Specific cerebral heat shock proteins and histamine receptor cross-talking mechanisms promote distinct lead-dependent neurotoxic responses in teleosts

Melatonin as an Ameliorative Agent Against Cadmium- and Lead-Induced Toxicity in Fish: an Overview

Diverse anthropogenic activities and lack of knowledge on its consequences have promoted serious heavy metal contaminations in different aquatic systems throughout the globe. The non-biodegradable nature of most of these toxic heavy metals has increased the concern on their possible bioaccumulation in aquatic organisms as well as in other vertebrates. Among these aquatic species, fish are most sensitive to such contaminated water that not only decreases their chance of survivability in the nature but also increases the probability of biomagnifications of these heavy metals in higher order food chain. After entering the fish body, heavy metals induce detrimental changes in different vital organs by impairing multiple physiological and biochemical pathways that are essential for the species. Such alterations may include tissue damage, induction of oxidative stress, immune-suppression, endocrine disorders, uncontrolled cell proliferation, DNA damage, and even apoptosis. Although uncountable reports have explored the toxic effects of different heavy metals in diverse fish species, but surprisingly, only a few attempts have been made to ameliorate such toxic effects. Since, oxidative stress seems to be the underlying common factor in such heavy metal-induced toxicity, therefore, a potent and endogenous antioxidant with no side effect may be an appropriate therapeutic solution. Apart from summarizing the toxic effects of two important toxicants, i.e., cadmium and lead in fish, the novelty of the present treatise lies in its arguments in favor of using melatonin, an endogenous free radical scavenger and indirect antioxidant, in ameliorating the toxic effects of heavy metals in any fish species.

Temperature- and chemical-induced neurotoxicity in zebrafish

Throughout their lives, humans encounter a plethora of substances capable of inducing neurotoxic effects, including drugs, heavy metals and pesticides. Neurotoxicity manifests when exposure to these chemicals disrupts the normal functioning of the nervous system, and some neurotoxic agents have been linked to neurodegenerative pathologies such as Parkinson's and Alzheimer's disease. The growing concern surrounding the neurotoxic impacts of both naturally occurring and man-made toxic substances necessitates the identification of animal models for rapid testing across a wide spectrum of substances and concentrations, and the utilization of tools capable of detecting nervous system alterations spanning from the molecular level up to the behavioural one. Zebrafish (Danio rerio) is gaining prominence in the field of neuroscience due to its versatility. The possibility of analysing all developmental stages (embryo, larva and adult), applying the most common "omics" approaches (transcriptomics, proteomics, lipidomics, etc.) and conducting a wide range of behavioural tests makes zebrafish an excellent model for neurotoxicity studies. This review delves into the main experimental approaches adopted and the main markers analysed in neurotoxicity studies in zebrafish, showing that neurotoxic phenomena can be triggered not only by exposure to chemical substances but also by fluctuations in temperature. The findings presented here serve as a valuable resource for the study of neurotoxicity in zebrafish and define new scenarios in ecotoxicology suggesting that alterations in temperature can synergistically compound the neurotoxic effects of chemical substances, intensifying their detrimental impact on fish populations.

Neurodegenerative Proteinopathies Induced by Environmental Pollutants: Heat Shock Proteins and Proteasome as Promising Therapeutic Tools

Environmental pollutants' (EPs) amount and diversity have increased in recent years due to anthropogenic activity. Several neurodegenerative diseases (NDs) are theorized to be related to EPs, as their incidence has increased in a similar way to human EPs exposure and they reproduce the main ND hallmarks. EPs induce several neurotoxic effects, including accumulation and gradual deposition of misfolded toxic proteins, producing neuronal malfunction and cell death. Cells possess different mechanisms to eliminate these toxic proteins, including heat shock proteins (HSPs) and the proteasome system. The accumulation and deleterious effects of toxic proteins are induced through HSPs and disruption of proteasome proteins' homeostatic function by exposure to EPs. A therapeutic approach has been proposed to reduce accumulation of toxic proteins through treatment with recombinant HSPs/proteasome or the use of compounds that increase their expression or activity. Our aim is to review the current literature on NDs related to EP exposure and their relationship with the disruption of the proteasome system and HSPs, as well as to discuss the toxic effects of dysfunction of HSPs and proteasome and the contradictory effects described in the literature. Lastly, we cover the therapeutic use of developed drugs and recombinant proteasome/HSPs to eliminate toxic proteins and prevent/treat EP-induced neurodegeneration.

