Zinc Inhibits Cholera Toxin–Induced, but NotEscherichia coliHeat‐Stable Enterotoxin–Induced, Ion Secretion in Human Enterocytes

Zinc in Human Health and Infectious Diseases

During the last few decades, the micronutrient zinc has proven to be an important metal ion for a well-functioning immune system, and thus also for a suitable immune defense. Nowadays, it is known that the main cause of zinc deficiency is malnutrition. In particular, vulnerable populations, such as the elderly in Western countries and children in developing countries, are often affected. However, sufficient zinc intake and homeostasis is essential for a healthy life, as it is known that zinc deficiency is associated with a multitude of immune disorders such as metabolic and chronic diseases, as well as infectious diseases such as respiratory infections, malaria, HIV, or tuberculosis. Moreover, the modulation of the proinflammatory immune response and oxidative stress is well described. The anti-inflammatory and antioxidant properties of zinc have been known for a long time, but are not comprehensively researched and understood yet. Therefore, this review highlights the current molecular mechanisms underlying the development of a pro-/ and anti-inflammatory immune response as a result of zinc deficiency and zinc supplementation. Additionally, we emphasize the potential of zinc as a preventive and therapeutic agent, alone or in combination with other strategies, that could ameliorate infectious diseases.

Role of Zinc in Mucosal Health and Disease: A Review of Physiological, Biochemical, and Molecular Processes

Zinc is an essential trace element of all highly proliferating cells in the human body. It is essential to the development and growth of all organisms. Zinc plays a critical role in modulating resistance to infectious agents and reduces the duration, severity, and risk of diarrheal disease via improved regeneration of intestinal epithelium, improved absorption of water and electrolytes, increased levels of brush border enzymes, and, possibly, an enhancement in the immune response allowing better clearance of pathogens. On the cellular level, zinc finger motifs play various roles including diverse functions that involve specific gene expression for ion channels throughout the body. It maintains the function and the structure of the membrane barrier by contributing to host defense, which is particularly crucial in the intestines due to the continuous exposure to noxious agents and pathogens. Zinc deficiency is characterized by impaired immune function, loss of appetite, and growth retardation. More severe cases cause diarrhea, delayed sexual maturation, hair loss, eye and skin lesions, impotence and hypogonadism in males, as well as weight loss, taste abnormalities, delayed healing of wounds, and mental lethargy. The objective of this study is a critical review of the molecular and genetic regulation of zinc in various cellular processes and organs, the association between zinc and diarrheal disease, the recommended dietary zinc intake, and the effects of zinc deficiency on the human body.

Potency of Oral Rehydration Solution in Inducing Fluid Absorption is Related to Glucose Concentration

Oral rehydration solutions (ORSs) is the key treatment of acute diarrhea in children, as it restores the electrolyte balance by stimulating the intestinal sodium/glucose transporter SGLT1 to induce fluid absorption. The World Health Organization (WHO) and The European Society for Paediatric Gastroenterology Hepatology and Nutrition (ESPGHAN) proposed ORSs with different chemical compositions. The main agent of childhood acute gastroenteritis is rotavirus (RV). We evaluate the effects of ORS with different concentration of glucose and sodium on RV induced secretion. Ussing chambers technique was used for electophysiology experiments to evaluate ion fluid flux. ESPGHAN ORS (sodium 60 mmol/L and glucose 111 mmol/L) induced a more potent proabsorptive effect in Caco-2 cells than WHO ORS, and this effect depended on the sodium/glucose ratio. Titration experiments showed that RV-induced fluid secretion can be reverted to a proabsorptive direction when sodium and glucose concentration fall in specific ranges, specifically 45–60 mEq/L and 80–110 mM respectively. The results were confirmed by testing commercial ORSs. These findings indicated that ORS proabsorptive potency depends on sodium and glucose concentrations. Optimal ORS composition should be tailored to reduce RV-induced ion secretion by also considering palatability. These in vitro data should be confirmed by clinical trials.

Enterotoxigenic Escherichia coli Heat-Stable Toxin Increases the Rate of Zinc Release from Metallothionein and Is a Zinc- and Iron-Binding Peptide

Enterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in children in low- to middle-income countries. Previous studies have identified heat-stable enterotoxin (ST)-producing ETEC as one of the major diarrhea-causing pathogens in children younger than five years. In this study, we examined iron and zinc binding by both human and porcine ST variants and determined how host metallothionein could detoxify ST. We found that ST purified from ETEC culture supernatants eluted as a doublet during C18 reverse-phase chromatography. Leading edge fractions of the ST doublet were found to be devoid of iron, while trailing edge fractions of the ST doublet were found to contain measurable iron. Next, we found that purified ST could be reconstituted with iron under reducing and anaerobic conditions, and iron-bound ST attenuated the induction of cGMP in T84 epithelial cells. Moreover, we demonstrated that supernatants of ETEC 214-4 grown under increasing iron concentrations were only able to induce cGMP at iron concentrations greater than 5 μM. In vitro studies also demonstrated that ST binds zinc, and once bound, zinc removal from ST required denaturing conditions. Zinc-bound ST also failed to induce cGMP. We found that ST contributes disulfide bonds to the perceived oxidized glutathione pool, increases the rate of zinc release from metallothionein, and can be detoxified by metallothionein. Lastly, we showed ST induces transcriptional changes in genes previously shown to be regulated by deferoxamine. These studies demonstrate ST ETEC pathogenesis may be tied intimately to host mucosal metal status.IMPORTANCE Enterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in children in low- to middle-income countries, deployed military personnel, and travelers to regions of endemicity. The heat-stable toxin (ST) is a small nonimmunogenic secreted peptide with 3 disulfide bonds. It has been appreciated that dietary disulfides modulate intestinal redox potential and that ST could be detoxified using exogenous reductants. Using biochemical and spectroscopic approaches, we demonstrated that ST can separately bind iron and zinc under reducing conditions, thereby reducing ST toxicity. Moreover, we demonstrated that ST modulates the glutathione (GSH)/oxidized glutathione (GSSG) ratio and that ST should be considered a toxin oxidant. ST can be detoxified by oxidizing zinc-loaded metallothionine, causing free zinc to be released. These studies help lay a foundation to understand how diarrheal pathogens modulate intestinal redox potential and may impact how we design therapeutics and/or vaccines for the pathogens that produce them.

