Low plasma lactate concentration as a biomarker of an incompetent brain-pull: a risk factor for weight gain in type 2 diabetes patients.

OBJECTIVE: Body weight development is closely regulated by central nervous mechanisms. As has been demonstrated recently, the capability of the brain to actively demand energy from the body (brain-pull) is indispensable for the maintenance of systemic homeostasis. A deficit in this brain-pull may result in compensatory ingestive behavior followed by weight gain in the medium or long term. The aim of this study was to establish a biomarker of such an incompetent brain-pull. Since lactate is an alternative cerebral energy substrate to glucose, we investigated whether low fasting plasma lactate concentrations are associated with weight gain and increased feelings of hunger in patients with type 2 diabetes over a 3-year period. METHODS: In a population based cohort study 134 type 2 diabetes patients were examined at baseline and 3-year follow-up. Plasma lactate concentrations and additional hormones associated with food intake such as e.g. insulin, or leptin, as well as psychological variables like hunger feelings before and after a standardized breakfast were measured. The relation between fasting plasma lactate concentrations and postprandial hunger as well as follow-up weight was analyzed. RESULTS: Low fasting plasma lactate concentrations predicted a higher 3-year follow-up weight (B=-1.268, SE=0.625, p=0.04). Moreover, low fasting plasma lactate concentrations were associated with more pronounced feelings of postprandial hunger (B=-0.406, SE=0.137, p<0.01). CONCLUSIONS: We conclude that low plasma lactate concentrations may represent a biomarker of an incompetent brain-pull, which is associated with weight gain and increased postprandial hunger in patients with type 2 diabetes mellitus. These results are in line with the view that plasma lactate can be used by the brain as an alternative energy substrate and thereby to some extent prevent overeating and obesity.

In vivo quantification of neuro-glial metabolism and glial glutamate concentration using 1H-[13C] MRS at 14.1T.

Astrocytes have recently become a major center of interest in neurochemistry with the discoveries on their major role in brain energy metabolism. An interesting way to probe this glial contribution is given by in vivo (13) C NMR spectroscopy coupled with the infusion labeled glial-specific substrate, such as acetate. In this study, we infused alpha-chloralose anesthetized rats with [2-(13) C]acetate and followed the dynamics of the fractional enrichment (FE) in the positions C4 and C3 of glutamate and glutamine with high sensitivity, using (1) H-[(13) C] magnetic resonance spectroscopy (MRS) at 14.1T. Applying a two-compartment mathematical model to the measured time courses yielded a glial tricarboxylic acid (TCA) cycle rate (Vg ) of 0.27 ± 0.02 μmol/g/min and a glutamatergic neurotransmission rate (VNT ) of 0.15 ± 0.01 μmol/g/min. Glial oxidative ATP metabolism thus accounts for 38% of total oxidative metabolism measured by NMR. Pyruvate carboxylase (VPC ) was 0.09 ± 0.01 μmol/g/min, corresponding to 37% of the glial glutamine synthesis rate. The glial and neuronal transmitochondrial fluxes (Vx (g) and Vx (n) ) were of the same order of magnitude as the respective TCA cycle fluxes. In addition, we estimated a glial glutamate pool size of 0.6 ± 0.1 μmol/g. The effect of spectral data quality on the fluxes estimates was analyzed by Monte Carlo simulations. In this (13) C-acetate labeling study, we propose a refined two-compartment analysis of brain energy metabolism based on (13) C turnover curves of acetate, glutamate and glutamine measured with state of the art in vivo dynamic MRS at high magnetic field in rats, enabling a deeper understanding of the specific role of glial cells in brain oxidative metabolism. In addition, the robustness of the metabolic fluxes determination relative to MRS data quality was carefully studied.

Genome-wide analysis of SREBP1 activity around the clock reveals its combined dependency on nutrient and circadian signals.

