Prucalopride is no more effective than placebo for children with functional constipation.

BACKGROUND & AIMS: Prucalopride is a selective, high-affinity agonist of the 5-hydroxytryptamine (serotonin) receptor 4 that enhances motility in the gastrointestinal tract. We performed a multicenter, randomized, placebo-controlled, double-blind, phase 3 trial to evaluate the efficacy and safety of prucalopride in children (6 months to 18 years old) with functional constipation. METHODS: Children with functional constipation, based on the Rome III criteria, were given prucalopride (children ≤ 50 kg were given a 0.04 mg/kg oral solution; children >50 kg were given a 2-mg tablet) or placebo once daily for 8 weeks. The primary efficacy end point was the proportion of children with toileting skills who had a mean of ≥ 3 spontaneous bowel movements/week and ≤ 1 episode of fecal incontinence/2 weeks, from study weeks 5-8 (responders). Adverse events, clinical laboratory values, and electrocardiograms were monitored. RESULTS: Efficacy and safety were assessed in 213 children (106 prucalopride, 107 placebo). Twenty-five percent were younger than 4 years old, 50% were 4-11 years old, and 25% were 12-18 years old; 55.4% were girls. At screening, 62.3% of patients in the prucalopride group and 55.1% in the placebo group had a history of fecal incontinence; 60.4% and 55.1% in the prucalopride and placebo groups, respectively, had a mean of ≤ 1 spontaneous bowel movements/week. The proportion of responders was similar between groups (prucalopride, 17.0% and placebo, 17.8%). There were no statistically significant differences in the primary efficacy end point when patients were stratified by sex, age group, or country. The incidence of treatment-emergent adverse events was similar in the prucalopride (69.8%) and placebo (60.7%) groups. CONCLUSIONS: Prucalopride, although generally well tolerated, was not more effective than placebo in children with functional constipation. ClinicalTrials.gov Number: NCT01330381.

Effect of prucalopride on the pharmacokinetics of oral contraceptives in healthy women.

BACKGROUND: Prucalopride is a selective, high-affinity, 5-hydroxytryptamine 4 (5-HT4) receptor agonist, which is approved for the symptomatic treatment of chronic constipation in women in whom laxatives fail to provide adequate relief. Women of childbearing potential, many of whom will be using oral contraceptives, comprise a large proportion of patients seeking medical therapy for constipation. OBJECTIVE: The aim of this study was to evaluate the effect of prucalopride on the absorption and steady-state pharmacokinetics of oral contraceptives in healthy women. METHODS: Sixteen women (aged 18-45 years) were enrolled in this open-label, two-way crossover trial (ClinicalTrials.gov identifier: NCT01036893) and given two 5-day treatments with a once-daily oral contraceptive (ethinylestradiol 0.035 mg + norethisterone 1 mg), alone and in combination with prucalopride 2 mg once daily. Treatments were separated by a 7 ± 2-day washout period. On days 1 and 5, blood samples were obtained pre-dose and at regular intervals post-dose up to 24 and 48 hours, respectively, to determine ethinylestradiol and norethisterone plasma concentrations. Prucalopride plasma concentrations were determined pre-dose and 3 hours post-dose on days 1 and 5, and 24 hours post-dose on day 6. Safety was assessed. RESULTS: Thirteen participants completed the study. One participant was thought to be non-compliant on days 3 and/or 4, and was excluded from the day 5 analysis. On days 1 and 5, maximum plasma concentrations of both oral contraceptive constituents were attained in ~1 hour and were unaffected by prucalopride administration. On day 5, steady-state prucalopride and oral contraceptive concentrations had been achieved. Prucalopride did not affect the pharmacokinetics of the oral contraceptives: point estimates for the maximum plasma concentration and area under the plasma concentration-time curve values and their associated 90 % confidence intervals were contained within predefined equivalence limits (80-125 %). Prucalopride was well tolerated, with a safety profile consistent with those observed in previous studies. CONCLUSION: Co-administration of prucalopride with an oral contraceptive did not result in any clinically meaningful pharmacokinetic interactions and was well tolerated.

Oral prucalopride in children with functional constipation.

