- Email: [email protected]
Apocynin, an NADPH Oxidase Inhibitor, Prevents Hepatic and Peripheral Insulin Resistance Induced by Short-Term Lipid Infusion
MONTREAL 2008 ABSTRACTS
| 305
ABSTRACT #94
ORAL PRESENTATIONS
C&SS
13
Apocynin, an NADPH Oxidase Inhibitor, Prevents Hepatic and Peripheral Insulin Resistance Induced by Short-Term Lipid Infusion SANDRA PEREIRA*, EDWARD PARK, ANTO MANGARDICH, LORETTA LAM, I. GEORGE FANTUS, ADRIA GIACCA, Department of Physiology, University of Toronto, Toronto, ON Free Fatty Acid (FFA)-induced oxidative stress causes hepatic and peripheral insulin resistance. Antioxidants can alleviate this insulin resistance through reactive oxygen species (ROS)-scavenging activity. The sources of ROS in in vivo FFA-induced insulin resistance are, however, unclear. We used apocynin, an inhibitor of NADPH oxidase, to test whether NADPH oxidase-derived ROS are involved in insulin resistance in a model of short-term (7h) lipid infusion in rodents. Chronically cannulated Wistar rats (250-300g, n=4-8/group), after an overnight fast, were intravenously infused with saline or Intralipid plus heparin (IH, 20% Intralipid + 20 U/ml heparin, 5.5ȝl/min) for 7h to increase plasma FFA by approximately twofold, with or without co-infusion of apocynin (0.5ȝmol·kg-1min-1). During the last 2h, a hyperinsulinemic (5 mU·kg-1min-1) euglycemic clamp with concomitant tritiated glucose methodology was performed to assess hepatic and peripheral insulin sensitivity. As expected, IH diminished whole body and peripheral insulin sensitivity, as measured by glucose infusion rate and glucose utilization, and decreased insulin-mediated suppression of endogenous glucose production (p<0.05). Apocynin reversed the IH-induced decrease in insulin-induced suppression of endogenous glucose production (% change from basal, IH: 2.8±10.8%; IH+Apocynin: -31.8±10.9%; p<0.05 vs IH) to levels that did not differ from controls (Saline: -31.2±3.9%). Co-infusion of IH and apocynin also restored whole body insulin sensitivity (p<0.05 vs IH), as indicated by the rate of glucose infusion during the clamp, and peripheral insulin sensitivity (Glucose utilization in ȝmol·kg-1min-1, Saline: 201±13, IH: 133±8, IH+Apocynin: 173±13, p<0.05 vs IH). Thus, 1) NADPH oxidase is causally implicated in hepatic and peripheral insulin resistance induced by short-term elevation of circulating FFA and 2) NADPH oxidase inhibitors may be of therapeutic interest to restore insulin sensitivity in conditions of high FFA flux, such as obesity-associated type 2 diabetes.
14 Attenuation of Hepatic Leptin Signalling Leads
to Improved Glucose Tolerance. SCOTT D. INSULIN ACTION/RESISTANCE *
COVEY, FRANK K. HUYNH , JASNA LEVI*, SARAH L. GRAY, PETER J. VOSHOL, MADELEINE SPECK, STREAMSON C. CHUA, TIMOTHY J. KIEFFER. Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC The hormone leptin plays a crucial role in the maintenance of body weight and lipid and glucose metabolism. The dramatic impact of leptin on metabolism is highlighted by the fact that leptin administration to leptin-deficient ob/ob mice acutely lowers plasma glucose prior to any change in body mass. In addition to the well-defined effects of leptin on the hypothalamus, leptin also acts at peripheral sites including the liver. Consistent with this, we and others have demonstrated that leptin has direct effects on cultured hepatocytes. Further, leptin treatment of leptin deficient ob/ob and lipodystrophic mice reduces liver triglyceride levels and improves hepatic insulin sensitivity. To further delineate the mechanisms by which leptin regulates body composition, lipid and glucose metabolism, we generated mice in which leptin signalling is attenuated in hepatocytes. The lack of hepatic leptin signalling did not impact weight gain or body composition. Interestingly, despite a great deal of evidence that leptin promotes lipid oxidation in tissues, the absence of hepatic leptin signalling did not increase liver cholesterol or triglyceride levels in year old mice. Also, loss of leptin signalling in the liver did not affect fasting triglyceride, cholesterol, or free fatty acid levels in 6 and 12 week old mice. Further, fasting and midnight randomfed blood glucose levels were unchanged in 6, 12, and 16 week old mice lacking hepatic leptin signalling. Surprisingly, the loss of hepatic leptin signalling did lead to an improvement in glucose tolerance in male mice on chow as well as a high-fat diet. Further, hyperinsulinemic-euglycemic clamp studies revealed an improvement in hepatic insulin sensitivity in relation to littermate controls. Collectively these data reveal that leptin action on the liver can influence lipid and glucose metabolism and that leptin sensitivity in the liver may contribute to aspects of type 2 diabetes.
