Probenecid Improves Cardiac Function in Patients With Heart Failure With Reduced Ejection Fraction In Vivo and Cardiomyocyte Calcium Sensitivity In Vitro

TRP (transient receptor potential) ion channel family: structures, biological functions and therapeutic interventions for diseases

Transient receptor potential (TRP) channels are sensors for a variety of cellular and environmental signals. Mammals express a total of 28 different TRP channel proteins, which can be divided into seven subfamilies based on amino acid sequence homology: TRPA (Ankyrin), TRPC (Canonical), TRPM (Melastatin), TRPML (Mucolipin), TRPN (NO-mechano-potential, NOMP), TRPP (Polycystin), TRPV (Vanilloid). They are a class of ion channels found in numerous tissues and cell types and are permeable to a wide range of cations such as Ca²⁺, Mg²⁺, Na⁺, K⁺, and others. TRP channels are responsible for various sensory responses including heat, cold, pain, stress, vision and taste and can be activated by a number of stimuli. Their predominantly location on the cell surface, their interaction with numerous physiological signaling pathways, and the unique crystal structure of TRP channels make TRPs attractive drug targets and implicate them in the treatment of a wide range of diseases. Here, we review the history of TRP channel discovery, summarize the structures and functions of the TRP ion channel family, and highlight the current understanding of the role of TRP channels in the pathogenesis of human disease. Most importantly, we describe TRP channel-related drug discovery, therapeutic interventions for diseases and the limitations of targeting TRP channels in potential clinical applications.

Probenecid affects muscle Ca2+ homeostasis and contraction independently from pannexin channel block

Tight control of skeletal muscle contractile activation is secured by the excitation-contraction (EC) coupling protein complex, a molecular machinery allowing the plasma membrane voltage to control the activity of the ryanodine receptor Ca2+ release channel in the sarcoplasmic reticulum (SR) membrane. This machinery has been shown to be intimately linked to the plasma membrane protein pannexin-1 (Panx1). We investigated whether the prescription drug probenecid, a widely used Panx1 blocker, affects Ca2+ signaling, EC coupling, and muscle force. The effect of probenecid was tested on membrane current, resting Ca2+, and SR Ca2+ release in isolated mouse muscle fibers, using a combination of whole-cell voltage-clamp and Ca2+ imaging, and on electrically triggered contraction of isolated muscles. Probenecid (1 mM) induces SR Ca2+ leak at rest and reduces peak voltage-activated SR Ca2+ release and contractile force by 40%. Carbenoxolone, another Panx1 blocker, also reduces Ca2+ release, but neither a Panx1 channel inhibitory peptide nor a purinergic antagonist affected Ca2+ release, suggesting that probenecid and carbenoxolone do not act through inhibition of Panx1-mediated ATP release and consequently altered purinergic signaling. Probenecid may act by altering Panx1 interaction with the EC coupling machinery, yet the implication of another molecular target cannot be excluded. Since probenecid has been used both in the clinic and as a masking agent for doping in sports, these results should encourage evaluation of possible effects on muscle function in treated individuals. In addition, they also raise the question of whether probenecid-induced altered Ca2+ homeostasis may be shared by other tissues.

Drug repurposing for cardiovascular diseases: New targets and indications for probenecid

The available pharmacological options in the management of cardiovascular diseases such as ischaemic heart disease and subsequent heart failure are effective in slowing the progression of this condition. However, the long-term prognosis is still poor, raising the demand for new therapeutic strategies. Drug repurposing is a time- and cost-effective drug development strategy that offers approved and abandoned drugs a new chance for new indications. Recently, drugs used for the management of gout-related inflammation such as canakinumab or colchicine have been considered for drug repurposing in cardiovascular indications. The old uricosuric drug, probenecid, has been identified as a novel therapeutic option in the management of specific cardiac diseases as well. Probenecid can modulate myocardial contractility and vascular tone and exerts anti-inflammatory properties. The mechanisms behind these beneficial effects might be related inhibition of inflammasomes, and to modulation purinergic-pannexin-1 signalling and TRPV2 channels, which are recently identified molecular targets of probenecid. In this review, we provide an overview on repurposing probenecid for ischaemic heart disease and subsequent heart failure by summarizing the related experimental and clinical data and propose its potential repurposing to treat cardiovascular diseases.

