Increased Plasma Concentrations of Midregional Proatrial Natriuretic Peptide Is Associated With Risk of Cardiorenal Dysfunction in Type 1 Diabetes

Original Article Increased Plasma Concentrations of Midregional Proatrial Natriuretic Peptide Is Associated With Risk of Cardiorenal Dysfunction in Type 1 Diabetes Simone Theilade, 1 Tine Willum Hansen, 1 Jens Peter Goetze, 2,3 and Peter Rossing 1,3,4 BACKGROUND To examine possible associations between midregional proatrial natriuretic peptide (MR-proANP) and diabetic complications at baseline and risk of mortality and end-stage renal disease (ESRD) during follow-up in type 1 diabetes. METHODS Observational study including 667 patients, with plasma MR-proANP measured at baseline. Complications were defined as micro- (n = 168) or macroalbuminuria (n = 190) (urinary albumin excretion rate (UAER) 30 299 or 300 mg/24 h), previous cardiovascular disease (CVD) (n = 143), cardiac autonomic dysfunction (heart rate variability < 11 beats/min) (n = 369), and retinopathy (n = 523). Adjustments included gender, age, systolic blood pressure, estimated glomerular filtration rate (egfr), UAER, HbA 1c, total cholesterol, 24-hour urinary sodium excretion (24h-U Na ), body mass index, daily insulin dose, antihypertensive treatment, and smoking in linear regression analyses and analysis of covariance models. Development of ESRD (dialysis, renal transplantation, or GFR/eGFR < 15 ml/min/1.73 m 2 ) and mortality was recorded through national registers. RESULTS The cohort included 293 (44%) females, aged 55 ± 13 years. Plasma MR-proANP (median (interquartile)) was 74.7 (49.2 116.8) pmol/l. Adjusted, MR-proANP correlated positively with age and UAER and negatively with egfr, 24h-U Na, total cholesterol, and HbA 1c (P < 0.05). Moreover, MR-proANP levels increased with albuminuria degree and were higher in patients with previous CVD (P 0.001), but similar in patients with or without autonomic dysfunction or retinopathy (P 0.076). During follow-up (3.5 (3.1 4.0) years), higher MR-proANP concentrations predicted ESRD and mortality combined (n = 35) adjusted for gender, age, systolic blood pressure, egfr, and previous CVD (hazard ratio per 1SD increase in loganp: 2.8 (1.6 4.7; P < 0.001)). CONCLUSIONS Increased plasma MR-proANP was associated with impaired renal function, increased albuminuria, and previous CVD. Moreover, MR-proANP concentrations were associated with increased risk of development of ESRD and mortality combined during follow-up. Keywords: atrial natriuretic peptide; blood pressure; diabetic complications; hypertension; natriuretic peptide, type 1 diabetes. doi:10.1093/ajh/hpu227 Atrial natriuretic peptide (ANP) is predominantly secreted from atrial myocytes in response to atrial stretch 1, regulates renal sodium and water secretion and reduces systemic blood pressure. 2,3 The hormone exerts its effects directly in the kidney and cardiovascular system as well as through inhibition of the renin-angiotensin-aldosterone system (RAAS) and sympathetic activity and by inducing endothelial modulation, 3 causing vasodilation, increased renal blood flow, and glomerular filtration (Figure 1). In hyperglycemia, RAAS activation induces raised blood pressure 4, which partly is counteracted by concurrent increased ANP secretion. 5 Interestingly, the overall opposing effect of ANP on blood pressure appears to be exaggerated in hypertension, 6 suggesting a general blood pressure regulatory effect. Despite the beneficial hormonal actions of ANP, higher concentrations in circulation may reflect hyposensitivity or increased release due to cardiac disease. This partly explains why higher concentrations are associated with worse outcome. In patients with type 1 diabetes, ANP concentrations are elevated, and incrementally so with presence of concurrent microalbuminuria, poor glycemic control, and hypertension. 7 In type 2 diabetes, higher ANP levels are associated with reduced kidney function and increased risk of cardiovascular events. 