Rubén Díaz-Rúa

Peripheral blood mononuclear cells as a potential source of biomarkers to test the efficacy of weight-loss strategies

Peripheral blood mononuclear cells (PBMC) constitute an easily obtainable blood cell fraction useful in nutrition and obesity studies. Our aim was to study the potential use of PBMC to reflect metabolic recovery associated with weight loss in rats.

Diet-induced obesity affects expression of adiponutrin/PNPLA3 and adipose triglyceride lipase, two members of the same family.

Background:Adiponutrin/PNPLA3 and adipose triglyceride lipase (ATGL) are proteins highly expressed in adipose tissue which have apparently different roles (lipogenic/lipolytic). Gene expression of both proteins and their nutritional regulation have been described to be altered in genetically obese animals.Methods:We studied adiponutrin and ATGL expression in 6-month-old rats made obese by cafeteria diet feeding, submitted to different feeding conditions (feeding/fasting/re-feeding), compared with normoweight animals. Adiponutrin and ATGL mRNA levels were determined in white adipose tissue depots (subcutaneous and visceral) and in interscapular brown adipose tissue, and ATGL protein levels in selected depots. In addition, basal adiponutrin and ATGL expression levels were compared between 6- and 3-month-old animals.Results:Obesity decreased adiponutrin and ATGL expression in different adipose depots. For adiponutrin, a tendency to lower mRNA levels was observed in the white adipose depots studied in obese animals, although the decrease was only significant in the subcutaneous depot. For ATGL, a generalized and significant lower expression was found in white and brown adipose tissue of cafeteria-obese rats. When considering nutritional regulation, according to a lipogenic role, adiponutrin mRNA expression decreased with fasting and was recovered by re-feeding in normoweight animals; this regulation was lost in obese rats. Expression of the lipolytic ATGL (mRNA and protein levels) was increased by fasting in normoweight animals in the mesenteric adipose depot, while no change was evident in obese rats. Moreover, adiponutrin and ATGL nutritional regulation was affected by age, and we report a downregulation of adiponutrin mRNA basal levels with age in internal adipose depots.Conclusions:Cafeteria diet-induced obesity and age alter adiponutrin and ATGL expression and their regulation by feeding conditions. These results reinforce the importance of a proper expression and regulation of both proteins for body weight maintenance and their role in energy metabolism.

Peripheral blood mononuclear cells as a source to detect markers of homeostatic alterations caused by the intake of diets with an unbalanced macronutrient composition

Peripheral blood mononuclear cells (PBMCs) are accessible in humans, and their gene expression pattern was shown to reflect overall physiological response of the body to a specific stimulus, such as diet. We aimed to study the impact of sustained intake (4months) of diets with an unbalanced macronutrient proportion (rich in fat or protein) administered isocalorically to a balanced control diet, as physiological stressors on PBMC whole-genome gene expression in rats, to better understand the effects of these diets on metabolism and health and to identify biomarkers of nutritional imbalance. Dietary macronutrient composition (mainly increased protein content) altered PBMC gene expression, with genes involved in immune response being the most affected. Intake of a high-fat (HF) diet decreased the expression of genes related to antigen recognition/presentation, whereas the high-protein (HP) diet increased the expression of these genes and of genes involved in cytokine signaling and immune system maturation/activation. Key energy homeostasis genes (mainly related to lipid metabolism) were also affected, reflecting an adaptive response to the diets. Moreover, HF diet feeding impaired expression of genes involved in redox balance regulation. Finally, we identified a common gene expression signature of 7 genes whose expression changed in the same direction in response to the intake of both diets. These genes, individually or together, constitute a potential risk marker of diet macronutrient imbalance. In conclusion, we newly show that gene expression analysis in PBMCs allows for detection of diet-induced physiological deviations that distinguish from a diet with a proper and equilibrated macronutrient composition.

