Pinocembrin attenuates MPP + -induced neurotoxicity by the induction of heme oxygenase-1 through ERK1/2 pathway

Therapeutic prospects of naturally occurring p38 MAPK inhibitors tanshinone IIA and pinocembrin for the treatment of SARS-CoV-2-induced CNS complications

P38 mitogen-activated protein kinase (p38 MAPK) signaling pathway is closely related to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) replication and hyperinflammatory responses in coronavirus disease 2019 (COVID-19). Therefore, blood-brain barrier-penetrating p38 MAPK inhibitors have good potential for the treatment of central nervous system (CNS) complications of COVID-19. The aim of the present study is the characterization of the therapeutic potential of tanshinone IIA and pinocembrin for the treatment of CNS complications of COVID-19. Studies published in high-quality journals indexed in databases Scopus, Web of Science, PubMed, and so forth were used to review the therapeutic capabilities of selected compounds. In continuation of our previous efforts to identify agents with favorable activity/toxicity profiles for the treatment of COVID-19, tanshinone IIA and pinocembrin were identified with a high ability to penetrate the CNS. Considering the nature of the study, no specific time frame was determined for the selection of studies, but the focus was strongly on studies published after the emergence of COVID-19. By describing the association of COVID-19-induced CNS disorders with p38 MAPK pathway disruption, this study concludes that tanshinone IIA and pinocembrin have great potential for better treatment of these complications. The inclusion of these compounds in the drug regimen of COVID-19 patients requires confirmation of their effectiveness through the conduction of high-quality clinical trials.

Therapeutic targeting of Ras/Raf/MAPK pathway by natural products: A systematic and mechanistic approach for neurodegeneration

BACKGROUND

Multiple dysregulated pathways are behind the pathogenesis of neurodegenerative diseases (NDDs); however, the crucial targets are still unknown. Oxidative stress, apoptosis, autophagy, and inflammation are the most dominant pathways that strongly influence neurodegeneration. In this way, targeting the Ras/Raf/mitogen-activated protein kinases (MAPKs) pathway appears to be a developing strategy for combating NDDs like Parkinson's disease, Alzheimer's disease, stroke, aging, and other NDDs. Accordingly, plant secondary metabolites have shown promising potentials for the simultaneous modulation of the Ras/Raf/MAPKs pathway and play an essential role in NDDs. MAPKs include p38 MAPK, extracellular signal-regulated kinase 1/2 (ERK 1/2), and c-Jun N-terminal kinase (JNK), which are important molecular players in neurodegeneration. Ras/Raf, which is located the upstream of MAPK pathway influences the initiation and progression of neurodegeneration and is regulated by natural products.

PURPOSE

Thus, the present study aimed to investigate the neuroprotective roles of plant- and marine-derived secondary metabolites against several NDDs through the modulation of the Ras/Raf/MAPK signaling pathway.

STUDY DESIGN AND METHODS

A systematic and comprehensive review was performed to highlight the modulatory roles of natural products on the Ras/Raf/MAPK signaling pathway in NDDs, according to the PRISMA guideline, using scholarly electronic databases, including PubMed, Scopus, and Web of Sciences. Associated reference lists were also searched for the literature review.

RESULTS

From a total of 1495 results, finally 107 articles were included in the present study. The results show that several natural compounds such as alkaloid, phenolic, terpenoids, and nanoformulation were shown to have modulatory effects on the Ras/Raf/MAPKs pathway.

CONCLUSION

Natural products are promising multi-targeted agents with on NDDs through Ras/Raf/MAPKs pathway. Nevertheless, additional and complementary studies are necessary to check its efficacy and potential side effects.

