direct peptides are an important tool for assessing the skin sensitization potential of chemical compounds. They are generally electrophilic and react with the nucleophile amino acid residues cysteine or lysine on proteins in the human epidermis, triggering an allergic contact dermatitis (ACD) response. The DPRA (OECD 442C) is an in-chemico test that evaluates the first key step in the skin sensitization Adverse Outcome Pathway, namely the reactivity of the compound with cysteine or lysine-containing synthetic peptides. Using LC/UV detection, the reactivity of the compound is monitored by measuring the depletion of the respective peptide in the reaction mixture. IIVS offers a fully automated service to perform the DPRA in compliance with the OECD 442C guideline and Good Laboratory Practices for regulatory submissions.

Molecular analysis of the lipids and glycoproteins in biological tissues and cells using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Peptide profiling in single neurons by combining MALDI-TOF and immunodetection. A strategy for enhancing the mass spectrometric sequencing of arginine-containing peptides with postsource decay MALDI-TOF. MALDI-TOF and MALDI-PSD mass spectrometric imaging of protein complexes in single mammalian cells and tissues. Rapid sequencing of peptides from single mammalian organelles with nanoliter chemistry and MALDI-TOF MS.

Neuropeptide expression and processing in a small neuronal network revealed by mass spectrometric characterization of aplysia brain peptidomes. Identification and characterization of interganglionically transported peptides in the Aplysia cerebral ganglion F cluster. A proteomic survey of neuroendocrine signaling in a single Aplysia ganglia cell using MALDI-TOF mass spectrometry. Processing and targeting of the insulin-related peptide prohormone in neurons producing it in the mollusk Aplysia californica.

The DPRA is a well-established in chemico assay to identify potent skin sensitizers. IIVS has extensive experience in the development, implementation and quality control of this method for screening chemicals with potential to cause skin sensitization. Moreover, the IVVS team is trained in the use of this method and is competent to perform the testing for the DPRA according to the OECD 442C guideline.

The DPRA is performed on a fully automated MALDI-TOF instrument. The procedure begins with the addition of a peptide solution to each sample, followed by the injection into the MALDI chamber. The sample is ionized by the interaction between the peptide and the ionic beam in the MALDI reflectron, with the fragment ions detected by the MALDI-TOF detector. To obtain accurate and reliable results, it is important to prepare the peptide and reagents correctly. To ensure this, the peptide solution is tested for solubility and purity prior to analysis, while the reagents are kept at a stable concentration by regular dilution of the stock solutions. The resulting peptide and reagent concentrations are recorded by the MALDI-TOF system to provide high-quality data. The peptide and reagent samples are then evaluated by the software to generate data, displaying an average value for each peptide. This result is the basis for identifying potent sensitizers.