Katsuyuki Yanagisawa

Progression of nephropathy in spontaneous diabetic rats is prevented by OPB-9195, a novel inhibitor of advanced glycation.

Levels of tissue advanced glycation end products (AGEs) that result from nonenzymatic reactions of glucose and proteins are high in both diabetic and aging people. Irreversible AGE formation is based on increases in AGE-derived protein-to-protein cross-linking and is considered to be a factor contributing to the complications of diabetes. A novel inhibitor of advanced glycation, OPB-9195, belongs to a group of thiazolidine derivatives, known as hypoglycemic drugs; however, they do not lower blood glucose levels. We did studies to determine if OPB-9195 would prevent the progression of nephropathy in spontaneous diabetic rats. In vitro inhibitory effects of OPB-9195 on AGE formation and AGE-derived cross-linking were examined by enzyme-linked immunosorbent assay (ELISA) and SDS-PAGE, respectively. Otsuka-Long-Evans-Tokushima-Fatty (OLETF) rats, a model of NIDDM, were used to evaluate the therapeutic effect of OPB-9195. Light microscopic findings by periodic acid-Schiff (PAS) staining, the extent of AGE accumulation detected by immunohistochemical staining in the kidneys, the levels of serum AGEs by AGE-specific ELISA, and urinary albumin excretion were examined. OPB-9195 effectively inhibited both AGE-derived cross-linking and the formation of AGEs, in a dose-dependent manner in vitro. In addition, the administration of OPB-9195 prevented the progression of glomerular sclerosis and AGE deposition in glomeruli. Elevation of circulating AGE levels and urinary albumin excretion were dramatically prevented in rats, even at 56 weeks of age and with persistent hyperglycemia. We concluded that a novel thiazolidine derivative, OPB-9195, prevented the progression of diabetic glomerular sclerosis in OLETF rats by lowering serum levels of AGEs and attenuating AGE deposition in the glomeruli.

Detection of noncarboxymethyllysine and carboxymethyllysine advanced glycation end products (AGE) in serum of diabetic patients.

BackgroundThe advanced stage of the Maillard reaction, which leads to the formation of advanced glycation end products (AGE), plays an important role in the pathogenesis of angiopathy in diabetic patients and in the aging process. Nϵ-(carboxymethyl)lysine (CML) is thought to be an important epitope for many of currently available AGE antibodies. However, recent findings have indicated that a major source of CML may be by pathways other than glycation. A distinction between CML and non-CML AGE may increase our understanding of AGE formation in vivo. In the present study, we prepared antibodies directed against CML and non-CML AGE.Materials and MethodsAGE-rabbit serum albumin prepared by 4, 8, and 12 weeks of incubation with glucose was used to immunize rabbits, and a high-titer AGE-specific antiserum was obtained without affinity for the carrier protein. To separate CML and non-CML AGE antibodies, the anti-AGE antiserum was subjected to affinity chromatography on a column coupled with AGE-BSA and CML-BSA. Two different antibodies were obtained, one reacting specifically with CML and the other reacting with non-CML AGE. Circulating levels of CML and non-CML AGE were measured in 66 type 2 diabetic patients without uremia by means of the competitive ELISA. Size distribution and clearance by hemodialysis detected by non-CML AGE and CML were assessed in serum from diabetic patients on hemodialysis. Results: The serum non-CML AGE level in type 2 diabetic patients was significantly correlated with the mean fasting blood glucose level over the previous 2 months (r = 0.498, p < 0.0001) or the previous 1 month (r = 0.446, p = 0.0002) and with HbA1c (r = 0.375, p = 0.0019), but the CML AGE level was not correlated with these clinical parameters. The CML and non-CML AGE were detected as four peaks with apparent molecular weights of 200, 65, 1.15, and 0.85 kD. The hemodialysis treatment did not affect the high-molecular-weight protein fractions. Although the low-molecular-weight peptide fractions (absorbance at 280 nm and fluorescence) were decreased by hemodialysis, there was no difference before and after dialysis in the non-CML AGE- and CML-peptide fractions (1.15 and 0.85 kD fractions).ConclusionsWe propose that both CML and non-CML AGE are present in the blood and that non-CML AGE rather than CML AGE should be more closely evaluated when investigating the pathophysiology of AGE-related diseases.

