State-dependent action of grayanotoxin I on Na(+) channels in frog ventricular myocytes

The efficacy and toxicity of grayanoids as analgesics: A systematic review

ETHNOPHARMACOLOGICAL RELEVANCE

Grayanoids are natural diterpenoids that are mostly found in the Ericaceae family, such as Rhododendron molle (Blume) G. Don (Relevant herb: nao yang hua), Rhododendron micranthum Turcz (also known as: zhao shan bai), which have traditionally been used to treat abdominal pain, cephalgia, and rheumatoid arthritis.

AIMS OF THE REVIEW

The review investigated advancements in notable anti-nociception, toxicity, and probable mechanisms of grayanoids. Meanwhile some binding sites of these compounds on voltage-gated sodium channels (VSGCs) were also analyzed and evaluated.

MATERIALS AND METHODS

The substantial grayanoids literature published before 2022, in SCI Finder, PubMed, Science Direct, Springer, Scopus, Wiley Online Library, J-Stage, and other literature databases had been exhaustively consulted and thoroughly screened.

RESULTS

More than 50 compounds in grayanoids exhibited exceptionally significant anti-nociception (intraperitoneal injection, less than 1 mg/kg), and the alteration of several substituents that were closely associated to the change in activity were investigated. Multiple possible mechanisms of analgesic action and toxicity had been proposed, with VSGCs playing a key part in both. As a result, the binding locations of these compounds on VGSCs (mostly grayanotoxin I and III) had been summarized.

CONCLUSIONS

The considerable anti-nociception, toxicity, and probable mechanisms of grayanoids, as well as the investigation of the binding sites on VSGCs, were discussed in this review. Furthermore, the homology of toxicity and anti-nociception of these substances was considered, as well as the possibility of grayanoids being developed as analgesics.

Evaluation of Electrocardiographic Parameters and the Presence of Interatrial Block in Patients with Mad Honey Intoxication

Mad honey intoxication (MHI) is a food-induced clinical condition that usually presents with cardiovascular symptoms and can lead to life-threatening arrhythmias if not diagnosed and treated early. No data exist in the literature on the presence of interatrial block (IAB) after food intoxication. In our study, we sought to investigate atrioventricular electrocardiography (ECG) parameters and determine the frequency of IAB in patients with MHI. In total, 76 patients diagnosed with MHI were included in our retrospective study. Twelve-lead ECGs were performed and participants were divided into two groups according to the presence of IAB in the reference ECG. The P maximum (P_max), P minimum (P_min), P dispersion (P_disp), T peak to T end (Tp-Te) interval and QT dispersion (QT_disp) values were compared between the two groups. IAB was detected in 28 (35.5%) of 76 MHI patients included in the final analysis. P_max duration (122 ± 8; p < 0.001) and PD (69 ± 11; p < 0.001) were significantly higher in the IAB ( +) group. During regression analysis, P_max [odds ratio (OR) 1.158, 95% confidence interval (CI) 1.036-1.294; p = 0.010] and Pd (OR 1.086, 95% CI 1.001-1.017; p = 0.046) were independently associated with IAB. P_max and Pd area under the receiver operating characteristic curve values for IAB prediction were 0.926 (95% CI 0.841-1,000; p < 0.001) and 0.872 (95% CI 0.765-0.974; p < 0.001), respectively. ECG changes are common in patients presenting with MHI. These patients need to be followed up clinically in terms of progression to arrhythmic events that may occur in the future.

Hydrophobic Drug/Toxin Binding Sites in Voltage-Dependent K+ and Na+ Channels

In the Na_v channel family the lipophilic drugs/toxins binding sites and the presence of fenestrations in the channel pore wall are well defined and categorized. No such classification exists in the much larger K_v channel family, although certain lipophilic compounds seem to deviate from binding to well-known hydrophilic binding sites. By mapping different compound binding sites onto 3D structures of Kv channels, there appear to be three distinct lipid-exposed binding sites preserved in K_v channels: the front and back side of the pore domain, and S2-S3/S3-S4 clefts. One or a combination of these sites is most likely the orthologous equivalent of neurotoxin site 5 in Na_v channels. This review describes the different lipophilic binding sites and location of pore wall fenestrations within the K_v channel family and compares it to the knowledge of Na_v channels.

