Differential Expression of miRNAs in the Hippocampi of Offspring Rats Exposed to Fluorine Combined with Aluminum during the Embryonic Stage and into Adulthood

Mononuclear Aluminum-Fluoride Ions, AlFx(+/-)-Study of Plausible Frameworks of Complexes with Biomolecules and Their In Vitro Toxicity

The importance of fluorine and aluminum in all aspects of daily life has led to an enormous increase in human exposure to these elements in their various forms. It is therefore important to understand the routes of exposure and to investigate and understand the potential toxicity. Of particular concern are aluminum-fluoride complexes (AlFx), which are able to mimic the natural isostructural phosphate group and influence the activity of numerous essential phosphoryl transferases. Our review of salts of ionic AlFx species, which plausibly form the framework of complexes with biomolecules, revealed that the octahedral configuration of aluminum in the active site of the enzyme is preferred over the trigonal-bipyramidal structure. The effects of varying concentrations of fluoride, aluminum and AlFx-from micromolar to millimolar levels-on the viability and apoptosis rate of THP-1 monocytes were investigated using phosphate buffer solution as a culture media to simulate physiological conditions. Our results suggest that aluminum can reduce the direct toxicity of fluoride through the formation of AlFx. In view of the results found, further in vitro studies are required to clarify the toxicity mechanisms of these species.

MicroRNAs in fluorosis pathogenesis: impact on dental, skeletal, and soft tissues

Fluoride-induced toxicity (fluorosis) poses a significant health concern globally, affecting millions of individuals. Understanding the molecular mechanisms underlying fluorosis, particularly the role of microRNAs (miRNAs), is crucial for developing effective preventive and therapeutic strategies. This review explores the pivotal role of miRNAs in the pathogenesis of fluorosis, particularly examining its impact on both hard (skeletal and dental) and soft (brain, liver, kidney, heart, and reproductive organs) tissues. Skeletal fluorosis manifests as abnormal bone mineralization and structure, while dental fluorosis affects enamel formation. In vitro and in vivo studies suggest a significant involvement of miRNAs in the progression of these conditions. For skeletal fluorosis, miR-124, miR-155, and miR-200c-3p have been identified as key regulators, while miR-296-5p and miR-214-3p are implicated in dental fluorosis. Moreover, soft tissue fluorosis encompasses a spectrum of adverse effects on various organs, including the brain, liver, kidneys, heart, and reproductive system. In soft tissues, miRNAs, such as miR-124, miR-200c-3p, miR-132, and miR-34b-5p, have been linked to cellular damage and dysfunction. Notably, miRNAs exert their effects through the modulation of critical pathways involved in fluorosis pathology, including Wnt signaling, apoptosis, cell cycle, and autophagy. Understanding the regulatory roles of miRNAs in fluorosis pathogenesis holds promise for identifying biomarkers and therapeutic targets. However, further research is needed to elucidate the molecular mechanisms underlying miRNA-mediated responses to fluoride exposure. Integration of miRNA research into fluorosis studies could facilitate the development of diagnostic tools and therapeutic interventions, thus mitigating the detrimental effects of fluorosis on both hard and soft tissues.

Epigenetic Mechanisms of Aluminum-Induced Neurotoxicity and Alzheimer's Disease: A Focus on Non-Coding RNAs

