RESUMO
BACKGROUND/AIMS: Flow restoration to ischemic myocardium reduces infarct size (IS), but it also promotes reperfusion injury. A burst of reactive oxygen species (ROS) and/or NHE-1 reactivation were proposed to explain this injury. Our study was aimed to shed light on this unresolved issue. METHODS: Regional infarction (40 min-ischemia/2 hs-reperfusion) was induced in isolated and perfused rat hearts. Maximal doses of N-(2-mercaptopropionyl)-glycine (MPG 2mmol/L, ROS scavenger), cariporide (10µmol/L, NHE-1 inhibitor), or sildenafil (1µmol/L, phosphodiesterase5A inhibitor) were applied at reperfusion onset. Their effects on IS, myocardial concentration of thiobarbituric acid reactive substances (TBARS), ERK1/2, p90(RSK), and NHE-1 phosphorylation were analyzed. RESULTS: All treatments decreased IS â¼ 50% vs. control. No further protection was obtained by combining cariporide or MPG with sildenafil. Myocardial TBARS increased after infarction and were decreased by MPG or cariporide, but unaffected by sildenafil. In line with the fact that ROS induce MAPK-mediated NHE-1 activation, myocardial infarction increased ERK1/2, p90(RSK), and NHE-1 phosphorylation. MPG and cariporide cancelled these effects. Sildenafil did not reduce the phosphorylated ERK1/2-p90(RSK) levels but blunted NHE-1 phosphorylation suggesting a direct dephosphorylating action. CONCLUSIONS: 1) Reperfusion injury would result from ROS-triggered MAPK-mediated NHE-1 phosphorylation (and reactivation) during reperfusion; 2) sildenafil protects the myocardium by favouring NHE-1 dephosphorylation and bypassing ROS generation.
Assuntos
Traumatismo por Reperfusão Miocárdica/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Trocadores de Sódio-Hidrogênio/metabolismo , Animais , Glicina/análogos & derivados , Glicina/uso terapêutico , Guanidinas/uso terapêutico , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Traumatismo por Reperfusão Miocárdica/tratamento farmacológico , Fosforilação , Piperazinas/uso terapêutico , Purinas/uso terapêutico , Ratos , Proteínas Quinases S6 Ribossômicas 90-kDa/metabolismo , Citrato de Sildenafila , Compostos de Sulfidrila/uso terapêutico , Sulfonas/uso terapêutico , Substâncias Reativas com Ácido Tiobarbitúrico/análise , Vasodilatadores/uso terapêuticoRESUMO
BACKGROUND/AIMS: This study aimed to identify the signaling pathway for the proposed link between phosphodiesterase-5A (PDE5A) inhibition and decreased cardiac Na(+)/H(+) exchanger (NHE-1) activity. METHODS: NHE-1 activity was assessed in rat isolated papillary muscles by the Na(+)-dependent initial pH(i) recovery from a sustained acidosis (ammonium prepulse). ERK1/2, p90RSK and NHE-1 phosphorylation state during acidosis was determined. RESULTS: PDE5A inhibition (1 µmol/L sildenafil, SIL) did not modify basal pH(i) but significantly blunted pH(i) recovery after sustained acidosis. Although preventing ERK1/2- p90RSK signaling pathway (10 µmol/L U0126) mimicked SIL effect, SIL did not blunt the acidosis-mediated increase in kinases activation. SIL+U0126 did not show additive effect on NHE-1 activity. Then, we hypothesized that SIL could be activating phophasatases (PP1 and/or PP2A) to directly dephosphorylate NHE-1 despite preserved ERK1/2-p90RSK activation. Non-specific phosphatases inhibition (1 µmol/L okadaic acid) canceled SIL effect on pH(i) recovery from acidosis. Same result was observed by inhibiting PP2A either with a lower dose of okadaic acid (1 nmol/L) or, more specifically, with 100 µmol/L endothall. Consistently, NHE-1 phosphorylation at Ser703 increased after acidosis, SIL prevented this effect and PP2A inhibition (endothall) reverted SIL effect. CONCLUSION: We suggest that PDE5A inhibitors decrease NHE-1 phosphorylation and activity through a mechanism that involves PP2A activation.
