The antidepressant-like effect of guanosine is dependent on GSK-3β inhibition and activation of MAPK/ERK and Nrf2/heme oxygenase-1 signaling pathways

Exploring the pathophysiological influence of heme oxygenase-1 on neuroinflammation and depression: A study of phytotherapeutic-based modulation

BACKGROUND

The heme oxygenase (HO) system plays a significant role in neuroprotection and reduction of neuroinflammation and neurodegeneration. The system, via isoforms HO-1 and HO-2, regulates cellular redox balance. HO-1, an antioxidant defense enzyme, is highlighted due to its association with depression, characterized by heightened neuroinflammation and impaired oxidative stress responses.

METHODOLOGY

We observed the pathophysiology of HO-1 and phytochemicals as its modulator. We explored Science Direct, Scopus, and PubMed for a comprehensive literature review. Bibliometric and temporal trend analysis were done using VOSviewer.

RESULTS

Several phytochemicals can potentially alleviate neuroinflammation and oxidative stress-induced depressive symptoms. These effects result from inhibiting the MAPK and NK-κB pathways - both implicated in the overproduction of pro-inflammatory factors - and from the upregulation of HO-1 expression mediated by Nrf2. Bibliometric and temporal trend analysis further validates these associations.

CONCLUSION

In summary, our findings suggest that antidepressant agents can mitigate neuroinflammation and depressive disorder pathogenesis via the upregulation of HO-1 expression. These agents suppress pro-inflammatory mediators and depressive-like symptoms, demonstrating that HO-1 plays a significant role in the neuroinflammatory process and the development of depression.

An insight into crosstalk among multiple signalling pathways contributing to the pathophysiology of PTSD and depressive disorders

Post-traumatic stress disorder (PTSD) and depressive disorders represent two significant mental health challenges with substantial global prevalence. These are debilitating conditions characterized by persistent, often comorbid, symptoms that severely impact an individual's quality of life. Both PTSD and depressive disorders are often precipitated by exposure to traumatic events or chronic stress. The profound impact of PTSD and depressive disorders on individuals and society necessitates a comprehensive exploration of their shared and distinct pathophysiological features. Although the activation of the stress system is essential for maintaining homeostasis, the ability to recover from it after diminishing the threat stimulus is also equally important. However, little is known about the main reasons for individuals' differential susceptibility to external stressful stimuli. The solution to this question can be found by delving into the interplay of stress with the cognitive and emotional processing of traumatic incidents at the molecular level. Evidence suggests that dysregulation in these signalling cascades may contribute to the persistence and severity of PTSD and depressive symptoms. The treatment strategies available for this disorder are antidepressants, which have shown good efficiency in normalizing symptom severity; however, their efficacy is limited in most individuals. This calls for the exploration and development of innovative medications to address the treatment of PTSD. This review delves into the intricate crosstalk among multiple signalling pathways implicated in the development and manifestation of these mental health conditions. By unravelling the complexities of crosstalk among multiple signalling pathways, this review aims to contribute to the broader knowledge base, providing insights that could inform the development of targeted interventions for individuals grappling with the challenges of PTSD and depressive disorders.

Glutathione-Mediated Neuroprotective Effect of Purine Derivatives

Numerous basic studies have reported on the neuroprotective properties of several purine derivatives such as caffeine and uric acid (UA). Epidemiological studies have also shown the inverse association of appropriate caffeine intake or serum urate levels with neurodegenerative diseases such as Alzheimer disease (AD) and Parkinson's disease (PD). The well-established neuroprotective mechanisms of caffeine and UA involve adenosine A2A receptor antagonism and antioxidant activity, respectively. Our recent study found that another purine derivative, paraxanthine, has neuroprotective effects similar to those of caffeine and UA. These purine derivatives can promote neuronal cysteine uptake through excitatory amino acid carrier protein 1 (EAAC1) to increase neuronal glutathione (GSH) levels in the brain. This review summarizes the GSH-mediated neuroprotective effects of purine derivatives. Considering the fact that GSH depletion is a manifestation in the brains of AD and PD patients, administration of purine derivatives may be a new therapeutic approach to prevent or delay the onset of these neurodegenerative diseases.

