Patricia Pérez-Matute

Eicosapentaenoic acid actions on adiposity and insulin resistance in control and high-fat-fed rats: role of apoptosis, adiponectin and tumour necrosis factor-α

n-3 PUFA have shown potential anti-obesity and insulin-sensitising properties. However, the mechanisms involved are not clearly established. The aim of the present study was to assess the effects of EPA administration, one of the n-3 PUFA, on body-weight gain and adiposity in rats fed on a standard or a high-fat (cafeteria) diet. The actions on white adipose tissue lipolysis, apoptosis and on several genes related to obesity and insulin resistance were also studied. Control and cafeteria-induced overweight male Wistar rats were assigned into two subgroups, one of them daily received EPA ethyl ester (1 g/kg) for 5 weeks by oral administration. The high-fat diet induced a very significant increase in both body weight and fat mass. Rats fed with the cafeteria diet and orally treated with EPA showed a marginally lower body-weight gain (P = 0.09), a decrease in food intake (P < 0.01) and an increase in leptin production (P < 0.05). EPA administration reduced retroperitoneal adipose tissue weight (P < 0.05) which could be secondary to the inhibition of the adipogenic transcription factor PPARgamma gene expression (P < 0.001), and also to the increase in apoptosis (P < 0.05) found in rats fed with a control diet. TNFalpha gene expression was significantly increased (P < 0.05) by the cafeteria diet, while EPA treatment was able to prevent (P < 0.01) the rise in this inflammatory cytokine. Adiposity-corrected adiponectin plasma levels were increased by EPA. These actions on both TNFalpha and adiponectin could explain the beneficial effects of EPA on insulin resistance induced by the cafeteria diet.

Reactive species and diabetes: counteracting oxidative stress to improve health.

Oxidative stress is at the very core of metabolism. Reactive species behave as true second messengers that control important cellular functions. However, under pathological conditions, abnormally large concentrations of these species may lead to permanent changes in signal transduction and gene expression. Attenuation of oxidative stress as a way to improve several diseases such as diabetes has flourished as one of the main challenges of research. The lack of evidence to prove the benefits from antioxidant compounds has led to boost these strategies. Inhibition of reactive oxygen species (ROS) production through the development of inhibitors against NADPH oxidase and mitochondria offers an alternative approach to conventional antioxidant therapies. There is a need to understand oxidative stress process to implement health-disorder approaches.

Role of obesity-associated dysfunctional adipose tissue in cancer: A molecular nutrition approach

Obesity is a complex disease caused by the interaction of a myriad of genetic, dietary, lifestyle and environmental factors, which favors a chronic positive energy balance, leading to increased body fat mass. There is emerging evidence of a strong association between obesity and an increased risk of cancer. However, the mechanisms linking both diseases are not fully understood. Here, we analyze the current knowledge about the potential contribution that expanding adipose tissue in obesity could make to the development of cancer via dysregulated secretion of pro-inflammatory cytokines, chemokines and adipokines such as TNF-α, IL-6, leptin, adiponectin, visfatin and PAI-1. Dietary factors play an important role in the risk of suffering obesity and cancer. The identification of bioactive dietary factors or substances that affect some of the components of energy balance to prevent/reduce weight gain as well as cancer is a promising avenue of research. This article reviews the beneficial effects of some bioactive food molecules (n-3 PUFA, CLA, resveratrol and lipoic acid) in energy metabolism and cancer, focusing on the molecular mechanisms involved, which may provide new therapeutic targets in obesity and cancer.

