Processing-independent analysis for pro-C-type natriuretic peptide

N-Terminal Pro-C-Type Natriuretic Peptide: The Novel Marker in Selected Disease Units

BACKGROUND

Amino-terminal pro C type natriuretic peptide (NT proCNP) is the N terminal fragment of the CNP precursor. NT proCNP occurs in an equimolar concentration with CNP in human plasma and is considered to be a marker of the extent of CNP biosynthesis. A recent study has shown associations between plasma NT proCNP and blood pressure; it is also an independent predictor of death and cardiac readmission in people with unstable angina. Beyond that, recent studies have focused on the applicability of assessing NT proCNP peptide levels in the diagnosis of diseases with different etiologies but the same denominator, i.e., inflammation.

METHODS

This study reviewed recent results on the usability of NT proCNP peptide levels in the diagnosis of diseases accompanied by statistical analysis of previously reported results.

RESULTS

The data obtained confirmed the applicability of the assessment of NT proCNP levels in biological fluids in diseases, such as Parkinson's disease, sepsis, meningitis, and asthenozoospermia.

CONCLUSION

The reported results demonstrated that NT-proCNP is helpful in a variety of diseases. Furthermore, changes in serum or CSF levels of NT-proCNP reflect only inflammatory states related to general inflammation. Local inflammation does not trigger an increase in NT proCNP level.

Sex-specific mortality prediction by pro-C-type natriuretic peptide measurement in a prospective cohort of patients with ST-elevation myocardial infarction

OBJECTIVE

To determine the predictive value of pro-C-type natriuretic peptide (pro-CNP) measurement in plasma sampled on admission from patients presenting with ST-elevation myocardial infarction (STEMI).

DESIGN

Prospective cohort study.

SETTING

Two University Hospitals in Denmark.

PARTICIPANTS

1760 consecutive patients (470 females and 1290 males) with confirmed STEMI.

MAIN OUTCOMES AND MEASURES

The main outcome was all-cause mortality at 1 year after presentation and the primary measure was pro-CNP concentration in plasma at admission in all patients and longitudinal measurements in a consecutive subgroup of 287 patients. A reference population (n=688) defined cut-off values of increased pro-CNP concentrations.

RESULTS

In all patients, an increased pro-CNP concentration was associated with a higher all-cause mortality after 1 year (HR 1.6, 95% CI 1.1 to 2.4, P_logrank=0.009) including an interaction of sex (p=0.03). In separate sex-stratified analyses, female patients showed increased all-cause mortality (HR_{1 year} 2.6, 95% CI 1.5 to 4.6), P_logrank <0.001), whereas no differences were found in male patients (HR_{1 year} 1.1, 95% CI 0.7 to 1.9, P_logrank=0.66). After adjusting for potential risk factors, we found increased pro-CNP concentrations≥the median value to be independently associated with increased risk of mortality in female patients within 1 year (HR per 1 pmol/L increase: 1.04, 95% CI 1.01 to 1.06, p=0.007). Moreover, we found indications of sex differences in pro-CNP concentrations over time (higher pro-CNP in males (4.4, 95% CI -0.28 to 9.1 pmol/L, p=0.07) and interaction of sex and time (p=0.13)), and that hypertension was independently associated with higher pro-CNP (4.5, 95% CI 0.6 to 8.4 pmol/L, p=0.03).

CONCLUSIONS

In female but not male patients presenting with STEMI, high concentrations of pro-CNP (≥median) at admission independently indicate a higher risk of all-cause mortality. The findings are remarkably specific for female patients, suggesting a different vascular phenotype beyond traditional measures of coronary artery flow compared with male patients.

Processing-independent analysis (PIA): a method for quantitation of the total peptide-gene expression

The translational product of protein-coding genes undergoes extensive posttranslational modifications. The modifications ensure an increased molecular and functional diversity at protein- and peptide-level. Prohormones are small pro-proteins that are expressed in many cell types, for instance endocrine cells, immune cells, myocytes and neurons. Here they mature to bioactive peptides (cytokines, hormones, growth factors, and neurotransmitters) that are released from the cells in an often regulated manner. The posttranslational processing of prohormones is cell-specific, however, and may vary during evolution and disease. Therefore, it is often inadequate to measure just a single peptide fragment as marker of endocrine, immune, and neuronal functions. In order to meet this challenge, we developed years back a simple "processing-independent analysis" (PIA) for accurate quantification of the total pro-protein product - irrespective of the degree and nature of the posttranslational processing. This review provides an overview of the PIA principle and describes examples of PIA results in different peptide systems.

