Ali Keshavarzian

Gut Microbiota Regulate Motor Deficits and Neuroinflammation in a Model of Parkinson’s Disease

The intestinal microbiota influence neurodevelopment, modulate behavior, and contribute to neurological disorders. However, a functional link between gut bacteria and neurodegenerative diseases remains unexplored. Synucleinopathies are characterized by aggregation of the protein α-synuclein (αSyn), often resulting in motor dysfunction as exemplified by Parkinsons disease (PD). Using mice that overexpress αSyn, we report herein that gut microbiota are required for motor deficits, microglia activation, and αSyn pathology. Antibiotic treatment ameliorates, while microbial re-colonization promotes, pathophysiology in adult animals, suggesting that postnatal signaling between the gut and the brain modulates disease. Indeed, oral administration of specific microbial metabolites to germ-free mice promotes neuroinflammation and motor symptoms. Remarkably, colonization of αSyn-overexpressing mice with microbiota from PD-affected patients enhances physical impairments compared to microbiota transplants from healthy human donors. These findings reveal that gut bacteria regulate movement disorders in mice and suggest that alterations in the human microbiome represent a risk factor for PD.

Intestinal barrier: an interface between health and disease.

Abstract  The intestine constitutes the largest interface between a person and his or her environment, and an intact intestinal barrier is thus essential in maintaining health and preventing tissue injury and several diseases. The intestinal barrier has various immunological and non‐immunological components. The epithelial barrier is one of the most important non‐immunological components. Hyperpermeability of this barrier is believed to contribute to the pathogenesis of several gastrointestinal disorders including inflammatory bowel disease, celiac disease and food allergy. Hence, assessing barrier integrity is of the utmost importance. One of the more quantitative gauges for this assessment is transepithelial permeability of various molecular probes, among which sugars are commonly used. Measures of intestinal permeability might also be useful as markers for assessment of prognosis and follow up in various gastrointestinal disorders. The present article is a review of the normal and abnormal functioning of the intestinal barrier, the diseases that can result from loss of barrier integrity, and some promising agents and strategies for restoring barrier normality and integrity.

Leaky gut in alcoholic cirrhosis: a possible mechanism for alcohol-induced liver damage

Objective: Only 30% of alcoholics develop cirrhosis, suggesting that the development of alcohol-induced liver injury requires one or more additional factors. Animal studies have shown that gut-derived endotoxin is one such factor. Because increased intestinal permeability has been shown to cause endotoxemia, we hypothesized that increased gastrointestinal permeability contributes to the pathogenesis of alcoholic liver disease. This study aimed to measure gastroduodenal and intestinal permeability in alcoholics with and without chronic liver disease and in nonalcoholic subjects with chronic liver disease. Methods: Gastroduodenal permeability was assessed by measurement of urinary excretion of sucrose after oral administration. Intestinal permeability was assessed by measurement of urinary lactulose and mannitol after oral administration of these sugars. Results: Alcoholics with no liver disease showed a small but significant increase in sucrose excretion. Alcoholics with chronic liver disease demonstrated a marked and highly significant increase in urinary sucrose excretion relative to the controls, to the alcoholics with no liver disease, and to the nonalcoholics with liver disease. Alcoholics with chronic liver disease demonstrated a marked and highly significant increase in both lactulose absorption and in the urinary lactulose/mannitol ratio (alcoholics 0.703 vs controls 0.019, p= 0.01). In contrast, alcoholics with no liver disease and nonalcoholics with liver disease showed normal lactulose absorption and normal lactulose/mannitol ratio. Conclusion: Because only the alcoholics with chronic liver disease had increased intestinal permeability, we conclude that a “leaky” gut may be a necessary cofactor for the development of chronic liver injury in heavy drinkers.

Disease-Specific Alterations in the Enteric Virome in Inflammatory Bowel Disease

Decreases in the diversity of enteric bacterial populations are observed in patients with Crohns disease (CD) and ulcerative colitis (UC). Less is known about the virome in these diseases. We show that the enteric virome is abnormal in CD and UC patients. In-depth analysis of preparations enriched for free virions in the intestine revealed that CD and UC were associated with a significant expansion of Caudovirales bacteriophages. The viromes of CD and UC patients were disease and cohort specific. Importantly, it did not appear that expansion and diversification of the enteric virome was secondary to changes in bacterial populations. These data support a model in which changes in the virome may contribute to intestinal inflammation and bacterial dysbiosis. We conclude that the virome is a candidate for contributing to, or being a biomarker for, human inflammatory bowel disease and speculate that the enteric virome may play a role in other diseases.

