Influence of racemic higenamine on the sinus node

The cellular function and molecular mechanism of formaldehyde in cardiovascular disease and heart development

As a common air pollutant, formaldehyde is widely present in nature, industrial production and consumer products. Endogenous formaldehyde is mainly produced through the oxidative deamination of methylamine catalysed by semicarbazide-sensitive amine oxidase (SSAO) and is ubiquitous in human body fluids, tissues and cells. Vascular endothelial cells and smooth muscle cells are rich in this formaldehyde-producing enzyme and are easily damaged owing to consequent cytotoxicity. Consistent with this, increasing evidence suggests that the cardiovascular system and stages of heart development are also susceptible to the harmful effects of formaldehyde. Exposure to formaldehyde from different sources can induce heart disease such as arrhythmia, myocardial infarction (MI), heart failure (HF) and atherosclerosis (AS). In particular, long-term exposure to high concentrations of formaldehyde in pregnant women is more likely to affect embryonic development and cause heart malformations than long-term exposure to low concentrations of formaldehyde. Specifically, the ability of mouse embryos to effect formaldehyde clearance is far lower than that of the rat embryos, more readily allowing its accumulation. Formaldehyde may also exert toxic effects on heart development by inducing oxidative stress and cardiomyocyte apoptosis. This review focuses on the current progress in understanding the influence and underlying mechanisms of formaldehyde on cardiovascular disease and heart development.

The cardiac electrophysiology effects of higenamine in guinea pig heart

BACKGROUND

Higenamine (HG) is an active compound derived from Aconiti root with a cardiotonic effect. It has been approved by the Chinese SFDA for clinical trials due to its effect as a potent inotropic and chronotropic agent in the heart. However, the direct mode of action of HG on cardiac electrophysiology is unclear.

METHODS

The experiments were performed at both cell levels and the isolated organ. The major cardiac ion currents and the action potential duration (APD) were measured using patch-clamps in single guinea-pig left ventricular myocytes. ECG was recorded in isolated guinea pig hearts.

RESULTS

In the left ventricular myocytes, HG increased I_Ca-L and I_Ks in concentration- and voltage-dependent manners in the left ventricular myocytes. It potentiated the I_Ca-L and I_Ks simultaneously for synchronization. The EC₅₀ values were 0.27 μM and 0.64 μM for the I_Ca-L and I_Ks, respectively. HG (0.1 μM, 0.5 μM and 1 μM) had no effect on the I_Kr and I_Na. HG slightly prolonged APD at lower concentrations, and shortened the APD at higher concentrations. HG can induce the delayed after depolarization (DAD), which showed some pro-arrhythmic effect. In the isolated perfused heart, HG increased the heart rate via an action on the sinoatrial node cells, but did not induce cardiac arrhythmias, even at high concentrations. The EC₅₀ value for the sinoatrial node that controls the heart rate was 0.13 μM. The sinoatrial node cells appeared to be more sensitive than ventricular myocytes to HG. The effects of HG on ventricular cells and sinoatrial node cells were both mediated through stimulation of β1-AR.

CONCLUSION

We show for the first time that HG produced a predominant action on the sinoatrial node. HG appears to control the cardiac electrophysiology through its predominant effect on the sinoarial node cells, without induction of the ectopic activity that causes cardiac arrhythmias. Thus, HG might be useful for the treatment of bradycardia.

Applications of Higenamine in pharmacology and medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Aconitum has been used as local and traditional medicines in many asian regions for the treatment of various diseases such as collapse, syncope, painful joints, oedema, bronchial asthma et al. Higenamine, a plant-based alkaloid, was initially isolated from Aconitum and identified as the active cardiotonic component of Aconitum. It has been tested as a candidate of pharmacologic stress agent in the detection of coronary artery diseases (CADs) and now researchers have just accomplished the phase III clinical studies successfully in China. Besides, a large number of studies have revealed the various pharmacological properties and potentially multi-spectral medical applications of higenamine. However, to date, no comprehensive review on higenamine has been published.

AIM OF THE REVIEW

This present paper aims to compile a comprehensive update regarding the biochemistry, pharmacokinetic features, pharmacological activities, clinical and potential clinical uses and toxicities on higenamine with the ultimate objective of providing a guide for future research on this drug.

MATERIALS AND METHODS

The selection of relevant data was made through a search using the keyword "higenamine" in "Web of science", "Pubmed", and "China Knowledge Resource Integrated (CNKI)". Information was also acquired from local classic herbal literature, government reports and conference papers.

RESULTS

In addition to Aconitum, higenamine also exists in many other plants including Tinospora crispa, Nandina domestica T_HUNBERG, Gnetum Parvifolium C.Y. Cheng, sarum Heterotropoides_,Nelumbo nucifera_,N.nucifera. The pharmacokinetic studies conducted in animals and humans showed that higenamine conformed to a two-compartment pharmacokinetic model. Studies over the last four decades on higenamine have revealed its various pharmacological properties such as positive inotropic and chronotropic effect, activating slow channel effect, vascular and tracheal relaxation effect, anti-thrombotic, anti-apoptotic and anti-oxidative effect, anti-inflammatory and immunomodulatory effect. This phytochemical constituent has shown its potential therapeutic effects for diseases like heart failure, disseminated intravascular coagulation (DIC), shock, arthritis, asthma, ischemia/reperfusion (I/R) injuries and erectile dysfunction.

CONCLUSIONS

Extensive basic and clinical studies on higenamine showed valuable therapeutic effects on different disorders. However, the underlying mechanisms of higenamine have not been established. Therefore, the safety, tolerability and efficacy of higenamine are as yet, not fully understood. Additionally, some of the studies were small sample-sized and unreliable. To sum up, there is a need for deeper investigation in the mechanisms of higenamine action, as well as well-designed preclinical and clinical trials studies to test the safety and clinical value of the drug.