Dipeptides in CSF and plasma: diagnostic and therapeutic potential in neurological diseases

Abstract

Dipeptides (DPs), composed of two amino acids (AAs), hold significant therapeutic potential but remain underexplored. Given the crucial role of AAs in central nervous system (CNS) function, this study investigated the presence of DPs in cerebrospinal fluid (CSF) and their correlation with corresponding AAs, potentially indicating their role as AA donors. Plasma and CSF samples were collected from 43 children with neurological or metabolic conditions of unknown origin, including 23 with epilepsy. A panel of 33 DPs was quantified using UPLC-MS/MS. Out of 33 DPs, 18 were detectable in CSF and 20 in plasma, displaying high inter-individual variance. Gly-Asp, Gly-Pro, and Ala-Glu were consistently found in all CSF samples, while only Gly-Asp was universally detectable in plasma. Anserine and carnosine were prominent in CSF and plasma, respectively, with no other histidine-containing DPs observed. Generally, DP concentrations were higher in plasma than in CSF; however, anserine and Gly-Pro had similar concentrations in both fluids. Significant correlations were observed between specific DPs and their corresponding AAs in CSF (Gly-Glu, Gly-Pro and Ser-Gln) and plasma (Glu-Glu and Glu-Ser). Notably, patients with epilepsy had elevated medium anserine concentrations in CSF. This study is the first to demonstrate the presence of numerous DPs in CSF and plasma. Further research is needed to determine if DP patterns can support the diagnosis of neurological diseases and whether DP administration can modulate amino acid availability in the brain, potentially offering new therapeutic options, such as for defects in the amino acid transporter.

Keywords: CSF; Dipeptide; Epilepsy.

Fig. 1

Dipeptide concentrations (fmol/µl) in CSF (A) and plasma (B) of 43 CSF samples from children with neurological or metabolic conditions of unknown origin. In CSF, out of 43 patients, anserine was detectably in 24 patients, Gly-Asp in 43, Carnosine in 4, γ-Glu-ε-Lys in 36, Asp-Gln in 26, Gly-Pro in 43, Glu-Ser in 21, Ser-Gln in 17, Ala-Glu in 43, Pro-Gly in 42, Gly-Glu in 23, Ala-Ala in 24, Ser-Ala in 13, Glu-Glu in 21, Gly-Phe in 3, Val-Tyr in 22, Phe-Ala in 3 and Leu-Pro in 13. In plasma, anserine was detectably in 12 patients, Gly-Asp in 43, Carnosine in 12, γ-Glu-ε-Lys in 3, Asp-Gln in 14, Gly-Pro in 42, Glu-Ser in 25, Ser-Gln in 17, Ala-Glu in 42, Pro-Gly in 39, Gly-Glu in 37, Ala-Ala in 28, Ser-Ala in 23, Glu-Glu in 37, Gly-Phe in 9, Val-Tyr in 21, Phe-Ala in 15, Ala-Gly in 27, Ala-Pro in 24 and Ala-Phe in 1. Displayed is a Tukey-Box-Plot

Fig. 2

The concentrations of the three DPs present in all patients, Gly-Asp (A), Gly-Pro (B) and Ala-Glu (C) and anserine (D), the DP with the highest concentration on average in CSF of patients without (w/o) and with epilepsy (in fmol/µl). Anserine was detectable in 12 patients without and with epilepsy, Gly-Asp, Gly-Pro and Ala-Glu in 20 patients without and in 23 patients with epilepsy. The mean values of these DPs tend to be higher for patients with epilepsy than for patients without epilepsy, but did only reach statistical significance in anserine. Mann–Whitney test was used for statistical evaluation. Displayed is mean ± SD. *p < 0.05. ns = not significant