Madecassoside ameliorates lipopolysaccharide-induced neurotoxicity in rats by activating the Nrf2-HO-1 pathway

Role of Natural Compounds Modulating Heme Catabolic Pathway in Gut, Liver, Cardiovascular, and Brain Diseases

The crucial physiological process of heme breakdown yields biliverdin (BV) and bilirubin (BR) as byproducts. BV, BR, and the enzymes involved in their production (the "yellow players-YP") are increasingly documented as endogenous modulators of human health. Mildly elevated serum bilirubin concentration has been correlated with a reduced risk of multiple chronic pro-oxidant and pro-inflammatory diseases, especially in the elderly. BR and BV per se have been demonstrated to protect against neurodegenerative diseases, in which heme oxygenase (HMOX), the main enzyme in the production of pigments, is almost always altered. HMOX upregulation has been interpreted as a tentative defense against the ongoing pathologic mechanisms. With the demonstration that multiple cells possess YP, their propensity to be modulated, and their broad spectrum of activity on multiple signaling pathways, the YP have assumed the role of an adjustable system that can promote health in adults. Based on that, there is an ongoing effort to induce their activity as a therapeutic option, and natural compounds are an attractive alternative to the goal, possibly requiring only minimal changes in the life style. We review the most recent evidence of the potential of natural compounds in targeting the YP in the context of the most common pathologic condition of adult and elderly life.

Insights on Natural Products Against Amyotrophic Lateral Sclerosis (ALS)

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that causes the death of motor neurons and consequent muscle paralysis. Despite many efforts to address it, current therapy targeting ALS remains limited, increasing the interest in complementary therapies. Over the years, several herbal preparations and medicinal plants have been studied to prevent and treat this disease, which has received remarkable attention due to their blood-brain barrier penetration properties and low toxicity. Thus, this review presents the therapeutic potential of a variety of medicinal herbs and their relationship with ALS and their physiopathological pathways.

Unraveling the Potential of Isorhamnetin as an Adjuvant in Depression Treatment with Escitalopram

Oxidative stress and inflammation are implicated in depression. While selective serotonin reuptake inhibitors (SSRIs) like escitalopram are commonly prescribed as first-line treatments, their inconsistent efficacy and delayed onset of action necessitates the exploration of adjunctive therapies. Isorhamnetin, a flavonol, has shown antioxidant and anti-inflammatory properties that makes exploring its antidepressant effect attractive. This study aims to investigate the adjuvant potential of isorhamnetin in combination with escitalopram to enhance its antidepressant efficacy in a lipopolysaccharide (LPS)-induced depression model using Swiss albino mice. Behavioral paradigms, such as the forced swim test and open field test, were employed to assess depressive symptoms, locomotion, and sedation. Additionally, enzyme-linked immunosorbent assays were utilized to measure Nrf2, BDNF, HO-1, NO, and IL-6 levels in the prefrontal cortex and hippocampus. The results demonstrate that isorhamnetin significantly improves the antidepressant response of escitalopram, as evidenced by reduced floating time in the forced swim test. Moreover, isorhamnetin enhanced antidepressant effects of escitalopram and effectively restored depleted levels of Nrf2, BDNF, and HO-1 in the cortex caused by LPS-induced depression. Isorhamnetin shows promise in enhancing the efficacy of conventional antidepressant therapy through antioxidant and anti-inflammatory effects.

