Oxidative stress modulates osteoblastic differentiation of vascular and bone cells

Uremic toxin and bone metabolism

Patients with end-stage renal disease (ESRD) develop various kinds of abnormalities in bone and mineral metabolism, widely known as renal osteodystrophy (ROD). Although the pathogenesis of ESRD may be similar in many patients, the response of the bone varies widely, ranging from high to low turnover. ROD is classified into several types, depending on the status of bone turnover, by histomorphometric analysis using bone biopsy samples [1,2]. In the mild type, bone metabolism is closest to that of persons with normal renal function. In osteitis fibrosa, bone turnover is abnormally activated. This is a condition of high-turnover bone. A portion of the calcified bone loses its lamellar structure and appears as woven bone. In the cortical bone also, bone resorption by osteoclasts is active, and a general picture of bone marrow tissue infiltration and the formation of cancellous bone can be observed. In osteomalacia, the bone surface is covered with uncalcified osteoid. This condition is induced by aluminum accumulation or vitamin D deficiency. The mixed type possesses characteristics of both osteitis fibrosa and osteomalacia. The bone turnover is so markedly accelerated that calcification of the osteoid cannot keep pace. In the adynamic bone type, bone resorption and bone formation are both lowered. While bone turnover is decreased, there is little osteoid. The existence of these various types probably accounts for the diversity in degree of renal impairment, serum parathyroid hormone (PTH) level, and serum vitamin D level in patients with ROD. However, all patients share a common factor, i.e., the presence of a uremic condition.

Vitamin D in chronic kidney disease: A systemic role for selective vitamin D receptor activation

Hyperparathyroidism occurs in most patients during the progression of chronic kidney disease (CKD) and one of its initiating events, reduced serum levels of 1,25-dihydroxyvitamin D, results from a decrease in renal 1alpha hydroxylase activity, which converts 25-hydroxyvitamin D to its activated form. The combination of persistently high parathyroid hormone (PTH) and low 1,25-dihydroxyvitamin D is associated with bone loss, cardiovascular disease, immune suppression and increased mortality in patients with end-stage kidney failure. Recent studies in dialysis patients suggest that paricalcitol, a selective activator of the vitamin D receptor (VDR), is associated with a more favorable efficacy to side effect profile than calcitriol, with less morbidity and better survival. One hypothesis derived from such studies suggests that systemic activation of VDRs may have direct effects on the cardiovascular system to decrease mortality in CKD. Although current guidelines for regulating serum calcium, phosphate and PTH recommend specific interventions at the various stages of CKD to prevent or postpone irreversible parathyroid disease and decrease cardiovascular morbidity and mortality, emerging data suggest that vitamin D therapy may prolong survival in this patient population by mechanisms that are independent of calcium, phosphate and PTH. It is suggested that a re-evaluation of current treatment recommendations is needed and that future research should focus on mechanisms that distinguish potential tissue specific benefits of selective VDR activators in patients with CKD.

Osteogenic oxysterols inhibit the adverse effects of oxidative stress on osteogenic differentiation of marrow stromal cells

The osteoporosis that occurs with aging is associated with reduced number and activity of osteoblastic cells. Aging, menopause, and osteoporosis are correlated with increased oxidative stress and reduced antioxidant defense mechanisms. We previously demonstrated that oxidative stress induced by a variety of compounds such as xanthine/xanthine oxidase (XXO) and minimally oxidized LDL (MM-LDL) inhibit the osteogenic differentiation of osteoprogenitor cells. Oxysterols are a family of products derived from cholesterol oxidation that have important biological activities. Recently, we reported that a specific oxysterol combination consisting of 22(S)- or 22(R)-hydroxycholesterol and 20(S)-hydroxycholesterol has potent osteogenic properties in vitro when applied to osteoprogenitor cells including M2-10B4 (M2) marrow stromal cells. We now demonstrate that this osteogenic combination of oxysterols prevents the adverse effects of oxidative stress on differentiation of M2 cells into mature osteoblastic cells. XXO and MM-LDL inhibited the osteogenic differentiation of M2 cells, demonstrated by the inhibition of markers of osteogenic differentiation: alkaline phosphatase activity, osteocalcin expression and mineralization. Treatment of M2 cells with osteogenic oxysterol combination 22(S)- and 20(S)-hydroxycholesterol both blocked and reversed the inhibition of osteogenic differentiation produced by XXO and MM-LDL in these cells. The protective effect of the oxysterols against oxidative stress was dependent on cyclooxygenase 1 and was associated with the osteogenic property of the oxysterols. These findings further demonstrate the ability of the osteogenic oxysterols to positively regulate osteogenic differentiation of cells, and suggests that the use of these compounds may be a novel strategy to prevent the adverse effects of oxidative stress on osteogenesis.

Evidence That Osteogenic Progenitor Cells in the Human Tunica Albuginea May Originate from Stem Cells: Implications for Peyronie Disease1

Tissue ossification in Peyronie disease (commonly known as Peyronie's disease [PD]), a localized fibrotic lesion within the tunica albuginea (TA) of the penis, may result from osteogenic differentiation of fibroblasts, myofibroblasts, and/or adult stem cells in the TA, and may be triggered by chronic inflammation, oxidative stress, and profibrotic factors like transforming growth factor beta 1 (TGFB1). In this study, we have investigated whether cultures of cells from normal TA and PD plaques undergo osteogenesis, express markers for stem cells, and originate other cell lineages via processes modulated by TGFB1. We found that TA and PD cells in osteogenic medium (OM) expressed osteogenic markers, alkaline phosphatase, and osteopontin and underwent calcification. PD cells, but not TA cells, formed foci in soft agar that were positive for alkaline phosphatase and calcification and expressed the mRNAs for osteoblast-specific factors pleiotrophin and periostin and bone morphogenic protein 2. Both cultures expressed stem cell marker CD34 antigen but not protein tyrosine phosphatase, receptor type c. TA and PD cells expressed smooth-muscle cell markers smoothelin and transgelin. None of the cultures underwent adipogenesis in adipogenic medium. Incubation with TGFB1 increased osteogenesis and myofibroblast differentiation and reduced CD34 antigen expression in both cultures. TA and PD cells modulated the differentiation of the multipotent C3H 10T(1/2) cells in dual cultures, into osteoblasts and myofibroblasts. In conclusion, both TA and PD cultures contain cells, presumably stem cells, that undergo osteogenic and myofibroblast differentiation, and may induce these processes by paracrine interactions. This may explain progression of fibrosis in the PD plaque and its eventual calcification.

