Effect of low-and non-calorie sweeteners on the gut microbiota: A review of clinical trials and cross-sectional studies

Use of non-nutritive sweeteners (NNSs) has increased worldwide in recent decades. However, evidence from preclinical studies shows that sweetener consumption may induce glucose intolerance through changes in the gut microbiota, which raises public health concerns. As studies conducted on humans are lacking, the aim of this review was to gather and summarize the current evidence on the effects of NNSs on human gut microbiota. Only clinical trials and cross-sectional studies were included in the review. Regarding NNSs (i.e, saccharin, sucralose, aspartame, and stevia), only two of five clinical trials showed significant changes in gut microbiota composition after the intervention protocol. These studies concluded that saccharin and sucralose impair glycemic tolerance. In three of the four cross-sectional studies an association between NNSs and the microbial composition was observed. All three clinical trials on polyols (i.e, xylitol) showed prebiotic effects on gut microbiota, but these studies had multiple limitations (publication date, dosage, duration) that jeopardize their validity. The microbial response to NNSs consumption could be strongly mediated by the gut microbial composition at baseline. Further studies in which the potential personalized microbial response to NNSs consumption is acknowledged, and that include longer intervention protocols, larger cohorts, and more realistic sweetener dosage are needed to broaden these findings

Estudios de trasplante de microbiota fecal en síndrome metabólico, obesidad y diabetes, ¿dónde nos encontramos?

Fundamento: El trasplante de microbiota fecal (FMT) consiste en la transferencia de las heces de un donante sano a otro paciente con el objetivo de cambiar o restablecer la composición y función de su microbiota. Su única aplicación clínica actualmente aceptada es el tratamiento de infección recurrente por Clostridium difficile. No obstante, se está estudiando su empleo en enfermedades como la enfermedad inflamatoria intestinal, el autismo y las enfermedades metabólicas. En este último grupo encontramos el síndrome metabólico, la obesidad y la diabetes tipo 2, tres enfermedades relacionadas entre sí y cada vez más prevalentes en nuestro tiempo. Las tres se caracterizan por cursar con una disbiosis de la microbiota intestinal y en este contexto surge la idea del empleo del FMT para su tratamiento. El objetivo de este Trabajo de Fin de Grado es conocer los estudios que se han realizado para evaluar el efecto del FMT con donantes humanos en síndrome metabólico, obesidad y diabetes. Metodología: Se ha llevado a cabo una revisión sistemática utilizando la base de datos PubMed, realizando tres búsquedas por términos MeSH relacionando “fecal microbiota transplantation” con “obesity”, “diabetes” y “metabolic syndrome” y aplicando las metodologías PRISMA y PICO para seleccionar los resultados de interés. Resultados: Se han valorado siete artículos de intervención que evalúan el efecto del FMT con donantes humanos y receptores humanos o animales. Existen pocos resultados concluyentes sobre el efecto del FMT en la microbiota del receptor, debido a que los artículos son heterogéneos y valoran parámetros diferentes. Conclusión: El FMT supone un avance en el conocimiento de la relación entre la microbiota y las enfermedades metabólicas y, conforme obtenemos más información de los estudios de intervención realizados, nos acercamos a la posibilidad de aplicar este procedimiento en el tratamiento de otras enfermedades además de la infección por Clostridium difficile.Background: The fecal microbiota transplantation (FMT) consists in the transfer of gastrointestinal microbiota from a healthy individual to another in order to change or restore the composition and function of the recipient’s microbiota. Nowadays this method is only accepted as a therapeutic option for Clostridium difficile infection. However, there are many studies evaluating its applicability in other diseases such as inflammatory bowel disease, irritable bowel syndrome, autism and metabolic disorders, like obesity, diabetes or metabolic syndrome. In this project we are focusing on these three metabolic diseases, which incidence has increased rapidly worldwide. They are characterized by a dysbiosis of the intestinal microbiota and that is the reason why the idea of fecal microbiota transplantation as a possible therapeutic option arises. The main objective of this project is to analyse the currently available studies that evaluate the effect of fecal microbiota transplantation, from humans to either humans or animals, in the physiopathology of obesity, diabetes and metabolic syndrome. Methodology: A systematic review was carried out using the PubMed database with three independent searches using MeSH terms relating “fecal microbiota transplantation” and “obesity”, “diabetes” and “metabolic syndrome”. PRISMA and PICO methodologies were applied to select the studies of interest. Results: Seven articles from intervention studies that evaluate FMT with human donors and human or animal recipients have been included in this systematic review. To date, there are few conclusive results due to the heterogeneity of the studies. Conclusion: New studies on FMT represent an advance in the knowledge of the relationship between the microbiota and metabolic disorders. As we obtain more information regarding the applicability of this technique and its effect, we approach the possibility of applying it in the treatment of other diseases a part from infection by Clostridium difficile

