No description available.

This study is based on a proposal concerning the feasibility of using aliphatic tertiary amine N-oxides as antiarrhythmic agent prodrugs. Lignocaine was selected as a candidate for prodrug development, because the N-oxide is a non-active, polar derivative of lignocaine and the drug of choice for ventricular arrhythmia, a symptom associated with ischaemic episodes leading to regions of transiently hypoxic heart tissue. An HPLC analytical method was developed to study the metabolism of lignocaine N-oxide. The rapid and sensitive analysis of lignocaine and its metabolites was demonstrated with good reproducibility, stability and high recovery. In this study, it was identified that lignocaine N-oxide can be reduced to its active parent compound, lignocaine with no other metabolites detected in the absence of oxygen. Under anaerobic conditions, no further metabolism of lignocaine was demonstrated in rat liver microsomes and heart S9 fractions suggesting no secondary metabolites were formed. The reduction of lignocaine N-oxide has been shown to be both enzymic and non-enzymic, NADPH dependent, oxygen sensitive and can be suppressed by CO, CN- and protein denaturation. Under anaerobic conditions, in vitro lignocaine N-oxide reduction was found to occur in NADPH supplemented rat liver homogenates, microsomal suspensions; rat heart homogenates, cytosolic solutions; human phenotyped cytochrome P450 isoforms; purified enzymes- cytochrome P450 reductase, xanthine oxidase, deoxymyoglobin and NADPHI ascorbate reduced protohaem (haemin). This reaction can be suppressed through the chemically mediated decrease ofP450 and bs levels in rat liver microsomes. Previous studies demonstrated that lignocaine N-oxide was non-active in aerobic rat heart in vivo and was potent under ischaemic conditions. In this study, high recovery of lignocaine N-oxide was found in the urine of normal rats suggesting low metabolism of the prodrug in oxic tissues. However, in hypoxic isolated rat hearts, lignocaine N-oxide was found to be reduced to lignocaine. The data presented suggested that the bioactivation of lignocaine N-oxide could be regulated by the prevailing oxygen tension in the ischaemic arrhythmic heart. Essentially the pro drug activation of lignocaine N-oxide may be triggered by the ischaemic state of the heart and terminated as the oxygen content in the heart returns to a more normal level. A controlled release and site-specific active drug delivery of lignocaine N-oxide, a hypoxia-mediated antiarrhythmic agent, may thus be achieved.

Abstract Atrial fibrillation (AF) is a common arrhythmia in the clinical setting with a population prevalence of 1–2%. AF significantly increases the risk of stroke and death, worsens coexistent heart diseases and may leave the patient with disabling symptoms. The treatment of AF consists of the control of the underlying conditions, prevention of complications and symptom relief by controlling heart rate (rate control) or by targeting normal rhythm (rhythm control), with the latter achieved either by antiarrhythmic drug (AAD) therapy or catheter ablation (CA). Ablation therapy has generally been applied and studied after failure of AAD therapy. The aim of this study was to evaluate the safety and efficacy of first-line CA in AF. The other objectives were to assess the safety of continuous warfarin therapy during CA and to identify prognostic markers for treatment outcome. A meta-analysis of all randomised studies and a secondary analysis of one randomised study comparing CA and AAD as first-line therapy were performed. In the first study, ablation therapy reduced AF recurrences more than AAD therapy (HR 0.63) when provided as first-line therapy; the rate of complications was similar with both therapies. Some of the complications of ablation therapy were more serious than those encountered with AADs. The second study revealed that the antiarrhythmic efficacy of ablation therapy was more durable. In the third study, the efficacies of continuous and interrupted warfarin therapy were compared in 228 procedures; both strategies were found to be equally safe during a three month follow-up. Furthermore, an analysis of 2317 AF episodes revealed a new electrocardiographic feature at AF initiation, which was associated with AF relapse after the initiation of therapy. Finally, a thorough echocardiographic examination was performed in 49 patients prior to ablation therapy. Mild diastolic dysfunction was associated with AF recurrence. In conclusion, CA was more effective as a first-line therapy than AADs but may cause more severe complications. Continuous warfarin therapy was found to be safe during CA. New electrocardiographic and echocardiographic markers for treatment outcome were recognised. / Tiivistelmä Eteisvärinä on yleinen rytmihäiriö, jonka esiintyvyys väestössä on 1–2 % luokkaa. Eteisvärinä lisää merkittävästi kuolleisuutta ja aivoinfarktiriskiä, vaikeuttaa muiden sydänsairauksien oireita ja saattaa aiheuttaa invalidisoivia oireita. Eteisvärinän hoito keskittyy liitännäissairauksien hoitoon ja komplikaatioiden estoon sekä oireiden lievitykseen joko syketaajuutta säätämällä (sykkeenhallinta) tai pyrkimällä normaaliin rytmiin (rytminhallinta). Rytminhallinnassa käytetään yleisesti joko rytmihäiriölääkkeitä tai katetriablaatiohoitoa. Eteisvärinän katetriablaatiota on useimmiten käytetty ja tutkittu tilanteessa, jossa rytmihäiriölääkitys on osoittautunut tehottomaksi. Tämän tutkimuksen tavoitteena oli arvioida eteisvärinän katetriablaatiohoidon tehoa ja turvallisuutta ensilinjan hoitona. Muina tavoitteina oli katetriablaation turvallisuuden arviointi jatkuvan varfariinihoidon aikana sekä löytää uusia katetriablaatiohoidon tehoa ennustavia tekijöitä. Teimme