Skin treatment composition

Abstract: Skin treatment compositions containing a system for enhancing sphingolipid production in skin containing N-acetyl-L-cysteine and an alpha hydroxy acid (or a salt, or an ester thereof).

Description: The invention relates to skin treatment compositions containing L-lactic acid or a salt thereof in combination with N-acetyl-L-cysteine, and the cosmetic use of these compositions for enhancing lipid biosynthesis in mammalian skin. BACKGROUND OF THE INVENTION: Layers of lipids in stratum corneum of the skin form a "water barrier" which prevents water loss from the skin. Known classes of stratum corneum lipids include sphingolipids, free fatty acids, sterols and sterol esters, and phospholipids, with sphingolipids being a major component. Sphingolipids, in turn, consist of four major classes of lipids: glycosphingolipids, ceramides, sphingomyelin and total sphingoid base. Ceramides and other sphingolipids play a major role in promoting cell differentiation and, thus, preventing, reducing, or eliminating skin dryness and wrinkles. Although several species of natural ceramides have been identified, these ceramides must be obtained through a lengthy process involving the extraction of ceramides from natural sources. Thus, the availability of natural ceramides is limited and their cost is very high. Several analogs of natural ceramides, known as pseudoceramides, have been synthesized. Pseudoceramides look similar but are not identical to ceramides. Unfortunately, pseudoceramides are still expensive, albeit not as expensive as natural ceramides. Recent work has shown the ability of cultured keratinocytes to synthesize sphingolipids. Due to the high cost of natural or synthetic sphingolipids, cosmetic compositions which can enhance biosynthesis of sphingolipids are desirable, in order to minimize or eliminate the need for exogenous application of sphingolipids. Skin treatment compositions are known which contain alpha hydroxy acids as ingredients for improving the appearance of dry, flaky, wrinkled, aged, photodamaged skin and for treating various disorders of skin, e.g., hyperkeratosis, ichthyosis, skin blemishes, acne, warts, herpes, psoriasis, eczema, pruritis. PCT application WO 93/04669 discloses compositions containing N-acetyl-L-cysteine or derivatives thereof. The compositions are said to efface and prevent wrinkles in mammalian skin. PCT Application WO 93/10755 discloses compositions containing salicylic acid as an essential ingredient in combination with an additional active component, which may be a N-acetyl-L-cysteine derivative. Many optional ingredients are disclosed, among which alpha hydroxy acids or derivatives thereof are mentioned. The compositions are said to regulate wrinkles and/or atrophy in mammalian skin. European patent application 0 280 606 discloses an antioxidant cosmetic composition comprising an ester of ascorbic acid, a complexing agent and N-acetyl cysteine. The art discussed above does not address the need for increasing sphingolipid biosynthesis in skin and does not envision skin treatment compositions based on a specific lipid biosynthesis enhancing system of N-acetyl-L-cysteine and L-lactic acid according to the present invention. The art does not teach or suggest that N-acetyl-L-cysteine is capable of enhancing lipid biosynthesis or that L-lactic acid further compliment the action of N-acetyl-L-cysteine. It was found, as part of the present invention, that compositions according to the PCT application 93/10755 do not attain a statistically significant increase in lipid biosynthesis. Accordingly, it is an object of the present invention to provide skin treatment compositions for increasing sphingolipid biosynthesis in mammalian skin. It is another object of the invention to provide a composition for improving skin condition by improving water barrier performance. It is another object of the present invention to provide compositions containing N-acetyl-L-cysteine and L-lactic acid as an active system capable of increasing sphingolipid biosynthesis in mammalian skin, while tailoring the rest of the composition so as to minimize or substantially eliminate any blocking effect on the active system. These and other objects of the invention will become more apparent from the detailed description and examples that follow. SUMMARY OF THE INVENTION: The above objects are attained by the present invention which includes, in part, a skin treatment composition containing (i) a sphingolipid biosynthesis enhancing system consisting essentially of: a) from 0.001% to 20% by weight of the composition of L-lactic acid or a salt thereof; and, b) from 0.001 to 20% by weight of N-acetyl-L-cysteine, and (ii) a cosmetically acceptable vehicle for the sphingolipid biosynthesis enhancing system; wherein the composition is free of salicylic acid. The invention is based, in part, on the discovery