Title: Use of ascorbyl glucoside for preventing the colouration of cutaneous blackheads.

Technical field

The present invention relates to the field of cosmetic products, which are more particularly intended for the prevention of cutaneous blackheads, in particular for inhibiting the appearance of the black or brown colour of comedones.

More particularly, the present invention is targeted at providing the non-therapeutic cosmetic use of a specific active agent as inhibitor of the black or brown colouration of comedones.

It also relates to a non-therapeutic cosmetic process for reducing and/or inhibiting the development of colour, for example brown or black colour, of cutaneous comedones and/or preventing the appearance of cutaneous blackheads, comprising the topical application to the skin of a composition comprising said active agent.

For the purposes of the present invention, the term "skin" is understood to denote all of the skin of the body, excluding the scalp and the mucous membranes. Preferably, "skin" is targeted at the skin of the face and/or of the hands, in particular the skin of the face, more particularly the skin of the forehead and/or of the alae of the nose and/or of the chin.

Prior art

There exist cosmetic compositions for combatting the appearance of cutaneous blackheads or for concealing them, in particular on the face. This is because this type of cutaneous imperfection, which relates to all skin typologies, is generally considered to be unattractive and thus undesirable. In view of its black, indeed even brown, colour, it is regarded as excessively visible and all the more so on a lightly pigmented skin.

To date, the source of the colour of the cutaneous blackhead has not been fully established. It is, on the other hand, known that the cutaneous blackhead results from the process of comedogenesis which affects pilosebaceous units of sebaceous follicle type, which are distributed predominantly on the face.

From a clinical perspective, a cutaneous blackhead is thus an open comedo (non inflammatory lesion) characterized by distension of the hair canal, sebum retention and excessive comification of the pilosebaceous duct. Hypercornification would result in sebum retention and in the accumulation of cell debris. A certain number of solutions for treating cutaneous blackheads have already been provided. Some of these solutions are based more particularly on the treatment of the blackheads with an active agent capable of preventing, altering or eliminating the blackheads. By way of illustration of these active agents, mention may in particular be made of the active agents capable of dissolving the lipids constituting the blackheads, such as the alkyl lactate derivatives described in the patent US 4 540567, the lipase enzyme, described in the application US 2006/051339, or else the neutralized fatty acids as described in the application EP 3 150 187. However, a certain number of these active agents have the drawback of impairing the organoleptic properties of the composition comprising them, in particular the odour and/or the colour of the composition, over time. These active agents also prove to be effective with regard to blackheads that have already appeared.

Moreover, other solutions proposed to date act in particular via mechanical extraction or use laser energy (LED).

As regards the extraction method, this relies on the use, for example, of a comedo suction device, a comedo extractor, or self-adhesive patches to be removed after a few minutes of contact with the skin. It clearly has the drawbacks of being painful and of generating redness or irritation.

A subject of the present invention is very particularly that of proposing novel active agents that are effective with regard to blackheads but are free from the above-mentioned drawbacks.

For the purposes of the present invention, the treatment of cutaneous blackheads involves the reduction or indeed even the inhibition of the development of the black or brown color of the comedones and/or the prevention of the appearance of the cutaneous blackheads.

Summary of the invention

Thus, according to a first aspect, the present invention relates to the cosmetic use of ascorbyl glucoside and also its solvates for reducing and/or inhibiting the development of colour, for example brown or black colour, of cutaneous comedones.

Against all expectations, ascorbyl glucoside has been characterized by the inventors as being capable of inhibiting the black or brown colouration of the comedones and hence of preventing the appearance of the black or brown colour of the cutaneous blackhead. This is because, as emerges from the examples below, the inventors have found that ascorbyl glucoside inhibits the formation of cutaneous blackheads by probably intervening in the process of oxidation of L-DOPA (3,4-dihydroxy-L-phenylalanine). For the record, L-DOPA is involved in the very complex melanogenesis mechanism. More specifically, the oxidation of L-DOPA, promoted by the microbial activity present in the comedo, is expressed by a colouring effect probably of dopachrome type, the latter being a coloured intermediate of the pathway for the biosynthesis of melanin. The ascorbyl glucoside in accordance with the invention appears to impair the formation of the product of the oxidation reaction in the comedones and thus inhibits the black or brown colouration of the latter. This effectiveness of ascorbyl glucoside is, to the knowledge of the inventors, characterized for the first time. Specifically, ascorbyl glucoside is already used in care products, in particular in the patent FR 2 913 198 B 1, but for the most part as an antioxidant active agent intended to combat the cutaneous signs of ageing and in particular to maintain and/or restore the biomechanical properties of the skin.

