Pecans and Its Polyphenols Prevent Obesity, Hepatic Steatosis and Diabetes by Reducing Dysbiosis, Inflammation, and Increasing Energy Expenditure in Mice Fed a High-Fat Diet

Pecans (Carya illinoinensis) are considered a functional food due to the high content of polyunsaturated fatty acids, dietary fiber and polyphenols. To determine the effect of whole pecans (WP) or a pecan polyphenol (PP) extract on the development of metabolic abnormalities in mice fed a high-fat (HF) diet, we fed C57BL/6 mice with a Control diet (7% fat), HF diet (23% fat), HF containing 30% WP or an HF diet supplemented with 3.6 or 6 mg/g of PP for 18 weeks. Supplementation of an HF diet with WP or PP reduced fat mass, serum cholesterol, insulin and HOMA-IR by 44, 40, 74 and 91%, respectively, compared to the HF diet. They also enhanced glucose tolerance by 37%, prevented pancreatic islet hypertrophy, and increased oxygen consumption by 27% compared to the HF diet. These beneficial effects were associated with increased thermogenic activity in brown adipose tissue, mitochondrial activity and AMPK activation in skeletal muscle, reduced hypertrophy and macrophage infiltration of subcutaneous and visceral adipocytes, reduced hepatic lipid content and enhanced metabolic signaling. Moreover, the microbial diversity of mice fed WP or PP was higher than those fed HF, and associated with lower circulating lipopolysaccharides (~83-95%). Additionally, a 4-week intervention study with the HF 6PP diet reduced the metabolic abnormalities of obese mice. The present study demonstrates that WP or a PP extract prevented obesity, liver steatosis and diabetes by reducing dysbiosis, inflammation, and increasing mitochondrial content and energy expenditure. Pecan polyphenols were mainly condensed tannin and ellagic acid derivatives including ellagitannins as determined by LC-MS. Herein we also propose a model for the progression of the HF diet-mediated metabolic disorder based on early and late events, and the possible molecular targets of WP and PP extract in preventive and intervention strategies. The body surface area normalization equation gave a conversion equivalent to a daily human intake dose of 2101-3502 mg phenolics that can be obtained from 110-183 g pecan kernels/day (22-38 whole pecans) or 21.6-36 g defatted pecan flour/day for an average person of 60 kg. This work lays the groundwork for future clinical studies.

The Role of the Unfolded Protein Response on Renal Lipogenesis in C57BL/6 Mice

Renal injury observed in several pathologies has been associated with lipid accumulation in the kidney. While it has been suggested that the accumulation of renal lipids depends on free fatty acids released from adipose tissue, it is not known whether in situ renal lipogenesis due to endoplasmic reticulum (ER) stress contributes to kidney injury. The aim of the present study was to elucidate the role of pharmacological ER stress in renal structure and function and its effect on renal lipid metabolism of C57BL/6 mice. ER stress increased serum creatinine and induced kidney structural abnormalities. Tunicamycin-administered mice developed hyperinsulinemia, augmented lipolysis and increased circulating leptin and adiponectin. Renal unfolded protein response (UPR) gene expression markers, the lipogenic transcription factor SREBP1 and the phosphorylation of eIF2α increased 8 h after tunicamycin administration. At 24 h, an increase in BiP protein content was accompanied by a reduction in p-eIF2α and increased SREBP-1 and FASn protein content, in addition to a significant increase in triglyceride content and a reduction in AMPK. Thus, ER stress induces in situ lipid synthesis, leading to renal lipid accumulation and functional alterations. Future pharmacological and/or dietary strategies must target renal ER stress to prevent kidney damage and the progression of metabolic diseases.

