Compositions of retinoic acids and tocopherol for prevention of dermatitis
BACKGROUND OF THE INVENTION 
     Retinoic acids such as 13-cis-retinoic acid and all-trans-retinoic acid are known to have beneficial dermatological effects, i.e. on human skin, and may be applied to retard the effects of photoaging on skin, or to combat acne, or in general to improve skin quality. However, repeated topical application of retinoic acids to human skin for these dermatological purposes may initially cause transient skin irritation (dermatitis) which may be characterized by erythema, scaling, pruritus, and sensations similar to sunburn (1,2). This problem is described in U.S. Pat. No. 4,888,342. Such results are also observed in animals after repeated topical dosing with retinoic acids. 
     The inflammatory component of retinoic acid induced skin irritation in animals can be demonstrated histologically by an influx of inflammatory cells into the skin. The effect can be quantified biochemically from measurement of increased myeloperoxidase (MPO) activity in skin biopsy punches (3) (MPO is a marker enzyme for neutrophils). In mice, for example, topical retinoic acid induced skin irritation is characterized by an inflammatory response and, after repeated topical applications, epidermal hyperproliferation. 
     Tocopherols, for example alpha tocopherol (Vitamin E), have long been recognized for their properties as free radical scavenging antioxidants (4). Also, it has been demonstrated that Vitamin E taken orally at a dose of 800 mg can reduce the toxic side effects of 13-cis-retinoic acid (100 mg/m 2 ) in patients who were treated with this retinoic acid for myelodysplastic syndrome (5). 
     SUMMARY OF THE INVENTION 
     The problem of retinoic acid induced dermatitis resulting from topical retinoic acid application for dermatological effects can be overcome by adding a tocopherol such as alpha tocopherol to the topical composition. 
     The subject invention therefore is directed to a composition of a retinoic acid and a tocopherol which is applied topically and has the desired dermatological effects of retinoic acid application with reduction in the undesired side effects of retinoic acid induced dermatitis or inflammation. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1: Topical irritation by 13-cis-retinoic acid in the mouse after eight (8) days. Skin irritation is measured by MPO activity (hatched upwards bar), and ear punch biopsy weight (hatched downwards bar). This graph demonstrates increasing irritant reactions to 13-cis-retinoic acid applied alone. 
     FIG. 2: Inhibition of 13-cis-retinoic acid induced mouse skin irritation by topical alpha tocopherol. Percent inhibition of MPO (hatched upwards bars) with increasing concentrations of alpha tocopherol 13-cis-RA, 20.0 μg. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention is drawn to compositions of a tocopherol and a retinoic acid, which compositions have the therapeutic dermatological effects of a retinoic acid, and avoid much of the skin irritation induced by retinoic acid. The retinoic acid is present in an amount effective for treating dermatological disorders. The tocopherol is present in an amount sufficient to reduce retinoic acid-induced skin irritation. Retinoic acid includes the retinoid all-trans retinoic acid, geometric isomers such as 13-cis-retinoic acid, and pharmaceutically acceptable esters. Also contemplated are those natural or synthetic retinoic acid analogues which have beneficial therapeutic effects on skin as described. 
     The liquid compositions can be applied in accordance with this invention to human skin in conventional topical compositions. The dermatological effects of retinoic acids are well known. These effects make retinoic acids useful in a range of applications. For example, retinoic acids may be used to treat dermatological disorders such as acne, photodamage (i.e., wrinkling) and epithelial carcinomas which can be reduced in size by treatment. 
     These topical compositions are in the form of liquid compositions suitable for topical administration (including for example creams, gels, ointments, microemulsions, shampoos, and solutions). 
     Any amount of retinoic acid effective to treat dermatological disorders, for example, acne and photodamage, is contemplated. Specifically, the concentration of retinoic acid, in particular 13-cis-retinoic acid, may be in a range of about 0.05% to about 0.2% by weight per volume of liquid composition, and the concentration of tocopherol, in particular alpha-tocopherol, may be in a range from about 0.005% to 5.0% by weight per volume of the liquid composition. In particular, the alpha tocopherol may be present in a range of about 0.01% to about 5.0% by weight per volume. 