8 Furthermore, higher levels of ANP are associated with arterial stiffness 1,9 and severity of hypertension 1 and with increased mortality in unselected acutely hospitalized patients, 10 patients with heart failure, 11 ischemic heart disease, 12 and in dialysis patients. 13 Correspondence: Simone Theilade (ktld@steno.dk). Initially submitted July 30, 2014; date of first revision August 25, 2014; accepted for publication October 20, 2014; online publication December 1, 2014. 1 Steno Diabetes Center, Gentofte, Denmark; 2 Department of Clinical Biochemistry, Rigshospitalet, Copenhagen, Denmark; 3 Faculty of Health Sciences, Aarhus University, Aarhus, Denmark; 4 Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark. American Journal of Hypertension, Ltd 2014. All rights reserved. For Permissions, please email: journals.permissions@oup.com 772 American Journal of Hypertension 28(6) June 2015

MR-proANP in Type 1 Diabetes Figure 1. Atrial natriuretic peptide (ANP) regulation. Diagram of the ANP activation and action. Abbreviations: BP, blood pressure; ECV, extracellular volume; GFR, glomerular filtration rate; SNS, sympathetic nerve system. Due to the short half-life of ANP, the hormonal precursor, proanp, is often measured as a surrogate marker for cardiac ANP. 2 Brain natriuretic peptide (BNP), another more thoroughly investigated natriuretic peptide, has previously been found to predict heart failure and mortality in type 1 and 2 diabetes. 8,14,15 However, ANP regulates BP and reduces cardiac hypertrophy, while BNP regulates cardiac remodeling, 16 hence the 2 natriuretic hormones may not be interchangeable. In accordance with this, ANP appears to have a BNPindependent predictive value 17 and may be superior to BNP as a prognostic marker for mortality in patients with heart failure. 17,18 However, ANP is much less investigated in particular in patients with diabetes. In the current study in patients with type 1 diabetes, we measured midregional proanp and examined the crosssectional association with diabetes duration and diabetic complications. Moreover, we assessed the predictive value of MR-proANP measurement in relation to all-cause mortality and end-stage renal disease (ESRD) during follow-up. METHODS Study design and population The cohort has previously been described. 19 Briefly, during 2009 2011, Caucasian patients with type 1 diabetes but without ESRD (dialysis, renal transplantation, or glomerular filtration rate/estimated glomerular filtration rate (GFR/ egfr) < 15 ml/min/1.73 m 2 ) attending the outpatient clinic at the Steno Diabetes Center were recruited to enter a study examining diabetic complications. Of 1,285 patients invited, 676 (52.6 %) accepted to participate. The study conformed to the Declaration of Helsinki was approved by the local ethics committee, and all patients gave written informed consent. Clinical and laboratory methods Office blood pressure was measured after 15 minutes supine rest as the average of 3 left brachial measurements (UA787, A&D Medical, San Jose, CA). All patients had blood samples and phenotypic characteristics collected. HbA 1c was measured by high-performance liquid chromatography (normal range: 4.1% 6.4%, 21 46 mmol/mol, Variant; Biorad Laboratories, Munich, Germany), plasma cholesterol and serum creatinine concentration by standardized methods. All participants had blood samples drawn and stored in EDTA plasma at 80 C for future analysis of biomarkers. After 1 thaw circle, MR-proANP was measured on the Kryptor platform (Thermo-Fisher, Germany) according to manufacturer s manual: The assay has been validated earlier in our laboratory (N-terminal proanp measurement in plasma suggests covalent modification). 