Agomelatine Exerts an Anti-inflammatory Effect by Inhibiting Microglial Activation Through TLR4/NLRP3 Pathway in pMCAO Rats

Mechanisms of inflammation after ischemic stroke in brain-peripheral crosstalk

Stroke is a devastating disease with high morbidity, disability, and mortality, among which ischemic stroke is more common. However, there is still a lack of effective methods to improve the prognosis and reduce the incidence of its complications. At present, there is evidence that peripheral organs are involved in the inflammatory response after stroke. Moreover, the interaction between central and peripheral inflammation includes the activation of resident and peripheral immune cells, as well as the activation of inflammation-related signaling pathways, which all play an important role in the pathophysiology of stroke. In this review, we discuss the mechanisms of inflammatory response after ischemic stroke, as well as the interactions through circulatory pathways between peripheral organs (such as the gut, heart, lung and spleen) and the brain to mediate and regulate inflammation after ischemic stroke. We also propose the potential role of meningeal lymphatic vessels (MLVs)-cervical lymph nodes (CLNs) as a brain-peripheral crosstalk lymphatic pathway in ischemic stroke. In addition, we also summarize the mechanisms of anti-inflammatory drugs in the treatment of ischemic stroke.

Agomelatine promotes differentiation of oligodendrocyte precursor cells and preserves white matter integrity after cerebral ischemic stroke

White matter injury contributes to neurological disorders after acute ischemic stroke (AIS). The repair of white matter injury is dependent on the re-myelination by oligodendrocytes. Both melatonin and serotonin antagonist have been proved to protect against post-stroke white matter injury. Agomelatine (AGM) is a multi-functional treatment which is both a melatonin receptor agonist and selective serotonin receptor antagonist. Whether AGM protects against white matter injury after stroke and the underlying mechanisms remain elusive. Here, using the transient middle cerebral artery occlusion (tMCAO) model, we evaluated the therapeutic effects of AGM in stroke mice. Sensorimotor and cognitive functions, white matter integrity, oligodendroglial regeneration and re-myelination in stroke hemisphere after AGM treatment were analyzed. We found that AGM efficiently preserved white matter integrity, reduced brain tissue loss, attenuated long-term sensorimotor and cognitive deficits in tMCAO models. AGM treatment promoted OPC differentiation and enhanced re-myelination both in vitro, ex vivo and in vivo, although OPC proliferation was unaffected. Mechanistically, AGM activated low density lipoprotein receptor related protein 1 (LRP1), peroxisome proliferator-activated receptor γ (PPARγ) signaling thus promoted OPC differentiation and re-myelination after stroke. Inhibition of PPARγ or knock-down of LRP1 in OPCs reversed the beneficial effects of AGM. Altogether, our data indicate that AGM represents a novel therapy against white matter injury after cerebral ischemia.

Unmoving and uninflamed: Characterizing neuroinflammatory dysfunction in the Wistar-Kyoto rat model of depression

Reductionistic research on depressive disorders has been hampered by the limitations of animal models. Recently, it has been hypothesized that neuroinflammation is a key player in depressive disorders. The Wistar-Kyoto (WKY) rat is an often-used animal model of depression, but no information so far exists on its neuroinflammatory profile. As such, we compared male young adult WKY rats to Wistar (WS) controls, with regard to both behavioral performance and brain levels of key neuroinflammatory markers. We first assessed anxiety- and depression-like behaviors in a battery consisting of the Elevated Plus Maze (EPM), the Novelty Suppressed Feeding (NSFT), Open Field (OFT), Social Interaction (SIT), Forced Swim (FST), Sucrose Preference (SPT), and Splash tests (ST). We found that WKY rats displayed increased NSFT feeding latency, decreased OFT center zone permanence, decreased EPM open arm permanence, decreased SIT interaction time, and increased immobility in the FST. However, WKY rats also evidenced marked hypolocomotion, which is likely to confound performance in such tests. Interestingly, WKY rats performed similarly, or even above, to WS levels in the SPT and ST, in which altered locomotion is not a significant confound. In a separate cohort, we assessed prefrontal cortex (PFC), hippocampus and amygdala levels of markers of astrocytic (GFAP, S100A10) and microglial (Iba1, CD86, Ym1) activation status, as well as of three key proinflammatory cytokines (IL-1β, IL-6, TNF-α). There were no significant differences between strains in any of these markers, in any of the regions assessed. Overall, results highlight that behavioral data obtained with WKY rats as a model of depression must be carefully interpreted, considering the marked locomotor activity deficits displayed. Furthermore, our data suggest that, despite WKY rats replicating many depression-associated neurobiological alterations, as shown by others, this is not the case for neuroinflammation-related alterations, thus representing a novel limitation of this model.

