Serum sialic acid concentration is elevated in IDDM especially in early diabetic nephropathy

Bioactives of Momordica charantia as Potential Anti-Diabetic/Hypoglycemic Agents

Momordica charantia L., a member of the Curcubitaceae family, has traditionally been used as herbal medicine and as a vegetable. Functional ingredients of M. charantia play important roles in body health and human nutrition, which can be used directly or indirectly in treating or preventing hyperglycemia-related chronic diseases in humans. The hypoglycemic effects of M. charantia have been known for years. In this paper, the research progress of M. charantia phytobioactives and their hypoglycemic effects and related mechanisms, especially relating to diabetes mellitus, has been reviewed. Moreover, the clinical application of M. charantia in treating diabetes mellitus is also discussed, hoping to broaden the application of M. charantia as functional food.

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.

Effect of Non-Surgical Periodontal Therapy on the Serum Sialic Acid Levels in Diabetic Patients with Periodontitis

Sialic acid (SA), a family of acetylated derivatives of neuraminic acid, an acute phase reactant by itself. It usually occurs as a terminal component at the non-reducing end of carbohydrate chains of glycoproteins and glycolipids. SA participates in multiple physiological functions, such as cell-to-cell interactions, cell migration and proliferation. Diabetes mellitus (DM) is a chronic metabolic disorder characterized by rise in blood glucose level. Periodontitis is a chronic inflammatory disease of the periodontal tissue, leading to destruction of bone surrounding the tooth and ultimately tooth loss. There is a two way relationship between diabetes mellitus and periodontitis. Periodontitis is the sixth complication of diabetes along with retinopathy, nephropathy, neuropathy, macrovascular disease, and altered wound healing. Inflammatory mediators like interleukin-6 and tumor necrosis factor-alpha produced during periodontal inflammation can interfere with the actions of insulin receptors and worsen the glycemic control of diabetic patients. Periodontitis is a major cause of tooth loss, affecting over 300 million people and bacteria associated with periodontitis are also linked with systemic problems like endocarditis, atherosclerosis. Recent work has highlighted a major role for the host sugar sialic acid in the biofilm physiology and host-pathogen interactions of T. forsithya, a key periodontal pathogen. There exists a need for a biomarker, for early detection of disease evolution and more robust therapy efficacy measurements. Serum sialic acids were estimated in Indian population by diphenylamine method and Thiobarbituric acid method. The average values were 68 ± 2.6 mg percent by DPA method and 56 ± 5 mg percent by TBA (thiobarbituric acid assay) method. Age and sex showed no influence on serum sialic acid level. Objectives of the present study was to compare (TSSA) level in healthy subjects, subjects with (CMP) with and without (NIDDM) and its effect on non-surgical periodontal therapy. In the present study, the participants were divided into three groups: Group A, B and C. Group A consists of systemically healthy subjects, Group B consists of subjects with (CMP) while Group C consists of subjects with (CMP) with (NIDDM) and results of this study indicated that, at baseline, there were significant differences between Group A, B and Group C with respect to all the clinical parameters, including (GI), (OHI-S), (PPD), (CAL), (TSSA) and (HbA1c) levels. Thus (TSSA) level could be considered as novel biomarker in the progression of periodontal disease and diabetic status. Periodontitis could be considered as a potential, modifiable, and independent risk factor for the development of diabetes. Early detection of elevated (TSSA) level may help in interpreting the progression of periodontitis, risk of development of diabetes mellitus in future and also to prevent complications.

Glycosylation of human plasma lipoproteins reveals a high level of diversity, which directly impacts their functional properties

AIMS

Human plasma lipoproteins are known to contain various glycan structures whose composition and functional importance are starting to be recognized. We assessed N-glycosylation of human plasma HDL and LDL and the role of their glycomes in cellular cholesterol metabolism.

METHODS

N-glycomic profiles of native and neuraminidase-treated HDL and LDL were obtained using HILIC-UHPLC-FLD. Relative abundance of the individual chromatographic peaks was quantitatively expressed as a percentage of total integrated area and N-glycan structures present in each peak were elucidated by MALDI-TOF MS. The capacity of HDL to mediate cellular efflux of cholesterol and the capacity of LDL to induce cellular accumulation of cholesteryl esters were evaluated in THP-1 cells.

RESULTS

HILIC-UHPLC-FLD analysis of HDL and LDL N-glycans released by PNGase F resulted in 22 and 18 distinct chromatographic peaks, respectively. The majority of N-glycans present in HDL (~70%) and LDL (~60%) were sialylated with one or two sialic acid residues. The most abundant N-glycan structure in both HDL and LDL was a complex type biantennary N-glycan with one sialic acid (A2G2S1). Relative abundances of several N-glycan structures were dramatically altered by the neuraminidase treatment, which selectively removed sialic acid residues. Native HDL displayed significantly greater efficacy in removing cellular cholesterol from THP-1 cells as compared to desialylated HDL (p < 0.05). Cellular accumulation of cholesteryl esters in THP-1 cells was significantly higher after incubations with desialylated LDL particles as compared to native LDL (p < 0.05).

CONCLUSIONS

N-glycome of human plasma lipoproteins reveals a high level of diversity, which directly impacts functional properties of the lipoproteins.

Elevated Serum Sialic Acid Levels Predict Prostate Cancer As Well As Bone Metastases

Objective: To evaluate the value of serum sialic acid (SA) in diagnosis of benign prostatic hyperplasia (BPH), prostate cancer (PCa), and bone metastases in PCa patients. Materials and Methods: Data from 540 patients who were newly diagnosed with PCa or BPH between November 2014 and March 2018 were retrospectively collected and analyzed. Pretreatment SA levels were compared across various groups, then, associations between SA levels and clinic parameters of patients were analyzed as well. Univariate and multivariate logistic regression analyses were further used to identify independent associations. Results: The mean SA levels in patients with PCa were significantly higher than with BPH (p = 0.013). Furthermore, PCa patients with bone metastases showed elevated SA levels compared with PCa without bone metastases (p < 0.001). A multivariate logistic regression model showed that: SA level > 52.35 mg/dL was identified to be independently associated with the diagnosis of PCa (HR = 1.645, p = 0.036), and SA level > 59 mg/dL was identified to be independent association with the presence of bone metastases in PCa patients (HR = 6.421, p = 0.012). Conclusions: Elevated SA level is an independent predictor of prostate cancer as well as its bone metastases. Therefore, SA level may be a promising diagnostic and prognostic biomarker for prostate cancer and bone metastases.

