Influence of Zinc on Calcium-Dependent Signal Transduction Pathways During Aluminium-Induced Neurodegeneration

Capsaicin and Zinc Signalling Pathways as Promising Targets for Managing Insulin Resistance and Type 2 Diabetes

The global burden of type 2 diabetes (T2DM) has led to significant interest in finding novel and effective therapeutic targets for this chronic disorder. Bioactive food components have effectively improved abnormal glucose metabolism associated with this disease. Capsaicin and zinc are food components that have shown the potential to improve glucose metabolism by activating signalling events in the target cells. Capsaicin and zinc stimulate glucose uptake through the activation of distinct pathways (AMPK and AKT, respectively); however, calcium signal transduction seems to be the common pathway between the two. The investigation of molecular pathways that are activated by capsaicin and zinc has the potential to lead to the discovery of new therapeutic targets for T2DM. Therefore, this literature review aims to provide a summary of the main signalling pathways triggered by capsaicin and zinc in glucose metabolism.

Capsaicin and Zinc Promote Glucose Uptake in C2C12 Skeletal Muscle Cells through a Common Calcium Signalling Pathway

Capsaicin and zinc have recently been highlighted as potential treatments for glucose metabolism disorders; however, the effect of these two natural compounds on signalling pathways involved in glucose metabolism is still uncertain. In this study, we assessed the capsaicin- or zinc- induced activation of signalling molecules including calcium/calmodulin-dependent protein kinase 2 (CAMKK2), cAMP-response element-binding protein (CREB), and target of rapamycin kinase complex 1 (TORC1). Moreover, the expression status of genes associated with the control of glucose metabolism was measured in treated cells. The activation of cell signalling proteins was then evaluated in capsaicin- or zinc treated cells in the presence or absence of cell-permeant calcium chelator (BAPTA-AM) and the CAMKK inhibitor (STO-609). Finally, capsaicin- and zinc-induced glucose uptake was measured in the cells pre-treated with or without BAPTA-AM. Our results indicate that calcium flux induced by capsaicin or zinc led to activation of calcium signalling molecules and promoting glucose uptake in skeletal muscle cells. Pharmacological inhibition of CAMKK diminished activation of signalling molecules. Moreover, we observed an increase in intracellular cAMP levels in the cells after treatment with capsaicin and zinc. Our data show that capsaicin and zinc mediate glucose uptake in C2C12 skeletal muscle cells through the activation of calcium signalling.

Evaluation of Cerebellar Function and Integrity of Adult Rats After Long-Term Exposure to Aluminum at Equivalent Urban Region Consumption Concentrations

High amounts of aluminum (Al) are found in soil and water. It is highly bioavailable, which makes it an important agent of environmental imbalance. Moreover, Al is considered a neurotoxic agent that is associated with several neurodegenerative diseases. Thus, this study investigated the effects of long-term Al chloride (AlCl₃) exposure on motor behavior, oxidative biochemistry, and cerebellar tissue parameters. For this, adult Wistar rats were divided into three groups: Al-D1 (8.3 mg kg^-1 day^-1), Al-D2 (5.2 mg kg^-1 day^-1), and control (distilled water); all groups were orally exposed for 60 days by intragastric gavage. After the exposure period, animals performed the open field, elevated plus maze, rotarod, and beam walking tests. Then, the blood and cerebellum were collected to evaluate Al levels and biochemical and morphological analyses, respectively. Our results demonstrate that animals exposed to Al doses presented a higher Al level in the blood. In the spontaneous locomotor activity, Al exposure groups had traveled a lower total distance when compared with the control group. There was no statistically significant difference (p > 0.05) between exposed and control groups when anxiogenic profile, forced locomotion, fine motor coordination/balance, pro-oxidative parameter, and density Purkinje cells were compared. Thus, aluminum exposure in equivalent doses to human consumption in urban regions did not promote significant changes in the cerebellum or motor parameters.

