Levels of serum sialic acid and thiobarbituric acid reactive substances in subjects with impaired glucose tolerance and type 2 diabetes mellitus

The connections of sialic acids and diabetes mellitus: therapeutic or diagnostic value?

Modulation of sialic acids is one of the important pathological consequences of both type 1 and type 2 diabetes mellitus with or without the micro- and macrovascular complications. However, the mechanistic, therapeutic and/or diagnostic implications of these observations are uncoordinated and possibly conflicting. This review critically analyses the scientific investigations connecting sialic acids with diabetes mellitus. Generally, variations in the levels and patterns of sialylation, fucosylation and galactosylation were predominant across various tissues and body systems of diabetic patients, but the immune system seemed to be most affected. These might be explored as a basis for differential diagnosis of various diabetic complications. Sialic acids are predominantly elevated in nearly all forms of diabetic conditions, particularly nephropathy and retinopathy, which suggests some diagnostic value but the mechanistic details were not unequivocal from the available data. The plausible mechanistic explanations for the elevated sialic acids are increased desialylation by sialidases, stimulation of hexosamine pathway and synthesis of acute phase proteins as well as oxidative stress. Additionally, sialic acids are also profoundly associated with glucose transport and insulin resistance in human-based studies while animal-based studies revealed that the increased desialylation of insulin receptors by sialidases, especially NEU1, might be the causal link. Interestingly, inhibition of the diabetes-associated NEU1 desialylation was beneficial in diabetes management and might be considered as a therapeutic target. It is hoped that the article will provide an informed basis for future research activities on the exploitation of sialic acids and glycobiology for therapeutic and/or diagnostic purposes against diabetes mellitus.

Association of Hypoglycemia with Biomarkers of Oxidative Stress and Antioxidants: An Observational Study

Hypoglycemia has been associated with complications from the vasculature. The contributing effects of oxidative stress (OS) on these actions have not been sufficiently studied, especially in daily, routine clinical practice. We examined the association of hypoglycemia encountered in daily clinical practice with biomarkers of OS and endogenous antioxidant activity in persons with diabetes [type 1 (T1D) or type 2 (T2D)], as well as individuals without diabetes, with a history of hypoglycemia. Several biomarkers of OS (MDA, ADMA, ox-LDL, 3-NT, protein carbonyls, 4-HNE, TBARS) and antioxidant capacity (TAC, superoxide scavenging capacity, hydroxyl radical scavenging capacity, reducing power, ABTS) were measured. Blood was drawn at the time of hypoglycemia detection and under euglycemic conditions on a different day. A total of 31 participants (mean age [±SD] 52.2 ± 21.1 years, 45.2% males) were included in the study. There were 14 (45.2%) persons with T2D, 12 (38.7%) with T1D, and 5 (16.1%) without diabetes. We found no differences in the examined biomarkers. Only TBARS, a biomarker of lipid peroxidation, showed lower values during hypoglycemia (p = 0.005). This finding needs confirmation in more extensive studies, given that MDA, another biomarker of lipid peroxidation, was not affected. Our study suggests that hypoglycemia encountered in daily clinical practice does not affect OS.

Association of serum sialic acid concentration with diabetic complications and cardiovascular risk factors in an Indian population

Introduction

Sialic acid (SA) is an acetylated product of neuraminic acid. It acts as a cofactor of many cell surface receptors (e.g. insulin receptors) and is positively associated with most of the serum acute phase reactants. Sialic acid is an important component of serum, which is elevated in diseases such as diabetes and certain malignancies. Diabetes mellitus (DM) is associated with an increase in SA concentration along with other complications. The present study was undertaken to assess the relationship between serum SA and type 2 diabetes.

Material and methods

A total of 200 type 2 DM patients, 145 males and 55 females, were included in the study. Also, 100 healthy individuals served as the control group. Parameters assessed included serum SA, lipid profile, urine microalbumin, LDL-C, lipoprotein(a), and serum fibrinogen. The relationship between serum SA and diabetic complications viz retinopathy, nephropathy, and neuropathy was also assessed.

Results

Type 2 DM patients had significantly higher levels (p < 0.01) of SA (77.35 ±4.6 mg%) as compared to the control group (68.23 ±7.9 mg%). Increased levels of serum SA were seen in patients with diabetic nephropathy and retinopathy. No correlation was seen between serum SA and diabetic neuropathy.

Conclusions

Elevated serum SA concentration is significantly related to type 2 DM and associated cardiovascular risk factors. Further study of acute-phase response markers and mediators as indicators or predictors of diabetic microvascular complications is therefore justified.

