Assessment of Murine Colon Inflammation Using Intraluminal Fluorescence Lifetime Imaging

Inflammatory bowel disease (IBD) is typically diagnosed by exclusion years after its onset. Current diagnostic methods are indirect, destructive, or target overt disease. Screening strategies that can detect low-grade inflammation in the colon would improve patient prognosis and alleviate associated healthcare costs. Here, we test the feasibility of fluorescence lifetime imaging (FLIm) to detect inflammation from thick tissue in a non-destructive and label-free approach based on tissue autofluorescence. A pulse sampling FLIm instrument with 355 nm excitation was coupled to a rotating side-viewing endoscopic probe for high speed (10 mm/s) intraluminal imaging of the entire mucosal surface (50-80 mm) of freshly excised mice colons. Current results demonstrate that tissue autofluorescence lifetime was sensitive to the colon anatomy and the colonocyte layer. Moreover, mice under DSS-induced colitis and 5-ASA treatments showed changes in lifetime values that were qualitatively related to inflammatory markers consistent with alterations in epithelial bioenergetics (switch between β-oxidation and aerobic glycolysis) and physical structure (colon length). This study demonstrates the ability of intraluminal FLIm to image mucosal lifetime changes in response to inflammatory treatments and supports the development of FLIm as an in vivo imaging technique for monitoring the onset, progression, and treatment of inflammatory diseases.

High-fat diet-induced colonocyte dysfunction escalates microbiota-derived trimethylamine N-oxide

A Western-style, high-fat diet promotes cardiovascular disease, in part because it is rich in choline, which is converted to trimethylamine (TMA) by the gut microbiota. However, whether diet-induced changes in intestinal physiology can alter the metabolic capacity of the microbiota remains unknown. Using a mouse model of diet-induced obesity, we show that chronic exposure to a high-fat diet escalates Escherichia coli choline catabolism by altering intestinal epithelial physiology. A high-fat diet impaired the bioenergetics of mitochondria in the colonic epithelium to increase the luminal bioavailability of oxygen and nitrate, thereby intensifying respiration-dependent choline catabolism of E. coli In turn, E. coli choline catabolism increased levels of circulating trimethlamine N-oxide, which is a potentially harmful metabolite generated by gut microbiota.

Vitamin A supplementation boosts control of antibiotic-resistant Salmonella infection in malnourished mice

Disseminated disease from non-typhoidal Salmonella enterica strains results in >20% mortality globally. Barriers to effective treatment include emerging multidrug resistance, antibiotic treatment failure, and risk factors such as malnutrition and related micronutrient deficiencies. Individuals in sub-Saharan Africa are disproportionately affected by non-typhoidal S. enterica bloodstream infections. To inform a clinical trial in people, we investigated vitamin A as a treatment in the context of antibiotic treatment failure in a mouse model of vitamin A deficiency. Vitamin A-deficient (VAD) mice exhibited higher systemic bacterial levels with a multidrug-resistant clinical isolate in comparison to mice on a control diet. Sex-specific differences in vitamin A deficiency and disseminated infection with S. enterica serotype Typhimurium (S. Typhimurium) were observed. VAD male mice had decreased weight gain compared to control male mice. Further, infected VAD male mice had significant weight loss and decreased survival during the course of infection. These differences were not apparent in female mice. In a model of disseminated S. Typhimurium infection and antibiotic treatment failure, we assessed the potential of two consecutive doses of vitamin A in alleviating infection in male and female mice on a VAD or control diet. We found that subtherapeutic antibiotic treatment synergized with vitamin A treatment in infected VAD male mice, significantly decreasing systemic bacterial levels, mitigating weight loss and improving survival. These results suggest that assessing vitamin A as a therapy during bacteremia in malnourished patients may lead to improved health outcomes in a subset of patients, especially in the context of antibiotic treatment failure.

