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

Glycation and drug binding by serum albumin

Accumulation of glycation products in patients with hyperglycaemic conditions can lead to their reaction with the proteins in the human system such as serum albumin, haemoglobin, insulin, plasma lipoproteins, lens proteins and collagen among others which have important biological functions. Therefore, it is important to understand if glycation of these proteins affects their normal action not only qualitatively, but also importantly quantitatively. Glycation of human serum albumin can easily be carried out over period of weeks and its drug transportability may be examined, in addition to characterisation of the amadori products. A combination of ultrasensitive isothermal titration calorimetry, differential scanning calorimetry, spectroscopy and chromatography provides structure-property-energetics correlations which are important to obtain mechanistic aspects of drug recognition, conformation of the protein, and role of amadori products under conditions of glycation. The role of advance glycation end products is important in recognition of antidiabetic drugs. Further, the extent of glycation of the protein and its implication on drug transportability investigated by direct calorimetric methods enables unravelling mechanistic insights into role of functionality on drug molecules in the binding process, and hinderance in the recognition process, if any, as a result of glycation. It is possible that the drug binding ability of the protein under glycation conditions may not be adversely affected, or may even lead to strengthened ability. Rigorous studies on such systems with diverse functionality on the drug molecules is required which is essential in deriving guidelines for improvements in the existing drugs or in the synthesis of new molecular entities directed towards addressing diabetic conditions.

Mechanistic physicochemical insights into glycation and drug binding by serum albumin: Implications in diabetic conditions

The drug binding ability of serum albumin might get affected as a result of its glycation under diabetic conditions. It requires not only an understanding of the effect of glycation of the protein upon association with the drug, but also calls for an assessment of structure-property-energetics relationships. A combination of ultrasensitive calorimetric, spectroscopic and chromatographic approach has been employed to correlate thermodynamic signatures with recognition, conformation and mechanistic details of the processes involved. An important observation from this work is that 3-(dansylamino) phenyl boronic acid (DnsPBA) assay cannot always determine the extent of glycation as evidenced by MALDI-TOF mass spectra of glycated HSA due to its selectivity for 1,2 or 1,3 cis-diol structures which may be absent in certain AGEs. Protein gets modified post glycation with the formation of advanced glycation end products (AGEs), which are monitored to be targeted by the guanidine group present in anti-diabetic drugs. AGEs formed in the third and fourth week of glycation are significant in the recognition of anti-diabetic drugs. The results with metformin and aminoguanidine suggest that the extent of binding depends upon the number of guanidine group(s) in the drug molecule. Open chain molecules having guanidine group(s) exhibit stronger affinity towards glycated HSA than closed ring entities like naphthalene or pyridine moiety. The observation that the drug binding ability of HSA is not adversely affected, rather strengthened upon glycation, has implications in diabetic conditions. A rigorous structure-property-energetics correlation based on thermodynamic signatures and identification of functional groups on drugs for recognition by HSA are essential in deriving guidelines for rational drug design addressing diabetes.

Reactivity and degradation products of tryptophan in solution and proteins

Tryptophan is one of the essential mammalian amino acids and is thus a required component in human nutrition, animal feeds, and cell culture media. However, this aromatic amino acid is highly susceptible to oxidation and is known to degrade into multiple products during manufacturing, storage, and processing. Many physical and chemical processes contribute to the degradation of this compound, primarily via oxidation or cleavage of the highly reactive indole ring. The central contributing factors are reactive oxygen species, such as singlet oxygen, hydrogen peroxide, and hydroxyl radicals; light and photosensitizers; metals; and heat. In a multi-component mixture, tryptophan also commonly reacts with carbonyl-containing compounds, leading to a wide variety of products. The purpose of this review is to summarize the current state of knowledge regarding the degradation and interaction products of tryptophan in complex liquid solutions and in proteins. For the purposes of context, a brief summary of the key pathways in tryptophan metabolism will be included, along with common methods and issues in tryptophan manufacturing. The review will focus on the conditions that lead to tryptophan degradation, the products generated in these processes, their known biological effects, and methods which may be applied to stabilize the amino acid.

