Many Western countries have been affected by the outbreak of COVID-19. Italy has been particularly hit at the beginning of the pandemic, immediately after China. In Italy and elsewhere women seem to be less affected then men by severe/fatal COVID-19 infection, regardless of their age. Despite the evidence that women and men are different fort this infection, very few studies consider different therapeutic approaches for the two sexes. Undoubtedly, understanding the mechanisms at the bases of these differences may help to find appropriate and sex specific therapies. Here we consider that other mechanisms but estrogen protection are involved. Several X-linked genes (such as ACE2) and Y-linked genes (SRY, SOX9) may explain sex differences. Cardiovascular comorbidities are among the major enhancers of virus lethality. In addition, the number of sex-independent non-genetic factors that can change susceptibility and mortality is enormous, and many other factors are likely to be considered, including gender and cultural habits in different countries.
Angiotensin converting enzyme-2 (ACE2) is the receptor for the coronavirus SARS-CoV-2, which causes COVID-19. We propose the following hypothesis: Imbalance in the action of ACE1- and ACE2-derived peptides, thereby enhancing Angiotensin-II (ANG II) signaling, a primary driver of COVID-19 pathobiology. ACE1/ACE2 imbalance occurs due to the binding of SARS-CoV-2 to ACE2, reducing ACE2-mediated conversion of ANG II to ANG peptides that counteract pathophysiological effects of ACE1-generated ANGII. This hypothesis suggests several approaches to treat COVID-19 by restoring ACE1/ACE2 balance: 1) ANG II receptor blockers (ARBs); 2) ACE1 inhibitors (ACEIs); 3) Agonists of receptors activated by ACE2-derived peptides [e.g., ANG (1-7), which activates MAS1]; 4) Recombinant human ACE2 or ACE2 peptides as decoys for the virus. Reducing ACE1/ACE2 imbalance is predicted to blunt COVID-19-associated morbidity and mortality, especially in vulnerable patients. Importantly, approved ARBs and ACEIs can be rapidly repurposed to test their efficacy in treating COVID-19.
The coronavirus disease 2019 (COVID-19) pandemic caused by SARS-CoV-2 infections has led to substantial unmet need for treatments, many of which will require testing in appropriate animal models of this disease. Vaccine trials are already underway, but there remains an urgent need to find other therapeutic approaches to either target SARS-CoV-2 or the complications arising from viral infection, particularly the dysregulated immune response and systemic complications which have been associated with progression to severe COVID-19. At the time of writing, in vivo studies of SARS-CoV-2 infection have been described using macaques, cats, ferrets, hamsters, and transgenic mice expressing human angiotensin I converting enzyme 2 (ACE2). These infection models have already been useful for studies of transmission and immunity, but to date only partially model the mechanisms implicated in human severe COVID-19. There is therefore an urgent need for development of animal models for improved evaluation of efficacy of drugs identified as having potential in the treatment of severe COVID-19. These models need to recapitulate key mechanisms of COVID-19 severe acute respiratory distress syndrome and reproduce the immunopathology and systemic sequelae associated with this disease. Here, we review the current models of SARS-CoV-2 infection and COVID-19-related disease mechanisms and suggest ways in which animal models can be adapted to increase their usefulness in research into COVID-19 pathogenesis and for assessing potential treatments.
The complement system is an ancient part of innate immunity sensing highly pathogenic coronaviruses by Mannan-binding lectin resulting in lectin pathway-activation and subsequent generation of the anaphylatoxins (AT) C3a and C5a as important effector molecules. Complement deposition in endothelial cells and high blood C5a serum levels have been reported in COVID-19 patients with severe illness, suggesting vigorous complement activation leading to systemic thrombotic microangiopathy (TMA). Strikingly, SARS-CoV-2-infected African Americans suffer from high mortality. Complement regulator gene variants prevalent in African Americans have been associated with a higher risk for severe TMA and multi-organ injury. These findings allow us to apply our knowledge from other complement-mediated diseases to COVID-19 infection to better understand severe disease pathogenesis. Here we will discuss the multiple aspects of complement activation, regulation, crosstalk with other parts of the immune system and the options to target complement in COVID-19 patients to halt disease progression and death.
