Ca2+-calmodulin increases RyR2 open probability yet reduces ryanoid association with RyR2

Comprehensive insight into the pharmacology, pharmacokinetics, toxicity, detoxification and extraction of hypaconitine from Aconitum plants

ETHNOPHARMACOLOGICAL RELEVANCE

Hypaconitine (HA), a diterpenoid alkaloid, mainly derived from Aconitum plants such as Acoitum carmichaeli Debx. And Aconitum nagarum Stapf., has recently piqued significant interest among the scientific community given its multifaceted attributes including anti-inflammatory, anticancer, analgesic, and cardio-protective properties.

AIM OF THE STUDY

This review presents a comprehensive exploration of the research advancements regarding the traditional uses, pharmacology, pharmacokinetics, toxicity, and toxicity reduction of HA. It aims to provide a thorough understanding of HA's multifaceted properties and its potential applications in various fields.

MATERIALS AND METHODS

A systematic literature search was conducted using several prominent databases including PubMed, Web of Science, NCBI, and CNKI. The search was performed using specific keywords such as "hypaconitine," "heart failure," "anti-inflammatory," "aconite decoction," "pharmacological," "pharmacokinetics," "toxicity," "detoxification or toxicity reduction," and "extraction and isolation." The inclusion of these keywords ensured a comprehensive exploration of relevant studies and enabled the retrieval of valuable information pertaining to the various aspects of HA.

RESULTS

Existing research has firmly established that HA possesses a range of pharmacological effects, encompassing anti-cardiac failure, anti-inflammatory, analgesic, and anti-tumor properties. The therapeutic potential of HA is promising, with potential applications in heart failure, ulcerative colitis, cancer, and other diseases. Pharmacokinetic studies suggest that HA exhibits high absorption rates, broad distribution, and rapid metabolism. However, toxic effects of HA on the nerves, heart, and embryos have also been observed. To mitigate these risks, HA needs attenuation before use, with the most common detoxification methods being processing and combined use with other drugs. Extraction methods for HA most commonly include cold maceration, soxhlet reflux extraction, and ultrasonic-assisted extraction. Despite the potential therapeutic benefits of HA, further research is warranted to elucidate its anti-heart failure effects, particularly in vivo, exploring aspects such as in vivo metabolism, distribution, and metabolites. Additionally, the therapeutic effects of HA monomers on inflammation-induced diseases and tumors should be validated in a more diverse range of experimental models, while the mechanisms underlying the therapeutic effects of HA should be investigated in greater detail.

CONCLUSION

This review serves to emphasize the therapeutic potential of HA and highlights the crucial need to address its toxicity concerns before considering clinical application. Further research is required to comprehensively investigate the pharmacological properties of HA, with particular emphasis on its anti-cardiac failure and anti-inflammatory activities. Such research endeavors have the potential to unveil novel treatment avenues for a broad spectrum of diseases.

Calmodulin variant E140G associated with long QT syndrome impairs CaMKIIδ autophosphorylation and L-type calcium channel inactivation

Long QT syndrome (LQTS) is a human inherited heart condition that can cause life-threatening arrhythmia including sudden cardiac death. Mutations in the ubiquitous Ca²⁺-sensing protein calmodulin (CaM) are associated with LQTS, but the molecular mechanism by which these mutations lead to irregular heartbeats is not fully understood. Here, we use a multidisciplinary approach including protein biophysics, structural biology, confocal imaging, and patch-clamp electrophysiology to determine the effect of the disease-associated CaM mutation E140G on CaM structure and function. We present novel data showing that mutant-regulated CaMKIIδ kinase activity is impaired with a significant reduction in enzyme autophosphorylation rate. We report the first high-resolution crystal structure of a LQTS-associated CaM variant in complex with the CaMKIIδ peptide, which shows significant structural differences, compared to the WT complex. Furthermore, we demonstrate that the E140G mutation significantly disrupted Ca_v1.2 Ca²⁺/CaM-dependent inactivation, while cardiac ryanodine receptor (RyR2) activity remained unaffected. In addition, we show that the LQTS-associated mutation alters CaM's Ca²⁺-binding characteristics, secondary structure content, and interaction with key partners involved in excitation-contraction coupling (CaMKIIδ, Ca_v1.2, RyR2). In conclusion, LQTS-associated CaM mutation E140G severely impacts the structure-function relationship of CaM and its regulation of CaMKIIδ and Ca_v1.2. This provides a crucial insight into the molecular factors contributing to CaM-mediated arrhythmias with a central role for CaMKIIδ.