Simulated Sunlight Selectively Modifies Maillard Reaction Products in a Wide Array of Chemical Reactions

The photochemical transformation of Maillard reaction products (MRPs) under simulated sunlight into mostly unexplored photoproducts is reported herein. Non-enzymatic glycation of amino acids leads to a heterogeneous class of intermediates with extreme chemical diversity, which is of particular relevance in processed and stored food products as well as in diabetic and age-related protein damage. Here, three amino acids (lysine, arginine, and histidine) were reacted with ribose at 100 °C in water for ten hours. Exposing these model systems to simulated sunlight led to a fast decay of MRPs. The photodegradation of MRPs and the formation of new compounds have been studied by fluorescence spectroscopy and nontargeted (ultra)high-resolution mass spectrometry. Photoreactions showed strong selectivity towards the degradation of electron-rich aromatic heterocycles, such as pyrroles and pyrimidines. The data show that oxidative cleavage mechanisms dominate the formation of photoproducts. The photochemical transformations differed fundamentally from "traditional" thermal Maillard reactions and indicated a high amino acid specificity.

Phototoxicity of environmental radiations in human lens: revisiting the pathogenesis of UV-induced cataract

The magnitude of cataract pathology is indeed significant as it is the principal cause of blindness worldwide. Also, the prominence of this concept escalates with the current aging population. The burden of the disease is more tangible in developing countries than developed ones. Regarding this concern, there is a gap in classifying the pathogenesis of the ultraviolet (UV) radiation-induced cataracts and explaining the possible cellular and subcellular pathways. In this review, we aim to revisit the effect of UV radiation on cataracts categorizing the cellular pathways involved. This may help for better pharmaceutical treatment alternatives and their wide-reaching availability. Also, in the last section, we provide an overview of the protecting agents utilized as UV shields. Further studies are required to enlighten new treatment modalities for UV radiation-induced pathologies in human lens.

Riboflavin-induced Type 1 photo-oxidation of tryptophan using a high intensity 365 nm light emitting diode

The mechanism of photo-oxidation of tryptophan (Trp) sensitized by riboflavin (RF) was examined employing high concentrations of Trp and RF, with a high intensity 365 nm light emitting diode (LED) source under N₂, 20% and 100% O₂ atmospheres. Dimerization of Trp was a major pathway under the N₂ atmosphere, though this occurred with a low yield (^Dφ_Trp = 5.9 × 10^-3), probably as a result of extensive back electron transfer reactions between RF^•- and Trp(H)^•+. The presence of O₂ decreased the extent of this back electron transfer reaction, and the extent of Trp dimerization. This difference is attributed to the formation of O₂^•- (generated via electron transfer from RF^•- to O₂) which reacts rapidly with Trp^• leading to extensive consumption of the parent amino acid and formation of peroxides and multiple other oxygenated products (N-formylkynurenine, alcohols, diols) of Trp, as detected by LC-MS. Thus, it appears that the first step of the Type 1 mechanism of Trp photo-oxidation, induced by this high intensity 365 nm light source, is an electron transfer reaction between the amino acid and ³RF, with the presence of O₂ modulating the subsequent reactions and the products formed, as a result of O₂^•- formation. These data have potential biological significance as LED systems and RF-based treatments have been proposed for the treatment of pathological myopia and keratitis.

Improved bactericidal capacity of UV-B radiation against E. coli strains by photosensitizing bacteria with fructosazine - An advanced Maillard reaction product

This study investigated the effect of UV-B irradiation and the combinational effect with glucosamine caramel, fructosazine and riboflavin on the antimicrobial activities against Bacillus subtilis (ATCC 6633) and two strains of Escherichia coli (AW 1.7 and ATCC 25922). The quantum yield of fructosazine was two times less than that of tryptophan, indicating its ability to emit fluorescent light but less efficiently than tryptophan. UV-B treatment alone was efficient to achieve a bactericidal effect for both E. coli stains tested, however no effect was found for Bacillus subtilis for up to 80 mJ/cm² UV-B. The combination of UV-B with photosensitizers fructosazine, glucosamine caramel and riboflavin enhanced the UV-B efficacy against E. coli strains at lower UV-B doses, while Bacillus subtilis ATCC 6633 was more resistant to the treatment combinations. High-performance liquid chromatography showed the production of different fructosazine reaction products occurred during irradiation, including the possible formation of endoperoxides.