Background and Purpose: Acute lung injury (ALI), acute respiratory distress syndrome (ARDS) and pulmonary fibrosis remain major causes of morbidity, mortality and healthcare burden in the critically ill patient. There is an urgent medical need for identifying factors of susceptibility and prognosis and for designing new therapeutic tools for treating these disorders. Here, we evaluate the capacity of the immunomodulatory neuropeptide cortistatin to regulate pulmonary inflammation and fibrosis in vivo. Experimental Approach: ALI/ARDS and pulmonary fibrosis were induced experimentally in wild-type and cortistatin-deficient mice by pulmonary infusion of the bacterial endotoxin LPS or the chemotherapeutic drug bleomycin, and the histopathological signs, pulmonary leukocyte infiltration and cytokines and fibrotic markers were evaluated. Key Results: Partially-deficient mice in cortistatin showed exacerbated pulmonary damage, pulmonary inflammation, alveolar oedema and fibrosis, and subsequent increased respiratory failure and mortality when challenged to LPS or bleomycin, even at low doses. Treatment with cortistatin reversed these aggravated phenotypes and protected from progression to severe ARDS and fibrosis after high-exposition to both injury agents. Moreover, cortistatin-deficient pulmonary macrophages and fibroblasts showed exaggerated ex vivo inflammatory and fibrotic responses. The anti-fibrotic protective effect of cortistatin was also observed in experimental scleroderma, in which lack of cortistatin predisposes to develop more severe dermal lesions and associated pulmonary fibrosis. Conclusion and Implications: We identify to cortistatin as an endogenous break of pulmonary inflammation and fibrosis. Deficiency in cortistatin could be a marker of poor-prognosis in inflammatory/fibrotic pulmonary disorders. Cortistatin-based therapies emerge as attractive candidates to treat severe ALI/ARDS, including SARS-Cov-2-associated ARDS.
COVID-19 is a complex disease and many difficulties are faced today especially in the proper choice of pharmacological treatments. The role of antiviral agents for COVID-19 is still being investigated. The evidence for immunomodulatory and anti-inflammatory drugs is quite conflicting, while the use of corticosteroids is supported by robust evidence. The use of heparins in hospitalized critically ill patients is preferred over other anticoagulants. Lastly, conflicting data were found regarding to the use of convalescent plasma and vitamin D. According to data shared by the WHO, many vaccines are under phase 3 clinical trials and some of them already received the marketing approval in EU countries and in the US. In conclusion, drugs repurposing has represented the main approach recently used in the treatment of patients with COVID-19. At this moment, the analysis of efficacy and safety data of drugs and vaccines used in real life context is strongly needed.
Background and Purpose: Despite availability of a variety of treatment options, many asthma patients have poorly controlled disease with frequent exacerbations. Proteinase-activated receptor-2 (PAR2) has been identified in pre-clinical animal models as important to asthma initiation and progression following allergen exposure. Proteinase activation of PAR2 induces intracellular Ca2+, mitogen activated protein kinase (MAPK) and -arrestin signaling the airway, leading to both inflammatory and protective effects. We have developed C391, a potent PAR2 antagonist effective in blocking peptidomimetic- and trypsin-induced PAR2 signaling in vitro as well as reducing inflammatory PAR2-associated pain in vivo. We hypothesized that PAR2 reduction with C391 would attenuate allergen-induced asthma indicators in murine models. Experimental Approach: We evaluated the ability for C391 to alter Alternaria alternata-induced PAR2 signaling pathways in vitro using a human airway epithelial cell line that naturally expresses PAR2 (16HBE14o-) and a transfected embryonic cell line (HEK 293). We next evaluated the ability for C391 to reduce A. alternata-induced asthma indicators in vivo in two murine strains. Key Results: C391 blocked A. alternata-induced, PAR2-dependent Ca2+ and MAPK signaling in 16HBE14o- cells, as well as -arrestin recruitment in HEK 293 cells. C391 effectively attenuated A. alternata-induced inflammation, mucus production, mucus cell hyperplasia and airway hyperresponsiveness in acute asthma murine models. Conclusions and Implications: To our knowledge, this is the first demonstration of pharmacological intervention of PAR2 to reduce allergen-induced asthma indicators in vivo. These data support further development of PAR2 antagonists as potential first-in-class allergic asthma drugs.
