In vivo influence of sodium fluoride on sperm chemotaxis in male mice

Effects of fluoride toxicity on the male reproductive system: A review

BACKGROUND

Fluoride toxicity and fluorosis is an emerging global problem. Fluoride has long been added to water for dental caries prevention; however, it has a variety of damaging consequences on human bodies. The aim of this paper is to analyse all the literature available on the effects of fluoride toxicity on male reproductive system.

METHODS

Research papers were collected using various methods of data collection like Pubmed, Scopus, and Google Scholar from 1980 to 2024, and then reviewed thoroughly.

RESULTS

Fluoride is known to cause various histopathological and biochemical alterations in the male reproductive system. It also affects fertility, semen quality, sperm number and quality,the process of spermatogenesis and spermiogenesis. Key changes caused by fluoride in male reproductive system include structural defects in the flagellum, acrosome, and nucleus of spermatids and epididymal spermatozoa. Degenerative changes in Leydig cells result in reduced testosterone production, causing regression of seminiferous tubules and structural damage to the epididymis, ultimately terminating spermatogenesis which leads to infertility. Decrease in levels of testosterone and activities of various antioxidant enzymes resulting in greater oxidative stress was also seen.

CONCLUSIONS

Fluoride has various detrimental effects on male reproductive system and overall reproductive health. This type of study is important for understanding the effects of fluoride toxicity so that health officials can guide public about safe fluoride exposure limits and the damages it can cause in higher concentrations. Studies using various natural and synthetic ameliorative substances mentioned in the text later can prove to be helpful for development of various therapeutic approaches to mitigate the effects of fluoride toxicity.

Effect of fluoride-induced testicular alteration in rats fed a high-fat diet

Previous research on the well-known environmental pollutant fluoride has demonstrated that fluoride exposure can lead to oxidative stress-related male infertility. Obesity is another public health issue that has a detrimental impact on male fertility. Previously, findings on fluoride toxicity in high-fat diet (HFD) conditions associated with oxidative stress have been evidenced. This study aimed to evaluate the impact of subchronic fluoride exposure (5 mg/kg) plus a HFD on testicular alteration in Wistar rats. Animals were divided into four groups (control, HFD, fluoride, and fluoride 5 mg/kg plus HFD). The HFD contained a 50% kcal increase in fat (saturated fat), after 90 days of co-exposure to fluoride plus HFD, the animals showed a significant decrease in the adiposity index. The co-exposed group showed oxidative damage assessed through decreased glutathione (GSH) concentration (p < 0.0001), increased concentrations of malondialdehyde (MDA) (p < 0.0001), and the oxidation of proteins (p < 0.0001) vs the control group. Finally, testicular histology exhibited a reduction in spermatogonia and spermatocytes. The results of the study indicate that under these conditions, subchronic co-exposure to fluoride under HFD conditions could protect against the accumulation of epididymal fat, however, oxidative alteration at the testicular level is maintained.

Microfluidics as an emerging paradigm for assisted reproductive technology: A sperm separation perspective

Millions of people are subject to infertility worldwide and one in every six people, regardless of gender, experiences infertility at some period in their life, according to the World Health Organization. Assisted reproductive technologies are defined as a set of procedures that can address the infertility issue among couples, culminating in the alleviation of the condition. However, the costly conventional procedures of assisted reproduction and the inherent vagaries of the processes involved represent a setback for its successful implementation. Microfluidics, an emerging tool for processing low-volume samples, have recently started to play a role in infertility diagnosis and treatment. Given its host of benefits, including manipulating cells at the microscale, repeatability, automation, and superior biocompatibility, microfluidics have been adopted for various procedures in assisted reproduction, ranging from sperm sorting and analysis to more advanced processes such as IVF-on-a-chip. In this review, we try to adopt a more holistic approach and cover different uses of microfluidics for a variety of applications, specifically aimed at sperm separation and analysis. We present various sperm separation microfluidic techniques, categorized as natural and non-natural methods. A few of the recent developments in on-chip fertilization are also discussed.

Exposure to Fluoride From in Utero to Puberty Alters Gonadal Structure and Steroid Hormone Expression in Offspring Rats

The reproductive toxicity of fluoride has been proven by a large number of studies. While the underlying mechanism of reproductive toxicity during pregnancy is still unclear. Hence, in this study, we investigated the effects of fluoride exposure on ovarian and testicular steroid hormone synthesis in young and adult rat offspring. We established a model of fluoride-exposed rat pups from in utero to puberty to explore the mechanisms of fluoride impacts on reproductive toxicity in the offspring. The results showed that NaF exposure did not affect the 3 weeks of age offspring. Whereas the body weight in both sexes significantly decreased, and the ovarian and testicular tissue structures were damaged at 11 weeks of age. In females, the total number of secondary follicles and mature follicles were significantly reduced after NaF exposure. Moreover, estradiol (E2) and follicle-stimulating hormone (FSH) levels in the females were significantly reduced in the 100 mg/L NaF exposure group. In males, the sperm viability and testosterone (T) were significantly decreased in the NaF exposure groups. Additionally, during steroidogenesis in ovaries and testes, fluoride remarkably decreased the expression levels of genes and proteins, including acute regulatory protein (StAR), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17a-hydroxylase (CYP17A1), and cholesterol side-chain cleavage enzyme (CYP11A1), while the mRNA levels of 17β-hydroxysteroid dehydrogenase (17β-HSD) decreased only in the testes. These results indicated that fluoride exposure disrupted the steroid hormone balance by changing several important steroidogenic-related genes associated with the development of the gonads, and damage the normal structure of the gonads in rat offspring.

