Dihydroquercetin alleviates dopamine neuron loss via regulating TREM2 activation.

BACKGROUND: Parkinson's disease (PD) is a prevalent neurodegenerative disorder, marked by the degeneration of dopamine (DA) neurons in the substantia nigra (SN). Current evidence strongly suggests that neuroinflammation, primarily mediated by microglia, contributes to PD pathogenesis. Triggering receptor expressed on myeloid cells 2 (TREM2) might serve as a promising therapeutic target for PD due to its ability to suppress neuroinflammation. Dihydroquercetin (DHQ) is an important natural dihydroflavone and confers apparent anti-inflammatory, antioxidant and anti-fibrotic effects. Recently, DHQ-mediated neuroprotection was exhibited. However, the specific mechanisms of its neuroprotective effects remain incompletely elucidated. METHODS: In this study, rat models were utilized to induce damage to DA neurons using lipopolysaccharide (LPS) and 6-hydroxydopamine (6-OHDA) to assess the impacts of DHQ on the loss of DA neurons. Furthermore, DA neuronal MN9D cells and microglial BV2 cells were employed to investigate the function of TREM2 in DHQ-mediated DA neuroprotection. Finally, TREM2 knockout mice were used to investigate whether the neuroprotective effects mediated by DHQ through a mechanism dependent on TREM2. RESULTS: The main findings demonstrated that DHQ effectively protected DA neurons against neurotoxicity induced by LPS and 6-OHDA and inhibited microglia-elicited neuroinflammation. Meanwhile, DHQ promoted microglial TREM2 signaling activation. Notably, DHQ failed to reduce inflammatory cytokines release and further present neuroprotection from DA neurotoxicity upon TREM2 silencing. Similarly, DHQ didn't exert DA neuroprotection in TREM2 knockout mice. CONCLUSIONS: These findings suggest that DHQ exerted DA neuroprotection by regulating microglia TREM2 activation.

Alterations of Spatial Memory and Gut Microbiota Composition in Alzheimer's Disease Triple-Transgenic Mice at 3, 6, and 9 Months of Age.

Alzheimer's disease (AD) is a progressive neurological disease. Gut microbial dysbiosis is associated with AD. This study involves the comparative assessment of spatial learning, ß-amyloid peptide accumulation, and fecal microbiota alterations in 3×Tg-AD mice from 3 age groups: AD asymptomatic stage (3 m), presymptomatic stage (6 m), and the symptomatic stage of AD (9 m). We demonstrate that spatial memory deficits, brain Aß accumulation, and weight gain in 3×Tg-AD mice gradually appear after 6 months of age. However, the total gut bacterial counts underwent changes from 3 to 6 months of age and were further altered at 9 months of age. Importantly, changes in gut bacteria abundance of Desulfobacterota and Actinobacteriota phyla in 6-month-old mice preceded apparent spatial memory deficits. In summary, Changes in the gut microbial community are one of the mechanisms of early AD pathology.

Synergistic effects of lipopolysaccharide and rotenone on dopamine neuronal damage in rats.

INTRODUCTION: The etiology of Parkinson's disease (PD) is still unknown. Until now, oxidative stress and neuroinflammation play a crucial role in the pathogenesis of PD. However, the specific synergistic role of oxidative stress and neuroinflammation in the occurrence and development of PD remains unclear. METHODS: The changes in motor behavior, dopamine (DA) neurons quantification and their mitochondrial respiratory chain, glial cells activation and secreted cytokines, Nrf2 signaling pathway, and redox balance in the brain of rats were evaluated. RESULTS: Lipopolysaccharide (LPS)-induced neuroinflammation and rotenone (ROT)-induced oxidative stress synergistically aggravated motor dysfunction, DA neuron damage, activation of glial cells, and release of related mediators, activation of Nrf2 signaling and destruction of oxidative balance. In addition, further studies indicated that after ROT-induced oxidative stress caused direct damage to DA neurons, LPS-induced inflammatory effects had stronger promoting neurotoxic effects on the above aspects. CONCLUSIONS: Neuroinflammation and oxidative stress synergistically aggravated DA neuronal loss. Furtherly, oxidative stress followed by neuroinflammation caused more DA neuronal loss than neuroinflammation followed by oxidative stress.

