Erythrocyte-derived measures of membrane lipid composition in healthy men: associations with arachidonic acid at low to moderate but not high insulin sensitivity

The lipid composition of erythrocyte membranes was explored as a surrogate for that of skeletal muscle in investigations into the influence of membrane fatty acid composition on insulin sensitivity. In a preliminary study (study 1), erythrocyte and monocyte/platelet membrane fatty acid percentages were compared with those of muscle membrane in 10 otherwise healthy men undergoing orthopedic surgery. In a further study (study 2), relationships between erythrocyte membrane fatty acid concentrations and insulin sensitivity, S(I), measured using the intravenous glucose tolerance test (IVGTT), were evaluated in 30 asymptomatic men. In study 1, significant positive correlations were found between muscle and erythrocyte membrane fatty acid percentages for 16:0 saturated fatty acid (r = 0.92, P <.001), and for the 18:2n-6, 20:4n-6, 20:5n-3, and 22:5n-3 polyunsaturated fatty acids (PUFAs) (r = 0.67 to 0.83, P <.05 to.01). There were fewer and weaker associations between muscle and monocyte/platelet membrane fatty acid compositions. In study 2, highly insulin-sensitive individuals (n = 8) had significantly lower erythrocyte membrane fatty acid concentrations than those with low/normal S(I). Among those with low/normal S(I) (n = 22), S(I) correlated positively with erythrocyte membrane arachidonic acid concentration (r = 0.57, P <.01) and with total PUFAs (r = 0.46, P <.05). Indices of delta 6 and delta 5 desaturase activities were significantly higher and lower, respectively, in high compared with low/normal S(I) individuals. For a range of fatty acids, erythrocyte membrane fatty acid composition shows close associations with that of muscle membranes. Measurements in erythrocyte membranes support a role for membrane arachidonic acid content in the modulation of insulin sensitivity, specifically at low/normal insulin sensitivities.     

Erythrocyte membrane phospholipid composition is related to hyperinsulinemia in obese nondiabetic women: effects of weight loss

The complex mechanisms by which obesity predisposes to insulin resistance are not clearly understood. According to a cell membrane hypothesis of insulin resistance, the defects in insulin action could be related to changes in membrane properties. The purpose of this work was to examine the relationship between 2 markers of insulin resistance (fasting plasma insulin [FPI] and homeostasis model assessment [HOMA IR]) and erythrocyte membrane lipid composition. In the first cross-sectional study, 24 premenopausal nondiabetic overweight women (body mass index [BMI], 32.5 +/- 0.9 kg/m(2); age, 35.7 +/- 2.2 years) were compared to 21 lean healthy women (BMI, 21 +/- 0.4 kg/m(2); age, 35.4 +/- 2.2 years). The second study examined whether a 3-month diet-induced weight loss, which usually improves insulin resistance, could also affect the membrane phospholipid (PL) composition and fluidity in the overweight group. Overweight women had significantly higher FPI levels (P <.0001), HOMA IR (P <.0001), membrane sphingomyelin (SM) (P <.05), and cholesterol (P <.05) contents than lean women. Baseline FPI and HOMA IR were positively correlated with membrane SM (P <.005), phosphatidylethanolamine (PE) (P <.005), and phosphatidylcholine (PC) (P <.05) contents, and negatively with phosphatidylinositol (PI) (P <.05) contents in the whole population. Multivariate regression analyses showed that 2 membrane parameters, PE and SM, were among the independent predictors of FPI or HOMA IR in the whole population, but also in the lean and the obese groups separately. Intervention induced a significant reduction in body weight (-5.7% +/- 0.7%), fat mass (-11.3% +/- 1.4%), and FPI (-10.2% +/- 5.4%). An improvement in membrane lipid composition was only observed in the insulin resistant subgroup (FPI > 9.55 mU/L). The reduction in FPI or HOMA IR was directly associated with reduction in SM and PE contents, a finding independent of the reduction in fat mass. A stepwise multiple regression analysis indicated that the changes in SM accounted for 26.6% of the variance in the changes in FPI as an independent predictor, with the changes in fat mass and PE as other determinants (27.8% and 20%, respectively, adjusted r(2) =.704, P <.0001). These results suggest that the abnormalities in the membrane PL composition could be included in the unfavorable lipid constellation of obesity which correlated with impaired insulin sensitivity.     

Is the erythrocyte membrane fatty acid composition a valid index of skeletal muscle membrane fatty acid composition?

