Chronic exposure to butyl-paraben causes photosensitivity disruption and memory impairment in adult zebrafish

Diethyl-hexyl-cyclohexane (Eco-DEHCH) is a safer phthalate alternative that does not elicit neuroendocrine disrupting effects

Alternative phthalates (APs) have been developed due to the reported adverse effects of conventional phthalates (CPs). However, whether APs are nontoxic and can replace CPs remains controversial due to their endocrine-disrupting (ED) effects. Herein, to investigate the ED potential of diethyl-hexyl-cyclohexane (DEHCH), a newly developed non-phthalate-structured AP, we employed in silico (molecular docking simulation), in vitro (cell-based assays for estrogen and androgen receptors), and in vivo (zebrafish embryo model) methods. We also compared the results with two CPs (di(2-ethylhexyl) phthalate [DEHP] and diisononyl phthalate [DINP]) and two previously proposed non-phthalate-structured APs (1,2-cyclohexane dicarboxylic acid diisononyl ester [DINCH] and di-2-ethylhexyl terephthalate [DEHTP]). DEHCH did not exhibit the highest binding affinity for any of the five receptors such as estrogen, androgen, glucocorticoid receptors, and thyroid receptor alpha and beta. None of the tested phthalates exhibited agonistic or antagonistic effects on estrogen and androgen receptors. In zebrafish larvae, DEHCH did not affect the expression of the nine endocrine-related genes and neurobehaviors, which correlates well with the lack of changes in the endogenous concentrations of the five neurosteroids. In contrast, DINCH, DEHP, and DEHTP induced hyperactivity, and except for DEHCH, four phthalates significantly upregulated at least one gene. In addition, DINCH significantly increased the expression of cortisol and DEHP increased progesterone, allopregnanolone, and cortisol. These findings demonstrate that DEHCH is safer than CPs and the previously proposed APs in terms of ED effects, including neuronal system dysregulation.

Neuroprotective potential of solanesol against tramadol induced zebrafish model of Parkinson's disease: insights from neurobehavioral, molecular, and neurochemical evidence

Parkinson's disease (PD) is a prevalent neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and subsequent depletion of dopamine in the striatum. Solanesol, an alcohol that acts as a precursor to coenzyme Q10, possesses potential applications in managing neurological disorders with antioxidant, anti-inflammatory, and neuromodulatory potential. In this study, a zebrafish model was employed to investigate the effects of solanesol in tramadol induced PD like symptoms. Zebrafish were administered tramadol injections (50 mg/kg) over a 20-day period. Solanesol was administered at doses of 25, 50, and 100 mg/kg, three hours prior to tramadol administration from day 11 to day 20. Behavioral tests assessing motor coordination were conducted on a weekly basis using open field and novel diving tank apparatus. On day 21, the zebrafish were euthanized, and brain tissues were examined for markers of oxidative stress, inflammation, and neurotransmitters level. Chronic tramadol treatment resulted in motor impairment, reduced antioxidant enzyme levels, enhanced release of proinflammatory cytokines in the striatum, and disrupted neurotransmitter balance. However, solanesol administration mitigated these effects and exhibited a neuroprotective effect against neurodegenerative alterations in the zebrafish model of PD. This was evident through improvements in behavior, modulation of biochemical markers, attenuation of neuroinflammation, restoration of neurotransmitters level, and enhancement of mitochondrial activity. The histopathological study also confirmed that solanesol dose dependently restored neuronal cell density which confirmed its neuroprotective potential. Further investigations are required to elucidate the underlying mechanisms of solanesol neuroprotective effects and evaluate its efficacy in human patients.

