Fluorides and bones

Fluorides began to be used in the treatment of osteoporosis in the sixties when it was found that in areas with a high fluoride content of drinking water the prevalence of this disease is low. Fluorides stimulate osteoblasts to form more osteoid, and moreover larger crystals of bone mineral are formed which are more resistant to resorption by osteoclasts. Fluorides must be, however, administered always in combination with calcium and vitamin D. In the eighties a certain group of osteologists started a "campaign" against fluorides and maintained that after fluorides bone is of poor quality and there in a greater risk of fractures. All was explained by the fact that these authors administered fluorides alone in large doses. Recently with the introduction of monofluorophosphate into treatment instead of NaF there was a revival of fluorides which in combination with calcium and vitamin D are among the best stimulators of new formation of bone; after fluorides the bone density improves and they are used also in osteoporosis and preventively to avoid fractures.     

Pathogenesis and immunopathology of rheumatoid polyarthritis

Etiology of rheumatoid arthritis remains unresolved. Initiating mechanisms include a genetic background of susceptibility, defined by HLA-DR4 and -DR1 antigens and also hormonal factors and infectious events. The synovitis is the hallmark of the disease. Lymphocytes infiltrating the synovial membrane are mainly memory CD4+ T cells associated to dominant clonotypes. The proliferation and cytokine production by synovial tissue T lymphocytes are weak. B cells produce locally auto-antibodies: rheumatoid factors, anti-keratin antibodies.... Type A and B synoviocytes constitute an hyperplastic synovial lining. They synthesize and release large amount of proteolytic enzymes and proinflammatory cytokines, largely participating to inflammation and tissue destruction. Understanding the pathogenesis of rheumatoid arthritis should offer novel approaches to treat rheumatoid arthritis patients.     

Bisphosphonate therapy in osteoporosis. Inhibition of trabecular perforation by aminobisphosphonate

After many years of experience with bisophosphonates in the treatment of "tumor osteopathy" and Paget's disease, these substances have now also been approved for use in the treatment of osteoporosis. Owing to their high affinity for calcium hydroxyapatite, the bisphosphonates are deposited in the bony surface, and the aminobisphosphonates exert their effect at the site of active resorption via direct inhibition of active osteoclasts. As a result of this inhibition of the osteoclastic bone resorption, trabecular perforation is reduced and during the course of bone remodelling by the activity of the osteoblasts, boneformation occurs. In addition to an increase in bone density, both etidronate and alendronate have been shown to inhibit vertebral fractures in patients with osteoporosis. In addition, in patients with preexisting fractures, alendronate is able, at the same time, to lower the incidence of fractures of the femoral neck. With proper administration, the associated occasional gastrointestinal side effects can be avoided. The introduction of bisphosphonates into the treatment of osteoporosis is definitely an enrichment of the therapeutic spectrum in conjunction with the basic treatment comprising calcium, vitamin D, diet and physical measures.     

Osteoblastic responses to TGF-beta during bone remodeling

Bone remodeling depends on the spatial and temporal coupling of bone formation by osteoblasts and bone resorption by osteoclasts; however, the molecular basis of these inductive interactions is unknown. We have previously shown that osteoblastic overexpression of TGF-beta2 in transgenic mice deregulates bone remodeling and leads to an age-dependent loss of bone mass that resembles high-turnover osteoporosis in humans. This phenotype implicates TGF-beta2 as a physiological regulator of bone remodeling and raises the question of how this single secreted factor regulates the functions of osteoblasts and osteoclasts and coordinates their opposing activities in vivo. To gain insight into the physiological role of TGF-beta in bone remodeling, we have now characterized the responses of osteoblasts to TGF-beta in these transgenic mice. We took advantage of the ability of alendronate to specifically inhibit bone resorption, the lack of osteoclast activity in c-fos-/- mice, and a new transgenic mouse line that expresses a dominant-negative form of the type II TGF-beta receptor in osteoblasts. Our results show that TGF-beta directly increases the steady-state rate of osteoblastic differentiation from osteoprogenitor cell to terminally differentiated osteocyte and thereby increases the final density of osteocytes embedded within bone matrix. Mice overexpressing TGF-beta2 also have increased rates of bone matrix formation; however, this activity does not result from a direct effect of TGF-beta on osteoblasts, but is more likely a homeostatic response to the increase in bone resorption caused by TGF-beta. Lastly, we find that osteoclastic activity contributes to the TGF-beta-induced increase in osteoblast differentiation at sites of bone resorption. These results suggest that TGF-beta is a physiological regulator of osteoblast differentiation and acts as a central component of the coupling of bone formation to resorption during bone remodeling.     