meta-analyysin kaikista randomisoiduista tutkimuksista ja sekundaarisen analyysin yhdestä randomisoidusta tutkimuksesta, jotka vertasivat rytmihäiriölääke- ja katetriablaatiohoitoa ensilinjan hoitona. Ensimmäisessä työssä ablaatiohoito esti eteisvärinän uusiutumista tehokkaammin (riskisuhde 0.63), eikä komplikaatioiden yleisyydessä ollut eroa hoitojen välillä. Jotkut ablaatiohoitoon liittyvät komplikaatiot olivat kuitenkin luonteeltaan vakavampia kuin lääkehoidossa. Ablaatiohoidon eteisvärinää estävä vaikutus todettiin pidempikestoiseksi toisessa työssämme. Kolmannessa työssä vertasimme jatkuvaa ja tauotettua varfariinihoitoa 228 ablaatiotoimenpiteen aikana. Molemmat lähestymistavat osoittautuivat yhtä turvallisiksi 3 kuukauden seuranta-aikana. Analysoimme edelleen 2317 eteisvärinäkohtausta ja löysimme osalla potilaista uuden eteisvärinäkohtauksen alkuun liittyvän ominaisuuden, joka oli yhteydessä rytminhallinnan tehottomuuteen. Lisäksi teimme 49 potilaalle laajan sydämen ultraäänitutkimuksen ennen katetriablaatiotoimenpidettä. Diastolisen dysfunktion havaittiin olevan yhteydessä eteisvärinän uusiutumiseen. Yhteenvetona totesimme että katetriablaatiohoito on rytmihäiriölääkehoitoa tehokkaampaa ensilinjan hoitona, mutta siihen mahdollisesti liittyvät komplikaatiot olivat luonteeltaan hankalampia. Jatkuva varfariinihoito todettiin turvalliseksi katetriablaation yhteydessä. Löysimme lisäksi sydänsähkökäyrästä ja sydämen ultraäänitutkimuksesta uusia hoidon tehoa ennustavia tekijöitä.

Bakgrund: Arytmi innebär en avvikande rytm hos hjärtat, alltså att det uppstått en avvikelse i impulsbildning och/eller impulsfortledning. Det kan inverka negativt på livskvalitén, orsaka följdsjukdomar eller leda till livshotande tillstånd. Utöver den konventionella behandlingen finns det behov av ytterligare alternativ. Magnesium är ett essentiellt mineralämne som är viktigt för hjärtats elektrofysiologi. Det har i tidigare studier visat sig att magnesium har haft effekt på postoperativt uppkomna arytmier och att låga nivåer av magnesium hos en frisk population har ökat risken för utvecklandet av olika arytmier. Magnesiums föreslagna antiarytmiska egenskaper är därför av intresse att studera vidare.  Syfte: Syftet med studien är att studera om magnesium har någon antiarytmisk effekt hos individer med arytmi.  Metod: En litteraturstudie genomfördes avseende relevanta artiklar publicerade i databasen PubMed från år 2000 och framåt. En relevansbedömning och kvalitetsgranskning genomfördes med utgångspunkt från Statens beredning för medicinsk och social utvärderings (SBU) metodbok.  Resultat: Tolv artiklar inkluderades i litteraturstudien varav sju uppvisade en antiarytmisk effekt av magnesium. En antiarytmisk effekt vid förmaksflimmer uppvisades i samtliga studier där det administrerades mer än 4 gram intravenöst magnesium. Eftersom magnesium i olika former har olika biotillgänglighet skulle formen eventuellt också kunna vara en bidragande faktor till effekten men studiematerialet var för litet gällande olika magnesiumformer. Vidare går det inte att särskilja om magnesium har olika effekt på olika arytmier då representationen av respektive arytmi var för liten. Slutsats: Magnesium har en antiarytmisk effekt vid administrering över 4 gram intravenöst. Huruvida detta gäller för fler arytmier än förmaksflimmer framkommer inte av denna litteraturstudie. Det finns ett behov av fler studier för att dels undersöka vilken som är den eventuella optimala formen och dosen av magnesium, dels för att utreda vilka typer av arytmier som verkar mottagliga för magnesium som behandlingsalternativ. / Background: Arrhythmia means a deviating rhythm in the heart, either in impulse formation and/or impulse conduction. It can adversely affect the quality of life, cause sequelae or lead to life-threatening conditions. In addition to the conventional treatment, there is a need for alternatives. Magnesium is an essential mineral that is important for the electrophysiology of the heart. Previous studies have shown that magnesium has had an effect on postoperative arrhythmias and that low levels of magnesium in a healthy population have increased the risk of developing various arrhythmias. The proposed antiarrhythmic properties of magnesium are therefore of interest for further study.  Aim: The aim of the study is to investigate whether magnesium has any antiarrhythmic effect in individuals with arrhythmias.  Methods: A literature study was conducted regarding relevant articles published in the PubMed database from the year 2000 and until today. Relevance assessment and quality review were carried out on the basis of  Swedish Agency for Health Technology Assessment and Assessment of Social Services (SBU) method book.  Results: Twelve articles were included in the literature study, seven of which showed an antiarrhythmic effect. An antiarrhythmic effect in atrial fibrillation was shown in all studies where more than 4 grams of intravenous magnesium was administered. Since magnesium in different forms has different bioavailability, the form could possibly also be a contributing factor to the effect, but the study material was too small for different forms of magnesium. Furthermore, it is not possible to distinguish whether magnesium has different effects on different arrhythmias as the representation of each arrhythmia was too small.  Conclusions: Magnesium has antiarrhythmic effect when administrated in excess of 4 gram intravenously. Whether this applies to more arrhythmias than atrial fibrillation does not emerge from this literature study. There is a need for more studies to investigate the possible optimal form and dose of magnesium, and to investigate which types of arrhythmias seem susceptible to magnesium as a treatment alternative.

Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2018-11-27T14:33:23Z No. of bitstreams: 2 Tese - Priscilla Regina Nasciutti - 2018.pdf: 3399119 bytes, checksum: 6cdbfee6b9cc1dffd41d48f821659dc3 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2018-11-28T09:56:34Z (GMT) No. of bitstreams: 2 Tese - Priscilla Regina Nasciutti - 2018.pdf: 3399119 bytes, checksum: 6cdbfee6b9cc1dffd41d48f821659dc3 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-11-28T09:56:35Z (GMT). No. of bitstreams: 2 Tese - Priscilla Regina Nasciutti - 2018.pdf: 3399119 bytes, checksum: 6cdbfee6b9cc1dffd41d48f821659dc3 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-02-23 / Fundação de Amparo à Pesquisa do Estado de Goiás - FAPEG / Mitral valve disease (MVD) is characterized by thickening in the valvular leaflets and may lead to heart failure. Pharmacological treatment of the disease with vasodilators, positive inotropes and diuretics is used in conjunction with dietary management. Omega 3 (ω-3) supplementation has been associated with modulation of blood pressure (BP) and heart rate, improvement of Doppler echocardiography, antiarrhythmic, anti-inflammatory and antidysiphyde effects. In the absence of prospective clinical studies, the objective was to evaluate the influence of ω-3 supplementation in dogs with MVD. For this purpose, 41 dogs were followed up every three months for 12 months by means of clinical evaluation, BP measurement, electrocardiography, Doppler echocardiography, chest radiography, laboratory tests, dosages of inflammatory mediators and cardiac biomarker. The dogs were classified in stages B1, B2 and C, according to the ACVIM consensus. Dogs were randomly divided into the ω-3 group, which received food for dogs with heart diseases supplemented with ω-3 and control group (even food without supplementation). In stage B1 only dogs from the ω-3 group were evaluated. At the end of 12 months, no changes were observed in the parameters evaluated. In dogs stage B2 and C, there was an increase in the serum levels of inflammatory mediators, in a larger amplitude in the control group. The ω-3 preserved body condition score, muscle condition score and reduced by 2.96 times the chance of developing arrhythmias. The DIVEdN and VHS measurements were higher in the control group and correlated with NTproBNP cardiac biomarker concentrations. It is concluded that the supplementation with ω-3 in patients in classes B2 and C, maintains the body condition, helps reduce volume overload, has an antiarrhythmic effect and keeps dogs with MVD in the firsts stages of the disease. / A doença valvar mitral (DVM) é caracterizada pelo espessamento nos folhetos valvares e pode levar ao desenvolvimento de insuficiência cardíaca. O tratamento farmacológico da doença com vasodilatadores, inotrópicos positivos e diuréticos é utilizado em conjunto com o manejo dietético. A suplementação com ômega 3 (ω-3) tem sido associada à modulação da pressão arterial (PA) e da frequência cardíaca, melhora de índices ecodopplercardiográficos, efeitos antiarrítmico, antinflamatório e antidislipidêmico. Diante da ausência de estudos clínicos prospectivos, o objetivo foi avaliar a influência da suplementação com ω-3 em cães portadores de DVM. Para tanto, 41 cães foram acompanhados trimestralmente durante 12 meses por meio de avaliação clínica, mensuração de PA, eletrocardiografia, ecodopplercardiografia, radiografia torácica, exames laboratoriais, dosagens de mediadores inflamatórios e de biomarcador cardíaco. Os cães foram classificados nos estágios B1, B2 e C, segundo o consenso do ACVIM. De maneira aleatória os cães foram dividis no grupo ω-3, que recebeu alimento para cães cardiopatas com suplementação com ω-3 e grupo controle (mesmo alimento sem a suplementação). No estágio B1 foram avaliados apenas os cães do grupo ω- 3. Ao final de 12 meses, não foram observadas alterações nos parâmetros avaliados. Nos cães estágio B2 e C ocorreu aumento nos níveis séricos de mediadores inflamatórios, em maior amplitude no grupo controle. O ω-3 preservou o ECC, ECM e reduziu em 2,96 vezes a chance de desenvolvimento de arritmias. As medidas DIVEdN e VHS foram superiores no grupo controle e se correlacionaram às concentrações do biomarcador cardíaco NT-proBNP. Concluise que a suplementação com ω-3 em pacientes nas classes B2 e C, atua mantendo a condição corporal, auxilia na redução da sobrecarga volumétrica, apresenta efeito antiarrítmico e mantem os cães portadores de DVM em estágios mais brandos da doença.

