Metabolic and oxidative impairments in human salivary gland cells line exposed to MeHg

Background/aimThe ingestion of contaminated seafood by MeHg is considered the main route of human exposure, turning the salivary gland one important target organ. The salivary glands play critical roles in maintaining oral health homeostasis, producing saliva that maintains the oral microbiota, initiation of the digestion of macromolecules, and being essential in maintaining the integrity of the adjacent soft tissues and teeth. Thus, this study aimed to investigate the effects of MeHg exposure on human salivary gland cells line.MethodsCells were exposed to 1–6 μM of MeHg for 24 h, and analysis of toxicity was performed. Based on these results, the LC50 was calculated and two concentrations were chosen (0.25 and 2.5 μM MeHg) to evaluate intracellular mercury (Hg) accumulation (THg), metabolic viability and oxidative stress parameters (GSH:GSSG ratio, lipid peroxidation, protein oxidation and DNA damage).ResultsThe results demonstrated accumulation of THg as we increased the MeHg concentrations in the exposure and, the higher the dose, the lower is the cell metabolic response. In addition, the 2.5 μM MeHg concentration also triggered oxidative stress in human salivary gland cells by depleting the antioxidant competence of GSH:GSSG ratio and increasing lipid peroxidation and proteins carbonyl levels, but no damages to DNA integrity.ConclusionIn conclusion, although these two elected doses did not show lethal effects, the highest dose triggered oxidative stress and new questionings about long-term exposure models are raised to investigate furthers cellular damages to human salivary gland cells caused by MeHg exposure to extrapolate in a translational perspective.     

Excess Manganese-Induced Apoptosis in Chicken Cerebrums and Embryonic Neurocytes

Methyl mercury (MeHg) is a developmental neurotoxin that causes irreversible cognitive damage in offspring of gestationally exposed mothers. Currently, no preventive drugs are established against MeHg developmental neurotoxicity. The neuroprotective effect of gestational administration of a flavanoid against in utero toxicity of MeHg is not explored much. Hence, the present study validated the effect of a bioactive flavanoid, fisetin, on MeHg developmental neurotoxicity outcomes in rat offspring at postnatal weaning age. Pregnant Wistar rats were simultaneously given MeHg (1.5 mg/kg b.w.) and two doses of fisetin (10 and 50 mg/kg b.w. in two separate groups) orally from gestational day (GD) 5 till parturition. Accordingly, after parturition, on postnatal day (PND) 24, weaning F₁ generation rats were studied for motor and cognitive behavioural changes. Biochemical and histopathological changes were also studied in the cerebral cortex, cerebellum and hippocampus on PND 25. Administration of fisetin during pregnancy prevented behavioural impairment due to transplacental MeHg exposure in weaning rats. Fisetin decreased the levels of oxidative stress markers, increased enzymatic and non-enzymatic antioxidant levels and increased the activity of membrane-bound ATPases and cholinergic function in F₁ generation rats. In light microscopic studies, fisetin treatment protected the specific offspring brain regions from significant morphological aberrations. Between the two doses of fisetin studied, 10 mg/kg b.w. was found to be more satisfactory and effective than 50 mg/kg b.w. The present study shows that intake of fisetin during pregnancy in rats ameliorated in utero MeHg exposure-induced neurotoxicity outcomes in postnatal weaning F₁ generation rats.     

A single exposure of rats to water-immersion restraint stress induces oxidative stress more severely in the thymus than in the spleen

Abstract

Objectives

We examined whether a single exposure of rats to water-immersion restraint stress (WIRS) induces oxidative stress in the thymus and spleen.

Methods

Vitamin E, ascorbic acid, reduced glutathione (GSH), and lipid peroxide (LPO) were assayed in the thymus and spleen of rats with and without 6 hours of WIRS.

Results

In unstressed rats, vitamin E, ascorbic acid, GSH, and LPO levels were higher in the thymus than in the spleen. Thymic ascorbic acid level was lower in stressed rats than in unstressed rats. Splenic ascorbic acid level was similar in both groups. Thymic and splenic GSH levels were lower in stressed rats than in unstressed rats but the reduced amount of GSH was lower in the spleen than in the thymus. Thymic vitamin E level was lower in stressed than in unstressed rats. Splenic vitamin E level was higher in stressed rats than in unstressed rats. Thymic and splenic LPO levels were higher in stressed rats than in unstressed rats but the increased amount of LPO was higher in the thymus than in the spleen.

