Stereochemistry of endogenous human RCTR1, RCTR2, and RCTR3. Gently minced human brain and spleen tissue sections were extracted, and levels of sulfido conjugates were assessed by lipid mediator metabololipidomics liquid chromatography–tandem mass spectrometry (MS-MS; Materials and Methods). A: Human brain identification of endogenous sulfido-conjugated products MCTR1, MCTR2, MCTR3, PCTR1, PCTR2, PCTR3, and RCTR3; representative multiple reaction monitoring (MRM) chromatograms from five human donors (Materials and Methods). B: Human spleen identification of endogenous MCTR1, MCTR2, PCTR1, RCTR1, RCTR2, and RCTR3; representative MRM chromatograms from seven human donors. C: Coinjections of synthetic and biological materials from human spleens. D: Human spleen identification of RCTR1, RCTR2, and RCTR3; representative MS-MS spectra. m/z, mass/charge ratio.