that a specific combination of actives enhances sphingolipid biosynthesis in skin. Although exogenously introduced N-acetyl-L-cysteine enhances sphingolipid biosynthesis even when used alone, L-lactic acid, as keratinocyte proliferation agent, compliment the action of N-acetyl-L-cysteine by providing more cells for N-acetyl-L-cysteine to act on. The invention also contains a discovery that salicylic acid blocks the beneficial effect on sphingolipid biosynthesis of the binary mixture of N-acetyl-L-cysteine (NAC) and L-lactic acid. Thus, according to the present invention, skin treatment compositions for the enhancement of lipid biosynthesis must be carefully tailored: the absence of salicylic acid in the inventive compositions is as critical as the presence of the lipid biosynthesis enhancement system, since if salicylic acid is present, the sphingolipid biosynthesis enhancing effect is substantially reduced or entirely obliterated. The amount of L-lactic acid is important in order to attain the lipid biosynthesis enhancement: if too little L-lactic acid is used, no significant improvement may be attained over the action of N-acetyl-L-cysteine alone. According to the present invention, by virtue of including an effective amount of L-lactic acid into N-acetyl-L-cysteine containing compositions, and by virtue of avoiding the blocking effect of salicylic acid the performance of the compositions is substantially improved. The inventive compositions include L-isomers of lactic acid. A further advantage of the present compositions is that lower levels of ceramides and/or other sphingolipids may be included in the composition containing sphingolipid biosynthesis enhancing system of the present invention to equal the performance of a similar formulation without the inventive system in order to minimize the cost of compositions. The present invention also includes the use of an active system based on a specific combination of L-lactic acid and N-acetyl-L-cysteine in skin care compositions for improving or preventing the appearance of wrinkled, flaky, aged, photodamaged skin and treating skin disorders. Compositions of the invention are intended for topical application to mammalian skin which is already in dry, flaky, wrinkled, aged, photodamaged condition or which suffers from a skin disorder, or, in the alternative, the inventive compositions may be applied prophylactically to normal healthy skin to prevent or reduce dryness and the deteriorative changes. DETAILED DESCRIPTION OF THE INVENTION: The first essential ingredient of the inventive composition is selected from the group consisting of L-lactic acid or a salt thereof. All the above listed suitable ingredients are collectively termed herein "alpha hydroxy acid." The alpha hydroxy acid (AHA) has the following structure: R 2 CHOHCOOR 1 wherein R 1 is H and R 2 is methyl. The alpha hydroxy acid may be present as a free acid or in a salt form with an organic base or an inorganic alkali. L stereoisomeric forms of lactic acid are employed in the inventive compositions. Suitable salts of L-lactic acid include but are not limited to sodium, potassium, ammonium, triethanolamine, calcium, lithium salts. The salts may be obtained commercially or they may be prepared by methods known in the art, e.g., neutralizing L-lactic acid with a suitable base, such as hydroxide bases of ammonium, potassium, sodium. It has been found, as part of the present invention, that an L-form of lactic acid is superior to the D-form of lactic acid. Preferred compositions according to the invention contain at least 60% of lactic acid in L-configuration, by weight of total alpha hydroxy acid. Preferably, in order to attain optimum performance, the inventive compositions contain from 60% to more than 99%, most preferably more than 99% of lactic acid by weight of total hydroxy acids in the composition is in the L-form. The total amount of L-lactic acid in the inventive compositions ranges from 0.001% to 20%, preferably from 0.1% to 15% by weight of the composition, in order to attain maximum performance at optimal cost. In general, the more active is L-lactic acid in promoting keratinocyte proliferation, the less of it may be required to enhance the action of N-acetyl-L-cysteine. Preferably, in order to attain a substantial benefit from the presence of N-acetyl-cysteine, the total concentration of L-lactic acid in the inventive compositions is at least 1-5% by weight of the composition. The second essential ingredient of inventive compositions is N-acetyl-L-cysteine ("NAC") of Formula I: NAC is employed in the inventive compositions in the amount effective to enhance lipid biosynthesis. Generally, the amount is in the range of from 0.001% to 20%. The precise amount will depend on the particular alpha hydroxy acid included in the inventive compositions. Preferably, the amount is in the range of from 0.1 % to 10% by