Zinc ameliorates intestinal barrier dysfunctions in shigellosis by reinstating claudin-2 and -4 on the membranes

Whether zinc (Zn²⁺) regulates barrier functions by modulating tight-junction (TJ) proteins when pathogens such as Shigella alter epithelial permeability is still unresolved. We investigated the potential benefits of Zn²⁺ in restoring impaired barrier function in vivo in Shigella-infected mouse tissue and in vitro in T84 cell monolayers. Basolateral Shigella infection triggered a time-dependent decrease in transepithelial resistance followed by an increase in paracellular permeability of FITC-labeled dextran and altered ion selectivity. This led to ion and water loss into the intestinal lumen. Immunofluorescence studies revealed redistribution of claudin-2 and -4 to an intracellular location and accumulation of these proteins in the cytoplasm following infection. Zn²⁺ ameliorated this perturbed barrier by redistribution of claudin-2 and -4 back to the plasma membrane and by modulating the phosphorylation state of TJ proteins t hough extracellular signal-regulated kinase (ERK)1/2 dependency. Zn²⁺ prevents elevation of IL-6 and IL-8. Mice challenged with Shigella showed that oral Zn²⁺supplementation diminished diverse pathophysiological symptoms of shigellosis. Claudin-2 and -4 were susceptible to Shigella infection, resulting in altered barrier function and increased levels of IL-6 and IL-8. Zn²⁺ supplementation ameliorated this barrier dysfunction, and the inflammatory response involving ERK-mediated change of phosphorylation status for claudin-2 and -4. Thus, Zn²⁺ may have potential therapeutic value in inflammatory diarrhea and shigellosis. NEW & NOTEWORTHY Our study addresses whether Zn²⁺ could be an alternative strategy to reduce Shigella-induced inflammatory response and epithelial barrier dysfunction. We have defined a mechanism in terms of intracellular signaling pathways and tight-junction protein expression by Zn²⁺. Claudin-2 and -4 are susceptible to Shigella infection, whereas in the presence of Zn²⁺ they are resistant to infection-related barrier dysfunction involving ERK-mediated change of phosphorylation status of claudins.

Zinc Deficiency and the Recurrence of Clostridium difficile Infection after Fecal Microbiota Transplant: A Retrospective Cohort Study

Background

Fecal microbiota transplant (FMT) is an effective therapy for recurrent Clostridium difficile infection (CDI). However, in 12% of patients treated with FMT, CDI recurs within one month. Zinc deficiency predicts increased diarrheal frequency in malnourished children, but little is known about its association with FMT outcome. We hypothesized that zinc levels were an independent predictor of CDI recurrence after FMT.

Methods

We performed a retrospective cohort study of 80 patients (mean age, 66; 59 women) receiving FMT for CDI from 9/2013–9/2016 at a tertiary care center. Zinc levels were measured within 90 days before FMT. The primary outcome was CDI recurrence within 90 days after FMT. We controlled for risk factors for FMT failure using Cox regression. We also analyzed the effect of zinc supplementation in individuals with deficiency.

Results

Forty-nine subjects had a normal zinc level, and 31 had a low level (<0.66 µg/mL). CDI recurred in 3/49 (6%) patients with normal zinc and 5/31 (16%) patients with low zinc (HR = 11.327, 95% CI = 2.162–59.336, p=0.004). Among low zinc subjects, 2 of 25 (8%) that received zinc supplements and 3 of 6 (50%) that did not receive zinc supplements had recurrence of CDI (HR = 0.102, 95% CI = 0.015–0.704, p=0.021).

Conclusion

Zinc deficiency was associated with increased CDI recurrence after FMT. Among zinc-deficient patients, supplementation was associated with reduced recurrence. Further study is needed to determine whether zinc deficiency represents a pathophysiologic mechanism and target for therapy.

Prevention and treatment of secretory diarrhea by the lysophosphatidic acid analog Rx100

IMPACT STATEMENT

A critical barrier in treating diarrheal disease is easy-to-use effective treatments. Rx100 is a first in class, novel small molecule that has shown efficacy after both subcutaneous and oral administration in a mouse cholera-toxin- and Citrobacter rodentium infection-induced diarrhea models. Our findings indicate that Rx100 a metabolically stable analog of the lipid mediator lysophosphatidic acid blocks activation of CFTR-mediated secretion responsible for fluid discharge in secretory diarrhea. Rx100 represents a new treatment modality which does not directly block CFTR but attenuates its activation by bacterial toxins. Our results provide proof-of-principle that Rx100 can be developed for use as an effective oral or injectable easy-to-use drug for secretory diarrhea which could significantly improve care by eliminating the need for severely ill patients to regularly consume large quantities of oral rehydration therapies and offering options for pediatric patients.

The Zn2+-sensing receptor, ZnR/GPR39, upregulates colonocytic Cl- absorption, via basolateral KCC1, and reduces fluid loss

Administration of zinc, as a complement to oral rehydration solutions, effectively diminishes duration and severity of diarrhea, but it is not known whether it merely fulfills a nutritional deficiency, or if zinc has a direct role of regulating solute absorption. We show that Zn2+ acts via a specific receptor, ZnR/GPR39, to reduce fluid loss. Intestinal fluid secretion triggered by cholera toxin (CTx) was lower in WT mice compared to ZnR/GPR39 KO. In the absence of dietary Zn2+ we observed similar fluid accumulation in WT and ZnR/GPR39 KO mice, indicating that Zn2+ and ZnR/GPR39 are both required for a beneficial effect of Zn2+ in diarrhea. In primary colonocytes and in Caco-2 colonocytic cells, activation of ZnR/GPR39 enhanced Cl- transport, a critical factor in diarrhea, by upregulating K+/Cl- cotransporter (KCC1) activity. Importantly, we show basolateral expression of KCC1 in mouse and human colonocytes, thus identifying a novel Cl- absorption pathway. Finally, inhibition of KCC-dependent Cl- transport enhanced CTx-induced fluid loss. Altogether, our data indicate that Zn2+ acting via ZnR/GPR39 has a direct role in controlling Cl- absorption via upregulation of basolateral KCC1 in the colon. Moreover, colonocytic ZnR/GPR39 and KCC1 reduce water loss during diarrhea and may therefore serve as effective drug targets.

Strategies and challenges to increase the precision in feeding zinc to monogastric livestock

Practical diets for monogastric livestock must be supplemented with zinc (Zn) due to their high contents of antagonistic substances like phytates. Current feeding recommendations include quite generous safety margins because of uncertainties regarding the gross Zn requirements under varying rearing conditions. Furthermore, the use of pharmacological Zn doses to stabilise animal performance and wellbeing is widespread. Taken together, modern diets for pigs and poultry contain considerably more Zn than necessary to meet animal requirements, which is associated with concerns related to the environment as well as animal and consumer safety. Therefore, European authorities most recently reduced the allowed upper limits for Zn in complete feed. To maintain animal productivity and wellbeing while reducing the Zn load in complete feed, all measures that stabilize feed Zn bioavailability must be applied. Most importantly, reliable information on the gross Zn requirement under practical conditions must be provided, considering the bioavailability of native or supplemented feed Zn, antagonisms with dietary factors as well as the physiological status of the animal.

Effects of zinc supplementation in the prevention of respiratory tract infections and diarrheal disease in Colombian children: A 12-month randomised controlled trial

BACKGROUND

Among the preventive strategies for lowering the incidence of upper respiratory tract infections (URTI) and acute diarrhoea episodes, two of the most common diseases in children, zinc supplementation has received special interest. However, there is a need for additional studies that determine the preventive effects of different doses of zinc on URTI and diarrhoeal disease episodes in children.

