Chronic atrial ionic remodeling by aldosterone: potentiation of L-type Ca2+ channels and its arrhythmogenic significance

Modulated Calcium Homeostasis and Release Events Under Atrial Fibrillation and Its Risk Factors: A Meta-Analysis

Background: Atrial fibrillation (AF) is associated with calcium (Ca²⁺) handling remodeling and increased spontaneous calcium release events (SCaEs). Nevertheless, its exact mechanism remains unclear, resulting in suboptimal primary and secondary preventative strategies.

Methods: We searched the PubMed database for studies that investigated the relationship between SCaEs and AF and/or its risk factors. Meta-analysis was used to examine the Ca²⁺ mechanisms involved in the primary and secondary AF preventative groups.

Results: We included a total of 74 studies, out of the identified 446 publications from inception (1982) until March 31, 2020. Forty-five were primary and 29 were secondary prevention studies for AF. The main Ca²⁺ release events, calcium transient (standardized mean difference (SMD) = 0.49; I² = 35%; confidence interval (CI) = 0.33–0.66; p < 0.0001), and spark amplitude (SMD = 0.48; I² = 0%; CI = −0.98–1.93; p = 0.054) were enhanced in the primary diseased group, while calcium transient frequency was increased in the secondary group. Calcium spark frequency was elevated in both the primary diseased and secondary AF groups. One of the key cardiac currents, the L-type calcium current (I_CaL) was significantly downregulated in primary diseased (SMD = −1.07; I² = 88%; CI = −1.94 to −0.20; p < 0.0001) and secondary AF groups (SMD = −1.28; I² = 91%; CI = −2.04 to −0.52; p < 0.0001). Furthermore, the sodium–calcium exchanger (I_NCX) and NCX1 protein expression were significantly enhanced in the primary diseased group, while only NCX1 protein expression was shown to increase in the secondary AF studies. The phosphorylation of the ryanodine receptor at S2808 (pRyR-S2808) was significantly elevated in both the primary and secondary groups. It was increased in the primary diseased and proarrhythmic subgroups (SMD = 0.95; I² = 64%; CI = 0.12–1.79; p = 0.074) and secondary AF group (SMD = 0.66; I² = 63%; CI = 0.01–1.31; p < 0.0001). Sarco/endoplasmic reticulum Ca²⁺-ATPase (SERCA) expression was elevated in the primary diseased and proarrhythmic drug subgroups but substantially reduced in the secondary paroxysmal AF subgroup.

Conclusions: Our study identified that I_CaL is reduced in both the primary and secondary diseased groups. Furthermore, pRyR-S2808 and NCX1 protein expression are enhanced. The remodeling leads to elevated Ca²⁺ functional activities, such as increased frequencies or amplitude of Ca²⁺ spark and Ca²⁺ transient. The main difference identified between the primary and secondary diseased groups is SERCA expression, which is elevated in the primary diseased group and substantially reduced in the secondary paroxysmal AF subgroup. We believe our study will add new evidence to AF mechanisms and treatment targets.

Modulating ALDH2 reveals a differential dependence on ROS for hypertrophy and SR Ca2+ release in aldosterone-treated cardiac myocytes

