Relation of serum sialic acid to lipid concentrations

High fat diet-induced inflammation and oxidative stress are attenuated by N-acetylneuraminic acid in rats

Background

Serum sialic acid levels are positively correlated with coronary artery disease and inflammation. Although sialic acid is a non-specific marker, it is considered sensitive likely due to its influence in sialylation of glycoprotein structures all over the body.

Objectives

We hypothesized that dietary supplementation with N-acetylneuraminic acid (Neu5Ac), a type of sialic acid, will have profound effects on high fat diet- (HFD-) induced inflammation and oxidative stress in view of the widespread incorporation of sialic acid into glycoprotein structures in the body.

Methods

HFD-fed rats with or without simvastatin or Neu5Ac (50 and 400 mg/kg/day) were followed up for 12 weeks. Lipid profiles, and markers of inflammation (C-reactive protein, interleukin-6, and tumor necrosis factor alpha), insulin resistance (serum insulin and adiponectin, oral glucose tolerance test and homeostatic model of insulin resistance) and oxidative stress (total antioxidant status and thiobarbituric acid reactive species) in the serum and liver were determined, while mRNA levels of hepatic antioxidant and inflammation genes were also quantified. Serum levels of alanine transaminase, aspartate transaminase, alkaline phosphatase, urea, creatinine and uric acid were also assessed.

Results

HFD feeding caused hyperlipidemia and insulin resistance, and worsened liver and kidney functions. HFD feeding also potentiated inflammation and oxidative stress, partly through modulation of hepatic gene expression, while Neu5Ac especially at higher doses and simvastatin attenuated HFD-induced changes, although Neu5Ac showed better outcomes.

Conclusions

Based on the present results, we surmised that Neu5Ac can prevent HFD-induced inflammation and oxidative stress, and may in fact be useful in the prevention of hyperlipidemia-associated inflammation and oxidative stress. However, the translational implications of these findings can only be determined after long-term effects are established. Hence, the use of Neu5Ac on obesity-related diseases requires additional attention.

Evaluation of oxidative stress via total antioxidant status, sialic acid, malondialdehyde and RT-PCR findings in sheep affected with bluetongue

INTRODUCTION

Bluetongue (BT) is a non-contagious infectious disease of ruminants. The disease agent bluetongue virus (BTV) is classified in the Reoviridae family Orbivirus.

AIMS AND OBJECTIVES

The aim of this study was to determine serum malondialdehyde (MDA), total antioxidative stres (TAS), total sialic acid (TSA), ceruloplasmin, triglyceride, alanine aminotransferase (ALT), aspartate aminotransferase (AST), γ-glutamyltransferase (GGT), cholesterol, creatinine, albumin, and total protein levels in sheep with and without bluetongue (BT).

MATERIALS AND METHODS

The study included 13 Sakiz crossbreed sheep, aged 1-4 years and usually in the last stage of pregnancy, as the BT group and a control group consisting of 10 healthy sheep. All sheep were clinically examined before collecting blood samples. Serum ALT, AST, cholesterol, triglyceride, albumin, GGT, total protein, creatinine and TAS levels were measured using commercially available kits as per manufacturer's recommendations using a Biochemistry Auto Analyzer (Sinnowa D280, China). Serum lipid peroxidation was estimated through a previously described method in which MDA reacts with thiobarbituric acid (TBA) to form a coloured complex at a maximum absorbance of 535 nm. The TSA value was measured at 549 nm using the method described by Warren (1959): sialic acid was oxidised to formyl-pyruvic acid, which reacts with TBA to form a pink product. The ceruloplasmin concentration was measured according to Sunderman and Nomoto (1970): ceruloplasmin and p-phenylenediamine formed a coloured oxidation product that was proportional to the concentration of serum ceruloplasmin. Real time RT-PCR and conventional RT-PCR were performed as described by Shaw and others (2007).

RESULTS

Biochemistry analysis of serum showed that in the BT group, TSA, MDA, triglyceride and ALT and AST were higher and that ceruloplasmin and TAS were lower than in the control group. Serum albumin, cholesterol, creatinine, total protein and GGT did not differ significantly between the two groups.

CONCLUSIONS

Serum triglyceride, ceruloplasmin, TSA, MDA and TAS concentrations may prove beneficial to the diagnosis, prognosis and biochemical analysis of BT.