Identifying candidate drugs effective in the new coronavirus disease 2019 (Covid-19) is crucial, pending a vaccine against SARS-CoV2. We suggest the hypothesis that Cannabidiol (CBD), a non-psychotropic phytocannabinoid, has the potential to limit the severity and progression of the disease for several reasons: 1) High-CBD Cannabis Sativa extracts are able to downregulate the expression of the two key receptors for SARS-CoV2 in several models of human epithelia 2) CBD exerts a wide range of immunomodulatory and anti-inflammatory effects and it can mitigate the uncontrolled cytokine production featuring Acute Lung Injury 3) Being a PPARΥ agonist, it can display a direct antiviral activity 4) PPARΥ agonists are regulators of fibroblast/myofibroblast activation and can inhibit the development of pulmonary fibrosis, thus ameliorating lung function in recovered patients. We hope our hypothesis, corroborated by several preclinical evidence, will inspire further targeted studies to test CBD as a support drug against the COVID-19 pandemic.
Epitranscriptomics is an exciting emerging area that studies biochemical modifications of RNA. The field is boosted by the technical efforts of the last decade to characterize and quantify RNA modifications which have led to a map of post-transcripcional RNA marks in normal cell fate and develoment. However, the scientific interest has been fueled by the discovery of aberrant epitranscriptomes associated with human diseases, mainly cancer. The challenge is now to see whether epitrancriptomics offers a tunable mechanims to be targeted by small- molecule intervention. In this review, we will describe the principal RNA modifications (with a focus on mRNA), summarize the latest scientific evidences of their dysregulation in cancer and provide an overview of the state-of-the-art drug discovery to target the epitranscriptome. Finally, we will discuss the principal challenges in the field of chemical biology and drug development to increase the potential of targeted-RNA for clinical benefit.
Background and Purpose: It is well established that both smokers and patients with COPD are at a significantly heightened risk of cardiovascular disease (CVD), although the mechanisms underpinning the onset and progression of comorbid CVD are largely unknown. Here, we explored whether cigarette smoke (CS) exposure impairs vascular function in mice and given the well-known pathological role for oxidative stress in COPD, whether the antioxidant compound ebselen prevents CS-induced vascular dysfunction in mice. Experimental Approach: Male BALB/c mice were exposed to either room air (sham) or CS generated from 9 cigarettes per day, 5 days a week for 8 weeks. Mice were treated with ebselen (10mg/kg, oral gavage once daily) or vehicle (5% w/v CM cellulose in water) 1 h prior to the first CS exposure of the day. Upon sacrifice, bronchoalveolar lavage fluid (BALF) was collected to assess pulmonary inflammation and the thoracic aorta was excised to investigate vascular endothelial and smooth muscle dilator responses ex-vivo. Key Results: CS exposure caused a significant increase in lung inflammation which was reduced by ebselen. CS also caused significant endothelial dysfunction in the thoracic aorta which was attributed to a downregulation of eNOS expression and increased vascular oxidative stress. Ebselen abolished the aortic endothelial dysfunction seen in CS-exposed mice by reducing the oxidative burden and preserving eNOS expression. Conclusion and Implications: Targeting CS-induced oxidative stress with ebselen may provide a novel means for treating the life-threatening pulmonary and cardiovascular manifestations associated with cigarette smoking and COPD.