Repurposing Probenecid for the Treatment of Heart Failure (Re-Prosper-HF): a study protocol for a randomized placebo-controlled clinical trial

BACKGROUND

Improving contractility in heart failure with reduced ejection fraction (HFrEF) has resurfaced as a potential treatment goal. Inotropic therapy is now better understood through its underlying mechanism as opposed to the observed effect of increasing contractility. Calcitropes are a subgroup of inotropes that largely depend on the stimulation of adenylyl cyclase to transform ATP into cyclic adenosine monophosphate (cAMP). At least two clinically relevant calcitropes-istaroxime and probenecid-improve contractility through an increase in systolic intracellular calcium without activating cAMP production. Probenecid, which has been safely used clinically for decades in non-cardiac conditions, has recently been identified as an agonist of the transient receptor potential vanilloid 2 channel. Translational studies have shown that it improves calcium cycling and contractility without activating noxious pathways associated with cAMP-dependent calcitropes and can improve cardiac function in patients with HFrEF.

METHODS

The Re-Prosper-HF study (Repurposing Probenecid for the Treatment of Heart Failure with Reduced Ejection Fraction) is a three-site double-blinded randomized-controlled trial that will test the hypothesis that probenecid can improve cardiac function in patients with HFrEF. Up to 120 patients will be randomized in this double-blind, placebo-controlled study that will assess whether oral probenecid administered at 1 g orally twice per day for 180 days in patients with NYHA II-III HFrEF improves systolic function (aim 1), functional status (aim 2), and self-reported health status (aim 3).

DISCUSSION

Findings from this study will provide data informing its use for improving symptomatology in patients with HFrEF as well as exploratory data for outcomes such as hospital admission rates.

TRIAL TEGISTRATION

The Re-Prosper HF Study (Re-Prosper HF) is registered on ClinicalTrials.gov with the identifier as NCT04551222. Registered on 9 September 2020.

Role of Known Transient Receptor Potential Vanilloid Channels in Modulating Cardiac Mechanobiology

The transient receptor potential (TRP) channels have been described in almost every mammalian cell type. Several members of the Vanilloid (TRPV) subtype have been found to play important roles in modulating cardiac structure and function through Ca²⁺ handling in response to systemic and local mechanobiological cues. In this review, we will consider the most studied TRPV channels in the cardiovascular field; transient receptor potential vanilloid 1 as a modulator of cardiac hypertrophy; transient receptor potential vanilloid 2 as a structural and functional protein; transient receptor potential vanilloid 3 in the development of hypertrophy and myocardial fibrosis; and transient receptor potential vanilloid 4 in its roles modulating the fibrotic and functional responses of the heart to pressure overload. Lastly, we will also review the potential overlapping roles of these channels with other TRP proteins as well as the advances in translational and clinical arenas associated with TRPV channels.

AIM2-driven inflammasome activation in heart failure

AIMS

Interleukin-1β (IL-1β) is an important pathogenic factor in cardiovascular diseases including chronic heart failure (HF). The CANTOS trial highlighted that inflammasomes as primary sources of IL-1 β are promising new therapeutic targets in cardiovascular diseases. Therefore, we aimed to assess inflammasome activation in failing hearts to identify activation patterns of inflammasome subtypes as sources of IL-1β.