Assuntos
Nucleotídeo Cíclico Fosfodiesterase do Tipo 5/metabolismo , Inibidores de Fosfodiesterase/farmacologia , Proteína Fosfatase 1/fisiologia , Proteína Fosfatase 2/fisiologia , Trocadores de Sódio-Hidrogênio/metabolismo , Acidose/tratamento farmacológico , Animais , Butadienos/farmacologia , Ácidos Dicarboxílicos/farmacologia , Concentração de Íons de Hidrogênio , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Nitrilas/farmacologia , Ácido Okadáico/farmacologia , Músculos Papilares/efeitos dos fármacos , Músculos Papilares/metabolismo , Fosforilação , Piperazinas/farmacologia , Proteína Fosfatase 1/antagonistas & inibidores , Proteína Fosfatase 1/metabolismo , Proteína Fosfatase 2/antagonistas & inibidores , Proteína Fosfatase 2/metabolismo , Purinas/farmacologia , Ratos , Proteínas Quinases S6 Ribossômicas 90-kDa/metabolismo , Citrato de Sildenafila , Sulfonas/farmacologiaRESUMO
The beneficial effect of phosphodiesterase 5A inhibition in ischemia/reperfusion injury and cardiac hypertrophy is well established. Inhibition of the cardiac Na(+)/H(+) exchanger (NHE-1) exerts beneficial effects on these same conditions, and a possible link between these therapeutic strategies was suggested. Experiments were performed in isolated cat cardiomyocytes to gain insight into the intracellular pathway involved in the reduction of NHE-1 activity by phosphodiesterase 5A inhibition. NHE-1 activity was assessed by the rate of intracellular pH recovery from a sustained acidic load in the absence of bicarbonate. Phosphodiesterase 5A inhibition with sildenafil (1 µmol/L) did not affect basal intracellular pH; yet, it did decrease proton efflux (J(H); in millimoles per liter per minute) after the acidic load (proton efflux: 6.97±0.43 in control versus 3.31±0.58 with sildenafil; P<0.05). The blockade of both protein phosphatase 1 and 2A with 100 nmol/L of okadaic acid reverted the sildenafil effect (proton efflux: 6.77±0.82). In contrast, selective inhibition of protein phosphatase 2A (1 nmol/L of okadaic acid or 100 µmol/L of endothall) did not (3.86±1.0 and 2.61±1.2), suggesting that only protein phosphatase 1 was involved in sildenafil-induced NHE-1 inhibition. Moreover, sildenafil prevented the acidosis-induced increase in NHE-1 phosphorylation without affecting activation of the extracellular signal-regulated kinase 1/2-p90(RSK) pathway. Our results suggest that phosphodiesterase 5A inhibition decreases NHE-1 activity, during intracellular pH recovery after an acidic load, by a protein phosphatase 1-dependent reduction in NHE-1 phosphorylation.
