Reassessing the increased glycation of hemoglobin in nondiabetic chronic renal failure patients: a hypothesis on the role of lipid peroxides

Oxidized LDL but not total LDL is associated with HbA1c in individuals without diabetes

OBJECTIVE

This study investigates the association between HbA1c, LDL and oxi-LDL in individuals without diabetes (DM).

METHODS

One hundred and ninety-six individuals, without DM, were enrolled and divided into three groups according to HbA1c and fasting plasma glucose values. HbA1c, oxi-LDL, LDL, and other biochemical measurements of lipid profile were also carried out.

RESULTS

oxi-LDL levels showed significant differences among all groups and group 3 presented higher values [34U/L (27-46); 44U/L (37-70); and 86U/L (49-136); p<0.001; for groups 1, 2 and 3, respectively]. There was also a significant difference in oxi-LDL/HDL and oxi-LDL/LDL ratios among all groups (p<0.001). There was no significant difference in total cholesterol (TC), triglycerides and LDL values among groups. HbA1c showed moderate positive associations with oxi-LDL (r=0.431; p<0.001), oxi-LDL/HDL ratio (r=0.423, p<0.001), and oxi-LDL/LDL ratio (r=0.359, p<0.001). There were lower associations between HbA1c and TC (r=0.142; p=0.048), triglycerides (r=0.155; p=0.030), LDL (r=0.148; p=0.039), non-HDL (r=0.192; p=0.007) and Apo B (r=0.171, p<0.001). The positive associations between HbA1c and oxi-LDL, oxi-LDL/HDL and oxi-LDL/LDL ratios remained significant even after adjustment by multiple linear regression analysis for the variables alcohol consumption, use of medicine, BMI, and age.

CONCLUSIONS

oxi-LDL levels are significantly associated with HbA1c in non-diabetic individuals. However, the levels of traditional atherogenic lipids only showed a weak association with HbA1c levels. Those at high risk of developing DM or cardiovascular disease have higher levels of oxi-LDL. These data favor to the use of HbA1c as a biomarker to identify individuals at risk of developing complications even in non-diabetic glycemic levels.

Influence of smoking and diet on glycated haemoglobin and 'pre-diabetes' categorisation: a cross-sectional analysis

BACKGROUND

The new HbA1c criteria for diagnosis of pre-diabetes have been criticised for misdiagnosis. It is possible that some elevation of HbA1c is not driven by hyperglycaemia. This study assesses associations of HbA1c, commonly assumed to relate solely to glucose concentration, with (i) smoking, a major source of reactive oxygen species (ROS) and (ii) fruit & vegetables consumption associated with improved redox status.

METHODS

One-way ANOVA, Chi-squared and multivariate linear regressions, adjusted for all known confounders were used to explore associations of HbA1c with self-reported smoking status and fruit & vegetables consumptions in the Scottish Health Surveys 2003-2010, among individuals without known diabetes and HbA1c < 6.5%.

RESULTS

Compared to non-smokers (n = 2831), smokers (n = 1457) were younger, consumed less fruit & vegetables, had lower physical activity levels, lower BMI, higher HbA1c and CRP (p < 0.05). HbA1c was higher in smokers by 0.25 SDs (0.08%), and 0.38 SDs higher (0.14%) in heavy smokers (>20 cigarettes/day) than non-smokers (p < 0.001 both). Smokers were twice as likely to have HbA1c in the 'pre-diabetic' range (5.7-6.4%) (p < 0.001, adj.model). Pre-diabetes and low grade inflammation did not affect the associations. For every extra 80 g vegetable portion consumed, HbA1c was 0.03 SDs (0.01%) lower (p = 0.02), but fruit consumption did not impact on HbA1c, within the low range of consumptions in this population.

CONCLUSION

This study adds evidence to relate smoking (an oxidative stress proxy) with protein glycation in normoglycaemic subjects, with implications for individuals exposed to ROS and for epidemiological interpretation of HbA1c.

Pathological aspects of lipid peroxidation

Lipid peroxidation (LPO) product accumulation in human tissues is a major cause of tissular and cellular dysfunction that plays a major role in ageing and most age-related and oxidative stress-related diseases. The current evidence for the implication of LPO in pathological processes is discussed in this review. New data and literature review are provided evaluating the role of LPO in the pathophysiology of ageing and classically oxidative stress-linked diseases, such as neurodegenerative diseases, diabetes and atherosclerosis (the main cause of cardiovascular complications). Striking evidences implicating LPO in foetal vascular dysfunction occurring in pre-eclampsia, in renal and liver diseases, as well as their role as cause and consequence to cancer development are addressed.