CPVT-associated calmodulin variants N53I and A102V dysregulate Ca2+ signalling via different mechanisms

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited condition that can cause fatal cardiac arrhythmia. Human mutations in the Ca2+ sensor calmodulin (CaM) have been associated with CPVT susceptibility, suggesting that CaM dysfunction is a key driver of the disease. However, the detailed molecular mechanism remains unclear. Focusing on the interaction with the cardiac ryanodine receptor (RyR2), we determined the effect of CPVT-associated variants N53I and A102V on the structural characteristics of CaM and on Ca2+ fluxes in live cells. We provide novel data showing that interaction of both Ca2+/CaM-N53I and Ca2+/CaM-A102V with the RyR2 binding domain is decreased. Ca2+/CaM-RyR23583-3603 high-resolution crystal structures highlight subtle conformational changes for the N53I variant, with A102V being similar to wild type (WT). We show that co-expression of CaM-N53I or CaM-A102V with RyR2 in HEK293 cells significantly increased the duration of Ca2+ events; CaM-A102V exhibited a lower frequency of Ca2+ oscillations. In addition, we show that CaMKIIδ (also known as CAMK2D) phosphorylation activity is increased for A102V, compared to CaM-WT. This paper provides novel insight into the molecular mechanisms of CPVT-associated CaM variants and will facilitate the development of strategies for future therapies.

Risk Compounds, Preclinical Toxicity Evaluation, and Potential Mechanisms of Chinese Materia Medica-Induced Cardiotoxicity

Chinese materia medica (CMM) has been applied for the prevention and treatment of diseases for thousands of years. However, arrhythmia, myocardial ischemia, heart failure, and other cardiac adverse reactions during CMM application were gradually reported. CMM-induced cardiotoxicity has aroused widespread attention. Our review aimed to summarize the risk compounds, preclinical toxicity evaluation, and potential mechanisms of CMM-induced cardiotoxicity. All relevant articles published on the PubMed, Embase, and China National Knowledge Infrastructure (CNKI) databases for the latest twenty years were searched and manually extracted. The risk substances of CMM-induced cardiotoxicity are relatively complex. A single CMM usually contains various risk compounds, and the same risk substance may exist in various CMM. The active and risk substances in CMM may be transformed into each other under different conditions, such as drug dosage, medication methods, and body status. Generally, the risk compounds of CMM-induced cardiotoxicity can be classified into alkaloids, terpenoids, steroids, heavy metals, organic acids, toxic proteins, and peptides. Traditional evaluation methods of chemical drug-induced cardiotoxicity primarily include cardiac function monitoring, endomyocardial biopsy, myocardial zymogram, and biomarker determination. In the preclinical stage, CMM-induced cardiotoxicity should be systematically evaluated at the overall, tissue, cellular, and molecular levels, including cardiac function, histopathology, cytology, myocardial zymogram, and biomarkers. Thanks to the development of systematic biology, the higher specificity and sensitivity of biomarkers, such as genes, proteins, and metabolic small molecules, are gradually applied for evaluating CMM-induced cardiotoxicity. Previous studies on the mechanisms of CMM-induced cardiotoxicity focused on a single drug, monomer or components of CMM. The interaction among ion homeostasis (sodium, potassium, and calcium ions), oxidative damage, mitochondrial injury, apoptosis and autophagy, and metabolic disturbance is involved in CMM-induced cardiotoxicity. Clarification on the risk compounds, preclinical toxicity evaluation, and potential mechanisms of CMM-induced cardiotoxicity must be beneficial to guide new CMM development and post-marketed CMM reevaluation.

