Blue light reduces organ injury from ischemia and reperfusion

Abstract

Evidence suggests that light and circadian rhythms profoundly influence the physiologic capacity with which an organism responds to stress. However, the ramifications of light spectrum on the course of critical illness remain to be determined. Here, we show that acute exposure to bright blue spectrum light reduces organ injury by comparison with bright red spectrum or ambient white fluorescent light in two murine models of sterile insult: warm liver ischemia/reperfusion (I/R) and unilateral renal I/R. Exposure to bright blue light before I/R reduced hepatocellular injury and necrosis and reduced acute kidney injury and necrosis. In both models, blue light reduced neutrophil influx, as evidenced by reduced myeloperoxidase (MPO) within each organ, and reduced the release of high-mobility group box 1 (HMGB1), a neutrophil chemotactant and key mediator in the pathogenesis of I/R injury. The protective mechanism appeared to involve an optic pathway and was mediated, in part, by a sympathetic (β3 adrenergic) pathway that functioned independent of significant alterations in melatonin or corticosterone concentrations to regulate neutrophil recruitment. These data suggest that modifying the spectrum of light may offer therapeutic utility in sterile forms of cellular injury.

Keywords: blue light; circadian rhythms; ischemia; organ injury; reperfusion.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Blue light before liver I/R attenuates liver injury and cellular necrosis. Mice were exposed to red, blue, or ambient light for 24 h and then subjected to hepatic I/R (10–12 total mice per group for all four experiments combined). (A) Serum was assayed for ALT concentration (IU/L). Bar, median. (B) Histology (H&E) of liver tissue (200× magnification) was performed to quantify cellular necrosis (representative image of three experiments). White dashed line demarcates regions of necrosis. Corresponding box plots provide summary estimates (bar, median; box, IQR 25–75% range; whiskers, 1.5× IQR) of necrosis. Statistical comparisons were made by nonparametric Mann–Whitney test.

Fig. 2.

Blue light before kidney I/R attenuates acute kidney injury and cellular necrosis. Mice were exposed to red, blue, or ambient light for 24 h and then subjected to unilateral kidney I/R (13 total mice per group for all four experiments combined). (A) Serum was assayed for cystatin C concentration (ng/mL). Bar, median. (B) Histology (H&E) of kidney cortical tissue (200× magnification) was performed to quantify cellular necrosis, blebbing, vacuolization, and cast formation (representative image of four experiments). Corresponding box plots provide summary estimates (bar, median; box, IQR 25–75% range; whiskers, 1.5× IQR) of necrosis. Statistical comparisons were made by nonparametric Mann–Whitney test.

Fig. 3.

Blue light functions through an optic pathway and reduces liver and kidney MPO activity during I/R. (A) Wild-type 129S1 (closed circles and squares) and Vsx2 Optic KO (open circles and squares) mice were exposed to red or blue light for 24 h and then subjected to hepatic I/R (10 total mice per group for all three experiments combined). Serum was assayed for ALT concentration (IU/L). Bar, median. (B) Liver tissue was assayed for MPO (ng/mg tissue protein). Bar, median. (C) Mice were exposed to red, blue, or ambient light for 24 h and then subjected to unilateral kidney I/R (12–14 total mice per group for all four experiments combined). Kidney tissue was assayed for MPO (ng/mg tissue protein). Bar, median. Statistical comparisons were made by nonparametric Mann–Whitney test.

Fig. 4.

Blue light attenuates HMGB1 release during hepatic and renal I/R. Mice were exposed to red, blue, or ambient light for 24 h and then subjected to (A) hepatic I/R (10–12 total mice per group for all four experiments combined) or (B) unilateral kidney I/R (13 total mice per group for all four experiments combined). Serum HMGB1 (29KD) expression (representative immunoblot of four experiments). Corresponding box plots provide summary estimates (bar, median; box, IQR 25–75% range; whiskers, 1.5× IQR) of densitometry of HMGB1 concentration. Statistical comparisons were made by nonparametric Mann–Whitney test.

Fig. 5.

Blue light does not alter serum melatonin or corticosterone concentration. Mice (C57BL/6) were exposed to red, blue, or ambient light for 24 h (six total mice per group for two experiments combined). Serum was isolated at CT5, CT13, CT20, and CT3 and analyzed for (A) melatonin (pg/mL) and (B) corticosterone (ng/mL) concentrations. Corresponding box plots provide summary estimates (bar, median; box, IQR 25–75% range; whiskers, 1.5× IQR) of melatonin and corticosterone concentrations. Statistical comparisons were made by nonparametric Mann–Whitney test.

Fig. S1.

Activity, heart rate, and heart rate variability (LF/HF) of mice exposed to blue and red spectrum light. Mice underwent laparotomy and implantation of a DSI HD-X11 telemetry device. After 24 h of recovery, mice were exposed to a 24-h photoperiod of high illuminance blue or red spectrum light and monitored for 24 h. Dark horizontal bar indicates circadian night (CT12 to CT24). White horizontal bar indicates circadian day (CT0 to CT12). (A) Activity of mice during exposure to blue or red light (n = 4 mice per group). (B) Heart rate of mice during exposure to blue or red light. Each point is a single measurement of a single mouse at a single time point. Lines and colored areas represent a fractional polynomial estimate of the mean ± 95% confidence interval of heart rate for each cohort of blue (n = 4) and red (n = 4) mice. (C) LF/HF ratio was calculated as a parameter of sympathetic tone. Each point is a single measurement of a single mouse at a single time point. Lines and colored areas represent a fractional polynomial estimate of the mean ± 95% confidence interval of LF/HF ratio for each cohort of blue (n = 4) and red (n = 4) mice.

Fig. 6.

Blue light functions through an adrenergic pathway. Mice were administered either equivolume saline (0.9%, i.p.) or the β3 agonist CL316,243 (1 mg/kg, i.p.), and exposed to red, blue, or ambient light for 24 h. Mice were then subjected to unilateral kidney I/R (nine total mice per group for all four experiments combined). (A) Serum was analyzed for cystatin C concentration (ng/mL). Bar, median. (B) Kidney tissue was analyzed for MPO concentration (ng/mg tissue protein). Bar, median. (C) Mice were administered either equivolume saline (0.9%, i.p.) or the β3 antagonist SR 59230A (5 mg/kg, i.p.) and then subjected to unilateral kidney I/R (six total mice per group for two experiments combined). Serum was analyzed for cystatin C concentration (ng/mL). Bar, median. Statistical comparisons were made by nonparametric Mann–Whitney test.

Fig. S2.

Intensity and spectrum of red, blue, and ambient lights. Spectroradiometric measurements of light intensity counts and wavelengths of each lighting condition were analyzed with an ISP-80-8-I integrating sphere (Ocean Optics). The sphere was placed into each cage to replicate the distance between the filtered light source and the animal population of each experimental condition. To avoid the intensity fluctuation of the light source, the measurement was integrated within 100 ms.

Fig. S3.

Temperature of red, blue, and ambient light experimental conditions. A thermometer was placed in the bottom of each cage, and temporal measurements of cage temperature were recorded over a 24-h period at the times indicated. Thermal measurements began at the same time that all experiments were initiated: CT2 (CT, circadian time set 0 as previous dawn and 12 previous dusk). Mean temperature of n = 3 independent experiments.