Oxytocin exerts harmful cardiac repolarization prolonging effects in drug-induced LQTS.

Background Oxytocin is used therapeutically in psychiatric patients. Many of these also receive anti-depressant or anti-psychotic drugs causing acquired long-QT-syndrome (LQTS) by blocking HERG/IKr. We previously identified an oxytocin-induced QT-prolongation in LQT2 rabbits, indicating potential harmful effects of combined therapy. We thus aimed to analyze the effects of dual therapy with oxytocin and fluoxetine/risperidone on cardiac repolarization. Methods Effects of risperidone, fluoxetine and oxytocin on QT/QTc, short-term variability (STV) of QT, and APD were assessed in rabbits using in vivo ECG and ex vivo monophasic AP recordings in Langendorff-perfused hearts. Underlying mechanisms were assessed using patch clamp in isolated cardiomyocytes. Results Oxytocin, fluoxetine and risperidone prolonged QTc and APD in whole hearts. The combination of fluoxetine + oxytocin resulted in further QTc- and APD-prolongation, risperidone + oxytocin tended to increase QTc and APD compared to monotherapy. Temporal QT instability, STVQTc was increased by oxytocin, fluoxetine / fluoxetine + oxytocin and risperidone / risperidone + oxytocin. Similar APD-prolonging effects were confirmed in isolated cardiomyocytes due to differential effects of the compounds on repolarizing ion currents: Oxytocin reduced IKs, fluoxetine and risperidone reduced IKr, resulting in additive effects on IKtotal-tail. In addition, oxytocin reduced IK1, further reducing the repolarization reserve. Conclusion Oxytocin, risperidone and fluoxetine prolong QTc / APD. Combined treatment further prolongs QTc/APD due to differential effects on IKs and IK1 (block by oxytocin) and IKr (block by risperidone and fluoxetine), leading to pronounced impairment of repolarization reserve. Oxytocin should be used with caution in patients in the context of acquired LQTS

Transgenic LQT2, LQT5, and LQT2-5 rabbit models with decreased repolarisation reserve for prediction of drug-induced ventricular arrhythmias

Background and Purpose Reliable prediction of pro‐arrhythmic side effects of novel drug candidates is still a major challenge. Although drug‐induced pro‐arrhythmia occurs primarily in patients with pre‐existing repolarisation disturbances, healthy animals are employed for pro‐arrhythmia testing. To improve current safety screening, transgenic long QT (LQTS) rabbit models with impaired repolarisation reserve were generated by overexpressing loss‐of‐function mutations of human HERG (HERG‐G628S , loss of IKr; LQT2), KCNE1 (KCNE1‐G52R , decreased IKs; LQT5), or both transgenes (LQT2‐5) in the heart. Experimental Approach Effects of K+ channel blockers on cardiac repolarisation and arrhythmia susceptibility were assessed in healthy wild‐type (WT) and LQTS rabbits using in vivo ECG and ex vivo monophasic action potential and ECG recordings in Langendorff‐perfused hearts. Key Results LQTS models reflect patients with clinically “silent” (LQT5) or “manifest” (LQT2 and LQT2‐5) impairment in cardiac repolarisation reserve: they were more sensitive in detecting IKr‐blocking (LQT5) or IK1/IKs‐blocking (LQT2 and LQT2‐5) properties of drugs compared to healthy WT animals. Impaired QT‐shortening capacity at fast heart rates was observed due to disturbed IKs function in LQT5 and LQT2‐5. Importantly, LQTS models exhibited higher incidence, longer duration, and more malignant types of ex vivo arrhythmias than WT. Conclusion and Implications LQTS models represent patients with reduced repolarisation reserve due to different pathomechanisms. As they demonstrate increased sensitivity to different specific ion channel blockers (IKr blockade in LQT5 and IK1 and IKs blockade in LQT2 and LQT2‐5), their combined use could provide more reliable and more thorough prediction of (multichannel‐based) pro‐arrhythmic potential of novel drug candidates

RET Proto-Oncogene Germline Mutation in Pheochromocytoma Patients - Incidence and Clinical Consequences