Ion channel gating in cardiac ryanodine receptors from the arrhythmic RyR2-P2328S mouse

Mutations in the cardiac ryanodine receptor Ca²⁺ release channel (RyR2) can cause deadly ventricular arrhythmias and atrial fibrillation (AF). The RyR2-P2328S mutation produces catecholaminergic polymorphic ventricular tachycardia (CPVT) and AF in hearts from homozygous RyR2^{P2328S/P2328S} (denoted RyR2^S/S) mice. We have now examined P2328S RyR2 channels from RyR2^S/S hearts. The activity of wild-type (WT) and P2328S RyR2 channels was similar at a cytoplasmic [Ca²⁺] of 1 mM, but P2328S RyR2 was significantly more active than WT at a cytoplasmic [Ca²⁺] of 1 µM. This was associated with a >10-fold shift in the half maximal activation concentration (AC₅₀) for Ca²⁺ activation, from ∼3.5 µM Ca²⁺ in WT RyR2 to ∼320 nM in P2328S channels and an unexpected >1000-fold shift in the half maximal inhibitory concentration (IC₅₀) for inactivation from ∼50 mM in WT channels to ≤7 μM in P2328S channels, which is into systolic [Ca²⁺] levels. Unexpectedly, the shift in Ca²⁺ activation was not associated with changes in sub-conductance activity, S2806 or S2814 phosphorylation or the level of FKBP12 (also known as FKBP1A) bound to the channels. The changes in channel activity seen with the P2328S mutation correlate with altered Ca²⁺ homeostasis in myocytes from RyR2^S/S mice and the CPVT and AF phenotypes.This article has an associated First Person interview with the first author of the paper.

Examining a new role for zinc in regulating calcium release in cardiac muscle

It is well established that mammalian cells contain a small but measurable pool of free or labile zinc in the cytosol that is buffered in the high picomolar range. Recent attention has focused on the fact that this pool of free zinc has signalling effects that can be evoked through extracellular stimuli posing the question as to whether zinc should be regarded as a second messenger. Our knowledge of the targets, the biological significance and the molecular mechanisms of zinc signalling is limited but recent evidence suggests that zinc homoeostasis may be intimately linked to intracellular calcium signalling. In this review, we discuss the role of zinc as an intracellular signalling molecule with an emphasis on the potential role of zinc in shaping calcium-dynamics in cardiac muscle. We also consider the evidence that the cardiac ryanodine receptor (RyR2) is a potential zinc signalling target.

FKBP12.6 activates RyR1: investigating the amino acid residues critical for channel modulation

We have previously shown that FKBP12 associates with RyR2 in cardiac muscle and that it modulates RyR2 function differently to FKBP12.6. We now investigate how these proteins affect the single-channel behavior of RyR1 derived from rabbit skeletal muscle. Our results show that FKBP12.6 activates and FKBP12 inhibits RyR1. It is likely that both proteins compete for the same binding sites on RyR1 because channels that are preactivated by FKBP12.6 cannot be subsequently inhibited by FKBP12. We produced a mutant FKBP12 molecule (FKBP12E31Q/D32N/W59F) where the residues Glu(31), Asp(32), and Trp(59) were converted to the corresponding residues in FKBP12.6. With respect to the functional regulation of RyR1 and RyR2, the FKBP12E31Q/D32N/W59F mutant lost all ability to behave like FKBP12 and instead behaved like FKBP12.6. FKBP12E31Q/D32N/W59F activated RyR1 but was not capable of activating RyR2. In conclusion, FKBP12.6 activates RyR1, whereas FKBP12 activates RyR2 and this selective activator phenotype is determined within the amino acid residues Glu(31), Asp(32), and Trp(59) in FKBP12 and Gln(31), Asn(32), and Phe(59) in FKBP12.6. The opposing but different effects of FKBP12 and FKBP12.6 on RyR1 and RyR2 channel gating provide scope for diversity of regulation in different tissues.