Assuntos
Inibidores da Fosfodiesterase 5 , Piperazinas/farmacologia , Proteína Fosfatase 1/metabolismo , Trocadores de Sódio-Hidrogênio/metabolismo , Sulfonas/farmacologia , Animais , Transporte Biológico/efeitos dos fármacos , Gatos , Células Cultivadas , Nucleotídeo Cíclico Fosfodiesterase do Tipo 5/metabolismo , Ácidos Dicarboxílicos/farmacologia , Inibidores Enzimáticos/farmacologia , Concentração de Íons de Hidrogênio , Immunoblotting , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , Miócitos Cardíacos/citologia , Miócitos Cardíacos/efeitos dos fármacos , Miócitos Cardíacos/metabolismo , Ácido Okadáico/farmacologia , Inibidores de Fosfodiesterase/farmacologia , Fosforilação/efeitos dos fármacos , Proteína Fosfatase 1/antagonistas & inibidores , Prótons , Purinas/farmacologia , Proteínas Quinases S6 Ribossômicas 90-kDa/metabolismo , Citrato de SildenafilaRESUMO
The sarcolemmal Na+/HCO3- cotransporter (NBC) plays an important role in intracellular pH (pH(i)) regulation in the heart. In the present work we studied, in isolated cat ventricular myocytes, the role of Angiotensin II (Ang II) and reactive oxygen species (ROS) production as potential activators of the NBC. pH(i) was measured in single cells in a medium with HCO3- using the fluorescent pH indicator BCECF. The NH4+ pulse method was used to induce an intracellular acid load and the acid efflux (JH) in the presence of the Na+/H+ exchanger blocker HOE642 (10 microM) was calculated as indicator of NBC activity. The following JH data are presented at pH(i) of 6.8 (* and # indicate p<0.05 after ANOVA vs. control and Ang II, respectively). The basal JH (1.03+/-0.12 mM/min, n=11) was significantly increased in the presence of 100 nM Ang II (1.70+/-0.15 mM/min, n=8*). This effect of Ang II was abolished when we added to the extracellular solution 2 mM MPG (ROS scavenger; 0.80+/-0.08 mM/min, n=11#), 300 microM apocynin (NADPH oxidase blocker; 0.80+/-0.13 mM/min, n=6#), 500 microM 5-hydroxidecanoate (mitochondrial ATP dependent K+ channel, mK(ATP), blocker; 0.97+/-0.21 mM/min, n=9#), or the inhibitor of the MAP kinase ERK pathway U0126 (10 microM; 0.56+/-0.18 mM/min, n=6#). We also determined the phosphorylation of ERK during the first min of acidosis and we detected that Ang II significantly enhanced the ERK phosphorylation levels, an effect that was cancelled by scavenging ROS with MPG. In conclusion, we propose that Ang II enhances the production of ROS through the activation of the NADPH oxidase, which in turn triggers mK(ATP) opening and mitochondrial ROS production ("ROS-induced ROS-release mechanism"). Finally, these mitochondrial ROS stimulate the ERK pathway, leading to the activation of the NBC.
Assuntos
Angiotensina II/farmacologia , Transporte Biológico/efeitos dos fármacos , Miócitos Cardíacos/efeitos dos fármacos , Miócitos Cardíacos/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Simportadores de Sódio-Bicarbonato/metabolismo , Vasoconstritores/farmacologia , Animais , Transporte Biológico/fisiologia , Gatos , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , Proteína Quinase 3 Ativada por Mitógeno/metabolismo , FosforilaçãoRESUMO
The effect of endurance training (swimming 90 min/d for 5 days a week for 60 days) on cardiac hypertrophy was investigated in the spontaneously hypertensive rat (SHR). Sedentary SHRs (SHR-Cs) and normotensive Wistar rats were used as controls. Exercise training enhanced myocardial hypertrophy assessed by left ventricular weight/tibial length (228+/-7 versus 251+/-5 mg/cm in SHR-Cs and exercised SHRs [SHR-Es], respectively). Myocyte cross-sectional area increased approximately 40%, collagen volume fraction decreased approximately 50%, and capillary density increased approximately 45% in SHR-Es compared with SHR-Cs. The mRNA abundance of atrial natriuretic factor and myosin light chain 2 was decreased by the swimming routine (100+/-19% versus 41+/-10% and 100+/-8% versus 61+/-9% for atrial natriuretic factor and myosin light chain 2 in SHR-Cs and SHR-Es, respectively). The expression of sarcoplasmic reticulum Ca(2+) pump was significantly augmented, whereas that of Na(+)/Ca(2+) exchanger was unchanged (93+/-7% versus 167+/-8% and 158+/-13% versus 157+/-7%, sarcoplasmic reticulum Ca(2+) pump and Na(+)/Ca(2+) exchanger in SHR-Cs and SHR-Es, respectively; P<0.05). Endurance training inhibited apoptosis, as reflected by a decrease in caspase 3 activation and poly(ADP-ribose) polymerase-1 cleavage, and normalized calcineurin activity without inducing significant changes in the phosphatidylinositol 3-kinase/Akt pathway. The swimming routine improved midventricular shortening determined by echocardiography (32.4+/-0.9% versus 36.9+/-1.1% in SHR-Cs and SHR-Es, respectively; P<0.05) and decreased the left ventricular free wall thickness/left ventricular cavity radius toward an eccentric model of cardiac hypertrophy (0.59+/-0.02 versus 0.53+/-0.01 in SHR-Cs and SHR-Es, respectively; P<0.05). In conclusion, we present data demonstrating the effectiveness of endurance training to convert pathological into physiological hypertrophy improving cardiac performance. The reduction of myocardial fibrosis and calcineurin activity plus the increase in capillary density represent factors to be considered in determining this beneficial effect.