Prevention of bone loss by phloridzin, an apple polyphenol, in ovariectomized rats under inflammation conditions

Aging and sex hormones related changes lead to inflammatory and oxidant conditions, which are involved in the pathogenesis of osteoporosis. Recent studies have suggested that polyphenols may exert a protective effect in such conditions. We assessed the effect of phloridzin (Phlo), a flavonoid exclusively found in apple, on bone metabolism in ovariectomized (OVX) or sham-operated (SH) rats with and without inflammation. Six-month-old Wistar rats were allocated to two equal groups that received either a control diet or a diet supplemented with 0.25% Phlo for 80 days. Three weeks before necropsy, inflammation was induced by subcutaneous injection of talc in 10 animals of each group. At necropsy, ovariectomy decreased both total (T-BMD) and metaphyseal (M-BMD) femoral bone mineral density (P < 0.01). Inflammation conditions, checked by an increase in the spleen weight and alpha1-acid glycoprotein concentration in OVX rats, exacerbated the decrease in T-BMD (g/cm2) (as well as M-BMD) observed in castrated animals (P < 0.05). Daily Phlo intake prevented ovariectomy-induced bone loss in conditions of inflammation as shown by T-BMD and M-BMD (P < 0.05). At the diaphyseal site, BMD was improved by Phlo in OVX rats with or without inflammation (P < 0.05). These results could be explained by changes in bone remodeling as the increased urinary deoxypyridinoline excretion in OVX and OVXinf animals was prevented by the polyphenol-rich diet (P < 0.001), while plasma osteocalcin concentration was similar in all experimental groups. In conclusion, Phlo consumption may provide protection against ovariectomy-induced osteopenia under inflammation conditions by improving inflammation markers and bone resorption.

Aortic valve calcification: association with bone mineral density and cardiovascular risk factors

BACKGROUND

Cardiovascular risk factors are reported to increase the incidence of aortic valve calcification. Among older women, low bone mineral density appears to be associated with increased prevalence of aortic calcification. We aimed to assess and compare cardiovascular risk factors and bone mineral density of patients with and without aortic valve calcification.

MATERIALS AND METHODS

Cardiovascular risk factors and bone mineral density measurements have been assessed in 49 patients with aortic valve calcification and in 65 patients without aortic valve calcification. All patients were subsequently referred to the nuclear medicine department to measure bone mineral density after echocardiographic evaluation.

RESULTS

No statistically significant differences were observed between the two groups with respect to sex, body mass index, history of coronary artery disease, diabetes mellitus, hypercholesterolemia, and smoking status. Although height and weight of the patients with aortic valve calcification were significantly lower than those of patients without aortic valve calcification, they were not independent risk factors. Age and hypertension were found to be independent positive risk factors for aortic valve calcification, whereas T score was found to be negatively associated with aortic valve calcification.

CONCLUSION

We have shown that aortic valve calcification is positively associated with age and hypertension, whereas bone mineral density is negatively associated with aortic valve calcification. The mechanism underlying the association between decreased bone mineral density and aortic valve calcification remains to be clarified in further studies.

Cross-regulation between Egr-1 and APE/Ref-1 during early response to oxidative stress in the human osteoblastic HOBIT cell line: evidence for an autoregulatory loop

The Early Growth Response protein (Egr-1) is a C(2)H(2)-zinc finger-containing transcriptional regulator involved in the control of cell proliferation and apoptosis. Its DNA-binding activity is redox regulated in vitro through the oxidation-reduction of Cys residues within its DNA-binding domain. APE/Ref-1 is a DNA-repair enzyme with redox modulating activities on several transcription factors. In this study, by evaluating the effects of different stimuli, we found a similar timing of activation being suggestive for a common and co-linear regulation for the two proteins. Indeed, we show that APE/Ref-1 increases the Egr-1 DNA-binding activity in unstimulated osteoblastic HOBIT cells. H(2)O(2) stimulation induces a strong interaction between Egr-1 and APE/Ref-1 at early times upon activation, as assayed by immunoprecipitation experiments. By using a cell transfection approach, we demonstrated the functional role of this interaction showing that two specific Egr-1 target genes, the PTEN phosphatase and the thymidine kinase (TK) genes promoters, are activated by contransfection of APE/Ref-1. Interestingly, by using a cell transfection approach and Chromatin immunoprecipitation assays, we were able to demonstrate that Egr-1 stimulates the transcriptional activity of APE/Ref-1 gene promoter by a direct interaction with specific DNA-binding site on its promoter. Taken together, our data delineate a new molecular mechanism of Egr-1 activation occurring soon after H(2)O(2) stimulation in osteoblastic cells and suggest a model for a positive loop between APE/Ref-1 and Egr-1 that could explain the early transcriptional activation of APE/Ref-1 gene expression.

Vascular calcification

PURPOSE OF REVIEW

Accumulating evidence suggests that the high cardiovascular mortality observed in patients with end-stage renal disease is due in part to the deleterious effects of vascular calcification that develops over time on dialysis. This review focuses on recent cell biological and animal studies that have shed light on the mechanisms and regulators of vascular smooth muscle cell calcification in end-stage renal disease.

RECENT FINDINGS

Clinical studies demonstrate that high circulating levels of phosphate or calcium predict vascular calcification. Recent cell biological studies have provided novel insights into how vascular smooth muscle cells regulate calcification in response to such insults. Vascular smooth muscle cell damage and subsequent vesicle release from viable and dying cells create an environment permissive for the nucleation of basic calcium phosphate mineral. This, combined with osteogenic conversion of vascular smooth muscle cells and consequent loss of their normal inhibitory processes/pathways, results in calcification. Circulating factors such as fetuin-A, with the potential to impact on vessel wall calcification, have also been identified. Animal studies suggest that the 'uremic milieu' potentiates calcification and have clearly established a link between vascular calcification and bone metabolism. However, our understanding of the factors that contribute to vascular smooth muscle cell calcification in end-stage renal disease remains incomplete.

SUMMARY

Systematic studies are required that integrate epidemiological studies to identify risk factors with in-vitro experiments to investigate mechanisms leading to vascular smooth muscle cell calcification in response to these factors. Animal and clinical studies can subsequently be used to assess how modifying risk factors under the complex physiological conditions of end-stage renal disease impacts on vessel wall health.

Inflammation and vascular calcification

Both vascular calcification and inflammation are common in patients with chronic kidney disease (CKD). In patients on dialysis, there is increased coronary artery and peripheral artery calcification compared to the general population. Both intimal (atherosclerotic) and medial calcification in CKD patients are associated with increased morbidity and mortality. Vascular calcification is an active cell-mediated process, and likely reflects a transformation of vascular smooth muscle cells to osteoblast-like cells. Pooled uremic serum can induce this transformation, but the mechanism by which it does so is not yet clear. Several mediators of inflammation such as oxidation, carbonyl stress, C-reactive protein, and cytokines may directly stimulate vascular calcification. In addition, inflammation itself reduces fetuin-A, a naturally occurring inhibitor of vascular calcification which binds excess mineral in serum. The combination of the acceleration of vascular calcification together with impaired defense mechanisms creates a uremic milieu primed for extra-osseous calcification.

Why Do Dialysis Patients Develop a Heart of Stone and Bone of China?

Vascular calcification is a common complication of end-stage renal disease (ESRD). The mechanisms responsible are complex and have so far been considered to be mainly the result of a passive mechanism due to elevated PO(4) levels and high Ca x PO(4) ion product resulting in saturated plasma. However, recent results suggest that also other features, commonly observed in the uremic milieu, such as chronic inflammation, hyperleptinemia and a dysregulation of various mineral-regulating proteins might also contribute to an enhanced calcification process. Moreover, as an inverse relationship between vascular calcification and bone density has been documented in ESRD, it could be speculated that pathologically low bone remodelling (adynamic bone disease) associated with active vitamin D treatment and low parathyroid hormone (PTH) levels may predispose to ectopic calcification of vessels, valves and heart. As patients with vascular calcification have a higher intake of calcium-containing PO(4) binders, novel, non-calcium containing PO(4) binders may diminish the risk of progressive vascular calcification in this patient group. Further studies are needed to elucidate the respective role of chronic inflammation, hyperleptinemia and PTH-lowering therapies in this fatal complication of ESRD.

