Obesity (Silver Spring). 2015 Jan;23(1):28-31

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

Reynés B, Díaz-Rúa R, Cifre M, Oliver P, Palou A.

Laboratory of Molecular Biology, Nutrition and Biotechnology (LBNB), Universitat de les Illes Balears and CIBER de Fisiopatología de la Obesidad y Nutrición (CIBERobn), Palma de Mallorca, Spain.



OBJECTIVES: 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.

METHODS: By real-time PCR, the fasting response of key energy homeostatic genes in PBMC samples of control and cafeteria-obese rats and of rats fed a control diet after the intake of a cafeteria diet (post-cafeteria model) was analyzed.

RESULTS: Fasting caused decreased mRNA expression of lipogenic (Fasn and Srebp1a) and adipogenic (Pparγ) genes in PBMC, whereas it increased the expression of the key beta-oxidation gene Cpt1a and the orexigenic gene Npy. Fasting response of the genes studied was impaired in cafeteria-obese animals but was recovered in post-cafeteria rats, which showed a significant body weight decrease and normalization of adipose and metabolic parameters. Npy expression analyzed in PBMC has been revealed to be especially useful as a marker of fasting sensitivity, as its fasting response is not affected by the age of the animals and it is recovered even after shorter time of exposure to a balanced diet.

CONCLUSIONS: PBMC reflect homeostatic balance recovery associated with weight loss in obese animals, when reverting from a hyperlipidic to a control balanced diet.

PMID: 25294800



Due to the dramatic worldwide increase in obesity, the interest in weight-loss strategies has increased. However, obesity is not only a problem of increased body weight, as this pathology is linked to metabolic syndrome and to metabolic dysfunction. Thus, weigh-loss programs would be implemented if, in addition of recording weight decrease, they included evaluation of other parameters, such as molecular parameters, apart from the metabolites classically analyzed in serum, in order to check metabolic improvement.

At molecular level, one of the characteristics of obesity is insensitivity to feeding conditions (fasting and re-feeding) (1). In normo-weight rodents, changes in feeding conditions affect gene expression profile in tissues as liver or adipose tissue with the aim of maintaining energy homeostasis. For example, fasting induces a down-regulation of lipogenic/adipogenic genes while induces an up-regulation of genes involved in lipolysis (2). However, this gene expression pattern is not observed in obese animals, and this fasting insensitivity could contribute to the inability to maintain a proper body weight. Interestingly, we have previously described by analyzing gene expression in key energy homeostatic tissues, that fasting insensitivity which appears in diet-induced obese animals can be reverted when the obesogenic diet is substituted by a control balanced diet (2). Thus, analysis of fasting response recovery appears as a good tool to analyze if weight loss is related to molecular metabolic improvement. However, to be applied in humans, this kind of studies using tissue samples would require of invasive techniques, such as biopsies. For this reason, it would be of interest to dispose of an easily available biological material to perform molecular metabolic recovery studies. In this sense, a biological sample which has received much attention for clinical diagnosis and, more recently, in molecular nutrition studies are peripheral blood mononuclear cells (PBMC).

PBMC constitute a fraction of blood cells mainly composed by lymphocytes and monocytes, which can be easily isolated from blood samples by differential centrifugation. These cells are part of the immune system, and they are able to reflect expression patterns characteristic of certain diseases, as those related to the immune system (3). Moreover, it is known that PBMC can express a large percentage of human genome genes (more than 80%), including tissue-specific transcripts, and can reflect metabolic response of other organs to changes in micro- and macro-environment (4). Particularly, wide amount of evidence show the utility of these cells in metabolic and nutritional studies, as PBMC are able to reveal, at gene expression level, specific effects of nutrients, metabolic response to fasting/re-feeding, obesity, or weight loss due to the intake of hypocaloric diets (4). Moreover, our laboratory has demonstrated that PBMC clearly show impairment in the response to feeding conditions related to obesity, even in early obese stages (5). With this background, in this study we aimed to study if PBMC were able to reflect not only obesity-related fasting insensitivity, but metabolic recovery (analyzed as recovery of fasting sensitivity) associated to weight loss in diet-induced obese animals after switching an obesogenic to a control balanced diet.

To perform our study we used adult male Wistar rats. Our control animals were fed with a balanced diet and we collected blood samples to obtain PBMC, in two different situations, ad libitum feeding and nocturnal 14-h fasting, time enough to observe a clear nutritional response. In fact, in PBMC from these animals, we observed the expected metabolic response to fasting when analyzing gene expression of fundamental genes involved in lipid metabolism. On the other hand, we used a group of rats chronically fed a cafeteria diet, a highly palatable hyperlipidic diet that mimics Western diet, and which induces persistent voluntary hyperphagia and a rapid and high weight gain. PBMC of these cafeteria obese animals showed a lack of response to fasting. Finally, we used a third group of animals, which were fed a cafeteria diet to induce obesity and afterwards with a control diet (post-cafeteria model). An evident body weight loss was observed in these animals, which were able to recover, in a major or lesser extent depending of the previous time of cafeteria feeding, that of controls. Gene expression analyzed in PBMC obtained from post-cafeteria rats followed the same fasting regulation as in lean control animals, evidencing that weight loss was associated to a recovery at molecular level. Apart from studying genes involved in lipid metabolism, we also analyzed expression of Npy, a gene which codes for a key orexigenic peptide mainly produced in the hypothalamus and with a clear nutritional regulation in this tissue. Interestingly, PBMC clearly reflected Npy increased expression with fasting in controls, fasting insensitivity in cafeteria obese and recovery of fasting response in post-cafeteria animals.

Taken together, results obtained in our study point to PBMC as a useful biological material to check metabolic normalization in obese subjects that lose weight after switching from an unhealthy hyperlipidic to a control balanced diet. PBMC can be simply collected in humans, thus, gene expression analysis in these cells obtained in feeding and fasted conditions in the same individual, at different stages of body weight loss, could easily help to verify if decreased adiposity is translated into metabolic recovery.

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This study was supported by the European Project BIOCLAIMS-FP7-244995. Authors belong to the University of the Balearic Islands (UIB) and CIBER de Fisiopatología de la Obesidad y Nutrición (CIBERobn), which is an initiative of the ISCIII.



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