Demonstration of differences in colonic volumes, transit, chyme consistency, and response to psyllium between healthy and constipated subjects using magnetic resonance imaging

BACKGROUND

In functional gastrointestinal disorders a lack of objective biomarkers limits evaluation of underlying mechanisms. We aimed to demonstrate the utility of magnetic resonance imaging for this task using psyllium, an effective constipation treatment, in patients and controls.

METHODS

Two crossover studies: (i) adults without constipation (controls, n = 9) took three treatments in randomized order for 6 days - maltodextrin (placebo), psyllium 3.5 g t.d.s and 7 g t.d.s., (ii) adults with chronic constipation (patients, n = 20) took placebo and psyllium 7 g t.d.s. for 6 days. MRI was performed fasting and postprandially on day 6. Measurements included small bowel and ascending colon water content, colonic volume, transit time, and MR relaxometry (T1, T2) to assess colonic chyme. Stool water percentage was measured.

RESULTS

7 g psyllium t.d.s. increased fasting colonic volumes in controls from median 372 mL (IQR 284-601) to 578 mL (IQR 510-882), and in patients from median 831 mL (IQR 745-934) to 1104 mL (847-1316), P < .05. Mean postprandial small bowel water was higher in controls and patients after 7 g psyllium t.d.s. vs placebo. Whole gut transit was slower in patients than controls (P < .05). T1 of the descending colon chyme (fasting) was lower in patients (213 ms, 176-420) than controls (440 ms, 352-884, P < .05) on placebo, but increased by 7 g psyllium t.d.s. (590 ms, 446-1338), P < .001. Descending colon T1 correlated with baseline stool water content and stool frequency on treatment.

CONCLUSIONS AND INFERENCES

MRI measurements can objectively demonstrate the mode of action of therapy targeting intestinal fluid content in constipation.

Linaclotide Attenuates Visceral Organ Crosstalk: Role of Guanylate Cyclase-C Activation in Reversing Bladder-Colon Cross-Sensitization

Bladder pain syndrome (BPS) is poorly understood; however, there is a female predominance and comorbidity with irritable bowel syndrome (IBS). Here we test the hypothesis that linaclotide, a guanylate cyclase-C (GC-C) agonist approved for the treatment of IBS with constipation (IBS-C), may represent a novel therapeutic for BPS acting through a mechanism involving an inhibition of visceral organ cross-sensitization. We showed previously that infusion of dilute protamine sulfate (PS) into the bladder increased sensitivity and permeability in the bladder and colon. PS was infused into the bladder of female rats; sensitivity was assessed via application of von Frey filaments applied to the suprapubic area and the frequency of withdrawal responses was recorded. Colonic sensitivity was measured via visceromotor behavioral response to graded pressures of colorectal distension (CRD). Permeability was measured in vitro via transepithelial electrical resistance (TEER) and conductance (G). Linaclotide (3 µg/kg, p.o.) or vehicle was administered daily for 7 days prior to experiments. Rats treated with PS bladder infusion exhibited visceral hyperalgesia, as shown by a significantly higher response frequency to individual von Frey filaments and increased behavioral responses to CRD. Linaclotide attenuated bladder and colonic hyperalgesia to control levels. PS infusion into the bladder increased bladder and colon permeability measured as a decrease in TEER and increased G. Linaclotide significantly inhibited PS-induced colonic hyperpermeability while having no effect on bladder hyperpermeability. Our findings suggest a novel treatment paradigm for GC-C agonism in IBS-C and BPS mediated through a mechanism involving visceral organ crosstalk.

Gene expression profiling and endothelin in acute experimental pancreatitis

AIM: To analyze gene expression profiles in an experimental pancreatitis and provide functional reversal of hypersensitivity with candidate gene endothelin-1 antagonists.

METHODS: Dibutyltin dichloride (DBTC) is a chemical used as a polyvinyl carbonate stabilizer/catalyzer, biocide in agriculture, antifouling agent in paint and fabric. DBTC induces an acute pancreatitis flare through generation of reactive oxygen species. Lewis-inbred rats received a single i.v. injection with either DBTC or vehicle. Spinal cord and dorsal root ganglia (DRG) were taken at the peak of inflammation and processed for transcriptional profiling with a cDNA microarray biased for rat brain-specific genes. In a second study, groups of animals with DBTC-induced pancreatitis were treated with endothelin (ET) receptor antagonists [ET-A (BQ123) and ET-B BQ788)]. Spontaneous pain related mechanical and thermal hypersensitivity were measured. Immunohistochemical analysis was performed using anti-ET-A and ET-B antibodies on sections from pancreatic tissues and DRG of the T10-12 spinal segments.

RESULTS: Animals developed acute pancreatic inflammation persisting 7-10 d as confirmed by pathological studies (edema in parenchyma, loss of pancreatic architecture and islets, infiltration of inflammatory cells, neutrophil and mononuclear cells, degeneration, vacuolization and necrosis of acinar cells) and the pain-related behaviors (cutaneous secondary mechanical and thermal hypersensitivity). Gene expression profile was different in the spinal cord from animals with pancreatitis compared to the vehicle control group. Over 260 up-regulated and 60 down-regulated unique genes could be classified into 8 functional gene families: circulatory/acute phase/immunomodulatory; extracellular matrix; structural; channel/receptor/transporter; signaling transduction; transcription/translation-related; antioxidants/chaperones/heat shock; pancreatic and other enzymes. ET-1 was among the 52 candidate genes up-regulated greater than 2-fold in animals with pancreatic inflammation and visceral pain-related behavior. Treatments with the ET-A (BQ123) and ET-B (BQ-788) antagonists revealed significant protection against inflammatory pain related mechanical and thermal hypersensitivity behaviors in animals with pancreatitis (P < 0.05). Open field spontaneous behavioral activity (at baseline, day 6 and 30 min after drug treatments (BQ123, BQ788) showed overall stable activity levels indicating that the drugs produced no undesirable effects on normal exploratory behaviors, except for a trend toward reduction of the active time and increase in resting time at the highest dose (300 μmol/L). Immunocytochemical localization revealed that expression of ET-A and ET-B receptors increased in DRG from animals with pancreatitis. Endothelin receptor localization was combined in dual staining with neuronal marker NeuN, and glia marker, glial fibrillary acidic protein. ET-A was expressed in the cell bodies and occasional nuclei of DRG neurons in naïve animals. However, phenotypic expression of ET-A receptor was greatly increased in neurons of all sizes in animals with pancreatitis. Similarly, ET-B receptor was localized in neurons and in the satellite glia, as well as in the Schwann cell glial myelin sheaths surrounding the axons passing through the DRG.

CONCLUSION: Endothelin-receptor antagonists protect against inflammatory pain responses without interfering with normal exploratory behaviors. Candidate genes can serve as future biomarkers for diagnosis and/or targeted gene therapy.