Background-Aldosteronism may account for oxi/nitrosative stress, a proinflammatory phenotype, and wasting in congestive heart failure. We hypothesized that aldosterone/1% NaCl treatment (ALDOST) in rats enhances

SUMMARYBone injury induces an inflammatory response that involves neutrophils, macrophages and other inflammatory cells. The recruitment of inflammatory cells to sites of injury occurs in response to specific signaling pathways. The CC chemokine receptor type 2 (CCR2) is crucial for recruiting macrophages, as well as regulating osteoclast function. In this study, we examined fracture healing in Ccr2-/-mice. We first demonstrated that the expression of Ccr2 transcripts and the filtration of macrophages into fracture calluses were most robust during the early phases of fracture healing. We then determined that the number of macrophages at the fracture site was significantly lower in Ccr2-/-mice compared with wild-type controls at 3 days after injury. As a result, impaired vascularization, decreased formation of callus, and delayed maturation of cartilage were observed at 7 days after injury in mutant mice. At day 14, Ccr2-/-mice had less bone in their calluses. At day 21, Ccr2-/-mice had larger calluses and more bone compared with wild-type mice, suggesting a delayed remodeling. In addition, we examined the effect of Ccr2 mutation on osteoclasts. We found that a lack of Ccr2 did not affect the number of osteoclasts within fracture calluses at 21 days after injury. However, Ccr2-/-osteoclasts exhibited a decreased ability to resorb bone compared with wild-type cells, which could contribute to the delayed remodeling of fracture calluses observed in Ccr2-/-mice. Collectively, these results indicate that a deficiency of Ccr2 reduces the infiltration of macrophages and impairs the function of osteoclasts, leading to delayed fracture healing.

Extracellular matrix (ECM) remodeling is important during bone development and repair. Because matrix metalloproteinase 13 (MMP13, collagenase-3) plays a role in long bone development, we have examined its role during adult skeletal repair. In this study we find that MMP13 is expressed by hypertrophic chondrocytes and osteoblasts in the fracture callus. We demonstrate that MMP13 is required for proper resorption of hypertrophic cartilage and for normal bone remodeling during non-stabilized fracture healing, which occurs via endochondral ossification. However, no difference in callus strength was detected in the absence of MMP13. Transplant of wild-type bone marrow, which reconstitutes cells only of the hematopoietic lineage, did not rescue the endochondral repair defect, indicating that impaired healing in Mmp13−/− mice is intrinsic to cartilage and bone. Mmp13−/− mice also exhibited altered bone remodeling during healing of stabilized fractures and cortical defects via intramembranous ossification. This indicates that the bone phenotype occurs independently from the cartilage phenotype. Taken together, our findings demonstrate that MMP13 is involved in normal remodeling of bone and cartilage during adult skeletal repair, and that MMP13 may act directly in the initial stages of ECM degradation in these tissues prior to invasion of blood vessels and osteoclasts.

Age significantly reduces the regenerative capacity of the skeleton, but the underlying causes are unknown. Here, we tested whether the functional status of inflammatory cells contributes to delayed healing in aged animals. We created chimeric mice by bone marrow transplantation after lethal irradiation. In this model, chondrocytes and osteoblasts in the regenerate are derived exclusively from host cells while inflammatory cells are derived from the donor. Using this model, the inflammatory system of middle-aged mice (12 month old) was replaced by transplanted bone marrow from juvenile mice (4 weeks old), or age-matched controls. We found that the middle-aged mice receiving juvenile bone marrow had larger calluses and more bone formation during early stages and faster callus remodeling at late stages of fracture healing, indicating that inflammatory cells derived from the juvenile bone marrow accelerated bone repair in the middle-aged animals. In contrast, transplanting bone marrow from middle-aged mice to juvenile mice did not alter the process of fracture healing in juvenile mice. Thus, the roles of inflammatory cells in fracture healing may be age-related, suggesting the possibility of enhancing fracture healing in aged animals by manipulating the inflammatory system. ß

