Background Lead (Pb) is an ubiquitous toxic pollutant in the environment, and studies have shown that Pb exposure induces microglia activation, causing neurological damage and increasing the risk of neurodegenerative diseases such as Alzheimer's disease. Microglia activation is regulated by nucleotide-binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome, but how to effectively inhibit NLRP3 inflammasome activation and prevent neuroinflammation is still unclear.

Objective To investigate whether epigallocatechin gallate (EGCG) can inhibit Pb-induced neuroinflammation mediated by NLRP3 inflammasome.

Methods A mouse model of lead acetate drinking exposure was established, and the mice were divided into 4 groups: control (Con), EGCG, Pb, and EGCG+Pb, with 18 mice in each group. The Pb group and the EGCG+Pb group were given 0.2% lead acetate drinking water, while the Con group and the EGCG group were given normal drinking water. The EGCG group and the EGCG+Pb group were given EGCG via gavage, three times a week for a month. The other groups were given saline via gavage under the same conditions. The lead acetate exposure and EGCG gavage intervention were conducted simultaneously. Blood lead levels were measured by graphite atomic absorption spectroscopy. Learning and memory of the mice were tested using Morris water maze, novel object recognition test, and fear conditioning box. Neuronal damage was observed using Western blot, immunofluorescence staining, and Golgi staining. The morphological changes of microglia activation were observed after immunofluorescence staining. The expression levels of inflammatory factors such as interleukin (IL)-1β, IL-18, tumor necrosis factor-α (TNF-α), and inducible nitric oxide synthase (iNOS), as well as NLRP3 inflammasome-related molecules such as NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC), and Caspase-1, were detected by PCR and Western blot to observe the effects of Pb exposure on microglia activation and NLRP3 inflammasome activation. The above indicators were re-examined after the EGCG gavage intervention to investigate the role of EGCG intervention in activating NLRP3 inflammasome and the development of neuroinflammation.

Results Compared to the Con group, the blood lead level increased in the Pb group (P < 0.05). In the Morris water maze, the platform quadrant dwelling time was shorter and the crossing times were reduced in the Pb group (P < 0.05). In the novel object recognition experiment, the discrimination index (DI) and recognition index (RI) of the Pb group decreased (P < 0.05). In the fear conditioning box experiment, the immobility index of the Pb group decreased (P < 0.05). The Golgi staining results showed that the density of dendritic spines decreased in the Pb group (P < 0.001). The immunofluorescence results showed that the number of neuronal nuclei (NeuN)-positive neurons decreased in the Pb group, while the expression of Iba1 increased (P < 0.001), and the activated microglia exhibited larger cell bodies and more shorter neurites (P < 0.05). The PCR and Western blot results showed that the expression levels of NLRP3, ASC, Caspase-1, IL-1β, IL-18, TNF-α, and iNOS mRNA and protein increased in the cortical area of the mice exposed to Pb (P < 0.05). After the EGCG intervention, the number of platform crossings and platform quadrant dwelling time increased in the EGCG+Pb group compared to the Pb group, the DI, RI, and immobility index increased, the density of dendritic spines increased, the number of NeuN-positive neurons increased, and the expression of Iba1 decreased (P < 0.05); the morphological changes of microglia were alleviated, and the expression levels of inflammatory factors such as IL-1β, IL-18, TNF-α, and iNOS, as well as inflammasome-related molecules such as NLRP3, ASC, and Caspase-1 mRNA and protein were all decreased (P < 0.05).

Conclusion Pb exposure can induce the activation of NLRP3 inflammasome and microglia, causing neuroinflammation and neuronal damage, leading to impairment of mouse's learning and memory ability. To some extent, EGCG intervention can inhibit the activation of NLRP3 inflammasome and the inflammatory response caused by the activation of microglia, thereby providing protection against neuronal damage and alleviating the impairment of learning and memory function caused by Pb exposure to some extent.