weight of the composition, most preferably in the range of from 0.1% to 5% to attain maximum performance at optimal cost. The ratio of NAC to L-lactic acid is such as to obtain a complimentary action of AHA and NAC. The ratio of L-lactic acid to NAC is generally in the range of from 1:100 to 100:1, preferably 1:5 to 5:1. The inventive compositions are free of salicylic acid. The absence of salicylic acid is critical in order to attain the sphingolipid biosynthesis enhancing benefit in the inventive compositions. Salicylic acid when used alone does not promote sphingolipid biosynthesis. When added to the sphingolipid biosynthesis enhancing system, salicylic acid substantially inhibits or eliminates the effect of the lipid biosynthesis enhancing system of the present invention. In this respect, it may be said that the inventive compositions consist essentially of the sphingolipid biosynthesis enhancing system as described above. The term "consists essentially of" means that the composition may include additional ingredients, but only if the additional ingredients do not materially alter the basic and novel characteristics of the claimed composition. The "consisting essentially of" language excludes the presence of salicylic acid. The skin treatment composition of the invention also includes a therapeutically acceptable vehicle or a carrier which is inert, usually an ingredient present in highest amounts, and functioning to deliver active or performance ingredients. The amount of vehicle may range from about 2 to about 99%, preferably from about 5 to about 80%, most preferably from about 25 to 80%, by weight of the total compositions. Surfactants, which are also sometimes designated as emulsifiers, may be incorporated into the cosmetic compositions of the present invention. Surfactants can comprise anywhere from about 0.5 to about 30%, preferably from about 1 to about 15% by weight of the total composition. Surfactants may be cationic, nonionic, anionic, or amphoteric in nature and combinations thereof may be employed. Illustrative of the nonionic surfactants are alkoxylated compounds based upon fatty alcohols, fatty acids and sorbitan. These materials are available, for instance, from the Shell Chemical Company under the "Neodol" designation. Copolymers of polyoxypropylene-polyoxyethylene, available under the Pluronic trademark sold by the BASF Corporation, are sometimes also useful. Alkyl polyglycosides available from the Henkel Corporation similarly can be utilized for the purposes of this invention. Anionic-type surfactants may include fatty acid soaps (polyglyceryl oleates), sodium lauryl sulphate, sodium lauryl ether sulphate, alkyl benzene sulphonate, mono and dialkyl acid phosphates and sodium fatty acyl isethionate. Amphoteric surfactants include such materials as dialkylamine oxide and various types of betaines (such as cocoamido propyl betaine). Emollients are often incorporated into cosmetic compositions of the present invention. Levels of such emollients may range from about 0.5 to about 50%, preferably between about 5 and 30% by weight of the total composition. Emollients may be classified under such general chemical categories as esters, fatty acids and alcohols, polyols and hydrocarbons. Esters may be mono- or di-esters. Acceptable examples of fatty di-esters include dibutyl adipate, diethyl sebacate, diisopropyl dimerate, and dioctyl succinate. Acceptable branched chain fatty esters include isostearyl neopentanoate, 2-ethyl-hexyl myristate, isopropyl stearate and isostearyl palmitate. Acceptable tribasic acid esters include triisopropyl trilinoleate and trilauryl citrate. Acceptable straight chain fatty esters include cetyl octanoate lauryl palmitate, myristyl lactate, oleyl erucate and stearyl oleate. Preferred esters include coco-caprylate/caprate (a blend of coco-caprylate and coco-caprate), propylene glycol myristyl ether acetate, diisopropyl adipate and cetyl octanoate. Suitable fatty alcohols and acids include those compounds having from 10 to 20 carbon atoms. Especially preferred are such compounds such as cetyl, myristyl, palmitic and stearyl alcohols and acids. Among the polyols which may serve as emollients are linear and branched chain alkyl polyhydroxyl compounds. For example, propylene glycol, sorbitol and glycerin are preferred. Also useful may be polymeric polyols such as polypropylene glycol and polyethylene glycol. Exemplary hydrocarbons which may serve as emollients are those having hydrocarbon chains anywhere from 12 to 30 carbon atoms. Specific examples include mineral oil, petroleum jelly, squalene and isoparaffins. Another category of functional ingredients within the cosmetic compositions of the present invention are thickeners. A thickener will usually be present in amounts anywhere from 0.1 to 20% by weight, preferably from about 0.5 to 10% by weight of the composition. Exemplary thickeners