Determination of histological, immunohistochemical and biochemical effects of acute and chronic grayanotoxin III administration in different doses in rats

Grayanotoxin (GTX)-III is a Na-channel neurotoxin. Grayanotoxins can be found in the nectar, pollen, and other plant parts of the Rhododendron genus plants from the Ericaceae family. It is widely believed that honey produced from these plants, which are concentrated in the Black Sea region, is traditionally characterized as enhancing sexual performance. It is thought that the effective factor is dose for this compound, which has both beneficial and toxic effects reported. Therefore, it is aimed to evaluate the histological, immunohistochemical, and biochemical effects of acute and chronic impact of GTX-III in different doses on testes tissue in this study. For this purpose, 100 Sprague-Dawley male rats were divided into 5 separate groups for acute and chronic research. While dose groups were (control, 0.1, 0.2, 0.4, ve 0.8 μg/kg/bw) for experimental groups, a single dose (i.p.) was administered for acute impact whereas the same doses were administered daily for 3 weeks to assess chronic effect. At the end of the experiment, Johnsen testicular biopsy scoring was performed on testicular tissue samples, seminiferous tubule diameters were measured, and apoptotic cells were evaluated by TUNEL method. Testosterone, LH, and FSH levels were measured by ELISA method in serum and tissue specimens. It was found that Johnsen score of acute doses was significantly lower than the control group, and the diameter of the seminiferous tubules decreased significantly in acute and chronic dose-administered groups compared to the control. Hemorrhage, epithelial shedding, irregularity in seminiferous epithelium, and vacuolization were observed in acute and chronic dose-administered groups, and increase in apoptotic cells was determined. Hormone levels varied depending on the dose. In conclusion, it was found that dose-dependent acute and chronic effects of GTX-III are different, and this factor should be taken into account in studies to be carried out due to the adverse effects of high doses.

Mad honey: uses, intoxicating/poisoning effects, diagnosis, and treatment

Honey has been used as a folk medicine since 2100 BC; however, mad honey is different from normal natural or commercially available honey as it is contaminated with grayanotoxins, which leads to intoxication/poisoning upon consumption. Grayanotoxin is generally found in Rhododendron genus (family: Ericaceae) and is extracted by bees from nectar and pollens of flowers. Mad honey has been commonly used as an aphrodisiac (sexual stimulant), in alternative therapy for gastrointestinal disorders (peptic ulcer disease, dyspepsia, and gastritis), and for hypertension for a long time. Grayanotoxin acts on sodium ion channels and muscarinic receptors, leading to cardiac disorders (hypotension and different rhythm disorders including bradycardia, bradydysrhythmias, atrial fibrillation, nodal rhythm, atrioventricular block, and complete atrioventricular block) and respiratory depression. Patients may also exhibit any one symptom out of or combination of dizziness, blurred vision, diplopia, nausea, vomiting, vertigo, headache, sweating/excessive perspiration, extremity paresthesia, impaired consciousness, convulsion, hypersalivation, ataxia, inability to stand, and general weakness. Mad honey intoxication is diagnosed with honey intake history before the appearance of the signs and symptoms (clinical presentation), and the treatment is symptomatic. Prompt treatment includes intravenous infusions of atropine sulfate and fluids (saline infusions or simultaneous infusion of saline with atropine sulfate) if the patient presents bradycardia and severe hypotension. In case of a complete atrioventricular block, a temporary pacemaker is employed. Except for a single case from Lanping County (Southwest China), the prognosis for mad honey intoxication is very good, and no fatalities have been reported in modern medical literature excluding a few in the 1800s. Although fatalities are very rare, mad honey ingestion may still lead to arrhythmias, which can be life-threatening and hard to recognize. This article provides a brief introduction to honey, mad honey and its uses, the effects of mad honey intoxication/poisoning, and its diagnosis, prognosis, and treatment.

Honey has been used as a folk medicine since 2100 BC; however, mad honey is different from normal natural or commercially available honey as it is contaminated with grayanotoxins, which leads to intoxication/poisoning upon consumption.

