Examining the neuroprotective effects of protocatechuic acid and chrysin on in vitro and in vivo models of Parkinson disease

Synthesis and protective effect of new ligustrazine-vanillic acid derivatives against CoCl2-induced neurotoxicity in differentiated PC12 cells

Ligustrazine-vanillic acid derivatives had been reported to exhibit promising neuroprotective activities. In our continuous effort to develop new ligustrazine derivatives with neuroprotective effects, we attempted the synthesis of several ligustrazine-vanillic acid amide derivatives and screened their protective effect on the injured PC12 cells damaged by CoCl₂. The results showed that most of the newly synthesized derivatives exhibited higher activity than ligustrazine, of which, compound VA-06 displayed the highest potency with EC₅₀ values of 17.39 ± 1.34 μM. Structure-activity relationships were briefly discussed.Graphical abstractNew series of ligustrazine-vanillic acid amide derivatives were synthesized and evaluated for their protective effect on the injured PC₁₂ cells damaged by CoCl₂. VA-06 was found to be the most active one.

Hormetic effect of panaxatriol saponins confers neuroprotection in PC12 cells and zebrafish through PI3K/AKT/mTOR and AMPK/SIRT1/FOXO3 pathways

Hormesis is an adaptive response of living organisms to a moderate stress. However, its biomedical implication and molecular mechanisms remain to be intensively investigated. Panaxatriol saponins (PTS) is the major bioactive components extracted from Panax notoginseng, a widely used herbal medicine for cerebrovascular diseases. This study aims to examine the hormetic and neuroprotective effects of PTS in PC12 cells and zebrafish Parkinson's disease (PD) models. Our results demonstrated that PTS stimulated PC12 cell growth by about 30% at low doses, while PTS at high doses inhibited cell growth, which is a typical hormetic effect. Moreover, we found that low dose PTS pretreatment significantly attenuated 6-OHDA-induced cytotoxicity and up-regulated PI3K/AKT/mTOR cell proliferation pathway and AMPK/SIRT1/FOXO3 cell survival pathway in PC12 cells. These results strongly suggested that neuroprotective effects of PTS may be attributable to the hormetic effect induced by PTS through activating adaptive response-related signaling pathways. Notably, low dose PTS could significantly prevent the 6-OHDA-induced dopaminergic neuron loss and improve the behavior movement deficiency in zebrafish, whereas relative high dose PTS exhibited neural toxicity, further supporting the hormetic and neuroprotective effects of PTS. This study indicates that PTS may have the potential in the development of future therapeutic medicines for PD.

Aqueous Extract of Clerodendranthus spicatus Exerts Protective Effect on UV-Induced Photoaged Mice Skin

Clerodendranthus spicatus (Thunb.) C.Y.Wu (CS) is commonly used to treat kidney diseases in traditional Chinese medicine for its prominent anti-inflammatory effect and nourishing function to kidneys. In this study, aqueous extract of CS was assessed for its protective effect on UV-induced skin damage of mice. The chemical compositions of CS aqueous extract were determined by HPLC-ESI-MS/MS, in which 10 components were identified. During the experimental period, CS (0.9, 1.8, and 3.6 g/mL) was externally applied to shaved dorsal skins of mice prior to UV irradiation, daily for ten weeks. The results presented that CS (3.6 g/mL) apparently improved photodamaged skin appearance such as erythema, edema, and coarseness. The abnormal epidermal thickening was significantly reduced, and the dermal structures became more complete. The underlying protective mechanisms were associated with improving antioxidant enzymes activities including superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px), downregulating inflammatory cytokines (IL-1β, IL-6, TNF-α, COX-2, and PGE₂) expressions, recovering collagen density, and reducing matrix metalloproteinases productions. Sun protection factor of CS (3.6 g/mL) was 16.21 ± 0.03. Our findings for the first time demonstrated that CS had therapeutic effect on the photoaged skin. The results indicated that CS is a potential agent for photoprotective cosmetics.

