Guanosine Protects Against Cortical Focal Ischemia. Involvement of Inflammatory Response

Spontaneously Hypertensive Rats Present Exacerbated Focal Stroke Behavioral Outcomes

This study aimed to analyze the effects of systemic arterial hypertension (SAH) in a model of permanent ischemic stroke (focal ischemia due to thermocoagulation of pial vessels) on sensorimotor function (cylinder test and patch removal test), behavioral tasks (novelty habituation memory open field task) and cerebral infarct size in adult male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) for 42 days after the occurrence of a stroke. We observed that the stroke caused asymmetry in the front paws and delayed adhesive removal. These effects were spontaneously reduced in WKY rats, but not in SHR. Short- and long-term novelty habituation memories were abolished by stroke in WYK and SHR. On the 3rd day after stroke, the size of the focal cerebral infarct was the same in WKY and SHR. However, on the 7th day, the infarct size decreased in WKY rats, but not SHR. These results suggested that SAH impairment of sensorimotor recovery in rats subjected to cerebral ischemia could be related to augmented focal cerebral infarct size. Moreover, the behavioral tasks used in this study were unaffected by Systemic Arterial Hypertension. Our results highlight the need for animal models of comorbidities in stroke research.

Constituents from Dolichos lablab L. Flowers and Their Anti-Inflammatory Effects via Inhibition of IL-1β Release

The occurrence of inflammation is closely related to the activation of the NLRP3 inflammasome. IL-1β produced during the activation of the NLRP3 inflammasome has strong pro-inflammatory activity and can also promote the release of inflammatory factors by other immune cells, exacerbating inflammatory damage to tissues. Utilizing IL-1β as the detection index to find small-molecule inhibitors targeting NLRP3 from natural products will benefit the search for drugs for inflammation-related diseases. During the exploration of anti-inflammatory active components derived from the flowers of Dolichos lablab L., an ingredient in traditional Chinese medicine with dual applications in both medicinal treatment and dietary consumption, fourteen compounds (1-14), including seven previously unreported ones, named flosdolilabnitrogenousols A-D (1-4) and flosdolilabsaponins A-C (5-7), were found. Their structures were established through extensive NMR spectra determination, HR-ESI-MS analysis, ECD calculations, and chemical reactions. Flosdolilabsaponin A (5) stands out as an exceptionally rare tetracyclic lactone oleane-type saponin. Additionally, the inhibitory activity on IL-1β release of all compounds, without cytotoxicity, was evaluated using BMDMs stimulated with LPS/Nigericin. An Elisa assay revealed that compounds 1, 8, 9, and 11-14 exhibited significant inhibition of IL-1β release at a concentration of 30 μM. Structure-activity relationships were also discussed. This study indicates that D. lablab flowers possess anti-inflammatory activity, which might exert its effect by suppressing the activation of the NLRP3 inflammasome.

Lessons from the physiological role of guanosine in neurodegeneration and cancer: Toward a multimodal mechanism of action?

Neurodegenerative diseases and brain tumours represent important health challenges due to their severe nature and debilitating consequences that require substantial medical care. Interestingly, these conditions share common physiological characteristics, namely increased glutamate, and adenosine transmission, which are often associated with cellular dysregulation and damage. Guanosine, an endogenous nucleoside, is safe and exerts neuroprotective effects in preclinical models of excitotoxicity, along with cytotoxic effects on tumour cells. However, the lack of well-defined mechanisms of action for guanosine hinders a comprehensive understanding of its physiological effects. In fact, the absence of specific receptors for guanosine impedes the development of structure-activity research programs to develop guanosine derivatives for therapeutic purposes. Alternatively, given its apparent interaction with the adenosinergic system, it is plausible that guanosine exerts its neuroprotective and anti-tumorigenic effects by modulating adenosine transmission through undisclosed mechanisms involving adenosine receptors, transporters, and purinergic metabolism. Here, several potential molecular mechanisms behind the protective actions of guanosine will be discussed. First, we explore its potential interaction with adenosine receptors (A1R and A2AR), including the A1R-A2AR heteromer. In addition, we consider the impact of guanosine on extracellular adenosine levels and the role of guanine-based purine-converting enzymes. Collectively, the diverse cellular functions of guanosine as neuroprotective and antiproliferative agent suggest a multimodal and complementary mechanism of action.

Investigating the Impact of SN-38 on Mouse Brain Metabolism Based on Metabolomics

Purpose

SN-38 (7-ethyl-10-hydroxycamptothecin), the active metabolite of irinotecan, has been extensively studied in drug delivery systems. However, its impact on neural metabolism remains unclear. This study aims to investigate the toxic effects of SN-38 on mouse brain metabolism.

Methods

Male mice were divided into an SN-38 group and a control group. The SN-38 group received SN-38 (20 mg/kg/day) via intraperitoneal injection, while the control group was given an equal volume of a blank solvent mixture (DMSO and saline, ratio 1:9). Gas chromatography-mass spectrometry (GC-MS) was employed to analyze differential metabolites in the cortical and hippocampal regions of the SN-38-treated mice.

Results

SN-38 induced metabolic disturbances in the central nervous system. Eighteen differential metabolites were identified in the hippocampus and twenty-four in the cortex, with six common to both regions. KEGG pathway enrichment analysis revealed statistically significant alterations in six metabolic pathways in the hippocampus and ten in the cortex (P<0.05).

Conclusion

This study is the first to demonstrate the neurotoxicity of SN-38 in male mice through metabolomics. Differential metabolites in the hippocampal and cortical regions were closely linked to purine metabolism, pyrimidine metabolism, amino acid metabolism, and glyceride metabolism, indicating disruptions in the blood-brain barrier, energy metabolism, and central signaling pathways.

Prevotella copri transplantation promotes neurorehabilitation in a mouse model of traumatic brain injury

BACKGROUND

The gut microbiota plays a critical role in regulating brain function through the microbiome-gut-brain axis (MGBA). Dysbiosis of the gut microbiota is associated with neurological impairment in Traumatic brain injury (TBI) patients. Our previous study found that TBI results in a decrease in the abundance of Prevotella copri (P. copri). P. copri has been shown to have antioxidant effects in various diseases. Meanwhile, guanosine (GUO) is a metabolite of intestinal microbiota that can alleviate oxidative stress after TBI by activating the PI3K/Akt pathway. In this study, we investigated the effect of P. copri transplantation on TBI and its relationship with GUO-PI3K/Akt pathway.

METHODS

In this study, a controlled cortical impact (CCI) model was used to induce TBI in adult male C57BL/6J mice. Subsequently, P. copri was transplanted by intragastric gavage for 7 consecutive days. To investigate the effect of the GUO-PI3K/Akt pathway in P. copri transplantation therapy, guanosine (GUO) was administered 2 h after TBI for 7 consecutive days, and PI3K inhibitor (LY294002) was administered 30 min before TBI. Various techniques were used to assess the effects of these interventions, including quantitative PCR, neurological behavior tests, metabolite analysis, ELISA, Western blot analysis, immunofluorescence, Evans blue assays, transmission electron microscopy, FITC-dextran permeability assay, gastrointestinal transit assessment, and 16 S rDNA sequencing.

RESULTS

P. copri abundance was significantly reduced after TBI. P. copri transplantation alleviated motor and cognitive deficits tested by the NSS, Morris's water maze and open field test. P. copri transplantation attenuated oxidative stress and blood-brain barrier damage and reduced neuronal apoptosis after TBI. In addition, P. copri transplantation resulted in the reshaping of the intestinal flora, improved gastrointestinal motility and intestinal permeability. Metabolomics and ELISA analysis revealed a significant increase in GUO levels in feces, serum and injured brain after P. copri transplantation. Furthermore, the expression of p-PI3K and p-Akt was found to be increased after P. copri transplantation and GUO treatment. Notably, PI3K inhibitor LY294002 treatment attenuated the observed improvements.

CONCLUSIONS

We demonstrate for the first time that P. copri transplantation can improve GI functions and alter gut microbiota dysbiosis after TBI. Additionally, P. copri transplantation can ameliorate neurological deficits, possibly via the GUO-PI3K/Akt signaling pathway after TBI.

Mechanistic insights into Qiteng Xiaozhuo Granules' regulation of autophagy for chronic glomerulonephritis treatment: Serum pharmacochemistry, network pharmacology, and experimental validation

ETHNOPHARMACOLOGICAL RELEVANCE

Qiteng Xiaozhuo Granules (QTXZG), a traditional Chinese medicine prescription, is widely acknowledged for its therapeutic efficacy and lack of discernible toxicity in clinical practice, substantiating its potential in the treatment of chronic glomerulonephritis (CGN). Nevertheless, the specific effectiveness and underlying mechanisms of QTXZG remain insufficiently explored.

AIM OF THE STUDY

The purpose of this study was to explore the mechanism of the QTXZG in the treatment of CGN via targeting autophagy based on serum pharmacochemistry, network pharmacology, and experimental validation.

METHODS

Serum samples from SD rats orally administered QTXZG were analyzed using UPLC-QE/MS to identify contained compounds. Network and functional enrichment analyses elucidated QTXZG's targets and biological mechanisms. Reliability was ensured through molecular docking, in vivo and in vitro experiments.

