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The airway epithelium plays a pivotal role in regulating mucosal immunity and inflammation. Epithelial barrier function, homeostasis of luminal fluid, and mucociliary clearance are major components of mucosal defense mechanisms. The epithelial sodium channel (ENaC) is one of the key players in controlling airway fluid volume and composition, and characteristic cytokines cause ENaC and barrier dysfunctions following pulmonary infections or allergic reactions. Given the limited understanding of the requisite duration and magnitude of cytokines to affect ENaC and barrier function, available treatment options for restoring normal ENaC activity are limited. Previous studies have demonstrated that distinct amino acids can modulate epithelial ion channel activities and barrier function in intestines and airways. Here, we have investigated the time- and concentration-dependent effect of representative cytokines for Th1- (IFN-γ and TNF-α), Th2- (IL-4 and IL-13), and Treg-mediated (TGF-β1) immune responses on ENaC activity and barrier function in human bronchial epithelial cells. When cells were exposed to Th1 and Treg cytokines, ENaC activity decreased gradually while barrier function remained largely unaffected. In contrast, Th2 cytokines had an immediate and profound inhibitory effect on ENaC activity that was subsequently followed by epithelial barrier disruption. These functional changes were associated with decreased membrane protein expression of α-, β-, and γ-ENaC, and decreased mRNA levels of β- and γ-ENaC. A proprietary blend of amino acids was developed based on their ability to prevent Th2 cytokine-induced ENaC dysfunction. Exposure to the select amino acids reversed the inhibitory effect of IL-13 on ENaC activity by increasing mRNA levels of β- and γ-ENaC, and protein expression of γ-ENaC. This study indicates the beneficial effect of select amino acids on ENaC activity in an in vitro setting of Th2-mediated inflammation suggesting these amino acids as a novel therapeutic approach for correcting this condition. [ABSTRACT FROM AUTHOR]

Summary: Iron deficiency (ID) and iron‐deficiency anaemia (IDA) are global public health concerns, most commonly afflicting children, pregnant women and women of childbearing age. Pathological outcomes of ID include delayed cognitive development in children, adverse pregnancy outcomes and decreased work capacity in adults. IDA is usually treated by oral iron supplementation, typically using iron salts (e.g. FeSO4); however, dosing at several‐fold above the RDA may be required due to less efficient absorption. Excess enteral iron causes adverse gastrointestinal side effects, thus reducing compliance, and negatively impacts the gut microbiome. Recent research has sought to identify new iron formulations with better absorption so that lower effective dosing can be utilized. This article outlines emerging research on oral iron supplementation and focuses on molecular mechanisms by which different supplemental forms of iron are transported across the intestinal epithelium and whether these transport pathways are subject to regulation by the iron‐regulatory hormone hepcidin. [ABSTRACT FROM AUTHOR]

Luminal isobutyrate, a relatively poor metabolized short-chain fatty acid (SCFA), induces HC[O.sub.3] secretion via a Cl-independent, DIDS-insensitive, carrier-mediated process as well as inhibiting both Cl-dependent and cAMP-induced HC[O.sub.3] secretion. The mechanism(s) responsible for these processes have not been well characterized. HC[O.sub.3] secretion was measured in isolated colonic mucosa mounted in Lucite chambers using pH stat technique and during microperfusion of isolated colonic crypts. [sup.14]C-labeled butyrate, [sup.14]C-labeled isobutyrate, and [sup.36]Cl uptake were also determined by apical membrane vesicles (AMV) isolated from surface and/or crypt cells. Butyrate stimulation of Cl-independent, DIDS-insensitive 5-nitro-3-(3-phenylpropyl-amino) benzoic acid-insensitive HC[O.sub.3] secretion is greater than that by isobutyrate, suggesting that both SCFA transport and metabolism are critical for HC[O.sub.3] secretion. Both lumen and serosal 25 mM butyrate inhibit cAMP-induced HC[O.sub.3] secretion to a comparable degree (98 vs. 90%). In contrast, Cl-dependent HC[O.sub.3] secretion is downregulated by lumen 25 mM butyrate considerably more than by serosal butyrate (98 vs. 37%). Butyrate did not induce HC[O.sub.3] secretion in isolated microperfused crypts, whereas an outward-directed HC[O.sub.3] gradient-driven induced [sup.14]C-butyrate uptake by surface but not crypt cell AMV. Both [sup.36]Cl/HC[O.sub.3] exchange and potential-dependent [sup.36]Cl movement in AMV were inhibited by 96-98% by 20 mM butyrate. We conclude that 1) SCFA-dependent HC[O.sub.3] secretion is the result of SCFA transport across the apical membrane via a SCFA/HC[O.sub.3] exchange more than intracellular SCFA metabolism: 2) SCFA-dependent HC[O.sub.3] secretion is most likely a result of an apical membrane SCFA/HC[O.sub.3] exchange in surface epithelial cells: 3) SCFA downregulates Cl-dependent and cAMP-induced HC[O.sub.3] secretion secondary to SCFA inhibition of apical membrane Cl/HC[O.sub.3] exchange and anion channel activity, respectively. Cl/HC[O.sub.3] exchange: short-chain fatty acid/HC[O.sub.3] exchange: anion channel: pH stat; colonic mucosa

