ECNI GC-MS analysis of picolinic and quinolinic acids and their amides in human plasma, CSF, and brain tissue

Abstract

To study the complex inter-relationships between inflammatory and apoptotic responses and the kynurenine pathway, we have utilized electron-capture negative ion mass spectrometry to develop trace analyses to concurrently quantify nicotinic acid (NIC), picolinic acid (PIC) and quinolinic acid (QUIN) in biological samples. We have shown that NIC and its amide nicotinamide (NAM) can be separately quantified by analyzing samples pre- and post-acid hydrolysis. We have now examined human plasma, CSF and brain tissue samples for the presence of putative picolinamide (PAM) and quinolinamide (QAM) by comparing PIC and QUIN concentrations pre- and post- gas phase hydrolysis. We report for the first time that, with respect to the free acids, relatively high concentrations of the amides (or, at least, hydrolysable precursors of the acids) are present in plasma and brain with marked relative increases in CSF. In normal control subjects (n=22) pre-hydrolysis plasma levels (± sem) of PIC and QUIN were 0.299 ± 0.034 and 0.47 ± 0.047 μmol/L respectively. Following hydrolysis the concentrations rose more than 4-fold to 1.33 ± 0.115 and 2.2 ± 0.27 μmol/L respectively. In CSF samples from patients with no sign of brain injury or pathology (n=10) pre-hydrolysis concentrations of PIC and QUIN were 0.017 ± 0.005 and 0.018 ± 0.006 μmol/L, respectively, which rose to 0.30 ± 0.06 and 0.06 ± 0.008 μmol/L respectively, after hydrolysis. In CSF samples from patients with a range of brain oedema or injury (eg subdural haemorrage, motor vehicle accident) (n=6) pre-hydrolysis concentrations of PIC and QUIN were 0.053 ± 0.03 and 0.29 ± 0.12 μmol/L, respectively. Following hydrolysis the concentrations were markedly increased to 6.06 ± 1.5 and 0.94 ± 0.63 μmol/L, respectively. The present investigation has shown for the first time that PAM and QAM are present endogenously with PAM being relatively higher than QAM, especially in CSF samples from patients with presumed brain inflammation. The site and mechanism of amidation of PIC and QUIN needs investigation.