Hydroxyl Free-Radical Formation during Vitrectomy

Abstract

 

Purpose

 

We are examining the formation of hydroxyl free-radicals (OHFR) in natural and artificial hydrogels during vitrectomy and expanding our knowledge of polymer and macromolecular sciences to the natural vitreous by evaluating the possibility of free-radical production as a mechanism of tissue damage during the vitrectomy.

 

Methods

 

Collagen gels and synthetic hydrogels [copolymer acrylamide/10 % sodium acrylate] were used as vitreous phamtoms during vitrectomy [ProCare Plus Vitrectomy System, Vision Care Devices] with a cut rate per minute of 3000 in the presence of a fiber-optic light source. This procedure was repeated up to ten times then the hydrogel was analyzed for OHFR formation; see Korotkova, [Int. J. Mol. Sci. 12, 401-409; 2011] where non-fluorescent terephthalic acid H2-TA is hydroxylated by OHFR to give the fluorophor TA-OH. The reaction in hydrogels was compared to and quantified by the Fenton reaction of iron and hydrogen peroxide free-radical production (Fe²⁺ + H₂O₂→Fe³⁺ + 2OHFR→2TA-OH).

 

Results

 

Measurable quantities of OHFR were produced during the hydrogel cutting procedure, which was proportional to the number of times the gel was passed through the vitrectomy cutter, see figure. The difference in the level of free-radical production is likely dependent on the concentration of material in the gels with the OHFR levels corresponding to ~0.5 (1cut)- 4.0 uM (10 cuts) in the Am copolymer gel.

 

Conclusions

 

Currently, increased partial pressure of oxygen, in the absence of the natural vitreous, is implicated in the pathogenesis of the increased incidence of nuclear sclerotic cataract and open angle glaucoma after vitrectomy [Beebe, Phil. Trans. R. Soc. B, 366, 1293-1300, 2011]. Mechanical disruption of polymers and macromolecules is known to generate free-radicals. It is possible that sufficient oxygen free-radicals are generated during vitrectomy to indiscriminately react with cellular components and cause their dysfunction depending on the redox buffer capacity (RBC) of cell and tissues. A combination of free-radical production along with the age-related decrease in RBC of tissues could offer an alternate hypothesis to formation of cataract post-vitrectomy.

 

 

Fluorescent detection of the production of hydroxyl free-radicals by the Fenton reaction with the hydroxylation of terephthalic acid.

 

 

Fluorescent detection of the production of hydroxyl free-radicals by the cutting of hydrogels with vitrectomy unit.

 

Keywords: 762 vitreoretinal surgery • 634 oxidation/oxidative or free radical damage