Aim: Isolated papillary muscles and enzymatically dissociated myocytes of guinea-pig hearts are routinely used for experimental cardiac research. The aim of our study is to investigate adult mammalian ventricular slices as an alternative preparation. Method: Vibratome cut ventricular slices (350 μm thick) were examined histologically and with 2-photon microscopy for fibre orientation. Intracellular action potentials were recorded with conventional glass microelectrodes, extracellular potentials were measured with tungsten platinum electrodes and multi-electrode arrays (MEA). Results: Dominant direction of fibre orientation was absent in vertical and horizontal transmural slices, but was longitudinal in tangential slices. Control action potential duration (APD90, 169.9 ± 4 ms) and drug effects on this parameter were similar to papillary muscles. The L-type Ca-channel blocker nifedipine shortened APD90 with a half maximal effective concentration (EC50) of 4.5 μM. The IKr blocker E4031 and neuroleptic drug risperidone prolonged APD90 with EC50 values of 31 nM and 0.67 μM, respectively. Mapping field potentials on multi-electrode arrays showed uniform spread of excitation with a mean conduction velocity of 0.47 m ⋅ s-1. Conclusion: Slices from adult mammalian hearts could become a useful routine model for electrophysiological and pharmacological research. / Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Objectif: Déterminer si l’efficacité de l’amiodarone pour le maintien du rythme sinusal varie selon la fonction systolique ventriculaire gauche. Contexte: Malgré un profil de sécurité établi en insuffisance cardiaque, nous ignorons si l’efficacité de l’amiodarone et son impact sur différentes issues cardiovasculaires sont modulés par la fonction ventriculaire gauche. Méthode: Nous avons effectué une analyse combinée de 3307 patients (âgés de 68,0±0,9 ans ; 31,1% de femmes) recrutés dans les études AFFIRM et AF-CHF qui ont été randomisés au contrôle du rythme par l’amiodarone (N=1107) ou au contrôle de la fréquence cardiaque (N=2200). Résultats: Chez les patients sous amiodarone, la survie sans fibrillation auriculaire était de 84% et de 45% à 1 et 5 ans respectivement, sans égard à la fraction d’éjection ventriculaire gauche (P=0,8754, ajusté). De façon similaire, la proportion moyenne ajustée de temps en fibrillation auriculaire (15,0±1,8%) n’a pas été influencée par la fraction d’éjection (P=0,6094). Durant le suivi, 1963 patients (59,4%) ont requis au moins une hospitalisation, incluant 1401 (42,6%) patients hospitalisés pour cause cardiovasculaire. Les taux ajustés d’hospitalisation pour toutes causes et pour cause cardiovasculaire étaient similaires entre les patients sous amiodarone et ceux dans le groupe de contrôle de la fréquence dans l’ensemble de la population ainsi que dans les sous-groupes de patients avec et sans dysfonction ventriculaire gauche sévère. De façon similaire, les taux ajustés de mortalité globale et cardiovasculaire étaient similaires entre chez les patients sous amiodarone et ceux traités par le contrôle de la fréquence dans l’ensemble de la population ainsi que dans les sous-groupes de patients avec et sans dysfonction ventriculaire gauche sévère. Conclusions: L’efficacité de l’amiodarone pour le maintien du rythme sinusal n’est pas influencée par la fonction ventriculaire gauche. Le contrôle du rythme avec l’amiodarone s’associe à des taux de mortalité et d’hospitalisation comparables au contrôle de la fréquence à la fois chez les patients avec et sans dysfonction ventriculaire gauche sévère. / Objectives: To determine whether amiodarone’s efficacy in maintaining sinus rhythm varies according to left ventricular systolic function. Background: Despite amiodarone’s established safety profile in heart failure, it is unknown whether its impact on cardiovascular outcomes is modulated by ventricular function. Methods: We conducted a pooled analysis of 3307 patients (age 68.0±0.9 years; 31.1% female) enrolled in AFFIRM and AF-CHF trials who were randomized to rhythm control with amiodarone (N=1107) or rate control (N=2200). Results: In amiodarone-treated patients, freedom from recurrent atrial fibrillation was 84% and 45% at 1 and 5 years, respectively, with no differences according to left ventricular function (adjusted P=0.8754). Similarly, the adjusted mean proportion of time in atrial fibrillation (15.0±1.8%) did not vary according to ventricular function (P=0.6094). During follow-up, 1963 (59.4%) patients required at least one hospitalization, with 1401 (42.6%) patients hospitalized for a cardiovascular reason. Adjusted all-cause and cardiovascular hospitalization rates were similar with amiodarone versus rate control in the overall population and in subgroups of patients with and without severe left ventricular dysfunction. Similarly adjusted all-cause and cardiovascular mortality rates were similar with amiodarone versus rate control, overall and in subgroups of patients with and without severe left ventricular dysfunction. Conclusions: Amiodarone’s efficacy in maintaining sinus rhythm and reducing the burden of atrial fibrillation is similar in patients with and without left ventricular dysfunction. Rhythm control with amiodarone was associated with similar mortality and hospitalisation rates when compared to rate control in patients with and without severe left ventricular dysfunction.

