Neurovaskulær dysregulering påvist hos ME patienter

Under motion skal venerne trække sig sammen, således veneblodet returneres til hjertet i tilstrækkeligt omfang. Hvis dette ikke sker, er der ikke blod nok til et fyldetryk i hjertekammeret. Det dysregulerede blodkredsløb medfører manglende iltforsyning til cellerne og hermed motionsintolerance. (engelsk: depressed cardiac output from impaired venous return - preload failure). 

Systrom's forskerteam har undersøgt om lægemidlet pyridostigmine kunne forbedre motionskapaciteten hos en gruppe ME patienter med lavt fyldetryk i højre hjertekammer (right artrial pressure (RAP) under 6,5 mm Hg. (1) 

45 ME patienter blev delt i to grupper. Begge grupper gennemgik invasiv kardiopulmonær motionstest (iCPET). Herefter fik den ene gruppe 60 mg pyridostigmine og den anden gruppe fik placebo. 50 minutter senere gennemgik alle en iCPET igen. Den maksimale iltoptagelse (peak Vo2 mL/min) blev målet under begge test. 

ME patientgruppen der fik pyridostigmine forbedrede den maksimale iltoptaglese ved test 2 med 13,3 mL/min i forhold til første test. ME placebogruppen havde en forrringet maksimal iltoptagelse ved test 2 på minus 40,2 mL/min i forhold til deres første test. Det vil sige behandlingsresponset af pyridostigmine var 53,6 mL/min. Forsøget viste også, at faldet i peak Vo2 hos placebogruppen var forårsaget af et fald i cardiac output og preload failure. 

De fysiologiske ændringer i iltoptagelsen er små og ikke klinisk relevante, men de fortæller os noget om ME sygdomsmekanismen (1): 

 "Interpretation: Pyridostigmine improves peak Vo2 in ME/CFS by increasing cardiac output and right ventricular filling pressures. Worsening peak exercise Vo2, cardiac output, and right atrial pressure following placebo may signal the onset of postexertional malaise. We suggest that treatable neurovascular dysregulation underlies acute exercise intolerance in ME/CFS." 

Reference:

1) Joseph P, Pari R, Miller S, Warren A, Stovall MC, Squires J, Chang CJ, Xiao W, Waxman AB, Systrom DM. Neurovascular Dysregulation and Acute Exercise Intolerance in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Randomized, Placebo-Controlled Trial of Pyridostigmine. Chest. 2022 Nov;162(5):1116-1126. doi: 10.1016/j.chest.2022.04.146. Epub 2022 May 6. 

https://pubmed.ncbi.nlm.nih.gov/35526605/

Læs også:

Lav arteriel-venøs iltindhold difference hos ME patienter

http://followmeindenmark.blogspot.com/2021/11/lav-arteriel-vens-iltindhold-difference.html

Efter motion har ME patienter forhøjet niveau af pyrroline-5-carboxylate

...fortsættelse. Læs først:
Metaboliske ændringer hos ME patienter før og efter to dages motion

http://followmeindenmark.blogspot.com/2022/04/metaboliske-ndringer-hos-me-patienter.html

Efter motion var niveauet af pyrroline-5-carboxylate (P5C) signifikant øget hos kvinder med ME i forhold til raske kontrolpersoner (1).

FC og p-værdier for P5C:

• D1PRE: FC = 1,18, p = 0,10
• D1POST: FC = 1,36, p = 0,009
• D2PRE: FC = 1,20, p = 0,13
• D2POST: FC  = 1,72, p = 0,0000122

P5C blev også fundet forhøjet hos ME patienter i Naviaux et al's studie (2).

P5C er et mellemprodukt i omsætning af aminosyrerne prolin, glutamat og ornitin.