No synergism between bis(propyl)-cognitin and rasagiline on protecting dopaminergic neurons in Parkinson's disease mice

Rasagiline, a monoamine oxidase-B inhibitor, and bis(propyl)-cognitin (B3C), a novel dimer are reported to be neuroprotective. Herein, the synergistical neuroprotection produced by rasagiline and B3C was investigated in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mice of Parkinsonism. By using neurobehavioural tests, high-performance liquid chromatography and western blot assay, we showed that B3C at 0.3 mg/kg, rasagiline at 0.02 mg/kg, as well as co-treatment with B3C and rasagiline prevented MPTP-induced behavioural abnormities, increased the concentrations of dopamine and its metabolites in the striatum, and up-regulated the expression of tyrosine hydroxylase in the substantia nigra. However, the neuroprotective effects of co-treatment were not significantly improved when compared with those of B3C or rasagiline alone. Collectively, we have demonstrated that B3C at 0.3 mg/kg and rasagline at 0.02 mg/kg could not produce synergistic neuroprotective effects.

Neuroprotective Role of MicroRNA-22 in a 6-Hydroxydopamine-Induced Cell Model of Parkinson's Disease via Regulation of Its Target Gene TRPM7

Parkinson's disease (PD), the second most prevalent neurodegenerative disorder with only symptomatic treatment available, is characterized by a progressive loss of dopaminergic neurons in the midbrain. Ample evidence indicated that microRNAs (miRs) could regulate post-transcriptional gene expression and neuronal disease. In the present study, we have evaluated the effects and mechanism of miR-22 in PC12 pheochromocytoma cells treated with 6-hydroxydopamine (6-OHDA) to mimic PD. RT-PCR results showed that the expression of miR-22 is downregulated in 6-OHDA-treated PC12 cells, and the overexpression of miR-22 significantly promoted the survival and proliferation of 6-OHDA-induced PC12 cells, whereas miR-22 inhibitor reversed these effects. In addition, PC12 cells were treated with miR-22 mimics or inhibitor following 6-OHDA administration, which medicated ROS production and upregulation or downregulation of caspase-3 activity, respectively. A luciferase reporter assay revealed that transient receptor potential melastatin 7 (TRPM7) is a direct target gene of miR-22, and miR-22 overexpression markedly downregulated the level of TRPM7. Strikingly, further analysis showed that miR-22 mediated 6-OHDA-induced PC12 cell survival and proliferation by targeting TRPM7. Taken together, the present study showed that miR-22 overexpression exhibited neuroprotective and reversal effects on the 6-OHDA-induced PC12 cell growth and apoptosis by targeting TRPM7.

Mitigating effect of chrysin loaded solid lipid nanoparticles against Amyloid β25-35 induced oxidative stress in rat hippocampal region: An efficient formulation approach for Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia. Amyloid-β25-35 (Aβ25-35), a well-established neurotoxicant, is reported to be involved in the etiology of AD. Chrysin (CN) with its wide range of biological activities in terms of reversing the neuronal damage once induced is limited due to its compromised bioavailability. Solid lipid nanoparticles (SLNs) on the other hand due to its improved protein stability, avoids proteolytic degradation, as well as sustained release of the incorporated molecules could be widely applied as a drug delivery vehicle. Hence, in the present investigation, we prepared CN loaded SLNs (CN-SLNs) and investigated its therapeutic role in alleviating Aβ25-35 administered neuronal damage. All the antioxidant enzymes and non-antioxidant enzyme in hippocampus were reduced significantly (P<0.01) in the Aβ25-35 injected group, whereas lipid peroxidation and acetylcholine esterase were increased significantly (P<0.01). These changes were restored significantly (P<0.01) by CN-SLNs (5mg/kg and 10mg/kg) and (P<0.05) by free CN (50mg/kg and 100mg/kg). Aβ25-35 also resulted in poor memory retention in behavioral tasks and histopathological sections of the hippocampal region showed the extent of neuronal loss which was thereby restored back on treatment with CN-SLNs and free CN. Our findings demonstrate that the therapeutic efficacy of CN could be attained at lower dose and also its oral bioavailability could be increased by encapsulating CN in SLNs. Thus the results suggest that CN-SLNs could be used as a potential therapeutic and a brain targeting strategy to combat the global burden of Alzheimer's disease.

