Elevated serum sialic acid concentration in NIDDM and its relationship to blood pressure and retinopathy

In view of the possible link between serum sialic acid and cardiovascular disease in the general population, we investigated whether serum total and lipid-associated sialic concentrations are elevated in NIDDM patients compared with normal subjects. We also investigated how sialic acid levels relate to glycemic control, blood pressure, microalbuminuria, retinopathy, and serum lipid levels.

We selected 20 NIDDM patients at random and matched them for age and sex with 20 normal subjects. The patients also had a similar BMI as the control subjects. A first morning blood sample was taken for sialic acid, glucose, fructosamine, and lipid analysis, as was a first morning urine sample for assessment of microalbuminuria. Retinopathy was assessed by fundoscopy.

Both total and lipid-associated sialic acid levels were elevated in the NIDDM patients compared with control subjects (mean +/- SD, total: 0.74 +/- 0.11 vs. 0.60 +/- 0.22 g/L, P < 0.02; lipid-associated: 0.18 +/- 0.04 vs 0.12 +/- 0.04 g/L, P < 0.001). Total serum sialic acid was correlated with systolic blood pressure (r = 0.58, P < 0.01) and diastolic blood pressure (r = 0.58, P < 0.02). There was no significant relationship of total sialic acid with age, duration of diabetes, BMI, microalbuminuria, serum triglyceride, blood glucose, or serum fructosamine. A relationship of lipid-associated sialic acid levels and systolic blood pressure did not reach significance (P = 0.09). In 9 patients with background retinopathy with or without maculopathy, the total serum sialic acid concentration was higher than in those without retinopathy (0.81 +/- 0.09 vs. 0.69 +/- 0.10 g/L, P < 0.008). Lipid-associated sialic acid levels were similar in those with and without retinopathy. (The conversion factor for standard units to SI units is 1 gL = 3.2 mM.)

Total serum sialic acid levels were significantly elevated in a relatively small group of NIDDM patients and were correlated with hypertension and retinopathy. A larger study of circulating sialic acid concentrations as a risk factor for the development or marker of diabetic angiopathy is therefore justified.