ABSTRACT 16
15 Comparing the correlation of measures of insulin sensitivity in youth. 1
2
MÉLANIE HENDERSON* , RÉMI RABASA-LHORET , JEAN3 4 PHILIPPE BASTARD , JEAN-PATRICE BAILLARGEON , JAMES 1 5, HANLEY , MARIE LAMBERT Dept. of Epidemiology, Biostatistics and
Occupational Health1, McGill U.; Dept. of Nutrition2, Pediatrics5, U. of Montreal; Montreal, Qc. Dept. of Biochemistry3, Tenon Hospital, Paris, France. Dept. of Medicine4, U. of Sherbrooke, Sherbrooke, Qc.
This study examined the correlation between four different methods of measuring insulin sensitivity (IS) in a group of children: the hyperinsulinemic-euglycemic (EUG) clamp, the frequently sampled intravenous glucose tolerance test (FSIVGTT), various indices derived from the OGTT, as well as fasting indices (HOMA-IR, QUICKI, and fasting insulin [INS0]). Twenty healthy children (mean (SD) age: 9(2) years) were studied: 9 boys and 11 girls. Their mean (SD) BMI z-score was 1.5 (0.8). No participant had impaired fasting glucose, glucose intolerance or diabetes. Each child underwent a 3-hour EUG clamp, an insulin modified minimal model FSIVGTT, and a 3hour OGTT. Correlations were established using Spearman’s rank correlations. The two clamp derived formulas considered were highly correlated (r=0.85). IS measured from the FSIVGTT was highly correlated with both clamp measures (r=0.69, 0.74). Of the 9 different indices derived from the OGTT considered, 4 showed high correlation with clamp results: ISI Matsuda (r=0.63, 0.69), ISI Belfiore (r=0.62, 0.64), SIisOGTT (r=0.62, 0.62) and Log sum insulin, the most closely correlated index (r=-0.67,-0.80). Fasting indices of IS had slightly lower correlations with clamp results: HOMA-IR (r=-0.55, -0.56), QUICKI (r=0.55, 0.57), and INS0 (r=-0.59, -0.63). Measurement of IS using the clamp, the FSIVGTT, and OGTT derived indices were highly correlated in this group of children. In particular, the Log sum insulin index was the most strongly correlated with clamp results, and appears to provide more valid information than either HOMA-IR or QUICKI. This suggests that OGTT derived indices provide valid, clinically feasible methods of estimating IS in youth.