METHODS

In a randomised, triple-blind clinical trial, we evaluated the efficacy of 12 months of daily zinc supplementation in the incidence of URTI and acute diarrhoea in a population of healthy children aged between 6 and 12 months living in Bogota, Colombia. The outcomes analysed were incidence of URTI, acute diarrhoeal disease episodes, and side effects of the interventions.

RESULTS

Between 2010 and 2013, a total of 355 children underwent randomisation, with 174 assigned to the zinc supplementation group and 181 to the control group. In the multivariate analyses, having been randomised to the non-supplemented control group (IRR 1.73, 95% CI 1.52-1.97, p<0.001), and nursery attendance (IRR 1.41, 95% CI 1.07-1.87, p=0.016) were independently linked to the number of URTI. Likewise, having been randomised to the non-supplemented group (IRR 1.43, 95% CI 1.20-1.71, p<0.001), and lower socioeconomic status (IRR 1.86, 95% CI 1.11-3.13, p=0.018) were independently associated to the number of diarrhoeal disease episodes.

CONCLUSIONS

Daily supplementation of 5mg of zinc during 12 months significantly decreased the incidence of URTI and diarrhoeal disease episodes in a healthy population of children aged between 6 and 12 months.

Crosstalk between Zinc Status and Giardia Infection: A New Approach

Zinc supplementation has been shown to reduce the incidence and prevalence of diarrhea; however, its anti-diarrheal effect remains only partially understood. There is now growing evidence that zinc can have pathogen-specific protective effects. Giardiasis is a common yet neglected cause of acute-chronic diarrheal illness worldwide which causes disturbances in zinc metabolism of infected children, representing a risk factor for zinc deficiency. How zinc metabolism is compromised by Giardia is not well understood; zinc status could be altered by intestinal malabsorption, organ redistribution or host-pathogen competition. The potential metal-binding properties of Giardia suggest unusual ways that the parasite may interact with its host. Zinc supplementation was recently found to reduce the rate of diarrhea caused by Giardia in children and to upregulate humoral immune response in Giardia-infected mice; in vitro and in vivo, zinc-salts enhanced the activity of bacitracin in a zinc-dose-dependent way, and this was not due to zinc toxicity. These findings reflect biological effect of zinc that may impact significantly public health in endemic areas of infection. In this paper, we shall explore one direction of this complex interaction, discussing recent information regarding zinc status and its possible contribution to the outcome of the encounter between the host and Giardia.

Acceptability and efficacy of a gel hypotonic oral rehydration solution in children with acute gastroenteritis

OBJECTIVE

Oral rehydration solution remains the mainstay of acute gastroenteritis therapy. The aim of this study was to investigate the acceptability of a new zinc-containing hypotonic super-oral rehydration solution (ORS) in a gel formulation and its efficacy in reducing the duration and severity of diarrhea in children.

METHODS

This was a randomized-controlled trial of children (5-36 months of age) observed for diarrhea lasting less than 24 h. Children were randomized to receive standard hypotonic ORS (group 1) or a gel hypotonic super-ORS containing zinc (group 2). The main study outcome was ORS intake in the first 24 h. ORS intake at 4 h, rate of diarrhea resolution at 72 h of treatment, total duration and severity of diarrhea, hospitalization, and adverse effects were also evaluated.

RESULTS

Eighty-three children were enrolled (group 1: 40; group 2: 43). The amount of ORS consumed at 24 h was significantly higher in group 2 than in group 1. A similar result was observed at 4 h. The number of children who refused ORS (<10 ml/kg/day) was lower in group 2 versus group 1 (P=0.001). The number of children presenting diarrhea after 72 h of treatment was lower in group 2 versus group 1 (P=0.028). Also, the mean duration of diarrhea was shorter in group 2 than in group 1 (P=0.001). The hypotonic super-ORS containing zinc in a gel formulation had a positive effect on the severity of diarrhea. No patient required hospitalization. No adverse events were observed in either of the two study groups.

CONCLUSION

The new zinc-containing hypotonic super-ORS in a gel formulation is effective in the management of childhood acute gastroenteritis.

Dose Effects of Apical versus Basolateral Zinc Supplementation on Epithelial Resistance, Viability, and Metallothionein Expression in Two Intestinal Epithelial Cell Lines

Zinc supplementation is used to reduce diarrhea incidence in piglets and it has been shown in vitro that the antisecretory effects are maximal after basolateral zinc application. To examine whether the application site and dose of zinc also influence passive ion permeability and viability, porcine (IPEC-J2) and human (Caco-2) intestinal epithelial cells were treated with increasing zinc concentrations (0-200 μM) at either the apical or basolateral side. Transepithelial electrical resistance and viability decreased and expression of metallothionein and the efflux zinc transporter 1 increased most prominently when zinc was added in high concentrations at the basolateral side of IPEC-J2 cells. Zinc transporter 4, a zinc importer, was not affected. Heat shock protein 70 mRNA expression increased only after basolateral addition of 200 μM zinc in IPEC-J2 cells. Thus, zinc can elicit toxic effects especially when added at the basolateral side, with IPEC-J2 cells being more susceptible than Caco-2 cells.

Infectious diarrhea: an overview

Diarrheal disease, which is most often caused by infectious pathogens, is a significant cause of morbidity and mortality worldwide, especially in children. This is particularly true in developing countries. Recent outbreaks of infectious diarrhea in developed countries, including the USA, are often attributed to food handling and distribution practices and highlight the need for continued vigilance in this area. Another common cause of infectious diarrhea, Clostridium difficile infection (CDI), has historically been associated with the use of antibiotics and exposure to a health-care setting but is now increasingly common in the community in persons who lack the typical risk factors. Recent scientific advances have also led to new and proposed new therapies for infectious diarrhea, including fecal microbiota transplant (FMT) for recurrent C. difficile infection (RCDI), probiotics for prevention of antibiotic-associated diarrhea (AAD) and CDI, and the use of zinc supplementation in the treatment of acute diarrhea in children. Other therapies that have been in use for decades, such as the oral rehydration solution (ORS), continue to be the targets of scientific advancement in an effort to improve delivery and efficacy. Finally, post-infectious irritable bowel syndrome (PI-IBS) is an increasingly recognized occurrence. Attempts to understand the mechanism behind this phenomenon are underway and may provide insight into potential treatment options.

