A mechanism for acute aluminium toxicity in fish

Aluminium is acutely toxic to fish in acid waters. The gill is the principal target organ and death is due to a combination of ionoregulatory, osmoregulatory and respiratory dysfunction. The toxic mechanism has hitherto received little direct consideration and is unknown. In this paper the mechanism of acute aluminium toxicity is approached from a chemical perspective. Symptomatic evidence of toxicity is taken from the literature and combined with our own research to elucidate a biochemically sound model to describe a possible mechanism of acute aluminium toxicity in fish. The proposed model delineates the chemical conditions immediately adjacent to the gill surface and emphasizes their importance in aluminium's toxic mode of action. The mechanism is shown to be bipartite. Aluminium binding to functional groups both apically located at the gill surface and intracellularly located within lamellar epithelial cells disrupts the barrier properties of the gill epithelium. The concomitant iono- and osmoregulatory dysfunction results in accelerated cell necrosis, sloughing and death of the fish. The mechanism of epithelial cell death is proposed as a general mechanism of aluminium-induced accelerated cell death.     

Multivessel system for cold-vapor mercury generation determination of mercury in hair and fish

A multivessel system for the determination of mercury (Hg) by cold-vapor atomic absorption spectrometry (CV-AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) was developed. The performance of the proposed device was tested by determining total Hg in quality-control samples of hair and fishes following acid digestion. Application of the apparatus to the determination of Hg by CV-AAS following alkaline digestion was studied as well. The detection limit obtained for CV-AAS was 0.11 ng/mL and for ICP-AES 1.39 ng/mL. The results show that the system is appropriate to be used in techniques involving cold-vapor generation of Hg.     

From distributed sensory processing to discrete motor representations in the diencephalon of the electric fish,Eigenmannia

Summary During their jamming avoidance response (JAR), weakly electric fish of the genusEigenmannia shift their electric organ discharge (EOD) frequency away from a similar EOD frequency of a neighboring fish. The behavioral rules and neural substrates for stimulus recognition and motor control of the JAR have been extensively studied (see review by Heiligenberg 1986). The diencephalic nucleus electrosensorius (nE) links sensory processing within the torus semicircularis and optic tectum with the mesencephalic prepacemaker nucleus which, in turn, modulates the medullary pacemaker nucleus and hence the EOD frequency. Two separate areas within the nE responsible for JAR-related EOD frequency rises and frequency falls, respectively, were identified by iontophoresis of the excitatory amino acid L-glutamate. Bilateral lesion of the areas causing EOD frequency rises resulted in elimination of JAR-related frequency rises above a baseline frequency obtained in the absence of a jamming stimulus. Similarly, bilateral lesion of the areas causing frequency falls resulted in a loss of JAR-related frequency falls below the baseline frequency. Whether these areas are also responsible for non-JAR-related frequency shifts is not known. The strength of response and spatial extent of the areas causing frequency shifts varied among fish and also varied in individual fish, reflecting the strength of JAR-related frequency shifts and the balance of activities in frequency-rise and frequency-fall areas. Local application of bicuculline-methiodide or GABA demonstrated a tonic inhibitory input to each area and suggests a reciprocal inhibitory interaction between the two ipsilateral areas, possibly accounting for much of the individual plasticity.The nE thus is a site for neuronal transformation from distributed, topographically organized processing within the laminated structures of the torus and tectum to discrete cell clusters which control antagonistic motor responses.Abbreviations EOD electric organ discharge - JAR jamming avoidance response - Df difference frequency between jamming signal and the fish's own EOD - nE nucleus electrosensorius - PPn prepacemaker nucleus     

DMPS and N-acetylcysteine induced renal toxicity in mice exposed to mercury

Acute effects of mercuric chloride (HgCl₂) were evaluated on mice. Mice received a single dose of HgCl₂ (4.6 mg/kg, subcutaneously) for three consecutive days. Thirty minutes after the last injection with HgCl₂, mice received one single injection of 2,3-dimercapto-1-propanesulfonic acid (DMPS) or N-acetylcysteine (NAC) or diphenyl diselenide (PhSe)₂. DMPS, NAC and (PhSe)₂ were utilized as therapy against mercury exposure. At 24 h after the last HgCl₂ injection, blood, liver and kidney samples were collected. δ-Aminolevulinate dehydratase (δ-ALA-D) and Na⁺, K_-⁺ ATPase activities, thiobarbituric acid-reactive substances (TBARS), non-protein thiols (NPSH) and ascorbic acid concentrations were evaluated. Plasma aspartate (AST) and alanine (ALT) aminotransferase activities, as well as urea and creatinine levels were determined. The group of mice exposed to Hg + (PhSe)₂ presented 100% of lethality. Exposure with HgCl₂ caused a decrease on the body weight gain and treatments did not modify this parameter. δ-ALA-D, AST and ALT activities, TBARS, ascorbic acid levels and NPSH (hepatic and erythrocytic) levels were not changed after HgCl₂ exposure. HgCl₂ caused an increase in renal NPSH content and therapies did not modify these levels. Mice treated with (PhSe)₂, Hg + NAC and Hg + DMPS presented a reduction in plasma NPSH levels. Creatinine and urea levels were increased in mice exposed to Hg + NAC, while Hg + DMPS group presented an increase only in urea level. Na⁺, K_-⁺ ATPase activity was inhibited in mice exposed to Hg + DMPS and Hg + NAC. In conclusion, therapies with (PhSe)₂, DMPS and NAC following mercury exposure must be better studied because the formation of more toxic complexes with mercury, which can mainly damage renal tissue.     