Excessive Production of Reactive Oxygen Metabolites by Inflamed Colon: Analysis by Chemiluminescence Probe

Reactive oxygen metabolites (ROMs) are involved in inflammatory diseases and are postulated to contribute to tissue injury in colitis. To determine whether excessive ROMs are generated by inflamed colonic mucosa and to identify possible sources and type of ROMs, mucosal ROMs were estimated in rats and humans using a chemiluminescence probe. Colitis was induced in rats by intracolonic injection of acetic acid or intraperitoneal injection of mitomycin C. Intact, inflamed colon in rats produced more ultraweak chemiluminescence than normal colon. Inflamed mucosal scrapings from both rat models produced significantly more luminol-enhanced chemiluminescence. Addition of catalase, an H2O2 scavenger, or azide, a myeloperoxidase inhibitor, into the media significantly decreased chemiluminescence from inflamed mucosal scrapings. Indomethacin, an antioxidant cyclo-oxygenase inhibitor, also decreased chemiluminescence, but MK-866, a 5-lipoxygenase inhibitor, had no effect. Colonic biopsy specimens obtained during colonoscopy from patients with ulcerative colitis also produced more catalase-inhibitable chemiluminescence than normal colonic mucosa. These data indicate that excessive ROMs are produced by inflamed colonic mucosa in both humans and rats, which may contribute to tissue injury.

Intestinal permeation and gastrointestinal disease.

The gastrointestinal tract constitutes one of the largest sites of exposure to the outside environment. The function of the gastrointestinal tract in monitoring and sealing the host interior from intruders is called the gut barrier. A variety of specific and nonspecific mechanisms are in operation to establish the host barrier; these include luminal mechanisms and digestive enzymes, the epithelial cells together with tight junctions in between them, and the gut immune system. Disruptions in the gut barrier follow injury from various causes including nonsteroidal anti-inflammatory drugs and oxidant stress, and involve mechanisms such as adenosine triphosphate depletion and damage to epithelial cell cytoskeletons that regulate tight junctions. Ample evidence links gut barrier dysfunction to multiorgan system failure in sepsis and immune dysregulation. Additionally, contribution of gut barrier dysfunction to gastrointestinal disease is an evolving concept and is the focus of this review. An overview of the evidence for the role of gut barrier dysfunction in disorders such as Crohns disease, celiac disease, food allergy, acute pancreatitis, non-alcoholic fatty liver disease, and alcoholic liver disease is provided, together with critical insight into the implications of this evidence as a primary disease mechanism.

Alpha-synuclein in colonic submucosa in early untreated Parkinson's disease.

The diagnosis of Parkinsons disease rests on motor signs of advanced central dopamine deficiency. There is an urgent need for disease biomarkers. Clinicopathological evidence suggests that α‐synuclein aggregation, the pathological signature of Parkinsons disease, can be detected in gastrointestinal tract neurons in Parkinsons disease. We studied whether we could demonstrate α‐synuclein pathology in specimens from unprepped flexible sigmoidoscopy of the distal sigmoid colon in early subjects with Parkinsons disease. We also looked for 3‐nitrotyrosine, a marker of oxidative stress. Ten subjects with early Parkinsons disease not treated with dopaminergic agents (7 men; median age, 58.5 years; median disease duration, 1.5 years) underwent unprepped flexible sigmoidoscopy with biopsy of the distal sigmoid colon. Immunohistochemistry studies for α‐synuclein and 3‐nitrotyrosine were performed on biopsy specimens and control specimens from a tissue repository (23 healthy subjects and 23 subjects with inflammatory bowel disease). Nine of 10 Parkinsons disease samples were adequate for study. All showed staining for α‐synuclein in nerve fibers in colonic submucosa. No control sample showed this pattern. A few showed light α‐synuclein staining in round cells. 3‐Nitrotyrosine staining was seen in 87% of Parkinsons disease cases but was not specific for Parkinsons disease. This study suggests a pattern of α‐synuclein staining in Parkinsons disease that was distinct from healthy subjects and those with inflammatory bowel disease. The absence of this pattern in subjects with inflammatory bowel disease suggests it is not a sequel of inflammation or oxidative stress. 3‐Nitrotyrosine immunostaining was common in all groups studied, suggesting oxidative stress in the colonic submucosa.

