Mutationer i muciner kan måske forklare øget immun aktivering og kemikalie intolerance hos ME patienter

Muciner er en gruppe glykoproteiner, som findes i slimhinderne i luftveje, tarm, skede urinrør og øjne.

Muciner sørger for at slimhinde-laget bliver tykt og højviskøst, så slimhinden bliver svær gennemtrængelig for virus, bakterier, skimmel og toxiner. Samtidig virker mucinerne som lokkemad for mikroorganismerne, der klistrer sig fast til sukkermolekylerne på mucinerne. Herved kan mikroorganismerne udstødes fra kroppen sammen med den slim, som kontinuerlig udskilles fra slimhinderne.

Under slimhindelaget findes et lag epitel med immunceller, som aktiveres hvis mikroorganismer eller toxiner alligevel slipper igennem slimhindelaget. Mutationer i muciner kan påvirke slimhindernes beskaffenhed, således at der sker en større indtrængning af mikroorganismer og toxiner til epitelet. Herved vil immunforsvaret hyppigt aktiveres (1).

Muciner og ME
Der er fundet mutationer i muciner hos ME patienter, og det danner baggrund for en ny hypotese: 

Mutations in ME/CFS nasal mucins result in compromised protective barriere

• an altered nasal microbiome
• a highly sensitive and irritated epithelial layer
• chronic low grade non-allergic inflammatory response
• exacerbation of ME/CFS symptomatology

Hypotesen er fremlagt i et webinar. Indslaget begynder til tiden cirka 1 time og 55 minutter:
INIM Webinar - Understanding ME/CFS Today: A Clinical & Research Approach
https://www.youtube.com/watch?v=QfrCF2atQxI&feature=youtu.be&t=8591

Forskerne bag studiet oplyser, at en mutation i mucin19 (MUC19) har særlig betydning for en beskadiget slimhinden i næse/øvre luftveje. Dette kan medføre øget følsomhed over for de kemikalier, som vi indånder. Det betyder at mutiple chemical sensitivity (MCS) kan forklares med hypotesen. MUC19 mutationen er nævnt i reference 2. 

Den nye mucin hypotese er forenelig med anden ME forskning: 

Der er tidligere fundet mutationer i IDO2 genet hos meget syge ME patienter, og det danner baggrund for IDO ME hypotesen (3). IDO har betydning for nasal tolerance (4).
Læs blog: IDO-ME hypotesen er forenelig med AHR-MCS hypotesen
http://followmeindenmark.blogspot.com/2019/06/ido-me-hypotesen-er-forenelig-med-ahr.html

Det er tidligere vist, at ME patienter har nedsat sygdomtolerance, og nasal stimulation kan afhjælpe ME symptomer (5).
Læs blog: Det inflammatoriske respons og induktion af sygdomstolerance er dysreguleret hos ME patienter
http://followmeindenmark.blogspot.com/2020/03/det-inflammatoriske-respons-og.html

Proteinet cathelicidin antimicrobial peptide (CAMP) kan påvises ved inflammatorisk respons. Det er f.eks. påvist i tarmens slimhinde hos patienter med inflammatory bowel disease (IBD). Plasma niveauet af CAMP er for forhøjet hos ME patienter (6).

Mere viden om CAMP:
Topical cathelicidin (LL-37) an innate immune peptide induces acute olfactory epithelium inflammation in a mouse model https://pubmed.ncbi.nlm.nih.gov/28837619/

Læs også om mucin studiet på Health Rising bloggen:
Surprise Gene Finding Could Give Pathogens and Toxins a Leg Up in ME/CFS
https://www.healthrising.org/blog/2020/07/11/mucosal-genes-chronic-fatigue-syndrome/


Referencer:
1) S K Linden, P Sutton, N G Karlsson, V Korolik, M A McGuckin: Mucins in the mucosal barrier to infection. Mucosal Immunol 2008 May;1(3):183-97. doi: 10.1038/mi.2008.5. Epub 2008 Mar 5. https://pubmed.ncbi.nlm.nih.gov/19079178/

2) Melanie Perez et al: Genetic Predisposition for Immune System, Hormone, and Metabolic Dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Pilot Study Front Pediatr. 2019 May 24;7:206. doi: 10.3389/fped.2019.00206. eCollection 2019. https://pubmed.ncbi.nlm.nih.gov/31179255/

