Development of gut microflora in obese and lean rats

The Role of Adipokines in Health and Disease

Adipokines are cell-signaling proteins secreted by adipose tissue that has been related to a low-grade state of inflammation and different pathologies. The present review aims to analyze the role of adipokines in health and disease in order to understand the important functions and effects of these cytokines. For this aim, the present review delves into the type of adipocytes and the cytokines produced, as well as their functions; the relations of adipokines in inflammation and different diseases such as cardiovascular, atherosclerosis, mental diseases, metabolic disorders, cancer, and eating behaviors; and finally, the role of microbiota, nutrition, and physical activity in adipokines is discussed. This information would allow for a better understanding of these important cytokines and their effects on body organisms.

Dietary fatty acids in gut health: Absorption, metabolism and function

In biological responses, fatty acids (FA) are absorbed and metabolized in the form of substrates for energy production. The molecular structures (number of double bonds and chain length) and composition of dietary FA impact digestion, absorption and metabolism, and the biological roles of FA. Recently, increasing evidence indicates that FA are essentially utilized as an energy source and are signaling molecules that exert physiological activity of gut microbiota and immune responses. In addition, FA could serve as natural ligands for orphan G protein-coupled receptors (GPCR), also called free fatty acid receptors (FFAR), which intertwine metabolic and immune systems via multiple mechanisms. The present review explores the recent findings on FA absorption and its impact on gut health, particularly addressing the mechanism by which dietary FA potentially influences intestinal microbiota and epithelial functions. Also, this work attempts to uncover research ideas for devising future strategies for manipulating the composition of dietary FA to regulate gut health and support a normal immune system for metabolic and immune disorders.

Jejunum: The understudied meeting place of dietary lipids and the microbiota

Although the jejunum is the main intestinal compartment responsible for lipid digestion and absorption, most of the studies assessing the impact of dietary lipids on the intestinal microbiota have been performed in the ileum, colon and faeces. This lack of interest in the jejunum is due to the much lower number of microbes present in this intestinal region and to the difficulty in accessing its lumen, which requires invasive methods. Recently, several recent publications highlighted that the whole jejunal microbiota or specific bacterial members are able to modulate lipid absorption and metabolism in enterocytes. This information reveals new strategies in the development of bacterial- and metabolite-based therapeutic interventions or nutraceutical recommendations to treat or prevent metabolic-related disorders, including obesity, cardiovascular diseases and malnutrition. This review is strictly focused on the following triad: dietary lipids, the jejunal epithelium and the jejunal microbiota. First, we will describe each member of the triad: the structure and functions of the jejunum, the composition of the jejunal microbiota, and dietary lipid handling by enterocytes and by microorganisms. Then, we will present the mechanisms leading to lipid malabsorption in small intestinal bacterial overgrowth (SIBO), a disease in which the jejunal microbiota is altered and which highlights the strong interactions among this triad. We will finally review the recent literature about the interactions among members of the triad, which should encourage research teams to further explore the mechanisms by which specific microbial strains or metabolites, alone or in concert, can mediate, control or modulate lipid absorption in the jejunum.

Maternal high fat diet and its consequence on the gut microbiome: A rat model

The biological changes that occur during pregnancy in the female mammal include shifts in hormonal regulation in preparation for parturition and lactation, and changes in energy metabolism. In women, studies have also shown that during pregnancy there is a reduction in bacterial species richness in the gut. In the current experiment rats were used to model the interaction of diet, reproductive status, and intestinal bacterial microbiota during pregnancy and lactation. In Experiment 1 rats were exposed to either standard chow or high-fat chow (60%) and were divided into two groups: unmated (NULL) or mated (RE). In Experiment 2, both NULL and RE rats were exposed to high-fat chow for a 30-day period. High-throughput sequencing of the 16S rRNA gene revealed that pregnancy impacted the gut microbiota in a similar manner to humans. The impact of reproductive status on microbiota composition, however, was stronger in rats fed a high-fat (HF) diet. Diet-induced changes replicated some of the changes observed in humans, such as increasing the Firmicutes/Bacteroidetes ratio. However, in contrast to humans, pregnancy in rats did not increase β-diversity between microbiota from different animals. These results indicate that during pregnancy in rats, the gut microbiota is altered in a similar manner to that which occurs in women, and that these changes are further exaggerated by exposure to a HF diet. Thus, the rat may allow modelling the effects of consumption of HF food during pregnancy and enable future studies to determine the risks of HF diets during pregnancy and its consequences on the offspring.

