Ahmed Menaouar

Treatment with brain natriuretic peptide prevents the development of cardiac dysfunction in obese diabetic db/db mice

Aims/hypothesisObesity and diabetes increase the risk of developing cardiovascular diseases and heart failure. These metabolic disorders are generally reflected by natriuretic peptide system deficiency. Since brain natriuretic peptide (BNP) is known to influence metabolism and cardioprotection, we investigated the effect of chronic exogenous BNP treatment on adverse myocardial consequences related to obesity and diabetes.MethodsTen-week-old C57BL/KsJ-db/db obese diabetic mice (db/db) and their lean control littermates (db/+) were treated with BNP (0.6xa0μgxa0kg−1xa0h−1) or saline for 12xa0weeks (nu2009=u200910/group). Serial blood and tomography analysis were performed. Cardiac function was determined by echocardiography, and biochemical and histological heart and fat analyses were also performed.ResultsBNP treatment resulted in an average increase in plasma BNP levels of 70xa0pg/ml. An improvement in the metabolic profile of db/db mice was observed, including a reduction in fat content, increased insulin sensitivity, improved glucose tolerance and lower blood glucose, despite increased food intake. db/db mice receiving saline displayed both early systolic and diastolic dysfunction, whereas these functional changes were prevented by BNP treatment. The cardioprotective effects of BNP were attributed to the inhibition of cardiomyocyte apoptosis, myocardial fibrosis, cardiac hypertrophy and the AGE–receptor for AGE (RAGE) system as well as normalisation of cardiac AMP-activated protein kinase and endothelial nitric oxide synthase activities.Conclusions/interpretationOur results indicate that chronic BNP treatment at low dose improves the metabolic profile and prevents the development of myocardial dysfunction in db/db mice.

Oxytocin treatment prevents the cardiomyopathy observed in obese diabetic male db/db mice.

Oxytocin (OT) is involved in the regulation of energy metabolism and in the activation of cardioprotective mechanisms. We evaluated whether chronic treatment with OT could prevent the metabolic and cardiac abnormalities associated with diabetes and obesity using the db/db mice model. Four-week-old male db/db mice and their lean nondiabetic littermates (db/+) serving as controls were treated with OT (125 ng/kg · h) or saline vehicle for a period of 12 weeks. Compared with db/+ mice, the saline-treated db/db mice developed obesity, hyperglycemia, and hyperinsulinemia. These mice also exhibited a deficient cardiac OT/natriuretic system and developed systolic and diastolic dysfunction resulting from cardiomyocyte hypertrophy, fibrosis, and apoptosis. These abnormalities were associated with increased reactive oxygen species (ROS) production, inflammation, and suppressed 5-adenosine monophosphate kinase signaling pathway. The db/db mice displayed reduced serum levels of adiponectin and adipsin and elevated resistin. OT treatment increased circulating OT levels, significantly reduced serum resistin, body fat accumulation (19%; P<.001), fasting blood glucose levels by (23%; P<.001), and improved glucose tolerance and insulin sensitivity. OT also normalized cardiac OT receptors, atrial natriuretic peptide, and brain natriuretic peptide, expressions and prevented systolic and diastolic dysfunction as well as cardiomyocyte hypertrophy, fibrosis, and apoptosis. Furthermore, OT reduced cardiac oxidative stress and inflammation and normalized the 5-adenosine monophosphate-activated protein kinase signaling pathway. The complete normalization of cardiac structure and function by OT treatment in db/db mice contrasted with only partial improvement of hyperglycemia and hyperinsulinemia. These results indicate that chronic treatment with OT partially improves glucose and fat metabolism and reverses abnormal cardiac structural remodeling, preventing cardiac dysfunction in db/db mice.

Urinary responses to acute moxonidine are inhibited by natriuretic peptide receptor antagonist

