Protopanaxtriol protects against 3-nitropropionic acid-induced oxidative stress in a rat model of Huntington's disease

Quercetin's Restorative Properties in Male Mice with 3-Nitropropionic Acid-induced Huntington-like Symptoms: Molecular Docking, Behavioral, and Biochemical Assessment

The neurotoxicity of 3-Nitropropionic acid (3-NP) is well known. Herein, the prophylactic versus therapeutic effects of quercetin (QCT) were investigated against 3-NP-induced behavioral anomalies and oxidative neural damage. Thirty male mice were assigned into five groups; the negative control group, the QCT group (25 mg/kg/day, p.o. for 21 days), the 3-NP group (17 days), the prophylactic group (QCT administration for 14 consecutive days, and then 3-NP was administrated), the therapeutic group (3-NP was administrated and then QCT for 21 days). At the end of the animal treatment, behavioral studies were assessed. Subsequently, the brain sample tissues were assessed for oxidative stress-related parameters and histological evaluation. Moreover, the potential interaction between 3-NP and tumor necrosis factor-alpha (TNF-α) was evaluated by using a molecular docking study. 3-NP markedly led to neurotoxicity which was indicated by behavioral deficits (motor behavior, depression-like behavior, memory dysfunction, and passive avoidance) and oxidative damage. Blind and targeted molecular docking results showed good interaction between 3-NP and TNF-α. However, the prophylactic effects of QCT were superior to the therapeutic effects for attenuating 3-NP-induced neurobehavioral and oxidative neural changes in experimental mice, which histological changes of the brain's striatum region approved our findings. Taken together, the antioxidant activity of QCT remarkably could attenuate 3-NP-induced neurobehavioral deficits and mitochondrial dysfunctions in mice.

Neuroprotective effects of silymarin in 3-nitropropionic acid-induced neurotoxicity in male mice: improving behavioral deficits by attenuating oxidative stress and neuroinflammation

3-Nitropropionic acid (3-NP) is strongly believed to be an irreversible inhibitor of mitochondrial complex II, leading to neural damage. This study aimed to investigate the neuroprotective effects of silymarin against 3-NP-induced neurotoxicity in male mice. Six-week-old mice received subacute doses of 3-NP intraperitoneally for 17 days. Mice were given silymarin (70 mg/kg/day, P.O.) for 2 weeks before 3-NP administration or for 4 weeks after 3-NP administration. At the end of the treatment schedule, animals were evaluated for behavioral alterations. Subsequently, neuronal damage in the hippocampus region of the brain tissues, oxidative stress-related parameters (lipid peroxidation, nitric oxide, superoxide dismutase, glutathione, and total antioxidant capacity), and pro-inflammatory cytokine (TNF-α, IL-17, and IL-1β) levels were evaluated. Our results indicated that 3-NP treatment significantly (p < 0.05) tended to reduce motor coordination, memory, and neuronal antioxidant status while increasing pro-inflammatory cytokine levels. However, silymarin in both treatment and pretreatment protocols markedly (p < 0.05) attenuated the behavioral deficits, oxidative stress status, and neuroinflammation. The results of the current study suggest that the neuroprotective effect of silymarin against 3-NP-induced neurotoxicity might be due to the mitigation of oxidative stress status and provide insight into the therapeutic potential of silymarin.

Effect of safranal or candesartan on 3-nitropropionicacid-induced biochemical, behavioral and histological alterations in a rat model of Huntington's disease

3-nitropropionic acid (3-NP) is a potent mitochondrial inhibitor mycotoxin. Systemic administration of 3-NP can induce Huntington's disease (HD)-like symptoms in experimental animals. Safranal (Safr) that is found in saffron essential oil has antioxidant, anti-inflammatory and anti-apoptotic actions. Candesartan (Cands) is an angiotensin receptor blocker that has the potential to prevent cognitive deficits. The present study aims to investigate the potential neuroprotective efficacy of Safr or Cands in 3-NP-induced rat model of HD. The experiments continued for nine consecutive days. Rats were randomly assigned into seven groups. The first group (Safr-control) was daily intraperitoneally injected with paraffin oil. The second group (Cands- and 3-NP-control) daily received an oral dose of 0.5% carboxymethylcellulose followed by an intraperitoneal injection of 0.9% saline. The third and fourth groups received a single daily dose of 50 mg/kg Safr (intraperitoneal) and 1 mg/kg Cands (oral), respectively. The sixth group was daily treated with 50 mg Safr kg/day (intraperitoneal) and was intraperitoneally injected with 20 mg 3-NP/ kg, from the 3rd till the 9th day. The seventh group was daily treated with 1 mg Cands /kg/day (oral) and was intraperitoneally injected with 20 mg 3-NP/ kg, from the 3rd till the 9th day. The present results revealed that 3-NP injection induced a considerable body weight loss, impaired memory and locomotor activity, reduced striatal monoamine levels. Furthermore, 3-NP administration remarkably increased striatal malondialdehyde and nitric oxide levels, whereas markedly decreased the total antioxidant capacity. Moreover, 3-NP significantly upregulated the activities of inducible nitric oxide synthase and caspase-3 as well as the Fas ligand, in striatum. On the contrary, Safr and Cands remarkably alleviated the above-mentioned 3-NP-induced alterations. In conclusion, Safr and Cands may prevent or delay the progression of HD and its associated impairments through their antioxidant, anti-inflammatory, anti-apoptotic and neuromodulator effects.

Osmundacetone Alleviates Cerebral Ischemia-Reperfusion Injury in Rats

Osmundacetone (DHBAc) is an antioxidant compound that has been shown to have neuroprotective and immunomodulatory activities. However, few studies have estimated its effect on cerebral ischemia-reperfusion (I/R) injury. In this study, we investigated the protective effect of DHBAc on the brain tissue of rats with cerebral I/R injury. Rats were respectively given nimodipine (NI), low dose (L-DHBAc) and high dose (H-DHBAc) Osmundacetone, and they were killed under anesthesia after 24 h of reperfusion. And neurological impairment scores, cerebral infarct size and cerebral pathological changes were respectively detected, and mRNA expression of recombinant kelch like ECH associated protein 1 (Keap1) and nuclear factor erythroid 2-related factor 2 (Nrf2), protein expression levels of caspase 3, cleaved caspase 3, heme oxygenase-1 (HO-1) and quinone oxidoreductase1 (NQO1) in ischemic brain tissue were measured. Compared with the I/R group, neurological impairment scores of the DHBAc groups were significantly decreased, and their infarct sizes were significantly smaller. DHBAc could improve the pathological status of brain tissue with cerebral I/R injury, including reducing number of inflammatory cells and area of vacuoles and restoring number of normal neurons. Expression levels of Keap1 mRNA and proteins of cleaved caspase3 were significantly decreased in the DHBAc groups than those of the I/R group, while expression levels of Nrf2 mRNA, HO-1 and NQO1 proteins were remarkably increased. The effect of H-DHBAc was similar to those of NI. These results suggest that DHBAc could mitigate damage to brain tissue in rats with cerebral I/R injury.