Alleviating effects of selenium on fluoride-induced testosterone synthesis disorder and reproduction toxicity in rats

Fluoride (F) exists widely in food, water and other natural resources, and can cause damage to the reproductive system of human and animals. Studies have shown that selenium (Se) is a necessary trace element to maintain the normal male reproductive system. However, it is not clear whether it can alleviate the damage of reproductive system induced by F. Hence, sodium fluoride (NaF) was administered singly in drinking water at 100 mg L^-1 alone and co-administered by drinking with sodium selenite (Na₂SeO₃) at 0.5, 1.0, 2.0 mg L^-1 for 10 consecutive weeks. The results demonstrated that the sperm deformity rate were increased significantly by F, however, it was improved significantly after the addition of 2.0 mg L^-1 Na₂SeO₃. The contents of glutathione peroxidase 4 (GPX-4), selenoprotein P (SePP), pregnenolone (PREG), androstenedione (ASD), and testosterone (T) were reduced obviously in the F group, however, it was increased significantly after adding 0.5, 1.0 and 2.0 mg L^-1 Na₂SeO₃. F decreased noticeably the mRNA and protein expression levels of steroidogenic acute regulatory protein (StAR), cytochrome P450 cholesterol side chain lyase (P450scc), 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17α-hydroxylase (P450c17) and 17β-hydroxysteroid dehydrogenase (17β-HSD), which was increased obviously after the addition of 1.0 and 2.0 mg L^-1 Na₂SeO₃. In summary, 2.0 mg L^-1 Na₂SeO₃ can alleviate testosterone synthesis disorder induced by F via reducing oxidative stress, increasing the level of selenoprotein in testis and regulating the content of related hormones and enzyme activity during testosterone synthesis pathway.

A systematic review on fluoride-induced epigenetic toxicity in mammals

Fluoride, one of the global groundwater contaminants, is ubiquitous in our day-to-day life from various natural and anthropogenic sources. Numerous in vitro, in vivo, and epidemiological studies are conducted to understand the effect of fluoride on biological systems. A low concentration of fluoride is reported to increase oral health, whereas chronic exposure to higher concentrations causes fluoride toxicity (fluorosis). It includes dental fluorosis, skeletal fluorosis, and fluoride toxicity in soft tissues. The mechanism of fluoride toxicity has been reviewed extensively. However, epigenetic regulation in fluoride toxicity has not been reviewed. This systematic review summarizes the current knowledge regarding fluoride-induced epigenetic toxicity in the in vitro, in vivo, and epidemiological studies in mammalian systems. We examined four databases for the association between epigenetics and fluoride exposure. Out of 932 articles (as of 31 March 2022), 39 met our inclusion criteria. Most of the studies focused on different genes, and overall, preliminary evidence for epigenetic regulation of fluoride toxicity was identified. We further highlight the need for epigenome studies rather than candidate genes and provide recommendations for future research. Our results indicate a correlation between fluoride exposure and epigenetic processes. Further studies are warranted to elucidate and confirm the mechanism of epigenetic alterations mediated fluoride toxicity.

Repression of autophagy leads to acrosome biogenesis disruption caused by a sub-chronic oral administration of polystyrene nanoparticles

As a new widespread contaminant, nanoplastics (NPs) pose a potential risk to human health. Nevertheless, the adverse effects of NPs on the male reproductive system are poorly understood. In this study, we aimed to determine the effects of polystyrene nanoplastics (PS-NPs) (50 nm) on sperm quality, with a focus on the acrosome defects. After 35 days of intragastric administration, sperm quality was decreased and testicular structures were impaired in mice exposed to PS-NPs in both the medium (1.0 mg/kg) and high dose (10 mg/kg) groups. No significant changes were observed in the low dose (0.2 mg/kg) group. Meanwhile, acrosome parameters including acrosome integrity and acrosome reaction were decreased after the administration of PS-NPs. These findings were consistent with the disruption of acrosome biogenesis, as identified by the changed testicular ultrastructure. Additionally, the findings were further validated using seven marker genes (Gba2, Pick1, Gopc, Hrb, Zpbp1, Spaca1 and Dpy19l2) essential for acrosome formation, which showed that two of these genes (Gopc and Dpy19l2) were significantly down-regulated. Moreover, repressed autophagy was observed in the testes of PS-NPs-exposed mice based on autophagy-related protein expression. This phenomenon was further verified in GC-2spd cells treated with PS-NPs (50 μg/mL, 100 μg/mL, 200 μg/mL for 24 h). The potential role of autophagy in such acrosome defects was explored by using the autophagy inhibitor 3-methyladenine (3-MA), autophagy activator rapamycin or beclin-1 siRNA. The results showed that Golgi-associated vesicle disorganization was exacerbated with the 3-MA and beclin-1 siRNA pretreatments, but decreased with the rapamycin pretreatment, and the expression of GOPC and DPY19L2 was also altered. These results indicated that autophagy might be involved in the PS-NPs-induced acrosome lesions based on the regulation of two key acrosome-formation proteins, GOPC and DPY19L2. Altogether, our results will provide new insights into the PS-NPs-induced male reproductive impairment.

Chemical Aspects of Human and Environmental Overload with Fluorine

Over the last 100-120 years, due to the ever-increasing importance of fluorine-containing compounds in modern technology and daily life, the explosive development of the fluorochemical industry led to an enormous increase of emission of fluoride ions into the biosphere. This made it more and more important to understand the biological activities, metabolism, degradation, and possible environmental hazards of such substances. This comprehensive and critical review focuses on the effects of fluoride ions and organofluorine compounds (mainly pharmaceuticals and agrochemicals) on human health and the environment. To give a better overview, various connected topics are also discussed: reasons and trends of the advance of fluorine-containing pharmaceuticals and agrochemicals, metabolism of fluorinated drugs, withdrawn fluorinated drugs, natural sources of organic and inorganic fluorine compounds in the environment (including the biosphere), sources of fluoride intake, and finally biomarkers of fluoride exposure.