Lipoic acid prevents body weight gain induced by a high fat diet in rats: Effects on intestinal sugar transport

Several studies have suggested that oxidative stress might cause and aggravate the inflammatory state associated with obesity and could be the link between excessive weight gain and its related disorders such as insulin resistance and cardiovascular diseases. Thus, antioxidant treatment has been proposed as a therapy to prevent and manage obesity and associated complications. Therefore, the aim of the present study was to investigate the effects of supplementation of a standard or high fat diet with the antioxidant lipoic acid (LA) during 56 days, on body weight gain, adiposity, feed efficiency and intestinal sugar absorption, in male Wistar rats. LA supplementation induced a lower body weight gain and adipose tissue size in both control or high fat fed rats accompanied by a reduction in food intake. The group fed on a high fat diet and treated with LA (OLIP group) showed a lower body weight gain than its corresponding Pair-Fed (PF) group (P<0.05), which received the same amount of food than LA-treated animals but with no LA. In fact, LA induced a reduction on feed efficiency and also significantly decreased intestinal α-methylglucoside (α-MG) absorption both in lean and obese rats. These results suggest that the beneficial effects of dietary supplementation with LA on body weight gain are mediated, at least in part, by the reduction observed in food intake and feed efficiency. Furthemore, the inhibitory action of LA on intestinal sugar transport could explain in part the lower feed efficiency observed in LA-treated animals and therefore, highlighting the beneficial effects of LA on obesity.ResumenVarios estudios han sugerido que el estrés oxidativo podría actuar como desencadenante y agravante del estado inflamatorio asociado a la obesidad y podría ser un potencial nexo de unión entre la excesiva ganancia de peso y las co-morbilidades asociadas. Así, se ha propuesto el tratamineto con antioxidantes naturales como posible terapia contra el desarrollo de obesidad así como sus complicaciones asociadas. Por ello, el objeto del presente trabajo fue investigar en ratas Wistar macho los efectos de la suplementación de una dieta estándar o alta en grasa con un antioxidante, el ácido lipoico (AL) (0,25g/ 100g de comida) durante 56 días sobre la ganancia de peso corporal, la adiposidad, la eficiencia metabólica y la absorción intestinal de azúcares. La suplementación de la dieta con AL indujo una menor ganacia de peso corporal y redujo el tamaño del tejido adiposo blanco total, tanto en ratas alimentadas con dieta control como alta en grasa. Además, disminuyó la ingesta. La ganancia de peso en el grupo alimentado con dieta alta en grasa y AL fue menor que la de su correspondiente grupoPair-Fed (P<0,05), el cual recibía la misma cantidad de comida que los animales tratados con AL pero sin este ácido. De hecho, la suplementación con ácido lipoico redujo la eficiencia metabólica y disminuyó significativamente la absorción intestinal de α-metilglucósido (α-MG) tanto en ratas control como obesas. Estos resultados sugieren que los efectos beneficiosos de la suplementación de la dieta con AL sobre la ganancia de peso corporal están mediados, al menos en parte, por la reducción observada en la ingesta de comida y en la eficiencia metabólica. Además, la acción inhibitoria del AL sobre el transporte intestinal de azúcares podría explicar, en parte, la menor eficiencia metabólica observada en los animales tratados con AL justificando, por consiguiente, los efectos beneficiosos del AL sobre la obesidad.

Effects of eicosapentaenoic acid (EPA) on adiponectin gene expression and secretion in primary cultured rat adipocytes