RESULTS

After oral administration of QTXZG, 39 enriched compounds in serum samples collected 1 h later were identified as potential active agents, with 508 potential targets recognized as QTXZG-specific targets. Through integration of various databases, intersection analysis of QTXZG targets, CGN-related genes, and autophagy-related targets identified 10 core autophagy-related targets for QTXZG in CGN. GO and KEGG analyses emphasized their roles in autophagy, inflammation, and immune processes, particularly emphasizing the enrichment of the AMPK/mTOR signaling pathway. Molecular docking results demonstrated strong binding affinities between QTXZG's key compounds and the predicted core targets. In animal experiments, QTXZG was found to ameliorate renal tissue damage in CGN model mice, significantly reducing serum creatinine (Scr) and blood urea nitrogen (BUN) levels. Importantly, both animal and cell experiments revealed QTXZG's ability to decrease excessive ROS and inflammatory factor release in mesangial cells. Furthermore, in vitro and in vivo experiments confirmed QTXZG's capacity to upregulate Beclin1 and LC3II/I expression, decrease p62 expression, and induce CGN autophagy through modulation of the AMPK/mTOR pathway.

CONCLUSIONS

This study indicated that QTXZG can induce autophagy in CGN by affecting the AMPK/mTOR pathway, and induction of autophagy may be one of the possible mechanisms of QTXZG's anti-CGN.

Hypothermia increases adenosine monophosphate and xanthosine monophosphate levels in the mouse hippocampus, preventing their reduction by global cerebral ischemia

Global cerebral ischemia (GCI) caused by clinical conditions such as cardiac arrest leads to delayed neuronal death in the hippocampus, resulting in physical and mental disability. However, the mechanism of delayed neuronal death following GCI remains unclear. To elucidate the mechanism, we performed a metabolome analysis using a mouse model in which hypothermia (HT) during GCI, which was induced by the transient occlusion of the bilateral common carotid arteries, markedly suppressed the development of delayed neuronal death in the hippocampus after reperfusion. Fifteen metabolites whose levels were significantly changed by GCI and 12 metabolites whose levels were significantly changed by HT were identified. Furthermore, the metabolites common for both changes were narrowed down to two, adenosine monophosphate (AMP) and xanthosine monophosphate (XMP). The levels of both AMP and XMP were found to be decreased by GCI, but increased by HT, thereby preventing their decrease. In contrast, the levels of adenosine, inosine, hypoxanthine, xanthine, and guanosine, the downstream metabolites of AMP and XMP, were increased by GCI, but were not affected by HT. Our results may provide a clue to understanding the mechanism by which HT during GCI suppresses the development of delayed neuronal death in the hippocampus.

Synergistic effect rescue animal model from NASH caused by diet-inflammation inducer

Excessive intake of pro-inflammatory fatty acids is related to the development of insulin resistance, impaired oxidative stress enzymes, and lipid disorders, leading to inflammation and development of non-alcoholic steatohepatitis (NASH). Diet and physical exercise are considered to prevent and treat metabolic disorders caused by chronic inflammatory states (responsible for insulin resistance and diabetes type 2) in individuals with obesity and nonalcoholic fatty liver diseases (NAFLD). Our investigation tested the hypothesis that Hass avocado oil, a monounsaturated fatty acid and a source of phytosterol, may improve liver and metabolic parameters without adverse effects when combined with physical exercise. Rats ingested a high-fat diet for seven weeks and were then subjected to more six weeks with a standard diet, Hass avocado-oil ingestion, and swimming. The intervention showed significantly improvements by synergistic effect between Hass avocado-oil and swimming exercise (P < 0.05), including improving adiponectin, leptin, and fasting blood glucose levels, alleviating insulin resistance, reducing serum TNF-α, improving glutathione enzyme levels, and decreasing lipotoxicity in the liver and blood and serum triacylglycerides in blood (P < 0.05). Liver tissue markers of apoptosis and necrosis such as CK-18 filaments and dimethylamine (DMA) were significantly higher in the intervention group (P < 0.05). We were unable to fully confirm our hypothesis. Although the synergistic effects between Hass avocado-oil and the swimming regimen offer a promising chance of recovering liver health by improving 10 health biological markers, we must not ignore the cellular damage due to apoptosis and necrosis in liver cells and DMA. The data on metabolomic profile and avocado-oil-treated livers highlight the need for further investigation.

Dynamic and Rapid Detection of Guanosine during Ischemia

Guanosine acts in both neuroprotective and neurosignaling pathways in the central nervous system; in this paper, we present the first fast voltammetric measurements of endogenous guanosine release during pre- and post-ischemic conditions. We discuss the metric of our measurements via analysis of event concentration, duration, and interevent time of rapid guanosine release. We observe changes across all three metrics from our normoxic to ischemic conditions. Pharmacological studies were performed to confirm that guanosine release is a calcium-dependent process and that the signaling observed is purinergic. Finally, we show the validity of our ischemic model via staining and fluorescent imaging. Overall, this paper sets the tone for rapid monitoring of guanosine and provides a platform to investigate the extent to which guanosine accumulates at the site of brain injury, i.e., ischemia.

Purinergic signaling: A gatekeeper of blood-brain barrier permeation

This review outlined evidence that purinergic signaling is involved in the modulation of blood-brain barrier (BBB) permeability. The functional and structural integrity of the BBB is critical for maintaining the homeostasis of the brain microenvironment. BBB integrity is maintained primarily by endothelial cells and basement membrane but also be regulated by pericytes, neurons, astrocytes, microglia and oligodendrocytes. In this review, we summarized the purinergic receptors and nucleotidases expressed on BBB cells and focused on the regulation of BBB permeability by purinergic signaling. The permeability of BBB is regulated by a series of purinergic receptors classified as P2Y₁, P2Y₄, P2Y₁₂, P2X4, P2X7, A₁, A_2A, A_2B, and A₃, which serve as targets for endogenous ATP, ADP, or adenosine. P2Y₁ and P2Y₄ antagonists could attenuate BBB damage. In contrast, P2Y₁₂-mediated chemotaxis of microglial cell processes is necessary for rapid closure of the BBB after BBB breakdown. Antagonists of P2X4 and P2X7 inhibit the activation of these receptors, reduce the release of interleukin-1 beta (IL-1β), and promote the function of BBB closure. In addition, the CD39/CD73 nucleotidase axis participates in extracellular adenosine metabolism and promotes BBB permeability through A₁ and A_2A on BBB cells. Furthermore, A_2B and A₃ receptor agonists protect BBB integrity. Thus, the regulation of the BBB by purinergic signaling is complex and affects the opening and closing of the BBB through different pathways. Appropriate selective agonists/antagonists of purinergic receptors and corresponding enzyme inhibitors could modulate the permeability of the BBB, effectively delivering therapeutic drugs/cells to the central nervous system (CNS) or limiting the entry of inflammatory immune cells into the brain and re-establishing CNS homeostasis.

Influence of Guanine-Based Purines on the Oxidoreductive Reactions Involved in Normal or Altered Brain Functions

The production of reactive oxygen species (ROS) in the brain is homeostatically controlled and contributes to normal neural functions. Inefficiency of control mechanisms in brain aging or pathological conditions leads to ROS overproduction with oxidative neural cell damage and degeneration. Among the compounds showing therapeutic potential against neuro-dysfunctions induced by oxidative stress are the guanine-based purines (GBPs), of which the most characterized are the nucleoside guanosine (GUO) and the nucleobase guanine (GUA), which act differently. Indeed, the administration of GUO to in vitro or in vivo models of acute brain injury (ischemia/hypoxia or trauma) or chronic neurological/neurodegenerative disorders, exerts neuroprotective and anti-inflammatory effects, decreasing the production of reactive radicals and improving mitochondrial function via multiple molecular signals. However, GUO administration to rodents also causes an amnesic effect. In contrast, the metabolite, GUA, could be effective in memory-related disorders by transiently increasing ROS production and stimulating the nitric oxide/soluble guanylate cyclase/cGMP/protein kinase G cascade, which has long been recognized as beneficial for cognitive function. Thus, it is worth pursuing further studies to ascertain the therapeutic role of GUO and GUA and to evaluate the pathological brain conditions in which these compounds could be more usefully used.

Purine nucleoside phosphorylase as a target to treat age-associated lower urinary tract dysfunction

The lower urinary tract (LUT), including the bladder, urethra and external striated muscle, becomes dysfunctional with age; consequently, many older individuals suffer from lower urinary tract disorders (LUTDs). By compromising urine storage and voiding, LUTDs degrade quality of life for millions of individuals worldwide. Treatments for LUTDs have been disappointing, frustrating both patients and their physicians; however, emerging evidence suggests that partial inhibition of the enzyme purine nucleoside phosphorylase (PNPase) with 8-aminoguanine (an endogenous PNPase inhibitor that moderately reduces PNPase activity) reverses age-associated defects in the LUT and restores the LUT to that of a younger state. Thus, 8-aminoguanine improves LUT biochemistry, structure and function by rebalancing the LUT purine metabolome, making 8-aminoguanine a novel potential treatment for LUTDs.

