Inherited Retinal Degeneration: PARP-Dependent Activation of Calpain Requires CNG Channel Activity.

Inherited retinal degenerations (IRDs) are a group of blinding diseases, typically involving a progressive loss of photoreceptors. The IRD pathology is often based on an accumulation of cGMP in photoreceptors and associated with the excessive activation of calpain and poly (ADP-ribose) polymerase (PARP). Inhibitors of calpain or PARP have shown promise in preventing photoreceptor cell death, yet the relationship between these enzymes remains unclear. To explore this further, organotypic retinal explant cultures derived from wild-type and IRD-mutant mice were treated with inhibitors specific for calpain, PARP, and voltage-gated Ca2+ channels (VGCCs). The outcomes were assessed using in situ activity assays for calpain and PARP and immunostaining for activated calpain-2, poly (ADP-ribose), and cGMP, as well as the TUNEL assay for cell death detection. The IRD models included the Pde6b-mutant rd1 mouse and rd1*Cngb1-/- double-mutant mice, which lack the beta subunit of the rod cyclic nucleotide-gated (CNG) channel and are partially protected from rd1 degeneration. We confirmed that an inhibition of either calpain or PARP reduces photoreceptor cell death in rd1 retina. However, while the activity of calpain was decreased by the inhibition of PARP, calpain inhibition did not alter the PARP activity. A combination treatment with calpain and PARP inhibitors did not synergistically reduce cell death. In the slow degeneration of rd1*Cngb1-/- double mutant, VGCC inhibition delayed photoreceptor cell death, while PARP inhibition did not. Our results indicate that PARP acts upstream of calpain and that both are part of the same degenerative pathway in Pde6b-dependent photoreceptor degeneration. While PARP activation may be associated with CNG channel activity, calpain activation is linked to VGCC opening. Overall, our data highlights PARP as a target for therapeutic interventions in IRD-type diseases.

Hippocampal cAMP regulates HCN channel function on two time scales with differential effects on animal behavior.

Hyperpolarization-activated cyclic nucleotide­gated (HCN) channels regulate neuronal excitability and represent a possible therapeutic target for major depressive disorder (MDD). These channels are regulated by intracellular cyclic adenosine monophosphate (cAMP). However, the relationship between cAMP signaling and the influence of HCN channels on behavior remains opaque. In this study, we investigated the role of hippocampal cAMP signaling on behavior using chemogenetic technology in mice. Acutely increasing cAMP limited spatial memory and motivated behavior by increasing HCN function. However, chronically elevated cAMP limited surface trafficking of HCN channels by disrupting the interaction between HCN and tetratricopeptide repeat-containing Rab8b-interacting protein (TRIP8b), an auxiliary subunit. Chronically increased cAMP in the dorsal hippocampus was also sufficient to rescue cognitive deficits induced by chronic stress in mice. These results reveal a behaviorally relevant form of regulation of HCN channel surface expression that has potential as a therapeutic target for cognitive deficits related to chronic stress.

Safety and Efficacy of AAV5 Vectors Expressing Human or Canine CNGB3 in CNGB3-Mutant Dogs.

Achromatopsia is an inherited retinal disorder of cone photoreceptors characterized by markedly reduced visual acuity, extreme light sensitivity, and absence of color discrimination. Approximately 50% of cases are caused by mutations in the cone photoreceptor-specific cyclic nucleotide gated channel beta subunit (CNGB3) gene. Studies in CNGB3-mutant dogs showed that subretinal injection of an AAV vector expressing human CNGB3, which has 76% amino acid identity with canine CNGB3, driven by a 2.1 kb human red cone opsin promoter (PR2.1) and packaged in AAV5 capsids (AAV5-PR2.1-hCNGB3) rescued cone photoreceptor function, but at high doses was associated with an inflammatory response (focal chorioretinitis) consistent with immune-mediated toxicity. AAV vectors containing the PR2.1 promoter packaged in AAV5 capsids and expressing either the native canine CNGB3 (AAV5-PR2.1-cCNGB3) or the human CNGB3 (AAV5-PR2.1-hCNGB3) were evaluated at different dose levels in CNGB3-mutant dogs. The vector expressing canine CNGB3 achieved somewhat better rescue of cone function but unexpectedly was associated with a greater degree of retinal toxicity than the vector expressing human CNGB3. Very low-level T-cell immune responses to some AAV or CNGB3 peptides were observed in animals that received the higher vector dose. There was a more than twofold increase in serum neutralizing antibodies to AAV in one of three animals in the low-dose group and in two of three animals in the high-dose group. No serum anti-hCNGB3 antibodies were detected in any animal. The results of this study do not support the hypothesis that the focal chorioretinitis seen with high doses of AAV5-PR2.1-hCNGB3 in the initial studies was due to an immune response to human CNGB3.