Growing evidence links high aldosterone levels with atrial fibrillation and other heart diseases. Here, we have investigated the functional consequences of culturing adult rat atrial myocytes with aldosterone, at the level of cell size, homeostasis of Ca2+, reactive oxygen species (ROS), and nitrogen oxide (NO). The protein levels of NO synthase (NOS), aldehyde dehydrogenase 2 (ALDH2), NADPH oxidase (NOX), and Na+-Ca2+ exchanger (NCX) were also studied. Aldosterone did not alter the expression of these proteins, except for the NCX, which was enhanced by nearly 100%. Additionally, the hormone inhibited and stimulated, respectively, the production of NO and ROS (the effect on ROS appeared after 24 h of treatment and reached a maximum by 4-6 days, with an EC50 of 1.2 nM). These changes in reactive species generation were blunted by tetrahydrobiopterin (BH4, a NOS cofactor), suggesting the involvement of an uncoupled NOS. An activator (Alda-1) and an inhibitor (daidzin) of ALDH2 were used, to determine if this enzyme activity is related to aldosterone effects, through possible modulation of ROS. Aldosterone produced a ∼10% increase in cell size and, remarkably, this hypertrophic effect, along with the corresponding changes in ROS and NO, were all mimicked by daidzin and prevented by Alda-1. Something different happened with SR Ca2+ release. Aldosterone increased both the magnitude of Ca2+ transients and the incidence of spontaneous Ca2+ oscillations, but these actions were not reproduced by daidzin. Moreover, rather than being prevented, they were further promoted by Alda-1, which also increased the rate of SR Ca2+ reuptake. These results suggest that NOS and ALDH2 may prevent some adverse consequences of aldosteronism (in the case of ALDH2, at the expense of exacerbating SR Ca2+ release). Our data also suggest a hierarchical model in which aldosterone promotes: SR Ca2+ release, then ROS production, and finally hypertrophy.

Interplay of pro-inflammatory cytokines, pro-inflammatory microparticles and oxidative stress and recurrent ventricular arrhythmias in elderly patients after coronary stent implantations

BACKGROUND

The roles of pro-inflammatory microparticles, pro-inflammatory cytokines and oxidative stress were unknown in elderly patients with recurrent ventricular arrhythmias (VA). We evaluated whether cross talk between oxidative stress, pro-inflammatory microparticles, and pro-inflammatory cytokines play the roles in elderly patients with recurrent VA after coronary stenting. This research sought to investigate the effects of oxidative stress, pro-inflammatory microparticles, and pro-inflammatory cytokines on recurrent VA in elderly patients after coronary stenting.

METHODS

In this study, we included 613 consecutive elderly patients with recurrent ventricular arrhythmias induced by coronary reocclusions after coronary stenting. We measured CD31⁺ endothelial microparticle (CD31⁺EMP), CD62E⁺ endothelial microparticle (CD62E⁺EMP), high-sensitivity C-reactive protein (hs-CRP), aldosterone (ALD), malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), soluble tumor necrosis factor receptor-1 (sTNFR-1) and soluble tumor necrosis factor receptor-2 (sTNFR-2) in elderly patients with recurrent VA and assessed impacts of pro-inflammatory microparticles, pro-inflammatory cytokines and oxidative stress on recurrent VA in elderly patients after coronary stenting.

RESULTS

The levels of CD31⁺EMP, CD62E⁺EMP, hs-CRP, ALD, MDA, TNF-α, sTNFR-1 and sTNFR-2 were increased in recurrent malignant ventricular arrhythmia, sustained ventricular tachycardia, multiple ventricular premature beat and left and right ventricular bundle branch block groups (P < 0.001) in elderly patients with coronary reocclusions after coronary stent implantation. Upregulation of pro-inflammatory microparticles, pro-inflammatory cytokines and oxidative stress markers induced recurrent VA in elderly patients after coronary stenting.

CONCLUSIONS

High levels of pro-inflammatory microparticles, pro-inflammatory cytokines and oxidative stress markers were associated with recurrent VA in elderly patients after coronary stenting. Our results suggested that the pro-inflammatory microparticles, pro-inflammatory cytokines and oxidative stress may simultaneously induce and aggravate recurrent VA in elderly patients after coronary stenting.