Aluminum (Al) is known to induce neurotoxic effects, potentially contributing to Alzheimer's disease (AD) pathogenesis. Recent studies suggest that epigenetic modification may contribute to Al neurotoxicity, although the mechanisms are still debatable. Therefore, the objective of the present study was to summarize existing data on the involvement of epigenetic mechanisms in Al-induced neurotoxicity, especially AD-type pathology. Existing data demonstrate that Al exposure induces disruption in DNA methylation, histone modifications, and non-coding RNA expression in brains. Alterations in DNA methylation following Al exposure were shown to be mediated by changes in expression and activity of DNA methyltransferases (DNMTs) and ten-eleven translocation proteins (TETs). Al exposure was shown to reduce histone acetylation by up-regulating expression of histone deacetylases (HDACs) and impair histone methylation, ultimately contributing to down-regulation of brain-derived neurotrophic factor (BDNF) expression and activation of nuclear factor κB (NF-κB) signaling. Neurotoxic effects of Al exposure were also associated with aberrant expression of non-coding RNAs, especially microRNAs (miR). Al-induced patterns of miR expression were involved in development of AD-type pathology by increasing amyloid β (Aβ) production through up-regulation of Aβ precursor protein (APP) and β secretase (BACE1) expression (down-regulation of miR-29a/b, miR-101, miR-124, and Let-7c expression), increasing in neuroinflammation through NF-κB signaling (up-regulation of miR-9, miR-125b, miR-128, and 146a), as well as modulating other signaling pathways. Furthermore, reduced global DNA methylation, altered histone modification, and aberrant miRNA expression were associated with cognitive decline in Al-exposed subjects. However, further studies are required to evaluate the contribution of epigenetic mechanisms to Al-induced neurotoxicity and/or AD development.

Fluoride-Induced Mitochondrial Dysfunction and Approaches for Its Intervention

Fluoride is present everywhere in nature. The primary way that individuals are exposed to fluoride is by drinking water. It's interesting to note that while low fluoride levels are good for bone and tooth growth, prolonged fluoride exposure is bad for human health. Additionally, preclinical studies link oxidative stress, inflammation, and programmed cell death to fluoride toxicity. Moreover, mitochondria play a crucial role in the production of reactive oxygen species (ROS). On the other hand, little is known about fluoride's impact on mitophagy, biogenesis, and mitochondrial dynamics. These actions control the growth, composition, and organisation of mitochondria, and the purification of mitochondrial DNA helps to inhibit the production of reactive oxygen species and the release of cytochrome c, which enables cells to survive the effects of fluoride poisoning. In this review, we discuss the different pathways involved in mitochondrial toxicity and dysfunction induced by fluoride. For therapeutic approaches, we discussed different phytochemical and pharmacological agents which reduce the toxicity of fluoride via maintained by imbalanced cellular processes, mitochondrial dynamics, and scavenging the ROS.

The miR-34b-5p-negative target Gnai2 aggravates fluorine combined with aluminum-induced apoptosis of rat offspring hippocampal neurons and NG108-15 cells

It is known that fluorine and aluminum are commonly found in the environment and that long-term overexposure can adversely affect the organism's nervous system, damaging the structure and function of brain tissue. Our previous study showed that fluorine combined with aluminum (FA) could trigger apoptosis in vitro and cause spatial learning and memory impairment and differentially expressed miRNAs (including miR-34b-5p) in the hippocampi in vivo. However, the detailed mechanism is unclear. Learning memory damage is implicated in excessive hippocampal neuron apoptosis, and miR-34b-5p participates in regulating the hippocampal neuron apoptosis. Thus, in the current research, Sprague-Dawley (SD) rats were subjected to FA, and NG108-15 control cells and NG108-15 cells pretransfected with miR-34b-5p agomir or antagomir were exposed to FA. We found that FA triggered apoptosis of rat hippocampal neurons and NG108-15 cells, increased miR-34b-5p expression, and decreased Gnai2, PKA, ERK and CREB expression. Inhibition of miR-34b-5p alleviated FA-induced NG108-15 cell apoptosis and further increased Gnai2, PKA, ERK, and CREB expression, and vice versa. Furthermore, miR-34b-5p modulated the level of Gnai2 by directly targeting its 3'-untranslated region (UTR), as verified through the dual Luciferase reporter assay. These outcomes suggested that miR-34b-5p participated in FA-induced neuronal apoptosis by targeting Gnai2 negatively, thereby inhibiting the PKA/ERK/CREB signaling pathway.

Role of microRNA-34b-5p in cancer and injury: how does it work?

