Krebs Cycle Enzyme Evidence (KGDHC, Aconitase)
1 Che et al. 2022 — α-KG and Succinate Elevated in ME/CFS Plasma
Full Citation:: Che X, Brydges CR, Yu Y, et al. Metabolomic Evidence for Peroxisomal Dysfunction and Dysregulation of the CDP-Choline Pathway in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. International Journal of Molecular Sciences. 2022;23(14):7906. (Che et al. 2022) DOI:: 10.3390/ijms23147906 Key Findings::
- Untargeted plasma metabolomics; $n = 106$ ME/CFS vs 91 frequency-matched controls
- Both $α$-ketoglutarate AND succinate elevated in ME/CFS plasma
- Pattern consistent with a functional KGDHC block: substrate ($α$-KG) accumulates upstream, product (succinate) accumulates downstream
- Also identified peroxisomal dysfunction and CDP-choline pathway disruption
- *Certainty: 0.50* — reasonable sample, but metabolite accumulation is consistent with multiple explanations (glutamine overflow, transamination imbalance)Relevance:: Strongest standalone metabolomic evidence for a KGDHC flux defect in ME/CFS. The simultaneous elevation of substrate and product is the metabolomic fingerprint of an enzyme bottleneck, though alternative explanations exist. Combined with the Germain 2022 exercise-provoked inverse \(α\)-KG trajectory, this constitutes converging indirect evidence for G17.
2 Ciregia et al. 2016 — Aconitase Protein Upregulated in CFS Proteomics
Full Citation:: Ciregia F, Kollipara L, Giusti L, Zahedi RP, et al. Bottom-up proteomics suggests an association between differential expression of mitochondrial proteins and chronic fatigue syndrome. Translational Psychiatry. 2016;6:e904. (Ciregia et al. 2016) DOI:: 10.1038/tp.2016.184 Key Findings::
- Three-phase proteomics: discovery (nano-LC-MS platelet mitochondria from monozygotic twins discordant for CFS, $n = 2$ pairs), pathway analysis, validation (Western blot $n = 45$ CFS vs 45 controls, saliva)
- Mitochondrial aconitase (ACON/ACO2) upregulated: fold change 3.1 (twins), 1.9 (cohort, $p = 0.02$)
- Protein *upregulation* amid documented high ROS is paradoxical unless interpreted as compensatory overexpression of an enzyme being oxidatively destroyed
- No aconitase activity assay performed
- Discovery phase is $n = 2$ twin pairs (extremely small); validation used saliva (not metabolically relevant tissue)
- *Certainty: 0.40* — confirms altered aconitase protein expression in CFS; cannot address the activity questionRelevance:: Combined with Yamano 2016 (reduced isocitrate implying reduced aconitase flux) and Shankar 2025 (elevated superoxide that would inactivate aconitase’s [4Fe-4S] cluster), this creates a three-way convergence: reduced product (metabolomics), elevated protein (proteomics), elevated inactivator (ROS). The predicted resolution — high protein, low activity — would confirm oxidative aconitase inactivation and close G16.
3 Tretter & Adam-Vizi 2005 — KGDHC as Target and Generator of Oxidative Stress
Full Citation:: Tretter L, Adam-Vizi V. Alpha-ketoglutarate dehydrogenase: a target and generator of oxidative stress. Philosophical Transactions of the Royal Society B. 2005;360(1464):2335–2345. (Tretter and Adam-Vizi 2005) DOI:: 10.1098/rstb.2005.1764 Key Findings::
- Core mechanistic paper on KGDHC vulnerability to ROS
- 40--50% inhibition at 0.1--0.5 mM H~2~O~2~ (physiologically relevant concentrations)
- HNE (4-hydroxynonenal, lipid peroxidation product) irreversibly modifies E2 lipoic acid residues
- Peroxynitrite nitrates E1/E2 tyrosines
- Elevated NADH/NAD^+^ ratio drives E3 to generate *more* ROS (positive feedback)
- *Certainty: 0.75* — rigorous in vitro biochemistry; core reference for KGDHC-ROS fieldRelevance:: Every inactivating condition described — elevated H2O2, HNE from lipid peroxidation, elevated NADH/NAD+ — is independently documented in ME/CFS (Shankar 2025: elevated ROS and HNE; Heng 2025: elevated NAD+ in PBMCs with impaired reduction). KGDHC is therefore mechanistically predicted to be impaired in ME/CFS, but has never been measured (G17). The positive feedback loop (KGDHC inhibition → less NADH reduction → more E3 ROS → more KGDHC inhibition) could sustain a self-amplifying vicious cycle.
4 Naegel et al. 2023 — Skeletal Muscle Energy Metabolism by Dynamic 31P MRS in COVID-19 and MS
Full Citation:: Naegel A, Ratiney H, Karkouri J, et al. Alteration of skeletal muscle energy metabolism assessed by 31P MRS in clinical routine: Part 2. Clinical application. NMR in Biomedicine. 2023;36(12):e5031. DOI:: 10.1002/nbm.5031 PMID:: 37797947 Sample Size:: n=19 COVID-19 patients, n=38 multiple sclerosis, n=40 matched healthy controls Key Findings::
- Dynamic 31P-MRS with exercise/recovery protocol showed reduced muscle oxidative capacity (prolonged $\tau$PCr, reduced Vmax) in both COVID-19 and MS vs controls
- Resting phosphocreatine differences were inconsistent (PCr lower in MS only); the robust membrane markers of oxidative impairment appeared in recovery dynamicsConclusion:: The muscle bioenergetic deficit in post-viral/neuroimmune fatigue is largely exercise-provoked and visible in recovery kinetics, reconciling the Godlewska resting-muscle null with the exercised-muscle deficit literature. Limitations:: COVID-19 cohort likely heterogeneous in severity/timing; advanced quality-control pipeline reduced final analyzable sample.