Satiating properties of a grape seed proanthocyanidin extract
- Autores: Joan Serrano López
- Directores de la Tesis: Anna Ardévol Grau (dir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: María Puy Portillo Baquedano (presid.), María Josepa Salvadó Rovira (secret.), Inge Depoortere (voc.)
- Programa de doctorado: Programa de Doctorado en Nutrición y Metabolismo por la Universidad Rovira i Virgili
- Materias:
- Enlaces
- Tesis en acceso abierto en: hdl.handle.net TDX
- Resumen
Overweight and obesity are increasingly prevalent in industrialized societies, but also affecting a large segment (35%) of the global population. Due to health issues associated, such as diabetes, cardiovascular disease and certain cancers, takes on special importance in our societies controlling body weight. Since body weight is a product of the energy balance between energy intake and energy expenditure, the first line of intervention for weight control is usually based on the recommendation of a healthy lifestyle, with a varied and controlled diet and moderate physical activity. However, with the increase in the prevalence of overweight is increasingly important to develop new approaches for weight control.
Pharmacological interventions that affect energy expenditure, as well as those that affect the mechanisms regulating food intake at the central nervous system mostly involve associated risks, so its use have not been approved or they were withdrawn from the market. This has focused current research in the development of therapies that reduce intake through modulation of certain gastrointestinal hormones that have important effects on appetite. Since gastrointestinal endocrine cells respond to food components arriving to the gastrointestinal lumen, a standpoint of current research interest is how to modulate the function of these cells through the use of food ingredients, which would allow extend the application of these ingredients for risk populations in the form of dietary supplements, functional foods or simple dietary recommendations. In this regard, our research group previously observed that the administration of an extract of proanthocyanidins from grape seeds (GSPE) increases the production of the intestinal hormone GLP-1 in rats, which is associated with a decrease in appetite.
This led us to hypothesize that the administration of this extract in rats would influence the secretion of major gastrointestinal hormones, thus influencing food intake and body weight. Given that the effects of proanthocyanidins, as well as other minor compounds present in GSPE (monomeric flavanols and phenolic compounds) on appetite and gastrointestinal hormones that control appetite had not been studied in depth, we decided to undertake this thesis. To carry this out, we set three specific objectives: to check whether the administration of this extract has an acute effect on intake; check whether the effective acute dose maintain its effect in the medium term; and to study its effects on the secretion of gastrointestinal hormones and the role of these hormones in the effects on food intake.
For intake studies we designed several studies with rats, while for secretion studies we used both rats, cell cultures and ex vivo tissue segments. Given our interest in the synthesis and secretion of hormones, we mostly used PCR and immunoassays (ELISA, RIA and EIA).
Early acute studies with female rats confirmed a satiating effect of GSPE with the same dose that was previously described to increase GLP-1 (1g/kg). Smaller doses showed satiating effects of GSPE from 0.35g/kg, when administered before the first meal of the animals. Similar results were observed with both male rats and rats subjected to a high-caloric, highly appetitive diet. Before proceeding to administer GSPE in a daily basis, we studied whether the effects on food intake were purely satiating or respond to an adverse, nauseous effect on animals. In this regard, we noted that the administration of 1g/kg GSPE produced no conditional taste aversion to a new flavor, nor induce to eat non-nutritive clay, two common tests to rule out the effect of any nauseating substance.
These results led us to continue the studies on GSPE in subchronic treatments of 8 consecutive days. In a first stage, we observed that both the dose of 1g/kg and 0.5g/kg GSPE maintained a satiating effect throughout the experiment, but in the dose of 1g/kg intake was reduced in the same extent as in the dose of 0.5g/kg (30%). Because proanthocyanidins may hinder the absorption of nutrients, in this experiment we also measured the amount of macronutrients excreted in the feces, observing that both doses of GSPE similarly reduced caloric absorption (2%). These effects resulted in a similar reduction in body weight in both groups, awakening an interest in the dose of 0.5g/kg and showing unnecessary the dose of 1g/kg.
