Measurement of the penetration of 56 cosmetic relevant chemicals into and through human skin using a standardized protocol.

OECD test guideline 428 compliant protocol using human skin was used to test the penetration of 56 cosmetic-relevant chemicals. The penetration of finite doses (10 µL/cm2 ) of chemicals was measured over 24 hours. The dermal delivery (DD) (amount in the epidermis, dermis and receptor fluid [RF]) ranged between 0.03 ± 0.02 and 72.61 ± 8.89 µg/cm2 . The DD of seven chemicals was comparable with in vivo values. The DD was mainly accounted for by the amount in the RF, although there were some exceptions, particularly of low DD chemicals. While there was some variability due to cell outliers and donor variation, the overall reproducibility was very good. As six chemicals had to be applied in 100% ethanol due to low aqueous solubility, we compared the penetration of four chemicals with similar physicochemical properties applied in ethanol and phosphate-buffered saline. Of these, the DD of hydrocortisone was the same in both solvents, while the DD of propylparaben, geraniol and benzophenone was lower in ethanol. Some chemicals displayed an infinite dose kinetic profile; whereas, the cumulative absorption of others into the RF reflected the finite dosing profile, possibly due to chemical volatility, total absorption, chemical precipitation through vehicle evaporation or protein binding (or a combination of these). These investigations provide a substantial and consistent set of skin penetration data that can help improve the understanding of skin penetration, as well as improve the prediction capacity of in silico skin penetration models.

Use of a Simple in vitro Test to Assess Loss of Chemical due to Volatility during an in vitro Human Skin Absorption Study.

BACKGROUND: We tested the cutaneous distribution of 50 chemicals in frozen human skin. The mass balance (MB) values for 48% of the chemicals were < 90%, possibly due to evaporation. METHODS: We confirmed the reduction in MB was due to evaporation for two chemicals tested in skin penetration experiments using a carbon filter above the skin to trap airborne chemical. An in vitro assay was used to predict the reduction in MB due to evaporation by comparing the recovery of chemicals after 4 h of incubation at room temperature in open and closed vials. RESULTS: Evaporative losses in vitro correlated well with measured MBs (i.e., < 90%) in skin penetration experiments (R2 = 0.81). There was a correlation of the MB with the vapour pressure (VP) which could be used to group chemicals according to their likelihood to evaporate during the course of a skin penetration study. There was also a correlation of MB with Henry's law constants, melting and boiling points. CONCLUSION: Our data support the use of a quick and simple test for volatility to account for the loss of MB in skin penetration experiment due to volatility. The best parameter to indicate the potential of a chemical to evaporate is the VP.

Activation of RNA metabolism-related genes in mouse but not human tissues deficient in SMN.

Mutations of the survival of motor neuron gene (SMN1) are responsible for spinal muscular atrophies (SMA), a frequent recessive autosomal motor neuron disease. SMN is involved in various processes including RNA metabolism. However, the molecular pathway linking marked deficiency of SMN to SMA phenotype remains unclear. Homozygous deletion of murine Smn exon 7 directed to neurons or skeletal muscle causes severe motor axonal or myofiber degeneration, respectively. With the use of cDNA microarrays, expression profiles of 8,400 genes were analyzed in skeletal muscle and spinal cord of muscular and neuronal mutants, respectively, and compared with age-matched controls. A high proportion of genes (20 of 429, 5%) was involved in pre-mRNA splicing, ribosomal RNA processing, or RNA decay, and 18 of them were upregulated in mutant tissues. By analyzing other neuromuscular disorders, we showed that most of them (14 of 18) were specific to the SMN defect. Quantitative PCR analysis of these transcripts showed that gene activation was an early adaptive response to the lack but not reduced amount of full-length SMN in mouse mutant tissues. In human SMA tissues, activation of this program was not observed, which could be ascribed to the reduction but not the absence of full-length SMN.