Measurement of Cardiac Mechanical Function in Isolated Ventricular Myocytes from Rats and Mice by Computerized Video-Based Imaging

Inhibition of ER stress using tauroursodeoxycholic acid rescues obesity-evoked cardiac remodeling and contractile anomalies through regulation of ferroptosis

Interrupted ER homeostasis contributes to the etiology of obesity cardiomyopathy although it remains elusive how ER stress evokes cardiac anomalies in obesity. Our study evaluated the impact of ER stress inhibition on cardiac anomalies in obesity. Lean and ob/ob obese mice received chemical ER chaperone tauroursodeoxycholic acid (TUDCA, 50 mg/kg/d, p.o.) for 35 days prior to evaluation of glucose sensitivity, echocardiographic, myocardial geometric, cardiomyocyte mechanical and subcellular Ca2+ property, mitochondrial integrity, oxidative stress, apoptosis, and ferroptosis. Intracellular Ca2+ governing domains including sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) were monitored by45Ca2+uptake and immunoblotting. Our results noted that TUDCA alleviated myocardial remodeling (fibrosis, hypertrophy, enlarged LVESD), echocardiographic anomalies (compromised fractional shortening and ejection fraction), cardiomyocyte contractile dysfunction (amplitude and velocity of cell shortening, relengthening time) and intracellular Ca2+ anomalies (compromised subcellular Ca2+ release, clearance and SERCA function), mitochondrial damage (collapsed membrane potential, downregulated mitochondrial elements and ultrastructural alteration), ER stress (GRP78, eIF2α and ATF4), oxidative stress, apoptosis and ferroptosis [downregulated SLC7A11, GPx4 and upregulated transferrin receptor (TFRC)] without affecting global glucose sensitivity and serum Fe2+ in obese mice. Obesity-evoked change in HSP90, phospholamban and Na+-Ca2+ exchanger was spared by the chemical ER chaperone. Moreover, in vitro results noted that TUDCA, PERK inhibitor GSK2606414, TFRC neutralizing antibody and ferroptosis inhibitor LIP1 mitigated palmitic acid-elicited changes in lipid peroxidation and mechanical function. Our findings favored a role for ferroptosis in obesity cardiomyopathy downstream of ER stress.

Elevated levels of alcohol dehydrogenase aggravate ethanol-evoked cardiac remodeling and contractile anomalies through FKBP5-yap-mediated regulation of ferroptosis and ER stress

Alcohol intake provokes severe organ injuries including alcoholic cardiomyopathy with hallmarks of cardiac remodeling and contractile defects. This study examined the toxicity of facilitated ethanol metabolism in alcoholism-evoked changes in myocardial morphology and contractile function, insulin signaling and various cell death domains using cardiac-selective overexpression of alcohol dehydrogenase (ADH). WT and ADH mice were offered an alcohol liquid diet for 12 weeks prior to assessment of cardiac geometry, function, ER stress, apoptosis and ferroptosis. Alcohol intake provoked pronounced glucose intolerance, cardiac remodeling and contractile anomalies with apoptosis, ER stress, and ferroptosis, the effects were accentuated by ADH with the exception of global glucose intolerance. Hearts from alcohol ingesting mice displayed dampened insulin-stimulated phosphorylation of insulin receptor (tyr1146) and IRS-1 (tyrosine) along with elevated IRS-1 serine phosphorylation, the effect was augmented by ADH. Alcohol challenge dampened phosphorylation of Akt and GSK-3β, and increased phosphorylation of c-Jun and JNK, the effects were accentuated by ADH. Alcohol challenge promoted ER stress, FK506 binding protein 5 (FKBP5), YAP, apoptosis and ferroptosis, the effects were exaggerated by ADH. Using a short-term ethanol challenge model (3 g/kg, i.p., twice in three days), we found that inhibition of FKBP5-YAP signaling or facilitated ethanol detoxification by Alda-1 alleviated ethanol cardiotoxicity. In vitro study revealed that the ethanol metabolite acetaldehyde evoked cardiac contractile anomalies, lipid peroxidation, and apoptosis, the effects of which were mitigated by Alda-1, inhibition of ER stress, FKBP5 and YAP. These data suggest that facilitated ethanol metabolism via ADH exacerbates alcohol-evoked myocardial remodeling, functional defects, and insulin insensitivity possibly through a FKBP5-YAP-associated regulation of ER stress and ferroptosis.

FBXL4 protects against HFpEF through Drp1-Mediated regulation of mitochondrial dynamics and the downstream SERCA2a

AIMS

Heart failure with preserved ejection fraction (HFpEF) is a devastating health issue although limited knowledge is available for its pathogenesis and therapeutics. Given the perceived involvement of mitochondrial dysfunction in HFpEF, this study was designed to examine the role of mitochondrial dynamics in the etiology of HFpEF.

METHOD AND RESULTS

Adult mice were placed on a high fat diet plus l-NAME in drinking water ('two-hit' challenge to mimic obesity and hypertension) for 15 consecutive weeks. Mass spectrometry revealed pronounced changes in mitochondrial fission protein Drp1 and E3 ligase FBXL4 in 'two-hit' mouse hearts. Transfection of FBXL4 rescued against HFpEF-compromised diastolic function, cardiac geometry, and mitochondrial integrity without affecting systolic performance, in conjunction with altered mitochondrial dynamics and integrity (hyperactivation of Drp1 and unchecked fission). Mass spectrometry and co-IP analyses unveiled an interaction between FBXL4 and Drp1 to foster ubiquitination and degradation of Drp1. Truncated mutants of FBXL4 (Delta-Fbox) disengaged interaction between FBXL4 and Drp1. Metabolomic and proteomics findings identified deranged fatty acid and glucose metabolism in HFpEF patients and mice. A cellular model was established with concurrent exposure of high glucose and palmitic acid as a 'double-damage' insult to mimic diastolic anomalies in HFpEF. Transfection of FBXL4 mitigated 'double-damage'-induced cardiomyocyte diastolic dysfunction and mitochondrial injury, the effects were abolished and mimicked by Drp1 knock-in and knock-out, respectively. HFpEF downregulated sarco(endo)plasmic reticulum (SR) Ca2+ uptake protein SERCA2a while upregulating phospholamban, RYR1, IP3R1, IP3R3 and Na+-Ca2+ exchanger with unaltered SR Ca2+ load. FBXL4 ablated 'two-hit' or 'double-damage'-induced changes in SERCA2a, phospholamban and mitochondrial injury.

CONCLUSION

FBXL4 rescued against HFpEF-induced cardiac remodeling, diastolic dysfunction, and mitochondrial injury through reverting hyperactivation of Drp1-mediated mitochondrial fission, underscoring the therapeutic promises of FBXL4 in HFpEF.

Metallothionein Alleviates Glutathione Depletion-Induced Oxidative Cardiomyopathy through CISD1-Dependent Regulation of Ferroptosis in Murine Hearts

This study was designed to discern the effect of heavy scavenger metallothionein on glutathione (GSH) deprivation-evoked cardiac anomalies and mechanisms involved with an emphasis on ferroptosis. Wild-type and cardiac metallothionein transgenic mice received GSH synthase inhibitor buthionine sulfoximine (BSO; 30 mmol/L in drinking water) for 14 days before assessment of myocardial morphology and function. BSO evoked cardiac remodeling and contractile anomalies, including cardiac hypertrophy, interstitial fibrosis, enlarged left ventricular chambers, deranged ejection fraction, fraction shortening, cardiomyocyte contractile capacity, intracellular Ca2+ handling, sarcoplasmic reticulum Ca2+ reuptake, loss of mitochondrial integrity (mitochondrial swelling, loss of aconitase activity), mitochondrial energy deficit, carbonyl damage, lipid peroxidation, ferroptosis, and apoptosis. Metallothionein itself did not affect myocardial morphology and function, although it mitigated BSO-provoked myocardial anomalies, loss of mitochondrial integrity and energy, and ferroptosis. Immunoblotting revealed down-regulated sarco(endo)plasmic reticulum Ca2+-ATPase 2a, glutathione peroxidase 4, the ferroptosis-suppressing iron-sulfur domain 1 (CISD1), and mitochondrial regulating glycogen synthase kinase-3β phosphorylation with elevated p53, myosin heavy chain-β isozyme, IκB phosphorylation, and SLC7A11 as well as unchanged SLC39A1, SLC1A5, and ferroptosis-suppressing protein 1 following BSO challenge, all of which, except glutamine transporter SLC7A11 and p53, were abrogated by metallothionein. Inhibition of CISD1 using pioglitazone nullified GSH-offered benefit against BSO-induced cardiomyocyte ferroptosis and contractile and intracellular Ca2+ derangement. Taken together, these findings support a regulatory modality for CISD1 in the impedance of ferroptosis in metallothionein-offered protection against GSH depletion-evoked cardiac aberration.

