Genotoxic effect of non-lethal concentrations of minocycline in human glial cell culture

Minocycline has been proposed as a neuroprotective agent with pleiotropic effects on several experimental models of neurodegenerative diseases, including microglial inhibition. However, although most studies have focused on the central actions of minocycline in affecting microglial functions, other central nervous system (CNS) cell types may also be affected by this drug toxicity. Hence, considering that glial cells play a pivotal role on CNS physiology and are the main responsible for neuronal integrity, a comprehensive investigation on the effects of minocycline treatment on human glial cells is mandatory before translational studies to afford neuroprotection in humans. Therefore, we explored the cytotoxic and genotoxic effects of minocycline at different concentrations in glial cells using an in vitro model. To achieve this, U87 glial cell were exposed to 10-50 μg/mL for 24 h. After exposure, cell viability, general metabolic status and genotoxic assays were performed. No changes were observed in cell viability, however, the general metabolic status decreased over 20 μg/mL. In addition, although no chromossome aberrations were observed, evidences of genotoxicity, such as increase on micronucleus, buds and bridges, were observed from 10 μg/mL. These results suggest that minocycline may induce genotoxic effects even at concentrations considered previously safe and should be used with caution in translational studies.

Long-Term Lead Exposure Since Adolescence Causes Proteomic and Morphological Alterations in the Cerebellum Associated with Motor Deficits in Adult Rats

Lead (Pb) is an environmental contaminant that presents a high risk for human health. We aimed to investigate the possible alterations triggered by the exposure to Pb acetate for a long period in motor performance and the possible relationship with biochemical, proteomic and morphological alterations in the cerebellum of rats. Male Wistar rats were exposed for 55 days, at 50 mg/Kg of Pb acetate, and the control animals received distilled water. Open field (OF) and rotarod tests; biochemistry parameters (MDA and nitrite); staining/immunostaining of Purkinje cells (PC), mature neurons (MN), myelin sheath (MS) and synaptic vesicles (SYN) and proteomic profile were analyzed. Pb deposition on the cerebellum area and this study drove to exploratory and locomotion deficits and a decrease in the number of PC, MN, SYN and MS staining/immunostaining. The levels of MDA and nitrite remained unchanged. The proteomic profile showed alterations in proteins responsible for neurotransmitters release, as well as receptor function and second messengers signaling, and also proteins involved in the process of apoptosis. Thus, we conclude that the long-term exposure to low Pb dose promoted locomotion and histological tracings, associated with alterations in the process of cell signaling, as well as death by apoptosis.

Proteomic approach underlying the hippocampal neurodegeneration caused by low doses of methylmercury after long-term exposure in adult rats

Methylmercury (MeHg) is an important toxicant that causes cognitive dysfunctions in humans. This study aimed to investigate the proteomic and biochemical alterations of the hippocampus associated with behavioural consequences of low doses of MeHg in a long-term exposure model, and to realistically mimic in vivo the result of human exposure to this toxicant. Adult Wistar male rats were exposed to a dose of MeHg at 0.04 mg kg-1 day-1 by gavage for 60 days. Total mercury (Hg) content was significantly increased in the hippocampal parenchyma. The increase in the Hg levels was capable of reducing neuron and astrocyte cell density in the CA1, CA3, hilus and dentate gyrus regions, increasing both malondialdehyde and nitrite levels and decreasing antioxidant capacity against peroxyl radicals. The proteomic analysis detected 1041 proteins with altered expression due to MeHg exposure, including 364 proteins with no expression, 295 proteins with de novo expression and 382 proteins with up- or down-regulated expression. This proteomic approach revealed alterations in pathways related to chemical synapses, metabolism, amino acid transport, cell energy, neurodegenerative processes and myelin maintenance. Therefore, even at low doses of MeHg exposure, it is possible to cause hippocampal damage in adult rats at many organisational levels, triggering oxidative stress and proteome misbalance, featuring a neurodegenerative process and culminating in long- and short-term memory and learning deficits.