Redox control of cardiac excitability

Reactive oxygen species (ROS) have been associated with various human diseases, and considerable attention has been paid to investigate their physiological effects. Various ROS are synthesized in the mitochondria and accumulate in the cytoplasm if the cellular antioxidant defense mechanism fails. The critical balance of this ROS synthesis and antioxidant defense systems is termed the redox system of the cell. Various cardiovascular diseases have also been affected by redox to different degrees. ROS have been indicated as both detrimental and protective, via different cellular pathways, for cardiac myocyte functions, electrophysiology, and pharmacology. Mostly, the ROS functions depend on the type and amount of ROS synthesized. While the literature clearly indicates ROS effects on cardiac contractility, their effects on cardiac excitability are relatively under appreciated. Cardiac excitability depends on the functions of various cardiac sarcolemal or mitochondrial ion channels carrying various depolarizing or repolarizing currents that also maintain cellular ionic homeostasis. ROS alter the functions of these ion channels to various degrees to determine excitability by affecting the cellular resting potential and the morphology of the cardiac action potential. Thus, redox balance regulates cardiac excitability, and under pathological regulation, may alter action potential propagation to cause arrhythmia. Understanding how redox affects cellular excitability may lead to potential prophylaxis or treatment for various arrhythmias. This review will focus on the studies of redox and cardiac excitation.

Effect of hypaconitine combined with liquiritin on the expression of calmodulin and connexin43 in rat cardiac muscle in vivo

OBJECTIVES

To study the effects of hypaconitine used alone and combined with liquiritin on calmodulin (CaM) expression and connexin43 (Cx43) phosphorylation on serine368 (Ser368), as well as to investigate the intervention of liquiritin on these hypaconitine-induced effects.

METHODS

Adult Wistar rats were orally administered hypaconitine (0.23, 0.69, 2.07 mg/kg per day), liquiritin (20 mg/kg per day), or hypaconitine (2.07 mg/kg per day) plus liquiritin (20 mg/kg per day) for seven consecutive days. The mRNA expression levels of CaM and Cx43 in rat myocardial tissue were determined by real-time quantitative PCR. The protein contents of CaM and phosphorylated Cx43 (Ser368) were determined by Western blot.

KEY FINDINGS

The results indicated that the mRNA and protein expression levels of CaM were significantly decreased by hypaconitine used alone and combined with liquiritin. Although CaM mRNA expression level was inhibited by liquiritin, its protein expression level was upregulated. Meanwhile, although no obvious effect on Cx43 mRNA expression was observed after the drug administration, the phosphorylation level of Cx43 (Ser368) was significantly inhibited. Furthermore, the coadministration of hypaconitine and liquiritin significantly reduced hypaconitine-induced inhibitory action on Cx43 (Ser368) phosphorylation.

CONCLUSIONS

The study indicated that hypaconitine could inhibit CaM expression and Cx43 (Ser368) phosphorylation, and liquiritin could interfere with this kind of effect by synergistically inhibiting CaM expression and by antagonizing Cx43 (Ser368) dephosphorylation induced by hypaconitine.

Ryanodol action on calcium sparks in ventricular myocytes

The action of ryanodol on single cardiac ryanodine receptor (RyR2) channels in bilayers and local RyR2-mediated Ca(2+) release events (Ca(2+) sparks) in ventricular myocytes was defined. At the single-channel level, ryanodol intermittently modified single channels into a long-lived subconductance state with an average duration of 3.8 +/- 0.2 s. Unlike ryanodine, ryanodol did not change the open probability (Po) of unmodified channels, and high concentrations did not promote full-channel closure. Ryanodol action was Po dependent with the K (D) varying roughly from 20 to 80 muM as Po changed from approximately 0.2 to 1, respectively. Ryanodol preferentially bound during long channel openings. In intact and permeabilized rat myocytes, ryanodol evoked trains of sparks at active release sites resulting in a significant increase in overall spark frequency. Ryanodol did not increase the number of active release sites. Long-lived Ca(2+) release events were observed but infrequently, and ryanodol action was readily reversed upon drug washout. We propose that ryanodol modifies a few channels during a Ca(2+) spark. These modified channels mediate a sustained low-intensity Ca(2+) release that repeatedly triggers sparks at the same release site. We conclude that ryanodol is an easily generated reversible probe that can be effectively used to explore RyR2-mediated Ca(2+) release in cells.