Discrimination between cutaneous pigmentation and erythema: comparison of the skin colorimeters Dermacatch and Mexameter.

BACKGROUND/PURPOSE: Reproducibility and specificity of the present skin colorimeters is still limited as alterations in erythema can bias the measurement of melanin and vice versa. Here, Dermacatch(®) , a new colorimeter covering the visible light spectrum, has been compared with Mexameter(®) , an established narrow-band reflectance spectrophotometer. METHODS: Repeated measurements with both devices were initially collected on colour charts. Then, measures were compared on 12 human volunteers before and after exposure to UVB, and/or modulation of skin erythema. RESULTS: In vitro sensitivity of Dermacatch to erythema/melanin covered a broader wavelength spectrum than Mexameter while in vivo sensitivity of both devices was similar. Interestingly, Mexameter's melanin and erythema values were falsely affected by an increase in erythema or variation in pigmentation respectively. On the contrary, Dermacatch's melanin and erythema values remained constant in the same circumstances. Furthermore, as Mexameter was at least twice less reproducible than Dermacatch, Mexameter showed an increased risk of a confusion over the detection of erythema or melanin fluctuations. CONCLUSION: The analysis of more than 18,000 measures indicated that, Dermacatch has a significantly higher specificity and reproducibility than Mexameter in the measurement of skin pigmentation and erythema.

Embryonic stem cell-based screen for small molecules: cluster analysis reveals four response patterns in developing neural cells.

Neural differentiation of embryonic stem cells (ESC) is considered a promising model to perform in vitro testing for neuroactive and neurotoxic compounds. We studied the potential of a dual reporter murine ESC line to identify bioactive and/or toxic compounds. This line expressed firefly luciferase under the control of the neural cell-specific tubulin alpha promoter (TUBA1A), and renilla luciferase under the control of the ubiquitous translation elongation factor 1-alpha-1 (EEF1A1) promoter. During neural differentiation, TUBA1A activity increased, while EEF1A1 activity decreased. We first validated our test system using the known neurotoxin methyl mercury. This compound altered expression of both reporter genes, with ESC-derived neural precursors being affected at markedly lower concentrations than undifferentiated ESCs. Analysis of a library of 1040 bioactive compounds picked up 127 compounds with altered EEF1A1 and/or TUBA1A promoter activity, which were classified in 4 clusters. Cluster 1 (low EEF1A1 and TUBA1A) was the largest cluster, containing many cytostatic drugs, as well as known neurodevelopmental toxicants, psychotropic drugs and endocrine disruptors. Cluster 2 (high EEF1A1, stable TUBA1A) was limited to three sulfonamides. Cluster 3 (high EEF1A1 and TUBA1A) was small, but markedly enriched in neuroactive and neurotoxic compounds. Cluster 4 (stable EEF1A1, high TUBA1A) was heterogeneous, containing endocrine disruptors, neurotoxic and cytostatic drugs. The dual reporter gene assay described here might be a useful addition to in vitro drug testing panels. Our two-dimensional testing strategy provides information on complex response patterns, which could not be achieved by a single marker approach.