- The Effect of Nitric Oxide on Insulin Binding and Insulin Receptor Recycling in Bovine Aortic Endothelial Cells.
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Hyuk Sang Kwon, Oak Kee Hong, Hee Soo Kim, Jung Min Lee, Sung Rae Kim, Sung Dae Moon, Sang Ah Jang, Hyun Shik Son, Kun Ho Yoon, Moo Il Kang, Bong Yun Cha, Kwang Woo Lee, Ho Young Son, Sung Koo Kang
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Korean Diabetes J. 2003;27(3):213-227. Published online June 1, 2003
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 Abstract
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- BACKGROUND
The coexistence of insulin resistance and endothelial dysfunction is commonly observed in a variety of metabolic and cardiovascular disorders, including athero-sclerosis and type 2 diabetes mellitus. Because nitric oxide (NO), or nitric oxide synthase (NOS), has been suggested as a significant contributing factor in the development of endothelial dysfunction and insulin resistance, reactive NO or NOS were investigated to see if they contribute to the insulin internalization pathway. METHODS: The production of NO (Nitrite), the expression of eNOS (endothelial NOS), insulin binding and the insulin receptor internalization and recycling, following 48 hours of incubation with bradykinin (BK), acetylcholine (Ach), NG-monomethyl- L-arginine (L-NMMA) and N-nitro-L-arginine methylester (L-NAME) in Bovine aortic endothelial cells (BAECs), were examined. RESULTS: The results were as follows: 1. In relation to the time course, the production of eNOS was increased, but was decreased after 8 hours of incubation. The production of eNOS in the L-NMMA and L-NAME treated groups was significantly decreased compared with that of the controls (p<0.05). 2. The specific insulin bindings to the receptors of the endothelial cells were maximized within 20 mins, and then decreased. At 20 mins, the binding rate of the L-NMMA treated group was significantly decreased compared to that of the controls. At a concentration of 0.4ng/ml of unlabelled insulin, the specific insulin binding of the L-NMMA treated group was significantly decreased compared to that of the controls (p<0.05). 3. The internalization of 125I-insulin into the endothelial cells, as assessed by the acid washing dissociation method, occurred rapidly. The internalized radioactivity of 125I-insulin, at 20 mins, was significantly increased in the BK and Ach groups compared with the controls (p<0.05). 4. The recycling of the internalized insulin receptors showed no significant differences between the study groups, but the recycling was slightly delayed compared with controls in the Ach group. CONCLUSION: In conclusion, the NO generating substances, BK and Ach, and the inhibitory substance, L-NMMA, may influence the binding and internalization of insulin-insulin receptors. Our results suggest that NO might contribute to the transcytosis of insulin in BAECs
- Effect of Oxidezed LDL in Insulin Binding, Internalization and Recycling of Insulin Receptor in Cultured Bovine Aortic Endothelial Cells.
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Sung Dae Moon, Bong Yun Cha, Hye Soo Kim, Sang Ah Jang, Yu Bae An, Ki Ho Song, Je Ho Han, Soon Jib You, Kun Ho Yoon, Moo Il Kang, Kwang Woo Lee, Ho Young Son, Sung Koo Kang
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Korean Diabetes J. 1999;23(3):243-255. Published online January 1, 2001
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Abstract
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- BACKGROUND
Endothelial dysfunction is perhaps one of the earliest manifestations of atherosclerosis. This abnormality is in part due to altered membrane signal transduction in endothelial cells. Oxidized LDL that is atherogenic may induce endothelial dysfunction, and its presence has been documented in atherosclerotic vessels. Many studies have shown that oxidized LDL inhibits signaling pathways mediated by inhibitory GTP-binding proteins (Gi- protein). It is also known that G-protein is involved in insulin recycling on cultured human umbilical vein endothelial cells. Therefore, to determine the effect of oxidized LDL on endothelial cells: insulin binding, internalization, and the recycling of insulin receptors were assessed in cultured bovine aortic endothelial cells treated with native LDL, oxidized LDL, and in some cells pretreated with pertussis toxin before the incubation with oxidized LDL. METHOD: Native LDL (density 1.019 1.063 g/mL) was obtained from using the rapid single discontinuous density gradient ultracentrifugation of plasma samples from a single donor. Oxidized LDL was prepared by exposing samples of native LDL to CuSO4 (5 uM) at 37't for 24 hours. Endothelial cells at 80% confluence were treated with the indicated concentrations of native LDL, oxidized LDL, and some cells were pretreated with pertussis toxin for 6 hrs before the incubation with oxidized LDL. These cells were incubated for 24 72 hours. RESULTS: 1. Binding of (125)I-insulin(0.17nM) to endothelial cells treated with increasing concentrations of oxidized LDL shows dose-dependent decrease. There were significant differences in insulin binding between native LDL and oxidized LDL-treated cells (p<0.05). Binding of 'I-insulin (0.17 nM) to endothelial cells treated with increasing culture time of oxidized LDL shows more decreased than that of native LDL significantly (p<0.05). And oxidized LDL had additive effect, but not significant, with pertussis toxin on the specific (125)I-insulin binding to bovine aortic endothelial cells. 