Dietary fructose-induced gut dysbiosis promotes mouse hippocampal neuroinflammation: a benefit of short-chain fatty acids

The Molecular and Mechanistic Insights Based on Gut-Liver Axis: Nutritional Target for Non-Alcoholic Fatty Liver Disease (NAFLD) Improvement

Non-alcoholic fatty liver disease (NAFLD) is recognized as the most frequent classification of liver disease around the globe. Along with the sequencing technologies, gut microbiota has been regarded as a vital factor for the maintenance of human and animal health and the mediation of multiple diseases. The modulation of gut microbiota as a mechanism affecting the pathogenesis of NAFLD is becoming a growing area of concern. Recent advances in the communication between gut and hepatic tissue pave novel ways to better explain the molecular mechanisms regarding the pathological physiology of NAFLD. In this review, we recapitulate the current knowledge of the mechanisms correlated with the development and progression of NAFLD regulated by the gut microbiome and gut-liver axis, which may provide crucial therapeutic strategies for NAFLD. These mechanisms predominantly involve: (1) the alteration in gut microbiome profile; (2) the effects of components and metabolites from gut bacteria (e.g., lipopolysaccharides (LPS), trimethylamine-N-oxide (TMAO), and N,N,N-trimethyl-5-aminovaleric acid (TMAVA)); and (3) the impairment of intestinal barrier function and bile acid homeostasis. In particular, the prevention and therapy of NAFLD assisted by nutritional strategies are highlighted, including probiotics, functional oligosaccharides, dietary fibers, ω-3 polyunsaturated fatty acids, functional amino acids (L-tryptophan and L-glutamine), carotenoids, and polyphenols, based on the targets excavated from the gut-liver axis.

Host-microbiota interaction helps to explain the bottom-up effects of climate change on a small rodent species

The population cycles of small rodents have puzzled biologists for centuries. There is a growing recognition of the cascading effects of climate change on the population dynamics of rodents. However, the ultimate cause for the bottom-up effects of precipitation is poorly understood, from a microbial perspective. Here, we conducted a precipitation manipulation experiment in the field, and three feeding trials with controlled diets in the laboratory. We found precipitation supplementation facilitated the recovery of a perennial rhizomatous grass (Leymus chinensis) species, which altered the diet composition and increase the intake of fructose and fructooligosaccharides for Brandt’s vole. Lab results showed that this nutrient shift was accompanied by the modulation of gut microbiota composition and functional pathways (especially for the degradation or biosynthesis of L-histidine). Particularly, the relative abundance of Eubacterium hallii was consistently increased after feeding voles with more L. chinensis, fructose or fructooligosaccharide. These modulations ultimately increased the production of short chain fatty acids (SCFAs) and boosted the growth of vole. This study provides evidence that the precipitation pulses cascades through the plant community to affect rodent gut microbiome. Our results highlight the importance of considering host-microbiota interaction when investigating rodent population responses to climate change.

Gut dysbiosis contributes to high fructose-induced salt-sensitive hypertension in Sprague-Dawley rats

OBJECTIVES

Although it is known that high fructose intake causes salt-sensitive hypertension, the underlying mechanism remains unclear. The aim of this study was to determine whether chronic intake of high fructose coupled with salt (HFS) might alter the structure of the gut microbiota, which contributes to elevated blood pressure.

METHODS

For 8 wk, Sprague-Dawley rats were given 20% fructose in drinking water and 4% sodium chloride in their diet to induce hypertension. A non-absorbable antibiotic vancomycin was used to modify gut microbiota. The 16 S rRNA sequencing for fecal samples was assessed and blood pressure was recorded. Enzyme-linked immunosorbent assay and quantitative polymerase chain reaction were used to examine the renin-angiotensin system in serum, urine, and the kidney.

RESULTS

Compared with the control group, HFS feeding resulted in gut dysbiosis by altering the diversity and richness of gut microbiota and decreased the ratio of Firmicutes to Bacteroidetes. Vancomycin reshaped dramatically the HFS-induced dysbiosis. And vancomycin (van) attenuated HFS-increased blood pressure (HFS: 121.3 ± 2.8 mm Hg; HFS-van: 111.1 ± 1.7 mm Hg) and heart rate (HFS: 360.5 ± 9.0 bpm; HFS-van: 318.7 ± 5.6 bpm) as well as the content of angiotensinogen, renin, and angiotensin II in the urine and the angiotensinogen mRNA level in renal cortical tissues. However, HFS-increased triacylglycerol, renin, and angiotensin II in serum were not decreased by vancomycin.