Heavy Metal Scavenger Metallothionein Rescues Against Cold Stress-Evoked Myocardial Contractile Anomalies Through Regulation of Mitophagy

Cold stress prompts an increased prevalence of cardiovascular morbidity yet the underneath machinery remains unclear. Oxidative stress and autophagy appear to contribute to cold stress-induced cardiac anomalies. Our present study evaluated the effect of heavy metal antioxidant metallothionein on cold stress (4 °C)-induced in cardiac remodeling and contractile anomalies and cell signaling involved including regulation of autophagy and mitophagy. Cold stress (3 weeks) prompted interstitial fibrosis, mitochondrial damage (mitochondrial membrane potential and TEM ultrastructure), oxidative stress (glutathione, reactive oxygen species and superoxide), lipid peroxidation, protein injury, elevated left ventricular (LV) end systolic and diastolic diameters, decreased fractional shortening, ejection fraction, Langendorff heart function, cardiomyocyte shortening, maximal velocities of shortening/relengthening, and electrically stimulated intracellular Ca2+ rise along with elongated relaxation duration and intracellular Ca2+ clearance, the responses of which were overtly attenuated or mitigated by metallothionein. Levels of apoptosis, cell death (Bax and loss of Bcl2, IL-18), and autophagy (LC3BII-to-LC3BI ratio, Atg7 and Beclin-1) were overtly upregulated with comparable p62 under cold stress. Cold stress also evoked elevated mitophagy (decreased TOM20, increased Parkin and FUNDC1 with unaltered BNIP3). Cold stress overtly dampened phosphorylation of autophagy/mitophagy inhibitory molecules Akt and mTOR, stimulated and suppressed phosphorylation of ULK1 and eNOS, respectively, in the absence of altered pan protein levels. Cold stress-evoked responses in cell death, autophagy, mitophagy and their regulatory domains were overtly attenuated or ablated by metallothionein. Suppression of autophagy and mitophagy with 3-methyladenine, bafilomycin A1, cyclosporine A, and liensinine rescued hypothermia-instigated cardiomyocyte LC3B puncta formation and mechanical anomalies. Our findings support a protective nature for metallothionein in deep hypothermia-evoked cardiac abnormalities associated with regulation of autophagy and mitophagy.

Cardiomyocyte-specific deletion of endothelin receptor A (ETA) obliterates cardiac aging through regulation of mitophagy and ferroptosis

Advanced aging evokes unfavorable changes in the heart including cardiac remodeling and contractile dysfunction although the underlying mechanism remains elusive. This study was conducted to evaluate the role of endothelin-1 (ET-1) in the pathogenesis of cardiac aging and mechanism involved. Echocardiographic and cardiomyocyte mechanical properties were determined in young (5-6 mo) and aged (26-28 mo) wild-type (WT) and cardiomyocyte-specific ETA receptor knockout (ETAKO) mice. GSEA enrichment identified differentially expressed genes associated with mitochondrial respiration, mitochondrial protein processing and mitochondrial depolarization in cardiac aging. Aging elevated plasma levels of ET-1, Ang II and suppressed serum Fe2+, evoked cardiac remodeling (hypertrophy and interstitial fibrosis), contractile defects (fractional shortening, ejection fraction, cardiomyocyte peak shortening, maximal velocity of shortening/relengthening and prolonged relengthening) and intracellular Ca2+ mishandling (dampened intracellular Ca2+ release and prolonged decay), the effects with the exception of plasma AngII, ET-1 and Fe2+ were mitigated by ETAKO. Advanced age facilitated O2- production, carbonyl protein damage, cardiac hypertrophy (GATA4, ANP, NFATc3), ER stress, ferroptosis, compromised autophagy (LC3B, Beclin-1, Atg7, Atg5 and p62) and mitophagy (parkin and FUNDC1), and deranged intracellular Ca2+ proteins (SERCA2a and phospholamban), the effects of which were reversed by ETA ablation. ET-1 provoked ferroptosis in vitro, the response was nullified by the ETA receptor antagonist BQ123 and mitophagy inducer CsA. ETA but not ETB receptor antagonism reconciled cardiac aging, which was abrogated by inhibition of mitophagy and ferroptosis. These findings collectively denote promises of targeting ETA, mitophagy and ferroptosis in the management of aging-associated cardiac remodeling and contractile defect.

Beneficial impact of cardiac heavy metal scavenger metallothionein in sepsis-provoked cardiac anomalies dependent upon regulation of endoplasmic reticulum stress and ferroptosis but not autophagy

AIMS

Sepsis represents a profound proinflammatory response with a major contribution from oxidative injury. Here we evaluated possible impact of heavy metal scavenger metallothionein (MT) on endotoxin lipopolysaccharide (LPS)-induced oxidative stress, endoplasmic reticulum (ER) stress, autophagy, and ferroptosis enroute to myocardial injury along with interplay among these stress domains.

MATERIALS AND METHODS

Echocardiographic, cardiomyocyte mechanical and intracellular Ca2+ responses were monitored in myocardia from WT and transgenic mice with cardiac-selective MT overexpression challenged with LPS. Oxidative stress, stress signaling (p38, ERK, JNK), ER stress, autophagy, and ferroptosis were scrutinized.

KEY FINDINGS

RNAseq analysis revealed discrepant patterns in ferroptosis between LPS-exposed and normal murine hearts. LPS insult enlarged LV end systolic dimension, suppressed fractional shortening, ejection fraction, maximal velocity of shortening/relengthening and peak shortening, as well as elongated relengthening along with dampened intracellular Ca2+ release and reuptake. In addition, LPS triggered oxidative stress (lowered glutathione/glutathione disulfide ratio and O2- production), activation of stress cascades (p38, ERK, JNK), ER stress (GRP78, PERK, Gadd153, and IRE1α), inflammation (TNFα and iNOS), unchecked autophagy (LCB3, Beclin-1 and Atg7), ferroptosis (GPx4 and SLC7A11) and interstitial fibrosis. Although MT overexpression itself did not reveal response on cardiac function, it attenuated or mitigated LPS-evoked alterations in echocardiographic, cardiomyocyte contractile and intracellular Ca2+ characteristics, O2- production, TNFα level, ER stress and ferroptosis (without affecting autophagy, elevated AMP/ATP ratio, and iNOS). In vitro evidence revealed beneficial effects of suppression of oxidative stress, ER stress and ferroptosis against LPS-elicited myocardial anomalies.

SIGNIFICANCE

These data strongly support the therapeutic promises of MT and ferroptosis in septic cardiomyopathy.

SGLT2 inhibitor empagliflozin alleviates cardiac remodeling and contractile anomalies in a FUNDC1-dependent manner in experimental Parkinson's disease

Recent evidence shows a close link between Parkinson's disease (PD) and cardiac dysfunction with limited treatment options. Mitophagy plays a crucial role in the control of mitochondrial quantity, metabolic reprogramming and cell differentiation. Mutation of the mitophagy protein Parkin is directly associated with the onset of PD. Parkin-independent receptor-mediated mitophagy is also documented such as BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (BNIP3) and FUN14 domain containing 1 (FUNDC1) for receptor-mediated mitophagy. In this study we investigated cardiac function and mitophagy including FUNDC1 in PD patients and mouse models, and evaluated the therapeutic potential of a SGLT2 inhibitor empagliflozin. MPTP-induced PD model was established. PD patients and MPTP mice not only displayed pronounced motor defects, but also low plasma FUNDC1 levels, as well as cardiac ultrastructural and geometric anomalies (cardiac atrophy, interstitial fibrosis), functional anomalies (reduced E/A ratio, fractional shortening, ejection fraction, cardiomyocyte contraction) and mitochondrial injury (ultrastructural damage, UCP2, PGC1α, elevated mitochondrial Ca2+ uptake proteins MCU and VDAC1, and mitochondrial apoptotic protein calpain), dampened autophagy, FUNDC1 mitophagy and apoptosis. By Gene set enrichment analysis (GSEA), we found overtly altered glucose transmembrane transport in the midbrains of MPTP-treated mice. Intriguingly, administration of SGLT2 inhibitor empagliflozin (10 mg/kg, i.p., twice per week for 2 weeks) in MPTP-treated mice significantly ameliorated myocardial anomalies (with exception of VDAC1), but did not reconcile the motor defects or plasma FUNDC1. FUNDC1 global knockout (FUNDC1-/- mice) did not elicit any phenotype on cardiac geometry or function in the absence or presence of MPTP insult, but it nullified empagliflozin-caused cardioprotection against MPTP-induced cardiac anomalies including remodeling (atrophy and fibrosis), contractile dysfunction, Ca2+ homeostasis, mitochondrial (including MCU, mitochondrial Ca2+ overload, calpain, PARP1) and apoptotic anomalies. In neonatal and adult cardiomyocytes, treatment with PD neurotoxin preformed fibrils of α-synuclein (PFF) caused cytochrome c release and cardiomyocyte mechanical defects. These effects were mitigated by empagliflozin (10 μM) or MCU inhibitor Ru360 (10 μM). MCU activator kaempferol (10 μM) or calpain activator dibucaine (500 μM) nullified the empagliflozin-induced beneficial effects. These results suggest that empagliflozin protects against PD-induced cardiac anomalies, likely through FUNDC1-mediated regulation of mitochondrial integrity.

Assessment of sarcomere shortening and calcium transient in primary human and dog ventricular myocytes

Understanding translation from preclinical observations to clinical findings is important for evaluating the efficacy and safety of novel compounds. Of relevance to cardiac safety is profiling drug effects on cardiomyocyte (CM) sarcomere shortening and intracellular Ca2+ dynamics. Although CM from different animal species have been used to assess such effects, primary human CM isolated from human organ donor heart represent an ideal non-animal alternative approach. We performed a study to evaluate primary human CM and have them compared to freshly isolated dog cardiomyocytes for their basic function and responses to positive inotropes with well-known mechanisms. Our data showed that simultaneous assessment of sarcomere shortening and Ca2+-transient can be performed with both myocytes using the IonOptix system. Amplitude of sarcomere shortening and Ca2+-transient (CaT) were significantly higher in dog compared to human CM in the basic condition (absence of treatment), while longer duration of sarcomere shortening and CaT were observed in human cells. We observed that human and dog CMs have similar pharmacological responses to five inotropes with different mechanisms, including dobutamine and isoproterenol (β-adrenergic stimulation), milrinone (PDE3 inhibition), pimobendan and levosimendan (increase of Ca2+sensitization as well as PDE3 inhibition). In conclusion, our study suggests that myocytes obtained from both human donor hearts and dog hearts can be used to simultaneously assess drug-induced effects on sarcomere shortening and CaT using the IonOptix platform.

