Neuroprotective effects of tert-butylhydroquinone on paraquat-induced dopaminergic cell degeneration in C57BL/6 mice and in PC12 cells

Protective Effects of Polyphenol-Rich Extracts against Neurotoxicity Elicited by Paraquat or Rotenone in Cellular Models of Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative disorder involving motor symptoms caused by a loss of dopaminergic neurons in the substantia nigra region of the brain. Epidemiological evidence suggests that anthocyanin (ANC) intake is associated with a low risk of PD. Previously, we reported that extracts enriched with ANC and proanthocyanidins (PAC) suppressed dopaminergic neuron death elicited by the PD-related toxin rotenone in a primary midbrain culture model. Here, we characterized botanical extracts enriched with a mixed profile of polyphenols, as well as a set of purified polyphenolic standards, in terms of their ability to mitigate dopaminergic cell death in midbrain cultures exposed to another PD-related toxicant, paraquat (PQ), and we examined underlying neuroprotective mechanisms. Extracts prepared from blueberries, black currants, grape seeds, grape skin, mulberries, and plums, as well as several ANC, were found to rescue dopaminergic neuron loss in PQ-treated cultures. Comparison of a subset of ANC-rich extracts for the ability to mitigate neurotoxicity elicited by PQ versus rotenone revealed that a hibiscus or plum extract was only neuroprotective in cultures exposed to rotenone or PQ, respectively. Several extracts or compounds with the ability to protect against PQ neurotoxicity increased the activity of the antioxidant transcription factor Nrf2 in cultured astrocytes, and PQ-induced dopaminergic cell death was attenuated in Nrf2-expressing midbrain cultures. In other studies, we found that extracts prepared from hibiscus, grape skin, or purple basil (but not plums) rescued defects in O₂ consumption in neuronal cells treated with rotenone. Collectively, these findings suggest that extracts enriched with certain combinations of ANC, PAC, stilbenes, and other polyphenols could potentially slow neurodegeneration in the brains of individuals exposed to PQ or rotenone by activating cellular antioxidant mechanisms and/or alleviating mitochondrial dysfunction.

The role of Nrf2/HO-1 signal pathway in regulating aluminum-induced apoptosis of PC12 cells

BACKGROUND

Aluminum has definite neurotoxicity and can lead to apoptosis of nerve cells, but the specific mechanism remains to be further explored. The aim of this study was to investigate the role of Nrf2/HO-1 signaling pathway in neural cell apoptosis induced by aluminum exposure.

METHODS

In this study, PC12 cells were used as the research object, aluminum maltol [Al(mal)₃] was used as the exposure agent, and tert-butyl hydroquinone (TBHQ), an agonist of Nrf2, was used as the intervention agent to construct an in vitro cell model. Cell viability was detected by CCK-8 method, cell morphology was observed by light microscope, cell apoptosis was measured by flow cytometry, and expression of Bax and Bcl-2 proteins and Nrf2/HO-1 signaling pathway proteins were investigated by western blotting.

RESULTS

With the increase of Al(mal)₃ concentration, PC12 cell viability decreased, the early apoptosis rate and total apoptosis rate increased, the ratio of Bcl-2 and Bax protein expression decreased, and Nrf2/HO-1 pathway protein expression decreased. The use of TBHQ could activate the Nrf2/HO-1 pathway and reverse the apoptosis of PC12 cells induced by aluminum exposure.

CONCLUSION

Nrf2/HO-1 signaling pathway plays a neuroprotective role in the apoptosis of PC12 cells caused by Al(mal)₃, which provides a possible target for the intervention of aluminum induced neurotoxicity.

Protective effects of polyphenol-rich extracts against neurotoxicity elicited by paraquat or rotenone in cellular models of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder involving motor symptoms caused by a loss of dopaminergic neurons in the substantia nigra region of the brain. Epidemiological evidence suggests that anthocyanin (ANC) intake is associated with a low risk of PD. Previously, we reported that extracts enriched with ANC and proanthocyanidins (PAC) suppressed dopaminergic neuron death elicited by the PD-related toxin rotenone in a primary midbrain culture model. Here, we characterized botanical extracts enriched with a mixed profile of polyphenols, as well as a set of purified polyphenolic standards, in terms of their ability to mitigate dopaminergic cell death in midbrain cultures exposed to another PD-related toxicant, paraquat (PQ), and we examined underlying neuroprotective mechanisms. Extracts prepared from blueberries, black currants, grape seeds, grape skin, mulberries, and plums, as well as several ANC, were found to rescue dopaminergic neuron loss in PQ-treated cultures. Comparison of a subset of ANC-rich extracts for the ability to mitigate neurotoxicity elicited by PQ versus rotenone revealed that a hibiscus or plum extract was only neuroprotective in cultures exposed to rotenone or PQ, respectively. Several extracts or compounds with the ability to protect against PQ neurotoxicity increased the activity of the antioxidant transcription factor Nrf2 in cultured astrocytes, and PQ-induced dopaminergic cell death was attenuated in Nrf2-expressing midbrain cultures. In other studies, we found that extracts prepared from hibiscus, grape skin, or purple basil (but not plums) rescued defects in O ₂ consumption in neuronal cells treated with rotenone. Collectively, these findings suggest that extracts enriched with certain combinations of ANC, PAC, stilbenes, and other polyphenols could potentially slow neurodegeneration in the brains of individuals exposed to PQ or rotenone by activating cellular antioxidant mechanisms and/or alleviating mitochondrial dysfunction.

