Effect of 297 nm Narrow-band LED Irradiation at Extremely Low Light Intensity of Microwatt on the Yield of Vitamin D3 Synthesis in Vitro
Objective To investigate the effects of power density and energy density on the yield of vitamin D3 synthesized in vitro by 297 nm narrow-band light-emitting diode(LED)irradiation at extremely low light intensity(power density).Methods Ethanol solution of 7-dehydrocholesterol(7-DHC),the classic paradigm of vitamin D3 synthesis in vitro was used as the study model.The 7-DHC ethanol solution with a concentration similar to that of human skin was placed in quartz colorimetric dishes with a light path of 1 cm.According to whether the solution was irradiated by ultraviolet light or not,it was divided into control group and experimental groups.The experimental groups were divided into 2 μW/cm2 group,4 μW/cm2 group,6 μW/cm2 group,and 8 μW/cm2 group according to power density,and 6 mJ/cm2 subgroup,12 mJ/cm2 subgroup,and 24 mJ/cm2 subgroup were set up under each power density group according to energy density.The solution was irradiated with 297 nm narrow-band LED according to the power density and energy density set by each group.After irradiation,the solution was transferred to an incubator at 37℃ for incubation for 4 days.The experiment was repeated for 3 times.The liquid chromatography-tandem mass spectrometry was used to determine the concentration of vitamin D3 and 7-DHC in solution,so as to calculate the yield of vitamin D3.Results No vitamin D3 was detected in the control solution.In experimental groups,there was no significant difference in the yield of vitamin D3 among 2 μW/cm2 group,4 μW/cm2 group,6 μW/cm2 group,and 8 μW/cm2 group when the energy density was the same(P＞0.05).However,when the power density was same,the yield of vitamin D3 of 24 mJ/cm2 subgroup was higher than that of 12 mJ/cm2 subgroup,and the yield of 12 mJ/cm2 group was higher than that of 6 mJ/cm2 subgroup,with statistically significant differences among the three groups(P＜0.001).The relationship between the yield of vitamin D3 and energy density was approximately linear,which can be expressed as the yield of vitamin D3=0.6483 × energy density(R2=0.9871).Conclusions When the power density is within 2～8 μW/cm2and the energy density is within 6～24 mJ/cm2,the change of power density will not affect the yield of vitamin D3 synthesized in vitro by 297 nm narrow-band LED irradiation,and energy density is the decisive optical parameter of the yield of vitamin D3.
Vitamin D37-dehydrocholesterol(7-DHC)Ultraviolet lightLight-emitting diode(LED)Extremely low power density
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