Free-Radical Formation during Vitrectomy Vitreous Substitutes

Abstract

 

Purpose

 

Complications such as nuclear sclerotic cataract and glaucoma are associated with vitrectomy in elderly patients. Increased oxygen tension in the vitreous cavity is associated with these complications, but causality is unclear. We have reported that significant hydroxyl free-radicals (OHFR) were formed during cutting of biomimetic vitreous hydrogels (ARVO #2144, 2013), and may provides an alternative mechanism of tissue damage during the vitrectomy. We have supplement previous data and have studied the quenching of free-radicals by naturally occurring anti-oxidants.

 

Methods

 

Synthetic acrylamide/acrylic acid cross-linked hydrogels were used as vitreous substitutes during vitrector cutting in the presence and absence of anti-oxidants. A cut rate 3000 cuts per minute was used, with variable suction pressures. Free-radical formation was followed by electron spin resonance (ESR), using 5,5-Dimethyl-1-Pyrroline-N-Oxide (DMPO) as a spin-trap and a magnetic field strength of 330-338 milli tesla (mT), focusing on the free-radical peaks between 333-334 mT. Separately, OHFR were calibrated using 40 uM FeSO4 plus H₂O₂, giving 80 uM of radicals. The anti-oxidants glutathione, lipoic acid and ascorbic acid were added at 80 uM concentration in the presence of the FeSO₄ and H₂O₂.

 

Results

 

Measurable quantities of OHFR were produced during the hydrogel cutting over a period of 20 minutes (Fig 1). Figure 2 suggests that glutathione is more effective than lipoic acid while ascorbate eliminated the OHFR peaks but produced its own ascorbyl FR peaks. The effect of glutathione and lipoic acid was additive, and the combination of all three also eliminated the OHFR and ascorbic acid FR peaks. The ESR signal produced by cutting in the presence of anti-oxidant was also quenched

 

Conclusions

 

Cutting of macromolecules by vitrector produces free radicals. Free radical production is mitigated in the presence of anti-oxidants. Ascorbic acid radicals were observed. Results indicate that it may be important to maintain a high antioxidant environment during vitrectomy, to prevent damage to the ocular tissues, especially in ageing patients where redox values are diminished. These results need to be validated in vivo.

 

 

Figure 1. OHFR signal with respect to time of cutting.

 

 

Figure 2. Quenching of OHFR free radical signal by ESR at 333-334 mT with anti-oxidants; lipoic acid (LA), glutathione (Glu) and ascorbic acid (Asc) singly and in combination.

 

Keywords: 634 oxidation/oxidative or free radical damage