Mitochondrial dysfunction and oxidative stress contribute to cross-generational toxicity of benzo(a)pyrene in Danio rerio

The potential for polycyclic aromatic hydrocarbons (PAHs) to have adverse effects that persist across generations is an emerging concern for human and wildlife health. This study evaluated the role of mitochondria, which are maternally inherited, in the cross-generational toxicity of benzo(a)pyrene (BaP), a model PAH and known mitochondrial toxicant. Mature female zebrafish (F0) were fed diets containing 0, 12.5, 125, or 1250 μg BaP/g at a feed rate of 1% body weight twice/day for 21 days. These females were bred with unexposed males, and the embryos (F1) were collected for subsequent analyses. Maternally-exposed embryos exhibited altered mitochondrial function and metabolic partitioning (i.e. the portion of respiration attributable to different cellular processes), as evidenced by in vivo oxygen consumption rates (OCRs). F1 embryos had lower basal and mitochondrial respiration and ATP turnover-mediated OCR, and increased proton leak and reserve capacity. Reductions in mitochondrial DNA (mtDNA) copy number, increases in mtDNA damage, and alterations in biomarkers of oxidative stress were also found in maternally-exposed embryos. Notably, the mitochondrial effects in offspring occurred largely in the absence of effects in maternal ovaries, suggesting that PAH-induced mitochondrial dysfunction may manifest in subsequent generations. Maternally-exposed larvae also displayed swimming hypoactivity. The lowest observed effect level (LOEL) for maternal BaP exposure causing mitochondrial effects in offspring was 12.5 µg BaP/g diet (nominally equivalent to 250 ng BaP/g fish). It was concluded that maternal BaP exposure can cause significant mitochondrial impairments in offspring.

A County-Level Program for the Evaluation of the Potential for Take-Home Lead Exposures Among Children in Michigan

OBJECTIVE

Take-home lead exposure involves lead dust inadvertently carried from the worksite by employees that becomes deposited in their homes and vehicles. We piloted a program in 2 counties in Michigan to investigate the countywide potential for take-home lead exposures across industries.

METHODS

During 2018-2020, we identified establishments through internet searches and industry-specific registries. We visited establishments with a physical storefront in-person; we attempted to contact the remaining establishments via telephone. We administered questionnaires at the establishment level to assess the presence of lead and the current use of practices meant to mitigate the potential for take-home lead exposures. We recruited workers for wipe sampling of lead dust from their vehicle floors to test for lead levels.

RESULTS

We identified 320 establishments with potential lead use or exposures. Questionnaire responses revealed widespread worker exposures to lead and a lack of education and implementation of best practices to prevent lead from leaving the worksite. Dust samples (n = 60) collected from employee vehicles showed a ubiquitous tracking of lead out of the workplace, with a range of 5.7 to 84 000 µg/ft2 and a geometric mean of 234 µg/ft2. Of the sample results, 95.0% were above the lead dust clearance levels for homes established by the US Environmental Protection Agency.

CONCLUSIONS

This work suggests that take-home lead exposures are widespread and may be important sources of lead exposure among children. It also demonstrates the feasibility of a program for the identification of establishments whose employees may be susceptible to taking lead dust home with them and whose children may subsequently be targeted for blood lead monitoring.

Zebrafish show long-term behavioral impairments resulting from developmental vitamin D deficiency

Vitamin D has been shown in a wide variety of species to play critical roles in neurodevelopment. Vitamin D deficiency disrupts development of the brain and can cause lasting behavioral dysfunction. Zebrafish have become an important model for the study of development in general and neurodevelopment in particular. Zebrafish were used in the current study to characterize the effects of developmental vitamin D deficiency on behavioral function. Adult zebrafish that had been chronically fed a vitamin D deficient or replete diets were bred and the offspring were continued on those diets. The offspring were behaviorally tested as adults. In the novel tank diving test the vitamin D deficient diet significantly lowered the vertical position of fish indicative of more anxiety-like behavior. In the novel tank diving test swimming activity was also significantly decreased by vitamin D deficiency. Startle response was increased by developmental vitamin D deficiency during the early part of the test. No significant effects of vitamin D deficiency were seen with social affiliation and predatory stimulus avoidance tests. These results indicate a phenotype of vitamin D deficiency characterized by more anxiety-like behavior. This result was relatively specific inasmuch as few or no behavioral effects were seen in other behavioral tests.

