Drugs targeting atrial-specific ion channels, Kv1.5 or Kir3.1/3.4, are being developed as new therapeutic strategies for atrial fibrillation. However, current preclinical studies carried out in non-cardiac cell lines or animal models may not accurately represent the physiology of a human cardiomyocyte (CM). In the current study, we tested whether human embryonic stem cell (hESC)-derived atrial CMs could predict atrial selectivity of pharmacological compounds. By modulating retinoic acid signaling during hESC differentiation, we generated atrial-like (hESC-atrial) and ventricular-like (hESC-ventricular) CMs. We found the expression of atrial-specific ion channel genes, KCNA5 (encoding Kv1.5) and KCNJ3 (encoding Kir 3.1), in hESC-atrial CMs and further demonstrated that these ion channel genes are regulated by COUP-TF transcription factors. Moreover, in response to multiple ion channel blocker, vernakalant, and Kv1.5 blocker, XEN-D0101, hESC-atrial but not hESC-ventricular CMs showed action potential (AP) prolongation due to a reduction in early repolarization. In hESC-atrial CMs, XEN-R0703, a novel Kir3.1/3.4 blocker restored the AP shortening caused by CCh. Neither CCh nor XEN-R0703 had an effect on hESC-ventricular CMs. In summary, we demonstrate that hESC-atrial CMs are a robust model for pre-clinical testing to assess atrial selectivity of novel antiarrhythmic drugs.

Background-Neutrophils may be an important source of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9), two matrix-degrading enzymes thought to be critical in the formation of an abdominal aortic aneurysm (AAA). The purpose of this investigation was to test the hypothesis that neutrophil depletion would limit experimental AAA formation by altering one or both of these enzymes. Methods and Results-Control, rabbit serum-treated (RS; nϭ27) or anti-neutrophil-antibody-treated (anti-PMN; nϭ25) C57BL/6 mice underwent aortic elastase perfusion to induce experimental aneurysms. Anti-PMN-treated mice became neutropenic (mean, 349 cells/L), experiencing an 84% decrease in the circulating absolute neutrophil count (PϽ0.001) before elastase perfusion. Fourteen days after elastase perfusion, control mice exhibited a mean aortic diameter (AD) increase of 104Ϯ14% (PϽ0.0001), and 67% developed AAAs, whereas anti-PMN-treated mice exhibited a mean AD increase of 42Ϯ33%, with 8% developing AAAs. The control group also had increased tissue neutrophils (20.3 versus 8.6 cells per 5 high-powered fields [HPFs]; Pϭ0.02) and macrophages (6.1 versus 2.1 cells per 5 HPFs, Pϭ0.005) as compared with anti-PMN-treated mice. There were no differences in monocyte chemotactic protein-1 or macrophage inflammatory protein-1␣ chemokine levels between groups by enzyme-linked immunosorbent assay. Neutrophil collagenase (MMP-8) expression was detected only in the 14-day control mice, with increased MMP-8 protein levels by Western blotting (Pϭ0.017), and MMP-8 -positive neutrophils were seen almost exclusively in this group. Conversely, there were no statistical differences in MMP-2 or MMP-9 mRNA expression, protein levels, enzyme activity, or immunostaining patterns between groups. When C57BL/6 wild-type (nϭ15) and MMP-8 -deficient mice (nϭ17) were subjected to elastase perfusion, however, ADs at 14 days were no different in size (134Ϯ7.9% versus 154Ϯ9.9%; Pϭ0.603), which suggests that MMP-8 serves only as a marker for the presence of neutrophils and is not critical for AAA formation. Conclusions-Circulating

There is a clear unmet medical need for new pharmacologic therapies for the treatment of atrial fibrillation (AF) with improved efficacy and safety. This article reviews the development of new and novel Kv1.5/ultra-rapid delayed-rectifier current (I Kur) inhibitors and presents evidence that Kv1.5 modulation provides an atrial-selective mechanism for treating AF. Academia and industry have invested heavily in Kv1.5 (>500 scientific publications and >50 patents published since 1993); however, to realize the full value of this therapeutic drug target, clinical efficacy and safety data are required for a selective Kv1.5 modulator. The reward for demonstrating clinical efficacy and safety in a pivotal Phase 3 trial, on regulatory approval, is "first in class" status.

