DNA Damage and Proteomic Profile Changes in Rat Salivary Glands After Chronic Exposure to Inorganic Mercury

Mercury (Hg) is a toxic metal that became a public health problem due to environmental contamination caused by anthropogenic activity. In this sense, oral homeostasis can undergo changes due to the toxic effects of metal on the salivary glands. Therefore, our objective was to investigate the proteomic and genotoxic changes in salivary glands after exposure to inorganic mercury (IHg). Forty Wistar rats that were divided into a control group, which received distilled water, and an exposed group, which received 0.375 mg/kg of mercury chloride for 45 days via orogastric gavage. After that, the animals were euthanized, and the parotid and submandibular glands were collected for analysis of the genotoxic effects, using the comet assay and proteome global profile assessment. The results showed that IHg promoted damage to cellular DNA associated with proteomic changes that showed events such as oxidative stress, mitochondrial dysfunction, changes in the cytoskeleton, and apoptosis. Therefore, these findings show a profile of molecular changes due to the interactions of IHg with several proteins and mechanisms inherent to the cell, which consequently may result in dysfunction of the salivary glands and impaired homeostasis of the oral cavity.

Effects of long-term fluoride exposure are associated with oxidative biochemistry impairment and global proteomic modulation, but not genotoxicity, in parotid glands of mice

BACKGROUND

Fluoride has become widely used in dentistry because of its effectiveness in caries control. However, evidence indicates that excessive intake interferes with the metabolic processes of different tissues. Thus, this study aimed to investigate the effects of long-term exposure to F on the parotid salivary gland of mice, from the analysis of oxidative, proteomic and genotoxic parameters.

MATERIALS AND METHODS

The animals received deionized water containing 0, 10 or 50 mg/L of F, as sodium fluoride, for 60 days. After, parotid glands were collected for analysis of oxidative biochemistry, global proteomic profile, genotoxicity assessment and histopathological analyses.

RESULTS

The results revealed that exposure to fluoride interfered in the biochemical homeostasis of the parotid gland, with increased levels of thiobarbituric acid reactive species and reduced glutathione in the exposed groups; as well as promoted alteration of the glandular proteomic profile in these groups, especially in structural proteins and proteins related to oxidative stress. However, genotoxic assessment demonstrated that exposure to fluoride did not interfere with DNA integrity in these concentrations and durations of exposure. Also, it was not observed histopathological alterations in parotid gland.

CONCLUSIONS

Thus, our results suggest that long-term exposure to fluoride promoted modulation of the proteomic and biochemical profile in the parotid glands, without inducing damage to the genetic component. These findings reinforce the importance of rationalizing the use of fluorides to maximize their preventative effects while minimizing the environmental risks.

Non-Lethal Concentration of MeHg Causes Marked Responses in the DNA Repair, Integrity, and Replication Pathways in the Exposed Human Salivary Gland Cell Line

In Brazilian northern Amazon, communities are potentially exposed and vulnerable to methylmercury (MeHg) toxicity through the vast ingestion of fish. In vivo and in vitro studies demonstrated that the salivary glands as a susceptible organ to this potent environmental pollutant, reporting alterations on physiological, biochemical, and proteomic parameters. However, the alterations caused by MeHg on the gene expression of the exposed human salivary gland cells are still unknown. Therefore, the goal was to perform the transcriptome profile of the human salivary gland cell line after exposure to MeHg, using the microarray technique and posterior bioinformatics analysis. The cell exposure was performed using 2.5 µM MeHg. A previously published study demonstrated that this concentration belongs to a range of concentrations that caused biochemical and metabolic alterations in this linage. As a result, the MeHg exposure did not cause lethality in the human salivary gland cells line but was able to alter the expression of 155 genes. Downregulated genes (15) are entirety relating to the cell metabolism impairment, and according to KEGG analysis, they belong to the glycosphingolipid (GSL) biosynthesis pathway. On the other hand, most of the 140 upregulated genes were related to cell-cycle progression, DNA repair, and replication pathway, or cellular defenses through the GSH basal metabolism. These genomic changes revealed the effort to the cell to maintain physiological and genomic stability to avoid cell death, being in accordance with the nonlethality in the toxicity test. Last, the results support in-depth studies on nonlethal MeHg concentrations for biomarkers identification that interpret transcriptomics data in toxicological tests serving as an early alert of physiological changes in vitro biological models.

