Disrupting effects of antibiotic sulfathiazole on developmental process during sensitive life-cycle stage of Chironomus riparius.

Antibiotics in the environment are a concern due to their potential to harm humans and interrupt ecosystems. Sulfathiazole (STZ), a sulfonamide antibiotic, is commonly used in aquaculture and is typically found in aquatic ecosystems. We evaluated the ecological risk of STZ by examining biological, molecular and biochemical response in Chironomus riparius. Samples were exposed to STZ for 12, 24 and 96 h, and effects of STZ were evaluated at the molecular level by analyzing changes in gene expression related to the endocrine system, cellular stress response and enzyme activity of genes on antioxidant and detoxification pathways. STZ exposure induced significant effects on survival, growth and sex ratio of emergent adults and mouthpart deformity in C. riparius. STZ caused concentration and time-dependent toxicity in most of the selected biomarkers. STZ exposure leads to significant heat-shock response of protein genes (HSP70, HSP40, HSP90 and HSP27) and to disruption by up-regulating selected genes, including the ecdysone receptor gene, estrogen-related receptors, ultraspiracle and E74 early ecdysone-responsive gene. Furthermore, STZ induced alteration of enzyme activities on antioxidant and detoxification responses (catalase, superoxide dismutase, glutathione peroxidase and peroxidase) in C. riparius. By inducing oxidative stress, antibiotic STZ disturbs the endocrine system and produces adverse effects in growth processes of invertebrates.

The influence of sulfathiazole on the macroalgae Ulva lactuca.

Sulfonamides (SA) are a class of antibiotics routinely found in environmental matrices and therefore their role as contaminants should be investigated in non-target organisms. With this purpose the present experimental work has evaluated the exposure of the chlorophycean Ulva lactuca L. to sulfathiazole (STZ), a SA drug commonly used in aquaculture, at two concentrations representing prophylactic (25 µg mL(-1)) and therapeutic (50 µg mL(-1)) administrations. Results showed that STZ exhibits high stability in seawater with only 18% degradation over the 5d assay at both dosages tested. Also, macroalgae demonstrated an efficient uptake capacity with constant internal concentrations after 24h regardless of the external solutions and thus should be considered as a bioindicator species in risk assessment. Both STZ concentrations induced a slight inhibition of the macroalgae growth after 96 h.

Gene expression of ribosomal protein mRNA in Chironomus riparius: effects of endocrine disruptor chemicals and antibiotics.

Ribosomal protein genes are essential for cellular development. To examine the effects of ribosomal protein genes under various cellular stress conditions in chironomids, ribosomal protein S3 (RpS3) and S6 (RpS6) cDNA from Chironomus riparius were characterized and their expression was analyzed during development. A comparative and phylogenetic study among different orders of insects was carried out by analysis of sequence databases. C. riparius RpS3 was highly conserved at the protein level and shared over 85% amino acid identity with homologous sequences from other insects. RpS6 also showed approximately 80% amino acid identity. The RpS3 and S6 transcripts were present during different developmental stages but were most abundant during the embryonic stage. Furthermore, expression of the previously reported ribosomal proteins RpL11, L13, and L15, as well as RpS3 and S6 was analyzed following exposure to various concentrations of three endocrine disruptor chemicals (EDCs), di(2-ethylhexyl) phthalate, bisphenol A, and 4-nonylphenol (4NP), and the veterinary antibiotics (VAs) fenbendazole, sulfathiazole, and lincomycin. Only RpS3 gene expression was up-regulated significantly in response to EDCs and fenbendazole. However, the C. riparius ribosomal proteins showed a limited response to cellular stress, following exposure to EDCs and VAs.

Potentials and mechanisms of genotoxicity of six pharmaceuticals frequently detected in freshwater environment.

Genotoxic potentials and the mechanisms of six pharmaceuticals, which are frequently detected in surface water worldwide, were investigated using isogenic chicken DT40 mutant cell lines. These pharmaceuticals include erythromycin, sulfamethazine, sulfathiazole, chlortetracycline, oxytetracycline, and diclofenac. The genotoxic effects of these pharmaceuticals were determined based on growth kinetics of several mutant cell lines. Genotoxic chemicals were expected to decrease the growth kinetics in at least one of the mutants more significantly than DNA-repair-proficient wild-type cells. The test pharmaceuticals sensitized the cells deficient in homologous recombination (HR) repair (RAD54⁻/⁻), nucleotide excision repair (XPA⁻/), or translesion DNA synthesis (REV3⁻/⁻), suggesting that these pharmaceuticals may induce bulky adducts covalently bound to duplex DNA, like ultraviolet (UV) light. Genotoxicity was confirmed again by analyzing chromosome aberrations (CAs) and γ-H2AX foci in both wild-type and the susceptible mutants (i.e., RAD54⁻/⁻ and XPA⁻/) following the exposure to all the test pharmaceuticals except for erythromycin. The data indicate that these pharmaceuticals induce the DNA damages that stall DNA replication, leading to chromosomal breaks as well as translesion DNA synthesis mediated mutagenesis in DT40 cells.

Acclimation to ultraviolet irradiation affects UV-B sensitivity of Daphnia magna to several environmental toxicants.

