Oral administration of inosine produces antidepressant-like effects in mice

Characterizing metabolomic and proteomic changes in depression: a systematic analysis

Despite the widespread use of metabolomics and proteomics to explore the molecular landscape of depression, there is a lack of consensus regarding dysregulated molecules with replicable evidence. Thus, this study aimed to identify robust metabolomic and proteomic features in depression by integrating evidence from large-scale studies. In this study, a knowledge base-mining approach was adopted to compile a list of dysregulated molecules derived from metabolomic and proteomic studies. A vote-counting approach was performed to identify consistently altered molecules in the blood and urine samples of patients with depression. A total of 2398 molecular entries were selected, comprising 857 unique metabolites and 468 unique proteins from 143 metabolomic and 23 proteomic studies in depression. The results of vote-counting analyses revealed that 11 metabolites in blood and 5 metabolites in urine exhibited consistent disturbances across studies. Circulating levels of glutamic acid and phosphatidylcholine (32:0) were elevated in depressive patients, whereas the levels of tryptophan, kynurenic acid, kynurenine, acetylcarnitine, serotonin, creatinine, inosine, phenylalanine, and valine were lower. Urinary levels of isobutyric acid, alanine, and nicotinic acid were higher, whereas the levels of N-methylnicotinamide and tyrosine were lower. Moreover, analysis of the proteomic dataset identified only one circulating protein, ceruloplasmin, that was consistently dysregulated. Convergence comparison prioritized tryptophan as the top-ranked circulating metabolite, followed by kynurenic acid, acetylcarnitine, creatinine, serotonin, and valine. Collectively, robust evidence of metabolomic changes was observed in patients with depression, pointing to a role as potential biomarkers. Further investigation of consensus proteomic features for depression is necessitated.

Investigating the neuroprotective effects of Dracocephalum moldavica extract and its effect on metabolomic profile of rat model of sporadic Alzheimer's disease

Alzheimer's disease (AD) is a progressive condition marked by multiple underlying mechanisms. Therefore, the investigation of natural products that can target multiple pathways presents a potential gate for the understanding and management of AD. This study aimed to assess the neuroprotective effects of the hydroalcoholic extract of Dracocephalum moldavica (DM) on cognitive impairment, biomarker changes, and putative metabolic pathways in a rat model of AD induced by intracerebroventricular streptozotocin (ICV-STZ). The DM extract was standardized and quantified based on examining total phenolic, total flavonoid, rosmarinic acid, and quercetin contents using colorimetry and high-performance liquid chromatography (HPLC) methods. The antioxidant potential of the extract was evaluated by 2,2-Diphenyl-1-picrylhydrazyl and nitric oxide radical scavenging assays. Male Wistar rats were injected with STZ (3 mg/kg, single dose, bilateral ICV) to induce a sporadic AD (sAD) model. Following model induction, rats were orally administered with DM extract (100, 200, and 400 mg/kg/day) or donepezil (5 mg/kg/day) for 21 days. Cognitive function was assessed using the radial arm water maze behavioral test. The histopathological evaluations were conducted in the cortex and hippocampus regions. Matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) was used to assess metabolite changes in various brain regions. DM extract significantly attenuated cognitive dysfunction induced by ICV-STZ according to behavioral and histopathological investigations. Thirty-two discriminating metabolites related to the amino acid metabolism; the glutamate/gamma-aminobutyric acid/glutamine cycle; nucleotide metabolism; lipid metabolism (glycerophospholipids, sphingomyelins, ceramides, phosphatidylserines, and prostaglandins), and glucose metabolic pathways were identified in the brains of rats with sAD simultaneously for the first time in this model. Polyphenols in DM extract may contribute to the regulation of these pathways. After treatment with DM extract, 10 metabolites from the 32 identified ones were altered in the brain tissue of a rat model of sAD, most commonly at doses of 200 and 400 mg/kg. In conclusion, this study demonstrates the neuroprotective potential of DM by upregulation/downregulation of various pathophysiological biomarkers such as adenine, glycerophosphoglycerol, inosine, prostaglandins, and sphingomyelin induced by ICV-STZ in sAD. These findings are consistent with cognitive behavioral results and histopathological outcomes.

Phlorizin ameliorates cognitive and behavioral impairments via the microbiota-gut-brain axis in high-fat and high-fructose diet-induced obese male mice

The long-term high-fat, high-sugar diet exacerbates type 2 diabetes mellitus (T2DM)-related cognitive impairments. Phlorizin, a well-studied natural compound found in apples and other plants, is recognized for its bioactive properties, including modulation of glucose and lipid metabolism. Despite its established role in mitigating metabolic disorders, the neuroprotective effects of phlorizin, particularly against diabetes-related cognitive dysfunction, have not been fully elucidated. Therefore, the present study aimed to investigate the effect of dietary supplementation of phlorizin on high-fat and high-fructose diet (HFFD)-induced cognitive dysfunction and evaluate the crucial role of the microbiota-gut-brain axis. We found that dietary supplementation of phlorizin for 14 weeks effectively prevented glucolipid metabolism disorder, spatial learning impairment, and memory impairment in HFFD mice. In addition, phlorizin improved the HFFD-induced decrease in synaptic plasticity, neuroinflammation, and excessive activation of microglia in the hippocampus. Transcriptomics analysis shows that the protective effect of phlorizin on cognitive impairment was associated with increased expression of neurotransmitters and synapse-related genes in the hippocampus. Phlorizin treatment alleviated colon microbiota disturbance, mainly manifested by an increase in gut microbiota diversity and the abundance of short-chain fatty acid (SCFA)-producing bacteria. The level of microbial metabolites, including SCFA, inosine 5'-monophosphate (IMP), and D (-)-beta-hydroxybutyric acid (BHB) were also significantly increased after phlorizin treatment. Integrating multiomics analysis observed tight connections between phlorizin-regulated genes, microbiota, and metabolites. Furthermore, removal of the gut microbiota via antibiotics treatment diminished the protective effect of phlorizin against HFFD-induced cognitive impairment, underscoring the critical role of the gut microbiota in mediating cognitive behavior. Importantly, supplementation with SCFA and BHB alone mimicked the regulatory effects of phlorizin on cognitive function. Therefore, phlorizin shows promise as a potential nutritional therapy for addressing cognitive impairment associated with metabolic disorders. Further research is needed to explore its effectiveness in preventing and alleviating neurodegenerative diseases.

Inosine reverses multidrug resistance in Gram-negative bacteria carrying mobilized RND-type efflux pump gene cluster tmexCD-toprJ

Antimicrobial resistance is rapidly increasing worldwide, highlighting the urgent need for pharmaceutical and nonpharmaceutical interventions to tackle different-to-treat bacterial infections. Tigecycline, a semi-synthesis glycylcycline for parenteral administration, is widely recognized as one of the few effective therapies available against pan-drug resistant Gram-negative pathogens. Regrettably, the efficacy of multiple drugs, including tigecycline, is currently being undermined due to the emergence of a recently discovered mobilized resistance-nodulation-division-type efflux pump gene cluster tmexCD1-toprJ1. Herein, by employing untargeted metabolomic approaches, we reveal that the expression of tmexCD1-toprJ1 disrupts bacterial purine metabolism, with inosine being identified as a crucial biomarker. Notably, the supplementation of inosine effectively reverses tigecycline resistance in tmexCD1-toprJ1-positive bacteria. Mechanistically, exogenous inosine enhanced bacterial proton motive force, which promotes the uptake of tigecycline. Furthermore, inosine enhances succinate biosynthesis by stimulating the tricarboxylic acid cycle. Succinate interacts with the two-component system EnvZ/OmpR and upregulates OmpK 36, thereby promoting the influx of tigecycline. These actions collectively lead to the increased intracellular accumulation of tigecycline. Overall, our study offers a distinct combinational strategy to manage infections caused by tmexCD-toprJ-positive bacteria.

IMPORTANCE

TMexCD1-TOprJ1, a mobilized resistance-nodulation-division-type efflux pump, confers phenotypic resistance to multiple classes of antibiotics. Nowadays, tmexCD-toprJ has disseminated among diverse species of clinical pathogens, exacerbating the need for novel anti-infective strategies. In this study, we report that tmexCD1-toprJ1-negative and -positive bacteria exhibit significantly different metabolic flux and characteristics, especially in purine metabolism. Intriguingly, the addition of inosine, a purine metabolite, effectively restores the antibacterial activity of tigecycline by promoting antibiotic uptake. Our findings highlight the correlation between bacterial mechanism and antibiotic resistance, and offer a distinct approach to overcome tmexCD-toprJ-mediated multidrug resistance.

