Molecular characterization of β-trace protein in human serum and urine: a potential diagnostic marker for renal diseases

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Abstract
We have isolated β-trace protein from cerebrospinal fluid, serum, plasma, and urine samples of normal volunteers and sera and hemofiltrate of patients with chronic renal failure. Blood-derived and urinary β-trace have significantly higher molecular weights than their cerebrospinal fluid counterpart, the amino acid sequences being identical. Oligosaccharide structural analysis revealed these molecular weight differences to be due to different N-glycosylation. β-Trace from hemofiltrate and urine has larger sugar chains and concurrently significantly higher sialylation than cerebrospinal fluid-β-trace which bears truncated “brain-type” oligosaccharide chains (published previously). β-Trace concentrations were about 40 ng/ml for normal sera and plasma. 2000–6000 ng/ml were measured in sera of dialysis patients whereas in normal human cerebrospinal fluid, β-trace concentration was about 8000 ng/ml. A reduced amount of 900 ng/ml was found in a single case of hydrocephalus cerebri. The sialylated glycoforms of β-trace detected in the blood are presumably derived from resorbed cerebrospinal fluid protein whereas β-TP-mole-cules bearing asialo-oligosaccharides are absent due to their hepatic clearance. The residual, sialylated β-TP-species are probably eliminated from the blood via the kidney. This physiological clearance mechanism for the sialylated glycoforms is disturbed in hemodialysis patients resulting in about 100-fold elevated serum concentrations. These results let us suggest β-trace may become a useful novel diagnostic protein in renal diseases.

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