Elaine Patterson

Transferring the blues: Depression-associated gut microbiota induces neurobehavioural changes in the rat.

The gut microbiota interacts with the host via neuroimmune, neuroendocrine and neural pathways. These pathways are components of the brain-gut-microbiota axis and preclinical evidence suggests that the microbiota can recruit this bidirectional communication system to modulate brain development, function and behaviour. The pathophysiology of depression involves neuroimmune-neuroendocrine dysregulation. However, the extent to which changes in gut microbiota composition and function mediate the dysregulation of these pathways is unknown. Thirty four patients with major depression and 33 matched healthy controls were recruited. Cytokines, CRP, Salivary Cortisol and plasma Lipopolysaccharide binding protein were determined by ELISA. Plasma tryptophan and kynurenine were determined by HPLC. Fecal samples were collected for 16s rRNA sequencing. A Fecal Microbiota transplantation was prepared from a sub group of depressed patients and controls and transferred by oral gavage to a microbiota-deficient rat model. We demonstrate that depression is associated with decreased gut microbiota richness and diversity. Fecal microbiota transplantation from depressed patients to microbiota-depleted rats can induce behavioural and physiological features characteristic of depression in the recipient animals, including anhedonia and anxiety-like behaviours, as well as alterations in tryptophan metabolism. This suggests that the gut microbiota may play a causal role in the development of features of depression and may provide a tractable target in the treatment and prevention of this disorder.

Gut microbiota, obesity and diabetes

The central role of the intestinal microbiota in the progression and, equally, prevention of metabolic dysfunction is becoming abundantly apparent. The symbiotic relationship between intestinal microbiota and host ensures appropriate development of the metabolic system in humans. However, disturbances in composition and, in turn, functionality of the intestinal microbiota can disrupt gut barrier function, a trip switch for metabolic endotoxemia. This low-grade chronic inflammation, brought about by the influx of inflammatory bacterial fragments into circulation through a malfunctioning gut barrier, has considerable knock-on effects for host adiposity and insulin resistance. Conversely, recent evidence suggests that there are certain bacterial species that may interact with host metabolism through metabolite-mediated stimulation of enteric hormones and other systems outside of the gastrointestinal tract, such as the endocannabinoid system. When the abundance of these keystone species begins to decline, we see a collapse of the symbiosis, reflected in a deterioration of host metabolic health. This review will investigate the intricate axis between the microbiota and host metabolism, while also addressing the promising and novel field of probiotics as metabolic therapies.

Impact of dietary fatty acids on metabolic activity and host intestinal microbiota composition in C57BL/6J mice

Different dietary fat and energy subtypes have an impact on both the metabolic health and the intestinal microbiota population of the host. The present study assessed the impact of dietary fat quality, with a focus on dietary fatty acid compositions of varying saturation, on the metabolic health status and the intestinal microbiota composition of the host. C57BL/6J mice (n 9-10 mice per group) were fed high-fat (HF) diets containing either (1) palm oil, (2) olive oil, (3) safflower oil or (4) flaxseed/fish oil for 16 weeks and compared with mice fed low-fat (LF) diets supplemented with either high maize starch or high sucrose. Tissue fatty acid compositions were assessed by GLC, and the impact of the diet on host intestinal microbiota populations was investigated using high-throughput 16S rRNA sequencing. Compositional sequencing analysis revealed that dietary palm oil supplementation resulted in significantly lower populations of Bacteroidetes at the phylum level compared with dietary olive oil supplementation (P< 0·05). Dietary supplementation with olive oil was associated with an increase in the population of the family Bacteroidaceae compared with dietary supplementation of palm oil, flaxseed/fish oil and high sucrose (P< 0·05). Ingestion of the HF-flaxseed/fish oil diet for 16 weeks led to significantly increased tissue concentrations of EPA, docosapentaenoic acid and DHA compared with ingestion of all the other diets (P< 0·05); furthermore, the diet significantly increased the intestinal population of Bifidobacterium at the genus level compared with the LF-high-maize starch diet (P< 0·05). These data indicate that both the quantity and quality of fat have an impact on host physiology with further downstream alterations to the intestinal microbiota population, with a HF diet supplemented with flaxseed/fish oil positively shaping the host microbial ecosystem.

Streptozotocin-induced type-1-diabetes disease onset in Sprague-Dawley rats is associated with an altered intestinal microbiota composition and decreased diversity.