MicroRNAs (miRNAs or miRs) are a class of noncoding single-stranded RNAs that can regulate gene expression by binding to the untranslated sequences at the 3 ' end of messenger RNAs. The microRNA-34 family is dysregulated in various human diseases. It is considered as a tumor-suppressive microRNA because of its synergistic effect with the well-known tumor suppressor p53. As a member of the miRNA-34 family, miR-34b-5p serves as a powerful regulator of a suite of cellular activities, including cell growth, multiplication, development, differentiation, and apoptosis. It promotes or represses disease occurrence and progression by participating in some important signaling pathways. This review aimed to provide an overview and update on the differential expression and function of miR-34b-5p in pathophysiologic processes, especially cancer and injury. Additionally, miR-34b-5p-mediated clinical trials have indicated promising consequences for the therapies of carcinomatosis and injury. With the application of the first tumor-targeted microRNA drug based on miR-34a mimics, it can be inferred that miR-34b-5p may become a crucial factor in the therapy of various diseases. However, further studies on miR-34b-5p should shed light on its involvement in disease pathogenesis and treatment options.

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.

Effect of Fluoride on Cytotoxicity Involved in Mitochondrial Dysfunction: A Review of Mechanism

Fluoride is commonly found in the soil and water environment and may act as chronic poison. A large amount of fluoride deposition causes serious harm to the ecological environment and human health. Mitochondrial dysfunction is a shared feature of fluorosis, and numerous studies reported this phenomenon in different model systems. More and more evidence shows that the functions of mitochondria play an extremely influential role in the organs and tissues after fluorosis. Fluoride invades into cells and mainly damages mitochondria, resulting in decreased activity of mitochondrial related enzymes, weakening of protein expression, damage of respiratory chain, excessive fission, disturbance of fusion, disorder of calcium regulation, resulting in the decrease of intracellular ATP and the accumulation of Reactive oxygen species. At the same time, the decrease of mitochondrial membrane potential leads to the release of Cyt c, causing a series of caspase cascade reactions and resulting in apoptosis. This article mainly reviews the mechanism of cytotoxicity related to mitochondrial dysfunction after fluorosis. A series of mitochondrial dysfunction caused by fluorosis, such as mitochondrial dynamics, mitochondrial Reactive oxygen species, mitochondrial fission, mitochondrial respiratory chain, mitochondrial autophagy apoptosis, mitochondrial fusion disturbance, mitochondrial calcium regulation are emphasized, and the mechanism of the effect of fluoride on cytotoxicity related to mitochondrial dysfunction are further explored.

Association between fluoride exposure and behavioural outcomes of school-age children: a pilot study in China

To assess the association between fluoride exposure and children's behavioural outcomes, we recruited 325 resident school-age children (7-13 years old) lived in Tongxu County of Henan Province in China. We measured urinary fluoride (UF) concentrations using the ion-selective electrode method. Children's behavioural outcomes were assessed by Conners' Parent Rating Scale-Revised, including conduct problems, learning problems, psychosomatic problems, impulsive-hyperactive, anxiety, and ADHD index. It turned out that each 1.0 mg/L increment in UF concentration corresponded with an elevation in the psychosomatic problem score of 4.01 (95% CI: 2.74, 5.28) and a 97% (OR = 1.97, 95% CI: 1.19, 3.27) increase in the prevalence of psychosomatic problems after adjusting for potential influencing factors. The sensitivity analysis results were consistent with those observed in our preliminary analysis. Our study suggests that fluoride exposure is positively related to the behavioural problem in school-age children, psychosomatic problem in particular.

