REVIEW | doi:10.20944/preprints202209.0458.v1
Subject: Medicine & Pharmacology, Pharmacology & Toxicology Keywords: kynurenine pathway; inflammatory biomarkers; inflammation; ADHD; neurobiology; kynurenine
Online: 29 September 2022 (08:11:33 CEST)
Attention deficit hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder that can diminish the quality of life of both children and adults in academic, occupational, and social contexts. The kynurenine pathway (KP) contains a set of enzymatic reactions involved in tryptophan (TRP) degradation. It is known to be associated with the risk of developing ADHD. This review will address the KP and underlying mechanism of inflammation in ADHD. Potential inflammatory biomarkers reported in the most recent studies are summarized. Although a strong neuroimmunological basis has been established due to advances of recent neurobiological research, the pathophysiology of ADHD remains unclear.
REVIEW | doi:10.20944/preprints201810.0014.v1
Subject: Medicine & Pharmacology, Clinical Neurology Keywords: IDO, kynurenine, pain, Sjögren’s syndrome, tryptophan
Online: 1 October 2018 (14:59:23 CEST)
For decades, neurologic and other extra glandular manifestations have been described in Sjögren’s syndrome (SS). More recently, neuropathic, psychological and cognitive alterations are being considered part of the disease. The lacrimal glands (LG), the ocular surface (OS), salivary glands (SG) and the central nervous system (CNS) are integrated to modulate the autonomic functions and, not just those organs, but also the hippocampus, which is linked to the autonomic nervous system, and modulate behavior responses appears to be compromised in the SS. Recent studies confirm that the tryptophan/kynurenine pathway (TKP) can be stimulated by interferon-γ (IFN-γ) and other cytokines, activating the indoleamine-pyrrole 2,3-dioxygenase (IDO) in SS. This pathway interferes on serotonergic and glutamatergic neurotransmission, mostly in the hippocampus, and other structures of the CNS. Although not demonstrated, it is plausible that this constant interference induces clinical signs of SS, and contributes to the discrepancy between symptoms and signs, towards manifestations of hyperalgesia and depression in patients with SS. Therapeutic strategies are being reexamined and new options designed and tested to regulate the involved steps of the TKP. In the future, the application of this concept may offer a clue to the mosaic of manifestations of SS.
ARTICLE | doi:10.20944/preprints202202.0249.v1
Subject: Life Sciences, Molecular Biology Keywords: HIV Nef; neurotoxicity; inflammatory cytokines; kynurenine metabolite
Online: 21 February 2022 (10:00:10 CET)
HIV-1 Nef is a multifunctional protein with well-known lethal properties. HIV infects various cells from the brain compartment and expressed nef is responsible for developing neuropathogenic potential. HIV-infected glial cells express nefvirotoxinand stimulate the cascade of various pathways to activate uninfected cells to release neurotoxic elements damaging cells themselves. A lot of genetic variabilities of this protein have been reported from patients with HIV-associated neurocognitive disorders. To determine the neurotoxic potential of subtype-specific nef plasmids and nef plasmids of clinical samples with and without HAND were transfected in normal human astrocytes (NHA) and monocyte-derived macrophages (MDM) using nef-pCMV-HA plasmid constructs. Supernatants from subtype-specific Nef plasmids indicated the upregulation of proinflammatory cytokines. The induced expression might be due to the nef genetic variability or variations in the transfection efficiency and expression levels of nef.The mRNA expression of IL-6, IP-10, and TNF-α indicated upregulation of 5.0-fold in NHA and 3-fold in MDM with respect to empty vector control transfection. Further, the kynurenine metabolites were also assessed from culture supernatants of NHA and MDM indicating the upregulation of IDO and KYNU in NHA by 3.0-fold and 3.2-fold in MDM.The expression levels of nef and cytokines at the translational level were confirmed by western blotting and bio-plex Pro cytokine estimation assay respectively along with controls expressing green fluorescent protein (GFP).The oxidative stress was also found to be elevated as compared to control cells as determined by the estimation of nitric oxide from the culture supernatant to confirm the neurotoxic potential of HIV nef plasmids. The downregulation in the levels of cytokines, as well as kynurenine metabolites, was observed in culture supernatants after blocking the expression of nef using HIV nef siRNA. Phylogenetic analysis of Nef sequences indicated subtype C predominance except one sequence showing the partial sequence of HIV-1 subtype B sequence forming BC recombinantThe upregulation in the cytokine and pathway-specific metabolites might be linked with the neurotoxic potential of HIV-1 Nef leading to neuropathogenesis. In conclusion, the variation in the transfection efficiency, nef expression levels, and the genetic variability of Nef might be responsible for upregulating the expression levels of cytokines and kynurenine metabolites in astrocytes and MDM.
