Immune System and Postmenopausal Bone Loss

The Role of Macrophage in the Pathogenesis of Osteoporosis

Osteoporosis is a systemic disease with progressive bone loss. The bone loss is associated with an imbalance between bone resorption via osteoclasts and bone formation via osteoblasts. Other cells including T cells, B cells, macrophages, and osteocytes are also involved in the pathogenesis of osteoporosis. Different cytokines from activated macrophages can regulate or stimulate the development of osteoclastogenesis-associated bone loss. The fusion of macrophages can form multinucleated osteoclasts and, thus, cause bone resorption via the expression of IL-4 and IL-13. Different cytokines, endocrines, and chemokines are also expressed that may affect the presentation of macrophages in osteoporosis. Macrophages have an effect on bone formation during fracture-associated bone repair. However, activated macrophages may secrete proinflammatory cytokines that induce bone loss by osteoclastogenesis, and are associated with the activation of bone resorption. Targeting activated macrophages at an appropriate stage may help inhibit or slow the progression of bone loss in patients with osteoporosis.

The Interplay between the bone and the immune system

In the last two decades, numerous scientists have highlighted the interactions between bone and immune cells as well as their overlapping regulatory mechanisms. For example, osteoclasts, the bone-resorbing cells, are derived from the same myeloid precursor cells that give rise to macrophages and myeloid dendritic cells. On the other hand, osteoblasts, the bone-forming cells, regulate hematopoietic stem cell niches from which all blood and immune cells are derived. Furthermore, many of the soluble mediators of immune cells, including cytokines and growth factors, regulate the activities of osteoblasts and osteoclasts. This increased recognition of the complex interactions between the immune system and bone led to the development of the interdisciplinary osteoimmunology field. Research in this field has great potential to provide a better understanding of the pathogenesis of several diseases affecting both the bone and immune systems, thus providing the molecular basis for novel therapeutic strategies. In these review, we reported the latest findings about the reciprocal regulation of bone and immune cells.

The use of raloxifene in osteoporosis treatment

INTRODUCTION

Osteoporosis is a common disease characterized by the occurrence of fragility fractures. Major osteoporotic fractures are associated with decreased quality of life and high costs.

AREAS COVERED

This review summarizes clinical data on raloxifene (RLX), a second generation selective estrogen-receptor modulator (SERM), currently approved for the treatment of postmenopausal osteoporosis. RLX has estrogen effects on bone and lipid profile, whereas it has anti-estrogen effects on uterus and breast cells. Its main side effects are hot flushes and venous thromboembolism. Literature searches were conducted to retrieve articles reporting RLX clinical trial data. For comparison of safety and efficacy, post-marketing studies on RLX were included.

EXPERT OPINION

RLX is effective in reducing vertebral fracture risk in osteoporotic women, it is safe and its ability to prevent breast cancer has to be considered in the analyses of cost/effect and of the ideal candidate to this treatment. RLX has to be avoided in patients with previous history of venous thromboembolism.