Changes in Gene and Protein Expression of Metalloproteinase-2 and -9 and Their Inhibitors TIMP2 and TIMP3 in Different Parts of Fluoride-Exposed Rat Brain

Fluoride (F) exposure decreases brain receptor activity and neurotransmitter production. A recent study has shown that chronic fluoride exposure during childhood can affect cognitive function and decrease intelligence quotient, but the mechanism of this phenomenon is still incomplete. Extracellular matrix (ECM) and its enzymes are one of the key players of neuroplasticity which is essential for cognitive function development. Changes in the structure and the functioning of synapses are caused, among others, by ECM enzymes. These enzymes, especially matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs), are involved in both physiological processes, such as learning or memory, and pathological processes like glia scare formation, brain tissue regeneration, brain-blood barrier damage and inflammation. Therefore, in this study, we examined the changes in gene and protein expression of MMP2, MMP9, TIMP2 and TIMP3 in the prefrontal cortex, hippocampus, striatum and cerebellum of rats (Wistar) exposed to relatively low F doses (50 mg/L in drinking water) during the pre- and neonatal period. We found that exposure to F during pre- and postnatal period causes a change in the mRNA and protein level of MMP2, MMP9, TIMP2 and TIMP3 in the prefrontal cortex, striatum, hippocampus and cerebellum. These changes may be associated with many disorders that are observed during F intoxication. MMPs/TIMPs imbalance may contribute to cognitive impairments. Moreover, our results suggest that a chronic inflammatory process and blood-brain barrier (BBB) damage occur in rats’ brains exposed to F.

Fluoride exposure alters the ultra-structure of sperm flagellum via reducing key protein expressions in testis

Excessive fluoride (F) ingestion via drinking water interfered with spermatogenesis and lowered sperm quality of human and animals. However, it is still unclear why the effects of fluoride on sperm quality focus on mostly sperm motility rather than sperm count. The objective of this study is to investigate the potential relationship between alteration in the structure and function of sperm flagellum and fluoride exposure in the environment. 40 male mice were allocated to four groups which were treated with 0, 25, 50, 100 mg/L NaF deionized water, respectively, for 8 weeks continuously. The testicular morphology, ultra-structure of fibrous sheath and axoneme of sperm flagellum, and eleven key function genes Akap3, Akap4, Dnah1, Eno4, Cfap43, Cfap44, Hydin, Spef2, Spag6, Spag16, and Cfap69 were examined by histology, transmission electron microscopy, and real-time PCR methods respectively. The results displayed that fluoride damaged the typical "9 + 2″ microtubule structure including fibrous sheathes and axoneme of sperm flagellum in testes of mice. Furthermore, the mRNA and protein expression levels of AKAP3 and AKAP4 related to fibrous sheathes formation, and CFAP43, CFAP44 and HYDIN in axoneme were down-regulated by fluoride exposure. Taken together, we revealed that fluoride altered the structures of the fibrous sheathes and axonemal in sperm flagellum via down-regulating the mRNA and protein expression levels of AKAP3, AKAP4, CFAP43, CFAP44, and HYDIN, which may be one of the reasons that fluoride lowered sperm quality and male reproductive function.

Fluoride Affects Dopamine Metabolism and Causes Changes in the Expression of Dopamine Receptors (D1R and D2R) in Chosen Brain Structures of Morphine-Dependent Rats

Disturbances caused by excess or shortages of certain elements can affect the cerebral reward system and may therefore modulate the processes associated with the development of dependence as was confirmed by behavioural studies on animals addicted to morphine. Earlier publications demonstrated and proved the neurodegenerative properties of both low and high doses of fluoride ions in animal experiments and in epidemiological and clinical studies. The aim of the experiments conducted in the course of the present study was to analyse the effect of pre- and postnatal exposure to 50 ppm F⁻ on the initiation/development of morphine dependence. For this purpose, the following were conducted: behavioural studies, the analysis of concentrations of dopamine and its metabolites, and the analyses of mRNA expression and dopamine receptor proteins D1 and D2 in the prefrontal cortex, striatum, hippocampus, and cerebellum of rats. In this study, it was observed for the first time that pre- and postnatal exposure to fluoride ions influenced the phenomenon of morphine dependence in a model expressing withdrawal symptoms. Behavioural, molecular, and neurochemical studies demonstrated that the degenerative changes caused by toxic activity of fluoride ions during the developmental period of the nervous system may impair the functioning of the dopaminergic pathway due to changes in dopamine concentration and in dopamine receptors. Moreover, the dopaminergic disturbances within the striatum and the cerebellum played a predominant role as both alterations of dopamine metabolism and profound alterations in striatal D1 and D2 receptors were discovered in these structures. The present study provides a new insight into a global problem showing direct associations between environmental factors and addictive disorders.

Flow-Free Microfluidic Device for Quantifying Chemotaxis in Spermatozoa

Current male fertility diagnosis tests focus on assessing the quality of semen samples by studying the concentration, total volume, and motility of spermatozoa. However, other characteristics such as the chemotactic ability of a spermatozoon might influence the chance of fertilization. Here we describe a simple, easy to fabricate and handle, flow-free microfluidic chip to test the chemotactic response of spermatozoa made out of a hybrid hydrogel (8% gelatin/1% agarose). A chemotaxis experiment with 1 μM progesterone was performed that significantly demonstrated that boar spermatozoa are attracted by a progesterone gradient.

Exposure of Fluoride with Streptozotocin-Induced Diabetes Aggravates Testicular Damage and Spermatozoa Parameters in Mice

Diabetes mellitus is the most common chronic disease worldwide that causes numerous complications, including male infertility. The prevalence of DM is 451 million people and estimated that would increase to 693 million in 2045. Fluorosis caused by drinking water contaminated with inorganic fluoride is a public health problem in many areas around the world. Previous studies have shown that fluoride exposure damages the male reproductive function. This study aimed to evaluate the fluoride sub-chronic exposure on the spermatozoa function in streptozotocin (STZ)-induced diabetic mice. After confirming diabetes by measuring blood glucose levels, the male mice received 45.2 ppm of fluoride added or deionized water. We evaluated several parameters in diabetic mice exposed to fluoride: standard quality analysis, the mitochondrial transmembrane potential (ψm), the caspase activity in spermatozoa, urinary fluoride excretion, and histological evaluation in the testes. After 60 days of fluoride-exposure, diabetic mice, significantly decreased sperm quality (motility, viability, and concentration). Spermatozoa from fluoride-exposure in diabetic mice presented a significant decrease in ψm and a significant increase in activity caspase 3/7. Urinary fluoride excretion was decreased in diabetic mice exposed to fluoride. Subchronic fluoride exposure of mice with STZ-induced diabetes aggravated testicular damage and the spermatozoa function.