Phototoxicity of several environmental contaminants by UV light has been reported in many studies. Nevertheless, field observations suggest the presence of certain defense mechanisms that would protect aquatic organisms against phototoxic damages. The current study was conducted to understand the responses of aquatic receptors to phototoxic chemicals in a natural environment where low dose UV light is present and long-term acclimation to UV might have been taken place. For this purpose, the water flea Daphnia magna was acclimated to a non-lethal, environmentally relevant level of UV-B light for >20 successive generations. The differences in toxicity response were evaluated between the UV-B acclimated and the non-acclimated daphnids when they were exposed to phototoxic compounds such as polynuclear aromatic hydrocarbons (fluoranthene and pyrene), a pharmaceutical (sulfathiazole), or metals (Cd and Cu) under UV-B light. Following the UV-B acclimation, toxicity of metals under UV-B light significantly decreased (P<0.1) suggesting the defense/repair system which might be developed through acclimation. For PAHs and sulfathiazole, however the acclimation rendered organisms more susceptible (P<0.05). The metabolic cost incurred during the acclimation to UV-B stress may in part explain the organisms' reduced capacity to deal with other stressors. Addition of vitamin C significantly increased the resistance of UV-B acclimated individuals against Cu, while no change was observed for the other chemicals, suggesting that the mode of Cu phototoxicity is different from those of the other phototoxicants under UV-B light. Two-dimensional gel electrophoresis analyses showed that long-term acclimation to UV-B lead to notable changes in protein expression, which may be further evaluated to explain varying susceptibilities of the acclimated daphnids to different phototoxicants.

Phototoxicity and oxidative stress responses in Daphnia magna under exposure to sulfathiazole and environmental level ultraviolet B irradiation.

Sulfonamide antibiotics frequently occur in aquatic environments. In this study, phototoxicity of sulfathiazole (STZ) and its mechanism of action were investigated using Daphnia magna. We evaluated the changes of molecular level stress responses by assessing gene expression, enzyme induction and lipid peroxidation, and the related organism-level effects in D. magna. In the presence of ultraviolet B (UV-B) light (continuous irradiation with 13.8+/-1.0microWcm(-2)d(-1)), STZ (at the nominal concentration of 94.9mg/L) caused a significant increase in reactive oxygen species (ROS) generation and lipid peroxidation. Catalase (CAT) and glutathione S-transferase (GST) showed concentration-dependent increases caused by the exposure. Exposure to STZ and UV-B light caused apparent up-regulation of alpha-esterase, hemoglobin, and vitellogenin mRNA. The survival of daphnids was significantly affected by the co-exposure to STZ and UV-B. The biochemical and molecular level observations in combination with organism-level effects suggest that the phototoxicity of STZ was mediated in part by ROS generated by oxidative stress in D. magna.

Environmental levels of ultraviolet light potentiate the toxicity of sulfonamide antibiotics in Daphnia magna.

We assessed the phototoxicity of several major sulfonamide antibiotics, i.e., sulfathiazole, sulfamethazine, and sulfamethoxazole, using acute 48 and 96 h Daphnia magna immobilization toxicity test under several indoor and outdoor lighting conditions. The lighting conditions were as follows: (1) fluorescent light only, (2) continuous irradiation with 15 microW/cm(2) UVB, (3) pulsed irradiation with 90 microW/cm(2) UVB for 4 h/d, and (4) natural sunlight (outdoors). Laboratory tests showed that phototoxicity resulting from exposure to continuous UVB light generally increased the acute toxicity of the sulfonamides in D. magna by up to 2.3-fold. However, pulsed UVB exposure resulted in a greater increase in phototoxicity. Compared to fluorescent light only (no UVB), pulsed UVB irradiation (96 h) resulted in 12.0-, 5.8-, and 4.4-fold increases in toxicity for sulfamethazine, sulfathiazole, and sulfamethoxazole, respectively. This suggests that the mode of UV irradiation is more important than the dose (UV-intensity x exposure time) for the photo-enhancement of sulfonamide toxicity. Natural sunlight enhanced the toxicity of the sulfonamides to an even greater degree, likely because of the contribution of UVA light. This study suggests that without taking into account the effects of UV irradiation, it is possible to underestimate the actual consequences of phototoxic sulfonamide antibiotics in the aquatic environment.

Skin sensitization testing: the relevance of rechallenge and pretreatment with sodium lauryl sulfate in the guinea pig maximization test.

The guinea pig maximization test is one of the preferred test methods for the identification of skin sensitizers. The OECD/EC test guidelines allow for the conduct of a rechallenge in case doubtful reactions are obtained after challenge. The relevance of rechallenging was investigated by performing multiple challenges (up to four) in the maximization test with four well-known sensitizers of varying strength: nickel sulfate, sulfathiazole, benzocaine, and 1-chloro-2,4-dinitrobenzene. In addition, the effect of sodium lauryl sulfate (SLS)-pretreatment during topical induction with weak sensitizers on rechallenging was investigated. In contrast to what has frequently been hypothesized, rechallenge did not result in an increase of skin reaction as compared with the reactions observed after the first treatment. SLS pretreatment was very effective in increasing the initial challenge response to weak sensitizers. Subsequent rechallenging in these cases however again showed a decrease in sensitivity of the animals.