20 Urinary albumin excretion rate (UAER) was measured in 2 sterile 24-hour urine collections obtained in connection with the study by enzyme immunoassay. Additional information on UAER was based on historical samples from medical records. Patients were stratified as normo-, micro-, or macroalbuminuric if UAER < 30 mg/24 h, 30 299 mg/24 h, or 300 mg/24 h, respectively, in 2 out of 3 consecutive measurements within 6 months, in the absence of other kidney or urinary tract diseases. Patients with a history of persistently elevated UAER, subsequently reduced with treatment, were categorized according to historic elevated samples. Urinary sodium excretion was also determined as a geometric mean from the 24-hour urine samples. egfr was calculated by the 4 variables Modification of Diet in Renal Disease adapted to isotope dilution mass spectrophotometry-traceable creatinine measurements. Cardiovascular disease (CVD) was history of myocardial infarction, revascularization, peripheral arterial disease, or stroke. Cardiac autonomic function was assessed by heart rate variability recorded during paced deep breathing. A heart rate variability < 11 beats/min defined autonomic dysfunction. 21 Retinopathy status was obtained from medical records. All patients had regular ophthalmological exams, where retinopathy was assessed from retinal photographs taken through dilated pupils. Presence of retinopathy was either simple, proliferative or blindness based on the worst eye. Information on antihypertensive treatment was retrieved from patients medical records and cross-checked with the patients. Antihypertensive treatment included renin-angiotensin blocking agents, alpha, beta, and calcium blockers, spironolactone, moxonidine, and diuretics. Based on standardized questionnaires, current smoking was 1 cigarettes/cigars/pipes per day. Information on antihypertensive treatment was obtained from questionnaires and cross checked with medical records at Steno Diabetes Center. Ascertainment of events On 1 April 2014, we ascertained vital status and incidence of ESRD for all patients through the electronic patient s records at Steno Diabetes Center. These records are linked to a nationwide electronic registration of admissions and medical records from hospitalizations and are continuously updated from the Danish Civil Registration System with information on vital status. American Journal of Hypertension 28(6) June 2015 773

Theilade et al. Statistical analysis Normally distributed variables are given as mean ± SD, whereas nonnormally distributed variables are given as median (interquartile range) and log transformed (base e) before analysis. Uni- and multivariate linear regression was used to compare levels of MR-proANP with covariates. Student s t-test, chi-square test, and analysis of variance were used for comparisons between groups, while analysis of covariance was applied for adjustment. Multiple logistic regression calculated odds ratios for diabetic complications per 1SD increase in loganp. All adjustments included gender, age, diabetes duration, systolic blood pressure, egfr, UAER, HbA 1c, total cholesterol, 24-hour urinary sodium excretion (24h-U Na ), body mass index, total daily insulin dose, antihypertensive treatment, and smoking. We modeled the risk of a combined end point of all-cause mortality or ESRD during follow-up in Cox regression analysis adjusted for gender, age, egfr, systolic blood pressure, and previous CVD (due to low number of events, no further adjustment was made). A 2-tailed P value < 0.05 was considered significant. Statistical analyses were performed using SPSS for Windows, version 20.0 (SPSS, Chicago, IL). RESULTS Characteristics Of the original cohort (n = 676), MR-proANP levels were available in 667 (98.7%) patients. In 9 patients, there was insufficient plasma for MR-proANP measurement. Table 1 shows characteristics of the analyzed cohort in total and divided into patients with normo-, micro-, and macroalbuminuria. Covariates Median (interquartile) MR-proANP was 74.7 (49.2 116.8) pmol/l. MR-proANP correlated significantly with egfr (r = 0.59), age (r = 0.49), pulse pressure (r = 0.38), diabetes duration (r = 0.37), UAER (r = 0.34), systolic blood pressure (r = 0.25), 24h-U Na (r = 0.20), total daily insulin dose (r = 0.17), diastolic blood pressure (r = 0.14), HbA 1c (r = 0.11), total cholesterol (r = 0.10), and heart rate (r = 0.08) (P 0.037 for all). MR-proANP levels were higher in smokers and in patients receiving