A comparison of the effect of glitazones on serum sialic acid in patients with type 2 diabetes

Although management of hyperglycaemia represents one of the principal treatment goals of diabetes therapy, the high incidence of cardiovascular (CV) complications in diabetes also needs effective management. Therefore, the present study was designed to determine and compare the effect of glitazones on serum sialic acid (SSA), a known risk marker for CV disease, along with fasting plasma glucose (FPG), glycohaemoglobin (HbA1-c) and blood lipids, in overweight, previously only diet-treated patients with type 2 diabetes (n=60). The study was conducted for a period of 12 months. Significant improvement in FPG and HbA1-c were shown by both rosiglitazone (p<0.003 and p<0.001, respectively) and pioglitazone (p<0.005 and p<0.001, respectively), compared with baseline, and pioglitazone showed greater beneficial effects on other parameters monitored, significantly reducing total cholesterol (TC) (p≤0.05). Both the drugs showed a decrease in SSA and no significant differences were observed between the groups. However, the decrease was significant only in the pioglitazone-treated group at month 12 (p≤0.05), compared with baseline. A significant decrease in SSA by pioglitazone indicates its greater cardioprotective effect compared with rosiglitazone.

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.

Sialic acid in cardiovascular diseases

Sialic acid, the acylated derivatives of 9-carbon sugar neuraminic acid, present as terminal component of oligosaccharide chains of many glycoproteins and glycolipids, has been recognized to be involved in the regulation of a great variety of biological phenomena. Studies have shown that serum sialic acid predicts both coronary heart disease and stroke mortality and reflects the existence or activity of an atherosclerotic process. Most of the studies have shown an elevation in serum sialic acid concentration in coronary heart disease and a positive correlation between the raised serum sialic acid and the severity of the coronary lesions is observed. However, a few contradictory reports are also available. Racial differences in serum sialic acid have also been reported and correlated with international differences in the prevalence of atherosclerosis. Reduced sialic acid content of platelets, erythrocytes and lipoproteins may play important role in the pathogenesis of atherosclerosis. Elucidation of the mechanism of alternation in sialic acid concentration may throw more light on its potential clinical utility. Hence more studies are needed to designates sialic acid as a cardiovascular risk factor/marker.

Type 2 diabetes mellitus: a disease of the innate immune system? An update

A few years ago a hypothesis was proposed suggesting that elements of the innate immune system, such as acute phase reactants, contribute to the development of Type 2 diabetes mellitus. Acute phase reactants such as C-reactive protein and sialic acid may thus predict risk of developing Type 2 diabetes mellitus, as well as being markers of diabetes microvascular and macrovascular complications. This article discusses these issues.

The role and potential of sialic acid in human nutrition

Sialic acids are a family of nine-carbon acidic monosaccharides that occur naturally at the end of sugar chains attached to the surfaces of cells and soluble proteins. In the human body, the highest concentration of sialic acid (as N-acetylneuraminic acid) occurs in the brain where it participates as an integral part of ganglioside structure in synaptogenesis and neural transmission. Human milk also contains a high concentration of sialic acid attached to the terminal end of free oligosaccharides, but its metabolic fate and biological role are currently unknown. An important question is whether the sialic acid in human milk is a conditional nutrient and confers developmental advantages on breast-fed infants compared to those fed infant formula. In this review, we critically discuss the current state of knowledge of the biology and role of sialic acid in human milk and nervous tissue, and the link between sialic acid, breastfeeding and learning behaviour.

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.

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.

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.

Growth hormone (GH) replacement therapy reduces serum sialic acid concentrations in adults with GH-deficiency: a double-blind placebo-controlled study

OBJECTIVES

Patients with adult GH-deficiency are thought to have an increased risk of cardiovascular disease. Sialic acid (SA) concentrations have been proposed as a marker of atherosclerotic disease probably related to an inflammatory response of the arterial wall. SA as a marker of cardiovascular disease in adult GH-deficiency and its relation to changes in fasting lipid profile and hormone concentrations have not yet been investigated.

PATIENTS

We performed a randomised, double-blind placebo-controlled study in 18 patients with adult GH-deficiency before and after 3 months GH replacement therapy (0.036 U/kg/d; GH-treated group: 6 females, 3 males; age: 47.3 +/- 5.4 years., mean +/- SEM; placebo-group: 5 females, 4 males; mean age 50.2 +/- 4.7). In addition, SA concentrations were measured in 18 sex and age matched healthy control subjects.