REVIEW | doi:10.20944/preprints202201.0134.v1
Subject: Medicine & Pharmacology, Psychiatry & Mental Health Studies Keywords: TRYCATs; MDD; MDE; Suicidal behavior; Kynurenine pathway
Online: 11 January 2022 (10:39:25 CET)
Kynurenine or tryptophan catabolite (TRYCAT) pathway contributes to the pathophysiology of major depression disorder (MDD) and major depressive episodes (MDE) in bipolar disorder and suicidal behaviors. The consequences of the overactivation of this pathway large reduced tryptophan (TRP) levels in peripheral blood and the CNS and increased levels of neurotoxic TRYCATs including kynurenine (KYN), 3-hydroxy kynurenine (3HK), quinolinic acid (QA), xanthurenic acid (XA), and picolinic acid (PA). However, other TRYCATs are protective, such as kynurenic acid (KA) and anthranilic acid (AA). Inflammation and cell-mediated immune activation along with oxidative and nitrosative stress (O&NS) may stimulate the first and rate-limiting enzyme of this pathway, namely indoleamine-2,3-dioxygenase (IDO). Therefore, during depression, balancing neuroprotective versus neurotoxic TRYCATs and balancing activation of the immune response system (IRS) versus the compensatory immune response system is crucial for achieving better treatment outcomes. Furthermore, targeting the causes of TRYCAT pathway activation (immune activation and O&NS) is probably the most effective strategy to treat depression. In the present review, we aim to provide a comprehensive explanation of the impact of TRYCATs in terms of pathophysiology and treatment of MDD and MDE.
REVIEW | doi:10.20944/preprints201805.0404.v2
Subject: Life Sciences, Other Keywords: microbiota; kynurenine pathway; serotonin; inflammation; gut motility
Online: 22 June 2018 (06:29:42 CEST)
The human gastrointestinal tract is inhabited by trillions of commensal bacteria collectively known as the gut microbiota. Our recognition of the significance of the complex interaction between the microbiota, and its host has grown dramatically over the past years. A balanced microbial community is a key regulator of the immune response, and metabolism of dietary components, which in turn, modulates several brain processes impacting mood and behavior. Consequently, it is likely that disruptions within the composition of the microbiota would remotely affect the mental state of the host. Here, we discuss how intestinal bacteria and their metabolites can orchestrate gut-associated neuroimmune mechanisms that influence mood and behavior leading to depression. In particular, we focus on microbiota-triggered gut inflammation and its implications in shifting the tryptophan metabolism towards kynurenine biosynthesis while disrupting the serotonergic signaling. We further investigate the gaps to be bridged in this exciting field of research in order to clarify our understanding of the multifaceted crosstalk in the microbiota-gut-brain interphase, bringing about a novel microbiota-targeted therapeutics for mental illnesses.
