at all. Yes, this substance has a wide spectrum of action, entering into a number of metabolic reactions. Nevertheless, to achieve a noticeable improvement in the general condition, for example, with acute respiratory infections, it is possible only with hypovitaminosis of L-ascorbic acid. In other cases, such therapy will be useless.
Cosmetic vitamin С
Ascorbic acid is a highly unstable compound, easily degraded in air or light. In addition, this vitamin hardly overcomes the hydro-lipid barrier of the skin, which leads to the need to increase its effective concentration in cosmetics for external use. However, the biochemical properties of this vitamin force cosmetic industry technologists to do everything possible to preserve this valuable ingredient in their products.
How to ensure the stability of vitamin C in products? There are several ways:
1. Storage of raw materials and finished products in a dark tightly closed container, without access to light and air.
2. Creation of a chemically inert atmosphere during the production and storage of drugs. This method allows you to maintain an effective concentration of vitamin C in individual products and products for injectable cosmetology.
3. Chemical modification of ascorbic acid. The essence of the method is to change the structure of the vitamin molecule by introducing radicals or forming esters. The advantage of the modification is to obtain a chemically stable vitamin with different solubility. For example, with the introduction of fatty acid residues – palmitic or stearic – fat-soluble ascorbic acid is obtained. This step allows you to introduce a valuable vitamin into the composition of creams and emulsions.
Let us analyze several types of stabilized ascorbic acid.
• Magnesium ascorbyl phosphate (MAP) is an ester of ascorbic and phosphoric acids bound to a magnesium ion. This modification allows you to increase the stability of vitamin C in water, and reduces the acidity of the solution. This leads to a decrease in the irritating effect of the acid. On the other hand, this ingredient in the form of an aqueous solution hardly penetrates into the deeper layers of the skin, which requires the complication of the composition of the cosmetic product.
Products containing magnesium ascorbyl phosphate actively stimulate the production of collagen and have a positive effect on the proliferation of skin fibroblasts. There are studies demonstrating the ability of this substance to regulate the process of methylation of DNA molecules, which has a positive effect on reducing the manifestations of age-related skin changes, as well as correcting its general condition. Sodium and calcium ascorbyl phosphates have a similar effect.
• Ascorbyl glucoside (AA2G) is vitamin C bound to glucose. This substance is quite stable, but has less pronounced acidic properties and biological activity compared to pure ascorbic acid. Widely used in moisturizing cosmetic formulas. It has a mild vascular effect, which allows it to be used in skin care products around the eyes.
• Fatty acid esters of vitamin C are compounds with intermediate stability, soluble in fats. These include ascorbyl tetraisopalmitate (VC-IP), ascorbyl stearate, and the like. This group of raw materials has found its place in the composition of anti-aging creams, serums and lotions. Nevertheless, there is a significant limitation for their use: ascorbic acid esters have a high ability to absorb UV radiation. This means that when using formulas based on them during daylight hours, the skin is subjected to additional oxidative stress, which negates the antioxidant effect of vitamin C.
Cosmetics based on esters of ascorbic acid will be a reliable tool for sun protection, photodamage repair and pigment spots. This spectrum of action is due to the activation of antioxidant mechanisms, as well as the pronounced whitening effect of ascorbic acid. Nevertheless, only when used in the evening and at night.
• Retinyl ascorbate is an ester of retinoic and ascorbic acids, which are ideal synergists with respect to each other. The effect of using cosmetics containing such a cocktail is manifested in the form of a reduction in wrinkles and an improvement in complexion. However, like fatty esters, it has high photosensitivity.
• Ethyl ascorbic acid is an example of a chemical modification of vitamin C molecule by introducing an ethyl radical. Conditionally stable substance, with minimal photophobia and high moisture absorption capacity. The main property of ethyl ascorbic acid is whitening and smoothing of the skin relief.
We have reviewed the most common modifications of ascorbic acid. Manufacturers of raw materials offer a variety of vitamin C derivatives with a wide spectrum of activity. Therefore, when choosing an active ingredient for cosmetic products, you should focus on the availability of quality certificates and declarations from the manufacturer. Basic information about the safety of the product is presented on its label in the form of an appropriate marking.
Mechanisms of action of vitamin C
We have already seen that vitamin C has a wide spectrum of action. Next, we will analyze what mechanisms are responsible for the implementation of such a variety of effects.
• Whitening
Vitamin C is a universal “bleach” for the skin, because its effectiveness is due to two mechanisms at once. In the case of combating hyperpigmentation, ascorbic acid is built into the synthesis of melanin, limiting the conversion of tyrosine to DOPA-chromium. This reaction is possible due to the reducing coenzyme activity of vitamin C.
