Abstract: The evolution of poison and venom had made the animal body system to deal effectively with defense mechanism primarily by molecular means. These chemical defences target the cell membrane receptors, block the physiological systems in body and cause paralysis. Evolution around years, led to the development of these peptides with effective functional properties that made them more selective and potent, but immunogenically poor, provide prolonged action and potent effect on preys. When a venom or toxin is enriched with these functionally effective peptides form 3D structure that are linked by disulphide brides. This structure is highly stable and they specifically target GPCRs, ion channels and other membrane receptors and it was proved to have indispensable pharmacological properties. The first drug Captopril discovered against hypertension was isolated from Brazilian viper, Bothrops juraraca. It is one of the most popular and accepted antihypertensive drug used world wide now-a-days. Since then peptides isolated from snake, scorpion, spider, bee and sea anemone toxin have proved to display potential immunomodulatory effects and were useful in treating rheumatoid arthritis, multiple sclerosis, lupus and psoriasis including autoimmune diseases in human. The present article in not intended to be a definitive review of entire field of zootoxins, but rather an overview, which emphasize on recent developments made in the field of zootoxins (venoms and toxins), their role in the treatment of diseases with a special focus towards exploring their potent immunodulatory and therapeutic potential in the field of drug development. Advances in the fields of analytic chemistry, molecular biotechnology and biochemistry are now making it possible to isolate and purify individual components, using a minute amount of a toxin.
INTRODUCTION
Since evolution, living system that is animals and humans developed a variety of adaptation ways for feeding and defense, which are the two basic aspects of life. The largest mammal of earth, elephants have a well developed tusks that helps in feeding also serves as a defense. Also reptiles like snakes and other animals have different evolutionary derived strategy to deal with feeding and defense. Animals venom have three potent activities such as prey-immobilization, prey digestion and defense (Wigger et al., 2002; Morgenstern and King, 2013).
When an animal posses special features such as stings, nematocysts, a special teeth, arrows or hairs to deliver the venom into the prey, then it is said to be venomous (Ericsson et al., 2006). Reptiles such as snakes, few lizards, insects and flies such as spiders and bees, sea creatres such as cone snails and octopuses produce toxic substances that help them in catching or trapping the prey and also as a self defense to protect themselves from getting preyed. In contrast, poisonous animals, lack any specific apparatus for injecting venom and toxins are distribted in their tissues which get activated once the animal is being ingested (Warrell, 2003). One of the venomous mammal is male duck-billed platypus in which the venom is carried inside their ankle spurs. Insights at molecular studies tells that the peptides in the toxin once injected into the vein will target the cardiac, nervous or respiratory systems in the the body, leading to blockage of the system followed by paralysis and death. These toxic peptides act precisely on ion channels, G-protein coupled receptors and other cell membrane receptors. Gradually, venom alongwith its various components had been known to act independently in various animal groups and have been reported to be specific for species, subspecies or even geographic-variation. These species- specific effects of venom, makes it difficult for researchers to transfer observations from animals to humans (Junghanss and Bodio, 1996). The basic molecular configuration of the venom remain unchanged though the years of evolution has made minor changes to these toxic compounds. The key molecules from blood, brain, digestive tract in the body have been proposed by nature to serve animals for predation or protection. Zootoxin is the only phenomenon in the field of medicine, which has fascinated both researchers and common men by enriching our knowledge in basic and applied science. As per WHO (2015), the cases of snake envenomisation alone may be around 2.5 million and number of death due to snake bite to be approx 20-125 thousand every year.
Animal venoms are conglomers of 20-25 different molecules and have peptides of 30-80 amino acid residues. The poisonous animal species have alkaloids in predominance that exhibit strong biological effects though they are small molecules. Table 1 represents a brief overview of zootoxins along with their respective sources, mechanism of action and chemical constituents. Paradoxically, the same venom which is a deadly hazard can be exploited to synthesise valuable medicine. Venoms and poisons contain pure toxic peptides which almost have specific action on biological systems making them an essential source for design and synthesis of therapeutic agents (Gomes et al., 2010). Marine species produce many biologically active peptides such as antimicrobial peptides (Matsunaga et al., 1985), neurotoxins (Tu, 1974), anti-tmour and anti-viral (Rinehart et al., 1981), cardiotonic peptide (Norton et al., 1976) and cardiotoxins (Bernheimer et al., 1982). The first of angiotensin converting enzyme i.e., captopril, a drug commonly used against hypertension and myocardial infarction owes it’s discovery to Brazilian viper, Bothrops juraraca. The present review reflects the recent developments made in the field of uses of zootoxins (venoms and toxins), their role in the treatment of diseases and disorders, cancer, autoimmune diseases, arthritis and other beneficial health applications with a special focus towards exploring their potent immunodulatory and therapeutic potentials in the field of drug development.
