Differentiating Cardiac Troponin Levels During Cardiac Myosin Inhibition or Cardiac Myosin Activation Treatments: Drug Effect or the Canary in the Coal Mine?

PURPOSE OF REVIEW: Cardiac myosin inhibitors (CMIs) and activators are emerging therapies for hypertrophic cardiomyopathy (HCM) and heart failure with reduced ejection fraction (HFrEF), respectively. However, their effects on cardiac troponin levels, a biomarker of myocardial injury, are incompletely understood. RECENT FINDINGS: In patients with HCM, CMIs cause substantial reductions in cardiac troponin levels which are reversible after stopping treatment. In patients with HFrEF, cardiac myosin activator (omecamtiv mecarbil) therapy cause modest increases in cardiac troponin levels which are reversible following treatment cessation and not associated with myocardial ischaemia or infarction. Transient changes in cardiac troponin levels might reflect alterations in cardiac contractility and mechanical stress. Such transient changes might not indicate cardiac injury and do not appear to be associated with adverse outcomes in the short to intermediate term. Longitudinal changes in troponin levels vary depending on the population and treatment. Further research is needed to elucidate mechanisms underlying changes in troponin levels.

[Positive inotropic agents for heart failure treatment: new avenues and questions]. / Positief-inotrope middelen bij hartfalen.

Although there are short term benefits of inotropic agents such as beta-stimulating agents and phosphodiesterase inhibitors type 3 for heart failure patients with reduced ejection fractions, their use is limited by adverse events and increased mortality. Safer inotropic agents such as omecamtiv mecarbil have been developed, that may utilize the inotropic reserve of the heart without increasing mortality. It enhances contractility by prolonging the interaction between myofilaments myosin and actin, so that the ejection time of the heart increases. The GALACTIC-HF trial (2021) demonstrated a small but significant improvement with a hazard ratio of 0.92 in the endpoint of death from cardiovascular cause or heart failure events, which in substudies appeared more relevant in advanced heart failure patients. These results, although still relevant, are now put into perspective, since the METEORIC trial (2022) failed to demonstrate a difference in VO2 max capacity in patients after 20 weeks of treatment.

The Heart Failure Knights.

The 2021 European Society of Cardiology guidelines for the diagnosis and treatment of acute and chronic heart failure (HF) have abandoned the sequential approach for optimal drug therapy and proposed four drug classes, the so-called 4 "pillars" (angiotensin-converting enzyme inhibitors; angiotensin receptor-neprilysin inhibitors; beta-blockers; mineralocorticoid receptor antagonists and sodium-glucose co-transporter 2 inhibitors) to be initiated and titrated in all patients with reduced ejection fraction HF (HFrEF). In addition, new molecules have been considered, derived from recently reported advances from trials in HFrEF. In this review, Authors examine in particular these new molecules, as further "knights" for HF. In particular, vericiguat, a novel oral soluble guanylate cyclase stimulator, has proved effective in patients with HFrEF who had recently been hospitalized or had received intravenous diuretic therapy. The selective cardiac myosin activator omecamtiv mecarbil and the cardiac myosin inhibitors aficamten and mavacamten are under investigation. Cardiac myosin stimulator, omecamtiv mecarbil, has shown efficacy in HFrEF, lowering HF related events or cardiovascular death, while the 2 inhibitors, mavacamten and aficamten have been shown to reduce hypercontractility and left ventricular outflow obstruction improving functional capacity in randomized trials targeting hypertrophic cardiomyopathy. These agents are the prototypes of active pipelines promising to deliver an array of molecules against HF in the near future.

Fluorescent hiPSC-derived MYH6-mScarlet cardiomyocytes for real-time tracking, imaging, and cardiotoxicity assays.

Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) hold great potential in the cardiovascular field for human disease modeling, drug development, and regenerative medicine. However, multiple hurdles still exist for the effective utilization of hiPSC-CMs as a human-based experimental platform that can be an alternative to the current animal models. To further expand their potential as a research tool and bridge the translational gap, we have generated a cardiac-specific hiPSC reporter line that differentiates into fluorescent CMs using CRISPR-Cas9 genome editing technology. The CMs illuminated with the mScarlet fluorescence enable their non-invasive continuous tracking and functional cellular phenotyping, offering a real-time 2D/3D imaging platform. Utilizing the reporter CMs, we developed an imaging-based cardiotoxicity screening system that can monitor distinct drug-induced structural toxicity and CM viability in real time. The reporter fluorescence enabled visualization of sarcomeric disarray and displayed a drug dose-dependent decrease in its fluorescence. The study also has demonstrated the reporter CMs as a biomaterial cytocompatibility analysis tool that can monitor dynamic cell behavior and maturity of hiPSC-CMs cultured in various biomaterial scaffolds. This versatile cardiac imaging tool that enables real time tracking and high-resolution imaging of CMs has significant potential in disease modeling, drug screening, and toxicology testing.