Uric acid and alterations of purine recycling disorders in Parkinson's disease: a cross-sectional study

The relationship between reduced serum uric acid (UA) levels and Parkinson's disease (PD), particularly purine metabolic pathways, is not fully understood. Our study compared serum and cerebrospinal fluid (CSF) levels of inosine, hypoxanthine, xanthine, and UA in PD patients and healthy controls. We analyzed 132 samples (serum, 45 PD, and 29 age- and sex-matched healthy controls; CSF, 39 PD, and 19 age- and sex-matched healthy controls) using liquid chromatography-tandem mass spectrometry. Results showed significantly lower serum and CSF UA levels in PD patients than in controls (p < 0.0001; effect size r = 0.5007 in serum, p = 0.0046; r = 0.3720 in CSF). Decreased serum hypoxanthine levels were observed (p = 0.0002; r = 0.4338) in PD patients compared to controls with decreased CSF inosine and hypoxanthine levels (p < 0.0001, r = 0.5396: p = 0.0276, r = 0.2893). A general linear model analysis indicated that the reduced UA levels were mainly due to external factors such as sex and weight in serum and age and weight in CSF unrelated to the purine metabolic pathway. Our findings highlight that decreased UA levels in PD are influenced by factors beyond purine metabolism, including external factors such as sex, weight, and age, emphasizing the need for further research into the underlying mechanisms and potential therapeutic approaches.

Increased functional connectivity following ingestion of dried bonito soup

Soup, including dried bonito broth, is customarily consumed as an umami taste during meals in Japan. Previous functional magnetic resonance imaging (fMRI) studies have investigated neuronal activation following human exposure to carbohydrates and umami substances. However, neuronal activity following ingestion of dried bonito soup has not been investigated. Additionally, recent progress in fMRI has enabled us to investigate the functional connectivity between two anatomically separated regions, such as the default mode network. In this study, we first investigated the altered functional connectivity after ingesting dried bonito soup in healthy volunteers. Functional connectivity in several brain regions, including the connection between the vermis, part of the cerebellum, and bilateral central opercular cortex, was markedly increased after ingesting dried bonito soup, compared to the ingestion of hot water. Physiological scaling showed that satiety was substantially increased by ingesting hot water rather than dried bonito soup. These results indicate that increased functional connectivity reflects the post-ingestive information pathway of dried bonito soup.

An Untargeted Metabolomic Analysis of Lacticaseibacillus (L.) rhamnosus, Lactobacillus (L.) acidophilus, Lactiplantibacillus (L.) plantarum and Limosilactobacillus (L.) reuteri Reveals an Upregulated Production of Inosine from L. rhamnosus

Lactic acid bacteria are considered an inexhaustible source of bioactive compounds; indeed, products from their metabolism are known to have immunomodulatory and anti-inflammatory activity. Recently, we demonstrated that Cell-Free Supernatants (CFS) obtained from Lactobacillus (L.) acidophilus, Lactiplantibacillus (L.) plantarum, Lacticaseibacillus (L.) rhamnosus, and Limosilactobacillus (L.) reuteri can impair Candida pathogenic potential in an in vitro model of epithelial vaginal infection. This effect could be ascribed to a direct effect of living lactic acid bacteria on Candida virulence and to the production of metabolites that are able to impair fungal virulence. In the present work, stemming from these data, we deepened our knowledge of CFS from these four lactic acid bacteria by performing a metabolomic analysis to better characterize their composition. By using an untargeted metabolomic approach, we detected consistent differences in the metabolites produced by these four different lactic acid bacteria. Interestingly, L. rhamnosus and L. acidophilus showed the most peculiar metabolic profiles. Specifically, after a hierarchical clustering analysis, L. rhamnosus and L. acidophilus showed specific areas of significantly overexpressed metabolites that strongly differed from the same areas in other lactic acid bacteria. From the overexpressed compounds in these areas, inosine from L. rhamnosus returned with the best identification profile. This molecule has been described as having antioxidant, anti-inflammatory, anti-infective, and neuroprotective properties. The biological significance of its overproduction by L. rhamnosus might be important in its probiotic and/or postbiotic activity.

Progress of depression mechanism based on Omics method

Depression is a very common disabling mental disorder, which is typically characterized by high rates of disability and mortality. Although research into the various mechanisms of depression was still underway, its physiopathology remains uncertain. The rapid developments in new technologies and the combined use of a variety of techniques will help to understand the pathogenesis of depression and explore effective treatment methods. In this review, we focus on the combination of proteomic and metabolomic approaches to analyze metabolites and proteins in animal models of depression induced by different modeling approaches, with the aim of broadening the understanding of the physiopathological mechanisms of depression using complementary "omics" strategy.

The Critical Role of Equilibrative Nucleoside Transporter-2 in Modulating Cerebral Damage and Vascular Dysfunction in Mice with Brain Ischemia-Reperfusion

BACKGROUND

Cerebral vascular protection is critical for stroke treatment. Adenosine modulates vascular flow and exhibits neuroprotective effects, in which brain extracellular concentration of adenosine is dramatically increased during ischemic events and ischemia-reperfusion. Since the equilibrative nucleoside transporter-2 (Ent2) is important in regulating brain adenosine homeostasis, the present study aimed to investigate the role of Ent2 in mice with cerebral ischemia-reperfusion.

METHODS

Cerebral ischemia-reperfusion injury was examined in mice with transient middle cerebral artery occlusion (tMCAO) for 90 minutes, followed by 24-hour reperfusion. Infarct volume, brain edema, neuroinflammation, microvascular structure, regional cerebral blood flow (rCBF), cerebral metabolic rate of oxygen (CMRO2), and the production of reactive oxygen species (ROS) were examined following the reperfusion.

RESULTS

Ent2 deletion reduced the infarct volume, brain edema, and neuroinflammation in mice with cerebral ischemia-reperfusion. tMCAO-induced disruption of brain microvessels was ameliorated in Ent2-/- mice, with a reduced expression of matrix metalloproteinases-9 and aquaporin-4 proteins. Following the reperfusion, the rCBF of the wild-type (WT) mice was quickly restored to the baseline, whereas, in Ent2-/- mice, rCBF was slowly recovered initially, but was then higher than that in the WT mice at the later phase of reperfusion. The improved CMRO2 and reduced ROS level support the beneficial effects caused by the changes in the rCBF of Ent2-/- mice. Further studies showed that the protective effects of Ent2 deletion in mice with tMCAO involve adenosine receptor A2AR.

CONCLUSIONS

Ent2 plays a critical role in modulating cerebral collateral circulation and ameliorating pathological events of brain ischemia and reperfusion injury.

Accelerated Extracellular Nucleotide Metabolism in Brain Microvascular Endothelial Cells in Experimental Hypercholesterolemia

Hypercholesterolemia affects the neurovascular unit, including the cerebral blood vessel endothelium. Operation of this system, especially in the context of energy metabolism, is controlled by extracellular concentration of purines, regulated by ecto-enzymes, such as e-NTPDase-1/CD39, ecto-5'-NT/CD73, and eADA. We hypothesize that hypercholesterolemia, via modulation of the activity of nucleotide metabolism-regulating ecto-enzymes, deteriorates glycolytic efficiency and energy metabolism of endothelial cells, which may potentially contribute to development of neurodegenerative processes. We aimed to determine the effect of hypercholesterolemia on the concentration of purine nucleotides, glycolytic activity, and activity of ecto-enzymes in the murine brain microvascular endothelial cells (mBMECs). We used 3-month-old male LDLR-/-/Apo E-/- double knockout mice to model hypercholesterolemia and atherosclerosis. The age-matched wild-type C57/BL6 mice were a control group. The intracellular concentration of ATP and NAD and extracellular activity of the ecto-enzymes were measured by HPLC. The glycolytic function of mBMECs was assessed by means of the extracellular acidification rate (ECAR) using the glycolysis stress test. The results showed an increased activity of ecto-5'-NT and eADA in mBMECs of the hypercholesterolemic mice, but no differences in intracellular concentration of ATP, NAD, and ECAR between the hypercholesterolemic and control groups. The changed activity of ecto-5'-NT and eADA leads to increased purine nucleotides turnover and a shift in their concentration balance towards adenosine and inosine in the extracellular space. However, no changes in the energetic metabolism of the mBMECs are reported. Our results confirm the influence of hypercholesterolemia on regulation of purine nucleotides metabolism, which may impair the function of the cerebral vascular endothelium. The effect of hypercholesterolemia on the murine brain microvascular endothelial cells (mBMECs). An increased activity of ecto-5'-NT and eADA in mBMECs of the LDLR-/-/Apo E-/- mice leads to a shift in the concentration balance towards adenosine and inosine in the extracellular space with no differences in intracellular concentration of ATP. Figure was created with Biorender.com.

