Cardiovascular effect of peripheral injected melittin in normotensive conscious rats: Mediation of the central cholinergic system

Vagus nerve stimulation modulates hippocampal inflammation caused by continuous stress in rats

Background

Previous studies have shown that vagus nerve stimulation (VNS) can attenuate inflammatory responses in peripheral tissues and also improve some neurological disorders and cognitive function in the brain. However, it is not clear how VNS is involved in neuropathological processes in brain tissues. Here, we investigated the regulatory effects of VNS on the production of proinflammatory cytokines in the hippocampus of an animal model of continuous stress (CS).

Methods

CS was induced by placing rats in cages immersed with water, and acute or chronic electrical stimulation was applied to the cervical vagus nerve of CS animals. Protein levels in the gastric and hippocampal tissues were measured by western blotting and protein signals analyzed by immunofluorescence staining. von Frey test and forced swimming test were performed to assess pain sensitivity and depressive-like behavior in rats, respectively.

Results

Levels of TNF-α, IL-1β, and IL-6 in the gastric and hippocampal tissues were significantly increased in CS animals compared to the untreated control and downregulated by acute VNS (aVNS). Iba-1-labeled microglial cells in the hippocampus of CS animals revealed morphological features of activated inflammatory cells and then changed to a normal shape by VNS. VNS elevated hippocampal expression of α7 nicotinic acetylcholine receptors (α7 nAChR) in CS animals, and pharmacological blockade of α7 nAChR increased the production of TNF-α, IL-1β, and IL-6, thus suppressing cholinergic anti-inflammatory activity that was mediated by VNS. Chronic VNS (cVNS) down-regulated the hippocampal production of active form of caspase 3 and 5-HT1A receptors and also decreased levels of TNF-α, IL-1β, and IL-6 in the gastric and hippocampal tissues of CS animals. Pain sensitivity and depressive-like behavior, which were increased by CS, were improved by cVNS.

Conclusions

Our data suggest that VNS may be involved in modulating pathophysiological processes caused by CS in the brain.

The intermediary role of the central cyclooxygenase / lipoxygenase enzymes in intracerebroventricular injected nesfatin-1-evoked cardiovascular effects in rats

That nesfatin-1 is a neuromodulatory peptide for the cardiovascular system is well documented. Several central receptors have been shown to mediate the cardiovascular effects of nesfatin-1. Immunohistochemistry and Western blot studies showed that nesfatin-1 activated the expression of the central cyclooxygenase (COX) -1, -2 and lipoxygenase (LOX). In addition, microdialysis study showed that nesfatin-1 increased the release of total prostaglandins and leukotrienes from the hypothalamus. The present study investigated whether the central COX and LOX enzymes have a direct mediating role in the MAP and HR responses of nesfatin-1. Intracerebroventricularly administered nesfatin-1 produced dose-dependent pressor and phasic HR responses in normotensive conscious rats Sprague Dawley. Central pretreatment with a COX1/2 inhibitor, ibuprofen, completely blocked the nesfatin-1-induced responses. However, central pretreatment with a nonselective LOX inhibitor, nordihydroguaiaretic acid, partially attenuated the cardiovascular responses induced by nesfatin-1. The results suggest that centrally administered nesfatin-1 activates the central enzymes COX and LOX, which may be involved in the cardiovascular responses as a novel central mechanism for nesfatin-1.

The mediation of central cyclooxygenase and lipoxygenase pathways in orexin-induced cardiovascular effects

Previously it was reported that central orexin (OX) and arachidonic acid (AA) signaling pathways played an active role in the control of the cardiovascular system. It was also reported that they have exhibited their cardiovascular control role by using similar central or peripheral mechanisms. However, there has been no study demonstrating the interaction between OX and AA signaling pathways in terms of cardiovascular control. The current study was designed to investigate the possible mediation of the central cyclooxygenase (COX) and lipoxygenase (LOX) pathways in OX-induced cardiovascular effects in the rats. Intracerebroventricular injection of OX increased blood pressure and heart rate in a dose-dependent manner in normotensive male Sprague Dawley rats. Moreover, the microdialysis study revealed that intracerebroventricular injected OX caused a time-dependent increase in the extracellular total prostaglandin concentrations in the posterior hypothalamus. Interestingly, central pretreatment with a non-selective COX inhibitor, ibuprofen, or a non-selective LOX inhibitor, nordihydroguaiaretic acid, partially reversed pressor and tachycardic cardiovascular responses evoked by central administration of OX. In summary, our findings show that the central treatment with OX causes pressor and tachycardic cardiovascular responses along with an increase in posterior hypothalamic extracellular total prostaglandin concentrations. Furthermore, our results also demonstrate that central COX and LOX pathways mediate, at least in part, centrally administered OX-evoked pressor and tachycardic responses, as well.

