Advanced glycation end-products and methionine sulphoxide in skin collagen of patients with type 1 diabetes

We determined whether oxidative damage in collagen is increased in (1) patients with diabetes; (2) patients with diabetic complications; and (3) subjects from the Diabetes Control and Complications Trial (DCCT)/Epidemiology of Diabetes Interventions and Complications (EDIC) study, with comparison of subjects from the former standard vs intensive treatment groups 4 years after DCCT completion.

Nuclear magnetic resonance-determined lipoprotein subclass profile in the DCCT/EDIC cohort:associations with carotid intima-media thickness

To relate nuclear magnetic resonance lipoprotein subclass profiles (NMR-LSP) and other lipoprotein-related factors with carotid intima-media thickness (IMT) in Type 1 diabetes.

Apolipoprotein C-III protein concentrations and gene polymorphisms in Type 1 diabetes:associations with microvascular disease complications in the DCCT/EDIC cohort

We investigated the associations of apolipoprotein C-III (apoCIII) protein and apoCIII gene variation with microvascular disease complications in Type 1 diabetes.

Serum lipoproteins in the diabetes control and complications trial/epidemiology of diabetes intervention and complications cohort:associations with gender and glycemia

To relate the nuclear magnetic resonance (NMR)-determined lipoprotein profile, conventional lipid and apolipoprotein measures, and in vitro oxidizibility of LDL with gender and glycemia in type 1 diabetes.

Effect of collagen turnover on the accumulation of advanced glycation end products

Collagen molecules in articular cartilage have an exceptionally long lifetime, which makes them susceptible to the accumulation of advanced glycation end products (AGEs). In fact, in comparison to other collagen-rich tissues, articular cartilage contains relatively high amounts of the AGE pentosidine. To test the hypothesis that this higher AGE accumulation is primarily the result of the slow turnover of cartilage collagen, AGE levels in cartilage and skin collagen were compared with the degree of racemization of aspartic acid (% d-Asp, a measure of the residence time of a protein). AGE (N(epsilon)-(carboxymethyl)lysine, N(epsilon)-(carboxyethyl)lysine, and pentosidine) and % d-Asp concentrations increased linearly with age in both cartilage and skin collagen (p <0.0001). The rate of increase in AGEs was greater in cartilage collagen than in skin collagen (p <0.0001). % d-Asp was also higher in cartilage collagen than in skin collagen (p <0.0001), indicating that cartilage collagen has a longer residence time in the tissue, and thus a slower turnover, than skin collagen. In both types of collagen, AGE concentrations increased linearly with % d-Asp (p <0.0005). Interestingly, the slopes of the curves of AGEs versus % d-Asp, i.e. the rates of accumulation of AGEs corrected for turnover, were identical for cartilage and skin collagen. The present study thus provides the first experimental evidence that protein turnover is a major determinant in AGE accumulation in different collagen types. From the age-related increases in % d-Asp the half-life of cartilage collagen was calculated to be 117 years and that of skin collagen 15 years, thereby providing the first reasonable estimates of the half-lives of these collagens.

Age-dependent increase in ortho-tyrosine and methionine sulfoxide in human skin collagen is not accelerated in diabetes. Evidence against a generalized increase in oxidative stress in diabetes

The glycoxidation products Nepsilon-(carboxymethyl)lysine and pentosidine increase in skin collagen with age and at an accelerated rate in diabetes. Their age-adjusted concentrations in skin collagen are correlated with the severity of diabetic complications. To determine the relative roles of increased glycation and/or oxidation in the accelerated formation of glycoxidation products in diabetes, we measured levels of amino acid oxidation products, distinct from glycoxidative modifications of amino acids, as independent indicators of oxidative stress and damage to collagen in aging and diabetes. We show that ortho-tyrosine and methionine sulfoxide are formed in concert with Nepsilon-(carboxymethyl)lysine and pentosidine during glycoxidation of collagen in vitro, and that they also increase with age in human skin collagen. The age-adjusted levels of these oxidized amino acids in collagen was the same in diabetic and nondiabetic subjects, arguing that diabetes per se does not cause an increase in oxidative stress or damage to extracellular matrix proteins. These results provide evidence for an age-dependent increase in oxidative damage to collagen and support previous conclusions that the increase in glycoxidation products in skin collagen in diabetes can be explained by the increase in glycemia alone, without invoking a generalized, diabetes-dependent increase in oxidative stress.

3-Deoxyfructose concentrations are increased in human plasma and urine in diabetes

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.

Platelet plasminogen activator inhibitor 1 in patients with type II diabetes

To compare platelet plasminogen activator inhibitor 1 (PAI-1) concentration in type II diabetic patients and healthy control subjects.