Advanced glycation end products and antioxidant status in nondiabetic and streptozotocin induced diabetic rats: effects of copper treatment

The effects of Cu(II) supplementation on glycemic parameters, advanced glycation end products (AGEs), antioxidant status (glutathione; GSH and total antioxidant capacity; TAOC) and lipid peroxidative damage (thiobarbituric acid-reactive substances, TBARS) were investigated in streptozotocin (STZ) induced diabetic rats. The study was carried out on Wistar albino rats grouped as control (n = 10), CuCl(2) treated (n = 9), STZ (n = 10) and STZ,CuCl(2) treated (n = 9). STZ was administered intraperitoneally at a single dose of 65 mg/kg and CuCl(2), 4 mg copper/kg, subcutaneously, every 2 days for 60 days. At the end of this period, glucose(mg/dl), Cu(microg/dl), TBARS(micromol/l), TAOC(mmol/l) were measured in plasma, GSH(mg/gHb) in erythrocytes and glycated hemoglobin (GHb)(%) in blood. Plasma AGE-peptides(%) were measured by HPLC flow system with spectrofluorimetric and spectrophotometric detectors connected on-line. Data were analyzed by the non-parametric Kruskal-Wallis and Mann-Whitney U test. In the STZ group glucose, GHb and AGE-peptide levels were all significantly higher than the control group (P < 0.01, P < 0.05, and P < 0.01, respectively). CuCl(2) treated group had significantly lower glucose but significantly higher GHb, TAOC and TBARS levels than the control group (P < 0.05, P < 0.001, P < 0.05 and P < 0.001, respectively). STZ,CuCl(2) treated group had significantly higher GHb, TAOC and TBARS levels compared with the control group (P < 0.001, P < 0.05 and P < 0.05, respectively); but only TAOC level was significantly higher than the STZ group (P < 0.01). This experimental study provides evidence that copper intake increases total antioxidant capacity in both nondiabetic and diabetic states. However despite the potentiated antioxidant defence, lipid peroxidation and glycation enhancing effects of CuCl(2) are evident under nondiabetic conditions.

A perspective on the Maillard reaction and the analysis of protein glycation by mass spectrometry: probing the pathogenesis of chronic disease

The Maillard reaction, starting from the glycation of protein and progressing to the formation of advanced glycation end-products (AGEs), is implicated in the development of complications of diabetes mellitus, as well as in the pathogenesis of cardiovascular, renal, and neurodegenerative diseases. In this perspective review, we provide an overview on the relevance of the Maillard reaction in the pathogenesis of chronic disease and discuss traditional approaches and recent developments in the analysis of glycated proteins by mass spectrometry. We propose that proteomics approaches, particularly bottom-up proteomics, will play a significant role in analyses of clinical samples leading to the identification of new markers of disease development and progression.

Attenuation of plasma dyslipidemia and oxidative damage by dietary caloric restriction in streptozotocin-induced diabetic rats

Oxidative stress has been proposed as the pathogenic mechanism linking insulin resistance with endothelial dysfunction during diabetes. The present study investigated the attenuation of plasma dyslipidemia and oxidative damage by caloric restriction in experimental diabetes. Forty male Wistar rats were divided into ad libitum and calorie-restricted groups. The calorie-restricted group was subjected to 30% caloric restriction for 63 days before induction of diabetes to 50% of both groups. Caloric restriction significantly (p<0.01) reduced the body weights, reactive oxygen species (ROS), catalase, total cholesterol levels and non-significantly reduced SOD activities in non-diabetic and diabetic rats. Caloric restriction was also found to improve blood glucose levels, glycated hemoglobin, malondialdehyde, triglyceride, oxidized glutathione and reduced glutathione levels and significantly (p<0.05) increased GPx and GR activities in the experimental animals. The non-diabetic rats fed ad libitum had the most significant increases in body weight which could be due to dyslipidemia. These results indicate that dietary caloric restriction attenuates the oxidative damage and dyslipidemia exacerbated during diabetes as evidenced by the significant reduction in their body weights, ROS, total cholesterol levels and the increases in GPx activity and redox status.

