Renal effects of venoms of Mexican coral snakes Micrurus browni and Micrurus laticollaris

The potential of phenothiazinium dyes as cytotoxicity markers in cisplatin-treated cells

Assessing the in vitro toxicity of compounds on cell cultures is an important step during the screening of candidate molecules for diverse applications. Among the strategies employed to determine cytotoxicity, MTT, neutral red, and resazurin are commonly used. Methylene blue (MB), a phenothiazinium salt, has several uses, such as dye, redox indicator, and even as treatment for human disease and health conditions, such as malaria and methemoglobinemia. However, MB has only been sparsely used as a cellular toxicity indicator. As a viability indicator, MB is mostly applied to fixed cultures at high concentrations, especially when compared to MTT or neutral red. Here we show that MB and its related compounds new methylene blue (NMB), toluidine blue O (TBO), and dimethylmethylene blue (DMMB) can be used as cytotoxicity indicators in live (non-fixed) cells treated for 72 h with DMSO and cisplatin. We compared dye uptake between phenothiazinium dyes and neutral red by analyzing supernatant and cell content via visible spectra scanning and microscopy. All dyes showed a similar ability to assess cell toxicity compared to either MTT or neutral red. Our method represents a cost-effective alternative to in vitro cytotoxicity assays using cisplatin or DMSO, indicating the potential of phenothiazinium dyes for the screening of candidate drugs and other applications.

Cardiac Effects of Micrurus corallinus and Micrurus dumerilii carinicauda (Elapidae) Venoms and Neutralization by Brazilian Coralsnake Antivenom and Varespladib

In this work, we examined the action of two South American coralsnake (Micrurus corallinus and Micrurus dumerilii carinicauda) venoms on rat heart function in the absence and presence of treatment with Brazilian coralsnake antivenom (CAV) and varespladib (VPL), a potent phospholipase A₂ inhibitor. Anesthetized male Wistar rats were injected with saline (control) or a single dose of venom (1.5 mg/kg, i.m.) and monitored for alterations in echocardiographic parameters, serum CK-MB levels and cardiac histomorphology, the latter using a combination of fractal dimension and histopathological methods. Neither of the venoms caused cardiac functional alterations 2 h after venom injection; however, M. corallinus venom caused tachycardia 2 h after venom injection, with CAV (given i.p. at an antivenom:venom ratio of 1:1.5, v/w), VPL (0.5 mg/kg, i.p.) and CAV + VPL preventing this increase. Both venoms increased the cardiac lesional score and serum CK-MB levels compared to saline-treated rats, but only the combination of CAV + VPL prevented these alterations, although VPL alone was able to attenuate the increase in CK-MB caused by M. corallinus venom. Micrurus corallinus venom increased the heart fractal dimension measurement, but none of the treatments prevented this alteration. In conclusion, M. corallinus and M. d. carinicauda venoms caused no major cardiac functional alterations at the dose tested, although M. corallinus venom caused transient tachycardia. Both venoms caused some cardiac morphological damage, as indicated by histomorphological analyses and the increase in circulating CK-MB levels. These alterations were consistently attenuated by a combination of CAV and VPL.

The edematogenic effect of Micrurus lemniscatus venom is dependent on venom phospholipase A2 activity and modulated by non-neurogenic factors

Coral snakes mainly cause neurotoxic symptoms in human envenomation, but experimental studies have already demonstrated several pharmacological activities in addition to these effects. This investigation was carried out with the aim of evaluating (1) non-neurogenic mechanisms involved in the inflammatory response induced by Micrurus lemniscatus venom (MLV) in rat hind paws, (2) participation of PLA₂ in this response, and (3) neutralizing efficiency of commercial anti-elapid antivenom on edema. MLV promoted a rapid, significant increase in vascular permeability, influx of leukocytes, and disorganization of collagen bundles, as demonstrated by histological analysis. Several pretreatments were applied to establish the involvement of inflammatory mediators in MLV-induced edema (5 µg/paw). Treatment of animals with chlorpromazine reduced MLV-induced edema, indicating participation of TNF-α. However, the inefficiency of other pharmacological treatments suggests that eicosanoids, leukotrienes, and nitric oxide have no role in this type of edema formation. In contrast, PAF negatively modulates this venom-induced effect. MLV was recognized by anti-elapid serum, but this antivenom did not neutralize edema formation. Chemical modification of MLV with p-bromophenacyl bromide abrogated the phospholipase activity and markedly reduced edema, demonstrating PLA₂ participation in MLV-induced edema. In conclusion, the non-neurogenic inflammatory profile of MLV is characterized by TNF-α-mediated edema, participation of PLA₂ activity, and down-regulation by PAF. MLV induces an influx of leukocytes and destruction of collagen fibers at the site of its injection.

Partial efficacy of a Brazilian coralsnake antivenom and varespladib in neutralizing distinct toxic effects induced by sublethal Micrurus dumerilii carinicauda envenoming in rats

In this work, we report the efficacy of a combination of Brazilian therapeutic coralsnake antivenom (CAV) and varespladib (phospholipase A₂ inhibitor - VPL) in partially neutralizing selected toxic effects of Micrurus dumerilii carinicauda coralsnake venom in rats. Venom caused local myonecrosis and systemic neurotoxicity, nephrotoxicity, and hepatotoxicity within 2 h of injection. CAV and VPL administered separately failed to prevent most of these alterations. However, a combination of CAV plus VPL offered variable protection against venom-induced coagulation disturbances, leukocytosis, and renal and hepatic morphological alterations.