are cross-linked polyacrylate materials available under the trademark Carbopol from the B.F. Goodrich Company. Gums may be employed such as xanthan, carrageenan, gelatin, karaya, pectin and locust beans gum. Under certain circumstances, the thickening function may be accomplished by a material also serving as a silicone or emollient. For instance, silicone gums in excess of 10 centistokes and esters such as glycerol stearate have dual functionality. Various types of active ingredients may be present in cosmetic compositions of the present invention. Actives are defined as skin benefit agents other than emollients and other than ingredients that merely improve the physical characteristics of the composition. Although not limited to this category, general examples include sunscreens, tanning agents, other skin anti-wrinkling agents, and anti-acne agents. Ceramides and/or other sphingolipids may be included in the inventive composition, although inventive compositions enhance the sphingolipid (including ceramide) biosynthesis in skin. Suitable ceramides and synthetic analogues thereof are disclosed in European Patent Application 534 286, European Patent Application 227 994, U.S. Patent 5,175,321, U.S. Patent 4,985,547, U.S. Patent 5,028,416, U.S. Patent 5,071,971, Japanese Patent Application 63192703, U.S. Patent 4,468,519, and U.S. Patent 4,950,688. Sphingolipids, including ceramides or their synthetic analogues, may be present in the inventive compositions at a level of from about 0.00001 to about 5%, preferably from about 0.0001 to about 1%, optimally from about .01 to .5%. Sunscreens include those materials commonly employed to block ultraviolet light. Illustrative compounds are the derivatives of PABA, cinnamate and salicylate. For example, octyl methoxycinnamate and 2-hydroxy-4-methoxy benzophenone (also known as oxybenzone) can be used. Octyl methoxycinnamate and 2-hydroxy-4-methoxy benzophenone are commercially available under the trademarks, Parsol MCX and Benzophenone-3, respectively. The exact amount of sunscreen employed in the emulsions can vary depending upon the degree of protection desired from the sun's UV radiation. Many cosmetic compositions, especially those containing water, must be protected against the growth of potentially harmful microorganisms. Preservatives are, therefore, necessary. Suitable preservatives include alkyl esters of p-hydroxybenzoic acid, hydantoin derivatives, propionate salts, and a variety of quaternary ammonium compounds. Particularly preferred preservatives of this invention are methyl paraben, propyl paraben, imidazolidinyl urea, sodium dehydroxyacetate and benzyl alcohol. Preservatives will usually be employed in amounts ranging from about 0.5% to 2% by weight of the composition. Other adjunct minor components may also be incorporated into the cosmetic compositions. These ingredients may include coloring agents, opacifiers and perfumes. Amounts of these materials may range anywhere from 0.001 up to 20% by weight of the composition. The composition according to the invention is intended primarily as a product for topical application to human skin, especially as an agent for reducing the permeability to water of the skin, particularly when the skin is dry or damaged, in order to reduce moisture loss and generally to enhance the quality and flexibility of skin. In particular, the composition can be used to cleanse the skin to In use, a small quantity of the composition, for example from 1 to 5ml, is applied to exposed areas of the skin, from a suitable container or applicator and, if necessary, it is then spread over and/or rubbed into the skin using the hand or fingers or a suitable device. The topical skin treatment composition of the invention can be formulated as a lotion having a viscosity of from 4,000 to 10,000 mPas, a fluid cream having a viscosity of from 10,000 to 20,000 mPas or a cream having a viscosity of from 20,000 to 100,000 mPas or above. The composition can be packaged in a suitable container to suit its viscosity and intended use by the consumer. For example, a lotion or fluid cream can be packaged in a bottle or a roll-ball applicator or a propellant-driven aerosol device or a container fitted with a pump suitable for finger operation. When the composition is a cream, it can simply be stored in a non-deformable bottle or squeeze container, such as a tube or a lidded jar. The following specific examples further illustrate the invention, but the invention is not limited thereto. EXAMPLES EXAMPLE 1 Effect of Alpha Hydroxy Acids on Keratinocyte Proliferation Keratinocyte proliferation (which is indicative of skin thickness and skin proliferative capacity) decreases with age. Thus, the increase in keratinocyte proliferation is beneficial to counteract skin aging (i.e., wrinkles, thickness, elasticity, and repair). According to the present invention, increased proliferation