Antithyroid and Goitrogenic Effects of Coal-Water Extracts from Iodine-Sufficient Goiter Areas

Abstract

Goiter in iodine-sufficient areas has been linked to water-borne goitrogens in watersheds and aquifers rich in coal and shale. In the present study, the potential antithyroid and goitrogenic effects of coal-water extracts (CWE) were investigated in vivo in rats after chronic and acute oral administration of CWE, and in vitro by a thyroid peroxidase (TPO) enzyme system. CWE was prepared by continuous extraction of ground (40 mesh) Appalachian coal with goitrogen-free water (GFW). Female Buffalo rats fed on Purina iodine-rich diet (12 μg I^-/day/rat), were given ad lib CWE (50 mg/ml; ∼ 20 mL/day/rat) or GFW (controls) for 2 months. At the end of the experiment, ¹²⁵I 1 μCi, was injected i.p. and 4 h later the thyroid glands were removed, weighed, and analyzed histologically and for total ¹²⁵I and ¹²⁵I-labeled compounds. Rats on CWE had larger thyroid glands [7.2 ± 0.3 mg/100 g (mean ± SE) vs 5.0 ± 0.5 controls; p < 0.005] with distinct histological changes of smaller thyroid follicles, some with columnar epithelium, and with more dense colloid than in controls, and had significant inhibition of the coupling mechanism for production of thyroid hormones [^l25MIT + DIT/ ¹²⁵T₃ + T₄: 5.1 ± 0.2 vs3.9 ± 0.1 controls,p < 0.005; and ¹²⁵T₃ + T₄(%): 10.6 ± 0.3 vs 12.6 ± 0.4 controls, p < 0.005]. Female Sprague-Dawley rats under the same conditions as Buffalo rats were given acutely by GI tube 2 mL of CWE (5 g/mL) or GFW (controls). Rats on CWE suppressed thyroid ¹²⁵I-organification [¹²⁵I (%): 56.2 ± 3.5 (mean ± SE) vs 45.6 ± 1.7 controls, p < 0.03; ¹²⁵MIT + DIT (%): 39.3 ± 3.9 vs 50.5 ± 1.5 controls, p < 0.03; and ¹²⁵I/¹²⁵MIT + DIT: 1.6 ± 0.3 vs 0.9 ± 0.06 controls, 0.05 >p < 0.10]. Aqueous extracts of 25 and 100 mg of coal produced 24.3 ±2.1% (mean ± SE) (p < 0.05) and 54.6 ± 6.3% (p < 0.01) inhibition, respectively, of TPO. These data provide direct experimental evidence that water-borne antithyroid and goitrogenic compounds are derived from coal, and are consistent with epidemiological observations of higher goiter prevalence in iodine-sufficient coal-rich areas than in areas devoid of organic rocks. Their contamination of water supplies could pose a serious threat of thyroid disorders.