Background/Purpose:

We
investigated osteoclastogenesis and osteoblastogenesis in peripheral blood
before and 6 months after TNF blocker treatment in seropositive RA patients.

Methods:

          
Seventeen seropositive RA patients who received TNF blocker treatment including
infliximab, adalimumab and etanercept were enrolled. Peripheral blood
mononuclear cells (PBMCs) were collected at baseline and 6 months after TNF
blocker treatment. For osteoblast culture, PBMCs were cultured and stained with
alizarin S to detect calcified nodules. The optical density (OD) of alizarin S
was measured for quantitative analysis. We also evaluated serum level of bone
formation markers including osteocalcin, bone specific alkaline phosphatase
(BSALP) using enzyme linked immunosorbent assay (ELISA). For osteoclast
culture, PBMCs (1 x 10⁶ cells/well) were cultured and stained with
tartrate resistant acid phosphatase (TRAP). TRAP positive cells with more than 3
nuclei were regarded as osteoclasts. To assess resorption potential of
osteoclasts, PBMCs were cultured on bone slices and resorption pits were
visualized with 0.1% toluidine blue. The areas of pits were quantified using
our own devised computerized image analysis program (Fig. 1). Inflammatory
markers including erythrocyte sedimentation rate (ESR), c-reactive protein
(CRP) and IL-6 were measured.

Results:

The
OD of calcified nodules and bone formation markers including osteocalcin and
BSALP all increased after TNF blocker treatment (Table 1). There was a positive
correlation between differences of osteocalcin and that of BSALP (p =
0.002, r = 0.696). The number of cultured osteoclasts and the area of
resorption pit by osteoclasts decreased after treatment. The difference of
numbers of circulating monocytes showed negative correlation with difference of
BSALP (p = 0.008, r= – 0.617) and that of osteocalcin (p = 0.005,
r= – 0.651). Inflammatory markers did not respond to the treatment.

Conclusion:

Increase
both in bone formation markers and optical density of calcified nodules by
cultured osteoblasts showed improved peripheral osteoblastogenesis after TNF
blocker treatment. The tendency of peripheral osteoclastogenesis which is
responsible for osteoporosis and bone erosion in RA was in downstream after
treatment. Although inflammatory markers did not respond to TNF blocker, the
peripheral osteoblastogenesis was markedly enhanced. There was a negative
correlation between changes of circulating monocytes, the osteoclast progenitor
cells and that of bone formation markers, suggesting a strong tie between bone
formation and resorption.

Table 1.

Figure 1