METHODS AND RESULTS

Out of the four major inflammasome sensors tested, expression of the inflammasome protein absent in melanoma 2 (AIM2) and NLR family CARD domain-containing protein 4 (NLRC4) increased in human HF regardless of the aetiology (ischaemic or dilated cardiomyopathy), while the NLRP1/NALP1 and NLRP3 (NLR family, pyrin domain containing 1 and 3) inflammasome showed no change in HF samples. AIM2 expression was primarily detected in monocytes/macrophages of failing hearts. Translational animal models of HF (pressure or volume overload, and permanent coronary artery ligation in rat, as well as ischaemia/reperfusion-induced HF in pigs) demonstrated activation pattern of AIM2 similar to that of observed in end-stages of human HF. In vitro AIM2 inflammasome activation in human Tohoku Hospital Pediatrics-1 (THP-1) monocytic cells and human AC16 cells was significantly reduced by pharmacological blockade of pannexin-1 channels by the clinically used uricosuric drug probenecid. Probenecid was also able to reduce pressure overload-induced mortality and restore indices of disease severity in a rat chronic HF model in vivo.

CONCLUSIONS

This is the first report showing that AIM2 and NLRC4 inflammasome activation contribute to chronic inflammation in HF and that probenecid alleviates chronic HF by reducing inflammasome activation. The present translational study suggests the possibility of repositioning probenecid for HF indications.

Cardiovascular risk associated with allopurinol vs. benzbromarone in patients with gout

Aims 

With the high prevalence of gout and associated cardiovascular (CV) diseases, information on the comparative CV safety of individual urate-lowering drugs becomes increasingly important. However, few studies examined the CV risk of uricosuric agents. We compared CV risk among patients with gout who initiated allopurinol vs. benzbromarone.

Methods and results 

Using the Korean National Health Insurance claims data (2002–17), we conducted a cohort study of 124 434 gout patients who initiated either allopurinol (n = 103 695) or benzbromarone (n = 20 739), matched on propensity score at a 5:1 ratio. The primary outcome was a composite CV endpoint of myocardial infarction, stroke/transient ischaemic attack, or coronary revascularization. To account for competing risk of death, we used cause-specific hazard models to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the outcomes comparing allopurinol initiators with benzbromarone. Over a mean follow-up of 1.16 years, 2258 patients developed a composite CV event. The incidence rate of the composite CV event was higher in allopurinol initiators (1.81 per 100 person-years) than benzbromarone (1.61 per 100 person-years) with a HR of 1.22 (95% CI 1.05–1.41). The HR for all-cause mortality was 1.66 (95% CI 1.43–1.93) among allopurinol initiators compared with benzbromarone.

Conclusion 

In this large population-based cohort of gout patients, allopurinol was associated with an increased risk of composite CV events and all-cause mortality compared to benzbromarone. Benzbromarone may reduce CV risk and mortality in patients with gout, although more studies are necessary to confirm our findings and to advance our understanding of the underlying mechanisms.

Uric acid as a cardiorenal mediator: pathogenesis and mechanistic insights

Introduction: The role of serum uric acid as a connector in cardiorenal interactions has been long debated and studied extensively in the past decade. Epidemiological, and clinical data suggest that hyperuricemia may be an independent risk factor as well as a strong predictor of morbidity and mortality in cardiovascular diseases (CVD) and renal diseases. New data suggesting that urate lowering therapies may improve outcomes in cardiovascular diseases have generated interest.Areas Covered: This review attempts to summarize the pathophysiological mechanisms by which hyperuricemia causes cardiorenal dysfunction. It also provides a summary of the recent evidence for urate lowering therapies and the possible underlying mechanisms which lead to cardiovascular benefits. This was a narrative review with essential references or cross references obtained via expert opinion.Expert Opinion: Emphasis on newer drugs that address the cardio-renal metabolic axis and the relation to their effects on uric acid may help further elucidate underlying mechanisms responsible for their cardiovascular and renal benefits. Once these benefits are well established, we will be able to come up with guidelines for targeting hyperuricemia. This can potentially lead to a change in clinical practice and can possibly lead to improved cardiovascular and renal outcomes.

