Pharmacological profile of rat pleurisy induced by Bothrops jararaca venom

Secreted Phospholipases A₂ from Animal Venoms in Pain and Analgesia

Animal venoms comprise a complex mixture of components that affect several biological systems. Based on the high selectivity for their molecular targets, these components are also a rich source of potential therapeutic agents. Among the main components of animal venoms are the secreted phospholipases A₂ (sPLA₂s). These PLA₂ belong to distinct PLA₂s groups. For example, snake venom sPLA₂s from Elapidae and Viperidae families, the most important families when considering envenomation, belong, respectively, to the IA and IIA/IIB groups, whereas bee venom PLA₂ belongs to group III of sPLA₂s. It is well known that PLA₂, due to its hydrolytic activity on phospholipids, takes part in many pathophysiological processes, including inflammation and pain. Therefore, secreted PLA₂s obtained from animal venoms have been widely used as tools to (a) modulate inflammation and pain, uncovering molecular targets that are implicated in the control of inflammatory (including painful) and neurodegenerative diseases; (b) shed light on the pathophysiology of inflammation and pain observed in human envenomation by poisonous animals; and, (c) characterize molecular mechanisms involved in inflammatory diseases. The present review summarizes the knowledge on the nociceptive and antinociceptive actions of sPLA₂s from animal venoms, particularly snake venoms.

Assessment of efficacy of bothropic antivenom therapy on microcirculatory effects induced by Bothrops jararaca snake venom

Intravenous administration of antibothropic antivenom (BAv) neutralises the systemic effects, but does not efficiently reverse the local symptoms elicited by the Bothrops jararaca venom (BjV). The mechanisms involved in this poor protection have not been clarified. In this work, intravital microscopy studies were carried out to determine the efficacy of different schedules of BAv treatment on local effects evoked by topical application of BjV in the microcirculatory network of the internal spermatic fascia of Wistar rats. Results demonstrated that BAv administration 15 min before, simultaneously with, or 15 min after BjV application did not totally reverse the local symptoms, represented by disturbances of coagulation, development of haemorrhage lesions, vascular permeability increase and increment on leukocyte-endothelium interactions. This lack of effectiveness neither reflects an inadequate amount of specific antibodies in the antivenom against toxins responsible for local effects nor an insufficient dose of circulating BAv during the assays. Administration of fluorescein isothiocyanate (FITC) labelled-BAv showed the dynamics of distribution of the antivenom in the microcirculatory network. Images obtained from prior and simultaneously treated animals showed that the antivenom remains at luminal side of vessels before venom application, and the latency time to antivenom leakage is coincidental to that for local effects evoked by the venom. In addition, images from posterior treatment demonstrated that the intense alterations in the microcirculatory network impair antivenom distribution at the site of injection. Together, our data show that the lack of effectiveness of antivenom therapy is due to impaired and delayed venom and antivenom interaction at the site of injury.

Cell adhesion molecules involved in the leukocyte recruitment induced by venom of the snake Bothrops jararaca

It has been shown that Bothrops jararaca venom (BjV) induces a significant leukocyte accumulation, mainly neutrophils, at the local of tissue damage. Therefore, the role of the adhesion molecules intercellular adhesion molecule-1 (ICAM-1), LECAM-1, CD18, leukocyte function-associated antigen-1 (LFA-1) and platelet endothelial cell adhesion molecule-1 (PECAM-1) on the BjV-induced neutrophil accumulation and the correlation with release of LTB4, TXA2, tumor necrosis factor-alpha, interleukin (IL)-1 and IL-6 have been investigated. Anti-mouse LECAM-1, LFA-1, ICAM-1 and PECAM-1 monoclonal antibody injection resulted in a reduction of 42%, 80%, 66% and 67%, respectively, of neutrophil accumulation induced by BjV (250 microg/kg, intraperitoneal) injection in male mice compared with isotype-matched control injected animals. The anti-mouse CD18 monoclonal antibody had no significant effect on venom-induced neutrophil accumulation. Concentrations of LTB(4), TXA(2), IL-6 and TNF-alpha were significant increased in the peritoneal exudates of animals injected with venom, whereas no increment in IL-1 was detected. This results suggest that ICAM-1, LECAM-1, LFA-1 and PECAM-1, but not CD18, adhesion molecules are involved in the recruitment of neutrophils into the inflammatory site induced by BjV. This is the first in vivo evidence that snake venom is able to up-regulate the expression of adhesion molecules by both leukocytes and endothelial cells. This venom effect may be indirect, probably through the release of the inflammatory mediators evidenced in the present study.

