Urine free sialic acid

The lysosomal disorder SASD is characterized by accumulation of the free acid monosaccharide sialic acid in the lysosomal compartment of the cell. Diagnosis is based on the demonstration of abnormal excretion of free, not OGS-bound sialic acid in urine, coupled with accumulation of free sialic acid in cultured fibroblasts, and on microscopic evidence of vacuoles (increased and swollen lysosomes filled with light electron-lucent material in skin biopsy and peripheral blood lymphocytes). The inheritance is autosomal recessive. There are different clinical forms of this disorder an adult form, called Salla disease (SD) or Finnish sialuria (OMIM 604369) infantile SASD (ISSD OMIM 269920) and an intermediate form, severe Salla disease [3,16]. 

Nonlysosomal sialuria (also called French-type sialuria) is characterized by massive excretion of free sialic acid in urine. Only four patients have been described. The defect is caused by a defective feedback inhibition of UDP-GlcNAc-2-epimerase... 

All determinations are performed in duplicate. For total (free plus bound ) sialic acid take 50 pi sample (distilled water blank or standard or urine sample ), add 50 pi H2S04 and incubate for 60 min at 80°C in closed reaction tubes. For free sialic acid, pipette the same without incubation at 80°C. 

The test is performed for diagnosis of all clinical forms of SASD. This analysis is usually done after an initial TLC screening test that is positive for free sialic acid, and an increased free sialic acid value in the quantitative urine determination test. The test is like the quantitative urine test performed with the periodate-TBA assay [5, 22]. However, in this case interference is decreased by prepurification of the sample using ion-exchange chromatography [12]. Fibroblasts are cultured under standardized conditions. Cell lysates are prepared by tip sonification in distilled water and the cleared lysates are applied to small Dowex columns. NeuAc is eluted, freeze dried,... 

Several alternative methods for the determination of sialic acid in body fluids and tissues have been described. Most of these methods make use of the classic periodate-TBA assay in combination with purification using HPLC [13]. Another method makes use of fluorometric HPLC of sialic acids after derivatization with a fluorogenic compound [9]. The most promising new method for the determination of free sialic acid in urine (and probably also other body fluids and tissues) is the HPLC-tandem mass spectrometry method [19]. This method is rapid, accurate, and sensitive, and is more robust than earlier methods. The only disadvantage is the expensive equipment that is required, which makes it only economical for specialized metabolic laboratories. Since this equipment is used for many different metabolic assays, the investment is certainly warranted, and nowadays almost essential for any metabolic laboratory. 

Valianpour F, Abeling NG, Duran M, Huijmans JG, Kulik W (2004) Quantification of free sialic acid in urine by HPLC-electrospray tandem mass spectrometry a tool for the diagnosis of sialic acid storage disease. Clin Chem 50 403-409... 

This Neu5Ac derivative lacking a glycosidic hydroxyl group at C2 has been found as free sialic acid in small quantities in blood serum, saliva and urine of man [5,8,13] and in tissue extracts of starfish [36] (Table 1). It is unknown, whether this compound, which is a potent competitive inhibitor of sialidases (see below), has a biological function. Its formation under physiological conditions has been described in section 2. 

Salla disease Psychomotor retardation, ataxia, abnormally high excretion of free sialic acid in the urine, rare and severe infantile form Free sialic acid Sialic acid transporter ... 

There is considerably more of a non-dialysable glycoprotein in the urine of germ-free rats than in the urine of normal animals. This mucin-like material contains residues of L-fucose (10.1 %), D-galactose (12.2%), 2-acetamido-2-deoxy-D-glucose (16.6%), 2-acetamido-2-deoxy-D-galactose (19.8%), sialic acid (11.9%), and sulphate (0.7 %). 

Another species of sialic acid found in human tissue is N,0-diacetylneuraminic acid, possibly the A-acetyl-4-O-acetylneuraminic acid, in urine (Carrion et al., 1969b 1970) and bile (Cabezas and Ramos, 1972). In the urine, the free form of the diacetyl derivative was detected. 

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