Occupational exposure to aluminum and its amyloidogenic link with cognitive functions

Unraveling the neuroprotective mechanisms of naltrexone against aluminum-induced neurotoxicity

Aluminum (Al) is a known neurotoxic trace element linked to Alzheimer's disease (AD). Naltrexone, an opioid antagonist, has shown promising effects in reducing neuroinflammation at lower doses than those prescribed for addiction. This study aimed to determine the neuroprotective effects of naltrexone on Al-induced neurotoxicity in an in vitro AD model. The SH-SY5Y cells were first cultivated in a standard growth medium. Subsequently, the cells were induced to differentiate by decreasing the concentration of fetal bovine serum and introducing retinoic acid (RA) into the culture media. Subsequently, the inclusion of brain-derived neurotrophic factor (BDNF) was implemented in conjunction with RA. The process of differentiation was concluded on the seventh day. Study groups (n = 3) were designed as the control group, naltrexone group, Al group, Al-Nal group, Alzheimer' model (AD) group, Alzheimer model + Al-exposed group (AD-Al), Alzheimer model + Nal applied group (AD-Nal) and Alzheimer model + Al-exposed + Nal applied group (AD-Al-Nal). Hyperphosphorylated Tau protein as the specific marker of AD was measured in all groups. Glycogen synthase kinase-3 (GSK-3)β, Protein phosphatase 2A (PP2A), Akt and Wnt signaling pathways were analyzed comparatively. In addition, oxidative stress parameters (total antioxidant capacity, lipid peroxidase, protein carbonyl and reactive oxygen species) were measured comparatively in the study groups. The results showed that naltrexone reduced hyperphosphorylated tau protein levels by regulating GSK-3β, PP2A, Akt and Wnt signaling. Also, exposure to naltrexone decreased oxidative stress parameters. Based on these results, naltrexone shows promise as a potential therapy for AD, subject to additional clinical assessments.

Diffusion Kurtosis Imaging in Evaluating the Mild Cognitive Impairment of Occupational Aluminum Workers

RATIONALE AND OBJECTIVES

To investigate whether diffusion kurtosis imaging (DKI) can distinguish mild cognitive impairment (MCI) from normal controls (NC) in aluminum (Al)-exposed workers, and to explore the association of DKI with cognitive performance and plasma Al concentration.

MATERIALS AND METHODS

28 patients with MCI and 25 NC at Al factory were enrolled in this study. All subjects underwent conventional MRI and DKI scans. The mean kurtosis (MK), axial kurtosis (Ka), radial kurtosis (Kr), mean diffusivity (MD) and fractional anisotropy (FA) parameters of the hippocampus, substantia nigra, red nucleus, thalamus, anterior cingulate gyrus, genu and crus of the corpus callosum, frontal, parietal and temporal lobe were measured. To compare the parameters between the two groups, the Mann-Whitney rank sum test was used. The correlation of parameter values with cognitive performance and plasma Al concentration was analyzed using Spearman correlation analysis. The receiver operating characteristic (ROC) curve and the Z-scores were used to evaluate the diagnostic efficacy of each parameter.

RESULTS

Compared with the NC group, the MK, Ka, Kr, and FA values in the MCI group were significantly decreased, and the MD values were significantly increased (p<0.05). For the diagnosis of MCI, MK in the right hippocampus showed the largest AUC (0.924). The MK, Kr, MD and FA values were correlated with the Montreal Cognitive Assessment (MoCA) scores, and MK values in the right hippocampus showed the greatest correlation with MoCA scores (r=0.744, p <0.001). Plasma Al in the MCI group was higher than that in the NC group, although there was no significant difference in plasma Al between the two groups (p=0.057). There was no correlation between DKI parameters and plasma Al.

CONCLUSION

The DKI method might be a sensitive imaging biomarker to discriminate MCI from NC, and could preliminarily assess the severity of cognitive impairment in Al-exposed workers. MK in the right hippocampus appeared to be the best independent predictor. The mechanism of cognitive decline is an important content of aluminum exposure research. This study indicates that the DKI technique could provide valuable information for the diagnosis of MCI.

Interaction between aluminum exposure and ApoEε4 gene on cognitive function of in-service workers

