Antiarrhythmic effect of newly synthesized compound 44Bu on model of aconitine-induced arrhythmia — Compared to lidocaine

Chinese herbal medicine for the treatment of cardiovascular diseases ─ targeting cardiac ion channels

Cardiovascular disease (CVD) remains the leading cause of morbidity and mortality, imposing an increasing global health burden. Cardiac ion channels (voltage-gated Na_V, Ca_V, K_Vs, and others) synergistically shape the cardiac action potential (AP) and control the heartbeat. Dysfunction of these channels, due to genetic mutations, transcriptional or post-translational modifications, may disturb the AP and lead to arrhythmia, a major risk for CVD patients. Although there are five classes of anti-arrhythmic drugs available, they can have varying levels of efficacies and side effects on patients, possibly due to the complex pathogenesis of arrhythmias. As an alternative treatment option, Chinese herbal remedies have shown promise in regulating cardiac ion channels and providing anti-arrhythmic effects. In this review, we first discuss the role of cardiac ion channels in maintaining normal heart function and the pathogenesis of CVD, then summarize the classification of Chinese herbal compounds, and elaborate detailed mechanisms of their efficacy in regulating cardiac ion channels and in alleviating arrhythmia and CVD. We also address current limitations and opportunities for developing new anti-CVD drugs based on Chinese herbal medicines.

Structural characterization, in vivo toxicity and biological activity of two new pyro-type diterpenoid alkaloids derived from 3-acetylaconitine

OBJECTIVE

The transformations that occur in diterpenoid alkaloids during the process of sand frying for Chinese herbal medicine preparation have yet to be clarified. This study investigated the structural changes that take place in 3-acetylaconitine during a simulation of heat-processing and evaluated the toxicity and biological activity of the pyrolysis products.

METHODS

The diterpenoid alkaloid 3-acetylaconitine was heated at 180 °C for 15 min to simulate the process of sand frying. The pyrolysis products were separated using column chromatography, and their structures were investigated using high-resolution electrospray ionization mass spectroscopy and nuclear magnetic resonance spectroscopy. Further, in vivo cardiotoxicity and acute toxicity of 3-acetylaconitine and its pyrolysis products were compared, and the aconitine-induced arrhythmia model was employed to evaluate the antiarrhythmic effect of the pyrolysis products.

RESULTS

Two new diterpenoid alkaloids, pyroacetylaconitine and 16-epi-pyroacetylaconitine, a pair of epimers at C-16, were isolated. After comparing the structures of these compounds, possible transformation pathways were proposed. Compared with the prototype compound, 3-acetylaconitine, the cardiotoxicity and acute toxicity of the heat-transformed products were significantly decreased. In the biological activity assay, the two pyrolysis products exhibited an effective increase in ventricular premature beat latency, a reduction in the occurrence of ventricular tachycardia, as well as an increase in the rate of arrhythmia inhibition, implying strong antiarrhythmic activity.

CONCLUSION

Compared with 3-acetylaconitine, its pyrolysis products displayed lower toxicity and good antiarrhythmic effects; thus, they have potential for being developed into antiarrhythmic medicines. Please cite this article as: Wang YJ, Wang Y, Tao P. Structural characterization, in vivo toxicity and biological activity of two new pyro-type diterpenoid alkaloids derived from 3-acetylaconitine. J Integr Med. 2023; Epub ahead of print.

