Pathological Roles of Advanced Glycation End Product Receptors SR-A and CD36

The pathological significance of advanced glycation end product (AGE)-modified proteins deposited in several lesions is generally accounted for by their cellular interaction via the AGE receptors and subsequent acceleration of the inflammatory process. In this study, we focused on two AGE receptors-specifically, the role of SR-A in pathogenesis of diabetic nephropathy and the role of CD36 in AGE-induced downregulation of leptin by adipocytes. In terms of SR-A, diabetic wild-type mice exhibited increased urinary albumin excretion, glomerular hypertrophy, and mesangial matrix expansion, whereas SR-A-knockout mice showed reduced glomerular size and mesangial matrix area. In these diabetic SR-A-knockout mice, the number of macrophages that infiltrated into glomeruli was remarkably reduced (P < 0.05), suggesting that SR-A-dependent glomerular migration of macrophages plays an important role in the pathogenesis of diabetic nephropathy. In terms of CD36, incubation of glycolaldehyde-modified bovine serum albumin (GA-BSA) with 3T3-L1 adipocytes reduced leptin secretion by these cells. The binding of GA-BSA to these cells and subsequent endocytic degradation were effectively inhibited by a neutralizing anti-CD36 antibody. AGE-induced downregulation of leptin was protected by N-acetyl-cysteine, an antioxidant. These results indicate that the interaction of AGE ligands with 3T3-L1 adipocytes via CD36 induces oxidative stress and leads to inhibition of leptin expression by these cells, suggesting a potential link of this phenomenon to exacerbation of the insulin sensitivity in metabolic syndrome.

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.

Conventional antibody against Nepsilon-(carboxymethyl)lysine (CML) shows cross-reaction to Nepsilon-(carboxyethyl)lysine (CEL): immunochemical quantification of CML with a specific antibody

Immunological strategies for the detection of N(epsilon)-(carboxymethyl)lysine (CML), one of the major antigenic structures of advanced glycation end products (AGE), are widely applied to demonstrate the contribution of CML to the pathogeneses of diabetic complications and atherosclerosis. Recent studies have indicated that methylglyoxal (MG), which is generated intracellularly through the Embden-Meyerhof and polyol pathways, reacts with proteins to form MG-derived AGE structures such as N(epsilon)-(carboxyethyl)lysine (CEL). In order to accurately measure the CML contents of the proteins by means of an immunochemical method, we prepared CML-specific antibodies since conventionally prepared polyclonal anti-CML antibody and monoclonal anti-CML antibody (6D12) cross-reacted with CEL. To prepare polyclonal CML-specific antibody, CML-keyhole limpet hemocyanin (CML-KLH) were immunized with rabbit and CEL-reactive antibody was removed by CEL-conjugated affinity chromatography. Monoclonal antibody specific for CML (CMS-10) was obtained by immunization with CML-KLH, followed by successive screening according to CML-bovine serum albumin (CML-BSA)-positive but CEL-BSA-negative criteria. Both polyclonal CML-specific antibody and CMS-10 significantly reacted with CML-proteins but not with CEL-proteins. It is likely therefore that these antibodies can recognize the difference of one methyl group between CML and CEL. Moreover, CMS-10 significantly reacted with BSA modified with several aldehydes and its reactivity was highly correlated with the CML content, which was determined by high performance liquid chromatography, whereas 6D12 showed a low correlation. These results indicate that CMS-10 can be used to determine the CML contents of modified proteins in a more specific way.