Adiponectin, a hormone produced by adipocytes, is involved in glucose metabolism and insulin sensitivity. The production of this adipokine is impaired in obesity and insulin resistance. Eicosapentaenoic acid (EPA) is a dietary n-3 polyunsaturated fatty acid that improves insulin sensitivity in several models of obesity and diabetes, which has been suggested to be related to adiponectin induction. An increase in adiponectin production has been also associated with an up-regulation of the transcriptional factor PPARγ. The aim of this trial was to evaluate the direct effects of EPA on adiponectin gene expression and protein secretion in isolated rat adipocytes as well as to explore the potential mechanisms involved. A comparative study with troglitazone, a PPARγ agonist, was also performed. For these purposes, primary rat adipocytes were cultured with EPA (100 and 200 μM) and with troglitazone (10 μM) for 96 hours. Both EPA and troglitazone improved glucose utilization by adipocytes. As expected, troglitazone enhanced adiponectin secretion and increased PPARγ gene expression. However, EPA significantly decreased adiponectin gene expression and protein secretion and reduced PPARγ mRNA levels, suggesting that the inhibition of adiponectin by EPA is likely to be secondary to the down-regulation of this adipogenic transcription factor. Moreover, these results suggest that other mechanisms different from the direct stimulation of adiponectin by the fatty acid are underlying the insulin-sensitizing properties observed after EPA treatment in vivo.ResumenLa adiponectina es una hormona producida por los adipocitos que esta implicada en el metabolismo de la glucosa y la sensibilidad a insulina. Situaciones de obesidad y resistencia insulínica se han asociado con hipoadiponectinemia. El ácido eicosapentaenoico (EPA) es un acido graso poliinsaturado omega-3 que mejora la sensibilidad a la insulina en diversos modelos de obesidad y diabetes, y se ha sugerido que esto podría estar relacionado con un incremento en la producción de adiponectina. Por otra parte, se ha observado que la activación del factor de transcripción PPARγ induce aumento en la producción de adiponectina. El objetivo del presente trabajo fue evaluar los efectos directos del EPA sobre la expresión génica y la secreción de adiponectina en adipocitos primarios de rata, así como investigar los potenciales mecanismos implicados. Además, se realizó un estudio comparativo con las acciones de la troglitazona, un agonista de PPARγ. Los adipocitos primarios de rata se cultivaron con EPA (100 y 200 μM) o con troglitazona (10 μM) durante 96 horas. Ambos tratamientos mejoraron la utilización de glucosa y como era de esperar, la troglitazona incrementó la secreción de adiponectina y la expresión de PPARγ. Sin embargo, el EPA disminuyó significativamente la secreción y expresión génica de adiponectina, además de reducir los niveles de ARNm de PPARγ, sugiriendo que la inhibición de la adiponectina causada por el EPA podría ser secundaria a la reducción del factor de transcripción PPARγ. Estos hallazgos sugieren que las propiedades insulino-sensibilizadoras observadas tras los tratamientos con EPA in vivo no derivan del incremento directo de la adiponectina.

Conjugated linoleic acid inhibits glucose metabolism, leptin and adiponectin secretion in primary cultured rat adipocytes

Conjugated linoleic acid (CLA) supplementation has been reported to induce insulin resistance in animals and humans, however, the underlying mechanisms remain unclear. The aim of this study was to examine the direct effects of CLA on leptin and adiponectin secretion, two hormones with actions known to influence insulin sensitivity. Isolated rat adipocytes were incubated with CLA (1-200microM) in the absence and presence of insulin (1.6nM). CLA inhibited both basal and insulin-stimulated leptin gene expression and secretion (-30 to -40%, P<0.05-0.01). CLA also inhibited basal adiponectin production (-20 to -40%, P<0.05-0.01), but not in the presence of insulin. CLA (50-200muM) decreased basal glucose uptake (P<0.05-0.01) and significantly increased the proportion of glucose metabolized to lactate (P<0.01). Insulin treatment partially prevented the inhibitory effects of CLA on glucose uptake and induced a significant increase (P<0.05-0.01) in the percentage of glucose metabolized to lactate. A strong inverse relationship was observed between the increase in the anaerobic utilization of glucose and the decreases of both leptin and adiponectin secretion. In addition, lipolysis and the expression of the adipogenic transcription factor PPARgamma were decreased by CLA. These results indicate that CLA inhibits leptin and adiponectin secretion and suggest that increased anaerobic metabolism of glucose may be involved in these effects. The inhibition of PPARgamma could also mediate the inhibition of adiponectin induced by CLA. Furthermore, the inhibition of leptin and adiponectin production induced by CLA may contribute to insulin resistance observed in CLA-treated animals and humans.

