Cosmetic Composition

The present invention relates to compositions for topical application to human skin and their cosmetic use. In particular, the invention relates to compositions of use in promoting the repair of photo-damaged skin and/or to reduce or prevent the damaging effects of ultra-violet light on skin and/or to lighten the skin. Compositions according to the invention are also of use in the treatment of aged skin.

Problems of hyperpigmentation of skin occur in many situations, including unwelcome general darkening of the skin due to exposure to ultra-violet (UV) light, to genetic makeup, to hyperpigmentation associated with wounds, to age including the appearance of so called `age spots` and to other factors. There is clearly a need for a safe and effective technique to reduce the degree of pigmentation of the skin in such cases.

Existing methods for reducing skin pigmentation generally involve either killing or damaging the cells which produce the pigment (the melanocytes) for example with hydroquinone or by inhibiting the enzyme, tyrosinase, which catalyses a key step in pigment synthesis for example with kojic acid, ascorbic acid, azelaic acid or catechol and derivatives.

JP 04/235112 (TAC Gijutsu Kagaku Kenkyusho) discloses a tyrosinase inhibitor comprising an active compound of the general formula ##STR2## wherein each of R.sub.A is hydrogen or a glucose residue and R.sub.B is hydrogen or the group ##STR3## with the proviso that at least one of the R.sub.A groups is hydrogen, however all of the R.sub.A and R.sub.B groups may not be hydrogen.

It is stated that this tyrosinase inhibitor is useful as skin whitening agent for cosmetics and also an agent for preventing darkening of foods.

We have now discovered that specified hydrochalcone structures, in particular dihydrophloretins are capable of suppressing melanin formation in vitro in cultured melanoma cells by a mechanism which involves competitive inhibition of the enzyme tyrosinase. They also have the capacity to act as an antioxidant, so reducing the damaging effects from UV radiation.

Accordingly the invention provides a composition suitable for the topical application to mammalian skin comprising a hydrocalchone of formula (I) ##STR4## wherein

R.sub.1, R.sub.2 and R.sub.3, which may be the same or different, represent H, --OH, --OR or --COR (where R is a C.sub.1-20 alkyl group);

R.sub.4, R.sub.5, R.sub.6 and R.sub.7, which may be the same or different, represent H or --COR (where R is a C.sub.1-20 alkyl group).

As used herein, a C.sub.1-20 alkyl group may be straight or branched chain and is conveniently C.sub.1-6, preferably C.sub.1-4 alkyl for example methyl. An alkoxy group is conveniently methoxy or ethoxy. A carboxyalkyl group is conveniently acetoxy.

A preferred class of compounds of formula (I) for use according to the invention has the formula (Ia) ##STR5## wherein R.sub.1, R.sub.2 and R.sub.3 are as defined herein for formula (I).

In a further preferred class of compounds of formula (I), R.sub.1 represents H or --OH.

R.sub.2 and R.sub.3 preferably represent H.

R.sub.4, R.sub.5, R.sub.6 and R.sub.7 preferably represent H.

Preferred hydrochalcones for use according to the invention include: .alpha.-deoxyphloretin (R.sub.1 -R.sub.7 =H).

A particularly preferred hydrochalcone is dihydrophloretin of formula (II). ##STR6##

It will be appreciated that compositions according to the present invention may suitably comprise two or more hydrochalcones of formula (I).

Conveniently the amount of hydrochalcone present in the composition according to the invention is from 0.001 to 20%, preferably from 0.01 to 5%, even more preferably from 0.1 to 2% by weight of the composition.

Compounds of formula (I) are either known compounds or may conveniently be prepared from known compounds by methods conventional in the art.

Dihydrophloretin may conveniently be prepared from phloretin (available from Sigma) using one of the following routes:

(a) Phloretin (25 mg) is dissolved in the minimum amount of methanol, diluted with water (3 ml) and treated with a slight excess of NaBH.sub.4. After 5 minutes the solution is carefully acidified, with ethyl acetate. The Organic phase is dried over Na.sub.2 SO.sub.4 and evaporated to dryness to give 17 mg of dihydrophloretin as white powder, homogeneous on TLC analysis (silica gel, CHCl.sub.3 /MeOH/H.sub.2 O 70:28:2).

(b) A solution of phloretin (1 g) in 80% ethanol (20 ml) containing 50 mg of 5% palladium on carbon is stirred under a hydrogen atmosphere. After 6 hrs the mixture is filtered, and the filtrate is concentrated under vacuo to give dihydrophloretin in about 90% yield.