Bee Venom: An Updating Review of Its Bioactive Molecules and Its Health Applications

Bee venom (BV) is usually associated with pain since, when humans are stung by bees, local inflammation and even an allergic reaction can be produced. BV has been traditionally used in ancient medicine and in acupuncture. It consists of a mixture of substances, principally of proteins and peptides, including enzymes as well as other types of molecules in a very low concentration. Melittin and phospholipase A2 (PLA2) are the most abundant and studied compounds of BV. Literature of the main biological activities exerted by BV shows that most studies focuses on the comprehension and test of anti-inflammatory effects and its mechanisms of action. Other properties such as antioxidant, antimicrobial, neuroprotective or antitumor effects have also been assessed, both in vitro and in vivo. Moreover, human trials are necessary to confirm those clinical applications. However, notwithstanding the therapeutic potential of BV, there are certain problems regarding its safety and the possible appearance of adverse effects. On this perspective, new approaches have been developed to avoid these complications. This manuscript is aimed at reviewing the actual knowledge on BV components and its associated biological activities as well as the latest advances on this subject.

Intracerebroventricularly injected nesfatin-1 activates central cyclooxygenase and lipoxygenase pathways

Nesfatin-1 is a multifunctional neuropeptide having crucial autonomic roles. It is well known that nesfatin-1 collaborates with other central neuromodulatory systems, such as central corticotropin-releasing hormone, melanocortin, oxytocin, and cholinergic systems to show its autonomic effects. Central arachidonic acid cascade plays an important role to provide the homeostasis by exhibiting similar autonomic effects to nesfatin-1. Based on these similarities, the current study was designed to show the effects of intracerebroventricularly (ICV) injected nesfatin-1 on the hypothalamic arachidonic acid (AA) cascade. Immunochemistry and western blot approaches demonstrated that ICV administration of nesfatin-1 provokes an increase in the hypothalamic cyclooxygenase (COX) -1, -2 and lipoxygenase (LOX) protein expression. Moreover, the microdialysis study demonstrated that centrally injected nesfatin-1 increased the posterior hypothalamic extracellular AA products. In conclusion, these findings report that while nesfatin-1 is generating its autonomic effects, it also might be using central prostaglandins and leukotrienes by activating central COX and LOX pathways.

Melittin-A Natural Peptide from Bee Venom Which Induces Apoptosis in Human Leukaemia Cells

Bee venom is a very complex mixture produced and secreted by the honeybee (Apis mellifera). Melittin is a major component of bee venom that accounts for about 52% of its dry mass. A vast number of studies have been dedicated to the effects of melittin’s regulation of apoptosis and to the factors that induce apoptosis in various types of cancer such as breast, ovarian, prostate, lung. The latest evidence indicates its potential as a therapeutic agent in the treatment of leukaemia. The aim of our present study is to evaluate melittin’s ability to induce apoptosis in leukaemia cell lines of different origin acute lymphoblastic leukaemia (CCRF-CEM) and chronic myelogenous leukaemia (K-562). We demonstrated that melittin strongly reduced cell viability in both leukaemia cell lines but not in physiological peripheral blood mononuclear cells (PMBCs). Subsequent estimated parameters (mitochondrial membrane potential, Annexin V binding and Caspases 3/7 activity) clearly demonstrated that melittin induced apoptosis in leukaemia cells. This is a very important step for research into the development of new potential anti-leukaemia as well as anticancer therapies. Further analyses on the molecular level have been also planned (analysis of proapoptotic genes expression and DNA damages) for our next research project, which will also focus on melittin.

The Influence of Bee Venom Melittin on the Functioning of the Immune System and the Contractile Activity of the Insect Heart-A Preliminary Study

Melittin (MEL) is a basic polypeptide originally purified from honeybee venom. MEL exhibits a broad spectrum of biological activity. However, almost all studies on MEL activity have been carried out on vertebrate models or cell lines. Recently, due to cheap breeding and the possibility of extrapolating the results of the research to vertebrates, insects have been used for various bioassays and comparative physiological studies. For these reasons, it is valuable to examine the influence of melittin on insect physiology. Here, for the first time, we report the immunotropic and cardiotropic effects of melittin on the beetle Tenebrio molitor as a model insect. After melittin injection at 10⁻⁷ M and 10⁻³ M, the number of apoptotic cells in the haemolymph increased in a dose-dependent manner. The pro-apoptotic action of MEL was likely compensated by increasing the total number of haemocytes. However, the injection of MEL did not cause any changes in the percent of phagocytic haemocytes or in the phenoloxidase activity. In an in vitro bioassay with a semi-isolated Tenebrio heart, MEL induced a slight chronotropic-positive effect only at a higher concentration (10⁻⁴ M). Preliminary results indicated that melittin exerts pleiotropic effects on the functioning of the immune system and the endogenous contractile activity of the heart. Some of the induced responses in T. molitor resemble the reactions observed in vertebrate models. Therefore, the T. molitor beetle may be a convenient invertebrate model organism for comparative physiological studies and for the identification of new properties and mechanisms of action of melittin and related compounds.

