Intra-arterial injection of Mesobuthus tamulus venom elicits cardiorespiratory reflexes involving perivascular afferents

Biochemical and Proteomic Characterization, and Pharmacological Insights of Indian Red Scorpion Venom Toxins

The Indian red scorpion (Mesobuthus tamulus) is one of the world's deadliest scorpions, with stings representing a life-threatening medical emergency. This species is distributed throughout the Indian sub-continent, including eastern Pakistan, eastern Nepal, and Sri Lanka. In India, Indian red scorpions are broadly distributed in western Maharashtra, Saurashtra, Kerala, Andhra Pradesh, Tamil Nadu, and Karnataka; however, fatal envenomations have been recorded primarily in the Konkan region of Maharashtra. The Indian red scorpion venom proteome comprises 110 proteins belonging to 13 venom protein families. The significant pharmacological activity is predominantly caused by the low molecular mass non-enzymatic Na+ and K+ ion channel toxins. Other minor toxins comprise 15.6% of the total venom proteome. Indian red scorpion stings induce the release of catecholamine, which leads to pathophysiological abnormalities in the victim. A strong correlation has been observed between venom proteome composition and local (swelling, redness, heat, and regional lymph node involvement) and systemic (tachycardia, mydriasis, hyperglycemia, hypertension, toxic myocarditis, cardiac failure, and pulmonary edema) manifestations. Immediate administration of antivenom is the preferred treatment for Indian red scorpion stings. However, scorpion-specific antivenoms have exhibited poor immunorecognition and neutralization of the low molecular mass toxins. The proteomic analysis also suggests that Indian red scorpion venom is a rich source of pharmacologically active molecules that may be envisaged as drug prototypes. The following review summarizes the progress made towards understanding the venom proteome of the Indian red scorpion and addresses the current understanding of the pathophysiology associated with its sting.

Ipsilateral somatic nerves mediate histamine-induced vasosensory reflex responses involving perivascular afferents in rat models

Reflex cardiorespiratory alterations elicited after instillation of nociceptive agents intra-arterially (i.a) are termed as ‘vasosensory reflex responses’. The present study was designed to evaluate such responses produced after i.a. instillation of histamine (1 mM; 10 mM; 100 mM) and to delineate the pathways i.e. the afferents and efferents mediating these responses. Blood pressure, electrocardiogram and respiratory excursions were recorded before and after injecting saline/histamine, in a local segment of femoral artery in urethane anesthetized rats. Paw edema and latencies of responses were also estimated. Separate groups of experiments were conducted to demonstrate the involvement of somatic nerves in mediating histamine-induced responses after ipsilateral femoral and sciatic nerve sectioning (+NX) and lignocaine pre-treatment (+Ligno). In addition, another set of experiments was performed after bilateral vagotomy (+VagX) and the responses after histamine instillation were studied. Histamine produced concentration-dependent hypotensive, bradycardiac, tachypnoeic and hyperventilatory responses of shorter latencies (2–7 s) favouring the neural mechanisms in eliciting the responses. Instillation of saline (time matched control) in a similar fashion produced no response, excluding the possibilities of ischemic/stretch effects. Paw edema was absent in both hind limbs indicating that the histamine did not reach the paws and did not spill out into the systemic circulation. +NX, +VagX, +Ligno attenuated histamine-induced cardiorespiratory responses significantly. These observations conclude that instillation of 10 mM of histamine produces optimal vasosensory reflex responses originating from the local vascular bed; afferents and efferents of which are mostly located in ipsilateral somatic and vagus nerves respectively.

Intra-arterial Instillation of a Nociceptive Agent Modulates Cardiorespiratory Parameters Involving 5-HT3 and TRPV1 Receptors in Anesthetized Rats

BACKGROUND

Since long back, it has been a matter of discussion regarding the role of peripheral blood vessels in the regulation of cardiorespiratory (CVR) system.

OBJECTIVE

The role of 5-HT3 and TRPV1 receptors present on perivascular nerves in elicitation of CVR reflexes was examined after intra-arterial instillation of bradykinin in urethane anesthetized rats.

MATERIALS AND METHODS

Femoral artery was cannulated retrogradely and was utilized for the instillation of saline/agonist/antagonist and recording of blood pressure (BP), using a double ported 24G cannula. BP, respiration and ECG were recorded for 30 min after bradykinin (1 μM) in the absence or presence of antagonists.