Fluoride exposure arrests the acrosome formation during spermatogenesis via down-regulated Zpbp1, Spaca1 and Dpy19l2 expression in rat testes

The exposure and health effects of fluoride are an ongoing topic that has attracted worldwide attention. Fluoride exposure disturbs the testicular development, sexual hormone levels and spermatogenesis. However, as to whether fluoride interferes with acrosome formation which is essential for production of capable spermatozoa during spermatogenesis still remains unclear. The objective was to determine the effects of fluoride on the acrosome formation and to further elucidate the potential mechanism of impaired reproductive function. For this, forty adult rats were assigned into four groups. The control group received distilled water, while the other three groups were treated with 25, 50 and 100 mg NaF/L via drinking water for 56 d, respectively. Testes were processed for total RNA extraction and western blot analysis. Three samples of each group were fixed in 2.5% glutaraldehyde solution for transmission electron microscopy analysis. From the results, we first found that fluoride decreased the expression of mRNA and protein levels of Zpbp1, Spaca1 and Dpy19l2 of seven markers during acrosome biogenesis in testes. Furthermore, fluoride damaged not only the acrosome structure, but also the structure of the nuclear lamina which was observed to be discontinuous and partially missing by transmission electron microscopy. Moreover, the results indicated that the altered structure in nuclear lamina maybe due to reduced LMNB2 expression in testis induced by fluoride. In a nutshell, fluoride exposure could restrain acrosome biogenesis during spermatogenesis and contribute to the elucidation of the underlying mechanisms of fluoride-induced male reproductive toxicity.

Trends of SHBG and ABP levels in male farmers: Influences of environmental fluoride exposure and ESR alpha gene polymorphisms

A number of epidemiological studies have reported that chronic exposure to high concentrations of fluoride not only causes dental and skeletal fluorosis but additionally affects serum levels of reproductive hormones. However, possible interaction between fluoride exposure and estrogen receptor alpha (ESRα) gene polymorphisms on sex hormone-binding globulin (SHBG) and androgen binding protein (ABP) of male farmers has not been detailed. Here, we conducted a cross-sectional study including 348 male farmers with different fluoride exposure levels from drinking water in Henan province of China to explore effects of fluoride exposure and ESRα genetic variation on serum SHBG and ABP levels. We found serum SHBG levels in male farmers from the high exposure group to be lower than those of the low exposure group. We also found that concentrations of SHBG affected ABP levels. Furthermore, fluoride exposure and single nucleotide polymorphisms at the XbaI and rs3798577 loci of the ESRα gene affected serum ABP levels. Our findings suggest that chronic fluoride exposure from drinking water is associated with alterations of serum SHBG and ABP concentrations in local male farmers and that the effect of fluoride exposure on ABP levels vary depending on ESRα gene polymorphisms.

Fluoride Interferes with the Sperm Fertilizing Ability via Downregulated SPAM1, ACR, and PRSS21 Expression in Rat Epididymis

Fluoride is a widespread environmental pollutant that can induce low sperm quality and fertilizing ability; however, the underlying mechanism still remains unclear. Hence, we aimed to investigate the influence of fluoride on the sperm fertilizing ability via some key proteins in the epididymis. For this, 40 adult rats were assigned randomly into four groups. The control group was given distilled water, while the other three groups were given 25, 50, and 100 mg of NaF/L via drinking water for 56 days, respectively. After 1 day, epididymides were processed for sperm-egg binding, RNA extraction, western blot, and immunofluorescence analysis. Fluoride exposure reduced the ability of sperm to break down the egg cumulus cell layer. A further study revealed that fluoride altered the expression levels of genes and proteins related to acrosome reaction in vivo, including SPAM1, ACR, and PRSS21. However, fluoride only affected the expression of the ACR protein only in the epididymis but not in the testis. Fluoride also affected the expression levels of the membrane proteins CD9 and CD81 of epididymosomes in the epididymis. From the results, it can be concluded that fluoride exposure reduced the ability of sperm to break down the egg cumulus cell layer, which could be one of the reasons for decreased fertility ability in males treated with fluoride. These results provide some theoretical guidance and new ideas for treatments of low fertility, infertility, and other reproductive diseases.

A hydrodynamic-stochastic model of chemotactic ciliated microorganisms

Biological systems like ciliated microorganisms are capable of responding to the external chemical gradients, a process known as chemotaxis. In this process, the internal signaling network of the microorganism is triggered due to binding of the chemoattractant molecules with the receptors on the surface of the body. This can alter the activity at the surface of the microorganism. We study the chemotaxis of ciliated microorganisms using the chiral squirmer model, a spherical body with a surface slip velocity. In the presence of a chemical gradient, the coefficients of the slip velocity get modified resulting in a change in the path followed by the body. We observe that the strength of the gradient is not the only parameter which controls the dynamics of the body but also the adaptation time plays a very significant role in the success of chemotaxis. The trajectory of the body is smooth if we ignore the discreteness in the ligand-receptor binding which is stochastic in nature. In the presence of the latter, the path is not only irregular but the whole dynamics of the body changes. We calculate the mean first passage time, by varying the strength of the chemical gradient and the adaptation time, to determine the success rate of chemotaxis.

Proteomic identification of sperm from mice exposed to sodium fluoride

Fluoride is a widespread environmental pollutant which can induce low sperm quality and fertilizing ability. However, effect of fluoride on proteomic changes of sperm is unknown. In this study, two-dimensional electrophoresis (2DE) and mass spectrometry (MS) were used to investigate the differently expressed proteins of sperm from mice exposed to fluoride. 180 male mice were randomly divided into three groups, and were administrated with the distilled water containing 0, 25, and 100 mg L^-1 NaF, respectively. After 45, 90 and 180 day's exposure, mice were sacrificed and sperm from the cauda epididymis and vas deferens were collected for 2DE. 16 differently expressed spots were picked up to identify using MS, 15 of which were successfully identified. Many of them are associated with the sperm function such as sperm motility, maturation, capacitation and acrosome reaction, lipid peroxidation, detoxification, inflammation, and stability of membrane structure. These results could contribute to the explanation and further research of mechanisms underlying sperm damage induced by fluoride.

