Advances in understanding colonic function

Region-Specific Effects of Metformin on Gut Microbiome and Metabolome in High-Fat Diet-Induced Type 2 Diabetes Mouse Model

The glucose-lowering drug metformin alters the composition of the gut microbiome in patients with type 2 diabetes mellitus (T2DM) and other diseases. Nevertheless, most studies on the effects of this drug have relied on fecal samples, which provide limited insights into its local effects on different regions of the gut. Using a high-fat diet (HFD)-induced mouse model of T2DM, we characterize the spatial variability of the gut microbiome and associated metabolome in response to metformin treatment. Four parts of the gut as well as the feces were analyzed using full-length sequencing of 16S rRNA genes and targeted metabolomic analyses, thus providing insights into the composition of the microbiome and associated metabolome. We found significant differences in the gut microbiome and metabolome in each gut region, with the most pronounced effects on the microbiomes of the cecum, colon, and feces, with a significant increase in a variety of species belonging to Akkermansiaceae, Lactobacillaceae, Tannerellaceae, and Erysipelotrichaceae. Metabolomics analysis showed that metformin had the most pronounced effect on microbiome-derived metabolites in the cecum and colon, with several metabolites, such as carbohydrates, fatty acids, and benzenoids, having elevated levels in the colon; however, most of the metabolites were reduced in the cecum. Thus, a wide range of beneficial metabolites derived from the microbiome after metformin treatment were produced mainly in the colon. Our study highlights the importance of considering gut regions when understanding the effects of metformin on the gut microbiome and metabolome.

The effect of claudin-15 deletion on cationic selectivity and transport in paracellular pathways of the cecum and large intestine

The large intestine plays a pivotal role in water and electrolyte balance. Paracellular transport may play a role in ion transport mechanisms in the cecum and large intestine; however, these molecular mechanisms and their physiological roles have not been fully studied. Claudin-15 forms a cation channel in tight junctions in the small intestine, but its role in the cecum and large intestine has not been investigated. This study aimed to explore the physiological role of claudin-15 in the cecum and large intestine using claudin-15 (Cldn15) KO mice. Electrical conductance, short-circuit current, Na⁺ flux, and dilution potential were assessed in isolated tissue preparations mounted in Ussing chambers. The induced short-circuit current of short-chain fatty acids, which are fermentative products in the intestinal tract, was also measured. Compared to wild type mice, the electrical conductance and paracellular Na⁺ flux was decreased in the cecum, but not the middle large intestine, while in both the cecum and the middle large intestine, paracellular Na⁺ permeability was decreased in Cldn15 KO mice. These results suggest that claudin-15 is responsible for Na⁺ permeability in the tight junctions of the cecum and large intestine and decreased Na⁺ permeability in the cecum may cause impaired absorption function.

The impact of colectomy on the risk of cardiovascular disease among patients without colorectal cancer

Cardiometabolic disorders were discussed and might be changed by microbiota in recent years. Since the colon acts as the primary reservoir of microbiota, we designed the present study to explore the association between colectomy and cardiovascular disease (CVD). We identified a total of 18,424 patients who underwent colectomy between 2000-2012 for reasons other than colorectal cancer from the National Health Insurance Research Database of Taiwan. Patients were matched with 18,424 patients without colectomy using a 1:1 propensity score by age, sex, and comorbidity. Cox proportional-hazards regression was used to assess the risk of CVD. Patients with colectomy were found to be at lower risk of CVD (hazard ratio [HR]: 0.95, 95% confidence interval [CI] = 0.90-0.99) than patients without colectomy. Stratified analysis according to the type of surgery revealed patients who underwent cecectomy and right hemicolectomy were at lower risk of CVD (cecectomy: adjusted HR [aHR] = 0.77, 95% CI = 0.64-0.94; right hemicolectomy: aHR = 0.88, 95% CI = 0.82-0.96). Patients who underwent left hemicolectomy were at higher risk of CVD (aHR = 1.19, 95% CI = 1.08-1.32). Our results indicate that the different colectomy procedures influence the risk for the CVD differently.

Gut Movements: A Review of the Physiology of Gastrointestinal Transit

The well-regulated mechanisms of intestinal transit favor aboral movement of intestinal contents during the formation of normal stool. Electrical pacemakers initiate mechanical smooth muscular propulsion under regulation by the enteric nervous system-a function of the "brain-gut axis." Several unique intestinal motor patterns function in concert to enhance the activities of intestinal transit. Development of pharmacologic targets of intestinal transit mechanisms afford clinicians control in the management of functional gastrointestinal disorders. This review highlights the important physiologic events of intestinal transit, discusses selected pharmacologic and neuromodulators involved in these processes, and provides relevant clinical correlates to physiologic events.

Short bowel syndrome in infants: the critical role of luminal nutrients in a management program

Short bowel syndrome develops when the remnant mass of functioning enterocytes following massive resections cannot support growth or maintain fluid–electrolyte balance and requires parenteral nutrition. Resection itself stimulates the intestine’s inherent ability to adapt morphologically and functionally. The capacity to change is very much related to the high turnover rate of enterocytes and is mediated by several signals; these signals are mediated in large part by enteral nutrition. Early initiation of enteral feeding, close clinical monitoring, and ongoing assessment of intestinal adaptation are key to the prevention of irreversible intestinal failure. The length of the functional small bowel remnant is the most important variable affecting outcome. The major objective of intestinal rehabilitation programs is to achieve early oral nutritional autonomy while maintaining normal growth and nutrition status and minimizing total parenteral nutrition related comorbidities such as chronic progressive liver disease. Remarkable progress has been made in terms of survivability and quality of life, especially in the context of coordinated multidisciplinary programs, but much work remains to be done.