The effects of chronic aluminum exposure on learning and memory of rats by observing the changes of Ras/Raf/ERK signal transduction pathway

Modulation of CREB and its associated upstream signaling pathways in pesticide-induced neurotoxicity

Human beings are exposed to various environmental xenobiotics throughout their life consisting of a broad range of physical and chemical agents that impart bodily harm. Among these, pesticide exposure that destroys insects mainly by damaging their central nervous system also exerts neurotoxic effects on humans and is implicated in the etiology of several degenerative disorders. The connectivity between CREB (cAMP Response Element Binding Protein) signaling activation and neuronal activity is of broad interest and has been thoroughly studied in various diseased states. Several genes, as well as protein kinases, are involved in the phosphorylation of CREB, including BDNF (Brain-derived neurotrophic factor), Pi3K (phosphoinositide 3-kinase), AKT (Protein kinase B), RAS (Rat Sarcoma), MEK (Mitogen-activated protein kinase), PLC (Phospholipase C), and PKC (Protein kinase C) that play an essential role in neuronal plasticity, long-term potentiation, neuronal survival, learning, and memory formation, cognitive function, synaptic transmission, and suppressing apoptosis. These elements, either singularly or in a cascade, can result in the modulation of CREB, making it a vulnerable target for various neurotoxic agents, including pesticides. This review provides insight into how these various intracellular signaling pathways converge to bring about CREB activation and how the activated or deactivated CREB levels can affect the gene expression of the upstream molecules. We also discuss the various target genes within the cascade vulnerable to different types of pesticides. Thus, this review will facilitate future investigations associated with pesticide neurotoxicity and identify valuable therapeutic targets.

Aluminum-Induced Electrophysiological Variation, Synaptic Plasticity Impairment, and Related Mechanism

Aluminum, an environmentally abundant non-redox trivalent cation, has long been reported to alter blood-brain barrier and gets deposited in different regions of the brain. Many reports strongly indicated that Al had an adverse impact on the central nervous system (CNS), particularly on cognitive ability. Until now, studies in animal models and cell cultures have revealed that Al exposure results in altered behavioral performance and memory damage. The present paper reviews the scientific literature linking aluminum and the impairment of electrophysiological variation and synaptic plasticity. The focus is on the changes of electrical excitability, voltage-operated ion channels, and synaptic plasticity induced by aluminum. A detailed mechanism of the role of aluminum in hippocampal LTP which is the most widely studied example of synaptic plasticity is highlighted. Evidence revealed that glutamate-NO-cGMP, PLC, Ca²⁺-CaM-CaMKII, MAPK, and Wnt pathway may be important in the mechanism underlying Al-induced long-term memory impairment. Further studies are required to establish the upstream activators and downstream effectors of these cascades and to answer how so many signaling cascades relate to the other signaling processes that might be involved in the Al-induced inhibition of synaptic plasticity.

Chlorogenic acid protects against aluminum toxicity via MAPK/Akt signaling pathway in murine RAW264.7 macrophages

Aluminum (Al), which may bring about damage to the macrophages, has been implicated in the development of immunological diseases. It has been reported that chlorogenic acid (CGA, 5‑caffeoylquinic acid, chemical formula: C₁₆H₁₈O₉) is a natural antioxidant and chelating agent with the capacity against Al (III)-induced biotoxicity. The present study was carried out to investigate whether CGA could reduce AlCl₃-induced cellular damage in RAW264.7 cells. After treatment with AlCl₃, the inhibition rate of viability and phagocytic activity of RAW264.7 cells was 54.5% and 27.6%, respectively. Administration of CGA significantly improved the integrity and phagocytic activity, and attenuated the accumulation of intracellular Al(III) level and oxidative stress in Al(III)-treated cells. Furthermore, CGA significantly inhibited Al(III)-induced increase of phospho-Jun N-terminal kinase (p-JNK), a pro-apoptotic Bcl-2 family protein (Bad), cytochrome c and decrease of extracellular regulated protein kinases (ERK1/2), protein kinase B (Akt) protein expressions. These results showed that CGA has a protective effect against Al(III)-induced cytotoxicity through mitogen-activated protein kinase (MAPK)/Akt-mediated caspase pathways in RAW264.7 cells.

The suppressive effects of aluminum chloride on the osteoblasts function

Aluminum (Al) exposure impairs bone formation, and bone formation is mediated by the osteoblasts. But effects of Al on the osteoblasts function remain elusive. The osteoblasts were exposed to 0, 0.0252, 0.126, 0.252mg/mL AlCl₃·6H₂O for 24h. The osteoblasts viability, TGF-β₁, BMP-2, IGF-I and Cbfα1 mRNA expressions, and GSH-P_x and SOD activities, ROS concentration were determined. The osteoblasts ultrastructural features were also observed. The results showed that AlCl₃ suppressed the osteoblasts viability, TGF-β₁, BMP-2, IGF-I and Cbfα1 mRNA expressions, GSH-P_x and SOD activities, and elevated ROS concentration compared with the CG. The ultrastructural features of osteoblasts in the HG showed mitochondrial swelling, foam-like structure, uneven distribution of chromatin, incomplete cell membrane and cytoplasm spillover compared with the CG. It indicates that AlCl₃ inhibits osteoblasts viability, growth regulation factors mRNA expressions, anti-oxidative function, and damaged the osteoblasts histology structure, impairing the osteoblasts function.

