Advanced glycation: an important pathological event in diabetic and age related ocular disease

Influence of diabetes and cardiovascular disease on the long-term incidence of cataract: the Blue Mountains eye study

PURPOSE

To assess associations between diabetes and selected cardiovascular risk factors and long-term incident cataract and cataract surgery.

METHODS

A cohort of initially 3654 elderly Australians were followed over a period of 10 years. Questionnaires ascertained relevant history and fasting blood samples were taken. Impaired fasting glucose (IFG) and metabolic syndrome were defined using World Health Organization criteria. Discrete logistic models were used to assess risk of incident cataract.

RESULTS

After controlling for age, sex, and other factors, baseline diabetes predicted nuclear cataract (relative risk, RR, 1.64; 95% confidence interval (CI), 1.02-2.64) and IFG predicted cortical cataract (RR, 2.01; CI, 1.20-3.36). Each standard deviation (SD) increase in glucose was positively associated with cortical cataract (RR, 1.13; CI, 1.01-1.27). Higher body mass index (BMI) was positively associated with posterior subcapsular cataract (RR per SD, 1.20; CI, 1.03-1.41). Persons using anti-hypertensive medication had a higher incidence of cataract surgery (RR, 1.61; CI, 1.18-2.20). Metabolic syndrome was associated with an increased risk of all 3 cataract subtypes. Few other significant associations were found between cardiovascular disease, cardiovascular risk factors, and incident cataract or cataract surgery.

CONCLUSIONS

We confirmed diabetes as a risk factor for age-related cataract and IFG as a possible risk factor for cortical cataract. BMI and hypertension were also related to incident cataract. Overall, few associations were found between cardiovascular risk factors and long-term incident cataract. A cluster of metabolic abnormalities attributable to insulin resistance appears more likely to contribute to cataract formation than any individual cardiovascular risk factor alone.

Dietary glycemic index and the risk of age-related macular degeneration

BACKGROUND

Dietary factors are known risk factors for age-related macular degeneration (AMD) -- the leading cause of visual loss among persons aged > or =65 y. High-glycemic-index diets have been hypothesized as a risk factor for AMD, but prospective data are unavailable.

OBJECTIVE

The objective was to examine the association between dietary glycemic index and the 10-y incidence of AMD in the Blue Mountain Eye Study population.

DESIGN

This was a population-based cohort study with 3,654 participants (> or =49 y) examined at baseline (1992-1994); 2,335 patients were reexamined after 5 y and 1952 after 10 y. The Wisconsin System was used to grade 10-y incident early and late AMD from retinal photographs. A food-frequency questionnaire was used to collect dietary information at baseline, and an Australian database was used to calculate the mean glycemic index.

RESULTS

Over 10 y, 208 of 1,810 persons (cumulative incidence: 14.1%) developed early AMD. After age, smoking, other risk factors, and dietary constituents were adjusted for, a higher mean dietary glycemic index was associated with an increased 10-y risk of early AMD in a comparison of quartiles 1 and 4 [relative risk (RR): 1.77; 95% CI: 1.13, 2.78; P for trend = 0.03]. Conversely, a greater consumption of cereal fiber (RR: 0.68; 95% CI: 0.44, 1.04; P for trend = 0.05) and breads and cereals (predominantly lower glycemic index foods such as oatmeal) (RR: 0.67; 95% CI: 0.44, 1.02; P for trend = 0.03) was associated with a reduced risk of incident early AMD. No relation was observed with late AMD.

CONCLUSIONS

A high-glycemic-index diet is a risk factor for early AMD -- the recognized precursor of sight-threatening late AMD. Low-glycemic-index foods such as oatmeal may protect against early AMD.

Could oxidative stress associate with age products in cataractogenesis?

BACKGROUND

Oxidative stress has been reported to contribute to aging and cataract formation in the lens. The aim was to determine the association of oxidative stress with advanced glycation end products (AGEs) in elderly diabetic and non-diabetic patients with cataract.

METHODS

In the present study, malondialdehyde, vitamin E, serum AGEs, and glycemic control were investigated. The study included 156 subjects. Out of them, 30 were normal elderly subjects, 31 were elderly diabetic patients without cataract, 33 were elderly diabetic patients with cataract, 32 were elderly non-diabetic with cataract, and 30 were normal young subjects. The patients were selected on clinical grounds from Eye Ward, Jinnah Postgraduate Medical Centre, Karachi, Pakistan.

RESULTS

Positive significant correlation was observed between s-AGEs and malondialdehyde in elderly diabetic and non-diabetic patients with cataract. Negative significant correlation was observed between s-AGEs and vitamin E in elderly diabetic and non-diabetic patients with cataract. However, the malondialdehyde and serum AGEs were found to be significantly increased (p < 0.001) in elderly diabetic and non-diabetic patients with and without cataract compared with elderly control subjects. In contrast to all four senile groups, the serum AGEs was significantly lower (p < 0.001) in young control subjects. Serum vitamin E was found to be significantly decreased (p < 0.001) in elderly diabetic patients with and without cataract compared with elderly control subjects. Fasting blood glucose, HbA(1C) and serum fructosamine levels were significantly increased (p < 0.001) in elderly diabetic patients with and without cataract compared with non-diabetic elderly patients with cataract and elderly control subjects.

CONCLUSIONS

This study revealed that increased AGEs were associated with oxidative stress in the elderly groups. AGE, as a result of oxidative stress, might have a role in cataract formation, which, in diabetic patients, occurs vigorously as compared with non-diabetic cataract patients.

A proposed new classification for diabetic retinopathy: the concept of primary and secondary vitreopathy

BACKGROUND

Many eyes with proliferative diabetic retinopathy (PDR) require vitreous surgery despite complete regression of new vessels with pan retinal laser photocoagulation (PRP). Changes in the vitreous caused by diabetes mellitus and diabetic retinopathy may continue to progress independent of laser regressed status of retinopathy. Diabetic vitreopathy can be an independent manifestation of the disease process.

AIM

To examine this concept by studying the long-term behavior of the vitreous in cases of PDR regressed with PRP.

MATERIALS AND METHODS

Seventy-four eyes with pure PDR (without clinically evident vitreous traction) showing fundus fluorescein angiography (FFA) proven regression of new vessels following PRP were retrospectively studied out of a total of 1380 eyes photocoagulated between March 2001 and September 2006 for PDR of varying severity. Follow-up was available from one to four years.

RESULTS

Twenty-three percent of eyes showing FFA-proven regression of new vessels with laser required to undergo surgery for indications produced by vitreous traction such as recurrent vitreous hemorrhage, tractional retinal detachment, secondary rhegmatogenous retinal detachment and tractional macular edema within one to four years.

CONCLUSION

Vitreous changes continued to progress despite regression of PDR in many diabetics. We identifies this as "clinical diabetic vitreopathy" and propose an expanded classification for diabetic retinopathy to signify these changes and to redefine the indications for surgery.

Effects of advanced glycation end products-inductor glyoxal and hydrogen peroxide as oxidative stress factors on rat retinal organ cultures and neuroprotection by UK-14,304

Retinal ganglion cell degeneration is supposed to be mediated by reactive oxygen species (ROS) and advanced glycation end products (AGEs). The alpha2-adrenergic agonist, 5-bromo-N-(4,5-dihydro-1H-imidazol-2-yl)-6-quinoxalinamine (brimonidine; UK-14,304), is said to exert a neuroprotective effect. To investigate these mechanisms in detail, we exposed rat whole mounts to glyoxal or H(2)O(2) and treated them with either UK-14,304 alone or additionally with the phosphatidylinositide 3 kinase (PI3) kinase inhibitor, 2-(4-Morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (Ly 294002). The accumulation of Nepsilon-[carboxymethyl] lysine (CML) was assessed immunohistochemically and changes in intracellular pH (pHi), mitochondrial transmembrane potential (MTMP) and ROS production in cell bodies of multipolar ganglion cell layer were studied by intravital fluorescence microscopy and confocal laser scanning microscopy. Ultrastructural changes in mitochondria of multipolar ganglion cell layer cell bodies were determined by transmission electron microscopy. We found that glyoxal and H(2)O(2) increased accumulation of CML-modified proteins and ROS production and decreased pHi and MTMP in cell bodies of multipolar ganglion cell layer. UK-14,304 could prevent production of ROS, accumulation of CML-modified proteins, ameliorate acidification, preserve MTMP and attenuate ultrastructural damages of ganglion cell mitochondria. Ly 294002 reversed the UK-14,304-mediated attenuation of CML and ROS production. We conclude that the protective effects of UK-14,304 seem partly to be mediated by PI3 kinase-dependent pathways.

