Endogenous hyaluronan in the normal and traumatized rabbit iris

Hyaluronan as a promising excipient for ocular drug delivery

Hyaluronan (HA) is a naturally occurring polysaccharide and well known for its exceptional properties such as high biocompatibility and biodegradability, along with a low immunogenicity. Besides its use for various biomedical applications it recently came into focus as a favorable excipient for the formulation of various ocular therapeutics. This review article summarizes the ocular distribution of HA and its most heavily investigated binding protein "cluster of differentiation 44" (CD44) which is the rationale for the clinical use of HA, primarily as an additive in ocular applications ranging from eye drops to contact lenses. Moreover, examples will be given for using HA in various pre-clinical approaches to generate entirely new therapeutics, most notably in the field of nanotechnology.

COX-2 inhibitors prolong trauma-induced elevations of iris hyaluronan

PURPOSE

To investigate whether and how treatment with COX-2 inhibitors influences hyaluronan responses to a standardized trauma, argon laser induced iritis, in rabbits.

METHODS

Two different COX-2 inhibitors were used, SC-236 and rofecoxib. The drugs were administered orally, 6 mg/kg/day and 1.5 mg/kg/day respectively. Iris and aqueous humor hyaluronan concentrations were measured with a radiometric assay at different time points after laser irradiation.

RESULTS

The hyaluronan concentration in the iris increased 3-4-fold with a peak concentration of 129.1 microg/g wet weight 2 days after laser irradiation. It then decreased to normal values after 1 week. In eyes treated with either of the COX-2 inhibitors, iris hyaluronan concentrations did not decrease as rapidly and were significantly higher at day 4 and 7 when compared to drug untreated eyes.

CONCLUSION

Treatment with COX-2 inhibitors prolongs trauma induced elevation of iris content of endogenous hyaluronan. This may be, at least partly, due to an inhibition of interstitial fluid pressure regulation.

Effects of sympathetic denervation on the hyaluronan content of the anterior segment in the normal and traumatized rabbit eye

PURPOSE

To determine whether there is any involvement of sympathetic nerves in the regulation of ocular hyaluronan production in the normal and traumatized rabbit iris.

METHODS

Unilateral sympathetic denervation was performed by removing the right superior cervical ganglion. Hyaluronan concentrations in the iris and aqueous were measured with a radiometric assay at various time intervals after denervation. Peripheral iridectomy was also performed in both denervated and non-denervated eyes.

RESULTS

Hyaluronan concentrations in the iris tissue after denervation were observed to have increased after 1 day, reaching a peak of 129.6 +/- 5.7 microg/g wet weight at day 3. Two weeks later, hyaluronan concentrations had fallen back to normal levels. Ocular trauma with peripheral iridectomy in denervated eyes caused an increase of hyaluronan content of up to 253.5 +/- 30.5 microg/g wet weight, which was not significantly different from hyaluronan concentrations observed after the same trauma in non-denervated eyes.

CONCLUSION

Cervical sympathetic denervation results in a moderate increase of the hyaluronan content in the rabbit iris and does not appear to influence the hyaluronan response of the iris to trauma.

Influence of laser irradiation on endogenous hyaluronan in rabbit iris and aqueous humor

PURPOSE

To monitor changes of endogenous hyaluronan in the iris tissue and aqueous humor after an isolated trauma to the iris by argon laser irradiation of the anterior surface of the iris.

METHODS

Iris and aqueous hyaluronan concentrations in rabbit were measured with a radiometric assay at different time points after laser irradiation.

RESULTS

Total hyaluronan content in iris tissue increased 3-fold to a peak concentration of 71-72 microg/g at 1 and 2 days after laser treatment. Aqueous hyaluronan increased to a maximum of about 1.6 microg/ml at 2 h and 12 h after laser irradiation of the iris.

CONCLUSIONS

The iris tissue responds with increased hyluronan synthesis to an isolated iris argon laser irradiation and it seems to be the most important source of aqueous hyaluronan.