In mammals, the circadian clock allows them to anticipate and adapt physiology around the 24 hours. Conversely, metabolism and food consumption regulate the internal clock, pointing the existence of an intricate relationship between nutrient state and circadian homeostasis that is far from being understood. The Sterol Regulatory Element Binding Protein 1 (SREBP1) is a key regulator of lipid homeostasis. Hepatic SREBP1 function is influenced by the nutrient-response cycle, but also by the circadian machinery. To systematically understand how the interplay of circadian clock and nutrient-driven rhythm regulates SREBP1 activity, we evaluated the genome-wide binding of SREBP1 to its targets throughout the day in C57BL/6 mice. The recruitment of SREBP1 to the DNA showed a highly circadian behaviour, with a maximum during the fed status. However, the temporal expression of SREBP1 targets was not always synchronized with its binding pattern. In particular, different expression phases were observed for SREBP1 target genes depending on their function, suggesting the involvement of other transcription factors in their regulation. Binding sites for Hepatocyte Nuclear Factor 4 (HNF4) were specifically enriched in the close proximity of SREBP1 peaks of genes, whose expression was shifted by about 8 hours with respect to SREBP1 binding. Thus, the cross-talk between hepatic HNF4 and SREBP1 may underlie the expression timing of this subgroup of SREBP1 targets. Interestingly, the proper temporal expression profile of these genes was dramatically changed in Bmal1-/- mice upon time-restricted feeding, for which a rhythmic, but slightly delayed, binding of SREBP1 was maintained. Collectively, our results show that besides the nutrient-driven regulation of SREBP1 nuclear translocation, a second layer of modulation of SREBP1 transcriptional activity, strongly dependent from the circadian clock, exists. This system allows us to fine tune the expression timing of SREBP1 target genes, thus helping to temporally separate the different physiological processes in which these genes are involved.

Exploring the mechanisms regulating nutrient bioavailability and lipid metabolism through a nutrigenomics approach

