PURPOSE OF REVIEW: The article is principally intended to describe the recent 
evolutions in the field of research concerned with the metabolic actions of 
thyroid hormones and those of some of their metabolites or derivatives. 
Mitochondria, as a result of their functions, represent the principal objective 
of scientists investigating the mechanisms underlying the effects of thyroid 
hormones or their metabolites/derivatives.
RECENT FINDINGS: Indeed, some important recent findings concern these 
organelles, and in particular mitochondrial uncoupling and its modulation by 
effectors. Traditionally, thyroxine (T4) and tri-iodo-L-thyronine (T3) were the 
only thyroid hormones considered to have metabolic effects, and they alone were 
considered for potential as agents that might counteract some important 
abnormalities such as dyslipidaemias and obesity. Several observations, however, 
led to a reconsideration of this idea. In recent years, studies dealing with the 
biological activities of some natural metabolites or structural analogues of 
thyroid hormones have revealed abilities to ameliorate some major worldwide 
medical problems, such as artherosclerosis, obesity and cardiovascular diseases. 
Among natural metabolites, 3,5-diiodothyronine (T2) has been shown to powerfully 
reduce adiposity and dyslipidaemia and to reverse hepatic steatosis without 
unfavourable side-effects usually observed when T3 or T4 is used. Examples of 
synthetic analogues are GC-1 (or sobetirome) and KB2115 (or eprotirome) which 
show ipolipidaemic and antiaterogenic capacities. Clinical trials are in 
progress for these last agents.
SUMMARY: In view of the above-mentioned actions, some of these compounds are now 
undergoing clinical trials and may have important implications for clinical 
practice or researches in the field of both endocrinology and metabolic-related 
abnormalities such as diabetes and dyslipidaemias.