Ileal losses of nitrogen and amino acids in humans and their importance to the assessment of amino acid requirements

BACKGROUND & AIMS: Irreversible amino acid losses at the human ileum are not taken into account when tracer-derived amino acid requirements are calculated because the data available are scarce. We have investigated amino acid losses at the ileal level in humans after ingestion of a protein meal. METHODS: Thirteen volunteers ingested a single meal of 15N milk or soy proteins. The appearance of 15N and 15N amino acids in the ileal effluents collected using an ileal tube was monitored for 8 hours. RESULTS: In the soy group, higher losses of endogenous nitrogen, especially originating from amino acids, were observed, as well as a higher flow rate of dietary non-amino acid nitrogen. With soy protein, the digestibilities of valine, threonine, histidine, tyrosine, alanine, and proline were significantly lower than with milk. Ileal losses of leucine, valine, and isoleucine amounted to 12, 10, and 7 mg x kg(-1) x day(-1), respectively. Threonine ileal loss (9-12 mg x kg(-1) x day(-1)) was particularly high compared with the current amino acid requirement. CONCLUSIONS: Amino acid losses at the human terminal ileum are substantial and depend on the type of dietary protein ingested. Although it remains unclear whether intact amino acids are absorbed in the colon, we suggest that ileal losses should be considered an important component of amino acid requirements.     

Comparison of FDG-PET/CT and MR with diffusion-weighted imaging for assessing peritoneal carcinomatosis from gastrointestinal malignancy

Objectives

To assess the accuracy of FDG-PET/CT and MR with diffusion-weighted imaging (MR-DWI) for diagnosing peritoneal carcinomatosis (PC) from gastrointestinal malignancies.

Methods

Thirty consecutive patients referred for staging of gastrointestinal malignancy underwent FDG-PET/CT and MR-DWI in this retrospective study. Extent of PC was characterised by dividing the peritoneal cavity into three sites in each patient: right and left supramesocolic areas and inframesocolic level (total 90 sites). Presence of PC was confirmed either by surgery (18/30) or by follow-up (12/30).

Results

PC was confirmed in 19 patients (19/30). At a total of 90 sites, 27 showed proven PC. On a patient-based analysis, sensitivity, specificity, PPV, NPV and accuracy were respectively 84%, 73%, 84%, 73% and 80% for PET/CT and 84%, 82%, 89%, 75% and 83% for MR-DWI. On a site-based analysis, overall sensitivity and specificity of PET/CT (63%, 90%) and MR-DWI (74%, 97%) were not statistically different (P?=?0.27). In the supramesocolic area, MR-DWI detected more sites involved than PET/CT (7/9 vs. 4/9). The sensitivities of PET and MR were lower for subcentimetre tumour implants (42%, 50%). Interobserver agreement was very good for PET/CT and good for MR-DWI.

Conclusions

FDG-PET/CT and MR-DWI showed similar high accuracy in diagnosing PC. Both techniques underestimated the real extent of PC because of decreased sensitivity for subcentimetre lesions.

Key Points

? FDG-PET/CT and MR-DWI showed similar high accuracy for diagnosing peritoneal carcinomatosis. ? In the supramesocolic area, MR-DWI could be more sensitive than PET/CT. ? Both techniques showed lower sensitivity for subcentimetre lesions. ? Interobserver agreement was very good for PET/CT and good for MR-DWI.     

Is-it possible to distinguish irritable bowel syndrome with constipation from functional constipation?

Background

The Rome III criteria classify patients complaining of constipation into two main groups: patients with functional constipation (FC) and patients with constipation predominant irritable bowel syndrome (IBS-C). The purpose of this study was to identify differences in the intensity of symptoms and total and segmental colonic transit time in these two types of patients.

Methods

We performed a prospective evaluation of 337 outpatients consecutively referred for chronic constipation and classified according to the Rome III criteria as FC or IBS-C. They were asked to report symptom intensity, on a 10-point Likert scale, for diarrhea, constipation, bloating and abdominal pain. Stool form was reported using the Bristol scale, and colonic transit time was measured by using multiple-ingestion single-marker single-film technique. Statistical analysis was completed by a discriminant analysis.

Results

Female gender and obstructed defecation was more frequent in IBS-C patients than in FC patients. IBS-C patients reported greater symptom intensity than FC patients, but stool form, and total and segmental colonic transit time were not different between the two groups. Multivariate logistic regression showed that only two parameters, bloating and abdominal pain, were related to the IBS-C or to the FC phenotype, and discriminant analysis showed that these two parameters were sufficient to give a correct classification of 71% of the patients.

Conclusions

Our study suggests that self-evaluation of abdominal pain and bloating is more helpful than colonic transit time in classifying patient as IBS‐C or FC.

     

Postprandial protein metabolism but not a fecal test reveals protein malabsorption in patients with pancreatic exocrine insufficiency

Background & aims

Pancreatic exocrine insufficiency (PEI) impairs fat absorption, but few data are available on protein absorption. We investigated this question in patients with chronic pancreatitis, both in the absence and presence of enzyme therapy, using a stable isotope sensitive method.

Methods

Eleven patients with sustained PEI and regular enzyme substitution were investigated at hospital, after a washout period without enzyme substitution, and later after reintroduction of substitution. The digestibility and postprandial metabolism of dietary protein were characterized after the ingestion of a semi-synthetic single meal containing 20 g ¹⁵N-labeled casein.

Results

At baseline, 20 ± 8% of dietary nitrogen was transferred to the metabolic pools vs. 24.5 ± 7% under enzyme treatment (P = 0.04). After treatment, the transfer of dietary nitrogen tended to increase in plasma amino acids, and increased significantly in plasma proteins and the deamination pool. In contrast, the fecal excretion of dietary nitrogen did not demonstrate any treatment effect. In patients not receiving insulin for diabetes, the treatment stimulated insulin secretion.

Conclusions

Protein malabsorption was mostly undetectable using standard fecal tests. The study of the postprandial fate of dietary protein revealed a moderate increase of its transfer to metabolic pools after enzyme substitution.     

Colon capsule endoscopy vs. colonoscopy in patients at average or increased risk of colorectal cancer

Aliment Pharmacol Ther 2010; 32: 1145–1153

Summary

Background Colon capsule endoscopy (CCE) is a new, non‐invasive technology. Aim To conduct a prospective, multicentre trial to compare CCE and colonoscopy in asymptomatic subjects enrolled in screening or surveillance programmes for the detection of colorectal neoplasia. Methods Patients underwent CCE on day one and colonoscopy (gold standard) on day two. CCE and colonoscopy were performed by independent endoscopists. Results A total of 545 patients were recruited. CCE was safe and well‐tolerated. Colon cleanliness was excellent or good in 52% of cases at CCE. Five patients with cancer were detected by colonoscopy, of whom two were missed by CCE. CCE accuracy for the detection of polyps ≥6 mm was 39% (95% CI 30–48) for sensitivity, 88% (95% CI 85–91) for specificity, 47% (95% CI 37–57) for positive predictive value and 85% (95% CI 82–88) for negative predictive value. CCE accuracy was better for the detection of advanced adenoma, in patients with good or excellent cleanliness and after re‐interpretation of the CCE videos by an independent expert panel. Conclusions Although well‐tolerated, CCE cannot replace colonoscopy as a first line investigation for screening and surveillance of patients at risk of cancer. Further studies should pay attention to colonic preparation (Clinicaltrial.gov number NCT00436514).