The ability of atropine to prevent and reverse the negative chronotropic effect of fingolimod in healthy subjects

WHAT IS KNOWN ABOUT THIS SUBJECT

• Clinical pharmacology and clinical therapeutic studies of fingolimod demonstrate that heart rate after the initial dose decreases by about 10–20% while normal circadian rhythm is preserved. With continued daily dosing, heart rate returns to normal over the next 2 weeks.
• This negative chronotropic effect is consistent with the binding of fingolimod-phosphate to the sphingosine-1-phosphate receptor on atrial myocytes.

WHAT THIS STUDY ADDS

• The present clinical pharmacology study demonstrates that atropine administered at usual therapeutic doses can prevent the decrease in heart rate when given concomitantly with fingolimod and can counteract the decrease in heart rate when give at the time of the typical heart rate nadir, 4 h after the fingolimod dose.
• Although therapeutic intervention is rarely needed for reduced heart rate in patients receiving fingolimod, atropine is an option, should this be desired.

AIMS

The authors determined whether intravenous atropine can prevent or counteract the negative chronotropic effect of the immunomodulator fingolimod.

METHODS

In this randomized, placebo-controlled, two-period, crossover study, 12 healthy subjects received 5 mg fingolimod orally concurrently with intravenous atropine (titrated to a heart rate of 110–120 beats min⁻¹) or intravenous placebo. A second group of 12 subjects received atropine/placebo 4 h after the fingolimod dose. Continuous telemetry measurements were made for 24 h after each fingolimod dose.

RESULTS

Fingolimod administration alone yielded a heart rate nadir of 51 ± 5 beats min⁻¹ at a median 4 h postdose with heart rate remaining depressed at 51–64 beats min⁻¹ over the rest of the day. Concurrent administration of fingolimod and atropine yielded a nadir of 66 ± 6 beats min⁻¹ resulting in an atropine : placebo ratio (90% confidence interval) of 1.30 (1.22, 1.36). When atropine was administered at the time of the nadir, it was able to reverse the negative chronotropic effect of fingolimod from a heart rate of 56 ± 9 beats min⁻¹ (placebo) to 64 ± 8 beats min⁻¹ (atropine) resulting in an atropine : placebo ratio of 1.15 (1.04, 1.26). Atropine had no influence on the pharmacokinetics of fingolimod.

CONCLUSIONS

Atropine administered concurrently with fingolimod prevented the heart rate nadir that typically occurs 4 h postdose. Atropine administered at the time of the heart rate nadir was able to reverse the negative chronotropic effect of fingolimod.     

小檗碱的负性变时作用

小檗碱(Ber)4mg/kg ⅳ使正常大鼠的血压(BP)降低,心率(HR)不变;迷走神经切断大鼠的BP降低,HR减慢;毁脊髓大鼠的HR减慢,BP不变。在离体豚鼠右心房,Ber产生负性变时作用,且不被阿托品对抗。Ber使异丙肾上腺素、组胺和CaCl_2正性变时作用的量效曲线非平行性右移,最大反应压低,呈非竞争性拮抗作用,其pD_2分别为4.82,4.51和4.68。结果表明Ber对正常大鼠的负性变时作用,可因其降压所致的反射性HR加快而抵消。Ber的负性变时作用可能与心肌M,β和H_2受体无关,也不是选择性阻滞Ca~(2+)内流所致。     

A theory of benzodiazepine dependence that can explain whether flumazenil will enhance or reverse the phenomena

Repeated administration of benzodiazepines (BDZs) produces dependence in man and animals and this is reflected in the phenomena of tolerance and withdrawal responses. In BDZ-dependent animals the BDZ-receptor antagonist flumazenil (Ro 15-1788) reverses the increased anxiety and decreased seizure threshold seen when benzodiazepine treatment is withdrawn. In contrast are reports that flumazenil enhances BDZ-withdrawal responses. Indirect influences on the direction of flumazenil's effects on anxiety are the duration and dose of BDZ treatment, whether tolerance has developed to its anxiolytic effect and whether there is an anxiogenic response on drug withdrawal. However, we conclude that the crucial factor is the anxiety level of the animal: when this is high flumazenil becomes anxiolytic; when this is low flumazenil is anxiogenic. These bidirectional effects of flumazenil can be seen in drug-naive and BDZ-dependent animals. We propose a theory of benzodiazepine dependence that can account for anxiogenic responses on drug withdrawal and for flumazenil's bidirectional effects; central to this theory is the assumption that flumazenil normalises the benzodiazepine receptor, returning it to a baseline state. Thus it is whether an animal's score lies above or below this baseline that will determine the direction of flumazenil's effect. The clinical implications of this theory are discussed. We suggest that during the development of benzodiazepine dependence, two independent adaptive biochemical mechanisms are triggered: one underlying the development of tolerance to the anxiolytic responses, the other underlying the incidence of increased anxiety on drug withdrawal. It is only changes in the latter that are induced by the administration of flumazenil.     

