Examining Potential Health Hazards of Circadian Disruption in Drosophila Melanogaster

Overview

Background: Environmental disruption of circadian rhythms can have deleterious consequences for human health. The extent to which artificial blue light from LED lighting, smartphones and tablets affects circadian biology and mental and physical health outcomes is not well known. The main goals of this project were to study the effects of varying blue light exposure on Drosophila melanogaster's (1) lifespan, (2) memory (3) propensity to consume caffeine containing media and (4) gut permeability. Methods: Four experimental groups were used: controls, flies with the tim01 mutation, which eliminates circadian behavioral rhythms, flies exposed to 8 hours (BL8) and 12 hours (BL12) of blue (460 nm) light. To assess the effect on lifespan, the percentage of flies surviving over time, within each group, was calculated. Preference for caffeine containing food was evaluated using a constructed choice chamber where caffeine-enriched and regular media were presented to flies. Loss of intestinal barrier function was detected by the presence of a non-absorbable blue food dye outside of the digestive tract after feeding. The aversive phototaxic suppression assay was used to assess learning/memory; flies learned to avoid light that is paired with an aversive stimulus. Group differences were analyzed with survival curves, t-tests, and Chi-square tests as needed. Results: Control flies lived significantly longer than the circadian mutants and flies exposed to blue light for 12 hours (p<0.001). Circadian mutant flies demonstrated significant impairment in short-term memory and learning compared to the control flies (P = 0.029) as did the BL12 (P =0.009) and BL8 (P = 0.008) groups. A preference for caffeine containing food, after 72 hours of exposure to it, was demonstrated by the circadian mutants (OR 10.52, p<0.0001) as well as the BL12 (OR 6.07, P<0.0007) and BL8 (OR 6.48, P=0.0003) groups. More flies with tim01 mutation and 12-hour exposure to blue light demonstrated impaired gut permeability compared to the controls. Conclusions: This study show that prolonged exposure to blue light can cause increased mortality, impaired memory, propensity to substance use and accelerated gut aging similar to known circadian mutants; the degree and spectrum of effects may depend on duration of exposure. The health implications of a digital world require closer biologic scrutiny.