Goat's Milk Intake Prevents Obesity, Hepatic Steatosis and Insulin Resistance in Mice Fed A High-Fat Diet by Reducing Inflammatory Markers and Increasing Energy Expenditure and Mitochondrial Content in Skeletal Muscle

Goat's milk is a rich source of bioactive compounds (peptides, conjugated linoleic acid, short chain fatty acids, monounsaturated and polyunsaturated fatty acids, polyphenols such as phytoestrogens and minerals among others) that exert important health benefits. However, goat's milk composition depends on the type of food provided to the animal and thus, the abundance of bioactive compounds in milk depends on the dietary sources of the goat feed. The metabolic impact of goat milk rich in bioactive compounds during metabolic challenges such as a high-fat (HF) diet has not been explored. Thus, we evaluated the effect of milk from goats fed a conventional diet, a conventional diet supplemented with 30% Acacia farnesiana (AF) pods or grazing on metabolic alterations in mice fed a HF diet. Interestingly, the incorporation of goat's milk in the diet decreased body weight and body fat mass, improved glucose tolerance, prevented adipose tissue hypertrophy and hepatic steatosis in mice fed a HF diet. These effects were associated with an increase in energy expenditure, augmented oxidative fibers in skeletal muscle, and reduced inflammatory markers. Consequently, goat's milk can be considered a non-pharmacologic strategy to improve the metabolic alterations induced by a HF diet. Using the body surface area normalization method gave a conversion equivalent daily human intake dose of 1.4 to 2.8 glasses (250 mL per glass/day) of fresh goat milk for an adult of 60 kg, which can be used as reference for future clinical studies.

Ethical Considerations in Animal Research: The Principle of 3R's

In the last century, progress in the knowledge of human diseases, their diagnosis and treatment have grown exponentially, due in large part to the introduction and use of laboratory animals. Along with this important progress, the need to provide training and guidance to the scientific community in all aspects related to the proper use of experimental animals has been indispensable. Animal research committees play a primary role in evaluating experimental research protocols, from their feasibility to the rational use of animals, but above all in seeking animal welfare. The Institutional Committee for the Care and Use of Animals (IACUC) has endeavored to share several relevant aspects in conducting research with laboratory animals. Here, we present and discuss the topics that we consider of utmost importance to take in the account during the design of any experimental research protocol, so we invite researchers, technicians, and undergraduate and graduate students to dive into the fascinating subject of proper animal care and use for experimentation. The main intention of these contributions is to sensitize users of laboratory animals for the proper and rational use of them in experimental research, as well as to disseminate the permitted and unpermitted procedures in laboratory animals. In the first part, the significance of experimental research, the main functions of IACUC, and the principle of the three R's (replacement, reduction, and refinement) are addressed.

Ethical Considerations in Animal Research: The Principle of 3R's

In the last century, progress in the knowledge of human diseases, their diagnosis and treatment have grown exponentially, due in large part to the introduction and use of laboratory animals. Along with this important progress, the need to provide training and guidance to the scientific community in all aspects related to the proper use of experimental animals has been indispensable. Animal research committees play a primary role in evaluating experimental research protocols, from their feasibility to the rational use of animals, but above all in seeking animal welfare. The Institutional Committee for the Care and Use of Animals (IACUC) has endeavored to share several relevant aspects in conducting research with laboratory animals. Here, we present and discuss the topics that we consider of utmost importance to take in the account during the design of any experimental research protocol, so we invite researchers, technicians, and undergraduate and graduate students to dive into the fascinating subject of proper animal care and use for experimentation. The main intention of these contributions is to sensitize users of laboratory animals for the proper and rational use of them in experimental research, as well as to disseminate the permitted and unpermitted procedures in laboratory animals. In the first part, the significance of experimental research, the main functions of IACUC, and the principle of the three R's (replacement, reduction, and refinement) are addressed.

Interaction between the amount of dietary protein and the environmental temperature on the expression of browning markers in adipose tissue of rats

Background

A low-protein diet increases the expression and circulating concentration of FGF21. FGF21 stimulates the browning process of WAT by enhancing the expression of UCP1 coupled with an increase in PGC1α. Interestingly, the consumption of a low-protein diet could stimulate WAT differentiation into beige/brite cells by increasing FGF21 expression and Ucp1 mRNA abundance. However, whether the stimulus of a low-protein diet on WAT browning can synergistically interact with another browning stimulus, such as cold exposure, remains elusive.