MiR-29b-3p aggravates NG108-15 cell apoptosis triggered by fluorine combined with aluminum

The mechanism of learning and memory impairment induced by the combination of fluorine and aluminum (FA) is not fully understood. The results of our previous research demonstrated that miR-29b-3p is a differentially expressed miRNA in the hippocampi of rat offspring exposed to FA; this miRNA is related to learning and memory and apoptosis. Based on these findings, in vitro studies were designed to assess the role of miR-29b-3p in neuronal apoptosis caused by the coexistence of FA. In the present study, the viability of mouse neuroblastoma-rat glioma hybrid cell (NG108-15 cell) was analyzed using Cell Counting Kit-8 (CCK-8). Apoptosis was detected by a Novocyte Flow Cytometer. Relative mRNA and protein expression levels were evaluated by real-time fluorescence quantitative PCR (qRT-PCR) and Western blotting (WB), respectively. The results showed that FA aggravated NG108-15 cell apoptosis by inhibiting dual-specificity phosphatase-2 (Dusp2) via increased miR-29b-3p. Accordingly, a dual-luciferase reporter assay showed that miR-29b-3p modulated Dusp2 protein levels by targeting its 3'-untranslated region. These findings show, for the first time, that miR-29b-3p is involved in neuronal apoptosis triggered by FA by targeting Dusp2.

Micro RNA (miRNA) Differential Expression and Exposure to Crude-Oil-Related Compounds

This review summarizes studies on miRNA differential regulation related to exposure to crude oil and 20 different crude oil chemicals, such as hydrocarbons, sulphur, nitrogen, and metal- containing compounds. It may be interesting to explore the possibility of using early post-transcriptional regulators as a potential novel exposure biomarker.

Crude oil has been defined as a highly complex mixture of solids, liquids, and gases. Given the toxicological properties of the petroleum components, its extraction and elaboration processes represent high-risk activities for the environment and human health, especially when accidental spills occur. The effects on human health of short-term exposure to petroleum are well known, but chronic exposure effects may variate depending on the exposure type (i.e., work, clean-up activities, or nearby residence).

As only two studies are focused on miRNA differential expression after crude-oil exposure, this review will also analyse the bibliography concerning different crude-oil or Petroleum-Related Compounds (PRC) exposure in Animalia L. kingdom and how it is related to differential miRNA transcript levels. Papers include in vitro, animal, and human studies across the world.

A list of 10 miRNAs (miR-142-5p, miR-126-3p, miR-24-3p, miR-451a, miR-16-5p, miR-28-5p, let-7b-5p, miR-320b, miR-27a-3p and miR-346) was created based on bibliography analysis and hypothesised as a possible “footprint” for crude-oil exposure. miRNA differential regulation can be considered a Big-Data related challenge, so different statistical programs and bioinformatics tools were used to have a better understanding of the biological significate of the most interesting data.

Synergistic oxidative impact of aluminum chloride and sodium fluoride exposure during early stages of brain development in the rat

Aluminum is widely used in industry and in cooking utensils, especially in countries with low economic and social standards. Fluoride is also used in industry, a major component of toothpaste and is added to the drinking water in many countries to fight teeth decay and cavities. Consequently, the coexistence of aluminum and fluoride is highly probable. Growing evidence indicates that environmental pollutants during the early stages of embryonic development may reprogram the offspring's brain capabilities to encounter oxidative stress during the rest of their postnatal life. This study investigated the impact of sodium fluoride (NaF, 0.15 g/L) and aluminum chloride (AlCl₃, 500 mg/L) added, individually or in combination, to the deionized drinking water starting from day 6 of gestation until just after weaning, or until the age of 70 days postnatal life. A significant decline was observed in tissue contents of vitamin C, reduced glutathione, GSH/GSSH ratio, and the total protein, as well as in the activities of Na⁺/K⁺-ATPase and superoxide dismutase (SOD) in almost all cases. On the contrary, lipid peroxidation and NO, as total nitrate, exhibited a significant increase in comparison with the corresponding control. Based on the present results, administration of Al and NaF, alone or in combination abated the quenching effects of the antioxidant system and induced oxidative stress in most brain regions under investigation. In conclusion, aluminum and fluoride are very noxious environmental pollutants that interfere with the proper functions of the brain neurons and their combination together aggravates their hazard.