Methylmercury-induced cytotoxicity and oxidative biochemistry impairment in dental pulp stem cells: the first toxicological findings

BACKGROUND

Methylmercury (MeHg) is a potent toxicant able to harm human health, and its main route of contamination is associated with the consumption of contaminated fish and other seafood. Moreover, dental amalgams are also associated with mercury release on human saliva and may contribute to the accumulation of systemic mercury. In this way, the oral cavity seems to be the primary location of exposure during MeHg contaminated food ingestion and dental procedures but there is a lack of literature about its effects on dental tissues and the impact of this toxicity on human health. In this way, this study aimed to analyze the effects of different doses of MeHg on human dental pulp stem cells after short-term exposure.

METHODS

Dental pulp stem cells from human exfoliated deciduous teeth (SHED) were treated with 0.1, 2.5 and 5 µM of MeHg during 24 h. The MeHg effects were assessed by evaluating cell viability with Trypan blue exclusion assay. The metabolic viability was indirectly assessed by MTT reduction assay. In order to evaluate an indicative of antioxidant defense impairment, cells exposed to 0.1 and 5 µM MeHg were tested by measuring glutathione (GSH) level.

RESULTS

It was observed that cell viability decreased significantly after exposure to 2.5 and 5 µM of MeHg, but the metabolic viability only decreased significantly at 5 µM MeHg exposure, accompanied by a significant decrease in GSH levels. These results suggest that an acute exposure of MeHg in concentrations higher than 2.5 µM has cytotoxic effects and reduction of antioxidant capacity on dental pulp stem cells.

Low doses of methylmercury exposure during adulthood in rats display oxidative stress, neurodegeneration in the motor cortex and lead to impairment of motor skills

Despite the vast distribution among tissues, the central nervous system (CNS) represents the main target of methylmercury (MeHg) toxicity. However, few studies have evaluated the effects of MeHg exposure on the CNS at equivalent doses to human environmental exposure. In our study, we evaluated the motor cortex, an important area of motor control, in adult rats chronically exposed to MeHg in a concentration equivalent to those found in fish-eating populations exposed to mercury (Hg). The parameters evaluated were total Hg accumulation, oxidative stress, tissue damage, and behavioral assessment in functional actions that involved this cortical region. Our results show in exposed animals a significantly greater level of Hg in the motor cortex; increase of nitrite levels and lipid peroxidation, associated with decreased antioxidant capacity against peroxyl radicals; reduction of neuronal and astrocyte density; and poor coordination and motor learning impairment. Our data showed that chronic exposure at low doses to MeHg is capable of promoting damages to the motor cortex of adult animals, with changes in oxidative biochemistry misbalance, neurodegeneration, and motor function impairment.

Physiological effects of marine natural organic matter and metals in early life stages of the North Pacific native marine mussel Mytilus trossulus; a comparison with the invasive Mytilus galloprovincialis

The role of seawater NOM in reducing metal toxicity for marine organisms is not well understood. We investigated the effects of five different marine NOMs (two autochthonous, one allochthonous, two of mixed origin, at 8 mg C/L), three metals (6 μg Cu/L; 20 μg Pb/L; 25 μg Zn/L), and combinations between them, to early life stages of Mytilus trossulus (a North Pacific native) in 48-h tests. Endpoints were whole body Ca²⁺+Mg²⁺-ATPase activity, carbonic anhydrase (CA) activity and lipid peroxidation. Comparisons were made with previously reported tests (identical conditions) on the invasive M. galloprovincialis. Unexposed M. trossulus had lower Ca²⁺+Mg²⁺-ATPase but similar baseline CA activity and lipid peroxidation to unexposed M. galloprovincialis. NOMs alone induced increased enzyme activities, and increased lipid peroxidation, but the latter did not occur with NOMs of mixed origin in M. trossulus. There was no clear difference in the sensitivity to various NOMs between species. In M. trossulus, all three metals by themselves caused increases in lipid peroxidation, as did many metal-NOM combinations. The origin of the NOMs influenced the nature of the responses to NOM-metal combinations in both species, but no clear relationship to NOM chemistry was apparent. Overall, M. trossulus was more sensitive to metals and NOM-metal combinations, with a greater number of significant responses (27 versus 22 treatment endpoints, out of a total of 72) and a greater proportion of negative effects (81% versus 50%) than in M. galloprovincialis. Therefore, marine NOMs by themselves, as well as metals by themselves and NOM-metal combinations, can induce both positive and negative physiological responses. Lipid peroxidation appears to be a particularly common negative response. In future studies, NOM quality and mussel species should be considered since native M. trossulus and invasive M. galloprovincialis exhibited markedly different responses after exposure to the same environmental conditions.