Sialic acid supplementation ameliorates puromycin aminonucleoside nephrosis in rats

Defects in sialylation are known to have serious consequences on podocyte function leading to collapse of the glomerular filtration barrier and the development of proteinuria. However, the cellular processes underlying aberrant sialylation in renal disease are inadequately defined. We have shown in cultured human podocytes that puromycin aminonucleoside (PAN) downregulates enzymes involved in sialic acid metabolism and redox homeostasis and these can be rescued by co-treatment with free sialic acid. The aim of the current study was to ascertain whether sialic acid supplementation could improve renal function and attenuate desialylation in an in vivo model of proteinuria (PAN nephrosis) and to delineate the possible mechanisms involved. PAN nephrotic rats were supplemented with free sialic acid, its precursor N-acetyl mannosamine or the NADPH oxidase inhibitor apocynin. Glomeruli, urine, and sera were examined for evidence of kidney injury and therapeutic efficacy. Of the three treatment regimens, sialic acid had the broadest efficacy in attenuating PAN-induced injury. Proteinuria and urinary nephrin loss were reduced. Transmission electron microscopy revealed that podocyte ultrastructure, exhibited less severe foot process effacement. PAN-induced oxidative stress was ameliorated as evidenced by a reduction in glomerular NOX4 expression and a downregulation of urine xanthine oxidase levels. Sialylation dysfunction was improved as indicated by reduced urinary concentrations of free sialic acid, restored electrophoretic mobility of podocalyxin, and improved expression of a sialyltransferase. These data indicate that PAN induces alterations in the expression of enzymes involved in redox control and sialoglycoprotein metabolism, which can be ameliorated by sialic acid supplementation possibly via its properties as both an antioxidant and a substrate for sialylation.

Correlation between sialic acid levels in the synovial fluid and the radiographic severity of knee osteoarthritis

Osteoarthritis (OA) is associated with the presence of inflammation. Sialic acid (SA), an acetylated derivative of neuraminic acid, is reported to be a useful biomarker of inflammation. The aim of the present study was to investigate the correlation between SA levels in the serum and synovial fluid (SF) and radiographic severity in patients with knee OA. A total of 234 patients with knee OA were recruited for the study, as well as 20 patients that had suffered a knee injury or fracture (without knee OA) and 160 healthy controls. Radiological grading of OA in the knee was conducted according to the Kellgren-Lawrence (KL) grading system. SA levels in the serum and SF were measured using Warren’s thiobarbituric acid assay. The results demonstrated that knee OA patients exhibited significantly elevated levels of serum SA when compared with the healthy controls, and also significantly elevated levels of SF SA when compared with the knee fracture patients. Higher SA levels in the SF were identified in knee OA patients with KL grade 4 as compared with patients with KL grade 2 or 3. In addition, OA patients of KL grade 3 had significantly higher SA levels in the SF as compared with patients with KL grade 2 (P<0.01). The SA levels in the SF of the knee OA patients positively correlated with the KL grades (r=0.353; P<0.01). However, there was no significant correlation identified between serum SA levels and KL grade. Therefore, SA levels in the SF positively correlated with the radiographic severity of OA, thus, SA levels in the SF may serve as a biomarker for the progression of OA.

Significance of serum and urine neuraminidase activity and serum and urine level of sialic acid in diabetic nephropathy

BACKGROUND

Prospective studies have reported associations among various markers of inflammation and the incidence of diabetes, and it has been proposed that inflammation has a causal role in the development of diabetes. The objective of this study was to investigate the significance of serum and urine neuraminidase activity (NA) and serum and urine sialic acid (SA) level in patients with Diabetic nephropathy.

METHODS

In a prospective study, 190 diabetic patients with established diabetic nephropathy, 30 type 2 diabetes patients without any diabetic related nephropathy, and 36 non-diabetic patients with diagnosed nephropathy were enrolled. Two hundred and forty healthy individuals without diabetes or kidney disease were also enrolled as control group. Fasting venous blood samples and urine samples were collected and checked for serum and urine NA and SA level.

RESULTS

In the diabetic nephropathy group, the mean value of serum and urine NA was 64.6 ± 2.6 and 11.7 ± 1.2 mU/ml, respectively, and mean values of serum and urine SA were 93.2 ± 3.6 and 17.7 ± 1.4 mg/dl, respectively. Serum and urine NA and SA levels were significantly higher in patient with diabetic nephropathy when compared to the other groups (P < 0.001).

CONCLUSIONS

Our study suggests that there is a strong association between elevated serum and urine NA and serum and urine SA levels with the presence of diabetic nephropathy in type 2 diabetic patients. Further investigations are needed on the diagnostic and prognostic significance of these two inflammatory markers.

Malondialdehyde Content and Circadian Variations in Brain, Kidney, Liver, and Plasma of Mice

In aerobic organisms, the use of oxygen (O(2)) to produce energy is associated with the production of Reactive Oxygen Species (ROS), which reacts with biological molecules to produce oxidized metabolites such as malondialdehyde (MDA). This experiment focused on male Swiss mice 12 weeks of age synchronized for 3 weeks by the 12 h light (rest)/12 h dark (activity) span. Different and comparable groups of animals (n=10) were sacrificed at six different circadian stages: 1, 5, 9, 13, 17, and 21 h after light onset (HALO). The 24 h mean MDA level varied among organs of mice in non-stress conditions and was comparable in brain and liver but lower than in kidney. As the MDA 24 h status constitutes only a part of ROS damages in sites differing by their oxygen use, lipid composition, and detoxification capacity, the temporal patterns of their MDA content were comparatively studied in relationship to the animal rest-activity cycle. The results revealed significant circadian rhythms with the peak time located during the rest span (approximately =5 HALO) for both brain and liver, but during the activity span for the kidney ( approximately =21 HALO) and plasma (approximately =13 HALO). This chronobiological study showed that under physiological conditions, lipid peroxidation depends on several factors. The MDA peak/trough might be used as a tool to detect moments of high/low sensitivity of tissues to ROS attack in rodents.