ARTICLE | doi:10.20944/preprints201810.0083.v2
Subject: Medicine & Pharmacology, Behavioral Neuroscience Keywords: immune, inflammation, natural IgM autoimmune, oxidative stress, kynurenine, schizophrenia, psychosis
Online: 8 October 2018 (13:51:40 CEST)
Schizophrenia is characterized by an interrelated activation of the immune-inflammatory response system (IRS) and the compensatory immune-regulatory reflex system (CIRS), which downregulates the IRS. Deficit schizophrenia is characterized by a deficit in natural regulatory autoimmune responses to tryptophan catabolites. The presence and correlates of IgM isotype antibodies to oxidative specific epitopes (OSEs), nitroso (NO) and nitro (NO2) adducts in schizophrenia remain unknown.This study measured IgM antibodies to malondialdehyde (MDA), azelaic acid, phosphatidylinositol, oleic acid, NO-tryptophan, NO-albumin, NO-cysteinyl and NO2-tyrosine in a sample of 80 schizophrenia patients, divided into those with and those without deficit schizophrenia, and 38 healthy controls.Deficit schizophrenia was characterized by significantly lower IgM antibody levels to all OSEs as compared with non-deficit schizophrenia and controls. Lowered IgM antibodies to MDA coupled with increased IgM levels to NO-cysteinyl and NO2-tyrosine strongly predict deficit schizophrenia versus non-deficit schizophrenia with an area under the ROC curve of 0.913. A large part of the variance (21.2 – 42.2 %) in the negative symptoms of schizophrenia and excitation is explained by IgM antibody titers to MDA (inversely) and NO-cysteinyl and/or NO2-tyrosine (both positively). Lower IgM antibodies to MDA are significantly associated with impairments in episodic memory including direct and delayed recall.These findings further indicate that deficit schizophrenia is a distinct phenotype of schizophrenia, which is characterized by lower natural IgM antibody levels to OSEs and relative increments in nitrosylation and nitration of proteins. It is concluded that deficits in lowered IgM responses to MDA and azelaic acid (part of the CIRS) attenuate the negative immune-regulatory feedback on the primary immune response and that this process may drive negative symptoms and impairments in episodic memory and thus deficit schizophrenia.
REVIEW | doi:10.20944/preprints202106.0128.v1
Subject: Medicine & Pharmacology, Allergology Keywords: chronic pain; nociceptive pain; neuropathic pain; nociplastic pain; psychogenic pain; neuroinflammation; kynurenine
Online: 4 June 2021 (09:09:26 CEST)
Chronic pain is an unpleasant sensory and emotional experience that persists or recurs more than three months and may extend beyond the expected time of healing. Recently nociplastic pain has been introduced as a descriptor of mechanism of pain, which is due to disturbance of neural processing without actual or potential tissue damage, appearing to replace a concept of psychogenic pain. An interdisciplinary task force of the International Association for the Study of Pain (IASP) compiled a systematic classification of clinical conditions associated with chronic pain, which was published in 2018 and will officially come into effect in 2022 in the 11th revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-11) by the World Health Organization. ICD-11 offers the option for recording the presence of psychological or social factors in chronic pain; however, cognitive, emotional, and social dimensions in the pathogenesis of chronic pain are missing. Earlier pain disorder was defined as a condition with chronic pain associated with psychological factors, but it was replaced with somatic symptom disorder with predominant pain in Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) in 2013. Recently clinical nosology is trending toward highlighting neurological pathology of chronic pain, discounting psychological or social factors in the pathogenesis of pain. This review article discusses components of the pain pathway, the component-based mechanisms of pain, central and peripheral sensitization, roles of chronic inflammation, and the involvement of tryptophan-kynurenine pathway metabolites, exploring participations of psychosocial and behavioral factors in central sensitization of diseases progressing into development of chronic pain, comorbid diseases that commonly present a symptom of chronic pain, and psychiatric disorders that manifest chronic pain without obvious actual or potential tissue damage.
REVIEW | doi:10.20944/preprints202207.0130.v1
Subject: Medicine & Pharmacology, Psychiatry & Mental Health Studies Keywords: Keywords: mitochondria; stress resilience; plasticity; stress; kynurenine; Alzheimer’s disease; neurodegenerative; depression; anxiety; psychiatric
Online: 8 July 2022 (03:56:36 CEST)
Nearly half a century has passed since the discovery of cytoplasmic inheritance of human chloramphenicol resistance. The inheritance was then revealed to take place maternally by mitochondrial DNA (mtDNA). Later, a number of mutations in mtDNA were identified as a cause of severe inheritable metabolic diseases with neurological manifestation, and the impairment of mitochondrial functions has been probed in the pathogenesis of a wide range of illnesses including neurodegenerative diseases. Recently growing number of preclinical studies has revealed that animal behaviors are influenced by the impairment of mitochondrial functions and possibly by the loss of mitochondrial stress resilience. Indeed, as high as 54% of patients with one of the most common primary mitochondrial diseases, mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome, present psychiatric symptoms including cognitive impairment, mood disorder, anxiety, and psychosis. Mitochondria are multifunctional organelles which produce cellular energy and play a major role in other cellular functions including homeostasis, cellular signaling, and gene expression, among other. Mitochondrial functions are observed to be compromised and to become less resilient under continuous stress. Meanwhile, stress and inflammation have been linked to the activation of the tryptophan (Trp)-kynurenine (KYN) metabolic system, which observably contributes to development of pathological conditions including neurological and psychiatric disorders. This narrative review discusses the functions of mitochondria and the Trp-KYN system, the interaction of the Trp-KYN system with mitochondria, and the current understanding of the involvement of mitochondria and the Trp-KYN system in preclinical and clinical studies of major neurological and psychiatric diseases.