SUMMARY Following the complete sequencing of the human genome, the field of nutrition has begun utilizing this vast quantity of information to comprehensively explore the interactions between diet and genes. This approach, coined nutrigenomics, aims to determine the influence of common dietary ingredients on the genome, and attempts to relate the resulting different phenotypes to differences in the cellular and/or genetic response of the biological system. However, complementary to defining the biological outcomes of dietary ingredients, we must also understand the influence of the multiple factors (such as the microbiota, bile, and function of transporters) that may contribute to the bioavailability, and ultimately bioefficacy, of these ingredients. The gastrointestinal tract (GIT) is the body's foremost tissue boundary, interacting with nutrients, exogenous compounds and microbiota, and whose condition is influenced by the complex interplay between these environmental factors and genetic elements. In order to understand GIT nutrient-gene interactions, our goal was to comprehensively elucidate the region-specific gene expression underlying intestinal functions. We found important regional differences in the expression of members of the ATP-binding cassette family of transporters in the mouse intestine, suggesting that absorption of dietary compounds may vary along the GIT. Furthermore, the influence of the microbiota on host gene expression indicated that this luminal factor predominantly influences immune function and water transport throughout the GIT; however, the identification of region-specific functions suggest distinct host-bacterial interactions along the GIT. Thus, these findings reinforce that to understand nutrient bioavailability and GIT function, one must consider the physiologically distinct regions of the gut. Nutritional molecules absorbed by the enterocytes of the GIT enter circulation and will be selectively absorbed and metabolised by tissues throughout the body; however, their bioefficacy in the body will depend on the unique and shared molecular mechanisms of the various tissues. Using a nutrigenomic approach, the biological responses of the liver and hippocampus of mice fed different long chain-polyunsaturated fatty acids diets revealed tissue-specific responses. Furthermore, we identified stearoyl-CoA desaturase as a hepatic target for arachidonic acid, suggesting a potentially novel molecular mechanism that may protect against diet-induced obesity. In summary, this work begins to unveil the fundamentally important role that nutrigenomics will play in unravelling the molecular mechanisms, and those exogenous factors capable of influencing these mechanisms, that regulate the bioefficacy of nutritional molecules. RÉSUMÉ Suite au séquençage complet du génome humain, le domaine de la nutrition a commencé à utiliser cette vaste quantité d'information pour explorer de manière globale les interactions entre la nourriture et les gènes. Cette approche, appelée « nutrigenomics », a pour but de déterminer l'influence d'ingrédients couramment utilisés dans l'alimentation sur le génome, et d'essayer de relier ces différents phénotypes, ainsi révélés, à des différences de réponses cellulaires et/ou génétiques. Cependant, en plus de définir les effets biologiques d'ingrédients alimentaires, il est important de comprendre l'influence des multiples facteurs (telle que la microflore, la bile et la fonction des transporteurs) pouvant contribuer à la bio- disponibilité et par conséquent à l'efficacité de ces ingrédients. Le tractus gastro-intestinal (TGI), qui est la première barrière vers les tissus, interagit avec les nutriments, les composés exogènes et la microflore. La fonction de cet organe est influencée par les interactions complexes entre les facteurs environnementaux et les éléments génétiques. Dans le but de comprendre les interactions entre les nutriments et les gènes au niveau du TGI, notre objectif a été de décrire de manière globale l'expression génique spécifique de chaque région de l'intestin définissant leurs fonctions. Nous avons trouvé d'importantes différences régionales dans l'expression des transporteurs de la famille des « ATP-binding cassette transporter » dans l'intestin de souris, suggérant que l'absorption des composés alimentaires puisse varier le long de l'intestin. De plus, l'étude des effets de la microflore sur l'expression des gènes hôtes a indiqué que ce facteur de la lumière intestinale influence surtout la fonction immunitaire et le transport de l'eau à travers l'intestin. Cependant, l'identification des fonctions spécifiques de chaque région suggère des interactions distinctes entre l'hôte et les bactéries le long de l'intestin. Ainsi, ces résultats renforcent l'idée que la compréhension de la bio-disponibilité des nutriments, et par conséquent la fonction du TGI, doit prendre en considération les différences régionales. Les molécules nutritionnelles transportées par les entérocytes jusqu'à la circulation sanguine, sont ensuite sélectivement absorbées et métabolisées par les différents tissus de l'organisme. Cependant, leur efficacité biologique dépendra du mécanisme commun ou spécifique de chaque tissu. En utilisant une approche « nutriogenomics », nous avons pu mettre en évidence les réponses biologiques spécifiques du foie et de l'hippocampe de souris nourris avec des régimes supplémentés avec différents acides gras poly-insaturés à chaîne longue. De plus, nous avons identifié la stearoyl-CoA desaturase comme une cible hépatique pour l'acide arachidonique, suggérant un nouveau mécanisme moléculaire pouvant potentiellement protéger contre le développement de l'obésité. En résumé, ce travail a permis de dévoiler le rôle fondamental qu'une approche telle que la « nutrigenomics » peut jouer dans le décryptage des mécanismes moléculaires et de leur régulation par des facteurs exogènes, qui ensemble vont contrôler l'efficacité biologique des nutriments.

Correlation between plasma concentration of cilazapril and haemodynamic and hormonal effects in healthy man.

1. The haemodynamic and humoral effects of cilazapril, a new angiotensin converting enzyme (ACE) inhibitor, were evaluated in normotensive healthy volunteers. 2. Single oral doses of 1.25, 2.5, 5 and 10 mg of cilazapril inhibited ACE by greater than or equal to 90% and induced the expected pattern of changes of the renin-angiotensin-aldosterone-system. 3. Cilazapril had a long duration of action, since some ACE inhibition was still present 72 h after drug intake. 4. Cilazapril administered intravenously at doses of 5 and 20 micrograms kg-1 for 24 h did not produce any significant effects. 5. During repeated administration of cilazapril for 8 days, no accumulation of cilazaprilat was observed and the clinical tolerance was excellent. 6. In normal volunteers, cilazapril administered orally acts as a potent inhibitor of converting enzyme.