Inhibition of cytokine-induced NO expression in RA-SMCs is associated with a selective, dose-dependent increase in MMP-9 expression and synthesis. These findings suggest that alterations in local NO synthesis may influence MMP-9-dependent vessel wall damage.

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Background and Purpose Inhibition of the G‐protein gated ACh‐activated inward rectifier potassium current, IK,ACh may be an effective atrial selective treatment strategy for atrial fibrillation (AF). Therefore, the anti‐arrhythmic and electrophysiological properties of a novel putatively potent and highly specific IK,ACh inhibitor, XAF‐1407 (3‐methyl‐1‐[5‐phenyl‐4‐[4‐(2‐pyrrolidin‐1‐ylethoxymethyl)‐1‐piperidyl]thieno[2,3‐d]pyrimidin‐6‐yl]azetidin‐3‐ol), were characterised for the first time in vitro and investigated in horses with persistent AF. Experimental Approach The pharmacological ion channel profile of XAF‐1407 was investigated using cell lines expressing relevant ion channels. In addition, eleven horses were implanted with implantable cardioverter defibrillators enabling atrial tachypacing into self‐sustained AF. The electrophysiological effects of XAF‐1407 were investigated after serial cardioversions over a period of 1 month. Cardioversion success, drug‐induced changes of atrial tissue refractoriness, and ventricular electrophysiology were assessed at baseline (day 0) and days 3, 5, 11, 17, and 29 after AF induction. Key Results XAF‐1407 potently and selectively inhibited Kir3.1/3.4 and Kir3.4/3.4, underlying the IK,ACh current. XAF‐1407 treatment in horses prolonged atrial effective refractory period as well as decreased atrial fibrillatory rate significantly (~20%) and successfully cardioverted AF, although with a decreasing efficacy over time. XAF‐1407 shortened atrioventricular‐nodal refractoriness, without effect on QRS duration. QTc prolongation (4%) within 15 min of drug infusion was observed, however, without any evidence of ventricular arrhythmia. Conclusion and Implications XAF‐1407 efficiently cardioverted sustained tachypacing‐induced AF of short duration in horses without notable side effects. This supports IK,ACh inhibition as a potentially safe treatment of paroxysmal AF in horses, suggesting potential clinical value for other species including humans.

The human electrophysiological and pharmacological properties of XEN-D0101 were evaluated to assess its usefulness for treating atrial fibrillation (AF). XEN-D0101 inhibited Kv1.5 with an IC50 of 241 nM and is selective over non-target cardiac ion channels (IC50 Kv4.3, 4.2 μM; hERG, 13 μM; activated Nav1.5, >100 μM; inactivated Nav1.5, 34 μM; Kir3.1/3.4, 17 μM; Kir2.1, >>100 μM). In atrial myocytes from patients in sinus rhythm (SR) and chronic AF, XEN-D0101 inhibited non-inactivating outward currents (Ilate) with IC50 of 410 and 280 nM, respectively, and peak outward currents (Ipeak) with IC50 of 806 and 240 nM, respectively. Whereas Ilate is mainly composed of IKur, Ipeak consists of IKur and Ito. Therefore, the effects on Ito alone were estimated from a double-pulse protocol where IKur was inactivated (3.5 µM IC50 in SR and 1 µM in AF). Thus, inhibition of Ipeak is because of IKur reduction and not Ito. XEN-D0101 significantly prolonged the atrial action potential duration at 20%, 50%, and 90% of repolarization (AF tissue only) and significantly elevated the atrial action potential plateau phase and increased contractility (SR and AF tissues) while having no effect on human ventricular action potentials. In healthy volunteers, XEN-D0101 did not significantly increase baseline- and placebo-adjusted QTc up to a maximum oral dose of 300 mg. XEN-D0101 is a Kv1.5/IKur inhibitor with an attractive atrial-selective profile.

TGF-beta 1 appears to regulate lysyl oxidase in cultured rat aortic smooth muscle cells. Increases in lysyl oxidase activity may be one of the mechanisms by which TGF-beta 1 contributes to arterial restenosis after vascular injury.