Conclusion

It is indicated that a single expose of rats to WIRS induces oxidative stress more severely in the thymus than in the spleen.     

The effects of UV radiation on the visual system of the crab Neohelice granulata: a protective role of melatonin

The first and main target-structure of ultraviolet (UV) radiation in animals is the body surface, including the skin and eyes. Here, we investigated cell damage in the visual system of the crab Neohelice granulata acclimated to constant light and exposed to UVA or UVB at 12:00 h for 30 min. The reactive oxygen species (ROS) production, antioxidant capacity against peroxyl radicals (ACAP), lipid peroxidation (LPO) damage, catalase (CAT) activity, and the melatonin immunohistochemical reactivity in the eyestalks were evaluated. The animals that received melatonin and were exposed to UVA and UVB radiation showed a decreased ROS concentration (p < 0.05).The ACAP test showed a decrease (p < 0.05) in their values when the animals received 2 pmol/crab of melatonin (physiological dose) before the exposure to UVA radiation. The animals exposed to UVB radiation after receiving the same dose of melatonin showed an increase (p < 0.05) in the ACAP test compared with the animals exposed to UVB radiation after receiving only crab physiological saline. The CAT activity increased (p < 0.05) in the animals that received melatonin and were exposed to UVA and UVB radiation. Animals exposed to UVA and UVB displayed an increase (p < 0.05) in the LPO levels, whereas animals treated with melatonin showed lower (p < 0.05) LPO levels when irradiated. The results indicate that the specific oxidative parameters altered by UV radiation can be modulated by a physiological dose of melatonin. Moreover, the melatonin regularly produced by virtually all eyestalk cells suggests that it may function to modulate the noxious effects of radiation, at least in the crab N. granulata.     

Modulation of lipid peroxidation and antioxidant enzymes in murine salivary gland by dietary fatty acid ethyl esters

The present study was undertaken to investigate the effect of n-9, n-6, and n-3 dietary fatty acid ethyl esters on basal (uninduced) and Fe2+/ascorbate (induced) lipid peroxidation (LPO) in salivary gland (SG) of mice. Feeding n-3 ethyl ester polyunsaturated fatty acids (PUFA) increased the uninduced and induced LPO in SG homogenates. In contrast, feeding olive oil ethyl esters (n-9) significantly lowered the induced and uninduced LPO in SG tissue. Salivary gland susceptibility to LPO increased in the order of: olive oil < corn oil < safflower oil < n-3 ethyl esters. Olive oil esters in the diet increased primarily the 18:1 levels in SG tissue. Whereas feeding n-3 PUFA notably increased the superoxide dismutase (SOD) and catalase activities in SG homogenates, no significant changes were seen between n-9 and n-6 PUFA-fed mice. Lower levels of Vitamin E (Vit E) in the tissues of n-3 PUFA-fed mice indicate that the higher the dietary lipid unsaturation, the higher the requirement for Vit E in the diet. Our results indicate that, similar to other organs, salivary gland susceptibility to uninduced or induced oxidation depends on the source of dietary PUFA. In conclusion, feeding olive oil increases the resistance of SGs to induced and uninduced LPO.     

Trace Element Concentrations in Beef Cattle Related to the Breed Aptitude

Environmental and occupational mercury exposure is considered a major public health issue. Despite being well known that MeHg exposure causes adverse effects in several physiologic functions, MeHg effects on salivary glands still not completely elucidated. Here, we investigated the cellular MeHg-induced damage in the three major salivary glands (parotid, submandibular, and sublingual) of adult rats after chronic, systemic and low doses of MeHg exposure. Rats were exposed by 0.04 mg/kg/day over 60 days. After that, animals were euthanized and all three glands were collected. We evaluated total Hg accumulation, metallothionein I/II (MT I/II), α-smooth muscle actin (α-SMA), and cytokeratin 18 (CK18) immune expression. Our results have showed that MeHg is able to disrupt gland tissue and to induce a protective mechanism by MT I/II expression. We also showed that cell MT production is not enough to protect gland tissue against cellular structural damage seen by reducing marking of cytoskeletal proteins as CK18 and α-SMA. Our data suggest that chronic MeHg exposure in low-daily doses is able to induce cellular damage in rat salivary glands.     

