Diabetic Cataract and the Total Antioxidant Status in Aqueous Humor Clin Chem Lab Med 2001; 39(2):143–145 © 2001 by Walter de Gruyter · Berlin · New York Hülya Aksoy 1 , Sait Keles 1 , Ibrahim Koçer 2 and Fatih Akçay 1 1 Department of Biochemistry, 2 Department of Ophthalmology, School of Medicine, Atatürk University, Erzurum, Turkey Some mechanisms have been proposed for cataract formation in diabetes mellitus such as excessive tissue sorbitol concentrations, abnormal glycosylation of lens proteins and increased free radical production in the intraocular region. We measured total antioxidant status and uric acid levels in aqueous humor from dia- betic (n=20) and non-diabetic subjects (n=16) with cataracts. The patients with diabetes and cataract had significantly lower aqueous humor total antioxidant status than those with senile cataract (p = 0.001). Serum and aqueous humor uric acid levels were sig- nificantly lower in the diabetic cataract group com- pared to the senile cataract group. In the diabetic cataract group, the aqueous humor antioxidant status correlated positively with the aqueous humor uric acid levels (p < 0.05). The results of this study suggest that reduced aqueous humor antioxidant status might be associated with reduced aqueous humor uric acid in patients with diabetic cataract. This decrease in aque- ous humor uric acid levels might lead to the accelera- tion of cataract formation. Key words: Diabetes, cataract; Antioxidant status; Aqueous humor; Uric acid. Abbreviations: ABTS, 2,2’-azino-di-(3-ethyl benzthiazo- line sulphonate); EDTA, ethylenediaminetetraacetic acid; HbA 1c , glycated haemoglobin; NADPH, nicoti- namide adenine dinucleotide phosphate; TAS, total an- tioxidant status. Introduction Oxidative mechanisms are claimed to play an impor- tant role in the pathogenesis of senile cataract. Mecha- nisms suggested for cataract formation in diabetes mellitus include excessive tissue sorbitol concentra- tion, abnormal glycosylation of lens proteins, alter- ations in the metabolism of phosphoinositides, and in- creased free radical production in the intraocular region (1). Free radical-mediated oxidative stress is in- creased in diabetes because of exposure to prolonged periods of hyperglycaemia which results in non-enzy- matic glycation of proteins. The resulting products are unstable and tend to generate free radicals. Oxidative stress has been implicated in the etiology of a large number of human chronic degenerative diseases (such as diabetes) including cataract (2). A variety of natural antioxidants exist which scavenge free radicals and prevent oxidative damage to biological structures. These include enzymes (superoxide dismutase and glutathione peroxidase) which are effective in the intra- cellular compartment, and small molecular weight molecules such as vitamin C, uric acid and vitamin E, which preferentially react with free radicals and are consumed in the process, especially in the extracellular environment (3). Previous studies have shown that in diabetic pa- tients antioxidant activity decreased compared with healthy controls (4, 5). McLauchlan et al . (6) have in- vestigated the suitability of the assay for total antioxi- dant status (TAS) to measure total antioxidant activity in the human aqueous humor. The study showed that the production of the 2,2’- azino-di-(3-ethyl benzthiazoline sulphonate)(ABTS) radical cation in the presence of human aqueous hu- mor followed lag phase kinetics consistent with this fluid acting as a sacrificial antioxidant. It also revealed that the assay responded in a predictable manner to two- and fourfold dilution of the aqueous humor, i.e., the lag phase decreased by two- and fourfold, respec- tively. Therefore, the assay was reliable for the mea- surement of total antioxidant activity in aqueous hu- mor (6). In the present study, we measured TAS and uric acid levels in aqueous humor from diabetic and non-dia- betic subjects with cataracts, in order to determine the role of oxidative stress in the pathogenesis of diabetic or non-diabetic cataract. Materials and Methods Aqueous humor was obtained from 20 type 2 diabetic (45–73 years) and 16 senile (55–75 years) patients with cataracts un- dergoing cataract extraction surgery. At the same time, blood samples were taken from the antecubital vein in the morning after overnight fasting. One aliquot was separated into EDTA- containing tubes for measurement of glycated haemoglobin (HbA 1c ). The rest of the blood was clotted and immediately centrifuged for 10 min at 3000 g to separate serum which was rapidly cooled and frozen at –80 °C until the assay of TAS and uric acid measurement. HbA 1c was measured using a com- mercially available chromatographic spectrophotometric as- say (Biosystems, Barcelona, Spain). Serum and aqueous hu- mor TAS was measured with the spectrophotometric method (Randox, Antrim, UK; lot no. 9976C). Briefly, the assay princi- ple is as follows: ABTS R is incubated with a peroxidase (met- myoglobin) and H 2 O 2 to produce the radical cation ABTS R+ . This has a relatively stable blue-green colour, which is mea- sured at 600 nm. Antioxidants in the added sample (serum or Brought to you by | New York University Bobst Library Technical Services Authenticated Download Date | 6/14/15 1:08 AM