1 We have previously shown that acute intravenous injections of moxonidine and clonidine increase plasma atrial natriuretic peptide (ANP), a vasodilator, diuretic and natriuretic hormone. We hypothesized that moxonidine stimulates the release of ANP, which would act on its renal receptors to cause diuresis and natriuresis, and these effects may be altered in hypertension. 2 Moxonidine (0, 10, 50, 100 or 150u2003μg in 300u2003μl saline) and clonidine (0, 1, 5 or 10u2003μg in 300u2003μl saline) injected intravenously in conscious normally hydrated normotensive Sprague–Dawley rats (SD, ∼200u2003g) and 12–14‐week‐old Wistar‐Kyoto (WKY) and spontaneously hypertensive rats (SHR) dose‐dependently stimulated diuresis, natriuresis, kaliuresis and cGMP excretion, with these effects being more pronounced during the first hour post‐injection. The actions of 5u2003μg clonidine and 50u2003μg moxonidine were inhibited by yohimbine, an α2‐adrenoceptor antagonist, and efaroxan, an imidazoline I1‐receptor antagonist. 3 Moxonidine (100u2003μg) stimulated (P<0.01) diuresis in SHR (0.21±0.04 vs 1.16±0.06u2003mlu2003h−1 100u2003g−1), SD (0.42±0.06 vs 1.56±0.19u2003mlu2003h−1 100u2003g−1) and WKY (0.12±0.04 vs 1.44±0.21u2003mlu2003h−1 100u2003g−1). Moxonidine‐stimulated urine output was lower in SHR than in SD and WKY. Moxonidine‐stimulated sodium and potassium excretions were lower in SHR than in SD, but not WKY, demonstrating an influence of strain but not of pressure. Pretreatment with the natriuretic peptide antagonist anantin (5 or 10u2003μg) resulted in dose‐dependent inhibition of moxonidine‐stimulated urinary actions. Anantin (10u2003μg) inhibited (P<0.01) urine output to 0.38±0.06, 0.12±0.01, and 0.16±0.04u2003mlu2003h−1 100u2003g−1 in SD, WKY, and SHR, respectively. Moxonidine increased (P<0.01) plasma ANP in SD (417±58 vs 1021±112u2003pgu2003ml−1) and WKY (309±59 vs 1433±187u2003pgu2003ml−1), and in SHR (853±96 vs 1879±229u2003pgu2003ml−1). 4 These results demonstrate that natriuretic peptides mediate the urinary actions of moxonidine through natriuretic peptide receptors.

Hemodynamic and Cardiac Effects of Chronic Eprosartan and Moxonidine Therapy in Stroke-Prone Spontaneously Hypertensive Rats

The renin-angiotensin and sympathetic nervous systems play critical interlinked roles in the development of left ventricular hypertrophy, fibrosis, and dysfunction. These studies investigated the hemodynamic and cardiac effects of monoblockade and coblockade of renin-angiotensin and sympathetic nervous systems. Stroke-prone spontaneously hypertensive rats (16 weeks old; male; n=12 per group) received the sympatholytic imidazoline compound, moxonidine (2.4 mg/kg per day); the angiotensin-receptor blocker eprosartan (30 mg/kg per day), separately or in combination; or saline vehicle for 8 weeks, SC, via osmotic minipumps. Blood pressure and heart rate were continuously measured by radiotelemetry. After 8 weeks, in vivo cardiac function and structure were measured by transthoracic echocardiography and a Millar conductance catheter, and the rats were then euthanized and blood and heart ventricles collected for various determinations. Compared with vehicle, the subhypotensive dose of moxonidine resulted in lower (P<0.01) heart rate, left ventricular hypertrophy, cardiomyocyte cross-sectional area, interleukin 1&bgr;, tumor necrosis factor-&agr;, and mRNA for natriuretic peptides. Eprosartan reduced pressure (P<0.01), as well as extracellular signal–regulated kinase (ERK) 44 phosphorylation, Bax/Bcl-2, and collagen I/III, and improved left ventricular diastolic function (P<0.03). Combined treatment resulted in greater reductions in blood pressure, heart rate, left ventricular hypertrophy, collagen I/III, and inhibited inducible NO synthase and increased endothelial NO synthase phosphorylation, as well as reduced left ventricular anterior wall thickness, without altering the other parameters. Thus, in advanced hypertension complicated with cardiac fibrosis, sympathetic inhibition and angiotensin II blockade resulted in greater reduction in blood pressure and heart rate, inhibition of inflammation, and improved left ventricular pathology but did not add to the benefits of angiotensin II blockade on cardiac function.

