
Studies have shown that exposure to light of different colors, or wavelengths, can positively influence the immune and inflammatory response in conditions such as sepsis and ischemia. The results showed that exposure to red light reduced platelet aggregation and activation, preventing clot formation. This represents a new frontier in the treatment and prevention of thrombotic conditions such as stroke.
Venous thromboembolism (VTE) is a condition that occurs when a blood clot forms in a vein, affecting millions of people around the world each year. This condition is a leading cause of preventable death in hospitals, despite ongoing efforts to improve prevention protocols.
In addition to VTE, arterial thrombosis, which can lead to stroke and heart attack, is equally prevalent. The challenge with both conditions is that current treatments, such as blood thinners and thrombolytic therapies, are often delayed or not recommended due to the risk of excessive bleeding.
Research suggests that the risk of thrombotic events, such as stroke and myocardial infarction, may vary with the daylight cycle. Ambient light plays a crucial role in regulating a number of biological processes, such as cardiovascular balance, hormone secretion and metabolism, which follow the rhythms of day and night.

Previous studies have shown that exposure to light, especially blue light, can positively influence the immune and inflammatory response in conditions such as sepsis and ischemia-reperfusion.
These effects suggest that light may also influence blood clotting and the prevention of bleeding, especially during times of increased activity or risk of injury. The mechanisms underlying thrombosis, both arterial and venous, share common features, such as the interaction between the innate immune system and coagulation.
Platelets, which are blood cells responsible for clotting, interact with neutrophils (a type of immune cell), creating a link between inflammation and coagulation. These interactions follow a circadian rhythm, that is, they fluctuate throughout the day, which opens up a new possibility for intervention to prevent clot formation.

Given the potential impact of light on the immune system and coagulation, researchers at the University of Pittsburgh Medical School, USA, investigated how exposure to different wavelengths of light could affect thrombus formation.
They conducted experiments with mice exposed to ambient, blue and red light for 72 hours, measuring how this affected platelet aggregation and activation.
They also looked at how these changes could influence thrombus formation in mouse models of venous thromboembolism and stroke.
The results showed that exposure to red light, which has a longer wavelength, reduced platelet aggregation and activation. This means that platelets became less likely to clump together and form clots.
This exposure also led to changes in platelet metabolism and decreased the formation of neutrophil extracellular traps, which are structures that contribute to clot formation.

Prophylactic exposure to long-wavelength light reduces thrombogenesis. (A) Schematic of the middle cerebral artery (MCA) occlusion model. (B) Stroke burden (infarct volume, mm2) after MCA occlusion after exposure to filtered white (gray circles), red (red squares), or blue (blue triangles) light. (C) Raw images of mouse brains visually demonstrate the effects of different light exposures (white, red, and blue) on the extent of brain damage caused by middle cerebral artery (MCA) occlusion. These images help illustrate the difference in infarct size (area of brain damage). (D) Benderson score. The Benderson score is a scale used to assess the degree of neurological impairment after stroke. In this context, the scores indicate the severity of motor and behavioral deficits in mice after MCA occlusion. The figure shows that mice exposed to red light had better Benderson scores (indicating less neurological impairment) than those exposed to white or blue light, suggesting that red light may have a protective effect against the neurological impact of stroke.
To understand whether these findings in mice could apply to humans, the researchers looked at a group of cataract patients who had been fitted with special intraocular lenses during cataract surgery.
These lenses were designed to filter out shorter wavelength light, such as blue light, while allowing longer wavelength light, such as red light, to pass through.
The researchers followed these patients over an eight-year period, paying particular attention to the incidence of venous thromboembolism. They found that patients with these lenses, especially those with a history of cancer, had a reduced risk of developing venous thromboembolism.

The reduced risk of venous thromboembolism in these patients suggests that modifying light exposure, using lenses that filter certain wavelengths, may positively influence the risk of blood clot formation.
This supports the idea that light, and specifically its wavelength, may play an important role in regulating blood clotting and potentially preventing thrombotic conditions in humans.
These findings suggest that light therapy, especially red light, may be a promising approach to preventing thrombosis by interfering with the interactions between the immune system and coagulation.
This represents a new frontier in the treatment and prevention of thrombotic conditions, offering a potentially less risky alternative to conventional treatments involving anticoagulants.
READ MORE:
Alterations in visible light exposure modulate platelet function and regulate thrombus formationAndraska, Elizabeth A. et al.Journal of Thrombosis and Haemostasis, Volume 23, Issue 1, 123 - 138
Abstract:
Variations in light exposure are associated with changes in inflammation and coagulation. The impact of light spectra on venous thrombosis (VT) and arterial thrombosis is largely unexplored. To investigate the impact of altering light spectrum on platelet function in thrombosis. Wild-type C57BL/6J mice were exposed to ambient (micewhite, 400 lux), blue (miceblue, 442 nm, 1400 lux), or red light (micered, 617 nm, 1400 lux) with 12:12 hour light:dark cycle for 72 hours. After 72 hours of light exposure, platelet aggregation, activation, transcriptomic, and metabolomic changes were measured. The ability of released products of platelet activation to induce thrombosis-generating neutrophil extracellular trap formation was quantified. Subsequent thrombosis was measured using murine models of VT and stroke. To translate our findings to human patients, light-filtering cataract patients were evaluated over an 8-year period for rate of venous thromboembolism with multivariable logistic regression clustered by hospital. Exposure to long-wavelength red light resulted in reduced platelet aggregation and activation. RNA-seq analysis demonstrated no significant transcriptomic changes between micered and micewhite. However, there were global metabolomic changes in platelets from micered compared with micewhite. Releasate from activated platelets resulted in reduced neutrophil extracellular trap formation. Micered also had reduced VT weight and brain infarct size following stroke. On subgroup analysis of cataract patients, patients with a history of cancer had a lower lifetime risk of venous thromboembolism after implantation with lenses that filter low-wavelength light. Light therapy may be a promising approach to thrombus prophylaxis by specifically targeting the intersection between innate immune function and coagulation.
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