Spontaneous generation of superoxide anion by human lens proteins and by calf lens proteins ascorbylated in vitro

Vitamin C supplementation for diabetes management: A comprehensive narrative review

Growing evidence suggests that vitamin C supplementation may be an effective adjunct therapy in the management of people with diabetes. This paper critically reviews the current evidence on effects of vitamin C supplementation and its potential mechanisms in diabetes management. Evidence from meta-analyses of randomized controlled trials (RCTs) show favourable effects of vitamin C on glycaemic control and blood pressure that may be clinically meaningful, and mixed effects on blood lipids and endothelial function. However, evidence is mostly of low evidence certainty. Emerging evidence is promising for effects of vitamin C supplementation on some diabetes complications, particularly diabetic foot ulcers. However, there is a notable lack of robust and well-designed studies exploring effects of vitamin C as a single compound supplement on diabetes prevention and patient-important outcomes (i.e. prevention and amelioration of diabetes complications). RCTs are also required to investigate potential preventative or ameliorative effects of vitamin C on gestational diabetes outcomes. Oral vitamin C doses of 500-1000 mg per day are potentially effective, safe, and affordable for many individuals with diabetes. However, personalisation of supplementation regimens that consider factors such as vitamin C status, disease status, current glycaemic control, vitamin C intake, redox status, and genotype is important to optimize vitamin C's therapeutic effects safely. Finally, given a high prevalence of vitamin C deficiency in patients with complications, it is recommended that plasma vitamin C concentration be measured and monitored in the clinic setting.

In vitro antioxidant and anticataractogenic potential of silver nanoparticles biosynthesized using an ethanolic extract of Tabernaemontana divaricata leaves

Silver nanoparticles (AgNPs) have been found useful in biological systems and in medicine since they possess a large surface area to volume ratio, which confers on them several unique properties. In the present study, AgNPs that had been biosynthesized using an ethanolic extract of Tabernaemontana divaricata leaf were evaluated for putative antioxidant potential and efficacy in preventing experimental in-vitro selenite-induced opacification of the ocular lens (cataractogenesis). The antioxidant potential of the AgNPs was evaluated in-vitro by looking for radical-scavenging activity on 1,1-diphenyl-2-picrylhydrazyl (DPPH) and hydrogen peroxide (H₂O₂) free radicals as well as by determining reducing power. The anticataractogenic potential of the AgNPs was evaluated in an in-vitro model of selenite-induced cataractogenesis in five groups of Wistar rat lenses cultured in Dulbecco's modified Eagle's medium (DMEM) for 24h: Group I lenses (negative control) were cultured in DMEM alone; Group II lenses were exposed to sodium selenite alone (100μM); Group III lenses were exposed simultaneously to sodium selenite and the T. divaricata extract (250μg/ml); Group IV lenses were exposed simultaneously to sodium selenite and the biosynthesized AgNPs (125μg/ml); and Group V lenses were exposed to the AgNPs alone. In these lenses, gross morphological changes, as well as activities of catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione-S-transferase (GST), and levels of reduced glutathione (GSH) and malondialdehyde (MDA), were determined. In-vitro, the AgNPs (which were spherical in shape with an average diameter ranging from 15 to 50nm) showed potent and concentration-dependent radical-scavenging activity on DPPH and H₂O₂ free radicals as well as reducing power. The gross morphological changes seen in the cultured rat lenses were: all eight control (Group I) lenses remained transparent; dense opacification was noted in all eight selenite-challenged untreated (Group II) lenses; in selenite-challenged, simultaneously T. divaricata extract-treated (Group III) lenses, no opacification occurred in seven of eight (87.5%) lenses and only minimal opacification in one (12.5%) lens; all the eight Group IV (selenite-challenged, simultaneously AgNPs-treated) lenses did not show any opacification; and all the eight Group V lenses (exposed to AgNPs alone) remained as transparent as control lenses. The mean activities of CAT, SOD, GPx and GST, and the mean levels of GSH, were significantly (p<0.05) lower in Group II lenses than those in Groups I, III, IV and V lenses, while the mean MDA level was significantly (p<0.05) higher in Group II lenses than those in Groups I, III, IV and V lenses; oxidative damage possibly occurred in Group II lenses, whereas this appears to have been prevented in Groups III and IV lenses. These observations suggest that the T. divaricata leaf ethanolic extract, and also the AgNPs biosynthesized using the T. divaricata extract, possess effective in-vitro antioxidant activity and the potential to prevent experimental selenite-induced opacification in cultured Wistar rat lenses.