Guanosine treatment prevents lipopolysaccharide-induced depressive-like behavior in mice

Guanosine is a purinergic nucleoside that has been shown to have neuroprotective effects, mainly through its ability to modulate the glutamatergic system. An increase in pro-inflammatory cytokine levels triggers the activation of the enzyme indoleamine 2,3-dioxygenase 1 (IDO-1), leading to glutamatergic excitotoxicity, which has important roles in the pathophysiology of depression. The aim of this study was to investigate the possible antidepressant-like effects and underlying mechanisms of action of guanosine against lipopolysaccharide (LPS)-induced depression in a mouse model. Mice were orally pre-treated with saline (0.9% NaCl), guanosine (8 or 16 mg/kg), or fluoxetine (30 mg/kg) for 7 days before LPS (0.5 mg/kg, intraperitoneal) injection. One day after LPS injection, mice were subjected to the forced swim test (FST), tail suspension test (TST), and open field test (OFT). After the behavioral tests, mice were euthanized and the levels of tumor necrosis factor-α (TNF-α), IDO-1, glutathione, and malondialdehyde in the hippocampus were measured. Pretreatment with guanosine was able to prevent LPS- induced depressive-like behaviors in the TST and FST. In the OFT, no locomotor changes were observed with any treatment. Both guanosine (8 and 16 mg/kg/day) and fluoxetine treatment prevented the LPS-induced increase in TNF-α and IDO expression and lipid peroxidation as well as decrease of reduced glutathione levels in the hippocampus. Taken together, our findings suggest that guanosine may have neuroprotective effects against LPS-induced depressive-like behavior through preventing oxidative stress and the expression of IDO-1 and TNF-α in the hippocampus.

Endurance-dependent urinary extracellular vesicle signature: shape, metabolic miRNAs, and purine content distinguish triathletes from inactive people

Extracellular vesicles (EVs) enriched with bioactive molecules have gained considerable attention in nanotechnology because they are critical to intercellular communication while maintaining low immunological impact. Among biological matrices, urine has emerged as a noninvasive source of extracellular-contained liquid biopsy, currently of interest as a readout for physiological adaptations. Therefore, we aimed to evaluate chronic adaptations of endurance sport practice in terms of urinary EV parameters and evaluated by food consumption assessment. Two balanced groups of 13 inactive controls vs. triathlon athletes were enrolled; their urinary EVs were obtained by differential ultracentrifugation and analyzed by dynamic light scattering and transmission electron and atomic force microscopy. The cargo was analyzed by means of purine and miRNA content through HPLC-UV and qRT-PCR. Specific urinary EV signatures differentiated inactive versus endurance-trained in terms of peculiar shape. Particularly, a spheroid shape, smaller size, and lower roughness characterize EVs from triathletes. Metabolic and regulatory miRNAs often associated with skeletal muscle (i.e., miR378a-5p, miR27a-3p, miR133a, and miR206) also accounted for a differential signature. These miRNAs and guanosine in urinary EVs can be used as a readout for metabolic status along with the shape and roughness of EVs, novel informative parameters that are rarely considered. The network models allow scholars to entangle nutritional and exercise factors related to EVs' miRNA and purine content to depict metabolic signatures. All in all, multiplex biophysical and molecular analyses of urinary EVs may serve as promising prospects for research in exercise physiology.