Integrated decision-tree testing strategies for acute systemic toxicity and toxicokinetics with respect to the requirements of the EU REACH legislation

Liverpool John Moores University and FRAME conducted a joint research project, sponsored by Defra, on the status of alternatives to animal testing with regard to the European Union REACH (Registration, Evaluation and Authorisation of Chemicals) system for the safety testing and risk assessment of chemicals. The project covered all the main toxicity endpoints associated with REACH. This paper focuses on the use of alternative (non-animal) methods (both in vitro and in silico) for acute systemic toxicity and toxicokinetic testing. The paper reviews in vitro tests based on basal cytotoxicity and target organ toxicity, along with QSAR models and expert systems available for this endpoint. The use of PBPK modelling for the prediction of ADME properties is also discussed. These tests are then incorporated into a decision-tree style, integrated testing strategy, which also includes the use of refined in vivo acute toxicity tests, as a last resort. The implementation of the strategy is intended to minimise the use of animals in the testing of acute systemic toxicity and toxicokinetics, whilst satisfying the scientific and logistical demands of the EU REACH legislation.     

From decision to action: Detailed modelling of frog tadpoles reveals neuronal mechanisms of decision-making and reproduces unpredictable swimming movements in response to sensory signals

How does the brain process sensory stimuli, and decide whether to initiate locomotor behaviour? To investigate this question we develop two whole body computer models of a tadpole. The “Central Nervous System” (CNS) model uses evidence from whole-cell recording to define 2300 neurons in 12 classes to study how sensory signals from the skin initiate and stop swimming. In response to skin stimulation, it generates realistic sensory pathway spiking and shows how hindbrain sensory memory populations on each side can compete to initiate reticulospinal neuron firing and start swimming. The 3-D “Virtual Tadpole” (VT) biomechanical model with realistic muscle innervation, body flexion, body-water interaction, and movement is then used to evaluate if motor nerve outputs from the CNS model can produce swimming-like movements in a volume of “water”. We find that the whole tadpole VT model generates reliable and realistic swimming. Combining these two models opens new perspectives for experiments.     

Toxicity of mercury: A comparative study in air-breathing and non air-breathing fish

Annual primary production was estimated from two years data. The results indicate a high primary productivity and a short turn over time for nitrogen.

     

Temperature and species differences in susceptibility of kidney cell cultures to mercury toxicity

The effect of temperature on inorganic mercury toxicity was investigated using kidney tissue culture systems. The relative susceptibility of rabbit (homeothermic) kidney to mercury intoxication was compared to that of Coho salmon (poikilothermic) kidney to mercury intoxication was compared to that of Coho salmon (poikilothermic) kidney over temperature ranges consistent with the habitat of each of the two species. It was demonstrated that susceptibility to mercury toxicity is species dependent; that is, the rabbit kidney cells tolerated higher mercury concentrations in the medium than did the fish-derived cells. Within a given species, susceptibility to mercury toxicity was temperature dependent. Decreasing the temperature increased the toxicity of mercury to cultures of rabbit kidney cells, whereas decreasing temperatures decreased the effect of mercury toxicity on the salmon kidney cells. As a consequence, fish taken from arctic waters are liable to be more toxic when introduced into mammalian food chains. Albumin was shown to act as a protective agent in vitro against inorganic mercury toxicity.     

