Snake antivenom serum proves to be three times more effective than the standard one

In Brazil, a group of researchers from the Federal University of São Paulo (UNIFESP) and the Butantan Institute have developed a new version of the antibothropic serum that is three times more effective than the version currently used to treat envenomation by snakes of the genus Bothrops, the jararaca (B. jararaca) being the most common.

The study is published in the Journal of Proteome Research.

“We combined classical techniques with the most modern ones to quantify and increase the proteins that neutralize the venom, as well as reducing other molecules that can cause side effects. As a result, we obtained a serum with increased action even in smaller quantities,” says Alexandre Tashima, professor at the university’s medical school (EPM-UNIFESP) and coordinator of the study.

Antivenom serums to combat snake poisoning have been produced for over a hundred years. A sublethal dose of venom is injected into large animals such as horses. The animal’s immune system then produces antibodies against the toxins present in the venom.

After a few days, doses of the now antibody-enriched blood are taken from the animal, processed and purified. The resulting product is called heterologous serum, the only scientifically proven treatment for snake poisoning.

However, not all of the components of the serum are antibodies that neutralize the venom. Studies by other groups indicate that only between 10% and 40% of the composition of anti-snake serums corresponds to proteins that target snake toxins.

Therefore, one of the first steps taken by Tashima’s group was to quantify these proteins in standard antibothropic serum. Using techniques such as affinity chromatography, surface plasmon resonance, and mass spectrometry, the researchers found that only 27.8% of the serum components interact with the toxins in jararaca venom.

Other non-specific antibodies make up a large portion of the remaining 72.2% of the serum. The second most abundant protein, accounting for 8.6% of the composition, was horse albumin.

Although it performs a number of important functions in mammals, albumin from one species can trigger an exacerbated response when it comes into contact with the immune system of another species.

“Although advances in purification have significantly reduced the incidence of adverse effects, they are still reported in 5% to 57% of cases. Most of these are due to the immune response to horse proteins such as albumin,” says Tashima.

Improved version

The researchers then subjected the standard antibothropic serum to a new purification phase. Using so-called affinity chromatography, the antibodies that bind to the venom were retained.

The new serum was then analyzed using the same techniques as the traditional serum. The improved version had 87% less albumin, while other proteins were reduced by between 37% and 83%.

Functional analysis showed that the new serum had a 2.9 times greater affinity for the toxins in the venom. In addition, poisoned mice treated with the new serum required a 2.8-fold lower dose to contain the toxins.

“This suggests that the improved serum has increased potency, requiring less serum to combat the same dose of poison. “This, together with the fact that it has fewer horse proteins, is a factor that could reduce the chances of adverse effects,” says Tassia Chiarelli, first author of the study, carried out during her master’s degree at EPM-UNIFESP.

The technologies used in this purification stage already exist and are widely used in the manufacture of other biopharmaceuticals. However, the clinical and regulatory research stages still must be completed before the research results can be translated into a new product.

Another factor on the horizon is the development of new technologies to treat snake poisoning, such as monoclonal antibodies. This is precisely the production of specific antibodies against the toxins. For example, monoclonal antibodies against SARS-CoV-2, the virus that causes COVID-19, are already on the market.

“The innovations we’re already seeing will probably lead to new treatments in the future. However, we’re aware of the time and cost of these innovations, which should mean that the heterologous serum will be used for a long time to come,” the researcher concludes.

Global estimates put the number of snakebite poisonings at over 5 million cases per year, with more than 100,000 deaths and 400,000 people disabled. Most of the victims are young rural workers and children from poor communities.

In 2017, the World Health Organization (WHO) reinstated snake poisoning to its list of neglected tropical diseases, a group of diseases that mainly affect poor people and receive little attention from the pharmaceutical industry.

The reinstatement is an incentive for the WHO itself, governments and humanitarian foundations to provide resources to NGOs, research groups and other organizations focused on reducing morbidity and mortality attributable to the problem.