Reversion to a control balanced diet is able to restore body weight and to recover altered metabolic parameters in adult rats long-term fed on a cafeteria diet

The increased intake of fat-rich foods is one of the causes of the increasing incidence of obesity. However, there are controversial data on the reversibility of diet-induced obesity and its metabolic complications when adopting a control energy-balanced diet. Our aim was to evaluate the ability to reset not only body weight but also metabolic disorders caused by a highly palatable high fat diet, cafeteria diet, administered to adult rats, when replaced by a control diet (post-cafeteria model). Four-months of cafeteria diet-feeding produced important metabolic alterations in comparison to a commercial purified high fat diet: a rapid, drastic increase in body weight, adiposity and related complications such as insulin resistance, decreased glucose tolerance and development of hepatic steatosis. At gene level, decreased lipogenic and increased lipolytic gene expression in key energy homeostatic tissues as a physiological adaptation to increased fat intake was observed. In addition, fasting response of serum parameters and of key genes in lipid metabolism was impaired in cafeteria-fed animals. Contrary to what we have previously described if cafeteria diet is administered early in life, when administered to adult animals, its replacement with a balanced diet is able to restore body weight. Cafeteria diet withdrawal also allows recovery from metabolic damage, gene expression regulation and fasting response, the degree of which is dependent on the time of exposure to the cafeteria diet. In conclusion, adherence to an ad libitum intake of a balanced standard diet can enable the recovery of healthy status in animals which were previously exposed to an unhealthy cafeteria diet in adult age.

Long-term intake of a high-protein diet increases liver triacylglycerol deposition pathways and hepatic signs of injury in rats☆☆☆

Intake of high-protein (HP) diets has increased over the last years, mainly due to their popularity for body weight control. Liver is the main organ handling ingested macronutrients and it is associated with the beginning of different pathologies. We aimed to deepen our knowledge on molecular pathways affected by long-term intake of an HP diet. We performed a transcriptome analysis on liver of rats chronically fed with a casein-rich HP diet and analyzed molecular parameters related to liver injury. Chronic increase in the dietary protein/carbohydrate ratio up-regulated processes related with amino acid uptake/metabolism and lipid synthesis, promoting a molecular environment indicative of hepatic triacylglycerol (TG) deposition. Moreover, changes in expression of genes involved in acid-base maintenance and oxidative stress indicate alterations in the pH balance due to the high acid load of the diet, which has been linked to liver/health damage. Up-regulation of immune-related genes was also observed. In concordance with changes at gene expression level, we observed increased liver TG content and increased serum markers of hepatic injury/inflammation (aspartate transaminase, C-reactive protein and TNF-alpha). Moreover, the HP diet strongly increased hepatic mRNA and protein levels of HSP90, a marker of liver injury. Thus, we show for the first time that long-term consumption of an HP diet, resulting in a high acid load, results in a hepatic transcriptome signature reflecting increased TG deposition and increased signs of health risk (increased inflammation, alterations in the acid-base equilibrium and oxidative stress). Persistence of this altered metabolic status could have unhealthy consequences.

Isocaloric high-fat feeding directs hepatic metabolism to handling of nutrient imbalance promoting liver fat deposition

Background/Objectives:Consumption of fat-rich foods is associated with obesity and related alterations. However, there is a group of individuals, the metabolically obese normal-weight (MONW) subjects, who present normal body weight but have metabolic features characteristic of the obese status, including fat deposition in critical tissues such as liver, recognized as a major cause for the promotion of metabolic diseases. Our aim was to better understand metabolic alterations present in liver of MONW rats applying whole genome transcriptome analysis.Methods:Wistar rats were chronically fed a high-fat diet isocaloric relative to Control animals to avoid the hyperphagia and overweight and to mimic MONW features. Liver transcriptome analysis of both groups was performed.Results:Sustained intake of an isocaloric high-fat diet had a deep impact on the liver transcriptome, mainly affecting lipid metabolism. Although serum cholesterol levels were not affected, circulating triacylglycerols were lower, and metabolic adaptations at gene expression level indicated adaptation toward handling the increased fat content of the diet, an increased triacylglycerol and cholesterol deposition in liver of MONW rats was observed. Moreover, gene expression pointed to increased risk of liver injury. One of the top upregulated genes in this tissue was Krt23, a marker of hepatic disease in humans that was also increased at the protein level.Conclusion:Long-term intake of a high-fat diet, even in the absence of overweight/obesity or increase in classical blood risk biomarkers, promotes a molecular environment leading to hepatic lipid accumulation and increasing the risk of suffering from hepatic diseases.