Temperature and species differences in susceptibility of kidney cell cultures to mercury toxicity

Summary The effect of temperature on inorganic mercury toxicity was investigated using kidney tissue culture systems. The relative susceptibility of rabbit (homeothermic) kidney to mercury intoxication was compared to that of Coho salmon (poikilothermic) kidney over temperature ranges consistent with the habitat of each of the two species. It was demonstrated that susceptibility to mercury toxicity is species dependent; that is, the rabbit kidney cells tolerated higher mercury concentrations in the medium than did the fish-derived cells. Within a given species, susceptibility to mercury toxicity was temperature dependent. Decreasing the temperature increased the toxicity of mercury to cultures of rabbit kidney cells, whereas decreasing temperatures decreased the effect of mercury toxicity on the salmon kidney cells. As a consequence, fish taken from arctic waters are liable to be more toxic when introduced into mammalian food chains. Albumin was shown to act as a protective agent in vitro against inorganic mercury toxicity. Research was supported in part by the University of Victoria Faculty Grant No. 08-869 and a Medical Staff Research and Education Fund Grant from Wayne County General Hospital, Eloise, Michigan.     

A review of the multi-level adaptations for maximizing aerobic dive duration in marine mammals: from biochemistry to behavior

Marine mammals exhibit multi-level adaptations, from cellular biochemistry to behavior, that maximize aerobic dive duration. A dive response during aerobic dives enables the efficient use of blood and muscle oxygen stores, but it is exercise modulated to maximize the aerobic dive limit at different levels of exertion. Blood volume and concentrations of blood hemoglobin and muscle myoglobin are elevated and serve as a significant oxygen store that increases aerobic dive duration. However, myoglobin is not homogeneously distributed in the locomotory muscles and is highest in areas that produce greater force and consume more oxygen during aerobic swimming. Muscle fibers are primarily fast and slow twitch oxidative with elevated mitochondrial volume densities and enhanced oxidative enzyme activities that are highest in areas that produce more force generation. Most of the muscle mitochondria are interfibriller and homogeneously distributed. This reduces the diffusion distance between mitochondria and helps maintain aerobic metabolism under hypoxic conditions. Mitochondrial volume densities and oxidative enzyme activities are also elevated in certain organs such as liver, kidneys, and stomach. Hepatic and renal function along with digestion and assimilation continue during aerobic dives to maintain physiological homeostasis. Most ATP production comes from aerobic fat metabolism in carnivorous marine mammals. Glucose is derived mostly from gluconeogenesis and is conserved for tissues such as red blood cells and the central nervous system. Marine mammals minimize the energetic cost of swimming and diving through body streamlining, efficient, lift-based propulsive appendages, and cost-efficient modes of locomotion that reduce drag and take advantage of changes in buoyancy with depth. Most dives are within the animal’s aerobic dive limit, which maximizes time underwater and minimizes recovery time at the surface. The result of these adaptations is increased breath-hold duration and enhanced foraging ability that maximizes energy intake and minimizes energy output while making aerobic dives to depth. These adaptations are the long, evolutionary legacy of an aquatic lifestyle that directly affects the fitness of marine mammal species for different diving abilities and environments.     

A hybrid molecule that prohibits amyloid fibrils and alleviates neuronal toxicity induced by beta-amyloid (1-42)

Inhibition of oligomeric amyloid beta (Abeta) peptide or fibril formation has emerged as a major therapeutic target for developing new drugs for Alzheimer's disease. We focused on developing inhibitors by synthesizing hybrid molecules of ferulic acid and styryl benzene, which has been known as a fibril binder. Initially, cell-based assay was carried out to evaluate the effective compound. A selected effector, 1, alleviated the Abeta-induced neuronal toxicity in differentiated SH-SY5Y human neuroblastoma cells. The effector could also inhibit Abeta fibril formation, monitored by thioflavin T fluorescence intensity assay and transmitted electron microscopic images. A strong binding affinity of 1 to non-fibrous monomer-like Abeta, which was immobilized to a surface chip, was measured using a surface plasmon resonance technique. The data suggest that the effector shifts the equilibrium of multimeric Abeta, inhibiting the pathogenic oligomer or fibril formation.     

Dietary self-selection in fish: a new approach to studying fish nutrition and feeding behavior

The principles of modern aquaculture encourage the development of fish feeds containing low fish meal content and several types of plant ingredients plus nutrients to avoid depleting global fish stocks and to reduce costs. However, food constituents can affect animal nutrition and feeding behavior, so the effect of different diets on fish behavior and growth needs to be understood to optimize the use of nutrients and to improve fish welfare. The development of multiple-choice self-feeding systems led to a new perspective for investigating these issues in aquaculture species. Our purpose with this review is to summarize the information that has been published to date on this topic and to identify gaps in knowledge where research is needed. Key subjects are assessed under the following major headings: How do we study dietary selection in fish? What food signals do fish use to choose the right diet? and How do fish respond to food challenges? The present review will provide a picture of the main results obtained to date in these studies in aquaculture fish species, as well as perspectives for future research in the field.     