Recent studies suggest that insulin sensitivity is related to the fatty acid composition of phospholipids in skeletal muscle (SM) membranes. Since it is difficult to obtain muscle biopsies, it may be useful to have information on the fatty acid composition using more accessible cells such as erythrocytes. This would be possible only if the composition of erythrocyte and muscle membranes are very similar. Since no comparative data are available, we evaluated the phospholipid fatty acid composition of erythrocyte and SM membranes in 16 individuals, 10 nondiabetics (male to female ratio, 4:6; age, 50 +/- 11 years; body mass index, 27 +/- 5 kg/m2; mean +/- SD) and 6 type 2 diabetic patients (male to female ratio, 2:4; age, 64 +/- 5 years; body mass index, 27 +/- 4 kg/m2). All patients underwent abdominal surgery, during which a biopsy of the abdominal rectus muscle (50 to 100 mg) was obtained. Erythrocyte and SM phospholipid fatty acids were extracted and then methylated; the methyl fatty acids were separated and quantified by gas chromatography. Compared with erythrocyte membranes, muscle membranes showed a significantly higher proportion of omega-6 polyunsaturated fatty acid ([PUFA] 43.0% +/- 3.1% v29.7% +/- 1.6%, P < .001) and lower saturated fatty acid ([SFA] 41.1% +/- 1.5% v 43.4% +/- 1.2%, P < .001), monounsaturated fatty acid ([MUFA] 11.5% +/- 1.7% v 20.0% +/- 1.9%, P < .001), and omega-3 PUFA (3.8% +/- 0.6% v 7.4% +/- 1.0%, P < .001). The greatest increase involved linoleic acid (26.9% +/- 2.8% v 10.3% +/- 1.6%, P < .001), whereas lignoceric acid (0.8% +/- 0.2% v 5.0% +/- 0.6%, P < .001) and oleic acid (10.4% +/- 1.6% v 13.5% +/- 1.3%, P < .001) were significantly lower. These results show that erythrocyte and muscle membrane phospholipid fatty acids are significantly different. Therefore, data on SM membranes cannot be extrapolated on the basis of measures of erythrocyte phospholipid fatty acid composition.     

Carbohydrate metabolism during exercise in females: effect of reduced fat availability

This study examined the effect of reduced plasma free fatty acid (FFA) availability on carbohydrate metabolism during exercise. Six untrained women cycled for 60 minutes at approximately 58% of maximum oxygen uptake after ingestion of a placebo (CON) or nicotinic acid (NA), 30 minutes before exercise (7.4 +/- 0.5 mg.kg(-1) body weight), and at 0 minutes (3.7 +/- 0.3 mg.kg(-1)) and 30 minutes (3.7 +/- 0.3 mg.kg(-1)) of exercise. Glucose kinetics were measured using a primed, continuous infusion of [6,6-(2)H] glucose. Plasma FFA (CON, 0.86 +/- 0.12; NA, 0.21 +/- 0.11 mmol.L(-1) at 60 minutes, P <.05) and glycerol (CON, 0.34 +/- 0.05; NA, 0.10 +/- 0.04 mmol.L(-1) at 60 minutes, P <.05) were suppressed throughout exercise. Mean respiratory exchange ratio (RER) during exercise was higher (P <.05) in NA (0.89 +/- 0.02) than CON (0.83 +/- 0.02). Plasma glucose and glucose production were similar between trials. Total glucose uptake during exercise was greater (P <.05) in NA (1,876 +/- 161 micromol.kg(-1)) than in CON (1,525 +/- 107 micromol.kg(-1)). Total fat oxidation was reduced (P <.05) by approximately 32% during exercise in NA. Total carbohydrate oxidized was approximately 42% greater (P <.05) in NA (412 +/- 40 mmol) than CON (290 +/- 37 mmol), of which, approximately 16% (20 +/- 10 mmol) could be attributed to glucose. Plasma insulin and glucagon were similar between trials. Catecholamines were higher (P <.05) during exercise in NA. In summary, during prolonged moderate exercise in untrained women, reduced FFA availability results in a compensatory increase in carbohydrate oxidation, which appears to be due predominantly to an increase in glycogen utilization, although there was a small, but significant, increase in whole body glucose uptake.     

Insulin-mediated changes in leg blood flow are coupled to capillary density in skeletal muscle in healthy 70-year-old men

The aim of this study was to investigate to what degree the capillarization in the skeletal muscle explains the leg blood flow (LBF) changes during hyperinsulinaemia. Fifteen normotensive men from a population-based cohort of 70-year-old men in Uppsala, Sweden, were investigated. Their metabolic status (oral glucose tolerance test and euglycemic, hyperinsulinaemic clamp test results), serum lipid profile, muscle fiber distribution (myosin adenosine triphosphatase staining), and capillary supply (amylase-periodic acid-Schiff method) was evaluated. Doppler ultrasound was used before and after the clamp test to detect insulin-induced changes in LBF. Physiologic hyperinsulinemia (serum insulin, 107 mU/L) caused a moderate increase in LBF (15% +/- 11%; P =.07). Change in LBF was closely related to capillary density (r =.66; P <.01) independent of obesity, smoking and level of physical activity. An association was observed between LBF and serum free fatty acid (FFA) concentrations (r = -.57; P <.05). In multiple regression analysis, capillary density and serum FFA level together explained 71% of the variation in insulin-mediated LBF changes. Capillary rarefaction and elevated serum FFA values were associated with a vasoconstrictive effect of insulin. In conclusion, capillarization in skeletal muscle and serum FFA concentration seem to be determinants of endothelial function.     

