Paul Krien

Electrochemical determination of femtomole amounts of free reduced and oxidized glutathione: Application to human hair follicles

A simple and sensitive high-performance liquid chromatographic technique has been developed for the quantification of free reduced and free oxidized glutathione in biological samples. After acidic extraction and isocratic separation of the compounds of interest on a reversed-phase column, both forms of glutathione are quantified with a coulometric detector working in the oxidative mode. The limit of detection is 125 fmol for reduced glutathione and 400 fmol for the oxidized form (signal-to-noise ratio of 3). This sensitivity allows the measurement of the small amount of glutathione present in a single hair follicle. The technique is well adapted to microsamples, i.e. for non-invasive sampling technique (hair, skin, tears, etc.) and can be adapted to various cells or tissues.

SUNSCREENS WITH BROAD-SPECTRUM ABSORPTION DECREASE THE trans TO cis PHOTOISOMERIZATION OF UROCANIC ACID IN THE HUMAN stratum corneum AFTER MULTIPLE UV LIGHT EXPOSURES

Abstract The trans to cis photoisomerization of urocanic acid (UCA) in skin is considered to play an important role in the mechanism of immunosuppression. We have investigated the effects of skin type and various sunscreens with low sun protection factor (SPF) on the UV‐induced cis‐UCA formation in human skin after exposure to artificial IJV light. The rate of cis‐UCA formation depends little on the skin type and is reduced by topical application of sunscreens. The rate of cis‐UCA formation decreases with increasing SPF and only broad‐spectrum, highly protective sunscreens offer protection against the UV‐induced formation of cis‐UCA, which accumulates in the stratum corneum after multiple UV exposures. A theoretical approach to estimate the distribution of cis‐UCA after irradiation indicates that this compound may diffuse into the deeper layers of the epidermis with D ∼ 10−17 m2/s, and that its elimination from the stratum corneum is mainly due to desquamation.

Direct comparison of DNA damage, isomerization of urocanic acid and edema in the mouse produced by three commonly used artificial UV light sources

Abstract— Exposure to sunlight can result in a number of harmful effects, including sunburn, erythema, premature aging of the skin, immune suppression and skin cancer. Studies designed to understand the underlying mechanisms often depend upon the use of artificial sources of UV radiation. Unfortunately, conclusions from different laboratories using different lamps often conflict, and it is entirely possible that the different spectra of sunlights used in each may be a source of conflict. To minimize confounding variables, we employed two of the more commonly used UY light sources, fluorescent sunlamps, such as the FS‐40 and Kodacel‐filtered FS‐40 sunlamps, and a xenon arc solar simulator and compared, in one series of standardized experiments, the effects of each light source on DNA damage, urocanic acid isomerization and edema formation. The dose‐response curves, calculated by linear regression or curve fitting were compared. The data indicate that DNA damage and urocanic acid isomerization were more sensitive to shorter wavelengths of UV than longer wavelengths, and the biological endpoint of edema most closely correlated with the induction of DNA damage. The results emphasize the dominance of shorter wavelengths within the UV spectrum in damaging biological tissues, even when the solar simulator, which contains significant amounts of UVA, was used and demonstrate that each light source has a characteristic pattern of induction of biochemical and biological endpoints.

Direct quantitative digital autoradiography—thin-layer chromatography of 3α,3β- and 5α-reduced and 17β-dehydrogenated androgens derived from testosterone metabolism

Abstract A digital autoradiographic—thin-layer chromatographic method involving simple steps is described for thorough separation of eight major androgens (testosterone, androstenedione, dihydrotestosterone, androsterone, epiandrosterone, androstanedione, 3α-androstanediol and 3β-androstanediol) derived from testosterone metabolism. Their direct quantification is performed by radioscanning, which avoids tedious plate-scraping and liquid scintillation counting. Satisfactory accuracy is obtained by both external standardization of plates by calibrated amounts of radiolabelled standard steroids and internal standardization of bioassays by radiolabelled squalane. Coefficients of variation are below 8.5% in the range 100–500 dpm. Some analytical criteria related to chromatographic conditions and quantification parameters depending on position-sensitive proportional counter are discussed.

Study of the re‐oiling process of hair with the replica technique

In the case of individuals with oily hair, the sebum excreted to the scalp surface spreads over the hair during the days following hair washing. The migration of sebum from the roots to the ends of hairs creates a gradient which may be measured by making casts on appropriate materials.