Rapid separation of gonadotropin-releasing hormone molecular forms by isocratic high-performance liquid chromatography on an ion-exchange column

Identification and quantification of sea lamprey gonadotropin-releasing hormones by electrospray ionization tandem mass spectrometry

Gonadotropin-releasing hormones (GnRH) are neuropeptide hormones that regulate reproduction in vertebrates. Twenty-five unique chordate GnRH isoforms have been identified, all with very similar molecular architecture. Identification and quantification of endogenous GnRH in biological samples is extremely challenging due to the high levels of sequence similarity among these GnRH peptides and complexity of the biological matrices laden with large numbers of other peptides and protein degradation fragments, and due to low levels of GnRH abundance. In this study, three lamprey GnRH (lGnRH-I, -II, and -III) were extracted from sea lamprey brain tissue and plasma samples by solid-phase extraction (SPE) and identified by a high resolution Q-TOF mass spectrometry (MS). A rapid quantitation method was developed and validated to determine the concentrations of these three lGnRHs by using a UPLC coupled tandem MS in positive ESI multiple reaction monitoring (MRM) mode. Luteinizing hormone-release hormone (LHRH, one of the mammalian GnRHs) was used as the internal standard. The developed quantitation method was fully validated for its recovery, matrix effect, linearity, repeatability, precision and accuracy, and storage stability. This method exhibited excellent linearity in a broad concentration range for all three lGnRHs (R(2)>0.99) and limits of detection (LOD; as low as 0.007 ng/mL). Brain and plasma samples from a total of 280 sea lampreys were analyzed with the developed method to investigate the biological relevance of the lGnRH levels. The concentrations of these three lGnRHs were detected at levels of pictogram per microgram brain tissue and milliliter of plasma. The obtained analytical performance parameters and collected data from real biological samples have proven that this is a robust, sensitive, and fully validated LC-MS/MS method to simultaneously quantify three neuropeptide hormones in complex biological matrices.

Chromatography of guanidino compounds

Guanidino compounds involved in the urea and guanidine cycles have been found in serum of nephritic patients, and some guanidino compounds have been suspected to be uremic toxins. The simultaneous analysis of naturally occurring metabolites is important for diagnosis of diseases. In this review, liquid chromatographic analysis of natural metabolites of guanidino compounds are described. the information about arginine as a precursor of nitric oxide are included. The reports of pharmaceutical compounds having a guanidino group, peptides containing arginine and aminoglycosides are summarized in Table 1.

Analysis of synthetic peptides by capillary zone electrophoresis in organic/aqueous buffers

Whereas synthetic peptides have been routinely analyzed for purity by reverse phase high performance liquid chromatography (RPHPLC) for a number of years, it is only in the last decade that the use of capillary zone electrophoresis (CZE) in aqueous buffers has been taken advantage of as an orthogonal method for the detection of impurities. However, we have found that hydrophobic amino acids and peptides often migrate as very broad, tailing absorbances or even precipitate in the aqueous buffers during CZE analysis. As a result, alternative buffer systems containing organic modifiers were sought. Varying concentrations of acetonitrile, methanol and isopropanol in sodium phosphate and triethylammonium phosphate buffers were used to study their effects on the electrophoretic migration of several synthetic peptides [gonadotropin releasing hormone (GnRH), corticotropin releasing factor (CRF) and analogs] and an enantiomeric synthetic amino acid. The organic/aqueous buffers used to obtain the best conditions for separation of porcine gonadotropin-releasing hormone (GnRH) and chicken II GnRH were then used to optimize a separation of nine native forms of GnRH decapeptides. Interestingly, several of these GnRHs have identical formal charges and yet could be separated. This suggests a mixed mechanism of separation that discriminates not only on the basis of peptide charge and structure but also of adsorptive properties (Van der Waals forces, dipole-dipole interactions and hydrogen bonding) of the capillaries.