The effect of amiloride on the cardiac chronotropic responses to isoproterenol in myocardial aggregate cells in culture

The purpose of this study was to test the hypothesis that amiloride alters the response of cardiac myocytes to isoproterenol. Myocardial cell aggregates were prepared from 7 day-old chick embryos maintained in culture for 72 hrs before study. Isoproterenol, 10-8 M to 10-5 M, significantly (P less than 0.05) increased contractile frequency of myocardial aggregates. The effects of isoproterenol were maximum within 5 min. of exposure and declined thereafter. In the absence of isoproterenol, amiloride, at 10-6 M and 10-7 M produced a transient decrease in contractile frequency while amiloride at 10-5 M produced a significant (P less than 0.05) decrease in contractile frequency. Amiloride significantly (P less than 0.05) increased the effect of isoproterenol on cardiac contractile frequency. There was a greater and more sustained response to isoproterenol in the presence of amiloride. Furthermore, the magnitude of these effects were greater with higher concentrations of amiloride. These data indicate that amiloride accentuates the cardiac chronotropic response to isoproterenol and suggest that, because amiloride inhibits sodium entry in these cells, change in intracellular sodium may be one of the mechanisms mediating the chronotropic action of isoproterenol on the heart.     

An in vivo investigation of the negative chronotropic effect of cholic acid in the rat

1. Experimental obstructive jaundice in the Wistar rat causes a significant decrease in heart rate. 2. Intravenous administration of cholic acid in vivo elicits a dose-dependent negative chronotropic effect. 3. Atropine or vagotomy significantly reduces, but does not abolish, the negative chronotropic effect of cholic acid. 4. Ganglion blockade and decerebration diminishes the negative chronotropic effect of cholic acid, but to a lesser extent than atropine or vagotomy. 5. Sympathetic depletion by reserpine slightly potentiates the response to cholic acid. 6. The effect of cholic acid injected cranially into the common carotid artery is less than when administered into the jugular vein. 7. The haemolysis caused by cholic acid does not appear to be involved in the negative chronotropic effect. 8. It is concluded that cholic acid causes both a direct as well as a vagally mediated negative chronotropic effect in the Wistar rat.     

Positive and negative chronotropic response of the S-A node to oxyfedrine.

Direct perfusion of the sinus node artery under a constant pressure of 100 mmHg was carried out in vagotomized dogs. "Selective" injection of L-3-methoxy-omega-(1-hydroxy-1-phenylisopropylamino) propiophenone hydrochloride (oxyfedrine) into the sinus node artery induced three types of chronotropic response; a pronounced sinus tachycardia, an initial bradycardia followed by sustained tachycarcia, or a definite sinus bradcardia alone. The paradoxical sinus bradycardia induced by oxyfedrine was more pronounced at higher doses of the compound, whereas it was nver produced by the injection of isoproterenol. The oxyfedrine-induced sinus tachycardia, which occurred even in reserpinized preparations, was not suppressed by the treatment with tetrodotoxin, hexamethonium or bretylium, but it was selectively inhibited by propranolol. Atropine, tetrodotoxin or hexamethonium did not prevent the occurrence of sinus bradycardia induced by oxyfedrine, and physostigmine failed to enhance the response. The present study indicates that the oxyfedrine-induced tachycardia is mediated mainly by a direct stimulating action on adrenergic beta-receptors, while the bradycardia appears to be induced by a direct depressant action on the S-A node.     

Potentiation of the negative chronotropic action of verapamil by ethanol

Ethanol and verapamil are both known to affect the transmembrane movement of Ca2+ in several biological systems. Both ethanol and verapamil have negative chronotropic actions on the isolated sinus node. The following study was designed to determine if these actions were synergistic. Studies on sinoatrial (SA) node-atrial preparations from rats pair-fed either sucrose or ethanol liquid diets showed that the preparations from the ethanol rats were more sensitive to verapamil. Studies on SA node-atrial preparations from control rats showed that acutely administered ethanol (20 mg/dl, 40 mg/dl) reduced spontaneous beating. In addition, verapamil had a greater negative chronotropic effect in the presence of ethanol (20 mg/dl, 40 mg/dl) than it did alone. It is hypothesized that the ethanol-verapamil interaction is mediated through a reduction in transmembrane Ca2+ movement.     