#118
Postprandial Free Fatty Acids (FFA) Metabolism Early in the Natural History of Type 2 Diabetes Mellitus (DM2). FRANÇOIS N. LAUZIERE*, SEBASTIEN L. MENARD, FREDERIQUE FRISH, INSULIN ACTION/RESISTANCE PASCAL BRASSARD, DENIS CYR, REGEN DROUIN, ANDRE C. CARPENTIER. Sherbrooke, Que., Canada.. We have shown that reduced suppression of plasma FFA appearance during enhanced intravascular lipolysis induced by iv fat infusion is among the earliest metabolic dysfunction seen in offspring of two parents with DM2 (FH+). Whether increased postprandial plasma FFA appearance occurs that early in the natural history of DM2 is unknown. Plasma palmitate appearance rate (Rapalmitate) was determined using intravenous [U- 13C]-palmitate during the last 2 hours of steady oral intake of a high-fat liquid meal over 6 hours (74, 169, and 70g of fat, carbohydrates and proteins) in five FH+ subjects (1 M, 4 F, BMI=28.6±1.6kg/m2) and compared to 10 healthy subjects without family history of DM2 (FH-: 6 M, 4 F, BMI=25.4±1.6kg/m2) and 7 subjects with DM2 (5 M, 2 F, BMI=33.0±3.1kg/m2). Postprandial plasma glucose, palmitate and FFA levels in FH+ were similar to FHbut lower than DM2 (P<0.05) (glucose: 5.3±0.2, 4.9±0.2 and 7.0±0.5mmol/l; palmitate: 37±6, 28±4 and 50±8 ȝmol/l; FFA: 197±54, 174±34 and 328±50ȝmol/l). Plasma insulin levels were similar between all groups. Rapalmitate in FH+ was also similar to FH- but lower than DM2 (P=0.07) (51±6, 55±7 and 80±1ȝmol/min). Plasma triglyceride levels were significantly elevated in FH+ compared to FH- (P<0.05) almost to a similar degree than in DM2 (1.91±0.28, 1.12±0.16 and 2.35±0.47mmol/l). We repeated these experiments using intravenous insulin and glucose infusion to keep postprandial glucose levels to ~6mmol/l in all participants but found similar results. These preliminary data show that postprandial increase in plasma FFA appearance seen in DM2 is not yet fully installed in FH+. The latter group displays postprandial hypertriglyceridemia that could contribute to lipotoxicity known to occur in these subjects. Acute normalization of plasma glucose does not reverse postprandial FFA abnormalities in DM2.
ABSTRACT #170
C&SS
C&SS METABOLISM
| 305
ABSTRACT #94
ORAL PRESENTATIONS
C&SS
13
Apocynin, an NADPH Oxidase Inhibitor, Prevents Hepatic and Peripheral Insulin Resistance Induced by Short-Term Lipid Infusion SANDRA PEREIRA*, EDWARD PARK, ANTO MANGARDICH, LORETTA LAM, I. GEORGE FANTUS, ADRIA GIACCA, Department of Physiology, University of Toronto, Toronto, ON Free Fatty Acid (FFA)-induced oxidative stress causes hepatic and peripheral insulin resistance. Antioxidants can alleviate this insulin resistance through reactive oxygen species (ROS)-scavenging activity. The sources of ROS in in vivo FFA-induced insulin resistance are, however, unclear. We used apocynin, an inhibitor of NADPH oxidase, to test whether NADPH oxidase-derived ROS are involved in insulin resistance in a model of short-term (7h) lipid infusion in rodents. Chronically cannulated Wistar rats (250-300g, n=4-8/group), after an overnight fast, were intravenously infused with saline or Intralipid plus heparin (IH, 20% Intralipid + 20 U/ml heparin, 5.5ȝl/min) for 7h to increase plasma FFA by approximately twofold, with or without co-infusion of apocynin (0.5ȝmol·kg-1min-1). During the last 2h, a hyperinsulinemic (5 mU·kg-1min-1) euglycemic clamp with concomitant tritiated glucose methodology was performed to assess hepatic and peripheral insulin sensitivity. As expected, IH diminished whole body and peripheral insulin sensitivity, as measured by glucose infusion rate and glucose utilization, and decreased insulin-mediated suppression of endogenous glucose production (p<0.05). Apocynin reversed the IH-induced decrease in insulin-induced suppression of endogenous glucose production (% change from basal, IH: 2.8±10.8%; IH+Apocynin: -31.8±10.9%; p<0.05 vs IH) to levels that did not differ from controls (Saline: -31.2±3.9%). Co-infusion of IH and apocynin also restored whole body insulin sensitivity (p<0.05 vs IH), as indicated by the rate of glucose infusion during the clamp, and peripheral insulin sensitivity (Glucose utilization in ȝmol·kg-1min-1, Saline: 201±13, IH: 133±8, IH+Apocynin: 173±13, p<0.05 vs IH). Thus, 1) NADPH oxidase is causally implicated in hepatic and peripheral insulin resistance induced by short-term elevation of circulating FFA and 2) NADPH oxidase inhibitors may be of therapeutic interest to restore insulin sensitivity in conditions of high FFA flux, such as obesity-associated type 2 diabetes.