Assessment of the CYP1A2 Inhibition-Mediated Drug Interaction Potential for Pinocembrin Using In Silico, In Vitro, and In Vivo Approaches

Pinocembrin, a bioflavonoid, is extensively used in complementary/alternative medicine. It turns out as a promising candidate against neurodegenerative diseases because of its multifaceted pharmacological action toward neuroprotection. However, literature evidence is still lacking for its inhibitory action on CYP1A2, which is responsible for xenobiotic metabolism leading to the generation of toxic metabolites and bioactivation of procarcinogens. In the present study, our aim was to evaluate the CYP1A2 inhibitory potential of pinocembrin via in silico, in vitro, and in vivo investigations. From the results of in vitro studies, pinocembrin is found to be a potent and competitive inhibitor of CYP1A2. In vitro-in vivo extrapolation results indicate the potential of pinocembrin to interact with CYP1A2 substrate drugs clinically. Molecular docking-based in silico studies demonstrate the strong interaction of pinocembrin with human CYP1A2. In in vivo investigations using a rat model, pinocembrin displayed a marked alteration in the plasma exposure of CYP1A2 substrate drugs, namely, caffeine and tacrine. In conclusion, pinocembrin has a potent CYP1A2 inhibitory action to cause drug interactions, and further confirmatory study is warranted at the clinical level.

A Pretreatment with Isoorientin Attenuates Redox Disruption, Mitochondrial Impairment, and Inflammation Caused by Chlorpyrifos in a Dopaminergic Cell Line: Involvement of the Nrf2/HO-1 Axis

The C-glucosyl flavone isoorientin (ISO) is obtained by humans from the diet and exhibits several cytoprotective effects, as demonstrated in different experimental models. However, it was not previously shown whether ISO would be able to prevent mitochondrial impairment in cells exposed to a chemical stressor. Thus, we treated the human neuroblastoma SH-SY5Y cells with ISO (0.5-20 µM) for 18 h before a challenge with chlorpyrifos (CPF) at 100 µM for additional 24 h. We observed that ISO prevented the CPF-induced lipid peroxidation and protein carbonylation and nitration in the membranes of mitochondria extracted from CPF-treated cells. ISO also attenuated the CPF-elicited increase in the production of reactive species in this experimental model. Moreover, ISO prevented the CPF-induced disruption in the activity of components of the oxidative phosphorylation (OXPHOS) system in the SH-SY5Y cells. ISO also promoted an anti-inflammatory action in the cells exposed to CPF. CPF caused a decrease in the activity of the enzyme heme oxygenase-1 (HO-1), a cytoprotective agent. On the other hand, ISO upregulated HO-1 activity in SH-SY5Y cells. Inhibition of HO-1 by zinc protoporphyrin-IX (ZnPP-IX) suppressed the cytoprotection induced by ISO in the CPF-treated cells. Besides, silencing of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2) abolished the ISO-induced HO-1 upregulation and mitochondrial benefits induced by this flavone on the CPF-challenged cells. Thus, ISO protected mitochondria of the CPF-treated cells by an Nrf2/HO-1-dependent fashion in the SH-SY5Y cells.

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.

Pinocembrin pretreatment counteracts the chlorpyrifos-induced HO-1 downregulation, mitochondrial dysfunction, and inflammation in the SH-SY5Y cells

Chlorpyrifos (CPF), an insecticide, induces pro-oxidant, pro-inflammatory, and pro-apoptotic effects in animal cells. Contamination with CPF occurs not only in farms, since CPF is found in the food consumed in homes. Recently, it was demonstrated that CPF affects the mitochondria, inhibiting components of the electron transfer chain (ETC), causing loss of mitochondrial membrane potential (MMP), and reducing the synthesis of adenosine triphosphate (ATP) by the Complex V. Pinocembrin (PB) is found in propolis and exhibits antioxidant, anti-inflammatory, and anti-apoptotic effects in mammalian cells. PB is a potent inducer of the nuclear factor erythroid 2-related factor 2 (Nrf2), which is a major transcription factor controlling the expression of heme oxygease-1 (HO-1), among others. In the present work, we investigated whether PB would be able to prevent the mitochondrial and immune dysfunctions in the human neuroblastoma SH-SY5Y cells exposed to CPF. PB was tested at 1-25 µM for 4 h before the administration of CPF at 100 µM for additional 24 h. We found that PB prevented the CPF-induced inhibition of ETC, loss of MMP, and decline in the ATP synthesis. PB also promoted anti-inflammatory actions in this experimental model. Silencing of Nrf2 or inhibition of HO-1 suppressed the PB-induced effects in the CPF-challenged cells. Thus, PB promoted beneficial effects by a mechanism dependent on the Nrf2/HO-1/CO + BR axis in the CPF-treated cells.