The interplay between lncRNA NR_030777 and SF3B3 in neuronal damage caused by paraquat

Paraquat (PQ) has been widely acknowledged as an environmental risk factor for Parkinson's disease (PD). However, the interaction between splicing factor and long non-coding RNA (lncRNA) in the process of PQ-induced PD has rarely been studied. Based on previous research, this study focused on splicing factor 3 subunit 3 (SF3B3) and lncRNA NR_030777. After changing the target gene expression level by lentiviral transfection technology, the related gene expression was detected by western blot and qRT-PCR. The expression of SF3B3 protein was reduced in Neuro-2a cells after PQ exposure, and the reactive oxygen species (ROS) scavenger N-acetylcysteine prevented this decline. Knockdown of SF3B3 reduced the PQ-triggered NR_030777 expression increase, and overexpression of NR_030777 reduced the transcriptional and translational level of Sf3b3. Then, knockdown of SF3B3 exacerbated the PQ-induced decrease in cell viability and aggravated the reduction of tyrosine hydroxylase (TH) protein expression. Overexpressing SF3B3 reversed the reduction of TH expression caused by PQ. Moreover, after intervention with the autophagy inhibitor Bafilomycin A1, LC3B-II protein expression was further increased in Neuro-2a cells with the knockdown of SF3B3, indicating that autophagy was enhanced. In conclusion, PQ modulated the interplay between NR_030777 and SF3B3 through ROS production, thereby impairing autophagic flux and causing neuronal damage.

Pharmacological Modulation of Nrf2/HO-1 Signaling Pathway as a Therapeutic Target of Parkinson's Disease

Parkinson’s disease (PD) is a complex neurodegenerative disorder featuring both motor and nonmotor symptoms associated with a progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Oxidative stress (OS) has been implicated in the pathogenesis of PD. Genetic and environmental factors can produce OS, which has been implicated as a core contributor to the initiation and progression of PD through the degeneration of dopaminergic neurons. The transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) orchestrates activation of multiple protective genes, including heme oxygenase-1 (HO-1), which protects cells from OS. Nrf2 has also been shown to exert anti-inflammatory effects and modulate both mitochondrial function and biogenesis. Recently, a series of studies have reported that different bioactive compounds were shown to be able to activate Nrf2/antioxidant response element (ARE) and can ameliorate PD-associated neurotoxin, both in animal models and in tissue culture. In this review, we briefly overview the sources of OS and the association between OS and the pathogenesis of PD. Then, we provided a concise overview of Nrf2/ARE pathway and delineated the role played by activation of Nrf2/HO-1 in PD. At last, we expand our discussion to the neuroprotective effects of pharmacological modulation of Nrf2/HO-1 by bioactive compounds and the potential application of Nrf2 activators for the treatment of PD. This review suggests that pharmacological modulation of Nrf2/HO-1 signaling pathway by bioactive compounds is a therapeutic target of PD.

Epigenetics in neurodegenerative disorders induced by pesticides

Neurodegenerative diseases are becoming major socio-economic burdens. However, most of them still have no effective treatment. Growing evidence indicates excess exposure to pesticides are involved in the development of various forms of neurodegenerative and neurological diseases through trigger epigenetic changes and inducing disruption of the epigenome. This review summaries studies on epigenetics alterations in nervous systems in relation to different kinds of pesticides, highlighting potential mechanism in the etiology, precision prevention and target therapy of various neurodegenerative diseases. In addition, the current gaps in research and future areas for study were also discussed.

Paraquat-induced oxidative stress regulates N6-methyladenosine (m6A) modification of circular RNAs

Paraquat (PQ), a widely used herbicide and well-known oxidative stress inducer, has been linked to numerous neurodegenerative diseases, but the underlying mechanism(s) remains unknown. Circular RNAs (circRNAs) have recently been reported to be associated with oxidative stress in Parkinson's disease. Herein, we performed methylated RNA immunoprecipitation and RNA sequencing assays for mouse neuroblastoma (Neuro-2a) cells and successfully established a positive link between the alteration of circRNAs driven by m⁶A modification and PQ-induced oxidative stress. We observed oxidative stress and antioxidative stress present distinct m⁶A modification pattern of circRNAs as well as biological effect. Gene ontology and pathway analysis predicted that differentially m⁶A-methylated and expressed circRNAs are highly clustered in pathways associated with function and development of nervous system, including axon cargo transport, nervous system development, long-term potentiation, and neurotrophic signaling pathways. Moreover, we demonstrated that the alteration of m⁶A-methylated circRNAs upon PQ exposure could be partially reversed by N-acetylcysteine pretreatment. The mechanistic analysis further demonstrated that N-acetylcysteine pretreatment attenuated the decreased expression of target genes (UBC and PPP2CA) induced by PQ. These findings revealed distinct patterns of differentially m⁶A-modified circRNAs, indicating that m⁶A could participate in a specific regulatory network of circRNAs to modulate the expression of downstream genes in response to PQ-induced oxidative stress. In conclusion, our work established a link between m⁶A modification of circRNAs and PQ-induced oxidative stress, and further studies are required to explore the underlying molecular mechanisms associated with PQ-induced neurotoxicity.

