In mice and rat models with spinal cord injury, the molecule led to recovery of sensory, motor functions

Spinal cord injury can now be repaired using a small molecule (TTK21) synthesised by a team led by Tapas Kumar Kundu from the Molecular Biology and Genetics Unit at Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bengaluru, a study has found. The small molecule tested both on mice and rat models promoted regeneration and growth of new sensory and motor axons leading to recovery of sensory and motor functions in the animals with spinal cord injury.

Since the small molecule cannot cross the blood–brain barrier and enter the brain, the researchers used 400 nanometre-size carbon nanospheres made using glucose, which is self-fluorescent, and attached the molecule to its surface. The non-toxic nature of the small molecule has already been demonstrated in animals.

The JNCASR researchers in collaboration with a French team had in October 2018 used the same molecule to recover long-term memory in mice with Alzheimer’s disease.

When the spinal cord is injured, the tails (axons) of nerve cells that stretch up and down the spine are either damaged or even completely cut. So signals from the brain can no longer travel beyond the site of injury when axons are severed, leading to paralysis.

According to anecdotal evidence, people with an active lifestyle have greater chances of recovering after spinal cord injury compared with those who are not active. Researchers tested this on animals by providing them with a larger cage, more mice to interact with, exercise (running) wheel, unidentified objects before inflicting an injury to the spinal cord. The environmental, physical or social stimuli were priming the cells and boosting their potential to regenerate such that five weeks after spinal injury, the damaged nerve fibres regenerated at the site of injury. Some axons regenerated so well that they expanded beyond the lesion site.

This finding in animal models prompted the researchers to investigate the underlying molecular mechanism to identify a therapeutic target to achieve recovery after spinal injury. They found that post spinal cord injury, animals that were earlier exposed to different stimuli expressed changes in the Cbp enzyme–mediated acetylation. This change brought about by the enzyme caused an increase in the expression of a set of genes associated with regeneration and growth of axons.

Even in the case of their previous work where new neurons are produced which help in recovering long-term memory in mice with Alzheimer’s, a similar set of genes are activated by the Cbp enzyme. “Modification in the level of Cbp–mediated acetylation plays an important role in several biological phenomena including memory recovery, making new neurons as well as extending the length of the axons which connect the injured neurons,” says Prof. Kundu, presently the Director of CSIR-Central Drug Research Institute, Lucknow.

“Mimicking the regenerative effect of environmental stimuli, we wanted to test if our small molecule could activate the Cbp enzyme and promote axon regeneration and recovery,” says Akash K. Singh, a PhD student at JNCASR and co-author of a paper published in the journal Science Translational Medicine.

In trials carried out in mice and rats, the small molecule injected four hours after the injury and once a week for five weeks resulted in regeneration and growth of axons at the site of injury. “The extent of regeneration and functional recovery of axons was nearly the same in both mice and rats. This proved our small molecule has a therapeutic effect,” says Dr. Sarmistha H. Sinha, post-doctoral fellow from JNCASR and co-author of the paper.

Behavioural tests

“Behavioural tests showed the mice could walk with fewer falls and slips due to imbalance. The number of times the animals slipped reduced with time. And on the floor, mice were also able to walk normally on the floor without limping,” says Prof. Kundu. “And the mice were able to quickly sense and remove the adhesive stuck to the hindpaws indicating recovery. When animals are paralysed they fail to sense the presence of the tape.”

“Along with the Imperial College London, we are exploring the possibility of conducting pre-clinical trials and jointly develop the molecule for therapeutic use in humans,” Prof. Kundu says.