MRL/lpr mice have alterations in brain metabolism as shown with [1H-13C] NMR spectroscopy

Cerebral glucose metabolism and cerebral blood flow are altered in patients with lupus who have neuropsychiatric manifestations. However, the dynamics of changes in glucose metabolism remain unclear. The present study was undertaken using 1H and 13C nuclear magnetic resonance (NMR) spectroscopy to determine the rates of incorporation of glucose into amino acids and lactate via cell-specific pathways in mice with lupus. In the well-established MRL/lpr lupus mouse model, 24-week-old mice had a significant increase of 30-80% (P < 0.001) in total brain glutamine, glutamate and lactate concentrations, while alanine, aspartate, N-acetyl aspartate (NAA) and γ-aminobutyric acid (GABA) remained unchanged as compared to the congenic MRL +/+ control mice. Although succinate concentration was increased in lupus brain, it did not reach statistical significance. Furthermore, 13C isotopomer analysis showed a selective increase of de novo synthesis of lactate from [1-13C] glucose through glycolysis resulting in 1.5-fold increased fractional 13C enrichments in lactate in MRL/lpr mice. [4-13C] Glutamate, which is synthesized mainly by the neuronal pyruvate dehydogenase, was selectively increased, while [2-13C] and [3-13C] GABA synthesis were decreased by 25% compared to controls. In accordance with the total concentrations, aspartate synthesis remained unaltered in brains of lupus mice, while alanine synthesis was elevated, indicating increased utilization of alanine. Creatine was unchanged in MRL/lpr mice as compared to controls. An interesting finding was a significant increase (158%, P < 0.005) in choline concentration in MRL/lpr mice while the myo-inositol concentration remained the same in both groups. Furthermore a significant increase in total brain water content was observed, indicative of possible edema. In conclusion, the cumulative effect of increased brain lactate synthesis, altered glucose metabolism and intracellular glutamine accumulation could be an important mechanism causing brain pathology in SLE. The alteration in metabolites could alter downstream pathways and cause neurological dysfunction. Future NMR spectroscopic studies using stable isotopes and real-time measurements of metabolic rates, along with levels of metabolites in plasma and cerebrospinal fluid, could be valuable in the elucidation of the cerebral metabolic consequences of systemic lupus erythematosis (SLE) in humans.