LncRNA NR_030777 Alleviates Paraquat-Induced Neurotoxicity by Regulating Zfp326 and Cpne5

Paraquat (PQ) is herbicide widely used in agricultural production. It is identified as an environmental toxicant that could lead to neurodegeneration damage. Parkinson's disease (PD) is a central nervous system degenerative disease that occurs in the elderly. Main risk factors for PD include genetic and environmental variables, but its specific mechanism is still not well understood. Emerging evidence suggests that long noncoding RNAs (lncRNAs) play an important role in PD. LncRNA NR_030777 has a full length of 2208 bp and is highly conserved among species. RNA profiling showed a significant alteration in lncRNA NR_030777 expression upon PQ-induced neurotoxicity. However, little is known on the functional relevance of lncRNA NR_030777 in the development of PQ. In this study, we discovered a vital protective role of lncRNA NR_030777 in PQ-induced neurotoxicity. The expression of NR_030777 correlates with elevated level of reactive oxygen species induced by PQ. In addition, activated expression of NR_030777 alleviates neurotoxicity by regulating the expression of Zfp326 and Copine 5. We report that lncRNA NR_030777 has a vital protective role in neurotoxicity induced by environmental toxicants such as PQ. This study could serve as an exemplary case for lncRNAs to be considered as a potential target for the prevention and treatment of PQ-induced neurodegenerative disorders such as PD.

Drp1-mediated mitochondrial fission contributes to mitophagy in paraquat-induced neuronal cell damage

Paraquat (PQ) is one of the most widely used herbicides in the world due to its excellent weed control effects. Accumulating evidence has revealed that long-term exposure to PQ can significantly increase the risk of Parkinson's disease (PD). However, the underlying molecular mechanisms are yet to be fully understood. Hence, we investigated the potential role of reactive oxygen species (ROS) and dynamin-related protein 1 (DRP1) in PQ-induced mitophagy, aiming to elaborate on possible molecular mechanisms involved in PQ-triggered neurotoxicity. Our results showed that ROS were increased, mitochondrial membrane potential was decreased at 100, 200, and 300 μM PQ concentrations, and autophagy pathways were activated at a concentration of 100 μM in neuronal cells. In addition, excessive mitophagy was observed in neurons exposed to 300 μM PQ for 24 h. Then, ROS-mediated mitochondrial fission was found to contribute to PQ-induced excessive mitophagy. Moreover, all aforementioned changes were significantly ameliorated by mdivi-1. Thus, our findings provide a novel neurotoxic mechanism and reveal the DRP1-mitochondrial fission pathway as a potential target for treatments of PQ-induced excessive mitophagy, serving as an alternative target for the prevention and treatment of Parkinson's disease. Because harmful substances are transmitted and enriched in the food chain, the toxic effect of environmental paraquat is nonnegligible, and more investigations are needed.

Paraquat increases Interleukin-1β in hippocampal dentate gyrus to impair hippocampal neurogenesis in adult mice

Paraquat (1,1'-dimethyl-4,4'-bipyridium dichloride, PQ), a non-selective and efficient herbicide, causes neuroinflammation, neurodegeneration and memory dysfunction. However, adverse effects of PQ on the neuroimmune interactions have rarely been investigated. Female adult C57/BL6 mice were divided into 3 groups and treated with PQ (intraperitoneal injection, 1 mg/kg or 5 mg/kg) or the vehicle (an equivalent volume of 0.9% saline) every two days, at day 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, for a total of 14 doses. We evaluated blood-brain barrier (BBB) integrity and PQ concentrations during the course of PQ exposure and tested interleukin-1β (IL-1β) concentrations in dentate gyrus (DG) after 28 days PQ exposure. In addition, memory function, neural stem cells (NSCs) proliferation, neurogenesis and microglia polarization were analyzed after PQ exposure. Furthermore, mice were intraperitoneal injections of anti-IL-1β during 5 mg/kg PQ exposure to test the rule of IL-1β. Blood-brain barrier (BBB) permeability and PQ concentrations increased gradually during PQ exposure (n = 6). Moreover, memory function, NSCs proliferation and neurogenesis were impaired after 5 mg/kg PQ exposure (n = 6). Further analyses revealed that 'classically' activated (M1) microglia and IL-1β concentrations in DG were increased after 5 mg/kg PQ treatment (n = 6). Moreover, we found that neutralization of IL-1β partly restored PQ-induced NSCs impairments and memory dysfunction (n = 6). In conclusion, our results revealed that PQ induced NSCs impairments and memory dysfunction in adult mice, which was related to the release of IL-1β by M1-polarized microglia in DG. These findings may help understand the neurotoxic effect of PQ.