Predictive value of estimated pulse wave velocity for cardiovascular and all-cause mortality in individuals with obesity.

BACKGROUND: Estimated pulse wave velocity (ePWV) has revealed excellent performance in predicting cardiovascular disease (CVD) risk. However, whether ePWV predicts all-cause mortality and CVD mortality in populations with obesity remains elusive. METHODS: We performed a prospective cohort including 49,116 participants from the National Health and Nutrition Examination Survey from 2005 to 2014. Arterial stiffness was evaluated by ePWV. Weighted univariate, multivariate Cox regression and receiver operating characteristic curve (ROC) analysis was used to assess the effects of ePWV on the risk of all-cause and CVD mortality. In addition, the two-piecewise linear regression analysis was used to describe the trend of ePWV affecting mortality and identify the thresholds that significantly affect mortality. RESULTS: A total of 9929 participants with obesity with ePWV data and 833 deaths were enrolled. Based on the multivariate Cox regression results, the high ePWV group had a 1.25-fold higher risk of all-cause mortality and a 5.76-fold higher risk of CVD mortality than the low-ePWV group. All-cause and CVD mortality risk increased by 123% and 44%, respectively, for every 1 m/s increase in ePWV. ROC results showed that ePWV had an excellent accuracy in predicting all-cause mortality (AUC = 0.801) and CVD mortality (AUC = 0.806). Furthermore, the two-piecewise linear regression analysis exhibited that the minimal threshold at which ePWV affected participant mortality was 6.7 m/s for all-cause mortality and 7.2 m/s for CVD mortality. CONCLUSIONS: ePWV was an independent risk factor for mortality in populations with obesity. High ePWV levels were associated with an increased all-cause and CVD mortality. Thus, ePWV can be considered a novel biomarker to assess mortality risk in patients with obesity.

Heat-killed Lactobacillus murinus confers neuroprotection against dopamine neuronal loss by targeting NLRP3 inflammasome.

The intestinal flora has become very active in studies related to Parkinson's disease (PD) in recent years. The microbe-gut-brain axis is closely related to the maintenance of brain homeostasis as well as PD pathogenesis. Alterations in gut bacteria can contribute to neuroinflammation and dopamine (DA) neurodegeneration. Lactobacillus murinus, a gram-positive bacterium, is a commensal gut bacteria present in the mammalian gut and considered as a potential probiotic due to its beneficial effects, including anti-inflammatory and antibacterial actions. In this study, the effects of live L. murinus and heat-killed L. murinus on DA neuronal damage in rats and the underlying mechanisms were investigated. Data showed that heat-killed L. murinus ameliorated 6-hydroxydopamine-induced motor dysfunctions and loss of substantia nigra DA neurons, while no protection was shown in live L. murinus treatment. At the same time, heat-killed L. murinus reduced the activation of NLRP3 inflammasome in microglia and the secretion of pro-inflammatory factors, thus inhibiting the development of neuroinflammation. Furthermore, heat-killed L. murinus failed to display its original neuroprotective properties in NLRP3 inflammasome knockout mice. Together, heat-killed L. murinus conferred neuroprotection against DA neuronal loss via the inhibition of microglial NLRP3 inflammasome activation. These findings provide a promising potential for future applications of L. murinus, and also beneficial strategy for PD treatment.

Dendrobium Nobile Lindl. Alkaloid Suppresses NLRP3-Mediated Pyroptosis to Alleviate LPS-Induced Neurotoxicity.