Amauroderma rugosum Extract Suppresses Inflammatory Responses in Tumor Necrosis Factor Alpha/Interferon Gamma-Induced HaCaT Keratinocytes

Keratinocytes form the physical barrier of the skin and play an important role in the inflammatory process. Amauroderma rugosum is an edible mushroom; however, its pharmacological properties have seldom been studied. Although the anti-inflammatory effect of the organic solvent extract of Amauroderma rugosum has been previously reported, it is not known whether the aqueous extract has a similar effect. In addition, the effect of Amauorderma rugosum extract on skin has never been explored. Therefore, the objectives of the present study were to evaluate the anti-inflammatory effects of the aqueous extract of Amauroderma rugosum on HaCaT keratinocytes, to explore its mechanisms of action, and to study the possible active ingredients involved. The results showed that the aqueous extract of Amauroderm rugosum at a concentration of 1.5 mg/mL was non-toxic to HaCaT cells and inhibited the release of cytokine interleukin-1β, and chemokines interleukin-8 and monocyte chemoattractant protein-1 in tumor necrosis factor (TNF)-α- and interferon (IFN)-γ-stimulated HaCaT cells. Amauroderma rugosum extract reduced the intracellular levels of reactive oxygen species. In addition, Amauroderma rugosum extract reduced the total protein expression of nuclear factor-kappa B (NF-κB) and B-cells inhibitor alpha in HaCaT keratinocytes and inhibited the phosphorylation of mitogen-activated protein kinase kinase (MEK) 1/2, extracellular signal-regulated kinase (ERK) 1/2, protein kinase B (Akt), and mammalian target of rapamycin (mTOR) in TNF-α- and INF-γ-stimulated HaCaT keratinocytes. Chemical analysis revealed that the aqueous extract of Amauroderma rugosum contains polysaccharides, triterpenes, and phenolic compounds. Anti-inflammatory compounds, such as gallic acid, guanosine, and uridine, were also present. The anti-inflammatory effect of Amauroderma rugosum could be mimicked by a combination of gallic acid, guanosine, and uridine. In conclusion, our study suggests that the aqueous extract of Amauroderma rugosum exerts anti-inflammatory effects on keratinocytes through its antioxidant and inhibitory effects on MEK/ERK-, Akt/mTOR-, and NF-κB-dependent signaling pathways.

Guanosine as a promising target for fast-acting antidepressant responses

Although the rapid-onset and sustained antidepressant responses elicited by ketamine have gained considerable attention in recent years, it has some knock-on effects that limit its widespread clinical use. Therefore, ketamine is considered the prototype for the new generation of glutamate-based rapid-acting antidepressants. Within this context, it has been demonstrated that guanosine, an endogenous guanine-based purine, has overlapping mechanisms of action with ketamine and is effective in eliciting fast antidepressant-like responses and even potentiating ketamine's actions in preclinical studies. Here, we review the recent findings regarding the ability of guanosine to produce rapid-acting antidepressant-like effects and we provide an overview of the molecular mechanisms underlying its antidepressant-like actions. Moreover, the neurobiological mechanisms underpinning the ability of guanosine in boosting the antidepressant-like and pro-synaptogenic effects elicited by ketamine are also reported. Taken together, this review opens perspectives for the use of guanosine alone or in combination with ketamine for the management of treatment-resistant depression.

Metabolomic Profiling Analysis of Physiological Responses to Acute Hypoxia and Reoxygenation in Juvenile Qingtian Paddy Field Carp Cyprinus Carpio Var Qingtianensis

The Qingtian paddy field carp (Cyprinus carpio var qingtianensis) is a local carp cultivated in the rice field of Qingtian county, Zhejiang province, China. The paddy field environment is distinct from the pond environment. Due to the inability to artificially increase oxygen, the dissolved oxygen greatly changes during the day. Therefore, investigating the physiological regulation to the changes of acute dissolved oxygen in Qingtian paddy field carp (PF-carp) will dramatically clarify how it adapts to the paddy breeding environment. The high tolerance of Qingtian paddy field carp to hypoxia makes it an ideal organism for studying molecular regulatory mechanisms during hypoxia process and reoxygenation following hypoxia in fish. In this study, we compared the changes of metabolites in the hepatopancreas during hypoxia stress and the following reoxygenation through comparative metabolomics. The results showed 131 differentially expressed metabolites between the hypoxic groups and control groups. Among them, 95 were up-regulated, and 36 were down-regulated. KEGG Pathway enrichment analysis showed that these differential metabolites were mainly involved in regulating lipid, protein, and purine metabolism PF-carps could require energy during hypoxia by enhancing the gluconeogenesis pathway with core glutamic acid and glutamine metabolism. A total of 63 differentially expressed metabolites were screened by a comparison between the reoxygenated groups and the hypoxic groups. Specifically, 15 were up-regulated, and 48 were down-regulated. The KEGG Pathway enrichment analysis supported that PF-carp could continue to gain energy by consuming glutamic acid and the glutamine accumulated during hypoxia and simultaneously weaken the ammonia-transferring effect of amino acids and the toxicity of ammonia. By consuming glycerophospholipids and maintaining the Prostaglandin E content, cell damage was improved, sphingosinol synthesis was reduced, and apoptosis was inhibited. Additionally, it could enhance the salvage synthesis and de novo synthesis of purine, reduce purine accumulation, promote the synthesis of nucleotide and energy carriers, and assist in recovering physiological metabolism. Overall, results explained the physiological regulation mechanism of PF-carp adapting to the acute changes of dissolved oxygen at the metabolic level and also provided novel evidence for physiological regulation of other fish in an environment with acute changes in dissolved oxygen levels.

System-level investigation of anti-obesity effects and the potential pathways of Cordyceps militaris in ovariectomized rats

BACKGROUND

Cordyceps species have been used as tonics to enhance energy, stamina, and libido in traditional Asian medicine for more than 1600 years, indicating their potential for improving reproductive hormone disorders and energy metabolic diseases. Among Cordyceps, Cordyceps militaris has been reported to prevent metabolic syndromes including obesity and benefit the reproductive hormone system, suggesting that Cordyceps militaris can also regulate obesity induced by the menopause. We investigated the effectiveness of Cordyceps militaris extraction (CME) on menopausal obesity and its mechanisms.

METHODS

We applied an approach combining in vivo, in vitro, and in silico methods. Ovariectomized rats were administrated CME, and their body weight, area of adipocytes, liver and uterus weight, and lipid levels were measured. Next, after the exposure of MCF-7 human breast cancer cells to CME, cell proliferation and the phosphorylation of estrogen receptor and mitogen-activated protein kinases (MAPK) were measured. Finally, network pharmacological methods were applied to predict the anti-obesity mechanisms of CME.

RESULTS

CME prevented overweight, fat accumulation, liver hypertrophy, and lowered triglyceride levels, some of which were improved in a dose-dependent manner. In MCF-7 cell lines, CME showed not only estrogen receptor agonistic activity through an increase in cell proliferation and the phosphorylation of estrogen receptors, but also phosphorylation of extracellular-signal-regulated kinase and p38. In the network pharmacological analysis, bioactive compounds of CME such as cordycepin, adenine, and guanosine were predicted to interact with non-overlapping genes. The targeted genes were related to the insulin signaling pathway, insulin resistance, the MARK signaling pathway, the PI3K-Akt signaling pathway, and the estrogen signaling pathway.

CONCLUSIONS

These results suggest that CME has anti-obesity effects in menopause and estrogenic agonistic activity. Compounds in CME have the potential to regulate obesity-related and menopause-related pathways. This study will contribute to developing the understanding of anti-obesity effects and mechanisms of Cordyceps militaris.

Functional Recovery Caused by Human Adipose Tissue Mesenchymal Stem Cell-Derived Extracellular Vesicles Administered 24 h after Stroke in Rats

Ischemic stroke is a major cause of death and disability, intensely demanding innovative and accessible therapeutic strategies. Approaches presenting a prolonged period for therapeutic intervention and new treatment administration routes are promising tools for stroke treatment. Here, we evaluated the potential neuroprotective properties of nasally administered human adipose tissue mesenchymal stem cell (hAT-MSC)-derived extracellular vesicles (EVs) obtained from healthy individuals who underwent liposuction. After a single intranasal EV (200 µg/kg) administered 24 h after a focal permanent ischemic stroke in rats, a higher number of EVs, improvement of the blood-brain barrier, and re-stabilization of vascularization were observed in the recoverable peri-infarct zone, as well as a significant decrease in infarct volume. In addition, EV treatment recovered long-term motor (front paws symmetry) and behavioral impairment (short- and long-term memory and anxiety-like behavior) induced by ischemic stroke. In line with these findings, our work highlights hAT-MSC-derived EVs as a promising therapeutic strategy for stroke.