Advanced glycation as a basis for understanding retinal aging and noninvasive risk prediction

The retina is exquisitely sensitive to age-related processes, and, in many cases, these can precipitate progressive and profound loss of vision. Many asymptomatic abnormalities that accrue in the outer retina as we get older can serve as a sinister preamble to age-related macular degeneration (AMD). This condition remains the leading cause of irreversible blindness in industrialized countries, but its precise pathogenesis has yet to be completely elucidated. Over recent years, increasing evidence has suggested that the accumulation of advanced glycation end products (AGEs) and activation of the receptor for AGEs in the outer retina could play a significant role in the initiation and progression of AMD. The current review outlines this evidence and indicates how products of Maillard chemistry could be used as robust markers for outer retinal aging and susceptibility to AMD. The utility of Raman spectroscopy to measure AGE adducts in human tissues is presented. The methodology reinforces the association between AGE formation and retinal aging and provides exciting possibilities for assessing these pathogenic agents in the living eye and, perhaps, for providing a valuable index for AMD susceptibility.

The effect of peptide glycation on local secondary structure

Protein glycation is a non-enzymatic reaction between reducing sugars and amino groups that occurs in vivo and has been implicated in a number of disease states and pathologies including Alzheimer's and diabetes. Although glycation is thought to alter protein structure and function, there is currently little information on the structural consequences of this modification. We have used a model alpha-helix and a model beta-hairpin peptide, and NMR analysis, to investigate the effects of glycation upon secondary structure. Glycation of the dilysine motif within the alpha-helix peptide occurred preferentially at one lysine residue and resulted in severe disruption to the local secondary structure. The area immediately around the site of modification was extremely flexible and the peptide did not adopt a preferred conformation in this area of the helix in 30% TFE. Significant glycation of the beta-hairpin peptide was not detected and the structure was unchanged. These results show that glycation results in local secondary structure distortion of alpha-helices and that preferential glycation occurs in a sequence specific manner. The findings will allow us to interrogate the local environment in other peptides/proteins to predict the likelihood of glycation, and to model the potential effects such modification might have upon structure/function.

Carbohydrate nutrition, glycemic index, and the 10-y incidence of cataract

BACKGROUND

Although dietary carbohydrates are thought to play a role in cataractogenesis, few epidemiologic studies have examined links between carbohydrate nutrition and cataract.

OBJECTIVES

We investigated the associations between dietary glycemic index (GI), glycemic load (GL), total carbohydrate intake, and 10-y incident nuclear, cortical, and posterior subcapsular cataract.

DESIGN

Of 3654 baseline participants in an Australian population aged >/=49 y (1992-1994), 933 were seen after 5 and/or 10 y, had completed a detailed semiquantitative food-frequency questionnaire, had no previous cataract surgery or baseline cataract, and had photographs taken to assess incident cataract with the Wisconsin Cataract Grading System. Dietary information was collected with a validated food questionnaire. GI was calculated from a customized database of Australian foods. GI, GL, and all other nutrients were energy adjusted. Hazard ratios (HRs) and 95% CIs were calculated with the use of discrete logistic models.

RESULTS

After age, sex, diabetes, and other factors were controlled for, each SD increase in GI significantly predicted incident cortical cataract (HR: 1.19; 95% CI: 1.01, 1.39). Participants within the highest compared with the lowest quartile of GI were more likely to develop incident cortical cataract (HR: 1.77; 95% CI: 1.13, 2.78; P for trend = 0.035). These findings were similar after excluding participants with diabetes, although they were slightly attenuated and marginally nonsignificant (HR: 1.16; 95% CI: 0.98, 1.37, per SD increase in GI). No association was found between GI and nuclear or posterior subcapsular cataract and between GL or carbohydrate quantity and any cataract subtype.

CONCLUSION

In an Australian cohort, poorer dietary carbohydrate quality, reflected by high GI, predicted incident cortical cataract.

Diagnostic utility of serum or cerebrospinal fluid levels of toxic advanced glycation end-products (TAGE) in early detection of Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in developed countries. AD is characterized pathologically by the presence of senile plaques and neurofibrillary tangles (NFTs), the major constituents of which are amyloid beta protein (A beta) and tau protein, respectively. Based on the disease pathology, numerous blood and cerebrospinal fluid (CSF) tests have been proposed for early detection of AD. However, there is no definite clinical method to determine in which patients with mild cognitive impairment will progress to AD with dementia. Therefore, to develop a novel promising biomarker for early diagnosis of AD is urgently needed. Several epidemiological studies have reported moderately increased risks for AD in diabetic patients compared with general population. In diabetes mellitus, the formation and accumulation of advanced glycation end-products (AGEs), senescent macroprotein derivatives, progress more rapidly. In addition, recent understanding of this process has confirmed that AGEs-their receptor (RAGE) interactions may play a role in the pathogenesis of neurodegenerative disorders including AD. In human AD brains, AGEs are distributed in the cytosol of neurons in the hippocampus and para-hippocampal gyrus. In this paper, we discuss the pathophysiological role for toxic AGEs (TAGE) in AD. We further review here the possibility that serum or cerebrospinal fluid levels of TAGE could become a promising biomarker for early detection of AD.

Proteolytic degradation of VE-cadherin alters the blood-retinal barrier in diabetes

OBJECTIVE

Increased vascular permeability due to alteration of the blood-retinal barrier (BRB) is one of the major complications in early diabetes. The aim of the present study was to determine whether diabetes alters the cellular expression and distribution of the adherens junction protein vascular endothelial (VE)-cadherin in retinal endothelial cells and if this alteration is mediated by proteinase activity.

RESEARCH DESIGN AND METHODS

Diabetes was induced in Brown Norway rats using streptozotocin, and retinal vascular permeability was measured by the Evans blue technique. The expression of matrix metalloproteinases (MMPs) and VE-cadherin was examined in isolated retinal vessels or cultured endothelial cells in response to diabetes and advanced glycation end products (AGEs). The cleavage of VE-cadherin from the endothelial cell surface was monitored by Western blotting following MMP or AGE treatment.

RESULTS

Retinal vascular permeability was significantly increased in rats following 2 weeks of diabetes coincident with a decrease of VE-cadherin expression. This increased vascular permeability could be inhibited with an MMP inhibitor. Treatment of endothelial cells with AGE-BSA led to a reduction of VE-cadherin staining on the cell surface and increased permeability, which was MMP mediated. Treatment of cells with specific MMPs or AGEs resulted in cleavage of VE-cadherin from the cell surface.

CONCLUSIONS

These observations suggest a possible mechanism by which diabetes contributes to BRB breakdown through proteolytic degradation of VE-cadherin. This may indicate a role for extracellular proteinases in alteration of the BRB seen in diabetic retinopathy.

