Faculty Bibliography

OBJECTIVES: Methotrexate (MTX) is considered the 'anchor drug' in the therapy of rheumatoid arthritis (RA), yet many physicians do not optimise MTX regimens in spite of high RA disease activity. The recent development of an auto-injector for the subcutaneous (subQ) administration of MTX has prompted re-evaluation of MTX utilisation. The purpose of this systematic literature review is to determine the optimal dose, drug level, and route of administration for MTX in the context of relevant pharmacokinetics and pharmacogenomics. METHODS: A systematic literature review was performed in Medline searching specifically for randomised controlled trials, systematic reviews, case control and cohort studies evaluating outcomes related to MTX dose and route of administration. Articles fulfilling these inclusion criteria were reviewed. Data on MTX dose, route of administration, clinical response, drug levels and adverse events were evaluated. RESULTS: Our search identified 420 articles of which 6 were eligible for inclusion using the above criteria. These included 2 systematic reviews, 2 randomised open label trials, one longitudinal study and one retrospective cohort study. CONCLUSIONS: Efficacy and toxicity for MTX appear related to absorbed dose of MTX, not to route of administration. While bioavailability is greater for parenteral MTX, there is no evidence yet that splitting the oral dose of MTX is less advantageous, less safe or less tolerable than administering parenteral MTX. However, there appear to be modest benefits in beginning with higher doses of MTX, and switching to parenteral MTX when the clinical response to an oral dose is inadequate.

Bone metabolism is a vital process that involves resorption by osteoclasts and formation by osteoblasts, which is closely regulated by immune cells. The neuronal guidance protein Netrin-1 regulates immune cell migration and inflammatory reactions, but its role in bone metabolism is unknown. During osteoclast differentiation, osteoclast precursors increase expression of Netrin-1 and its receptor Unc5b. Netrin-1 binds, in an autocrine and paracrine manner, to Unc5b to promote osteoclast differentiation in vitro, and absence of Netrin-1 or antibody-mediated blockade of Netrin-1 or Unc5b prevents osteoclast differentiation of both murine and human precursors. We confirmed the functional relationship of Netrin-1 in osteoclast differentiation in vivo using Netrin-1-deficient (Ntn1(-/-) ) or wild-type (WT) bone marrow transplanted mice. Notably, Ntn1(-/-) chimeras have markedly diminished osteoclasts, as well as increased cortical and trabecular bone density and volume compared with WT mice. Mechanistic studies revealed that Netrin-1 regulates osteoclast differentiation by altering cytoskeletal assembly. Netrin-1 increases regulator of Rho-GEF subfamily (LARG) and repulsive guidance molecule (RGMa) association with Unc5b, which increases expression and activation of cytoskeletal regulators RhoA and focal adhesion kinase (FAK). Netrin-1 and its receptor Unc5b likely play a role in fusion of osteoclast precursors because Netrin-1 and DC-STAMP are tightly linked. These results identify Netrin-1 as a key regulator of osteoclast differentiation that may be a new target for bone therapies. (c) 2015 American Society for Bone and Mineral Research.

Promoting bone regeneration and repair of bone defects is a need that has not been well met to date. We have previously found that adenosine, acting via A2A receptors (A2AR) promotes wound healing and inhibits inflammatory osteolysis and hypothesized that A2AR might be a novel target to promote bone regeneration. Therefore, we determined whether direct A2AR stimulation or increasing endogenous adenosine concentrations via purine transport blockade with dipyridamole regulates bone formation. We determined whether coverage of a 3 mm trephine defect in a mouse skull with a collagen scaffold soaked in saline, bone morphogenetic protein-2 (BMP-2; 200 ng), 1 muM CGS21680 (A2AR agonist, EC50 = 160 nM), or 1 muM dipyridamole (EC50 = 32 nM) promoted bone regeneration. Microcomputed tomography examination demonstrated that CGS21680 and dipyridamole markedly enhanced bone regeneration as well as BMP-2 8 wk after surgery (60 +/- 2%, 79 +/- 2%, and 75 +/- 1% bone regeneration, respectively, vs. 32 +/- 2% in control, P < 0.001). Blockade by a selective A2AR antagonist (ZM241385, 1 muM) or deletion of A2AR abrogated the effect of CGS21680 and dipyridamole on bone regeneration. Both CGS21680 and dipyridamole treatment increased alkaline phosphatase-positive osteoblasts and diminished tartrate resistance acid phosphatase-positive osteoclasts in the defects. In vivo imaging with a fluorescent dye for new bone formation revealed a strong fluorescent signal in treated animals that was equivalent to BMP-2. In conclusion, stimulation of A2AR by specific agonists or by increasing endogenous adenosine levels stimulates new bone formation as well as BMP-2 and represents a novel approach to stimulating bone regeneration.-Mediero, A., Wilder, T., Perez-Aso, M., Cronstein, B. N. Direct or indirect stimulation of adenosine A2A receptors enhances bone regeneration as well as bone morphogenetic protein-2.