Calcium/calcimimetic via calcium-sensing receptor ameliorates cholera toxin-induced secretory diarrhea in mice.

BACKGROUND: Enterotoxins produce diarrhea through direct epithelial action and indirectly by activating the enteric nervous system. Calcium-sensing receptor (CaSR) inhibits both actions. The latter has been well documented in vitro but not in vivo. The hypothesis to be tested was that activating CaSR inhibits diarrhea in vivo. AIM: To determine whether CaSR agonists ameliorate secretory diarrhea evoked by cholera toxin (CTX) in mice. METHODS: CTX was given orally to C57BL/6 mice to induce diarrhea. Calcium and calcimimetic R568 were used to activate CaSR. To maximize their local intestinal actions, calcium was administered luminally via oral rehydration solution (ORS), whereas R568 was applied serosally using an intraperitoneal route. To verify that their actions resulted from the intestine, effects were also examined on Cre-lox intestine-specific CaSR knockouts. Diarrhea outcome was measured biochemically by monitoring changes in fecal Cl- or clinically by assessing stool consistency and weight loss. RESULTS: CTX induced secretory diarrhea, as evidenced by increases in fecal Cl-, stool consistency, and weight loss following CTX exposure, but did not alter CaSR, neither in content nor in function. Accordingly, calcium and R568 were each able to ameliorate diarrhea when applied to diseased intestines. Intestinal CaSR involvement is suggested by gene knockout experiments where the anti-diarrheal actions of R568 were lost in intestinal epithelial CaSR knockouts (villinCre/Casrflox/flox) and neuronal CaSR knockouts (nestinCre/Casrflox/flox). CONCLUSION: Treatment of acute secretory diarrheas remains a global challenge. Despite advances in diarrhea research, few have been made in the realm of diarrhea therapeutics. ORS therapy has remained the standard of care, although it does not halt the losses of intestinal fluid and ions caused by pathogens. There is no cost-effective therapeutic for diarrhea. This and other studies suggest that adding calcium to ORS or using calcimimetics to activate intestinal CaSR might represent a novel approach for treating secretory diarrheal diseases.

Very early onset perinatal constipation: Can it be cow's milk protein allergy?

Delayed passage of meconium or constipation during the perinatal period is traditionally regarded as a signal to initiate further work up to evaluate for serious diagnoses such as Hirschsprung's disease (HD), meconium ileus due to Cystic Fibrosis, etc. The diagnosis of HD particularly warrants invasive testing to confirm the diagnosis, such as anorectal manometry or rectal suction biopsy. What if there was another etiology of perinatal constipation, that is far lesser known? Cow's milk protein allergy (CMPA) is often diagnosed in infants within the first few weeks of life, however, there are studies that show that the CMPA allergen can be passed from mother to an infant in-utero, therefore allowing symptoms to show as early as day one of life. The presentation is more atypical, with perinatal constipation rather than with bloody stools, diarrhea, and vomiting. The diagnosis and management would be avoidance of cow's milk protein within the diet, with results and symptom improvement in patients immediately. Therefore, we discuss whether an alternative pathway to address perinatal constipation should be further discussed and implemented to potentially avoid invasive techniques in patients. This entails first ruling out CMPA with safe, noninvasive techniques with diet modification, and if unsuccessful, then moving forward with further diagnostic modalities.

Gastric electrical stimulation: An emerging therapy for children with intractable gastroparesis.

Management of gastroparesis remains challenging, particularly in pediatric patients. Supportive care and pharmacological therapies for symptoms remain the mainstay treatment. Although they are effective for mild and some moderately severe cases, often time they do not work for severe gastroparesis. There are a few prokinetics available, yet the use of these drugs is limited by a lack of persistent efficacy and/or safety concerns. Currently, the only modality for adult patients with severe intractable gastroparesis is surgery, e.g., pyloroplasty and partial gastrectomy, however, this option is generally considered too radical for a growing child. Novel therapeutic approaches, particularly those which are less invasive, are needed. This article explores gastric electrical stimulation (GES), a new therapy for gastroparesis. Unlike others, it neither needs medications nor gastrectomy; rather, it treats through the use of microelectrodes to deliver high-frequency low energy electric stimulation to the pacemaker area of the stomach. Thus, it is tolerated and safe in children. Like in adult patients, GES appears to work in releasing symptoms, improving nutrition, and enhancing the quality of life; it also helps wean off medications and eliminate many needs for hospitalization. Considering the transient nature of gastroparesis in children in many occasions, GES is considered a "bridging" therapy after failed medical interventions and before surgery.