BACKGROUND AND OBJECTIVES: Prucalopride is a selective, high-affinity 5-HT4 receptor agonist with gastrointestinal prokinetic activities. The aim of this study was to evaluate the pharmacokinetics, efficacy, safety, and tolerability of prucalopride oral solution in children, ages 4 years or older to 12 years or younger, with functional constipation. METHODS: A single oral dose of 0.03 mg/kg prucalopride was administered to 38 children to characterize prucalopride pharmacokinetics (NCT01674166). Thereafter, 37 children entered an open-label extension period in which 0.01 to 0.03 mg/kg of prucalopride was administered once per day for 8 weeks to investigate efficacy, safety, and tolerability (NCT01670669). RESULTS: Mean (standard deviation [SD]) Cmax, tmax, and AUC∞ (area under the plasma concentration-time curve from time 0 to infinity) were 3.8 (0.6) ng/mL, 1.8 (0.9) hour, and 65.3 (10.6) ng · h · mL, respectively, with limited (16%) variability in Cmax and AUC∞. Mean (SD) t1/2 was 19.0 (3.1) hours. On average, mean (SD) renal clearance (0.25 [0.08] L · h · kg) accounted for 54% of the apparent total plasma clearance (0.46 [0.07] L · h · kg). The apparent volume of distribution was 12.6 (2.6) L/kg. Prucalopride treatment resulted in a mean bowel movement frequency of 6.8/week, normal stool consistency, and reduced frequency of fecal incontinence. During the 8-week extension, 70% of study participants had at least 1 adverse event (all but 1 of mild/moderate intensity, 19% considered related to prucalopride). No children discontinued prucalopride because of adverse events. CONCLUSIONS: The pharmacokinetic profile of a single dose of prucalopride oral solution (0.03 mg · kg · day) generally resembled the profile in adults (2-mg tablet) but reflected lower systemic exposure in children. Prucalopride treatment for 8 weeks demonstrated an apparent favorable efficacy and tolerability profile in children with functional constipation.

Assessment of the cardiac safety of prucalopride in healthy volunteers: a randomized, double-blind, placebo- and positive-controlled thorough QT study.

AIMS: To assess steady-state effects of therapeutic and supra-therapeutic doses of prucalopride on the QT interval using a novel design involving a parallel placebo group with nested crossover for positive control. METHODS: A double-blind, double-dummy, placebo- and active-controlled study was conducted in 120 healthy male and female volunteers (NCT00903747). Volunteers were randomized to receive prucalopride 2-10 mg once daily (therapeutic and supratherapeutic doses, respectively) (group 1), placebo with 400 mg moxifloxacin on day 1 (group 2a), or placebo with moxifloxacin on day 15 (group 2b). Twelve-lead 24 h Holter ECGs recorded at various time-points were evaluated blind and centrally. RESULTS: Estimated mean difference in study specific corrected QT interval (QT(c)SS) time-matched change from baseline between prucalopride (2 and 10 mg) and placebo was <5 ms at all time points (maximum mean difference: 3.83 ms at 3.5 h post dose on day 5 with 2 mg [90% Cl -0.33, 6.38 ms]). Upper limits of the two-sided 90% CI for QT(c)SS were all <10 ms. There were no outlying QT(c)SS values >450 ms and no subjects had an increase >60 ms following prucalopride. Moxifloxacin produced the expected significant changes in QT(c)SS (>5 ms, maximum of +12.7 ms at 5 h post dose) at all time-points except 1 h post dose. Prucalopride resulted in small increases in heart rate (maximum of 5.8 beats min(-1)), which were similar for 2 and 10 mg. Prucalopride was well tolerated after first day of treatment. CONCLUSION: Prucalopride at both therapeutic and supra therapeutic doses has no clinically significant effects on cardiac repolarisation in healthy volunteers.

Design and synthesis of a series of piperazine-1-carboxamidine derivatives with antifungal activity resulting from accumulation of endogenous reactive oxygen species.

In this study, we screened a library of 500 compounds for fungicidal activity via induction of endogenous reactive oxygen species (ROS) accumulation. Structure-activity relationship studies showed that piperazine-1-carboxamidine analogues with large atoms or large side chains substituted on the phenyl group at the R(3) and R(5) positions are characterized by a high ROS accumulation capacity in Candida albicans and a high fungicidal activity. Moreover, we could link the fungicidal mode of action of the piperazine-1-carboxamidine derivatives to the accumulation of endogenous ROS.

Re-expression of alpha skeletal actin as a marker for dedifferentiation in cardiac pathologies.

