Palatability and glucose, insulin and satiety responses of chickpea flour and extruded chickpea flour bread eaten as part of a breakfast

Objective: To determine the effect of adding chickpea flour or extruded chickpea flour to white bread on palatability and postprandial glycaemia, insulinaemia and satiety.

Design: A randomised, single-blind, cross-over study of four 50 g available carbohydrate breakfasts.

Setting: School of Exercise and Nutrition Sciences, Deakin University.

Subjects: In all, 12 healthy subjects were recruited through posted notices. Totally, 11 (nine male, two female) completed the study (meanplusminuss.e.m.; age 32±2 y; body mass index, 24.7±0.8 kg/m²).

Intervention: After overnight fasting, subjects consumed a control (white) bread (WB) breakfast twice, a chickpea bread (CHB) breakfast once and an extruded chickpea bread (EXB) breakfast once. Palatability and postprandial blood glucose, insulin and satiety responses were determined. Following this, food intakes from an ad libitum buffet and for the remainder of the day were assessed.

Results: A trend towards a lower incremental area under the curve (IAUC) of glucose for the CHB breakfast compared to the WB breakfast was observed (P=0.087). The IAUC of insulin and insulinaemic index (II) of the CHB breakfast were higher (P<0.05) than for the WB breakfast. No differences in glycaemic index (GI), satiety response, food intake or palatability were observed.

Conclusions: CHB and EXB demonstrated acceptable palatability. CHB demonstrated some hypoglycaemic effect compared to WB, but neither CHB nor EXB demonstrated effects on satiety or food intake. The hyperinsulinaemic effect of CHB observed in this study requires further investigation.

cGMP phosphodiesterase inhibition improves the vascular and metabolic actions of insulin in skeletal muscle

There is considerable support for the concept that insulin-mediated increases in microvascular blood flow to muscle impact significantly on muscle glucose uptake. Since the microvascular blood flow increases with insulin have been shown to be nitric oxide-dependent inhibition of cGMP-degrading phosphodiesterases (cGMP PDEs) is predicted to enhance insulin-mediated increases in microvascular perfusion and muscle glucose uptake. Therefore, we studied the effects of the pan-cGMP PDE inhibitor zaprinast on the metabolic and vascular actions of insulin in muscle. Hyperinsulinemic euglycemic clamps (3 mU·min−1·kg−1) were performed in anesthetized rats and changes in microvascular blood flow assessed from rates of 1-methylxanthine metabolism across the muscle bed by capillary xanthine oxidase in response to insulin and zaprinast. We also characterized cGMP PDE isoform expression in muscle by real-time PCR and immunostaining of frozen muscle sections. Zaprinast enhanced insulin-mediated microvascular perfusion by 29% and muscle glucose uptake by 89%, while whole body glucose infusion rate during insulin infusion was increased by 33% at 2 h. PDE2, -9, and -10 were the major isoforms expressed at the mRNA level in muscle, while PDE1B, -9A, -10A, and -11A proteins were expressed in blood vessels. Acute administration of the cGMP PDE inhibitor zaprinast enhances muscle microvascular blood flow and glucose uptake response to insulin. The expression of a number of cGMP PDE isoforms in skeletal muscle suggests that targeting specific cGMP PDE isoforms may provide a promising avenue for development of a novel class of therapeutics for enhancing muscle insulin sensitivity.

The role of Ca2+ in insulin-stimulated glucose transport in 3T3-L1 cells.

