Masako Sasaki

Increasing trend of biologically active solar ultraviolet-B irradiance in mid-latitude Japan in the 1990s

Ground-based global solar ultraviolet-B (UV-B: 290 to 320 nm) irradiance has been measured by a narrow band UV-B radiometer at Tokai University, Hiratsuka, Japan (35°218N, 139°168E) for a 10-year period from October 1990 to September 2000. A precise calibration of the UV-B radiometer was periodically performed, and the yearly decay in sensitivity was found to be 23.7%. Using this decay rate, the measured UV-B irradiance was corrected, and the long-term trends of the UV-B irradiance were estimated. When the seasonal variation was eliminated by taking 12-month moving averages, an increasing trend in the UV-B irradiance was demonstrated to be 1.57 % per year. Moreover, to re- move quasibiennial oscillation (QBO), 26-month moving averages were applied to the UV-B irradiance normalized by the global total (300 to 3000 nm) solar irradiance. An increasing trend in the normalized UV-B irradiance was found to be 1.22 % per year. In winter, the clearly increas- ing trend of the UV-B irradiance was statistically significant, although the increasing tendency of the UV-B irradiance in other seasons (spring, summer, and fall) is not clear. A significant inverse correlation was con- firmed between the UV-B irradiance normalized by the global total solar irradiance and the effective ozone amount defined as total ozone amount 3secu, where u is the solar zenith angle. These findings give supporting evidence for a direct relationship between solar UV-B irradiance and the stratospheric ozone amount. In conclusion, the increasing trend of global solar UV-B irradiance, especially in winter, was confirmed in response to stratospheric ozone loss in mid-latitude Japan in the 1990s.

INTRACELLULAR TARGET FOR α‐TERTHIENYL PHOTOSENSITIZATION: INVOLVEMENT OF LYSOSOMAL MEMBRANE DAMAGE

Abstract— Intracellular targets for the photosensitizer α‐terthienyl (αT) were examined by fluorescence microscopy and microfluorospectrometry using human nonkeratinized buccal cells. Intracellular distribution of αT was observed as fluorescent patches widely dispersed in the cytoplasm. The distribution of the fluorescent patches was compared with that of acid phosphatase activity visualized as an azo dye produced by the fast garnet 2‐methyl‐4‐[(2‐methyl‐phenyl)azo]benzenediasonium sulfate reaction. Because both the distribution sites coincided, lysosomes were the likely sites of intracellular affinity of αT. However, because acid phosphatase is not a specific lysosomal marker, we tried to detect another lysosomal enzyme, β‐galactosidase, to confirm if the fluorescent patches were lysosomes, using fluorescein‐di‐(β‐D‐galactopyranoside) (FDG) as a fluorogenic substrate. Without UV‐A (320–400 nm) irradiation of the cells after uptake of αT and FDG, no significant fluorescence was observed. In contrast, with prior UV‐A irradiation in the presence of αT and FDG, the bright yellow fluorescence of fluorescein, which is the digested product of FDG, was clearly detected in the cells by fluorescence microscopy. This observation implied that inflow of external FDG into the lysosomes is caused by lysosomal membrane damage on αT photosensitization. The present results indicated that lysosomes are the primary photosensitization site of αT.

Spectroscopic mimicry for the protonated retinal Schiff base in vivo with modified amphiphilic clay interlayers as a possible model of opsin environment.

Abstract— We have found that clay acts as a novel model matrix for the amphiphilic protein‐opsin to mimic the visible absorption spectrum of a protonated retinal Schiff base (RSB) in vivo. Without strong acids at ambient temperature, a visible broad absorption spectrum with a LDmax at 530 nm covering the range from 400 to 680 nm was achieved for the protonated RSB with cationic surfactant‐modified montmorillonite clay. The interlayers of the dimethyloctadecylamine (DOA) modified clay were found to provide amphiphilic space allowing the amphiphilic RSB to be intercalated easily and sequentially and protonated by the DOA. It is proposed that the visible absorption spectrum at LD, 530 nm was attributable to electrostatic effects, permitting the appropriate distance between the nitrogen of the protonated RSB and the negatively charged clay interlayers and also to the anisotropic orientation of the RSB molecules in the interlayers.

Evidence for uptake of 8-methoxypsoralen and 5-methoxypsoralen by cellular nuclei

The fluorescent appearance of oral mucosa cells treated with 8-methoxypsoralen (8-MOP) and 5-methoxypsoralen (5-MOP) was observed by means of fluorescence microscopy. Fluorescence at the nuclei was weakened in 8-MOP-treated cells, while it was intensified in 5-MOP-treated cells. These findings were consistent with changes in the fluorescence intensities on association of the psoralen derivatives with DNA in aqueous solution. This intensity change of fluorescence and also the blue shift of the fluorescence maximum of the derivatives on association suggested that the environment around the psoralen molecules is as little polar as methanol. From the results of these fluorescence microscopic observations and spectroscopic analysis of fluorescence of derivatives interacting with DNA during equilibrium dialysis, we concluded that 8-MOP, as well as 5-MOP, is incorporated by nuclei of human cells.

