Thymoquinone alleviates arsenic induced hippocampal toxicity and mitochondrial dysfunction by modulating mPTP in Wistar rats

Minocycline as a Neuroprotective Agent in Arsenic-Induced Neurotoxicity in PC12 Cells

Arsenic is a naturally occurring metalloid that exists in water, soil, food, and air. Humans can be exposed to arsenic through occupational, medical, or nutritional routes. Both acute and chronic forms of toxicity with severe outcomes are likely following arsenic exposure. Neurotoxicity is one of the serious manifestations of arsenic toxicity. In our study, the effect of minocycline, a widely used antimicrobial agent with antioxidant aspects and the ability to cross the blood-brain barrier, was evaluated against arsenic-induced neurotoxicity. PC12 cell line was used as the cellular model of this study. Cells were pre-treated with minocycline (50 nM-1 µM) for 2 h, and then incubated for 24 h after adding sodium arsenite (10 µM). The MTT assay and fluorimetry were performed to study cytotoxicity and reactive oxygen species generation, respectively. Finally, Western blotting was done to determine the levels of caspase-8, Bax, Bcl-2, and caspase-3. Once exposed to arsenic, the cell viability was significantly reduced, the intracellular oxidative balance was significantly disrupted, and the levels of proteins caspase-8, Bax/Bcl-2, and caspase-3 were significantly increased. Minocycline not only attenuated arsenic-induced cytotoxicity and reduced oxidative stress, but also led to lower levels of caspase-8, Bax/Bcl-2, and caspase-3 proteins compared with the arsenic-treated cells. Minocycline can significantly protect cells against arsenic-induced neurotoxicity by antioxidant and anti-apoptosis properties via both intrinsic and extrinsic caspase-dependent apoptotic pathways; therefore, at this point, it's worth considering it as a promising agent for the treatment of arsenic toxicity.

The protective effect of natural or chemical compounds against arsenic-induced neurotoxicity: Cellular and molecular mechanisms

Arsenic is a notorious metalloid that exists in the earth's crust and is considered toxic for humans and the environment. Both cancerous and non-cancerous complications are possible after arsenic exposure. Target organs include the liver, lungs, kidney, heart, and brain. Arsenic-induced neurotoxicity, the main focus of our study, can occur in central and peripheral nervous systems. Symptoms can develop in a few hours, weeks, or years depending on the quantity of arsenic and the duration of exposure. In this review, we aimed to gather all the compounds, natural and chemical, that have been studied as protective agents in cellular, animal, and human reports. Oxidative stress, apoptosis, and inflammation are frequently described as destructive mechanisms in heavy metal toxicity. Moreover, reduced activity of acetylcholinesterase, the altered release of monoamine neurotransmitters, down-regulation of N-methyl-D-aspartate receptors, and decreased brain-derived neurotrophic factor are important underlying mechanisms of arsenic-induced neurotoxicity. As for neuroprotection, though some compounds have yet limited data, there are others, such as curcumin, resveratrol, taurine, or melatonin which have been studied more deeply and might be closer to a reliable protective agent. We collected the available information on all protective agents and the mechanisms by which they fight against arsenic-induced neurotoxicity.

Neuroprotective Efficacy of Edaravone against Arsenic-Induced Behavioral and Neurochemical Deficits in Rats: Amelioration of Cholinergic and Mitochondrial Functions

BACKGROUND

A substantial amount of evidence indicates that long-term arsenic exposure leads to various types of pathological complications, especially cognitive dysfunction.

OBJECTIVE

The present study was designed to assess the neuroprotective potential of edaravone (a potent free radical scavenger) against arsenic-induced neurotoxicity in Wistar rats.

METHODS

Adult male Wistar rats were randomly divided into five groups. Arsenic (20 mg/kg/day; p.o.) and Edaravone (5 and 10 mg/kg/day; i.p.) were administered in different experimental groups for 28 days.

RESULTS

The results of various behavioral test paradigms revealed that arsenic caused significant learning and memory deficits, along with anxiety-like behavior. In biochemical analysis, we found marked elevations of oxidative-nitrosative stress (indicated by augmentation of lipid peroxidation and nitrite) and a reduction of glutathione levels in the hippocampus and frontal cortex region of arsenictreated rats. Moreover, arsenic administration caused mitochondrial complexes impairment and reduction of acetylcholinesterase level. On the other hand, chronic treatment with edaravone (10 mg/kg) significantly ameliorated the arsenic-induced behavioral deficits and neurochemical anomalies.