Wstęp Dotychczasowe badania wskazują, że częstość zespołu mnogiej gruczolakowatości (MEN 2), w skład którego wchodzi guz chromochłonny, jest większa niż dotychczas sądzono. Zespół ten dziedziczony jest w sposób autosomalny dominujący i wywołuje go mutacja protoonkogenu RET. Celem pracy jest ocena częstości występowania oraz kliniczne znaczenie mutacji protoonkogenu RET u chorych z guzem chromochłonnym. Materiał i metody Badania genetyczne w kierunku mutacji protoonkogenu RET przeprowadzono u 106 chorych (średni wiek: 49 ± 14,1 roku, 26M, 80K) z rozpoznanym i potwierdzonym histopatologicznie guzem chromochłonnym. Pacjenci ci byli uprzednio hospitalizowani i leczeni w Klinice Chorób Wewnętrznych i Nadciśnienia Tętniczego Akademii Medycznej w Warszawie w latach 1957–1998 oraz w Klinice Nadciśnienia Tętniczego Instytutu Kardiologii w Warszawie od roku 1980 do 2001. Oceniano również stężenie kalcytoniny (CT), zarówno w warunkach podstawowych, jak i po stymulacji pentagastryną, oraz stężenie parathormonu. Wyniki Obecność mutacji protoonkogenu RET wykazano u 8 chorych (7,4%) - w eksonie 11, w kodonie 634, TGC na CGC u 5 chorych, u pozostałych 3 odpowiednio - w eksonie 11, kodonie 634, TGC na GGC, w eksonie 11, kodonie 634, TGC na TGG oraz w eksonie 13, kodonie 791, TAT na CGC. Nadczynność komórek C potwierdzoną dodatnim testem pentagastrynowym stwierdzono u 5 nosicieli, u 2 chorych wynik testu był wątpliwy, jedynie u 1 chorego stężenie kalcytoniny było prawidłowe. Prawidłowe stężenie CT obserwowano u chorego z mutacją w eksonie 13, kodonie 791, TAT na CGC. U 4 nosicieli potwierdzono histopatologicznie obecność raka rdzeniastego tarczycy (biopsja cienkoigłowa). U 3 chorych wykonano totalną tyroidektomię, dwóch nie wyraziło zgody na dalsze leczenie (w tym jeden z pozytywnym wynikiem biopsji). Pozostali chorzy zostali poinformowani o konieczności totalnej tyroidektomii. U żadnego nosiciela nie stwierdzono nadczynności przytarczyc. Wnioski Wyniki badań autorów potwierdzają doniesienia o konieczności poddawania przesiewowym badaniom genetycznym oceniającym obecność mutacji protoonkogenu RET pacjentów z guzem chromochłonnym. Potwierdzenie nosicielstwa tej mutacji stanowi wskazanie do wykonania totalnej tyroidektomii. Genetyczne badania przesiewowe mogą mieć również znaczenie w wykrywaniu zespołu MEN 2 oraz ustaleniu dalszego postępowania u członków rodzin, u których stwierdza się mutację protoonkogenu RET.Background In patients with pheochromocytoma there may exist more often than expected the autosomal dominant cancer syndrome — multiple endocrine neoplasia type 2 (MEN 2). The susceptibility gene for MEN 2 is the RET proto-oncogene. Germline mutations can be identified by analysis of exons 10, 11, 13–16 of the RET gene. The aim of the study was to evaluate the frequency of these mutations in patients with pheochromocytoma and to report on the conclusions which patients and physicians have drawn. Material and methods We screened for germline mutations in the RET proto-oncogene and clinically evaluated 106 unselected patients with pheochromocytoma (mean age: 49 ± 14,1 years, 26 male, 80 female) histopathologically confirmed, diagnosed and treated in the years 1957–1998 in the Department of Internal Medicine and Hypertension, Warsaw School of Medicine and in the years 1980/81–2001 in the Department of Hypertension, Institute of Cardiology, Warsaw. Determination of calcitonin concentration (CT) was performed in basal conditions and after pentagastrin stimulation; parathormone level was also determined. Results Genetic testing revealed germline mutations in the RET proto-oncogene in 8 patients (7,4%). Carriers had mutation of exon 11, codon 634: TGC to CGC (5 patients), exon 11, codon 634: TGC to GGC (1 patient), exon 11, codon 634: TGC to TGG (1 patient) and in exon 13, codon 791: TAT to TTT (1 patient). Hyperactivity of thyroid C-cells was found in 5 carriers, borderline values of basal and after pentagastrin CT were found in 2 carriers and in only one patient CT concentration was normal. In four patients with RET proto-oncogene mutations, MTC was confirmed histopathologically in fine-needle biopsy. In three of them total thyroidectomy was performed. Two patients refused to be surgically treated (one with positive result of biopsy); the next three RET proto-oncogene germline mutation carriers have been informed that prophylactic total thyroidectomy should be considered. In none of the carriers hyperparathyroidism was observed. Conclusions Our study indicates that patients with pheochromocytoma should be genetically screened for mutations of the RET proto-oncogene. The carriers of these mutations should undergo thyroidectomy. In addition, genetic studies can be useful for the screening of the carriers families

Transgenic LQT2, LQT5, and LQT2-5 rabbit models with decreased repolarisation reserve for prediction of drug-induced ventricular arrhythmias.