Lipoic Acid Improves Mitochondrial Function in Nonalcoholic Steatosis through the Stimulation of Sirtuin 1 and Sirtuin 3

Nonalcoholic steatosis is an important hepatic complication of obesity linked to mitochondrial dysfunction and oxidative stress. Lipoic acid (LA) has been reported to have beneficial effects on mitochondrial function and to attenuate oxidative stress. The sirtuin (SIRT) family has been demonstrated to play an important role in the regulation of mitochondrial function and in the activation of antioxidant defenses. In this study, we analyzed the potential protective effect of LA supplementation, via the modulation of mitochondrial defenses through the SIRT pathway, against oxidative stress associated with high‐fat feeding. Wistar rats were fed a standard diet (control group (C), n = 10), a high‐fat diet (obese group (OB), n = 10) and a high‐fat diet supplemented with LA (OLIP, n = 10). A group pair‐fed to the latter group (pair‐fed OLIP group (PFO), n = 6) was also included. LA prevented hepatic triglyceride (TG) accumulation (−68.2%) and liver oxidative damage (P < 0.01) through the inhibition of hydroperoxide (H2O2) production (P < 0.001) and the stimulation of mitochondrial antioxidant defenses. LA treatment upregulated manganese superoxide dismutase (SOD2) (60.6%) and glutathione peroxidase (GPx) (100.2%) activities, and increased the reduced glutathione (GSH): oxidized glutathione (GSSG) ratio and UCP2 mRNA levels (P < 0.001–P < 0.01). Moreover, this molecule reduced oxidative damage in mitochondrial DNA (mtDNA) and increased mitochondrial copy number (P < 0.001– P < 0.01). LA treatment decreased the acetylation levels of Forkhead transcription factor 3a (Foxo3a) and PGC1β (P < 0.001–P < 0.01) through the stimulation of SIRT3 and SIRT1 (P < 0.001). In summary, our results demonstrate that the beneficial effects of LA supplementation on hepatic steatosis could be mediated by its ability to restore the oxidative balance by increasing antioxidant defenses through the deacetylation of Foxo3a and PGC1β by SIRT1 and SIRT3.

Effects of eicosapentaenoic acid ethyl ester on visfatin and apelin in lean and overweight (cafeteria diet-fed) rats

Previous studies have demonstrated that the n-3 fatty acid EPA improves insulin resistance induced by high-fat diets. The aim of the present study was to investigate the potential role of visfatin and apelin in the insulin-sensitising effects of EPA ethyl ester. The effects of EPA on muscle and adipose GLUT mRNA, as well as on liver glucokinase (GK) and glucose-6-phosphatase (G6Pase) activity, were investigated. Male Wistar rats fed on a standard diet or a high-fat cafeteria diet were daily treated by oral administration with EPA ethyl ester (1 g/kg) for 5 weeks. A significant decrease (P < 0.01) in white adipose tissue (WAT) visfatin mRNA levels was found in the cafeteria-fed rats, which was reversed by EPA administration (P < 0.05). Moreover, a negative relationship was observed between homeostatic model assessment (HOMA) and the visfatin:total WAT ratio. In contrast, cafeteria-diet feeding caused a significant increase (P < 0.01) in apelin mRNA in visceral WAT. EPA increased (P < 0.01) apelin gene expression, and a negative relationship between HOMA index with visceral apelin mRNA and serum apelin:total WAT ratio was also observed. EPA treatment did not induce changes in skeletal muscle GLUT1, GLUT4 or insulin receptor mRNA levels. Neither liver GK and G6Pase activity nor the GK:G6Pase ratio was modified by EPA. These data suggest that somehow the insulin-sensitising effects of EPA could be related to its stimulatory action on both visfatin and apelin gene expression in visceral fat, while changes in skeletal muscle GLUT, as well as in hepatic glucose production, are not likely to be the main contributing factors in the improvement in insulin resistance induced by EPA.