CONCLUSION

This study suggests that edaravone confers neuroprotection against arsenic-induced memory impairment and anxiety-like behavior, which may be attributed to the inhibition of oxidativenitrosative stress and amelioration of cholinergic and mitochondrial functions.

NMDA receptors mediate synaptic plasticity impairment of hippocampal neurons due to arsenic exposure

Endemic arsenism is a worldwide health problem. Chronic arsenic exposure results in cognitive dysfunction due to arsenic and its metabolites accumulating in hippocampus. As the cellular basis of cognition, synaptic plasticity is pivotal in arsenic-induced cognitive dysfunction. N-methyl-D-aspartate receptors (NMDARs) serve physiological functions in synaptic transmission. However, excessive NMDARs activity contributes to exitotoxicity and synaptic plasticity impairment. Here, we provide an overview of the mechanisms that NMDARs and their downstream signaling pathways mediate synaptic plasticity impairment due to arsenic exposure in hippocampal neurons, ways of arsenic exerting on NMDARs, as well as the potential therapeutic targets except for water improvement.

Thymoquinone in Ocular Neurodegeneration: Modulation of Pathological Mechanisms via Multiple Pathways

Thymoquinone is a naturally occurring compound and is the major component of Nigella sativa, also known as black seed or black cumin. For centuries thymoquinone has been used especially in the Middle East traditionally to treat wounds, asthma, allergies, fever, headache, cough, hypertension, and diabetes. Studies have suggested beneficial effects of thymoquinone to be attributed to its antioxidant, antibacterial, anti-oxidative stress, anti-inflammatory, and neuroprotective properties. Recently, there has been a surge of interest in thymoquinone as a treatment for neurodegeneration in the brain, such as that seen in Alzheimer’s (AD) and Parkinson’s diseases (PD). In vitro and in vivo studies on animal models of AD and PD suggest the main neuroprotective mechanisms are based on the anti-inflammatory and anti-oxidative properties of thymoquinone. Neurodegenerative conditions of the eye, such as Age-related Macular Degeneration (AMD) and glaucoma share at least in part similar mechanisms of neuronal cell death with those occurring in AD and PD. This review aims to summarize and critically analyze the evidence to date of the effects and potential neuroprotective actions of thymoquinone in the eye and ocular neurodegenerations.

Thymoquinone: A Review of Pharmacological Importance, Oxidative Stress, COVID-19, and Radiotherapy

Widely consumed worldwide, Nigella sativa (NS) is a medicinal herb commonly used in various alternative medicine systems such as Unani and Tibb, Ayurveda, and Siddha. Recommended for regular use in Tibb-e-Nabwi (Prophetic Medicine), NS is considered one of the most notable forms of healing medicine in Islamic literature. Thymoquinone (TQ), the main component of the essential oil of NS, has been reported to have many properties such as antioxidant, anti-inflammatory, antiviral, and antineoplastic. Its chemical structure indicates antiviral potential against many viruses, including the hepatitis C virus, human immunodeficiency virus, and other coronavirus diseases. Interestingly, molecular docking studies have demonstrated that TQ can potentially inhibit the development of the coronavirus disease 2019 (COVID-19) by binding to the receptor site on the transmembrane serine proteinase 2 (the activator enzyme that attaches the virus to the cell). In addition, TQ has been shown to be effective against cancer cells due to its inhibitory effect by binding to the different regions of MDM2, according to the proposed molecular docking study. Detailed in this review is the origin of TQ, its significance in alternative medicine, pharmacological value, potential as a cancer anti-proliferative agent, use against the coronavirus disease 2019 (COVID-19), and treatment of other diseases.