Sodium fluoride exposure exerts toxic effects on porcine oocyte maturation

Excessive long-term fluoride intake is associated with several health problems, including infertility. However, limited information is available on the toxic effects of fluoride exposure on the female reproductive system, especially oocyte maturation. In this study, we investigated the toxic effect of sodium fluoride (NaF) exposure on porcine oocyte maturation and its possible underlying mechanisms. Our results showed that NaF exposure during porcine oocyte maturation inhibited cumulus cell expansion and impaired polar body extrusion. Cell cycle analysis showed that NaF exposure blocked meiotic resumption, disturbed spindle dynamics, disrupted chromosome separation, and increased aneuploidy in porcine oocytes. Moreover, NaF exposure disturbed mitochondrial function, triggered DNA damage response, and induced early apoptosis in porcine oocytes. NaF exposure also induced oxidative stress, decreased GSH level, and increased cathepsin B activity in and impaired the further development potential of porcine oocytes, as indicated by a decrease in blastocyst formation rate, increase in apoptosis, and inhibition of cell proliferation. Together, these results indicate that NaF exposure impairs the maturation capacity of porcine oocytes by inhibiting cumulus cell expansion, disturbing cytoskeletal dynamics, and blocking nuclear and cytoplasmic maturation, thus decreasing the quality and affecting the subsequent embryonic development potential of porcine oocytes.

Fluoride-Induced Autophagy via the Regulation of Phosphorylation of Mammalian Targets of Rapamycin in Mice Leydig Cells

Fluoride is known to impair testicular function and decrease testosterone levels, yet the underlying mechanisms remain inconclusive. The objective of this study is to investigate the roles of autophagy in fluoride-induced male reproductive toxicity using both in vivo and in vitro Leydig cell models. Using transmission electron microscopy and monodansylcadaverine staining, we observed increasing numbers of autophagosomes in testicular tissue, especially in Leydig cells of fluoride-exposed mice. Further study revealed that fluoride increased the levels of mRNA and protein expression of autophagy markers LC3, Beclin1, and Atg 5 in primary Leydig cells. Furthermore, fluoride inhibited the phosphorylation of mammalian targets of rapamycin and 4EBP1, which in turn resulted in a decrease in the levels of AKT and PI3K mRNA expression, as well as an elevation of the level of AMPK expression in both testes and primary Leydig cells. Additionally, fluoride exposure significantly changed the mRNA expression of the PDK1, TSC, and Atg13 regulator genes in primary Leydig cells but not in testicular cells. Taken together, our findings highlight the roles of autophagy in fluoride-induced testicular and Leydig cell damage and contribute to the elucidation of the underlying mechanisms of fluoride-induced male reproductive toxicity.

Fluoride exposure changed the structure and the expressions of HSP related genes in testes of pubertal rats

Previous studies have indicated that fluoride exposure damaged the male reproductive function; however, the cellular mechanism of fluoride-induced testicular toxicity is still unclear. In this study, twenty-two female pregnant Wistar rats were allotted randomly to two groups: control (deionized water) and sodium fluoride (NaF, contain F^-: 67.86 mg/L) groups. After delivery, the dosage was continued for 15 weeks for puppies. Twelve rats in each group were tested at 6 and 9 (pubertal); 12 and 15 (mature) weeks of age. Our results suggested that organ coefficient of epididymis was significantly decreased in the mature (12 and 15 week-old) rats. Epididymal sperm abnormality and femur fluoride concentration were increased with the concomitant decrease in sperm motility and concentration in these experimental periods. Compared to the control, in the NaF group, the seminiferous tubules of each age were reduced in terms of diameter and thickness. The sperm cells were lost and shedding and finally disappeared after 9 weeks. mRNA and protein levels of HSP27 and 90 were decreased with a concomitant increase in HSP70 and HSF mRNA and protein levels in NaF exposed rats. The mRNA and protein levels of HSP27 and HSF (only mRNA) were significantly increased in NaF treated rats at 9 and 15 weeks of age, respectively. In summary, these results emphasize that NaF induces testicular and sperm abnormalities through the involvement of HSPs especially during the pubertal period.

Alterations in epididymal proteomics and antioxidant activity of mice exposed to fluoride

It is well known that high fluoride results in low fertility. Epididymis is the important place for spermatozoa maturation, which is essential for successful fertilization. In the previous studies, fluoride was reported to damage the epididymal structure of mouse and rabbit. However, the mechanism underlying sodium fluoride (NaF)-induced epididymal toxicity has not yet been well elucidated. The aim of this study is to explore the global protein alterations in epididymis of mice exposed to NaF using the iTRAQ technique. Results showed that 211 proteins were differentially expressed in both 25 and 100 mg/L NaF groups. Some of them have been proved to be important for reproduction, such as low-density lipoprotein receptor-related protein 2 (Lrp2), cytochrome c, testis-specific (Cyct), sorbitol dehydrogenase (Sord), glutathione S-transferases (GSTs), acrosin, beta-defensin 126, cysteine-rich secretory protein (Crisp) 1, and Crisp2. Gene ontology (GO) analysis suggested cellular process, organelle and catalytic activity account for high percent and number of differentially expressed proteins. 171 pathways were found after the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, among which the representative maps, such as ribosome, focal adhesion, and phagosome, were involved. Different functional categories post-translational modification, protein turnover, chaperones; translation, ribosomal structure and biogenesis; cytoskeleton; energy production and conversion are implicated in the Cluster of Orthologous Groups (COG) of proteins analysis. Subsequently, the effect of NaF on the antioxidant activity in epididymis, especially glutathione and glutathione-related enzymes, was evaluated. Results exhibited high fluoride caused low total antioxidant capacity (T-AOC), high methane dicarboxylic aldehyde (MDA), decreased reduced glutathione (GSH), and the glutathione-related enzymes [GSH peroxidase (GPx), GSH reductase (GR), and GSH S-transferase (GST)] changes in activity, protein, and mRNA expressions. In summary, NaF decreased the antioxidant activity of epididymis, especially glutathione and glutathione-related enzymes, as well as iTRAQ results, providing new explanations for the low sperm quality induced by fluoride.