Active secretion and protective effect of salivary nitrate against stress in human volunteers and rats

Up to 25% of the circulating nitrate in blood is actively taken up, concentrated, and secreted into saliva by the salivary glands. Salivary nitrate can be reduced to nitrite by the commensal bacteria in the oral cavity or stomach and then further converted to nitric oxide (NO) in vivo, which may play a role in gastric protection. However, whether salivary nitrate is actively secreted in human beings has not yet been determined. This study was designed to determine whether salivary nitrate is actively secreted in human beings as an acute stress response and what role salivary nitrate plays in stress-induced gastric injury. To observe salivary nitrate function under stress conditions, alteration of salivary nitrate and nitrite was analyzed among 22 healthy volunteers before and after a strong stress activity, jumping down from a platform at the height of 68 m. A series of stress indexes was analyzed to monitor the stress situation. We found that both the concentration and the total amount of nitrate in mixed saliva were significantly increased in the human volunteers immediately after the jump, with an additional increase 1 h later (p<0.01). Saliva nitrite reached a maximum immediately after the jump and was maintained 1 h later. To study the biological functions of salivary nitrate and nitrite in stress protection, we further carried out a water-immersion-restraint stress (WIRS) assay in male adult rats with bilateral parotid and submandibular duct ligature (BPSDL). Intragastric nitrate, nitrite, and NO; gastric mucosal blood flow; and gastric ulcer index (UI) were monitored and nitrate was administrated in drinking water to compensate for nitrate secretion in BPSDL animals. Significantly decreased levels of intragastric nitrate, nitrite, and NO and gastric mucosal blood flow were measured in BPSDL rats during the WIRS assay compared to sham control rats (p<0.05). Recovery was observed in the BPSDL rats upon nitrate administration. The WIRS-induced UI was significantly higher in the BPSDL animals compared to controls, and nitrate administration rescued the WIRS-induced gastric injury in BPSDL rats. In conclusion, this study suggests that stress promotes salivary nitrate secretion and nitrite formation, which may play important roles in gastric protection against stress-induced injury via the nitrate-dependent NO pathway.     

Influence of the dark/light rhythm on the effects of UV radiation in the eyestalk of the crab Neohelice granulata

Crustaceans are interesting models to study the effects of ultraviolet (UV) radiation, and many species may be used as biomarkers for aquatic contamination of UV radiation reaching the surface of the Earth. Here, we investigated cell damage in the visual system of crabs Neohelice granulata that were acclimated to either 12L:12D, constant light, or constant dark, and were exposed to UVA or UVB at 12:00 h (noon). The production of reactive oxygen species (ROS), antioxidant capacity against peroxyl radicals (ACAP), lipid peroxidation (LPO) damage, catalase activity, and pigment dispersion in the eye were evaluated. No significant differences from the three groups of controls (animals acclimated to 12L:12D, or in constant light, or not exposed to UV radiation) were observed in animals acclimated to 12L:12D, however, crabs acclimated to constant light and exposed to UV radiation for 30 min showed a significant increase in ROS concentration, catalase activity, and LPO damage, but a decrease in ACAP compared with the controls. Crabs acclimated to constant darkness and exposed to UV for 30 min showed a significantly increased ROS concentration and LPO damage, but the ACAP and catalase activity did not differ from the controls (animals kept in the dark while the experimental group was being exposed to UV radiation). Pigment dispersion in the pigment cells of eyes of animals acclimated to constant light was also observed. The results indicate that UVA and UVB alter specific oxidative parameters; however, the cell damage is more evident in animals deviated from the normal dark/light rhythm.     