Molecular Mechanism of Arsenic-Induced Neurotoxicity including Neuronal Dysfunctions

Arsenic is a key environmental toxicant having significant impacts on human health. Millions of people in developing countries such as Bangladesh, Mexico, Taiwan, and India are affected by arsenic contamination through groundwater. Environmental contamination of arsenic leads to leads to various types of cancers, coronary and neurological ailments in human. There are several sources of arsenic exposure such as drinking water, diet, wood preservatives, smoking, air and cosmetics, while, drinking water is the most explored route. Inorganic arsenic exhibits higher levels of toxicity compared its organic forms. Exposure to inorganic arsenic is known to cause major neurological effects such as cytotoxicity, chromosomal aberration, damage to cellular DNA and genotoxicity. On the other hand, long-term exposure to arsenic may cause neurobehavioral effects in the juvenile stage, which may have detrimental effects in the later stages of life. Thus, it is important to understand the toxicology and underlying molecular mechanism of arsenic which will help to mitigate its detrimental effects. The present review focuses on the epidemiology, and the toxic mechanisms responsible for arsenic induced neurobehavioral diseases, including strategies for its management from water, community and household premises. The review also provides a critical analysis of epigenetic and transgenerational modifications, mitochondrial oxidative stress, molecular mechanisms of arsenic-induced oxidative stress, and neuronal dysfunction.

Bisphenol-A inhibits mitochondrial biogenesis via impairment of GFER mediated mitochondrial protein import in the rat brain hippocampus

Mitochondrial biogenesis relies on different protein import machinery, as mitochondrial proteins are imported from the cytosol. The mitochondrial intermembrane space assembly (MIA) pathway consists of GFER/ALR and CHCHD4/Mia40, responsible for importing proteins and their oxidative folding inside the mitochondria. The MIA pathway plays an essential role in complex IV (COX IV) biogenesis via importing copper chaperone COX17, associated with the respiratory chain. BPA, an environmental toxicant, found in consumable plastics, causes neurotoxicity via impairment in mitochondrial dynamics, neurogenesis, and cognitive functions. We studied the levels of key regulatory proteins of mitochondrial import pathways and mitochondrial biogenesis after BPA exposure in the rat hippocampus. BPA caused a significant reduction in the levels of mitochondrial biogenesis proteins (PGC1α, and TFAM) and mitochondrial import protein (GFER). Immunohistochemical analysis showed reduced co-localization of NeuN with GFER, PGC-1α, and TFAM suggesting impaired mitochondrial biogenesis and protein import. BPA exposure resulted in damaged mitochondria with distorted cristae in neurons and caused a significant reduction in GFER localization inside IMS as depicted by immunogold electron microscopy. The reduced levels of GFER resulted in defective COX17 import. The translocation of cytochrome c into the cytosol and increased cleaved caspase-3 levels triggered apoptosis due to BPA toxicity. Overall, our study implicates GFER as a potential target for impaired mitochondrial protein machinery, biogenesis, and apoptosis against BPA neurotoxicity in the rat hippocampus.

Black Cumin (Nigella sativa L.): A Comprehensive Review on Phytochemistry, Health Benefits, Molecular Pharmacology, and Safety

Mounting evidence support the potential benefits of functional foods or nutraceuticals for human health and diseases. Black cumin (Nigella sativa L.), a highly valued nutraceutical herb with a wide array of health benefits, has attracted growing interest from health-conscious individuals, the scientific community, and pharmaceutical industries. The pleiotropic pharmacological effects of black cumin, and its main bioactive component thymoquinone (TQ), have been manifested by their ability to attenuate oxidative stress and inflammation, and to promote immunity, cell survival, and energy metabolism, which underlie diverse health benefits, including protection against metabolic, cardiovascular, digestive, hepatic, renal, respiratory, reproductive, and neurological disorders, cancer, and so on. Furthermore, black cumin acts as an antidote, mitigating various toxicities and drug-induced side effects. Despite significant advances in pharmacological benefits, this miracle herb and its active components are still far from their clinical application. This review begins with highlighting the research trends in black cumin and revisiting phytochemical profiles. Subsequently, pharmacological attributes and health benefits of black cumin and TQ are critically reviewed. We overview molecular pharmacology to gain insight into the underlying mechanism of health benefits. Issues related to pharmacokinetic herb-drug interactions, drug delivery, and safety are also addressed. Identifying knowledge gaps, our current effort will direct future research to advance potential applications of black cumin and TQ in health and diseases.