Taurine reverses sodium fluoride-mediated increase in inflammation, caspase-3 activity, and oxidative damage along the brain-pituitary-gonadal axis in male rats

Excessive exposure to fluoride is associated with male reproductive dysfunction in humans and animals. Taurine (2-aminoethane sulfonic acid) is a free intracellular β-amino acid with antioxidant, anti-inflammatory, and neuroprotective properties. However, the effect of taurine on fluoride-induced reproductive toxicity has not been reported. The present study investigated the influence of taurine on sodium fluoride (NaF)-induced functional changes along the brain-pituitary-gonadal axis in male rats. NaF was administered singly in drinking water at 15 mg·L^-1 alone or orally co-administered by gavage with taurine at 100 and 200 mg·(kg body mass)^-1 for 45 consecutive days. Results showed that taurine significantly prevented NaF-induced increase in oxidative stress indices as well as augmented antioxidant enzymes activities and glutathione level in the brain, testes, and epididymis of the treated rats. Moreover, taurine reversed NaF-induced elevation in inflammatory biomarkers and caspase-3 activity as well as histological damage in the brain, testes, and epididymis of the treated rats. The significant reversal of NaF-induced decreases in testosterone level and testicular activities of acid phosphatase, alkaline phosphatase, and lactate dehydrogenase by taurine was accompanied by enhancement of sperm functional characteristics in the treated rats. Taurine may be a possible chemopreventive candidate against reproductive dysfunction resulting from fluoride exposure.

Cell cycle arrest and gene expression profiling of testis in mice exposed to fluoride

Exposure to fluoride results in low reproductive capacity; however, the mechanism underlying the impact of fluoride on male productive system still remains obscure. To assess the potential toxicity in testis of mice administrated with fluoride, global genome microarray and real-time PCR were performed to detect and identify the altered transcriptions. The results revealed that 763 differentially expressed genes were identified, including 330 up-regulated and 433 down-regulated genes, which were involved in spermatogenesis, apoptosis, DNA damage, DNA replication, and cell differentiation. Twelve differential expressed genes were selected to confirm the microarray results using real-time PCR, and the result kept the same tendency with that of microarray. Furthermore, compared with the control group, more apoptotic spermatogenic cells were observed in the fluoride group, and the spermatogonium were markedly increased in S phase and decreased in G2/M phase by fluoride. Our findings suggested global genome microarray provides an insight into the reproductive toxicity induced by fluoride, and several important biological clues for further investigations. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1558-1565, 2017.

Effects of Fluoride on Expression of P450, CREM and ACT Proteins in Rat Testes

Fluoride (F) is an essential trace element that humans and animals ingest from water, air, and fluoride-containing products; however, excessive fluoride absorption can damage a variety of organs and tissues, including the male reproductive system. Our previous studies found that fluoride exposure lowered sperm quality and interfered with spermatogenesis; however, the exact mechanism remained unclear. Proteins cytochrome P450 (P450), cAMP-responsive element modulator (CREM), and activator of CREM in testis (ACT) play the key roles in spermatogenesis and sperm motility. To investigate whether fluoride affects the expression of P450, CREM, and ACT, we used immunohistochemical techniques to determine expression levels of these proteins in testes of rats administered 100 mg NaF/L for 2 weeks via drinking water. The results showed that P450 expression was decreased while CREM and ACT expression was increased in the fluoride group, compared to the control. These data suggest that fluoride can impair male reproduction by affecting expression of P450, CREM, and ACT in the testes.

Choline supplementation alleviates fluoride-induced testicular toxicity by restoring the NGF and MEK expression in mice

Fluoride is known to cause male reproductive toxicity, and the elucidation of its underlying mechanisms is an ongoing research focus in reproductive toxicology and epidemiology. Choline, an essential nutrient, has been extensively studied for its benefits in nervous system yet was rarely discussed for its prospective effect in male reproductive system. This study aims to explore the potential protective role of choline against NaF-induced male reproductive toxicity via MAPK pathway. The male mice were administrated by 150mg/L NaF in drinking water, 5.75g/kg choline in diet, and their combination respectively from maternal gestation to postnatal 15weeks. The results showed that fluoride exposure reduced body weight growth, lowered sperm count and survival percentages, altered testicular histology, down-regulated the mRNA expressions of NGF, Ras, Raf, and MEK genes in testes, as well as significantly decreased the expressions of both NGF and phosphor-MEK proteins in testes. Examination of data from choline-treated mice revealed that choline supplementation ameliorated these fluoride-induced changes. Taken together, our findings suggest that choline supplementation alleviates fluoride-induced testicular toxicity by restoring the NGF and phosphor-MEK expression. The suitable dosage and supplementation periods of choline await further exploration.

Fluoride exposure changed the structure and the expressions of Y chromosome related genes in testes of mice

It is known that during spermatogenesis, pluripotent germ cells differentiate to become efficient delivery vehicles to the oocyte of paternal DNA, and the process is easily damaged by external poison. In this study, the effects of fluoride on the body weight, fluoride content in femur, testosterone levels in serum and testis, sperm quality, and the expressions of Y chromosome microdeletion genes and protein levels were examined in testes of Kunming male mice treated with different concentrations of 0, 25, 50, 100 mg/L of NaF in drinking water for 11 weeks, respectively. The results showed that compared with the control group, fluoride contents in three treatment groups were significantly increased and the structure of testes was seriously injured. The testosterone contents and the sperm count were decreased. Sperm malformation ratio was distinctly elevated. The expressions of Sly and HSF2 mRNA were markedly reduced in 100 mg/L NaF group and Ssty2 mRNA expression was dramatically decreased in 50 and 100 mg/L NaF groups. Meanwhile, the protein levels of Ssty2 and Sly were significantly reduced in 50 and 100 mg/L NaF groups and HSF2 protein levels were significantly decreased in 100 mg/L NaF group. These studies indicated that fluoride had toxic effects on male reproductive system by reducing the testosterone and sperm count, and increasing the sperm malformation ratio, supported by the damage of testicular structure, as a consequence of depressed HSF2 level, which resulted in the down-regulation of Ssty2 and Sly mRNA and protein.