3) Kashi AA Davis RW and, Phair RD: The IDO Metabolic Trap Hypothesis for the Etiology of ME/CFS. Diagnostics (Basel). 2019 Jul 26;9(3). pii: E82. doi: 10.3390/diagnostics9030082. https://www.mdpi.com/2075-4418/9/3/82

4) van der Marel AP1, Samsom JN, Greuter M, van Berkel LA, O'Toole T, Kraal G, Mebius RE. Blockade of IDO inhibits nasal tolerance induction. J Immunol. 2007 Jul 15;179(2):894-900.
https://www.ncbi.nlm.nih.gov/pubmed/17617580

5) Lucie S.T. Rodriguez, Christian Pou, Tadepally Lakshmikanth, Jingdian Zhang, Constantin Habimana Mugabo, Jun Wang, Jaromir Mikes, Axel Olin, Yang Chen, Joanna Rorbach, Jan-Erik Juto, Tie Qiang Li, Per Julin, Petter Brodin: Achieving symptom relief in patients with Myalgic encephalomyelitis by targeting the neuro-immune interface and inducing disease tolerance
doi: https://doi.org/10.1101/2020.02.20.958249
https://www.biorxiv.org/content/10.1101/2020.02.20.958249v1.abstract

6) Milica Milivojevic et al: Plasma proteomic profiling suggests an association between antigen driven clonal B cell expansion and ME/CFS. PLoS One . 2020 Jul 21;15(7):e0236148. doi: 10.1371/journal.pone.0236148. eCollection 2020. https://pubmed.ncbi.nlm.nih.gov/32692761/

Kynurenine skal afprøves til behandling af ME patienter

Open Medicine Foundation finansierer et nyt placebo-kontrolleret studie, hvor ME patienter skal behandles med kynurenine:

Kynurenine Clinical Trial for ME/CFS
https://omfcanada.ngo/kynurenine-clinical-trial-for-me-cfs/

Jonas Bergquist, MD, PhD, direktør for det svenske ME/CFS forskningscenter i Uppsala, skal stå for studiet.

Baggrunden for studiet er Dr. Robert Phair's ME- hypotese "den metaboliske fælde", der beskriver, at ME patienter ikke omsætter aminosyren tryptofan i tilstrækkelig omfang i nogle af vores celletyper (1). Blogindlæg om den metaboliske fælde:

ME hypotese: The Metabolic Trap - den metaboliske fælde
https://followmeindenmark.blogspot.com/2019/06/me-hypotese-metabolic-trap-den.html

Kynurenine metabolitter opstår ved omsætning af tryptofan, og disse metabolitter er vigtige for normal funktion af bl.a. hjerne og immunforsvar. Dette er vist i dette blogindlæg: 

Tryptofan metabolitten kynureninsyre har immunmodulerende egenskaber
https://followmeindenmark.blogspot.com/2019/06/tryptofan-metabolitten-kynureninsyre.html


Yderligere blogindlæg om kynurenine og den metaboliske fælde:

Is the ME hypothesis "the metabolic trap" able to explain endothelial dysfunction?
https://followmeindenmark.blogspot.com/2019/06/is-me-hypothesis-metabolic-trap-able-to.html

Kynurenine metabolisme påvirkes af motion
https://followmeindenmark.blogspot.com/2019/06/kynurenine-metabolisme-pavirkes-af.html

Omsætning af tryptofan og forgrenede aminosyrer hos ME patienter under motion
https://followmeindenmark.blogspot.com/2019/06/omstning-af-tryptofan-og-forgrenede.html

Is the kynurenic acid responsive Gpr35 involved in the ME pathomechanism?
https://followmeindenmark.blogspot.com/2019/06/is-kynurenic-acid-responsive-gpr35.html

IDO-ME hypotesen er forenelig med AHR-MCS hypotesen
https://followmeindenmark.blogspot.com/2019/06/ido-me-hypotesen-er-forenelig-med-ahr.html

Mutations in the IDO2 gene and DNA methylations in genes in the NAD/NADP synthesis pathway in ME
https://followmeindenmark.blogspot.com/2019/07/mutations-in-ido2-gene-and-dna.html

Reference: 
1) Kashi AA Davis RW and, Phair RD: The IDO Metabolic Trap Hypothesis for the Etiology of ME/CFS. Diagnostics (Basel). 2019 Jul 26;9(3). pii: E82. doi: 10.3390/diagnostics9030082. https://www.mdpi.com/2075-4418/9/3/82

Serum fra ME patienter udviser antiviral aktivitet

Et nyt studie af Schreiner et al har vist, at serum fra ME patienter udviser antiviral aktivitet mod både DNA- og RNA-virus i en cellekultur. Samtidig blev det observeret, at serummet inducerer et fragmenteret mitokondriel netværk og nedsat cellulær ATP produktion (1).

