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Objectives: The kynurenine (KYN) pathway has been attracting attention as a relevant pathway in schizophrenia (SZ), bipolar disorder (BD), and major depressive disorder (MDD). We conducted a systematic review and meta-analysis of studies examining KYN pathway metabolites from cerebrospinal fluid (CSF) samples in SZ, BD, and MDD. Methods: The PubMed and Scopus databases were systematically searched to identify peer-reviewed case-control studies published until April 2022 that assessed KYN metabolites, namely, tryptophan (TRP), KYN, kynurenic acid (KA), quinolinic acid (QA), and 3-hydroxykynurenine (3-HK), in subjects with SZ, BD, or MDD compared with healthy controls (HC). The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines were followed. The random effects model method was selected for comparison of standardized mean differences (SMD) between two groups. Results: Twenty-three articles met the inclusion criteria (k = 8, k = 8, k = 11, for SZ, BD, and MDD, respectively). In SZ, KA levels were increased (SMD = 2.64, confidence interval [CI] = 1.16 to 4.13, p = 0.0005, I2 = 96%, k = 6, n=384). TRP (k = 5) and KYN (k = 4) did not differ significantly. In BD, TRP levels (k = 7) did not differ significantly. The level of KA was increased in MDD (k = 2), but the small number of studies precluded evaluation of statistical significance. Finally, in MDD, although some studies tended to show an increased level of KYN in those with remission vs. decreased levels in those with current depression, no significant difference was found in any KYN metabolite levels. Similarly, an increased level of QA was found, but the number of studies (k = 2) was small. Conclusion: KA, which has possibly neuroprotective effects, is increased in SZ. QA, which has neurotoxic effects, may be increased in MDD. There were no alterations in BD. Alterations in the KYN pathway may occur based on population characteristics and mood states. Future studies should explore the utility of these metabolites as biomarkers.
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BackgroundThe pathogenesis of depression remains not fully understood， and previous studies have suggested that the kynurenine pathway （KP） plays an important role in the pathogenesis of major depressive disorder. ObjectiveTo study the difference in serum KP metabolites level between patients with first-episode and recurrent major depressive disorder， and to testify the correlation between KP metabolites level with the severity of depressive symptoms， so as to provide references for the prevention of recurrence. MethodsA total of 136 patients with major depressive disorder who attended the outpatient clinics of the Affiliated Brain Hospital of Guangzhou Medical University from November 2016 to December 2018 and met the diagnostic criteria of the Diagnostic and Statistical Manual of Mental Disorders， fifth edition （DSM-5） diagnostic criteria were included， including 62 patients in the first-episode group and 74 patients in the recurrent group. Meanwhile， 60 healthy subjects were included as control group. All patients were assessed by Hamilton Depression Scale-17 item （HAMD-17）， and serum concentrations of tryptophan （TRP）， kynurenine （KYN） and kynurenic acid （KYNA） were measured by liquid chromatography tandem mass spectrometry （LC-MS/MS）. Then the correlation of HAMD-17 total score and individual item scores with the levels of KP metabolites was tested using partial correlation coefficient. ResultsCompared with the control group， the first-episode group and recurrent group showed a marked decline in TRP concentration （t=-3.044， -4.477， P<0.05 or 0.01） and an increase in KYN/TRP ratio （t=2.343， 3.644， P<0.05 or 0.01）， with significant differences. The KYNA concentrations （t=2.490， 2.636， P<0.05 or 0.01） and KYNA/KYN ratio （t=2.894， 2.616， P<0.01） in first-episode group and control group were notably elevated compared to recurrent group， with statistical difference. Partial correlation analysis in patients with first-episode major depressive disorder demonstrated that KYN/TRP ratio was positively correlated with the HAMD-17 anxiety/somatization factor score （r=0.261， P<0.05）， and KYNA/KYN ratio was negatively