Stimulation of osteoclast formation by 1,25-dihydroxyvitamin D requires its binding to vitamin D receptor (VDR) in osteoblastic cells: studies using VDR knockout mice

Previous studies have shown that 1,25-dihydroxyvitamin D [1,25(OH)2D] plays important roles in the formation of osteoclasts through its actions on osteoblastic cells. We have generated mice lacking vitamin D receptor (VDR) by gene targeting (VDR-/-). These mice had tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts, and exhibited similar levels of parameters for bone resorption to those in wild type mice. The present studies were undertaken to clarify whether effects of 1,25(OH)2D on osteoclast formation require VDR in osteoblasts, and to examine mechanisms of the formation of osteoclasts without VDR-mediated actions using VDR-/- mice. When wild-type calvarial osteoblasts and spleen cells were co-cultured with 1,25(OH)2D, TRAP-positive osteoclasts were formed regardless of the genotypes of spleen cells. In contrast, when osteoblasts from VDR-/- mice were co-cultured, no osteoclasts could be formed even with wild-type spleen cells. Parathyroid hormone and interleukin-1alpha stimulated osteoclast formation by co-cultures from VDR-/- mice, and the generated osteoclasts showed resorbing activity. These results demonstrate that VDR-mediated actions of 1,25(OH)2D in osteoblasts are essential for osteoclast formation by 1,25(OH)2D, and that functionally intact osteoclasts can be formed without 1,25(OH)2D actions under stimulations by other agents. It is suggested that osteoclastic bone resorption can be maintained without 1,25(OH)2D actions by other stimulatory agents.     

Ultrastructural evaluation of the interaction of glucocorticoids and vitamin D on bone cells in thyroparathyroidectomized rats

To determine the direct effects of cortisol on bone, rats were thyroparathyroidectomized (T(X)PT(X)), fed a low-calcium diet, and given high (50 mg/kg) or low (8 mg/kg) pharmacologic levels of cortisol with or without excess vitamin D3 (15,000 IU). Rats given vitamin D had osteoblasts and osteocytes interpreted ultrastructurally to be actively engaged in matrix synthesis, mineralization of matrix, and in calcium mobilization. Osteoclasts were numerous on metaphyseal trabeculae and in vascular channels of cortical bone. In T(X)PT(X) rats not given vitamin D, osteoblasts and osteocytes were interpreted to have reduced metabolic activity with minimal evidence of participation in bone formation or resorption. Cortisol at both dose levels failed to alter the electron microscopic appearance of osteoblasts, osteocytes, and osteoclasts with or without vitamin D. Bone turnover indicated by urinary hydroxyproline excretion was unaffected by cortisol treatment. These findings suggest that glucocorticoids have little direct action on bone cells and that their effects on calcium metabolism are probably mediated by an interference in intestinal calcium transport and by secondary hyperparathyroidism.     

