Thyroid hormones play a critical role in development and functioning of the nervous system. Deiodinases (type 2 [D2] and type 3 [D3]) contribute to the control of thyroid hormone action in the nervous system by regulating the local concentrations of triiodothyronine (T(3)), the main active thyroid hormone. Most brain T(3) is indeed locally formed by deiodination of thyroxine (T(4)). This reaction is catalyzed by D2 expressed in astrocytes throughout the brain and in tanycytes in the mediobasal hypothalamus. D3, which inactivates both T(4) and T(3), is mainly expressed in neurons also throughout the brain, with high expression in hippocampus and pyriform cortex. The regulation of deiodinases by many factors in addition to the thyroid hormones indicate that their role is not limited to mitigate the fluctuations in plasma T(4) and T(3). In contrast to the brain, deiodinases are not expressed in the adult peripheral nerve. Nerve lesions induce D2 in peripheral nerve sheaths and D3 in the endoneurial compartment containing Schwann cells. On the basis of available data summarized in this review, D2 and D3 clearly contribute to determine T(3) concentrations depending on the area of the nervous system, the state of development, and the pathophysiologic conditions.

In cancer patients, appetite and immune status are significantly weakened. Two experimental fermented formulations without (group A, named as FSWW08) and with (group B, FSWW08) an extract from yam root were investigated against a placebo formulation with casein (group C) in a clinical study conducted in six cancer hospitals where cancer patients underwent radio or chemotherapy (patients undergoing radiation therapy n=78, patients undergoing chemotherapy n=184, total 262). IgG and IgA were increased by formulation A in patients despite receiving radio- or chemotherapy. Group A experienced statistically significant increases in lymphocyte transformation rates, whereas group B and group C did not. Formulations A and B either inhibited or lessened statistically significant decreases in white blood counts, whereas the placebo group experienced substantial decreases. Hemoglobin and platelet decreases were inhibited in group A, although not statistically significantly. Patients in group A received no blood transfusions, whereas many patients from the placebo group received blood transfusions. Appetite loss was reduced in group A from 57.9% to 13.3% and in group B from 70% to 35.8%. In the placebo group, an increase in appetite loss was detected under chemo and radiation therapy from 41.8% to 70.9%.