Tadao Taguchi

Inhibition of advanced protein glycation by a Schiff base between aminoguanidine and pyridoxal.

Aminoguanidine is a well-known inhibitor of the formation of advanced glycation end products and is considered to be promising for the treatment of diabetic complications. We recently reported, however, that administration of aminoguanidine caused the formation of a Schiff base adduct between aminoguanidine and pyridoxal phosphate in the liver and kidney of mice and a concomitant decrease in the amount of liver pyridoxal phosphate. Our study led us to hypothesize that the Schiff base adduct and/or another Schiff base adduct formed from aminoguanidine and pyridoxal might be a better compound than aminoguanidine. In the present study, we examined the in vitro inhibitory potency of the latter adduct against advanced glycation end product formation and its effect on the tissue contents of pyridoxal and its phosphate. Aminoguanidine-pyridoxal phosphate adduct was not employed in this study because of its poor solubility in water. Aminoguanidine-pyridoxal adduct was hydrolyzed by only about 15% during 10 days at pH 7.4 and 37 degrees C. The adduct at 1 mM did not inhibit Amadori product formation induced by incubation of albumin with 100 mM mannose for 10 days. The adduct, when tested at 1 and 2 mM, dose-dependently inhibited advanced glycation end product formation induced by incubation of albumin with mannose; and the inhibitory potency of the adduct was similar to or higher than that of aminoguanidine. The presence of an appreciable amount of aminoguanidine-pyridoxal adduct in the kidney of mice given the adduct suggested that at least part of the adduct administered was absorbed from the gastrointestinal duct. The amounts of pyridoxal and its phosphate in tissues were not at all decreased by administration of the aminoguanidine-pyridoxal Schiff base. We conclude that the Schiff base may be a more promising inhibitor of advanced protein glycation than aminoguanidine.

Determination of d-Mannose in Plasma by HPLC

d-Mannose is an essential monosaccharide in the structure of glycoproteins, cell-surface glycoconjugates, and glycosylated phosphatidylinositide anchors. Several stud-ies have focused on plasma or serum mannose concentrations in patients with invasive candidiasis (1)(2), diabetes mellitus (3)(4)(5)(6)(7)(8), or congenital disorders of glycosylation type 1 (9). There are various methods to determine mannose concentrations in human plasma or serum: enzymatic methods (4)(5)(7)(10), gas-liquid chromatography (2)(11), high-resolution liquid chromatography (12), gas-liquid chromatography–mass spectrometry (6), and capillary electrophoresis (13). None of these methods is fully suitable for routine use for various reasons, e.g., the incomplete or time-consuming elimination of the ∼100-fold excess of blood glucose, the use of instruments with limited availability, and the need for a large sample volume. We investigated whether a HPLC assay using an anion-exchange column would be appropriate for plasma mannose determinations. With the procedure described below, mannose could be rapidly and accurately determined in small amounts of plasma. Boric acid, guanidine hydrochloride, sodium metaperiodate, and acetonitrile were purchased from Wako Pure Chemicals Co. Ltd. d-Mannose was obtained from Sigma Chemical Co. We obtained blood samples from healthy individuals and from nondiabetic and diabetic patients after receiving their informed consent for this study. After collection of venous blood in tubes containing disodium EDTA (an anticoagulant) and NaF (a glycolysis inhibitor), plasma was separated by centrifugation. The plasma was mixed with an equal volume of 0.6 mol/L perchloric acid, a protein-precipitating reagent. The mixture was centrifuged at 8000 g for 10 min at 4 °C, and the protein-free supernatant was used for the analysis of mannose. We used a HPLC system (Gulliver system with a JASCO PU-980 pump) equipped …

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.

Plasma mannose level, a putative indicator of glycogenolysis, and glucose tolerance in Japanese individuals

Mannose is a monosaccharide constituent of glycoproteins and glycolipids. Experiments in rats have shown previously that the plasma mannose level decreases after glucose load, but does not decrease in diabetic rats, and that hepatic glycogenolysis is a source of this plasma mannose; however, these results are not fully elucidated in humans. Plasma mannose levels before/after glucose loading in humans with various degrees of glucose intolerance were examined to analyze their association with clinical factors.

Glyceraldehyde Is Present in Rat Lens and Its Level Is Increased in Diabetes Mellitus

Purpose: OP-lysine, a glycation product of lysine residues of proteins, has been reported to be formed with glyceraldehyde and glycolaldehyde as precursors in the lens, and has been suggested to play a role in senile cataracts. However, there has been no reliable information regarding the content of glyceraldehyde in tissues. This study determined the glyceraldehyde levels in the lenses of normal and diabetic rats. Methods: Glyceraldehyde was derivatized to a fluorescent compound, and the compound was then quantified by high-performance liquid chromatography. Results: The lens glyceraldehyde levels in normal and diabetic rats were 0.75 ± 0.06 and 1.26 ± 0.21 nmol/g wet weight (means ± standard deviations of 6 animals, p < 0.01), respectively. Isolated rat lenses accumulated a higher level of glyceraldehyde when cultured for 6 days in 25.5 mM glucose than when cultured in 5.5 mM glucose. Conclusions: Glyceraldehyde was found to be present in the lens and was increased in diabetes mellitus. OP-lysine is thus likely to be a potential risk factor for senile and diabetic cataracts.

Determination of pseudo-α- and pseudo-β-dl-glucose by gas-liquid chromatography, high-performance liquid chromatography, and enzymatic colorimetry with glucose 2-oxidase

Abstract Three methods have been developed for measuring pseudo-α- and pseudo-β- dl -glucose (pseudo-β- d -glucose), synthetic compounds in which the ring oxygens of α- and β- dl -glucose (β- d -glucose) have been replaced by a methylene group. Moderate sensitivity in the determination of these pseudo-glucoses dissolved in human serum was obtained by GLC (0.1 nmol) and HPLC (0.5 nmol). The colorimetric determination with glucose 2-oxidase, peroxidase, and 2,2′-azino-di-(3-ethylbenzothiazoline-6-sulfonic acid) was satisfactory for the assay of pseudo-α- and pseudo-β- dl -glucose (respective sensitivities: 25 and 5 nmol). The addition of hexokinase to the colorimetric assay system made it possible to eliminate glucose present in the sample, such as serum, and the remaining pseudo-α- or pseudo-β- dl -glucose in the sample solution could then be measured by a colorimetric method using glucose 2-oxidase. The methods described can be used for biochemical studies involving pseudo-α- and pseudo-β- dl -glucose.