Catheter-based pulmonary vein isolation fails to prevent transient atrial arrhythmogenic changes related to acute obstructive respiratory events in a porcine model

AIMS

Pulmonary vein isolation (PVI) is the corner stone of modern rhythm control strategies in patients with atrial fibrillation (AF). Sleep-disordered breathing (SDB) is prevalent in more than 50% of patients undergoing AF ablation and studies have indicated a greater recurrence rate after PVI in patients with SDB. Herein, we study the effect of catheter-based PVI on AF in a pig model for SDB.

METHODS AND RESULTS

In 11 sedated spontaneously breathing pigs, obstructive apnoeas were simulated by 75 seconds of intermittent negative upper airway pressure (INAP) applied by a negative pressure device connected to the endotracheal tube. INAPs were performed before and after PVI. AF-inducibility and atrial effective refractory periods (aERP) were determined before and during INAP by programmed atrial stimulation. PVI prolonged the aERP by 48 ± 27 ms in the right atrium (RA) (p < 0.0001) and by 40 ± 34 ms in the left atrium (LA) (p = 0.0004). Following PVI, AF-inducibility dropped from 28 ± 26% to 0% (p = 0.0009). INAP was associated with a transient aERP-shortening (ΔaERP) in both atria, which was not prevented by PVI (INAP indued ΔaERP after PVI in the RA: -57 ± 34 ms, p = 0.0002; in the LA: -42 ± 24 ms, p < 0.0001). INAP was associated with a transient increase in AF-inducibility (from 28 ± 26% to 69 ± 21%; p = 0.0008), which was not attenuated by PVI (INAP-associated AF-inducibility after PVI: 58 ± 33% (p = 0.5)).

CONCLUSION

Transient atrial arrhythmogenic changes related to acute obstructive respiratory events are not prevented by electrical isolation of the pulmonary veins, which partially explains the increased AF recurrence in patients with SDB after PVI procedures.

Inhibition of the acetylcholine-regulated potassium current prevents transient apnea-related atrial arrhythmogenic changes in a porcine model

BACKGROUND

More than 50% of patients with atrial fibrillation (AF) suffer from sleep disordered breathing (SDB). Obstructive respiratory events contribute to a transient, vagally mediated atrial arrhythmogenic substrate, which is resistant to most available antiarrhythmic drugs.

OBJECTIVE

The purpose of this study was to investigate the effect of pharmacologic inhibition of the G-protein-gated acetylcholine-regulated potassium current (IK,ACh) with and without acute autonomic nervous system activation by nicotine in a pig model for obstructive respiratory events.

METHODS

In 21 pigs, SDB was simulated by applying an intermittent negative upper airway pressure (INAP). AF inducibility and atrial effective refractory periods (aERPs) were determined before and during INAP by an S1S2 atrial pacing-protocol. Pigs were randomized into 3 groups-group 1: vehicle (n = 4); group 2: XAF-1407 (IK,ACh inhibitor) (n = 7); and group 3: nicotine followed by XAF-1407 (n = 10).

RESULTS

In group 1, INAP shortened aERP (ΔaERP -42.6 ms; P = .004) and transiently increased AF inducibility from 0% to 31%. In group 2, XAF-1407 prolonged aERP by 25.2 ms (P = .005) during normal breathing and prevented INAP-induced aERP shortening (ΔaERP -3.6 ms; P = .3) and AF inducibility. In group 3, INAP transiently shortened aERP during nicotine perfusion (ΔaERP -33.6 ms; P = .004) and increased AF inducibility up to 61%, which both were prevented by XAF-1407.

CONCLUSION

Simulated obstructive respiratory events transiently shorten aERP and increase AF inducibility, which can be prevented by the IK,ACh-inhibitor XAF-1407. XAF-1407 also prevents these arrhythmogenic changes induced by obstructive respiratory events during nicotine perfusion. Whether IK,ACh channels represent a target for SDB-related AF in humans warrants further study.

3D-electroanatomical mapping of the left atrium and catheter-based pulmonary vein isolation in pigs: A practical guide

Aim

To propose a standardized workflow for 3D-electroanatomical mapping guided pulmonary vein isolation in pigs.

Materials and methods

Danish female landrace pigs were anaesthetized. Ultrasound-guided puncture of both femoral veins was performed and arterial access for blood pressure measurement established. Fluoroscopy- and intracardiac ultrasound-guided passage of the patent foramen ovale or transseptal puncture was performed. Then, 3D-electroanatomical mapping of the left atrium was conducted using a high-density mapping catheter. After mapping all pulmonary veins, an irrigated radiofrequency ablation catheter was used to perform ostial ablation to achieve electrical pulmonary vein isolation. Entrance- and exit-block were confirmed and re-assessed after a 20-min waiting period. Lastly, animals were sacrificed to perform left atrial anatomical gross examination.

Results

We present data from 11 consecutive pigs undergoing pulmonary vein isolation. Passage of the fossa ovalis or transseptal puncture was uneventful and successful in all animals. Within the inferior pulmonary trunk 2-4 individual veins as well as 1-2 additional left and right pulmonary veins could be cannulated. Electrical isolation by point-by-point ablation of all targeted veins was successful. However, pitfalls including phrenic nerve capture during ablation, ventricular arrhythmias during antral isolation close to the mitral valve annulus and difficulties in accessing right pulmonary veins were encountered.

Conclusion

Fluoroscopy- and intracardiac ultrasound-guided transseptal puncture, high-density electroanatomical mapping of all pulmonary veins and complete electrical pulmonary vein isolation can be achieved reproducibly and safely in pigs when using current technologies and a step-by-step approach.

Pharmacological inhibition of SK-channels with AP14145 prevents atrial arrhythmogenic changes in a porcine model for obstructive respiratory events

BACKGROUND

Obstructive sleep apnea (OSA) creates a complex substrate for atrial fibrillation (AF), which is refractory to many clinically available pharmacological interventions. We investigated atrial antiarrhythmogenic properties and ventricular electrophysiological safety of small-conductance Ca²⁺ -activated K⁺ (SK)-channel inhibition in a porcine model for obstructive respiratory events.

METHODS

In spontaneously breathing pigs, obstructive respiratory events were simulated by intermittent negative upper airway pressure (INAP) applied via a pressure device connected to the intubation tube. INAP was applied for 75 s, every 10 min, three times before and three times during infusion of the SK-channel inhibitor AP14145. Atrial effective refractory periods (AERP) were acquired before (pre-INAP), during (INAP) and after (post-) INAP. AF-inducibility was determined by a S1S2 atrial pacing protocol. Ventricular arrhythmicity was evaluated by heart rate adjusted QT-interval duration (QT-paced) and electromechanical window (EMW) shortening.

RESULTS

During vehicle infusion, INAP transiently shortened AERP (pre-INAP: 135 ± 10 ms vs. post-INAP 101 ± 11 ms; p = .008) and increased AF-inducibility. QT-paced prolonged during INAP (pre-INAP 270 ± 7 ms vs. INAP 275 ± 7 ms; p = .04) and EMW shortened progressively throughout INAP and post-INAP (pre-INAP 80 ± 4 ms; INAP 59 ± 6 ms, post-INAP 46 ± 10 ms). AP14145 prolonged baseline AERP, partially prevented INAP-induced AERP-shortening and reduced AF-susceptibility. AP14145 did not alter QT-paced at baseline (pre-AP14145 270 ± 7 ms vs. AP14145 268 ± 6 ms, p = .83) or QT-paced and EMW-shortening during INAP.

CONCLUSION

In a pig model for obstructive respiratory events, the SK-channel-inhibitor AP14145 prevented INAP-associated AERP-shortening and AF-susceptibility without impairing ventricular electrophysiology. Whether SK-channels represent a target for OSA-related AF in humans warrants further study.

Sympatho-vagal activation during obstructive respiratory events in pigs and blunted atrial arrhythmogenic effects by pharmacological IKACh-inhibition

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Novo nordisk foundation

Background

Obstructive sleep apnea (OSA) is associated with a sympatho-vagal activation which is suspected to create a complex substrate for atrial fibrillation (AF).