Alongside this, as disclosed by the patent US 2009/018200 Al, compositions have already been proposed comprising ascorbyl glucoside in combination with phenanthrenol as active agents for the skin, for the purposes of depigmenting and/or whitening the latter, and thus for an effect very distinct from that found according to the invention, namely preventing the appearance of cutaneous blackheads by inhibiting the appearance of the brown or black colour in the comedones.

Patent application US 2006/057092 Al discloses a cosmetic use for the care of greasy skin of a composition comprising (a) a water-soluble ascorbic acid compound and (b) porous polyamide particles. This document merely focuses on treating greasy skin, and is thus silent regarding reducing and/or inhibiting the development of colour of cutaneous comedones. To the inventor, the porous polyamide particles should be responsible for the effect suggested therein on sebum excess.

It is important to emphasize that these distinct effects involve very different routes of action. Thus, the depigmentation of the skin is carried out by inhibition of the pathway for the biosynthesis of human melanin, in particular via the inhibition of the expression of tyrosinase, whereas the prevention of the brown or black colouration of the comedones is carried out, as mentioned above, by impairing the formation of dopachrome. The term "inhibitor of the black or brown colouration of the comedones" is understood to denote, for the purposes of the present invention, a compound capable of slowing down, indeed even preventing, the appearance of the black or brown colour of the comedones. In particular, a compound is considered an inhibitor of the black or brown colouration of the comedones if the percentage of inhibition with regard to the development of the colour is at least 15%, preferably at least 20%, more particularly at least 25%, in particular as evaluated according to the protocol detailed in the examples below.

According to a second aspect, the present invention relates to a cosmetic process for reducing and/or inhibiting the development of colour, for example brown or black colour, of cutaneous comedones, comprising the topical application to the skin of a cosmetic composition comprising ascorbyl glucoside.

The cosmetic uses and processes considered according to the invention are non-therapeutic. Preferably, the skin is the skin of the face and/or of the body, in particular of the face and/or of the hands, preferably of the face, and more particularly of the forehead and/or of the alae of the nose and/or of the chin.

According to a first alternative form, the skin is greasy and/or shiny skin, in particular skin exhibiting secretion and excessive excretion of sebum. According to this alternative form, the skin is in particular greasy and/or shiny skin, especially of phototype 1, 2, 3 or 4, in particular greasy and/or shiny skin of the face and/or of the hands, more particularly greasy and/or shiny skin of the forehead and/or of the alae of the nose and/or of the chin. According to a second alternative form, the skin is non-acneic skin, namely healthy skin devoid of the clinical manifestations of acne, namely acne lesions, such as the presence of numerous acne pimples. This is because blackheads constitute cutaneous imperfections of the skin, distinct from ailments of the skin, such as acne. In particular, the blackhead is not an inflammatory lesion of the skin, in contrast to the lesions characteristic of acne. Furthermore, the regions of the face which are favourable to the development of blackheads, namely the alae of the nose more particularly, precisely do not constitute regions that favour the development of acne.

Brief description of the drawings

[Fig 1] represents a graph of the measurement of the optical density (OD) at 475 nm as a function of time for compositions 1 (containing Cutibacterium acnes extract at a concentration of 1.5 mg/ml), 2 (containing L-DOPA at a concentration of 125 mg/ml), and the reference composition (containing a combination of Cutibacterium acnes extract at a concentration of 1.5 mg/ml and L-DOPA at a concentration of 125 pg/ml).

Detailed description ASCORBYL GLUCOSIDE

As mentioned above, the present invention relates to the cosmetic use of ascorbyl glucoside. [Chem 1]

The term "ascorbyl glucoside" is understood to mean the product of condensation of glucose, in D form, i.e. in the form of a- or b-glucopyranose or of a- or b-furanose, or in L form, with ascorbic acid, preferably in L form.

Ascorbyl glucoside is provided in particular by the company Hayashibara or by the company Macrocare under the name "Ascorbic acid glucoside" at a content of 100% active material. It is in reality the 2-O-a-D-glucopyranoside of L-ascorbic acid. This isomer is preferred for use in the context of the present invention.