NMDA receptor-mediated modulation on glutamine synthetase and glial glutamate transporter GLT-1 is involved in the antidepressant-like and neuroprotective effects of guanosine

Guanosine has been reported to elicit antidepressant-like responses in rodents, but if these actions are associated with its ability to afford neuroprotection against glutamate-induced toxicity still needs to be fully understood. Therefore, this study investigated the antidepressant-like and neuroprotective effects elicited by guanosine in mice and evaluated the possible involvement of NMDA receptors, glutamine synthetase, and GLT-1 in these responses. We found that guanosine (0.05 mg/kg, but not 0.01 mg/kg, p. o.) was effective in producing an antidepressant-like effect and protecting hippocampal and prefrontocortical slices against glutamate-induced damage. Our results also unveiled that ketamine (1 mg/kg, but not 0.1 mg/kg, i. p, an NMDA receptor antagonist) effectively elicited antidepressant-like actions and protected hippocampal and prefrontocortical slices against glutamatergic toxicity. Furthermore, the combined administration of sub-effective doses of guanosine (0.01 mg/kg, p. o.) with ketamine (0.1 mg/kg, i. p.) promoted an antidepressant-like effect and augmented glutamine synthetase activity and GLT-1 immunocontent in the hippocampus, but not in the prefrontal cortex. Our results also showed that the combination of sub-effective doses of ketamine and guanosine, at the same protocol schedule that exhibited an antidepressant-like effect, effectively abolished glutamate-induced damage in hippocampal and prefrontocortical slices. Our in vitro results reinforce that guanosine, ketamine, or sub-effective concentrations of guanosine plus ketamine protect against glutamate exposure by modulating glutamine synthetase activity and GLT-1 levels. Finally, molecular docking analysis suggests that guanosine might interact with NMDA receptors at the ketamine or glycine/d-serine co-agonist binding sites. These findings provide support for the premise that guanosine has antidepressant-like effects and should be further investigated for depression management.

The Nrf2 Pathway in Depressive Disorders: A Systematic Review of Animal and Human Studies

There is increasing interest in the involvement of antioxidative systems in protecting from depression. Among these, Nrf2 occupies a central place. We aimed to review the role of Nrf2 in depression. For this reason, we conducted a PubMed search using as search strategy (psychiatr*[ti] OR schizo*[ti] OR psychot*[ti] OR psychos*[ti] OR depress*[ti] OR MDD[ti] OR BD[ti] OR bipolar[ti] OR Anxiety[ti] OR antidepress*[ti] OR panic[ti] OR obsess*[ti] OR compulsio*[ti] OR “mood disord*”[ti] OR phobi*[ti] OR agoraphob*[ti] OR anorex*[ti] OR anorect*[ti] OR bulimi*[ti] OR “eating disorder*”[ti] OR neurodevelopm*[ti] OR retardation[ti] OR autism[ti] OR autistic[ti] OR ASM[ti] OR adhd[ti] OR “attention-deficit”[ti]) AND nrf2, which on the 9th of March produced 208 results of which 89 were eligible for our purposes. Eligible articles were studies reporting data of Nrf2 manipulations or content by any treatment in human patients or animals with any animal model of depression. Most studies were on mice only (N = 58), 20 on rats only, and three on both rats and mice. There were two studies on cell lines (in vitro) and one each on nematodes and fish. Only four studies were conducted in humans, one of which was post mortem. Most studies were conducted on male animals; however, human studies were carried out on both men and women. The results indicate that Nrf2 is lower in depression and that antidepressant methods (drugs or other methods) increase it. Antioxidant systems and plasticity-promoting molecules, such as those in the Nrf2–HO-1, BDNF–TrkB, and cyclic AMP–CREB pathways, could protect from depression, while glycogen synthase kinase-3β and nuclear factor κB oppose these actions, thus increasing depressive-like behaviours. Since Nrf2 is also endowed with tumorigenic and atherogenic potential, the balance between benefits and harms must be taken into account in designing novel drugs aiming at increasing the intracellular content of Nrf2.

