Th17-Related Cytokines Involved in Fluoride-Induced Cecal and Rectal Barrier Damage of Ovariectomized Rats.

To investigate fluoride (F)-induced intestine barrier damage and the role of estrogen deficiency in this progress, a rat model of estrogen deficiency was established through bilateral surgical removal of ovaries. The F exposure model was then continued by adding sodium fluoride (0, 25, 50, and 100 mg/L, calculated on a fluorine ion basis) to drinking water for 90 days. Afterward, intestinal mucosal structure, barrier function, and inflammatory cytokines were evaluated. The results showed that excessive F decreased the developmental parameters (crypt depth) of the cecum and rectum and inhibited the proliferation capacity of the intestinal epithelia, which are more obvious in the state of estrogen deficiency. The distribution of goblet cells and glycoproteins in the intestinal mucosa decreased with the increase in F concentration, and estrogen deficiency led to a further decline, especially in the rectum. Using the immunofluorescence method, the study showed that excessive F caused interleukin-17A (IL-17A) significantly decrease in the cecum and increase in the rectum. Meanwhile, F treatment remarkably upregulated the expression of intestinal IL-1ß, IL-23, and IL-22, while the level of IL-6 was downregulated. In addition, estrogen deficiency increased IL-1ß, IL-6, IL-23, and IL-22, but decreased IL-17A expression in the cecum and rectum. Collectively, F exposure damaged intestinal morphological structure, inhibited epithelial cell proliferation and mucus barrier function, and resulted in the disturbance of T helper (Th) 17 cell-related cytokines expression. Estrogen deficiency may further aggravate F-induced damage to the cecum and rectum.

Estrogen deficiency aggravates fluoride-induced small intestinal mucosa damage and junctional complexes proteins expression disorder in rats.

To investigate the effect of estrogen deficiency on the small intestinal mucosal barrier induced by fluoride (F), F exposure models of ovariectomy (OVX) rats (surgically removed ovaries) and non-OVX rats (normal condition) were established by adding sodium fluoride (NaF) (0, 25, 50, and 100 mg/L, calculated by F ion) in drinking water for 90 days. The intestinal mucosal histomorphology, mucosal barrier function, and protein expression levels of tight junctions (TJs), adhesion junctions (AJs), and desmosomes were evaluated in the duodenum, jejunum, and ileum. Hematoxylin-eosin (HE) staining and 5-Bromo-2-deoxyUridine (BrdU) measurement showed that excessive F-induced damage to intestinal epithelial cells and inhibited the proliferation of intestinal epithelial cells, eventually decreasing the number of goblet cells and decreasing glycoprotein secretion, as indicated by Alcian blue and periodic acid-Schiff (AB-PAS) and periodic acid-Schiff (PAS) staining. Further immunofluorescence analysis demonstrated that excessive F decreased the protein expression levels of occludin, zonula occludens-1 (ZO-1), E-cadherin, and desmoplakin (P < 0.05, P < 0.01) and enhanced the expression of claudin-2 (P < 0.01), suggesting that cell-to-cell junctions were disrupted. Collectively, F exposure impaired the small intestinal mucosal barrier by inducing damage to intestinal epithelial cells and inhibiting intestinal epithelial cell proliferation. Disorders in the junctional complex protein expression blocked the synergy between intercellular communication and aggravated mucosal injury. In particular, estrogen deficiency exacerbated F-induced enterotoxicity, which provides new explanations for the development and severity of intestinal disease in postmenopausal women with high-F areas.