Kynurenine pathway is altered in BDNF Val66Met knock-in mice: Effect of physical exercise

Prenatal MAM exposure raises kynurenic acid levels in the prefrontal cortex of adult rats

BACKGROUND

Elevated brain levels of kynurenic acid (KYNA), a metabolite in the kynurenine pathway, are associated with cognitive dysfunctions, which are nowadays often considered as fundamental characteristics of several psychopathologies; however, the role of KYNA in mental illnesses, such as schizophrenia, is not fully elucidated. This study aimed to assess KYNA levels in the prefrontal cortex (PFC) of rats prenatally treated with methylazoxymethanol (MAM) acetate, i.e., a well-validated neurodevelopmental animal model of schizophrenia. The effects of an early pharmacological modulation of the endogenous cannabinoid system were also evaluated.

METHODS

Pregnant Sprague-Dawley rats were treated with MAM (22 mg/kg, ip) or its vehicle at gestational day 17. Male offspring were treated with the cannabinoid CB1 receptor antagonist/inverse agonist AM251 (0.5 mg/kg/day, ip) or with the typical antipsychotic haloperidol (0.6 mg/kg/day, ip) from postnatal day (PND) 19 to PND39. The locomotor activity and cognitive performance were assessed in the novel object recognition test and the open field test in adulthood. KYNA levels in the PFC of prenatally MAM-treated rats were also assessed.

RESULTS

A significant cognitive impairment was observed in prenatally MAM-treated rats (p < 0.01), which was associated with enhanced PFC KYNA levels (p < 0.05). The peripubertal AM251, but not haloperidol, treatment ameliorated the cognitive deficit (p < 0.05), by normalizing the PFC KYNA content in MAM rats.

CONCLUSIONS

The present findings suggest that the cognitive deficit observed in MAM rats may be related to enhanced PFC KYNA levels which could be, in turn, mediated by the activation of cannabinoid CB1 receptor. These results further support the modulation of brain KYNA levels as a potential therapeutic strategy to ameliorate the cognitive dysfunctions in schizophrenia.

Kynurenines, Neuronal Excitotoxicity, and Mitochondrial Oxidative Stress: Role of the Intestinal Flora

The intestinal flora has been the focus of numerous investigations recently, with inquiries not just into the gastrointestinal aspects but also the pathomechanism of other diseases such as nervous system disorders and mitochondrial diseases. Mitochondrial disorders are the most common type of inheritable metabolic illness caused by mutations of mitochondrial and nuclear DNA. Despite the intensive research, its diagnosis is usually difficult, and unfortunately, treating it challenges physicians. Metabolites of the kynurenine pathway are linked to many disorders, such as depression, schizophrenia, migraine, and also diseases associated with impaired mitochondrial function. The kynurenine pathway includes many substances, for instance kynurenic acid and quinolinic acid. In this review, we would like to show a possible link between the metabolites of the kynurenine pathway and mitochondrial stress in the context of intestinal flora. Furthermore, we summarize the possible markers of and future therapeutic options for the kynurenine pathway in excitotoxicity and mitochondrial oxidative stress.

The function of previously unappreciated exerkines secreted by muscle in regulation of neurodegenerative diseases

The initiation and progression of neurodegenerative diseases (NDs), distinguished by compromised nervous system integrity, profoundly disrupt the quality of life of patients, concurrently exerting a considerable strain on both the economy and the social healthcare infrastructure. Exercise has demonstrated its potential as both an effective preventive intervention and a rehabilitation approach among the emerging therapeutics targeting NDs. As the largest secretory organ, skeletal muscle possesses the capacity to secrete myokines, and these myokines can partially improve the prognosis of NDs by mediating the muscle-brain axis. Besides the well-studied exerkines, which are secreted by skeletal muscle during exercise that pivotally exert their beneficial function, the physiological function of novel exerkines, e.g., apelin, kynurenic acid (KYNA), and lactate have been underappreciated previously. Herein, this review discusses the roles of these novel exerkines and their mechanisms in regulating the progression and improvement of NDs, especially the significance of their functions in improving NDs' prognoses through exercise. Furthermore, several myokines with potential implications in ameliorating ND progression are proposed as the future direction for investigation. Elucidation of the function of exerkines secreted by skeletal muscle in the regulation of NDs advances the understanding of its pathogenesis and facilitates the development of therapeutics that intervene in these processes to cure NDs.