Effect on oxidative stress, hepatic chemical metabolizing parameters, and genotoxic damage of mad honey intake in rats

A total of 66 male Wistar rats were used and six groups (control: 10 animals and experimental: 12 animals) were formed. While a separate control group was established for each study period, mad honey application to the animals in the experimental group was carried out with a single dose (12.5 g kg−1 body weight (b.w.); acute stage), at a dose of 7.5 g kg−1 b.w. for 21 days (subacute stage), and at a dose of 5 g kg−1 b.w. for 60 days (chronic stage). Tissue and blood oxidative stress markers (malondialdehyde (MDA), nitric oxide (NO), 4-hydroxynonenal (HNE), superoxide dismutase, catalase, glutathione (GSH) peroxidase, and glucose-6-phosphate dehydrogenase), hepatic chemical metabolizing parameters in the liver (cytochrome P450 2E1, nicotinamide adenine dinucleotide (NADH)-cytochrome b5 reductase, nicotinamide adenine dinucleotide phosphate (NADPH)-cytochrome c reductase (CYTC), GSH S-transferase (GST), and GSH), and micronucleus and comet test in some samples were examined. Findings from the study showed that single and repeated doses given over the period increased MDA, NO, and HNE levels while decreasing/increasing tissue and blood antioxidant enzyme activities. From hepatic chemical metabolizing parameters, GST activity increased in the subacute and chronic stages and CYTC activity increased in the acute period, whereas GSH level decreased in the subacute stage. Changes in tail and head intensities were found in most of the comet results. Mad honey caused oxidative stresses for each exposure period and made some significant changes on the comet test in certain periods for some samples obtained. In other words, according to the available research results obtained, careless consumption of mad honey for different medical purposes is not appropriate.

The pharmacology of voltage-gated sodium channel activators

Toxins and venom components that target voltage-gated sodium (Na_V) channels have evolved numerous times due to the importance of this class of ion channels in the normal physiological function of peripheral and central neurons as well as cardiac and skeletal muscle. Na_V channel activators in particular have been isolated from the venom of spiders, wasps, snakes, scorpions, cone snails and sea anemone and are also produced by plants, bacteria and algae. These compounds have provided key insight into the molecular structure, function and pathophysiological roles of Na_V channels and are important tools due to their at times exquisite subtype-selectivity. We review the pharmacology of Na_V channel activators with particular emphasis on mammalian isoforms and discuss putative applications for these compounds. This article is part of the Special Issue entitled 'Venom-derived Peptides as Pharmacological Tools.'

Analysis of grayanatoxin in Rhododendron honey and effect on antioxidant parameters in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Rhododendron honey, locally known as "mad honey", contains gryanotoksin (GTX) and thus induces toxic effects when consumed in large amounts. But, it is still popularly used for treating medical conditions such as high blood pressure or gastro-intestinal disorders. The aim of this study was to evaluate the effect of GTX on antioxidant parameters measured from rats fed with Rhododendron honey.

MATERIAL AND METHODS

A total of sixty Sprague-Dawley female rats were divided into five groups of 12 rats each, one being the control group (Group 1) and the others being the experimental groups (Groups 2 to 5). Group 2 was treated with 0.015 mg/kg/bw of Grayanotoxin-III (GTX-III) standard preparation via intraperitoneal injection. Groups 3, 4 and 5 were respectively given Rhododendron honey (RH) at doses of 0.1, 0.5, and 2.5 g/kg/bw via oral gavage. After one hour, blood samples were collected from the rats. Glutathione peroxidase (GSh-Px), superoxide dismutase (SOD), catalase (CAT) activities and malondialdehyde (MDA) contents were examined in blood, heart, lungs, liver, kidney, testicles, epididiymis, spleen and brain specimens.

RESULTS

The data from the rats in Groups 2 (GTX) and 5 (RH at 2.5 g/kg/bw) showed negative effect on the antioxidants parameters in blood and all tissue samples examined at the specified doses and time period. Administration of GTX to rats at dose of 0.015 mg/kg/bw resulted in lipid peroxidation. (This part needs to be enhanced more).

CONCLUSION

It has been observed that both Grayanotoxin and high dose Rhododendron honey treatments showed oxidant effect on blood plasma and organ tissues investigated.

Electroencephalographic and behavioral effects of intracerebroventricular or intraperitoneal injections of toxic honey extract in adult Wistar rats and GAERS

