Lupeol derivative mitigates Echis carinatus venom-induced tissue destruction by neutralizing venom toxins and protecting collagen and angiogenic receptors on inflammatory cells.

BACKGROUND: Echis carinatus bite is a serious threat in South-Asian countries including India, as it causes highest number of deaths and terrifying long-term tissue destruction at the bitten site. Although venom metalloproteinases and hyaluronidases are the suggested key players, studies on the effect of venom on polymorphonuclear cells, peripheral blood mononuclear cells and platelets, and their role in long-term tissue destruction are still in infancy. While, the effect of venom on collagen receptors, integrin α2ß1/GP VI/DDR1 and CX3CR1 chemokine receptor present on these cells is an untouched area. METHODS: Lupeol, lupeol acetate, its synthetic derivatives 2-8 were screened for inhibition of E. carinatus venom induced-hemorrhage in mouse model where compound 8 was found to be the most potent. Further, compound 8 efficiently neutralized venom induced hemorrhage, edema, dermonecrosis, myonecrosis, myotoxicity, pro-coagulant, oxidative stress, inflammatory cytokines and cleavage of collagen and CX3CR1 receptors on inflammatory cells in in vivo, in silico, ex vivo and in vitro studies. CONCLUSIONS: This study for the first time demonstrated the cleavage of collagen receptors and the receptor for angiogenesis and wound healing by the venom and its inhibition by compound 8, as these are important for firm adhesion of inflammatory cells at the damaged site to resolve inflammation and promote tissue repair. GENERAL SIGNIFICANCE: This study provides a lead in venom pharmacology, wherein, compound 8 could be a therapeutic agent for the better management of viper venom-induced long-term tissue destruction.

Oxidative stress-induced methemoglobinemia is the silent killer during snakebite: a novel and strategic neutralization by melatonin.

Oxidative stress-induced methemoglobinemia remained an untouched area in venom pharmacology till date. This study for the first time explored the potential of animal venoms to oxidize hemoglobin to methemoglobin. In in vitro whole-blood assay, methemoglobin forming ability of venoms varied as Naja naja > Ophiophagus hannah > Echis carinatus > Daboia russellii > Apis mellifera > Mesobuthus tamulus > Hippasa partita. Being highly potential, N. naja venom was further studied to observe methemoglobin formation in RBCs and in combinations with PMNs and PBMCs, where maximum effect was observed in RBCs + PMNs combination. Naja naja venom/externally added methemoglobin-induced methemoglobin formation was in parallel with ROS generation in whole blood/RBCs/RBCs + PMNs/RBCs + PBMCs. In in vivo studies, the lethal dose (1 mg/kg body weight, i.p.) of N. naja venom readily induced methemoglobin formation, ROS generation, expression of inflammatory markers, and hypoxia-inducible factor-3α. Although the mice administered with three effective doses of antivenom recorded zero mortality; the methemoglobin and ROS levels remained high. However, one effective dose of antivenom when administered along with melatonin (1:50; venom/melatonin, w/w), not only offered 100% survival of experimental mice, but also significantly reduced methemoglobin level, and oxidative stress markers including hypoxia-inducible factor-3α. This study provides strong drive that, complementing melatonin would not only reduce the antivenom load, but for sure greatly increase the success rate of antivenom therapy and drastically minimize the global incidence of snakebite deaths. However, further detailed investigations are needed before translating the combined therapy towards the bed side.

Melatonin inhibits snake venom and antivenom induced oxidative stress and augments treatment efficacy.

Snakebite is a neglected health hazard. Its patho-physiology has largely been focused on systemic and local toxicities; whereas, venom and antivenom induced oxidative stress has long been ignored. Antivenom therapy although neutralizes venom lethality and saves many lives, remains ineffective against oxidative stress. This prompted us to complement antivenom with an antioxidant molecule melatonin that would protect against oxidative stress and increase the efficacy of the existing snakebite therapy. Here we show that D. russelli and E. carinatus venoms induce strong oxidative stress that persists even after antivenom administration in mice model. Additionally, antivenoms also induce oxidative stress. Polyvalent antivenom induce more oxidative stress than monovalent antivenom. Strikingly, antivenom and melatonin together not only inhibit venom and antivenom induced oxidative stress but also significantly reduce the neutralizing antivenom dose. This study provides a therapeutic potential for enhancing the existing snakebite therapy. The combined treatment of antivenom+melatonin would prevent the upsurge of oxidative stress as well as minimize the antivenom load. Thus the investigation offers immense scope for physicians and toxinologists to reinvestigate, design new strategies and think beyond the conventional mode of antivenom therapy.

NETosis and lack of DNase activity are key factors in Echis carinatus venom-induced tissue destruction.

Indian Echis carinatus bite causes sustained tissue destruction at the bite site. Neutrophils, the major leukocytes in the early defence process, accumulate at the bite site. Here we show that E. carinatus venom induces neutrophil extracellular trap (NET) formation. The NETs block the blood vessels and entrap the venom toxins at the injection site, promoting tissue destruction. The stability of NETs is attributed to the lack of NETs-degrading DNase activity in E. carinatus venom. In a mouse tail model, mice co-injected with venom and DNase 1, and neutropenic mice injected with the venom, do not develop NETs, venom accumulation and tissue destruction at the injected site. Strikingly, venom-induced mice tail tissue destruction is also prevented by the subsequent injection of DNase 1. Thus, our study suggests that DNase 1 treatment may have a therapeutic potential for preventing the tissue destruction caused by snake venom.