title: Albumin heterogeneity in low-abundance fluids. The case of urine and cerebro-spinal fluid.
abstract: BACKGROUND
  Serum albumin is a micro-heterogeneous protein composed of at least 40 isoforms. Its heterogeneity is even more pronounced in biological fluids other than serum, the major being urine and cerebrospinal fluid. Modification 'in situ' and/or selectivity of biological barriers, such as in the kidney, determines the final composition of albumin and may help in definition of inflammatory states.
  
  
  METHODS
  This review focuses on various aspects of albumin heterogeneity in low 'abundance fluids' and highlights the potential source of information in diseases.
  
  
  CONCLUSIONS
  The electrical charge of the protein in urine and CSF is modified but with an opposite change and depending on clinical conditions. In normal urine, the bulk of albumin is more anionic than in serum for the presence of ten times more fatty acids that introduce equivalent anionic charges and modify hydrophobicity of the protein. At the same time, urinary albumin is more glycosylated compared to the serum homolog. Finally, albumin fragments can be detected in urine in patients with proteinuria. For albumin in CSF, we lack information relative to normal conditions since ethical problems do not allow normal CSF to be studied. In multiple sclerosis, the albumin charge in CSF is more cationic than in serum, this change possibly involving structural anomalies or small molecules bindings.
  
  
  CONCLUSIONS
  Massively fatty albumin could be toxic for tubular cells and be eliminated on this basis. Renal handling of glycosylated albumin can alter the normal equilibrium of filtration/reabsorption and trigger mechanisms leading to glomerulosclerosis and tubulo-interstitial fibrosis. This article is part of a Special Issue entitled Serum Albumin.
authors.affiliation: Division of Nephrology, Dialysis, and Transplantation, Istituto Giannina Gaslini, Genoa, Italy; Laboratory on Pathophysiology of Uremia, Istituto Giannina Gaslini, Genoa, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Bruschi
authors.forename: Laura
authors.initials: L
authors.lastname: Santucci
authors.forename: Giovanni
authors.initials: G
authors.lastname: Candiano
authors.forename: Gian Marco
authors.initials: GM
authors.lastname: Ghiggeri
mesh_terms: D006801:Humans; D008958:Models, Molecular; D011507:Proteinuria / Q000652:urine*; D012709:Serum Albumin / Q000032:analysis* / Q000134:cerebrospinal fluid
chemical_list: D012709:Serum Albumin
keywords: Anionic albumin; CSF; Diabetic microalbuminuria; Glycosyl albumin; Nephrotic syndrome; Non-enzymatic glycosylation; cerebrospinal fluid; ioelectric point; pI