Acute psychotic symptoms in HIV-1 infected patients are associated with increased levels of kynurenic acid in cerebrospinal fluid

Important role of microglia in HIV-1 associated neurocognitive disorders and the molecular pathways implicated in its pathogenesis

The development of effective combined anti-retroviral therapy (cART) led to a significant reduction in the death rate associated with human immunodeficiency virus type 1 (HIV-1) infection. However, recent studies indicate that considerably more than 50% of all HIV-1 infected patients develop HIV-1-associated neurocognitive disorder (HAND). Microglia are the foremost cells infected by HIV-1 in the central nervous system (CNS), and so, are also likely to contribute to the neurotoxicity observed in HAND. The activation of microglia induces the release of pro-inflammatory markers and altered secretion of cytokines, chemokines, secondary messengers, and reactive oxygen species (ROS) which activate signalling pathways that initiate neuroinflammation. In turn, ROS and inflammation also play critical roles in HAND. However, more efforts are required to understand the physiology of microglia and the processes involved in their activation in order to better understand the how HIV-1-infected microglia are involved in the development of HAND. In this review, we summarize the current state of knowledge about the involvement of oxidative stress mechanisms and role of HIV-induced ROS in the development of HAND. We also examine the academic literature regarding crucial HIV-1 pathogenicity factors implicated in neurotoxicity and inflammation in order to identify molecular pathways that could serve as potential therapeutic targets for treatment of this disease. KEY MESSAGES Neuroinflammation and excitotoxicity mechanisms are crucial in the pathogenesis of HAND. CNS infiltration by HIV-1 and immune cells through the blood brain barrier is a key process involved in the pathogenicity of HAND. Factors including calcium dysregulation and autophagy are the main challenges involved in HAND.

Cerebrospinal fluid metabolomics: detection of neuroinflammation in human central nervous system disease

The high morbidity and mortality of neuroinflammatory diseases drives significant interest in understanding the underlying mechanisms involved in the innate and adaptive immune response of the central nervous system (CNS). Diagnostic biomarkers are important to define treatable neuroinflammation. Metabolomics is a rapidly evolving research area offering novel insights into metabolic pathways, and elucidation of reliable metabolites as biomarkers for diseases. This review focuses on the emerging literature regarding the detection of neuroinflammation using cerebrospinal fluid (CSF) metabolomics in human cohort studies. Studies of classic neuroinflammatory disorders such as encephalitis, CNS infection and multiple sclerosis confirm the utility of CSF metabolomics. Additionally, studies in neurodegeneration and neuropsychiatry support the emerging potential of CSF metabolomics to detect neuroinflammation in common CNS diseases such as Alzheimer's disease and depression. We demonstrate metabolites in the tryptophan-kynurenine pathway, nitric oxide pathway, neopterin and major lipid species show moderately consistent ability to differentiate patients with neuroinflammation from controls. Integration of CSF metabolomics into clinical practice is warranted to improve recognition and treatment of neuroinflammation.

The Kynurenine Pathway is Differentially Activated in Children with Lyme Disease and Tick-Borne Encephalitis

In children, tick-borne encephalitis and neuroborreliosis are common infections affecting the central nervous system. As inflammatory pathways including cytokine expression are activated in these children and appear to be of importance for outcome, we hypothesized that induction of the kynurenine pathway may be part of the pathophysiological mechanism. Inflammatory biomarkers were analyzed in cerebrospinal fluid from 22 children with tick-borne encephalitis (TBE), 34 children with neuroborreliosis (NB) and 6 children with no central nervous system infection. Cerebrospinal fluid levels of kynurenine and kynurenic acid were increased in children with neuroborreliosis compared to the comparison group. A correlation was seen between expression of several cerebrospinal fluid cytokines and levels of kynurenine and kynurenic acid in children with neuroborreliosis but not in children with tick-borne encephalitis. These findings demonstrate a strong induction of the kynurenine pathway in children with neuroborreliosis which differs from that seen in children with tick-borne encephalitis. The importance of brain kynurenic acid (KYNA) in both immune modulation and neurotransmission raises the possibility that abnormal levels of the compound in neuroborreliosis might be of importance for the pathophysiology of the disease. Drugs targeting the enzymes of this pathway may open the venue for novel therapeutic interventions.

Quantification of Plasma Kynurenine Metabolites Following One Bout of Sprint Interval Exercise

The kynurenine pathway of tryptophan degradation produces several neuroactive metabolites suggested to be involved in a wide variety of diseases and disorders, however, technical challenges in reliably detecting these metabolites hampers cross-comparisons. The main objective of this study was to develop an accurate, robust and precise bioanalytical method for simultaneous quantification of ten plasma kynurenine metabolites. As a secondary aim, we applied this method on blood samples taken from healthy subjects conducting 1 session of sprint interval exercise (SIE). It is well accepted that physical exercise is associated with health benefits and reduces risks of psychiatric illness, diabetes, cancer and cardiovascular disease, but also influences the peripheral and central concentrations of kynurenines. In line with this, we found that in healthy old adults (n = 10; mean age 64 years), levels of kynurenine increased 1 hour (P = .03) after SIE, while kynurenic acid (KYNA) concentrations were elevated after 24 hours (P = .02). In contrast, no significant changes after exercise were seen in young adults (n = 10; mean age 24 years). In conclusion, the described method performs well in reliably detecting all the analyzed metabolites in plasma samples. Furthermore, we also detected an age-dependent effect on the degree by which a single intense training session affects kynurenine metabolite levels.

Indoleamine 2, 3-Dioxygenase-Mediated Tryptophan Catabolism: A Leading Star or Supporting Act in the Tuberculosis and HIV Pas-de-Deux?

Progression from latency to active Tuberculosis (TB) disease is mediated by incompletely understood host immune factors. The definitive characteristic of progressive human immunodeficiency virus (HIV) disease is a severe loss in number and function of T lymphocytes. Among the many possible mediators of T lymphocyte loss and ineffective function is the activity of the immune-modulatory enzyme indoleamine 2,3-dioxygenase (IDO). IDO is the rate-limiting enzyme converting tryptophan to kynurenine. IDO activity was initially recognized to mediate tolerance at the foeto-maternal interface. Recently, IDO activity has also been noted to play a critical role in immune tolerance to pathogens. Studies of host immune and metabolic mediators have found IDO activity significantly elevated in HIV and TB disease. In this review, we explore the link between IDO-mediated tryptophan catabolism and the presence of active TB disease in HIV-infected patients. We draw attention to increased IDO activity as a key factor marking the progression from latent to active TB disease in HIV-infected patients.