Redox toxicology of environmental chemicals causing oxidative stress

Living organisms are surrounded with heavy metals such as methylmercury, manganese, cobalt, cadmium, arsenic, as well as pesticides such as deltamethrin and paraquat, or atmospheric pollutants such as quinone. Extensive studies have demonstrated a strong link between environmental pollutants and human health. Redox toxicity is proposed as one of the main mechanisms of chemical-induced pathology in humans. Acting as both a sensor of oxidative stress and a positive regulator of antioxidants, the nuclear factor erythroid 2-related factor 2 (NRF2) has attracted recent attention. However, the role NRF2 plays in environmental pollutant-induced toxicity has not been systematically addressed. Here, we characterize NRF2 function in response to various pollutants, such as metals, pesticides and atmospheric quinones. NRF2 related signaling pathways and epigenetic regulations are also reviewed.

Nrf2-regulated miR-380-3p Blocks the Translation of Sp3 Protein and Its Mediation of Paraquat-Induced Toxicity in Mouse Neuroblastoma N2a Cells

Laboratorial and epidemiological research has established a relationship between paraquat (PQ) exposure and a risk for Parkinson's disease. Previously, we have investigated the effects of nuclear factor erythroid 2 related factor 2 (Nrf2) and microRNAs in PQ-induced neurotoxicity, addressing the function of miR-380-3p, a microRNA dysregulated by PQ, as well as Nrf2 deficiency. Nrf2 is known to mediate the expression of a variety of genes, including noncoding genes. By chromatin immunoprecipitation, we identified the relationship between Nrf2 and miR-380-3p in transcriptional regulation. qRT-PCR, Western blots, and dual-luciferase reporter gene assay showed that miR-380-3p blocked the translation of the transcription factor specificity protein-3 (Sp3) in the absence of degradation of Sp3 mRNA. Results based on cell counting analysis, annexin v-fluorescein isothiocyanate/propidium iodide double-staining assay, and propidium iodide staining showed that overexpression of miR-380-3p inhibited cell proliferation, increased the apoptotic rate, induced cell cycle arrest, and intensified the toxicity of PQ in mouse neuroblastoma (N2a [Neuro2a]) cells. Knockdown of Sp3 inhibited cell proliferation and eclipsed the alterations induced by miR-380-3p in cell proliferation. Two mediators of apoptosis and cell cycle identified in previous studies as Sp3-regulated, namely cyclin-dependent kinase inhibitor 1 (p21) and calmodulin (CaM), were dysregulated by PQ, but not Sp3 deficiency. In conclusion, Nrf2-regulated miR-380-3p inhibited cell proliferation and enhanced the PQ-induced toxicity in N2a cells potentially by blocking the translation Sp3 mRNA. We conclude that CaM and p21 were involved in PQ-induced toxicity.

The significance of serum HMGB1 level in humans with acute paraquat poisoning

High-mobility group box 1 (HMGB1) mediates acute lung injury in a mouse model of paraquat poisoning. However, published reports showing a clinically relevant association between HMGB1 and paraquat exposure are lacking. The objective of the present study was to investigate the potential role of serum HMGB1 level as a prognostic marker of mortality in patients with paraquat poisoning in a clinical setting. This retrospective observational cohort study included a convenience sample of 92 patients with acute paraquat poisoning admitted to the emergency room (ER) of The First Hospital of Jilin University between January 2014 and December 2016. Baseline serum HMGB1 levels and other laboratory parameters were measured on admission. Cumulative incidence of mortality during the first 30 days after admission was 50% (n = 46/92). Serum HMGB1 levels were higher in fatalities than survivors (P = 0.015), 30-day mortality increased with increasing baseline serum HMGB1 level (P < 0.001), and higher serum HMGB1 levels were associated with an increase in 30-day mortality on Kaplan-Meier analysis. Multivariate Cox regression analysis identified baseline serum HMGB1 levels, white blood cell count, and serum lactic acid levels as independent prognostic markers of 30-day mortality. These data suggest that serum HMGB1 levels measured on admission to the ER are an independent predictor of 30-day mortality in patients with acute paraquat poisoning.

Evaluation of Nrf2 with Exposure to Nanoparticles

Transcription factor Nrf2, nuclear factor (erythroid-derived 2)-like 2, is considered a master regulator of redox homeostasis and plays a central role in antioxidant and anti-inflammatory defence. It has been largely reported that oxidative stress is implicated in nanoparticle-induced toxicity with the involvement of Nrf2. Several basic methods for Nrf2 evaluation with exposure to nanoparticles are described in this chapter including real-time reverse transcription-polymerase chain reaction (RT-PCR), western blotting, immunofluorescence staining, electrophoretic mobility shift assay, DNase I footprinting, dimethylsulfate footprinting, protein pulse-chase analysis, and tert-butylhydroquinone treatment.