Maillard reaction products and their relation to complications in insulin-dependent diabetes mellitus

Glycation, oxidation, and browning of proteins have all been implicated in the development of diabetic complications. We measured the initial Amadori adduct, fructoselysine (FL); two Maillard products, N epsilon-(carboxymethyl) lysine (CML) and pentosidine; and fluorescence (excitation = 328 nm, emission = 378 nm) in skin collagen from 39 type 1 diabetic patients (aged 41.5 +/- 15.3 [17-73] yr; duration of diabetes 17.9 +/- 11.5 [0-46] yr, [mean +/- SD, range]). The measurements were related to the presence of background (n = 9) or proliferative (n = 16) retinopathy; early nephropathy (24-h albumin excretion rate [AER24] > or = 20 micrograms/min; n = 9); and limited joint mobility (LJM; n = 20). FL, CML, pentosidine, and fluorescence increased progressively across diabetic retinopathy (P <0.05, P <0.001, P <0.05, P <0.01, respectively). FL, CML, pentosidine, and fluorescence were also elevated in patients with early nephropathy (P <0.05, P <0.001, P <0.01, P <0.01, respectively). There was no association with LJM. Controlling for age, sex, and duration of diabetes using logistic regression, FL and CML were independently associated with retinopathy (FL odds ratio (OR) = 1.06, 95% confidence interval (CI) = 1.01-1.12, P <0.05; CML OR = 6.77, 95% CI = 1.33-34.56, P <0.05) and with early nephropathy (FL OR = 1.05, 95% CI = 1.01-1.10, P <0.05; CML OR = 13.44, 95% CI = 2.00-93.30, P <0.01). The associations between fluorescence and retinopathy and between pentosidine and nephropathy approached significance (P = 0.05). These data show that FL and Maillard products in skin correlate with functional abnormalities in other tissues and suggest that protein glycation and oxidation (glycoxidation) may be implicated in the development of diabetic retinopathy and early nephropathy.

Accumulation of Maillard reaction products in skin collagen in diabetes and aging

To investigate the contribution of glycation and oxidation reactions to the modification of insoluble collagen in aging and diabetes, Maillard reaction products were measured in skin collagen from 39 type 1 diabetic patients and 52 nondiabetic control subjects. Compounds studied included fructoselysine (FL), the initial glycation product, and the glycoxidation products, N epsilon-(carboxymethyl) lysine (CML) and pentosidine, formed during later Maillard reactions. Collagen-linked fluorescence was also studied. In nondiabetic subjects, glycation of collagen (FL content) increased only 33% between 20 and 85 yr of age. In contrast, CML, pentosidine and fluorescence increased five-fold, correlating strongly with age. In diabetic patients, collagen FL was increased threefold compared with nondiabetic subjects, correlating strongly with glycated hemoglobin but not with age. Collagen CML, pentosidine and fluorescence were increased up to twofold in diabetic compared with control patients: this could be explained by the increase in glycation alone, without invoking increased oxidative stress. There were strong correlations among CML, pentosidine and fluorescence in both groups, providing evidence for age-dependent chemical modification of collagen via the Maillard reaction, and acceleration of this process in diabetes. These results support the description of diabetes as a disease characterized by accelerated chemical aging of long-lived tissue proteins.

Effect of diabetes and aging on carboxymethyllysine levels in human urine

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)

Metabolism of very low- and low-density lipoproteins isolated from normolipidaemic type 2 (non-insulin-dependent) diabetic patients by human monocyte-derived macrophages

The very low- and low-density lipoprotein fractions were isolated from 16 normolipidaemic Type 2 (non-insulin-dependent) diabetic patients in good to fair glycaemic control and from corresponding age-, sex-, and race-matched, non-diabetic control subjects. Rates of cholesteryl ester synthesis averaged 268 +/- 31 vs 289 +/- 40 pmol 14C-cholesteryl oleate.mg cell protein-1.20 h-1 for very low- and 506 +/- 34 vs 556 +/- 51 pmol 14C-cholesteryl oleate.mg cell protein-1.20 h-1 for low-density lipoproteins isolated from the Type 2 diabetic patients and control subjects, respectively, when they were incubated with human macrophages. A group of approximately one-third of the patients was selected for separate analyses because very low-density lipoproteins isolated from these patients did stimulate more cholesteryl ester synthesis when incubated with macrophages. There were no significant differences in the lipid composition of the lipoproteins isolated from the three groups of subjects. The relative proportion of apoprotein C to apoprotein E was significantly decreased (p less than 0.002) in the very low-density lipoproteins from diabetic patients and was further decreased in samples from these selected diabetic patients. The apoprotein C-I content of very low-density lipoproteins isolated from diabetic patients was increased compared to control subjects and was further increased in samples from the selected diabetic patients (p less than 0.02). There were no significant differences in the proportions of apoproteins C-III-0, C-III-1, or C-III-2 among the three groups. These studies suggest that in normolipidaemic Type 2 diabetic patients, the apoprotein composition of VLDL is abnormal and this may alter VLDL macrophage interactions and thus contribute to the increased prevalence of atherosclerosis in diabetic patients.