Ved iltmangel (hypoxia) fungerer P5C og prolin  som et redoxpar, der påvirker NADP+/NADPH ratioen (3):

Figure 1. The metabolic pathways of P5C—physiological intracellular intermediate of the interconversion of proline, ornithine, and glutamate. Acetyl-CoA—acetyl coenzyme A, ATP—adenosine triphosphate, α-KG—α-ketoglutarate, Glu—glutamate, GSAL—L-glutamate-γ-semialdehyde, METC—mitochondrial electron transport chain, NAD+—oxidized form of nicotinamide adenine dinucleotide, NADH—reduced form of nicotinamide adenine dinucleotide, NADP+ –oxidized form of nicotinamide adenine dinucleotide phosphate, NADPH—reduced form of nicotinamide adenine dinucleotide phosphate, ORN—ornithine, P5C—∆ 1 -pyrroline-5-carboxylate, P5CDH—P5C dehydrogenase, P5CS—P5C synthase, PAT1—proton-coupled amino acid transporter 1, PRODH/POX—proline dehydrogenase/oxidase, PROT—L-proline transporter PROT, PYCR1/2/L—P5C reductase 1/2/L, ROS—reactive oxygen species, SIT1—sodium/imino-acid transporter 1, SNAT1/2—sodium-coupled neutral amino acid transporter 1/2, TCA cycle—tricarboxylic acid cycle, δOAT—ornithine δ-aminotransferase. Reference: Chalecka M, Kazberuk A, Palka J, Surazynski A. P5C as an Interface of Proline Interconvertible Amino Acids and Its Role in Regulation of Cell Survival and Apoptosis. Int J Mol Sci. 2021 Oct 29;22(21):11763. doi: 10.3390/ijms222111763. PMID: 34769188; PMCID: PMC8584052. https://www.mdpi.com/1422-0067/22/21/11763

Efter motion på 2. dagen var niveauet af proline signifikant øget hos kvinder med ME i forhold til raske kontrolpersoner (1): 

FC og p-værdier for proline: 

• D1PRE: FC = 1,03, p = 0,76
• D1POST: FC = 1,04, p = 0,88
• D2PRE: FC = 1,15, p = 0,13
• D2POST: FC = 1,18, p = 0,03

Pyrroline-5-carboxylate synthase (P5CS) katalyserer syntesen af P5C. P5CS mærker cellestress og tilpasser metabolismen ved at regulere mitokondriel respiration. P5CS er nødvendig for den oxidative respiration i mitokondrierne (4).

Hvad betyder det øgede niveau af P5C og proline hos ME patienter? Har det forbindelse til hypoxia? Stiger niveauet af P5C, fordi den oxidative respiration i mitokondrierne er udfordret af ME sygdom-mekanismen?


Læs også:
Lav arteriel-venøs iltindhold difference hos ME patienter

http://followmeindenmark.blogspot.com/2021/11/lav-arteriel-vens-iltindhold-difference.html

Andre gode artikler om P5C:
Proline synthesis through PYCR1 is required to support cancer cell proliferation and survival in oxygen-limiting conditions

https://pubmed.ncbi.nlm.nih.gov/35108535/

Perspectives, past, present and future: the proline cycle/proline-collagen regulatory axis

https://pubmed.ncbi.nlm.nih.gov/34825974/

Referencer

1) Germain A, Giloteaux L, Moore GE, Levine SM, Chia JK, Keller BA, Stevens J, Franconi CJ, Mao X, Shungu DC, Grimson A, Hanson MR. Plasma metabolomics reveals disrupted response and recovery following maximal exercise in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. JCI Insight. 2022 Mar 31:e157621. doi: 10.1172/jci.insight.157621. Epub ahead of print. PMID: 35358096.

https://insight.jci.org/articles/view/157621 

2) Naviaux RK, Naviaux JC, Li K, Bright AT, Alaynick WA, Wang L, Baxter A, Nathan N, Anderson W, Gordon E. Metabolic features of chronic fatigue syndrome. Proc Natl Acad Sci U S A. 2016 Sep 13;113(37):E5472-80. doi: 10.1073/pnas.1607571113. Epub 2016 Aug 29. Erratum in: Proc Natl Acad Sci U S A. 2017 May 2;114(18):E3749. PMID: 27573827; PMCID: PMC5027464.

https://pubmed.ncbi.nlm.nih.gov/27573827/

3) Chalecka M, Kazberuk A, Palka J, Surazynski A. P5C as an Interface of Proline Interconvertible Amino Acids and Its Role in Regulation of Cell Survival and Apoptosis. Int J Mol Sci. 2021 Oct 29;22(21):11763. doi: 10.3390/ijms222111763. PMID: 34769188; PMCID: PMC8584052.