Net increase of lactate and glutamate concentration in activated human visual cortex detected with magnetic resonance spectroscopy at 7 tesla.

After the landmark studies reporting changes in the cerebral metabolic rate of glucose (CMRGlc ) in excess of those in oxygen (CMRO2 ) during physiological stimulation, several studies have examined the fate of the extra carbon taken up by the brain, reporting a wide range of changes in brain lactate from 20% to 250%. The present study reports functional magnetic resonance spectroscopy measurements at 7 Tesla using the enhanced sensitivity to study a small cohort (n = 6). Small increases in lactate (19% ± 4%, P < 0.05) and glutamate (4% ± 1%, P < 0.001) were seen within the first 2 min of activation. With the exception of glucose (12% ± 5%, P < 0.001), no other metabolite concentration changes beyond experimental error were significantly observed. Therefore, the present study confirms that lactate and glutamate changes during physiological stimulation are small (i.e. below 20%) and shows that the increased sensitivity allows reproduction of previous results with fewer subjects. In addition, the initial rate of glutamate and lactate concentration increases implies an increase in CMRO2 that is slightly below that of CMRGlc during the first 1-2 min of activation.

Substrate metabolism, nutrient balance and obesity development in children and adolescents: a target for intervention?

Obesity results from the organism's inability to maintain energy balance over a long term. Childhood obesity and its related factors and pathological consequences tend to persist into adulthood. A cluster of factors, including high energy density in the diet (high fat intake), low energy expenditure, and disturbed substrate oxidation, favour the increase in fat mass. Oxidation of three major macronutrients and their roles in the regulation of energy balance, particularly in children and adolescents, are discussed. Total glucose oxidation is not different between obese and lean children; exogenous glucose utilization is higher whereas endogenous glucose utilization is lower in obese compared with lean children. Carbohydrate composition of the diet determines carbohydrate oxidation regardless of fat content of the diet. Both exogenous and endogenous fat oxidation are higher in obese than in lean subjects. The influence of high fat intake on accumulation of fat mass is operative rather over a long term. Several future directions are addressed, such that a combination of increased physical activity and modification in diet composition, in terms of energy density and glycemic index, is recommended for children and adolescents.

Ad libitum intake of a high-carbohydrate or high-fat diet in young men: effects on nutrient balances.

The effect of diet composition [high-carbohydrate, low-fat (HC) and high-fat, low-carbohydrate (HF) diets] on macronutrient intakes and nutrient balances was investigated in young men of normal body weight. Eleven subjects were studied on two occasions for 48 h in a whole-body indirect calorimeter in a crossover design. Subjects selected their meals from a list containing a large variety of common food, which had a food quotient > 0.85 for the HC diet and < 0.85 for the HF diet. The average ad libitum intake was 14.41 +/- 0.85 MJ/d (67%, 18%, and 15% of energy as carbohydrate, fat, and protein, respectively) with the HC diet and 18.25 +/- 0.90 MJ/d (26%, 61%, and 13% of energy as carbohydrate, fat, and protein, respectively) with the HF diet. Total energy expenditure was not significantly influenced by diet composition: 10.46 +/- 0.27 and 10.97 +/- 0.22 MJ/d for the HC and HF diets, respectively. During the 2 test days, cumulative carbohydrate storage was 418 +/- 72 and 205 +/- 47 g, and fat balance was 29 +/- 17 and 291 +/- 29 g with the HC and HF diets, respectively. Only the HF diet induced a significantly positive fat balance. These results emphasize the important role of the dietary fat content in body fat storage.

Binding of low concentration of peptide to H-2Kd produced in insect cells requires mouse beta 2-microglobulin co-expression.