Alzheimer's disease (AD) is a neurodegenerative disorder recognized as a global public health priority. Although available treatments temporarily relieve the symptoms, they could not prevent the progression of cognitive decline. Natural compounds have been rich sources for drug discovery. Dendrobium nobile Lindl. alkaloid (DNLA) is the main active compound in Dendrobium nobile Lindl, a traditional Chinese herbal medicine. Recent studies indicated that DNLA produced neuroprotection. However, the mechanisms underlying DNLA-generated neuroprotection remain unknown. To investigate neuroprotection and the underlying mechanisms of DNLA, mouse hippocampus injection of lipopolysaccharide (LPS)-induced neuronal damage was performed. DNLA protected hippocampus neurons and working memory disorder against LPS-induced neurotoxicity. In addition, DNLA suppressed cell undergoing membrane lysis and cell swelling and inhibited the essential mediator of pyroptosis GSDMD-N expressions. Furthermore, DNLA-mediated neuroprotection was dependent on the inhibition of NLRP3 inflammasome activation, as evidenced by the fact that DNLA reduced pro-inflammatory factor (IL-18 and IL-1ß) production and inhibited the expression of related proteins. DNLA-exerted neuroprotection against LPS-induced neuronal damage, and cognitive impairment was not observed in NLRP3 knockout mice. Together, this study suggested that DNLA attenuated NLRP3-mediated pyroptosis to generate neuroprotection against LPS-induced neuronal damage and cognitive impairment.

Potential neuroprotection by Dendrobium nobile Lindl alkaloid in Alzheimer's disease models.

At present, treatments for Alzheimer's disease can temporarily relieve symptoms but cannot prevent the decline of cognitive ability and other neurodegenerative changes. Dendrobium nobile Lindl alkaloid is the main active component of Dendrobium nobile Lindl. Dendrobium nobile Lindl alkaloid has been shown to resist aging, prolong life span, and exhibit immunomodulatory effects in animals. This review summarizes the mechanisms behind the neuroprotective effects reported in Alzheimer's disease animal models. The neuroprotective effects of Dendrobium nobile Lindl alkaloid have not been studied in patients. The mechanisms by which Dendrobium nobile Lindl alkaloid has been reported to improve cognitive dysfunction in Alzheimer's disease animal models may be associated with extracellular amyloid plaque production, regulation of tau protein hyperphosphorylation, inhibition of neuroinflammation and neuronal apoptosis, activation of autophagy, and enhanced synaptic connections.

Physiological Concentration of H2O2 Supports Dopamine Neuronal Survival via Activation of Nrf2 Signaling in Glial Cells.

Traditionally, hydrogen peroxide (H2O2) was formed from cellular oxidative metabolism and often viewed as toxic waste. In fact, H2O2 was a benefit messenger for neuron-glia signaling and synaptic transmission. Thus, H2O2 was a double-edged sword and neuroprotection vs. neurotoxicity produced by H2O2 was difficult to define. Nuclear factor erythroid 2-related factor 2 (Nrf2) has been implicated as an intracellular regulator of neuronal growth. Inactivation of Nrf2 participated in the development of Parkinson's disease (PD). Thus, suitable activation of Nrf2 was essential for the prevention and treatment of PD. This study aimed to explore whether H2O2-conferred neuroprotective effects to support neuronal survival. H2O2 were added into primary neuron-glia, neuron-astroglia and neuron-microglia co-cultures in concentration- and time-dependent manners. H2O2 increased dopamine (DA) neuronal survival in concentration- and time-dependent manners. In addition, glial cells Nrf2 activation involved in H2O2-supported DA neuronal survival with the following phenomenons. First, H2O2 activated Nrf2 signaling pathway. Second, H2O2 generated beneficial neuroprotection in neuron-glia, neuron-astroglia and neuron-microglia co-cultures but not in neuron-enriched cultures. Third, silence of Nrf2 in glial cells abolished H2O2-conferred DA neuronal survival. This study demonstrated that physiological concentration of H2O2-supported DA neuronal survival via activation of Nrf2 signaling in glial cells. Our data permit to re-evaluate the role of H2O2 in the pathogenesis and therapeutic strategies for PD.

Dendrobium nobile Lindl alkaloid attenuates 6-OHDA-induced dopamine neurotoxicity.

