WO2001017507A1 - Preserved liposomes - Google Patents

Abstract

The invention is directed to a preserved cosmetic composition comprising lipid vesicles having lumens, in which the lipid vesicle lumens include a cosmetic-effective amount of an active ingredient; a preservative-effective amount of a combination of sorbic acid and salicylic acid or water-soluble salts thereof; a base in an amount which provides a lipid vesicle lumen pH of about 5 to about 6; and water.

Description

PRESERVED LIPOSOMES BACKGROUND OF THE INVENTION

The present invention relates to the preservation of liposomal preparations against microbial contamination. More particularly, the present invention relates to a cosmetic liposomal preparations containing active ingredients which have previously been difficult to preserve, such as magnesium ascorbyl phosphate.

Liposomes are spherical vesicles composed of lipid bilayers. Active ingredients inside the liposomes can be delivered to the skin by topical application of the liposomes. A general reference for the application of liposomes to cosmetics is Hayward, J.A. and Smith, W.P. Potential Applications of Liposomes in Cosmetic Science, in Cosmetic and Toiletries, 105:47-54, 1990. U.S. Pat. No. 5,585,109 to Hayward et al. teaches the cosmetic delivery of un-neutralized salicylic acid by a liposome formulation including a preservative.

Liposome formulations are typically difficult to preserve against microbiological contamination. An 8-week challenge study is considered a standard measure of preservative efficacy within the cosmetic industry. All percentages given in the specification are percent by weight of the total composition weight, unless otherwise noted. SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a preserved liposomal composition, particularly a topical formulation, that ensures against microbial growth during storage, even in the presence of added microbial contaminants. Other objects and features of the present invention will become apparent when considered in combination with the following summary and detailed description of certain preferred embodiments of the present invention.

The foregoing and related objects are achieved by providing a preserved cosmetic composition comprising: a) a vesicle-forming amount of lipids known to form, either alone or in combination, unilamellar vesicles; b) a cosmetic-effective amount of an active ingredient; c) a preservative-effective amount of a combination of sorbic acid and salicylic acid or water-soluble salts thereof; d) a base in an amount which provides a pH of about 5 to about 6 to the composition; and e) water. The cosmetic liposomes of the invention can optionally contain other ingredients conventionally employed in cosmetic products. Examples of other ingredients include, but are not limited to, perfumes, colorants such as staining dyes and pigments, humectants, anti- dandruff agents, anti-acne agents, germicides, sunscreens, emollients, vitamins, sterols and other lipids. Once the liposome composition has been formed such that the interior of the liposomes, the limposome lumens, contain the active ingredient and the combination of sorbic acid and salicylic acid in a pH of about 5 to about 6, one of skill in the art is well able to alter the characteristics of the solution exterior to the liposomes by the addition of compounds, dilution, dialysis or other known methods, without altering the content of the liposomes. Preferred lipids include the synthetic or natural phospholipids, phosphatidylthanolamines, phosphatidylserines, cereamides, cerebrosides, phophatidylglycerides and non-ionic surfactants. Particularly preferred lipids are natural phospholipids such as soya lecithin, in an amount of 0.5 to 10%. Most preferred are natural phospholipids which have been substantially purified to increase the phosphatidylcholine content. Preferred active ingredients include any ingredient known for cosmetic use through topical application. Examples of active ingredients for use in the cosmetic liposomes of the invention include, but are not limited to, vitamins, herbal extracts, enzymes, growth factors, anti-dandruff agents, anti-acne agents, germicides and sterols. A "cosmetic-effective amount" of an active ingredient is that amount which is required in a liposome preparation for the active ingredient to have a discernible cosmetic effect upon topical application.

A "preservative-effective amount" of a combination of sorbic acid and salicylic acid or water-soluble salts thereof is at least 0.1% of sorbic acid or a water-soluble salt of sorbic acid in combination with at least 0.1% of salicylic acid or a water-soluble salt of salicylic acid. Preferably, sorbic acid is present in an amount from 0.1% to 5%, and salicylic acid or its water-soluble salt are present in an amount from 0.1% to 10%.