Preventive effect of Abelmoschus manihot (L.) Medik. on bone loss in the ovariectomised rats

Because the biggest culprit in pathogenesis of osteoporosis is oestrogen deficiency, hormone replacement therapy remained the mainstay for prevention. However most of postmenopausal women are more inclined to use natural alternative. We thus investigated the ability of Abelmoschus manihot, a herbal medicine to prevent bone loss in ovariectomised rats. Female Wistar rats were sham operated (SH: 8) or ovariectomised (OVX: 24). On day 0, OVX rats were randomly assigned to groups as follows: eight received 10% Abelmoschus manihot leaves in their diet, eight were given 15% Abelmoschus manihot leaves and eight were untreated (OVX). Compounds were mixed with a soy protein-free diet and given orally for 3 months. At necropsy, bone mineral density (BMD) in the femur and in its metaphyseal zone was lower in OVX than SH (p<0.05). This osteopenia was prevented by consumption of the highest dose of Abelmoschus manihot leaves. Bone mineral content (BMC) in the total femur and its metaphyseal and diaphyseal subregions was improved, as well (p<0.05). This could be explained by a trend towards decreased bone resorption. The lowest dose did not elicit any significant effect. In conclusion, Abelmoschus manihot consumption, at the dose of 15% in the diet, provided bone-sparing effects by improving both BMD and BMC.

Reactive Oxygen Species Stimulates Receptor Activator of NF-κB Ligand Expression in Osteoblast

It has been established that reactive oxygen species (ROS) such as H2O2 or superoxide anion is involved in bone loss-related diseases by stimulating osteoclast differentiation and bone resorption and that receptor activator of NF-kappaB ligand (RANKL) is a critical osteoclastogenic factor expressed on stromal/osteoblastic cells. However, the roles of ROS in RANKL expression and signaling mechanisms through which ROS regulates RANKL genes are not known. Here we report that increased intracellular ROS levels by H2O2 or xanthine/xanthine oxidase-generated superoxide anion stimulated RANKL mRNA and protein expression in human osteoblast-like MG63 cell line and primary mouse bone marrow stromal cells and calvarial osteoblasts. Further analysis revealed that ROS promoted phosphorylation of cAMP response element-binding protein (CREB)/ATF2 and its binding to CRE-domain in the murine RANKL promoter region. Moreover, the results of protein kinase A (PKA) inhibitor KT5720 and CREB1 RNA interference transfection clearly showed that PKA-CREB signaling pathway was necessary for ROS stimulation of RANKL in mouse osteoblasts. In human MG63 cells, however, we found that ROS promoted heat shock factor 2 (HSF2) binding to heat shock element in human RANKL promoter region and that HSF2, but not PKA, was required for ROS up-regulation of RANKL as revealed by KT5720 and HSF2 RNA interference transfection. We also found that ROS stimulated phosphorylation of extracellular signal-regulated kinases (ERKs) and that PD98059, the inhibitor for ERKs suppressed ROS-induced RANKL expression either in mouse osteoblasts or in MG63 cells. These results demonstrate that ROS stimulates RANKL expression via ERKs and PKA-CREB pathway in mouse osteoblasts and via ERKs and HSF2 in human MG63 cells.

Platelets can neutralize hydrogen peroxide in an acute toxicity model with cells involved in granulation tissue formation

Platelets play a key role in the replacement of the blood clot with granulation tissue during the early steps of bone regeneration. We hypothesized that activated platelets can neutralize locally produced reactive oxygen species, thereby protecting cells involved in granulation tissue formation. The potential of platelet-released supernatant (PRS) to neutralize hydrogen peroxide (H(2)O(2)) was tested in an acute toxicity model with osteogenic, inflammatory, and endothelial cells. In the human fetal osteoblastic cell line 1.19 (hFOB), considerable morphological changes, cell shedding, and dysfunction of the respiratory chain were observed when cells were exposed to 3 mM H(2)O(2). Caspase-3 and poly-(ADP-ribose)-polymerase were not activated, suggesting that cell death occurred by necrosis. Preincubation of osteogenic cells, leukocytes, or endothelial cells with PRS decreased the acute toxicity of H(2)O(2). The capacity of platelets to release H(2)O(2)-detoxifying activity was retained for up to 72 h. Aminotriazole, an inhibitor of catalase, decreased the cytoprotective activity of PRS, whereas blocking of glutathione peroxidase by mercaptosuccinate had no effect. These results suggest that platelet-released catalase can rapidly neutralize cytotoxic amounts of H(2)O(2), a process that may play a role during the early stages of bone regeneration.

Vascular ossification-calcification in metabolic syndrome, type 2 diabetes mellitus, chronic kidney disease, and calciphylaxis-calcific uremic arteriolopathy: the emerging role of sodium thiosulfate

Background

Vascular calcification is associated with metabolic syndrome, diabetes, hypertension, atherosclerosis, chronic kidney disease, and end stage renal disease. Each of the above contributes to an accelerated and premature demise primarily due to cardiovascular disease. The above conditions are associated with multiple metabolic toxicities resulting in an increase in reactive oxygen species to the arterial vessel wall, which results in a response to injury wound healing (remodeling). The endothelium seems to be at the very center of these disease processes, acting as the first line of defense against these multiple metabolic toxicities and the first to encounter their damaging effects to the arterial vessel wall.

Results

The pathobiomolecular mechanisms of vascular calcification are presented in order to provide the clinician – researcher a database of knowledge to assist in the clinical management of these high-risk patients and examine newer therapies. Calciphylaxis is associated with medial arteriolar vascular calcification and results in ischemic subcutaneous necrosis with vulnerable skin ulcerations and high mortality. Recently, this clinical syndrome (once thought to be rare) is presenting with increasing frequency. Consequently, newer therapeutic modalities need to be explored. Intravenous sodium thiosulfate is currently used as an antidote for the treatment of cyanide poisioning and prevention of toxicities of cisplatin cancer therapies. It is used as a food and medicinal preservative and topically used as an antifungal medication.

Conclusion

A discussion of sodium thiosulfate's dual role as a potent antioxidant and chelator of calcium is presented in order to better understand its role as an emerging novel therapy for the clinical syndrome of calciphylaxis and its complications.