Objectif: Déterminer si l’efficacité de l’amiodarone pour le maintien du rythme sinusal varie selon la fonction systolique ventriculaire gauche. Contexte: Malgré un profil de sécurité établi en insuffisance cardiaque, nous ignorons si l’efficacité de l’amiodarone et son impact sur différentes issues cardiovasculaires sont modulés par la fonction ventriculaire gauche. Méthode: Nous avons effectué une analyse combinée de 3307 patients (âgés de 68,0±0,9 ans ; 31,1% de femmes) recrutés dans les études AFFIRM et AF-CHF qui ont été randomisés au contrôle du rythme par l’amiodarone (N=1107) ou au contrôle de la fréquence cardiaque (N=2200). Résultats: Chez les patients sous amiodarone, la survie sans fibrillation auriculaire était de 84% et de 45% à 1 et 5 ans respectivement, sans égard à la fraction d’éjection ventriculaire gauche (P=0,8754, ajusté). De façon similaire, la proportion moyenne ajustée de temps en fibrillation auriculaire (15,0±1,8%) n’a pas été influencée par la fraction d’éjection (P=0,6094). Durant le suivi, 1963 patients (59,4%) ont requis au moins une hospitalisation, incluant 1401 (42,6%) patients hospitalisés pour cause cardiovasculaire. Les taux ajustés d’hospitalisation pour toutes causes et pour cause cardiovasculaire étaient similaires entre les patients sous amiodarone et ceux dans le groupe de contrôle de la fréquence dans l’ensemble de la population ainsi que dans les sous-groupes de patients avec et sans dysfonction ventriculaire gauche sévère. De façon similaire, les taux ajustés de mortalité globale et cardiovasculaire étaient similaires entre chez les patients sous amiodarone et ceux traités par le contrôle de la fréquence dans l’ensemble de la population ainsi que dans les sous-groupes de patients avec et sans dysfonction ventriculaire gauche sévère. Conclusions: L’efficacité de l’amiodarone pour le maintien du rythme sinusal n’est pas influencée par la fonction ventriculaire gauche. Le contrôle du rythme avec l’amiodarone s’associe à des taux de mortalité et d’hospitalisation comparables au contrôle de la fréquence à la fois chez les patients avec et sans dysfonction ventriculaire gauche sévère. / Objectives: To determine whether amiodarone’s efficacy in maintaining sinus rhythm varies according to left ventricular systolic function. Background: Despite amiodarone’s established safety profile in heart failure, it is unknown whether its impact on cardiovascular outcomes is modulated by ventricular function. Methods: We conducted a pooled analysis of 3307 patients (age 68.0±0.9 years; 31.1% female) enrolled in AFFIRM and AF-CHF trials who were randomized to rhythm control with amiodarone (N=1107) or rate control (N=2200). Results: In amiodarone-treated patients, freedom from recurrent atrial fibrillation was 84% and 45% at 1 and 5 years, respectively, with no differences according to left ventricular function (adjusted P=0.8754). Similarly, the adjusted mean proportion of time in atrial fibrillation (15.0±1.8%) did not vary according to ventricular function (P=0.6094). During follow-up, 1963 (59.4%) patients required at least one hospitalization, with 1401 (42.6%) patients hospitalized for a cardiovascular reason. Adjusted all-cause and cardiovascular hospitalization rates were similar with amiodarone versus rate control in the overall population and in subgroups of patients with and without severe left ventricular dysfunction. Similarly adjusted all-cause and cardiovascular mortality rates were similar with amiodarone versus rate control, overall and in subgroups of patients with and without severe left ventricular dysfunction. Conclusions: Amiodarone’s efficacy in maintaining sinus rhythm and reducing the burden of atrial fibrillation is similar in patients with and without left ventricular dysfunction. Rhythm control with amiodarone was associated with similar mortality and hospitalisation rates when compared to rate control in patients with and without severe left ventricular dysfunction.