Ocular fundus auto-fluorescence observations at different wavelengths in patients with age-related macular degeneration and diabetic retinopathy

BACKGROUND

Post-translational protein modification by lipid peroxidation products or glycation is a feature of aging as well as pathologic processes in postmitotic cells at the ocular fundus exposed to an oxidative environment. The accumulation of modified proteins such as those found in lipofuscin and advanced glycation end products (AGEs) contribute greatly to the fundus auto-fluorescence. The distinct fluorescence spectra of lipofuscin and AGE enable their differentiation in multispectral fundus fluorescence imaging.

METHOD

A dual-centre consecutive case series of 78 pseudo-phacic patients is reported. Digital colour fundus photographs as well as auto-fluorescence images were taken from 33 patients with age related macular degeneration (AMD), 13 patients with diabetic retinopathy (RD), or from 32 cases without pathologic findings (controls). Fluorescence was excited at 475-515 nm or 476-604 nm and recorded in the emission bands 530-675 nm or 675-715 nm, respectively. Fluorescence images excited at 475-515 nm were taken by a colour CCD-camera (colour-fluorescence imaging) enabling the separate recording of green and red fluorescence. The ratio of green versus red fluorescence was calculated within a representative region of each image.

RESULTS

The 530-675 nm auto-fluorescence in AMD patients was dominated by the red emission (green vs. red ratio, g/r = 0.861). In comparison, the fluorescence of the diabetics was green-shifted (g/r = 0.946; controls: g/r = 0.869). Atrophic areas (geographic atrophy, laser scars) showed massive hypo-fluorescence in both emission bands. Hyper-fluorescent drusen and exudates, unobtrusive in the colour fundus images as well as in the fluorescence images with emission >667 nm, showed an impressive green-shift in the colour-fluorescence image.

CONCLUSIONS

Lipofuscin is the dominant fluorophore at long wavelengths (>675 nm or red channel of the colour fluorescence image). In the green spectral region, we found an additional emission of collagen and elastin (optic disc, sclera) as well as deposits in drusen and exudates. The green shift of the auto-fluorescence in RD may be a hint of increased AGE concentrations.

Advanced glycation end products and sorbitol in blood from differently compensated diabetic dogs

Canine diabetes mellitus (DM) is a common metabolic disorder with long term complications, most of which are caused by glycosylation of structural proteins, decreases in antioxidant concentrations, altered osmotic balance and hypoxia due to impaired oxygen transport. Previous studies have demonstrated that under hyperglycemic conditions canine erythrocytes undergo swelling, probably due to activation of the polyol pathway. The present work aimed to assess the plasma concentration of advanced glycation end (AGE) products, stable Amadori-products generated by non-enzymatic glycosylation of proteins and the intracellular concentration of sorbitol, produced by the activation of polyol pathway in 34 blood samples from diabetic dogs and in 14 controls. AGE products were significantly higher (p<0.01) in plasma from diabetic dogs compared with control animals. The sorbitol concentration in erythrocytes was also significantly higher in diabetic dogs and, in particular, in poorly compensated animals and in dogs with ketonuria. In five cases that were analysed before and after clinical improvement, sorbitol concentration was found to correlate with improvement. These results suggest that non-specific glycosylation is increased and that the polyol pathway is activated in diabetic dogs in a manner that is proportionate to the severity of disease. Moreover, the concentration of AGE products and sorbitol may be useful for monitoring the onset of diabetic complications and assessing the most appropriate therapeutic approaches for management of canine DM.

Drevogenin D prevents selenite-induced oxidative stress and calpain activation in cultured rat lens

PURPOSE

Selenite-induced cataractogenesis is mediated by oxidative stress, accumulation of calcium and activation of lenticular calpains. Calpains are a super family of Ca2+ dependent proteases, which are involved in lens protein proteolysis and insolubilization. Many inhibitors could prevent calpain-induced proteolysis of alpha- and beta-crystallins in rodent cataracts. Evaluating natural sources with antioxidant property and subsequent prevention of calpain activation may lead to the development of safer and more effective agents against cataractogenesis. There are no reports on the protective role of bioactive components against calpain-mediated proteolysis and subsequent cataractogenesis. The purpose of the study was to evaluate the role of Drevogenin D, a triterpenoid aglycone, isolated from Dregea volubilis in preventing selenite-induced, calcium-activated, calpain-mediated proteolysis in cultured rat lenses.

METHODS

Lenses were extracted from Sprague-Dawley strain rats at the age of one month and were organ cultured in M-199 medium with HEPES buffer. The lenses were divided into three groups with eight lenses in each group as follows: lenses cultured in a normal medium (GI), lenses cultured in a sodium selenite supplemented medium (GII), and lenses cultured in a medium supplemented with sodium selenite and Drevogenin D-treated (GIII). Changes to transparency and opacity formation of lenses were monitored under microscopic observation. At the end of the experiment, biochemical parameters such as activity of lens superoxide dismutase (SOD), lens Ca2+ ATPase, concentration of Ca2+, levels of sulfhydryl content, and thiobarbituric acid reacting substances (TBARS) were determined. Changes to casein zymography for calpains, immunoblot for Lp82, and SDS-PAGE of lens water soluble protein fraction (WSF) were also done.

RESULTS

Microscopic evaluation of lens morphology showed that Drevogenin D prevented the opacification in G-III. Drevogenin D inhibited the accumulation of calcium, the activation of calpain system, and lipid peroxidation. Activity of Ca2+ ATPase, SOD, and SDS-PAGE profile of water soluble proteins was normalized following treatment with Drevogenin D.

CONCLUSIONS

Selenite-induced cataractogenesis is mediated by oxidative stress leading to a decrease in the activity of Ca2+ ATPase, resulting in the accumulation of calcium and the subsequent activation of lenticular calpains. The results obtained indicated that Drevogenin D treatment was effective in protecting the lens proteins by controlling stress-induced protein oxidation, maintenance of Ca2+ ATPase activity, calcium accumulation, lipid peroxidation, and prevention of calpain activation. Hence, Drevogenin D can be used as a potential therapeutic agent against oxidative stress-induced cataract.

Pathogenesis and classification of proliferative diabetic vitreoretinopathy

PURPOSE

To review the current knowledge regarding the pathogenesis of proliferative diabetic vitreoretinopathy (PDVR) and to present recommendations for its clinical staging.

DESIGN

Focused literature review and authors' clinical experience.

RESULTS

Although several biochemical mediators may be responsible for the pathogenesis of PDVR, no common biochemical pathway exists. Of those mediators, vascular endothelial growth factor is the one most studied so far. However, since in proliferative diabetic retinopathy (PDR) the thickened posterior vitreous cortex is one of the main factors in the development of proliferations, a consequent shrinkage of the posterior vitreous cortex leads to hemorrhages and tractive retinal detachments. Therefore, PDR should be called PDVR. In consequence, the authors present a new morphological classification of PDVR.

CONCLUSIONS

There is no consensus about the biochemical pathway responsible for the progression of PDVR. Although several classifications are described in the literature, the classification suggested here is important in the judgment of, the communication about and the therapy of diabetic retinopathy. Furthermore, it is the only reliable classification for predicting the surgical outcome in diabetics.

Advanced glycation end products cause increased CCN family and extracellular matrix gene expression in the diabetic rodent retina

AIMS/HYPOTHESIS

Referred to as CCN, the family of growth factors consisting of cystein-rich protein 61 (CYR61, also known as CCN1), connective tissue growth factor (CTGF, also known as CCN2), nephroblastoma overexpressed gene (NOV, also known as CCN3) and WNT1-inducible signalling pathway proteins 1, 2 and 3 (WISP1, -2 and -3; also known as CCN4, -5 and -6) affects cellular growth, differentiation, adhesion and locomotion in wound repair, fibrotic disorders, inflammation and angiogenesis. AGEs formed in the diabetic milieu affect the same processes, leading to diabetic complications including diabetic retinopathy. We hypothesised that pathological effects of AGEs in the diabetic retina are a consequence of AGE-induced alterations in CCN family expression.

