Electrophysiological actions of the plant alkaloid 6-benzoylheteratisine in rat hippocampal slices

Neuropharmacological Potential of Diterpenoid Alkaloids

This study provides a narrative review of diterpenoid alkaloids (DAs), a family of extremely important natural products found predominantly in some species of Aconitum and Delphinium (Ranunculaceae). DAs have long been a focus of research attention due to their numerous intricate structures and diverse biological activities, especially in the central nervous system (CNS). These alkaloids originate through the amination reaction of tetra or pentacyclic diterpenoids, which are classified into three categories and 46 types based on the number of carbon atoms in the backbone structure and structural differences. The main chemical characteristics of DAs are their heterocyclic systems containing β-aminoethanol, methylamine, or ethylamine functionality. Although the role of tertiary nitrogen in ring A and the polycyclic complex structure are of great importance in drug-receptor affinity, in silico studies have emphasized the role of certain sidechains in C13, C14, and C8. DAs showed antiepileptic effects in preclinical studies mostly through Na⁺ channels. Aconitine (1) and 3-acetyl aconitine (2) can desensitize Na⁺ channels after persistent activation. Lappaconitine (3), N-deacetyllapaconitine (4), 6-benzoylheteratisine (5), and 1-benzoylnapelline (6) deactivate these channels. Methyllycaconitine (16), mainly found in Delphinium species, possesses an extreme affinity for the binding sites of α7 nicotinic acetylcholine receptors (nAChR) and contributes to a wide range of neurologic functions and the release of neurotransmitters. Several DAs such as bulleyaconitine A (17), (3), and mesaconitine (8) from Aconitum species have a drastic analgesic effect. Among them, compound 17 has been used in China for decades. Their effect is explained by increasing the release of dynorphin A, activating the inhibitory noradrenergic neurons in the β-adrenergic system, and preventing the transmission of pain messages by inactivating the Na⁺ channels that have been stressed. Acetylcholinesterase inhibitory, neuroprotective, antidepressant, and anxiolytic activities are other CNS effects that have been investigated for certain DAs. However, despite various CNS effects, recent advances in developing new drugs from DAs were insignificant due to their neurotoxicity.

Personalized approach in arrhythmology by genetic-based data: a case report

The results of molecular genetic testing may affect recommended treatment or therapeutic decisions and risk assessment, may help with identification of family members at risk. Here, we report a case of a young patient with a paradoxical combination of two inherited arrhythmic syndromes and demonstrate the role of genetic testing as one of the basis of personalized approach in diagnosis, treatment and prevention complications of inherited channelopathies complications. Integration of genetic testing results into clinical practice is a successful example of the concept of personalized medicine.

An Intentional Aconite Overdose: A Case Report

BACKGROUND

Aconite is one of the most toxic known herbs, widely used for centuries as an essential Chinese medicine, but also for deliberate poisoning throughout history. Clinically indicated in herbal medicine for a range of ailments from headaches to muscle spasm, unfortunately the narrow therapeutic window may lead to a range of toxic presentations. The mechanism of action of the pharmacologically active compounds in Aconite relate to the activation of voltage gated sodium channels within a range of tissue including myocardial, neuronal and smooth muscle leading to persistent cellular activity.

CASE PRESENTATION

We report on a rare case of a fifty year old male with intentional aconite overdose presenting with refractory cardiovascular instability from persistent life threatening arrhythmias, respiratory failure and seizure activity.

CONCLUSION

An overview of Aconite, its history, pharmacological effects, treatment of overdose and outcomes is presented.

A review on phytochemistry, pharmacology and toxicology studies of Aconitum

Objectives

A number of species belonging to herbal genus Aconitum are well-known and popular for their medicinal benefits in Indian, Vietnamese, Korean, Japanese, Tibetan and Chinese systems of medicine. It is a valuable drug as well as an unpredictable toxic material. It is therefore imperative to understand and control the toxic potential of herbs from this genus. In this review, the ethnomedicinal, phytochemistry, pharmacology, structure activity relationship and toxicology studies of Aconitum were presented to add to knowledge for their safe application.

