PARP Inhibition Prevents Ethanol-Induced Neuroinflammatory Signaling and Neurodegeneration in Rat Adult-Age Brain Slice Cultures

Friedelin and Glutinol induce neuroprotection against ethanol induced neurotoxicity in pup's brain through reduction of TNF-α, NF-kB, caspase-3 and PARP-1

Ethanol administration triggers an inflammatory response that leads to a complex series of immune responses including the release of an excessive amount of inflammatory mediators particularly tumor necrosis factor (TNF-α) and nuclear factor-kB (NF-KB) which produce a large amount of reactive oxygen species. The inflammatory-induced cytotoxicity is increased when the PI3-kinase/Akt pathway is inhibited. Some studies have also shown that ethanol suppresses the PI3-kinase signaling pathway induced by receptor activation. Friedelin and Glutinol belong to pentacyclic triterpenoid class and are known for their anti-inflammatory and antioxidant properties. The present study was aimed to elucidate the effects of these phytoconstituents on one of the key ethanol-induced neuronal damage pathways. The pups having (5-7 g average body weight) were used and randomly divided into groups. The control and ethanol treated pups were administered 0.9% normal saline while treated pups received glutinol and friedelin (30 mg/kg subcutaneously) respectively. After four hours all the experimental animals were sacrificed and their brains were collected carefully for protein expression analysis of p-Akt, TNF-α, NF-KB, caspase-3 and PARP-1 employing immunoblotting technique. Hemolytic, DNA protection, chelating power and β-carotene assays results revealed that freidelin and glutinol are safe for parenteral administration. Glutinol administration with ethanol significantly abridged the ethanol induced over expression of TNF-α, caspase-3 and PARP-1 in pup's brain. Similarly, freidelin attenuated the neurodegeneration by inhibiting the ethanol induced p-JNK and NF-kB expression in pups' brain. This protection may be attributed to the revival of p-Akt signaling for cell survival. It is concluded that the present study demonstrates the neuro-protective effects of friedelin and glutinol via modulating the capase-3 and PARP-1 expression and modulating the neuronal apoptotic pathways.

Synergistic toxicity of ethanol and 2,4-dichlorophenoxyacetic acid enhances oxidant status, DNA damage, inflammation, and apoptosis in rats

Clarifying the interactions between substances as a result of exposure to multiple xenobiotics and determining the impacts on health are important from the toxicological point of view. Therefore, the aim of the study was to investigate the synergistic toxic effects of ethanol and 2,4-dichlorophenoxyacetic acid (2,4-D) in male albino rats. A total number of 28 Wistar male rats were divided into 4 groups (7/each), and 2,4-D (5 mg/kg) and ethanol (3 g/kg) were administered orally to rats for 60 days, either alone or in combination. Co-administration of ethanol and 2,4-D increased liver functional enzyme levels and lipid peroxidation in blood and tissues while decreased glutathione and antioxidant enzyme activities when compared to individual applications. Furthermore, co-administration of ethanol and 2,4-D caused DNA damage as well as the increase in apoptotic and proinflammatory cytokine gene expressions. Furthermore, histopathological examination of the tissues especially liver and kidney revealed that these two substances induced more serious damage. In conclusion, co-administration of ethanol and 2,4-D resulted in strong toxic effects on tissues (especially liver) with a synergistic interaction and give rise to serious toxicological drawbacks.

Resolution Potential of Necrotic Cell Death Pathways

During tissue damage caused by infection or sterile inflammation, not only damage-associated molecular patterns (DAMPs), but also resolution-associated molecular patterns (RAMPs) can be activated. These dying cell-associated factors stimulate immune cells localized in the tissue environment and induce the production of inflammatory mediators or specialized proresolving mediators (SPMs). Within the current prospect of science, apoptotic cell death is considered the main initiator of resolution. However, more RAMPs are likely to be released during necrotic cell death than during apoptosis, similar to what has been observed for DAMPs. The inflammatory potential of many regulated forms of necrotic cell death modalities, such as pyroptosis, necroptosis, ferroptosis, netosis, and parthanatos, have been widely studied in necroinflammation, but their possible role in resolution is less considered. In this review, we aim to summarize the relationship between necrotic cell death and resolution, as well as present the current available data regarding the involvement of certain forms of regulated necrotic cell death in necroresolution.