MATERIALS AND METHODS

CCN gene expression levels were studied at the mRNA and protein level in retinas of control and diabetic rats using real-time quantitative PCR, western blotting and immunohistochemistry at 6 and 12 weeks of streptozotocin-induced diabetes in the presence or absence of aminoguanidine, an AGE inhibitor. In addition, C57BL/6 mice were repeatedly injected with exogenously formed AGE to establish whether AGE modulate retinal CCN growth factors in vivo.

RESULTS

After 6 weeks of diabetes, Cyr61 expression levels were increased more than threefold. At 12 weeks of diabetes, Ctgf expression levels were increased twofold. Treatment with aminoguanidine inhibited Cyr61 and Ctgf expression in diabetic rats, with reductions of 31 and 36%, respectively, compared with untreated animals. Western blotting showed a twofold increase in CTGF production, which was prevented by aminoguanidine treatment. In mice infused with exogenous AGE, Cyr61 expression increased fourfold and Ctgf expression increased twofold in the retina.

CONCLUSIONS/INTERPRETATION

CTGF and CYR61 are downstream effectors of AGE in the diabetic retina, implicating them as possible targets for future intervention strategies against the development of diabetic retinopathy.

Calpains and their multiple roles in diabetes mellitus

Type 2 diabetes mellitus (T2DM) can lead to death without treatment and it has been predicted that the condition will affect 215 million people worldwide by 2010. T2DM is a multifactorial disorder whose precise genetic causes and biochemical defects have not been fully elucidated, but at both levels, calpains appear to play a role. Positional cloning studies mapped T2DM susceptibility to CAPN10, the gene encoding the intracellular cysteine protease, calpain 10. Further studies have shown a number of noncoding polymorphisms in CAPN10 to be functionally associated with T2DM while the identification of coding polymorphisms, suggested that mutant calpain 10 proteins may also contribute to the disease. Here we review recent studies, which in addition to the latter enzyme, have linked calpain 5, calpain 3, and its splice variants, calpain 2 and calpain 1 to T2DM-related metabolic pathways along with T2DM-associated phenotypes, such as obesity and impaired insulin secretion, and T2DM-related complications, such as epithelial dysfunction and diabetic cataract.

Accelerated aging in glaucoma: immunohistochemical assessment of advanced glycation end products in the human retina and optic nerve head

PURPOSE

This study aimed to determine the association between advanced glycation end products (AGEs) and glaucoma based on the known synergism between oxidative stress with AGEs and the evidence of oxidative stress during glaucomatous neurodegeneration.

METHODS

The extent and cellular localization of immunolabeling for AGEs and their receptor, RAGE, were determined in histologic sections of the retina and optic nerve head obtained from 38 donor eyes with glaucoma and 30 eyes from age-matched donors without glaucoma.

RESULTS

The extent of AGE and RAGE immunolabeling was greater in older than in younger donor eyes. However, compared with age-matched controls, an enhanced accumulation of AGEs and an up-regulation of RAGE were detectable in the glaucomatous retina and optic nerve head. Although some retinal ganglion cells (RGCs) and glia exhibited intracellular immunolabeling for AGEs, increased AGE immunolabeling in glaucomatous eyes was predominantly extracellular and included laminar cribriform plates in the optic nerve head. Some RAGE immunolabeling was detectable on RGCs; however, increased RAGE immunolabeling in glaucomatous eyes was predominant on glial cells, primarily Müller cells.

CONCLUSIONS

Given that the generation of AGEs is an age-dependent event, increased AGE accumulation in glaucomatous tissues supports that an accelerated aging process accompanies neurodegeneration in glaucomatous eyes. One of the potential consequences of AGE accumulation in glaucomatous eyes appears to be its contribution to increased rigidity of the lamina cribrosa. The presence of RAGE on RGCs and glia also makes them susceptible to AGE-mediated events through receptor-mediated signaling, which may promote cell death or dysfunction during glaucomatous neurodegeneration.

Hypertension aggravates glomerular dysfunction with oxidative stress in a rat model of diabetic nephropathy

Oxidative stress may contribute to the pathogenesis of diabetic nephropathy (DN), although the detailed mechanism of reactive oxygen species (ROS) regulation is still unclear. This study examined the effect of high-salt diet on ROS production and expression of antioxidant enzymes in control and experimentally diabetic rats. Wistar fatty rats (WFR) as a type 2 diabetes mellitus model and Wistar lean rats (WLR) as a control were fed a normal-salt diet (NS) and high-salt diet (HS) from the age of 6 to 14 weeks. We then examined the blood pressure, urinary albumin excretion (UAE), and urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels. The expression of antioxidant enzymes including alpha-catalase (CAT), Cu-Zn superoxide dismutase (SOD), Mn SOD, and glutathione peroxidase (GPx) were analyzed in the glomeruli of the rats using Western blotting. The expression of NAD(P)H oxidase p47(phox) and NFkappaB p65 was evaluated using immunohistochemical staining. By 14 weeks of age, the WFR-HS group exhibited hypertension and markedly increased UAE. The level of 8-OHdG, a marker of oxidative damage, in the WFR-HS group was also higher than that in the WLR groups or WFR-NS group. The expression of alpha-CAT and Mn SOD proteins was significantly decreased in isolated glomeruli in the WFR-HS group. GPx and Cu-Zn SOD expression did not differ between the WFR and WLR groups. High expression of ROS and decreases in antioxidants were seen in the glomeruli of diabetic rats with hypertension, suggesting that oxidative stress may be involved in the development of DN.

Skin autofluorescence, a novel marker for glycemic and oxidative stress-derived advanced glycation endproducts: an overview of current clinical studies, evidence, and limitations

BACKGROUND

Advanced glycation endproducts (AGEs) predict long-term complications in agerelated diseases. However, there are no clinically applicable markers for measuring AGEs in vivo.

METHODS

We have recently introduced the AGE-Reader (DiagnOptics B.V., Groningen, The Netherlands) to noninvasively measure AGE accumulation in the human skin of the forearm, making use of the characteristic autofluorescence (AF) pattern that AGEs encompass. Skin AF is calculated as a ratio of mean intensities detected from the skin between 420-600 nm and 300-420 nm. It correlates with collagen-linked fluorescence and specific skin AGE levels from skin biopsies in diabetes, renal failure, and control subjects. Skin AF levels are increased in patients with diabetes and renal failure and are associated with the presence of vascular complications. Additionally, skin AF is strongly related to the progression of coronary heart disease and mortality, independently of traditional risk factors. Since skin pigmentation might influence skin AF, we have investigated the relation of relative skin reflectance (R%) to skin AF in subjects with varying skin phototypes (SPT).

RESULTS

The data presented in this article suggest that only in subjects with an SPT of V and VI or R% <12%, no reliable measurement can be performed. Therefore, the current prototype of the AGE-Reader is suitable for subjects with SPT I-IV or R% >12%, and more research is needed for a broader application.

CONCLUSION

The AGE-Reader is useful as a noninvasive clinical tool for assessment of risk for long-term vascular complications in diabetes and in other conditions associated with AGE accumulation.

Toxic advanced glycation end products (TAGE) theory in Alzheimer's disease

Several epidemiological studies have reported moderately increased risks of Alzheimer's disease (AD) in diabetic patients compared with general population. In diabetes mellitus, the formation and accumulation of advanced glycation end products (AGEs) progress more rapidly. Recent understanding of this process has confirmed that interactions between AGEs and their receptor (RAGE) may play a role in the pathogenesis of diabetic complications and AD. The authors have recently found that glyceraldehyde-derived AGEs (AGE-2), which is predominantly the structure of toxic AGEs (TAGE), show significant toxicity on cortical neuronal cells and that the neurotoxic effect of diabetic serum is completely blocked by neutralizing antibody against the AGE-2 epitope. Moreover, in human AD brains, AGE-2 is distributed in the cytosol of neurons in the hippocampus and parahippocampal gyrus. These results suggest that TAGE is involved in the pathogenesis of AD as well as other age-related diseases. In this review, the authors discuss the molecular mechanisms of AD, especially focusing on TAGE-RAGE system.