Pinocembrin Promotes OPC Differentiation and Remyelination via the mTOR Signaling Pathway

The exacerbation of progressive multiple sclerosis (MS) is closely associated with obstruction of the differentiation of oligodendrocyte progenitor cells (OPCs). To discover novel therapeutic compounds for enhancing remyelination by endogenous OPCs, we screened for myelin basic protein expression using cultured rat OPCs and a library of small-molecule compounds. One of the most effective drugs was pinocembrin, which remarkably promoted OPC differentiation and maturation without affecting cell proliferation and survival. Based on these in vitro effects, we further assessed the therapeutic effects of pinocembrin in animal models of demyelinating diseases. We demonstrated that pinocembrin significantly ameliorated the progression of experimental autoimmune encephalomyelitis (EAE) and enhanced the repair of demyelination in lysolectin-induced lesions. Further studies indicated that pinocembrin increased the phosphorylation level of mammalian target of rapamycin (mTOR). Taken together, our results demonstrated that pinocembrin promotes OPC differentiation and remyelination through the phosphorylated mTOR pathway, and suggest a novel therapeutic prospect for this natural flavonoid product in treating demyelinating diseases.

Pinocembrin attenuates benzo(a)pyrene-induced CYP1A1 expression through multiple pathways: An in vitro and in vivo study

Benzo(a)pyrene [B(a)P], which is a carcinogen, is a substance most typically known in cigarette smoke and considered as an important intermediary of lung cancer. The enzyme CYP1A1 is crucial for the metabolic conversion of B(a)P into the intermediates that induce carcinogenesis. Stimulation of the aryl hydrocarbon receptor, which is regulated by B(a)P, is thought to induce numerous signaling cascades. Interruption in the mitogen-activated protein kinase (MAPK) pathway causes changes in cellular processes and may alter the AhR pathway. The aim of this investigation is to examine the potential ability of a flavonoid pinocembrin (PCB) to alleviate B(a)P toxicity and analyze the underlying molecular mechanisms. We found that PCB inhibited DNA adduct formation by attenuating CYP1A1 expression through the suppression of the AhR/Src/ERK pathways. PCB mitigated the B(a)P-stimulated DNA damage, inhibited Src and ERK1/2 expression, decreased CYP1A1 expression, and reduced the B(a)P-induced stimulation of NF-κB and MAPK signaling in lung epithelial cells. Finally, the activity of CYP1A1 and Src in lung tissues from mice supplemented with PCB was noticeably decreased and lower than that in lung tissues from mice supplemented with B(a)P alone. Collectively, these data suggest that PCB may alleviate the toxic effects of PAHs, which are important environmental pollutants.

Apitherapy for Parkinson's Disease: A Focus on the Effects of Propolis and Royal Jelly

The vast increase of world's aging populations is associated with increased risk of age-related neurodegenerative diseases such as Parkinson's disease (PD). PD is a widespread disorder characterized by progressive loss of dopaminergic neurons in the substantia nigra, which encompasses a wide range of debilitating motor, emotional, cognitive, and physical symptoms. PD threatens the quality of life of millions of patients and their families. Additionally, public welfare and healthcare systems are burdened with its high cost of care. Available treatments provide only a symptomatic relief and produce a trail of noxious side effects, which increase noncompliance. Hence, researchers have recently focused on the use of nutraceuticals as safe adjunctive treatments of PD to limit its progress and associated damages in affected groups. Propolis is a common product of the beehive, which possesses a large number of therapeutic properties. Royal jelly (RJ) is a bee product that is fed to bee queens during their entire life, and it contributes to their high physical fitness, fertility, and long lifespan. Evidence suggests that propolis and RJ can promote health by preventing the occurrence of age-related debilitating diseases. Therefore, they have been used to treat various serious disorders such as diabetes mellitus, cardiovascular diseases, and cancer. Some evolving studies used these bee products to treat PD in animal models. However, a clear understanding of the collective effect of propolis and RJ as well as their mechanism of action in PD is lacking. This review evaluates the available literature for the effects of propolis and RJ on PD. Whenever possible, it elaborates on the underlying mechanisms through which they function in this disorder and offers insights for fruitful use of bee products in future clinical trials.