Methylmercury Alters the Activities of Hsp90 Client Proteins,Prostaglandin E Synthase/p23 (PGES/23) and nNOS

Methylmercury (MeHg) is a persistent pollutant with known neurotoxic effects. We have previously shown that astrocytes accumulate MeHg and play a prominent role in mediating MeHg toxicity in the central nervous system (CNS) by altering glutamate signaling, generating oxidative stress, depleting glutathione (GSH) and initiating lipid peroxidation. Interestingly, all of these pathways can be regulated by the constitutively expressed, 90-kDa heat shock protein, Hsp90. As Hsp90 function is regulated by oxidative stress, we hypothesized that MeHg disrupts Hsp90-client protein functions. Astrocytes were treated with MeHg and expression of Hsp90, as well as the abundance of complexes of Hsp90-neuronal nitric oxide synthase (nNOS) and Hsp90-prostaglandin E synthase/p23 (PGES/p23) were assessed. MeHg exposure decreased Hsp90 protein expression following 12 h of treatment while shorter exposures had no effect on Hsp90 protein expression. Interestingly, following 1 or 6 h of MeHg exposure, Hsp90 binding to PGES/p23 or nNOS was significantly increased, resulting in increased prostaglandin E₂ (PGE₂) synthesis from MeHg-treated astrocytes. These effects were attenuated by the Hsp90 antagonist, geldanmycin. NOS activity was increased following MeHg treatment while cGMP formation was decreased. This was accompanied by an increase in •O₂ ⁻ and H₂O₂ levels, suggesting that MeHg uncouples NO formation from NO-dependent signaling and increases oxidative stress. Altogether, our data demonstrates that Hsp90 interactions with client proteins are increased following MeHg exposure, but over time Hsp90 levels decline, contributing to oxidative stress and MeHg-dependent excitotoxicity.     

Oxidative stress in zinc-induced dopaminergic neurodegeneration: Implications of superoxide dismutase and heme oxygenase-1

Abstract

The study was undertaken to investigate the effect of zinc (Zn) on glutathione S-transferase (GST) and superoxide dismutases (SOD) activities and on the expressions of cytosolic Cu, Zn-SOD (SOD1), mitochondrial Mn-SOD (SOD2), γ-glutamyl cysteine synthetase (γ-GCS) and heme oxygenase-1 (HO-1) in the nigrostriatal tissue of rats. Additionally, Zn-induced alterations in the neurobehavioral parameters, lipid peroxidation (LPO), striatal dopamine and its metabolites and tyrosine hydroxylase (TH) protein expression were measured to assess their correlations with the oxidative stress. Zn exposure reduced the locomotor activity, rotarod performance, striatal dopamine and its metabolites and TH protein expression. LPO, total SOD, SOD1 and SOD2 activities were increased while GST and catalase were reduced in a dose and time dependent manner. Expressions of SOD1 and HO-1 were increased while no change was observed in SOD2 and γ-GCS expressions. The results obtained suggest that Zn-induced augmentation of total SOD, SOD1, SOD2 and HO-1 was associated with increased oxidative stress and neurodegenerative indexes indicating the involvement of both cytosolic and mitochondrial machinery in Zn-induced oxidative stress leading to dopaminergic neurodegeneration.     

Nigella sativa oil attenuates chronic nephrotoxicity induced by oral sodium nitrite: Effects on tissue fibrosis and apoptosis

Objectives: Sodium nitrite, a food preservative, has been reported to increase oxidative stress indicators such as lipid peroxidation, which can affect different organs including the kidney. Here, we investigated the toxic effects of oral sodium nitrite on kidney function in rats and evaluated potential protective effects of Nigella sativa oil (NSO).

Methods: Seventy adult male Sprague–Dawley rats received 80?mg/kg sodium nitrite orally in the presence or absence of NSO (2.5, 5, and 10?ml/kg) for 12 weeks. Morphological changes were assessed by hematoxylin and eosin, Mallory trichome, and periodic acid–Schiff staining. Renal tissues were used for measurements of oxidative stress markers, C-reactive protein, cytochrome C oxidase, transforming growth factor (TGF)-beta1, monocyte chemotactic protein (MCP)-1, pJNK/JNK, and caspase-3.

Results: NSO significantly reduced sodium nitrite-induced elevation in serum urea and creatinine, as well as increasing normal appearance of renal tissue. NSO also prevented reductions in glycogen levels caused by sodium nitrite alone. Moreover, NSO treatment resulted in dose-dependent significant reductions in fibrosis markers after sodium nitrite-induced 3- and 2.7-fold increase in MCP-1 and TGF-beta1, respectively. Finally, NSO partially reduced the elevated caspase-3 and pJNK/JNK.

Discussion: NSO ameliorates sodium nitrite-induced nephrotoxicity through blocking oxidative stress, attenuation of fibrosis/inflammation, restoration of glycogen level, amelioration of cytochrome C oxidase, and inhibition of apoptosis.     

