Testing the potential of sodium fluoride to affect spermatogenesis: a morphometric study

Intertubular morphometric and ultrastructural testes analyses in mdx mice

Duchenne Muscular Dystrophy (DMD) reproductive alterations and the influence of antioxidant treatments may aid in understanding morphometry testicular quantification. In this context, the aim of the present study was to characterize the intertubular compartment (ITC) morphometry of animal testes in mdx mice supplemented with ascorbic acid (AA). Sixteen mice were used, namely the C57BL/10 (non-dystrophic) and C57BL/10Mdx (dystrophic) lineages, distributed into the following groups: Control (C60), Dystrophic (D60), Control supplemented with AA (CS60), Dystrophic supplemented with AA (DS60). A total of 200 mg/kg of AA were administered to mice for 30 days. Subsequently, the testicles were collected, weighed, and fragmented. The obtained fragments were fixed in Karnovsky's solution (pH 7.2) and embedded in historesin for morphometric and transmission electron microscopy assessments. Leydig cells were hypertrophic in the D60 group, but was reverted by AA supplementation in the DS60 group. The DS60 group also exhibited increased intertubular volume compared to the CS60 group. The ultrastructural images identified multilamellar bodies in dystrophic animals (lipid storage) and telocyte cells (transport substances) in both control and dystrophic animals. Morphometric alterations were, therefore, noted in the intertubular compartment due to Duchenne muscular dystrophy (DMD), with AA administration capable of altering Leydig cells in this condition.

Vitamin C and E supplementation can ameliorate NaF mediated testicular and spermatozoal DNA damages in adult Wistar rats

OBJECTIVE

Present study was designed to explore the efficacy of vitamin C and E (VC&VE) against fluoride mediated testicular, epididymal and spermatozoal anomalies.

MATERIALS AND METHODS

Thirty two adult Wistar rats were divided into four groups. Group-I was control; Group-II received sodium fluoride (NaF) at 15 mg/kg/day dose; Group-III was provided with VC (200 mg/kg/day) and VE (400 mg/kg/day) plus NaF; Group-IV received only VC&VE. Structural integrity and oxidative stress markers (superoxide dismutase, catalase, malondialdehyde and protein carbonyl) of testis and epididymis were assessed. Spermatozoal parameters (count, motility, viability and hypo-osmotic swelling) were evaluated. Testicular functional maker enzymes (acid phosphatase, alkaline phosphatase and lactate dehydrogenase) were also assessed. Integrity of testicular and spermatozoal DNA were evaluated. Testicular fluoride content was measured.

RESULT

Fluoride induced structural changes and alterations of oxidative stress markers were observed in testis and epididymis. Spermatozoal potentials were altered and reduced activities of testicular functional marker enzymes were observed. Fluoride caused testicular and spermatozoal DNA damages. VC&VE supplementation resulted in protectionfrom all fluoride mediated alterations and helped in attenuating testicular fluoride accumulation.

CONCLUSION

Antioxidant properties of VC&VE ameliorated fluoride mediated reproductive damages but only supplementation did not exhibit any notable effect compared to control rats.

Glycine alleviates fluoride-induced oxidative stress, apoptosis and senescence in a porcine testicular Sertoli cell line

Glycine is a well-known free radical scavenger in the cellular antioxidant system that prevents oxidative damage and apoptosis. Excessive fluoride exposure is associated with multiple types of cellular damage in humans and animals. The objective of the present study was to investigate the protective effects of glycine on sodium fluoride (NaF) exposure and the possible underlying mechanisms in a porcine testicular Sertoli cell line model. Cellular viability and proliferation were examined following NaF exposure and glycine supplementation, and glycine dramatically ameliorated the decreases in NaF-induced porcine testicular Sertoli cell viability and proliferation. Further investigations revealed that glycine decreased NaF-induced intracellular reactive oxygen species production, DNA fragment accumulation and the apoptosis incidence in the porcine testicular Sertoli cell line; in addition, glycine improved mitochondrial function and ATP production. Notably, results of the SPiDER-β-Gal analysis suggested that glycine alleviated NaF-induced cellular senescence and downregulated P53, P21, HMGA2 and P16INK4a gene expression in the porcine testicular Sertoli cell line. Collectively, the beneficial effects of glycine alleviate NaF-induced oxidative stress, apoptosis and senescence, and together with our previous findings, support the hypothesis that glycine plays an important role in protecting against NaF exposure-induced impairments in the porcine testicular Sertoli cell line.