correlated with HAMD-17 total score and block factor score （r=-0.286， -0.282， P<0.05）. In patients with recurrent major depressive disorder， KYN/TRP ratio was positively correlated with HAMD-17 anxiety/somatization factor score （r=0.280， P<0.05）. ConclusionKP metabolites in serum differ between first-episode and recurrent major depressive disorder patients， and patients with recurrent episodes experience severe KP metabolite abnormalities. Therefore， KP metabolites are considered to be potential biomarker candidates to assist clinicians in the diagnosis and recurrent prediction of major depressive disorder. ［Funded by National Key Research and Development Program Precision Medicine Research Project （number， 2016YFC0906300）］
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Objective: Changes in the kynurenine pathway are recognized in psychiatric disorders, but their role in Alzheimer's disease (AD) is less clear. We aimed to conduct a systematic review and meta-analysis to determine whether tryptophan and kynurenine pathway metabolites are altered in AD. Methods: We performed a systematic review and random-effects meta-analyses. Inclusion criteria were studies that compared AD and cognitively normal (CN) groups and assessed tryptophan or kynurenine pathway metabolites in cerebrospinal fluid or peripheral blood. Results: Twenty-two studies with a total of 1,356 participants (664 with AD and 692 CN individuals) were included. Tryptophan was decreased only in peripheral blood. The kynurenine-to-tryptophan ratio was only increased in peripheral blood of the AD group. 3-Hydroxykynurenine was decreased only in cerebrospinal fluid and showed higher variability in the CN group than the AD group. Kynurenic acid was increased in cerebrospinal fluid and decreased in peripheral blood. Finally, there were no changes in kynurenine and quinolinic acid between the groups. Conclusions: Our results suggested a shift toward the kynurenine pathway in both the brain and in the periphery, as well as a shift towards increased kynurenic acid production in the brain but decreased production in peripheral blood. In addition, our analysis indicated dissociation between the central and peripheral levels, as well as between plasma and serum for some of these metabolites. Finally, changes in the kynurenine pathway are suggested to be a core component of AD. More studies are warranted to verify and consolidate our results.
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Objective:To establish an isotope dilution liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS) method for the determination of L-tryptophan and its metabolites in serum.Methods:The methodology was established and evaluated using serum samples collected from 166 healthy subjects undergoing physical examinations at West China Hospital from November 2022 to January 2023 were collected. Isotope-labeled markers of L-tryptophan (Trp), L-kynurenine (Kyn), and kynurenic acid (KA) were used as internal standards. After protein precipitation treatment of serum samples, LC-MS/MS was used to determine Trp, Kyn, and KA simultaneously. The selectivity, specificity, linearity, detection limit (LOD), quantification limit (LOQ), carry-over, precision, recovery rate, matrix effect, and dilution integrity of the method were evaluated.Results:The linearity of Trp, Kyn, and KA was demonstrated to be 0.999. The LODs were 0.10 μmol/L, 0.01 μmol/L and 1.00 nmol/L, respectively. The LOQs were 0.20 μmol/L, 0.04 μmol/L and 2.00 nmol/L, respectively. The intra-batch precision and inter-batch precision were below<10%. The average recovery rate and the relative matrix effect were all about 100%. The samples over the upper limit of quantitation can be diluted up to 16 times. The Trp concentration, Kyn concentration, KA concentration, Kyn/Trp ratio, and KA/Kyn ratio in serum of healthy subjects were 59.55±10.92 μmol/L, 1.85±0.43 μmol/L, 39.89±17.93 nmol/L, (31.64±8.19)×10 -3 and 21.51±6.72, respectively. Conclusion:An ID-LC-MS/MS method was successfully established for the quantitative determination of Trp, Kyn, and KA in serum. The method proved to be simple, rapid, sensitive, accurate, and reliable, providing robust support for clinical research related to these analytes.