The antidepressant-like effect of guanosine involves the modulation of adenosine A1 and A2A receptors

Guanosine has been considered a promising candidate for antidepressant responses, but if this nucleoside could modulate adenosine A₁ (A₁R) and A_2A (A_2AR) receptors to exert antidepressant-like actions remains to be elucidated. This study investigated the role of A₁R and A_2AR in the antidepressant-like response of guanosine in the mouse tail suspension test and molecular interactions between guanosine and A₁R and A₂AR by docking analysis. The acute (60 min) administration of guanosine (0.05 mg/kg, p.o.) significantly decreased the immobility time in the tail suspension test, without affecting the locomotor performance in the open-field test, suggesting an antidepressant-like effect. This behavioral response was paralleled with increased A₁R and reduced A_2AR immunocontent in the hippocampus, but not in the prefrontal cortex, of mice. Guanosine-mediated antidepressant-like effect was not altered by the pretreatment with caffeine (3 mg/kg, i.p., a non-selective adenosine A₁R/A_2AR antagonist), 8-cyclopentyl-1,3-dipropylxanthine (DPCPX - 2 mg/kg, i.p., a selective adenosine A₁R antagonist), or 4-(2-[7-amino-2-{2-furyl}{1,2,4}triazolo-{2,3-a}{1,3,5}triazin-5-yl-amino]ethyl)-phenol (ZM241385 - 1 mg/kg, i.p., a selective adenosine A_2AR antagonist). However, the antidepressant-like response of guanosine was completely abolished by adenosine (0.5 mg/kg, i.p., a non-selective adenosine A₁R/A_2AR agonist), N-6-cyclohexyladenosine (CHA - 0.05 mg/kg, i.p., a selective adenosine A₁ receptor agonist), and N-6-[2-(3,5-dimethoxyphenyl)-2-(methylphenyl)ethyl]adenosine (DPMA - 0.1 mg/kg, i.p., a selective adenosine A_2A receptor agonist). Finally, docking analysis also indicated that guanosine might interact with A₁R and A_2AR at the adenosine binding site. Overall, this study reinforces the antidepressant-like of guanosine and unveils a previously unexplored modulation of the modulation of A₁R and A_2AR in its antidepressant-like effect.

Neferine alleviates chronic stress-induced depression by regulating monoamine neurotransmitter secretion and gut microbiota structure

Neferine (Nef) might possess anti-depressive properties; however, its therapeutic effects are yet to be elucidated. Therefore, in this study, we aimed to explore the anti-depressant property of Nef using a mouse model of chronic stress-induced depression. Fifteen depression-prone mice were randomly selected and divided into three groups, namely, the model, Nef, and fluoxetine (Flu) groups. We observed that in tail suspension and forced swimming tests, the Nef and Flu treatments significantly decreased the immobility time of the depressed mice, and increased their sucrose preference indices. Moreover, both Nef and Flu treatments induced significant increases in the levels of anti-depressant neurotransmitters, including dopamine (DA), serotonin (5-HT), and norepinephrine (NE), and also reduced pathological damage to the hippocampus of the depressed mice. Incidentally, Illumina MiSeq sequencing analysis demonstrated that the relative abundance of Lactobacillus in the intestinal microbiota of depressed mice was restored after Nef/Flu treatment. Moreover, colonic Lactobacillus abundance was positively correlated with the levels of DA, 5-HT, and NE in the hippocampus of the mice. In conclusion, Nef improved monoamine neurotransmitter secretion and modulated the intestinal flora structure, particularly the abundance of Lactobacillus. Hence, it showed considerable anti-depressant potential, and might be a prospective anti-depressant therapeutic agent.

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.

Catalpol Exerts Antidepressant-Like Effects by Enhancing Anti-oxidation and Neurotrophy and Inhibiting Neuroinflammation via Activation of HO-1