Transcutaneous electrical acupoint stimulation alleviates cerebral ischemic injury through the TLR4/MyD88/NF-κ B pathway

This study was to explore whether transcutaneous electrical acupoint stimulation (TEAS) treatment could mediate inflammation, apoptosis, and pyroptosis of neuronal cells and microglia activation through the TLR4/MyD88/NF-κB pathway in the early stage of ischemic stroke. TEAS treatment at Baihui (GV20) and Hegu (LI4) acupoints of the affected limb was administered at 24, 48, and 72 h following middle cerebral artery occlusion/reperfusion (MCAO/R), with lasting for 30 min each time. Neurological impairment scores were assessed 2 h and 72 h after ischemia/reperfusion (I/R). TTC staining was used to evaluate the volume of brain infarction. The histopathologic changes of hippocampus were detected by H&E staining. WB analysis was performed to assess the levels of TLR4, MyD88, p-NF-κB p65/NF-κB p65, and inflammation, apoptosis, pyroptosis-related proteins. TLR4 expression was measured using immunohistochemistry. The expression of inflammation-related proteins was also measured using ELISA. Immunofluorescence was used to detect the expression level of Iba1. Our findings demonstrated that TEAS intervention after I/R improved neurological function, reduced the volume of brain infarction, and mitigated pathological damage. Moreover, TEAS reduced the levels of TLR4, MyD88, p-NF-κB p65/NF-κB p65, TNF-α, IL-6, Bax, NLRP3, cleaved caspase-1/pro caspase-1, IL-1β, IL-18, GSDMD, and Iba1 while enhancing Bcl-2 expression. Moreover, the protective effects of TEAS could be counteracted by lipopolysaccharide (LPS, a TLR4 agonist). In conclusion, TEAS can reduce cerebral damage and suppress inflammation, cell death, and microglia activation after ischemic stroke via inhibiting the TLR4/MyD88/NF-κB pathway.

Microglial TLR4/NLRP3 Inflammasome Signaling in Alzheimer's Disease

Alzheimer's disease is a pervasive neurodegenerative disease that is estimated to represent approximately 70% of dementia cases worldwide, and the molecular complexity that has been highlighted remains poorly understood. The accumulation of extracellular amyloid-β (Aβ), intracellular neurofibrillary tangles formed by tau hyperphosphorylation, and neuroinflammation are the major pathological features of Alzheimer's disease (AD). Over the years, there has been no apparent breakthrough in drug discovery based on the Aβ and tau hypotheses. Neuroinflammation has gradually become a hot spot in AD treatment research. As the primary cells of innate immunity in the central nervous system, microglia play a key role in neuroinflammation. Toll-like receptor 4 (TLR4) and nucleotide-binding oligomerization domain-like receptor 3 (NLRP3) inflammasomes are vital molecules in neuroinflammation. In the pathological context of AD, the complex interplay between TLR4 and the NLRP3 inflammasomes in microglia influences AD pathology via neuroinflammation. In this review, the effect of the activation and inhibition of TLR4 and NLRP3 in microglia on AD pathology, as well as the cross-talk between TLR4 and the NLRP3 inflammasome, and the influence of essential molecules in the relevant signaling pathway on AD pathology, were expounded. In addition, the feasibility of these factors in representing a potential treatment option for AD has been clarified.

The melatonin receptor agonist agomelatine protects against acute pancreatitis induced by cadmium by attenuating inflammation and oxidative stress and modulating Nrf2/HO-1 pathway