Results

In the present study, rats were fed 6% (low), 20% (adequate), or 50% (high) dietary protein for 10 days and subsequently exposed to 4 °C for 72 h. Body weight, food intake, and energy expenditure were measured, as well as WAT browning and BAT thermogenesis markers and FGF21 circulating levels. The results showed that during cold exposure, the consumption of a high-protein diet reduced UCP1, TBX1, Cidea, Cd137, and Prdm16 in WAT when compared with the consumption of a low-protein diet. In contrast, at room temperature, a low-protein diet increased the expression of UCP1, Cidea, and Prdm16 associated with an increase in FGF21 expression and circulating levels when compared with a consumption of a high-protein diet. Consequently, the consumption of a low-protein diet increased energy expenditure.

Conclusions

These results indicate that in addition to the environmental temperature, WAT browning is nutritionally modulated by dietary protein, affecting whole-body energy expenditure.

Graphical abstract

PPARα Downregulates Hepatic Glutaminase Expression in Mice Fed Diets with Different Protein:Carbohydrate Ratios

BACKGROUND

Glutamine is catabolized in the liver by glutaminase 2 (GLS2). Evidence suggests that peroxisome proliferator-activated receptor α (PPARα) represses the expression of several amino acid-catabolizing enzymes, but for Gls2 this is unknown.

OBJECTIVE

The aim of the study was to assess whether PPARα regulates Gls2 expression.

METHODS

For 8 d, 7-9-wk-old male C57BL/6 wild-type (WT) and Ppara-null mice weighing 23.4 ± 0.5 g were fed diets with different dietary protein:carbohydrate (DP:DCH) ratios (6%:77%, 20%:63%, or 50%:33%). Liver samples were obtained after 16 h of feed deprivation or 3 h of refeeding, and microarrays were performed. Hepatic glutaminase expression was measured by quantitative polymerase chain reaction and Western blotting. Cotransfection analyses in hepatocellular carcinoma cell line (HepG2) cells with PPARα and hepatocyte nuclear factor 4α (HNF4α) expression vectors were performed.

RESULTS

The microarray results showed that Gls2 was the only upregulated gene in WT mice, but not in the Ppara-null mice. In the feed-deprived WT mice, the Gls2 mRNA and protein abundances in the 50%:33% group were 2.5- and 1.1-fold greater (P < 0.05), respectively, than those in the 20%:63% group, which were 2.3- and 0.4-fold greater than those in the 6%:77% group (P < 0.01). Gls2 mRNA expression in the 6%:77% group of feed-deprived Ppara-null mice was 33-fold greater than that in the same group of WT mice (P < 0.0001). GLS2 protein abundance in HepG2 cells was 78% greater than that in the controls (P < 0.0001) after HNF4α overexpression, and it was 99% greater after transfection with a short hairpin targeting PPARα.

CONCLUSIONS

In Ppara-null mice, Gls2 mRNA expression was greater than in WT mice, regardless of the DP:DCH ratio. In HepG2 cells overexpressing HNF4α, Gls2 expression increased, an effect repressed by overexpression of PPARα. This suggests that Gls2 depends on the PPARα/HNF4α counterregulatory transcriptional control.

Hepatic amino acid-degrading enzyme expression is downregulated by natural and synthetic ligands of PPARα in rats

Body nitrogen retention is dependent on the amount of dietary protein consumed, as well as the fat and carbohydrate content in the diet, due to the modulation of amino acid oxidation. PPARα is a transcription factor involved in the upregulation of the expression of enzymes of fatty acid oxidation. However, the role of putative PPARα response elements (PPREs) in the promoter of several amino acid-degrading enzymes (AADEs) is not known. The aim of this work was to study the effect of the synthetic ligand Wy 14643 and the natural ligands palmitate, oleate, and linoleate in rats fed graded concentrations of dietary protein (6, 20, or 50 g/100 g of total diet) on the expression of the AADEs histidase, serine dehydratase, and tyrosine aminotransferase. Thus, we fed male Wistar rats diets containing 6, 20, or 50% casein for 10 d. The results showed that addition of Wy 14643 to the diet significantly reduced the expression of the AADEs. Furthermore, the incubation of hepatocytes with natural ligands of PPARα or feeding rats with diets containing soybean oil, safflower oil, lard, or coconut oil as sources of dietary fat significantly repressed the expression of the AADEs. Gene reporter assays and mobility shift assays demonstrated that the PPRE located at -482 bp of the histidase gene actively bound PPARα in rat hepatocytes. These data indicate that PPARα ligands may reduce amino acid catabolism in rats.