Role of 6-gingerol in reduction of cholera toxin activity in vitro and in vivo

Vibrio cholerae is one of the major bacterial pathogens responsible for the devastating diarrheal disease called cholera. Chemotherapy is often used against V. cholerae infections; however, the emergence of V. cholerae with multidrug resistance (MDR) toward the chemotherapeutic agents is a serious clinical problem. This scenario has provided us with the impetus to look into herbal remediation, especially toward blocking the action of cholera toxin (CT). Our studies were undertaken to determine the antidiarrheal potential of 6-gingerol (6G) on the basis of its effect on CT, the virulence factor secreted by V. cholerae. We report here that 6G binds to CT, hindering its interaction with the GM1 receptor present on the intestinal epithelial cells. The 50% inhibitory concentration (IC50) was determined to be 10 μg/ml. The detailed mechanistic study was conducted by enzyme-linked immunosorbent assay (ELISA), fluorescence spectroscopy, and isoelectric focusing. These results were validated with in vitro studies performed with the CHO, HeLa, and HT-29 cell lines, whereas a rabbit ileal loop assay was done to estimate the in vivo action, which confirms the efficacy of 6G in remediation of the choleragenic effects of CT. Thus, 6G can be an effective adjunctive therapy with oral rehydration solution for severe CT-mediated diarrhea.

Zinc: Role in the management of diarrhea and cholera

Diarrhea and cholera are major health problems. Vibrio cholera, the causative agent of cholera, infects the small intestine, resulting in vomiting, massive watery diarrhea and dehydration. Reduced water and electrolyte absorption is also due to zinc deficiency. Zinc has an important role in recovery from the disease. The combination of zinc with cholera vaccine and oral rehydration solutions has a positive impact on cholera and diarrhea. It has led to a decrease in the mortality and morbidity associated with diarrhea.

Effects of zinc on epithelial barrier properties and viability in a human and a porcine intestinal cell culture model

Zinc is an essential trace element with a variety of physiological and biochemical functions. Piglets are commonly supplemented, during the weaning period, with doses of zinc above dietary requirements with positive effects on health and performance that might be attributed to anti-secretory and barrier-enhancing effects in the intestine. For a better understanding of these observations increasing zinc sulfate (ZnSO4; 0-200μM) concentrations were used in an in vitro culture model of porcine (IPEC-J2) and human (Caco-2) intestinal epithelial cells and effects on barrier function, viability, and the mRNA expression of one selected heat shock protein (Hsp) were assessed. When treated apically with zinc sulfate, the transepithelial electrical resistance (TEER) did not change significantly. In contrast, cell viability measured by lactate dehydrogenase (LDH) leakage, by ATP and by WST-1 conversion in postconfluent IPEC-J2 monolayers was affected after a 24-h treatment with 200μM ZnSO4. Caco-2 cells were more resistant to Zn. ZnSO4 did not induce any effect on viability, except when it was used at the highest concentration (200μM), and only in preconfluent cells. Furthermore, ZnSO4 induced Hsp70 mRNA expression at 200μM and was more pronounced in preconfluent cells. The observed dose-related effects of zinc are cell-line specific and depended on the differentiation status of the cells. The IPEC-J2 cell line appears to be a suitable in vitro model to characterize specific effects on porcine intestinal cells.

Bioavailability of trace elements in beans and zinc-biofortified wheat in pigs

The objectives of this experiment were to study bioavailability of trace elements in beans and wheat containing different levels of zinc and to study how the water solubility of trace elements was related to the bioavailability in pigs. Three wheat and two bean types were used: wheat of Danish origin as a control (CtrlW), two Turkish wheat types low (LZnW) and high (HZnW) in zinc, a common bean (Com), and a faba bean (Faba). Two diets were composed by combining 81 % CtrlW and 19 % Com or Faba beans. Solubility was measured as the trace element concentration in the supernatant of feedstuffs, and diets incubated in distilled water at pH 4 and 38°C for 3 h. The bioavailability of zinc and copper of the three wheat types and the two bean-containing diets were evaluated in the pigs by collection of urine and feces for 7 days. The solubility of zinc was 34-63 %, copper 18-42 %, and iron 3-11 %. The zinc apparent digestibility in pigs was similar in the three wheat groups (11-14 %), but was significantly higher in the CtrlW+Faba group (23 %) and negative in the CtrlW+Com group (-30 %). The apparent digestibility of copper was higher in the HZnW (27 %) and CtrlW+Faba (33 %) groups than in the CtrlW (17 %) and LZnW (18 %) groups. The apparent copper digestibility of the CtrlW+Com diet was negative (-7 %). The solubility and digestibility results did not reflect the concentration in feedstuffs. The in vitro results of water solubility showed no relationship to the results of trace mineral bioavailability in pigs.

Mechanisms of action of zinc on rat intestinal epithelial electrogenic ion secretion: insights into its antidiarrhoeal actions

OBJECTIVES

Zinc is a useful addition to oral rehydration therapy for acute diarrhoea. We have assessed the mechanism of its epithelial antisecretory action when intestinal epithelial tight junctions were pharmacologically opened.

METHODS

Rat isolated ileal and colonic mucosae were mounted in Ussing chambers and exposed to ZnSO(4) (Zn(2+) ) in the presence of secretagogues and inhibition of short circuit current (I(sc) ) was measured.

KEY FINDINGS

Pre-incubation with basolateral but not apical Zn(2+) reduced I(sc) stimulated by forskolin, carbachol and A23187. In the presence of the tight junction-opener, cytochalasin D, antisecretory effects of apically-applied Zn(2+) were enabled in colon and ileum. The apparent permeability coefficient (P(app) ) of Zn(2+) was increased 1.4- and 2.4-fold across rat ileum and colon, respectively, by cytochalasin D. Basolateral addition of Zn(2+) also reduced the I(sc) stimulated by nystatin in rat colon, confirming K channel inhibition. In comparison with other inhibitors, Zn(2+) was a relatively weak blocker of basolateral K(ATP) and K (Ca2+) channels. Exposure of ileum and colon to Zn(2+) for 60 min had minimal effects on epithelial histology.

CONCLUSIONS

Antisecretory effects of Zn(2+) on intestinal epithelia arose in part through nonselective blockade of basolateral K channels, which was enabled when tight junctions were open.

Infective and inflammatory diarrhoea: mechanisms and opportunities for novel therapies

There have been significant advances in unravelling the cellular mechanisms of diarrhoea in common gut infections and colonic inflammation, as well as in the identification of targets for potential antidiarrhoeal drugs. Infective diarrhoea reflects activation of electrogenic Cl⁻ secretion, inhibition of electroneutral NaCl absorption and in some cases, downregulation of tight junctional proteins and increased apoptosis. In colonic inflammation, diarrhoea mainly reflects impairment of colonic Na⁺ and Cl⁻ absorption by inflammatory cytokines, leading to decreased water absorption. Stimulation of endogenous opiate-dependent pathways, manipulation of epithelial ion (Na⁺, K⁺ and Cl⁻) channels and suppression of proinflammatory cytokine production by a variety of drugs and novel molecules, offer opportunities to move evaluation of these potential antisecretory and anti-inflammatory agents from the laboratory into clinical trials.