Neuroprotective Effects of Guanosine in Ischemic Stroke-Small Steps towards Effective Therapy

Guanosine (Guo) is a nucleotide metabolite that acts as a potent neuromodulator with neurotrophic and regenerative properties in neurological disorders. Under brain ischemia or trauma, Guo is released to the extracellular milieu and its concentration substantially raises. In vitro studies on brain tissue slices or cell lines subjected to ischemic conditions demonstrated that Guo counteracts destructive events that occur during ischemic conditions, e.g., glutaminergic excitotoxicity, reactive oxygen and nitrogen species production. Moreover, Guo mitigates neuroinflammation and regulates post-translational processing. Guo asserts its neuroprotective effects via interplay with adenosine receptors, potassium channels, and excitatory amino acid transporters. Subsequently, guanosine activates several prosurvival molecular pathways including PI3K/Akt (PI3K) and MEK/ERK. Due to systemic degradation, the half-life of exogenous Guo is relatively low, thus creating difficulty regarding adequate exogenous Guo distribution. Nevertheless, in vivo studies performed on ischemic stroke rodent models provide promising results presenting a sustained decrease in infarct volume, improved neurological outcome, decrease in proinflammatory events, and stimulation of neuroregeneration through the release of neurotrophic factors. In this comprehensive review, we discuss molecular signaling related to Guo protection against brain ischemia. We present recent advances, limitations, and prospects in exogenous guanosine therapy in the context of ischemic stroke.

Neuroinflammation in Ischemic Stroke: Inhibition of cAMP-Specific Phosphodiesterases (PDEs) to the Rescue

Ischemic stroke is caused by a thromboembolic occlusion of a major cerebral artery, with the impaired blood flow triggering neuroinflammation and subsequent neuronal damage. Both the innate immune system (e.g., neutrophils, monocytes/macrophages) in the acute ischemic stroke phase and the adaptive immune system (e.g., T cells, B cells) in the chronic phase contribute to this neuroinflammatory process. Considering that the available therapeutic strategies are insufficiently successful, there is an urgent need for novel treatment options. It has been shown that increasing cAMP levels lowers neuroinflammation. By inhibiting cAMP-specific phosphodiesterases (PDEs), i.e., PDE4, 7, and 8, neuroinflammation can be tempered through elevating cAMP levels and, thereby, this can induce an improved functional recovery. This review discusses recent preclinical findings, clinical implications, and future perspectives of cAMP-specific PDE inhibition as a novel research interest for the treatment of ischemic stroke. In particular, PDE4 inhibition has been extensively studied, and is promising for the treatment of acute neuroinflammation following a stroke, whereas PDE7 and 8 inhibition more target the T cell component. In addition, more targeted PDE4 gene inhibition, or combined PDE4 and PDE7 or 8 inhibition, requires more extensive research.

Guanosine and uridine alleviate airway inflammation via inhibition of the MAPK and NF-κB signals in OVA-induced asthmatic mice

Asthma is one of the most common respiratory diseases. Lack of response or poor adherence to corticosteroids demands the development of new drug candidates for asthma. Endogenous nucleosides could be potential options since uridine has been reported to have an anti-inflammatory effect in asthma model. However, its molecular pathways and whether other nucleosides have similar therapeutic effects remain untouched. Thus, we herein report our investigation into the anti-inflammatory effects of guanosine and uridine, and the related inner signaling pathways in asthma model. Present study shows that administration of guanosine or uridine can reduce lung inflammation in OVA-challenged mice. Total cell counts in BALF, cytokines such as IL-4, IL-6, IL-13, OVA-specific IgE and mRNA level of Cxcl1, Cxlc3, IL-17 and Muc5ac were decreased in asthmatic mice after treatment. Besides, the production of IL-6 in LPS/IFN-γ induced THP-1 cells was also decreased by both nucleosides. In vivo and in vitro expressions of key molecules in the MAPK and NF-κB pathways were reduced after the treatment of both compounds. These findings suggest that guanosine has a similar potential therapeutic value in asthma as uridine and they exert anti-inflammatory effects through suppression of the MAPK and NF-κB pathways.

Purines and Pyrimidines: Metabolism, Function and Potential as Therapeutic Options in Neurodegenerative Diseases

Various neurodegenerative disorders have various molecular origins but some common molecular mechanisms. In the current scenario, there are very few treatment regimens present for advanced neurodegenerative diseases. In this context, there is an urgent need for alternate options in the form of natural compounds with an ameliorating effect on patients. There have been individual scattered experiments trying to identify potential values of various intracellular metabolites. Purines and Pyrimidines, which are vital molecules governing various aspects of cellular biochemical reactions, have been long sought as crucial candidates for the same, but there are still many questions that go unanswered. Some critical functions of these molecules associated with neuromodulation activities have been identified. They are also known to play a role in foetal neurodevelopment, but there is a lacuna in understanding their mechanisms. In this review, we have tried to assemble and identify the importance of purines and pyrimidines, connecting them with the prevalence of neurodegenerative diseases. The leading cause of this class of diseases is protein misfolding and the formation of amyloids. A direct correlation between loss of balance in cellular homeostasis and amyloidosis is yet an unexplored area. This review aims at bringing the current literature available under one umbrella serving as a foundation for further extensive research in this field of drug development in neurodegenerative diseases.

Effects of intranasal guanosine administration on brain function in a rat model of ischemic stroke

Ischemic stroke is a major cause of morbidity and mortality worldwide and only few affected patients are able to receive treatment, especially in developing countries. Detailed pathophysiology of brain ischemia has been extensively studied in order to discover new treatments with a broad therapeutic window and that are accessible to patients worldwide. The nucleoside guanosine (Guo) has been shown to have neuroprotective effects in animal models of brain diseases, including ischemic stroke. In a rat model of focal permanent ischemia, systemic administration of Guo was effective only when administered immediately after stroke induction. In contrast, intranasal administration of Guo (In-Guo) was effective even when the first administration was 3 h after stroke induction. In order to validate the neuroprotective effect in this larger time window and to investigate In-Guo neuroprotection under global brain dysfunction induced by ischemia, we used the model of thermocoagulation of pial vessels in Wistar rats. In our study, we have found that In-Guo administered 3 h after stroke was capable of preventing ischemia-induced dysfunction, such as bilateral suppression and synchronicity of brain oscillations and ipsilateral cell death signaling, and increased permeability of the blood-brain barrier. In addition, In-Guo had a long-lasting effect on preventing ischemia-induced motor impairment. Our data reinforce In-Guo administration as a potential new treatment for brain ischemia with a more suitable therapeutic window.

Guanosine modulates SUMO2/3-ylation in neurons and astrocytes via adenosine receptors

SUMOylation is a post-translational modification (PTM) whereby members of the Small Ubiquitin-like MOdifier (SUMO) family of proteins are conjugated to lysine residues in target proteins. SUMOylation has been implicated in a wide range of physiological and pathological processes, and much attention has been given to its role in neurodegenerative conditions. Due to its reported role in neuroprotection, pharmacological modulation of SUMOylation represents an attractive potential therapeutic strategy in a number of different brain disorders. However, very few compounds that target the SUMOylation pathway have been identified. Guanosine is an endogenous nucleoside with important neuromodulatory and neuroprotective effects. Experimental evidence has shown that guanosine can modulate different intracellular pathways, including PTMs. In the present study we examined whether guanosine alters global protein SUMOylation. Primary cortical neurons and astrocytes were treated with guanosine at 1, 10, 100, 300, or 500 μM at four time points, 1, 6, 24, or 48 h. We show that guanosine increases global SUMO2/3-ylation in neurons and astrocytes at 1 h at concentrations above 10 μM. The molecular mechanisms involved in this effect were evaluated in neurons. The guanosine-induced increase in global SUMO2/3-ylation was still observed in the presence of dipyridamole, which prevents guanosine internalization, demonstrating an extracellular guanosine-induced effect. Furthermore, the A1 adenosine receptor antagonist DPCPX abolished the guanosine-induced increase in SUMO2/3-ylation. The A2A adenosine receptor antagonist ZM241385 increased SUMOylation per se, but did not alter guanosine-induced SUMOylation, suggesting that guanosine may modulate SUMO2/3-ylation through an A1-A2A receptor interaction. Taken together, this is the first report to show guanosine as a SUMO2/3-ylation enhancer in astrocytes and neurons.

Guanosine enhances glutamate uptake and oxidation, preventing oxidative stress in mouse hippocampal slices submitted to high glutamate levels

Glutamate (Glu) is the main mammalian brain neurotransmitter. Concerning the glutamatergic neurotransmission, excessive levels of glutamate in the synaptic cleft are extremally harmful. This phenomenon, named as excitotoxicity is involved in various acute and chronic brain diseases. Guanosine (GUO), an endogenous guanine nucleoside, possesses neuroprotective effects in several experimental models of glutamatergic excitotoxicity, an effect accompanied by an increase in astrocytic glutamate uptake. Therefore, the objective of this study was to investigate the involvement of an additional putative parameter, glutamate oxidation to CO₂, involved in ex-vivo GUO neuroprotective effects in mouse hippocampal slices submitted to glutamatergic excitotoxicity. Mice were sacrificed by decapitation, the hippocampi were removed and sliced. The slices were incubated for various times and concentrations of Glu and GUO. First, the concentration of Glu that produced an increase in L-[¹⁴C(U)]-Glu oxidation to CO₂ without cell injury was determined at different time points (between 0 and 90 min); 1000 μM Glu increased Glu oxidation between 30 and 60 min of incubation without cell injury. Under these conditions (Glu concentration and incubation time), 100 μM GUO increased Glu oxidation (35%). Additionally, 100 μM GUO increased L-[3,4-3H]-glutamate uptake (45%) in slices incubated with 1000 μM Glu (0-30 min). Furthermore, 1000  μM Glu increased reactive species levels, SOD activity, and decreased GPx activity, and GSH content after 30 and 60 min; 100 μM GUO prevented these effects. This is the first study demonstrating that GUO simultaneously promoted an increase in the uptake and utilization of Glu in excitotoxicity-like conditions preventing redox imbalance.