Promoter characterization and role of CRE in the basal transcription of the rat SNAT2 gene

Small neutral amino acid transporter 2 (SNAT2) is the most abundant and ubiquitous transporter for zwitterionic short-chain amino acids. The activity of this amino acid transporter is stimulated in vivo or in vitro by glucagon or cAMP analogs. However, it is not known whether the increase in activity at the protein level is due to an increase in SNAT2 gene transcription. Thus, the aim of the present work was to study whether cAMP was able to stimulate SNAT2 gene expression and to localize and characterize the presence of cAMP response elements (CRE) in the promoter that controls the expression of the rat SNAT2 gene. We found that consumption of a high-protein diet that increased serum glucagon concentration or the administration of glucagon or incubation of hepatocytes with forskolin increased the SNAT2 mRNA level. We then isolated the 5' regulatory region of the SNAT2 gene and determined that the transcriptional start site was located 970 bp upstream of the translation start codon. We identified two potential CRE sites located at -354 and -48 bp. Our results, using deletion analysis of the 5' regulatory region of the SNAT2 gene, revealed that the CRE site located at -48 bp was fully responsible for SNAT2 regulation by cAMP. This evidence was strongly supported by mutation of the CRE site and EMSA and ChIP analysis. Alignment of rat, mouse, and human sequences revealed that this CRE site is highly conserved among species, indicating its essential role in the regulation of SNAT2 gene expression.

Changes in messenger RNA abundance of amino acid transporters in rat mammary gland during pregnancy, lactation, and weaning

During lactation, the mammary gland increases the needs for nutrients to fulfill the milk production requirements. Among these nutrients, amino acids play an important role for the synthesis of milk proteins. Amino acids are supplied to the mammary gland through amino acid transporters, although some are synthesized in situ. The purpose of this study was to establish the pattern of changes in messenger RNA abundance of the amino acid transporters ASC, system L, EAAC1, GLAST, CAT-1, and Tau in the mammary gland of the rat during different stages of pregnancy and lactation. Rats were fed during pregnancy and lactation a 20% casein diet. Food intake increased significantly during the lactation period. Amino acid transporter ASC expression increased during the first days of pregnancy about 2-fold, and it was increased in a lesser extent again during the peak of lactation. The expression of system L (LAT-1) and CAT-1 transporters was increased only during the lactation period. On the other hand, the expression of the transporters for anionic amino acids EAAC1 and GLAST was low during both stages. Finally, taurine transporter expression decreased during pregnancy; and it was significantly lower during lactation. These results showed that amino acid transporters were not expressed similarly in the mammary gland during pregnancy and lactation, indicating that the expression of these transporters did not respond only to the metabolic needs of the gland but depended on the dietary protein supply and possibly the specific hormonal changes that occur during pregnancy and lactation.

Characterization and regulation of the gene expression of amino acid transport system A (SNAT2) in rat mammary gland