Role of IL-17 Pathways in Immune Privilege: A RNA Deep Sequencing Analysis of the Mice Testis Exposure to Fluoride

We sequenced RNA transcripts from the testicles of healthy male mice, divided into a control group with distilled water and two experimental groups with 50 and 100 mg/l NaF in drinking water for 56 days. Bowtie/Tophat were used to align 50-bp paired-end reads into transcripts, Cufflinks to measure the relative abundance of each transcript and IPA to analyze RNA-Sequencing data. In the 100 mg/l NaF-treated group, four pathways related to IL-17, TGF-β and other cellular growth factor pathways were overexpressed. The mRNA expression of IL-17RA, IL-17RC, MAP2K1, MAP2K2, MAP2K3 and MAPKAPK2, monitored by qRT-PCR, increased remarkably in the 100 mg/L NaF group and coincided with the result of RNA-Sequencing. Fluoride exposure could disrupt spermatogenesis and testicles in male mice by influencing many signaling pathways and genes, which work on the immune signal transduction and cellular metabolism. The high expression of the IL-17 signal pathway was a response to the invasion of the testicular immune system due to extracellular fluoride. The PI3-kinase/AKT, MAPKs and the cytokines in TGF-β family were contributed to control the IL-17 pathway activation and maintain the immune privilege and spermatogenesis. All the findings provided new ideas for further molecular researches of fluorosis on the reproduction and immune response mechanism.

Altered miRNAs expression profiling in sperm of mice induced by fluoride

The reproductive toxicity of fluoride has become a major concern in the world. Fluoride can decrease the abilities of sperm capacitation, hyperactivation, chemotaxis, acrosome reaction and fertilization, but the studies on the responses of sperm small noncoding RNAs (sncRNAs), especially miRNAs, to fluoride exposure are lacking. miRNAs are demonstrated to influence sperm quality and male fertility by regulating gene expression at post-transcriptional levels or translational repression. The objective of this study is to analyze miRNA profiling in sperm of mice administrated with 25 and 100 mg L(-1) sodium fluoride (NaF) for 60 d using high-throughput sequencing technology. Along with reduced sperm concentration, survival, motility, and mitochondrial membrane potential, 31 differentially expressed known miRNAs were identified in fluoride groups, compared with the control group. 671 predicted target genes against the 16 altered miRNAs were mainly involved in protease inhibitor activity, apoptosis, ubiquitin mediated proteolysis, and signaling pathways of calcium, JAK-STAT, MAPK, p53, Wnt, which were proved to be directly related to sperm quality. These findings suggested that the altered sperm miRNAs could be potential biomarkers for fluoride reproductive toxicity.

Chronic fluoride exposure-induced testicular toxicity is associated with inflammatory response in mice

Previous studies have indicated that fluoride (F) can affect testicular toxicity in humans and rodents. However, the mechanism underlying F-induced testicular toxicity is not well understood. This study was conducted to evaluate the sperm quality, testicular histomorphology and inflammatory response in mice followed F exposure. Healthy male mice were randomly divided into four groups with sodium fluoride (NaF) at 0, 25, 50, 100 mg/L in the drinking water for 180 days. At the end of the exposure, significantly increased percentage of spermatozoa abnormality was found in mice exposed to 50 and 100 mg/L NaF. Disorganized spermatogenic cells, vacuoles in seminiferous tubules and loss and shedding of sperm cells were also observed in the NaF treated group. In addition, chronic F exposure increased testicular interleukin-17(IL-17), interleukin-17 receptor C (IL-17RC), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in transcriptional levels, as well as IL-17 and TNF-α levels in translational levels. Interestingly, we observed that F treated group elevated testicular inducible nitric oxide synthase (iNOS) mRNA level and nitric oxide (NO) concentration. Taken together, these results indicated that testicular inflammatory response could contribute to chronic F exposure induced testicular toxicity in mice.

Sodium fluoride and sulfur dioxide affected male reproduction by disturbing blood-testis barrier in mice

Fluoride and sulfur dioxide (SO2), two well-known environmental toxicants, have been implicated to have adverse effects on male reproductive health in humans and animals. The objective of this study to investigate if the BTB is one of the pathways that lead to reproductive toxicity of sodium fluoride and sulfur dioxide alone or in combination, in view of the key role of blood testis barrier (BTB) in testis. The results showed that a marked decrease in sperm quality, and altered morphology and ultrastructure of BTB in testis of mice exposure to fluoride (100 mg NaF/L in drinking water) or/and sulfur dioxide (28 mg SO2/m(3), 3 h/day). Meanwhile, the mRNA expression levels of some vital BTB-associated proteins, including occluding, claudin-11, ZO-1, Ncadherin, α-catenin, and connexin-43 were all strikingly reduced after NaF exposure, although only the reduction of DSG-2 was statistically significant in all treatment groups. Moreover, the proteins expressions also decreased significantly in claudin-11, N-cadherin, α-catenin, connexin-43 and desmoglein-2 in mice treated with fluoride and/or SO2. These changes in BTB structure and constitutive proteins may therefore be connected with the low sperm quality in these mice. The role of fluoride should deserves more attention in this process.

Excessive apoptosis and defective autophagy contribute to developmental testicular toxicity induced by fluoride

Fluoride, a ubiquitous environmental contaminant, is known to impair testicular functions and fertility; however the underlying mechanisms remain obscure. In this study, we used a rat model to mimic human exposure and sought to investigate the roles of apoptosis and autophagy in testicular toxicity of fluoride. Sprague-Dawley rats were developmentally exposed to 25, 50, or 100 mg/L sodium fluoride (NaF) via drinking water from pre-pregnancy to post-puberty, and then the testes of offspring were excised on postnatal day 56. Our results demonstrated that developmental NaF exposure induced an enhanced testicular apoptosis, as manifested by a series of hallmarks such as caspase-3 activation, chromatin condensation and DNA fragmentation. Further study revealed that fluoride exposure elicited significant elevations in the levels of cell surface death receptor Fas with a parallel increase in cytoplasmic cytochrome c, indicating the involvement of both extrinsic and intrinsic apoptotic pathways. Intriguingly, fluoride treatment also simultaneously increased the number of autophagosomes and the levels of autophagy marker LC3-II but not Beclin1. Unexpectedly, the expression of p62, a substrate that is degraded by autophagy, was also significantly elevated, suggesting that the accumulated autophagosomes resulted from impaired autophagy degradation rather than increased formation. Importantly, these were associated with marked histopathological lesions including spermatogenic failure and germ cell loss, along with severe ultrastructural abnormalities in testes. Taken together, our findings provide deeper insights into roles of excessive apoptosis and defective autophagy in the aggravation of testicular damage, which could contribute to a better understanding of fluoride-induced male reproductive toxicity.