Management of heart failure.

Heart failure is a complex clinical syndrome, with diagnosis based on typical symptoms, signs and supportive investigations. Investigations may include an electrocardiogram and chest x-ray, but echocardiography is the definitive test. Plasma B-type natriuretic peptide levels may also be useful in diagnosis among patients with breathlessness, particularly as a rule-out test.Mainstay therapy for heart failure comprises lifestyle modification, pharmacotherapy and referral to a multidisciplinary heart failure program.Drug therapies focused on blockade of key activated neurohormonal systems are well established in systolic heart failure. First-line pharmacotherapy consists of angiotensin-converting enzyme (ACE) inhibitors (or angiotensin receptor blockers if the patient is intolerant to ACE inhibitors) and ß-blockers. These medications should be commenced at a low dose and slowly up-titrated to the maximal tolerated dose. In selected patients, device-based therapies are a useful adjunct in systolic heart failure. The most common of these are implantable cardioverter defibrillators and cardiac resynchronisation therapy. Most patients will receive both, as the indications overlap. Multidisciplinary approaches, including involvement of the patient's general practitioner, are strongly recommended.

'Inappropriate' sinus tachycardia: does the 100 beats per min cut-off matter?

Sinus tachycardia is commonly encountered in clinical practice and when persistent, can result in significant symptoms and impaired quality of life, warranting further evaluation. On the other hand, a growing body of epidemiological and clinical evidence has shown that high resting heart rate (HR) within the accepted normal range is independently associated with increased risk of all-cause and cardiovascular mortality. However, higher HR as a risk factor for adverse cardiovascular outcomes is frequently underappreciated. In this review, we focus on two challenging problems that span the spectrum of abnormally fast sinus HR. The first section reviews inappropriate sinus tachycardia, a complex disorder characterized by rapid sinus HR without a clear underlying cause, with particular emphasis on current management options. The latter section discusses the prognostic significance of elevated resting HR and reviews clinical evidence aimed at modifying this simple, yet highly important risk factor.

[Effect of ivabradin on heart rate, left ventricular function a NT-proBNP concentration in patients with systolic chronic heart failure--case reports]. / Efekt ivabradinu na tepovou frekvenci, vývoj funkce levé komory a koncentraci NT-proBNP u pacientu se systolickým chronickým srdecním selháním - príklady z praxe.

Ivabradin is indicated in patients with compensated chronic heart failure and sinus rhythm with resting heart rate 75 beats per minute despite maximal tolerated beta-blocker dose. Three case reports show favourable effect of ivabradin therapy on heart rate, reverse cardiac remodeling and B-type natriuretic peptide concentration in patients with systolic heart failure.

Recent developments in the management of heart failure.

The typical presentation of heart failure in primary care is insidious, with progressive breathlessness on exertion, ankle swelling, orthopnoea or paroxysmal nocturnal dyspnoea. Not all patients will have all these symptoms, and in many patients there may be other causes. If a GP suspects heart failure, then the key blood test is B-type natriuretic peptide (BNP). If the BNP is normal then heart failure is unlikely and other diagnoses should be considered. If it is raised, or if there is a past history of myocardial infarction, the patient requires further assessment, which must include echocardiography and a specialist assessment. The underlying cardiac abnormality should be identified. An ECG is often very useful and if it is completely normal it makes heart failure less likely. Both the NICE and the ESC guidance emphasise the importance of lifestyle management (regular appropriate exercise, avoiding excessive salt and alcohol consumption). ACE inhibitors (or angiotensin receptor blockers) and beta-blockers licensed for heart failure (carvedilol, bisoprolol, nebivolol) remain the mainstay of treatment in addition to as small a dose of diuretic as possible to control any fluid retention. Aldosterone antagonism is recommended by the 2012 ESC guidance for all patients who remain symptomatic despite an ACE inhibitor and beta-blocker. If the rhythm is sinus but the heart rate is 75 beats per minute, therapy needs to be optimised, perhaps by increasing the beta-blocker dose, if possible, or by the addition of ivabradine.