Serum Small Extracellular Vesicles Proteome of Tuberculosis Patients Demonstrated Deregulated Immune Response

PURPOSE

Detailed understanding of host pathogen interaction in tuberculosis is an important avenue for identifying novel therapeutic targets. Small extracellular vesicles (EVs) like exosomes that are rich in proteins, nucleic acids and lipids, act as messengers and may show altered composition in disease conditions.

EXPERIMENTAL DESIGN

In this case control study, small EVs are isolated from serum of 58 subjects (all male, 33 (15-70) in years) including drug naïve active tuberculosis (ATB: n = 22), non-tuberculosis (NTB: n = 18), and healthy subjects (n = 18). Serum small EVs proteome analysis is carried out using isobaric tag for relative and absolute quantification (iTRAQ) experiments and an independent sample (n = 36) is used for validation.

RESULTS

A set of 132 and 68 proteins are identified in iTRAQ-I (ATB/Healthy) and iTRAQ-II (ATB/NTB) experiments, respectively. Four proteins (KYAT3, SERPINA1, HP, and APOC3) show deregulation (log₂ -fold change > ±0.48, p < 0.05) in ATB with respect to healthy controls and Western blot data corroborated mass spectrometry findings.

CONCLUSIONS AND CLINICAL RELEVANCE

These important proteins, involved in neutrophil degranulation, plasma heme scavenging, kynurenine, and lipid metabolism, show deregulation in ATB patients. Identification of such a protein panel in circulating small EVs besides providing novel insights into their role in tuberculosis may prove to be useful targets to develop host-directed therapeutic intervention.

Potential Role of Antipsychotic-Galantamine-Memantine Combination in the Treatment of Positive, Cognitive, and Negative Symptoms of Schizophrenia

Schizophrenia is, in part, a cognitive illness. There are no approved medications for cognitive impairments associated with schizophrenia (CIAS) and primary negative symptoms. Cholinergic and glutamatergic systems, alpha-7 nicotinic acetylcholine (α-7nACh) and N-methyl-D-aspartate (NMDA) receptors, kynurenic acid (KYNA), and mismatch negativity have been implicated in the pathophysiology of CIAS and negative symptoms. Galantamine is an acetylcholinesterase inhibitor that is also a positive allosteric modulator at the α4β2 and α7nACh receptors. Memantine is a noncompetitive NMDA receptor antagonist. Galantamine and memantine alone and in combination were effective for cognition in animals and people with Alzheimer's disease. The objective of this article is to critically dissect the published randomized controlled trials with galantamine and memantine for CIAS to highlight the efficacy signal. These studies may have failed to detect a clinically meaningful efficacy signal due to limitations, methodological issues, and possible medication nonadherence. There is evidence from a small open-label study that the galantamine-memantine combination may be effective for CIAS with kynurenine pathway metabolites as biomarkers to detect the severity of cognitive impairments. Given that there are no available treatments for cognitive impairments and primary negative symptoms in schizophrenia, testing of this "five-pronged strategy" (quintuple hypotheses: dopamine, nicotinic-cholinergic, glutamatergic/NMDA, GABA, and KYNA) is a "low-risk high-gain" approach that could be a major breakthrough in the field. The galantamine-memantine combination has the potential to treat positive, cognitive, and negative symptoms, and targeting the quintuple hypotheses concurrently may lead to a major scientific advancement - from antipsychotic treatment to antischizophrenia treatment.

Cerebrospinal fluid kynurenine and kynurenic acid concentrations are associated with coma duration and long-term neurocognitive impairment in Ugandan children with cerebral malaria

Background

One-fourth of children with cerebral malaria (CM) retain cognitive sequelae up to 2 years after acute disease. The kynurenine pathway of the brain, forming neuroactive metabolites, e.g. the NMDA-receptor antagonist kynurenic acid (KYNA), has been implicated in long-term cognitive dysfunction in other CNS infections. In the present study, the association between the kynurenine pathway and neurologic/cognitive complications in children with CM was investigated.

Methods

Cerebrospinal fluid (CSF) concentrations of KYNA and its precursor kynurenine in 69 Ugandan children admitted for CM to Mulago Hospital, Kampala, Uganda, between 2008 and 2013 were assessed. CSF kynurenine and KYNA were compared to CSF cytokine levels, acute and long-term neurologic complications, and long-term cognitive impairments. CSF kynurenine and KYNA from eight Swedish children without neurological or infectious disease admitted to Astrid Lindgren’s Children’s Hospital were quantified and used for comparison.

Results

Children with CM had significantly higher CSF concentration of kynurenine and KYNA than Swedish children (P < 0.0001 for both), and CSF kynurenine and KYNA were positively correlated. In children with CM, CSF kynurenine and KYNA concentrations were associated with coma duration in children of all ages (P = 0.003 and 0.04, respectively), and CSF kynurenine concentrations were associated with worse overall cognition (P = 0.056) and attention (P = 0.003) at 12-month follow-up in children ≥5 years old.

Conclusions

CSF KYNA and kynurenine are elevated in children with CM, indicating an inhibition of glutamatergic and cholinergic signaling. This inhibition may lead acutely to prolonged coma and long-term to impairment of attention and cognition.

Central Nervous System Infection with Borna Disease Virus Causes Kynurenine Pathway Dysregulation and Neurotoxic Quinolinic Acid Production