Amino acid transport via system A plays an important role during lactation, promoting the uptake of small neutral amino acids, mainly alanine and glutamine. However, the regulation of gene expression of system A [sodium-coupled neutral amino acid transporter (SNAT)2] in mammary gland has not been studied. The aim of the present work was to understand the possible mechanisms of regulation of SNAT2 in the rat mammary gland. Incubation of gland explants in amino acid-free medium induced the expression of SNAT2, and this response was repressed by the presence of small neutral amino acids or by actinomycin D but not by large neutral or cationic amino acids. The half-life of SNAT2 mRNA was 67 min, indicating a rapid turnover. In addition, SNAT2 expression in the mammary gland was induced by forskolin and PMA, inducers of PKA and PKC signaling pathways, respectively. Inhibitors of PKA and PKC pathways partially prevented the upregulation of SNAT2 mRNA during adaptive regulation. Interestingly, SNAT2 mRNA was induced during pregnancy and to a lesser extent at peak lactation. beta-Estradiol stimulated the expression of SNAT2 in mammary gland explants; this stimulation was prevented by the estrogen receptor inhibitor ICI-182780. Our findings clearly demonstrated that the SNAT2 gene is regulated by multiple pathways, indicating that the expression of this amino acid transport system is tightly controlled due to its importance for the mammary gland during pregnancy and lactation to prepare the gland for the transport of amino acids during lactation.

Regulation by glucagon of the rat histidase gene promoter in cultured rat hepatocytes and human hepatoblastoma cells

Histidase (Hal), the amino acid-degrading enzyme of histidine, is regulated by the protein content of the diet and by hormones such as glucocorticoids and glucagon. However, glucagon can activate the following two possible transduction pathways: protein kinase A (PKA) and protein kinase C (PKC). The aim of this study was to isolate the 5'-flanking region of rat Hal gene to locate possible cAMP- and glucocorticoid-responsive elements and to identify whether the activation of the Hal promoter by glucagon occurs via PKA or PKC. The results showed that glucagon was able to induce Hal expression 1.5-fold in primary hepatocytes. The addition of phorbol 12-myristate,13-acetate (PMA) and forskolin to hepatocytes increased Hal mRNA concentration by 100 and 40%, respectively. To identify the Hal gene regulatory region, a 1248-bp fragment of the 5'-region was obtained. The transcription initiation site was located at 404 bp from ATG. The sequence did not show consensus TATA-like or CAAT-like boxes in the first 100 bp upstream from the transcription start site. The promoter contained six GC rich boxes, seven putative AP1 binding sites, and four glucocorticoid-responsive elements. The putative Hal promoter region was cloned into the pGL3basic vector and transfected into HepG2 cells. Luciferase expression was significantly stimulated by glucagon (0.9-fold), forskolin (0.9-fold), PMA (2.0-fold), and dexamethasone (2.9-fold). This evidence supports that the Hal gene is turned on by glucocorticoids and by glucagon either via PKC or PKA, but prefers the PKA pathway.

[Peroxisome proliferator-activated receptors (PPARs) in obesity and insulin resistance development]

The peroxisome proliferator-activated receptors (PPARs) are a family of nuclear transcription factors that belong to the steroid receptor superfamily. PPARs family includes PPARalpha, PPARbeta/delta, PPARgamma1 and PPARgamma2. PPARs form an heterodimer with the 9-cis retinoic acid receptor (RXR) and bind to response elements present in target genes activated by these transcription factors. PPARs control the expression of genes involved in fatty acid synthesis, oxidation and storage. PPARs are present in most tissues, where PPARalpha is most abundant in liver and skeletal muscle, whereas PPARgamma is found mainly in adipose tissue. Natural ligands for PPARs are polyunsaturated fatty acids (PUFAs) and some eicosanoids, however they are also activated by compounds such as fibrates and thiazolidinediones (TZDs). In this review is shown the different PPARs isoforms, identification, and regulation of their expression and activity. Also shows which are the natural ligands, and the chemical compounds that activate PPARs. Finally, it shows the target genes activated by the different isoforms of PPARs, the metabolic integration between the different PPAR isoforms to maintain a balance between fatty acid synthesis and oxidation and the association with the development of obesity and insulin resistance. Also shows information about the nutritional requirements of PUFAs that are the main natural ligands of PPARs.