Inosine attenuates rotenone-induced Parkinson's disease in rats by alleviating the imbalance between autophagy and apoptosis

Growing evidence points to impaired autophagy as one of the major factors implicated in the pathophysiology of Parkinson's disease (PD). Autophagy is a downstream target of adenosine monophosphate-activated protein kinase (AMPK). Inosine has already demonstrated a neuroprotective effect against neuronal loss in neurodegenerative diseases, mainly due its anti-inflammatory and antioxidant properties. We, herein, aimed at investigating the neuroprotective effects of inosine against rotenone-induced PD in rats and to focus on the activation of AMPK-mediated autophagy. Inosine successfully increased p-AMPK/AMPK ratio in PD rats and improved their motor performance and muscular co-ordination (assessed by rotarod, open field, and grip strength tests, as well as by manual gait analysis). Furthermore, inosine was able to mitigate the rotenone-induced histopathological alterations and to restore the tyrosine hydroxylase immunoreactivity in PD rats' substantia nigra. Inosine-induced AMPK activation resulted in an autophagy enhancement, as demonstrated by the increased striatal Unc-S1-like kinase1 and beclin-1 expression, and also by the increment light chain 3II to light chain 3I ratio, along with the decline in striatal mammalian target of rapamycin and p62 protein expressions. The inosine-induced stimulation of AMPK also attenuated neuronal apoptosis and promoted antioxidant activity. Unsurprisingly, these neuroprotective effects were antagonized by a preadministration of dorsomorphin (an AMPK inhibitor). In conclusion, inosine exerted neuroprotective effects against the rotenone-induced neuronal loss via an AMPK activation and through the restoration of the imbalance between autophagy and apoptosis. These findings support potential application of inosine in PD treatment.

Dopaminergic neuroprotective effects of inosine in MPTP-induced parkinsonian mice via brain-derived neurotrophic factor upregulation

Parkinson's disease (PD) is the second most common neurodegenerative disease. However, no curative or modifying therapy is known. Inosine is a purine nucleoside that increases brain-derived neurotrophic factor (BDNF) expression in the brain through adenosine receptors. Herein, we investigated the neuroprotective effects of inosine and elucidated the mechanisms underlying its pharmacological action. Inosine rescued SH-SY5Y neuroblastoma cells from MPP⁺ injury in a dose-dependent manner. Inosine protection correlated with BDNF expression and the activation of its downstream signaling cascade, as the TrkB receptor inhibitor, K252a and siRNA against the BDNF gene remarkably reduced the protective effects of inosine. Blocking the A₁ or A_2A adenosine receptors diminished BDNF induction and the rescuing effect of inosine, indicating a critical role of adenosine A₁ and A_2A receptors in inosine-related BDNF elevation. We assessed whether the compound could protect dopaminergic neurons from MPTP-induced neuronal injury. Beam-walking and challenge beam tests revealed that inosine pretreatment for 3 weeks reduced the MPTP-induced motor function impairment. Inosine ameliorated dopaminergic neuronal loss and MPTP-mediated astrocytic and microglial activation in the substantia nigra and striatum. Inosine ameliorated the depletion of striatal dopamine and its metabolite following MPTP injection. BDNF upregulation and the activation of its downstream signaling pathway seemingly correlate with the neuroprotective effects of inosine. To our knowledge, this is the first study to demonstrate the neuroprotective effects of inosine against MPTP neurotoxicity via BDNF upregulation. These findings highlight the therapeutic potential of inosine in dopaminergic neurodegeneration in PD brains.

Inosine attenuates post-stroke neuroinflammation by modulating inflammasome mediated microglial activation and polarization

To date, various agents and molecules have been developed to treat post-stroke neuroinflammation; however, none of them are clinically successful. Post-stroke neuroinflammation is primarily attributed to microglial polarization as the generation of inflammasome complexes shifts microglia to their M1 phenotype and regulate the downstream cascade. Inosine, an adenosine derivative reported to maintain cellular energy homeostasis in stressed condition. Although, the exact mechanism is still unexplored, various studies have reported that it can stimulate axonal sprouting in different neurodegenerative diseases. Hence, our present study aims to decipher the molecular mechanism of inosine mediated neuroprotection by modulating inflammasome signaling towards altered microglial polarization in ischemic stroke. Inosine was administered intraperitoneally to male Sprague Dawley rats at 1 h post ischemic stroke and were further evaluated for neurodeficit score, motor coordination and long-term neuroprotection. Brains were harvested for infarct size estimation, biochemical assays and molecular studies. Inosine administration at 1 h post ischemic stroke decreased infarct size, neurodeficit score, and improved motor co-ordination. Normalization of biochemical parameters were achieved in the treatment groups. Microglial polarization towards its anti-inflammatory phenotype and modulation of inflammation were evident by relevant gene and protein expression studies. The outcome provides preliminary evidence of inosine mediated alleviation of post-stroke neuroinflammation via modulation of microglial polarization towards its anti-inflammatory form through regulating the inflammasome activation.

The adenosine hypothesis of schizophrenia into its third decade: From neurochemical imbalance to early life etiological risks

The adenosine hypothesis of schizophrenia was conceptualized about two decades ago in an attempt to integrate two prominent theories of neurochemical imbalance that attribute the pathogenesis of schizophrenia to hyperfunction of the mesocorticolimbic dopamine neurotransmission and hypofunction of cortical glutamate neurotransmission. Given its unique position as an endogenous modulator of both dopamine and glutamate signaling in the brain, adenosine was postulated as a potential new drug target to achieve multiple antipsychotic actions. This new strategy may offer hope for improving treatment, especially in alleviating negative symptoms and cognitive deficits of schizophrenia that do not respond to current medications. To date, however, the adenosine hypothesis has yet led to any significant therapeutic breakthroughs. Here, we address two possible reasons for the impasse. First, neither the presence of adenosine functional deficiency in people with schizophrenia nor its causal relationship to symptom production has been satisfactorily examined. Second, the lack of novel adenosine-based drugs also impedes progress. This review updates the latest preclinical and clinical data pertinent to the construct validity of the adenosine hypothesis and explores novel molecular processes whereby dysregulation of adenosine signaling could be linked to the etiology of schizophrenia. It is intended to stimulate and revitalize research into the adenosine hypothesis towards the development of a new and improved generation of antipsychotic drugs that has eluded us for decades.

The impact of inosine on hippocampal synaptic transmission and plasticity involves the release of adenosine through equilibrative nucleoside transporters rather than the direct activation of adenosine receptors

Inosine has robust neuroprotective effects, but it is unclear if inosine acts as direct ligand of adenosine receptors or if it triggers metabolic effects indirectly modifying the activity of adenosine receptors. We now combined radioligand binding studies with electrophysiological recordings in hippocampal slices to test how inosine controls synaptic transmission and plasticity. Inosine was without effect at 30 μM and decreased field excitatory post-synaptic potentials by 14% and 33% at 100 and 300 μM, respectively. These effects were prevented by the adenosine A₁ receptor antagonist DPCPX. Inosine at 300 (but not 100) μM also decreased the magnitude of long-term potentiation (LTP), an effect prevented by DPCPX and by the adenosine A_2A receptor antagonist SCH58261. Inosine showed low affinity towards human and rat adenosine receptor subtypes with K_i values of > 300 µM; only at the human and rat A₁ receptor slightly higher affinities with K_i values of around 100 µM were observed. Affinity of inosine at the rat A₃ receptor was higher (K_i of 1.37 µM), while it showed no interaction with the human orthologue. Notably, the effects of inosine on synaptic transmission and plasticity were abrogated by adenosine deaminase and by inhibiting equilibrative nucleoside transporters (ENT) with dipyridamole and NBTI. This shows that the impact of inosine on hippocampal synaptic transmission and plasticity is not due to a direct activation of adenosine receptors but is instead due to an indirect modification of the tonic activation of these adenosine receptors through an ENT-mediated modification of the extracellular levels of adenosine.

Exercise hormone irisin prevents physical inactivity-induced cognitive decline in mice

We previously reported that physical inactivity (PI) induces cognitive decline and depressive states, which were ameliorated by regular exercise. However, the mechanism underlying the preventive effect of exercise remains unelucidated. Irisin has recently been identified as an exercise-inducible myokine that improves cognitive impairment. Plasma irisin levels increase during physical exercise; therefore, PI could lead to a decline in cognitive function by reducing plasma irisin. Therefore, this study aimed to examine whether irisin is associated with cognitive decline and mental deterioration altered by PI and exercise. The mice were housed for eight weeks in the PI cage, whose living space was one-sixth that of a standard cage. Simultaneously, the mice were subjected to regular exercise in the presence or absence of an irisin-neutralizing antibody. PI increased the epididymal fat mass without increasing body weight, muscle mass, or plasma corticosterone levels. Additionally, PI induced anxiety, depressive states, and a decline in working memory. In contrast, regular exercise after PI elevated irisin levels in plasma and increased fibronectin type III domain-containing 5 (FNDC5) and peroxisome proliferator-activated receptor gammacoactivator 1α expression in skeletal muscle. Regular exercise also increased hippocampal brain-derived neurotrophic factor (BDNF) expression and BrdU-positive cells, alleviating cognitive decline and mental deterioration induced by PI. The beneficial effects of exercise were compromised by the administration of an irisin-neutralizing antibody. Moreover, plasma irisin level was positively correlated with working memory, hippocampal BDNF levels, and hippocampal cell proliferation. These findings suggest that exercise-inducible irisin is critical for maintaining cognitive function in the PI state.