The occurrence and development of cognitive impairment, the early stage of AD, may be affected both by factors of environmental (aluminum exposure) and genetic (ApoEε4 gene). But whether there is an interaction between the two factors on cognitive function is still unknown. To explore the interaction between the two factors on cognitive function of in-service workers. A total of 1121 in-service workers in a large aluminum factory were investigated in Shanxi Province. Cognitive function was assessed by the Mini-mental State Examination (MMSE), the clock-drawing test (CDT), the Digit Span Test (DST, including DSFT and DSBT), the fuld object memory evaluation (FOM), and the verbal fluency task (VFT). The plasma-Al (p-Al) concentrations were measured by inductively coupled plasma-mass spectrometry (ICP-MS) as an internal exposure indicator, and the participants were divided into four Al exposure groups according to the quartile of p-Al concentrations, namely Q1, Q2, Q3, and Q4. ApoE genotype was determined by Ligase Detection Reaction (LDR). The multiplicative model was fitted using non-conditional logistic regression and additive model was fitted using crossover analysis to analyze the interaction between p-Al concentrations and the ApoEε4 gene. Finally, a dose-response relationship between p-Al concentrations and cognitive impairment was observed, with the p-Al concentrations increased, cognitive function performance gradually becomes worse (P_trend＜0.05), and the risk of cognitive impairment gradually increases (P_trend＜0.05), mainly in executive/visuospatial impairment, auditory memory impairment (particularly the working memory impairment). And ApoEε4 gene may be a risk factor for cognitive impairment, while no association between the ApoEε2 gene and cognitive impairment is observed. Additionally, an additive but no multiplicative interaction between p-Al concentrations and ApoEε4 gene is observed, and when the two factors work together, the risk of cognitive impairment further increased, of which 44.2% can be attributed to the interaction effect.

The Palmitoylation/Depalmitoylation Cycle is Involved in the Inhibition of AMPA Receptor Trafficking Induced by Aluminum In Vitro

To study the effect of the palmitoylation/depalmitoylation cycle on the inhibition of ɑ-amino-3-hydroxy-5-methyl-4-isoxazolpropionic acid (AMPA) receptor trafficking induced by aluminum (Al) in vitro. Five different doses of aluminum-maltolate complex (Al(mal)₃) were administered to rat adrenal pheochromocytoma cells (PC12 cells) for three exposure time durations, and the cell activity was measured by the CCK-8 method to obtain the optimal doses and time of Al(mal)₃ exposure. Following Al(mal)₃ exposure, membrane protein (M) and total protein (T) were extracted. The expression levels of GluR1 and GluR2, which are AMPA receptor subunits, were determined by Western blot analysis, and the levels with respect to membrane and total protein were calculated. The ratio of membrane protein to total protein (M/T) was used to measure the rate of AMPA receptor transport. The palmitoylation levels of GluR1 and GluR2 were detected by immunoprecipitation-acyl-biotin exchange (IP-ABE) assay. Western blotting was performed to detect the protein expression of acyltransferase (zDHHC3) and palmitoyl protein thioesterase 1 (PPT1). Following depalmitoylation inhibitor (palmostatin B) treatment of PC12 cells, the effect of aluminum on AMPA receptor trafficking was detected through the aforementioned methods. With increasing Al(mal)₃ doses administered to PC12 cells, a gradual decrease in the trafficking of AMPA receptor subunits GluR1 and GluR2 and in the palmitoylation levels of GluR1 and GluR2 was found; the expression of zDHHC3 was decreased; and the expression of PPT1 was increased. In addition, palmostatin B reduced the effects of Al(mal)₃ on AMPA receptor palmitoylation and trafficking. Al can inhibit the trafficking of the AMPA receptor in vitro, and a decrease in the palmitoylation level of the AMPA receptor may be a mechanism of Al action. The palmitoylation/depalmitoylation cycle of the AMPA receptor is influenced by Al through the actions of zDHHC3 and PPT1.

Effect of the Reelin-Dab1 signaling pathway on the abnormal metabolism of Aβ protein induced by aluminum

Aluminum (Al) is a common neurotoxic element that can exacerbate intracellular β-amyloid (Aβ) deposition. Reelin is a highly conserved extracellular glycoprotein that is involved in intracellular Aβ deposition. However, the action of Reelin on aluminum-induced Aβ deposition is not fully understood. Here, we investigated the effects of the Reelin-Dab1 signaling pathway on Aβ deposition in aluminum maltol (Al(mal)₃) exposure in rat pheochromocytoma-derived cells (PC12). Our results showed that Al(mal)₃ exposure decreased activity of PC12, increased expression of Aβ₄₂, and decreased expression of Aβ₄₀. Moreover, Al(mal)₃ exposure in PC12 induced Reelin-Dab1 signaling pathway-associated proteins changed, decreased expression of Reelin and Dab1, and increased expression of pdab1. Moreover, the expression of Reelin, Dab1, and Aβ₄₀ was found to be elevated in PC12 exposed to Al(mal)₃ and corticosterone compared to those exposed to Al(mal)₃. Also, the expression of Reelin, Dab1, and Aβ₄₀ was found to be depressed in PC12 exposed to Al(mal)₃ and streptozotocin compared with cells exposed to Al(mal)₃ alone. These results suggested that Al(mal)₃ inhibits the expression of the Reelin-Dab1 signaling pathway, promoting Aβ deposition. Thus, our findings provided important evidence to better understand how the Reelin-Dab1 signaling pathway may be a potential mechanism of Aβ deposition induced by aluminum.