Gallic Acid Inhibits Mesaconitine-Activated TRPV1-Channel-Induced Cardiotoxicity

Aconiti Kusnezoffii Radix (Caowu) is often combined or processed with Chebulae Fructus (Hezi) to achieve attenuation purposes in Mongolian medicine. Mesaconitine (MA), a main bioactive ingredient of Caowu, is also famous for its high cardiotoxicity while exerting good anti-inflammatory and analgesic properties. Gallic acid (GA), one of the leading chemical components in Hezi, possesses cardiac protection. This study aimed to clarify the detoxification effects of GA from Hezi on MA-induced cardiotoxicity and whether the detoxification mechanism is related to the TRPV1 channel. Cell viability was determined by methyl thiazol tetrazolium (MTT), and lactate dehydrogenase (LDH) leakage rate was determined by ELISA. Hoechst 33258, JC-1, DCFH-DA, and Fluo-3 AM staining were conducted to detect apoptosis, mitochondrial membrane potential, reactive oxygen species (ROS), and Ca2+ respectively; TRPV1 channel current was recorded by whole-cell patch-clamp technology to observe the effect of GA and MA alone or in combination on TRPV1 channel. The results showed that GA exhibited pronounced detoxification effects on MA-induced cardiotoxicity. GA significantly inhibited the MA-induced decrease in cell viability; suppressed the MA-induced LDH leakage rate, apoptosis, and the release of ROS and Ca2+; and alleviated the reduction of mitochondrial membrane potential. We found that MA-induced cardiotoxicity was significantly attenuated in H9c2 cells pretreated with the TRPV1 antagonist BCTC. In the whole-cell patch-clamp experiment, the TRPV1 channel current increase was caused by the GA and MA treatment, whereas it was reduced by the cotreatment of GA and MA. Our data demonstrate that GA in Hezi can reduce MA-induced cardiotoxicity by inhibiting intracellular Ca2+ influx, restoring mitochondrial membrane potential, and reducing apoptosis. The detoxification mechanism may be related to the desensitization of the TRPV1 channel by the combined application of MA and GA.

Attenuated Structural Transformation of Indaconitine during Sand Frying Process and Anti-Arrhythmic Effects of Its Transformed Products

The transformation pathways of diterpenoid alkaloids have been clarified clearly in the boiling and steaming process, but remain to be determined in the sand frying process. The aims of the study were to investigate the transformation pathways of indaconitine in the sand frying process, as well as examine the cardiotoxicity and anti-arrhythmic activity of indaconitine and its transformed products. The transformed product was separated by column chromatography, and the structure was identified by ¹H NMR, ¹³C NMR, and HR-ESI-MS. The cardiotoxicity of indaconitine and its transformed products was clarified by observing the electrocardiogram (ECG) changes at the same dose. Furthermore, the anti-arrhythmic activity of the transformed products was investigated using an aconitine-induced rat arrhythmia model. Consequently, Δ¹⁵⁽¹⁶⁾-16-demethoxyindaconitine, a new diterpenoid alkaloid, was isolated from processed indaconitine. Intravenous injection of 0.06 mg/kg indaconitine induced arrhythmias in SD rats, while Δ¹⁵⁽¹⁶⁾-16-demethoxyindaconitine did not exhibit arrhythmias at the same dose. In the anti-arrhythmic assay, mithaconitine, obtained in the previous research, together with Δ¹⁵⁽¹⁶⁾-16-demethoxyindaconitine, could dose-dependently delay the onset time of ventricular premature beat (VPB) and reduce the incidence of ventricular tachycardia (VT), combined with the increasing arrhythmia inhibition rate, exhibiting strong anti-arrhythmic activities. These results indicated that two or more pathways exist in the sand frying process, and the transformed products exhibited lower cardiotoxicity and strong anti-arrhythmic activities, which had the possibility of being developed into anti-arrhythmic drugs.

Design, synthesis, and biological evaluation of arylmethylpiperidines as Kv1.5 potassium channel inhibitors

Kv1.5 potassium channel, encoded by KCNA5, is a promising target for the treatment of atrial fibrillation, one of the common arrhythmia. A new series of arylmethylpiperidines derivatives based on DDO-02001 were synthesised and evaluated for their ability to inhibit Kv1.5 channel. Among them, compound DDO-02005 showed good inhibitory activity (IC₅₀ = 0.72 μM), preferable anti-arrhythmic effects and favoured safety. These results indicate that DDO-02005 can be a promising Kv1.5 inhibitor for further studies.