RESULTS

Instillation of bradykinin produced immediate hypotensive (40%), bradycardiac (17%), tachypnoeic (45%) and hyperventilatory (96%) responses of shorter latencies (5-8 s) favoring the neural mechanisms in producing the responses. In lignocaine (2%) pretreated animals, bradykinin- induced hypotensive (10%), bradycardiac (1.7%), tachypnoeic (13%) and hyperventilatory (13%) responses attenuated significantly. Pretreatment with ondansetron (100 μg/kg), 5-HT3-antagonist attenuated the hypotensive (10%), bradycardiac (1.7%), tachypnoeic (11%) and hyperventilatory (11%) responses significantly. Pretreatment with capsazepine (1 mg/kg), transient receptor potential vanilloid 1- antagonist blocked the hypotensive (5%), bradycardiac (1.2%), tachypnoeic (6%) and hyperventilatory (6%) responses significantly.

CONCLUSION

In conclusion, presence of a nociceptive agent in the local segment of an artery evokes vasosensory reflex responses modulating CVR parameters involving TRPV1 and 5-HT3 receptors present on the perivascular sensory nerve terminals in anesthetized rats.

Instillation of bradykinin into femoral artery elicits cardiorespiratory reflexes involving perivascular afferents in anesthetized rats

The physiology of baroreceptors and chemoreceptors present in large blood vessels of the heart is well known in the regulation of cardiorespiratory functions. Since large blood vessels and peripheral blood vessels are of the same mesodermal origin, therefore, involvement of the latter in the regulation of cardiorespiratory system is expected. The role of perivascular nerves in mediating cardiorespiratory alterations produced after intra-arterial injection of a nociceptive agent (bradykinin) was examined in urethane-anesthetized male rats. Respiratory frequency, blood pressure, and heart rate were recorded for 30 min after the retrograde injection of bradykinin/saline into the femoral artery. In addition, paw edema was determined and water content was expressed as percentage of wet weight. Injection of bradykinin produced immediate tachypneic, hypotensive and bradycardiac responses of shorter latency (5-8 s) favoring the neural mechanisms involved in it. Injection of equi-volume of saline did not produce any responses and served as time-matched control. Paw edema was observed in the ipsilateral hind limb. Pretreatment with diclofenac sodium significantly attenuated the bradykinin-induced responses and also blocked the paw edema. Ipsilateral femoral and sciatic nerve sectioning attenuated bradykinin-induced responses significantly, indicating the origin of responses from the local vascular bed. Administration of bradykinin in the segment of an artery produced reflex cardiorespiratory changes by stimulating the perivascular nociceptors involving prostaglandins. This is a novel study exhibiting the role of peripheral blood vessels in the regulation of the cardiorespiratory system.

Correlation of Venom Toxinome Composition of Indian Red Scorpion (Mesobuthus tamulus) with Clinical Manifestations of Scorpion Stings: Failure of Commercial Antivenom to Immune-Recognize the Abundance of Low Molecular Mass Toxins of This Venom

The Indian red scorpion (Mesobuthus tamulus), with its life-threatening sting, is the world's most dangerous species of scorpion. The toxinome composition of M. tamulus venom was determined by tandem mass spectrometry (MS) analysis of venom protein bands separated by SDS-PAGE. A total of 110 venom toxins were identified from searching the MS data against the Buthidae family (taxid: 6855) of toxin entries in nonredundant protein databases. The Na⁺ and K⁺ ion channel toxins taken together are the most abundant toxins (76.7%) giving rise to the neurotoxic nature of this venom. The other minor toxin classes in the M. tamulus venom proteome are serine protease-like protein (2.9%), serine protease inhibitor (2.2%), antimicrobial peptide (2.3%), hyaluronidase (2.2%), makatoxin (2.1%), lipolysis potentiating peptides (1.2%), neurotoxin affecting Cl^- channel (1%), parabutoporin (0.6%), Ca²⁺ channel toxins (0.8%), bradykinin potentiating peptides (0.2%), HMG CoA reductase inhibitor (0.1%), and other toxins with unknown pharmacological activity (7.7%). Several of these toxins have been shown to be promising drug candidates. M. tamulus venom does not show enzymatic activity (phospholipase A₂, l-amino acid oxidase, adenosine tri-, di-, and monophosphatase, hyaluronidase, metalloproteinase, and fibrinogenolytic), in vitro hemolytic activity, interference with blood coagulation, or platelet modulation properties. The clinical manifestations post M. tamulus sting have been described in the literature and are well correlated with its venom proteome composition. An abundance of low molecular mass toxins (3-15 kDa) are responsible for exerting the major pharmacological effects of M. tamulus venom, though they are poorly immune-recognized by commercial scorpion antivenom. This is a major concern for the development of effective antivenom therapy against scorpion stings.

