Therapeutic Use of Crystallin Biomaterials

Abstract

Crystallin proteins are traditionally known to maintain transparency and modulate the refractive index in the vertebrate eye lens. Human crystallins have also been shown to be therapeutic and can reduce oxidative stress, inflammation and apoptosis, as well as stabilise proteins. Hoki-derived crystallin proteins are a plentiful and sustainable source of crystallin proteins, as hoki fish heads are a low-value waste product of the commercial fishing industry. However, unlike human crystallins, the therapeutic properties of this protein source are unknown. This research focuses on utilising crystallin proteins obtained from a low-cost source, hoki (Macruronus novaezelandiae), as a novel biomaterial with therapeutic potential. Crystallinbased hydrogels may be used to provide sustained drug delivery to the eye through action as a therapeutic carrier. In this thesis, a novel crystallin hydrogel was successfully developed using poly ethylene glycol diacrylate (PEGDA). Moreover, the therapeutic effects of hoki crystallin were shown for the first time. This thesis demonstrates the ability of hoki crystallins to increase proliferation and protect against oxidative stress in human corneal epithelial cells (HCEC). Furthermore, the biocompatibility and physical properties of crystallin-based PEGDA hydrogels were characterised. Fourier transform infrared spectroscopy (FTIR) was used to confirm crosslinking following photopolymerisation, and circular dichroism (CD) was used to confirm the maintenance of the native secondary structure of incorporated crystallin proteins. Scanning electron microscopy (SEM) showed the developed material to have a smooth surface, and swelling studies demonstrated that the hydrogels can swell up to 400%. The swelling potential of the hydrogels was dependent on the concentration of protein, where higher concentrations of crystallin resulted in lower swelling. Crystallin-PEGDA hydrogels were also shown to be biocompatible under the tested conditions. As a proof of concept and to verify the ability of the developed crystallin-PEGDA hydrogels to act as a therapeutic drug delivery vehicle, the release profile of tetracycline hydrochloride (TH) and crystallin proteins was investigated. The hydrogels provided sustained delivery of model drug TH for 6 hours and crystallin protein for 2 weeks. TH released from the material maintained its antibacterial activity. This work demonstrated the potential of hoki crystallins both as a therapeutic agent and as a low-cost protein crystallin source to develop biomaterials with broad applications.