More particularly, 2-O-a-D-glucosyl-L-ascorbic acid, also known under the name ascorbic acid 2-glucoside, is a compound made up of a molecule of D-glucose bonded to the hydroxyl group in the C2 position of L-ascorbic acid (vitamin C) by an a-glucosidic bond. Advantageously, in this cosmetic use, said ascorbyl glucoside is present in the cosmetic composition in a content ranging from 0.01% to 10% by weight, preferably from 0.1% to 5% by weight, better still from 0.2% to 5% by weight, relative to the total weight of the cosmetic composition.

COMPOSITION

According to one aspect of the invention, the ascorbyl glucoside can be incorporated into a cosmetic composition intended for a topical application, in order to prevent the formation of cutaneous blackheads, in particular in order to inhibit the development of the black or brown colour of comedones.

Thus, the present invention is targeted at a cosmetic use in which at least the ascorbyl glucoside employed according to the invention is present in a cosmetic composition intended to prevent the black or brown colouration of comedones.

Preferably, the ascorbyl glucoside employed according to the invention, when it is present within a composition, can be formulated in a physiologically acceptable medium.

Such a medium is considered to be physiologically acceptable when it does not cause any tingling, tautness or discomfort unacceptable for the user.

A composition used according to the invention can be provided in any formulation form normally used in the cosmetics field.

It can in particular be in the form of an aqueous or aqueous/alcoholic solution, which is optionally gelled, of a dispersion of the lotion type, which is optionally a two-phase lotion, of an oil-in-water or water-in-oil or multiple emulsion, of an aqueous gel, of a dispersion of oils in an aqueous phase, in particular by means of spherules, it being possible for these spherules to be polymer particles or, better still, lipid vesicles of ionic and/or non-ionic type, or else in the form of a powder, of a serum, of a paste or of a flexible rod or also of a stick. It can be of solid, pasty or more or less fluid liquid consistency.

Thus, the composition can comprise any constituent normally employed in the topical application and administration envisaged.

Mention may in particular be made of water, solvents, compounds forming a fatty phase which is liquid at ambient temperature, for example oils of mineral, animal and/or vegetable origin, waxes, in particular, pigments, fillers, surfactants, thickeners, gelling agents, preservatives and mixtures thereof in any proportions.

A composition according to the invention can advantageously be provided in the form of an emulsion, in particular obtained by dispersion of an aqueous phase in a fatty phase (W/O) or of a fatty phase in an aqueous phase (O/W), of liquid or semi-liquid consistency of the milk type, or of soft, semi- solid or solid consistency of the cream or gel type, or also of multiple emulsion (W/O/W or O/W/O). These compositions are prepared according to the usual methods.

A composition used according to the invention can advantageously comprise at least one fatty phase which is liquid at ambient temperature and atmospheric pressure. Such a fatty phase can comprise at least one non-volatile ether oil having from 10 to 40 carbon atoms and/or at least one non-volatile monoester oil.

For the purposes of the present invention, the term " non-volatile oil " is understood to denote an oil, the vapour pressure of which at ambient temperature and atmospheric pressure is non zero and less than 10 ³ mmHg (0.13 Pa).

Mention may in particular be made, as example of ethers having from 10 to 40 carbon atoms, of dicaprylyl ether (CTFA name: Dicaprylyl ether).

Mention may in particular be made, as preferred monoesters, of isononyl isononanoate, oleyl erucate and/or 2-octyldodecyl neopentanoate, preferably isononyl isononanoate.

The amount of fatty phase which is liquid at ambient temperature and atmospheric pressure present in the compositions according to the invention can range, for example, from 0.01% to 50% by weight and preferably from 0.1% to 30% by weight, relative to the total weight of the composition.

The emulsions according to the invention can comprise at least one emulsifier chosen from amphoteric, anionic, cationic or non-ionic emulsifiers, used alone or as a mixture. Advantageously, the emulsifiers are appropriately chosen according to the emulsion to be obtained (W/O or O/W). The emulsifiers are generally present in the composition in a proportion which can range from 0.3% to 30% by weight and preferably from 0.5% to 20% by weight, relative to the total weight of the composition.