The correlation between blood oxidative stress and sialic acid content in diabetic patients with nephropathy, hypertension, and hyperlipidemia

This clinical study was designed to find out the correlation between oxidative stress and sialic acid (SA) content of plasma and RBCs in patients with type 2 diabetes. We evaluated SA concentration and oxidative stress biomarkers in healthy subjects and diabetic patients with and without complications in a cross-sectional survey. Significant changes in oxidative stress biomarkers and RBC-SA were revealed in the diabetic patients compared to those in the healthy group. Plasma SA significantly increased with an increase in lipid peroxidation of RBCs (LPO-RBC) (P < 0.001) in the diabetic patients without complication. RBC-SA significantly decreased with an elevation in LPO-RBC (P < 0.001) in all the diabetic patients and those with nephropathy. There was no significant correlation between plasma and RBC-SA and other oxidative stress biomarkers in the diabetic subjects. In multiple logistic regression analysis, RBC-SA was independently related to LPO-RBC in all the diabetic patients and those with nephropathy. We conclude that the induction of LPO-RBC in diabetic patients and those with nephropathy may influence the SA decomposition of RBC membrane, thereby altering its functions and transporter activities. Therefore, LPO-RBC and SA levels in RBCs can be used for prediction of diabetic nephropathy, and further studies to evaluate other factors contributing to desialylation of RBC membrane are justified.

Comprehensive metabolic profiling of chronic low-grade inflammation among generally healthy individuals

BACKGROUND

Inflammation occurs as an immediate protective response of the immune system to a harmful stimulus, whether locally confined or systemic. In contrast, a persisting, i.e., chronic, inflammatory state, even at a low-grade, is a well-known risk factor in the development of common diseases like diabetes or atherosclerosis. In clinical practice, laboratory markers like high-sensitivity C-reactive protein (hsCRP), white blood cell count (WBC), and fibrinogen, are used to reveal inflammatory processes. In order to gain a deeper insight regarding inflammation-related changes in metabolism, the present study assessed the metabolic patterns associated with alterations in inflammatory markers.

METHODS

Based on mass spectrometry and nuclear magnetic resonance spectroscopy we determined a comprehensive panel of 613 plasma and 587 urine metabolites among 925 apparently healthy individuals. Associations between inflammatory markers, namely hsCRP, WBC, and fibrinogen, and metabolite levels were tested by linear regression analyses controlling for common confounders. Additionally, we tested for a discriminative signature of an advanced inflammatory state using random forest analysis.

RESULTS

HsCRP, WBC, and fibrinogen were significantly associated with 71, 20, and 19 plasma and 22, 3, and 16 urine metabolites, respectively. Identified metabolites were related to the bradykinin system, involved in oxidative stress (e.g., glutamine or pipecolate) or linked to the urea cycle (e.g., ornithine or citrulline). In particular, urine 3'-sialyllactose was found as a novel metabolite related to inflammation. Prediction of an advanced inflammatory state based solely on 10 metabolites was well feasible (median AUC: 0.83).

CONCLUSIONS

Comprehensive metabolic profiling confirmed the far-reaching impact of inflammatory processes on human metabolism. The identified metabolites included not only those already described as immune-modulatory but also completely novel patterns. Moreover, the observed alterations provide molecular links to inflammation-associated diseases like diabetes or cardiovascular disorders.

Leukocyte Telomere Length in the Neonatal Offspring of Mothers with Gestational and Pre-Gestational Diabetes

Aims

Telomeres undergo shortening with cell division, accelerated by increased oxidative stress. We aimed to demonstrate shortened telomeres in the offspring of mothers who have diabetes as a consequence of exposure to increased oxidative stress during intrauterine development.

Methods

We examined the level of glycaemia (glucose, HbA1c, fructosamine), oxidative stress (lipid peroxidation) and the levels of antioxidant enzymes (Superoxide dismutase (SOD) and Selenium dependent glutathione peroxidase) and correlate these findings with mean telomere length (TL) in maternal and foetal blood in groups of pregnant women with pre-gestational diabetes (PGD), gestational diabetes (GD) and a euglycaemic control group.

Results

Foetal and maternal glucose, maternal HbA1c, and foetal insulin and C-peptide were higher in the PGD group with the GD group being intermediate. Markers of oxidative stress did not vary between groups with the exception of foetal SOD activity that was highest in the GD group. There were no detectable differences in maternal or foetal TL between study groups. An exploratory analysis looking at correlations between glycaemic and oxidative stress parameters and TL revealed a negative correlation between maternal and foetal glucose and TL across the whole study population. This relationship held for the short-term marker of glycaemic control, fructosamine.

Conclusions

We were unable to show significant telomere shortening in the offspring of mothers with PGD or GD. Exploratory analysis revealed a relationship between foetal TL and short-term glycaemia particularly in PGD. It is possible that increased telomerase activity can compensate for long-term increased oxidative stress but not for short-term dysglycaemia.