METHODS

Blood samples were obtained after an overnight fast. Serum SA, triglycerides and cholesterol were measured using enzymatic methods. Lipoprotein classes were separated by ultracentrifugation. Insulin and IGF-I were determined by radioimmunoassay, HbA1C was measured by anion exchange liquid chromatography.

RESULTS

SA concentrations of the patients with adult GH-deficiency were not significantly different compared to the control group (GH-deficient group: 2.29 +/- 0.02 mmol/l, mean +/- SEM vs. control group: 2.09 +/- 0.13 mmol/l, P = 0.25). Before GH replacement therapy SA concentrations correlated positively with the patients age (r = 0.45; P < 0.04) and fasting insulin concentrations (r = 0.5; P < 0.03) but not with fasting lipid profile. GH replacement therapy significantly increased IGF-I (GH: + 27 +/- 2.6 vs. placebo: + 1.0 +/- 0.8 nmol/l, P < 0.001) and fasting insulin concentrations (GH: + 71.9 +/- 8.0 vs. placebo: + 19.6 +/- 22.6 pmol/l, P < 0.04) compared to placebo therapy. SA concentrations (GH: - 0.41 +/- 0.15 vs. placebo: - 0.01 +/- 0.12 mmol/l, P < 0.05), total cholesterol (GH: - 0.71 +/- 0.16 vs. placebo: 0.23 +/- 0.21 mmol/l, P < 0.003) and LDL-cholesterol (- 0.71 +/- 0.14 vs. placebo: - 0.12 +/- 0.21 mmol/l P < 0.04) significantly decreased after GH replacement therapy compared to placebo therapy. No significant correlation between changes in SA concentrations and changes in lipid profile were observed following GH replacement therapy.

CONCLUSION

These results suggest that, firstly, GH replacement therapy may have a beneficial effect on the pathogenesis of atherosclerosis despite the increase in insulin concentrations, a surrogate marker of insulin resistance, secondly, the proposed beneficial effect of GH on the atherosclerotic process is likely to be multifactorial and cannot only be explained by changes in lipid profile and finally, SA might be a useful marker for the process of atherosclerotic disease in interventional studies.

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.

Elevated plasma lipid hydroperoxides in patients with coronary artery disease

Sustained presence of lipid peroxides in the circulation and their plasma carrier is a controversial issue. Particularly, there is no firm evidence for an increased plasma lipid peroxide level in patients with atherosclerosis. In this study, a strong correlation was found between plasma total lipid hydroperoxide and lipid hydroperoxide content of LDL cholesterol (r = 0.882; p < 0.001; n = 16). Lipid hydroperoxides in plasma were carried almost exclusively (89%) in LDL. In 70 patients tested 3 months after coronary artery bypass graft surgery with a specific assay, plasma lipid hydroperoxide levels were significantly increased when compared with matched healthy controls (4.31 +/- 0.23 nmol/ml and 2.34 +/- 0.13 nmol/ml, p < 0.0001, patients vs controls, respectively). These concentrations are 10 times lower than those detected by the nonspecific thiobarbituric acid assay. However, considering the in vitro concentration range in which oxidized LDL exerts important atherogenic effects, the elevated plasma lipid hydroperoxide levels measured in atherosclerotic patients have pathologic significance.

Effect of eicosapentaenoic acid intake on the relationship between lnterleukin-6 and acute phase proteins in serum in youths

Twenty male volunteers 20-25 years old were examined to determine their serum concentrations of interleukin-6 (IL-6), acute phase proteins and lipids before, immediately after and one hour after a load of 90 watts for 20 minutes using a Monark ergometer, and the same parameters were reexamined after eicosapentaenoic acid (EPA) intake of 1.125 g/day for 2 weeks. By EPA intake, EPA level of the membranes of red blood cells increased significantly by 75.6% and docosahexanoic acid (DHA) by 53.8%. The IL-6 level increased significantly by 17% and C-reactive protein (CRP) by 11.7%, but fibrinogen (Fbg) decreased by 9.6%. After EPA intake, at one hour after the load, the change rate of IL-6 decreased to that of before EPA. The change rate of α(1)-acid glycoprotein ( α(1)-AGP) increased in the group in which IL-6 was unchanged and did so significantly in the group in which it increased, but tended to increase in the group in which it decreased. Thus the change rate of sialic acids (SA) increased significantly in both the IL-6 unchanged and increased groups. It is suggested that EPA activated IL-6, which was related to the increase of α(1)-AGP as an activator of immunity. The change rate of sialic acid (SA) as an index of acute phase protiens was correlated significantly and positively with that of total cholesterol and HDL-cholesterol.