Despite having reached a similar body weight, after 8 days of treatment the growth profiles of the two groups showed differences. The group previously treated with 1g/kg GSPE fattened faster than the group treated with 0.5g/kg, until resuming the body weight of the control group. Once thereafter we proceeded to a second treatment, which highlighted the differences between the two doses. While the dose of 0.5g/kg kept presenting its satiating effect and reduced body weight, the dose of 1g/kg had no effect at all. Furthermore, by indirect calorimetry we observed that despite eating less, the group treated with 0.5g/kg GSPE burnt more energy and fat than the control group, an effect not observed in the group of 1g/kg. Yet, this study shows that GSPE presents interesting effects under daily administration, but only under the right dose.
To consider whether the administration of GSPE modifies gastrointestinal hormone secretion, we analyzed the concentration of three satiating hormones, CCK, PYY and GLP-1, as well as ghrelin, a hormone stimulating appetite, after an acute dose 1g/kg GSPE. Confirming previous results, the administration of GSPE increased the levels of GLP-1, as well as decreased CCK and increased ghrelin. In subchronic studies we focused on the secretion of ghrelin, noting that after 8 days of administration of GSPE this was reduced both in a group treated with 0.5g/kg GSPE and in a group treated with 1g/kg GSPE after 24h of the last dose, both at plasma and gene expression levels.
Given the importance of this hormone in the induction of appetite, and considering that the effects of GSPE had never been studied in depth, we screened the effects of different compounds of GSPE in ghrelin secretion in a cell line producing ghrelin. In this model we observed that the monomeric flavanols stimulate the secretion of ghrelin through interaction with bitter taste receptors, a fact that could explain the observed increase in plasma ghrelin after acute treatments, but also at short-term after a subchronic treatment with GSPE. Moreover, both GSPE, proanthocyanidins and gallic acid proved to inhibit the secretion of ghrelin. In the case of GSPE, we observed similar inhibitory effects working with segments of intestinal tissue.
Since gallic acid not only is found freely in GSPE, but is also formed by microbial degradation of certain proanthocyanidins in the colon, we postulated that this compound could be a bioactive compound of GSPE, which could explain the reduction in ghrelin 24h after the last dose of GSPE in subchronic studies. In this regard, we observed that gallic acid also inhibited the secretion of ghrelin in segments of intestinal tissue and in plasma of rats just after the last dose of an 8 days study. Despite this fact, intake studies on this compound showed a satiating effect only the first day of administration, followed by a gradual adaptation and a total loss of the effect on intake, emphasizing the importance of remaining compounds present in GSPE to maintain a subchronic effect.
In order to determine the role of each hormone in the observed effects in appetite, we used two different approaches in acute and subchronic studies. Acutely, we found that the effects of GSPE and gallic acid are blocked by prior administration of an antagonist of the GLP-1 receptor, targeting this signaling mechanism as responsible for the acute satiating effect observed. Given the impossibility of working subchronically with antagonists or in knock-out models, we made a statistical study of gastrointestinal and hypothalamic gene expressions associated with appetite in rats treated with 0.5 g/kg and 1 g/kg GSPE. The results of these analyses show that the decline in ghrelin and increased GLP-1 signaling in the hypothalamus are related to the decrease in intake in the 0.5g/kg group, as well as the increase of lipolytic activity in subcutaneous adipose tissue. Moreover, the results of this study indicate a counter-regulation of hypothalamic anorexigenic neurons towards excessive GLP-1 signaling, which would explain the resistance to the treatment in the 1g/kg group.
In conclusion, in this thesis we showed that GSPE has a satiating effect in rats under a proper dosage. This effect is dependent of GLP-1 acutely and is related to the decrease in ghrelin and to GLP-1 signaling in the hypothalamus subchronically, which is also related to the lipolytic effect of GSPE. The ranges of effective doses observed, as well as the pathways involved in appetite regulation and the observed the effects of different molecules that make up GSPE will be useful for translational studies in humans.
