# Systemic Effects of Vascular Photobiomodulation on Early Macrophage Recruitment During Skeletal Muscle Repair

## TL;DR

This study shows that a non-invasive light therapy can speed up muscle repair by influencing immune cells called macrophages.

## Contribution

The novel finding is that preventive vascular photobiomodulation accelerates macrophage recruitment and pro-regenerative inflammation after muscle injury.

## Key findings

- Preventive VPBM increases early CD68+ macrophage recruitment and CD206+ polarization.
- VPBM promotes a pro-regenerative inflammatory response, potentially improving tissue repair.
- Therapeutic VPBM application shows delayed macrophage resolution compared to preventive use.

## Abstract

Muscle injuries involve a complex inflammatory response in which macrophages are essential for proper tissue repair. Dysregulation of this process can impair regeneration. This study investigated the effects of vascular photobiomodulation (VPBM), a non‐invasive therapy applied via the caudal vein/artery, on macrophage dynamics in acute skeletal muscle injury. Wistar rats were divided into Control, Injury, Pre‐VPBM+Injury, and Injury+Post‐VPBM groups. VPBM (780 nm, 40 mW, 3.2 J) was applied preventively or therapeutically. Animals were euthanized on days 1, 2, 5, and 7 post‐injury for CD68+ and CD206+ immunostaining. CD68+ cells peaked on day 1 in the Pre‐VPBM+Injury group, while the Injury group maintained higher levels at day 7. CD206+ cells were elevated early in both VPBM groups, especially Pre‐VPBM. On day 7, CD206+ remained higher in the Injury group, indicating delayed resolution. In summary, the study demonstrates that preventive VPBM application accelerates macrophage recruitment and promotes a pro‐regenerative inflammatory response.

Preventive vascular photobiomodulation accelerates macrophage recruitment and enhances pro‐regenerative inflammation after skeletal muscle injury, suggesting its potential to improve tissue repair through timely modulation of the immune response.