Opposite regulation of brain and C-type natriuretic peptides in the streptozotocin-diabetic cardiopathy

Molecular Correlates of Early Onset of Diabetic Cardiomyopathy: Possible Therapeutic Targets

Diabetes mellitus (DM) is associated with mitochondrial dysfunction and oxidative stress that can lead to diabetic cardiomyopathy (DCM), which can often remain undetected until late stages of the disease. However, myocardial injury occurs before the onset of measurable cardiac dysfunction, although its molecular correlates are poorly understood. In this study, we made a DM rat induced by a high-fat diet combined with low and high doses of streptozotocin (STZ) to emulate pre and early DCM. RNA-sequencing analysis of ventricular tissue revealed a differential transcriptome profile and abnormal activation of pathways involved in fatty acid metabolism, oxidative phosphorylation, cardiac structure and function, insulin resistance, calcium signalling, apoptosis, and TNF signalling. Moreover, using high glucose-treated human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM), we recapitulated the cardiac cellular phenotype of DM and identified several molecular correlates that may promote the development of DCM. In conclusion, we have developed an experimental framework to target pathways underlying the progression of DCM.

Characteristics of dendroaspis natriuretic peptide and its receptor in streptozotocin-induced diabetic rats

Dendroaspis natriuretic peptide (DNP) shares a functionally important sequence homology with other natriuretic peptides. However, the characteristics of DNP and its receptor in the context of diabetes remafin to be fully elucidated. In the present study, alterations in the plasma levels and tissue contents of DNP and the properties of its receptor in diabetic rats, induced by streptozotocin (STZ) injection, were investigated. The plasma levels of DNP were 90.01 ± 4.12 and 196.68 ± 5.60 pg/ml in the control and STZ-induced diabetic rats, respectively. The tissue contents of DNP in the cardiac atrium, ventricle, renal cortex and inner medulla of the STZ-induced diabetic rats were also significantly increased compared with the control rats. Specific (125)I-DNP-binding sites were located predominantly in the glomeruli and inner medulla of the rat kidney. In the glomeruli of the kidney, the apparent dissociation constants (Kd) of (125)I-DNP in the control and STZ-induced diabetic rats were 0.41 ± 0.03 and 0.56 ± 0.06 nM, respectively. The maximum binding capacities (Bmax) of (125)I-DNP in control and STZ-induced diabetic rats were 2.98 ± 0.21 and 6.22 ± 1.06 fmol/mg protein, respectively. However, no differences were observed in the apparent Kd and Bmax of (125)I-DNP in the inner medulla of the kidney between the control and STZ-induced diabetic rats. In the glomerular and inner medullary kidney membranes, DNP stimulated the production of cyclic guanosine monophosphate (cGMP) in a dose-dependent manner. The magnitude of cGMP production in glomerular membranes was greater in the STZ-induced diabetic rats, whereas the magnitude of cGMP production in the inner medullary membranes was lower in the STZ-induced diabetic rats compared with the control rats. These results indicated that STZ-induced diabetes modulate DNP and its receptor, and also suggested that modulation of the DNP system is involved in the renal function of diabetic animals via the intracellular domain of the kidney NP receptor.

Alterations in atrial natriuretic peptide and its receptor levels in long-term, streptozotocin-induced, diabetes in rats

Diabetes mellitus (DM) shows a markedly increased incidence of cardiovascular pathology that leads to hypertension, endothelial macro- and microangiopathy, diabetic nephropathy, and myocardial infarction. Atrial natriuretic peptide (ANP), is a 28 amino acid peptide hormone synthesized mainly by the heart atria and ventricles. It has potent diuretic and natriuretic properties. In this article the effect of long-term DM on blood plasma, kidney, and heart atrial and ventricular ANP concentrations were evaluated in streptozotocin (STZ)-induced 8-month diabetic and control rats by using radioimmunoassay (RIA). Moreover, ANP receptors in STZ-induced, 8-month diabetic rat kidneys were studied by receptor autoradiography. In addition, the expression of ANP concentrations in the kidney of diabetic and control rats was evaluated by means of immunohistochemistry. Body weight loss and increased blood glucose levels were used as indices of DM in the STZ-induced diabetic rats. Our results showed significantly higher ANP concentrations in diabetic plasma (P < 0.05), kidney (P < 0.01), heart atria (P < 0.05), and ventricles (P < 0.01) compared to controls. We also demonstrated a significant decrease in ANP receptors in the outer cortex (P < 0.05), juxtaglomerular medulla (P < 0.05), and papilla (P < 0.05) of 8-month diabetic rat kidneys compared to controls. The observed increase in ANP levels in plasma and kidney could play a role in the development of diabetic nephropathy: probably by reducing the levels of ANP receptors in diabetic kidney. Furthermore, the role of ANP in the STZ-induced diabetic heart merits additional study.

