INDUCTION and DISAPPEARANCE OF THYMINE DIMERS IN HUMAN SKIN EXPOSED TO UVB RADIATION: FLOW CYTOMETRIC MEASUREMENTS IN REPLICATING and NONREPLICATING EPIDERMAL CELLS

We have earlier reported on determining UV-induced DNA damage in murine epidermal cell suspensions by flow cytometric analysis of the fluorescence from a fluorescein isothiocyanate-labeled antibody (H3) directed against thymine dimers (T>2-M-phase cells can further be distinguished from cell doublets by pulse-shape discrimination. Thus, T>(i.e. G₀-G₁, S or G₂-M phases) can be determined after in vivo exposure of human skin to environmentally relevant UVB (280–315nm) doses. The method was applied to measure the decrease of T>0-G₁ phase) and replicating cells (S phase or G₂-M phase) from seven volunteers exposed to twice their minimal erythema dose. The reduction in the average T>0-G₁ cells and 70% (ranging between 37% and 100%) for the S + G₂-M cells. The difference was statistically highly significant. Determination of individual DNA repair capacities with this method can become a convenient diagnostic tool for patients with DNA repair disorders, or it may even be used to identify individuals with low repair proficiencies and increased risk of developing skin cancers.     

TUMORIGENESIS BY A LONG WAVELENGTH UV-A SOURCE

Albino hairless mice (Skh-hr1) were exposed daily to radiation from a high-power long wavelength UV-A source (wavelengths longer than 340 nm). The irradiations lasted 2 h per day. The daily dose was 220 kJ/m2. Heavy scratching marks were observed in 13 out of 48 animals. However during the experiment 31 of the animals developed tumors of 1 mm or larger before any scratching was observed. The median induction time was 265 days for 1 mm tumors.     

FOLLOW UP ON SYSTEMIC INFLUENCE OF PARTIAL PRE-IRRADIATION ON UV-TUMORIGENESIS

Abstract— In a previous paper we presented experimental data which showed that partial pre-irradiation of a mouse enhanced subsequent UV-tumorigenesis in formerly unexposed skin areas: a systemic effect. In those experiments pre-irradiation was carried out up to the point where tumors started to appear in the pre-irradiated skin areas. Here we present the results of an experiment in which pre-irradiation was discontinued long before the appearance of tumors. The systemic effect induced by the pre-irradiation remained detectable, though-it was weaker than in the previous experiment. It is suspected that the observed systemic effect affects the initiation of tumors rather than the growth. A discussion is presented on how changes in initiation may best be detected, which may also prove to be useful for the design of other comparative studies on UV-tumorigenesis.     

UV doses of young adults

Since 1986, people have been informed that they get about 80% of their lifetime ultraviolet (UV) dose by the age of 18. This belief originated from the mathematical conclusion that diligent use of sunscreens (sun protection factor 15 or higher) during the first 18 years of life would reduce the lifetime incidence of nonmelanoma skin cancers by 78%. These data were misconstrued to mean that individuals also got about 80% of their lifetime dose of UV by the age of 18 (linear relationship). However, these calculations were based on the incidence of nonmelanoma skin cancers being related to the square of the UV dose. Careful analysis of UV exposure data shows that Americans actually get less than 25% of their lifetime UV dose by the age of 18. This finding also appears to be true worldwide because Australia, UK and The Netherlands report a similar UV exposure pattern. UV-initiated damage early in life can be promoted by subsequent exposures to progress into tumors later in life. For example, the nonmelanoma skin cancer, squamous cell carcinoma, is dependent on the cumulative UV dose. Thus, a better educational approach for reducing skin cancers would be to instruct fair-skinned individuals to protect themselves throughout their lives from being exposed to too much UV radiation.     

Strengths of electromagnetic transitions between bound states for a < 45

A recent review of the strengths of about 600 γ-ray transitions between bound states in the A = 21–44 region is extended in the present paper by including (i) the A<21 region, (ii) recent data on the A = 21–44 region, (iii) E0 transitions, (iv) magnetic transitions of which the (experimentally unknown) mixing ratio can be assumed to be negligibly small. The present addition concerns 350 transitions. Interesting new groups are the isovector E2 transitions (9 cases), and the isoscalar M2 transitions (7 cases). For magnetic transitions, the dependence of isospin retardation on multipolarity is stronger than expected theoretically. Recommended upper limits are presented for the 11 groups with reasonably good statistics. Because the strengths in the A<21 and A = 21–44 regions differ but little, the same upper limits can be used for the two regions.     

The deuteron binding energy

The ¹H(n, γ)²H γ-ray energy has been measured relative to ⁴⁸V and ¹⁴⁴Ce γ-rays, which are both based on the gold standard for γ-ray energies. The ensuing deuteron binding energy, $\text{B(}{}^2\text{H}\text{= 2224575 ± 9}\text{eV}$, confirms (with higher accuracy) the value from one of two conflicting recent precision measurements. This value has been used to recalculate the energies of γ-rays from thermal-neutron capture in ²H, ¹²C, ¹³C and ¹⁴N, which serve as mass-based γ-ray energy standards.     

THE DOSE-RESPONSE RELATIONSHIP OF TUMORIGENESIS BY ULTRAVIOLET RADIATION OF 254 nm

Abstract— Groups of albino hairless mice, Skh-hrl, were exposed daily to UVC radiation from low pressure Hg arcs (Philips TUV 40W). These lamps emit predominantly radiation of 254 nm. Three groups of animals were used in the experiments, each receiving a different daily dose.
The results were described with the Weibull probability function. As in earlier studies with UVB. the tumor induction time was proportional to a power of the daily dose. The exponent turned out to be as low as -0.2. This implies that the induction time varied only a little with the daily dose. The average number of tumors per animal was proportional to a power of time. A sample of 73 tumors of at least 4 mm in diameter were investigated histologically. The large majority were classified as squamous cell carcinomas.
A comparison was made with the results of an earlier reported experiment with Westinghouse FS40 sunlamps. Throughout the whole range of daily doses used in the present experiment, UVC was less carcinogenic than UVB. An intriguing difference between the two types of radiation was that the tumors induced by UVC appeared much more scattered over the irradiated parts of the animals than the UVB-induced tumors.