Catalpol is an iridoid glycoside with rich content, rich nutrition, and numerous biological activities in Rehmanniae Radix contained in classic antidepressant prescriptions in Chinese clinical medicine. Catalpol has been confirmed previously its exact antidepressant-like effect involved heme oxygenase (HO)-1, but its antidepressant molecular targets and mechanism are still unclear. Here, catalpol's antidepressant-like molecular target was diagnosed and confirmed by ZnPP intervention [the antagonist of HO-1, (10 μg/rat), intracerebroventricular] for the first time, and its molecule mechanism network was determined through HO-1 related pathway and molecules in the hippocampus. Results showed that ZnPP significantly abolished catalpol's (10 mg/kg) reversal on depressive-like behaviors of chronic unpredictable mild stress rats, abolished catalpol's up-regulation on the phosphorylation level of extracellular regulated protein kinases (ERK)1/2 and brain-derived neurotrophic factor (BDNF)'s receptor tropomyosin-related kinase B (TrkB), the nuclear expression level of nuclear factor E 2-related factor 2 (Nrf2), the levels of anti-oxidant factors (such as HO-1, SOD, GPX, GST, GSH) and BDNF, and abolished catalpol's down-regulation on the levels of peroxide and neuroinflammation factors [cyclooxygenase-2 (COX-2), induced nitrogen monoxide synthase (iNOS), nitric oxide (NO)]. Thus, HO-1 could serve as an important potential molecular target for catalpol's antidepressant-like process, and the antidepressant-like mechanism of catalpol could at least involve the activation of HO-1 triggering the up-regulation of the ERK1/2/Nrf2/HO-1 pathway-related factors to enhance the anti-oxidant defense, triggering the down-regulation of the COX-2/iNOS/NO pathway-related factors to inhibit neuroinflammation, and triggering the up-regulation of the BDNF/TrkB pathway to enhance neurotrophy.

Role of heme oxygenase-1 in the antidepressant-like effect of ursolic acid in the tail suspension test

OBJECTIVES

This study investigated the involvement of heme oxygenase-1 (HO-1) in the antidepressant-like effects of ursolic acid (UA), a plant-derived compound with neuroprotective and antidepressant-like properties.

METHODS

Mice received intracerebroventricular injections of zinc protoporphyrin IX (ZnPP) or cobalt protoporphyrin IX (CoPP) to inhibit or induce HO-1, respectively, together with effective (0.1 mg/kg, p.o.) or sub-effective (0.01 mg/kg, p.o.) doses of UA or fluoxetine (10 mg/kg, p.o.). Immobility time was assessed using the tail suspension test (TST) and the ambulatory behaviour with the open field test. HO-1 immunocontent was evaluated in mice hippocampus and prefrontal cortex.

KEY FINDINGS

ZnPP prevented the anti-immobility effects of UA and fluoxetine. Combined treatment with a sub-effective dose of CoPP and UA synergistically exerted antidepressant-like effects in the TST. Acute administration of UA or CoPP, but not fluoxetine, increased the HO-1 immunocontent in the hippocampus. None of the treatments altered the HO-1 immunocontent in the prefrontal cortex.

CONCLUSIONS

In conclusion, this work shows that increased hippocampal HO-1 content and activity mediate the antidepressant-like effect of UA in the TST.

A low-dose combination of ketamine and guanosine counteracts corticosterone-induced depressive-like behavior and hippocampal synaptic impairments via mTORC1 signaling

Ketamine exhibits rapid and sustained antidepressant responses, but its repeated use may cause adverse effects. Augmentation strategies have been postulated to be useful for the management/reduction of ketamine's dose and its adverse effects. Based on the studies that have suggested that ketamine and guanosine may share overlapping mechanisms of action, the present study investigated the antidepressant-like effect of subthreshold doses of ketamine and guanosine in mice subjected to repeated administration of corticosterone (CORT) and the role of mTORC1 signaling for this effect. The ability of the treatment with ketamine (0.1 mg/kg, i.p.) plus guanosine (0.01 mg/kg, p.o.) to counteract the depressive-like behavior induced by CORT (20 mg/kg, p.o., for 21 days) in mice, was paralleled with the prevention of the CORT-induced reduction on BDNF levels, Akt (Ser⁴⁷³) and GSK-3β (Ser⁹) phosphorylation, and PSD-95, GluA1, and synapsin immunocontent in the hippocampus. No changes on mTORC1 and p70S6K immunocontent were found in the hippocampus and prefrontal cortex of any experimental group. No alterations on BDNF, Akt/GSK-3β, mTORC1/p70S6K, and synaptic proteins were observed in the prefrontal cortex of mice. The antidepressant-like and pro-synaptogenic effects elicited by ketamine plus guanosine were abolished by the pretreatment with rapamycin (0.2 nmol/site, i.c.v., a selective mTORC1 inhibitor). Our results showed that the combined administration of ketamine and guanosine at low doses counteracted CORT-induced depressive-like behavior and synaptogenic disturbances by activating mTORC1 signaling. This study supports the notion that the combined administration of guanosine and ketamine may be a useful therapeutic strategy for the management of MDD.

