A simple enzymatic determination of urinary sialic acid--its significance in the diagnosis of disorders of sialic acid metabolism

Sialic acid in hemolymph and affinity purified lectins from two marine bivalves

Sialic acids have been implicated in a variety of complex biological regulatory and signalling events and their functional importance is reflected by their presence in a wide variety of phyla. Potentially they may inhibit intermolecular and intercellular interactions. Lectins that exhibit specificity for sialic acid or sialoglycoconjugates are ubiquitous in the body fluids of invertebrates and this has supported the assumption that these lectins are involved in defense against microbes that express sialic acids on their surfaces. This biological function has also been inferred from the absence of sialic acids in lower invertebrates. However, most invertebrate lectins are heterogeneous and may also bind other ligands. The biological significance of the different carbohydrate specificities are not yet known. We have demonstrated the presence of sialic acids in hemolymph from two marine bivalves, the Pacific oyster Crassostrea gigas (approximately 15 micrograms ml-1) and the horse mussel Modiolus modiolus (48-100 micrograms ml-1) by several different assays. The sialic acid was mostly in free form. Affinity purified lectins from the horse mussel also contained bound sialic acids (2-5 mumol g-1). Oyster hemolymph stimulated the in vitro phagocytosis of bacteria by oyster hemocytes. The stimulation by hemolymph is facilitated by a dialyzable component, that apparently is active irrespective of the binding to sialic acid (BSM). Addition of sialic acid had no significant effect on the in vitro phagocytosis of bacteria by oyster hemocytes.

Juvenile galactosialidosis in a white male: a new variant

We describe a 19-year-old white male with juvenile galactosialidosis. He presented with hip arthralgia and was found to have facial "coarseness," corneal clouding, mitral and aortic insufficiency, and hepatosplenomegaly. Ultrastructural studies of skin biopsy and peripheral blood lymphocytes showed membrane-bound inclusions containing sparse fibrillogranular material. Biochemical analysis showed elevated urinary sialyloligosaccharides and no free sialic acid. Fibroblast enzyme analysis showed low activities of both alpha-neuraminidase and beta-galactosidase. To date, most patients with juvenile galactosialidosis have been Japanese. However, unlike those patients, our patient did not have macular cherry-red spots, neurologic abnormalities, or mental retardation. We speculate that this young man represents a new subtype of juvenile galactosialidosis with a potentially different molecular defect from that of the Japanese variant.

Urinary sialic acid screening in neurologic disorders

Urine sialic acid was measured in 246 patients evaluated for possible neurodegenerative disorders. Total, free, and bound sialic acid excretion declined significantly with patients' ages. Among 11 patients (4.5%) with age-related excretion rates greater than 2 standard deviations above the mean, 5 had the following disorders: free sialic acid storage disease, mucolipidosis type II, pseudohypoparathyroidism, sinus histiocytosis, and probable Sanfilippo syndrome. Although the remaining 6 were undiagnosed, 2 exhibited deteriorating courses and the other 4 presented variable combinations of organomegaly, developmental delay or mental retardation, seizures, facial dysmorphism, or bony abnormalities. Thus, these individuals also may have metabolic disorders with abnormal excretions of sialic acid-containing compounds. With awareness of age-related excretion rates, sialic acid screening is most useful for the sialidoses, mucolipidoses, and disorders of free sialic acid metabolism.

Evaluation of a fully mechanized enzymatic kinetic determination of sialic acid

The enzymatic determination of sialic acid, commercially introduced recently as an end point method, has been considerably improved by the development of initial rate and peak rate modifications of the kinetic method, respectively, and adapted to a centrifugal analyser (Cobas Bio). The assay is completed within 3 min, takes 3 microliter sample volume and is reduced to a total reaction volume of 153 microliter. The costs per test thereby are lowered to about 10% of the original procedure. Within-run and day-to-day imprecisions (means = 0.81 g/l) are 2% and 3.9%, respectively; inaccuracy is between +1% and -2%. The detection limit is 0.012 g/l, i.e. about 3 times higher than that of the thiobarbituric acid method (0.0037 g/l) for sialic acid determination. The enzymatic-kinetic assay correlates well with the latter method (r = 0.973). There was no measurable interference by EDTA (less than 3 mg/l), bilirubin (less than 160 mumol/l), haemolysis (haemoglobin less than 5.25 g/l), or triglycerides (less than 3.50 g/l). The reference range (2.5th to 97.5th percentile) for sialic acid in sera of adults is 0.51 to 0.84 g/l (median 0.63 g/l) with no significant sex-related differences. The reference range for sialic acid in spontaneous urine samples is 0.01-0.13 g/l.