Purpose

In pigs, we investigated atrial arrhythmogenic consequences of simulated obstructive respiratory events by intermittent negative upper airway pressure (INAP) application and tested antiarrhythmic properties of an atria-specific IK,ACh-inhibitor.

Methods

In spontaneously breathing pigs, obstructive respiratory events were simulated by intermittent negative upper airway pressure (INAP) applied via a pressure device connected to the intubation tube. INAP was applied for 75 seconds, every 10 minutes, three times before (vehicle) and two times following infusion of an IK,ACh-inhibitor. P-wave, PQ-duration, atrial effective refractory periods (AERP) and left ventricular hemodynamic parameters (maximum upstroke velocity, minimal downslope velocity and systole duration) were acquired before (Pre-INAP), during (INAP) and after (Post-) INAP. AF-inducibility was determined by a S1S2 atrial pacing protocol.

Results

During vehicle infusion, INAP transiently shortened AERP (Pre-INAP: 147±8ms vs. Post-INAP 105±12 ms; p=0.021) and increased AF-inducibility (Pre-INAP: 10±6% vs. Post-INAP 57±15%; p=0.018). Whereas p-wave duration remained stable, PQ-duration prolonged (Pre-INAP: 130±6ms vs. Post-INAP 142±7ms; p=0.03). Left ventricular maximum upstroke velocity increased (Pre-INAP: 1990±118 mmHg/s vs. Post-INAP 3980±704 mmHg/s; p=0.04), minimal downslope velocity decreased and systole duration shortened (Pre-INAP: 236±6 ms vs. Post-INAP 202±12 ms; p=0.04).

The IK,ACh-inhibitor increased AERP (vehicle 147±8ms vs. IK,ACh-inhibitor 171±9ms; p=0.05) and sufficiently prevented INAP-associated AERP-shortening (Pre-INAP: 171±9ms vs. Post-INAP 180±9ms; p=0.219) and PQ-duration prolongation (Pre-INAP: 116±8ms vs. Post-INAP 113±7ms; p=0.76). INAP-induced changes of left ventricular maximum upstroke/minimal downslope velocity and systole duration remained unaffected in the presence of the IK,ACh-inhibitor.

Conclusion

During obstructive respiratory events simulated by INAP in pigs, left ventricular hemodynamic changes demonstrated elevated sympathetic tone, while atrial electrophysiological parameters resemble elevated parasympathetic tone at the same time. This was associated with increased AF-susceptibility. Pharmacological IK,ACh-inhibition blunted INAP-induced impairment of atrial electrophysiology without affecting left ventricular hemodynamic changes. Hence, pharmacological IKACh-inhibition may constitute a promising treatment strategy in AF-patients with OSA.

Pharmacological inhibition of SK-channels with AP14145 prevents atrial arrhythmogenic changes in a porcine model for obstructive respiratory events

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): This work was supported by the Novo Nordisk Foundation (Tandem Programme; #31634).

Background

Obstructive sleep apnea (OSA) creates a complex substrate for atrial fibrillation (AF), which is refractory to many clinically available pharmacological interventions.

Purpose

To investigate atrial antiarrhythmogenic properties and ventricular electrophysiological safety of small-conductance Ca2+ -activated K+ (SK)- channel inhibition in a porcine model for obstructive respiratory events.

Methods

In spontaneously breathing pigs, obstructive respiratory events were simulated by intermittent negative upper airway pressure (INAP) applied via a pressure device connected to the intubation tube. INAP was applied for 75 seconds, every 10 minutes, three times before and three times during infusion of the SK-channel inhibitor AP14145. Atrial effective refractory periods (AERP) were acquired before (Pre-INAP), during (INAP) and after (Post-) INAP. AF-inducibility was determined by a S1S2 atrial pacing protocol. For the purpose of drug safety, ventricular arrhythmicity was evaluated by heart rate adjusted QT-interval duration (QT-paced) and electromechanical window (EMW) calculation.

Results

During vehicle infusion, INAP transiently shortened AERP (Pre-INAP: 135±10 ms vs. Post-INAP 101±11 ms; p=0.008) and increased AF-inducibility. QT-paced prolonged during INAP (Pre-INAP 270±7 ms vs. INAP 275±7 ms; p=0.04) and EMW shortened progressively throughout INAP and Post-INAP (Pre-INAP 80±4 ms; INAP 59±6 ms, Post-INAP 46±10 ms). AP14145 prolonged baseline AERP, partially prevented INAP-induced AERP-shortening and reduced AF-susceptibility. AP14145 did neither alter QT-paced (Pre-AP14145 270±7 ms vs. AP14145 268±6 ms, p=0.83) nor INAP-induced QT-paced prolongation, but blunted Post-INAP associated EMW-shortening.

Conclusion

In a pig model for obstructive respiratory events, the SK-channel-inhibitor AP14145 prevented INAP-associated AERP-shortening and AF-susceptibility without impairing ventricular electrophysiology. Hence, SK-channels may represent a promising target for OSA-related AF.

Differential effects of positive and negative upper airway pressure application on atrial electrophysiology: implications for CPAP-therapy in OSA-patients

Funding Acknowledgements

Type of funding sources: Foundation. Main funding source(s): Novo nordisk foundation

Background

Obstructive sleep apnea (OSA) is closely associated with atrial fibrillation (AF) and OSA-treatment by continuous positive airway pressure (CPAP) is believed to reduce the AF burden in OSA-patients. While negative upper airway pressure during obstructive respiratory events have been shown to increase AF susceptibility, atrial electrophysiological effects of positive upper airway pressure during CPAP-therapy are unknown.

Purpose

In pigs, we investigated differential atrial electrophysiological effects of increasing levels of CPAP-applications compared to obstructive respiratory events.

Methods

In sedated and spontaneously breathing pigs, obstructive respiratory events were simulated by intermittent negative upper airway pressure (INAP) applied via a pressure device connected to the intubation tube. INAP was applied for 75 seconds with a 10 minute resting period in-between. After four INAP-applications, during which atrial electrophysiological responses to INAP were recorded, continuous positive airway pressure was applied in increasing pressure stages for a duration of 20 minutes for each pressure level (4, 8, 12 and 16 mbar). Atrial effective refractory periods (AERP) were recorded at the free wall of the right atrium (RA) and in the distal area of the coronary sinus (CS) before (Pre-INAP), during (INAP) and after (Post-) INAP and every 10 minutes throughout the stepwise increase of CPAP.

Results

AERP shortened due to INAP application in the RA (Pre-INAP 134±7ms vs. INAP 95±7ms; p=0.008, Fig.1.), but not in the CS (Pre-INAP 132±8ms vs. INAP 110±9ms; p=0.144, Fig.2). Stepwise increases of CPAP-application up until 12 mbar did neither result in changes of RA- nor CS-AERP. Only CPAP-application at 16 mbar (CPAP16) resulted in transiently shortened CS-AERP (CPAP-baseline 140±6ms versus CPAP16 115±10ms; p=0.0081, Fig.2.), but not RA-AERPs (p=0.31, Fig.1.).

Conclusion

While simulation of obstructive respiratory events by INAP were reproducibly associated with a predominantly right atrial shortening of refractoriness, high-pressure CPAP-application of 16 mbar was associated with an isolated moderate shortening of left atrial refractoriness. These findings may have important implications for CPAP treatment in patients with AF, which should be considered in the design of future clinical studies.

Renal Denervation Prevents Atrial Arrhythmogenic Substrate Development in CKD

BACKGROUND

In patients with chronic kidney disease (CKD), atrial fibrillation (AF) is highly prevalent and represents a major risk factor for stroke and death. CKD is associated with atrial proarrhythmic remodeling and activation of the sympathetic nervous system. Whether reduction of the sympathetic nerve activity by renal denervation (RDN) inhibits AF vulnerability in CKD is unknown.