There is a growing appreciation that microbiota composition can significantly affect host health and play a role in disease onset and progression. This study assessed the impact of streptozotocin (STZ)-induced type-1-diabetes (T1D) on intestinal microbiota composition and diversity in Sprague-Dawley rats, compared with healthy controls over time. T1D was induced by injection of a single dose (60 mg STZ kg(-1)) of STZ, administered via the intraperitoneal cavity. Total DNA was isolated from faecal pellets at weeks 0 (pre-STZ injection), 1, 2 and 4 and from caecal content at week 5 from both healthy and T1D groups. High-throughput 16S rRNA sequencing was employed to investigate intestinal microbiota composition. The data revealed that although intestinal microbiota composition between the groups was similar at week 0, a dramatic impact of T1D development on the microbiota was apparent post-STZ injection and for up to 5 weeks. Most notably, T1D onset was associated with a shift in the Bacteroidetes : Firmicutes ratio (P<0.05), while at the genus level, increased proportions of lactic acid producing bacteria such as Lactobacillus and Bifidobacterium were associated with the later stages of T1D progression (P<0.05). Coincidently, T1D increased caecal lactate levels (P<0.05). Microbial diversity was also reduced following T1D (P<0.05). Principle co-ordinate analyses demonstrated temporal clustering in T1D and control groups with distinct separation between groups. The results provide a comprehensive account of how T1D is associated with an altered intestinal microbiota composition and reduced microbial diversity over time.

Influence of GABA and GABA-producing Lactobacillus brevis DPC 6108 on the development of diabetes in a streptozotocin rat model

The aim of this study was to investigate if dietary administration of γ-aminobutyric acid (GABA)-producing Lactobacillus brevis DPC 6108 and pure GABA exert protective effects against the development of diabetes in streptozotocin (STZ)-induced diabetic Sprague Dawley rats. In a first experiment, healthy rats were divided in 3 groups (n=10/group) receiving placebo, 2.6 mg/kg body weight (bw) pure GABA or L. brevis DPC 6108 (~10(9)microorganisms). In a second experiment, rats (n=15/group) were randomised to five groups and four of these received an injection of STZ to induce type 1 diabetes. Diabetic and non-diabetic controls received placebo [4% (w/v) yeast extract in dH2O], while the other three diabetic groups received one of the following dietary supplements: 2.6 mg/kg bw GABA (low GABA), 200 mg/kg bw GABA (high GABA) or ~10(9) L. brevis DPC 6108. L. brevis DPC 6108 supplementation was associated with increased serum insulin levels (P<0.05), but did not alter other metabolic markers in healthy rats. Diabetes induced by STZ injection decreased body weight (P<0.05), increased intestinal length (P<0.05) and stimulated water and food intake. Insulin was decreased (P<0.05), whereas glucose was increased (P<0.001) in all diabetic groups, compared with non-diabetic controls. A decrease (P<0.01) in glucose levels was observed in diabetic rats receiving L. brevis DPC 6108, compared with diabetic-controls. Both the composition and diversity of the intestinal microbiota were affected by diabetes. Microbial diversity in diabetic rats supplemented with low GABA was not reduced (P>0.05), compared with non-diabetic controls while all other diabetic groups displayed reduced diversity (P<0.05). L. brevis DPC 6108 attenuated hyperglycaemia induced by diabetes but additional studies are needed to understand the mechanisms involved in this reduction.

Renal angiotensin II type 1 receptor expression and associated hypertension in rats with minimal SHR nuclear genome

Angiotensin II (AII) has been linked as a causal factor in several experimental models of hypertension (HT) including Okamoto spontaneously hypertensive rats (SHR). The transmission and expression of AII type 1 receptors (AT1r) in SHR and the development of genetic HT remain unknown. It is hypothesized that tissue‐specific expression of renin–angiotensin system (RAS) genes derived from SHR are linked to HT in offspring of SHR crossed with Brown Norway (BN) rats. Hypertensive female progeny of BN/SHR matings was backcrossed with founder BN males to generate the F1 and five backcross generations (BN/SHR‐mtSHR). Progeny were phenotyped according to normotension (NT: systolic arterial pressure [SAP] ≤ 124 mmHg), borderline hypertension (BHT: 124 ≤ SAP < 145 mmHg), and HT (SAP ≥ 145 mmHg). Six generations produced more HT (n = 88; 46%) than NT (n = 21; 11%) offspring. The mRNA expression of the RAS was evaluated in NT (n = 20) and HT (n = 20) BN/SHR‐mtSHR across several generations. Quantitative real‐time polymerase chain reaction analysis of kidney tissue showed increased expression of AII, type 1 receptors (Agtr1a) (~2.5‐fold) in HT versus NT rats, while other members of both the renal and systemic RAS pathway were not different. Western blot analysis from kidney homogenates showed that AT1r protein levels were higher (P < 0.05) in backcross generation 3 (BC3) HT versus NT rats. Evaluation of SAP as a function of AT1r expression by linear regression indicated positive correlation (P < 0.05) in kidney of BC3 BN/SHR‐mtSHR rats. Thus, elevated kidney AT1r expression may be involved in the development of HT in BN/SHR‐mtSHR rats.

