Ingrid Hunter

N-terminal Pro–Atrial Natriuretic Peptide Measurement in Plasma Suggests Covalent Modification

BACKGROUND The N-terminal fragment of cardiac-derived pro-B-type natriuretic peptide is a glycosylated polypeptide. It is unknown whether N-terminal pro-atrial natriuretic peptide (proANP) fragments are also covalently modified. We therefore evaluated the clinical performance of 2 distinctly different proANP assays on clinical outcome. METHODS We examined 474 elderly patients with symptoms of heart failure presenting in a primary healthcare setting. Samples were analyzed with an automated immunoluminometric midregion proANP (MR-proANP) assay and a new processing-independent assay (PIA) developed in our laboratory. The results were compared with Bland-Altman plots, and clinical performance was assessed by generating ROC curves for different clinical outcomes. RESULTS Despite linear regression results indicating a good correlation (r = 0.85; P < 0.0001), the PIA measured considerably more proANP than the MR-proANP assay (mean difference, 663 pmol/L; SD, 478 pmol/L). In contrast, the clinical performances of the 2 assays [as assessed by the area under the ROC curve (AUC)] in detecting left ventricular dysfunction were similar [proANP PIA, 0.71 (95% CI, 0.63-0.79); MR-proANP assay, 0.74 (95% CI, 0.66-0.81); P = 0.32]. The prognostic ability to report cardiovascular mortality during a 10-year follow-up revealed AUC values of 0.66 (95% CI, 0.60-0.71) for the proANP PIA and 0.69 (95% CI, 0.63-0.74) for the MR-proANP assay (P = 0.08, for comparing the 2 assays). CONCLUSIONS Our data suggest that N-terminal proANP fragments in patient plasma differ from the calibrator peptides used but that the difference does not affect ROC curves in an elderly cohort of patients with mild to moderate heart failure. We suggest that human N-terminal proANP fragments can be covalently modified.

Measurement of the total proANP product in mammals by processing independent analysis

The cellular processing of natriuretic propeptides is attenuated in heart disease, resulting in release of a mixture of unprocessed precursor, partially processed fragments, and the bioactive hormone. Here, we report a species-independent method for quantification of pro-atrial natriuretic peptide (proANP) and its products irrespective of variable post-translational processing. The processing-independent assay (PIA) was developed raising mono-specific antibodies against the C-terminus of sequence 1-16 in proANP. The assay procedure included plasma extraction followed by tryptic cleavage, which releases the assay epitope from the N-terminal region. The PIA was tested in elderly patients with symptoms of heart failure (n=450), in pigs with acute myocardial infarction (n=21), and in normal dogs and dogs with heart failure (n=77). The epitope specificity permitted reliable measurement in man, dog, cat and pig. In human plasma, the PIA correlated well with an established proANP analysis (r=0.86, P<0.0001) but with a 5.5-fold difference in plasma level (P<0.0001). In pigs, the PIA measured 9.2-fold higher concentrations compared to a human assay (804 versus 87pmol/L, P<0.0001). The basal proANP concentration was 396pmol/L in dogs: a dramatic increase was seen in canine heart failure. Our new processing- and species-independent proANP assay allows for the measurement of the total proANP product, irrespective of changes in post-translational maturation. We suggest that this tool should be used for comparative studies between human patients and porcine and canine models of human cardiac disease.

Human and equine cardiovascular endocrinology: beware to compare

Cardiac biomarkers such as troponins and natriuretic peptides are routinely used in human medicine for the evaluation of myocardial damage and heart failure. Recently, these markers have also been introduced in veterinary medicine. Comparison between human and equine cardiac biomarker studies show important species differences, which can partly be explained by variations in physiology or pathophysiology. Most important are physiological differences in heart rate, cardiovascular response to exercise, food and water intake, and molecular elimination in plasma. Pathological differences are even more prominent. In humans, troponins and natriuretic peptides are mostly used for the diagnosis of acute coronary syndromes and heart failure. These cardiac entities, however, are rare in horses. In this species, cardiac biomarkers are rather proposed for the assessment of valvular or myocardial disease. In conclusion, these species differences corroborate that extrapolation of cardiac biomarker data should always be performed with caution and species-specific data should be applied whenever possible.

ProANP plasma measurement predicts all-cause mortality in acutely hospitalised patients: a cohort study

Importance The association of natriuretic peptide measurement with all-cause mortality in a broad selection of acutely admitted patients has not yet been examined. Objective To test the risk association between pro-atrial natriuretic peptide (ANP) and short-term and long-term mortality and its predictive value in acutely hospitalised patients and compare this to N-terminal B-type natriuretic peptide (NT-proBNP). Design, setting and patients Participants were selected from the Copenhagen Hospital Heart Failure Study (n=3644). Medical history, satisfactory echocardiography and blood samples were available on 2193 participants in 1998–1999 where NT-proBNP was measured. Vital status after discharge was obtained from national central data registers. A total of 1337 participants with eligible blood samples were selected in 2010–2011 for proANP measurement. Among these, 1255 (94%) were acutely hospitalised in 1998–1999. Main outcome measure(s) 1-year and long-term mortality. Results Median follow-up period was 11.5 years. At the end of follow-up, 926 patients had died, 239 during the first year. ProANP quartiles to 2–4 (median proANP levels 594 pmol/L, 990 pmol/L and 2052 pmol/L, respectively) associated with a stepwise increase in risk of 1-year and long-term mortality compared to the first quartile (336 pmol/L) in multivariable adjusted Cox proportional regression models (HR 1.53 95% CI 1.30 to 1.81 and HR 1.26 95% CI 1.17 to 1.36, respectively). An addition of NT-proBNP attenuated proANPs association with mortality in the models (HR 1.24 95% CI 1.01 to 1.53 and 1.14 95% CI 1.03 to 1.26, respectively). The increased risk was observed in participants with the highest proANP levels (fourth quartile). Similar results were observed in subgroups of participants with no evidence of cardiovascular disease (CVD). ProANP in quartiles improved discrimination when added to traditional risk factors in prediction models for 1-year (integrated discrimination improvement (IDI) 0.141 95% CI 0.085 to 0.197; C-index 0.753 95% CI 0.724 to 0.783, P for improvement 0.003) and long-term mortality (IDI 0.053 95% CI 0.032 to 0.074; C-index 0.736 95% CI 0.720 to 0.752, P for improvement <0.001) with similar results in subgroups. Discrimination was best in a combined model with proANP as well as NT-proBNP included. Conclusions and relevance High plasma proANP concentrations are associated with and predict short-term and long-term all-cause mortality in acutely hospitalised patients irrespective of CVD status at admission.

