97th DOG Annual Meeting 1999



C. Erb1,3, W. M. Nau2, J. Flammer1

To determine the role of ascorbic acid (AA) as a free-radical scavenger in aqueous humour (AH) and to characterize its reactivity.

Methods: Fresh porcine AH was taken within 2 minutes after death and frozen at -70ºC to avoid chemical changes of the AH. With a pooled volume of 20 ml we used spectrophotometry to quantify the AA concentration (lmax = 266 nm; c=600 µM) and to monitor its decay. The activity of AA upon free radicals was determined with time-resolved fluorimetry (laser excitation at 351 nm) using diazabicyclooctene (DBO) as a probe and an optically matched reference solution of AA in phosphate-based solution (PBS).

Results: The UV absorption of AA in AH was constant at l=266 nm. The lifetime of the radical probe DBO was reduced from 325 ns in neat aerated PBS to 197 ns in AH (kq=2.05 x109 M-1s-1). The same lifetime shortening was observed for the AA reference solution (225 ns). The AA decay in AH was found to be 17 µM/h, ten times faster than the decay in a freshly self-mixed PBS solution (pH=7.2), i.e. 1.7 µM/h.

Conclusion: The activity of AH toward the radical probe DBO matched that of the reference solution with identical AA concentrations, thus providing evidence that AA is the main radical scavanger in the AH. Therefore, AA seems to be the most important substance to protect the eye from radical-induced cell-damage.

1University Eye Clinic Basel, Switzerland
2Institute of Physical Chemistry, University Basel, Switzerland
3Eye Clinic, Medizinische Hochschule Hannover, Germany