Occupational Exposure to Solar UVB and Seasonal Monitoring of Serum Levels of 25-hydroxy Vitamin D3: A Case–Control Study

To characterize the relationship between occupational sun exposure and seasonal variations in serum 25-OH-D3, four consecutive measurements of 25-OH-D3, one per season, were taken in 122 outdoor and 104 indoor Israeli workers. Continuous UVB measurements, taken in Beer Sheva, Israel, provided the average daily standard erythema dose (SED) of ambient solar UVB. The average daily exposure of the outdoor and indoor workers to solar UVB was 4.4 ± 1.6 h (4.0–37.6 SED) and 0.9 ± 0.5 h (0.6–8.2 SED), respectively. At each season mean 25-OH-D3 were significantly higher among outdoor workers than among indoor workers. Mean 25-OH-D3 increased significantly from spring to autumn in both gender and occupational groups. Adjusting for confounders, high (>median) 25-OH-D3 among males was significantly associated with occupational sun exposure in the autumn (odds ratio [OR] 4.31; 95% confidence interval [CI] 1.4–13.3), and among females in the spring (OR 3.35; 95% CI 1.53–7.32). Among this working population optimal vitamin D status (≥30 ng mL⁻¹) was approached only in summer by males working either outdoor or indoor. In the rest of the year 25-OH-D3 ranged between ≥20.0 and 29.0 ng mL⁻¹. Monitoring 25-OH-D3 may disclose undesirable vitamin D status following reduced sun exposure for skin cancer prevention among outdoor workers.     

Serum Levels of 25‐Hydroxy‐Vitamin D3 Among Sun‐protected Outdoor Workers in Israel

The objective of this study was to evaluate the effect of reduced sun exposure of outdoor workers on vitamin D status using different modalities of sun protection, for primary prevention of skin cancer. 25‐OH‐D3 measurements were performed in two successive winters, 8 (interim) and 20 months after initiation of the study, in three groups of male outdoor workers, enrolled in either a complete, partial or minimal sun protection program. Ambient solar UVB radiation was monitored simultaneously. No intragroup or intergroup differences were observed between the interim‐ and postintervention measurements of mean 25‐OH‐D3, which were close to 30 ng mL^?1. Significant risk factors for postintervention 25‐OH‐D3 levels >33.8 ng mL^?1 (a surrogate for reduced sun protection) were: previous sunburn episodes (OR 2.5; 95% CI 1.01–6.3; P = 0.05) and younger age (OR 0.92; 95 CI 0.86–0.98; P = 0.009). Outdoor workers of Western, compared with those of Eastern paternal origin had a borderline significant risk (OR 2.4; 95% CI 0.9–6.3; P = 0.07). A borderline significant effect (OR 2.9; 95% CI 0.97–10.1; P = 0.085) was also noted for those in the minimal intervention group. In conclusion, sun protection among outdoor workers following a successful intervention did not suppress mean winter 25‐OH‐D3.     

Uniform Stability of Local Extrema of an Integral Curve of an ODE of Second Order

A second-order equation can have singular sets of first and second type, S₁ and S₂ (see the introduction), where the integral curve x(y) does not exist in the ordinary sense but where it can be extended by using the first integral [1–-5]. Denote by Y the Cartesian axis y=0. If the function x(y) has a derivative at a point of local extremum of this function, then this point belongs to S ₁∪Y. The extrema at which y'(x) does not exist can be placed on S ₂. In [5–-8], the stability and instability of extrema on S ₁∪ S ₂ under small perturbations of the equation were considered, and the stability of the mutual arrangement of the maxima and minima of x(y) on the singular set was studied (locally as a rule, i.e., in small neighborhoods of singular points). In the present paper, sufficient conditions for the preservation of type of a local extremum on the finite part of S ₁ or S ₂ are found for the case in which the perturbation on all of this part does not exceed some explicitly indicated quantity which is the same on the entire singular set.     

Some qualitative properties of the Van der Pol equation inferred from its singular set

It is shown that the singular set of an extended “inverse” integral curve x(y) of the Van der Pol equation is covered with local extrema of x(y) that are stable with respect to small perturbations in the equation. As a consequence, the qualitative behavior of x(y) can be determined and some of its important properties can be understood.     

Extremal Points of Integral Curves of Second-Order Ordinary Differential Equations and Their Local Stability

In [1--3] an extension of the solution of the equation , to the singular set , is defined in terms of the first integral. In this case all stationary points and all local extrema of the integral curve such that the function has a derivative at the extreme point belong to a set , where Y is the line . We study the local stability of local extrema of different types in the families of equations small enough. Introduce the notation . By abuse of language, we talk about the stability of local extrema when S is replaced with . Some sufficient conditions for stability and instability are found.     

Serine Conjugates of Chlorophyll and Bacteriochlorophyll: Photocytotoxicity in vitro and Tissue Distribution in Mice Bearing Melanoma Tumors

Chlorophyll (Chl) and bacteriochlorophyll (Bchl) have been made water soluble by transesterfication with serine (Ser) at the propionyl residue and tested as potential reagents for photodynamic therapy (PDT). Photocytotoxicity of the conjugates Chl-Ser and Bchl-Ser in M2R mouse melanoma was tested in cell cultures. Tissue uptake and clearance of the photosensitizers in CD1 nude and C57B1 mice implanted with M2R tumors are described. Photocytotoxicity in cell cultures was determined microscopically and by [³H]thymidine incorporation. The LD₅₀ values in vitro were 0.05-0.1 μM for both sensitizers while that of the commercially available hematoporphyrin derivative (HPD, Photosan) was over 100 times higher for the same light intensity (45 mW/cm²). Pigment concentrations were determined fluorometrically in acetone extracts of the tissues of interest at different times after intraperitoneal injection of 20 mg pigment/kg body weight. The distribution pattern of Chl-Ser in the different tissues resembled that reported for Photofrin, chlorin and bacteriochlorin derivatives. Clearance from normal tissues was essentially completed within 16 h for Bchl-Ser and 72 h for Chl-Ser with mean half-lives (t_1/2) of about 2 and 7 h, respectively. In contrast, the clearance rates of these pigments and their metabolites from melanoma tumor tissue were significantly longer: t_1/2= 20 h for Chl-Ser and 15 h for Bchl-Ser and metabolites. The clearance rates showed biphasic or single exponential decay patterns in normal tissues and in tumors, respectively. Cumulatively the high phototoxicity, simple mode of delivery and fast tissue clearance rates reported here suggest that polar conjugates of Chl and Bchl promise to be highly effective PDT reagents.