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) is a newly identified coronavirus which has spread from China to the rest of the world causing the pandemic coronavirus disease 19 (COVID-19). It has fatality rate that floats from 5 to 15% and the symtoms are fever, cough, myalgia and/or fatigue up to dyspnea, responsible for hospitalization and in most of the cases of artificial oxygenation. In the attempt to understand how the virus spreads and how to pharmacologically abolish it, it was highlighted that SARS-CoV2 infects human cells by means of angiotensin converting enzyme 2 (ACE2), transmembrane protease serine 2 (TMPRSS2) and 3-chymotrypsin-like protease (3CLpro), also known as Mpro. Once bound to its receptor ACE2, the other two proteases, in concert with the receptor-mediated signaling, allow virus replication and spread throughout the body. Our attention has been focused on the role of ACE2 in that its blockade by the virus increases Bradykinin and its metabolites, well known to facilitate inflammation in the lung (responsible for cough and fever), facilitate both the coagulation and complement system, three mechanisms that are typical of angioedema, cardiovascular dysfunction and sepsis, pathologies which symptoms occur in COVID-19 patients. Thus, we propose to pharmacologically block the kallicrein-kinin system upstream bradykinin and the ensuing inflammation, coagulation and complement activation by means of lanadelumab, which is a clinically approved drug for hereditary angioedema.
Intense effort is underway to evaluate potential therapeutic agents for the treatment of COVID-19. In order to respond quickly to the crisis, the repurposing of existing drugs is the primary pharmacological strategy. Despite the urgent clinical need for these therapies, it is imperative to consider potential safety issues. This is important due to the harm-benefit ratios that may be encountered when treating COVID-19, which can depend on the stage of the disease, when therapy is administered and underlying clinical factors in individual patients. Treatments are currently being trialled for a range of scenarios from prophylaxis (where benefit must greatly exceed risk) to severe life-threatening disease (where a degree of potential risk may be tolerated if it is exceeded by the potential benefit). In this perspective, we have reviewed some of the most widely-researched repurposed agents in order to identify potential safety considerations using existing information in the context of COVID-19.
Background and Purpose: Resurgence in the use of chloroquine as a putative treatment for COVID-19 has seen recent cases of fatal toxicity due to unintentional overdoses. Protocols for the management of poisoning recommend diazepam, although there are uncertainties in its pharmacology and efficacy in this context. The aim was to assess the effects of diazepam in experimental models of chloroquine cardiotoxicity. Experimental Approach: In vitro experiments involved cardiac tissues isolated from rats and incubated with chloroquine, alone, or in combination with diazepam. In vivo models of toxicity involved chloroquine administered intravenously to pentobarbitone-anaesthetised rats and rabbits. Randomised, controlled interventional studies in rats assessed diazepam, clonazepam and Ro5-4864 administered: (i) prior, (ii) during, and (iii) after chloroquine; and the effects of diazepam: (iv) at high dose, (v) in urethane-anaesthetised rats, and (vi) co-administered with adrenaline. Key Results: Chloroquine decreased the developed tension of left atria, prolonged the effective refractory period of atria, ventricular tissue and right papillary muscles, and caused dose-dependent impairment of haemodynamic and electrocardiographic parameters. Cardiac arrhythmias indicated impairment of atrioventricular conduction. Studies (i), (ii) and (v) showed no differences between interventions and control. Diazepam increased heart rate in study (iv) and, as with clonazepam, also prolonged the QTc interval in study (iii). Combined administration of diazepam and adrenaline in study (vi) improved cardiac contractility but caused hypokalaemia. Conclusion and Implications: Neither diazepam, nor other ligands for benzodiazepine binding sites, protect against or attenuate chloroquine cardiotoxicity. However, diazepam may augment the effects of positive inotropes in reducing chloroquine cardiotoxicity.