CONCLUSION

The present results demonstrated that gut dysbiosis develops after chronic fructose plus salt intake and contributes to the increase of blood pressure and the activation of the intrarenal renin-angiotensin system. Therefore, targeting gut microbiota provides a helpful therapy method to improve HFS-induced hypertension.

The progress of gut microbiome research related to brain disorders

There is increasing evidence showing that the dynamic changes in the gut microbiota can alter brain physiology and behavior. Cognition was originally thought to be regulated only by the central nervous system. However, it is now becoming clear that many non-nervous system factors, including the gut-resident bacteria of the gastrointestinal tract, regulate and influence cognitive dysfunction as well as the process of neurodegeneration and cerebrovascular diseases. Extrinsic and intrinsic factors including dietary habits can regulate the composition of the microbiota. Microbes release metabolites and microbiota-derived molecules to further trigger host-derived cytokines and inflammation in the central nervous system, which contribute greatly to the pathogenesis of host brain disorders such as pain, depression, anxiety, autism, Alzheimer’s diseases, Parkinson’s disease, and stroke. Change of blood–brain barrier permeability, brain vascular physiology, and brain structure are among the most critical causes of the development of downstream neurological dysfunction. In this review, we will discuss the following parts:

Overview of technical approaches used in gut microbiome studies

Microbiota and immunity

Gut microbiota and metabolites

Microbiota-induced blood–brain barrier dysfunction

Neuropsychiatric diseases

■ Stress and depression

■ Pain and migraine

■ Autism spectrum disorders

Neurodegenerative diseases

■ Parkinson’s disease

■ Alzheimer’s disease

■ Amyotrophic lateral sclerosis

■ Multiple sclerosis

Cerebrovascular disease

■ Atherosclerosis

■ Stroke

■ Arteriovenous malformation

Conclusions and perspectives

Antibiotic Treatment Does Not Ameliorate the Metabolic Changes in Rats Presenting Dysbiosis After Consuming a High Fructose Diet

High fructose consumption is one of the hallmarks of Western diets and has been found to induce MeS symptoms in parallel to gut microbial dysbiosis. However, the causality between those two is still elusive. Here, we studied whether a significant modification of gut microbial composition by antibiotics can influence the fructose-induced metabolic changes. Male Sprague-Dawley (SD) rats were divided into four groups including controls, controls + antibiotics, high fructose diet (HFrD, 60% fructose), HFrD + antibiotics (n = 7-8 in each group) for a period of 8-weeks. The high fructose diet increased blood pressure (BP), triglyceride (TG), fatty liver and the expression of hepatic genes related to lipogenesis, and fructose transport and metabolism. In addition, fructose changed the microbial composition and increased acetic and butyric acids in fecal samples but not in the blood. Antibiotic treatment significantly reduced microbial diversity and modified the microbial composition in the samples. However, minimal or no effect was seen in the metabolic phenotypes. In conclusion, high fructose consumption (60%) induced metabolic changes and dysbiosis in rats. However, antibiotic treatment did not reverse the metabolic phenotype. Therefore, the metabolic changes are probably independent of a specific microbiome profile.

Demystifying the manipulation of host immunity, metabolism, and extraintestinal tumors by the gut microbiome

The trillions of microorganisms in the gut microbiome have attracted much attention recently owing to their sophisticated and widespread impacts on numerous aspects of host pathophysiology. Remarkable progress in large-scale sequencing and mass spectrometry has increased our understanding of the influence of the microbiome and/or its metabolites on the onset and progression of extraintestinal cancers and the efficacy of cancer immunotherapy. Given the plasticity in microbial composition and function, microbial-based therapeutic interventions, including dietary modulation, prebiotics, and probiotics, as well as fecal microbial transplantation, potentially permit the development of novel strategies for cancer therapy to improve clinical outcomes. Herein, we summarize the latest evidence on the involvement of the gut microbiome in host immunity and metabolism, the effects of the microbiome on extraintestinal cancers and the immune response, and strategies to modulate the gut microbiome, and we discuss ongoing studies and future areas of research that deserve focused research efforts.