Stress response mechanisms in protein misfolding diseases: Profiling a cellular model of Huntington's disease

Stress response pathways like the integrated stress response (ISR), the mitochondrial unfolded protein response (UPRmt) and the heat shock response (HSR) have emerged as part of the pathophysiology of neurodegenerative diseases, including Huntington's disease (HD) - a currently incurable disease caused by the production of mutant huntingtin (mut-Htt). Previous data from HD patients suggest that ISR is activated while UPRmt and HSR are impaired in HD. The study of these stress response pathways as potential therapeutic targets in HD requires cellular models that mimic the activation status found in HD patients of such pathways. PC12 cells with inducible expression of the N-terminal fragment of mut-Htt are among the most used cell lines to model HD, however the activation of stress responses remains unclear in this model. The goal of this study is to characterize the activation of ISR, UPRmt and HSR in this HD cell model and evaluate if it mimics the activation status found in HD patients. We show that PC12 HD cell model presents reduced levels of Hsp90 and mitochondrial chaperones, suggesting an impaired activation or function of HSR and UPRmt. This HD model also presents increased levels of phosphorylated eIF2α, the master regulator of the ISR, but overall similar levels of ATF4 and decreased levels of CHOP - transcription factors downstream to eIF2α - in comparison to control, suggesting an initial activation of ISR. These results show that this model mimics the ISR activation and the impaired UPRmt and HSR found in HD patients. This work suggests that the PC12 N-terminal HD model is suitable for studying the role of stress response pathways in the pathophysiology of HD and for exploratory studies investigating the therapeutic potential of drugs targeting stress responses.

Neuroprotective potency of mangiferin against 3-nitropropionic acid induced Huntington's disease-like symptoms in rats: possible antioxidant and anti-inflammatory mechanisms

Huntington's disease (HD), a neurodegenerative disease, normally starts in the prime of adult life, followed by a gradual occurrence of psychiatric disturbances, cognitive and motor dysfunction. The daily performances and life quality of HD patients have been severely interfered by these clinical signs and symptoms until the last stage of neuronal cell death. To the best of our knowledge, no treatment is available to completely mitigate the progression of HD. Mangiferin, a naturally occurring potent glucoxilxanthone, is mainly isolated from the Mangifera indica plant. Considerable studies have confirmed the medicinal benefits of mangiferin against memory and cognitive impairment in neurodegenerative experimental models such as Alzheimer's and Parkinson's diseases. Therefore, this study aims to evaluate the neuroprotective effect of mangiferin against 3-nitropropionic acid (3-NP) induced HD in rat models. Adult Wistar rats (n = 32) were randomly allocated equally into four groups of eight rats each: normal control (Group I), disease control (Group II) and two treatment groups (Group III and Group IV). Treatment with mangiferin (10 and 20 mg/kg, p. o.) was given for 14 days, whereas 3-NP (15 mg/kg, i. p.) was given for 7 days to induce HD-like symptoms in rats. Rats were assessed for cognitive functions and motor coordination using open field test (OFT), novel object recognition (NOR) test, neurological assessment, rotarod and grip strength tests. Biochemical parameters such as oxidative stress markers and pro-inflammatory markers in brain hippocampus, striatum and cortex regions were evaluated. Histopathological study on brain tissue was also conducted using hematoxylin and eosin (H&E) staining. 3-NP triggered anxiety, decreased recognition memory, reduced locomotor activity, lower neurological scoring, declined rotarod performance and grip strength were alleviated by mangiferin treatment. Further, a significant depletion in brain malondialdehyde (MDA) level, an increase in reduced glutathione (GSH) level, succinate dehydrogenase (SDH), superoxide dismutase (SOD) and catalase (CAT) activities, and a decrease in tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β) and interleukin-6 (IL-6) levels were observed in mangiferin treated groups. Mangiferin also mitigated 3-NP induced histopathological alteration in the brain hippocampus, striatum and cortex sections. It could be inferred that mangiferin protects the brain against oxidative damage and neuroinflammation, notably via antioxidant and anti-inflammatory activities. Mangiferin, which has a good safety profile, may be an alternate treatment option for treating HD and other neurodegenerative disorders. The results of the current research of mangiferin will open up new avenues for the development of safe and effective therapeutic agents in diminishing HD.

A Preclinical Model for Parkinson’s Disease Based on Transcriptional Gene Activation via KEAP1/NRF2 to Develop New Antioxidant Therapies

Investigations of the effect of antioxidants on idiopathic Parkinson’s disease have been unsuccessful because the preclinical models used to propose these clinical studies do not accurately represent the neurodegenerative process of the disease. Treatment with certain exogenous neurotoxins induces massive and extremely rapid degeneration; for example, MPTP causes severe Parkinsonism in just three days, while the degenerative process of idiopathic Parkinson´s disease proceeds over many years. The endogenous neurotoxin aminochrome seems to be a good alternative target since it is formed in the nigrostriatal system neurons where the degenerative process occurs. Aminochrome induces all the mechanisms reported to be involved in the degenerative processes of idiopathic Parkinson’s disease. The presence of neuromelanin-containing dopaminergic neurons in the postmortem brain of healthy elderly people suggests that neuromelanin synthesis is a normal and harmless process despite the fact that it requires oxidation of dopamine to three ortho-quinones that are potentially toxic, especially aminochrome. The apparent contradiction that neuromelanin synthesis is harmless, despite its formation via neurotoxic ortho-quinones, can be explained by the protective roles of DT-diaphorase and glutathione transferase GSTM2-2 as well as the neuroprotective role of astrocytes secreting exosomes loaded with GSTM2-2. Increasing the expression of DT-diaphorase and GSTM2-2 may be a therapeutic goal to prevent the degeneration of new neuromelanin-containing dopaminergic neurons. Several phytochemicals that induce DT-diaphorase have been discovered and, therefore, an interesting question is whether these phytochemical KEAP1/NRF2 activators can inhibit or decrease aminochrome-induced neurotoxicity.

Glycyrrhizin prevents 3-nitropropionic acid-induced neurotoxicity by downregulating HMGB1/TLR4/NF-κB p65 signaling, and attenuating oxidative stress, inflammation, and apoptosis in rats

AIMS

Glycyrrhizin (Glyc) is a saponin triterpenoid that has signified its efficacy against Huntington's disease (HD). Nonetheless, its mechanism has not been fully clarified. Accordingly, this study was designed to evaluate the plausible mechanism of action of Glyc against 3-nitropropionic acid (3-NP)-induced HD.

MAIN METHODS

Rats were treated with Glyc (50 mg/kg, i.p.) for 3 weeks and 3-NP (10 mg/kg, i.p.) was administered at the latter 2 weeks alongside to induce HD.

KEY FINDINGS

Animals exposed to 3-NP revealed a reduction in body weight, neurobehavioral abnormalities, and various deleterious effects related to overexpression of HMGB1 such as oxidative stress, apoptosis, and inflammation. Promisingly, Glyc administration provided valuable effects by reversing the decline in body weight with improved neurobehavioral deficits. Ameliorating oxidative stress via restoring GSH, SOD, and Nrf2 alongside with MDA suppression was evident. Furthermore, Glyc switched the HMGB1/TLR4/NF-κB p65 signaling off, reduced IL-6, IL-β, TNF-α, caspase-3, and increased Bcl-2 as well as BDNF. All these beneficial effects were mirrored by a better histopathological picture upon using Glyc that suppressed gliosis by reducing GFAP expression as observed in the immunohistochemistry results.

SIGNIFICANCE

Accordingly, the current study demonstrated a promising neuroprotective effect of Glyc against experimentally induced HD through alleviating deleterious events by diverse mechanisms.