Pancreatitis is a serious effect of the heavy metal cadmium (Cd) and inflammation and oxidative stress (OS) are implicated in Cd-induced pancreatic injury. This study evaluated the effect of the melatonin receptor agonist agomelatine (AGM) on Cd-induced acute pancreatitis (AP), pointing to its modulatory effect on inflammation, OS, and Nrf2/HO-1 pathway. Rats were supplemented with AGM orally for 14 days and a single injection of cadmium chloride (CdCl2) on day 7. Cd increased serum amylase and lipase and caused pancreatic endocrine and exocrine tissue injury. Malondialdehyde (MDA), nitric oxide (NO) and myeloperoxidase (MPO) were elevated, nuclear factor (NF)-kB p65, inducible NO synthase (iNOS), interleukin (IL)-6, tumor necrosis factor (TNF)-α and CD40 were upregulated, and antioxidants were decreased in the pancreas of Cd-administered rats. AGM ameliorated serum amylase and lipase and pancreatic OS, NF-kB p65, CD40, pro-inflammatory mediators and caspase-3, prevented tissue injury and enhanced antioxidants. AGM downregulated Keap1 and enhanced Nrf2 and HO-1 in the pancreas of Cd-administered rats. In silico findings revealed the binding affinity of AGM with Keap1, HO-1, CD40L and caspase-3. In conclusion, AGM protected against AP induced by Cd by preventing inflammation, OS and apoptosis and modulating Nrf2/HO-1 pathway.

Non-Excitatory Amino Acids, Melatonin, and Free Radicals: Examining the Role in Stroke and Aging

The aim of this review is to explore the relationship between melatonin, free radicals, and non-excitatory amino acids, and their role in stroke and aging. Melatonin has garnered significant attention in recent years due to its diverse physiological functions and potential therapeutic benefits by reducing oxidative stress, inflammation, and apoptosis. Melatonin has been found to mitigate ischemic brain damage caused by stroke. By scavenging free radicals and reducing oxidative damage, melatonin may help slow down the aging process and protect against age-related cognitive decline. Additionally, non-excitatory amino acids have been shown to possess neuroprotective properties, including antioxidant and anti-inflammatory in stroke and aging-related conditions. They can attenuate oxidative stress, modulate calcium homeostasis, and inhibit apoptosis, thereby safeguarding neurons against damage induced by stroke and aging processes. The intracellular accumulation of certain non-excitatory amino acids could promote harmful effects during hypoxia-ischemia episodes and thus, the blockade of the amino acid transporters involved in the process could be an alternative therapeutic strategy to reduce ischemic damage. On the other hand, the accumulation of free radicals, specifically mitochondrial reactive oxygen and nitrogen species, accelerates cellular senescence and contributes to age-related decline. Recent research suggests a complex interplay between melatonin, free radicals, and non-excitatory amino acids in stroke and aging. The neuroprotective actions of melatonin and non-excitatory amino acids converge on multiple pathways, including the regulation of calcium homeostasis, modulation of apoptosis, and reduction of inflammation. These mechanisms collectively contribute to the preservation of neuronal integrity and functions, making them promising targets for therapeutic interventions in stroke and age-related disorders.

Partial blood replacement ameliorates middle cerebral artery occlusion generated neurological aberrations by intervening TLR4 and NLRP3 cascades in rats

Acute ischemic stroke is a catastrophic medical condition that causes severe disability and mortality if the sufferer escapes treatment within a stipulated timeframe. While timely intervention with clot-bursting agents like tissue-plasminogen activators abrogates some post-stroke neurologic deficits, no neuroprotective therapy is yet promisingly addresses the post-recanalization neuroinflammation in post-stroke survivors. Herein, we investigated the effect of partial blood replacement therapy (BRT), obtained from healthy and treadmill-trained donor rats, on neurological deficits, and peripheral and central inflammatory cascades using the ischemia-reperfusion animal paradigm. The cerebral ischemia-reperfusion was induced in rats by occlusion of the middle cerebral artery (MCAO) for 90 min, followed by reperfusion. Rats underwent MCAO surgery displayed remarkable sensorimotor and motor deficits in rotarod, foot fault, adhesive removal, and paw whisker tests till 5 days post-surgery. These behavior abnormalities were ameliorated in the BRT-recipient MCAO rats. BRT also reduced the infarct volume and neuronal death in the ipsilateral hemisphere revealed by TTC and cresyl violet staining compared to the MCAO group. Rats received BRT infusion exhibited the reduced expression of glial fibrillary acidic protein, ionized calcium-binding adaptor molecule-1 (Iba-1), and MyD88 on day 5 post-MCAO in immunohistochemistry and immunofluorescent assays. Moreover, elevated levels of toll-like receptor 4 (TLR4) and mRNA expression of IL-1β, TNF-α, matrix metalloproteinase-9 and NLRP3, and decreased levels of zonula occludens-1 in MCAO rats, were reversed following BRT. These findings suggest that the partial BRT may rescind MCAO-induced neurological dysfunctions and cerebral injury by intervening in the TLR4 and NLRP3 pathways in rats.