REVIEW | doi:10.20944/preprints202103.0231.v1
Subject: Biology, Anatomy & Morphology Keywords: Tryptophan metabolism; Kynurenine; Indoleamine 2,3-dioxygenase; Aryl hydrocarbon receptor; Microbiome; Indole; Colon cancer.
Online: 8 March 2021 (15:55:29 CET)
Tryptophan metabolism, via the kynurenine (Kyn) pathway, and microbial transformation of tryptophan to indolic compounds, are fundamental for host health; both of which are altered in colon carcinogenesis. Alterations in tryptophan metabolism begin early in colon carcinogenesis as an adaptive mechanism for the tumor to escape immune surveillance and metastasize. The microbial community is a key part of the tumor microenvironment and influences cancer initiation, promotion and treatment response. A growing awareness of the impact of the microbiome on tryptophan (Trp) metabolism in the context of carcinogenesis has prompted this review. We first compare the different metabolic pathways of Trp under normal cellular physiology to colon carcinogenesis, in both the host cells and the microbiome. Second, we review how the microbiome, specifically indoles, influence host tryptophan pathways under normal and oncogenic metabolism. We conclude by proposing several dietary, microbial and drug therapeutic modalities that can be utilized in combination to abrogate tumorigenesis.
ARTICLE | doi:10.20944/preprints202203.0327.v1
Subject: Medicine & Pharmacology, Psychiatry & Mental Health Studies Keywords: tryptophan; kynurenine; kynurenic acid; passive avoidance; cognitive domain; memory; cognitive enhancer; neurotransmission; receptor blockers; translational
Online: 24 March 2022 (08:57:45 CET)
Kynurenic acid (KYNA) is an endogenous tryptophan (Trp) metabolite known to possess neuroprotective property. KYNA plays critical roles in nociception, neurodegeneration, and neuroinflammation. A lower level of KYNA is observed in patients with neurodegenerative diseases such as Alzheimer’s and Parkinson’s diseases or psychiatric disorders such as depression and autism spectrum disorders, whereas a higher level of KYNA is associated with the pathogenesis of schizophrenia. Little is known about the optimal concentration for neuroprotection and the threshold for neurotoxicity. In this study the effects of KYNA on memory functions were investigated by passive avoidance test in mice. Six different doses of KYNA were administered intracerebroventricularly to previously trained CFLP mice and they were observed following 24 hours. High doses of KYNA (i.e., 20-40 μg/2 μl) significantly decreased the avoidance latency, whereas a low dose of KYNA (0.5 μg/2 μl) significantly elevated it compared with controls, suggesting that the low dose of KYNA enhanced memory function. Furthermore, six different receptor blockers were applied to reveal the mechanisms underlying the memory enhancement induced by KYNA. The series of tests revealed the possible involvement of the serotonergic, dopaminergic, α and β adrenergic, and opiate systems in the nootropic effect. The study confirmed that a low dose of KYNA improved a memory component of cognitive domain, which was mediated by, at least in part, four systems of neurotransmission in an animal model of learning and memory.