Abstract Osteoclasts are multinuclear bone degrading cells differentiated from monocytes which can be isolated from bone marrow and peripheral blood. Complex signaling between osteoclast precursors and other bone cells, such as mesenchymal stromal cells (MSC) occurs during the differentiation. Gap junctional communication (GJC) is one of the mechanisms in the cell fusion. GJC can be modulated with several substances such as the specific GJC stimulators, antiarrhythmic peptides (AAP). Due to their promising clinical value in the treatment of cardiac disorders, the effects of AAPs in cardiac tissue are studied extensively. This study was conducted in order to investigate the roles of GJC and AAPs in bone cell cultures. Further, the contribution of the MSCs on the effects of AAPs was studied along with comparison of two types of osteoclastogenesis cultures with differing quantities of MSCs. GJC in osteoclastogenesis was studied with both GJC inhibitors and stimulators in mouse monocyte line RAW 264.7 cells and primary cultures with bone marrow hematopoietic cells. The following studies were made with human monocytes from peripheral blood and bone marrow where the effects of AAP10 were investigated in normal and acidic environments. In addition, comparison of osteoclastogenesis from bone marrow and peripheral blood monocytes was carried out in in vitro cell cultures on bovine or human bone slices. The cells were analyzed with regard to multinuclearity, bone resorption and the expression of several osteoclast markers. The results show that GJC is utilized in osteoclastogenesis, but it is not indispensable. GJC in monocytes can be stimulated with the AAPs during osteoclastogenesis, but the effects depend on the culture conditions as well as on the presence of MSCs in the culture. The AAPs can also activate the MSCs leading to indirect regulation of osteoclastogenesis, as the MSCs produce several molecules affecting the differentiation. Further, monocytes from peripheral blood showed increased potential for osteoclastogenic differentiation compared to bone marrow derived monocytes. This can be explained by the presence of the osteoclastogenesis-controlling MSCs in the bone marrow culture, while the peripheral blood cultures contain only few of these cells and thus lack their regulatory effects. / Tiivistelmä Osteoklastit ovat monitumaisia luuta hajottavia soluja, jotka ovat erilaistuneet monosyyteistä. Monosyyttejä voidaan eristää luuytimestä tai perifeerisestä verestä. Erilaistumisen aikana osteoklastien esiastesolujen sekä muiden luusolujen, kuten mesenkymaalisten stroomasolujen (MSC) välillä tapahtuu monimutkaista signalointia. Aukkoliitoskommunikointi (GJC) on eräs solufuusiossa tapahtuvista mekanismeista. GJC:tä voidaan muunnella useilla aineilla, esimerkiksi spesifisillä stimulaattoreilla, antiarytmisillä peptideillä (AAP). AAP-yhdisteiden vaikutuksia on tutkittu laajalti sydänkudoksessa johtuen niiden lupaavista kliinisistä ominaisuuksista sydänperäisten oireiden hoidossa. Tämän tutkimuksen tarkoituksena oli selvittää GJC:n ja AAP-yhdisteiden roolia luusoluviljelmissä. Lisäksi tutkittiin MSC-solujen osallistumista AAP-yhdisteiden vaikutuksiin sekä vertailtiin kahta erilaista osteoklastogeneesiviljelmää, joissa oli eri määrä MSC-soluja. GJC:tä osteoklastogeneesissä tutkittiin sekä sitä estävillä että stimuloivilla yhdisteillä hiiren monosyyttilinjan RAW 264.7 -soluissa sekä luuytimen hematopoieettisten solujen primääriviljelmissä. Seuraavat tutkimukset tehtiin ihmisen luuytimen ja perifeerisen veren monosyyteillä, ja niissä selvitettiin AAP10-yhdisteen vaikutuksia fysiologisissa sekä happamissa olosuhteissa. Lisäksi vertailtiin luuytimen ja perifeerisen veren monosyyttien osteoklastogeneesiä. In vitro -soluviljelmät tehtiin naudan tai ihmisen luulastujen päällä, ja soluista analysoitiin monitumaisuus, luun resorptio sekä useiden osteoklastimarkkereiden ilmentyminen. Tulokset osoittavat, että GJC:tä hyödynnetään osteoklastogeneesissä, mutta se ei ole korvaamaton mekanismi. GJC:tä voidaan stimuloida AAP-yhdisteillä osteoklastogeneesin aikana, mutta vaikutukset riippuvat viljelyolosuhteista sekä MSC-solujen läsnäolosta. AAP-yhdisteet voivat aktivoida myös MSC-soluja johtaen osteoklastogeneesin epäsuoraan säätelyyn, kun MSC-solut tuottavat useita erilaistumiseen vaikuttavia molekyylejä. Lisäksi perifeerisen veren monosyyteillä havaittiin korkeampi osteoklastogeeninen erilaistumispotentiaali verrattuna luuytimen monosyytteihin. Tulokset voidaan selittää osteoklastogeneesiä säätelevien MSC-solujen läsnäololla luuydinviljelmissä, kun taas perifeerisen veren monosyyttiviljelmissä näitä soluja on vain vähän, jolloin myös niiden säätelyominaisuudet puuttuvat.