Low doses of ketamine and guanosine abrogate corticosterone-induced anxiety-related behavior, but not disturbances in the hippocampal NLRP3 inflammasome pathway

RATIONALE

Guanosine has been shown to potentiate ketamine's antidepressant-like actions, although its ability to augment the anxiolytic effect of ketamine remains to be determined.

OBJECTIVE

This study investigated the anxiolytic-like effects of a single administration with low doses of ketamine and/or guanosine in mice subjected to chronic administration of corticosterone and the role of NLRP3-driven signaling.

METHODS

Corticosterone (20 mg/kg, p.o.) was administered for 21 days, followed by a single administration of ketamine (0.1 mg/kg, i.p.), guanosine (0.01 mg/kg, p.o.), or ketamine (0.1 mg/kg, i.p.) plus guanosine (0.01 mg/kg, p.o.). Anxiety-like behavior and NLRP3-related targets were analyzed 24 h following treatments.

RESULTS

Corticosterone reduced the time spent in the open arms and the central zone in the elevated plus-maze test and open-field test, respectively. Corticosterone raised the number of unsupported rearings and the number and time of grooming, and decreased the latency to start grooming in the open-field test. Disturbances in regional distribution (increased rostral grooming) and grooming transitions (increased aborted and total incorrect transitions) were detected in corticosterone-treated mice. These behavioral alterations were accompanied by increased immunocontent of Iba-1, ASC, NLRP3, caspase-1, TXNIP, and IL-1β in the hippocampus, but not in the prefrontal cortex. The treatments with ketamine, guanosine, and ketamine plus guanosine were effective to counteract corticosterone-induced anxiety-like phenotype, but not disturbances in the hippocampal NLRP3 pathway.

CONCLUSIONS

Our study provides novel evidence that low doses of ketamine and/or guanosine reverse corticosterone-induced anxiety-like behavior and shows that the NLRP3 inflammasome pathway is likely unrelated to this response.

Catalpol Weakens Depressive-like Behavior in Mice with Streptozotocin-induced Hyperglycemia via PI3K/AKT/Nrf2/HO-1 Signaling Pathway

Depression has huge social risks of high incidence, disability, and suicide. Its prevalence and harm in people with hyperglycemia are 2-3 times higher than in normal people. However, antidepressants with precise curative effects and clear mechanisms for patients with hyperglycemia are currently lacking. Prescriptions containing Rehmannia glutinosa, a traditional medicinal herb with a wide range of nutritional and medicinal values, are often used as antidepressants in Chinese clinical medicine. Catalpol is one of the main effective compounds of R. glutinosa, with multiple biological activities such as hypoglycemia. Here, the antidepressant effect of catalpol on the pathological state of streptozotocin (STZ)-induced hyperglycemia and the underlying molecular mechanisms were analyzed. Results showed that administering catalpol orally to hyperglycemic mice for 21 consecutive days significantly reversed the abnormalities in tail suspension, forced swimming, and open field tests. Catalpol also reversed the abnormal phosphorylation of phosphoinositide 3-kinase (PI3K) and protein kinase B (AKT) and the abnormal levels of nuclear factor erythroid 2-related factor 2 (Nrf2) protein, heme oxygenase-1 (HO-1), and antioxidants, including superoxide dismutase, glutathione peroxidase, glutathione-s transferase, reduced glutathione, and malondialdehyde in the hippocampus and frontal cortex of STZ-induced hyperglycemic mice. Thus, catalpol attenuates depressive-like behavior in pathological hyperglycemic state, and the antidepressant mechanism could at least be partly attributed to the upregulation of the PI3K/AKT/Nrf2/HO-1 signaling pathway in both brain regions, thus restoring the balance between oxidative and antioxidant damage. These data expanded the scientific understanding of catalpol and provided preclinical experimental evidence for its application.