The second mechanism allows you to smooth out the external manifestations of rosacea, dark circles under the eyes, puffiness. This is due to the ability of vitamin C to restructure vascular epithelial cells and stimulate the growth of fibroblasts. This mechanism allows to normalize the permeability and structure of the capillary network, which leads to the normalization of skin pigmentation.
• Antioxidant activity
One of the most obvious mechanisms. We have already found out that vitamin C is characterized by coenzyme activity. This substance independently neutralizes the superoxide radical to hydrogen peroxide, and takes part in the detoxification of hepatocytes with the participation of cytochrome P450. This mechanism allows you to correct and prevent age-related changes in the skin.
• Restoration of skin structure
Restoration of the microrelief, including the smoothing of scars and wrinkles, is possible only through the formation of the correct polypeptide sequence of the collagen fiber. Vitamin C is responsible for the process of hydroxylation of amino acids, maintaining the activity of the enzymes necessary for the synthesis and ensuring the correct formation of this functional biopolymer.
• Lipolysis
That is right! Habitual ascorbic acid is a promising lipolytic. Studies are gaining popularity that describe two mechanisms for the interaction of this vitamin with adipose tissue. In the first case, we are talking about starting the process of adipocyte apoptosis, which leads to a decrease in volume due to the self-destruction of fat cells. The reason for the process is a violation of glucose metabolism and leptin production. In combination with drainage components that ensure the removal of adipocyte decay products, this method of dealing with local fat deposits looks quite acceptable.
Another mechanism describes the effect of vitamin C on the formation of adipose tissue. It has been shown that ascorbic acid affects the storage and release of triglycerides in the later stages of lipogenesis. There is still no precise understanding of the nature of this mechanism. Some researchers associate it with the antioxidant activity of ascorbic acid, others with the ability of the vitamin to transmembrane transitions in aging fat cells.
On the other hand, ascorbic acid has a pronounced local irritating effect on areas with local fat deposits, which leads to the development of inflammatory reactions. Therefore, these mechanisms require caution in the selection of formulations and methods of drug administration.
When using such a multifunctional ingredient as vitamin C for therapeutic purposes, the full composition of care and corrective products, as well as their method of application, should be considered. It will not be superfluous to collect a complete history of your patient in order to avoid possible adverse events. The most pronounced effect from the use of vitamin C is achieved with combined anti-age therapy.
Literature
1. P. Humbert et. al. Bateman purpura (dermatoporosis): a localized scurvy treated by topical vitamin C – Double blind randomized placebo-controlled clinical trial. doi: 10.1111/jdv.14525.
2. M. Zasada et al. Preliminary randomized controlled trial of antiaging effects of L‐ascorbic acid applied in combination with no-needle and microneedle mesotherapy. J Cosmet Dermatol. 2018;00:1–7.
3. K. Byoungkae et al. Adipogenic and Lipolytic Effects of Ascorbic Acid in Ovariectomized Rats. Yonsei Med J 2018 Jan;59(1):85-91.
4. K. Morisaki, S. Ozaki. Design of novel hybrid Vitamin C derivatives: Thermal stability and biological activity. Chem. Pharm. Bull. 44 (9) 1647 – 1655 (1996)
5. R. Yin et al. Ascorbic Acid Enhances Tet-Mediated 5‑Methylcytosine Oxidation and Promotes DNA Demethylation in Mammals. J. Am. Chem. Soc. 135 (2013) 10396−10403
6. Wen-Ying Huang et al. Stability studies of ascorbic acid 2-glucoside in cosmetic lotion using surface response methodology. Bioorganic & Medicinal Chemistry Letters 23 (2013) 1583–1587
7. D. F. Garcia-Diaz et al. Vitamin C in the Treatment and/or Prevention of Obesity. J Nutr Sci Vitaminol 60 (2014) 367-379
8. A. Wojcik et al. Influence of the complex of retinol–vitamin C on skin surface lipids. J of Cosmetic Dermatology 14 (2015) 92-99
9. A. Jaros et al. Evaluation of selected skin parameters following the application of 5% vitamin C concentrate. J Cosmet Dermatol. 2018;00:1–6.
10. Min-Jung Bae et al. Baicalein induces CD4+Foxp3+ T cells and enhances intestinal barrier function in a mouse model of food allergy. Sci Rep. 2016; 6: 32225.
Figure 1. The structure of vitamin C: a) L-ascorbic acid; b) D-ascorbic acid.
Figure 2. Treatment of Bateman's purpura with topical serum containing 5% vitamin C.
Источник: P. Humbert et. al. Bateman purpura (dermatoporosis): a localized scurvy treated by topical vitamin C – Double blind randomized placebo-controlled clinical trial