Retrograde cannulation of femoral artery: A novel experimental design for precise elicitation of vasosensory reflexes in anesthetized rats

Vasosensory reflex responses are elicited by instillation of nociceptive agents in a segment of peripheral blood vessel. A novel method for the stimulation of perivascular afferents was designed by retrograde cannulation of femoral artery, using a 24G, double ported polyethylene cannula. The vertical port of which was used to inject the algogen into the artery and horizontal port to measure the BP continuously, as this port was connected to the pressure transducer. Previously, separate carotid artery cannulation was used for the BP recording. But our experimental design excluded the need for carotid artery cannulation that might compromise the circulation to the CNS centers mediating cardiorespiratory reflex responses. After cannulation, the proximal end of femoral artery became an end artery and the drugs were instilled retrogradely. The volume of chemicals was kept minimal (100 µl) and the ipsilateral femoral vein was also ligated. These measures made sure that the instilled drug remained in a local segment of femoral artery and did not spill out to the systemic circulation. Further, there was no increase in the water content of ipsilateral paw as compared to the contralateral paw. This finding also substantiates our proposition regarding minimal systemic spillage.•

The femoral artery is cannulated by a double ported cannula.

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This cannula helps instillation of algogen and BP measurement simultaneously.

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Retrograde instillation helps to deposit the algogen in a local segment of femoral artery.

B1-kinin receptors modulate Mesobuthus tamulus venom-induced vasosensory reflex responses in anesthetized rats

OBJECTIVE

Intra-arterial injection of Mesobuthus tamulus (BT) venom produces reflex vasosensory responses modulating cardiorespiratory parameters in albino rats. The present study was conducted to understand the role of kinin receptors in modulating vasosensory reflexes evoked by BT venom.

MATERIALS AND METHODS

In urethane-anesthetized rats, tracheostomy was performed to keep the airway patent. The femoral artery was cannulated proximally, as well as distally, to record the blood pressure (BP) and to inject the chemicals, respectively. Electrocardiographic and respiratory excursions were recorded to compute the heart rate (HR) and respiratory rate (RR). A group of animals was pretreated with saline/kinin receptor antagonists intra-arterially (B1/B2 receptor antagonists) before the injection of venom.

RESULTS

After intra-arterial injection of BT venom (1 mg/kg), there was an immediate increase in RR, which reached to 40% within 30 s, followed by a decrease of 40%. Further, there was sustained increase in RR (50%) up to 60 min. The BP started to increase at 40 s, peaking at 5 min (50%), and remained above the initial level up to 60 min. The bradycardiac response started after 5 min which peaked (50% of initial) at 25 min and remained at that level up to 60 min. In B1 receptor antagonist (des-Arg) pretreated animals, venom-induced cardiovascular responses were attenuated (by 20-25% in mean arterial pressure and HR) significantly but not in B2 receptor antagonist (Hoe-140) pretreated animals. Either of the antagonists failed to alter the RR responses.

CONCLUSIONS

BT venom-induced vasosensory reflex responses modulating cardiovascular parameters are mediated via B1-kinin receptors in anesthetized rats.

Different types of toxins targeting TRPV1 in pain

The transient receptor potential vanilloid 1(TRPV1) channels are members of the transient receptor potential (TRP) superfamily. Members of this family are expressed in primary sensory neurons and are best known for their role in nociception and sensory transmission. Multiple painful stimuli can activate these channels. In this review, we discussed the mechanisms of different types of venoms that target TRPV1, such as scorpion venom, botulinum neurotoxin, spider toxin, ciguatera fish poisoning (CFP) and neurotoxic shellfish poisoning (NSP). Some of these toxins activate TRPV1; however, some do not. Regardless of TRPV1 inhibition or activation, they occur through different pathways. For example, BoNT/A decreases TRPV1 expression levels by blocking TRPV1 trafficking to the plasma membrane, although the exact mechanism is still under debate. Vanillotoxins from tarantula (Psalmopoeus cambridgei) are proposed to activate TRPV1 via interaction with a region of TRPV1 that is homologous to voltage-dependent ion channels. Here, we offer a description of the present state of knowledge for this complex subject.