METHODS

Left atrial (LA) fibrosis was analyzed in samples from patients with AF and concomitant CKD (estimated GFR, <60 mL/min per 1.73 m²) using picrosirius red and compared with AF patients without CKD and patients with sinus rhythm with and without CKD. In a translational approach, male Sprague Dawley rats were fed with 0.25% adenine (AD)-containing chow for 16 weeks to induce CKD. At week 5, AD-fed rats underwent RDN or sham operation (AD). Rats on normal chow served as control. After 16 weeks, cardiac function and AF susceptibility were assessed by echocardiography, radiotelemetry, electrophysiological mapping, and burst stimulation, respectively. LA tissue was histologically analyzed for sympathetic innervation using tyrosine hydroxylase staining, and LA fibrosis was determined using picrosirius red.

RESULTS

Sirius red staining demonstrated significantly increased LA fibrosis in patients with AF+CKD compared with AF without CKD or sinus rhythm. In rats, AD demonstrated LA structural changes with enhanced sympathetic innervation compared with control. In AD, LA enlargement was associated with prolonged duration of induced AF episodes, impaired LA conduction latency, and increased absolute conduction inhomogeneity. RDN treatment improved LA remodeling and reduced LA diameter compared with sham-operated AD. Furthermore, RDN decreased AF susceptibility and ameliorated LA conduction latency and absolute conduction inhomogeneity, independent of blood pressure reduction and renal function.

CONCLUSIONS

In an experimental rat model of CKD, RDN inhibited progression of atrial structural and electrophysiological remodeling. Therefore, RDN represents a potential therapeutic tool to reduce the risk of AF in CKD, independent of changes in renal function and blood pressure.

Pharmacological inhibition of acetylcholine-regulated potassium current (IK,ACh) prevents atrial arrhythmogenic changes in a rat model of repetitive obstructive respiratory events

Background

In obstructive sleep apnea (OSA), intermittent hypoxemia and intrathoracic pressure fluctuations may increase atrial fibrillation (AF) susceptibility by cholinergic activation.

Objective

To investigate short-term atrial electrophysiological consequences of obstructive respiratory events, simulated by intermittent negative upper airway pressure (INAP), and the role of atrial acetylcholine-regulated potassium current (I_K,ACh) activated by the M₂ receptor.

Methods

In sedated (2% isoflurane), spontaneously breathing rats, INAP was applied noninvasively by a negative pressure device for 1 minute, followed by a resting period of 4 minutes. INAP was applied repeatedly throughout 70 minutes, followed by a 2-hour recovery period. Atrial effective refractory period (AERP) and AF inducibility were determined throughout the protocol. To study INAP-induced I_K,ACh activation, protein levels of protein kinase C (PKC_Ɛ) were determined in membrane and cytosolic fractions of left atrial (LA) tissue by Western blotting. Moreover, an I_K,ACh inhibitor (XAF-1407: 1 mg/kg) and a muscarinic receptor inhibitor (atropine: 1 μg/kg) were investigated.

Results

In vehicle-treated rats, repetitive INAP shortened AERP (37 ± 3 ms vs baseline 44 ± 3 ms; P = .001) and increased LA membrane PKC_Ɛ content relative to cytosolic levels. Upon INAP recovery, ratio of PKC_Ɛ membrane to cytosol content normalized and INAP-induced AERP shortening reversed. Both XAF-1407 and atropine increased baseline AERP (control vs XAF-1407: 61 ± 4 ms; P > .001 and control vs atropine: 58 ± 3 ms; P = .011) and abolished INAP-associated AERP shortening.

Conclusion

Short-term simulated OSA is associated with a progressive, but transient, AERP shortening and a PKC_Ɛ translocation to LA membrane. Pharmacological I_K,ACh and muscarinic receptor inhibition prevented transient INAP-induced AERP shortening, suggesting an involvement of I_K,ACh in the transient arrhythmogenic AF substrate in OSA.

Arrhythmogenic mechanisms of acute obstructive respiratory events in a porcine model of drug-induced long QT

BACKGROUND

Obstructive sleep apnea is associated with increased risk of sudden cardiac death.

OBJECTIVE

The purpose of this study was to elucidate changes in ventricular repolarization and electromechanical interaction during obstructive respiratory events simulated by intermittent negative upper airway pressure (INAP) in pigs. We also investigated the effect of a reduced repolarization reserve in drug-induced long QT (LQT) following INAP-induced changes in ventricular repolarization.

METHODS

In sedated spontaneously breathing pigs, 75 seconds of INAP was applied by a negative pressure device connected to the endotracheal tube. Ventricular electromechanical coupling was determined by the electromechanical window (EMW) before (pre-INAP), during (INAP), and after INAP (post-INAP). Incidence rates of premature ventricular contractions (PVCs) were measured respectively. A drug-induced LQT was modeled by treating the pigs with the hERG1 blocker dofetilide (DOF).

RESULTS

Whereas QT interval increased during and decreased after INAP (pre-INAP: 273 ± 5 ms; INAP 281 ± 6 ms; post-INAP 254 ± 9 ms), EMW shortened progressively throughout INAP and post-INAP periods (pre-INAP 81 ± 4 ms; post-INAP 44 ± 7 ms). DOF shortened EMW at baseline. Throughout INAP, EMW decreased in a comparable fashion as before DOF (pre-INAP/+DOF 61 ± 7 ms; post-INAP/+DOF 14 ± 9 ms) but resulted in shorter absolute EMW levels. Short EMW levels were associated with increased occurrence of PVCs (pre-INAP 7 ± 2 ms vs post-INAP 26 ± 6 ms; P = .02), which were potentiated in DOF pigs (pre-INAP/+DOF 5 ± 2 ms vs post-INAP/+DOF 40 ± 8 ms; P = .006). Administration of atenolol prevented post-INAP EMW shortening and decreased occurrence of PVCs.

CONCLUSION

Transient dissociation of ventricular electromechanical coupling during simulated obstructive respiratory events creates a dynamic ventricular arrhythmogenic substrate, which is sympathetically mediated and aggravated by drug-induced LQT.

Nocturnal hypoxemic burden during positive airway pressure treatment across different central sleep apnea etiologies

INTRODUCTION

Nocturnal hypoxemia is associated with increased cardiovascular mortality. Here, we assess whether positive airway pressure by adaptive servo-ventilation (ASV) reduces nocturnal hypoxemic burden in patients with primary central sleep apnea (primary CSA), or heart failure related central sleep apnea (CSA-HF) and treatment emergent central sleep apnea (TECSA).

METHODS

Overnight oximetry data from 328 consecutive patients who underwent ASV initiation between March 2010 and May 2018 were retrospectively analyzed. Patients were stratified into three groups: primary CSA (n = 14), CSA-HF (n = 31), TECSA (n = 129). Apnea hypopnea index (AHI) and time spent below 90% SpO₂ (T90) was measured. Additionally, T90 due to acute episodic desaturations (T90_Desaturation) and due to non-specific and non-cyclic drifts of SpO₂ (T90_Non-specific) were assessed.

RESULTS

ASV reduced the AHI below 15/h in all groups. ASV treatment significantly shortened T90 in all three etiologies to a similar extent. T90_Desaturation, but not T90_Non-specific, was reduced by ASV across all three patient groups. AHI was identified as an independent modulator for ΔT90_Desaturation upon ASV treatment (B (95% CI: -1.32 (-1.73; -0.91), p < 0.001), but not for ΔT90 or ΔT90_Non-specific. Body mass index was one independent predictor of T90.

CONCLUSIONS

Across different central sleep apnea etiologies, ASV reduced AHI, but nocturnal hypoxemic burden remained high due to a non-specific component of T90 not related to episodic desaturation. Whether adjunct risk factor management such as weight-loss can further reduce T90 warrants further study.