     This invention provides a method for topically applying retinoic acid to skin to treat dermatological disorders without inducing skin irritation caused by said retinoic acid by applying topically a liquid composition containing retinoic acid and alpha tocopherol, said composition being applied in an amount sufficient to produce the dermatological effects of said retinoic acid, and said alpha tocopherol being present in an amount sufficient to reduce the skin irritation caused by the retinoic acid. Also included is a method for providing a composition for topical application to treat dermatological disorders by mixing retinoic acid with an amount of alpha tocopherol sufficient to reduce the skin irritation induced by the retinoic acid, which itself is present in a dermatologically effective amount. Alpha-tocopherol and 13-cis-retinoic acid are preferred in these methods. Effective amounts of retinoic acid for a particular application are well-known in the art (U.S. Pat. Nos. 5,075,333; 4,888,342; 4,487,782; 4,603,146; and 4,877,805), or can be determined empirically by assays or tests such as those described in Examples 1 and 2. The amount of alpha tocopherol sufficient to reduce skin irritation can be similarly determined. The amounts used may be those above for the liquid compositions described above, specifically about 0.01% to about 5.0% by weight tocopherol and about 0.05% to about 0.2% by weight retinoic acid. 
     These liquid compositions may be applied to the skin of the body, in particular face, legs, arms and hands. They may be administered in any conventional topical preparations, i.e., in combination with any suitable conventional carrier useful for topical administration. Such topical compositions include cream, ointment, soap, solutions, lotions, emulsions, shampoo and any other conventional topical preparations. In formulating the preparations, any conventional non-toxic dermatologically acceptable base or carrier in which these compositions are stable is acceptable. 
     Preferred compositions may contain conventional cosmetically active ingredients. Examples of conventional cosmetically active materials are sunscreens, penetration enhancers, moisturizers, surfactants, emollients, colorants, conditioners, bacteriocides, astringents, detergents and other such materials. Any conventional sunscreen may be included in the claimed composition. 
     These topical composition can contain any conventional excipients and additives commonly used in preparing skin compositions. Among the conventional additives or excipients are preservatives, thickeners, perfumes and the like. In addition, conventional anti-oxidants such as butylated hydroxy anisoles (BHA), ascorbyl palmitate, propyl gallate, citric acid, butylated hydroxytoluene (BHT), ethoxyquin, and the like can be incorporated into these compositions. These compositions may contain thickening agents, solubilizers, humectants, emulsifiers and viscosity stabilizers, any of which are well known in the art. In addition, these compositions can contain flavoring, perfuming, or coloring agents conventionally used. 
     The topical compositions should be applied to the skin with a frequency to be determined for an individual patient. In general, the particular regimen for application will depend on the age, weight, and skin condition of the individual. However, an exemplary regimen for retinoic acid application to reverse sun damage and reduce wrinkling is at least one application to the skin at least 2 to 3 times weekly for at least 5 months, and thereafter as needed to maintain skin elasticity. For acne treatment, an exemplary regimen is one or more applications daily for about four to six weeks. 
     This invention is further illustrated in the following examples. These examples are for illustration only and are intended not to limit the claimed invention. 
     EXAMPLE 1 
     Example 1 demonstrates that skin irritation caused by topical application of retinoic acid can be reduced if the retinoic acid is applied with alpha-tocopherol. Skin irritation is determined from the amount of inflammation developed in the area of application, specifically the ear. The amount of inflammation is related to the increase in the number of inflammatory cells (neutrophils) in ear tissues caused by retinoic acid application. Increase in neutrophils is directly proportional to MPO activity (MPO is a neutrophil marker enzyme), which activity is quantified colorimetrically by adding substrate and measuring optical density resulting from the MPO reacting on the substrate. Increased ear weight due to inflammation is another measure of the amount of inflammation caused by retinoic acid application. 