A recombinant baculovirus expressing the murine class I MHC heavy chain H-2Kd cDNA under the transcriptional control of Autografa californica nuclear polyhedrosis virus (AcNPV) polyhedrin promoter has been isolated and used to infect Sf9 lepidopteran cells either alone or in association with a previously isolated virus expressing mouse beta 2-microglobulina (beta 2-ma). When infected with the heavy chain-encoding virus alone, H-2Kd was produced in a beta 2-m-free conformation detected on the surface of infected cells by conformation-independent antibodies. When Sf9 cells were co-infected with both viruses, approximately 10% of the heavy chain pool was engaged in the formation of native heterodimeric MHC class I molecules, which were glycosylated and transported to the cell surface as demonstrated by radio-binding experiments and flow cytometry. The assembly of the recombinant class I molecule was dependent on peptide, since heterodimer formation was brought about by H-2Kd-specific peptide ligands both in vivo, upon incubation with dually infected cells, and in vitro, in cell-free detergent extracts. In addition, a change in heavy chain conformation was brought about upon incubation with high concentrations (100 microM) of an H-2Kd-restricted octapeptide epitope from Plasmodium berghei. Furthermore, using low concentrations (3 nM) of a photoaffinity label derivative of this peptide, we show direct binding to cells co-expressing class I heavy chain and mouse beta 2-m but not to cells expressing free heavy chain only.

Effect of chronic hypoglycaemia on glucose concentration and glycogen content in rat brain: A localized 13C NMR study.

While chronic hypoglycaemia has been reported to increase unidirectional glucose transport across the blood-brain barrier (BBB) and to increase GLUT1 expression at the endothelium, the effect on steady-state brain d-glucose and brain glycogen content is currently unknown. Brain glucose and glycogen concentrations were directly measured in vivo using localized 13C magnetic resonance spectroscopy (MRS) following 12-14 days of hypoglycaemia. Brain glucose content was significantly increased by 48%, which is consistent with an increase in the maximal glucose transport rate, Tmax, by 58% compared with the sham-treated animals. The localized 13C NMR measurements of brain glucose were directly validated by comparison with biochemically determined brain glucose content after rapid focused microwave fixation (1.4 s at 4 kW). Both in vivo MRS and biochemical measurements implied that brain glycogen content was not affected by chronic hypoglycaemia, consistent with brain glucose being a major factor controlling brain glycogen content. We conclude that the increased glucose transporter expression in chronic hypoglycaemia leads to increased brain glucose content at a given level of glycaemia. Such increased brain glucose concentrations can result in a lowered glycaemic threshold of counter-regulation observed in chronic hypoglycaemia.

Influence of sex and age on T3 receptors and T3 concentration in the pituitary gland of the rat: consequences on TSH secretion.

A reduced secretion of thyroid hormones with age has been documented in humans and animals with no substantial increase in TSH secretion, which may be indicative of an age-related impairment of the pituitary sensitivity to the negative control exerted by thyroid hormones. We have evaluated in rats the influence of sex and age on pituitary T3 nuclear receptors--known to be determinant in the regulation of TSH secretion--as well as on T3 concentration in the pituitary gland. As regards sex, the density of T3 receptors and the concentration of T3 in pituitary gland and plasma were greater in females than in males whereas pituitary and plasma TSH concentrations were less. As for age, the density of T3 receptors was greater in old male rats than in young ones with no changes in pituitary T3 and plasma TSH concentrations. In old female rats in contrast, there was no significant increase in T3 receptors but pituitary T3 was less and plasma TSH greater than in young female rats. In both sexes plasma thyroid hormones and pituitary TSH were reduced with age whereas TSH response to TRH was not altered. These results illustrate sex and age differences in pituitary T3 receptors and pituitary T3 concentration as well as in TSH secretion. In young animals of both sexes an inverse correlation is observed between the density of pituitary T3 receptors and plasma TSH. In contrast, in old animals the absence of this correlation is suggestive of an age-related impairment of T3 action on the thyrotrophs or of changes pertaining to other factors modulating TSH secretion.