Long-term exposure to lead reduces antioxidant capacity and triggers motor neurons degeneration and demyelination in spinal cord of adult rats

Lead is a toxic metal found in environment with great neurotoxic potential. The main effect is associated with impairments in hippocampus and cerebellum, driving to cognitive and motor dysfunctions, however, there is a lack of evidences about the effects over the spinal cord. In this way, we aimed to investigate in vivo the effects of long-term exposure to lead acetate in oxidative biochemistry and morphology of rats' spinal cord. For this, 36 male Wistar rats (Rattus norvegicus) were divided into the group exposed to 50 mg/kg of lead acetate and control group, which received only distilled water, both groups through intragastric gavage, for 55 days. After the exposure period, the animals were euthanized and the spinal cords were collected to perform the analyses of lead levels quantification, oxidative biochemistry evaluation by levels of malondialdehyde (MDA), nitrites and the antioxidant capacity against peroxyl radicals (ACAP). Besides, morphological evaluation with quantitative analysis of mature and motor neurons and reactivity to myelin basic protein (MBP). Our results showed high levels of lead in spinal cord after long-term exposure; there was a reduction on ACAP level; however, there was no difference observed in MDA and nitrite levels. Moreover, there was a reduction of mature and motor neurons in all three regions, and a reduction of immunolabeling of MBP in the thoracic and lumbar segments. Therefore, we conclude that long-term exposure to lead is able of increasing the levels of the metal in spinal cord, affecting the antioxidant capacity and inducing morphological impairments in spinal cord parenchyma. Our results also suggest that the tissue impairments triggered by lead may be resultant from others molecular mechanisms besides the oxidative stress.

Spinal cord neurodegeneration after inorganic mercury long-term exposure in adult rats: Ultrastructural, proteomic and biochemical damages associated with reduced neuronal density

Mercury chloride (HgCl₂) is a chemical pollutant widely found in the environment. This form of mercury is able to promote several damages to the Central Nervous System (CNS), however the effects of HgCl₂ on the spinal cord, an important pathway for the communication between the CNS and the periphery, are still poorly understood. The aim of this work was to investigate the effects of HgCl₂ exposure on spinal cord of adult rats. For this, animals were exposed to a dose of 0.375 mg/kg/day, for 45 days. Then, they were euthanized, the spinal cord collected and we investigated the mercury concentrations in medullary parenchyma and the effects on oxidative biochemistry, proteomic profile and tissue structures. Our results showed that exposure to this metal promoted increased levels of Hg in the spinal cord, impaired oxidative biochemistry by triggering oxidative stress, mudulated antioxidant system proteins, energy metabolism and myelin structure; as well as caused disruption in the myelin sheath and reduction in neuronal density. Despite the low dose, we conclude that prolonged exposure to HgCl₂ triggers biochemical changes and modulates the expression of several proteins, resulting in damage to the myelin sheath and reduced neuronal density in the spinal cord.

Methylmercury intoxication and cortical ischemia: Pre-clinical study of their comorbidity

Stroke is one of the main causes of human disability worldwide. Ischemic stroke is mostly characterized by metabolic collapse and fast tissue damage, followed by secondary damage in adjacent regions not previously affected. Heavy metals intoxication can be associated with stroke incidence, because of their damaging action in the vascular system. Mercury, in particular, possesses a high tropism by metabolically active regions, such as the brain. In the present study we sought to evaluate whether methylmercury (MeHg) intoxication can aggravate the tissue damage caused by an ischemic stroke induced by microinjections of endothelin-1 (ET-1) into the motor cortex of adult rats. Following MeHg intoxication by gavage (0.04 mg/kg/day) during 60 days, the animals were injected with ET-1 (1 μl, 40 pmol/μl) or vehicle (1 μl). After 7 days, all animals were submitted to behavioral tests and then their brains were processed to biochemical and immunohistochemical analyses. We observed that long-term MeHg intoxication promoted a significant Hg deposits in the motor cortex, with concomitant increase of microglial response, followed by reduction of the neuronal population following ischemia and MeHg intoxication, as well as disturbance in the antioxidant defense mechanisms by misbalance of oxidative biochemistry with increase of both lipid peroxidation and nitrite levels, associated to behavioral deficits. MeHg exposure and cortical ischemia demonstrated that both injuries are able of causing significant neurobehavioural impairments in motor coordination and learning accompanied of an exacerbated microglial activation, oxidative stress and neuronal loss in the motor cortex, indicating that MeHg as a source of metabolic disturbance can act as an important increasing factor of ischemic events in the brain.

