Immunoautoradiographic localisation of enkephalinase (EC 3.4.24.11) in rat gastrointestinal tract

Gelatin Tannate for Acute Childhood Gastroenteritis: A Randomized, Single-Blind Controlled Trial

BACKGROUND

Oral rehydration therapy is the recommended treatment for acute childhood gastroenteritis. The aim of this study was to assess the efficacy and safety of gelatin tannate plus oral rehydration compared with oral rehydration alone.

METHODS

We conducted a multicenter, parallel, randomized, controlled, single-blind, prospective, open-label trial. A central randomization center used computer generated tables to allocate treatments. The study was performed in two medical centers in Italy. Sixty patients 3-72 months of age with acute gastroenteritis were recruited (median age 18 months; age range 3-66 months): 29 received an oral rehydration solution (ORS) and 31 an ORS plus gelatin tannate (ORS + G). The primary outcome was the number of bowel movements 48 and 72 h after initiating treatment. Secondary outcomes were: duration of diarrhea, stool characteristics and adverse events.

RESULTS

No patient was lost at follow-up. No significant difference in the number of bowel movements after 48 h was reported (2.7 ± 1.3 ORS + G; 3.2 ± 0.8 ORS; p = 0.06), although the ORS + G group showed a significant improvement in stool consistency (3.7 ± 1.0 vs. 4.3 ± 0.8; p = 0.005). At 72 h, a significant reduction in bowel movements was reported in the ORS + G group compared with the ORS group (1.0 ± 1.4 vs. 2.0 ± 1.7; p = 0.01). Mean duration of diarrhea was significantly lower in the ORS + G group than in the ORS only group (76.8 ± 19.2 vs. 108 ± 24.0 h; p < 0.0001). No adverse events were reported.

CONCLUSIONS

Gelatin tannate added to oral rehydration in children with acute diarrhea was associated with a significant decrease in bowel movements at 72 h, with an early improvement in the stool consistency and shorter disease duration.

CLINICAL TRIAL REGISTRATION

NCT02644200-Gelatin Tannate as Treatment for Acute Childhood Gastroenteritis ( https://www.clinicaltrials.gov ).

Use of preproenkephalin knockout mice and selective inhibitors of enkephalinases to investigate the role of enkephalins in various behaviours

RATIONALE

The most simple and efficient method to study the physiological role of enkephalins is to increase the lifetime of these endogenous opioid peptides by inhibiting their inactivating enzymes. Enkephalins are degraded by the concomitant action of two metallopeptidases: neutral endopeptidase (NEP, EC3.4.21.11) and aminopeptidase N (APN, EC3.4.11.2), both enzymes releasing inactive metabolites.

OBJECTIVES

Potent dual inhibitors have been developed, such as RB101. However, NEP and APN have a broad specificity and can cleave various peptides in vitro. Therefore, it was essential to investigate the specific involvement of enkephalins in the various pharmacological responses induced by dual inhibitors.

MATERIALS AND METHODS

We compared the pharmacological responses induced by RB101 in wild-type and preproenkephalin-deficient mice (Penk1-/-) using several behavioural assays.

RESULTS

In all the tests used (hot plate test, force swim test, castor-oil-induced diarrhoea), RB101 induced strong effects in wild-type animals, whereas slight effects were observed in Penk1-/- animals. These residual effects are blocked by pre-administration of the opioid antagonist naloxone, supporting the involvement of the opioid receptors in the responses observed.

CONCLUSIONS

The pharmacological effects induced by dual inhibitors acting on both NEP and APN are mainly due to the protection of the endogenous enkephalins at supraspinal and peripheral levels. It could be speculated that the residual effects observed in Penk1-/- mice after RB101 administration could be due to the direct action of other opioid peptides or through an indirect effect involving the protection of other peptide substrates of NEP or APN, as substance P or angiotensin.

A blind, randomized comparison of racecadotril and loperamide for stopping acute diarrhea in adults

AIM

Racecadotril is a specific enkephalinase inhibitor that exhibits intestinal antisecretory activity without affecting intestinal transit. Loperamide is an effective anti-diarrheal agent, but it usually induces constipation. This study is to compare the efficacy, safety, and tolerability of racecadotril versus loperamide in the outpatient treatment of acute diarrhea in adults.

METHODS

A two-center, randomized, parallel-group, single-blind study was carried out to compare the efficacy, tolerability, and safety of racecadotril (100 mg thrice daily) and loperamide (2.0 mg 2 twice daily) in 62 adult patients suffering from acute diarrhea. The main efficacy criterion used was the duration of diarrhea after beginning the treatment (in hours). Other signs and symptoms were also evaluated.

RESULTS

The clinical success rates for these anti-diarrheal treatments were 95.7% and 92.0% for racecadotril and loperamide respectively. Patients on racecadotril had a median duration of diarrhea of 19.5 h compared with a median of 13 h for patients on loperamide. Rapid improvement in anal burn and nausea was found for each drug. However, more patients on loperamide suffered from reactive constipation (29.0% vs 12.9%). Itching, another adverse event was notably higher in the racecadotril group (28.6% vs 0%). With regard to other adverse events, the two medications showed similar occurrence rates and similar concomitant medication usage rates.