Cardiac-specific overexpression of catalase attenuates lipopolysaccharide-induced cardiac anomalies through reconciliation of autophagy and ferroptosis

Lipopolysaccharide (LPS) from Gram-negative bacteria is a major contributor to cardiovascular failure, but the signaling mechanisms underlying its stress response are not fully understood. This study aimed to investigate the effect of the antioxidant enzyme catalase on LPS-induced cardiac abnormalities and the mechanisms involved, with particular focus on the interplay between autophagy, ferroptosis, and apoptosis. Cardiac-specific catalase (CAT) overexpression and wild-type (WT) mice were stimulated with LPS (6 mg/kg, intravenous injection), and cardiac morphology and function were evaluated. Oxidative stress, ferroptosis, apoptosis, and mitochondrial status were monitored, and survival curves were plotted based on the results of LPS stimulation. The results showed that, compared with WT mice, mice overexpressing catalase had a higher survival rate under LPS stimulation. Ultrasound echocardiography, cardiomyocyte characteristics, and Masson's trichrome staining showed that LPS inhibited cardiac function and caused cardiac fibrosis, while catalase alleviated these adverse effects. LPS increased apoptosis (TUNEL, caspase-3 activation, cleaved caspase-3), increased O₂^·- production, induced inflammation (TNF-α), autophagy, iron toxicity, and carbonyl damage, and significantly damaged mitochondria (mitochondrial membrane potential, mitochondrial proteins, and ultrastructure). These effects were significantly alleviated by catalase. Interestingly, the antioxidant N-acetylcysteine, autophagy inhibitor 3-methyladenine, and ferroptosis inhibitor lipostatin-1 all eliminated the LPS-induced contraction dysfunction and ferroptosis (using lipid peroxidation). Induction of ferroptosis could eliminate the cardioprotective effect of NAC. In conclusion, catalase rescues LPS-induced cardiac dysfunction by regulating oxidative stress, autophagy, ferroptosis, apoptosis, and mitochondrial damage in cardiomyocytes.

Syntaxin17 contributes to obesity cardiomyopathy through promoting mitochondrial Ca2+ overload in a Parkin-MCUb-dependent manner

OBJECTIVE

Uncorrected obesity is accompanied by unfavorable structural and functional changes in the heart, known as obesity cardiomyopathy. Recent evidence has revealed a crucial role for mitochondria-associated endoplasmic reticulum membranes (MAMs) in obesity-induced cardiac complication. Syntaxin 17 (STX17) serves as a scaffolding molecule localized on MAMs although its role in obesity heart complication remains elusive.

METHODS AND MATERIALS

This study examined the role of STX17 in MAMs and mitochondrial Ca²⁺ homeostasis in HFD-induced obesity cardiomyopathy using tamoxifen-induced cardiac-specific STX17 knockout (STX17^cko) and STX17 overexpression mice using intravenously delivered recombinant adeno-associated virus serotype-9 (AAV9-cTNT-STX17).

RESULTS

STX17 levels were significantly elevated in plasma from obese patients and heart tissues of HFD-fed mice. Our data revealed that cardiac STX17 knockout alleviated cardiac remodeling and dysfunction in obese hearts without eliciting any notable effect itself, while STX17 overexpression aggravated cardiac dysfunction in obese mice. STX17 deletion and STX17 overexpression annihilated and aggravated, respectively, HFD-induced oxidative stress (O₂^- production) and mitochondrial injury in the heart. Furthermore, STX17 transfection facilitated obesity-induced MAMs formation in cardiomyocytes and evoked excess mitochondrial Ca²⁺ influx, dependent upon interaction with mitochondrial Ca²⁺ uniporter dominant negative β (MCUb) through Habc domain. Our data also suggested that STX17 promoted ubiquitination and degradation of MCUb through the E3 ligase parkin in the face of palmitate challenging.

CONCLUSION

Taken together, our results identified a novel role for STX17 in facilitating obesity-induced MAMs formation, and subsequently mitochondrial Ca²⁺ overload, mitochondrial O₂^- accumulation, lipid peroxidation, resulting in cardiac impairment. Our findings denoted therapeutic promises of targeting STX17 in obesity.

Enzastaurin cardiotoxicity: QT interval prolongation, negative inotropic responses and negative chronotropic action

Several clinical trials observed that enzastaurin prolonged QT interval in cancer patients. However, the mechanism of enzastaurin-induced QT interval prolongation is unclear. Therefore, this study aimed to assess the effect and mechanism of enzastaurin on QT interval and cardiac function. The Langendorff and Ion-Optix MyoCam systems were used to assess the effects of enzastaurin on QT interval, cardiac systolic function and intracellular Ca²⁺ transient in guinea pig hearts and ventricular myocytes. The effects of enzastaurin on the rapid delayed rectifier (I_Kr), the slow delayed rectifier K⁺ current (I_Ks), transient outward potassium current (I_to), action potentials, Ryanodine Receptor 2 (RyR2) and the sarcoplasmic/endoplasmic reticulum Ca²⁺ ATPase 2a (SERCA2a) expression and activity in HEK 293 cell system and primary cardiomyocytes were investigated using whole-cell recording technique and western blotting. We found that enzastaurin significantly prolonged QT interval in guinea pig hearts and increased the action potential duration (APD) in guinea pig cardiomyocytes in a dose-dependent manner. Enzastaurin potently inhibited I_Kr by binding to the human Ether-à-go-go-Related gene (hERG) channel in both open and closed states, and hERG mutant channels, including S636A, S631A, and F656V attenuated the inhibitory effect of enzastaurin. Enzastaurin also moderately decreased I_Ks. Additionally, enzastaurin also induced negative chronotropic action. Moreover, enzastaurin impaired cardiac systolic function and reduced intracellular Ca²⁺ transient via inhibition of RyR2 phosphorylation. Taken together, we found that enzastaurin prolongs QT, reduces heart rate and impairs cardiac systolic function. Therefore, we recommend that electrocardiogram (ECG) and cardiac function should be continuously monitored when enzastaurin is administered to cancer patients.

Empagliflozin attenuates trastuzumab-induced cardiotoxicity through suppression of DNA damage and ferroptosis

Trastuzumab (TZM) is commonly used for target therapy in breast cancer patients with high HER2 although the cardiotoxicity restricts its clinical usage. DNA damage and ferroptosis are implicated in anti-tumor drug cardiotoxicity. Given the emerging use of SGLT2 inhibitors in clinical cardiology, this study evaluated the impact of SGLT2 inhibitor Empagliflozin on TZM-induced cardiotoxicity, and mechanism involved with a focus on DNA damage and ferroptosis. Adult C57BL/6 mice were challenged with TZM (10 mg/kg/week, i.p.) or saline for six weeks. A cohort of mice received Empagliflozin (10 mg/kg, i.p.) at the same time. Myocardial function, morphology, ultrastructure, mitochondrial integrity, oxidative stress, DNA damage and various cell death domains were evaluated in TZM-challenged mice with or without Empagliflozin treatment. Our data revealed that TZM challenge overtly increased levels of serum LDH and troponin I, promoted adverse myocardial remodeling (increased heart weight, chamber size, cardiomyocyte area and interstitial fibrosis), contractile dysfunction and intracellular Ca²⁺ mishandling, oxidative stress, lipid peroxidation, mitochondrial ultrastructural damage, DNA damage, apoptosis and ferroptosis, the effects of which were greatly attenuated or mitigated by Empagliflozin with little effects from Empagliflozin itself. In vitro study indicated that induction of DNA damage mimicked TZM-induced lipid peroxidation and cardiomyocyte contractile dysfunction while the ferroptosis inducer erastin mitigated Empagliflozin-offered protection against lipid peroxidation and cardiomyocyte dysfunction (but not DNA damage). Likewise, in vivo and in vitro inhibition of ferroptosis recapitulated Empagliflozin-offered cardioprotection against TZM exposure. Taken together, these data demonstrated that Empagliflozin may be possible candidate drug for TZM cardiotoxicity likely through a DNA damage-ferroptosis-mediated mechanism.

NDP52 Protects Against Myocardial Infarction-Provoked Cardiac Anomalies Through Promoting Autophagosome-Lysosome Fusion via Recruiting TBK1 and RAB7

Aims: Acute myocardial infarction (MI), caused by acute coronary artery obstruction, is a common cardiovascular event leading to mortality. Nuclear dot protein 52 (NDP52) is an essential selective autophagy adaptor, although its function in MI is still obscure. This study was designed to examine the function of NDP52 in MI and the associated mechanisms. Results: Our results revealed that MI challenge overtly impaired myocardial geometry and systolic function, along with cardiomyocyte apoptosis, myocardial interstitial fibrosis, and mitochondrial damage, and NDP52 nullified such devastating responses. Further studies showed that the blockade of mitochondrial clearance is related to MI-induced buildup of damaged mitochondria. Mechanistic approaches depicted that 7-day MI induced abnormal mitophagy flux, resulting in poor lysosomal clearance of injured mitochondria. NDP52 promoted mitophagy flux through the recruitment of Ras-associated protein RAB7 (RAB7) and TANK-binding kinase 1 (TBK1). On protein co-localization, TBK1 phosphorylated RAB7, in line with the finding that chloroquine or a TBK1 inhibitor reversed NDP52-dependent beneficial responses. Innovation: This study denoted a novel mechanism that NDP52 promotes cardioprotection against ischemic heart diseases through interaction with TBK1 and RAB7, leading to RAB7 phosphorylation, induction of mitophagy to clear ischemia-induced impaired mitochondria, thus preventing cardiomyocyte apoptosis in MI. Conclusion: Our results indicate that NDP52 promotes autophagic flux and clears damaged mitochondria to diminish reactive oxygen species and cell death in a TBK1/RAB7-dependent manner and thus limits MI-induced injury. Antioxid. Redox Signal. 36, 1119-1135.