HPLC-PDA-MS/MS profiling of secondary metabolites from Opuntia ficus-indica cladode, peel and fruit pulp extracts and their antioxidant, neuroprotective effect in rats with aluminum chloride induced neurotoxicity

Opuntia ficus-indica (L.) Mill. (OFI), also known as Indian fig Opuntia or prickly pear, is a member of the family Cactaceae that produces edible, nutritionally rich sweet fruits. It has been traditionally used to treat several health disorders and is considered to possess various therapeutic properties. In this work, we have characterized 37 secondary metabolites using HPLC-MS/MS, identified the polysaccharide from the fruits and cladodes pulp, and estimated the neuroprotective activity. All tested extracts exhibited substantial antioxidant activities in-vitro and neuroprotective potential in AlCl₃ induced Alzheimer's condition. Administration of OFI extracts attenuated AlCl₃ induced learning and memory impairment as confirmed from passive avoidance test and counteracted the oxidative stress as manifested from decreasein the elevated MDA level, increased TAC, GSH, SOD and CAT levels. OFI extracts significantly decreased the elevated brain levels of proinflammatory cytokines (NF-κβ and TNF-α), increased anti-inflammatory cytokine (IL-10), and monoamine neurotransmitters (NE, DA, 5-HT) as compared to positive control group. The extracts showed a significant decrease in acetylcholinesterase level (AChE) as compared with AlCl_3. Furthermore, molecular docking was performed to investigate the ability of the major constituents of OFI extracts to interact with acetylcholinesterase (AChE) and serotonin transporter (SERT). Among the tested extracts, cladodes contain highest phenolic content and exhibited the highest antioxidant, anti-inflammatory and neuroprotective activities, which could be attributed to presence of several polyphenols, which could function as AChE and SERT inhibitors. Opuntia ficus-indica might be promising candidate for treating Alzheimer disease, which makes it a subject for more detailed studies.

Elevated circulating magnesium levels in patients with Parkinson's disease: a meta-analysis

BACKGROUND

The association between circulating magnesium (Mg) and Parkinson's disease (PD) remains ambiguous and controversial. Thus, a meta-analysis was conducted to evaluate the circulating Mg levels in PD patients and to clarify whether high circulating Mg levels should be considered as a potential risk factor for PD.

METHODS

In this study, 17 case-control published studies were selected in our meta-analysis by searching the electronic databases of Web of Science, PubMed, and China National Knowledge Infrastructure (CNKI) before June 1, 2018. Overall, 848 PD cases and 784 healthy controls (HC), 1,023 PD cases and 911 HC, and 180 PD cases and 144 HC met the inclusion criteria for this study Mg levels in serum, peripheral blood, and cerebrospinal fluid (CSF), respectively. Standardized mean difference (SMD) in random-effects model and 95% CI were used to assess the correlation strength through the comparison of the two groups.

RESULTS

Meta-analysis showed that the serum Mg levels in PD cases were significantly higher than those in HC individuals (SMD =1.09, 95% CI =0.52, 1.66). Furthermore, this result was further confirmed by the combined analysis of serum and whole blood studies together (SMD =0.64, 95% CI =0.10, 1.19). In addition, the higher CSF Mg levels in patients of PD were observed in comparison with normal range (SMD =0.55, 95% CI =0.21, 0.88). However, this data did not further discuss and analyze because of the smaller sample size of CSF studies.

CONCLUSION

Our findings supported the notion that the increase of circulating Mg levels appears in the patients with PD.

Neuroprotective effect of Moringa oleifera leaf extract on aluminium-induced temporal cortical degeneration