Toxic honey, containing grayanotoxin, is obtained from nectar and polen of rhododendron. Consumed in excess it produces seizures and convulsions. In order to investigate whether the toxic honey extract can be used as a seizure model, we examined the electroencephalographic (EEG) and motor effects of intracerebroventricular (icv) or intraperitoneal (ip) injection of toxic honey extract in Wistar rats or in genetic absence epilepsy rats from Strasbourg (GAERS). Male Wistar rats or GAERS were stereotaxically implanted with bilateral cortical recording electrodes in all ip groups and cannula in the icv groups. Based on the previous study, an extract was obtained from the non-toxic and toxic honey. After the injection of the non-toxic or toxic honey extract, seizure stages and changes in EEG were evaluated from 9 am to noon. The icv administration of toxic honey extract produced stage 4 seizures and bilateral cortical spikes within 30-60 min and these effects disappeared after 120 min in Wistar rats or GAERS. The mean of bilateral cortical spike acitivity in EEG of Wistar rats was 804.2 ± 261.0 s in the 3-h period. After the icv administration of toxic honey extract to GAERS, the mean duration of spike-and-wave discharges (SWDs) in GAERS significantly decreased during the first 60 min and then returned to baseline level. Ip injection of toxic honey extract caused no seizure and no change in EEG in either GAERS or Wistars. These results suggest that the icv administration of toxic honey extract can be used as a seizure model.

The genus Rhododendron: an ethnopharmacological and toxicological review

ETHNOPHARMACOLOGICAL RELEVANCE

The vast genus Rhododendron includes species that have been used in traditional medicine for the treatment of inflammatory conditions, pain, gastro-intestinal disorders, common cold, asthma, skin disease, etc. Rhododendrons are also well known for their toxicity and some species have been traditionally used as poison.

AIM OF THE REVIEW

The work reviews and analyses the traditional use, biological activities with the corresponding chemical constituents, and toxicological data on Rhododendron species. The review aims at characterizing the ethnopharmacology of the genus in relation to its toxicity in order to identify the therapeutic potential of Rhododendron species and future directions for research.

METHODS

Data regarding Rhododendron spp. was collected using electronic databases (SciFinder, PubMed, Google Scholar) and library search for selected peer-reviewed articles. Plant taxonomy was validated by the databases The Plant List, Tropicos, eFloras, Flora Iberica and Flora Europaea (RBGE). Additional information on traditional use and botany was obtained from published books. The review encompasses literature, mainly regarding biological activity and toxicological data, from 1898 to the end of December 2012.

RESULTS

Rhododendrons have been used in Asian, North American and European traditional medicine mainly against inflammation, pain, skin ailments, common cold and gastro-intestinal disorders. In vivo and in vitro testing of plant extracts and isolated compounds determined diverse biological activities including anti-inflammatory, analgesic, anti-microbial, anti-diabetic, insecticidal and cytotoxic activity. Rhododendron spp. can cause intoxications in humans following intake of rhododendron honey or medicinal preparations. The toxicity is due to grayanotoxins, diterpenes which activate voltage-gated sodium channels and lead to gastro-intestinal, cardiac and central nervous system symptoms.

CONCLUSION

Rhododendron species are useful traditional remedies for the treatment of inflammation, pain, skin ailments, common cold and gastro-intestinal disorders. Pharmacological data has validated most indications of rhododendrons in ethnomedicine and toxicology studies have confirmed the toxicity observed by traditional use. Ethnopharmacological data point to the therapeutic potential of the genus Rhododendron for the treatment of inflammatory conditions and pain and, thus, research should focus on identification of active compounds and related mechanistic studies. Prolonged and high dose intake of traditional formulations containing rhododendrons should be avoided until more in depth toxicity studies become available.

Food Poisoning

Food poisoning is encountered throughout the world. Many of the toxins responsible for specific food poisoning syndromes are no longer limited to isolated geographic locations. With increased travel and the ease of transporting food products, it is likely that a patient may present to any emergency department with the clinical effects of food poisoning. Recognizing specific food poisoning syndromes allows emergency health care providers not only to initiate appropriate treatment rapidly but also to notify health departments early and thereby prevent further poisoning cases. This article reviews several potential food-borne poisons and describes each agent's mechanism of toxicity, expected clinical presentation, and currently accepted treatment.

Sodium Channel Inactivation: Molecular Determinants and Modulation

Voltage-gated sodium channels open (activate) when the membrane is depolarized and close on repolarization (deactivate) but also on continuing depolarization by a process termed inactivation, which leaves the channel refractory, i.e., unable to open again for a period of time. In the “classical” fast inactivation, this time is of the millisecond range, but it can last much longer (up to seconds) in a different slow type of inactivation. These two types of inactivation have different mechanisms located in different parts of the channel molecule: the fast inactivation at the cytoplasmic pore opening which can be closed by a hinged lid, the slow inactivation in other parts involving conformational changes of the pore. Fast inactivation is highly vulnerable and affected by many chemical agents, toxins, and proteolytic enzymes but also by the presence of β-subunits of the channel molecule. Systematic studies of these modulating factors and of the effects of point mutations (experimental and in hereditary diseases) in the channel molecule have yielded a fairly consistent picture of the molecular background of fast inactivation, which for the slow inactivation is still lacking.

