An autoantibody against N(ε)-(carboxyethyl)lysine (CEL): possible involvement in the removal of CEL-modified proteins by macrophages.

Advanced glycation end products (AGEs) are believed to play a significant role in the development of diabetic complications. In this study, we measured the levels of autoantibodies against several AGE structures in healthy human plasma and investigated the physiological role of the autoantibodies. A high titer of the autoantibody against N(ε)-(carboxyethyl)lysine (CEL) was detected in human plasma compared with other AGE structures such as CML and pentosidine. The purified human anti-CEL autoantibody reacted with CEL-modified human serum albumin (CEL-HSA), but not CML-HSA. A rabbit polyclonal anti-CEL antibody, used as a model autoantibody against CEL, accelerated the uptake of CEL-HSA by macrophages, but did not enhance the uptake of native HSA. Furthermore, when (125)I-labeled CEL-HSA was injected into the tail vein of mice, accumulation of (125)I-CEL-HSA in the liver was accelerated by co-injection of the rabbit anti-CEL antibody. These results demonstrate that the autoantibody against CEL in plasma may play a role in the macrophage uptake of CEL-modified proteins.

Structural insights into differences in drug-binding selectivity between two forms of human alpha1-acid glycoprotein genetic variants, the A and F1*S forms.

Human α(1)-acid glycoprotein (hAGP) in serum functions as a carrier of basic drugs. In most individuals, hAGP exists as a mixture of two genetic variants, the F1*S and A variants, which bind drugs with different selectivities. We prepared a mutant of the A variant, C149R, and showed that its drug-binding properties were indistinguishable from those of the wild type. In this study, we determined the crystal structures of this mutant hAGP alone and complexed with disopyramide (DSP), amitriptyline (AMT), and the nonspecific drug chlorpromazine (CPZ). The crystal structures revealed that the drug-binding pocket on the A variant is located within an eight-stranded ß-barrel, similar to that found in the F1*S variant and other lipocalin family proteins. However, the binding region of the A variant is narrower than that of the F1*S variant. In the crystal structures of complexes with DSP and AMT, the two aromatic rings of each drug interact with Phe-49 and Phe-112 at the bottom of the binding pocket. Although the structure of CPZ is similar to those of DSP and AMT, its fused aromatic ring system, which is extended in length by the addition of a chlorine atom, appears to dictate an alternative mode of binding, which explains its nonselective binding to the F1*S and A variant hAGPs. Modeling experiments based on the co-crystal structures suggest that, in complexes of DSP, AMT, or CPZ with the F1*S variant, Phe-114 sterically hinders interactions with DSP and AMT, but not CPZ.

Effect of reactive-aldehydes on the modification and dysfunction of human serum albumin.

Advanced glycation end products (AGEs) are generated not only from glucose but also from several aldehydes such as methylglyoxal, glyoxal, and glycolaldehyde. The aim of the present study was to investigate the effect of several aldehydes on human serum albumin (HSA) in terms of the physicochemical properties and formation of AGE structures. HSA modified with methylglyoxal, generated by the glycolysis pathway and degradation of the Schiff base, showed the highest increase in the molecular weight and net negative charge, whereas glucose modification caused a small increase in the molecular weight even incubation for after 4 weeks. N(epsilon)-(carboxymethyl)lysine (CML), N(epsilon)-(carboxyethyl)lysine (CEL), and imidazolone increased in modified HSA in correlation with their lysine and arginine modification, whereas high amounts of GA-pyridine was detected in HSA modified with glycolaldehyde. Furthermore, the binding ability of HSA to warfarin and ketoprofen was more effectively decreased by methylglyoxal modification than the other aldehydes. These results indicated that changes in the physicochemical properties and the formation of AGE structures are highly dependent on the aldehydes.