Elevated glutamate and decreased glutamine levels in the cerebrospinal fluid of patients with MELAS syndrome

Background Mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) syndrome is a genetically heterogeneous disorder caused by mitochondrial DNA (mtDNA) mutations in the MT-TL1 gene. The pathophysiology of neurological manifestations is still unclear, but neuronal hyperexcitability and neuron-astrocyte uncoupling have been suggested. Glutamatergic neurotransmission is linked to glucose oxidation and mitochondrial metabolism in astrocytes and neurons. Given the relevance of neuron-astrocyte metabolic coupling and astrocyte function regulating energetic metabolism, we aimed to assess glutamate and glutamine CSF levels in MELAS patients. Methods This prospective observational case-control study determined glutamate and glutamine CSF levels in patients with MELAS syndrome and compared them with controls. The plasma and CSF levels of the remaining amino acids and lactate were also determined. Results Nine adult patients with MELAS syndrome (66.7% females mean age 35.8 +/- 3.2 years) and 19 controls (63.2% females mean age 42.7 +/- 3.8 years) were included. The CSF glutamate levels were significantly higher in patients with MELAS than in controls (18.48 +/- 1.34 vs. 5.31 +/- 1.09 mu mol/L, p < 0.001). Significantly lower glutamine concentrations in patients with MELAS than controls were shown in CSF (336.31 +/- 12.92 vs. 407.06 +/- 15.74 mu mol/L, p = 0.017). Moreover, the CSF levels of alanine, the branched-chain amino acids (BCAAs) and lactate were significantly higher in patients with MELAS. Conclusions Our results suggest the glutamate-glutamine cycle is altered probably due to metabolic imbalance, and as a result, the lactate-alanine and BCAA-glutamate cycles are upregulated. These findings might have therapeutic implications in MELAS syndrome.

Automated summary

This study found that levels of glutamate were significantly elevated and glutamine levels were significantly decreased in the cerebrospinal fluid of patients with MELAS syndrome. Additionally, levels of alanine, branched-chain amino acids, and lactate were found to be significantly higher in MELAS patients. These findings suggest an altered glutamate-glutamine cycle and upregulated lactate-alanine and branched-chain amino acid-glutamate cycles, which may have therapeutic implications in MELAS syndrome.