Therapeutic perspective of thymoquinone: A mechanistic treatise

The higher utilization of fruits and vegetables is well known to cure human maladies due to the presence of bioactive components. Among these compounds, thymoquinone, a monoterpene and significant constituent in the essential oil of Nigella sativa L., has attained attention by the researchers due to their pharmacologies perspectives such as prevention from cancer, antidiabetic and antiobesity, prevention from oxidative stress and cardioprotective disorder. Thymoquinone has been found to work as anticancer agent against different human and animal cancer stages including propagation, migration, and invasion. Thymoquinone as phytochemical also downregulated the Rac1 expression, mediated the miR-34a upregulation, and increased the levels of miR-34a through p53, as well as also regulated the pro- and antiapoptotic genes and decreased the phosphorylation of NF-κB and IKKα/β. In addition, thymoquinone also lowered the metastasis and ERK1/2 and PI3K activities. The present review article has been piled by adapting narrative review method and highlights the diverse aspects of thymoquinone such as hepatoprotective, anti-inflammatory, and antiaging through various pathways, and further utilization of this compound in diet has been proven effective against different types of cancers.

Curcumin alleviates arsenic-induced toxicity in PC12 cells via modulating autophagy/apoptosis

Arsenic is a recognized highly toxic contaminant, responsible for numerous human diseases and affecting many millions of people in different parts of the world. Contrarily, curcumin is a natural dietary polyphenolic compound and the main active ingredient in turmeric. Recently it has drawn great attention due to its diverse biological activities, strong antioxidant properties and therapeutic potential against many human ailments. In this study, we aimed to explore the protective effects and the regulatory role of curcumin on arsenic-induced toxicity and gain insights into biomolecular mechanism/s. Arsenic (10 μM) treatment in PC12 cells for 24 h induced cytotoxicity by decreasing cell viability and intracellular glutathione level and increasing lactate dehydrogenase activity and DNA fragmentation. In addition, arsenic caused apoptotic cell death in PC12 cells, which were confirmed from flow cytometry results. Moreover, arsenic (10 μM) treatment significantly down-regulated the inhibition factors of autophagy/apoptosis; mTOR, Akt, Nrf2, ERK1, Bcl-x, Xiap protein expressions, up-regulated the enhanced factors of autophagy/apoptosis; ULK, LC3, p53, Bax, cytochrome c, caspase 9, cleaved caspase 3 proteins and eventually caused autophagic and apoptotic cell death. However, curcumin (2.5 μM) pretreatment with arsenic (10 μM) effectively saves PC12 cells against arsenic-induced cytotoxicity through increasing cell viability, intracellular GSH level and boosting the antioxidant defense system, and limiting the LDH activity and DNA damage. Furthermore, pretreatment of curcumin with arsenic expressively alleviated arsenic-induced toxicity and cell death by reversing the expressions of proteins; mTOR, Akt, Nrf2, ERK1, Bcl-x, Xiap, ULK, LC3, p53, Bax, cytochrome c, caspase 9 and cleaved caspase 3. Our findings indicated that curcumin showed antioxidant properties through the Nrf2 antioxidant signaling pathway and alleviates arsenic-triggered toxicity in PC12 cells by regulating autophagy/apoptosis.

Thymoquinone Induces Mitochondrial Damage and Death of Cerebellar Granule Neurons

Thymoquinone (TQ) exhibits a wide spectrum of biological activities. Most studies on the neurotoxic action of TQ have been carried out in cancer cell lines. Here, we studied the toxic effect of TQ in primary neuronal cultures in vitro. Incubation with 0.04-0.05 mM TQ for 24 h induced the death of cultured cerebellar granule neurons (CGNs) in a dose-dependent manner. Neuronal death was preceded by an increase in the reactive oxygen species (ROS) generation, as demonstrated using CellROX Green and MitoSOX Red. Confocal and electron microscopy showed that incubation with 0.05 mM TQ for 5 h induced changes in the intracellular localization of mitochondria and mitochondria hypertrophy and cell swelling. The antioxidant N-acetyl-L-cysteine (2 mM) protected CGNs from the toxic action of TQ. Taken together, these facts suggest that TQ is toxic for normal neurons, while ROS-induced changes in the mitochondria can be one of the major causes of the TQ-induced neuronal damage and death.