NT-proCNP as a new indicator of asthenozoospermia

PURPOSE

C-type natriuretic peptide (CNP) is a proinflammatory peptide. The highest concentration of CNP is found in male reproductive organs. This study aims to analyze the role of N-terminal C-type natriuretic propeptide (NT-proCNP) as a new indicator of asthenozoospermia.

MATERIAL/METHODS

Semen was collected after 3-5 days of sexual abstinence from 86 men. The participants were between 25 and 38 years old, 51 of which had asthenozoospermia and 35 of which had normal sperm motility. Semen was analyzed for the concentrations of NT-proCNP, spermatozoa, percentages of live sperm, and sperm exhibiting a specific type of movement. The laboratory tests and analyses were performed using accepted methods and under appropriate conditions.

RESULTS

A significant difference in the concentration and motility of spermatozoa was observed between the focus and control groups. The concentration of spermatozoa in the focus group was significantly lower than in the control group (median: 38.5 vs. 69.8mln/ml [p=0.016] respectively). The progressive motility of spermatozoa demonstrated a significantly lower performance in the focus group than in the control group (median: 10.4% vs. 45% respectively). The concentration of NT-proCNP was significantly higher in the focus group (median: 29.1 vs. 17.9pmol/l; p<0.001). The Area under the Receiver Operating Characteristic (AUROC) curve for the concentration of NT-proCNP - as an indicator of asthenozoospermia - was 0.733. Participants with a concentration of NT-proCNP higher than 28.8pmol/l had asthenozoospermia with 52.9% sensitivity and 94.3% specificity.

CONCLUSIONS

NT-proCNP - an indicator of inflammatory reaction - should be evaluated as an indicator of asthenozoospermia.

C-type natriuretic peptide and its precursor: potential markers in human prostate cancer

AIM

Seminal plasma offer a more organ-specific matrix for markers in prostatic disease. We hypothesized that C-type natriuretic peptide (CNP) expression may constitute such a new target.

METHODS

Patients with benign prostatic hyperplasia, clinically localized and metastatic prostate cancer were examined for CNP and CNP precursor (proCNP) concentrations in blood and seminal plasma. Furthermore, CNP and the CNP receptor (NPR-B) mRNA contents in tissue from prostate and seminal vesicles were analyzed by qPCR.

RESULTS

CNP and NPR-B concentrations decreased with increasing tumor burden (p = 0.0027 and p = 0.0096, respectively). In contrast, seminal plasma CNP and proCNP concentrations were markedly increased with increased tumor burden (p < 0.0001 and p < 0.0001, respectively).

CONCLUSION

CNP/proCNP could be new markers in human prostate cancer.

N-terminal pro-C-type natriuretic peptide in serum associated with bone destruction in patients with multiple myeloma

Aim: To examine whether N-terminal proCNP concentrations in serum is associated with bone destruction in patients with multiple myeloma. Materials & methods: N-terminal proCNP and biochemical bone markers were measured in 153 patients. Radiographic bone disease and skeletal-related events were evaluated at specific time-points. Results: N-terminal proCNP concentrations increased with age. High N-terminal proCNP concentrations were associated with high-risk disease and renal impairment. Renal function explained 22% of the variation. N-terminal proCNP concentrations correlated with serum bone ALP and serum PINP, but lacked association with bone resorption markers, radiographic bone disease and skeletal-related events. Conclusion: Serum N-terminal proCNP are associated with bone formation activity in patients with multiple myeloma, but should be interpreted with caution in patients with renal impairment.

Cardiac C-type natriuretic peptide gene expression and plasma concentrations in neonatal piglets

BACKGROUND

C-type natriuretic peptide (CNP) is a member of the natriuretic peptide family. Cardiac ANP and BNP expressions are firmly established, whereas CNP expression in the mammalian heart remains controversial. In the present report, we used a porcine model of the neonatal period with high expressions of cardiac ANP and BNP in order to elucidate the cardiac CNP expression profile.

METHODS

Plasma and cardiac tissue were obtained from newborn piglets during the first 72 h of life. The chamber-specific CNP mRNA contents were quantified by real-time PCR analysis. The proCNP concentrations in plasma and cardiac tissue extracts were quantified by a porcine-specific radioimmunoassay.

RESULTS

Cardiac CNP mRNA contents (n=24) were low compared to sites of known expression, where porcine seminal vesicle CNP mRNA contents were 200-fold higher. In addition, plasma proCNP concentrations in the newborn piglets (n=44) were exceedingly low compared to proANP concentrations (5.3 pmol/L (3.2-8.6) vs. 3438 pmol/L (2790-5418), p<0.0001). The proCNP concentrations in atrial tissue extracts were barely detectable (≤0.06 pmol/g) (n=2) compared to ventricular proANP (130 pmol/g (101-159)) and atrial proANP (12,303 pmol/g (10,623-15,412)).