Temperature and hypoxia on oxidative stress responses in pacu Piaractus mesopotamicus

The aim of this study was to verify the effects of the interaction between different temperatures and levels of dissolved oxygen in the oxidative stress parameters of pacu juveniles. A total of 81 pacu juveniles (61.7 ± 9.1 g) were exposed to three temperatures (18, 23, and 28 °C), acclimated for a period of 30 days, and then submitted to three levels of dissolved oxygen: control or normoxia (7 mg L⁻¹); moderate hypoxia (4 mg L⁻¹); and severe hypoxia (2 mg L⁻¹) for 12 h. Glutathione-S-transferase (GST) activity, total antioxidant capacity against peroxyl radicals (ACAP), and protein thiol content (PSH) and LPO (lipid peroxidation) [measured by the TBARS] were measured in gill, liver, muscle and brain. The results indicated that the interaction between different temperatures and dissolved oxygen levels caused alterations in the antioxidant system and induced lipid and protein damage in pacu juveniles. In addition, the effects were organ specific. In conclusion, exposure to moderate and severe hypoxia affect oxidative stress parameters and have been shown to be organ-specific in pacu juveniles. The interaction between 23 °C and hypoxia caused greater disturbances in oxidative stress markers, such as PSH in the gills and liver and LPO in the muscle.     

Comparative-physiological study of leukocyte participation in initiation of lipid peroxidation during nitrite intoxication in rats and muskrats

The study is carried out on Wistar white rats non-adapted to oxygen deficit and on semiaquatic rodents muskrats adapted to periodic arrest of respiration during diving under conditions of Nembutal narcosis. It has been revealed that 1 h after a subcutaneous injection of sodium nitrite (3 mg/100 g body mass), intensification of lipid peroxidation (LPO) in the muskrat brain is absent, the activity of the antioxidant enzyme catalase increasing 16 times (p < 0.01) as compared with control injected with equivalent saline volume. In heart and liver, there was a statistically significant decrease of the content of LPO products active in the test with 2-thiobarbituric acid; in the femoral muscle tissue, the LPO intensity did not change. In rats, unlike muskrats, after injection of sodium nitrite, an increase of LPO is recorded in brain, while a decrease of the LPO product content in the femoral muscle; in liver the LPO intensity did not change. In muskrats, the sodium nitrite administration led to a decrease of the leukocyte spontaneous mobility, of lymphocyte cytokine-producing activity, and of neutrophil bactericidal activity (by the content of cationic proteins in neutrophilic phagocytes), whereas in rats the leukocyte mobility did not change, only the blood neutrophil bactericidal activity decreased. The ability of neutrophils to produce the superoxide anion during the nitrite intoxication did not change both in rats and in muskrats. The obtained data allow concluding that under conditions of Nembutal narcosis the leukocyte functional activity on the background of nitrite intoxication is suppressed to the greater degree in the muskrats genotypically adapted to oxygen deficit than in immunocompetent cells of the rodents not adapted to hypoxia.     

Plant components can reduce methylmercury toxication: A mini-review

BackgroundMethylmercury (MeHg) is a ubiquitous environmental pollutant, with the nervous system as its main target; however, the neurotoxic mechanisms of MeHg have not been fully elucidated, and no effective therapeutic and preventive drugs are available to mitigate its toxicity. Recent evidence suggests a reduction in the toxicity of MeHg by natural plant extracts.Scope of reviewThe aim of this review is to provide an overview of effective natural plant extracts and their putative biochemical mechanisms for blocking gut absorption, enhancing excretion and minimizing toxic effects of MeHg.Major conclusionsNatural plant extracts may act as potential therapeutics in response to MeHg exposure. The roles plant components play in the reduction of MeHg toxicity may be multifaceted including: (1) attenuating neurobehavioral deficits; (2) facilitating demethylation of MeHg to inorganic mercury; (3) reducing MeHg absorption from the gastrointestinal tract; (4) redistributing MeHg to less sensitive target organs and tissues; (5) promoting enterohepatic circulation of MeHg to increase its biliary and intestinal excretion; (6) restoring intracellular redox status.General significanceThe possible protective effects of natural plant components contribute to the understanding of mechanisms of MeHg toxicity and to the development of novel therapeutic strategies.     