Antidepressant-like effect of guanosine involves activation of AMPA receptor and BDNF/TrkB signaling

Guanosine is a purine nucleoside that has been shown to exhibit antidepressant effects, but the mechanisms underlying its effect are not well established. We investigated if the antidepressant-like effect induced by guanosine in the tail suspension test (TST) in mice involves the modulation of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor, voltage-dependent calcium channel (VDCC), and brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) pathway. We also evaluated if the antidepressant-like effect of guanosine is accompanied by an acute increase in hippocampal and prefrontocortical BDNF levels. Additionally, we investigated if the ability of guanosine to elicit a fast behavioral response in the novelty suppressed feeding (NSF) test is associated with morphological changes related to hippocampal synaptogenesis. The antidepressant-like effect of guanosine (0.05 mg/kg, p.o.) in the TST was prevented by DNQX (AMPA receptor antagonist), verapamil (VDCC blocker), K-252a (TrkBantagonist), or BDNF antibody. Increased P70S6K phosphorylation and higher synapsin I immunocontent in the hippocampus, but not in the prefrontal cortex, were observed 1 h after guanosine administration. Guanosine exerted an antidepressant-like effect 1, 6, and 24 h after its administration, an effect accompanied by increased hippocampal BDNF level. In the prefrontal cortex, BDNF level was increased only 1 h after guanosine treatment. Finally, guanosine was effective in the NSF test (after 1 h) but caused no alterations in dendritic spine density and remodeling in the ventral dentate gyrus (DG). Altogether, the results indicate that guanosine modulates targets known to be implicated in fast antidepressant behavioral responses (AMPA receptor, VDCC, and TrkB/BDNF pathway).

Protective Effect of Lemon Peel Extract on Oxidative Stress in H9c2 Rat Heart Cell Injury

Aim

Lemon peel, a traditional Chinese medicine, was tested in this study for its novel application in inhibiting cellular oxidative stress, and the effect of lemon peel extract (LPE) on protecting H9c2 rat heart cells from oxidative stress was investigated.

Methods

The scavenging effects of LPE on 1,1-diphenyl-2-picryhydrazyl (DPPH) and 2,2’-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) free radicals were measured in extracellular experiments. The 3-(4,5-dimethyl-2-thiazolinyl)-2,5-diphenyl-2-h-tetrazolylammonium bromide (MTT) assay was used to detect the cell survival rate. The cell supernatant and intracellular oxidation-related indicators were detected by a kit, and the mRNA expression in H9c2 cells was detected by quantitative polymerase chain reaction (qPCR). The chemical substances of LPE were analyzed by high-performance liquid chromatography (HPLC).

Results

The results showed that LPE exhibited better DPPH and ABTS free radical scavenging abilities than vitamin C. Compared with the cells in the normal state (control group), the cell survival rate in the model group decreased, and the level of lactate dehydrogenase (LDH) increased, the levels of superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) decreased, and the content of malondialdehyde (MDA) increased. Compared with the control group, the expression of Bcl-2-related X protein (Bax), caspase-3, nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) in the model group was increased, and the expression of B-cell lymphoma-2 (Bcl-2) was reduced. Compared with the model group, LPE treatment improved the cell survival rate, reduced the levels of LDH and MDA, increased the levels of SOD, CAT, and GSH, downregulated the expression of Bax, caspase-3, Nrf2 and HO-1, and upregulated the expression of Bcl-2. The composition analysis showed that LPE contained catechin, rutin, naringin, quercetin, and hesperidin.

Conclusion

The results indicated that LPE could protect H9c2 cells from oxidative stress through five active components. LPE has the potential to be developed into natural medicine or health food for the inhibition of cell oxidative damage.