Paraquat and MPTP induce alteration in the expression profile of long noncoding RNAs in the substantia nigra of mice: Role of the transcription factor Nrf2

Parkinson's disease (PD) is a common age-related degenerative disease of the central nervous system caused mainly by hereditary, pesticides, metals, and polychlorinated biphenyls. Paraquat (PQ), a widely used herbicide, causes PD. Long noncoding RNAs (lncRNAs) are nonprotein-coding transcripts, expressed in the brain and play irreplaceable roles in neurodegenerative diseases. NF-E2-related factor-2 (Nrf2) is an important genetic transcription regulator in oxidative stress. We aimed to discover novel PQ or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-Nrf2-related lncRNAs and explore their association with PD. 17157 lncRNAs and 13707 mRNAs (fold change ≥2, P < 0.05) were identified by Microarray. And the expressions of six lncRNAs were confirmed by using qRT-PCR and two by FISH. Coding-noncoding analysis and qRT-PCR were applied to discover the functions of lncRNAs and predict the targeted genes. In mice, PQ and MPTP exposure caused alteration of the lncRNA expression profile, suggesting lncRNAs may be involved in PQ- and MPTP-induced neurotoxicity. The changes in their lncRNA expression were distinct but related. PQ caused lncRNA expression profiling alteration in the substantia nigra (SN) through an interaction with Nrf2, thus changing the NR_027648/Zc3h14/Cybb and NR_030777/Zfp326/Cpne5 mRNA pathways. Similarly, MPTP caused lncRNA expression profiling alteration in SN through an interaction with Nrf2. Nrf2 may be involved in the development of neurodegeneration induced by PQ and MPTP via interaction with lncRNAs as the molecular mechanism. Our findings indicate the potential roles of lncRNAs in the development of PD by PQ or MPTP and provide positive insights into future mechanism studies.

Tert-butylhydroquinone post-treatment attenuates neonatal hypoxic-ischemic brain damage in rats

Hypoxic-ischemic (HI) encephalopathy is a leading cause of dire mortality and morbidity in neonates. Unfortunately, no effective therapies have been developed as of yet. Oxidative stress plays a critical role in pathogenesis and progression of neonatal HI. Previously, as a Nrf2 activator, tert-butylhydroquinone (TBHQ) has been demonstrated to exert neuroprotection on brain trauma and ischemic stroke models, as well as oxidative stress-induced cytotoxicity in neurons. It is, however, still unknown whether TBHQ administration can protect against oxidative stress in neonatal HI brain injury. This study was undertaken to determine the neuroprotective effects and mechanisms of TBHQ post-treatment on neonatal HI brain damage. Using a neonatal HI rat model, we demonstrated that TBHQ markedly abated oxidative stress compared to the HI group, as evidenced by decreased oxidative stress indexes, enhanced Nrf2 nuclear accumulation and DNA binding activity, and up-regulated expression of Nrf2 downstream antioxidative genes. Administration of TBHQ likewise significantly suppressed reactive gliosis and release of inflammatory cytokines, and inhibited apoptosis and neuronal degeneration in the neonatal rat cerebral cortex. In addition, infarct size and neuronal damage were attenuated distinctly. These beneficial effects were accompanied by improved neurological reflex and motor coordination as well as amelioration of spatial learning and memory deficits. Overall, our results provide the first documentation of the beneficial effects of TBHQ in neonatal HI model, in part conferred by activation of Nrf2 mediated antioxidative signaling pathways.

Paraquat and MPTP alter microRNA expression profiles, and downregulated expression of miR-17-5p contributes to PQ-induced dopaminergic neurodegeneration

Recent evidence indicates that microRNAs (miRNAs) play a key role in neurodegenerative diseases. However, the toxic effects of paraquat (PQ) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) on miRNA expression profiles in dopaminergic neurons have not been investigated. In the present study, we used microarray analysis to show that PQ and MPTP induce alterations of miRNA expression in neuro-2a cells. The results reveal that treatment with 300 μm PQ caused miRNA deregulation, such that 60 miRNAs were upregulated and 228 miRNAs were downregulated. Following treatment with 300 μm MPTP, a total of 576 miRNAs were dysregulated, of which 506 were upregulated and 70 were downregulated. Alterations in the expression of miR-17-5p, miR-210-3p, miR-374-5p, miR-378-3p and miR-503-5p were verified by real-time quantitative reverse transcriptase polymerase chain reaction. Moreover, overexpression of miR-17-5p in Neuro-2a cells enhanced cell proliferation, suppressed apoptosis and promoted S phase transition of the cell cycle after PQ treatment. Taken together, our study demonstrates that characteristic changes in miRNA expression profiles occur after PQ and MPTP treatment, which suggests that miRNAs may be involved in the development of PQ- and MPTP-induced neurodegeneration. Downregulated miR-17-5p expression contributes to PQ-induced dopaminergic neurodegeneration.

