The hepatoprotective effect of sodium butyrate on hepatic inflammatory injury mediated by the NLRP3 inflammatory pathway in subchronic fluoride-exposed mice

Excessive subchronic fluoride exposure can cause severe damage to detoxification organs, including the liver. Sodium butyrate has anti-inflammatory, antitumor, antioxidant and immunomodulatory properties. However, relatively few studies have investigated the effects of sodium butyrate on liver injury caused by subchronic fluoride exposure. The purpose of this research was to investigate the effect and mechanism of sodium butyrate on fluoride-induced hepatic inflammatory injury via the expression of nod-like receptor protein 3 (NLRP3).

Mice were subjected to randomization into four groups, control group (C), fluorosis group (F), sodium butyrate alone group (S), and treatment group (Y). The mice in groups F and F + S drank 100 mg/L sodium fluoride-containing distilled water freely every day. After fluoride exposure lasted for 3 months, the mice in group S and F + S were gavaged with sodium butyrate daily at a concentration of 1000 mg/kg. Following the treatment regimen, liver specimens were collected for analysis. The mRNA and protein expression levels of inflammatory factors and NLRP3 and its downstream gene were measured by RT-qPCR and western blotting.

The histological hematoxylin and eosin (H&E) staining of liver showed that the subchronic fluoride-exposed group were chronic inflammation. The liver of treatment group were less vacuolar degeneration and inflammatory infiltration. The results of the biochemical assay showed that the subchronic fluoride-exposed group were liver injury. In addition, the detection of oxidative stress indicators showed that chronic subchronic fluoride exposure could lead to an increase in the level of oxidative stress in the liver, and the treatment alleviated this increase. RT-qPCR results showed that compared with those in the control group, the mRNA levels of the inflammatory factors TNF-α, IL-6 and IL-1β, the NLRP3 inflammasome and its downstream factors NLRP3, caspase-1, gasdermin D (GSDMD) and IL-18 increased in the liver tissue of mice in the subchronic fluoride-exposed group. Sodium butyrate released inflammatory factors during subchronic fluoride exposure and inhibited the protein expression of activated NLRP3 to a certain extent.

Sodium butyrate may play a protective role by antagonizing the production of activated inflammasomes and their downstream inflammatory factors in the livers of subchronic fluoride-exposed mice.