Preferably compositions according to the invention additionally comprise a cosmetically acceptable vehicle to act as a diluent, dispersant or carrier for other materials present in the composition, so as to facilitate their distribution when the composition is applied to the skin.

Vehicles other than water can include liquid or solid emollients, solvents, humectants, thickeners and powders. Examples of each of these types of vehicle, which can be used singly or as mixtures of one or more vehicles, are as follows:

Emollients, such as stearyl alcohol, glyceryl monoricinoleate, mink oil, cetyl alcohol, isopropyl isostearate, stearic acid, isobutyl palmirate, isocetyl stearate, oleyl alcohol, isopropyl laurate, hexyl laurate, decyl oleate, octadecan-2-ol, isocetyl alcohol, eicosanyl alcohol, behenyl alcohol, cetyl palmitate, silicone oils such as dimethylpolysiloxane, di-n-butyl sebacate, isopropyl myristate, isopropyl palmitate, isopropyl stearate, butyl stearate, polyethylene glycol, triethylene glycol, lanolin, cocoa butter, corn oil, cotton seed oil, olive oil, palm kernel oil, rapeseed oil, safflower seed oil, evening primrose oil, soybean oil, sunflower seed oil, avocado oil, sesame seed oil, coconut oil, arachis oil, castor oil, acetylated lanolin alcohols, petroleum jelly, mineral oil, butyl myristate, isostearic acid, palmitic acid, isopropyl linoleate, lauryl lactate, myristyl lactate, decyl oleate, myristyl myristate;

Propellants, such as air, propane, butane, isobutane, dimethyl ether, carbon dioxide, nitrous oxide;

Solvents, such as ethyl alcohol, isopropanol, acetone, ethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether;

Powders, such as chalk, talc, fuller's earth, kaolin, starch, gums, colloidal silica sodium polyacrylate, tetra alkyl and/or trialkyl aryl ammonium smectites, chemically modified magnesium aluminium silicate, organically modified montmorillonite clay, hydrated aluminium silicate, fumed silica, carboxyvinyl polymer, sodium carboxymethyl cellulose, ethylene glycol monostearate.

The cosmetically acceptable vehicle will usually form from 10 to 99.9%, preferably from 50 to 99% by weight of the emulsion, and can, in the absence of other cosmetic adjuncts, form the balance of the emulsion.

The composition of the invention optionally can comprise an organic sunscreen further to enhance the benefit of the composition in providing protection from the harmful effects of excessive exposure to sunlight.

Examples of suitable organic sunscreens, when required, include those set out in Table 1 below, and mixtures thereof.

The composition of the invention can accordingly comprise from 0.1 to 10%, preferably from 1 to 5% by weight of an organic sunscreen material.

The composition according to the invention optionally can also comprise as a sunscreen ultrafine titanium dioxide in either of two forms, namely water-dispersible titanium dioxide and oil-dispersible titanium dioxide.

Water-dispersible titanium dioxide is ultrafine titanium dioxide, the particles of which are uncoated or which are coated with a material to impart a hydrophilic surface property to the particles. Examples of such materials include aluminium oxide and aluminium silicate.

Oil-dispersible titanium dioxide is ultrafine titanium dioxide, the particles of which exhibit a hydrophobic surface property, and which, for this purpose, can be coated with metal soaps such as aluminium stearate, aluminium laurate or zinc stearate, or with organosilicone compounds.

By "ultrafine titanium dioxide" is meant particles of titanium dioxide having an average particle size of less than 100 nm, preferably from 10 to 40 nm and most preferably from 15 to 25 nm.

By topical application to the skin of a mixture of both water-dispersible ultrafine titanium dioxide and oil-dispersible ultrafine titanium dioxide, synergically enhanced protection of the skin against the harmful effects of both UV-A and UV-B rays is achievable.

It is believed that this unexpected benefit is due to the deposition of each type of titanium dioxide on different regions of the skin surface, water-dispersible titanium dioxide being preferentially retained by hydrophilic regions of the skin's surface, while oil-dispersible titanium dioxide is retained preferentially by hydrophobic regions of the skin's surface. The combined overall effect is that more efficient physical coverage of the skin's surface is attainable and this can be demonstrated by measurement of the Sun Protection Factor (SPF).

In order to achieve the enhanced, synergistic benefit, as herein described, the weight ratio of water-dispersible titanium dioxide to oil-dispersible titanium dioxide should be from 1:4 to 4:1, preferably from 1:2 to 2:1 and ideally about equal weight proportions.

The total amount of titanium dioxide that can optionally can be incorporated in the composition according to the invention is from 1 to 25%, preferably from 2 to 10% and ideally from 3 to 7% by weight of the composition.