Epigenética en obesidad y diabetes tipo 2: papel de la nutrición, limitaciones y futuras aplicaciones

In the last years, epigenetics is helping to explain the mechanisms non dependent on the genetic sequence by which the nutrients and other environmental factors contribute to modulate gene expression and disease development. Obesity and type 2 diabetes are two diseases that have been linked to changes in epigenetic marks (particularly DNA methylation, covalent modifications of histones and miRNAs). These epigenetic changes appear to be influenced, mainly in the perinatal period but also in adulthood, by environmental factors such as hyperglycemia or the diet. Among the food compounds that have been linked to epigenetic modifications, there are methyl donor groups, excessive or deficient caloric intake, short chain fatty acids, some minerals and antioxidant vitamins, and various compounds of plant origin, as catechins, isoflavones or isothiocyanates. EWAS studies, that analyze the methylation of thousands of CpG sites in thousands of individuals, will contribute in the next years to identify some of the epigenetic marks that can be used as early predictors of metabolic risk, as well as some intimate mechanisms that explain the development of obesity, type 2 diabetes and its complications. Moreover, epigenetic marks, among them the CpG-SNPs, can be heritable but some of them could be potentially reversible. One of the medium-term objectives is to develop drug or diet-related treatments that could delay or even reverse these epigenetic changes

Interplay of early-life nutritional programming on obesity, inflammation and epigenetic outcomes

The huge health burden accompanying obesity is not only attributable to inadequate dietary and sedentary lifestyle habits, since a predisposing genetic make-up and other putative determinants concerning easier weight gain and fat deposition have been reported. Thus, several investigations aiming to understand energy metabolism and body composition maintenance have been performed considering the participation of perinatal nutritional programming and epigenetic processes as well as inflammation phenomena. The Developmental Origins of Health and Disease hypothesis and inheritance-oriented investigations concerning gene–nutrient interactions on energy homoeostasis and metabolic functions have suggested that inflammation could be not only a comorbidity of obesity but also a cause. There are several examples about the role of nutritional interventions in pregnancy and lactation, such as energetic deprivation, protein restriction and excess fat, which determine a cluster of disorders affecting energy efficiency in the offspring as well as different metabolic pathways, which are mediated by epigenetics encompassing the chromatin information encrypted by DNA methylation patterns, histone covalent modifications and non-coding RNA or microRNA. Epigenetic mechanisms may be boosted or impaired by dietary and environmental factors in the mother, intergenerationally or transiently transmitted, and could be involved in the obesity and inflammation susceptibility in the offspring. The aims currently pursued are the early identification of epigenetic biomarkers concerned in individual's disease susceptibility and the description of protocols for tailored dietary treatments/advice to counterbalance adverse epigenomic events. These approaches will allow diagnosis and prognosis implementation and facilitate therapeutic strategies in a personalised ‘epigenomically modelled’ manner to combat obesity and inflammation

Implication of miR-612 and miR-1976 in the regulation of TP53 and CD40 and their relationship in the response to specific weight-loss diets