The Role of High Mobility Group Box 1 (HMGB1) in Neurodegeneration: A Systematic Review

BACKGROUND

High mobility group box 1 (HMGB1) protein is a damage-associated molecular pattern (DAMP) that plays an important role in the repair and regeneration of tissue injury. It also acts as a pro-inflammatory cytokine through the activation of toll-like receptor 4 (TLR4) and receptor for advanced glycation end products (RAGE), to elicit the neuroinflammatory response. HMGB1 may aggravate several cellular responses, which may lead to pathological inflammation and cellular death. Thus, there have been a considerable amount of research into the pathological role of HMGB1 in diseases. However, whether the mechanism of action of HMGB1 is similar in all neurodegenerative disease pathology remains to be determined.

OBJECTIVE

Therefore, this systematic review aimed to critically evaluate and elucidate the role of HMGB1 in the pathology of neurodegeneration based on the available literature.

METHODS

A comprehensive literature search was performed on four databases; EMBASE, PubMed, Scopus, and CINAHL Plus.

RESULTS

A total of 85 articles were selected for critical appraisal, after subjecting to the inclusion and exclusion criteria in this study. The selected articles revealed that HMGB1 levels were found elevated in most neurodegeneration except in Huntington's disease and Spinocerebellar ataxia, where the levels were found decreased. This review also showcased that HMGB1 may act on distinctive pathways to elicit its pathological response leading to the various neurodegeneration processes/ diseases.

CONCLUSION

While there have been promising findings in HMGB1 intervention research, further studies may still be required before any HMGB1 intervention may be recommended as a therapeutic target for neurodegenerative diseases.

DSS-induced inflammation in the colon drives a proinflammatory signature in the brain that is ameliorated by prophylactic treatment with the S100A9 inhibitor paquinimod

Background

Inflammatory bowel disease (IBD) is established to drive pathological sequelae in organ systems outside the intestine, including the central nervous system (CNS). Many patients exhibit cognitive deficits, particularly during disease flare. The connection between colonic inflammation and neuroinflammation remains unclear and characterization of the neuroinflammatory phenotype in the brain during colitis is ill-defined.

Methods

Transgenic mice expressing a bioluminescent reporter of active caspase-1 were treated with 2% dextran sodium sulfate (DSS) for 7 days to induce acute colitis, and colonic, systemic and neuroinflammation were assessed. In some experiments, mice were prophylactically treated with paquinimod (ABR-215757) to inhibit S100A9 inflammatory signaling. As a positive control for peripheral-induced neuroinflammation, mice were injected with lipopolysaccharide (LPS). Colonic, systemic and brain inflammatory cytokines and chemokines were measured by cytokine bead array (CBA) and Proteome profiler mouse cytokine array. Bioluminescence was quantified in the brain and caspase activation was confirmed by immunoblot. Immune cell infiltration into the CNS was measured by flow cytometry, while light sheet microscopy was used to monitor changes in resident microglia localization in intact brains during DSS or LPS-induced neuroinflammation. RNA sequencing was performed to identify transcriptomic changes occurring in the CNS of DSS-treated mice. Expression of inflammatory biomarkers were quantified in the brain and serum by qRT-PCR, ELISA and WB.

Results

DSS-treated mice exhibited clinical hallmarks of colitis, including weight loss, colonic shortening and inflammation in the colon. We also detected a significant increase in inflammatory cytokines in the serum and brain, as well as caspase and microglia activation in the brain of mice with ongoing colitis. RNA sequencing of brains isolated from DSS-treated mice revealed differential expression of genes involved in the regulation of inflammatory responses. This inflammatory phenotype was similar to the signature detected in LPS-treated mice, albeit less robust and transient, as inflammatory gene expression returned to baseline following cessation of DSS. Pharmacological inhibition of S100A9, one of the transcripts identified by RNA sequencing, attenuated colitis severity and systemic and neuroinflammation.

Conclusions

Our findings suggest that local inflammation in the colon drives systemic inflammation and neuroinflammation, and this can be ameliorated by inhibition of the S100 alarmin, S100A9.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-021-02317-6.

