Endocrinology and Metabolism

Myung Jun Kim (Kim MJ)

3 Articles

The Effect of Epicatechin on the High Glucose-induced TSP-1 Expression and MMP-2 Activity in Rat Vascular Smooth Muscle Cells.: Gyeong Ryul Ryu, Jung Hoon Kang, Kyong Ja Hong, In Kyung Jeong, Hwa In Jang, Duck Joo Rhie, Shin Hee Yoon, Sang June Hahn, Myung Suk Kim, Yang Hyeok Jo, Myung Jun Kim; J Korean Endocr Soc. 2006;21(4):302-310. Published online August 1, 2006; DOI: https://doi.org/10.3803/jkes.2006.21.4.302

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BACKGROUND
The incidence of atherosclerosis is well correlated with the progression of type 2 diabetes mellitus. High plasma glucose in uncontrolled diabetic patients evokes many vascular complications such as atherosclerosis. Specifically, high glucose was reported to induce thrombospondin-1 (TSP-1), which activates matrix metalloproteinase-2 (MMP-2) and leads to the invasion of vascular smooth muscle cells (VSMCs) into the intima. Catechins with antioxidant effects are known to inhibit MMP-2 activity. Therefore, this study was aimed at revealing the effect of epicatechin, one of catechins, on high glucose-induced TSP-1 and the invasiveness of VSMCs. METHODS: VSMCs were primarily isolated from Sprague-Dawley rat aorta. The VSMCs were incubated with different doses (30, 100 and 300 micrometer) of epicatechin under high glucose concentration (30 mM). The TSP-1 protein and mRNA expressions were analyzed by performing Western blotting and Northern blot analyses, respectively. RT-PCR was performed to observe the MMP-2 mRNA expression. Gelatin zymography was performed for the measurement of MMP-2 activity. Invasion assays were performed to evaluate the invasiveness of VSMCs. RESULTS: Epicatechin inhibited the high glucose-induced TSP-1 expression and the MMP-2 activity in a dose-dependent manner. Also, epicatechin inhibited the high glucose-induced invasiveness of VSMCs across the matrix barrier in a dose-dependent fashion. CONCLUSION: Collectively, epicatechin may prevent the high glucose-induced proliferation and invasion of VSMCs by inhibiting the TSP-1 expression and the MMP-2 activity. Therefore, epicatechin appears to play a protective role in the development of atherosclerosis.

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(‐)‐Epicatechin maintains endurance training adaptation in mice after 14 days of detraining
Maik Hüttemann, Icksoo Lee, Moh H. Malek
The FASEB Journal.2012; 26(4): 1413. CrossRef

Role of Protein kinase C in Desensitization of Somatostatin-induced Calcium Signalling in NG108-15 Cells.: Kyoung Mi Kim, Jong Ho Sung, Myung Jun Kim, Duck Joo Rhie, Yang Hyeok Jo, Sang June Hahn, Myung Suk Kim, Shin Hee Yoon, Bu Seung Kim; J Korean Endocr Soc. 2005;20(4):353-361. Published online August 1, 2005; DOI: https://doi.org/10.3803/jkes.2005.20.4.353

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Abstract PDF: BACKGROUND
Activation of G-protein coupled-somatostatin receptors induces the release of calcium from inositol 1, 4, 5-trisphosphate-sensitive intracelluar stores. G-protein-coupled receptor signaling decreases with prolonged exposure to an agonist. SEBJECTS and METHODS: Fura-2-based digital Ca2+ imaging was used to study the effects of prolonged exposure to an agonist on the somatostatin-induced intracellular Ca2+ concentration([Ca2+]i) increases in NG108-15 cells, which were differentiated with CO2-independent medium and 10micrometer forskolin. RESULTS: Exposure to somatostatin(1micrometer) for 30 min completely desensitized the NG108-15 cells to a second somatostatin-induced response. The cells recovered gradually over 20 min following washout of the somatostatin. The desensitization was not due to depletion of the intracellular Ca2+ stores, and pretreatment for 30 min with bradykinin(100nM), which activates phospholipase C, or DADLE(D-Ala2-D-Leu5 enkephalin, 1microM), which activates phospholipase C, failed to cross-desensitize the somatostatin-evoked [Ca2+]i increases. Treatment with 8-cpt-cAMP(0.1mM) for 30min did not influence the somatostatin-induced[Ca2+]i increases. Phorbol 12, 13-dibutyrate(PdBu, 1microM) blocked the response completely. Down-regulation of PKC due to 24 h exposure of PdBu (1microM) inhibited the somatostatin-induced desensitization. CONCLUSION: Prolonged exposure of somatostatin to NG108-15 cells desensitized the somatostatin-induced release of Ca2+ from the intracelluar store, with protein kinase C also involved in the desensitization.

Effect fo Nitric Oxide on Control of Insulin Secretion in Rat Pancreas.: Myung Jun Kim, Jong Ho Sung, Yang Hyeok Jo; J Korean Endocr Soc. 1999;14(4):719-728. Published online January 1, 2001

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Abstract PDF: BACKGROUND
NO (nitric oxide), derived from L-arginine through the action of nitric oxide synthase (NOS), is a short-lived free radical transmitting cellular signals for vasodilation, neurotransmission, and cytotoxicity. Recently, this molecule has been reported to be involved in the various glandular secretion. Although the relationship between NO and the pancreatic endocrine secretion has been widely investigated, the role of NO on insulin secretion has not been elucidated. Therefore, the present study was designed to reveal the precise action of NO on the secretion and synthesis of insulin following administration of NAME (L-NG -nitroarginine methyl ester) or L-arginine using immunocytochemistry and in situ hybridization techniques. METHODS: NAME or L-arginine was administered into jugular vein of the male Sprague-Dawley rat (180~200 g, b,w.) exhibiting normoglycemia (80~120mg/dL). Blood glucose concentrations were measured at intervals of 30 minutes for 2 hours after drug treatment. The pancreatic tissues were taken out at 30 and 90 minutes following drugs administration for insulin immunocytochemistry and in situ hybridization. RESULTS: Both NAME and L-arginine treatments diminished blood glucose levels. The decrease of blood glucose level was more prominent in NAME-treated rats than that of L-arginine. Insulin immunoreactivity in drugs-treated rat pancreas decreased compared to that in normal control, while the expression of insulin mRNA was significantly increased. CONCLUSION: On the basis of present study, it is concluded that the transient changes of NO con-centration, regardless of increase or decrease, in Langerhans islet might act as a potent stimulant in insulin secretion and its synthesis.

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