Venom based curative therapies-historical developments: Venom-based cures and their use dates back to ancient era as evident from their mention in Sanskrit scriptures Charak samhita, Vagbata samita and Saranghara samita (Pal et al., 2002; Gomes et al., 2010). It is believed that during the primedivial period, Mithradates VI of Pontus whose wounds in battle field are healed by administration of steppe viper venom by shamans (Now-a-days crystallized snake venom is exported from Azerbaijan as a medicine). In indian medicine cobra venom, has been useful in Dushyodara and Jalodara (ascites). In unani field of medicine cobra venom is being used as hepatic stimulant, tonic, aphrodiasic and for resuscitation in collapsed conditions (Debnath et al., 1972). Venom of spider, bee and snake are routinely used in homeopathy (Pal et al., 2002). Bee venom was by hyppocrates to treat arthritis and joint pain. But the curative dose which he used was just within the limit of the pathogenic dose. The development in science of synthesising therapeutic peptides from venoms started in 1960s, when Hugh Alistair Reid, an English clinician who suggested that the venom extracted from the Malayan pit viper (Ancistrodon rhodostoma) may be used to treat deep-vein thrombosis condition (Hawgood, 1998). In the year 1968, Hugh named this defibrinating derivative of A. rhodostoma venom as Arvin (ancrod) which was used clinically as a clot-busting drug in Europe.
| Table 1: | Zootozins, their sources and mechanism of action |
These days Arvin has been substituted by other venom anticoagulants. In 1970’s, Brazilian pit viper (Bothrops jararaca) venom led to the development of a class of antihypertensives, ACE inhibitors. Finally, in 1975 a more synthetic version, captopril the first oral drug was approved as an antihypertensive in human (Blankley, 1985). Recently prialt and byetta has replaced catptopril in the market after integrillin and aggrastat.
Immunomodulatory potential of snake venom: There are nearly more than 2000 species of snakes in the world among which approximately 300 are venomous belonging to families, Elapidae (coral snake, cobra, krait, tiger snake, mamba and taipan), Colubridae (boomslang), Hydrophidae (sea snakes), Viperidae (old world vipers, saw scaled viper, Gaboon viper, Russell's viper and puff adder) and Crotalidae (pit vipers, cotton mouth, copper head and rattle snakes) (Karalliedde, 1995). Local and systemic hemorrhages are the classic indication of envenoming by the viperid snakes. Snake venom metalloproteinases (SVMPs) in the microvasculature are specifically in capillaries responsible for the hemorrhagic activity (Herrera et al., 2015). Venoms generally aim to cause paralysis leading to death, but some venoms also elicit acute pain. The venoms target somatosensory nerve terminals and stimulate the nociceptive neural pathways (Bohlen and Julius, 2012).
