Difference between total and intact assays for N-terminal propeptide of type I procollagen reflects degradation of pN-collagen rather than denaturation of intact propeptide.
BACKGROUND
The concentration of N-terminal propeptide of type I procollagen (PINP) in the serum reflects the rate of type I collagen formation. Intact PINP assay measures the trimeric propeptide while total P1NP assay measures both trimeric and monomeric forms. In this study we compared these two assays emphasizing the possible differences.


METHODS
Intact and total PINP were measured from serum in healthy Finnish blood donors (n = 34) and in the patients with chronic renal failure before and after haemodialysis (n = 39). In addition, the serum of a normal man, pooled hospital serum samples and the serum of a patient with haemodialysis treatment were fractioned by gel filtration and trimeric and monomeric forms were located. Fractions were lyophilized and intact and total PINP were measured in each fraction. Samples from bedridden geriatric patients (n = 173) were also measured using intact and total PINP assays and a degradation marker of type I collagen (ICTP).


RESULTS
The correlation between intact and total PINP in controls was 0.89 and their PINP concentrations were similar. In haemodialysis or bedridden geriatric patients, the PINP methods gave significantly different results. In gel filtration studies, intact PINP hardly measured monomeric form even if its concentration was disproportionately increased in haemodialysis patients. In bedridden geriatric patients, the difference of total and intact PINP correlated significantly to degradation marker ICTP.


CONCLUSIONS
Difference between total and intact assays for PINP seem to reflect degradation of pN-collagen rather than denaturation of intact propeptide.
Koivula
Marja-Kaisa
MK
Institute of Diagnostics, Department of Clinical Chemistry, University of Oulu, Finland.
Ruotsalainen
Vesa
V
Björkman
Mikko
M
Nurmenniemi
Sini
S
Ikäheimo
Risto
R
Savolainen
Kari
K
Sorva
Antti
A
Risteli
Juha
J
D000328:Adult; D001774:Blood Chemical Analysis / Q000379:methods; D024042:Collagen Type I / Q000032:analysis / Q000097:blood / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009994:Osmolar Concentration; D010446:Peptide Fragments / Q000032:analysis / Q000097:blood / Q000737:chemistry / Q000378:metabolism; D010748:Phosphopeptides / Q000032:analysis* / Q000097:blood / Q000378:metabolism; D011347:Procollagen / Q000032:analysis / Q000097:blood / Q000737:chemistry / Q000378:metabolism*; D011489:Protein Denaturation / Q000502:physiology; D011499:Protein Processing, Post-Translational / Q000502:physiology*; D006435:Renal Dialysis; D013048:Specimen Handling / Q000379:methods / Q000592:standards; D055815:Young Adult
D024042:Collagen Type I; C062121:N-propeptide type I collagen; D010446:Peptide Fragments; D010748:Phosphopeptides; D011347:Procollagen