https://www.mdpi.com/1422-0067/22/21/11763

4) Yang Z, Zhao X, Shang W, Liu Y, Ji JF, Liu JP, Tong C. Pyrroline-5-carboxylate synthase senses cellular stress and modulates metabolism by regulating mitochondrial respiration. Cell Death Differ. 2021 Jan;28(1):303-319. doi: 10.1038/s41418-020-0601-5. Epub 2020 Aug 7. PMID: 32770108; PMCID: PMC7853148.

https://www.nature.com/articles/s41418-020-0601-5

ME patienter har lavt niveau af tridecenedioate

 ...fortsættelse. Læs først:

Metaboliske ændringer hos ME patienter før og efter to dages motion

http://followmeindenmark.blogspot.com/2022/04/metaboliske-ndringer-hos-me-patienter.html

En af metabolitterne fra figur 4 er tridecenedioate (C13:1-DC). Figuren viser metabolitter, hvor niveauet er signifikant forskelligt hos kvinder med ME i forhold til raske kontrolpersoner (1). 

Data for tridecenedioate fremgår af supplerende tabel 4:

D1PRE (dag 1 før motion)

• p = 0,0000244
• q = 0,000685
• FC = 0,540

D2POST (dag 2 efter motion)

• p = 0,000000516
• q = 0,000580
• FC = 0,453

Det betyder, at vi er meget sikre på, at kvinder med ME kun har halvt så meget af denne metabolit i forhold til raske kontrolpersoner.

Tridecenedioate er en monoumættet dicarboxylic fedtsyre, som menes at have neuroproktektive egenskaber (2).

Et studie har vist, at fodboldatleter med gentagne hovedskader havde et lavere niveau af denne fedtsyre. Det lave niveau var associeret med en stigning i det inflammatoriske mir-505. Ydermere kunne data relateres til skanninger af hovedet. Se figur fra artiklen (2): 

Synopsis figure summarizing the interplay between moderation variables. Repetitive head acceleration events (HAE) in football athletes have been related to changes in brain homeostasis, as evidenced by neuroimaging studies. In the present study, significant moderation effects were observed with default mode network (DMN) fingerprint similarity, miR-505, VR balance task performance, and tridecenedioate. Tridecenedioate, a dicarboxylic fatty acid with one double bond, significantly decreased from Pre to Post-season. The double bond in this metabolite is hypothesized to act as a reactive oxygen species (ROS) scavenger. Indeed, previous research supports an increase in reactive oxygen species (ROS) following repetitive exposure to head impacts; therefore, a depletion of tridecenedioate would support its role as an ROS scavenger. Even with scavenging, ROS can still remain elevated and cause damage to neurophysiological systems. This may ultimately result in damage to neuronal connectivity as observed by decreased similarity in DMN and interactions with VR balance task performance. Together, these complex relationships may explain why behavioral changes in subconcussed athletes are not consistently observed, but how repetitive, long-term exposure to HAE, chronic increases of inflammatory-miRNAs, and acute changes to resting state networks could result in behavioral disturbances later in life.

Reference: Sumra Bari, Nicole L. Vike, Khrystyna Stetsiv, Alexa Walter, Sharlene Newman, Keisuke Kawata, Jeffrey J. Bazarian, Linda Papa, Eric A. Nauman, Thomas M. Talavage, Semyon Slobounov, Hans C. Breiter,

Integrating multi-omics with neuroimaging and behavior: A preliminary model of dysfunction in football athletes,
Neuroimage: Reports,Volume 1, Issue 3,2021,100032,ISSN 2666-9560,
https://doi.org/10.1016/j.ynirp.2021.100032.
(https://www.sciencedirect.com/science/article/pii/S2666956021000301)

Hvad betyder det lave niveau af tridecenedioate for ME patienter?