The underlying rationality of Chinese medicine herb pair Coptis chinensis and Dolomiaea souliei: From the perspective of metabolomics and intestinal function

ETHNOPHARMACOLOGICAL RELEVANCE

The combination of Coptis chinensis (RC) and Dolomiaea souliei (VR) has long been used as a classic herb pair for the treatment of gastrointestinal diseases, but the underlying mechanisms remain unknown.

MATERIALS AND METHODS

In this study, the rationality of evidence-based RC and VR combination was explored from the perspective of metabolism, gut microbiota and gastrointestinal function.

RESULTS

After 5 weeks treatment, VR extracts (700 mg/kg) and RC alkaloids (800 mg/kg) showed no toxic effect on mice. However, RC administration significantly decreased the body weight of mice. Gastric emptying, gastrointestinal motility function and the absorption of FITC dextran were retarded in the mice of RC group, taking RC along with low dose VR (RC-VRL) and high dose VR (RC-VRH) reversed the impaired gastrointestinal function caused by RC. RC administration significantly increased villus height/crypt depth value. Notably, VR administration increased the number of crypts in mice ileum and reduced villus height/crypt depth value in VR and RC combination group. RC treatment significantly increased the expression of occludin compared to NC group; RC-VRL treatment reversed this tendency. While, VR administration increased ZO1 expression by 99.4% compared to NC mice. As for gut microbiota, RC gavage decreased the gut microbiota diversity, but gut microbiota in VR group was similar to NC group, and VR and RC combination increased gut microbiota diversity. RC administration obviously increased the proportion of Akkermansia muciniphila, Bacteroides thetaiotaomicron, Parabacteroides distasonis, and Escherichia coli, compared to NC mice. VR treatment increased the richness of Bacteroides thetaiotaomicron, Parabacteroides distasonis. RC-VRL and RC-VRH treatment dose-dependently increased the richness of Rikenellaceae RC9, Lactobacillus, and decreased the abundance of Psychrobacter, Bacteroides and Ruminococcus in mice. Serum metabolomic analysis revealed that RC gavage significantly down regulated 76 metabolites and up regulated 31 metabolites. VR treatment significantly down regulated 30 metabolites and up regulated 12 metabolites. Weight loss caused by RC may attribute to the elevated methylxanthine level in mice. The potential adverse effects caused by high dose RC intake may partially alleviate by high serum contents of adenosine, inosine and urolithin A resulted from VR coadministration.

CONCLUSION

VR may alleviate RC caused "fluid retention" via normalizing gastrointestinal function, gut microbiota and modulating the perturbed metabolism.

Regular Low-Intensity Exercise Prevents Cognitive Decline and a Depressive-Like State Induced by Physical Inactivity in Mice: A New Physical Inactivity Experiment Model

Regular exercise has already been established as a vital strategy for maintaining physical health via experimental results in humans and animals. In addition, numerous human studies have reported that physical inactivity is a primary factor that causes obesity, muscle atrophy, metabolic diseases, and deterioration in cognitive function and mental health. Regardless, an established animal experimental method to examine the effect of physical inactivity on physiological, biochemical, and neuroscientific parameters is yet to be reported. In this study, we made a new housing cage, named as the physical inactivity (PI) cage, to investigate the effect of physical inactivity on cognitive function and depressive-like states in mice and obtained the following experimental results by its use. We first compared the daily physical activity of mice housed in the PI and standard cages using the nano-tag method. The mice’s physical activity levels in the PI cage decreased to approximately half of that in the mice housed in the standard cage. Second, we examined whether housing in the PI cage affected plasma corticosterone concentration. The plasma corticosterone concentration did not alter before, 1 week, or 10 weeks after housing. Third, we investigated whether housing in the PI cage for 10 weeks affected cognitive function and depressive behavior. Housing in an inactive state caused a cognitive decline and depressive state in the mice without increasing body weight and plasma corticosterone. Finally, we examined the effect of regular low-intensity exercise on cognitive function and depressive state in the mice housed in the PI cage. Physical inactivity decreased neuronal cell proliferation, blood vessel density, and gene expressions of vascular endothelial growth factors and brain-derived neurotrophic factors in the hippocampus. In addition, regular low-intensity exercise, 30 min of treadmill running at a 5–15 m/min treadmill speed 3 days per week, prevented cognitive decline and the onset of a depressive-like state caused by physical inactivity. These results showed that our novel physical inactivity model, housing the mice in the PI cage, would be an adequate and valuable experimental method for examining the effect of physical inactivity on cognitive function and a depressive-like state.

Metformin modulates microbiota-derived inosine and ameliorates methamphetamine-induced anxiety and depression-like withdrawal symptoms in mice

BACKGROUND

Metformin exhibits therapeutic potential in behavioural deficits induced by methamphetamine (METH) in rats. Emerging studies suggest gut microbiota may impact psychiatric symptoms, but there is no direct evidence supporting metformin's participation in the pathophysiology of withdrawal symptoms via modulation of gut microbiota.

METHODS

In order to define the functional impacts of gut microbiota and metformin to the behavioural deficits during METH withdrawal, we utilized a combination of fecal microbiota transplantation (FMT), high-throughput sequencing, and untargeted metabolomics technologies.

RESULTS

First, METH addicts exhibited higher α diversity and distinct microbial structures compared to healthy controls. In particular, the relative abundance of Rikenellaceae was positively correlated with the severity of anxiety and depression. Second, both human-to-mouse and mouse-to-mouse FMTs confirmed that METH-altered-microbiota transplantation is sufficient to promote anxiety and depression-like behaviours in recipient germ-free mice, and these behavioural disturbances could be ameliorated by metformin. In-depth analysis revealed that METH significantly altered the bacterial composition and structure as well as relative abundance of several bacterial taxa and metabolites, including Rikenellaceae and inosine, respectively, whereas add-on metformin could remodel these alterations. Finally, the inosine complementation successfully restored METH-induced anxiety and depression-like behaviours in mice.

CONCLUSION

This study demonstrates that METH withdrawal-induced anxiety and depression-like behaviours are reversible and transmissible via gut microbiota in a mouse model. The therapeutic effects of metformin on psychiatric manifestations are associated with microbiota-derived metabolites, highlighting the role of the gut microbiota in substance use disorders and the pathophysiology of withdrawal symptoms.

Inosine attenuates 3-nitropropionic acid-induced Huntington's disease-like symptoms in rats via the activation of the A2AR/BDNF/TrKB/ERK/CREB signaling pathway

Huntington's disease (HD) is an autosomal dominant inherited neurodegenerative disease characterized by involuntary bizarre movements, psychiatric symptoms, dementia, and early death. Several studies suggested neuroprotective activities of inosine; however its role in HD is yet to be elucidated. The current study aimed to demonstrate the neuroprotective effect of inosine in 3-nitropropionic acid (3-NP)-induced neurotoxicity in rats while investigating possible underlying mechanisms. Rats were randomly divided into five groups; group 1 received i.p. injections of 1% DMSO, whereas groups 2, 3, 4, and 5 received 3-NP (10 mg/kg, i.p.) for 14 days, concomitantly with inosine (200 mg/kg., i.p.) in groups 3, 4, and 5, SCH58261, a selective adenosine 2A receptor (A2AR) antagonist, (0.05 mg/kg, i.p.) in group 4, and PD98059, an extracellular signal-regulated kinase (ERK) inhibitor, (0.3 mg/kg, i.p.) in group 5. Treatment with inosine mitigated 3-NP-induced motor abnormalities and body weight loss. Moreover, inosine boosted the striatal brain-derived neurotrophic factor (BDNF) level, p-tropomyosin receptor kinase B (TrKB), p-ERK, and p-cAMP response element-binding protein (CREB) expression, which subsequently suppressed oxidative stress biomarkers (malondialdehyde and nitric oxide) and pro-inflammatory cytokines (tumor necrosis factor alpha and interleukin-1β) and replenished the glutathione content. Similarly, histopathological analyses revealed decreased striatal injury score, the expression of the glial fibrillary acidic protein, and neuronal loss after inosine treatment. These effects were attenuated by the pre-administration of SCH58261 or PD98059. In conclusion, inosine attenuated 3-NP-induced HD-like symptoms in rats, at least in part, via the activation of the A2AR/BDNF/TrKB/ERK/CREB signaling pathway.

