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Biomedical subjects

R Roelandts

Publications and source records attributed to R Roelandts.

At least 37 records · Page 2Linked to original sources
PubMed1989

Modification of sunburn cell production in 8-MOP sensitized mouse epidermis: a method of assessing UVA sunscreen efficacy.

The UVA(320-400 nm) photoprotection of four commercially available sunscreens with different sun protection factors was evaluated in 8-methoxypsoralen (8-MOP) treated mouse epidermis with the number of sunburn cells (SBCs) as the end-point. SBC production in 8-MOP sensitized mouse epidermis with and without application of sunscreens is dose-related. The difference between the slopes of the dose-response curves of the control group and the four sunscreens was highly significant (p less than 0.001). It appears that the SBC production was modified both by the dose of the UVA irradiation administered and by the UVA photoprotection of the four sunscreens. It could be concluded that the number of SBCs in 8-MOP sensitized mouse epidermis is a useful parameter to quantify the degree of UVA photoprotection of sunscreens.

Animals↗
PubMed1988

Photophysical, photochemical and photobiological properties of pyrrolocoumarins; a new class of photoactive compounds.

With the aim of finding new photoactive compounds that may reduce the side effects of 8-methoxypsoralen photochemotherapy we report on some photophysical, photochemical and photobiological properties of recently synthesized pyrrolocoumarins, in particular 4-methyl-N-ethyl-pyrrolo[3,2-g]coumarin (PCNEt) which has an absorption maximum in the UV-A (320-400 nm). Laser (347 nm) flash photolysis studies showed triplet transients that were quenched by O2 and by ground state PCNEt. Singlet minus triplet spectra were broad (350-550 nm) and, at 700 nm, indicated solvated electron and radical production. PCNEt complexes with DNA in the dark and photobinds to thymine but does not form DNA cross-links. PCNEt was phototoxic in yeast with an action spectrum similar to its absorption spectrum. PCNEt showed photohaemolytic activity but was not phototoxic on guinea pig skin. These data suggest that PCNEt may photosensitize via several mechanisms: direct DNA photobinding, photodynamic action, or photoproduction of radicals.

Candida albicans↗
PubMed1988

Silver polish: another source of contact dermatitis reactions to thiourea.

A cleaning woman in a restaurant became sensitized to thiourea in a silver polish. The dermatitis persisted for several months and occasionally flared up after exposure to sunlight, even after she no longer used the product. Patch testing and photopatch testing showed that she had both contact and photocontact allergy.

Administration, Topical↗
PubMed1988

[Is accurate UVA dosimetry in photobiology and photodermatology an illusion?].

Accurate UVA dosimetry is of primary importance for photobiological research as well as for UVA phototherapy and photochemotherapy. For the former, it is necessary because the success or failure of an experiment can depend on the UVA dose, and for the latter, the carcinogenic risks are dependent upon the cumulative dosage, as is the evaluation of the therapy. Experience has shown that the UVA meters used in different photodermatological and photobiological centers give divergent values when exposed to the same UVA source. One Joule/cm2 does not seem to be the same thing everywhere, and it can vary by as much as 400 p. 100.

Humans↗
PubMed1987

Contact and photocontact sensitivity problems associated with thiourea and its derivatives: a review of the literature and case reports.

Thiourea and its derivatives have been widely used in industry since the beginning of this century, but it was only in the late 1960s that reports of cases of contact dermatitis to these compounds began to appear in the literature. This literature is reviewed. We have observed eight cases of diphenylthiourea sensitivity in patients sensitive to adhesive tape. Four cases are presented of sensitivity to thiourea compounds in diazo-sensitized paper. Three of these patients were contact allergic to dimethylthiourea, and the other was contact and photocontact allergic to thiourea. These skin problems were mainly induced by airborne contact.

Adult↗
PubMed1987

[Carcinogenic risks of phototherapy and photochemotherapy].

The data in the literature regarding the carcinogenic risks involved in both UVB phototherapy and 8-methoxypsoralen plus UVA photochemotherapy are discussed. Both modes of treatment can be mutagenic and can induce immunosuppression. Which of the two factors (the initiator or the promoter effect) is more responsible for the carcinogenic risks involved in phototherapy or photochemotherapy is a subject of much controversy. In addition to discussing the theoretical background, the present article also takes into consideration the long-term clinical studies that have been performed. Practical guidelines are given on how to apply phototherapy and photochemotherapy as safely as possible.