Recombinant Incretin-Secreting Microbe Improves Metabolic Dysfunction in High-Fat Diet Fed Rodents

AbstactThe gut hormone glucagon-like peptide (GLP)-1 and its analogues represent a new generation of anti-diabetic drugs, which have also demonstrated propensity to modulate host lipid metabolism. Despite this, drugs of this nature are currently limited to intramuscular administration routes due to intestinal degradation. The aim of this study was to design a recombinant microbial delivery vector for a GLP-1 analogue and assess the efficacy of the therapeutic in improving host glucose, lipid and cholesterol metabolism in diet induced obese rodents. Diet-induced obese animals received either Lactobacillus paracasei NFBC 338 transformed to express a long-acting analogue of GLP-1 or the isogenic control microbe which solely harbored the pNZ44 plasmid. Short-term GLP-1 microbe intervention in rats reduced serum low-density lipoprotein cholesterol, triglycerides and triglyceride-rich lipoprotein cholesterol substantially. Conversely, extended GLP-1 microbe intervention improved glucose-dependent insulin secretion, glucose metabolism and cholesterol metabolism, compared to the high-fat control group. Interestingly, the microbe significantly attenuated the adiposity associated with the model and altered the serum lipidome, independently of GLP-1 secretion. These data indicate that recombinant incretin-secreting microbes may offer a novel and safe means of managing cholesterol metabolism and diet induced dyslipidaemia, as well as insulin sensitivity in metabolic dysfunction.

The influence of rosuvastatin on the gastrointestinal microbiota and host gene expression profiles

Statins are the most widely prescribed medications worldwide for the treatment of hypercholesterolemia. They inhibit the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-R), an enzyme involved in cholesterol synthesis in higher organisms and in isoprenoid biosynthesis in some bacteria. We hypothesized that statins may influence the microbial community in the gut through either direct inhibition or indirect mechanisms involving alterations to host responses. We therefore examined the impact of rosuvastatin (RSV) on the community structure of the murine gastrointestinal microbiota. RSV was orally administered to mice and the effects on the gut microbiota, host bile acid profiles, and markers of inflammation were analyzed. RSV significantly influenced the microbial community in both the cecum and feces, causing a significant decrease in α-diversity in the cecum and resulting in a reduction of several physiologically relevant bacterial groups. RSV treatment of mice significantly affected bile acid metabolism and impacted expression of inflammatory markers known to influence microbial community structure (including RegIIIγ and Camp) in the gut. This study suggests that a commonly used statin (RSV) leads to an altered gut microbial composition in normal mice with attendant impacts on local gene expression profiles, a finding that should prompt further studies to investigate the implications of statins for gut microbiota stability and health in humans.NEW & NOTEWORTHY This work demonstrates that rosuvastatin administration in mice affects the gastrointestinal microbiota, influences bile acid metabolism, and alters transcription of genes encoding factors involved in gut homeostasis and immunity in the gastrointestinal tract.

Dietary Supplementation with a Magnesium-Rich Marine Mineral Blend Enhances the Diversity of Gastrointestinal Microbiota

Accumulating evidence demonstrates that dietary supplementation with functional food ingredients play a role in systemic and brain health as well as in healthy ageing. Conversely, deficiencies in calcium and magnesium as a result of the increasing prevalence of a high fat/high sugar “Western diet” have been associated with health problems such as obesity, inflammatory bowel diseases, and cardiovascular diseases, as well as metabolic, immune, and psychiatric disorders. It is now recognized that modulating the diversity of gut microbiota, the population of intestinal bacteria, through dietary intervention can significantly impact upon gut health as well as systemic and brain health. In the current study, we show that supplementation with a seaweed and seawater-derived functional food ingredient rich in bioactive calcium and magnesium (0.1% supplementation) as well as 70 other trace elements, significantly enhanced the gut microbial diversity in adult male rats. Given the significant impact of gut microbiota on health, these results position this marine multi-mineral blend (MMB) as a promising digestive-health promoting functional food ingredient.