Bradykinin is involved in hyperalgesia induced by Bothrops jararaca venom

Bradykinin is involved in hyperalgesia (pain hypersensitivity) induced by Bothrops jararaca venom-intraplantar injection of B. jararaca venom (5microg/paw) in rats caused hyperalgesia, which peaked 1h after venom injection. This phenomenon was not modified by promethazine (H(1) receptor antagonist), methysergide (5-HT receptor antagonist), guanethidine (sympathetic function inhibitor), anti-TNF-alpha or anti-interleukin-1 antibodies or by the chelating agent CaNa(2)EDTA. Venom-induced hyperalgesia was blocked by the bradykinin B(2) receptor antagonist HOE 140. On the other hand, des-Arg(9), [Leu(8)]-bradykinin, a bradykinin B(1) receptor antagonist, did not modify the hyperalgesic response. These results suggest that bradykinin, acting on B(2) receptor, is a mediator of hyperalgesia induced by B. jararaca venom.

The role of migrating leukocytes in IL-1 beta-induced up-regulation of kinin B(1) receptors in rats

1. The present study examines the role of migrating leukocytes in the ability of IL-1 beta to induce the functional up-regulation of B(1) receptors, as assessed by kinin B(1) agonist-induced oedema in the rat paw. 2. Pre-treatment with the PAF receptor antagonist WEB 2086 inhibited des-Arg(9)-BK-induced oedema in IL-1 beta-treated paws, while the LTB(4) receptor antagonist CP105696 had no effect. Des-Arg(9)-BK-induced paw oedema was also inhibited by pre-treatment with the selectin blocker fucoidin or by an anti-CD-18 monoclonal antibody. 3. I.d. injection of IL-1 beta produced a 5 - 10-fold increase of myeloperoxidase (MPO) activity in the rat paw. The increase in MPO activity was significantly inhibited by WEB 2086 (46 +/- 9%), fucoidin (68 +/- 5%) or the CD-18 antibody (84 +/- 3%). In contrast, i.d. injection of TNF alpha a dose known to upregulate the B(1) receptor functionally did not induce any significant increase in MPO activity. 4. Des-Arg(9)-BK alone had no effect in MPO activity but enhanced (by about 40%) the response induced by IL-1 beta, an effect prevented by the B(1) receptor antagonist des-Arg(9)-[Leu(8)]-BK. 5. The concentration of TNF-alpha was increased in the paws after i.d. injection of IL-1 beta. Pre-treatment with fucoidin, WEB 2086, anti-CD-18 or CP 105695, significantly reversed the local increases in TNF-alpha concentrations (80 +/- 2; 75 +/- 4, 73 +/- 3 and 40 +/- 2%), respectively. 6. Finally, IL-1 beta induced an increase of B(1) receptor mRNA levels in the rat paw, an effect which was prevented by fucoidin treatment. 7. Taken together, these results indicate that up-regulation of B(1) receptors in the rat paw following IL-1 beta seems to involve the local recruitment of neutrophils and subsequent local TNF-alpha production. The cross-talk between kinins, cytokines and leukocytes implicate B(1) receptors in chronic inflammatory diseases.

Pharmacological characterisation of arthritis induced by Bothrops jararaca venom in rabbits: a positive cross talk between bradykinin, nitric oxide and prostaglandin E2

BACKGROUND

Our previous results showed that nitric oxide (NO) and bradykinin (BK) mediate the arthritis induced by Bothrops jararaca venom (BjV) in rabbits. In this study, we investigated the contribution of each receptor of BK as well as the inter-relationship between NO and eicosanoids in BjV-induced arthritis.