DNA damage and regulation of protein homeostasis

The accumulation of unrepaired DNA lesions is associated with many pathological outcomes in humans, particularly in neurodegenerative diseases and in normal aging. Evidence supporting a causal role for DNA damage in the onset and progression of neurodegenerative disease has come from rare human patients with mutations in DNA damage response genes as well as from model organisms; however, the generality of this relationship in the normal population is unclear. In addition, the relevance of DNA damage in the context of proteotoxic stress-the widely accepted paradigm for pathology during neurodegeneration-is not well understood. Here, observations supporting intertwined roles of DNA damage and proteotoxicity in aging-related neurological outcomes are reviewed, with particular emphasis on recent insights into the relationships between DNA repair and autophagy, the ubiquitin proteasome system, formation of protein aggregates, poly-ADP-ribose polymerization, and transcription-driven DNA lesions.

ADP-ribosylation in evasion, promotion and exacerbation of immune responses

ADP-ribosylation is the addition of one or more (up to some hundreds) ADP-ribose moieties to acceptor proteins. This evolutionary ancient post-translational modification (PTM) is involved in fundamental processes including DNA repair, inflammation, cell death, differentiation and proliferation, among others. ADP-ribosylation is catalysed by two major families of enzymes: the cholera toxin-like ADP-ribosyltransferases (ARTCs) and the diphtheria toxin-like ADP-ribosyltransferases (ARTDs, also known as PARPs). ARTCs sense and use extracellular NAD, which may represent a danger signal, whereas ARTDs are present in the cell nucleus and/or cytoplasm. ARTCs mono-ADP-ribosylate their substrates, whereas ARTDs, according to the specific family member, are able to mono- or poly-ADP-ribosylate target proteins or are devoid of enzymatic activity. Both mono- and poly-ADP-ribosylation are dynamic processes, as specific hydrolases are able to remove single or polymeric ADP moieties. This dynamic equilibrium between addition and degradation provides plasticity for fast adaptation, a feature being particularly relevant to immune cell functions. ADP-ribosylation regulates differentiation and functions of myeloid, T and B cells. It also regulates the expression of cytokines and chemokines, production of antibodies, isotype switch and the expression of several immune mediators. Alterations in these processes involve ADP-ribosylation in virtually any acute and chronic inflammatory/immune-mediated disease. Besides, pathogens developed mechanisms to contrast the action of ADP-ribosylating enzymes by using their own hydrolases and/or to exploit this PTM to sustain their virulence. In the present review, we summarize and discuss recent findings on the role of ADP-ribosylation in immunobiology, immune evasion/subversion by pathogens and immune-mediated diseases.

Neurotoxic Effect of Flavonol Myricetin in the Presence of Excess Copper

Oxidative stress (OS) induced by the disturbed homeostasis of metal ions is one of the pivotal factors contributing to neurodegeneration. The aim of the present study was to investigate the effects of flavonoid myricetin on copper-induced toxicity in neuroblastoma SH-SY5Y cells. As determined by the MTT method, trypan blue exclusion assay and measurement of ATP production, myricetin heightened the toxic effects of copper and exacerbated cell death. It also increased copper-induced generation of reactive oxygen species, indicating the prooxidative nature of its action. Furthermore, myricetin provoked chromatin condensation and loss of membrane integrity without caspase-3 activation, suggesting the activation of both caspase-independent programmed cell death and necrosis. At the protein level, myricetin-induced upregulation of PARP-1 and decreased expression of Bcl-2, whereas copper-induced changes in the expression of p53, p73, Bax and NME1 were not further affected by myricetin. Inhibitors of ERK1/2 and JNK kinases, protein kinase A and L-type calcium channels exacerbated the toxic effects of myricetin, indicating the involvement of intracellular signaling pathways in cell death. We also employed atomic force microscopy (AFM) to evaluate the morphological and mechanical properties of SH-SY5Y cells at the nanoscale. Consistent with the cellular and molecular methods, this biophysical approach also revealed a myricetin-induced increase in cell surface roughness and reduced elasticity. Taken together, we demonstrated the adverse effects of myricetin, pointing out that caution is required when considering powerful antioxidants for adjuvant therapy in copper-related neurodegeneration.

