Altered developmental toxicity caused by three carrier solvents

Assessing differences in toxicity and teratogenicity of three phthalates, Diethyl phthalate, Di-n-propyl phthalate, and Di-n-butyl phthalate, using Xenopus laevis embryos

Phthalates, compounds used to add flexibility to plastics, are ubiquitous in the environment. In particular, the diethyl (DEP), di-n-propyl (DnPP), and di-n-butyl (DBP) phthalates were found to exert detrimental effects in both mammalian and non-mammalian studies, with toxic effects varying according to alkyl chain length. Embryos of Xenopus laevis, the African clawed frog, have been used to assess toxicity and teratogenicity of several compounds and serves as a model for assessing adverse and teratogenic effects of ortho-phthalate esters. The purpose of this study was to develop a model for comparison of developmentally toxic effects of ortho-phthalate esters using Xenopus embryos. In this study developing Xenopus laevis embryos were exposed to increasing concentrations of DEP, DnPP, and DBP using the 96-h Frog Embryo Teratogenesis Assay-Xenopus (FETAX), with 96-h lethal concentrations, effective concentrations to induce malformations, teratogenic indices, and concentrations to inhibit growth determined. DEP, DnPP, and DBP showed enhanced toxicity with increasing ester length. Developing Xenopus laevis exposed to DEP, DnPP, and DBP showed similar malformations that also occurred at lower concentrations with increasing alkyl chain length. Teratogenic risk did not change markedly with alkyl chain length, with data showing only DBP to be teratogenic.

Zebrafish as a Model for Systems Medicine R&D: Rethinking the Metabolic Effects of Carrier Solvents and Culture Buffers Determined by (1)H NMR Metabolomics

Zebrafish is a frequently employed model organism in systems medicine and biomarker discovery. A crosscutting fundamental question, and one that has been overlooked in the field, is the "system-wide" (omics) effects induced in zebrafish by metabolic solvents and culture buffers. Indeed, any bioactivity or toxicity test requires that the target compounds are dissolved in an appropriate nonpolar solvent or aqueous media. It is important to know whether the solvent or the buffer itself has an effect on the zebrafish model organism. We evaluated the effects of two organic carrier solvents used in research with zebrafish, as well as in drug screening: dimethyl sulfoxide (DMSO) and ethanol, and two commonly used aqueous buffers (egg water and Hank's balanced salt solution). The effects of three concentrations (0.01, 0.1, and 1%) of DMSO and ethanol were tested in the 5-day-old zebrafish embryo using proton nuclear magnetic resonance ((1)H NMR) based metabolomics. DMSO (1% and 0.1%, but not 0.01%) exposure significantly decreased the levels of adenosine triphosphate (ATP), betaine, alanine, histidine, lactate, acetate, and creatine (p < 0.05). By contrast, ethanol exposure did not alter the embryos' metabolome at any concentration tested. The two different aqueous media noted above impacted the zebrafish embryo metabolome as evidenced by changes in valine, alanine, lactate, acetate, betaine, glycine, glutamate, adenosine triphosphate, and histidine. These results show that DMSO has greater effects on the embryo metabolome than ethanol, and thus is used with caution as a carrier solvent in zebrafish biomarker research and oral medicine. Moreover, the DMSO concentration should not be higher than 0.01%. Careful attention is also warranted for the use of the buffers egg water and Hank's balanced salt solution in zebrafish. In conclusion, as zebrafish is widely used as a model organism in life sciences, metabolome changes induced by solvents and culture buffers warrant further attention for robust systems science, and precision biomarkers that will stand the test of time.

Chlorpyrifos and malathion have opposite effects on behaviors and brain size that are not correlated to changes in AChE activity

Organophosphates, a type of neurotoxicant pesticide, are used globally for the treatment of pests on croplands and are therefore found in a large number of conventional foods. These pesticides are harmful and potentially deadly if ingested or inhaled in large quantities by causing a significant reduction in acetylcholinesterase (AChE) activity in the central and peripheral nervous system. However, much less is known about the effects of exposure to small quantities of the pesticides on neural systems and behavior during development. In the current study we used zebrafish larvae in order to determine the effects of two of the most widely used organophosphates, chlorpyrifos and malathion, on zebrafish behavior and AChE activity. Embryos and larvae were exposed to the organophosphates during different time points in development and then tested at 5 days post-fertilization for behavioral, neurodevelopmental and AChE abnormalities. The results of the study indicate that chlorpyrifos and malathion cause opposing behaviors in the larvae such as swim speed (hypoactivity vs. hyperactivity) and rest. Additionally, the pesticides affect only certain behaviors, such as thigmotaxis, during specific time points in development that are unrelated to changes in AChE activity. Larvae treated with malathion but not chlorpyrifos also had significantly smaller forebrain and hindbrain regions compared to controls by 5 days post-fertilization. We conclude that exposure to very low concentrations of organophosphate pesticides during development cause abnormalities in behavior and brain size.