Protective Effects of Otophylloside N on Pentylenetetrazol-Induced Neuronal Injury In vitro and In vivo

Approximately 30% of epileptic patients worldwide are medically unable to control their seizures. In addition, repeated epileptic seizures generally lead to neural damage. Pentylenetetrazol (PTZ) is a clinical circulatory and respiratory stimulant that is experimentally used to mimic epileptic convulsion in epilepsy research. Here, we systematically explore the neuroprotective effects of a pure compound isolated from Cynanchum otophyllum Schneid (Qingyangshen), Otophylloside N (OtoN), against PTZ-induced neuronal injury. We used three models: in vitro primary cortical neurons, in vivo mice, and in vivo zebrafish. Our results revealed that OtoN treatment may attenuate PTZ-induced morphology changes, cell death, LDH efflux in embryonic neuronal cells of C57BL/6J mice, and convulsive behavior in zebrafish. Additionally, our Western blot and RT-PCR results demonstrated that OtoN may attenuate PTZ-induced apoptosis and neuronal activation in neuronal cells, mice, and zebrafish. OtoN may reduce PTZ-induced cleavage of poly ADP-ribose polymerase and upregulation of the Bax/Bcl-2 ratio and decrease the expression level of c-Fos. This study is the first investigation of the neuroprotective effects of OtoN, which might be developed as a novel antiepileptic drug.

Multifunction of Chrysin in Parkinson's Model: Anti-Neuronal Apoptosis, Neuroprotection via Activation of MEF2D, and Inhibition of Monoamine Oxidase-B

Chrysin, a flavonoid compound existing in several plants, is applied as a dietary supplement because of its beneficial effects on general human health and alleviation of neurological disorders. However, mechanisms underlying neuroprotection of chrysin has not been fully elucidated, and the effects of chrysin on the Parkinson's disease (PD) model in vivo have not been investigated. It is here shown that chrysin protects primary granular neurons against 1-methyl-4-phenylpyridinium ion insult via antiapoptosis by reversing the dysregulated expression of Bcl-2, Bax, and caspase 3. The mechanisms also involved activating transcriptional factor myocyte enhancer factor 2D (MEF2D) via regulation of AKT-GSK3β signaling. In this in vivo model of PD, chrysin rescued the dopaminergic neurons loss and alleviated the decrease in dopamine level induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice. Moreover, chrysin markedly inhibited monoamine oxidase-B activity in vitro and in vivo. In conclusion, chrysin exerts beneficial effects to PD, possibly through multitarget mechanisms including antineuronal apoptosis, activation of the AKT-GSK3β/MEF2D pathway, and inhibition of the MAO-B activity.

The neurotoxicity of iron, copper and cobalt in Parkinson's disease through ROS-mediated mechanisms

Parkinson's disease (PD) is the second most common neurodegenerative disease with gradual loss of dopaminergic neurons. Despite extensive research in the past decades, the etiology of PD remains elusive. Nevertheless, multiple lines of evidence suggest that oxidative stress is one of the common causes in the pathogenesis of PD. It has also been suggested that heavy metal-associated oxidative stress may be implicated in the etiology and pathogenesis of PD. Here we review the roles of redox metals, including iron, copper and cobalt, in PD. Iron is a highly reactive element and deregulation of iron homeostasis is accompanied by concomitant oxidation processes in PD. Copper is a key metal in cell division process, and it has been shown to have an important role in neurodegenerative diseases such as PD. Cobalt induces the generation of reactive oxygen species (ROS) and DNA damage in brain tissues.

SIRT2 mediates NADH-induced increases in Nrf2, GCL, and glutathione by modulating Akt phosphorylation in PC12 cells

SIRT2 plays important roles in multiple biological processes. It is unclear whether SIRT2 affects antioxidant capacity by modulating Nrf2, a key transcription factor for multiple antioxidant genes. By studying NADH-treated differentiated PC12 cells, we found that NADH induced a significant increase in the nuclear Nrf2, which was prevented by both SIRT2 siRNA and SIRT2 inhibitor, AGK2. SIRT2 siRNA also blocked the NADH-induced increases in glutamate cysteine ligase (GCL) and glutathione. Moreover, SIRT2 siRNA and AGK2 blocked NADH-induced Akt phosphorylation, and inhibition of Akt phosphorylation prevented NADH-induced increases in the nuclear Nrf2 and glutathione. Collectively, our study shows that SIRT2 regulates nuclear Nrf2 levels by modulating Akt phosphorylation, thus modulating the levels of GCL and total glutathione.

mTOR Signaling in Parkinson's Disease

As a key regulator of cell metabolism and survival, mechanistic target of rapamycin (mTOR) emerges as a novel therapeutic target for Parkinson's disease (PD). A growing body of research indicates that restoring perturbed mTOR signaling in PD models can prevent neuronal cell death. Nevertheless, molecular mechanisms underlying mTOR-mediated effects in PD have not been fully understood yet. Here, we review recent progress in characterizing the association of mTOR signaling with PD risk factors and further discuss the potential roles of mTOR in PD.