Background and Purpose: The development of effective therapeutic strategies against Alzheimer’s disease (AD) remains a challenge. I2 Imidazoline receptors (I2-IR) ligands have a neuroprotective role in AD. While co-treatment of acetylcholinesterase inhibitors with neuroprotective agents have shown better effects on the prevention of dementia. Here, we assessed the potential therapeutic effect of the I2-IR ligand LSL60101, donepezil and their combination in 5XFAD mice. Experimental Approach: 5XFAD female mice were treated with low doses of LSL60101 (1mg/kg/day), donepezil (1mg/kg/day), and donepezil plus LSL60101 (1+1mg/kg/day), during 4 weeks per os. Novel object recognition, Morris water maze, open field, elevated plus maze and three-chamber tests were employed to evaluate the cognitive and behavioural status of the mice after treatment. The effects of the treatments on AD-like pathology were assessed with immunohistochemistry, Western blot and qPCR. Key results: Chronic low-dose treatment with LSL60101 and donepezil reversed cognitive deficits and impaired social behaviour. LSL60101 treatment did not affect anxiety-like behaviour in contrast to donepezil. In the 5XFAD brains, LSL60101 and donepezil/LSL60101 treatments decreased Aβ-pathology and Tau hyperphosphorylation, and these alterations were accompanied by decreased microglia marker Iba-1 levels and increased Trem2 gene expression. LSL60601 and donepezil decreased glial fibrillary acidic protein (GFAP) astrocytic marker reactivity. However, only LSL60601 treatment significantly increased the levels of the synaptic markers post-density 95 (PSD95) and synaptophysin (SYN). Conclusion and implications: Our results suggest that chronic low dose treatment with selective I2-IR ligands can be an effective treatment for AD and provide insights into combination treatments of symptomatic and disease-modifying drugs
Acute respiratory distress syndrome (ARDS) is the main cause of morbidity and mortality in Coronavirus disease 19 (Covid-19) for which as of now there is no effective treatment. ARDS is caused and sustained by an uncontrolled inflammatory activation characterized by a massive release of cytokines (cytokine storm), diffuse lung edema, inflammatory cell infiltraton and disseminated coagulation. Macrophage and T lymphocyte dysfunction plays a central role in this syndrome. In several experimental in vitro and in vivo models, many of these pathophysiological changes are triggered by stimulation of the P2X7 receptor. We hypothesize that this receptor might be an ideal candidate to target in Covid-19-associated ARDS.
Nitric oxide (NO) is a unique signaling molecule in the mammalian species. NO is produced by a variety of cell types to elicit distinct physiological actions. In the vascular system, NO is produced by the endothelium, a single layer of cells forming the inner lining of all blood vessels. Endothelium-derived NO has several different functions, one of which is vascular smooth muscle relaxation, resulting in vasodilation and a consequent decrease in blood pressure and increase in local blood flow. In the erectile tissue, NO is released as a neurotransmitter from the nerves innervating the corpus cavernosum during sexual stimulation, and causes profound smooth muscle relaxation and increased blood flow to the erectile tissue. This results in engorgement with blood and consequent penile erection.The uniqueness of NO as a signaling molecule derives, at least in part, by the fact that it is a gaseous molecule in its native state. However, despite being a gas, NO, like oxygen (O2), elicits its pharmacological effects as a solute in aqueous solution. Another unique characteristic of NO is its fleeting action because of its highly unstable chemical nature and reactivity. Unlike many other signaling molecules, NO elicits its wise array of physiological effects by distinct mechanisms. For example, vascular and nonvascular smooth muscle relaxation, and inhibition of platelet function are mediated by intracellular cyclic GMP (cyclic 3’, 5’-guanosine monophosphate). NO elicits many cyclic GMP-independent effects as well. For example, nitric oxide is a reactive free radical that can covalently modify protein function. One good example is protein S-nitrosylation, which can result in both regulatory and aberrant effects. By this and a variety of other mechanisms, NO also reacts with other molecules, such as reactive oxygen species, in invading cells such as bacteria, parasites and viruses to kill them or inhibit their replication or spread.The first pharmacological action of nitric oxide, demonstrated several years before it’s production in mammals was actually discovered, was vascular and nonvascular smooth muscle relaxation. One of many examples of the latter is the smooth muscle enveloping the sinusoidal cavities within the corpus cavernosum. Another important example is the airway smooth muscle