Organic osmolytes increase expression of specific tight junction proteins in skin and alter barrier function in keratinocytes.

BACKGROUND: The epidermal barrier is important for water conservation, failure of which is evident in dry-skin conditions. Barrier function is fulfilled by the stratum corneum, tight junctions (TJs, which control extracellular water) and keratinocyte mechanisms, such as organic osmolyte transport, which regulate intracellular water homeostasis. Organic osmolyte transport by keratinocytes is largely unexplored and nothing is known regarding how cellular and extracellular mechanisms of water conservation may interact. OBJECTIVES: We aimed to characterize osmolyte transporters in skin and keratinocytes, and, using transporter inhibitors, to investigate whether osmolytes can modify TJs. Such modification would suggest a possible link between intracellular and extracellular mechanisms of water regulation in skin. METHODS: Immunostaining and quantitative polymerase chain reaction of organic osmolyte-treated organ-cultured skin were used to identify changes to organic osmolyte transporters, and TJ protein and gene expression. TJ functional assays were performed on organic osmolyte-treated primary human keratinocytes in culture. RESULTS: Immunostaining demonstrated the expression of transporters for betaine, taurine and myo-inositol in transporter-specific patterns. Treatment of human skin with either betaine or taurine increased the expression of claudin-1, claudin-4 and occludin. Osmolyte transporter inhibition abolished this response. Betaine and taurine increased TJ function in primary human keratinocytes in vitro. CONCLUSIONS: Treatment of skin with organic osmolytes modulates TJ structure and function, which could contribute to the epidermal barrier. This emphasizes a role for organic osmolytes beyond the maintenance of intracellular osmolarity. This could be harnessed to enhance topical therapies for diseases characterized by skin barrier dysfunction.

Differential expression and functionality of ATP-binding cassette transporters in the human hair follicle.

BACKGROUND: ATP-binding cassette (ABC) transporters are involved in the active transport of an extremely diverse range of substrates across biological membranes. These transporters are commonly implicated in the development of multidrug resistance and are also involved in numerous physiological and homeostatic processes, including lipid transport, cell migration and differentiation. OBJECTIVES: To close the knowledge gap in the expression of ABC transporters in the human hair follicle (HF). METHODS: Quantitative polymerase chain reaction (qPCR) of ABC genes and immunofluorescence microscopy analysis of cryosections of human HFs. RESULTS: By qPCR analysis, numerous members of the ABC transporter superfamily, such as ABCB1, ABCG2 and ABCA12, were found to be transcribed in full-length human scalp HFs. Immunofluorescence microscopy demonstrated that the intrafollicular protein expression of different xenobiotic ABC transporters (ABCB1, ABCC1, ABCC4, ABCG2) varies greatly, with ABCG2 expression restricted primarily to the epithelial stem cell region of the outer root sheath (bulge), whereas expression of ABCB1, ABCC1 and ABCC4 was more widespread. Lipid transporters ABCA1, ABCA12 and ABCA4 were almost uniformly expressed throughout the HF epithelium. Functional ABCB1/G2 activity was demonstrated by exclusion of the substrate dye, Hoechst 33342. In the bulge, this was reversed by ABCB1 and ABCG2 inhibition. CONCLUSIONS: These data encourage further investigation of ABC transporters as potentially important regulators of HF epithelial biology. Clinically, pharmacological modulation of the activity of selected intrafollicular ABC transporters may permit novel therapeutic interventions, such as protecting HF stem cells from chemotherapy-induced damage, counteracting cholesterol-associated hypertrichosis, and manipulating the intrafollicular prostaglandin balance in androgenetic alopecia.

Expression of the ABC transport proteins MDR1 (ABCB1) and BCRP (ABCG2) in bovine rumen.

Rumen fermentation of plant-based forage in bovines is the major site for generation and absorption of short-chain fatty acids. Consequentially, the rumen is also the site for initial exposure to toxins released from diet. Accordingly, we have investigated the expression of bovine ABC transporters in the rumen associated with cytoprotection against xenobiotic exposure, namely MDR1 (ABCB1), MRP2 (ABCC2) and BCRP (ABCG2). Bovine rumen samples from the ventral sac were obtained post-mortem from a commercial slaughterhouse after humane killing. Rumen papilla samples were then prepared for total RNA isolation for RT-PCR, SDS-PAGE/Western blotting and immunohistochemistry. PCR products of the predicted size were observed for both MDR1 and BCRP, but not for MRP2 using bovine-specific primers. ß-actin was used as a control transcript. Western blot analysis using C219 primary monoclonal antibody revealed MDR1 protein expression in bovine rumen (Mapp, of ~170-180 kD). Immunolocalisation of MDR1 using UIC2 monoclonal antibody within cryosections of bovine rumen showed extensive membrane staining in the cells of the stratum granulosum, stratum spinosum and stratum basale. MDR1 expression was absent from outer stratum corneum. Protein expression and immunolocalisation were also confirmed for BCRP, with prevalent staining in the stratum basale, becoming weaker in the stratum spinosum and stratum granulosum.

Intestinal ciprofloxacin efflux: the role of breast cancer resistance protein (ABCG2).