Assessing the accuracy of the death certificate injury at work box for identifying fatal occupational injuries in Michigan

BACKGROUND

Death certificates contain a box labeled "Injury at Work" which is to be marked "Yes" for all fatal occupational injuries. The accuracy of this box in Michigan is not fully characterized.

METHODS

The accuracy of the Injury at Work box on the Michigan death certificate was compared to deaths identified from 2001 through 2016 by the Michigan Fatality Assessment and Control Evaluation multi-source surveillance system. The sensitivity was calculated across this time period, while specificity and positive and negative predictive values were derived for 2011-2016. Univariate and multivariate regression were used to examine differences in the sensitivity over time and across demographic variables, industry, and the type of death.

RESULTS

We found a sensitivity for the Injury at Work box of 73.1% among 2156 deaths. The sensitivity showed a significant declining trend over the 17 years, from 79.8% to 63.1%. Sensitivity varied significantly across incident type (aircraft, animal-related, drug overdose, motor vehicle, and suicides having particularly lower sensitivities, and electrocutions, falls, and machine-related incidents having higher sensitivities), and industry sector (construction, manufacturing, public safety, transportation, and trade sectors having higher sensitivities, and agriculture and services sectors showing lower sensitivities). Across nearly all categories the sensitivity was significantly below 1.

CONCLUSIONS

The Injury at Work box on the Michigan death certificate was often incorrectly completed and has become less accurate with time, though the degree of this inaccuracy varies by the industry of the victim and the type of incident.

Developmental exposure of zebrafish to vitamin D receptor acting drugs and environmental toxicants disrupts behavioral function

Vitamin D receptor (VDR) signaling is important for optimal neurobehavioral development. Disruption of VDR signaling by environmental toxicants during early development might contribute to the etiology of behavioral dysfunction. In the current set of studies, we examined ten compounds known to affect VDR function in vitro for neurobehavioral effects in vivo in zebrafish. Zebrafish embryos were exposed to concentrations of the compounds in their water during the first 5 days post-fertilization. On day 5, the embryos were tested in an alternating light-dark locomotor assay using a computerized video tracking system. We found that most of the compounds produced significant changes in locomotor behavior in exposed zebrafish larvae, although the direction of the effect (i.e., hypo- or hyperactivity) and the sensitivity of the effect to changes in illumination condition varied across the compounds. The nature of the behavioral effects generally corresponded to the effects these compounds have been shown to exert on VDR. These studies lay a foundation for further investigation to determine whether behavioral dysfunction persists into adulthood and if so which behavioral functions are affected. Zebrafish can be useful for screening compounds identified in high throughput in vitro assays to provide an initial test for how those compounds would affect construction and behavioral function of a complex nervous system, helping to bridge the gap between in vitro neurotoxicity assays and mammalian models for risk assessment in humans.

Dopamine D1 and D2 receptor antagonism during development alters later behavior in zebrafish