Structural and functional alteration of human αA-crystallin after exposure to full spectrum solar radiation and preventive role of lens antioxidants

The chronically exposure of eye lenses to ultra violet and visible light of the solar radiation is an important risk factor for development of the senile cataract diseases. Various photosensitizer molecules including riboflavin (RF) play a significant role in photo-oxidative damages of lens proteins underlying development of opacity in the lenticular tissues. In the current study, RF-mediated photo-oxidation of human αA-crystallin (αA-Cry) was assessed using SDS-PAGE analysis, dynamic light scattering and other spectroscopic assessments. The RF-photosensitized reactions led to non-disulfide covalent cross-linking, oligomerization and significant structural changes in αA-Cry. The photo-damaging of αA-Cry under solar radiation was also accompanied by the reduction in both Trp and Tyr fluorescence intensities which followed by the formation of new photosensitizer chromophores. The solvent exposed hydrophobic patches, secondary structures and chaperone-like activity of αA-Cry were significantly altered after exposure to the solar radiation in the presence of RF. Although glutathione and ascorbate were capable to partially protect the photo-induced structural damages of human αA-Cry, they also disrupted its chaperone function when co-exposed with this protein to the solar radiation. Also, the most promising data were obtained with cysteine which its availability in the lenticular tissues is a rate limiting factor for the biosynthesis of glutathione. Overall our results suggest that glutathione and ascorbate, as the major anti-oxidant compounds within lenticular tissues, demonstrate controversial effect on structure and chaperone-like activity of human αA-Cry. Elucidation of this effect may demand further experiments.

Corneal collagen crosslinking for corneal ectasias: a review

PURPOSE

To review the published literature on corneal collagen crosslinking (CXL).

METHODS

Importance has been placed on seminal publications, systemic reviews, meta-analyses, and randomized controlled clinical trials. Where such evidence was not available, cohort studies, case-controlled studies, and case series with follow-up greater than 12 months were examined.

RESULTS

Corneal collagen crosslinking with riboflavin and ultraviolet A (UVA) 370 nm radiation appears to be capable of arresting the progression of ectatic corneal disorders, with most studies reporting significant improvements in visual, keratometric, and topographic measurements. Its mode of action at the molecular level is undetermined. Follow-up is limited to 5-10 years but suggests sustained stability and enhancement in corneal shape with time. Nearly all published long-term data and comparative studies are with epithelium-off techniques. Epithelium-on investigations suggest some efficacy but less than with epithelium-off treatments and long-term data are unavailable. Accelerated techniques with higher UVA fluencies and shorter treatments times, delivering the same UVA energy dosage, are the subject of recent investigation, with some laboratory and clinical studies suggesting reduced efficacy compared to the standard 3 mW/cm2 for 30 minutes irradiation procedure. Combined methodologies of CXL with techniques such as photorefractive keratectomy and intrastromal rings show promise but long-term follow-up is indicated. Sight-threatening complications of CXL are rare.

CONCLUSIONS

Studies of epithelium-off CXL with irradiation at 3 mW/cm2 for 30 minutes support its efficacy. Refinement in techniques may allow for safer and more rapid procedures with less patient discomfort but require further investigation.

UVA light-excited kynurenines oxidize ascorbate and modify lens proteins through the formation of advanced glycation end products: implications for human lens aging and cataract formation

Advanced glycation end products (AGEs) contribute to lens protein pigmentation and cross-linking during aging and cataract formation. In vitro experiments have shown that ascorbate (ASC) oxidation products can form AGEs in proteins. However, the mechanisms of ASC oxidation and AGE formation in the human lens are poorly understood. Kynurenines are tryptophan oxidation products produced from the indoleamine 2,3-dioxygenase (IDO)-mediated kynurenine pathway and are present in the human lens. This study investigated the ability of UVA light-excited kynurenines to photooxidize ASC and to form AGEs in lens proteins. UVA light-excited kynurenines in both free and protein-bound forms rapidly oxidized ASC, and such oxidation occurred even in the absence of oxygen. High levels of GSH inhibited but did not completely block ASC oxidation. Upon UVA irradiation, pigmented proteins from human cataractous lenses also oxidized ASC. When exposed to UVA light (320-400 nm, 100 milliwatts/cm(2), 45 min to 2 h), young human lenses (20-36 years), which contain high levels of free kynurenines, lost a significant portion of their ASC content and accumulated AGEs. A similar formation of AGEs was observed in UVA-irradiated lenses from human IDO/human sodium-dependent vitamin C transporter-2 mice, which contain high levels of kynurenines and ASC. Our data suggest that kynurenine-mediated ASC oxidation followed by AGE formation may be an important mechanism for lens aging and the development of senile cataracts in humans.