WITHDRAWN: Effect of HSPA8 on the proliferation, apoptosis and immune function of chicken macrophages

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Early-life lead exposure induces long-term toxicity in the central nervous system: From zebrafish larvae to juveniles and adults

Lead induced neurotoxicity has been extensively investigated. However, the potential connections between early-life lead exposure and the frequently observed aberrant neurobehavior in juveniles and adults remain unclear. In this study, zebrafish model was used to explore the immediate and long-term effects of early-life exposure to environmental levels of lead on the central nervous system, and the cellular and molecular mechanisms underlying the consequent abnormal neurobehavior. Lead exposed zebrafish larvae exhibited neurologic damage and defective neurobehavior. Consistent with clinical studies, despite being raised in lead-free conditions, the juvenile and adult fish experienced lead exposure earlier, presented ADHD-like symptoms, and the adult fish exhibited remarkably affected vitality and shoaling behavior. Their anxiety levels were elevated, whereas their social interaction, as well as learning and memory were strongly depressed. The expression profiles of key genes involved in neurodevelopment and neurotransmitter systems were significantly modulated, in similar patterns as in the larval stage. Notably, the density of neurons was decreased and varicosities in neuronal axons were frequently observed in the lead-exposed groups. It's tempting to speculate that the disruption of early neurodevelopment as well as the prolonged modulation of neuromorphic and neurotransmitter systems contribute to the lead-induced neurobehavioral disorders observed in juveniles and adulthood.

Urtica dioica extracts abolish scopolamine-induced neuropathies in rats

Alzheimer's disease (AD) is characterized by alterations in monoamines, oxidative stress, and metabolic dysfunctions. We aim to assess the therapeutic impacts of roots or leaf extract from Urtica dioica (UD; stinging nettle) against scopolamine (SCOP)-induced memory dysfunction, amnesia, and oxidative stress in rats. Spatial memory was assessed by Y maze test. Tissue analyses of norepinephrine (NE), dopamine (DA), serotonin (5-HT), malondialdehyde (MDA), nitric oxide (NO), glutathione (GSH, GSSG), AMP, ADP, and ATP were assessed by HPLC. mRNA levels of Tau and Hsp70 were estimated by PCR. UD extracts particularly nettle root (NR) significantly normalized the SCOP-induced memory deficits even more potent than sermion (SR) and donepezil (DON). Similarly, NR had potent therapeutic impacts on the levels of cortical and hippocampal monoamines e.g. DA, NE, and 5-HT. SCOP induced a dramatic oxidative stress as measured by MDA, NO, and GSSG levels; however, UD extracts showed significant anti-oxidative stress impacts. Additionally, UD extracts restored ATP levels and reduced the levels of AMP and ADP compared to SCOP-treated rats. Furthermore, cortical Tau and hippocampal Hsp70 were modulated by UD extracts particularly NR compared to the SCOP group. In conclusion, UD extracts particularly roots have potential therapeutic impacts against SCOP-induced neuroinflammatory and/or Alzheimer-like phenotype in rats.

Lead toxicity in seawater teleosts: A morphofunctional and ultrastructural study on the gills of the Ornate wrasse (Thalassoma pavo L.)

Lead is one of the most alarming toxic pollutants for the environment due to its acute toxicity and high bioaccumulation tendency. Despite legislative efforts, world lead production has more than doubled since the early 1970s to 2016. Due to extensive exploitation and human activity, the coastal and estuarine regions belong to marine environments that are mostly and more rapidly deteriorated by pollutants including lead. A limited number of studies examined the effects of lead in fishes, compared to other aquatic models and even fewer studies have been dedicated to seawater fishes especially regarding Pb adsorption and accumulation in specific organs. Fish gills, key compartments involved in several crucial functions such as gas exchange, osmoregulation, and excretion, are also the organs in which Pb is mainly accumulated. Herein, we investigated the morphofunctional and ultrastructural modifications in the gills of a marine teleost (Thalassoma pavo) after acute exposure (48, 96, 192 h) to three lead concentrations. We showed that pathological alterations can be detected in all the examined samples. The most common modifications observed were: the curling of the lamellae and the dilation of their apical tips, the lamellar edema, the proliferation and the hypertrophy of CCs, the progressive epithelial disorganization with detachment of the epithelium from connective tissue. This study also demonstrates that there is a weak influence on the expression pattern of Na⁺/K⁺-ATPase and AQP3 biomarker enzymes while high metallothioneins expression has been observed. The described alterations may adversely affect gas exchange and ionic balance, with a long chain of cascading effects. This is the first evidence of the effects exerted by lead on gills of seawater fishes that highlights the harmful properties of this metal, even at low concentration.

