Aim: 

In rats feeding high fat diet (HFD), long-term administration of 3,5-diiodo-L-thyronine (T₂) was shown to reduce body-weight gain, fat mass and hepatic lipid accumulation and to prevent liver oxidative stress associated with increased fat metabolism. In this study, the direct effects of T₂ were investigated in vitro using primary cultures of rat hepatocytes.

Methods: 

Lipid accumulation was induced by incubating isolated hepatocytes for 24 h in DMEM supplemented with 1 mM Oleic/0.5 mM Palmitic acids (O/P). Afterwards cells were exposed for different times to two doses (10^-5M and 10^-6M) of T₂ or T₃ (3,3',5-triiodo-L-thyronine), for comparison. An integrated approach consisting of optical microscopy, UV spectroscopy and 'real-time' RT-PCR allowed to assess lipid droplet accumulation, enzymatic activity and gene expression.

Results: 

The fat accumulation induced by O/P treatment in hepatocytes was decreased by short exposure to T₂ that both reduced the lipid content (Oil Red-O staining) and modified lipid droplet morphology (adipocyte differentiation-related protein-ADRP immunostaining). Moroever, O/P-cultured hepatocytes showed: i) an increase in acyl-CoA oxidase activity that was reduced by T₂ ii) an increase in catalase activity that was not modified by T₂; iii) an increased expression of the MT isoforms MT-1 and MT-2 that was reduced by T₂. Results recorded for T₂ were compared with those obtained with T₃.

Conclusion: 

Our results suggest that T₂ plays a direct role in decreasing the lipid accumulation in rat hepatocytes cultured in fat-supplemented medium.