Neurochemical dysfunction in motor cortex and hippocampus impairs the behavioral performance of rats chronically exposed to inorganic mercury

Chronic exposure to mercury chloride (HgCl₂) has been shown to promote oxidative stress and cell death in the central nervous system of adult rats displaying motor and cognitive impairments. However, there are no investigations about neurochemical function after this type of exposure in rodents that may be associated with those behavioral changes already reported. Thus, the aim of this study was to analyze glutamatergic and GABAergic dysfunctions in the motor cortex and hippocampus of adult rats, in a model of chronic exposure to HgCl₂ in. Twenty rats were exposed to a daily dose of 0.375 mg/kg for 45 days. After this period, they were submitted to motor and cognitive functions tests and euthanized to collect the motor cortex and hippocampus for measurement of mercury (Hg) levels in the parenchyma and neurochemical assays for analysis of glutamatergic and GABAergic functions. It was observed that chronic exposure to HgCl₂ promoted increase in total Hg levels in these two brain areas, with changes in glutamatergic transport, but without changes in GABAergic transport. Functionally this model of exposure caused the decrease of the spontaneous motor locomotion and in the process of learning and memory. In this way, our results provide evidences that glutamatergic neurochemical dysfunction can be pointed out as a strong causal factor of motor and cognitive deficits observed in rats exposed to this HgCl₂.

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.

Methylmercury Intoxication Promotes Metallothionein Response and Cell Damage in Salivary Glands of Rats

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.

Efficacy of Hank's balanced salt solution compared to other solutions in the preservation of the periodontal ligament. A systematic review and meta-analysis

This systematic review and meta-analysis (MA) aimed to verify the capacity of different storage media to preserve viability of periodontal ligament cells in comparison to Hank’s Balanced Salt Solution. The searches, selection process, data extraction and Risk of Bias control were conducted according to Preferred Reporting Items for Systematic Review and Meta-Analysis guidelines. Five MA were conducted to compare the cell viability between milk versus Hank's balanced salt solution (HBSS) in a dichotomous (1) or continuous (2) data model; tap water versus HBSS (3); medicinal herbals versus HBSS (4); and saline solution versus HBSS (5). 693 potentially studies were identified, with 18 studies included in the qualitative and 8 studies included in the quantitative analysis. Most of the articles presented a low risk of bias. HBSS medium showed a superior ratio of cell viability compared to tap water (RR 0.26; 95% CI [0.21, 0.32]; p < 0.00001; I2 = 96%) and saline solution (RR 0.76; 95% CI [0.69, 0.84]; p < 0.0001; I2 = 99%). Herbal medicines showed a similar ratio of cell viability when compared to HBSS (RR 0.97; 95% CI [0.94, 1.00]; p = 0.08; I² = 50%). Mixed results were observed between milk and HBSS: a superior ratio of HBSS was observed in an overall evaluation (RR 0.26; 95% CI [0.21, 0.32]; p < 0.00001; I² = 96%), and a similar ratio was achieved when periodontal ligament (PDL) cells were removed prior to immersion in the solution (RR 0.94; 95% CI [0.87, 1.01]; p = 0.10; I2 = 0%) or rinsed in tap water or maintained in open air prior to immersion (RR 0.63; 95% CI [0.35, 1.12]; p = 0.11; I2 = not applicable). This systematic review and MA suggests that milk and herbal medicines could represent an alternative to HBSS. However, more studies are necessary to obtain a reliable conclusion.

Chronic intoxication by methylmercury leads to oxidative damage and cell death in salivary glands of rats

Methylmercury (MeHg) is one of the most toxic species of mercury, causing several systemic damages; however, its effect on the salivary glands has rarely been explored to date. This study was aimed at analyzing the mercury deposit, oxidative stress markers, and cell viability in parotid and submandibular rat salivary glands after chronic methylmercury intoxication. Herein, forty male Wistar rats (40 days old) were used in the experiment. The animals of the experimental group were intoxicated by intragastric gavage with MeHg at a dose of 0.04 mg per kg body weight per day for 35 days, whereas the control group received only corn oil, a diluent. After the period of intoxication, the glands were obtained for evaluation of total mercury deposit, cell viability, and the malondialdehyde (MDA) and the nitrite levels. Our results indicated mercury deposits in salivary glands, with a decrease in cell viability, higher levels of MDA in both glands of intoxicated animals, and a higher concentration of nitrite only in the submandibular gland of the mercury group. Thus, the intoxication by MeHg was able to generate deposits and oxidative stress in salivary glands that resulted in a decrease in cell viability in both types of glands.