Key findings

A total of about 76 of all aconite species growing in China and surrounding far-east and Asian countries are used for various medical purposes. The main ingredients of aconite species are alkaloids, flavonoids, free fatty acids and polysaccharides. The tuberous roots of genus Aconitum are commonly applied for various diseases such as rheumatic fever, painful joints and some endocrinal disorders. It stimulates the tip of sensory nerve fibres. These tubers of Aconitum are used in the herbal medicines only after processing. There remain high toxicological risks of the improper medicinal applications of Aconitum. The cardio and neurotoxicities of this herb are potentially lethal. Many analytical methods have been reported for quantitatively and qualitatively characterization of Aconitum.

Summary

Aconitum is a plant of great importance both in traditional medicine in general and in TCM in particular. Much attention should be put on Aconitum because of its narrow therapeutic range. However, Aconitum's toxicity can be reduced using different techniques and then benefit from its pharmacological activities. New methods, approaches and techniques should be developed for chemical and toxicological analysis to improve its quality and safety.

Sodium-channel blockers might contribute to the prevention of ventricular tachycardia in patients with long QT syndrome type 2: a description of 4 cases

Four patients with long QT type 2, aged 11 to 18 years from unrelated families, with recurrent syncope and polymorhic ventricular tachycardia were studied. Long QT syndrome was diagnosed in these children at ages 4 to 7 years. Syncope, QT prolongation on electrocardiogram (corrected QT interval ≥ 490 milliseconds), notched T-wave morphology, bradycardia, and polymorphic ventricular arrhythmia were found in all of the patients. The KCNH2-L586M; KCNH2-G604S, KCNH2-L1045F; and a combined mutation KCNH2 T613M + SCN5A R190G were genotyped. Syncope, implantable cardioverter-defibrillator shocks, and tachycardia persisted in these patients, although they were receiving a full dose of β-blocker therapy. Adding a sodium-channel blocker (IC class) led to a reduction in the polymorphic ventricular arrhythmia. No syncope episodes were registered during the patients' 8 to 60 months of follow-up on the combined antiarrhythmic therapy. Further studies are needed to better define the possible role of sodium-channel blockers in patients with long QT type 2.

Aconitum in traditional Chinese medicine: a valuable drug or an unpredictable risk?

Aconitum species have been used in China as an essential drug in Traditional Chinese Medicine (TCM) for 2000 years. Reviewing the clinical application of Aconitum, their pharmacological effects, toxicity and detoxifying measures, herb-herb interactions, clinical taboos, famous herbal formulas, traditional and current herbal processing methods based upon a wide range of literature investigations serve as a case study to explore the multidisciplinary implications of botanicals used in TCM. The toxicological risk of improper usage of Aconitum remains very high, especially in countries like China, India and Japan. The toxicity of Aconitum mainly derives from the diester diterpene alkaloids (DDAs) including aconitine (AC), mesaconitine (MA) and hypaconitine (HA). They can be decomposed into less or non-toxic derivatives through Chinese traditional processing methods (Paozhi), which play an essential role in detoxification. Using Paozhi, the three main forms of processed aconite -- yanfuzi, heishunpian and baifupian -- can be obtained (CPCommission, 2005). Moreover, some new processing techniques have been developed in China such as pressure-steaming. The current development of fingerprint assays, in particular HPLC, has set a good basis to conduct an appropriate quality control for TCM crude herbs and their ready-made products. Therefore, a stipulation for a maximum level of DDA content of Aconitum is highly desirable in order to guarantee the clinical safety and its low toxicity in decoctions. Newly developed HPLC methods have made the accurate and simultaneous determination and quantification of DDA content interesting.

