A 24-hour exposure to bright blue light before surgery reduces inflammation and organ damage at the cellular level in mice, a new study shows.
The findings suggest that pre-treatment light therapy could improve outcomes for patients undergoing procedures that involve a period of blood restriction, such as liver resection or organ transplantation.
“We were incredibly surprised by our results,” says Matthew R. Rosengart, associate professor of surgery and critical care medicine at the University of Pittsburgh School of Medicine. “There’s long been evidence suggesting that light and circadian rhythms profoundly influence our biology, and specifically the physiological response to stress.
“So while we were expecting to find some correlation with light spectrum and the immune response, we were not expecting results quite so striking.”
Light is complex and consists of intensity, duration of exposure, and wavelength. The new study, published in the Proceedings of the National Academy of Sciences, is one of the first that accounts for this complexity and derives results that could guide future clinical trials in humans.
Researchers compared what happened when mice were exposed to red light, ambient white fluorescent light similar to that in hospitals, and high-intensity blue light 24 hours before kidney or liver surgery involving periods of blood restriction and restoration.
The high-intensity blue light outperformed the red and white light, attenuating cellular and organ injury through at least two cellular mechanisms. The blue light brought about a reduction in the influx of neutrophils, a type of white blood cell involved in inflammation, which can lead to organ damage and other problems.
It also inhibited dying cells from releasing a protein called HMGB1 that triggers organ-damaging inflammation.
They then tested whether the blue light was acting through the optic pathway or some other mechanism, like the skin. Blind mice had the same healing response regardless of whether they were exposed to blue or red light, indicating that the protective impact of blue light does, indeed, act through the optic pathway.
The team then looked at whether one color of light might disrupt the circadian rhythm, which is linked to immunity, more than another. Blood from mice exposed to red, white, and blue light had similar concentrations of melatonin and corticosteroid hormones. Furthermore, the mice under each of the lights also had similar activity levels. These data indicate the effects of blue light were not mediated by a disruption of sleep, activity, or circadian rhythms.
Rosengart stresses that mice are nocturnal animals with visual, circadian, and immune biology that is distinct from humans. So, the results of the study should not be broadly extended to patients or hospital settings until robust clinical trials have been performed to show whether or not pre-treatment with intensive blue light is safe.
Other researchers from University of Pittsburgh and from Central South University are coauthors of the study, which was funded by the National Institutes of Health.
Source: University of Pittsburgh