Ascorbic acid and protein glycation in vitro

The aim of the study was to compare the effects of ascorbic acid (AA) in vitro in the absence and in the presence of cell-dependent recycling. In a cell-free system, AA enhanced glycoxidation of bovine serum albumin (BSA) by glucose and induced BSA glycation in the absence of sugars. On the other hand, AA did not affect erythrocyte hemolysis, glycation of hemoglobin and erythrocyte membranes, and inactivation of catalase, protected against inactivation of acetylcholinesterase of erythrocytes incubated with high glucose concentrations and enhanced the loss of glutathione. These results can be explained by assumption that AA acts as a proglycating agent in the absence of recycling while is an antiglycating agent when metabolic recycling occurs.

High-dose supplements of vitamins C and E, low-dose multivitamins, and the risk of age-related cataract: a population-based prospective cohort study of men

We examined the associations of high-dose supplements of vitamins C and E and low-dose multivitamins with the risk of age-related cataract among 31,120 Swedish men, aged 45-79 years, in a population-based prospective cohort. Dietary supplement use was assessed from a questionnaire at baseline in 1998. During follow-up (January 1998-December 2006), 2,963 incident age-related cataract cases were identified. The multivariable-adjusted hazard ratio for men using vitamin C supplements only was 1.21 (95% confidence interval (CI): 1.04, 1.41) in a comparison with that of non-supplement users. The hazard ratio for long-term vitamin C users (≥10 years before baseline) was 1.36 (95% CI: 1.02, 1.81). The risk of cataract with vitamin C use was stronger among older men (>65 years) (hazard ratio = 1.92, 95% CI: 1.41, 2.60) and corticosteroid users (hazard ratio = 2.11, 95% CI: 1.48, 3.02). The hazard ratio for vitamin E use only was 1.59 (95% CI: 1.12, 2.26). Use of multivitamins only or multiple supplements in addition to vitamin C or E was not associated with cataract risk. These results suggest that the use of high-dose (but not low-dose) single vitamin C or E supplements may increase the risk of age-related cataract. The risk may be even higher among older men, corticosteroid users, and long-term users.

Kynurenines: from the perspective of major psychiatric disorders

Psychiatric disorders are documented to be associated with a mild pro-inflammatory state. Pro-inflammatory mediators could activate the tryptophan breakdown and kynurenine pathway with a shift toward the neurotoxic arm where excitotoxic N-methyl-D-aspartate receptor agonist quinolinic acid is formed. An unbalanced metabolism in terms of neuroprotective and neurotoxic effects, such as reduced kynurenic acid to kynurenine ratio, has been demonstrated in the major psychiatric disorders such as unipolar depression, bipolar manic-depressive disorder and schizophrenia, and in drug-induced neuropsychiatric side effects such as interferon-α treated patients. The changes in serum or plasma are shown to be associated with central changes such as in the cerebrospinal fluid and certain brain areas. While currently available antidepressants and mood stabilizers could not efficiently improve these neurochemical changes within the same period that could induce clinical improvement, some antipsychotic treatments could reverse certain metabolic imbalances. Some of these changes were tested also in animal models. In this review the role of this unbalanced kynurenine metabolism through interactions with other neurochemicals is discussed as a major contributing pathophysiological mechanism in psychiatric disorders. Moreover, the biomarker role of kynurenine metabolites and future therapeutic opportunities are also discussed.

In vivo inhibition of l-buthionine-(S,R)-sulfoximine-induced cataracts by a novel antioxidant, N-acetylcysteine amide

The effects of N-acetylcysteine amide (NACA), a free radical scavenger, on cataract development were evaluated in Wistar rat pups. Cataract formation was induced in these animals with an intraperitoneal injection of a glutathione (GSH) synthesis inhibitor, l-buthionine-(S,R)-sulfoximine (BSO). To assess whether NACA has a significant impact on BSO-induced cataracts, the rats were divided into four groups: (1) control, (2) BSO only, (3) NACA only, and (4) NACA+BSO. The control group received only saline ip injections on postpartum day 3, the BSO-only group was given ip injections of BSO (4mmol/kg body wt), the NACA-only group received ip injections of only NACA (250mg/kg body wt), and the NACA+BSO group was given a dose of NACA 30min before administration of the BSO injection. The pups were sacrificed on postpartum day 15, after examination under a slit-lamp microscope. Their lenses were analyzed for selective oxidative stress parameters, including glutathione (reduced and oxidized), protein carbonyls, catalase, glutathione peroxidase, glutathione reductase, and malondialdehyde. The lenses of pups in both the control and the NACA-only groups were clear, whereas all pups within the BSO-only group developed well-defined cataracts. It was found that supplemental NACA injections during BSO treatment prevented cataract formation in most of the rat pups in the NACA+BSO group. Only 20% of these pups developed cataracts, and the rest retained clear lenses. Further, GSH levels were significantly decreased in the BSO-only treated group, but rats that received NACA injections during BSO treatment had these levels of GSH replenished. Our findings indicate that NACA inhibits cataract formation by limiting protein carbonylation, lipid peroxidation, and redox system components, as well as replenishing antioxidant enzymes.

