Infliximab induces apoptosis in monocytes from patients with chronic active Crohn's disease by using a caspase-dependent pathway.
OBJECTIVE
Treatment with a chimeric anti-tumor necrosis factor (TNF) antibody (infliximab) has been shown to be highly efficient for patients with steroid-refractory Crohn's disease (CD). However, the mechanism of action remains largely unknown. As monocytopenia is commonly observed after treatment with infliximab, we investigated the role of infliximab-induced monocyte apoptosis.


METHODS
Peripheral blood monocytes from healthy volunteers and patients with chronic active CD (CDAI > 250) were isolated by density gradient centrifugation methods. Apoptosis was determined by annexin V staining DNA-laddering, and transmission electron microscopy. Activation of caspases and mitochondrial release of cytochrome C was determined by immunoblotting. Transcriptional activation of members of the Bcl-2 family have been analyzed by ribonuclease protection assay.


RESULTS
Treatment with infliximab at therapeutic concentrations resulted in monocyte apoptosis in patients with chronic active CD in a dose-dependent manner. Infliximab-induced monocyte-apoptosis required the activation of members of the caspase-family since activation of caspase-8, -9, and -3 could be determined. Caspase activation was induced by a CD95/CD95L independent signaling pathway with mitochondrial release of cytochrome C. Cytochrome C release seemed to be triggered by transcriptional activation of Bax and Bak. Monocyte apoptosis in vivo as determined by annexin-V binding and caspase-3 activation could be shown in patients with chronic active CD as soon as 4 hours after treatment with infliximab.


CONCLUSIONS
Monocyte apoptosis induced by infliximab may be an important mechanism that could explain the powerful anti-inflammatory properties of infliximab in patients with chronic active CD.
Lügering
A
A
Department of Medicine, University of Münster, Münster, Germany.
Schmidt
M
M
Lügering
N
N
Pauels
H G
HG
Domschke
W
W
Kucharzik
T
T
D000911:Antibodies, Monoclonal / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects*; D020169:Caspases / Q000502:physiology*; D002478:Cells, Cultured; D002908:Chronic Disease; D003424:Crohn Disease / Q000097:blood / Q000188:drug therapy*; D003574:Cytochrome c Group / Q000378:metabolism; D004789:Enzyme Activation; D053222:Fas Ligand Protein; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D006801:Humans; D000069285:Infliximab; D018950:Lipopolysaccharide Receptors / Q000502:physiology; D008562:Membrane Glycoproteins / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics; D009000:Monocytes / Q000187:drug effects* / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2; D015533:Transcriptional Activation; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors* / Q000378:metabolism; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein
D000911:Antibodies, Monoclonal; C494772:BAK1 protein, human; C494826:BAX protein, human; D003574:Cytochrome c Group; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D005765:Gastrointestinal Agents; D018950:Lipopolysaccharide Receptors; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D014409:Tumor Necrosis Factor-alpha; D050998:bcl-2 Homologous Antagonist-Killer Protein; D051028:bcl-2-Associated X Protein; D000069285:Infliximab; D020169:Caspases