Pentacyclic triterpene oleanolic acid protects against cardiac aging through regulation of mitophagy and mitochondrial integrity

Advanced aging exhibits altered cardiac geometry and function involving mitochondrial anomaly. Natural compounds display promises in the regulation of cardiac homeostasis via governance of mitochondrial integrity in aging. This study examined the effect of oleanolic acid (OA), a natural pentacyclic triterpenoid with free radical scavenging and P450 cyclooxygenase-regulating properties, on cardiac aging and mechanisms involved with a focus on mitophagy. Young (4-5 month-old) and old (22-24 month-old) mice were treated with OA for 6 weeks prior to assessment of cardiac function, morphology, ultrastructure, mitochondrial integrity, cell death and autophagy. Our data revealed that OA treatment alleviated aging-induced changes in myocardial remodeling (increased heart weight, chamber size, cardiomyocyte area and interstitial fibrosis), contractile function and intracellular Ca²⁺ handling, apoptosis, necroptosis, inflammation, autophagy and mitophagy (LC3B, p62, TOM20 and FUNDC1 but not BNIP3 and Parkin). OA treatment rescued aging-induced anomalies in mitochondrial ultrastructure (loss of myofilament alignment, swollen mitochondria, increased circularity), mitochondrial biogenesis and O₂^- production without any notable effect at young age. Interestingly, OA-offered benefit against cardiomyocyte aging was nullified by deletion of the mitophagy receptor FUNDC1 using FUNDC1 knockout mice, denoting an obligatory role for FUNDC1 in OA-elicited preservation of mitophagy. OA reconciled aging-induced changes in E3 ligase MARCH5 but not FBXL2, and failed to affect aging-induced rises in IP3R3. Taken together, our data indicated a beneficial role for OA in attenuating cardiac remodeling and contractile dysfunction in aging through a FUNDC1-mediated mechanism.

Cell Shortening and Calcium Homeostasis Analysis in Adult Cardiomyocytes via a New Software Tool

Intracellular calcium (Ca2+) is the central regulator of heart contractility. Indeed, it couples the electrical signal, which pervades the myocardium, with cardiomyocytes contraction. Moreover, alterations in calcium management are the main factors contributing to the mechanical and electrical dysfunction observed in failing hearts. So, simultaneous analysis of the contractile function and intracellular Ca2+ is indispensable to evaluate cardiomyocytes activity. Intracellular Ca2+ variations and fraction shortening are commonly studied with fluorescent Ca2+ indicator dyes associated with microscopy techniques. However, tracking and dealing with multiple files manually is time-consuming and error-prone and often requires expensive apparatus and software. Here, we announce a new, user-friendly image processing and analysis tool, based on ImageJ-Fiji/MATLAB® software, to evaluate the major cardiomyocyte functional parameters. We succeeded in analyzing fractional cell shortening, Ca2+ transient amplitude, and the kinematics/dynamics parameters of mouse isolated adult cardiomyocytes. The proposed method can be applied to evaluate changes in the Ca2+ cycle and contractile behavior in genetically or pharmacologically induced disease models, in drug screening and other common applications to assess mammalian cardiomyocyte functions.

CD74 ablation rescues type 2 diabetes mellitus-induced cardiac remodeling and contractile dysfunction through pyroptosis-evoked regulation of ferroptosis

Type 2 diabetes mellitus (T2D) contributes to sustained inflammation and myopathic changes in the heart although the precise interplay between the two remains largely unknown. This study evaluated the impact of deficiency in CD74, the cognate receptor for the regulatory cytokine macrophage migration inhibitory factor (MIF), in T2D-induced cardiac remodeling and functional responses, and cell death domains involved. WT and CD74-/- mice were fed a high fat diet (60% calorie from fat) for 8 weeks prior to injection of streptozotocin (STZ, 35 mg/kg, i.p., 3 consecutive days) and were maintained for another 8 weeks. KEGG analysis for differentially expressed genes (DEGs) reported gene ontology term related to ferroptosis in T2D mouse hearts. T2D patients displayed elevated plasma MIF levels. Murine T2D exerted overt global metabolic derangements, cardiac remodeling, contractile dysfunction, apoptosis, pyroptosis, ferroptosis and mitochondrial dysfunction, ablation of CD74 attenuated T2D-induced cardiac remodeling, contractile dysfunction, various forms of cell death and mitochondrial defects without affecting global metabolic defects. CD74 ablation rescued T2D-evoked NLRP3-Caspase1 activation and oxidative stress but not dampened autophagy. In vitro evidence depicted that high glucose/high fat (HGHF) compromised cardiomyocyte function and promoted lipid peroxidation, the effects were ablated by inhibitors of NLRP3, pyroptosis, and ferroptosis but not by the mitochondrial targeted antioxidant mitoQ. Recombinant MIF mimicked HGHF-induced lipid peroxidation, GSH depletion and ferroptosis, the effects of which were reversed by inhibitors of MIF, NLRP3 and pyroptosis. Taken together, these data suggest that CD74 ablation protects against T2D-induced cardiac remodeling and contractile dysfunction through NLRP3/pyroptosis-mediated regulation of ferroptosis.

Catecholamine-induced cardiotoxicity: A critical element in the pathophysiology of stroke-induced heart injury

Cerebrovascular diseases such as ischemic stroke, brain hemorrhage, and subarachnoid hemorrhage provoke cardiac complications such as heart failure, neurogenic stress-related cardiomyopathy and Takotsubo cardiomyopathy. With regards to the pathophysiology of stroke-induced heart injury, several mechanisms have been postulated to contribute to this complex interaction between brain and heart, including damage from gut dysbiosis, immune and systematic inflammatory responses, microvesicle- and microRNA-mediated vascular injury and damage from a surge of catecholamines. All these cerebrovascular diseases may trigger pronounced catecholamine surges through diverse ways, including stimulation of hypothalamic-pituitary adrenal axis, dysregulation of autonomic system, and secretion of adrenocorticotropic hormone. Primary catecholamines involved in this pathophysiological response include norepinephrine (NE) and epinephrine. Both are important neurotransmitters that connect the nervous system with the heart, leading to cardiac damage via myocardial ischemia, calcium (Ca²⁺) overload, oxidative stress, and mitochondrial dysfunction. In this review, we will aim to summarize the molecular mechanisms behind catecholamine-induced cardiotoxicity including Ca²⁺ overload, oxidative stress, apoptosis, cardiac hypertrophy, interstitial fibrosis, and inflammation. In addition, we will focus on how synchronization among these pathways evokes cardiotoxicity.

FUNDC1 insufficiency sensitizes high fat diet intake-induced cardiac remodeling and contractile anomaly through ACSL4-mediated ferroptosis

OBJECTIVE

Ferroptosis is indicated in cardiovascular diseases. Given the prominent role of mitophagy in the governance of ferroptosis and our recent finding for FUN14 domain containing 1 (FUNDC1) in obesity anomalies, this study evaluated the impact of FUNDC1 deficiency in high fat diet (HFD)-induced cardiac anomalies.

METHODS AND MATERIALS

WT and FUNDC1-/- mice were fed HFD (45% calorie from fat) or low fat diet (LFD, 10% calorie from fat) for 10 weeks in the presence of the ferroptosis inhibitor liproxstatin-1 (LIP-1, 10 mg/kg, i.p.).

RESULTS

RNAseq analysis for differentially expressed genes (DEGs) reported gene ontology term related to ferroptosis and mitophagy in obese rat hearts, which was validated in obese rodent and human hearts. Although 10-week HFD intake did not alter global metabolism, cardiac geometry and function, ablation of FUNDC1 unmasked metabolic derangement, pronounced cardiac remodeling, contractile, intracellular Ca2+ and mitochondrial anomalies upon HFD challenge, the effects of which with exception of global metabolism were attenuated or mitigated by LIP-1. FUNDC1 ablation unmasked HFD-evoked rises in fatty acid synthase ACSL4, necroptosis, inflammation, ferroptosis, mitochondrial O2- production, and mitochondrial injury as well as dampened autophagy and DNA repair enzyme 8-oxoG DNA glycosylase 1 (OGG1) but not apoptosis, the effect of which except ACSL4 and its regulator SP1 was reversed by LIP-1. In vitro data noted that arachidonic acid, an ACSL4 substrate, provoked cytochrome C release, cardiomyocyte defect, and lipid peroxidation under FUNDC1 deficiency, the effects were interrupted by inhibitors of SP1, ACSL4 and ferroptosis.

CONCLUSIONS

These data suggest that FUNDC1 deficiency sensitized cardiac remodeling and dysfunction with short-term HFD exposure, likely through ACSL4-mediated regulation of ferroptosis.

Dense optical flow software to quantify cellular contractility

Cell membrane deformation is an important feature that occurs during many physiological processes, and its study has been put to good use to investigate cardiomyocyte function. Several methods have been developed to extract information on cardiomyocyte contractility. However, no existing computational framework has provided, in a single platform, a straightforward approach to acquire, process, and quantify this type of cellular dynamics. For this reason, we develop CONTRACTIONWAVE, high-performance software written in Python programming language that allows the user to process large data image files and obtain contractility parameters by analyzing optical flow from images obtained with videomicroscopy. The software was validated by using neonatal, adult-, and human-induced pluripotent stem-cell-derived cardiomyocytes, treated or not with drugs known to affect contractility. Results presented indicate that CONTRACTIONWAVE is an excellent tool for examining changes to cardiac cellular contractility in animal models of disease and for pharmacological and toxicology screening during drug discovery.