Brain-Protective Mechanisms of Transcription Factor NRF2: Toward a Common Strategy for Neurodegenerative Diseases

Neurodegenerative diseases are characterized by the loss of homeostatic functions that control redox and energy metabolism, neuroinflammation, and proteostasis. The transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) is a master controller of these functions, and its overall activity is compromised during aging and in these diseases. However, NRF2 can be activated pharmacologically and is now being considered a common therapeutic target. Many gaps still exist in our knowledge of the specific role that NRF2 plays in specialized brain cell functions or how these cells respond to the hallmarks of these diseases. This review discusses the relevance of NRF2 to several hallmark features of neurodegenerative diseases and the current status of pharmacological activators that might pass through the blood-brain barrier and provide a disease-modifying effect. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Plant-Derived Natural Compounds for the treatment of Amyotrophic Lateral Sclerosis: An Update

Background

Amyotrophic lateral sclerosis (ALS) is a motor neuron disease (MND) that typically causes death within 3-5 years after diagnosis. Regardless of the substantial scientific knowledge accrued more than a century ago, truly effective therapeutic strategies remain distant. Various conventional drugs are being used but are having several adverse effects.

Objective/Aim

The current study aims to thoroughly review plant-derived compounds with well-defined ALS activities and their structure-activity relationships. Moreover, the review also focuses on complex genetics, clinical trials, and the use of natural products that might decrypt the future and novel therapeutics in ALS.

Methods

The collection of data for the compilation of this review work was searched in PubMed Scopus, Google Scholar, and Science Direct.

Results

Results showed that phytochemicals like-Ginkgolides, Protopanaxatriol, Genistein, epigallocatechingallate, resveratrol, cassoside, and others possess Amyotrophic lateral sclerosis (ALS) activity by various mechanisms.

Conclusion

These plant-derived compounds may be considered as supplements for conventional (ALS). Moreover, further preclinical and clinical studies are required to understand the structure-activity relationships, metabolism, absorption, and mechanisms of plant-derived natural agents.

Microglial Polarization: Novel Therapeutic Strategy against Ischemic Stroke

Ischemic stroke, which is the second highest cause of death and the leading cause of disability, represents ~71% of all strokes globally. Some studies have found that the key elements of the pathobiology of stroke is immunity and inflammation. Microglia are the first line of defense in the nervous system. After stroke, the activated microglia become a double-edged sword, with distinct phenotypic changes to the deleterious M1 types and neuroprotective M2 types. Therefore, ways to promote microglial polarization toward M2 phenotype after stroke have become the focus of attention in recent years. In this review, we discuss the process of microglial polarization, summarize the alternation of signaling pathways and epigenetic regulation that control microglial polarization in ischemic stroke, aiming to find the potential mechanisms by which microglia can be transformed into the M2 polarized phenotype.

Loss of NRF2 accelerates cognitive decline, exacerbates mitochondrial dysfunction, and is required for the cognitive enhancing effects of Centella asiatica during aging

The water extract of Centella asiatica (CAW) improves cognitive and mitochondrial function and activates the nuclear factor erythroid 2-related factor 2 (NRF2) regulated antioxidant response pathway in aged mice. Here we investigate whether NRF2 activation is required for the cognitive and mitochondrial effects of prolonged CAW exposure during aging. Five-month-old NRF2 knockout (NRF2KO) and wild-type mice were treated with CAW for 1, 7, or 13 months. Each cohort underwent cognitive testing and hippocampal mitochondrial analyses. Age-related cognitive decline was accelerated in NRF2KO mice and while CAW treatment improved cognitive performance in wild-type mice, it had no effect on NRF2KO animals. Hippocampal mitochondrial function also declined further with age in NRF2KO mice and greater hippocampal mitochondrial dysfunction was associated with poorer cognitive performance in both genotypes. Long-term CAW treatment did not affect mitochondrial endpoints in animals of either genotype. These data indicate that loss of NRF2 results in accelerated age-related cognitive decline and worsened mitochondrial deficits. NRF2 also appears to be required for the cognitive enhancing effects of CAW during aging.

