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.

The intake of high-fat diets induces the acquisition of brown adipocyte gene expression features in white adipose tissue.

BACKGROUND/OBJECTIVE: White-to-brown adipose tissue remodeling (browning) in response to different stimuli constitutes an active research area for obesity treatment. The emergence in traditional white adipose tissue (WAT) depots of multilocular adipocytes that express uncoupling protein 1 (UCP1) and resemble brown adipocytes, the so called 'brite' adipocytes, could contribute to increased energy expenditure. In rodents, obesogenic stimuli such as the intake of hyperlipidic diets can increase brown adipose tissue (BAT) thermogenic capacity and contribute to maintaining body weight. The aim of this study was to investigate the potential of two different hyperlipidic diets, a commercial high-fat (HF) diet and a highly palatable cafeteria (CAF) diet, to induce WAT browning. METHODS: We analyzed gene expression of a wide number of brown/brite adipocyte markers in different WAT depots, in BAT and in peripheral blood mononuclear cells (PBMCs) increasingly being used in nutrition studies as a potential source of biomarkers of physiological effects. We also performed morphological analysis of adipose tissue. RESULTS: Both HF diets studied were able to increase the expression of the markers studied in WAT in a depot-specific manner, as well as in BAT; some of these changes were also reflected in PBMCs. This increased browning capacity was translated into the appearance of UCP1- and CIDE-A (cell death-inducing DFFA-like effector A)-positive brite adipocytes in retroperitoneal WAT. Administration of the CAF diet, associated with higher adiposity, produced the strongest impact on the parameters studied while its withdrawal restored basal conditions. CONCLUSIONS: Acquisition of brown adipocyte features in WAT could evidence an adaptation to try to counteract increased adiposity due to the intake of HF diets. Additionally, PBMCs could constitute an interesting easily obtainable material to assess the effect of nutritional interventions on browning capacity.

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.