Inosine and its methyl derivatives: Occurrence, biogenesis, and function in RNA

Inosine is one of the most common post-transcriptional modifications. Since its discovery, it has been noted for its ability to contribute to non-Watson-Crick interactions within RNA. Rapidly accumulating evidence points to the widespread generation of inosine through hydrolytic deamination of adenosine to inosine by different classes of adenosine deaminases. Three naturally occurring methyl derivatives of inosine, i.e., 1-methylinosine, 2'-O-methylinosine and 1,2'-O-dimethylinosine are currently reported in RNA modification databases. These modifications are expected to lead to changes in the structure, folding, dynamics, stability and functions of RNA. The importance of the modifications is indicated by the strong conservation of the modifying enzymes across organisms. The structure, binding and catalytic mechanism of the adenosine deaminases have been well-studied, but the underlying mechanism of the catalytic reaction is not very clear yet. Here we extensively review the existing data on the occurrence, biogenesis and functions of inosine and its methyl derivatives in RNA. We also included the structural and thermodynamic aspects of these modifications in our review to provide a detailed and integrated discussion on the consequences of A-to-I editing in RNA and the contribution of different structural and thermodynamic studies in understanding its role in RNA. We also highlight the importance of further studies for a better understanding of the mechanisms of the different classes of deamination reactions. Further investigation of the structural and thermodynamic consequences and functions of these modifications in RNA should provide more useful information about their role in different diseases.

Increased inosine levels in drug-free individuals with at-risk mental state: A serum metabolomics study

AIM

At-risk mental state (ARMS) has been recently attracting attention with respect to the improvement of the management and outcome of psychiatric diseases, such as schizophrenia. Since only a few studies have reported on biological alterations in ARMS, serum metabolomics was carried out in ARMS subjects and healthy controls using liquid chromatography with high-resolution mass spectrometry.

METHODS

Serum samples were collected from ARMS subjects (n = 24; male: 12; female 12) and age- and sex-matched healthy controls (n = 23 male: 11, female: 12). After serum pre-treatment, liquid chromatography with high-resolution mass spectrometry was performed. Multivariate analyses, such as orthogonal partial least-squares discriminant and volcano plot analyses, were performed.

RESULTS

Serum inosine, lactate, taurine, 2,3-dihydroxypropanoate and glutamate levels differed between the two groups. A significant increase in inosine levels was detected in the positive- and negative-ion modes; however, significant differences were not observed in the levels of other purine-related metabolites (hypoxanthine, xanthine and urate) between the two groups.

CONCLUSION

Increased inosine levels may serve as biological markers for ARMS, in addition to alterations in the levels of lactate and certain amino acids.

Investigating the Effect of Inosine on Brain Purinergic Receptors and Neurotrophic and Neuroinflammatory Parameters in an Experimental Model of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative pathology characterized by progressive impairment of memory, associated with neurochemical alterations and limited therapy. The aim of this study was to evaluate the effects of inosine on memory, neuroinflammatory cytokines, neurotrophic factors, expression of purinergic receptors, and morphological changes in the hippocampus and cerebral cortex of the rats with AD induced by streptozotocin (STZ). Male rats were divided into four groups: I, control; II, STZ; III, STZ plus inosine (50 mg/kg); and IV, STZ plus inosine (100 mg/kg). The animals received intracerebroventricular injections of STZ or buffer. Three days after the surgical procedure, animals were treated with inosine (50 mg/kg or 100 mg/kg) for 25 days. Inosine was able to prevent memory deficits and decreased the immunoreactivity of the brain A2A adenosine receptor induced by STZ. Inosine also increased the levels of brain anti-inflammatory cytokines (IL-4 and IL-10) and the expression of brain-derived neurotrophic factor and its receptor. Changes induced by STZ in the molecular layer of the hippocampus were attenuated by treatment with inosine. Inosine also protected against the reduction of immunoreactivity for synaptophysin induced by STZ in CA3 hippocampus region. However, inosine did not prevent the increase in GFAP in animals exposed to STZ. In conclusion, our findings suggest that inosine has therapeutic potential for AD through the modulation of different brain mechanisms involved in neuroprotection.

Inosine mitigated diabetic peripheral neuropathy via modulating GLO1/AGEs/RAGE/NF-κB/Nrf2 and TGF-β/PKC/TRPV1 signaling pathways

Inosine is a dietary supplement that is widely used for managing numerous central neurological disorders. Interestingly, recent experimental investigation of inosine revealed its potential to promote peripheral neuroprotection after sciatic nerve injury. Such investigation has guided the focus of the current study to expose the potential of inosine in mitigating diabetic peripheral neuropathy (DPN) in rats and to study the possible underlying signaling pathways. Adult male Wistar rats were arbitrarily distributed into four groups. In the first group, animals received saline daily for 15 days whereas rats of the remaining groups received a single injection of both nicotinamide (50 mg/Kg/i.p.) and streptozotocin (52.5 mg/Kg/i.p.) for DPN induction. Afterward, inosine (10 mg/Kg/p.o.) was administered to two groups, either alone or in combination with caffeine (3.75 mg/Kg/p.o.), an adenosine receptor antagonist. As a result, inosine showed a hypoglycemic effect, restored the sciatic nerve histological structure, enhanced myelination, modulated conduction velocities and maintained behavioral responses. Furthermore, inosine increased GLO1, reduced AGE/RAGE axis and oxidative stress which in turn, downregulated NF-κB p65 and its phosphorylated form in the sciatic nerves. Inosine enhanced Nrf2 expression and its downstream molecule HO-1, resulting in increased CAT and SOD along with lowered MDA. Moreover, pain was relieved due to suppression of PKC and TRPV1 expression, which ultimately lead to reduced SP and TGF-β. The potential effects of inosine were nearly blocked by caffeine administration; this emphasizes the role of adenosine receptors in inosine-mediated neuroprotective effects. In conclusion, inosine alleviated hyperglycemia-induced DPN via modulating GLO1/AGE/RAGE/NF-κB p65/Nrf2 and TGF-β/PKC/TRPV1/SP pathways.

Impact of Inosine on Chronic Unpredictable Mild Stress-Induced Depressive and Anxiety-Like Behaviors With the Alteration of Gut Microbiota

Current antidepressants do not confer a clear advantage in children and adolescents with major depressive disorder (MDD). Accumulating evidence highlights the potential antidepressant-like effects of inosine on adult MDD, and gut microbiomes are significantly associated with MDD via the microbiota-gut-brain axis. However, few studies have investigated possible associations between inosine and gut microbiota in adolescents with MDD. The current study investigated the potential antidepressant effects of inosine in adolescent male C57BL/6 mice. After 4 weeks of chronic unpredictable mild stress (CUMS) stimulation, the mice were assessed by body weight, the sucrose preference test (SPT), open field test, and the elevated plus maze (EPM). The microbiota compositions of feces were determined by 16S rRNA gene sequencing. Inosine significantly improved CUMS-induced depressive and anxiety-like behaviors in adolescent mice including SPT and EPM results. Fecal microbial composition differed in the CON+saline, CUMS+saline, and CUMS+inosine groups, which were characterized by 126 discriminative amplicon sequence variants belonging to Bacteroidetes and Firmicute at the phylum level and Muribaculaceae and Lachnospiraceae at the family level. Muribaculaceae was positively associated with depressive and anxiety-like behaviors. KEGG functional analysis suggested that inosine might affect gut microbiota through carbohydrate metabolism and lipid metabolism pathways. The results of the study indicated that inosine improved depressive and anxiety-like behaviors in adolescent mice, in conjunction with the alteration of fecal microbial composition. Our findings may provide a novel perspective on the antidepressant effects of inosine in children and adolescents.

WS6 Induces Adult Hippocampal Neurogenesis in Correlation to its Antidepressant Effect on the Alleviation of Depressive-like Behaviors of Rats

Major depressive disorder (MDD) is one of the most common psychiatric disorders. However, the effective drugs for MDD have not yet been developed. WS6 is originally designed with a similar structure as Resveratrol and Pterostilbene. The present study aims to investigate the neuroprotective and ameliorating effects of WS6 treatment in a rat model of chronic unpredictable mild stress (CUMS) induced depression. The results show that CUMS is effective in producing depressive-like behavior in rats as indicated by decreased responses in the locomotor activity, sucrose preference test and increased immobility time. However, WS6 treatment significantly ameliorated these behavioral alterations associated with CUMS-induced depression. Moreover, the reduction in neurogenesis, GABAergic neurons, dendrite complexity, spine density and synaptic plasticity-associate protein 95 (PSD95) by CUMS can be reversed by treatment with WS6. Taken together, this study highlights the neuroprotective and antidepressant-like effects of WS6 against CUMS-induced depression, and suggest a possible mechanism for this protection via changes in neurogenesis within the hippocampus. These finding reveal the therapeutic protection of WS6 for use in clinical trials in the treatment of neuronal deterioration in MDD.

Inosine as a Tool to Understand and Treat Central Nervous System Disorders: A Neglected Actor?

