Colonic epithelial ion transport is not affected in patients with diverticulosis

Short-term oxycodone treatment does not affect electrogenic ion transport in isolated mucosa from the human rectosigmoid colon

OBJECTIVE

Opioid therapy is associated with altered secretion and motility of the gut. The relative contribution of decreased secretion to the development of opioid-induced constipation remains unknown.

MATERIALS AND METHODS

Twenty-five healthy males were treated with oxycodone for 5 d in a placebo-controlled, randomised cross-over design. Gastrointestinal adverse effects were assessed with validated questionnaires (bowel function index and gastrointestinal symptom rating scale). Rectosigmoid mucosal biopsies were taken at baseline and on day 5 during both treatments and mounted in Ussing chambers. Electrogenic ion transport parameters (short circuit current (SCC) and slope conductance) were measured after addition of secretagogues (prostaglandin E2 (PGE2) (6 μm), theophylline (400 μm)), and an inhibitor (ouabain (200 μm)). Additionally, morphine (50 μm) was added to investigate the direct opioid effect on colonic mucosa.

RESULTS

Questionnaires showed pronounced bowel symptoms, including constipation during oxycodone treatment (eight-fold increase in bowel function index score from day 1 to day 5 (p < 0.001) while no significant change occurred during placebo treatment (p = 0.47). Basal SCC and slope conductance did not differ between treatments (all p > 0.05) and application with PGE2, theophylline, and ouabain yielded comparable results on all examinations (all p > 0.05). Morphine application consistently did not evoke a change in ion transport.

CONCLUSION

Compared to placebo, epithelial electrogenic ion transport is not altered in mucosal biopsies from the rectosigmoid colon following 5-d oxycodone treatment. The secretory mechanisms in isolated mucosa appear to play a negligible role in the development of opioid-induced constipation.

Clinical potential of naloxegol in the management of opioid-induced bowel dysfunction

Opioid-induced bowel dysfunction (OIBD) is a burdensome condition which limits the therapeutic benefit of analgesia. It affects the entire gastrointestinal tract, predominantly by activating opioid receptors in the enteric nervous system, resulting in a wide range of symptoms, such as reflux, bloating, abdominal cramping, hard, dry stools, and incomplete evacuation. The majority of studies evaluating OIBD focus on constipation experienced in approximately 60% of patients. Nevertheless, other presentations of OIBD seem to be equally frequent. Furthermore, laxative treatment is often insufficient, which in many patients results in decreased quality of life and discontinuation of opioid treatment. Novel mechanism-based pharmacological approaches targeting the gastrointestinal opioid receptors have been marketed recently and even more are in the pipeline. One strategy is prolonged release formulation of the opioid antagonist naloxone (which has limited systemic absorption) and oxycodone in a combined tablet. Another approach is peripherally acting, μ-opioid receptor antagonists (PAMORAs) that selectively target μ-opioid receptors in the gastrointestinal tract. However, in Europe the only PAMORA approved for OIBD is the subcutaneously administered methylnaltrexone. Alvimopan is an oral PAMORA, but only approved in the US for postoperative ileus in hospitalized patients. Finally, naloxegol is a novel, oral PAMORA expected to be approved soon. In this review, the prevalence and pathophysiology of OIBD is presented. As PAMORAs seem to be a promising approach, their potential effect is reviewed with special focus on naloxegol's pharmacological properties, data on safety, efficacy, and patient-focused perspectives. In conclusion, as naloxegol is administered orally once daily, has proven efficacious compared to placebo, has an acceptable safety profile, and can be used as add-on to existing pain treatment, it is a welcoming addition to the targeted treatment possibilities for OIBD.

