Abstract
Some of the edible plants like apricot kernel, flaxseed, and cassava generate hydrogen cyanide (HCN) when cyanogenic glycosides are hydrolyzed. Rhodanese (thiosulfate: cyanide sulfurtransferases of TSTs; EC: 2.8.1.1) is a sulfide-detoxifying enzymes that converts cyanides into thiocyanate and sulfite. This enzyme exists in a liver and kidneys in abundance. The present study is to evaluate the conversion of apricot cyanogenic glycosides into thiocyanate by human hepatic (HepG2) and colonal (HT-29) cells, and the induction of the enzymes in the rat. The effects of short term exposure of amygdalin to rats have also been investigated. Cytosolic, mitochondrial, and microsomal fractions from HepG2 and HT-29 cells and normal male Spraque-Dawley rats were used. When apricot kernel extract was used as substrate, the rhodanese activity in liver cells was higher than the activity in colon cells, both from established human cell line or animal tissue. The cytosolic fractions showed the highest rhodanese activity in all of the cells, exhibiting two to three times that of microsomal fractions. Moreover, the cell homogenates could metabolize apricot extract to thiocyanate suggesting cellular hydrolysis of cyanogenic glycoside to cyanide ion, followed by a sulfur transfer to thiocyanate. After the consumption of amygdalin for 14 days, growth of rats began to decrease relative to that of the control group though a significant change in thyroid has not been observed. The resulting data support the conversion to thiocyanate, which relate to the thyroid dysfunction caused by the chronic dietary intake of cyanide. Because Korean eats a lot of Brassicaceae vegetables such as Chinese cabbage and radish, the results of this study might indicate the involvement of rhodanese in prolonged exposure of cyanogenic glycosides.
Highlights
Some edible plants, including bitter almond, apricot, and cassava, contain cyanogenic glycosides
Rhodanese is a sulfide-detoxifying enzyme that converts cyanides into thiocyanate and Correspondence to: Hoonjeong Kwon, Department of Food and Nutrition, Research Institute of Human Ecology, Seoul National University, Seoul 151-742, Korea E-mail: hjkwon@snu.ac.kr occurs in abundance in the liver and kidneys (Ogata et al, 1990)
The objective of this study is to evaluate the conversion of apricot cyanogenic glycosides into thiocyanate by human hepatic (HepG2) and colonal (HT-29) cells, and the induction of the enzymes using rats
Summary
Some edible plants, including bitter almond, apricot, and cassava, contain cyanogenic glycosides. When these compounds are hydrolyzed by β-glycosidase found in microbes or plant tissue, cyanide (HCN) is released (Montgomery, 1965; Osuntokun et al, 1970). Rhodanese is a sulfide-detoxifying enzyme that converts cyanides into thiocyanate and. If ingested in sublethal quantities, cyanide is detoxified to thiocyanate within the cells of the organism. Chronic exposure to cyanogenic glycosides can be goitrogenic, because the thiocyanate, the metabolite, competes with iodide in the thyroid gland, inhibiting the synthesis and clearance of thyroid hormones (Dohan et al, 2000). Cassava was suspected of having goitrogenic properties for the first time in Nigeria in 1966, where iodine deficiency alone could not account for the frequency of goiter (Ekpechi et al, 1966).
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