Données nouvelles sur la prévention nutritionnelle de l’ostéoporose

With the human race experiencing a progressive increase in life expectancy, we are facing a growing prevalence of chronic age-related conditions, among which osteoporosis is a generalised condition of bone, whose hallmark is increased bone fragility. Based on the overwhelming body of evidence emphasising that gonadal failure at the time of menopause causes osteopenia and the administration of estrogens in postmenopausal women prevents this loss, hormone replacement therapy (HRT) has been widely recommended. However HRT should be limited due to its potential adverse effects. In this light, an effort should be made to integrate alternative therapies of proven values to provide new options for women in midlife. Research in nutrition over the past 30 years has led to exciting and significant progress. Although the primary role of diet is to provide sufficient nutrients to fulfill the metabolic requirements of an individual, there is an emerging rationale to support the hypothesis that, by modulating specific target functions in the body, diet can help to achieve optimal health and also play an important role in reducing the risk of disease. Specifically, it has been recognized that human diet contains, in addition to essential macro- and micronutrients, a complex array of naturally occurring bioactive molecules, the phytochemicals, that may confer significant long-term health benefits. Indeed, besides calcium, micronutrients such as vitamins, polyphenols, phytoestrogens, trace elements or minerals remain a source for putative new and innovative dietary health intervention in the nutritional prevention of osteoporosis.

Spatial heterogeneity of endothelial phenotypes correlates with side-specific vulnerability to calcification in normal porcine aortic valves

Calcific aortic valve sclerosis involves inflammatory processes and occurs preferentially on the aortic side of endothelialized valve leaflets. Although the endothelium is recognized to play critical roles in focal vascular sclerosis, the contributions of valvular endothelial phenotypes to aortic valve sclerosis and side-specific susceptibility to calcification are poorly understood. Using RNA amplification and cDNA microarrays, we identified 584 genes as differentially expressed in situ by the endothelium on the aortic side versus ventricular side of normal adult pig aortic valves. These differential transcriptional profiles, representative of the steady state in vivo, identify globally distinct endothelial phenotypes on opposite sides of the aortic valve. Several over-represented biological classifications with putative relevance to endothelial regulation of valvular homeostasis and aortic-side vulnerability to calcification were identified among the differentially expressed genes. Of note, multiple inhibitors of cardiovascular calcification were significantly less expressed by endothelium on the disease-prone aortic side of the valve, suggesting side-specific permissiveness to calcification. However, coexisting putative protective mechanisms were also expressed. Specifically, enhanced antioxidative gene expression and the lack of differential expression of proinflammatory molecules on the aortic side may protect against inflammation and lesion initiation in the normal valve. These data implicate the endothelium in regulating valvular calcification and suggest that spatial heterogeneity of valvular endothelial phenotypes may contribute to the focal susceptibility for lesion development.

Impact of inflammation and oxidative stress on vascular calcifications in chronic kidney disease

Vascular and/or valvular calcifications in patients with chronic kidney disease (CKD) appear to indicate a poor prognosis in terms of overall survival and cardiovascular morbidity and mortality. Inflammation and oxidative stress represent new features of the arterial and/or valvular calcification process. However, only limited observational and epidemiological data are available in these areas. Therefore, the link between inflammation, oxidation and vascular and/or valvular calcifications deserves careful consideration in CKD patients, since they may become targets for the development of new therapeutic strategies.

Oxidative stress and vascular permeability in steroid-induced osteonecrosis model

We focused on the role of oxidative stress in the pathogenesis of steroid-induced osteonecrosis (ON) and the possibility of preventing this condition by antioxidant administration. Methylprednisolone 4 mg/kg was injected only once into Japanese white rabbits. The involvement of oxidative stress and the presence/absence of bone circulatory impairment were investigated in groups of 10 rabbits killed at 3, 5, and 14 days each and in 10 rabbits administered the antioxidant glutathione. Reduced blood glutathione and lipid peroxide levels were determined biochemically, and the presence/absence of advanced glycation end-product expression was determined immunohistochemically. Vascular permeability in bone was confirmed by finding albumin leakage into the stroma. These blood biochemical and immunohistochemical studies clarified that the oxidative stress in this model developed 3-5 days after steroid administration. Elevated vascular permeability was observed in the 5- and 14-day groups. Hence, circulatory disturbance in bone was noted 5 days after steroid administration, coinciding with the onset of oxidative stress. The rate of ON development, which was 70% in the steroid-alone 14-day group, was significantly reduced to 0% in the steroid + antioxidant group. These results suggest the involvement of oxidative stress and vascular permeability in this steroid-induced ON model and the possibility of its prevention by suppression of oxidative stress.

Oxidative stress and nutritional prevention in autoimmune rheumatic diseases

The hypothesis that oxidative stress favours flogistic and immune processes inducing autoimmune rheumatic diseases (ARDs) and their complications is still under discussion. In this review we take into consideration both the aetiopathological role of the diet in such diseases and the possible efficacy of dietary supports as adjuvants for the usual specific therapies. Moreover, we shall examine the hypothetical pathophysiological role of oxidative stress on ARDs and their complications, the methods for its evaluation and the possibility of intervening on oxidative pathways by means of nutritional modulation. It is possible that in the future we will be able to control connective pathology by associating an immuno-modulating therapy ('re-educating') with natural products having an anti-oxidant activity to current immunosuppressive treatment (which has potentially toxic effects).

The influence of 4-hydroxy-2-nonenal on proliferation, differentiation and apoptosis of human osteosarcoma cells

The product of lipid peroxidation, 4-hydroxy-2-nonenal (HNE) is known to cause cell death at high concentrations, while at lower concentrations it can influence cell proliferation and differentiation. In our experiments we used human osteosarcoma cells (HOS), to test the influence of HNE on cell proliferation, differentiation and induction of apoptosis. Apoptosis induction was estimated by TiterTACS TUNEL test. The cells were in parallel counted and the DAPI staining method was used to distinguish between apoptotic and necrotic cells as well as to define the proportion of cells in mitosis. To test the influence of HNE on HOS cell differentiation, cells were treated every second day with HNE. After 10 days, the cells were stained for alkaline phosphatase, a marker for osteoblast differentiation. Cell growth inhibition was caused by supraphysiological concentrations of 10 or 100 microM HNE, while apoptosis was induced with supraphysiological as well as by the physiological amount of the aldehyde (1 microM). Necrosis appeared when cells were treated with 10 or 100 microM, but not with 1 microM HNE. The proportion of cells in mitosis gradually declined with increased HNE concentration. Multiple exposures of HOS cells to 10 microM HNE prevented HOS cell differentiation. These results indicated that HNE inhibits proliferation and differentiation of HOS cells in the same concentration dependent manner as it causes apoptosis. We thus assume that HNE might be one of the important signaling molecules regulating the growth of the human osteosarcoma cells.

Biochanin A Stimulates Osteoblastic Differentiation and Inhibits Hydrogen Peroxide-Induced Production of Inflammatory Mediators in MC3T3-E1 Cells

Phytoestrogens are plant chemicals that are structurally analogous to estrogen and are known to affect estrogenic activity. Biochanin A, a naturally occurring isoflavone, has been identified and detected in various diets and plant species. We examined the effects of biochanin A on the differentiation of osteoblastic MC3T3-E1 cells and the production of local factors in osteoblasts. Biochanin A (1-50 microM) caused a significant elevation of cell growth, alkaline phosphatase (ALP) activity, collagen content, and osteocalcin secretion in osteoblastic MC3T3-E1 cells (p<0.05). The effect of biochanin A (10 microM) in increasing ALP activity and collagen content was completely prevented by the presence of 10(-6) M cycloheximide and 10(-6) M tamoxifen, suggesting that biochanin A's effect results from a newly synthesized protein component and might be partly involved in estrogen action. We then examined the effect of biochanin A on the H2O2-induced production of inflammatory mediators in osteoblasts. Biochanin A (1-10 microM) decreased the 0.2 mM H2O2-induced production of TNF-alpha, IL-6 and NO in osteoblasts. These results suggest that biochanin A may be useful as potential phytoestrogens, which play important physiological roles in the prevention of postmenopausal osteoporosis.