Ginsenoside Rb1 alleviates aluminum chloride-induced rat osteoblasts dysfunction

Osteoblasts dysfunction, induced by aluminum (Al), plays a critical role in the osteoporosis etiology. Ginsenoside Rb1 (Rb1) has the therapeutic properties for osteoporosis. This study aimed to assess the efficiency of Rb1 in ameliorating Al-induced osteoblasts dysfunction. The osteoblasts were divided into four groups: Rb1-treated group (RG, 0.0145mg/mL Rb1), control group (CG, 0), AlCl₃-treated group (AG, 0.126mg/mL AlCl₃·6H₂O), AlCl₃+Rb1-treated group (ARG, 0.0145mg/mL Rb1 and 0.126mg/mL AlCl₃·6H₂O). After 24h of culture, the osteoblasts viability, the transforming growth factor-β1 (TGF-_β1), bone morphogenetic protein-2 (BMP-2), the insulin-like growth factor I (IGF-I), core-binding factor α1 (Cbfα1) mRNA expressions, glutathione perioxidase (GSH-P_x) and superoxide dismutase (SOD) activities, and reactive oxygen species (ROS) concentration were determined. The osteoblasts ultrastructural features were also observed. In the ARG, the osteoblasts viability, TGF-_β1, BMP-2, IGF-I and Cbfα1 mRNA expressions and the GSH-P_x and SOD activities were significantly increased, the ROS concentration was significantly decreased, and osteoblasts histology lesion was attenuated compared with the AG. These results demonstrated that Rb1 could significantly reverse osteoblasts viability and osteoblasts growth regulation factor, inhibit oxidative stress, and attenuate histology lesion in the osteoblasts with AlCl₃. These results indicate that Rb1 can effectively alleviate the AlCl₃-induced osteoblasts dysfunction.

The History, Status, Gaps, and Future Directions of Neurotoxicology in China

BACKGROUND

Rapid economic development in China has produced serious ecological, environmental, and health problems. Neurotoxicity has been recognized as a major public health problem. The Chinese government, research institutes, and scientists conducted extensive studies concerning the source, characteristics, and mechanisms of neurotoxicants.

OBJECTIVES

This paper presents, for the first time, a comprehensive history and review of major sources of neurotoxicants, national bodies/legislation engaged, and major neurotoxicology research in China.

METHODS

Peer-reviewed research and pollution studies by Chinese scientists from 1991 to 2015 were examined. PubMed, Web of Science and Chinese National Knowledge Infrastructure (CNKI) were the major search tools.

RESULTS

The central problem is an increased exposure to neurotoxicants from air and water, food contamination, e-waste recycling, and manufacturing of household products. China formulated an institutional framework and standards system for management of major neurotoxicants. Basic and applied research was initiated, and international cooperation was achieved. The annual number of peer-reviewed neurotoxicology papers from Chinese authors increased almost 30-fold since 2001.

CONCLUSIONS

Despite extensive efforts, neurotoxicity remains a significant public health problem. This provides great challenges and opportunities. We identified 10 significant areas that require major educational, environmental, governmental, and research efforts, as well as attention to public awareness. For example, there is a need to increase efforts to utilize new in vivo and in vitro models, determine the potential neurotoxicity and mechanisms involved in newly emerging pollutants, and examine the effects and mechanisms of mixtures. In the future, we anticipate working with scientists worldwide to accomplish these goals and eliminate, prevent and treat neurotoxicity.

CITATION

Cai T, Luo W, Ruan D, Wu YJ, Fox DA, Chen J. 2016. The history, status, gaps, and future directions of neurotoxicology in China. Environ Health Perspect 124:722-732; http://dx.doi.org/10.1289/ehp.1409566.

Effects of chronic manganese exposure on the learning and memory of rats by observing the changes in the hippocampal cAMP signaling pathway