Aluminum Oxide Nanoparticles Impair Working Memory and Neuronal Activity through the GSK3β/BDNF Signaling Pathway of Prefrontal Cortex in Rats

Studies demonstrated that alumina nanoparticles (alumina NPs) impair spatial cognition and hippocampus-dependent synaptic plasticity. Although alumina NPs accumulate in the prefrontal cortex (PFC), their effects on PFC-mediated neuronal and cognitive function have been not yet documented. Here, alumina NPs (10 or 20 μg/kg of body weight) were bilaterally injected into the medial PFC (mPFC) of adult rats, and the levels of glycogen synthase kinase 3β (GSK3β) and the brain-derived neurotrophic factor (BDNF) were detected. The PFC-dependent working memory task with one-minute or three-minute delay time was conducted. Meanwhile, the neuronal correlates of working memory performance were recorded. The specific expression of neuronal BDNF was assessed by colabeled BDNF expression with the neuronal nuclear antigen (NeuN). Whole-cell patch-clamp recordings were employed to detect neuronal excitability. Intra-mPFC alumina NP infusions significantly enhanced the expression of GSK3β but reduced the phosphorylation of GSK3β (pGSK3β) and BDNF levels more severely at a dose of 20 μg/kg. Alumina NPs acted in a dose-dependent manner to impair working memory. The neuronal expression of BDNF in the 20 μg/kg group was markedly declined compared with the 10 μg/kg group. During the delay time, the neuronal frequency of pyramidal cells but not interneurons was significantly weakened. Furthermore, both the frequency and amplitude of the excitatory postsynaptic currents (EPSCs) were descended in the mPFC slices. Additionally, the infusion of GSK3β inhibitor SB216763 or BDNF could effectively attenuate the impairments in neuronal correlate, neuronal activity, and working memory. From the perspective of the identified GSK3β/BDNF pathway, these findings demonstrated for the first time that alumina NPs exposure can be a risk factor for prefrontal neuronal and cognitive functions.

Association of both prenatal and early childhood multiple metals exposure with neurodevelopment in infant: A prospective cohort study

BACKGROUND

Impaired neurodevelopment of children has become a growing public concern; however, the associations between metals exposure and neurocognitive function have remained largely unknown.

OBJECTIVES

We systematically evaluated the associations of multiple metals exposure during pregnancy and childhood on the neurodevelopment of children aged 2-3 years.

METHODS

We measured 22 metals in the serum and urine among703 mother-child pairs from the Guangxi Birth Cohort Study. The neurocognitive development of children was assessed by the Gesell Development Diagnosis Scale (GDDS; Chinese version). Multiple linear regression models were used to evaluate the relationship between the metals (selected by elastic net regression) and the outcomes. The Bayesian kernel machine regression (BKMR) was used to evaluate the possible joint effect between the multiple metal mixture and the outcomes.

RESULTS

Prenatal aluminum (Al) exposure was negatively associated with the fine motor developmental quotient (DQ) (β = -1.545, 95%CI: 2.231, -0.859), adaption DQ (β = -1.182, 95%CI: 1.632, -0.732), language DQ (β = -1.284, 95% CI: 1.758, -0.809), and social DQ (β = -1.729, 95% CI: 2.406, -1.052) in the multi-metal model. Prenatal cadmium (Cd) exposure was negatively associated with gross motor DQ (β = -2.524, 95% CI: 4.060, -0.988), while postpartum Cd exposure was negatively associated with language DQ (β = -1.678, 95% CI: 3.227, -0.129). In stratified analyses, infants of different sexes had different sensitivities to metal exposure, and neurobehavioral development was more significantly affected by metal exposure in the first and second trimester. BKMR analysis revealed a negative joint effect of the Al, Cd, and selenium (Se) on the language DQ score; postpartum Cd exposure played a major role in this relationship.

CONCLUSION

Prenatal exposure to Al, Ba, Cd, molybdenum (Mo), lead (Pb), antimony (Sb), and strontium (Sr), and postpartum exposure to cobalt (Co), Cd, stannum (Sn), iron (Fe), nickel (Ni), and Se are associated with neurological development of infants. The first and second trimester might be the most sensitive period when metal exposure affects neurodevelopment.