Pharmacological inhibition of acetylcholine-regulated potassium current (IK,ACh) and associated A1- and M2-pathways prevent atrial arrhythmogenic changes in a rat model for obstructive sleep apnea

Background

In obstructive sleep apnea (OSA), intermittent hypoxemia and intrathoracic pressure fluctuations may increase vagal tone and adenosine release, potentially resulting in an increased acetylcholine-regulated potassium current (IK,ACh). Here we elucidated acute atrial electrophysiological effects of obstructive respiratory events simulated by intermittent negative upper airway pressure (INAP) and the role of atrial IKACh activation by A1-receptor and M2-receptor activation.

Methods

In sedated spontaneously breathing rats (2% isoflurane), either IK,ACh-inhibitor (XAF-1407: 1mg/kg), M2-receptor inhibitor (atropine; 1μg/kg), A1-receptor inhibitor (Rolofylline; 1μg/kg) or a buffer-based vehicle was perfused (Control). INAP was applied non-invasively by a negative pressure device 14 times throughout 70 minutes. Simulated apneas were maintained for one minute with a four minute resting period. Atrial effective refractory period (AERP) and atrial activation time were acquired by a programmed atrial pacing protocol before, during and after applied INAP throughout the study.

Results

Independent of IK,Ach-inhibition, single INAP applications prolonged transiently atrial activation times (Control: INAP vs. pre-INAP p=0.034; XAF-1407: INAP vs. pre-INAP p=0.039). In control-rats, seventy minutes of repetitive INAP decreased AERP by 15.45±0.06% (vs. baseline p=0.0015), which was reversible upon 1 hour of recovery. AERP shortening correlated with the cumulative pressure applied per body weight (Pearson r=−0.773; p=0.025). Whilst only XAF-1407 and atropine increased baseline AERP, all drug interventions, XAF-1407, atropine and Rolofylline could prevent INAP-associated AERP shortening (end INAP-protocol vs. respective baseline XAF-1407 p=0.994; atropine p=0.984; Rolofylline p=0.951). Drops in oxygen saturation and applied INAP were comparable in all groups.

Conclusion

Short-term simulated OSA is associated with progressive AERP shortening, which was determined by the cumulative negative airway pressure applied. This potentially represents an important insight in future OSA treatment. Pharmacological IK,ACh inhibition prevented INAP-associated AERP-shortening suggesting an involvement in acute atrial arrhythmogenesis in OSA. However, if IK,Ach and its potential upstream activating A1- and M2-pathway pose a pharmacological treatment target for OSA-patients with AF, requires further investigation.

Funding Acknowledgement

Type of funding source: None

Obstructive respiratory events transiently impair electromechanical coupling and increase premature ventricular contraction rate in a drug-induced Long-QT-2 pig model

Background

Obstructive sleep apnea (OSA) is characterized by intermittent negative thoracic pressure fluctuations and intermittent hypoxemic events. Recent findings associate OSA with impaired ventricular repolarization during sleep and increased risk of sudden cardiac death, which may have special implications for Long-QT-2-syndrome patients. Therefore, we elucidated changes in ventricular repolarization and electromechanical coupling (electromechanical window; EMW) during either obstructive respiratory events simulated by intermittent negative upper airway pressure (INAP) or hypoxemic events simulated by intermittent hypoxia (IH) in vehicle (VEH) and dofetilide (DOF) treated pigs, as a simulation of drug induced Long-QT-2 syndrome.

Methods

In sedated spontaneously breathing pigs, either VEH or DOF (50 μg/kg) was perfused and INAP was applied by a negative pressure device connected to the intubation tube. For IH-application the device was connected and left turned off. INAP or IH was maintained for 75 seconds followed by a ten-minute resting period. In order to evaluate the electromechanical window, the time difference between electrical (QT-duration) and mechanical systole (Q-wave to the end of left ventricular pressure signal, QLVPend) was measured before (pre-INAP/-IH), during and 60 seconds after INAP/IH (post-INAP/-IH). Incidence rates of premature ventricular contractions (PVC) and ventricular tachycardia were compared pre- to post-INAP/-IH.

Results

In VEH-pigs, EMW shortened throughout INAP and post-INAP periods steadily (VEH: pre-INAP: 81.69±2.31ms; INAP: 55.65±6.13ms; post-INAP: 38±8.89ms. p=0.008). EMW shortening during post-INAP was associated with an increase in PVCs (VEH: pre-INAP 5.41±1.87 vs. post-INAP 26.5±8.15; p=0.04). In DOF-pigs, INAP-associated EMW-shortening was further potentiated (DOF: pre-INAP: 61.16±7.18ms; INAP: 38.09±9.84ms; post-INAP: 14.93±9.24ms. p=0.016), which was associated with an increase in PVCs (DOF: pre-INAP 4.75±2.36 vs. post-INAP 36.58±10.92; p=0.017). Administration of Atenolol could prevent post-INAP shortening of the EMW and decrease counts of premature ventricular contractions. While desaturations were comparable in INAP and IH, IH did not result in EMW-shortening or increased arrhythmia risk.

Conclusion

Transient dissociation of the ventricular electromechanical coupling during a simulated obstructive apnea, but not during IH, creates a dynamic and sympathetically driven arrhythmogenic substrate. Apnea associated ventricular electromechanical uncoupling was aggravated in a drug-induced Long-QT-2 simulation. Whether OSA represents a modifiable arrhythmogenic risk factor in Long-QT-2-patients warrants further studies.

Funding Acknowledgement

Type of funding source: Foundation. Main funding source(s): Novo nordisk fonden

Inhibition of sodium-proton-exchanger subtype 3-mediated sodium absorption in the gut: A new antihypertensive concept

Arterial hypertension is one of the main contributors to cardiovascular diseases, including stroke, heart failure, and coronary heart disease. Salt plays a major role in the regulation of blood pressure and is one of the most critical factors for hypertension and stroke. At the individual level, effective salt reduction is difficult to achieve and available methods for managing sodium balance are lacking for many patients. As part of the ingested food, salt is absorbed in the gastrointestinal tract by the sodium proton exchanger subtype 3 (NHE3 also known as Slc9a3), influencing extracellular fluid volume and blood pressure. In this review, we discuss the beneficial effects of pharmacological inhibition of NHE3-mediated sodium absorption in the gut and focus on the effect on blood pressure and end-organ damage.

Cathepsin A contributes to left ventricular remodeling by degrading extracellular superoxide dismutase in mice

In the heart, the serine carboxypeptidase cathepsin A (CatA) is distributed between lysosomes and the extracellular matrix (ECM). CatA-mediated degradation of extracellular peptides may contribute to ECM remodeling and left ventricular (LV) dysfunction. Here, we aimed to evaluate the effects of CatA overexpression on LV remodeling. A proteomic analysis of the secretome of adult mouse cardiac fibroblasts upon digestion by CatA identified the extracellular antioxidant enzyme superoxide dismutase (EC-SOD) as a novel substrate of CatA, which decreased EC-SOD abundance 5-fold. In vitro, both cardiomyocytes and cardiac fibroblasts expressed and secreted CatA protein, and only cardiac fibroblasts expressed and secreted EC-SOD protein. Cardiomyocyte-specific CatA overexpression and increased CatA activity in the LV of transgenic mice (CatA-TG) reduced EC-SOD protein levels by 43%. Loss of EC-SOD-mediated antioxidative activity resulted in significant accumulation of superoxide radicals (WT, 4.54 μmol/mg tissue/min; CatA-TG, 8.62 μmol/mg tissue/min), increased inflammation, myocyte hypertrophy (WT, 19.8 μm; CatA-TG, 21.9 μm), cellular apoptosis, and elevated mRNA expression of hypertrophy-related and profibrotic marker genes, without affecting intracellular detoxifying proteins. In CatA-TG mice, LV interstitial fibrosis formation was enhanced by 19%, and the type I/type III collagen ratio was shifted toward higher abundance of collagen I fibers. Cardiac remodeling in CatA-TG was accompanied by an increased LV weight/body weight ratio and LV end diastolic volume (WT, 50.8 μl; CatA-TG, 61.9 μl). In conclusion, CatA-mediated EC-SOD reduction in the heart contributes to increased oxidative stress, myocyte hypertrophy, ECM remodeling, and inflammation, implicating CatA as a potential therapeutic target to prevent ventricular remodeling.

