Vidarabine, an anti-herpes agent, prevents occlusal-disharmony-induced cardiac dysfunction in mice

We recently reported a positive relationship between occlusal disharmony and cardiovascular disease via activation of β-adrenergic signaling in mice. Furthermore, inhibition of type 5 adenylyl cyclase (AC5), a major cardiac subtype in adults, protects the heart against oxidative stress. Here, we examined the role of AC5 in the development of occlusal-disharmony-induced cardiovascular disease in bite-opening (BO) mice, prepared by cementing a suitable appliance onto the mandibular incisor. We first examined the effects of BO treatment on cardiac function in mice treated or not treated for 2 weeks with vidarabine, which we previously identified as an inhibitor of cardiac AC. Cardiac function was significantly decreased in the BO group compared to the control group, but vidarabine ameliorated the dysfunction. Cardiac fibrosis, myocyte apoptosis and myocyte oxidative DNA damage were significantly increased in the BO group, but vidarabine blocked these changes. The BO-induced cardiac dysfunction was associated with increased phospholamban phosphorylation at threonine-17 and serine-16, as well as increased activation of the Ca2+-calmodulin-dependent protein kinase II/receptor-interacting protein 3 signaling pathway. These data suggest that AC5 inhibition with vidarabine might be a new therapeutic approach for the treatment of cardiovascular disease associated with occlusal disharmony.

Electropharmacological Characterization of Aciclovir in the Halothane-Anesthetized Dogs: A Proposal of Evaluation Method for Cardiovascular Safety Pharmacology of Anti-virus Drugs

Given limited information regarding the pathophysiology underlying aciclovir-associated, clinically observed cardiovascular adverse events including chest pain, tachycardia, bradycardia, palpitation, arrhythmia, hypertension and hypotension, we investigated its electropharmacological effects using the halothane-anesthetized beagle dogs. Aciclovir in doses of 2 and 20 mg/kg was sequentially infused over 10 min with an interval of 20 min (n = 4), which would achieve sub-therapeutic to supra-therapeutic levels of plasma concentrations. Aciclovir decreased the total peripheral vascular resistance along with the blood pressure in a dose-related manner, which increased the heart rate, ventricular contraction and atrioventricular nodal conduction speed probably via a reflex-mediated increase of sympathetic tone. No significant change was detected in the intra-atrial or intra-ventricular conduction, indicating that aciclovir may not inhibit atrial or ventricular I_Na. Aciclovir prolonged the repolarization period in a dose-related as well as in a reverse frequency-dependent manners, indicating that aciclovir may inhibit I_Kr, which was supported by the T_peak - T_end prolongation. Aciclovir transiently prolonged the J - T_peakc possibly through a reflex-mediated increase of sympathetic tone, indicating an increase of net inward current in the early repolarization phase. Thus, aciclovir may directly inhibit I_Kr, and also have the potential to indirectly induce Ca²⁺ overload leading to early afterdepolarization. These in vivo electropharmacological profile of aciclovir would partly explain the onset mechanism of clinical adverse events.

Cardiac Arrhythmias and Antiarrhythmic Drugs: An Autophagic Perspective

Degradation of cellular material by lysosomes is known as autophagy, and its main function is to maintain cellular homeostasis for growth, proliferation and survival of the cell. In recent years, research has focused on the characterization of autophagy pathways. Targeting of autophagy mediators has been described predominantly in cancer treatment, but also in neurological and cardiovascular diseases. Although the number of studies is still limited, there are indications that activity of autophagy pathways increases under arrhythmic conditions. Moreover, an increasing number of antiarrhythmic and non-cardiac drugs are found to affect autophagy pathways. We, therefore, suggest that future work should recognize the largely unaddressed effects of antiarrhythmic agents and other classes of drugs on autophagy pathway activation and inhibition.

Vidarabine, an anti-herpesvirus agent, prevents catecholamine-induced arrhythmias without adverse effect on heart function in mice

Sympathetic activation causes clinically important arrhythmias including atrial fibrillation (AF) and ventricular tachyarrhythmia. Although the usefulness of β-adrenergic receptor blockade therapy is widely accepted, its multiple critical side effects often prevent its initiation or continuation. The aim of this study is to determine the advantages of vidarabine, an adenylyl cyclase (AC)-targeted anti-sympathetic agent, as an alternative treatment for arrhythmia. We found that vidarabine, which we identified as a cardiac AC inhibitor, consistently shortens AF duration and reduces the incidence of sympathetic activation-induced ventricular arrhythmias. In atrial and ventricular myocytes, vidarabine inhibits adrenergic receptor stimulation-induced RyR2 phosphorylation, sarcoplasmic reticulum (SR) Ca²⁺ leakage, and spontaneous Ca²⁺ release from SR, the last of which has been considered as a potential arrhythmogenic trigger. Moreover, vidarabine also inhibits sympathetic activation-induced reactive oxygen species (ROS) production in cardiac myocytes. The pivotal role of vidarabine's inhibitory effect on ROS production with regard to its anti-arrhythmic property has also been implied in animal studies. In addition, as expected, vidarabine exerts an inhibitory effect on AC function, which is more potent in the heart than elsewhere. Indexes of cardiac function including ejection fraction and heart rate were not affected by a dosage of vidarabine sufficient to exert an anti-arrhythmic effect. These findings suggest that vidarabine inhibits catecholamine-induced AF or ventricular arrhythmia without deteriorating cardiac function in mice.