We have examined the requirement for Ca2+ in the signaling and trafficking pathways involved in insulin-stimulated glucose uptake in 3T3-L1 adipocytes. Chelation of intracellular Ca2+, using 1,2-bis (o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra (acetoxy- methyl) ester (BAPTA-AM), resulted in >95% inhibition of insulin-stimulated glucose uptake. The calmodulin antagonist, W13, inhibited insulin-stimulated glucose uptake by 60%. Both BAPTA-AM and W13 inhibited Akt phosphorylation by 70-75%. However, analysis of insulin-dose response curves indicated that this inhibition was not sufficient to explain the effects of BAPTA-AM and W13 on glucose uptake. BAPTA-AM inhibited insulin-stimulated translocation of GLUT4 by 50%, as determined by plasma membrane lawn assay and subcellular fractionation. In contrast, the insulin-stimulated appearance of HA-tagged GLUT4 at the cell surface, as measured by surface binding, was blocked by BAPTA-AM. While the ionophores A23187 or ionomycin prevented the inhibition of Akt phosphorylation and GLUT4 translocation by BAPTA-AM, they did not overcome the inhibition of glucose transport. Moreover, glucose uptake of cells pretreated with insulin followed by rapid cooling to 4 °C, to promote cell surface expression of GLUT4 and prevent subsequent endocytosis, was inhibited specifically by BAPTA-AM. This indicates that inhibition of glucose uptake by BAPTA-AM is independent of both trafficking and signal transduction. These data indicate that Ca2+ is involved in at least two different steps of the insulin-dependent recruitment of GLUT4 to the plasma membrane. One involves the translocation step. The second involves the fusion of GLUT4 vesicles with the plasma membrane. These data are consistent with the hypothesis that Ca2+/calmodulin plays a fundamental role in eukaryotic vesicle docking and fusion. Finally, BAPTA-AM may inhibit the activity of the facilitative transporters by binding directly to the transporter itself.

Saturated, but not n-6 polyunsaturated, fatty acids induce insulin resistance: role of intramuscular accumulation of lipid metabolites

Consumption of a Western diet rich in saturated fats is associated with obesity and insulin resistance. In some insulin-resistant phenotypes this is associated with accumulation of skeletal muscle fatty acids. We examined the effects of diets high in saturated fatty acids (Sat) or n-6 polyunsaturated fatty acids (PUFA) on skeletal muscle fatty acid metabolite accumulation and whole-body insulin sensitivity. Male Sprague-Dawley rats were fed a chow diet (16% calories from fat, Con) or a diet high (53%) in Sat or PUFA for 8 wk. Insulin sensitivity was assessed by fasting plasma glucose and insulin and glucose tolerance via an oral glucose tolerance test. Muscle ceramide and diacylglycerol (DAG) levels and triacylglycerol (TAG) fatty acids were also measured. Both high-fat diets increased plasma free fatty acid levels by 30%. Compared with Con, Sat-fed rats were insulin resistant, whereas PUFA-treated rats showed improved insulin sensitivity. Sat caused a 125% increase in muscle DAG and a small increase in TAG. Although PUFA also resulted in a small increase in DAG, the excess fatty acids were primarily directed toward TAG storage (105% above Con). Ceramide content was unaffected by either high-fat diet. To examine the effects of fatty acids on cellular lipid storage and glucose uptake in vitro, rat L6 myotubes were incubated for 5 h with saturated and polyunsaturated fatty acids. After treatment of L6 myotubes with palmitate (C16:0), the ceramide and DAG content were increased by two- and fivefold, respectively, concomitant with reduced insulin-stimulated glucose uptake. In contrast, treatment of these cells with linoleate (C18:2) did not alter DAG, ceramide levels, and glucose uptake compared with controls (no added fatty acids). Both 16:0 and 18:2 treatments increased myotube TAG levels (C18:2 vs. C16:0, P < 0.05). These results indicate that increasing dietary Sat induces insulin resistance with concomitant increases in muscle DAG. Diets rich in n-6 PUFA appear to prevent insulin resistance by directing fat into TAG, rather than other lipid metabolites.

Blood plasma concentrations of metabolic hormones and glucose during extended lactation in grazing cows or cows fed a total mixed ration

An experiment was conducted to measure the effect of diet on circulating concentrations of metabolic hormones and metabolites in cows undergoing extended lactations. Two groups of 6 Holstein-Friesian cows managed for lactations of 670 d were used in the experiment. One group was fully fed on a total mixed ration (TMR), whereas the other group grazed fresh pasture supplemented with grain (P+G). On 7 occasions between 332 and 612 d in milk, concentrations of metabolic hormones and glucose were measured in the blood plasma of each cow. Cows fed TMR gained more weight and body condition than P+G cows, but did not produce more milk during the study period. Only 3 of the TMR cows continued to lactate until 612 d in milk compared with all 6 of the P+G cows. Blood plasma from cows fed TMR had higher concentrations of glucose, insulin, glucagon, insulin-like growth factor 1, and leptin, but lower concentrations of growth hormone, than that from P+G cows. These changes were consistent with the preferential deposition of energy into adipose tissue at the expense of milk production and presumably were induced by a diet that provided precursors for gluconeogenesis that were in excess of the requirements for maintenance and prevailing milk production. The mechanism responsible for some TMR cows putting on excess weight and reducing or ceasing milk production is uncertain, but this observation has important implications for the nutritional management of cows in extended lactation programs.