14 Attenuation of Hepatic Leptin Signalling Leads
to Improved Glucose Tolerance. SCOTT D. INSULIN ACTION/RESISTANCE *
COVEY, FRANK K. HUYNH , JASNA LEVI*, SARAH L. GRAY, PETER J. VOSHOL, MADELEINE SPECK, STREAMSON C. CHUA, TIMOTHY J. KIEFFER. Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC The hormone leptin plays a crucial role in the maintenance of body weight and lipid and glucose metabolism. The dramatic impact of leptin on metabolism is highlighted by the fact that leptin administration to leptin-deficient ob/ob mice acutely lowers plasma glucose prior to any change in body mass. In addition to the well-defined effects of leptin on the hypothalamus, leptin also acts at peripheral sites including the liver. Consistent with this, we and others have demonstrated that leptin has direct effects on cultured hepatocytes. Further, leptin treatment of leptin deficient ob/ob and lipodystrophic mice reduces liver triglyceride levels and improves hepatic insulin sensitivity. To further delineate the mechanisms by which leptin regulates body composition, lipid and glucose metabolism, we generated mice in which leptin signalling is attenuated in hepatocytes. The lack of hepatic leptin signalling did not impact weight gain or body composition. Interestingly, despite a great deal of evidence that leptin promotes lipid oxidation in tissues, the absence of hepatic leptin signalling did not increase liver cholesterol or triglyceride levels in year old mice. Also, loss of leptin signalling in the liver did not affect fasting triglyceride, cholesterol, or free fatty acid levels in 6 and 12 week old mice. Further, fasting and midnight randomfed blood glucose levels were unchanged in 6, 12, and 16 week old mice lacking hepatic leptin signalling. Surprisingly, the loss of hepatic leptin signalling did lead to an improvement in glucose tolerance in male mice on chow as well as a high-fat diet. Further, hyperinsulinemic-euglycemic clamp studies revealed an improvement in hepatic insulin sensitivity in relation to littermate controls. Collectively these data reveal that leptin action on the liver can influence lipid and glucose metabolism and that leptin sensitivity in the liver may contribute to aspects of type 2 diabetes.
ABSTRACT 16
15 Comparing the correlation of measures of insulin sensitivity in youth. 1
2
MÉLANIE HENDERSON* , RÉMI RABASA-LHORET , JEAN3 4 PHILIPPE BASTARD , JEAN-PATRICE BAILLARGEON , JAMES 1 5, HANLEY , MARIE LAMBERT Dept. of Epidemiology, Biostatistics and
Occupational Health1, McGill U.; Dept. of Nutrition2, Pediatrics5, U. of Montreal; Montreal, Qc. Dept. of Biochemistry3, Tenon Hospital, Paris, France. Dept. of Medicine4, U. of Sherbrooke, Sherbrooke, Qc.