Vitamin C supplements and the risk of age-related cataract: a population-based prospective cohort study in women

BACKGROUND

Experimental animal studies have shown adverse effects of high-dose vitamin C supplements on age-related cataract.

OBJECTIVE

We examined whether vitamin C supplements (approximately 1000 mg) and multivitamins containing vitamin C (approximately 60 mg) are associated with the incidence of age-related cataract extraction in a population-based, prospective cohort of women.

DESIGN

Our study included 24,593 women aged 49-83 y from the Swedish Mammography Cohort (follow-up from September 1997 to October 2005). We collected information on dietary supplement use and lifestyle factors with the use of a self-administrated questionnaire. Cataract extraction cases were identified by linkage to the cataract extraction registers in the geographical study area.

RESULTS

During the 8.2 y of follow-up (184,698 person-years), we identified 2497 cataract extraction cases. The multivariable hazard ratio (HR) for vitamin C supplement users compared with that for nonusers was 1.25 (95% CI: 1.05, 1.50). The HR for the duration of >10 y of use before baseline was 1.46 (95% CI: 0.93, 2.31). The HR for the use of multivitamins containing vitamin C was 1.09 (95% CI: 0.94, 1.25). Among women aged > or = 65 y, vitamin C supplement use increased the risk of cataract by 38% (95% CI: 12%, 69%). Vitamin C use among hormone replacement therapy users compared with that among nonusers of supplements or of hormone replacement therapy was associated with a 56% increased risk of cataract (95% CI: 20%, 102%). Vitamin C use among corticosteroid users compared with that among nonusers of supplements and corticosteroids was associated with an HR of 1.97 (95% CI: 1.35, 2.88).

CONCLUSION

Our results indicate that the use of vitamin C supplements may be associated with higher risk of age-related cataract among women.

Lens aging: effects of crystallins

The primary function of the eye lens is to focus light on the retina. The major proteins in the lens--alpha, beta, and gamma-crystallins--are constantly subjected to age-related changes such as oxidation, deamidation, truncation, glycation, and methylation. Such age-related modifications are cumulative and affect crystallin structure and function. With time, the modified crystallins aggregate, causing the lens to increasingly scatter light on the retina instead of focusing light on it and causing the lens to lose its transparency gradually and become opaque. Age-related lens opacity, or cataract, is the major cause of blindness worldwide. We review deamidation, and glycation that occur in the lenses during aging keeping in mind the structural and functional changes that these modifications bring about in the proteins. In addition, we review proteolysis and discuss recent observations on how crystallin fragments generated in vivo, through their anti-chaperone activity may cause crystallin aggregation in aging lenses. We also review hyperbaric oxygen treatment induced guinea pig and 'humanized' ascorbate transporting mouse models as suitable options for studies on age-related changes in lens proteins.

Glycation by ascorbic acid oxidation products leads to the aggregation of lens proteins