Læs også:

A metabolomic measure of energy metabolism moderates how an inflammatory miRNA relates to rs-fMRI network and motor control in football athletes

https://arxiv.org/abs/2006.14930

Referencer

1)Germain A, Giloteaux L, Moore GE, Levine SM, Chia JK, Keller BA, Stevens J, Franconi CJ, Mao X, Shungu DC, Grimson A, Hanson MR. Plasma metabolomics reveals disrupted response and recovery following maximal exercise in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. JCI Insight. 2022 Mar 31:e157621. doi: 10.1172/jci.insight.157621. Epub ahead of print. PMID: 35358096. 

https://pubmed.ncbi.nlm.nih.gov/35358096/

https://insight.jci.org/articles/view/157621

2) Sumra Bari, Nicole L. Vike, Khrystyna Stetsiv, Alexa Walter, Sharlene Newman, Keisuke Kawata, Jeffrey J. Bazarian, Linda Papa, Eric A. Nauman, Thomas M. Talavage, Semyon Slobounov, Hans C. Breiter,
Integrating multi-omics with neuroimaging and behavior: A preliminary model of dysfunction in football athletes,
Neuroimage: Reports,
Volume 1, Issue 3,2021,100032,ISSN 2666-9560,
https://doi.org/10.1016/j.ynirp.2021.100032.
https://www.sciencedirect.com/science/article/pii/S2666956021000301

Metaboliske ændringer hos ME patienter før og efter to dages motion

Der er blevet udført et studie, hvor ME patienter og kontrolpersoner motionerede to dage i træk. Der blev udtaget blodprøver lige før og lige efter motion begge dage. De fire tidspunkter blev benævnt

• D1PRE
• D1POST
• D2PRE
• D2POST

Blodprøverne blev undersøgt for indhold af metabolitter (metabolomics). 

Mængden af en metabolit hos ME patienter i forhold til kontrolpersoner er angivet som FoldChange (FC):

• FC mellem 0,9 og 1,1 - niveauet anses for uændret
• FC over 1,1 - niveauet af metabolitten er højere hos ME patienter
• FC under 0,9 - niveauet af metabolitten er lavere hos ME patienter

FC er signifikant ændret, når p-værdien er under 0,05. Der kan dog forekomme falsk positive værdier, der er derfor udført en Wilcoxon ranksum test. Denne angives ved en q-værdi, som skal være under 0,05. Denne grænse er meget konservativt sat og kan udelukke data, som er værd at kigge nærmere på. Derfor er q-værdier under 0,15 også angivet i artiklen. 

Den første blodprøve før motion på dag 1 (D1PRE) viste, at kvinder med ME havde 7 metabolitter, der var signifikant forskellige fra kontrolpersoner. Se figur 4 i artiklen https://insight.jci.org/articles/view/157621/pdf

Efter 2 dage med motion (D2POST) var 56 metabolitter hos kvinder med ME ændrede. Se figur 3 i artiklen https://insight.jci.org/articles/view/157621/pdf

Mange biokemiske stiveje var påvirkede hos kvinder med ME. Se figur 2 i det supplerende materiale https://insight.jci.org/articles/view/157621/sd/5

Det her studie er meget værdifuldt, og jeg er sikker på, at vi kommer til at høre meget mere om det. 

Reference

Germain A, Giloteaux L, Moore GE, Levine SM, Chia JK, Keller BA, Stevens J, Franconi CJ, Mao X, Shungu DC, Grimson A, Hanson MR. Plasma metabolomics reveals disrupted response and recovery following maximal exercise in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. JCI Insight. 2022 Mar 31:e157621. doi: 10.1172/jci.insight.157621. Epub ahead of print. PMID: 35358096. 

https://pubmed.ncbi.nlm.nih.gov/35358096/

https://insight.jci.org/articles/view/157621

Lav arteriel-venøs iltindhold difference hos ME patienter

Hjertet pumper iltet blod fra lungerne rundt i kroppen. Det iltrige blod føres ud i kroppen gennem arterier og kaldes for arterielt blod. Det iltfattige blod føres tilbage til hjertet gennem vener, for igen af blive pumpet ud i lungerne til iltning. Det iltfattige blod i venerne kaldes venøst blod.

Forskellen i iltindhold mellem arterielt blod og venøst blod kaldes på engelsk: 

"arterial-venous oxygen content difference".

Det er hæmoglobin, der bærer ilt og iltindhold differencen skal vurderes i forhold til hæmoglobin koncentrationen. Der for ser formlen for iltindhold difference således ud: 

"(Ca-vO2) / koncentrationen af Hb".

Hvis den arteriel-venøse iltindhold difference er stor, så har kroppen optaget en masse ilt fra blodet. Og omvendt, hvis differencen er lav, betyder det, at det venøse blod vender tilbage til hjertet uden, at der er optaget så meget ilt.