Effects of fluoride and aluminum on expressions of StAR and P450scc of related steroidogenesis in guinea pigs' testis

A lot of studies have shown that fluoride and aluminum have toxic effect on male reproductive system, but the mechanism of which and the interaction between fluoride and aluminum is still unknown. This study investigated the effects of fluoride (NaF) or/and aluminum (AlCl3) on serum testosterone level, gene and protein expression levels of Steroidogenic Acute Regulatory Protein (StAR) and Cytochrome P450 cholesterol side chain cleavage enzyme (P450scc) in the testes of guinea pigs. Fifty-two guinea pigs were divided randomly into four groups (Control, HiF, HiAl and HiF + HiAl). Fluoride (150 mg NaF/L) or/and aluminum (300 mg AlCl3/L) were orally administrated to male guinea pigs for 13 weeks. The results showed that F and Al reduced number and elevated abnormal ratio of sperm. Meanwhile, the concentrations of serum testosterone in all experimental groups were decreased. P450scc protein expression was significantly reduced in all treatment groups, and StAR expression was decreased remarkably in HiF group and HiF + HiAl group. The levels of StAR mRNA in three groups were reduced by 53.9%, 21.4% and 33.4%, respectively, while the expressions of P450scc mRNA were reduced by 67.8%, 17.0% and 47.8%. Therefore, we concluded that F induced the reduction in testosterone and sperm amount, and thus in lower fertility, which might occur as a consequence of depressed StAR and P450scc mRNA expression. There were no synergistic effects between F and Al, instead, Al weakened the toxicity of F to some extents. The results indicated that Al had antagonism effects on F.

Fluoride exposure changed the structure and the expressions of reproductive related genes in the hypothalamus-pituitary-testicular axis of male mice

Numerous studies have shown that fluoride exposure adversely affected the male reproductive function, while the molecular mechanism is not clear. The present study was to investigate the effects of fluoride exposure (60 days) on the expressions of reproductive related genes, serum sex hormone levels and structures of the hypothalamus-pituitary-testicular axis (HPTA), which plays a vital role in regulating the spermatogenesis in male mice. In this study, 48 male mice were administrated with 0, 25, 50, and 100 mg/L NaF through drinking water. Results showed that the malformation ratio of sperm was significantly increased (P<0.05). At transcriptional level, the expression levels of follicle-stimulating hormone receptor (FSHR), luteinizing hormone receptor (LHR), inhibin alpha (INHα), inhibin beta-B (INHβB), and sex hormone binding globulin (SHBG) mRNA in testis were significantly decreased (P<0.05). Moreover, histological lesions in testis and ultrastructural alterations in hypothalamus, pituitary and testis were obvious. However, the same fluoride exposure did not lead to significant changes of related mRNA expressions in hypothalamus and pituitary (P>0.05). Also, there were no marked changes in serum hormones. Taken together, we conclude that the mechanism of HPTA dysfunction is mainly elucidated through affecting testes, and its effect on hypothalamus and pituitary was secondary at exposure for 60 days.

Long-Term Fluoride Release from Dental Resins Affects STRO-1+ Cell Behavior

Fluoride-releasing restorative dental materials can be beneficial to remineralize dentin and help prevent secondary caries. However, the effects of fluoride release from dental materials on the activity of dental pulp stem cells are not known. Here we investigate whether different fluoride release kinetics from dental resins supplemented with modified hydrotalcite (RK-F10) or fluoride-glass filler (RK-FG10) could influence the behavior of a human dental pulp stem cell subpopulation (STRO-1(+) cells) known for its ability to differentiate toward an odontoblast-like phenotype. The 2 resins, characterized by similar physicochemical properties and fluoride content, exhibited different long-term fluoride release kinetics. Our data demonstrate that long-term exposure of STRO-1(+) cells to a continuous release of a low amount of fluoride by RK-F10 increases their migratory response to transforming growth factor β1 (TGF-β1) and stromal cell-derived factor 1 (SDF-1), both important promoters of pulp stem cell recruitment. Moreover, the expression patterns of dentin sialoprotein (dspp), dentin matrix protein 1 (dmp1), osteocalcin (ocn), and matrix extracellular phosphoglycoprotein (mepe) indicate a complete odontoblast-like cell differentiation only when STRO-1(+) cells were cultured on RK-F10. On the contrary, RK-FG10, characterized by an initial fluoride release burst and reduced lifetime of the delivery, did not elicit any significant effect on both STRO-1(+) cell migration and differentiation. Taken together, our results highlight the importance of taking into account fluoride release kinetics in addition to fluoride concentration when designing new fluoride-restorative materials.

Effect of sodium fluoride on male mouse fertility

Sodium fluoride (NaF), an environmental pollutant, has been tested for its impact on fertility in several species of laboratory animals. A literature demonstrated that NaF adversely affects sperm motility, morphology, capacitation, and the acrosome reaction. However, the molecular mechanisms underlying these alterations have not yet been elucidated. Therefore, present study was designed to evaluate the regulatory pathways involved in the effect of NaF on sperm function and fertilization. In this in vitro study, mouse spermatozoa were incubated with a range of concentrations (2.5, 5, and 10 mm) of NaF for 90 min in media that support in vitro fertilization. Our results showed that NaF was associated with reduced intracellular ATP generation, motility, and motion kinematics. Likewise, short-term exposure of spermatozoa to NaF significantly reduced the intracellular calcium concentration, protein kinase-A activity, and tyrosine phosphorylation of sperm proteins, which were associated with a significant decrease in the rate of capacitation and the acrosome reaction. Finally, NaF significantly reduced the fertilization and blastocyst formation during early embryonic development. On the basis of these results, we propose that NaF reduces sperm motility, capacitation, and the acrosome reaction leading to poor fertilization and suppressed embryonic development.