Human peripheral blood mononuclear cell in vitro system to test the efficacy of food bioactive compounds: Effects of polyunsaturated fatty acids and their relation with BMI

SCOPE To analyse the usefulness of isolated human peripheral blood mononuclear cells (PBMC) to rapidly/easily reflect n-3 long-chain polyunsaturated fatty acid (LCPUFA) effects on lipid metabolism/inflammation gene profile, and evaluate if these effects are body mass index (BMI) dependent. METHODS AND RESULTS PBMC from normoweight (NW) and overweight/obese (OW/OB) subjects were incubated with physiological doses of docosahexaenoic (DHA), eicosapentaenoic acid (EPA), or their combination. PBMC reflected increased beta-oxidation-like capacity (CPT1A expression) in OW/OB but only after DHA treatment. However, insensitivity to n-3 LCPUFA was evident in OW/OB for lipogenic genes: both PUFA diminished FASN and SREBP1C expression in NW, but no effect was observed for DHA in PBMC from high-BMI subjects. This insensitivity was also evident for inflammation gene profile: all treatments inhibited key inflammatory genes in NW; nevertheless, no effect was observed in OW/OB after DHA treatment, and EPA effect was impaired. SLC27A2, IL6 and TNFα PBMC expression analysis resulted especially interesting to determine obesity-related n-3 LCPUFA insensitivity. CONCLUSION A PBMC-based human in vitro system reflects n-3 LCPUFA effects on lipid metabolism/inflammation which is impaired in OW/OB. These results confirm the utility of PBMC ex vivo systems for bioactive-compound screening to promote functional food development and to establish appropriate dietary strategies for obese population.

Cold exposure down-regulates adiponutrin/PNPLA3 mRNA expression and affects its nutritional regulation in adipose tissues of lean and obese Zucker rats

Adiponutrin/PNPLA3 is a protein highly produced in adipose tissue whose expression is under tight nutritional regulation. It possesses lipogenic/lipolytic capacity and, although adiponutrin polymorphisms are related to obesity, its physiological role is not clear. To help clarify its role, we studied the effect of acute cold exposure on adiponutrin mRNA expression in different adipose tissues of lean/obese Zucker rats subjected to feeding/fasting/refeeding. The effect of cold on the expression of key lipogenic enzymes and on uncoupling protein-1 (UCP1) was evaluated in selected adipose depots. Adiponutrin mRNA levels were also determined in the adipose tissue of isoprenaline-treated rats and in cultured adipocytes treated with noradrenaline, isoprenaline and a selective β3-adrenoceptor (AR) agonist. Adiponutrin expression was strongly down-regulated by cold in the different adipose depots in lean animals, while this down-regulation was impaired in obese rats. Adiponutrin pattern of expression in response to cold correlated positively with that of the lipogenic enzymes and negatively with UCP1 expression. Acute intraperitoneal administration of isoprenaline also produced a decrease in adiponutrin expression in adipose tissue. In vitro data suggest that adiponutrins inhibitory effect could be mediated, at least in part, by the sympathetic system via β1/β2-AR. In addition, improvement in metabolic parameters related to obesity in cold-exposed animals was related to an improvement in adiponutrin nutritional regulation. Thus, cold inhibition of adiponutrin expression in adipose tissue (which correlates with the response of lipogenic enzymes) supports a physiological role for this protein in lipogenesis. Moreover, alterations in adiponutrin expression and regulation in adipose tissue are related to obesity.