Small intestinal motility

Evaluation of bowel peristalsis by dynamic cine MRI: detection of relevant functional disturbances--initial experience

PURPOSE

To investigate the diagnostic performance of a cine magnetic resonance imaging (MRI) sequence in the visualization and detection of impaired bowel peristalsis.

MATERIALS AND METHODS

In all, 91 consecutive patients (mean age 45 years) were prospectively examined on a 1.5 T system and stratified into a surgery group (n = 22) and a nonsurgery group (n = 69). A coronal fast imaging with steady-state precession (TrueFISP) sequence with 30 acquisitions per slice covered the abdomen in 10-15 slices each 7-12 mm thick (temporal resolution: 6-8 sec per frame). Image evaluation for reduced bowel peristalsis and relevant bowel stenosis was compared to surgical findings or clinical follow-up.

RESULTS

Cine MRI reached 96% accuracy (94% sensitivity; 100% specificity) in detecting a relevant reduction in bowel peristalsis and 85% of relevant stenosis was identified in the surgery group. Twenty of 69 patients of the nonsurgery group showed reduced peristalsis on cine MR which was attributed to underlying disease; 49/69 patients in this group had no findings on cine MR and were uneventfully followed up.

CONCLUSION

Cine MRI of the bowel provides functional information of bowel passage. The visualization of a reduction in peristalsis may improve the assessment of the functional impact of suspected bowel adhesions or stenosis. Standard bowel MR protocols can be easily complemented by cine MR, extending scan time by <4 minutes.

Non-invasive, dynamic imaging of murine intestinal motility

BACKGROUND

After intravenous (i.v.) administration, indocyanine green (ICG) is known to be secreted into bile from the liver via the biliary tracts, enabling fluorescent delineation of the intestine. In addition, ICG is a near-infrared (NIR) excitable fluorophore, capable of providing exogenous contrast for rapid NIR fluorescence imaging. We sought to quantify the intestinal motility using dynamic NIR fluorescence imaging after injection of ICG.

METHODS

C57BL6 mice were dynamically imaged immediately before and up to 24h after i.v. and intradermal (i.d.) injection of 50 and 10μL of ICG, respectively. Necropsy was also performed 1h postinjection and the entire gastrointestinal tract was isolated and exposed for ex vivo fluorescence imaging.

KEY RESULTS

The secretion of ICG-laden fluorescent bile into the duodenum was observed in vivo and confirmed in situ. Different patterns of the intestinal motility, such as peristaltic and segmental motions, were dynamically imaged in vivo. Our imaging data showed that the frequency of contractions ranged from 27 to 35cyclesmin(-1) and the propagation velocity of peristaltic waves ranged from 0.82±0.5 to 2.04±1.12cms(-1) .

CONCLUSIONS & INFERENCES

Dynamic NIR fluorescence imaging with injection of ICG can provide a method for diagnostic motility testing for intestinal motility disorders or dysfunction and for potential evaluation of therapeutic agents.

Endotoxin-binding affinity of sevelamer: a potential novel anti-inflammatory mechanism

Chronic inflammation is highly prevalent in patients with chronic kidney disease (CKD), and is associated with increased cardiovascular morbidity and mortality. There are numerous causes of inflammation in CKD, including the potential exposure to bacterial lipopolysaccharide (LPS) in the bloodstream from the intestinal tract as a result of uremia-related increases in intestinal permeability. Sevelamer, a commonly prescribed non-calcium, non-metal-based phosphate binder in CKD, also possesses putative anti-inflammatory properties, as its use has been associated with a reduction in systemic markers of inflammation. Emerging studies have provided direct evidence that sevelamer shows in vitro LPS-binding properties. Indirect clinical evidence suggests that sevelamer might also limit translocation of LPS from the intestinal lumen into the bloodstream. This review focuses on bacterial LPS as a source of chronic inflammation in CKD, and proposes that sevelamer might possess novel anti-inflammatory properties as a result of LPS binding in the intestinal tract. The proposed hypothesis that intestinal LPS-binding by sevelamer may lower circulating LPS, and in turn systemic inflammation, requires further evaluation in a clinical trial.

