Myalgic encephalopathy/chronic fatigue syndrome (ME/CFS) is a debilitating disease of unknown etiology, with hallmark symptoms including postexertional malaise and poor recovery. Metabolic dysfunction is a plausible contributing factor. We hypothesized that changes in serum amino acids may disclose specific defects in energy metabolism in ME/CFS. Analysis in 200 ME/CFS patients and 102 healthy individuals showed a specific reduction of amino acids that fuel oxidative metabolism via the TCA cycle, mainly in female ME/CFS patients. Serum 3-methylhistidine, a marker of endogenous protein catabolism, was significantly increased in male patients. The amino acid pattern suggested functional impairment of pyruvate dehydrogenase (PDH), supported by increased mRNA expression of the inhibitory PDH kinases 1, 2, and 4; sirtuin 4; and PPARδ in peripheral blood mononuclear cells from both sexes. Myoblasts grown in presence of serum from patients with severe ME/CFS showed metabolic adaptations, including increased mitochondrial respiration and excessive lactate secretion. The amino acid changes could not be explained by symptom severity, disease duration, age, BMI, or physical activity level among patients. These findings are in agreement with the clinical disease presentation of ME/CFS, with inadequate ATP generation by oxidative phosphorylation and excessive lactate generation upon exertion.
Øystein Fluge, Olav Mella, Ove Bruland, Kristin Risa, Sissel E. Dyrstad, Kine Alme, Ingrid G. Rekeland, Dipak Sapkota, Gro V. Røsland, Alexander Fosså, Irini Ktoridou-Valen, Sigrid Lunde, Kari Sørland, Katarina Lien, Ingrid Herder, Hanne Thürmer, Merete E. Gotaas, Katarzyna A. Baranowska, Louis M.L.J. Bohnen, Christoph Schäfer, Adrian McCann, Kristian Sommerfelt, Lars Helgeland, Per M. Ueland, Olav Dahl, Karl J. Tronstad
Hypothetic mechanism of ME/CFS linked to amino acid catabolism.
According to this model, ME/CFS is caused by immune interference with an unidentified target, potentially a signaling factor, which ultimately causes metabolic dysfunction and induction of secondary rescue mechanisms. We hypothesize that aberrant PDK and SIRT4-mediated inhibition of PDH, and consequent obstruction(s) in central energy metabolism, occurs early during ME/CFS pathogenesis, followed by metabolic adaptations serving to maintain ATP production. The result will be increased consumption of amino acids not depending on PDH to fuel oxidative metabolism via the TCA cycle. Such a mechanism would expectedly change the serum amino acid profile in patients, depending on the different entry stages of the amino acids into the catabolic pathway. Accordingly, for the purpose of serum amino acid profiling, the 20 standard amino acids were assigned into three categories: category I amino acids that may convert to pyruvate (i.e., dependent on PDH; Gly, Ser, Thr, Cys, Ala); category II amino acids that may metabolize to acetyl-CoA and fuel the TCA cycle (i.e., independent of PDH; Lys, Leu, Ile, Phe, Tyr, Trp); and category III amino acids that are anaplerotic and serve to replenish TCA cycle intermediates (i.e., independent of PDH; His, Pro, Met, Val, Glu + Gln = Glx, Asp + Asn = Asx). The asterisk indicates amino acids that were significantly reduced in serum of ME/CFS patients compared with healthy controls in this study (see