Nicotinic acid-induced insulin resistance is related to increased circulating fatty acids and fat oxidation but not muscle lipid content

Insulin resistance is associated with increased circulating lipids and skeletal muscle lipid content. Chronic nicotinic acid (NA) treatment reduces insulin sensitivity and provides a model of insulin resistance. We hypothesized that the reduction in insulin sensitivity occurs via elevation of circulating nonesterified fatty acids (NEFAs) and an increase in intramyocellular lipid (IMCL). A total of 15 nondiabetic males (mean age 27.4 +/- 1.6 years) were treated with NA (500 mg daily for 1 week, 1 g daily for 1 week). Insulin sensitivity (glucose infusion rate [GIR]) was determined pre- and post-NA by euglycemic-hyperinsulinemic clamp. Substrate oxidation was determined by indirect calorimetry. Skeletal muscle lipid was assessed by estimation of long-chain acyl-CoA (LCACoA) and triglyceride (TG) content and by (1)H-magnetic resonance spectroscopy quantification of IMCL (n = 11). NA reduced GIR (P =.03) and nonoxidative glucose disposal (P <.01) and increased fasting NEFAs (P =.01). The decrease in GIR related significantly to the increase in fasting NEFAs (r(2) =.30, P =.03). The intrasubject increase in basal and clamp fat oxidation correlated with the decrease in GIR (r(2) =.45, P <.01 and r(2) =.63, P <.01). There were no significant changes in muscle LCACoA, TG, or IMCL content. Therefore, induction of insulin resistance by NA occurs with increased availability of circulating fatty acids to muscle rather than with increased muscle lipid content.     

Insulin-mediated increase in glucose 1,6-bisphosphate is attenuated in skeletal muscle of insulin-resistant man

The purpose of this study was to determine the effect of insulin infusion on the glucose 1,6-bisphosphate (glucose 1,6-P2) content in skeletal muscle of insulin resistant man. Euglycemic (approximately 100 mg/dL) hyperinsulinemic clamps were performed on seven men with chronically elevated fasting plasma glycemia (228 +/- 13 mg/dL, mean +/- SE) who were insulin resistant (HIR) and five men with normal fasting glycemia (115 +/- 5 mg/dL) who were insulin resistant (NIR). Insulin was infused at successive rates of 40 and 400 mU/m2/min, and biopsies were obtained from the quadriceps femoris muscle before and after insulin infusion. The results were compared with those of normoglycemic insulin-sensitive (NIS) men. The insulin-resistant groups had significantly higher percent body fat values than did the NIS group. Glucose 1,6-P2 increased from 70 +/- 6, 49 +/- 9, and 67 +/- 3 mumols/kg dry weight in the basal state to 135 +/- 12 (P less than .001 v basal), 67 +/- 11 (P greater than .05) and 79 +/- 3 (P greater than .05) after 40 mU insulin in NIS, HIR, and NIR, respectively. Glucose 1,6-P2 increased to 147 +/- 12 (P less than .001 v basal), 91 +/- 15 (P less than .01) and 99 +/- 13 (P less than .05) mumols/kg dry weight after 400 mU insulin in NIS, HIR, and NIR, respectively. The increase in glucose 1,6-P2 in response to 40 mU insulin was only 28% and 18% in HIR and NIR, respectively, of that in NIS.(ABSTRACT TRUNCATED AT 250 WORDS)     

Alteration of muscle fiber composition linking to insulin resistance and hypertension in fructose-fed rats.

The aim of this study was to examine the role of muscle fiber composition in insulin resistance and the effect of a calcium channel antagonist on insulin sensitivity in fructose-induced insulin resistant and hypertensive rats. Six-week-old male Sprague-Dawley rats were fed either normal rat chow (control) or fructose-rich diet (FFR). For the last 2 weeks of a 6-week period of either diet, the rats were treated, by gavage, with gum arabic solution (control or FFR) or a dihydropyridine calcium channel antagonist, benidipine hydrochloride (3 mg/kg/day: FFR + Ca), then the euglycemic hyperinsulinemic glucose clamp technique was performed to evaluate insulin sensitivity. Blood pressure was measured weekly for 6 weeks. At the end of the glucose clamp, the soleus muscle was dissected out for determination of muscle fiber composition by ATPase methods. Blood pressure was elevated at 2 weeks after the start of fructose-rich chow feeding and persisted thereafter throughout the study. Blood pressure at the glucose clamp in the FFR was significantly higher than that in the control group (142 +/- 2 v 155 +/- 2 mm Hg, P < .01) and the calcium antagonist significantly lowered blood pressure of FFR (136 +/- 6 mm Hg for FFR +/- Ca, P < .05). The average rate of glucose infusion during glucose clamp, as a measure of insulin sensitivity (M value), was significantly lower in the FFR than in the control (15.4 +/- 0.4 v 10.9 +/- 0.6 mg/kg/min, P < .01). The calcium channel antagonist partially improved the M value compared to that of FFR (13.4 +/- 0.7 mg/kg/min in FFR +/- Ca, P < .01 compared to FFR, P < .05 compared to control). The composite ratio of type I fiber in soleus muscle was significantly decreased in FFR compared to control (81.7 +/- 1.5% v 75.0 +/- 1.7%, P < .01), and the composite ratio of type I fiber in rats treated with the calcium channel antagonist (FFR +/- Ca) recovered to the control level (79.9 +/- 1.1%, P < .05 compared to FFR). The M value was significantly correlated with the compositions of type I and type II fibers (for type I fibers, r = 0.80, P < .01; for type II fibers, r = -0.81, P < .01). These results suggest that fiber composition of skeletal muscle links insulin resistance and that a calcium channel antagonist may modulate muscle fiber composition in hypertensive animal model, fructose-fed rats.     