Parkinson's disease (PD) is one of the most common central nervous system (CNS) degenerative disease and is characterized by a progressive loss of midbrain substantia nigra dopamine (DA) neurons. Dendrobium nobileLindl alkaloid (DNLA) is an active component extracted from D. nobile Lindl, which is a traditional Chinese herb. The various pharmacological effects of D. nobile are beneficial for human health. Recently, DNLA-mediated neuroprotective effects have been reported. However, the neuroprotection of DNLA on 6-hydroxydopamine (6-OHDA)-induced DA neurotoxicity is still unknown. This study aimed to explore the neuroprotective effects of DNLA on DA neurotoxicity induced by 6-OHDA. In PD rat model, continuous intragastric administration of DNLA (20 mg/kg) for 7 days significantly ameliorated 6-OHDA-induced DA neurons loss in the midbrain substantia nigra. In addition, primary rat midbrain neuron-glia cocultures were used to explore the mechanisms underlying DNLA-related DA neuroprotection. The studies on neuron-glia cocultures revealed that neuroprotective effects of DNLA (2.5 ng/mL) were mediated by inhibiting the release of proinflammatory cytokines. Taken together, DNLA holds neuroprotective effect on 6-OHDA-induced neurons neurodegeneration by selectively inhibiting the production of proinflammatory factors and could be a potential compound for PD treatment.

Corrigendum: Combination Treatment of Icariin and L-DOPA Against 6-OHDA-Lesioned Dopamine Neurotoxicity.

[This corrects the article DOI: 10.3389/fnmol.2018.00155.].

Ellagic acid protects dopamine neurons from rotenone-induced neurotoxicity via activation of Nrf2 signalling.

Parkinson's disease (PD) is the second most prevalent central nervous system (CNS) degenerative disease. Oxidative stress is one of key contributors to PD. Nuclear factor erythroid-2-related factor 2 (Nrf2) is considered to be a master regulator of many genes involved in anti-oxidant stress to attenuate cell death. Therefore, activation of Nrf2 signalling provides an effective avenue to treat PD. Ellagic acid (EA), a natural polyphenolic contained in fruits and nuts, possesses amounts of pharmacological activities, such as anti-oxidant stress and anti-inflammation. Recent studies have confirmed EA could be used as a neuroprotective agent in neurodegenerative diseases. Here, mice subcutaneous injection of rotenone (ROT)-induced DA neuronal damage was performed to investigate EA-mediated neuroprotection. In addition, adult Nrf2 knockout mice and different cell cultures including MN9D-enciched, MN9D-BV-2 and MN9D-C6 cell co-cultures were applied to explore the underlying mechanisms. Results demonstrated EA conferred neuroprotection against ROT-induced DA neurotoxicity. Activation of Nrf2 signalling was involved in EA-mediated DA neuroprotection, as evidenced by the following observations. First, EA activated Nrf2 signalling in ROT-induced DA neuronal damage. Second, EA generated neuroprotection with the presence of astroglia and silence of Nrf2 in astroglia abolished EA-mediated neuroprotection. Third, EA failed to produce DA neuroprotection in Nrf2 knockout mice. In conclusion, this study identified EA protected against DA neuronal loss via an Nrf2-dependent manner.

Age-Associated Dopaminergic Neuron Loss and Midbrain Glia Cell Phenotypic Polarization.

In response to changes in brain micro-environment caused by aging, microglia could polarize into proinflammatory M1 phenotype and anti-inflammatory M2 phenotype. Besides, astroglia could polarize into A1 phenotype, exhibiting neurotoxicity, or A2 phenotype, showing neuroprotection. This study aimed to investigate the change of glial cells and dopaminergic (DA) neuron in midbrain with age. Two-, 6-, 18- and 28- months old rat brains were collected. The DA neurons were detected using anti-TH and anti-DAT antibodies. The expressions of astroglia markers (glial fibrillary acidic protein, GFAP), microglia markers (ionized calcium binding adaptor molecule 1, Iba-1), M1 markers (tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß), M2 markers (arginase 1 (Arg1) and IL-10), A1 markers (lipocalin-2 (Lcn2) and complement C3 (C3), A2 markers (brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) were examined by real time RT-PCR and Western Blotting. DA neuron expressions decreased in 18-, 28- months old rat brains. In addition, microglia and astroglia have different degrees of activation with age. Besides, M1 markers (TNF-α and IL-1ß) increased and M2 markers (Arg1 and IL-10) decreased in aged rats. Furthermore, A2 markers (BDNF and GDNF) decreased and A1 markers (Lcn2 and C3) increased in aged rats. Age induced DA neuron loss and influenced midbrain glial cells phenotypic polarization, which might account for the occurrence and pathogenesis of Parkinson's diseases.

Ellagic acid supports neuron by regulating astroglia Nrf2.

