Aqueous humor hydrogen peroxide analysis with dichlorophenol-indophenol

Area of Science:

• Biochemistry
• Analytical Chemistry
• Ophthalmology

Background:

• Hydrogen peroxide (H2O2) has been reported as a normal component of aqueous humor.
• The dichlorophenol-indophenol assay is a common method for H2O2 quantification.
• Previous studies have relied on this method without fully addressing its limitations.

Purpose of the Study:

• To critically evaluate the dichlorophenol-indophenol assay for measuring H2O2 in aqueous humor.
• To identify and quantify sources of error in the assay, specifically spontaneous H2O2 generation and ascorbate interference.
• To determine the accuracy of previously reported H2O2 concentrations in aqueous humor.

Main Methods:

• Analysis of aqueous humor using the dichlorophenol-indophenol method.
• Quantification of spontaneous H2O2 generation by monitoring absorbance changes in the absence of sample.
• Assessment of ascorbate's role in the assay and its interference with H2O2 measurement.
• Evaluation of aqueous humor's effect on the auto-oxidation rate of dichlorophenol-indophenol.

Main Results:

• The dichlorophenol-indophenol method exhibits spontaneous H2O2 generation (0.03 nmol min-1 microM-1) independent of ascorbate.
• Ascorbate auto-oxidation is not the source of spontaneous H2O2; it is consumed by dichlorophenol-indophenol.
• Assay results show an artifactual positive correlation between ascorbate and H2O2 levels.
• Rabbit aqueous humor H2O2 measurements using this method, without corrections, yield inaccurate high values (e.g., 25.3 microM).

Conclusions:

• The dichlorophenol-indophenol assay has significant limitations, including spontaneous H2O2 generation and ascorbate interference, leading to overestimation.
• Previous H2O2 concentrations reported for aqueous humor using this method are likely incorrect.
• Appropriate corrections for spontaneous H2O2 generation and ascorbate levels are necessary for accurate H2O2 quantification in aqueous humor.