Cardiotoxic Potential of Hydroxychloroquine, Chloroquine and Azithromycin in Adult Human Primary Cardiomyocytes

Substantial efforts have been recently committed to develop coronavirus disease-2019 (COVID-19) medications, and Hydroxychloroquine alone or in combination with Azithromycin has been promoted as a repurposed treatment. Although these drugs may increase cardiac toxicity risk, cardiomyocyte mechanisms underlying this risk remain poorly understood in humans. Therefore, we evaluated the proarrhythmia risk and inotropic effects of these drugs in the cardiomyocyte contractility-based model of the human heart. We found Hydroxychloroquine to have a low proarrhythmia risk, whereas Chloroquine and Azithromycin were associated with high risk. Hydroxychloroquine proarrhythmia risk changed to high with low level of K+, whereas high level of Mg2+ protected against proarrhythmic effect of high Hydroxychloroquine concentrations. Moreover, therapeutic concentration of Hydroxychloroquine caused no enhancement of elevated temperature-induced proarrhythmia. Polytherapy of Hydroxychloroquine plus Azithromycin and sequential application of these drugs were also found to influence proarrhythmia risk categorization. Hydroxychloroquine proarrhythmia risk changed to high when combined with Azithromycin at therapeutic concentration. However, Hydroxychloroquine at therapeutic concentration impacted the cardiac safety profile of Azithromycin and its proarrhythmia risk only at concentrations above therapeutic level. We also report that Hydroxychloroquine and Chloroquine, but not Azithromycin, decreased contractility while exhibiting multi-ion channel block features, and Hydroxychloroquine's contractility effect was abolished by Azithromycin. Thus, this study has the potential to inform clinical studies evaluating repurposed therapies, including those in the COVID-19 context. Additionally, it demonstrates the translational value of the human cardiomyocyte contractility-based model as a key early discovery path to inform decisions on novel therapies for COVID-19, malaria, and inflammatory diseases.

Effects of omecamtiv mecarbil on calcium-transients and contractility in a translational canine myocyte model

Omecamtiv mecarbil (OM) is a selective cardiac myosin activator (myotrope), currently in Phase 3 clinical investigation as a novel treatment for heart failure with reduced ejection fraction. OM increases cardiac contractility by enhancing interaction between myosin and actin in a calcium-independent fashion. This study aims to characterize the mechanism of action by evaluating its simultaneous effect on myocyte contractility and calcium-transients (CTs) in healthy canine ventricular myocytes. Left ventricular myocytes were isolated from canines and loaded with Fura-2 AM. With an IonOptix system, contractility parameters including amplitude and duration of sarcomere shortening, contraction and relaxation velocity, and resting sarcomere length were measured. CT parameters including amplitude at systole and diastole, velocity at systole and diastole, and duration at 50% from peak were simultaneously measured. OM was tested at 0.03, 0.1, 0.3, 1, and 3 µmol\L concentrations to simulate therapeutic human plasma exposure levels. OM and isoproterenol (ISO) demonstrated differential effects on CTs and myocyte contractility. OM increased contractility mainly by prolonging duration of contraction while ISO increased contractility mainly by augmenting the amplitude of contraction. ISO increased the amplitude and velocity of CT, shortened duration of CT concurrent with increasing myocyte contraction, while OM did not change the amplitude, velocity, and duration of CT up to 1 µmol\L. Decreases in relaxation velocity and increases in duration were present only at 3 µmol\L. In this translational myocyte model study, therapeutically relevant concentrations of OM increased contractility but did not alter intracellular CTs, a mechanism of action distinct from traditional calcitropes.

Multiparametric Mechanistic Profiling of Inotropic Drugs in Adult Human Primary Cardiomyocytes

Effects of non-cardiac drugs on cardiac contractility can lead to serious adverse events. Furthermore, programs aimed at treating heart failure have had limited success and this therapeutic area remains a major unmet medical need. The challenges in assessing drug effect on cardiac contractility point to the fundamental translational value of the current preclinical models. Therefore, we sought to develop an adult human primary cardiomyocyte contractility model that has the potential to provide a predictive preclinical approach for simultaneously predicting drug-induced inotropic effect (sarcomere shortening) and generating multi-parameter data to profile different mechanisms of action based on cluster analysis of a set of 12 contractility parameters. We report that 17 positive and 9 negative inotropes covering diverse mechanisms of action exerted concentration-dependent increases and decreases in sarcomere shortening, respectively. Interestingly, the multiparametric readout allowed for the differentiation of inotropes operating via distinct mechanisms. Hierarchical clustering of contractility transient parameters, coupled with principal component analysis, enabled the classification of subsets of both positive as well as negative inotropes, in a mechanism-related mode. Thus, human cardiomyocyte contractility model could accurately facilitate informed mechanistic-based decision making, risk management and discovery of molecules with the most desirable pharmacological profile for the correction of heart failure.

Human Heart Cardiomyocytes in Drug Discovery and Research: New Opportunities in Translational Sciences

In preclinical drug development, accurate prediction of drug effects on the human heart is critically important, whether in the context of cardiovascular safety or for the purpose of modulating cardiac function to treat heart disease. Current strategies have significant limitations, whereby, cardiotoxic drugs can escape detection or potential life-saving therapies are abandoned due to false positive toxicity signals. Thus, new and more reliable translational approaches are urgently needed to help accelerate the rate of new therapy development. Renewed efforts in the recovery of human donor hearts for research and in cardiomyocyte isolation methods, are providing new opportunities for preclinical studies in adult primary cardiomyocytes. These cells exhibit the native physiological and pharmacological properties, overcoming the limitations presented by artificial cellular models, animal models and have great potential for providing an excellent tool for preclinical drug testing. Adult human primary cardiomyocytes have already shown utility in assessing drug-induced cardiotoxicity risk and helping in the identification of new treatments for cardiac diseases, such as heart failure and atrial fibrillation. Finally, strategies with actionable decision-making trees that rely on data derived from adult human primary cardiomyocytes will provide the holistic insights necessary to accurately predict human heart effects of drugs.

Considerations for an In Vitro, Cell-Based Testing Platform for Detection of Drug-Induced Inotropic Effects in Early Drug Development. Part 2: Designing and Fabricating Microsystems for Assaying Cardiac Contractility With Physiological Relevance Using Human iPSC-Cardiomyocytes

Contractility of the myocardium engines the pumping function of the heart and is enabled by the collective contractile activity of its muscle cells: cardiomyocytes. The effects of drugs on the contractility of human cardiomyocytes in vitro can provide mechanistic insight that can support the prediction of clinical cardiac drug effects early in drug development. Cardiomyocytes differentiated from human-induced pluripotent stem cells have high potential for overcoming the current limitations of contractility assays because they attach easily to extracellular materials and last long in culture, while having human- and patient-specific properties. Under these conditions, contractility measurements can be non-destructive and minimally invasive, which allow assaying sub-chronic effects of drugs. For this purpose, the function of cardiomyocytes in vitro must reflect physiological settings, which is not observed in cultured cardiomyocytes derived from induced pluripotent stem cells because of the fetal-like properties of their contractile machinery. Primary cardiomyocytes or tissues of human origin fully represent physiological cellular properties, but are not easily available, do not last long in culture, and do not attach easily to force sensors or mechanical actuators. Microengineered cellular systems with a more mature contractile function have been developed in the last 5 years to overcome this limitation of stem cell-derived cardiomyocytes, while simultaneously measuring contractile endpoints with integrated force sensors/actuators and image-based techniques. Known effects of engineered microenvironments on the maturity of cardiomyocyte contractility have also been discovered in the development of these systems. Based on these discoveries, we review here design criteria of microengineered platforms of cardiomyocytes derived from pluripotent stem cells for measuring contractility with higher physiological relevance. These criteria involve the use of electromechanical, chemical and morphological cues, co-culture of different cell types, and three-dimensional cellular microenvironments. We further discuss the use and the current challenges for developing and improving these novel technologies for predicting clinical effects of drugs based on contractility measurements with cardiomyocytes differentiated from induced pluripotent stem cells. Future research should establish contexts of use in drug development for novel contractility assays with stem cell-derived cardiomyocytes.

Maternal obesity impairs fetal cardiomyocyte contractile function in sheep

Obesity is a major public health problem worldwide. In the United States, one-third of women of reproductive age are obese. Human studies show that maternal obesity (MO) predisposes offspring to cardiovascular disease. However, the underlying mechanisms remain unclear. Given the similarities between pregnancy in sheep and humans, we studied sheep to examine the impact of MO on fetal cardiomyocyte contractility at term. We observed that MO impaired cardiomyocyte contractility by reducing peak shortening and shortening/relengthening velocity, prolonging time to relengthening. MO disrupted Ca²⁺ homeostasis in fetal cardiomyocytes, increasing intracellular Ca²⁺ and inducing cellular Ca²⁺ insensitivity. The Ca²⁺-release channel was impaired, but Ca²⁺ uptake was unaffected by MO. The upstream kinases that phosphorylate the Ca²⁺-release channel-ryanodine receptor-2, PKA, and calmodulin-dependent protein kinase II-were activated in MO fetuses. Contractile dysfunction was associated with an increased ratio of myosin heavy chain (MHC)-β to MHC-α and upregulated cardiac troponin (cTn)-T and tropomyosin, as well as cTn-I phosphorylation. In summary, this is the first characterization of the effects of MO on fetal cardiomyocyte contractility. Our findings indicate that MO impairs fetal cardiomyocyte contractility through altered intracellular Ca²⁺ handling, overloading fetal cardiomyocyte intracellular Ca²⁺ and aberrant myofilament protein composition. These mechanisms may contribute to developmental programming by MO of offspring cardiac function and predisposition to later life cardiovascular disease in the offspring.-Wang, Q., Zhu, C., Sun, M., Maimaiti, R., Ford, S. P., Nathanielsz, P. W., Ren, J., Guo, W. Maternal obesity impairs fetal cardiomyocyte contractile function in sheep.

