현대 성인의 대표적 에너지 대사이상 질환인 인슐린 비의존형 당뇨(non insulin dependent diabetes mellitus, NIDDM)의 의과학적 치료방법은 지속적으로 발전되고 있지만 현재까지 완치율을 보이는 약물은 없으며, 대부분 장기복용이 불가피하여 심각하고 다양한 부작용을 동반하고 있는 실정이다. 이런 문제를 극복하기 위한 시도로서 항당뇨 효과가 있으면서 부작용을 줄일 수 있는 천연물에 대한 연구는 오랫동안 계속되어 왔다.
이 연구에서는 세포내에서 당 이용 및 분해대사촉진을 통해 항당뇨 기능을 보일 수 있는 소재를 검증하기 위하여 1) 세포내 당 분해대사와 관련된 주요 효소들의 활성을 증가시킬 수 있는 천연소재들을 발굴하여 기작을 검증하고 2) 이 소재들을 배합첨가 하였을 때 실제로 당 분해대사가 증가하는가를 검증하였다. 3) 또한 당 분해대사 증가시 생성되는 과잉의 acetyl-CoA들의 소변배출을 증가시켜 지방으로의 전환을 억제시킬 수 있는 대사조절 가능성을 조사하기 위하여 nicotinamide N-methyltransferase (NNMT) 활성을 억제할 수 있는 소재를 발굴검증하였다.
Glucose uptake는 대조군에 비해 SB가 225%, MC가 209%로 유의적으로 높았으며, 작용기작을 확인하기 위한 glucose transporter 2 (GLUT2)와 hepatocyte nuclear factors 1 alpha (HNF-1α) 단백질 발현증가를 보여 현재까지 알려진 작용기작적 변화가 있음을 확인하였다. GK 활성은 대조군에 비해 AS 150%, MC 135%로 유의적으로 높았으며, 작용기작을 확인하기 위한 phosphoinositide 3-kinase (PI3K)와 sterol regulatory element-binding protein 1C (SREBP-1C) 단백질 발현증가를 보여 현재까지 알려진 작용기작적 변화가 있음을 확인하였다. PDH 활성은 대조군에 비해 LCR이 131%로 유의적으로 높았으며, 작용기작을 확인하기 위한 pPDH 단백질 발현이 91%로 감소, PDH 단백질 발현이 127% 증가를 보여 알려진 작용기작적 변화가 있음을 확인하였다. ACL 단백질 발현은 대조군에 비해 MCA가 135%로 유의적 증가를 확인하였다. NNMT 활성은 RR 1 mg/mL 첨가시 40% 억제됨을 알 수 있었으며 처리시간에 따라 NNMT 활성이 5%에서 75%까지 억제할 수 있음도 확인하였다. 세포내 당 분해대사와 관련된 주요 효소들의 활성을 증가시킨 선발된 소재들을 이용하여 배합첨가한 실험을 통해 phospho-acetyl-CoA carboxylase (pACC) 단백질 발현감소, ACC 단백질 발현증가, malonyl-CoA 함량이 증가하는 것이 확인되었다. 또한 NNMT 활성을 억제시키는 RR을 배합한 경우 pACC 단백질 발현 증가, ACC 단백질 발현 감소, malonyl-CoA 함량이 감소하는 것이 확인되어 선발된 소재의 배합첨가가 당 분해대사 증가와 당 분해대사 증가로 인해 생성되는 과잉의 acetyl-CoA의 지방전환을 억제할 수 있음을 입증할 수 있었다.
이번 연구결과는 HepG2 세포에서 당 분해대사 관련 소재들의 첨가가 당의 분해속도를 증가시킬 수 있음을 알 수 있었으며 이로 인해 mitochondria로부터 생성이 증가되는 acetyl-CoA도 NNMT 억제소재를 이용하면 지방산으로의 전환저장을 억제할 수 있음을 확인하였다. 이 결과는 향후 동물실험 및 임상실험 등을 통해 재 확인되어야하지만 천연소재 물 추출물들이 세포내 당대사 및 과잉의 acetyl-CoA가 지방산으로 합성저장을 억제할 수 있음을 확인하여 향후 당뇨와 같은 당대사이상 질환의 개선에 중요한 소재로 활용될 가능성이 있음을 알 수 있었다.

The medical and scientific treatments for non-insulin dependent diabetes mellitus (NIDDM), the most frequently occurring metabolic disease of adults nowadays, are constantly advancing. Nonetheless, there is no drug at present that offers full recovery, and most drugs necessitate long-term administration which accompanies serious and various side effects. In an attempt to overcome such problems, studies have lasted long since focused on natural substances that exhibit antidiabetic effects but with less side effects.
In this study, to identify a natural substance that can confer antidiabetic function through facilitating the metabolic activities for use and degradation of sugar in the cells, 1) the natural sources that can increase the activities of major enzymes involved in cellular sugar metabolism were searched and their mechanisms verified; 2) whether the addition of a mixture of sources actually increases sugar catabolism was tested; and 3) a natural source that can inhibit NNMP activity was searched and tested in order to investigate the possibility of metabolic regulation that can inhibit the transformation into lipids by increasing the amount of excess acetyl-CoA produced during increased sugar catabolism via urine excretion.
The glucose uptake was significantly higher than the control in SB by 225 % and in MC by 209 %. In the experiment measuring glucose transporter 2 (GLUT2) protein expression to verify the mechanism, an increase by 143 % in SB and that by 147 % in MC were shown. An increase by 133 % in SB and that by 120 % in MC were also shown in the experiment where hepatocyte nuclear factors 1 alpha (HNF-1α) protein expression was measured, indicating that there has been a change in the currently known mechanism. The increased activities in the water extracts of the selected natural sources in this study were confirmed by the SB which increased glucose uptake; the AS which increased MC and GK; the LCR which increased MC and PDH; the MCA which increased ACL, and those were proved by verifying the mechanisms behind the changes in the activities of each enzyme. It was confirmed that the NNMT activity was inhibited by 40 % upon adding 1 mg/mL RR, and depending on the treatment time, the activity could be inhibited between 5 % and 75 %. In the experiment based on the addition of a mixture of selected sources that increased the activities of major enzymes involved in cellular sugar metabolism, treating the cells with mixtures resulted in reduction in pACC protein expression, increase in ACC protein expression and malonyl-CoA content, all confirming that the treatment enhanced sugar catabolism. In addition, when the added mixture contained RR that inhibits NNMT activity, i.e. treating the cells with mixtures led to increase in pACC protein expression, reduction in ACC protein expression and reduction in malonyl-CoA content. This proved that the addition of the mixture of selected sources can inhibit the increase of sugar catabolism itself and can prevent the excess acetyl-CoA, which is produced by an increase of sugar catabolism, from turning into lipids.
The findings of this study revealed that the addition of natural sources participating in the sugar metabolism in HepG2 cells can increase the rate of sugar catabolism, and that the consequently increased production of acetyl-CoA in mitochondria can be prevented from leading to their conversion into fatty acids for storage by using a source that can inhibit NNMT activity. Despite the need for reconfirmation of the results in future studies through animal experiments or clinical trials, it is notable that the present study has verified the effects of the water extracts of natural sources on cellular sugar metabolism and the synthesis of fatty acids from the excess acetyl-CoA for storage, thereby suggesting that the selected natural sources can be potentially valuable for improving sugar metabolic disorders such as diabetes.