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PubMed2002

A computational study of physical and biological characterization of common UV sources and filters, and their relevance for substituting sunlight.

Sunlight is the most important environmental UV source, affecting not only human health but also the whole terrestrial ecosystem. The use of artificial sources is advantageous since it is independent of geographical location and seasonal variations, however, in some photobiological/photochemical studies the choice of a specific UV source in relation to the biological end-point studied is sometimes questionable. Furthermore, it is often difficult to compare the results obtained in different laboratories due to 'slight' differences in the physical characteristics of the UV sources used. In an attempt to address these issues we calculated and compared the physical characteristics and the biological efficiency in UV-B and UV-A regions for two biological end-points (CPD and Fpg-sensitive sites formation) for frequently used UV-B, UV-A sources and solar light simulators (SLS). Our calculation shows that FS20 lamp is appropriate for studying the biological effects of UV-B radiation although differences in spectral characteristics of the associated filters may lead to at least 2-fold yields in CPD production. Furthermore, the use of a SLS with a Kodacel filter alone is inadequate for studying environmental UV effects. A metal-halide source with a Schott WG345 filter is appropriate for studies on biological effects due to UV-A region. Relative exposure duration was calculated to achieve equal amount of CPD or Fpg-sensitive sites, provided equal, total UV-(A+B) irradiance for the different UV sources.

Animals↗
PubMed1998

The potential role for urocanic acid and sunlight in the immune suppression associated with protein malnutrition.

Irradiation of skin by sunlight or ultraviolet B (UVB, 290-320 nm) brings about a downregulation of cell-mediated immunity. An action spectrum for photoimmune suppression in mice indicates that trans-urocanic acid absorbs UV photons and is isomerized to the cis-isomer in the stratum corneum. Cis-urocanic acid is subsequently shown to suppress cellular immunity in mice. When histidine is elevated in a mouse diet, a higher level of urocanic acid is detected in mouse skin. These mice are more susceptible to photoimmune suppression. There is evidence that humans and animals experiencing protein malnutrition have very high levels of urocanic acid and/or histidine. Urocanic acid is formed by deamination of histidine in one enzymatic step. We discuss the protein malnutrition of kwashiorkor patients. They experience suppressed immunity and disturbed histidine metabolism. Here, we present a testable hypothesis: one cause of the immune deficiency observed in humans with protein malnutrition is the photoconversion by UVB of increased levels of trans-urocanic acid in skin to cis-urocanic acid, which suppresses the cellular immune system.

Animals↗
PubMedDate not supplied

Stability of enzymes and proteins in dried glassy systems: effect of simulated sunlight conditions.

The purpose of the present work was to study the effects of simulated sunlight conditions on enzyme inactivation and structural damage in dehydrated glassy systems. Freeze-dried samples containing different enzymes (lactase, invertase, lysozyme and amyloglucosidase) were exposed to light using a medium-pressure metal halide HPA 400 W lamp. After 1 h of light exposure, the samples showed a significant reduction (more than 50%) in the denaturation peak area as analyzed by DSC, and this could be attributed to protein denaturation. For most of the pure enzymes, the loss of enzymic activity after 1 h of light exposure was around 50%. In the case of enzymes included in anhydrous model systems (trehalose, raffinose, maltodextrin, and dextran), the remaining activity also decreased dramatically during the light treatment. We showed that the light exposure in dehydrated systems generated both the loss of enzymic activity and structural changes such as denaturation (observed by DSC) and protein fragmentation and aggregation (observed by electrophoresis). Overall, we can conclude that a short exposure to the light produces dramatic changes in the enzymic activity in dehydrated systems with or without protective matrices.

Calorimetry, Differential Scanning↗
PubMed2003

Conversion of fogwater and aerosol organic nitrogen to ammonium, nitrate, and NOx during exposure to simulated sunlight and ozone.