Gene Transfer in Isolated Adult Cardiomyocytes

During the past few decades, gene delivery using recombinant virus has made tremendous progress. With a higher than 80 % transduction efficiency, even in non-dividing cells, viral transduction has become the method of choice for efficient gene transfer into cardiomyocytes. However, in vitro gene delivery is dependent on a robust cell isolation protocol, as prolonged cultivation is needed to initiate gene expression and target specific cellular processes. This chapter describes some of the important steps that need to be considered for successful in vitro gene transfer into adult cardiomyocytes. Included are detailed protocols for isolating cells, maintaining rod shaped cardiomyocytes in culture over several days, and employing adenovirus for gene transduction.

Adult Human Primary Cardiomyocyte-Based Model for the Simultaneous Prediction of Drug-Induced Inotropic and Pro-arrhythmia Risk

Cardiac safety remains the leading cause of drug development discontinuation. We developed a human cardiomyocyte-based model that has the potential to provide a predictive preclinical approach for simultaneously predicting drug-induced inotropic and pro-arrhythmia risk.

Methods: Adult human primary cardiomyocytes from ethically consented organ donors were used to measure contractility transients. We used measures of changes in contractility parameters as markers to infer both drug-induced inotropic effect (sarcomere shortening) and pro-arrhythmia (aftercontraction, AC); contractility escape (CE); time to 90% relaxation (TR90). We addressed the clinical relevance of this approach by evaluating the effects of 23 torsadogenic and 10 non-torsadogenic drugs. Each drug was tested separately at four multiples of the free effective therapeutic plasma concentration (fETPC).

Results: Human cardiomyocyte-based model differentiated between torsadogenic and non-torsadogenic drugs. For example, dofetilide, a torsadogenic drug, caused ACs and increased TR90 starting at 10-fold the fETPC, while CE events were observed at the highest multiple of fETPC (100-fold). Verapamil, a non-torsadogenic drug, did not change TR90 and induced no AC or CE up to the highest multiple of fETPCs tested in this study (222-fold). When drug pro-arrhythmic activity was evaluated at 10-fold of the fETPC, AC parameter had excellent assay sensitivity and specificity values of 96 and 100%, respectively. This high predictivity supports the translational safety potential of this preparation and of the selected marker. The data demonstrate that human cardiomyocytes could also identify drugs associated with inotropic effects. hERG channel blockers, like dofetilide, had no effects on sarcomere shortening, while multi-ion channel blockers, like verapamil, inhibited sarcomere shortening.

Conclusions: Isolated adult human primary cardiomyocytes can simultaneously predict risks associated with inotropic activity and pro-arrhythmia and may enable the generation of reliable and predictive data for assessing human cardiotoxicity at an early stage in drug discovery.

Calcium homeostasis and endoplasmic reticulum stress are involved in Salvianolic acid B-offered protection against cardiac toxicity of arsenic trioxide

Arsenic trioxide (ATO) is a potent anticancer agent used to treat acute promyelocytic leukemia. However, its cardiotoxicity limits ATO’s widespread clinical use. Previous studies demonstrated that ATO may aggravate Ca²⁺ overload and promote endoplasmic reticulum stress (ERS). Salvianolic acid B (Sal B) is cardioprotective against ATO and enhances ATO’s anticancer activities. The present study assessed whether the Sal B protective effect was related to maintenance of Ca²⁺ homeostasis and inhibition of ER stress. Male BALB/c mice were injected with ATO or ATO+Sal B once a day via the tail vein for 2 weeks. We then detected the effects of Sal B in real time using adult rat ventricular cardiomyocytes in vitro using an IonOptix MyoCam system. Sal B treatment alleviated ATO-induced abnormal cardiac contractions and Ca²⁺ homeostasis imbalance. Sal B increased sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) activity, regulated Ca²⁺ handling protein expression, and decreased expression of ERS proteins. Our results demonstrate that the cardioprotective effect of Sal B correlates with SERCA modulation, maintenance of Ca²⁺ homeostasis, and inhibition of ER stress. These findings suggest Sal B may ameliorate ATO cardiotoxicity during clinical application.

A novel SOD mimic with a redox-modulating mn (II) complex, ML1 attenuates high glucose-induced abnormalities in intracellular Ca2+ transients and prevents cardiac cell death through restoration of mitochondrial function

A key contributor to the pathophysiology of diabetic cardiomyopathy, mitochondrial superoxide can be adequately countered by Mn-superoxide dismutase, which constitutes the first line of defense against mitochondrial oxidative stress. Our group has recently synthesized low molecular weight SOD mimics, demonstrating superior protection against oxidative damages to kidney cells. In the current study, we sought to evaluate the protective effect of the SOD mimic ML1 against high glucose induced cardiomyopathy in diabetes. Mechanistic studies using rat cardiac myoblast H9c2 showed that ML1 markedly inhibited High Glucose (HG) induced cytotoxicity. This was associated with increased Mn-SOD expression along with decreased mitochondrial [Formula: see text], ONOO- and Ca²⁺ accumulation, unveiling its anti-oxidant potentials. ML1 also attenuated HG-induced loss of mitochondrial membrane potential (ΔΨ_m) and release of cytochrome c, suggesting that ML1 effectuates its cytoprotective action via the preservation of mitochondrial function. In an ex-vivo model normal adult rat ventricular myocytes (ARVMs) were isolated and cultured in either normal glucose (5.5 mmol/l glucose) or HG (25.5 mmol/l glucose) conditions and the efficiency of ML-1 was analyzed by studying contractile function and calcium indices. Mechanical properties were assessed using a high-speed video-edge detection system, and intracellular Ca²⁺ transients were recorded in fura-2-loaded myocytes. Pretreatment of myocytes with ML1 (10 nM) ameliorated HG induced abnormalities in relaxation including depressed peak shortening, prolonged time to 90% relenghthening, and slower Ca²⁺ transient decay. Thus, ML1 exhibits significant cardio protection against oxidative damage, perhaps through its potent antioxidant action via activation of Mn-SOD.

Biomechanics of Cardiac Function

The heart pumps blood to maintain circulation and ensure the delivery of oxygenated blood to all the organs of the body. Mechanics play a critical role in governing and regulating heart function under both normal and pathological conditions. Biological processes and mechanical stress are coupled together in regulating myocyte function and extracellular matrix structure thus controlling heart function. Here, we offer a brief introduction to the biomechanics of left ventricular function and then summarize recent progress in the study of the effects of mechanical stress on ventricular wall remodeling and cardiac function as well as the effects of wall mechanical properties on cardiac function in normal and dysfunctional hearts. Various mechanical models to determine wall stress and cardiac function in normal and diseased hearts with both systolic and diastolic dysfunction are discussed. The results of these studies have enhanced our understanding of the biomechanical mechanism in the development and remodeling of normal and dysfunctional hearts. Biomechanics provide a tool to understand the mechanism of left ventricular remodeling in diastolic and systolic dysfunction and guidance in designing and developing new treatments.

α,β-Unsaturated aldehyde pollutant acrolein suppresses cardiomyocyte contractile function: Role of TRPV1 and oxidative stress

Air pollution is associated with an increased prevalence of heart disease and is known to trigger a proinflammatory response via stimulation of transient receptor potential vanilloid cation channels (TRPV1, also known as the capsaicin receptor). This study was designed to examine the effect of acrolein, an essential α,β-unsaturated aldehyde pollutant, on myocardial contractile function and the underlying mechanism involved with a focus on TRPV1 and oxidative stress. Cardiomyocyte mechanical and intracellular Ca(2+) properties were evaluated using an IonOptix MyoCam® system including peak shortening (PS), maximal velocity of shortening/relengthening (± dL/dt), time-to-PS (TPS), time-to-90% relengthening (TR90 ), fura-2 fluorescence intensity (FFI) and intracellular Ca(2+) decay. Changes in apoptosis and TRPV1 were evaluated using Western blot analysis. The degree of oxidative stress was assessed using the ratio between reduced and oxidized glutathione. Results obtained revealed that exposure of cardiomyocytes to acrolein acutely compromised contractile and intracellular Ca(2+) properties including depressed PS, ± dL/dt and ΔFFI, as well as prolonged TR90 and intracellular Ca(2+) decay. In addition, acrolein exposure upregulated TRPV1 associated with an increase in both apoptosis and oxidative stress. However, the acrolein-induced cardiomyocyte contractile and intracellular Ca(2+) anomalies, as well as apoptosis (as evidenced by Bcl-2, Bax, FasL, Caspase-3 and -8), were negated by the reactive oxygen species (ROS) scavenger glutathione or the TRPV1 antagonist capsazepine. Collectively these data suggest that the α,β-unsaturated aldehyde pollutant acrolein may play a role in the pathogenesis and sequelae of air pollution-induced heart disease via a TRPV1- and oxidative stress-dependent mechanism.

A device for rapid and quantitative measurement of cardiac myocyte contractility

Cardiac contractility is the hallmark of cardiac function and is a predictor of healthy or diseased cardiac muscle. Despite advancements over the last two decades, the techniques and tools available to cardiovascular scientists are limited in their utility to accurately and reliably measure the amplitude and frequency of cardiomyocyte contractions. Isometric force measurements in the past have entailed cumbersome attachment of isolated and permeabilized cardiomyocytes to a force transducer followed by measurements of sarcomere lengths under conditions of submaximal and maximal Ca(2+) activation. These techniques have the inherent disadvantages of being labor intensive and costly. We have engineered a micro-machined cantilever sensor with an embedded deflection-sensing element that, in preliminary experiments, has demonstrated to reliably measure cardiac cell contractions in real-time. Here, we describe this new bioengineering tool with applicability in the cardiovascular research field to effectively and reliably measure cardiac cell contractility in a quantitative manner. We measured contractility in both primary neonatal rat heart cardiomyocyte monolayers that demonstrated a beat frequency of 3 Hz as well as human embryonic stem cell-derived cardiomyocytes with a contractile frequency of about 1 Hz. We also employed the β-adrenergic agonist isoproterenol (100 nmol l(-1)) and observed that our cantilever demonstrated high sensitivity in detecting subtle changes in both chronotropic and inotropic responses of monolayers. This report describes the utility of our micro-device in both basic cardiovascular research as well as in small molecule drug discovery to monitor cardiac cell contractions.