Serum sialic acid changes in non-insulin-dependant diabetes mellitus (NIDDM) patients following bitter melon (Momordica charantia) and rosiglitazone (Avandia) treatment

Diabetes mellitus is associated with an increase in sialic acid concentration along with other complications. Sialic acid changes in NIDDM patients were investigated following bitter melon (55 ml/24h) and rosiglitazone (4 mg/24h) treatment. A total of 25 patients of both sexes were used in each experimental group. Patients following bitter melon treatment showed no significant difference of serum sialic acid (57.95+/-4.90 vs. 57.6+/-5.56 mg/dl, p=0.17) and serum glucose concentration (93.7+/-9.63 vs. 88.35+/-6.31 mg/dl, p=0.78) as compared to control subjects. However, the concentration of total cholesterol was significantly high in these patients as compared to control subjects (192+/-14.23 vs. 170.6+/-15.1mg/dl, p<0.03) but within normal range (160-200mg/dl), suggesting the significant hypoglycemic and lipid-lowering properties of bitter melon. The patients following rosiglitazone treatment showed a significant increase of serum sialic acid concentration (60.2+/-5.80 vs. 57.6+/-5.56 mg/dl, p=0.01) along with glucose (112+/-6.2 vs. 88.35+/-6.31 mg/dl, p<0.04) and total cholesterol concentration (216.45+/-20.2 vs. 170.6+/-15.1mg/dl, p<0.01) as compared to control subjects. In addition six of the patients had retinopathy, two of whom were suffering also from myocardial infarction and they still had a higher serum sialic acid (61.05+/-1.20mg/dl), glucose (187+/-2.11 mg/dl), total cholesterol (239.10+/-5.04 mg/dl) and triglyceride (183+/-4.14 mg/dl) concentration, indicating a poor response of these patients to rosiglitazone. Comparison of serum sialic acid concentration of patients, following bitter melon and rosiglitazone treatment revealed no significant difference but the study showed that bitter melon could be more effective in the management of diabetes and its related complications as compared to rosiglitazone.

Relationship between plasma sialic acid and fibrinogen concentration and incident micro- and macrovascular complications in type 1 diabetes. The EURODIAB Prospective Complications Study (PCS)

AIMS/HYPOTHESIS

Type 1 diabetes is associated with an increased risk of vascular complications. This increased risk could be explained by sialic acid and/or fibrinogen. It is also not clear what explains the abolition of sex-related differences affecting risk of CHD in the presence of type 1 diabetes. Therefore, we examined whether fibrinogen and sialic acid are related to incident micro- and macrovascular complications in patients with type 1 diabetes.

METHODS

A subset (n=2329) of the EURODIAB Prospective Complications Study was analysed. Sialic acid and fibrinogen concentrations were measured at baseline. The main outcomes after 7 years were development of albuminuria, retinopathy, neuropathy and CHD.

RESULTS

Univariable and multivariable models using Cox proportional survival analyses showed that an SD unit increase in sialic acid and fibrinogen levels was significantly associated with CHD in men only. Adjusted standardised hazard ratios (sHRs) were 1.50 (95% CI 1.05-2.15) and 1.40 (95% CI 1.06-1.86) for sialic acid and fibrinogen, respectively. Initial associations between (1) sialic acid and incident retinopathy [standardised odds ratio (sOR) men 1.68, 95% CI 1.10-2.57], (2) fibrinogen and retinopathy (sOR women 1.37, 95% CI 1.06-1.78) and (3) sialic acid and neuropathy (sOR men 1.37, 95% CI 1.06-1.77) were shown, but became non-significant in multivariable models.

CONCLUSIONS/INTERPRETATION

Sialic acid and fibrinogen are strong predictors of CHD in men with type 1 diabetes, beyond the effect of established risk factors. The associations found with microvascular complications were not independent of other risk factors.

Serum level of sialic acid (SA) and carbohydrate-deficient transferrin (CDT) in type 2 diabetes mellitus with microvascular complications

Sialic acid (SA) is responsible for the composition of different isoforms of transferrin and is reported to be a marker of microvascular complications in type 2 diabetes mellitus. Therefore, we explored the serum concentration of SA, and the less sialylated isoforms of transferrin, termed carbohydrate-deficient transferrin (CDT), in relation to the presence of microvascular complications in type 2 diabetes mellitus. We studied 21 patients with type 2 diabetes with microangiopathy and 22 patients without complications who were hospitalized at a diabetic clinic. The prevalence of microvascular complications was based on clinical history, fundoscopy, and laboratory tests. Blood samples were taken for measurements of SA, CDT, total transferrin, glucose, HbA1c, fibrinogen, C-reactive protein (CRP), and indicators of renal dysfunction (i.e., creatinine, urea, albumin excretion rate (AER), and glomerular filtration rate (GFR)). A rise in serum SA and a decrease in CDT concentrations were observed in both diabetic groups with and without complications, and there were no differences between the two groups of patients. There was a statistically significant correlation between serum SA and CDT in diabetic subjects with microvascular complications, but not in patients without such complications. This proves that the serum changes in CDT and SA levels in the course of type 2 diabetes mellitus are associated with each other in the presence of microangiopathy.

Relationship between sialic acid and metabolic variables in Indian type 2 diabetic patients

Background

Plasma sialic acid is a marker of the acute phase response. Objective is to study the relationship between sialic acid relationship with metabolic variables in Indian type 2 diabetes with and without microvascular complications.

Research design and Methods

Fasting Venous blood samples were taken from 200 subjects of which 50 were of diabetes mellitus (DM) and nephropathy patients, 50 patients with type 2 diabetes and retinopathy, 50 patients with type 2 diabetes without any complications and 50 healthy individuals without diabetes. The Indian subject's aged 15–60 years with type 2 diabetes were recruited for the study. Simultaneously urine samples were also collected from each of the subjects. All the blood samples were analyzed for total cholesterol, triglyceride (TG), low-density lipoprotein (LDL), high-density lipoprotein (HDL), fasting and postprandial glucose on fully automated analyzer. Serum and urine sialic acid along with microalbumin levels were also estimated.