Although organic nitrogen (ON) compounds are apparently ubiquitous in the troposphere, very little is known about their fate and transformations. As one step in addressing this issue, we have studied the transformations of bulk (uncharacterized) organic nitrogen in fogwaters and aerosol aqueous extracts during exposure to simulated sunlight and O3. Our results show that over the course of several hours of exposure a significant portion of condensed-phase organic nitrogen is transformed into ammonium, nitrite, nitrate, and NOx. For nitrite, there was both photochemical formation and destruction, resulting in a slow net loss. Ammonium and nitrate were formed at initial rates on the order of a few micromolar per hour in the bulk fogwaters, corresponding to formation rates of approximately 10 and 40 ng m(-3) h(-1), respectively, in ambient fog. The average initial formation rate (expressed as ng (m of air)(-3) h(-1)) of NH4+ in the aqueous extracts of fine particles (PM2.5) was approximately one-half of the corresponding fogwater value. Initial formation rates of NOx (i.e., NO + NO2) were equivalent to approximately 2-11 pptv h(-1) in the three fogwaters tested. Although the formation rates of ammonium and nitrate were relatively small as compared to their initial concentrations in fogwaters (approximately 200-2000 microM) and aerosol particles (approximately 400-1500 ng m(-3)), this photochemical mineralization and "renoxification" from condensed-phase organic N is a previously uncharacterized source of inorganic N in the atmosphere. This conversion also represents a new component in the biogeochemical cycle of nitrogen that might have significant influences on atmospheric composition, condensed-phase properties, and the ecological impacts of N deposition.

Aerosols↗
PubMed2005

Photolysis study of perfluoro-2-methyl-3-pentanone under natural sunlight conditions.

The UV-vis and infrared absorption cross sections of perfluoro-2-methyl-3-pentanone (CF3CF2C(O)CF(CF3)2, 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-penta none), has been obtained, and a photolysis study was carried out under natural sunlight conditions in the European simulation chamber, Valencia, Spain (EUPHORE). The photolysis loss rate, J(photol), equaled (6.4 +/- 0.3) x 10(-6) s(-1) in the period of 10-14 GMT, July 14, 2003 in Valencia (0.5 W, 39.5 N) and corresponded to an effective quantum yield of photolysis of 0.043 +/- 0.011 over the wavelength range of 290-400 nm; the error limits correspond to 2sigma from the statistical analyses. The atmospheric lifetime of CF3CF2C(O)CF(CF3)2 is estimated to be around 1 week, and the global warming potential of the compound is negligible.

Flame Retardants↗
PubMed2003

Effect of sunlight exposure and aging on skin surface lipids and urate.

Free fatty acids (FFA), squalene, squalene hydroperoxide, and uric acid in the methanol extracts from human skin surface were measured. Levels of FFA and squalene were significantly lower in the older (83.7 +/- 9.4 years) than in the younger (22.2 +/- 3.9 years) group. FFA are mostly saturated, and linoleic acid is an exclusive polyunsaturated fatty acid. The composition of linoleic acid decreased in the older group by 40%, suggesting age-dependent loss of oxidatively vulnerable polyunsaturated fatty acid. Even monounsaturated acids such as palmitoleic and oleic acids decreased significantly in the older group. This could be interesting because 2-nonenal is the oxidation product of palmitoleic acid and has been identified as the major aged body odor component. Sunlight exposure for 1.5 h did not change levels of FFA and squalene, or FFA composition. However, squalene hydroperoxide increased by 60-fold, as reported previously, suggesting that hydroperoxide is produced by singlet oxygen. Uric acid increased by two-fold, which may be the adaptive response against photo-oxidative stress because uric acid is a good scavenger of singlet oxygen and oxygen radicals.

Aging↗
PubMed1997

p53 mutations implicate sunlight in post-transplant skin cancer irrespective of human papillomavirus status.

Mutations in p53 were detected in 11/23 (48%) of non melanoma skin cancers in renal allograft recipients and in 5/8 (63%) of sporadic tumours from immune competent patients. 9/12 (75%) of mutations in transplant patients and all 5 mutations in non transplant tumours were consistent with damage caused by ultraviolet (u.v.) irradiation. DNA sequences, predominantly of the epidermodysplasia verruciformis (EV) subgroup, were detected in 9/23 (39%) of transplant tumours and in 2/8 (25%) of eight non-transplant tumours. There was no relationship between HPV status and p53 mutation, HPV DNA being present in 5/16 (31%) of tumours with p53 mutation and 6/15 (40%) of tumours lacking p53 mutation. These data are consistent with an important role for sunlight in the development of post-transplant skin cancer, and with limited functional data suggesting that E6 proteins of the cutaneous and EV-related papillomaviruses do not target p53 for ubiquitin-mediated degradation.

DNA Damage↗
PubMed2005

PROPHIS: parabolic trough-facility for organic photochemical syntheses in sunlight.

The PROPHIS facility is an efficient tool for the synthesis of chemicals with moderately concentrated sunlight on a semi-technical scale. The feasibility of selected solar photochemical reaction classes--including heterogeneous and homogeneous reactions--has been demonstrated using various set-ups of the plant. This paper outlines the potential of solar photochemistry by representative examples.