Adipose tissue, hepatic, and skeletal muscle insulin sensitivity in extremely obese subjects with acanthosis nigricans

We evaluated insulin action in skeletal muscle (glucose disposal), liver (glucose production), and adipose tissue (lipolysis) in 5 extremely obese women with acanthosis nigricans (AN), who had normal oral glucose tolerance, and 5 healthy lean subjects, by using a 5-stage pancreatic clamp and stable isotopically labeled tracer infusion. Basal plasma insulin concentration was much greater in obese subjects with AN than lean subjects (54.8 +/- 4.5 vs 8.0 +/- 1.3 microU/mL, P < .001), but basal glucose and free fatty acid concentrations were similar in both groups. During stage 1 of the clamp, glucose rate of appearance (R(a)) (2.6 +/- 0.3 vs 3.7 +/- 0.3 micromol x kg FFM(-1) x min(-1), P = .02) and palmitate R(a) (2.4 +/- 0.6 vs 7.0 +/- 1.5 micromol x kg FFM(-1) x min(-1), P < .05) were greater in obese subjects with AN than lean subjects despite slightly greater plasma insulin concentration in subjects with AN (3.0 +/- 0.7 vs 1.1 +/- 0.4 microU/mL, P < .05). The area under the curve for palmitate R(a) (1867 +/- 501 vs 663 +/- 75 micromol x kg FFM(-1) x 600 min(-1), P = .03) and glucose R(a) (1920 +/- 374 vs 1032 +/- 88 micromol x kg FFM(-1) x 600 min(-1), P = .02) during the entire clamp procedure was greater in subjects with AN than lean subjects. During intermediate insulin conditions (plasma insulin, approximately 35 microU/mL), palmitate R(a) was 5-fold greater in subjects with AN than in lean subjects (2.6 +/- 1.1 vs 0.5 +/- 0.2 micromol x kg FFM(-1) x min(-1), P = .05). Maximal glucose disposal was markedly lower in obese subjects with AN than in lean subjects (13.0 +/- 0.8 vs 23.4 +/- 1.8 mg x kg FFM(-1) x min(-1), P = .01) despite greater peak plasma insulin concentration (1842 +/- 254 vs 598 +/- 38 microU/mL, P < .05). These data demonstrate obese young adults with AN have marked insulin resistance in multiple tissues. However, marked insulin hypersecretion can compensate for impaired insulin action, resulting in normal glucose and fatty acid metabolism during basal conditions.     

Effect of ovariectomy and estradiol replacement on skeletal muscle enzyme activity in female rats

In female rats, ovariectomy (OVX) is associated with increased body fat and insulin resistance, and estradiol replacement prevents these alterations. These metabolic changes related to the estrogen-deficient state might be due, in part, to alterations in skeletal muscle substrate metabolism. We tested the hypothesis that estradiol affects the regulation of enzymes involved in substrate oxidation and storage within skeletal muscle. Specifically, we examined enzymes involved in the regulation of glycogen synthesis (glycogen synthase [GS]), glycolysis (phosphofructokinase [PFK]), tricarboxylic acid cycle activity (citrate synthase [CS]), and beta-oxidation (beta-hydroxyacyl-CoA dehydrogenase [beta-HADH]). Twenty-two, female Sprague-Dawley rats (7 to 8 weeks old) were separated into 3 groups: OVX + placebo (P; n = 8), OVX + estradiol (E(2); n = 8), and sham-operated (S; n = 6). Rats from E(2) and P groups were pair-fed to the S group to control for OVX-induced changes in food intake. After 16 days, activities of GS, PFK, CS, and beta-HADH were measured in vastus medialis muscle. GS fractional velocity was significantly lower (P <.05) in P (mean +/- SE; 39.7% +/- 6.2%) compared with both S (61.9% +/- 8.8%) and E(2) (65.8% +/- 8.4%) rats. In addition, E(2) rats (41.4 +/- 2.0) had significantly higher (P <.05) CS activity than P (34.9 +/- 2.0) and S (33.9 +/- 1.4 micromol/min/g) groups. There was no effect of OVX or estradiol replacement on beta-HADH or PFK. Our results suggest that, independent of alterations in food intake, estradiol availability affects the regulation of enzymes involved in nonoxidative glucose disposal (GS) and oxidative metabolism (CS) in skeletal muscle.     