Chronic manganese exposure can produce cognitive deficits; however, the underlying mechanism remains unclear; reliable peripheral biomarker of Mn neurotoxicity have not yet been fully developed. Hence, this study aimed to investigate the mechanism of Mn-induced cognitive deficits and the potential biomarker of Mn neurotoxicity in rats. Thirty-two male Sprague Dawley rats were divided into four groups; these groups received intraperitoneal injections of 0, 5, 10 and 20 mg Mn/kg once daily, five days/week for 18 weeks. Learning and memory were assessed via Morris water maze test. Hippocampal and plasma Mn concentrations were measured through graphite furnace atomic absorption spectrometry. The levels of plasma BDNF, hippocampal BDNF, cAMP, protein kinase A, and pCREB were assessed through ELISA or Western blot. Results showed that the Mn concentrations in the hippocampus and plasma of the Mn-treated rats were higher than those of the control rats. Mn exposure impaired the learning and memory of rats. Plasma BDNF levels and hippocampal BDNF, cAMP, protein kinase A, and pCREB levels were significantly lower in the Mn-treated rats than in the control rats. Plasma BDNF levels were negatively correlated with the escape latency and the hippocampal and plasma Mn concentrations. By contrast, plasma BDNF levels were positively correlated with the number of platform crossings and the hippocampal cAMP and BDNF levels. Therefore, Mn impaired learning and memory probably by inhibiting the hippocampal cAMP signaling pathway in rats. Plasma BDNF levels may also be a potential effect biomarker of Mn neurotoxicity.

Systematic review of potential health risks posed by pharmaceutical, occupational and consumer exposures to metallic and nanoscale aluminum, aluminum oxides, aluminum hydroxide and its soluble salts

Abstract Aluminum (Al) is a ubiquitous substance encountered both naturally (as the third most abundant element) and intentionally (used in water, foods, pharmaceuticals, and vaccines); it is also present in ambient and occupational airborne particulates. Existing data underscore the importance of Al physical and chemical forms in relation to its uptake, accumulation, and systemic bioavailability. The present review represents a systematic examination of the peer-reviewed literature on the adverse health effects of Al materials published since a previous critical evaluation compiled by Krewski et al. (2007) . Challenges encountered in carrying out the present review reflected the experimental use of different physical and chemical Al forms, different routes of administration, and different target organs in relation to the magnitude, frequency, and duration of exposure. Wide variations in diet can result in Al intakes that are often higher than the World Health Organization provisional tolerable weekly intake (PTWI), which is based on studies with Al citrate. Comparing daily dietary Al exposures on the basis of "total Al"assumes that gastrointestinal bioavailability for all dietary Al forms is equivalent to that for Al citrate, an approach that requires validation. Current occupational exposure limits (OELs) for identical Al substances vary as much as 15-fold. The toxicity of different Al forms depends in large measure on their physical behavior and relative solubility in water. The toxicity of soluble Al forms depends upon the delivered dose of Al(+3) to target tissues. Trivalent Al reacts with water to produce bidentate superoxide coordination spheres [Al(O2)(H2O4)(+2) and Al(H2O)6 (+3)] that after complexation with O2(•-), generate Al superoxides [Al(O2(•))](H2O5)](+2). Semireduced AlO2(•) radicals deplete mitochondrial Fe and promote generation of H2O2, O2 (•-) and OH(•). Thus, it is the Al(+3)-induced formation of oxygen radicals that accounts for the oxidative damage that leads to intrinsic apoptosis. In contrast, the toxicity of the insoluble Al oxides depends primarily on their behavior as particulates. Aluminum has been held responsible for human morbidity and mortality, but there is no consistent and convincing evidence to associate the Al found in food and drinking water at the doses and chemical forms presently consumed by people living in North America and Western Europe with increased risk for Alzheimer's disease (AD). Neither is there clear evidence to show use of Al-containing underarm antiperspirants or cosmetics increases the risk of AD or breast cancer. Metallic Al, its oxides, and common Al salts have not been shown to be either genotoxic or carcinogenic. Aluminum exposures during neonatal and pediatric parenteral nutrition (PN) can impair bone mineralization and delay neurological development. Adverse effects to vaccines with Al adjuvants have occurred; however, recent controlled trials found that the immunologic response to certain vaccines with Al adjuvants was no greater, and in some cases less than, that after identical vaccination without Al adjuvants. The scientific literature on the adverse health effects of Al is extensive. Health risk assessments for Al must take into account individual co-factors (e.g., age, renal function, diet, gastric pH). Conclusions from the current review point to the need for refinement of the PTWI, reduction of Al contamination in PN solutions, justification for routine addition of Al to vaccines, and harmonization of OELs for Al substances.

Disturbance of intracellular calcium homeostasis and CaMKII/CREB signaling is associated with learning and memory impairments induced by chronic aluminum exposure

Aluminum-induced neuronal injury has been implicated in various neurodegenerative disorders. However, the underlying mechanism involved in this pathogenesis still remains unknown. Our present findings demonstrated that chronic aluminum exposure resulted in spatial learning impairment and significantly increased intracellular calcium level in the hippocampus of rats. Examination of the associated protein molecules essential for induction and maintenance of long-term potentiation revealed that aluminum exposure could increase the expression level of calmodulin (CaM), but the expression levels of CaM-dependent protein kinase II (CaMKII), and phosphorylated cAMP-responsive element binding protein (CREB) were significantly reduced, whereas the total protein levels of CaMKII and CREB did not change in the aluminum-treated hippocampus. Thus, we provide a previously unrecognized mechanism whereby chronic aluminum exposure impairs hippocampal learning and memory, at least in part, through disruption of intracellular calcium homeostasis and CaM/CaMKII/CREB signaling pathway.