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Antithyroid effects in vivo and in vitro of babassu and mandioca: a staple food in goiter areas of Brazil

Gaitan E, Cooksey RC, Legan J, Lindsay RH, Ingbar SH, Medeiros-Neto G. Antithyroid effects in vivo and in vitro of babassu and mandioca: a staple food in goiter areas of Brazil. Eur J Endocrinol 1994;131:138–44. ISSN 0804–4643

Babassu (Orbignya phalerata), a palm-tree coconut fruit, mixed with mandioca (Manihot utilissima) is the staple food of people living in the endemic goiter area of Maranhao in Brazil, where goiter prevalence among schoolchildren was still 38% in 1986 despite an adequate iodine intake in most of the population. Therefore, the question arose as to whether or not the ingestion of babassu alone or mixed with mandioca contributed to the persistence of endemic goiter in this area of Brazil. In this investigation we examined the potential antithyroid effects of babassu and mandioca by means of in vivo studies in Sprague-Dawley rats, in vitro studies in porcine thyroid slices and using a purified porcine thyroid peroxidase (TPO) system. Samples of various edible parts of babassu and mandioca flour were homogenized and extracted in goitrogen-free water (GFW) for in vivo experiments, and in methanol (100 g/l), GFW or 0.06 mol/l phosphate buffer (pH 7.0) for in vitro experiments. The edible parts of babassu produced significant in vivo antithyroid effects (p < 0.05–< 0.001) in rats on a high iodine intake (14 µg I^– day^–1 · rat^–1), as well as distinct and reproducible antithyroid and anti-TPO activities in both in vitro systems, their action being similar to that of the thionamide-like antithyroid drugs propylthiouracil and methimazole. The antithyroid action of aqueous extracts of mandioca flour in vivo and in thyroid slices in vitro was also evident by significant (p < 0.01–< 0.001) and pronounced inhibition of the iodide organification process; however, in contrast to babassu, methanol and aqueous extracts of mandioca flour caused little inhibition in vitro in the TPO system. Little or no effect was produced by babassu or mandioca on thyroid iodide transport by thyroid slices or in vivo in the rat, indicating that neither thiocyanate nor perchlorate-like compounds are responsible for their antithyroid effects. Results of this study provide direct experimental evidence, both in vivo and in vitro, of antithyroid effects of babassu and mandioca, supporting the hypothesis that this staple food is responsible, at least in part, for the persistence of goiter in the iodine-supplemented endemic region of Maranhao in Brazil.

Eduardo Gaitan, Endocrinology Section (151), VA Medical Center, 1500 E. Woodrow Wilson Drive, Jackson, MS 39216, USA