Mediating role of brain functional connectivity in cognitive decline induced by occupational aluminum exposure in workers

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.