Tumor necrosis factor-alpha mediates osteopenia caused by depletion of antioxidants

We recently found that estrogen deficiency leads to a lowering of thiol antioxidant defenses in rodent bone. Moreover, administration of agents that increase the concentration in bone of glutathione, the main intracellular antioxidant, prevented estrogen-deficiency bone loss, whereas depletion of glutathione by buthionine sulfoximine (BSO) administration provoked substantial bone loss. It has been shown that the estrogen-deficiency bone loss is dependent on TNFalpha signaling. Therefore, a model in which estrogen deficiency causes bone loss by lowering antioxidant defenses predicts that the osteopenia caused by lowering antioxidant defenses should similarly depend on TNFalpha signaling. We found that the loss of bone caused by either BSO administration or ovariectomy was inhibited by administration of soluble TNFalpha receptors and abrogated in mice deleted for TNFalpha gene expression. In both circumstances, lack of TNFalpha signaling prevented the increase in bone resorption and the deficit in bone formation that otherwise occurred. Thus, depletion of thiol antioxidants by BSO, like ovariectomy, causes bone loss through TNFalpha signaling. Furthermore, in ovariectomized mice treated with soluble TNFalpha receptors, thiol antioxidant defenses in bone remained low, despite inhibition of bone loss. This suggests that the low levels of antioxidants in bone seen after ovariectomy are the cause, rather than the effect, of the increased resorption. These experiments are consistent with a model for estrogen-deficiency bone loss in which estrogen deficiency lowers thiol antioxidant defenses in bone cells, thereby increasing reactive oxygen species levels, which in turn induce expression of TNFalpha, which causes loss of bone.

Regulation of human osteoclast differentiation by thioredoxin binding protein-2 and redox-sensitive signaling

Differential expression of TBP-2 and Trx-1 occurs during osteoclastogenesis. Adenoviral overexpression of TBP-2 in osteoclast precursors inhibits Trx-1 expression, osteoclast formation, and AP-1 binding activity. TBP-2 and Trx-1 are key regulators of osteoclastogenesis.

INTRODUCTION

Thioredoxin binding protein-2 (TBP-2) negatively regulates thioredoxin-1 (Trx-1), a key endogenous modulator of cellular redox and signaling. In gene array analysis, we found that TBP-2 expression was reduced during human osteoclast differentiation compared with macrophage differentiation. Our aim was to determine the roles of TBP-2 and Trx-1 in human osteoclastogenesis and RANKL signaling.

MATERIALS AND METHODS

Osteoclasts or macrophages were generated from colony-forming unit-granulocyte macrophage (CFU-GM) precursors treated with sRANKL and macrophage-colony-stimulating factor (M-CSF), or M-CSF alone, respectively. Expression of TBP-2 and Trx-1 was quantified by real-time PCR and Western analysis. Adenoviral gene transfer was used to overexpress TBP-2 in precursors. NF-kappaB and activator protein 1 (AP-1) signaling was assessed with EMSA.

RESULTS

In the presence of sRANKL, expression of TBP-2 was decreased, whereas Trx-1 expression was increased. The antioxidant N-acetylcysteine reversed this pattern and markedly inhibited osteoclastogenesis. Adenoviral overexpression of human TBP-2 in precursors inhibited osteoclastogenesis and Trx-1 expression, inhibited sRANKL-induced DNA binding of AP-1, but enhanced sRANKL-induced DNA binding of NF-kappaB.

CONCLUSIONS

These data support significant roles for TBP-2 and the Trx system in osteoclast differentiation that are mediated by redox regulation of AP-1 transcription. A likely mechanism of stress signal induction of bone resorption is provided. Modulators of the Trx system such as antioxidants have potential as antiresorptive therapies.

Strategies for directing the differentiation of stem cells into the osteogenic lineage in vitro

A major area in regenerative medicine is the application of stem cells in bone reconstruction and bone tissue engineering. This will require well-defined and efficient protocols for directing the differentiation of stem cells into the osteogenic lineage, followed by their selective purification and proliferation in vitro. The development of such protocols would reduce the likelihood of spontaneous differentiation of stem cells into divergent lineages on transplantation, as well as reduce the risk of teratoma formation in the case of embryonic stem cells. Additionally, such protocols could provide useful in vitro models for studying osteogenesis and bone development, and facilitate the genetic manipulation of stem cells for therapeutic applications. The development of pharmokinetic and cytotoxicity/genotoxicity screening tests for bone-related biomaterials and drugs could also use protocols developed for the osteogenic differentiation of stem cells. This review critically examines the various strategies that could be used to direct the differentiation of stem cells into the osteogenic lineage in vitro.

Olive oil and its main phenolic micronutrient (oleuropein) prevent inflammation-induced bone loss in the ovariectomised rat

The present study was designed to evaluate the effect of olive oil and its main polyphenol (oleuropein) in ovariectomised rats with or without inflammation. Rats (6 months old) were ovariectomised or sham-operated as control. Ovariectomised rats were separated into three groups receiving different diets for 3 months: a control diet with 25 g peanut oil and 25 g rapeseed oil/kg (OVX), the control diet with 50 g olive oil/kg or the control diet with 0.15 g oleuropein/kg. The sham-operated group was given the same control diet as OVX. Inflammation was induced 3 weeks before the end of the experiment by subcutaneous injections of talc (magnesium silicate) in one-half of each group. The success of ovariectomy was verified at necropsy by the atrophy of uterine horns. Inflammation, oleuropein or olive oil intakes did not have any uterotrophic activity, as they had had no effect on uterus weight. The plasma concentration of alpha-1-acid glycoprotein (an indicator of inflammation) was increased in OVX rats with inflammation. With regard to bone variables, osteopenia in OVX was exacerbated by inflammation, as shown by a decrease in metaphyseal and total femoral mineral density. Both oleuropein and olive oil prevented this bone loss in OVX rats with inflammation. At necropsy, oleuropein and olive oil consumption had had no effect on plasma osteocalcin concentrations (marker of bone formation) or on urinary deoxypyridinoline excretion (marker of bone resorption). In conclusion, oleuropein and olive-oil feeding can prevent inflammation-induced osteopenia in OVX rats.

Relation of low bone mineral density and carotid atherosclerosis in postmenopausal women

Due to the lack of convincing data about the association between atherosclerosis and osteoporosis, we evaluated the association between carotid atherosclerosis and bone mineral density in a sample of apparently healthy postmenopausal women who underwent health-screening in our hospital. We also evaluated a bone turnover marker, osteocalcin; we divided the population into 2 groups according to osteocalcin levels. We found a high prevalence of carotid atherosclerosis in subjects with high osteocalcin levels and low bone mineral density.

