Vitamina C estabilizada, sí o no?

[labenplantada]

Lo siento porque está en inglés, pero de acuerdo con este estudio, las formas estabilizadas de Vit C tipo MAP, SAP, etc. no sirven para nada. Lo único que vale es hacerse una exfoliación con una solución a AA al 20% con ph inferior a 3.5 cada 4 días como máximo si queremos que la vit C haga algún efecto.

[magoo68]

labemplantada, aunque los derivados tiene menor poder de conversión a AA en la piel, sí son efectivos, mira los resultados de estos estudios:

Skin Res Technol. 2008 Aug;14(3):376-80. In vitro antioxidant activity and in vivo efficacy of topical formulations containing vitamin C and its derivatives studied by non-invasive methods. Campos PM, Gonçalves GM, Gaspar LR. Faculdade de Ciências Farmacêuticas de Ribeirão Preto, Universidade de São Paulo, São Paulo, Brazil. pmcampos@usp.br

BACKGROUND/PURPOSE: Vitamins C and its derivatives, mainly due to their antioxidant properties, are being used in cosmetic products to protect and to reduce the signs of ageing. However, there are no studies comparing the effects of vitamin C [ascorbic acid (AA)] and its derivatives, magnesium ascorbyl phosphate (MAP) and ascorbyl tetra-isopalmitate (ATIP), when vehiculated in topical formulations, mainly using objective measurements, which are an important tool in clinical efficacy studies. Thus, the objective of this study was to determine the in vitro antioxidant activity of AA and its derivatives, MAP and ATIP, as well as their in vivo efficacy on human skin, when vehiculated in topical formulations. METHODS: The study of antioxidant activity in vitro was performed with an aqueous and a lipid system. The in vivo methodology consisted of the application of these formulations on human volunteers' forearm skin and the analysis of the skin conditions after 4-week period daily applications in terms of transepidermal water loss (TEWL), stratum corneum moisture content and viscoelasticity using a Tewameter, Corneometer and Cutometer, respectively. RESULTS: In vitro experiments demonstrated that in an aqueous system, AA had the best antioxidant potential, and MAP was more effective than ATIP, whereas in the lipid system ATIP was more effective than MAP. In in vivo studies, all formulations enhanced stratum corneum moisture content after a 4-week period daily applications when compared with baseline values; however, only the formulation containing AA caused alterations in TEWL values. The formulations containing MAP caused alterations in the viscoelastic-to-elastic ratio, which suggested its action in the deeper layers of the skin. CONCLUSION: AA and its derivates presented an in vitro antioxidant activity but AA had the best antioxidant effect. In in vivo efficacy studies, only the formulation containing AA caused alterations in TEWL values and the formulation containing MAP caused alterations in the viscoelastic-to-elastic ratio. This way, vitamin C derivatives did not present the same effects of AA on human skin; however, MAP showed other significant effect-improving skin hydration, which is very important for the normal cutaneous metabolism and also to prevent skin alterations and early ageing

Photochem Photobiol. 1998 Jun;67(6):669-75. Postadministration protective effect of magnesium-L-ascorbyl-phosphate on the development of UVB-induced cutaneous damage in mice. Kobayashi S, Takehana M, Kanke M, Itoh S, Ogata E. Kyoritsu College of Pharmacy, Tokyo, Japan. kobayashi-sz@kyoritsu-ph.ac.jp

The effects of stable vitamin C, magnesium-L-ascorbyl-2-phosphate (MAP), administered after acute and chronic exposure to UVB irradiation were investigated using hairless mice. Intraperitoneal administration of 100 mg/kg of MAP immediately after acute exposure to 15 kJ/m2 of UVB significantly prevented increases of UVB-induced lipid peroxidation in skin and sialic acid in serum, an inflammation marker. Administration of 50 mg/kg of MAP immediately after each exposure significantly delayed skin tumor formation and hyperplasia induced by chronic exposure to 2 kJ/m2 of UVB. Intraperitoneal administration of 200 mg/kg of MAP produced an increase in ascorbic acid (As) levels in the serum, liver and skin within 15 min. Serum As levels quickly returned to normal, but hepatic and cutaneous levels remained elevated before returning to normal after 24 h, suggesting that MAP was converted to As in the serum and in those tissues. Ultraviolet B-induced hydroxyl radical generation in murine skin homogenates was scavenged by As-Na addition, which was directly detected by electron spin resonance (ESR). These results suggest that postadministration of MAP delays progression of skin damage induced by UVB irradiation. It is presumed that MAP, once converted to As, exhibits such inhibitory effects by scavenging hydroxyl and lipid radicals generated as a direct or indirect result of UVB exposure

Photochem Photobiol. 1996 Jul;64(1):224-8. Protective effect of magnesium-L-ascorbyl-2 phosphate against skin damage induced by UVB irradiation. Kobayashi S, Takehana M, Itoh S, Ogata E. Kyoritsu College of Pharmacy, Tokyo, Japan.