Nonalcoholic Fatty Liver Disease Is Exacerbated in High-Fat Diet-Fed Gnotobiotic Mice by Colonization with the Gut Microbiota from Patients with Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is a serious liver disorder associated with the accumulation of fat and inflammation. The objective of this study was to determine the gut microbiota composition that might influence the progression of NAFLD. Germ-free mice were inoculated with feces from patients with nonalcoholic steatohepatitis (NASH) or from healthy persons (HL) and then fed a standard diet (STD) or high-fat diet (HFD). We found that the epididymal fat weight, hepatic steatosis, multifocal necrosis, and inflammatory cell infiltration significantly increased in the NASH-HFD group. These findings were consistent with markedly elevated serum levels of alanine transaminase, aspartate transaminase, endotoxin, interleukin 6 (IL-6), monocyte chemotactic protein 1 (Mcp1), and hepatic triglycerides. In addition, the mRNA expression levels of Toll-like receptor 2 (Tlr2), Toll-like receptor 4 (Tlr4), tumor necrosis factor alpha (Tnf-α), Mcp1, and peroxisome proliferator-activated receptor gamma (Ppar-γ) significantly increased. Only abundant lipid accumulation and a few inflammatory reactions were observed in group HL-HFD. Relative abundance of Bacteroidetes and Firmicutes shifted in the HFD-fed mice. Furthermore, the relative abundance of Streptococcaceae was the highest in group NASH-HFD. Nevertheless, obesity-related Lactobacillaceae were significantly upregulated in HL-HFD mice. Our results revealed that the gut microbiota from NASH Patients aggravated hepatic steatosis and inflammation. These findings might partially explain the NAFLD progress distinctly was related to different compositions of gut microbiota.

Dietary Whole Egg Consumption Attenuates Body Weight Gain and Is More Effective than Supplemental Cholecalciferol in Maintaining Vitamin D Balance in Type 2 Diabetic Rats

Background: Type 2 diabetes (T2D) is characterized by vitamin D insufficiency owing to excessive urinary loss of 25-hydroxycholecalciferol [25(OH)D]. We previously reported that a diet containing dried whole egg, a rich source of vitamin D, was effective at maintaining circulating 25(OH)D concentrations in rats with T2D. Furthermore, whole egg consumption reduced body weight gain in rats with T2D.Objective: This study was conducted to compare whole egg consumption with supplemental cholecalciferol with respect to vitamin D balance, weight gain, and body composition in rats with T2D.Methods: Male Zucker diabetic fatty (ZDF) rats (n = 24) and their lean controls (n = 24) were obtained at 5 wk of age and randomly assigned to 3 treatment groups: a casein-based diet (CAS), a dried whole egg-based diet (WE), or a casein-based diet containing supplemental cholecalciferol (CAS+D) at the same amount of cholecalciferol provided by WE (37.6 μg/kg diet). Rats were fed their respective diets for 8 wk. Weight gain and food intake were measured daily, circulating 25(OH)D concentrations were measured by ELISA, and body composition was analyzed by dual X-ray absorptiometry.Results: Weight gain and percentage of body fat were reduced by ∼20% and 11%, respectively, in ZDF rats fed WE compared with ZDF rats fed CAS or CAS+D. ZDF rats fed CAS had 21% lower serum 25(OH)D concentrations than lean rats fed CAS. In ZDF rats, WE consumption increased serum 25(OH)D concentrations 130% compared with CAS, whereas consumption of CAS+D increased serum 25(OH)D concentrations 35% compared with CAS.Conclusions: Our data suggest that dietary consumption of whole eggs is more effective than supplemental cholecalciferol in maintaining circulating 25(OH)D concentrations in rats with T2D. Moreover, whole egg consumption attenuated weight gain and reduced percentage of body fat in ZDF rats. These data may support new dietary recommendations targeting the prevention of vitamin D insufficiency in T2D.