Colonic microbiome is altered in alcoholism

Several studies indicate the importance of colonic microbiota in metabolic and inflammatory disorders and importance of diet on microbiota composition. The effects of alcohol, one of the prominent components of diet, on colonic bacterial composition is largely unknown. Mounting evidence suggests that gut-derived bacterial endotoxins are cofactors for alcohol-induced tissue injury and organ failure like alcoholic liver disease (ALD) that only occur in a subset of alcoholics. We hypothesized that chronic alcohol consumption results in alterations of the gut microbiome in a subgroup of alcoholics, and this may be responsible for the observed inflammatory state and endotoxemia in alcoholics. Thus we interrogated the mucosa-associated colonic microbiome in 48 alcoholics with and without ALD as well as 18 healthy subjects. Colonic biopsy samples from subjects were analyzed for microbiota composition using length heterogeneity PCR fingerprinting and multitag pyrosequencing. A subgroup of alcoholics have an altered colonic microbiome (dysbiosis). The alcoholics with dysbiosis had lower median abundances of Bacteroidetes and higher ones of Proteobacteria. The observed alterations appear to correlate with high levels of serum endotoxin in a subset of the samples. Network topology analysis indicated that alcohol use is correlated with decreased connectivity of the microbial network, and this alteration is seen even after an extended period of sobriety. We show that the colonic mucosa-associated bacterial microbiome is altered in a subset of alcoholics. The altered microbiota composition is persistent and correlates with endotoxemia in a subgroup of alcoholics.

Increased intestinal permeability correlates with sigmoid mucosa alpha-synuclein staining and endotoxin exposure markers in early Parkinson's disease.

Parkinsons disease (PD) is the second most common neurodegenerative disorder of aging. The pathological hallmark of PD is neuronal inclusions termed Lewy bodies whose main component is alpha-synuclein protein. The finding of these Lewy bodies in the intestinal enteric nerves led to the hypothesis that the intestine might be an early site of PD disease in response to an environmental toxin or pathogen. One potential mechanism for environmental toxin(s) and proinflammatory luminal products to gain access to mucosal neuronal tissue and promote oxidative stress is compromised intestinal barrier integrity. However, the role of intestinal permeability in PD has never been tested. We hypothesized that PD subjects might exhibit increased intestinal permeability to proinflammatory bacterial products in the intestine. To test our hypothesis we evaluated intestinal permeability in subjects newly diagnosed with PD and compared their values to healthy subjects. In addition, we obtained intestinal biopsies from both groups and used immunohistochemistry to assess bacterial translocation, nitrotyrosine (oxidative stress), and alpha-synuclein. We also evaluated serum markers of endotoxin exposure including LPS binding protein (LBP). Our data show that our PD subjects exhibit significantly greater intestinal permeability (gut leakiness) than controls. In addition, this intestinal hyperpermeability significantly correlated with increased intestinal mucosa staining for E. coli bacteria, nitrotyrosine, and alpha-synuclein as well as serum LBP levels in PD subjects. These data represent not only the first demonstration of abnormal intestinal permeability in PD subjects but also the first correlation of increased intestinal permeability in PD with intestinal alpha–synuclein (the hallmark of PD), as well as staining for gram negative bacteria and tissue oxidative stress. Our study may thus shed new light on PD pathogenesis as well as provide a new method for earlier diagnosis of PD and suggests potential therapeutic targets in PD subjects. Trial Registration Clinicaltrials.gov NCT01155492

Alcohol, intestinal bacterial growth, intestinal permeability to endotoxin, and medical consequences: summary of a symposium.

This report is a summary of the symposium on Alcohol, Intestinal Bacterial Growth, Intestinal Permeability to Endotoxin, and Medical Consequences, organized by National Institute on Alcohol Abuse and Alcoholism, Office of Dietary Supplements, and National Institute of Diabetes and Digestive and Kidney Diseases of National Institutes of Health in Rockville, Maryland, October 11, 2006. Alcohol exposure can promote the growth of Gram-negative bacteria in the intestine, which may result in accumulation of endotoxin. In addition, alcohol metabolism by Gram-negative bacteria and intestinal epithelial cells can result in accumulation of acetaldehyde, which in turn can increase intestinal permeability to endotoxin by increasing tyrosine phosphorylation of tight junction and adherens junction proteins. Alcohol-induced generation of nitric oxide may also contribute to increased permeability to endotoxin by reacting with tubulin, which may cause damage to microtubule cytoskeleton and subsequent disruption of intestinal barrier function. Increased intestinal permeability can lead to increased transfer of endotoxin from the intestine to the liver and general circulation where endotoxin may trigger inflammatory changes in the liver and other organs. Alcohol may also increase intestinal permeability to peptidoglycan, which can initiate inflammatory response in liver and other organs. In addition, acute alcohol exposure may potentiate the effect of burn injury on intestinal bacterial growth and permeability. Decreasing the number of Gram-negative bacteria in the intestine can result in decreased production of endotoxin as well as acetaldehyde which is expected to decrease intestinal permeability to endotoxin. In addition, intestinal permeability may be preserved by administering epidermal growth factor, l-glutamine, oats supplementation, or zinc, thereby preventing the transfer of endotoxin to the general circulation. Thus reducing the number of intestinal Gram-negative bacteria and preserving intestinal permeability to endotoxin may attenuate alcoholic liver and other organ injuries.