Attenuation of Endoplasmic Reticulum Stress, Impaired Calcium Homeostasis, and Altered Bioenergetic Functions in MPP+-Exposed SH-SY5Y Cells Pretreated with Rutin

Oxidative stress and dysregulated long noncoding RNAs in the pathogenesis of Parkinson's disease

Parkinson's disease (PD) is a progressive age-related neurodegenerative disease whose annual incidence is increasing as populations continue to age. Although its pathogenesis has not been fully elucidated, oxidative stress has been shown to play an important role in promoting the occurrence and development of the disease. Long noncoding RNAs (lncRNAs), which are more than 200 nucleotides in length, are also involved in the pathogenesis of PD at the transcriptional level via epigenetic regulation, or at the post-transcriptional level by participating in physiological processes, including aggregation of the α-synuclein, mitochondrial dysfunction, oxidative stress, calcium stabilization, and neuroinflammation. LncRNAs and oxidative stress are correlated during neurodegenerative processes: oxidative stress affects the expression of multiple lncRNAs, while lncRNAs regulate many genes involved in oxidative stress responses. Oxidative stress and lncRNAs also affect other processes associated with neurodegeneration, including mitochondrial dysfunction and increased neuroinflammation that lead to neuronal death. Therefore, modulating the levels of specific lncRNAs may alleviate pathological oxidative damage and have neuroprotective effects. This review discusses the general mechanisms of oxidative stress, pathological mechanism underlying the role of oxidative stress in the pathogenesis of PD, and teases out the mechanisms through which lncRNAs regulate oxidative stress during PD pathogenesis, as well as identifies the possible neuroprotective mechanisms of lncRNAs. Reviewing published studies will help us further understand the mechanisms underlying the role of lncRNAs in the oxidative stress process in PD and to identify potential therapeutic strategies for PD.

Neuroprotective effects of flavonoids: endoplasmic reticulum as the target

The incidence of neurological disorders, particularly age-related neurodegenerative pathologies, exhibits an alarming upward trend, while current pharmacological interventions seldom achieve curative outcomes. Despite their diverse clinical presentations, neurological diseases often share a common pathological thread: the aberrant accumulation of misfolded proteins within the endoplasmic reticulum (ER). This phenomenon, known as ER stress, arises when the cell's intrinsic quality control mechanisms fail to cope with the protein-folding burden. Consequently, misfolded proteins accumulate in the ER lumen, triggering a cascade of cellular stress responses. Recognizing this challenge, researchers have intensified their efforts over the past two decades to explore natural compounds that could potentially slow or even reverse these devastating pathologies. Flavonoids constitute a vast and heterogeneous class of plant polyphenols, with over 10,000 identified from diverse natural sources such as wines, vegetables, medicinal plants, and organic products. Flavonoids are generally divided into six different subclasses: anthocyanidins, flavanones, flavones, flavonols, isoflavones, and flavonols. The diverse family of flavonoids, featuring a common phenolic ring backbone adorned with varying hydroxyl groups and additional modifications, exerts its antioxidant activity by inhibiting the formation of ROS, as evidenced by research. Also, studies suggest that polyphenols such as flavonoids can regulate ER stress through apoptosis and autophagy. By understanding these mechanisms, we can unlock the potential of flavonoids as novel therapeutic agents for neurodegenerative disorders. Therefore, this review critically examines the literature exploring the modulatory effects of flavonoids on various steps of the ER stress in neurological disorders.

Azoramide prevents MPP+-induced dopaminergic neuronal death via upregulating ER chaperone BiP expression

Progressive death of dopaminergic (DA) neurons is the main cause of Parkinson's disease (PD). The discovery of drug candidates to prevent DA neuronal death is required to address the pathological aspects and alter the process of PD. Azoramide is a new small molecule compound targeting ER stress, which was originally developed for the treatment of diabetes. In this study, pre-treatment with Azoramide was found to suppress mitochondria-targeting neurotoxin MPP+-induced DA neuronal death and locomotor defects in zebrafish larvae. Further study showed that pre-treatment with Azoramide significantly attenuated MPP+-induced SH-SY5Y cell death by reducing aberrant changes in nuclear morphology, mitochondrial membrane potential, intracellular reactive oxygen species, and apoptotic biomarkers. The mechanistic study revealed that Azoramide was able to up-regulate the expression of ER chaperone BiP and thereby prevented MPP+-induced BiP decrease. Furthermore, pre-treatment with Azoramide failed to suppress MPP+-induced cytotoxicity in the presence of the BiP inhibitor HA15. Taken together, these results suggested that Azoramide is a potential neuroprotectant with pro-survival effects against MPP+-induced cell death through up-regulating BiP expression.

