Anti-diabetic effects of DMC-derivatives by activation of AMP-activated protein kinase and peroxisome proliferator activated receptor

Abstract

Abstract

Type 2 diabetes is caused by insulin resistance and beta-cell dysfunction, leading to hyperglycemia. It is a complex metabolic disorder with various etiological pathways, impacting ectopic lipid depositions. Insulin resistance is very closely linked with T2D because it is predictor and therapeutic target of T2D. To treat and prevent T2D, insulin resistance and insulin signaling are needed to be improved. There are two representative insulin sensitizers in the market, metformin and TZDs. Metformin works as activator of AMPK which is a master regulator of energy metabolism. It is activated by increasing phosphorylation of AMPKα at Thr-172. Activation of AMPK increases fatty acid oxidation in skeletal muscle and regulates the hepatic glucogenesis in liver. TZDs work as activator of peroxisome proliferator activated receptor, PPARγ which is a nuclear receptor and is predominantly expressed in adipose tissues. Expressions of lipid transport related proteins are increased by its activation. It reduces lipid contents in circulation and improves insulin sensitivity by reducing lipotoxicity. However, TZDs have several side effects such as weight gain and fluid retention. In previous study, my lab studied about antidiabetic effects of DMC which is isolated from cleistocalyx operculatus plant by screening 14 putative PPARγ agonists. DMC worked as dual agonist of PPARγ and AMPK, increasing PPARγ transcriptional activity and AMPK activation. It also suppressed differentiation of adipocytes, promoted glucose uptake and increased the fatty acid oxidation in myotubes by AMPK activation in cell cultured system. It also improved insulin sensitivity in high fed diet (HFD) induced obese mice. I received the B series of DMC derivatives form department of chemical engineering in Choong-Ang University. They were designed and synthesized with different functional groups according to the degree of electronic effect, hydroxylation, hydrophobicity and hydrophilicity. Purpose of my study is to investigate the antidiabetic effects of the B series of DMC derivatives in vitro and in vivo, having more efficacy than DMC. In in vitro experiment, most of DMC derivatives increased FAO ratio and phosphorylation of AMPK as much as DMC and AICAR. They also inhibited adipogenesis as much as DMC but they showed lower PPARγ transcriptional activities than DMC. For in vivo study, B1 and B7 selected as increasing FAO ratio as much as DMC and AICAR. In in vivo experiment, DMC derivatives showed similar effects on blood glucose tolerance with DMC. They tended to increase FAO in GM and decrease triglyceride (TG) levels in liver. In conclusion, the antidiabetic effects of B series of DMC derivatives were mainly mediated by AMPK activation.

Keywords: DMC, insulin resistance, type2 diabetes, metformin, TZDs, PPARγ, AMPK, fatty acid oxidation

국문초록

대사성 질환인 제 2형 당뇨병은 인슐린 저항성과 밀접한 연관관계를 갖고 있다. 대표적인 인슐린 증감제로는 Metformin 과 TZDs가 존재한다. Metformin은 대사성 질환의 주요 표적인 AMP-dependent protein kinase (AMPK) 인산화를 촉진시키며 대사조절과 밀접하게 연관되어 있는 표적장기에 관여하며 인슐린 저항성을 개선시킨다. TZDs는 PPARγ의 활성을 증가시켜 지방세포를 분화시키고 피하지방에 유리지방산을 축적시킴으로써 인해 혈중 유리지방산을 낮추어 인슐린 저항성을 개선한다. 이전 실험에서 Cleistocalyx operculatus 라는 작물에서 추출된 단일화합물 DMC (2,4-dihydroxy-6-methoxy-3,5-dimethylchalcone) 의 효능을 기반으로 본 연구가 시작되었다. DMC 물질은 PPARγ와 AMPK의 이중작용제로서 인슐린 저항성을 개선시키는 것을 최진우 박사에 의하여 입증되었다. DMC 보다 더 효능이 좋은 DMC 유사 물질을 찾기 위해 본 연구가 시작되었다. DMC유사물질은 중앙대학교 화학과에서 전자효과에 따른 작용기의 치환을 통해 만들어졌다. B 시리즈 DMC 유사물질은 근육세포내에서 지방산 산화와 AMPK의 인산화를 DMC 만큼 촉진 시켰으며 지방세포 분화를 억제하는 작용도 DMC와 유사한 결과를 보였다. 다음으로 14주간 고지방사료를 먹인 동물모델에서 B 시리즈의 DMC유사물질을 4주간 동물모델에 경구 투여한 후 인슐린 저항성의 미치는 영향을 관찰하였다. 비록 B 시리즈 DMC 유사물질이 DMC 보다 더 크게 인슐린 저항성을 개선시키지 못하였지만 간에서 중성지방 수치를 감소시키는 경향을 보였고 골격근에서 지방산 산화를 증가시키는 경향을 보였다. 결론적으로 B 시리즈의 항 당뇨적인 효능은 주로 AMPK 활성에 의해 매개되었다. DMC 유사물질을 연구함으로써 비만, 체액 저류 등의 부작용 없이 인슐린 저항성을 개선시키는 새로운 치료제 개발에 큰 도움이 될 것으로 기대된다.

주요어 : DMC, 인슐린 저항성, 제 2 형 당뇨병, metformin, TZDs, PPARγ, AMPK, 지방산 산화