A systematic review of the toxic potential of parabens in fish

Parabens are the most prevalent ingredients in cosmetics and personal care products (PCPs). They are colorless and tasteless and exhibit good stability when combined with other components. Because of these unique physicochemical properties, they are extensively used as antimicrobial and antifungal agents. Their release into the aquatic ecosystem poses potential threats to aquatic organisms, including fish. We conducted an electronic search in PubMed (http://www.ncbi.nlm.nih.gov/pubmed) using the search term parabens and fish and sorted 93 articles consisting of methyl paraben (MTP), ethyl paraben (ETP), propyl paraben (PPP), butyl paraben (BTP), and benzyl paraben (BNP) in several fish species. Furthermore, we confined our search to six fish species (common carp, Cyprinus carpio; fathead minnows, Pimephales promelas; Japanese medaka, Oryzias latipes; rainbow trout, Oncorhynchus mykiss; Nile tilapia, Oreochromis niloticus; and zebrafish, Danio rerio) and four common parabens (MTP, ETP, PPP, and BTP) and sorted 48 articles for review. Our search indicates that among all six fish, zebrafish was the most studied fish and the MTP was the most tested paraben in fish. Moreover, depending on the alkyl chain length and linearity, long-chained parabens were more toxic than the parabens with short chains. Parabens can be considered endocrine disruptors (EDs), targeting estrogen-androgen-thyroid-steroidogenesis (EATS) pathways, blocking the development and growth of gametes, and causing intergenerational toxicity to impact the viability of offspring/larvae. Paraben exposure can also induce behavioral changes and nervous system disorders in fish. Although the USEPA and EU limit the use of parabens in cosmetics and pharmaceuticals, their prolonged persistence in the environment may pose an additional health risk to humans.

Impact of butylparaben on growth dynamics and microcystin-LR production in Microcystis aeruginosa

The presence of butylparaben (BP), a prevalent pharmaceutical and personal care product, in surface waters has raised concerns regarding its impact on aquatic ecosystems. Despite its frequent detection, the toxicity of BP to the cyanobacterium Microcystis aeruginosa remains poorly understood. This study investigates the influence of BP on the growth and physiological responses of M. aeruginosa. Results indicate that low concentrations of BP (below 2.5 mg/L) have negligible effects on M. aeruginosa growth, whereas higher concentrations (5 mg/L and 10 mg/L) lead to significant growth inhibition. This inhibition is attributed to the severe disruption of photosynthesis, evidenced by decreased Fv/Fm values and chlorophyll a content. BP exposure also triggers the production of reactive oxygen species (ROS), resulting in elevated activity of antioxidant enzymes. Excessive ROS generation stimulates the production of microcystin-LR (MC-LR). Furthermore, lipid peroxidation and cell membrane damage indicate that high BP concentrations cause cell membrane rupture, facilitating the release of MC-LR into the environment. Transcriptome analysis reveals that BP disrupts energy metabolic processes, particularly affecting genes associated with photosynthesis, carbon fixation, electron transport, glycolysis, and the tricarboxylic acid cycle. These findings underscore the profound physiological impact of BP on M. aeruginosa and highlight its role in stimulating the production and release of MC-LR, thereby amplifying environmental risks in aquatic systems.

Use of Cosmetics in Pregnancy and Neurotoxicity: Can It Increase the Risk of Congenital Enteric Neuropathies?

Pregnancy is a particularly vulnerable period for the growing fetus, when exposure to toxic agents, especially in the early phases, can decisively harm embryo development and compromise the future health of the newborn. The inclusion of various chemical substances in personal care products (PCPs) and cosmetic formulations can be associated with disruption and damage to the nervous system. Microplastics, benzophenones, parabens, phthalates and metals are among the most common chemical substances found in cosmetics that have been shown to induce neurotoxic mechanisms. Although cosmetic neurotoxin exposure is believed to be minimal, different exposure scenarios of cosmetics suggest that these neurotoxins remain a threat. Special attention should be paid to early exposure in the first weeks of gestation, when critical processes, like the migration and proliferation of the neural crest derived cells, start to form the ENS. Importantly, cosmetic neurotoxins can cross the placental barrier and affect the future embryo, but they are also secreted in breast milk, so babies remain exposed for longer periods, even after birth. In this review, we explore how neurotoxins contained in cosmetics and PCPs may have a role in the pathogenesis of various neurodevelopmental disorders and neurodegenerative diseases and, therefore, also in congenital enteric aganglionosis as well as in postnatal motility disorders. Understanding the mechanisms of these chemicals used in cosmetic formulations and their role in neurotoxicity is crucial to determining the safety of use for cosmetic products during pregnancy.