Chinese Herbs and Repurposing Old Drugs as Therapeutic Agents in the Regulation of Oxidative Stress and Inflammation in Pulmonary Diseases

Several pro-inflammatory factors and proteins have been characterized that are involved in the pathogenesis of inflammatory diseases, including acute respiratory distress syndrome, chronic obstructive pulmonary disease, and asthma, induced by oxidative stress, cytokines, bacterial toxins, and viruses. Reactive oxygen species (ROS) act as secondary messengers and are products of normal cellular metabolism. Under physiological conditions, ROS protect cells against oxidative stress through the maintenance of cellular redox homeostasis, which is important for proliferation, viability, cell activation, and organ function. However, overproduction of ROS is most frequently due to excessive stimulation of either the mitochondrial electron transport chain and xanthine oxidase or reduced nicotinamide adenine dinucleotide phosphate (NADPH) by pro-inflammatory cytokines, such as interleukin-1β and tumor necrosis factor α. NADPH oxidase activation and ROS overproduction could further induce numerous inflammatory target proteins that are potentially mediated via Nox/ROS-related transcription factors triggered by various intracellular signaling pathways. Thus, oxidative stress is considered important in pulmonary inflammatory processes. Previous studies have demonstrated that redox signals can induce pulmonary inflammatory diseases. Thus, therapeutic strategies directly targeting oxidative stress may be effective for pulmonary inflammatory diseases. Therefore, drugs with anti-inflammatory and anti-oxidative properties may be beneficial to these diseases. Recent studies have suggested that traditional Chinese medicines, statins, and peroxisome proliferation-activated receptor agonists could modulate inflammation-related signaling processes and may be beneficial for pulmonary inflammatory diseases. In particular, several herbal medicines have attracted attention for the management of pulmonary inflammatory diseases. Therefore, we reviewed the pharmacological effects of these drugs to dissect how they induce host defense mechanisms against oxidative injury to combat pulmonary inflammation. Moreover, the cytotoxicity of oxidative stress and apoptotic cell death can be protected via the induction of HO-1 by these drugs. The main objective of this review is to focus on Chinese herbs and old drugs to develop anti-inflammatory drugs able to induce HO-1 expression for the management of pulmonary inflammatory diseases.

Diffusion kurtosis imaging to evaluate the effect and mechanism of tetramethylpyrazine on cognitive impairment induced by lipopolysaccharide in rats

Using diffusion kurtosis imaging (DKI) to evaluate the brain changes, the therapeutic effect and mechanism of tetramethylpyrazine in rats with dementia induced by lipopolysaccharide. Thirty-six male Sprague-Dawley rats were randomly divided into control group and five groups pretreated with sham operation, lipopolysaccharide(150ug) and three doses of tetramethylpyrazine(5, 10, and 20 mg/mL respectively). The Morris water maze test was used to evaluate cognitive ability. DKI and histology were performed. Low-dose of tetramethylpyrazine pretreated rats showed lower escape latency(6th day: 15.92seconds(s) vs. 5.11 s, P = 0.001), spent more time in the target quadrant(15.67 s vs. 29.83 s, P = 0.009) and crossed the platform area more frequently(3.50 vs. 9.17, P = 0.001) than rats in the LPS-treated group. Compared to sham group, the fractional anisotropy (FA), axial diffusion (Da), mean kurtosis (MK), and axial kurtosis (Ka) values in the cortex of lipopolysaccharide group were lower (P = 0.021,0.003,0.003,0.001,respectively).The MK, Ka, Kr, and FA values in the hippocampus of the lipopolysaccharide group were higher (P = 0.01, 0.026,0.007,0.003,respectively),while MD and Da values were lower (P = 0.045,0.044, respectively). Tetramethylpyrazine-pretreated rats showed higher values of FA, MD, Da, MK, and Ka in the cortex, lower MK, Ka, Kr, and FA values and higher MD,Da values in the hippocampus than the lipopolysaccharide group. Histologically, prominent inflammatory cells infiltration in the brain parenchyma of lipopolysaccharide group were observed, while groups pretreated using tetramethylpyrazine were alleviated. Tetramethylpyrazine can improve cognitive dysfunction induced by lipopolysaccharide. DKI can sensitively detect microstructure integrity of brain parenchyma in a non-invasive manner.