Citat fra artiklen (1), side 213: 
"... we showed that serum from ME/CFS patients contained an activity that produced mitochondrial fragmentation, decreased mitochondrial ATP production, and induced a powerful antiviral state."

Det er ukendt, hvad det er i serum, som udløser og udøver den antivirale aktivitet. Schreiner et al har en hypotese om, at en delvis aktivering af herpesvirus (HHV-6) kan være årsag til den kroniske immunaktivering hos ME patienter. Forskerne understøtter hypotesen med et forsøg, hvor en cellekultur udsat for delvis aktivering af HHV-6 udskilder et stof som har samme effekt som serum fra ME patienter (1). 

Citat fra artiklen (1), side 206:
"...These results showed that cells containing latent HHV-6A DNA that had been transactivated by TSA (trichostatin-A) secreted a potent activity that could be adoptively transferred and induce mitochondrial fragmentation and a proinflammatory CDR (cell danger response) in naive responder cells, conferring strong protection from both DNA and RNA virus infections."

ME er tidligere sat i forbindelse med kronisk herpes infektion (2).

Schreiner et al foreslår, at nye forsøg skal vise om ME patienter har en produktion af HHV-6 proteiner (ikke hele, levende HHV-6).

Citat fra artiklen (1), side 213:
"Larger multicohort studies involving ME/CFS patients from different age groups should be carried out in the future and should include methods for detecting and quantifying both productive and nonproductive (incomplete) viral reactivation events. Furthermore, potential factors affecting mitochondrial dynamics in ME/CFS patients should be systematically evaluated for their ability to induce a powerful antiviral state."

Læs også:

For ME/CFS Patients, Viral Immunities Come at a Devastating, Lifelong Cost
https://health.ucsd.edu/news/releases/Pages/2020-04-27-for-me-cfs-patients-viral-immunities-come-at-lifelong-cost.aspx

Explaining ME/CFS? Prusty / Naviaux Study Ties Infections to Energy Breakdowns
https://www.healthrising.org/blog/2020/04/26/explaining-chronic-fatigue-syndrome-naviaux-prusty/

Viden om fragmenteret mitokondriel netværk:
Mitochondria in Innate Immune Responses
https://pubmed.ncbi.nlm.nih.gov/21597473/

Figur: https://pubmed.ncbi.nlm.nih.gov/21597473/#&gid=article-figures&pid=figure-2-uid-1

Referencer:

1) Philipp Schreiner, Thomas Harrer, Carmen Scheibenbogen, Stephanie Lamer, Andreas Schlosser, Robert K. Naviaux and Bhupesh K. Prusty
Human Herpesvirus-6 Reactivation, Mitochondrial Fragmentation, and the Coordination of Antiviral and Metabolic Phenotypes in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome
Immunohorizons. 2020 Apr 23;4(4):201-215.
DOI: 10.4049/immunohorizons.2000006

PMID: 32327453 

2) Nuno Sepúlveda, Jorge Carneiro,  Eliana Lacerda, Luis Nacul Myalgic Encephalomyelitis/Chronic Fatigue Syndrome as a Hyper-Regulated Immune System Driven by an Interplay Between Regulatory T Cells and Chronic Human Herpesvirus Infections
Front Immunol 2019 Nov 21;10:2684. doi: 10.3389/fimmu.2019.02684. eCollection 2019.
https://www.frontiersin.org/articles/10.3389/fimmu.2019.02684/full

ME - a failure of inducing exercise tolerance?

ME hypothesis from Karolinska Institutet and Karolinska University Hospital in Sweden (1):

"ME - a failure of inducing disease tolerance upon chronic immune activation"

My question:
Is ME also a failure of inducing exercise tolerance?