Previous studies from this laboratory have shown that there are striking similarities between the yellow chromophores, fluorophores and modified amino acids released by proteolytic digestion from calf lens proteins ascorbylated in vitro and their counterparts isolated from aged and cataractous lens proteins. The studies reported in this communication were conducted to further investigate whether ascorbic acid-mediated modification of lens proteins could lead to the formation of lens protein aggregates capable of scattering visible light, similar to the high molecular aggregates found in aged human lenses. Ascorbic acid, but not glucose, fructose, ribose or erythrulose, caused the aggregation of calf lens proteins to proteins ranging from 2.2 x 10(6) up to 3.0 x 10(8 )Da. This compared to proteins ranging from 1.8 x 10(6) up to 3.6 x 10(8 )Da for the water-soluble (WS) proteins isolated from aged human lenses. This aggregation was likely due to the glycation of lens crystallins because [U-(14)C] ascorbate was incorporated into the aggregate fraction and because NaCNBH(3), which reduces the initial Schiff base, prevented any protein aggregation. Reactions of ascorbate with purified crystallin fractions showed little or no aggregation of alpha-crystallin, significant aggregation of beta(H)-crystallin, but rapid precipitation of purified beta(L)- and gamma-crystallin. The aggregation of lens proteins can be prevented by the binding of damaged crystallins to alpha-crystallin due to its chaperone activity. Depending upon the ratios between the components of the incubation mixtures, alpha-crystallin prevented the precipitation of the purified beta(L)- and gamma-crystallin fractions during ascorbylation. The addition of at least 20% of alpha-crystallin by weight into glycation mixtures with beta(L)-, or gamma-crystallins completely inhibited protein precipitation, and increased the amount of the high molecular weight aggregates in solution. Static and dynamic light scattering measurements of the supernatants from the ascorbic acid-modified mixtures of alpha- and beta(L)-, or gamma-crystallins showed similar molar masses (up to 10(8 )Da) and hydrodynamic diameter (up to 80( )nm). These data support the hypothesis, that if the lens reducing environment is compromised, the ascorbylation of lens crystallins can significantly change the short range interactions between different classes of crystallins leading to protein aggregation, light scattering and eventually to senile cataract formation.

Effect of methylglyoxal modification and phosphorylation on the chaperone and anti-apoptotic properties of heat shock protein 27

Heat shock protein 27 (Hsp27) is a stress-inducible protein in cells that functions as a molecular chaperone and also as an anti-apoptotic protein. Methylglyoxal (MGO) is a reactive dicarbonyl compound produced from cellular glycolytic intermediates that reacts non-enzymatically with proteins to form products such as argpyrimidine. We found considerable amount of Hsp27 in phosphorylated form (pHsp27) in human cataractous lenses. pHsp27 was the major argpyrimidine-modified protein in brunescent cataractous lenses. Modification by MGO enhanced the chaperone function of both pHsp27 and native Hsp27, but the effect on Hsp27 was at least three-times greater than on pHsp27. Phosphorylation of Hsp27 abolished its chaperone function. Transfer of Hsp27 using a cationic lipid inhibited staurosporine (SP)-induced apoptotic cell death by 53% in a human lens epithelial cell line (HLE B-3). MGO-modified Hsp27 had an even greater effect (62% inhibition). SP-induced reactive oxygen species in HLE-B3 cells was significantly lower in cells transferred with MGO-modified Hsp27 when compared to native Hsp27. In vitro incubation experiments showed that MGO-modified Hsp27 reduced the activity of caspase-9, and MGO-modified pHsp27 reduced activities of both caspase-9 and caspase-3. Based on these results, we propose that Hsp27 becomes a better anti-apoptotic protein after modification by MGO, which may be due to multiple mechanisms that include enhancement of chaperone function, reduction in oxidative stress, and inhibition of activity of caspases. Our results suggest that MGO modification and phosphorylation of Hsp27 may have important consequences for lens transparency and cataract development.

alpha-Crystallin binding in vitro to lipids from clear human lenses

The association of alpha-crystallin to lens membranes increases with age and cataract. Lipid compositional changes also occur with age, cataract, and diabetes. In this study we determined the influence of lipid compositional differences on the binding capacity of alpha-crystallin to lipid vesicles in vitro. Lipids were extracted from pools of human lenses from younger (22+/-4 y, n=30) and older (69+/-3 y, n=26) nondiabetic donors as well as from diabetics taking insulin (60+/-9 y, n=26) and diabetics not taking insulin (58+/-9 y, n=20). Diabetics were insulin dependent for an average of 6 years. Extracted lipids were extruded into large unilamellar vesicles. alpha-Crystallin was mixed with the lipid at 36 degrees C, allowed to bind for about 12 h, and centrifuged at 14,000 g. This centrifugal force was low enough to not pellet free alpha-crystallin but high enough to pellet the lipid and bound alpha-crystallin. alpha-Crystallin-lipid binding was characterized by comparing the amount alpha-crystallin in the pellets of samples with and without lipid. Protein was measured using an assay that minimized interference from lipids. Lipid composition was determined by 31P-NMR spectroscopy. The binding capacity of alpha-crystallin to lipids was 12, 19, 8.9, 17 microg bound/mg lipid for lens lipids extracted from younger, older, insulin-treated and nontreated diabetic donors, respectively. The amount of alpha-crystallin in the pellet (bound alpha-crystallin) was significantly lower for the lipids from the younger group of lenses, p=0.033 and insulin-treated group, p=0.006, compared with the older group of lenses. Higher binding capacity was associated with a higher relative amount of sphingolipid and lower relative amounts of phosphatidylethanolamine-related lipid and phosphatidylcholine. The binding capacity of alpha-crystallin to lens lipids, measured in vitro, increases with age and decreases in diabetic donors that were treated with insulin. Our data support the idea that with age and perhaps certain types of diabetes, more alpha-crystallin is bound to the membrane and serves as a condensation point to which other crystallins bind and then become oxidized.

