Occurrence of sialic acids in healthy humans and different disorders

Abstract

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.

Sialic acid in cardiovascular diseases

“…In human beings it is present in body fluids (blood plasma, breast milk, gallbladder excretions, synovial fluid, sweat, gastric juices and urine) and tissues (erythrocytes, leucocytes, platelets, salivary glands, throat, stomach, cervix, colon, cartilage etc. (15). In blood plasma a large quantity of sialic acids are present in orosomucoid, fibrinogen, haptoglobin, ceruloplasmin, α 1 -antitrypsin, complement proteins and transferrin (16,17).…”

“…Serum sialic acid levels are influenced by nonpathological factors like aging, pregnancy, smoking etc (15). Moreover, sialic acid is not specific for a given disease as variations in serum sialic acid levels have been found in various diseases such as cancer, diabetes, chronic renal failure, alcohol abuse, Salla's disease etc.…”

“…Moreover, sialic acid is not specific for a given disease as variations in serum sialic acid levels have been found in various diseases such as cancer, diabetes, chronic renal failure, alcohol abuse, Salla's disease etc. (15).…”

NMR analysis on the sialic acid‐binding mechanism of an R‐type lectin mutant by natural evolution‐mimicry

“…Striking changes in sialylation features on tumor cells have been shown to serve as useful 'tumor markers' [2,3]. Influenza virus infections are mediated by specific interactions between the viral hemagglutinin and cell oligosaccharides containing Sia residues.…”

Serum Total Sialic Acid in Pigs: New Possibilities for an Old Inflammatory Biomarker

“…13 Sialic acid is a 9-carbon monosaccharide mainly attached to the oligosaccharide side-chains of many glycoprotein and glycolipids. 13 In humans, it is known that serum-sialicacid concentration rises during the acute-phase reaction, because of an increase in serum concentration of sialicacid-carrying APPs, as well as a higher degree of sialylation of these proteins. 2,13 Hence, sialic acid is considered an acute-phase marker in human medicine.…”