Sevoflurane Exposure Induces Neuronal Cell Parthanatos Initiated by DNA Damage in the Developing Brain via an Increase of Intracellular Reactive Oxygen Species

The safety of volatile anesthetics in infants and young children has been drawing increasing concern due to its potential neurotoxicity in the developing brain. Neuronal death is considered a major factor associated with developmental neurotoxicity after exposure to volatile anesthetics sevoflurane, but its mechanism remains elusive. Parthanatos, a new type of programmed cell death, resulting from poly (ADP-ribose) polymerase 1 (PARP-1) hyperactivation in response to DNA damage, was found to account for the pathogenesis of multiple neurological disorders. However, the role of Parthanatos in sevoflurane-induced neonatal neuronal cell death has not been investigated. To test it, neuronal cells treated with 2, 4, and 8% sevoflurane for 6, 12, and 24 h and postnatal day 7 rats exposed to 2.5% sevoflurane for 6 h were used in the present study. Our results found sevoflurane exposure induced neuronal cell death, which was accompanied by PARP-1 hyperactivation, cytoplasmic polymerized ADP-ribose (PAR) accumulation, mitochondrial depolarization, and apoptosis-inducing factor (AIF) nuclear translocation in the neuronal cells and hippocampi of rats. Pharmacological or genetic inhibition of PAPR-1 significantly alleviated sevoflurane-induced neuronal cell death and accumulation of PAR polymer and AIF nuclear translocation, which were consistent with the features of Parthanatos. We observed in vitro and in vivo that sevoflurane exposure resulted in DNA damage, given that 8-hydroxydeoxyguanosine (8-OHdG) and phosphorylation of histone variant H2AX (γH2AX) were improved. Moreover, we detected that sevoflurane exposure was associated with an overproduction of intracellular reactive oxygen species (ROS). Inhibition of ROS with antioxidant NAC markedly alleviated DNA damage caused by sevoflurane, indicating that ROS participated in the regulation of sevoflurane-induced DNA damage. Additionally, sevoflurane exposure resulted in upregulation of Parthanatos-related proteins and neuronal cell death, which were significantly attenuated by pretreatment with NAC. Therefore, these results suggest that sevoflurane exposure induces neuronal cell Parthanatos initiated by DNA damage in the developing brain via the increase of intracellular ROS.

Modulation of Poly ADP Ribose Polymerase (PARP) Levels and Activity by Alcohol Binge-Like Drinking in Male Mice

Binge drinking is a frequent pattern of ethanol consumption within Alcohol Use Disorders (AUDs). Binge-like ethanol exposure increases Poly(ADP-ribose) polymerase (PARP) expression and activity. PARP enzymes have been implicated in addiction and serve multiple roles in the cell, including gene expression regulation. In this study, we examined the effects of binge-like alcohol consumption in the prefrontal cortex (PFC) of adult C57BL/6J male mice via a 4-day Drinking-in-the-Dark (DID) paradigm. The role of PARP in associated gene expression and behavioral changes was assessed by administering the PARP inhibitor ABT-888 on the last DID day. We then conducted an RNA-seq analysis of the PFC gene expression changes associated with DID-consumed ethanol or ABT-888 treatment. A separate cohort of mice was inoculated with an HSV-PARP1 vector in the PFC and subject to a DID experiment to verify whether overexpressed PARP1 increased ethanol drinking. We confirmed that alcohol increases Parp1 gene expression and PARP activity in the PFC. RNA-seq showed significantly altered expression of 41 genes by DID-consumed ethanol, and of 48 genes by ABT-888. These results were confirmed by qPCR in 7 of the 10 genes validated, 4 of which have been previously associated with addiction. ABT-888 reduced, and overexpression of PFC PARP1 increased DID ethanol consumption. In our model, alcohol binge drinking induced specific alterations in the PFC expression of genes potentially involved in addiction. Pharmacological PARP inhibition proved effective in reversing these changes and preventing further alcohol consumption. Our results suggest an involvement of ethanol-induced PARP1 in reinforcing binge-like addictive behavior.