Fluoride induced testicular toxicities in adult Wistar rats

Fluoride is essential for the development of teeth and bone but its excessive exposure causes reprotoxic effects. We have studied the graded effects of different doses of sodium fluoride (NaF) on 24 adult Wistar rats which were randomly divided into four groups (n = 6). All the rats were given normal diet prepared in our laboratory. Control (group I) rats were received vehicle only and treated rats (group II, III, and IV) were administered NaF orally at 10, 15, and 20 mg/kg/d doses, respectively, for 30 consecutive days. Gravimetric index of testis was decreased significantly in group III and IV rats but such changes were not observed in the accessory reproductive organs. Marked alterations in number, motility, viability, and plasma membrane functional integrity of caudal spermatozoa were noted in most of the treated groups. Noticeable alterations in testicular histoarchitecture were observed in group III and IV rats. Graded Changes of testicular redox homeostasis were noted by assessment of enzymatic (superoxide dismutase [SOD], catalase, glutathione s-transferase [GST], and glutathione peroxidase [GPx]) and nonenzymatic (malondialdehyde [MDA] and protein carbonyl [PC]) markers. Changes of testicular functional markers (acid phosphatase [ACP], alkaline phosphatase [ALP], and lactate dehydrogenase (LDH) activity) were noted in group III and IV rats. DNA fragmentation assay proved the possibility of DNA damage caused by oxidative stress, as evidenced by prominent trailing pattern of fragmented testicular genomic DNA from group III and IV rats. The study concludes that fluoride-mediated oxidative stress not only impedes the structural and functional facets of testis but also results in testicular DNA damage.

Fluoride-induced testicular degeneration and sperm quality deteriorations: Salutary role of Cyperus esculentus tubers (tiger nut) extract in animal model

OBJECTIVE

Chronic exposure to fluoride causes tissue damage induced by oxidative imbalance, Cyperus esculentus (CE) possess anti-inflammatory and immunostimulatory properties. This study focused on Salutary role of Cyperus esculentus in sodium fluoride (NaF) induced testicular degeneration and sperm quality deteriorations.

METHODS

Sexually mature male Sprague-Dawley rats were randomly divided into four groups (n=6). Animals in control group received 2 mls of normal saline per day; CE group received 500mg/kg bw of CE; NaF group received 5mg/kg bw of NaF; NaF+CE group received 500mg/kg bw of CE (for 14 days pre-treatment) and NaF co-treatment till 56 days via gastric gavage. Parameters tested include: testicular histology, sperm parameters, sex hormone, fertility test, malondialdehyde (MDA), superoxide dismutase (SOD), reduced glutathione, glutathione peroxidase (GPX), catalase (CAT), testicular fluoride and testicular cholesterol.

RESULTS

Sodium fluoride significantly (p<.05) decrease testicular antioxidant (SOD, CAT, GSH and GPx), sperm quality, hormone profiles (TT, FSH, LH, estrogen levels), testicular cholesterol, morphometric parameters, Johnsen's Score and number of implantations in female rats with corresponding (p<.05) increase in oxidative stress makers and abnormal sperm morphology. Also depleted seminiferous epithelium and degenerate spermatogenic cells. Pretreatment with 500mg/kg bw of CE lowered NaF toxicity by significantly reducing the lipid peroxidation products, fluoride accumulation in the testis, histopathological changes of the testes and spermatozoa abnormalities and reverted observed NaF-induced inhibition in antioxidant parameters and weight of accessory sex organs.

CONCLUSIONS

Cyperus esculentus attenuated NaF-induced testicular injuries and protected the seminiferous epithelium, reduced oxidative stress and promoted spermatogenesis.

Toxicity of fluoride: critical evaluation of evidence for human developmental neurotoxicity in epidemiological studies, animal experiments and in vitro analyses