Long-term and age-dependent restoration of visual function in a mouse model of CNGB3-associated achromatopsia following gene therapy.

Mutations in the CNGB3 gene account for >50% of all known cases of achromatopsia. Although of early onset, its stationary character and the potential for rapid assessment of restoration of retinal function following therapy renders achromatopsia a very attractive candidate for gene therapy. Here we tested the efficacy of an rAAV2/8 vector containing a human cone arrestin promoter and a human CNGB3 cDNA in CNGB3 deficient mice. Following subretinal delivery of the vector, CNGB3 was detected in both M- and S-cones and resulted in increased levels of CNGA3, increased cone density and survival, improved cone outer segment structure and normal subcellular compartmentalization of cone opsins. Therapy also resulted in long-term improvement of retinal function, with restoration of cone ERG amplitudes of up to 90% of wild-type and a significant improvement in visual acuity. Remarkably, successful restoration of cone function was observed even when treatment was initiated at 6 months of age; however, restoration of normal visual acuity was only possible in younger animals (e.g. 2-4 weeks old). This study represents achievement of the most substantial restoration of visual function reported to date in an animal model of achromatopsia using a human gene construct, which has the potential to be utilized in clinical trials.

Clinical trials update from the European Society of Cardiology Meeting 2010: SHIFT, PEARL-HF, STAR-heart, and HEBE-III.

This article provides information and a commentary on key trials relevant to the pathophysiology, prevention, and treatment of heart failure (HF) presented at the annual meeting of the European Society of Cardiology held in Stockholm in 2010. Unpublished reports should be considered as preliminary, since analyses may change in the final publication. The SHIFT study supports the use of ivabradine in patients with HF due to left ventricular systolic dysfunction and resting sinus rhythm rate ≥70 b.p.m. despite treatment with beta-blockers or where beta-blockers are contra-indicated. Results from PEARL-HF suggest that the potassium binding polymer RLY5016 may be useful for both prevention and treatment of hyperkalaemia in HF patients with or without concomitant chronic kidney disease. The STAR-heart study provides encouraging observational data about the potential for intracoronary stem cell transplantation in patients with HF. Results from HEBE-III showed no effect of erythropoietin on ejection fraction measured 6 weeks post-MI; although there were fewer cardiovascular events in patients assigned to erythropoietin, the study was too small to provide conclusive evidence of effect.

Achromatopsia as a potential candidate for gene therapy.

Achromatopsia is an autosomal recessive retinal disease involving loss of cone function that afflicts approximately 1 in 30,000 individuals. Patients with achromatopsia usually have visual acuities lower than 20/200 because of the central vision loss, photophobia, complete color blindness and reduced cone-mediated electroretinographic (ERG) amplitudes. Mutations in three genes have been found to be the primary causes of achromatopsia, including CNGB3 (beta subunit of the cone cyclic nucleotide-gated cation channel), CNGA3 (alpha subunit of the cone cyclic nucleotide-gated cation channel), and GNAT2 (cone specific alpha subunit of transducin). Naturally occurring mouse models with mutations in Cnga3 (cpfl5 mice) and Gnat2 (cpfl3 mice) were discovered at The Jackson Laboratory. A natural occurring canine model with CNGB3 mutations has also been found. These animal models have many of the central phenotypic features of the corresponding human diseases. Using adeno-associated virus (AAV)-mediated gene therapy, we and others show that cone function can be restored in all three models. These data suggest that human achromatopsia may be a good candidate for corrective gene therapy.

Ivabradine as an alternative therapeutic trial in the therapy of inappropriate sinus tachycardia: a case report.

Inappropriate sinus tachycardia is a disease which is relatively rarely found and sometimes difficult to treat. Up to now it has been mostly treated with a beta-blocker or verapamil. If this did not work sinus node modulation was considered. Since the relatively new selective IF-stream blocker ivabradine has been approved for the therapy of chronic stable angina pectoris, a new therapeutic option is available. As ivabradine is well tolerated and only few side effects are known, it may become a new therapeutic step between medication and the invasive sinus node modulation. We report the case of a young female patient with inappropriate sinus tachycardia where a sustained therapeutic success was achieved with ivabradine medication as an alternative therapeutic trial after various ineffective medications.