For the O/W emulsions, examples of emulsifiers that may be mentioned include non-ionic surfactants, and especially esters of polyols and of fatty acids with a saturated or unsaturated chain comprising, for example, from 8 to 24 carbon atoms and better still from 12 to 22 carbon atoms, and the oxyalkylenated derivatives thereof, i.e. derivatives comprising oxyethylenated and/or oxypropylenated units, for example the glyceryl esters of C8-C24 fatty acids, and the oxyalkylenated derivatives thereof; the polyethylene glycol esters of C8-C24 fatty acids, and the oxyalkylenated derivatives thereof; the sorbitol esters of C8-C24 fatty acids, and the oxyalkylenated derivatives thereof; the sugar (sucrose, glucose or alkylglucose) esters of C8-C24 fatty acids, and the oxyalkylenated derivatives thereof; fatty alcohol ethers; the sugar ethers of C8-C24 fatty alcohols, and mixtures thereof in any proportions.

A composition according to the invention can additionally comprise at least one silicone elastomer, in particular the products sold under the KSG names by Shin-Etsu, under the Trefil, BY29 or EPSX names by Dow Coming or under the Gransil names by Grant Industries.

A composition used according to the invention can additionally contain one or more adjuvants commonly used in the cosmetics field, in particular sequestering agents, odour absorbers, UV-screening agents, fragrances, mattifying agents, and abrasive fillers or exfoliating agents, and mixtures thereof in any proportions.

A composition used according to the invention can advantageously comprise at least one additional active agent.

It can in particular be at least one active agent for caring for greasy skin.

It can also advantageously comprise at least one additional active agent for caring for aged skin.

The expression "additional active agent" is understood to mean, in the context of the present invention, a compound which has, by itself, that is to say not requiring the intervention of an external agent in order to activate it, a biological activity which can in particular be:

- a desquamating activity (which makes possible the opening of the comedones), and/or

- an antimicrobial activity (in particular with regard to C. acnes ), and/or

- a soothing or anti-irritant activity, and/or

- a sebum-regulating or anti-seborrhoeic activity, and/or

- an astringent activity, and/or

- an activity intended to combat and/or prevent the signs of ageing, in particular chronobiological ageing, for example wrinkles and fine lines.

The additional active agent which can be used in the compositions of the invention is preferentially chosen from desquamating agents, soothing agents, anti-irritant agents, sebum-regulating or anti-seborrhoeic agents, astringent agents and mixtures thereof in any proportions.

The additional active agent for caring for greasy skin used in the composition according to the invention can represent from 0.0001% to 20%, preferably from 0.01% to 10% and better still from 0.01% to 5% by weight, relative to the total weight of the composition.

Mention may in particular be made, as examples of such an additional active agent, of salicylic acid and pro-xylane, namely C-D-xylopyranoside-2-hydroxypropane (INCI name: hydroxypropyl tetrahydropyrantriol), in particular extracted from rye seeds. Moreover, a composition employed according to the invention can advantageously comprise from 5% to 80% by weight and preferably from 35% to 75% by weight of water, relative to the total weight of said composition.

The pH of said composition is advantageously less than or equal to 8, preferably ranging from 4 to 7, even better still ranging from 4.5 to 6.5.

A composition according to the invention can additionally comprise retinol, otherwise known as vitamin A, preferably all-trans-retinol.

More particularly, a composition according to the invention can comprise an amount of retinol ranging from 0.02% to 5.0% by weight, in particular from 0.05% to 3.0% by weight, relative to the total weight of the composition.

Thus, a composition employed according to the invention can comprise at least one additional active agent, in particular chosen from salicylic acid, hydroxypropyl tetrahydropyrantriol (pro-xylane), retinol and mixtures thereof.

A composition according to the invention can additionally comprise at least one polyol, namely an organic molecule comprising at least two free hydroxyl groups, in particular chosen from ethylene glycol, propylene glycol, propane- 1,3-diol, 1,3-butylene glycol, isoprene glycol, 1,2-pentylene glycol, hexylene glycol, caprylyl glycol, dipropylene glycol, glycerol, pentaerythritol, trimethylolpropane, polyglycerols, polyethylene glycols and mixtures thereof.

A composition according to the invention can additionally comprise at least one gelling agent, in particular a hydrophilic gelling agent, namely a compound capable of gelling the aqueous phase of the compositions according to the invention. Mention may be made, as examples of hydrophilic gelling agents, of the polymers and copolymers of 2-acrylamido-2- methylpropanesulfonic acid, which are crosslinked and/or neutralized, polysaccharides and mixtures thereof.

