A new chromatographic method for the fractionation of hyaluronic acid

Physicochemical Properties of Hyaluronic Acid-Based Lubricant Eye Drops

Purpose

To assess the physicochemical properties of hyaluronic acid (HA)-based artificial tears.

Methods

The average molecular weight (MW) and polydispersion index (PDI) of HA in 18 commercially available artificial tears were determined by light scattering/high-performance liquid chromatography. Osmolality, pH, viscosity, and sodium concentration were determined using an osmometer, pH meter, rheometer, and inductively coupled plasma mass spectrometer, respectively.

Results

The MW of HA varied considerably between formulations. The PDI was >2.0 in two formulations (2.28 and 4.94), suggesting the presence of a copolymer and/or HA size variability. Three formulations exhibited viscosity exceeding the blur threshold at different shear rates. Viscosity at low shear rates was generally highest in formulations containing high-MW HA. Correlations were found between observed viscosity and a predictive/calculated value, except for four copolymer-containing formulations, and osmolality (range, 154–335 mOsm/kg) and sodium concentration (range, 22–183 mM), with two exceptions. Compared with organic osmolytes, adding sodium decreased viscosity, particularly at lower shear rates.

Conclusions

In the context of the literature, our findings suggest that for most patients with dry eye disease, the ideal HA-based artificial tear should include high-MW HA with a low PDI and exhibit enhanced viscosity at low shear rate (without exceeding the blur threshold). The inclusion of synergistic copolymers and a low sodium concentration may increase viscosity, but whether any of these physicochemical properties or correlations can predict clinical efficacy will require further investigation.

Translational Relevance

Understanding the properties of HA-based artificial tears will support the development of unique formulations that target specific ocular surface conditions.

Extracellular mammalian polysaccharides: glycosaminoglycans and proteoglycans

This review of the mammalian extracellular matrix polysaccharides covered the glycosaminoglycans (GAGs) and their association into proteoglycans. As they necessarily pertain to the chromatographic and electrophoretic separations of these molecules, the structural features of the five principal GAGs were briefly reviewed. Much of the current structural work as well as the separation technology has been concerned with the sulfation state and copolymeric sequences of the individual classes of GAGs. The separation methods discussed included electrophoresis by agarose, acrylamide and cellulose acetate, high-performance liquid chromatography (HPLC), ion-exchange, gel permeation and biospecific affinity methods. Since detection systems are an integral part of chemical separation technology, current thoughts about the best methods to assay GAGs or detect column fractions were discussed. These included polysaccharide-specific detection systems such as Alcian blue dye, 1,9-dimethylmethylene blue, bovine serum albumin-Coomassie blue, as well as non-specific carbohydrate detection systems such as the carbazole or indole hydrochloride methods. Instrumentation used in the detection of chromatography fractions for these molecules was discussed, since the usual ultraviolet detector, standard with HPLC equipment, is often unsatisfactory. The most sensitive specific detection method for GAGs is the use of monoclonal antibodies, which are only now becoming commercially available. The use of these antibodies, combined with HPLC separation, appears to be the best available biochemical technology for studying the extracellular matrix polysaccharides. Finally, the association between proteoglycans, GAGs and mammalian disease processes was reviewed, emphasizing mucopolysaccharidoses and arthritis. The early detection of both of these diseases is desired for effective counselling and treatment. Many of the methods discussed here have been applied, but others are yet to be tried in efforts to further that goal.

Conformational differences between hyaluronates of gel and liquid human vitreous: fractionation and circular dichroism studies

Post-mortem human vitreous samples (liquid and gel) of comparable intrinsic viscosity values (n approximately equal to 3000 cc/g) were chromatographed on DEAE-Sephacel columns at 4 degrees C using a linear salt gradient ranging from 0----0.4 M NaCl. All samples examined produced numerous discrete hyaluronic acid (HA) fractions. The HA fractions from liquid vitreous were eluted at lower salt concentrations than those from gel vitreous. Several HA fractions from vitreous analyzed by circular dichroism (CD) displayed CD minima at 210 nm, with an ellipticity value of 14 to 16 X 10(3) deg X cm2d mole-1. However, all HA fractions from liquid vitreous showed lower ellipticity values and a weak positive signal above 240 nm. This signal was absent in HA fractions from gel vitreous. Results suggest that subtle but definite conformational differences involving carboxylic groups exist between gel and liquid vitreous hyaluronate.