Gene expression of heat shock protein 70, interleukin-1β and tumor necrosis factor α as tools to identify immunotoxic effects on Xenopus laevis: a dose-response study with benzo[a]pyrene and its degradation products

The exposure to benzo[a]pyrene (B[a]P) results in an alteration of immune function in mammals and fish, and the analysis of cytokine mRNA levels has been suggested for predicting the immunomodulatory potential of chemicals. To obtain evidence of the innate immune responses to B[a]P in Xenopus laevis, the present study monitored the mRNA expression of interleukin 1-β (IL-1β), tumor necrosis factor α (TNF-α) and heat shock protein 70 (HSP70) in a laboratorial exposure. Tadpoles exposed to 8.36, 14.64, 89.06 and 309.47 μg/L of B[a]P,were used for detecting hsp70, IL-1β and TNF-α mRNA induction. A dose-response increase in the expression of hsp70 and IL-1β mRNA was found. The results of this study confirmed the use of hsp70 and IL-1β, but not TNF-α, as sensitive indicators of immunotoxic effect of B[a]P in X. laevis. Further research would be required for the validation of these endpoints.

Sub-lethal effects of acetone on Daphnia magna

There is increasing concern about the sub-lethal effect of hydrophobic chemicals in the water medium. Even though acetone is a commonly used solvent in toxicity testing, few studies have focussed on its chronic toxicity to Daphnia magna and the available results are often contradictory. In this study, acetone was tested on D. magna in a 21-day exposure experiment and the effects on mortality, fertility and morphology of exposed organisms (F(0)) and offspring (F(1)-F(2), reared without acetone) were evaluated. No significant reduction of survival was observed with increasing concentrations, and no significant reduction in fecundity in any treatment group in terms of average number of daphnids per mother was observed. Abnormal development of second antennae was observed on F(1) from F(0) exposed to 79 mg l(-1) solvent. The ET50 of acetone on the number of mothers that produced deformed offspring over time was 12.5 days. Our results suggest that the acetone concentration should not exceed 7.9 mg l(-1), which is 10 times less than the allowed concentration as determined by OECD chronic assays on D. magna. More attention should be paid to small, water-soluble molecules usually considered of low concern for chronic toxicity because they might affect other metabolic pathways.

Dimethyl sulfoxide is a potent modulator of estrogen receptor isoforms and xenoestrogen biomarker responses in primary culture of salmon hepatocytes

Dimethyl sulfoxide (DMSO) has been frequently used as carrier solvent in toxicological experiments where the most compelling DMSO attributes are its exceptionally low toxicity and environmental impact. We were inspired by recent and consistent observations that ethanol and DMSO modulate endocrine-disruptor biomarker responses in both in vitro and in vivo studies in our laboratory, to take a critical evaluation of these effects. Quantitative (real-time) polymerase chain reaction (PCR) method with specific primer pairs was used in this study to measure DMSO-induced time-dependent modulation of estrogen receptor (ER) isoforms, vitellogenin (Vtg) and zona radiata-protein (Zr-protein) gene expression patterns in primary culture of salmon hepatocytes. In addition, immunochemical analysis, using indirect enzyme linked immunosorbent assay (ELISA) with monoclonal (Vtg) and polyclonal (Zr-proteins) antibodies was used to detect and measure Vtg and Zr-proteins secreted in culture media. Salmon hepatocytes were isolated by a two-step collagenase perfusion method and exposed to 0.1% or 10 microL/L of DMSO after 48 h pre-culture. Cells were harvested at 12, 24, 48 and 72 h after exposure and analysed for ERalpha, ERbeta, Vtg and Zr-protein gene expression using real-time PCR method. Media samples were collected at similar time-intervals for protein analysis. Our data show that DMSO-induced significant increase in ERalpha, ERbeta, Vtg and Zr-protein genes in a time-dependent manner. Indirect ELISA analysis showed a time-specific effect of DMSO. The use of DMSO as carrier solvent in fish endocrine disruption studies should be re-evaluated. We recommend more investigation, using other endocrine-disruptor biomarkers in order to validate the suitability of common carrier solvents used in toxicology with the aim of setting new maximum allowable concentrations. In particular, given the high sensitivity of genomic approaches in toxicology, these results may have serious consequences for the interpretation of biomarker responses.