Carbachol-induced colonic mucus formation requires transport via NKCC1, K⁺ channels and CFTR

The colonic mucosa protects itself from the luminal content by secreting mucus that keeps the bacteria at a distance from the epithelium. For this barrier to be effective, the mucus has to be constantly replenished which involves exocytosis and expansion of the secreted mucins. Mechanisms involved in regulation of mucus exocytosis and expansion are poorly understood, and the aim of this study was to investigate whether epithelial anion secretion regulates mucus formation in the colon. The muscarinic agonist carbachol was used to induce parallel secretion of anions and mucus, and by using established inhibitors of ion transport, we studied how inhibition of epithelial transport affected mucus formation in mouse colon. Anion secretion and mucin exocytosis were measured by changes in membrane current and epithelial capacitance, respectively. Mucus thickness measurements were used to determine the carbachol effect on mucus growth. The results showed that the carbachol-induced increase in membrane current was dependent on NKCC1 co-transport, basolateral K(+) channels and Cftr activity. In contrast, the carbachol-induced increase in capacitance was partially dependent on NKCC1 and K(+) channel activity, but did not require Cftr activity. Carbachol also induced an increase in mucus thickness that was inhibited by the NKCC1 blocker bumetanide. However, mice that lacked a functional Cftr channel did not respond to carbachol with an increase in mucus thickness, suggesting that carbachol-induced mucin expansion requires Cftr channel activity. In conclusion, these findings suggest that colonic epithelial transport regulates mucus formation by affecting both exocytosis and expansion of the mucin molecules.

The effect of acute hypoxia on short-circuit current and epithelial resistivity in biopsies from human colon

BACKGROUND AND AIMS

In isolated colonic mucosa, decreases in short-circuit current (ISC) and transepithelial resistivity (RTE) occur when hypoxia is either induced at both sides or only at the serosal side of the epithelium. We assessed in human colon biopsies the sensitivity to serosal-only hypoxia and mucosal-only hypoxia and whether Na, K-ATPase blockade with ouabain interacts with hypoxia.

MATERIALS AND METHODS

Biopsy material from patients undergoing colonoscopy was mounted in an Ussing chamber for small samples (1-mm2 window). In a series of experiments we assessed viability and the electrical response to the mucolytic, dithiothreitol (1 mmol/l). In a second series, we explored the effect of hypoxia without and with ouabain. In a third series, we evaluated the response to a cycle of hypoxia and reoxygenation induced at the serosal or mucosal side while keeping the oxygenation of the opposite side.

RESULTS

1st series: Dithiothreitol significantly decreased the unstirred layer and ISC but increased RTE. 2nd series: Both hypoxia and ouabain decreased ISC, but ouabain increased RTE and this effect on RTE prevailed even during hypoxia. 3rd series: Mucosal hypoxia caused lesser decreases of ISC and RTE than serosal hypoxia; in the former, but not in the latter, recovery was complete upon reoxygenation.

CONCLUSIONS

In mucolytic concentration, dithiothreitol modifies ISC and RTE. Oxygen supply from the serosal side is more important to sustain ISC and RTE in biopsy samples. The different effect of hypoxia and Na, K-ATPase blockade on RTE suggests that their depressing effect on ISC involves different mechanisms.

An ex vivo method for studying mucus formation, properties, and thickness in human colonic biopsies and mouse small and large intestinal explants

The colon mucus layers minimize the contact between the luminal flora and the epithelial cells, and defects in this barrier may lead to colonic inflammation. We now describe an ex vivo method for analysis of mucus properties in human colon and mouse small and large intestine. Intestinal explants were mounted in horizontal perfusion chambers. The mucus surface was visualized by adding charcoal particles on the apical side, and mucus thickness was measured using a micropipette. Mucus thickness, adhesion, and growth rate were recorded for 1 h. In mouse and human colon, the ability of the mucus to act as a barrier to beads the size of bacteria was also evaluated. Tissue viability was monitored by transepithelial potential difference. In mouse ileum, the mucus could be removed by gentle aspiration, whereas in colon ∼40 μm of the mucus remained attached to the epithelial surface. Both mouse and human colon had an inner mucus layer that was not penetrated by the fluorescent beads. Spontaneous mucus growth was observed in human (240 μm/h) and mouse (100 μm/h) colon but not in mouse ileum. In contrast, stimulation with carbachol induced a higher mucus secretion in ileum than colon (mouse ileum: Δ200 μm, mouse colon: Δ130 μm, human colon: Δ140 μm). In conclusion, while retaining key properties from the mucus system in vivo, this setup also allows for studies of the highly dynamic mucus system under well-controlled conditions.