The effect of insulin and exercise on c-Cbl protein abundance and phosphorylation in insulin-resistant skeletal muscle in lean and obese Zucker rats.

Aims/hypothesis: Recruitment of the protein c-Cbl to the insulin receptor (IR) and its tyrosine phosphorylation via a pathway that is independent from phosphatidylinositol 3prime-kinase is necessary for insulin-stimulated GLUT4 translocation in 3T3-L1 adipocytes. The activation of this pathway by insulin or exercise has yet to be reported in skeletal muscle. Methods: Lean and obese Zucker rats were randomly assigned to one of three treatment groups: (i) control, (ii) insulin-stimulated or (iii) acute, exhaustive exercise. Hind limb skeletal muscle was removed and the phosphorylation state of IR, Akt and c-Cbl measured.  Results:   Insulin receptor phosphorylation was increased 12-fold after insulin stimulation (p<0.0001) in lean rats and threefold in obese rats. Acute exercise had no effect on IR tyrosine phosphorylation. Similar results were found for serine phosphorylation of Akt. Exercise did not alter c-Cbl tyrosine phosphorylation in skeletal muscle of lean or obese rats. However, in contrast to previous studies in adipocytes, c-Cbl tyrosine phosphorylation was reduced after insulin treatment (p<0.001). Conclusions/interpretation: We also found that c-Cbl associating protein expression is relatively low in skeletal muscle of Zucker rats compared to 3T3-L1 adipocytes and this could account for the reduced c-Cbl tyrosine phosphorylation after insulin treatment. Interestingly, basal levels of c-Cbl tyrosine phosphorylation were higher in skeletal muscle from insulin-resistant Zucker rats (p<0.05), but the physiological relevance is not clear. We conclude that the regulation of c-Cbl phosphorylation in skeletal muscle differs from that previously reported in adipocytes.

Glucose ingestion during exercise blunts exercise-induced gene expression of skeletal muscle fat oxidative genes.

Ingestion of carbohydrate during exercise may blunt the stimulation of fat oxidative pathways by raising plasma insulin and glucose concentrations and lowering plasma free fatty acid (FFA) levels, thereby causing a marked shift in substrate oxidation. We investigated the effects of a single 2-h bout of moderate-intensity exercise on the expression of key genes involved in fat and carbohydrate metabolism with or without glucose ingestion in seven healthy untrained men (22.7 ± 0.6 yr; body mass index: 23.8 ± 1.0 kg/m²; maximal O2 consumption: 3.85 ± 0.21 l/min). Plasma FFA concentration increased during exercise (P < 0.01) in the fasted state but remained unchanged after glucose ingestion, whereas fat oxidation (indirect calorimetry) was higher in the fasted state vs. glucose feeding (P < 0.05). Except for a significant decrease in the expression of pyruvate dehydrogenase kinase-4 (P < 0.05), glucose ingestion during exercise produced minimal effects on the expression of genes involved in carbohydrate utilization. However, glucose ingestion resulted in a decrease in the expression of genes involved in fatty acid transport and oxidation (CD36, carnitine palmitoyltransferase-1, uncoupling protein 3, and 5'-AMP-activated protein kinase-α2; P < 0.05). In conclusion, glucose ingestion during exercise decreases the expression of genes involved in lipid metabolism rather than increasing genes involved in carbohydrate metabolism.

Activation of MAP kinase by insulin and vanadate in adipocytes from young and old rats

Vanadate has insulin-like effects in adipocytes without stimulating insulin receptor kinase activity. However, it activates IRS-1 associated PI 3-kinase, suggesting that it mimics insulin effects by stimulating signaling elements downstream of PI 3-kinase. Here we analysed the stimulation of MAPK by insulin and vanadate and observed that both elicit a rapid 3.5–4 fold activation which is abolished by wortmannin and PD98059. Simultaneous addition of insulin and vanadate does not result in an additive effect neither on MAPK nor in MEK. Whereas insulin action is transient, vanadate stimulation lasts up to 20 min. In insulin-resistant adipocytes from old rats, insulin stimulates poorly MAPK, whereas a normal activation is achieved with vanadate. We conclude that: (a) insulin and vanadate use a common signaling pathway from PI 3-kinase to MEK and MAPK; (b) vanadate but not insulin, elicits a sustained activation of both enzymes; (c) this pathway is functional in old rat adipocytes.