Differential Epigenetic Changes in the Dorsal Hippocampus of Male and Female SAMP8 Mice: A Preliminary Study

Alzheimer's disease (AD) is the most common age-related neurodegenerative disease characterized by memory loss and cognitive impairment. The causes of the disease are not well understood, as it involves a complex interaction between genetic, environmental, and epigenetic factors. SAMP8 mice have been proposed as a model for studying late-onset AD, since they show age-related learning and memory deficits as well as several features of AD pathogenesis. Epigenetic changes have been described in SAMP8 mice, although sex differences have never been evaluated. Here we used western blot and qPCR analyses to investigate whether epigenetic markers are differentially altered in the dorsal hippocampus, a region important for the regulation of learning and memory, of 9-month-old male and female SAMP8 mice. We found that H3Ac was selectively reduced in male SAMP8 mice compared to male SAMR1 control mice, but not in female mice, whereas H3K27me3 was reduced overall in SAMP8 mice. Moreover, the levels of HDAC2 and JmjD3 were increased, whereas the levels of HDAC4 and Dnmt3a were reduced in SAMP8 mice compared to SAMR1. In addition, levels of HDAC1 were reduced, whereas Utx and Jmjd3 were selectively increased in females compared to males. Although our results are preliminary, they suggest that epigenetic mechanisms in the dorsal hippocampus are differentially regulated in male and female SAMP8 mice.

An Evaluation of MINDFIT—A Student Therapeutic Running Group as a Multi-Layered Intervention in the United Kingdom

Background: Mental health is an ever-increasing concern for UK Universities and is underreported. Creative and dynamic approaches to tackle student wellbeing are important. In 2018, Sheffield Hallam University (SHU) Student Wellbeing Service initiated a pilot study of a therapeutic running programme ‘MINDFIT’ that combined physical activity, led by a counsellor, alongside a psychoeducation approach to support student mental health. Methods: Mixed methods were used which included the Patient Health Questionnaire-9 (PHQ-9), evaluating low mood and depression, and Generalized Anxiety Disorder Scale-7 (GAD-7), evaluating levels of anxiety. Results: A total of 28 students were triaged onto a weekly programme over three semesters. Overall, 86% of the participants completed the programme. A promising reduction in the scores for PHQ-9 and GAD-7 was found at the end of the programme. Focus groups, with student participants, were held to gather qualitative data for analysis. After thematic analysis, three main themes emerged: “Creating a safe community”, “Making progress” and “Pathways to success”. Conclusions: MINDFIT was an effective and engaging multi-layered therapeutic approach. Recommendations identified the importance and effectiveness of the triage process in recruiting students and sustainability of the programme through the continued engagement of students post programme. More research is required to identify the long-term effects of the MINDFIT approach and how applicable it is to higher education contexts.

Recent advances on the molecular mechanisms of exercise-induced improvements of cognitive dysfunction

Physical exercise is of great significance for maintaining human health. Exercise can provide varying degrees of benefits to cognitive function at all stages of life cycle. Currently, with the aging of the world's population and increase of life expectancy, cognitive dysfunction has gradually become a disease of high incidence, which is accompanied by neurodegenerative diseases in elderly individuals. Patients often exhibit memory loss, aphasia and weakening of orientation once diagnosed, and are unable to have a normal life. Cognitive dysfunction largely affects the physical and mental health, reduces the quality of life, and causes a great economic burden to the society. At present, most of the interventions are aimed to maintain the current cognitive level and delay deterioration of cognition. In contrast, exercise as a nonpharmacological therapy has great advantages in its nontoxicity, low cost and universal application. The molecular mechanisms underlying the effect of exercise on cognition are complex, and studies have been extensively centered on neural plasticity, the direct target of exercise in the brain. In addition, mitochondrial stability and energy metabolism are essential for brain status. Meanwhile, the organ-brain axis responds to exercise and induces release of cytokines related to cognition. In this review, we summarize the latest evidence on the molecular mechanisms underlying the effects of exercise on cognition, and point out directions for future research.