Increased plasma malondialdehyde and fructosamine in iron deficiency anemia: effect of treatment

Glycation and lipid peroxidation are spontaneous reactions that are believed to play a key role in the pathogenesis of many clinical disorders. Glycation of proteins is enhanced by elevated glucose concentrations. However, increased glycated hemoglobin levels have been documented in iron deficiency anemic patients without any history of diabetes. Collective evidences reveal that lipid peroxidation can modulate protein glycation. This study was undertaken to unravel the possible association of malondialdehyde and fructosamine in iron deficient anemic patients and to observe the possible alteration in malondialdehyde and fructosamine levels in these patients after one month supplementation with iron. Twenty non-diabetic anemic patients and 16 age-matched healthy subjects were enrolled for this study. Plasma lipid peroxides, fasting glucose, fructosamine, iron, ferritin and hemoglobin were analyzed in both the groups. Partial correlation analysis was performed to predict the independent association of malondialdehyde and fasting glucose on fructosamine. In anemic patients, while fructosamine and malondialdehyde levels were found to be significantly increased, hemoglobin, iron and ferritin levels decreased significantly when compared to before treatment. Fructosamine was found to have a significant positive correlation with malondialdehyde even after nullifying the effect of glucose. After one month supplementation with iron, both fructosamine and malondialdehyde levels decreased significantly when compared to before treatment. There was a significant increase in iron, ferritin and hemoglobin levels in anemic patients after one month of treatment. In conclusion, an increased level of fructosamine and malondialdehyde was found in anemic patients. These data suggest that fructosamine levels are closely associated with malondialdehyde concentrations in iron deficient anemic patients.

Increased plasma malondialdehyde and fructosamine in anemic H pylori infected patients: Effect of treatment

AIM: To unravel the possible association of malon-dialdehyde (MDA) and fructosamine in anemic H pylori infected patients and to observe the alteration in MDA and fructosamine levels in these patients after treatment for one month.

METHODS: Fructosamine, MDA and glucose were estimated in 22 anemic H pylori infected patients and 16 healthy controls. Hematological parameters were also evaluated in both the groups using Sysmex-K-100 automated cell counter. The H pylori infected patients were randomly divided into two groups. H pylori infected patients in GroupIreceived both iron supplementation and anti-H pylori therapy, while patients in Group II received only iron supplementation. All the biochemical and hematological parameters were estimated after one month of treatment.

RESULTS: In anemic H pylori infected patients, while MDA (5.41 ± 2.16 vs 2.26 ± 0.50; P < 0.05) and fructosamine (2.64 ± 0.93 vs 1.60 ± 0.35; P < 0.05) were significantly increased, iron (32.72 ± 14.93 vs 110.25 ± 26.58; P < 0.05), hemoglobin (6.9 ± 2.6 vs 12.66 ± 0.74; P < 0.05) and ferritin (28.82 ± 16.27 vs 140.43 ± 30.72; P < 0.05) levels were significantly decreased compared with the controls. With partial correlation analysis, fructosamine was found to have a significant positive correlation with MDA. In GroupI, while MDA level decreased significantly (3.11 ± 1.73 vs 5.50 ± 2.46; P < 0.05), there was a significant increase in iron (84.09 ± 29.51 vs 36.09 ± 17.81; P < 0.05), hemoglobin (10.40 ± 1.11 vs 7.42 ± 1.90; P < 0.05) and ferritin (116.91 ± 63.34 vs 30.46 ± 17.81; P < 0.05) levels after one month. There was no significant change in the levels of fructosamine in groupIafter treatment. Similarly, no significant alterations were noted in the levels of MDA, fructosamine, hemoglobin or ferritin in Group II patients after one month of treatment.

CONCLUSION: An increased level of fructosamine and MDA was found in anemic H pylori infected patients. Present data supports the premise that lipid peroxides per se do play a role in the glycation of plasma proteins. Furthermore, the findings from this study indicate that treatment for both anemia and H pylori infections is required for lowering the levels of lipid peroxides in these patients.

Increased glycation of hemoglobin and plasma proteins in normotensive, non-diabetic obese Indian subjects: putative role of lipid peroxides

BACKGROUND

Glycation and lipid peroxidation are spontaneous reactions believed to contribute to the pathogenesis of many clinical disorders. The purpose of the present study was to evaluate the levels of lipid peroxides and glycated proteins in normotensive, non-diabetic obese Indian subjects and to assess possible associations between them.

METHODS

A total of 28 obese male subjects and 20 non-obese subjects were included in the present study. Whole blood glycated hemoglobin, plasma lipid peroxides and fructosamine levels were estimated in both groups.

RESULTS

Lipid peroxides, glycated hemoglobin and fructosamine levels were significantly higher in obese subjects in comparison with non-obese subjects. We also found a significant association between malondialdehyde and body mass index (r=0.424, p=0.025). Partial correlation analysis revealed that malondialdehyde was significantly correlated with glycated hemoglobin (r=0.590, p=0.01) and fructosamine (r=0.442, p=0.021) after controlling for glucose.

CONCLUSIONS

Increased glycation of proteins was found in normotensive, non-diabetic obese Indian subjects. These data also support the premise that lipid peroxides per se play a role in the glycation of hemoglobin and plasma proteins.

