Transplantation of Microbes of Fecal Origin for Prevention and Treatment of Metabolic Syndrome and Non Alcoholic Fatty Liver Disease

Obesity and obesity-related disorders such as metabolic syndrome, Type 2 Diabetes (DM2), and NAFLD are of increasing concern worldwide. Metabolic syndrome refers to the clustering of 3 out of 5 parameters - abdominal obesity, elevated blood pressure, elevated fasting glucose, elevated triglyceride level, and low high-density lipoprotein cholesterol (HDL-C) level. The prevalence of metabolic syndrome is approximately 20-25% in North America. Those with metabolic syndrome are at increased risk for DM2 and cardiovascular disease.

Metabolic syndrome, DM2 and NAFLD are all marked by insulin resistance and are intricately linked with obesity. NAFLD is currently the most common liver disease in developed countries such as Canada. About 10-20% of patients with NAFLD progress to non-alcoholic steatohepatitis (NASH) which is characterized by inflammation and fat deposition. Unfortunately, NASH is a major cause of cirrhosis in North America.

Gut Microbiota, Obesity, DM2, and NAFLD Very strong support for the hypothesis of the gut microbiome inducing insulin resistance was found in a recent randomized control trial which showed that fecal transplantation from lean healthy donors into human patients with metabolic syndrome resulted in improved insulin sensitivity. This improvement correlated to an increase in the prevalence of butyrate-producing bacteria. Since butyrate helps prevent programmed cell death in the mucosal cells of the colon, preserving the integrity of the intestinal mucosa may prevent migration of endotoxin from the gut to the liver and induction of insulin resistance. Larger metagenome wide association studies of the fecal microbiome confirmed this finding that butyrate-producing bacteria including Clostridiales spp,C. rectales, Faecalibacterium prausnitzii, Roseburia intestinalis and R.inulinvorans appear to be less prevalent in DM2 than in healthy controls.

Differences in the microbiome between obese patients and those with DM2 versus those with a normal body mass index have been reported in many publications. There is evidence that the altered flora can increase the efficiency of release of calories from food. In a study of obese human twins, the decrease in Bacteroidetes proportion with increase in Firmicutes proportion correlated with the enrichment of microbial genes encoding key enzymes involved in carbohydrate metabolism, potentially leading to increased digestion of food and supply of energy in the form of short chain fatty acids (SCFA) to the host. Transfer of the gut microbiota from obese mice or from obese humans into germ-free mice reproduced the obese phenotype. Differences in microbiota composition have even been documented between children with obesity and those children who are lean, suggesting that microbiota changes may occur early in life. Decrease in the ratio of the number of firmicutes/bacteroidetes were associated with weight loss in humans. Other human gut organisms such as Akkermansia muciniphilia and Enterobacter cloacae B29 have been implicated with obesity and DM2. A high concentration of gut Beta proteobacteria was associated with the development of diabetes possibly via an inflammatory response incited by the endotoxin within these Gram negative rods. In fact antibiotic administration in some animal models has led to reduced numbers of both aerobic and anaerobic bacteria which increases insulin sensitivity as well as in plasma adiponectin levels, which correlate with insulin sensitivity. Changes in the gut microbiota associated with obesity have been found to activate Toll like receptors and thus GI inflammation with resulting insulin resistance. Very recently it was found that artificial sweeteners despite being "no-calorie" can exacerbate glucose intolerance, the effect mediated via a change in the microbiome.

Compared to both healthy controls and simple steatosis patients, patients with NASH have a lower percentage of the phylum Bacteroidetes, a finding similar to that of the gut microbial flora in obese human subjects. Microbial fermentation products like ethanol in the gut are key factors to induce obesity in mice and may be related to the pathogenesis of fatty liver disease. Elevated systemic ethanol levels even in the absence of any ethanol ingestion have been noted in patients with NASH compared to controls, suggesting that ethanol-producing microbes might be related to the pathogenesis of NASH in humans.Certain microbiomes can also lead to higher monosaccharide absorption from the gut lumen, which can promote de novo fatty acid and triglyceride production in the liver. It has been found that the hepatic kupffer cell activation in mice seems to contribute to the pathogenesis of NAFLD and that this can be induced by microbial endotoxin-related chronic inflammation. Chronic endotoxemia is associated with the severity of NAFLD. Increased intestinal permeability has similarly been documented in DM2 and metabolic syndrome and likely plays a key role in the pathophysiology of these disorders. Overall these findings suggest that preventive or therapeutic interventions such as fecal transplantation may lead to improvement in the status of obesity, metabolic syndromes, and NASH or NAFLD,and possibly even atherosclerosis.