Acyclic Monoterpenes↗
PubMed2000

The protective role of Langerhans' cells and sunlight in multiple sclerosis.

The low prevalence of multiple sclerosis in equatorial areas may be the consequence of a physiological immunosuppression induced by ultraviolet radiation on the epidermal Langerhans' cells, which are the antigen-presenting cells. Multiple sclerosis appears to be the consequence of an immune response to an environmental antigen during childhood in the absence of two protective factors: a genetic factor conferred by the HLA haplotypes of Langerhans' cells, and an environmental factor conferred by ultraviolet radiation in sunlight. In the presence of these two factors, T lymphocytes are physiologically immunosuppressed. Their association may play a key role in protection against multiple sclerosis. The varying combinations of these two factors may provide an explanation for the differences in incidence and prevalence of the disease noted within a single region or from one region to another throughout the globe. The hypothetical pathogenic mechanism developed in this article opens up new fields of research, particularly those concerning its therapeutic applications.

Humans↗
PubMed1987

Effect of natural sunlight on adrenaline and noradrenaline excretion in man.

Sympathoadrenal activity was evaluated in 6 healthy subjects by excretory rate of adrenaline and noradrenaline in 6 hour samples of urine throughout three consecutive days. Subjects were exposed to natural sunlight for 4 hours on the second day of experiment, the first and third days served for control measurements. Sunbath caused erythema in all subjects and it had no impact adrenaline on excretion. However, significantly higher no radrenalineexcretion was present during 6 hours after exposition to sunshine when compared to control days.

Adult↗
PubMed1985

Sunlight exposure as risk factor for intraocular malignant melanoma.

In a case-control study, we compared 444 patients with intraocular malignant melanoma with matched controls to evaluate the role of exposure to ultraviolet radiation and other risk factors in the pathogenesis of this tumor. Persons born in the southern United States had a relative risk of 2.7 (95 per cent confidence interval, 1.3 to 5.9) as compared with those born in the North. Subjects with brown eyes were protected as compared with those with blue eyes (relative risk, 0.6; 95 per cent confidence interval, 0.4 to 0.8), but complexion and hair color were not important risk factors. Patients with intraocular malignant melanoma were also more likely to have spent time outdoors in their gardens, to have sunbathed, and to have used sunlamps. Rarely wearing hats, visors, or sunglasses while in the sun was a risk factor for the disease (relative risk, 1.9; 95 per cent confidence interval, 1.6 to 2.2). These data suggest that sunlight exposure is an important risk factor for intraocular melanoma.

Eyeglasses↗
PubMed2006

Autonomous artificial nanomotor powered by sunlight.

Light excitation powers the reversible shuttling movement of the ring component of a rotaxane between two stations located at a 1.3-nm distance on its dumbbell-shaped component. The photoinduced shuttling movement, which occurs in solution, is based on a "four-stroke" synchronized sequence of electronic and nuclear processes. At room temperature the deactivation time of the high-energy charge-transfer state obtained by light excitation is approximately 10 micros, and the time period required for the ring-displacement process is on the order of 100 micros. The rotaxane behaves as an autonomous linear motor and operates with a quantum efficiency up to approximately 12%. The investigated system is a unique example of an artificial linear nanomotor because it gathers together the following features: (i) it is powered by visible light (e.g., sunlight); (ii) it exhibits autonomous behavior, like motor proteins; (iii) it does not generate waste products; (iv) its operation can rely only on intramolecular processes, allowing in principle operation at the single-molecule level; (v) it can be driven at a frequency of 1 kHz; (vi) it works in mild environmental conditions (i.e., fluid solution at ambient temperature); and (vii) it is stable for at least 10(3) cycles.

Absorption↗
PubMed2006

The significance of direct sunlight and polarized skylight in the ant's celestial system of navigation.

As textbook knowledge has it, bees and ants use polarized skylight as a backup cue whenever the main compass cue, the sun, is obscured by clouds. Here we show, by employing a unique experimental paradigm, that the celestial compass system of desert ants, Cataglyphis, relies predominantly on polarized skylight. If ants experience only parts of the polarization pattern during training but the full pattern in a subsequent test situation, they systematically deviate from their true homeward courses, with the systematics depending on what parts of the skylight patterns have been presented during training. This "signature" of the polarization compass remains unaltered, even if the ants can simultaneously experience the sun, which, if presented alone, enables the ants to select their true homeward courses. Information provided by direct sunlight and polarized skylight is picked up by different parts of the ant's compound eyes and is channeled into two rather separate systems of navigation.