Paraquat and MPTP induce neurodegeneration and alteration in the expression profile of microRNAs: the role of transcription factor Nrf2

Both transcription factors (TFs) and microRNAs (miRNAs) can exert a widespread impact on gene expression. In the present study, we investigated the role of Nrf2 in paraquat-induced intracorporeal neurodegeneration and miRNA expression by exposing Nrf2 wild-type and knockout mice to paraquat (PQ) or 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Exposure to 10 mg/kg PQ or 30 mg/kg MPTP caused damage to nerve cells in the substantia nigra (SN) in both Nrf2 (+/+) and Nrf2 (−/−) ICR mice, which included cell morphological changes, detectable apoptosis and a significant reduction in the number of dopaminergic (DA) neurons. When mice were exposed to the same PQ dose of 10 mg/kg, significant fewer tyrosine hydroxylase (TH)-positive DA neurons were observed in the Nrf2 (−/−) mice than that in the Nrf2 (+/+) mice. Both Nrf2 deficiency and PQ or MPTP exposure could alter miRNA expression profile in the SN, suggesting the potential involvement of Nrf2 in the PQ-induced or MPTP-induced miRNA expression alteration. The expression of miR-380-3p was altered by the Nrf2-MPTP interaction effect. miR-380-3p/Sp3-mRNA pathway is likely part of the mechanism of MPTP-induced neurodegeneration. Collectively, our results corroborated the protective role of Nrf2 and also demonstrated the essential interaction of Nrf2 with miRNAs in intracorporal neurodegeneration induced by neurotoxicants.

The gene expression regulators Nrf2 and small regulatory RNA molecule miR-380-3p protect nerve cells from damage caused by neurotoxins. Huangyuan Li, at Fujian Medical University, China, and colleagues examined the effects of paraquat and MPTP (1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine), two chemicals known to induce parkinsonism, in mice lacking Nrf2, a key mediator of antioxidant and anti-inflammatory responses. They found that after MPTP or paraquat exposure, the extent of neuronal loss in the substantia nigra was greater in mice lacking Nrf2 than in wild-type controls. Moreover, Nrf2 deficiency prevented an upregulation of miR-380-3p following MPTP exposure. These findings implicate miR-380-3p in the mechanism through which Nrf2 protects the brain from Parkinson’s disease-related cell death and opens new avenues of investigation for developing more effective neuroprotective therapies.

Pikuni-Blackfeet traditional medicine: Neuroprotective activities of medicinal plants used to treat Parkinson's disease-related symptoms

ETHNOPHARMACOLOGICAL RELEVANCE

Parkinson's disease (PD) is a multifactorial neurodegenerative disorder affecting 5% of the population over the age of 85 years. Current treatments primarily involve dopamine replacement therapy, which leads to temporary relief of motor symptoms but fails to slow the underlying neurodegeneration. Thus, there is a need for safe PD therapies with neuroprotective activity. In this study, we analyzed contemporary herbal medicinal practices used by members of the Pikuni-Blackfeet tribe from Western Montana to treat PD-related symptoms, in an effort to identify medicinal plants that are affordable to traditional communities and accessible to larger populations.

AIM OF THE STUDY

The aims of this study were to (i) identify medicinal plants used by the Pikuni-Blackfeet tribe to treat individuals with symptoms related to PD or other CNS disorders, and (ii) characterize a subset of the identified plants in terms of antioxidant and neuroprotective activities in cellular models of PD.

MATERIALS AND METHODS

Interviews of healers and local people were carried out on the Blackfeet Indian reservation. Plant samples were collected, and water extracts were produced for subsequent analysis. A subset of botanical extracts was tested for the ability to induce activation of the Nrf2-mediated transcriptional response and to protect against neurotoxicity elicited by the PD-related toxins rotenone and paraquat.

RESULTS

The ethnopharmacological interviews resulted in the documentation of 26 medicinal plants used to treat various ailments and diseases, including symptoms related to PD. Seven botanical extracts (out of a total of 10 extracts tested) showed activation of Nrf2-mediated transcriptional activity in primary cortical astrocytes. Extracts prepared from Allium sativum cloves, Trifolium pratense flowers, and Amelanchier arborea berries exhibited neuroprotective activity against toxicity elicited by rotenone, whereas only the extracts prepared from Allium sativum and Amelanchier arborea alleviated PQ-induced dopaminergic cell death.

CONCLUSIONS

Our findings highlight the potential clinical utility of plants used for medicinal purposes over generations by the Pikuni-Blackfeet people, and they shed light on mechanisms by which the plant extracts could slow neurodegeneration in PD.

HMGB1-TLR4-IL23-IL17A axis promotes paraquat-induced acute lung injury by mediating neutrophil infiltration in mice

Paraquat is a poisoning herbicide that primarily targets lung, leading to severe acute lung injury characterized by extensive neutrophil infiltration. However, the mechanisms underlying the neutrophil infiltration is not clear. In this study, we demonstrated the significance of the signaling cascade from high-mobility group box 1 (HMGB1), to Toll-like receptor 4 (TLR4), interleukin-23 (IL-23), and lastly to IL-17A during the paraquat-induced neutrophil infiltration and the subsequent lung injury in mice. Paraquat challenge significantly elevated serum levels of IL-17A and IL-23, the percentage of IL-17A-producing γδT cells in the lung, and the level of HMGB1 in bronchoalveolar lavage fluid. Reducing IL-17A production using an anti-γδT antibody, targeting IL-23 with the neutralizing antibody against IL-23p19, and blocking HMGB1 signaling by using glycyrrhizin or TLR4^-/- mice all dramatically inhibited the infiltration of neutrophils and attenuated lung injury. These novel findings not only reveal the critical role of HMGB1-TLR4-IL-23-IL-17A axis in the pathogenesis of paraquat-induced acute lung injury, but also provide promising therapeutic targets for treating paraquat poisoning.