CONCLUSION

Racecadotril and loperamide are rapid, equally effective treatments for acute diarrhea in adults, but loperamide treatment is associated with a higher incidence of treatment-related constipation.

[Effect of racecadotril in the management of acute diarrhea in infants and children]

BACKGROUND

The treatment of diarrhoea relies on the maintenance or restoration of hydration with maintenance of an adequate nutritional intake. Racecadotril has been shown to reduce the stools output during acute diarrhoea. The present work was aimed at measuring the number of emergency department visits for acute diarrhoea either the children received racecadotril or not.

METHOD

Racecadotril and rehydration were compared with rehydration alone in children aged three months to three years who had acute diarrhoea and were evaluated in the emergency department (ED). The primary end point was the number of medical exams during the week after starting treatment. Secondary end points were the number of stools during the first 48 hours, the duration of the diarrhoea and the weight on day 7.

RESULTS

One hundred and sixty-six children were alternatively randomized to the treated and the control groups. There was no difference for age, degree of dehydration and length of illness before the first visit between the groups. Whatever type of rehydration (oral or i.v.), the treated group had a significant lower number of stools (p < 0.001) and a faster recovery (p < 10(-9)). The children receiving racecadotril needed less additional ED visits for the same episode (p < 0.05). There was no difference for the weight-gain on day 7.

CONCLUSIONS

This study demonstrates the efficacy of racecadotril as adjuvant therapy to oral and i.v. rehydration in the treatment of acute diarrhoea and a fewer emergency department second visit before recovery.

Efficacy and tolerability of racecadotril in acute diarrhea in children

BACKGROUND & AIMS

Oral rehydration therapy is the only treatment recommended by the World Health Organization in acute diarrhea in children. Antisecretory drugs available could not be used because of their side effects, except for racecadotril, which is efficient in acute diarrhea in adults.

METHODS

The efficacy and tolerability of racecadotril (1.5 mg/kg administered orally 3 times daily) as adjuvant therapy to oral rehydration were compared with those of placebo in 172 infants aged 3 months to 4 years (mean age, 12.8 months) who had acute diarrhea. The treatment groups were comparable in terms of age, duration of diarrhea, number of stools, and causative microorganism at inclusion.

RESULTS

During the first 48 hours of treatment, patients receiving racecadotril had a significantly lower stool output (grams per hour) than those receiving placebo. The 95% confidence interval was 43%-88% for the full data set (n = 166; P = 0.009) and 33%-75% for the per-protocol population (n = 116; P = 0.001). There was no difference between treatments depending on rotavirus status. Significant differences between treatment groups were also found after 24 hours of treatment: full data set (n = 167; P = 0.026) and per-protocol population (n = 121; P = 0.015). Tolerability was good in both groups of patients.

CONCLUSIONS

This study demonstrates the efficacy (up to 50% reduction in stool output) and tolerability of racecadotril as adjuvant therapy to oral rehydration solution in the treatment of severe diarrhea in infants and children.

Racecadotril: a new approach to the treatment of diarrhoea

Since enkephalins were discovered in 1975, it has become clear that they play an antisecretory role in the gastrointestinal tract. Hence a rational research programme was directed at the development of a drug that would preserve these neurotransmitter peptides in the gut by preventing their inactivation. This research programme has resulted in the development of the enkephalinase inhibitor, racecadotril. Preclinical studies have demonstrated the efficacy of racecadotril in two models of hypersecretory diarrhoea: infusion of cholera toxin and castor oil-induced diarrhoea. Moreover, unlike loperamide, racecadotril did not prolong transit time in the small intestine or colon. Further experiments have shown that racecadotril does not promote bacterial overgrowth in the small intestine. Racecadotril lacks any potential for neurotoxicity, and radiolabelled studies have demonstrated that the drug does not enter the brain after oral administration. No potential for abuse or physical dependence has been seen. It is concluded that racecadotril demonstrates specificity of antisecretory action on the gastrointestinal tract without any adverse effect on gastrointestinal motility, and that the results of the preclinical studies indicate the potential usefulness in the treatment of hypersecretory diarrhoea in man.

Evidence for peptidase activity in the rat intestine

1. Cholinergic contraction was induced in segments of rat jejunum by transmural stimulation (10 Hz, 1 ms for 8 s). The synthetic delta-opiate agonist, DADLE (100 nM), caused a prolonged inhibition of the cholinergic response. 2. The naturally occurring opioid peptides, dynorphin A (1-13) (200 nM), leu-enkephalin (400 nM), met-enkephalin (200 nM) and the synthetic delta-agonist, DSLET (30 nM), also caused large inhibitions in the response. 3. Each of these peptides lost a significant amount of their original activity at 6 min, which was reduced by a mixture of peptidase inhibitors consisting of bestatin (30 microM), thiorphan (10 microM), captopril (10 microM) and L-leucyl-L-leucine (2 mM). 4. The enkephalinase inhibitor, thiorphan (10 microM), significantly lengthened the time at which met-enkephalin was active, but not to the same extent as the mixture of peptidase inhibitors. However, the mixture of peptidase inhibitors did not significantly alter the cholinergic contraction in the absence of opioid peptides. 5. It is concluded that peptidases, including enkephalinase, are present in the rat intestine. However, the model presently described does not release functional amounts of endogenous opioid peptides, nor does it become tolerant to the effect of stimulating its delta-opioid receptors.