Music stimuli lead to increased levels of nitrite in unstimulated mixed saliva

Concentration of salivary nitrate is approximately 10-fold to that of serum. Many circumstances such as acute stress could promote salivary nitrate secretion and nitrite formation. However, whether other conditions can also be used as regulators of salivary nitrate/nitrite has not yet been explored. The present study was designed to determine the influence of exposure to different music on the salivary flow rate and nitrate secretion and nitrite formation. Twenty-four undergraduate students(12 females and 12 males) were exposed to silence, rock music, classical music or white noise respectively on four consecutive mornings. The unstimulated salivary flow rate and stimulated salivary flow rate were measured. Salivary ionic(Na+, Ca2+Cl-,and PO3-4) content and nitrate/nitrite levels were detected. The unstimulated salivary flow rate was significantly increased after classical music exposure compared to that after silence. Salivary nitrite levels were significantly higher upon classical music and white noise stimulation than those under silence in females. However, males were more sensitive only to white noise with regard to the nitrite increase. In conclusion, this study demonstrated that classical music stimulation promotes salivary nitrite formation and an increase in saliva volume was observed. These observations may play an important role in regulating oral function.     

Microwave radiation (2.45 GHz)-induced oxidative stress: Whole-body exposure effect on histopathology of Wistar rats

Man-made microwave and radiofrequency (RF) radiation technologies have been steadily increasing with the growing demand of electronic appliances such as microwave oven and cell phones. These appliances affect biological systems by increasing free radicals, thus leading to oxidative damage. The aim of this study was to explore the effect of 2.45 GHz microwave radiation on histology and the level of lipid peroxide (LPO) in Wistar rats. Sixty-day-old male Wistar rats with 180 ± 10 g body weight were used for this study. Animals were divided into two groups: sham exposed (control) and microwave exposed. These animals were exposed for 2 h a day for 35 d to 2.45 GHz microwave radiation (power density, 0.2 mW/cm²). The whole-body specific absorption rate (SAR) was estimated to be 0.14 W/kg. After completion of the exposure period, rats were sacrificed, and brain, liver, kidney, testis and spleen were stored/preserved for determination of LPO and histological parameters. Significantly high level of LPO was observed in the liver (p < 0.001), brain (p < 0.004) and spleen (p < 0.006) in samples from rats exposed to microwave radiation. Also histological changes were observed in the brain, liver, testis, kidney and spleen after whole-body microwave exposure, compared to the control group.

Based on the results obtained in this study, we conclude that exposure to microwave radiation 2 h a day for 35 d can potentially cause histopathology and oxidative changes in Wistar rats. These results indicate possible implications of such exposure on human health.     

Variation in the biological half-life of methylmercury in humans: Methods,measurements and meaning

BackgroundUnderstanding methylmercury (MeHg) toxicity requires a complete understanding of its fundamental toxicokinetic and toxicodynamic characteristics in the human body. The biological half-life (t_1/2) of MeHg is a kinetic property that directly influences the body burden of Hg that results from repeated exposures such as can occur with fish and seafood consumption. The t_1/2 of MeHg in humans is approximately 50 days, equivalent to an elimination rate (k_el) of 0.014 day⁻¹. However, numerous studies report a wide range of half-life values (t_1/2 < 30 to >120 days), demonstrating that significant variation in the biological process of MeHg elimination exists. This variation is a source of considerable uncertainty in deriving a meaningful reference dose for MeHg applicable to all individuals in a population.Scope of reviewFirst, we summarize fundamentals of MeHg toxicokinetics, emphasizing the central role that biological half-life plays in MeHg dosimetry. We next present important considerations for how kinetic analyses are performed. We provide an example of how MeHg half-life variation directly influences the body burden and, in certain contexts, can result in MeHg levels exceeding the US EPA Reference Dose. We then survey existing studies that report MeHg half-life determinations in people.Major conclusionsRecent advances in methods of determining MeHg kinetics in people have made individualized assessment of MeHg elimination rates more accurate and readily obtainable.General significanceCharacterization of MeHg half-life, particularly in vulnerable individuals, such as pregnant women and children, will diminish the remaining toxicokinetic uncertainty surrounding MeHg exposures and will better inform the risk assessment process.