Apitherapy for Age-Related Skeletal Muscle Dysfunction (Sarcopenia): A Review on the Effects of Royal Jelly, Propolis, and Bee Pollen

The global pandemic of sarcopenia, skeletal muscle loss and weakness, which prevails in up to 50% of older adults is increasing worldwide due to the expansion of aging populations. It is now striking young and midlife adults as well because of sedentary lifestyle and increased intake of unhealthy food (e.g., western diet). The lockdown measures and economic turndown associated with the current outbreak of Coronavirus Disease 2019 (COVID-19) are likely to increase the prevalence of sarcopenia by promoting sedentarism and unhealthy patterns of eating. Sarcopenia has multiple detrimental effects including falls, hospitalization, disability, and institutionalization. Although a few pharmacological agents (e.g., bimagrumab, sarconeos, and exercise mimetics) are being explored in different stages of trials, not a single drug has been approved for sarcopenia treatment. Hence, research has focused on testing the effect of nutraceuticals, such as bee products, as safe treatments to prevent and/or treat sarcopenia. Royal jelly, propolis, and bee pollen are common bee products that are rich in highly potent antioxidants such as flavonoids, phenols, and amino acids. These products, in order, stimulate larval development into queen bees, promote defenses of the bee hive against microbial and environmental threats, and increase royal jelly production by nurse bees. Thanks to their versatile pharmacological activities (e.g., anti-aging, anti-inflammatory, anticarcinogenic, antimicrobial, etc.), these products have been used to treat multiple chronic conditions that predispose to muscle wasting such as hypertension, diabetes mellitus, cardiovascular disorder, and cancer, to name a few. They were also used in some evolving studies to treat sarcopenia in laboratory animals and, to a limited degree, in humans. However, a collective understanding of the effect and mechanism of action of these products in skeletal muscle is not well-developed. Therefore, this review examines the literature for possible effects of royal jelly, bee pollen, and propolis on skeletal muscle in aged experimental models, muscle cell cultures, and humans. Collectively, data from reviewed studies denote varying levels of positive effects of bee products on muscle mass, strength, and function. The likely underlying mechanisms include amelioration of inflammation and oxidative damages, promotion of metabolic regulation, enhancement of satellite stem cell responsiveness, improvement of muscular blood supply, inhibition of catabolic genes, and promotion of peripheral neuronal regeneration. This review offers suggestions for other mechanisms to be explored and provides guidance for future trials investigating the effects of bee products among people with sarcopenia.

Natural Products and Their Bioactive Compounds: Neuroprotective Potentials against Neurodegenerative Diseases

In recent years, natural products, which originate from plants, animals, and fungi, together with their bioactive compounds have been intensively explored and studied for their therapeutic potentials for various diseases such as cardiovascular, diabetes, hypertension, reproductive, cancer, and neurodegenerative diseases. Neurodegenerative diseases, including Alzheimer's disease, Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis are characterized by the progressive dysfunction and loss of neuronal structure and function that resulted in the neuronal cell death. Since the multifactorial pathological mechanisms are associated with neurodegeneration, targeting multiple mechanisms of actions and neuroprotection approach, which involves preventing cell death and restoring the function to damaged neurons, could be promising strategies for the prevention and therapeutic of neurodegenerative diseases. Natural products have emerged as potential neuroprotective agents for the treatment of neurodegenerative diseases. This review focused on the therapeutic potential of natural products and their bioactive compounds to exert a neuroprotective effect on the pathologies of neurodegenerative diseases.

