Endocrine Abstracts

Patients with glucocorticoids (GC) excess develop central obesity, insulin resistance and hepatic steatosis in up to 20% of cases. Current dogma suggests that GCs cause insulin resistance in all tissues. However, we have previously demonstrated that GCs induce insulin sensitisation in adipose tissue in vitro, whilst causing insulin resistance in skeletal muscle. In rodent hepatocytes, GCs enhance insulin stimulated lipogenesis but studies in human hepatocytes have not been performed and the cellular mechanisms underpinning these observations have not been determined.

Cryopreserved human hepatocytes were purchased from Celsis in vitro Technologies (Baltimore, USA) and incubated with variable doses of cortisol (0–1000 nM) for 24 h in the presence and absence of insulin (5 nM). Insulin signalling gene expression levels were quantified by real-time PCR and western blotting was performed to determine total and phospho PKB/akt protein expression levels. De novo lipogenesis (DNL) was measured by 1-(14C) acetate incorporation in triglyceride.

GC receptor, IRS1/2, insulin receptor and AKT1/2 were all expressed in primary cultures. Incubation with cortisol alone or in combination with insulin did not significantly alter gene expression levels. However, whilst cortisol treatment did not alter total PKB/akt levels, insulin stimulated phosphorylation of PKB/akt at serine 473 increased following cortisol pre-treatment in a dose dependant manner (1.23-fold (100 nM), 1.68-fold (250 nM), 2.44-fold (1000 nM) vs control n=4 P<0.05). Increasing doses of cortisol increased insulin stimulated lipogenesis (43.9±12.7% (250 nM), 66.13±9.8% (1000 nM) vs control (23.61±10.7%), P<0.05).

We have demonstrated that in primary human hepatocytes GC treatment enhances insulin signalling through increased serine phosphorylation of PKB/akt and that GCs and insulin can act synergistically to promote lipogenesis. Whilst translation to the clinical setting is crucially important, this mechanism may be fundamental in explaining the interaction between GCs and insulin to drive lipogenesis. Furthermore, this may contribute to the pathogenesis of non-alcoholic fatty liver disease with GC excess.

Declaration of funding: Medical research council (senior clinical fellowship Ref.g0802765,J W T).