A method for evaluating sunscreen protection from longwave ultraviolet

Molecular pathogenesis of pulmonary arterial hypertension

Recent clinical and experimental studies are redefining the cellular and molecular bases of pulmonary arterial hypertension (PAH). The genetic abnormalities first identified in association with the idiopathic form of PAH--together with a vast increase in our understanding of cell signaling, cell transformation, and cell-cell interactions; gene expression; microRNA processing; and mitochondrial and ion channel function--have helped explain the abnormal response of vascular cells to injury. Experimental and clinical studies now converge on the intersection and interactions between a genetic predisposition involving the BMPR2 signaling pathway and an impaired metabolic and chronic inflammatory state in the vessel wall. These deranged processes culminate in an exuberant proliferative response that occludes the pulmonary arterial (PA) lumen and obliterates the most distal intraacinar vessels. Here, we describe emerging therapies based on preclinical studies that address these converging pathways.

Evaluating the UVA protection of sunscreens

Because the protection factor of sunscreens concerns only UVB protection, usually nothing is known about the protection offered in the UVA range. Using different methods, we compared six commercially available sunscreens to determine the UVA protection factor and, thus, to select the most appropriate sunscreen. Two clinical methods on human skin (inhibition of UVA-induced tanning with the use of a high-intensity UVA source and inhibition of methoxsalen plus UVA-induced phototoxicity) were compared with a method in animals (inhibition of UVA-induced sunburn cell production in mice treated with methoxsalen) and with two in vitro techniques (solution-dilution and sandwich spectrophotometry). We conclude that all five methods used give a quantitative estimate of UVA protection, but none can be accepted as a standard because the UVA protection factor varies according to the method used and the reading time.

Assessment by mouse model of the ultraviolet A protective effect of topical sunscreens

We have developed an animal model to assess the ultraviolet A (UVA) protective effect of topical sunscreens with the use of BALB/cJ mice in which contact photosensitivity to 3, 3', 4', 5 tetrachlorosalicylanilide had been induced. The mice were sensitized on the clipped dorsal skin and challenged on the ears. Changes in ear thickness after challenge were used to measure the degree of photosensitivity. The efficacy of two doses of each topical sunscreen was assessed by the degree of suppression of the contact photosensitivity response at challenge. Control studies were performed with the base of each sunscreen. Some but not all sunscreens that contained UVA-absorbing chemicals showed active suppression of contact photosensitivity in this test system. Several sunscreens gave greater suppression at 5 microliters/cm2 than at 2 microliters/cm2, which suggests a dose-related effect. One sunscreen, however, gave greater suppression at 2 microliters/cm2. Several of the bases tested also suppressed the contact photosensitivity response. An unexpected finding was an enhancement of the contact photosensitivity reaction by two of the bases tested.

An animal model for evaluation of topical photoprotection against ultraviolet A (320-380 nm) radiation

Recent studies reporting UVA (ultraviolet A radiation 320-380 nm) as an integral part of the cumulative sun-induced damage in human skin have prompted an interest in developing effective UVA photoprotective agents. The development of such compounds has been impeded by the absence of a clinically relevant animal model for evaluating their efficacy. This report describes the development and use of such a laboratory animal system. Selected concentrations of oxybenzone (2-hydroxy-4-methoxybenzophenone) in vehicle (0.1% to 6%) or vehicle alone were applied to the depilated dorsal skin of 30 Hartley strain female albino guinea pigs. The skin was irradiated with solar simulated UVA from a xenon light source. Acute radiation-induced damage was assayed by erythema grading and inhibition of [3H]thymidine incorporation into epidermal DNA. Data from erythema grading studies indicated that a significant degree of photoprotection was achieved with 6%, 3%, and 1% solutions of benzophenone compared with the control vehicle; the 6% solution was significantly more photoprotective than the 3% and 1% solutions. A 6% solution afforded significant photoprotection when assayed by [3H]thymidine incorporation.

Efficacy of a sunscreen containing butyl methoxydibenzoylmethane against ultraviolet A radiation in photosensitized subjects

Topical formulations containing a new chemical entity, the ultraviolet A absorber Parsol 1789 (butyl methoxydibenzoylmethane), were evaluated as agents for protecting human skin against ultraviolet A (UVA) radiation. Healthy subjects were photosensitized to UVA radiation by ingestion of 8-methoxypsoralen (0.6 mg/kg). After 90 minutes, five formulations (vehicle, vehicle + butyl methoxydibenzoylmethane, vehicle + butyl methoxydibenzoylmethane + padimate O, vehicle + padimate O, and a marketed sunscreen containing padimate O, oxybenzone, and octyl salicylate) were applied in a randomized, double-blind manner to areas on the lower part of the back. Thirty minutes later, sites in the five treated areas and in a sixth unprotected area were exposed to graduated doses of UVA radiation. Test sites were evaluated for erythema 48 and 72 hours after UVA exposure, and for melanogenesis approximately 2 weeks later. The combination of butyl methoxydibenzoylmethane + padimate O demonstrated significantly greater protection than the combination of padimate O, oxybenzone, and octyl salicylate.

An evaluation of sunscreens in patients with broad action-spectrum photosensitivity

The photoprotection afforded by three sunscreens available by prescription in the U.K. has been studied in patients with severe broad action-spectrum photosensitivity. All products investigated exhibited high protection against UV-B radiation in accordance with the protection factors quoted by the respective manufacturers. On the other hand, the protection against UV-A ranged only from fair to poor. The need for a sunscreen which has good protection against UV-A is shown to be important for the satisfactory management of patients with severe broad action spectrum photosensitivity.

Mouse screening test for evaluating protection to longwave ultraviolet radiation

Albino mice photosensitized to psoralens were used for evaluating a sun-barrier preparation for use against longwave ultraviolet radiation. The difference in thickness of the treated and control ears at various times after irradiation was used as a measure of photoprotection.