APP palmitoylation is involved in the increase in Aβ1-42 induced by aluminum

The increase in Aβ_1-42 is a neurotoxic effect induced by aluminum which can lead to impairment of learning and memory, but its mechanism has yet to be fully elucidated. Studies have shown that APP palmitoylation is appears to be involved in the production process of Aβ_1-42. Here, we investigated whether APP palmitoylation is related to the increase in Aβ caused by aluminum and its specific mechanism of action. In this study, APP palmitoylation was studied in the setting of aluminum-induced increases in Aβ_1-42 from two perspectives: whole animal experiments and in vitro cell experiments. First, the learning and memory of rats were impaired and the number of rat cortical neurons was decreased after staining with aluminum. Second, the expression of palmitoyl APP, APP in lipid rafts and palmitoyl acyltransferase zDHHC7 both in rat cerebral cortex and PC12 cells increased with the production of Aβ_1-42 induced by aluminum in a dose-dependent manner. Finally, the intervention with the palmitoylation inhibitors 2-BP and siRNA zDHHC7 in PC12 cells reduced levels of palmitoyl APP, the expression of APP in lipid rafts and the content of Aβ_1-42 induced by aluminum to a certain extent. Our results indicate that increased APP palmitoylation levels may be related to the increase in Aβ_1-42 caused by aluminum, and the mechanism may involve APP palmitoylation promoting the accumulation of APP protein on lipid rafts and the cleavage of APP by BACE1 in amyloidogenic pathway. The increase in expression of zDHHC7 may be one of the reasons for the increase in levels of APP palmitoylation caused by aluminum.

The GSK-3β/β-Catenin Signaling-Mediated Brain-Derived Neurotrophic Factor Pathway Is Involved in Aluminum-Induced Impairment of Hippocampal LTP In Vivo

The neurotoxic effects of aluminum (Al) are associated with the impairment of synaptic plasticity, the biological basis of learning and memory, the major form of which is long-term potentiation (LTP). The canonical glycogen synthase kinase-3β (GSK-3β)/β-catenin signaling-mediated brain-derived neurotrophic factor (BDNF) pathway has been suggested to play important roles in memory. Thus, Al may affect LTP through this pathway. In this study, a Sprague-Dawley rat model of neurotoxicity was established through intracerebroventricular (i.c.v.) injection of aluminum maltol (Al(mal)₃), which was achieved by preimplantation of a cannula into the lateral ventricle. The rats in the control and Al-treated groups received a daily injection of SB216763, an inhibitor of GSK-3β. Electrophysiology and western blot analysis were used to investigate the regulatory effect of the GSK-3β/β-catenin signaling-mediated BDNF pathway on LTP impairment induced by Al(mal)₃. The results confirmed that i.c.v. injection of Al(mal)₃ significantly suppressed the field excitatory postsynaptic potential (fEPSP) amplitude, as indicated by a decrease in BDNF protein expression, which was accompanied by dose-dependent decreases in β-catenin protein expression and the phosphorylation of GSK-3β at Ser9. Rats that received SB216763, a GSK-3β inhibitor, exhibited higher fEPSP amplitudes than control rats. Furthermore, SB216763 treatment upregulated the hippocampal protein expression of BDNF and β-catenin while increasing the ratio of p-GSK-3β/GSK-3β. From the perspective of the identified β-catenin-BDNF axis, Al impairs hippocampal LTP, possibly through the GSK-3β/β-catenin signaling-mediated BDNF pathway.

Relationship between the expression of TNFR1-RIP1/RIP3 in peripheral blood and cognitive function in occupational Al-exposed workers: A mediation effect study

Aluminium (Al), not essential for biological activities, accumulates in the tissues. It exerts toxic effects on the nervous system, inducing in humans' irreversible cognitive impairment. In this study, a cluster sampling method was used to observe the cognitive function of long-term occupational Al-exposed workers in a large Al factory, and determine the expression of peripheral blood tumour necrosis factor receptor 1 (TNFR1), receptor-interacting protein 1 (RIP1), and RIP3. TNF-alpha, expressed in blood macrophages and microglia, with its receptors TNFR1, TR1 and TR3, enhances the necroptosis of neurons. Additionally, the relationship between the expression of TNFR1, RIP1, and RIP3 in the peripheral blood of long-term occupational Al-exposed workers and changes in their cognitive function was explored. The differences in the distributions of clock drawing test (CDT) scores among the three groups were statistically significant (P < 0.05). The results of correlation analysis showed that RIP1 and RIP3 protein contents were negatively correlated with mini-mental state examination (MMSE) and CDT scores (P < 0.05). Plasma Al content was positively correlated with other biological indicators (P < 0.05), and negatively correlated with MMSE and CDT scores (P < 0.05). Results showed that RIP3 protein had an incomplete mediation effect between plasma Al content and cognitive function. This suggests that Al may affect cognitive function by influencing the expression of TNFR1, RIP1, and RIP3 in the nervous system.

Longitudinal study of the effects of occupational aluminium exposure on workers' cognition

OBJECTIVE

To explore the effects of occupational aluminium(Al) exposure on workers' cognition through a longitudinal study.

METHODS

The study population consisted of 276 workers in an Al factory. In 2014, we used inductively coupled plasma mass spectrometry (ICP-MS) to determine the plasma aluminium (P-Al) concentration of the workers, and a combined questionnaire to test the workers' cognitive function. Followed-up in 2016, the workers were tested again for cognitive function. Generalized linear regression was used to assess the association between P-Al concentration and cognitive scores, and multivariable logistic regression was used to assess the risk of cognitive decline caused by Al exposure.

