Effect of commercial breakfast fibre cereals compared with corn flakes on postprandial blood glucose, gastric emptying and satiety in healthy subjects: a randomized blinded crossover trial

<p>Abstract</p> <p>Background</p> <p>Dietary fibre food intake is related to a reduced risk of developing diabetes mellitus. However, the mechanism of this effect is still not clear. The aim of this study was to evaluate the effect of commercial fibre cereals on the rate of gastric emptying, postprandial glucose response and satiety in healthy subjects.</p> <p>Methods</p> <p>Gastric emptying rate (GER) was measured by standardized real time ultrasonography. Twelve healthy subjects were assessed using a randomized crossover blinded trial. The subjects were examined after an 8 hour fast and after assessment of normal fasting blood glucose level. Satiety scores were estimated and blood glucose measurements were taken before and at 0, 20, 30, 40, 60, 80, 100 and 120 min after the end of the meal. GER was calculated as the percentage change in the antral cross-sectional area 15 and 90 min after ingestion of sour milk with corn flakes (GER1), cereal bran flakes (GER2) or wholemeal oat flakes (GER3).</p> <p>Results</p> <p>The median value was, respectively, 42% for GER1, 33 % for GER2 and 51% for GER3. The difference between the GER after ingestion of bran flakes compared to wholemeal oat flakes was statistically significant (p = 0.023). The postprandial delta blood glucose level was statistically significantly lower at 40 min (p = 0.045) and 120 min (p = 0.023) after the cereal bran flakes meal. There was no statistical significance between the areas under the curve (AUCs) of the cereals as far as blood glucose and satiety were concerned.</p> <p>Conclusion</p> <p>The result of this study demonstrates that the intake of either bran flakes or wholemeal oat flakes has no effect on the total postprandial blood glucose response or satiety when compared to corn flakes. However, the study does show that the intake of cereal bran flakes slows the GER when compared to oat flakes and corn flakes, probably due to a higher fibre content. Since these products do not differ in terms of glucose response and satiety on healthy subjects, they should be considered equivalent in this respect.</p> <p>Trial registration</p> <p>ISRCTN90535566</p

<i>Drosophila</i> Spidey/Kar Regulates Oenocyte Growth via PI3-Kinase Signaling

<div><p>Cell growth and proliferation depend upon many different aspects of lipid metabolism. One key signaling pathway that is utilized in many different anabolic contexts involves Phosphatidylinositide 3-kinase (PI3K) and its membrane lipid products, the Phosphatidylinositol (3,4,5)-trisphosphates. It remains unclear, however, which other branches of lipid metabolism interact with the PI3K signaling pathway. Here, we focus on specialized fat metabolizing cells in <i>Drosophila</i> called larval oenocytes. In the presence of dietary nutrients, oenocytes undergo PI3K-dependent cell growth and contain very few lipid droplets. In contrast, during starvation, oenocytes decrease PI3K signaling, shut down cell growth and accumulate abundant lipid droplets. We now show that PI3K in larval oenocytes, but not in fat body cells, functions to suppress lipid droplet accumulation. Several enzymes of fatty acid, triglyceride and hydrocarbon metabolism are required in oenocytes primarily for lipid droplet induction rather than for cell growth. In contrast, a very long chain fatty-acyl-CoA reductase (FarO) and a putative lipid dehydrogenase/reductase (Spidey, also known as Kar) not only promote lipid droplet induction but also inhibit oenocyte growth. In the case of Spidey/Kar, we show that the growth suppression mechanism involves inhibition of the PI3K signaling pathway upstream of Akt activity. Together, the findings in this study show how Spidey/Kar and FarO regulate the balance between the cell growth and lipid storage of larval oenocytes.</p></div

Kar is required to restrain oenocyte endoreplication.

<p>(A) <i>PromE-GAL4</i> driven Kar RNAi or FarO RNAi in NR larvae leads to a significant (**p<0.001) increase in oenocyte nuclear volume. (B) <i>PromE-GAL4</i> driven Kar RNAi or PI3K overexpression (Dp110) in NR larvae increases endoreplication (EdU nuclear incorporation) in oenocytes (marked with mGFP). Note that in larvae of the control genotype, endoreplication is shut down by NR in almost all cells of the salivary gland (outlined in white) but not in all oenocytes. Examples of EdU-positive oenocytes are indicated (white arrowheads). Scale bar is 10 μm.</p

Kar and FarO decrease oenocyte size and stimulate lipid droplet induction.

<p>(A) Oenocyte-specific RNAi knockdown (<i>PromE-GAL4</i>) for Kar or FarO in oenocytes increases their cell size in both Fed₄₈ and NR₆₆ larvae (insets) and markedly decreases the induction of lipid droplets (LipidTOX) in NR larvae. Note that oenocytes from Fed₄₈ Kar RNAi larvae also display a small increase in lipid droplets, as is also seen with Acc RNAi. Scale bar is 10μm (B) Graph showing quantitation of larval oenocyte volumes and a significant (**p<0.001) increase in Fed₄₈ and NR cell volumes for Kar RNAi and FarO RNAi. See <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1006154#pgen.1006154.s001" target="_blank">S1 Fig</a> for quantitations.</p

Kar is required to dampen the expression of membrane phospho-Akt.