Effects of brain natriuretic peptide on contraction and intracellular Ca2+ in ventricular myocytes from the streptozotocin-induced diabetic rat

The streptozotocin (STZ)-treated rat is a widely studied experimental model of diabetes mellitus (DM). Its pathophysiology includes hypoinsulinemia, hyperglycemia, cardiac hypertrophy, and a cardiomyopathy that is characterized by the presence of diastolic and/or systolic contractile dysfunction. As part of their endocrine function cardiomyocytes in the heart produce and secrete a family of related peptide hormones called the natriuretic peptides that include A-type natriuretic peptide (ANP) and B-type natriuretic peptide (BNP). ANP and BNP levels are variously augmented in patients with hypertension, cardiac overload, in the ventricles of failing or hypertrophied heart, in cardiac heart failure, in acute myocardial infarction (MI), and in some circumstances in DM. In this article, the effects of BNP on ventricular myocyte contraction and Ca2+ transport in STZ-induced diabetic rats have been investigated. BNP concentration was significantly increased in blood plasma and in atrial muscle in STZ-induced diabetic rats compared to age-matched controls. BNP was 11.9 +/- 0.9 ng/mL in plasma from diabetic rats compared to 6.7 +/- 1.6 ng/mL in controls and 15.8 +/- 2.0 ng/mg protein in diabetic atrial muscle compared to 8.5 +/- 1.0 ng/mg protein in controls. The heart weight to body weight ratio, an indicator of hypertrophy, was significantly increased in diabetic rat heart (4.3 +/- 0.1 mg/g) compared to controls (3.7 +/- 0.04 mg/g). The amplitude of shortening was not significantly altered in diabetic myocytes (10.3 +/- 0.4%) compared to controls (10.9 +/- 0.4%). BNP reduced the amplitude of shortening to a greater extent in diabetic myocytes (8.1 +/- 0.6%) compared to controls (10.1 +/- 0.4%). The time to peak (TPK) shortening was significantly prolonged in diabetic myocytes (254 +/- 8 ms) compared to controls (212 +/- 5 ms) and was not additionally altered by BNP. The time to half relaxation of shortening was also significantly prolonged in diabetic myocytes (131 +/- 8 ms) compared to controls (111 +/- 5 ms). BNP (10(-8) to 10(-6) M) normalized the time to half relaxation of shortening in diabetic myocytes to that of controls. Time to peak (TPK) shortening of Ca2+ was not different between diabetic and control rats. However, BNP (10(-7) M) increases TPK of Ca2+ significantly. The amplitude of the Ca2+ transient was significantly increased in diabetic myocytes (0.42 +/- 0.02 Ratio units [RU]) compared to controls (0.36 +/- 0.02 RU) and was not additionally altered by BNP. BNP may have a protective role in STZ-induced diabetic rat heart.

Does the C-Type Natriuretic Peptide Have Prognostic Value in Chagas Disease and Other Dilated Cardiomyopathies?

Atrial natriuretic peptides (ANP) and brain natriuretic peptides (BNP) are powerful neurohormonal indicators of left-ventricular function and prognosis in heart failure (HF). Chagas disease (CD) caused by the protozoan Trypanosoma cruzi remains a major cause of HF in Latin America. We assessed whether the plasma concentration of the third natriuretic peptide, C-type natriuretic peptide (CNP), also has diagnostic and prognostic properties in patients with CD or other dilated cardiomyopathies (DCM). Blood samples were obtained from 66 patients with CD, 50 patients with DCM from other causes, and 30 gender- and age-matched healthy subjects. Patients were subdivided according to the New York Heart Association (NYHA) class. The CNP concentration was determined by radioimmunoassay (Immundiagnostik, Bensheim, Germany). The main duration of follow-up was 31.4 months (range 13 to 54 months); 19 patients had died and 11 patients received a heart transplant. CNP concentrations were only significantly altered in patients with DCM or CD of the NYHA classes III and IV (P < 0.05). The Pearson correlation of echocardiographic data with CNP revealed an association only with the left-ventricular end systolic volume (P = 0.03) in patients with DCM. Furthermore, CNP did not predict mortality or the necessity for heart transplant. Our data are the first to demonstrate the raised levels of the third natriuretic peptide CNP in CD and other DCM. Whereas ANP and BNP have a high predictive value for mortality in both diseases, CNP is without any predictive potency.