Antiarrhythmic effects of newly developed propafenone derivatives

It is well known that the presence of different chemical groups in drug molecules influences their pharmacological properties. The aim of our study is to investigate whether newly synthesized derivatives of propafenone, with changes in benzyl moiety, have a different effect upon arrhythmia, compared to propafenone. 5OCl-PF and 5OF-PF are derivatives of propafenone with -Cl or -F substituent on the ortho position of the benzyl moiety. For verification of their antiarrhythmic effect, we used an in vivo rat model of aconitine-induced arrhythmia. 5OCl-PF speeded the appearance of supraventricular premature beats (SVPB) and death more than aconitine. All animals treated with 5OCl-PF developed ventricular premature beats in salvos (VPBS), bigeminies (VPBB) and paroxysmal ventricular tachycardia (PVT). 5OF-PF had a negative chronotropic effect and potentiated atrial excitability (more SVPB). It had a positive effect on the occurrence and onset time of supraventricular tachycardia, VPBS, and PVT. Based on the obtained results, it can be concluded that newly synthesized propafenone derivatives have no better antiarrhythmic effect than the parent compound. In the future, our research will be focused on the synthesis of different derivatives and examining their antiarrhythmic effects.

Attenuation and Structural Transformation of Crassicauline A During Sand Frying Process and Antiarrhythmic Effects of its Transformed Products

To ensure safety and efficacy, most Aconitum herbs should be processed before clinical application. The processing methods include boiling, steaming, and sand frying. Among these methods, the transformation pathways of diterpenoid alkaloids in the process of sand frying are more complicated. Therefore, crassicauline A, a natural product with two ester bonds, was chosen as the experimental object. Consequently, a known alkaloid, together with three new alkaloids, was derived from crassicauline A. Meanwhile, the cardiotoxicity of converted products was reduced compared with their parent compound. Interestingly, some diterpenoid alkaloids have similar structures but opposite effects, such as arrhythmia and antiarrhythmic. Considering the converted products are structural analogues of crassicauline A, herein, the antiarrhythmic activity of the transformed products was further investigated. In a rat aconitine-induced arrhythmia assay, the three transformed products, which could dose-dependently delay the ventricular premature beat (VPB) incubation period, reduce the incidence of ventricular tachycardia (VT), combined with the increasing arrhythmia inhibition rate, exhibited prominent antiarrhythmic activities. Our experiments speculated that there might be at least two transformation pathways of crassicauline A during sand frying. The structure-activity data established in this paper constructs the critical pharmacophore of diterpenoid alkaloids as antiarrhythmic agents, which could be helpful in searching for the potential drugs that are equal or more active and with lower toxicity, than currently clinical used antiarrhythmic drugs.

Attenuated Structural Transformation of Aconitine during Sand Frying Process and Antiarrhythmic Effect of Its Converted Products

The transformation pathways of diterpenoid alkaloids have been clarified in the boiling and steaming process. Aconitine, a famous diterpenoid alkaloid, is successively transformed into benzoylaconine and aconine during the processes of boiling and steaming, but the transformation pathway remains to be determined in the sand frying process. The present study aims at investigating the transformation pathways of aconitine in the process of sand frying, as well as assessing the cardiotoxicity and antiarrhythmic activity of aconitine and its converted products. The parameters of temperature and time for the structural transformation of aconitine were confirmed by HPLC. The converted products were further separated and identified by column chromatography, NMR, and HR-ESI-MS. Furthermore, by observing the lead II electrocardiogram (ECG) changes in rats under an equivalent dose, the cardiotoxicity of aconitine and its converted products were compared. Ultimately, the antiarrhythmic effect of the converted products was investigated by employing the model of aconitine-induced arrhythmia. Consequently, the structure of aconitine was converted when processed at 120°C–200°C for 1–40 min. Two diterpenoid alkaloids, a pair of epimers, namely, pyroaconitine and 16-epi-pyroaconitine, were further isolated from processed aconitine. 0.03 mg/kg aconitine induced arrhythmias in normal rats, while the converted products did not exhibit arrhythmias under an equal dose. In the antiarrhythmic assay, 16-epi-pyroaconitine could dose-dependently delay the onset time of VPB, reduce the incidence of VT, and increase the arrhythmia inhibition rate, demonstrating comparatively strong antiarrhythmic activity. Conclusively, compared with the prototype compound aconitine, the converted products exhibited lower cardiotoxicity. Further investigations on the cardiotoxicity indicated that pyroaconitine with β configuration had a stronger cardiotoxicity than 16-epi-pyroaconitine with α configuration. Furthermore, 16-epi-pyroaconitine could antagonize the arrhythmogenic effect caused by the prototype compound aconitine; the antiarrhythmic effect of 16-epi-pyroaconitine was stronger than lidocaine and propafenone, which had the potential to be developed as antiarrhythmic drugs.