REVIEW | doi:10.20944/preprints202011.0147.v1
Subject: Medicine & Pharmacology, Allergology Keywords: antineuronal autoantibodies; autoimmune diseases; autoimmune encephalitis; food antigens; kynurenine pathway; microbiota; prolactin; cytokines; schizophrenia; stress
Online: 3 November 2020 (12:53:38 CET)
The review analyzes a possible role of autoimmune processes in the pathogenesis of schizophrenia and evolution of concepts on this issue from its origin to present. Risks of autoimmune processes causing schizophrenia are associated with several factors: an impaired functioning of dopaminergic and glutamatergic systems in the brain, kynurenine pathway disorder with overproduction of quinolinic, anthranilic and kynurenic acids (possibly altering both neurons and T-regulators), increased intestinal permeability, as well as food antigens’ effects, stress and infections with various pathogens at different stages of ontogenesis. An increase in the levels of proinflammatory cytokines and chemokines as well as a decrease in the levels of anti-inflammatory ones also may contribute to schizophrenia risks. Schizophrenia often occurs in those patients having various autoimmune diseases and their first-degree relatives. Cases of schizophrenia resulted from autoimmune pathogenesis (including autoimmune encephalitis caused by autoantibodies against various neuronal antigens) are characterized by quite severe cognitive and psychotic symptoms and less favorable prognosis. This severe course may result from the chronic immune damage of the neuronal receptors such as NMDA, GABA, and others and depend on hyperprolactinemia, induced by antipsychotics, but aggravating autoimmune processes [with 2 tables, 4 figures, bibliography: 99 references].
REVIEW | doi:10.20944/preprints202007.0425.v1
Subject: Medicine & Pharmacology, Psychiatry & Mental Health Studies Keywords: autism spectrum disorder; neuroinflammation; kynurenine pathway; microglia; oxidative stress; mitochondrial disorder; immune deregulation; QUIN (quinolinic acid); KYNA (kynurenic acid); tryptophan catabolites
Online: 19 July 2020 (19:19:31 CEST)
Autism Spectrum Disorder etiopathogenesis is still unclear and no effective preventive and treatment measures have been identified. Research has focused on the potential role of neuroinflammation and kynurenine pathway. Here we review the nature of these interactions. Pre-natal or neonatal infections would induce microglial activation, with secondary consequences on behavior, cognition and neurotransmitter networks. Peripherally, higher levels of pro-inflammatory cytokines and anti-brain antibodies have been identified. Increased frequency of autoimmune diseases, allergies, and recurring infections have been demonstrated both in autistic patients and in their relatives. Genetic studies, also, have identified some important polymorphisms in chromosome loci related to human leukocyte antigen (HLA) system. The persistence of immune-inflammatory deregulation would lead to mitochondrial dysfunction and oxidative stress, creating a self-sustaining cytotoxic loop. Chronic inflammation activates kynurenine pathway with increase in neurotoxic metabolites and excitotoxicity, causing long-term changes in glutamatergic system, trophic support and synaptic function. Furthermore, overactivation of kynurenine’s branch induces depletion of melatonin and serotonin worsening ASD symptoms. In this scenario, kynurenine pathway appears as a pharmacological target to treat and prevent ASD. Thus, in genetically predisposed subjects aberrant neurodevelopment may derives from a complex interplay between inflammatory process, mitochondrial dysfunction, oxidative stress and kynurenine pathway overexpression. To validate previous hypothesis a new translational research approach is necessary.
ARTICLE | doi:10.20944/preprints202207.0058.v1
Subject: Life Sciences, Biophysics Keywords: human interferon gamma; human interferon gamma receptor; receptor binding; heparan sulfate; co-receptor; molecular dynamics simulations; sodium chlorate; kynurenine antiproliferative assays; hIFNγ signalling
Online: 5 July 2022 (04:43:05 CEST)
The extremely controversial conclusions about the function of human interferon-gamma (hIFNγ) C-terminus as well as the lack of a consistent model explaining its role in the receptor binding prompted us to scrutinize the interaction of hIFNγ with its extracellular receptor hIFNGR1 in different scenarios by means of molecular dynamics simulations. We find that the two molecules alone fail to form a stable complex but the presence of heparan-sulfate-like oligosaccharides largely facilitates the process by both demobilizing the highly flexible C-termini of the cytokine and assisting in the proper positioning of its globule between the receptor subunits. An antiproliferative-activity essay on cells depleted from surface sulfation confirms qualitatively the simulation-based multistage complex-formation model. Our results reveal the key role of HS and its proteoglycans in all processes involving hIFNγ signalling.
