Tityus serrulatus, the Yellow scorpion, causes more deaths than any other venomous animal in Brazil. Its sting can induce heart attack and pulmonary edema, especially in children and the elderly. According to the Brazilian Health Ministry, more than 156,000 cases of scorpion envenomation, 169 fatal, were reported in the country in 2019.
Researchers at the University of São Paulo (USP) have demonstrated for the first time that in severe cases of scorpion envenomation a systemic neuroimmune reaction produces inflammatory mediators leading to the release of neurotransmitters. A paper reporting the results of their study is publishedin Nature Communications. It suggests the inflammatory process can be inhibited by administration of a corticosteroid almost immediately after the patient is stung.
Besides local inflammation that causes acute pain but does not lead to death, scorpion venom may also trigger a systemic inflammatory reaction resulting in pulmonary edema (excess fluid in the lungs), heart failure and shortness of breath.
"Although a previous study by our group described the inflammatory mechanism that leads to pulmonary edema and death in severe cases, the impact of envenomation on the heart and the link between neurotransmitters and inflammatory mediators weren't entirely elucidated," said Lúcia Helena Faccioli, a professor at USP's Ribeirão Preto School of Pharmaceutical Sciences and principal investigator for the study. "There was no consensus as to whether neurotransmitters or inflammatory mediators were the villains, and whether pulmonary edema leads to cardiac alterations or the other way around. This study suggests inflammatory mediators produced in the lungs not only induce pulmonary edema but also affect the heart via neurotransmitters. The inflammatory process causes various kinds of damage and can lead to death unless it's blocked very swiftly."
The study was conducted with São Paulo Research Foundation—FAPESP's support during the Ph.D. research of Mouzarllem Barros dos Reis as part of a Thematic Project for which Faccioli is principal investigator.
This was an in vitro and in vivo study in mice focusing on an investigation of the inflammatory process triggered by envenomation and its association with neurotransmitters. The scorpion venom spreads rapidly from the sting site into the bloodstream. In severe cases, recognition of the venom by macrophages (immune cells) results in the release of inflammatory mediators, especially interleukin-1beta (IL-1β), leading to release of prostaglandin E2 (PGE2), which in turn induces production of the neurotransmitter acetylcholine. Produced in the lungs, these mediators cause both pulmonary edema and cardiac alterations.
"The mediators produced in the lungs in response to the venom activate production of acetylcholine, a neurotransmitter that has a strong effect on the heart due to its association with the control of cardiac muscle tone," Faccioli explained. "This neurotransmitter makes the heart beat irregularly. In one and the same process we have pulmonary edema and heart disturbances."
In a previous study, published in 2016, the same research group showed that pulmonary edema resulted from release of IL-1β due to activation of the inflammasome, a protein complex present in immune cells, and that regulation of this process by lipidic mediators involves activation by PGE2 and inhibition by leukotriene B4 (LTB4). It remained to demonstrate the neuroimmune interaction and the key role played by acetylcholine.
Rapid inhibition of the neuroimmune processThe study also highlighted the need to inhibit the neuroimmune process triggered by inflammatory mediators as quickly as possible, so that the patient does not reach the "point of no return", when the effects of the mediators are so critical that improvement is no longer possible.
"We demonstrated that administration of the anti-inflammatory corticosteroid dexamethasone not more than 30 minutes after envenomation can avoid death in mice," Faccioli said. "The aim was to block the inflammatory process before it became irreversible. It's important to note that this study used a murine model and the time to the point of no return can't be extrapolated for humans."
Almost immediate administration of the drug does not avert the need for antivenom. "Dexamethasone will block the process that releases acetylcholine and mitigate damage to the lungs and heart. The antivenom is important to inhibit other possible effects of the toxins that may damage tissues and other parts of the organism," Faccioli said.
"In previous studies, we showed that indomethacin and celecoxib can prevent or at least minimize the inflammatory reaction triggered by envenomation, and avoid death. However, these drugs may not be effective for all patients.
Dexamethasone is far more efficient, despite possible adverse side-effects for a small proportion of patients." Improper use of corticosteroids can entail significant risks to the organism. Dosage and the duration of treatment should be prescribed by a physician.
Previous research by Faccioli and her group also showed that venom from the pit viper Bothrops moojeni and the South American rattlesnake Crotalus durissus terrificus contains lipids as well as toxins (i.e. proteins and polypeptides), potentially explaining several biological effects of envenomation.
"The presence of lipids points to a biological function," Faccioli said. "Biochemical analysis of pit viper and rattlesnake venom showed that one of the lipids resembled platelet aggregation factor [PAF], so thrombus formation after a snake bite may be due to the presence of these lipids. This is typically what follows a snake bite: blood clotting and thrombosis."
This study, published in Archives of Toxicology, extended scientists' understanding of the mechanisms that lead to complications of envenomation. "The PAF-like lipid is also important to induce inflammation," Faccioli said.
The analysis was based on ultra high performance liquid chromatography and mass spectrometry using equipment funded by FAPESP that enabled the scientists to identify several lipids for the first time in snake venom.
It was conducted as part of the postdoctoral research of Tanize dos Santos Acunha, with FAPESP's support via the Thematic Project mentioned earlier.
Faccioli explained that venom is a complex substance comprising molecules with several biological functions that cause local and systemic manifestations. A great deal of research has been done on venom composition and effects, but most studies focus on the toxins and ignore or are unaware of the lipids.
More information: Mouzarllem B. Reis et al, Interleukin-1 receptor-induced PGE2 production controls acetylcholine-mediated cardiac dysfunction and mortality during scorpion envenomation, Nature Communications (2020). DOI: 10.1038/s41467-020-19232-8
Journal information: Nature Communications
Provided by FAPESP