Central nervous system infection of neonatal and adult rats with Borna disease virus (BDV) results in neuronal destruction and behavioral abnormalities with differential immune-mediated involvement. Neuroactive metabolites generated from the kynurenine pathway of tryptophan degradation have been implicated in several human neurodegenerative disorders. Here, we report that brain expression of key enzymes in the kynurenine pathway are significantly, but differentially, altered in neonatal and adult rats with BDV infection. Gene expression analysis of rat brains following neonatal infection showed increased expression of kynurenine amino transferase II (KATII) and kynurenine-3-monooxygenase (KMO) enzymes. Additionally, indoleamine 2,3-dioxygenase (IDO) expression was only modestly increased in a brain region- and time-dependent manner in neonatally infected rats; however, its expression was highly increased in adult infected rats. The most dramatic impact on gene expression was seen for KMO, whose activity promotes the production of neurotoxic quinolinic acid. KMO expression was persistently elevated in brain regions of both newborn and adult BDV-infected rats, with increases reaching up to 86-fold. KMO protein levels were increased in neonatally infected rats and colocalized with neurons, the primary target cells of BDV infection. Furthermore, quinolinic acid was elevated in neonatally infected rat brains. We further demonstrate increased expression of KATII and KMO, but not IDO, in vitro in BDV-infected C6 astroglioma cells. Our results suggest that BDV directly impacts the kynurenine pathway, an effect that may be exacerbated by inflammatory responses in immunocompetent hosts. Thus, experimental models of BDV infection may provide new tools for discriminating virus-mediated from immune-mediated impacts on the kynurenine pathway and their relative contribution to neurodegeneration.IMPORTANCE BDV causes persistent, noncytopathic infection in vitro yet still elicits widespread neurodegeneration of infected neurons in both immunoincompetent and immunocompetent hosts. Here, we show that BDV infection induces expression of key enzymes of the kynurenine pathway in brains of newborn and adult infected rats and cultured astroglioma cells, shunting tryptophan degradation toward the production of neurotoxic quinolinic acid. Thus, our findings newly implicate this metabolic pathway in BDV-induced neurodegeneration. Given the importance of the kynurenine pathway in a wide range of human infections and neurodegenerative and neuropsychiatric disorders, animal models of BDV infection may serve as important tools for contrasting direct viral and indirect antiviral immune-mediated impacts on kynurenine pathway dysregulation and the ensuing neurodevelopmental and neuropathological consequences.

Tryptophan Metabolism Along the Kynurenine Pathway Downstream of Toll-like Receptor Stimulation in Peripheral Monocytes

Tryptophan degradation along the kynurenine pathway is of central importance for the immune function. Toll-like receptors (TLRs), representing the first line of immune defence against pathogens, are expressed in various cell types. The most abundant expression is found on monocytes, macrophages and dendritic cells. The aim of this study was to investigate whether stimulation with different TLR ligands induces the kynurenine pathway in human peripheral monocytes. Cell supernatants were analysed using a liquid chromatography/mass spectrometry to measure kynurenine, kynurenic acid (KYNA), quinolinic acid (QUIN) and tryptophan. Stimulation of TLR-2, TLR-3, TLR-4, TLR-7/8 and TLR-9 was found to induce the production of kynurenine, but only stimulation of TLR-3 increased levels of further downstream metabolites, such as KYNA and QUIN. Stimulation of TLR-1, TLR-5 and TLR-6 did not induce the kynurenine pathway. Taken together, this study provides novel evidence demonstrating that TLR activation induces a pattern of downstream tryptophan degradation along the kynurenine pathway in monocytes. The results of this study may implicate that TLRs can be used as new drug targets for the regulation of aberrant tryptophan metabolism along this pathway, a potential therapeutic strategy that may be of importance in several disorders.

Polymorphism of Kynurenine Pathway-Related Genes, Kynurenic Acid, and Psychopathological Symptoms in HIV

HIV-infection is associated with neuroinflammation and greater psychopathological symptoms, which may be mediated by imbalances in the kynurenic pathway (KP). Two key KP enzymes that catabolize kynurenine include kynurenine-aminotransferase II (KATII), which yields antioxidative kynurenine acid [KYNA] in astrocytes, and kynurenine-3-monooxygenase (KMO), which produces neurotoxic metabolites in microglia. The relationships between polymorphisms in KMO and KATII, psychopathological symptoms, and cerebrospinal fluid (CSF) [KYNA] were evaluated in subjects with and without HIV-infection. Seventy-two HIV-positive and 72-seronegative (SN) participants were genotyped for KATII-rs1480544 and KMO-rs1053230. Although our participants were not currently diagnosed with depression or anxiety, they were assessed for psychopathological distress with Center for Epidemiologic Studies-Depression scale and Symptom Checklist-90-Revised. CSF-[KYNA] was also measured in 100 subjects (49 HIV/51 SN). HIV-participants had more psychopathological distress than SN, especially for anxiety. KATII-by-HIV interactions were found on anxiety, interpersonal sensitivity and obsessive compulsivity; KATII-C-carriers had lower scores than TT-carriers in SN but not in HIV. In contrast, the KMO-polymorphism had no influence on psychopathological symptoms in both groups. Overall, CSF-[KYNA] increased with age independently of HIV-serostatus, except KATII-TT-carriers tended to show no age-dependent variations. Therefore, the C-allele in KATII-rs1480544 appears to be protective against psychopathological distress in SN but not in HIV individuals, who had more psychopathological symptoms and likely greater neuroinflammation. The age-dependent increase in CSF-[KYNA] may reflect a compensatory response to age-related inflammation, which may be deficient in KATII-TT-carriers. Targeted treatments that decrease neuroinflammation and increase KYNA in at risk KATII-TT-carriers may reduce psychopathological symptoms in HIV.

Tryptophan Catabolism in Chronic Viral Infections: Handling Uninvited Guests

l-Tryptophan (l-Trp) is an essential amino acid that possesses diverse metabolic, neurological, and immunological roles spanning from the synthesis of proteins, neurotransmitter serotonin, and neurohormone melatonin, to its degradation into immunosuppressive catabolites by indoleamine-2, 3-dioxygenase (IDO) in the kynurenine pathway (KP). Trp catabolites, by activating aryl hydrocarbon receptor (AhR), play an important role in antimicrobial defense and immune regulation. IDO/AhR acts as a double-edged sword by both depleting l-Trp to starve the invaders and by contributing to the state of immunosuppression with microorganisms that were not cleared during acute infection. Pathogens experiencing Trp deprivation by IDO-mediated degradation include certain bacteria, parasites, and less likely viruses. However, chronic viral infections highjack the host immune response to create a state of disease tolerance via kynurenine catabolites. This review covers the latest data involving chronic viral infections such as human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), herpes, and cytomegalovirus (CMV) and their cellular interplay with Trp catabolites. Strategies developed by viruses to escape immune control also represent new avenues for therapeutic interventions based on Trp metabolism.