Anti-hypertrophic effects of oxytocin in rat ventricular myocytes

BACKGROUNDnOxytocin (OT) and functional OT receptor (OTR) are expressed in the heart and are involved in blood pressure regulation and cardioprotection. Cardiac OTR signaling is associated with atrial natriuretic peptide (ANP) and nitric oxide (NO) release. During the synthesis of OT, its precursor, termed OT-Gly-Lys-Arg (OT-GKR), is accumulated in the developing rat heart. Consequently, we hypothesized that an OT-related mechanism of ANP controls cardiomyocyte (CM) hypertrophy.nnnMETHODSnThe experiments were carried out in newborn and adult rat CM cultures. The enhanced protein synthesis and increased CM volume were mediated by a 24-h treatment with endothelin-1 or angiotensin II.nnnRESULTSnThe treatment of CM with OT or its abundant cardiac precursor, OT-GKR, revealed ANP accumulation in the cell peri-nuclear region and increased intracellular cGMP. Consequently, the CM hypertrophy was abolished by the treatment of 10nM OT or 10nM OT-GKR. The ANP receptor antagonist (anantin) and NO synthases inhibitor (l-NAME) inhibited cGMP production in CMs exposed to OT. STO-609 and compound C inhibition of anti-hypertrophic OT effects in CMs indicated the contribution of calcium-calmodulin kinase kinase and AMP-activated protein kinase pathways. Moreover, in ET-1 stimulated cells, OT treatment normalized the reduced Akt phosphorylation, prevented abundant accumulation of ANP and blocked ET-1-mediated translocation of nuclear factor of activated T-cells (NFAT) into the cell nuclei.nnnCONCLUSIONncGMP/protein kinase G mediates OT-induced anti-hypertrophic response with the contribution of ANP and NO. OT treatment represents a novel approach in attenuation of cardiac hypertrophy during development and cardiac pathology.

Molecular mechanisms underlying oxytocin-induced cardiomyocyte protection from simulated ischemia-reperfusion.

Oxytocin (OT) stimulates cardioprotection. Here we investigated heart-derived H9c2 cells in simulated ischemia-reperfusion (I-R) experiments in order to examine the mechanism of OT protection. I-R was induced in an anoxic chamber for 2 hours and followed by 2u2009h of reperfusion. In comparison to normoxia, I-R resulted in decrease of formazan production by H9c2 cells to 63.5u2009±u20091.7% (MTT assay) and in enhanced apoptosis from 1.7u2009±u20090.3% to 2.8u2009±u20090.4% (Tunel test). Using these assays it was observed that treatment with OT (1-500u2009nM) exerted significant protection during I-R, especially when OT was added at the time of ischemia or reperfusion. Using the CM-H2DCFDA probe we found that OT triggers a short-lived burst in reactive oxygen species (ROS) production in cells but reduces ROS production evoked by I-R. In cells treated with OT, Western-blot revealed the phosphorylation of Akt (Thr 308, p-Akt), eNOS and ERK 1/2. Microscopy showed translocation of p-Akt and eNOS into the nuclear and perinuclear area and NO production in cells treated with OT. The OT-induced protection against I-R was abrogated by an OT antagonist, the Pi3K inhibitor Wortmannin, the cGMP-dependent protein kinase (PKG) inhibitor, KT5823, as well as soluble guanylate cyclase (GC) inhibitor, ODQ, and particulate GC antagonist, A71915. In conditions of I-R, the cells with siRNA-mediated reduction in OT receptor (OTR) expression responded to OT treatment by enhanced apoptosis. In conclusion, the OTR protected H9c2 cells against I-R, especially if activated at the onset of ischemia or reperfusion. The OTR-transduced signals include pro-survival kinases, such as Akt and PKG.

Control of left ventricular mass by moxonidine involves reduced DNA synthesis and enhanced DNA fragmentation

Left ventricular hypertrophy (LVH) is a maladaptive process associated with increased cardiovascular risk. Regression of LVH is associated with reduced complications of hypertension. Moxonidine is an antihypertensive imidazoline compound that reduces blood pressure primarily by central inhibition of sympathetic outflow and by direct actions on the heart to release atrial natriuretic peptide, a vasodilator and an antihypertrophic cardiac hormone. This study investigated the effect of moxonidine on LVH and the mechanisms involved in this effect.