Differentiation of foetal cardiomyocytes is accompanied by sequential actin isoform expression, i.e. down-regulation of the 'embryonic' alpha smooth muscle actin, followed by an up-regulation of alpha skeletal actin (alphaSKA) and a final predominant expression of alpha cardiac actin (alphaCA). Our objective was to detect whether re-expression of alphaSKA occurred during cardiomyocyte dedifferentiation, a phenomenon that has been observed in different pathologies characterized by myocardial dysfunction. Immunohistochemistry of alphaCA, alphaSKA and cardiotin was performed on left ventricle biopsies from human patients after coronary bypass surgery. Furthermore, actin isoform expression was investigated in left ventricle samples of rabbit hearts suffering from pressure- and volume-overload and in adult rabbit ventricular cardiomyocytes during dedifferentiation in vitro. Atrial goat samples up to 16 weeks of sustained atrial fibrillation (AF) were studied ultrastructurally and were immunostained for alphaCA and alphaSKA. Up-regulation of alphaSKA was observed in human ventricular cardiomyocytes showing down-regulation of alphaCA and cardiotin. A patchy re-expression pattern of alphaSKA was observed in rabbit left ventricular tissue subjected to pressure- and volume-overload. Dedifferentiating cardiomyocytes in vitro revealed a degradation of the contractile apparatus and local re-expression of alphaSKA. Comparable alphaSKA staining patterns were found in several areas of atrial goat tissue during 16 weeks of AF together with a progressive glycogen accumulation at the same time intervals. The expression of alphaSKA in adult dedifferentiating cardiomyocytes, in combination with PAS-positive glycogen and decreased cardiotin expression, offers an additional tool in the evaluation of myocardial dysfunction and indicates major changes in the contractile properties of these cells.

Efficacy of a single oral dose of 200 mg pramiconazole in vulvovaginal yeast infections: an exploratory phase IIa trial.

Pramiconazole (R126638) is a novel azole with potent antifungal activity against yeasts, dermatophytes and many other fungal species. The aim of this study was to evaluate the efficacy and tolerance of a single oral dose of 200 mg pramiconazole in acute and recurrent vulvovaginal yeast infections. Thirty-two patients (15 acute and 17 recurrent cases) were KOH microscopy- and culture-positive at inclusion. Clinical cure was 53% at one week and 66% at one month. Mycological eradication was obtained in 88% at one week, whereas at one month 75% of the patients were still culture-negative. Effects in both acute and recurrent cases appeared to be similar for mycological cure. The composite sign and symptom score (sum of scores for oedema, erythema, excoriation pruritus, burning and irritation) had a median value of 7.5 (range 2-17) at inclusion. At one week this value was reduced to 1.0 (range 0-8) and at one month a further reduction to 0 (range 0-11) was seen. p-values compared with baseline at both follow-up visits were <0.001. The drug was well tolerated and the reported adverse events were rare and minimal. In conclusion, the results of this trial indicate that pramiconazole possesses properties that warrant further clinical studies in a larger number of patients with acute and recurrent vulvo notvaginal yeast infection to confirm its efficacy and tolerability.

Miconazole induces changes in actin cytoskeleton prior to reactive oxygen species induction in yeast.

The antifungal compound miconazole inhibits ergosterol biosynthesis and induces reactive oxygen species (ROS) in susceptible yeast species. To further uncover the mechanism of miconazole antifungal action and tolerance mechanisms, we screened the complete set of haploid Saccharomyces cerevisiae gene deletion mutants for mutants with an altered miconazole sensitivity phenotype. We identified 29 S. cerevisiae genes, which when deleted conferred at least 4-fold hypersensitivity to miconazole. Major functional groups encode proteins involved in tryptophan biosynthesis, membrane trafficking including endocytosis, regulation of actin cytoskeleton, and gene expression. With respect to the antifungal activity of miconazole, we demonstrate an antagonism with tryptophan and a synergy with a yeast endocytosis inhibitor. Because actin dynamics and induction of ROS are linked in yeast, we further focused on miconazole-mediated changes in actin cytoskeleton organization. In this respect, we demonstrate that miconazole induces changes in the actin cytoskeleton, indicative of increased filament stability, prior to ROS induction. These data provide novel mechanistic insights in the mode of action of a ROS-inducing azole.

A pilot study on seborrheic dermatitis using pramiconazole as a potent oral anti-Malassezia agent.