Ethanol extracts from Ilex pubescens promotes cerebral ischemic tolerance via modulation of TLR4-MyD88/TRIF signaling pathway in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Pubescent Holly Root is the dry root of Ilex pubescens Hook. et Arn. It is clinically using in the treatment for stroke and coronary artery disease. It remains unclear whether the ethanol extracts of Ilex pubescens(IPEE) treatment can promote cerebral ischemic tolerance (CIT) and exert endogenous neuroprotective effects and thus to alleviate the nerve injury caused by the subsequent persistent cerebral ischemic attacks.

AIM OF THE STUDY

To investigate the effects of IPEE on CIT and its underlying molecular mechanisms.

MATERIALS AND METHODS

Adult male Wistar rats were used in the present study. The bilateral common carotid arteries were blocked for 10 min followed a subsequent reperfusion to create the cerebral ischemic preconditioning (CIP); After 3 days post CIP, rats were subjected to middle cerebral artery occlusion/reperfusion (MCAO/R)-injury. Rats were continuously fed with IPEE for 5 days throughout the experiment period at the dose of 100 mg/kg and 200 mg/kg, respectively. Then, the brain infarct volume, histopathology, neurological deficits, and the gene/protein expression related with the TLR4-MyD88/TRIF signaling pathway were evaluated after 24 h of MCAO/R experiment.

RESULTS

IPEE pretreatment significantly reduced the cerebral infarct volume, the neurological deficit scores, and the plasma level of neuron specific enolase (NSE) at the dose of 100 mg/kg. Meanwhile, IPEE pretreatment significantly decreased the levels of inflammatory cytokines including TNF-α, IL-6, MCP-1, MIP-1α and RANTES, while it increased the levels of anti-inflammatory cytokines, such as IL-10 and TGF-β, when compared with the group with CIP treatment alone. Moreover, the effect of IPEE treatment on CIT was in a dose-dependent manner, showing as a better effect in the group pretreated with IPEE with the dose of 100 mg/kg than that in group pretreated with IPEE with the dose of 200 mg/kg. In addition, IPEE pretreatment significantly inhibited the expressions of MyD88 mRNA and the protein expression of COX-2 and NF-κBp65, while it strengthened the expressions of TRIF mRNA and protein. The effects of IPEE pretreatment on the expression of these genes were better than that in the group treated with CIP alone.

CONCLUSIONS

The present study demonstrates that IPEE pretreatment can enhance cerebral ischemic tolerance with a underlying mechanism involved in the toll-like receptor 4 (TLR4) signaling pathway through inhibiting the production of proteins or cytokines in the downstream of MyD88 and activating TRIF dependent anti-inflammatory pathways.

Adenosine A1-A2A Receptor-Receptor Interaction: Contribution to Guanosine-Mediated Effects

Guanosine, a guanine-based purine nucleoside, has been described as a neuromodulator that exerts neuroprotective effects in animal and cellular ischemia models. However, guanosine's exact mechanism of action and molecular targets have not yet been identified. Here, we aimed to elucidate a role of adenosine receptors (ARs) in mediating guanosine effects. We investigated the neuroprotective effects of guanosine in hippocampal slices from A2AR-deficient mice (A2AR-/-) subjected to oxygen/glucose deprivation (OGD). Next, we assessed guanosine binding at ARs taking advantage of a fluorescent-selective A2AR antagonist (MRS7396) which could engage in a bioluminescence resonance energy transfer (BRET) process with NanoLuc-tagged A2AR. Next, we evaluated functional AR activation by determining cAMP and calcium accumulation. Finally, we assessed the impact of A1R and A2AR co-expression in guanosine-mediated impedance responses in living cells. Guanosine prevented the reduction of cellular viability and increased reactive oxygen species generation induced by OGD in hippocampal slices from wild-type, but not from A2AR-/- mice. Notably, while guanosine was not able to modify MRS7396 binding to A2AR-expressing cells, a partial blockade was observed in cells co-expressing A1R and A2AR. The relevance of the A1R and A2AR interaction in guanosine effects was further substantiated by means of functional assays (i.e., cAMP and calcium determinations), since guanosine only blocked A2AR agonist-mediated effects in doubly expressing A1R and A2AR cells. Interestingly, while guanosine did not affect A1R/A2AR heteromer formation, it reduced A2AR agonist-mediated cell impedance responses. Our results indicate that guanosine-induced effects may require both A1R and A2AR co-expression, thus identifying a molecular substrate that may allow fine tuning of guanosine-mediated responses.

Guanosine prevents oxidative damage and glutamate uptake impairment induced by oxygen/glucose deprivation in cortical astrocyte cultures: involvement of A1 and A2A adenosine receptors and PI3K, MEK, and PKC pathways

Glial cells are involved in multiple cerebral functions that profoundly influence brain tissue viability during ischemia, and astrocytes are the main source of extracellular purines as adenosine and guanosine. The endogenous guanine-based nucleoside guanosine is a neuromodulator implicated in important processes in the brain, such as modulation of glutamatergic transmission and protection against oxidative and inflammatory damage. We evaluated if the neuroprotective effect of guanosine is also observed in cultured cortical astrocytes subjected to oxygen/glucose deprivation (OGD) and reoxygenation. We also assessed the involvement of A₁ and A_2A adenosine receptors and phosphatidylinositol-3 kinase (PI3K), MAPK, and protein kinase C (PKC) signaling pathways on the guanosine effects. OGD/reoxygenation decreased cell viability and glutamate uptake and increased reactive oxygen species (ROS) production in cultured astrocytes. Guanosine treatment prevented these OGD-induced damaging effects. Dipropyl-cyclopentyl-xanthine (an adenosine A₁ receptor antagonist) and 4-[2-[[6-amino-9-(N-ethyl-β-D-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl] benzenepropanoic acid hydrochloride (an adenosine A_2A receptor agonist) abolished guanosine-induced protective effects on ROS production, glutamate uptake, and cell viability. The PI3K pathway inhibitor 2-morpholin-4-yl-8-phenylchromen-4-one, the extracellular-signal regulated kinase kinase (MEK) inhibitor 2'-amino-3'-methoxyflavone, or the PKC inhibitor chelerythrine abolished the guanosine effect of preventing OGD-induced cells viability reduction. PI3K inhibition partially prevented the guanosine effect of reducing ROS production, whereas MEK and PKC inhibitions prevented the guanosine effect of restoring glutamate uptake. The total immunocontent of the main astrocytic glutamate transporter glutamate transporter-1 (GLT-1) was not altered by OGD and guanosine. However, MEK and PKC inhibitions also abolished the guanosine effect of increasing cell-surface expression of GLT-1 in astrocytes subjected to OGD. Then, guanosine prevents oxidative damage and stimulates astrocytic glutamate uptake during ischemic events via adenosine A₁ and A_2A receptors and modulation of survival signaling pathways, contributing to microenvironment homeostasis that culminates in neuroprotection.

2',3'-cGMP exists in vivo and comprises a 2',3'-cGMP-guanosine pathway

The discovery in 2009 that 2',3'-cAMP exists in biological systems was rapidly followed by identification of 2',3'-cGMP in cell and tissue extracts. To determine whether 2',3'-cGMP exists in mammals under physiological conditions, we used ultraperformance LC-MS/MS to measure 2',3'-cAMP and 2',3'-cGMP in timed urine collections (via direct bladder cannulation) from 25 anesthetized mice. Urinary excretion rates (means ± SE) of 2',3'-cAMP (15.5 ± 1.8 ng/30 min) and 2',3'-cGMP (17.9 ± 1.9 ng/30 min) were similar. Mice also excreted 2'-AMP (3.6 ± 1.1 ng/20 min) and 3'-AMP (9.5 ± 1.2 ng/min), hydrolysis products of 2',3'-cAMP, and 2'-GMP (4.7 ± 1.7 ng/30 min) and 3'-GMP (12.5 ± 1.8 ng/30 min), hydrolysis products of 2',3'-cGMP. To validate that the chromatographic signals were from these endogenous noncanonical nucleotides, we repeated these experiments in mice (n = 18) lacking 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), an enzyme known to convert 2',3'-cyclic nucleotides to their corresponding 2'-nucleotides. In CNPase-knockout mice, urinary excretions of 2',3'-cAMP, 3'-AMP, 2',3'-cGMP, and 3'-GMP were increased, while urinary excretions of 2'-AMP and 2'-GMP were decreased. Infusions of exogenous 2',3'-cAMP increased urinary excretion of 2',3'-cAMP, 2'-AMP, 3'-AMP, and adenosine, whereas infusions of exogenous 2',3'-cGMP increased excretion of 2',3'-cGMP, 2'-GMP, 3'-GMP, and guanosine. Together, these data suggest the endogenous existence of not only a 2',3'-cAMP-adenosine pathway (2',3'-cAMP → 2'-AMP/3'-AMP → adenosine), which was previously identified, but also a 2',3'-cGMP-guanosine pathway (2',3'-cGMP → 2'-GMP/3'-GMP → guanosine), observed here for the first time. Because it is well known that adenosine and guanosine protect tissues from injury, our data support the concept that both pathways may work together to protect tissues from injury.