2. Internalization of insulin receptors reached rapidly to its maximal level around 30min at 37'C. At 60 min, oxidized-LDL treated cells was less increased in internalization of insulin receptors than that of native LDL treated cells [59.1+1.9% of total cell associated insulin (mean+SE) vs. 67.5+1.1%, p<0.05]. There were additive effects, but not significant differences, between oxidized LDL and pretreated with pertussis toxin before the incubation with oxidized LDL. 3. After 30 min of incubation with unlabeled insulin (33 nM), insulin binding in oxidized LDL treated cells was significantly higher compared to native LDL treated cells (69.0+2.5% of control values vs. 63.7+1.2%, p<0.05), suggesting that oxidized-LDL decreased internalization of insulin receptors. And during the process of recycling, there were significant differences in insulin receptor recycling between the oxidized LDL and native LDL treated cells, but oxidized LDL had an additive effect, but not significant, with pertussis toxin on insulin receptor recycling to the bovine aortic endothelial cells. CONCLUSION: 1. The findings in this study suggest that oxidized LDL may play a causative role to produce the insulin resistance by inhibiting insulin binding, internalization and recycling of insulin receptor in cultured bovine aortic endothelial cells 2. This study suggests that the effect of oxidized LDL to the bovine aortic endothelial cells in insulin binding and receptor-mediated transcytosis is caused by inhibiting pertussis toxin sensitive Gi-protein.
- The Effect of Metformin Monotherapy in Patients with NIDDM.
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Yu Bae Ahn, Sung Dae Moon, Sang Ah Jang, Jong Min Lee, Hyun Shik Son, Kun Ho Yoon, Moo Il Kang, Bong Yun Cha, Kwang Woo Lee, Ho Young Son, Sung Koo Kang
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Korean Diabetes J. 1997;21(2):185-193. Published online January 1, 2001
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- BACKGROUND
We performed this study to investigate the effect of metformin on glycemia, insulin secretion and body weight in patients with non-insulin-dependent diabetes melltus(NIDDM) who could not aehieve satisfactory glycemic control by sulfonylurea or diet therapy. METHODS: A total of 167 patients with NIDDM were included in this study. At baseline the patients underwent anthropometry and a 75g oral glucose tolerance test. Jn addition, levels of hemoglobin Alc (HbAlc), setum lipids, fasting and postprandial 2hr glucose were measured. Metformin was given in an initial dose of 500mg twice daily and increased by 500mg every month as long as the fasting blood sugar(FBS) concentration exceeded 7.8mmol/L and the side effects were tolerable. After 3 rnonths of metformin therapy we defined a responder as a patient who experienced a FBS of under 7.8 mmol/L or a HbAlc of under 7%. Patients who failed to respond to metformin monotherapy were excluded in the study. Anthrapometric changes and results of a 75 g oral glucose tolerance test were reevaluated in the responder group after 6 months of metformin treatment. RESULTS: I) The overall response rate to metformin mono-therapy was 55.6%(79/142) in the study population. 2) There were significant changes in body weight (64.4+/-8.2 vs 62.9+/-8.4 kg, p(0.01) and body mass index(25.3+/-2.3 vs 24.6+/-2.3kg/m, p<0.01) during metformin treatment. 3) There were significant decreases in the fasting, postprandial 2hr serum glucose(10.1+/-2.8 vs 7.9+1.6, 15,2+/-5.0 vs 12.2+/-3.9 mmol/L, p 0.01) and HbAlc levels(8.4+/-1.7 vs 6.5+/-0.9%, p<0.05) after 6 months of metformin treatment. 4) There were significant decreases in the levels of AUC[g](59.2+/-15.5 vs 49.4+/-9.4mmol L-1. Min-1, p =C0.01) without changes of AUC[I] and AUC[I]/ AUC[g] ratio (558.0+486.0 vs 536.4+374.4 pmol.L-1. Min-1, p=0.71, 11.7+/-13.0 vs 11.8+/-10.0, p=0.89). 5) The incidence of side effects was 25% in the study population, but most of them were mild and fade away with continuous use of metformin, CONCLUSION: Metforrnin monotherapy improved glycemic control in NlDDM patients who failed to respond to diet or sulfonylurea therapy and may be a useful hypoglycemic agent for the treatment of NIBDM.
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