Effect of Uric Acid-Lowering Agents on Patients With Heart Failure: A Systematic Review and Meta-Analysis of Randomised Controlled Trials

Background: Elevated serum uric acid (SUA) level is considered an independent predictor of all-cause mortality and the combined endpoint of death or readmission in cardiovascular disease patients. However, the causal relationship between uric acid-lowering therapies (ULTs) and heart failure is still controversial.

Design: Meta-analyses were performed to systematically compile available evidence to determine the overall effect of ULTs on heart failure patients.

Method: We conducted this systematic review following the PRISMA statement guidelines. Databases were searched to identify randomised controlled trials related to the influence of a ULT intervention in people with heart failure. Data extracted from the included studies were subjected to a meta-analysis to compare the effects of ULTs to a control.

Results: Pooled analysis of left ventricular ejection fraction (LEVF) showed an insignificant result towards the ULT group (MD, 1.63%; 95%CI, −1.61 to 4.88; p = 0.32; three studies). Pooled analysis of the 6-Minute Walk Test (6MWT) showed an insignificant result towards the ULT group (MD, 4.59; 95%CI, −12.683 to 22.00; p = 0.61; four studies). Pooled analysis of BNP/NT-pro-BNP led to a nearly statistically significant result towards the ULT group (SMD, −0.30; 95%CI, −0.64 to 0.04; p = 0.08; five studies). Pooled analysis of all-cause mortality and cardiovascular death between ULTs (all XOIs) and placebo did not show a significant difference (RR, 1.26; 95% CI, 0.74 to 2.15, p = 0.39).

Conclusion: ULTs did not improve LVEF, BNP/NT-pro-BNP, 6MWT, all-cause mortality, and CV death in heart failure patients. UA may just be a risk marker of heart failure.

Probenecid Improves Cardiac Function in Subjects with a Fontan Circulation and Augments Cardiomyocyte Calcium Homeostasis

Subjects with functionally univentricular circulation who have completed staged single ventricle palliation, with the final stage culminating in the Fontan procedure, are often living into adulthood. However, high morbidity and mortality remain prevalent in these patients, as diastolic and systolic dysfunction of the single systemic ventricle are linked to Fontan circulatory failure. We presently investigated the effects of probenecid in post-Fontan patients. Used for decades for the treatment of gout, probenecid has been shown in recent years to positively influence cardiac function via effects on the Transient Receptor Potential Vanilloid 2 (TRPV2) channel in cardiomyocytes. Indeed, we observed that probenecid improved cardiac function and exercise performance in patients with a functionally univentricular circulation. This was consistent with our findings from a retrospective cohort of patients with single ventricle physiology where TRPV2 expression was increased. Experiments in isolated cardiomyocytes associated these positive actions to augmentation of diastolic calcium homeostasis.

Investigational drugs in early phase clinical trials targeting thermotransient receptor potential (thermoTRP) channels

INTRODUCTION

Thermo transient receptor potential (thermoTRP) channels are some of the most intensely pursued therapeutic targets of the past decade. They are considered promising targets of numerous diseases including chronic pain and cancer. Modulators of these proteins, in particular TRPV1-4, TRPM8 and TRPA1, have reached clinical development, but none has been approved for clinical practice yet.

AREAS COVERED

The therapeutic potential of targeting thermoTRP channels is discussed. The discussion is centered on our experience and on available data found in SciFinder, PubMed, and ClinicalTrials.gov database from the past decade. This review focuses on the therapeutic progress concerning this family of channels, including strategies to improve their therapeutic index for overcoming adverse effects.

EXPERT OPINION

Although thermoTRPs are pivotal drug targets, translation to the clinic has faced two key problems, (i) unforeseen side effects in Phase I trials and, (ii) poor clinical efficacy in Phase II trials. Thus, there is a need for (i) an enhanced understanding of the physiological role of these channels in tissues and organs and (ii) the development of human-based pre-clinical models with higher clinical translation. Furthermore, progress in nanotechnology-based delivery strategies will positively impact thermoTRP human pharmacology.

