Cardiac electrophysiological effects of citalopram in guinea pig papillary muscle comparison with clomipramine

Drug-induced fatal arrhythmias: Acquired long QT and Brugada syndromes

Since the early 1990s, the concept of primary "inherited" arrhythmia syndromes or ion channelopathies has evolved rapidly as a result of revolutionary progresses made in molecular genetics. Alterations in genes coding for membrane proteins such as ion channels or their associated proteins responsible for the generation of cardiac action potentials (AP) have been shown to cause specific malfunctions which eventually lead to cardiac arrhythmias. These arrhythmic disorders include congenital long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, short QT syndrome, progressive cardiac conduction disease, etc. Among these, long QT and Brugada syndromes are the most extensively studied, and drugs cause a phenocopy of these two diseases. To date, more than 10 different genes have been reported to be responsible for each syndrome. More recently, it was recognized that long QT syndrome can be latent, even in the presence of an unequivocally pathogenic mutation (silent mutation carrier). Co-existence of other pathological conditions in these silent mutation carriers may trigger a malignant form of ventricular arrhythmia, the so called torsade de pointes (TdP) that is most commonly brought about by drugs. In analogy to the drug-induced long QT syndrome, Brugada type 1 ECG can also be induced or unmasked by a wide variety of drugs and pathological conditions; so physicians may encounter patients with a latent form of Brugada syndrome. Of particular note, Brugada syndrome is frequently associated with atrial fibrillation whose therapeutic agents such as Vaughan Williams class IC drugs can unmask the dormant and asymptomatic Brugada syndrome. This review describes two types of drug-induced arrhythmias: the long QT and Brugada syndromes.

Low proarrhythmic potential of citalopram and escitalopram in contrast to haloperidol in an experimental whole-heart model

In several case reports proarrhythmic effects of citalopram and escitalopram have been reported. Systematic analyses on prorarrhythmic effects of these drugs are not yet available. The aim of the present study was to investigate if application of citalopram, escitalopram or haloperidol provokes polymorphic ventricular tachycardia in a sensitive model of proarrhythmia. In isolated rabbit hearts monophasic action potentials and ECG showed a significant QT-prolongation after application of citalopram (2µM: +47ms, 4µM: +56ms, P<0.05) accompanied by an increase of action potential duration (APD) but not dispersion of repolarization. Reduced potassium concentration in bradycardic AV-blocked hearts provoked early afterdepolarizations (EAD) in 2 of 12 hearts but no polymorphic ventricular tachycardia (pVT). Application of escitalopram also increased QT-interval (2µM: +3ms, 4µM: +30ms, P<0.05) and APD without effects on dispersion. 3 of 10 hearts showed EAD and pVT in 2 of 10 hearts (32 episodes). The results were compared to 12 rabbits treated with haloperidol which led to an increase in QT-interval (1µM:+62ms; 2µM:+96ms; P<0.01), APD and dispersion (1µM:+15ms, 2µM:+40ms; P<0.01) and induced EAD in all 12 and pVT in 10 of 12 hearts (152 episodes). Citalopram and escitalopram demonstrated a rather safe electrophysiologic profile despite significant QT prolongation. In contrast, haloperidol led to significant increase of dispersion of repolarization while this parameter remained stable under the influence of citalopram or escitalopram. These results imply that application of citalopram or escitalopram is not as proarrhythmic as some case reports might suggest while haloperidol is torsadogenic.

New screening system for selective blockers of voltage-gated K(+) channels using recombinant cell lines dying upon single action potential

To develop a simple screening system for blockers of voltage-gated Kv1.3 and Kv1.5 channels, new cell lines co-expressing mutated Nav1.5 (IFM/Q3), Kir2.1 (Kir), and Kv1.3 or Kv1.5 were introduced as IFM/Q3+Kir+Kv1.3 and IFM/Q3+Kir+Kv1.5, respectively. Electrical stimulation (ES) of a cell line, IFM/Q3+Kir, induced prolonged action potentials due to the slow inactivation of IFM/Q3 and subsequent cell death. Additional co-expression of Kv1.3 or Kv1.5 to IFM/Q3+Kir shortened the evoked action potentials and prevented cell death. In the presence of margatoxin, a selective Kv1.3-blocker, ES induced cell death in IFM/Q3+Kir+Kv1.3, but not in IFM/Q3+Kir+Kv1.5. In the presence of 4-aminopyridine, a non-selective Kv-channel blocker, ES application elicited cell death in both cell lines. The IC50s of acacetin, a Kv1.5-blocker, was 10.2 μM in IFM/Q3+Kir+Kv1.3 and almost identical to that in IFM/Q3+Kir+Kv1.5 (7.6 μM). The IC50s of citalopram, a 5-HT uptake-inhibitor, were 1.8 μM in IFM/Q3+Kir+Kv1.3 and 1.5 μM in IFM/Q3+Kir+Kv1.5, respectively. These IC50s were comparable to those determined electrophysiologically. In conclusion, acacetin and citalopram block both Kv1.3 and Kv1.5 without selectivity. The Kv1.3 or Kv1.5 channel inhibition assay using these new cell lines may be applicable to high-throughput screening because of its simplicity, accuracy, and high cost-performance.