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Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide. Fat accumulation "sensitizes" the liver to insult and leads to nonalcoholic steatohepatitis (NASH). G protein-coupled receptor 35 (GPR35) is involved in metabolic stresses, but its role in NAFLD is unknown. We report that hepatocyte GPR35 mitigates NASH by regulating hepatic cholesterol homeostasis. Specifically, we found that GPR35 overexpression in hepatocytes protected against high-fat/cholesterol/fructose (HFCF) diet-induced steatohepatitis, whereas loss of GPR35 had the opposite effect. Administration of the GPR35 agonist kynurenic acid (Kyna) suppressed HFCF diet-induced steatohepatitis in mice. Kyna/GPR35 induced expression of StAR-related lipid transfer protein 4 (STARD4) through the ERK1/2 signaling pathway, ultimately resulting in hepatic cholesterol esterification and bile acid synthesis (BAS). The overexpression of STARD4 increased the expression of the BAS rate-limiting enzymes cytochrome P450 family 7 subfamily A member 1 (CYP7A1) and CYP8B1, promoting the conversion of cholesterol to bile acid. The protective effect induced by GPR35 overexpression in hepatocytes disappeared in hepatocyte STARD4-knockdown mice. STARD4 overexpression in hepatocytes reversed the aggravation of HFCF diet-induced steatohepatitis caused by the loss of GPR35 expression in hepatocytes in mice. Our findings indicate that the GPR35-STARD4 axis is a promising therapeutic target for NAFLD.
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Objective:To study the effect of sevoflurane inhalation anesthesia on stress reaction and kynurenic acid ( KYNA) level in serum of the patients with laparoscopic cholecystectomy .Methods:Totally 48 patients undergoing laparoscopic cholecystectomy were randomly divided into two groups.Group S(n=24) received sevoflurane inhalation and group V (n=24) received intravenous general anesthesia.The levels of norepinephrine (NE), epinephrine (E), cortisol (Cor), KYNA and neutrophil and the neutrophil/lympho-cyte ratio were measured at five time points, namely T1(before the anesthesia), T2 (just after the surgery) , T3(in the morning of the first day after the surgery ) , T4 ( in the morning of the second day after the surgery ) and T5 ( in the morning of the third day after the surgery).The correlation of Cor, NE, E and NLR with KYNA was studied as well.Results:The levels of Cor, NE and E at the three time points after the surgery (T2, T3 and T4) in group V were significantly higher than those before the surgery (T1) with statistically significant difference (P0.05).And the levels of Cor, NE and E at the three time points after the surgery (T2, T3 and T4) in group S were markedly lower than those in group V at the same time point (P<0.05).After the surgery (T2, T3, T4 and T5), KYNA levels in group V were significantly decreased and NLR values in group V were significantly increased when compared with those of T 1.In group S, KYNA levels and NLR values after the surgery (T2, T3, T4 and T5) were markedly increased , which were higher than those in group V at the same time point with statistically significant difference (P<0.05).The correlation analysis indicated the level of KYNA displayed positive correlation with the levels of NLR , Cr, Z and E (P<0.05).Conclusion:Sevoflurane inhalation anesthesia can inhibit the increase of stress reaction and KYNA level in the patients with laparoscopic cholecystectomy , which may be related with its anti-in ammatory properties .
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Tryptophan-kynurenine metabolic pathways are involved in a series of enzymatic reactions,generate a variety of bioactive compounds and participate in some complex pathophysiological processes.In recent years,studies have shown that kynurenine metabolic pathways may be associated with the pathogenesis of migraine and treatment.This article reviews the advances in research on the relationship between tryptophankynurenine metabolic pathways and migraines.
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The kynurenine metabolic pathway involves in a cascade of enzyme reaction generated multiple biologically-active compounds.These metabolites are called"kynurenines" which participate in diverse pathophysiological processes,particularly in the central nervous system.The kynurenines have important physiological functions.For example.quinolinic acid is an Nmethyl-D-aspartate(NMDA)receptor agonist.and it can be largely accumulated in the central nervous system in many infectious nervous system diseases,resulting in neuronal excitotoxicity and death.Kynurenic acid antagonizes excitatory glutamate receptors to reduce excitotoxicityinduced neuronal death.This article reviews the related researches of the effects of kynurenine metabolic pathway on the central nervous system.
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0.05).The concentration of urinary KYNA,metabolite of the KYN,was significantly lower in SHRs compared to WKYs(7.8?1.8 vs 19.9?3.5 ?mol/24 h P=0.013).Both KAT activity in renal cortex and KYNA content in urine were negatively correlated to blood pressure(r=-0.418,P=0.023;r=-0.723,P=0.001).Conclusion The declined activity of KAT in renal cortex and the deficiency of KYNA concentration in urinary may affect blood pressure regulation in SHR by renal metabolite of the KYN.
