Researchers at the University of Colorado Anschutz Medical Campus have found that intense light amplifies a specific gene — Period 2 (PER2) — that makes the metabolism of mice and humans more oxygen-efficient. This amplification could offer protection against injury to the heart muscle if the light therapy were given before high-risk cardiac and noncardiac surgery. The scientists sought to develop a cardio-protective strategy using light to target and manipulate the function of the PER2 gene, which is expressed in a circadian pattern in the part of the brain that controls circadian rhythms. They investigated intense light exposure protocols in mice and found that housing mice under intense light conditions (10,000 lux, full spectrum, UV filter, L (light):D (dark) phase 14:10 h) enhanced cardio-protection, which was reflected in a time-dependent decrease in infarct size and troponin levels. Mice that were blind, however, gained no cardio-protection when exposed to intense light, indicating a need for visual light perception. Next, the researchers investigated whether intense light had similar effects on healthy human volunteers. The subjects were exposed to 30 minutes of intense light — 10,000 lux— on five consecutive days. The light therapy increased PER2 levels in the human subjects as it did in mice. Plasma triglycerides, a surrogate for insulin sensitivity and carbohydrate metabolism, significantly decreased. Overall, the therapy improved metabolism. Intense light-mediated cardio-protection requires endothelial-specific PER2. Intense light-elicited PER2 transcriptionally reprograms the endothelium. Endothelial PER2 regulates respiration and barrier function during hypoxia. Courtesy of Cell Reports/Tobias Eckle et al. By amplifying the PER2 gene through light, the researchers found that it could protect cardiovascular tissues against low oxygen conditions like myocardial ischemia. They also discovered that the light increased cardiac adenosine, a chemical that plays a role in blood flow regulation. “We already knew that intense light can protect against heart attacks, but now we have found the mechanism behind it,” professor Tobias Eckle, M.D., said. Eckle said that the study showed, on a molecular level, that intensive light therapy could offer a promising strategy for treating or preventing low oxygen conditions like myocardial ischemia. “Giving patients light therapy for a week before surgery could increase cardio protection,” Eckle said. “Drugs could also be developed that offer similar protections based on these findings. However, future studies in humans will be necessary to understand the impact of intense light therapy and its potential for cardio-protection.” The research was published in Cell Reports (https://doi.org/10.1016/j.celrep.2019.07.020).