Naja Naja Atra Venom (NNAV) regulates the immune system by precise increase in Th1 and Th2 cytokines (IFN-γ and IL-4, respectively) by secretion and inhibition of Th17 cytokine (IL-17) production which in turn raises the innate and humoral immune responses and inhibits the CD4 Th17 and CD8 T cell actions, thus implying a possible therapeutic agent for autoimmune diseases (Kou et al., 2014). Bungarus caeruleus snake venom (BCV) treatment significantly increases the production of TNF-α, IFN-γ, ROS, NO mediated through immunomodulatory activity associating the macrophages (Bhattacharya et al., 2013). The venom from Crotalus durissus cascavella and Bothrops erythromelas induces a distinct immunomodulatory effect in vitro through production of NO and cytokines. Bothrops erythromelas stimulates a proinflammatory response whereas C. durissus cascavella stimulates an anti-inflammatory effect (Luna et al., 2011). In an in vitro study conducted by Ribeiro et al. (2014) in PBMC’s of human, the C. durissus collineatus venom lead to increased production of IL-10 and TNF that resulted in cell death suggesting their proinflammatory and anti inflammatory activity. Hannalgesin isolated from Ophiophagus hannah venom exerts its effect by binding to the SS1 or SS2 subunit of the sodium channel (Pu et al., 1995). The two main components phospholipases A2 and metalloproteases of Bothrops snake venom mediates the inflammatory response (Teixeira et al., 2003, 2009; 2005; Correa-Netto et al., 2010). Studies also suggest that Bothrops asper activates the complement system (Farsky et al., 2000) Batroxobin, inhibits the conversion of fibrinogen to fibrin is a serine protease isolated from Bothrops atrox moojeni venom. Bothrojaracin, isolated from Bothrops jararaca exerts its anti-thrombin activity by binding to the two thrombin anion binding exosites I and II at fibrinogen and antithrombin respectively (Zingali et al., 2006). Lebecetin, a C-type lectin-like protein exclusively binds to the platelet anti-glycoprotein Ib (GP1b) was isolated from Macrovipera lebetina. Ecarin is a 1A prothrombin activator metalloproteinase isolated from Echis carinatus venom that aids in the detection of von Willebrand disease (Schieck et al., 1972). Pseutarin C, extracted from venom of Pseudonaja textiles by incitement of prothombin converts prothrombin to thrombin. Salmosin, isolated from Gloydius ussuriensis venom strongly inhibits tumor-derived angiogenesis, attachment and generation of tumor cells. Rhodostomin, hampers angiogenesis induced by basic fibroblast growth factor and abolished the murine melanoma B16-F10 tumor growth is derived from the venom of Calloselasma rhodostoma (Yeh et al., 2001). Textilinin, a reversible plasmin inhibitor and can be harvested as an anti-bleeding agent is a highly potent venom of from Australian brown snake Pseudonaja textilis (Millers et al., 2009). Arvin extracted from Malaysian pit viper Caloselasma rhodostoma suppress the chronic inflammatory responses mainly arthritis (Ford et al., 1970).
Immunomodulatory potential of scorpion venom: Scorpion envenomisation leads to induction of systemic immune response and augment the excitability of muscle and nerve cells by release of noradrenaline, acetylcholine and serotonin or action on ion channels (Adam and Weiss, 1959). The alpha and beta scorpion toxins prolong the action potential through delaying inactivation of sodium channels, but beta toxins in addition also affect the activation of sodium channels. The sodium channel is activated at membrane potential level in which the channel would be regularly closed (Jover et al., 1980). Mexican scorpion toxin was the first toxin observed to block voltage-dependent potassium channels. Chloride channels are also serve as receptors for scorpion toxin.
Harald Sontheimer isolated the peptide chlorotoxin from Leiurus quinquestriatus (the giant Israeli Scorpion) venom which specifically killed only the cancerous cells leaving the healthy cells intact, thus exploring it as a potent anticancer drug (Soroceanu et al., 1998). Agitoxin-2, anuroctoxin, charybdotoxin (ChTX), hongotoxin, kaliotoxin, margatoxin (MgTX), noxiustoxin (NTX) and orthochirus scrobiculosus toxin 1 (OSK1) also block KV1.3 channels (Wulff and Zhorov, 2008; Zhao et al., 2015).