Effect of Pre- and Post-Weaning High-Fat Dietary Manipulation on Intestinal Microflora and Alkaline Phosphatase Activity in Male Rats

We investigated the impact of a high-fat (HF) diet during pre- and post-weaning periods on the intestinal microbiota and alkaline phosphatase (AP) activity in male rats. Nutrition from birth was influenced by feeding rat dams with either a standard or HF diet. After weaning male pups nursed by control dams continued on a standard diet (CC) or HF diet (C→HF), while offspring nursed by HF dams continued on HF diet (HF) or standard diet (HF→C). The numbers of Bacteroides/Prevotella (BAC) and Lactobacillus/Enterococcus (LAB) in the gut were determined by FISH technique. HF pups displayed enhanced adiposity and increased AP activity (19 %), as well as higher LAB (P<0.001) and lower numbers of BAC (P<0.001) in the jejunum and colon than controls. In HF→C rats, post-weaning lower fat intake resulted in decreased fat deposition accompanied by reduced AP activity (20 %) compared to HF rats. Composition of the intestinal microbiota in these rats was not influenced. In contrast, in comparison with controls, C→HF rats displayed higher LAB (P<0.001) and lower BAC (P<0.001) together with increased adiposity and AP activity (14 %). These results indicate that consumption of diet with different fat content could modulate gut microbial/functional conditions depending on the period when the nutritional manipulation occurs.

Role of Gut Microbiota in the Aetiology of Obesity: Proposed Mechanisms and Review of the Literature

The aetiology of obesity has been attributed to several factors (environmental, dietary, lifestyle, host, and genetic factors); however none of these fully explain the increase in the prevalence of obesity worldwide. Gut microbiota located at the interface of host and environment in the gut are a new area of research being explored to explain the excess accumulation of energy in obese individuals and may be a potential target for therapeutic manipulation to reduce host energy storage. Several mechanisms have been suggested to explain the role of gut microbiota in the aetiology of obesity such as short chain fatty acid production, stimulation of hormones, chronic low-grade inflammation, lipoprotein and bile acid metabolism, and increased endocannabinoid receptor system tone. However, evidence from animal and human studies clearly indicates controversies in determining the cause or effect relationship between the gut microbiota and obesity. Metagenomics based studies indicate that functionality rather than the composition of gut microbiota may be important. Further mechanistic studies controlling for environmental and epigenetic factors are therefore required to help unravel obesity pathogenesis.

Changes in gut microbiota in rats fed a high fat diet correlate with obesity-associated metabolic parameters

The gut microbiota is emerging as a new factor in the development of obesity. Many studies have described changes in microbiota composition in response to obesity and high fat diet (HFD) at the phylum level. In this study we used 16s RNA high throughput sequencing on faecal samples from rats chronically fed HFD or control chow (n = 10 per group, 16 weeks) to investigate changes in gut microbiota composition at the species level. 53.17% dissimilarity between groups was observed at the species level. Lactobacillus intestinalis dominated the microbiota in rats under the chow diet. However this species was considerably less abundant in rats fed HFD (P<0.0001), this being compensated by an increase in abundance of propionate/acetate producing species. To further understand the influence of these species on the development of the obese phenotype, we correlated their abundance with metabolic parameters associated with obesity. Of the taxa contributing the most to dissimilarity between groups, 10 presented significant correlations with at least one of the tested parameters, three of them correlated positively with all metabolic parameters: Phascolarctobacterium, Proteus mirabilis and Veillonellaceae, all propionate/acetate producers. Lactobacillus intestinalis was the only species whose abundance was negatively correlated with change in body weight and fat mass. This species decreased drastically in response to HFD, favouring propionate/acetate producing bacterial species whose abundance was strongly correlated with adiposity and deterioration of metabolic factors. Our observations suggest that these species may play a key role in the development of obesity in response to a HFD.

Effect of repeated fasting/refeeding on obesity development and health complications in rats arising from reduced nest

BACKGROUND

Overnutrition during postnatal life represents a risk factor for later obesity and associated metabolic disorders.

AIM

We investigated the interaction between postnatal and later-life nutrition on body composition, blood pressure and the jejunal enzyme activities in male Sprague-Dawley rats.

METHODS

From birth, we adjusted the number of pups in the nest to 4 (small litters-SL; overfeeding) or to 10 pups (normal litters-NL; controls), and from day 50 until 70, the SL (SL-R) and NL (NL-R) rats were subjected to 1 day fasting and 1 day refeeding cycles (RFR). Their body composition was determined by magnetic resonance imaging, and enzyme activity was assayed histochemically.