Inhibition of the INa/K and the activation of peak INa contribute to the arrhythmogenic effects of aconitine and mesaconitine in guinea pigs

Aconitine (ACO), a main active ingredient of Aconitum, is well-known for its cardiotoxicity. However, the mechanisms of toxic action of ACO remain unclear. In the current study, we investigated the cardiac effects of ACO and mesaconitine (MACO), a structurally related analog of ACO identified in Aconitum with undocumented cardiotoxicity in guinea pigs. We showed that intravenous administration of ACO or MACO (25 μg/kg) to guinea pigs caused various types of arrhythmias in electrocardiogram (ECG) recording, including ventricular premature beats (VPB), atrioventricular blockade (AVB), ventricular tachycardia (VT), and ventricular fibrillation (VF). MACO displayed more potent arrhythmogenic effect than ACO. We conducted whole-cell patch-clamp recording in isolated guinea pig ventricular myocytes, and observed that treatment with ACO (0.3, 3 μM) or MACO (0.1, 0.3 μM) depolarized the resting membrane potential (RMP) and reduced the action potential amplitude (APA) and durations (APDs) in a concentration-dependent manner. The ACO- and MACO-induced AP remodeling was largely abolished by an I_Na blocker tetrodotoxin (2 μM) and partly abolished by a specific Na⁺/K⁺ pump (NKP) blocker ouabain (0.1 μM). Furthermore, we observed that treatment with ACO or MACO attenuated NKP current (I_Na/K) and increased peak I_Na by accelerating the sodium channel activation with the EC₅₀ of 8.36 ± 1.89 and 1.33 ± 0.16 μM, respectively. Incubation of ventricular myocytes with ACO or MACO concentration-dependently increased intracellular Na⁺ and Ca²⁺ concentrations. In conclusion, the current study demonstrates strong arrhythmogenic effects of ACO and MACO resulted from increasing the peak I_Na via accelerating sodium channel activation and inhibiting the I_Na/K. These results may help to improve our understanding of cardiotoxic mechanisms of ACO and MACO, and identify potential novel therapeutic targets for Aconitum poisoning.

L-Type Calcium Channel Inhibition Contributes to the Proarrhythmic Effects of Aconitine in Human Cardiomyocytes

Aconitine (ACO) is well-known for causing lethal ventricular tachyarrhythmias. While cardiac Na⁺ channel opening during repolarization has long been documented in animal cardiac myocytes, the cellular effects and mechanism of ACO in human remain unexplored. This study aimed to assess the proarrhythmic effects of ACO in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). ACO concentration-dependently (0.3 ~ 3.0 μM) shortened the action potentials (AP) durations (APD) in ventricular-like hiPSC-CMs by > 40% and induced delayed after-depolarization. Laser-scanning confocal calcium imaging analysis showed that ACO decreased the duration and amplitude of [Ca²⁺]_i transients and increased in the beating frequencies by over 60%. Moreover, ACO was found to markedly reduce the L-type calcium channel (LTCC) currents (I_Ca,L) in hiPSC-CMs associated with a positive-shift of activation and a negative shift of inactivation. ACO failed to alter the peak and late Na⁺ currents (I_Na) in hiPSC-CMs while it drastically increased the late I_Na in Guinea-pig ventricular myocytes associated with enhanced activation/delayed inactivation of I_Na at -55 mV~ -85 mV. Further, the effects of ACO on I_Ca,L, I_Na and the rapid delayed rectifier potassium current (I_kr) were validated in heterologous expression systems by automated voltage-clamping assays and a moderate suppression of I_kr was observed in addition to concentration-dependent I_Ca,L inhibition. Lastly, increased beating frequency, decreased Ca²⁺ wave and shortened field potential duration were recorded from hiPSC-CMs by microelectrode arrays assay. In summary, our data demonstrated that LTCC inhibition could play a main role in the proarrhythmic action of ACO in human cardiomyocytes.

