Light Therapy Could Treat Vascular Constriction Diseases

A new study describes a receptor on blood vessels that cause them to relax in response to light, making it potentially useful in treating vascular diseases.

Researchers at Johns Hopkins University (JHU; Baltimore, MD, USA) used polymerase chain reaction (PCR) to demonstrate that melanopisn (Opn4, a member of a group of non-image-forming light receptors) is expressed in blood vessels in mice via a photorelaxation mechanism. Further force-tension myography tests in the mice tails demonstrated that vessels in mice that lacked Opn4 failed to display photorelaxation, which was also inhibited by an Opn4-specific small-molecule inhibitor.

The researchers also found that vasorelaxation is wavelength-specific, with a maximal response at about 430–460 nm. Blue light (455 nm) was found to regulate tail artery vasoreactivity ex vivo and tail blood blood flow in vivo, supporting a potential physiological role for this signaling system. The researchers also discovered that photorelaxation did not involve endothelial-, nitric oxide-, carbon monoxide-, or cytochrome p450-derived vasoactive prostanoid signaling, but was associated with vascular hyperpolarization. The study was published in the November 17, 2014, issue of Proceedings of the National Academy of Sciences of the United States of America (PNAS).

“If we can develop novel ways of delivering light to blood vessels, this molecular switch for relaxation could be harnessed in all types of vascular disease treatment,” said senior author Dan Berkowitz, MD, of the JHU departments of anesthesiology, critical care, and biomedical engineering. “We plan to use high-intensity light-emitting diodes (LEDs) incorporated into gloves as a potential mode of therapy for these patients. Additionally, socks with LEDs could be used in diabetic patients to potentially enhance blood flow and heal chronic ischemic ulcers.”

Melanopsin is also in found intrinsically photosensitive retinal ganglion cells, which do perceive light but are much slower to react to visual changes than the better-known rod and cone cells. They have been linked to a number of behavioral responses to light, including circadian photo-entrainment, light suppression of activity in nocturnal animals, and alertness in diurnal animals. Another type of melanopsin based receptor is involved in the association between light sensitivity and migraine pain.

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