Since the 1970s, when ATP was identified as a co-transmitter in sympathetic and parasympathetic nerves, it and its active metabolite adenosine have been considered relevant signaling molecules in biological and pathological processes in the central nervous system (CNS). Meanwhile, inosine, a naturally occurring purine nucleoside formed by adenosine breakdown, was considered an inert adenosine metabolite and remained a neglected actor on the purinergic signaling scene in the CNS. However, this scenario began to change in the 1980s. In the last four decades, an extensive group of shreds of evidence has supported the importance of mediated effects by inosine in the CNS. Also, inosine was identified as a natural trigger of adenosine receptors. This evidence has shed light on the therapeutic potential of inosine on disease processes involved in neurological and psychiatric disorders. Here, we highlight the clinical and preclinical studies investigating the involvement of inosine in chronic pain, schizophrenia, epilepsy, depression, anxiety, and in neural regeneration and neurodegenerative diseases, such as Parkinson and Alzheimer. Thus, we hope that this review will strengthen the knowledge and stimulate more studies about the effects promoted by inosine in neurological and psychiatric disorders.

Gastrodia elata Blume water extract modulates neurotransmitters and alters the gut microbiota in a mild social defeat stress-induced depression mouse model

Gastrodia elata Blume has multiple bioactive functions, such as antioxidant and antidepressant activities, immune modulation, neuroplasticity, and neuroprotection. We previously found that the water extract of G. elata exerts antidepressant-like effects in unpredictable chronic mild stress models and animals exposed to the forced swimming test. We aimed to investigate the mechanisms by which the water extract of G. elata protects against subchronic- and mild-social defeat-stress-induced dysbiosis. After a 10-day subchronic and mild-social-defeat-stress program, oral treatment with the water extract of G. elata (500 mg/kg bw) resulted in reversal of depression-like behavior. In addition, monoamine analyses showed that the water extract of G. elata normalized the 5-hydroxyindoleacetic acid:5-HT ratio in the prefrontal cortex and colon and reduced the defeat-stress-induced kynurenine:tryptophan ratio in the colon. After the 10-day subchronic and mild social-defeat-stress program, the water extract of G. elata altered the intestinal microbiome by increasing Actinobacteria levels, modulating intestinal inflammation, and shifting the relative abundances of multiple bacterial groups in the gut. Our results suggest that the water extract of G. elata exhibits a potent antidepressant-like effect via the regulation of monoaminergic neurotransmission and alteration of gut microbiota composition and function, and that it may be an effective prevention for depression.

Inosine in Biology and Disease

The nucleoside inosine plays an important role in purine biosynthesis, gene translation, and modulation of the fate of RNAs. The editing of adenosine to inosine is a widespread post-transcriptional modification in transfer RNAs (tRNAs) and messenger RNAs (mRNAs). At the wobble position of tRNA anticodons, inosine profoundly modifies codon recognition, while in mRNA, inosines can modify the sequence of the translated polypeptide or modulate the stability, localization, and splicing of transcripts. Inosine is also found in non-coding and exogenous RNAs, where it plays key structural and functional roles. In addition, molecular inosine is an important secondary metabolite in purine metabolism that also acts as a molecular messenger in cell signaling pathways. Here, we review the functional roles of inosine in biology and their connections to human health.

Purinergic transmission in depressive disorders

Purinergic signaling involves the actions of purine nucleotides and nucleosides (such as adenosine) at P1 (adenosine), P2X, and P2Y receptors. Here, we present recent data contributing to a comprehensive overview of the association between purinergic signaling and depression. We start with background information on adenosine production and metabolism, followed by a detailed characterization of P1 and P2 receptors, with an emphasis on their expression and function in the brain as well as on their ligands. We provide data suggestive of altered metabolism of adenosine in depressed patients, which might be regarded as a disease biomarker. We then turn to considerable amount of preclinical/behavioral data obtained with the aid of the forced swim test, tail suspension test, learned helplessness model, or unpredictable chronic mild stress model and genetic activation/inactivation of P1 or P2 receptors as well as nonselective or selective ligands of P1 or P2 receptors. We also aimed to discuss the reason underlying discrepancies observed in such studies.

Effects of inosine monophosphate and exercise training on neuronal nitric oxide synthase in the mouse brain

Recently, the purine nucleoside inosine has been demonstrated to have several neuroprotective effects. Similarly, exercise training has well-known beneficial effects on mental health and cognitive function. Neuronal nitric oxide synthase (nNOS) is a key neuronal messenger in several brain regions, and the downregulation of nNOS has been shown to improve brain function. However, whether inosine and exercise training have combined effects on nNOS pathway-related proteins in the brain remains unknown. We found, for the first time, that inosine monophosphate (IMP), which is a precursor of inosine, decreases nNOS levels in the ventral hippocampus (vHp) and the cerebellum (Ce), but not in the dorsal hippocampus (dHp). In the vHp, the phosphorylation of cAMP response element-binding protein (CREB) was also upregulated, which negatively correlated with nNOS protein levels. In the cerebral cortex (Cx), no significant activation of the nNOS pathway was observed. In the dHp, vHp, Cx, and Ce, no interactions between the effects of IMP and exercise on nNOS protein and CREB phosphorylation levels were observed. The phosphorylation of nNOS was regulated by the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathway. Although IMP induced minor changes in Akt phosphorylation, nNOS phosphorylation was unchanged by either IMP or exercise. In conclusion, in the vHp, which is associated with emotional behavior, IMP decreased nNOS levels and activated CREB, suggesting that IMP can elicit anxiolytic effects.

Purinergic Signaling and Related Biomarkers in Depression

It is established that purinergic signaling can shape a wide range of physiological functions, including neurotransmission and neuromodulation. The purinergic system may play a role in the pathophysiology of mood disorders, influencing neurotransmitter systems and hormonal pathways of the hypothalamic-pituitary-adrenal axis. Treatment with mood stabilizers and antidepressants can lead to changes in purinergic signaling. In this overview, we describe the biological background on the possible link between the purinergic system and depression, possibly involving changes in adenosine- and ATP-mediated signaling at P1 and P2 receptors, respectively. Furthermore, evidence on the possible antidepressive effects of non-selective adenosine antagonist caffeine and other purinergic modulators is reviewed. In particular, A2A and P2X7 receptors have been identified as potential targets for depression treatment. Preclinical studies highlight that both selective A2A and P2X7 antagonists may have antidepressant effects and potentiate responses to antidepressant treatments. Consistently, recent studies feature the possible role of the purinergic system peripheral metabolites as possible biomarkers of depression. In particular, variations of serum uric acid, as the end product of purinergic metabolism, have been found in depression. Although several open questions remain, the purinergic system represents a promising research area for insights into the molecular basis of depression.

Inosine protects against impairment of memory induced by experimental model of Alzheimer disease: a nucleoside with multitarget brain actions

RATIONALE

Inosine is a naturally occurring purine nucleoside formed by adenosine breakdown. This nucleoside is reported to exert potent effects on memory and learning, possibly through its antioxidant and anti-inflammatory actions.

OBJECTIVE

The objective is to evaluate the effects of inosine on the behavioral and neurochemical parameters in a rat model of Alzheimer's disease (AD) induced by streptozotocin (STZ).

METHODS

Adult male rats were divided into four groups: control (saline), STZ, STZ plus inosine (50 mg/kg), and STZ plus inosine (100 mg/kg). STZ (3 mg/kg) was administered by bilateral intracerebroventricular injection. The animals were treated intraperitoneally with inosine for 25 days. Memory, oxidative stress, ion pump activities, acetylcholinesterase (AChE), and choline acetyltransferase (ChAT) activities and expression were evaluated in the cerebral cortex and hippocampus.

RESULTS

The memory impairment induced by STZ was prevented by inosine. An increase in the Na⁺, K⁺-ATPase, and Mg-ATPase activities and a decrease in the Ca²⁺-ATPase activity were induced by STZ in the hippocampus and cerebral cortex, and inosine could prevent these alterations in ion pump activities. Inosine also prevented the increase in AChE activity and the alterations in AChE and ChAT expression induced by STZ. STZ increased the reactive oxygen species, nitrite levels, and superoxide dismutase activity and decreased the catalase and glutathione peroxidase activities. Inosine treatment conferred protection from these oxidative alterations in the brain.

CONCLUSIONS

Our findings demonstrate that inosine affects brain multiple targets suggesting that this molecule may have therapeutic potential against cognitive deficit and tissue damage in AD.

Anti-depressant activity of Erythrina variegata bark extract and regulation of monoamine oxidase activities in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Erythrina variegata, commonly referred to as 'Indian coral tree' belongs to the Fabaceae family. It is a plant native to the coast of India, China and is distributed in tropical and subtropical regions worldwide. In traditional medicine, E. variegata is known to exhibit anxiolytic and anti-convulsant activities and has been used as a nervine sedative. As per the Indian Materia Medica, E. variegata barks have been traditionally known to act on the central nervous system. However, there is a lack of data demonstrating this.

