Biology subjects

Bartlett, K. E.

Publications and source records attributed to Bartlett, K. E..

6 recordsLinked to original sources

bioRxiv2024

Snake venom metalloproteinases are predominantly responsible for the cytotoxic effects of certain African viper venoms

AbstractSnakebite envenoming is a neglected tropical disease that causes substantial mortality and morbidity globally. The puff adder (Bitis arietans) and saw-scaled viper (Echis romani) have cytotoxic venoms that cause permanent injury via tissue-destructive dermonecrosis around the bite site. Identification of cytotoxic toxins within these venoms will allow development of targeted treatments, such as small molecule inhibitors or monoclonal antibodies to prevent snakebite morbidity. Venoms from both species were fractionated using gel filtration chromatography, and a combination of cell-based cytotoxicity approaches, SDS-PAGE gel electrophoresis, and enzymatic assays were applied to identify venom cytotoxins in the resulting fractions. Our results indicated that snake venom metalloproteinase (SVMP) toxins are predominately responsible for causing cytotoxic effects across both venoms, but that the PII subclass of SVMPs are likely the main driver of cytotoxicity following envenoming by B. arietans, whilst the structurally distinct PIII subclass of SVMPs are responsible for conveying this effect in E. romani venom. Identification of distinct SVMPs as the primary cytotoxicity-causing toxins in these two African viper venoms will facilitate the future design and development of novel therapeutics targeting these medically important venoms, which in turn could help to mitigate the severe life and limb threatening consequences of tropical snakebite. Key ContributionSVMP toxins were identified as the primary cytotoxicity-causing toxins in the venoms of the puff adder (Bitis arietans) and saw-scaled viper (Echis romani); PII and PIII SVMPs, respectively. This cytotoxicity can be prevented using the metalloproteinase-inhibiting chelator EDTA, suggesting targeted drugs/antibodies may be a viable option for future treatment.

pharmacology and toxicology↗

bioRxiv2024

Intraspecific venom variation in the medically important puff adder (Bitis arietans): comparative venom gland transcriptomics, in vitro venom activity and immunological recognition by antivenom

BackgroundVariation in snake venoms is well documented, both between and within species, with intraspecific venom variation often correlated with geographically distinct populations. The puff adder, Bitis arietans, is found widely distributed across sub-Saharan Africa and into the Arabian Peninsula where it is considered a leading cause of the [~]310,000 annual snakebites across the region, with its venom capable of causing substantial morbidity and mortality. Despite its medical importance and wide geographic distribution, there is little known about venom variation between different B. arietans populations and the potential implications of this variation on antivenom efficacy. MethodologyWe applied a range of analyses, including venom gland transcriptomics, in vitro enzymatic assays and reverse phase chromatography to comparatively analyse B. arietans venoms originating from Nigeria, Tanzania, and South Africa. Immunological assays and in vitro enzymatic neutralisation assays were then applied to investigate the impact of venom variation on the potential efficacy of three antivenom products; SAIMR Polyvalent, EchiTAb-Plus and Fav-Afrique. FindingsThrough the first comparison of venom gland transcriptomes of B. arietans from three geographically distinct regions (Nigeria, Tanzania, and South Africa), we identified substantial variation in toxin expression. Findings of venom variation were further supported by chromatographic venom profiling, and the application of enzymatic assays to quantify the activity of three pathologically relevant toxin families. However, the use of western blotting, ELISA, and in vitro enzymatic inhibition assays revealed that variation within B. arietans venom does not appear to substantially impact upon the efficacy of three African polyvalent antivenoms. ConclusionsThe large distribution and medical importance of B. arietans makes this species ideal for understanding venom variation and the impact this has on therapeutic efficacy. The findings in this study highlight the likelihood for considerable venom toxin variation across the range of B. arietans, but that this may not dramatically impact upon the utility of treatment available in the region. Author SummaryThe puff adder (Bitis arietans) is found across sub-Saharan Africa and the Arabian Peninsula and is capable of causing life threatening pathology due to its potent venom. The extensive range of B. arietans exposes populations to different ecological pressures which may impact upon the composition of venom toxins. In this study, we examined the venom composition of B. arietans from three countries separated by large geographic distance: Nigeria, Tanzanian and South Africa. By integrating venom gland transcriptomes, venom chromatography, and in vitro functional assays to profile B. arietans venom composition, we uncovered extensive variation between the three locales. Given that venom variation can have a significant impact on the efficacy of antivenom treatment, we also investigated the ability of three African antivenoms to recognise and inhibit in vitro venom activity. Through these analyses, we were able to determine that venom variation did not have a substantial impact on the neutralising effect of selected antivenoms. This study has highlighted the potentially extensive venom variation found across the range of B. arietans and initiated valuable investigations into the efficacy of African antivenoms to protect human populations vulnerable to snakebite envenoming.

molecular biology↗

bioRxiv2023

Dermonecrosis caused by spitting cobra snakebite is the result of toxin potentiation and is prevented by the repurposed drug varespladib