Effect of sertraline on ouabain-induced arrhythmia in isolated guinea-pig atria

BACKGROUND

The effect of sertraline a selective serotonin reuptake inhibitor antidepressant was studied on ouabain-induced toxicity (arrhythmia) in spontaneously beating isolated guinea-pig atria.

METHODS

The guinea-pig atrium was dissected out and suspended in modified Krebs solution under physiological conditions. Drugs were added into solutions. The changes in rate and force of contractions were measured using a physiograph.

RESULTS

Sertraline (2-16 microg/mL) caused a dose-dependent decrease in the rate of contractions (17-46%) and in the contractile force (26-48%). Ouabain alone (1.2 microg/mL) produced arrhythmia at 7.8 min and asystole at 22 min. Pre- administration of the atria with sertraline (8 microg/mL) significantly increased the time required to produce arrhythmia by ouabain to 20.5 min, prolonged the beating of atria to more than 64.5 min and delayed the occurrence of asystolia. The pattern of contractile force induced by sertraline + ouabain was more regular than that produced by ouabain alone.

CONCLUSIONS

These findings indicate that sertraline produces direct cardiac action, probably due to the inhibition of cardiac Na(+) and Ca(2+) channels. Our results suggest that sertraline may reduce the membrane conduction through inhibition of ionic channels which decrease ouabain-induced arrhythmia.

Drugs and Brugada syndrome patients: review of the literature, recommendations, and an up-to-date website (www.brugadadrugs.org)

BACKGROUND

Worldwide, the Brugada syndrome has been recognized as an important cause of sudden cardiac death in individuals at a relatively young age. Importantly, many drugs have been reported to induce the characteristic Brugada syndrome-linked ECG abnormalities and/or (fatal) ventricular tachyarrhythmias.

OBJECTIVE

The purpose of this study was to review the literature on the use of drugs in Brugada syndrome patients, to make recommendations based on the literature and on expert opinion regarding drug safety, and to ensure worldwide online and up-to-date availability of this information to all physicians who treat Brugada syndrome patients.

METHODS

We performed an extensive review of the literature, formed an international expert panel to produce a consensus recommendation to each drug, and initiated a website (www.brugadadrugs.org).

RESULTS

The literature search yielded 506 reports for consideration. Drugs were categorized into one of four categories: (1) drugs to be avoided (n = 18); (2) drugs preferably avoided (n = 23); (3) antiarrhythmic drugs (n = 4); and (4) diagnostic drugs (n = 4). Level of evidence for most associations was C (only consensus opinion of experts, case studies, or standard-of-care) as there are no randomized studies and few nonrandomized studies in Brugada syndrome patients.

CONCLUSION

Many drugs have been associated with adverse events in Brugada syndrome patients. We have initiated a website (www.brugadadrugs.org) to ensure worldwide availability of information on safe drug use in Brugada syndrome patients.

The hERG potassium channel as a therapeutic target

The hERG (human ether-à-go-go-related gene) potassium channel has elicited intense scientific interest due to its counter-intuitive kinetics and its association with arrhythmia and sudden death. hERG blockade is involved in both antiarrhythmic pharmacotherapy and the pathogenesis of familial and acquired long QT syndrome (LQTS). Short QT syndrome (SQTS), muscular atrophy and many forms of cancer have also been associated with hERG as a target. Molecular models of both the channel and its blocker pharmacophores exist, revealing methods to design hERG liability out of potential drug molecules. Future developments will synthesise preclinical data on hERG with other criteria to determine net arrhythmogenic risk. Also, the molecular actions of hERG and its genetics will be elucidated in detail to allow clinical risk reduction.