RESULTS

Generalized linear regression results showed that a non-significant association was found between the P-Al concentration and cognitive test scores (P > 0.05) in 2014. Two years later, each 10-fold increase in P-Al concentration was inversely associated with the score of Mini-Mental state examination (MMSE) (β: -0.53, 95% CI: -0.86, -0.20) and Fuld object memory evaluation (FOME) (β: -0.93, 95% CI: -1.62, -0.24). Each 10-fold increase in P-Al concentration was inversely associated with MMSE_2016-2014 (β: -0.38, 95% CI: -0.74, -0.01) and FOME_2016-2014 (β: -1.20, 95% CI: -1.95, -0.45). There was a statistically significant difference in the average annual rate of change of MMSE and FOME with the tertile of P-Al concentration increase (P < 0.05). The multivariable logistic regression results showed that as the P-Al concentration increased, the risk of a FOME score decline increased (P_trend = 0.009).

CONCLUSIONS

Continuous occupational Al exposure can damage workers' overall cognitive ability, especially episodic memory function.

Cross-sectional study based on occupational aluminium exposure population

To evaluate the different characteristics of cognitive impairment caused by occupational aluminium exposure at different ages, we surveyed 1660 workers in Shanxi Aluminium Plant, China, and assessed their cognitive function and plasma aluminium concentration. In multiple linear regression, the scores of the digit-span test (DST) and digit-span backward test (DSBT) were negatively correlated with plasma aluminium concentration when concentration reached 34.52 μg/L in younger group (＜40 years), while in the middle-aged group (≥40 years) only found when concentration reached 42.25 μg/L (β<0, P < 0.05). In logistic regression, when plasma aluminum concentration reached 42.25μg/L, odds ratios (95 % confidence interval) were 1.695 (1.062-2.705) and 3.270 (1.615-6.620) for DST, 7.644 (3.846-15.192) and 15.308 (4.180-56.059) for DSBT in middle-aged group and younger group, respectively. These results showed that aluminium exposures were associated with cognitive impairment among aluminium-exposed workers, particularly for young workers who were more susceptible.

Association between aluminium exposure and cognitive functions: A systematic review and meta-analysis

INTRODUCTION

Chronic Aluminium (Al) exposure is reported to be linked with neuro-cognitive impairment. However, there is limited synthesized information on the role of chronic Al exposure on individual cognitive domains. This knowledge gap is explored here by systematic review and meta-analysis of the published literature.

METHODS

Observational studies that reported the association between Al exposure and cognitive functions were systematically searched in PubMed, Scopus and Embase databases since inception to June 2019 and updated on September 2020. PRISMA guidelines were adhered in this study. Meta-analysis was performed using a random-effect model if the included studies exhibited heterogeneity, in the absence of heterogeneity fixed effect model was used. Heterogeneity was assessed using Cochran-Q test and I² statistic. Risk of bias was assessed using the risk of bias in non-randomized studies of exposures. Sub-group analysis and meta regression analysis were explored.

RESULTS

Twenty-three studies including 1781 Al exposed and 1186 unexposed were part of the final results. The pooled standardized mean difference of global cognitive scores (-0.65, 95%CI: -1.09 to -0.22, I² = 91.09%), memory (-0.45, 95% CI: -0.69 to -0.21, I² = 81.67%), working memory (-0.3, 95%CI: -0.45 to -0.15, I² = 0%) and processing speed domains were significantly inferior among Al exposed as compared to unexposed. The other evaluated cognitive domains, such as cognitive flexibility, visuospatial abilities and psychomotor functions did not significantly differ between the two groups. We observed a serious risk of bias in most of the included studies.

CONCLUSION

Current pieces of evidence suggest an association between chronic Al exposure and impaired cognitive function in majority of domains including memory, processing speed and working memory while no significant influence in other cognitive domains. However, considering high heterogeneity and low quality of primary evidence, further high-quality studies are necessary for conclusive evidence in this regard.

Derivation of Biomonitoring Equivalents for aluminium for the interpretation of population-level biomonitoring data

Aluminium is widely used in many consumer products, however the primary source of aluminium exposure to the Canadian general population is through food. Aluminium can cause neurotoxicity and reproductive toxicity at elevated exposure levels. Health-based exposure guidance values have been established for oral exposure to aluminium, including a Minimal Risk Level (MRL) by the Agency for Toxic Substances and Disease Registry (ATSDR), a Provincial Tolerable Weekly Intake (PTWI) by the Joint FAO/WHO Expert Committee on Food Additives (JECFA) and a Tolerable Weekly Intake (TWI) by the European Food Safety Authority (EFSA). Aluminium concentration in blood and urine can be used as a tool for exposure characterization in a population. A pharmacokinetic (PK) model was developed based on human dosing data to derive blood Biomonitoring Equivalents (BEs), whereas a mass balance approach was used to derive urine BEs for the above guidance values. The BEs for blood for daily intake consistent with the MRL, PTWI and TWI were 18, 16 and 8 μg/L, respectively. BEs for urine for the same guidance values were 137, 123 and 57 μg/L, respectively. The derived BEs may be useful in interpreting population-level biomonitoring data in a health risk context and thereby screening and prioritizing substances for human health risk assessment and risk management.