Resistance of corneal RFUVA–cross-linked collagens and small leucine-rich proteoglycans to degradation by matrix metalloproteinases

PURPOSE

Extracellular matrix metalloproteinases (MMPs) are thought to play a crucial role in corneal degradation associated with the pathological progression of keratoconus. Currently, corneal cross-linking by riboflavin and ultraviolet A (RFUVA) has received significant attention for treatment of keratoconus. However, the extent to which MMPs digest cross-linked collagen and small leucine-rich proteoglycans (SLRPs) remains unknown. In this study, the resistance of RFUVA-cross-linked collagens and SLRPs to MMPs has been investigated.

METHODS

To investigate the ability of MMPs to digest cross-linked collagen and SLRPs, a model reaction system using purified collagen type I, type IV, and nonglycosylated, commercially available recombinant SLRPs, keratocan, lumican, mimecan, decorin, and biglycan in solution in vitro has been compared using reactions inside an intact bovine cornea, ex vivo.

RESULTS

Our data demonstrate that corneal cross-linked collagen type I and type IV are resistant to cleavage by MMP-1, MMP-2, MMP-9, and MMP-13, whereas non-cross-linked collagen I, IV, and natively glycosylated SLRPs are susceptible to degradation by MMPs. In addition, both cross-linked SLRPs themselves and cross-linked polymers of SLRPs and collagen appear able to resist degradation. These results suggest that the interactions between SLRPs and collagen caused by RFUVA protect both SLRPs and collagen fibrils from cleavage by MMPs.

CONCLUSIONS

A novel approach for understanding the biochemical mechanism whereby RFUVA cross-linking stops keratoconus progression has been achieved.

State diagrams for improving processing and storage of foods, biological materials, and pharmaceuticals (IUPAC Technical Report)

Supplemented temperature/composition phase diagrams include the non-equilibrium glass-transition temperature (Tg) curve and equilibrium ice-melting and solubility curves. The inclusion of the non-equilibrium curve allows one to establish relationships with the time coordinate and, thus, with the dynamic behavior of systems, provided that the thermal history of such systems is known. The objective of this report is to contribute to the potential applications of supplemented state diagrams for aqueous glass-formers, in order to describe the influence of water content, nature of vitrifying agents, and temperature on the physico-chemical properties of foods and biological and pharmaceutical products. These data are helpful to develop formulations, processing strategies, or storage procedures in order to optimize the stability of food ingredients and pharmaceutical formulations. Reported experimental data on phase and state transitions for several food and pharmaceutical systems were analyzed. Some methodological aspects and the effect of phase and state transitions on the main potential chemical reactions that can alter those systems during processing and/or storage are discussed.

Effects of ultraviolet-A and riboflavin on the interaction of collagen and proteoglycans during corneal cross-linking

Corneal cross-linking using riboflavin and ultraviolet-A (RFUVA) is a clinical treatment targeting the stroma in progressive keratoconus. The stroma contains keratocan, lumican, mimecan, and decorin, core proteins of major proteoglycans (PGs) that bind collagen fibrils, playing important roles in stromal transparency. Here, a model reaction system using purified, non-glycosylated PG core proteins in solution in vitro has been compared with reactions inside an intact cornea, ex vivo, revealing effects of RFUVA on interactions between PGs and collagen cross-linking. Irradiation with UVA and riboflavin cross-links collagen α and β chains into larger polymers. In addition, RFUVA cross-links PG core proteins, forming higher molecular weight polymers. When collagen type I is mixed with individual purified, non-glycosylated PG core proteins in solution in vitro and subjected to RFUVA, both keratocan and lumican strongly inhibit collagen cross-linking. However, mimecan and decorin do not inhibit but instead form cross-links with collagen, forming new high molecular weight polymers. In contrast, corneal glycosaminoglycans, keratan sulfate and chondroitin sulfate, in isolation from their core proteins, are not cross-linked by RFUVA and do not form cross-links with collagen. Significantly, when RFUVA is conducted on intact corneas ex vivo, both keratocan and lumican, in their natively glycosylated form, do form cross-links with collagen. Thus, RFUVA causes cross-linking of collagen molecules among themselves and PG core proteins among themselves, together with limited linkages between collagen and keratocan, lumican, mimecan, and decorin. RFUVA as a diagnostic tool reveals that keratocan and lumican core proteins interact with collagen very differently than do mimecan and decorin.

