Identification of antiparkinsonian drugs in the 6-hydroxydopamine zebrafish model

Parkinson's disease (PD) is known as a movement disorder due to characteristic motor features. Existing therapies for PD are only symptomatic, and their efficacy decreases as disease progresses. Zebrafish, a vertebrate in which parkinsonism has been modelled, offers unique features for the identification of molecules with antiparkinsonian properties. Here, we developed a screening assay for the selection of neuroactive agents with antiparkinsonian potential. First, we performed a pharmacological validation of the phenotypes exhibited by the 6-hydroxydopamine zebrafish model, by testing the effects of known antiparkinsonian agents. These drugs were also tested for disease-modifying properties by whole mount immunohistochemistry to TH⁺ neurons and confocal microscopy in the dopaminergic diencephalic cluster of zebrafish. Next, we optimized a phenotypic screening using the 6-hydroxydopamine zebrafish model and tested 1600 FDA-approved bioactive drugs. We found that 6-hydroxydopamine-lesioned zebrafish larvae exhibit bradykinetic and dyskinetic-like behaviours that are rescued by the administration of levodopa, rasagiline, isradipine or amantadine. The rescue of dopaminergic cell loss by isradipine was also verified, through the observation of a higher number of TH⁺ neurons in 6-OHDA-lesioned zebrafish larvae treated with this compound as compared to untreated lesioned larvae. The phenotypic screening enabled us to identify several compounds previously positioned for PD, as well as, new molecules with potential antiparkinsonian properties. Among these, we selected stavudine, tapentadol and nabumetone as the most promising candidates. Our results demonstrate the functional similarities of the motor impairments exhibited by 6-hydroxydopamine-lesioned zebrafish with mammalian models of PD and with PD patients, and highlights novel molecules with antiparkinsonian potential.

Nash Equilibria in the Response Strategy of Correlated Games

In nature and society, problems that arise when different interests are difficult to reconcile are modeled in game theory. While most applications assume that the players make decisions based only on the payoff matrix, a more detailed modeling is necessary if we also want to consider the influence of correlations on the decisions of the players. We therefore extend here the existing framework of correlated strategies by giving the players the freedom to respond to the instructions of the correlation device by probabilistically following or not following its suggestions. This creates a new type of games that we call “correlated games”. The associated response strategies that can solve these games turn out to have a rich structure of Nash equilibria that goes beyond the correlated equilibrium and pure or mixed-strategy solutions and also gives better payoffs in certain cases. We here determine these Nash equilibria for all possible correlated Snowdrift games and we find these solutions to be describable by Ising models in thermal equilibrium. We believe that our approach paves the way to a study of correlations in games that uncovers the existence of interesting underlying interaction mechanisms, without compromising the independence of the players.

Temporal variability of radon in a remediated tailing of uranium ore processing--the case of Urgeiriça (central Portugal)

Radon monitoring at different levels of the cover of the Urgeiriça tailings shows that the sealing is effective and performing as desired in terms of containing the strongly radioactive waste resulting from uranium ore processing. However, the analysis of the time series of radon concentration shows a very complex temporal structure, particularly at depth, including very large and fast variations from a few tens of kBq m(-3) to more than a million kBq m(-3) in less than one day. The diurnal variability is strongly asymmetric, peaking at 18 h/19 h and decreasing very fast around 21 h/22 h. The analysis is performed for summer and for a period with no rain in order to avoid the potential influence of precipitation and related environmental conditions on the radon variability. Analysis of ancillary measurements of temperature, relative humidity, wind speed and wind direction, as well as atmospheric pressure reanalysis data shows that the daily averaged radon concentration in the taillings material is anti-correlated with the atmospheric pressure and that the diurnal amplitude is associated with the magnitude of atmospheric pressure daily oscillations.

A Novel Behavioral Fish Model of Nociception for Testing Analgesics

Pain is a major symptom in many medical conditions, and often interferes significantly with a person's quality of life. Although a priority topic in medical research for many years, there are still few analgesic drugs approved for clinical use. One reason is the lack of appropriate animal models that faithfully represent relevant hallmarks associated with human pain. Here we propose zebrafish (Danio rerio) as a novel short-term behavioral model of nociception, and analyse its sensitivity and robustness. Firstly, we injected two different doses of acetic acid as the noxious stimulus. We studied individual locomotor responses of fish to a threshold level of nociception using two recording systems: a video tracking system and an electric biosensor (the MOBS system). We showed that an injection dose of 10% acetic acid resulted in a change in behavior that could be used to study nociception. Secondly, we validated our behavioral model by investigating the effect of the analgesic morphine. In time-course studies, first we looked at the dose-response relationship of morphine and then tested whether the effect of morphine could be modulated by naloxone, an opioid antagonist. Our results suggest that a change in behavioral responses of zebrafish to acetic acid is a reasonable model to test analgesics. The response scales with stimulus intensity, is attenuated by morphine, and the analgesic effect of morphine is blocked with naloxone. The change in behavior of zebrafish associated with the noxious stimulus can be monitored with an electric biosensor that measures changes in water impedance.