antihypertensive treatment (P 0.028), but similar in men and women and did not correlate with body mass index (P 0.56). In multivariate analysis, MR-proANP levels correlated positive with age and UAER and negatively with egfr, 24h- U Na, total cholesterol, and HbA 1c (P 0.021). Diabetes duration Normoalbuminuric patients (n = 309) were split into patients with short (<10 years) (n = 94) and long diabetes duration (n = 215). MR-proANP levels were lower in patients with short vs. long diabetes duration (48.8 (38.2 68.8) vs. 67.6 (47.3 94.0) pmol/l; P < 0.001; Figure 2); however this attenuated after adjustment (P = 0.58; Figure 3). Moreover, adjusted analyses of diabetes duration as a continuous variable in both normoalbuminuric and all patients did not reveal any relationship between MR-proANP levels and diabetes duration (P 0.70). Complications MR-proANP increased with albuminuria degree, the levels for patients with normo-, micro-, and macroalbuminria were: 62.2 (43.7 88.5), 75.8 (52.0 129.3), and 108.5 (70.5 166.3) pmol/l (P < 0.001; Figure 2). This difference remained significant after adjustment (not including UAER in the model) (P = 0.001; Figure 3). Per 1SD increase in proanp, the odds ratio for albuminuria (micro- and macroalbuminuria combined) was 1.9 (P < 0.001; Table 2). Moreover, MR-proANP levels were higher in patients with (n = 143) vs. without previous CVD (116.5 (70.4 183.1) vs. 68.0 (46.8 102.5) pmol/l; P < 0.001, adjusted P < 0.001; Figures 2 and 3). Per 1SD increase in proanp, the odds ratio for previous CVD was 1.7 (P = 0.002; Table 2). Including pulse pressure and heart rate in the adjusted models did not alter the results (data not shown). Cardiac autonomic function was assessed in 623 patients. In patients with vs. without autonomic dysfunction (n = 369), MR-proANP levels were higher (90.7 (61.2 138.2) vs. 55.0 (40.4 79.6) pmol/l; P < 0.001; Figure 2). However, this difference disappeared after adjustment (P= 0.15). Retinopathy status was available in 664 patients. In patients with (n = 523) vs. without (n = 141) retinopathy, MR-proANP levels were higher (81.7 (53.1 125.0) vs. 61.2 (42.0 92.9) pmol/l; P < 0.001; Figure 2). But, adjustment attenuated the significance of this difference (P = 0.076). Follow-up During a median follow-up of 3.5 (3.1 4.0) years, 22 (3.3%) patients died and 13 (1.9%) developed ESRD. None of the patients who developed ESRD died subsequently during the follow-up period. The MR-proANP concentrations in patients that experienced the combined event of death or ESRD were 195.2 (127.1 268.7) pmol/l compared with 72.3 (48.5 111.6) pmol/l in patients without an event (P < 0.001; Figure 2). This difference remained significant following adjustment for gender, age, systolic blood pressure, and egfr (P < 0.001; Figure 3). Including pulse pressure and heart rate instead of or additional to systolic blood pressure did not alter the results (data not shown). In Cox regression, higher MR-proANP (per 1SD increase) predicted the combined event independent of gender, age, egfr, systolic blood pressure, and previous CVD (hazard ratio: 2.77 (1.62 4.74; P < 0.001)). Including beta-blocker, calcium-blocker, and diuretic treatment in the model did not alter the results (hazard ratio: 2.80 (1.62 4.89)). Nor did exchanging systolic blood pressure with pulse pressure (hazard ratio: 2.70 (1.57 4.65)). 774 American Journal of Hypertension 28(6) June 2015

MR-proANP in Type 1 Diabetes Table 1. Baseline characteristics All patients (n = 667) Normoalbuminuria (n = 309) Microalbuminuria (n = 168) Macroalbuminuria (n = 190) P value Female (%) 44 49 39 42 0.11 Age (years) 55 ± 13 53 ± 14 58 ± 13 55 ± 10 0.001 Diabetes duration (years) 33 ± 16 28 ± 17 35 ± 15 38 ± 11 <0.001 egfr (ml/min/1.73 m 2 ) 83 ± 28 93 ± 22 85 ± 26 63 ± 29 <0.001 UAER (mg/24 h) a 17 (8 65) 8 (6 12) 33 (17 61) 136 (33 479) HbA 1c (mmol/mol) 64 ± 13 62 ± 11 65 ± 13 68 ± 14 <0.001 HbA 1c (%) 8.0 ± 1.2 7.8 ± 1.0 8.1 ± 1.2 8.4 ± 1.2 <0.001 Total daily insulin dose (international units) 42 (32 59) 40 (30 55) 43 (33 62) 46 (34 60) 