Sevelamer hydrochloride use and circulating endotoxin in hemodialysis patients: a pilot cross-sectional study

OBJECTIVE

There is a growing interest in the potential anti-inflammatory properties of sevelamer hydrochloride, a commonly used phosphate binder for patients with chronic kidney failure. This study explores the hypothesis that sevelamer hydrochloride binds bacterial endotoxin in the intestinal tract, leading to lower circulating endotoxin levels, and offering a novel anti-inflammatory mechanism.

METHODS

We performed a cross-sectional study in medically stable patients with chronic kidney failure undergoing maintenance hemodialysis. Blood samples were collected before 2 consecutive dialysis sessions, and plasma was tested for endotoxin, interleukin-6 and C-reactive protein. Linear regression analyses were used to examine patient-related and dialysis-related factors associated with plasma endotoxin level.

RESULTS

Forty-six patients met our eligibility criteria. Their mean age was 62 years, 41% were diabetic, and 65% reported the use of sevelamer hydrochloride. The mean plasma endotoxin level was significantly lower in patients using sevelamer hydrochloride compared with those who were not (0.23 +/- 0.01 vs. 0.30 +/- 0.01 EU/mL, P = .001). However, plasma interleukin-6 and C-reactive protein levels were not significantly different between the two groups. According to multivariate analysis, the use of sevelamer hydrochloride was associated with a lower plasma endotoxin level after adjustment for race, gender, age, dialysis vintage, total cholesterol level, and white blood cell count.

CONCLUSIONS

This proof-of-concept pilot study demonstrates that the use of sevelamer hydrochloride is associated with a lower plasma endotoxin level, supporting the hypothesis that this agent binds to endotoxin in the intestinal lumen. Although this may be an important mechanism by which sevelamer hydrochloride attenuates systemic inflammation, a clinical trial is required to test this hypothesis.

Insights into mechanisms of intestinal segmentation in guinea pigs: a combined computational modeling and in vitro study

Segmentation in the guinea pig small intestine consists of a number of discrete motor patterns including rhythmic stationary contractions that occur episodically at specific locations along the intestine. The enteric nervous system regulates segmentation, but the exact circuit is unknown. Using simple computer models, we investigated possible circuits. Our computational model simulated the mean neuron firing rate in the feedforward ascending and descending reflex pathways. A stimulus-evoked pacemaker was located in the afferent pathway or in a feedforward pathway. Output of the feedforward pathways was fed into a simple model to determine the response of the muscle. Predictions were verified in vitro by using guinea pig jejunum, in which segmentation was induced with luminal fatty acid. In the computational model, local stimuli produced an oral contraction and anal dilation, similar to in vitro responses to local distension, but did not produce segmentation. When the stimulus was distributed, representing a nutrient load, the result was either a tonic response or globally synchronized oscillations. However, when we introduced local variations in synaptic coupling, stationary contractions occurred around these locations. This predicts that severing the ascending and descending pathways will induce stationary contractions. An acute lesion in our in vitro model significantly increased the number of stationary contractions immediately oral and anal to the lesion. Our results suggest that spatially localized rhythmic contractions arise from a local imbalance between ascending excitatory and descending inhibitory muscle inputs and require a distributed stimulus and a rhythm generator in the afferent pathway.

Microbial communities in the human small intestine: coupling diversity to metagenomics

The gastrointestinal tract is the main site where the conversion and absorption of food components takes place. The host-derived physiological processes and the residing microorganisms, especially in the small intestine, contribute to this nutrient supply. To circumvent sampling problems of the small intestine, several model systems have been developed to study microbial diversity and functionality in the small intestine. In addition, metagenomics offers novel possibilities to gain insight into the genetic potential and functional properties of these microbial communities. Here, an overview is presented of the most recent insights into the diversity and functionality of the microorganisms in the human gastrointestinal tract, with a focus on the small intestine.