Two polyclonal antisera detect different AGE epitopes in human plasma samples

Immunogenicity of advanced glycation end products in diabetic patients and in nephropathic non-diabetic patients on hemodialysis or after renal transplantation

Advanced glycation end products (AGE) increase as a consequence of diabetic hyperglycemia and, in nephropathic patients, following renal function loss. Protein-bound AGE behave as immunogens, inducing formation of specific antibodies (Ab-AGE). In this work AGE immunogenicity was studied in 42 diabetic patients, 26 nephropathic patients on hemodialysis and 26 patients with end-stage renal disease who underwent kidney transplantation and in 20 normal subjects. Non-oxidation-derived AGE (nox-AGE), oxidation-derived AGE (ox-AGE) and Ab-AGE were measured by competitive or direct enzyme-linked immunosorbent assay (ELISA) and circulating immune complexes (CIC) by C1q ELISA. Nox- AGE increased significantly in all patient groups (p < or = 0.05 to < or = 0.0001) except in patients on hemodialysis for less than 6 yr. Ox-AGE were only significantly increased in patients transplanted more than 3 yr previously (p < 0.05). Ab-AGE were significantly lower than controls in both diabetic groups and in patients on hemodialysis for more than 6 yr (p < 0.005 to < 0.0001) and not unlike controls in the other groups. These results demonstrate that hemodialysis or renal transplantation can, initially, reduce either nox- or ox-AGE levels, which however go back to being high in time. Renal transplantation fails to normalize nox-AGE. More importantly, plasma Ab-AGE levels are reduced or unchanged in all patient groups in comparison with controls, despite higher circulating AGE levels. This suggests the importance of tissue-bound AGE as Ab-AGE targets. Additional interventions are needed to control AGE levels in treated nephropathic patients. The search and quantification of specific Ab-AGE would give more meaningful results if performed over specific tissue specimens.

A novel advanced glycation index and its association with diabetes and microangiopathy

Formation of advanced glycation end products (AGEs) is an important mechanism by which chronic exposure to high glucose levels leads to vascular complications. Measurement of AGEs is hence of great importance for clinicians and researchers concerned with the management and prevention of diabetic vascular disease. The aim of this study was to evaluate a simple methodology to detect AGEs in the serum and to correlate their levels with diabetes and microangiopathy, specifically retinopathy and nephropathy. We studied 157 subjects, which included nondiabetic control subjects (n = 38), type 2 diabetic patients without microangiopathy (n = 65), and type 2 diabetic subjects with retinopathy (n = 29) or both retinopathy and nephropathy (n = 25). All subjects were assessed for their glycemic and lipid status. Serum AGEs were monitored by recording the Maillard-specific fluorescence that resulted from sequential addition of serum into the buffer. The resultant linear regression was modeled to yield the slope values that were termed advanced glycation index (AGI) in arbitrary units. The serum levels of AGI (mean +/- SD) were higher in diabetic subjects without complications (6.0 +/- 1.6 units) compared with nondiabetic subjects (4.6 +/- 1.0 units), still higher among diabetic subjects with retinopathy (7.6 +/- 1.2 units) and highest in diabetic subjects with both retinopathy and nephropathy (8.3 +/- 2.0 units). Among diabetic subjects, AGI had a significant positive correlation with duration of diabetes (r = 0.25, P = .006), glycated hemoglobin (r = 0.27, P = .004), cholesterol (r = 0.24, P = .009), triglycerides (r = 0.23, P = .014), and serum creatinine (r = 0.30, P = .001), and a significant negative correlation with creatinine clearance (r = -0.27, P = .003). Logistic regression analysis using diabetic microangiopathy as the dependent variable showed an association with AGI even after including age, duration of diabetes, and glycated hemoglobin (P < .001) into the model. Advanced glycation index is a simple method to detect AGEs, and it correlates well with diabetes, particularly with microangiopathy.

Therapeutic potential of breakers of advanced glycation end product-protein crosslinks

Long-lived structural proteins, collagen and elastin, undergo continual non-enzymatic crosslinking during aging and in diabetic individuals. This abnormal protein crosslinking is mediated by advanced glycation end products (AGEs) generated by non-enzymatic glycosylation of proteins by glucose. The AGE-derived protein crosslinking of structural proteins contributes to the complications of long-term diabetes such as nephropathy, retinopathy, and neuropathy. AGE-crosslinks have also been implicated in age-related cardiovascular diseases. Potential treatment strategies for these AGE-derived complications include prevention of AGE-formation and breaking of the existing AGE-crosslinks. The therapeutic potential of the AGE-inhibitor, pimagedine (aminoguanidine), has been extensively investigated in animal models and in Phase 3 clinical trials. This review presents the pre-clinical and clinical studies using ALT-711, a highly potent AGE-crosslink breaker that has the ability to reverse already-formed AGE-crosslinks. Oral administration of ALT-711 has resulted in a rapid improvement in the elasticity of stiffened myocardium in experimental animals. Topical administration of ALT-711 was effective in improving the skin hydration of aged rats. The therapeutic potential of crosslink breakers for cardiovascular complications and dermatological alterations associated with aging and diabetes is discussed.