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Glycated and Oxidized Protein Degradation Products Are Indicators of Fasting and Postprandial Hyperglycemia in Diabetes

¹ Department of Biological Sciences, University of Essex, Colchester, Essex, U.K.
² Section of Endocrinology, Diabetes and Metabolism, Dartmouth Medical School and Dartmouth-Hitchcock Medical Center, Lebanon, New Hampshire

Address correspondence and reprint requests to Paul J. Beisswenger, MD, Professor of Medicine, Dartmouth Medical School, Dartmouth-Hitchcock Medical Center, 1 Medical Center Dr., Lebanon, NH 03756. E-mail: paul.j.beisswenger{at}dartmouth.edu

	ABSTRACT

TOP ABSTRACT INTRODUCTION RESEARCH DESIGN AND METHODS RESULTS CONCLUSIONS References

 
OBJECTIVE—To assess the relative importance of fasting and postprandial hyperglycemia to vascular dysfunction in diabetes, we have measured indicators of glycation, oxidative and nitrosative stress in subjects with type 1 diabetes, and different postprandial glucose patterns.

RESEARCH DESIGN AND METHODS—Plasma and urinary levels of specific arginine- and lysine-derived advanced glycation end products, as well as oxidative and nitrosative products, were measured by liquid chromatography with triple quadrupole mass spectrometric detection (LC-MS/MS) after 2 months of treatment with insulin lispro or human regular insulin in 21 subjects participating in a cross-over study. Hb-bound early glycation (Amadori) products were also measured after each treatment period by high-performance liquid chromatography (fructosyl-valine Hb or HbA_1c [A1C]:Diamat) and fructosyl-lysine Hb by LC-MS/MS (A1C:fructosyl-lysine).

RESULTS—In diabetic patients, the concentrations of protein glycation and oxidation-free adducts increased up to 10-fold, while urinary excretion increased up to 15-fold. Decreasing postprandial hyperglycemia with lispro gave 10–20% decreases of the major free glycation adducts, hydroimidazolones derived from methylglyoxal and 3-deoxyglucosone, and glyoxal-derived N-carboxymethyl-lysine. No differences were observed in A1C:Diamat or A1C:fructosyl-lysine with lispro or regular insulin therapy in spite of significant decreases in postprandial glycemia with lispro.

CONCLUSIONS—We conclude that the profound increases in proteolytic products of proteins modified by advanced glycation endproducts in diabetic patients are responsive to changes in mean hyperglycemia and also show responses to changes in postprandial hyperglycemia.

Abbreviations: 3-DG, 3-deoxyglucosone • 3DG-H, 3-DG–derived hydroimidazolone N-(5-hydro-5-[2,3,4-trihydroxybutyl]-4-imidazolon-2-yl)ornithine • 3-NT, 3-nitrotyrosine • AGE, advanced glycation end product • CEL, N-carboxyethyl-lysine • CML, N-carboxymethyl-lysine • FPG, fasting plasma glucose • G-H1, glyoxal-derived hydroimidazolone N-(5-hydro-4-imidazolon-2-yl)ornithine • LC-MS/MS, liquid chromatography with triple quadrupole mass spectrometric detection • MetSo, methionine sulfoxide • MG-H1, methylglyoxal-derived hydroimidazolone N-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine • MPG, mean plasma glucose • NFK, N-formylkynurenine • PPG, postprandial glucose

	INTRODUCTION

TOP ABSTRACT INTRODUCTION RESEARCH DESIGN AND METHODS RESULTS CONCLUSIONS References

 
Vascular complications of diabetes, including retinopathy, neuropathy, nephropathy, and macrovascular disease, are the major cause of morbidity and mortality in diabetic patients, with macrovascular disease being a major cause of premature death (1,2). Dysfunction of the key cells responsible for vascular function, including endothelial cells, pericytes, and vascular smooth muscle cells, can be induced by increased cellular concentrations of glucose during hyperglycemia. This can activate multiple pathways of biochemical dysfunction (3,4) leading to increased glycation of proteins (5,6). Oxidative stress can also lead to cellular protein modification and damage and can be initiated by mitochondrial dysfunction, activation of vascular NADPH oxidase, and uncoupling of endothelial nitric oxide synthase (3,7,8).