The neurological toxicity of heavy metals: A fish perspective

The causes of neurodegenerative diseases are complex with likely contributions from genetic susceptibility and environmental exposures over an organism's lifetime. In this review, we examine the role that aquatic models, especially zebrafish, have played in the elucidation of mechanisms of heavy metal toxicity and nervous system function over the last decade. Focus is applied to cadmium, lead, and mercury as significant contributors to central nervous system morbidity, and the application of numerous transgenic zebrafish expressing fluorescent reporters in specific neuronal populations or brain regions enabling high-resolution neurodevelopmental and neurotoxicology research.

Host condition and accumulation of metals by acanthocephalan parasite Echinorhynchus gadi in cod Gadus morhua from the southern Baltic Sea

In this study, we analyzed the relationship between concentration of metals in the host-parasite system (cod - acanthocephalan Echinorhynchus gadi) and Fulton's condition factor (FCF) of the host. The relationship between metal (Ca, Cd, Cr, Cu, Fe, Hg, K, Mg, Mn, Na, Pb, Sr, Zn) concentrations in E. gadi and cod tissues was expressed as a bioconcentration factor (BCF), the ratio of the concentration in the parasite tissue to that in host tissues. Acanthocephalans accumulated mainly toxic metals (Cd, Pb), as well as Sr, Ca, Na. Cadmium showed the highest bioconcentration in parasites (BCF >200) compared to fish muscle. Significant negative correlation was detected between FCF and the concentration of Cd and Hg in cod liver. In contrast, FCF was positively correlated with the concentration of Hg in acanthocephalan tissues.

Cross-species coherence in effects and modes of action in support of causality determinations in the U.S. Environmental Protection Agency's Integrated Science Assessment for Lead

The peer-reviewed literature on the health and ecological effects of lead (Pb) indicates common effects and underlying modes of action across multiple organisms for several endpoints. Based on such observations, the United States (U.S.) Environmental Protection Agency (EPA) applied a cross-species approach in the 2013 Integrated Science Assessment (ISA) for Lead for evaluating the causality of relationships between Pb exposure and specific endpoints that are shared by humans, laboratory animals, and ecological receptors (i.e., hematological effects, reproductive and developmental effects, and nervous system effects). Other effects of Pb (i.e., cardiovascular, renal, and inflammatory responses) are less commonly assessed in aquatic and terrestrial wildlife limiting the application of cross-species comparisons. Determinations of causality in ISAs are guided by a framework for classifying the weight of evidence across scientific disciplines and across related effects by considering aspects such as biological plausibility and coherence. As illustrated for effects of Pb where evidence across species exists, the integration of coherent effects and common underlying modes of action can serve as a means to substantiate conclusions regarding the causal nature of the health and ecological effects of environmental toxicants.

Lead-induced neurodegenerative events and abnormal behaviors occur via ORXRergic/GABA(A)Rergic mechanisms in a marine teleost

The hindering effects of metals and in particular lead (Pb) are representing a growing threat to aquatic organisms such as fish. This observation derives from toxic concentrations of Pb accounting for altered neurophysiological activities of some interesting teleost models like Thalassoma pavo, a fish species highly known for its host-cleaning symbiosis. In this study, the nominal PbNO(3) concentration of 1.6 mg/L was capable of reducing feeding and resting bouts as early as 24 h of exposure while hyperactive swimming episodes were also detected. Such abnormal behaviors were tightly correlated to up-regulated orexin receptor (ORXR) mRNA expression levels in some brain areas such as the lateral thalamic nucleus (+213%) and the optic tectum (+90%) with respect to controls. Interestingly, these transcriptional effects seemed to be attenuated when Pb-exposed fish received either 100 ng/g of ORX-A (-70%) or 0.1 μg/g of γ-aminobutyric acid(A) receptor (GABA(A)R) agonist muscimol (MUS; -97%) compared to fish exposed to Pb alone. Moreover, a net neurodegenerative process of the different brain areas was reported after Pb exposure as displayed by their marked amino cupric silver stained cells while these cells were devoid of any staining reaction after treatment with MUS only. Conversely, addition of the GABA(A)R antagonist bicuculline (BIC; 1 μg/g) moderately (p<0.05) enhanced Pb-dependent behavioral and neurodegenerative actions. Overall, these first indications strongly point to altered ORXR/GABA(A)R interactions during neurotoxic events of a metal that by evoking harmful neurobiological dysfunctions may endanger the survival of commercially valuable fish with eventual repercussions on human health.

