fructosyl-lysine and Diabetes-Mellitus--Type-1

Part of the fructosamines that are bound to intracellular proteins are repaired by fructosamine 3-kinase (FN3K). Because subject-to-subject variations in erythrocyte FN3K activity could affect the level of glycated haemoglobin independently of differences in blood glucose level, we explored if such variability existed, if it was genetically determined by the FN3K locus on 17q25 and if the FN3K activity correlated inversely with the level of glycated haemoglobin.. The mean erythrocyte FN3K activity did not differ between normoglycaemic subjects (n = 26) and type 1 diabetic patients (n = 31), but there was a wide interindividual variability in both groups (from about 1 to 4 mU/g haemoglobin). This variability was stable with time and associated (P < 0.0001) with two single nucleotide polymorphisms in the promoter region and exon 6 of the FN3K gene. There was no significant correlation between FN3K activity and the levels of HbA1c, total glycated haemoglobin (GHb) and haemoglobin fructoselysine residues, either in the normoglycaemic or diabetic group. However, detailed analysis of the glycation level at various sites in haemoglobin indicated that the glycation level of Lys-B-144 was about twice as high in normoglycaemic subjects with the lowest FN3K activities as compared to those with the highest FN3K activities.. Interindividual variability of FN3K activity is substantial and impacts on the glycation level at specific sites of haemoglobin, but does not detectably affect the level of HbA1c or GHb. As FN3K opposes one of the chemical effects of hyperglycaemia, it would be of interest to test whether hypoactivity of this enzyme favours the development of diabetic complications.

Topics: Adult; Base Sequence; Diabetes Mellitus, Type 1; DNA Primers; Erythrocytes; Female; Genetic Variation; Genotype; Glycated Hemoglobin; Glycosylation; Humans; Lysine; Male; Middle Aged; Phosphotransferases (Alcohol Group Acceptor); Polymorphism, Genetic; Reference Values

A differing individual expression of fructosyllysine-specific receptors has been found on the monocytes of 90 insulin-dependent diabetic patients and 101 healthy control subjects. The degree of receptor expression is neither age- nor sex-dependent; however, in the diabetic group it correlates significantly with the severity and age of onset of diabetic microangiopathy. To interpret the results of the human study, spontaneously diabetic and non-diabetic BB/OK rats were used to estimate tissue content of glucose-modified proteins and capillary basement membrane thickness in relation to the receptor expression on macrophages. In non-diabetic and diabetic rats no correlation was found between receptor expression and tissue content (i.e. artery, nerve) of fructosyllsine and fluorescent advanced glycation end products. However, animals which express the fructosyllysine receptor showed a greater increase in muscle capillary basement membrane thickness. There are indications that fructosyllysine receptor expression is positively associated with indices of diabetic complications such as microangiopathy and/or capillary basement membrane thickening.

Topics: Adult; Age of Onset; Animals; Blood Glucose; Body Weight; Diabetes Mellitus, Type 1; Diabetic Nephropathies; Diabetic Neuropathies; Diabetic Retinopathy; Female; Fructosamine; Glycated Hemoglobin; Humans; Lysine; Macrophages; Male; Membrane Proteins; Middle Aged; Monocytes; Nuclear Proteins; Probability; Rats; Rats, Inbred BB; Reference Values; RNA-Binding Proteins

3-Deoxyglucosone (3-DG) is a reactive dicarbonyl sugar thought to be a key intermediate in the nonenzymatic polymerization and browning of proteins by glucose. 3-DG may be formed in vivo from fructose, fructose 3-phosphate, or Amadori adducts to protein, such as N epsilon-fructoselysine (FL), all of which are known to be elevated in body fluids or tissues in diabetes. Modification of proteins by 3-DG formed in vivo is thought to be limited by enzymatic reduction of 3-DG to less reactive species, such as 3-deoxyfructose (3-DF). In this study, we have measured 3-DF, as a metabolic fingerprint of 3-DG, in plasma and urine from a group of diabetic patients and control subjects. Plasma and urinary 3-DF concentrations were significantly increased in the diabetic compared with the control population (0.853 +/- 0.189 vs. 0.494 +/- 0.072 microM, P < 0.001, and 69.9 +/- 44.2 vs. 38.7 +/- 16.1 nmol/mg creatinine, P < 0.001, respectively). Plasma and urinary 3-DF concentrations correlated strongly with one another, with HbA1c (P < 0.005 in all cases), and with urinary FL (P < 0.02 and P = 0.005, respectively). The overall increase in 3-DF concentrations in plasma and urine in diabetes and their correlation with other indexes of glycemic control suggest that increased amounts of 3-DG are formed in the body during hyperglycemia in diabetes and then metabolized to 3-DF. These observations are consistent with a role for increased formation of the dicarbonyl sugar 3-DG in the accelerated browning of tissue proteins in diabetes.