Madecassoside Inhibits Body Weight Gain via Modulating SIRT1-AMPK Signaling Pathway and Activating Genes Related to Thermogenesis

BACKGROUND

Pre-clinical research studies have shown that Madecassoside (MA) has favorable therapeutic effects on arthritis, acne, vitiligo and other diseases. However, the effects of MA on obesity have not yet been studied. This study mainly aimed to investigate the effects of MA in protecting against obesity and its underlying mechanism in reducing obesity.

METHODS

Obese diabetic KKay/TaJcl mice model was adopted to the study. The body weight of all animals was recorded daily, and the blood glucose, blood lipid, and serum aminotransferase levels were examined, respectively. The expression of P-AMPK, SIRT1, P-LKB1, P-ACC, and P-HSL in abdominal fat, mesenteric fat, and epididymal fat was measured by western blotting, and the levels of PPARα, CPT1a, PGC-1α, UCP-1, Cidea, Cox7a1, and Cox8b were examined by real-time quantitative PCR (RT-qPCR).

RESULTS

The results revealed that the body weight of the mice in MA group was significantly reduced, and the body mass index (BMI) showed significant difference between the two groups after 8 weeks of MA treatment. Further research revealed that it affected the mesenteric fat and epididymis fat by activating SIRT1/AMPK signaling pathway, and then promoted fatty acid oxidation of epididymal fat (PPARα ↑, CPT1a↑, and PGC-1α↑). Last but not the least, it also promoted the expression of UCP-1 and stimulated thermoregulatory genes (Cidea, Cox7a1, and Cox8b) in brown fat and mesenteric fat.

CONCLUSIONS

Taken together, these findings suggest that MA can inhibit the weight gain in obese diabetic mice, and reduce triglyceride levels, inhibit lipogenesis of mesenteric fat, promote epididymal fat lipolysis and fatty acid oxidation. Furthermore, MA treatment might promote mesenteric fat browning and activate mitochondrial function in brown fat as well as mesenteric fat.

RTA-408 protects against propofol-induced cognitive impairment in neonatal mice via the activation of Nrf2 and the inhibition of NF-κB p65 nuclear translocation

OBJECTIVE

To explore the effect of RTA-408 on the propofol-induced cognitive impairment of neonatal mice via regulating Nrf2 and NF-κB p65 nuclear translocation.

METHODS

C57BL/6 neonatal mice were randomized into intralipid, propofol, vehicle + propofol, and RTA-408 + propofol groups. The learning and memory ability was inspected by Morries water maze (MWM) test. TUNEL staining was performed to examine the apoptosis of neurons in hippocampus. The gene and protein expressions in hippocampus were detected by immunohistochemistry, qRT-PCR, or Western blotting. The activities of glutathione peroxidase (GPx), superoxide dismutase (SOD), and catalase (CAT) were tested by the corresponding kits.

RESULTS

Propofol prolonged escape latency of mice, decreased the times of crossing the platform, and shortened the time of staying in the target quadrant, while RTA-408 treatment improved the above-mentioned situation. Besides, Nrf2 protein in hippocampus of mice induced by propofol was decreased with the increased NF-κB p65 nuclear translocation, which was reversed by RTA-408. Meanwhile, RTA-408 decreased the apoptosis of neurons accompanying with the down-regulation of Caspase-3 and the up-regulations of neuronal-specific nuclear protein (NeuN), microtubule-associated protein 2 (Map2), Ca₂⁺ /Calmodulin-dependent Protein Kinase II (CaMKII), and parvalbumin (PV) immunostaining in hippocampus. Besides, propofol-induced high levels of proinflammatory cytokines and antioxidase activities in hippocampus were reduced by RTA-408.

CONCLUSION

RTA-408 improved propofol-induced cognitive impairment in neonatal mice via enhancing survival of neurons, reducing the apoptosis of hippocampal neurons, mitigating the inflammation and oxidative stress, which may be correlated with the activation of Nrf2 and the inhibition of NF-κB p65 nuclear translocation.