BACKGROUND: Seborrheic dermatitis is considered to be a Malassezia-driven disease. Little objective information is available so far from biometrological quantitative assessments of this skin condition. Pramiconazole is a novel triazole with potent in vitro antifungal activity, especially against Malassezia spp. OBJECTIVE: To study the sequential effects of pramiconazole on Malassezia, inflammation and epidermal changes. METHOD: This study was performed in 2 groups of subjects suffering from seborrheic dermatitis. The first group (n = 17) remained untreated and was used as control. Clinical, mycological and biometrological assessments were performed at inclusion and during the following 2 weeks. The second group of subjects (n = 10) received a single 200-mg oral dose of pramiconazole at inclusion. Clinical, mycological and biometrological evaluations were performed before and during 1 month following the single antifungal intake. For both parts of the study, several parameters were assessed including yeast density, desquamation, erythema, itching and sebum excretion. RESULTS: In the control group, no significant changes were observed in any of the parameters during the observation period. The findings were markedly different in the pramiconazole-treated subjects. The yeast density was significantly improved on days 3, 7 and 28. Desquamation, erythema, itching, and the global clinical evaluation as assessed by the patients and investigators became significantly improved on days 7 and 28. A trend in decrease of scaliness was noted. No effect on sebum excretion was evidenced. In conclusion, a single 200-mg dose of pramiconazole exhibitsin vivo efficacy in controlling some important clinical aspects of seborrheic dermatitis. Following a reduction in the number of yeasts on day 3, a decrease in the severity of clinical signs and symptoms occurred from day 7 onwards. Sebum excretion appeared uninvolved in the clearing process of seborrheic dermatitis. CONCLUSION: A single 200-mg dose of pramiconazole appears to abate seborrheic dermatitis. The density in Malassezia present on lesional skin is first decreased, followed by clearing of the clinical signs.

Absence of an active metabolite for the triazole antifungal pramiconazole.

Pramiconazole is an antifungal with high potential for the treatment of dermatophyte and yeast infections of the skin. It is currently not known whether pramiconazole is active alone as the parent agent or assisted by active metabolites. The in vitro metabolism as well as the metabolic stability of pramiconazole was investigated in subcellular liver fractions and isolated hepatocytes of several species. Results indicate that the metabolism of pramiconazole was slow, since the enzyme-mediated disappearance of pramiconazole was rather slow. To investigate whether pramiconazole was converted into an active metabolite in humans, serum samples from healthy volunteers receiving a daily dose of 100 or 200 mg pramiconazole for one week were assayed with an agar diffusion bioassay and liquid chromatography-tandem mass spectrometry. It was concluded that there was no active metabolite present in serum samples from healthy volunteers after oral dosing of pramiconazole.

Serial cardioversion by class IC Drugs during 4 months of persistent atrial fibrillation in the goat.

INTRODUCTION: The success rate of pharmacological cardioversion of atrial fibrillation (AF) in patients depends on the duration of AF. It is unknown to what extent AF-induced structural atrial remodeling contributes to this loss of efficacy. METHODS AND RESULTS: In 10 goats, persistent AF was induced by repetitive burst pacing. During a time period of 16 weeks, the efficacy of flecainide and cibenzoline to cardiovert AF was investigated by serial cardioversion. The drugs were administered intravenously at a rate of 0.1 mg/kg/min. AF cycle length (AFCL) was continuously monitored. Drug infusion was continued until AF was successfully cardioverted or the QRS duration was prolonged about twofold. The average atrial cycle length during persistent AF was 104 +/- 10 msec and did not change during the 16-week period. The success rate of cardioversion by flecainide and cibenzoline decreased with the duration of AF from 60% to 17% and from 80% to 63%. In goats that failed to cardiovert, sinus rhythm was not restored despite a twofold prolongation of the AF cycle length (respectively from 96 +/- 5 msec to 168 +/- 30 msec (flecainide) and 203 +/- 26 msec (cibenzoline)). The sensitivity of AF for Class IC drugs was not altered with time, and the dose-dependent effect on AFCL remained the same (flecainide: 8 +/- 5 vs 7 +/- 2 msec/mg/kg (P = 0.70) and cibenzoline: 13 +/- 3 vs 13 +/- 5 msec/mg/kg (P = 0.95)). In animals in which cardioversion remained possible, the critical AFCL at which cardioversion occurred increased from 96 +/- 5 msec to 211 msec (flecainide) and 189 +/- 24 msec (cibenzoline). CONCLUSIONS: The progressive loss of efficacy of Class IC drugs to cardiovert AF of longer duration is not due to a decrease in the sensitivity of remodeled atrial myocardium for Class IC drugs. Failure of cardioversion was due to an increase in the critical AF cycle length required for pharmacological cardioversion.