<p>(A) Oenocyte clusters from NR larvae expressing <i>Kar</i> RNAi (<i>PromE>Kar RNAi</i>) and marked with GFP (mGFP) display higher intensity P-Akt staining than those from NR larvae of a control genotype. Single confocal sections are shown and insets correspond to a higher magnification of the boxed region. (B) The three rows of panels show two oenocyte clusters from a single NR larva, one of which is a Flp-out clone for Kar RNAi (marked with nlsGFP) that includes all oenocytes of one cluster. The nlsGFP-positive oenocyte cluster displays a decrease in lipid droplets (LipidTOX) and an increase in membrane p-Akt staining, compared to its neighboring control nlsGFP-negative oenocyte cluster. Nuclei are marked with DAPI and the scale bar is 10 μm. (C) Proposed model for the cross regulation between Kar and PI3K signaling in oenocytes. Diagrams depict the genetic interactions between Kar and PI3K signaling that balance cell growth and lipid droplet induction in fed (left panel) and nutrient restricted (right panel) states. In the fed state, cell growth predominates over lipid droplets as dietary nutrients stimulate high PI3K activity, which is prevented from becoming even higher by Kar mediated negative feedback, but also suppresses lipid droplet induction. In the nutrient restricted state, lipid droplets predominate over cell growth as Kar remains active, albeit at lower expression, but PI3K signaling is insufficient to promote substantial cell growth or to inhibit the lipid droplet induction process. Note that this model does not explain the genetic interactions underlying the aberrant accumulation of oenocyte lipid droplets in the fed state, as observed following Acc or Kar knockdown. Arrows indicate genetic interactions that are not necessarily mediated by the known enzymatic activities of the proteins (see text for details).</p

Fatty acid, triglyceride and hydrocarbon metabolism regulate oenocyte lipid droplets.

<p>(A) Simplified presentation of the pathway for long chain (LCFA) and very long chain (VLCFA) fatty acid, triglyceride (TAG) and hydrocarbon synthesis. See text for details of the <i>Drosophila</i> enzymes (blue) analyzed in this study. The questionmark indicates that the enzyme activity of Kar has not yet been directly established. (B) Oenocyte clusters (mGFP labeled) from Fed₄₈ and NR₆₆ larvae expressing <i>PromE-GAL4</i> driven <i>UAS-RNAi</i> for <i>Acc</i>, <i>Dgat1</i>, <i>Cyp4g1</i> or <i>Cpr</i> indicating decreased or blocked induction of lipid droplets (LipidTOX) during NR. <i>PromE-GAL4</i> driven <i>UAS-Acc RNAi</i> or <i>UAS-Lsd2</i> are the only manipulations that gave a modest increase in oenocyte lipid droplets in Fed₄₈ larvae. Scale bar is 10 μm (C) Oenocyte cluster from a <i>Cyp4g1</i>^<i>Δ4</i> hemizygous larva (<i>Cyp4g1</i> mutant) showing a decrease in lipid droplet (Oil Red O) induction during NR. (D) Graph of relative oenocyte volumes for the five genetic manipulations in B showing no significant changes in cell size in NR₆₆ larvae. In this and subsequent graphs, error bars represent 1 s.d. and asterisks show statistical significance in Student t tests (*p<0.05, and **p<0.001) compared to the black control bar unless otherwise indicated. See <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1006154#pgen.1006154.s001" target="_blank">S1 Fig</a> for quantifications.</p

Genetic interactions between Kar and PI3K.

<p>(A) In Fed₄₈ larvae, both <i>PromE>Kar Ri</i> and <i>PromE>Dp110</i>^<i>DN</i> genotypes accumulate low levels of oenocyte lipid droplets and this is also seen in <i>PromE>Kar Ri Dp110</i>^<i>DN</i>. In NR larvae, <i>PromE>Dp110</i>^<i>DN</i> does not noticeably alter lipid droplet induction and thus inhibition of NR droplet induction is similar in <i>PromE>Kar Ri</i> and in <i>PromE>Kar Ri Dp110</i>^<i>DN</i>. Oenocyte volume in both Fed₄₈ and NR larvae is increased in <i>PromE>Kar Ri</i> but decreased in <i>PromE>Kar Ri Dp110</i>^<i>DN</i> to a similar extent as for <i>PromE>Dp110</i>^<i>DN</i> alone. Panels show single confocal sections and the scale bar is 10 μm. (B) Relative neutral lipid content of oenocytes in Fed₄₈ larvae of the genotypes in panel A. (C) Oenocyte volumes of the genotypes in panel A in Fed₄₈ and NR₆₆ larvae, demonstrating that <i>PromE-GAL4</i> driving the expression of Dp110^DN is epistatic to Kar RNAi with respect to cell size. Statistical significance in Student t tests is indicated with asterisks (*p<0.05 and **p<0.001). See <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1006154#pgen.1006154.s001" target="_blank">S1 Fig</a> for LipidTOX quantifications.</p