     Male CD-1 mice (5 weeks old) were dosed topically on the dorsal side of the right ear daily for eight (8) days with 25 μl of an acetone solution containing both 0.08% (20 μg/25 μl) 13-cis-retinoic acid and various doses of alpha tocopherol (Vitamin E), ranging from 0.01% to 5.0% (2.5 μg to 1.2 mg). Eight animals per group were used. Control groups were treated either with a solution of 0.08% 13-cis-retinoic acid alone or with the solvent (acetone). On day nine (9) the animals were sacrificed by CO 2  inhalation and biopsy punches (6 mm diameter) were removed from the treated ears. The biopsy punches were weighed, homogenized, and the homogenate was assayed for MPO activity, according to the method of Bradley, et al. (3) which was adapted to 96 well microtiter plates. MPO activity was determined by measuring the change in optical density of the reaction mixture at 450 nm in a 96 well plate reader (SLT Lab instruments) over a period of two minutes. The data are expressed as percent inhibition of alpha tocopherol (Vitamin E) treated groups relative to the control groups according to the formula 1  : ##EQU1## 
    
     Topical application of 13-cis-retinoic acid for eight (8) days to mouse ears resulted in a dose related increase in infiltration of polymorphonuclear neutrophils, as indicated by the increase in MPO activity. Ear wet weight was also increased in a dosed-related manner and this increase was partially due to ear inflammation and epidermal hyperproliferation in response to the retinoic acid. FIG. 1 shows MPO activity and wet weight in mouse ear punches increasing with increasing doses of 13-cis-retinoic acid. MPO activity is a measure of the inflammatory response, as discussed above. Alpha-tocopherol, at concentrations from 0.01% to 5.0%, inhibited the retinoic acid-induced increase in MPO activity (neutrophil infiltration) in a dose related manner. FIG. 2 shows retinoic acid-induced MPO activity in mouse ears decreasing with increasing doses of alpha-tocopherol. Maximum inhibition (70%) of 13-cis-retinoic acid-induced neutrophil infiltration was obtained at an alpha-tocopherol concentration of 5.0%. These data clearly demonstrate that topical alpha tocopherol (optimum doses) can ameliorate the inflammatory component induced by repeated topical application of 13-cis-retinoic acid. 
     EXAMPLE 2 
     The liquid compositions described herein can be provided for topical application in creams, lotions, shampoos, and any other topical formulation. The percentages given in these examples are percent by weight based on the total volume of the liquid composition. Specific formulations are described below. However, any conventional formulation can be used for the claimed composition. 
     
         ______________________________________                                    
a.    Liposomal Formulations                                              
      Ingredient            % by Weight                                   
______________________________________                                    
      Isotretinoin          0.050-1.000                                   
      Vitamin E             0.005-5.000                                   
      L-α-Dimyristyl Phosphatidyl Choline                           
                            0.062                                         
      Cholesterol           0.062                                         
      T-Butyl Alcohol       31.089                                        
      Lactose               6.000                                         
      Purified Water q.s. to                                              
                            100.000                                       
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b.  Water in Oil Cream                                                    
    Ingredient               % by Weight                                  
______________________________________                                    
    Isotretinoin             0.050-1.000                                  
    Vitamin E                0.005-5.000                                  
    Propylene Glycol Dicaprylate/Dicaprate                                
                             20.000                                       
    and Stearalkonium Bentonite (and)                                     
    Propylene Carbonate                                                   
    Caprylic/Capric Triglyceride                                          
                             20.000                                       
    Isostearyl Diglyceryl Succinate                                       
                              5.000                                       
    Purified Water q.s. to   100.000                                      
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c.    Hair Conditioning Gel                                               
      Ingredient          % by Weight                                     
______________________________________                                    
      Isotretinoin        0.050-1.000                                     
      Vitamin E           0.005-5.000                                     
      PEG-7-Glyceryl Cocoate                                              
                          10.000                                          
      Ethanol, Anhydrous  24.000                                          
      Methyl pyrol        5.000                                           
      Dimyristyl Phosphatidyl Choline                                     
                          0.030                                           
      Sodium Ascorbate    0.030                                           
      Citric Acid         0.100                                           
      Carbomer 940        0.500                                           
      B-Alanine           0.500                                           
      Purified Water q.s. to                                              
                          100.000                                         