Dietary carbohydrate intake and glycemic index in relation to cortical and nuclear lens opacities in the Age-Related Eye Disease Study

BACKGROUND

Little is known about the association between dietary carbohydrates and cataract in nondiabetic persons.

OBJECTIVE

The aim was to test whether recent dietary carbohydrate intakes or glycemic index (GI; a measure of carbohydrate intake quality) was associated with the presence of cortical or nuclear opacities.

DESIGN

A modified Block food-frequency questionnaire was used to obtain dietary information from 3377 participants (aged 60-80 y; 56% were women) in the Age-Related Eye Disease Study (AREDS). Lens status was evaluated by using the AREDS System for Classifying Cataracts. Associations were examined for eyes with only a single, or pure, type of lens opacity by using the generalized estimating approach to logistic regression to account for the lack of independence between the eyes of a person.

RESULTS

For participants in the highest quartile, dietary GI was associated with a higher prevalence of all pure nuclear opacities [grade >2; odds ratio (OR): 1.29; 95% CI: 1.04, 1.59; P for trend = 0.02] and moderate nuclear opacities (grade > or =4; OR: 1.43; 95% CI: 0.96, 2.14; P for trend = 0.052). The OR in a comparison of the highest with the lowest quartile of intake was 1.27 (95% CI: 0.99, 1.63; P for trend = 0.09) for cortical opacities of any severity (>0% of area opaque), and the OR increased somewhat for moderate cortical opacities (>5% of area opaque; OR: 1.71; 95% CI: 1.00, 2.95; P for trend = 0.056).

CONCLUSIONS

Results from the cross-sectional analysis of AREDS baseline data suggest that dietary glycemic quality and dietary carbohydrate quantity may be associated with prevalent nuclear and cortical opacities, respectively.

Dietary glycemic index and carbohydrate in relation to early age-related macular degeneration

BACKGROUND

Several dietary factors have been linked to age-related maculopathy (ARM), the early form of age-related macular degeneration, and there is reason to think that dietary carbohydrate may play a role in the development of ARM.

OBJECTIVE

The purpose of the present study was to examine the relation between dietary carbohydrate quality, as measured by dietary glycemic index (GI) or total carbohydrate intake, and ARM.

DESIGN

From the Nurses' Health Study, 1036 eyes from 526 Boston-area participants without a previous ARM diagnosis were included in the present study. The presence and degree of ARM were classified by the Age-Related Eye Diseases Study system. Long-term dietary information was based on data from an average of 4 food-frequency questionnaires collected over a 10-y period before the assessment of ARM. With eyes as the unit of analysis, we used a generalized estimating approach to logistic regression to estimate the odds ratios for ARM in a manner that accounted for the lack of independence between the 2 eyes from the same subject.

RESULTS

After multivariate adjustment, dietary GI was related to ARM (specifically to retinal pigmentary abnormalities), whereas total carbohydrate intake was not. The odds ratio for ARM being in the highest tertile of dietary GI (> or =77.0) versus the lowest (<74.6) was 2.71 (95% CI: 1.24, 5.93; P for trend = 0.01). Neither dietary GI nor total carbohydrate intake was related to drusen.

CONCLUSION

Our results suggest that dietary GI may be an independent risk factor for ARM.

Association between systemic arterial stiffness and age-related macular degeneration

BACKGROUND

A number of epidemiological studies suggest that age-related macular degeneration (AMD) and cardiovascular disease share the same risk factors. Systemic arterial stiffness is a clear indicator of cardiovascular disease. We investigated whether there is an association between directly measured systemic arterial stiffness and the presence of AMD.

METHODS

We used a SphygmoCor 2000 system to noninvasively measure two indicators of the systemic arterial stiffness, the arterial pulse wave velocity (PWV) and the central aortic blood pressure waveform, from which the augmentation pressure is determined. We studied 50 patients with AMD (12 men, 38 women, aged 60 to 91 years, mean 77 years) and 11 age-matched control subjects (3 men, 8 women, aged 66 to 92 years, mean 75 years). All study subjects received a complete ophthalmic examination including digital fundus photography. All of the patients with AMD were classified as stage 3 or worse in at least one eye according to the AREDS system.

RESULTS

Pulse wave velocity was significantly higher in the patients with AMD (8.2+/-1.1 m/s, mean +/- SD) compared with controls (7.1+/-0.8 m/s, p=0.0025), indicating increased arterial stiffness. There was no significant difference in PWV in AMD patients with and without choroidal neovascularization. There was no association between PWV and the presence of hypertension in either the patients or the controls. The central aortic augmentation pressure was significantly higher in the AMD patients than in the controls (p=0.040), also indicating increased arterial stiffness.

CONCLUSIONS

Patients with AMD have increased systemic arterial stiffness compared with age-matched controls. Treatments aimed at preventing or reversing systemic arterial stiffness may also be effective in preventing the onset or slowing the progression of AMD.

Decrease in the glyceraldehyde derived advanced glycation end products in the sera of patients with Vogt-Koyanagi-Harada disease

BACKGROUND/AIMS

Advanced glycation end products (AGEs) are considered to act as mediators of both age related pathologies and diabetic complications. It was recently reported that glyceraldehyde derived AGE (AGE-2) has a strong biological effect on various diseases. The aim of this study was to investigate the serum AGE-2 levels in Vogt-Koyanagi-Harada (VKH) disease.

METHODS

Sera were obtained from 31 patients with active VKH. 20 of these 31 patients were treated with systemic corticosteroids. As controls, 33 healthy volunteers were also examined. The serum AGE-2 levels were determined with a competitive enzyme linked immunosorbent assay using AGE-2 polyclonal antibody.

RESULTS

The mean AGE-2 level in the sera of patients with VKH disease was 4.91 (SD 2.23) U/ml, which was significantly lower than that of the healthy control subjects (8.32 (2.94), p<0.001). The average serum AGE-2 level significantly increased to 13.49 (2.17) U/ml after the patients were treated with systemic corticosteroids (p<0.001).

CONCLUSIONS

These results suggest that AGE-2 may be involved in the onset of VKH disease.

Expression of functionally phagocyte-type NAD(P)H oxidase in pericytes: effect of angiotensin II and high glucose

BACKGROUND INFORMATION

A growing body of evidence demonstrates the involvement of the oxidative stress in the development of vascular complications associated with diabetes, such as hypertension, retinopathy, nephropathy, neuropathy and atherosclerosis. However, the molecular mechanisms accountable for the increased production of reactive oxygen species (ROS) remain uncertain. Among others, the NAD(P)H oxidase is one of the most important sources of superoxide anion (O2-) that induce dysfunction of vascular cells. Pericytes (PCs) have an essential role in the capillary dysfunction in retinopathy and other vascular complications in diabetes. We questioned whether PCs express a functional phagocyte-type NAD(P)H oxidase, and examined the role of angiotensin II and high glucose on the activity of the oxidase complex and expression of the essential subunit p22(phox).

RESULTS

The mRNA expression of p22(phox), p47(phox), p67(phox) and NOX 1 subunits, and the lack of gp91(phox) component, were detected in PCs by reverse transcriptase PCR. Western-blotting analysis demonstrated the protein expression of p22(phox), p47(phox) and p67(phox) subunits. As compared with the normal condition, stimulation of PCs with angiotensin II or high glucose induced: (i) an increase in ROS production and NAD(P)H oxidase activity, and (ii) an up-regulation of p22(phox) mRNA and protein expression.