is beneficial because it provides more cells for N-acetyl-L-cysteine to act on to induce sphingolipid biosynthesis, resulting in enhanced sphingolipid biosynthesis. Human keratinocytes were seeded at a relatively low density in wells of microtiter plates. The next day, cells were treated with various concentrations of a specific alpha hydroxy acid in keratinocyte basal medium containing 0.15 mM calcium. After 4 days of treatment the media was removed and the cells were lysed by repeated freeze thawing. The number of keratinocytes were determined by a fluorescent dye which binds to the cell's DNA. The amount of fluorescense is directly proportional to the number of cells present. Control cells were analyzed in the absence of any alpha hydroxy acids. The results that were obtained are summarized in Table 1 and indicate the response of the most effective concentration tested. The data in Table 1 indicates that L-lactic acid and other alpha hydroxy acids promote keratinocyte proliferation, and that the L-form of alpha hydroxy acid is significantly superior to the D-form in eliciting keratinocyte proliferation. Furthermore, dicarboxylic alpha hydroxy acids (i.e., L-tartaric, L-malic) are more potent promoters of proliferation than mono alpha hydroxy acids (i.e., citric, glycolic, lactic). EXAMPLE 2 N-acetyl-L-cysteine, salicylic acid and DL-lactic acid are purchased from Sigma Chemical Co., St. Louis, MO. Stock solutions of NAC, salicylic acid and lactic acid were made at 1.0M and pH adjusted to 7.0. Stock solutions were diluted into culture medium to the designated concentrations before the treatment. Keratinocyte culture medium is from GIBCO BRL. Grand Island, NY. 14 C-acetate is from DuPont NEN Research Products. Boston, MA. Human keratinocytes were cultured in GIBCO Keratinocyte-SFM (serum-free keratinocyte medium containing 0.09 mM calcium chloride), 37°C, 5% CO 2 to confluent, treated with two components (lactic acid, and NAC), and three components (Salicylic acid, lactic acid, and NAC) for 24 hours, respectively. The concentrations of chemicals used in this experiment were, salicylic acid, 0.5 mM; lactic acid, 0.5 mM; and NAC, 2.0 mM. 14 C-acetate (10 µ Ci/ml) was used to label epidermal lipids synthesized during the period of treatment. At the end of the incubation, cells were harvested and lipids were extracted using Bligh/Dyer method and subject to analysis on a standard TLC plate. The separated lipids on the plates were then quantified by Bioscan, system 200 imaging scanner. Specific epidermal lipids were identified by comparing with the lipid standards after charing of the plate. The results that were obtained are summarized in Table 2. The results in table 2 indicate that 13% of increase in ceramides biosynthesis was induced by the 24 hours period of treatment with the two components (lactic acid and NAC) within the scope of the invention as compared to the control. Almost no effect on ceramides level increase was observed from the three component treatment, which is not within the scope of the invention. The results indicate that combination of lactic acid and NAC stimulated keratinocyte ceramides biosynthesis at a substantially higher level as compared to the three component system. EXAMPLE 3 This example illustrates an oil-in-water cream incorporating the inventive composition. EXAMPLE 4 This example illustrates a suncare cream incorporating the lipid enhancement system of the invention: Accordingly, reference should be made to the following appended claims in determining the full scope of the invention.

Claims: A skin treatment composition comprising (i) a sphingolipid biosynthesis enhancing system consisting essentially of: a) from 0.001% to 20% by weight of the composition of L-lactic acid or a salt thereof; and b) from 0.001 to 20% by weight of the composition of N-acetyl-L-cysteine; and, (ii) a cosmetically acceptable vehicle for the sphingolipid biosynthesis enhancing system; wherein the composition is free of salicylic acid. The composition according to claim 1 wherein the amount of ingredient (b) is at least 0.1% by weight of the composition. The composition according to any preceding claim wherein the weight ratio of (a) to (b) is in the range of from 1:100 to 100:1. Use cosmetic of L-lactic acid and N-acetyl-L-cysteine in skin care compositions for enhancing lipid biosynthesis in skin. Use cosmetic of L-lactic acid and N-acetyl-L-cysteine in skin care compositions for improving or preventing the appearance of wrinkled, flaky, aged, photodamaged skin and treating skin disorders.

Inventors: BARTOLONE JOHN, KOSTURKO RICHARD, RAWLINGS ANTHONY VINCENT, ZHANG KELLY HUA, BARTOLONE, JOHN, KOSTURKO, RICHARD, RAWLINGS, ANTHONY VINCENT, ZHANG, KELLY HUA
Applicants: UNILEVER NV, UNILEVER PLC, UNILEVER N.V.
Application year: 1995
Main classification: A61K7
IPC codes: A61K31, A61Q5, A61Q19, A61K8, A61P17, A61P43