Glutamate Transport and Preterm Brain Injury

Preterm birth complications are the leading cause of child death worldwide and a top global health priority. Among the survivors, the risk of life-long disabilities is high, including cerebral palsy and impairment of movement, cognition, and behavior. Understanding the molecular mechanisms of preterm brain injuries is at the core of future healthcare improvements. Glutamate excitotoxicity is a key mechanism in preterm brain injury, whereby the accumulation of extracellular glutamate damages the delicate immature oligodendrocytes and neurons, leading to the typical patterns of injury seen in the periventricular white matter. Glutamate excitotoxicity is thought to be induced by an interaction between environmental triggers of injury in the perinatal period, particularly cerebral hypoxia-ischemia and infection/inflammation, and developmental and genetic vulnerabilities. To avoid extracellular build-up of glutamate, the brain relies on rapid uptake by sodium-dependent glutamate transporters. Astrocytic excitatory amino acid transporter 2 (EAAT2) is responsible for up to 95% of glutamate clearance, and several lines of evidence suggest that it is essential for brain functioning. While in the adult EAAT2 is predominantly expressed by astrocytes, EAAT2 is transiently upregulated in the immature oligodendrocytes and selected neuronal populations during mid-late gestation, at the peak time for preterm brain injury. This developmental upregulation may interact with perinatal hypoxia-ischemia and infection/inflammation and contribute to the selective vulnerability of the immature oligodendrocytes and neurons in the preterm brain. Disruption of EAAT2 may involve not only altered expression but also impaired function with reversal of transport direction. Importantly, elevated EAAT2 levels have been found in the reactive astrocytes and macrophages of human infant post-mortem brains with severe white matter injury (cystic periventricular leukomalacia), potentially suggesting an adaptive mechanism against excitotoxicity. Interestingly, EAAT2 is suppressed in animal models of acute hypoxic-ischemic brain injury at term, pointing to an important and complex role in newborn brain injuries. Enhancement of EAAT2 expression and transport function is gathering attention as a potential therapeutic approach for a variety of adult disorders and awaits exploration in the context of the preterm brain injuries.

Subsecond detection of guanosine using fast-scan cyclic voltammetry

Guanosine is an important neuromodulator and neuroprotector in the brain and is involved in many pathological conditions, including ischemia and neuroinflammation. Traditional methods to detect guanosine in the brain, like HPLC, offer low limits of detection and are robust; however, subsecond detection is not possible. Here, we present a method for detecting rapid fluctuations of guanosine concentration in real-time using fast-scan cyclic voltammetry (FSCV) at carbon-fiber microelectrodes. The optimized waveform scanned from -0.4 V to 1.3 V and back at a rate of 400 V s-1 and application frequency of 10 Hz. Potential limits were chosen to increase selectivity of guanosine over the structurally similar interferent adenosine. Two oxidation peaks were detected with the optimized waveform: the primary oxidation reaction occurred at 1.3 V and the secondary oxidation at 0.8 V. Guanosine detection was stable over time with a limit of detection of 30 ± 10 nM, which permits its use to monitor low nanomolar fluctuations in the brain. To demonstrate the feasibility of the method for in-tissue detection, guanosine was exogenously applied and detected within live rat brain slices. This paper demonstrates the first characterization of guanosine using FSCV, and will be a valuable method for measuring signaling dynamics during guanosine neuromodulation and protection.

Novel Targets for Fast Antidepressant Responses: Possible Role of Endogenous Neuromodulators

The available medications for the treatment of major depressive disorder have limitations, particularly their limited efficacy, delayed therapeutic effects, and the side effects associated with treatment. These issues highlight the need for better therapeutic agents that provide more efficacious and faster effects for the management of this disorder. Ketamine, an N-methyl-D-aspartate receptor antagonist, is the prototype for novel glutamate-based antidepressants that has been shown to cause a rapid and sustained antidepressant effect even in severe refractory depressive patients. Considering the importance of these findings, several studies have been conducted to elucidate the molecular targets for ketamine's effect. In addition, efforts are under way to characterize ketamine-like drugs. This review focuses particularly on evidence that endogenous glutamatergic neuromodulators may be able to modulate mood and to elicit fast antidepressant responses. Among these molecules, agmatine and creatine stand out as those with more published evidence of similarities with ketamine, but guanosine and ascorbic acid have also provided promising results. The possibility that these neuromodulators and ketamine have common neurobiological mechanisms, mainly the ability to activate mechanistic target of rapamycin and brain-derived neurotrophic factor signaling, and synthesis of synaptic proteins in the prefrontal cortex and/or hippocampus is presented and discussed.

Neuromodulatory Effects of Guanine-Based Purines in Health and Disease

The function of guanine-based purines (GBPs) is mostly attributed to the intracellular modulation of heteromeric and monomeric G proteins. However, extracellular effects of guanine derivatives have also been recognized. Thus, in the central nervous system (CNS), a guanine-based purinergic system that exerts neuromodulator effects, has been postulated. The thesis that GBPs are neuromodulators emerged from in vivo and in vitro studies, in which neurotrophic and neuroprotective effects of these kinds of molecules (i.e., guanosine) were demonstrated. GBPs induce several important biological effects in rodent models and have been shown to reduce seizures and pain, stabilize mood disorder behavior and protect against gliomas and diseases related with aging, such as ischemia or Parkinson and Alzheimer diseases. In vitro studies to evaluate the protective and trophic effects of guanosine, and of the nitrogenous base guanine, have been fundamental for understanding the mechanisms of action of GBPs, as well as the signaling pathways involved in their biological roles. Conversely, although selective binding sites for guanosine have been identified in the rat brain, GBP receptors have not been still described. In addition, GBP neuromodulation may depend on the capacity of GBPs to interact with well-known membrane proteins in glutamatergic and adenosinergic systems. Overall, in this review article, we present up-to-date GBP biology, focusing mainly on the mechanisms of action that may lead to the neuromodulator role of GBPs observed in neurological disorders.

Guanosine Attenuates Behavioral Deficits After Traumatic Brain Injury by Modulation of Adenosinergic Receptors

Traumatic brain injury (TBI) is a leading cause of disability worldwide, triggering chronic neurodegeneration underlying cognitive and mood disorder still without therapeutic prospects. Based on our previous observations that guanosine (GUO) attenuates short-term neurochemical alterations caused by TBI, this study investigated the effects of chronical GUO treatment in behavioral, molecular, and morphological disturbances 21 days after trauma. Rats subject to TBI displayed mood (anxiety-like) and memory dysfunction. This was accompanied by a decreased expression of both synaptic (synaptophysin) and plasticity proteins (BDNF and CREB), a loss of cresyl violet-stained neurons, and increased astrogliosis and microgliosis in the hippocampus. Notably, chronic GUO treatment (7.5 mg/kg i.p. daily starting 1 h after TBI) prevented all these TBI-induced long-term behavioral, neurochemical, and morphological modifications. This neuroprotective effect of GUO was abrogated in the presence of the adenosine A₁ receptor antagonist DPCPX (1 mg/kg) but unaltered by the adenosine A_2A receptor antagonist SCH58261 (0.05 mg/kg). These findings show that a chronic GUO treatment prevents the long-term mood and memory dysfunction triggered by TBI, which involves adenosinergic receptors.

Neuroprotective Effects of Guanosine Administration on In Vivo Cortical Focal Ischemia in Female and Male Wistar Rats

Guanosine (GUO) has neuroprotective effects in experimental models of brain diseases involving glutamatergic excitotoxicity in male animals; however, its effects in female animals are poorly understood. Thus, we investigated the influence of gender and GUO treatment in adult male and female Wistar rats submitted to focal permanent cerebral ischemia in the motor cortex brain. Female rats were subdivided into non-estrogenic and estrogenic phase groups by estrous cycle verification. Immediately after surgeries, the ischemic animals were treated with GUO or a saline solution. Open field and elevated plus maze tasks were conducted with ischemic and naïve animals. Cylinder task, immunohistochemistry and infarct volume analyses were conducted only with ischemic animals. Female GUO groups achieved a full recovery of the forelimb symmetry at 28-35 days after the insult, while male GUO groups only partially recovered at 42 days, in the final evaluation. The ischemic insult affected long-term memory habituation to novelty only in female groups. Anxiety-like behavior, astrocyte morphology and infarct volume were not affected. Regardless the estrous cycle, the ischemic injury affected differently female and male animals. Thus, this study points that GUO is a potential neuroprotective compound in experimental stroke and that more studies, considering the estrous cycle, with both genders are recommended in future investigation concerning brain diseases.