The relative importance of fasting and postprandial hyperglycemia to vascular dysfunction in diabetes, including protein glycation and oxidative stress, remains controversial. In a number of prospective clinical trials, postprandial glucose (PPG) excursions have been linked to increased risk of mortality from cardiovascular disease (9–12), and decreasing PPG by intensive therapy with therapeutic agents such as the fast-acting insulin lispro or with oral hypoglycemic agents decreased the progression of retinopathy, neuropathy, and nephropathy in diabetic subjects (13,14). It is crucial, therefore, to quantify the contributions of increased fasting plasma glucose (FPG) and PPG to biochemical dysfunction linked to the development of macrovascular and microvascular complications of diabetes (15).

High plasma glucose concentrations in the postprandial periods can further increase the levels of glycation and oxidative damage to cellular and plasma proteins in diabetes. Glycation of proteins is a complex series of reactions where early-stage reactions lead to the formation of the early glycation adduct, fructosyl-lysine and NH₂-terminal fructosyl-amino acids, and later-stage reactions form advanced glycation end products (AGEs) (5). Fructosyl-lysine and its Schiff’s base degrade slowly to form AGEs. Physiological -dicarbonyls, including glyoxal, methylglyoxal, and 3-deoxyglucosone (3-DG), are also potent glycating agents that are formed by the degradation of glycated proteins, glycolytic intermediates, and lipid peroxidation and react with proteins to form AGEs directly. Important AGEs quantitatively are hydroimidazolones derived from arginine residues modified by glyoxal, methylglyoxal, and 3DG-N-(5-hydro-4-imidazolon-2-yl)ornithine (G-H1), N-(5-hydro-5-methyl-4-imidazolon-2-yl)ornithine (MG-H1), and N-(5-hydro-5-[2,3,4-trihydroxybutyl]-4-imidazolon-2-yl)ornithine (3DG-H) and related structural isomers, respectively. Other important and widely studied lysine-derived AGEs are N-carboxymethyl-lysine (CML), N-carboxyethyl-lysine (CEL), and pentosidine (6). Major quantitative markers of oxidative damage to proteins are methionine sulfoxide (MetSO) and N-formylkynurenine (NFK), formed by the oxidation of methionine and tryptophan, respectively (16,17), and a widely studied marker of nitration damage to proteins is 3-nitrotyrosine (3-NT) (18). Detection of protein glycation, oxidation, and nitration adducts by liquid chromatography with triple quadrupole mass spectroscopy (LC-MS/MS) has been reported previously in the quantitative screening of protein glycation, oxidation, and nitration adducts, measured as adduct residues in proteins and free adducts in physiological fluids (6). In diabetes, protein glycation adducts residues have been shown to be increased in cytosolic proteins at sites of development of vascular complications including renal glomeruli, retina, and nerves (6,19). Cells maintain the quality and functional integrity of proteins by degradation and replacement of proteins damaged by oxidation and glycation (6,20). This occurs by proteolysis, liberating the oxdized, glycated, and nitrated amino acids as free adducts, which in turn are released into blood plasma and excreted in urine (6).

We have previously shown that decreasing postprandial hyperglycemia with insulin lispro therapy decreases postprandial glucose, methylglyoxal, and 3-DG levels, but not HbA_1c (A1C) (21) in subjects with type 1 diabetes, suggesting that specific AGEs related to these chemically reactive precursors may also be decreased. To investigate the impact of reducing postprandial levels of glucose and dicarbonyls on a number of related AGEs, we have investigated the levels of the arginine-derived AGEs G-H1, MG-H1, and 3DG-H, the lysine-derived AGEs CML and CEL, and the levels of oxidative products (3-NT, NFK, and MetSO) in subjects with lower postprandial glucose excursions secondary to insulin lispro therapy.