The Emerging Landscape of Natural Small-molecule Therapeutics for Huntington's Disease

Huntington's disease (HD) is a rare and fatal neurodegenerative disorder with no diseasemodifying therapeutics. HD is characterized by extensive neuronal loss and is caused by the inherited expansion of the huntingtin (HTT) gene that encodes a toxic mutant HTT (mHTT) protein having expanded polyglutamine (polyQ) residues. Current HD therapeutics only offer symptomatic relief. In fact, Food and Drug Administration (FDA) approved two synthetic small-molecule VMAT2 inhibitors, tetrabenazine (1) and deutetrabenazine (2), for managing HD chorea and various other diseases in clinical trials. Therefore, the landscape of drug discovery programs for HD is evolving to discover disease- modifying HD therapeutics. Likewise, numerous natural products are being evaluated at different stages of clinical development and have shown the potential to ameliorate HD pathology. The inherent anti-inflammatory and antioxidant properties of natural products mitigate the mHTT-induced oxidative stress and neuroinflammation, improve mitochondrial functions, and augment the anti-apoptotic and pro-autophagic mechanisms for increased survival of neurons in HD. In this review, we have discussed HD pathogenesis and summarized the anti-HD clinical and pre-clinical natural products, focusing on their therapeutic effects and neuroprotective mechanism/s.

Activated AMPK mitigates diabetes-related cognitive dysfunction by inhibiting hippocampal ferroptosis

Clinical and preclinical interest in Type 2 diabetes (T2D)-associated cognitive dysfunction (TDACD) has grown in recent years. However, the precise mechanisms underlying TDACD need to be further elucidated. Ferroptosis was reportedly involved in neurodegenerative diseases and diabetes-related organ injuries; however, its role in TDACD remains elusive. In this study, mice fed with a high-fat-diet combined with streptozotocin (HFD-STZ) were used as a T2D model to assess the role of ferroptosis in cognitive dysfunction. We found that ferroptosis was mainly activated in hippocampal neurons but not in microglia or astrocytes. Accordingly, increased levels of transferrin receptor and decreased levels of ferritin, GPX4, and SLC7A11 were observed in hippocampal neurons. In addition, pre-treatment with liproxstatin-1, a ferroptosis inhibitor, attenuated iron accumulation and oxidative stress response, which resulted in improved cognitive function in the HFD-STZ group. Furthermore, we found that p-AMP-activated protein kinase (AMPK) was decreased in the HFD-STZ group. Pre-treatment with AMPK agonist increased the expression of AMPK and GPX4, but decreased lipocalin 2 (LCN2) in the hippocampus that resulted in improved spatial learning ability in the HFD-STZ group. Taken together, we found that activation of neuronal ferroptosis in the hippocampus contributed to cognitive impairment of HFD-STZ mice. Furthermore, AMPK activation may reduce hippocampal ferroptosis, and consequently improve cognitive performance in diabetic mice.

The Role of Voltage-Gated Calcium Channels in Basal Ganglia Neurodegenerative Disorders

Calcium (Ca2+) plays a central role in regulating many cellular processes and influences cell survival. Several mechanisms can disrupt Ca2+ homeostasis to trigger cell death, including oxidative stress, mitochondrial damage, excitotoxicity, neuroinflammation, autophagy, and apoptosis. Voltage-gated Ca2+ channels (VGCCs) act as the main source of Ca2+ entry into electrically excitable cells, such as neurons, and they are also expressed in glial cells such as astrocytes and oligodendrocytes. The dysregulation of VGCC activity has been reported in both Parkinson's disease (PD) and Huntington's (HD). PD and HD are progressive neurodegenerative disorders (NDs) of the basal ganglia characterized by motor impairment as well as cognitive and psychiatric dysfunctions. This review will examine the putative role of neuronal VGCCs in the pathogenesis and treatment of central movement disorders, focusing on PD and HD. The link between basal ganglia disorders and VGCC physiology will provide a framework for understanding the neurodegenerative processes that occur in PD and HD, as well as a possible path towards identifying new therapeutic targets for the treatment of these debilitating disorders.

Targeting the Nrf2 signaling pathway using phytochemical ingredients: A novel therapeutic road map to combat neurodegenerative diseases

BACKGROUND

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a classical nuclear transcription factor that regulates the system's anti-oxidative stress response. The activation of Nrf2 induces the expression of antioxidant proteins and improves the system's anti-oxidative stress ability. Accumulating evidence suggests that Nrf2-centered signaling pathways may be a key pharmacological target for the treatment of neurodegenerative diseases (NDDs). However, phytochemicals as new therapeutic agents against NDDs have not been clearly delineated.

PURPOSE

To review the therapeutic effects of phytochemical ingredients on NDDs by activating Nrf2 and reducing oxidative stress injury.

METHODS

A comprehensive search of published articles was performed using various literature databases including PubMed, Google Scholar, and China National Knowledge Infrastructure. The search terms included "Nrf2", "phytochemical ingredients", "natural bioactive agents", "neurodegenerative diseases", "Antioxidant", "Alzheimer's disease", "Parkinson's disease", "Huntington's disease", "amyotrophic lateral sclerosis" "multiple sclerosis", "toxicity", and combinations of these keywords. A total of 769 preclinical studies were retrieved until August 2022, and we included 39 of these articless on phytochemistry, pharmacology, toxicology and other fields.

RESULTS

Numerous in vivo and in vitro studies showed that phytochemical ingredients could act as an Nrf2 activator in the treatment of NDDs through the antioxidant defense mechanism. These phytochemical ingredients, such as salidroside, naringenin, resveratrol, sesaminol, ellagic acid, ginsenoside Re, tanshinone I, sulforaphane, curcumin, naringin, tetramethylpyrazine, withametelin, magnolol, piperine, and myricetin, had the potential to improve Nrf2 signaling, thereby combatting NDDs.

CONCLUSION

As Nrf2 activators, phytochemical ingredients may provide a novel potential strategy for the treatment of NDDs. Here, we reviewed the interaction between phytochemical ingredients, Nrf2, and its antioxidant damaging pathway in NDDs and explored the advantages of phytochemical ingredients in anti-oxidative stress, which provides a reliable basis for improving the treatment of NDDs. However, further clinical trials are needed to determine the safety and efficacy of Nrf2 activators for NDDs.

The Emerging Landscape of Small-Molecule Therapeutics for the Treatment of Huntington's Disease

Huntington's disease (HD) is a progressive neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin gene (HTT). The new insights into HD's cellular and molecular pathways have led to the identification of numerous potent small-molecule therapeutics for HD therapy. The field of HD-targeting small-molecule therapeutics is accelerating, and the approval of these therapeutics to combat HD may be expected in the near future. For instance, preclinical candidates such as naphthyridine-azaquinolone, AN1, AN2, CHDI-00484077, PRE084, EVP4593, and LOC14 have shown promise for further optimization to enter into HD clinical trials. This perspective aims to summarize the advent of small-molecule therapeutics at various stages of clinical development for HD therapy, emphasizing their structure and design, therapeutic effects, and specific mechanisms of action. Further, we have highlighted the key drivers involved in HD pathogenesis to provide insights into the basic principle for designing promising anti-HD therapeutic leads.

Nrf2 Pathway in Huntington's Disease (HD): What Is Its Role?

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease that occurs worldwide. Despite some progress in understanding the onset of HD, drugs that block or delay symptoms are still not available. In recent years, many treatments have been proposed; among them, nuclear transcriptional factor-2 (Nrf2) enhancer compounds have been proposed as potential therapeutic agents to treat HD. Nrf2 triggers an endogenous antioxidant pathway activated in different neurodegenerative disorders. Probably, the stimulation of Nrf2 during either the early phase or before HD symptoms' onset, could slow or prevent striatum degeneration. In this review, we present the scientific literature supporting the role of Nrf2 in HD and the potential prophylactic and therapeutic role of this compound.