The base used may be either organic or inorganic. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In a preferred embodiment, a liposome composition of the cosmetic active ingredient magnesium ascorbyl phosphate is preserved by the addition of sorbic acid and salicylic acid. Previously known preservative systems were unsuccessful in preserving liposome compositions of magnesium ascorbyl phosphate.

Magnesium ascorbyl phosphate functions to deliver a stabilized form of Vitamin C (ascorbic acid) to the skin. The stabilized Vitamin C functions as an antioxidant, skin tightener and pigment promoter. EXAMPLE 1 Mg Ascorbyl Phosphate Liposomes Preserved with 0.2% Salicylic Acid and 0.2% Sorbic Acid

Ingredient Content Substantially Purified Soya Lecithin 80 grams

Sorbic Acid 2 grams

Salicylic Acid 2 grams

NaOH to pH 5.5

Water QS to 1 kilogram Mg Ascorbyl Phosphate 10 grams

To compound the formula, the sorbic acid and the salicylic acid were dissolved in water. The pH was then adjusted to a pH of 5.5 using the base. The active ingredient, Mg ascorbyl phosphate, was then added. Finally, the lecithin is added under agitation, and the mixture is processed by high shear homogenization or microfulidization until a particle size of between 100 nm and 300 nm is reached. The particle size was monitored by a Horiba LA-90 particle size analyzer (Horiba Instruments, Inc., Irvine, California).

As a comparison for testing, Mg ascorbyl phosphate liposomes were also prepared using two prior art preservatives, Phenonip (Nipa-Hardwicke, Inc., Wilmington, Deleware), and the combination of Dowicil (Dow Chemical USA, Midland, Michigan), methyl paraben and propyl paraben. COMPARATIVE EXAMPLE 1 Mg Ascorbyl Phosphate Liposomes Preserved with 1.0% Phenonip

Ingredient Content

Substantially Purified Soya Lecithin 80 grams Phenonip 10 grams

Water QS to 1 kilogram

Mg Ascorbyl Phosphate 10 grams

To compound the formula, the Phenonip was dissolved in water. The active ingredient, Mg ascorbyl phosphate, was then added. Finally, the lecithin is added under agitation, and the mixture is processed by high shear homogenization or microfiilidization until a particle size of between 100 nm and 300 nm is reached. The particle size was monitored by a Horiba LA-90 particle size analyzer.

COMPARATIVE EXAMPLE 2 Mg Ascorbyl Phosphate Liposomes Preserved with 0.2% Dowicil 200, 0.2% Methyl Paraben, 0.05% Propyl Paraben

Ingredient Content

Substantially Purified Soya Lecithin 80 grams Dowicil 200 2 grams

Methyl Paraben 2 grams Propyl Paraben 0.5 grams

Water QS to 1 kilogram

Mg Ascorbyl Phosphate 10 grams

To compound the formula, the Dowicil 200, methyl paraben and propyl paraben were dissolved in water. The active ingredient, Mg ascorbyl phosphate, was then added. Finally, the lecithin is added under agitation, and the mixture is processed by high shear homogenization or microfiilidization until a particle size of between 100 nm and 300 nm is reached. The particle size was monitored by a Horiba LA-90 particle size analyzer.

EXAMPLE 2 Eight Week Challenge Study of Preservative Effectiveness Samples of the preserved liposome compositions of Example 1, Comparative Example

1 and Comparative Example 2 were each inoculated with standardized cultures to provide a final concentration of 5.0 x 10⁵ gram positive bacteria per gram, 5.0 x 10⁵ gram negative bacteria per gram, 5.0 x 10⁵ yeast per gram and 5.0 x 10⁴ mold spores per gram. The inoculum was distributed uniformly throughout the preserved samples in a manner which minimized aeration. The samples were then stored at room temperature for the duration of the eight week study.