	RESEARCH DESIGN AND METHODS

TOP ABSTRACT INTRODUCTION RESEARCH DESIGN AND METHODS RESULTS CONCLUSIONS References

 
The recruitment of diabetic patients for this study has been described previously (21). Briefly, 21 type 1 diabetic patients on multiple insulin injections were studied using a randomized cross-over design. There were 15 males and 6 females with mean age 40 ± 10 years and mean diabetes duration of 16.6 ± 9.4 years. Insulin lispro or biosynthetic human regular insulin (Humulin; Eli Lilly, Indianapolis, IN) combined with intermediate (NPH or Lente) or long-acting (Ultralente) insulin was given over an initial 2-month period before switching to the alternate rapid-acting insulin. Subjects performed self-monitoring of blood glucose and recorded their results on a daily basis. Glucose values were determined five times daily (before breakfast, lunch, and supper and 2 h post breakfast and supper) to facilitate adjustments of insulin dosage, and seven blood glucose readings per day (before each meal, 1 and 2 h after breakfast, and 1 and 2 h postsupper) were measured once weekly to assess long-term postprandial glucose excursions. Postprandial glycemic excursions are expressed as the mean of the sum of the difference between preprandial glucose values and the postbreakfast and postsupper plasma glucose values utilizing the seven blood glucose profiles during the 2nd month of each study period (21). Fasting glucose levels were determined for each subject as the mean of all recorded fasting glucose values. Mean glucose levels were calculated based on all of the glucose determinations on the days that seven values were determined during the 2nd month of each study period.

As described in our prior study, we also determined plasma levels of 3-DG, methylglyoxal, and the methylglyoxal metabolite, D-lactic acid, at the end of each 2-month study period in the fasting state and 1 and 2 h after a standard test meal. Their postprandial excursions were calculated based on fasting, 1-, and 2-h values. A1C was measured at the end of each 2-month study period during which the subject received insulin lispro or regular insulin. Twelve normal healthy control subjects were also studied: six men and six women with mean age 52 ± 12 years.

Blood and urine samples.
Venous blood samples with heparin anticoagulant and 24-h urine collections were taken from diabetic patients and normal healthy control subjects. Blood cells were sedimented by centrifugation and plasma removed. Urine samples were collected at ambient temperature. Validation studies showed that <10% of analyte amounts were lost during this period. Plasma and urine samples were stored at –80°C before analysis. Urinary and plasma creatinine were determined by colorimetric assay (diagnostic kit 510; Sigma, St. Louis, MO). The study protocol conformed to the ethical guidelines of the latest Declaration of Helsinki and was approved by the local Committee for the Protection of Human Subjects. Informed consent was obtained from all participants.

Assessment of A1C.
At baseline and at the end of each 2-month study period, A1C was measured by high-performance liquid chromatography (Diamat method; BioRad, Irvine, CA) in the clinical laboratory at the Dartmouth-Hitchcock Medical Center (22). This determines the percentage of Hb with a fructosyl-valine residue on the NH₂-terminus of the ß-chain and will be referred to as A1C:Diamat. This accounts typically for 60% of fructosamine residues in Hb (23), the remaining 40% being fructosyl-lysine residues, mostly on lys-61 of the -chain (24). Total fructosyl-lysine residues in Hb (and not fructosyl-valine) are determined by the LC-MS/MS technique described below and will be referred to as A1C:fructosyl-lysine.

Protein glycation, oxidation, and nitrosation-free adduct determination by LC-MS/MS.
The following glycation adducts were determined: fructosyl-lysine, MG-derived AGEs (MG-H1, CEL, argpyrimidine, and methylglyoxal-derived lysine dimer), glyoxal-derived AGEs (G-H1 and CML), 3-DG–derived AGEs (3DG-H), and pentosidine. Protein oxidation adducts, MetSO, NFK, and dityrosine, the marker of nitrosative stress 3-NT, and amino acids lys, arg, tyr, met, and trp were also determined. Stable isotope standards for internal standardization were purchased and synthesized as described (6). Free glycation adducts were determined by assay of analytes in ultrafiltrate (12-kDa filter cutoff, 50 µl aliquot) of plasma and urine. Analytes released by self-digestion of proteases in assay blanks were subtracted from analyte estimates.