Neuroprotective Potential of Hydroalcoholic Extract of Centella asiatica Against 3-Nitropropionic Acid-Induced Huntington's Like Symptoms in Adult Zebrafish

Huntington's disease (HD) is an inherited neurodegenerative disease. 3-Nitropropionic acid (3-NP) causes increased reactive oxygen species production and neuroinflammation. Centella asiatica (CA) is a strong antioxidant. The aim of this study is to investigate the effect of hydroalcoholic extract of C. asiatica (HA-CA) on 3-NP-induced HD in adult zebrafish. Adult zebrafish (∼5-6 months old) weighing 470 to 530 mg was used and treated with 3-NP (5 mg/kg intraperitoneal [i.p.]). The animals received HA-CA (80 and 100 mg/L) daily for up to 28 days in water. Tetrabenazine (3 mg/kg i.p.) was used as a standard drug. We have done an open field test (for locomotor activity), a novel tank diving test (for anxiety), and a light and dark tank test (for memory), followed by biochemical analysis (acetyl-cholinesterase [AchEs], nitrite, lipid peroxidation [LPO], and glutathione [GSH]) and histopathology to further confirm memory dysfunctions. 3-NP-treated zebrafish exhibit reductions in body weight, progressive neuronal damage, cognition, and locomotor activity. The HA-CA group significantly reduced the 3-NP-induced increase in LPO, AchEs, and nitrite levels while decreasing GSH levels. Oral administration of HA-CA (80 or 100 mg/L) significantly reduces 3-NP-induced changes in body weight and behaviors, in addition to neuroinflammation in the brain by lowering tumor necrosis factor-α and interleukin-1β levels. Moreover, HA-CA significantly decreases the 3-NP-induced neuronal damage in the brain. HA-CA ameliorates neurotoxicity and neurobehavioral deficits in 3-NP-induced HD-like symptoms in adult zebrafish.

Neurohormetic phytochemicals in the pathogenesis of neurodegenerative diseases

The world population is progressively ageing, assuming an enormous social and health challenge. As the world ages, neurodegenerative diseases are on the rise. Regarding the progressive nature of these diseases, none of the neurodegenerative diseases are curable at date, and the existing treatments can only help relieve the symptoms or slow the progression. Recently, hormesis has increased attention in the treatment of age-related neurodegenerative diseases. The concept of hormesis refers to a biphasic dose-response phenomenon, where low levels of the drug or stress exert protective of beneficial effects and high doses deleterious or toxic effects. Neurohormesis, as the adaptive aspect of hormetic dose responses in neurons, has been shown to slow the onset of neurodegenerative diseases and reduce the damages caused by aging, stroke, and traumatic brain injury. Hormesis was also observed to modulate anxiety, stress, pain, and the severity of seizure. Thus, neurohormesis can be considered as a potentially innovative approach in the treatment of neurodegenerative and other neurologic disorders. Herbal medicinal products and supplements are often considered health resources with many applications. The hormesis phenomenon in medicinal plants is valuable and several studies have shown that hormetic mechanisms of bioactive compounds can prevent or ameliorate the neurodegenerative pathogenesis in animal models of Alzheimer’s and Parkinson’s diseases. Moreover, the hormesis activity of phytochemicals has been evaluated in other neurological disorders such as Autism and Huntington’s disease. In this review, the neurohormetic dose–response concept and the possible underlying neuroprotection mechanisms are discussed. Different neurohormetic phytochemicals used for the better management of neurodegenerative diseases, the rationale for using them, and the key findings of their studies are also reviewed.

GSK-3β-mediated regulation of Nrf2/HO-1 signaling as a new therapeutic approach in the treatment of movement disorders

Movement disorders are neurological conditions characterized by involuntary motor movements, such as dystonia, ataxia, chorea myoclonus, tremors, Huntington's disease (HD), and Parkinson's disease (PD). It is classified into two categories: hypokinetic and hyperkinetic movements. Globally, movement disorders are a major cause of death. The pathophysiological process is initiated by excessive ROS generation, mitochondrial dysfunction, neuroinflammation, and neurotransmitters imbalance that lead to motor dysfunction in PD and HD patients. Several endogenous targets including Nrf2 maintain oxidative balance in the body. Activation of Nrf2 signaling is regulated by the enzyme glycogen synthase kinase (GSK-3β). In the cytoplasm, inhibition of GSK-3β regulates cellular proliferation, homeostasis, and apoptotic process by stimulating the nuclear factor erythroid 2 (Nrf2) pathway which is involved in the elevation of the cellular antioxidant enzymes which controls the ROS generation. The activation of Nrf2 increases the expression of antioxidant response elements (ARE), such as (Hemeoxygenase-1) HO-1, which decreases excessive cellular stress, mitochondrial dysfunction, apoptosis, and neuronal degeneration, which is the major cause of motor dysfunction. The present review explores the GSK-3β-mediated neuroprotection in various movement disorders through the Nrf2/HO-1 antioxidant pathway. This review provides a link between GSK-3β and the Nrf2/HO-1 signaling pathway in the treatment of PD and HD. In addition to that it highlights various GSK-3β inhibitors and the Nrf2/HO-1 activators, which exert robust neuroprotection against motor disorders. Therefore, the present review will help in the discovery of new therapy for PD and HD patients.

Diapocynin neuroprotective effects in 3-nitropropionic acid Huntington's disease model in rats: emphasis on Sirt1/Nrf2 signaling pathway

Background and Aim

Huntington's disease (HD) is a rare inherited disease portrayed with marked cognitive and motor decline owing to extensive neurodegeneration. NADPH oxidase is considered as an important contributor to the oxidative injury in several neurodegenerative disorders including HD. Thus, the present study explored the possible neuroprotective effects of diapocynin, a specific NADPH oxidase inhibitor, against 3-nitropropionic acid (3-NP) model of HD in rats.

Methods

Animals received diapocynin (10 mg/kg/day, p.o), 30 min before 3-NP (10 mg/kg/day, i.p) over a period of 14 days.

Results

Diapocynin administration attenuated 3-NP-induced oxidative stress with significant increase in reduced glutathione, glutathione-S-transferase, nuclear factor erythroid 2-related factor 2, and brain-derived neurotrophic factor striatal contents contrary to NADPH oxidase (NOX2; gp91phox subunit) diminished expression. Moreover, diapocynin mitigated 3-NP-associated neuroinflammation and glial activation with prominent downregulation of nuclear factor-Кβ p65 and marked decrement of inducible nitric oxide synthase content in addition to decreased immunoreactivity of ionized calcium binding adaptor molecule 1 and glial fibrillary acidic protein; markers of microglial and astroglial activation, respectively. Treatment with diapocynin hindered 3-NP-induced apoptosis with prominent decrease in tumor suppressor protein and Bcl-2-associated X protein contents whereas the anti-apoptotic marker; B-cell lymphoma-2 content was noticeably increased. Diapocynin neuroprotective effects could be attributed to silent information regulator 1 upregulation which curbed 3-NP-associated hazards resulting in improved motor functions witnessed during open field, rotarod, and grip strength tests as well as attenuated 3-NP-associated histopathological derangements.

Conclusion

The present findings indicated that diapocynin could serve as an auspicious nominee for HD management.

Graphical abstract

Restoration of BDNF, DARPP32, and D2R Expression Following Intravenous Infusion of Human Immature Dental Pulp Stem Cells in Huntington's Disease 3-NP Rat Model

Huntington's disease (HD) is a neurodegenerative inherited genetic disorder, which leads to the onset of motor, neuropsychiatric and cognitive disturbances. HD is characterized by the loss of gamma-aminobutyric acid (GABA)ergic medium spiny neurons (MSNs). To date, there is no treatment for HD. Mesenchymal stem cells (MSCs) provide a substantial therapeutic opportunity for the HD treatment. Herein, we investigated the therapeutic potential of human immature dental pulp stem cells (hIDPSC), a special type of MSC originated from the neural crest, for HD treatment. Two different doses of hIDPSC were intravenously administrated in a subacute 3-nitropropionic acid (3NP)-induced rat model. We demonstrated hIDPSC homing in the striatum, cortex and subventricular zone using specific markers for human cells. Thirty days after hIDPSC administration, the cells found in the brain are still express hallmarks of undifferentiated MSC. Immunohistochemistry quantities analysis revealed a significant increase in the number of BDNF, DARPP32 and D2R positive stained cells in the striatum and cortex in the groups that received hIDPSC. The differences were more expressive in animals that received only one administration of hIDPSC. Altogether, these data suggest that the intravenous administration of hIDPSCs can restore the BDNF, DARPP32 and D2R expression, promoting neuroprotection and neurogenesis.