Chaperone-Dependent Mechanisms as a Pharmacological Target for Neuroprotection

Modern pharmacotherapy of neurodegenerative diseases is predominantly symptomatic and does not allow vicious circles causing disease development to break. Protein misfolding is considered the most important pathogenetic factor of neurodegenerative diseases. Physiological mechanisms related to the function of chaperones, which contribute to the restoration of native conformation of functionally important proteins, evolved evolutionarily. These mechanisms can be considered promising for pharmacological regulation. Therefore, the aim of this review was to analyze the mechanisms of endoplasmic reticulum stress (ER stress) and unfolded protein response (UPR) in the pathogenesis of neurodegenerative diseases. Data on BiP and Sigma1R chaperones in clinical and experimental studies of Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Huntington's disease are presented. The possibility of neuroprotective effect dependent on Sigma1R ligand activation in these diseases is also demonstrated. The interaction between Sigma1R and BiP-associated signaling in the neuroprotection is discussed. The performed analysis suggests the feasibility of pharmacological regulation of chaperone function, possibility of ligand activation of Sigma1R in order to achieve a neuroprotective effect, and the need for further studies of the conjugation of cellular mechanisms controlled by Sigma1R and BiP chaperones.

GSK2606414 attenuates PERK/p-eIF2α/ATF4/CHOP axis and augments mitochondrial function to mitigate high glucose induced neurotoxicity in N2A cells

Neuronal dysfunction and subsequent apoptosis under high glucose conditions during diabetes contribute majorly to the manifestation of diabetic peripheral neuropathy (DPN). PERK (protein kinase RNA (PKR)-like ER kinase) one among the three canonical arms of unfolded protein response (UPR), is believed to play a crucial role in determining the cell fate during endoplasmic reticulum stress (ERS/ER stress) conditions. We evaluated the role of PERK inhibitor GSK2606414 in high glucose (30 ​mM) treated neuroblastoma (N2A) cells. High glucose resulted in disruption of ER proteostasis by activation of UPR which is evident through increased (p ​< ​0.001) expression of GRP78, p-PERK, p-eIF2α, ATF-4 and CHOP when compared to normal cells. It is accompanied with enhanced GRP78 localization in Endoplasmic Reticulum (ER) lumen evident from ER labeling Immunofluorescence (IF) staining. PERK activation resulted in altered mitochondrial function evident by increased mitochondrial superoxide production and compromised mitochondrial homeostasis with decrease in Mfn-2 levels. Additionally, ER stress induced neuronal apoptosis was attenuated by GSK2606414 treatment via inhibiting the PERK-eIF2α-ATF4-CHOP axis that not only curtailed the levels of apoptotic proteins like Bax and caspase 3 but also elevated the levels of anti-apoptotic Bcl-2. Collectively, our findings revealed the neuroprotective potential of GSK2606414 against high glucose induced neurotoxicity in N2A cells.

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Unregulated ER stress drives neuronal (N2A) apoptosis following high glucose (HG) exposure (30 ​mM).

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Mitochondrial dysfunction aggravated by ER stress under hyperglycemic conditions.

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PERK/p-eIF2α/ATF4/CHOP axis underlies the apoptosis of N2A cells upon HG exposure.

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GSK2606414 attenuates PERK/p-eIF2α/ATF4/CHOP axis to mitigate HG induced neurotoxicity in N2A cells.

Inhibition of γH2AX, COX-2 and regulation of antioxidant enzymes in MPP+-exposed SH-SY5Y cells pre-treated with rutin

Many plant-derived bioactive compounds such as rutin are reportedly effective in attenuating neuronal death in most neurodegenerative disorders. Parkinson's disease (PD) is characterized by the gradual degeneration of dopaminergic neurons in the substantia nigra of the midbrain, and has previously been modelled in-vitro through the specific neurotoxic activity of 1-methyl-4-phenylpyridinium (MPP⁺) on dopaminergic neurons. Rutin is a bioflavonoid with multiple pharmacological effects, and this study investigated the neuroprotective effects of rutin in the human dopaminergic SH-SY5Y cell line using the neurotoxin MPP⁺. SH-SY5Y cells pretreated with rutin, were exposed to MPP⁺ and evaluated for cell viability, nitric oxide (NO), reactive oxygen species (ROS) and antioxidant enzymes activities. In addition, western blot techniques were used to determine the protein expression levels of γH2AX and COX-2. Rutin significantly attenuated MPP⁺-induced loss of cell viability, mitigated ROS and NO production and inhibited the disruption of antioxidant enzymes activity. It was also observed that rutin significantly reduced protein expression levels of γH2AX and COX-2 in SH-SY5Y cells treated with MPP⁺. Taken together, findings from this study tend to suggest that rutin is a promising neuroprotective compound for the treatment of PD through its effects on some of the mechanisms that characterize this neurodegenerative disease.

