Probing paracellular -versustranscellular tissue barrier permeability using a gut mucosal explant culture system

Abstract

Intestinal permeation enhancers (PEs), i.e. agents improving oral delivery of therapeutic drugs with poor bioavailability, may typically act by two principally different mechanisms: to increase either transcellular -or paracellular passage across the epithelium. With the aim to define these different modes of action in a small intestinal mucosal explant system, the transcellular-acting PE sodium dodecyl sulfate (SDS) was compared to the paracellular-acting PE ethylenediaminetetraacetic acid (EDTA), using several fluorescent polarand lipophilic probes. Here, SDS rendered the enterocyte cell membranes leaky for the relatively small polar tracers Lucifer yellow and a 3 kD Texas red-conjugated dextran, but most conspicuously SDS blocked constitutive endocytosis from the brush border. In contrast, the main action of EDTA was to increase paracellular passage across the epithelium of both polar probes, including 10and 70 kDa dextrans and lipophilic probes, visualized by distinct stripy lateral staining of enterocytes and/or accumulation in the lamina propria. In addition, EDTA caused a loss of epithelial cell polarity by opening tight junctions for diffusion of domain-specific basolateral/apical cell membrane protein markers into the opposite domains. By transmission electron microscopy, SDS caused the formation of vacuoles and vesicle-like structures at the lateral cell membranes. In contrast, EDTA led to a bulging of the whole enterocyte apex, resulting in a "cobblestone" appearance of the epithelium, probably caused by an extreme contraction of the perijunctional actomyosin ring. We conclude that the mucosal explant system is a convenient model for predicting transcellular/paracellular modes of action of novel prospective PEs. ARTICLE HISTORYIntestinal permeation enhancers (PEs); ethylenediaminetetraacetic acid (EDTA); sodium dodecyl sulphate (SDS); small intestine; enterocyte; brush border CONTACT E. Michael Danielsen

Short-term tissue permeability actions of dextran sulfate sodium studied in a colon organ culture system

“…11 To this end, organ culture of colon explants lends itself as an in vivo-like model system enabling direct observations of changes occurring within as short a time period as 1-2 h. In recent works, intestinal organ culture has proved particularly useful for studying paracellular-and transcellular permeability effects of a number of luminally-acting permeation enhancers, using a variety of polarand lipophilic fluorescent probes. [12][13][14][15][16] In the present work, using colon obtained from pig and mouse, we observed that DSS within 1-2 h increased the paracellular permeability of FITCconjugated dextrans, suggesting a rapid action of DSS on tight junction function between neighboring colonocytes. In addition, and more surprising, FITC-conjugated DSS itself permeated into the lamina propria and strongly accumulated in nuclei of cells scattered within this mucosal region.…”

Prevention of Rat Intestinal Injury with a Drug Combination of Melatonin and Misoprostol

“…The mechanism of SDS-induced injury is related to its surfactant properties-monomers are incorporated into the epithelial bilayer, causing destabilization of the membrane and the tight junction protein complex [23][24][25]. This increases the passive intestinal transport of a range of compounds in both absorptive and secretory directions and blocks constitutive endocytosis [20,26,27]. The effects on intestinal permeability after exposure to SDS are both concentration-and time-dependent and accompanied by biochemical and histological features of intestinal injury [19,22].…”

Transient Permeation Enhancer® (TPE®) technology for oral delivery of octreotide: a technological evaluation

“…[37] used a cannulated rat model to assess absorption of a series of hydrophilic FITC-labeled dextran (FDs) polysaccharides of MW ranging from 4 to 70 kDa in the presence of TPE ® . FDs are established as transmucosal probes [44] and have very low flux across intestinal TJs under normal conditions. Moreover, these conjugates tend to be stable during flux due to poly-(α-D-1,6-glucose) bonds [44].…”

“…FDs are established as transmucosal probes [44] and have very low flux across intestinal TJs under normal conditions. Moreover, these conjugates tend to be stable during flux due to poly-(α-D-1,6-glucose) bonds [44]. Permeation of FDs across rat GI epithelia was increased by TPE ® , indicative of an enabled transmucosal flux [45], although this data alone is not proof of a paracellular mechanism because PEs that act via transcellular perturbation can also increase the flux of FDs.…”