The association of total sialic acid and malondialdehyde levels with metabolic and anthropometric variables in obesity

Serum sialic acid levels are abnormally high in pathological states that exhibit tissue destruction, tissue proliferation or inflammation. We measured total serum sialic acid levels in 139 women and 125 men. Subjects were divided into quartiles according to their body mass index (BMI): Q1 (18-24.9 kg/m(2)), Q2 (25-29.9 kg/m(2)), Q3 (30-39.9 kg/m(2)) and Q4 (> 40 kg/m(2)). The patients in Q1 constituted the control group. Serum sialic acid levels of subjects in Q2, Q3 and Q4 were significantly higher than those in Q1. Higher BMI quartiles also were associated with higher levels of serum glucose, insulin, total cholesterol, LDL-cholesterol, triglycerides, high-sensitivity C-reactive protein, malondialdehyde levels, waist circumference, blood pressure and homeostasis model assessment of insulin resistance in both women and men. Lower BMI quartiles were associated with higher levels of serum HDL-cholesterol levels in both women and men. We found positive associations among serum sialic acid levels, BMI and oxidative stress. Serum sialic acid also is related to some conventional cardiovascular risk factors including elevated lipid profile, increased blood pressure, increased serum glucose and insulin levels, and insulin resistance in obese people.

Therapeutic effects of stem cell on hyperglycemia, hyperlipidemia, and oxidative stress in alloxan-treated rats

Diabetes mellitus is the most common endocrine disorder that affects more than 285 million people worldwide. The purpose of this study was to investigate the effect of mesenchymal stem cells (MSCs) from the bone marrow of albino rats, on hyperglycemia, hyperlipidemia, and oxidative stress induced by intraperitoneal injection (i.p.) of alloxan at a dose of 150 mg/kg in rats. Injection of alloxan into rats resulted in a significant increase in serum glucose, total cholesterol, triglyceride, low density lipoprotein cholesterol, and sialic acid level and a significant decrease in serum insulin, high density lipoprotein-cholesterol, vitamin E, and liver glycogen as compared to their corresponding controls. Also, oxidative stress was noticed in pancreatic tissue as evidenced by a significant decrease in glutathione level, superoxide dismutase, glutathione-S-transferase activities, also a significant increase in malondialdehyde and nitric oxide levels when compared to control group. Treatment of diabetic rats with MSCs stem cells significantly prevented these alterations and attenuated alloxan-induced oxidative stress. In conclusion, rat bone marrow harbors cells that have the capacity to differentiate into functional insulin-producing cells capable of controlling hyperglycemia, hyperlipidemia, and oxidative stress in diabetic rats. This may be helpful in the prevention of diabetic complications associated with oxidative stress.

Sialic acid levels in the blood in pregnant women with impaired glucose tolerance test

PURPOSE

Gestational diabetes (GDM) is a metabolic disease characterized by the impairment of glucose tolerance during pregnancy. Sialic acid (SA) is a component of glycolipid and glycoproteins found in hormone and enzymes in serum and tissues and high serum SA levels are observed in diabetic patients.

METHODS

Serum SA levels were investigated in three groups, namely 61 normal pregnant women with normal 50 gr glucose loading test (group 1: gr 1), 36 patients with high 50 gr test values and normal 100 gr test (group 2: gr 2: group with impaired glucose tolerance test, IGT), and 8 patients with diagnosis of GDM (group 3:gr 3).

RESULTS

According to Kruskal-Wallis test, significant difference was observed in SA levels between gr1 and gr2-gr3 (p = 0.001). Difference was observed between groups with respect to age (p < 0.001), the number of pregnancies (p = 0.001), BMI (p = 0.001), and diabetes history in the family (p = 0.001) (Table 1). Table 1 Summary of results and statistical relationship Variable Group 1 (n = 61) Group 2 (n = 36) Group 3 (n = 8) p Age 24 (18-38) 28 (19-38) 31 (20-38) <0.001 Pregnancy week 26 (24-29) 26 (24-32) 26,5 (24-29) 0.126 Pregnancy number 2 (0-6) 2 (1-5) 3.5 (1-5) <0.001 BMI 23.7 (17.9-38.2) 27.6 (17.04-41.14) 30.8 (21.9-43.8) <0.001 Weight taken 7 (1-13) 6 (2-12) 6 (4-10) 0.954 Sialic acids 2.66 (1.2-4.59) 3.22 (2.34-5.04) 3.05 (2.67-3.49) <0.001 Fetal weight 3,380 (2,310-4,290) 3,400 (2,650-4,600) 3,655 (3,270-3,960) 0.092 Smoking 5 (%8.2) 2 (%5.6) 0 (%0) 1 Family history 22 (%36.1) 10 (%27.8) 8 (%100) <0.001.