Tert-buthylhydroquinone pre-conditioning exerts dual effects in old female rats exposed to 3-nitropropionic acid

The brain is a very susceptible organ to structural and functional alterations caused by oxidative stress and its vulnerability increases with age. Understanding the antioxidant response activated by the transcription factor Nrf2 has become very important in the aging field in order to activate cellular protection. However, the role of Nrf2 inducers during old age has not been completely understood. Our aim was to activate the Nrf2 pathway by pre-treating old rats with a widely used Nrf2-inducer, tert-buthylhydroquinone (tBHQ), prior to 3-nitropropionic acid (3-NP) insult, in order to evaluate its effects at a behavioral, morphological and biochemical levels. 3-NP has been used to reproduce the biochemical and pathophysiological characteristics of Huntington's disease due to an oxidative effect. Our results suggest that tBHQ confers an important protective effect against 3-NP toxicity; nevertheless, Nrf2 seems not to be the main protective pathway associated to neuroprotection. Hormetic responses include the activation of more than one transcription factor. Nrf2 and NFκB are known to simultaneously initiate different cellular responses against stress by triggering parallel mechanisms, therefore NFκB nuclear accumulation was also evaluated.

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Old rats are able to activate an hormetic response against 3NP toxicity.

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tBHQ pre-conditioning exerts an antioxidant-prooxidant, dual role in old rats.

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tBHQ activates a crosstalk mechanism between NFκB and Nrf2.

t-BHQ Provides Protection against Lead Neurotoxicity via Nrf2/HO-1 Pathway

The neurotoxicity of lead has been well established, and oxidative stress is strongly associated with lead-induced neurotoxicity. Nrf2 is important for protection against oxidative stress in many disease models. We applied t-BHQ, which is an Nrf2 activator, to investigate the possible role of Nrf2 in the protection against lead neurotoxicity. t-BHQ significantly attenuated the oxidative stress in developmental rats by decreasing MDA level, as well as by increasing SOD activity and GSH content, in the hippocampus and frontal cortex. Furthermore, neuronal apoptosis was detected by Nissl staining, and Bax expression was inhibited in the t-BHQ-treated group. Results showed that t-BHQ suppressed ROS production and caspase 3/7 activity but increased intracellular GSH content, in SH-SY5Y cells under lead exposure. Moreover, in vivo and in vitro, t-BHQ enhanced the nuclear translocation of Nrf2 and binding to ARE areas but did not induce Nrf2 transcription. These phenomena were confirmed using RT-PCR, EMSA, Western blot, and immunofluorescence analyses. Subsequent upregulation of the expression of HO-1, NQO1, and GCLC was observed. However, knockdown of Nrf2 or HO-1 adversely affected the protective effects of t-BHQ against lead toxicity in SH-SY5Y cells. Thus, t-BHQ can protect against lead neurotoxicity, depending on the Nrf2/HO-1 pathway.

The antioxidant compound tert-butylhydroquinone activates Akt in myocardium, suppresses apoptosis and ameliorates pressure overload-induced cardiac dysfunction

Tert-butylhydroquinone (TBHQ) is an antioxidant compound which shows multiple cytoprotective actions. We evaluated the effects of TBHQ on pathological cardiac remodeling and dysfunction induced by chronic overload. Pressure overload was created by transverse aortic constriction (TAC) in male C57BL/6 mice. TBHQ was incorporated in the diet and administered for 4 weeks. TBHQ treatment prevented left ventricular dilatation and cardiac dysfunction induced by TAC, and decreased the prevalence of myocardial apoptosis. The beneficial effects of TBHQ were associated with an increase in Akt activation, but not related to activations of Nrf2 or AMP-activated protein kinase. TBHQ-induced Akt activation was accompanied by increased phosphorylation of Bad, glycogen synthase kinase-3β (GSK-3β) and mammalian target of rapamycin (mTOR). Mechanistically, we showed that in cultured H9c2 cells and primary cardiac myocytes, TBHQ stimulated Akt phosphorylation and suppressed oxidant-induced apoptosis; this effect was abolished by wortmannin or an Akt inhibitor. Blockade of the Akt pathway in vivo accelerated cardiac dysfunction, and abrogated the protective effects of TBHQ. TBHQ also reduced the reactive aldehyde production and protein carbonylation in stressed myocardium. We suggest that TBHQ treatment may represent a novel strategy for timely activation of the cytoprotective Akt pathway in stressed myocardium.