Extracellular Calcium Dictates Onset, Severity, and Recovery of Diarrhea in a Child with Immune-Mediated Enteropathy.

Diarrhea causes monovalent and divalent ion losses that can influence clinical outcome. Unlike the losses of monovalent ions, such as Na+, K+, Cl-, and [Formula: see text], which are generally large in quantity (osmoles) and therefore determine the severity of diarrhea, the losses of divalent ions are relatively small in osmoles and are often overlooked during diarrheal treatment. Studies now suggest that despite divalent ions being small in osmoles, their effects are large due to the presence of divalent ion-sensing receptors and their amplifying effects in the gut. As a result, losses of these divalent ions without prompt replacement could also significantly affect the onset, severity, and/or recovery of diarrheal disease. Herein, we report a case of a malnourished child with an immune-mediated enteropathy who developed episodes of "breakthrough" diarrhea with concurrent hypocalcemia while on appropriate immunotherapy. Interestingly, during these periods of diarrhea, stool volume fluctuated with levels of blood Ca2+. When Ca2+ was low, diarrhea occurred; when Ca2+ levels normalized with replacement, diarrhea stopped. Based on this and other observations, a broader question arises as to whether the Ca2+ lost in diarrhea should be replaced promptly in these patients.

Calcimimetic R568 inhibits tetrodotoxin-sensitive colonic electrolyte secretion and reduces c-fos expression in myenteric neurons.

AIMS: Calcium-sensing receptor (CaSR) is expressed on neurons of both submucosal and myenteric plexuses of the enteric nervous system (ENS) and the CaSR agonist R568 inhibited Cl- secretion in intestine. The purpose of this study was to localize the primary site of action of R568 in the ENS and to explore how CaSR regulates secretion through the ENS. MATERIALS AND METHODS: Two preparations of rat proximal and distal colon were used. The full-thickness preparation contained both the submucosal and myenteric plexuses, whereas for the "stripped" preparation the myenteric plexus with the muscle layers was removed. Both preparations were mounted onto Ussing chambers and Cl- secretory responses were compared by measuring changes in short circuit current (Isc). Two tissue-specific CaSR knockouts (i.e., neuron-specific vs. enterocyte-specific) were generated to compare the effect of R568 on expression of c-fos protein in myenteric neurons by immunocytochemistry. KEY FINDINGS: In full-thickness colons, tetrodotoxin (TTX) inhibited Isc, both in proximal and distal colons. A nearly identical inhibition was produced by R568. However, in stripped preparations, while the effect of TTX on Isc largely remained, the effect of R568 was nearly completely eliminated. In keeping with this, R568 reduced c-fos protein expression only in myenteric neurons of wild type mice and mutant mice that contained CaSR in neurons (i.e., villinCre/Casrflox/flox mice), but not in myenteric neurons of nestinCre/Casrflox/flox mice in which neuronal cell CaSR was eliminated. SIGNIFICANCE: These results indicate that R568 exerts its anti-secretory effects predominantly via CaSR-mediated inhibition of neuronal activity in the myenteric plexus.

Calcium-sensing receptor: A new target for therapy of diarrhea.

Management of acute diarrhea remains a global challenge, particularly in resource-limiting countries. Oral rehydration solution (ORS), a passive rehydrating therapy developed approximately 40 years ago, remains the mainstay treatment. Although ORS is effective for hydration, since it does not inhibit enterotoxin-mediated excessive secretion, reduced absorption and compromised barrier function - the primary mechanisms of diarrhea, ORS does not offer a rapid relief of diarrhea symptom. There are a few alternative therapies available, yet the use of these drugs is limited by their expense, lack of availability and/or safety concerns. Novel anti-diarrheal therapeutic approaches, particularly those simple affordable therapies, are needed. This article explores intestinal calcium-sensing receptor (CaSR), a newly uncovered target for therapy of diarrhea. Unlike others, targeting this host antidiarrheal receptor system appears "all-inclusive": it is anti-secretory, pro-absorptive, anti-motility, and anti-inflammatory. Thus, activating CaSR reverses changes of both secretory and inflammatory diarrheas. Considering its unique property of using simple nutrients such as calcium, polyamines, and certain amino acids/oligopeptides as activators, it is possible that through targeting of CaSR with a combination of specific nutrients, novel oral rehydrating solutions that are inexpensive and practical to use in all countries may be developed.