Cadmium cardiotoxicity is associated with oxidative stress and upregulated TLR-4/NF-kB pathway in rats; protective role of agomelatine

Cardiotoxicity is one of the hazardous effects of the exposure to the heavy metal cadmium (Cd). Inflammation and oxidative injury are implicated in the cardiotoxic mechanism of Cd. The melatonin receptor agonist agomelatine (AGM) showed promising effects against oxidative and inflammatory responses. This study evaluated the effect of AGM on Cd-induced cardiotoxicity in rats, pointing to its modulatory effect on TLR-4/NF-kB pathway and HSP70. Rats received AGM for 14 days and a single dose of Cd on day 7 and blood and heart samples were collected for analyses. Cd increased serum CK-MB, AST and LDH and caused cardiac tissue injury. Cardiac malondialdehyde (MDA), nitric oxide (NO) and MPO were elevated and GSH, SOD and GST decreased in Cd-administered rats. AGM ameliorated serum CK-MB, AST and LDH and cardiac MDA, NO and MPO, prevented tissue injury and enhanced antioxidants. AGM downregulated serum CRP and cardiac TLR-4, NF-kB, iNOS, IL-6, TNF-α and COX-2 in Cd-administered rats. HSP70 was upregulated in the heart of Cd-challenged rats treated with AGM. In silico findings revealed the binding affinity of AGM with TLR-4 and NF-kB. In conclusion, AGM protected against Cd cardiotoxicity by preventing myocardial injury and oxidative stress and modulating HSP70 and TLR-4/NF-kB pathway.

Agomelatine: A Potential Multitarget Compound for Neurodevelopmental Disorders

Agomelatine (AGM) is one of the latest atypical antidepressants, prescribed exclusively for the treatment of depression in adults. AGM belongs to the pharmaceutical class of melatonin agonist and selective serotonin antagonist ("MASS"), as it acts both as a selective agonist of melatonin receptors MT1 and MT2, and as a selective antagonist of 5-HT2C/5-HT2B receptors. AGM is involved in the resynchronization of interrupted circadian rhythms, with beneficial effects on sleep patterns, while antagonism on serotonin receptors increases the availability of norepinephrine and dopamine in the prefrontal cortex, with an antidepressant and nootropic effect. The use of AGM in the pediatric population is limited by the scarcity of data. In addition, few studies and case reports have been published on the use of AGM in patients with attention deficit and hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Considering this evidence, the purpose of this review is to report the potential role of AGM in neurological developmental disorders. AGM would increase the expression of the cytoskeleton-associated protein (ARC) in the prefrontal cortex, with optimization of learning, long-term memory consolidation, and improved survival of neurons. Another important feature of AGM is the ability to modulate glutamatergic neurotransmission in regions associated with mood and cognition. With its synergistic activity a melatoninergic agonist and an antagonist of 5-HT2C, AGM acts as an antidepressant, psychostimulant, and promoter of neuronal plasticity, regulating cognitive symptoms, resynchronizing circadian rhythms in patients with autism, ADHD, anxiety, and depression. Given its good tolerability and good compliance, it could potentially be administered to adolescents and children.

The effectiveness of anti-inflammatory agents in reducing chemotherapy-induced cognitive impairment in preclinical models - A systematic review

Chemotherapy-induced cognitive impairment (CICI) is a debilitating condition resulting from chemotherapy administration for cancer treatment. CICI is characterised by various cognitive impairments, including issues with learning, memory, and concentration, impacting quality of life. Several neural mechanisms are proposed to drive CICI, including inflammation, therefore, anti-inflammatory agents could ameliorate such impairments. Research is still in the preclinical stage; however, the efficacy of anti-inflammatories to reduce CICI in animal models is unknown. Therefore, a systematic review was conducted, with searches performed in PubMed, Scopus, Embase, PsycInfo and Cochrane Library. A total of 64 studies were included, and of the 50 agents identified, 41 (82%) reduced CICI. Interestingly, while non-traditional anti-inflammatory agents and natural compounds reduced impairment, the traditional agents were unsuccessful. Such results must be taken with caution due to the heterogeneity observed in terms of methods employed. Nevertheless, preliminary evidence suggests anti-inflammatory agents could be beneficial for treating CICI, although it may be critical to think beyond the use of traditional anti-inflammatories when considering which specific compounds to prioritise in development.