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gestive heart failure (CHF) is a clinical syndrome with origins rooted in a salt-avid state largely mediated by effector hormones of the circulating renin-angiotensin-aldosterone system. Other participating neurohormones include catecholamines, endothelin-1, and arginine vasopressin. CHF is accompanied by a systemic illness of uncertain causality. Features include the appearance of oxidative/nitrosative stress and a wasting of tissues including bone. Herein we hypothesized that inappropriate (relative to dietary Na ϩ ) elevations in plasma aldosterone (Aldo) contribute to an altered redox state, augmented excretion of divalent cations, and in turn, a loss of bone minerals and strength. In uninephrectomized rats that received chronic Aldo and 1% NaCl treatment for 4 -6 wk, we monitored plasma ␣1-antiproteinase activity, which is an inverse correlate of oxidative/nitrosative stress; plasma concentrations of ionized Mg 2ϩ and Ca 2ϩ ; urinary Mg 2ϩ and Ca 2ϩ excretion; and bone mineral composition and strength to flexure stress. Compared with controls, we found reductions in plasma ␣1-antiproteinase activity and ionized Mg 2ϩ and Ca 2ϩ together with persistently elevated urinary Mg 2ϩ and Ca 2ϩ excretion, a progressive loss of bone mineral density and content with reduced Mg 2ϩ and Ca 2ϩ concentrations, and a reduction in cortical bone strength. Thus the hypermagnesuria and hypercalciuria that accompany chronic Aldo-1% NaCl treatment contribute to the systemic appearance of oxidative/nitrosative stress and a wasting of bone minerals and strength. aldosterone; congestive heart failure; peripheral blood mononuclear cells; antiproteinase; parathyroid hormone CONGESTIVE HEART FAILURE (CHF), a clinical syndrome with characteristic signs and symptoms, arises from circulating renin-angiotensin-aldosterone system activation (38) and is accompanied by a systemic illness that includes oxidative/ nitrosative stress in the heart, systemic organs, circulating immune cells, and blood (10,20,34,37) and a catabolic state with wasting of lean tissue, fat, and bone (2, 3, 22, 32). Aldosteronism in rats, which is defined as inappropriate (relative to dietary Na ϩ ) and chronic elevations in plasma aldosterone (Aldo) comparable to those seen in CHF, ultimately leads to a proinflammatory coronary vascular phenotype with evidence of oxidative/nitrosative stress (e.g., 3-nitrotyrosine labeling) in invading inflammatory cells (36). These vascular lesions are preceded by an immunostimulatory state that involves activated peripheral blood mononuclear cells (PBMCs) and is induced by Ca 2ϩ loading and transduced by reactive oxygen species in these cells (1, 16). Herein we hypothesized that enhanced urinary excretion of Mg 2ϩ and Ca 2ϩ accompanies chronic Aldo with 1% NaCl treatment (Aldost) and leads to yet another component of this illness, namely, bone wasting. MATERIALS AND METHODSMale 8-wk-old Sprague-Dawley rats (Harlan, IN) were used in this study, which was approved by the institution's Animal Care and Use Committee. Unoperated and untr...

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Molecules absorbed on the surface of particulate wear debris may contribute to inflammatory reactions that lead to aseptic loosening of implants. Lipopolysaccharide (LPS), a bacterial endotoxin, can attach to many biomaterials and stimulate macrophages to secrete osteoclast-activating cytokines. We tested the adsorption of LPS by polyethylene particles in vitro and examined the biological effects of LPS absorption on bone remodeling around implants in vivo. Polyethylene particles were incubated in radiolabeled LPS solutions, and adsorption of LPS by the particles was quantified by radioassay. Because polyethylene particles are hydrophobic and less dense than water, they floated and clumped when incubated in a water solution of LPS, resulting in low adsorption of LPS. However, when particles were incubated in an ethanol solution of LPS, most of the LPS was adsorbed by the particles, and was resistant to washing with water. Triton X-100 (10%), however, effectively washed the LPS off the particles. In a rat model, the presence of polyethylene particles around the implant in the femoral canal decreased bone attachment to the implant at 6 weeks. Incubating the particles with LPS before implantation, or intermittent administration of LPS systemically, further decreased bone-implant attachment to similar extents, but had no effect on the bone density of the control side femurs. Our data indicate that polyethylene particles have high affinity for LPS, depending on many factors, especially the solvents of the LPS. Intermittent systemic administration of LPS affects bone remodeling but only occurs in the area containing polyethylene particles and titanium implants, supporting the hypothesis that the presence of polyethylene particles around implants can result in accumulation of LPS from exogenous sources. This may cause local levels of LPS that are high enough to affect bone remodeling around implants. ß