Se tolerance. In order to elucidate the 548-04-9 underlying mechanisms causative for the development of myocardial steatosis we have recently performed a standardized hyperglycemic clamp test in healthy subjects. We could demonstrate that endogenous hyperinsulinemia in response to hyperglycemia induces an acute increase in MYCL content. [14]. In the present study, we observed a strong correlation between MedChemExpress 307538-42-7 glucose concentrations at day 1 and MYCL at day 10 of IT. Insulin forcefully stimulates myocardial glucose uptake via increased GLUT 4 translocation to the cellular membrane fostering substrate competition between fatty acids and glucose [36,37]. The resulting switch in mitochon-drial substrate utilization from fatty acid- to glucose utilization is mediated mainly by malonyl-CoA. Malonyl-CoA is generated by acetyl-CoA carboxylase (ACC 2) and inhibits CPT I (carnitine palmitoyltransferase) [36], which controls the rate limiting step of mitochondrial FFA-uptake and in turn xidation. Insulin also exerts a direct stimulatory effect on ACC, thereby potently suppressing mitochondrial lipid oxidation in the presence of hyperglycemia [38]. In addition increased insulin-mediated uptake of circulating FFA and stimulation of intracellular triglyceride synthesis likely contributed to myocardial lipid accumulation [26]. Our results confirm myocardial steatosis in the expected range in patients with T2DM (OT-group) [21]. However, in subjects with secondary failure of oral glucose lowering therapy MYCL content was in the normal range at baseline. Relative insulin deficiency due to progressive b-cell dysfunction [39] in the ITgroup likely contributed to unexpectedly normal (low) MYCL stores in patients with longstanding T2DM.Figure 2. Intramyocardial lipid- (MYCL, given in of water signal [w. s.]) (a) and intrahepatic lipid concentration (IHCL, given in of water signal [w. s.]) at baseline, day 10 of IT and during follow up (181?9 days) (b). Gray bars indicate IT-group 1676428 and empty bar the OTgroup; error bars delineate SEM. doi:10.1371/journal.pone.0050077.gInsulin Alters Myocardial Lipids and MorphologyFigure 3. Association between mean glucose concentrations at day 1 and MYCL 24272870 content at day 10 of IT. doi:10.1371/journal.pone.0050077.gAt follow up improvement of metabolic control might have returned MYCL to baseline. These results are in accordance with previous data showing a parallel decrease in MYCL and HbA1c during treatment with pioglitazone and insulin in patients with T2DM [15]. Insulin therapy did not induce an acute rise in hepatic lipid content in the present study, suggesting that myocardial lipids are more sensitive to insulin compared to hepatic lipids. Since the muscle-type CPT1B is 10?00 fold more sensitive to malonyl-CoA compared to liver-type CPT1A [40] the heart might be especially susceptible to substrate competition between fatty acids and glucose. Therefore, insulin might preferentially induce myocardial steatosis in the presence of hyperglycemia. In our study myocardial mass and thickness acutely increased in response to IT leading to morphological changes of the left ventricle. In accordance, investigations in animal models have shown that exogenous insulin supply induces myocardial hypertrophy and interstitial fibrosis by activation of key mitogenic signaling pathways including angiotensin, MAPK-ERK1/2 and S6K1 [41?3]. However, in the present study metabolic and structural changes of the myocardium due to IT were not associated with a.Se tolerance. In order to elucidate the underlying mechanisms causative for the development of myocardial steatosis we have recently performed a standardized hyperglycemic clamp test in healthy subjects. We could demonstrate that endogenous hyperinsulinemia in response to hyperglycemia induces an acute increase in MYCL content. [14]. In the present study, we observed a strong correlation between glucose concentrations at day 1 and MYCL at day 10 of IT. Insulin forcefully stimulates myocardial glucose uptake via increased GLUT 4 translocation to the cellular membrane fostering substrate competition between fatty acids and glucose [36,37]. The resulting switch in mitochon-drial substrate utilization from fatty acid- to glucose utilization is mediated mainly by malonyl-CoA. Malonyl-CoA is generated by acetyl-CoA carboxylase (ACC 2) and inhibits CPT I (carnitine palmitoyltransferase) [36], which controls the rate limiting step of mitochondrial FFA-uptake and in turn xidation. Insulin also exerts a direct stimulatory effect on ACC, thereby potently suppressing mitochondrial lipid oxidation in the presence of hyperglycemia [38]. In addition increased insulin-mediated uptake of circulating FFA and stimulation of intracellular triglyceride synthesis likely contributed to myocardial lipid accumulation [26]. Our results confirm myocardial steatosis in the expected range in patients with T2DM (OT-group) [21]. However, in subjects with secondary failure of oral glucose lowering therapy MYCL content was in the normal range at baseline. Relative insulin deficiency due to progressive b-cell dysfunction [39] in the ITgroup likely contributed to unexpectedly normal (low) MYCL stores in patients with longstanding T2DM.Figure 2. Intramyocardial lipid- (MYCL, given in of water signal [w. s.]) (a) and intrahepatic lipid concentration (IHCL, given in of water signal [w. s.]) at baseline, day 10 of IT and during follow up (181?9 days) (b). Gray bars indicate IT-group 1676428 and empty bar the OTgroup; error bars delineate SEM. doi:10.1371/journal.pone.0050077.gInsulin Alters Myocardial Lipids and MorphologyFigure 3. Association between mean glucose concentrations at day 1 and MYCL 24272870 content at day 10 of IT. doi:10.1371/journal.pone.0050077.gAt follow up improvement of metabolic control might have returned MYCL to baseline. These results are in accordance with previous data showing a parallel decrease in MYCL and HbA1c during treatment with pioglitazone and insulin in patients with T2DM [15]. Insulin therapy did not induce an acute rise in hepatic lipid content in the present study, suggesting that myocardial lipids are more sensitive to insulin compared to hepatic lipids. Since the muscle-type CPT1B is 10?00 fold more sensitive to malonyl-CoA compared to liver-type CPT1A [40] the heart might be especially susceptible to substrate competition between fatty acids and glucose. Therefore, insulin might preferentially induce myocardial steatosis in the presence of hyperglycemia. In our study myocardial mass and thickness acutely increased in response to IT leading to morphological changes of the left ventricle. In accordance, investigations in animal models have shown that exogenous insulin supply induces myocardial hypertrophy and interstitial fibrosis by activation of key mitogenic signaling pathways including angiotensin, MAPK-ERK1/2 and S6K1 [41?3]. However, in the present study metabolic and structural changes of the myocardium due to IT were not associated with a.