Involvement of the anti-inflammatory, anti-apoptotic, and anti-secretory activity of bee venom in its therapeutic effects on acetylsalicylic acid-induced gastric ulceration in rats

Acetylsalicylic acid (ASA) is the most highly consumed pharmaceutical product worldwide. Importantly, gastrointestinal ulceration due to ASA is a major complication. Hence, the present work aimed to examine, for the first time, the healing properties of bee venom (BV) in acute gastric ulceration induced by ASA. Forty adult male Sprague-Dawley rats were divided into four groups that received distilled water only, ASA (500 mg/kg BW) twice daily for 3 days, ASA for 3 days followed by BV (2 mg/kg BW) for 7 days, or ASA for 3 days followed by ranitidine hydrochloride (50 mg/kg BW) for 7 days. Haematological analysis, haemostatic evaluation, and inflammatory marker estimation were performed. Rat stomachs were collected for ulcer scoring, gene expression analysis, oxidative stress assays, histopathological and immunohistochemical examinations, and tissue eosinophil scoring. The results revealed that BV markedly decreased the ulcer index, pro-inflammatory cytokine levels, malondialdehyde levels, BAX distribution, caspase-3 expression, and tissue eosinophil levels. Additionally, significant increases in antioxidant enzymes and heat shock protein 70 localization in gastric tissue were evident following BV treatment after ASA exposure. Also, BV has been found to attenuate the haematological, haemostatic, and histopathological alterations induced by ASA. Our findings collectively indicate that the gastroprotective effect of BV against ASA-induced ulceration in rats is mediated by its antioxidant, anti-inflammatory, anti-apoptotic, and anti-secretory properties.

Production of antibacterial peptide from bee venom via a new strategy for heterologous expression

Honey bee is important economic insect that not only pollinates fruits and crops but also provides products with various physiological activities. Bee venom is a functional agent that is widely applied in clinical treatment and pharmacy. Secapin is one of these agents that have a significant role in therapy. The functions of secapin from the bee venom have been documented, but little information is known about its heterologous expression under natural condition. Moreover, few scholars verified experimentally the functions of secapin from bee venom in vitro. In this study, we successfully constructed a heterologous expression vector, which is different from conventional expression system. A transgenic approach was established for transformation of secapin gene from the venom of Apis mellifera carnica (Ac-sec) into the edible fungi, Coprinus cinereus. Ac-sec was encoded by a 234 bp nucleotide that contained a signal peptide domain and two potential phosphorylation sites. The sequence exhibited highly homology with various secapins characterized from honey bee and related species. Southern blot data indicated that Ac-sec was present as single or multiple copy loci in the C. cinereus genome. By co-transformation and double-layer active assay, Ac-sec was expressed successfully in C. cinereus and the antibacterial activity of the recombinants was identified, showing notable antibacterial activities on different bacteria. Although Ac-sec is from the venom of Apidae, phylogenetic analysis demonstrated that Ac-sec was more closely related to that of Vespid than to bee species from Apidae. The molecular characteristics of Ac-sec and the potential roles of small peptides in biology were discussed.

Centrally administered CDP-choline induced cardiovascular responses are mediated by activation of the central phospholipase-prostaglandin signaling cascade