The Nrf2/HO-1 Axis as Targets for Flavanones: Neuroprotection by Pinocembrin, Naringenin, and Eriodictyol

Flavanones are a group of flavonoids that derive from their immediate chalcone precursors through the action of chalcone isomerase enzymes. The Aromatic A and B rings, C4-keto group, and the 15-carbon flavonoid skeleton are all evident in flavanones, but a notable absence of C2-C3 double bond and a lack of oxygenation at C-3 position of the C-ring makes them distinctively different from other groups such as flavonols (e.g., quercetin). On the basis of oxygenation level in the B ring, flavanones can vary from each other as exemplified by pinocembrin (no oxygenation), naringenin (4′-hydroxyl), or eriodictyol (3′,4′-dihydroxyl substitution). These groups are generally weaker free radical scavengers as compared to quercetin and derivatives though eriodictyol has a better free radical scavenging profile within the group due to the presence of the catechol functional moiety. In this communication, their antioxidant potential through the induction of antioxidant defenses is scrutinized. These compounds as exemplified by pinocembrin could induce the nuclear factor erythroid 2-related factor 2- (Nrf2-) heme oxygenase-1 (HO-1) axis leading to amelioration of oxidative stress in cellular and animal models. Their neuroprotective effect through such mechanism is discussed.

Evidence on the Health Benefits of Supplemental Propolis

Propolis is a honey-related product with reported health benefits such as improved immunity, lowered blood pressure, treated allergies and skin conditions. A literature review and narrative synthesis were conducted to investigate the evidence on the reported health benefits and future direction of propolis products. Using a predefined search strategy we searched Medline (OvidSP), Embase and Central for quantitative and qualitative studies (1990-2018). Citation, reference, hand searches and expert consultation were also undertaken. Studies of randomised control trials and observational data on humans with health-related outcomes were included. Collected data were entered into NVivo software (Version 12, QRS International) and analysed using a thematic framework and a narrative synthesis of emergent themes. A total of 63 publications were discussed. The majority were cell-based and animal studies, with a few key human trials conducted. There is significant promise for propolis as an effective antioxidant and anti-inflammatory agent with particular promise in cardiometabolic health.

Advances in Biosynthesis, Pharmacology, and Pharmacokinetics of Pinocembrin, a Promising Natural Small-Molecule Drug

Pinocembrin is one of the most abundant flavonoids in propolis, and it may also be widely found in a variety of plants. In addition to natural extraction, pinocembrin can be obtained by biosynthesis. Biosynthesis efficiency can be improved by a metabolic engineering strategy and a two-phase pH fermentation strategy. Pinocembrin poses an interest for its remarkable pharmacological activities, such as neuroprotection, anti-oxidation, and anti-inflammation. Studies have shown that pinocembrin works excellently in treating ischemic stroke. Pinocembrin can reduce nerve damage in the ischemic area and reduce mitochondrial dysfunction and the degree of oxidative stress. Given its significant efficacy in cerebral ischemia, pinocembrin has been approved by China Food and Drug Administration (CFDA) as a new treatment drug for ischemic stroke and is currently in progress in phase II clinical trials. Research has shown that pinocembrin can be absorbed rapidly in the body and easily cross the blood-brain barrier. In addition, the absorption/elimination process of pinocembrin occurs rapidly and shows no serious accumulation in the body. Pinocembrin has also been found to play a role in Parkinson's disease, Alzheimer's disease, and specific solid tumors, but its mechanisms of action require in-depth studies. In this review, we summarized the latest 10 years of studies on the biosynthesis, pharmacological activities, and pharmacokinetics of pinocembrin, focusing on its effects on certain diseases, aiming to explore its targets, explaining possible mechanisms of action, and finding potential therapeutic applications.

Effects of Pinocembrin Pretreatment on Connexin 43 (Cx43) Protein Expression After Rat Myocardial Ischemia-Reperfusion and Cardiac Arrhythmia

Background

Cardiac infarction frequently leads to arrhythmia and ischemia/reperfusion (I/R) aggravates cardiac injury. Pinocembrin can resist cerebral ischemia and decrease cardiac infarction area. This study thus generated a rat myocardial I/R model to assess the effect on ventricular rhythm and expression of gap junction connexin (Cx43).