In vitro activity of R126638 and ketoconazole against Malassezia species.

The in vitro activity of a new triazole R126638 against Malassezia yeasts was compared with that of ketoconazole. With the agar dilution technique, minimal inhibitory concentrations were lower for R126638 compared with ketoconazole against Malassezia globosa, M. obtusa, M. slooffiae, M. restricta and two strains of M. sympodialis. On human stratum corneum in vitro, both R126638 and ketoconazole were very effective in reducing the production of hyphae from 15% to 1% with R126638 and to 2% with ketoconazole. Scanning electron microscopy did not reveal obvious surface differences between untreated cultures and cultures exposed to ketoconazole or R126638 in the concentration range 0.01-1 microg/ml. However, transmission electron microscopy showed partial to complete necrosis of the cytoplasmic organelles of Malassezia yeasts. The combined scanning electron microscopy and transmission electron microscopy findings confirm earlier observations of the "mummifying" effect of azoles against Malassezia spp. In conclusion, R126638 is an interesting new triazole with high activity against the Malassezia yeasts, which are involved in pityriasis versicolor and seborrhoeic dermatitis.

Synthesis and in vitro and in vivo structure-activity relationships of novel antifungal triazoles for dermatology.

In search for new compounds with potential for clinical use as antifungal agents in dermatology, a series of 12 azole compounds were synthesized stereospecifically and investigated specifically for their activity against dermatophyte fungal infections in animal models. This panel of azoles was studied in vitro and compared with itraconazole and terbinafine for their antifungal activity using a panel of 24 Candida spp. and 182 dermatophyte isolates. Three azoles (1c, 2c, and 4c) showed in vitro antifungal potency equivalent to itraconazole, but superior to terbinafine, against a panel of 24 Candida spp. with comparable or lower activity than that of itraconazole and terbinafine against 182 dermatophyte isolates and only rare activity against other pathogenic fungi. However, in vivo 1c and 4c, both given orally, demonstrated antifungal activity at least three times greater than itraconazole and were superior compared to terbinafine in M. canis infected guinea pigs. In a mouse model infected by T. mentagrophytes, again 4c, but not 1c, showed 5-fold superior activity over itraconazole and terbinafine. Compound 2c was effective in both models but less effective than itraconazole in these models. On the basis of these promising results, 4c is currently being clinically investigated for its potential as a novel antifungal agent against dermatophytosis.

Atrial ultrastructural changes during experimental atrial tachycardia depend on high ventricular rate.

INTRODUCTION: Atrial structural and electrophysiologic changes occur during atrial tachycardia. The role of high ventricular rate in these processes remains to be established. METHODS AND RESULTS: Six goats were subjected to 4 weeks of rapid atrioventricular (AV) pacing at an atrial and ventricular rate of 240 beats/min, resulting in development of congestive heart failure. In another five goats, AV block was created. These goats then were subjected to 4 weeks of atrial pacing, also at 240 beats/min while the ventricular rate was kept low and regular at 80 beats/min (A-paced). Pacing was interrupted only for measurement of atrial effective refractory period and right atrial diameter. The ultrastructure of both atria was examined by light and electron microscopy, including quantification of the percentage of atrial extracellular matrix (%ECM). A group of six goats served as controls. In the AV-paced group, severe structural remodeling occurred in the atria, including severe loss of sarcomeres, glycogen accumulation, disruption of sarcoplasmic reticulum, and appearance of numerous small mitochondria and nuclei with homogeneously distributed chromatin. In contrast, structural changes were virtually absent in the atria of A-paced goats. Only a redistribution of nuclear chromatin and the appearance of numerous mitochondria were observed. The ultrastructure was normal in control animals. The%ECM was increased in AV-paced goats (29%) compared to A-paced animals (18%) and controls (17%) (P < 0.05). Finally, right atrial diameter increased by 51% in AV-paced goats but was unchanged in A-paced goats (P < 0.05). In both experimental groups, atrial effective refractory period shortened during pacing. CONCLUSION: Structural remodeling during chronic atrial tachycardia is related to the concomitant presence of a high ventricular rate and hence the occurrence of congestive heart failure rather than a high atrial rate. Electrical remodeling can occur in the absence of significant structural changes.

