Decreased P-glycoprotein (P-gp/MDR1) expression in inflamed human intestinal epithelium is independent of PXR protein levels.
BACKGROUND
Altered P-glycoprotein expression (P-gp/MDR1) and/or function may contribute to the pathogenesis of gastrointestinal inflammatory disorders. Low intestinal mRNA levels of the pregnane X receptor (PXR) have been linked to low MDR1 mRNA levels in patients with ulcerative colitis (UC). Here we compared intestinal MDR1 mRNA and protein expression in uninflamed and inflamed intestinal epithelium (IE) of patients with gastrointestinal inflammatory disorders to healthy controls.


METHODS
Intestinal mucosal biopsies were obtained from patients with Crohn's disease (CD, n = 20), UC (n = 10), diverticulitis (n = 3), collagenous colitis (n = 3), and healthy controls (n = 10). MDR1, iNOS, MRP1, CYP3A4, and PXR expression was determined using real-time reverse-transcriptase polymerase chain reaction (RT-PCR), Western blotting, and/or immunohistochemistry. Furthermore, MDR1 expression was determined in human intestinal biopsies and the human colon carcinoma cell line DLD-1 after exposure to cytokines (TNF-alpha, IFN-gamma, and/or IL-1beta).


RESULTS
MDR1 mRNA levels in uninflamed colon of UC patients were comparable to healthy controls, while they were slightly decreased in ileum and slightly increased in colon of CD patients. MDR1 expression, however, was strongly decreased in inflamed IE of CD, UC, collagenous colitis, and diverticulitis patients. A cytokine-dependent decrease of MDR1 expression was observed in human intestinal biopsies, but not in DLD-1 cells. Remarkably, PXR protein levels were equal in uninflamed and inflamed tissue of CD and UC patients despite low PXR mRNA levels in inflamed tissue.


CONCLUSIONS
MDR1 expression is strongly decreased in inflamed IE of patients with gastrointestinal disorders and this is independent of PXR protein levels. Low MDR1 levels may aggravate intestinal inflammation.
Blokzijl
Hans
H
Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
Vander Borght
Sara
S
Bok
Lisette I H
LI
Libbrecht
Louis
L
Geuken
Mariska
M
van den Heuvel
Fiona A J
FA
Dijkstra
Gerard
G
Roskams
Tania A D
TA
Moshage
Han
H
Jansen
Peter L M
PL
Faber
Klaas Nico
KN
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000096:biosynthesis / Q000235:genetics*; D000293:Adolescent; D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000378:metabolism; D001706:Biopsy; D015153:Blotting, Western; D004848:Epithelium / Q000378:metabolism / Q000473:pathology; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D007150:Immunohistochemistry; D015212:Inflammatory Bowel Diseases / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D007413:Intestinal Mucosa / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000235:genetics*; D011987:Receptors, Steroid / Q000096:biosynthesis / Q000235:genetics*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D015415:Biomarkers; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D011987:Receptors, Steroid