Poly(ADP-ribose) polymerase inhibition: past, present and future

The process of poly(ADP-ribosyl)ation and the major enzyme that catalyses this reaction, poly(ADP-ribose) polymerase 1 (PARP1), were discovered more than 50 years ago. Since then, advances in our understanding of the roles of PARP1 in cellular processes such as DNA repair, gene transcription and cell death have allowed the investigation of therapeutic PARP inhibition for a variety of diseases - particularly cancers in which defects in DNA repair pathways make tumour cells highly sensitive to the inhibition of PARP activity. Efforts to identify and evaluate potent PARP inhibitors have so far led to the regulatory approval of four PARP inhibitors for the treatment of several types of cancer, and PARP inhibitors have also shown therapeutic potential in treating non-oncological diseases. This Review provides a timeline of PARP biology and medicinal chemistry, summarizes the pathophysiological processes in which PARP plays a role and highlights key opportunities and challenges in the field, such as counteracting PARP inhibitor resistance during cancer therapy and repurposing PARP inhibitors for the treatment of non-oncological diseases.

Ethanol Stimulation of Microglia Release Increases ERK1/2-Dependent Neuronal cPLA2 Activity in Immature Cultured Cortical Preparations

Ethanol consumption typically begins during adolescence and is associated with age-dependent responses and maladaptive neuronal consequences. Our previous work established the role of a putative signaling cascade involving cytoplasmic phospholipase A₂ (cPLA₂), arachidonic acid (AA) and novel protein kinase C isoforms in adolescent hypnotic sensitivity. The current study aimed to further delineate this pathway by ascertaining the cellular specificity as well as the upstream activators of cPLA₂ using an immature cultured cortical preparation. A threefold increase in cPLA₂ was detected within 2 min of 100 mM ethanol exposure as measured by phosphorylation of serine 505 (Ser505). Increases in cPLA₂ activity were further observed to be primarily confined to neuronal cells. Increases in the number of neurons co-expressing cPLA2 Ser505 phosphorylation were prevented by preincubation with an ERK1/2 inhibitor, but not P38 MAPK inhibition. Finally, conditioned media studies were used to determine whether glial cells were involved in the ethanol-induced neuronal cPLA₂ activity. Rapid increases in neuronal cPLA2 activity appears to be initiated through ethanol stimulated microglial, but not astrocytic releasable factors. Taken together, these data extend the proposed signaling cascade involved in developmental ethanol responding.

PARP inhibition in vivo blocks alcohol-induced brain neurodegeneration and neuroinflammatory cytosolic phospholipase A2 elevations

Chronic alcoholism promotes brain damage that impairs memory and cognition. High binge alcohol levels in adult rats also cause substantial neurodamage to memory-linked regions, notably, the hippocampus (HC) and entorhinal cortex (ECX). Concurrent with neurodegeneration, alcohol elevates poly (ADP-ribose) polymerase-1 (PARP-1) and cytosolic phospholipase A2 (cPLA2) levels. PARP-1 triggers necrosis when excessively activated, while cPLA2 liberates neuroinflammatory ω-6 arachidonic acid. Inhibitors of PARP exert in vitro neuroprotection while suppressing cPLA2 elevations in alcohol-treated HC-ECX slice cultures. Here, we examined in vivo neuroprotection and cPLA2 suppression by the PARP inhibitor, veliparib, in a recognized adult rat model of alcohol-binging. Adult male rats received Vanilla Ensure containing alcohol (ethanol, 7.1 ± 0.3 g/kg/day), or control (dextrose) ± veliparib (25 mg/kg/day), by gavage 3x daily for 4 days. Rats were sacrificed on the morning after the final binge. HC and ECX neurodegeneration was assessed in fixed sections by Fluoro-Jade B (FJB) staining. Dorsal HC, ventral HC, and ECX cPLA2 levels were quantified by immunoblotting. Like other studies using this model, alcohol binges elevated FJB staining in the HC (dentate gyrus) and ECX, indicating neurodegeneration. Veliparib co-treatment significantly reduced dentate gyrus and ECX neurodegeneration by 79% and 66%, respectively. Alcohol binges increased cPLA2 in the ventral HC by 34% and ECX by 72%, which veliparib co-treatment largely prevented. Dorsal HC cPLA2 levels remained unaffected by alcohol binges, consistent with negligible FJB staining in this brain region. These in vivo results support an emerging key role for PARP in binge alcohol-induced neurodegeneration and cPLA2-related neuroinflammation.