Animals↗
PubMed1986

Prophylaxis against vitamin D deficiency in the elderly by regular sunlight exposure.

The effects of regular sunlight exposure on levels of vitamin D metabolites and on other indices of calcium metabolism have been studied in elderly rest-home residents. Fifteen subjects who formerly went outdoors very infrequently were studied over a 4-week period while spending 0, 15 or 30 minutes daily sitting on the rest-home verandah. During this time, levels of 25-hydroxyvitamin D [25(OH)D] rose by 7.4 +/- 1.2 (s.e.m.) microgram/1 in the group spending 30 minutes per day outdoors (P less than 0.005) and there was a smaller but nonsignificant increase in the 15 minutes per day group also. Serum 1,25 (OH)2D levels did not change during the study but serum ionized calcium and alkaline phosphatase showed small, but significant, decreases. Intestinal strontium absorption increased in both treatment groups (P less than 0.05), indicating a similar change in calcium absorption. It is concluded that 30 minutes spent outdoors each day leads to a substantial increase in 25(OH)D levels in elderly subjects and that this has significant effects upon other indices of calcium metabolism. This regimen provides a safe and inexpensive method for the prevention of osteomalacia in frail elderly subjects.

Aged↗
PubMed1983

Sunlight and vitamin D status in normal Saudi subjects.

Serum levels of the circulating form of vitamin D3, 25-hydroxycholecalciferol [25-(OH)D3], were determined in 59 university students, 26 males and 33 females, aged 18 to 26 yr and in 24 elderly subjects, 13 males and 11 females, with a mean age of 62 +/- 13 yr. The level of 25-(OH)D3 was significantly lower in the elderly persons (p less than 0.001) than in young students of both sexes, and was significantly higher in females than in males. Serum levels of 1, 25- and 24, 25-dihydroxycholecalciferol were measured in adult males and found to be within the normal range. A group of elderly patients were exposed to natural uv light, and the circulating levels of 25-(OH)D3, serum phosphorus, and alkaline phosphatase were determined both before and 1 day after the last exposure. The exposure to natural uv light resulted in a 2 1/2-fold increase in the level of 25-(OH)D3 and a significant decrease in the activity of alkaline phosphatase, but no significant change in serum phosphorus concentrations was observed. It is concluded that the low vitamin D3 status in Saudis is mainly due to avoidance of sunlight exposure and other factors discussed below.

24,25-Dihydroxyvitamin D 3↗
PubMed2004

Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease.

Most humans depend on sun exposure to satisfy their requirements for vitamin D. Solar ultraviolet B photons are absorbed by 7-dehydrocholesterol in the skin, leading to its transformation to previtamin D3, which is rapidly converted to vitamin D3. Season, latitude, time of day, skin pigmentation, aging, sunscreen use, and glass all influence the cutaneous production of vitamin D3. Once formed, vitamin D3 is metabolized in the liver to 25-hydroxyvitamin D3 and then in the kidney to its biologically active form, 1,25-dihydroxyvitamin D3. Vitamin D deficiency is an unrecognized epidemic among both children and adults in the United States. Vitamin D deficiency not only causes rickets among children but also precipitates and exacerbates osteoporosis among adults and causes the painful bone disease osteomalacia. Vitamin D deficiency has been associated with increased risks of deadly cancers, cardiovascular disease, multiple sclerosis, rheumatoid arthritis, and type 1 diabetes mellitus. Maintaining blood concentrations of 25-hydroxyvitamin D above 80 nmol/L (approximately 30 ng/mL) not only is important for maximizing intestinal calcium absorption but also may be important for providing the extrarenal 1alpha-hydroxylase that is present in most tissues to produce 1,25-dihydroxyvitamin D3. Although chronic excessive exposure to sunlight increases the risk of nonmelanoma skin cancer, the avoidance of all direct sun exposure increases the risk of vitamin D deficiency, which can have serious consequences. Monitoring serum 25-hydroxyvitamin D concentrations yearly should help reveal vitamin D deficiencies. Sensible sun exposure (usually 5-10 min of exposure of the arms and legs or the hands, arms, and face, 2 or 3 times per week) and increased dietary and supplemental vitamin D intakes are reasonable approaches to guarantee vitamin D sufficiency.

Adolescent↗