Sequential Upregulation of Superoxide Dismutase 2 and Heme Oxygenase 1 by tert-Butylhydroquinone Protects Mitochondria during Oxidative Stress

Oxidative stress is linked to mitochondrial dysfunction in aging and neurodegenerative conditions. The transcription factor nuclear factor E2-related factor 2 (Nrf2)-antioxidant response element (ARE) regulates intracellular antioxidative capacity to combat oxidative stress. We examined the effect of tert-butylhydroquinone (tBHQ), an Nrf2-ARE signaling pathway inducer, on mitochondrial function during oxidative challenge in neurons. tBHQ prevented glutamate-induced cytotoxicity in an HT-22 neuronal cell line even with an 8-hour exposure delay. tBHQ blocked glutamate-induced intracellular reactive oxygen species (ROS) and mitochondrial superoxide accumulation. It also protected mitochondrial function under glutamate toxicity, including maintaining mitochondrial membrane potential, mitochondrial Ca(2+) hemostasis, and mitochondrial respiration. Glutamate-activated, mitochondria-mediated apoptosis was inhibited by tBHQ as well. In rat primary cortical neurons, tBHQ protected cells from both glutamate and buthionine sulfoximine toxicity. We found that tBHQ scavenged ROS and induced a rapid upregulation of superoxide dismutase 2 (SOD2) expression and a delayed upregulation of heme oxygenase 1 (HO-1) expression. In HT-22 cells with a knockdown of SOD2 expression, delayed treatment with tBHQ failed to prevent glutamate-induced cell death. Briefly, tBHQ rescues mitochondrial function by sequentially increasing SOD2 and HO-1 expression during glutamate-mediated oxidative stress. This study is the first to demonstrate the role of tBHQ in preserving mitochondrial function during oxidative challenge and provides a clinically relevant argument for using tBHQ against acute neuron-compromising conditions.

Tert-butylhydroquinone attenuates scrotal heat-induced damage by regulating Nrf2-antioxidant system in the mouse testis

Tert-butylhydroquinone (tBHQ), a widely used nuclear factor erythroid 2-related factor 2 (Nrf2) activator, was always employed to investigate the potential protective role of Nrf2 activation. In this study, to elucidate the effect of tBHQ on scrotal heat-induced damage and Nrf2-antioxidant system in mouse testes, eight-week-old mice were administrated with or without dietary tBHQ (1%w/w) for 1week and afterward subjected to a single scrotal heat treatment (42°C for 25min). Trunk blood and testes were collected 3h or 1, 2, or 7days later. Mice displayed less germ cell loss in testes, higher relative testis weight and lower testosterone concentration on day 2 in tBHQ treatment group. Before heat treatment, there were significant increases in malondialdehyde (MDA) concentration in tBHQ treatment group. After heat treatment, mice in tBHQ treatment group showed lower MDA concentration than those in non-tBHQ treatment group. In addition, both tBHQ pretreatment and scrotal heat treatment induced markedly increased Nrf2 protein expression in cytoplasm and nuclei of interstitial cells, accompanying with elevated mRNA expression of Nrf2 and Nrf2-regulated genes in mice testes. Our data indicated that pretreatment to tBHQ induced a mild oxidative stress, and further enhanced the cellular antioxidative ability to protect testicular cells against scrotal heat-induced damage via a mechanism that might involve the Nrf2-antioxidant system in mice testes.

The role of calpain in an in vivo model of oxidative stress-induced retinal ganglion cell damage

PURPOSE

In this study, we set out to establish an in vivo animal model of oxidative stress in the retinal ganglion cells (RGCs) and determine whether there is a link between oxidative stress in the RGCs and the activation of calpain, a major part of the apoptotic pathway.

MATERIALS AND METHODS

Oxidative stress was induced in the RGCs of C57BL/6 mice by the intravitreal administration of 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH, 30mM, 2μl). Control eyes were injected with 2μl of vehicle. Surviving Fluorogold (FG)-labeled RGCs were then counted in retinal flat mounts. Double staining with CellROX and Annexin V was performed to investigate the co-localization of free radical generation and apoptosis. An immunoblot assay was used both to indirectly evaluate calpain activation in the AAPH-treated eyes by confirming α-fodrin cleavage, and also to evaluate the effect of SNJ-1945 (a specific calpain inhibitor: 4% w/v, 100mg/kg, intraperitoneal administration) in these eyes.

RESULTS

Intravitreal administration of AAPH led to a significant decrease in FG-labeled RGCs 7days after treatment (control: 3806.7±575.2RGCs/mm(2), AAPH: 3156.1±371.2RGCs/mm(2), P<0.01). CellROX and Annexin V signals were co-localized in the FG-labeled RGCs 24h after AAPH injection. An immunoblot assay revealed a cleaved α-fodrin band that increased significantly 24h after AAPH administration. Intraperitoneally administered SNJ-1945 prevented the cleavage of α-fodrin and had a neuroprotective effect against AAPH-induced RGC death (AAPH: 3354.0±226.9RGCs/mm(2), AAPH+SNJ-1945: 3717.1±614.6RGCs/mm(2), P<0.01).

CONCLUSION

AAPH administration was an effective model of oxidative stress in the RGCs, showing that oxidative stress directly activated the calpain pathway and induced RGC death. Furthermore, inhibition of the calpain pathway protected the RGCs after AAPH administration.