Assessment of diphenhydramine toxicity - Is its mode of action conserved between human and zebrafish?

Effects of diphenhydramine exposure on reproduction of mature Japanese medaka (Oryzias latipes)

Diphenhydramine (DPH) is an antihistamine drug. It has been frequently detected in the environment, because it is not completely degraded in wastewater treatment plants. Recent studies have shown the adverse effects of DPH exposure to various aquatic organisms; however, its chronic effects on fish have been poorly elucidated. In this study, several pairs of mature Japanese medaka (Oryzias latipes) were exposed to DPH for a long period to determine the effects of DPH exposure on the subsequent generations, number of spawned and fertilized eggs, expression of sex-related genes, feeding behavior, embryo development, hatching rate, malformations among the hatched larvae, and mortality rate. The number of spawned eggs significantly decreased, when the parent fish were continuously exposed to 31.6 μg/L DPH for over 46 days. DPH exposure also altered the feeding behavior of medaka individuals, and increased the larval mortality rate. The effects of DPH exposure to fish may occur to some extent in the actual aquatic environment, although the risk evaluations in the field are limited.

Amitriptyline ecotoxicity in Danio rerio (Hamilton, 1822) embryos - similar toxicity profile in the presence of nanoplastics

Interaction of nanoplastics (NPls) with other environmental contaminants could affect their uptake by the organisms and their toxicity. Thus, the present study aims to investigate the polystyrene NPls (44 nm) interaction with the antidepressant amitriptyline (AMI) and its toxicity to Danio rerio embryos. A similar toxicological profile for NPls + AMI exposure was found for most of the evaluated endpoints, comparing with AMI single exposure, showing that the presence of NPls did not modulate the AMI toxicity. However, the behavioral assessment showed a different pattern with hypoactivity for the NPls + AMI exposure (NPls - hyperactivity; AMI - no effect). Interaction effects between NPls and AMI were also found in the protein contents (antagonism) and in the total glutathione content (synergism). This study highlights the complexity and unpredictability of NPls interaction with pharmaceuticals, important for an accurate environmental risk assessment and for the developing of effective strategies and interventions against plastic pollution.

Effects of carbamazepine on the central nervous system of zebrafish at human therapeutic plasma levels

The fish plasma model (FPM) facilitated the environmental risk assessment of human drugs by using existing data on human therapeutic plasma concentrations (HTPCs) and predicted fish plasma concentrations (FPCs). However, studies on carbamazepine (CMZ) with both the mode of action (MOA) based biological effects at molecular level (such as neurotransmitter and gene level) and measured FPCs are lacking. Bioconcentration of CMZ in adult zebrafish demonstrated that the FPM underestimated the bioconcentration factors (BCFs) in plasma at environmental CMZ exposure concentrations (1-100 μg/L). CMZ significantly increased Glu and GABA, decreased ACh and AChE as well as inhibited the transcription levels of gabra1, grin1b, grin2b, gad1b, and abat when the actual FPCs were in the ranges of 1/1000 HTPC to HTPC. It is the first read-across study of CMZ integrating MOA-based biological effects at molecular level and FPCs. This study facilitates model performance against a range of different drug classes.

Nanoplastics increase the toxicity of a pharmaceutical, at environmentally relevant concentrations - A mixture design with Daphnia magna

In aquatic environments, nanoplastics (NPls) can adsorb pharmaceuticals. However, throughout the scientific community, there is scarce knowledge about the interactive effects of the mixture nanoplastics (NPls) with pharmaceuticals to aquatic organisms. Therefore, this study aimed to investigate if the pharmaceutical diphenhydramine (DPH) toxicological effects alters when in presence of polystyrene NPls (PSNPls). To achieve this, Daphnia magna immobilization and different biochemical biomarkers (48-hours exposure) were assessed. Synergistic interactions occurred at environmentally relevant concentrations, PSNPls+DPH induced oxidative damage, whereas no effect was observed at single exposures. With the increase of PSNPls concentration, the DPH concentration causing 50% of effect (EC50) for organisms' immobilization decreased to 0.001 mg/L. In silico analysis suggested that the DPH toxicity to D. magna occurs via the sodium-dependent serotonin transporter. The results showed interactive effects between PSNPls and DPH (implying harmful effects on D. magna), allowing more thoughtful decisions by society and policymakers regarding plastics and pharmaceuticals.

