Method for the selective measurement of amino-terminal variants of procalcitonin.
BACKGROUND
Procalcitonin (PCT) is an established marker for diagnosing and monitoring bacterial infections. Full-length PCT [116 amino acids that make up procalcitonin (PCT1-116)] can be truncated, leading to des-Ala-Pro-PCT (des-Alanin-Prolin-Procalcitonin; PCT3-116). Current immunoassays for PCT ("total PCT") use antibodies directed against internal epitopes and are unable to distinguish amino-terminal PCT variants. Here we describe the development of monoclonal antibodies recognizing the amino-termini of PCT1-116 and PCT3-116 and their use in the selective measurement of these PCT species.


METHODS
With newly developed monoclonal antibodies against the amino-termini of PCT1-116 and PCT3-116, and an antibody against the katacalcin moiety of PCT, we developed and characterized immunoluminometric assays for the 2 PCT peptides. We comparatively assessed the kinetics of PCT variants in a human endotoxemia model.


RESULTS
Monoclonal antibodies against the amino-termini of PCT1-116 and PCT3-116 showed <1% cross-reactivity with other PCT-related peptides. The sandwich assays for PCT1-116 and PCT3-116 had functional assay sensitivities of 5 and 1.2 pmol/L, respectively, and exhibited recoveries within 20% of expected values. Plasma PCT1-116 was stable for 6 h at 22 degrees C and 24 h at 4 degrees C, and PCT3-116 was stable for at least 24 h at both temperatures. During experimental endotoxemia in healthy people, both PCT1-116 and PCT3-116 increased early in parallel with total PCT, but further increases in PCT1-116 were significantly slower than for PCT3-116 (P = 0.0049) and total PCT (P = 0.0024).


CONCLUSIONS
The new assays selectively measure PCT1-116 and PCT3-116. Both PCT species increase early during endotoxemia but differ in their kinetics thereafter. The selective measurement of PCT species with different in vivo kinetics may be useful in improving PCT-guided therapies.
Struck
Joachim
J
Research Department, BRAHMS Aktiengesellschaft, Hennigsdorf/Berlin, Germany. j.struck@brahms.de
Strebelow
Martina
M
Tietz
Sonja
S
Alonso
Christine
C
Morgenthaler
Nils G
NG
van der Hoeven
Johannes G
JG
Pickkers
Peter
P
Bergmann
Andreas
A
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology*; D002116:Calcitonin / Q000032:analysis* / Q000737:chemistry / Q000276:immunology; D015740:Calcitonin Gene-Related Peptide; D003429:Cross Reactions; D019446:Endotoxemia / Q000097:blood; D000939:Epitopes / Q000737:chemistry / Q000276:immunology; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007700:Kinetics; D008969:Molecular Sequence Data; D011498:Protein Precursors / Q000032:analysis* / Q000737:chemistry / Q000276:immunology; D014409:Tumor Necrosis Factor-alpha / Q000097:blood
D000911:Antibodies, Monoclonal; C000606589:CALCA protein, human; D000939:Epitopes; D011498:Protein Precursors; D014409:Tumor Necrosis Factor-alpha; D002116:Calcitonin; D015740:Calcitonin Gene-Related Peptide