BACKGROUND AND PURPOSE Reliable prediction of pro-arrhythmic side effects of novel drug candidates is still a major challenge. Although drug-induced pro-arrhythmia occurs primarily in patients with pre-existing repolarisation disturbances, healthy animals are employed for pro-arrhythmia testing. To improve current safety screening, transgenic long QT (LQTS) rabbit models with impaired repolarisation reserve were generated by overexpressing loss-of-function mutations of human HERG (HERG-G628S, loss of IKr ; LQT2), KCNE1 (KCNE1-G52R, decreased IKs ; LQT5), or both transgenes (LQT2-5) in the heart. EXPERIMENTAL APPROACH Effects of K+ channel blockers on cardiac repolarisation and arrhythmia susceptibility were assessed in healthy wild-type (WT) and LQTS rabbits using in vivo ECG and ex vivo monophasic action potential and ECG recordings in Langendorff-perfused hearts. KEY RESULTS LQTS models reflect patients with clinically "silent" (LQT5) or "manifest" (LQT2 and LQT2-5) impairment in cardiac repolarisation reserve: they were more sensitive in detecting IKr -blocking (LQT5) or IK1 /IKs -blocking (LQT2 and LQT2-5) properties of drugs compared to healthy WT animals. Impaired QT-shortening capacity at fast heart rates was observed due to disturbed IKs function in LQT5 and LQT2-5. Importantly, LQTS models exhibited higher incidence, longer duration, and more malignant types of ex vivo arrhythmias than WT. CONCLUSION AND IMPLICATIONS LQTS models represent patients with reduced repolarisation reserve due to different pathomechanisms. As they demonstrate increased sensitivity to different specific ion channel blockers (IKr blockade in LQT5 and IK1 and IKs blockade in LQT2 and LQT2-5), their combined use could provide more reliable and more thorough prediction of (multichannel-based) pro-arrhythmic potential of novel drug candidates

Pronounced effects of HERG-blockers E-4031 and erythromycin on APD, spatial APD dispersion and triangulation in transgenic long-QT type 1 rabbits.

Prolongation of action potential duration (APD), increased spatial APD dispersion, and triangulation are major factors promoting drug-induced ventricular arrhythmia. Preclinical identification of HERG/IKr-blocking drugs and their pro-arrhythmic potential, however, remains a challenge. We hypothesize that transgenic long-QT type 1 (LQT1) rabbits lacking repolarizing IKs current may help to sensitively detect HERG/IKr-blocking properties of drugs.Hearts of adult female transgenic LQT1 and wild type littermate control (LMC) rabbits were Langendorff-perfused with increasing concentrations of HERG/IKr-blockers E-4031 (0.001-0.1 µM, n=9/7) or erythromycin (1-300 µM, n=9/7) and APD, APD dispersion, and triangulation were analyzed.At baseline, APD was longer in LQT1 than in LMC rabbits in LV apex and RV mid. Erythromycin and E-4031 prolonged APD in LQT1 and LMC rabbits in all positions. However, erythromycin-induced percentaged APD prolongation related to baseline (%APD) was more pronounced in LQT1 at LV base-lateral and RV mid positions (100 µM, LQT1, +40.6 ± 9.7% vs. LMC, +24.1 ± 10.0%, p<0.05) and E-4031-induced %APD prolongation was more pronounced in LQT1 at LV base-lateral (0.01 µM, LQT1, +29.6 ± 10.6% vs. LMC, +19.1 ± 3.8%, p<0.05) and LV base-septal positions. Moreover, erythromycin significantly increased spatial APD dispersion only in LQT1 and increased triangulation only in LQT1 in LV base-septal and RV mid positions. Similarly, E-4031 increased triangulation only in LQT1 in LV apex and base-septal positions.E-4031 and erythromycin prolonged APD and increased triangulation more pronouncedly in LQT1 than in LMC rabbits. Moreover, erythromycin increased APD dispersion only in LQT1, indicating that transgenic LQT1 rabbits could serve as sensitive model to detect HERG/IKr-blocking properties of drugs

Spatial Correlation of Action Potential Duration and Diastolic Dysfunction in Transgenic and Drug-induced LQT2 Rabbits

Focus Issue: Sudden Cardiac DeathInternational audienceEnhanced dispersion of action potential duration (APD) is a major contributor to long-QT-(LQTS)-related arrhythmias.We aimed at investigating spatial correlations of regional heterogeneities in cardiac repolarization and mechanical function in LQTS.Female transgenic LQT2 (n=11) and wildtype (LMC) rabbits (n=9/10 without/with E4031) were subjected to phase contrast MRI to assess regional myocardial velocities. In the same rabbits' hearts, monophasic APDs were assessed in corresponding segments.In LQT2 and E4031 rabbits, APD was longer in all LV segments (p<0.01) and APD dispersion was greater than in LMC (p<0.01). In diastole, peak radial velocities (Vr) were reduced in LQT2 and E4031 compared to LMC in base and mid (cm/s, LQT2, -3.36±0.4, p<0.01, E4031, -3.24±0.6, p<0.0001, LMC, -4.42±0.5) - indicating an impaired diastolic function. Regionally heterogeneous diastolic Vr correlated with APD (LQT2, CC 0.3

Erythromycin-induced changes in triangulation of monophasic action potential in LQT1 and LMC rabbits.

<p>Exemplary, representative MAP triangulation in (A) LQT1 and LMC rabbit at baseline. Exemplary, representative MAP triangulation in (B) LQT1 rabbit and (C) LMC rabbit at baseline and during 300 µM erythromycin. Triangulation of MAP at increasing concentrations of erythromycin in LQT1 (n = 9) and LMC (n = 7) rabbits in (D) LV apex, (E) LV mid, (F) LV base septal, and (G) RV mid position. t =  trend (p<0.1), *p<0.05, **p<0.01.</p