in the trachea and bronchioles of the lungs. Indeed, inhalation of NO gas causes bronchodilation and increased delivery of air into the lungs. However, perhaps more significant than the bronchodilator effect of inhaled NO is its vasodilator effect. In fact, advantage was taken of the vasodilator action of NO in the lungs by Warren Zapol, MD, from the Massachusetts General Hospital in Boston, who discovered that inhalation of very small amounts of NO gas by newborn babies with life-threatening, persistent pulmonary hypertension (PPHN) results in a dramatic and permanent reversal of pulmonary vasoconstriction. Inhaled NO (INO) literally turned blue babies into pink babies. Without INO, most babies would have died while others would have required highly invasive procedures (extracorporeal membrane oxygenation; ECMO) to oxygenate their lungs, and may not have survived.Regarding its antiviral action, NO has been shown to increase the survival rate of mammalian cells infected with SARS-CoV (Severe Acute Respiratory Syndrome caused by coronavirus). In an in vitrostudy, NO donors (i.e., S-nitroso-N-acetylpenicillamine) greatly increased the survival rate of SARS-CoV-infected eukaryotic cells, suggesting direct antiviral effects of NO (1). In this study, NO significantly inhibited the replication cycle of SARS CoV in a concentration-dependent manner. NO also inhibited viral protein and RNA synthesis. Furthermore, NO generated by inducible nitric oxide synthase inhibited the SARS CoV replication cycle. The coronavirus responsible for SARS-CoV shares most of the genome of COVID- 19 indicating potential effectiveness of inhaled NO therapy in these patients.In 2004, during the SARS-CoV outbreak in China, the administration of inhaled NO reversed pulmonary hypertension, improved severe hypoxia and shortened the length of ventilatory support as compared to matched control patients with SARS-CoV (2). The mechanism of action was thought to be pulmonary vasodilation and consequent improved oxygenation in the blood of the lungs, thereby killing the virus, which does not do well in a high oxygen environment. In addition, however, I would offer the opinion that the NO also interacts directly with the virus to kill it and/or inhibit its replication, as shown in a prior study (1).Although studies have not yet been reported with COVID-19, NO has been shown to have an antiviral effect on several DNA and RNA virus families (3). The NO-mediated S-nitrosylation of viral molecules might be an intriguing general mechanism for the control of the virus life cycle. In this regard, it is conceivable that NO could nitrosylate cysteine-containing enzymes and proteins, including nucleocapsid proteins and glycoproteins, present in the coronavirus.In view of the knowledge gained by treating SARS-CoV patients with INO, it follows that INO might be effective in patients with the current SARS CoV-2 (COVID-19) infection. Indeed, a clinical trial of inhaled nitric oxide in patients with moderate to severe COVID-19 with pneumonia and under assisted ventilatory support recently received IRB (Institutional Review Board) approval at the Massachusetts General Hospital. Warren Zapol is director of this project. This trial has now been expanded to include at least two additional hospitals in the U.S. In the successful treatment of persistent pulmonary hypertension in newborns, the amount of NO inhaled is generally one ppm (part per million). In the clinical trial using COVID-19 patients, the amount of NO will be approximately 100-fold higher, about 100 ppm. This is a safe dose of INO, which could prove to be effective in killing the virus and allowing recovery of the patient. The effective use of INO would also lessen the need for oxygen, ventilators, and beds in the ICU.One thing I urge everyone to practice during this coronavirus pandemic is to breathe or inhale through your NOSE and exhale through your mouth. Swedish investigators at the Karolinska Institute in Stockholm have shown that the cells and tissues in the nasal sinusoids, but not the mouth, constantly and continuously produce nitric oxide, which is a gas, and can be easily detected in the exhaled breath. The physiological significance of this is that nasally-derived NO, when inhaled through the nose, improves oxygen delivery into the lungs by causing bronchodilation. This physiological action of inhaled NO is well-known by competitive athletes, especially runners. Moreover, when inhaling through the nose, your nasal nitric oxide is inhaled into your lungs where it stands a chance of meeting up with the coronavirus particles and killing them or inhibiting their replication. Inhaling through your mouth will NOT accomplish this. By the same token, exhaling through your nose is highly wasteful in that you would be expelling the NO away from the lungs, where it is needed most.“INHALE THROUGH YOUR NOSE, AND EXHALE THROUGH YOUR MOUTH!”