741Pharmacological inhibition of the acetylcholine-regulated potassium channel (IK,ACh) prevents atrial arrhythmogenic changes in a rat model for obstructive sleep apnea

Background

In obstructive sleep apnea (OSA), intermittent hypoxemia and intrathoracic pressure fluctuations may increase vagal tone, resulting in an increased acetylcholine-regulated potassium current (IK,ACh). Here we elucidated acute atrial electrophysiological effects of obstructive respiratory events simulated by intermittent negative upper airway pressure (INAP) and the role of atrial IKACh activation.

Methods

In sedated spontaneously breathing rats (2% isoflurane), either IK,ACh-inhibitor (XAF-1407: 1mg/kg) or a buffer-based vehicle was perfused (Control). INAP was applied non-invasively by a negative pressure device 14 times throughout 70 minutes. Simulated apneas were maintained for one minute with a four minute resting period. Atrial effective refractory period (AERP), inducible atrial fibrillation (AF)-durations and atrial activation time were acquired by a programmed atrial pacing protocol before, during and after applied INAP throughout the study.

Results

During single INAP applications atrial activation times prolonged transiently in both groups (Control: INAP vs. pre-INAP p = 0.034; XAF-1407: INAP vs. pre-INAP p = 0.039). In control-rats, seventy minutes of repetitive INAP prolonged P-wave duration (+10.8 ± 2.7% vs. baseline, p = 0.008) and decreased AERP by 14.6 ± 3.1% (vs. baseline p = 0.001). AERP shortening correlated with the cumulative pressure applied per body weight (Pearson r= -0.773; p= 0.025). XAF-1407 could prevent P-wave prolongation and AERP shortening. Inducible AF-durations (CTR 0.94 ± 0.34s vs. XAF-1407 0.1 ± 0.09s p = 0.049) were shorter in XAF-1407 treated rats. Drops in oxygen saturation or applied INAP were comparable in control and XAF-1407 rats.

Conclusion

Short-term simulated OSA is associated with AF-related arrhythmogenic changes, which could be prevented by pharmacological IK,ACh inhibition. Moreover, the cumulative negative airway pressure applied determined aERP shortening and may represent a target for OSA treatment. These findings have important implications for the antiarrhythmic management of AF patients with OSA.

Pharmacological inhibition of sodium-proton-exchanger subtype 3-mediated sodium absorption in the gut reduces atrial fibrillation susceptibility in obese spontaneously hypertensive rats

Background

Increased sodium uptake has been shown to contribute to hypertension and cardiac end-organ damage. The sodium-proton-exchanger subtype 3 (NHE3) is an important mediator of intestinal sodium absorption. Whether a reduction in intestinal sodium absorption can prevent the development of an atrial arrhythmogenic substrate in hypertension is unknown.

Methods

Eight-week-old obese spontaneously hypertensive rats (SHR-ob) were treated for six weeks with the gut-specific NHE3-inhibitor SAR (1-(β-D-glucopyranosyl)-3-{3-[(4S)-6,8-dichloro-2-methyl-1,2,3,4-tetrahydroiso-chinolin-4-yl]phenyl}urea, 1 mg/kg/d in chow, SHR-ob SAR, n = 7) and compared to aged-matched placebo-treated SHR-ob (SHR-ob PLAC, n = 8). Cardiac magnetic resonance imaging was performed at the end of the treatment period to assess atrial emptying function. Afterwards, local conduction disturbances and inducible atrial fibrillation (AF) duration were determined and histological analysis to quantify atrial fibrosis amount were performed.

Results

Inhibition of intestinal NHE3 by SAR increased fecal sodium excretion, resulted in marked changes in feces electrolyte concentrations and water content, reduced blood pressure and preserved atrial emptying function (active total percent emptying: SHR-ob SAR: 0.47 ± 0.05% vs. SHR-ob PLAC: 0.38 ± 0.007, p < 0.0001). Atrial fibrosis content was lower (21.4 ± 2.5% vs. 36.7 ± 1.2%, p < 0.0001) and areas of slow conduction were smaller (2.5 ± 0.09% vs. 5.3 ± 0.2%, p < 0.0001) in SHR-ob SAR compared to SHR-ob PLAC. Left atrial burst stimulation resulted in shorter inducible AF-durations in SHR-ob SAR compared to SHR-ob PLAC.

Conclusions

Reduction of intestinal sodium absorption and subsequent changes in feces milieu by pharmacological NHE3 inhibition in the gut preserved atrial emptying function and reduced AF susceptibility. Whether pharmacological NHE3 inhibition in the gut prevents AF in humans warrants further study.

P2561Withdrawal of simulated obstructive sleep apnea partially reverses atrial arrhythmogenic substrate in rats

Background

Obstructive sleep apnea (OSA) is associated with structural alterations of the left atria (LA) and increased occurrence of atrial fibrillation (AF). Obstructive respiratory events lead to intermittent hypoxia (IH) and ineffective inspiration against the occluded upper airways, which result in intrathoracic and cardiac transmural pressure changes. Data on reversibility of LA-structural remodeling processes after withdrawal of OSA are still missing.

Objectives

Aim of the study was to develop a novel AF animal model mimicking intrathoracic pressure changes in addition to IH and to analyze the effect of OSA-withdrawal on atrial remodeling reversibility.

Method

In sedated rats (2% isoflurane), IH (n=9) was applied by intermittent increase in the respiratory dead volume. Standardized obstructive respiratory events were induced by defined intermittent negative upper airway pressure (INAP = inverse CPAP) applied via a customized mask connected to a negative pressure device (n=9). One minute of IH or INAP was followed by a rest period of nine minutes for four hours every second day. Rats with comparable anesthesia were used as controls (CTR). After three weeks, the animals were sacrificed. To analyze atrial structural remodeling reversibility, additional INAP-rats (n=5) were sacrificed after INAP-withdrawal of three weeks and compared to respective CTR (n=7).

Result

Blood pressure was not affected by IH or INAP. Intermittent desaturation and post-apneic hyperventilation were comparable in INAP- and IH-rats, but INAP-rats showed significantly higher breathing efforts during apneas compared to IH-rats. LA connexin43 (Cx43) protein expression assessed by quantitative immunofluorescence was reduced in both groups compared to CTR (0.77±0.07% in CTR vs. 0.45±0.06% in IH, p=0.02; CTR vs. 0.39±0.06% in INAP, p=0.005). However, LA interstitial fibrosis content (7.03±0.58% vs. CTR, p=0.01) and LA myocyte diameters (13.23±0.34μm vs. CTR, p=0.03) were increased in INAP-rats, but not in IH-rats. This was associated with longer inducible AF-durations in INAP-rats (11.65±4.43s vs. 0.72±0.33s in CTR, p=0.03) but not in IH-rats (1.28±0.33s vs. CTR, p=0.31). Three weeks of INAP-withdrawal (INAP-W) normalized interstitial fibrosis content (INAP-W vs. CTR, p=0.50) and LA-myocyte diameter (INAP-W vs. CTR, p=0.31). However, LA Cx43 protein expression remained low after three weeks of INAP withdrawal and inducible AF-episodes were still prolonged compared to respective CTR.

Conclusion

Application of INAP in rats mimics important components of OSA beyond IH and allows the study of an arrhythmogenic substrate in the atrium independent of the development of risk factors. In our model, withdrawal of INAP resulted in partial reversibility of structural LA remodeling but was not sufficient to abolish inducible AF-episodes completely. Future clinical studies are warranted to determine the anti-arrhythmic effect of isolated sleep apnea treatment in AF-patients.