Non-typhoidal Salmonella serotypes generally cause diarrhea in people. However, there are certain factors that make people at risk of developing a more severe infection where the bacteria can enter the blood and cause fever and whole-body symptoms. Patients with this infection are usually hospitalized, and about one in five patients do not survive. The factors that make this bloodstream infection possible include pathogen features like resistance to antibiotics and patient factors like a malnourished state. Better treatments are needed. In this study, the authors assess vitamin A as a treatment during antibiotic treatment failure in a mouse model. Vitamin A-deficient male mice have better outcomes with vitamin A and antibiotic co-therapy, whereas female mice do not benefit. Despite similar levels of bacteria causing infection systemically, female mice show better outcomes in terms of weight loss and survival than male mice overall. This research provides evidence that a clinical study assessing vitamin A as a treatment in people could lead to improved survival for malnourished patients presenting with severe bloodstream infection.

High-Fat Diet and Antibiotics Cooperatively Impair Mitochondrial Bioenergetics to Trigger Dysbiosis that Exacerbates Pre-inflammatory Bowel Disease

The clinical spectra of irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) intersect to form a scantily defined overlap syndrome, termed pre-IBD. We show that increased Enterobacteriaceae and reduced Clostridia abundance distinguish the fecal microbiota of pre-IBD patients from IBS patients. A history of antibiotics in individuals consuming a high-fat diet was associated with the greatest risk for pre-IBD. Exposing mice to these risk factors resulted in conditions resembling pre-IBD and impaired mitochondrial bioenergetics in the colonic epithelium, which triggered dysbiosis. Restoring mitochondrial bioenergetics in the colonic epithelium with 5-amino salicylic acid, a PPAR-γ (peroxisome proliferator-activated receptor gamma) agonist that stimulates mitochondrial activity, ameliorated pre-IBD symptoms. As with patients, mice with pre-IBD exhibited notable expansions of Enterobacteriaceae that exacerbated low-grade mucosal inflammation, suggesting that remediating dysbiosis can alleviate inflammation. Thus, environmental risk factors cooperate to impair epithelial mitochondrial bioenergetics, thereby triggering microbiota disruptions that exacerbate inflammation and distinguish pre-IBD from IBS.

Increased Epithelial Oxygenation Links Colitis to an Expansion of Tumorigenic Bacteria

Intestinal inflammation is a risk factor for colorectal cancer formation, but the underlying mechanisms remain unknown. Here, we investigated whether colitis alters the colonic microbiota to enhance its cancer-inducing activity. Colitis increased epithelial oxygenation in the colon of mice and drove an expansion of Escherichia coli within the gut-associated microbial community through aerobic respiration. An aerobic expansion of colibactin-producing E. coli was required for the cancer-inducing activity of this pathobiont in a mouse model of colitis-associated colorectal cancer formation. We conclude that increased epithelial oxygenation in the colon is associated with an expansion of a prooncogenic driver species, thereby increasing the cancer-inducing activity of the microbiota.IMPORTANCE One of the environmental factors important for colorectal cancer formation is the gut microbiota, but the habitat filters that control its cancer-inducing activity remain unknown. Here, we show that chemically induced colitis elevates epithelial oxygenation in the colon, thereby driving an expansion of colibactin-producing Escherichia coli, a prooncogenic driver species. These data suggest that elevated epithelial oxygenation is a potential risk factor for colorectal cancer formation because the consequent changes in the gut habitat escalate the cancer-inducing activity of the microbiota.

Microbiota-activated PPAR-γ signaling inhibits dysbiotic Enterobacteriaceae expansion

Perturbation of the gut-associated microbial community may underlie many human illnesses, but the mechanisms that maintain homeostasis are poorly understood. We found that the depletion of butyrate-producing microbes by antibiotic treatment reduced epithelial signaling through the intracellular butyrate sensor peroxisome proliferator-activated receptor γ (PPAR-γ). Nitrate levels increased in the colonic lumen because epithelial expression of Nos2, the gene encoding inducible nitric oxide synthase, was elevated in the absence of PPAR-γ signaling. Microbiota-induced PPAR-γ signaling also limits the luminal bioavailability of oxygen by driving the energy metabolism of colonic epithelial cells (colonocytes) toward β-oxidation. Therefore, microbiota-activated PPAR-γ signaling is a homeostatic pathway that prevents a dysbiotic expansion of potentially pathogenic Escherichia and Salmonella by reducing the bioavailability of respiratory electron acceptors to Enterobacteriaceae in the lumen of the colon.