Electrical alternans and hemodynamics in the anesthetized guinea pig can discriminate the cardiac safety of antidepressants

INTRODUCTION

The arrhythmogenic risk of fluoxetine, citalopram, and venlafaxine were evaluated through preclinical assays measuring hERG, blood pressure and electrical alternans over their respective clinical unbound concentration ranges.

METHODS

Anesthetized guinea pigs were instrumented with jugular and carotid cannulae for drug infusion and blood pressure monitoring respectively; a thoracotomy was performed for placement of a monophasic action potential probe on the left ventricle and for placement of pacing wires on the left ventricular apex. Drugs were infused as a 5-min loading dose immediately followed by a 10-min maintenance dose to achieve clinically relevant plasma concentrations; blood samples were taken at the end of each maintenance dose. Ventricular pacing was performed twice at baseline and at each dose level as follows: 50 preconditioning-beats at S1=220 (or 240) ms immediately followed by 30 test-beats at S2=200 ms. This S1-S2 protocol was repeated for S2=190 to 140 ms. HERG and calcium current measurements were recorded in HEK-293 cells stably expressing hERG potassium currents and freshly isolated guinea pig cardiac myocytes using the whole-cell configuration of the patch clamp technique.

RESULTS

Physiologically relevant inhibition (IC(20)) of hERG occurred at concentrations 22-fold (fluoxetine), 9-fold (citalopram), and 11-fold (venlafaxine) beyond their respective clinically effective concentration (C(eff)). At the highest achievable levels, fluoxetine (20-fold C(eff)) and citalopram (28-fold C(eff)) significantly decreased heart rate and/or blood pressure as well as increasing electrical alternans by 5 and 18 ms respectively. Venlafaxine increased blood pressure at only 1.3-fold C(eff), but did not increase electrical alternans at the highest achievable dose (3.1-fold C(eff)).

DISCUSSION

These data suggest that evaluating other dose limiting side effects in relation to a drug's therapeutic range may be crucial for accurate assessment of arrhythmia liability.

Inhibitory effect of the DA uptake blocker GBR 12909 on sodium channels of hippocampal neurons

The effect of the selective dopamine uptake inhibitor GBR 12909 on TTX-sensitive sodium channels of cultured hippocampal neurons was investigated using whole cell patch-clamp technique. GBR 12909 dose-dependently inhibited sodium currents evoked by trains of depolarizing pulses with an IC50 of 6.3 microM. A weaker inhibition (IC50 = 17-35 microM) could be observed when currents were evoked by either single pulse depolarization or from hyperpolarized holding membrane potential. These data indicate that the extent of inhibition caused by GBR 12909 depends on the physiological activity pattern of neurons. Our results suggest that caution is needed for the interpretation of data when GBR 12909 is used for the inhibition of dopamine uptake at concentrations above the submicromolar range.

Age-related differences in the side effect profile of citalopram

The authors evaluated the autonomic and cardiovascular side effects of citalopram with particular emphasis on their relation to the age of treated patients. The data that formed the basis for the U.S. Food and Drug Administration approval of citalopram were provided by Lundbeck (Copenhagen, Denmark). This database included placebo-controlled short- and long-term studies in major depressed patients. The list of side effects comprised all "heart rate and rhythm disorders" as well as "autonomic nervous system disorders" that had been reported by at least 5% more than that reported for the placebo group of subjects. The database encompassed 1344 subjects treated with citalopram (20-60 mg/day) for a period of no less than 6 weeks. Statistically significant age-related distribution was found for five side effects: bradycardia, nausea, diarrhea, sweating and headache. Bradycardia was more prevalent in elderly (>65 years) patients as compared to the younger population (2.4% vs. 0.2%, P<.05), whereas gastrointestinal side effects, sweating and headache were less prevalent in the elderly. The age-related differences in the side effect profile may be attributable to altered sensitivity of the serotonergic system.