The novel Nrf2 activator CDDO-EA attenuates cerebral ischemic injury by promoting microglia/macrophage polarization toward M2 phenotype in mice

The aim of present study was to explore whether 2‐cyano‐3, 12‐dioxooleana‐1, 9‐dien‐28‐oic acid (CDDO)‐ethylamide (CDDO‐EA) attenuates cerebral ischemic injury and its possible mechanisms using a middle cerebral artery occlusion (MCAO) model in C57BL/6 mice. Our results showed that intraperitoneal injection (i.p.) of CDDO‐EA (2 and 4 mg/kg) augmented NFE2‐related factor 2 (Nrf2) and heme oxygenase‐1 (HO‐1) expression in ischemic cortex after MCAO. Moreover, CDDO‐EA (2 mg/kg, i.p.) significantly enhanced Nrf2 nuclear accumulation, associated with increased cytosolic HO‐1 expression, reduced neurological deficit and infarct volume as well as neural apoptosis, and shifted polarization of microglia/macrophages toward an antiinflammatory M2 phenotype in ischemic cortex after MCAO. Using an in vitro model, we confirmed that CDDO‐EA (100 μg/mL) increased HO‐1 expression and primed microglial polarization toward M2 phenotype under inflammatory stimulation in BV2 microglial cells. These findings suggest that a novel Nrf2 activator CDDO‐EA confers neuroprotection against ischemic injury.

Secondary Metabolites with Antioxidant Activities for the Putative Treatment of Amyotrophic Lateral Sclerosis (ALS): "Experimental Evidences"

Amyotrophic lateral sclerosis (ALS) is a fatal motor neuron disorder that is characterized by progressive loss of the upper and lower motor neurons at the spinal or bulbar level. Oxidative stress (OS) associated with mitochondrial dysfunction and the deterioration of the electron transport chain are factors that contribute to neurodegeneration and perform a potential role in the pathogenesis of ALS. Natural antioxidant molecules have been proposed as an alternative form of treatment for the prevention of age-related neurological diseases, in which ALS is included. Researches support that regulations in cellular reduction/oxidation (redox) processes are being increasingly implicated in this disease, and antioxidant drugs are aimed at a promising pathway to treatment. Among the strategies used for obtaining new drugs, we can highlight the isolation of secondary metabolite compounds from natural sources that, along with semisynthetic derivatives, correspond to approximately 40% of the drugs found on the market. Among these compounds, we emphasize oxygenated and nitrogenous compounds, such as flavonoids, coumarins, and alkaloids, in addition to the fatty acids, that already stand out in the literature for their antioxidant properties, consisting in a part of the diets of millions of people worldwide. Therefore, this review is aimed at presenting and summarizing the main articles published within the last years, which represent the therapeutic potential of antioxidant compounds of natural origin for the treatment of ALS.

β-Asarone Exerts Antioxidative Effects on H2O2-Stimulated PC12 Cells by Activating Nrf2/HO-1 Pathway

Oxidative stress-mediated neuron damage is considered an important contributor to the pathogenesis and development of neurodegenerative diseases. Although β-asarone is widely known for its neuroprotective pharmacological properties, the exact mechanism of β-asarone against oxidative stress has not been fully elucidated. The aim of the present study was to investigate underlying mechanisms of β-asarone against oxidative damage in PC12 cells. Our results demonstrated that the treatment of β-asarone significantly alleviated the reduction in cell viability and the excessive accumulation of lactate dehydrogenase (LDH), malondialdehyde (MDA) and reactive oxygen species (ROS) by increasing the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH). Moreover, β-asarone pretreatment also activated nuclear factor 2 erythroid-related factor 2 (Nrf2) and its downstream target heme oxygenase-1 (HO-1), which was involved in quenching reactive oxygen to inhibit oxidative stress. Furthermore, when silenced by Nrf2 siRNA, the protective effect of β-asarone was reduced and the oxidative stress induced by H2O2 was enhanced. In conclusion, our findings revealed that β-asarone could reduce oxidative stress via activating Nrf2/HO-1 pathway in PC12 cells, highlighting the potential therapeutic role of β-asarone in neurodegenerative diseases.