Shockwave stimulates oxygen radical-mediated osteogenesis of the mesenchymal cells from human umbilical cord blood

Human umbilical cord blood (HUCB) mesenchymal progenitor cells expressed stro-1 or CD44 or CD29, and subsequently, differentiated toward osteogenic lineage. Physical shockwave treatment increased osteogenic activity of HUCB mesenchymal progenitor cells through superoxide-mediated TGF-beta1 induction. Transplantation of shockwave-treated HUCB mesenchymal progenitor cells enhanced healing of segmental femoral defect in severe combined immunodeficiency disease (SCID) mice.

INTRODUCTION

Mesenchymal progenitor cells (MPCs) in the bone marrow are precursors to bone development. It remains uncertain whether MPCs are present in human umbilical cord blood (HUCB) and are capable of differentiating into osteogenic cell lineage. Extending from a model of shockwave (SW) promotion of bone marrow stromal cell differentiation toward osteoprogenitors in rats, we further investigated how physical SW mediated biological responses in regulating osteogenic differentiation of HUCB MPCs.

MATERIALS AND METHODS

HUCB was subjected to SW treatment at different energy flux densities and impulses. Colony-forming units-stroma (CFU-Stroma), osteogenic activities (Cbfa1/Runx2 expression, bone alkaline phosphatase activity, and bone nodule formation), and bone formation by heterologous transplantation into SCID mice were assessed.

RESULTS

Few CD34+ stem cells (1.3%) and stro-1+ cells (1.0%) were present in the freshly prepared mononuclear cells (MNCs) from HUCB. The number of stro-1+ cells, but not CD34+, increased to 72.4% in the adherent cell culture over 6 days. Stro-1+ cells co-expressed CD44 and CD29 markers and grew into CFU-Stroma that matured into bone nodules. We found that the SW treatment (0.16 mJ/mm2 energy flux density, 200 impulses) elicited superoxide production and promoted formation of CFU-Stroma, but not of hematopoietic CFU-Mix. SW also enhanced the production of transforming growth factor (TGF)-beta1, but not of interleukin (IL)-3 or granulocyte monocyte-colony stimulating factor (GM-CSF). Neutralization of TGF-beta1 significantly reduced SW-promoted CFU-Stroma formation. Superoxide scavenging by superoxide dismutase blocked SW enhancement of TGF-beta1 production and formation of CFU-Stroma. Administration of SW-treated HUCB MPCs to SCID mice with femoral segmental defects facilitated dense, bridging callus and gap closure.

CONCLUSION

HUCB MPCs subjected to SW treatment is a potential source for stem cells useful in the treatment of orthopedic disorders. An optimal physical SW treatment enhanced osteogenesis through superoxide-mediated TGF-beta1 production. Physical stimulation is an alternative method for extending mesenchymal stem cells of HUCB.

Mitral annular calcification is associated with osteoporosis in women

BACKGROUND

Few studies have suggested association between mitral annular calcification (MAC) and osteoporosis in women who are post-menopausal. However, the association of MAC with osteoporosis in women, in relation to bone resorption, as assessed by using the dual-energy x-ray absorptiometry method (DEXA), have not been performed. We sought to examine the association between MAC and osteoporosis.

METHODS

In this prospective, observational study carried out in a tertiary referral center, 340 women (mean age +/- SD, 56 +/- 10 years; age range, 33-85 years) underwent echocardiography, with specific assessment of MAC and bone mineral density measurement (T-scores) using DEXA.

RESULTS

MAC was absent in 123 patients (group I) and present in 217 patients (group II). Compared with the control group, the group with MAC had a significantly higher prevalence and severity of osteoporosis (18.2% vs 55.5%, P <.001). Severe osteoporosis was significantly more common in the severe MAC subgroup (n = 66) than in the control subjects (65.2% vs 17.1%; Pearson chi2, 70.02; df = 4; P <.001). With multivariate analysis, only T-scores and age were highly predictive of MAC, with an odds ratio of 2.66 (95 % CI, 1.85-3.83) and 1.04 (95% CI, 1.01-1.07), respectively.

CONCLUSIONS

MAC is associated with osteoporosis. Bone mineral density measurement (T-scores) and age were highly predictive of MAC in women.

Osteogenic regulation of vascular calcification: an early perspective

Cardiovascular calcification is a common consequence of aging, diabetes, hypercholesterolemia, mechanically abnormal valve function, and chronic renal insufficiency. Although vascular calcification may appear to be a uniform response to vascular insult, it is a heterogenous disorder, with overlapping yet distinct mechanisms of initiation and progression. A minimum of four histoanatomic variants-atherosclerotic (fibrotic) calcification, cardiac valve calcification, medial artery calcification, and vascular calciphylaxis-arise in response to metabolic, mechanical, infectious, and inflammatory injuries. Common to the first three variants is a variable degree of vascular infiltration by T cells and macrophages. Once thought benign, the deleterious clinical consequences of calcific vasculopathy are now becoming clear; stroke, amputation, ischemic heart disease, and increased mortality are portended by the anatomy and extent of calcific vasculopathy. Along with dystrophic calcium deposition in dying cells and lipoprotein deposits, active endochondral and intramembranous (nonendochondral) ossification processes contribute to vascular calcium load. Thus vascular calcification is subject to regulation by osteotropic hormones and skeletal morphogens in addition to key inhibitors of passive tissue mineralization. In response to oxidized lipids, inflammation, and mechanical injury, the microvascular smooth muscle cell becomes activated. Orthotopically, proliferating stromal myofibroblasts provide osteoprogenitors for skeletal growth and fracture repair; however, in valves and arteries, vascular myofibroblasts contribute to cardiovascular ossification. Current data suggest that paracrine signals are provided by bone morphogenetic protein-2, Wnts, parathyroid hormone-related polypeptide, osteopontin, osteoprotegerin, and matrix Gla protein, all entrained to endocrine, metabolic, inflammatory, and mechanical cues. In end-stage renal disease, a "perfect storm" of vascular calcification often occurs, with hyperglycemia, hyperphosphatemia, hypercholesterolemia, hypertension, parathyroid hormone resistance, and iatrogenic calcitriol excess contributing to severe calcific vasculopathy. This brief review recounts emerging themes in the pathobiology of vascular calcification and highlights some fundamental deficiencies in our understanding of vascular endocrinology and metabolism that are immediately relevant to human health and health care.