Synergistic effects of the membrane actions of cecropin-melittin antimicrobial hybrid peptide BP100

BP100 (KKLFKKILKYL-NH(2)) is a short cecropin A-melittin hybrid peptide, obtained through a combinatorial chemistry approach, which is highly effective in inhibiting both the in vitro and in vivo growth of economically important plant pathogenic Gram-negatives. The intrinsic Tyr fluorescence of BP100 was taken advantage of to study the peptide's binding affinity and damaging effect on phospholipid bilayers modeling the bacterial and mammalian cytoplasmic membranes. In vitro cytotoxic effects of this peptide were also studied on mammalian fibroblast cells. Results show a stronger selectivity of BP100 toward anionic bacterial membrane models as indicated by the high obtained partition constants, one order of magnitude greater than for the neutral mammalian membrane models. For the anionic systems, membrane saturation was observed at high peptide/lipid ratios and found to be related with BP100-induced vesicle permeabilization, membrane electroneutrality, and vesicle aggregation. Occurrence of BP100 translocation was unequivocally detected at both high and low peptide/lipid ratios using a novel and extremely simple method. Moreover, cytotoxicity against mammalian models was reached at a concentration considerably higher than the minimum inhibitory concentration. Our findings unravel the relationships among the closely coupled processes of charge neutralization, permeabilization, and translocation in the mechanism of action of antimicrobial peptides.

The joint effect of polycyclic aromatic hydrocarbons on fish behavior

Polycyclic aromatic hydrocarbons (PAHs) are one of the most widespread organic environmental pollutants that pose a potential risk to marine biota. Although they occur as mixtures in the marine environment, only little information exists about their joint action on fish behavior. In 4-day tests with juvenile gilthead seabream (Sparus aurata) concentration-response analyses were performed for three PAH compounds--fluorene (FE), phenanthrene (PHE), and pyrene (PY). Responses of fish to these compounds were assessed by recording visually the changes in their locomotory activities and social behaviors. Based on these concentration-response data, mixture effects were predicted by applying the model of concentration addition. The mixture was tested using a fixed-ratio design, and the resulting effects were compared to the predictions. The single compounds and the mixture were accumulated in fish muscle and produced a clear change in the overall behavioral performance of fish, as all individual parameters were affected in a dose-response way. For lethargy and swimming, we determined regression fits for all single compounds, with PY the most potent (EC(10)=0.031 microM for swimming and 0.039 microM for lethargy) and FE the least (EC(10)=0.29 microM for swimming and 0.26 microM for lethargy). Also, changes in the number of lethargic fish were always the most sensitive parameter and social interaction the least. The mixture study revealed for lethargy and swimming a good agreement between the predicted and observed effect changes, and statistically significant deviations could not be identified.

Mixtures of estrogenic chemicals enhance vitellogenic response in sea bass

BACKGROUND

The potential impact of natural and synthetic estrogens on aquatic ecosystems has attracted considerable attention because it is currently accepted that their joint effects are more severe when they are present in mixtures. Although it is well-known that they occur as mixtures in the marine environment, there is little information about the combined effects of estrogenic chemicals on marine biota.

OBJECTIVE

In 14-day tests with juvenile sea bass, we analyzed singly and in combination the estrogenic activity of estradiol (E(2)), ethynylestradiol (EE(2)), and bisphenol A (BPA) using vitellogenin induction as an end point.

METHODS

Fish were exposed to each compound, and on the basis of these concentration-response data, we predicted mixture effects by applying the model of concentration addition. The mixtures were tested using a fixed-ratio design, and the resulting mixture effects were compared to the predictions.

RESULTS

EE(2) was the most potent steroid, with an EC(50) (median effective concentration) of 0.029 microg/L, 3.6 times more potent than E(2) (EC(50) = 0.104 microg/L); BPA was the least potent chemical, with an EC(50) of 77.94 microg/L. The comparative assessment yielded a good agreement between observed and predicted mixture effects.