LDL oxidation is associated with increased blood hemoglobin A1c levels in diabetic patients

AIM

To investigate whether levels of blood HbA1c in diabetic patients are associated with susceptibility of LDL to oxidation.

METHODS

LDL was separated from blood of 40 diabetic patients with known blood glucose and HbA1c levels. The tendency to undergo lipid peroxidation was assessed via lag time required for initiation of LDL oxidation. HbA1c formation was measured in vitro following incubation of red blood cell (RBC) hemolysate for 3 months with increasing concentrations of glucose in the absence or presence of LDL or oxidized LDL.

RESULTS

Lag time for copper-induced LDL oxidation was twice as long in normal subjects compared to diabetic patients. Correlation analyses between LDL oxidation lag time and HbA1c blood levels revealed an R value of 0.74. Incubation of RBC hemolysate with high glucose concentration (up to 400 mg/dl) resulted in increased blood HbA1c concentration by up to 107%. Addition of LDL to this hemolysate over a period of 3 months resulted in LDL oxidation and an increase in HbA1c levels by up to 168%. Similarly, addition of oxidized LDL to the hemolysate increased HbA1c by up to 240%.

CONCLUSIONS

Increased tendency of LDL to undergo lipid peroxidation in diabetic patients contributes to increased levels of blood HbA1c, mainly in those with HbA1c<7.3.

Evidence for the role of lipid peroxides on glycation of hemoglobin and plasma proteins in non-diabetic asthma patients

BACKGROUND

Collective evidences reveal that malondialdehyde (MDA), reduced glutathione (GSH) and ascorbic acid can modulate protein glycation. We investigated the concentrations of MDA, GSH, ascorbic acid and protein glycation in asthma patients to delineate the possible association among these parameters.

METHODS

Blood was collected from 18 asthma patients and 16 age and sex matched control subjects. Glycated hemoglobin (HbA1C), GSH, MDA, vitamin C, fructosamine and glucose were assessed in both groups. The effect of H2O2 on glycation of hemoglobin was studied by incubating normal healthy erythrocytes with either 5 or 50 mmol/l glucose concentration.

RESULTS

Plasma of asthma patients revealed significantly higher concentrations of lipid peroxides and fructosamine concentrations than the matched controls. Glycated hemoglobin concentrations were also found to be significantly increased. Ascorbic acid and GSH concentrations were decreased significantly in the test group when compared with the healthy control group. When the effects of fasting glucose, GSH and ascorbic acid on the concentrations of HbA1C and fructosamine were refuted by partial correlation analysis, MDA was found to be a significant determinant of HbA1c and fructosamine in patients with asthma. The in vitro model with human erythrocytes showed an enhancement of protein glycation by H2O2.

CONCLUSION

An increased glycation of proteins was found in asthma patients. These data also support the premise that lipid peroxides per se do have a role to play in glycation of hemoglobin and plasma proteins.

Effect of lipid peroxides and antioxidants on glycation of hemoglobin: an in vitro study on human erythrocytes

BACKGROUND

Glycation and lipid peroxidation are two important processes known to play a key role in complications of many pathophysiological process. We sought to assess the possibility of an interaction between these processes in vitro and to examine the effect of lipoic acid and taurine on the glycation of hemoglobin and lipid peroxidation.

METHODS

Human erythrocytes in phosphate buffered saline (pH 7.4) were incubated with 5 or 50 mmol/l glucose. To study the effect of antioxidants on glycation of hemoglobin, erythrocytes were incubated with either lipoic acid or taurine and then exposed to glucose concentration of either 5 or 50 mmol/l. To clarify if lipid peroxides per se enhances the glycated hemoglobin level, an in vitro study was performed by incubating erythrocyte suspension containing either 5 or 50 mmol/l glucose with or without MDA. Lipid peroxides and glycated hemoglobin levels were determined in the glucose treated cells.

RESULTS

Glycated hemoglobin levels were higher in erythrocytes incubated with 50 mmol/l glucose concentrations than in erythrocytes incubated with 5 mmol/l glucose. The increase in glycated hemoglobin levels was blocked significantly when erythrocytes were pretreated with either lipoic acid or taurine. Both the antioxidants used in the present study markedly reduced the MDA levels. The level of glycated hemoglobin in erythrocyte incubated in the presence of MDA was increased significantly when compared to erythrocyte incubated with glucose alone.

CONCLUSIONS

Lipid peroxides per se may have a role to play in glycation of hemoglobin and antioxidants (lipoic acid and taurine) can partially inhibit the formation of glycated hemoglobin by lowering the levels of lipid peroxides.