Results

There was a significantly increasing trend of plasma and urine sialic acid with severity of nephropathy (P < 0.001) and with degree of urinary albumin excretion (P < 0.001). Serum sialic acid correlated with increasing serum creatinine concentration (P < 0.001). Elevated serum sialic acid concentrations were also associated with several risk factors for diabetic vascular disease: diabetes duration, HbA₁c, serum triglyceride and cholesterol concentrations, waist-to-hip ratio and hypertension. Significant correlations were found between sialic acid concentration and cardiovascular risk factors like LDL and TG in the diabetic subjects.

Conclusion

The main finding of this study is that elevated serum and urinary sialic acid and microalbumin concentrations were strongly related to the presence of microvascular complications like diabetic nephropathy and retinopathy and cardiovascular risk factors in Indian type 2 diabetic subjects. Further study of acute-phase response markers and mediators as indicators or predictors of diabetic microvascular complications is therefore justified.

Age-dependent relation of serum sialic acid concentration to aortic pulse wave velocity in type 2 diabetes

OBJECTIVE

The purpose of this study was to determine whether age affects the significance of serum sialic acid concentration as a marker of atherosclerosis in patients with diabetes.

METHODS

In this cross-sectional study, we investigated the relationship of serum sialic acid concentration to aortic pulse wave velocity (a-PWV) and the effects of age on this relationship in patients with type 2 diabetes.

RESULTS

In the elderly (70 years or over) diabetic patients, a-PWV showed a significant positive correlation with serum sialic acid. This relationship was also significant after adjustment for age, duration of diabetes, body mass index, systolic blood pressure, LDL cholesterol, HDL cholesterol and fibrinogen levels. In elderly diabetic patients, a-PWV also showed a significant positive correlation with age and duration of diabetes and a significant negative correlation with serum HDL cholesterol level. On the other hand, in the younger (31-60 years) diabetic patients, there was no significant correlation between serum sialic acid level and a-PWV, while a-PWV showed significant positive correlations with age, duration of diabetes and plasma fibrinogen level.

CONCLUSIONS

Serum sialic acid level reflects atherosclerosis in elderly diabetic patients but not in younger diabetic patients. This may explain recent controversial findings regarding the relationship between serum sialic acid level and incidence of coronary heart disease in diabetes.

Association of serum sialic acid with cardiovascular metabolic risk factors in Kuwaiti children and adolescents with type 1 diabetes

The aim of the present study was to investigate the relation of serum total sialic acid (TSA) concentrations with cardiovascular metabolic risk factors in Kuwaiti children and adolescents with uncomplicated type 1 diabetes. This case-control study included 150 (57 males and 93 females) type 1 diabetic children aged 6 to 18 years matched by age and sex to 150 nondiabetic children as controls. Measured variables included weight, height, systolic, diastolic blood pressure, and biochemical variables: blood glucose, glycated hemoglobin (HbA(1C)), triglycerides (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL), apolipoproteins (apo) A1 and B, and urine microalbumin. There was no significant difference between mean serum TSA of the type 1 diabetic children (671.0 mg/L) and their controls (663.7 mg/L). In diabetic children, mean serum TSA was significantly higher in females (699.1 mg/L) than in males (625.2 mg/L) (P =.003). Significant correlations were found between serum TSA and the cardiovascular risk factors TC (P =.002), TG (P <.001), and apo B (P =.008). TSA mean level was significantly higher in diabetic children with poor glycemic control (HbA(1C) > 9.0%; P =.015), raised TC (P =.013), raised TG (P =.014), and in children with family history of cardiovascular disease (CVD; P =.02). In conclusion, the study suggests that serum TSA levels were not elevated in young type 1 diabetic children as compared with controls. The study also confirmed significant correlation of TSA concentrations with CVD risk factors TC, TG, and apo B, and as such serum TSA may be considered as a marker for CVD risk, especially in diabetic patients. A long-term prospective study is recommended to ascertain the longitudinal relationship of serum TSA with the adverse metabolic changes in type 1 diabetic children as complications prevail.

Relation of serum sialic acid to blood coagulation activity in type 2 diabetes

The level of serum sialic acid, which is known to reflect atherosclerotic progress and to be related to the incidence of cardiovascular diseases, is increased in patients with diabetes. To elucidate the mechanism of the relation of serum sialic acid to fibrinogen, the relationship between serum sialic acid and markers of blood coagulation activity was investigated in type 2 diabetic patients. The concentration of serum sialic acid showed significant positive correlations with blood platelet count and with plasma concentrations of fibrinogen, D-dimer, thrombin-antithrombin III complex and plasmin-alpha2 plasmin inhibitor complex. These relationships were still significant after adjustment for age, sex, smoking history, body mass index, hemoglobin A, mean arterial pressure and low-density lipoprotein cholesterol. The correlation coefficient of blood fibrinogen with serum sialic acid was still significant after adjustment for D-dimer, thrombin-antithrombin III complex or plasmin-alpha2 plasmin inhibitor complex. On the contrary, blood fibrinogen showed no significant correlation with D-dimer, thrombin-antithrombin III complex or plasmin-alpha2 plasmin inhibitor complex, although an increase in blood fibrinogen is known to be an atherosclerotic risk factor. These results suggest that the serum sialic acid level reflects blood coagulation activity in type 2 diabetic patients and is related to blood fibrinogen level independently of blood coagulation activity.