This study examined the correlation between four different methods of measuring insulin sensitivity (IS) in a group of children: the hyperinsulinemic-euglycemic (EUG) clamp, the frequently sampled intravenous glucose tolerance test (FSIVGTT), various indices derived from the OGTT, as well as fasting indices (HOMA-IR, QUICKI, and fasting insulin [INS0]). Twenty healthy children (mean (SD) age: 9(2) years) were studied: 9 boys and 11 girls. Their mean (SD) BMI z-score was 1.5 (0.8). No participant had impaired fasting glucose, glucose intolerance or diabetes. Each child underwent a 3-hour EUG clamp, an insulin modified minimal model FSIVGTT, and a 3hour OGTT. Correlations were established using Spearman’s rank correlations. The two clamp derived formulas considered were highly correlated (r=0.85). IS measured from the FSIVGTT was highly correlated with both clamp measures (r=0.69, 0.74). Of the 9 different indices derived from the OGTT considered, 4 showed high correlation with clamp results: ISI Matsuda (r=0.63, 0.69), ISI Belfiore (r=0.62, 0.64), SIisOGTT (r=0.62, 0.62) and Log sum insulin, the most closely correlated index (r=-0.67,-0.80). Fasting indices of IS had slightly lower correlations with clamp results: HOMA-IR (r=-0.55, -0.56), QUICKI (r=0.55, 0.57), and INS0 (r=-0.59, -0.63). Measurement of IS using the clamp, the FSIVGTT, and OGTT derived indices were highly correlated in this group of children. In particular, the Log sum insulin index was the most strongly correlated with clamp results, and appears to provide more valid information than either HOMA-IR or QUICKI. This suggests that OGTT derived indices provide valid, clinically feasible methods of estimating IS in youth.
#118
Postprandial Free Fatty Acids (FFA) Metabolism Early in the Natural History of Type 2 Diabetes Mellitus (DM2). FRANÇOIS N. LAUZIERE*, SEBASTIEN L. MENARD, FREDERIQUE FRISH, INSULIN ACTION/RESISTANCE PASCAL BRASSARD, DENIS CYR, REGEN DROUIN, ANDRE C. CARPENTIER. Sherbrooke, Que., Canada.. We have shown that reduced suppression of plasma FFA appearance during enhanced intravascular lipolysis induced by iv fat infusion is among the earliest metabolic dysfunction seen in offspring of two parents with DM2 (FH+). Whether increased postprandial plasma FFA appearance occurs that early in the natural history of DM2 is unknown. Plasma palmitate appearance rate (Rapalmitate) was determined using intravenous [U- 13C]-palmitate during the last 2 hours of steady oral intake of a high-fat liquid meal over 6 hours (74, 169, and 70g of fat, carbohydrates and proteins) in five FH+ subjects (1 M, 4 F, BMI=28.6±1.6kg/m2) and compared to 10 healthy subjects without family history of DM2 (FH-: 6 M, 4 F, BMI=25.4±1.6kg/m2) and 7 subjects with DM2 (5 M, 2 F, BMI=33.0±3.1kg/m2). Postprandial plasma glucose, palmitate and FFA levels in FH+ were similar to FHbut lower than DM2 (P<0.05) (glucose: 5.3±0.2, 4.9±0.2 and 7.0±0.5mmol/l; palmitate: 37±6, 28±4 and 50±8 ȝmol/l; FFA: 197±54, 174±34 and 328±50ȝmol/l). Plasma insulin levels were similar between all groups. Rapalmitate in FH+ was also similar to FH- but lower than DM2 (P=0.07) (51±6, 55±7 and 80±1ȝmol/min). Plasma triglyceride levels were significantly elevated in FH+ compared to FH- (P<0.05) almost to a similar degree than in DM2 (1.91±0.28, 1.12±0.16 and 2.35±0.47mmol/l). We repeated these experiments using intravenous insulin and glucose infusion to keep postprandial glucose levels to ~6mmol/l in all participants but found similar results. These preliminary data show that postprandial increase in plasma FFA appearance seen in DM2 is not yet fully installed in FH+. The latter group displays postprandial hypertriglyceridemia that could contribute to lipotoxicity known to occur in these subjects. Acute normalization of plasma glucose does not reverse postprandial FFA abnormalities in DM2.
ABSTRACT #170
C&SS
C&SS METABOLISM