Herbal Resources to Combat a Progressive & Degenerative Nervous System Disorder- Parkinson's Disease

Parkinson's disease is one of the most common adult-onset, a chronic disorder involving neurodegeneration, which progressively leads to deprivation of dopaminergic neurons in substantia nigra, causing a subsequent reduction of dopamine levels in the striatum resulting in tremor, myotonia, and dyskinesia. Genetics and environmental factors are believed to be responsible for the onset of Parkinson's disease. The exact pathogenesis of Parkinson's disease is quite complicated and the present anti-Parkinson's disease treatments appear to be clinically insufficient. Comprehensive researches have demonstrated the use of natural products such as ginseng, curcumin, ashwagandha, baicalein, etc. for the symptomatic treatment of this disease. The neuroprotective effects exhibited by these natural products are mainly due to their ability to increase dopamine levels in the striatum, manage oxidative stress, mitochondrial dysfunction, glutathione levels, clear the aggregation of α- synuclein, induce autophagy and decrease the pro-inflammatory cytokines and lipid peroxidation. This paper reviews various natural product studies conducted by scientists to establish the role of natural products (both metabolite extracts as well as pure metabolites) as adjunctive neuroprotective agents.

Regulation of AKT/AMPK signaling, autophagy and mitigation of apoptosis in Rutin-pretreated SH-SY5Y cells exposed to MPP. Metab Brain Dis 2021;36:315-326. [PMID: 33146846 DOI: 10.1007/s11011-020-00641-z]

Accumulating evidence suggest that apoptosis, autophagy and dysregulation of signaling pathways are common mechanisms involved in Parkinson's disease (PD) pathogenesis, and thus development of therapeutic agents targeting these mechanisms may be useful for the treatment of this disease. Although rutin (a bioflavonoid) is reported to have pharmacological benefits such as antioxidant, anti-inflammatory and antitumor activities, there are very few reports on the activity of this compound in 1-methyl-4-phenylpyridinium (MPP⁺)-induced PD models. Accordingly, we investigated the effects of rutin on apoptosis, autophagy and cell signaling markers (AKT/AMPK) in SH-SY5Y cells exposed to MPP⁺. Results show reduced changes in nuclear morphology and mitigation of caspase 3/7 and 9 activities in rutin pre-treated cells exposed to MPP⁺. Likewise, rutin regulated cell signaling pathways (AKT/AMPK) and significantly decreased protein expression levels of cleaved PARP, cytochrome c, LC3-II and p62. Also, rutin significantly increased protein expression levels of full-length caspase 3 in SH-SY5Y cells treated with MPP⁺. Transmission electron microscope (TEM) images demonstrated a reduction in autophagosomes in rutin-pretreated SH-SY5Y cells exposed to MPP⁺. These results provide experimental support for rutin's neuroprotective activity against MPP⁺-induced toxicity in SH-SY5Y cells, which is as a promising therapeutic agent for clinical trials in humans.

Role of Flavonoids in Neurodegenerative Diseases: Limitations and Future Perspectives

BACKGROUND

Flavonoids, a group of natural dietary polyphenols, are known for their beneficial effects on human health. By virtue of their various pharmacological effects, like anti-oxidative, antiinflammatory, anti-carcinogenic and neuroprotective effects, flavonoids have now become an important component of herbal supplements, pharmaceuticals, medicinals and cosmetics. There has been enormous literature supporting neuroprotective effect of flavonoids. Recently their efficacy in various neurodegenerative diseases, like Alzheimer's disease and Parkinson diseases, has received particular attention.

OBJECTIVE

The mechanism of flavanoids neuroprotection might include antioxidant, antiapoptotic, antineuroinflammatory and modulation of various cellular and intracellular targets. In in-vivo systems, before reaching to brain, they have to cross barriers like extensive first pass metabolism, intestinal barrier and ultimately blood brain barrier. Different flavonoids have varied pharmacokinetic characteristics, which affect their pharmacodynamic profile. Therefore, brain accessibility of flavonoids is still debatable.