Determination of kynurenic acid in rat cerebrospinal fluid by HPLC with fluorescence detection

A sensitive HPLC method using fluorescence detection was developed to determine kynurenic acid (KYNA) level in rat cerebrospinal fluid (CSF). The method development was accomplished by screening different columns, optimizing zinc acetate concentration and determining the optimal HPLC flow rate. This method allowed direct injection of the CSF samples onto an Xselect C18 column and KYNA levels were measured fluorometrically by forming a fluorescent complex with zinc acetate that was delivered post-column. The limit of quantitation was 0.2 n m with 30 μL injection, corresponding to 6 fmol (signal-to-noise ratio = 10). The improved sensitivity enabled the measurement of KYNA in naive and drug-treated rat CSF.

Kynurenine 3-Monooxygenase: An Influential Mediator of Neuropathology

Mounting evidence demonstrates that kynurenine metabolism may play an important pathogenic role in the development of multiple neurological and neuropsychiatric disorders. The kynurenine pathway consists of two functionally distinct branches that generate both neuroactive and oxidatively reactive metabolites. In the brain, the rate-limiting enzyme for one of these branches, kynurenine 3-monooxygenase (KMO), is predominantly expressed in microglia and has emerged as a pivotal point of metabolic regulation. KMO substrate and expression levels are upregulated by pro-inflammatory cytokines and altered by functional genetic mutations. Increased KMO metabolism results in the formation of metabolites that activate glutamate receptors and elevate oxidative stress, while recent evidence has revealed neurodevelopmental consequences of reduced KMO activity. Together, the evidence suggests that KMO is positioned at a critical metabolic junction to influence the development or trajectory of a myriad of neurological diseases. Understanding the mechanism(s) by which alterations in KMO activity are able to impair neuronal function, and viability will enhance our knowledge of related disease pathology and provide insight into novel therapeutic opportunities. This review will discuss the influence of KMO on brain kynurenine metabolism and the current understanding of molecular mechanisms by which altered KMO activity may contribute to neurodevelopment, neurodegenerative, and neuropsychiatric diseases.

A role for inflammatory metabolites as modulators of the glutamate N-methyl-D-aspartate receptor in depression and suicidality

BACKGROUND

Patients with depression and suicidality suffer from low-grade neuroinflammation. Pro-inflammatory cytokines activate indoleamine 2,3-dioxygenase, an initial enzyme of the kynurenine pathway. This pathway produces neuroactive metabolites, including quinolinic- and kynurenic acid, binding to the glutamate N-methyl-d-aspartate-receptor, which is hypothesized to be part of the neural mechanisms underlying symptoms of depression. We therefore hypothesized that symptoms of depression and suicidality would fluctuate over time in patients prone to suicidal behavior, depending on the degree of inflammation and kynurenine metabolite levels in the cerebrospinal fluid (CSF).

METHODS

We measured cytokines and kynurenine metabolites in CSF, collected from suicide attempters at repeated occasions over 2 years (total patient samples n=143, individuals n=30) and healthy controls (n=36). The association between the markers and psychiatric symptoms was assessed using the Montgomery Asberg Depression Rating Scale and the Suicide Assessment Scale.

RESULTS

Quinolinic acid was increased and kynurenic acid decreased over time in suicidal patients versus healthy controls. Furthermore, we found a significant association between low kynurenic acid and severe depressive symptoms, as well as between high interleukin-6 levels and more severe suicidal symptoms.

CONCLUSIONS

We demonstrate a long-term dysregulation of the kynurenine pathway in the central nervous system of suicide attempters. An increased load of inflammatory cytokines was coupled to more severe symptoms. We therefore suggest that patients with a dysregulated kynurenine pathway are vulnerable to develop depressive symptoms upon inflammatory conditions, as a result the excess production of the NMDA-receptor agonist quinolinic acid. This study provides a neurobiological framework supporting the use of NMDA-receptor antagonists in the treatment of suicidality and depression.

The kynurenine pathway as a therapeutic target in cognitive and neurodegenerative disorders

Understanding the neurochemical basis for cognitive function is one of the major goals of neuroscience, with a potential impact on the diagnosis, prevention and treatment of a range of psychiatric and neurological disorders. In this review, the focus will be on a biochemical pathway that remains under-recognized in its implications for brain function, even though it can be responsible for moderating the activity of two neurotransmitters fundamentally involved in cognition - glutamate and acetylcholine. Since this pathway - the kynurenine pathway of tryptophan metabolism - is induced by immunological activation and stress, it also stands in a unique position to mediate the effects of environmental factors on cognition and behaviour. Targeting the pathway for new drug development could, therefore, be of value not only for the treatment of existing psychiatric conditions, but also for preventing the development of cognitive disorders in response to environmental pressures.

Kynurenic Acid levels in cerebrospinal fluid from patients with Alzheimer's disease or dementia with lewy bodies

Kynurenic acid (KYNA) is implicated in cognitive functions. Altered concentrations of the compound are found in serum and cerebrospinal fluid (CSF) of patients with Alzheimer’s disease (AD). Further studies to determine whether KYNA serves as a biomarker for cognitive decline and dementia progression are required. In this study, we measured CSF KYNA levels in AD patients (n = 19), patients with dementia with Lewy bodies (DLB) (n = 18), and healthy age-matched controls (Ctrls)) (n = 20) to further explore possible correlations between KYNA levels, cognitive decline, and well-established AD and inflammatory markers. Neither DLB patients nor AD patients showed significantly altered CSF KYNA levels compared to Ctrls. However, female AD patients displayed significantly higher KYNA levels compared to male AD patients, a gender difference not seen in the Ctrl or DLB group. Levels of KYNA significantly correlated with the AD-biomarker P-tau and the inflammation marker soluble intercellular adhesion molecule-1 (sICAM-1) in the AD patient group. No associations between KYNA and cognitive functions were found. Our study shows that, although KYNA was not associated with cognitive decline in AD or DLB patients, it may be implicated in AD-related hyperphosphorylation of tau and inflammation. Further studies on larger patient cohorts are required to understand the potential role of KYNA in AD and DLB.

