Ronald E. Davies

Lipid oxidation: Biologic effects and antioxidants—A review

The detection and measurement of lipid oxidation in biological systems and some biologic effects of this oxidation are reviewed. The role of lipid oxidation in the process of photocarcinogenesis and the protective effect of antioxidants against this process also are discussed. The mechanism of such protection is unknown and studies directed at elucidating the mechanism of antioxidant effect in photocarcinogenesis and in some other pathological conditions believed to involve, lipid oxidation are needed. In addition to this, epoxidation of lipids observed in monolayer studies requires further investigation, particularly in the presence of some other unsaturated molecules. The possible significance of such a study—particularly in the presence of polycyclic aromatic hydrocarbon carcinogens, where formation of epoxides is generally accepted as active intermediates-is also discussed. In addition, present knowledge on the role of lipid peroxides in the destruction of proteins and biomembranes, in chemically induced toxicity and in generation of singlet oxygen is presented.

An action spectrum for uv photocarcinogenesis

Abstract— Hairless mice were irradiated repeatedly by exposure to unfiltered black‐light (FR74T12 PUVA) fluorescent lamps and the time to development of skin tumors was determined. For several groups of animals the treatment variable was the size of the weekly dose. A similar approach had been used previously to determine dose‐response characteristics for other ultraviolet radiation emitting sources: a xenon arc solar simulator (with a series of five cut‐off filters producing five source spectra), and a fluorescent (FS40T12) “sunlamp”. The median tumor latent period (time period for just more than one half of the animals to develop at least one tumor each) was accurately predicted for all these ultraviolet radiation emitting sources by a mathematical equation incorporating the spectral source description and a spectral weighting function. The weighting function judged most appropriate for ultraviolet radiation‐induced photocarcinogenesis was the action spectrum, determined previously, for acute (single dose) skin edema in hairless mice. The mathematical equation assigns no effectiveness to wavelengths greater than 330 nm. There was no evidence for wavelength interaction in the spectral range of 26MW nm. Our data, combined with results of others, lead us to conclude that radiation with wavelength greater than 330 nm has an average relative efficacy (297 nm =1.0) less than 0.0002, and that this efficacy is not detectable with sources in which at least 2% of the UV radiation is in the UV‐B range.

Enhancement of experimental photocarcinogenesis by topical retinoic acid.

Topical application of retinoic acid (RA) solutions greatly enhanced the response of hairless mouse skin to a moderate dose of simulated sunlight. Tumors appeared much earlier, and in much greater numbers, in animals treated daily with 1 or 10 micrograms of RA in methanol immediately after 2 h exposure to a xenon arc filtered through 2 mm of Schott WG 320 glass (approximately equivalent in human erythema effectiveness to 5 min of mid-summer noon solar exposure in northern mid-latitudes), compared to mice treated with light and methanol only. The higher amount of RA, in combination with light, produced moderate epidermal hyperplasia and some scaling and transient erythema, but no gross ulceration or inflammation of skin. The lower amount of RA, though about equally effective in carcinogenesis, produced minimal epidermal hyperplasia compared to the ultraviolet radiation + methanol control.

Comparison of action spectra for acute cutaneous responses to ultraviolet radiation: man and albino hairless mouse.

Abstract The hairless mouse has been used as an experimental model for photocarcinogenesis for about 20 years. Although the carcinogenesis action spectra for mice and man are not known, acute responses to ultraviolet radiation (UVR) in the biologically active UVB and UVC region (wavelengths below 320 nm) can be compared. Vascular response (predominantly edema) action spectra for monochromatic radiation in the Skh:HR‐l (albino hairless) male mouse were determined. These action spectra were found to be very similar to the human erythema action spectrum that had been developed using the same monochromator. The accuracy of this experimentally derived action spectrum was tested with a series of polychromatic source spectra. The mice were exposed to radiation from a long arc Xe lamp filtered by varying thicknesses of Schott WG320 filters, which yielded a wide range of biologically effective spectra. Spectral irradiance measurements, when weighted with the mouse edema and human erythema action spectra and multiplied by the irradiation time required to elicit a threshold response (edema), yielded a constant weighted dose regardless of irradiation spectral quality. The integrated effective dose was approximately 200 J/m2 of 297 nm equivalent energy, agreeing with requirements for the monochromatic 297 nm dose in the mice as well as for minimal human erythema. These data suggest a commonality in the UVR chromophores of mice and men as they relate to the acute responses described, and a direct additivity of effectiveness from the UVR components in a polychromatic beam, at least over the portion of the UVR spectrum tested (λ > 295 nm).