Oxidative stress inhibits osteoblastic differentiation of bone cells by ERK and NF-kappaB

Signaling pathways involved in oxidative stress-induced inhibition of osteoblast differentiation are not known. We showed in this report that H(2)O(2) (0.1-0.2mM)-induced oxidative stress suppressed the osteoblastic differentiation process of primary rabbit bone marrow stromal cells (BMSC) and calvarial osteoblasts, manifested by a reduction of differentiation markers including alkaline phosphatase (ALP), type I collagen, colony-forming unit-osteoprogenitor (CFU-O) formation, and nuclear phosphorylation of Runx2. H(2)O(2) treatment stimulated phospholipase C-gamma1 (PLC-gamma1), extracellular signal-regulated kinase 1/2 (ERK1/2), and NF-kappaB signaling but inhibited p38 mitogen-activated protein kinase (MAPK) activation. In the presence of 20microM PD98059 or 50microM caffeic acid phenethyl ester (CAPE), specific inhibitor for ERKs or NF-kappaB, respectively, could significantly reverse the decrease of above-mentioned osteoblastic differentiation markers elicited by H(2)O(2) (0.1mM). Furthermore, PD98059 also suppressed H(2)O(2)-stimulated NF-kappaB signaling in this process. These data suggest that ERK and ERK-dependent NF-kappaB activation is required for oxidative stress-induced inhibition of osteoblastic differentiation in rabbit BMSC and calvarial osteoblasts.

Regulation of cardiovascular calcification

Vascular calcification is highly correlated with cardiovascular disease (CVD) and is a significant predictor of cardiovascular events, especially in high risk patients such as the end stage renal disease (ESRD) population. Vascular calcification can lead to serious problems including valve stenosis, decreased vascular compliance, calciphylaxis, and even sudden death. However, the contribution of vascular calcification to progression of atherosclerosis is unknown and needs more study. Biochemical, histological, and genetic studies indicate that vascular calcification is actively regulated and involves both positive and negative modulators. Several nonmutually exclusive theories to account for vascular calcification based on current studies are discussed.

Osteoporosis and cardiovascular disease: brittle bones and boned arteries, is there a link?

Both osteoporosis and cardiovascular disease (CVD) are major public health problems leading to increased morbidity and mortality. Although traditionally viewed as separate disease entities that increase in prevalence with aging, accumulating evidence indicates that there are similar pathophysiological mechanisms underlying both diseases. In addition to menopause and advanced age, other risk factors for CVD such as dyslipidemia, oxidative stress, inflammation, hyperhomocystinemia, hypertension, and diabetes have also been associated with increased risk of low bone mineral density (LBMD). Elevated LDL and low HDL cholesterol are associated with LBMD, altered lipid metabolism is associated with both bone remodeling and the atherosclerotic process, which might explain, in part, the co-existence of osteoporosis and atherosclerosis in patients with dyslipidemia. Similarly, inflammation plays a pivotal role in both atherosclerosis and osteoporosis. Elevated plasma homocysteine levels are associated with both CVD and osteoporosis. Nitric oxide (NO), in addition to its known atheroprotective effects, appears to also play a role in osteoblast function and bone turnover. Supporting this notion, in a small randomized controlled trial, nitroglycerine (an NO donor) was found to be as effective as estrogen in preventing bone loss in women with surgical menopause. Statins, agents that reduce atherogenesis, also stimulate bone formation. Furthermore, bis- phosphonates, used in the treatment of osteoporosis, have been shown to inhibit atherogenesis. Intravenous bisphosphonate therapy significantly decreases serum LDL and increases HDL in postmenopausal women The exciting possibilities of newer pharmacological agents that effectively treat both osteoporosis and CVD hold considerable promise. However, it is important to emphasize that the current evidence linking both of these diseases is far from conclusive. Therefore, additional research is necessary to further characterize the relationship between these two common illnesses.

Lycopene II--effect on osteoblasts: the carotenoid lycopene stimulates cell proliferation and alkaline phosphatase activity of SaOS-2 cells

We explored the possibility that lycopene, a carotenoid that is abundant in tomatoes, has effects on proliferation and differentiation of osteoblasts, the cells responsible for bone formation. Human osteoblast-like osteosarcoma SaOS-2 cells were cultured for 24 hours, after which varying doses of a water-dispersible microemulsion preparation of lycopene or vehicle of the same dilution were added. The cells were further cultured for 24 to 144 hours, and then the cell numbers were counted. Lycopene at 10(-6) and 10(-5) M had significant stimulatory effects on cell numbers, compared with the corresponding vehicle treatment, at all time points from 24 to 144 hours. The effects of lycopene on activity of the differentiation marker alkaline phosphatase activity in the absence or presence of dexamethasone were shown to be dependent on the stage of cell differentiation. This is the first report on the effects of lycopene on osteoblasts of human origin; the results may have important applications in the prevention of osteoporosis.

A crucial role for thiol antioxidants in estrogen-deficiency bone loss

The mechanisms through which estrogen prevents bone loss are uncertain. Elsewhere, estrogen exerts beneficial actions by suppression of reactive oxygen species (ROS). ROS stimulate osteoclasts, the cells that resorb bone. Thus, estrogen might prevent bone loss by enhancing oxidant defenses in bone. We found that glutathione and thioredoxin, the major thiol antioxidants, and glutathione and thioredoxin reductases, the enzymes responsible for maintaining them in a reduced state, fell substantially in rodent bone marrow after ovariectomy and were rapidly normalized by exogenous 17-beta estradiol. Moreover, administration of N-acetyl cysteine (NAC) or ascorbate, antioxidants that increase tissue glutathione levels, abolished ovariectomy-induced bone loss, while l-buthionine-(S,R)-sulphoximine (BSO), a specific inhibitor of glutathione synthesis, caused substantial bone loss. The 17-beta estradiol increased glutathione and glutathione and thioredoxin reductases in osteoclast-like cells in vitro. Furthermore, in vitro NAC prevented osteoclast formation and NF-kappaB activation. BSO and hydrogen peroxide did the opposite. Expression of TNF-alpha, a target for NF-kappaB and a cytokine strongly implicated in estrogen-deficiency bone loss, was suppressed in osteoclasts by 17-beta estradiol and NAC. These observations strongly suggest that estrogen deficiency causes bone loss by lowering thiol antioxidants in osteoclasts. This directly sensitizes osteoclasts to osteoclastogenic signals and entrains ROS-enhanced expression of cytokines that promote osteoclastic bone resorption.

Effects of adrenomedullin, C-type natriuretic peptide, and parathyroid hormone-related peptide on calcification in cultured rat vascular smooth muscle cells

To clarify the regulating mechanism of vascular calcification, the investigators observed the effects of three vasoactive peptides, adrenomedullin (ADM), C-type natriuretic peptide (CNP), and parathyroid hormone-related peptide (PTHrP) on calcification in rat vascular smooth muscle cells (VSMCs). Beta-glycerophosphate stimulated growth and calcification in VSMCs. Adrenomedullin and CNP lowered beta-glycerophosphate-induced increase in VSMC growth. All three vasoactive peptides attenuated the increases of 45Ca accumulation, calcium content, and alkaline phosphatase activity in calcified VSMCs. As for comparing the inhibitory effects, the strongest was PTHrP. Both ADM and PTHrP increased cyclic adenosine monophosphate (cAMP) content in calcified VSMCs, but CNP upregulated cyclic guanosine monophosphate (cGMP) content. The PKA inhibitor PKAI completely reversed the inhibition of ADM on cell growth and all inhibitory effects of PTHrP on the parameters of calcification. The PKG inhibitor H8, however, strongly antagonized all the inhibitory effects of CNP on calcification. These data suggested that beta-glycerophosphate-induced calcification in VSMCs was inhibited by ADM, CNP, and PTHrP. Adrenomedullin and PTHrP inhibited VSMC calcification partially through the cAMP/PKA pathway, whereas CNP inhibited VSMC calcification through the cGMP/PKG pathway. This study could be of help in understanding the pathogenesis of vascular calcification, and providing new target for clinical treatment of cardiovascular diseases associated with vascular calcification.