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d.  Oil in Water Cream                                                    
    Ingredient               % by Weight                                  
______________________________________                                    
    Isotretinoin              0.05-1.00                                   
    Vitamin E                0.005-5.00                                   
    Propylene Glycol Dicaprylate/Dicaprate                                
                             8.95                                         
    Stearyl Alcohol          0.75                                         
    Glyceryl Stearate        4.00                                         
    Ceteareth-12             0.50                                         
    Ceteareth-20             0.50                                         
    Propylparaben            0.10                                         
    Methylparaben            0.15                                         
    Disodium Edetate         0.03                                         
    Glycerin                 5.00                                         
    Purified Water q.s. to   100.000                                      
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         ______________________________________                                    
e.     Cream (Anhydrous)                                                  
       Ingredient         % by Weight                                     
______________________________________                                    
       Isotretinoin        0.05-1.00                                      
       Vitamin E          0.005-5.00                                      
       Caprylic/Capric/Stearic                                            
                          29.00                                           
       Triglyceride                                                       
       Glyceryl Cocoate (and)                                             
                          43.00                                           
       Ceteareth-25                                                       
       Propylene Glycol Dicaprylate/                                      
                          8.95                                            
       Dicaprate                                                          
       Mineral Oil q.s. to                                                
                          100.000                                         
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f.     Oil in Water Microemulsion                                         
       Ingredient         % by Weight                                     
______________________________________                                    
       Isotretinoin        0.05-1.00                                      
       Vitamin E          0.005-5.00                                      
       DEA-Oleth-3 Phosphate                                              
                          8.95                                            
       Oleth-20           1.00                                            
       Oleth-10           15.00                                           
       Mineral Oil        4.00                                            
       Propylene Glycol Dicaprylate/                                      
                          8.00                                            
       Dicaprate                                                          
       BHT                0.03                                            
       Hexetidine         0.10                                            
       Citric Acid        0.05                                            
       Sodium Ascorbate   0.10                                            
       Sorbic Acid        0.10                                            
       Glycerin           5.00                                            
       Purified Water q.s. to                                             
                          100.000                                         
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g.     Topical Solution                                                   
       Ingredient       % by Weight                                       
______________________________________                                    
       Isotretinoin     0.050-1.000                                       
       Vitamin E        0.005-5.000                                       
       PEG-7-Glyceryl Cocoate                                             
                        10.000                                            
       Ethanol, Anhydrous                                                 
                        25.000                                            
       Purified Water q.s. to                                             
                        100.000                                           
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     REFERENCES 
     1. Weiss, J. S., Ellis, C. N., Headington, J. T., Tincoff, T., Hamilton, T. A., and Voorhees, J. J., Topical tretinoin improves photoaged skin: A double-blind vehicle controlled study. JAMA 1988; 259:527-32. 
     2. Weiss, J. S., Ellis, C. N., Headington, J. T., and Voorhees, J. J., Topical tretinoin in the treatment of aging skin. J. Am. Acad. Dermatol. 1988; 19:169-75. 
     3. Bradley, P. P., Priebat, D. A., Christensen, R. D. and Rothstein G. Measurement of cutaneous inflammation: Estimation of neutrophil content with an enzyme marker. J. Invest. Dermatol. 1982; 78:206-209. 
     4. Witting, L. A. Vitamin E and Lipid Anti-Oxidants in Free Radical Initiated Reactions, in: Free Radicals in Biology, Vol. IV (W. A. Pryor ed.) Academic Press, 1980. 
     5. Besa, E. C., Abrahm, J. L., Bartholomew, M. J., Hyzinski, M. and Nowell, P. C. Treatment with 13-cis-retinoic acid in transfusion-dependent patients with myelodysplastic syndrome and decreased toxicity with addition of alpha tocopherol. Amer. J. Med. 1990; 89:739-746.