0.027 Total cholesterol (mmol/l) 4.7 ± 0.9 4.7 ± 0.8 4.7 ± 0.9 4.6 ± 1.0 0.33 Urinary sodium excretion (mmol/24 h) 151 (118 194) 151 (118 194) 155 (121 201) 148 (112 188) 0.45 Body mass index (kg/m 2 ) 25.3 ± 4.0 24.8 ± 3.6 25.7 ± 4.1 25.7 ± 4.5 0.031 Antihypertensive medication, any (%) 72 46 90 98 <0.001 Beta-blocker treatment (%) 13 9 14 19 0.003 Calcium-blocker treatment (%) 31 16 45 44 <0.001 Diuretic treatment (%) 50 27 56 83 <0.001 Smokers (%) 21 18 19 25 0.17 Systolic blood pressure (mm Hg) 132 ± 17 129 ± 16 134 ± 18 135 ± 19 0.008 Diastolic blood pressure (mm Hg) 74 ± 9 75 ± 9 73 ± 9 74 ± 10 0.025 MR-proANP (pmol/l) 74.7 (49.2 116.8) 62.2 (43.7 88.5) 75.8 (52.2 130.1) 107.5 (70.4 166.3) <0.001 Data represent percentage (%), mean ± SD, or median (interquartile range). P values are for unadjusted comparisons (ANOVA or chi-square test) between normo-, micro-, and macroalbuminuric patients. Abbreviations: ANOVA, analysis of variance; egfr, estimated glomerular filtration rate; MR-proANP, midregional proatrial natriuretic peptide; UAER, urinary albumin excretion rate. a Some patients with previously persistent macro- or macroalbuminuria had values <30 and <300 mg/24 h, respectively, at the time of investigation. American Journal of Hypertension 28(6) June 2015 775

Theilade et al. 300 250 MR-proANP (pmol/ml) 200 150 100 50 0 Figure 2. MR-proANP levels in patient groups. Bars showing median (interquartile range) levels of MR-proANP in different patient groups. P values are unadjusted ANOVA. : <0.001. Abbreviations: ANOVA, analysis of variance; ESRD, end-stage renal disease; MR-proANP, midregional proatrial natriuretic peptide. Figure 3. Adjusted MR-proANP (logarithmic) in patient groups. Bars showing adjusted marginal means and 95% confidence intervals in different patient groups. P values are adjusted ANCOVA. : <0.001, : <0.05. $: Adjusted for gender, age, diabetes duration, systolic blood pressure, egfr, UAER, HbA 1c, total cholesterol, 24-hour urinary sodium excretion (24h-U Na ), body mass index, total daily insulin dose, antihypertensive treatment, and smoking. #: Adjusted for gender, age, diabetes duration, systolic blood pressure, egfr, HbA 1c, total cholesterol, 24-hour urinary sodium excretion (24h-U Na ), body mass index, total daily insulin dose, antihypertensive treatment, and smoking. *: Adjusted for gender, age, egfr, systolic blood pressure, and previous CVD. Abbreviations: ANCOVA, analysis of covariance; CVD, cardiovascular disease; egfr, estimated glomerular filtration rate; ESRD, end-stage renal disease; MR-proANP, midregional proatrial natriuretic peptide; UAER, urinary albumin excretion rate. DISCUSSION In the current study, we examined the possible relationship between MR-proANP and diabetes duration and diabetic complications in patients with type 1 diabetes. Furthermore, we investigated the predictive value of MR-proANP measurement for the combined end point of ESRD and all-cause mortality during follow-up. We found that proanp concentrations were (i) independent of diabetes duration after adjustment, (ii) higher with increased degree of albuminuria and lower egfr, (iii) higher in patients with previous CVD, and (iv) associated with increased risk of all-cause mortality and ESRD combined. 776 American Journal of Hypertension 28(6) June 2015

MR-proANP in Type 1 Diabetes Table 2. Odds ratios for diabetic complications per 1SD increase in MR-proANP in 665 type 1 diabetic patients Odds ratio 95% Confidence interval P value Albuminuria (n = 358) a 1.93 1.41 2.66 <0.001 Cardiovascular disease (n = 143) 1.66 1.21 2.26 0.002 Autonomic dysfunction (n = 369) 1.20 1.86 1.66 0.29 Retinopathy (n = 523) 0.72 0.48 1.07 0.11 All adjustments included gender, age, diabetes duration, systolic blood pressure, egfr, urinary albumin excretion rate, HbA 1c, total cholesterol, 24-hour urinary sodium excretion, body mass index, total daily insulin dose, antihypertensive treatment, and smoking. Abbreviations: egfr, estimated glomerular filtration rate; MR-proANP, midregional proatrial natriuretic peptide a