Background: Non-coding RNAs (i.e., miRNAs) play a role in the development of obesity and related comorbidities and the regulation of body weight. Objective: To identify candidate miRNA biomarkers throughout omics approaches in order to predict the response to specific weight-loss dietary treatments. Design: Genomic DNA and cDNA isolated from white blood cells of a subset from the RESMENA nutritional intervention study (Low-responders (LR) vs High-responders (HR)) was hybridized in Infinium Human Methylation450 BeadChip and in Illumina Human HT-12 v4 gene expression BeadChips arrays respectively. A bioinformatic prediction of putative target sites of selected miRNAs was performed by applying miRBase algorithms. HEK-293T cells were co-transfected with expression vectors containing the 3'-UTR of candidate genes to validate the binding of miRNAs to its target sites. Results: 134 miRNAs were differentially methylated between HR and LR in the methylation array, whereas 44 miRNAs were differentially expressed between both groups in the expression array. Specifically, miR-1237, miR-1976, miR-642, miR-636, miR-612 and miR-193B were simultaneously hypomethylated and overexpressed in HR. miR-612 and miR-1976 showed greatest differences in methylation and expression levels, respectively. The bioinformatic prediction revealed that TP53 was a putative target gene of miR-612 and CD40 of miR-1976. Moreover, TP53 was downregulated in the expression array when comparing HR vs LR expression levels adjusted by sex, diet, age and baseline weight, and CD40 showed a statistical trend. Furthermore, gene expression levels of TP53 and CD40 in white blood cells, when measured by qPCR, were also downregulated in HR. Finally, miR-612 and miR-1976 potently repressed TP53 and CD40 respectively by targeting its 3'-UTR regions. Conclusion: miR-612 and miR-1976 levels could be prospective biomarkers of response to specific weight-loss diets and might regulate the gene expression of TP53 and CD40

One-carbon metabolism and nonalcoholic fatty liver disease: The crosstalk between nutrients, microbiota, and genetics

The prevalence of nonalcoholic fatty liver disease (NAFLD) is increasing worldwide. Its etiology includes nutritional, genetic, and lifestyle factors. Several mechanisms may link onecarbon metabolism – the associated metabolic pathways of folate, methionine, and choline – to the onset of NAFLD. In this review, we attempted to assess how choline, folate, methionine, and betaine affect NAFLD development, mainly through their role in the secretion of very low-density lipoproteins (VLDL) from the liver. We also reviewed recent articles that have described the relation between microbiota metabolism and NAFLD progression. Moreover, we describe the effect of single-nucleotide polymorphisms (SNP) in genes related to one-carbon metabolism and disease prevalence. We additionally seek SNP identified by genome-wide associations that may increase the risk of this disease. Even though the evidence available is not entirely consistent, it seems that the concentrations of choline, methionine, folate, and betaine may affect the progression of NAFLD. Since there is no effective therapy for NAFLD, further investigations into the link between nutrition, gut microbiota, genetic factors, and NAFLD are still necessary, with a particular emphasis on methyl donors

Fat-to-glucose interconversion by hydrodynamic transfer of two glyoxylate cycle enzyme genes

The glyoxylate cycle, which is well characterized in higher plants and some microorganisms but not in vertebrates, is able to bypass the citric acid cycle to achieve fat-to-carbohydrate interconversion. In this context, the hydrodynamic transfer of two glyoxylate cycle enzymes, such as isocytrate lyase (ICL) and malate synthase (MS), could accomplish the shift of using fat for the synthesis of glucose. Therefore, 20 mice weighing 23.37 +/- 0.96 g were hydrodinamically gene transferred by administering into the tail vein a bolus with ICL and MS. After 36 hours, body weight, plasma glucose, respiratory quotient and energy expenditure were measured. The respiratory quotient was increased by gene transfer, which suggests that a higher carbohydrate/lipid ratio is oxidized in such animals. This application could help, if adequate protocols are designed, to induce fat utilization for glucose synthesis, which might be eventually useful to reduce body fat depots in situations of obesity and diabete

Dietary factors, epigenetic modifications and obesity outcomes: Progresses and perspectives