Molecular pathways of major depressive disorder converge on the synapse

Major depressive disorder (MDD) is a psychiatric disease of still poorly understood molecular etiology. Extensive studies at different molecular levels point to a high complexity of numerous interrelated pathways as the underpinnings of depression. Major systems under consideration include monoamines, stress, neurotrophins and neurogenesis, excitatory and inhibitory neurotransmission, mitochondrial dysfunction, (epi)genetics, inflammation, the opioid system, myelination, and the gut-brain axis, among others. This review aims at illustrating how these multiple signaling pathways and systems may interact to provide a more comprehensive view of MDD's neurobiology. In particular, considering the pattern of synaptic activity as the closest physical representation of mood, emotion, and conscience we can conceptualize, each pathway or molecular system will be scrutinized for links to synaptic neurotransmission. Models of the neurobiology of MDD will be discussed as well as future actions to improve the understanding of the disease and treatment options.

Acute stress induces an aberrant increase of presynaptic release of glutamate and cellular activation in the hippocampus of BDNFVal/Met mice

Stressful life events are considered major risk factors for the development of several psychiatric disorders, though people differentially cope with stress. The reasons for this are still largely unknown but could be accounted for by individual genetic variants, previous life events, or the kind of stressors. The human brain-derived neurotrophic factor (BDNF) Val66Met variant, which was found to impair intracellular trafficking and activity-dependent secretion of BDNF, has been associated with increased susceptibility to develop several neuropsychiatric disorders, although there is still some controversial evidence. On the other hand, acute stress has been consistently demonstrated to promote the release of glutamate in cortico-limbic regions and altered glutamatergic transmission has been reported in psychiatric disorders. However, it is not known if the BDNF Val66Met single-nucleotide polymorphism (SNP) affects the stress-induced presynaptic glutamate release. In this study, we exposed adult male BDNF^Val/Val and BDNF^Val/Met knock-in mice to 30 min of acute restraint stress. Plasma corticosterone levels, glutamate release, protein, and gene expression in the hippocampus were analyzed immediately after the end of the stress session. Acute restraint stress similarly increased plasma corticosterone levels and nuclear glucocorticoid receptor levels and phosphorylation in both BDNF^Val/Val and BDNF^Val/Met mice. However, acute restraint stress induced higher increases in hippocampal presynaptic release of glutamate, phosphorylation of cAMP-response element binding protein (CREB), and levels of the immediate early gene c-fos of BDNF^Val/Met compared to BFNF^Val/Val mice. Moreover, acute restraint stress selectively increased phosphorylation levels of synapsin I at Ser⁹ and at Ser⁶⁰³ in BDNF^Val/Val and BDNF^Val/Met mice, respectively. In conclusion, we report here that the BDNF Val66Met SNP knock-in mice display an altered response to acute restraint stress in terms of hippocampal glutamate release, CREB phosphorylation, and neuronal activation, compared to wild-type animals. Taken together, these results could partially explain the enhanced vulnerability to stressful events of Met carriers reported in both preclinical and clinical studies.

Can kynurenine pathway be considered as a next-generation therapeutic target for Parkinson's disease? An update information

By far, no revolutionary breakthrough in the treatment of Parkinson's disease (PD) was found. It is indeed a knotty problem to select a satisfactory strategy for treating some patients with advanced stage PD. Development of novel therapeutic targets against PD has been an urgent task faced by global PD researchers. Targets in the tryptophan-kynurenine pathway (KP) were then considered. Metabolites in the KP are liposoluble. Some neurotoxic metabolites, including 3-hydroxykynurenine and its downstream 3-hydroxyanthranilic acid and quinolinic acid, are mainly produced peripherally. They can easily cross the blood-brain barrier (BBB) and exert their neurotoxic effects in the central neuron system (CNS), which is considered as a potential pathophysiological mechanism of neurodegenerative diseases. Hence, agents against the targets in the KP have two characteristics: (1) being independent from the dopaminergic system and (2) being seldom affected by the BBB. Inspiringly, one agent, namely, the inhibitor of indoleamine 2,3-dioxygenase 1, has been currently reported to present satisfactory efficacy comparable to levodopa, implying that the KP might be a potential novel target for PD. This review collected and summarized the updated information regarding the association of the KP with PD, which is helpful for understanding the clinical value of the KP in the PD scenario.

