Ulrika Andersson

AMP-activated Protein Kinase Plays a Role in the Control of Food Intake

AMP-activated protein kinase (AMPK) is the downstream component of a protein kinase cascade that acts as an intracellular energy sensor maintaining the energy balance within the cell. The finding that leptin and adiponectin activate AMPK to alter metabolic pathways in muscle and liver provides direct evidence for this role in peripheral tissues. The hypothalamus is a key regulator of food intake and energy balance, coordinating body adiposity and nutritional state in response to peripheral hormones, such as leptin, peptide YY-(3–36), and ghrelin. To date the hormonal regulation of AMPK in the hypothalamus, or its potential role in the control of food intake, have not been reported. Here we demonstrate that counter-regulatory hormones involved in appetite control regulate AMPK activity and that pharmacological activation of AMPK in the hypothalamus increases food intake. In vivo administration of leptin, which leads to a reduction in food intake, decreases hypothalamic AMPK activity. By contrast, injection of ghrelin in vivo, which increases food intake, stimulates AMPK activity in the hypothalamus. Consistent with the effect of ghrelin, injection of 5-amino-4-imidazole carboxamide riboside, a pharmacological activator of AMPK, into either the third cerebral ventricle or directly into the paraventricular nucleus of the hypothalamus significantly increased food intake. These results suggest that AMPK is regulated in the hypothalamus by hormones which regulate food intake. Furthermore, direct pharmacological activation of AMPK in the hypothalamus is sufficient to increase food intake. These findings demonstrate that AMPK plays a role in the regulation of feeding and identify AMPK as a novel target for anti-obesity drugs.

Endosperm and whole grain rye breads are characterized by low post-prandial insulin response and a beneficial blood glucose profile

BackgroundRye products have previously been shown to induce comparatively low post-prandial insulin responses; irrespectively of their glycaemic indices (GI). However, the mechanism behind this lowered insulin demand remains unknown. An improved insulin economy might contribute to the benefits seen in epidemiological studies with whole grain diets on metabolic risk factors and weight regulation. The objective of this study was to explore the mechanism for a reduced post-prandial insulin demand with rye products.Methods12 healthy subjects were given flour based rye products made from endosperm, whole grain or bran, produced with different methods (baking, simulated sour-dough baking and boiling) as breakfasts in random order in a cross-over design. White wheat bread (WWB) was used as a reference. Blood glucose, serum insulin, plasma ghrelin and subjective satiety were measured during 180 minutes. To evaluate the course of post-meal glycaemia, a measure of the glycaemic profile (GP) was introduced defined as the duration for the incremental post-prandial blood glucose response divided with the blood glucose incremental peak (min/mM).ResultsThe study shows that whole grain rye breads and endosperm rye products induced significantly (p < 0.05) lower insulinaemic indices (IIs) than WWB. Rye bran bread (RBB) produced significantly higher II compared with all the other rye products. Furthermore, the acute insulin response showed better correlations with the GP than with the GI of the products. The endosperm rye bread and the whole grain rye bread with lactic acid induced a significantly higher GP than RBB, WWB, white wheat- and whole grain rye porridge, respectively. A low insulin incremental peak was associated with less severe late post-prandial hypoglycaemia (r = 0.38, p < 0.001), and hypoglycaemia was negatively correlated to subjective satiety at 180 min (r = -0.28, p < 0.05). A low insulin incremental peak was also associated with a milder recovery of plasma ghrelin in the late post-prandial phase (180 min, r = 0.34, p < 0.01).ConclusionOur study shows that endosperm and wholegrain rye products induce low acute insulinaemic responses and improved glycaemic profiles. The results also suggest that the rye products possess beneficial appetite regulating properties. Further studies are needed to identify the unknown property or bioactive component(s) responsible for these beneficial metabolic features of rye.

Trehalose-6-phosphate phosphorylase is part of a novel metabolic pathway for trehalose utilization in Lactococcus lactis.

Lactococcus lactis splits phosphorylated trehalose by the action of inorganic phosphate-dependent trehalose-6-phosphate phosphorylase (TrePP) in a novel catabolic pathway. TrePP was found to catalyze the reversible conversion of trehalose 6-phosphate into β-glucose 1-phosphate and glucose 6-phosphate by measuring intermediate sugar phosphates in cell extracts from trehalose-cultivated lactococci. According to native PAGE and SDS-PAGE, TrePP was shown to be a monomeric enzyme with a molecular mass of 94 kDa. Reaction kinetics suggested that the enzyme follows a ternary complex mechanism with optimal phosphorolysis at 35 °C and pH 6.3. The equilibrium constants were found to be 0.026 and 0.032 at pH 6.3 and 7.0, respectively, favoring the formation of trehalose 6-phosphate. The Michaelis-Menten constants of TrePP for trehalose 6-phosphate, inorganic phosphate, β-glucose 1-phosphate, and glucose 6-phosphate were determined to be 6, 32, 0.9, and 4 mm, respectively. The TrePP-encoding gene, designated trePP, was localized in a putative trehalose operon of L. lactis. This operon includes the gene encoding β-phosphoglucomutase in addition to three open reading frames believed to encode a transcriptional regulator and two trehalose-specific phosphotransferase system components. The identity of trePP was confirmed by determining the N-terminal amino acid sequence of TrePP and by its overexpression inEscherichia coli and L. lactis, as well as the construction of a lactococcal trePP knockout mutant. Furthermore, both TrePP and β-phosphoglucomutase activity were detected in Enterococcus faecalis cell extract, indicating that this bacterium exhibits the same trehalose assimilation route asL. lactis.

