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Ermans
Antithyroid sulfurated compoundsErmans AM, Bourdoux in Environmental Goitrogens by E Gaitan, ed, 1989, pp 15-31.
"Natural thioglucosides (also called glucosinolates) were found as the main source of goitrogens present in plants of the Cruciferae family of which cabbage, turnips, and swedes were most often implicated. Hydrolysis of these thioglucosides releases a series of sulfurated compounds, some of which (thiocyanate, isothiocyanate, and thiooxazolidone) exhibit a clear antithyroid activity.
"Another important source of naturally occurring goitrogens is constituted by a series of cyanogenic glucosides present in several vegetable foodstuffs, such as cassava (manioc) and sorgho, which are staple foods in many countries of the world. Antithyroid activity of the cyanogenic glucosides is related to the endogenous detoxification of the cyanide released by the hydrolysis of these compounds leading to the synthesis of thiocyanate....
"Antithyroid compounds identified in vegetable foodstuffs can be divided into two categories according to the way they act on iodine metabolism: (1) thiocyanate and thiocyanate-like compounds primarily inhibit the active concentrating mechanism of iodide. These ions have a molecular volume and charge similar to those of iodide. Their goitrogenic activity can be overcome by iodine administration. L-5 vinyl-2 thiooxazolidone or goitrin acts as a thionamide-like goitrogen, hence as thiourea; it interferes with the process of iodine organification and the coupling of iodotyrosines to form the active hormones. Its action cannot usually be antagonized by iodine."
"THIOCYANATE.... Because of similarities in chemical and physical properties with the halides, a series of ions are termed pseudo-halides. The pseudo-halides include cyanide, cyanate, thiocyanate, selenocyanate, tellurocyanate, and azide.... The wide reactivity of the ion and preparation of organic thiocyanates have led to an extensive use of thiocyanate derivatives in the field of herbicides, defoliants, pesticides, dyes, synthetic fibers, etc."
"Glucosinolates.... Mihailovsky [et al]... have extensively investigated the thiocyanate content of Brassicae plants. the average thiocyanate content in milligrams per 100 g is about 3 for kohlrabi, 4 for cabbage, 8 for cauliflower, and 20 for kale. The glucosinolate content of Brassica vegetables is stimulated by the addition of sulfate in the presence of an adequate mitrate level.
"The ingestion of the foliage of Brassica, such as cabbage or of pure glucobrassicin, cause a rise of thiocyanate in the blood, followed by its appearance in the urine. One feeding of Brassica to guinea pigs caused an inhibition of the iodine uptake by the thyroid gland. However, a quantitative estimation of the thiocyanate content of the plants in relation to the extent of thyroid inhibition suggested that other goitrogens were present in the Brassica tested. Further identification of thiooxazolidone and isothiocyanate in the same foodstuffs validated this assumption. An additive antithyroid effect of thiocyanate, isothiocyanate, and goitrin in groups of rats force-fed with various combinations of these naturally occurring goitrogens has been observed."
"Cyanogenic Glucosides. Another important source of thiocyanate is the cyanogenic glucosides. The CN component of thiocyanate may indeed originate from inorganic cyanide and sulfur donors through the enzymatic action of rhodanese or thiosulfate-cyanide sulfur transferase. Cyanide detoxification function seems to be a primary role in this enzyme.
"Cyanide is not free in intact plants. It originates from the hydrolysis of cyanogenic glucosides which are present in a large number of plants. It is released when the plant tissue containing the glucosides is crushed or autolized. The accidental poisoning of humans who eat cyanophoric foodstuffs, such as bitter almonds, peaches, or apricot kernels, is well known. Moreover, chronic cyanide ingestion in conjunction with a poor diet has been implicated in tropical neuropathies; insufficient supply of sulfur donors possibly limits cyanide conversion into thiocyanate which otherwise is nearly complete.
"The principal vegetables containing cyanogenic glucosides are cassava, lima beans, linseed, bamboo shoots, and sweet potatoes. Cassava (or manioc) is one of the main sources of cyanoglucosides absorbed by man and animals. It is almost exclusively cultivated in the developing countries and represents the essential source of calories for more than 300 million people living in the tropics."
"Large doses of thiocyanate produce an overloading of the renal excretory system for thiocyanate.... In the case of a prolonged overload of thiocyanate in rats and in human beings, a renal adaptative mechanism prevents the plasma level of thiocyanate from rising to more than a concentration of 10 to 15 mcg/ml."
"In the thyroid, thiocyanate is rapidly converted to sulfate. Administration of the thyroid stimulating hormone (TSH) increases the intrathyroidal catabolism of thiocyanate and is even capabel of reversing the block in uptake induced by this ion. TSH probably accelerates the oxidation of thiocyanate to sulfate.