Estrogens and bone metabolism

The authors present a review referring to cellular and biochemical control systems of bone remodeling as well as the effect of estrogens on modulation of bone metabolism. Systemic and local control factors such as PTH, calcitonin, vitamin D, prostaglandins, insulin-like growth factor-1, transforming growth factor-beta are analyzed as possible indirect targets for the estrogen induced inhibition of bone resorption. A direct receptor-linked action of estrogens on the osteoblast-lining cell unit, the most important modulator or bone metabolism, is furtherwise examined. The precise mechanism of the beneficial effect of estrogens for the prevention of postmenopausal bone loss and the treatment of established osteoporosis has not yet been clearly identified, but it seems likely that multiple mechanisms may be involved since postmenopausal osteoporosis itself appears as a heterogenic clinical condition related to multiple pathogenetic factors.     

Somatic mosaicism in the central nervous system in spinocerebellar ataxia type 1 and Machado-Joseph disease

Glucocorticoids (GC) are widely used for anti-inflammatory and immunosuppressive therapy. Thirty to 50% of GC-treated patients develop osteoporosis. Potential mechanisms of GC-induced osteoporosis (GC-OP) include abnormalities in calcium balance, vitamin D metabolism, parathyroid hormone release and activity, prostaglandin E2 and cytokine synthesis, interference with c-fos and p-53 expression in osteoblasts, and hypogonadism. Early diagnosis and detection of patients at risk are accomplished with rapid, safe and non-invasive bone density measurements. Preventive measures include maintaining a positive calcium balance, vitamin D supplementation (if indicated) and treatment of hypogonadism. The shortest duration and the smallest doses possible of GC for a particular condition are advisable. For high-risk patients and those with established GC-OP calcitonin or bisphosphonate therapy is recommended.     

Glucocorticoid-induced osteoporosis: prevention and treatment

Glucocorticoid excess carries the risk of inducing secondary osteoporosis. In endogenous Cushing's syndrome, osteoporosis may be the presenting symptom of the underlying disease. Bone loss may reverse after the condition is cured, but often active treatment of established osteoporosis is necessary. In long-term glucocorticoid treatment at therapeutic doses, bone loss is likely and should be prevented; if prevention is ineffective, treatment is necessary. Hypercortisolism impairs calcium homeostasis and bone metabolism in a complex, multifactorial way: Glucocorticoids diminish calcium absorption and increase renal calcium excretion; this negative calcium balance leads to secondary hyperparathyroidism and osteoclast activation. Osteoblast activity is directly impaired by glucocorticoids, which lower activity of the gonadal hormone axis so that hypogonadism also contributes to bone loss. Glucocorticoids lead to muscle atrophy and decreased muscle strength with negative consequences for bone formation. For prevention and treatment, two different strategies have been used. The pathophysiological approach substitutes calcium and vitamin D in the first step; if bone loss nevertheless continues, bone formation is stimulated by fluorides. The alternative pharmaco-dynamic approach uses antiresorptives-calcitonin or, for preference, bisphosphonates. Clinically it is mandatory to monitor all patients in whom glucocorticoids are used (e.g., organ transplant recipients) before and after the initiation of treatment to stabilize bone metabolism as early as possible.     

Inflammatory bowel disease and osteoporosis

The relation between inflammatory bowel disease (IBD) and osteoporosis has received increasing attention during the past decade. The prevalence of low bone mass in patients with IBD has been reported to be more than 50%. The development of a quick non-invasive method to diagnose osteoporosis (dual-energy X-ray absorptiometry) provides a practical tool to identify the patient who needs special attention. The aetiology of the bone disease in patients with IBD has still not been elucidated, but corticosteroids may play a major role. Studies on the prevention/treatment of IBD-related osteoporosis are scarce. In a single uncontrolled study hormone replacement therapy proved effective in preventing bone loss in peri- and post-menopausal women with IBD. A placebo-controlled study showed that supplementation with calcium and vitamin D prevents bone loss in patients with Crohn's disease. The present paper reviews our current knowledge on the mechanisms and epidemiology of IBD-related bone disease.     