In vitro glucose-induced cataract in copper-zinc superoxide dismutase null mice

The purpose of this study was to evaluate the involvement of the superoxide radical in glucose-induced cataract using lenses from mice lacking the cytosolic copper-zinc superoxide dismutase (SOD1). Lenses from wild-type mice and SOD1 null mice were kept in organ culture with either 5.6 or 55.6 mM glucose for 6 days. The cataract formation was followed with digital image analysis and ocular staging. The lens damage was further quantified by analysis of the leakage of lactate dehydrogenase into the medium by the uptake of 86Rb and by determining the water content of the lenses. The formation of superoxide radicals in the lenses was assessed with lucigenin-derived chemiluminescence. Immunohistochemical staining for SOD1 was also performed on murine lenses. The SOD1 null lenses exposed to high glucose developed more cataract showed an increased leakage of lactate dehydrogenase and developed more oedema compared to the control lenses. At 5.6 mM glucose there was no difference between the SOD1 null and wild-type lenses. Staining for SOD1 was seen primarily in the cortex of the wild-type lens. This in vitro model suggests an involvement of the superoxide radical and a protective effect of SOD1 in glucose-induced cataract formation.

Oxygen tension in the rabbit lens and vitreous before and after vitrectomy

Oxygen is believed to be one of the potential causative agents for the development of nuclear cataract following vitrectomy. The aim of this study was to determine the partial pressure of oxygen (pO2) in different compartments of the rabbit eye, and to describe the changes following vitrectomy. Twenty-six rabbits (3.5-5.3 kg) were anesthetized and oxygen tension was probed using a fiber-optic oxygen sensor system (optode). A micromanipulator was employed to ascertain the exact position of the probe within the eye. Measurements were taken pre- and post-vitrectomy at several defined positions within the vitreous, the lens and the anterior chamber. Follow-up measurements were performed 2 and 8 weeks after vitrectomy. The contralateral eye served as a control. Measurements in the normal rabbit eye showed that oxygen tension in the globe is asymmetrical with the lowest pO2 in the nucleus of the lens (10.4 mmHg+/-3.0). The region of the lens near the posterior capsule has an oxygen tension close to the values of the vitreous directly behind the posterior capsule (12.4 mmHg+/-3.1). The highest pO2 within the posterior compartment of the eye was measured close to the retinal surface (40-l60 mmHg) depending on neighboring large vessels. The tension drops off rapidly to 20 mmHg some 0.5 mm from the retina. From that position to the posterior surface of the lens there is a shallow gradient of decreasing pO2. Immediately following vitrectomy the pO2 in the BSS replacement varied from ca. 90-140 mmHg, and decreased over approximately 30 min. to levels that were 2-3 times that of normal vitreous. Two weeks after vitrectomy the pO2 values in the lens were 2-3 times as high as in the control eye (p < 0.05). In addition there is no longer a gradient in the vitreous cavity, except close to the retina. Eight weeks after vitrectomy, pO2 levels in the lens were decreased but still remained higher than in the normal eye (13.83 mmHg+/-0.02). The pO2 gradient in the vitreous was not detectable anymore. Overall the results provide evidence that oxygen levels in the lens increase significantly after vitrectomy in rabbits. If this occurs in humans it may contribute to cataract formation following surgery.

