RESUMEN
Phlorizin is a type of flavonoids and has a peroxynitrite scavenging effect. This study aimed to elucidate the effects of phlorizin on ischemia-induced ventricular tachyarrhythmia (VT). Optical signals from the epicardial surface of the ventricle or left ventricular end diastolic pressure (LVEDP) were recorded during acute global ischemia in 42 Langendorff-perfused guinea pig hearts. Experiments were performed in the control condition and in the presence of phlorizin or N-2-mercaptopropionylglycine (2-MPG), a peroxynitrite scavenger, respectively. Mean action potential duration at 20 min of ischemia did not differ among the three interventions. Impulse conduction time-dependently slowed during 20 min of ischemia in the control. Phlorizin but not 2-MPG improved the ischemic conduction slowing at 15 and 20 min of ischemia. Programmed stimulation induced VT at 20 min of ischemia in the control and in the presence of 2-MPG but not in the presence of phlorizin (p<0.05). LVEDP was increased during 30 min of ischemia in the control and in the presence of 2-MPG but not in the presence of phlorizin. These results indicate that phlorizin prevents VT through the improvement of impulse conduction slowing during ischemia. Phlorizin may be more useful for ischemia-induced VT than 2-MPG.
Asunto(s)
Antiarrítmicos/uso terapéutico , Isquemia Miocárdica/complicaciones , Florizina/uso terapéutico , Taquicardia Ventricular/prevención & control , Potenciales de Acción/efectos de los fármacos , Animales , Antiarrítmicos/administración & dosificación , Presión Sanguínea/efectos de los fármacos , Calcio/metabolismo , Estimulación Eléctrica , Electrocardiografía , Electrodos , Cobayas , Sistema de Conducción Cardíaco/efectos de los fármacos , Isquemia Miocárdica/metabolismo , Isquemia Miocárdica/fisiopatología , Perfusión , Florizina/administración & dosificación , Taquicardia Ventricular/etiología , Taquicardia Ventricular/metabolismo , Taquicardia Ventricular/fisiopatología , Función Ventricular Izquierda/efectos de los fármacos , Imagen de Colorante Sensible al VoltajeRESUMEN
Sodium glucose co-transporter 1 (SGLT1) plays a dominant role in the absorption of glucose in the gut and is considered a promising target in the development of therapeutic options for postprandial hyperglycemia. Previously, we reported potent and selective SGLT1 inhibitors 1 and 2 showing efficacy in oral carbohydrate tolerance tests in diabetic rat models. In a pharmacokinetic (PK) study of 2, excessive systemic exposure to metabolites of 2 was observed, presumably due to the high permeability of its aglycone (2a). To further improve SGLT1 inhibitory activity and reduce aglycone permeability, a series of 4-benzyl-5-isopropyl-1H-pyrazol-3-yl ß-D-glycopyranoside derivatives bearing novel hydrophilic substitution groups on the phenyl ring were synthesized and their inhibitory activity toward SGLTs was evaluated. Optimized compound 14c showed an improved profile satisfying both higher activity and lower permeability of its aglycone (22f) compared with initial leads 1 and 2. Moreover, the superior efficacy of 14c in various carbohydrate tolerance tests in diabetic rat models was confirmed compared with acarbose, an α-glucosidase inhibitor (α-GI) widely used in the clinic.
Asunto(s)
Diseño de Fármacos , Glicósidos/farmacología , Transportador 1 de Sodio-Glucosa/antagonistas & inhibidores , Relación Dosis-Respuesta a Droga , Glicósidos/síntesis química , Glicósidos/química , Humanos , Interacciones Hidrofóbicas e Hidrofílicas , Estructura Molecular , Relación Estructura-ActividadRESUMEN
Sodium glucose co-transporter 1 (SGLT1) plays a dominant role in the absorption of glucose in the gut and is considered a promising target in the development of treatments for postprandial hyperglycemia. A series of 4-benzyl-1H-pyrazol-3-yl ß-d-glucopyranoside derivatives have been synthesized, and its inhibitory activity toward SGLTs has been evaluated. By altering the substitution groups at the 5-position of the pyrazole ring, and every position of the phenyl ring, we studied the structure-activity relationship (SAR) profiles and identified a series of potent and selective SGLT1 inhibitors. Representative derivatives showed a dose-dependent suppressing effect on the escalation of blood glucose levels in oral mixed carbohydrate tolerance tests (OCTT) in streptozotocin-nicotinamide-induced diabetic rats (NA-STZ rats).