Osteoporosis in rheumatoid arthritis

Patients with rheumatoid arthritis (RA) develop both periarticular and generalized osteoporosis. Periarticular osteopenia in appendicular bones occurs early in the course of RA and is one of the earliest radiological signs of RA. An uncoupled state in bone resorption-formation linkage, contributes to the development of periarticular osteopenia and it might be mediated through an increased productions of cytokines and prostaglandins by synovium and bone marrow. Accordingly, early suppression of rheumatoid synovitis is necessary for the prevention of periarticular osteopenia. Generalized osteoporosis is also common in RA and leads to increased risk of fractures. Generalized osteoporosis considered to be multifactorial and factors contributing to lumbar osteoporosis might be different from those to loss of appendicular bones, such as femur and radius. Corticosteroids and menopausal state are important risk factors for lumbar osteoporosis. Rheumatoid activity and reduced physical activity are also important determinants. According to the previous studies, however, the influence of functional impairment is more prominent in the femoral BMD compared to spinal BMD. In addition to control of RA and maintenance of physical activity, hormone replacement therapy (HRT) and bisphosphonate are possible agents for the treatment of osteoporosis in RA patients, especially postmenopausal women.     

Transient gene transfer of IL-12 regulates chemokine expression and disease severity in experimental arthritis

Murine collagen-induced arthritis (CIA) is characterized by pannus formation, cell infiltration, and cartilage erosion, and shares histologic and immunologic features with rheumatoid arthritis. Numerous cytokines are reportedly associated with RA and/or CIA; however, their mechanistic role is not clear. To determine the role of IL-12 in CIA, DBA/1 LacJ mice were administered 3 x 10(8) plaque-forming units of mIL-12 i.p. in a nonreplicating adenoviral vector (AdIL-12) on day 25 following primary type II collagen immunization. Our studies demonstrated that systemic transient overexpression of IL-12 accelerated disease progression and augmented the arthritis severity relative to mice expressing a replication-deficient, E1-deleted Ad5 construct. A likely mechanism for this increase in pathology was the increase in the expression of cytokines and chemokines known to play a proinflammatory role in disease. In particular, levels of murine IFN-gamma were significantly increased in mice overexpressing AdIL-12 relative to the replication-deficient, E1-deleted Ad5 construct. Interestingly, the C-X-C chemokine murine macrophage inflammatory protein-2, as well as the C-C chemokines murine monocyte chemoattractant protein-1 and murine macrophage inflammatory protein-1alpha were up-regulated by AdIL-12 relative to controls. In an additional set of studies, neutralization of endogenous IL-12 in CIA mice was shown to delay disease onset and attenuate disease severity. IFN-gamma levels in the mice receiving anti-IL-12 were significantly decreased in joint homogenates. These studies demonstrate that IL-12 is an important cytokine involved in controlling the production of chemokines/cytokines leading to the evolution of experimental arthritis.     

Inflammation and joint destruction during rheumatoid polyarthritis: what relation?

A QUESTION REVISITED: It is generally accepted that acute then chronic joint inflammation leads to the development of a synovial pannus and secondarily to characteristic degenerative joint disease en rheumatoid arthritis. However accumulating clinical and biological evidence would question the real relationship between inflammation and joint destruction, and suggest therapeutic strategies might need to be revisited. THE CAUSAL EVENTS: Synovial proliferation is the fundamental event in joint lesions. The contact between the synovial pannus and the cartilage leads to characteristic joint damage mediated by pro-inflammatory cytokines (TNF alpha and IL 1) and enzyme secretion, particularly metalloproteases. ROLE OF T CELLS: The role of T-lymphocytes is a question of much debate. Although it is generally accepted that T cells are crucial in the initial phases of rheumatoid arthritis, several arguments suggest that the process of synovial proliferation and joint destruction in advanced stage disease would be independent of T cell activity. Synovial macrophages and fibroblasts, and perhaps chondrocytes, play a central role at this phase. THERAPEUTIC IMPLICATIONS: A direct mandatory relationship between inflammation and joint destruction appears to be excluded, although complex and poorly understood links exist between these events in rheumatoid arthritis. A better understanding of the mechanisms involved would be very useful for the development of more adapted therapeutic strategies in rheumatoid arthritis.     