Lipolysis in skeletal muscle is decreased in high-fat-fed rats

The intracellular triglyceride content in skeletal muscle is increased in insulin-resistant states such as obesity or high-fat feeding. It has been hypothesized that increased fatty acid oxidation resulting from increased lipolysis of intramyocellular triglycerides may be responsible for this insulin resistance. This study was undertaken to examine whether insulin resistance is associated with increased lipolysis in skeletal muscle in rats fed a high-fat diet. Sprague-Dawley rats were fed a high-fat diet for 5 weeks. Lipolysis in skeletal muscle and adipose tissue was determined by measuring the interstitial glycerol concentrations using a microdialysis method in basal and hyperinsulinemic-euglycemic clamp conditions. In the basal state, plasma free fatty acid (FFA) levels were higher in high-fat-fed rats than in low fat-fed rats (P <.05). In contrast, plasma glycerol levels (P <.001) and interstitial glycerol concentrations of skeletal muscle (P <.05) and adipose tissue (P <.01) were lower in high fat-fed rats than in low fat-fed rats. Plasma (P <.05) and interstitial glycerol concentrations (P <.05 for skeletal muscle, P <.01 for adipose tissue) during the hyperinsulinemic euglycemic clamps were also lower in the high-fat diet group. These results do not support the idea that increased fatty acid oxidation resulting from increased lipolysis of intramyocellular triglycerides is responsible for the insulin resistance in high fat-fed rats.     

Postnatal growth and fatty acid synthesis in overgrown rat pups induced by fetal hyperinsulinemia

Fetal hyperinsulinemia in the rat results in increased body weight, lipid content, and enhanced lipogenesis in liver and carcass. The purpose of our study was to determine whether the macrosomia and enhancement of fatty acid (FA) synthesis and/or content persisted postnatally in this animal model. Fetal hyperinsulinemia was produced in Sprague-Dawley rats by injecting fetuses with 2 units of insulin at 20.5 days of gestation. Alternate pups in the same litter were injected with saline. Pups were delivered surgically at 22.5 days of gestation, were weighed daily and sacrificed on day 15. FA content and synthesis rates of liver and skeletal muscle were measured. We found: (1) At birth, insulin-treated pups were 12% heavier than saline littermates, (5.88 +/- 0.14 g v 5.26 +/- 0.14 g, P less than .01); and (2) The enhanced growth associated with prenatal insulin treatment persisted during the suckling period, ie, compared with saline-treated controls, insulin pups were 15.7% heavier at 15 days of age (P less than .01); growth velocity of insulin pups, beginning on day 3, significantly exceeded that of control pups (P less than .05). FA contents of liver and muscle in insulin pups, (62.6 +/- 5.7 mumol/g and 62.7 +/- 13.2 mumol/g) were significantly greater (P less than .05) than in saline littermates (45.1 +/- 5.6 mumol/g and 30.2 +/- 4.7 mumol/g, respectively). We conclude that.(ABSTRACT TRUNCATED AT 250 WORDS)     

Epinephrine stimulates human muscle lipoprotein lipase activity in vivo

Lipoprotein lipase (LPL) is involved in lipoprotein metabolism and nutrient partitioning in both adipose tissue and skeletal muscle, and LPL activity is regulated by various hormones and the nutritional state. However, the action of catecholamines has not been thoroughly investigated in humans. Therefore, the effects of exogenous epinephrine on skeletal muscle LPL (SM-LPL) activity and whole-body lipid oxidation were studied. Muscle biopsies were obtained from eight healthy subjects before, during, and after epinephrine infusion. Somatostatin was infused to suppress endogenous insulin production and insulin was infused at a constant rate to maintain basal insulin levels throughout the study. After an equilibrium period (120 minutes), epinephrine (0.05 microg/kg/min) was infused for another 120 minutes. Epinephrine stimulated SM-LPL activity by 21.8%+/-6.8% above basal levels from 1.44+/-0.25 to 1.69+/-0.28 micromol free fatty acid (FFA)/h/g muscle (P<.02), increased plasma FFA 270% from 0.147 to 0.544 mmol/L (P<.05), and increased lipid oxidation 45% from 4.37 to 6.36 mg/kg/min (P<.05). The increase in SM-LPL activity was positively correlated with the increase in whole-body lipid oxidation (R=.75, P<.05). Finally, lipid oxidation and SM-LPL activity were negatively correlated with whole-body glucose oxidation. Overall, the results demonstrate that epinephrine is able to stimulate SM-LPL activity in humans, and thus may have opposite effects on adipose tissue and SM-LPL activity.     