CONCLUSIONS

Taken together, the present study provides the first evidence that PCs express a functional phagocyte-type NAD(P)H oxidase, which is up-regulated by both angiotensin II and high glucose. Given the importance of ROS in vascular physiology and pathology, the NAD(P)H oxidase complex could be an important therapeutic target in the treatment of microvascular disorders.

Changes in aqueous humor dynamics with age and glaucoma

Changes in aqueous humor dynamics with age and in glaucoma have been studied for several decades. More recently, techniques have been developed which confirm earlier studies showing that outflow facility decreases with age and in glaucoma and add the newer finding that uveoscleral outflow also decreases. Morphologic studies in aging and glaucoma eyes have shown an increase in accumulation of extracellular material in both the trabecular meshwork and ciliary muscle and a loss of trabecular meshwork cells, which contribute to this reduction in outflow and result in an increase in intraocular pressure. A reduction in hyaluronic acid and increases in fibronectin and thrombospondin contribute to the change in the extracellular environment. Imbalances in responses to age-related stresses such as oxidative damage to long-lived molecules, protein cross-linking and loss of elasticity could trigger excess production of factors such as transforming growth factor beta, interleukin-1 and CD44S that could stimulate pathways leading to increases in fibronectin, transformation of trabecular meshwork cells to a myoepithelial state and decrease the breakdown in extracellular matrix material, allowing excess to accumulate. Ultimately trabecular outflow and uveoscleral outflow are reduced and intraocular pressure becomes elevated, adding more stress and perpetuating the pathological condition. Future research to identify additional factors and clarify their roles in these processes could lead to alternative therapies for age and glaucoma related changes in the eye.

Immunohistochemical localization of advanced glycation end products in pinguecula

BACKGROUND

Advanced glycation end products (AGEs) are known to be deposited in the target organ of ageing. In addition, the deposition of AGEs accelerate the process of ageing. We investigated the immunohistochemical localization of AGEs in pinguecula, one of the ocular changes related with ageing process.

METHODS

Surgical specimens of conjunctiva with or without pinguecula were prepared from nine patients, respectively. Immunohistochemical localization of AGEs was investigated using monoclonal antibodies to N(epsilon)-(carboxymethyl)lysine, pentosidine, imidazolone, and pyrraline.

RESULTS

Moderate to strong immunoreactivities to AGEs were detected in the subepithelial amorphous deposits of all the surgical specimens with pinguecula. In contrast, no or weak immunoreactivities to AGEs were detected in the surgical specimens without pinguecula.

CONCLUSIONS

Pinguecula is an aggregation of AGEs-modified proteins. The presence of pinguecula would be an index of local irradiation of ultraviolet rays and decreased antioxidant activities.

Levels of pentosidine in the vitreous of eyes with proliferative diabetic retinopathy, proliferative vitreoretinopathy and retinal detachment

BACKGROUND

Advanced glycosylation end products (AGEs) are thought to play an important role in the pathophysiology of diabetes. Particularly, these products have been implicated in the pathogenesis of proliferative diabetic retinopathy. The majority of these products are formed from a vast range of precursor molecules, the variable chemical nature of which contributes to AGE heterogeneity. There is a growing population of structurally defined AGE adducts such as pyrraline, pentosidine, CML and crossline that have been found to be elevated in diabetic tissues. In the present study, the levels of the glycoxidation product pentosidine were determined in vitreous samples obtained during vitrectomy from eyes with proliferative diabetic retinopathy (PDR), proliferative vitreoretinopathy (PVR), and retinal detachment (RD). Samples from cadaveric control eyes were also included in the study. The levels of pentosidine were compared among the groups.

METHODS

Seventy-three vitreous samples were collected from eyes undergoing vitrectomy for PDR (n=33), PVR (n=28) and RD (n=12). Eighteen samples from cadaveric control eyes were also included in the study. A modified Bradford's method was used to assay protein content, and vitreous levels of pentosidine were determined by high-performance liquid chromatography after acid hydrolysis and pretreatment with SP-Sephadex. Statistical analyses were performed using a two-sided Mann-Whitney U test.

RESULTS

The levels of pentosidine [median (interquartile range)] were 0.92 (0.55-1.26) pmol/mg of protein in the PDR cases, 1.12 (0.46-1.80) pmol/mg of protein in PVR, and 1.02 (0.24-1.44) pmol/mg of protein in RD. In the cadaveric control eyes pentosidine levels were 0.97 (0.68-1.30) pmol/mg of protein. The pentosidine levels of the four groups did not differ significantly.

CONCLUSIONS

The levels of the glycoxidation product pentosidine (expressed as pmol/mg of protein) in the vitreous of eyes with PDR do not differ significantly from those in the vitreous of eyes with PVR, RD or cadaveric control eyes. Although these results do not refute the findings of previous studies that evaluated globally total AGE levels and the existence of diabetic vitreopathy, further investigation is needed to fully understand their relevance in this multifactorial disorder.

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.

Carbohydrate intake and glycemic index in relation to the odds of early cortical and nuclear lens opacities

BACKGROUND

Animal studies suggest a role for dietary carbohydrate in cataractogenesis. However, few published human studies have evaluated associations between carbohydrate nutrition and lens opacification.

OBJECTIVE

Our objective was to test the hypothesis that long-term carbohydrate intake and dietary glycemic index are associated with the odds of early cortical and nuclear opacities.

DESIGN

Subjects were 417 Boston-area members of the Nurses' Health Study cohort aged 53-73 y. Dietary information was based on an average from 5 semiquantitative food-frequency questionnaires collected over a 14-y period. Opacities were assessed by using the Lens Opacity Classification System III (LOCS III). We used eyes (n = 711) as the unit of analysis and generated odds ratios by using a generalized estimating approach to logistic regression to account for the lack of independence between the 2 eyes of each subject.

RESULTS

After multivariate adjustment, the odds of cortical opacities (LOCS III >/=1.0) among women in the highest tertile of carbohydrate intake (>/=200 g/d) was 2.46 times (95% CI: 1.30, 4.64; P for trend = 0.005) that among women in the lowest tertile (<185 g/d). This association was not affected by adjustment for dietary glycemic index, which was not associated with early cortical opacities. Carbohydrate nutrition was not associated with the odds of nuclear opacities (LOCS III >/=2.5).

CONCLUSIONS

These data suggest that carbohydrate quantity, but not carbohydrate quality, is associated with early cortical opacities, and that neither the quantity nor the quality of dietary carbohydrate affects the risk of nuclear opacities in middle-aged women.

Sodium fluorescein as a retinal pH indicator?

Retinal neovascularization is a symptom associated with various diseases revealing ocular fundus manifestation. Often, these neovascularizations originate from retinal hypoxia. A concomitant phenomenon of hypoxia is acidosis. To recognise this would permit the identification and treatment of hypoxic fundus areas long before first vascular modifications are seen. Thus, the goal of this investigation was to elucidate whether sodium fluorescein could be used as a retinal pH indicator. Sodium fluorescein solution was diluted in PBS (ratio: 1:150,000). The pH was varied from 6.5 to 8.6 by supplementation of HCl or NaOH, respectively. The fluorescence was excited by a pulsed diode laser (wavelength: 446 nm, pulse width: 100 ps) and detected by time-correlated single photon counting (TCSPC) technique. A least-squares fit of the measured fluorescence decay versus time by an exponential function results in the fluorescence lifetime. Ten measurements were taken at each pH for statistical analysis. The dependence of the fluorescence lifetime on the temperature and the concentration of sodium fluorescein was investigated in the same way. The fluorescence lifetime was found to rise from 3.775 ns to 4.11 ns with increasing pH (6.5 to 8.6). However, the gradient decreases with increasing pH. We found highly significant differences (Student's t-test, P<0.0005) of the fluorescence lifetimes for pH values with a mean difference of 0.125 at pH<7.65 whereas the differences were still significant (P<or=0.02) at pH>7.65 and mean pH differences of 0.2. The fluorescence lifetime was independent of the temperature (22 degrees C to 37 degrees C) and the concentration of sodium fluorescein (dilution 1:150,000 to 1:2000). The fluorescence lifetime of sodium fluorescein depends on the pH but not on temperature and concentration. Thus, the discrimination of areas with retinal acidosis should be possible by combination of the TCSPC technique with scanning laser ophthalmoscopy. Further investigations have to clarify whether the accuracy of the measurement at the fundus in vivo is sufficient.