A portion of each sample was taken one week after the first inoculation and every week thereafter until the eighth week. Each portion was diluted and plated on a series of petri dishes containing media which were selective for each of gram positive bacteria, gram negative bacteria, yeast and mold. The series of plates were then incubated. Following incubation, the number of colonies on the plates was determined using a colony counter and used to calculate the number of organisms per gram for each class of gram positive bacteria, gram negative bacteria, yeast and mold.

The fourth week after the inoculation, after the weekly portion was removed for diluting and plating, the samples were reinoculated with standardized cultures to provide an additional 5.0 x 10⁵ gram positive bacteria per gram, 5.0 x 10⁵ gram negative bacteria per gram, 5.0 x 10⁵ yeast per gram and 5.0 x 10⁴ mold spores per gram.

If, at any point during the challenge study, the number of colonies on the series of plates from a sample were too numerous to count (TNTC), this indicated a failure of the preservative system, and the study was discontinued for that sample. The results of the eight week challenge study are shown in Table 1, below.

Table 1

20 As can be seen from Table 1, the salicylic acid/sorbic acid of Example 1 provided a stable preservative for the liposomes, even in the face of repeated challenges with bacteria, yeast, and mold spores. In contrast, the phenonip preserved and Dowicil 200/methyl paraben/propyl paraben preserved liposomes failed to provide adequate protection from even one challenge.

25 The invention has been described in connection with certain preferred embodiments which illustrate the principals of the invention. However, it should be understood that various modifications and changes may readily occur to those skilled in the art, and it is not intended to so limit the invention. Accordingly, modifications and equivalents may be considered as falling within the scope of the invention as defined by the claims hereinbelow.

Claims

WHAT IS CLAIMED IS:

1. A preserved cosmetic composition comprising lipid vesicles having lumens, wherein the lipid vesicle lumens contain: a) a cosmetic-effective amount of an active ingredient; b) a preservative-effective amount of a combination of sorbic acid and salicylic acid or water-soluble salts thereof; c) a base in an amount which provides a lipid vesicle lumen pH of about 5 to about 6; and d) water.

2. The preserved cosmetic composition of claim 1, wherein the active ingredient is magnesium ascorbyl phosphate.

3. The preserved cosmetic composition of claim 1, wherein the sorbic acid is present in an amount of at least 0.1% by weight of the composition and the salicylic acid or water soluble salt thereof is present in an amount of at least 0.1% by weight of the composition.

4. The preserved cosmetic composition of claim 1, wherein the sorbic acid is present in the amount of from about 0.1% to about 5.0 % by weight of the composition and the salicylic acid or water soluble salt thereof is present in the amount of from about 0.1% to about 10% by weight of the composition.

5. The preserved cosmetic composition of claim 1, wherein the lipid vesicles have a particle size of from about 100 to about 300 nm.

6. A preserved cosmetic composition comprising: a) an vesicle-forming amount of lipids known to form, either alone or in combination, unilamellar vesicles; b) a cosmetic-effective amount of an active ingredient; c) a preservative-effective amount of a combination of sorbic acid and salicylic acid or water-soluble salts thereof; d) a base in an amount which provides a pH of about 5 to about 6 to the composition; g and e) water.

7. The preserved cosmetic composition of claim 6, wherein the active ingredient is magnesium ascorbyl phosphate.

5 8. The preserved cosmetic composition of claim 6, wherein the sorbic acid is present in an amount of at least 0.1% by weight of the composition and the salicylic acid or water soluble salt thereof is present in an amount of at least 0.1% by weight of the composition.

9. The preserved cosmetic composition of claim 6, wherein the sorbic acid is present in 10 the amount of from about 0.1% to about 5.0 % by weight of the composition and the salicylic acid or water soluble salt thereof is present in the amount of from about 0.1% to about 10% by weight of the composition.

10. The preserved cosmetic composition of claim 6, wherein the lipid vesicles have a particle size of from about 100 to about 300 nm.

15 11. The preserved cosmetic composition of claim 6, wherein the lipids are natural phospholipids in an amount of about 0.5 to about 10% by weight of the composition.

12. The preserved cosmetic composition of claim 11, wherein the natural phospholipids are soya lecithin.