The present study was designed to determine the involvement of central prostaglandin synthesis on the pressor and bradycardic effect of cytidine 5'-diphosphocholine (CDP-choline). Intracerebroventricular (i.c.v.) administration of CDP-choline was made and blood pressure and heart rate were recorded in male Sprague Dawley rats throughout this study. Microdialysis and immunohistochemical studies were performed to measure extracellular total prostaglandin concentration and to show cyclooxygenase-1 and -2 (COX-1 and -2) immunoreactivities, respectively, in the posterior hypothalamic area. Moreover, rats were pretreated (i.c.v) with mepacrine [a phospholipase A2 (PLA2) inhibitor], ibuprofen [a nonselective COX inhibitor], neomycine [a phospholipase C (PLC) inhibitor] or furegrelate [a thromboxane A2 (TXA2) synthesis inhibitor] 5 min prior to the injection of CDP-choline to determine the effects of these inhibitors on cardiovascular responses to CDP-choline. Control rats were pretreated (i.c.v) with saline. CDP-choline caused a dose- and time-dependent increase in blood pressure and decrease in heart rate. Immunohistochemical studies showed that CDP-choline increased COX-1 and -2 immunoreactivities in the posterior hypothalamic area. CDP-choline also elevated hypothalamic extracellular total prostaglandin concentration by 62%, as shown in microdialysis studies. Mepacrine or ibuprofen pretreatments almost completely blocked the pressor and bradycardic responses to CDP-choline while neomycine or furegrelate partially attenuated the drug-induced cardiovascular effects. The results suggest that CDP-choline may stimulate prostaglandin synthesis through the activation of PLA2, cyclooxygenases (COX-1 and -2) and prostaglandins and at least TXA2, may mediate the drug׳s cardiovascular effects.

The effect of centrally injected CDP-choline on respiratory system; involvement of phospholipase to thromboxane signaling pathway

CDP-choline is an endogenous metabolite in phosphatidylcholine biosynthesis. Exogenous administration of CDP-choline has been shown to affect brain metabolism and to exhibit cardiovascular, neuroendocrine neuroprotective actions. On the other hand, little is known regarding its respiratory actions and/or central mechanism of its respiratory effect. Therefore the current study was designed to investigate the possible effects of centrally injected CDP-choline on respiratory system and the mediation of the central cholinergic receptors and phospholipase to thromboxane signaling pathway on CDP-choline-induced respiratory effects in anaesthetized rats. Intracerebroventricularly (i.c.v.) administration of CDP-choline induced dose- and time-dependent increased respiratory rates, tidal volume and minute ventilation of male anaesthetized Spraque Dawley rats. İ.c.v. pretreatment with atropine failed to alter the hyperventilation responses to CDP-choline whereas mecamylamine, cholinergic nicotinic receptor antagonist, mepacrine, phospholipase A2 inhibitor, and neomycin phospholipase C inhibitor, blocked completely the hyperventilation induced by CDP-choline. In addition, central pretreatment with furegrelate, thromboxane A2 synthesis inhibitor, also partially blocked CDP-choline-evoked hyperventilation effects. These data show that centrally administered CDP-choline induces hyperventilation which is mediated by activation of central nicotinic receptors and phospholipase to thromboxane signaling pathway.

Effect of melittin on mice stomach

Melittin, the main bee venom component, has many positive biological effects and a relatively low toxicity in various cell types. However, there is no evidence of the effect of melittin on gastrointestinal cells. In the present study, we investigated the histological and immuonohistochemical effects of melittin on mice stomach. Adult male mice (Albino Swiss) were randomly divided into two groups (7 mice for each group): control group and melittin only treated group (10 and 40 μg/kg). These mice were sacrificed, then samples from the stomach were collected and prepared for histopathological studies by using alcian blue stain and immuonohistochemical studies by using smooth muscle actin (SMA) antibody. Treatment with melittin alone do not cause any harmful effect on the stomach tissue where the microscopic examination of Alcian blue stained section showed the normal distribution of the mucous secreting cells of the stomach tissues. On other hand, no changes were observed on smooth muscle cells. This study demonstrated the safety of using melittin on gastrointestinal tissues if used in definite dose and for suitable duration, which offers an opportunity for its use as a treatment for many diseases of the gastrointestinal tract.

Bee venom and its component apamin as neuroprotective agents in a Parkinson disease mouse model

Bee venom has recently been suggested to possess beneficial effects in the treatment of Parkinson disease (PD). For instance, it has been observed that bilateral acupoint stimulation of lower hind limbs with bee venom was protective in the acute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD. In particular, a specific component of bee venom, apamin, has previously been shown to have protective effects on dopaminergic neurons in vitro. However, no information regarding a potential protective action of apamin in animal models of PD is available to date. The specific goals of the present study were to (i) establish that the protective effect of bee venom for dopaminergic neurons is not restricted to acupoint stimulation, but can also be observed using a more conventional mode of administration and to (ii) demonstrate that apamin can mimic the protective effects of a bee venom treatment on dopaminergic neurons. Using the chronic mouse model of MPTP/probenecid, we show that bee venom provides sustained protection in an animal model that mimics the chronic degenerative process of PD. Apamin, however, reproduced these protective effects only partially, suggesting that other components of bee venom enhance the protective action of the peptide.

