Engineered Nanobody Blocks Cholera Toxin, Offers New Hope Against Diarrhea.

Since 1961, the world has been grappling with a persistent cholera pandemic. In 2022, cases surged again, highlighting the limitations of current prevention tools. Caused by the bacterium Vibrio cholerae, cholera is best known for causing intense, watery diarrhea triggered by the cholera toxin (CTX). While oral vaccines exist, demand has outstripped supply, especially in outbreak-prone areas, prompting the search for alternative defenses.

One promising route is the use of single-domain antibodies, also known as VHHs or nanobodies. Found in animals like camels, llamas, and alpacas, these antibodies differ from typical human antibodies by consisting solely of heavy chains. Their small size, high specificity, and resilience in the gut environment make them especially attractive for oral delivery.

A recent collaborative effort among the Technical University of Denmark, Harvard Medical School, and the biotech company Bactolife has led to the creation of an orally administered VHH protein that targets CTX. The research team, led by Marcus Petersson and Sandra Wingaard Thrane, engineered a protein that blocks the toxin’s interaction with intestinal receptors, effectively halting the chain reaction that causes diarrhea. Their findings, published in Nature Communications, propose that this protein could act as a dietary supplement to help manage cholera symptoms.

CTX comprises five B-subunits (CTXB), which latch onto the GM1 ganglioside receptors on gut cells, and a single A-subunit that enters the cells and triggers the disease’s characteristic symptoms. The researchers focused on stopping the CTXB–GM1 interaction. To do this, they immunized two alpacas with CTXB and created a library of VHHs, screening for the most effective binders.

Among several strong candidates, one nanobody stood out: BL3.1, a monovalent binder. To improve its efficacy, the team connected two BL3.1 units to form a bivalent version, BL3.2, which showed greater affinity. BL3.2 remained stable in simulated stomach conditions and successfully prevented CTX from binding to GM1 in human intestinal cell assays.

Encouraged by the lab results, the team tested BL3.2 in infant mice, a suitable model for mimicking human cholera due to their undeveloped immune systems. Mice that received oral doses of BL3.2 before and after CTX exposure exhibited no diarrhea, lost less weight, and showed reduced fluid buildup compared to untreated controls.

Further testing with a 2022 clinical isolate of V. cholerae confirmed that BL3.2 offered similar protection. Notably, mice treated with the protein also had ten times fewer bacteria colonizing their intestines, suggesting that the nanobody may reduce infection severity beyond just neutralizing the toxin.

Michiel Harmsen, a consultant experienced in VHH-based therapies, praised the increased potency of the bivalent design and speculated whether toxin aggregation, rather than receptor blocking alone, could contribute to its effect. This opens the door to additional investigations into how these proteins work at the molecular level.

Looking ahead, the researchers aim to optimize dosing and explore applications against other gut pathogens. “This represents an exciting new tool—not only to protect against diarrheal outbreaks, but also to deepen our understanding of bacterial pathogenesis,” said Thrane.

Source:https://www.the-scientist.com/new-cholera-toxin-binding-protein-stops-diarrhea-in-its-tracks-73059

This is non-financial/medical advice and made using AI so could be wrong.