Kazushi Misawa

Production and characterization of antibodies to advanced glycation products on proteins.

Antibodies directed against advanced glycation products formed during Maillard reaction have been generated and characterized. These antibodies reacted specifically with advanced glycation products in common among proteins incubated with glucose, but not early-stage compounds such as a Schiff base adduct and Amadori rearrangement products. Incubation of bovine serum albumin with glucose caused a time-related increase in immunoreactivity and a concomitant increase in fluorescence intensity. These antibodies may serve as a useful tool to elucidate pathophysiological roles of advanced Maillard reaction in diabetic complications and aging processes.

Characterization of antibodies to advanced glycosylation end products on protein.

Antibodies directed against advanced glycosylation end products (AGEs) formed during a Maillard reaction have been generated and characterized. Since protein-bound AGEs recognized by the antibodies were labile to acid hydrolysis, the antibodies were further characterized by using the AGE-alpha-acetyl-L-lysine methyl ester (AGE-ALME) with a brown and fluorescent property as well as the AGE-proteins. The antibodies reacted with fluorescent compounds, rather than brown pigment compounds, in the AGE-ALME. The fluorescent compounds in the AGE-ALME were separated into four fluorescent compounds by reversed-phase thin layer chromatography (TLC). Of the fluorescent compounds tested, compound 3 (Rf = 0.63), as designated on a TLC plate, showed the highest affinity for the antibodies. In addition, the antibody recognition to the cross-linked oligomers with fluorescence in the AGE-protein was investigated by using bovine pancreatic ribonuclease A (RNase), which is known as a model protein for studying AGE-induced cross-linking. Fluorescence in the AGE-RNase existed in both of the oligomers and the monomer. The cross-linked oligomers exhibited higher affinity to the antibodies than did the monomer, which has a similar degree of fluorescent intensity. These results indicate that our antibodies against cross-linked protein-bound AGEs may serve as a useful tool to elucidate pathophysiological roles of advanced Maillard reaction in diabetic complications and aging processes.

Radioimmunoassay for the determination of glycated haemoglobin

SummaryA competitive radioimmunoassay for the quantitative determination of glycated haemoglobin was developed. The antiserum, obtained by immunizing guinea pigs with reduced glycated human albumin, was capable of identifying and quantitating the glucitollysine residues of glycated Hb after reduction with sodium borohydride. To simplify the sample preparation we introduced trichloroacetic acid precipitation to remove unreacted sodium borohydride instead of using dialysis or gel filtration. Using this procedure, our radioimmunoassay became relatively simple and provided satisfactory within- and between-run (1.3–2.8% and 1.9–5.4% coefficient of variation, respectively). The radioimmunoassay method was compared to the measurement of HbA1c by high performance liquid chromatography which is the most widely used method for quantitating glycated Hb. For this purpose glycated Hb was measured in normal glucose tolerance, impaired glucose tolerance, and diabetes mellitus groups based on WHO criteria. Both assays were able to discriminate between the normal and diabetic groups. In addition, while the determination of glycated Hb by the radioimmunoassay method was able to clearly discriminate between the normal and impaired glucose tolerance groups, the determination of HbA1c by the high performance liquid chromatography method failed to discriminate between these two groups. Moreover, 15 of the 20 impaired glucose tolerance patients exceeded the upper normal range (mean normal values + 2 SD) in radioimmunoassay. But all 20 patients with impaired glucose tolerance were within the upper normal range in HbA1c values.These results demonstrate that the measurement of glycated Hb by radioimmunoassay is more sensitive than the measurement of HbA1c by high performance liquid chromatography since it can discriminate between the normal and impaired glucose tolerance groups.

Radioimmunoassay for nonenzymatically glycated protein in human serum.

Recent studies have shown that posttranslational, nonenzymatic glycation of a variety of serum and structural proteins occur in normal and to a much greater extent in diabetic subjects. The glycation of serum albumin is of noteworthy clinical interest, since the extent of serum albumin glycation provides a useful means for accurately assessing the mean blood glucose level of diabetic subjects over short periods of time [l-3]. Therefore, it may be important to quantitate it accurately. Recently, Curtiss and Witztum [4] reported an elegant method for generating region-specific monoclonal antibodies to reductively glycated proteins, and quantifying glucitollysine residues on the total plasma proteins and isolated lipoproteins of normal and diabetic subjects after reduction of the proteins. In this report, we describe a radioimmunoassay (RIA) for glycated human serum protein using antiserum readily obtained by immunizing guinea pigs with reductively glycated human albumin. The antiserum was also capable of identifying and quantitating glucitollysine residues of human serum albumin after reduction of’ the protein with sodium borohydride (NaBH,).

Antibodies to nonenzymatically glucosylated albumin in the human serum.

The existence of antibodies to nonenzymatically glucosylated albumin was investigated in nondiabetic and diabetic subjects. The sera from both the nondiabetic and the diabetic subjects were shown to contain the proteins which bound to reductively glucosylated albumin. An enzyme-linked immunosorbent assay demonstrated that the antibodies specific for reductively glucosylated albumin existed in the sera containing the binding proteins. For binding the antibodies glucitollysine as the glucose adduct in reductively glucosylated albumin was an effective competitor. The hexose alcohol epimers glucitol and mannitol were also effective competitors compatible with glucitollysine. Our results suggest that the antibodies to reductively glucosylated albumin are widely present not only in the diabetic subjects but also in the nondiabetic subjects and cross-react with the hexose alcohol.

A radioimmunoassay for an advanced glycosylation endproduct

A competitive radioimmunoassay for an advanced glycosylation endproduct, 2-(2-furoyl)-4(5)-(2-furanyl)-1H-imidazole (FFI) was developed. The immunogen was prepared by coupling of 4-furanyl-2-furoyl-1H-imidazole-1-hexanoic acid to keyhole limpet hemocyanin. The antiserum obtained by immunizing guinea pigs with the immunogen exhibited high affinity binding to FFI, but no cross-reactivity was observed for structurally related compounds containing an imidazole ring or furan ring(s). By using the radioimmunoassay, the levels of FFI in bovine serum albumin incubated with glucose for varying lengths of time were measured. A time-dependent increase was obtained in the amount of acid-liberated FFI and fluorescence. The radioimmunoassay described here had satisfactory reproducibility as judged by the intra-assay precision of 3.4-6.4% and the interassay precision of 7.3-8.9%. The method allows to quantitate FFI on the modified proteins that have been implicated in the complications of diabetes and in normal aging as well.