Amniotic fluid insulin-like growth factor binding-protein 3 concentration as early indicator of fetal growth restriction

Rapport de synthèse : Introduction : La croissance foetale infra-utérine dépend d'un grand nombre de facteurs maternels, placentaires et foetaux. Une inadéquation d'un ou plusieurs de ces facteurs peut induire un retard de croissance infra-utérin (RCIU) ou au contraire une macrosomie. Les principales causes de RCIU comprennent les infections maternelles, l'éclampsie, les cardiovasculopathies maternelles, la toxicomanie, les malformations foetales et les insuffisances placentaires. Les facteurs endocriniens constituent un petit pourcentage des causes de RCIU, mais méritent que l'on s'y intéresse de plus près. Les facteurs hormonaux les plus importants pour la croissance fatale sont l'insuline et les insuline-like growth factors (IGFs) et non l'hormone de croissance (GH) qui joue un rôle majeur dans la croissance postnatale. Notre attention s'est portée sur IGF-1 qui joue un rôle important dans la croissance intrautérine. Sa biodisponibilité dépend de plusieurs protéines plasmatiques, les IGF-binding proteins (IGFBP 1 à 9). IGFBP-3 est la principale de ces IGFBPs, autant d'un point de vue quantitatif que fonctionnel. Nous avons cherché à déterminer si les concentrations d'IGF-1 et d'IGFBP-3 dans le liquide amniotique au début du deuxième trimestre étaient prédictives de la croissance infra-utérine. Les gènes codant pour IGF-1 et IGFBP-3 contenant certaines séquences polymorphiques, nous avons également étudié leur influence sur la croissance foetale. L'analyse du liquide amniotique présente l'avantage de pouvoir être effectuée dès la 14ème semaine d'aménorrhée alors que la biométrie foetale échographique ne permet pas à ce stade de déceler des anomalies de la croissance infra-utérine. Méthode : Nous avons analysé des échantillons de liquide amniotique prélevés entre la 14ème et la 18ème semaine de grossesse chez 196 patientes. Les concentrations d'IGF-1 et d'IGFBP-3 ont été dosées par ELISA, les polymorphismes analysés par PCR. Ces résultats ont été ensuite analysés en fonction du poids de naissance des nouveaux-nés, répartis en trois groupes normal pour l'âge gestationnel (AGA), petit pour l'âge gestationnel (SGA) et grand pour l'âge gestationnel (LGA). Résultats : Les concentrations d'IGFBP3 dans le liquide amniotique sont significativement plus élevées (p = 0.030) dans le groupe SGA par rapport au groupe AGA, d'autant plus quand les taux sont ajustés en fonction de paramètres tels que l'âge gestationnel lors de l'amniocentèse (ANCOVA analysis : p = 0.009). La distribution du polymorphisme VNTR (variable number of tandem repeat) dans la région promotrice d'IGF-1 au sein du groupe SGA est significativement différente de celle du groupe AGA (p = 0.029). En effet, la fréquence de l'association allélique 19CA/20CA est diminuée dans le groupe SGA. Nous n'avons pas identifié de différence de distribution des séquences polymorphiques d'IGFBP-3 entre les différents groupes. Conclusion : Une concentration élevée d'IGFBP-3 dans le liquide amniotique au début du deuxième trimestre est associée à un risque plus élevé de retard de croissance alors que l'association allélique 19CA/20CA dans la région polymorphique IGF-1 VNTR est un facteur protecteur.

Personalized modeling for drug concentration prediction using Support Vector Machine

Building a personalized model to describe the drug concentration inside the human body for each patient is highly important to the clinical practice and demanding to the modeling tools. Instead of using traditional explicit methods, in this paper we propose a machine learning approach to describe the relation between the drug concentration and patients' features. Machine learning has been largely applied to analyze data in various domains, but it is still new to personalized medicine, especially dose individualization. We focus mainly on the prediction of the drug concentrations as well as the analysis of different features' influence. Models are built based on Support Vector Machine and the prediction results are compared with the traditional analytical models.