Preprint Augmentation of Anaerobic Pentose Phosphate Pathway Dysregulates Tetrahydrobiopter in Metabolism in ME/CFS Patients with OI..., 2023, Roy et al

Augmentation of Anaerobic Pentose Phosphate Pathway Dysregulates Tetrahydrobiopterin Metabolism in Myalgic Encephalomyelitis/ Chronic Fatigue Syndrome (ME/CFS) Patients with Orthostatic Intolerance: A Pilot Study

Sarojini Bulbule, Carl Gunnar Gottschalk, Molly E Drosen, Daniel Peterson, Leggy A Arnold, Avik Roy

Tetrahydrobiopterin (BH4), an essential cofactor of amino acid metabolism, was found to be strongly elevated in ME/CFS patients with Orthostatic intolerance (ME + OI). However, the molecular mechanism of BH4 upregulation is poorly understood in ME + OI patients.

Here, we report that the activation of the non-oxidative pentose phosphate pathway (PPP) plays a critical role in the biosynthesis of BH4 in ME + OI patients. Microarray-based gene screening followed by real-time PCR-based validation, ELISA assay, and finally enzyme kinetic studies of glucose-6-phosphate dehydrogenase (G6PDH), transaldolase (TALDO1), and transketolase (TK) enzymes revealed that the augmentation of anaerobic PPP is critical in the pathogenesis of ME + OI.

Along with the upregulated anaerobic PPP enzymes, we observed that biopterin metabolites such as BH4 and dihydrobiopterin (BH2) are strongly upregulated suggesting the disruption of biopterin homeostasis in ME + OI patients. To explore the molecular role of anaerobic PPP in biopterin metabolism, we devised a novel cell culture strategy to induce non-oxidative PPP by treating human microglial cells with ribose-5-phosphate (R5P) under a hypoxic condition of 85%N2/10%CO2/5%O2 followed by the analysis of BH4 and BH2 upregulation via ELISA, immunoblot and dual immunocytochemical analyses. These results confirmed that the activation of non-oxidative PPP is indeed required for the upregulation of both BH4 and BH2.

Moreover, the siRNA knocking down of the taldo1 gene strongly inhibited the expression of GTP cyclohydrolase 1 (GTPCH1) and subsequent production of BH4 and its metabolic conversion to BH2 in R5P-treated and hypoxia-induced C20 human microglia cells. To test the functional role of ME + OI plasma-derived biopterins, exogenously added plasma samples of ME + OI plasma with high BH4 upregulated inducible nitric oxide synthase (iNOS) and nitric oxide (NO) in human microglial cells indicating that the non-oxidative PPP-induced-biopterins could stimulate inflammatory response in ME + OI patients.

https://www.researchsquare.com/article/rs-3716093/v1

 

Years ago I read that BH4 is involved in an alternative loop for forming methionine if there are issues with folate and B12 . I may be misremembering , but it's part of a very complex interdependent system for many compounds , some compromised by genetics and epigenetic expression .

We need to look at all of these as interdependent.

 

Another impact re BH4 availability - reduced recycling of BH2 to BH4 if folate availability is reduced.

uncoupling of NOS by either too little BH4 or too little arginine produces not only superoxide and but also BH2 (a partially oxidized pterin). Both BH4 and BH2 bind to iNOS with equal affinity but only BH4 provides the desired enzymatic effect of producing NO. Therefore, BH2 can block BH4 from binding to iNOS. unbound BH4 is exposed to superoxide which converts the BH4 to peroxynitrite. So BH2 promotes more oxidative stress. To maintain BH4 homeostasis, BH2 is normally recycled back into BH4 by quinoid dihydropteridin reductase (QDPR) using dihydrofolate (DHF). This recycling pathway is also important because the use of BH4 as a co-factors in the production of neurotransmitters (serotonin, dopamine, norepinephrine, and epinephrine) always produces BH2 as an output. This recycling pathway is therefore a major source of BH4 and must remain reliably functional. However, efficiency is reduced by two types of genetic mutations -
mutations of QDPR have been shown to impair this recycling pathway.
folate mutations (chiefly MTHFR C677T and MTHFR A1298C) and/or a diet deficient in fresh green vegetables can reduce the availability of dihydrofolate for the recycling pathway .

If BH2 is upregulated as suggested in the paper, then having the above genetic mutations may underlie this or exacerbate it ?