Samples were assayed by LC-MS/MS using a 2690 Separation Module with a Quattro Ultima triple quadrupole mass spectrometric detector (Waters-Micromass, Manchester, U.K.) as described (6). The only modification was a change of acetonitrile gradient (linear gradient of 10–50% acetonitrile from 0 to 15 min and isocratic 50% acetonitrile thereafter) for the detection of argpyrimidine, pentosidine, dityrosine, and 3-NT. Pentosidine, NFK, and trp were determined by liquid chromatography with fluorimetric detection using a Waters 2475 multichannel fluorescence detector (Waters-Micromass). The mobile phase was 0.1% trifluoroacetic acid with isocratic 10% acetonitrile from 0 to 20 min and then a linear gradient of 10–50% acetonitrile from 20 to 50 min eluted through column one only at a flow rate of 0.4 ml/min. The retention time, detection excitation and emission wavelengths (_ex/_em), and limits of detection for the analytes were pentosidine 25.7 min, 320/385 nm, and 6 fmol; NFK 43.7 min, 330/437 nm, and 13 pmol; and tryptophan 46.2 min, 286/400 nm, and 29 pmol. Authentic standard pentosidine and NFK were prepared as described (6,25).

Statistical analysis.
Significance of difference between means and medians of diabetic patients on regular insulin and lispro therapy were assessed by a paired t test and Wilcoxon signed rank, respectively. Correlation analysis was performed by calculating Spearman’s statistic.

	RESULTS

TOP ABSTRACT INTRODUCTION RESEARCH DESIGN AND METHODS RESULTS CONCLUSIONS References

 
The impact of decreased postmeal glucose excursions from insulin lispro treatment, on glycation, oxidation, and nitration-free adduct levels in plasma
The concentration of fructosyl-lysine–free adduct in plasma was decreased by lispro therapy, relative to regular insulin, although this change did not achieve statistical significance. The concentration of CML-free adduct was decreased significantly (19%) by lispro therapy (Table 1), however, whereas CEL-free adduct concentration was decreased 11% by lispro therapy, and this decrease was not statistically significant. The increase in 3DG-H–free adduct concentration seen in diabetes was significantly reversed (by 23%) by lispro therapy (Table 1), and the concentrations of G-H1–and MG-H1–free adducts were decreased by 29 and 24%, respectively, although these changes did not quite achieve statistical significance (Table 1). The MetSO-free adduct level in plasma was not changed significantly by the switch to lispro therapy (Table 1).

Fractional excretion of protein glycation and oxidation-free adducts were deduced to assess the efficiency of renal elimination. Extreme values of fractional excretions were for fructosyl-lysine (>100%) and MetSO (<1%). The efficiency of renal elimination in diabetes was increased for MG-H1–and 3DG-H–free adducts and decreased for CML, CEL, and G-H1 (regular insulin therapy only). Therapy with lispro in diabetes increased the efficiency of renal elimination of CML-free adduct.

Levels of standard indicators of glycemic control associated with regular and lispro therapy.
We investigated the levels of five indicators of glycemic control (A1C determined by the Diamat method [A1C:Diamat] and fructosyl-lysine in Hb [A1C:fructosyl-lysine], mean FPG, mean overall plasma glucose values [MPG], and mean PPG excursions) achieved in subjects on regular insulin or lispro treatment. As is seen in Table 3, no significant difference was observed in levels of A1C:Diamat, A1C:fructosyl-lysine, or mean fasting glucose in the face of highly significant differences in mean PPG levels and modest decreases in overall mean glucose levels with lispro therapy.

MPG also correlated with 24-h urinary excretion of fructosyl-lysine–free adduct, as well as with dityrosine, while a significant negative correlation was seen between MPG and 3-NT (Table 3). PPG also showed a significant negative correlation with excretion of urinary-free 3-NT (Table 3).

Correlations between indicators of glycemic control and A1C in diabetic subjects
As shown in Table 3, we observed statistically significant relationships between A1C (Diamat and fructosyl-lysine) with MPG, while mean PPG showed no such relationship (P values of 0.73 and 0.27) for A1C Diamat and fructosyl-lysine, respectively.

	CONCLUSIONS

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Protein glycation was viewed originally as a posttranslational modification that accumulated mostly on extracellular proteins. AGEs were thought to be formed slowly throughout life, and the concentrations of AGEs found represent a life-long accumulation of the glycation adducts. This applies to chemically stable AGEs formed on long-lived proteins. However, fructosyl-lysine and some AGEs (hydroimidazolones for example) have relatively shorter chemical half-lives under physiological conditions (2–6 weeks), and they may also be formed on cellular and short-lived extracellular proteins. The concentrations of these glycation adducts, therefore, reflect the rate of the respective glycation process in the 2–6 weeks before sampling. Proteins modified by glycation, oxidation, and nitration are degraded by cellular proteolysis, releasing free protein glycation, oxidation, and nitration glycation adducts (6,20).