A composition according to the invention can also comprise at least one derivative of polyethylene glycol and of mono-, di- and triglycerides of an acid comprising at least one alkyl chain ranging from Ce to C _½ , and having at least two ethylene oxide groups, in particular chosen from derivatives of polyethylene glycol and of mono-, di- and triglycerides of caprylic acid and of capric acid, for example that comprising 6 ethylene oxide groups (INCI name: PEG-6 caprylic/capric glycerides), sold under the name Softigen 767 by Sasol. A composition according to the invention can also comprise at least one colourant chosen, for example, from pigments, pearlescent agents, dyes, effect materials and mixtures thereof in any proportions.

These colourants can be present in a content ranging from 0.01% to 50% by weight and preferably from 0.01% to 30% by weight, relative to the total weight of the composition.

A composition according to the invention can additionally comprise at least one filler, in particular in a content ranging from 0.01% to 50% by weight, preferably ranging from 0.01% to 30% by weight, relative to the total weight of the composition.

These fillers can be inorganic or organic and of any shape, platelet, spherical or oblong, whatever the crystallographic form (for example lamellar, cubic, hexagonal, orthorhombic or amorphous).

Of course, a person skilled in the art will take care to choose the optional additional compound(s), and/or the amount thereof, in such a way that the advantageous properties of the ascorbyl glucoside according to the invention are not, or not substantially, detrimentally affected by the envisaged addition and that the properties of the compositions resulting therefrom are compatible with the topical administration route.

A composition of the invention can advantageously exhibit a firm and compact feel when taken up. It can be thick on application and subsequently be transformed, melt and release freshness.

According to another alternative form, a composition of the invention can advantageously be provided in the form of a more or less wide stick, such as a pencil, for example.

A composition can alternatively have the form of a product for caring for or making up the face and/or the body, and be packaged, for example, in the form of cream in ajar or of fluid in a tube or as a pump-action bottle.

A composition according to the invention can be manufactured by any known process generally used in the cosmetics field.

The ingredients are mixed before they are shaped, in the order and under conditions which are easily determined by a person skilled in the art.

According to a specific form of the invention, other agents intended to make the appearance and/or the texture of the skin more attractive can also be added to the composition according to the invention. COSMETIC PROCESSES

As mentioned above, the present invention relates to a cosmetic process for preventing the black or brown colouration of comedones, comprising the topical application to the skin of a cosmetic composition comprising at least ascorbyl glucoside.

The cosmetic process of the invention is carried out by administering, by the topical route, a composition comprising at least ascorbyl glucoside according to the invention, preferably in a physiologically acceptable medium.

The topical administration consists of the external application to the skin of cosmetic compositions according to the usual techniques for use of these compositions.

By way of illustration, the cosmetic process according to the invention can be carried out by topical application, for example daily, of at least ascorbyl glucoside in accordance with the invention, which can, for example, be formulated in the form of a cream, gel, serum, lotion, emulsion, make-up-removing milk, stick or aftersun composition.

According to one embodiment, the application is repeated, for example, 1 to 2 times daily for one day or more and generally over an extended period of at least 4 weeks, indeed even 4 to 15 weeks, with, if appropriate, one or more periods of interruption.

According to another embodiment, the application is daily (once per day) and generally over an extended period of at least 4 weeks, indeed even 4 to 15 weeks, with, if appropriate, one or more periods of interruption.

According to another embodiment, the composition including at least ascorbyl glucoside as defined above will be applied to skin regions which have been cleansed beforehand, for example using an appropriate soap, and/or freed beforehand from at least one blackhead, for example using an adhesive patch or a mechanical action.

Furthermore, treatment combinations with optionally topical forms, in order to complement or to reinforce the activity of the ascorbyl glucoside, can be envisaged.

It might be possible to imagine a topical treatment with a composition containing at least ascorbyl glucoside in accordance with the invention, combined with a supplementary composition dedicated to a topical application and containing at least one active agent distinct from ascorbyl glucoside.

Thus, the present descreiption also describes a cosmetic process for preventing the black or brown colouration of comedones, comprising: a) a step of topical application to the skin of a cosmetic composition comprising at least ascorbyl glucoside; and b) a step of topical application of a composition different from the composition applied in step a) and containing at least one active agent distinct from ascorbyl glucoside.