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Objective A method was developed for the simultaneous determination of tryptophan(Trp) and its metabolites kynurenine(Kyn) and kynurenic acid(Kyna) by high performance liquid chromatography with fluorescence detection(HPLC-FD),and testing serum levels of Trp metabolites in systemic lupus erythematosus(SLE) patients.Methods Serum samples were deproteinized by equal volume of 0.624 mol/L perchloric acid.The analytical column was Hypersil C18 column,and the mobile phase was 0.20 mol/L zinc acetate,8.3 mmol/L acetic acid,and 2.5% acetonitrile;flow rate was 1.5 ml/min.The excitation and emission wave length of fluorescence detector were 365 nm and 480 nm in 0~11 min,344 nm and 404 nm in 11~15.5 min,254 nm and 404 nm in 15.5~20 min,respectively.Results The linear range of Trp was 0.610~196 ?mol/L,the detection limit was 0.005 ?mol/L,and the average recovery was 103.71%.The linear range of Kyn was 0.049~98 ?mol/L,the detection limit 0.025 ?mol/L,and the average recovery was 97.45%.The linear range of Kyna was 1.050~1047 ?mol/L,the detection limit was 0.050 nmol/L,and the average recovery was 100.60%.Inter-and intra-day precisions were both less than 5%.Phenylalanine,tyrosine,and 5-hydroxytryptamine had no interference.The assay was employed to analyze serum samples of SLE patients.The result showed significant difference in Trp,Kyn,and Kyna content,Kyn/Trp ratio between SLE patients and control group.Conclusions A new method was established for simultaneous determination of Trp,Kyn,and Kyna in serum.The method is simple,fast,sensitive,specific,and suitable for applicability to clinical measurement.
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The basic mechanism for the excitation of the peripheral vestibular receptors following acute hypotension induced by sodium nitroprusside (SNP) or hemorrhage was investigated in anesthetized rats. Electrical activity of the afferent vestibular nerve was measured after pretreatment with kynurenic acid, an NMDA receptor antagonist. The activity of the vestibular nerve at rest following acute hypotension induced by SNP or simulating hemorrhage was a greater increase than in control animals. The gain of the vestibular nerve with sinusoidal rotation following acute hypotension increased significantly compared to control animals. The acute hypotension induced by SNP or hemorrhage did not change the activity of the afferent vestibular nerve after kynurenic acid injection. These results suggest that acute hypotension produced excitation of the vestibular hair cells via glutamate excitotoxicity in response to ischemia.
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Animals , Rats , Glutamic Acid , Hair Cells, Vestibular , Hemorrhage , Hypotension , Ischemia , Kynurenic Acid , N-Methylaspartate , Nitroprusside , Vestibular NerveABSTRACT
It has been well documented that transient forebrain global ischemia causes selective neuronal degeneration in hippocampal CA1 pyramidal neurons with a delay of a few days. The mechanism of this delayed hippocampal CA1 pyramidal neuronal death (DND) is still controversial. To delineate the mechanisms of the DND, the effects of treatment with MK-801, an NMDA receptor antagonist, kynurenic acid, a NMDA/non-NMDA receptor antagonist, and/or cycloheximide, a protein synthesis inhibitor, on the DND were investigated in male Wistar rats. To examine the participation of apoptotic neuronal death in the DND, TUNEL staining was performed in ischemic brain section. Global ischemia was induced by 4-vessel occlusion for 20 min. All animals in this study showed the DND 3 and 7 days after the ischemic insult. The DND that occurred 3 days and 7 days after the ischemia were not affected by pretreatment with MK-801 (I mg/kg), but markedly attenuated by the pretreatment with kynurenic acid (500 mg/kg). Treatment with cycloheximide (1 mg/kg) also markedly inhibited the DND. The magnitudes of attenuation by the two drugs were similar. The magnitude of attenuation by co-treatments with kynurenic acid and cycloheximide was not greater than that with any single treatment. TUNEL staining was negative in the sections obtained 1 or 2 days after the ischemic insults, but it was positive at hippocampal CA1 pyramidal cells in sections collected 3 days after the ischemia. These results suggested that the DND should be mediated by the activation of non-NMDA receptor, not by the activation of NMDA receptor and that the activation of AMPA receptor should induce the apoptotic process in the DND.