Behavioral disturbances in adult mice following neonatal virus infection or kynurenine treatment--role of brain kynurenic acid

Exposure to infections in early life is considered a risk-factor for developing schizophrenia. Recently we reported that a neonatal CNS infection with influenza A virus in mice resulted in a transient induction of the brain kynurenine pathway, and subsequent behavioral disturbances in immune-deficient adult mice. The aim of the present study was to investigate a potential role in this regard of kynurenic acid (KYNA), an endogenous antagonist at the glycine site of the N-methyl-D-aspartic acid (NMDA) receptor and at the cholinergic α7 nicotinic receptor. C57BL/6 mice were injected i.p. with neurotropic influenza A/WSN/33 virus (2400 plaque-forming units) at postnatal day (P) 3 or with L-kynurenine (2×200 mg/kg/day) at P7-16. In mice neonatally treated with L-kynurenine prepulse inhibition of the acoustic startle, anxiety, and learning and memory were also assessed. Neonatally infected mice showed enhanced sensitivity to D-amphetamine-induced (5 mg/kg i.p.) increase in locomotor activity as adults. Neonatally L-kynurenine treated mice showed enhanced sensitivity to D-amphetamine-induced (5 mg/kg i.p.) increase in locomotor activity as well as mild impairments in prepulse inhibition and memory. Also, D-amphetamine tended to potentiate dopamine release in the striatum in kynurenine-treated mice. These long-lasting behavioral and neurochemical alterations suggest that the kynurenine pathway can link early-life infection with the development of neuropsychiatric disturbances in adulthood.

Sustained elevation of kynurenic Acid in the cerebrospinal fluid of patients with herpes simplex virus type 1 encephalitis

Herpes simplex virus (HSV) type 1 encephalitis (HSE) is a viral infectious disease with commonly occurring neurodegeneration and neurological/cognitive long-term sequelae. Kynurenic acid (KYNA) is a neuroactive tryptophan metabolite, which is elevated in the cerebrospinal fluid (CSF) during viral infection as a result of immune activation. The aim of the study was to investigate the role of endogenous brain KYNA for the long-term outcome of the disease. CSF KYNA concentration was analyzed in 25 HSE patients along the course of the disease and compared with that of 25 age-matched healthy volunteers. Within 3 weeks of admission CSF KYNA of HSE patients was markedly elevated (median 33.6 nM) compared to healthy volunteers (median 1.45 nM). Following a decline observed after 1-2 months, levels of CSF KYNA were elevated more than 1 year after admission (median 3.4 nM range: 1-9 years). A negative correlation was found between initial CSF KYNA concentrations and severity of the long-term sequelae. This study show a marked elevation in CSF KYNA from patients with HSE, most pronounced during the acute phase of the disease and slowly declining along the recovery. We propose that brain KYNA might potentially protect against neurodegeneration while causing a long-lasting loss in cognitive function associated with the disease.

Activation of kynurenine pathway in ex vivo fibroblasts from patients with bipolar disorder or schizophrenia: cytokine challenge increases production of 3-hydroxykynurenine

Accumulating data suggest a causative link between immune stimulation, disturbed metabolism of tryptophan, and pathogenesis of bipolar disorder and schizophrenia. The goal of this study was to examine the production of kynurenic acid (KYNA), 3-hydroxykynurenine (3-HK) and the expression of kynurenine pathway enzymes involved in their synthesis and metabolism in cultured skin fibroblasts obtained from patients with bipolar disorder, schizophrenia or from healthy control individuals. The assessment was performed under basal conditions or following treatment with interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, or their combinations, in cells exposed to exogenous kynurenine. In both groups of patients, the baseline production of KYNA and 3-HK was increased, as compared to control subjects. Case-treatment analyses revealed significant interactions between bipolar case status and IL-1β, IL-6, IFN-γ + TNF-α, or IFN-γ + IL-1β, as well as between schizophrenia case status and IL-1β, IFN-γ + TNF-α, or IFN-γ + IL-1β, in terms of higher 3-HK. Noteworthy, no case-treatment interactions in terms of KYNA production were found. Observed changes did not appear to correlate with the expression of genes encoding kynurenine aminotransferases (KATs), kynureninase (KYNU) or kynurenine-3-monooxygenase (KMO). The single nucleotide polymorphisms (SNPs), rs1053230 and rs2275163, in KMO influenced KYNA levels yet did not explain the case-treatment discrepancies. In conclusion, our present findings indicate the utility of skin-derived fibroblasts for kynurenines research and support the concept of kynurenine pathway alterations in bipolar disorder and schizophrenia. The increase in ratio between neurotoxic 3-HK and neuroinhibitory/neuroprotective KYNA following exposure to cytokines may account for altered neurogenesis and structural abnormalities characteristic for both diseases.

Kynurenic acid in plasma and endometrium in bitches with pyometra

Kynurenic acid (KYNA) is produced enzymatically in humans and animals from kynurenine. Reports concerning changes of kynurenine metabolism during inflammation are available in the literature. Pyometra is a pathological condition characterized by the accumulation of pus in the uterine lumen and bacterial infection. The objective of the study was to compare the serum and endometrial KYNA concentrations in healthy bitches and those with pyometra. KYNA was determined by means of high-performance liquid chromatography with fluorometric detection. The serum content of KYNA in bitches with pyometra was significantly higher than in healthy bitches. The KYNA content in the endometrium of bitches with pyometra was higher, yet the difference was not statistically significant. Our result indicates that determination of KYNA might be a marker of pyometra in bitches.

Kynurenic acid in synovial fluid and serum of patients with rheumatoid arthritis, spondyloarthropathy, and osteoarthritis

OBJECTIVE

Previously we demonstrated that kynurenic acid (KYNA), an endogenous metabolite of kynurenine, is present in the synovial fluid of patients with rheumatoid arthritis (RA). KYNA inhibits proliferation of synoviocytes in vitro. The goal of our study was to compare KYNA concentrations in synovial fluid and blood of patients with RA, inflammatory spondyloarthropathies (SpA), and osteoarthritis (OA).

METHODS

Serum and synovial fluid samples were obtained from 189 patients with RA, 56 patients with SpA, and 32 patients with OA. KYNA was separated using a high-performance liquid chromatography system and measured fluorometrically.

RESULTS

KYNA concentration in synovial fluid obtained from patients with RA and SpA was significantly lower than that in patients with OA (p < 0.05). The concentration of KYNA in serum of patients with RA, SpA, and OA did not differ among all groups studied. The positive correlation between KYNA content in synovial fluid and serum was found in patients with RA (p < 0.05). Univariate linear regression analysis demonstrated that fibrinogen was significantly associated with KYNA in synovial fluid (p < 0.05), and red blood cell counts, morning stiffness, and pain scores were significantly associated with KYNA level in serum (all p < 0.05). Multivariate regression analysis revealed correlation between the following independent variables: hemoglobin level, hematocrit, red blood cell count in conjunction with age and KYNA content in synovial fluid. A lack of correlation was observed between KYNA content in synovial fluid of patients with RA and other clinical and laboratory measures of disease activity.

