Effects of embryonic exposure to polychlorinated biphenyls on zebrafish skeletal development

Environmental Chemicals and their Association with Hyperparathyroidism

BACKGROUND

The incidence of hyperparathyroidism has increased in the USA. The previous work from our institution detected environmental chemicals (EC) within hyperplastic parathyroid tumors. The National Health and Nutrition Examination Survey (NHANES) is a program designed to assess the health status of people in the USA and includes measurements of EC in serum. Our aim was to determine which EC are associated with elevated parathyroid hormone (PTH) and calcium levels within NHANES.

METHODS

NHANES was queried from 2003-2016 for our analysis with calcium. A separate subgroup was queried from 2003-2006 that included PTH levels. Subjects with elevated calcium, and elevated PTH and normal Vitamin D levels were identified. Wilcoxon rank sum tests were used to analyze levels of EC in those with elevated calcium, and those with elevated PTH in the subgroup. All EC with p < 0.05 were then included in separate multivariate models adjusting for serum vitamin D and creatinine for PTH and albumin for calcium.

RESULTS

There were 51,395 subjects analyzed, and calcium was elevated in 2.1% (1080) of subjects. Our subgroup analysis analyzed 14,681 subjects, and PTH was elevated without deficient Vitamin D in 9.4% (1,377). Twenty-nine different polychlorinated biphenyls and the organochlorine pesticides hexachlorobenzene, transnonachlor, oxychlordane, and p,p'-dichlorodiphenyldichloroethylene (DDE) were found to be associated with elevated calcium and separately with elevated PTH (all p < 0.05).

CONCLUSION

In NHANES, 33 ECs were found to be associated with elevated calcium as well as elevated PTH levels on our subgroup analysis. These chemicals may lead us toward a causal link between environmental factors and the development of hyperparathyroidism and should be the focus of future studies looking at chemical levels within specimens.

Acute exposure to 4-OH-A, not PCB1254, alters brain aromatase activity but does not adversely affect growth in zebrafish

Acute developmental exposure to pharmaceuticals or environmental contaminants can have deleterious, long lasting effects. Many of these compounds are endocrine disruptors (EDCs) that target estrogen signaling, with effects on reproductive and non-reproductive tissues. We recently reported that zebrafish larvae transiently exposed to the pharmaceutical EDC 4-OH-A display visual deficits as adults. Here, we examine whether these long-term effects are due to compound-induced morphological and/or cellular changes. Zebrafish aged 24 h, 48 h, 72 h, or 7 days post-fertilization (larvae) or 3-4mos (adults) were exposed to either 4-OH-A or PCB₁₂₅₄ for 24 h. After that time, notochord length, eye diameter, inter-eye distance, and heart rate were measured from larvae; and aromatase (estrogen synthase) activity was measured in homogenates of adult brain tissue. In general, indices of larval growth and development were not altered by 24 h exposure to either compound. 4-OH-A potently inhibited aromatase activity, while PCB₁₂₅₄ did not, with inhibition continuing even after removal from treatment. These results support differential function of EDCs and indicate that developmental exposure to 4-OH-A causes sustained inhibition of aromatase, which could be associated with altered adult behaviors.

Effects of embryonic exposure to polychlorinated biphenyls (PCBs) on anxiety-related behaviors in larval zebrafish

The zebrafish (Danio rerio) is an excellent model system for assessing the effects of toxicant exposure on behavior and neurodevelopment. In the present study, we examined the effects of sub-chronic embryonic exposure to polychlorinated biphenyls (PCBs), a ubiquitous anthropogenic pollutant, on anxiety-related behaviors. We found that exposure to the PCB mixture, Aroclor (A) 1254, from 2 to 26h post-fertilization (hpf) induced two statistically significant behavioral defects in larvae at 7 days post-fertilization (dpf). First, during 135min of free swimming, larvae that had been exposed to 2ppm, 5ppm or 10ppm A1254 exhibited enhanced thigmotaxis (edge preference) relative to control larvae. Second, during the immediately ensuing 15-min visual startle assay, the 5ppm and 10ppm PCB-exposed larvae reacted differently to a visual threat, a red 'bouncing' disk, relative to control larvae. These results are consistent with the anxiogenic and attention-disrupting effects of PCB exposure documented in children, monkeys and rodents and merit further investigation.

Effects of embryonic exposure to polychlorinated biphenyls (PCBs) on larval zebrafish behavior

Developmental disorders such as anxiety, autism, and attention deficit hyperactivity disorders have been linked to exposure to polychlorinated biphenyls (PCBs), a ubiquitous anthropogenic pollutant. The zebrafish is widely recognized as an excellent model system for assessing the effects of toxicant exposure on behavior and neurodevelopment. In the present study, we examined the effect of sub-chronic embryonic exposure to the PCB mixture, Aroclor (A) 1254 on anxiety-related behaviors in zebrafish larvae at 7 days post-fertilization (dpf). We found that exposure to low concentrations of A1254, from 2 to 26 h post-fertilization (hpf) induced specific behavioral defects in two assays. In one assay with intermittent presentations of a moving visual stimulus, 5 ppm and 10 ppm PCB-exposed larvae displayed decreased avoidance behavior but no significant differences in thigmotaxis or freezing relative to controls. In the other assay with intermittent presentations of a moving visual stimulus and a stationary visual stimulus, 5 ppm and 10 ppm PCB-exposed larvae had elevated baseline levels of thigmotaxis but no significant differences in avoidance behavior relative to controls. The 5 ppm larvae also displayed higher terminal levels of freezing relative to controls. Collectively, our results show that exposure to ecologically valid PCB concentrations during embryonic development can induce functional deficits and alter behavioral responses to a visual threat.