Prefoldin 5 is required for normal sensory and neuronal development in a murine model

Molecular chaperones and co-chaperones are crucial for cellular development and maintenance as they assist in protein folding and stabilization of unfolded or misfolded proteins. Prefoldin (PFDN), a ubiquitously expressed heterohexameric co-chaperone, is necessary for proper folding of nascent proteins, in particular, tubulin and actin. Here we show that a genetic disruption in the murine Pfdn5 gene, a subunit of prefoldin, causes a syndrome characterized by photoreceptor degeneration, central nervous system abnormalities, and male infertility. Our data indicate that a missense mutation in Pfdn5, may cause these phenotypes through a reduction in formation of microtubules and microfilaments, which are necessary for the development of cilia and cytoskeletal structures, respectively. The diversity of phenotypes demonstrated by models carrying mutations in different PFDN subunits suggests that each PFDN subunit must confer a distinct substrate specificity to the prefoldin holocomplex.     

Metallothioneins are required for formation of cross-adaptation response to neurobehavioral toxicity from lead and mercury exposure in nematodes

Metallothioneins (MTs) are small, cysteine-rich polypeptides, but the role of MTs in inducing the formation of adaptive response is still largely unknown. We investigated the roles of metallothionein genes (mtl-1 and mtl-2) in the formation of cross-adaptation response to neurobehavioral toxicity from metal exposure in Caenorhabditis elegans. Pre-treatment with mild heat-shock at L2-larva stage effectively prevented the formation of the neurobehavioral defects and the activation of severe stress response in metal exposed nematodes at concentrations of 50 and 100 μM, but pre-treatment with mild heat-shock did not prevent the formation of neurobehavioral defects in 200 μM of metal exposed nematodes. During the formation of cross-adaptation response, the induction of mtl-1 and mtl-2 promoter activity and subsequent GFP gene expression were sharply increased in 50 μM or 100 μM of metal exposed Pmtl-1::GFP and Pmtl-2::GFP transgenic adult animals after mild heat-shock treatment compared with those treated with mild heat-shock or metal exposure alone. Moreover, after pre-treatment with mild heat-shock, no noticeable increase of locomotion behaviors could be observed in metal exposed mtl-1 or mtl-2 mutant nematodes compared to those without mild heat-shock pre-treatment. The defects of adaptive response to neurobehavioral toxicity induced by metal exposure formed in mtl-1 and mtl-2 mutants could be completely rescued by the expression of mtl-1 and mtl-2 with the aid of their native promoters. Furthermore, over-expression of MTL-1 and MTL-2 at the L2-larval stage significantly suppressed the toxicity on locomotion behaviors from metal exposure at all examined concentrations. Therefore, the normal formation of cross-adaptation response to neurobehavioral toxicity induced by metal exposure may need the enough accumulation of MTs protein in animal tissues.     

Antitumor activity and toxicity of peroxo heteroligand vanadates(V) in relation to biochemistry of vanadium

A selected set of 14 V(V) complexes was tested for toxicity and antitumor activity against L1210 murine leukemia, to examine the biological properties of peroxoheteroligand vanadates(V) of the formula (NH4)4[O(VO(O2)2)2], M3I[VO(O2)2C2O4], and MI[VO(O2)L], L = malate, citrate, iminodiacetate, nitrilotriacetate, and EDTA. The x-ray structure is known for five of these compounds. A relationship has been found between the chemical composition and the biological activity (antitumor activity-toxicity) of these complexes. Activity in the L1210 system is defined as greater than or equal to 25% increase in life span, and this was seen with (NH4)4[O(VO(O2)2)2]; M3[VO(O2)2(C2O4)]2H2O, M = K, NH4; and NH4[VO(O2)Malato]H2O. These observations are important for the biochemistry of vanadium. The special nature of electron transfer within the V(V)-peroxo moiety is proposed to be responsible for this phenomenon. Peroxo heteroligand vanadates(V) therefore represent a model system for studying some biochemical interactions of vanadium in living matter.     

A lateral-displacement flume for fish behavior and stranding studies during simulated pulsed flows

In regulated rivers, fluctuating water depths associated with pulsed discharges may strand small fish in side channels and pools. Quantitative assessments of stranded fish are difficult in field studies (e.g., due to unknown effects of avian and terrestrial vertebrate predators). To assess such lateral displacement and stranding on juvenile stream fishes, we designed, constructed, and tested (with three species) a 2 × 1-m, lateral-displacement flume. The flume featured a main channel that never drained and a raised, wide “floodplain” channel that alternately flooded, with a simulated pulse, and became dewatered. The floodplain contained four pools, with different shapes and draining capacities, in which fish could become stranded as the water level subsided. Fish-stranding rates (8%) in this relatively compact laboratory flume, after exposure to simulated pulsed stream flows, were comparable to those observed in past investigations using larger, artificial streams.