Environmental pollution of paraben needs attention: A study of methylparaben and butylparaben co-exposure trigger neurobehavioral toxicity in zebrafish

Parabens (PBs) are commonly utilized as preservatives in various commodities. Of all the PBs, methylparaben (MeP) and butylparaben (BuP) are usually found together at similar levels in the aqueous environment. Although a few studies have demonstrated that PBs are neurotoxic when present alone, the neurobehavioral toxic effects and mechanisms of coexisting MeP and BuP at environmental levels has not been determined. Neurobehavior is a sensitive indicator for identifying neurotoxicity of environmental pollutants. Therefore, adult female zebrafish (Danio rerio) were chronic co-exposure of MeP and BuP at environmental levels (5, 50, and 500 ng/L) for 60 d to investigate the effects on neurobehavior, histopathology, oxidative stress, mitochondrial function, neurotransmitters and gene expression. The results demonstrated that chronic co-exposure of MeP and BuP interfered with several behaviors (learning-memory, anxiety, fear, aggressive and shoaling behavior) in addition to known mechanisms of producing oxidative stress and disrupting energy. More intriguingly, chronic co-exposure of MeP and BuP caused retinal vacuolization and apoptosis in the optic tectum zone. It even has further effects on the phototransduction pathway, impairing optesthesia and leading to neurotransmitters dysregulation. These are critical underlying mechanisms resulting in neurobehavioral abnormalities. This study confirms that the pollution of multiple PBs by chronic co-exposure in aquatic environments can result neurobehavioral toxicity. It also suggests that the prolonged effects of PBs on aquatic ecosystems and health require close attention.

Endocrine disrupting effects of parabens in zebrafish (Danio rerio): New insights from transcriptomics, metabolomics, and molecular dynamics simulation

Parabens (PBs), a group of widely used synthetic preservatives with potential endocrine disrupting activity, have been detected with increasing frequency in organisms and environmental matrices. This study assessed the hormone interference effects of four typical PBs, namely methylparaben (MeP), ethylparaben (EtP), propylparaben (PrP), and butylparaben (BuP), in zebrafish and elucidated the probable underlying mechanisms. Transcriptomic and metabolomic analyses showed that the differentially expressed genes and metabolites were associated with the tyrosine metabolism, arachidonate metabolism, and glycerophospholipid metabolism, indicating they were essential precursors of steroid hormone biosynthesis and metabolism. Histopathological analysis revealed impaired gonad development in the zebrafish exposed to PBs, as evidenced by the significantly increased vitellogenin (VTG) and estradiol (E2) levels. Furthermore, molecular dynamics simulation suggested that the four PBs could preferentially activate the zebrafish estrogen receptor, zfERβ2, to regulate the downstream pathways. Disruption of the amino acid metabolism and lipid metabolism, and activation of zfERβ2 signaling pathway were found to be the key mechanisms for the endocrine disrupting effects of PBs. The hormone interference effects of PBs were apparently dependent on the shared oxybenzene on their structures, with the degree of interference determined largely by the length of their alkyl chains. These findings provide new insights into the endocrine disrupting effects of PBs and could help better assess their risk to human health.