Recently, epidemiological studies have suggested that fluoride is a human developmental neurotoxicant that reduces measures of intelligence in children, placing it into the same category as toxic metals (lead, methylmercury, arsenic) and polychlorinated biphenyls. If true, this assessment would be highly relevant considering the widespread fluoridation of drinking water and the worldwide use of fluoride in oral hygiene products such as toothpaste. To gain a deeper understanding of these assertions, we reviewed the levels of human exposure, as well as results from animal experiments, particularly focusing on developmental toxicity, and the molecular mechanisms by which fluoride can cause adverse effects. Moreover, in vitro studies investigating fluoride in neuronal cells and precursor/stem cells were analyzed, and 23 epidemiological studies published since 2012 were considered. The results show that the margin of exposure (MoE) between no observed adverse effect levels (NOAELs) in animal studies and the current adequate intake (AI) of fluoride (50 µg/kg b.w./day) in humans ranges between 50 and 210, depending on the specific animal experiment used as reference. Even for unusually high fluoride exposure levels, an MoE of at least ten was obtained. Furthermore, concentrations of fluoride in human plasma are much lower than fluoride concentrations, causing effects in cell cultures. In contrast, 21 of 23 recent epidemiological studies report an association between high fluoride exposure and reduced intelligence. The discrepancy between experimental and epidemiological evidence may be reconciled with deficiencies inherent in most of these epidemiological studies on a putative association between fluoride and intelligence, especially with respect to adequate consideration of potential confounding factors, e.g., socioeconomic status, residence, breast feeding, low birth weight, maternal intelligence, and exposure to other neurotoxic chemicals. In conclusion, based on the totality of currently available scientific evidence, the present review does not support the presumption that fluoride should be assessed as a human developmental neurotoxicant at the current exposure levels in Europe.

Screening of Human Proteins for Fluoride and Aluminum Binding

Previous studies showed that prolonged exposure to fluoride (F-) and aluminum (Al3+) ions is associated with numerous diseases including neurological disorders. They don't have any known biological function. But they can bind with proteins that interact with ions similar to them. Such unwanted interactions affect the normal biological function of the target proteins, as well as their downstream protein-protein interactions. Several studies show the detrimental effects posed by them including Alzheimer's disease. However, their target proteins have never been reported. Here, we have screened for the human protein targets subjected to F- and Al3+ interactions by using data-driven prediction tools. We have identified 20 different proteins that directly bind with them (10 interact with fluoride and 10 with aluminum). In addition, protein-protein interaction has been explored to find the proteins that indirectly interact with F- and Al3+. We have found 86 indirect targets for F- and 90 for Al3+. Furthermore, 19 common protein targets have been identified, including proteins (9 out of 19) associated with neurodegenerative disorders. However, wet lab experiments are beyond our scopes to validate the binding networks. Additional studies must be warranted.

Fluoride Exposure Aggravates the Testicular Damage and Sperm Quality in Diabetic Mice: Protective Role of Ginseng and Banaba

Fluoride toxicity is known to pose infertility in fluoride-intoxicated animals as well as in people residing in fluoride endemic zones. The present study addresses the degree of impairments caused due to co-exposure of high fluoride toxicity in diabetic mice. Swiss mice, Mus musculus, were subjected to fluoride toxicity by providing fluoride-supplemented drinking water (600 ppm NaF) for a period of 30 days after the confirmation of streptozotocin-induced diabetes(STZ, 50 mg/kgbw). Consequently, aggravated hyperglycemia and tissue fluoride accumulation were witnessed in fluoride-intoxicated diabetic mice; later, these toxicated mice were treated with ginseng extract (GE) and banaba leaf extract, (BLE) at dose of 150 mg/kgbw/day alone and in combination for 15 and 30-day duration to check the efficacy of phytoextracts in reversing the toxicity. The spermatological indices studied, such as sperm density, motility, viability and morphology as well as the testicular biochemical parameters showed enhanced impairment in reproductive status of fluoride-intoxicated diabetic mice. Further, 15-days administration of GE and BLE in combination at a dose of 150 mg/kgbw/day was found to be beneficial in normalizing the alterations observed upon fluoride intoxication to diabetic mice. However, the correlates showed moderate association between blood glucose levels and the spermatological as well as biochemical indices wherein the tissue fluoride levels correlate least.

Does Fluoride Affect Serum Testosterone and Androgen Binding Protein with Age-Specificity? A Population-Based Cross-Sectional Study in Chinese Male Farmers

Many studies have demonstrated that exposure to excess fluoride was associated with a variety of diseases. Little is known about the variation of testosterone (T) levels caused by fluoride exposure. The aim of this study is to explore the association of fluoride exposure and age with serum T and androgen-binding protein (ABP) levels in male farmers. A cross-sectional study was conducted in a county of Henan Province, China, including high fluoride exposure from drinking water villages and control villages. Male farmers aged 18-55 years old who lived in these villages were recruited by cluster sampling and divided into a higher fluoride exposure group (HFG) and a lower fluoride exposure group (LFG) according to the level of urinary fluoride. Levels of T and ABP in serum were measured using chemiluminescence immunoassay (CLIA) and enzyme-linked immunosorbent assay (ELISA) respectively. Markedly lower T levels were observed in male farmers from the HFG than in those from the LFG (t = 2.496, P < 0.05). Furthermore, younger farmers, 18-29 and 30-39 years old, may be the most likely to have lower T levels when exposed to fluoride (P < 0.05). No significant differences were observed in serum ABP levels in all male farmers between the two groups with different fluoride exposure. These results supported that excess fluoride exposure decreased serum T levels of male farmers with age-specificity.

