22 SKIN CARE
compartments of the cell, respectively, and they synergistically limit chronic UV damage by significantly reducing both cell apoptosis and thymine dimer formation.3,6 A combination of 0.5% ferulic acid (a potent
antioxidant of plant origin) with 15% vitamin C and 1% vitamin E can increase the efficacy of vitamin C eight-fold. It has been noted that this triple combination is very useful for the reduction of acute and chronic photodamage, and could be used for prevention of skin cancer in the future.3 Vitamin C is essential for collagen
biosynthesis. It has been proposed that it influences quantitative collagen synthesis in addition to stimulating qualitative changes in the collagen molecule. Vitamin C serves as a co-factor for prolysyl and lysyl hydroxylase, the enzymes responsible for stabilising and cross- linking the collagen molecules. It also stimulates lipid peroxidation, and the product of this process, malondialdehyde, in turn stimulates collagen gene expression.2 Vitamin C also directly activates the
transcription of collagen synthesis and stabilises procollagen mRNA. This helps to regulate collagen synthesis, the impairment of which is a symptom of scurvy. Clinical studies have shown that the topical use of vitamin C increases collagen production in both young and aged human skin.3,6 When choosing a depigmenting agent, it is important to differentiate between substances that are toxic to the melanocyte and substances that interrupt the key steps of melanogenesis. Vitamin C falls into the latter category. It interacts with copper ions at the tyrosinase-active site and inhibits action of the enzyme tyrosinase, thereby decreasing melanin formation.
Vitamin C also acts on the perifollicular
pigment. However, it is an unstable compound and is often combined with other depigmenting agents, such as soy and liquorice, for better depigmenting effect.5,7,8 As mentioned above, vitamin C inhibits
NFkB, which is responsible for the activation of a number of pro-inflammatory cytokines such as TNF-α, IL1, IL6 and IL8. Therefore, it has a potential anti-inflammatory activity and can be
OH O OH OH OH D-Glucose OH OH OH OH OH D-Glucuronate OH OH L-Gluconate OH OH O HO OH OH O OH O OH OH OH D-Glucose OH O HO HO HO D-Fructose (Choice of simple sugars as starting points)
Several steps
GDP-L-Galactose OH H HO O O L-Galactonolatone HO OH OH Ascorbic acid Figure 2: Plant synthesis of ascorbic acid
used in conditions like acne vulgaris and rosacea. It can promote wound healing and prevent post- inflammatory hyperpigmentation.2,3
Topical formulations of vitamin C Vitamin C is available in the market as a variety of creams, serums and transdermal patches. Only serums contain active vitamin C, in an almost colourless form. This is unstable and, on exposure to light, is oxidised to dehydro ascorbic acid (DHAA), which imparts a yellow colour. Vitamin C is kept stable by maintaining a pH of <3.5, which removes the ionic charge on the molecule and enables it to be transported well across the stratum corneum.3,5,9 From a clinical point of view, it is important
to note that the efficacy of the serum is proportional to the concentration, but only up to 20%.3
maximum concentration is four days. The half-life in the skin after achieving A persistent reservoir of vitamin C is
important for adequate photoprotection, and can be achieved by regular eight-hourly applications.1,5
As UV light lowers tissue
vitamin C levels, topical vitamin C is best used after exposure to UV light and not prior.1-3
A
combination of tyrosine, zinc and vitamin C has been shown to increase the bioavailability of vitamin C by 20 times over vitamin C alone.2 A variety of creams with vitamin C
derivatives are available in the market. Not all preparations are physiologically effective. Some are not delivered into the dermis in adequate quantities, while others do not chemically convert to the biologically active form of vitamin C in the skin.1,2,4 Magnesium ascorbyl phosphate (MAP) is the
most stable and preferred ascorbyl ester. This lipophilic molecule is easily absorbed into the skin, and the rate-limiting step for absorption is its release from the vehicle, not the rate of diffusion across the stratum corneum. as one might suppose. MAP has a hydrating effect on the skin and
decreases trans-epidermal water loss. It is also a free radical scavenger that is photoprotective and increases collagen production under laboratory test conditions.1,3
Other useful, stable, esterified OH H HO O O
Spontanious Conversion
2-Keto-Gulonolactone HO OH Ascorbic Acid Figure 3: Vertebrate synthesis of ascorbic acid PERSONAL CARE November 2021 Oxidation by enzyme L-gulonolactone oxidase L-Galactonolatone
derivatives include: ■ Sodium ascorbyl phosphate ■ Ascorbyl 6 palmitate, a lipophilic free radical scavenger that hydrolyses to vitamin C and palmitic acid3,8 ■ Disodium isostearyl 2-0 L-ascorbyl phosphate (VCP-IS-Na), another reliable and popular derivative of vitamin C with a C8
alkyl
chain attached to the stable ascorbyl moiety. This ensures increased permeability across the epidermis ■ Ascorbic acid sulfate1 Tetraisopalmitoyl ascorbic acid, a lipophilic
provitamin, and sodium ascorbate, are derivatives that are currently under research.
www.personalcaremagazine.com L-Galactose OH OH O OH L-Galactonolatone-1-P CH2 OH OH OH HO HO OH D-Mannose OH O OH
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104
