1-Amino-1-deoxy-d-fructose ("fructosamine") and its derivatives

Fructosamine has long been considered as a key intermediate of the Maillard reaction, which to a large extent is responsible for specific aroma, taste, and color formation in thermally processed or dehydrated foods. Since the 1980s, however, as a product of the Amadori rearrangement reaction between glucose and biologically significant amines such as proteins, fructosamine has experienced a boom in biomedical research, mainly due to its relevance to pathologies in diabetes and aging. In this chapter, we assess the scope of the knowledge on and applications of fructosamine-related molecules in chemistry, food, and health sciences, as reflected mostly in publications within the past decade. Methods of fructosamine synthesis and analysis, its chemical, and biological properties, and degradation reactions, together with fructosamine-modifying and -recognizing proteins are surveyed.

Resorcylidene aminoguanidine induces antithrombotic action that is not dependent on its antiglycation activity

There is good evidence supporting the notion that aminoguanidine(AG)-derived compounds prevent glycation/glycooxidation-dependent processes and therefore inhibit late diabetic complications. The aim of the present work was to analyse the antithrombotic action and antiglycation activity of beta-resorcylidene aminoguanidine (RAG) in comparison with another commonly used aminoguanidine (AG)-derived compound, pyridoxal aminoguanidine (PAG). In vitro RAG and PAG prevented exhaustive glycation and glycooxidation of BSA to a similar extent. However, merely RAG showed almost complete binding to sepharose-immobilized heparin, while PAG and other AG derivatives had much poorer affinities. In the model of in vivo thrombosis in Wistar rats with extracorporeal circulation RAG (i.v. 30 mg/kg), but not PAG, produced sustained (2 h) antithrombotic effect, which was abrogated by indomethacin (5 mg/kg) and rofecoxib (1 mg/kg). The 60-day treatment of streptozotocin-diabetic animals with RAG (p.o. 4 mg/kg) significantly decreased plasma concentration of a thromboxane B(2) and reduced whole blood platelet aggregability triggered by ADP or collagen. In conclusion, although RAG and PAG displayed similar antiglycation and antioxidation activities in vitro, only RAG showed antithrombotic activity in vivo that involved activation of COX-2/PGI(2) pathway. Our results indicate that designing novel RAG derivatives with optimal antithrombotic and antiglycation activities may prove useful to treat diabetic complications.

High glucose contributes to aspirin insensitivity in streptozotocin-diabetic rats: a multiparametric aggregation study

The effect of chronic hyperglycaemia on blood platelet response to acetylsalicylic acid was studied in rats with experimental diabetes. Platelet aggregation was determined in non-diabetic and streptozotocin-diabetic rats treated orally with 4 or 40 mg aspirin (ASA)/kg per day (for 8 weeks from the eighth day of diabetes) using whole blood impedance aggregometry with arachidonic acid or ADP as platelet agonists. The dose-dependent effect of ASA 'therapy' on ADP-agonized platelets was significant only in non-diabetic animals, while in diabetic rats both doses were ineffective in reducing ADP-stimulated platelet aggregation. ASA-mediated increased acetylation of platelet proteins favoured reduced platelet aggregation and slower platelet disaggregation (Pr < 0.025 or less). Interestingly, however, the occupation of platelet protein-free amino groups was significantly higher in control rats compared with diabetic rats (P < 0.001), pointing out that proteins of platelets in non-diabetic animals were more vulnerable for the ASA-induced acetylation. We conclude that chronic hyperglycaemia interferes with preventive effects of ASA on platelet reactivity. Our data validate the suggestion that the relationship between aspirin ineffectiveness and poor metabolic control, first revealed in humans, concerns also other animals' platelets and holds regardless of the model or type of diabetes.

Increased protein glycation in diabetes mellitus is associated with decreased aspirin-mediated protein acetylation and reduced sensitivity of blood platelets to aspirin

Reduced effectiveness of the most common antiplatelet drug, acetylsalicylic acid (ASA, aspirin), in diabetes mellitus has been associated with a lowered platelet sensitivity to ASA and related to glycemic control in diabetic patients. Our objectives were (a) to monitor the chemical background of how chronic hyperglycemia affects platelet response to ASA in diabetes and (b) to study a chemical competition between the amount of bound acetyl residues and the extent of protein glycation in blood platelets. Using whole-blood impedance aggregometry and platelet function analyzer (PFA-100) we observed a reduced platelet response to ASA in diabetic patients (14% vs. 79% for PFA-100 collagen-epinephrine occlusion time) and an association between the index of glycemic control and platelet refractoriness to ASA (r(S) = -0.378). Impaired platelet response to ASA was related to enhanced platelet protein glycation (3.6+/-0.4 in diabetes vs. 2.3+/-0.4 micromol fructosamine/microg protein in control) and reduced incorporation of acetyl residue into proteins of platelets from diabetic patients (47.4+/-2.0 in control vs. 33.1+/-0.7 micromol acetyl/microg protein in diabetic subjects). Incubation of blood platelets with increasing concentrations of glucose and ASA under in vitro conditions led to excessive modification in protein amino groups: glucose and ASA competed with each other in the course of nonenzymatic modifications, glycosylation, or acetylation, and their contributions to the occupancy of protein amino groups (R2 = 0.22 for glucose, R2 = 0.43 for ASA) were dependent upon the concentrations of glucose and ASA. Overall the effects of high glucose and high ASA on the overall occupancy of protein free amino groups are not additive. While at higher concentrations ASA overcomes the effects of hyperglycemia and retards glycation, high glucose makes acetylation less efficient, and therefore the resultant chemical modification becomes greatly reduced. In conclusion, diminished susceptibility of various platelet proteins and receptors on blood platelet membranes to acetylation and high ambient glucose might underlie the apparently differentiated sensitivity of blood platelets to ASA and determine platelet "insensitivity to aspirin" in diabetic patients.

Fructosamine assay using albumin extracted from serum

Albumin extracted from serum by a simple technique using trichloroacetic acid and ethanol has been applied to a fructosamine assay using nitroblue tetrazolium. A fructosamine assay using extracted albumin sample was carried out without interference from low molecular weight substances with reducing activities and other proteins with varying concentrations, half-lives and reducing activities. 1-Deoxy-1-p-toluidino-D-fructose (DTF) was selected as a calibrator for the assay because it is a stable Amadori reaction product with a constant glycation rate. Albumin fructosamine value was calculated using the calibration curve of DTF. The corrected albumin fructosamine value was expressed as the amount of albumin fructosamine per gram of extracted albumin taking into consideration the variation in albumin concentrations in sera from patients. The corrected albumin fructosamine values correlated more closely with the fasting blood glucose levels (r=0.735) than the serum fructosamine values corrected for albumin concentrations (r=0.514) (p<0.05).