Probiotics lower plasma glucose in the high-fat fed C57BL/6J mouse.

Today, the gut microbiota is considered a key organ in host nutritional metabolism and recent data have suggested that alterations in gut microbiota contribute to the development of type 2 diabetes and obesity. Accordingly, a whole range of beneficial effects relating to inflammation and gut health have been observed following administration of probiotics to both humans and different animal models. The objective of this study was to evaluate the metabolic effects of an oral probiotic supplement, Lactobacillus plantarum DSM 15313, to high-fat diet (HFD) fed C57BL/6J mice, a model of human obesity and early diabetes. The mice were fed the experimental diets for 20 weeks, after which the HFD had induced an insulin-resistant state in both groups compared to the start of the study. The increase in body weight during the HFD feeding was higher in the probiotic group than in the control group, however, there were no significant differences in body fat content. Fasting plasma glucose levels were lower in the group fed the probiotic supplement, whereas insulin and lipids were not different. Caecal levels of short-chain fatty acids were not significantly different between the groups. An oral glucose tolerance test showed that the group fed probiotics had a significantly lower insulin release compared to the control group, although the rate of glucose clearance was not different. Taken together, these data indicate that L. plantarum DSM 15313 has anti-diabetic properties when fed together with an HFD.

Physiological Role of β-Phosphoglucomutase in Lactococcus lactis

ABSTRACT A β-phosphoglucomutase (β-PGM) mutant of Lactococcus lactis subsp. lactis ATCC 19435 was constructed using a minimal integration vector and double-crossover recombination. The mutant and the wild-type strain were grown under controlled conditions with different sugars to elucidate the role of β-PGM in carbohydrate catabolism and anabolism. The mutation did not significantly affect growth, product formation, or cell composition when glucose or lactose was used as the carbon source. With maltose or trehalose as the carbon source the wild-type strain had a maximum specific growth rate of 0.5 h−1, while the deletion of β-PGM resulted in a maximum specific growth rate of 0.05 h−1 on maltose and no growth at all on trehalose. Growth of the mutant strain on maltose resulted in smaller amounts of lactate but more formate, acetate, and ethanol, and approximately 1/10 of the maltose was found as β-glucose 1-phosphate in the medium. Furthermore, the β-PGM mutant cells grown on maltose were considerably larger and accumulated polysaccharides which consisted of α-1,4-bound glucose units. When the cells were grown at a low dilution rate in a glucose and maltose mixture, the wild-type strain exhibited a higher carbohydrate content than when grown at higher growth rates, but still this content was lower than that in the β-PGM mutant. In addition, significant differences in the initial metabolism of maltose and trehalose were found, and cell extracts did not digest free trehalose but only trehalose 6-phosphate, which yielded β-glucose 1-phosphate and glucose 6-phosphate. This demonstrates the presence of a novel enzymatic pathway for trehalose different from that of maltose metabolism in L. lactis.

Physiological function of the maltose operon regulator, MalR, in Lactococcus lactis

BackgroundMaltose metabolism is initiated by an ATP-dependent permease system in Lactococcus lactis. The subsequent degradation of intracellular maltose is performed by the concerted action of Pi-dependent maltose phosphorylase and β-phosphoglucomutase. In some Gram-positive bacteria, maltose metabolism is regulated by a maltose operon regulator (MalR), belonging to the LacI-GalR family of transcriptional regulators. A gene presumed to encode MalR has been found directly downstream the maltose phosphorylase-encoding gene, malP in L. lactis. The purpose of this study was to investigate the physiological role of the MalR protein in maltose metabolism in L. lactis.ResultsA L. lactis ssp. lactis mutant, TMB5004, deficient in the putative MalR protein, was physiologically characterised. The mutant was not able to ferment maltose, while its capability to grow on glucose as well as trehalose was not affected. The activity of maltose phosphorylase and β-phosphoglucomutase was not affected in the mutant. However, the specific maltose uptake rate in the wild type was, at its lowest, five times higher than in the mutant. This difference in maltose uptake increased as the maltose concentration in the assay was increased.ConclusionAccording to amino acid sequence similarities, the presumed MalR is a member of the LacI-GalR family of transcriptional regulators. Due to the suggested activating effect on maltose transport and absence of effect on the activities of maltose phosphorylase and β-phosphoglucomutase, MalR of L. lactis is considered rather as an activator than a repressor.

Metabolic effects of whole grain wheat and whole grain rye in the C57BL/6J mouse.