Evidence for a correlation between ambient cholesterol levels and soluble plasma sialyltransferase enzyme activity

While soluble forms of the sialyltransferase (sialyl-T) enzyme have been detected in significant quantities in serum, the exact source(s) of the enzyme, or the factors controlling its secretion are poorly understood. In this study, we have examined the relationship between ambient plasma cholesterol concentrations and sialyl-T-activities and also levels of constituent plasma sialoglycoproteins (SGP). There was an inverse relationship between levels of the alpha 2, 6 sialyl-T enzyme and both total plasma cholesterol and HDL, although no such relationship was observed for the alpha 2,3 enzyme. While there was no correlation between total cholesterol and the levels of plasma SGPs, there was an inverse relationship between the HDL component and alpha 2,3 SGPs.

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

OBJECTIVES

Elevated serum sialic acid concentration is a strong predictor of cardiovascular mortality in non-diabetic subjects. Because patients with insulin-dependent diabetes mellitus (IDDM) and albuminuria have a highly increased cardiovascular morbidity and mortality, we hypothesized that IDDM patients with albuminuria would have an increased concentration of serum sialic acid.

DESIGN

Cross-sectional study.

SETTING

Outpatient clinic at Steno Diabetes Centre, Gentofte, Denmark.

SUBJECTS

Twenty-six non-diabetic controls and 74 IDDM patients with normoalbuminuria (urinary albumin excretion [UAE] < 30 mg 24 h-1; n = 37), incipient nephropathy (UAE 30-300 mg 24 h-1; n = 20) and clinical nephropathy (UAE > 300 mg 24 h-1; n = 17), matched for sex, age and body mass index (BMI).

MAIN OUTCOME MEASURES

Serum sialic acid concentration, concurrent fasting blood glucose, glycated haemoglobin (HbA1c), serum creatinine, plasma fibrinogen and erythrocyte sedimentation rate.

RESULTS

Normoalbuminuric patients had a higher serum sialic acid concentration (mmol L-1) than non-diabetic controls (1.83 +/- 0.24 vs. 1.67 +/- 0.26; P < 0.02). Serum sialic acid concentration was further increased in patients with incipient nephropathy (2.02 +/- 0.37; P < 0.03) and in patients with clinical nephropathy (2.13 +/- 0.33; P < 0.002) compared with normoalbuminuric IDDM patients. Serum sialic acid correlated strongly with plasma fibrinogen (r = 0.78; P < 0.0001) and erythrocyte sedimentation rate (r = 0.62; P < 0.0001). In a multiple regression analysis including UAE, retinopathy status, fasting blood glucose, HbA1c, mean blood pressure, serum creatinine, age, BMI, duration and smoking. UAE and fasting blood glucose were the independent variables which correlated significantly with serum sialic acid concentration (P < 0.0001 and P < 0.05, respectively).

CONCLUSION

Serum sialic acid is elevated in IDDM especially in albuminuric patients. Whether elevated serum sialic acid is predictive for early diabetic nephropathy and cardiovascular disease in IDDM has to be shown in the future.

Plasma sialic acid and acute-phase proteins in patients with myocardial infarction

Plasma total sialic acid (TSA) and lipid-associated sialic acid (LASA) were measured in 19 patients with a myocardial infarction (MI) on days 1, 2, and 5 and in 19 normal subjects. On each day plasma TSA was elevated in the MI patients as compared with that of normal subjects, although no significant difference was seen in the plasma LASA between the two groups. The following plasma acute-phase proteins were also assayed in the MI patients and the normal subjects: C-reactive protein (CRP), alpha-1 acid glycoprotein (AGP), alpha-1 antichymotrypsin (ACT), alpha-2 macroglobulin (AMG), and fibrinogen (FIB). Significantly elevated plasma concentrations were found in the MI patients as compared with normal subjects. Furthermore, a significant correlation was found between some of these plasma acute-phase proteins (ACT, AMG, and FIB) and plasma TSA in the MI patients and also in normal subjects (ACT, AMG, CRP, and FIB). However, no significant difference was noted in any of the plasma acute-phase proteins, or plasma TSA, or plasma LASA between survivors and patients who died of their MI.