Snakebite envenoming is a neglected tropical disease that causes substantial mortality and morbidity globally. The venom of African spitting cobras often causes permanent injury via tissue-destructive dermonecrosis at the bite site, which is ineffectively treated by current antivenoms. To address this therapeutic gap, we identified the aetiological venom toxins responsible for causing local dermonecrosis. While cytotoxic three-finger toxins were primarily responsible for causing spitting cobra cytotoxicity in cultured keratinocytes, their potentiation by phospholipases A2 toxins was essential to cause dermonecrosis in vivo. This evidence of probable toxin synergism suggests that a single toxin-family inhibiting drug could prevent local envenoming. We show that local injection with the repurposed phospholipase A2-inhibiting drug varespladib significantly prevents local tissue damage caused by several spitting cobra venoms in murine models of envenoming. Our findings therefore provide a new therapeutic strategy to more effectively prevent life-changing morbidity caused by snakebite in rural Africa. Significance StatementSpitting cobra venoms cause extensive local tissue damage surrounding the site of a snakebite. This damage cannot be effectively prevented with current antivenom treatments, and patients are often left with life-changing wounds. In this study we used cellular and mouse experiments to determine which toxins in African spitting cobra venom are responsible for causing tissue damage, revealing that a combination of two different types of toxins are required to cause pathology in vivo. We then showed that the repurposed drug, varespladib, which targets one of these toxin types, effectively prevents skin and muscle damage in mouse models of envenoming. Collectively these findings suggest that varespladib could be an effective new type of therapy for preventing snakebite morbidity in Africa.

pharmacology and toxicology↗

bioRxiv2023

Machine-learning guided Venom Induced Dermonecrosis Analysis tooL: VIDAL

Snakebite envenoming is a global public health issue that causes significant morbidity and mortality, particularly in low-income regions of the world. The clinical manifestations of envenomings vary depending on the snakes venom, with paralysis, haemorrhage, and necrosis being the most common and medically relevant effects. To assess the efficacy of antivenoms against dermonecrosis, a preclinical testing approach involves in vivo mouse models that mimic local tissue effects of cytotoxic snakebites in humans. However, current methods for assessing necrosis severity are time-consuming and susceptible to human error. To address this, we present the Venom Induced Dermonecrosis Analysis tool (VIDAL), a machine-learning-guided image-based solution that can automatically identify dermonecrotic lesions in mice, adjust for lighting biases, scale the image, extract lesion area and discolouration, and calculate the severity of dermonecrosis. We also introduce a new unit, the dermonecrotic unit (DnU), to better capture the complexity of dermonecrosis severity. Our tool is comparable to the performance of state-of-the-art histopathological analysis, making it an accessible, accurate, and reproducible method for assessing dermonecrosis. Given the urgent need to address the neglected tropical disease that is snakebite, high-throughput technologies such as VIDAL are crucial in developing and validating new and existing therapeutics for this debilitating disease.

pharmacology and toxicology↗

bioRxiv2022

Repurposed drugs and their combinations prevent morbidity-inducing dermonecrosis caused by diverse cytotoxic snake venoms

Morbidity from snakebite envenoming affects approximately 400,000 people annually. Tissue damage at the bite-site often leaves victims with catastrophic life-long injuries and is largely untreatable by currently available antivenoms. Repurposing small molecule drugs that inhibit specific snake venom toxins offers a potential new treatment strategy for tackling this neglected tropical disease. Using human skin cell assays as an initial model for snakebite-induced dermonecrosis, we show that the repurposed drugs 2,3-dimercapto-1-propanesulfonic acid (DMPS), marimastat, and varespladib, alone or in combination, reduce the cytotoxic potency of a broad range of medically important snake venoms up to 5.7-fold. Thereafter, using a preclinical murine model of dermonecrosis, we demonstrate that the dual therapeutic combinations of DMPS or marimastat with varespladib potently inhibit the dermonecrotic activity of three geographically distinct and medically important snake venoms. These findings strongly support the future translation of repurposed drug combinations as broad-spectrum therapeutics for preventing morbidity caused by snakebite.

pharmacology and toxicology↗

bioRxiv2020

A combination of two small molecule toxin inhibitors provides pancontinental preclinical efficacy against viper snakebite

Snakebite is a medical emergency causing high mortality and morbidity in rural tropical communities that typically experience delayed access to unaffordable therapeutics. Viperid snakes are responsible for the majority of envenomings, but extensive interspecific variation in venom composition dictates that different antivenom treatments are used in different parts of the world, resulting in clinical and fiscal snakebite management challenges. Here, we show that a number of repurposed Phase 2-approved small molecules are capable of broadly neutralizing distinct viper venom bioactivities in vitro by inhibiting different enzymatic toxin families. Furthermore, using multiple in vivo models of envenoming, we demonstrate that a single dose of a rationally-selected dual inhibitor combination consisting of marimastat and varespladib prevents lethality caused by venom from the most medically-important vipers of Africa, South Asia and Central America. Our findings strongly support the translation of combinations of safe and affordable enzyme inhibitors as novel broad-spectrum therapeutics for snakebite.

pharmacology and toxicology↗