Association between serum total and lipid-bound sialic acid concentration and the severity of coronary atherosclerosis

Serum total sialic acid has recently been shown to be a cardiovascular risk factor. Increased levels of this substance are associated with higher cardiovascular mortality and with cerebrovascular disease. It has also been shown that serum concentrations of total and lipid-associated sialic acid are significantly increased in hypertriglyceridemia. On the other hand, several circulating lipoproteins have been suggested to be related to the severity of coronary atherosclerosis, but contradictory results have been reported in the possible relationship between the concentrations of sialic acid and the severity of coronary lesions in patients with coronary heart disease. The purpose of this study was to investigate the possible relationship between serum total sialic acid concentration, recently shown to be a cardiovascular risk factor, and serum lipid-bound sialic acid concentration and the severity of coronary lesions. The study comprised 90 subjects, divided into three subgroups according to angiography results: 30 patients with no vessel disease, 30 patients with single-vessel disease, and 30 patients with double/triple-vessel disease. Serum total sialic acid determination was carried out with the thiobarbituric acid method of Warren; lipid-associated sialic acid was assayed with the method of Katopodis. Mean serum total sialic acid levels in patients with single-vessel disease (P <.05) and patients with double/triple-vessel disease (P <.001) were found to be significantly increased compared with that in patients with no vessel disease, whereas mean serum lipid-bound sialic acid levels were found to be significantly different between patients with double- or triple-vessel disease and patients with no vessel disease (P <.001). We also noted a significant difference between the levels of serum total sialic acid (P <.001) and lipid-bound sialic acid (P <.001) in patients with single-vessel disease and patients with double/triple-vessel disease. We found a significant correlation only between serum lipid-bound sialic acid and coronary angiographic score in patients with double/triple-vessel disease (r = 0.425, P <.05). Although the concentration of serum total sialic acid is increased proportionally with the number of diseased coronary arteries, only the concentration of serum lipid-bound sialic acid is related to the severity of coronary atherosclerosis, especially in patients with double/triple-vessel disease.

The response of serum sialic acid and other acute phase reactants to an oral fat load in healthy humans

BACKGROUND

Elevated serum total sialic acid (TSA) has been shown to be associated with increased cardiovascular mortality. It has been postulated that atherogenesis is a postprandial phenomenon. We tested the hypothesis that serum TSA and other acute phase proteins, namely C-reactive protein (CRP) and fibrinogen, may be related to the postprandial state.

METHODS

Ten healthy male subjects, aged 24-48 years, were fed 62.5 g of total fat (saturates 12 g, monounsaturates 35.3 g and polyunsaturates 12.5 g) in the form of strawberry flavoured Calogen. Venous blood was sampled hourly for 5 h. Concentrations of serum triglyceride, TSA and acute phase proteins were measured.

RESULTS

Serum triglyceride concentration increased postprandially, peaking at 240 min. Serum CRP and plasma fibrinogen did not significantly increase after the oral fat load. However, serum TSA did increase from baseline (0.599+/-0.051 g/l) in response to the oral fat load, peaking at 120 min post-oral fat load (0.633+/-0.066 g/l, P<0.02). There was a significant correlation between serum TSA and plasma fibrinogen at baseline (rho=0.62, P=0.05) but not for serum CRP (rho=-0.22) or triglyceride (rho=0.21).

CONCLUSIONS

We conclude that serum TSA increases postprandially and this finding gives further insight as to why the former is considered to be a cardiovascular risk factor.

Hyperglycemia-induced production of acute phase reactants in adipose tissue

Chronic elevation of systemic levels of acute phase reactants and inflammatory cytokines found in patients with diabetes and the often-associated metabolic syndrome X (hypertriglyceridemia, low serum high density lipoprotein cholesterol, hypertension, and accelerated atherosclerosis) may be responsible for the increased incidence of cardiovascular problems in this population. Here we examine the contribution of adipose tissue to the systemic elevation of acute phase reactants associated with chronic hyperglycemia. We demonstrate that adipose tissue expresses a number of acute phase reactants at high levels, including serum amyloid A3 (SAA3), alphal-acid glycoprotein, the lipocalin 24p3 as well as plasminogen activator inhibitor-1 (PAI-1). Additionally, we show SAA3 is expressed at low levels under normal conditions but in the diabetic state is dramatically up-regulated in adipose tissue while down-regulated in liver. Furthermore, pro-inflammatory stimuli and high glucose can lead to the induction of SAA3 in adipose tissue in vivo as well as in the 3T3-L1 adipocyte cell line. Adipose tissue may therefore play a major role in the pathogenic sequelae of Type II diabetes, in particular the cardiovascular problems associated with prolonged hyperglycemia.

Reaction conditions affecting the relationship between thiobarbituric acid reactivity and lipid peroxides in human plasma

The thiobarbituric acid (TBA) reactivity of human plasma was studied to evaluate its adequacy in quantifying lipid peroxidation as an index of systemic oxidative stress. Two spectrophotometric TBA tests based on the use of either phosphoric acid (pH 2.0, method A) or trichloroacetic plus hydrochloric acid (pH 0.9, method B) were employed with and without sodium sulfate (SS) to inhibit sialic acid (SA) reactivity with TBA. To correct for background absorption, the absorbance values at 572 nm were subtracted from those at 532 nm, which represent the absorption maximum of the TBA:MDA adduct. Method B gave values of TBA-reactive substances (TBARS) 2-fold higher than those detected with method A. SS lowered TBARS by about 50% with both methods, indicating a significant involvement of SA in plasma TBA reactivity. Standard SA, at a physiologically relevant concentration of 1.5 mM, reacted with TBA, creating interference problems, which were substantially eliminated by SS plus correction for background absorbance. When method B was carried out in the lipid and protein fraction of plasma, SS inhibited by 65% TBARS formation only in the latter. Protein TBARS may be largely ascribed to SA-containing glycoproteins and, to a minor extent, protein-bound MDA. Indeed, EDTA did not affect protein TBARS assessed in the presence of SS. TBA reactivity of whole plasma and of its lipid fraction was instead inhibited by EDTA, suggesting that lipoperoxides (and possibly monofunctional lipoperoxidation aldehydes) are involved as MDA precursors in the TBA test. Pretreatment of plasma with KI, a specific reductant of hydroperoxides, decreased TBARS by about 27%. Moreover, aspirin administration to humans to inhibit prostaglandin endoperoxide generation reduced plasma TBARS by 40%. In conclusion, reaction conditions affect the relationship between TBA reactivity and lipid peroxidation in human plasma. After correction for the interfering effects of SA in the TBA test, 40% of plasma TBARS appears related to in vivo generated prostaglandin endoperoxides and only about 60% to lipoperoxidation products. Thus, the TBA test is not totally specific to oxidant-driven lipid peroxidation in human plasma.