Thymoquinone as a Potential Neuroprotector in Acute and Chronic Forms of Cerebral Pathology

Thymoquinone is one of the main active components of the essential oil from black cumin (Nigella sativa) seeds. Thymoquinone exhibits a wide range of pharmacological activities, including neuroprotective action demonstrated in the models of brain ischemia/reperfusion, Alzheimer's and Parkinson's diseases, and traumatic brain injury. The neuroprotective effect of thymoquinone is mediated via inhibition of lipid peroxidation, downregulation of proinflammatory cytokines, maintenance of mitochondrial membrane potential, and prevention of apoptosis through inhibition of caspases-3, -8, and -9. Thymoquinone-based mitochondria-targeted antioxidants are accumulated in the mitochondria and exhibit neuroprotective properties in nanomolar concentrations. Thymoquinone reduces the negative effects of acute and chronic forms of brain pathologies. The mechanisms of the pharmacological action of thymoquinone and its chemical derivatives require more comprehensive studying. In this paper, we formulated the prospects of application of thymoquinone and thymoquinone-based drugs in the therapy of neurodegenerative diseases.

Arsenic-induced neurotoxicity: a mechanistic appraisal

Arsenic is a metalloid found in groundwater as a byproduct of soil/rock erosion and industrial and agricultural processes. This xenobiotic elicits its toxicity through different mechanisms, and it has been identified as a toxicant that affects virtually every organ or tissue in the body. In the central nervous system, exposure to arsenic can induce cognitive dysfunction. Furthermore, iAs has been linked to several neurological disorders, including neurodevelopmental alterations, and is considered a risk factor for neurodegenerative disorders. However, the exact mechanisms involved are still unclear. In this review, we aim to appraise the neurotoxic effects of arsenic and the molecular mechanisms involved. First, we discuss the epidemiological studies reporting on the effects of arsenic in intellectual and cognitive function during development as well as studies showing the correlation between arsenic exposure and altered cognition and mental health in adults. The neurotoxic effects of arsenic and the potential mechanisms associated with neurodegeneration are also reviewed including data from experimental models supporting epidemiological evidence of arsenic as a neurotoxicant. Next, we focused on recent literature regarding arsenic metabolism and the molecular mechanisms that begin to explain how arsenic damages the central nervous system including, oxidative stress, energy failure and mitochondrial dysfunction, epigenetics, alterations in neurotransmitter homeostasis and synaptic transmission, cell death pathways, and inflammation. Outlining the specific mechanisms by which arsenic alters the cell function is key to understand the neurotoxic effects that convey cognitive dysfunction, neurodevelopmental alterations, and neurodegenerative disorders.

Ochratoxin A causes mitochondrial dysfunction, apoptotic and autophagic cell death and also induces mitochondrial biogenesis in human gastric epithelium cells

Ochratoxin A (OTA) is a common natural contaminant found in human and animal food worldwide. Our previous work has shown that OTA can cause oxidative DNA damage, G₂ arrest and malignant transformation of human gastric epithelium (GES-1) cells. Mitochondria are considered to be target for the action of many cytotoxic agents. However, the role of mitochondria in the cytotoxicity of OTA remains unknown. The aim of this study is to explore the putative role of mitochondria on OTA cytotoxicity by analyzing mitochondrial changes in GES-1 cells. The results showed that OTA treatment (5, 10, 20 µM) for different times caused increases in the production of reactive oxygen species, and induced mitochondrial damage, shown by loss of mitochondrial membrane potential (ΔΨM), and decrease in cellular ATP concentration. Subsequently, the mitochondrial apoptotic pathway was activated, presented by increase of apoptotic rate and activation of apoptotic proteins. Autophagic cell death was also triggered, demonstrated by the conversion of light chain 3B (LC3B)-I to LC3B-II and elevated levels of green fluorescent protein-LC3 (GFP-LC3) puncta. Moreover, Parkin-dependent mitophagy was also activated presented by the colocalization of MitoTracker with LysoTracker or GFP-LC3 puncta. The inhibition of autophagy and mitophagy by inhibitors or siRNA attenuated the toxic effect of OTA on cell growth. Interestingly, OTA treatment also enhanced mitochondrial biogenesis confirmed by activation of AMPK/PGC-1α/TFAM pathway and promoted cell survival. Collectively, the effects of OTA on mitochondria of GES-1 cells are complex. OTA could cause mitochondrial function disturbance, apoptotic and autophagic cell death and also induce mitochondrial biogenesis.