Role of zinc in pediatric diarrhea

Zinc supplementation is a critical new intervention for treating diarrheal episodes in children. Recent studies suggest that administration of zinc along with new low osmolarity oral rehydration solutions / salts (ORS), can reduce the duration and severity of diarrheal episodes for up to three months. The World Health Organization (WHO) and UNICEF recommend daily 20 mg zinc supplements for 10 – 14 days for children with acute diarrhea, and 10 mg per day for infants under six months old, to curtail the severity of the episode and prevent further occurrences in the ensuing -two to three months, thereby decreasing the morbidity considerably. This article reviews the available evidence on the efficacy and safety of zinc supplementation in pediatric diarrhea and convincingly concludes that zinc supplementation has a beneficial impact on the disease outcome.

Oral rehydration salts, zinc supplement and rota virus vaccine in the management of childhood acute diarrhea

Acute diarrhea remains a major cause of morbidity and mortality in children. Since the introduction of oral rehydration salts (ORS) mortality has dropped to less than 50% worldwide. Low osmolarity ORS improved the outcome and reduced the hospitalization further. Zinc difficiency has been found to be associated with severe episodes of acute diarrhea. Zinc supplement in developing countries did reduce the incidence and prevalence of diarrhea. In addition, Zinc supplement significantly reduced the severity of diarrhea and duration of the episode. In the Americas and Europe, Rota virus vaccine was 90% effective in preventing severe episodes of severe rotavirus gastroenteritis. This review concludes that low osmolarilty ORS, zinc supplementation and rotavirus vaccine are major factors in reducing the morbidity, mortality and hospitalization resulting from to acute gastroenteritis in childhood.

Cobalamin status modifies the effect of zinc supplementation on the incidence of prolonged diarrhea in 6- to 30-month-old north Indian children

The observed effect of zinc supplementation on diarrheal morbidity varies between trials and there is a need to identify subgroups most likely to benefit from improved zinc nutriture. In a randomized, double-blind trial in 2296 children in New Delhi, India, we assessed whether baseline cobalamin or folate status modified the effect of zinc supplementation on the incidence of prolonged (≥ 7 d duration) and acute diarrhea. Children aged 6-30 mo received zinc or placebo daily for 4 mo. We measured plasma concentrations of folate, cobalamin, total homocysteine (tHcy), and methylmalonic acid (MMA) at enrollment and assessed the efficacy of zinc supplementation in subgroups based on these variables. The efficacy of zinc on reducing the risk of prolonged diarrhea was higher in those with plasma cobalamin concentrations below the 25th percentile and in those with tHcy and MMA concentrations above the 75th percentile. The OR (95% CI) for children below and above the 25th percentile for cobalamin were 0.53 (0.35-0.78) and 0.90 (0.73-1.11), respectively (P-interaction = 0.015). There were similar differences for the OR when comparing efficacy in those above and below the 75th percentile for tHcy and MMA (P-interaction = 0.045 and 0.188, respectively). Baseline folate status did not modify the effect of zinc on prolonged diarrhea. Neither cobalamin nor folate status influenced the effect of zinc on acute diarrhea. Children with poor cobalamin status benefited more from zinc supplementation for the prevention of prolonged diarrhea.

Treatment of cholera-like diarrhoea with oral rehydration

Cholera diarrhoea remains a major global health problem that has caused seven pandemics. The pathogenesis of cholera is attributable to the production of cholera toxin by the causative pathogen, Vibrio cholerae. The toxin causes increased production of cyclic adenosine monophosphate and this results in massive water and electrolyte secretion into the intestinal lumen. These changes manifest clinically as the painless defecation of voluminous stools that resemble 'rice water', leading to severe dehydration. The cornerstone in the management of cholera diarrhoea is the use of oral rehydration solutions (ORS) to replace the water and electrolytes lost as stools. The World Health Organization recommends the use of ORS of 'reduced osmolarity' for the treatment of acute non-cholera diarrhoea and the use of rice-based ORS for the management of cholera diarrhoea. Although several attempts have been made to improve ORS, studies to evaluate some of the modifications, which include the addition of amylase-resistant starch, the use of amino acids (such as glycine, alanine and glutamine) as sodium cotransporters, and zinc-supplemented ORS, are still needed.

Efficacy of a new hypotonic oral rehydration solution containing zinc and prebiotics in the treatment of childhood acute diarrhea: a randomized controlled trial

OBJECTIVE

To evaluate the efficacy of a hypotonic oral rehydration solution (ORS) containing zinc and prebiotics for treatment of acute diarrhea in children.

STUDY DESIGN

We conducted a single-blind, prospective, controlled trial including children (age range, 3-36 months) with acute diarrhea randomly assigned to standard hypotonic ORS (group 1) or to new hypotonic ORS containing zinc and prebiotics (group 2). The main outcome was the rate of resolution of diarrhea at 72 hours.

RESULTS

A total of 60 children in group 1 (34 male; mean age, 18.58 months; 95% CI, 15.5-21.6) and 59 in group 2 (36 male; mean age, 19.26 months; 95% CI, 15.9-22.6) completed the study protocol. The rate of diarrhea resolution at 72 hours was higher in group 2 (50% versus 72.9%, P = .010). Total ORS intake in the first 24 hours was higher in group 2 (50 mL/kg; 95% CI, 41-59 versus 22 mL/kg; 95% CI, 17-29; P < .001). The mean number of missed working days by the parents of children in group 2 was lower (0.39; 95% CI, 0.08-0.70 versus 1.45; 95% CI 1.02-1.88; P < .001). Fewer patients in group 2 needed adjunctive drugs for the treatment of diarrhea 6/59 versus 19/60, P = .004. No adverse events were observed in either of the two groups.

CONCLUSION

The addition of zinc and prebiotics to ORS limits diarrhea duration in children.

Mechanisms of action of zinc in acute diarrhea

PURPOSE OF REVIEW

For over a decade, the importance of zinc in the treatment of acute diarrhea has been recognized. More recently, the mechanisms of action of zinc are becoming clearer. This review is focused on the new evidence on the mechanisms of action of zinc in acute diarrhea.

RECENT FINDINGS

The vast majority of data derive from in-vitro studies using intestinal cell lines or from animal model. The positive action by zinc in acute diarrhea derives from a regulation of intestinal fluid transport, mucosal integrity, immunity, gene expression, and oxidative stress. A complex homeostatic network is also able to regulate zinc status at cellular and extracellular level.

SUMMARY

All these data support the use of zinc in the treatment of acute diarrhea, but further clinical studies are needed to explore the selective effects of zinc against specific pathogens responsible for diarrhea.

Mechanisms of diarrhea

Diarrhea is a symptom common to a wide variety of gastrointestinal illnesses, and is an important public health challenge in underdeveloped regions of the world. Normal intestinal absorption is a complex process. Recent research offers new insights into normal physiology and pathophysiology. The role of the enteric nervous system and neurotransmitters in the pathogenesis of diarrhea in inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS) is being actively investigated. In patients with IBD, ileal and sigmoid biopsies showed altered transepithelial sodium and fluid transport, specifically from decreased expression of the NHE3, NHERF-1, and NHE1 epithelial Na channel. This results in changes in normal intestinal electroneutral NaCl absorption and may be an additional factor contributing to the diarrhea in patients with IBD. Physiologic studies in humans suggest that primary bile acid malabsorption may be caused by an abnormal feedback system resulting in the increased bile salts, which may explain the watery diarrhea. Finally, the role of zinc in treatment of infectious diarrhea led to studies of its effect on intracellular human enterocyte ion secretion. Understanding such basic mechanisms may lead to better and novel therapies for treatment of diarrhea.