Interaction of the structurally related aconitum alkaloids, aconitine and 6-benzyolheteratisine, in the rat hippocampus

Aconitine is a highly toxic diterpenoid alkaloid occurring in plants of the Aconitum genus. Aconitine is known to shift the voltage-dependence of the voltage-dependent Na(+) channel towards hyperpolarized direction, thereby leading to a permanent activation of the channel. 6-benzoylheteratisine is a plant alkaloid which is structurally related with aconitine. The aim of the present study was to investigate the interaction of aconitine and 6-benzoylheteratisine in the rat hippocampus. The experiments were carried out as extracellular recordings of stimulus evoked population spikes and field excitatory postsynaptic potential (EPSP) in rat hippocampal slices. Aconitine (10-100 nM) exerted a concentration-dependent decrease in the amplitude of the orthodromic population spike. When aconitine was applied in presence of 6-benzoylheteratisine (3 microM), the concentration-response curve was shifted to the right. Furthermore, the complete suppression of the population spike evoked by 100 nM aconitine was reversed by 10 microM 6-benzoylheteratisine. The closely related alkaloid heteratisine (3 and 30 microM), however, was not capable to antagonize the aconitine action. 6-benzoylheteratisine shifted the input-output relationship of the presynaptic fiber spike as function of the stimulation intensity and the input-output relationship of the field EPSP as function of the presynaptic fiber spike to the right. Thus, electrophysiologically this alkaloid seems to inhibit predominantly the excitability of the afferent fibres and, in consequence, neurotransmission between Schaffer collaterals and the CA1 neurons, thereby suppressing the firing of the latter. Spontaneously occurring epileptiform activity in area CA3 elicited by omission of Mg(2+) and elevation of K(+) was attenuated by 6-benzoylheteratisine (1 and 10 microM). Patch clamp studies performed on cultured rat hippocampal pyramidal cells revealed an inhibitory action of 6-benzoylheteratisine on whole cell Na(+) currents. It is concluded that the inhibitory and antiepileptiform effect of ajacine and lappaconitine is mediated by an inhibition of the voltage-dependent Na(+) channel which might be important for filtering high frequency bursts of action potentials characteristic for epileptiform activity in the hippocampus. Thus, 6-benzoylheteratisine seems to be a naturally occurring antagonist of the Na(+) channel activator aconitine.

The alkaloid 6-benzoylheteratisine inhibits voltage-gated Na+ channels in rat brain synaptosomes

The effects of the Aconitum alkaloid 6-benzoylheteratisine on the aconitine-, veratridine-, oubain- and KCl-induced alterations in free synaptosomal Na + ([Na+]i) and Ca2+ ([Ca2+]i) and the release of endogenous glutamate from rat cerebrocortical synaptosomes were investigated. [Na+]i and [Ca2+]i were fluorometrically determined employing SBFI and Fura-2 as the Na+ and Ca2+ sensitive dyes, respectively. Glutamate was detected by a continuous enzyme-linked fluorometric assay. The study revealed a concentration-dependent inhibitory effect of 6-benzoylheteratisine on aconitine-induced increases in [Na+]i, [Ca2+]i and the release of glutamate. The IC50 values were 4.1 microM (Na+), 4.8 microM (Ca2+) and 4.8 microM (glutamate release). Application of 100 microM 6-benzoylheteratisine after stimulation with 5 microM veratridine also reduced the induced [Na+]i and [Ca2+]i with half-lives of 72.1 and 44.7 s, respectively. Furthermore, 100 microM 6-benzoylheteratisine reduced the ouabain-induced Na+ influx to the same extent as the Na+ channel inhibitor tetrodotoxin, which points to an inhibition of non-activated Na+ channels by 6-benzoylheteratisine. Additionally, 100 microM 6-benzoylheteratisine failed to affect the release of glutamate and the increase in [Ca2+]i induced by 30 mM KCl, indicating that voltage-gated Ca2+ channels were not affected by 6-benzoylheteratisine. The data suggest an inhibitory effect of 6-benzoylheteratisine on voltage-gated Na+ channels as the only target, whereas mechanisms of Na+ and Ca2+ homoeostasis and pathways of glutamate release seem not to be affected by the drug.