Hemostatic alterations with exercise conditioning in NIDDM

Various parameters of coagulation and fibrinolysis were measured in 13 men (aged 54 +/- 3 yr) with non-insulin-dependent diabetes mellitus (NIDDM) before and after 12-14 wk of exercise training. Subjects exercised for 30 min 3 times/wk at 70% of maximum O2 consumption (VO2max). Training increased VO2max by 12.5% but did not alter body weight, relative body fat, blood pressure, cholesterol, triglycerides, or high-density lipoprotein cholesterol. Slight downward trends were apparent for fasting glucose and insulin, but glycosylated hemoglobin was unchanged. There were no changes in coagulation parameters of plasminogen, hematocrit, or alpha 2-antiplasmin. Plasma fibrinogen (303 +/- 24.2 vs. 256 +/- 12.3 mg/dl) and fibronectin (380 +/- 41.9 vs. 301 +/- 22.2 micrograms/ml) were significantly reduced (P less than 0.02) by exercise conditioning. Three assays of fibrinolytic activity (tissue plasminogen activator, euglobulin lysis time, and an isotopic measure of fibrinolysis) confirmed that neither basal fibrinolysis nor the fibrinolytic responses to venous occlusion and maximal exercise were significantly altered. Exercise conditioning may have antithrombotic effects in NIDDM by reducing plasma fibrinogen and fibronectin. Although the significance of the fall in fibronectin awaits further studies, the reduction in plasma fibrinogen gives a rationale for the use of exercise training in men with NIDDM.

Stimulation of cholesteryl ester synthesis in human monocyte-derived macrophages by low-density lipoproteins from type 1 (insulin-dependent) diabetic patients:the influence of non-enzymatic glycosylation of low-density lipoproteins

Diabetes mellitus is an independent risk factor in the development of atherosclerosis. In this study we aimed to demonstrate whether there is an abnormal interaction between low-density lipoproteins from diabetic patients and human macrophages. We measured cholesteryl ester synthesis and cholesteryl ester accumulation in human monocyte-derived macrophages (obtained from non-diabetic donors) incubated with low density lipoproteins from Type 1 (insulin-dependent) diabetic patients in good or fair glycaemic control. Low density lipoproteins from the diabetic patients stimulated more cholesteryl ester synthesis than low density lipoproteins from non-diabetic control subjects (7.19 +/- 1.19 vs 6.11 +/- 0.94 nmol/mg cell protein/20 h, mean +/- SEM, p less than 0.05). The stimulation of cholesteryl ester synthesis by low density lipoproteins isolated from diabetic patients was paralleled by a significant increase in intracellular cholesteryl ester accumulation (p less than 0.02). There were no significant differences in the lipid composition of low density lipoproteins between the diabetic and control groups. Non-enzymatic glycosylation of low density lipoproteins was higher in the diabetic group (p less than 0.01) and correlated significantly with cholesteryl ester synthesis (r = 0.58). Similarly, low-density lipoproteins obtained from non-diabetic subjects and glycosylated in vitro stimulated more cholesteryl ester synthesis in macrophages than control low density lipoproteins. The increase in cholesteryl ester synthesis and accumulation by cells exposed to low density lipoproteins from diabetic patients seems to be mediated by an increased uptake of these lipoproteins by macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)

Glycosylation of low density lipoprotein in patients with type 1 (insulin-dependent) diabetes:correlations with other parameters of glycaemic control

Glycosylation of low density lipoproteins obtained from 16 patients with Type 1 (insulin-dependent) diabetes and from 16 age-, sex-, and race-matched controls, was determined. The diabetic patients were normolipaemic and were in good or fair glycaemic control. Eleven patients performed home blood glucose monitoring. Glycosylation of low density lipoproteins in the diabetic patients was significantly higher (p less than 0.001) than in the control subjects, and was significantly correlated with haemoglobin A1c, (p less than 0.01), glycosylation of plasma proteins, (p less than 0.001), and mean home blood glucose, (p less than 0.01). This study confirms that, in diabetic patients, increased glycosylation of low density lipoprotein occurs to an extent which correlates closely with other commonly used indices of glycaemic control.