Asunto(s)
Glucósidos/química , Hipoglucemiantes/síntesis química , Transportador 1 de Sodio-Glucosa/antagonistas & inhibidores , Animales , Glucemia/análisis , Cristalografía por Rayos X , Diabetes Mellitus Experimental/tratamiento farmacológico , Glucósidos/síntesis química , Glucósidos/uso terapéutico , Humanos , Hiperglucemia/tratamiento farmacológico , Hipoglucemiantes/química , Hipoglucemiantes/uso terapéutico , Conformación Molecular , Ratas , Transportador 1 de Sodio-Glucosa/metabolismo , Transportador 2 de Sodio-Glucosa/metabolismo , Inhibidores del Cotransportador de Sodio-Glucosa 2 , Relación Estructura-ActividadRESUMEN
In cardiac myocytes, LTCCs (L-type calcium channels) form a functional signalling complex with ryanodine receptors at the JM (junctional membrane). Although the specific localization of LTCCs to the JM is critical for excitation-contraction coupling, their targeting mechanism is unclear. Transient transfection of GFP (green fluorescent protein)-α(1S) or GFP-α(1C), but not P/Q-type calcium channel α(1A), in dysgenic (α(1S)-null) GLT myotubes results in correct targeting of these LTCCs to the JMs and restoration of action-potential-induced Ca2+ transients. To identify the sequences of α(1C) responsible for JM targeting, we generated a range of α(1C)-α(1A) chimaeras, deletion mutants and alanine substitution mutants and studied their targeting properties in GLT myotubes. The results revealed that amino acids L(1681)QAGLRTL(1688) and P(1693)EIRRAIS(1700), predicted to form two adjacent α-helices in the proximal C-terminus, are necessary for the JM targeting of α(1C). The efficiency of restoration of action-potential-induced Ca2+ transients in GLT myotubes was significantly decreased by mutations in the targeting motif. JM targeting was not disrupted by the distal C-terminus of α(1C) which binds to the second α-helix. Therefore we have identified a new structural motif in the C-terminus of α(1C) that mediates the targeting of cardiac LTCCs to JMs independently of the interaction between proximal and distal C-termini of α(1C).
Asunto(s)
Canales de Calcio Tipo L/química , Canales de Calcio Tipo L/metabolismo , Potenciales de Acción , Secuencias de Aminoácidos , Secuencia de Aminoácidos , Animales , Canales de Calcio Tipo L/genética , Señalización del Calcio , Línea Celular , Membrana Celular/metabolismo , Ratones , Modelos Moleculares , Mutagénesis , Miocitos Cardíacos/metabolismo , Estructura Secundaria de Proteína , Subunidades de Proteína , Conejos , Proteínas Recombinantes de Fusión/química , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismoRESUMEN
Dihydropyridine Ca(2+) channel antagonists (DHPs) block Ca(V)1.2 L-type Ca(2+) channels (LTCCs) by stabilizing their voltage-dependent inactivation (VDI); however, it is still not clear how DHPs allosterically interact with the kinetically distinct (fast and slow) VDI. Thus, we analyzed the effect of a prototypical DHP, nifedipine on LTCCs with or without the Timothy syndrome mutation that resides in the I-II linker (L(I)-(II)) of Ca(V)1.2 subunits and impairs VDI. Whole-cell Ba(2+) currents mediated by rabbit Ca(V)1.2 with or without the Timothy mutation (G436R) (analogous to the human G406R mutation) were analyzed in the presence and absence of nifedipine. In the absence of nifedipine, the mutation significantly impaired fast closed- and open-state VDI (CSI and OSI) at -40 and 0 mV, respectively, but did not affect channels' kinetics at -100 mV. Nifedipine equipotently blocked these channels at -80 mV. In wild-type LTCCs, nifedipine promoted fast CSI and OSI at -40 and 0 mV and promoted or stabilized slow CSI at -40 and -100 mV, respectively. In LTCCs with the mutation, nifedipine resumed the impaired fast CSI and OSI at -40 and 0 mV, respectively, and had the same effect on slow CSI as in wild-type LTCCs. Therefore, nifedipine has two mechanistically distinct effects on LTCCs: the promotion of fast CSI/OSI caused by L(I-II) at potentials positive to the sub-threshold potential and the promotion or stabilization of slow CSI caused by different mechanisms at potentials negative to the sub-threshold potential.