NO-1886 (ibrolipim), a lipoprotein lipase activator, increases the expression of uncoupling protein 3 in skeletal muscle and suppresses fat accumulation in high-fat diet-induced obesity in rats

Although the lipoprotein lipase (LPL) activator NO-1886 shows antiobesity effects in high-fat-induced obese animals, the mechanism remains unclear. To clarify the mechanism, we studied the effects of NO-1886 on the expression of uncoupling protein (UCP) 1, UCP2, and UCP3 in rats. NO-1886 was mixed with a high-fat chow to supply a dose of 100 mg/kg to 8-month-old male Sprague-Dawley rats. The animals were fed the high-fat chow for 8 weeks. At the end of the administration period, brown adipose tissue (BAT), mesenteric fat, and soleus muscle were collected and levels of UCP1, UCP2, and UCP3 messenger RNA (mRNA) were determined. NO-1886 suppressed the body weight increase seen in the high-fat control group after the 8-week administration (585 +/- 39 vs 657 +/- 66 g, P < .05). NO-1886 also suppressed fat accumulation in visceral (46.9 +/- 10.4 vs 73.7 +/- 14.5 g, P < .01) and subcutaneous (43.1 +/- 18.1 vs 68.9 +/- 18.8 g, P < .05) tissues and increased the levels of plasma total cholesterol and high-density lipoprotein cholesterol in comparison to the high-fat control group. In contrast, NO-1886 decreased the levels of plasma triglycerides, nonesterified free fatty acid, glucose, and insulin. NO-1886 increased LPL activity in soleus muscle (0.082 +/- 0.013 vs 0.061 +/- 0.016 mumol of free fatty acid per minute per gram of tissue, P < .05). NO-1886 increased the expression of UCP3 mRNA in soleus muscle 3.14-fold (P < .01) compared with the high-fat control group without affecting the levels of UCP3 in mesenteric adipose tissue and BAT. In addition, NO-1886 did not affect the expression of UCP1 and UCP2 in BAT, mesenteric adipose tissue, and soleus muscle. In conclusion, NO-1886 increased the expression of UCP3 mRNA and LPL activity only in skeletal muscle. Therefore, a possible mechanism for NO-1886's antiobesity effects in rats may be the enhancement of LPL activity in skeletal muscle and the accompanying increase in UCP3 expression.     

Dietary intervention increases n-3 long-chain polyunsaturated fatty acids in skeletal muscle membrane phospholipids of obese subjects. Implications for insulin sensitivity

OBJECTIVE: Cross-sectional studies suggest that the fatty acid (FA) composition of phospholipids in skeletal muscle cell membrane may modulate insulin sensitivity in humans. We examined the impact of a hypocaloric low-fat dietary intervention on membrane FA composition and insulin sensitivity. DESIGN Muscle membrane FA profiles were determined in muscle (vastus lateralis) biopsies from 21 obese subjects before and after 6 months of dietary restriction. Diet instructions emphasized low intake of FA of marine origin by recommending lean fish and prohibiting fatty fish and fish oil supplements. Insulin resistance was estimated by the homeostasis model assessment (HOMA-IR). RESULTS The mean weight loss was 5.1 kg (range -15.3 to +1.3 kg). BMI decreased from 36.5 to 34.9 kg/m(2) (P=0.003). Saturated FA (SFA) decreased 11% (P=0.0001). Polyunsaturated FA (PUFA)n-6 increased 4% (P =0.003). Long-chain PUFAn-3 increased 51% (P= 0.0001), mainly due to a 75% increase (P<0.0001) in docosahexaenoic acid. Changes in HOMA-IR correlated significantly with changes in long-chain PUFAn-3 (R=-0.57, P< 0.01), SFA (R=0.58, P<0.01) and waist circumference (R=0.46, P<0.05). A multivariate linear regression analysis that included changes in weight, fat mass, waist circumference, plasma lipids, PUFA, SFA and long-chain PUFAn-3 indicated that SFA and long-chain PUFAn-3 were independent predictors of HOMA-IR (R(2)=0.33, P<0.01). CONCLUSIONS: A hypocaloric low-fat dietary intervention programme increased incorporation of long-chain PUFAn-3 and reduced SFA in skeletal muscle membrane phospholipids of obese subjects, a setting that may impact on insulin action.     