Developmental toxicity of the emerging contaminant cyclophosphamide and the integrated biomarker response (IBRv2) in zebrafish

The safety of cyclophosphamide (CP) in the early developmental stages is not studied yet; it is important to study the responses at these stages because they might have relevance to CP-administered humans. We studied the developmental toxicity of CP by analysing physiological, morphological, and oxidative stress, neurotransmission enzymes, gene expression and histological endpoints in zebrafish embryos/larvae. The study lasted for 120 hpf at environmentally relevant concentrations of CP. No visible alterations were noticed in the control group. Delayed hatching, slow heart rate, yolk sac oedema, pericardial oedema, morphological deformities, the incompetence of oxidative stress biomarkers, excessive generation of ROS, apoptosis, inhibition of neurotransmitters and histopathological anomalies were observed in CP-treated groups. These alterations were found to be concentration- and duration-dependent effects for physiological and morphological endpoints, whereas concentration-dependent effects were antioxidants, ROS, apoptosis and histological endpoints. Biomarkers and gene expression were standardised using the integrated biomarker response-IBRv2 index. The IBRv2 index showed a concentration-dependent behaviour. A non-lethal developmental and teratogenic effect was observed in CP-treated zebrafish embryos/larvae at the studied concentrations. The studied biomarkers are sensitive, and the responses are interrelated; thus, their responses are useful to assess veiled and unseen hazards of pharmaceuticals.

Cocktail effects of emerging contaminants on zebrafish: Nanoplastics and the pharmaceutical diphenhydramine

Nanoplastics (NPLs) became ubiquitous in the environment, from the air we breathe to the food we eat. One of the main concerns about the NPLs risks is their role as carrier of other environmental contaminants, potentially increasing their uptake, bioaccumulation and toxicity to the organisms. Therefore, the main aim of this study was to understand how the presence of polystyrene NPLs (∅ 44 nm) will influence the toxicity (synergism, additivity or antagonism) of the antihistamine diphenhydramine (DPH), towards zebrafish (Danio rerio) embryos, when in dual mixtures. After 96 hours (h) exposure, at the organismal level, NPLs (0.015 or 1.5 mg/L) + DPH (10 mg/L) induced embryo mortality (90%) and malformations (100%) and decreased hatching (80%) and heartbeat rates (60%). After 120 h exposure, NPLs (0.015 or 1.5 mg/L) + DPH (0.01 mg/L) decreased larvae swimming distance (30-40%). At the biochemical level, increased glutathione S-transferases (55-122%) and cholinesterase (182-343%) activities were found after 96 h exposure to NPLs (0.015 or 1.5 mg/L) + DPH (0.01 mg/L). However, catalase (CAT) activity remained similar to the control group in the mixtures, inhibiting the effects detected after the exposure to 1.5 mg/L NPLs alone (increased 230% of CAT activity). In general, the effects of dual combination - NPLs + DPH (even at concentrations as low as 10 μg/L of DPH) - were more harmful than the correspondent individual exposures, showing the synergistic interactions of the dual mixture and answering to the main question of this work. The obtained results, namely the altered toxicity patterns of NPLs + DPH compared with the individual exposures, show the importance of an environmental risk assessment considering NPLs as a co-contaminant due to the potential NPLs role as vector for other contaminants.

First approach to assess the effects of nanoplastics on the soil species Folsomia candida: A mixture design with bisphenol A and diphenhydramine