CONCLUSIONS

This study demonstrates the potential hazard of these compounds to seawater life by their ability to act together in an additive manner. It provides evidence that concentration addition can be used as a predictive tool for assessing the combined effects of estrogenic chemicals in marine ecosystems.

Multi-level assessment of chronic toxicity of estuarine sediments with the amphipod Gammarus locusta: I. Biochemical endpoints

We report on biomarker responses conducted as part of a multi-level assessment of the chronic toxicity of estuarine sediments to the amphipod Gammarus locusta. A companion article accounts for organism and population-level effects. Five moderately contaminated sediments from two Portuguese estuaries, Sado and Tagus, were assessed. Three of them were muddy and two were sandy sediments. The objective was to assess sediments that were not acutely toxic. Three of the sediments met this criterion, the other two were diluted (50% and 75%) with clean sediment until acute toxicity was absent. Following 28-d exposures, the amphipods were analysed for whole-body metal bioaccumulation, metallothionein induction (MT), DNA strand breakage (SB) and lipid peroxidation (LP). Two of the muddy sediments did not cause chronic toxicity. These findings were consistent with responses at organism and population levels that showed higher growth rates and improvement of reproductive traits for amphipods exposed to these two sediments. Two other sediments, one muddy and one sandy, exhibited pronounced chronic toxicity, affecting SB, MT induction (in muddy sediment), survival and reproduction. Potential toxicants involved in these effects were identified. The last sandy sediment exhibited some loss of DNA integrity, however growth was also enhanced. Present results, together with the organism/population-level data, and also benthic communities information, were analysed under a weight-of-evidence approach. By providing evidence of exposure (or lack of it) to contaminants in sediments, the biomarkers here applied assisted in distinguishing toxicants' impacts in test organisms from the confounding influence of other geochemical features of the sediments.

Multi-level assessment of chronic toxicity of estuarine sediments with the amphipod Gammarus locusta: II. Organism and population-level endpoints

This study aimed to test the performance of the amphipod Gammarus locusta (L.) in chronic sediment toxicity tests. It constitutes part of a multi-level assessment of chronic toxicity of estuarine sediments, integrating organism and population-level endpoints with biochemical markers responses. Here we account for organism and population-level effects, while biomarker responses were reported in a companion article. Five moderately contaminated sediments from Sado and Tagus estuaries were tested, comprising 3 muddy and 2 sandy sediments. These sediments either did not show acute toxicity or were diluted with control sediment as much as required to remove acute toxicity. Subsequent chronic tests consisted of 28-day exposures with survival, individual growth and reproductive traits as endpoints. Two of the muddy sediments induced higher growth rates in the amphipods, and improved reproductive traits. This was understood to be a consequence of the amount of organic matter in the sediment, which was nutritionally beneficial to the amphipods, while concurrently decreasing contaminant bioavailability. Biomarker responses did not reveal toxicant-induced stress in amphipods exposed to these sediments. One of the sandy sediments was acutely toxic at 50% dilution, but in contrast stimulated amphipod growth when diluted 75%. This was presumed to be an indication of a hormetic response. Finally the two remaining contaminated sediments showed pronounced chronic toxicity, affecting survival and reproduction. The sex ratio of survivors was highly biased towards females, and offspring production was severely impaired. The particulars of the responses of this amphipod were examined, as well as strengths versus limitations of the sediment test. This study illustrates the utility of this chronic test for toxicity assessment of contaminated estuarine sediments, with potential application all along Atlantic Europe.

Studies on biomarkers of copper exposure and toxicity in the marine amphipod Gammarus locusta (Crustacea): I. Induction of metallothionein and lipid peroxidation