METHODS

This review emphasized on current trends of research and development on flavonoids, especially in neurodegenerative diseases, possible challenges and strategies to encounter using novel drug delivery system.

RESULTS

Various flavonoids have elicited their therapeutic potential against neurodegenerative diseases, however by using nanotechnology and novel drug delivery systems, the bioavailability of favonoids could be enhanced.

CONCLUSION

This study bridges a significant opinion on medicinal chemistry, ethanopharmacology and new drug delivery research regarding use of flavonoids in management of neurodegeneration.

Protective effects of diet containing rutin against trichlorfon-induced muscle bioenergetics disruption and impairment on fatty acid profile of silver catfish Rhamdia quelen

Trichlorfon is an organophosphate insecticide that is widely used on fish farms to control parasitic infections. It has been detected in freshwater ecosystems as well as in fishery products. There is a growing body of evidence to suggest that certain feed additives may reduce or prevent pesticide-induced toxicity in fish. The aim of the present study was to determine whether acute exposure to trichlorfon would alter bioenergetic homeostasis and alter fatty acid profiles in muscles of silver catfish (Rhamdia quelen). We also sought to determine whether rutin prevents or reduces these effects. Cytosolic and mitochondrial creatine kinase (CK) and activities of complexes II-III and IV in muscle were significantly inhibited by exposure to 11 mg/L trichlorfon for 48 h compared to effects in the unexposed group. Total content of polyunsaturated fatty acids (omega-3 and omega-6) were significantly lower in muscle of silver catfish exposed to 11 mg/L trichlorfon for 48 h than in the unexposed group. Addition of 3 mg rutin/kg feed increased CK activity and prevented inhibition of complex IV activity, as well as preventing all alterations of muscle fatty acid profiles elicited by exposure to trichlorfon. No significant differences were observed between groups with respect to muscle adenylate kinase or pyruvate kinase activities, as well as total content of saturated and monounsaturated fatty acids. Our findings suggest that exposure (48 h) to 11 mg trichlorfon/L water inhibits cytosolic and mitochondrial CK activity in muscle. Trichlorfon also affects activities of complexes II-III and IV in respiratory chain, with important consequences for adenosine triphosphate production. The pesticide alters fatty acid profiles in the fish and endangers human consumers of the product. The most important finding of the present study is that inclusion of rutin improves bioenergetic homeostasis and muscle fatty acid profiles, suggesting that it reduces trichlorfon-induced muscle damage.

The Endoplasmic Reticulum Stress/Unfolded Protein Response and Their Contributions to Parkinson's Disease Physiopathology

Parkinson’s disease (PD) is a multifactorial age-related movement disorder in which defects of both mitochondria and the endoplasmic reticulum (ER) have been reported. The unfolded protein response (UPR) has emerged as a key cellular dysfunction associated with the etiology of the disease. The UPR involves a coordinated response initiated in the endoplasmic reticulum that grants the correct folding of proteins. This review gives insights on the ER and its functioning; the UPR signaling cascades; and the link between ER stress, UPR activation, and physiopathology of PD. Thus, post-mortem studies and data obtained by either in vitro and in vivo pharmacological approaches or by genetic modulation of PD causative genes are described. Further, we discuss the relevance and impact of the UPR to sporadic and genetic PD pathology.

Ghrelin mitigates MPP+-induced cytotoxicity: Involvement of ERK1/2-mediated Nrf2/HO-1 and endoplasmic reticulum stress PERK signaling pathway