Tityus serrulatus scorpion envenomation induces the inflammatory mediators which affect the local and systematic immune response. Tityus serrulatus (TsV) toxins Ts1 and Ts6 induced the production of NO, Interleukin (IL)-6 and tumor necrosis factor alpha (TNF-α) in combination with lipopolysaccharide (LPS) in stimulated J774.1 cells, however, Ts2 toxin and LPS combination showed opposite to this effect. Also, Ts2 alone showed anti-infllamatory effect by induction of IL-10 (Zoccal et al., 2011). The Ts1 has a crucial immunomodulatory response on macrophages (Petricevich et al., 2007). The Ts2 (TsTX-III) and Ts6 (TsTX-IV) depend on lipid mediator and cytokine production mechanism to induce inflammation (Zoccal et al., 2013). The Ts2 may show a regulatory role and Ts6 a pro-inflammatory activity, hence, may be harnessed as a therapeutic agent for immunological disorders. Similarly, Tityus serrulatus scorpion crude venom (Tsv) injected subcutaneously in mice induced the blood neutrophils recruitment and serum IL-6, IL-10 and TNF-α (Fialho et al., 2011). Casella-Martins et al. (2015) studied that TsV was found to activate peritoneal macrophages of mouse expressing the lymphocytic role in envenomation. HsTX1 toxin, isolated from the Heterometrus spinnifer scorpion, reveals potentially attractive candidature for the treatment of autoimmune diseases i.e., multiple sclerosis and rheumatoid arthritis, as it has been shown to block KV1.3 channels (Rashid et al., 2014). A potent immunosuppressive toxin Kaliotoxin (KTX) is beneficially effective on the neurological symptoms of autoimmune encephalomyelitis and treating bone resorption in periodontitis. The KTX that blocks Kv1.3 might establish a potential therapy to prevent alveolar bone injury in periodontal disease (Zhao et al., 2015). Indian red scorpion venom was reported to have the property to treat Freunds complete adjuvant induced arthritis in rat model (Nipate et al., 2014). Androctonus australis hector venom (Aah venom) of scorpion induces the release of cytokines such as IL-6, TNF-alph a leading to tissue damage (Raouraoua-Boukari et al., 2012).
Immunomodulatory potential of spider venom: Alpha latrotoxin from black widow spider venom, cause depletion of synaptic vesicles at neurotransmitter junction. This mechanism of action is exerted by the polypeptide toxins of the venom that acts on presynaptic nerve terminals leading to extensive release of transmitter from the cationic channels (Clark et al., 1972). Similarly, the Agatoxins isolated from Agelenidae (Australian funnel-web spider) affects synaptic transmission acting on calcium channels, blocking access of calcium into presynaptic terminals and inhibiting release of inhibitory transmitters such as glycine and GABA (Adams et al., 1990). Heminecrolysin, a sphingomyelinase D (SMaseD), released during Hemiscorpius lepturus (H.) envenomation causes the major pathological effects in man. Lycosa singoriensis, a wolf spider more common in north western regions of china produces rashes and pain in animals and humans around the site of bite (Lu and Zhang, 2001). Antimicrobial peptides lycotoxin I ans II forms pore in the synaptsomoses leading to outflow of calcium ions (Yan and Adams, 1998). In addition these peptides also has antimicrobial property that inhibits the growth of microbes (Liu et al., 2009). The exposure of phosphatidylserine effect on human nucleated Jurkat T cells, stimulates pro-inflammatory secretions (TNF-α, IL-6) and anti-inflammatory cytokines (IL-10) and stimulates a disseminated intravascular coagulation effect on chorioallantoic membrane inoculated chick embryo model (Borchani et al., 2013). Lachesana tarabaevi spider venom, Latarcins (Ltc) is a linear cytolytic peptide which also has been reported to reveal immunomodulatory effect (Dubovskii et al., 2015).
Immunomodulatory potential of bee toxins: Bee venom consists of histamine, mellitin, apamin, adolapin and phospholipase A2 causing cytolytic effect on skin mast cells leads to release of histamine (Markovic and Rexova, 1963). A high concentration of >100 μg mL–1 causes lymphocyte instability while lower concentration of same don't cause oxidative damage. This bee venom therapy has been since time immemorial to alleviate pain in rheumatoid arthritis and multiple sclerosis (Mohammadi et al., 2015). Mellitin which comprises of 50% of the dry weight of bee venom exerts its anti-arthritis effects by inhibition of nuclear factor kappaβ (NF-κβ), decrease in the production of pro-inflammatory cytokines (TNF-α, IL-6 and IL-1β), cyclooxygenase and phospholipase enzymes and Reactive Oxygen Species (ROS) (Mohammadi et al., 2015). It also suppresses the expression of Toll-like receptor-2 (TLR-2) and CD14; reduces the binding activity of Activator Protein (AP-1) and nuclear factor-κβ (NF-κβ) and decreased the production of TNF-α and IL-1β (An et al., 2014). It accelerates the differentiation of FOXP3-expressing cells both from fresh CD4 T cells and mature CD4 thymocytes, a tract that may commit to the VIT s space to spread circulating Tregs in allergic individuals (Caramalho et al., 2015). In another study, the bee venom and mellitin showed its anti-cancer effect by inducing the apoptotic cell death of SKOV3 and PA-1 human ovarian cancer cells through enhaced expression of DR3, DR4 and DR6, in addition it inhibit the STAT3 pathway (Jo et al., 2012).