Role of the sympathetic and renin angiotensin systems in the glucose-induced increase of blood pressure in rats

The pressor effect induced by acute hyperglycemia is not well understood, therefore, it was of interest to study the effect of intravenous glucose infusion on the mean arterial pressure of anesthetized Wistar rats. Animals received glucose (100 mg/kg/min, i.v.), mannitol or saline during 30 min, but only glucose increased the mean arterial pressure (about 40 mm Hg), plasma glucose, insulin and nitric oxide (NO). Pretreatment with reserpine or indorenate (a central antihypertensive) inhibited completely the pressor effect of glucose. Reserpine also decreased the plasma NO levels. Pretreatment with ramipril or with streptozotocin decreased the late phase of the glucose-induced pressor response and the NO levels, the latter treatment also abolishes insulin plasma concentrations. The present results suggest that the pressor effect induced by glucose has an early phase due to an increase of efferent sympathetic discharges and a delayed phase produced by the activation of the renin angiotensin system.

Cardiac gene expression of natriuretic substances is altered in streptozotocin-induced diabetes during angiotensin II-induced pressure overload

OBJECTIVE

To gain insight into the cardiac adaptive mechanisms in diabetes, we studied whether angiotensin II (Ang II) alters expression of the atrial natriuretic peptide (ANP), B-type natriuretic peptide (BNP) and adrenomedullin (AM) genes in the left ventricle of the diabetic rat heart.

METHODS

Diabetes was induced by streptozotocin (STZ; 60 mg/kg body weight intravenously). During the last 24 h of 2.5 or 7 weeks of treatment of male Wistar rats with STZ or vehicle, Ang II (33 microg/kg per h) was administered via osmotic minipumps.

RESULTS

Diabetes was associated with an increased left ventricular weight to body weight (LV/BW) ratio, an index of left ventricular hypertrophy, at week 7 but not at week 2.5, and with increased ANP mRNA content at 2.5 weeks, but not with altered expression of the AM and BNP genes. Mean arterial pressure and LV/BW ratio were increased by Ang II in all groups except in the 7-week diabetic group. Levels of ANP mRNA were increased fourfold (P < 0.001) and threefold (P < 0.05) by Ang II at 2.5 and 7 weeks in control animals, respectively, and 11-fold (P < 0.001) and sevenfold (P < 0.001) at 2.5 and 7 weeks in diabetic animals, respectively. Ang II increased ventricular concentrations of BNP mRNA in control and diabetic animals at 2.5 weeks (1.3-fold, P < 0.001; and 1.6-fold, P < 0.001) and at 7 weeks (1.3-fold, P < 0.05; and 1.8-fold, P < 0.001), respectively. Left ventricular levels of adrenomedullin mRNA were increased by treatment with Ang II for 24 h in 2.5-week diabetic animals.

CONCLUSION

Ang II markedly increased the levels of natriuretic peptide mRNAs in the left ventricle of normal and diabetic rat hearts, whereas it increased adrenomedullin mRNA levels only in 2.5-week diabetic rats and failed to cause hypertension in 7-week diabetic rats. Left ventricular levels of ANP and BNP mRNA were increased by Ang II in diabetic animals more than the additive effects of diabetes and Ang II alone, showing that Ang II induced an amplified response with respect to cardiac concentrations of ANP and BNP in diabetes.

B-type natriuretic peptide prevents acute hypertrophic responses in the diabetic rat heart: importance of cyclic GMP

Stimulation of cardiomyocyte guanosine 3',5'-cyclic monophosphate (cyclic GMP) via endothelial-derived nitric oxide (NO) is an important mechanism by which bradykinin and ACE inhibitors prevent hypertrophy. Endothelial NO dysfunction and cardiac hypertrophy are morbid features of diabetes not entirely prevented by ACE inhibitors. In cardiomyocyte/endothelial cell cocultures, bradykinin efficacy is abolished by high-glucose-induced endothelial NO dysfunction. We now demonstrate that antihypertrophic actions of natriuretic peptides, which stimulate cyclic GMP independently of NO, are preserved in cardiomyocytes despite high-glucose-induced endothelial dysfunction. Further, streptozotocin-induced diabetes significantly impairs the effectiveness of acute antihypertrophic strategies in isolated rat hearts. In hearts from citrate-treated control rats, angiotensin II-stimulated [(3)H]phenylalanine incorporation and atrial natriuretic peptide and beta-myosin heavy chain mRNA expression were prevented by B-type natriuretic peptide (BNP), bradykinin, the ACE inhibitor ramiprilat, and the neutral endopeptidase inhibitor candoxatrilat. These antihypertrophic effects were accompanied by increased left ventricular cyclic GMP. In age-matched diabetic hearts, the antihypertrophic and cyclic GMP stimulatory actions of bradykinin, ramiprilat, and candoxatrilat were absent. However, the blunting of hypertrophic markers and accompanying increases in cyclic GMP stimulated by BNP were preserved in diabetes. Thus BNP, which increases cyclic GMP independently of NO, is an important approach to prevent growth in the diabetic myocardium, where endothelium-dependent mechanisms are compromised.