A subset of histamine receptor ligands improve thermotolerance of the yeast Saccharomyces cerevisiae

AIMS

Histamine interacts with the stress response in eukaryotes. This study investigated the effects of antihistamines on the heat shock (HS) response in yeast, thereby exploring their functions in a well-established histamine receptor (H(x) R)-free model.

METHODS AND RESULTS

Stress response was evaluated by determining growth and viability of postlogarithmic phase grown yeast cultures after HS at 53°C for 30 min. The effects of H(x) R ligands were investigated following short- and long-term administration. The H(1) R antagonist dimethindene exerted dose-related antifungal actions, whereas the H(2) R antagonist ranitidine failed to elicit any effect. In contrast, the H(3/4) R and H(4) R ligands, thioperamide and JNJ7777120, respectively, induced the thermotolerant phenotype. The circumvention of thermotolerance by cycloheximide and the induction of Hsp70 and Hsp104 expression indicated the contribution of de novo protein synthesis in the adaptive process, likely directed towards alterations in Hsp expression.

CONCLUSIONS

The data provide evidence for the differential function of H(x) R ligands in thermotolerance induction in yeast.

SIGNIFICANCE AND IMPACT OF THE STUDY

First demonstration of the action of antihistamines in the HS response in yeast. The work supports the potential H(x) R-independent functions of histaminergic compounds in fungal adaptation and stimulates research on the prospect of their exploitation in eukaryotic (patho)physiology.

Histamine H3 receptor antagonists in relation to epilepsy and neurodegeneration: a systemic consideration of recent progress and perspectives

The central histaminergic actions are mediated by H(1) , H(2) , H(3) and H(4) receptors. The histamine H(3) receptor regulates the release of histamine and a number of other neurotransmitters and thereby plays a role in cognitive and homeostatic processes. Elevated histamine levels suppress seizure activities and appear to confer neuroprotection. The H(3) receptors have a number of enigmatic features like constitutive activity, interspecies variation, distinct ligand binding affinities and differential distribution of prototypic splice variants in the CNS. Furthermore, this Gi/Go-protein-coupled receptor modulates several intracellular signalling pathways whose involvement in epilepsy and neurotoxicity are yet to be ascertained and hence represent an attractive target in the search for new anti-epileptogenic drugs. So far, H(3) receptor antagonists/inverse agonists have garnered a great deal of interest in view of their promising therapeutic properties in various CNS disorders including epilepsy and related neurotoxicity. However, a number of experiments have yielded opposing effects. This article reviews recent works that have provided evidence for diverse mechanisms of antiepileptic and neuroprotective effects that were observed in various experimental models both in vitro and in vivo. The likely reasons for the apparent disparities arising from the literature are also discussed with the aim of establishing a more reliable basis for the future use of H(3) receptor antagonists, thus improving their utility in epilepsy and associated neurotoxicity.

Developmental lead acetate exposure induces embryonic toxicity and memory deficit in adult zebrafish

Lead is a persistent metal and commonly present in our living environment. The present study was aimed to investigate lead-induced embryonic toxicity, behavioral responses, and adult learning/memory deficit in zebrafish. Lead acetate (PbAc) induced malformations such as uninflated swim bladder, bent spine and yolk-sac edema with an EC₅₀ of 0.29 mg/L at 120 h post fertilization (hpf). Spontaneous movement as characterized by tail bend frequency was significantly altered in zebrafish embryos following exposure to PbAc. Behavior assessment demonstrated that lead exposure changed behavioral responses in zebrafish larvae, as hyperactivity was detected within the first minute of light-to-dark transition in the fish exposed to PbAc from 6 to 96 hpf, and a different dose-dependent change was found in swimming speeds in the dark and in the light at 120 hpf following lead exposure. Learning/memory task assay showed that embryos exposed to PbAc from 6 to 120 hpf developed learning/memory deficit at adulthood as exhibited by a significant decrease in accuracy rate to find the food and a significant increase in finding time. Overall, our results suggested that low dose of developmental lead exposure resulted in embryonic toxicity, behavioral alteration, and adult learning/memory deficit in zebrafish.