The switch from regular insulin to lispro therapy of type 1 diabetic patients and the associated decrease in PPG produced significant decreases in protein glycation–free adducts of MG-H1, 3DG-H, and CML in plasma and urine. This confirms that decreasing postprandial glucose concentrations, as well as the previously observed decreases in methylglyoxal and 3-DG levels by therapy with lispro, can also decrease the levels of their specific AGEs (21). In this study population, we previously observed that the mean postprandial excursions of glucose, methylglyoxal, and 3-DG were 55, 15, and 13% of the corresponding fasting concentrations. The limited time period over which these elevations occur in the postprandial period may explain why the diabetes-associated increases in AGEs derived from these glycating agents were reversed by only 10–20% with lispro therapy. The observed reduction in AGEs with lispro treatment appears to relate to the decreased area under the curve for the meal-related variation of methylglyoxal, 3-DG, and glycoxidation (assuming oxidative degradation of fructosyl-lysine is the major precursor of CML in vivo). The modest changes of protein glycation and glycoxidation adducts found herein, therefore, are in keeping with the extent to which therapy with lispro decreases daily glucose exposure in our study. The hydroimidazolones MG-H1 and 3DG-H emerged as sensitive indicators of this because the concentrations of their precursors increase rapidly (21) in response to increased glucose concentration. Hydroimidazolones are also the major quantitative glycation adducts formed from these precursors, with diabetes-associated MG-H1–free adduct concentrations achieving levels 3- to 10-fold higher than other free AGE adducts, as shown in the present and prior studies (26,39). CML probably emerged as an indicator sensitive to PPG because oxidative stress enhanced in the postprandial period increased the rate of degradation of fructosyl-lysine to CML. Although we observed a strong relationship between urinary levels of dityrosine and mean glucose levels, the limited data on oxidative stress in this study, including measurement of 3-NT, dityrosine, and MetSO, did not confirm this hypothesis, although many other independent studies have shown that postprandial hyperglycemia and hyperlipidemia enhances oxidative stress (27–31). These findings are in contrast to the relative insensitivity of the Amadori product, represented by fructosyl-lysine residues of Hb or A1C (N-fructosyl-valine + fructosyl-lysine residues), which were not significantly decreased by lispro treatment (Table 3 and [21]). It is of interest that most other conventional markers of glycemic control were not sensitive to significant decreases in postprandial glycemia. These include markers such as mean fasting blood glucose levels as well as A1C:Diamat and A1C:fructosyl-lysine, all of which were unchanged by reducing glucose levels in the postprandial state. We did observe a modest change in mean daily glucose concentrations in association with lispro therapy however, although this was not sufficient to decrease A1C levels.

We did observe significant correlations between FPG and MPG levels and fructosyl-lysine–free adducts in plasma and urine and MPG with A1C:fructosyl-lysine and A1C:Diamat, confirming that the formation of Amadori products are strongly related to overall glycemia. Fasting glucose levels also correlated with MG-HI and CEL, demonstrating that methylglyoxal-related AGEs are indicators of mean blood glucose as well as postprandial glycemia. The only plasma AGE–free adduct that correlated with PPG was 3DG-H, while plasma fructosyl-lysine–free adduct demonstrated a significant negative relationship with PPG, confirming that it is an insensitive marker for postprandial glucose fluctuations.

The fractional excretion of fructosyl-lysine–free adduct was >100% in diabetic patients. In diabetes, there may be increased fructosyl-lysine–free adduct released by tubular epithelial cell proteolysis of protein in the glomerular filtrate (32). In contrast, the fractional excretion of MetSO was very low, reflecting the efficient conversion of MetSO to methionine by methionine sulfoxide reductase in the kidney (33). Lispro therapy increased the fractional excretion of CML-free adduct in diabetes, suggesting that the decreased urinary excretion of CML-free adduct was due to decreased formation of CML-free adduct rather than a decline in the efficiency of excretion.