Cataract formation and prevention

Cataract, a leading cause of blindness worldwide, is a multifactorial eye disease. In developing countries the incidence of cataract among young generations is not uncommon due to malnutrition, excess exposure to ultraviolet radiation and so on. In developed countries, age-related cataract affecting the population over 65 years of age is a major concern. Oxidative stress was suggested to inflict damage to the lens and induce opacification, and a variety of antioxidant nutrients were tested for the prevention or delay of cataract development. Although promising results were obtained in animal studies of various antioxidants, epidemiological studies on human populations do not seem to support their protective effects unequivocally. It is unlikely that age-related cataract in man, similar to the ageing process itself, will be prevented or delayed by therapeutic drugs in the foreseeable future. At present, keeping a health-conscious life style (i.e., no smoking) may be the most effective and least expensive strategy to prevent the onset of age-related cataract.

Oxidative modification of rat eye lens proteins by peroxyl radicals in vitro: protection by the chain-breaking antioxidants stobadine and Trolox

In an attempt to model the processes of free radical-mediated cataractogenesis, we investigated the oxidative modification of rat eye lens proteins by peroxyl radicals generated by thermal decomposition of 2,2'-azobis(2-amidinopropane)hydrochloride (AAPH) under aerobic conditions. When incubated with AAPH, the soluble eye lens proteins precipitated in a time-dependent manner. The insolubilisation was accompanied by the accumulation of protein free carbonyls and the diminution of sulfhydryls, yet the processes were shifted in time. The SDS-PAGE analysis of the AAPH-treated proteins revealed the presence of high molecular weight cross-links and, to a lesser extent, fragments. The aggregation and cross-linking of proteins along with the generation of free carbonyls was significantly inhibited by the chain-breaking antioxidants stobadine and Trolox. On the other hand, the AAPH-initiated sulfhydryl consumption was much less sensitive to the antioxidants studied. The results point to a complex mechanism of peroxyl-radical-mediated modification of eye lens proteins with implications for cataract development and they indicate a potentially protective role of antioxidants.

Advanced glycation endproduct crosslinking in the cardiovascular system: potential therapeutic target for cardiovascular disease

Advanced glycation endproducts (AGEs) are formed by a reaction between reducing sugars and biological amines. Because of their marked stability, glycated proteins accumulate slowly over a person's lifespan, and can contribute to age-associated structural and physiological changes in the cardiovascular system such as increased vascular and myocardial stiffness, endothelial dysfunction, altered vascular injury responses and atherosclerotic plaque formation. The mechanisms by which AGEs affect the cardiovascular system include collagen crosslinking, alteration of low-density lipoprotein molecules and impairment of cellular nitric oxide signalling through their interaction with AGE receptors (RAGEs). Thus, the accumulation of AGEs may help to explain the increased cardiac risk associated with aging as well as diabetes mellitus and hypertension, two conditions that accelerate and enhance AGE formation. A variety of new pharmacological approaches are being developed to reduce the pathophysiological impact of AGEs. These agents can prevent AGE and AGE crosslink formation, break pre-existing AGE crosslinks, and block the interaction between AGEs and RAGEs. Such agents have been shown to reduce vascular and myocardial stiffness, inhibit atherosclerotic plaque formation and improve endothelial function in animal models. Improvement in vascular compliance has also been demonstrated with AGE crosslink breakers in clinical trials. These studies offer promise to reduce the cardiac risk associated with isolated systolic hypertension, diastolic dysfunction and diabetes.

Calpains: targets of cataract prevention?

There is emerging evidence to suggest that the unregulated Ca(2+)-mediated proteolysis of essential lens proteins by calpains might be a major contributor to some forms of cataract in both animals and humans. Moreover, recently solved calpain structures have revealed molecular-level details of the activation mechanism used by these proteases, enabling the structure-based design of potent calpain inhibitors with the potential to act as anti-cataract agents. These agents offer the first real hope of an urgently needed alternative to the surgical treatment of at least some forms of cataract and relief from a life-depreciating condition on a global scale.

Advanced glycation end product cross-linking: pathophysiologic role and therapeutic target in cardiovascular disease

Advanced glycation end products (AGEs) form by a nonenzymatic reaction between reducing sugars and biological proteins. These stable compounds accumulate slowly throughout the life span and contribute to structural and physiologic changes in the cardiovascular system such as increased vascular and myocardial stiffness, endothelial dysfunction, altered vascular injury responses, and atherosclerotic plaque formation. Mechanisms underlying these alterations include AGE cross-linking of collagen and AGE interactions with circulating proteins and AGE receptors. The clinical manifestations of AGE accrual-isolated systolic hypertension, endothelial and diastolic dysfunction, and atherosclerosis-underscore their role in increased cardiovascular risk associated with aging as well as diabetes and hypertension, conditions that enhance AGE formation. New pharmacologic agents that prevent AGE, break cross-links, or block AGE receptors reduce vascular and myocardial stiffness, inhibit atherosclerotic plaque formation, and improve endothelial function. These agents promise to reduce the risk of isolated systolic hypertension, diastolic dysfunction, and diabetes, and thus, heart failure.

Carnosine disaggregates glycated alpha-crystallin: an in vitro study

Protein glycation, which promotes aggregation, involves the unwanted reaction of carbohydrate oxidation products with proteins. Glycation of lens alpha-crystallin occurs in vivo and may contribute to cataractogenesis. Anti-glycation compounds such as carnosine may be preventive, but interestingly carnosine reverses lens opacity in human trials. The mechanism for this observation may involve carnosine's ability to disaggregate glycated protein. We investigated this hypothesis using glycated alpha-crystallin as our in vitro model. Methylglyoxal-induced glycation of alpha-crystallin caused aggregation as evidenced by increased 90 degrees light scattering. After addition of carnosine, light scattering returned to baseline levels suggesting that the size of the glycation-induced aggregates decreased. Additionally, carnosine decreased tryptophan fluorescence polarization of glycated alpha-crystallin, suggesting that carnosine increased peptide chain mobility, which may contribute to the controlled unfolding of glycated protein. Comparatively, guanidine-HCl and urea had no effect. Our data support the hypothesis that carnosine disaggregates glycated alpha-crystallin.

Stimulation of glucose utilization and inhibition of protein glycation and AGE products by taurine

AIM

Pathological effects of the process of non-enzymatic glycation of proteins are reflected in chronic complications of diabetes mellitus. We investigated the antiglycating effect of taurine in high fructose fed rats in vivo and the inhibiting potency of taurine in the process of in vitro glycation. Additionally, we investigated whether taurine enhances glucose utilization in the rat diaphragm.

METHODS

Rats fed a high fructose diet (60% total calories) were provided 2% taurine solution for 30 days. The effects of taurine on plasma glucose, fructosamine, protein glycation and glycosylated haemoglobin in high fructose rats were determined. For in vitro glycation a mixture of 25 mm glucose and 25 mm fructose was used as glycating agent, bovine serum albumin as the model protein and taurine as the inhibitor. Incubations were carried out in a constant temperature bath at 37 degrees C for 3-30 days. Amadori products and advanced glycation end products (AGEs) formed were measured. In vitro utilization of glucose was carried out in the rat diaphragm in the presence and absence of insulin in which taurine was used as an additive.