Humans↗
PubMed1986

Light on the persistent light reaction-photosensitivity dermatitis-actinic reticuloid syndrome.

In this article are reviewed the various hypotheses concerning the etiology of the persistent light reaction and photosensitivity dermatitis, which occurs among older people and is characterized by an extreme photosensitivity that sometimes evolves into a pseudolymphoma, that is, actinic reticuloid. An etiologic agent can sometimes be demonstrated, but the precise pathogenetic mechanism is unknown. Clinical experience and experimental research indicate that the cause is most probably multifactoral: contact allergenic, photoallergenic, phototoxic, immunologic, and metabolic factors are involved, but their precise roles in the origin of the extreme photosensitivity are still unclear. Localized persistent light reactivity could result from the continued effects of the original photoallergen, but generalized photosensitivity is more difficult to account for. Among the many different hypotheses, two are of special interest: autosensitization of skin proteins with endogenous photosensitizers and cellular hypersensitivity to light, as is manifested by fibroblast cultures of actinic reticuloid patients.

Allergens↗
PubMed1986

Status of ultraviolet A dosimetry in methoxsalen plus ultraviolet A therapy.

The carcinogenic risk of methoxsalen plus ultraviolet A treatment (PUVA) is almost certainly related to the cumulative UVA exposure dose. A reliable estimate of UVA dose is a major component, therefore, in determining the long-term safety of this treatment modality. Thirty-one UVA meters from twenty-nine different PUVA treatment centers were compared with a calibrated UVA meter. The results inferred that 95% of UVA meters used in PUVA centers are reading between 57% and 159% of the true UVA irradiance, a factor of 2.8 in relative sensitivity. This wide variation in accuracy between the UVA meters gives cause for concern. These variations were attributed to differences in calibration procedure, optical properties of the sensors, and, most importantly, poor quality control by the manufacturers. The situation that appears to have existed since the introduction of PUVA therapy can be improved only if dermatologists agree that the present inaccurate and uncertain approach to UVA measurements is unsatisfactory. Manufacturers of UVA meters should be encouraged to provide instruments as reliable as the dosimeters used in radiotherapy, in which the prescribed dose is probably within 5% of the true value. Ideally, a standard type of UVA meter with appropriate physical properties and an agreed calibration procedure should be used by all centers engaged in PUVA treatment.

Humans↗
PubMed1985

Standardizing 8-methoxypsoralen plasma profiles by using an emulsion form.

Uniform 8-methoxypsoralen (8-MOP) absorption from the gastrointestinal tract is necessary to avoid day-to-day variations in 8-MOP plasma levels when treating patients with psoriasis by photochemotherapy. Because of its low water solubility, particle size and crystal form of the 8-MOP can significantly influence its bioavailability. The presentation form is also important, as is shown by the present study in which 8-MOP plasma levels were compared in thirty patients after oral administration in three different forms: formulation A consisted of gelatin capsules containing 8-MOP with a mean particle size of 200 mu; formulation B consisted of gelatin capsules containing 8-MOP in microcrystalline form with particle size between 20 mu and 30 mu; formulation C contained the same microcrystalline 8-MOP but in an emulsion base. Significantly higher plasma levels were found with formulations B and C than with formulation A. Furthermore, the individual differences in plasma profiles were markedly less with the emulsion base than with the capsule forms. Therefore, the clinical use of 8-MOP in emulsion form would constitute a major step in 8-MOP dose standardization and could lead to better control of subjective side effects and better therapeutic results.

Emulsions↗
PubMed1985

A pharmacokinetic comparison in dogs of seven brands of 8-MOP and five new formulations.

A pharmacokinetic comparison was carried out with 7 commercially available brands of 8-methoxypsoralen and 5 new formulations. The purpose of the study was to determine the brand or formulation with the least interindividual variation and thus the best standardized 8-methoxypsoralen plasma levels. The experiment was performed on dogs and not on human subjects because each of the 12 preparations had to be given to the same individual. The 8-methoxypsoralen plasma levels were measured by high performance liquid chromatography. One commercial and one self-made formulation showed a significantly earlier peaking time and higher peak concentration than the other brands tested. At 1 hour after administration the same commercial preparation and 4 self-made formulations showed significantly higher plasma levels than the other formulations. At 2 h, however, 10 of the 12 brands or formulations did not show statistically significant differences in 8-methoxypsoralen plasma levels.

Animals↗