The novel azole R126638 is a selective inhibitor of ergosterol synthesis in Candida albicans, Trichophyton spp., and Microsporum canis.

R126638 is a novel triazole with in vitro activity similar to that of itraconazole against dermatophytes, Candida spp., and Malassezia spp. In animal models of dermatophyte infections, R126638 showed superior antifungal activity. R126638 inhibits ergosterol synthesis in Candida albicans, Trichophyton mentagrophytes, Trichophyton rubrum, and Microsporum canis at nanomolar concentrations, with 50% inhibitory concentrations (IC(50)s) similar to those of itraconazole. The decreased synthesis of ergosterol and the concomitant accumulation of 14 alpha-methylsterols provide indirect evidence that R126638 inhibits the activity of CYP51 that catalyzes the oxidative removal of the 14 alpha-methyl group of lanosterol or eburicol. The IC(50)s for cholesterol synthesis from acetate in human hepatoma cells were 1.4 microM for itraconazole and 3.1 microM for R126638. Compared to itraconazole (IC(50) = 3.5 microM), R126638 is a poor inhibitor of the 1 alpha-hydroxylation of 25-hydroxyvitamin D(3) (IC(50) > 10 microM). Micromolar concentrations of R126638 and itraconazole inhibited the 24-hydroxylation of 25-hydroxyvitamin D(3) and the conversion of 1,25-dihydroxyvitamin D(3) into polar metabolites. At concentrations up to 10 microM, R126638 had almost no effect on cholesterol side chain cleavage (CYP11A1), 11 beta-hydroxylase (CYP11B1), 17-hydroxylase and 17,20-lyase (CYP17), aromatase (CYP19), or 4-hydroxylation of all-trans retinoic acid (CYP26). At 10 microM, R126638 did not show clear inhibition of CYP1A2, CYP2A6, CYP2D6, CYP2C8, CYP2C9, CYP2C10, CYP2C19, or CYP2E1. Compared to itraconazole, R126638 had a lower interaction potential with testosterone 6 beta hydroxylation and cyclosporine hydroxylation, both of which are catalyzed by CYP3A4, whereas both antifungals inhibited the CYP3A4-catalyzed hydroxylation of midazolam similarly. The results suggest that R126638 has promising properties and merits further in vivo investigations for the treatment of dermatophyte and yeast infections.

Troponin I isoform expression in human and experimental atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) is accompanied by re-expression of fetal genes and activation of proteolytic enzymes. In this study both aspects were addressed with respect to troponin I (TnI) isoform expression. METHODS AND RESULTS: Western blotting and real-time reverse transcription-polymerase chain reaction were used to study TnI isoform expression in patients with paroxysmal or chronic AF and in goats after 1, 2, 4, 8, and 16 weeks of AF. In addition to cardiac TnI (cTnI), low expression of slow-twitch skeletal TnI (ssTnI) protein was found in 60% of patients in sinus rhythm or paroxysmal AF and in 8% of patients with chronic AF. In adult goat atrium, ssTnI protein expression was undetectable. Calcium-dependent degradation of cTnI protein was found in 1 or 2 of 6 animals after 1 to 4 weeks of AF. Although always low, ssTnI mRNA levels were significantly higher in patients who expressed ssTnI protein than in those who did not. Relative ssTnI mRNA expression was significantly lower in patients with paroxysmal AF and chronic AF than in those in sinus rhythm. In goats there was a tendency toward higher relative levels of ssTnI at the onset of AF followed by a normalization when AF had become sustained. CONCLUSIONS: Atrial re-expression of ssTnI during paroxysmal AF in patients and during the first 2 weeks of pacing-induced AF in goats does not seem to be part of the process of AF-associated cardiomyocyte dedifferentiation but seems to result from transient cardiomyocyte stress at the onset of AF.

Reverse structural and gap-junctional remodeling after prolonged atrial fibrillation in the goat.

