Reducing Complexity? Cysteine Reduction and S-Alkylation in Proteomic Workflows: Practical Considerations

Identification of Cross-Species Marker Peptides for the Detection of Mammalian and Poultry Meat in Vegan and Vegetarian Foods

Authentication of vegan and vegetarian foods is important since these increasingly popular food items could be adulterated with cheap meat to increase profit margins. In this study, nine marker peptides for the detection of meat (several species) were identified applying liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). These marker peptides enable the crucial differentiation of beef versus milk and chicken meat versus egg, demonstrated by the investigation of 19 commercial vegetarian meat substitutes containing milk and egg. Extensive experimental testing proved the presence of the cross-species meat marker peptides in 19 food-relevant types of mammals and poultry as well as their absence in more than 136 plant-based ingredients for the production of vegan and vegetarian foods. An authentic vegan sausage matrix based on an actual retail product was produced and spiked with 5.0%, w/w meat to confirm the high signal intensities and the heat stability of the marker peptides.

An improved sample extraction method reveals that plasma receptor for advanced glycation end-products (RAGE) modulates circulating free oxytocin in mice

The receptor for advanced glycation end-products (RAGE) binds oxytocin (OT) and transports it from the blood to the brain. As RAGE's OT-binding capacity was lost in RAGE knockout (KO) mice, we predicted that circulating concentrations of unbound (free) OT should be elevated compared to wild-type (WT) mice. However, this hypothesis has not yet been investigated. Unfortunately, the evaluation of the dynamics of circulating free and bound plasma OT is unclear in immunoassays, in part because of interference from plasma proteins. A radioimmunoassay (RIA) is considered the gold standard method for overcoming this issue, but is more challenging to implement; thus, commercially available enzyme-linked immunosorbent assays (ELISAs) are more commonly used. Here, we developed a pre-treatment method to remove the interference-causing components from plasma before performing ELISA. The acetonitrile protein precipitation (PPT) approach was reliable, with fewer steps needed to measure free OT concentrations than by solid-phase extraction of plasma samples. PPT-extracted plasma samples yielded higher concentrations of OT in RAGE KO mice than in WT mice using ELISA. After peripheral OT injection, free OT plasma levels spiked immediately then rapidly declined in WT mice, but remained high in KO mice. These results suggest that plasma samples with PPT pre-treatment appear to be superior and that circulating soluble RAGE can most likely serve as a buffer for plasma OT, which indicates a novel physiological function of RAGE.