The relationship of serum total sialic acid with serum acute phase proteins and lipoprotein (a) in patients with severe hypertriglyceridaemia

Total serum sialic acid (TSA), recently shown to be a cardiovascular risk factor, was measured in 15 patients with severe hypertriglyceridaemia (fasting triglyceride > 2.3 mmol l-1) and 15 age and sex matched normal control subjects. To test the hypothesis that serum TSA is related in some way to serum acute phase proteins we also measured five acute phase proteins, namely alpha-1-antichymotrypsin (ACT), alpha-1-acid-glycoprotein (AGP), alpha-2-macroglobulin (AMG), C-reactive protein (CRP) and haptoglobin (HAP) in both groups. Of note was the significantly elevated serum TSA in the severely hypertriglyceridaemic group as compared to normal subjects. Serum TSA being 71.9 +/- 11.7 mg dl-1 and 59.6 +/- 10.2 mg dl-1 respectively (P < 0.01 Mann-Whitney test). Serum CRP was significantly elevated in the type IV patients as compared to controls (6.4 +/- 4.5 mg l-1 vs. 3.3 +/- 1.9 mg l-1 P < 0.05 Mann Whitney test) as was serum AMG (2.1 +/- 0.89 g l-1 vs. 1.5 +/- 0.53 g l-1 P < 0.05 Mann Whitney test). There was no correlation between serum TSA and lipoprotein (a) in either the normal or severely hypertriglyceridaemic subjects. We suggest that serum TSA could in part be related to hypertriglyceridaemia and serum acute phase proteins but that its property as a cardiovascular risk factor is not related to serum lipoprotein (a) concentrations.

Serum sialic acid concentration and atherosclerotic risk factors

To clarify the significance of increased blood sialic acid in atherosclerotic cardiovascular disease, we investigated the relationship between serum sialic acid level and atherosclerotic risk factors such as serum uric acid, fasting blood glucose, systolic and diastolic blood pressure, atherogenic index, and white blood cell count. By simple regression analysis, the serum sialic acid level was found to correlate significantly with these parameters. The mean sialic acid level was significantly higher in the highest quartile for serum uric acid than in its lowest quartile and also for fasting blood glucose concentration in comparison with its other three quartiles. A tendency was noted for the mean serum sialic acid level of each quartile to become higher with an increase in the quartiles of systolic or diastolic blood pressure, atherogenic index, and white blood cell count. Multiple regression analysis showed the correlations to be significant for the relationship of serum sialic acid to atherogenic index, mean arterial pressure and white blood cell count. From these results and previous findings of higher serum sialic acid levels in smokers, patients with diabetic angiopathies, and patients with hyperlipidemia, it is suggested that serum sialic acid reflects the degree of atherosclerotic progress involving inflammation processes.

Serum sialic acid and acute phase proteins in type 1 and type 2 diabetes mellitus

Serum sialic acid is a risk factor for cardiovascular disease in the general population. Serum total sialic acid concentrations were therefore measured in 20 type 1 diabetic patients and in 20 age- and sex-matched non-diabetic subjects. Serum sialic acid were not significantly different in the type 1 diabetic patients and the normal subjects (2.00 +/- 0.37 vs. 1.98 +/- 0.67 mmol/l), but was significantly correlated with serum total cholesterol (r = 0.55, P < 0.02) and serum triglyceride concentration (r = 0.63, P < 0.01) in the type 1 diabetic patients. There was no relationship of sialic acid levels to age, duration of diabetes, smoking, body mass index, systolic or diastolic blood pressure, plasma glucose, serum fructosamine, or daily insulin dosage. Six of the type 1 diabetic patients with retinopathy had higher total serum sialic acid concentrations than those patients without retinopathy (2.38 +/- 0.33 vs. 1.85 +/- 0.26 mmol/l, P < 0.01). A further study of 16 type 1 and 16 type 2 diabetic patients matched for serum fructosamine and blood glucose concentrations and without tissue complications showed that the serum total sialic acid concentration was significantly higher in the type 2 diabetic patients compared with the type 1 patients (2.32 +/- 0.41 vs. 1.84 +/- 0.24 mmol/l, P < 0.001). Although the serum concentrations of the non-sialylated acute phase protein, C-reactive protein, was higher in type 2 than type 1 diabetes, sialylated acute phase protein levels did not explain differences in serum total sialic acid in diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)