Metabolic characteristics of soleus muscle in relation to insulin action in the offspring of hypertensive parents

Insulin resistance affecting skeletal muscle metabolism is present in the prehypertensive state. The aim of our study was to test the hypothesis that blood pressure value is related to skeletal muscle composition, measured by (31)P magnetic resonance (MR) spectroscopy, and to insulin sensitivity in the offspring of hypertensive parents (OH) and healthy controls. Study groups consisted of 10 healthy young lean OH with normal glucose tolerance, confirmed with oral glucose tolerance test, and 13 controls matched for age, sex, and body mass index. Insulin action was estimated as glucose disposal (M), glucose metabolic clearance rate (MCR), and insulin sensitivity index (M/I) during a 10-hour hyperinsulinemic euglycemic clamp. The sum of immunoreactive insulin values from the oral glucose tolerance test was calculated. (31)P MR spectroscopy was performed on a whole-body MR scanner (Siemens Vision, Erlangen, Germany) operating at 1.5 T and equipped with actively shielded gradient coils. There were no differences in common metabolic and anthropometric parameters between OH and controls except for the blood pressure, which was in the range of normal to high-normal level in OH. Mean blood pressure was significantly higher in OH (95.73 +/- 4.39 vs 83.76 +/- 3.95 mm Hg; P < .001). Trend toward insulin resistance was registered in OH with significantly lower M/I (0.74 +/- 0.47 vs 1.42 +/- 0.65 mg x kg(-1) x min(-1) x mIU(-1) x L(-1); P < .05). There were no significant differences in total serum magnesium (sMg) levels between OH and controls, although a positive correlation exists between sMg and insulin sensitivity expressed as M (r = 0.63, P < .01), MCR (r = 0.54, P < .01), and M/I (r = 0.51, P < .05). No differences in signal intensities of phosphocreatine (PCr), phosphomonoesters, phosphodiesters, inorganic phosphates (Pi), adenosine triphosphates (Patp and betaATP), and calculated concentrations of intracellular ionized magnesium (Mgi) and H(+) ions between the groups were detected. Systolic blood pressure correlates positively with PCr/Patp (r = 0.43, P < .05), Pi/Patp (r = 0.413, P < .05), and Pi/betaATP (r = 0.48, P < .05). Diastolic blood pressure correlates positively only with the ratio Pi/betaATP (r = 0.42, P < .05). The sum of immunoreactive insulin values correlates with PCr/betaATP (r = 0.53, P < .01) and with Pi/betaATP (r = 0.6, P < .01). In conclusion, increase in blood pressure and insulin resistance were confirmed in offspring of OH. Insulin sensitivity is related to sMg and the elevation of blood pressure is associated with the activation of energy metabolism in skeletal muscle. The relationship between muscle energetic characteristics and markers of insulin resistance suggests that the alteration of energy metabolism may be present in early stages of metabolic syndrome.     

Time course of alterations in phospholipid fatty acids and number of beta-adrenoceptors in the rat heart during adrenergic stimulation in vivo.

The purpose of this study was to test the hypothesis that catecholamine induced down-regulation of beta-adrenoceptors in cardiac muscle is facilitated by modifications of the lipid milieu in cellular membranes. The time course of down-regulation of beta -adrenoceptors and changes in the fatty acid composition of phospholipids was examined in the rat heart during adaptation to repeated epinephrine administration. By this we studied a possible relationship between modulation of the membrane phospholipids and the properties of beta-adrenoceptors during 7 days of epinephrine administration. The fatty acid composition of cardiac membrane phosphatidylcholine (PC) and phosphatidylethanolamine (PE) and Bmax and Kd of [3H]dihydroalprenolol binding to beta -adrenoceptors were measured in rats after 1, 2, 3, 5 and 7 days of epinephrine administration. The in vivo adrenergic stimulation led to a significant response of phospholipid fatty acyl chains. In both PC and PE the linoleic acid (18:2n-6) level decreased markedly. The docosahexanoic acid (22:6n-3) level increased in PE and the arachidonic acid (20:4n-6) level increased in PC. These fatty acid changes were all significant after 3-5 days of epinephrine administration. During the 7 day epinephrine administration, the polyunsaturated fatty acid levels in the phospholipids of purified cardiac sarcolemma changed in the same way as in the phospholipids of whole ventricular muscle. The number of binding sites of beta -adrenoceptors (Bmax) decreased as expected. The decrease in Bmax occurred later than the changes in their lipid environment and was only significant after 7 days of epinephrine administration. The conclusion is that during adaptation to epinephrine administration, the down-regulation of beta-adrenoceptors is preceded by alterations in the polyunsaturated fatty acid composition of phospholipids in heart muscle. This supports the concept of a regulatory role of membrane lipids in the response of beta-adrenoceptors to prolonged stimulation.     

The role of plasma fatty acid composition in endogenous glucose production in patients with type 2 diabetes mellitus