Interaction of MDIMP with the Voltage-Gated Calcium Channels

Amino acid-derived isoindolines are synthetic compounds that were created with the idea of investigating their biological actions. The amino acid moiety was included on the grounds that it may help to avoid toxic effects. Recently, the isoindoline MDIMP was shown to inhibit both cardiac excitation-contraction coupling and voltage-dependent calcium channels. Here, we revealed that MDIMP binds preferentially to low-voltage-activated (LVA) channels. Using a holding potential of -90 mV, the following IC₅₀ values were found (in micromolars): >1000 (Ca_V2.3), 957 (Ca_V1.3), 656 (Ca_V1.2), 219 (Ca_V3.2), and 132 (Ca_V3.1). Moreover, the isoindoline also promoted both accelerated inactivation kinetics of high-voltage-activated Ca²⁺ channels and a modest upregulation of Ca_V1.3 and Ca_V2.3. Additional data indicate that although MDIMP binds to the closed state of the channels, it has more preference for the inactivated one. Concerning Ca_V3.1, the compound did not alter the shape of the instantaneous current-voltage curve, and substituting one or two residues in the selectivity filter drastically increased the IC₅₀ value, suggesting that MDIMP binds to the extracellular side of the pore. However, an outward current failed in removing the inhibition, which implies an alternative mechanism may be involved. The enantiomer (R)-MDIMP [methyl (R)-2-(1,3-dihydroisoindol-2-yl)-4-methylpentanoate], on the other hand, was synthesized and evaluated, but it did not improve the affinity to LVA channels. Implications of these findings are discussed in terms of the possible underlying mechanisms and pharmacological relevance. SIGNIFICANCE STATEMENT: We have studied the regulation of voltage-gated calcium channels by MDIMP, which disrupts excitation-contraction coupling in cardiac myocytes. The latter effect is more potent in atrial than ventricular myocytes, and this could be explained by our results showing that MDIMP preferentially blocks low-voltage-activated channels. Our data also provide mechanistic insights about the blockade and suggest that MDIMP is a promising member of the family of Ca²⁺ channel blockers, with possible application to the inhibition of subthreshold membrane depolarizations.

Long-Term Regulation of Excitation-Contraction Coupling and Oxidative Stress in Cardiac Myocytes by Pirfenidone

Pirfenidone (PFD) is used to treat human pulmonary fibrosis. Its administration to animals with distinct forms of cardiovascular disease results in striking improvement in cardiac performance. Here, its functional impact on cardiac myocytes was investigated. Cells were kept 1–2 days under either control culture conditions or the presence of PFD (1 mM). Subsequently, they were subjected to electrical stimulation to assess the levels of contractility and intracellular Ca²⁺. The PFD treatment promoted an increase in both peak contraction and kinetics of shortening and relaxation. Moreover, the amplitude and kinetics of Ca²⁺ transients were enhanced as well. Excitation–contraction coupling (ECC) was also investigated, under whole-cell patch-clamp conditions. In keeping with a previous report, PFD increased twofold the density of Ca²⁺ current (I_Ca). Notably, a similar increase in the magnitude of Ca²⁺ transients was also observed. Thus, the gain of ECC was unaltered. Likewise, PFD did not alter the peak amplitude of caffeine-induced Ca²⁺ release, indicating stimulation of Ca²⁺-induced–Ca²⁺-release (CICR) at constant sarcoplasmic reticulum Ca²⁺ load. A phase-plane analysis indicated that PFD promotes myofilament Ca²⁺ desensitization, which is being compensated by higher levels of Ca²⁺ to promote contraction. Interestingly, although the expression of the Na⁺/Ca²⁺ exchanger (NCX) was unaffected, the decay of Ca²⁺ signal in the presence of caffeine was 50% slower in PFD-treated cells (compared with controls), suggesting that PFD downregulates the activity of the exchanger. PFD also inhibited the production of reactive oxygen species, under both, basal conditions and the presence of oxidative insults (acetaldehyde and peroxide hydrogen). Conversely, the production of nitric oxide was either increased (in atrial myocytes) or remained unchanged (in ventricular myocytes). Protein levels of endothelial and neuronal nitric oxide synthases (eNOS and nNOS) were also investigated. eNOS values did not exhibit significant changes. By contrast, a dual regulation was observed for nNOS, which consisted of inhibition and stimulation, in ventricular and atrial myocytes, respectively. In the latter cells, therefore, an up-regulation of nNOS was sufficient to stimulate the synthesis of NO. These findings improve our knowledge of molecular mechanisms of PFD action and may also help in explaining the corresponding cardioprotective effects.