Now showing 1 - 3 of 3
  • Publication
    Mechanisms of Action of Zinc on Intestinal Epithelial Electrogenic Ion Secretion: Insights into its Anti-Diarrheal 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 ZnSO4 (Zn2+) in the presence of secretagogues and inhibition of short circuit current (Isc) was measured. Key findings  Pre-incubation with basolateral but not apical Zn2+ reduced Isc stimulated by forskolin, carbachol and A23187. In the presence of the tight junction-opener, cytochalasin D, antisecretory effects of apically-applied Zn2+ were enabled in colon and ileum. The apparent permeability coefficient (Papp) of Zn2+ was increased 1.4- and 2.4-fold across rat ileum and colon, respectively, by cytochalasin D. Basolateral addition of Zn2+ also reduced the Isc stimulated by nystatin in rat colon, confirming K channel inhibition. In comparison with other inhibitors, Zn2+ was a relatively weak blocker of basolateral KATP and K Ca2+ channels. Exposure of ileum and colon to Zn2+ for 60 min had minimal effects on epithelial histology. Conclusions  Antisecretory effects of Zn2+ on intestinal epithelia arose in part through nonselective blockade of basolateral K channels, which was enabled when tight junctions were open.
    Scopus© Citations 13  380
  • Publication
    An Assessment of the Permeation Enhancer, 1-phenyl-piperazine (PPZ), on Paracellular Flux Across Rat Intestinal Mucosae in Ussing Chambers
    (American Association of Pharmaceutical Scientists, 2016-07) ;
    Purpose: 1-phenyl piperazine (PPZ) emerged from a Caco-2 monolayer screen as having high enhancement potential due to a capacity to increase permeation without significant toxicity. Our aim was to further explore the efficacy and toxicity of PPZ in rat ileal and colonic mucosae in order to assess its true translation potential. Methods: Intestinal mucosae were mounted in Ussing chambers and apparent permeability coefficient (Papp) values of [14C]-mannitol and FITC-dextran 4 kDa (FD-4) and transepithelial electrical resistance (TEER) values were obtained following apical addition of PPZ (0.6–60 mM). Exposed issues were assessed for toxicity by histopathology and lactate dehydrogenase (LDH) release. Mucosal recovery after exposure was also assessed using TEER readings. Results: PPZ reversibly increased the Papp of both agents across rat ileal and distal colonic mucosae in concentration–dependent fashion, accompanied by TEER reduction, with acceptable levels of tissue damage. The complex mechanism of tight junction opening was part mediated by myosin light chain kinase, stimulation of transepithelial electrogenic chloride secretion, and involved activation of 5-HT4 receptors. Conclusions: PPZ is an efficacious and benign intestinal permeation enhancer in tissue mucosae. However, its active pharmacology suggest that potential for further development in an oral formulation for poorly permeable molecules will be difficult.
    Scopus© Citations 16  596
  • Publication
    CriticalSorb promotes permeation of flux markers across isolated rat intestinal mucosae and Caco-2 monolayers
    Purpose CriticalSorb™ is a novel absorption enhancer based on Solutol® HS15, one that has been found to enhance the nasal transport. It is in clinical trials for nasal delivery of human growth hormone. The hypothesis was that permeating enhancement effects of the Solutol®HS15 component would translate to the intestine. Methods Rat colonic mucosae were mounted in Ussing chambers and Papp values of [14C]-mannitol, [14C]-antipyrine, FITC-dextran 4000 (FD-4), and TEER values were calculated in the presence of CriticalSorb™. Tissues were fixed for H & E staining. Caco-2 monolayers were grown on Transwells™ for similar experiments. Results CriticalSorb™(0.01% v/v) significantly increased the Papp of [14C]-mannitol, FD-4 [14C]-antipyrine across ileal and colonic mucosae, accompanied by a decrease in TEER. In Caco-2 monolayers, it also increased the Papp of [14C]-mannitol FD-4 and [14C]-antipyrine over 120 min. In both monolayers and tissues, it acted as a moderately effective P-glycoprotein inhibitor. There was no evidence of cytotoxicity in Caco-2 at concentrations of 0.01% for up to 24 h and histology of tissues showed intact epithelia at 120 min. Conclusions Solutol® HS15 is the key component in CriticalSorb™ that enables non-cytotoxic in vitro intestinal permeation and its mechanism of action is a combination of increased paracellular and transcellular flux.
      676Scopus© Citations 23