Comparative embryotoxicity and proteotoxicity of three carrier solvents to zebrafish (Danio rerio) embryos

The present study examines the effects of ethanol (ETOH), dimethyl sulfoxide (DMSO), and acetone on zebrafish embryos and the implications of the observed results on the use of these solvents to zebrafish early life stage tests. The embryos were exposed to different concentrations (0.0, 0.0001, 0.001, 0.01, 0.1, 0.05, 1, 1.5, and 2.0% v/v) of the respective solvents by diluting reagent-grade solvent with reconstituted water [DIN 38415-6-Suborganismische Testverfahren (Gruppe T) Teil 6: Giftigkeit gegenüber Fischen. Deutsches Institute für Normung e.V]. The following endpoints were investigated (mortality, hatching rate, abnormalities, heart rate, and hsp 70 induction). No effect on survival was recorded for both acetone and DMSO even up to the highest concentration. On the other hand, embryos exposed to 1.5% and 2.0% ethanol showed a significant reduction in survival rate. No developmental defects occurred with any of the solvents at the 0.1% concentration. However, starting with 1.0%, weak to very pronounced abnormalities (weak pigmentation, edema, crooked bodies, eye defect, tail defect, reduced heartbeat, and abnormal hatching) were observed depending on the solvent type and the concentration used. Ethanol has been shown to be the most embryotoxic solvent while DMSO and acetone have comparably lesser effects. Heat shock protein 70 was induced by all solvents but at different concentration ranges. DMSO has been shown to be the most potent inducer of stress proteins. Based on the study, the chemicals tested here may be used as carrier solvents in the zebrafish embryo assay at levels below 1.5, 1.5, and 1% v/v for acetone, DMSO, and ethanol, respectively. For stress protein analysis of the exposed embryos, however, the solvent levels should be below 0.1%, 0.01%, and 1.5%, respectively. Additional and separate investigations utilizing other biomarkers should be carried out to further validate the suitability of using these solvents in a typical zebrafish embryo assay.

Acute and chronic effects of carrier solvents in aquatic organisms: a critical review

Recognising the scientific and regulatory need for testing relatively hydrophobic or 'difficult substances', the OECD currently recommends that selected organic solvents may be used in aquatic toxicity testing in order to help achieve more effective dispersion of the toxicant. The OECD recommends a maximum solvent concentration of 100 microl l(-1) (with specific gravity equivalents to 100 microl l(-1) in parentheses) for acetone (79 mg l(-1)), dimethylformamide (95 mg l(-1)), dimethylsulfoxide (1.10 mg l(-1)), ethanol (78.9 mg l(-1)), methanol (79.2 mg l(-1)) and triethylene glycol (1.12 mg l(-1)). While this recommendation is supported by historical data, we have recently observed evidence that some solvents may affect the reproduction of certain fish species, and also impact biomarkers of endocrine disruption. This review presents available data on the effects of solvents in aquatic organisms, supplemented by relevant information from mammalian studies (e.g. effects on liver enzyme induction potentially altering the metabolism of sex hormones). In conclusion, it is recommended that maximum effort should be given to avoiding the use of carrier solvents wherever possible, for example through the use of saturation columns or other physical methods (e.g. stirring or ultrasonification). Where solvent use is necessary, however, it is recommended that in reproduction studies with aquatic organisms, the maximum solvent concentration should not exceed 20 microl l(-1) of dilution water.

A comparative study of the toxicity of mercury dichloride and methylmercury, assayed by the Frog Embryo Teratogenesis Assay--Xenopus (FETAX)

The Frog Embryo Teratogenesis Assay-Xenopus (FETAX) is a powerful and flexible bioassay that makes use of the embryos of the anuran amphibian Xenopus laevis. The FETAX can detect xenobiotics that affect embryonic development, when mortality, teratogenicity and growth inhibition are used as endpoints. The FETAX was used to compare the embryotoxic and teratogenic potentials of two chemical species of mercury, inorganic mercury(II) chloride (HgCl2) and organic methylmercury chloride (MeHgCl). A higher toxicity of MeHgCl (the estimated median lethal concentration [LC50] and median teratogenic concentration [TC50] were 0.313microM and 0.236microM, respectively) over HgCl2, with estimated LC50 and TC50 values of 0.601microM and 0.513microM, respectively). On the basis of these results, HgCl2 and MeHgCl can be classified as "slightly teratogenic compounds", as the ratio of LC50/TC50 is less than 1.5. There was a significant deviation from the commonly described monotonic behaviour of the concentration-response curves, suggesting a hormetic effect of both species of mercury. Uptake experiments, followed by neutron activation analysis, showed a higher incorporation of mercury in embryos exposed to MeHgCl compared with those exposed to HgCl2. Interestingly, Hg- exposed embryos showed a higher content of selenium and zinc than did control embryos.