[Homocysteine metabolism and risk of cardiovascular diseases: importance of the nutritional status on folic acid, vitamins B6 and B12]

Homocysteine is a thiol-containing amino acid derived from methionine metabolism that can be degraded through two enzymatic pathways: remethylation and trans-sulfuration. In remethylation, homocysteine regenerates methionine. In the trans-sulfuration pathway, homocysteine forms cysteine. Due to the rapid metabolic utilization, the plasma concentration of this amino acid is low. Homocysteine circulates as free thiol, homocystine, or bound to free cysteine or to cysteine residues of proteins. Genetic defects of some enzymes in the homocysteine metabolism, or nutritional deficiencies of folic acid, vitamin B6 and B12 lead to an increase in homocysteine plasma concentration and is associated to an increment in cardiovascular diseases. On the basis of clinical and epidemiological studies, homocysteine plasma concentration is considered to be an independent risk factor for the development of atherothrombotic and cardiovascular diseases. The present review describes the homocysteine metabolism, the epidemiological evidence showing the association between homocysteine and the incidence of cardiovascular diseases. The mechanisms by which homocysteine produces vascular damage are indicated. Finally, some recommendations are given for the nutritional therapy of patients with hyperhomocysteinemia.

Regulation of histidase gene expression by glucagon, hydrocortisone and protein-free/high carbohydrate diet in the rat

The effect of glucagon and hydrocortisone was investigated to understand the mechanism of induction of hepatic histidase gene. In this study, glucagon (0.6 mg/100 g body wt/d) was injected to rats fed 10% casein diet. After 3 h of the last injection, histidase activity and amount of enzyme were induced by 3 fold and histidase mRNA concentration by 6 fold. Injection of hydrocortisone (2 mg/100 g body wt/d) increased 100% histidase activity and mRNA concentration and by 150% the amount of enzyme after 3 h of the last injection. These results indicate that glucagon is a better inductor of histidase gene expression than hydrocortisone. Another purpose of the study was to evaluate if a protein-free/high carbohydrate diet could reverse the induction of Hal expression produced by a high protein diet. Hal activity, amount of enzyme and mRNA concentration was repressed by 68, 88 and 95% respectively by a protein-free/high carbohydrate diet. Injection of glucagon reversed partially the effect of a high carbohydrate diet, however, injection of hydrocortisone under the concentration used in these experiments did not reverse the effect of a high carbohydrate diet. These results support the evidence that hepatic histidase gene expression is probably regulated transcriptionally by hormones.

Histidase expression is regulated by dietary protein at the pretranslational level in rat liver

The effect of dietary protein on the expression of histidase (Hal) was investigated to understand the mechanism of induction of histidase by a high protein diet. In this study, we examined the following: 1) the effect of 0, 6, 18, 35 and 50% casein diets on hepatic and epidermal Hal activity, amount of the enzyme and Hal-mRNA; 2) the effect of a high histidine diet (1.25%) on Hal expression; 3) the response of Hal expression in rats fed a 10% casein diet and injected with glucagon (0.6 mg /(100 g body wt.d); and 4) the half-lives of the enzyme and Hal-mRNA in rats fed an 80% casein diet for 7 d followed by a protein-free diet. Hal activity increased as the protein content in the diet increased (r = 0.986, P < 0.001) and was associated with a significant increase in Vmax without a change in Km. The dietary regulation was liver specific because skin Hal was unresponsive. Increments in hepatic Hal activity were accompanied by concomitant significant increases in the amount of histidase and its mRNA. The response was more pronounced in rats fed diets containing >18% casein. Rats fed a 12% casein diet containing 1.25% histidine did not have different Hal activity and mRNA levels compared with rats fed a 12% casein diet, indicating that Hal expression is not modified by its substrate. Injection of glucagon into rats fed the 10% casein diet increased Hal activity threefold and Hal- mRNA expression fivefold compared with uninjected rats fed the same diet. The apparent half-life of hepatic histidase in protein-depleted rats previously fed an 80% casein diet was 2.8 d, whereas the half-life of Hal-mRNA was 17 h. In summary, these data support the hypothesis that Hal expression is regulated by dietary protein at the pretranslational level in rat liver, and that glucagon is one of the hormones involved in the induction of Hal.