Marc R. Bomhof

Low-Dose Aspartame Consumption Differentially Affects Gut Microbiota-Host Metabolic Interactions in the Diet-Induced Obese Rat

Aspartame consumption is implicated in the development of obesity and metabolic disease despite the intention of limiting caloric intake. The mechanisms responsible for this association remain unclear, but may involve circulating metabolites and the gut microbiota. Aims were to examine the impact of chronic low-dose aspartame consumption on anthropometric, metabolic and microbial parameters in a diet-induced obese model. Male Sprague-Dawley rats were randomized into a standard chow diet (CH, 12% kcal fat) or high fat (HF, 60% kcal fat) and further into ad libitum water control (W) or low-dose aspartame (A, 5–7 mg/kg/d in drinking water) treatments for 8 week (n = 10–12 animals/treatment). Animals on aspartame consumed fewer calories, gained less weight and had a more favorable body composition when challenged with HF compared to animals consuming water. Despite this, aspartame elevated fasting glucose levels and an insulin tolerance test showed aspartame to impair insulin-stimulated glucose disposal in both CH and HF, independently of body composition. Fecal analysis of gut bacterial composition showed aspartame to increase total bacteria, the abundance of Enterobacteriaceae and Clostridium leptum. An interaction between HF and aspartame was also observed for Roseburia ssp wherein HF-A was higher than HF-W (P<0.05). Within HF, aspartame attenuated the typical HF-induced increase in the Firmicutes:Bacteroidetes ratio. Serum metabolomics analysis revealed aspartame to be rapidly metabolized and to be associated with elevations in the short chain fatty acid propionate, a bacterial end product and highly gluconeogenic substrate, potentially explaining its negative affects on insulin tolerance. How aspartame influences gut microbial composition and the implications of these changes on the development of metabolic disease require further investigation.

Combined effects of oligofructose and Bifidobacterium animalis on gut microbiota and glycemia in obese rats

Prebiotics and probiotics may be able to modify an obesity‐associated gut microbiota. The aim of this study was to examine the individual and combined effects of the prebiotic oligofructose (OFS) and the probiotic Bifidobacterium animalis subsp. lactis BB‐12 (BB‐12) on gut microbiota and host metabolism in obese rats.

Chronic coffee consumption in the diet-induced obese rat: impact on gut microbiota and serum metabolomics.

Epidemiological data confirms a strong negative association between regular coffee consumption and the prevalence of type 2 diabetes. Coffee is initially absorbed in the stomach and small intestine but is further fermented in the colon by gut microbiota. The bioavailability, production and biological activity of coffee polyphenols is modulated, in part, by gut microbiota. The purpose of this study was to determine if chronic coffee consumption could mitigate negative gut microbiota and metabolomic profile changes induced by a high-fat diet. Male Sprague-Dawley rats were randomized to chow (12% kcal fat) or high-fat (60% kcal fat) diet. Each group was further divided into water or caffeinated coffee for 10 weeks. Coffee consumption in high-fat-fed rats was associated with decreased body weight, adiposity, liver triglycerides and energy intake. Despite a more favorable body composition, rats displayed profound systemic insulin resistance, likely due to caffeine. Coffee consumption attenuated the increase in Firmicutes (F)-to-Bacteroidetes (B) ratio and Clostridium Cluster XI normally associated with high-fat feeding but also resulted in augmented levels of Enterobacteria. In the serum metabolome, coffee had a distinct impact, increasing levels of aromatic and circulating short-chain fatty acids while lowering levels of branched-chain amino acids. In summary, coffee consumption is able to alter gut microbiota in high-fat-fed rats although the role of these changes in reducing diabetes risk is unclear given the increased insulin resistance observed with coffee in this study.

Diet-induced changes in maternal gut microbiota and metabolomic profiles influence programming of offspring obesity risk in rats.

Maternal obesity and overnutrition during pregnancy and lactation can program an increased risk of obesity in offspring. In this context, improving maternal metabolism may help reduce the intergenerational transmission of obesity. Here we show that, in Sprague-Dawley rats, selectively altering obese maternal gut microbial composition with prebiotic treatment reduces maternal energy intake, decreases gestational weight gain, and prevents increased adiposity in dams and their offspring. Maternal serum metabolomics analysis, along with satiety hormone and gut microbiota analysis, identified maternal metabolic signatures that could be implicated in programming offspring obesity risk and highlighted the potential influence of maternal gut microbiota on maternal and offspring metabolism. In particular, the metabolomic signature of insulin resistance in obese rats normalized when dams consumed the prebiotic. In summary, prebiotic intake during pregnancy and lactation improves maternal metabolism in diet-induced obese rats in a manner that attenuates the detrimental nutritional programming of offspring associated with maternal obesity. Overall, these findings contribute to our understanding of the maternal mechanisms influencing the developmental programming of offspring obesity and provide compelling pre-clinical evidence for a potential strategy to improve maternal and offspring metabolic outcomes in human pregnancy.

Exercise training modifies gut microbiota in normal and diabetic mice.

Cecal microbiota from type 2 diabetic (db/db) and control (db/(+)) mice was obtained following 6 weeks of sedentary or exercise activity. qPCR analysis revealed a main effect of exercise, with greater abundance of select Firmicutes species and lower Bacteroides/Prevotella spp. in both normal and diabetic exercised mice compared with sedentary counterparts. Conversely, Bifidobacterium spp. was greater in exercised normal but not diabetic mice (exercise × diabetes interaction). How exercise influences gut microbiota requires further investigation.