Ligustrazine ameliorates lipopolysaccharide‑induced neurocognitive impairment by activating autophagy via the PI3K/AKT/mTOR pathway

Autophagy is a lysosome-mediated cell content- dependent degradation pathway that leads to enhanced inflammation in an uncontrolled state. This study examined the role of autophagy in lipopolysaccharide (LPS)-induced brain inflammation and the effects of the traditional Chinese medicine ligustrazine on LPS-induced neurocognitive impairment in rats. Furthermore, the molecular mechanisms by which ligustrazine influences neurocognitive impairments were explored. The production of the inflammatory mediators interleukin (IL)-1β and tumor necrosis factor (TNF)-α was analyzed using ELISAs, and the expression levels of the autophagy marker microtubule-associated protein light chain 3 (LC3) II/I were analyzed using western blotting. LPS exposure upregulated the expression of IL-1β and TNF-α and downregulated the expression of LC3 II/I. Ligustrazine activated autophagy by preventing the expression of phosphoinositide 3-kinase (PI3K), phosphorylated protein kinase B (p-AKT), and phosphorylated mammalian target of rapamycin (p-mTOR). The present results suggest that ligustrazine improved LPS-induced neurocognitive impairments by activating autophagy and ameliorated neuronal injury by regulating the PI3K/AKT/mTOR signaling pathway. These findings provide an important reference for the prevention and treatment of neuroinflammation.

NRF2 as a Therapeutic Target in Neurodegenerative Diseases

Increased reactive oxygen species production and oxidative stress have been implicated in the pathogenesis of numerous neurodegenerative conditions including among others Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, Friedrich’s ataxia, multiple sclerosis, and stroke. The endogenous antioxidant response pathway protects cells from oxidative stress by increasing the expression of cytoprotective enzymes and is regulated by the transcription factor nuclear factor erythroid 2-related factor 2 (NRF2). In addition to regulating the expression of antioxidant genes, NRF2 has also been shown to exert anti-inflammatory effects and modulate both mitochondrial function and biogenesis. This is because mitochondrial dysfunction and neuroinflammation are features of many neurodegenerative diseases as well NRF2 has emerged as a promising therapeutic target. Here, we review evidence for a beneficial role of NRF2 in neurodegenerative conditions and the potential of specific NRF2 activators as therapeutic agents.

Intravoxel Incoherent Motion Imaging Study of Madecassoside in Improving Lipopolysaccharide-Induced Cognitive Impairment in Rats

BACKGROUND

Central nervous system inflammation is associated with neurodegenerative diseases and is thought to play a part in the pathophysiological cascade leading to cognitive impairment. Madecassoside (MA) has shown potential for the treatment of neuroinflammation. Lipopolysaccharide (LPS) can be used to establish an animal model of cognitive dysfunction induced by neuroinflammation. Intravoxel incoherent motion (IVIM) may potentially provide diffusion and perfusion data.

PURPOSE

To investigate the effect of MA on neurocognitive impairment induced by LPS in rats, and to explore the changes of brain microstructure and microcirculatory perfusion by IVIM imaging.

STUDY TYPE

Prospective.

POPULATION

Thirty-six male Sprague-Dawley rats were randomly divided into six groups (control group, sham operation group, LPS group, low-dose MA group, middle-dose MA group, and high-dose MA group) in a model of neurocognitive impairment induced by LPS (150 μg / 5 μL, 5 μL).

FIELD STRENGTH/SEQUENCE

IVIM-DWI sequence at 3.0T MRI; the scan time was 2 minutes and 17 seconds.