A review on Huntington protein Insight into protein aggregation and therapeutic interventions

Huntington disease (HD) is a distressing, innate neurodegenerative disease that descends from CAG repeat expansion in the huntingtin gene causing behavioral changes, motor dysfunction, and dementia in children and adults. Mutation in huntingtin (HTT) protein has been suggested to cause neuron loss in the cortex and striatum through various mechanisms including abnormal regulation of transcription, proteasomal dysfunction, post-translational modification, and other events, regulating toxicity. Pathogenesis of HD involves cleavage of the huntingtin protein followed by the neuronal accumulation of its aggregated form. Several research groups made possible efforts to reduce huntingtin gene expression, protein accumulation, and protein aggregation using inhibitors and molecular chaperones as developing drugs against HD. Herein, we review the mechanism proposed towards the formation of HTT protein aggregation and the impact of therapeutic strategies for the treatment of HD.

Traditional Chinese Medicine Targeting Heat Shock Proteins as Therapeutic Strategy for Heart Failure

Heart failure (HF) is the terminal stage of multifarious heart diseases and is responsible for high hospitalization rates and mortality. Pathophysiological mechanisms of HF include cardiac hypertrophy, remodeling and fibrosis resulting from cell death, inflammation and oxidative stress. Heat shock proteins (HSPs) can ameliorate folding of proteins, maintain protein structure and stability upon stress, protect the heart from cardiac dysfunction and ameliorate apoptosis. Traditional Chinese medicine (TCM) regulates expression of HSPs and has beneficial therapeutic effect in HF. In this review, we summarized the function of HSPs in HF and the role of TCM in regulating expression of HSPs. Studying the regulation of HSPs by TCM will provide novel ideas for the study of the mechanism and treatment of HF.

Inhibition of Brain GTP Cyclohydrolase I Attenuates 3-Nitropropionic Acid-Induced Striatal Toxicity: Involvement of Mas Receptor/PI3k/Akt/CREB/ BDNF Axis

GTP cyclohydrolase I (GTPCH I) is the rate-limiting enzyme for tetrahydrobiopterin (BH4) biosynthesis; the latter is an essential factor for iNOS activation that contributes neuronal loss in Huntington’s disease (HD). The aim of the study was to investigate the neuroprotective effect of 2,4-diamino-6-hydroxypyrimidine (DAHP), GTPCH I enzyme inhibitor, against neuronal loss in 3-nitropropinic acid (3-NP)-induced HD in rats and to reveal the possible involved mechanisms mediated through PI3K/Akt axis and its correlation to Mas receptor (MasR). Rats received 3-NP (10 mg/kg/day; i.p.) with or without administration of DAHP (0.5 g/kg/day; i.p.) or wortmannin (WM), a PI3K inhibitor, (15 μg/kg/day; i.v.) for 14 days. DAHP improved cognitive, memory, and motor abnormalities induced by 3-NP, as confirmed by striatal histopathological specimens and immunohistochemical examination of GFAP. Moreover, DAHP treatment inhibited GTPCH I activity, resulting in decreased BH4 levels and iNOS activation. Also, DAHP upregulated the protein expression of survival protein; p85/p55 (pY458/199)-PI3K and pS473-Akt that, in turn, boosted the activation of striatal neurotrophic factors and receptor, pS133-CREB, BDNF and pY515-TrKB, which positively affect MasR protein expression and improve mitochondrial dysfunction, as indicated by enhancing both SDH and PGC-1α levels. Indeed, DAHP attenuates oxidative stress by increasing SOD activity and Nrf2 expression in addition to reducing neuro-inflammatory status by inhibiting NF-κB p65 and TNF-α expression. Interestingly, all the previous effects were blocked by co-administration of WM with DAHP. In conclusion, DAHP exerts neuroprotective effect against neuronal loss induced by 3-NP administration via inhibition of GTPCH I and iNOS activity and activation of MasR/PI3K/Akt/CREB/BDNF/TrKB axis besides its antioxidant and anti-inflammatory effect.

Identification of cyclin D1 as a major modulator of 3-nitropropionic acid-induced striatal neurodegeneration

Mitochondria dysfunction occurs in the aging brain as well as in several neurodegenerative disorders and predisposes neuronal cells to enhanced sensitivity to neurotoxins. 3-nitropropionic acid (3-NP) is a naturally occurring plant and fungal neurotoxin that causes neurodegeneration predominantly in the striatum by irreversibly inhibiting the tricarboxylic acid respiratory chain enzyme, succinate dehydrogenase (SDH), the main constituent of the mitochondria respiratory chain complex II. Significantly, although 3-NP-induced inhibition of SDH occurs in all brain regions, neurodegeneration occurs primarily and almost exclusively in the striatum for reasons still not understood. In rodents, 3-NP-induced striatal neurodegeneration depends on the strain background suggesting that genetic differences among genotypes modulate toxicant variability and mechanisms that underlie 3-NP-induced neuronal cell death. Using the large BXD family of recombinant inbred (RI) strains we demonstrate that variants in Ccnd1 - the gene encoding cyclin D1 - of the DBA/2 J parent underlie the resistance to 3-NP-induced striatal neurodegeneration. In contrast, the Ccnd1 variant inherited from the widely used C57BL/6 J parental strain confers sensitivity. Given that cellular stress triggers induction of cyclin D1 expression followed by cell-cycle re-entry and consequent neuronal cell death, we sought to determine if the C57BL/6 J and DBA/2 J Ccnd1 variants are differentially modulated in response to 3-NP. We confirm that 3-NP induces cyclin D1 expression in striatal neuronal cells of C57BL/6 J, but this response is blunted in the DBA/2 J. We further show that striatal-specific alternative processing of a highly conserved 3'UTR negative regulatory region of Ccnd1 co-segregates with the C57BL/6 J parental Ccnd1 allele in BXD strains and that its differential processing accounts for sensitivity or resistance to 3-NP. Our results indicate that naturally occurring Ccnd1 variants may play a role in the variability observed in neurodegenerative disorders involving mitochondria complex II dysfunction and point to cyclin D1 as a possible therapeutic target.

Ursodeoxycholic acid as a potential alternative therapeutic approach for neurodegenerative disorders: Effects on cell apoptosis, oxidative stress and inflammation in the brain

Ursodeoxycholic acid (UDCA) is a bile acid component with anti-apoptotic, anti-oxidant and anti-inflammatory properties. It has been used in clinical medicine for liver diseases for centuries. In neurodegenerative diseases, increased cell apoptosis, oxidative stress and inflammation are frequently observed as well. Due to those beneficial effects of UDCA, recent studies have started to investigate the effects of UDCA in pre-clinical models of neurodegeneration. On this account, I review the data reported so far to investigate the role of UDCA in regulating apoptosis, oxidative stress and inflammation in pre-clinical models of neurodegeneration, as well as in homeostatic state. Evidence have shown that UDCA can reduce apoptosis, inhibit reactive oxygen species and tumor necrosis factor - α production in neurodegenerative models. In addition, UDCA is able to induce apoptosis of brain blastoma cells in homeostatic conditions. Overall, this review suggests the therapeutic potential of UDCA in neurodegenerative disorders, proposing UDCA as a potential alternative therapeutic approach for patients suffering from these diseases.