Simultaneous chemical and photochemical protein crosslinking induced by irradiation of eye lens proteins in the presence of ascorbate: the photosensitizing role of an UVA-visible-absorbing decomposition product of vitamin C

Exposure to light has been implicated as a risk factor during aging of the eye lens and in cataract generation. In order to visualize the actual effect of UVA-visible light on this tissue, we incubated water-soluble eye lens proteins with ascorbate in the presence and absence of UVA-visible light for 3, 6 and 9 days at low oxygen concentration. The samples incubated in the presence of light were characterized by an initially small but continuous increase over time of the protein crosslinking. This was not the result of more extensive glycation because the decrease in amino group content of the proteins and the decomposition of ascorbate was the same in both irradiated and unirradiated samples. The augmented crosslinking capacity observed in the presence of UVA-visible light is due to the generation of a chromophore from the decomposition of ascorbate. This chromophore, obtained after 3, 6 and 9 days of incubation of solutions containing only ascorbate, induces both protein-crosslinking and oxidation after exposure to UVA-visible light in the presence of lens proteins. The extent of the crosslinking was proportional to the amount of the chromophore present in the solution. The presence of this chromophore was also determined when ascorbate was incubated with four-fold higher concentrations of N-α-acetyl lysine and N-α-acetyl arginine. When these samples were used as photosensitizers, the crosslinking degree was conditioned by the presence of this chromophore; nonetheless, the ascorbate-mediated advanced glycation end product (AGE) generation also made a contribution. The results of this work indicate that ascorbate oxidation, which generates the AGEs responsible for the chemical crosslinking of the lens proteins, also simultaneously produces a chromophore that can act as a photosensitizer, further increasing the protein crosslinking.

Mechanisms of corneal tissue cross-linking in response to treatment with topical riboflavin and long-wavelength ultraviolet radiation (UVA)

PURPOSE

Treatment of de-epithelialized human corneas with riboflavin (RF) + long-wavelength ultraviolet light (UVA; RFUVA) increases corneal stroma tensile strength significantly. RFUVA treatment retards the progression of keratoconus, perhaps by cross-linking of collagen molecules, but exact molecular mechanisms remain unknown. Research described here tested possible chemical mechanisms of cross-linking.

METHODS

Corneas of rabbits and spiny dogfish sharks were de-epithelialized mechanically, subjected to various chemical pretreatments, exposed to RFUVA, and then subjected to destructive tensile stress measurements. Tensile strength was quantified with a digital force gauge to measure degree of tissue cross-linking.

RESULTS

For both rabbit and shark corneas, RFUVA treatment causes significant cross-linking by mechanism(s) that can be blocked by the presence of sodium azide. Conversely, such cross-linking is greatly enhanced in the presence of deuterium oxide (D(2)O), even when RF is present at only one tenth the currently used clinical concentrations. Blocking carbonyl groups preexisting in the stroma with 2,4-dinitrophenylhydrazide or hydroxylamine blocks essentially all corneal cross-linking. In contrast, blocking free amine groups preexisting in the stroma with acetic anhydride or ethyl acetimidate does not affect RFUVA corneal cross-linking. When both carbonyl groups are blocked and singlet oxygen is quenched, no RFUVA cross-linking occurs, indicating the absence of other cross-linking mechanisms.

CONCLUSIONS

RFUVA catalyzes cross-linking reactions that require production of singlet oxygen ((1)O(2)), whose half-life is extended by D(2)O. Carbonyl-based cross-linking reactions dominate in the corneal stroma, but other possible reaction schemes are proposed. The use of D(2)O as solution media for RF would enable concentration decreases or significant strength enhancement in treated corneas.