A breaker of advanced glycation end products attenuates diabetes-induced myocardial structural changes

The formation of advanced glycation end products (AGEs) on extracellular matrix components leads to accelerated increases in collagen cross linking that contributes to myocardial stiffness in diabetes. This study determined the effect of the crosslink breaker, ALT-711 on diabetes-induced cardiac disease. Streptozotocin diabetes was induced in Sprague-Dawley rats for 32 weeks. Treatment with ALT-711 (10 mg/kg) was initiated at week 16. Diabetic hearts were characterized by increased left ventricular (LV) mass and brain natriuretic peptide (BNP) expression, decreased LV collagen solubility, and increased collagen III gene and protein expression. Diabetic hearts had significant increases in AGEs and increased expression of the AGE receptors, RAGE and AGE-R3, in association with increases in gene and protein expression of connective tissue growth factor (CTGF). ALT-711 treatment restored LV collagen solubility and cardiac BNP in association with reduced cardiac AGE levels and abrogated the increase in RAGE, AGE-R3, CTGF, and collagen III expression. The present study suggests that AGEs play a central role in many of the alterations observed in the diabetic heart and that cleavage of preformed AGE crosslinks with ALT-711 leads to attenuation of diabetes-associated cardiac abnormalities in rats. This provides a potential new therapeutic approach for cardiovascular disease in human diabetes.

Overexpression of apolipoprotein B in the heart impedes cardiac triglyceride accumulation and development of cardiac dysfunction in diabetic mice

The heart secretes apolipoprotein B (apoB) containing lipoproteins. Herein, we examined whether the overexpression of a human apoB transgene in the heart affects triglyceride accumulation and development of cardiac dysfunction in streptozotocin-treated diabetic mice. Blood glucose, plasma free fatty acids, and plasma triglycerides were similarly affected in diabetic wild type mice and diabetic apoB transgenic mice as compared with non-diabetic mice of the same genotype. After 12 weeks, heart triglycerides were increased by 48% in diabetic wild type mice. These mice displayed an increased expression of brain natriuretic peptide and deterioration of heart function on echocardiography. In diabetic apoB transgenic mice, heart triglyceride levels were identical to those in non-diabetic wild type and apoB transgenic mice, and brain natriuretic peptide expression as well as echocardiographic indexes of heart function were only marginally affected or unaffected. The findings suggest that triglyceride accumulation in the heart is important for development of diabetic cardiomyopathy in mice, and that lipoprotein formation by cardiomyocytes plays an integrated role in cardiac lipid metabolism.

Chamber-dependent expression of brain natriuretic peptide and its mRNA in normal and diabetic pig heart

Brain natriuretic peptide (BNP) is produced in cardiac myocytes, and increased secretion is closely associated with cardiac dysfunction. However, several fundamental aspects of BNP expression in the myocardium have not yet been resolved. In the present study, we report the presence of a precursor BNP mRNA transcript and a mature BNP mRNA transcript in normal porcine hearts. In normal pigs, the amount of precursor BNP mRNA was similar in atrial and ventricular myocardium, whereas the mature BNP transcript was 10- to 50-fold more abundant in atrial than in ventricular myocardium. Quantitation of proBNP in normal porcine hearts by radioimmunoassay disclosed abundant proBNP in the atria, whereas proBNP was undetectable in the ventricles. Laser confocal microscopy revealed proBNP in secretory granules of atrial but not in the ventricular myocardium of normal pigs. Mild streptozotocin-induced diabetes doubled the expression of BNP mRNA in porcine atrial myocardium (P=0.03), but was without effect on BNP mRNA in the ventricular myocardium. The data suggest that BNP mRNA processing and proBNP storage differ between the atrial and ventricular myocardium. The results also imply that diabetes increases cardiac BNP expression in a chamber-dependent manner.