Muscle-specific differences in the response of mitochondrial proteins to β-GPA feeding: an evaluation of potential mechanisms

Beta-Guanadinopropionic acid (beta-GPA) feeding leads to reductions in skeletal muscle phosphagen concentrations and has been used as a tool with which to study the effects of energy charge on skeletal muscle metabolism. Supplementing standard rodent diets with beta-GPA leads to increases in mitochondrial enzyme content in fast but not slow-twitch muscles from male rats. Given this apparent discrepancy between muscle types we used beta-GPA feeding as a model to study signaling pathways involved in mitochondrial biogenesis. We hypothesized that beta-GPA feeding would result in a preferential activation of p38 MAPK and AMPK signaling and reductions in RIP140 protein content in triceps but not soleus muscle. Despite similar reductions in high-energy phosphate concentrations, 6 wk of beta-GPA feeding led to increases in mitochondrial proteins in triceps but not soleus muscles. Differences in the response of mitochondrial proteins to beta-GPA feeding did not seem to be related to a differential activation of p38 MAPK and AMPK signaling pathways or discrepancies in the induction of PPARgamma coactivator (PGC)-1alpha and -1beta. The protein content and expression of the nuclear corepressor RIP140 was reduced in triceps but not soleus muscle. Collectively our results indicate that chronic reductions in high-energy phosphates lead to the activation of p38 MAPK and AMPK signaling and increases in the expression of PGC-1alpha and -1beta in both soleus and triceps muscles. The lack of an effect of beta-GPA feeding on mitochondrial proteins in the soleus muscles could be related to a fiber type-specific effect of beta-GPA on RIP140 protein content.

Metabolomic Modeling To Monitor Host Responsiveness to Gut Microbiota Manipulation in the BTBRT+tf/j Mouse

The microbiota, the entirety of microorganisms residing in the gut, is increasingly recognized as an environmental factor in the maintenance of health and the development of disease. The objective of this analysis was to model in vivo interactions between gut microbiota and both serum and liver metabolites. Different genotypic models (C57BL/6 and BTBR(T+tf/j) mice) were studied in combination with significant dietary manipulations (chow vs ketogenic diets) to perturb the gut microbiota. Diet rather than genotype was the primary driver of microbial changes, with the ketogenic diet diminishing total bacterial levels. Fecal but not cecal microbiota profiles were associated with the serum and liver metabolomes. Modeling metabolome-microbiota interactions showed fecal Clostridium leptum to have the greatest impact on host metabolism, significantly correlating with 10 circulating metabolites, including 5 metabolites that did not correlate with any other microbes. C. leptum correlated negatively with serum ketones and positively with glucose and glutamine. Interestingly, microbial groups most strongly correlated with host metabolism were those modulating gut barrier function, the primary site of microbe-host interactions. These results show very robust relationships and provide a basis for future work wherein the compositional and functional associations of the microbiome can be modeled in the context of the metabolome.

Improvement in adiposity with oligofructose is modified by antibiotics in obese rats

Given the intimate link between gut microbiota and host physiology, there is growing interest in understanding the mechanisms by which diet influences gut microbiota and affects human metabolic health. Using antibiotics and the prebiotic oligofructose, which has been shown to counteract excess fat mass, we explored the gut microbiota‐dependent effects of oligofructose on body composition and host metabolism. Diet‐induced obese male Sprague Dawley rats, fed a background high‐fat/sucrose diet, were randomized to one of the following diets for 6 wk: 1) high‐energy control; 2) 10% oligofructose; 3) ampicillin; 4) ampicillin + 10% oligofructose; 5) ampicillin/neomycin; or 6) ampicillin/neomycin + 10% oligofructose. Combining oligofructose with ampicillin treatment blunted the decrease in adiposity seen with oligofructose. Although ampicillin did not affect total bacteria, ampicillin impeded oligofructose‐induced increases in Bifidobacterium and Lactobacillus. In contrast, the combination of ampicillin and neomycin reduced total bacteria but did not abrogate the oligofructose‐induced decrease in adiposity. Oligofructose‐mediated effects on host adiposity and metabolic health appear to be in part dependent on the presence of specific microbial species within the gut.—Bomhof, M. R., Paul, H. A., Geuking, M. B., Eller, L. K., Reimer, R. A. Improvement in adiposity with oligofructose is modified by antibiotics in obese rats. FASEB J. 30, 2720‐2732 (2016). www.fasebj.org

Potential Impact of Metabolic and Gut Microbial Response to Pregnancy and Lactation in Lean and Diet-Induced Obese Rats on Offspring Obesity Risk

SCOPE Maternal obesity programs metabolic dysfunction in offspring, increasing their susceptibility to obesity and metabolic diseases in later life. Moreover, pregnancy and lactation are associated with many metabolic adaptations, yet it is unclear how diet-induced maternal obesity may interrupt these processes. METHODS AND RESULTS 1 H NMR serum metabolomics analysis was performed on samples collected pre-pregnancy and in pregnant and lactating lean and high fat/sucrose (HFS) diet-induced obese Sprague-Dawley rats to identify maternal metabolic pathways associated with developmental programming of offspring obesity. Gut microbial composition was assessed using qPCR. Offspring of HFS dams had nearly 40% higher adiposity at weaning compared to offspring of lean dams. While pregnancy and lactation were associated with distinct maternal metabolic changes common to both lean and obese dams, we identified several metabolic differences, potentially implicating dysregulated one-carbon and mammary gland metabolism in the metabolic programming of obesity. Gut microbial composition was significantly altered with obesity, and both gestation and lactation were accompanied by changes in gut microbiota. CONCLUSION Diet-induced maternal obesity and consumption of an obesogenic maternal diet results in differential metabolic and gut microbial adaptations to pregnancy and lactation; these maladaptations may be directly involved in maternal programming of offspring susceptibility to obesity.