At cellular level disease and inflammation result in increased reactive oxygen species (ROS) production. Stress-response pathways are countermeasures to ROS. Exercise also leads to increased ROS levels. The antioxidant enzyme superoxide dismutase 2 (SOD2) is one the primary mechanisms against ROS generated during exercise.

Quote from a review "Impact of oxidative stress on exercising skeletal muscle" (2):
"It is well established that muscle contractions during exercise lead to elevated levels of reactive oxygen species (ROS) in skeletal muscle. These highly reactive molecules have many deleterious effects, such as a reduction of force generation and increased muscle atrophy. Since the discovery of exercise-induced oxidative stress several decades ago, evidence has accumulated that ROS produced during exercise also have positive effects by influencing cellular processes that lead to increased expression of antioxidants. These molecules are particularly elevated in regularly exercising muscle to prevent the negative effects of ROS by neutralizing the free radicals. In addition, ROS also seem to be involved in the exercise-induced adaptation of the muscle phenotype.

Chronic oxidative stress is associated with an increase in protein loss and muscle atrophy. High ROS levels cause a sustained activation of NF-κB and of FoxO which then activate two muscle-specific E3 ubiquitin ligases, atrogin-1 or muscle atrophy F-box (MAFbx) and muscle RING (Really Interesting New Gene)-finger protein 1 (MuRF-1) [52]. MAFbx and MuRF-1 then degrade various proteins, such as titin, nebulin, troponin, myosin-binding protein C, myosin light chains 1 and 2 and myosin heavy chain [53,54]. Recently, it was demonstrated that excessive oxidative stress also enhances the transcription factor C/EBP homology protein (CHOP). This transcription factor also enhances expression of MuRF1, which again results in increased protein degradation [35]."

It seems like ME patients have increased muscle protein degradation:

Increased serum and urine 3-methylhistidine in ME patients
http://followmeindenmark.blogspot.com/2020/03/increased-serum-and-urine-3.html

Increased plasma N,N,N-trimethyl-L-alanyl-L-proline betaine in ME patients
https://followmeindenmark.blogspot.com/2020/02/increased-plasma-nnn-trimethyl-l-alanyl.html

Proline, P5C and 4-hydroxyglutamate in ME
http://followmeindenmark.blogspot.com/2020/02/proline-p5c-and-4-hydroxyglutamate-in-me.html

And do remember the transcription profile analysis of skeletal muscle from ME patients (3), quote:
"In an effort to establish which pathways might be involved in the onset and development of muscle symptoms, we used global transcriptome analysis to identify genes that were differentially expressed in the vastus lateralis muscle of female and male CFS patients. We found that the expression of genes that play key roles in mitochondrial function and oxidative balance, including superoxide dismutase 2, were altered, as were genes involved in energy production, muscular trophism and fiber phenotype determination. Importantly, the expression of a gene encoding a component of the nicotinic cholinergic receptor binding site was reduced, suggesting impaired neuromuscular transmission. We argue that these major biological processes could be involved in and/or responsible for the muscle symptoms of CFS."

Are the inflammatory reponse to disease and the adaptive response to exercise dysregulated in ME through the same pathways?

Reference

1) Lucie S.T. Rodriguez, Christian Pou, Tadepally Lakshmikanth, Jingdian Zhang, Constantin Habimana Mugabo, Jun Wang, Jaromir Mikes, Axel Olin, Yang Chen, Joanna Rorbach, Jan-Erik Juto, Tie Qiang Li, Per Julin, Petter Brodin: Achieving symptom relief in patients with Myalgic encephalomyelitis by targeting the neuro-immune interface and inducing disease tolerance
doi: https://doi.org/10.1101/2020.02.20.958249
https://www.biorxiv.org/content/10.1101/2020.02.20.958249v1.abstract

2) Peter Steinbacher, Peter Eckl:
Impact of Oxidative Stress on Exercising Skeletal Muscle

DOI: 10.3390/biom5020356
https://pubmed.ncbi.nlm.nih.gov/25866921-impact-of-oxidative-stress-on-exercising-skeletal-muscle/
https://www.mdpi.com/2218-273X/5/2/356

3) T Pietrangelo 1, R Mancinelli, L Toniolo, G Montanari, J Vecchiet, G Fanò, S Fulle
Transcription Profile Analysis of Vastus Lateralis Muscle From Patients With Chronic Fatigue Syndrome. Int J Immunopathol Pharmacol, Vol 22 (3), 795-807, 2009
https://pubmed.ncbi.nlm.nih.gov/19822097-transcription-profile-analysis-of-vastus-lateralis-muscle-from-patients-with-chronic-fatigue-syndrome/
https://journals.sagepub.com/doi/abs/10.1177/039463200902200326