Neuroprotective effect of total flavonoids from Ilex pubescens against focal cerebral ischemia/reperfusion injury in rats

Ilex pubescens is commonly used in traditional Chinese medicine to treat cardiovascular and cerebrovascular diseases, such as coronary artery disease and stroke. However, the underlying mechanisms remain to be fully elucidated. The aim of the present study was to investigate the effects of Ilex pubescens total flavonoids (IPTF) on neuroprotection and the potential mechanisms in a rat model of focal cerebral ischemia/reperfusion (I/R) injury. Rats were pretreated with intragastric administration of IPTF at doses of 200 and 100 mg/kg for 5 days; middle cerebral artery occlusion surgery was then performed to induce cerebral I/R injury. Neurological deficits were determined using the 5‑point neurological function score evaluation system, brain infarct sizes were determined by 2,3,5‑triphenyltetrazolium chloride staining and alterations in brain histology were determined by hematoxylin and eosin staining. The neurological deficit score, the infarcted area and the brain tissue pathological injury were significantly reduced when the rats were pretreated with IPTF. In addition, inflammatory mediators and neurotrophic factors in the brain were investigated. IPTF pretreatment decreased the activities of total nitric oxide synthase (TNOS), induced NOS (iNOS) and constitutive NOS (cNOS), and the levels of nitric oxide (NO), interleukin‑1β (IL‑1β) and tumor necrosis factor‑α (TNF‑α), however, it increased the levels of IL‑10 in brain tissues. Furthermore, pretreatment with IPTF also increased the protein expressions of brain‑derived neurotrophic factor, glial cell‑derived neurotrophic factor and vascular endothelial growth factor, when compared with the model group. In conclusion, the results of the present study demonstrated that IPTF has a neuroprotective effect against focal cerebral I/R injury in rats. The mechanism may be associated with the decreased production of certain proinflammatory cytokines including NO, IL‑1β, TNF‑α, TNOS, iNOS and cNOS, the increased production of the anti‑inflammatory cytokine IL‑10 and the increased secretion of neurotrophic factors.

Antiparkinsonian Efficacy of Guanosine in Rodent Models of Movement Disorder

Guanosine (GUO) is a guanine-based purine nucleoside with important trophic functions and promising neuroprotective properties. Although the neuroprotective effects of GUO have been corroborated in cellular models of Parkinson’s disease (PD), its efficacy as an antiparkinsonian agent has not been fully explored in PD animal models. Accordingly, we evaluated the effectiveness of GUO in reversing motor impairments in several rodent movement disorder models, including catalepsy, tremor, and hemiparkinsonism. Our results showed that orally administered GUO antagonized reserpine-mediated catalepsy, reduced reserpine-induced tremulous jaw movements, and potentiated the number of contralateral rotations induced by L-3,4-dihydroxyphenylalanine in unilaterally 6-hydroxidopamine-lesioned rats. In addition, at 5 and 7.5 mg/kg, GUO inhibited L-DOPA-induced dyskinesia in rats chronically treated with a pro-dopaminergic agent. Overall, we describe the therapeutic potential of GUO, which may be effective not only for reversing parkinsonian motor impairments but also for reducing dyskinesia induced by treatment for PD.

Delayed administration of guanosine improves long‑term functional recovery and enhances neurogenesis and angiogenesis in a mouse model of photothrombotic stroke

Guanosine (GUO) is neuroprotective when administered acutely for the treatment of cerebral ischemia. The aim of the present study was to investigate whether delayed administration of GUO improved long‑term functional recovery following stroke, as well as to explore the potential underlying mechanisms. GUO (8 mg/kg) or a vehicle was administered intraperitoneally for 7 consecutive days beginning 24 h prior to photothrombosis‑induced stroke in male C57/B6J mice. Behaviour tests were performed at days 1, 3, 7, 14 and 28 post‑stroke. Infarct volume was measured using Nissl staining at day 7 post‑stroke. Neurogenesis and angiogenesis were evaluated by co‑labelling bromodeoxyuridine (BrdU) with doublecortin (DCX), neuronal nuclei (NeuN) and von Willebrand factor, in immunohistochemical studies. Brain‑derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) levels in the ipsilesional brain at day 28 post‑stroke were detected by western blot analysis. Delayed administration of GUO did not reduce infarct volume or affect neurological function at day 7 post‑stroke; however, it did improve functional recovery from day 14 post‑stroke, when compared with the vehicle group. GUO significantly increased the number of BrdU+ and BrdU+/DCX+ cells in the subventricular zone and subgranular zone at all examined time points, the number of Brdu+/NeuN+ cells in the peri‑infarction region at days 14 and 28 post‑stroke and microvessel density in the peri‑infarction region at day 28 post‑stroke compared with the vehicle group. In addition, the BDNF and VEGF levels in the ipsilesional brain were significantly elevated. Delayed administration of GUO at 24 h post‑stroke enhanced neurogenesis and angiogenesis, and increased BDNF and VEGF levels, which likely contributes to long‑term functional recovery following stroke.

Cortical Bilateral Adaptations in Rats Submitted to Focal Cerebral Ischemia: Emphasis on Glial Metabolism

This study was performed to evaluate the bilateral effects of focal permanent ischemia (FPI) on glial metabolism in the cerebral cortex. Two and 9 days after FPI induction, we analyze [¹⁸F]FDG metabolism by micro-PET, astrocyte morphology and reactivity by immunohistochemistry, cytokines and trophic factors by ELISA, glutamate transporters by RT-PCR, monocarboxylate transporters (MCTs) by western blot, and substrate uptake and oxidation by ex vivo slices model. The FPI was induced surgically by thermocoagulation of the blood in the pial vessels of the motor and sensorimotor cortices in adult (90 days old) male Wistar rats. Neurochemical analyses were performed separately on both ipsilateral and contralateral cortical hemispheres. In both cortical hemispheres, we observed an increase in tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), and glutamate transporter 1 (GLT-1) mRNA levels; lactate oxidation; and glutamate uptake and a decrease in brain-derived neurotrophic factor (BDNF) after 2 days of FPI. Nine days after FPI, we observed an increase in TNF-α levels and a decrease in BDNF, GLT-1, and glutamate aspartate transporter (GLAST) mRNA levels in both hemispheres. Additionally, most of the unilateral alterations were found only in the ipsilateral hemisphere and persisted until 9 days post-FPI. They include diminished in vivo glucose uptake and GLAST expression, followed by increased glial fibrillary acidic protein (GFAP) gray values, astrocyte reactivity, and glutamate oxidation. Astrocytes presented signs of long-lasting reactivity, showing a radial morphology. In the intact hemisphere, there was a decrease in MCT2 levels, which did not persist. Our study shows the bilateralism of glial modifications following FPI, highlighting the role of energy metabolism adaptations on brain recovery post-ischemia.

Guanosine Protects Against Traumatic Brain Injury-Induced Functional Impairments and Neuronal Loss by Modulating Excitotoxicity, Mitochondrial Dysfunction, and Inflammation

Traumatic brain injury (TBI) is one of the most common types of brain injuries that cause death or persistent neurological disturbances in survivors. Most of the promising experimental drugs were not effective in clinical trials; therefore, the development of TBI drugs represents a huge unmet need. Guanosine, an endogenous neuroprotective nucleoside, has not been evaluated in TBI to the best of our knowledge. Therefore, the present study evaluated the effect of guanosine on TBI-induced neurological damage. Our findings showed that a single dose of guanosine (7.5 mg/kg, intraperitoneally (i.p.) injected 40 min after fluid percussion injury (FPI) in rats protected against locomotor and exploratory impairments 8 h after injury. The treatment also protected against neurochemical damage to the ipsilateral cortex, glutamate uptake, Na⁺/K⁺-ATPase, glutamine synthetase activity, and alterations in mitochondrial function. The inflammatory response and brain edema were also reduced by this nucleoside. In addition, guanosine protected against neuronal death and caspase 3 activation. Therefore, this study suggests that guanosine plays a neuroprotective role in TBI and can be exploited as a new pharmacological strategy.

Rodent Gymnastics: Neurobehavioral Assays in Ischemic Stroke

Despite years of research, most preclinical trials on ischemic stroke have remained unsuccessful owing to poor methodological and statistical standards leading to "translational roadblocks." Various behavioral tests have been established to evaluate traits such as sensorimotor function, cognitive and social interactions, and anxiety-like and depression-like behavior. A test's validity is of cardinal importance as it influences the chance of a successful translation of preclinical results to clinical settings. The mission of choosing a behavioral test for a particular project is, therefore, imperative and the present review aims to provide a structured way to evaluate rodent behavioral tests with implications in ischemic stroke.

Guanosine: a Neuromodulator with Therapeutic Potential in Brain Disorders

Guanosine is a purine nucleoside with important functions in cell metabolism and a protective role in response to degenerative diseases or injury. The past decade has seen major advances in identifying the modulatory role of extracellular action of guanosine in the central nervous system (CNS). Evidence from rodent and cell models show a number of neurotrophic and neuroprotective effects of guanosine preventing deleterious consequences of seizures, spinal cord injury, pain, mood disorders and aging-related diseases, such as ischemia, Parkinson’s and Alzheimer’s diseases. The present review describes the findings of in vivo and in vitro studies and offers an update of guanosine effects in the CNS. We address the protein targets for guanosine action and its interaction with glutamatergic and adenosinergic systems and with calcium-activated potassium channels. We also discuss the intracellular mechanisms modulated by guanosine preventing oxidative damage, mitochondrial dysfunction, inflammatory burden and modulation of glutamate transport. New and exciting avenues for future investigation into the protective effects of guanosine include characterization of a selective guanosine receptor. A better understanding of the neuromodulatory action of guanosine will allow the development of therapeutic approach to brain diseases.