Correlation of chemical structure with reproductive and developmental toxicity as it relates to the use of the threshold of toxicological concern

In the absence of toxicological data on a chemical, the threshold of toxicological concern (TTC) approach provides a system to estimate a conservative exposure below which there is a low probability of risk for adverse health effects. The original toxicology dataset underlying the TTC was based on NOELs from repeat dose studies. Subsequently there have been several efforts to assess whether or not these limits are also protective for reproductive/developmental effects. This work expands the database of chemicals with reproductive and developmental data, presents these data in a comprehensive and transparent format and groups the chemicals according to the TTC "Cramer Class" rules. Distributions of NOAELs from each of these classes were used to assess whether the previously proposed TTC values based on repeat dose data are protective for reproductive/developmental toxicity endpoints as well. The present analysis indicates that, for each Cramer Class, the reproductive and developmental endpoints would be protected at the corresponding general TTC tiers derived by Munro et al. (1996).

Effect of duration of fluoride exposure on the reproductive system in male rabbits

BACKGROUND AND OBJECTIVES:

Fluorosis has become an endemic problem worldwide. Fluoride has its effect on various organs, including the reproductive system, although there are controversial reports over it. Thus, the present study was designed to study the effect of sodium fluoride (NaF) exposure for different durations.

MATERIALS AND METHODS:

30 healthy rabbits were divided into three equal groups. Group I was fed on a standard diet for 30 days, Group II was fed on sodium fluoride (20 mg/kg body weight) for 30 days and Group III was fed on sodium fluoride (20 mg/kg body weight) for 60 days. Sperm count, motility, progressive motility and weight of testis and epididymis were measured and compared with the control group.

RESULTS:

We observed that in the group exposed to NaF for 30 days (Group II), there was a significant decrease in all the parameters except the testicular weight and in the group on exposure of 60 days (Group III), there was a significant decrease in all the parameters when compared with the control group (Group I). On applying the Tukey post-hoc test between Groups II and III, we observed that there was a significant decrease in the sperm count while the other parameters showed a non-significant decrease. Testicular histology was confirmatory for the above findings.

CONCLUSION:

The present study demonstrates that fluoride hampers the reproductive functions of male rabbits and is proportional to the duration of fluoride exposure.

Effect of long-term fluoride exposure on lipid peroxidation and histology of testes in first- and second-generation rats

This experiment was designed to investigate the histological and lipid peroxidation effects of chronic fluorosis on testes tissues of first- and second-generation rats. Sixteen virgin female Wistar rats were mated with eight males (2:1) for approximately 12 h to obtain first-generation rats. Pregnant rats were divided into two groups: controls and fluoride-given group, each of which containing five rats. Pregnant rats in the fluoride-given group were exposed to a total dose of 30 mg/l sodium fluoride (NaF) in commercial drinking water containing 0.07 mg/l of NaF throughout the gestation and lactation periods. After the lactation period, the young animals (first generation, F1) were exposed to the same dose of NaF in drinking water for 4 months. At the end of the 4 months of experimental period, nine randomly chosen male rats (F1) were killed and testes tissues were taken for histopathological and biochemical analysis. The remaining eight female rats were mated with four males (2:1) for approximately 12 h to obtain second-generation rats. Six female were identified as pregnant and treated with similarly throughout the gestation and the lactation periods. After the lactation period, the young male animals (second generation, F2) were also treated in the same way for 4 months. At the end of the 4 months of experimental period, nine randomly chosen male rats (F2) were killed and testes tissues were collected for histopathological and biochemical analysis. The rats in the control group were applied the same procedure without NaF administration. In biochemical analysis of the fluoride given F1 and F2 rats, it has been found that plasma fluoride levels and testes thiobarbituric acid reactive substance levels were significantly increased when compared with the control group. In F1 and F2 rats, similar histopathological changes were observed. In both groups, spermatogenesis was severely reduced. Spermatogonia and primary spermatocytes were normal, however, there was a widespread degeneration in other spermatogenic cell lines of the seminiferous epithelium. The histological structures of the Sertoli and interstitial Leydig cells were normally observed. It is concluded that chronic fluorosis exposure leads to a remarkable destruction in testes tissues of F1 and F2 rats via lipid peroxidation.