Local estradiol metabolism in osteoblast- and osteoclast-like cells

Bone is an estradiol-responsive tissue. Estrogen withdrawal during the menopause causes loss of bone mass and clinically relevant osteoporosis in a third of all women. Sufficient or impaired local production, as well as degradation of estradiol in cells present in the bone microenvironment might be an important mechanism of rescue or might contribute to the development of osteoporosis, respectively. We therefore investigated aromatase and 17beta-hydroxysteroid dehydrogenase type IV (17beta-HSD IV) expression in osteoblast- and osteoclast-like cells. Aromatase mRNA was increasingly expressed in myeloid THP 1 cells differentiated along the monocyte/phagocyte pathway exploiting vitamin D and either granulocyte-macrophage-stimulating factor (GMCSF) or macrophage-stimulating factor (MCSF). In long-term cultures, when sequentially exposed to vitamin D (days 0-21) and GMCSF (days 5-10) and plated on collagen, the amount of expression of aromatase mRNA steadily increased along with the increasing expression of osteopontin mRNA, alpha(v) integrin mRNA, c-fms (MCSF-receptor) mRNA and multinucleated cells developing. The conversion of estradiol from testosterone (10(-7) M/l) in the supernatants of dishes mirrored changes in aromatase mRNA expression and by day 21 rose to 30,000 ng/10(7) cells/24 h. 17Beta-HSD IV mRNA expression was abundant in undifferentiated THP 1 cells and was decreased to approximately 50% by day 21. Unstimulated SV-40 immortalized fetal osteoblasts did not express aromatase mRNA, but the expression was stimulated by the addition of the phorbol ester phorbol myristate acetate (PMA). Unstimulated osteoblasts from primary cultures did not express aromatase mRNA. Osteoblast-like osteosarcoma cells MG 63 expressed faint levels of aromatase mRNA in contrast to the osteosarcoma cell line HOS 58. 17Beta-HSD IV mRNA was expressed in fetal osteoblasts as well as in osteoblasts from primary culture, MG 63 and HOS 58 cells. In summary, we can show the expression of estradiol metabolizing enzymes in cells which are present in the bone microenvironment. Impaired aromatase expression and/or enhanced expression of 17beta-HSD IV may contribute to the pathogenesis of osteoporosis.     

Chiasmatic specificity in the regenerating mammalian optic nerve

Bone-resorbing multinucleated cells were efficiently formed in primary culture of cells isolated from synovial tissues of patients with rheumatoid arthritis in 2-3 weeks in the presence of 1,25(OH)2vitaminD3 without any additional stromal cells, and that formation was further facilitated by macrophage-colony stimulating factor. Furthermore, we show that osteoclast-like cells are formed in co-culture of peripheral blood mononuclear cells and rheumatoid synovial fibroblasts obtained by continued sub-cultures. The multinucleated cells showed all the phenotypical and functional characteristics of osteoclasts including the expression of tartrate resistant acid phosphatase, vitronectin receptors, receptors for human calcitonin and the ability to resorb bone. These results indicate that synovial macrophages are capable of differentiating into osteoclasts in the presence of rheumatoid synovial fibroblasts which can support differentiation of monocytes/ macrophages, implicating that osteoclasts generated within the synovial membrane are probably involved in bone destruction in rheumatoid arthritis.     