Effect of dietary modificatio of muscle long-chainN-3 fatty acid on plasma insulin and lipid metabolite, carcass traits, and fat deposition in lambs

In a previous study we showed that feeding fish meal significantly increased muscle long chain n-3 fatty acids (FA) and hot carcass weight. In this study we compared the effect of fish meal and fish oil on increasing muscle long-chain FA. We also investigated whether the increase in carcass weight was due to the effect of dietary enrichment of muscle long-chain n-3 FA on muscle membrane phospholipids and(or) to rumen by-pass protein provided by fish meal. Forty crossbred ([Merino x Border Leicester] x Poll Dorset) wether lambs between 26 and 33 kg BW were randomly assigned to one of five treatments: 1) basal diet of oaten:lucerne chaff (Basal); 2) Basal + fish meal (9% DM) = FM; 3) Basal + fish oil (1.5% DM) with protected sunflower meal (9% DM ) = FOSMP; 4) Basal + fish oil (1.5% DM) = FO; or 5) Basal + protected sunflower meal (10.5% DM) = SMP. Daily intake of ME (9.60 - 10.5 MJ ME/d) and CP (150 to 168 g/d) in all treatments was kept similar by varying the ratio of oaten:lucerne chaff and by feeding the animals at 90% ad libitum intake. Blood samples were collected at the start of the experiment and on the day (d 42) prior to slaughter. Lambs were then slaughtered at a commercial abattoir. At 24 h postmortem carcass traits were measured and longis-simus thoracis muscle taken for analysis of FA of phospholipid and triglyceride fractions. Lambs fed FO and FOSMP showed a marked increase in muscle longchain n-3 FA (P < 0.001) and a reduction in magnitude of the rise in insulin concentration (P < 0.001) after feeding compared with lambs fed Basal and SMP diets. Lambs in FM had a moderate increase (P < 0.001) in muscle long-chain n-3 FA content. Compared with Basal diet, both plasma total cholesterol (P < 0.02) and high-density lipoprotein cholesterol (P < 0.001) levels were greater in SMP and less in FO and FOSMP treat- ments. The i.m. fat content was reduced (P < 0.05) in FM and FO treatments, but carcass weight was increased only with fish meal (P < 0.03). Adding SMP to FO produced muscle with an intermediate level of i.m. fat, whereas muscle long-chain n-3 FA, i.m. fat, and insulin concentration were unchanged with SMP treatment. These results indicate that an increase in carcass weight in FM may be due to the supply of ruminally undegraded protein. They also suggest that fish oil along with fish meal can increase long-chain n-3 FA content in phospholipid of muscle membrane. This may be associated with reduced i.m. fat content and altered insulin action and lipoprotein metabolism.

Deleterious associations of sitting time and television viewing time with cardiometabolic risk biomarkers

We examined the associations of sitting time and television (TV) viewing time with continuously measured biomarkers of cardio-metabolic risk in Australian adults. Waist circumference, BMI, resting blood pressure, triglycerides, HDL cholesterol, fasting and 2-h postload plasma glucose, and fasting insulin were measured in 2,761 women and 2,103 men aged ≥30 years (mean age 54 years) without clinically diagnosed diabetes from the 2004-2005 Australian Diabetes, Obesity and Lifestyle (AusDiab) study. Multivariate linear regression analyses examined associations of self-reported sitting time and TV viewing time (hours per day) with these biomarkers, adjusting for potential confounding variables. For both women and men, sitting time was detrimentally associated with waist circumference, BMI, systolic blood pressure, fasting triglycerides, HDL cholesterol, 2-h postload plasma glucose, and fasting insulin (all P < 0.05), but not with fasting plasma glucose and diastolic blood pressure (men only). With the exception of HDL cholesterol and systolic blood pressure in women, the associations remained significant after further adjustment for waist circumference. TV viewing time was detrimentally associated with all metabolic measures in women and all except HDL cholesterol and blood pressure in men. Only fasting insulin and glucose (men only) remained deleteriously associated with TV viewing time after adjustment for waist circumference. In women and men, sitting time and TV viewing time were deleteriously associated with cardio-metabolic risk biomarkers, with sitting time having more consistent associations in both sexes and being independent of central adiposity. Preventive initiatives aimed at reducing sitting time should focus on both nonleisure and leisure-time domains.