Photoisomerization of the rhodopsin chromophore in clay interlayers at 77 K

Abstract In rhodopsins, cis–trans photoisomerization of the retinal chromophore occurs in the specific protein environment even at low temperature, where molecular motions are significantly prohibited. In this study, we found that illumination of the rhodopsin chromophore in clay interlayers at 77 K results in formation of a bathochromic product, which is reverted to the original state by light in a manner similar to what is observed in the rhodopsins. Infrared spectral changes suggest that the chromophore is protonated in clay, and that trans–cis isomerization occurs at 77 K. The clay interlayer thus works to mimic the primary photochemical reaction in rhodopsin.

ESTIMATION OF AN INDEX OF HYDROPHOBICITY OF DNA INTERIOR USING 5‐METHOXYPSORALEN AS A FLUORESCENT PROBE

The index of hydrophobicity of DNA interior was estimated by measuring fluorescence spectra of psoralen derivatives associated with DNA. The environment around 5‐MOP associated with DNA was as hydrophobic (Dk= 34) as methanol, suggesting that the molecules reside at the space between the base‐pairs in B‐form DNA. This is also true for 8‐MOP. Thus, planar and aromatic molecules of 5‐ and 8‐MOP are more stable in the interior of DNA than in aqueous medium due to hydrophobic affinity.

Determination of action spectrum for sparfloxacin‐photosensitized single‐strand breaks in plasmid pBR322 DNA

Background: Various drugs have been reported to induce photosensitivity as a side effect. Sparfloxacin (SPFX) is well known to trigger dermatological phototoxicity upon solar radiation exposure.

Photocleavage of DNA by Chlorophylls and Porphyrins: Electron Transfer from Nucleic Acid Base to Dyes in the Singlet Excited States

Plasmid DNA has been efficiently photocleaved under anaerobic condition by water-soluble pheophorbides (sodium pheophorbides, Na-Phde) a and b and a novel coproporphyrin III with zinc (zinc phyrin) produced by Strep-tomyces sp. Singlet oxygen production sensitized by Na-Phde a or b cannot be observed in the aqueous media, although zinc phyrin produced singlet oxygen in about 17% quantum yield. Direct evidence for the electron capture from the nucleic acid bases adenine and guanine by porphyrin derivatives in the singlet excited states has been first obtained by using nucleobase-attached porphyrins. A guanine-attached porphyrin showed the strongest reduction of fluorescence derived from the porphyrin ring, and an adenine-attached porphyrin showed the second strongest reduction. This is the first evidence in support of the electron transfer mechanism for the oxygen-independent photocleavage of DNA. Fluorescence microscopic observation has shown a rapid incorporation of Na-Phde a and zincphyrin into the nuclei, mitochondria, and lysosomes of human oral mucosa cells, although Na-Phde b has been incorporated only into the plasma membrane. Red fluorescence from Na-Phde a and zincphyrin rapidly decayed during the microscopic observation, indicating that some photochemical reactions take place in the organelle.

Long-term trends of global solar ultraviolet-B, ultraviolet-A and total irradiances measured in Japan since 2001

Global and diffuse solar ultraviolet-B, ultraviolet-A, and Total irradiances have been measured at Shonan Campus of Tokai University (Kanagawa, Japan, 35°21’N, 139°11’E) since 1990. Analysis of data recorded from Apr. 2001 to Dec. 2015 shows that daily integrated global UV-B irradiance has decreasing in the long-term as -0.381 %/year for the 95 % confidence interval in this period. More detail evaluation is made on the data recorded from Jan. 2009 to Dec. 2015. In this period, an increase trend in global UV-B irradiance was obtained (+0.607 %/year). This result suggests that critical factor on increase in UV-B irradiance is not only ozone amount but also amount of aerosols, sunshine duration and solar cycle.

Estimation of global solar UV index from UV-B irradiance measured with a narrow-band UV-B radiometer

The global solar UV index is an indicator for notifying the level of harmful solar ultraviolet radiation reaching the surface of the earth and the general public. It was proposed by the WHO/WMO/UNEP/ICNIRP and was standardized by the CIE in 2003. This index is derived from the product of the spectral solar UV irradiance from 250 to 400 nm and the CIE standard of reference erythema spectrum. For calculation of the UV index, the measurement of spectral solar UV irradiance is needed. Spectral radiometry is the best method of measurement of solar UV irradiance, however spectral radiometers are cost prohibitive. On the other hand, a narrow-band solar UV-B radiometer is widely used for measurement of solar UV-B irradiance in the world. The Tokai Solar Radiation Monitoring Network, and the UV Monitoring Network-Japan performed by the National Institute for Environmental Studies are two examples of monitoring networks using narrow-band solar UV-B radiometer in Japan. In this paper an estimation method of the UV index from the measured UV-B irradiance with the narrow-band UV-B radiometer.