Cardiac Dysfunction in a Porcine Model of Pediatric Malnutrition.

Background Half a million children die annually of severe acute malnutrition and cardiac dysfunction may contribute to the mortality. However, cardiac function remains poorly examined in cases of severe acute malnutrition. Objective To determine malnutrition-induced echocardiographic disturbances and longitudinal changes in plasma pro-atrial natriuretic peptide and cardiac troponin-T in a pediatric porcine model. Methods and Results Five-week old piglets (Duroc-x-Danish Landrace-x-Yorkshire) were fed a nutritionally inadequate maize-flour diet to induce malnutrition (MAIZE, n = 12) or a reference diet (AGE-REF, n = 12) for 7 weeks. Outcomes were compared to a weight-matched reference group (WEIGHT-REF, n = 8). Pro-atrial natriuretic peptide and cardiac troponin-T were measured weekly. Plasma pro-atrial natriuretic peptide decreased in both MAIZE and AGE-REF during the first 3 weeks but increased markedly in MAIZE relative to AGE-REF during week 5–7 (p≤0.001). There was overall no difference in plasma cardiac troponin-T between groups. However, further analysis revealed that release of cardiac troponin-T in plasma was more frequent in AGE-REF compared with MAIZE (OR: 4.8; 95%CI: 1.2–19.7; p = 0.03). However, when release occurred, cardiac troponin-T concentration was 6.9-fold higher (95%CI: 3.0–15.9; p<0.001) in MAIZE compared to AGE-REF. At week 7, the mean body weight in MAIZE was lower than AGE-REF (8.3 vs 32.4 kg, p<0.001), whereas heart-weight relative to body-weight was similar across the three groups. The myocardial performance index was 86% higher in MAIZE vs AGE-REF (p<0.001) and 27% higher in MAIZE vs WEIGHT-REF (p = 0.025). Conclusions Malnutrition associates with cardiac dysfunction in a pediatric porcine model by increased myocardial performance index and pro-atrial natriuretic peptide and it associates with cardiac injury by elevated cardiac troponin-T. Clinical studies are needed to see if the same applies for children suffering from malnutrition.

Total plasma proANP increases with atrial dilatation in horses

Equine atrial natriuretic peptide (ANP) plasma concentrations are correlated with left atrial size. However, species-specific assays are lacking and the results from human assays are poorly reproducible. A new methodology called processing independent analysis (PIA) that measures the total proANP product in plasma has proven to be successful in human medicine, but has never been used in horses. The aims were to establish an equine proANP reference interval by measurement of the total proANP product using PIA and to examine the proANP concentrations in horses with atrial dilatation. Sample stability was studied by comparison of storage at −80°C and −20°C. Plasma samples were obtained from 23 healthy horses, 12 horses with moderate or severe valvular regurgitation without atrial dilatation and 42 horses with valvular regurgitation and atrial dilatation. The proANP concentration was significantly (P<0.001) higher in horses with atrial dilatation (761.4 (442.1–1859.1) pmol/l) than in healthy horses (491.6 (429.5–765.9) pmol/l; P<0.001) or horses with cardiac disease but without atrial dilatation (544.4 (457.0–677.6) pmol/l). A cut-off value (573.8 pmol/l) for detection of atrial dilatation was calculated. Sample storage at −80°C did not differ from sample storage at −20°C. The measurement of total proANP in plasma detects atrial dilatation in horses and may be useful for clinical evaluation in equine medicine.

Processing-independent proANP measurement for low concentrations in plasma: reference intervals and effect of body mass index and plasma glucose

Abstract Background: Decreased concentrations of pro-atrial-derived natriuretic peptides (proABP) in plasma have been associated with obesity and suggested as a predictor of type 2 diabetes. However, assays for measuring proANP are generally aimed to quantitate higher concentrations of proANP associated with cardiac disease. Therefore, we aimed to measure plasma proANP concentrations in a non-obese Scandinavian reference material and evaluate potential associations of plasma proANP with body mass index (BMI) and plasma glucose, respectively. Methods: We report an optimized processing-independent assay (PIA) for proANP in the lower concentration range. The assay was optimized by raising the amount of radioactive tracer and modifying the mixing ratio of resuspended plasma and buffer. Blood samples from a Scandinavian plasma cohort of 693 healthy subjects were then analyzed and age and gender-specific reference intervals were determined. Results: Simple linear regression analyses of proANP and both BMI and plasma glucose in fasting subjects displayed insignificant associations. Multiple regression analyses supported these findings. However, a higher median plasma concentration of proANP was noted among women <50 years compared to men, whereas no gender-specific differences were seen in other age groups. Conclusions: Our results show that in a healthy non-obese population, BMI and plasma glucose in fasting subjects do not affect plasma proANP concentrations. Our method should be considered for future studies on low proANP concentration studies, e.g. in obesity and diabetes.