Rapid multislice T1 mapping of mouse myocardium: Application to quantification of manganese uptake in α-Dystrobrevin knockout mice

PURPOSE

The aim of this study was to develop a rapid, multislice cardiac T1 mapping method in mice and to apply the method to quantify manganese (Mn(2+)) uptake in a mouse model with altered Ca(2+) channel activity.

METHODS

An electrocardiography-triggered multislice saturation-recovery Look-Locker method was developed and validated both in vitro and in vivo. A two-dose study was performed to investigate the kinetics of T1 shortening, Mn(2+) relaxivity in myocardium, and the impact of Mn(2+) on cardiac function. The sensitivity of Mn(2+)-enhanced MRI in detecting subtle changes in altered Ca(2+) channel activity was evaluated in a mouse model with α-dystrobrevin knockout.

RESULTS

Validation studies showed strong agreement between the current method and an established method. High Mn(2+) dose led to significantly accelerated T1 shortening. Heart rate decreased during Mn(2+) infusion, while ejection ratio increased slightly at the end of imaging protocol. No statistical difference in cardiac function was detected between the two dose groups. Mice with α-dystrobrevin knockout showed enhanced Mn(2+) uptake in vivo. In vitro patch-clamp study showed increased Ca(2+) channel activity.

CONCLUSION

The saturation recovery method provides rapid T1 mapping in mouse hearts, which allowed sensitive detection of subtle changes in Mn(2+) uptake in α-dystrobrevin knockout mice.

The effect of SN-6, a novel sodium-calcium exchange inhibitor, on contractility and calcium handling in isolated failing rat ventricular myocytes

BACKGROUND AND PURPOSE

Specific Na(+) /Ca(2+) exchanger (NCX) inhibition is a potential strategy to correct reduced contractility and depleted sarcoplasmic reticulum (SR) Ca(2+) content in heart failure (HF). SN-6, a benzyloxyphenyl derivative and proposed selective NCX inhibitor, could be used for this purpose. This study aimed to evaluate the effects of SN-6 on contractility and Ca(2+) handling in normal and failing rat cardiomyocytes.

EXPERIMENTAL APPROACH

HF was induced in rats by coronary artery ligation. Left ventricular myocytes were isolated and superfused with increasing concentrations of SN-6.

KEY RESULTS

Sarcomere shortening, induced by field-stimulation, was reduced in amplitude with increasing concentrations of SN-6 compared with control solution. This effect was greater in failing cells. Kinetics of contractility (time to 90% peak and time to 50% relaxation) were significantly faster. Despite this, intracellular Ca(2+) transients demonstrated no change in the peak amplitude at low concentrations of SN-6, suggesting that SN-6 may affect myofilament sensitivity to Ca(2+) . Ten micro molar SN-6 significantly reduced peak Ca(2+) amplitude by 61.57% and 64.73% in normal and failing cells, respectively. Diastolic Ca(2+) was significantly increased at 1 μM SN-6. SR Ca(2+) content, assessed by rapid application of caffeine, was reduced in failing cells with 1 μM SN-6. Peak ICa , measured by whole-cell patch clamping, was significantly reduced in normal and failing myocytes at 1 μM SN-6.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that SN-6 is not a selective inhibitor of NCX and impairs contractility and Ca(2+) handling. Its use, together with similar putative NCX blockers, in correcting the contractile abnormalities of heart failure requires further studies.

Effect of the total saponins of Aralia elata (Miq) Seem on cardiac contractile function and intracellular calcium cycling regulation

ETHNOPHARMACOLOGICAL RELEVANCE

Total saponins of Aralia elata (Miq) Seem (AS) from the Chinese traditional herb Longya Aralia chinensis L. can improve cardiac function, although the active mechanism remains poorly understood. The present study aimed to determine the direct effect of AS on cardiac function in dogs and the effects on Ca2+ transient and contractions in isolated rat cardiomyocytes.

MATERIAL AND METHODS

In anesthetized dogs, hemodynamic indexes and myocardial oxygen consumption were determined before and after AS was administered. In isolated adult rat cardiomyocytes, contractile and intracellular Ca2+ properties were determined simultaneously in real time by using an IonOptix MyoCam system.

RESULTS

Our results showed that AS directly induced a positive inotropic effect and improved coronary blood flow and energy metabolism, indicating that AS induced a beneficial effect to treat myocardial ischemia/reperfusion injury. Moreover, AS increased sarcomere shortening, maximal velocity of shortening/relengthening (±dL/dt), amplitude of [Ca2+]i transients and SERCA activity in a concentration-dependent manner. PKCε was also activated after the cells were treated with AS.

CONCLUSION

These findings revealed the positive inotropic effect of AS on canine myocardium and isolated rat cardiomyocytes. This effect was possibly associated with an increase in amplitude of the [Ca2+]i transient and PKCε-dependent signaling pathway.

α,β-Unsaturated aldehyde crotonaldehyde triggers cardiomyocyte contractile dysfunction: role of TRPV1 and mitochondrial function

Recent evidence has suggested that cigarette smoking is associated with an increased prevalence of heart diseases. Given that cigarette smoking triggers proinflammatory response via stimulation of the capsaicin-sensitive transient receptor potential cation channel TRPV1, this study was designed to evaluate the effect of an essential α,β-unsaturated aldehyde from cigarette smoke crotonaldehyde on myocardial function and the underlying mechanism with a focus on TRPV1 and mitochondria. Cardiomyocyte mechanical and intracellular Ca2+ properties were evaluated including peak shortening (PS), maximal velocity of shortening/relengthening (±dL/dt), time-to-PS (TPS), time-to-90% relengthening (TR90), fura-2 fluorescence intensity (FFI), intracellular Ca2+ decay and SERCA activity. Apoptosis and TRPV1 were evaluated using Western blot analysis. Production of reactive oxygen species (ROS) and DNA damage were measured using the intracellular fluoroprobe 5-(6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate and 8-hydroxy-2'-deoxyguanosine (8-OHdG), respectively. Our data revealed that crotonaldehyde interrupted cardiomyocyte contractile and intracellular Ca2+ property including depressed PS, ±dL/dt, ΔFFI and SERCA activity, as well as prolonged TR90 and intracellular Ca2+ decay. Crotonaldehyde exposure increased TRPV1 and NADPH oxidase levels, promoted apoptosis, mitochondrial injury (decreased aconitase activity, PGC-1α and UCP-2) as well as production of ROS and 8-OHdG. Interestingly, crotonaldehyde-induced cardiac defect was obliterated by the ROS scavenger glutathione and the TRPV1 inhibitor capsazepine. Capsazepine (not glutathione) ablated crotonaldehyde-induced mitochondrial damage. Capsazepine, glutathione and the NADPH inhibitor apocynin negated crotonaldehyde-induced ROS accumulation. Our data suggest a role of crotonaldehyde compromises cardiomyocyte mechanical function possibly through a TRPV1- and mitochondria-dependent oxidative stress mechanism.

Inhibition of protein kinase C βII isoform ameliorates methylglyoxal advanced glycation endproduct-induced cardiomyocyte contractile dysfunction

AIMS

Accumulation of advanced glycation endproduct (AGE) contributes to diabetic complication including diabetic cardiomyopathy although the precise underlying mechanism still remains elusive. Recent evidence depicted a pivotal role of protein kinase C (PKC) in diabetic complications. To this end, this study was designed to examine if PKCβII contributes to AGE-induced cardiomyocyte contractile and intracellular Ca(2+) aberrations.

MAIN METHODS

Adult rat cardiomyocytes were incubated with methylglyoxal-AGE (MG-AGE) in the absence or presence of the PKCβII inhibitor LY333531 for 12h. Contractile and intracellular Ca(2+) properties were assessed using an IonOptix system including peak shortening (PS), maximal velocity of shortening/relengthening (±dL/dt), time-to-PS (TPS), time-to-90% relengthening (TR90), rise in intracellular Ca(2+) Fura-2 fluorescence intensity and intracellular Ca(2+) decay. Oxidative stress, O2(-) production and mitochondrial integrity were examined using TBARS, fluorescence imaging, aconitase activity and Western blotting.

KEY FINDINGS

MG-AGE compromised contractile and intracellular Ca(2+) properties including reduced PS, ±dL/dt, prolonged TPS and TR90, decreased electrically stimulated rise in intracellular Ca(2+) and delayed intracellular Ca(2+) clearance, the effects of which were ablated by the PKCβII inhibitor LY333531. Inhibition of PKCβII rescued MG-AGE-induced oxidative stress, O2(-) generation, cell death, apoptosis and mitochondrial injury (reduced aconitase activity, UCP-2 and PGC-1α). In vitro studies revealed that PKCβII inhibition-induced beneficial effects were replicated by the NADPH oxidase inhibitor apocynin and were mitigated by the mitochondrial uncoupler FCCP.

SIGNIFICANCE

These findings implicated the therapeutic potential of specific inhibition of PKCβII isoform in the management of AGE accumulation-induced myopathic anomalies.