Hyperexcitability-related diseases include epilepsies, pain syndromes, neuromuscular disorders, and cardiac arrhythmias. Sodium channel inhibitors can be used to treat these conditions, however, their applicability is limited by their nonspecific effect on physiological function. They act by channel block (obstructing ion conduction, since the binding site is within the channel pore), and by modulation (delaying recovery from the non-conducting inactivated state). Channel block inhibits healthy and pathological tissue equally, while modulation can preferentially inhibit pathological activity. Therefore, an ideal sodium channel inhibitor drug would act by modulation alone. Unfortunately, thus far no such drug has been known to exist. Here we present evidence that riluzole acts by this “ideal” mechanism, “non-blocking modulation” (NBM). We propose that, being a relatively small molecule, riluzole is able to stay bound to the binding site, but nonetheless stay off the conduction pathway, by residing in one of the “fenestrations” (cavities connecting the central cavity to the membrane phase). Using precisely timed UV pulses to photolabel specific conformations of the channel, we show that association to the local anesthetic binding site requires prior inactivation. We discuss why kinetics of binding is crucial for selective inhibition of pathological activity, and how the NBM mechanism can be recognized using a special voltage- and drug application-protocol. Our results identify riluzole as the prototype of this new class of sodium channel inhibitors. Drugs of this class are expected to selectively prevent hyperexcitability, while having minimal effect on cells firing at a normal rate from a normal resting potential.
Background and Purpose: Heart failure can reflect impaired contractile function at the myofilament level. In healthy hearts, myofilaments become more sensitive to Ca2+ as cells are stretched. This represents a fundamental property of myocardium that contributes to the Frank-Starling response, although the molecular mechanisms underlying the effect remain unclear. Mavacamten is a drug that binds to myosin, which is under investigation as a potential therapy for cardiovascular disease. We tested how mavacamten affects the sarcomere-length dependence of Ca2+-sensitive isometric contraction to determine how mavacamten might modulate the Frank-Starling mechanism. Experimental Approach: Multicellular preparations from the left ventricular free wall of hearts procured from organ donors were chemically permeabilized and Ca2+-activated in the presence or absence of 0.5 μM mavacamten at 1.9 or 2.3 µm sarcomere length (37°C). Isometric force and frequency-dependent viscoelastic myocardial stiffness measurements were made. Key Results: At both sarcomere lengths, mavacamten reduced maximal force and Ca2+-sensitivity of contraction. In the presence and absence of mavacamten, Ca2+-sensitivity of force increased as sarcomere length increased. This suggests that the length-dependent activation response was maintained in human myocardium, even though mavacamten reduced Ca2+-sensitivity. There were subtle effects of mavacamten reducing force values under relaxed conditions (pCa 8.0), as well as slowing myosin cross-bridge recruitment and speeding cross-bridge detachment under maximally activated conditions (pCa 4.5). Conclusion and Implications: Mavacamten did not eliminate sarcomere length-dependent increases in the Ca2+-sensitivity of contraction in myocardial strips from organ donors at physiological temperature. Pharmaceuticals that modulate myofilament function may be useful therapies for cardiovascular disease.