Relationship between plasma sialic acid concentration and microvascular and macrovascular complications in type 1 diabetes: the EURODIAB Complications Study

OBJECTIVE

To test the hypothesis that an increased plasma concentration of sialic acid, a marker of the acute-phase response, is related to the presence of diabetic micro- and macrovascular complications in type 1 diabetes.

RESEARCH DESIGN AND METHODS

We investigated the relationship between plasma sialic acid concentration and nephropathy, retinopathy, neuropathy, and coronary heart disease (CHD) in a cross-sectional survey of 1,369 people with type 1 diabetes. Subjects were participants in the EURODIAB IDDM Complications Study, which involved 31 centers in 16 European countries.

RESULTS

There was a significantly increasing trend of plasma sialic acid with severity of retinopathy (P < 0.001 in men) and with degree of urinary albumin excretion (P < 0.001 men, P < 0.01 women). Plasma sialic acid correlated with increasing plasma creatinine concentration (P < 0.009 men, P < 0.0002 women), and men with neuropathy had a higher plasma sialic acid concentration than those without (P < 0.006). There was no significant correlation between plasma sialic acid and CHD in either sex. Elevated plasma sialic acid concentrations were also associated with several risk factors for diabetic vascular disease: diabetes duration, HbA1c, plasma triglyceride and cholesterol concentrations, waist-to-hip ratio, hypertension and smoking (in men), and low physical exercise (in women). In multiple logistic regression analysis, plasma sialic acid was independently related to proliferative retinopathy and urinary albumin excretion rate in men.

CONCLUSIONS

We conclude that an elevated plasma sialic concentration is strongly related to the presence of microvascular complications in type 1 diabetes, especially retinopathy and nephropathy. Further study of acute-phase response markers and mediators as indicators or predictors of diabetic microvascular complications is therefore justified.

Serum total and lipid-bound sialic acid levels following acute myocardial infarction

Although serum total sialic acid has been shown to be a cardiovascular risk factor, with elevated levels associated with increased cardiovascular mortality and also with cerebrovascular disease, the reason for the elevation in serum sialic acid content remains obscure. It has been shown that an increased output of serum proteins by the liver due to some type of acute phase reaction may be one of the possible sources of an increased serum sialic acid concentration in patients with myocardial infarction. An increase in the activity of sialidase, which cleaves the terminal sialic acid residues from oligosaccharides, glycoproteins and gangliosides, may also play an important role in the elevation of serum total sialic acid in myocardial infarction. Elevated serum total sialic acid in the blood might result either from the shedding or secreting of sialic acid from the cell membrane surface, or releasing of cellular sialic acid from the cell into the bloodstream due to cell damage after myocardial infarction. The purpose of the present study is to investigate serum total and lipid-bound sialic acid and the enzymes serum lactate dehydrogenase, creatine kinase and aspartate aminotransferase in patients with acute myocardial infarction, at 24 h post-infarction (day 1), 48 h post-infarction (day 2) and 72 h post-infarction (day 3). A possible role of cell damage in the elevation of serum total and lipid-bound sialic acid levels in these patients was also evaluated. In this study, 40 patients with myocardial infarction ranging in age from 42 to 68 years, and 26 healthy volunteers ranging in age from 45 to 71 years were included. Serum total sialic acid determination was carried out by the thiobarbituric acid method of Warren and lipid-bound sialic acfd by the method of Katopodis. Our data shows that a) there is a gradual increase in the levels of serum total sialic acid and lipid-bound sialic acid during the first three days after the acute myocardial infarction and b) the elevation in serum total sialic acid levels correlates with the elevation in lactate dehydrogenase activity only on day 1 following infarction. Therefore, either the shedding or secreting of sialic acid from the cell or cell membrane surface may be partly responsible for an increased serum sialic acid concentration especially on day 1 following myocardial infarction.

Relation of serum total sialic acid concentrations with diabetic complications and cardiovascular risk factors in Kuwaiti Type 2 diabetic patients

Serum total sialic acid is a marker of the acute phase response. Elevated levels have also been associated with cardiovascular disease in the general Caucasian population and especially in Type 2 diabetic subjects. The purpose of this study was to estimate serum total sialic acid concentrations among Kuwaiti Type 2 diabetic subjects and to investigate its association with macro and microvascular diabetes-related complications in that population. Serum total sialic acid levels were estimated by an enzymatic spectro-photometric assay in two groups of subjects: (i) 358 Kuwaiti Type 2 diabetics (156 men and 202 women) referred for their annual evaluation to the specialised diabetic clinic at the main university teaching hospital in Kuwait, and (ii) 47 healthy age and sex matched non-diabetic Kuwaiti control population (13 men and 34 women). Serum sialic acid levels were significantly higher (P<0.001) among the diabetic patients (mean+/-S.D.) (81.2+/-13.2 mg/dl) compared to the non-diabetic controls (66.9+/-11.0 mg/dl). Kuwaiti diabetic women had significantly higher concentrations compared to diabetic men (85.2+/-12.1 vs. 75.9+/-13.0 mg/dl, P<0.001). Among the controls there was no significant gender difference in sialic acid levels of women, (68.3+/-11.6 mg/dl) versus men (63.2+/-8.2 mg/dl). The gender difference in the diabetic patients was unrelated to the degree of obesity. Significant correlations were found between serum total sialic acid concentrations and such cardiovascular risk factors as plasma levels of apolipoprotein B, low density lipoprotein cholesterol, triglycerides and uric acid in the diabetic subjects. Furthermore, there was a significant elevation in serum total sialic acid concentrations with increasing urinary albumin excretion, P<0.001, but not with retinopathy or neuropathy.