Antidepressant-Like Effects of Chronic Guanosine in the Olfactory Bulbectomy Mouse Model

Major depressive disorder (MDD) leads to pervasive changes in the health of afflicted patients. Despite advances in the understanding of MDD and its treatment, profound innovation is needed to develop fast-onset antidepressants with higher effectiveness. When acutely administered, the endogenous nucleoside guanosine (GUO) shows fast-onset antidepressant-like effects in several mouse models, including the olfactory bulbectomy (OBX) rodent model. OBX is advocated to possess translational value and be suitable to assess the time course of depressive-like behavior in rodents. This study aimed at investigating the long-term behavioral and neurochemical effects of GUO in a mouse model of depression induced by bilateral bulbectomy (OBX). Mice were submitted to OBX and, after 14 days of recovery, received daily (ip) administration of 7.5 mg/kg GUO or 40 mg/kg imipramine (IMI) for 45 days. GUO and IMI reversed the OBX-induced hyperlocomotion and recognition memory impairment, hippocampal BDNF increase, and redox imbalance (ROS, NO, and GSH levels). GUO also mitigated the OBX-induced hippocampal neuroinflammation (IL-1, IL-6, TNF-α, INF-γ, and IL-10). Brain microPET imaging ([¹⁸F]FDG) shows that GUO also prevented the OBX-induced increase in hippocampal FDG metabolism. These results provide additional evidence for GUO antidepressant-like effects, associated with beneficial neurochemical outcomes relevant to counteract depression.

Guanosine-Based Nucleotides, the Sons of a Lesser God in the Purinergic Signal Scenario of Excitable Tissues

Purines are nitrogen compounds consisting mainly of a nitrogen base of adenine (ABP) or guanine (GBP) and their derivatives: nucleosides (nitrogen bases plus ribose) and nucleotides (nitrogen bases plus ribose and phosphate). These compounds are very common in nature, especially in a phosphorylated form. There is increasing evidence that purines are involved in the development of different organs such as the heart, skeletal muscle and brain. When brain development is complete, some purinergic mechanisms may be silenced, but may be reactivated in the adult brain/muscle, suggesting a role for purines in regeneration and self-repair. Thus, it is possible that guanosine-5′-triphosphate (GTP) also acts as regulator during the adult phase. However, regarding GBP, no specific receptor has been cloned for GTP or its metabolites, although specific binding sites with distinct GTP affinity characteristics have been found in both muscle and neural cell lines. Finally, even if the cross regulation mechanisms between the two different purines (ABP and GBP) are still largely unknown, it is now possible to hypothesize the existence of specific signal paths for guanosine-based nucleotides that are capable of modulating the intensity and duration of the intracellular signal, particularly in excitable tissues such as brain and muscle.

Honey as Source of Nitrogen Compounds: Aromatic Amino Acids, Free Nucleosides and Their Derivatives

The content of selected major nitrogen compounds including nucleosides and their derivatives was evaluated in 75 samples of seven varieties of honey (heather, buckwheat, black locust, goldenrod, canola, fir, linden) by targeted ultra-high performance liquid chromatography-diode array detector - high-resolution quadrupole time-of-flight mass spectrometry (UHPLC-DAD-QqTOF-MS) and determined by UHPLC-DAD. The honey samples contained nucleosides, nucleobases and their derivatives (adenine: 8.9 to 18.4 mg/kg, xanthine: 1.2 to 3.3 mg/kg, uridine: 17.5 to 51.2 mg/kg, guanosine: 2.0 to 4.1 mg/kg; mean amounts), aromatic amino acids (tyrosine: 7.8 to 263.9 mg/kg, phenylalanine: 9.5 to 64.1 mg/kg; mean amounts). The amounts of compounds significantly differed between some honey types. For example, canola honey contained a much lower amount of uridine (17.5 ± 3.9 mg/kg) than black locust where it was most abundant (51.2 ± 7.8 mg/kg). The presence of free nucleosides and nucleobases in different honey varieties is reported first time and supports previous findings on medicinal activities of honey reported in the literature as well as traditional therapy and may contribute for their explanation. This applies, e.g., to the topical application of honey in herpes infections, as well as its beneficial activity on cognitive functions as nootropic and neuroprotective, in neuralgia and is also important for the understanding of nutritional values of honey.