Snake Envenomation

SNAKE ENVENOMATION REPRESENTS AN IMPORTANT HEALTH PROBLEM IN much of the world. In 2009, it was recognized by the World Health Organization (WHO) as a neglected tropical disease, and in 2017, it was elevated into Category A of the Neglected Tropical Diseases list, further expanding access to funding for research and antivenoms. However, snake envenomation occurs in both tropical and temperate climates and on all continents except Antarctica. Worldwide, the estimated number of annual deaths due to snake envenomation (80,000 to 130,000) is similar to the estimate for drug-resistant tuberculosis and for multiple myeloma.^, In countries with adequate resources, deaths are infrequent (e.g., <6 deaths per year in the United States, despite the occurrence of 7000 to 8000 bites), but in countries without adequate resources, deaths may number in the tens of thousands. Venomous snakes kept as pets are not rare, and physicians anywhere might be called on to manage envenomation by a nonnative snake. Important advances have occurred in our understanding of the biology of venom and the management of snake envenomation since this topic was last addressed in the Journal two decades ago. For the general provider, it is important to understand the spectrum of snake envenomation effects and approaches to management and to obtain specific guidance, when needed.

In vivo treatment with varespladib, a phospholipase A2 inhibitor, prevents the peripheral neurotoxicity and systemic disorders induced by Micrurus corallinus (coral snake) venom in rats

In this study, we investigated the action of varespladib (VPL) alone or in combination with a coral snake antivenom (CAV) on the local and systemic effects induced by Micrurus corallinus venom in rats. Adult male Wistar rats were exposed to venom (1.5 mg/kg - i.m.) and immediately treated with CAV (antivenom:venom ratio 1:1.5 'v/w' - i.p.), VPL (0.5 mg/kg - i.p.), or both of these treatments. The animals were monitored for 120 min and then anesthetized to collect blood samples used for haematological and serum biochemical analysis; after euthanasia, skeletal muscle, renal and hepatic tissue samples were collected for histopathological analysis. M. corallinus venom caused local oedema without subcutaneous haemorrhage or apparent necrosis formation, although there was accentuated muscle morphological damage; none of the treatments prevented oedema formation but the combination of CAV and VPL reduced venom-induced myonecrosis. Venom caused neuromuscular paralysis and respiratory impairment in approximately 60 min following envenomation; CAV alone did not prevent the neurotoxic action, whereas VPL alone prevented neurotoxic symptoms developing as did the combination of CAV and VPL. Venom induced significant increase of serum CK and AST release, mostly due to local and systemic myotoxicity, which was partially prevented by the combination of CAV and VPL. The release of hepatotoxic serum biomarkers (LDH and ALP) induced by M. corallinus venom was not prevented by CAV and VPL when individually administered; their combination effectively prevented ALP release. The venom-induced nephrotoxicity (increase in serum creatinine concentration) was prevented by all the treatments. VPL alone or in combination with CAV significantly prevented the venom-induced lymphocytosis. In conclusion, VPL shows to be effective at preventing the neurotoxic, nephrotoxic, and inflammatory activities of M. corallinus venom. In addition, VPL acts synergistically with antivenom to prevent a number of systemic effects caused by M. corallinus venom.

Phosphodiesterase-5 inhibitor sildenafil attenuates kidney injury induced by Bothrops alternatus snake venom

Acute kidney injury pathogenesis in envenoming by snakes is multifactorial and involves immunologic reactions, hemodynamic disturbances, and direct nephrotoxicity. Sildenafil (SFC), a phosphodiesterase 5 inhibitor, has been reported to protect against pathological kidney changes.

OBJECTIVE

This study aimed to investigate the protective effect of sildenafil against Bothrops alternatus snake venom (BaV)-induced nephrotoxicity.

METHODS

Kidneys from Wistar rats (n = 6, weighing 260-300 g) were isolated and divided into four groups: (1) perfused with a modified Krebs-Henseleit solution (MKHS) containing 6 g% of bovine serum albumin; (2) administered 3 μg/mL SFC; (3) perfused with 3 μg/mL BaV; and (4) administered SFC + BaV, both at 3 μg/mL. Subsequently, the perfusion pressure (PP), renal vascular resistance (RVR), urinary flow (UF), glomerular filtration rate (GFR), and percentage of electrolyte tubular sodium and chloride transport (%TNa⁺, %TCl^-, respectively) were evaluated. The cyclic guanosine monophosphate (cGMP) levels were analyzed in the perfusate, and the kidneys were removed to perform oxidative stress and histopathological analyses.

RESULTS

All renal parameters evaluated were reduced with BaV. In the SFC + BaV group, SFC restored PP to normal values and promoted a significant increase in %TNa⁺ and %TCl^-. cGMP levels were increased in the SFC + BaV group. The oxidative stress biomarkers, malondialdehyde (MDA) and glutathione (GSH), were reduced by BaV. In the SFC + BaV group, a decrease in MDA without an increase in GSH was observed. These findings were confirmed by histological analysis, which showed improvement mainly in tubulis.

CONCLUSION

Our data suggest the involvement of phosphodiesterase-5 and cGMP in BaV-induced nephrotoxicity since its effects were attenuated by the administration of SFC.