OBJECTIVE A diet rich in whole grain cereals is suggested to protect against type 2 diabetes and facilitate body weight regulation. However, little is known about the impact of different cereals and the underlying mechanisms. The objective of this study was to compare the long-term metabolic effects of diets supplemented with whole grain wheat or whole grain rye in the C57BL/6J mouse. METHODS Mice were fed the whole grain supplements in a low-fat background diet for 22 wk. Oral and intravenous glucose tolerance tests were performed during the study and in vitro insulin secretion assays were performed at the end of the study. Body weight, energy intake, body fat content, and plasma parameters were measured during the study. RESULTS A dietary supplement of whole grain rye suppressed body weight gain and resulted in significantly decreased adiposity, plasma leptin, total plasma cholesterol, and triacylglycerols compared with a supplement of whole grain wheat. Also, a slight improvement in insulin sensitivity was observed in the rye group compared with the wheat group. The decreases in body weight and adiposity were observed in the absence of differences in energy intake. CONCLUSION Long-term administration of whole grain rye evokes a different metabolic profile compared with whole grain wheat in the C57BL/6J mouse, the primary difference being that whole grain rye reduces body weight and adiposity compared with whole grain wheat. In addition, whole grain rye slightly improves insulin sensitivity and lowers total plasma cholesterol.

Rye bran alkylresorcinols suppress adipocyte lipolysis and hormone-sensitive lipase activity

The effects of alkylresorcinols (ARs) isolated from rye bran on adipocyte lipolysis, hormone-sensitive lipase activity and phosphorylation and on phosphorylation of protein kinase A substrates were studied. Preincubation with ARs for 18 h suppressed catecholamine-stimulated lipolysis in 3T3-L1 adipocytes. Furthermore, phosphorylation of hormone-sensitive lipase (HSL), a key lipase responsible for stimulated lipolysis, and phosphorylation of protein kinase A substrates, were diminished after preincubation with ARs, whereas HSL protein expression was unaltered. ARs were also shown to inhibit HSL activity in an in vitro assay.

Effects of rose hip intake on risk markers of type 2 diabetes and cardiovascular disease: a randomized, double-blind, cross-over investigation in obese persons

BACKGROUND/OBJECTIVES:In studies performed in mice, rose hip powder has been shown to both prevent and reverse high-fat diet-induced obesity and glucose intolerance as well as reduce plasma levels of cholesterol. The aim of this study was to investigate whether daily intake of rose hip powder over 6 weeks exerts beneficial metabolic effects in obese individuals.SUBJECTS/METHODS:A total of 31 obese individuals with normal or impaired glucose tolerance were enrolled in a randomized, double-blind, cross-over study in which metabolic effects of daily intake of a rose hip powder drink over 6 weeks was compared with a control drink. Body weight, glucose tolerance, blood pressure, blood lipids and markers of inflammation were assessed in the subjects.RESULTS:In comparison with the control drink, 6 weeks of daily consumption of the rose hip drink resulted in a significant reduction of systolic blood pressure (−3.4%; P=0.021), total plasma cholesterol (−4.9%; P=0.0018), low-density lipoprotein (LDL) cholesterol (−6.0%; P=0.012) and LDL/HDL ratio (−6.5%; P=0.041). The Reynolds risk assessment score for cardiovascular disease was decreased in the rose hip group compared with the control group (−17%; P=0.007). Body weight, diastolic blood pressure, glucose tolerance, and plasma levels of high-density lipoprotein (HDL) cholesterol, triglycerides, incretins and markers of inflammation did not differ between the two groups.CONCLUSIONS:Daily consumption of 40 g of rose hip powder for 6 weeks can significantly reduce cardiovascular risk in obese people through lowering of systolic blood pressure and plasma cholesterol levels.

Rose hip exerts antidiabetic effects via a mechanism involving downregulation of the hepatic lipogenic program

The aim of this study was to investigate the metabolic effects of a dietary supplement of powdered rose hip to C57BL/6J mice fed a high-fat diet (HFD). Two different study protocols were used; rose hip was fed together with HFD to lean mice for 20 wk (prevention study) and to obese mice for 10 wk (intervention study). Parameters related to obesity and glucose tolerance were monitored, and livers were examined for lipids and expression of genes and proteins related to lipid metabolism and gluconeogenesis. A supplement of rose hip was capable of both preventing and reversing the increase in body weight and body fat mass imposed by a HFD in the C57BL/6J mouse. Oral and intravenous glucose tolerance tests together with lower basal levels of insulin and glucose showed improved glucose tolerance in mice fed a supplement of rose hip compared with control mice. Hepatic lipid accumulation was reduced in mice fed rose hip compared with control, and the expression of lipogenic proteins was downregulated, whereas AMP-activated protein kinase and other proteins involved in fatty acid oxidation were unaltered. Rose hip intake lowered total plasma cholesterol as well as the low-density lipoprotein-to-high-density lipoprotein ratio via a mechanism not involving altered gene expression of sterol regulatory element-binding protein 2 or 3-hydroxymethylglutaryl-CoA reductase. Taken together, these data show that a dietary supplement of rose hip prevents the development of a diabetic state in the C57BL/6J mouse and that downregulation of the hepatic lipogenic program appears to be at least one mechanism underlying the antidiabetic effect of rose hip.