A caffeine analogue (1,3,7-trimethyl-6-thioxo-2-oxopurine) with a negative inotropic and chronotropic effect

Cardiac effects of thio-xanthine derivatives, S-caffeine and S-theophylline, were studied on isolated guinea-pig atria and on partially purified cardiac cAMP phosphodiesterase enzymes. Theophylline and caffeine were taken as reference compounds. On electrically driven left atria S-caffeine (0.01-1 mmol/l) decreased contractile tension in a concentration dependent manner. On spontaneously beating atria, the same concentrations of S-caffeine showed negative inotropic as well as negative chronotropic effects. On electrically driven left atria, S-theophylline (0.01-1 mmol/l) increased heart contractile tension but, at higher concentrations, a reversal of the stimulating effect was observed. Both S-caffeine and S-theophylline inhibited bovine heart cAMP phosphodiesterase activity to a comparable extent. Their inhibitory potencies were about three and nine times higher than those of theophylline or caffeine but consistently lower than that of IBMX. The results show that the replacement of O with S in the methylxanthine molecule drastically modifies the effects induced by the drugs on cardiac function without changing those on cAMP phosphodiesterase.     

A mechanistic study of the effect of transferrin conjugation on cytotoxicity of targeted liposomes

Abstract

This study was performed to prepare 5-fluorouracil (5FU) containing targeted liposomes for the safety and efficacy enhancement. Liposomes were prepared using thin layer method and transferrin (Tf) was employed as the targeting ligand. Morphology of 5FU-loaded liposomes was assessed by transmission electron microscopy (TEM). The in vitro cytotoxicity was investigated via MTT assay on HT-29, CT26 and fibroblast cells. Mitochondrial membrane and cell death evaluations were also investigated. Resulted showed that the encapsulation efficiency (EE%) and particle size of the liposomes were 40.12% and 130?nm, respectively. TEM image implied that liposomes were spherical in shape. In cancer cells, targeted liposomes triggered the mitochondrial apoptotic pathway by lower production of reactive oxygen species (ROS) (63.58 vs 84.95 fluorescence intensity), reduced mitochondrial membrane potential and releasing of cytochrome c (68.66 vs 51.13?ng/mL). The results of this study indicated that Tf-targeted 5FU liposomes can be employed as promising nanocarrier for the delivery of drugs to cancer cells.     

The effect of aging on the positive chronotropic response to amitriptyline

Amitriptyline (AT) increases sinus heart rate (SHR) due to inhibition of the reuptake of norepinephrine in combination with an antimuscarinic blockade of cardiac vagal inhibition. After 150 mg/day AT for 28 days, the change in SHR was negatively correlated with age in 42 depressed patients who were 18–85 years of age. This finding is consistent with observations that the tachycardic response to antimuscarinics and catecholamines decreases with aging.     

The effect of thyroid dysfunction on the chronotropic response to noradrenaline

Dose-response curves to noradrenaline in the presence and absence of beta-receptor antagonists were established with isolated atria from euthyroid, hypothyroid and hyperthyroid rats. Baseline atrial rate and Emax were significantly lower than normal in the hypothyroid group and significantly higher than normal in the hyperthyroid group. Differences between the groups were minimal for pD2 and range of response to noradrenaline. The response to beta-receptor antagonists was the same in all 3 groups with the exception of the hypothyroid group which showed an attenuated increase in baseline atrial rate with compounds possessing partial agonist activity. This was particularly marked for practolol. These results do not provide evidence for an altered responsiveness to catecholamines due to altered thyroid status but suggest that thyroid hormones have a direct action on cardiac tissue.     

Inhibition of the negative chronotropic action of adenosine by caffeine in the dog

The sinus node artery was perfused in situ in 15 dogs. Injection of adenosine into the sinus node artery induced a negative chronotropic effect at doses of 1, 3 and 10 μg. The negative chronotropic response to adenosine was blocked by 300 μg to of caffeine given into the same artery. On the contrarym, the negative chronotropic response to ACh was not inhibited but rather enhanced by caffeine, so that the atrial fibrillation threshold to ACh was lowered. Neither norepinephrine nor calcium when injected into the sinus node artery inhibited the deceleration response to adenosine.     