Autoantibodies against the β3-adrenoceptor protect from cardiac dysfunction in a rat model of pressure overload

β₃-adrenoceptors (β₃-ARs) mediate a negative inotropic effect in human ventricular cardiomyocytes, which is opposite to that of β₁- and β₂-ARs. It has been previously demonstrated that autoantibodies against the β_1/β₂-AR exist in the sera of some patients with heart failure (HF) and these autoantibodies display agonist-like effects. Our aim in this study was to observe whether autoantibodies against the β₃-AR (β₃-AR Abs) exist in the sera of patients with HF and to assess the effects of β₃-AR Abs on rat model of pressure overload cardiomyopthy. In the present study, the level of β₃-AR Abs in the sera of HF patients was screened by ELISA. β₃-AR Abs from HF patients were administrated to male adult rats with abdominal aortic banding (AAB), and the cardiac function was measured by echocardiographic examination and hemodynamic studies. The biological effects of this autoantibody on cardiomyocytes were evaluated using a motion-edge detection system, intracellular calcium transient assay, and patch clamp techniques. Compared to healthy subjects, the frequency of occurrence and titer of β₃-AR Abs in the sera of HF patients were greatly increased, and β₃-AR Abs could prevent LV dilation and improve the cardiac function of rats with AAB. β₃-AR Abs exhibited negative chronotropic and inotropic effects and were accompanied by a decreased intracellular Ca²⁺ transient and membrane L-type Ca²⁺ current in cardiomyocytes. Our results demonstrated the existence of β₃-AR Abs in the sera of patients with HF and found that this autoantibody could alleviate the cardiac dysfunction induced by pressure-overload in AAB rats.

Inhibition of protein kinase C βII isoform rescues glucose toxicity-induced cardiomyocyte contractile dysfunction: role of mitochondria

AIMS

Hyperglycemia leads to cytotoxicity in the heart. Although theories were postulated for glucose toxicity-induced cardiomyocyte dysfunction including oxidative stress, the mechanism involved still remains unclear. Recent evidence has depicted a role of protein kinase C (PKC) in diabetic complications while high concentrations of glucose stimulate PKC. This study examined the role of PKCβII in glucose toxicity-induced cardiomyocyte contractile and intracellular Ca(2+) aberrations.

MAIN METHODS

Adult rat cardiomyocytes were maintained in normal (NG, 5.5 mM) or high glucose (HG, 25.5 mM) medium for 12 h. Contractile and intracellular Ca(2+) properties were measured using a video edge-detection system including peak shortening (PS), maximal velocity of shortening/relengthening (±dL/dt), time-to-PS (TPS), time-to-90% relengthening (TR90), rise in intracellular Ca(2+) Fura-2 fluorescence intensity and intracellular Ca(2+) decay. Production of ROS/O2(-) and mitochondrial integrity were examined using fluorescence imaging, aconitase activity and Western blotting.

KEY FINDINGS

High glucose triggered abnormal contractile and intracellular Ca(2+) properties including reduced PS, ±dL/dt, prolonged TR90, decreased electrically-stimulated rise in intracellular Ca(2+) and delayed intracellular Ca(2+) clearance, the effects of which were ablated by the PKCβII inhibitor LY333531. Inhibition of PKCβII rescued glucose toxicity-induced generation of ROS and O2(-), apoptosis, cell death and mitochondrial injury (reduced aconitase activity, UCP-2 and PGC-1α). In vitro studies revealed that PKCβII inhibition-induced beneficial effects were mimicked by the NADPH oxidase inhibitor apocynin and were canceled off by mitochondrial uncoupling using FCCP.

SIGNIFICANCE

These findings suggest the therapeutic potential of specific inhibition of PKCβII isoform in the management of hyperglycemia-induced cardiac complications.

Decoy peptides targeted to protein phosphatase 1 inhibit dephosphorylation of phospholamban in cardiomyocytes

Cardiac sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) plays a crucial role in Ca(2+) handling in cardiomyocytes. Phospholamban (PLB) is an endogenous inhibitor of SERCA2a and its inhibitory activity is enhanced via dephosphorylation by protein phosphatase 1 (PP1). Therefore, the inhibition of PP1-mediated dephosphorylation of PLB might be an efficient strategy for the restoration of reduced SERCA2a activity in failing hearts. We sought to develop decoy peptides that would mimic phosphorylated PLB and thus competitively inhibit the PP1-mediated dephosphorylation of endogenous PLB. The phosphorylation sites Ser16 and Thr17 are located within the flexible loop region (amino acids 14-22) of PLB. We therefore synthesized a 9-mer peptide derived from this region (ΨPLB-wt) and two pseudo-phosphorylated peptides where Ser16 was replaced with Glu (ΨPLB-SE) or Thr17 was replaced with Glu (ΨPLB-TE). These peptides were coupled to the cell-permeable peptide TAT to facilitate cellular uptake. Treatment of adult rat cardiomyocytes with ΨPLB-SE or ΨPLB-TE, but not with ΨPLB-wt, significantly elevated the phosphorylation levels of PLB at Ser16 and Thr17. This increased phosphorylation of PLB correlated with an increase in contractile parameters in vitro. Furthermore, the perfusion of isolated rat hearts with ΨPLB-SE or ΨPLB-TE, but not with ΨPLB-wt, significantly improved left ventricular developed pressure that had been previously impaired by ischemia. These data indicate that ΨPLB-SE and ΨPLB-TE efficiently prevented dephosphorylation of PLB by serving as decoys for PP1. Therefore, these peptides may provide an effective modality to regulate SERCA2a activity in failing hearts.

Longstanding hyperthyroidism is associated with normal or enhanced intrinsic cardiomyocyte function despite decline in global cardiac function

Thyroid hormones (THs) play a pivotal role in cardiac homeostasis. TH imbalances alter cardiac performance and ultimately cause cardiac dysfunction. Although short-term hyperthyroidism typically leads to heightened left ventricular (LV) contractility and improved hemodynamic parameters, chronic hyperthyroidism is associated with deleterious cardiac consequences including increased risk of arrhythmia, impaired cardiac reserve and exercise capacity, myocardial remodeling, and occasionally heart failure. To evaluate the long-term consequences of chronic hyperthyroidism on LV remodeling and function, we examined LV isolated myocyte function, chamber function, and whole tissue remodeling in a hamster model. Three-month-old F1b hamsters were randomized to control or 10 months TH treatment (0.1% grade I desiccated TH). LV chamber remodeling and function was assessed by echocardiography at 1, 2, 4, 6, 8, and 10 months of treatment. After 10 months, terminal cardiac function was assessed by echocardiography and LV hemodynamics. Hyperthyroid hamsters exhibited significant cardiac hypertrophy and deleterious cardiac remodeling characterized by myocyte lengthening, chamber dilatation, decreased relative wall thickness, increased wall stress, and increased LV interstitial fibrotic deposition. Importantly, hyperthyroid hamsters demonstrated significant LV systolic and diastolic dysfunction. Despite the aforementioned remodeling and global cardiac decline, individual isolated cardiac myocytes from chronically hyperthyroid hamsters had enhanced function when compared with myocytes from untreated age-matched controls. Thus, it appears that long-term hyperthyroidism may impair global LV function, at least in part by increasing interstitial ventricular fibrosis, in spite of normal or enhanced intrinsic cardiomyocyte function.

Contractility assessment in enzymatically isolated cardiomyocytes

The use of enzymatically isolated cardiac myocytes is ubiquitous in modern cardiovascular research. Parallels established between cardiomyocyte shortening responses and those of intact tissue make the cardiomyocyte an invaluable experimental model of cardiac function. Much of our understanding regarding the fundamental processes underlying heart function is owed to our increasing capabilities in single-cell stimulation and direct or indirect observation, as well as quantitative analysis of such cells. Of the many important mechanisms and functions that can be readily assessed in cardiomyocytes at all stages of development, contractility is the most representative and one of the most revealing. The purpose of this review is to provide a survey of various methodological approaches in the literature used to assess adult and neonatal cardiomyocyte contractility. The various methods employed to evaluate the contractile behavior of enzymatically isolated mammalian cardiac myocytes can be conveniently divided into two general categories-those employing optical (image)-based systems and those that use transducer-based technologies. This survey is by no means complete, but we have made an effort to include the most popular methods in terms of reliability and accessibility. These techniques are in constant evolution and hold great promise for the next generation of breakthrough studies in cell biology for the prevention, treatment, and cure of cardiovascular diseases.

Ca+2/calmodulin-dependent protein kinase mediates glucose toxicity-induced cardiomyocyte contractile dysfunction

(1) Hyperglycemia leads to cytotoxicity in the heart. Although several theories are postulated for glucose toxicity-induced cardiomyocyte dysfunction, the precise mechanism still remains unclear. (2) This study was designed to evaluate the impact of elevated extracellular Ca²⁺ on glucose toxicity-induced cardiac contractile and intracellular Ca²⁺ anomalies as well as the mechanism(s) involved with a focus on Ca²⁺/calmodulin (CaM)-dependent kinase. Isolated adult rat cardiomyocytes were maintained in normal (NG, 5.5 mM) or high glucose (HG, 25.5 mM) media for 6-12 hours. Contractile indices were measured including peak shortening (PS), maximal velocity of shortening/relengthening (±dL/dt), time-to-PS (TPS), and time-to-90% relengthening (TR₉₀). (3) Cardiomyocytes maintained with HG displayed abnormal mechanical function including reduced PS, ±dL/dt, and prolonged TPS, TR₉₀ and intracellular Ca²⁺ clearance. Expression of intracellular Ca²⁺ regulatory proteins including SERCA2a, phospholamban and Na⁺-Ca²⁺ exchanger were unaffected whereas SERCA activity was inhibited by HG. Interestingly, the HG-induced mechanical anomalies were abolished by elevated extracellular Ca²⁺ (from 1.0 to 2.7 mM). Interestingly, the high extracellular Ca²⁺-induced beneficial effect against HG was abolished by the CaM kinase inhibitor KN93. (4) These data suggest that elevated extracellular Ca²⁺ protects against glucose toxicity-induced cardiomyocyte contractile defects through a mechanism associated with CaM kinase.