Asunto(s)
Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio Tipo L/efectos de los fármacos , Síndrome de QT Prolongado/genética , Nifedipino/farmacología , Sindactilia/genética , Regulación Alostérica , Animales , Trastorno Autístico , Canales de Calcio Tipo L/metabolismo , Células HEK293 , Humanos , Potenciales de la Membrana , Mutación , Conejos , RatasRESUMEN
The high-affinity sodium glucose cotransporter (SGLT1) plays a critical role in glucose absorption from the gastrointestinal tract. We have developed 3-(3-{4-[3-(ß-D-glucopyranosyloxy)-5-isopropyl-1H-pyrazol-4-ylmethyl]-3-methylphenoxy}propylamino)propionamide (KGA-2727), which has a pyrazole-O-glucoside structure, as the first selective SGLT1 inhibitor. KGA-2727 inhibited SGLT1 potently and highly selectively in an in vitro assay using cells transiently expressing recombinant SGLTs. In a small intestine closed loop absorption test with normal rats, KGA-2727 inhibited the absorption of glucose but not that of fructose. After oral intake of starch along with KGA-2727 in normal rats, the residual content of glucose in the gastrointestinal tract increased. In the oral glucose tolerance test with streptozotocin-induced diabetic rats, KGA-2727 attenuated the elevation of plasma glucose after glucose loading, indicating that KGA-2727 improved postprandial hyperglycemia. In Zucker diabetic fatty (ZDF) rats, chronic treatments with KGA-2727 reduced the levels of plasma glucose and glycated hemoglobin. Furthermore, KGA-2727 preserved glucose-stimulated insulin secretion and reduced urinary glucose excretion with improved morphological changes of pancreatic islets and renal distal tubules in ZDF rats. In addition, the chronic treatment with KGA-2727 increased the level of glucagon-like peptide-1 in the portal vein. Taken together, our data indicate that the selective SGLT1 inhibitor KGA-2727 had antidiabetic efficacy and allow us to propose KGA-2727 as a candidate for a novel and useful antidiabetic agent.
Asunto(s)
Diabetes Mellitus Experimental/tratamiento farmacológico , Glucósidos/farmacología , Hipoglucemiantes/farmacología , Pirazoles/farmacología , Transportador 1 de Sodio-Glucosa/antagonistas & inhibidores , Animales , Diabetes Mellitus Experimental/metabolismo , Péptido 1 Similar al Glucagón/metabolismo , Glucosa/metabolismo , Glucósidos/metabolismo , Hemoglobina Glucada/metabolismo , Humanos , Hiperglucemia/tratamiento farmacológico , Hiperglucemia/metabolismo , Hipoglucemiantes/química , Insulina/metabolismo , Absorción Intestinal/efectos de los fármacos , Intestino Delgado/efectos de los fármacos , Intestino Delgado/metabolismo , Islotes Pancreáticos/efectos de los fármacos , Islotes Pancreáticos/metabolismo , Masculino , Ratas , Ratas Wistar , Ratas Zucker , Transportador 1 de Sodio-Glucosa/metabolismoRESUMEN
L-type Ca(2+) channels (LTCCs) play an essential role in the excitation-contraction coupling of ventricular myocytes. We previously found that t-tubular (TT) LTCC current density was halved by the activation of protein phosphatase (PP)1 and/or PP2A, whereas surface sarcolemmal (SS) LTCC current density was increased by the inhibition of PP1 and/or PP2A activity in failing ventricular myocytes of mice chronically treated with isoproterenol (ISO mice). In the present study, we examined the possible involvement of inhibitory heterotrimeric G proteins (G(i/o)) in these abnormalities by chronically administrating pertussis toxin (PTX) to ISO mice (ISO + PTX mice). Compared with ISO mice, ISO + PTX mice exhibited significantly higher fractional shortening of the left ventricle. The expression level of Gα(i2) proteins was not altered by the treatment of mice with ISO and/or PTX. ISO + PTX myocytes had normal TT and SS LTCC current densities because they had higher and lower availability and/or open probability of TT and SS LTCCs than ISO myocytes, respectively. A selective PKA inhibitor, H-89, did not affect LTCC current densities in ISO + PTX myocytes. A selective PP2A inhibitor, fostriecin, did not affect SS or TT current density in control or ISO + PTX myocytes but significantly increased TT but not SS LTCC current density in ISO myocytes. These results indicate that chronic receptor-mediated activation of G(i/o) in vivo decreases basal TT LTCC activity by activating PP2A and increases basal SS LTCC activity by inhibiting PP1 without modulating PKA in heart failure.