CONCLUSION

Our data show a local deficit of KYNA in inflammatory states.

Elevated cerebrospinal fluid kynurenic acid levels in patients with tick-borne encephalitis

BACKGROUND

Kynurenic acid (KYNA) is a neuroactive metabolite of tryptophan that is thought to regulate cognitive functions. Previous studies have shown that levels of KYNA increase during virus infection and that this metabolite interacts with the immune system.

OBJECTIVE

The aim of the study was to investigate whether patients with tick-borne encephalitis (TBE), a viral infectious disease associated with long-term cognitive impairment, have increased levels of KYNA in the cerebrospinal fluid (CSF).

METHODS

CSF KYNA was analysed using high-performance liquid chromatography in 108 patients with TBE and 52 age-matched controls. Patients were classified according to the severity of TBE: mild (47%), moderate (44%) or severe (9%).

RESULTS

Concentrations of CSF KYNA were considerably higher in patients with TBE (5.3 nmol L(-1) ) than in control subjects (0.99 nmol L(-1) ). KYNA concentration in the CSF varied greatly amongst individuals with TBE and increased (P < 0.05) with the severity of disease.

CONCLUSIONS

This is the first study to demonstrate increased levels of CSF KYNA in patients with TBE. The importance of brain KYNA in both immune modulation and neurotransmission raises the possibility that abnormal levels of the compound in TBE might play a part in the pathophysiology of the disease. A detailed knowledge of endogenous brain KYNA during the course of CNS infection might yield further insights into the neuroimmunological role of the compound and may also provide new pharmacological approaches for the treatment of cognitive symptoms.

Cognitive dysfunction among HIV positive and HIV negative patients with psychosis in Uganda

BACKGROUND

Cognitive impairment is an established phenomenon in HIV infected individuals and patients that have psychosis. However there is need to establish the severity of the impairment if patients are co morbid with both conditions.

AIM

To compare cognitive function among HIV positive individuals and HIV negative individuals with psychosis.

METHODS

We recruited patients with psychosis at two national referral hospitals. A standardized demographics questionnaire and psychiatric, physical, and laboratory assessments were conducted. Types of psychosis were diagnosed using the Mini International Neuropsychiatric Inventory-PLUS while cognitive functioning was determined using the Mini mental state examination (MMSE) and a neuropsychological test battery. Follow-up assessments on cognitive function and severity of psychiatric illness were performed at 3 and 6 months. Pairwise comparison and multivariable logistic regression analysis were used to determine the differences between the HIV positive and HIV negative individuals.

RESULTS

There were 156 HIV positive and 322 HIV negative participants. The mean age was 33 years for the HIV positive group and 29 years for the HIV negative group (p<0.001). The HIV positive individuals were almost three times (OR = 2.62 CI 95% 1.69-4.06) more likely to be cognitively impaired on the MMSE as well as the following cognitive tests:- WHO-UCLA Auditory Verbal Learning Test (OR 1.79, 95% CI 1.09-2.92), Verbal Fluency (OR 3.42, 95% CI 2.24-5.24), Color Trails 1 (OR 2.03, 95% CI 1.29-3.02) and Color Trails 2 (OR 3.50 95% 2.00-6.10) all p = 0.01. There was improvement in cognitive function at follow up; however the impairment remained higher for the HIV positive group (p<0.001).

CONCLUSION

Cognitive impairment in psychosis was worsened by HIV infection. Care plans to minimize the effect of this impairment should be structured for the management of individuals with HIV and psychosis.

Effect of systemic kynurenine on cortical spreading depression and its modulation by sex hormones in rat

BACKGROUND

The aura symptoms in migraine are most likely due to cortical spreading depression (CSD). CSD is favored by NMDA receptor activation and increased cortical excitability. The latter probably explains why migraine with aura may appear when estrogen levels are high, like during pregnancy. Kynurenic acid, a derivative of tryptophan metabolism, is an endogenous NMDA receptor antagonist whose cerebral concentrations can be augmented by systemic administration of its precursor L-kynurenine.

OBJECTIVE

To determine if exogenous administration of L-kynurenine is able to influence KCl-induced CSD in rat, if the effect is sex-dependent and if it differs in females between the phases of the estrous cycle.

METHODS

Adult Sprague-Dawley rats (n=8/group) received intraperitoneal (i.p.) injections of L-kynurenine (L-KYN, 300 mg/kg), L-KYN combined with probenecid (L-KYN+PROB) that increases cortical concentration of KYNA by blocking its excretion from the central nervous system, probenecid alone (PROB, 200 mg/kg) or NaCl. Cortical kynurenic acid concentrations were determined by HPLC (n=7). Thirty minutes after the injections, CSDs were elicited by application of 1M KCl over the occipital cortex and recorded by DC electrocorticogram. In NaCl and L-KYN groups, supplementary females were added and CSD frequency was analyzed respective to the phases of the estrous cycle determined by vaginal smears.

RESULTS

In both sexes, PROB, L-KYN and L-KYN+PROB increased cortical kynurenic acid level. PROB, L-KYN and L-KYN+PROB with increasing potency decreased CSD frequency in female rats, while in males such an effect was significant only for L-KYN+PROB. The inhibitory effect of L-KYN on CSD frequency in females was most potent in diestrus.

CONCLUSION

L-Kynurenine administration suppresses CSD, most likely by increasing kynurenic acid levels in the cortex. Females are more sensitive to this suppressive effect of L-kynurenine than males. These results emphasize the role of sex hormones in migraine and open interesting novel perspectives for its preventive treatment.

Kynurenine 3-monooxygenase polymorphisms: relevance for kynurenic acid synthesis in patients with schizophrenia and healthy controls

BACKGROUND

Patients with schizophrenia show increased brain and cerebrospinal fluid (CSF) concentrations of the endogenous N-methyl-D-aspartate receptor antagonist kynurenic acid (KYNA). This compound is an end-metabolite of the kynurenine pathway, and its formation indirectly depends on the activity of kynurenine 3-monooxygenase (KMO), the enzyme converting kynurenine to 3-hydroxykynurenine.