Plasma levels and negative chronotropic effect of metoprolol following single doses of a conventional and sustained-release formulation

Summary Plasma levels and associated reduction in exercise-induced tachycardia have been examined following the administration of single doses of metoprolol in conventional and slow-release tablets at different times to six healthy male subjects. The study was carried out in two parts. Initially, the tablets were given at 9 a. m. and the subjects were studied up to 14 h and then at 24 h. Subsequently, the same doses were given at 9 p. m. and the subjects were studied 12–24 h after drug administration (i. e. 9 a. m.–9 p. m. the next day). After giving the slow-release tablets the peak plasma levels were significantly lower but the drug persisted in the plasma at higher levels than after the conventional tablet. However, the beta-blocking effect was comparable from the two dosages. The results obtained for the period 12–24 h after the evening dose differed from the corresponding values after morning administration in that the plasma levels were higher and the betablocking effects more marked. Furthermore, the half-life values calculated from these data were significantly longer.     

Demonstration of two different types of beta1-receptors in man (selective blockade of the positively inotropic and the positively chronotropic effect of isoproterenol).

The hemodynamic effect of a beta-receptor blockade with mepindolol--a noncardioselective beta-receptor blocker--was studied in 6 male test subjects age 25 to 30 years with an increasing dose of isoproterenol. The cardiac output per min, the heart rate and the stroke volume, the wet blood pressure and the contractility parameters dp/dt max in the right and left ventricles were measured as part of the study. It was found that a dissociated right shift of the dose-effect curves occurred for the stroke volume, contractility parameters and heart rate. The following major conclusions can be made from an exact analysis of this result: 1. Evidence was produced that a distinction must be made in man with respect to the so-called beta1-receptors between those which mediate a specific effect on the heart rate and those which mediate a primarily positively inotropic effect. 2. There are apparently some beta-receptor blockers which inhibit the frequency receptors primarily and the inotropic receptors to a lesser extent. 3. Through their beta 2-effect, noncardioselective beta-receptor blockers can partly compensate for their negatively inotropic effect on the heart by maintaining the Frank Starling mechanism.     

Investigation of the negative chronotropic action of SK&F 86466 in the pithed normotensive rat

SK&F 86466, 6-chloro-3-methyl-2,3,4,5-tetrahydro-1-H-3-benzazepine, is a potent and selective antagonist of the α₂-adrenoceptor in vitro. This compound produced a small pressor response accompanied by a marked bradycardia when administered i.v. to the pithed normotensive rat. The pressor response was not affected by reserpine treatment, pretreatment with α- or β-adrenoceptor antagonists, atropine, or hexamethonium. The bradycardia was markedly reduced by bilateral vagotomy and pretreatment with atropine and attenuated by hexamethonium. The negative chronotropic action of SK&F 86466 was abolished by a combination of vagotomy and atropine. Mediation of the bradycardia by a baroreceptor reflex was ruled out by the observations that a lack of change in heart rate was associated with the vasopressor response to phenylephrine in the pithed rat pretreated with propranolol. It is concluded that the negative chronotropic action of SK&F 86466 in the pithed rat is mediated indirectly by activation of the cholinergic innervation of the heart.     

A mechanistic study of tumor-targeted corrole toxicity

HerGa is a self-assembled tumor-targeted particle that bears both tumor detection and elimination activities in a single, two-component complex (Agadjanian et al. Proc. Natl. Acad. Sci. U.S.A.2009, 106, 6105-6110). Given its multifunctionality, HerGa (composed of the fluorescent cytotoxic corrole macrocycle, S2Ga, noncovalently bound to the tumor-targeted cell penetration protein, HerPBK10) has the potential for high clinical impact, but its mechanism of cell killing remains to be elucidated, and hence is the focus of the present study. Here we show that HerGa requires HerPBK10-mediated cell entry to induce toxicity. HerGa (but not HerPBK10 or S2Ga alone) induced mitochondrial membrane potential disruption and superoxide elevation, which were both prevented by endosomolytic-deficient mutants, indicating that cytosolic exposure is necessary for corrole-mediated cell death. A novel property discovered here is that corrole fluorescence lifetime acts as a pH indicator, broadcasting the intracellular microenvironmental pH during uptake in live cells. This feature in combination with two-photon imaging shows that HerGa undergoes early endosome escape during uptake, avoiding compartments of pH < 6.5. Cytoskeletal disruption accompanied HerGa-mediated mitochondrial changes whereas oxygen scavenging reduced both events. Paclitaxel treatment indicated that HerGa uptake requires dynamic microtubules. Unexpectedly, low pH is insufficient to induce release of the corrole from HerPBK10. Altogether, these studies identify a mechanistic pathway in which early endosomal escape enables HerGa-induced superoxide generation leading to cytoskeletal and mitochondrial damage, thus triggering downstream cell death.