Asunto(s)
Canales de Calcio Tipo L/metabolismo , Subunidades alfa de la Proteína de Unión al GTP Gi-Go/fisiología , Insuficiencia Cardíaca/enzimología , Microtúbulos/metabolismo , Fosfoproteínas Fosfatasas/metabolismo , Sarcolema/metabolismo , Ácido 3-piridinacarboxílico, 1,4-dihidro-2,6-dimetil-5-nitro-4-(2-(trifluorometil)fenil)-, Éster Metílico/farmacología , Agonistas Adrenérgicos beta/farmacología , Algoritmos , Animales , Presión Sanguínea/efectos de los fármacos , Agonistas de los Canales de Calcio/farmacología , Canales de Calcio Tipo L/efectos de los fármacos , Proteínas Quinasas Dependientes de AMP Cíclico/metabolismo , Subunidades alfa de la Proteína de Unión al GTP Gi-Go/efectos de los fármacos , Insuficiencia Cardíaca/diagnóstico por imagen , Frecuencia Cardíaca/efectos de los fármacos , Isoproterenol/farmacología , Masculino , Potenciales de la Membrana/efectos de los fármacos , Ratones , Ratones Endogámicos C57BL , Microtúbulos/efectos de los fármacos , Miocardio/patología , Miocitos Cardíacos/fisiología , Técnicas de Placa-Clamp , Toxina del Pertussis/farmacología , Fosfoproteínas Fosfatasas/antagonistas & inhibidores , Receptores Acoplados a Proteínas G/efectos de los fármacos , Sarcolema/efectos de los fármacos , UltrasonografíaRESUMEN
In some forms of cardiac hypertrophy and failure, the gain of Ca(2+)-induced Ca(2+) release [CICR; i.e., the amount of Ca(2+) released from the sarcoplasmic reticulum normalized to Ca(2+) influx through L-type Ca(2+) channels (LTCCs)] decreases despite the normal whole cell LTCC current density, ryanodine receptor number, and sarcoplasmic reticulum Ca(2+) content. This decrease in CICR gain has been proposed to arise from a change in dyad architecture or derangement of the t-tubular (TT) structure. However, the activity of surface sarcolemmal LTCCs has been reported to increase despite the unaltered whole cell LTCC current density in failing human ventricular myocytes, indicating that the "decreased CICR gain" may reflect a decrease in the TT LTCC current density in heart failure. Thus, we analyzed LTCC currents of failing ventricular myocytes of mice chronically treated with isoproterenol (Iso). Although Iso-treated mice exhibited intact t-tubules and normal LTCC subunit expression, acute occlusion of t-tubules of isolated ventricular myocytes with osmotic shock (detubulation) revealed that the TT LTCC current density was halved in Iso-treated versus control myocytes. Pharmacological analysis indicated that kinases other than PKA or Ca(2+)/calmodulin-dependent protein kinase II insufficiently activated, whereas protein phosphatase 1/2A excessively suppressed, TT LTCCs in Iso-treated versus control myocytes. These results indicate that excessive ß-adrenergic stimulation causes the decrease in TT LTCC current density by altering the regulation of TT LTCCs by protein kinases and phosphatases in heart failure. This phenomenon might underlie the decreased CICR gain in heart failure.