Normalization of Up‐Regulated Cardiac Imidazoline I1‐Receptors and Natriuretic Peptides by Chronic Treatment with Moxonidine in Spontaneously Hypertensive Rats

Abstract: The effect of treatment with moxonidine (120 mg/kg/h sc, 4 weeks) on cardiac I1‐receptors and natriuretic peptide synthesis was evaluated in spontaneously hypertensive rats (SHR). I1‐receptor protein (85 kD) was up‐regulated in SHR atria, and normalized in right and left atria by moxonidine. Similarly, moxonidine normalized atrial and ventricular atrial natriuretic peptide messenger RNA (mRNA) and brain natriuretic peptide mRNA. This study shows that cardiac I1‐receptors are functional, being regulated by hypertension and by chronic exposure to agonist, and that cardiac natriuretic peptides may be regulated by I1‐receptor‐mediated mechanisms.

Cardiac Effects of Moxonidine in Spontaneously Hypertensive Obese Rats

Abstract: Moxonidine, an imidazoline receptor agonist that acts centrally to inhibit sympathetic activity, has been shown to reduce effectively blood pressure, fasting insulin levels, and free fatty acids. In this study, we investigated the long‐term effects of moxonidine treatment on cardiac natriuretic peptides (ANP and BNP) in Spontaneously Hypertensive Obese Rats (SHROBs), a rat model that resembles human Syndrome X. SHROBs expressing spontaneous hypertension, insulin resistance, and genetic obesity (weight 590 6 20 g, at 30 weeks) received moxonidine in chow at 4 mg/kg/day for 15 days. Moxonidine significantly reduced not only systolic blood pressure (187 6 6 versus 156 6 5 mm Hg, P < 0.05) but also plasma ANP (1595 6 371 versus 793 6 131 pg/mL, P < 0.05) and BNP (22 6 3 versus 14 6 1 pg/mL, P < 0.04), without influencing cardiac content of either peptide. Semi‐quantitative PCR revealed that atrial ANPmRNA/GAPDHmRNA decreased to 39% 6 10% of pair‐fed controls, P < 0.03. In left ventricles, moxonidine also decreased ANP mRNA to 69% 6 7% and BNP mRNA to 74% 6 6% of control, P < 0.02, but right ventricular ANP and BNP mRNA were not affected. These findings indicate that chronic inhibition of sympathetic activity with moxonidine in SHROB is associated with decreased ventricular natriuretic peptide transcription, consistent with the cardioprotective effects of moxonidine given the role of ANP and BNP as markers of cadiac disease. Moxonidine also improves the metabolic profile in these rats, thus it may be considered the drug of choice in treatment of metabolic syndrome X.

Chronic Imidazoline Receptor Activation in Spontaneously Hypertensive Rats

BACKGROUNDnAcute intravenous administration of moxonidine, an imidazoline I1-receptor agonist, reduces blood pressure (BP) in normotensive and hypertensive rats, induces diuresis and natriuresis, and stimulates plasma atrial natriuretic peptide (ANP). In these studies we investigated the involvement of natriuretic peptides (ANP and brain natriuretic peptide) in the effects of chronic activation of imidazoline receptors.nnnMETHODSnSpontaneously hypertensive rats (SHR; 12 to 14 weeks old) received 7-day moxonidine treatment at various doses (10, 20, 60, and 120 microg/kg/h) via subcutaneously implanted osmotic minipumps.nnnRESULTSnHemodynamic parameters (continuously monitored by telemetry) revealed that, compared with saline-treated rats, moxonidine dose-dependently decreased blood pressures (BPs). Maximal blood pressure lowering effect was achieved by day 4 of treatment, at which point 60 microg/kg/h reduced mean arterial pressure (MAP) by 14.5 +/- 6.8 mm Hg as compared with basal levels. The decrease in MAP was influenced by a drop in both diastolic and systolic pressures. Moxonidine treatment did not alter daily urinary sodium and potassium excretions, but 120 microg/kg/h moxonidine decreased urine volume after 2 days and increased cyclic guanosine 35monophosphate excretion on days 4 to 7 of treatment. Chronic moxonidine treatment dose-dependently increased plasma ANP to reach, at 120 microg/kg/h, a 40% increase (P < .01) above that of corresponding saline-treated SHR, with a concomitant increase in left and right atrial ANP mRNA (more than twofold). Plasma BNP increased by 120 microg/kg/h moxonidine (11.0 +/- 1.1 v 16.5 +/- 1.9 pg/mL, P < .002) without significant increases in atrial and ventricular BNP mRNA.nnnCONCLUSIONSnANP and BNP may be involved in the antihypertensive effect of chronic moxonidine treatment. Accordingly, natriuretic peptides may contribute to the sympatholytic and cardioprotective effects of chronic activation of imidazoline I1-receptors.