Probenecid treatment improves outcomes in a novel mouse model of peripartum cardiomyopathy

Probenecid has been used for decades in the treatment of gout but recently has also been found to improve outcomes in patients with heart failure via stimulation of the transient receptor potential vanilloid 2 (TRPV2) channel in cardiomyocytes. This study tested the use of probenecid on a novel mouse model of peripartum cardiomyopathy (PPCM) as a potential treatment option. A human mutation of the human heat shock protein 20 (Hsp20-S10F) in mice has been recently shown to result in cardiomyopathy, when exposed to pregnancies. Treatment with either probenecid or control sucrose water was initiated after the first pregnancy in both wild type and Hsp20-S10F mice. Serial echocardiography was performed during subsequent pregnancies and hearts were collected after the third pregnancies for staining and molecular analysis. Hsp20-S10F mice treated with probenecid had decreased mortality, hypertrophy, TRPV2 expression and molecular parameters of heart failure. Probenecid treatment also decreased apoptosis as evidenced by an increase in the level of Bcl-2/Bax. Probenecid improved survival in a novel mouse model of PPCM and may be an appropriate therapy for humans with PPCM as it has a proven safety and tolerability in patients with heart failure.

TRPV2 channel as a possible drug target for the treatment of heart failure

Heart transplantation is currently the only viable option available for the treatment of severe heart failure conditions such as dilated cardiomyopathy. Hence, novel drugs for treating such conditions need to be developed urgently. Recent studies suggest that Ca²⁺ overload is involved in the onset and progression of dilated cardiomyopathy, and thus heart failure. The expression and activation of the Ca²⁺ permeable channel, transient receptor potential vanilloid 2 (TRPV2) channel have been found to play an essential role in sustained intracellular Ca²⁺ concentration increase, leading to heart failure. However, since there have been no TRPV2-specific inhibitors available until recently, the effect of TRPV2 inhibition on the pathology has not been clearly elucidated. Recent reports show that inhibiting TRPV2 activity effectively improves cardiac function, suppressing myocardial fibrosis and ameliorating the prognosis in animal models of cardiomyopathy with heart failure. In addition to that, inflammation is reported to be involved in the development of heart failure. Here, we review the recent findings on TRPV2 in cardiomyocytes and immune cells involved in the development of heart failure and discuss the current progress of drug development for the treatment of heart failure via targeting TRPV2.

The Control of Diastolic Calcium in the Heart: Basic Mechanisms and Functional Implications

Normal cardiac function requires that intracellular Ca²⁺ concentration be reduced to low levels in diastole so that the ventricle can relax and refill with blood. Heart failure is often associated with impaired cardiac relaxation. Little, however, is known about how diastolic intracellular Ca²⁺ concentration is regulated. This article first discusses the reasons for this ignorance before reviewing the basic mechanisms that control diastolic intracellular Ca²⁺ concentration. It then considers how the control of systolic and diastolic intracellular Ca²⁺ concentration is intimately connected. Finally, it discusses the changes that occur in heart failure and how these may result in heart failure with preserved versus reduced ejection fraction.

Potential roles in cardiac physiology and pathology of the cation channel TRPV2 expressed in cardiac cells and cardiac macrophages: a mini-review