Advanced glycation endproducts as UVA photosensitizers of tryptophan and ascorbic acid: consequences for the lens

Upon aging, the lens accumulates brown fluorophores, mainly derived from the Maillard reaction between vitamin C oxidation products and crystallins lysine residues. At the same time, the concentration of UVA filters decreases, allowing some radiation to be absorbed by lenticular advanced glycation endproducts (AGEs). This paper quantifies the photosensitizing activity of AGEs at various oxygen pressures, and compares it to that of lenticular riboflavin (RF). Solutions containing the sensitizer and the substrates tryptophan (Trp) and ascorbate (AH(-)) were irradiated at 365 nm. We show that the AGEs-photosensitized Trp oxidation rate increases with AGEs concentration and is optimal at 5% oxygen, the pressure in the lens. By contrast, for AH(-), the photooxidation rate increases with oxygen concentration. Despite the higher quantum yield of RF-depending reactions, its low concentration as compared to that of AGEs in aging lenses induces significantly higher Trp and AH(-) photodegradation rates with AGEs than with RF. As ascorbate is more rapidly photodegraded than Trp, the antioxidant competitively protects Trp from oxidation up to 1 mM, although not absolutely. We conclude that in the aging lens, AH(-) exerts a strong UVA protecting activity, but does not impede some Trp residue to be photodegraded proportionally to the AGEs concentration.

Blood and lens lipid peroxidation and antioxidant status in normal individuals, senile and diabetic cataractous patients

PURPOSE

Oxidative mechanisms are believed to play an important role in the pathogenesis of cataract, the most important cause of visual impairment at advanced age. To determine the body's antioxidant status as well as its lipid peroxidation levels, both blood and lens parameters were evaluated.

METHODS

This study was performed on the blood samples and lenses obtained from 46 patients diagnosed as having cataract and 20 control subjects. The control group was composed of 10 women and 10 men who do not smoke. Control subjects without any lens opacity or vacuoles when observed with a slit lamp were recruited on the same exclusion criteria as far as disease and treatment were concerned. No antioxidant medicines were used. They were all healthy individuals without any systemic diseases. Superoxide dismutase (SOD), glucose-6-phosphate dehydrogenase (G6PD), glutathione reductase (GSSG-Red) activities in red blood cell (RBC) lysates as well as whole blood glutathione (GSH) and plasma thiobarbituric acid reactive substances (TBARS), the indicator of lipid peroxidation concentrations, were determined quantitatively both in the blood samples and the lenses of the patients with senile and diabetic cataracts.

RESULTS

Whole blood GSH values, and erythrocyte SOD activities were significantly lower in the cataractous patients than those in the control group. The values in the diabetic cataractous group were also less than those in the senile cataractous group. Significantly decreased erythrocyte GSSG-Red and G6PD activities were detected in the diabetic cataractous group. Plasma TBARS values were higher both in the senile and diabetic groups when compared to those in the control group. Significantly decreased values were observed for GSSG-Red activities and TBARS values in the lenses of the senile cataractous patients in comparison with those in the diabetic cataractous patients. The lens GSH values were found to be higher in the senile cataractous group than the values obtained in the diabetic cataractous group.

CONCLUSIONS

A strong correlation was found between lens GSH and lens TBARS concentrations in the diabetic group. This emphasized the vital role of GSH as an antioxidant in the lens over the other antioxidant parameters, e.g., enzymes, and the oxidative stress is at the highest level in lens.

Early glycation products produce pentosidine cross-links on native proteins. novel mechanism of pentosidine formation and propagation of glycation

Bovine lens alpha-crystallin was immobilized on EAH-Sepharose gel and glycated using d-ribose. Incubation with 500 and 100 mm d-ribose for 2 and 15 days produced short-term glycated (STGP gel) and long-term glycated proteins (LTGP gel). Both STGP and LTGP gels produced oxygen free radicals. Hydroxyl radical production was twice that in STGP gel compared with the LTGP gel. Incubation with the glycated gels produced pentosidine in a mixture of N-alpha-acetylarginine + N-alpha-acetyllysine, bovine lens proteins (BLP), and lysozyme; the amounts measured with STGP gel were higher than those with LTGP gel. Reactive oxygen species scavengers decreased the formation of pentosidine. Pentosidine was also formed in BLP when incubated with water-insoluble proteins extracted from aged or brunescent human lenses. Early glycated proteins from aged or diabetic lenses were bound to a boronate affinity column, the protein-containing gel was incubated with BLP, and pentosidine was measured in the incubation mixtures. With this method we found that diabetic lens proteins produced more pentosidine on BLP than did aged lens proteins. Further investigation indicates that two and three carbon carbohydrates possibly formed from oxidative cleavage of early glycation products are involved in pentosidine formation. Based on our findings, we propose a novel pathway for pentosidine formation on native proteins from glycated proteins.