The present invention relates to a cosmetic process for preventing the black or brown colouration of comedones, comprising: a) a step of topical application to the skin of a cosmetic composition comprising at least ascorbyl glucoside, said ascorbyl glucoside being present therein in a content ranging from 0.01 to 10% by weight, relative to the total weight of said cosmetic composition; and b) a step of topical application of a composition different from the composition applied in step a) and containing at least one active agent distinct from ascorbyl glucoside.

In particular, said ascorbyl glucoside is present in the cosmetic composition applied during step a) in a content ranging from 0.1% to 5% by weight, preferably from 0.2 to 5% by weigh, relative to the total weight of the cosmetic composition.

Advantageously, the cosmetic composition applied during step a), can be as defined hereabove.

Such a composition applied in step b) can be described as "supplementary composition". Steps a) and b) defined above can be carried out simultaneously or successively.

This supplementary composition, which is different from the composition employed according to the invention, and applicable by the topical route, can in particular be in the form of an emulsified oil-in-water gel, comprising retinol; at least one polyol; at least one hydrophilic gelling agent; at least one derivative of polyethylene glycol and of mono-, di- and triglycerides of an acid comprising at least one alkyl chain ranging from Ce to C _½ , and having at least two ethylene oxide groups; at least one non-volatile ether oil having from 10 to 40 carbon atoms; and at least one non-volatile monoester oil.

Throughout the description, including the claims, the expressions "between ... and ..." and "ranging from ... to ..." should be understood as meaning limits included, unless otherwise specified. The examples which follow illustrate the present invention without limiting the scope thereof.

EXAMPLE

Methodology on a reconstructed epidermis for characterization of the appearance of dark- coloured structures and its development over time

For the purposes of the present invention, the term "dark-coloured structures" is understood to denote the structures responsible for the colouration of blackheads.

This method is targeted at characterizing the change over time, in the expression of colour, brought about by an intracellular extract of bacteria of Cutibacterium acnes type (formerly listed under the name Propionibacterium acne ) in the presence of 3,4-dihydroxy-L- phenylalanine (L-DOPA), which extract is deposited at the surface of an EpiSkin ™ reconstituted epidermis.

To do this, an intracellular extract of bacteria of Cutibacterium acnes CIP 53.117 type, stored at 4°C in lyophilized form, is suspended in IX PBS (Dulbecco's Phosphate Buffered Saline, supplied by Gibco BRL, Life Technologies) at a concentration of 6 mg/ml. This extract is subsequently deposited at the surface of an EpiSkin epidermis in the presence of 3,4- dihydroxy-L-phenylalanine (L-DOPA - supplied by Sigma- Aldrich) at 1 mg/ml.

The expression of a colouring effect and its development towards a dark colour are observed visually, starting from 48 hours of incubation.

In vitro methodology used for the evaluation of the ability to inhibit the development of the colour

This method is based on the measurement of absorbance, over time, carried out directly on a composition formed of a mixture of intracellular extract of bacteria of Cutibacterium acnes type, of 3,4-dihydroxy-L-phenylalanine (L-DOPA) and of the compound to be tested.

The measurements are compared with those carried out for a mixture of an intracellular extract of bacteria of Cutibacterium acnes type and of 3,4-dihydroxy-L-phenylalanine (L- DOPA), in the absence of compound to be tested (reference).

The method is adapted from a method for the enzymatic assay of the tyrosinase activity (Behbahani et al. , Microchemical Journal (1993), 47, 251), which is based on the absorbance properties at 475 nm of a coloured intermediate of the pathway for the biosynthesis of melanin starting from L-DOPA, namely dopachrome, a product of the oxidation of L-DOPA.

Preparation of the reference composition

An intracellular extract of bacteria of Cutibacterium acnes CIP 53.117 type, stored at 4°C in lyophilized form, is suspended in IX PBS (supplied by Gibco BRL, Life Technologies) at a concentration of 6 mg/ml.

A solution of L-DOPA at a concentration of 0.5 mg/ml is prepared by bringing together L- DOPA (supplied by Sigma- Aldrich) and milliQ water, so as to have an L-DOPA concentration of 1 mg/ml, and then diluting with IX PBS (Dulbecco's Phosphate Buffered Saline, supplied by Gibco BRL, Life Technologies).

The mixture of 50 pi of these two solutions and of 100 mΐ of IX PBS (Dulbecco's Phosphate Buffered Saline supplied by Gibco BRL, Life Technologies) results in a composition with a total volume of 200 mΐ containing L-DOPA (at a concentration of 125 pg/ml) and the Cutibacterium acnes extract (at a concentration of 1.5 mg/ml).