Cladosporium cladosporioides XJ-AC03, an aconitine-producing endophytic fungus isolated from Aconitum leucostomum

The endophytic fungus XJ-AC03, which was isolated from the healthy roots of Aconitum leucostomum, produced aconitine when grown in potato dextrose agar (PDA) medium. The presence of aconitine was confirmed by the chromatographic and spectroscopic analyses. The yield of aconitine was recorded as 236.4 μg/g by high performance liquid chromatography (HPLC). The mass spectrometry was shown to be identical to authentic aconitine. Further analysis with nuclear magnetic resonance (NMR) spectroscopy to show the chemical structure of the fungal aconitine indicated that the fungal aconitine produced an NMR spectrum identical to that of authentic aconitine. Strain XJ-AC03 was identified as Cladosporium cladosporioides by its characteristic culture morphology and ITS rDNA sequence analysis.

Aconitine blocks HERG and Kv1.5 potassium channels

ETHNOPHARMACOLOGICAL RELEVANCE

Aconitum has been widely used to treat various diseases in China for a long time. However, improper use of this drug results in severe intoxication. Aconitine (ACO), a diterpenoid alkaloid from aconitum, mainly contributes to cardio-toxic effects of aconitum and has also been commonly known to induce arrhythmias in animal models. However, its pro-arrhythmic mechanisms are not clear.

AIM OF THE STUDY

The effects of ACO on HERG and Kv1.5 channels were investigated.

MATERIALS AND METHODS

HERG and Kv1.5 channels were expressed in Xenopus laevis oocytes, and the resulting currents were recorded using a two-microelectrode voltage clamp technique.

RESULTS

In HERG channels, ACO exhibited a blockade in a voltage- and time-dependent manner. The blockade was enhanced by further activation of currents, which were consistent with an open-channel blockade. In Kv1.5 channels, ACO produced a voltage-, time-, and frequency-dependent inhibition. The blockade was enhanced by higher rates of stimulation, consistent with preferential binding of the drug to the open state. In addition, ACO blocked Kv1.5 and HERG channels in a concentration-dependent manner with an IC(50) of 0.796+/-0.123 and 1.801+/-0.332 microM, respectively.

CONCLUSIONS

ACO blocks HERG and Kv1.5 potassium channels in the open state. Blockade of potassium channels, particular the HERG channel, may be one of the important mechanisms of how ACO induces arrhythmias.

Effect of Newly Synthesized Compounds 44Bu and 444 on QRS-Complex Width and Fast Sodium Current: Differences between Isomers

Two newly synthesized short-acting agents 44Bu and 444 were observed to suppress the aconitine-induced arrhythmias and block the fast sodium currentINain the rat heart. No data about their effect on the electrocardiographic parameters are available. In this study, we explored the effect of both racemates and particular isomers of 44Bu and 444 on the QRS-complex widthin vivoin rats and onINain isolated rat ventricular myocytes. All variants of 44Bu and 444 (1.5 mg/kg) caused a significant QRS-widening reaching the peak effect at the 1st or 2nd min after their intravenous administration. 44Bu racemate widened the QRS-complex from 16.8 ± 0.4 to 26.3 ± 0.5 ms (by 57%), significantly more than R- (33%-widening) and S-isomer (36%-widening). 444 racemate widened the QRS-complex from 20.8 ± 1.0 to 34.1 ± 0.9 ms (by 64%), which was comparable to S-isomer (63%-widening), however, substantially more than R-isomer (40%-widening). Regarding the effect onINa, 44Bu caused a significantly deeperINa- block compared to 444 when applied at the same concentration of 3 μmol/l (~0.1 mg/kg). 44Bu racemate and R-isomer blockedINasimilarly (91.7 ± 0.8 and 91.8 ± 1.6%-block, respectively) and significantly more than S-isomer (82.4 ± 2.3%-block). 444 R-isomer blockedINaless than racemate and S-isomer (by 31.7 ± 3.9% vs. 48.3 ± 4.7 and 50.2 ± 4.1%, respectively). We conclude that both racemates and particular isomers of 44Bu and 444 induce a QRS-widening and blockINain the rat heart, however, their effects notably differed. The relative widening of the QRS-complex after application of 44Bu did not conform to the level ofINa-block observed in isolated cardiomyocytes which stresses the importance ofin vivoexperiments in the pre-clinical testing of new drugs.

