Novel biomarkers of perchlorate exposure in zebrafish

Abstract

Perchlorate inhibits iodide uptake by thyroid follicles and lowers thyroid hormone production. Although several effects of perchlorate on the thyroid system have been reported, the utility of these pathologies as markers of environmental perchlorate exposures has not been adequately assessed. The present study examined time-course and concentration-dependent effects of perchlorate on thyroid follicle hypertrophy, colloid depletion, and angiogenesis; alterations in whole-body thyroxine (T4) levels; and somatic growth and condition factor of subadult and adult zebrafish. Changes in the intensity of the colloidal T4 ring previously observed in zebrafish also were examined immunohistochemically. Three-month-old zebrafish were exposed to ammonium perchlorate at measured perchlorate concentrations of 0, 11, 90, 1,131, and 11,480 ppb for 12 weeks and allowed to recover in clean water for 12 weeks. At two weeks of exposure, the lowest-observed-effective concentrations (LOECs) of perchlorate that induced angiogenesis and depressed the intensity of colloidal T4 ring were 90 and 1,131 ppb, respectively; other parameters were not affected (whole-body T4 was not determined at this time). At 12 weeks of exposure, LOECs for colloid depletion, hypertrophy, angiogenesis, and colloidal T4 ring were 11,480, 1,131, 90, and 11 ppb, respectively. All changes were reversible, but residual effects on angiogenesis and colloidal T4 ring intensity were still present after 12 weeks of recovery (LOEC, 11,480 ppb). Whole-body T4 concentration, body growth (length and weight), and condition factor were not affected by perchlorate. The sensitivity and longevity of changes in colloidal T4 ring intensity and angiogenesis suggest their usefulness as novel markers of perchlorate exposure. The 12-week LOEC for colloidal T4 ring is the lowest reported for any perchlorate biomarker in aquatic vertebrates.

Effects of elevated nitrate on endocrine function in Atlantic salmon, Salmo salar

“…Despite changes in thyroid morphology that were suggestive of impaired thyroid function, plasma T 4 concentrations did not differ significantly between the beginning and end of the exposure (Morris et al, 2011). In zebrafish (Danio rerio), exposure to perchlorate, another NIS inhibitor, caused clear changes in thyroid histology, but no significant reduction in T 4 concentration (Mukhi et al, 2005). In contrast, female Wistar rats exposed to various concentrations of NO 3 − in their drinking water for 30 weeks showed depressed TH concentrations at exposures as low as 50 mg/L NO 3 − (Eskiocak et al, 2005).…”

“…It is possible that a 27-day exposure to elevated NO 3 -N was not sufficient to elicit a response in TT 4 or TT 3 in the current study. Because T 4 can be stored within the colloid of thyroid follicles, a reduction in plasma TH may not be manifested until those stores are depleted (Mukhi et al, 2005). More sensitive measures of thyroid function, including histological analyses of follicle structure and immunostaining for T 4 within the colloid, have been suggested (Mukhi et al, 2005).…”

“…Because T 4 can be stored within the colloid of thyroid follicles, a reduction in plasma TH may not be manifested until those stores are depleted (Mukhi et al, 2005). More sensitive measures of thyroid function, including histological analyses of follicle structure and immunostaining for T 4 within the colloid, have been suggested (Mukhi et al, 2005). While histological endpoints were not included in the present study, recent work on nitrate exposure during embryonic development suggests that early thyroid tissue development in Atlantic salmon is not impaired at concentrations up to 93 mg/L NO 3 -N (unpublished data).…”

Developmental timing of sodium perchlorate exposure alters angiogenesis, thyroid follicle proliferation and sexual maturation in stickleback

“…In sufficient concentration and with chronic exposure, perchlorate effectively inhibits the synthesis of thyroid hormones (TH: thyroxine, T4 and triiodothyronine, T3), which are essential regulators of metabolism, growth, development and metamorphosis in vertebrates (Carr et al, 2005; Choksi et al, 2003; Wolff, 1998). Lack of iodide uptake halts production of T4 and can lead to increased thyroid stimulating hormone due to lack of negative feedback to the hypothalamus and pituitary as well as hypothyroidism and changes in thyroid tissue morphology; these changes include follicle cell hypertrophy, proliferation of follicles and surrounding tissue, increased vasculature, and reduced colloid (Blanton and Specker, 2007; Choksi et al, 2003; Mukhi et al, 2005; Tietge et al, 2010). …”

Assessing reproductive and endocrine parameters in male largescale suckers (Catostomus macrocheilus) along a contaminant gradient in the lower Columbia River, USA

“…Digital images of thyroid follicles were taken with an Olympus® digital camera (DP10; Tokyo, Japan) attached to a compound microscope. All measurements were conducted digitally using Image-Pro® Express Software (Media Cybernetics, Silver Spring, MD, USA) as previously described by Mukhi et al (2005). Briefly, five follicles per fish were chosen for all analyses according to their histological integrity and quality, and appropriate angle of cut.…”