CONCLUSION

Our study demonstrated that SA values are increased in GDM and IGT groups, which demonstrates that inflammatory disorders may occur also in IGT group, which is considered like normal pregnancy, and that this group may be considered in the same way as GDM.

Cardiovascular risk assessment in patients with type 2 diabetes mellitus and metabolic syndrome: role of biomarkers

OBJECTIVES

Metabolic syndrome (MetS) and type 2 diabetes mellitus (DM) are associated with a high incidence of cardiovascular diseases. The aim of this study was to determine paraoxonase (PON), total sialic acid (TSA), and nitric oxide (NO) levels in addition to conventional risk markers in patients with DM, MetS and DM plus MetS.

MATERIAL AND METHODS

The study has been carried out over 78 subjects which divided into four groups; control (n=18), DM (n=20), newly diagnosed MetS (n=20) and DM plus MetS patient groups (n=20).

RESULTS

Both insulin and triglyceride concentrations were significantly higher in DM+MetS group than in control and DM groups and serum HDL-C concentrations were significantly lower in DM+MetS group than other groups. Patients with MetS had higher LDL-C, total cholesterol and hsCRP concentrations than in the other groups. Interestingly, in addition to body mass index and waist circumference values, LDL-C, total cholesterol and hsCRP concentrations were decreased in patients who have both DM and MetS. Serum NO and TSA levels were higher in MetS and DM+MetS groups compared to control subjects. Unexpectedly, PON activity has been found lower in control group when compared to other groups.

CONCLUSIONS

Although there is no doubt that association of DM and MetS elevates the risk of cardiovascular disease, occurrence of DM in patients with undiagnosed MetS might be encouraging patients to change their life styles and dietary habits.

Protective potential of Royal Jelly against carbon tetrachloride induced-toxicity and changes in the serum sialic acid levels

Royal Jelly (RJ) is used in the Turkish folk medicine for the treatment of number of disorders. The present study describes the hepatoprotective and antioxidant activities of the RJ against carbon tetrachloride (CCl(4))-induced acute liver damage. Sprague-Dawley rats were used for the experiment. CCl(4) (0.8 ml/kg; s.c.) and RJ (50, 100, 200mg/kg; orally) were given every other day, for 20 days. Malondialdehyde, reduced glutathione in whole blood and tissues; ceruloplasmin, sialic acid, ascorbic acid, retinol, β-carotene and liver enzymes levels in serum were measured. Additionally, histopathological alterations in the liver were examined. RJ exerted the significant protective effect on liver damage as well as on oxidative stress induced by CCl(4), resulting in reduced lipid peroxidation and improved endogenous antioxidant defence systems. It also reduced the elevated levels of liver enzymes. Histopathological study further confirmed the hepatoprotective effect of RJ, when compared with the CCl(4) treated control groups. In conclusion, present study reveals biological evidence that supports the use of RJ in the treatment of chemical-induced hepatotoxicity.

Sialic acid modification of adiponectin is not required for multimerization or secretion but determines half-life in circulation

Adiponectin is an adipocyte-secreted, insulin-sensitizing hormone the circulating levels of which are reduced in conditions of insulin resistance and diabetes. Previous work has demonstrated the importance of posttranslational modifications, such as proline hydroxylation and lysine hydroxylation/glycosylation, in adiponectin oligomerization, secretion, and function. Here we describe the first functional characterization of adiponectin sialylation. Using a variety of biochemical approaches we demonstrated that sialylation occurs on previously unidentified O-linked glycans on Thr residues of the variable domain in human adiponectin. Enzymatic removal of sialic acid or its underlying O-linked sugars did not affect adiponectin multimer composition. Expression of mutant forms of adiponectin (lacking the modified Thr residues) or of wild-type adiponectin in cells defective in sialylation did not compromise multimer formation or secretion, arguing against a structural role for this modification. Activity of desialylated adiponectin was comparable to control adiponectin in L6 myotubes and acute assays in adiponectin(-/-) mice. In contrast, plasma clearance of desialylated adiponectin was accelerated compared with that of control adiponectin, implicating a role for this modification in determining the half-life of circulating adiponectin. Uptake of desialylated adiponectin by isolated primary rat hepatocytes was also accelerated, suggesting a role for the hepatic asialoglycoprotein receptor. Finally, after chronic administration in adiponectin(-/-) mice steady-state levels of desialylated adiponectin were lower than control adiponectin and failed to recapitulate the improvements in glucose and insulin tolerance tests observed with control adiponectin. These data suggest an important role for sialic acid content in the regulation of circulating adiponectin levels and highlight the importance of understanding mechanisms regulating adiponectin sialylation/desialylation.