HC[O.sup.-.sub.3] secretion has long been recognized in the mammalian colon, but it has not been well characterized. Although most studies of colonic HC[O.sup.-.sub.3] secretion have revealed evidence of lumen [Cl.sup.-] dependence, suggesting a role for apical membrane [Cl.sup.-]/HC[O.sup.-.sub.3] exchange, direct examination of HC[O.sup.-.sub.3] secretion in isolated crypt from rat distal colon did not identify [Cl.sup.-]-dependent HC[O.sup.-.sub.3] secretion but did reveal cAMP-induced, [Cl.sup.-] -independent HC[O.sup.-.sub.3] secretion. Studies were therefore initiated to determine the characteristics of HC[O.sup.-.sub.3] secretion in isolated colonic mucosa to identify HC[O.sup.-.sub.3] secretion in both surface and crypt cells. HC[O.sup.-.sub.3] secretion was measured in rat distal colonic mucosa stripped of muscular and serosal layers by using a pH star technique. Basal HC[O.sup.-.sub.3] secretion (5.6 [+ or -] 0.03 [micro]eq x [h.sup.-1] x [cm.sup.-2]) was abolished by removal of either lumen [Cl.sup.-] or bath HC[O.sup.-.sub.3]; this [Cl.sup.-]-dependent HC[O.sup.-.sub.3] secretion was also inhibited by 100 [micro]M DIDS (0.5 [+ or -] 0.03 [micro]eq x [h.sup.-1] x [cm.sup.-2]) but not by 5-nitro-3-(3-phenylpropyl-amino) benzoic acid (NPPB), a [Cl.sup.-] channel blocker. 8-Bromo-cAMP induced [Cl.sup.-] -independent HC[O.sup.-.sub.3] secretion (and also inhibited [Cl.sup.-] dependent HC[O.sup.-.sub.3] secretion), which was inhibited by NPPB and by glibenclamide, a CFTR blocker, but not by DIDS. Isobutyrate, a poorly metabolized short-chain fatty acid (SCFA), also induced a [Cl.sup.-] -independent. DIDS-insensitive, saturable HC[O.sup.-.sub.3] secretion that was not inhibited by NPPB. Three distinct HC[O.sup.-.sub.3] secretory mechanisms were identified: 1) [Cl.sup.-] -dependent secretion associated with apical membrane [Cl.sup.-]/HC[O.sup.-.sub.3] exchange, 2) cAMP-induced secretion that was a result of an apical membrane anion channel, and 3) SCFA-dependent secretion associated with an apical membrane SCFA/HC[O.sup.-.sub.3] exchange. chloride/bicarbonate exchange; short-chain fatty acid/bicarbonate exchange; anion channel; pH stat

Colonic [K.sup.+] secretion stimulated by cholinergic agents requires activation of muscarinic receptors and the release of intracellular [Ca.sup.2+]. However, the precise mechanisms by which this rise in [Ca.sup.2+] leads to [K.sup.+] efflux across the apical membrane are poorly understood. In the present study, Northern blot analysis of rat proximal colon revealed the presence of transcripts encoding rSK2 [small conductance (SK)], rSK4 [intermediate conductance (IK)], and rSlo [large conductance (BK)] [Ca.sup.2+]-activated [K.sup.+] channels. In dietary [K.sup.+]-depleted animals, only rSK4 mRNA was reduced in the colon. On the basis of this observation, a cDNA encoding the [K.sup.+] channel rSK4 was cloned from a rat colonic cDNA library. Transfection of this cDNA into Chinese hamster ovary (CHO) cells led to the expression of [Ca.sup.2+]-activated [K.sup.+] channels that were blocked by the IK channel inhibitor clotrimazole (CLT). Confocal immunofluorescence confirmed the presence of IK channels in proximal colonic crypts, and Western blotting demonstrated that IK protein sorted to both the apical and basolateral surfaces of colonic epithelia. In addition, transcellular active [K.sup.+] secretion was studied on epithelial strips of rat proximal colon using unidirectional [sup.86][Rb.sup.+] fluxes. The addition of thapsigargin or carbachol to the serosal surface enhanced net [sup.86][Rb.sup.+] secretion. The mucosal addition of CLT completely inhibited carbachol-induced net [sup.86][Rb.sup.+] secretion. In contrast, only partial inhibition was observed with the BK and SK channel inhibitors, iberiotoxin and apamin, respectively. Finally, in parallel with the reduction in SK4 message observed in animals deprived of dietary [K.sup.+], carbachol-induced [.sup.86][Rb.sup.+] secretion was abolished in dietary [K.sup.+]-depleted animals. These results suggest that the rSK4 channel mediates [K.sup.+] secretion induced by muscarinic agonists in the rat proximal colon and that transcription of the rSK4 channel is downregulated to prevent [K.sup.+] loss during dietary [K.sup.+] depletion. intermediate conductance [Ca.sup.2+]-activated [K.sup.+] channel; intermediate-conductance channel; carbachol; clotrimazole; [sup.86][RB.sup.+] flux; [K.sup.+] depletion