Det inflammatoriske respons og induktion af sygdomstolerance er dysreguleret hos ME patienter

Forskere fra Karolinska Instituttet og Karolinska Universitetshospital har beskrevet en ME hypotese (1):

"ME - a failure of inducing disease tolerance upon chronic immune activation"

Sygdomstolerance er en overordnet betegnelse for en række stress-respons stiveje. Disse skal sørge for at begrænse skade fra patogene mikroorganismer og fra kroppens inflammationsproces.

Vagusnerve og hjernestamme regulerer systemisk inflammation ved at skrue op eller ned for den inflammatoriske refleks. Nerver der fører fra kroppen (afferent vagus nerve endings) til hjernestamme sender besked om immunstatus i kroppen. Nerverne kan f.eks. sende besked om aktivitet fra patogene mikroorganismer i tarmen. Nerver der fører fra hjernestamme (efferente) til kroppen  sender signaler via acetylcholin om at dæmpe inflammationen. 

Det er kendt viden, at påvirkning af vagusnerven kan dæmpe inflammatoriske tilstande.

Forskerne fra Karolinska afprøvede Intranasal Mekanisk Stimulation (INMEST) på en gruppe ME patienter. INMEST udstyret består af et tyndt plasticrør, som placeres i næsen. Udstyret vibrerer og danner en turbulent luftstrøm. Dette inducerer en nervereflex, som påvirker vagusnerven. Behandlingen dæmpede nogle ME symptomer (men ikke fatigue), og blodprøver fra patienterne viste normalisering af inflammatoriske tilstande (1).

En analyse af sygdomstoleranceprogrammer viste, at INMEST behandling opregulerede disse programmer.

Forskerene påpegede, at årsagen til den manglende induktion af tolerance hos ME patienter skal klarlægges. Samtidig henviser de til forskningen i IDO2 enzymet, som netop er involveret i regulering af sygdomstolerance.



Mere viden om emnet kan findes her:

Neural Reflexes in Inflammation and Immunity
https://pubmed.ncbi.nlm.nih.gov/22665702-neural-reflexes-in-inflammation-and-immunity/

The Vagus Nerve and the Inflammatory Reflex--Linking Immunity and Metabolism
https://pubmed.ncbi.nlm.nih.gov/23169440-the-vagus-nerve-and-the-inflammatory-reflex-linking-immunity-and-metabolism/

Er der behandlingsmuligheder i lægemidler, der øger aktivitet i acetylcholin-stiveje?:

Central and peripheral anti-inflammatory effects of acetylcholinesterase inhibitors
https://www.sciencedirect.com/science/article/abs/pii/S0028390820300861

Aryl Hydrocarbon Receptor Control of a Disease Tolerance Defence Pathway
https://pubmed.ncbi.nlm.nih.gov/24930766-aryl-hydrocarbon-receptor-control-of-a-disease-tolerance-defence-pathway/


Relevante blogindlæg:

Indånding af skimmel er noget, der kan gøre en ME/MCS patient ganske syg. IDO er med til at inducere tolerance i næsens slimhinder, og mutationer i IDO-generne har betydning for kroppens reaktion på skimmel infektion (AHR = Arylhydrocarbon receptor, MCS = multiple chemical sensitivity): 

IDO-ME hypotesen er forenelig med AHR-MCS hypotesen

http://followmeindenmark.blogspot.com/2019/06/ido-me-hypotesen-er-forenelig-med-ahr.html

Tryptofan metabolitten kynureninsyre har immunmodulerende egenskaber

http://followmeindenmark.blogspot.com/2019/06/tryptofan-metabolitten-kynureninsyre.html

Reference

1) Lucie S.T. Rodriguez, Christian Pou, Tadepally Lakshmikanth, Jingdian Zhang, Constantin Habimana Mugabo, Jun Wang, Jaromir Mikes, Axel Olin, Yang Chen, Joanna Rorbach, Jan-Erik Juto, Tie Qiang Li, Per Julin, Petter Brodin: Achieving symptom relief in patients with Myalgic encephalomyelitis by targeting the neuro-immune interface and inducing disease tolerance
doi: https://doi.org/10.1101/2020.02.20.958249
https://www.biorxiv.org/content/10.1101/2020.02.20.958249v1.abstract

Increased serum and urine 3-methylhistidine in ME patients

3-metylhistidine is a breakdown product of muscle contractile proteins. Serum or urine 3-methylhistidine is used as a biomarker of muscle protein degradation (1).