The functional effects of nutrients on enterocyte proliferation and intestinal ion transport in early infancy

Nutrition has a key role in the modulation of the developing intestine in early infancy, and nutrients are able to modulate several intestinal functions including nutrient absorption, ion transport, cell growth and differentiation, motility and immunomodulation. Such modulation is exerted in part through a direct interaction between a single nutrient and the enterocyte. Two functions--ion transport and cell growth--are closely connected and appear to be modulated by nutrients. This is supported by the finding that a single nutrient (e.g. zinc) stimulates ion absorption and also promotes enterocyte growth. Interestingly, intracellular signalling for either effect is similar and involves mitogen-activated protein kinase. Other nutrients also modulate enterocyte function and there is evidence that their effect may depend on their side of action (apical or basolateral) and concentration. Knowledge of the interaction between nutrients and enterocytes may be exploited to obtain clinical effects using nutrition as a long-term treatment for intestinal and non-intestinal conditions.

Influence of zinc supplementation in acute diarrhea differs by the isolated organism

Zinc supplementation is recommended in all acute diarrheas in children from developing countries. We aimed to assess whether zinc supplementation would be equally effective against all the common organisms associated with acute diarrheas. We used data on 801 children with acute diarrhea recruited in a randomized, double blind controlled trial (ISRCTN85071383) of zinc and copper supplementation. Using prespecified subgroup analyses, multidimensionality reduction analyses, tests of heterogeneity, and stepwise logistic regression for tests of interactions, we found that the influence of zinc on the risk of diarrhea for more than 3 days depended on the isolated organism—beneficial in Klebsiella, neutral in Esherichia coli and parasitic infections, and detrimental in rotavirus coinfections. Although we found similar results for the outcome of high stool volume, the results did not reach statistical significance. Our findings suggest that the current strategy of zinc supplementation in all cases of acute diarrheas in children may need appropriate fine tuning to optimize the therapeutic benefit based on the causative organism, but further studies need to confirm and extend our findings.

Therapeutic value of zinc supplementation in acute and persistent diarrhea: a systematic review

BACKGROUND

For over a decade, the importance of zinc in the treatment of acute and persistent diarrhea has been recognized. In spite of recently published reviews, there remain several unanswered questions about the role of zinc supplementation in childhood diarrhea in the developing countries. Our study aimed to assess the therapeutic benefits of zinc supplementation in the treatment of acute or persistent diarrhea in children, and to examine the causes of any heterogeneity of response to zinc supplementation.

METHODS AND FINDINGS

EMBASE, MEDLINE and CINAHL databases were searched for published reviews and meta-analyses on the use of zinc supplementation for the prevention and treatment of childhood diarrhea. Additional RCTs published following the meta-analyses were also sought. The reviews and published RCTs were qualitatively mapped followed by updated random-effects meta-analyses, subgroup meta-analyses and meta-regression to quantify and characterize the role of zinc supplementation with diarrhea-related outcomes. We found that although there was evidence to support the use of zinc to treat diarrhea in children, there was significant unexplained heterogeneity across the studies for the effect of zinc supplementation in reducing important diarrhea outcomes. Zinc supplementation reduced the mean duration of diarrhea by 19.7% but had no effect on stool frequency or stool output, and increased the risk of vomiting. Our subgroup meta-analyses and meta-regression showed that age, stunting, breast-feeding and baseline zinc levels could not explain the heterogeneity associated with differential reduction in the mean diarrheal duration. However, the baseline zinc levels may not be representative of the existing zinc deficiency state.

CONCLUSIONS

Understanding the predictors of zinc efficacy including the role of diarrheal disease etiology on the response to zinc would help to identify the populations most likely to benefit from supplementation. To improve the programmatic use of zinc, further evaluations of the zinc salts used, the dose, the frequency and duration of supplementation, and its acceptability are required. The significant heterogeneity of responses to zinc suggests the need to revisit the strategy of universal zinc supplementation in the treatment children with acute diarrhea in developing countries.

Zinc inhibits calcium-mediated and nitric oxide-mediated ion secretion in human enterocytes

Zn(2+) is effective in the treatment of acute diarrhea, but its mechanisms are not completely understood. We previously demonstrated that Zn(2+) inhibits the secretory effect of cyclic adenosine monophosphate but not of cyclic guanosine monophosphate in human enterocytes. The aim of the present study was to investigate whether Zn(2+) inhibits intestinal ion secretion mediated by the Ca(2+) or nitric oxide pathways. To investigate ion transport we evaluated the effect of Zn(2+) (35 microM) on electrical parameters of human intestinal epithelial cell monolayers (Caco2 cells) mounted in Ussing chambers and exposed to ligands that selectively increased intracellular Ca(2+) (carbachol 10(-6)M) or nitric oxide (interferon-gamma 300 UI/ml) concentrations. We also measured intracellular Ca(2+) and nitric oxide concentrations. Zn(2+) significantly reduced ion secretion elicited by carbachol (-87%) or by interferon-gamma (-100%), and inhibited the increase of intracellular Ca(2+) and nitric oxide concentrations. These data indicate that Zn(2+) inhibits ion secretion elicited by Ca(2+) and nitric oxide by directly interacting with the enterocyte. They also suggest that Zn(2+) interferes with three of the four main intracellular pathways of intestinal ion secretion that are involved in acute diarrhea.

Secretory state regulates Zn2+ transport in gastric parietal cell of the rabbit

Secretory compartments of neurons, endocrine cells, and exocrine glands are acidic and contain high levels of labile Zn2+. Previously, we reported evidence that acidity is regulated, in part, by the content of Zn2+ in the secretory [i.e., tubulovesicle (TV)] compartment of the acid-secreting gastric parietal cell. Here we report studies focusing on the mechanisms of Zn2+ transport by the TV compartment in the mammalian (rabbit) gastric parietal cell. Uptake of Zn2+ by isolated TV structures was monitored with a novel application of the fluorescent Zn2+ reporter N-(6-methoxy-8-quinolyl)-para-toluenesulfonamide (TSQ). Uptake was suppressed by removal of external ATP or blockade of H+-K+-ATPase that mediates luminal acid secretion. Uptake was diminished with dissipation of the proton gradient across the TV membrane, suggesting Zn2+/H+ antiport as the connection between Zn2+ uptake and acidity in the TV lumen. In isolated gastric glands loaded with the reporter fluozin-3, inhibition of H+-K+-ATPase arrested the flow of Zn(2+) from the cytoplasm to the TV compartment and secretory stimulation with forskolin enhanced vectorial movement of cytoplasmic Zn2+ into the tubulovesicle/lumen (TV/L) compartment. Our findings suggest that Zn2+ accumulation in the TV/L compartment is physiologically coupled to secretion of acid. These findings offer novel insight into mechanisms regulating Zn2+ homeostasis in the gastric parietal cell and potentially other cells in which acidic subcellular compartments serve signature functional roles.