METHODS

We analyzed the association between KMO gene polymorphisms and CSF concentrations of KYNA in patients with schizophrenia and healthy controls. Fifteen single nucleotide polymorphisms (SNPs) were selected covering KMO and were analyzed in UNPHASED.

RESULTS

We included 17 patients with schizophrenia and 33 controls in our study. We found an association between a KMO SNP (rs1053230), encoding an amino acid change of potential importance for substrate interaction, and CSF concentrations of KYNA.

LIMITATIONS

Given the limited sample size, the results are tentative until replication.

CONCLUSION

Our results suggest that the nonsynonymous KMO SNP rs1053230 influences CSF concentrations of KYNA.

Neonatal infection with neurotropic influenza A virus induces the kynurenine pathway in early life and disrupts sensorimotor gating in adult Tap1-/- mice

Epidemiological studies suggest that early life infections may contribute to the development of neuropsychiatric disorders later in life. Experimental studies employing infections during neonatal life support this notion by reporting persistent changes in the behaviour of adult animals, including deficits in sensorimotor gating. We have previously described an induction of the kynurenine pathway in neonatal wild-type (WT) mice following a systemic infection with neurotropic influenza A/WSN/33 virus. Here, we use the same model of infection in both WT and Tap1-/- mice (expressing reduced levels of MHC class I) and study long-term effects of the infection on sensorimotor gating, as determined by measuring prepulse inhibition (PPI). Moreover, transcription of genes encoding enzymes in the kynurenine pathway and levels of kynurenic acid (KYNA), in the brain of Tap1-/- mice were investigated. In mice infected on postnatal day (P)3 or P4, the levels of several transcripts in the kynurenine pathway were altered at P7, P13 and P24. Transcripts encoding indoleamine-pyrrole 2,3-dioxygenase (IDO), degrading tryptophan in the first step of the kynurenine pathway were consistently up-regulated at all time-points investigated. The changes in transcript levels were accompanied by a transient elevation of KYNA in the brain of infected mice at P13. At age 5-6 months, neonatally infected Tap1-/-, but not WT, mice exhibited a reduction in PPI. The present data show that a neonatal infection targeting the brain can induce the kynurenine pathway and that such an infection can disrupt sensorimotor gating in adulthood in genetically vulnerable mice.

Elevated levels of kynurenic acid in the cerebrospinal fluid of patients with bipolar disorder

BACKGROUND

Patients with schizophrenia show elevated brain levels of the neuroactive tryptophan metabolite kynurenic acid (KYNA). This astrocyte-derived mediator acts as a neuroprotectant and modulates sensory gating and cognitive function. We measured the levels of KYNA in the cerebrospinal fluid (CSF) of patients with bipolar disorder and healthy volunteers to investigate the putative involvement of KYNA in bipolar disorder.

METHODS

We obtained CSF by lumbar puncture from 23 healthy men and 31 euthymic men with bipolar disorder. We analyzed the samples using high-performance liquid chromatography.

RESULTS

Patients with bipolar disorder had increased levels of KYNA in their CSF compared with healthy volunteers (1.71 nM, standard error of the mean [SEM] 0.13 v. 1.13 nM, SEM 0.09; p = 0.002. The levels of KYNA were positively correlated with age among bipolar patients but not healthy volunteers.

LIMITATIONS

The influence of ongoing drug treatment among patients cannot be ruled out. We conducted our study during the euthymic phase of the disease.

CONCLUSION

Brain KYNA levels are increased in euthymic men with bipolar disorder. In addition, KYNA levels increased with age in these patients. These findings indicate shared mechanisms between bipolar disorder and schizophrenia. Elevated levels of brain KYNA may provide further insight to the pathophysiology and progression of bipolar disorder.

Treatment considerations for psychiatric syndromes associated with HIV infection

Psychiatric syndromes associated with HIV disease were recognized early in the AIDS epidemic. Public education, new technologies and antiretroviral therapies have resulted in earlier recognition and therapautic interventions of HIV infection, improving the physical health for individuals living with HIV. While HIV-associated psychiatric symptoms have been recognized for more than 20 years, our understanding of the mechanisms underlying psychiatric symptoms among HIV-infected individuals and treatments for these symptoms have not kept pace with advances in HIV therapies. In this article, we discuss current knowledge of the psychiatric symptoms occurring with HIV disease, specifically mood, anxiety and psychotic disorders, evidence-based treatments and treatment considerations, new strategies for the treatments of psychiatric symptoms in HIV disease are also discussed.

Pharmacological manipulation of kynurenic acid: potential in the treatment of psychiatric disorders

The kynurenine pathway constitutes the main route of tryptophan degradation and generates the production of several neuroactive compounds; quinolinic acid is an excitotoxic NMDA receptor agonist, 3-hydroxykynurenine is a free-radical generator and kynurenic acid (KYNA) is an antagonist at glutamate and nicotinic receptors. In low micromolar concentrations, KYNA blocks the glycine site of the NMDA receptor and the nicotinic alpha(7) acetylcholine receptor. Knowledge regarding kynurenine metabolites and their involvement in neurophysiological processes has increased dramatically in recent years. In particular, endogenous KYNA appears to tightly control firing of midbrain dopamine neurons and to be involved in cognitive functions. Thus, decreased endogenous levels of rat brain KYNA have been found to reduce firing of these neurons, and mice with a targeted deletion of kynurenine aminotransferase II display low endogenous brain KYNA levels concomitant with an increased performance in cognitive tests. It is also suggested that kynurenines participate in the pathophysiology of psychiatric disorders. Thus, elevated levels of KYNA have been found in the CSF as well as in the post-mortem brain of patients with schizophrenia. Advantages in understanding how kynurenines can be pharmacologically manipulated may provide new possibilities in the treatment of psychiatric disorders, such as schizophrenia.

Kynurenine pathway metabolites in humans: disease and healthy States

Tryptophan is an essential amino acid that can be metabolised through different pathways, a major route being the kynurenine pathway. The first enzyme of the pathway, indoleamine-2,3-dioxygenase, is strongly stimulated by inflammatory molecules, particularly interferon gamma. Thus, the kynurenine pathway is often systematically up-regulated when the immune response is activated. The biological significance is that 1) the depletion of tryptophan and generation of kynurenines play a key modulatory role in the immune response; and 2) some of the kynurenines, such as quinolinic acid, 3-hydroxykynurenine and kynurenic acid, are neuroactive. The kynurenine pathway has been demonstrated to be involved in many diseases and disorders, including Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, AIDS dementia complex, malaria, cancer, depression and schizophrenia, where imbalances in tryptophan and kynurenines have been found. This review compiles most of these studies and provides an overview of how the kynurenine pathway might be contributing to disease development, and the concentrations of tryptophan and kynurenines in the serum, cerebrospinal fluid and brain tissues in control and patient subjects.

