27 September 2013

Defibrillators and pacemakers might soon use light instead of electricity to restart your heart

Closed-chest electric defibrillators - i.e. the normal defibrillators that you usually see on TV - have been around for decades. They can be effective at restoring normal heart rhythm, but come at a price: even with fine-tuned pulse shapes and sequences, they are typically very painful when active. Researchers have been looking to scrap these devices altogether by switching to a softer, smarter technology that instead uses light to activate special, genetically engineered light-sensitive stem cells that have been grafted to the heart.

Detailed computer models of the heart have played a huge role in defibrillator technology. By stimulating in the right place at the right time, much less current needs to be used, and inconveniences like external burn marks have largely become a thing of the past. Using these models, it is possible to pinpoint where to add the new light-sensitive cells, and how many must be used to achieve a desired effect. If compared to packets of explosives, the placement of these modified cells might be likened to clearing the slopes of avalanches before a ski resort opens for the day - you want full activation, but don’t want to blow the works to bits.

A team of researchers from Johns Hopkins recently published a paper in Nature Communications where they describe what they call “multiscale models” for opto-cardiac modulation. Their models take much of the mystery out of light source delivery, and subsequent scattering within tissues. These issues have been the traditional bugbears of the technology when attempts have been made to apply it to the brains of larger animals. Another group of researchers, from Stanford, have already moved beyond modelling and are preparing to test these ideas in real tissues. They have just received a $600,000 grant award from NSF to develop these technologies. Perhaps just as importantly, the larger concept is to segue the technology into other major organ systems. Stanford is where the original optogenetic experiments in the brain were done by Karl Deisseroth’s lab in 2005. The original cellular-optic switch they developed there has since blossomed into a complete toolkit of proteins that are responsive at many different wavelengths, and able to ramp cell voltages either up or down. These now allow for the selective activation of proteins within the same tissue volume.

More than four million Americans have some significant degree of heart rhythm abnormality, and there are many more with subclinical conditions that would benefit tremendously from an optogenetic retrofit. Once the heart is no longer the limiting factor in the lifestyle of any given senior, the next weak link in the activity chain may also be assisted optogenetically. Switching on natural insulin or energy sources have already been proposed, and other applications await. Light-activated collagens or other proteins in the muscles and joints might be fair game, as would be targeting the peripheral nerves that activate them, and similarly return the emissaries of pain when we overextend. The success of optogenetics in the lab, where new memories have been both created and destroyed in mammalian brains, suggests that similar finesse in other organs will soon follow.

Research paper: doi:10.1038/ncomms3370 – “A comprehensive multiscale framework for simulating optogenetics in the heart”

Now read: Regenerated human heart tissue beats on its own, leads towards replacement hearts and other organs


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