Gut microbiota: a key player in health and disease. A review focused on obesity

Gut microbiota, its evolutive dynamics and influence on host through its protective, trophic and metabolic actions, has a key role in health and opens unique opportunities for the identification of new markers of the physiopathological state of each individual. Alterations in gut microbiota composition have been associated with plenty disorders. Of interest, the vast number of studies demonstrates the role of microbiota in obesity, a serious public health problem that has reached epidemic proportions in many developed and middle-income countries. The economic and health costs of this condition and its comorbidities such as fatty liver, insulin resistance/diabetes, or cardiovascular events are considerable. Therefore, every strategy designed to reduce obesity would imply important savings. Targeting microbiota, in order to restore/modulate the microbiota composition with antibiotics, probiotics, prebiotics, or even fecal transplants, is considered as a promising strategy for the development of new solutions for the treatment of obesity. However, there is still lot to do in this field in order to identify the exact composition of microbiota in “health” and the specific mechanisms that regulate the host-microbiotal crosstalk. In addition, it is important to note that changes not only in the gut microbiota profile (abundance) but also in its metabolism and functions need to be taken into account in the context of contribution in the physiopathology of obesity and related disorders.

Serum and gene expression levels of leptin and adiponectin in rats susceptible or resistant to diet-induced obesity

The aim of the present study was to identify the role of leptin and adiponectin in the development of resistance or susceptibility to diet-induced obesity in rats. For this purpose, male Wistar rats were fed with standard laboratory diet (control group) or cafeteria diet. After 15 days, two groups of rats with different response respect to the cafeteria diet were identified, and were assigned as diet-induced obesity (DIO) and diet resistant (DR) rats. The high-fat diet induced a very dignificant increase in both body and fat mass weight in DIO group. However, DR rats, gained even less weight than control-fed animals. Food intake was increased in cafeteria-fed rats (both DIO and DR) in comparison to control group; but hyperphagia was higher in DIO rats. In addition, feed efficiency (the ratio of weight gained to calories consumed) was significantly decreased in DR as compared to DIO rats. Regarding leptin, a significant increase in both adipose tissue gene expression and serum levels was observed in DIO rats in comparison with other groups (control and DR). A significant increase in both adiponectin circulating levels and adipose tissue mRNA expression was also observed in DIO animals as compared with the other groups. These data suggest that the susceptibility to obesity of DIO rats might be secondary, at least in part, to an earlier development of leptin resistance, which could lead to alterations in food intake (hyperphagia) and energetic metabolism. However, neither changes in leptin or adiponectin seem to be involved in the adaptive mechanisms that confer resistance to high fat intake.ResumenEn el presente trabajo, se estudia el papel de la leptina y la adiponectina en la resistencia o susceptibilidad a la obesidad inducida por la dieta. Para ello, se alimentaron ratas Wistar macho con una dieta de laboratorio (grupo control) o con una dieta rica en grasa (dieta de cafetería). Tras 15 días, se identificaron dos grupos de ratas con diferente respuesta a la dieta de cafetería, los cuales fueron designados como susceptibiles (DIO) o resistentes (DR) al desarrollo de obesidad. Así, se observó un incremento muy significativo en el peso y la masa grasa corporal en el grupo DIO, mientras que los animales del grupo DR ganaron menos peso corporal que los animales control. La ingesta calórica fue significativamente superior en los grupos DR y DIO respecto del grupo control, aunque la hiperfagia fue significativamente superior en los animales susceptibles. Además, la eficiencia metabólica fue significativamente inferior en las ratas DR. En cuanto a la leptina y a la adiponectina, las ratas DIO mostraron un incremento significativo tato en la expresión de los genes correspondientes en tejido adiposo como en los niveles séricos de ambas hormonas. Esto datos sugieren que la susceptibilidad a la obesidad en las ratas DIO podría ser secundaria a un desarrollo temprano de resistencia a la leptina, que puede ir acompañada tanto de alteraciones en la ingesta (hiperfagia) como en el metabolismo energético. Sin embargo, ni los cambios en la leptina ni en la adiponectina parecen estar implicados en los mecanismos de adaptación que provocan resistencia a la obesidad.