The terrestrial environment is one of the main recipients of plastic waste. However, limited research has been performed on soil contamination by plastics and even less assessing the effects of nanoplastics (NPls). Behind the potential toxicity caused per se, NPls are recognized vectors of other environmental harmful contaminants. Therefore, the main aim of the present study is to understand whether the toxicity of an industrial chemical (bisphenol A - BPA) and a pharmaceutical (diphenhydramine - DPH) changes in the presence of polystyrene NPls to the terrestrial invertebrate Folsomia candida. Assessed endpoints encompassed organismal (reproduction, survival and behavior) and biochemical (neurotransmission and oxidative stress) levels. BPA or DPH, 28 d single exposures (1 to 2000 mg/kg), induce no effect on organisms' survival. In terms of reproduction, the calculated EC50 (concentration that causes 50% of the effect) and determined LOEC (lowest observed effect concentration) were higher than the environmental concentrations, showing that BPA or DPH single exposure may pose no threat to the terrestrial invertebrates. Survival and reproduction effects of BPA or DPH were independent on the presence of NPls. However, for avoidance behavior (48 h exposure), the effects of the tested mixtures (BPA + NPls and DPH + NPls) were dependent on the NPls concentration (at 0.015 mg/kg - interaction: no avoidance; at 600 mg/kg - no interaction: avoidance). Glutathione S-transferase activity increased after 28 d exposure to 100 mg/kg DPH + 0.015 mg/kg NPls (synergism). The increase of lipid peroxidation levels found after the exposure to 0.015 mg/kg NPls (a predicted environmental concentration) was not detected in the mixtures (antagonism). The results showed that the effects of the binary mixtures were dependent on the assessed endpoint and the tested concentrations. The findings of the present study show the ability of NPls to alter the effects of compounds with different natures and mechanisms of toxicity towards soil organisms, showing the importance of environmental risk assessment considering mixtures of contaminants.

Influence of hypomagnetic field on the heartbeat in zebrafish embryos

The magnetic environment may influence the functioning of the cardiovascular system. It was reported that low-frequency and static magnetic fields affect hemodynamics, heart rate, and heart rate variability in animals and humans. Moreover, recent data suggest that magnetic fields affect the circadian rhythms of physiological processes. The influence of the magnetic environment on heart functionating during early development has been studied insufficiently. We utilized transparent zebrafish embryos to evaluate the effect of the hypomagnetic field on the characteristics of cardiac function using a noninvasive optical approach based on photoplethysmographic microscopic imaging. The embryos were exposed to the geomagnetic and hypomagnetic fields from the second to the 116th hour post fertilization under a 16 h light/8 h dark cycle or constant illumination. The exposure of embryos to the hypomagnetic field in both lighting modes led to increased embryo mortality, the appearance of abnormal phenotypes, and a significant increase in the embryo’s heartbeat rate. The difference between maximal and minimal heartbeat intervals, maximal to minimal heartbeat intervals ratio, and the coefficient of variation of heartbeat rate were increased in the embryos exposed to the hypomagnetic field under constant illumination from 96 to 116 h post fertilization. The dynamics of heartbeat rate changes followed a circadian pattern in all studied groups except zebrafish exposed to the hypomagnetic field under constant illumination. The results demonstrate the importance of natural magnetic background for the early development of zebrafish. The possible mechanisms of observed effects are discussed.

Comprehensive study of pydiflumetofen in Danio rerio: Enantioselective insight into the toxic mechanism and fate

Pydiflumetofen (PYD) is primarily used to control fungal disease. The potential risks posed by PYD enantiomers to the aquatic ecosystem are currently unclear. In this study, the enantioselective toxicity and fate of PYD in Danio rerio were investigated, and the enantioselective toxic mechanism and metabolic pathway were explored. The acute toxicity of R-PYD was 10.7-14.7-fold than that of S-PYD against Danio rerio embryos, larvae, and adults. Meanwhile, R-PYD presented a stronger effect on embryo hatching and abnormalities, adult tissue damage and oxidative stress. R-PYD inhibited the succinate dehydrogenase (SDH) activity more than S-PYD because of its better interaction with SDH with a lower binding free energy (-59.35 kcal/mol), explaining the mechanism of enantioselective toxicity. Remarkable enantioselectivity was observed in uptake, distribution, and elimination. R-PYD showed preferential uptake with the higher uptake rate constants and slow metabolism with a longer half-life, resulting in the bioaccumulation of R-PYD with higher BCF_k (7.37 at 0.05 mg/L and 14.69 at 0.2 mg/L). Besides, muscle is an important tissue for PYD accumulation, existing potential food risk. Eleven PYD metabolites were qualitatively identified, and the metabolic pathway was proposed, including hydroxylation, N-demethylation, demethoxylation, hydrolysation (phase Ⅰ), and acetylation and glucuronidation (phase Ⅱ). The predicted toxicity of the metabolite indicated that several highly toxic metabolites need to be considered in the future. This study provides a new perspective for evaluating the ecological and human health risks of chiral pesticides.