New research suggests a new way to prevent a tick-borne bacterial infection that most antibiotics just can’t seem to do. Treatment uses tiny molecules, which are called nanobodies, which are created to mimic antibody structures and functions to block the disease.
Known as human monocytic ehrlichiosis (HME), this infection is the most known and potentially life-threatening of all tick-borne disease within the United States. Symptoms normally begin with feeling like you’re coming down with the flu, and if left untreated, in rare cases, it can even lead to death.
What makes it difficult to treat is because most antibiotics aren’t sufficient or at a high enough concentration to actually kill the Ehrlichia chafeensis, which is the infection-causing bacteria that determines it. This is mostly due to the microbes that live in and multiply within the human immune cells. Unlike other common bacterial pathogens or diseases like E. colior Streptococcus, which impart their damage outside of human or hosts cells, rather than within.
During a study at Ohio State University, a research group developed nanobodies precisely meant to target the protein that’s known to make the E. chaffeensis bacteria infectious. Throughout a series of experiments done in mice and cell cultures, the results showed that there was one particular nanobody they had developed in the lab that managed to stop the infection by blocking the protein in the three ways that allows the bacteria to penetrate and take over the immune cells.
Professor of veterinary biosciences at Ohio State and the study lead author, Yasuko Rikihisa, explains, “If multiple mechanisms are blocked, that’s better than just stopping one function, and it gives us more confidence that these nanobodies will really work.”
Although the study has proven to add valuable insight and support for the possibility of nanobody-based ehrlichiosis treatment, experts still say that much more research is still required before this type of treatment could be used on humans. The team also published their research recently in Proceedings of the National Academy of Sciences.
The current treatment available is the antibiotic doxycycline, which is why there is some urgency in finding other alternatives. Part of the issue is that broad-spectrum antibiotics are generally unsafe for children and pregnant women due to their ability to cause extreme side effects.
Rikihisa shares, “With only a single antibiotic available as a treatment for this infection, if antibiotic resistance were to develop in these bacteria, there is no treatment left. It’s very scary.”
The Start of New Treatment Breakthrough
The ehrlichiosis bacteria is actually part of the obligatory intracellular bacteria family. In order to survive, the E. chaffeensis needs to have internal access to a cell while blocking the ‘host cell’s ability to program their own death with a function called apoptosis – which would kill the bacteria.’
According to Rikihisa, “Infected cells normally would commit suicide by apoptosis to kill the bacteria inside. But these bacteria block apoptosis and keep the cell alive so they can multiply hundreds of times very rapidly and then kill the host cell.”
Professor Rikihisa has been a specialist on the Rickettsiales family of bacteria for a very long time, which is where the E. chaffeensis falls under. Back in the 1980s, Rikihisa managed to create the exact culture conditions in the lab that allowed the bacteria to properly grow. In the process, a dozen discoveries were made that explain the way these diseases work. One such finding was the ‘identification of proteins that help E. chaffeensis block immune cells’ programmed cell death.’
With the help of Jeffrey Lakritz, who also happens to be a professor of veterinary medicine at Ohio State, the researchers amalgamated one protein called Etf-1 in order to develop a vaccine-style agent which they used to immunize a llama. Lamas, alpacas and camels are known to make single-chain antibodies that ‘include a large antigen binding site on the tip.’
They then cut apart some segments of that same binding site in order to make a library of nanobodies that had the potential to work as antibodies that know how to recognize and adhere to Etf-1 protein in order to block or stop the infection caused by E. chaffeensis.
According to Rikihisa, “They function similarly to our own antibodies, but they’re tiny, tiny nano-antibodies. Because they are small, they get into nooks and crannies and recognize antigens much more effectively. Big antibodies cannot fit inside a cell. And we don’t need to rely on nanobodies to block extracellular bacteria because they are outside and accessible to ordinary antibodies binding to them.”
After evaluating the candidates to see how effective they were, the research team found a single nanobody that ‘attached to Eft-1 in cell cultures and inhibited three of its functions.’ The team was able to make nanobodies in the E. coli cells’ fluids, which Rikihisa said her lab could then produce at an industrial scale and pace if required, by packing them by the millions in just a small drop.
In collaboration with co-author and professor of chemistry and biochemistry at Ohio State, Dehua Pei, they combined ‘the tiny molecules with a cell-penetrating peptide that enabled the nanobodies to be safely delivered to mouse cells.’
They took mice that had weakened immune systems and immunized them with a very deadly strain of E. chaffeensis. After, they gave it intracellular nanobody treatments on the first and second day after the infection. As compared to the mice that were given control treatments, those that were given the highest effective nanobody displayed substantially lowered levels of bacteria within two weeks from the time of infection.
The study managed to prove the principle that nanobodies have the ability to inhibit E. chaffeensis infection when targeting a single protein. And yet Rikihisa also said that there are a number of other targets that may give even more protection when nanobodies are delivered alone, or when they are given in combination. The lead author also claims that this study can also be widely relevant and suitable when it comes to other intracellular diseases.
She said, “Cancers and neurodegenerative diseases work in our cells, so if we want to block an abnormal process or abnormal molecule, this approach may work.”
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