The compositions of the invention optionally can comprise an inorganic sunscreen in addition to ultrafine titanium dioxide as herein defined.

Examples of other inorganic sunscreens include:

zinc oxide, having an average particle size of from 1 to 300 nm,

iron oxide, having an average particle size of from 1 to 300 nm,

silica, such as fumed silica, having an average particle size of from 1 to 100 nm.

It should be noted that silica, when used as an ingredient in the emulsion according to the invention can provide protection from infra-red radiation.

Compositions according to the invention may also optionally comprise other skin whitening agents.

Examples of skin-lightening agents include:

L-ascorbic acid, and derivatives thereof

Kojic acid, and derivatives thereof

Hydroquinone and derivatives thereof

Extract of placenta

Arbutin

dioic acids, especially C.sub.6-22 dioic acids

.alpha. hydroxy acids, such as lactic, malic, tartaric, hydroxycaprylic, citric acids

phloretin

phloridzin

liquorice extract

cysteaminylphenol and derivatives thereof

Niacin

Niacinamide, and

Compounds having the structure (III) ##STR7## where R.sub.8 represents H, or an ether group represented by OR.sub.10,

R.sub.9 and R.sub.10 are the same or different and each represents a group chosen from branched or unbranched alkyl or alkenyl groups having up to 20 carbon atoms.

In a preferred aspect, the composition according to the invention may additionally comprise retinol or a derivative thereof having the structure (IV) ##STR8## where X represents H or --COR.sub.11 where R.sub.11 represents a group chosen from branched or unbranched, alkyl or alkenyl groups having up to 20 carbon atoms.

In addition to retinol itself, examples of derivatives of retinol include:

Retinyl acetate

Retinyl butyrate

Retinyl propionate

Retinyl octanoate

Retinyl laurate

Retinyl palmitate

Retinyl oleate

Retinyl linoleate

The amount of retinol, or a derivative thereof, present in the composition according to the invention is from 0,001 to 10% and preferably 0,005 to 1% by weight of the composition, most preferably 0.01 to 0.5% by weight of the composition.

Preferably the composition comprises retinol, most preferable the composition comprises the trans-isomer of retinol.

A particularly convenient form of the composition according to the invention is an emulsion, in which case an oil or oily material will normally be present, together with an emulsifier to provide either a water-in-oil emulsion or an oil-in-water emulsion, depending largely on the average hydrophilic-lipophilic balance (HLB) of the emulsifier employed.

The composition according to the invention can optionally comprise one or more oils or other materials having the properties of an oil.

Examples of suitable oils include mineral oil and vegetable oils, and oil materials, such as those already proposed herein as emollients. Other oils or oily materials include silicone oils, both volatile and non-volatile, such as polydimethyl siloxanes.

The oil or oily material, when present for the purposes for forming an emulsion, will normally form up to 90%, preferably from 10 to 80% by volume of the composition.

The composition according to the invention can also optionally comprise one or more emulsifiers the choice of which will normally determine whether a water-in-oil or and oil-in-water emulsion is formed.

When a water-in-oil emulsion is required, the chosen emulsifier or emulsifiers should normally have an average HLB value of from 1 to 6. When an oil-in-water emulsion is required, a chosen emulsifier or emulsifiers should have an average HLB value of >6.

Examples of suitable emulsifiers are set below in Table 2 in which the chemical name of the emulsifiers is given together with an example of a trade name as commercially available, and the average HLB value.

The foregoing list of emulsifiers is not intended to be limiting and merely exemplifies selected emulsifiers which are suitable for use in accordance with the invention.

It is to be understood that two or more emulsifiers can be employed if desired.

The amount of emulsifier or mixtures thereof, that optionally can be incorporated in the composition of the invention is from 1 to 50%, preferably from 2 to 20% and most preferably from 2 to 10% by weight of the composition.

The composition of the invention can also comprise water, usually up to 80%, preferably from 5 to 80% by volume.

Emulsifiers or surfactants in the form of silicone polymers may be incorporated into compositions of the invention in place of or in addition to the optional emulsifier(s) already mentioned.

Suitable silicone surfactants are high molecular weight polymers, particularly of dimethyl polysiloxane with polyoxyethylene and/or polyoxypropylene side chains having a molecular weight of from 10,000 to 50,000.

The dimethyl polysiloxane polymer is conveniently provided as a dispersion in a volatile siloxane, the dispersion comprising, for example, from 1 to 20% by volume of the polymer and from 80 to 99% by volume of the volatile siloxane. Ideally, the dispersion consists of a 10% by volume of the polymer dispersed in the volatile siloxane.