Tryptophan Metabolism in Depression: A Narrative Review with a Focus on Serotonin and Kynurenine Pathways

Depression is a common and serious disorder, characterized by symptoms like anhedonia, lack of energy, sad mood, low appetite, and sleep disturbances. This disease is very complex and not totally elucidated, in which diverse molecular and biological mechanisms are involved, such as neuroinflammation. There is a high need for the development of new therapies and gaining new insights into this disease is urgent. One important player in depression is the amino acid tryptophan. This amino acid can be metabolized in two important pathways in the context of depression: the serotonin and kynurenine pathways. These metabolic pathways of tryptophan are crucial in several processes that are linked with depression. Indeed, the maintenance of the balance of serotonin and kynurenine pathways is critical for the human physiological homeostasis. Thus, this narrative review aims to explore tryptophan metabolism (particularly in the serotonin and kynurenine pathways) in depression, starting with a global overview about these topics and ending with the focus on these pathways in neuroinflammation, stress, microbiota, and brain-derived neurotrophic factor regulation in this disease. Taken together, this information aims to clarify the metabolism of tryptophan in depression, particularly the serotonin and kynurenine pathways.

Exerkines and long-term synaptic potentiation: Mechanisms of exercise-induced neuroplasticity

Physical exercise may improve cognitive function by modulating molecular and cellular mechanisms within the brain. We propose that the facilitation of long-term synaptic potentiation (LTP)-related pathways, by products induced by physical exercise (i.e., exerkines), is a crucial aspect of the exercise-effect on the brain. This review summarizes synaptic pathways that are activated by exerkines and may potentiate LTP. For a total of 16 exerkines, we indicated how blood and brain exerkine levels are altered depending on the type of physical exercise (i.e., cardiovascular or resistance exercise) and how they respond to a single bout (i.e., acute exercise) or multiple bouts of physical exercise (i.e., chronic exercise). This information may be used for designing individualized physical exercise programs. Finally, this review may serve to direct future research towards fundamental gaps in our current knowledge regarding the biophysical interactions between muscle activity and the brain at both cellular and system levels.

Alterations in rat prefrontal cortex kynurenic acid levels are involved in the enduring cognitive dysfunctions induced by tetrahydrocannabinol exposure during the adolescence

INTRODUCTION

Cannabis abuse during adolescence is a risk factor for cognitive impairments in psychiatric disorders later in life. To date, the possible causal relationship between cannabinoids, kynurenic acid (KYNA; i.e., a neuroactive metabolite of tryptophan degradation) and cognition has not been investigated in adolescence. Early exposure to delta 9-tetrahydrocannabinol (THC; i.e., the main psychotropic component of cannabis) causes enduring cognitive deficits, which critically involve impaired glutamatergic function in the prefrontal cortex (PFC). In addition, prenatal cannabis exposure results in enduring increases in PFC KYNA levels. Based on these findings, the effects of chronic THC exposure in rats, during another critical period of neurodevelopment particularly sensitive to perturbation by exogenous stimuli, such as adolescence, have been investigated.

METHODS

Male Wistar rats were chronically treated with vehicle or ascending intraperitoneal (i.p.) doses of THC starting on postnatal day (PND) 35 until PND 45. In adulthood (PND 75), cognitive assessment (Y-maze) and extracellular KYNA/glutamate levels were measured in the PFC by in vivo microdialysis, before and after a challenge with KYN (5 mg/kg i.p., the biological precursor of KYNA). By using the selective, brain-penetrable KAT II inhibitor PF-04859989, we then examined whether blockade of KYNA neosynthesis prevents the cognitive impairment.

RESULTS

Compared to vehicle-treated controls, extracellular basal KYNA levels were higher in the PFC of adult rats chronically exposed to THC in adolescence (p < 0.01). No changes were observed in extracellular glutamate levels. Following a challenge with KYN, extracellular KYNA levels similarly increased in both groups (i.e., vehicle- and THC-treated; p < 0.001 and p < 0.01, respectively). Chronic adolescent THC exposure negatively affected short-term memory (reduced spontaneous alternation), in adult animals (p < 0.001), while PF-04859989 (30 mg/kg i.p.) restored the cognitive impairment (p < 0.05).

DISCUSSION

We propose that the observed alterations in PFC KYNA signaling might be involved in the cognitive dysfunction induced by the exposure to THC during the adolescence. In the translational realm, these experiments raise the prospect of prevention of KYNA neosynthesis as a possible novel approach to counteract some of the detrimental long-term effects of adolescence cannabis use.