BACKGROUND: Prolonged atrial fibrillation (AF) results in electrical, structural, and gap-junctional remodeling. We examined the reversibility of the changes in (ultra)structure and gap junctions. METHODS AND RESULTS: Four groups of goats were used: (1) sinus rhythm (SR), (2) 4 months' AF (4 mo AF), (3) 2 months' SR after 4 mo AF (2 mo post-AF), and (4) 4 months' SR after 4 mo AF (4 mo post-AF). Atria were characterized electrophysiologically, (ultra)structure was studied by light and electron microscopy, and structural and gap-junctional protein expression was studied by immunohistochemistry or Western blotting. The atrial effective refractory period had completely returned to normal values 2 mo post-AF. Induced AF episodes still lasted for minutes at 2 and 4 mo post-AF, compared with seconds in the SR group. Structural abnormalities were still present at 2 and 4 mo post-AF, although to a lesser extent. The increased atrial myocyte diameter was back to normal at 4 mo post-AF. The number of myocytes with severe myolysis had almost normalized 4 mo post-AF, whereas myocytes with mild myolysis remained significantly increased. Extracellular matrix area fraction after 4 mo AF was similar to SR. However, the extracellular matrix fraction per myocyte had increased after 4 mo AF and remained higher post-AF. Changes in expression of structural proteins were partially restored post-AF. The reduction of connexin 40 that was observed during AF was completely reversed at 4 mo post-AF. CONCLUSIONS: Recovery from structural remodeling after 4 mo AF is a slow process and is still incomplete 4 mo post-AF. Several months post-AF, the duration of AF episodes is still prolonged (minutes).

Electrical and contractile remodeling during the first days of atrial fibrillation go hand in hand.

BACKGROUND: The mechanisms of the atrial contractile dysfunction induced by atrial fibrillation (AF) are not completely understood. In particular, the relation between the atrial dysfunction and electrical remodeling has not yet been studied. METHODS AND RESULTS: Seven goats were chronically instrumented with electrodes sutured to the atria and with ultrasonic piezoelectric crystals to record the atrial diameters. A pressure transducer was implanted in the right atrium. After 5 minutes, 3 hours, and throughout the first 5 days of artificially maintained AF, atrial contractile function was measured and the atrial effective refractory period (AERP) was monitored for comparison. Also, the positive inotropic effects of the L-type Ca2+-channel agonist BayY5959 and short trains of rapid atrial pacing were studied. After resumption of sinus rhythm, the recovery of atrial contractile function was followed. After 5 minutes of AF, atrial contractility was decreased by approximately 55% but recovered completely within 10 minutes. Five days of AF nearly completely abolished the atrial contractile function, and recovery took 2 days. During the first days of AF, the development of the contractile dysfunction followed the same time course as the shortening of AERP (electrical remodeling). In remodeled atria, BayY5959 increased atrial contractility to the same extent as it prolonged AERP. The inotropic effect of short trains of rapid atrial pacing was similar in normal and remodeled atria. CONCLUSIONS: Depending on the duration of AF, different mechanisms contribute to the AF-induced atrial hypocontractility. Atrial contractile remodeling during several days of AF goes hand in hand with electrical remodeling and might be caused by a reduction of the L-type Ca2+-current.

Electrical, contractile and structural remodeling during atrial fibrillation.

The natural history of atrial fibrillation (AF) is characterized by a gradual worsening with time. The recent finding that AF itself produces changes in atrial function and structure has provided a possible explanation for the progressive nature of this arrhythmia. Electrical remodeling (shortening of atrial refractoriness) develops within the first days of AF and contributes to an increase in stability of AF. However, 'domestication of AF' must also depend on a 'second factor' since the persistence of AF continues to increase after electrical remodeling has been completed. Atrial contractile remodeling (loss of contractility) leads to a reduced atrial transport function after cardioversion of AF. An important clinical consequence is that during several days after restoration of sinus rhythm, the risk of atrial thrombus formation is still high. In addition, the reduction of atrial contractility during AF may enhance atrial dilatation which may add to the persistence of AF. Tachycardia-induced structural remodeling takes place in a different time domain (weeks to months). Myolysis probably contributes to the loss of atrial contractile force. Although it might explain the loss of efficacy of pharmacological cardioversion and the development of permanent AF, the role of structural remodeling in the progression of AF is still unclear. Atrial structural remodeling also occurs as a result of heart failure and other underlying cardiovascular diseases. The associated atrial fibrosis might explain intra-atrial conduction disturbances and the susceptibility for AF. Thus, both AF itself and the underlying heart disease are responsible for the development of the arrhythmogenic substrate. New strategies for prevention and termination of AF should be build on our knowledge of the mechanisms and time course of AF-induced atrial remodeling.