Does aluminum exposure affect cognitive function? a comparative cross-sectional study

OBJECTIVES

This study assessed the cognitive function of aluminum-exposed participants from an alum mining zone, compared them with unexposed subjects, and aimed to elucidate the effect of aluminum exposure on cognition.

DESIGN

This was a comparative cross-sectional study. Univariate analyses were used to assess the differences between the aluminum-exposed and unexposed groups. Binary logistic regression models were applied to analyze the effect of aluminum exposure.

SETTING

The aluminum-exposed participants were included from an alum mining zone and the unexposed subjects were residents from another district without alum-mine-related factories.

PARTICIPANTS

We included 539 aluminum-exposed participants (254 men, 285 women) and 1720 unexposed participants (692 men, 1028 women).

RESULTS

The mean cognition score on Mini-Mental State Examination was 21.34 (± 6.81) for aluminum-exposed participants. The exposed group had 6.77 times (95% confidence interval, 5.09-9.00) more risk of cognitive impairment than the unexposed group, after adjusting for age, sex, and educational level. No statistically significant association was found between exposure duration and cognition.

CONCLUSIONS

This study demonstrated a significant association between aluminum exposure and lower cognitive function.

Aluminum-Induced Cognitive Impairment and PI3K/Akt/mTOR Signaling Pathway Involvement in Occupational Aluminum Workers

Epidemiological studies indicate that long-term occupational exposure to aluminum (Al) causes neurotoxicity and cognitive impairment. While the molecular underpinnings associated with workers' cognitive impairment is unclear, one mechanism may involve Al-induced PI3K/Akt/mTOR activation and neuronal cell death, which impairs learning and memory in rats. Here, we sought to determine whether PI3K/Akt/mTOR is also associated with cognitive impairment in Al-exposed occupational workers. Cognitive function was screened by Mini-Mental State Examination (MMSE) and Clock-Drawing Test (CDT), and serum Al and PI3K/Akt/mTOR-associated gene expression was quantified. A negative correlation between serum Al and scores of MMSE and CDT was found, which might relate with downregulation of PI3K/Akt/mTOR. To determine the role of the PI3K/Akt/mTOR pathway cognitive function, we treated zebrafish with Al and observed a profound impairment in learning and memory. Increased brain Al levels was associated with decreased expression of PI3K/Akt/mTOR in Al-exposed zebrafish. Finally, rapamycin, an mTOR inhibitor, was added to isolate the role of mTOR specifically in the Al exposed zebrafish. The results suggested that Al induces learning and memory deficits by downregulating PI3K, Akt, and mTOR1 expression and inducing neuronal cell death like rapamycin group. This study indicates that aluminum exposure can cause cognitive impairment through PI3K/Akt/mTOR pathway, with mTOR activity being a critical player involved in this mechanism. Future studies are necessary to further characterize the role of PI3K/Akt/mTOR1 signaling in Al-induced neurocognitive decline among Al occupational workers. These findings draw attention to Al risk exposure among occupational workers and the need to implement novel safety and protective measures to mitigate neurocognitive health risks in the Al industrial workspace.

Cognitive impairment of workers in a large-scale aluminium factory in China: a cross-sectional study

OBJECTIVES

To investigate the prevalence of mild cognitive impairment and the relationship with plasma aluminium among aluminium workers.

DESIGN

This was a cross-sectional case-control study in the SH Aluminium Factory, China.

SETTING

The university and affiliated hospital cooperated in the study.

PARTICIPANTS

There were 910 aluminium workers on duty, among whom 853 participated in our study. Participants, such as those with cerebral vascular disease, epilepsy, brain trauma, Parkinson's and mental diseases, aluminium-containing drug and mental drug use, and any family history of dementia in first-degree relatives were excluded.

PRIMARY AND SECONDARY OUTCOME MEASURES

Blood samples were collected, and plasma aluminium was measured by inductively coupled plasma-mass spectrometry. For each case, four age-matched controls were evaluated to determine the relationship between aluminium exposure and mild cognitive impairment. Conditional logistic regression was used to explore influential factors in mild cognitive impairment.