Topics: Adolescent; Adult; Aged; Biomarkers; Blood Glucose; Diabetes Mellitus; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Glycated Hemoglobin; Humans; Ketoses; Lysine; Middle Aged; Reference Values; Regression Analysis

Low density lipoprotein (LDL) from Type 1 and Type 2 diabetic patients, unlike LDL from healthy subjects, caused a 1.5- to 2.5-fold increase in the cholesterol content of cells cultured from unaffected human aortic intima, i.e. possessed atherogenic potential. LDL were further divided into two subfractions by affinity chromatography on Ricinus communis agglutinin-agarose. The amount of bound LDL was significantly higher in diabetic patients as compared with healthy subjects. Bound LDLs differed from unbound ones by significantly lowered sialic acid content, i.e. were desialylated lipoproteins. Desialylated, but not sialylated LDL subfraction induced massive cholesterol accumulation in cultured cells. Desialylated LDL subfraction in diabetic patients was also characterized by a higher degree of nonenzymatic glycation as compared to LDL subfraction with normal sialic acid level. Desialylated LDL had significantly decreased levels of free and esterified cholesterol, triglycerides and phosphatidylcholine and elevated amounts of lysophosphatidylcholine. These disturbances in lipid constituent of LDL were weak in healthy subjects, but conspicuous in diabetic patients. The results of this study have shown that there is in vivo modified LDL subfraction in the blood of diabetic patients which is characterized by crucial changes in protein and lipid moiety and are able to induce massive cholesterol accumulation in cultured cells.

Topics: Cells, Cultured; Cholesterol; Diabetes Mellitus, Type 1; Diabetes Mellitus, Type 2; Humans; Lipids; Lipoproteins, LDL; Lysine; N-Acetylneuraminic Acid; Phospholipids; Sialic Acids

Carboxymethyllysine (CML) has been identified as a modified amino acid that accumulates with age in human lens proteins and collagen. CML may be formed by oxidation of fructoselysine (FL), the Amadori adduct formed on nonenzymatic glycosylation of lysine residues in protein, or by reaction of ascorbate with protein under autoxidizing conditions. We proposed that measurements of tissue and urinary CML may be useful as indices of oxidative stress or damage to proteins in vivo. To determine the extent to which oxidation of nonenzymatically glycosylated proteins contributes to urinary CML, we measured the urinary concentrations of FL and CML in diabetic (n = 26) and control (n = 28) patients. The urinary concentration of FL correlated strongly with HbA1 measurements and was significantly higher in diabetic compared with control samples (9.2 +/- 6.5 and 4.0 +/- 2.8 micrograms/mg creatinine, respectively; P less than 0.0001). There was also a strong correlation between the concentrations of CML and FL in both diabetic and control urine (r = 0.67, P less than 0.0001) but only a weakly significant increase in the CML concentration in diabetic compared with control urine (1.2 +/- 0.5 and 1.0 +/- 0.3 micrograms/mg creatinine, respectively; P = 0.05). The molar ratio of CML to FL was significantly lower in diabetic compared with control patients (0.25 +/- 0.12 and 0.43 +/- 0.16, respectively; P less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adolescent; Adult; Aged; Aging; Diabetes Mellitus, Type 1; Humans; Lysine; Middle Aged; Oxidation-Reduction

Glycation, oxidation, and nonenzymatic browning of protein have all been implicated in the development of diabetic complications. The initial product of glycation of protein, fructoselysine (FL), undergoes further reactions, yielding a complex mixture of browning products, including the fluorescent lysine-arginine cross-link, pentosidine. Alternatively, FL may be cleaved oxidatively to form N(epsilon)-(carboxymethyl)lysine (CML), while glycated hydroxylysine, an amino-acid unique to collagen, may yield N(epsilon)-(carboxymethyl)hydroxylysine (CMhL). We have measured FL, pentosidine, fluorescence (excitation = 328 nm, emission = 378 nm), CML, and CMhL in insoluble skin collagen from 14 insulin-dependent diabetic patients before and after a 4-mo period of intensive therapy to improve glycemic control. Mean home blood glucose fell from 8.7 +/- 2.5 (mean +/- 1 SD) to 6.8 +/- 1.4 mM (P less than 0.005), and mean glycated hemoglobin (HbA1) from 11.6 +/- 2.3% to 8.3 +/- 1.1% (P less than 0.001). These changes were accompanied by a significant decrease in glycation of skin collagen, from 13.2 +/- 4.3 to 10.6 +/- 2.3 mmol FL/mol lysine (P less than 0.002). However, levels of browning and oxidation products (pentosidine, CML, and CMhL) and fluorescence were unchanged. These results show that the glycation of long-lived proteins can be decreased by improved glycemic control, but suggest that once cumulative damage to collagen by browning and oxidation reactions has occurred, it may not be readily reversed. Thus, in diabetic patients, institution and maintenance of good glycemic control at any time could potentially limit the extent of subsequent long-term damage to proteins by glycation and oxidation reactions.

Topics: Arginine; Blood Glucose; Collagen; Diabetes Mellitus, Type 1; Humans; Hyperglycemia; Lysine; Maillard Reaction; Skin