"Halmi, Wollman, and Scranton et al, showed that thiocyanate, in low concentrations inhibited iodide transport by increasing the velocity constant of the iodine efflux from the gland.... At high concentrations, the iodide efflux is greatly accelerated and the thiocyanate inhibits the unidirectional clearance of iodide in the gland. At these high concentration, thiocyanate also inhibits the incorporation of iodide into thyroglobulin; the competition between iodide and thiocyanate is at the level of peroxidase.
"The phenomenon of iodide-thiocyanate competition has also been studied in other tissues that concentrate iodide, i.e., the salivary and mammary glands, stomach, and placenta. Thiocyante and perchlorate inhibit nonthyroidal iodide transport but in different degrees in different organs and different species.
"Extensive experimental studies performed on the goitrogenic action of vegetable foodstuffs containing glucosinolates or cyanogenic glucosides did not at present provide clearcut evidence of the role of thiocyanate in the etiology of endemic goiter. In particular, thiocyanate concentrations found in populations consuming these goitrogenic foodstuffs are indeed much lower than those which are able to inhibit consistently the iodide incorporation into the gland. It has been therefore suggested that increased concentration of thiocyanate in blood and urine primarily constitutes the marker of the presence of other more potent antithyroid compounds."
"These observations therefore indicate that under a prolonged administration of low doses of thiocyanate in rats, the reduction of radioiodine uptake is not an appropriate index of the antithyroid activity of thiocyanate. Moreover, in these studies, thyroid abnormalities mainly correspond to an increased iodide spillage from the gland when the iodide supply is deficient."
"ISOTHIOCYANATES. Isothiocyanates from many thioglucosides are easily recognized because of their pungency, a characteristic of mustard oils which has been long recognized and sought after in condiments. They are fairly widespread in the vegetable kingdom.... Conversion of mustard oil to thiocyanate is one of the mechanisms of the detoxification of isothiocyanate.... Most of the sulfur of certain other isothiocyanates is contrariwise oxidized to sulfate."
"GOITRIN.... The parent thioglucoside of goitrin is progoitrin which is a typical glucosinate. Progoitrin is found in turnip, cabbage, and in other Brassicae. Conversion of progoitrin into goitrin is carried out by a myrosinase present in the plant; progoitrin does not have any antithyroid activity per se. However, a marked antithyroid activity may be observed when progoitrin is administered orally without added myrosinase; hydrolysis of progoitrin probably takes place by normal bacterial inhabitants of the gastrointestinal tract."
"ALIPHATIC DISULFIDES. The small aliphatic disulfides (R-S-S-R; R = methyl-. ethyl-, n-propyl-, phenyl-_, the major components of onion and garlic, exert marked antithyroid activity in the rat.... Disulfides are also present in high concentration (0.3 to 0.5 g/l) in aqueous effluents from coal-conversion processes. Disulfides have also been identified as water contaminants in the US and in water supplying a Colombian district with endemic goiter."
"Another difficulty lies in the need to discriminate between the action of these vegetable antithyroid compounds from the influence of iodine deficiency itself taking into account that some degree of iodine deficiency constitutes a permissive factor for the goitrogenic action of some of these compounds. Moreover,... thyroid abnormalities induced by these vegetable goitrogens are not specific and because of the longstanding ingestion of the suspected vegetables, the question always arises whether the observed thyroid abnormalities are a direct consequence of the effect of the goitrogenic compounds or the result of adaptative mechanisms of the thyroid gland.
"For these different reasons, a tremendous gap persists between the well-documented biochemical knowledge of these vegetable goitrogenic compounds and their potential action in human beings. This gap is very important from a public health point of view."
[Goitrogens of vegetable origin as possible aetiological factors in endemic goiter (author's transl)]Ermans AM. Ann Endocrinol (Paris). 1981 Oct-Nov;42(4-5):435-8. French. [abstract only]
"Ingestion of unsoaked cassava is followed by an increase of the thiocyanate production in men and in rats. Even a moderate increase of serum SCN concentration induces, in chronic conditions, a clearcut goitrogenic effect characterized by the aggravation of the effects of a preexisting iodine deficiency. The mechanism of the antithyroid action of SCN at low concentrations, lies in an acceleration of the exit rate of thyroidal iodide; this effect cannot be identified by the usual clinical investigation with Iodine131."
Goitrogenic action of cyanogenic glucosides present in cassava: a possible etiologic factor of endemic goiter in the Idjwi island.Ermans AM, Delange F, Van der Velden M, Kinthaert J. Acta Endocrinol Suppl (Copenh). 1973 Oct;179:31. [citation only]
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