Cardiac arrhythmias are disorders of the electrical system of the heart and an often clinically-challenging group of disorders. Atrial fibrillation (AF) is the most common cardiac arrhythmia in the general population; it is associated with significant morbidity and mortality. Available antiarrhythmic drugs (AADs) for the treatment of AF are older molecules with sub- optimal efficacy and safety profiles. Recent advances in basic electrophysiology and the development of sophisticated mathematical modeling approaches could help in expanding our understanding of the basic mechanisms of AF and assist in the development of novel AF- selective AADs. The purpose of this thesis was to utilize computational approaches to the understanding of the consequences and opportunities of ion channel properties, with a special emphasis on AF. The cardiac action potential is the basic functional unit of the electrical system of the heart and is the manifestation of coordinated current fluxes through specialized proteins known as ion channels. Antiarrhythmic drugs act through modulation of ion channel properties. We hypothesized that mathematical modeling could be used to study and optimize the pharmacodynamic properties of AADs for the treatment of AF. We demonstrated that the pharmacodynamic properties (binding/unbinding characteristics) of a state-dependent Na+- channel blocker modulate the drug’s anti-/proarrhythmic actions with inactivated-state blockers being optimally AF-selective. The optimized drug’s selectivity for AF was the result of its rate- selectivity (stronger effects at fast vs slow cardiomyocyte activation rates) with relatively mild atrial-selective (stronger effects in atrial vs ventricular cardiomyocytes) actions. We found that the optimally AF-selective Na+-channel blocker had sub-optimal anti-AF efficacy, but that slightly less selective drugs had favorable AF-termination rates. We then sought to explore potential current-block combinations with synergistic AF- selective properties. Using mathematical modeling and laboratory experiments, we demonstrated that the combination of optimized state-dependent Na+-channel block and K+- channel block had synergistic effects, significantly augmenting AF termination rates for any level of AF-selectivity vs pure Na+-channel block. The mechanisms of these synergistic effects were found to be mediated by the functional interaction between the action potential prolonging- v effects of K+-channel block, the Na+-channel blocker’s voltage-dependent binding/unbinding properties and the Na+ channel’s inactivation characteristics, highlighting the non-linear nature of the cardiac action potential’s dynamics. Traditional K+ currents targeted by AADs have significant ventricular proarrhythmic liabilities. Using recent experimental observations, we updated the mathematic formulation for the inactivation dynamics of the ultra-rapid delayed-rectifier K+ current (IKur), an atrial-specific current. Using this model, we showed that, contrary to what had been proposed in the published literature, IKur rate-dependent properties are mediated by its activation properties with minimal contribution from inactivation, under physiological conditions. We also demonstrated that the contribution of IKur to action potential repolarization is preserved, or even increased, in the setting of electrical remodeling-induced IKur downregulation. Finally, we described the mechanisms of the forward rate-dependent of IKur block, mediated by functional non-linear interactions with the rapid delayed inward-rectifier K+ current (IKr), the only K+ current with such properties. Until recently, fibroblasts were considered to be electrically inactive. More recently, experimental work demonstrated the presence of functional ionic current on the fibroblast and possible cardiomyocyte-fibroblast coupling. Here, we described a novel kind of heart failure- induced electrical remodeling involving the fibroblasts ion channels. This was characterized by downregulation of the fibroblast voltage-dependent K+ current (IKv,fb) and upregulation of the fibroblast inward-rectifier K+ current (IKir,fb). We then implemented our experimental findings into a mathematical model of cardiomyocyte-fibroblast coupling and found fibroblast electrical remodeling to have significant effects on the cardiomyocyte’s electrophysiological properties. In a 2-dimension model of simulated AF, downregulation of IKv,fb had an antiarrhythmic effect whereas IKir,fb upregulation was found to be proarrhythmic. The studies presented here utilized mathematical modeling to study non-linear systems in cardiac electrophysiology to tackle questions that would have been difficult to approach with traditional laboratory-based experimentation. They also showcased how theoretical results can help orient and receive confirmation with subsequent experimental work or, conversely, novel experimental findings results be implemented into a mathematical model to investigate potential consequences. Mathematical modeling is a promising tool to help in studying the complex and vi non-linear effects of pharmacological modulation of ion channel properties and assist in the development of optimized antiarrhythmics for the treatment of AF, a major unmet need in clinical medicine. As models increase in sophistication to better represent the cardiomyocyte’s electrophysiology, they will almost certainly play an ever-growing role in expanding our understanding of the mechanisms of complex arrhythmias. / Les arythmies cardiaques représentent une famille de pathologies du système électrique cardiaque. La fibrillation auriculaire (FA), est l’arythmie cardiaque la plus fréquente dans la population