International Union of Basic and Clinical Pharmacology. CI. Structures and Small Molecule Modulators of Mammalian Adenylyl Cyclases

Adenylyl cyclases (ACs) generate the second messenger cAMP from ATP. Mammalian cells express nine transmembrane AC (mAC) isoforms (AC1-9) and a soluble AC (sAC, also referred to as AC10). This review will largely focus on mACs. mACs are activated by the G-protein Gαs and regulated by multiple mechanisms. mACs are differentially expressed in tissues and regulate numerous and diverse cell functions. mACs localize in distinct membrane compartments and form signaling complexes. sAC is activated by bicarbonate with physiologic roles first described in testis. Crystal structures of the catalytic core of a hybrid mAC and sAC are available. These structures provide detailed insights into the catalytic mechanism and constitute the basis for the development of isoform-selective activators and inhibitors. Although potent competitive and noncompetitive mAC inhibitors are available, it is challenging to obtain compounds with high isoform selectivity due to the conservation of the catalytic core. Accordingly, caution must be exerted with the interpretation of intact-cell studies. The development of isoform-selective activators, the plant diterpene forskolin being the starting compound, has been equally challenging. There is no known endogenous ligand for the forskolin binding site. Recently, development of selective sAC inhibitors was reported. An emerging field is the association of AC gene polymorphisms with human diseases. For example, mutations in the AC5 gene (ADCY5) cause hyperkinetic extrapyramidal motor disorders. Overall, in contrast to the guanylyl cyclase field, our understanding of the (patho)physiology of AC isoforms and the development of clinically useful drugs targeting ACs is still in its infancy.

Vidarabine, an Anti-Herpes Virus Agent, Protects Against the Development of Heart Failure With Relatively Mild Side-Effects on Cardiac Function in a Canine Model of Pacing-Induced Dilated Cardiomyopathy

BACKGROUND

In heart failure patients, chronic hyperactivation of sympathetic signaling is known to exacerbate cardiac dysfunction. In this study, the cardioprotective effect of vidarabine, an anti-herpes virus agent, which we identified as a cardiac adenylyl cyclase inhibitor, in dogs with pacing-induced dilated cardiomyopathy (DCM) was evaluated. In addition, the adverse effects of vidarabine on basal cardiac function was compared to those of the β-blocker, carvedilol.Methods and Results:Vidarabine and carvedilol attenuated the development of pacing-induced systolic dysfunction significantly and with equal effectiveness. Both agents also inhibited the development of cardiac apoptosis and fibrosis and reduced the Na⁺-Ca²⁺exchanger-1 protein level in the heart. Importantly, carvedilol significantly enlarged the left ventricle and atrium; vidarabine, in contrast, did not. Vidarabine-treated dogs maintained cardiac response to β-AR stimulation better than carvedilol-treated dogs did.

CONCLUSIONS

Vidarabine may protect against pacing-induced DCM with less suppression of basal cardiac function than carvedilol in a dog model. (Circ J 2016; 80: 2496-2505).

A Food and Drug Administration-Approved Antiviral Agent that Inhibits Adenylyl Cyclase Type 5 Protects the Ischemic Heart Even When Administered after Reperfusion

A Food and Drug Administration-approved antiviral agent, known as vidarabine or adenine 9-β-D-arabinofuranoside (AraA), has features of inhibiting adenylyl cyclase type 5 (AC5) and protects against chronic coronary artery occlusion (CAO). The goal of this investigation was to determine whether AraA protects against myocardial ischemia, even when delivered after coronary artery reperfusion (CAR). AraA, delivered after CAR in wild-type mice, reduced infarct size by 55% compared with vehicle-treated controls, whereas an equal dose of adenosine reduced infarct size only when administered before CAR. A 5-fold greater dose of adenosine was required to reduce infarct size when delivered after CAR, which also reduced arterial pressure by 15%, whereas AraA did not affect pressure. The reduction in infarct size with AraA was prevented by a MEK/extracellular signal-regulated kinase blocker, a pathway also involved in the mechanism of protection of the AC5 knockout (KO) model. Infarct size was also reduced in cardiac-specific AC5 KO mice similarly in the presence and absence of AraA, further suggesting that AraA protection involves the AC5 pathway. AraA reduced infarct size in chronically instrumented conscious pigs when delivered after CAR, and in this model, it also reduced post-CAR coronary hyperemia, which could be another mechanism for cardioprotection (i.e., by reducing oxidative stress during CAR). Thus, AraA inhibits AC5 and exhibits unique cardioprotection when delivered after CAR, which is critical for clinical translation.