Fluge et al found increased serum 3-metylhistidine in male ME patients (2).

McGregor et al found increased urine 3-metylhistidine in post-exertional malaise (PEM) ME patients (1).

Quote from McGregor et al (1):
"The findings that the PEM is associated with a loss of metabolites, reduction in acetylation, deregulation of purine metabolism, increased contractile protein breakdown and bacteremia associated with exercise suggest that treatments such as graded exercise may be more detrimental than beneficial as claimed in some studies [39,40]. Until such time as these biological changes can be further investigated, the use of graded exercise as a therapy for those with severe forms of ME/CFS should be considered potentially harmful. In support of this, the use of graded exercise therapy has caused significant protest by ME/CFS sufferers as they see it as harmful [41,42]."


Further reading about possible breakdown of skeletal muscles in ME patients :

Proline, P5C and 4-hydroxyglutamate in ME
http://followmeindenmark.blogspot.com/2020/02/proline-p5c-and-4-hydroxyglutamate-in-me.html

Increased plasma N,N,N-trimethyl-L-alanyl-L-proline betaine in ME patients
https://followmeindenmark.blogspot.com/2020/02/increased-plasma-nnn-trimethyl-l-alanyl.html



Referencer
1) McGregor et al: Post-Exertional Malaise Is Associated with Hypermetabolism, Hypoacetylation and Purine Metabolism Deregulation in ME/CFS Cases Diagnostics (Basel). 2019 Jul 4;9(3). pii: E70. doi: 10.3390/diagnostics9030070. https://www.ncbi.nlm.nih.gov/pubmed/31277442

2) Fluge et al: Metabolic profiling indicates impaired pyruvate dehydrogenase function in myalgic encephalopathy / chronic fatigue syndrome. JCI Insight. 2016; 1(21):e89376. Doi 10.1172/jci.insight.89276

Increased plasma N,N,N-trimethyl-L-alanyl-L-proline betaine in ME patients

N,N,N-trimethyl-L-alanyl-L-proline betaine (TMAP) is a plasma biomarker of reduced kidney function (1).

Quote from ref 1:
"TMAP was the most consistently cleared metabolite by all hemodialysis modalities in our untargeted metabolomics analysis. Although the biological origin of TMAP has not been identified, we suggest that TMAP may be produced from degradation of myosin light chain (MYL) proteins. N,N,N-trimethylalanine is mainly found in myosin light chain (MYL) proteins and in each of the four MYL isoforms (MYL1, MYL2, MYL3, and MYL4), the c-terminus of N,N,N-trimethylalanine forms a peptide bond with proline (26). Therefore, MYL protein degradation may be responsible for the release of TMAP. Further study is necessary to determine the biological origin and potential physiological effects of TMAP."

Myosin light chains are components of macromcular myosin complexes. Fx. myosin II is the myosin type responsible for producing muscle contractions in muscle cells. Myosin II contains two heavy chains and four ligtht chains. ( Wikipedia. Myosin )

Plasma TMAP was increased in ME patients in Germain et al's metabolomic study (2020) (2).

As far as I know, ME patients have normal kidney function, so why is TMAP increased? Is the turnover of myosin light chains increased? And/or do the increased TMAP level reflect the breakdown of skeletal muscles?


Further reading about possible breakdown of skeletal muscles in ME patients :

Proline, P5C and 4-hydroxyglutamate in ME

http://followmeindenmark.blogspot.com/2020/02/proline-p5c-and-4-hydroxyglutamate-in-me.html

References:

1) 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

2) Arnaud Germain , Dinesh K Barupal , Susan M Levine , Maureen R Hanson: Comprehensive Circulatory Metabolomics in ME/CFS Reveals Disrupted Metabolism of Acyl Lipids and Steroids. Metabolites 2020, 10(1), 4; https://doi.org/10.3390/metabo10010034
https://www.mdpi.com/2218-1989/10/1/34