Zinc and copper supplementation in acute diarrhea in children: a double-blind randomized controlled trial

BACKGROUND

Diarrhea causes an estimated 2.5 million child deaths in developing countries each year, 35% of which are due to acute diarrhea. Zinc and copper stores in the body are known to be depleted during acute diarrhea. Our objectives were to evaluate the efficacy of zinc and copper supplementation when given with standard treatment to children with acute watery or bloody diarrhea.

METHODS

We conducted a double-blind randomized controlled clinical trial in the Department of Pediatrics at Indira Gandhi Government Medical College Nagpur, India. Eight hundred and eight children aged 6 months to 59 months with acute diarrhea were individually randomized to placebo (Pl), zinc (Zn) only, and zinc and copper (Zn+Cu) together with standard treatment for acute diarrhea.

RESULTS

The mean duration of diarrhea from enrollment and the mean stool weight during hospital stay were 63.7 hours and 940 grams, respectively, and there were no significant differences in the adjusted means across treatment groups. Similarly, the adjusted means of the amount of oral rehydration solution or intravenous fluids used, the proportion of participants with diarrhea more than 7 days from onset, and the severity of diarrhea indicated by more than three episodes of some dehydration or any episode of severe dehydration after enrollment, did not differ across the three groups.

CONCLUSION

The expected beneficial effects of zinc supplementation for acute diarrhea were not observed. Therapeutic Zn or Zn and Cu supplementation may not have a universal beneficial impact on the duration of acute diarrhea in children.

Colon in acute intestinal infection

The colon is actively implicated in intestinal infections not only as a target of enteric pathogens and their products but also as a target organ for treatment. In the presence of diarrhea, both of osmotic and secretory nature, the colon reacts with homeostatic mechanisms to increase ion absorption. These mechanisms can be effectively exploited to decrease fluid discharge. A model of intestinal infections using rotavirus (RV) in colonic cells was set up and used to define a dual model of secretory and osmotic diarrhea in sequence. Using this model, antidiarrheal drugs were tested, namely zinc and the enkephalinase inhibitor racecadotril. Zinc was able to decrease the enterotoxic activity responsible for secretory diarrhea. It also inhibited the cytotoxic effect of RV. The mechanism of zinc was related at least in part to the activation of MAPK activity, but also a direct antiviral effect was observed. Racecadotril showed a potent and selective inhibition of active secretion, being particularly effective in the first phase of RV diarrhea. The use of drugs active at the colonic level, therefore, offers effective options to treat intestinal infections in childhood. In addition, the colon is the natural site of colonic microflora, a target of probiotic therapy, which is the first line of approach recommended by the European Society for Paediatric Gastroenterology, Hepatology and Nutrition to treat infectious diarrhea.

Zinc and diarrheal disease: current status and future perspectives

PURPOSE OF REVIEW

To evaluate clinical data indicating the benefits of oral zinc supplementation to prevent and/or treat diarrhea in children and extend these findings to adults.

RECENT FINDINGS

Zinc plays an important role in modulating host resistance to infectious agents and reducing the risk, severity, and duration of diarrheal diseases. Zinc is important in the developing world and in low-income and middle-income countries where mild-to-moderate zinc deficiency is highly prevalent.The WHO/UNICEF recommendations for zinc supplementation are based on meta-analyses of randomized, controlled intervention trials on children: 20 mg zinc/day for 10-14 days for children with acute diarrhea and 10 mg/day for infants under 6 months of age. Effective forms include sulfate, gluconate, or acetate. No similar studies have been conducted on adults. Thus, carefully conducted clinical trials are necessary to ascertain the efficacy of zinc in prevention of acute and persistent diarrhea in adults.

SUMMARY

Faced with rising antibiotic resistance and the lack of effective antidiarrheal vaccines, oral zinc provides substantial benefit in the reduction of stool output and disease duration combined with safety, selectivity of action, and low cost. Thus, oral zinc supplementation is a practical therapeutic intervention for the treatment of diarrhea in children, and by extension, should be provided to adults.

Altered fluid, electrolyte and mineral status in tropical disease, with an emphasis on malaria and leptospirosis

Fluid, electrolyte and mineral perturbations are prevalent features of tropical disease. Hemodynamic alterations, fever, nitrogen wasting, and changes in membrane transport and acid-base balance contribute to these perturbations. Models of malaria and leptospirosis have been used to show that common hemodynamic changes in tropical disease include decreased systemic vascular resistance, increased cardiac output and increased renal vascular resistance. Blood volume is initially increased, but it decreases as disease progresses. Response to fluid loading is decreased. Diabetes insipidus is occasionally observed in malaria. Hyponatremia occurs frequently in tropical diseases, as a result of increased levels of antidiuretic hormone (vasopressin), entry of sodium into cells, sodium loss and resetting of osmoreceptors. Natriuresis and kaliuresis are observed in patients with leptospirosis. Large amounts of sodium and potassium are lost in stool as a result of diarrhea. Hypernatremia is uncommon, whereas hypokalemia caused by hyperventilation is often observed (more frequently in patients with leptospirosis and kaliuresis). During severe tropical infective episodes, hyperkalemia results from intravascular hemolysis or rhabdomyolysis, and occasionally from decreased activity of Na+,K+-ATPase. Hypocalcemia, hypomagnesemia and hypophosphatemia are common features of both malaria and leptospirosis. Loss of magnesium in the urine is uniquely associated with leptospiral nephropathy. Hypozincemia and hypocupremia can also develop during tropical infection, and might interfere with a patient's immune response. These electrolyte and mineral perturbations are transient and quickly resolve when the disease is controlled.

A meta-analysis of the effects of oral zinc in the treatment of acute and persistent diarrhea

OBJECTIVE

Children in developing countries are at a high risk for zinc deficiency. Supplemental zinc has previously been shown to provide therapeutic benefits in diarrhea. The objective of this study was to examine the efficacy and safety of supplemental oral zinc therapy during recovery from acute or persistent diarrhea.

METHODS

We conducted a meta-analysis of randomized, controlled trials to compare the efficacy and safety of supplementary oral zinc with placebo in children with acute and persistent diarrhea. Results were reported using a pooled relative risk or a weighted mean difference. A total of 22 studies were identified for inclusion: 16 examined acute diarrhea (n = 15,231), and 6 examined persistent diarrhea (n = 2968).