An Overview of the Nrf2/ARE Pathway and Its Role in Neurodegenerative Diseases

Nrf2 is a basic region leucine-zipper transcription factor that plays a pivotal role in the coordinated gene expression of antioxidant and detoxifying enzymes, promoting cell survival in adverse environmental or defective metabolic conditions. After synthesis, Nrf2 is arrested in the cytoplasm by the Kelch-like ECH-associated protein 1 suppressor (Keap1) leading Nrf2 to ubiquitin-dependent degradation. One Nrf2 activation mechanism relies on disconnection from the Keap1 homodimer through the oxidation of cysteine at specific sites of Keap1. Free Nrf2 enters the nucleus, dimerizes with small musculoaponeurotic fibrosarcoma proteins (sMafs), and binds to the antioxidant response element (ARE) sequence of the target genes. Since oxidative stress, next to neuroinflammation and mitochondrial dysfunction, is one of the hallmarks of neurodegenerative pathologies, a molecular intervention into Nrf2/ARE signaling and the enhancement of the transcriptional activity of particular genes are targets for prevention or delaying the onset of age-related and inherited neurogenerative diseases. In this study, we review evidence for the Nrf2/ARE-driven pathway dysfunctions leading to various neurological pathologies, such as Alzheimer’s, Parkinson’s, and Huntington’s diseases, as well as amyotrophic lateral sclerosis, and the beneficial role of natural and synthetic molecules that are able to interact with Nrf2 to enhance its protective efficacy.

Ginsenoside Rg1 exerts neuroprotective effects in 3-nitropronpionic acid-induced mouse model of Huntington's disease via suppressing MAPKs and NF-κB pathways in the striatum

Huntington's disease (HD) is one of main neurodegenerative diseases, characterized by striatal atrophy, involuntary movements, and motor incoordination. Ginsenoside Rg1 (Rg1), an active ingredient in ginseng, possesses a variety of neuroprotective effects with low toxicity and side effects. In this study, we investigated the potential therapeutic effects of Rg1 in a mouse model of HD and explored the underlying mechanisms. HD was induced in mice by injection of 3-nitropropionic acid (3-NP, i.p.) for 4 days. From the first day of 3-NP injection, the mice were administered Rg1 (10, 20, 40 mg·kg^-1, p.o.) for 5 days. We showed that oral pretreatment with Rg1 alleviated 3-NP-induced body weight loss and behavioral defects. Furthermore, pretreatment with Rg1 ameliorated 3-NP-induced neuronal loss and ultrastructural morphological damage in the striatum. Moreover, pretreatment with Rg1 reduced 3-NP-induced apoptosis and inhibited the activation of microglia, inflammatory mediators in the striatum. We revealed that Rg1 exerted neuroprotective effects by suppressing 3-NP-induced activation of the MAPKs and NF-κΒ signaling pathways in the striatum. Thus, our results suggest that Rg1 exerts therapeutic effects on 3-NP-induced HD mouse model via suppressing MAPKs and NF-κΒ signaling pathways. Rg1 may be served as a novel therapeutic option for HD.

Naringenin mitigates behavioral alterations and provides neuroprotection against 3-nitropropinoic acid-induced Huntington's disease like symptoms in rats

BACKGROUND

Naringenin is a powerful antioxidant and anti-inflammatory flavonoid which has been widely used as a therapeutic agent in various toxic models. However, few studies have clearly discussed the neuromodulatory effects of naringenin against different neurodegenerative disorders.

AIM

We investigated the neuroprotective efficacy of naringenin against 3-nitropropionic acid (3-NP)-induced neurobehavioral, biochemical and histopathological alterations in rats.

METHODS

Albino Wistar rats were randomly divided into three experimental groups. Group 1, the vehicle administered group, received saline. Group 2 received 3-NP (20 mg/kg body weight, i.p.) for 4 consecutive days. Group 3 received naringenin (50 mg/kg body weight, p.o.) twice daily for a period of 4 days, 30 min before and 6 h after the 3-NP administration. On the 5th day, neurobehavioral experiments were performed to access the behavioral outcomes and the striatum tissue was used for analysis of the monoamine oxidase (MAO) activity and serotonin (5-HT) levels. In addition, astrocytes activation was observed by glial fibrillary acidic protein (GFAP) immunostaining.

RESULTS

Our results showed that naringenin co-treatment provides neuroprotection against 3-NP-induced neurological disorders. Naringenin also increased the MAO activity and 5-HT levels in the striatum. Moreover, co-treatment with naringenin reduced the expression of GFAP protein in the striatal part and significantly attenuated the neuronal cell death. The findings of the present study suggest that naringenin provides neuroprotection and mitigates neurobehavioral alterations in experimental rats.

CONCLUSION

The results show that co-treatment with naringenin ameliorates 3-NP-induced HD-like symptoms in rats.

Mitochondrial and Redox-Based Therapeutic Strategies in Huntington's Disease

Significance: The molecular processes that determine Huntington's disease (HD) pathogenesis are not yet fully understood, and until now no effective neuroprotective therapeutic strategies have been developed. Mitochondria are one of most important organelles required for neuronal homeostasis, by providing metabolic pathways relevant for energy production, regulating calcium homeostasis, or controlling free radical generation and cell death. Because augmented reactive oxygen species (ROS) accompanied by mitochondrial dysfunction are relevant early HD mechanisms, targeting these cellular mechanisms may constitute relevant therapeutic approaches. Recent Advances: Previous findings point toward a close relationship between mitochondrial dysfunction and redox changes in HD. Mutant huntingtin (mHTT) can directly interact with mitochondrial proteins, as translocase of the inner membrane 23 (TIM23), disrupting mitochondrial proteostasis and favoring ROS production and HD progression. Furthermore, abnormal brain and muscle redox signaling contributes to altered proteostasis and motor impairment in HD, which can be improved with the mitochondria-targeted antioxidant mitoquinone or resveratrol, an SIRT1 activator that ameliorates mitochondrial biogenesis and function. Critical Issues: Various antioxidants and metabolic enhancers have been studied in HD; however, the real outcome of these molecules is still debatable. New compounds have proven to ameliorate mitochondrial and redox-based signaling pathways in early stages of HD, potentially precluding selective neurodegeneration. Future Directions: Unraveling the molecular etiology of deregulated mitochondrial function and dynamics, and oxidative stress opens new prospects for HD therapeutics. In this review, we explore the role of redox unbalance and mitochondrial dysfunction in HD progression, and further describe advances on clinical trials in HD based on mitochondrial and redox-based therapeutic strategies.

The bile acid TUDCA and neurodegenerative disorders: An overview

Bear bile has been used in Traditional Chinese Medicine for thousands of years due to its therapeutic potential and clinical applications. The tauroursodeoxycholic acid (TUDCA), one of the acids found in bear bile, is a hydrophilic bile acid and naturally produced in the liver by conjugation of taurine to ursodeoxycholic acid (UDCA). Several studies have shown that TUDCA has neuroprotective action in several models of neurodegenerative disorders (ND), including Alzheimer's disease, Parkinson's disease, and Huntington's disease, based on its potent ability to inhibit apoptosis, attenuate oxidative stress, and reduce endoplasmic reticulum stress in different experimental models of these illnesses. Our research extends the knowledge of the bile acid TUDCA actions in ND and the mechanisms and pathways involved in its cytoprotective effects on the brain, providing a novel perspective and opportunities for treatment of these diseases.

