Lipid-bound sialic acid in diabetes

Circulating levels of ganglioside GM3 in metabolic syndrome: A pilot study

SUMMARY

BACKGROUND

Insulin resistance is a characteristic feature of metabolic syndrome. Ganglioside GM3 [α-Neu5Ac-(2-3)-β-Gal-(1-4)-β-Glc-(1-1)-ceramide] may impair insulin sensitivity in adipose tissue. We investigated the relationship between serum GM3 levels and adiposity indices, as well as between serum GM3 levels and metabolic risk variables.

METHODS

Study 1: we assessed serum GM3 levels in normal subjects and in patients with hyperglycemia and/or hyperlipidemia (HL). Study 2: we investigated the relationship between serum GM3 levels and metabolic risk variables in patients with type 2 diabetes.

RESULTS

Study 1: serum GM3 levels were higher in hyperglycemic patients (1.4-fold), hyperlipidemic patients (1.4-fold) and hyperglycemic patients with hyperlipidemia (1.6-fold), than in normal subjects. Study 2: serum GM3 levels were significantly increased in type 2 diabetic patients with severe obesity (visceral fat area (VFA) >200 cm(2), BMI > 30). The GM3 level was positively correlated with LDL-c (0.403, p = 0.012) in type 2 diabetes mellitus, but not affected by blood pressure. In addition, the high levels of small dense LDL (>10 mg/dL) were associated with the elevation of GM3.

CONCLUSIONS

Serum GM3 levels was affected by glucose and lipid metabolism abnormalities and by visceral obesity. GM3 may be a useful marker for severity of metabolic syndrome.

Plasma and urine sialic acid in non-insulin dependent diabetes mellitus

Urinary excretions of albumin, glycosaminoglycans (GAGS), total sialic acid (TSA), and lipid associated sialic acid (LASA) were measured in 78 non-insulin dependent diabetic patients (NIDDM) and 28 healthy subjects. TSA excretion was significantly higher in normoalbuminuric and microalbuminuric diabetic subjects than the control subjects and TSA excretion was correlated with urinary albumin excretion rate (AER). In normoalbuminuric diabetics, the duration of diabetes correlated significantly with both sialicaciduria and albuminuria. Although serum TSA levels were significantly higher in both diabetic groups than the control subjects, there was no correlation between serum and urinary TSA levels.

Measurement of sialic acid in serum and urine: clinical applications and limitations

Many recent studies have examined the sialic acid content of serum or urine in various pathological states. We have briefly reviewed the substances which contribute to the observed total sialic acid concentration, and given an overview of assay methods used. Three major areas of clinical interest in sialic acid metabolism are discussed. Serum total sialic acid, 'lipid-bound' and 'protein bound' sialic acid have all been proposed as tumour markers; but the usefulness of any of these tests is severely limited by changes due to accompanying inflammatory processes. Serum total sialic acid is not a valuable simple marker of an acute phase response. Urinary free and bound sialic acid measurements should be included in screening protocols for inherited disorders of lysosomal metabolism. Current developments in research and potential applications within the clinical biochemistry laboratory are briefly discussed.

Total and ganglioside-bound sialic acid content of lymphocytes from non-insulin-dependent diabetic patients

The total and ganglioside-bound sialic acid content of unfractionated blood lymphocytes obtained from normal-weight healthy subjects (n = 17) and non-insulin-dependent diabetic patients on oral hypoglycemic drugs arbitrarily divided into normal-weight (n = 11), moderately overweight (n = 14) and severely overweight (n = 17) subgroups were examined. In normal-weight diabetics the level of lipid-bound sialic acid (gangliosides) of lymphocytes was found to be reduced (p less than 0.01). A more pronounced decrease (p less than 0.001) was observed for the lymphocyte total sialic acid of normal-weight and moderately overweight diabetics as compared to healthy subjects. In severely overweight non-insulin-dependent diabetics the decrease of total sialic acid was less pronounced compared to that found in healthy subjects. Whether this finding was due to obesity in these patients remains to be clarified.