CONCLUSION

Our data show that the heart is not a major source of circulating proCNP in neonatal piglets.

Next generation natriuretic peptide measurement

Plasma measurement of natriuretic peptides is a "must" for clinical laboratories. For the next generation measurement, the unraveling of the molecular complexity of the peptides points toward a more qualitative assessment, as the posttranslational processing also changes with disease. Changes in the molecular heterogeneity could in itself contain valuable information of clinical status, and the time seems right for industry and dedicated researchers in the field to get together and discuss the next generation natriuretic peptide measurement. In such an environment, new strategies can be developed with the mutual aim of making already very good plasma markers even better.

Urinary osteocalcin and serum pro-C-type natriuretic peptide predict linear catch-up growth in infants

Preterm (PT) infants are at risk of growth failure despite advanced early care and nutrition. In addition to poor weight gain, slow postnatal linear growth also is associated with adverse neurological outcome. Markers distinguishing infants at risk for impaired catch-up growth are needed. The aim of this longitudinal study was to determine the extent to which postnatal levels of circulating cartilage (serum pro-C-type natriuretic peptide [S-proCNP]) and urinary bone metabolic markers (urinary osteocalcin [MidOC] and two forms of C-terminal cross-linked telopeptide of type I collagen [U-α-CTX-I and U-β-CTX-I]) predict catch-up growth in infancy in 67 PT and 58 full-term (FT) infants. PT infants were significantly shorter than FT infants during the first 6 months of life, but no statistically significant difference was found at the corrected age of 14 months (M14). At the age of 3 months (M3), S-ProCNP and U-MidOC levels, but not U-α-CTX-I and U-β-CTX-I levels, correlated positively with prospective growth velocity from M3 to M14 (ρ = 0.460, p < 0.001 and ρ = 0.710, p < 0.001, respectively). In predicting slow linear growth (growth velocity at the lowest quartile), the area under the S-ProCNP ROC curve was 0.662 and that of U-MidOC 0.891. Thus, U-MidOC, and to lesser extent S-ProCNP at M3 are predictors of catch-up growth in infancy.

B-type natriuretic peptide: from posttranslational processing to clinical measurement

BACKGROUND

Plasma cardiac natriuretic peptides and peptide fragments from their molecular precursors are markers of heart disease. Clinical studies have defined the current diagnostic utility of these markers, whereas biochemical elucidation of peptide structure and posttranslational processing has revealed new plasma peptide forms of potential clinical use.

CONTENT

Natriuretic propeptide structures undergo variable degrees of endo- and exoproteolytic cleavages as well as amino acid modifications, which leave the plasma phase of the peptides highly heterogeneous and dependent on cardiac pathophysiology and capacity. An ongoing characterization of the molecular heterogeneity may not only help us to appreciate the biosynthetic capacity of the endocrine heart but may also lead to the discovery of new and more disease-specific targets for future molecular diagnosis.

SUMMARY

Peptides derived from pro-atrial natriuretic peptide and pro-B-type natriuretic peptide are useful plasma markers in heart failure. New data have defined cardiac myocytes as competent endocrine cells in posttranslational processing and cellular secretion.

Corin is present in the normal human heart, kidney, and blood, with pro-B-type natriuretic peptide processing in the circulation

BACKGROUND

B-type natriuretic peptide (BNP), which is activated in heart failure (HF), is processed to an active form by corin. The corin gene is expressed in the human heart and kidney, but corin protein expression in the heart, kidney, and circulation, along with whether proBNP is processed by circulating corin, remains unknown.

METHODS

We examined corin protein expression by immunostaining and Western blot in human heart and kidney, and we assessed the circulating corin concentration by ELISA. We examined histidine-tagged (His-tag) proBNP(1-108) processing in serum and plasma by immunoprecipitation and Western blot and sequenced the processed form.

RESULTS

Normal human heart and kidney displayed the presence of corin, especially in cells around the vasculature. Both corin and proBNP(1-108) were present in the plasma of healthy human subjects, with circulating corin significantly higher in men than women (P < 0.0001) and a positive correlation of corin to age (P = 0.0497, r = 0.27). In fresh normal plasma and serum, His-tag proBNP(1-108) was processed to a lower molecular weight form confirmed to be BNP. Processed BNP was higher in men than women (P = 0.041) and was positively correlated to plasma corin concentrations (P = 0.041, r = 0.65).

CONCLUSIONS

Our results support the concept that proBNP(1-108) may be processed outside of the heart in the circulation where the proprotein convertase is present. Moreover, sex may impact this process, since corin concentrations are higher in men. These findings may have important physiologic and pathophysiologic implications for the proBNP/corin system in the human.