Assuntos
Cardiomegalia/patologia , Cardiomegalia/fisiopatologia , Hipertensão/patologia , Hipertensão/fisiopatologia , Resistência Física/fisiologia , Animais , Apoptose/fisiologia , Calcineurina/metabolismo , Cardiomegalia/terapia , Regulação para Baixo/fisiologia , Expressão Gênica/fisiologia , Hipertensão/terapia , Masculino , Ratos , Ratos Endogâmicos SHR , Ratos Wistar , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/genética , Transdução de Sinais/fisiologia , Trocador de Sódio e Cálcio/genética , Natação/fisiologiaRESUMO
Na(+)/H(+) exchanger (NHE-1) inhibition was demonstrated to induce the regression of cardiac hypertrophy (CH) in several experimental models and to inhibit mitochondrial death pathway in "in-vitro" experiments. Since recent reports show that NHE-1 inhibition delays the transition from CH to failure, and apoptosis plays a key role in this process, we investigated the effect of chronic treatment with the NHE-1 blocker cariporide on CH and apoptosis in the SHR. One month of cariporide treatment (30 mg x kg(-1) x day(-1)) induced the regression of CH (cardiomyocyte cross-sectional area: 468 +/- 20 vs. 285 +/- 9 microm(2) in untreated and cariporide-treated spontaneously hypertensive rats; P < 0.05). Apoptosis was assessed by TUNEL staining, the expression of Bcl-2, Bax, and activation of caspase-3 and PARP-1 by immunoblot. Cariporide treatment decreased the TUNEL-positive cells, the Bax-to-Bcl-2 ratio (3.16 +/- 0.32 vs. 1.70 +/- 0.17, untreated and cariporide-treated, respectively; P < 0.05); caspase-3 and PARP-1 activation (465 +/- 62 vs. 260 +/- 22 and 2,239 +/- 62 vs. 1,683 +/- 85 AU, untreated and cariporide-treated, respectively; P < 0.05). Angiotensin II, a growth factor and apoptotic stimulus, was used to induce O(2)(-) production that activated the ERK1/2-p90(RSK) pathway, increasing NHE-1 phosphorylation. These effects were prevented by losartan, N-(2-mercaptopropionyl)-glycine, and cariporide. In conclusion, we present data demonstrating that chronic NHE-1 inhibition with cariporide decreases both hypertrophy and apoptosis susceptibility in the spontaneously hypertensive rat heart. The antiapoptotic effect would be the consequence of two different actions of cariporide: the prevention of cytosolic Na(+) and Ca(2+) overload due to the inhibition of the sarcolemmal NHE-1 and a direct mitochondrial effect preventing mitochondrial permeability transition pore opening.