Hymenoptera stings often leads to death by immune dysfunction thus by the venom allergens react with cell-bound IgE and induces the huge release of histamine, prostaglandins, leukotrienes, chemotactic factors and a myriad of many different factors (Wasserman, 1983). Apitherapy (opitoxin) is used to treat the patients who suffer from inflammatory or degenerative diseases such as arthritis. It provides a soothing relief against arthritis and other systemic inflammations. Moreover, bee venom toxin can soften the scar tissues and break them down, has a local anti-inflammatory effect and can treat both acute injuries such as tendonitis and chronic neck pain. Also apitoxin was found to treat cancer. It was suggested that the venom peptides target the tumour cells and the cell exhibits its cytotoxic on activation by these peptides and establishes its anti-tumour activity, also induces apoptosis of the tumour cell (Orsolic, 2012)
Immunomodulatory potential of marine snail and sea anemone venom: Conantokins and conotoxins from snail venom helps to alleviate the pain in people with epileptic seizures and cancer, respectively. The α-conopeptides target particular subtypes of nicotinic receptors (Myers et al., 1991), also both are protective against Parkinson’s and Alzheimer’s diseases, nicotine addiction and depression (Livett et al., 2004). The δ-conopeptides delay inactivation (Shon et al., 1994) whereas μ- and μO-conopeptides restrict voltage-gated sodium channels (NaV) (McIntosh et al., 1995; Cruz et al., 1989), σ-conopeptides block 5-HT3Rs (type 3 serotonin receptors) (England et al., 1998), similarly ω-conopeptides block the subtypes of voltage-gated calcium channels (CaV) (Olivera et al., 1984; McCleskey et al., 1987), likewise κ- and κα-conopeptides block voltage-gated AShaker@ potassium channels (KV) (Olivera et al., 1984), conantokins inhibit N-methyl-D-aspartate receptors (NMDARs) (Jimenez et al., 2002) and norepinephrine transporter got inhibited by χ-conopeptides, conopressins and contulakin-G are act as an agonists at vasopressin receptors (Cruz et al., 1987) and neurotensin receptors (Craig et al., 1999) respectively, whereas the ρ-conopeptides inhibit α-adrenergic receptors.
Stichodactyla toxin (ShK) is a peptide toxin isolated from sea anemone (Stichodactyla helianthus) that restricts the voltage-gated potassium (Kv) channels i.e., Kv1.1, Kv1.3, Kv1.6, Kv3.2 and KCa3.1. The ShK is a potent immunosuppressant which can be exploited for the treatment of autoimmune diseases such as multiple sclerosis (Beeton et al., 2011). Similary, The venom isolated from sun anemone has also been useful against human autoimmune diseases, such as multiple sclerosis, rheumatoid arthritis, psoriasis and lupus. Moreover, the Dalazatide (ShK-186) a reconfigured peptide can be used against multiple autoimmune diseases like rheumatoid arthritis, psoriasis, atopic dermatitis, psoriatic arthritis, multiple sclerosis, inflammatory bowel diseases, lupus, type 1 diabetes mellitus, asthma, autoimmune uveitis and vasculitis1.
CONCLUSION
All venoms and toxins (zootoxins) have a multifaceted and multitasking effect. In the evolutionary struggle between competing sets of co-evolving species, i.e., race between predator and prey, weapons and defenses are constantly tugged. However, deadly venom also is enriched with properties that make it valuable for therapy. Venom or toxins often act specifically on the particular target in the same manner just like a lock and key fitting model for therapeutic cure. Currently, it’s a challenge for scientists and health professionals to discover the active principle of the toxin that hits only the certain target and then exploit the same active molecule to design a cure for deadly diseases. New molecules for the treatments of autoimmune diseases, diabetes, heart diseases, cancer and chronic pain could be available within a decade. It won=t be an exaggeration to state that venom will serve as a stepping stone to future medicine. Finally, the peptides in zootoxins have enriched us a boon in the field of health and medicine.