METHODS

The arthritis was induced in rabbits with 16 microg of BjV injected intra-articularly. Prostaglandin E2 (PGE2), thromboxane B2 (TxB2), leukotriene B4 (LTB4) (radioimmunoassay) and nitrite/nitrate concentrations (NO2/NO3) (Griess reaction) were evaluated in the synovial fluid 4 h later. The animals were prior treated with NO synthase inhibitor (L-NAME; 20 mg/kg/day for 14 days), the B2 antagonist of BK (HOE-140) and the B1 antagonist of BK (des-Arg9[Leu8]-bradykinin), both at a dose of 0.3mg/kg, 30 min prior to the venom injection.

RESULTS

Data show that L-NAME and HOE-140 treatment were equally able to reduce PGE2 and NO2/NO3 levels without interfering with TxB2 and LTB4 production. On the contrary, the B1 antagonist of BK inhibited TxB2 and LTB4 production, and did not alter PGE2 and NO metabolites levels in the inflamed joint.

DISCUSSIONS

The results presented clarify the contribution of the kinin system, mainly through the B2 receptor, to the local inflammatory response induced by BjV, as well as its positive interaction with PGE2 and NO production.

Role of kinins and nitric oxide on the rabbit arthritis induced by Bothrops jararaca venom

The effects of the nitric oxide synthase inhibitor N(omega)Nitro-L-arginine-methyl ester (L-NAME) and of the bradykinin B(2) receptor antagonist HOE 140 were evaluated in the inflammatory reaction induced by Bothrops jararaca venom (BjV) in New Zealand White rabbits. Arthritis was induced by injecting 0.5 ml of a sterile solution of BjV (1-64 microg/ml) into the knee intraarticular cavity. The contralateral joint was injected with bovine serum albumin (BSA) diluted in sterile saline. At selected times thereafter (4, 24 and 48 h), the vascular permeability and the leukocyte influx in both the synovial fluid and synovium were evaluated. BjV caused a dose-dependent increase in both leukocyte influx and protein extravasation which reached a maximal response at 16 microg. Bothrops jararaca venom also induced the increase in the leukocyte accumulation in the synovium and in the concentration of both NO(2)/NO(3) in the synovial fluid. Chronic administration of L-NAME (20 mg/kg/day in the drinking water for 2 weeks) markedly reduced the leukocyte accumulation (90%), protein leakage (44%), and NO(2)/NO(3) (50%) levels in the synovial fluid, measured at the 4th h. Hoe 140, given i.v. (0.3 mg/kg, 30 min before) also reduced leukocyte accumulation (75%), protein leakage (48%), and NO(2)/NO(3) (79%) levels in the synovial fluid, measured at the 4th h. Similar results were obtained with acute administration of L-NAME (30 mg/kg, i.v., 30 min before). These results indicate that arthritis induced by BjV is triggered by kinin formation and that the increase in both vascular permeability and leukocyte accumulation is modulated by NO release.

Local haemorrhage induced by Bothrops jararaca venom: relationship to neurogenic inflammation

We investigated morphological alterations induced by s.c. injection of 2.5 microg of Bothrops jararaca venom in rats. Intense disorganisation of collagen fibres was observed 1 min after the venom injection, particularly at regions near vessels and nerves. Mast cells were degranulated, and erythrocytes were seen leaving venules throughout the endothelial junctions. At this time, damaged endothelial cells were not observed. In rats envenomed as above, but immediately after cardiorespiratory failure induced by deep ether anaesthesia, alterations in the connective tissue structures, as previously described, were not observed. The mediation of this haemorrhage was investigated by injecting the venom into the foot pad of mice and compared to the mediation of oedema. Local haemorrhage was significantly reduced in mice pre-treated with capsaicin or guanethidine or submitted to a surgical section of sciatic and saphenous nerves. In these animals, oedema was not affected. Groups treated with methysergide or morphine showed both haemorrhage and oedema significantly reduced. Indomethacin or dexamethasone pre-treatments significantly reduced the oedema, but not the haemorrhage. Moreover, in animals treated with promethazine or mepyramine, oedema and haemorrhage were not affected. These data suggest that local haemorrhage induced by Bothrops jararaca venom is partially controlled by serotonin and neurohumoral mediators. Furthermore, results indicate that haemorrhage and oedema are mediated by different pharmacological systems.