Although the effect of decreasing postprandial hyperglycemia on protein glycation was modest, this study demonstrates that some AGEs, unlike fructosamines, are responsive to control of PPG. Since we have shown that some of the largest increases of protein glycation–free adducts in diabetes occurs for plasma concentration and urinary excretion of CML, MG-H1, and 3DG-H, it is not surprising that these glycation-related variables are most sensitive to change in glycemic control with lispro therapy. It was somewhat surprising, however, that lispro produced significant decreases in plasma and urinary excretion of glycation-free adducts but no significant reduction of glycation adduct residues of plasma protein or Hb. The latter observation could be related to our prior observation that increases in AGE residues in Hb tended to be modest in diabetes, possibly secondary to protection and repair of Hb from glycation damage by glyoxalase I and fructosamine 3-phosphokinase activities in erythrocytes (34–36). Plasma proteins damaged by AGE formation may suffer preferential cellular proteolysis and hence the modest changes in glycation damage are more readily detected in proteolysis products than in glycation adduct residues of plasma protein. The changes observed in this study also occurred in a relatively short 2-month time period, and longer periods of reduction in postprandial glucose levels could be associated with greater changes in AGE levels. In recent studies we have found that postprandial methylglyoxal levels are significantly decreased by treatment with nateglinide in type 2 diabetes (37), suggesting that decreases in methylglyoxal-derived AGEs may also occur with other treatments targeting postprandial glycemia. Since postprandial increases in ,ß-dicarbonyls and their associated AGEs can lead to direct cellular damage, decreasing their levels with lispro as well as decreasing postprandial oxidative lipemia and oxidative stress (27–29,31,38) could potentially lead to a reduction in long-term vascular complications.

	Acknowledgments

 
We thank the Juvenile Diabetes Research Fund and the Wellcome Trust, Eli Lilly, and the American Diabetes Association for support for our research.

	Footnotes

 
P.J.T. and P.J.B. are cosenior authors of this study.

P.J.B. has received honoraria and grant support from Eli Lilly. S.K.H. has received grant support from Eli Lilly.

A table elsewhere in this issue shows conventional and Système International (SI) units and conversion factors for many substances.

Received for publication April 14, 2005. Accepted for publication July 2, 2005.

	References

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1. Donnelly R, Emslie-Smith AM, Gardner ID, Morris AD: ABC of arterial and venous disease: vascular complications of diabetes (Review). BMJ 320:1062–1066, 2000[Free Full Text]
   
2. Haffner SM, Lehto S, Ronnemaa T, Pyorala K, Laakso M: Mortality from coronary heart disease in subjects with type 2 diabetes and in nondiabetic subjects with and without prior myocardial infarction (Comment). N Engl J Med 339:229–234, 1998[Abstract/Free Full Text]
   
3. Nishikawa T, Edelstein D, Du X, Yamagishi S, Matsumura T, Kaneda Y, Yorek M, Beebe D, Oates P, Hammes H, Giardino I, Brownlee M: Normalizing mitochondrial superoxide production blocks three pathways of hyperglycemic damage. Nature 404:787–790, 2000[Medline]
   
4. Brownlee M: Biochemistry and molecular cell biology of diabetic complications. Nature 414:813–820, 2001[Medline]
   
5. Thornalley PJ: Clinical significance of glycation. Clin Lab 45:263–273, 1999
   
6. Thornalley PJ, Battah S, Ahmed N, Karachalias N, Agalou S, Babaei-Jadidi R, Dawnay A: Quantitative screening of advanced glycation endproducts in cellular and extracellular proteins by tandem mass spectrometry. Biochem J 375:581–592, 2003[Medline]
   
7. Baynes J, Thorpe S: Role of oxidative stress in diabetic complications: a new perspective on an old paradigm. Diabetes 48:1–9, 1999[Abstract]
   
8. Hink U, Li H, Mollnau H, Oelze M, Matheis E, Hartmann M, Skatchkov M, Thaiss F, Stahl RA, Warnholtz A, Meinertz T, Griendling K, Harrison DG, Forstermann U, Munzel T: Mechanisms underlying endothelial dysfunction in diabetes mellitus. Circ Res 88:E14–E22, 2001
   
9. DECODE Study Group: Glucose tolerance and mortality: comparison of WHO and American Diabetes Association diagnostic criteria. European Diabetes Epidemiology Group. Diabetes Epidemiology: collaborative analysis of diagnostic criteria in Europe. Lancet 354:617–621, 1999[Medline]
   
