FLAVONOIDS EXTRACTED FROM FONIO MILLET (DIGITARIA-EXILIS) REVEAL POTENT ANTITHYROID PROPERTIES

Digitaria exilis (fonio) is a tiny variety of millet commonly eaten by inhabitants of semiarid regions. A sample of fonio collected right in the middle of a severely iodine-depleted goitrous endemic was submitt ed to phytochemical investigations in order to assess the potential co ntributory roles played by vegetable molecules to the goitrogenic proc esses. The total content of flavonoids amounts to 500 mg/kg of the edi ble whole cereal grains. Their extraction and identification fail to d etect the C-glycosylflavones described in other millet varieties hut p oint out the presence of apigenin (A = 150 mg/kg) and of luteolin (L(1 ) = 350 mg/kg). Ten percent of A and 80% of L(1) are present in free f orm, whereas the remaining 90% of A and 20% of L(1) are bound as O-gly cosylflavones. Both A and L(1) aglycones manifest strong anti-thyroid peroxidase (TPO) activities, resulting in a significant reduction of t he hormonogenic capacity of this enzyme. In addition, L(1) significant ly depresses the cyclic AMP phosphodiesterase, implying a concomitant overproduction of the thyrotropin-dependent nucleotide. These last unr eported data are regarded as counteracting to some extent the TPO-medi ated goitrogenic properties of L(1). Since fonio is devoid of other mo lecules likely to interfere with the thyroid function, our results art : directly and causally attributed to A and L(1) found in the customar y diet.