Bothrops asper snake venom and its metalloproteinase BaP-1 activate the complement system. Role in leucocyte recruitment

The venom of the snake Bothrops asper, the most important poisonous snake in Central America, evokes an inflammatory response, the mechanisms of which are not well characterized. The objectives of this study were to investigate whether B. asper venom and its purified toxins--phospholipases and metalloproteinase--activate the complement system and the contribution of the effect on leucocyte recruitment. In vitro chemotaxis assays were performed using Boyden's chamber model to investigate the ability of serum incubated with venom and its purified toxins to induce neutrophil migration. The complement consumption by the venom was evaluated using an in vitro haemolytic assay. The importance of complement activation by the venom on neutrophil migration was investigated in vivo by injecting the venom into the peritoneal cavity of C5-deficient mice. Data obtained demonstrated that serum incubated with crude venom and its purified metalloproteinase BaP-1 are able to induce rat neutrophil chemotaxis, probably mediated by agent(s) derived from the complement system. This hypothesis was corroborated by the capacity of the venom to activate this system in vitro. The involvement of C5a in neutrophil chemotaxis induced by venom-activated serum was demonstrated by abolishing migration when neutrophils were pre-incubated with antirat C5a receptor antibody. The relevance of the complement system in in vivo leucocyte mobilization was further demonstrated by the drastic decrease of this response in C5-deficient mice. Pre-incubation of serum with the soluble human recombinant complement receptor type 1 (sCR 1) did not prevent the response induced by the venom, but abolished the migration evoked by metalloproteinase-activated serum. These data show the role of the complement system in bothropic envenomation and the participation of metalloproteinase in the effect. Also, they suggest that the venom may contain other component(s) which can cause direct activation of C5a.

Pharmacological effects of the leaf-nosed viper snake (Eristocophis macmahoni) venom and its HPLC fractions

Crude venom from Eristocophis macmahoni was demonstrated to exert a potent inhibition of human blood platelet aggregation mediated by adenosine diphosphate (ADP), platelet activating factor (PAF) and arachidonic acid (AA). The venom caused lysis of the platelets, however, the red blood cells were not lysed by the venom. Substantial oedema was produced upon injection of the venom into the rat hind paw. Contrarily, the intraperitoneal injection of the venom to the rats caused an inhibition of the carrageenin-induced rat paw oedema. However, an 100% lethality within 24 h was observed with a dose of 40 mg/kg body weight. The venom was fractionated by reverse phase high pressure liquid chromatography (HPLC) and the fractions were analyzed for their effect on ADP-induced platelet aggregation. The fraction eluted at 15.5 min (20% acetonitrile concentration) exhibited an inhibitory effect of several-fold greater potency than that of the crude venom. Fractions eluted at 18.5 min (25.4% acetonitrile concentration) and onward showed a proaggregatory but insignificant effect. It is suggested that although the venom contains pro aggregatory components, inhibition of platelet aggregation seems to be its predominant activity.

Characterization of local tissue damage evoked by Bothrops jararaca venom in the rat connective tissue microcirculation: an intravital microscopic study

The aim of this study was to investigate the dynamic of the effects after topical application of Bothrops jararaca venom (BjV) on the microcirculation of the internal spermatic fascia of Wistar rats. The administration of 1 microg of BjV induced marked disturbances in capillaries and postcapillary venules, characterized by vasodilatation, fibrin clot formation, hemorrhagic lesions and alterations in the leukocyte-endothelial interactions. The installation and development of these effects occurred simultaneously. The application of higher dose of venom (10 microg) induced more intense effects, observed by the time-course of the beginning, evolution and intensity of the effects. The time-course of events suggests that an interaction of different effects occurs during the development of local symptoms following the exposure of tissues to BjV.