Astroglia support neuron by providing substrates for neuronal metabolism, glutamate clearance, and antioxidative protection. Nuclear factor erythroid 2-related factor 2 (Nrf2) participates in the antioxidative defense response. Also, Nrf2 signaling is recognized to activate the neurotrophic pathway to replace/protect damaged organelles. Ellagic acid (EA), an extraction component of fruits and nuts, presents many pharmacological activities such as anti-inflammation, antioxidation, and neuroprotection. However, few studies have been focused on the neurotrophic properties of EA. Our study investigated whether EA could increase neuronal survival and the target cells. Thus, primary neuron-enriched cultures and primary astroglia-enriched cultures were applied to detect whether EA-elicited neurotrophic effects were mediated by astroglia Nrf2. This study indicated that EA promoted neuronal survival. Further, astroglia Nrf2 participate in EA-elicited neuronal survival with the following scenarios. First, EA elicited astroglia proliferation, glial cell line-derived neurotrophic factor (GDNF) release, and Nrf2 activation. Second, after silencing astroglia Nrf2, EA-induced astrogliosis, GDNF release, and neuronal survival disappeared. Thus, EA-mediated astroglia Nrf2 activation is important to enhance neurotrophic effects on neurons, which might provide new insights for neurodegenerative disease.

Naringenin Produces Neuroprotection Against LPS-Induced Dopamine Neurotoxicity via the Inhibition of Microglial NLRP3 Inflammasome Activation.

Background: Parkinson's disease (PD) is the second most prevalent central nervous system (CNS) degenerative disease and characterized by slow and progressive loss of dopamine (DA) neurons in the midbrain substantia nigra. Microglia-mediated neuroinflammation has been considered as the major central event in the process of DA neuronal loss. Thus, inhibition of neuroinflammation could possess a more viable strategy for PD treatment. Naringenin (NAR), a natural flavanoid contained in citrus fruit and grapefruits, possesses amounts of pharmacological activities. Recent studies indicated that NAR produced neuroprotection against several neurological disorders. However, the mechanisms underlying NAR-generated neuroprotection are not fully illuminated. Methods: In the present study, rat nigral stereotaxic injection of lipopolysaccharide (LPS)-induced DA neuronal loss was performed to investigate NAR-mediated neuroprotection. In addition, BV-2 and MN9D cell lines were applied to explore the underlying mechanisms. Results: NAR protected DA neurons against LPS-induced neurotoxicity. Also, NAR suppressed microglial nod-like receptor protein 3 (NLRP3) inflammasome signaling activation and the subsequent pro-inflammatory factors release. In addition, NAR-mediated DA neuroprotection was dependent on the inhibition of microglial NLRP3 inflammasome activation, as evidenced by the observations that NAR-reduced pro-inflammatory factors production and further NAR-exerted DA neuroprotection against LPS-induced neuronal damage was not discerned after microglial NLRP3 siRNA treatment. Conclusions: This study demonstrated that NAR targeted microglial NLRP3 inflammasome to protect DA neurons against LPS-induced neurotoxicity. These findings suggest NAR might hold a promising therapeutic potential for PD.

Icariin targets Nrf2 signaling to inhibit microglia-mediated neuroinflammation.

Microglia-mediated neuroinflammation is an important contributor to the pathogenesis of neurodegenerative diseases. Inhibition of neuroinflammation has been proved to be effective in neurodegenerative diseases treatment. Nuclear factor erythroid 2 related factor 2 (Nrf2) is a key mediator of endogenous inducible defense systems in the body. In response to oxidative stress, Nrf2 translocates to the nucleus and binds to specific DNA sites termed as anti-oxidant response elements to initiate transcription of cytoprotective genes, such as hemeoxygenase-1 (HO-1) and nicotinamide adenine dinucleotide phosphate: quinine oxidoreductase-1 (NQO1). However, insufficient Nrf2 activation has been closely associated with the progress of neurodegenerative diseases. New findings have linked activation of Nrf2 signaling to anti-inflammatory effects. Icariin (ICA), a natural compound derived from Herba Epimedii, possesses amounts of pharmacological activities, such as anti-aging, anti-oxidation and anti-inflammatory effects. Recent studies have confirmed that ICA exerted neuroprotection against neurodegenerative diseases. However, the mechanisms underlying ICA-mediated neuroprotection were not fully understood. In the present study, microglia BV-2 cell lines were performed to investigate the anti-neuroinflammatory effects of ICA and the mechanisms of actions. Results showed that ICA suppressed lipopolysaccharide (LPS)-induced microglial pro-inflammatory factors production. In addition, activation of Nrf2 signaling pathway participated in ICA-mediated anti-neuroinflammation, as evidenced by the following observations. First, Nrf2 siRNA reversed ICA-reduced microglial activation and pro-inflammatory factors release. Second, a selective inhibitor of HO-1 abolished ICA-mediated anti-neuroinflammatory actions. This study will give us an insight into the potential of Nrf2 and neuroinflammation in terms of opening up an alternative therapeutic strategy for neurodegenerative diseases.

