Structure of advanced Maillard reaction products and their pathological role

Abstract

In this article we review recent progress and controversies relating to three areas of the field of advanced glycosylation end-products (AGE). A controversy exists as to whether pyrraline, an AGE detectable by immunohistochemistry in kidneys from patients with renal failure, exists in vivo. Recent data from the authors' laboratory revealed that pyrraline is present in alkaline or protease digests from human skin and plasma. However, the amounts are very low and pyrraline was found to undergo further reactions to form an ether with itself (dipyrraline) as well as a thioether with cysteine. This high reactivity of pyrraline may explain the difficulty of quantitating it accurately in biological material. In contrast, the glycoxidation products carboxymethyllysine (CML) and pentosidine are stable, very resistant to acid hydrolysis and easy to quantitate. They are present in elevated concentrations in the extracellular matrix in diabetes mellitus and ageing. In the diabetic human lens, CML is not elevated, in contrast to pentosidine, suggesting a different mechanism of formation. Recent data in diabetic dogs have shown that pentosidine is elevated only in lenses from poorly controlled dogs, in contrast to LM-1, a fluorophore thought to arise from ascorbate. Further studies are needed to clarify the intracellular mechanism of glycoxidation. The greatest concentrations of AGEs and glycoxidation products are found in patients with end-stage renal disease, and they are almost completely normalized by renal transplantation. Comparison of peritoneal dialysis (PD) with haemodialysis (HD) showed that PD is associated with lower plasma protein pentosidine, possibly due to selective transport of pentosidine-rich protein across the peritoneal wall. Fractionation of plasma proteins from ESRD patients by size showed that 90% of pentosidine is linked to HMW protein and 1-2% is in free form. The mechanism of accelerated glycoxidation in ESRD is still not understood.

Early Glycation Products Produce Pentosidine Cross-links on Native Proteins

“…Among the carbohydrates tested, glyceraldehyde produced the highest levels of pentosidine followed by glycolaldehyde and glyoxal (Table II). 1 H NMR (D 2 O) and UV absorption spectra of the product from glyceraldehyde were fully compatible with those reported for ribosederived pentosidine (43) (data not shown). In the case of glycolaldehyde and glyoxal, spectroscopic characterization is necessary to confirm the formation of pentosidine.…”

“…1 The reaction products include amino acid cross-links, fluorophores, and chromophores on proteins (1,2). AGEs can bind to specific receptors on cells to cause intracellular oxidative stress as well as the synthesis of growth factors and cytokines (3)(4)(5)(6), and the end result is usually damage to the affected tissues (7,8).…”

Amides Are Novel Protein Modifications Formed by Physiological Sugars

“…After 2 min 190 l of phosphate buffer (50 mM, pH 6.6) were added, and the solution was mixed and immediately subjected to the second HPLC system. The Knauer column was used with the mobile phase consisting of H 2 Protein Incubations-For the detection of GOLD the postcolumn derivatization system described above was used. For the detection of GOLA a two-stage HPLC system was used.…”

“…A variety of stable end products, known as advanced glycation end products, or AGEs, 1 form as a result (1). However, the few AGEs identified in vivo cannot account for the extensive protein modifications found in target tissues (2,3). Since AGEs are recognized by cellular receptors, they can also damage tissues by triggering the production of reactive oxygen species (4).…”

Determination of Advanced Glycation End Products in Serum by Fluorescence Spectroscopy and Competitive ELISA

“…Finally, advanced glycation endproducts are formed as a mixture of protein-bound nitrogen and oxygen-containing heterocyclic compounds through a complex cascade of dehydration, condensation, fragmentation, oxidation and cyclization reactions (1,2). A variety of chemical advanced glycation endproduct structures have been elucidated, some of which are non-fluorescent like N e -(carboxymethyl)lysine, pyralline or imidazolone, or fluorescent like pentosidine or the crosslinks (3,4).…”