AIM OF THE STUDY

Our study focuses on previously unreported anti-depressant activity of E. variegata bark ethanolic extract (EBE) and determination of its mechanism of action possibly through regulation of monoamine oxidase activity in mouse brain homogenates.

MATERIALS AND METHODS

EBE was characterized using standard protocols for phytochemical analysis, followed by liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS) analysis. The compounds in EBE (previously reported for anti-depressant activity), were further studied by LC-MS/MS and GC-MS/MS analysis. Anti-depressant activity of EBE (50, 100, 200 and 500 mg/kg) was evaluated in Swiss albino mice using acute and chronic tail suspension test (TST) and forced swim test (FST) models. Furthermore, the possible mechanism of action of EBE was evaluated using the chronic unpredictable mild stress (CUMS) model, wherein inhibitory effects on monoamine oxidase (MAO) A and B were assessed by spectrophotometric-chemical analysis in mouse whole brain homogenates.

RESULTS

EBE showed significant reduction in immobility time periods in both TST (acute: 50, 100 and 200 mg/kg and chronic: 100 and 200 mg/kg) and FST (acute: 200 mg/kg and chronic: 100, 200 and 500 mg/kg) models. Moreover, the locomotor activity test confirmed that acute and chronic administration of EBE did not significantly affect the motor activity of mice. In the CUMS model, EBE when administered alone (100 and 200 mg/kg) and in combination (50, 100 and 200 mg/kg) with escitalopram (15 mg/kg), showed significant reductions in immobility time periods compared to the control group, in the acute FST performed on 22nd day of CUMS. Furthermore, when administered alone (50, 100 and 200 mg/kg), EBE showed significant inhibition in MAO-A and B activities compared to the control group. When used in combination, EBE (50, 100 and 200 mg/kg) showed synergistic action with escitalopram (15 mg/kg), resulting in significantly greater inhibition of MAO-A and B activities, compared to both EBE alone and escitalopram alone. Phytochemical analysis of EBE revealed presence of sugars, steroids, glycosides, alkaloids and tannins. LC-MS, LC-MS/MS, GC-MS and GC-MS/MS analysis identified components in EBE, previously reported for their anti-depressant activity.

CONCLUSIONS

The study thus concluded the anti-depressant like activity of EBE. The study identified components present in EBE that may be responsible for its anti-depressant activity. The possible mechanism of action of EBE was also investigated in the CUMS model, wherein inhibitory effects of EBE on MAO-A and B activities in the mouse brain were demonstrated. Furthermore, the study confirms the traditional use of E. variegata barks in CNS related activities through its anti-depressant like activity.

Deletion of equilibrative nucleoside transporter-2 protects against lipopolysaccharide-induced neuroinflammation and blood-brain barrier dysfunction in mice

Neuroinflammation is a common pathological feature of many brain diseases and is a key mediator of blood-brain barrier (BBB) breakdown and neuropathogenesis. Adenosine is an endogenous immunomodulator, whose brain extracellular level is tightly controlled by equilibrative nucleoside transporters-1 (ENT1) and ENT2. This study was aimed to investigate the role of ENTs in the modulation of neuroinflammation and BBB function. The results showed that mRNA level of Ent2 was significantly more abundant than that of Ent1 in the brain (hippocampus, cerebral cortex, striatum, midbrain, and cerebellum) of wild-type (WT) mice. Ent2^-/- mice displayed higher extracellular adenosine level in the hippocampus than their littermate controls. Repeated lipopolysaccharide (LPS) treatment induced microglia activation, astrogliosis and upregulation of proinflammatory cytokines, along with aberrant BBB phenotypes (including reduced tight junction protein expression, pericyte loss, and immunoglobulin G extravasation) and neuronal apoptosis in the hippocampus of WT mice. Notably, Ent2^-/- mice displayed significant resistance to LPS-induced neuroinflammation, BBB breakdown, and neurotoxicity. These findings suggest that Ent2 is critical for the modulation of brain adenosine tone and deletion of Ent2 confers protection against LPS-induced neuroinflammation and neurovascular-associated injury.

The protective effect of inosine against rotenone-induced Parkinson's disease in mice; role of oxido-nitrosative stress, ERK phosphorylation, and A2AR expression

Parkinson's disease (PD) is a severe disabling syndrome in which neuroinflammation and various signaling pathways are believed to mediate dopaminergic neurodegeneration. Here, the possible disease-modifying effects of the purine nucleoside inosine were examined against rotenone-induced PD. Mice were allocated into six groups, namely, a normal control group receiving dimethylsulfoxide, a PD control group receiving rotenone, a standard treatment group receiving L-dopa/carbidopa together with rotenone, and three treatment groups receiving inosine in low, medium, and high doses together with rotenone. At the end of the experimental protocol, three behavioral tests were performed to assess PD motor manifestations, namely, wire-hanging test, wood-walking test, and stair test. After performing the behavioral study, mice striata were isolated for the colorimetric assay of hypoxanthine, the enzyme-linked immunosorbent assay of dopamine, tumor necrosis factor-α, interleukin-6 and nitrite, the Western blot estimation of total and phosphorylated extracellular signal-regulated kinase (tERK and pERK), the polymerase chain reaction estimation of adenosine A_2A receptor (A2AR) expression, as well as the histopathological examination of substantia nigra and striatal tissue. Inosine protected against PD progression in a dose-dependent manner, with the effect comparable to the standard treatment L-dopa/carbidopa, evidenced by behavioral, biochemical, and histologic findings. The beneficial antiparkinsonian effect of inosine could be attributed to the ability of the drug to ameliorate neuroinflammation and oxido-nitrosative stress, together with suppression of ERK phosphorylation and down-regulation of A2AR expression. Inosine could therefore be considered as a disease-modifying agent against PD, but further studies are claimed to confirm such effects clinically.

Inosine Accelerates the Regeneration and Anticipates the Functional Recovery after Sciatic Nerve Crush Injury in Mice

Trauma to the peripheral nervous system (PNS) results in loss of motor and sensory functions. After an injury, a complex series of events begins, allowing axonal regeneration and target reinnervation. However, this regenerative potential is limited by several factors such as age, distance from the lesion site to the target and severity of lesion. Many studies look for ways to overcome these limitations. Inosine, a purine nucleoside derived from adenosine, emerges as a potential treatment, due to its capacity to regulate axonal growth, neuroprotection and immunomodulation, contributing to motor recovery. However, no studies demonstrated their effects on PNS. C57/Black6 mice were submitted to sciatic nerve crush and received intraperitoneal injections of saline or inosine (70 mg/kg), one hour after injury and daily for one week. To evaluate axonal regeneration and functional recovery, electroneuromyography, Sciatic Function Index (SFI), rotarod and pinprick tests were performed. Our results showed that the inosine group presented a higher number of myelinated fibers and a large amount of fibers within the ideal G-ratio. In addition, the results of electroneuromyography showed greater amplitude of the compound muscle action potentials in the first and second weeks, suggesting anticipation of regeneration in the inosine group. We also observed in the inosine group, motor and sensory neurons survival, reduction in the number of macrophages and myelin ovoids in the sciatic nerves, and an early recovery of motor and sensory functions. Thus, we conclude that the use of inosine accelerates axonal regeneration promoting an early recovery of motor and sensory functions.

A comprehensive metabolomics investigation of hippocampus, serum, and feces affected by chronic fluoxetine treatment using the chronic unpredictable mild stress mouse model of depression

A metabolomic investigation of depression and chronic fluoxetine treatment was conducted using a chronic unpredictable mild stress model with C57BL/6N mice. Establishment of the depressive model was confirmed by body weight measurement and behavior tests including the forced swim test and the tail suspension test. Behavioral despair by depression was reversed by four week-treatment with fluoxetine. Hippocampus, serum, and feces samples collected from four groups (control + saline, control + fluoxetine, model + saline, and model + fluoxetine) were subjected to metabolomic profiling based on ultra-high performance liquid chromatography-quadrupole-time-of-flight mass spectrometry. Alterations in the metabolic patterns were evident in all sample types. The antidepressant effects of fluoxetine appeared to involve various metabolic pathways including energy metabolism, neurotransmitter synthesis, tryptophan metabolism, fatty acid metabolism, lipid metabolism, and bile acid metabolism. Predictive marker candidates of depression were identified, including β-citryl-L-glutamic acid (BCG) and docosahexaenoic acid (DHA) in serum and chenodeoxycholic acid and oleamide in feces. This study suggests that treatment effects of fluoxetine might be differentiated by altered levels of tyramine and BCG in serum, and that DHA is a potential serum marker for depression with positive association with hippocampal DHA. Collectively, our comprehensive study provides insights into the biochemical perturbations involved in depression and the antidepressant effects of fluoxetine.