Icariin attenuates neuroinflammation and exerts dopamine neuroprotection via an Nrf2-dependent manner.

BACKGROUND: Oxidative stress and neuroinflammation are considered the major central events in the process of Parkinson's disease (PD). Nrf2 is a key regulator of endogenous defense systems. New finds have contacted activation of Nrf2 signaling with anti-inflammatory activities. Therefore, the outstanding inhibition of neuroinflammation or potent Nrf2 signaling activation holds a promising strategy for PD treatment. Icariin (ICA), a natural compound derived from Herba Epimedii, presents a number of pharmacological properties, including anti-oxidation, anti-aging and anti-inflammatory actions. Recent studies have confirmed ICA exerted neuroprotection against neurodegenerative disorders. However, the underlying mechanisms were not fully elucidated. METHODS: In the present study, mouse nigral stereotaxic injection of 6-hydroxydopamine (6-OHDA)-induced PD model was performed to investigate ICA-conferred dopamine (DA) neuroprotection. In addition, adult Nrf2 knockout mice and primary rat midbrain neuron-glia co-culture was applied to elucidate whether ICA-exerted neuroprotection was through an Nrf2-dependent mechanism. RESULTS: Results indicated that ICA attenuated 6-OHDA-induced DA neurotoxicity and glial cells-mediated neuroinflammatory response. Furtherly, activation of Nrf2 signaling pathway in glial cells participated in ICA-produced neuroprotection, as revealed by the following observations. First, ICA enhanced Nrf2 signaling activation in 6-OHDA-induced mouse PD model. Second, ICA failed to generate DA neuroprotection and suppress glial cells-mediated pro-inflammatory factors production in Nrf2 knockout mice. Third, ICA exhibited neuroprotection in primary neuron-glia co-cultures but not in neuron-enriched cultures (without glial cells presence). Either, ICA-mediated neuroprotection was not discerned after Nrf2 siRNA treatment in neuron-glia co-cultures. CONCLUSIONS: Our findings identify that ICA attenuated glial cells-mediated neuroinflammation and evoked DA neuroprotection via an Nrf2-dependent manner.

Activation of Nrf2 signaling by Icariin protects against 6-OHDA-induced neurotoxicity.

Nerve damage is the main pathogenesis of neurodegenerative diseases. Recently, in search for a promising therapeutic target that could stop neurodegenerative diseases progression, the antioxidant signaling pathway regulated by transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) has attracted new hopes. Icariin (ICA) exhibited a battery of pharmacological properties, including antioxidation, anti-aging, and anti-inflammation activities. Recent studies indicate ICA conferred neuroprotection against brain ischemic injury and neurodegenerative diseases. However, the mechanisms underlying ICA-mediated neuroprotection remain unelucidated. This study aimed at analyzing whether ICA evoked neuroprotection against 6-hydroxydopamine (6-OHDA)-induced neurotoxicity in PC12 cells and the mechanisms of action. ICA protected against 6-OHDA-induced neuronal damage, accompanied by the inhibition of cell apoptosis through the marked decreases in the Bax/Bcl-2 ratio, cytochrome c release, and caspase-3 cleavage. In addition, the activation of Nrf2 signaling pathway was responsible for ICA-mediated neuroprotection. First, ICA relieved reactive oxygen species accumulation and increased superoxide dismutase generation via the activation of Nrf2 signaling. Second, Nrf2 knockdown by siRNA reversed ICA-mediated neuroprotection. Together, these results suggested ICA-mediated neuroprotection might be attributable to the activation of Nrf2 pathway via antioxidative signaling pathways.

