ABSTRACT
Background Occupational aluminum exposure may associate with cognitive impairment in workers. At present, brain functional imaging data are not available for evaluating cognitive dysfunction in workers with occupational exposure to aluminum. The role of brain functional connectivity in cognitive decline associated with occupational aluminum exposure is not clear yet. Objective To explore potential mediating effect of brain functional connectivity value on cognitive decline induced by occupational aluminum exposure, to assess the relationship between cognitive impairment and brain functional connectivity, and to identify appropriate imaging evidence of early cognitive changes induced by occupational aluminum exposure. Methods This study used a subset data from a previous cross-sectional survey. Based on the data of aluminum-exposed workers, over 40 years old, aluminum-exposed working years >1 year, Montreal International Cognitive Assessment (MoCA) (Beijing version) score <26 points, 20 workers were selected as the case group, and 40 healthy workers with the same basic conditions (age, smoking, drinking, etc.) in non-aluminum production were selected as the control group with a 1∶2 matching ratio. The basic information of the subjects was collected, plasma aluminum level and cognitive function level were evaluated, and different brain functional connectivity values of default mode network (DMN) were measured by magnetic resonance imaging. The mediating effect analysis was conducted to examine the role of brain functional connectivity in the relationship between aluminum exposure and cognitive function. Results The plasma aluminum concentration of the case group was 1.76 times higher than that of the control group [(33.04±12.02) µg·L−1 vs (18.74±8.95) µg·L−1, P<0.05]; the MoCA score was 9.5 points lower [(18.35±2.64) vs (27.85±0.92), P<0.05]. The mean functional connection values of DMN1 and DMN2 in the case group were lower than those in the control group (P<0.05). The mean functional connection values of the left precuneus, left middle cingulate cortex, left superior medial gyrus, left precentral gyrus, and left cerebellum also decreased in the case group compared with the control group (P<0.05). Plasma aluminum concentration was negatively correlated with DMN1 functional connectivity value and MoCA scores (b=−0.004, 95%CI: −0.008–−0.001; b=−0.15, 95%CI: −0.233–−0.067; P<0.05). The mean functional connection values of DMN1 and DMN2 were positively correlated with MoCA scores (b=10.945, 95%CI: 5.574–16.316; b=10.107, 95%CI: 2.457–17.758; P<0.05). With the increase of plasma aluminum concentration, MoCA score decreased, but when the plasma aluminum concentration exceeded 19.50 µg·L−1, MoCA score decreased slowly. With the increase of the mean functional connectivity value of DMN1, MoCA score increased, but when the mean functional connectivity value of DMN1 exceeded 1.05 and continued to increase, the increase of MoCA score slowed down. The results of mediating effect analysis showed that the functional connectivity value of DMN1 partially mediated the relationship between plasma aluminum concentration and MoCA score, and the mediating effect was 25.80%. Conclusion Cognitive impairment in occupational aluminum-exposed workers is closely related to brain resting-state functional connectivity. There is a dose-response relationship of plasma aluminum concentration with DMN1 functional connectivity value and MoCA scores, and DMN1 functional connectivity value partially mediates the relationship between plasma aluminum concentration and MoCA scores. The brain functional connectivity value can be used as meaningful imaging data to study the cognitive decline induced by chronic aluminum exposure.
ABSTRACT
Background Occupational aluminum exposure is closely related to cognitive impairment, and alcohol consumption is also closely related to cognitive dysfunction. Objective To explore the effects of types of alcohol consumption on cognitive function of occupational aluminum exposed workers. Methods A total of 181 workers aged from 23 to 56 years were selected by cluster sampling method in an electrolytic aluminum workshop of an aluminum plant in a region and in a maintenance workshop of another plant in the same region from July to August, 2019. Venous blood was collected, and plasma aluminum concentration was determined by inductively coupled plasma mass spectrometry. The study subjects were divided into low and high exposure groups based on the median blood aluminum level and type of work. Their basic information was collected by occupational health examination. Workers' cognitive function was assessed using the Montreal Cognitive Assessment Scale-Beijing Edition. Logistic regression was used to analyze the association between plasma aluminum concentration and cognitive impairment, and between the types of alcohol consumption (including Baijiu, red wine, and beer) and cognitive impairment, Unconditional logistic regression was used to fit multiplicative interaction model as well as additive interaction model of plasma aluminum concentration and the types of alcohol consumption, and to calculate the relative excess relative risk due to interaction (RERI) and attributable proportion due to interaction (AP). Results The M (P25, P75) concentrations of plasma aluminum were 40.01 (25.05, 60.56) µg·L−1 in the total study subjects, 25.16 (17.13, 34.78) µg·L−1 in the low exposure group and 60.56 (47.40, 68.53) µg·L−1 in the high exposure group. After adjusting the type of alcohol consumption, drinking, age, duration of exposure to aluminum, education, marital status, and smoking, the odds ratios for impairments of attention, language expression, and overall cognitive function in the high exposure group were 4.295 (95%CI: 1.912-9.648), 5.687 (95%CI: 1.355-23.867), and 2.720 (95%CI: 1.225-6.040) times of the low exposure group respectively. Besides, after adjusting blood aluminum concentration, total alcohol consumption, age, duration of exposure to aluminum, education, marital status, and smoking, the risk of attention impairment of the Baijiu drinkers was 2.613 (95%CI: 1.054 to 6.837) times of the non-Baijiu drinkers; the risks of impairment of visuospatial abilities and execution functions, language expression, delayed recall, and overall cognitive function of the beer drinkers were 3.165 (95%CI: 1.285-7.797), 17.898 (95%CI: 1.590-201.480), 3.118 (95%CI: 1.215-8.003), and 3.824 (95%CI: 1.736-8.423) times of the non-beer drinkers. There were both additive [RERI (95%CI): 1.745 (1.394-2.097), AP (95%CI): 0.415 (0.201-0.630)] and multiplicative (OR=3.591, 95%CI: 1.393-9.255) interactions between Baijiu intake and plasma aluminum concentration levels on the attention domain. The cognitive impairment attributed to the interactive effects of drinking Baijiu and plasma aluminum concentration in individuals with attention impairment accounted for 41.5%. There were both additive [RERI (95%CI): 5.955 (0.562-11.328), AP (95%CI): 0.829 (0.577-1.081)] and multiplicative (OR=42.174, 95%CI: 5.469-325.252) interactions between beer drinking and plasma aluminum concentration on the overall cognitive function. Among the individuals with overall cognitive impairment, the cognitive impairment caused by the interaction of beer drinking and plasma aluminum concentration accounted for 82.9%. Conclusion Occupation aluminum exposed workers' attention, language expression, and overall cognitive function are closely related to their plasma aluminum concentration. Plasma aluminum concentrations have interactions with Baijiu and beer consumption on cognitive impairment of workers.