RESULTS

Mean duration of acute diarrhea and persistent diarrhea was significantly lower for zinc compared with placebo. Presence of diarrhea between zinc and placebo at day 1 was not significantly different in acute diarrhea or persistent diarrhea trials. At day 3, presence was significantly lower for zinc in persistent diarrhea trials (n = 221) but not in acute diarrhea trials. Vomiting after therapy was significantly higher for zinc in 11 acute diarrhea trials (n = 4438) and 4 persistent diarrhea trials (n = 2969). Those who received zinc gluconate in comparison with zinc sulfate/acetate vomited more frequently. Overall, children who received zinc reported an 18.8% and 12.5% reduction in average stool frequency, 15.0% and 15.5% shortening of diarrhea duration, and a 17.9% and 18.0% probability of reducing diarrhea over placebo in acute and persistent trials, respectively.

CONCLUSIONS

Zinc supplementation reduces the duration and severity of acute and persistent diarrhea; however, the mechanisms by which zinc exerts its antidiarrheal effect have not been fully elucidated.

Serosal zinc attenuate serotonin and vasoactive intestinal peptide induced secretion in piglet small intestinal epithelium in vitro

This study addressed the mechanisms by which dietary zinc affects diarrhoea and aimed to study possible interactions between zinc status and the presence of zinc in vitro on secretagogue-induced secretion from piglet intestinal epithelium in Ussing chambers. In addition, it was studied from which side of the epithelium zinc would perform an effect and if copper caused similar effects. Twenty-four piglets (28 days of age) were weaned and fed diets containing 100 or 2500 mg zinc/kg (as ZnO) for 5 or 6 days (12 piglets per group). Intestinal epithelium underwent the following 5 treatments: zinc at the mucosal side (M(Zn)), zinc at the serosal side (S(Zn)), zinc at both sides (MS(Zn)), copper at both sides (MS(Cu)) or water at both sides (control). Provoked secretion in terms of short circuit responses to serotonin (5-HT) and vasoactive intestinal peptide (VIP) were measured. Zinc at the serosal or both sides of the epithelium reduced the 5-HT induced secretion (P<0.001); however, due to interactions (P=0.05) the effect of zinc in vitro was only present in the ZnO(100) group. The secretion caused by VIP was not affected by the diet (P=0.33), but zinc at the serosal side or both sides reduced the response to VIP (P<0.001). Copper reduced the 5-HT and VIP induced secretion to a larger extent than zinc. However, copper also disturbed intestinal barrier function as demonstrated by increased transepithelial conductance and increased short circuit current, which was unaffected by zinc. In conclusion, zinc at the serosal side of piglet small intestinal epithelium attenuated 5-HT and VIP induced secretion in vitro. These in vitro studies indicate that in vivo there will be no positive acute effect of increasing luminal Zn concentration on secretagogue-induced chloride secretion and that zinc status at the serosal side of the epithelium has to be increased to reduce secretagogue-induced chloride secretion and thereby diarrhoea.

Differential expression of intestinal membrane transporters in cholera patients

Vibrio cholerae causes the cholera disease through secretion of cholera toxin (CT), resulting in severe diarrhoea by modulation of membrane transporters in the intestinal epithelium. Genes encoding membrane-spanning transporters identified as being differentially expressed during cholera disease in a microarray screening were studied by real-time PCR, immunohistochemistry and in a CaCo-2 cell model. Two amino acid transporters, SLC7A11 and SLC6A14, were upregulated in acute cholera patients compared to convalescence. Five other transporters were downregulated; aquaporin 10, SLC6A4, TRPM6, SLC23A1 and SLC30A4, which have specificity for water, serotonin (5-HT), magnesium, vitamin C and zinc, respectively. The majority of these changes appear to be attempts of the host to counteract the secretory response. Our results also support the concept that epithelial cells are involved in 5-HT signalling during acute cholera.

Probiotics and zinc in acute infectious gastroenteritis in children: are they effective?

OBJECTIVE

Several studies in recent decades have assessed the effects of different probiotics in acute gastroenteritis, showing that specific strains of Lactobacilli (mainly Lactobacillus casei GG) and Saccharomyces boulardii may exert some beneficial therapeutic actions, mainly when used in rotavirus gastroenteritis, at a high dose, and in the early phase. The mechanisms of action of probiotics are not completely elucidated but seem to involve a complex interaction among epithelial, molecular, metabolic, and immune responses. Data on the prevention of community-acquired, nosocomial, and travelers' diarrhea are currently conflicting. Because each micro-organism has different properties, an accurate selection of the strain, dose, and patient should be cautiously considered.

METHODS AND RESULTS

Several reports from developing countries have demonstrated that supplements of zinc also provide significant reduction in stool output and duration, persistency, and severity of diarrhea. In view of the published data and of the different actions of zinc (such as improvement of the immune status, intestinal permeability, epithelial and enzymatic function, and electrolyte transport), the use of zinc as adjunctive therapy to oral rehydration solution has the potential to improve the management of diarrhea and decrease complications in children worldwide. In contrast to probiotics, which most trials in the developed world have used, there has been no trial with zinc performed in developed countries.

CONCLUSION

Data on the effect of a combined administration of zinc and probiotics in acute gastroenteritis are urgently needed.

Zinc fights diarrhoea in HIV-1-infected children: in-vitro evidence to link clinical data and pathophysiological mechanism

Diarrhoea-related morbidity is reduced by zinc supplementation in HIV-1-infected children. The mechanisms of this effect are largely undefined. We provide evidence for role for Tat (transactivating peptide produced by HIV-1) in the pathogenesis of diarrhoea in AIDS patients. In this study we showed that zinc, preventing Tat-induced fluid secretion, directly limits a specific mechanism of HIV-1-related diarrhoea. Our data support a 'zinc approach' in adjunct to specific antiretroviral therapy in HIV-1-infected children.

Zinc supplementation for the treatment of diarrhea in infants in Pakistan, India and Ethiopia

OBJECTIVE

This randomized, placebo controlled trial was designed to assess the safety and efficacy of 10-mg zinc supplementation for the treatment of acute diarrhea in infants.

METHODS

A total of 1110 infants aged 28 days to 5 months with acute diarrhea were enrolled and randomized to receive either zinc (n = 554) or placebo (n = 556) for 14 days. Diarrhea history, anthropometric status, breast-feeding status and socioeconomic indicators were assessed at baseline. The homes of all infants were visited every 3 days until the diarrhea episode was over. The number of stools, presence of blood and additional illnesses were recorded daily.

RESULTS

The geometric mean duration of the diarrhea episode was 0.21 days longer among infants receiving zinc versus those receiving placebo, but this was not statistically significant and no difference was observed after controlling for sex, exclusive breast-feeding and length for age Z score. There were no differences in any subgroup (ie, sex, baseline length for age Z score, exclusive breast-feeding or site after controlling for the remaining subgroup variables). There were no differences in reported stool frequency or among the proportion of episodes lasting longer than 7 days. Rates of vomiting were similar in the zinc and placebo groups.

CONCLUSIONS

Young infants do not appear to benefit from zinc supplementation for the treatment of diarrhea.