Molecular interactions of paraben family of pollutants with embryonic neuronal proteins of Danio rerio: A step ahead in computational toxicity towards adverse outcome pathway

The paraben family of endocrine disruptors exhibit persistent behaviours in aquatic matrices, having bio-accumulative effects and necessitating toxicity analysis and safe use, as well as prevention of food web penetration. In this study, the toxicity effects of 9 different parabens (Methyl, Ethyl, Propyl, Butyl, Heptyl, Isopropyl, Isobutyl, benzyl parabens and p-hydroxybenzoic acid) were studied against 17 neuronal proteins (Neurog1, Ascl1a, DLA, Syn2a, Ntn1a, Pitx2, and SoxB1, Her/Hes, Zic family) expressed during the early embryonic developmental stage of Danio rerio. The neuronal genes were selected as a biomarker to study the inhibitory effects on the cascade of genes expressed in the early developmental stage. The study uses trRossetta software to predict protein structures of neuronal genes, followed by structural refinement, energy minimisation, and active site prediction, evaluated using energy value, RC plot and ERRAT scores of PROCHECK and ERRAT programs. Compared to raw structures, highly confident predicted structures and quality scores were observed for refined protein with few exceptions. Based on the polarity and charge of the aminoacids, the probable pockets were identified using active site prediction, which were then used for molecular docking analysis. Further, the ADMET analysis, ligand likeliness and toxicological test revealed the paraben family of compounds as one of the most susceptible toxic and mutagenic compounds. The molecular docking results showed an interesting pattern of increasing binding affinity with increase in the carbon chains of paraben molecules. Benzyl Paraben showed higher binding affinities across all 17 neuronal proteins. Finally, gene co-occurrence/co-expression and protein-protein interaction studies using the STRING database depict that all proteins are functionally related and play essential roles in standard biological processes or pathways, conserved and expressed in diverse organisms. The interaction between paraben compounds and neuronal genes indicates high risks of inhibiting reactions in embryonic stages, emphasising the need for effective treatment measures and strict regulations.

Effects of butyl paraben on behavior and molecular mechanism of Chinese striped-necked turtle (Mauremys sinensis)

Butyl paraben (BuP) is widely used in cosmetics, drugs, and food preservation. Recently it is an identified new pollutant that affects various aspects of reproduction, lipid metabolism, and nervous system. Behavioral activity serves as a pre-warning biomarker for predicting water quality. So, in this study, the changes in some behaviors and its neurotransmitters and cell apoptosis in the brain of Chinese striped-necked turtles (Mauremys sinensis) were studied when the turtles were exposed to BuP concentrations of 0, 5, 50, 500, and 5000 µg/L for 21 weeks. The results showed that, the basking time and altering scores to external stimuli in the groups of 50, 500, and 5000 µg/L were significantly reduced, while the time for body-righting was significantly increased, compared with the control (0 µg/L), indicating that the turtles exhibited depression and inactive behavior. The analysis of neurotransmitter in the brain showed that 5-hydroxytryptamine (5-HT) contents in the groups of 500 and 5000 µg/L were significantly higher than the other groups, which was due to an increase in the mRNA relative expression levels of the 5-HT receptor gene (5-HTR), neurotransmitter transporter genes (Drd4, Slc6a4), and neurotransmitter synthase tryptophan hydroxylase (TPH). Furthermore, GABA transaminase (GABA-T) activity increased in the 500 and 5000 µg/L groups, and tyrosine hydroxylase (TH) activity increased dramatically in the 5000 µg/L group. However, acetyl-CoA (AChE) activity was significantly reduced in these four BuP exposure groups. These changes could be attributed to decreased movement velocity and increased inactivity. Meanwhile, the mRNA expression level of BAX, Bcl-2, caspase-9 and TUNEL assay indicated the occurrence of cell apoptosis in the brains of the higher BuP exposed groups, which may play an important role in neuronal death inducing behavior change. In summary, these findings offer fundamental insights into turtle ecotoxicology and serve as a foundation for a comprehensive assessment of the ecological and health risks associated with BuP.

