No evidence for proteolytic venom resistance in southern African ground squirrels

Raptors without resistance: No evidence for endogenous inhibition of rattlesnake venom metalloproteinases in a Great Plains raptor assemblage

Snake venoms are complex biochemical secretions under strong selection for prey subjugation, and venoms are tightly linked to the biotic communities that snakes inhabit. Physiological adaptations for venom resistance have been identified in various snake prey species, but fewer snake predators, with research in this area largely biased towards mammalian species. Fewer investigations have assayed for the presence of resistance mechanisms in avian systems. Birds of prey (hereafter "raptors"; orders Accipitriformes, Falconiformes, and Strigiformes) represent major sources of predation for snakes. Raptor dietary habits range from snake specialists to non-snake feeders, and this continuum of snake predation frequency among species creates the ideal system in which to explore the presence and strength of venom resistance. We assayed sera from a suite of Great Plains raptors against snake venom metalloproteinases (SVMPs) of the Prairie rattlesnake (Crotalus v. viridis) to test the general hypotheses that 1) raptor sera will display elevated SVMP inhibition compared to a naïve avian model (domestic chicken; Gallus gallus) and 2) raptor species with high levels of rattlesnake predation will more effectively inhibit SVMP activity than those that are not known to feed on rattlesnakes. We found that raptors do possess elevated SVMP inhibition in comparison to a naïve avian model, but this level of inhibition remains low and is unlikely to be biologically significant in detoxifying venoms. We found no evidence suggesting that inhibitory potential of different raptor sera corresponds to the level of rattlesnake predation associated with each species. The widespread lack of SVMP inhibition in diverse raptors underscores the complexity of venom resistance dynamics in natural systems and further suggests that physiological venom resistance mechanisms may be poorly developed in birds more broadly.

A plethora of rodents: Rattlesnake predators generate unanticipated patterns of venom resistance in a grassland ecosystem

Predation has the potential to impart strong selective pressures on organisms within their environments, resulting in adaptive changes in prey that minimize risk of predation. Pressures from venomous snakes present an exceptional challenge to prey, as venom represents a unique chemical arsenal evolutionarily tailored to incapacitate prey. In response, venom resistance has been detected in various snake prey species, and to varying degrees. This study analyzes venom resistance in an eastern Colorado grassland habitat, where the Prairie Rattlesnake (Crotalus viridis) and Desert Massasauga Rattlesnake (Sistrurus tergeminus edwardsii) co-occur with a suite of grassland rodents. We test for venom resistance across rodent and snake pairings using two geographically distant field sites to determine the role of 1) predation pressure and trophic ecology, and 2) sympatric and allopatric patterns of venom resistance. Resistance was measured using serum-based metalloproteinase inhibition assays to determine potential inhibition of proteolytic activity, augmented by median lethal dose (LD50) assays on rodent species to assess toxicity of crude venoms. Resistance is present in several rodent species, with strong resistance present in populations of Eastern Woodrat (Neotoma floridana), Ord's Kangaroo Rat (Dipodomys ordii), and Northern Grasshopper Mouse (Onychomys leucogaster). Resistance is less developed in other species, including the House Mouse (Mus musculus) and Plains Pocket Mouse (Perognathus flavescens). An unexpected differential is present, where Lincoln County Kangaroo Rats are highly resistant to venom of co-occurring Prairie Rattlesnakes yet are sensitive to an allopatric population of Prairie Rattlesnakes in Weld County. Lincoln Co. Northern Grasshopper Mice also demonstrate extremely elevated resistance to Weld Co. Prairie Rattlesnake venoms, and they may possess resistance mechanisms for myotoxin a, an abundant component of Weld Co. C. v viridis venoms. This study illustrates the complexity of venom resistance in biological communities that can exist when incorporating multiple species interactions. Future studies aimed at characterizing resistance mechanisms at the molecular level will provide a more detailed physiological context for understanding mechanisms by which resistance to venoms occurs.

Naja annulifera Snake: New insights into the venom components and pathogenesis of envenomation

Background

Naja annulifera is a medically important venomous snake occurring in some of the countries in Sub-Saharan Africa. Accidental bites result in severe coagulation disturbances, systemic inflammation and heart damage, as reported in dogs, and death, by respiratory arrest, in humans. Despite the medical importance of N. annulifera, little is known about its venom composition and the pathogenesis of envenomation. In this paper, the toxic, inflammatory and immunogenic properties of N. annulifera venom were analyzed.

Methodology/Principal findings

Venom proteomic analysis identified 79 different proteins, including Three Finger Toxins, Cysteine Rich Secretory Proteins, Metalloproteinases, Phospholipases A₂ (PLA₂), Hyaluronidase, L-amino-acid oxidase, Cobra Venom Factor and Serine Proteinase. The presence of PLA₂, hyaluronidase, fibrinogenolytic and anticoagulant activities was detected using functional assays. The venom was cytotoxic to human keratinocytes. In an experimental murine model of envenomation, it was found that the venom induced local changes, such as swelling, which was controlled by anti-inflammatory drugs. Moreover, the venom caused death, which was preceded by systemic inflammation and pulmonary hemorrhage. The venom was shown to be immunogenic, inducing a strong humoral immune response, with the production of antibodies able to recognize venom components with high molecular weight and to neutralize its lethal activity.

Conclusions/Significance

The results obtained in this study demonstrate that N. annulifera venom contains toxins able to induce local and systemic inflammation, which can contribute to lung damage and death. Moreover, the venom is immunogenic, an important feature that must be considered during the production of a therapeutic anti-N. annulifera antivenom.

N. annulifera is a dangerous snake that belongs to the Elapidae family. It is found in some of the countries in Sub-Saharan Africa and has caused accidents in humans and dogs. In this study, we characterized some of the biochemical, toxic and immunogenic properties of N. annulifera venom. We showed that the venom is composed of several proteins, some of which display enzymatic activities, such as phospholipase A2, hyaluronidase, metalloproteinases and serine proteinases. The venom promoted disturbances in the human coagulation system and was cytotoxic to human epidermal cells. Using a mouse model, we showed that the venom promotes local reactions that were reduced with anti-inflammatory drugs. The venom caused systemic inflammation, lung hemorrhage and death. Further, the venom stimulated production of high antibody titers when injected into mice and the antiserum produced was able to inhibit venom-induced death. This study demonstrated that N. annulifera venom contains toxins that trigger inflammatory process, which may contribute to the envenomation pathology. Moreover, the venom is immunogenic, an important aspect for the production of an efficient N. annulifera antivenom.