Aluminium (Al), one of the metals implicated in neurodegeneration easily gain access to the nervous system through its presence in many manufactured foods, medicines and drinking water, and causes neurotoxicity utilizing the reactive oxygen specie pathway. The need to curtail these effects on the nervous system motivated the use of the plant Moringa oleifera (MO). This study thus, investigated the neuroprotective effects of MO leaf extract on aluminium-induced temporal cortical degeneration in rats. 24 male albino Wistar rats were grouped (n = 6) into control (1 ml/kg distilled water), l00 mg/kg aluminium chloride (AlCl₃), 300 mg/kg MO, and 100 mg/kg AlCl₃ and 300 mg/kg MO groups. The administration lasted for 28 days and the rats were sacrificed on day 29 by perfusion-fixation after blood was obtained for serum Al estimation. The brain tissues were then routinely processed for some histological and immunnolabelling studies. There was no significant difference in serum Al in the test groups. Histological results showed atrophied and karyorrhetic cells with loss of Nissl substance in the temporal cortex of the AlCl₃ group, while no adverse effect was observed in the cytoarchitecture of the temporal cortex and Nissl substance of the MO group. However, groups which were administered AlCl₃ simultaneously with MO extract showed less degenerative features in the cyto-architecture of the temporal cortex with normal Nissl substance staining. There was increased neuron specific enolase (NSE) and glial fibrillary acidic protein (GFAP) expressions in the AlCl₃ group, while the MO group also showed increased NSE but decreased GFAP expression. However, the group which were administered AlCl₃ simultaneously with MO extract showed less expression of NSE and GFAP. In conclusion, MO protects against Al-induced neurotoxicity of the temporal cortex of rats.

Identification of Cerebral Metal Ion Imbalance in the Brain of Aging Octodon degus

The accumulation of redox-active transition metals in the brain and metal dyshomeostasis are thought to be associated with the etiology and pathogenesis of several neurodegenerative diseases, and Alzheimer’s disease (AD) in particular. As well, distinct biometal imaging and role of metal uptake transporters are central to understanding AD pathogenesis and aging but remain elusive, due inappropriate detection methods. We therefore hypothesized that Octodon degus develop neuropathological abnormalities in the distribution of redox active biometals, and this effect may be due to alterations in the expression of lysosomal protein, major Fe/Cu transporters, and selected Zn transporters (ZnTs and ZIPs). Herein, we report the distribution profile of biometals in the aged brain of the endemic Chilean rodent O. degus—a natural model to investigate the role of metals on the onset and progression of AD. Using laser ablation inductively coupled plasma mass spectrometry, our quantitative images of biometals (Fe, Ca, Zn, Cu, and Al) appear significantly elevated in the aged O. degus and show an age-dependent rise. The metals Fe, Ca, Zn, and Cu were specifically enriched in the cortex and hippocampus, which are the regions where amyloid plaques, tau phosphorylation and glial alterations are most commonly reported, whilst Al was enriched in the hippocampus alone. Using whole brain extracts, age-related deregulation of metal trafficking pathways was also observed in O. degus. More specifically, we observed impaired lysosomal function, demonstrated by increased cathepsin D protein expression. An age-related reduction in the expression of subunit B2 of V-ATPase, and significant increases in amyloid beta peptide 42 (Aβ42), and the metal transporter ATP13a2 were also observed. Although the protein expression levels of the zinc transporters, ZnT (1,3,4,6, and 7), and ZIP7,8 and ZIP14 increased in the brain of aged O. degus, ZnT10, decreased. Although no significant age-related change was observed for the major iron/copper regulator IRP2, we did find a significant increase in the expression of DMT1, a major transporter of divalent metal species, 5′-aminolevulinate synthase 2 (ALAS2), and the proto-oncogene, FOS. Collectively, our data indicate that transition metals may be enriched with age in the brains of O. degus, and metal dyshomeostasis in specific brain regions is age-related.

Combination of DFP and Taurine Counteracts the Aluminum-Induced Alterations in Oxidative Stress and ATPase in Cortex and Blood of Rats

The study investigated the combined effect of 1,2-dimethyl-3-hydroxypyrid-4-one (DFP) and taurine on aluminum (Al) toxicity in cortex and blood of rats. The control group received 1 ml/kg/day saline solution for 8 weeks. Other animals were exposed to Al at a dose of 281.40 mg/kg/day orally for 4 weeks. Then, they were administered with 1 ml/kg/day saline solution, 400 mg/(kg·day) taurine, 13.82 mg/(kg·day) DFP, 27.44 mg/(kg·day) DFP, 400 mg/(kg·day) taurine +13.82 mg/(kg·day) DFP, and 400 mg/(kg·day) taurine +27.44 mg/(kg·day) DFP for 4 weeks. The changes in markers of oxidative stress, activities of antioxidant enzymes, and triphosphatase (ATPase) in the cortex and blood were determined. Administration of Al led to significant increase in the malondialdehyde (MDA) level and decrease in the activities of antioxidant enzymes, Na⁺K⁺-ATPase, Mg²⁺-ATPase, and Ca²⁺-ATPase in the cortex and blood, compared with the control group. DFP was observed to reverse alteration of these parameters except for Ca²⁺-ATPase activity. Treatment with taurine caused significant increase of GSH-Px activity and decrease of the MDA level in the cortex and serum and rise of Na⁺K⁺-ATPase in the blood. Effects of DFP combined with taurine were investigated and found to provide a more significant benefit than either drug alone. Combined intake of taurine and DFP could achieve an optimum effect of therapy for Al exposure.