In vitro and in vivo evaluation of buccal bioadhesive films containing salbutamol sulphate

The aim of present study was to prepare and evaluate buccal bioadhesive films of salbutamol sulphate (SS) for the treatment of asthma. The films were designed to release the drug for a prolonged period of time so as to reduce the frequency of administration of the available conventional dosage forms of SS. The different proportions of sodium carboxymethylcellulose (SCMC) and Carbopol 940P (CP 940P) were used for the preparation of films. Carbopol was used to incorporate the desired bioadhesiveness in the films. The films were prepared by solvent casting method and evaluated for bioadhesion, in vitro drug release and anti asthmatic effect (bronchoprotection) in histamine induced bronchospasm of guinea pigs. In vitro drug release from the film was determined using a modified Franz diffusion cell while bioadhesiveness was evaluated with a modified two-arm balance using guinea pig buccal mucosa as a model tissue. Films containing SCMC : CP 940P ratio of 76 : 24 was found to be the best with moderate swelling along with favorable bioadhesion force and in vitro drug release. The drug release mechanism was found to follow non-Fickian diffusion as release mechanism. The prolonged in vivo effect (bronchoprotection) obtained from the buccal bioadhesive film of SS administered via buccal route may improve the treatment of asthmatic disorders by reducing the frequency of administration which is associated with the tolerance effect of SS. Additionally for the clinical benefit, it is also expected to reduce the major adverse effects of SS such as tachycardia and arrhythmias via buccal absorption.

Buthus tamulus venom-induced vasosensory reflexes are mediated through efferent pathways in sympathetic and vagal parasympathetics

Present study was conducted to identify the efferents mediating the vasosensory reflexes evoked by intra-arterial (i.a.) injection of Mesobuthus tamulus (BT; 1mg/kg) venom in the distal segment of femoral artery. Blood pressure (BP), electrocardiogram (ECG) and respiratory movements were recorded for 60 min after the i.a. injection of venom in urethane anaesthetised rats. Intra-arterial injection of venom produces immediate-tachypnoeic, intermediate-hypertensive and delayed-bradycardiac responses. Respiratory changes manifested as immediate increase (by 40%) in respiratory frequency (RF) followed by a decrease (by 40%) within 1 min and subsequent sustained increase (50%) up to 60 min. Increase in BP began after the respiratory changes, peaked (50%) at 5 min and remained at that level throughout. The decrease in heart rate (HR) began after 5 min, peaked (60%) at 10 min and recovered subsequently (40%) but remained below the initial level. In terazosin pretreated animals, the venom-induced cardiorespiratory changes were attenuated significantly. Whereas in vagotomized group, venom-induced respiratory changes and HR changes were blocked but not the BP changes. The findings suggest that the venom-induced vasosensory responses involve alpha(1)-adrenoceptors for BP and vagal efferents for HR changes.

Estrogen modulates in vitro atrial bradycardia induced by Indian red scorpion venom via G-protein coupled mechanisms

Role of estrogen on cardiac dysrhythmia produced by Indian red scorpion (Mesobuthus tamulus) venom was examined using rat right atrial preparations in vitro. In females, the M. tamulus venom produced an increase, a decrease and an increase in rate at 0.03, 0.3 and 3 microg/ml of venom, respectively, producing N-shaped response curve, whereas no such response pattern was observed in males. Force of contraction in females was increased at all the concentrations of the venom, while in males the increase was seen only at 3 microg/ml. Castration of male rats did not alter the venom response to female type, while 'estrogenisation of castrated male rats' (pseudofemales) produced a response similar to females. Tamoxifen reversed the venom-induced responses both in females and pseudofemales. Further in females, the venom action at 0.3 microg/ml was blocked by atropine. Response at this concentration was also blocked by pertussis toxin and methylene blue. Results suggest that the cholinergic component of venom response is modulated by estrogen receptors via G(i)-protein-guanylyl cyclase mechanism.