Inosine - a Multifunctional Treatment for Complications of Neurologic Injury

Spinal cord injury (SCI) caused by trauma or disease leads to motor and sensory abnormalities that depend on the level, severity and duration of the lesion. The most obvious consequence of SCI is paralysis affecting lower and upper limbs. SCI also leads to loss of bladder and bowel control, both of which have a deleterious, life-long impact on the social, psychological, functional, medical and economic well being of affected individuals. Currently, there is neither a cure for SCI nor is there adequate management of its consequences. Although medications provide symptomatic relief for the complications of SCI including muscle spasms, lower urinary tract dysfunction and hyperreflexic bowel, strategies for repair of spinal injuries and recovery of normal limb and organ function are still to be realized. In this review, we discuss experimental evidence supporting the use of the naturally occurring purine nucleoside inosine to improve the devastating sequelae of SCI. Evidence suggests inosine is a safe, novel agent with multifunctional properties that is effective in treating complications of SCI and other neuropathies.

Imbalance in amino acid and purine metabolisms at the hypothalamus in inflammation-associated depression by GC-MS

Hypothalamic dysfunction is a key factor in depression; increasing evidence highlights neuroinflammation abnormalities as well as imbalances in neurotransmitters and the purinergic system in the pathophysiology of depression. However, little is known about the metabolomic changes in the hypothalamus of depressed patients with neuroinflammation. Herein, taking advantage of the well-established lipopolysaccharide (LPS)-induced depression mouse model, we measured metabolic changes in the hypothalamus using gas chromatography-mass spectrometry (GC-MS). Sucrose preference test (SPT), open field test (OFT), forced swimming test (FST), and tail suspension test (TST) were conducted to assess our depressive model. To better understand the metabolic disturbances occurring in the hypothalamus of depressed mice, multivariate statistics were applied to analyse the clinical significance of differentially expressed metabolites in the hypothalamus of mice with LPS-induced depression. Bioinformatic analysis was conducted to detect potential relationships among the changed metabolites. The data confirmed that mice with LPS-induced depression were good mimics of depression patients in some characteristic symptoms such as decreased sucrose intake and increased immobility. In our study, 27 differentially expressed metabolites were identified in the hypothalamus of mice with LPS-induced depression. Herein, seventeen of these metabolites decreased, whereas 10 metabolites increased. These molecular changes were closely related to perturbations in the amino acid and purine metabolisms. Our data indicate that dysfunction of amino acid and purine metabolisms is one of main characteristics of inflammation-mediated depression. These results provide new insights into the mechanisms underlying depression, which may shed some light on the role of the hypothalamus in the pathogenesis of inflammation-mediated depression.

Adenosine A2A Receptor Deletion Blocks the Beneficial Effects of Lactobacillus reuteri in Regulatory T-Deficient Scurfy Mice

The lack of a functional Foxp3 transcription factor and regulatory T (Treg) cells causes lethal, CD4+ T cell-driven autoimmune diseases in scurfy (SF) mice and humans. Recent studies have shown that adenosine A2A receptor activation limits inflammation and tissue damage, thereby playing an anti-inflammatory role. However, the role of the adenosine A2A receptor in the development of disease in SF mice remains unclear. Using a genetic approach, we found that adenosine A2A receptor deletion in SF mice (SF[Formula: see text]) does not affect early life events, the development of a lymphoproliferative disorder, or hyper-production of pro-inflammatory cytokines seen in the Treg-deficiency state. As shown previously, Lactobacillus reuteri DSM 17938 treatment prolonged survival and reduced multiorgan inflammation in SF mice. In marked contrast, A2A receptor deletion completely blocked these beneficial effects of L. reuteri in SF mice. Altogether, these results suggest that although absence of the adenosine A2A receptor does not affect the development of disease in SF mice, it plays a critical role in the immunomodulation by L. reuteri in Treg-deficiency disease. The adenosine A2A receptor and its activation may have a role in treating other Treg dysfunction-mediated autoimmune diseases.

Uric acid contributes greatly to hepatic antioxidant capacity besides protein

Uric acid is the end-product of purine nucleotide metabolism and an increase in uric acid concentration in the body results in hyperuricemia, ultimately leading to gout. However, uric acid is a potent antioxidant and interacts with reactive oxygen species (ROS) to be non-enzymatically converted to allantoin. Uric acid accounts for approximately 60 % of antioxidant capacity in the plasma; however, its contribution to tissue antioxidant capacity is unknown. In this study, the contribution of uric acid to tissue antioxidant capacity and its conversion to allantoin by scavenging ROS in tissue were examined. The results showed that a decrease in hepatic uric acid content via allopurinol administration significantly reduced hepatic total-radical trapping antioxidant parameter (TRAP) content in protein-free cytosol. Additionally, treating protein-free cytosol with uricase led to a further reduction of hepatic TRAP content. Allantoin was also detected in the solution containing protein-free cytosol that reacted with ROS. These findings suggest that in the absence of protein, uric acid contributes greatly to antioxidant capacity in the liver, where uric acid is converted to allantoin by scavenging ROS.

Insight into the metabolic mechanism of Diterpene Ginkgolides on antidepressant effects for attenuating behavioural deficits compared with venlafaxine

Depression is a severe and chronic mental disorder, affecting about 322 million individuals worldwide. A recent study showed that diterpene ginkgolides (DG) have antidepressant-like effects on baseline behaviours in mice. Here, we examined the effects of DG and venlafaxine (VLX) in a chronic social defeat stress model of depression. Both DG and VLX attenuated stress-induced social deficits, despair behaviour and exploratory behaviour. To elucidate the metabolic changes underlying the antidepressive effects of DG and VLX, we investigated candidate functional pathways in the prefrontal cortex using a GC-MS-based metabolomics approach. Metabolic functions and pathways analysis revealed that DG and VLX affect protein biosynthesis and nucleotide metabolism to enhance cell proliferation, with DG having a weaker impact than VLX. Glutamate and aspartate metabolism played important roles in the antidepressant effects of DG and VLX. Tyrosine degradation and cell-to-cell signaling and interaction helped discriminate the two antidepressants. L-glutamic acid was negatively correlated, while hypoxanthine was positively correlated, with the social interaction ratio. Understanding the metabolic changes produced by DG and VLX should provide insight into the mechanisms of action of these drugs and aid in the development of novel therapies for depression.

Comparison of the Human A2A Adenosine Receptor Recognition by Adenosine and Inosine: New Insight from Supervised Molecular Dynamics Simulations

Adenosine deaminase converts adenosine into inosine. In contrast to adenosine, relatively little attention has been paid to the physiological roles of inosine. Nevertheless, recent studies have demonstrated that inosine has neuroprotective, cardioprotective, immunomodulatory, and antidepressive effects. Inosine was recently shown to be a less potent agonist than adenosine at the A_2A adenosine receptor. To better depict the differences in the mechanisms of receptor recognition between adenosine and inosine, we carried out supervised molecular dynamics (SuMD) simulations, and the results are analyzed herein.

A fully integrated new paradigm for lithium's mode of action - lithium utilizes latent cellular fail-safe mechanisms

It is proposed that lithium's therapeutic effects occur indirectly by augmenting a cascade of protective "fail-safe" pathways pre-configured to activate in response to a dangerous low cell [Mg⁺⁺] situation, eg, posttraumatic brain injury, alongside relative cell adenosine triphosphate depletion. Lithium activates cell protection, as it neatly mimics a lowered intracellular [Mg⁺⁺] level.

Resetting microbiota by Lactobacillus reuteri inhibits T reg deficiency-induced autoimmunity via adenosine A2A receptors

Regulatory T (T reg) cell deficiency causes lethal, CD4+ T cell-driven autoimmune diseases. Stem cell transplantation is used to treat these diseases, but this procedure is limited by the availability of a suitable donor. The intestinal microbiota drives host immune homeostasis by regulating the differentiation and expansion of T reg, Th1, and Th2 cells. It is currently unclear if T reg cell deficiency-mediated autoimmune disorders can be treated by targeting the enteric microbiota. Here, we demonstrate that Foxp3+ T reg cell deficiency results in gut microbial dysbiosis and autoimmunity over the lifespan of scurfy (SF) mouse. Remodeling microbiota with Lactobacillus reuteri prolonged survival and reduced multiorgan inflammation in SF mice. L. reuteri changed the metabolomic profile disrupted by T reg cell deficiency, and a major effect was to restore levels of the purine metabolite inosine. Feeding inosine itself prolonged life and inhibited multiorgan inflammation by reducing Th1/Th2 cells and their associated cytokines. Mechanistically, the inhibition of inosine on the differentiation of Th1 and Th2 cells in vitro depended on adenosine A2A receptors, which were also required for the efficacy of inosine and of L. reuteri in vivo. These results reveal that the microbiota-inosine-A2A receptor axis might represent a potential avenue for combatting autoimmune diseases mediated by T reg cell dysfunction.