Protective Effect of Natural Products against Huntington's Disease: An Overview of Scientific Evidence and Understanding Their Mechanism of Action

Huntington's disease (HD), a neurodegenerative disease, normally starts in the prime of adult life, followed by a gradual occurrence of characteristic psychiatric disturbances and cognitive and motor dysfunction. To the best of our knowledge, there is no treatment available to completely mitigate the progression of HD. Among various therapeutic approaches, exhaustive literature reports have confirmed the medicinal benefits of natural products in HD experimental models. Building on this information, this review presents a brief overview of the neuroprotective mechanism(s) of natural products against in vitro/in vivo models of HD. Relevant studies were identified from several scientific databases, including PubMed, ScienceDirect, Scopus, and Google Scholar. After screening through literature from 2005 to the present, a total of 14 medicinal plant species and 30 naturally isolated compounds investigated against HD based on either in vitro or in vivo models were included in the present review. Behavioral outcomes in the HD in vivo model showed that natural compounds significantly attenuated 3-nitropropionic acid (3-NP) induced memory loss and motor incoordination. The biochemical alteration has been markedly alleviated with reduced lipid peroxidation, increased endogenous enzymatic antioxidants, reduced acetylcholinesterase activity, and increased mitochondrial energy production. Interestingly, following treatment with certain natural products, 3-NP-induced damage in the striatum was ameliorated, as seen histologically. Overall, natural products afforded varying degrees of neuroprotection in preclinical studies of HD via antioxidant and anti-inflammatory properties, preservation of mitochondrial function, inhibition of apoptosis, and induction of autophagy.

Sodium hydrogen sulfide upregulates cystathionine β-synthase and protects striatum against 3-nitropropionic acid-induced neurotoxicity in rats

OBJECTIVES

Hydrogen sulfide (H2S) is a neuromodulator that plays a protective role in multiple neurodegenerative diseases including Alzheimer's (AD) and Parkinson's (PD). However, the precise mechanisms underlying its effects against Huntington's disease (HD) are still questioned.This study aimed to examine the neuroprotective effects of sodium hydrogen sulfide (NaHS; H2S donor) against 3-nitropropionic acid (3NP)-induced HD like pathology in rats. Methods: Male Wistar rats were randomly allocated into four groups; (1) normal control receiving saline; (2) NaHS control receiving (0.5 mg/kg/day, i.p.) for 14 days; (3,4) receiving 3NP (10 mg/kg/day, i.p.) for 14 days, with NaHS 30 min later in group 4.

KEY FINDINGS

NaHS improved cognitive and locomotor deficits induced by 3NP as confirmed by the striatal histopathological findings. These former events were biochemically supported by the increment in cystathionine β-synthase (CBS) gene expression, reduction of glutamate (Glu), dopamine (DA), malondialdehyde (MDA), tumour necrosis factor-alpha (TNF-α), cytochrome-c, cleaved caspase-3 and pc-FOS indicating antioxidant, anti-inflammatory as well as anti-apoptotic effects. Furthermore, NaHS pretreatment improved cholinergic dysfunction and increased brain-derived neurotropic factor (BDNF) and nuclear factor erythroid-2-related factor 2 (Nrf2).

CONCLUSIONS

These findings suggest that appropriate protection with H2S donors might represent a novel approach to slow down HD-like symptoms.

Neuroprotection: Targeting Multiple Pathways by Naturally Occurring Phytochemicals

With the increase in the expectancy of the life span of humans, neurodegenerative diseases (NDs) have imposed a considerable burden on the family, society, and nation. In defiance of the breakthroughs in the knowledge of the pathogenesis and underlying mechanisms of various NDs, very little success has been achieved in developing effective therapies. This review draws a bead on the availability of the nutraceuticals to date for various NDs (Alzheimer's disease, Parkinson's disease, Amyotrophic lateral sclerosis, Huntington's disease, vascular cognitive impairment, Prion disease, Spinocerebellar ataxia, Spinal muscular atrophy, Frontotemporal dementia, and Pick's disease) focusing on their various mechanisms of action in various in vivo and in vitro models of NDs. This review is distinctive in its compilation to critically review preclinical and clinical studies of the maximum phytochemicals in amelioration and prevention of almost all kinds of neurodegenerative diseases and address their possible mechanism of action. PubMed, Embase, and Cochrane Library searches were used for preclinical studies, while ClinicalTrials.gov and PubMed were searched for clinical updates. The results from preclinical studies demonstrate the efficacious effects of the phytochemicals in various NDs while clinical reports showing mixed results with promise for phytochemical use as an adjunct to the conventional treatment in various NDs. These studies together suggest that phytochemicals can significantly act upon different mechanisms of disease such as oxidative stress, inflammation, apoptotic pathways, and gene regulation. However, further clinical studies are needed that should include the appropriate biomarkers of NDs and the effect of phytochemicals on them as well as targeting the appropriate population.

Mitochondrial retrograde signalling in neurological disease

Neuronal mitochondrial dysfunction causes primary mitochondrial diseases and likely contributes to neurodegenerative diseases including Parkinson's and Alzheimer's disease. Mitochondrial dysfunction has also been documented in neurodevelopmental disorders such as tuberous sclerosis complex and autism spectrum disorder. Only symptomatic treatments exist for neurodevelopmental disorders, while neurodegenerative diseases are largely untreatable. Altered mitochondrial function activates mitochondrial retrograde signalling pathways, which enable signalling to the nucleus to reprogramme nuclear gene expression. In this review, we discuss the role of mitochondrial retrograde signalling in neurological diseases. We summarize how mitochondrial dysfunction contributes to neurodegenerative disease and neurodevelopmental disorders. Mitochondrial signalling mechanisms that have relevance to neurological disease are discussed. We then describe studies documenting retrograde signalling pathways in neurons and glia, and in animal models of neuronal mitochondrial dysfunction and neurological disease. Finally, we suggest how specific retrograde signalling pathways can be targeted to develop novel treatments for neurological diseases. This article is part of the theme issue 'Retrograde signalling from endosymbiotic organelles'.

Harmine Acts as an Indirect Inhibitor of Intracellular Protein Aggregation

Protein aggregation and oxidative stress are two pathological hallmarks of a number of protein misfolding diseases, including Huntington's disease (HD). Whether protein aggregation precedes elevation of oxidative stress or follows it remains ambiguous. We have investigated the role of harmine, a beta-carboline alkaloid, in aggregation of a mutant huntingtin fragment (103Q-htt) in a yeast model of HD. We observed that harmine was able to decrease intracellular aggregation of 103Q-htt, and this reduction was higher than that observed with trehalose, a conventional protein stabilizer. The presence of harmine also decreased prion formation. Decreased protein aggregation was accompanied by reduction in oxidative stress. However, harmine had no effect on aggregation of the mutant huntingtin fragment in vitro. Thus, based on experimental data, we conclude that the antioxidant harmine lowers aggregation-induced elevation in oxidative stress, which slows down intracellular protein aggregation.

Effects of Ginseng on Neurological Disorders

Ginseng (Panax ginseng Meyer), a famous traditional medicinal herb, has been widely used for many centuries. Numerous studies have shown that ginseng has a positive effect on the prevention and treatment of neurological disorders. In this review, we summarized the effects of ginseng in treating neurological diseases, particularly the anti-depressant effects of ginseng. Furthermore, its potential mechanism was also outlined. Therefore, this review may provide new insight into the treatment of ginseng on neurological diseases.