The α2-adrenergic receptor pathway modulating depression influences the risk of arterial thrombosis associated with BDNFVal66Met polymorphism

Depression is associated with thrombotic risk and arterial events, its proper management is strongly recommended in coronary artery disease (CAD) patients. We have previously shown that the Brain-Derived Neurotrophic Factor (BDNF)Val66Met polymorphism, related to depression, is associated with arterial thrombosis in mice, and with an increased risk of acute myocardial infarction in humans. Herein, expanding the previous findings on BDNFVal66Met polymorphism, we show that desipramine, a norepinephrine reuptake-inhibitor, rescues behavioral impairments, reduces the arterial thrombosis risk, abolishes pathological coagulation and platelet hyper-reactivity, normalizes leukocyte, platelet, and bone marrow megakaryocyte number and restores physiological norepinephrine levels in homozygous knock-in BDNF Val66Met (BDNF^Met/Met) mice. The in vitro data confirm the enhanced procoagulant activity and the alpha_2A-adrenergic receptor (α_2A-ADR) overexpression found in BDNF^Met/Met mice and we provide evidence that, in presence of Met variant, norepinephrine is crucial to up-regulate procoagulant activity and to enhance platelet generation. The α₂-ADR antagonist rauwolscine rescues the prothrombotic phenotype in BDNF^Met/Met mice and reduces procoagulant activity and platelet generation in cells transfected with BDNF^Met plasmid or exposed to pro-BDNF^Met peptide. Finally, we show that homozygous BDNF^Met/Met CAD patients have hyper-reactive platelets overexpressing abundant α_2A-ADR. The great proplatelet release from their megakaryocytes well reflects their higher circulating platelet number compared to BDNF^Val/Val patients. These data reveal an unprecedented described role of Met allele in the dysregulation of norepinephrine/α_2A-ADR pathway that may explain the predisposition to arterial thrombosis. Overall, the development of α_2A-ADR inhibitors might represent a pharmacological treatment for depression-associated thrombotic conditions in this specific subgroup of CAD patients.

All roads lead to Rome - a review of the potential mechanisms by which exerkines exhibit neuroprotective effects in Alzheimer's disease

Age-related neurodegenerative disorders such as Alzheimer’s disease (AD) have become a critical public health issue due to the significantly extended human lifespan, leading to considerable economic and social burdens. Traditional therapies for AD such as medicine and surgery remain ineffective, impractical, and expensive. Many studies have shown that a variety of bioactive substances released by physical exercise (called “exerkines”) help to maintain and improve the normal functions of the brain in terms of cognition, emotion, and psychomotor coordination. Increasing evidence suggests that exerkines may exert beneficial effects in AD as well. This review summarizes the neuroprotective effects of exerkines in AD, focusing on the underlying molecular mechanism and the dynamic expression of exerkines after physical exercise. The findings described in this review will help direct research into novel targets for the treatment of AD and develop customized exercise therapy for individuals of different ages, genders, and health conditions.

Negative Correlation between Serum Brain-derived Neurotrophic Factor Levels and Obesity Predictor Markers and Inflammation Levels in Females with Obesity

BACKGROUND: Obesity has been widely associated with structural and functional changes in the brain, whereas inflammation is one of the potential mechanisms involved in these changes. OBJECTIVE: This study aims to prove the relationship between serum brain-derived neurotrophic factor (BDNF) levels and obesity predictor markers (body mass index and waist to hip ratio) and inflammation (interleukin-6 and Tumor Necrosis Factor-alpha) levels in females with obesity. METHODS: This study used a cross-sectional study method using 33 females with obesity aged 19-23 years, body mass index (BMI) > 27.5 kg/m2, normal blood pressure, normal resting heart rate (RHR), normal hemoglobin (Hb), and fasting blood glucose (FBG) ≤ 100 mg/dL. The examination of serum BDNF, IL-6, and TNF-α levels using the Enzyme-Linked Immunosorbent Assay (ELISA) method. The data were analyzed using Pearson product-moment test with a significant levels p<0.05. RESULTS: The results indicated that there is a negative correlation between serum BDNF levels and BMI (r = –0.759; p<0.001), WHR (r = –0.675; p<0.001), IL-6 levels (r = –0.530; p<0.001) and TNF-α levels (r = –0.561; p<0.001). CONCLUSION: Based on the results of the study, there is a negative correlation between serum BDNF levels and BMI, waist to hip ratio, and inflammation (interleukin-6 and Tumor Necrosis Factor-alpha) levels in females with obesity. Further studies are needed to confirm the present findings.