TRPV2 is a well-conserved channel protein expressed in almost all tissues. Cardiomyocyte TRPV2 is expressed in the intercalated disks of the cardiac sarcomeres, where it is involved in maintaining the proper mechanoelectric coupling and structure. It is also abundantly expressed in the intracellular pools, mainly the endoplasmic reticulum. Under pathological conditions, TRPV2 is translocated to the sarcolemma, where it mediates an abnormal [Ca]²⁺ entry that may contribute to disease progression. In addition, an intracellularly diffused TRPV2 expression is present in resident cardiac macrophages. Upon infection or inflammation, TRPV2 is engaged in early phagosomes and is, therefore, potentially involved in protecting the cardiac tissue. Following acute myocardial infarction, a profound elevated expression of TRPV2 is observed on the cell membrane of the peri-infarct macrophages. The macrophage TRPV2 may harbor a detrimental effect in cardiac recovery by increasing unfavorable migration and phagocytosis processes in the injured heart. Most reports suggest that while cardiac TRPV2 activation may be beneficial under specific physiological conditions, both cardiac- and macrophage-related TRPV2 blocking can significantly ameliorate disease progression in various pathological states. To verify this possibility, the time frame of TRPV2 overexpression and its mediated signaling need to be fully characterized in both cardiomyocyte and cardiac macrophage populations.

Probenecid: An Oral Inotrope for End-Stage Heart Failure in a Case With Myotonic Dystrophy

A 56-year-old man with multiple cardiac manifestations of type 1 myotonic dystrophy, including severe, nonischemic cardiomyopathy, presented in refractory cardiogenic shock requiring inotropic therapy. Given his wishes to die without having any intravenous medications, he was started on oral probenecid therapy, which allowed for successful elimination of his intravenous therapies. (Level of Difficulty: Intermediate.)

In Vitro Negative Inotropic Effect of Low Concentrations of Bupivacaine Relates to Diminished Ca2+ Sensitivity but Not to Ca2+ Handling or β-Adrenoceptor Signaling

BACKGROUND

Systemic toxicity of local anesthetics is predominantly complicated by their myocardial toxicity. Especially long-acting local anesthetics exert a negative inotropic effect that has been described at lower concentrations than defined for blockade of myocardial ion channels. We evaluated the negative inotropic effect of bupivacaine at a concentration described for clinical toxicity testing the hypothesis that negative inotropy is a result of reduced Ca sensitivity rather than blockade of ion channels.

METHODS

We simultaneously measured force development and action potentials in guinea pig right papillary muscles (n = 5 to 7). L-type Ca currents (n = 8 to 16) and Ca transients (n = 10 to 11) were measured in isolated cardiomyocytes. Sensitivity of myofilaments to Ca was assessed in skinned fibers (n = 10). Potential effects of bupivacaine on 3',5'-cyclic adenosine monophosphate concentrations were measured using Förster Resonance Energy Transfer (n = 12 to 14) microscopy.

RESULTS

Bupivacaine reduced force in a concentration-dependent manner from 173 ± 119 µN at baseline to 28 ± 13 µN at 300 µM (mean ± SD). At concentrations giving half-maximum negative inotropic effects (5 µM), the maximum upstroke velocity of action potentials, as a surrogate of sodium channel activity, was unaffected. Maximum positive inotropic effects of isoprenaline were also reduced to 50%. Neither basal nor isoprenaline-induced 3',5'-cyclic adenosine monophosphate accumulation, L-type Ca currents, or Ca transients were affected by 5 µM bupivacaine, but this concentration significantly decreased Ca sensitivity of myofilaments, changing the negative logarithm of the half-maximum effective Ca concentrations from 5.66 to 5.56 -log[M].

CONCLUSIONS

We provide evidence that the negative inotropic effect of bupivacaine may be caused mainly by a reduction in myofilament sensitivity to Ca.

Treatment of Cardiorenal Syndrome

The treatment of cardiorenal syndrome is as complex as the various mechanisms underlying its pathophysiology. Randomized controlled data typically focus on the treatment of heart failure with cardiac specific endpoints and a lack of worsening renal function used as a surrogate for efficacy. When heart failure is considered the inciting event, the acute state is managed with vasodilators, inotropic support, and decongestion; whereas neurohormonal axis inhibition is more commonly applied to chronic state. A recent shift in thought process regarding the interplay of cardiac and renal dysfunction suggests that renal congestion may be the primary driver of worsening renal function.