Procoagulant activities of skeletal and cardiac muscle myosin depend on contaminating phospholipid.

Recent reports indicate that suspended skeletal and cardiac myosin, such as might be released during injury, can act as procoagulants by providing membrane-like support for factors Xa and Va in the prothrombinase complex. Further, skeletal myosin provides membrane-like support for activated protein C. This raises the question of whether purified muscle myosins retain procoagulant phospholipid through purification. We found that lactadherin, a phosphatidyl-l-serine-binding protein, blocked >99% of prothrombinase activity supported by rabbit skeletal and by bovine cardiac myosin. Similarly, annexin A5 and phospholipase A2 blocked >95% of myosin-supported activity, confirming that contaminating phospholipid is required to support myosin-related prothrombinase activity. We asked whether contaminating phospholipid in myosin preparations may also contain tissue factor (TF). Skeletal myosin supported factor VIIa cleavage of factor X equivalent to contamination by ∼1:100 000 TF/myosin, whereas cardiac myosin had TF-like activity >10-fold higher. TF pathway inhibitor inhibited the TF-like activity similar to control TF. These results indicate that purified skeletal muscle and cardiac myosins support the prothrombinase complex indirectly through contaminating phospholipid and also support factor X activation through TF-like activity. Our findings suggest a previously unstudied affinity of skeletal and cardiac myosin for phospholipid membranes.

Genetic differences in bone marrow-derived lymphoid lineages control susceptibility to experimental autoimmune myocarditis.

Bone marrow (BM) transplantation has been used to study the cellular basis of genetic control of autoimmune diseases, but conclusions remain elusive due to the contradictory findings in different animal models. In the current study, we found that BM cells from myocarditis-susceptible A.SW mice can render irradiated, myocarditis-resistant B10.S recipient mice susceptible to myosin-induced myocarditis, indicating that hematopoietic cells express the genetic differences controlling susceptibility to autoimmune myocarditis. We then sought to differentiate the role of lymphoid vs nonlymphoid components of BM in the pathogenesis of myocarditis by comparing mixed chimeras receiving BM from A.SW wild-type or RAG(-/-) mice mixed with BM from B10.S wild-type mice. This experiment clearly demonstrated that T and B lymphocytes were indispensable for transferring the susceptible phenotype to disease-resistant recipients. Our findings significantly narrow the cellular expression of genetic polymorphisms controlling the EAM phenotype.

Microarray analysis reveals the role of matrix metalloproteinases in mouse experimental autoimmune myocarditis induced by cardiac myosin peptides.

Autoimmune myocarditis develops after the presentation of heart-specific antigens to autoaggressive CD4(+) T cells and after inflammation has infiltrated the tissues. To shed light on global changes in the gene expression of autoimmune myocarditis and to gain further insight into the molecular mechanisms underlying the genesis of myocarditis, we conducted a comprehensive microarray analysis of mRNA using an experimental mouse autoimmune myocarditis model via immunization with alpha-myosin heavy chain-derived peptides. Of over 39,000 transcripts on a high density oligonucleotide microarray, 466 were under-expressed and 241 over-expressed by >or= 1.5-fold compared with the controls in BALB/C mouse with autoimmune myocarditis. In this paper, we list the top 50 up-regulated genes related to the immune response. These altered genes encode for leukocyte-specific markers and receptors, the histocompatibility complex, cytokines/receptors, chemokines/receptors, adhesion molecules, components of the complement cascade, and signal transduction-related molecules. Interestingly, matrix metalloproteinases (MMPs) such as MMP-3 and MMP-9 were up-regulated, as further revealed by the reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemistry assays. This indicates that MMPs may act as major regulators of the cytokine profile. Together, these findings provide new insight into the molecular events associated with the mechanism of the autoimmune genesis of myocarditis.