Fluoride-induced disruption of reproductive hormones in men

Fluoride-induced reproductive effects have been reported in experimental models and in humans. However, these effects were found in heavily exposed scenarios. Therefore, in this work our objective was to study reproductive parameters in a population exposed to fluoride at doses of 3-27 mg/day (high-fluoride-exposed group-HFEG). Urinary fluoride levels, semen parameters, and reproductive hormones in serum (LH, FSH, estradiol, prolactin, inhibin-B, free and total testosterone) were measured. Results were compared with a group of individuals exposed to fluoride at lower doses: 2-13 mg/day (low-fluoride-exposed group-LFEG). A significant increase in FSH (P<0.05) and a reduction of inhibin-B, free testosterone, and prolactin in serum (P<0.05) were noticed in the HFEG. When HFEG was compared to LFEG, a decreased sensitivity was found in the FSH response to inhibin-B (P<0.05). A significant negative partial correlation was observed between urinary fluoride and serum levels of inhibin-B (r=-0.333, P=0.028) in LFEG. Furthermore, a significant partial correlation was observed between a chronic exposure index for fluoride and the serum concentrations of inhibin-B (r=-0.163, P=0.037) in HFEG. No abnormalities were found in the semen parameters studied in the present work, neither in the HFEG, nor in the LFEG. The results obtained indicate that a fluoride exposure of 3-27 mg/day induces a subclinical reproductive effect that can be explained by a fluoride-induced toxic effect in both Sertoli cells and gonadotrophs.

Developmental toxicity of sodium fluoride measured during multiple generations

Sodium fluoride (NaF) has been used to fluoridate drinking water in the United States since the mid 1940s. Because of the lack of reliable studies on the multigeneration effects of the compound, NaF (0, 25, 100, 175 or 250 ppm in drinking water) was given to rats continuously during three generations. Parental (F0) generation rats were treated for 10 weeks and mated within groups. At gestation day 20, caesarean sections were performed and eight F0 females per group and their litters (F1) were observed for implant status, fetal weight and length, sex and morphological development. The remaining F0 females (29-32 per group) were allowed to litter. F1 offspring (36 of each sex per group) were mated within groups, and caesarean sections were performed at gestation day 20. The F1 females and their litters (F2) were observed for implant status, fetal weight and length, sex and morphological development. In addition, F2 fetuses were evaluated for internal (soft-tissue) and skeletal development. Decreased fluid consumption for F0 and F1 dams at 175 and 250 ppm was attributed to decreased palatability of the solution. No dose-related effects in feed consumption or mean body weight gain were observed in either F0 or F1 females. Numbers of corpora lutea, implants, viable fetuses and fetal morphological development were similar in all groups. No dose-related anomalies in internal organs were observed in F2 fetuses. Ossification of the hyoid bone of F2 fetuses was significantly decreased at 250 ppm. Because of the decreased ossification of the hyoid bone, 250 ppm is considered the effect level.

Multigenerational evaluation of sodium fluoride in rats

Since the mid 1940s, fluoride has been added to tap water in American communities in an effort to reduce the incidence of dental caries in the population. When the levels of fluoride in drinking water were tested and set, water was the only measurable source of fluoride for most communities. Now, adults and children ingest fluoride with foods and beverages prepared with fluoridated water, and they are exposed to fluoride-containing dental products. As a result, exposure to fluoride is greater than had been anticipated. In the early 1990s, the existing reproductive studies were reviewed in several reports and were considered to be inadequate to determine potential reproductive or developmental hazards. The effects of sodium fluoride ingestion at 0, 25, 100, 175 or 250 ppm in drinking water measured in rats throughout three generations are reported here. Feed and fluid consumption, body weights and clinical signs were recorded at regular intervals. Decreased fluid consumption observed at 175 and 250 ppm was attributed to decreased palatability and did not affect reproduction. No cumulative effects were observed in the three generations. Mating, fertility and survival indices were not affected. Organ-to-body-weight ratios and organ-to-brain weight ratios were not affected. Sodium fluoride up to 250 ppm did not affect reproduction in rats.