Acknowledgement/Funding

Else Kröner-Fresenius-Stiftung, SFB-TRR219-M02/S-02

The association between different features of sleep-disordered breathing and blood pressure: A cross-sectional study

Sleep disordered breathing (SDB) is highly prevalent in patients with high blood pressure (BP). Severity of SDB can be evaluated by the number of apneas and hypopneas per hour (AHI) or by measures of hypoxia. The objective of this study was to assess the association between different measures of SDB and BP. In 134 consecutive patients, polygraphy was performed to determine the AHI. Pulse oximetry was used to determine hypoxemic burden (time below 90% oxygen saturation [T90] and hypoxia load [HL], representing the integrated area above the curve of desaturation). AHI did not correlate with systolic and diastolic BP or pulse pressure. In contrast, HL correlated with pulse pressure during the day (P = .01) and night (P = .0034) before and after adjustment for body mass index. The correlation between systolic BP and HL at night disappeared following adjustment for body mass index. This study generates the hypothesis that nocturnal hypoxemic burden may represent a suitable marker of BP pattern and a potential treatment target in hypertensive patients.

Concomitant Obesity and Metabolic Syndrome Add to the Atrial Arrhythmogenic Phenotype in Male Hypertensive Rats

Background

Besides hypertension, obesity and the metabolic syndrome have recently emerged as risk factors for atrial fibrillation. This study sought to delineate the development of an arrhythmogenic substrate for atrial fibrillation in hypertension with and without concomitant obesity and metabolic syndrome.

Methods and Results

We compared obese spontaneously hypertensive rats (SHR‐obese, n=7–10) with lean hypertensive controls (SHR‐lean, n=7–10) and normotensive rats (n=7–10). Left atrial emptying function (MRI) and electrophysiological parameters were characterized before the hearts were harvested for histological and biochemical analyses. At the age of 38 weeks, SHR‐obese, but not SHR‐lean, showed increased body weight and impaired glucose tolerance together with dyslipidemia compared with normotensive rats. Mean blood pressure was similarly increased in SHR‐lean and SHR‐obese when compared with normotensive rats (178±9 and 180±8 mm Hg [not significant] versus 118±5 mm Hg, P<0.01 for both), but left ventricular end‐diastolic pressure was more increased in SHR‐obese than in SHR‐lean. Impairment of left atrial emptying function, increase in total atrial activation time, and conduction heterogeneity, as well as prolongation of inducible atrial fibrillation durations, were more pronounced in SHR‐obese as compared with SHR‐lean. Histological and biochemical examinations revealed enhanced triglycerides and more pronounced fibrosis in the left atrium of SHR‐obese. Besides increased expression of profibrotic markers in SHR‐lean and SHR‐obese, the profibrotic extracellular matrix protein osteopontin was highly upregulated only in SHR‐obese.

Conclusions

In addition to hypertension alone, concomitant obesity and metabolic syndrome add to the atrial arrhythmogenic phenotype by impaired left atrial emptying function, local conduction abnormalities, interstitial atrial fibrosis formation, and increased propensity for atrial fibrillation.

Update: Kardiovaskuläre Schlafmedizin

The prevalence of sleep-disordered breathing (SDB) is high in patients with cardiovascular diseases. Typical symptoms like daytime sleepiness can be absent and those patients may report unspecific, therapy-resistant symptoms related to their underlying disease. Particularly sleep-related symptoms like nocturia, nocturnal dyspnea and pectangina can be present. Based on the results of recently published studies, the treatment of central sleep apnea in patients with symptomatic, systolic heart failure by adaptive servo-ventilation is no longer recommended. Although the treatment of obstructive sleep apnea did not prevent cardiovascular events, it improved snoring, daytime sleepiness and health-related quality of life. Furthermore, studies imply that treatment of SDB should be considered as an adjunct treatment modality in patients with hypertension and atrial fibrillation. Due to the high prevalence, screening for SDB can help to identify patients at high cardiovascular risk.

Progression of kidney injury and cardiac remodeling in obese spontaneously hypertensive rats: the role of renal sympathetic innervation

BACKGROUND

Hypertension and metabolic syndrome (MetS) are associated with increased sympathetic activation possibly contributing to the progression of renal damage and cardiac remodeling. Renal sympathetic denervation (RDN) decreases sympathetic renal efferent and afferent nerve activity.

METHODS

Obese spontaneously hypertensive rats (SHRs-ob) were subjected to RDN at the age of 34 weeks (SHRs-ob + RDN) and were compared with sham-operated SHRs-ob and their normotensive lean controls (Ctrs). Blood pressure was measured by telemetry. Kidney and heart function were determined by magnetic resonance imaging (MRI). Renal and cardiac remodeling were characterized by immunohistochemical analyses. Animals were killed at the age of 48 weeks.

RESULTS

In SHRs-ob, RDN attenuated the progressive increase in blood pressure and preserved a mean blood pressure of 156±7mm Hg compared with 220±8mm Hg in sham-operated SHRs-ob at 100 days after RDN, whereas heart rate, body weight, and metabolic parameters remained unchanged. Renal catecholamine and tyrosine hydroxylase levels were significantly reduced after RDN, suggesting effective renal denervation. Progression of renal dysfunction as characterized by increased urinary albumin/creatinine ratio and reduced glomerular filtration rate were attenuated by RDN. In SHRs-ob, renal perfusion was significantly reduced and normalized by RDN. Cardiac fibrosis and cardiac diastolic dysfunction measured by MRI and invasive pressure measurements were significantly attenuated by RDN.

CONCLUSIONS

In SHRs-ob, progressive increase in blood pressure and progression of renal injury and cardiac remodelling are mediated by renal sympathetic activation as they were attenuated by RDN.

Experimental Evidence Of The Role Of Renal Sympathetic Denervation For Treating Atrial Fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia and is associated with significant morbidity and mortality. In addition to mechanisms such as atrial stretch and atrial remodeling, also the activity of the autonomic nervous system has been suggested to contribute to the progression from paroxysmal to persistent AF. Catheter-based renal denervation (RDN) was introduced as a minimally invasive approach to reduce renal and whole body sympathetic activation which may result in atrial antiarrhythmic effects under some pathophysiological conditions. This review focuses on the potential effects of RDN on different arrhythmogenic mechanisms in the atrium and discusses potential anti-remodeling effects in hypertension, heart failure, and sleep apnea.

Effect of obstructive respiratory events on blood pressure and renal perfusion in a pig model for sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) is associated with hypertension and the progression of chronic kidney disease (CKD). Renal sympathetic innervation contributes to either condition.

METHODS

We investigated the effect of renal sympathetic denervation (RDN) on blood pressure (BP), renal perfusion, and neurohumoral responses during and after repetitive obstructive apneas in a pig model for OSA. BP, femoral artery, and renal artery flow were measured in 29 spontaneously breathing urethane-chloralose-anesthetized pigs. The effect of RDN (n = 14) and irbesartan (n = 3) was investigated. Repetitive tracheal occlusions for 2 minutes with applied negative tracheal pressure at -80 mbar were performed over 4 hours.

RESULTS

Spontaneous breathing attempts during tracheal occlusion caused an intra-apneic breathing synchronous oscillating pattern of renal flow. Renal flow oscillations were > 2-fold higher compared with femoral flow that almost showed changes proportional to the BP alterations (2.9%/mm Hg vs. 1.3%/mm Hg; P < 0.0001). A marked postapneic BP rise from 102 ± 3 to 172 ± 8 mm Hg (P < 0.00001) was associated with renal hypoperfusion (from 190 ± 24 to 70 ± 20 ml/min; P < 0.00001) occurring after application of obstructive respiratory events. RDN, but not irbesartan, inhibited postapneic BP rises and renal hypoperfusion and attenuated increased plasma renin activity and aldosterone concentration induced by repetitive tracheal occlusions. Additionally, increased urinary protein/creatinine ratio was significantly reduced by RDN, whereas intra-apneic hemodynamic changes or blood gases were not modified by RDN.

