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The heart is a source of circulating cardiotrophin-1 in humans
1Diagnostic Department, Shionogi and Company, Ltd., 2-5-1 Mishima, Settsu-shi, Osaka, 566-0022, Japan.
Insights
A new radioimmunoassay (RIA) was developed to measure Cardiotrophin-1 (CT-1) levels in human plasma. This assay confirms the heart secretes CT-1, paving the way for clinical studies.
Area of Science:
- Cardiovascular Biology
- Cytokine Signaling
- Biochemical Assays
Background:
- Cardiotrophin-1 (CT-1) is an interleukin-6 family cytokine with known cardiac hypertrophic and survival effects.
- The clinical relevance of CT-1 is limited by the lack of specific and sensitive measurement assays.
- Understanding CT-1's role in cardiovascular health requires reliable quantification methods.
Purpose of the Study:
- To develop a competitive radioimmunoassay (RIA) for quantifying human Cardiotrophin-1 (CT-1) in plasma.
- To validate the specificity and sensitivity of the developed RIA for CT-1.
- To investigate the origin and molecular form of circulating CT-1.
Main Methods:
- Development of a competitive RIA using rabbit antiserum against human CT-1 and recombinant CT-1 as a calibrator.
- Testing for cross-reactivity with other interleukin-6 family cytokines.
- Measurement of CT-1 plasma levels in healthy volunteers and analysis of CT-1 from aortic and coronary sinus samples.
Main Results:
- The developed RIA is specific for CT-1, showing no cross-reactivity with related cytokines.
- The assay has a low detection limit (43 fmol/ml) and a working range of 120-8300 fmol/ml.
- Mean plasma CT-1 levels in healthy volunteers were 571 +/- 75 fmol/ml, with the primary circulating form matching recombinant CT-1.
- Significantly higher CT-1 concentrations were found in the aorta and coronary sinus compared to peripheral circulation, indicating cardiac secretion.
Conclusions:
- A specific and sensitive RIA for human CT-1 has been successfully developed.
- The heart is confirmed as a source of circulating CT-1, secreted into the coronary sinus.
- This RIA provides a crucial tool for future research into the clinical significance of CT-1 in cardiovascular diseases.
Abstract:
Cardiotrophin-1 (CT-1) is a new member of the interleukin (IL)-6 family of cytokines and one of the endogenous ligands for gp130 signaling pathways in the heart, which has potent hypertrophic and survival effects on cardiac myocytes. However, the clinical significance of CT-1 is poorly understood, mainly because there is no widely applicable specific and sensitive assay system for measuring plasma levels of circulating CT-1. We therefore developed a competitive radioimmunoassay (RIA) for human CT-1 with rabbit antiserum recognizing the N-terminus region of human CT-1 and using recombinant human CT-1 as a calibrator. The assay displays no cross-reactivities with any of the IL-6 family of cytokines including IL-11, leukemia inhibitory factor, ciliary neurotrophic factor, and oncostatin M. The lower detection limit in buffer was found to be 43 fmol/ml, and the working range was 120-8300 fmol/ml (CV < 15%). This RIA directly recognizes CT-1-like immunoreactivity in human plasma with a mean value of 571 +/- 75 fmol/ml (mean +/- SD) in healthy volunteers. The RIA coupled with gel filtration chromatographic analyses showed that the major molecular form of circulating CT-1 corresponds to recombinant full-length human CT-1. Moreover, there is a significant increase in the plasma CT-1 concentration from the aorta and coronary sinus, which clearly indicates that the heart secretes CT-1 via the coronary sinus into the peripheral circulation. This RIA should serve as a powerful tool for investigating the clinical significance of CT-1.