RESULTS

Among 910 workers, 93.74% participated in stage 1; 53 cases were finally diagnosed. The crude prevalence of mild cognitive impairment among aluminium workers on duty was 6.21%. There was a significant difference in plasma aluminium concentration between the two groups. In the multivariate analysis, we found that a higher level of plasma aluminium was associated with a high risk of cognitive impairment when compared with a lower aluminium level (AOR=2.24, 95% CI=1.17 to 4.26), and a high education level was a protective factor (AOR=0.36, 95% CI=0.18 to 0.70). No other factor was statistically significant.

CONCLUSIONS

Mild cognitive impairment is no longer a disease specific to elderly people. High plasma aluminium exposure might be associated with an increased risk of cognitive impairment, but a reduced risk was observed with a high education level. The cognitive function of aluminium workers on duty must be considered seriously.

Lycopene attenuates aluminum-induced hippocampal lesions by inhibiting oxidative stress-mediated inflammation and apoptosis in the rat

Aluminum (Al) causes hippocampal lesions by oxidative stress, which is widely accepted as the primary pathogenesis of Al neurotoxicity. Lycopene (LYC), a naturally carotenoid, has received extensive attention due to its antioxidant effect. In this study, the neuroprotective effects and mechanisms of LYC against aluminum chloride (AlCl₃)-induced hippocampal lesions were explored. First, oral administration of LYC (4 mg/kg) alleviated AlCl₃-induced (150 mg/kg) cognition impairment and histopathological changes of the hippocampus in rats. Then, LYC significantly attenuated AlCl₃-induced oxidative stress, presenting as the reduced reactive oxygen species, malondialdehyde and 8-hydroxy-2'-deoxyguanosine levels, and increased glutathione level and superoxide dismutase activity. Moreover, LYC also protected the hippocampus from AlCl₃-induced apoptosis and neuroinflammation, as assessed by protein levels of p53, Bcl-2-associated X protein (Bax), B-cell lymphoma gene 2 (Bcl-2), Cytochrome c (Cyt c), cleaved caspase-3 and nuclear factor kappa B, as well as the mRNA levels of Bax, Bcl-2, tumor necrosis factor alpha, interleukin-6 and interleukin-1 beta. Finally, LYC increased nuclear factor-erythroid-2-related factor 2 (Nrf2) nuclear translocation and its downstream gene expression, including heme oxygenase-1, NAD(P)H: quinone oxidoreductase 1, glutamate cysteine ligase catalytic subunit and superoxide dismutase 1, which were involved in antioxidant, anti-apoptosis, and anti-inflammation. Overall, our findings demonstrate LYC attenuates Al-induced hippocampal lesions by inhibiting oxidative stress-mediated inflammation and apoptosis in the rat.

Effects of occupational exposure to aluminium on some oxidative stress and DNA damage parameters

Aim:

The aim of this work was to investigate the relationships between aluminium levels, oxidative status and DNA damage in workers occupationally exposed to aluminium.

Subjects and methods:

This study was conducted in a secondary aluminium smelter. It included 96 male workers occupationally exposed to aluminium fume and dust compared to 96 male nonexposed individuals. Full history and clinical examination were done for all participants. Laboratory investigations in the form of serum aluminium, total antioxidant capacity (TAC), urinary 8-hydroxy-2′-deoxyguanosine (8-OHdG) and comet assay test were performed.

Results:

Serum aluminium level ranged from 4 to 30 µg/L of median: 10 µg/L; urinary 8-OHdG ranged from 2.7 to 17.2 ng/mg creatinine of median: 7.6 ng/mg creatinine; comet tail length (CTL) ranged from 19.7 to 50.5 µm of median: 45 µm, were statistically significantly increased in the exposed group compared to nonexposed group. In exposed workers, a statistically significant positive correlations were found between serum aluminium level and urinary 8-OHdG ( r = 0.75, p < 0.001); aluminium level and CTL ( r = 0.71, p < 0.001); and urinary 8-OHdG and CTL ( r = 0.71, p < 0.001). There was a statistically significant negative correlation between serum aluminium and TAC ( r = −0.76, p < 0.001).

Conclusion:

Occupational exposure to aluminium in secondary aluminium smelters was related to the induction of oxidative stress and DNA damage. This may promote the development of adverse health hazards in the exposed workers

The relationship between cognition and depressive symptoms, and factors modifying this association, in Alzheimer's disease: A multivariate multilevel model

OBJECTIVES

To examine whether there was a bidirectional association between cognition and depressive symptoms in Alzheimer's disease (AD), and to explore the role of socio-demographic factors and daily performance in this association.

METHODS

We conducted a longitudinal study of 104 community-dwelling patients with confirmed AD from Taiyuan, China. We assessed cognition and depressive symptoms (dependent variables) with the Montreal Cognitive Assessment (MoCA) and the Geriatric Depression Scale-30 (GDS-30), respectively. Socio-demographic information and daily performance were treated as explanatory variables. A multivariate multilevel model was built to investigate the interrelationship between patients' cognition and depression, as well as the effect of related factors on both outcomes.