Neuronal sodium channels in ventricular heart cells are localized near T-tubules openings

Cardiac voltage-dependent sodium channels (VDSC) are known to be tetrodotoxin (TTX)-resistant. However, recent immunochemical studies suggest the presence of TTX-sensitive neuronal-type VDSC in the heart. Scanning ion conductance microscopy (SICM) coupled to electrophysiology was used to obtain more direct functional evidence. TTX sensitivities of whole-cell sodium currents (I(Na)) in control and detubulated cells were compared. Addition of 200 nM TTX decreased I(Na) of control cells by 20%, whereas detubulated cells were hardly effected. The remaining current peaked slightly earlier and inactivation decay was faster (as in neuronal VDSC) than in detubulated cells. Single-channel activity was first assayed at random on the plasmalemma, and after topography had been revealed by SICM, at patched T-tubules openings. In the latter case, a single-channel conductance of 11-12pS was observed with a higher rate of success. This study provides independent evidence for neuronal VDSC in cardiomyocytes where they could rapidly and synchronously couple T-tubule and cell surface depolarizations.

Distinct sites regulating grayanotoxin binding and unbinding to D4S6 of Na(v)1.4 sodium channel as revealed by improved estimation of toxin sensitivity

Grayanotoxin (GTX) exerts selective effects on voltage-dependent sodium channels by eliminating fast sodium inactivation and causing a hyperpolarizing shift in voltage dependence of channel activation. In this study, we adopted a newly developed protocol that provides independent estimates of the binding and unbinding rate constants of GTX (k(on) and k(off)) to GTX sites on the sodium channel protein, important in the molecular analysis of channel modification. Novel GTX sites were determined in D2S6 (Asn-784) and D3S6 (Ser-1276) by means of site-directed mutagenesis; the results suggested that the GTX receptor consists of the S6 transmembrane segments of four homologous domains facing the ion-conducting pore. We systematically introduced at two sites in D4S6 (Na(v)1.4-Phe-1579 and Na(v)1.4-Tyr-1586) amino acid substituents with residues containing hydrophobic, aromatic, charged, or polar groups. Generally, substitutions at Phe-1579 increased both k(on) and k(off), resulting in no prominent change in dissociation constant (K(d)). It seems that the smaller the molecular size of the residue at Na(v)1.4-Phe-1579, the larger the rates of k(on) and k(off), indicating that this site acts as a gate regulating access of toxin molecules to a receptor site. Substitutions at Tyr-1586 selectively increased k(off) but had virtually no effect on k(on), thus causing a drastic increase in K(d). At position Tyr-1586, a hydrophobic or aromatic amino acid side chain was required to maintain normal sensitivity to GTX. These results suggest that the residue at position Tyr-1586 has a more critical role in mediating GTX binding than the one at position Phe-1579. Here, we propose that the affinity of GTX to Na(v)1.4 sodium channels might be regulated by two residues (Phe and Tyr) at positions Phe-1579 and Tyr-1586, which, respectively, control access and binding of GTX to its receptor.

Structural determinants for the action of grayanotoxin in D1 S4-S5 and D4 S4-S5 intracellular linkers of sodium channel alpha-subunits

We located a novel binding site for grayanotoxin on the cytoplasmic linkers of voltage-dependent cardiac (rH1) or skeletal-muscle (mu 1) Na(+) channel isoforms (segments S4-S5 in domains D1 and D4), using the alanine scanning substitution method. GTX-modification of Na(+) channels, transiently expressed in HEK 293 cells, was evaluated under whole-cell voltage clamp, from the ratio of maximum chord conductance for modified and unmodified Na(+) channels. In mu 1, mutations K237A, L243A, S246A, K248A, K249A, L250A, S251A, or T1463A, caused a moderate, but statistically significant decrease in this ratio. On making corresponding mutations in rH1, only L244A dramatically reduced the ratio. Because in mu 1, the serine at position 251 is the only heterologous residue with respect to rH1 (Ala-252), we made a double mutant L243A&S251A to match the sequence of mu 1 and rH1 in S4-S5 linkers of both domains. This double mutation resulted in a significant decrease in the ratio, to the same extent as L244A substitution in rH1 did, indicating that the site at Leu-244 in rH1 or at Leu-243 in mu 1 is a novel one, exhibiting a synergistic effect of grayanotoxin.