Parkinson's disease (PD) is a common progressive and multifactorial neurodegenerative disease. Current pharmacological therapies for PD are inadequate and often accompanied by serious side effects. In search of neuroprotective agents being considered to be beneficial to PD therapy. Ghrelin confers neuroprotective effect in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned PD model, but the underlying mechanism remains not fully elucidated. Here, we utilized human neuroblastoma SH-SY5Y cells exposed to MPP⁺ as a PD model to investigate the underlying mechanism of Ghrelin. In our present work, cell viability, cell apoptosis, oxidative stress-related indicators, and the level of Nrf2, HO-1, PERK, eIF2α, ATF4, CHOP, and ERK1/2 were examined. The results showed that Ghrelin attenuated MPP⁺-induced change of cell viability, apoptosis, coupled with decreased Cytochrome c, caspase-9, and caspase-3 expressions. Consistently, Ghrelin suppressed MPP⁺-induced oxidative stress. Moreover, Ghrelin markedly enhanced Nrf2 expression and nuclear accumulation as well as HO-1 induction. Further investigations showed that Ghrelin significantly inhibited the endoplasmic reticulum stress PERK-eIF2α-ATF4-CHOP pathway. Interestingly, we then found that Ghrelin promoted phosphorylation of ERK1/2, and pharmacological inhibition of ERK signaling abolished the cytoprotective effect of Ghrelin. Furthermore, we also found promoting the activation of the Nrf2/ HO-1 pathway and suppressing of the PERK pathway were mediated by ERK1/2. These findings provided novel insights into the underlying mechanisms of Ghrelin exerted protective effect, suggesting its potential as a novel therapeutic strategy against PD.

Natural polyphenols prevent indomethacin-induced and diclofenac-induced Caco-2 cell death by reducing endoplasmic reticulum stress regardless of their direct reactive oxygen species scavenging capacity

Objectives

Indomethacin (INDO) and diclofenac (DIC) can induce intestinal cell death through induction of oxidative stress-mediated ER stress and mitochondrial dysfunction. This study investigated the cytoprotective potential of 11 polyphenols, namely caffeic acid (CAF), curcumin (CUR), epigallocatechin gallate (EGCG), gallic acid (GAL), hypophyllanthin (HYPO), naringenin (NAR), phyllanthin (PHY), piperine (PIP), quercetin (QUE), rutin (RUT) and silymarin (SLY) against these two NSAIDs in Caco-2 cells.

Methods

Reactive oxygen species (ROS) production was determined with fluorescence spectroscopy using specific probes (DHE, DCFH-DA, HPF). Cell viability and mitochondrial function were assessed by MTT and TMRE assays. The mRNA levels of Bax, Bcl-2 and CHOP proteins were determined by quantitative real-time polymerase chain reaction technique.

Key findings

All test polyphenols reduced NSAIDs-mediated ROS production. Only EGCG, QUE and RUT protected INDO-/DIC-induced cell death. These three polyphenols suppressed Bax/Bcl-2 mRNA ratio, CHOP up-regulation and MMP disruption in NSAIDs-treated cells. CAF and NAR prevented cytotoxicity from INDO, but not DIC. The cytoprotective effect of NAR, but not CAF, involved alteration of Bax/Bcl-2 mRNA ratio or MMP disruption, but not CHOP transcription.

Conclusion

The cytoprotective activity of polyphenols against NSAIDs-induced toxicity stemmed from either suppression of CHOP-related ER and mitochondria stresses or other CHOP-independent pathways, but not from the intrinsic ROS scavenging capacity.

The role of iron in Parkinson's disease monkeys assessed by susceptibility weighted imaging and inductively coupled plasma mass spectrometry

Mounting evidences indicated that elevated iron levels in the substantia nigra (SN) have been concerned as the underlying mechanisms of neurodegenerative diseases, including Parkinson's disease (PD). The present study used the 1-Methyl-4-phenyl-1, 2, 3, 6 -tetrahydropyridine (MPTP)-treated cynomolgus monkeys for PD to evaluate the usability of SWI for assessing iron deposition in the cerebral nuclei of PD. The results showed that susceptibility-weighted imaging (SWI) phase values of the ipsilateral (MPTP-lesion side) SN of MPTP-treated monkeys were lower than those in the contralateral SN of MPTP-treated monkeys and the same side of Control monkeys, suggesting that iron deposition were elevated in the affected side SN of MPTP-treated monkeys. Whereas MPTP has not effects on the SWI phase values in other detected brain regions of monkeys, including red nucleus (RN), putamen (PUT) and caudate nucleus (CA). Furthermore, ICP-MS results showed that MPTP increased the iron levels in MPTP injection side, but no in the ipsilateral striatum. Additionally, MPTP treatment did not affect the calcium and manganese levels in the detected brain regions of monkeys. However, Pearson correlation analysis results indicated that there were not relationship between SWI phase values in MPTP-lesion side of SN with the behavioral score, tyrosine hydroxylase (TH)-positive cells number and iron levels in the MPTP-lesion side of midbrain. Taken together, the results confirm the involvement of SN iron accumulations in the MPTP-treated monkey models for PD, and indirectly verify the usability of SWI for the measurement of iron deposition in the cerebral nuclei of PD.