Neuroimmune signaling in alcohol use disorder

Alcohol use disorder (AUD) is a widespread disease with limited treatment options. Targeting the neuroimmune system is a new avenue for developing or repurposing effective pharmacotherapies. Alcohol modulates innate immune signaling in different cell types in the brain by altering gene expression and the molecular pathways that regulate neuroinflammation. Chronic alcohol abuse may cause an imbalance in neuroimmune function, resulting in prolonged perturbations in brain function. Likewise, manipulating the neuroimmune system may change alcohol-related behaviors. Psychiatric disorders that are comorbid with AUD, such as post-traumatic stress disorder, major depressive disorder, and other substance use disorders, may also have underlying neuroimmune mechanisms; current evidence suggests that convergent immune pathways may be involved in AUD and in these comorbid disorders. In this review, we provide an overview of major neuroimmune cell-types and pathways involved in mediating alcohol behaviors, discuss potential mechanisms of alcohol-induced neuroimmune activation, and present recent clinical evidence for candidate immune-related drugs to treat AUD.

Hydrogen‑rich medium alleviates high glucose‑induced oxidative stress and parthanatos in rat Schwann cells in vitro

Diabetic peripheral neuropathy (DPN) is considered to be the most common cause of microvascular diabetic complications, for which no effective therapies currently exist. Previous studies have identified that oxidative stress is the common pathway in all possible hypotheses for the induction of DPN, and poly(ADP-ribose) (PAR) polymerase-1 (PARP-1)-dependent cell death (parthanatos) is key in the pathogenic mechanisms of neurodegenerative disease. The aim of the present study was to investigate the protective effects and corresponding mechanisms of hydrogen-rich medium (HM) on high glucose (HG)-induced oxidative stress and parthanatos in primary rat Schwann cells (RSCs) in vitro. The RSCs were divided into groups and treated for 48 h. Cell counting kit-8 and lactate dehydrogenase assays were used to detect cell viability and cytotoxicity, respectively; intracellular OH⁻ levels were measured using a DCFH-DA assay; concentrations of peroxynitrite (ONOO⁻) and 8-hydroxy deoxyguanosine (8-OHdG) were evaluated with an enzyme-linked immunosorbent assay; relative expression levels of parthanatos-related proteins [PAR, nucleus apoptosis-inducing factor (AIF) and total AIF] were analyzed using western blot analysis, and immunofluorescence was used to determine the nuclear translocation of AIF. After 48 h, HG was shown to induce severe oxidative stress and promote marked levels of parthanatos in the RSCs. Treatment with HM inhibited HG-induced oxidative stress by reducing the production of OH⁻ and ONOO⁻ and suppressed parthanatos by downregulating the levels of 8-OHdG, the expression of PAR and the nuclear translocation of AIF. HM improved cell viability and inhibited cytotoxicity under the HG condition. These results indicate that HM effectively reduces HG-induced oxidative stress in RSCs and protects them against parthanatos. Therefore, HM may be a novel treatment for DPN.

Regional Differences and Similarities in the Brain Transcriptome for Mice Selected for Ethanol Preference From HS-CC Founders

The high genetic complexity found in heterogeneous stock (HS-CC) mice, together with selective breeding, can be used to detect new pathways and mechanisms associated with ethanol preference and excessive ethanol consumption. We predicted that these pathways would provide new targets for therapeutic manipulation. Previously (Colville et al., 2017), we observed that preference selection strongly affected the accumbens shell (SH) genes associated with synaptic function and in particular genes associated with synaptic tethering. Here we expand our analyses to include substantially larger sample sizes and samples from two additional components of the “addiction circuit,” the central nucleus of the amygdala (CeA) and the prelimbic cortex (PL). At the level of differential expression (DE), the majority of affected genes are region-specific; only in the CeA did the DE genes show a significant enrichment in GO annotation categories, e.g., neuron part. In all three brain regions the differentially variable genes were significantly enriched in a single network module characterized by genes associated with cell-to-cell signaling. The data point to glutamate plasticity as being a key feature of selection for ethanol preference. In this context the expression of Dlg2 which encodes for PSD-93 appears to have a key role. It was also observed that the expression of the clustered protocadherins was strongly associated with preference selection.