Excretion of β2-glycoprotein i (apolipoprotein H) in renal tubular disease

Abstract

β2-Glycoprotein I (β2GI) was identified as a major urinary protein excreted by patients with several renal tubular diseases, including adult Fanconi syndrome, nephrocalcinosis associated with autoimmune diseases, Lowe's syndrome, and Dent's disease (a familial renal tubular disease). Sixteen patients excreted between 2 and 40 mg of β2GI per millimole of creatinine. In contrast, 18 healthy controls had undetectable amounts of β2GI in urine. Isoelectric focusing followed by immunoblotting demonstrated multiple forms of β2GI with pls between 6.4 and 8.2. These pis are higher than for several other "tubular proteins"; β2GI may therefore be less retarded than more-anionic proteins by the glomerular charge-barrier. This could explain why large quantities of β2GI are excreted despite its relatively high molecular mass (50 kDa). Excretion of β2GI was easily demonstrated by routine electrophoresis of urine proteins. β2GI migrates in the beta-gamma region and may be confused with Bence Jones protein. β2GI is stable for at least two years in urine frozen at -25 °C.