Ecotoxicological soil evaluation by FETAX

The frog embryo teratogenesis assay-Xenopus (FETAX) is a powerful and flexible bioassay that makes use of the embryos of the anuran Xenopus laevis. FETAX satisfies the requirements of low cost, reliability and reproducibility and, thanks to its three endpoints (i.e., mortality, teratogenicity and growth inhibition) can detect the xenobiotics that affect embryonic development. In this paper, we have used FETAX to evaluate samples of soils collected in an oil-contaminated area. Embryos were exposed directly to the soil to be tested. Particular attention was devoted to provide a statistical procedure for analysing mortality and malformation data as well as growth retardation.

Effects of pond water, sediment, and sediment extracts from minnesota and vermont, USA, on early development and metamorphosis of xenopus

In recent studies, a high incidence of amphibian mortality and malformation has been reported in the field, suggesting that toxic and/or bioactive agents are present in the environment of the affected amphibians. This study provides evidence for this hypothesis, because it applies to several affected ponds in Minnesota and Vermont, USA. Three developmental bioassays were carried out on samples from three reference and three test sites in Minnesota and one reference and three test sites, in Vermont. The bioassays utilized Xenopus as a model system, measuring altered developmental patterns during the first 4 d of development (frog embryo teratogenesis assay-Xenopus [FETAX]), hind-limb development over a 30-d period, and tail length resorption over a 14-d period. Strong correlations were observed among the results for all three in vitro bioassays, as well as between adverse developmental effects in vitro and in the field.

The effect of photomirex on the in vitro perfused ovary of the rat

Photomirex, a photodegradation product of the insecticide mirex, is an environmental contaminant that has been identified in Great Lakes fish, soil, and human adipose tissue. Because of the potential for human exposure, the present study was designed to investigate the short-term effects of photomirex on the in vitro perfused ovary of the rat. Adult Sprague-Dawley rat ovaries were isolated and perfused for a total of 6 h with Medium 199. Following a 2-h baseline period, 10(-4) M of photomirex was administered to the medium. Control ovaries received medium or DMSO (vehicle control). Significant effects of perfusion and chemical intervention were identified using lactate dehydrogenase enzyme, glucose utilization, lactate, pyruvate, and flow:pressure ratio as markers of toxicity (P < 0.05). Lactate:pyruvate ratio, glutathione, and oxygen consumption did not demonstrate significant effects. Post hoc tests showed that there were significant differences between the DMSO + photomirex group and the control group (M199) using lactate dehydrogenase as a marker of toxicity. Pyruvate concentration was also reduced significantly after perfusion with DMSO + photomirex compared to M199 only and DMSO only (P < 0.05). Histopathologic changes were not discernible by light microscopy. These results suggest that metabolic and respiratory processes of the ovary are acutely sensitive to perturbation with photomirex in the in vitro perfused rat ovary model.

Synergistic interaction of glycoalkaloids alpha-chaconine and alpha-solanine on developmental toxicity in Xenopus embryos

The embryo toxicities of two major potato glycoalkaloids, alpha-chaconine and alpha-solanine, were examined individually and in mixtures using the frog embryo teratogenesis assay-Xenopus. Calculations of toxic units (TUs) were used to assess possible antagonism, synergism or response addition of several mixtures ranging from approximately 3:1 to 1:20 TUs of alpha-chaconine to alpha-solanine. Some combinations exhibited strong synergism in the following measures of developmental toxicity: (a) 96-hr LC50, defined as the median concentration causing 50% embryo lethality; (b) 96-hr EC50 (malformation), defined as the concentration causing 50% malformation of the surviving embryos; and (c) teratogenic index which is equal to LC50/EC50 (malformation). The results indicated that each of the mixtures caused synergistic mortality or malformation. Furthermore, these studies suggested that the synergism observed for a specific mixture cannot be used to predict possible synergism of other mixtures with different ratios of the two glycoalkaloids; toxicities observed for individual glycoalkaloids may not be able to predict toxicities of mixtures; and specific combinations found in different potato varieties need to be tested to assess the safety of a particular cultivar.

Joint action of t-retinoic and valproic acids on Xenopus embryo development

The joint action of all-trans retinoic acid (RA) with valproic acid (VPA) was examined at malformation-inducing concentrations for Xenopus embryos. The compounds were selected for testing to evaluate malformation as an endpoint for the developmental toxicity of chemical mixtures and to help assess whether joint action types can be related to modes or mechanisms of chemical toxicity for Xenopus. Three mixtures (3:1, 1:1, and 1:3 RA:VPA) were tested in 96 hr static-renewal exposures. Three separate tests were conducted on each mixture. Positive controls were also tested (i.e., 1:0 and 0:1 solutions). Using toxic unit analysis, the joint action for induction of malformations of all types, craniofacial malformations, and microcephaly was response addition, indicating the chemicals are dissimilar and non-interactive. The results support recent joint action studies in providing evidence that similar acting chemicals might be defined as chemicals with the same biochemical/molecular mechanism of action in inducing malformations in Xenopus embryos.