REVIEW | doi:10.20944/preprints202106.0344.v1
Subject: Medicine & Pharmacology, Allergology Keywords: chronic inflammation; low grade inflammation; immune tolerance; inflammatory factor; kynurenine; kynurenic acid; depression; bipolar disorder; substance use disorder; post-traumatic stress disorder; schizophrenia; autism spectrum disorder
Online: 14 June 2021 (10:06:50 CEST)
The tryptophan (TRP)-kynurenine (KYN) metabolic pathway is a main player of TRP metabolism through which more than 95% of TRP is catabolized. The pathway is activated by acute and chronic immune responses leading to a wide range of illnesses including cancer, immune diseases, neurodegenerative diseases, and psychiatric disorders. The TRP-KYN pathway synthesizes multifarious metabolites including oxidants, antioxidants, neurotoxins, neuroprotectants, and immunomodulators. The immunomodulators are known to facilitate the immune system towards a tolerogenic state, resulting in chronic low-grade inflammation (LGI) that is commonly present in obesity, poor nutrition, exposer to chemicals or allergens, prodromal stage of various illnesses, and chronic diseases. KYN, kynurenic acid, xanthurenic acid, and cinnabarinic acid are aryl hydrocarbon receptor ligands that serve as immunomodulators. Furthermore, TRP-KYN pathway enzymes are known to be activated by the stress hormone cortisol and inflammatory cytokines, and genotypic variants were observed to contribute to inflammation and thus various diseases. The tryptophan 2,3-dioxygenase, the indoleamine 2, 3-oxygenases, and the kynurenine-3-monooxygenase are main enzymes in the pathway. This review article discusses the TRP-KYN pathway with special emphasis on its interaction with the immune system and the tolerogenic shift towards chronic LGI and overviews the major symptoms, pro- and anti-inflammatory cytokines, and toxic and protective KYNs to explore the linkage between chronic LGI, KYNs, and major psychiatric, including depressive disorder, bipolar disorder, substance use disorder, post-traumatic stress disorder, schizophrenia, and autism spectrum disorder.
HYPOTHESIS | doi:10.20944/preprints202005.0144.v1
Subject: Medicine & Pharmacology, Other Keywords: COVID-19, SARS-CoV-2, pyridoxal 5'-phosphate, pyridoxine, vitamin B6, immune response, IL-6, TNF, type I interferon, lymphopenia, blood clotting, coagulopathy, cytokine storm, sphingosine-1-phosphate, kynurenine, inflammasome, serine hydroxymethyltransferase 2 (SHMT2), hypertension, angiotensin
Online: 8 May 2020 (12:36:03 CEST)
Although most cases of COVID-19 are paucisymptomatic, severe disease is characterized by immune dysregulation, with a decreased type I interferon response, increased inflammatory indicators, surging IL-6, IL-10 and TNFα suggestive of cytokine storm, progressive lymphopenia, and abnormal blood clotting. Factors determining susceptibility to severe disease are poorly understood, although mortality correlates with increasing age and co-morbidities including diabetes and cardiovascular disease (CVD). Pyridoxal 5'-phosphate (PLP) tends to be insufficient in populations particularly vulnerable to COVID-19, including the elderly, the institutionalized, and people with diabetes and CVD, and PLP becomes further depleted during infection and inflammation. In turn, low PLP results in immune imbalance, as PLP is an essential cofactor in pathways regulating cytokine production, in particular type I interferons and IL-6, and in lymphocyte trafficking and endothelial integrity. Furthermore, normalizing PLP levels attenuates abnormalities in platelet aggregation and clot formation. Finally, PLP insufficiency induces excess secretion of renin and angiotensin, and hypertension. In inflammatory disease, pharmacological doses of PLP decrease circulating TNFα, IL-6 and D-dimer, and animal studies demonstrate that supplemental PLP shortens the duration and severity of viral pneumonia. Severe COVID-19 manifests as an imbalance in the immune response and the clotting system. Pharmacological PLP supplementation may therefore mitigate COVID-19 symptoms by alleviating both the immune suppression underlying viral spread and the pathological hypersecretion of inflammatory cytokines, as well as directly bolstering endothelial integrity and preventing hypercoagulability.