Nutritional factors play a life-long role in human health. Indeed, there is growing evidence that one of the mechanisms by which nutrients and bioactive compounds affect metabolic traits is epigenetics. Complex interactions among food components and histone modifications, DNA methylation, non-coding RNA expression and chromatin remodeling factors lead to a dynamic regulation of gene expression that controls the cellular phenotype. Although perinatal period is the time of highest phenotypic plasticity, contributing largely to developmental programming, also during adulthood there is evidence about a nutritional influence on epigenetic regulation. Similarly to type 2 diabetes, hypertension, atherosclerosis and other metabolic disorders, obesity predisposition and weight loss outcomes have been repeatedly associated to changes in epigenetic patterns. Different non-nutritional risk factors that usually accompany obesity seem also to be involved in these epigenetic modifications, especially hyperglycemia, inflammation, hypoxia and oxidative stress. There are currently three major objectives in epigenetic research in relation to obesity: to search for epigenetic biomarkers to predict future health problems or detect the individuals at most risk, to understand the obesity-related environmental factors that could modulate gene expression by affecting epigenetic mechanisms, and to study novel therapeutic strategies based on nutritional or pharmacological agents that can modify epigenetic marks. At this level, the major tasks are: development of robust epigenetic biomarkers of weight regulation, description of those epigenetic marks more susceptible to be modified by dietary exposures, identification of the active ingredients (and the doses) that alter the epigenome, assessment of the real importance of other obesity-related factors on epigenetic regulation, determination of the period of life in which best results are obtained, and understanding the importance of the inheritance of these epigenetic marks

Implication of Trimethylamine N-Oxide (TMAO) in disease: Potential biomarker or new therapeutic target

Trimethylamine N-oxide (TMAO) is a molecule generated from choline, betaine, and carnitine via gut microbial metabolism. The plasma level of TMAO is determined by several factors including diet, gut microbial flora, drug administration and liver flavin monooxygenase activity. In humans, recent clinical studies evidence a positive correlation between elevated plasma levels of TMAO and an increased risk for major adverse cardiovascular events. A direct correlation between increased TMAO levels and neurological disorders has been also hypothesized. Several therapeutic strategies are being explored to reduce TMAO levels, including use of oral broad spectrum antibiotics, promoting the growth of bacteria that use TMAO as substrate and the development of target-specific molecules. Despite the accumulating evidence, it is questioned whether TMAO is the mediator of a bystander in the disease process. Thus, it is important to undertake studies to establish the role of TMAO in human health and disease. In this article, we reviewed dietary sources and metabolic pathways of TMAO, as well as screened the studies suggesting possible involvement of TMAO in the etiology of cardiovascular and neurological disorders, underlying the importance of TMAO mediating inflammatory processes. Finally, the potential utility of TMAO as therapeutic target is also analyzed

Dietary supplementation with methyl donors reduces fatty liver and modifies the fatty acid synthase DNA methylation profile in rats fed an obesogenic diet

Non-alcoholic fatty liver disease (NAFLD) is one of the first hepatic manifestations of metabolic syndrome, whose progression can lead to cirrhosis and hepatic carcinoma. Interestingly, methyl donor supplementation could improve obesogenic diet-induced hepatic triglyceride accumulation. The aim of this research is to describe methyl donor effects on a high-fat-sucrose (HFS) diet in both sexes and epigenetic changes induced on fatty acid synthase (FASN) promoter methylation pattern as well as gene expression of NAFLD key metabolic genes. Twenty-four male and 28 female Wistar rats were assigned to three dietary groups: control, HFS, and HFS supplemented with methyl donors (choline, betaine, vitamin B12, and folic acid). After 8 weeks of treatment, somatic, biochemical, mRNA, and epigenetic measurements were performed. Rats fed the HFS diet presented an overweight phenotype and alterations in plasma biochemical measurements. Methyl donor supplementation reverted the HFS-diet-induced hepatic triglyceride accumulation. Analysis of FASN promoter cytosine methylation showed changes in both sexes due to the obesogenic diet at -1,096, -780, -778, and -774 CpG sites with respect to the transcriptional start site. Methyl donor supplementation modified DNA methylation at -852, -833, -829, -743, and -733 CpGs depending on the sex. RT-PCR analysis confirmed that FASN expression tended to be altered in males. Our findings reinforce the hypothesis that methyl donor supplementation can prevent hepatic triglyceride accumulation induced by obesogenic diets in both sexes. Changes in liver gene expression profile and epigenetic-mediated mechanisms related to FASN DNA hypermethylation could be involved in methyl donor-induced NAFLD improvement