Researchers have found that oxidative stress and biomarkers increased neurotoxicity in tadpoles exposed to severe coronavirus respiratory syndrome 2 (SARS-CoV-2) spike protein peptides.
SARS-CoV-2, the causative pathogen of coronavirus 2019 (COVID-19), is spread mainly by ingestion of virus droplets from an infected person. However, the virus can live on different surfaces (also known as ‘fomites’) for several days. Contact with such a contaminated surface can also spread virus.
Environmental transmission of the virus can occur through indirect contact with the urine or stool of infected people. Studies around the world have found that the virus contains ribonucleic acid (RNA) in sewage and waste water. So household waste from hospitals and large buildings can catch the virus and its ecotoxicological effect is not yet known.
Therefore, there is an urgent need to study the impact of the virus on aquatic organisms living close to such spreads. However, there are almost no aquatic animal models to test and understand the effects of the virus on aquatic spines.
SARS-CoV-2 increased oxidative stress in tadpoles
To study how SARS-CoV-2 affects aquatic animals, a team of researchers used previously developed synthetic peptides of SARS-CoV-2 spike proteins to study the its effect on tadpoles Physalaemus cuvieri. The team published their results in the bioRxiv * preprint server.
The tadpole is found in freshwater throughout Brazil and South America and has a stable and abundant population. Previous studies have used this animal to study the effects of water pollution.
The authors divided the tadpoles into seven groups of 50 animals each, including a control group. They put two different concentrations of the three synthetic spike protein peptides into water and kept the tadpoles in the spike water for a day. Using biomarkers for oxidative stress and neurotoxicity, they evaluated the toxic effects of the virus on the tadpoles. The team also estimated the relationship and binding mode of the synthesized peptides with the oxidative stress and neurotoxic biomarkers using chemoinformatic scratches and molecular docking simulations.
The teams found major biochemical changes in the tadpoles exposed to two of the peptides after 24 h. They found an increase in the production of nitrite and hydrogen peroxide, reflecting an increase in oxidative stress processes in the animals. They also found an increase in the levels of the enzymes catalase and superoxide dismutase, which are antioxidants produced against oxidative stress.
These results agree with previous studies that have shown that SARS-CoV-2 can induce oxidative stress in disease and show that the peptides can induce metabolic changes in the tadpoles.
The antioxidant levels extracted were insufficient to counteract oxidative stress. The authors hypothesize that this may be due to the fact that the peptides caused functional changes and were related to the antioxidant enzyme; this idea is supported by molecular docking simulations. The increase in nitrite may be due to a normal response to SARS-CoV-2 by the immune system, thus an increase in the proinflammatory cytokines.
Neurotoxicity in tadpoles
The authors evaluated neurotoxicity in the animals by measuring acetylcholinesterase (AChE), an indicator for cholinergic action. At the higher concentration, all peptides caused increased AChE production, ranging from 200% to 700%.
This result differs from previous studies, which reported an increase in AChE production, possibly due to the reduction in neurotransmission damage and oxidation. The results seen in the tadpoles may be due to activity on the cholinergic anti-inflammatory pathway. This is seen as helping to prevent inflammatory conditions in animal models and the pathway can control inflammation by releasing the neurotransmitter acetylcholine. This mechanism has also been reported in COVID-19 patients.
The activity of the cholinergic system of the tadpoles may be the result of the direct interaction of the peptides with AChE. Molecular docking analysis showed that there is a strong relationship between the two. However, more studies are needed to determine whether this interaction altered the binding and catalysis mechanism or increased enzyme efficiency due to increased substrate relationship with the active site.
Thus, the results indicate that SARS-CoV-2 protein fragments have a strong adverse effect on tadpoles. However, many questions remain about the impact of the virus on the aquatic environment, such as the effects of prolonged exposure, the impact on other animal models, and other toxic biomarkers, which can be addressed in future studies. This knowledge can help to understand the impact of SARS-CoV-2 on the environment and the ecosystem.
* Important message
bioRxiv publish preliminary scientific reports that are not peer-reviewed and, therefore, should not be seen as final, guiding health-related clinical practice / behavior, or be treated as information established.