Hepatic insulin resistance and increased endogenous glucose production (EGP) are associated with increased plasma free fatty acids (FFA). However, the contribution of FFA composition to the regulation of EGP is not known. Six obese nondiabetic subjects and 6 patients with type 2 diabetes mellitus (DM2) were studied after an overnight and a 3-day fast. Plasma insulin concentrations after an overnight fast were similar in the DM2 and nondiabetic patients (88.8 +/- 26.4 v 57.6 +/- 12.6 pmol/L, not significant [NS]) despite increased plasma glucose (9.9 +/- 1.8 v 5.1 +/- 0.1 mmol/L, P <.01) and EGP (510.3 +/- 77.7 v 298.3 +/- 18.3 micromol x m(-2) x min(-1), P <.05) in the patients with DM2. Absolute rates of gluconeogenesis using the heavy water method were also increased in the patients with DM2 (346.8 +/- 74.9 v 198.8 +/- 16.4 micromol x m(-2). min(-1), P <.05). No differences were observed in plasma polyunsaturated fatty acids (PUFA) between the diabetic and nondiabetic subjects. However, total saturated fatty acid (SFA) concentrations (350 +/- 37.4 v 230.9 +/- 33.3 micromol/L, P <.02) were significantly increased in the diabetic subjects. Rates of EGP were correlated with total plasma FFA concentration (r =.71, P <.01) and the concentration of SFA (r =.71, P <.01), but not monounsaturated fatty acids or PUFA. Rates of gluconeogenesis were also correlated with plasma FFA (r =.64, P <.05) and SFA (r =.67, P <.05). We observed no relationship between EGP and either total FFA or fatty acid composition after a 3-day fast. We conclude that increases in EGP are associated with concentrations of plasma SFA after an overnight fast.     

Skeletal muscle neuronal nitric oxide synthase micro protein is reduced in people with impaired glucose homeostasis and is not normalized by exercise training

Skeletal muscle inducible nitric oxide synthase (NOS) protein is greatly elevated in people with type 2 diabetes mellitus, whereas endothelial NOS is at normal levels. Diabetic rat studies suggest that skeletal muscle neuronal NOS (nNOS) micro protein expression may be reduced in human insulin resistance. The aim of this study was to determine whether skeletal muscle nNOSmicro protein expression is reduced in people with impaired glucose homeostasis and whether exercise training increases nNOSmicro protein expression in these individuals because exercise training increases skeletal muscle nNOSmicro protein in rats. Seven people with type 2 diabetes mellitus or prediabetes (impaired fasting glucose and/or impaired glucose tolerance) and 7 matched (sex, age, fitness, body mass index, blood pressure, lipid profile) healthy controls aged 36 to 60 years participated in this study. Vastus lateralis muscle biopsies for nNOSmicro protein determination were obtained, aerobic fitness was measured (peak pulmonary oxygen uptake [Vo(2) peak]), and glucose tolerance and insulin homeostasis were assessed before and after 1 and 4 weeks of cycling exercise training (60% Vo(2) peak, 50 minutes x 5 d wk(-1)). Skeletal muscle nNOSmicro protein was significantly lower (by 32%) in subjects with type 2 diabetes mellitus or prediabetes compared with that in controls before training (17.7 +/- 1.2 vs 26.2 +/- 3.4 arbitrary units, P < .05). The Vo(2) peak and indicators of insulin sensitivity improved with exercise training in both groups (P < .05), but there was no effect of exercise training on skeletal muscle nNOSmicro protein in either group. In conclusion, individuals with impaired glucose homeostasis have reduced skeletal muscle nNOSmicro protein content. However, because exercise training improves insulin sensitivity without influencing skeletal muscle nNOSmicro protein expression, it seems that changes in skeletal muscle nNOSmicro protein are not central to the control of insulin sensitivity in humans and therefore may be a consequence rather than a cause of diabetes.     

Rosiglitazone enhances glucose tolerance by mechanisms other than reduction of fatty acid accumulation within skeletal muscle

We hypothesized that improved glucose tolerance with rosiglitazone treatment would coincide with decreased levels of i.m. triacylglycerol (IMTG), diacylglycerol, and ceramide. Obese Zucker rats were randomly divided into two experimental groups: control (n = 9) and rosiglitazone (n = 9), with lean Zucker rats (n = 9) acting as a control group for obese controls. Rats received either vehicle or 3 mg/kg rosiglitazone for 6 wk. Glucose tolerance was impaired (P < 0.01) in obese compared with lean rats, but was normalized after rosiglitazone treatment. IMTG content was higher in obese compared with lean rats (70.5 +/- 5.1 vs. 27.5 +/- 2.0 micromol/g dry mass; P < 0.05) and increased an additional 30% (P < 0.05) with rosiglitazone treatment. Intramuscular fatty acid composition shifted toward a higher proportion of monounsaturates (P < 0.05) in obese rosiglitazone-treated rats due to an increase in palmitoleate (16:1; P < 0.05). Rosiglitazone treatment increased (P < 0.05) skeletal muscle diacylglycerol and ceramide levels by 65% and 100%, respectively, compared with obese rats, but elevated muscle diacylglycerol was not associated with changes in the total or membrane contents of the diacylglycerol-sensitive protein kinase C isoforms theta;, delta, alpha, and beta. In summary, we observed a disassociation among skeletal muscle IMTG, diacylglycerol and ceramide content, and glucose tolerance with rosiglitazone treatment in obese Zucker rats. Our data suggest, therefore, that rosiglitazone enhances glucose tolerance by mechanisms other than reduction of fatty acid accumulation within skeletal muscle.