générale et est associée à un fardeau de morbidité et mortalité cardiovasculaire important. Les médicaments antiarythmiques utilisées dans le traitement de la FA sont de vieilles molécules avec une efficacité sous-optimale et des effets secondaires importants. Les avancées récentes en électrophysiologie cardiaque fondamentale et le développement d’outils de modélisation mathématique ont le potentiel d’élargir notre compréhension des mécanismes pathophysiologiques en FA et contribuer au développement de nouveaux médicaments antiarythmiques optimisés pour le traitement de la FA. L’objectif global de cette thèse est d’utiliser les méthodes de modélisation mathématique pour étudier les conséquences et opportunités thérapeutiques de la modulation des canaux ioniques cardiaques, avec une emphase sur la FA. Le potentiel d’action cardiaque est l’unité fonctionnelle de base du système électrique cardiaque ; il est le résultat du flux coordonné de courants électriques à travers de protéines spécialisées, les canaux ioniques. Les molécules antiarythmiques agissent à travers la modulation des canaux ioniques cardiaques. Nous avons posé l’hypothèse que des modèles mathématiques pourraient être utilisés pour étudier et optimiser les propriétés pharmacodynamiques d’un médicament antiarythmique pour le traitement de la FA. Nous avons démontré que les propriétés pharmacodynamiques (propriétés de liage et déliage) d’un bloqueur des canaux Na+ état-dépendant modulent les effets anti- et pro-arythmiques de la molécule ; un bloqueur Na+ sélectif pour l’état inactivé du canal serait maximalement FA-sélectif. Cette sélectivité pour la FA est la conséquence de la sélectivité pour la fréquence (effet thérapeutique plus important à des fréquences d’activation du cardiomyocyte élevées vs basses) avec une contribution relativement faible de la sélectivité auriculaire (effet thérapeutique plus important sur les cardiomyocytes auriculaires vs ventriculaires). Par la suite, nous avons exploré des combinaisons de bloqueurs ioniques ayant des propriétés anti-FA synergiques. En utilisant des modèles mathématiques et des expériences en laboratoire, nous avons démontré que la combinaison d’un bloqueur des canaux Na+ et d’un iii bloqueur des canaux K+ a des effets synergiques, augmentant de façon importante l’efficacité anti-FA pour un même degré de sélectivité vs un bloqueur des canaux Na+ seul. Le mécanisme de synergie a été élucidé et consiste d’effets fonctionnels médiés par l’interaction du prolongement de la durée du potentiel d’action causé par le bloque des canaux K+, les propriétés voltage-dépendantes du liage et déliage du bloqueur des canaux Na+ ainsi que des propriétés d’inactivation des canaux Na+, démontrant la nature hautement non-linéaire des dynamiques du potentiel d’action cardiaque. Les courants K+ ciblés par les médicaments antiarythmiques ont des effets proarythmiques ventriculaires importants. En utilisant des données expérimentales récentes, nous avons proposé une formulation mise à jour des dynamiques d’inactivation du courant K+ IKur, un courant auriculo-sélectif. En utilisant ce modèle, nous avons démontré que, contrairement à ce qui avait été précédemment proposé, les propriétés fréquence-dépendantes du courant IKur dépendent de ses caractéristiques d’activation avec une contribution négligeable de ses propriétés d’inactivation, sous conditions physiologiques normales. Nous avons également démontré que la contribution de IKur à la repolarisation du potentiel d’action est maintenue, voir augmentée, dans le contexte de la diminution de IKur en situation de remodelage électrique induit par la FA. Finalement, nous avons décrit le mécanisme qui sous-tend les propriétés fréquence-dépendantes du bloque de IKur, l’unique courant K+ avec de telles caractéristiques. Jusqu’à très récemment, les fibroblastes cardiaques étaient considérés comme électriquement inactifs. Des travaux expérimentaux ont démontré la présence de canaux ioniques sur la surface de ces fibroblastes ainsi que la possibilité de couplage électrique entre cardiomyocytes et fibroblastes. Nous avons décrit un nouveau type de remodelage électrique en situation d’insuffisance cardiaque, le remodelage des courants ioniques des fibroblastes cardiaques. Ce remodelage est caractérisé par une diminution du courant K+ voltage-dépendant IKv,fb et une augmentation du courant K+ IKir,fb. Nous avons par la suite incorporé ces trouvailles expérimentales dans un modèle mathématique simulant l’interaction électrique entre cardiomyocytes et fibroblastes et montré que le remodelage électrique des fibroblastes peut avoir un impact important sur les propriétés électrophysiologiques des cardiomyocytes. Dans iv un modèle 2-dimensionel de FA, nous avons trouvé que la diminution de IKv,fb a un effet antiarythmique alors que l’augmentation de IKir,fb a des effets proarythmiques. Les études ici présentées utilisent les méthodes de modélisation mathématique pour l’étude de systèmes non-linéaires en électrophysiologie cardiaque et aborder des avenues de recherche difficilement accessibles aux méthodes de laboratoire traditionnelles. Elles démontrent également comment des résultats théoriques peuvent orienter et trouver confirmation dans des travaux expérimentaux subséquents ou, à l’inverse, des trouvailles expérimentales peuvent être implémentées dans les modèles mathématiques pour investiguer les conséquences de celles-ci. La modélisation mathématique est un outil prometteur pour l’étude des effets complexes et non-linéaires de la modulation pharmacologique des canaux ioniques et ainsi contribuer au développement de médicaments antiarythmiques optimisés pour le traitement de la FA, un besoin clinique majeur.