Agomelatine ameliorates cadmium-induced toxicity through the modification of HMGB-1/TLR-4/NFκB pathway

Cadmium (Cd) has potential hazards on human beings. Consequently, this study was performed to explore the protective effects of agomelatine (AGO), a melatonin receptor agonist, against Cd-induced toxicity in rats. AGO (40 mg/kg/day) was administered orally concomitant with intra peritoneal injection of Cd (0.4 mg/kg/day) for 14 days. Then, blood, biochemical parameters and histological examination of affected organs including, heart and testis, were evaluated. Interestingly, AGO significantly counteracted Cd-induced elevation of serum cardiac enzymes. Similarly, AGO significantly improved the deterioration of serum testosterone level with Cd administration. The oxidative balance was corrected by AGO, as evidenced by decrease malondialdehyde (MDA), and superoxide dismutase activity in cardiac and testicular tissues. Additionally, AGO increased silent information regulator 1 protein (SIRT-1) and decreased High mobility group box 1 (HMGB1), Toll like receptor-4 (TLR-4), and Myd88 levels that subsequently reduced expression of nuclear factor-κB (NF-κB). Moreover, level of apoptotic marker; caspase-3 was inhibited by AGO. In accordance with the biochemical and molecular results, AGO restored structure of cardiac myofibers and seminiferous tubules. Collectively, AGO mitigated cardiac and testicular toxicity of Cd via modulation of SIRT-1/HMGB1 and its downstream pathway.

Contact Lenses Loaded with Melatonin Analogs: A Promising Therapeutic Tool against Dry Eye Disease

Melatonin analogs topically administered evoke a potent tear secretagogue effect in rabbits. This route of drug administration requires high drug concentration and frequent dosing due to its reduced ocular surface retention. Therefore, contact lenses (CLs) have emerged as an alternative drug-delivery system that prolongs drug retention in the cornea, improving its therapeutic performance. This study explores the in vitro ability of five commercially available hydrogel CLs to act as a delivery system for melatonin analogs and the in vivo secretagogue effect of melatonin analog-loaded CLs. We soaked CLs with melatonin or melatonin analog solutions (1 mM) for 12 h. Spectroscopic assays showed that IIK7-loaded CLs led to the inadequate delivery of this compound. Conventional hydrogel lenses loaded with agomelatine released more agomelatine than silicone ones (16–33% more). In contrast, the CLs of silicone materials are more effective as a delivery system of 5-MCA-NAT than CLs of conventional materials (24–29%). The adaptation of CLs loaded with agomelatine or 5-MCA-NAT in rabbits triggered a higher tear secretion than the corresponding eye drops (78% and 59% more, respectively). These data suggest that CLs preloaded with melatonin analogs could be an adequate strategy to combat aqueous tear deficient dry eye disease.

NLRP3 Inflammasome Activation: A Therapeutic Target for Cerebral Ischemia–Reperfusion Injury

Millions of patients are suffering from ischemic stroke, it is urgent to figure out the pathogenesis of cerebral ischemia–reperfusion (I/R) injury in order to find an effective cure. After I/R injury, pro-inflammatory cytokines especially interleukin-1β (IL-1β) upregulates in ischemic brain cells, such as microglia and neuron. To ameliorate the inflammation after cerebral I/R injury, nucleotide-binding oligomerization domain (NOD), leucine-rich repeat (LRR), and pyrin domain-containing protein 3 (NLRP3) inflammasome is well-investigated. NLRP3 inflammasomes are complicated protein complexes that are activated by endogenous and exogenous danger signals to participate in the inflammatory response. The assembly and activation of the NLRP3 inflammasome lead to the caspase-1-dependent release of pro-inflammatory cytokines, such as interleukin (IL)-1β and IL-18. Furthermore, pyroptosis is a pro-inflammatory cell death that occurs in a dependent manner on NLRP3 inflammasomes after cerebral I/R injury. In this review, we summarized the assembly and activation of NLRP3 inflammasome; moreover, we also concluded the pivotal role of NLRP3 inflammasome and inhibitors, targeting the NLRP3 inflammasome in cerebral I/R injury.