Coherent and Contradictory Facts, Feats and Fictions Associated with Metal Accumulation in Parkinson's Disease: Epicenter or Outcome, Yet a Demigod Question

Unwarranted exposure due to liberal use of metals for maintaining the lavish life and to achieve the food demand for escalating population along with an incredible boost in the average human life span owing to orchestrated progress in rejuvenation therapy have gradually increased the occurrence of Parkinson's disease (PD). Etiology is albeit elusive; association of PD with metal accumulation has never been overlooked due to noteworthy similitude between metal-exposure symptoms and a few cardinal features of disease. Even though metals are entailed in the vital functions, a hysterical shift, primarily augmentation, escorts the stern nigrostriatal dopaminergic neurodegeneration. An increase in the passage of metals through the blood brain barrier and impaired metabolic activity and elimination system could lead to metal accumulation in the brain, which eventually makes dopaminergic neurons quite susceptible. In the present article, an update on implication of metal accumulation in PD/Parkinsonism has been provided. Moreover, encouraging and paradoxical facts and fictions associated with metal accumulation in PD/Parkinsonism have also been compiled. Systematic literature survey of PD is performed to describe updated information if metal accumulation is an epicenter or merely an outcome. Finally, a perspective on the association of metal accumulation with pesticide-induced Parkinsonism has been explained to unveil the likely impact of the former in the latter.

Multifaceted effects of aluminium in neurodegenerative diseases: A review

Aluminium (Al) is the most common metal and widely distributed in our environment. Al was first isolated as an element in 1827, and its use began only after 1886. Al is widely used for industrial applications and consumer products. Apart from these it is also used in cooking utensils and in pharmacological agents, including antacids and antiperspirants from which the element usually enters into the human body. Evidence for the neurotoxicity of Al is described in various studies, but still the exact mechanism of Al toxicity is not known. However, the evidence suggests that the Al can potentiate oxidative stress and inflammatory events and finally leads to cell death. Al is considered as a well-established neurotoxin and have a link between the exposure and development of neurodegenerative diseases, including Amyotrophic Lateral Sclerosis (ALS), Alzheimer's disease (AD), dementia, Gulf war syndrome and Parkinsonism. Here, we review the detailed possible pathogenesis of Al neurotoxicity. This review summarizes Al induced events likewise oxidative stress, cell mediated toxicity, apoptosis, inflammatory events in the brain, glutamate toxicity, effects on calcium homeostasis, gene expression and Al induced Neurofibrillary tangle (NFT) formation. Apart from these we also discussed animal models that are commonly used for Al induced neurotoxicity and neurodegeneration studies. These models help to find out a better way to treat and prevent the progression in Al induced neurodegenerative diseases.

Zinc Improves Cognitive and Neuronal Dysfunction During Aluminium-Induced Neurodegeneration