Effect of citalopram on ouabain-induced arrhythmia in isolated guinea-pig atria

The effect of citalopram (CTP) a selective serotonin reuptake inhibitor agent was studied on ouabain-induced arrhythmia in spontaneously beating isolated guinea-pig atria. CTP (2-32 microg/ml) produced a dose-dependent decrease in the force of contractions (7-62%), and in the rate of contractions (11-72%). Pre-administration of the atria with CTP inhibited the ouabain-induced arrhythmia in isolated atria. Ouabain alone (1.2 microg/ml) produced arrhythmia at 4.5 min, and asystole at 20.7 min. Pretreatment with CTP (8 microg/ml) significantly increased the time of onset of arrhythmia to 9.5 min. In addition CTP prolonged the beating of atria (survival time) to more than 56 min, and inhibited the occurrence of asystole. These findings indicate that CTP produces direct cardiac action, probably due to the inhibition of cardiac Na(+) and Ca(2+) channels. Moreover our results suggest that CTP may reduce the membrane conductance through inhibition of ionic channels which decrease ouabain-induced arrhythmia.

Inhibitory actions of the selective serotonin re-uptake inhibitor citalopram on HERG and ventricular L-type calcium currents

Using whole-cell patch clamp recording of heterologous HERG-mediated currents in transfected mammalian cells, we observed that the selective serotonin re-uptake inhibitor citalopram blocks HERG with an IC(50) of 3.97 microM. This is slightly less potent than fluoxetine in our system (IC(50) of 1.50 microM). In isolated guinea pig ventricular cardiomyocytes citalopram inhibited L-type calcium current (I(Ca,L)). The voltage dependence of I(Ca,L) inactivation in the presence of 100 microM citalopram was shifted significantly leftward. As a result, the I(Ca,L) 'window' in citalopram was found to be (a) smaller and (b) leftward-shifted compared to control. The effects of citalopram on both calcium current amplitude and the I(Ca,L) 'window' may help to explain citalopram's good cardiac safety profile, given its propensity to block HERG at excessive dosages.

Selective serotonin-reuptake inhibitor antidepressants increase the risk of falls and hip fractures in elderly people by inhibiting cardiovascular ion channels

Surprising results from recently published retrospective studies show that the use of new selective serotonin-reuptake inhibitor antidepressants (SSRIs), similarly to the older tricyclic antidepressants (TCAs), increases the risk of falls and hip fractures among elderly people.The mechanism whereby antidepressants increase this risk is complex and may include orthostatic hypotension, arrhythmias, sedation and confusion. The increased risk of falls and hip fractures with the use of TCAs is not surprising considering their well-known cardiovascular, anticholinergic and antihistaminergic side-effects. But the increased risk of falls with SSRIs is highly unexpected since these drugs are believed to be free from the disadvantages of TCAs. We hypothesized that the new SSRI antidepressants may also have cardiovascular effects similarly to the older TCA compounds, which may be an explanation for the increased rate of falls and hip fractures. The experimental and clinical evidence in support of this hypothesis are discussed.

Serotonin reuptake inhibitors fluoxetine and citalopram relax intestinal smooth muscle

Selective serotonin reuptake inhibitor antidepressants (SSRIs) exert depressant effects on cardiac myocytes and vascular smooth muscle cells by inhibiting Ca2+ channels. We hypothesized that the SSRIs fluoxetine and citalopram affect the contractile activity of intestinal smooth muscle by interfering with Ca2+ entry and (or) signaling pathways. The effects of fluoxetine and citalopram on contractions of guinea-pig ileum longitudinal muscle-myenteric plexus preparations (LMMP) were compared with the effects of the voltage-operated Ca2+ channel inhibitors nifedipine and diltiazem. In a concentration-dependent manner, nifedipine, diltiazem, fluoxetine, and citalopram elicited relaxation of LMMPs contracted by electrical field stimulation (EC50 values of 4 × 10–7 M, 1.4 × 10–6 M, 1.4 × 10–5, and 6.8 × 10–6 M, respectively). Nifedipine, diltiazem, fluoxetine, and citalopram also relaxed LMMPs contracted with a depolarizing concentration of KCl (48 mM; EC50 values of 1.8 × 10–8 M, 1.4 × 10–7 M, 3.7 × 10–6 M, and 6.3 × 10–6, respectively), a response that could be reversed by increasing the extracellular Ca2+ concentration (2.5–30 mM). These data suggest that fluoxetine and citalopram elicit relaxation of intestinal smooth muscle, likely by inhibiting Ca2+ channel(s). This effect may be of clinical importance.Key words: fluoxetine (Prozac(r)), citalopram (Seropram(r)), nifedipine, diltiazem, L-type Ca2+ channels, intestinal smooth muscle.