Age-related change in relationship between body-mass index, serum sialic acid, and atherogenic risk factors

In order to clarify the significance of obesity in atherosclerotic risk at different ages, the relationship between the body-mass index, serum sialic acid concentration, and various atherosclerotic risk factors were investigated for healthy subjects in three different age groups, 35-39, 40-49 and 50-59 years old. The body-mass index correlated significantly with mean arterial blood pressure, fasting blood sugar, serum triglycerides, atherogenic index and serum uric acid in all age groups. The magnitudes of the association of body-mass index with mean arterial blood pressure, fasting blood sugar and serum triglycerides decreased with age, while those of the association with atherogenic index and serum uric acid were not different among the three age groups. Body-mass index did not show significant correlation with white blood cell count, platelet count or smoking in any of the age groups. Simple and multiple regression analyses showed that body-mass index was significantly correlated with serum sialic acid in the 35-39-year-old group, but not in the other two groups. Neither the percentage of obese subjects (body-mass index > 26.4) nor the mean values of body-mass index were different among the three groups. These results suggest that for younger people, the body-mass index is related more closely with some atherosclerotic risk factors (e.g. blood pressure, blood sugar and serum triglycerides), and obesity may be possibly more involved in the progression of atherosclerosis, compared to more elderly people.

Serum sialic acid in young type-1 diabetic patients

It is well established that serum total sialic acid (TSA) is elevated in patients with type-2 diabetes mellitus (NIDDM) compared to non-diabetics. However, it is not clear whether serum TSA is also elevated in type-1 diabetic patients (IDDM). Twenty-one type-1 patients were studied along with age and sex matched normal non-diabetic subjects (ten males and 11 females). Their ages were 24.8+/-3.4 years (20-30) and 23.5+/-3.9 years (18-30) respectively. The duration of diabetes mellitus was 12.6+/-6.7 years (1-24) with a HBA1c of 9.0+/-2.2% (6.0-14.9). There was no significant difference in serum TSA of the type-1 diabetic patients 689+/-107 mg/l versus 670+/-119 mg/l in the normal subjects. Nor was there a significant correlation between serum TSA with patient age (r = -0.31), urine albumin/creatinine ratio (ACR) (r = 0.25), HBA1c (r = 0.36), plasma random glucose (r = -0.04) or diabetes duration (r = -0.09) in the diabetic patients. However, there was a significant correlation between serum TSA and mean daily insulin dose (r = 0.51, P<0.02) and also serum cholesterol and triglyceride (r = 0.58, P<0.01 and r = 0.49, P<0.04, respectively) in the type-1 diabetic patients. In summary, we conclude that serum TSA is not elevated in young type-1 diabetic patients compared with normal age and sex matched control subjects. However, the relationship between serum TSA and serum lipids and also mean daily insulin dose merits further research.

No difference in serum sialic acid in type 2 diabetic patients from the United Arab Emirates with and without diabetic retinopathy

Serum total sialic acid (TSA) has recently been shown to be related to diabetic retinopathy. However, there is some controversy as this may be true in European Type 2 diabetic patients but not South Asians. There are few data looking at serum TSA expression in Arab Type 2 diabetic patients from the United Arab Emirates (UAE) and we wished to test the hypothesis that there may be different serum TSA expression in Arab Type 2 diabetic patients as regard to retinopathy. Sixty-five Type 2 diabetic patients from the UAE were studied (19 male and 46 female, age 57.5+/-9.8 (45-74) years, duration of diabetes 9.4+/-5.7 (0-22) years. The serum TSA in 13 patients with diabetic retinopathy was 757+/-130 mg/l and 782+/-163 mg/l in those without retinopathy (NS). There was no significant correlation between serum TSA and patient age, serum fructosamine, diabetes duration, or blood pressure. As in South Asians serum TSA does not appear to be elevated in Type 2 diabetic patients from the United Arab Emirates with diabetic retinopathy.

Serum Sialic Acid in a Random Sample of the General Population

Background: The serum sialic acid (SA) concentration has been reported to be a potentially useful but nonspecific disease marker. We wanted to study which factors influence SA concentration in a well-characterized healthy population.

Methods: SA was determined in 97 women and 96 men with a colorimetric Warren method.

Results: The mean ± SD concentrations of SA were 634 ± 109 (95% confidence interval, 612–656) and 630 ± 106 (95% confidence interval, 608–651) mg/L for women and men, respectively. The serum SA showed a significant positive association with body mass index and with systolic and diastolic blood pressure among both women and men. SA also correlated significantly with the use of contraceptive pills and age among women and with smoking among men.

Conclusions: Our study suggests that SA does not increase with age in men but appears to increase with female menopause. The strong positive association with blood pressure may explain why SA predicts cardiovascular mortality.

Plasma sialic acid and coronary artery atheromatous load in patients with stable chest pain

Serum or plasma sialic acid and C-reactive protein have recently been shown to be cardiovascular risk factors. Our aim was to determine whether plasma sialic acid or C-reactive protein concentration correlate with atheromatous load on coronary angiography. Plasma sialic acid concentration and plasma C-reactive protein concentration were determined in 128 consecutive patients attending day case coronary angiography. Patients were excluded for previous coronary angioplasty, coronary artery bypass grafting, recent myocardial infarction, acute or chronic inflammatory disease and proximal occlusions precluding analysis of distal coronary anatomy. Total cholesterol, triglyceride, HDL cholesterol and glucose concentrations were assayed on fasting samples of venous blood. Angiograms were graded according to a semisubjective scoring system. There was no significant correlation between plasma sialic acid (r = 0.19, P = 0.07), or C-reactive protein concentration (r = 0.17, P = 0.13) and atheromatous load. There was no significant correlation between sialic acid (P = 0.13), or C-reactive protein concentration (P = 0.32) and the number of diseased coronary vessels. The difference in plasma sialic acid concentration between those with normal coronary angiograms and those with coronary artery disease did not reach significance (P = 0.08). Plasma sialic acid concentration correlated with C-reactive protein (r = 0.58, P = 0.0001), serum triglyceride (r = 0.32, P = 0.002), and blood cholesterol concentration (r = 0.22, P = 0.04). Plasma sialic acid concentration does not correlate with atheromatous load on coronary angiography in patients with stable angina.