Metals are considered as important components of a physiologically active cell, and imbalance in their levels can lead to various diseased conditions. Aluminium (Al) is an environmental neurotoxicant, which is etiologically related to several neurodegenerative disorders like Alzheimer's, whereas zinc (Zn) is an essential trace element that regulates a large number of metabolic processes in the brain. The objective of the present study was to understand whether Zn provides any physiological protection during Al-induced neurodegeneration. Male Sprague Dawley rats weighing 140-160 g received either aluminium chloride (AlCl₃) orally (100 mg/kg b.wt./day), zinc sulphate (ZnSO₄) in drinking water (227 mg/L) or combined treatment of aluminium and zinc for 8 weeks. Al treatment resulted in a significant decline in the cognitive behaviour of rats, whereas zinc supplementation caused an improvement in various neurobehavior parameters. Further, Al exposure decreased (p ≤ 0.001) the levels of neurotransmitters, acetylcholinesterase activity, but increased (p ≤ 0.001) the levels of L-citrulline as well as activities of nitric oxide and monoamine oxidase in the brain. However, zinc administration to Al-treated animals increased the levels of neurotransmitters and regulated the altered activities of brain markers. Western blot of tau, amyloid precursor protein (APP), glial fibrillary acidic protein (GFAP), ubiquitin, α-synuclein and Hsp 70 were also found to be elevated after Al exposure, which however were reversed following Zn treatment. Al treatment also revealed alterations in neurohistoarchitecture in the form of loss of pyramidal and Purkinje cells, which were improved upon zinc co-administration. Therefore, the present study demonstrates that zinc improves cognitive functions by regulating α-synuclein and APP-mediated molecular pathways during aluminium-induced neurodegeneration.

Modulation of (14) C-labeled glucose metabolism by zinc during aluminium induced neurodegeneration

Aluminium (Al) is one of the most prominent metals in the environment and is responsible for causing several neurological disorders, including Alzheimer's disease. On the other hand, zinc (Zn) is an essential micronutrient that is involved in regulating brain development and function. The present study investigates the protective potential of Zn in the uptake of (14) C-labeled amino acids and glucose and their turnover in rat brain slices during Al intoxication. Male Sprague Dawley rats (140-160 g) were divided into four different groups: normal control, Al treated (100 mg/kg body weight/day via oral gavage), Zn treated (227 mg/liter in drinking water), and Al + Zn treated. Radiorespirometric assay revealed an increase in glucose turnover after Al exposure that was attenuated after Zn treatment. Furthermore, the uptake of (14) C-labeled glucose was increased after Al treatment but was appreciably decreased upon Zn supplementation. In addition, the uptakes of (14) C-lysine, (14) C-leucine, and (14) C-aspartic acid were also found to be elevated following Al exposure but were decreased after Zn treatment. Al treatment also caused alterations in the neurohistoarchitecture of the brain, which were improved after Zn coadministration. Therefore, the present study suggests that Zn provides protection against Al-induced neurotoxicity by regulating glucose and amino acid uptake in rats, indicating that Zn could be a potential candidate for the treatment of various neurodegenerative disorders.

Zinc modulates aluminium-induced oxidative stress and cellular injury in rat brain

Dysregulation of metal homeostasis has been perceived as one of the key factors in the progression of neurodegeneration. Aluminium (Al) has been considered as a major risk factor, which is linked to several neurodegenerative diseases, especially Alzheimer's disease, whereas zinc (Zn) has been reported as a vital dietary element, which regulates a number of physiological processes in central nervous system. The present study was conducted to explore the protective potential of zinc, if any, in ameliorating neurotoxicity induced by aluminium. Male Sprague Dawley rats received either aluminium chloride (AlCl3) orally (100 mg kg(-1) b.wt. per day), zinc sulphate (ZnSO4) at a dose level of 227 mg L(-1) in drinking water or combined treatment of aluminium and zinc for 8 weeks. Aluminium treatment significantly elevated the levels of lipid peroxidation and reactive oxygen species as well as the activities of catalase, superoxide dismutase and glutathione reductase, which however were decreased following Zn co-treatment of Al-treated rats. In contrast, Al treatment decreased the activities of glutathione-S-transferase as well as the levels of reduced glutathione, oxidised glutathione and total glutathione, but co-administration of Zn to Al-treated animals increased these levels. Furthermore, Al treatment caused a significant increase in the levels of Fe and Mn as well as of Al but decreased the Zn and metallothionein levels. In the Zn-supplemented animals, the levels of Al, Fe, Mn were found to be significantly decreased, whereas the levels of metallothionein as well as Zn were increased. Moreover, histopathological alterations such as vacuolization and loss of Purkinje cells were also evident following Al treatment, which showed improvement upon Zn supplementation. Therefore, zinc has the potential to alleviate aluminium-induced neurodegeneration.