Carbon monoxide: a critical physiological regulator sensitive to light

摘要

The mechanism by which humans absorb therapeutic light in winter seasonal and nonseasonal depression is unknown. Bright-light-induced release and generation of blood-borne gasotransmitters such as carbon monoxide (CO) may be one mechanism. Here, 24 healthy female volunteers had peripheral blood samples drawn. Samples were collected in a dimly lit room and protected from light exposure. Samples were analyzed for CO concentrations by gas chromatography after 2?h of continuous exposure to darkness vs. bright white light. In a similar confirmatory study, 11 additional volunteers had samples analyzed for CO concentrations after 2?h of continuous exposure to gentle rocking in darkness vs. in bright white light. In the first study, light-unexposed peripheral blood had a mean CO concentration of 1.8?±?0.4 SD?ppm/g. Identically treated samples with 2?h of rocking and exposure to bright white light at illuminance 10,000?lux had a mean CO of 3.6?±?1.2?ppm/g (p??0.0001). Post hoc analysis of that study showed that time of day was significantly inversely associated with increase in CO concentration under bright light vs. dark (p??0.04). In a smaller confirmatory study of 11 healthy female volunteers, after 2?h of rocking, light-unexposed peripheral blood had a mean CO of 1.4?±?0.5 SD?ppm/g. Identically treated blood samples with 2?h of exposure to bright white light at illuminance 10,000?lux had a mean CO of 2.8?±?1.7?ppm/g (p??0.02). In conclusion, bright-light exposure robustly increases human blood CO in vitro. This supports the putative role of CO as a physiological regulator of circadian rhythms and light’s antidepressant effects. This human evidence replicates earlier data from a preclinical in vivo model. This effect may be stronger in the morning than in the afternoon.