Material/Methods

Male SD rats were randomly assigned into sham, model, and pinocembrin (30 mg/kg) pretreatment groups (N=15 each). The I/R model was generated by ligation of the left anterior descending coronary artery for 30 min. The pinocembrin group received intravenous injection 10 min before surgery. Heart rate (HR), mean artery pressure (MAP), rate pressure product (RPP), and arrhythmia were observed at 10 min before ischemia, 30 min after ischemia, and at 30, 60, and 120 min after reperfusion. ELISA was used to assess serum CK-MB and cTnI levels. Na⁺-K⁺ATPase and Ca⁺-Mg²⁺ATPase levels were quantified by spectrometry, followed by HE staining, IHC approach for Cx43 expression, and Western blot for Kir2.1 protein expression.

Results

Model rats had significantly lower HR, MAP, and RPP than in the sham group, and the pinocembrin pretreatment group had higher serum indexes. Arrhythmia index, CK-MB, and cTnI were higher in the model and pinocembrin groups, while Na⁺-K⁺ATPase, Ca⁺-Mg²⁺ATPase, Cx43, and Kir2.1 proteins were lower (p<0.05).

Conclusions

Pinocembrin alleviated ventricular arrhythmia in I/R rats via enhancing Na⁺-K⁺ATPase and Ca⁺-Mg²⁺ATPase activity and upregulating Cx43 and Kir2.1 protein expression.

Gallic Acid Protects 6-OHDA Induced Neurotoxicity by Attenuating Oxidative Stress in Human Dopaminergic Cell Line

Gallic acid is one of the most important polyphenolic compounds, which is considered an excellent free radical scavenger. 6-Hydroxydopamine (6-OHDA) is a neurotoxin, which has been implicated in mainly Parkinson's disease (PD). In this study, we investigated the molecular mechanism of the neuroprotective effects of gallic acid on 6-OHDA induced apoptosis in human dopaminergic cells, SH-SY5Y. Our results showed that 6-OHDA induced cytotoxicity in SH-SY5Y cells was suppressed by pre-treatment with gallic acid. The percentage of live cells (90%) was high in the pre-treatment of gallic acid when compared with 6-OHDA alone treated cell line. Moreover, gallic acid was very effective in attenuating the disruption of mitochondrial membrane potential, elevated levels of intracellular ROS and apoptotic cell death induced by 6-OHDA. Gallic acid also lowered the ratio of the pro-apoptotic Bax protein and the anti-apoptotic Bcl-2 protein in SH-SY5Y cells. 6-OHDA exposure was up-regulated caspase-3 and Keap-1 and, down-regulated Nrf2, BDNF and p-CREB, which were sufficiently reverted by gallic acid pre-treatment. These findings indicate that gallic acid is able to protect the neuronal cells against 6-OHDA induced injury and proved that gallic acid might potentially serve as an agent for prevention of several human neurodegenerative diseases caused by oxidative stress and apoptosis.

Pinocembrin Attenuates Mitochondrial Dysfunction in Human Neuroblastoma SH-SY5Y Cells Exposed to Methylglyoxal: Role for the Erk1/2-Nrf2 Signaling Pathway

Pinocembrin (PB; 5,7-dihydroxyflavanone) is found in propolis and exhibits antioxidant activity in several experimental models. The antioxidant capacity of PB is associated with the activation of the nuclear factor erythroid 2-related factor 2/antioxidant response element (Nrf2/ARE) signaling pathway. The Nrf2/ARE axis mediates the expression of antioxidant and detoxifying enzymes, such as glutathione peroxidase (GPx), glutathione reductase (GR), heme oxygenase-1 (HO-1), and the catalytic (GCLC) and regulatory (GCLM) subunits of the rate-limiting enzyme in the synthesis of glutathione (GSH), γ-glutamate-cysteine ligase (γ-GCL). Nonetheless, it is not clear how PB exerts mitochondrial protection in mammalian cells. Human neuroblastoma SH-SY5Y cells were pretreated (4 h) with PB (0-25 µM) and then exposed to methylglyoxal (MG; 500 µM) for further 24 h. Mitochondria were isolated by differential centrifugation. PB (25 µM) provided mitochondrial protection (decreased lipid peroxidation, protein carbonylation, and protein nitration in mitochondrial membranes; decreased mitochondrial free radical production; enhanced the content of GSH in mitochondria; rescued mitochondrial membrane potential-MMP) and blocked MG-triggered cell death by a mechanism dependent on the activation of the extracellular-related kinase (Erk1/2) and consequent upregulation of Nrf2. PB increased the levels of GPx, GR, HO-1, and mitochondrial GSH. The PB-induced effects were suppressed by silencing of Nrf2 with siRNA. Therefore, PB activated the Erk1/2-Nrf2 signaling pathway resulting in mitochondrial protection in SH-SY5Y cells exposed to MG. Our work shows that PB is a strong candidate to figure among mitochondria-focusing agents with pharmacological potential.

