Biotechnological production of hyaluronic acid: a mini review by Jun Hui Sze, Jeremy C. Brownlie, and Christopher A. Love
Hyaluronic acid (HA) is a polysaccharide found in the extracellular matrix of vertebrate epithelial, neural and connective tissues. Due to the high moisture retention, biocompatibility and viscoelasticity properties of this polymer, HA has become an important component of major pharmaceutical, biomedical and cosmetic products with high commercial value worldwide. For example, HA with high molecular weight (greater than 10 kDa) is desirable for products used in ophthalmology, orthopaedic, cosmetics and tissue engineering (Allison and Grande-Allen 2006; Fagien and Cassuto 2012; Kogan et al. 2007) whereas HA with low molecular weight (about 5 kDa and below) are useful for producing substances that promote angiogenesis, inhibit tumour progression or induce expression of pro-inflammatory mediators (Jagannath and Ramachandran 2010; Tammi et al. 2008). Currently there are two production processes employed to obtain HA polymer in commercial quantities: extraction from animal tissues, or more recently though the application of bacterial expression systems in Streptococcus Extraction from animal tissues Since the early 1930s when HA was first isolated from bovine vitreous humor (Meyer and Palmer 1934), extraction of HA has been widely carried out using other animal tissues including human umbilical cord, rooster comb, and bovine synovial fluid. HA derived from animal tissues have naturally high molecular weights Disadvantages of animal-derived HA First, the extraction processes have always experience technical limitations due to harsh extraction conditions that comes with grinding, acid treatment, and repeated extraction with organic solvents. This uncontrolled degradation technique greatly affects not only the yield but also the polydispersity (range of sizes) of HA (Boeriu et al. 2013). A second problem is that animal HA may still be bound to cellular proteins including hyaluronidase, a HA-specific binding protein (Fraser et al. 1997). These contaminant proteins are undesirable as there may be a chance that these will illicit an immune response. Moreover, there is a potential risk of contamination with nucleic acids, prions (bovine) and viruses (avian) which could result in the transmission of infectious disease (Shiedlin et al. 2004). Finally, extracting HA from animal tissues is costly as it takes considerable time to complete, is labour intensive and requires large facilities that can accommodate processes involved from collection of tissue from the animal to extraction and purification of HA. As a consequence of these technical and safety issues, biotechnological production of HA is seen as a preferred method of producing HA. Bacterial expression systems in Streptococci The has（HA synthase）operon was first discovered in early 1990s when a gene encoding the enzyme responsible for HA synthesis, denoted as HA synthase or HAS, was identified from Group A Streptococcus (S. pyogenes) (DeAngelis et al. 1993). This gene is part of an operon containing the hasA gene that encodes HA synthase, hasB gene that encodes UDP-glucose dehydrogenase, and the hasC gene that encodes UDP-glucose pyrophosphorylase (Crater et al. 1995; Dougherty and van de Rijn 1993). The has operon in other streptococci, such as S. zooepidemicus, contain two additional genes, hasD and hasE that encode a bi-functional enzyme (acetyltransferase and pyrophosphorylase) and phosphoglucoisomerase respectively, allowing HA to be synthesised by additional metabolic pathway. The addition of these two genes to the hasoperon are thought to have been facilitated by intragenomic gene duplication together with frequent homologous recombination (Blank et al. 2008). And it's now the major production method of HA, owning advantages of low cost, high yield and animal-origin free. Medical Sodium Hyaluronate Gel produced by Singclean are animal-origin free medical polymer materials extracted and refined by high-tech bio-engineering from streptococcal fermentation metabolites with high viscoelasticity, lubricity, physical alterability and good biocompatibility. HA market in healthcare industry HA’s essential functions in the human eye, synovial fluid of joints and in the epidermal layers, has led to considerable interest in developing new methods to successfully synthesise and deliver HA. A recent market analysis report predicted that as a consequence of an aging population and an increase in osteoarthritis the global market for HA visco-supplementation in humans alone was estimated to be more than $2.5 billion by 2017 (MRG.Net 2013).