Aim: 

To study whether mitochondrial oxidation of FFA and/or CPT1 activity and expression are affected during severe steatosis.

Methods: 

Rats were fed a control or a MCD diet and sacrificed after 4 weeks. Phospholipids, total cholesterol and triacylglycerols (TAG) were determined in serum and liver tissue. Measurement of acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), diacylglycerol acyltransferase (DGAT), 3-hydroxyacyl-CoA dehydrogenase (3-HAD) activities were conducted spectrophotometrically in rat liver. CPT1 enzymatic activity, together with its sensitivity for malonyl-CoA, was also determined. CPT1 expression was evaluated by Real Time RT-PCR and Western Blot.

Results: 

Cholesterol phospholipids and TAG were reduced in serum, but increased in liver of MCD-fed rats, with respect to controls. ACC and FAS activities were lower in MCD-fed rats, as well as 3-HAD activity, while DGAT activity was similar in both groups. CPT1 activity was lower of 35% in MCD-fed rats, together with a reduction of malonyl-CoA inhibiting effect. Moreover, CPT1 mRNA was increased of about 70% in MCD-fed rats when compared to controls, even though the protein expression was reduced.

Discussion: 

Increased lipids accumulation (mainly as TAG) observed in severe steatosis induced by MCD diet is not dependent on an increase in FFA synthesis, but on the impairment of mitochondria b-oxidation. This could be the result of a reduction in the transport of FFA into mitochondria, as demonstrated by a reduced CPT1 activity. An impairment of CPT1 may occur, as suggested by an increase in the mRNA matched with a decrease of the protein level.