Acto-myosin cross-bridge kinetics are important for beat-to-beat regulation of cardiac contractility; however, physiological and pathophysiological mechanisms for regulation of contractile kinetics are incompletely understood. Here we explored whether thin filament-mediated Ca sensitization influences cross-bridge kinetics in permeabilized, osmotically compressed cardiac muscle preparations. We used a murine model of hypertrophic cardiomyopathy (HCM) harboring a cardiac troponin C (cTnC) Ca-sensitizing mutation, Ala8Val in the regulatory N-domain. We also treated wild-type murine muscle with bepridil, a cTnC-targeting Ca sensitizer. Our findings suggest that both methods of increasing myofilament Ca sensitivity increase cross-bridge cycling rate measured by the rate of tension redevelopment (k); force per cross-bridge was also enhanced as measured by sinusoidal stiffness and I/I ratio from X-ray diffraction. Computational modeling suggests that Ca sensitization through this cTnC mutation or bepridil accelerates k primarily by promoting faster cross-bridge detachment. To elucidate if myofilament structural rearrangements are associated with changes in k, we used small angle X-ray diffraction to simultaneously measure myofilament lattice spacing and isometric force during steady-state Ca activations. Within in vivo lattice dimensions, lattice spacing and steady-state isometric force increased significantly at submaximal activation. We conclude that the cTnC N-domain controls force by modulating both the number and rate of cycling cross-bridges, and that the both methods of Ca sensitization may act through stabilization of cTnC's D-helix. Furthermore, we propose that the transient expansion of the myofilament lattice during Ca activation may be an additional factor that could increase the rate of cross-bridge cycling in cardiac muscle. These findings may have implications for the pathophysiology of HCM.

BACKGROUND: Autoantibodies to cardiac troponins (TnAAbs) could negatively affect cardiac troponin I (cTnI) measurements by TnAAbs-sensitive immunoassays. We investigated the epitope specificity of TnAAbs and its influence on cTnI immunodetection in patients with acute myocardial infarction (AMI).

Netakimab (NTK) is a humanized anti-interleukin-17A monoclonal antibody. To date, the drug has been approved to treat ankylosing spondylitis (AS), psoriatic arthritis, and plaque psoriasis. The paper gives the data obtained during 52-week follow-up of AS patients in the phase III ASTERA study.Objective: to study the efficacy and safety of NTK when used long in patients with active AS.Patients and methods. The investigation enrolled 228 patients with active AS, in whom nonsteroidal anti-inflammatory drugs or biological agents were ineffective. The patients were randomized in a 1:1 ratio to receive NTK 120 mg or placebo. The drug was administered subcutaneously at weeks 0, 1, 2, and then once every 2 weeks. Patients who received placebo and achieved a 20% improvement according to the ASAS criteria (ASAS20) were excluded from the study at week 16. At this week, patients who took placebo and did not achieve an ASAS20 response were switched to subcutaneous NTK at 120 mg dose once every two weeks. The follow-up period was 52 weeks.Results and discussion. Patients with active AS who received NTK were more likely to respond to treatment than those who took placebo. The proportion of people who achieved 40% improvement (ASAS40) during treatment with NTK increased throughout the follow-up period and amounted to 80.7% at week 52. Positive changes were achieved in all used clinical and laboratory parameters of AS activity. There was also a decrease in inflammatory changes, as shown by magnetic resonance imaging (MRI). The adverse events (AEs) were mainly laboratory abnormalities and upper respiratory tract infections. Treatment-related AEs were recorded in no more than one third of patients and they were mild to moderate. Severe AEs were singular.Conclusion. Response to NTK therapy generates in the first weeks of drug use and increases throughout a year. The safety profile of NTK when used long is generally favorable.