Comprehensive characterization and simultaneous analysis of overall lipids in reconstructed human epidermis using NPLC/HR-MSn: 1-O-E (EO) Cer, a new ceramide subclass.

Stratum corneum lipids are responsible for the skin's barrier function. They are the final product of epidermis lipid biosynthesis. During this process, lipids evolve from simple to complex structures in three main levels respectively (stratum basal level, stratum granulosum level, and stratum corneum level). Our aim was to simultaneously analyze and characterize the structure of total epidermis lipids. A powerful analytical method (normal-phase liquid chromatography coupled with high-resolution mass spectrometry (NPLC/HR-MSn)) was developed in order to separate, in a single run, lipid classes with a wide polarity range. Chromatographic conditions were particularly designed to analyze lipids of intermediate polarity such as ceramides. Rich information was obtained about the molecular structure of keratinocyte differentiation biomarkers such as ceramides, glucosylceramides, and sphingomyelins and the microstructures of reconstructed human epidermis lipids using HR-MSn. A new subclass of ceramides, 1-O-Acyl Omega-linoleoyloxy ceramides [1-O-E (EO) Cer] has been highlighted. This class is double esterified on the 1-O-position of sphingoid base with long to very long chain acyl residues (1-O-E) and on the position of ω-hydroxyl group of fatty acid with the linolenic acid (EO). Considering its chemical structure and hydrophobicity, this subclass can contribute to the skin barrier. In addition, we detected a new epidermis sphingomyelins. Our lipidomic approach offers a direct access to epidermis biomarkers.

To what extent does freezing impact the mid-infrared signature of urine? Case of patients attending urology department.

Urine is a very interesting and attractive biofluid for biomarker discovery and medical diagnosis research due to its non-invasiveness collection and richness of potential biomarkers. Fourier-Transform Infrared (FTIR) spectroscopy applied on urine samples is a promising tool that could be used as a screening method for various diseases. However, during method development, frozen urine is more accessible, especially for inter-laboratory studies, whereas in routine application fresh urine is more convenient. Here, the objective of our work is to evaluate the freezing impact on mid-infrared signature of urine samples. Therefore, both fresh and frozen urine samples from twenty patients were analysed in a dried form. These samples were collected from patients consulting for cystoscopy examination. Simultaneously, centrifugation was also conducted on 10 of all included patients. Principal component analysis (PCA) revealed that patient inter-variabilities are higher than variability due to the freezing step. Then, Euclidean distance between fresh and frozen urine of each patient highlighted that the impact of freezing is different from one patient to another. Adding the centrifugation step slightly minimized intra-patient variability compared to not centrifugated samples. This study contributes to define experimental conditions for urine analysis development for translational application in biomedical field.