Forskere fra Havard Medical School er eksperter i at måle iltindhold differencen under motion hos mennesker med motionsintolerance. Dette gøres ved en invasiv kardiopulmonær motionstest. Iltindhold differencen er under motionstest målt hos ME patienter:

Insights From Invasive Cardiopulmonary Exercise Testing of Patients With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

https://journal.chestnet.org/article/S0012-3692(21)00256-7/fulltext

Forskerne udvalgte data fra en patientgruppe, der både havde lavt fyldetryk i højre hjertekammer ("right arterial pressure" under 6,5 mm Hg) og som opfyldte ME diagnosekriterierne. Analyse af data viste, at ME patienterne under motion havde en lav arteriel-venøs iltindhold difference. Det betyder, at ME patienterne ikke optog/udnyttede ilten i blodet i tilstrækkelig grad. Dette medfører motionsintolerance. Forskerne udelukker dekonditionering som årsag til motionsintolerancen hos ME patienterne. I stedet peger de på mulige årsager, der kan bidrage til motionsintolerancen: 

 - Under motion bliver veneblodet ikke returneret til hjertet i tilstrækkeligt omfang, og der er herved ikke nok blod til et fyldetryk i hjertekammeret (engelsk: depressed cardiac output from impaired venous return - preload failure).

- Manglende ilt udnyttelse fordi blodet passerer fra arterier til vener uden at komme ud i de helt små blodkar (kapillærer), hvor en stor del af ilten udnyttes. Fænomenet kaldes arteriel-venøs shunting (AV-shunting). AV-shunting kan forekomme ved småfiber neuropati, som blev påvist hos en del ME patienter i artiklen.

Reference: 

Joseph P, Arevalo C, Oliveira RKF, Faria-Urbina M, Felsenstein D, Oaklander AL, Systrom DM. Insights From Invasive Cardiopulmonary Exercise Testing of Patients With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Chest. 2021 Aug;160(2):642-651. doi: 10.1016/j.chest.2021.01.082. Epub 2021 Feb 10. PMID: 33577778.

ZFR suppresses the antiviral response, but not in ME? Is macroH2A1/H2AFY involved?

ME peripheral blood mononuclear cell (PBMC) proteomes reveal decreased level of zinc finger RNA-binding protein (ZFR), foldchange = 0,52, p-value = 0,00047 (1).

ZFR suppresses interferon-beta induction and the antiviral response. ZFR controls interferon signaling by preventing aberrant splicing and nonsense-mediated decay (NMD) of histone variant macroH2A1/H2AFY mRNAs (2).

Serum from ME patients contains an activity which induces a powerful antiviral state, but it seems like the interferon response has been ruled out in the ME pathomechanism (3, 4).

However, macroH2A1 has also been shown to bind and repress interferon-stimulated genes (ISG) promoters, raising the possibility that the constitutive ISG induction in ZFR-depleted cells could be partially due to loss of direct action of macroH2A1 on these genes. Taking the available data together, macroH2A1 appears to both suppress the initiation of type I interferon signaling by inhibiting IFNB1 transcription and by modulating the consequences of IFNB1 transcription by directly repressing ISG promoters (2).

The gene macroH2A1/H2AFY is differentially methylated in PBMC from ME patients. Read the blogpost:

H2AFY and ME

https://followmeindenmark.blogspot.com/2018/10/h2afy-and-me.html

Is dysregulated macroH2A1/H2AFY involved in the ME pathomechanism?

MacroH2A1 can buffer transcriptional noise associated with the antiviral response

Knockdown of macroH2A causes a dramatic change in the antiviral gene expression program. Genes that normally do not respond to virus infection get activated or repressed (5).