The mediation of the central histaminergic system in the pressor effect of intracerebroventricularly injected melittin, a phospholipase A2 activator, in normotensive rats

Melittin is a polypeptide component of bee venom that leads to an increase in arachidonic acid release and subsequently in prostaglandin synthesis by activating phospholipase A(2). Recently we demonstrated that centrally or peripherally administrated melittin caused pressor effect and central thromboxane A(2) (TXA(2)) and cholinergic system mediated these effects of melittin. Also centrally injected histamine leads to pressor and bradycardic response by activating central histamine receptors in normotensive rats and central cholinergic system involved the effects of histamine. The present study demonstrates an involvement of the central histaminergic system in melittin-induced cardiovascular effect in normotensive rats. Experiments were carried out in male Sprague Dawley rats. Intracerebroventricularly (i.c.v.) injected melittin (0.5, 1 and 2 nmol) caused dose- and time-dependent increases in mean arterial pressure (MAP) and decrease in heart rate (HR) as we reported previously. Moreover, H(2) receptor antagonist ranitidine (50 nmol; i.c.v.) almost completely and H(3)/H(4) receptor antagonist thioperamide (50 nmol; i.c.v.) partly blocked melittin-evoked cardiovascular effects, whereas H(1) receptor blocker chlorpheniramine (50 nmol; i.c.v.) had no effect. Also centrally injected melittin was accompanied by 28% increase in extracellular histamine concentration in the posterior hypothalamus, as shown in microdialysis studies. In conclusion, results show that centrally administered melittin causes pressor and bradycardic response in conscious rats. Moreover, according to our findings, there is an involvement of the central histaminergic system in melittin-induced cardiovascular effects.

The role of the central arachidonic acid-thromboxane A2 cascade in cardiovascular regulation during hemorrhagic shock in rats

The aim of the current study was to elucidate the underlying central mechanism(s) of the cardiovascular effects evoked by centrally injected melittin and arachidonic acid (AA) in hemorrhaged hypotensive condition, specifically, from central AA release from the cell membrane under the influence of phospholipase A(2) (PLA(2)) to central thromboxane A(2) (TXA(2)) signaling via the cyclooxygenase (COX) pathway. As the main control of the study, melittin (3 μg) or AA (150 μg) was injected intracerebroventricularly (i.c.v.) after the hemorrhage procedure, which was performed by withdrawing a total volume of 2.2 ml of blood/100g body weight over a period of 10 min. Both treatments generated a pressor response and abolished the hypotension-induced hemorrhage. Pretreatment with the PLA(2) inhibitor mepacrine (500 μg; i.c.v.) completely blocked the pressor response to melittin in the hemorrhagic hypotensive state. Pretreatments with the nonselective COX inhibitor indomethacin (200 μg; i.c.v.) or the TXA(2) synthesis inhibitor furegrelate (250 or 500 μg; i.c.v.) were made to test the role of central COX activity and, subsequently, the TXA(2) signaling pathway in the melittin- or AA-mediated reversal of hemorrhagic hypotension. Indomethacin completely prevented the pressor response to melittin and AA in the hemorrhaged, hypotensive state, but furegrelate did so only partially. In conclusion, these findings suggest that central COX activity and, subsequently, the central TXA(2) signaling pathway, are, at least in part, involved in the melittin- or AA-induced reversal effect during hemorrhagic shock.

Central mechanism underlying pressor and bradycardic effect of intracerebroventricularly injected arachidonic acid

The aim of the current study was to determine the central cyclooxygenase (COX) pathway and central thromboxane signaling in the cardiovascular effects evoked by arachidonic acid (AA). As a main control for the study, different doses of AA (75, 150, or 300 µg) were administered intracerebroventricularly (i.c.v.). Centrally injected AA dose- and time-dependently increased mean arterial pressure and decreased heart rate in conscious normotensive Sprague–Dawley rats. The maximal cardiovascular effects of AA were observed at min 10 of the injection and lasted almost 30 min. To investigate the central mechanism of the AA-induced cardiovascular effect in conscious normotensive animals, pretreatment with nonselective COX inhibitor indomethacin (200 µg; i.c.v.), thromboxane A2 (TXA2) synthesis inhibitor furegrelate (250 or 500 µg; i.c.v.), or TXA2 receptor antagonist SQ-29548 (8 or 16 µg; i.c.v.) was carried out 15 min before AA (150 µg; i.c.v.) injection. While indomethacin completely prevented the pressor and bradycardic responses to AA, furegrelate and SQ-29548 attenuated these effects in part in awake normotensive rats. In conclusion, these findings suggest that the pressor and bradycardic cardiovascular effects of centrally injected AA are dependent on COX activity being totally central and the TXA2 signaling pathway being subsequently central, at least in part.