Plant-Derived Natural Products for Parkinson's Disease Therapy

Plant-derived natural products have made their own niche in the treatment of neurological diseases since time immemorial. Parkinson's disease (PD), the second most prevalent neurodegenerative disorder, has no cure and the treatment available currently is symptomatic. This chapter thoughtfully and objectively assesses the scientific basis that supports the increasing use of these plant-derived natural products for the treatment of this chronic and progressive disorder. Proper considerations are made on the chemical nature, sources, preclinical tests and their validity, and mechanisms of behavioural or biochemical recovery observed following treatment with various plants derived natural products relevant to PD therapy. The scientific basis underlying the neuroprotective effect of 6 Ayurvedic herbs/formulations, 12 Chinese medicinal herbs/formulations, 33 other plants, and 5 plant-derived molecules have been judiciously examined emphasizing behavioral, cellular, or biochemical aspects of neuroprotection observed in the cellular or animal models of the disease. The molecular mechanisms triggered by these natural products to promote cell survivability and to reduce the risk of cellular degeneration have also been brought to light in this study. The study helped to reveal certain limitations in the scenario: lack of preclinical studies in all cases barring two; heavy dependence on in vitro test systems; singular animal or cellular model to establish any therapeutic potential of drugs. This strongly warrants further studies so as to reproduce and confirm these reported effects. However, the current literature offers scientific credence to traditionally used plant-derived natural products for the treatment of PD.

Nrf2--a therapeutic target for the treatment of neurodegenerative diseases

The brain is very sensitive to changes in redox status; thus maintaining redox homeostasis in the brain is critical for the prevention of accumulating oxidative damage. Aging is the primary risk factor for developing neurodegenerative diseases. In addition to age, genetic and environmental risk factors have also been associated with disease development. The primary reactive insults associated with the aging process are a result of oxidative stress (OS) and nitrosative stress (NS). Markers of increased oxidative stress, protein and DNA modification, inflammation, and dysfunctional proteostasis have all been implicated in contributing to the progression of neurodegeneration. The ability of the cell to combat OS/NS and maintain a clearance mechanism for misfolded aggregating proteins determines whether or not it will survive. A critical pathway in this regard is the Nrf2 (nuclear factor erythroid 2-related factor 2)- antioxidant response element (ARE) pathway. Nrf2 activation has been shown to mitigate a number of pathologic mechanisms associated with Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, and multiple sclerosis. This review will focus on the role of Nrf2 in these diseases and the potential for Nrf2 activation to attenuate disease progression.

Neuroprotective effects of chrysin: From chemistry to medicine

The World Health Organization estimated that the proportion of older people (over 60 years) will increase from 11% to 22% during next 40 years throughout the world. With respect to this, the morbidity and mortality rates of age-related diseases will increase. Mental diseases are the most common and important health problems among elderly people. Therefore, much attention has been paid to the discovery of neuroprotective drugs with high efficacy and negligible adverse effects. A growing body of scientific evidence has shown that phytochemicals possess neuroprotective effects and also mitigate neurodegeneration under both in vivo and in vitro conditions. Polyphenolic compounds, especially flavonoids, are known as most common chemical class of phytochemicals which possess a multiple range of health promoting effects. Chrysin, belonging to the flavone class, is one of the most important bioactive constituents of different fruits, vegetables and even mushrooms. Chrysin possesses potent neuroprotective effects and suppress neuroinflammation. In addition, chrysin improves cognitive decline and possesses a potent anti-amyloidogenic and neurotrophic effects. Furthermore, beneficial effects of chrysin on both depression and epilepsy have been reported. The present paper aimed to critically review the available literature data regarding the neuroprotective effects of chrysin as well as its chemistry, sources and bioavailability.

Green tea polyphenols and their potential role in health and disease

There is a growing body of evidence that plant polyphenols such as resveratrol, anthocyanins, catechins, and terpenes like taxol are effectively used in the treatment of chronic conditions including cancer, Alzheimer, Parkinsonism, diabetes, aging, etc. The link between oxidative stress and inflammation is well accepted. Thus, the mechanism of action of these natural products is partly believed to be through their significant antioxidant properties. The main constituent of green tea, with clinical significance, is epigallocatechin gallate (EGCG). It has been associated with antitumor, anti-Alzheimer, and anti-aging properties, improve redox status at the tissue level possibly preventing system level structural damage. This review focuses on EGCG and its potential therapeutic role in health and disease.