Detection of kynurenine modifications in proteins using a monoclonal antibody

N-formylkynurenine and kynurenine are oxidation products of tryptophan formed from the reaction catalyzed by indoleamine 2,3-dioxygenase. These kynurenines react with proteins to produce chemical modifications in the lens. We developed a novel monoclonal antibody that detects a kynurenine modification in proteins. The antibody recognized proteins (human lens proteins, RNase A and BSA) that were modified by either kynurenine or N-formylkynurenine. The antibody also reacted strongly with N-formylkynurenine-modified N(alpha)-acetyl histidine and weakly with N-formylkynurenine-modified N(alpha)-acetyl lysine, N(alpha)-acetyl cysteine and N(alpha)-acetyl arginine. The antibody recognized kynurenine and N-formylkynurenine but not other tryptophan oxidation products. We isolated and purified a major antigen from the reaction mixture of N(alpha)-acetyl histidine and N-formylkynurenine and identified the product as N-acetyl-1-[3-(2-aminophenyl)-1-carboxy-3-oxopropyl]-histidine. We then used our purified antibody to detect kynurenine modifications in kynurenine-treated human lens epithelial cells and human lens. We found epithelial immunoreactivity in a lens from an aged donor but not in one from a very young donor. This would suggest that the antibody detects age-related changes in lens proteins altered by kynurenines. We believe that our antibody could be used to establish the importance of kynurenine modifications in diseases where tryptophan oxidation is enhanced.

Photosensitizing Activity of Advanced Glycation Endproducts on Tryptophan, Glucose 6-phosphate Dehydrogenase, Human Serum Albumin and Ascorbic Acid Evaluated at Low Oxygen Pressure†

A comparative study of the photosensitizing activity of advanced glycation endproducts (AGEs) prepared by incubating glucose (Glc), threose (Threo) and ascorbate (AH-) in the presence of lysine (Lys) was performed. Photochemical activity was evaluated under low oxygen pressure with the aim to simulate the conditions of the eye lens. AGE-sensitized tryptophan and AH- photodecomposition and glucose 6-phosphate dehydrogenase inactivation were studied. In all systems, glucose-derived AGEs showed the highest photosensitizing efficiency, followed by ascorbate and threose. The presence of different sensitizers in glycation products mixtures was investigated. For this purpose, Trp decomposition quantum yields were determined at 344 and 367 nm. The values obtained at 344 nm are between three and six times higher than those observed at 367 nm, confirming the presence of at least two compounds with different photosensitizing activities in the mixtures. The chemiluminescence associated with the AGE-mediated oxidation of free Trp and Trp residues in human serum albumin was also studied, and a good correlation between the emission of light and the extent of Trp decomposition was found. In conclusion, it is demonstrated that glucose derived AGEs, which can be formed in vivo in the eye lens of diabetic patients and are accumulated in elderly lenses, have a higher photosensitizing efficiency, at low oxygen pressure, than those arising from ascorbate and threose. This high efficiency is especially significant when proteins are employed as photochemical targets, indicating that protein-sensitizer interaction and the local environment around the sensitizers play an important role.

Fluorescence from the Maillard Reaction and its Potential Applications in Food Science

The chemistry of the Maillard reaction involves a complex set of steps, and its interpretation represents a challenge in basic and applied aspects of Food Science. Fluorescent compounds have been recognized as important early markers of the reaction in food products since 1942. However, the recent advances in the characterization of fluorophores' development were observed in biological and biomedical areas. The in vivo non-enzymatic glycosylation of proteins produces biological effects, promoting health deterioration. The characteristic fluorescence of advanced glycosylation end products (AGEs) is similar to that of Maillard food products and represents an indicator of the level of AGE-modified proteins, but the structure of the fluorescent groups is, typically, unknown. Application of fluorescence measurement is considered a potential tool for addressing key problems of food deterioration as an early marker or index of the damage of biomolecules. Fluorophores may be precursors of the brown pigments and/or end products. A general scheme of the Maillard reaction is proposed in this article, incorporating the pool concept. A correct interpretation of the effect of environmental and compositional conditions and their influences on the reaction kinetics may help to define the meaning of fluorescence development for each particular system.

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.