This study sought to examine the long-term behavioral impacts of dopamine D₁ and D₂ receptor antagonism during development in zebrafish (Danio rerio). Zebrafish embryos of both the AB* and 5D strains were exposed via immersion to either the D₁ receptor antagonist SCH-23,390 or the D₂ receptor antagonist haloperidol, at either 0.5 or 1.5-μM, from 5 h post-fertilization to 5 days post-fertilization. Aquarium water served as a control. Fish were then either tested as larvae on day 6 post-fertilization on a light/dark locomotor assay, or were grown to adulthood and tested on a behavioral battery that included assays for novel environment exploration, startle habituation, social affiliation, and predator escape (AB* strain only). Overall, developmental exposure to dopamine D₁ and D₂ receptor antagonists caused clear effects in larval locomotor behavior, driving hyperactivity in dark phases and hypoactivity in light phases. Additionally, control fish from the two strains were significantly different from each other (p < 0.05) with the AB* fish being more active than SD during the dark periods of the test. In the adult behavioral battery, developmental exposure to 1.5-μM of the D₁ antagonist SCH-23390 significantly reduced activity (p < 0.05) in the predator escape assay. Despite the fact that embryonic exposure to D₁ and D₂ receptor antagonists caused clear behavioral alterations in larval activity there were much more subtle effects persisting into adulthood.

Developmental exposure to an organophosphate flame retardant alters later behavioral responses to dopamine antagonism in zebrafish larvae

Human exposure to organophosphate flame retardants (OPFRs) is widespread, including pregnant women and young children with whom developmental neurotoxic risk is a concern. Given similarities of OPFRs to organophosphate (OP) pesticides, research into the possible neurotoxic impacts of developmental OPFR exposure has been growing. Building upon research implicating exposure to OP pesticides in dopaminergic (DA) dysfunction, we exposed developing zebrafish to the OPFR tris(1,3-dichloroisopropyl) phosphate (TDCIPP), during the first 5 days following fertilization. On day 6, larvae were challenged with acute administration of dopamine D₁ and D₂ receptor antagonists and then tested in a light-dark locomotor assay. We found that both developmental TDCIPP exposure and acute dopamine D₁ and D₂ antagonism decreased locomotor activity separately. The OPFR and DA effects were not additive; rather, TDCIPP blunted further D₁ and D₂ antagonist-induced decreases in activity. Our results suggest that TDCIPP exposure may be disrupting dopamine signaling. These findings support further research on the effects of OPFR exposure on the normal neurodevelopment of DA systems, whether these results might persist into adulthood, and whether they interact with OPFR effects on other neurotransmitter systems in producing the developmental neurobehavioral toxicity.

Developmental exposure to a complex PAH mixture causes persistent behavioral effects in naive Fundulus heteroclitus (killifish) but not in a population of PAH-adapted killifish

Acute exposures to some individual polycyclic aromatic hydrocarbons (PAHs) and complex PAH mixtures are known to cause cardiac malformations and edema in the developing fish embryo. However, the heart is not the only organ impacted by developmental PAH exposure. The developing brain is also affected, resulting in lasting behavioral dysfunction. While acute exposures to some PAHs are teratogenically lethal in fish, little is known about the later life consequences of early life, lower dose subteratogenic PAH exposures. We sought to determine and characterize the long-term behavioral consequences of subteratogenic developmental PAH mixture exposure in both naive killifish and PAH-adapted killifish using sediment pore water derived from the Atlantic Wood Industries Superfund Site. Killifish offspring were embryonically treated with two low-level PAH mixture dilutions of Elizabeth River sediment extract (ERSE) (TPAH 5.04 μg/L and 50.4 μg/L) at 24h post fertilization. Following exposure, killifish were raised to larval, juvenile, and adult life stages and subjected to a series of behavioral tests including: a locomotor activity test (4 days post-hatch), a sensorimotor response tap/habituation test (3 months post hatch), and a novel tank diving and exploration test (3months post hatch). Killifish were also monitored for survival at 1, 2, and 5 months over 5-month rearing period. Developmental PAH exposure caused short-term as well as persistent behavioral impairments in naive killifish. In contrast, the PAH-adapted killifish did not show behavioral alterations following PAH exposure. PAH mixture exposure caused increased mortality in reference killifish over time; yet, the PAH-adapted killifish, while demonstrating long-term rearing mortality, had no significant changes in mortality associated with ERSE exposure. This study demonstrated that early embryonic exposure to PAH-contaminated sediment pore water caused long-term locomotor and behavioral alterations in killifish, and that locomotor alterations could be observed in early larval stages. Additionally, our study highlights the resistance to behavioral alterations caused by low-level PAH mixture exposure in the adapted killifish population. Furthermore, this is the first longitudinal behavioral study to use killifish, an environmentally important estuarine teleost fish, and this testing framework can be used for future contaminant assessment.

