Clare Wilson : New Scientist : 10 Jul 2015
The effect on cells of near-infrared light, which has a wavelength of 670 nanometres, was first reported 40 years ago. The light causes mitochondria, the cell's powerhouses, to produce more ATP, a compound that provides the cell's energy. Until now, the best explanation was that an important respiration enzyme called cytochrome C is affected by the near-infrared energy, but we now know that it doesn't absorb light at quite the right frequency.
Thinner than water
The work from Sommer's team now points at the water within the cell. Normally the layer of water next to any solid object has high surface tension, making it viscous. "It's like molasses," says Sommer. His team found that when surface layers of water are illuminated with the red light, it increases the distance between each water molecule, making the liquid become "runnier".
Mitochondria are powered by an enzyme bound into their membranes. It spins like a molecular turbine, and being surrounded by runnier water should make it turn more easily, generating more ATP. Because it is hard to measure water inside a living cell, the team measured the effect of near-infrared light on thin layers of water by examining the friction on a diamond probe as it pushed through water and into a metal block (see picture above). Illuminating the water cut the force needed to push in the probe by 72 per cent.
"It's highly significant," says Horst-Dieter Försterling of the Philipp University of Marburg in Germany. "This is the first explanation of how the light might work."
Healing with light
Other research groups are investigating this phenomenon as a way to speed up the healing of skin wounds and to repair burns to the eye. It may also be able to reduce pain and inflammation in tissues underneath the skin. Others are investigating whether red light shone into mice's heads using fibre optics can help with Parkinson's disease.
A better understanding of how red light affects cells should make it easier to expand its medical uses, says Sommer. "If we start from an incorrect model then everything is trial and error." One of the next applications could be in helping couples undergoing IVF because of problems with male fertility. Some men's sperm do not have enough energy to fertilise an egg in a lab, even though they only have to swim 1 millimetre to reach it, says IVF doctor Friedrich Gagsteiger of the Fertility Centre in Ulm.
Gagsteiger has previously investigated other ways of giving sperm more oomph, such as using caffeine - which does make them swim faster but also seems to be toxic. Gagsteiger is now starting tests of irradiating sperm with the near-infrared light before fertilisation. "We hope this will increase the chance of the sperm finding the eggs," he says.
Journal reference: Scientific Reports, DOI: 10.1038/srep12029