The protective effects of incadronate on inflammation and joint destruction in established rat adjuvant arthritis

[Remarkable improvement of the hip joint lesion in a patient with rheumatoid arthritis by the treatment with anti-TNF-α agents]

22-year old woman who was previously diagnosed as having juvenile idiopathic arthritis (JIA) was treated with anti-TNF-α agents. Her disease activity was assessed as Stage IV and Class III by Steinbrocker's classification and resistant to steroids and methotrexate. Initially clinical findings responded well to infliximab (IFX), but polyarthritis recurred 15 months after the start of the treatment, and IFX was switched to etanercept (ETN) with good response. On the other hand, effects on the osteoarticular lesions were continuously observed through the period of the treatment with these two biologics. It was thought very rare that weight-bearing joint like the hip joint was restored as was seen in this case, while its mechanism is unknown. Because mechanism for inhibition of inflammation or joint destruction might be independent, we should investigate further the relationship between inflammation and joint destruction in the future.

RANKL increases the level of Mcl-1 in osteoclasts and reduces bisphosphonate-induced osteoclast apoptosis in vitro

INTRODUCTION

Bisphosphonates are the most widely used class of drug for inhibiting osteoclast-mediated bone loss, but their effectiveness at preventing joint destruction in rheumatoid arthritis has generally been disappointing. We examined whether the ability of bisphosphonates to induce osteoclast apoptosis and inhibit bone resorption in vitro is influenced by the cytokine receptor activator of nuclear factor-kappa B ligand (RANKL), an important mediator of inflammation-induced bone loss.

METHODS

Rabbit osteoclasts were treated with the bisphosphonates clodronate or alendronate for up to 48 hours in the absence or presence of RANKL. Changes in cell morphology and induction of apoptosis were examined by scanning electron microscopy, whilst resorptive activity was determined by measuring the area of resorption cavities. Changes in the level of anti-apoptotic proteins, including Mcl-1, Bcl-2, and Bcl-x>L, were determined in rabbit osteoclasts and in cytokine-starved mouse osteoclasts by Western blotting.

RESULTS

RANKL significantly attenuated the ability of both clodronate and alendronate to induce osteoclast apoptosis and inhibit bone resorption. Treatment of rabbit osteoclasts with RANKL was associated with an increase in the anti-apoptotic protein Mcl-1 but not Bcl-2. A role for Mcl-1 in osteoclast survival was suggested using osteoclasts generated from mouse bone marrow macrophages in the presence of RANKL + macrophage colony-stimulating factor (M-CSF) since cytokine deprivation of mouse osteoclasts caused a rapid loss of Mcl-1 (but not Bcl-2 or Bcl-xL), which preceded the biochemical and morphological changes associated with apoptosis. Loss of Mcl-1 from mouse osteoclasts could be prevented by factors known to promote osteoclast survival (RANKL, M-CSF, tumour necrosis factor-alpha [TNF-alpha], or lipopolysaccharide [LPS]).

CONCLUSIONS

RANKL protects osteoclasts from the apoptosis-inducing and anti-resorptive effects of bisphosphonates in vitro. The ability of RANKL (and other pro-inflammatory factors such as TNF-alpha and LPS) to increase the level of Mcl-1 in osteoclasts may explain the lack of effectiveness of some bisphosphonates in preventing inflammation-induced bone loss.

Variations in articular calcified cartilage by site and exercise in the 18-month-old equine distal metacarpal condyle

OBJECTIVES

To interrelate articular calcified cartilage thickness, mineralisation density, tidemark count and tidemark linear accretion rate by site in the equine third metacarpal distal condyle. To determine the effects of exercise during early life on articular calcified cartilage.

METHOD

Six of 12 pasture-raised Thoroughbred horses were exercised from 10 days old. Calcein labels were given 19 and 8 days prior to euthanasia at 18 months old. Osteochondral specimens were cut from the distal third metacarpal condyle and imaged using confocal scanning light microscopy (CSLM) and quantitative backscattered electron scanning electron microscopy (qBSE). Articular calcified cartilage thickness and total thickness mineralisation density were measured on montaged qBSE image sets, and inter-label mineralisation density, tidemark count and linear accretion rate measured on registered CSLM-qBSE image pairs.

RESULTS

Calcified cartilage thickness, mineralisation density, tidemark count and linear accretion rate varied significantly between sites. Regions with thinner calcified cartilage had greater linear accretion rates, hence rapid chondroclastic resorption. Mineralisation density was positively correlated with linear accretion rate. Fewer multiple tidemarks were counted in regions with greater linear accretion rates. Lag time between the tidemark and cement line was estimated (180 days; in the range of 0-648 days). Exercise had little effect on measured parameters.

CONCLUSION

The major determinant of articular calcified cartilage thickness is the rate of chondroclastic resorption, not tidemark linear accretion rate. Our evidence supports coupled, mechanosensitive regulation of chondroclastic resorption and linear accretion rate in articular calcified cartilage. Exercising pasture-reared foals causes little additional adaptation in distal third metacarpal articular calcified cartilage.

Transmigration: a new property of mature multinucleated osteoclasts

Even though it is assumed that multinucleated osteoclasts are migrating cells on the bone surface to be resorbed, we show that they can also selectively transmigrate through layers of cells usually found in the bone microenvironment. This activity is associated with c-src and MMPs and can be stimulated by bone metastatic breast cancer cells, a process blocked by bisphosphonate treatment.

INTRODUCTION

Osteoclasts have an hematopoietic origin and are bone-resorbing cells. Monocytic precursors migrate to the bone surface where they fuse to form multinucleated osteoclasts able to migrate over the bone surface. We studied whether multinucleated osteoclasts were also able to transmigrate through tissues.

MATERIALS AND METHODS

Murine spleen-derived and green fluorescent protein (GFP)-Raw derived osteoclasts were seeded on osteoblasts and several other cell types. The cells were fixed for 20 minutes, 4 or 12 h after osteoclast seeding, and stained with phalloidin to visualize actin using confocal microscopy. Drugs such as PP2 and GM6001, inhibitors of c-src and matrix metalloproteinases (MMPs), respectively, and risedronate were used to determine osteoclast transmigration regulating factors.

RESULTS

We observed by confocal microscopy that multinucleated osteoclasts specifically transmigrate through confluent layers of various cell types present in the bone microenvironment in vitro. This is an efficient process associated with c-src and MMPs but is independent of podosomes. Moreover, conditioned medium from bone metastatic breast cancer cells stimulates osteoclast transmigration in vitro, a process inhibited by bisphosphonate treatment.

CONCLUSIONS

Our data describe a new property of mature multinucleated osteoclasts to transmigrate through various cell types. The ability to control this highly regulated osteoclast transmigration process may offer new therapeutic strategies for bone diseases associated with an imbalance in bone remodeling caused by excessive osteoclast resorption.