Effects of acute and chronic waterborne lead exposure on the swimming performance and aerobic scope of fathead minnows (Pimephales promelas)

Fathead minnows were subjected to an incremental velocity test using swim tunnel respirometry for the analysis of aerobic scope and swimming performance, as critical aerobic swim speed (U(crit)), following chronic exposures (33-57 ) to 0.9±0.4, 157±18 or 689±66 nmol L⁻¹ Pb and an acute exposure (24 h) to 672±35 nmol L⁻¹ Pb (mean±SEM). Assessment of Pb-induced anemia and neurological impairment were evaluated by blood hemoglobin (Hb) concentrations and a cost of transport (COT) analysis, respectively. Fish from the acute 672±35 nmol L⁻¹ Pb (24.4±1.2 BL s⁻¹) and chronic 689±66 nmol L⁻¹ Pb (24.6±0.9 BL s⁻¹) treatments exhibited reduced U(crits) compared to control fish (27.6±0.8 BL s⁻¹). Aerobic scope was reduced by acute Pb exposure (8.6±2.6 μmol O₂ g⁻¹ h⁻¹ vs. 22.6±3.8 μmol O₂ g⁻¹ h⁻¹ from controls) owing to a decrease in maximum oxygen consumption rate (38.8±0.8 μmol O₂ g⁻¹ h⁻¹ vs. 54.0±4.2 μmol O₂ g⁻¹ h⁻¹ from controls). However, no effect on aerobic scope was observed with fish chronically exposed to Pb. Significant differences were not observed for Hb concentrations or COT. These findings suggest that the impaired swimming performances arising from acute and chronic Pb exposures reflect different mechanisms of toxicity.

Characterization of two heat shock proteins (Hsp70/Hsc70) from grass carp (Ctenopharyngodon idella): evidence for their differential gene expression, protein synthesis and secretion in LPS-challenged peripheral blood lymphocytes

Two cDNAs, encoding the stress-inducible 70-kDa heat shock protein (Hsp70) and the constitutively expressed 70-kDa heat shock cognate protein (Hsc70), were isolated from grass carp. The Hsp70 and Hsc70 cDNAs were 2250 bp and 2449 bp in length and contained 1932 bp and 1953 bp open reading frames, respectively. Tissue distribution results showed that Hsp70/Hsc70 was highly expressed in gill, kidney, head kidney and peripheral blood lymphocytes (PBLs). Using grass carp PBLs as a cell model, effects of lipopolysaccharide (LPS) on the mRNA and protein levels of Hsp70/Hsc70 were examined. In this case, LPS increased the mRNA expression of Hsp70 in a time- and dose-dependent manner, but had no effect on Hsc70 mRNA expression. In agreement with this, LPS elevated the intracellular Hsp70 markedly, but not the Hsc70 protein levels in parallel experiments. Furthermore, Hsp70 protein was also detected in culture medium. Moreover, inhibition of LPS on Hsp70 release in a time-dependent manner was observed, indicating that there may be a dynamic balance between Hsp70 stores and Hsp70 release in grass carp PBLs following exposure to LPS. Taken together, these results not only shed new insights into the different regulations of LPS on Hsp70/Hsc70 gene expression, protein synthesis and release, but also provide a basis for further study on the functional role of Hsp70 in fish immune response.

Lungfish aestivating activities are locked in distinct encephalic γ-aminobutyric acid type A receptor α subunits

Ammonia in dipnoans plays a crucial role on neuronal homeostasis, especially for those brain areas that maintain torpor and awakening states in equilibrium. In the present study, specific α subunits of the major neuroreceptor inhibitory complex (GABA(A) R), which predominated during some phases of aestivation of the lungfish Protopterus annectens, turned out to be key adaptive factors of this species. From the isolation, for the first time, of the encoding sequence for GABA(A) R α₁, α₄ , and α₅ subunits in Protopterus annectens, qPCR and in situ hybridization levels of α₄ transcript in thalamic (P < 0.001) and mesencephalic (P < 0.01) areas proved to be significantly higher during long aestivating maintenance states. Very evident α₅ mRNA levels were detected in diencephalon during short inductive aestivating states, whereas an α₄ /α₁ turnover characterized the arousal state. Contextually, the recovery of physiological activities appeared to be tightly related to an evident up-regulation of α₁ transcripts in telencephalic and cerebellar sites. Surprisingly, TUNEL and amino cupric silver methods corroborated apoptotic and neurodegenerative cellular events, respectively, above all in telencephalon and cerebellum of lungfish exposed to long maintenance aestivating conditions. Overall, these results tend to underlie a novel GABAergic-related ON/OFF molecular switch operating during aestivation of the lungfish, which might have a bearing on sleeping disorders.