Albuminuria was micro- (30 299 mg/24 h) and macroalbuminuria ( 300 mg/24 h) combined. Adjustments did not include urinary albumin excretion rate when examining the relationship between albuminuria and MR-proANP. Under physiological conditions, higher ANP concentrations in circulation reduce systemic blood pressure. Under pathological states in connection with CVD, however, high ANP concentrations are present 22 without the same effect on blood pressure control. The biological mechanisms are several, including altered ANP degradation, 23 concurrent increased intrarenal RAAS activation counteracting ANP activity, 24 increased sympathetic tone-blunting ANP response, 25 and reduced renal ANP receptors. 26 Finally, the paradoxical high concentrations of natriuretic peptides in the absence of peripheral effects may likely also be caused by impaired cardiac maturation of the natriuretic prohormones, as is seen in hyperinsulinemia with and increased proinsulin release. Higher proanp levels are associated with CVD events and impaired renal function in type 2 diabetes 8 and predict mortality in patients with CVD and ESRD. 11 13 We now demonstrate similar relationships in patients with type 1 diabetes. ANP blocks tubular protein reabsorption and increases glomerular filtration and permeability, 27,28 which may explain the association between albuminuria and proanp. 29 Hyperfiltration is an early occurrence in the development of diabetic nephropathy, 30 and as proanp stimulates GFR, it may be an early marker of diabetic kidney disease. Furthermore, in patients with microalbuminuria, ANP stimulation alters basal membrane properties leading to altered charge and size selectivity, ultimately increasing proteinuria and transcapillary escape of plasma proteins. 31 The concept of a cardiorenal syndrome, in which systemic, cardiac, or renal disease contributes to development of concurrent cardiac and renal disease, has previously been established. 32,33 Our data confirm this interaction between cardiac and renal disease. Moreover, as shown by others, 34 elevations of natriuretic peptides are not merely a result of impaired glomerular filtration as the relationship between MR-proANP and cardiorenal disease is independent of egfr. We did not measure BNP in the current cohort. BNP is already an established biomarker for impaired renal function, heart failure, and mortality (CVD and all-cause) in type 1 and 2 diabetes. 8,14,15 BNP is also secreted from the cardiac atria and reflects ventricular systolic function, while ANP is secreted also in response to diastolic dysfunction. 35 As diastolic dysfunction is frequent in asymptomatic type 1 diabetes, 36 progression of diastolic dysfunction to heart failure is potentially reversible with improved diabetes control. 37 Moreover, studies have shown that ANP may provide additional diagnostic value to BNP for heart failure 38 and may be superior to BNP in predicting mortality in heart failure patients. 17,18 Hence, ANP may be an early biomarker for screening patients at long-term risk of heart failure and thus suitable for intensified diabetes management. As ANP counteracts RAAS, endothelin synthesis, and sympathetic activity, 39 the hormone constitutes a potential therapeutic target in management of hypertension and CVD. Currently, only 1 single ANP analogue is commercially available. Carperitide has shown promising cardiorenal effects in patients with acute heart failure and patients undergoing coronary bypass surgery. 40,41 Neutral endopeptidases are enzymes that breakdown ANP. Recently, the PARADIGM HF trial, examining the effect of enalapril vs. a neutral endopeptidase inhibitor in combination with valsartan on outcome in patients with heart failure, was stopped prematurely due to overwhelming improved outcome in the combination treatment arm. However, although ANP therapy may potentially improve blood pressure control and cardiorenal function, the side effects of neutral endopeptidase inhibition therapy may be significant, 42 and data on drug interference with the ANP activity are still limited. However, although not a major pharmacologic target at present, ANP remains a strong biomarker for cardiorenal failure. 