Age-related bone loss and senile osteoporosis: evidence for both secondary hyperparathyroidism and skeletal growth factor deficiency in the elderly

Aging is characterized by a decrease in bone volume, implying that net bone resorption exceeds net bone formation. This age-related bone loss can be regarded as the main determinant of hip fracture risk in the elderly. In the concept of senile osteoporosis, a key role has been attributed to vitamin D deficiency. Lack of vitamin D activity may affect femoral strength through impaired mineralization as well as through a hyperparathyroidism-mediated increase in bone resorption. In addition to vitamin D-related mechanisms, recent evidence has indicated a decline in the skeletal content of anabolic growth factors--such as insulin-like growth factor-I (IGF-I)--in femoral (cortical) bone, suggesting that skeletal growth factor deficiency may contribute to the age-related bone loss in the proximal femur as well. It is tempting to speculate that skeletal IGF-I loss might, at least partially, be accounted for by growth hormone deficiency. However, critical evidence does not yet support the concept that the decreased activity of the growth hormone-IGF-I-axis alters bone remodeling, and the extent to which serum concentrations of growth factors are reflective of skeletal activity remains to be clarified.     

OX-40: life beyond the effector T cell stage

Juvenile rheumatoid arthritis (JRA), unlike rheumatoid arthritis of adulthood (RA), is a heterogenous disease comprising at least five subtypes that differ in clinical course and prognosis, and require different therapeutical approaches. As compared to RA, the production of local and systemic cytokines in JRA have not yet been as extensively investigated. In this article we review the available literature on cytokine expression in serum and synovial fluid in all five different subtypes of JRA. Even though the data are still fragmentary, the evidence so far suggests that the determination of serum cytokines yields relevant information as to clinical subtype and inflammatory activity of the disease. Furthermore, the cytokine data suggest that the pathogenesis of JRA may even by more heterogenous than defined by the clinical subtypes. Finally, future directions of research in this area are proposed, and-based on the latest results-arguments for (anti)cytokine therapies in JRA are critically discussed.     

Effect of vitamin D receptor gene alleles on bone loss in early rheumatoid arthritis

OBJECTIVE: Rheumatoid arthritis (RA) is a polygenic disease characterized by localized joint destruction and generalized osteoporosis resulting in increased fracture risk. The pathogenetic mechanisms that determine the severity of generalized bone loss in RA are poorly understood. Polymorphisms in the vitamin D receptor (VDR) gene have been described as a significant determinant of bone turnover and mass. In this prospective study we describe VDR gene allele effects on bone loss in patients with early RA. METHODS: We recruited 232 patients with early RA. Bone mineral density measurements were repeated in 167 patients. Serial clinical and laboratory measures were recorded during the period of followup. DNA extraction, polymerase chain reaction amplification, and restriction fragment length polymorphism analysis of VDR alleles were performed using standard techniques. Presence of the Taq restriction site for both alleles was denoted "tt", and absence "TT". RESULTS: In women with RA the tt genotype group lost bone more rapidly than subjects with TT genotype at both the lumbar spine (-0.1 vs -4.9% p.a, respectively; p < 0.05) and femoral neck (-3.9 vs -9.6%, respectively; p < 0.01). The effect was independent of other disease characteristics. CONCLUSION: The presence of the VDR gene "t" allele in female patients with RA was associated with accelerated bone loss.     

Corticosteroid osteoporosis in the adult]

EARLY BONE LOSS: Bone loss is greatest in patients given supra-physiological doses of corticosteroids during the first months of treatment. The rate of loss then tapers off but persists throughout the duration of the treatment because of depressed osteoblast activity. EVALUATE THE RISK: Corticosteroid-induced osteoporosis is a multifactorial phenomenon depending in part on the duration and the dose of the treatment and in part on prior bone status and the causal disease. Young subjects can expect to recover bone mass partially or completely after withdrawal. Menopaused women not taking hormone replacement therapy have a low bone mass and are high risk patients. PREVENTION: Preventive measures against corticosteroid-induced osteoporosis should begin with treatment onset. Patients should be given calcium and vitamin D supplements, hormone replacement therapy (menopaused women) or androgens (hypogonadic men), and biphosphonates (for young patients at risk or in case of bone mass despite the preceding measures).