Preparation of a composition 1 comprising only a Cutibacterium acnes extract The 6 mg/ml Cutibacterium acnes extract was diluted with IX PBS (Dulbecco's Phosphate Buffered Saline supplied by Gibco BRL, Life Technologies) so as to form a 200 mΐ composition with a concentration of 1.5 mg/ml of Cutibacterium acnes.

Preparation of a composition 2 comprising only L-DOPA

The 0.5 mg/ml L-DOPA solution was also diluted with IX PBS (Dulbecco's Phosphate Buffered Saline supplied by Gibco BRL, Life Technologies) so as to form a 200 mΐ composition with a concentration of 125 pg/ml of L-DOPA.

Absorbance measurement

The compositions to be tested and the reference composition are introduced separately into wells of a 96-well microplate suitable for reading in visible spectrophotometry, and placed at a temperature of 32°C.

The formation of a coloured product is then monitored over time by spectrophotometry. To do this, the absorbance, or optical density (O.D.), is measured at 475 nm from the time 0 to the time 2 hours by means of a Spectra Max M5 ^e reader and the Spectra Max software (the time 0 corresponds to the addition of composition 1 or the introduction of the composition into the wells).

In the graph of figure 1, the formation of a coloured product for the reference composition, the product of the oxidation of L-DOPA, is visually observed.

However, no appearance of a significant colouring effect over time is noted for compositions 1 and 2 comprising solely a Cutibacterium acnes extract and solely L-DOPA, respectively. This confirms the catalytic activity of the bacterial extract of Cutibacterium acnes on the development of the dark colour by oxidation of L-DOPA.

It is thus possible to monitor the formation of the coloured intermediate of the melanin biosynthesis pathway by virtue of its properties of absorption at 475 nm. The effectiveness of a compound in preventing the development of colour of cutaneous blackheads can be evaluated by this means.

Parameters studied for the evaluation of the effectiveness of the various compounds to be tested

The ability to inhibit the development of colour of a given compound was assessed by comparing the absorbance measurements obtained for the test compositions with those obtained for the reference composition.

More specifically, the inhibitory effect of the compound to be tested was evaluated by comparing the initial rate of oxidation of the L-DOPA under the action of the bacterial extract at 475 nm for the test composition with that of the reference composition in order to obtain a corresponding percentage of inhibition.

In practice, the initial rate (Vi) of the oxidation reaction is calculated from the linear part of the curve of the graph of the absorbance values. As this part lies between 10 and 40 minutes (see the graph in Figure 1), the initial rate of the oxidation reaction is determined using the following relationship:

[Math 1]

The percentage of inhibition (%inhib) of a given compound with regard to the formation of the coloured product is subsequently obtained using the values of the initial rate of the oxidation reaction for the reference composition (Vi _ref ) and for the test composition (Vi _test ) according to the following relationship:

[Math 2] 100 For the purposes of the invention, a compound is considered to have an inhibitory effect if the %inhib value is at least 15%.

Example 1 - In vitro evaluation of the ability of the ascorbyl glucoside to inhibit the development of the colour Three test compositions, 1, 2, and 3, comprising ascorbyl glucoside, AG, (reference ASCORBYL GLUCOSIDE AA2G® supplied by Hayashibara) at respective concentrations of 0.125, 0.25 and 0.5 mg/ml were prepared. These compositions, with a total volume of 200 pi, also contain L-DOPA (25 pg), the Cutibacterium acnes extract (0.3 mg) and the PBS buffer which are mentioned in the methodology part above. The change in the optical density at 475 nm of these three compositions, and also the reference composition, is then measured according to the protocol indicated in the methodology part above.

The measured optical density values are collated in the following table.

[Table 1]

The percentage of inhibition values, calculated from the mathematical formulae detailed in the methodology part above, are presented in Table 2 below.

[Table 2]

An effectiveness of the ascorbyl glucoside which increases with the concentration of AG, up to more than 50% with an AG concentration of 0.5 mg/ml, is effectively observed.

Example 2 - Cosmetic compositions comprising at least ascorbyl glucoside in accordance with the invention

A composition for topical application is prepared which comprises:

[Table 3]

The composition applied to the skin makes it possible to prevent the black or brown colouration of the comedones.