PHOTOCARCINOGENESIS IN HAIRLESS MICE: DOSE-RESPONSE AND THE INFLUENCE OF DOSE-DELIVERY‡

Abstract— Albino hairless (Skh:HR) mice were exposed to a series of daily (5 days/wk) doses of ultraviolet radiation (UVR) from a bank of fluorescent sun lamps (type FS40T12); the 24 animals in each group were examined weekly and skin changes, including tumor locations and sizes, were recorded. Primary endpoints were time to reach a specified proportion of mice bearing one or more tumors, (incidence) and time to reach a specified number of tumors per survivor (tumor yield). By these criteria, the effectiveness of the treatment increased over the range in which the skin could tolerate exposures without exhibiting overt damage (e.g. ulceration). For the 6 tolerated daily dose levels, corresponding tumor median latent periods (time to 50% incidence) described a linear relationship with log dose. A second study tested the effect of dose‐delivery (time‐dose reciprocity). Three groups of animals were treated with a weekly dose, delivered entirely either on 1 day, or one‐third on each of 3 days, or one‐fifth on each of 5 days, chosen so that the 1‐day exposure did not produce overt damage. This weekly dose coincided with the 4th of the 6 dose levels in the first experiment. Effectiveness of treatment increased directly with the number of fractions per week. The basis for this dose reciprocity failure is not known, but we expect to investigate the ratio of sublethal to lethal damage in epidermal cells, and to evaluate tumor growth promotion by single vs fractionated exposures.

Phototoxicity testing of fragrance raw materials

Abstract Of 160 fragrance raw materials tested for phototoxicity by a procedure involving topical application of the test agents to the skin of hairless mice and miniature swine, followed by exposure of the skin either to simulated sunlight or to near-ultraviolet light (UV-A), 21 elicited a phototoxic response. Of these, 20 were members of the botanical families Rutaceae or Umbelliferae; the single exception was from the family Verbenaceae. Several selected materials were tested, in sunlight and under three laboratory light sources, on the skin of mouse, man and miniature swine. Mouse skin was the most sensitive, reactions in human and swine skin being qualitatively and quantitatively similar.

Inhibition of Ultraviolet Radiation-Induced Skin Tumors in Hairless Mice by Topical Application of the Sunscreen 2-Ethyl Hexyl-P-Methoxycinnamate

AbstractThis study used simulated solar ultraviolet radiation (UVR) exposure of hairless mice to produce skin tumors and 12-o-tetradecanoyl-phorbol-13-acetate (TPA) to increase the likelihood of tumor expression. We evaluated the protection afforded by several concentrations of a sunscreen ingredient (by measuring reduction of “promotable” effects initiated by UVR); the data show that 2-ethyl hexyl-p-methoxycinnamate (2-EHMC) provided protection against photocarcinogenesis (the level of protection increasing with concentration of sunscreen). A second sample of 2-EHMC (drawn from a different production batch) also suppressed photocarcinogenesis but less effectively than the first sample. The study was also useful for evaluating whether the test agents could act as initiators in the two-stage process of tumorigenesis. The data show that repeated applications of TPA did not promote tumor growth in skin pretreated with any sunscreen ingredients alone (i.e., either sample of 2-EHMC in the absence of UVR).

PHOTOOXIDATION OF 8‐METHOXYPSORALEN WITH SINGLET OXYGEN

Abstract— The in vitro photooxidation of 8‐methoxypsoralen (8‐MOP) with singlet oxygen is studied. Irradiation of 8‐MOP(295–400 or320–400 nm) in the presence of oxygen for 72 h results in the formation of a product (1.4%) which is identified as 6‐formyl‐7‐hydroxy‐8‐methoxycoumarin by aid of IR, NMR, MS and co‐chromatography with an authentic sample. A study of this reaction in the presence of l,4‐diazobicyclo(2,2,2)octane, a singlet oxygen scavenger, indicates the involvement of 1O2 in the formation of this compound. In addition to this, formation of a novel dimer of 8‐MOP is reported.

Effect of Indoor Lighting on Normal Skin

A small but measurable component of some indoor lighting is ultraviolet radiation (UVR); whether it is sufficient to modify the indoor workers risk for chronic skin changes is not directly answerable with available technology. A first approach to this question involves a) estimating a range of annual background solar exposure for indoor workers currently at risk; b) determining whether, and at what levels, UVR exposure is a part of specified indoor lighting; and c) calculating the increment in risk implied by a and b. This algorithm predicts that some lighting conditions that meet NIOSH recommended standards would still result in significant increases in the risk of cumulative UVR damage, including skin cancer. More information concerning actual exposure conditions, the relation of spectral effectiveness for luminosity and UVR production, and dose-time reciprocity are required to improve our predictions of long-term cutaneous effects of indoor lighting.

Skin-tumour promoting activity of methyl ethyl ketone peroxide—a potent lipid-peroxidizing agent

The tumour-promoting activity of methyl ethyl ketone peroxide (MEKP) was tested on the skin of hairless mice using a two-stage initiation-promotion protocol. When ultraviolet radiation in the UVB region (280-320 nm) was used as tumour initiator, MEKP showed weak promoting activity. The promotional activity of MEKP was potentiated by diethyl maleate, which is known to deplete intracellular glutathione, suggesting that lipid peroxidation may be important in the tumour promotion.