Specific fluorescence assay for advanced glycation end products in blood and urine of diabetic patients

Late rearrangement products that accumulate by glycation of proteins, known as advanced glycation end products (AGEs), have been implicated in the pathogenesis of complications related to diabetes. Circulating AGEs, especially in the form of a small peptide (AGE-peptide) of less than 10 kd, increase in the blood of diabetic patients with end-stage renal disease (ESRD). The aim of the study was to evaluate AGE-peptide levels by measuring AGE-specific fluorescence (excitation at 370 nm and emission at 440 nm) and to examine the relationship between AGE-peptide and diabetic nephropathy. AGE-specific fluorescence in serum and urine were examined in diabetic subjects with various levels of renal complications of varying severity: normoalbuminuria (N), microalbuminuria (Mi), macroalbuminuria (Ma), chronic renal failure (C), and hemodialysis (HD). We also assessed correlations among the AGE-peptide level and age, duration of diabetes, hemoglobin A1c (HbA1c), serum creatinine, and creatinine clearance. Serum and urine AGE-peptide levels in C and HD were significantly higher than in N, Mi, and Ma. Serum AGE-peptide levels were significantly correlated with serum creatinine (r=.866, P < .0001) and creatinine clearance (r=-.720, P < .0001) but not with duration of diabetes or age. There was a significant correlation between AGE-peptide levels measured by enzyme-linked immunosorbent assay (ELISA) and levels determined from the specific fluorescence intensity (r=.688, P < .0001). These findings suggest that renal function may play a greater role in the accumulation of AGEs than persistent hyperglycemia in diabetic patients. Measurement of AGE-specific fluorescence (ie, AGE-peptide) may serve as a simple and useful test to assess circulating AGE levels and monitor AGE excretion.

Advanced glycation endproducts and diabetic nephropathy

Diabetic nephropathy is currently the single largest cause of endstage renal disease (ESRD) in the United States and many European countries. The primary cause for the development of diabetic complications (including diabetic nephropathy) is persistent exposure to hyperglycemia, although genetic and other incompletely understood factors also play an important role. Although much consideration has been given to the pathogenesis and genetics of the disease itself, the mechanisms by which persistent exposure to hyperglycemia cause biochemical and metabolic alterations have been very sketchily understood. Recently, a growing body of evidence has linked the accumulation of the late products of glucose-protein interaction to a variety of chronic complications, including diabetic nephropathy. The formation of irreversible advanced glycosylation endproducts (AGEs) resulting from the spontaneous reaction between glucose and proteins occur most noticeably on long-lived structural proteins. Recent studies demonstrate that the pathogenesis of diabetic nephropathy is caused by the hyperglycemia-accelerated formation of AGEs. Also, reactive AGE peptides in the circulation are thought to play a role as a new version of so called middle molecule toxic substances. This evidence is opening a new window for our understanding of the pathogenesis of diabetic nephropathy.

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.

Quantitative enzyme-linked immunosorbent assay (ELISA) for non-enzymatically glycated serum protein

A competitive ELISA for quantitative determination of glucitollysine, the reduced hexose alcohol form of glucose conjugated to the epsilon amino group of lysine was developed. We applied it to measure non-enzymatically glycated serum proteins. The antiserum obtained by immunizing guinea pigs with reductively glycated human albumin was capable of identifying and quantitating glucitollysine residues of serum proteins in normal and diabetic subjects after reduction of the proteins with sodium borohydride. The ELISA assay developed here had satisfactory reproducibility as judged by the intra-assay precision of 2.3-7.6% and the interassay precision of 6.7-9.8%. Results from this assay procedure correlated well with those from the radioimmunoassay and the boronate affinity chromatography procedure. The data suggested that diabetic serum proteins contained at least three times as much immunochemically detectable glucitollysine residues as normal serum proteins after reduction of the proteins with sodium borohydride. This method allows to quantitate glucitollysine residues on any of the proteins that have been implicated in the pathological sequelae of diabetes.

Switching to multiple daily injection therapy with glulisine improves glycaemic control, vascular damage and treatment satisfaction in basal insulin glargine-injected diabetic patients

Basal and bolus insulin therapy is required for strict blood control in diabetic patients, which could lead to prevention of vascular complications in diabetes. However, the optimal combination regimen is not well established.

A glycation inhibitor, aminoguanidine and pyridoxal adduct, suppresses the development of diabetic nephropathy

Abstract We examined the effect of a Schiff base adduct (PL–AG) between aminoguanidine (AG) and pyridoxal on the severity of nephropathy in streptozotocin (STZ)-induced diabetic mice using an anti-advanced glycation end product antibody. We also assessed the in vitro antioxidant activity of AG and PL–AG. Neither drug altered glycemic control. AG significantly lessened the increase in glomerular volume, fractional mesangial volume, and glomerular basement thickness, but did not alter the urinary albumin excretion (UAE). On the other hand, PL–AG significantly improved UAE. The antioxidant activity of PL–AG was superior to that of AG in all evaluation methods we employed. The findings suggest that PL–AG is superior to AG for the treatment of diabetic complications because it not only prevents vitamin B 6 deficiency, but also is better at controlling diabetic nephropathy. The preventive effect of this adduct against diabetic nephropathy would be mediated via inhibition of both oxidative stress and glycation.

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.