Intestinal secretory movement of the fluoroquinolone antibiotic, ciprofloxacin, may limit its oral bioavailability. Active ATP-binding cassette (ABC) transporters such as breast cancer resistance protein (BCRP) have been implicated in ciprofloxacin transport. The aim of this study was to test the hypothesis that BCRP alone mediates intestinal ciprofloxacin secretion. The involvement of ABC transport proteins in ciprofloxacin secretory flux was investigated with the combined use of transfected cell lines [bcrp1/BCRP-Madin-Darby canine kidney II (MDCKII) and multidrug resistance-related protein 4 (MRP4)-human embryonic kidney (HEK) 293] and human intestinal Caco-2 cells, combined with pharmacological inhibition using 3-(6-isobutyl-9-methoxy-1,4-dioxo-1,2,3,4,6, 7,12,12a-octahydropyrazino[1',2':1,6]pyrido[3,4-b]indol-3-yl)-propionic acid tert-butyl ester (Ko143), cyclosporine, 3-[[3-[2-(7-chloroquinolin-2-yl)vinyl]phenyl]-(2-dimethylcarbamoylethylsulfanyl)methylsulfanyl] propionic acid (MK571), and verapamil as ABC-selective inhibitors. In addition, the regional variation in secretory capacity was investigated using male Han Wistar rat intestine mounted in Ussing chambers, and the first indicative measurements of ciprofloxacin transport by ex vivo human jejunum were made. Active, Ko143-sensitive ciprofloxacin secretion was observed in bcrp1-MDCKII cell layers, but in low-passage (BCRP-expressing) Caco-2 cell layers only a 54% fraction was Ko143-sensitive. Ciprofloxacin accumulation was lower in MRP4-HEK293 cells than in the parent line, indicating that ciprofloxacin is also a substrate for this transporter. Ciprofloxacin secretion by Caco-2 cell layers was not inhibited by MK571. Secretory flux showed marked regional variability in the rat intestine, increasing from the duodenum to peak in the ileum. Ciprofloxacin secretion was present in human jejunum and was reduced by Ko143 but showed marked interindividual variability. Ciprofloxacin is a substrate for human and rodent BCRP. An additional pathway for ciprofloxacin secretion exists in Caco-2 cells, which is unlikely to be MRP(4)-mediated. BCRP is likely to be the dominant transport mechanism for ciprofloxacin efflux in both rat and human jejunum.

Induction of P-glycoprotein expression and function in human intestinal epithelial cells (T84).

Intestinal induction of Pgp is known to limit the oral availability of certain drug compounds and give rise to detrimental drug-drug interactions. We have investigated the induction of P-glycoprotein (Pgp; MDR1) activity in a human intestinal epithelial cell line (T84) following pre-exposure to a panel of drug compounds, reported to be Pgp substrates, inhibitors or inducers. Human MDR1-transfected MDCKII epithelial monolayers were used to assess Pgp substrate interactions and inhibition of digoxin secretion by the selected drug compounds. The T84 cell line was used to assess induction of Pgp-mediated digoxin secretion following pre-exposure to the same compounds. Changes in gene expression (MDR1, MRP2, PXR and CAR) were determined by quantitative RT-PCR. Net transepithelial digoxin secretion was increased (1.3 fold, n=6, P<0.05) following pre-exposure to the PXR activator hyperforin (100nM, 72h), as was MDR1 mRNA expression (3.0 fold, n=4, P<0.05). A number of Pgp substrates (quinidine, amprenavir, irinotecan, topotecan, atorvastatin and erythromycin) induced net digoxin secretion, as did the non-Pgp substrate artemisinin. Various non-Pgp substrates demonstrated inhibition of digoxin secretion (verapamil, mifepristone, clotrimazole, mevastatin, diltiazem and isradipine) but did not induce Pgp-mediated digoxin secretion. Of the compounds that increased Pgp secretion, quinidine, topotecan, atorvastatin and amprenavir pre-exposure also elevated MDR1 mRNA levels, whereas erythromycin, irinotecan and artemisinin displayed no change in transcript levels. This indicates possible post-translational regulation of digoxin secretion. Finally, a strong correlation between drug modulation of MRP2 and PXR mRNA expression levels was evident.

Rifampin and digoxin induction of MDR1 expression and function in human intestinal (T84) epithelial cells.

BACKGROUND AND PURPOSE: Oral drug bioavailability is limited by intestinal expression of P-glycoprotein (MDR1, Pgp, ABCB1) whose capacity is regulated via nuclear receptors e.g. the pregnane X receptor (PXR, SXR, NR1I2). In order to study dynamic regulation of MDR1 transport capacity we have identified the T84 epithelial cell-line as a model for human intestine co-expressing MDR1 with PXR. The ability of rifampin, a known PXR agonist and digoxin, a model MDR1 substrate, to regulate MDR1 expression and transport activity has been tested, in these T84 cells. EXPERIMENTAL APPROACH: Transport was assayed by bi-directional [(3)H]-digoxin transepithelial fluxes across epithelial layers of T84 cells seeded onto permeable filter supports following pre-exposure to rifampin and digoxin. Quantitative real-time PCR, Western blotting and immunocytochemistry were used to correlate induction of MDR1 transcript and protein levels with transport activity. KEY RESULTS: Rifampin exposure (10 microM, 72 hours) increased MDR1 transcript levels (3.4 fold), MDR1 total protein levels (4.4 fold), apical MDR1 protein (2.7 fold) and functional activity of MDR1 (1.2 fold). Pre-incubation with digoxin (1 microM, 72 hours) potently induced MDR1 transcript levels (92 fold), total protein (7 fold), apical MDR1 protein (4.7 fold) and functional activity (1.75 fold). Whereas PXR expression was increased by rifampin incubation (2 fold), digoxin reduced PXR expression (0.3 fold). CONCLUSIONS AND IMPLICATIONS: Chronic digoxin pre-treatment markedly upregulates MDR1 expression and secretory capacity of T84 epithelia. Digoxin-induced changes in MDR1 levels are distinct from PXR-mediated changes resulting from rifampin exposure.