Plasma and cerebrospinal fluid correlation for tryptophan and its metabolites and their expression in neurodegenerative, demyelinating, infectious diseases and CNS tumors.

BACKGROUND

To clarify the cerebrospinal fluid (CSF) and plasma correlation for tryptophan and its major metabolites in real clinical setting, and to explore their expression across common types of neurological disorders.

METHODS

181 paired CSF and plasma samples from patients with neurological diseases and 67 plasma samples from healthy controls were collected. Tryptophan, serotonin, 5-hydroxyindoleacetic acid (5-HIAA), melatonin, and kynurenic acid (KYNA) in those samples were measured using LC-MS/MS. Age- and sex-effects on plasma levels of those analytes were evaluated in healthy control. Pearson correlation analysis was used to assess CSF and plasma correlation. Patients were grouped into neurodegenerative, demyelinating, tumors, and infectious diseases for group comparisons.

RESULTS

CSF and plasma correlation were weak but still statistically significant for most analytes (r = 0.15-0.3, p < 0.05); but no significant correlation was observed for 5-HIAA. In healthy controls plasma tryptophan and was higher in males than in females, but 5-HIAA was higher in females. The plasma concentrations of these analytes showed no significant differences among different diseases, nor between the disease groups and the control group. However, the level of 5-HIAA were significantly lower in all disease groups compared with the control group. By contrast, CSF tryptophan and KYNA levels in patients with CNS tumors were significantly higher than in patients with other diseases.

CONCLUSIONS

Plasma tryptophan and its metabolites do not reliably reflect their CSF levels. The selective elevation of CSF tryptophan and KYNA in tumor patients may reflect tumor-associated changes in metabolism, but their biological significance requires further investigation.