CONCLUSIONS

Repetitive obstructive respiratory events result in postapneic BP rises and renal hypoperfusion, as well as neurohumoral responses and increased protein/creatinine ratio. These changes are mainly sympathetically driven because they could be attenuated by RDN.

Obstructive sleep apnea and atrial arrhythmogenesis

Atrial fibrillation (AF) is the most common sustained arrhythmia and is associated with relevant morbidity and mortality. Besides hypertension, valvular disease and cardiomyopathy, mainly ischemic and dilated, also other conditions like obesity, alcohol abusus, genetic factors and obstructive sleep apnea (OSA) are discussed to contribute to the progression from paroxysmal to persistent AF. The prevalence of OSA among patients with AF is 40-50%. OSA is characterized by periodic or complete cessation of effective breathing during sleep due to obstruction of the upper airways. Obstructive respiratory events result in acute intrathoracic pressure swings and profound changes in blood gases together leading to atrial stretch and acute sympatho-vagal dysbalance resulting in acute apnea related to electrophysiological and hemodynamic alterations. Additionally, repetitive obstructive events in patients with OSA may lead to sympathetic and neurohumoral activation and subsequent structural and functional changes in the atrium creating an arrhythmogenic substrate for AF in the long run.

This review focuses on the acute and chronic effects of negative thoracic pressure swings, changes in blood pressure and sympatho-vagal dysbalance induced by obstructive respiratory events on atrial electrophysiology and atrial structure in patients with obstructive sleep apnea.

Blood-brain barrier in vitro models as tools in drug discovery: assessment of the transport ranking of antihistaminic drugs

In the course of our validation program testing blood-brain barrier (BBB) in vitro models for their usability as tools in drug discovery it was evaluated whether an established Transwell model based on porcine cell line PBMEC/C1-2 was able to differentiate between the transport properties of first and second generation antihistaminic drugs. First generation antihistamines can permeate the BBB and act in the central nervous system (CNS), whereas entry to the CNS of second generation antihistamines is restricted by efflux pumps such as P-glycoprotein (P-gP) located in brain endothelial cells. P-gP functionality of PBMEC/C1-2 cells grown on Transwell filter inserts was proven by transport studies with P-gP substrate rhodamine 123 and P-gP blocker verapamil. Subsequent drug transport studies with the first generation antihistamines promethazine, diphenhydramine and pheniramine and the second generation antihistamines astemizole, ceterizine, fexofenadine and loratadine were accomplished in single substance as well as in group studies. Results were normalised to diazepam, an internal standard for the transcellular transport route. Moreover, effects after addition of P-gP inhibitor verapamil were investigated. First generation antihistamine pheniramine permeated as fastest followed by diphenhydramine, diazepam, promethazine and second generation antihistaminic drugs ceterizine, fexofenadine, astemizole and loratadine reflecting the BBB in vivo permeability ranking well. Verapamil increased the transport rates of all second generation antihistamines, which suggested involvement of P-gP during their permeation across the BBB model. The ranking after addition of verapamil was significantly changed, only fexofenadine and ceterizine penetrated slower than internal standard diazepam in the presence of verapamil. In summary, permeability data showed that the BBB model based on porcine cell line PBMEC/C1-2 was able to reflect the BBB in vivo situation for the transport of antihistaminc drugs and to distinguish between first and second generation antihistamines.

Helicobacter pylori Sequences Reflect Past Human Migrations

The long association between the stomach bacterium Helicobacter pylori and humans, in combination with its predominantly within-family transmission route and its exceptionally high DNA sequence diversity, make this bacterium a reliable marker for discerning both recent and ancient human population movements. As much of the diversity in H. pylori sequences is generated by recombination and mutation on a local scale, the partitioning of H. pylori sequences from a large globally distributed data set into six geographic populations enabled the detection of recent ( < 500 years) human population movements including the European colonial expansion and the slave trade. The further separation of bacterial populations into distinct sub-populations traced prehistoric population movements like the settlement of the Americas by Asians across the Bering Strait and the Bantu migrations in Africa. The ability to deduce ancestral population structure from modern sequences was a key development that allowed the detection of zones of admixture, such as Europe, and the inference of multiple migration waves into these zones. The significantly similar global population structure of both H. pylori and humans confirmed not only an evolutionary time-scale association between host and parasite, but also that humans had carried H. pylori in their stomachs on their migrations out of Africa.

[Population identification of Helicobacter pilory isolates from Russia]

Using multilocus sequence typing (MLST), 22 Helicobacter pylori isolates from Russia have been characterized. All of the Russian strains were assigned to a single population, hpEurope.

Fit genotypes and escape variants of subgroup III Neisseria meningitidis during three pandemics of epidemic meningitis

The genetic variability at six polymorphic loci was examined within a global collection of 502 isolates of subgroup III, serogroup A Neisseria meningitidis. Nine "genoclouds" were identified, consisting of genotypes that were isolated repeatedly plus 48 descendent genotypes that were isolated rarely. These genoclouds have caused three pandemic waves of disease since the mid-1960s, the most recent of which was imported from East Asia to Europe and Africa in the mid-1990s. Many of the genotypes are escape variants, resulting from positive selection that we attribute to herd immunity. Despite positive selection, most escape variants are less fit than their parents and are lost because of competition and bottlenecks during spread from country to country. Competition between fit genotypes results in dramatic changes in population composition over short time periods.

Frequent interspecific genetic exchange between commensal Neisseriae and Neisseria meningitidis

Natural sequence variation was investigated among serogroup A subgroup IV-1 Neisseria meningitidis isolated from diseased patients and healthy carriers in The Gambia, West Africa. The frequencies of DNA import were analysed by sequencing fragments of four linked genes encoding the immunogenic outer membrane proteins TbpB (transferrin binding protein B) and OpaA (an adhesin) plus two housekeeping enzymes. Seventeen foreign tbpB alleles were independently imported into the 98 strains tested, apparently due to immune selection. The median size of the imported DNA fragments was 5 kb, resulting in the occasional concurrent import of linked housekeeping genes by hitchhiking. Sequences of tbpB from other strains of N. meningitidis as well as commensal Neisseria lactamica and Neisseria spp. isolated from the same geographical area revealed that these species share a common tbpB gene pool and identified several examples of interspecific genetic exchange. These observations indicate that recombination can be more frequent between related species than within a species and indicate that effective vaccination against serogroup B meningococcal disease may be difficult to achieve.

Post-termination ribosome interactions with the 5'UTR modulate yeast mRNA stability

A novel form of post-transcriptional control is described. The 5' untranslated region (5'UTR) of the Saccharomyces cerevisiae gene encoding the AP1-like transcription factor Yap2 contains two upstream open reading frames (uORF1 and uORF2). The YAP2-type of uORF functions as a cis-acting element that attenuates gene expression at the level of mRNA turnover via termination-dependent decay. Release of post-termination ribosomes from the YAP2 5'UTR causes accelerated decay which is largely independent of the termination modulator gene UPF1. Both of the YAP2 uORFs contribute to the destabilization effect. A G/C-rich stop codon context, which seems to promote ribosome release, allows an uORF to act as a transferable 5'UTR-destabilizing element. Moreover, termination-dependent destabilization is potentiated by stable secondary structure 3' of the uORF stop codon. The potentiation of uORF-mediated destabilization is eliminated if the secondary structure is located further downstream of the uORF, and is also influenced by a modulatory mechanism involving eIF2. Destabilization is therefore linked to the kinetics of acquisition of reinitiation-competence by post-termination ribosomes in the 5'UTR. Our data explain the destabilizing properties of YAP2-type uORFs and also support a more general model for the mode of action of other known uORFs, such as those in the GCN4 mRNA.