Evaluation of Tacrolimus' Adverse Effects on Zebrafish in Larval and Adult Stages by Using Multiple Physiological and Behavioral Endpoints

Tacrolimus (FK506) is a common immunosuppressant that is used in organ transplantation. However, despite its importance in medical applications, it is prone to adverse side effects. While some studies have demonstrated its toxicities to humans and various animal models, very few studies have addressed this issue in aquatic organisms, especially zebrafish. Here, we assessed the adverse effects of acute and chronic exposure to tacrolimus in relatively low doses in zebrafish in both larval and adult stages, respectively. Based on the results, although tacrolimus did not cause any cardiotoxicity and respiratory toxicity toward zebrafish larvae, it affected their locomotor activity performance in light-dark locomotion tests. Meanwhile, tacrolimus was also found to slightly affect the behavior performance, shoaling formation, circadian rhythm locomotor activity, and color preference of adult zebrafish in a dose-dependent manner. In addition, alterations in the cognitive performance of the fish were also displayed by the treated fish, indicated by a loss of short-term memory. To help elucidate the toxicity mechanism of tacrolimus, molecular docking was conducted to calculate the strength of the binding interaction between tacrolimus to human FKBP12. The results showed a relatively normal binding affinity, indicating that this interaction might only partly contribute to the observed alterations. Nevertheless, the current research could help clinicians and researchers to further understand the toxicology of tacrolimus, especially to zebrafish, thus highlighting the importance of considering the toxicity of tacrolimus prior to its usage.

Teleosts as behaviour test models for social stress

Stress is an important aspect of our everyday life and exposure to it is an unavoidable occurrence. In humans, this can come in the form of social stress or physical stress from an injury. Studies in animal models have helped researchers to understand the body's adaptive response to stress in human. Notably, the use of behavioural tests in animal models plays a pivotal role in understanding the neural, endocrine and behavioural changes induced by social stress. Under socially stressed conditions, behavioural parameters are often measured physiological and molecular parameters as changes in behaviour are direct responses to stress and are easily assessed by behavioural tests. Throughout the past few decades, the rodent model has been used as a well-established animal model for stress and behavioural changes. Recently, more attention has been drawn towards using fish as an animal model. Common fish models such as zebrafish, medaka, and African cichlids have the advantage of a higher rate of reproduction, easier handling techniques, sociability and most importantly, share evolutionary conserved genetic make-up, neural circuitry, neuropeptide molecular structure and function with mammalian species. In fact, some fish species exhibit a clear diurnal or seasonal rhythmicity in their stress response, similar to humans, as opposed to rodents. Various social stress models have been established in fish including but not limited to chronic social defeat stress, social stress avoidance, and social stress-related decision-making. The huge variety of behavioural patterns in teleost also aids in the study of more behavioural phenotypes than the mammalian species. In this review, we focus on the use of fish models as alternative models to study the effects of stress on different types of behaviours. Finally, fish behavioural tests against the typical mammalian model-based behavioural test are compared and discussed for their viability.

Zebrafish: A Pharmacological Model for Learning and Memory Research

Learning and memory are essential to organism survival and are conserved across various species, especially vertebrates. Cognitive studies involving learning and memory require using appropriate model organisms to translate relevant findings to humans. Zebrafish are becoming increasingly popular as one of the animal models for neurodegenerative diseases due to their low maintenance cost, prolific nature and amenability to genetic manipulation. More importantly, zebrafish exhibit a repertoire of neurobehaviors comparable to humans. In this review, we discuss the forms of learning and memory abilities in zebrafish and the tests used to evaluate the neurobehaviors in this species. In addition, the pharmacological studies that used zebrafish as models to screen for the effects of neuroprotective and neurotoxic compounds on cognitive performance will be summarized here. Lastly, we discuss the challenges and perspectives in establishing zebrafish as a robust model for cognitive research involving learning and memory. Zebrafish are becoming an indispensable model in learning and memory research for screening neuroprotective agents against cognitive impairment.