10. Hanefeld M, Fischer S, Julius U, Schulze J, Schwanebeck U, Schmechel H, Ziegelasch HJ, Lindner J: Risk factors for myocardial infarction and death in newly detected NIDDM: the Diabetes Intervention Study, 11-year follow-up. Diabetologia 39:1577–1583, 1996[Medline]
    
11. Muggeo M, Verlato G, Bonora E, Zoppini G, Corbellini M, de Marco R: Long-term instability of fasting plasma glucose, a novel predictor of cardiovascular mortality in elderly patients with non-insulin-dependent diabetes mellitus: the Verona Diabetes Study. Circulation 96:1750–1754, 1997[Abstract/Free Full Text]
    
12. Del Prato S: In search of normoglycaemia in diabetes: controlling postprandial glucose. Int J Obes Relat Metab Disord 26 (Suppl. 3):S9–S17, 2002
    
13. Chiasson JL, Josse RG, Gomis R, Hanefeld M, Karasik A, Laakso M, Group S-NTR: acarbose treatment and the risk of cardiovascular disease and hypertension in patients with impaired glucose tolerance: the STOP-NIDDM trial. JAMA 290:486–494, 2003[Abstract/Free Full Text]
    
14. Shichiri M, Kishikawa H, Ohkubo Y, Wake N: Long-term results of the Kumamoto Study on optimal diabetes control in type 2 diabetic patients. Diabetes Care 23 (Suppl. 2):B21–B29, 2000
    
15. Kahn R: Postprandial blood glucose. Diabetes Care 24:775–778, 2001[Free Full Text]
    
16. Wells-Knecht MC, Lyons TJ, McCance DR, Thorpe SR, Baynes JW: 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. J Clin Invest 100:839–846, 1997[Medline]
    
17. Geibauf A, Van Wickern B, Simat T, Steinhart H, Esterbauer H: Formation of N-formylkynurenine suggests the involvement of apolipoprotein B-100 centered tryptophan radicals in the initiation of LDL lipid peroxidation. FEBS Lett 389:136–140, 1996[Medline]
    
18. Gaut JP, Byun J, Tran HD, Heinecke JW: Artifact-free quantification of free 3-chlorotyrosine, 3-bromotyrosine, and 3-nitrotyrosine in human plasma by electron capture-negative chemical ionization gas chromatography mass spectrometry and liquid chromatography-electrospray ionization tandem mass spectrometry. AnalBiochem 300:252–259, 2002[Medline]
    
19. Karachalias N, Babaei-Jadidi R, Ahmed N, Thornalley PJ: Accumulation of fructosyl-lysine and advanced glycation end products in the kidney, retina and peripheral nerve of streptozotocin-induced diabetic rats. Biochem Soc Trans 31:1423–1425, 2003[Medline]
    
20. Goldberg AL: Protein degradation and protection against misfolded or damaged proteins (Review). Nature 426:895–899, 2003[Medline]
    
21. Beisswenger p, Howell S, O’Dell R, Wood M, Touchette A, Szwergold B: Dicarbonyls increase in the postprandial period and reflect the degree of hyperglycemia. Diabetes Care 24:726–732, 2001[Abstract/Free Full Text]
    
22. Halwachs-Baumann G, Katzensteiner S, Schnedl W, Purstner P, Pieber T, Wilders-Truschnig M: Comparative evaluation of three assay systems for automated determination of hemoglobin A1c. Clin Chem 43:511–517, 1997[Abstract/Free Full Text]
    
23. Roberts NB, Amara AB, Morris M, Green BN: Long-term evaluation of electrospray ionization mass spectrometric analysis of glycated hemoglobin. Clin Chem 47:316–321, 2001[Abstract/Free Full Text]
    
24. Zhang X, Medzihradszky KF, Cunningham J, Lee PD, Rognerud CL, Ou CN, Harmatz P, Witkowska HE: Characterization of glycated hemoglobin in diabetic patients: usefulness of electrospray mass spectrometry in monitoring the extent and distribution of glycation. J Chromatogr B Biomed Sci 759:1–15, 2001
    
25. Simat T, Meyer K, Steinhart H: Synthesis and analysis of oxidation and carbonyl condensation products of tryptophan. J Chromatogr A 661:93–99, 1994
    
