Organic compounds

Abstract

A skin care composition comprising low molecular weight acetylated hyaluronic acid or its sodium salt having a weight average molecular weight less than 50 kDa, and a degree of acetylation of at least 3.6 is useful in the treatment of the visible effects of age on human skin.

1 . A skin care composition comprising low molecular weight acetylated hyaluronic acid or its-sodium salt thereof, wherein:
 the low molecular weight acetylated hyaluronic acid or its sodium salt h a weight average molecular weight of 50 kDa or less and an average degree of acetylation of greater than 3.6.   
     
     
         2 . The skin care composition of  claim 1 , wherein:
 the low molecular weight acetylated hyaluronic acid or its sodium salt has an average degree of acetylation of 3.7 or greater.   
     
     
         3 . The skin care composition of  claim 1 , wherein:
 the low molecular weight acetylated hyaluronic acid or its sodium salt has a weight average molecular weight of 35 kDa or less.   
     
     
         4 . The skin care composition of  claim 1 , wherein:
 the low molecular weight acetylated hyaluronic acid or its sodium salt a polydispersity index that is less than 2.0.   
     
     
         5 . The skin care composition of  claim 1 , wherein:
 the degree of acetylation is determined by quantitative 2D NMR.   
     
     
         6 . A method of preparing low molecular weight acetylated hyaluronic acid or sodium salt thereof having a weight average molecular weight of 50 kDa or less and an average degree of acetylation of greater than 3.6, comprising the steps of:
 (i) providing a low molecular weight hyaluronic acid having a molecular weight of 50 kDa or less;   (ii) subjecting it to acetylation conditions; and   (iii) isolating the low molecular weight acetylated hyaluronic acid.   
     
     
         7 . The method of  claim 6 , comprising the further step of:
 (iv) reacting the low molecular weight acetylated hyaluronic acid with a base that provides a source of sodium ions to obtain a solution of sodium acetyl hyaluronate.   
     
     
         8 . The method of  claim 7 , wherein the reaction of low molecular weight acetylated hyaluronic acid with a base to obtain the solution of sodium acetyl hyaluronate is carried out at a pH that does not exceed 9. 
     
     
         9 . The method of  claim 7  comprising the further step of:
 (v) dehydrating the solution by lyophilization or spray-drying. 
 
     
     
         10 . Low molecular weight acetylated hyaluronic acid or sodium salt thereof having a weight average molecular weight of 50 kDa or less and an average degree of acetylation of greater than 3.6, in the form of a white powder having an L* value of about 90 or more, and a b* value of less than about 8. 
     
     
         11 . A method of inhibiting the degradation of the skin's extracellular matrix associated with elevated levels of matrix-degrading enzymes, said method comprising the step of:
 applying to the skin an effective amount of the skin care composition according to  claim 1 .   
     
     
         12 . The method of  claim 11 , which method causes a reduction in the visible signs of aging on the skin. 
     
     
         13 . The method of  claim 11 ,
 wherein the matrix-degrading enzymes are metalloproteinases.   
     
     
         14 . The method of  claim 11 , wherein the acetylated hyaluronic acid or sodium salt thereof in the skin care composition applied to the skin inhibits the degradation of collagen in the extra-cellular matrix. 
     
     
         15 . The skin care composition of  claim 2 , wherein the average degree of acetylation is 3.8 or greater. 
     
     
         16 . The skin care composition of  claim 3 , wherein the average molecular weight is about 30 kDa or less. 
     
     
         17 . The skin care composition of  claim 4 , wherein the polydispersity index is less than 1.8. 
     
     
         18 . The method of  claim 6 , wherein the acetylation conditions comprise:
 reacting the low molecular weight hyaluronic acid with an acetic acid/acetic anhydride mixture in the presence of a strong acid.   
     
     
         19 . A method of inhibiting the degradation of the skin's extracellular matrix associated with elevated levels of matrix-degrading enzymes, said method comprising the step of:
 applying to the skin an effective amount of the low molecular weight acetylated hyaluronic acid or its sodium salt according to  claim 10 .   
     
     
         20 . The method of  claim 13 , wherein the metalloproteinases are MMP-1 and/or MMP-3.