Occurrence of sialic acids in healthy humans and different disorders

Sialic acid (SA), N-acetylated derivatives of neuraminic acid, play a central role in the biomedical functioning of humans. The normal range of total sialic acid (TSA) level in serum/plasma is 1.58-2.22 mmol L-1, the free form of SA only constituting 0.5-3 mumol L-1 and the lipid-associated (LSA) forms 10-50 mumol L-1. Notably, considerably higher amounts of free SA are found in urine than in serum/plasma (approximately 50% of the total SA). In inherited SA storage diseases such as Salla's disease, SA levels are elevated many times over, and their determination during clinical investigation is well established. Furthermore, a number of reports describe elevated SA levels in various other diseases, tentatively suggesting broader clinical utility for SA markers. Increased SA concentrations have been reported during inflammatory processes, probably resulting from increased levels of richly sialylated acute-phase glycoproteins. A connection between increased SA levels and elevated stroke and cardiovascular mortality risk has also been reported. In addition, SA levels are slightly increased in cancer, positively correlating with the degree of metastasis, as well as in alcohol abuse, diabetes, chronic renal failure and chronic glomerulonephritis. Several different mechanisms are assumed to underlie the elevated SA concentrations in these disorders. The apparent non-specificity of SA to a given disease limits the potential clinical usefulness of SA determination. In addition, some non-pathological factors, such as aging, pregnancy and smoking, may cause changes in SA concentrations. The absolute increases in SA levels are also rather small (save those in inherited SA storage disorders); this further limits the clinical potential of SA as a marker. Tentatively, SA markers might serve as adjuncts, when combined with other markers, in disease screening, disease progression follow-up, and in the monitoring of treatment response. To become clinically useful, however, the existing SA determination assays need to be considerably refined to reduce interferences, to be specific for certain SA forms, and to be more easy to use.

Lipoprotein desialylation simultaneously enhances the cell cholesterol uptake and impairs the reverse cholesterol transport system: in vitro evidences utilizing neuraminidase-treated lipoproteins and mouse peritoneal macrophages

Desialylation of low density lipoprotein (LDL) brings about accumulation of cholesterol in cultured cells. The influence of the neuraminidase-treated lipoprotein (LP) on the reverse cholesterol transport system was investigated in vitro utilizing very low density lipoprotein (VLDL), LDL, total high density lipoprotein (HDL) and its subfractions, HDL2 and HDL3, isolated from healthy donor plasma and mouse peritoneal macrophages. It was found that LP desialylation significantly: (1) decreased the capacity of total HDL and of HDL2, but not of HDL3, to efflux cellular cholesterol; (2) lowered the cholesterol esterification rate by lecithin:cholesterol acyltransferase (LCAT) without modifying the intrinsic LCAT activity of HDL; (3) increased the cholesteryl ester transfer from HDL to apo B-containing LP mediated by cholesteryl ester transfer protein (CETP); (4) enhanced the uptake by macrophages of cholesterol from HDL and LDL, although the amount of cholesterol taken up by the cells was much greater from the desialylated LDL than from desialylated HDL. Taken together, these in vitro evidences indicate that, in addition to enhancing the cell cholesterol LP uptake, desialylation may contribute to the premature development of atherosclerosis by impairing the reverse cholesterol transport system.

Sialic acid, diabetes, and aging: a study on the erythrocyte membrane

Sialic acid (SA) content and Na+/K+-ATPase activity of red blood cell (RBC) membranes were studied in 26 normoalbuminuric patients with insulin-dependent diabetes mellitus (IDDM), 25 normoalbuminuric patients with non-insulin-dependent diabetes mellitus (NIDDM), and 40 healthy nondiabetic subjects with a negative family history for diabetes. A decrease in RBC membrane SA content and Na+/K+-ATPase activity was observed in older control subjects compared with younger controls. A significant correlation between age, Na+/K+-ATPase activity, and SA content was also found. No difference was observed in RBC membrane SA content between IDDM and NIDDM subjects, but Na+/K+-ATPase activity was significantly lower in IDDM patients. SA content was increased in NIDDM subjects compared with healthy subjects of similar age, whereas Na+/K+-ATPase activity was significantly lower in both IDDM and NIDDM subjects compared with controls. In NIDDM, Na+/K+-ATPase activity was significantly correlated with age, whereas both Na+/K+-ATPase activity and SA content were significantly correlated in IDDM and NIDDM patients. Hemoglobin A1c, (HbA1c) levels did not show any significant correlation either with Na+/K+-ATPase or with SA content in diabetic patients. The modified SA content and Na+/K+-ATPase activity in elderly subjects described in the present study indicate a similar behavior of the erythrocyte membrane during both RBC senescence and aging of subjects.

Cohort study of predictive value of urinary albumin excretion for atherosclerotic vascular disease in patients with insulin dependent diabetes

OBJECTIVE

To examine whether slightly elevated urinary albumin excretion precedes development of atherosclerotic vascular disease in patients with insulin dependent diabetes independently of conventional atherogenic risk factors and of diabetic nephropathy.

DESIGN

Cohort study with 11 year follow up.

SETTING

Diabetes centre in Denmark.

SUBJECTS

259 patients aged 19-51 with insulin dependent diabetes of 6-34 years' duration and without atherosclerotic vascular disease or diabetic nephropathy at baseline.

MAIN OUTCOME MEASURES

Baseline variables: urinary albumin excretion, blood pressure, smoking habits, and serum concentrations of total cholesterol, high density lipoprotein cholesterol, sialic acid, and von Willebrand factor.

END POINT

atherosclerotic vascular disease assessed by death certificates, mailed questionnaires, and hospital records.

RESULTS

Thirty patients developed atherosclerotic vascular disease during follow up of 2457 person year. Elevated urinary albumin excretion was significantly predictive of atherosclerotic vascular disease (hazard ratio 1.06 (95% confidence interval 1.02 to 1.18) per 5 mg increase in 24 hour urinary albumin excretion, P = 0.002). Predictive effect was independent of age; sex; blood pressure; smoking; serum concentrations of total cholesterol, high density lipoprotein cholesterol, sialic acid, and von Willebrand factor; level of haemoglobin A(lc); insulin dose, duration of diabetes, and diabetic nephropathy (hazard ratio 1.04 (1.01 to 1.08) per 5 mg increase