The role of C16:0 ceramide in the development of obesity and type 2 diabetes: CerS6 inhibition as a novel therapeutic approach

Suryaprakash Raichur, Bodo Brunner, Maximilian Bielohuby, Gitte Hansen, Anja Pfenninger, Bing Wang, Jens C. Bruning, Philip Just Larsen, Norbert Tennagels

Oversupply of saturated fats induces excess ceramide accumulation that leads to impaired insulin signaling and energy homeostasis, and eventually to insulin resistance and type 2 diabetes. The ceramide species C16:0 ceramide plays a key role in the development of insulin resistance. Raichur, Brunner, and colleagues investigated if the specific inhibition of ceramide synthase 6 (CerS6) might be suitable for a drug intervention approach using CerS6 antisense oligonucleotides to knock down CerS6. They report that CerS6 mediated C16:0 ceramide reduction could be an attractive target for the treatment of insulin resistance, obesity, and type 2 diabetes.

Objective: Ectopic fat deposition is associated with increased tissue production of ceramides. Recent genetic mouse studies suggest that specific sphingolipid C16:0 ceramide produced by ceramide synthase 6 (CerS6) plays an important role in the development of insulin resistance. However, the therapeutic potential of CerS6 inhibition not been demonstrated. Therefore, we pharmacologically investigated the selective ablation of CerS6 using antisense oligonucleotides (ASO) in obese insulin resistance animal models.

Methods: We utilized ASO as therapeutic modality, CerS6 ASO molecules designed and synthesized were initially screened for in-vitro knock-down (KD) potency and cytotoxicity. ASOs with >85% inhibition of CerS6 mRNA were selected for further investigations. Most promising ASOs verified for in-vivo KD efficacy in healthy mice. CerS6 ASO (AAGATGAGCCGCACC) was found most active with hepatic reduction of CerS6 mRNA expression. Prior to longitudinal metabolic studies, we performed a dose titration target engagement analysis with CerS6 ASO in healthy mice to select the optimal dose. Next, we utilized leptin deficiency ob/ob and high fat diet (HFD) induced obese mouse models for pharmacological efficacy study.

Results: CerS6 expression were significantly elevated in the liver and brown adipose, this was correlated with significantly elevated C16:0 ceramide concentrations in plasma and liver. Treatment with CerS6 ASO selectively reduced CerS6 expression by ∼90% predominantly in the liver and this CerS6 KD resulted in a significant reduction of C16:0 ceramide by about 50% in both liver and plasma. CerS6 KD resulted in lower body weight gain and accompanied by a significant reduction in whole body fat and fed/fasted blood glucose levels (1% reduction in HbA1c). Moreover, ASO-mediated CerS6 KD significantly improved oral glucose tolerance (during oGTT) and mice displayed improved insulin sensitivity. Thus, CerS6 appear to play an important role in the development of obesity and insulin resistance.

Conclusions: Our investigations identified specific and selective therapeutic valid ASO for CerS6 ablation in in-vivo. CerS6 should specifically be targeted for the reduction of C16:0 ceramides, that results in amelioration of insulin resistance, hyperglycemia and obesity. CerS6 mediated C16:0 ceramide reduction could be a potentially attractive target for the treatment of insulin resistance, obesity and type 2 diabetes.