Assuntos
Antiarrítmicos/uso terapêutico , Apoptose/efeitos dos fármacos , Cardiomegalia/tratamento farmacológico , Cardiomegalia/patologia , Guanidinas/uso terapêutico , Trocadores de Sódio-Hidrogênio/antagonistas & inibidores , Sulfonas/uso terapêutico , Angiotensina II/farmacologia , Animais , Western Blotting , Núcleo Celular/patologia , Núcleo Celular/ultraestrutura , Marcação In Situ das Extremidades Cortadas , Masculino , Mitocôndrias Cardíacas/efeitos dos fármacos , Miocárdio/metabolismo , Miocárdio/patologia , Miócitos Cardíacos/patologia , Miócitos Cardíacos/ultraestrutura , Ratos , Ratos Endogâmicos SHR , Trocador 1 de Sódio-Hidrogênio , Superóxidos/metabolismo , Proteína X Associada a bcl-2/metabolismoRESUMO
The aim of this work was to assess the possible correlation between oxidative damage and the development of cardiac hypertrophy in heart tissue from young (40-d-old) and older (4-, 11- and 19-month-old) spontaneously hypertensive rats (SHR) in comparison with age-matched Wistar (W) rats. To this end, levels of thiobarbituric acid reactive substances (TBARS), nitrotyrosine contents, NAD(P)H oxidase activity, superoxide production, and the activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) were determined. Compared to age-matched normotensive rats, SHR showed a significant increase in systolic blood pressure from 40 d of age and left ventricular hypertrophy (LVH) was significantly evident from 4 months of age. W rats (11- and 19-month-old) also showed an increase in LVH with aging. TBARS and nitrotyrosine levels were similar in young rats from both strains and were significantly increased with age in both strains, with the values in SHR being significantly higher than those in age-matched W rats. NAD(P)H activity was similar in young SHR and W rats, whereas it was higher in aged SHR compared with age-matched W rats. Compared to W rats, superoxide production was higher in aged SHR, and was abolished by NAD(P)H inhibition with apocynin. CAT activity was increased in the hearts of 4-month-old SHR compared to age-matched W rats and was decreased in the hearts of the oldest SHR compared to the oldest W rats. SOD and GPx activities decreased in both rat strains with aging. Moreover, an increase in collagen deposition with aging was evident in both rat strains. Taken together, these data showed that aged SHR exhibited higher cardiac hypertrophy and oxidative damage compared to W rats, indicating that the two undesirable effects are associated. That is, oxidative stress appears to be a cause and/or consequence of hypertrophy development in this animal model.
Assuntos
Cardiomegalia/metabolismo , Estresse Oxidativo , Animais , Cardiomegalia/etiologia , Catalase/metabolismo , Colágeno/análise , Glutationa Peroxidase/metabolismo , Peroxidação de Lipídeos , Masculino , NADPH Oxidases/metabolismo , Ratos , Ratos Endogâmicos SHR , Ratos Wistar , Superóxido Dismutase/metabolismo , Superóxidos/metabolismoRESUMO
The possibility of a direct mitochondrial action of Na(+)/H(+) exchanger-1 (NHE-1) inhibitors decreasing reactive oxygen species (ROS) production was assessed in cat myocardium. Angiotensin II and endothelin-1 induced an NADPH oxidase (NOX)-dependent increase in anion superoxide (O(2)(-)) production detected by chemiluminescence. Three different NHE-1 inhibitors [cariporide, BIIB-723, and EMD-87580] with no ROS scavenger activity prevented this increase. The mitochondria appeared to be the source of the NOX-dependent ROS released by the "ROS-induced ROS release mechanism" that was blunted by the mitochondrial ATP-sensitive potassium channel blockers 5-hydroxydecanoate and glibenclamide, inhibition of complex I of the electron transport chain with rotenone, and inhibition of the permeability transition pore (MPTP) by cyclosporin A. Cariporide also prevented O(2)(-) production induced by the opening of mK(ATP) with diazoxide. Ca(2+)-induced swelling was evaluated in isolated mitochondria as an indicator of MPTP formation. Cariporide decreased mitochondrial swelling to the same extent as cyclosporin A and bongkrekic acid, confirming its direct mitochondrial action. Increased O(2)(-) production, as expected, stimulated ERK1/2 and p90 ribosomal S6 kinase phosphorylation. This was also prevented by cariporide, giving additional support to the existence of a direct mitochondrial action of NHE-1 inhibitors in preventing ROS release. In conclusion, we report a mitochondrial action of NHE-1 inhibitors that should lead us to revisit or reinterpret previous landmark observations about their beneficial effect in several cardiac diseases, such as ischemia-reperfusion injury and cardiac hypertrophy and failure. Further studies are needed to clarify the precise mechanism and site of action of these drugs in blunting MPTP formation and ROS release.