References

preprint 1) Eiren Sweetman, Torsten Kleffmann, Christina Edgar, Michel de Lange, Rosamund Vallings Howick Warren Tate: A SWATH-MS analysis of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome peripheral blood mononuclear cell proteomes reveals mitochondrial dysfunction
https://assets.researchsquare.com/files/rs-52172/v1/6b319d19-80fb-46e3-b56e-3687ae1c7203.pdf

2) Haque N, Ouda R, Chen C, Ozato K, Hogg JR. ZFR coordinates crosstalk between RNA decay and transcription in innate immunity. Nat Commun. 2018;9(1):1145. Published 2018 Mar 20. doi:10.1038/s41467-018-03326-5
https://www.nature.com/articles/s41467-018-03326-5

3) Schreiner P, Harrer T, Scheibenbogen C, et al. Human Herpesvirus-6 Reactivation, Mitochondrial Fragmentation, and the Coordination of Antiviral and Metabolic Phenotypes in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Immunohorizons. 2020;4(4):201-215. Published 2020 Apr 23. doi:10.4049/immunohorizons.2000006
https://pubmed.ncbi.nlm.nih.gov/32327453/

4) Corbitt M, Eaton-Fitch N, Staines D, Cabanas H, Marshall-Gradisnik S. A systematic review of cytokines in chronic fatigue syndrome/myalgic encephalomyelitis/systemic exertion intolerance disease (CFS/ME/SEID). BMC Neurol. 2019;19(1):207. Published 2019 Aug 24. doi:10.1186/s12883-019-1433-0

5) Lavigne MD, Vatsellas G, Polyzos A, et al. Composite macroH2A/NRF-1 Nucleosomes Suppress Noise and Generate Robustness in Gene Expression. Cell Rep. 2015;11(7):1090-1101. doi:10.1016/j.celrep.2015.04.022

Atrogin 1 mRNA is elevated in muscle biopsies of ME patients

 Quote reference 1):
"Levels of Atrogin 1 mRNA were significantly elevated in muscle biopsies of patients with ME/CFS compared with HCs (Healthy Controls) suggesting an increase in protein degradation processes in muscles of patients with ME/CFS compared with HCs. Atrogin-1 binds to polyubiquitinated proteins to direct them for subsequent degradation by the 26S proteasome and as such is an important regulator of ubiquitin-mediated protein degradation in skeletal muscle (69). Increased levels of Atrogin-1 mRNA are associated with reduced muscle mass (69) and in this study Atrogin-1 was associated with a significant reduction in muscle fibre size, although a detailed examination of muscle protein degradation was not undertaken."

Atrogin 1, also known as muscle atrophy F-box (MAFbx), is encoded by FBXO32. Atrogin 1 degrades various muscle proteins, such as titin, nebulin, troponin, myosin-binding protein C, myosin light chains 1 and 2 and myosin heavy chains (2).

Increased degradation of myosin light chain proteins may lead to increased plasma N,N,N-trimethyl-L-alanyl-L-proline betaine (TMAP) (3). 


Read the blogpost:
Increased plasma N,N,N-trimethyl-L-alanyl-L-proline betaine in ME patients
http://followmeindenmark.blogspot.com/2020/02/

References:
preprint: 1) Arief Gusnanto, Kate Elizabeth Earl, George K Sakellariou, Daniel J Owens, Adam Lightfoot, Sandra A Fawcett, Euan Owen, Caroline A Staunton, Tu Shu, Fiona C Croden, Manuel Fenech, Melanie A Sinclair, Libuse Ratcliffe, Kasia A Whysall, Rebecca I Haynes, Nicola M Wells, Malcolm J Jackson, Graeme L Close, Clare L Lawton, Michael BJ Beadsworth, Louise Dye, Anne MCARDLE:
Discriminatory cytokine profiles predict muscle function, fatigue and cognitive function in patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)
doi: https://doi.org/10.1101/2020.08.17.20164715
https://www.medrxiv.org/content/10.1101/2020.08.17.20164715v1

2) Steinbacher and Eckl: Impact of oxidative stress on exercising skeletal muscle. Biomolecules  2015 Apr 10;5(2):356-77.
doi: 10.3390/biom5020356.
https://pubmed.ncbi.nlm.nih.gov/25866921/

3) Velenosi, T.J., Thomson, B.K.A., Tonial, N.C. et al. Untargeted metabolomics reveals N, N, N-trimethyl-L-alanyl-L-proline betaine (TMAP) as a novel biomarker of kidney function. Sci Rep 9, 6831 (2019). https://www.nature.com/articles/s41598-019-42992-3
https://doi.org/10.1038/s41598-019-42992-3 PMID: 31048706 PMCID: PMC6497643