43,44 Our data expand the present knowledge by documenting that higher MR-proANP concentrations are related to impaired renal function and presence of CVD in patients with type 1 diabetes. Interestingly, diabetes duration did not appear to affect proanp concentrations and was unrelated to autonomic dysfunction and retinopathy. Regardless, proanp may prove to be a useful biomarker for monitoring outcome of diabetes. Furthermore, continued attempts at developing novel pharmacologic agents targeting ANP-RAAS homeostasis may improve the management of diabetes altogether. Strengths and limitations We used the propeptide (proanp) as a surrogate for ANP, as it has a longer half-life and is stable in vitro. However, levels of proanp generally correspond well to levels of the active hormone. 2 MR-proANP levels were measured from stored samples after 3.5 years, following only 1 thawing cycle. But, levels of appear to be stable after freeze-thaw cycles. 45 Patients were not fasting prior to blood sampling, although food American Journal of Hypertension 28(6) June 2015 777

Theilade et al. intake has been shown to affect MR-proANP levels in healthy individuals. 46 However, given the patients type 1 diabetes status, this would not have been a safe option for all. Blood tests were not drawn at a specific time in all patients. However, plasma ANP does not show significant diurnal variation. 47 We did not measure N-terminal-proBNP, as the primary aim was to assess the relationship of MR-proANP and diabetic complications, hence we cannot compare the 2 markers in this study. Previous CVD was based on patient recollection and medical records. Thus, we may have underestimated the prevalence of CVD (silent ischemia). Furthermore, we dichotomized presence of retinopathy and autonomic dysfunction and only used 1 test to define autonomic function. Thus, all 3 measures of complications are crude, and weakened the retinopathy and autonomic function variables. However, the majority of patients had been followed at the Steno Diabetes Center for more than a decade, rendering the information on diabetic complications very reliable. Moreover, follow-up data were acquired from the Steno Diabetes Center electronic patient record, which is linked to nationwide electronic databases, consequently no patients were lost to follow-up. Number of follow-up events were few, hence we created the combined end point of all-cause mortality and ESRD, which we have used in a previous publication, 48,49 and yet we were still only able to include a limited number of variables in the adjusted model. Moreover, we did not asses the development of heart failure. Importantly, the current cohort only included Caucasian patients, and as MR-proANP levels differ significantly between races, 50 our results may not be suited for extrapolation to non-caucasian races. Major strengths are the large cohort and single-center setup. CONCLUSIONS In the current cohort, increased MR-proANP concentrations were associated with impaired renal function, increased albuminuria degree, and presence of CVD. Moreover, higher MR-proANP was associated with increased risk of all-cause mortality and ESRD combined during follow-up. Although, being a potential agent against cardiovascular and renal disease, ANP may also be a risk marker for CVD and other complications in patients with type 1 diabetes, when levels are elevated beyond physiological control. DISCLOSURE The authors declared no conflict of interest. REFERENCES 1. Khaleghi M, Saleem U, Morgenthaler NG, Turner ST, Bergmann A, Struck J, Mosley TH, Kullo IJ. Plasma midregional pro-atrial natriuretic peptide is associated with blood pressure indices and hypertension severity in adults with hypertension. Am J Hypertens 2009; 22:425 431. 2. Rosenzweig A, Seidman CE. Atrial natriuretic factor and related peptide hormones. Annu Rev Biochem 1991; 60:229 255. 3. 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