Assuntos
Mitocôndrias Cardíacas/metabolismo , Miocárdio/metabolismo , Trocadores de Sódio-Hidrogênio/antagonistas & inibidores , Superóxidos/metabolismo , Angiotensina II/farmacologia , Animais , Antiarrítmicos/farmacologia , Cloreto de Cálcio/farmacologia , Gatos , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Guanidinas/farmacologia , Técnicas In Vitro , Mitocôndrias Cardíacas/efeitos dos fármacos , Dilatação Mitocondrial/efeitos dos fármacos , NADPH Oxidases/metabolismo , Fosforilação , Espécies Reativas de Oxigênio/metabolismo , Proteínas Quinases S6 Ribossômicas 90-kDa/metabolismo , Sulfonas/farmacologiaRESUMO
The enhanced activity of the cardiac Na+/H+ exchanger (NHE-1) after myocardial stretch is considered a key step of the intracellular signaling pathway leading to the slow force response to stretch as well as an early signal for the development of cardiac hypertrophy. We propose that the chain of events triggered by stretch begins with the release of small amounts of Angiotensin II (Ang II)/endothelin (ET) and ends with the increase in intracellular Ca2+ concentration ([Ca2+]i) through the Na+/Ca2+ exchanger in reverse mode (NCX(rev)), which triggers cardiac hypertrophy by activation of widely recognized Ca2+-dependent intracellular signaling pathways.
Assuntos
Cardiomegalia/fisiopatologia , Trocadores de Sódio-Hidrogênio/fisiologia , Adulto , Angiotensina II/fisiologia , Fenômenos Biomecânicos , Cardiomegalia/genética , Ventrículos do Coração/fisiopatologia , Humanos , Hipertrofia Ventricular Direita/fisiopatologia , Obesidade/genética , Pressorreceptores/fisiologia , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais , Função VentricularRESUMO
When the length of the myocardium is increased, a biphasic response to stretch occurs involving an initial rapid increase in force followed by a delayed slow increase called the slow force response (SFR). Confirming previous findings involving angiotensin II in the SFR, it was blunted by AT1 receptor blockade (losartan). The SFR was accompanied by an increase in reactive oxygen species (ROS) of approximately 30% and in intracellular Na(+) concentration ([Na(+)](i)) of approximately 2.5 mmol l(-1) over basal detected by H(2)DCFDA and SBFI fluorescence, respectively. Abolition of ROS by 2-mercapto-propionyl-glycine (MPG) and EUK8 suppressed the increase in [Na(+)](i) and the SFR, which were also blunted by Na(+)/H(+) exchanger (NHE-1) inhibition (HOE642). NADPH oxidase inhibition (apocynin or DPI) or blockade of the ATP-sensitive mitochondrial potassium channels (5HD or glybenclamide) suppressed both the SFR and the increase in [Na(+)](i) after stretch, suggesting that endogenous angiotensin II activated NADPH oxidase leading to ROS release by the ATP-sensitive mitochondrial potassium channels, which promoted NHE-1 activation. Supporting the notion of ROS-mediated NHE-1 activation, stretch increased the ERK1/2 and p90rsk kinases phosphorylation, effect that was cancelled by losartan. In agreement, the SFR was cancelled by inhibiting the ERK1/2 signalling pathway with PD98059. Angiotensin II at a dose that mimics the SFR (1 nmol l(-1)) induced an increase in .O(2)(-) production of approximately 30-40% detected by lucigenin in cardiac slices, an effect that was blunted by losartan, MPG, apocynin, 5HD and glybenclamide. Taken together the data suggest a pivotal role of mitochondrial ROS in the genesis of the SFR to stretch.