RESULTS

MoCA scores were negatively correlated with GDS-30 both at the subject level (correlation coefficient r₃=-0.68, χ²=19.26, P<0.001) and time point level (r₂=-0.35, χ²=35.68, P<0.001) in patients with AD. Multivariate analysis showed several significant factors for cognitive function, including educational level, personality, hobbies, exercise, reading, aluminum utensil use, dietary restriction and hypertension (regression coefficients: 0.60, 0.52, 0.51, 0.48, 0.45, -0.48, 0.67, and -0.74, respectively). Significant factors for depressive symptoms included family status, employment before retirement, homemaking, reading, aluminum utensil use, dietary restriction, and hypertension (regression coefficients: 3.09, -1.33, -1.62, -1.31, 0.96, -1.15, and 1.14, respectively).

CONCLUSION

These findings indicated that cognition was negatively associated with depression in patients with AD, and both were influenced by reading, aluminum utensil use, dietary restriction, and hypertension. Considering patient factors may help to slow the progression of dementia.

Metal ions influx is a double edged sword for the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a common form of dementia in aged people, which is defined by two pathological characteristics: β-amyloid protein (Aβ) deposition and tau hyperphosphorylation. Although the mechanisms of AD development are still being debated, a series of evidence supports the idea that metals, such as copper, iron, zinc, magnesium and aluminium, are involved in the pathogenesis of the disease. In particular, the processes of Aβ deposition in senile plaques (SP) and the inclusion of phosphorylated tau in neurofibrillary tangles (NFTs) are markedly influenced by alterations in the homeostasis of the aforementioned metal ions. Moreover, the mechanisms of oxidative stress, synaptic plasticity, neurotoxicity, autophagy and apoptosis mediate the effects of metal ions-induced the aggregation state of Aβ and phosphorylated tau on AD development. More importantly, imbalance of these mechanisms finally caused cognitive decline in different experiment models. Collectively, reconstructing the signaling network that regulates AD progression by metal ions may provide novel insights for developing chelators specific for metal ions to combat AD.

Brain biometals and Alzheimer's disease - boon or bane?

Alzheimer's disease (AD) is the most common form of dementia. Several hypotheses have been put forward to explain the basis of disease onset and progression. A complicated array of molecular events has been implicated in the pathogenesis of AD. It is attributed to a variety of pathological conditions that share similar critical processes, such as oxidative stress, proteinaceous aggregations, mitochondrial dysfunctions and energy failure. There is increasing evidence suggesting that metal homeostasis is dysregulated in the pathology of AD. Biometals play an important role in the normal body functioning but AD may be mediated or triggered by disproportion of metal ions leading to changes in critical biological systems and initiating a cascade of events finally leading to neurodegeneration and cell death. The link is multifactorial, and although the source of the shift in oxidative homeostasis is still unclear, current evidence points to changes in the balance of redox transition metals, especially iron, copper (Cu) and other trace metals. Their levels in the brain are found to be elevated in AD. In other neurodegenerative disorders, Cu, zinc, aluminum and manganese are involved. This paper is a review of recent advances of the role of metals in the pathogenesis and pathophysiology of AD and related neurodegenerative diseases.

Ibuprofen targets neuronal pentraxins expresion and improves cognitive function in mouse model of AlCl3-induced neurotoxicity

Aluminum is known to exert neurotoxic effects associated with various neurodegenerative disorders, including Alzheimer's disease (AD). Ibuprofen is a well-known non-steroidal anti-inflammatory drug, which has demonstrated potential efficacy in the treatment of numerous inflammatory and neurodegenerative disorders, including AD. The present study aimed to investigate the protective effects of ibuprofen on cognitive function, and the expression levels of neuronal pentraxins (NPs) and interleukin (IL)-1β in an aluminum chloride (AlCl₃)-induced mouse model of neurotoxicity. The effects of ibuprofen (100 mg/kg/day for 12 days) on learning and memory were evaluated in the AlCl₃-induced neurotoxic mice using a Morris water maze and open field tests. In addition, ibuprofen was assessed for its effects on the expression levels of NPs and IL-1β in the hippocampus, cortex and amygdala of the brain. Treatment of the AlCl₃-treated mice with ibuprofen decreased anxiety levels (6.90±0.34 min) compared with the AlCl₃-treated group (1.80±0.29 min), as indicated by the time spent in the central area in an open field test. Furthermore, the expression levels of NP1 (1.32±0.47) and IL-1β (0.99±0.21) were significantly decreased in the hippocampus of mice following ibuprofen treatment, as compared with the AlCl₃-treated mice (8.62±1.54 and 7.47±0.53, respectively). In the present study, ibuprofen was able to target novel structures in order to attenuate the inflammation associated with an AlCl₃-induced mouse model of neurotoxicity; thus suggesting that ibuprofen may be considered a potential therapeutic option for the treatment of neurodegenerative diseases, including AD.