Guanosine and its role in neuropathologies

Guanosine is a purine nucleoside thought to have neuroprotective properties. It is released in the brain under physiological conditions and even more during pathological events, reducing neuroinflammation, oxidative stress, and excitotoxicity, as well as exerting trophic effects in neuronal and glial cells. In agreement, guanosine was shown to be protective in several in vitro and/or in vivo experimental models of central nervous system (CNS) diseases including ischemic stroke, Alzheimer's disease, Parkinson's disease, spinal cord injury, nociception, and depression. The mechanisms underlying the neurobiological properties of guanosine seem to involve the activation of several intracellular signaling pathways and a close interaction with the adenosinergic system, with a consequent stimulation of neuroprotective and regenerative processes in the CNS. Within this context, the present review will provide an overview of the current literature on the effects of guanosine in the CNS. The elucidation of the complex signaling events underlying the biochemical and cellular effects of this nucleoside may further establish guanosine as a potential therapeutic target for the treatment of several neuropathologies.

The Guanine-Based Purinergic System: The Tale of An Orphan Neuromodulation

Guanine-based purines (GBPs) have been recently proposed to be not only metabolic agents but also extracellular signaling molecules that regulate important functions in the central nervous system. In such way, GBPs-mediated neuroprotection, behavioral responses and neuronal plasticity have been broadly described in the literature. However, while a number of these functions (i.e., GBPs neurothophic effects) have been well-established, the molecular mechanisms behind these GBPs-dependent effects are still unknown. Furthermore, no plasma membrane receptors for GBPs have been described so far, thus GBPs are still considered orphan neuromodulators. Interestingly, an intricate and controversial functional interplay between GBPs effects and adenosine receptors activity has been recently described, thus triggering the hypothesis that GBPs mechanism of action might somehow involve adenosine receptors. Here, we review recent data describing the GBPs role in the brain. We focus on the involvement of GBPs regulating neuronal plasticity, and on the new hypothesis based on putative GBPs receptors. Overall, we expect to shed some light on the GBPs world since although these molecules might represent excellent candidates for certain neurological diseases management, the lack of putative GBPs receptors precludes any high throughput screening intent for the search of effective GBPs-based drugs.

Guanosine Exerts Neuroprotective Effect in an Experimental Model of Acute Ammonia Intoxication

The nucleoside guanosine (GUO) increases glutamate uptake by astrocytes and acts as antioxidant, thereby providing neuroprotection against glutamatergic excitotoxicity, as we have recently demonstrated in an animal model of chronic hepatic encephalopathy. Here, we investigated the neuroprotective effect of GUO in an acute ammonia intoxication model. Adult male Wistar rats received an intraperitoneal (i.p.) injection of vehicle or GUO 60 mg/kg, followed 20 min later by an i.p. injection of vehicle or 550 mg/kg of ammonium acetate. Afterwards, animals were observed for 45 min, being evaluated as normal, coma (i.e., absence of corneal reflex), or death status. In a second cohort of rats, video-electroencephalogram (EEG) recordings were performed. In a third cohort of rats, the following were measured: (i) plasma levels of glucose, transaminases, and urea; (ii) cerebrospinal fluid (CSF) levels of ammonia, glutamine, glutamate, and alanine; (iii) glutamate uptake in brain slices; and (iv) brain redox status and glutamine synthetase activity in cerebral cortex. GUO drastically reduced the lethality rate and the duration of coma. Animals treated with GUO had improved EEG traces, decreased CSF levels of glutamate and alanine, lowered oxidative stress in the cerebral cortex, and increased glutamate uptake by astrocytes in brain slices compared with animals that received vehicle prior to ammonium acetate administration. This study provides new evidence on mechanisms of guanine-derived purines in their potential modulation of glutamatergic system, contributing to GUO neuroprotective effects in a rodent model of by acute ammonia intoxication.

Effect of a trans fatty acid-enriched diet on biochemical and inflammatory parameters in Wistar rats

PURPOSE

Recent data regarding trans fatty acids (TFAs) have implicated these lipids as particularly deleterious to human health, causing systemic inflammation, endothelial dysfunction and possibly inflammation in the central nervous system (CNS). We aimed to clarify the impact of partially hydrogenated soybean oil (PHSO) with different TFA concentrations on cerebrospinal fluid (CSF), serum and hepatic parameters in adult Wistar rats.

METHODS

Wistar rats (n = 15/group) were fed either a normolipidic diet or a hyperlipidic diet for 90 days. The normolipidic and hyperlipidic diets had the same ingredients except for fat compositions, concentrations and calories. We used lard in the cis fatty acid group and PHSO in the trans fatty acid group. The intervention groups were as follows: (1) low lard (LL), (2) high lard (HL), (3) low partially hydrogenated soybean oil (LPHSO) and (4) high partially hydrogenated soybean oil (HPHSO). Body weight, lipid profiles and the inflammatory responses in the CSF, serum and liver tissue were analyzed.

RESULTS

Surprisingly, with the PHSO diet we observed a worse metabolic response that was associated with oxidative stress in hepatic tissue as well as impaired serum and CSF fluid parameters at both PHSO concentrations. In many analyses, there were no significant differences between the LPHSO and HPHSO diets.

CONCLUSIONS

Dietary supplementation with PHSO impaired inflammatory parameters in CSF and blood, induced insulin resistance, altered lipid profiles and caused hepatic damage. Overall, these findings suggest that fat composition is more important than the quantity of fat consumed in terms of cis and trans fatty acid diets.

Intranasal guanosine administration presents a wide therapeutic time window to reduce brain damage induced by permanent ischemia in rats

In addition to its intracellular roles, the nucleoside guanosine (GUO) also has extracellular effects that identify it as a putative neuromodulator signaling molecule in the central nervous system. Indeed, GUO can modulate glutamatergic neurotransmission, and it can promote neuroprotective effects in animal models involving glutamate neurotoxicity, which is the case in brain ischemia. In the present study, we aimed to investigate a new in vivo GUO administration route (intranasal, IN) to determine putative improvement of GUO neuroprotective effects against an experimental model of permanent focal cerebral ischemia. Initially, we demonstrated that IN [(3)H] GUO administration reached the brain in a dose-dependent and saturable pattern in as few as 5 min, presenting a higher cerebrospinal GUO level compared with systemic administration. IN GUO treatment started immediately or even 3 h after ischemia onset prevented behavior impairment. The behavior recovery was not correlated to decreased brain infarct volume, but it was correlated to reduced mitochondrial dysfunction in the penumbra area. Therefore, we showed that the IN route is an efficient way to promptly deliver GUO to the CNS and that IN GUO treatment prevented behavioral and brain impairment caused by ischemia in a therapeutically wide time window.

Purine nucleosides in neuroregeneration and neuroprotection

In the present review, we stress the importance of the purine nucleosides, adenosine and guanosine, in protecting the nervous system, both centrally and peripherally, via activation of their receptors and intracellular signalling mechanisms. A most novel part of the review focus on the mechanisms of neuronal regeneration that are targeted by nucleosides, including a recently identified action of adenosine on axonal growth and microtubule dynamics. Discussion on the role of the purine nucleosides transversally with the most established neurotrophic factors, e.g. brain derived neurotrophic factor (BDNF), glial derived neurotrophic factor (GDNF), is also focused considering the intimate relationship between some adenosine receptors, as is the case of the A2A receptors, and receptors for neurotrophins. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Guanosine inhibits LPS-induced pro-inflammatory response and oxidative stress in hippocampal astrocytes through the heme oxygenase-1 pathway

Guanosine, a guanine-based purine, is an extracellular signaling molecule that is released from astrocytes and has been shown to promote central nervous system defenses in several in vivo and in vitro injury models. Our group recently demonstrated that guanosine exhibits glioprotective effects in the C6 astroglial cell line by associating the heme oxygenase-1 (HO-1) signaling pathway with protection against azide-induced oxidative stress. Astrocyte overactivation contributes to the triggering of brain inflammation, a condition that is closely related to the development of many neurological disorders. These cells sense and amplify inflammatory signals from microglia and/or initiate the release of inflammatory mediators that are strictly related to transcriptional factors, such as nuclear factor kappa B (NFκB), that are modulated by HO-1. Astrocytes also express toll-like receptors (TLRs); TLRs specifically recognize lipopolysaccharide (LPS), which has been widely used to experimentally study inflammatory response. This study was designed to understand the glioprotective mechanism of guanosine against the inflammatory and oxidative damage induced by LPS exposure in primary cultures of hippocampal astrocytes. Treatment of astrocytes with LPS resulted in deleterious effects, including the augmentation of pro-inflammatory cytokine levels, NFκB activation, mitochondrial dysfunction, increased levels of oxygen/nitrogen species, and decreased levels of antioxidative defenses. Guanosine was able to prevent these effects, protecting the hippocampal astrocytes against LPS-induced cytotoxicity through activation of the HO-1 pathway. Additionally, the anti-inflammatory effects of guanosine were independent of the adenosinergic system. These results highlight the potential role of guanosine against neuroinflammatory-related diseases.