Epidemiology and pathophysiology of diverticular disease

Diverticular disease is common and thought to result from structural abnormalities of the colonic wall, disordered intestinal motility, or deficiencies of dietary fiber. Signs and symptoms of inflammation include fever, abdominal pain, and leukocytosis.

Relationships between body mass index and short-circuit current in human duodenal and colonic mucosal biopsies

AIM

Retrospectively, to investigate the relationship between body mass index (BMI) and basal electrogenic transport as measured by short-circuit current (SCC) in human duodenal and colonic mucosal biopsies.

METHODS

The study included biopsies from mucosa of normal appearance in the sigmoid colon and/or distal duodenum. Patients were referred for routine endoscopy (predominantly for monosymptomatic abdominal pain) and had normal endoscopic findings. Biopsies were mounted in miniaturized Ussing chambers and basal SCC was recorded. Patients were divided into two groups on the basis of BMI (≤25 and >25 kg m⁻²). Statistical significance was assessed by the unpaired t-test or Wilcoxon rank-sum test. Correlation coefficients were calculated by Pearson product moment correlation.

RESULTS

In colonic biopsies, basal SCC (mean ± standard deviation) was significantly higher in 59 biopsies from 30 patients with low BMI than in 32 biopsies from 23 patients with high BMI (45 ± 29 μA cm⁻² vs. 27 ± 21 μA cm⁻², P = 0.016). In duodenal biopsies, mean basal SCC was numerically lower in 38 biopsies from 15 patients with low BMI than in 46 biopsies from 19 patients with high BMI (54 ± 26 μA cm⁻² vs. 74 ± 39 μA cm⁻², P = 0.069). The correlation coefficient between BMI and SCC was -0.26 (P = 0.06) in colonic biopsies and +0.44 (P = 0.001) in duodenal biopsies.

CONCLUSION

Basal intestinal active electrogenic transport is related to BMI and this relationship may differ in different segments of the intestinal tract.

Prostaglandin E2-induced colonic secretion in patients with and without colorectal neoplasia

Background

The pathogenesis for colorectal cancer remains unresolved. A growing body of evidence suggests a direct correlation between cyclooxygenase enzyme expression, prostaglandin E₂ metabolism and neoplastic development. Thus further understanding of the regulation of epithelial functions by prostaglandin E₂ is needed. We hypothesized that patients with colonic neoplasia have altered colonic epithelial ion transport and express functionally different prostanoid receptor levels in this respect.

Methods

Patients referred for colonoscopy were included and grouped into patients with and without colorectal neoplasia. Patients without endoscopic findings of neoplasia served as controls. Biopsy specimens were obtained from normally appearing mucosa in the sigmoid part of colon. Biopsies were mounted in miniaturized modified Ussing air-suction chambers. Indomethacin (10 μM), various stimulators and inhibitors of prostanoid receptors and ion transport were subsequently added to the chamber solutions. Electrogenic ion transport parameters (short circuit current and slope conductance) were recorded. Tissue pathology and tissue damage before and after experiments was assessed by histology.

Results

Baseline short circuit current and slope conductance did not differ between the two groups. Patients with neoplasia were significantly more sensitive to indomethacin with a decrease in short circuit current of 15.1 ± 2.6 μA·cm^-2 compared to controls, who showed a decrease of 10.5 ± 2.1 μA·cm^-2 (p = 0.027). Stimulation or inhibition with theophylline, ouabain, bumetanide, forskolin or the EP receptor agonists prostaglandin E₂, butaprost, sulprostone and prostaglandin E₁ (OH) did not differ significantly between the two groups. Histology was with normal findings in both groups.

Conclusions

Epithelial electrogenic transport is more sensitive to indomethacin in normal colonic mucosa from patients with previous or present colorectal neoplasia compared to colonic mucosa from control patients. Stimulated epithelial electrogenic transport through individual prostanoid subtype receptors EP1, EP2, EP3, and EP4 is not significantly different between neoplasia diseased patients and controls. This indicates that increased indomethacin-sensitive mechanisms in colonic mucosa from neoplasia diseased patients are not related to differences in functional expression of EP receptor subtypes.