The original UV biodosimeter for an in situ monitoring of the vitamin-D-synthetic capacity of sunlight and/or artificial UV sources is based on the same photoreaction in vitro by which vitamin D is synthesized in human skin from initial provitamin D via photo- and thermo-induced monomolecular isomerizations. Therefore, targets for UV photons in the biodosimeter are the provitamin D molecules embedded in specially designed UV transparent and stable matrix. The dosimeter response to UV radiation is photoinduced conversion of provitamin D into previtamin D which is immediate precursor of vitamin D. Thus, biological ‘antirachitic’ UV dose is determined by the amount of accumulated previtamin D. To follow the photoreaction course in real time three operation modes of varying complexity have been developed.
The practice of indoor tanning has led to the development of a large artificial tanning industry. In addition to
psychological benefits, exposure to UVB light helps the body produce the activated form of vitamin D, which is
necessary for many cellular functions. But uncontrolled tanning and UV overexposure can increase the risk of skin
cancer. For direct checkout of the vitamin D synthetic capacity of a UV source the bio-equivalent UV dosimeter has
been developed that is based on the same molecular photochemistry from which vitamin D is photosynthesized in
human skin and makes possible both instrumental and visual indication of vitamin D synthesis.
Excessive UV doses have adverse effects on human health, but proper amount of UV is beneficial for people and is
essential in the natural production of vitamin D# in skin. Most of broadband UV-radiometers that have an output in
sunburn units are incapable to record correctly the vitamin D synthetic capacity of sunlight because of the difference
between the CIE erythema and 'Vitamin D synthesis' action spectra. The liquid-crystalline UV sensor based on
provitamin D photoconversions has been developed for direct observation of vitamin D synthesis under UV irradiation.
UV-induced transformation of provitamin D in cholesteric liquid-crystalline matrix is accompanied by the change of
cholesteric pitch value in the LC cell. The developed UV biosensor makes possible both instrumental and visual
monitoring of the vitamin D synthetic capacity of sunlight and/or artificial UV source.
Response of cholesteric sensor materials to biologically active UV radiation has been studied. The sensor mixture comprised a cholesteric liquid crystalline matrix doped with provitamin D, and changes in the maximum selective reflection wavelength λmax caused by the photochemical reaction of provitamin D → vitamin D transformation were recorded. Using a UV source (DRT-240 lamp) calibrated accounting for the specific irradiation geometry, λmax shifts were obtained as function of UV illuminance dose (in J/cm2). Using a set of optical filters cutting off specified parts of the provitamin D absorption spectrum, effects of the spectral composition of UV radiation upon the response characteristics of sensor were determined. The results obtained support our earlier considerations of the developed sensor
material as "bioequivalent".
UV irradiation is widely used in phototherapy. Regardless of the fact that UV overexposure is liable to cause adverse health effect, in appropriate doses UV radiation initiates synthesis of vitamin D in skin that is absolutely essential for human health. As it proved, most people in northern industrial countries have a level of vitamin D in their bodies that is insufficient for optimum health, especially in winter. These low levels of vitamin D are now known to be associated with a wide spectrum of serious disease much of which leads on to premature death. The diseases associated with D deficiency involve more than a dozen types of cancer including colon, breast and prostate, as well as the classic bone diseases: rickets, osteoporosis and osteomalacia. Irradiation with artificial UV sources can prevent the vitamin D deficiency. However, in view of different irradiation spectra of UV lamps, their ability to initiate vitamin D synthesis is different. The reliable method based on an in vitro model of vitamin D synthesis has been developed for direct measurement in situ of the vitamin D synthetic capacity of artificial UV sources during a phototherapeutic procedure
Selective reflection spectra have been studied for cholesteric matrices doped with certain steroids of vitamin D group, and substantial effect of the dopants upon the helical pitch was noted. Under UV irradiation, shifts of selective reflection peaks were observed. It is argued that the effect studied can be used for monitoring of vitamin D formation reactions induced by UV irradiation, thus being a base of bioequivalent UV dosimetry.
The nematic liquid crystals (LCs) can be converted into cholesteric LCs by different chiral dopants. For the first time the dynamics of a cholesteric phase induction was investigated on dissolution of the single steroid crystal (vitamin D isomers and relative compounds) at the nematic droplet and the new effect of the crystal rotation has been discovered. In all cases the correlation between the rotation direction and screw sense of the cholesteric helix was found. A theoretical model and interpretation of the rotation effect has been proposed.
Solar ultraviolet radiation (UVR) gives rise to beneficial or adverse health effects depending on the dose. Excessive UV exposures are associated with acute and chronic health effect but in appropriate doses UV sunlight is advisable. Important biological function of UVR is initiation of endogenous synthesis of vitamin D in human skin. A useful method based on an in vitro model of vitamin D synthesis ('D-dosimeter') has been specially developed to measure the vitamin D synthetic capacity of sunlight in situ. For the first time laboratory and field tests have been performed to link commonly used erythemal units (MEDs) and previtamin D accumulation.
Variations of solar ultraviolet (UV) radiation by clouds and aerosols that have a comparable effect on UVB (280-315 nm) caused by variations in stratospheric ozone hinder accurate detecting mid-latitude UVB trends. In this connection it is desirable to use a UVB dosimeter that has at least two independent parameters, namely, a parameter responding to the integral intensity of UVB radiation and an additional one exclusively sensitive to the short wavelength variations in solar UV spectrum related to ozone depletion. The desired spectral selectivity is intrinsic in D-dosimeter that was recently introduced for an in situ monitoring of vitamin D synthetic capacity of solar UVB radiation. D-dosimeter is based on an in vitro model of vitamin D synthesis. The photoreaction rate (decay of provitamin D and formation of previtamin D) depends upon the integral UV intensity whereas maximum achievable concentration of previtamin D is solely dictated by the spectral position of the short-wave edge of solar spectrum. This makes it possible to reveal ozone depletion under conditions of opaque atmosphere when clouds and aerosols attenuate solar UV flux like a gray filter.
The new biosensor of vitamin D synthetic capacity of solar/artificial UV-B radiation is based on liquid crystal with provitamin D dopant. Nematic liquid crystals (LC-805, ZLI-1695) are converted into induced cholesteric phase using photosensitive steroid biomolecules of provitamin D3 (7- dehydrocholesterol). During UV exposure remarkable decrease in the number of the Cano-Grandjean stripes has been observed in the wedge-like cell as a result of UV initiated photoisomerization of provitamin D3 that changed helical twisting power of the dopant molecules.
An in vitro model of the well-known reaction of previtamin D photosynthesis in presence of UVB (280 to 315 nm) irradiation is proposed for the measuring of solar (and artificial) UVB radiation. The detailed study of the wavelength effect on the reaction kinetics using laser irradiation, as well as computer simulations, confirms the potential of the photoreaction as spectrally selective monitor of solar UVB. A method of express spectral analysis of the photoisomer mixture has been developed to promote realization of the proposal.
The effect of the irradiation intensity on the kinetics of provitamin D photoisomerization was studied by picosecond laser excitation. The changes in reaction kinetics were revealed as the intensity of laser irradiation increased from 1012 up to 2. 5 x 1014 W/m2 and model calculations gave evidence that there changes were due to the significant reduction of side product tachysterol formation. We attribute there observations to the excitation of provitamin being in non-equilibrium conformational distribution. The results obtained are believed to provide challenging possibilities for the control of photoproducts in triene photochemistry. 1.
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