Antiarrhythmic effect of acute oxygen-ozone administration to rats

The antiarrhythmic effects of 100; 150; and 300microg/kg i.p. oxygen/ozone mixture were tested on arrhythmias induced by i) ischemia; ii) ischemia/reperfusion; iii) aconitine (15microg/kg/i.v.); potassium chloride (1.5% i.v.) in rats. 25min of cardiac left descending coronary artery ischemia caused severe incidence of ventricular tachycardia, ventricular fibrillation and mortality. These were significantly reduced by pre-treatment of rats with oxygen/ozone mixture at doses of 150 and 300microg/kg. In separate experiments using a protocol of 5min ischemia followed by 8min reperfusion this caused arrhythmias starting within 6+/-1s. The incidence of ventricular tachycardia was 100%, while ventricular fibrillation occurred in 75% of the animals and lasted 85+/-14s. The mortality was 62.5%. These figures were significantly (P<0.01) reduced in animals treated with 150microg/kg oxygen/ozone and a substantial increase observed with 300microg/kg, whilst not affected by the lower dose of 100microg/kg. 150 and 300microg/kg oxygen/ozone prolonged the onset time for the appearance of arrhythmias induced by aconitine (300microg/kg oxygen/ozone, approximately 81% longer). Oxygen/ozone also reduced the ventricular tachycardia duration, ventricular fibrillation incidence, arrhythmia score, and increased the rat's survival rate. As for example, this latter was increased from 25% (aconitine) to 50% (aconitine+oxygen/ozone 150microg/kg). 100microg/kg oxygen/ozone was without effect. None of the oxygen/ozone doses affected the arrhythmias caused by potassium chloride 1.5% i.v. All the oxygen/ozone antiarrhythmic effects were similar to those observed with lidocaine (1.5mg/kg i.v.). In conclusion, oxygen/ozone has antiarrhythmic effects against arrhythmias caused by aconitine, myocardial ischemia and ischemia/reperfusion.

A single exposure to particulate or gaseous air pollution increases the risk of aconitine-induced cardiac arrhythmia in hypertensive rats

Epidemiological studies demonstrate an association between arrhythmias and air pollution. Aconitine-induced cardiac arrhythmia is widely used experimentally to examine factors that alter the risk of arrhythmogenesis. In this study, Wistar-Kyoto (WKY) and spontaneously hypertensive (SH) rats acutely exposed to synthetic residual oil fly ash (s-ROFA) particles (450 mug/m(3)) were "challenged" with aconitine to examine whether a single exposure could predispose to arrhythmogenesis. Separately, SH rats were exposed to varied particulate matter (PM) concentrations (0.45, 1.0, or 3.5 mg/m(3) s-ROFA), or the irritant gas acrolein (3 ppm), to better assess the generalization of this challenge response. Rather than directly cause arrhythmias, we hypothesized that inhaled air pollutants sensitize the heart to subsequent dysrhythmic stimuli. Twenty-four hour postexposure, urethane-anesthetized rats were monitored for heart rate (HR), electrocardiogram, and blood pressure (BP). SH rats had higher baseline HR and BP and significantly longer PR intervals, QRS duration, QTc, and JTc than WKY rats. PM exposure caused a significant increase in the PR interval, QRS duration, and QTc in WKY rats but not in SH rats. Heart rate variability was significantly decreased in WKY rats after PM exposure but increased in SH rats. Cumulative dose of aconitine that triggered arrhythmias in air-exposed SH rats was lower than WKY rats and even lower for each strain postexposure. SH rats exposed to varied concentrations of PM or acrolein developed arrhythmia at significantly lower doses of aconitine than controls; however, there was no PM concentration-dependent response. In conclusion, a single exposure to air pollution may increase the sensitivity of cardiac electrical conduction to disruption. Moreover, there seem to be host factors (e.g., cardiovascular disease) that increase vulnerability to triggered arrhythmias regardless of the pollutant or its concentration.