Naringenin targets on astroglial Nrf2 to support dopaminergic neurons.

Astroglia serve as a critical role in metabolic and neurotrophic support to neurons. The loss of astroglia-derived neurotrophic effects could be a primary contributor to Parkinson's disease (PD). Thus, understanding astroglia functions is an important strategy for enhancing neuronal survival. Nuclear factor erythroid 2-related factor 2 (Nrf2) plays a key role in neuronal resistance to oxidative stress and glutamate-induced excitotoxicity. Balancing oxidative stress by up-regulation of Nrf2 has been demonstrated to be effective in neurodegenerative disease treatment. Naringenin (NAR), a dietary flavonoid, displays anti-oxidant, cardioprotective, anti-inflammatory and neuroprotective activities. However, the molecular mechanisms underlying NAR-mediated neuroprotection against neurodegeneration remain unelucidated. Here, the present study investigated whether NAR promoted astroglial neurotrophic effects to support neurons and the underlying mechanisms as well. In primary rat midbrain neuron-glia co-cultures, NAR conferred neurotrophic effects to support dopaminergic (DA) neurons survival in the concentration- and time-dependent manners. Furtherly, astroglia were essential for NAR-mediated neurotrophic actions. Also, NAR elicited astrogliosis and neurotrophic factors release in primary neuron-glia co-cultures and astroglia-enriched cultures. Mechanistically, astroglial Nrf2 activation participated in NAR-mediated neurotrophic actions to support DA neurons evidenced by the following observations: 1) NAR increased Nrf2 mRNA and protein expressions both in neuron-glia and astroglia-enriched cultures; 2) Nrf2-siRNA inhibited NAR-mediated astrogliosis and neurotrophic factors release; 3) astroglial Nrf2-siRNA abolished NAR-mediated neurotrophic effects on DA neurons. Together, this study demonstrates NAR enhanced astroglial neurotrophic effects on DA neurons through the regulation of Nrf2 activation, and these findings might open new potential promising avenues for neurotrophic factor-based treatment of PD.

Combination Treatment of Icariin and L-DOPA Against 6-OHDA-Lesioned Dopamine Neurotoxicity.

Until now, the dopamine (DA) precursor, L-3,4-dihydroxyphenylalanine (L-DOPA), remains the gold standard effective drug therapy for Parkinson's disease (PD) patients. Nevertheless, long-term chronic L-DOPA administration leads to the drug efficacy loss and severe adverse effects, such as L-DOPA-induced dyskinesia (LID). Icariin (ICA), a flavonoid that is extracted from Epimedium, has been proved to evoke neuroprotection against DA neuronal loss in PD animal models. Here, the present study detected the effects of ICA combined with L-DOPA on 6-hydroxydopamine (6-OHDA)-elicited DA neurotoxicity and L-DOPA-induced motor dysfunction as well. PC12 cells were applied to investigate the combination treatment of ICA and L-DOPA against 6-OHDA-lesioned neurotoxicity. In addition, rat substantia nigral stereotaxic injection of 6-OHDA-induced DA neuronal injury was performed to explore the neuroprotective effects mediated by ICA combined with L-DOPA. The pathological movement triggered by L-DOPA was determined by the abnormal involuntary movements (AIM) scores analysis. In PC12 cells, ICA combined with L-DOPA produced better neuroprotection from 6-OHDA-induced neurotoxicity than ICA or L-DOPA alone treatment. In parkinsonian 6-OHDA lesioned rats, ICA conferred DA neuroprotection as monotherapy and an enhancement benefit of L-DOPA treatment after daily administration of L-DOPA and ICA for 21 days. Moreover, ICA ameliorated the development of LID as evidenced by the lowered AIM scores without affecting L-DOPA-mediated efficacy. Furtherly, ICA attenuated neuroinflammation in 6-OHDA-induced DA neuronal loss and the development of LID in vivo. In conclusion, these findings suggest ICA might be a potential promising adjuvant to enhance L-DOPA efficacy and attenuate L-DOPA-produced adverse effects in PD.