RESULTS

The contents of glucose, glycated protein, glycosylated haemoglobin and fructosamine were significantly lowered by taurine treatment to high fructose rats. Taurine prevented in vitro glycation and the accumulation of AGEs. Furthermore, taurine enhanced glucose utilization in the rat diaphragm. This effect was additive to that of insulin and did not interfere with the action of insulin.

CONCLUSIONS

These results underline the potential use of taurine as a therapeutic supplement for the prevention of diabetic pathology.

The influence of ageing on the insulin signalling system in rat lacrimal and salivary glands

PURPOSE

Ageing adversely affects the structure and function of lacrimal and salivary glands (LG and SG) and leads to marked insulin resistance that correlates with reduced insulin signal transduction. The aim of this study was to investigate whether ageing affects insulin signal transduction in LG and SG in vivo.

METHODS

Male Wistar rats aged 20 months and 2 months (control group) were compared (n=8/group). Samples were removed under anaesthesia after i.v. injection of insulin, homogenized, immunoprecipitated with anti-insulin receptor (IR), Shc and STAT-1 antibodies and immunoblotted with antiphosphotyrosine antibody.

RESULTS

The 20-month-old rats were significantly hyperinsulinaemic and presented a reduced rate of blood glucose disappearance in response to insulin, compared to the 2-month-old rats. The level of phosphorylation determined by densitometry in the older group of rats showed that ageing significantly reduced insulin-induced IR phosphorylation in LG and SG and STAT-1 phosphorylation in SG, compared to in the control group, but did not alter Shc phosphorylation.

CONCLUSIONS

Ageing influences insulin signal transduction in the LG and SG of rats. Considering the major anabolic actions of insulin, these observations may help to explain the mechanisms of LG and SG dysfunctions observed in ageing.

Glucose, glycation and aging

Glycation, a deleterious form of post-translational modification of macromolecules has been linked to diseases such as diabetes, cataract, Alzheimer's, dialysis related amyloidosis (DRA), atherosclerosis and Parkinson's as well as physiological aging. This review attempts to summarize the data on glycation in relation to its chemistry, role in macromolecular damage and disease, dietary sources and its intervention. Macromolecular damage and biochemical changes that occur in aging and age-related disorders point to the process of glycation as the common event in all of them. This is supported by the fact that several age-related diseases show symptoms manifested by hyperglycemia. Free radical mediated oxidative stress is also known to arise from hyperglycemia. There is evidence to indicate that controlling hyperglycemia by antidiabetic biguanides prolongs life span in experimental animals. Caloric restriction, which appears to prolong life span by bringing about mild hypoglycemia and increased insulin sensitivity further strengthens the idea that glucose via glycation is the primary damaging molecule.

Changes in oxidative balance in rat pericytes exposed to diabetic conditions

Recent data indicate that the oxidative stress plays an important role in the pathogenesis of diabetes and its complications such as retinopathy, nephropathy and accelerated atherosclerosis. In diabetic retinopathy, it was demonstrated a selective loss of pericytes accompanied by capillary basement membrane thickening, increased permeability and neovascularization. This study was designed to investigate the role of diabetic conditions such as high glucose, AGE-Lysine, and angiotensin II in the modulation of antioxidant enzymes activities, glutathione level and reactive oxygen species (ROS) production in pericytes. The activity of antioxidant enzymes: superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and total glutathione (GSH) was measured spectrophotometrically. The production of ROS was detected by spectrofluorimetry and fluorescence microscopy after loading the cells with 2'-7' dichlorofluoresceine diacetate; as positive control H2O2 was used. Intracellular calcium was determined using Fura 2 AM assay. The results showed that the cells cultured in high glucose alone, do not exhibit major changes in the antioxidant enzyme activities. The presence of AGE-Lys or Ang II induced the increase of SOD activity. Their combination decreased significantly GPx activity and GSH level. A three times increase in ROS production and a significant impairment of intracellular calcium homeostasis was detected in cells cultured in the presence of the three pro-diabetic agents used. In conclusion, our data indicate that diabetic conditions induce in pericytes: (i) an increase of ROS and SOD activity, (ii) a decrease in GPx activity and GSH level, (iii) a major perturbation of the intracellular calcium homeostasis. The data may explain the structural and functional abnormalities of pericytes characteristic for diabetic retinopathy.

Glucose-mediated in vitro glycation modulates biomechanical integrity of the soft tissues but not hard tissues

Glycation induced crosslinking of connective tissue collagen is thought to be involved in the pathogenesis of various disorders associated with diabetes and aging. Although the formation of the glycation related collagen crosslinks appears to be universal for all tissues, currently it is unknown whether differences exist between soft and hard tissue biomechanics in response to glucose-mediated in vitro glycation. In this study, the impact of non-enzymatic glycation was investigated on tendons and bones, using them as models for soft and hard tissue respectively. Achilles tendons from rabbits, and femur and tibia from rats, were subjected to in vitro glycation with glucose. Sixty days following glycation, the matrix integrity of the tendons and bones was evaluated and compared with the respective non-glycated tissue (n=10 in each group). The results revealed that the impact of glycation was significant on the tendon but not on the bone. Measurements of the biomechanical stability of glycated tendons indicated a significant increase in maximum load (21%), Young's modulus of elasticity (72%), energy to yield (35%) and toughness (68%) compared to the non-glycated tendons. No significant differences were found in breaking strength, bending stiffness, energy to yield and toughness between glycated and non-glycated femurs or tibias. The deformation of both soft and hard tissue was unaffected by the glycation. Measurements at ultimate tissue failure (break point) revealed that glycated tendons bore significantly higher load and energy absorption than non-glycated tendons. In contrast, the deformation of the glycated tendons at break point was considerably reduced as compared to control tendons. However, glycation had no significant effects on the hard tissue biomechanical properties at break point. The results of this study demonstrate that in vitro glycation influences the biomechanical properties of soft tissue but not hard tissue.

Advanced glycation endproducts in human diabetic and non-diabetic cataractous lenses

BACKGROUND

Advanced glycation endproduct (AGE) formation is thought to contribute to aging and cataract formation in the lens. In this study, we evaluated AGE immunoreactivity in human diabetic (n=14) and nondiabetic (n=31) cataractous lenses in relation to high-molecular-weight (HMW) protein content, which is believed to contribute to the onset of cataract.

METHODS

AGE immunoreactivity was detected in alkali-soluble individual lens samples. Competitive ELISA with polyclonal anti-AGE antibody was performed to estimate AGEs. SDS-PAGE was used to detect changes in lens protein composition on the basis of molecular size.

RESULTS

Regression analysis of data from nondiabetic lenses showed a significant correlation between lens AGE content and patient age (r=0.665, P<0.001). The curve exhibited exponential regression ( y=0.272.e(0.025x)). The level of nonspecified AGEs measured in diabetic lenses showed an overall increase compared with nondiabetic lenses (4.03+/-1.85 vs 1.78+/-0.71 AU/mg protein, P<0.0078). SDS-PAGE showed the occurrence of HMW proteins in both diabetic and nondiabetic lens samples. However, in diabetic patients, who had a higher level of AGEs, a significantly higher proportion of HMW proteins was also observed. The levels of AGE and percent of HMW aggregates showed a very significant correlation ( r=0.68, P<0.007) in the diabetic group, whereas in nondiabetics the correlation, although positive, did not reach statistical significance.

CONCLUSION

The AGE distribution, with a higher proportion in the samples of lenses rich in HMW aggregates, corroborates the hypothesis that the advanced glycation process might have a role in degenerative changes in eye lens, which in diabetic patients occur vigorously and much earlier than in those without diabetes.