RESULTS

At 50 and 70 days, SL rats were found to be overweight (p < 0.001), with higher adiposity (p < 0.001) and blood pressure (p < 0.01). Moreover, despite significantly decreased daily food intake during RFR (SL-R 39 %, NL-R 23 %), higher fat deposition (p < 0.001) and blood pressure (p < 0.05) was detected in SL-R rats. Activity of alkaline phosphatase (AP) functionally involved in lipid absorption was significantly higher in SL than NL rats (p < 0.001) but substantially decreased in RFR groups (SL-R p < 0.001, NL-R p < 0.01). However, despite these enzymatic adaptations to reduced food intake, the SL-R rats displayed significantly higher AP activity in comparison with NL-R rats (p < 0.01) on day 70.

CONCLUSIONS

Our results demonstrate that postnatal overfeeding predisposes the ontogeny of intestinal function, which may promote the probability of obesity risk. Accordingly, in these animals, efficient fat deposition and elevated blood pressure were not diminished in response to dietary restrictions in later life.

Two-Generation Diet-Induced Obesity Model Producing Mice With Increased Amount of Body Fat in Early Adulthood

The aim of our study was to develop a model producing obese mice in early adulthood (4-6 weeks) based on their over-nutrition during fetal and early postnatal development. The fertilized dams of the parental generation were fed the standard diet supplemented with high-energy nutritional product Ensure Plus during gestation and lactation. Delivered weanlings were then fed with standard or supplemented diet and assessed for body fat deposits using EchoMRI at the time of early and late adulthood. Maternal over-feeding during the period before weaning had the most significant effect on obesity development in the filial generation. In weanlings, significantly higher body fat deposits and average body weight were recorded. Later, further significant increase in percentage of body fat in both male and female mice was observed. Withdrawal of the Ensure Plus supplement caused a decrease in the percentage of body fat in part of the filial generation. In offspring fed the standard diet, higher fat deposits persisted till the time of late adulthood. We conclude that this diet-induced obesity model might be used in exploration of the effects of elevated body fat on physiological functions of various organ systems during juvenile and early adulthood periods of life of a human being.

Lactobacillus species shift in distal esophagus of high-fat-diet-fed rats

AIM: To analyze the microbiota shift in the distal esophagus of Sprague-Dawley rats fed a high-fat diet.

METHODS: Twenty Sprague-Dawley rats were divided into high-fat diet and normal control groups of 10 rats each. The composition of microbiota in the mucosa from the distal esophagus was analyzed based on selective culture. A variety of Lactobacillus species were identified by molecular biological techniques. Bacterial DNA from Lactobacillus colonies was extracted, and 16S rDNA was amplified by PCR using bacterial universal primers. The amplified 16S rDNA products were separated by denaturing gradient gel electrophoresis (DGGE). Every single band was purified from the gel and sent to be sequenced.

RESULTS: Based on mucosal bacterial culturing in the distal esophagus, Staphylococcus aureus was absent, and total anaerobes and Lactobacillus species were decreased significantly in the high-fat diet group compared with the normal control group (P < 0.01). Detailed DGGE analysis on the composition of Lactobacillus species in the distal esophagus revealed that Lactobacillus crispatus, Lactobacillus gasseri (L. gasseri) and Lactobacillus reuteri (L. reuteri) comprised the Lactobacillus species in the high-fat diet group, while the composition of Lactobacillus species in the normal control group consisted of L. gasseri, Lactobacillus jensenii and L. reuteri.

CONCLUSION: High-fat diet led to a mucosal microflora shift in the distal esophagus in rats, especially the composition of Lactobacillus species.

The remarkable capacity for gut microbial and host interactions

The stunning complexity of the resident microbiota and the intricate pathways of microbial and host interactions provide a massive adaptive capacity for mammals. In this addendum we reflect on our recent publication on Toll-like receptor 2 deficiency related colonic mucosal epigenetic, immunologic and microbiomic changes. Our findings underscored the tremendous flexibility of the gut and its microbiota. This flexibility can provide means to overcome significant environmental or genetic challenges. In the meantime, the challenged intestinal system may become vulnerable to otherwise tolerable insults. In such instances, the fine-tuned mutualistic balance between the gut and its microflora may collapse leading to dysbiosis and disease. The ultimate challenge for biomedical research in these cases is to find optimal means for the restoration and maintenance of healthy host physiology.