Roles of poly (ADP-ribose) polymerase 1 activation and cleavage in induction of multi-oocyte ovarian follicles in the mouse by 3-nitropropionic acid

3-nitropropionic acid (3-NPA) is known to be a mitochondrial toxin produced by plants and fungi, which may produce DNA damage in cells. However, studies of its reproductive toxicology are lacking. We know that poly(ADP-ribose) polymerase (PARP) plays an important role in a large variety of physiological processes and is involved in DNA repair pathways. The present study was therefore aimed at exploring the involvement of PARP-1 activation and cleavage after 3-NPA stimulation in female mice. We observed an increased number of atretic follicles and multi-oocyte follicles (MOFs) after treatment with 3-NPA and serum concentrations of 17β-oestradiol and progesterone were significantly reduced. Our results provide evidence that PARP-1 cleavage and activational signals are involved in pathological ovarian processes stimulated by 3-NPA. In addition, total superoxide dismutase, glutathione peroxidase and catalase activities were significantly increased, whereas succinate dehydrogenase was decreased in a dose-dependent manner. Results from our in vitro study similarly indicated that 3-NPA inhibited the proliferation of mouse granulosa cells and increased apoptosis in a dose-dependent manner. In summary, 3-NPA induces granulosa cell apoptosis, follicle atresia and MOFs in the ovaries of female mice and causes oxidative stress so as to disrupt endogenous hormonal systems, possibly acting through PARP-1 signalling.

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.

Human Immunodeficiency Virus Infection in Huntington's Disease is Associated with an Earlier Age of Symptom Onset

BACKGROUND

Huntington Disease (HD) and human immunodeficiency virus (HIV) are both associated with neurodegeneration in the cerebral cortex and striatum. The rate of striatal degeneration is a known predictor of symptom onset in HD indicating a potential neurobiological link between HD and HIV.

OBJECTIVE

To determine if the presence of pre-existing HIV infection would trigger a significantly earlier age of symptom onset (ASO) in HD-mutation carriers when compared to non-infected HD subjects.

METHODS

This was a retrospective analysis of the Enroll-HD database that included participants with a CAG repeat of at least 36. Participants with HD and a comorbidity of HIV that was diagnosed prior to their reported ASO were identified and compared to participants with HD who did not have HIV. An ANCOVA analysis was performed to investigate the differences in ASO between the HIV and non-HIV groups. Sex, drug use, and CAG repeat number were used as covariates.

RESULTS

The average ASO of HD subjects with previous HIV infection (n = 8) was 9.1 years earlier than non-HIV infected HD subjects (n = 3259) [F (1, 3267) =10.05, p = 0.002]. Despite low numbers of participants in the HIV group, the calculated effect size of this difference was 1.07.

CONCLUSION

The known neurobiological changes caused by HIV seem to hasten the ASO in patients with HD. These results may enhance our understanding of the neuropathology of HD in a way that will help with the identification of novel targets for future therapies.

NADPH oxidase regulates paraquat and maneb-induced dopaminergic neurodegeneration through ferroptosis

The activation of NADPH oxidase contributes to dopaminergic neurodegeneration induced by paraquat and maneb, two concurrently used pesticides in agriculture. However, the mechanisms remain unclear. Ferroptosis, a recently recognized form of regulated cell death, has been implicated in the pathogenesis of multiple neurodegenerative diseases. This study is designed to investigate whether ferroptosis is involved in NADPH oxidase-regulated dopaminergic neurotoxicity. In vitro study showed that paraquat and maneb exposure induced ferroptosis in SHSY5Y dopaminergic cells, which was associated with activation of NADPH oxidase. Inhibition of NADPH oxidase by apocynin or diphenyleneiodonium (DPI), two widely used NADPH oxidase inhibitors mitigated paraquat and maneb-induced ferroptotic cell death. Consistently, stimulating activation of NADPH oxidase by phorbol myristate acetate (PMA) or supplementation of H₂O₂ exacerbated ferroptosis in paraquat and maneb-treated SHSY5Y cells. Mechanistic inquiry revealed that NADPH oxidase activation elicited lipid peroxidation, a main driving force for ferroptosis, since both apocynin and DPI greatly reduced MDA contents and simultaneously recovered levels of glutathione and glutathione peroxidase 4 (GPX4) in paraquat and maneb-treated SHSY5Y cells. The contribution of NADPH oxidase on ferroptosis of dopaminergic neurons was further verified in vivo by showing reduced iron content, lipid peroxidation, neuroinflammation and dopaminergic neurodegeneration, which are all involved in ferroptosis, in combined apocynin and paraquat and maneb-treated mice compared with paraquat and maneb alone group. Altogether, our findings showed that NADPH oxidase contributed to paraquat and maneb-induced dopaminergic neurodegeneration through ferroptosis, providing a novel mechanism for pesticide-induced dopaminergic neurotoxicity.

Topiramate mitigates 3-nitropropionic acid-induced striatal neurotoxicity via modulation of AMPA receptors

Prevalence of glutamate receptor subunit 2 (GluR2)-lacking alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors is a hallmark of excitotoxicity-related neurodegenerative diseases. Topiramate (TPM) is a structurally novel anticonvulsant with a well-known modulatory effects on AMPA/kainate subtypes of glutamate receptors. The present study aimed at investigating the neuroprotective potential of TPM on 3-nitropropionic acid (3-NP)-induced striatal neurodegeneration and Huntington's disease-like symptoms. Rats were injected with 3-NP (10 mg/kg/i.p.) for 14 days. TPM (50 mg/kg/p.o.) was given once a day, 1 h before 3-NP. TPM amended 3-NP induced changes in neurobehavioral performance, striatal neurotransmitters levels and histopathological injury. 3-NP control rats showed a significant ablation in the mRNA expression of Ca²⁺-impermeable Glu2R subunit along with an elevation in its regulatory protein (protein interacting with C kinase-1) PICK1, an effect that was largely reversed by TPM. TPM in addition, enhanced the phosphorylation of the protein kinase B/glycogen synthase kinase-3β/cAMP response element binding protein (Akt/GSK-3β/CREB) cue. Moreover, improvement in oxidative status, suppression of caspase-3 activity and restoration of striatal BDNF were noticed following treatment with TPM. The current study revealed that TPM boosted the neuroprotective (Akt/GSK-3β/CREB) pathway by its negative modulatory effect on AMPA glutamate receptors as well as its direct antioxidant property.

Emerging signals modulating potential of ginseng and its active compounds focusing on neurodegenerative diseases

Common features of neurodegenerative diseases (NDDs) include progressive dysfunctions and neuronal injuries leading to deterioration in normal brain functions. At present, ginseng is one of the most frequently used natural products. Its use has a long history as a cure for various diseases because its extracts and active compounds exhibit several pharmacological properties against several disorders. However, the pathophysiology of NDDs is not fully clear, but researchers have found that various ion channels and specific signaling pathways might have contributed to the disease pathogenesis. Apart from the different pharmacological potentials, ginseng and its active compounds modulate various ion channels and specific molecular signaling pathways related to the nervous system. Here, we discuss the signal modulating potential of ginseng and its active compounds mainly focusing on those relevant to NDDs.

Modulation of Nrf2 by Olive Oil and Wine Polyphenols and Neuroprotection

Strong adherence to a Mediterranean diet is associated with improved cognitive function and a lower prevalence of mild cognitive impairment. Olive oil and red wine are rich sources of polyphenols which are responsible in part for the beneficial effects on cognitive functioning. Polyphenols induce endogenous antioxidant defense mechanisms by modulating transcription factors such as the nuclear factor (erythroid-derived 2)-like 2 (Nrf2). This review discusses the scientific data supporting the modulating effect of olive oil and red wine polyphenols on Nrf2 expression, and the potential health benefits associated with cognitive functioning.