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

This version was published on 1 January 2010

Ann Clin Biochem 2010;47:67-71
© 2010 Association for Clinical Biochemistry


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Original Articles

Marja-Kaisa Koivula1,2,
Vesa Ruotsalainen3,
Mikko Björkman4,
Sini Nurmenniemi1,
Risto Ikäheimo5,
Kari Savolainen6,
Antti Sorva7 and
Juha Risteli1

1 Institute of Diagnostics, Department of Clinical Chemistry, University of Oulu;
2 TYKSLAB, Turku University Central Hospital, Turku;
3 Orion Diagnostica Oy, Oulu;
4 Clinics of Internal Medicine and Geriatrics, Helsinki University Central Hospital, Helsinki;
5 Institute of Clinical Medicine, Department of Internal Medicine, University of Oulu, Oulu;
6 Eastern Finland Laboratory Centre (ISLAB), Kuopio;
7 Department of Long-Term Care, Helsinki City Hospital, Helsinki, Finland

Corresponding author: Juha Risteli, Professor of Clinical Chemistry, Institute of Diagnostics, University of Oulu, PO Box 5000, FI-90014 Oulu, Finland. Email: juha.risteli{at}oulu.fi

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 totalP1NP assay measures both trimeric and monomeric forms. In thisstudy we compared these two assays emphasizing the possibledifferences.

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 assaysand a degradation marker of type I collagen (ICTP).

Results: The correlation between intact and total PINP in controls was0.89 and their PINP concentrations were similar. In haemodialysisor bedridden geriatric patients, the PINP methods gave significantlydifferent results. In gel filtration studies, intact PINP hardlymeasured monomeric form even if its concentration was disproportionatelyincreased in haemodialysis patients. In bedridden geriatricpatients, the difference of total and intact PINP correlatedsignificantly to degradation marker ICTP.

Conclusions: Difference between total and intact assays for PINP seem toreflect degradation of pN-collagen rather than denaturationof intact propeptide.

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