Action of enkephalinase (EC 3.4.24.11) inhibition on the pre- and post-prandial electromyographic patterns of colon in rats

Endogenous opioids are an important regulatory factor for the digestive tract and specially for its motility pattern. Enkephalin degradation includes an enkephalinase (EC 3.4.24. 11) and the effects on the colic electromyographic profile of its inhibition by acetorphan has been investigated in the unrestrained rat. Electromyogram consisted of Long Spike Bursts (LSB). In fasted state, they propagated indifferently in both aboral or oral directions from any point of the colon. Feeding privileges LSB which start near the cecal junction and propagated aborally to the distal colon. The acetorphan treatment (A) increases the percentage of LSB propagating aborally on the entire colon in fasted state and (B) reinforces the increased percentage of LSB which propagated down on the entire colon induced by feeding. All the actions of acetorphan on colic motility pattern disappear after inhibition of opioid receptors by naloxone. That may account for involvement of enkephalins in acetorphan properties on the pattern of the colic electrical activity.

Polarized distribution of neutral endopeptidase 24.11 at the cell surface of cultured human intestinal epithelial Caco-2 cells

The human colon cancer cell line Caco-2 undergoes spontaneous enterocytic differentiation during growth, and expresses a number of brush-border-membrane-associated hydrolases typical of a differentiated phenotype. Among these are alkaline phosphatase, dipeptidyl peptidase IV and sucrase-isomaltase (sucrase, EC 3.2.1.48). Neutral endopeptidase 24.11 [EC 3.4.24.11, neprilysin (NEP)] is another abundant protease of normal enterocytes but its presence in Caco-2 cells has not been fully documented yet. In this paper, we show that Caco-2 cell extracts hydrolyse tritiated [D-Ala2Leu5]enkephalin with a Km of 180 microM, very close to the value obtained for the NEP present in the rabbit kidney (118 microM). Western-blot analysis of brush-border membranes purified from post-confluent cells revealed a protein with an apparent molecular mass of 94000 Da similar to that of the rabbit kidney NEP. The amount of enzyme in cell extracts increased as a function of the age of the culture, indicating that NEP expression is correlated with the degree of cell differentiation as is also the case for sucrase and dipeptidylpeptidase IV (DPP-IV). Binding of a radiolabelled antibody to Caco-2 cell monolayers grown on semi-permeable filters indicated that 95% of NEP molecules present at the cell surface are on the apical side. Immunocytochemical and flow cytometric analysis of intact and permeabilized cells were also used to investigate the presence of NEP and DPP-IV at the surface of Caco-2 cells. Whereas DPP-IV staining appeared to be homogeneous throughout the entire cell population, NEP-related fluorescence exhibited a bimodal distribution which indicates an uneven expression of the protein at the cell surface. Permeabilization of monolayers with saponin before staining restored a labelling pattern for NEP similar to the one obtained for DPP-IV. This suggests that although DPP-IV and NEP follow similar patterns of expression when enzymic activities are measured on whole-cell extracts, targeting of these brush-border proteins to the cell surface appears to be regulated in different ways.

Endogenous opiates: 1991

This paper is the fourteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1991 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.

Effects of acetorphan, an antidiarrhoeal enkephalinase inhibitor, on oro-caecal and colonic transit times in healthy volunteers

Acetorphan is a potent enkephalinase inhibitor displaying antidiarrhoeal activity attributable to its intestinal antisecretory action mediated by endogenous enkephalins. The effect of acetorphan on digestive motility was studied in 12 healthy volunteers. Oro-caecal transit time was evaluated using the sulphasalazine/sulphapyridine method and colonic transit times using radiopaque markers. These measurements were successively performed after one week treatment with an antidiarrhoeal dose of acetorphan (100 mg t.d.s.) or placebo. There was no significant modification in transit time linked to acetorphan treatment: total oro-caecal times were 303 +/- 32 min vs. 287 +/- 27 min and colonic transit times 25.8 +/- 5.8 h vs. 31.3 +/- 5.5 h after acetorphan and placebo, respectively (means +/- S.E.M.). There was no significant modification either in right colonic, left colonic or rectosigmoid segmental transit times, or in the mean number of stools. These results, consistent with those from animal studies, confirm that, unlike classical antidiarrhoeal mu opiate receptor agonists, which act by delaying intestinal transit, acetorphan does not affect the transit. Antidiarrhoeal activity not accompanied by a delayed intestinal transit could have beneficial therapeutic consequences in the management of infectious diarrhoea. In addition, we show that the sulphasalazine and radiopaque markers methods can be simultaneously applied in the same study.