Sublethal exposures of the marine amphipod Gammarus locusta to a concentration range of copper (Cu) in water (4 days' exposure; 3, 5 and 10 micro g Cu l(-1)) or spiked sediments (28 days' exposure; 1, 3 and 6 mg Cu kg(-1) dry weight) were performed, and the resulting bioaccumulation of Cu and effects on putative metallothionein (MT) and lipid peroxidation (LP) were investigated. A time-course exposure study (over 10 days) to a single water-borne concentration of Cu (4 micro g l(-1)) was also carried out. MT and LP were quantified, respectively, by differential pulse polarography and as thiobarbituric acid-reactive malondialdehyde equivalents. The increasing levels of Cu in water and sediment exposures resulted in enhanced uptake of the metal by G. locusta. Synthesis of putative MT occurred in response to exposure to water-borne Cu, the levels being higher (p < 0.05) over the dose range of Cu compared with controls. A positive correlation was observed between putative MT levels and the Cu body-burden concentration (p < 0.001). However, no increase in LP was observed in these animals. In contrast, in the time-course experiment, LP levels increased within 1 day of exposure, subsequently peaking at 4 days (68% greater than control, p < 0.001), before returning to control values by day 6. Higher levels of MT were also observed in this exposure, but at days 6 and 10 (55% and 38%, respectively), paralleling the decrease in LP. No increase in MT levels was recorded with exposure to Cu-contaminated sediments, whereas higher levels of LP were seen in comparison with controls (p < 0.001). Overall, the inverse relationship between putative MT induction and the occurrence of LP indicates that MT may protect against the prooxidant effects of Cu. It is concluded that MT and LP offer potential for application as biomarkers in G. locusta.

Effects of sediment geochemical properties on the toxicity of copper-spiked sediments to the marine amphipod Gammarus locusta

The contribution of some sediment features, namely acid-volatile sulfide (AVS) and total organic carbon (TOC) in order to explain the toxicity of copper-spiked sediments was investigated. A 10-day assay with the marine amphipod Gammarus locusta was performed with three selected sediment types that consisted of different proportions of fine fractions (FF) and TOC (0.5% FF/1% TOC; 25% FF/2% TOC; and 75% FF/4% TOC). Copper toxic effects were observed for 0.5% FF/25% FF sediments when simultaneously extracted copper (SEM(Cu)) minus acid volatile sulfide (SEM(Cu) - AVS) were 0.3 and 3.4 micromol/g, respectively. However, no significant mortality was observed for 75% FF sediment even when the sulfide binding capacity was exceeded (1.1 micromol/g < or = SEM(Cu) - AVS < or = 8.9 micromol/g). These results indicate that mortality could not be described solely as a function of the SEM(Cu) - AVS, suggesting the presence of other binding phases in addition to AVS. Results of the normalized LC50 values to total organic carbon indicated that this component probably also interferes in the amphipod survival, although not completely. The estimated LC50 values were close (2 mg Cu/g C and 8 mg Cu/g C, respectively for 0% FF and 25% FF sediment) although there was still a fourfold difference between them. Considering that none of these sediment features by itself could fully explain copper toxicity, an attempt was made to describe G. locusta mortality as a function of simultaneous SEM(Cu) - AVS and copper concentrations normalized to TOC. Nevertheless, the limited set of data available from this study prevented an attempt to model toxicity as a function of both of these factors. These findings reinforce the need to develop integrated models that include more than one binding phase, sulfide and organic carbon, and also other compartments of the system (e.g. interstitial water) to improve current methodologies for predicting copper toxicity based on sediment geochemical features.

Acute marine sediment toxicity: a potential new test with the amphipod Gammarus locusta

Although amphipod toxicity tests have been successfully used in the United States to assess coastal sediment toxicity, few tests have been developed with European species. The authors have been working with the amphipod Gammarus locusta, a widely spread species along European coastal areas that is particularly abundant in the Portuguese Sado estuary. This amphipod fulfills the most important requirements of a test species. It can be easily reproduced in laboratory and it is tolerant to a broad range of sediment types. A series of tests demonstrated its sensitivity to copper and gamma-hexachlorocyclohexane (lindane) in the sediment (LC50 = 6.8 mg Cu/dry kg, 0.9% total volatile solids; LC50 = 60.5 micrograms HCH/dry kg, 2% total volatile solids) and to some heavily contaminated field sediments. After assessment of the species sensitivity to several noncontaminant variables, an experimental protocol was designed to conduct acute sediment toxicity tests that are briefly described. Proposed is a 10-day static toxicity test at 15 degrees C and 33-34/1000 salinity, with laboratory-produced juveniles and mortality as the endpoint. General assay performance is identical to the American Society for Testing and Materials (ASTM) standard for sediment toxicity tests with marine and estuarine amphipods. The results previously obtained revealed a strong potential for this amphipod to be used in toxicological testing. Considering the wide geographic distribution of this species and its amenability for culturing, it may be an alternative or complementary test for ecotoxicological studies in other European coastal systems where the existing tests cannot be applied or do not offer a definitive solution.