ASSESSMENT

The escape latency times of a Morris water maze test was used to evaluate the cognitive impairment rat model and the changes of learning ability of rats treated with different doses of MA (30 mg/kg, 60 mg/kg, 120 mg/kg). A GE postprocessing workstation (adw 4.5) was used to analyze the changes of each parameter (f value, D value, and D* value) in the IVIM data of each group.

STATISTICAL TESTS

All the data were analyzed by one-way and two-way analysis of variance (ANOVA).

RESULTS

The escape latency of the LPS group was significantly longer than the sham group (P = 0.05, 0.001, 0.006, and 0.042, respectively), and the high-dose group was significantly shorter than the LPS group on the sixth day (P = 0.034). Compared with the control group, the D values and f values of cerebral cortex and hippocampus were decreased significantly in the LPS group (P = 0.043 and 0.003; P = 0.029 and 0.016, respectively). With the increasing dose of MA, the D and f values of hippocampus and cortex increased, and there was a significant difference between the high-dose MA group and LPS group (D values: P = 0.038, 0.036; f values: P = 0.048, 0.039, respectively) DATA CONCLUSION: MA can improve the cognitive impairment induced by LPS by reducing neuroinflammation, and the changes of microcirculation and microperfusion in the brain tissue of these rats can be detected by IVIM imaging.

LEVEL OF EVIDENCE

1 Technical Efficacy Stage: 4 J. Magn. Reson. Imaging 2020;51:1836-1843.

Achyranthes bidentata polypeptide k suppresses neuroinflammation in BV2 microglia through Nrf2-dependent mechanism

Background

Activated microglia play a critical role in regulating neuroinflammatory responses in central nervous system. Previous studies have shown that Achyranthes bidentata polypeptide k's (ABPPk's) neuroprotective effects are partly due to its anti-inflammatory effect, but the mechanism remains unknown. This study is aimed to investigate the anti-inflammatory effect of ABPPk on lipopolysaccharide (LPS)-activated neuroinflammation in BV2 microglia.

Methods

We pretreated BV2 microglia with different concentrations of ABPPk (0.04-5 µg/mL) for 30 minutes, and then stimulated microglia with LPS for 24 hours. Pro-inflammatory mediators including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), nitric oxide (NO) and prostaglandin E₂ (PGE₂) production were measured by enzyme-linked immunosorbent assay (ELISA) kits. Inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), phosphorylated nuclear factor kappa B (NF-κB), heme oxygenase-1 (HO-1) and nuclear factor erythroid 2-related factor 2 (Nrf2) expression levels were detected by western blot. Glutathione (GSH) level was measured by GSH-Glo™ Glutathione assay. Immunofluorescent staining was used to detect the nuclear translocation of NF-κB and Nrf2. BV2 microglia transfected with Nrf2 siRNA were used to investigate the effect of Nrf2 on the anti-inflammatory activity of ABPPk.

Results

ABPPk (0.2-5 µg/mL) reduced the iNOS mediated NO and COX-2 mediated PGE₂ production significantly in LPS-activated BV2 microglia. ABPPk (1 and 5 µg/mL) also suppressed the production of TNF-α and IL-6 significantly. NF-κB is phosphorylated and translocated into nuclear in LPS-activated BV2 microglia, but ABPPk is shown to inhibit the phosphorylation and translocation of NF-κB in a concentration-dependent way. ABPPk increased the protein expression levels of HO-1 and Nrf2, as well as the GSH content in BV2 microglia. Immunofluorescent staining showed that ABPPk also promoted nuclear translocation of Nrf2. After knocking down Nrf2 in BV2 cells with siRNA interference, ABPPk's inhibitory effect on pro-inflammatory mediators also disappeared.

Conclusions

The present study suggests that ABPPk inhibits neuroinflammation in BV2 microglia through Nrf2-dependent mechanism. This provides some strong evidence for the potential of this neuroprotective natural compound to treat neurodegenerative diseases such as ischemic stroke and Parkinson's disease.