Systemic TNF blockade does not modulate synovial expression of the pro-inflammatory mediator HMGB1 in rheumatoid arthritis patients--a prospective clinical study.
BACKGROUND
High-mobility group box chromosomal protein 1 (HMGB1) has recently been identified as an endogenous mediator of arthritis. TNF and IL-1beta, pivotal cytokines in arthritis pathogenesis, both have the ability to induce the release of HMGB1 from myeloid and dendritic cells. It was, therefore, decided to investigate whether treatment based on TNF blockade in rheumatoid arthritis (RA) affects the expression of synovial HMGB1.


METHODS
Repeated arthroscopy-guided sampling of synovial tissue was performed in nine patients with RA before and nine weeks after initiation of anti-TNF mAb (infliximab) therapy. Synovial biopsy specimens were analysed for HMGB1 protein by immunohistochemical staining and for HMGB1 mRNA expression by real-time reverse transcriptase PCR (RT-PCR). Statistical evaluations were based on Wilcoxon's signed rank tests or Spearman rank sum tests.


RESULTS
Aberrant, extranuclear HMGB1 and constitutive nuclear HMGB1 expression, with histological signs of inflammation, were evident in all biopsies obtained before infliximab therapy. Signs of inflammation were still evident in the second biopsies obtained nine weeks after initiation of infliximab therapy. The cytoplasmic and extracellular expression of HMGB1 decreased in five patients, remained unchanged in one patient and increased in three patients, making the overall change in HMGB1 protein expression not significant. No correlation between the clinical response, as measured by disease activity score calculated for 28 joints (DAS28) or the American College of Rheumatology response criteria (ACR 20, 50, and 70), and the direction of change of HMGB1 expression in individual patients could be discerned. In addition, infliximab therapy did not alter HMGB1 mRNA synthesis.


CONCLUSIONS
Pro-inflammatory HMGB1 expression during rheumatoid synovitis was not consistently influenced by TNF-blocking therapy with infliximab. This suggests that TNF is not the main inducer of extranuclear HMGB1 during synovitis and that HMGB1 may represent a TNF-independent molecule that could be considered as a possible target for future therapeutic intervention in RA.
Sundberg
Erik
E
Department of Woman and Child Health, Pediatric Rheumatology Research Unit, Karolinska Institutet/Karolinska University Hospital, Stockholm, Sweden. erik.sundberg@ki.se
Grundtman
Cecilia
C
Af Klint
Erik
E
Lindberg
Johan
J
Ernestam
Sofia
S
Ulfgren
Ann-Kristin
AK
Harris
Helena Erlandsson
HE
Andersson
Ulf
U
D000328:Adult; D000368:Aged; D000911:Antibodies, Monoclonal / Q000627:therapeutic use*; D018501:Antirheumatic Agents / Q000627:therapeutic use*; D001172:Arthritis, Rheumatoid / Q000188:drug therapy / Q000378:metabolism*; D001182:Arthroscopy; D005260:Female; D015870:Gene Expression; D024243:HMGB1 Protein / Q000096:biosynthesis* / Q000187:drug effects; D006801:Humans; D007150:Immunohistochemistry; D000069285:Infliximab; D007719:Knee Joint / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D012333:RNA, Messenger / Q000032:analysis / Q000187:drug effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013583:Synovial Membrane / Q000187:drug effects / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000037:antagonists & inhibitors* / Q000187:drug effects
D000911:Antibodies, Monoclonal; D018501:Antirheumatic Agents; D024243:HMGB1 Protein; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D000069285:Infliximab