Identification and developmental expression of a 5'-3' exoribonuclease from Drosophila melanogaster

In multicellular organisms, very little is known about the role of mRNA stability in development, and few proteins involved in degradation pathways have been characterized. We have identified the Drosophila homologue of XRN1, which is the major cytoplasmic 5'-3' exoribonuclease in Saccharomyces cerevisiae. The protein sequence of this homologue (pacman) has 59% identity to S. cerevisiae XRN1 and 67% identity to the mouse homologue (mXRN1p) in certain regions. Sequencing of this cDNA revealed that it includes a trinucleotide repeat (CAG)9 which encodes polyglutamine. By directly measuring pacman exoribonuclease activity in yeast, we demonstrate that pacman can complement the yeast XRN1 mutation. Northern blots show a single transcript of approximately 5.2 kb which is abundant only in 0-8-h embryos and in adult males and females. In situ hybridization analysis revealed that the pcm transcripts are maternally derived, and are expressed at high levels in nurse cells. During early embryonic syncytial nuclear divisions, pcm transcripts are homogenously distributed. pcm mRNA is expressed abundantly and ubiquitously throughout the embryo during gastrulation, with high levels in the germ band and head structures. After germ band retraction, pcm transcripts are present at much lower levels, in agreement with the Northern results. Our experiments provide the first example of an exoribonuclease which is differentially expressed throughout development.

The yeast transcription factor genes YAP1 and YAP2 are subject to differential control at the levels of both translation and mRNA stability

Two forms of post-transcriptional control direct differential expression of the Saccharomyces cerevisiae genes encoding the AP1-like transcription factors Yap1p and Yap2p. The mRNAs of these genes contain respectively one (YAP1 uORF) and two (YAP2 uORF1 and uORF2) upstream open reading frames. uORF-mediated modulation of post-termination events on the 5'-untranslated region (5'-UTR) directs differential control not only of translation but also of mRNA decay. Translational control is defined by two types of uORF function. The YAP1 -type uORF allows scanning 40S subunits to proceed via leaky scanning and re-initiation to the major ORF, whereas the YAP2 -type acts to block ribosomal scanning by promoting efficient termination. At the same time, the YAP2 uORFs define a new type of mRNA destabilizing element. Both post-termination ribosome scanning behaviour and mRNA decay are influenced by the coding sequence and mRNA context of the respective uORFs, including downstream elements. Our data indicate that release of post-termination ribosomes promotes largely upf -independent accelerated decay. It follows that translational termination on the 5'-UTR of a mature, non-aberrant yeast mRNA can trigger destabilization via a different pathway to that used to rid the cell of mRNAs containing premature stop codons. This route of control of non-aberrant mRNA decay influences the stress response in yeast. It is also potentially relevant to expression of the sizable number of eukaryotic mRNAs that are now recognized to contain uORFs.

Disruption of ribosomal scanning on the 5'-untranslated region, and not restriction of translational initiation per se, modulates the stability of nonaberrant mRNAs in the yeast Saccharomyces cerevisiae

Translation and mRNA decay constitute key players in the post-transcriptional control of gene expression. We examine the mechanisms by which the 5'-untranslated region (UTR) of nonaberrant mRNAs acts to modulate both these processes in Saccharomyces cerevisiae. Two classes of functional relationship between ribosome-5'-UTR interactions and mRNA decay are identifiable. In the first of these, elements in the main open reading frame (ORF) dictate how the decay process reacts to inhibitory structures in the 5'-UTR. The same types of stability modulation can be elicited by trans-regulation of translation via inducible binding of the iron-regulatory protein to an iron-responsive element located 9 nucleotides from the 5' cap. A eukaryotic translational repressor can therefore modulate mRNA decay via the 5'-UTR. In contrast, translational regulation mediated via changes in the activity of the cap-binding eukaryotic translation initiation factor eIF-4E bypasses translation-dependent pathways of mRNA degradation. Thus modulation of mRNA stability via the 5'-UTR depends on disruption of the scanning process, rather than changes in translational initiation efficiency per se. In the second class of pathway, an upstream ORF (uORF) functions as a powerful destabilizing element, inducing termination-dependent degradation that is apparently independent of any main ORF determinants but influenced by the efficiencies of ribosomal recognition of the uORF start and stop codons. This latter mechanism provides a regulatable means to modulate the stability of nonaberrant mRNAs via a UPF-dependent pathway.

Mutants of eukaryotic initiation factor eIF-4E with altered mRNA cap binding specificity reprogram mRNA selection by ribosomes in Saccharomyces cerevisiae

Recognition of the 5'-end of eukaryotic mRNA by the ribosomal 43 S preinitiation complex involves the eukaryotic translation initiation factor eIF-4E (eIF-4alpha). Deletion mutants of the eIF-4E gene of Saccharomyces cerevisiae (CDC33) encoded proteins with reduced affinity for the 5'-cap. One of these mutant proteins lacked any detectable binding to a cap analogue binding column, yet was still able to support cell growth. More than 17% of the total eIF-4E amino acid sequence could be removed without fully inactivating this factor. At least 30 of the N-terminal amino acids are not essential for function. The minimal functional eIF-4E protein segment therefore comprises at most 176 amino acids. The translation and growth defects of the deletion mutants could be at least partially compensated by increases in eIF-4E synthesis, possibly due to a mass-action effect on mRNA binding. Electroporation of yeast spheroplasts with in vitro synthesized mRNA allowed us to characterize the ability of eIF-4E mutant strains to distinguish between capped and uncapped mRNAs in vivo. Our data show that the cap specificity of eIF-4E determines to what extent the translational apparatus differentiates between capped and uncapped mRNAs and indicate the minimum relative mRNA (cap) binding activity of eIF-4E required for yeast cell viability.

Theoretical and experimental basis for the development of a dynamic airway stent

Three major problems are currently associated with airway stents: mucostasis, formation of granulation tissue, and migration. We wanted to determine whether these problems could be solved by a different stent design. Based on theoretical considerations of an idealized trachea, we developed a dynamic bifurcation stent made of silicone which incorporates horseshoe-shaped steel struts. A flexible posterior membrane enables dynamic compression during cough, whilst the clasps maintain the airway lumen in the face of external compression. The design of the stent cast was based upon computed tomographic (CT)-scan studies of the central airways. Its complex shape provides a smoother distribution of pressure on the mucosa; thereby, lowering the stimulus for granulation formation. The bronchial limbs saddle on the carina, preventing displacement. The mechanical behaviours of the new stent and two commercially available stents were compared in an ex-vivo model, utilizing freshly excised tracheae and new visualization techniques. Dynamic (artificial coughs) and static loads (simulating tumour compression or pleural pressures) were applied on excised human tracheae with different stents. Our dynamic stent preserved effective compression of the posterior membrane in response to cough, and also provided lumen stability against extrinsic compression. In comparison, the two commercially available stents did not provide both functions equally well. In conclusion, our newly designed dynamic bifurcation stent shows characteristics which should prove useful in avoiding problems currently associated with airway stents.

Theoretical and experimental basis for the development of a dynamic airway stent

Three major problems are currently associated with airway stents: mucostasis, formation of granulation tissue, and migration. We wanted to determine whether these problems could be solved by a different stent design. Based on theoretical considerations of an idealized trachea, we developed a dynamic bifurcation stent made of silicone which incorporates horseshoe-shaped steel struts. A flexible posterior membrane enables dynamic compression during cough, whilst the clasps maintain the airway lumen in the face of external compression. The design of the stent cast was based upon computed tomographic (CT)-scan studies of the central airways. Its complex shape provides a smoother distribution of pressure on the mucosa; thereby, lowering the stimulus for granulation formation. The bronchial limbs saddle on the carina, preventing displacement. The mechanical behaviours of the new stent and two commercially available stents were compared in an ex-vivo model, utilizing freshly excised tracheae and new visualization techniques. Dynamic (artificial coughs) and static loads (simulating tumour compression or pleural pressures) were applied on excised human tracheae with different stents. Our dynamic stent preserved effective compression of the posterior membrane in response to cough, and also provided lumen stability against extrinsic compression. In comparison, the two commercially available stents did not provide both functions equally well. In conclusion, our newly designed dynamic bifurcation stent shows characteristics which should prove useful in avoiding problems currently associated with airway stents.