Persistent behavioral effects following early life exposure to retinoic acid or valproic acid in zebrafish

BACKGROUND

Moderate to severe dysregulation in retinoid signaling during early development is associated with a constellation of physical malformations and/or neural tube defects, including spina bifida. It is thought that more subtle dysregulation of this system, which might be achievable via dietary (i.e. hypervitaminosis A) or pharmacological (i.e. valproic acid) exposure in humans, will manifest on behavioral domains including sociability, without overt physical abnormalities.

METHODS

During early life, zebrafish were exposed to low doses of two chemicals that disrupt retinoid signaling. From 0 to 5dpf, larvae were reared in aqueous solutions containing retinoic acid (0, 0.02, 0.2 or 2nM) or valproic acid (0, 0.5, 5.0 or 50μM). One cohort of zebrafish was assessed using a locomotor activity screen at 6-dpf; another was reared to adulthood and assessed using a neurobehavioral test battery (startle habituation, novel tank exploration, shoaling, and predator escape/avoidance).

RESULTS

There was no significant increase in the incidence of physical malformation among exposed fish compared to controls. Both retinoic acid and valproic acid exposures during development disrupted larval activity with persisting behavioral alterations later in life, primarily manifesting as decreased social affiliation.

CONCLUSIONS

Social behavior and some aspects of motor function were altered in exposed fish; the importance of examining emotional or psychological consequences of early life exposure to retinoid acting chemicals is discussed.

Teratogenic, bioenergetic, and behavioral effects of exposure to total particulate matter on early development of zebrafish (Danio rerio) are not mimicked by nicotine

Cigarette smoke has been associated with a number of pathologies; however, the mechanisms leading to developmental effects are yet to be fully understood. The zebrafish embryo is regarded as a 'bridge model'; however, not many studies examined its applicability to cigarette smoke toxicity. This study examined the effects of total particulate matter (TPM) from 3R4F reference cigarettes on the early development of zebrafish (Danio rerio). Zebrafish embryos were exposed to two concentrations of TPM (0.4 and 1.4 μg/mL equi-nicotine units) or nicotine at equivalent doses. The exposures began at 2h post-fertilization (hpf) and lasted until 96 hpf. Several physiological parameters were assessed during or after the exposure. We show that TPM increased mortality, delayed hatching, and increased the incidence of deformities in zebrafish. TPM exposure also increased the incidence of hemorrhage and disrupted the angiogenesis of the major vessels in the brain. Moreover, TPM exposure reduced the larval body length, decreased the heart rate, and reduced the metabolic rate. Biomarkers of xenobiotic metabolism and oxidative stress were also affected. TPM-exposed zebrafish also differed behaviorally: at 24 hpf the embryos had a higher frequency of spontaneous contractions and at 144 hpf the larvae displayed swimming hyperactivity. This study demonstrates that TPM disrupts several aspects of early development in zebrafish. The effects reported for TPM were not attributable to nicotine, since embryos treated with nicotine alone did not differ significantly from the control group. Collectively, our work illustrates the utility of zebrafish as an alternative model to evaluate the toxic effects of cigarette smoke constituents.

Neurobehavioral impairments caused by developmental imidacloprid exposure in zebrafish

BACKGROUND

Neonicotinoid insecticides are becoming more widely applied as organophosphate (OP) insecticides are decreasing in use. Because of their relative specificity to insect nicotinic receptors, they are thought to have reduced risk of neurotoxicity in vertebrates. However, there is scant published literature concerning the neurobehavioral effects of developmental exposure of vertebrates to neonicotinoids.