Physiological effects of five different marine natural organic matters (NOMs) and three different metals (Cu, Pb, Zn) on early life stages of the blue mussel (Mytilus galloprovincialis)

Metals are present in aquatic environments as a result of natural and anthropogenic inputs, and may induce toxicity to organisms. One of the main factors that influence this toxicity in fresh water is natural organic matter (NOM) but all NOMs are not the same in this regard. In sea water, possible protection by marine NOMs is not well understood. Thus, our study isolated marine NOMs by solid-phase extraction from five different sites and characterized them by excitation-emission fluorescence analysis—one inshore (terrigenous origin), two offshore (autochthonous origin), and two intermediate in composition (indicative of a mixed origin). The physiological effects of these five NOMS alone (at 8 mg/L), of three metals alone (copper, lead and zinc at 6 µg Cu/L, 20 µg Pb/L, and 25 µg Zn/L respectively), and of each metal in combination with each NOM, were evaluated in 48-h exposures of mussel larvae. Endpoints were whole body Ca²⁺+Mg²⁺-ATPase activity, carbonic anhydrase activity and lipid peroxidation. By themselves, NOMs increased lipid peroxidation, Ca²⁺+Mg²⁺-ATPase, and/or carbonic anhydrase activities (significant in seven of 15 NOM-endpoint combinations), whereas metals by themselves did not affect the first two endpoints, but Cu and Pb increased carbonic anhydrase activities. In combination, the effects of NOMs predominated, with the metal exerting no additional effect in 33 out of 45 combinations. While NOM effects varied amongst different isolates, there was no clear pattern with respect to optical or chemical properties. When NOMs were treated as a single source by data averaging, NOM had no effect on Ca²⁺+Mg²⁺-ATPase activity but markedly stimulated carbonic anhydrase activity and lipid peroxidation, and there were no additional effects of any metal. Our results indicate that marine NOMs may have direct effects on this model marine organism, as well as protective effects against metal toxicity, and the quality of marine NOMs may be an important factor in these actions.

Early biochemical biomarkers for zinc in silver catfish (Rhamdia quelen) after acute exposure

Contamination of aquatic ecosystems by metals causes various biochemical changes in aquatic organisms, and fish are recognized as indicators of environmental quality. Silver catfish were exposed to six concentrations of zinc (Zn): 1.0, 2.5, 5.0, 7.5, 10.0 and 12.5 mg/L for 96 h to determine the mean lethal concentration (LC50). The value obtained was 8.07 mg/L. In a second experiment, fish were exposed to concentrations of 1.0 or 5.0 mg/L Zn and a control for 96 h. Afterward, the tissues were collected for biochemical analysis. Lipid peroxidation, as indicated by thiobarbituric acid-reactive substance (TBARS), decreased in the liver and brain for all Zn concentrations tested, while in the gills TBARS levels increased at 1.0 mg/L and declined at 5.0 mg/L. Zn increased protein carbonyls in the muscle of silver catfish and decreased it in the other tissues. The enzyme superoxide dismutase increased in both exposed groups. However, catalase did not change. Glutathione S-transferase decreased in the liver and increased in the gills (1.0 mg/L), muscle (5.0 mg/L) and brain (1.0 and 5.0 mg/L). Nonprotein thiols changed only in brain and muscle tissue. Zn exposure inhibited acetylcholinesterase (AChE) activity in the brain at both concentrations tested, but did not change it in muscle. Exposure to Zn inhibited the activity of Na(+)/K(+)-ATPase in the gills and intestine at both concentrations tested. Our results demonstrate that Zn alters biochemical parameters in silver catfish and that some parameters such as AChE and Na(+)/K(+)-ATPase could be considered as early biomarkers of waterborne Zn toxicity.

[Neurocryptococcosis caused by nonencapsulated Cryptococcus neoformans]

The case of a patient with meningoencephafalitis due to a nonencapsulated strain of Cryptococcus neoformans is reported; he had no risk factors for the disease or AIDS. Clinical examination showed a chronic meningoencephalitis first diagnosed as tuberculosis. In the second cerebrospinal fluid (CSF) examination after a week from admission yeasts appeared inside macrophage cells. CSF culture in Sabouraud medium disclosed nonencapsulated Cryptococcus neoformans (biochemical identification). Sample inoculation in mouse (intraperitoneal) evidenced a capsule that disappeared in several consecutive cultures. The morphology of the yeast was studied by electronic microscopy. After treatment with amphotericin B and 5-fluorocytosine the patient had a favorable evolution. The significance of capsular material is discussed.