Pinocembrin Provides Mitochondrial Protection by the Activation of the Erk1/2-Nrf2 Signaling Pathway in SH-SY5Y Neuroblastoma Cells Exposed to Paraquat

Pinocembrin (PB; 5,7-dihydroxyflavanone; C₁₅H₁₂O₄) is a flavonoid found in propolis and exerts antioxidant, anti-inflammatory, and antimicrobial effects. Furthermore, PB has been studied as a neuroprotective agent. However, it remains to be understood whether and how PB would induce mitochondrial protection in mammalian cells. Therefore, we investigated here the mechanism involved in the protective effects elicited by PB in paraquat (PQ; 100 μM)-treated SH-SY5Y neuroblastoma cells. PB (25 μM) pretreatment (for 4 h) downregulated the levels of Bcl-2-associated X protein (Bax), blocked the release of cytochrome c to the cytosol, and inhibited the PQ-induced activation of caspase-9 and caspase-3. Besides, PB prevented mitochondrial dysfunction by suppressing the PQ-elicited inhibition of complexes I and V. Moreover, PB abrogated the loss of mitochondrial membrane potential (MMP) and the decline in ATP levels in the cells exposed to PQ. PB exerted antioxidant effects on mitochondria by decreasing the levels of redox impairment markers in mitochondrial membranes. Importantly, PB enhanced the levels of mitochondrial reduced glutathione (GSH). Upregulation of enzymes involved in the synthesis of GSH was seen in the cells exposed to PB. PB afforded mitochondrial protection by activating the extracellular signal-regulated kinase/nuclear factor erythroid 2-related factor 2 (Erk1/2-Nrf2) axis, since inhibition of Erk1/2 or silencing of Nrf2 abrogated these effects. Therefore, PB exerted mitochondrial and cellular protection by an Erk1/2-Nrf2-dependent mechanism.

Inhibition of beta-amyloid-induced neurotoxicity by pinocembrin through Nrf2/HO-1 pathway in SH-SY5Y cells

Amyloid beta peptide (Aβ) can cause neurotoxicity in Alzheimer's disease (AD). It evokes a cascade of oxidative damage to neurons. Pinocembrin (PCB), the most abundant flavonoid in propolis, has been proven to have neuroprotective effects in vivo and in vitro. In the present study, we investigated the neuroprotective effects of PCB on Aβ25-35-induced neurotoxicity. Exposure of SH-SY5Y cells to 25μM Aβ25-35 for 24h caused viability loss, apoptotic increase and reactive oxygen species (ROS) increase, pre-treatment with PCB for 4h significantly reduced the viability loss, apoptotic rate and attenuated Aβ-mediated ROS production. PCB strikingly inhibited Aβ25-35-induced mitochondrial dysfunctions, including lowered membrane potential, decreased Bcl-2/Bax ratio. In addition, PCB suppressed the release of cytochrome c and the cleavage of caspase-3. PCB treatment also resulted in an increase in Nrf2 protein levels and subsequent induction of heme oxygenase-1(HO-1) expression in SH-SY5Y cells. RNA interference-mediated knockdown of Nrf2 expression suppressed the PCB-induced HO-1 expression. Notably, we found that the HO-1 inhibitor zinc protoporphyrin IX (ZnPP) markedly diminished the neuroprotective effect of PCB against Aβ-mediated neurotoxicity. Taken together, these results indicated that PCB protects SH-SY5Y cells from Aβ25-35-induced neurotoxicity through activation of Nrf2/HO-1 pathways. Thus, activation of Nrf2/HO-1 pathways and inhibition of mitochondria-dependent apoptosis together may protect cells from Aβ25-35-induceded neurotoxicity.