METHODS

Using zebrafish, we investigated the neurobehavioral effects of developmental exposure to imidacloprid, a prototypic neonicotinoid pesticide. Nicotine was also administered for comparison. Zebrafish were exposed via immersion in aqueous solutions containing 45 μM or 60 μM of imidacloprid or nicotine (or vehicle control) from 4h to 5d post fertilization. The functional effects of developmental exposure to both imidacloprid and nicotine were assessed in larvae using an activity assay and during adolescence and adulthood using a battery of neurobehavioral assays, including assessment of sensorimotor response and habituation in a tactile startle test, novel tank swimming, and shoaling behavior.

RESULTS

In larvae, developmental imidacloprid exposure at both doses significantly decreased swimming activity. The 5D strains of zebrafish were more sensitive to both nicotine and imidacloprid than the AB* strain. In adolescent and adult fish, developmental exposure to imidacloprid significantly decreased novel tank exploration and increased sensorimotor response to startle stimuli. While nicotine did not affect novel tank swimming, it increased sensorimotor response to startle stimuli at the low dose. No effects of either compound were found on shoaling behavior or habituation to a startling stimulus.

DISCUSSION

Early developmental exposure to imidacloprid has both early-life and persisting effects on neurobehavioral function in zebrafish. Its developmental neurotoxicity should be further investigated.

Pharmacological analyses of learning and memory in zebrafish (Danio rerio)

Over the last decade, zebrafish (Danio rerio) have become valuable as a complementary model in behavioral pharmacology, opening a new avenue for understanding the relationships between drug action and behavior. This species offers a useful intermediate approach bridging the gap between in vitro studies and traditional mammalian models. Zebrafish offer great advantages of economy compared to their rodent counterparts, their complex brains and behavioral repertoire offer great translational potential relative to in vitro models. The development and validation of a variety of tests to measure behavior, including cognition, in zebrafish have set the stage for the use of this animal for behavioral pharmacology studies. This has led to research into the basic mechanisms of cognitive function as well as screening for potential cognition-improving drug therapies, among other lines of research. As with all models, zebrafish have limitations, which span pharmacokinetic challenges to difficulties quantifying behavior. The use, efficacy and limitations associated with a zebrafish model of cognitive function are discussed in this review, within the context of behavioral pharmacology.

Long-term behavioral impairment following acute embryonic ethanol exposure in zebrafish

BACKGROUND

Developmental exposure to ethanol has long been known to cause persisting neurobehavioral impairment. However, the neural and behavioral mechanisms underlying these deficits and the importance of exposure timing are not well-characterized. Given the importance of timing and sequence in neurodevelopment it would be expected that alcohol intoxication at different developmental periods would result in distinct neurobehavioral consequences.

METHODS

Zebrafish embryos were exposed to ethanol (0%, 1%, 3%) at either 8-10 or 24-27 h post-fertilization (hpf) then reared to adolescence and evaluated on several behavioral endpoints. Habituation to a repeated environmental stimulus and overall sensorimotor function were assessed using a tap startle test; measurements of anxiety and exploration behavior were made following introduction to a novel tank; and spatial discrimination learning was assessed using aversive control in a three-chambered apparatus. Overt signs of dysmorphogenesis were also scored (i.e. craniofacial malformations, including eye diameter and midbrain-hindbrain boundary morphology).

RESULTS

Ethanol treated fish were more active both at baseline and following a tap stimulus compared to the control fish and were hyperactive when placed in a novel tank. These effects were more prominent following exposure at 24-27 hpf than with the earlier exposure window, for both dose groups. Increases in physical malformation were only present in the 3% ethanol group; all malformed fish were excluded from behavioral testing.

DISCUSSION

These results suggest specific domains of behavior are affected following ethanol exposure, with some but not all of the tests revealing significant impairment. The behavioral phenotypes following distinct exposure windows described here can be used to help link cellular and molecular mechanisms of developmental ethanol exposure to functional neurobehavioral effects.