The protective effect of magnesium-L-ascorbyl-2-phosphate (MAP) on cutaneous photodamage such as lipid peroxidation and inflammation induced by ultraviolet B (UVB) exposure (290-320 nm, max. 312 nm) was investigated using hairless mice. When MAP was administered intraperitoneally to mice at a dose of 100 mg of ascorbic acid (AS) per kg body weight base immediately before irradiation (15 kj/m2), the expected increases in thiobarbituric acid reactive substance (TBARS) formation in skin and serum sialic acid, indices of lipid peroxidation and inflammatory reaction, respectively, were significantly reduced. However, the expected decrease in the level of cutaneous AS was unchanged. Similar results were observed for animals given 100 mg of AS-Na per kg body weight before UVB irradiation. When MAP was administered intracutaneously immediately before irradiation, the expected UVB-induced increases in TBARS and sialic acid were again significantly prevented. Ascorbic acid-Na had a less protective effect than intracutaneous MAP administration. The cutaneous AS level was significantly higher in the MAP-treated mice than in the controls, and the UVB-induced decrease in tissue AS was prevented by intracutaneous MAP administration. These results suggest that MAP protects against UVB irradiation-induced lipid peroxidation and inflammation in cutaneous tissue, regardless of the drug administration route. We found, in an in vitro experiment, that MAP was converted to AS as it crossed the epidermis, but that AS-Na did not pass through the epidermis. Furthermore, MAP was also converted to AS in serum. These results suggest that the protective effect of MAP on UVB-induced cutaneous damage is due to conversion of MAP to AS

J Am Acad Dermatol. 1996 Jan;34(1):29-33. Inhibitory effect of magnesium L-ascorbyl-2-phosphate (VC-PMG) on melanogenesis in vitro and in vivo. Kameyama K, Sakai C, Kondoh S, Yonemoto K, Nishiyama S, Tagawa M, Murata T, Ohnuma T, Quigley J, Dorsky A, Bucks D, Blanock K. Department of Dermatology, Kitasato University School of Medicine, Sagamihara, Japan.

BACKGROUND: An inhibitory effect of ascorbic acid (AsA) on melanogenesis has been described. However, AsA is quickly oxidized and decomposed in aqueous solution and thus is not generally useful as a depigmenting agent. OBJECTIVE: Our purpose was to examine the effect on pigmentation of magnesium-L-ascorbyl-2-phosphate (VC-PMG), a stable derivative of AsA. METHODS: Percutaneous absorption of VC-PMG was examined in dermatomed human skin, and its effect on melanin production by mammalian tyrosinase and human melanoma cells in culture was also measured. A 10% VC-PMG cream was applied to the patients. RESULTS: VC-PMG suppressed melanin formation by tyrosinase and melanoma cells. In situ experiments demonstrated that VC-PMG cream was absorbed into the epidermis and that 1.6% remained 48 hours after application. The lightening effect was significant in 19 of 34 patients with chloasma or senile freckles and in 3 of 25 patients with normal skin. CONCLUSION: VC-PMG is effective in reducing skin hyperpigmentation in some patients

Skin Pharmacol. 1993;6(1):65-71. Regulation of collagen synthesis in human dermal fibroblasts by the sodium and magnesium salts of ascorbyl-2-phosphate. Geesin JC, Gordon JS, Berg RA. Department of Biochemistry, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, Piscataway 08854.

Ascorbic acid has been shown to stimulate collagen synthesis in dermal fibroblasts by increasing the rate of transcription of collagen genes. Experiments involving the use of ascorbic acid require daily supplementation due to the instability of the molecule in aqueous solutions. In order to provide a more stable alternative to ascorbic acid, two salts of ascorbyl-2-phosphate, having a greater chemical stability than ascorbic acid, were tested for their ability to stimulate collagen synthesis in monolayer fibroblast cultures. The concentration and time dependence of their activities were compared with ascorbic acid.The magnesium salt of ascorbyl-2-phosphate was found to be equivalent to ascorbic acid in stimulating collagen synthesis in these assays, while the sodium salt required at least a tenfold greater concentration to produce the same effect as ascorbic acid. Solutions of either ascorbic acid or the ascorbyl-2-phosphate analogs (at 10 mM) in phosphate-buffered saline (PBS) were relatively stable as shown by their decay rates and their ability to stimulate collagen synthesis even after nine days in solution prior to testing their effects on cultured cells. Ascorbic acid was unstable at neutral pH compared to solutions of either sodium or magnesium ascorbyl-2-phosphate. These data support the use of magnesium ascorbyl-2-phosphate in experiments where stability of ascorbic acid is a concern, e.g. in long-term cultures or in in vivo studies

Y según esto otro, la efectividad depende de la formulación. Ahí es donde entran las sinergias, los péptidos, la súper óxido dismutasa, el resveratrol, el picnogenol, los liposomas, las ceramidas. Los agentes que ayudan a la penetración multiplican el efecto de los activos, por el lado natural el monocaprilato de glicerilo, derivado del ácido cáprico, y el propanediol, por el lado químico el isosórbido de dimetilo (DMI), el etoxidiglicol, el propolenglicol, el butilenglicol, el dietilenglicol y el sulfóxido de dimetilo (DMSO), que también son solventes.

According to the American Academy of Dermatology, Magnesium Ascorbyl Phosphate is deeply absorbed into the skin and stays in the skin's cellular layers for up to 48 hours, provided that it is properly formulated with specific liposomes and oligomers. This sustained continuous-action complex bathes both the exterior wall and the interior of the cell with active Vitamin-C. In fact, studies have shown that, when properly formulated with specific oligomers, Magnesium Ascorbyl Phosphate is the only form of Vitamin-C that simultaneously penetrates the cell wall and coats the exterior of the cell, while remaining both stable and bioavailable for a prolonged period of time. With effective penetration occurring at a relatively neutral pH of approximately 5, Magnesium Ascorbyl Phosphate is gentle on the skin and does not cause any inflammation or associated skin aging.

[labenplantada]

... pues habrá que agregar un poco de propylene glycol junto con el MAP. Lo que me pregunto es si para producción de colágeno también hay que usar MAP al 10%. Los estudios que mencionan esa concentración sólo hablan de blanquear la piel.