The Developmental Neuro-and Reproductive Toxicities Induced By Fluoride Exposure And Their Underlying Mechanisms

Part1Low glucose utilization and neurodegenerative changes caused by sodium fluoride exposure in rat’s developmental brainObjective:Fluorine, a toxic and reactive element, is widely prevalent throughout the environment and can induce toxicity when absorbed into the body. This study was to explore the possible mechanisms of developmental neurotoxicity in rats treated with different levels of sodium fluoride (NaF).Methods:Sprague-Dawley rats were administered with NaF at25,50and100mg/L via drinking water from pre-pregnancy (10days before mating) to gestation, birth and finally to post-puberty (Postnatal day56). The offspring’s learning and memory, as well as changes in neuronal morphology, glucose utilization, and functional genes expression within the brain were determined using the Morris water maze test, transmission electron microscopy (TEM), small-animal magnetic resonance imaging (MRI) and Positron emission tomography/computed tomography (PET/CT), and Western blotting techniques.Results:Fluoride treatment impaired learning and memory in offspring rats, as evidenced by increased latency time and total distance swam in the place navigation test, as well as decreased ratios (the time in the platform quadrant compared to the total time and the distance travelled in the platform quadrant compared to the total distance traveled) in the spatial probe test. In addition, MRI results showed an increase in the T2-weighted signal intensity in some areas of the lateral ventricle, suggestive of enlargement of the lateral ventricle. Also, PET/CT fusion imaging desmontrated lower glucose utilization with the standardized uptake values (SUV, fold of control) significantly reduced. Furthermore, TEM analysis revealed that fluoride caused neuronal degeneration and demyelination, together with apparent hippocampal CA1vacuolation. Functional genes analysis indicated that fluoride down-regulated the protein expression of glucose transporterl (GLUT1) and glial fibrillary acidic protein (GFAP), and up-regulated the level of brain-derived neurotrophic factor (BDNF) in both cerebral cortex and hippocampus of rat brains.Conclusions:The developmental neurotoxicity of fluoride may be closely associated with low glucose utilization and neurodegenerative changes. Part2Fluoride-elicited developmental testicular toxicity in rats:roles of endoplasmic reticulum stress and inflammatory responseObjective:Long-term excessive fluoride intake is known to be toxic and can damage a variety of organs and tissues in the human body. However, the molecular mechanisms underlying fluoride-induced male reproductive toxicity are not well understood. In this study, we used a rat model to simulate the situations of human exposure and aimed to evaluate the roles of endoplasmic reticulum (ER) stress and inflammatory response in fluoride-induced testicular injury.Methods:Sprague-Dawley rats were administered with sodium fluoride (NaF) at25,50and100mg/L via drinking water from pre-pregnancy (10days before mating) to gestation, birth and finally to post-puberty (postnatal day56). And then the testes of male offspring were collected, one part of the testis was used for histopathological and immunohistochemical analysis or Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, another part was applied for ultrastructural analysis, while the left testis was used for RNA isolation and protein extraction to determine the expression of markers for ER stress and unfolded protein response, as well as imflammatory response.Results:Our results demonstrated that fluoride treatment increased MDA accumulation, decreased SOD activity, and enhanced germ cell apoptosis. In addition, fluoride elevated mRNA and protein levels of glucose-regulated protein78(GRP78), inositol requiring ER-to-nucleus signal kinase1(IRE1), and C/EBP homologous protein (CHOP), indicating activation of ER stress signaling. Furthermore, fluoride also induced testicular inflammation, as manifested by gene up-regulation of tumor necrosis factor-a (TNF-a), interleukin-1β (IL-1β), inducible nitric oxide synthase (iNOS), cyclooxygenase-2(COX-2) and, in a nuclear factor-κB (NF-κB)-dependent manner. These were associated with marked histopathological lesions including injury of spermatogonia, decrease of spermatocytes and absence of elongated spermatids, as well as severe ultrastructural abnormalities in testes.Conclusions:Our results provide compelling evidence that ER stress and inflammation would be novel and significant mechanisms responsible for fluoride-induced disturbance of spermatogenesis and germ cell loss in addition to oxidative stress.