ESPE Abstracts

Introduction: The impact of increased exposure to blue light (BL) from infancy over the past decade on growth and epiphyseal plate maturation is not well understood. This study aims to experimentally investigate the effects of BL exposure and duration during the prepubertal period on the epiphyseal plate.

Materials and Methods: Eighteen female and eighteen male Sprague Dawley rats, aged 21-days postnatal, were divided into six groups with six rats each: Control Group (CG), Blue Light-6 hours (BL-6), and Blue Light-12 hours (BL-12). The CG was kept under standard conditions with a 12/12 hour light-dark cycle. The BL-6 and BL-12 groups were exposed to BL (450-470nm, irradiance 0.03uW/cm²) for 6 hours and 12 hours respectively. The rats were exposed to BL until the first signs of puberty, after which they were euthanized. The femur and tibia were dissected and measured for length. The femur epiphyseal plate and proliferation zone were measured, and the expression levels of IGF1 and IGFBP3 in the femur epiphyseal plate were assessed using immunohistochemistry. SerumIGF1 andIGFBP3 levels were measured using ELISA.

Results: Females: The median days for the onset of puberty were 38^th, 32^nd, and 30^th for CG, BL-6, and BL-12 respectively (P = 0.001). The occipital tail length difference (%) was greater in BL-6 and BL-12 compared to CG (P = 0.029, P = 0.006). Femur length in BL-6 was greater than in CG (P = 0.04). No differences were found in serum IGF1 and IGFBP3 levels among the groups (P = 0.83, P = 0.61). The epiphyseal plate length*, proliferation zone length^¶, and IGF1, IGFBP3 expression in BL-12 were higher than in CG (P = 0.0004*, P = 0.0004^¶). Males: The median days for the onset of puberty were 38^th,30^th, and 28^th for CG, BL-6, and BL-12 respectively(P = 0.0001). The tail length difference (%) in BL-12 was greater than in CG(P = 0.02) while serum IGFBP3 levels in BL-6 were higher than in CG (P = 0.03). The epiphyseal plate length*, proliferation zone length^¶, and IGF1, IGFBP3 expression in BL-12 were higher than in CG (P = 0.0002*, P = 0.0002^¶). Degeneration and calcification consistent with changes in the proliferation zone were observed in both sexes.

Conclusion: This is the first study to demonstrate the effects of BL exposure on the epiphyseal plate. Blue light increases growth and proliferation in the epiphyseal plate. While this may appear beneficial, it also accelerates bone maturation. Prior to the physical signs of puberty, rapid maturation observed in ovarian and testicular tissues in previous studies was also seen in bone tissue. These findings suggest that blue light may have an accelerating effect on the pubertal process in tissues.