26. Ahmed N, Argirov OK, Minhas HS, Cordeiro CA, Thornalley PJ: Assay of advanced glycation endproducts (AGEs): surveying AGEs by chromatographic assay with derivatization by 6-aminoquinolyl-N-hydroxysuccinimidyl-carbamate and application to Nepsilon-carboxymethyl-lysine- and Nepsilon-(1-carboxyethyl)lysine-modified albumin. Biochem J 364:1–14, 2002[Medline]
    
27. Blackburn P, Cote M, Lamarche B, Couillard C, Pascot A, Tremblay A, Bergeron J, Lemieux I, Despres JP: Impact of postprandial variation in triglyceridemia on low-density lipoprotein particle size. Metabolism 52:1379–1386, 2003[Medline]
    
28. Nappo F, Esposito K, Cioffi M, Giugliano G, Molinari AM, Paolisso G, Marfella R, Giugliano D: Postprandial endothelial activation in healthy subjects and in type 2 diabetic patients: role of fat and carbohydrate meals. J Am Coll Cardiol 39:1145–1150, 2002[Abstract/Free Full Text]
    
29. Teno S, Uto Y, Nagashima H, Endoh Y, Iwamoto Y, Omori Y, Takizawa T: Association of postprandial hypertriglyceridemia and carotid intima-media thickness in patients with type 2 diabetes. Diabetes Care 23:1401–1406, 2000[Abstract/Free Full Text]
    
30. Ceriello A, Bortolotti N, Motz E, Pieri C, Marra M, Tonutti L, Lizzio S, Feletto F, Catone B, Taboga C: Meal-induced oxidative stress and low-density lipoprotein oxidation in diabetes: the possible role of hyperglycemia. Metabolism 48:1503–1508,1999
    
31. Mohanty P, Hamouda W, Garg R, Aljada A, Ghanim H, Dandona P: Glucose challenge stimulates reactive oxygen species (ROS) generation by leucocytes. J Clin Endocrinol Metab 85:2970–2973, 2000[Abstract/Free Full Text]
    
32. Cha T, Tahara Y, Yamato E, Yoneda H, Ikegami H, Noma Y, Shima K, Ogihara T: Renal handling of glycated albumin in non-insulin-dependent diabetes mellitus with nephropathy. Diabetes Res Clin Pract 12:149–156, 1991[Medline]
    
33. Hansel A, Heinemann SH, Hoshi T: Heterogeneity and function of mammalian MSRs: enzymes for repair, protection and regulation (Review). Biochim Biophys Acta 2:239–247, 2005
    
34. Thornalley P, Langborg A, Minhas H: Formation of glyoxal, methylglyoxal and 3-deoxyglucosone in the glycation of proteins by glucose. Biochem J 344:109–116, 1999
    
35. Szwergold BS, Howell S, Beisswenger PJ: Human fructosamine-3-kinase: purification, sequencing, substrate specificity, and evidence of activity in vivo. Diabetes 50:2139–2147, 2001[Abstract/Free Full Text]
    
36. Delpierre G, Rider M, Collard F, Stroobant V, Vanstapel F, Santos H, Van Schaftingen E: Identification, cloning, and heterologous expression of a mammalian fructosamine-3-kinase. Diabetes 49:1627–1634, 2000[Abstract]
    
37. Beisswenger P, Tamber M, LaPoint N, Keshavarz T, Howell S, Baron M: Nateglinide reduces post-prandial glucose and methylglyoxal levels in type 2 diabetes (Abstract). Diabetes 53 (Suppl. 2):A471, 2004
    
38. Ceriello A, Quagliaro L, Piconi L, Assaloni R, Da Ros R, Maier A, Esposito K, Giugliano D: Effect of postprandial hypertriglyceridemia and hyperglycemia on circulating adhesion molecules and oxidative stress generation and the possible role of simvastatin treatment. Diabetes 53:701–710, 2004[Abstract/Free Full Text]
    
39. Ahmed N, Babaei-Jadidi R, Howell SK, Beisswenger PJ, Thornalley PJ: Degradation products of proteins damaged by glycation, oxidation and nitration in clinical type 1 diabetes. Diabetologia 48:1590–1603, 2005[Medline]
    

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