Inhibition of Free Radical Degradation in Medical Grade Hyaluronic Acid - Hyaluronic Acid for Biomedical and Pharmaceutical Applications - page 103

5 Inhibition of Free Radical Degradation

in Medical Grade Hyaluronic Acid

Tamer Mahmoud Tamer, Katarína Valachová and
Ladislav Šoltés

5.1 Introduction

Hyaluronan, also known as hyaluronic acid (HA) ( Figure 5.1 ) is
an unbranched endogenous polysaccharide consisting of repeating
disaccharide units of b-1,4- d -glucuronic acid and b-1,3- N -acetyl-
d -glucosamine. HA is a glycosaminoglycan (GAG). Most GAG are
synthesised in the endoplasmic reticulum and Golgi apparatus. In
contrast, HA is synthesised at the cell membrane [1, 2]. To build
up the HA polymer, the synthesis of HA is catalysed by hyaluronan
synthases, the enzymes which utilise both sugar substrates [3].
Hyaluronan synthases (HAS1, HAS2 and HAS3) are predicted to have
multiple membrane spanning domains with a large intracellular loop
on the inner face of the plasma membrane. Hyaluronan molecules are
extruded into the extracellular matrix as they are synthesized [4], but
they also exist intracellularly. In the extracellular matrix, HA exists
in a number of different forms. For example, in vertebrates it can be
intercalated within a proteoglycan complex, referred to as glycocalyx,
or it can be bound to membrane receptors of the cell surface. HA
can also interact with binding proteins in the extracellular matrix,
the so-called hyaladherins, which is also the case for intracellular
hyaluronan [5].

Historically, the first report about HA was written in 1880, when
the French chemist Portes observed a mucin in the vitreous body,