Metabolomic analysis of the cerebrospinal fluid reveals changes in phospholipase expression in the CNS of SIV-infected macaques

HIV infiltrates the CNS soon after an individual has become infected with the virus, and can cause dementia and encephalitis in late-stage disease. Here, a global metabolomics approach was used to find and identify metabolites differentially regulated in the cerebrospinal fluid (CSF) of rhesus macaques with SIV-induced CNS disease, as we hypothesized that this might provide biomarkers of virus-induced CNS damage. The screening platform used a non-targeted, mass-based metabolomics approach beginning with capillary reverse phase chromatography and electrospray ionization with accurate mass determination, followed by novel, nonlinear data alignment and online database screening to identify metabolites. CSF was compared before and after viral infection. Significant changes in the metabolome specific to SIV-induced encephalitis were observed. Metabolites that were increased during infection-induced encephalitis included carnitine, acyl-carnitines, fatty acids, and phospholipid molecules. The elevation in free fatty acids and lysophospholipids correlated with increased expression of specific phospholipases in the brains of animals with encephalitis. One of these, a phospholipase A2 isoenzyme, is capable of releasing a number of the fatty acids identified. It was expressed in different areas of the brain in conjunction with glial activation, rather than linked to regions of SIV infection and inflammation, indicating widespread alterations in infected brains. The identification of specific metabolites as well as mechanisms of their increase illustrates the potential of mass-based metabolomics to address problems in CNS biochemistry and neurovirology, as well as neurodegenerative diseases.

Quality of life and immune activation in patients with HIV-infection

Depression and impaired quality of life (QoL) are frequently observed in patients suffering from HIV-infection. As an enhanced degradation of the serotonin precursor tryptophan is well documented in HIV-infected patients, disturbances in tryptophan metabolism may be causally linked to HIV-related depression. In this study, the relationship between QoL, depression, various laboratory parameters and tryptophan metabolism was investigated. To estimate QoL and mood, 152 HIV-infected patients (classified according to CDC-criteria) were requested to complete the following psychological questionnaires: BDI and MQoL-HIV. Disease progression was monitored by determination of viral load (VL), CD4(+) cell counts, haemoglobin and urinary/plasma neopterin, tryptophan and kynurenine concentrations. Increasing VL, decreasing CD4(+) cell counts, and enhanced tryptophan degradation reflected disease progression. Forty-one patients presented with mild, 22 with moderate and 14 with severe depression. BDI and MQoL scores were associated strongly with each other (rs=-0.838; p<0.001). Patients without depression had significantly lower plasma neopterin concentrations, higher CD4(+) cell counts and haemoglobin concentrations and better QoL scores (all p<0.01) than depressive patients. Furthermore, they showed lower rates of tryptophan degradation (p<0.05). Significant associations were observed between tryptophan degradation and immune activation. Haemoglobin and viral load were predictive for impaired QoL, while high urinary neopterin concentrations and low haemoglobin were the best predictors for depression. In HIV-infected patients, depressive mood and impaired QoL appear to be related to clinical parameters like immune activation, haemoglobin values and viral load.

The high-affinity niacin receptor HM74A is decreased in the anterior cingulate cortex of individuals with schizophrenia

The pathway for de novo synthesis of the suite of niacin congeners, the kynurenine pathway, has been shown to be upregulated in prior studies of postmortem brain tissue from individuals with schizophrenia. The cause of the upregulation is unknown, but one factor may be a defect in feedback regulation via receptors responsive to niacin. A high-affinity and low-affinity receptor for niacin have been identified, HM74A and HM74, respectively. We used RT-QPCR and Western blots to quantify expression of HM74A and HM74 receptors in brain tissue obtained postmortem from patients with schizophrenia (N=12) or bipolar disorder (N=14) and from normal controls (N=14). Although the protein for the HM74 receptor was unchanged, the protein for HM74A was significantly decreased in the schizophrenia group, both when normalized to GAPDH protein or to HM74 as an internal control for degradation and gel-loading error (0.56-fold+/-0.36, p=0.016 and 0.58-fold+/-0.19 the mean control value, p=0.001, respectively). In contrast, the transcript for HM74A was significantly increased, revealing a striking dysregulation between gene transcription and final protein product. No significant differences in HM74A were found for the bipolar group relative to controls. These results are consistent with the blunted niacin flush response reported for individuals with schizophrenia and may be relevant to different rates of comorbid disease.

Alterations in kynurenine precursor and product levels in schizophrenia and bipolar disorder

Increased concentrations of kynurenine pathway metabolites have been reported by several groups for disorders involving psychosis, including schizophrenia and bipolar disorder. To identify components of the pathway that may be relevant as biomarkers or may underlie the etiology of psychosis, it is essential to characterize the extent of kynurenine pathway activation and to investigate known regulators of one of the key kynurenine-producing enzymes, tryptophan 2,3-dioxygenase (TDO2), previously shown in this laboratory to be increased commensurate with kynurenine in postmortem anterior cingulate brain tissue from individuals with schizophrenia. Using this same anterior cingulate sample set from individuals with schizophrenia, bipolar disorder, depression and controls (N=12-14 per group), we measured the precursor of kynurenine and two downstream products. The precursor, tryptophan, was significantly increased only in the schizophrenia group (1.54-fold the mean control value, p=0.02), and through substrate-induced activation, may be one cause of the increased kynurenine and kynurenine metabolites. This finding for tryptophan differs from some, but not all, previous reports and methodological reasons for the discrepancies are discussed. A product of kynurenine metabolism, 3-OH-anthranilic acid was also significantly increased only in the schizophrenia group (1.68-fold the mean control value, p=0.03). 3-OH-anthranilic acid is a reactive species with cytotoxic properties, although the threshold for such effects is not known for neurons. Analysis of major pre- and post-mortem variables showed that none were confounding for these between-group experimental comparisons. Nicotinamide, a pathway end product, did not differ between groups but was associated with cause of death (suicide) within the bipolar group (p=0.03).