Examples of the volatile siloxanes in which the polysiloxane polymer can be dispersed include polydimethyl siloxane (pentamer and/or hexamer).

A particularly preferred silicone surfactant is cyclomethicone and dimethicone copolyol, such as DC 3225C Formulation Aid available from DOW CORNING. Another is laurylmethicone copolyol, such as DC Q2-5200, also available from Dow Corning.

The amount of silicone surfactant, when present in the composition will normally be up to 25%, preferably from 0.5 to 15% by weight of the emulsion.

Examples of conventional adjuncts which can optionally be employed include preservatives, such as para-hydroxy benzoate esters; antioxidants, such butylated hydroxytoluene; humectants, such as glycerol, sorbitol, 2-pyrrolidone-5-carboxylic acid, dibutylphthalate, gelatin, polyethylene glycol, such as PEG 200-600; buffers, such as lactic acid together with a base such as triethanolamine or sodium hydroxide; waxes, such as beeswax, ozokerite wax, paraffin wax; plant extracts, such as aloe vera, cornflower, witch hazel, elderflower, cucumber; thickeners; activity enhancers; colourants; and perfumes. Cosmetic adjuncts can form the balance of the composition.

The composition according to the invention is intended primarily as a skin-care product for topical application to human skin to repair photo-damaged skin and to prevent photo-damage to skin due to exposure to sunlight. In particular, the composition can be used to reduce skin blotchiness and mottling due to hyperpigmentation, to improve skin texture with reductions in fine wrinkling and otherwise to improve skin colour. In general, the composition, when topically applied to skin, is useful in the prevention and or treatment of actinic damage to all skin cells.

Accordingly, the invention provides the cosmetic use of a composition comprising a hydrochalcone having the general structure (I) as hereinbefore defined.

In an alternative aspect the invention provides the use of a composition comprising a hydrochalcone of formula (I) in the manufacture of a medicament for treating skin.

The invention further provides a method of treating skin comprising topically administering thereto a composition comprising a hydrocalchone having the general structure (I).

The compositions according to the invention may be formulated in conventional manner using one or more cosmetically and/or pharmaceutically acceptable carriers or excipients.

Test method--In vitro melanocyte cell culture

Pigment producing cells derived from a mammalian melanoma are grown in culture by standard methods. Preferred cell lines are B16 or S-91 cells, but other lines or primary mouse or human melanocytes can be used.

Melanoma cells are grown in cell culture medium such as RPMI 1640 (GIBCO) supplemented with fetal calf serum and glutamine to approximately 1/3 confluence. The active is dissolved in culture medium, the pH adjusted as required and sterile filtered. The solution is then added to the cells.

The cells are cultured for a further period of 4 days and the amount of melanin produced assayed by measuring the absorbance at 540 nm of the melanin released into the medium.

Cell viability in the presence of the inhibitor is tested using neutral red (3-amino-7-dimethylamino-2-methyl phenazine hydrochloride) a water soluble vital dye which passes through the intact plasma membrane and becomes concentrated in lysosomes of viable cells. For any culture, the amount of dye taken up is proportional to the number of viable cells and agents that damage cell and lysosomal membranes inhibit dye incorporation.

The cells are incubated in 50 .mu.g/ml neutral red solution for 3 hours at 37.degree. C. in 5% CO.sub.2 in air. The solution is aspirated, the cells washed once in saline and to them added a solvent (50% H.sub.2 O, 49% ethanol, 1% acetic acid) to solubilise the dye. The amount of neutral red dye is quantified by measuring absorbance at 540 nm.

Results

The above procedure was used to assess the ability of compositions of (a) dihydrophloretin alone and (b) dihydrophloretin plus retinol to reduce the amount of melanin produced. No adverse effects are seen on cell viability at any level of dihydrophloretin or retinol tested, indicating that pigment inhibition is due to specific inhibition of melanogenisis and not cell toxicity.

The results for melanin production were calculated as percentages of control which contained medium alone. Results are given in Tables 3 to 5. There was no effect on viability at the concentrations of actives reported.

This example illustrates a lotion according to the invention.

This example illustrates a fluid cream according to the invention.

This example illustrates a cream according to the invention.

In the same manner, a cream containing 0.1% w/w retinol in place of the retinyl palmirate and 0.1% w/w dihydrophloretin in place of .alpha.-deoxyphloretin may be prepared.

This example illustrates a lotion according to the invention.

This example also illustrates a sunscreen cream in accordance with the invention.