Growth and cellular differentiation: a physico-biochemical conundrum? The example of the hand

Currently, the predominant hypothesis explains cellular differentiation as an essentially genetic intracellular process. The goal of this paper is to suggest that cell growth and differentiation may be, simply, the result of physical and chemical constraints. Bone growth occurs at the level of cartilage conjunction (growth plate) in a zone of lesser constrain. It appears that this growth also induces muscle, tendon, nerve and skin elongation. This cartilage growth by itself seems to explain the elongation of the hand. Growth stops at puberty likely because of feed-back from an increasing muscle load. The ossification (that is differentiation of cartilage into bone) appears to result from the shear stress induced. The study of bone age, obtained by X-ray picture of the hand, shows that ossification of epiphyses is very precise both in time and space. Computer modelization suggests that this ossification occurs where shear stress is greatest. The cartilage which does not ossify (joint, nose, larynx, ear, bronchus, etc.) is not exposed to high shear. Shear stress induces the secretion of extracellular matrix and a change of the biochemical environment of the cell. Precipitation of calcium phosphate, as in ossification, seems related to the alkalosis induced by shear stress. To speak in more general terms, loss of cellular differentiation, as occurs with cancer, can result from a change in the physical-chemical environments.

Possible role of oxidized lipids in osteoporosis: could hyperlipidemia be a risk factor?

Several years ago we hypothesized that products of lipid and lipoprotein oxidation may contribute to pathophysiology of osteoporosis (F. Parhami, Curr. Opin. Lipidol. 8 (1997) 312), and that their effects on artery wall and bone cells may explain the parallel development of osteoporosis and atherosclerosis in the same subjects (R. Boukhris, JAMA 219 (1972) 1307; M.A. Frye, Bone Miner. 19 (1992) 185). Since then, new evidence has accumulated in support of this hypothesis and its possibility is being further tested by investigators in both vascular and bone fields (A.D. Watson, J. Biol. Chem. 272 (1997) 13597). This review will summarize the evidence to date that support the role of oxidized lipids in osteoporosis, and will address some of the issues that need further examination in order to establish whether hyperlipidemia and susceptibility to lipid oxidation may serve as risk factors for osteoporosis.

Lovastatin stimulates human vascular smooth muscle cell expression of bone morphogenetic protein-2, a potent inhibitor of low-density lipoprotein-stimulated cell growth

Bone morphogenetic proteins (BMPs) stimulate ectopic bone formation in skeletal muscle. Here we show that human vascular smooth muscle cells (VSMC) abundantly express mRNA encoding for BMP receptor type II, BMP-2, and BMP-7 proteins. Treatment with the 3-hydroxy-3-methylglutaryl coenzyme A inhibitor lovastatin (34 microM) increased BMP-2 gene transcription >14-fold as measured by real-time PCR analysis (P<0.05 vs. solvent control). Moreover, VSMC proliferation stimulated with native low-density lipoprotein (100 microg of protein/mL) was prevented by either human recombinant BMP-2 or BMP-7 at concentrations of 100 ng/mL (P<0.05). Both BMPs also inhibited basal cell proliferation (P<0.05). Induction of BMPs and subsequent inhibition of VSMC growth and/or induction of vascular bone formation could contribute to the mechanisms by which statins increase plaque stability in patients with coronary atherosclerosis.

Role of the cholesterol biosynthetic pathway in osteoblastic differentiation of marrow stromal cells

Cholesterol is an important molecule that plays a key role in regulating cellular differentiation and function. Although the possible role of lipids has been implicated in regulating osteoblastic cells, the role of cholesterol in that process is not well defined. In this study we have examined the role of the cellular cholesterol biosynthetic pathway on osteoblastic differentiation of marrow stromal cells (MSCs). Treatment of pluripotent mouse MSCs M2-10B4 with inhibitors of the cholesterol biosynthetic pathway mevastatin or mevinolin inhibited the maturation of these cells into functional osteoblastic cells. This was determined by the inhibition of the activity and expression of alkaline phosphatase (ALP), a key enzyme involved in differentiation and mineralization of osteoblastic cell cultures, as well as inhibition of mineralization. Mevastatin treatment did not affect expression of the osteoblast-specific gene osteocalcin (OCN). Furthermore, promoter-reporter studies in MSCs showed that mevastatin inhibited activity of the ALP gene promoter, suggesting regulation by derivatives of the cholesterol biosynthetic pathway. The effects of mevastatin and mevinolin were reversed by mevalonate but not by geranylgeraniol or farnesol, intermediates in the cholesterol biosynthetic pathway. Altogether, these results suggest that products of the cholesterol biosynthetic pathway are important for proper development of MSCs into functional osteoblastic cells capable of forming a mineralized matrix. Identification of those molecules may provide new therapeutic approaches to prevent the decline in osteoblastic activity in osteoporosis and aging.

Novel mechanisms in accelerated vascular calcification in renal disease patients

PURPOSE OF REVIEW

Vascular calcification occurs more often and earlier in patients with end-stage renal disease than in normal controls. It is a regulated biological process following many of the cellular and molecular programs in osteogenesis. This review summarizes some of the regulatory mechanisms that may explain its severity in renal patients.

RECENT FINDINGS

A subpopulation of cells from arteries and cardiac valves produce a mineralizing matrix and undergo osteoblastic differentiation. Osteogenic differentiation regulators are found in calcified but not normal arteries. Phosphate levels have dramatic effects on vascular calcification in vitro, through a sodium phosphate transporter signaling molecular changes. Atherogenic oxidized lipids promote osteoblastic differentiation of vascular cells and inhibit bone mineralization. In uremic patients, the severity of dyslipidemia corresponds with the progression of vascular calcification. Oxidative stress and inflammatory mediators may underlie the effects of oxidized lipids. In dialysis patients, the degree of cardiac valvular calcification corresponds with levels of C-reactive protein. Genetic factors may also contribute. Polymorphisms of the inflammatory adhesion molecule, E-selectin, associate with coronary calcification in young women. Mice deficient in matrix GLA protein, which inhibits bone morphogenetic protein activity, develop complete ossification of the aorta, presumably as a result of unopposed osteogenic activity on vascular mesenchyme. Since matrix GLA protein function requires gamma-carboxylation of its glutamate residues by a vitamin K dependent carboxylase, warfarin treatment may affect vascular calcification by blocking vitamin K and hence matrix GLA protein activity.

SUMMARY

These findings indicate that vascular calcification is regulated both positively and negatively by a wide variety of mechanisms affecting patients with renal disease.

Monocyte/macrophage regulation of vascular calcification in vitro

BACKGROUND

Calcification is a common complication of atherosclerosis and other chronic inflammatory processes that involves infiltration of monocytes and accumulation of macrophages.

METHODS AND RESULTS

To determine whether these cells modulate vascular calcification in vitro, calcifying vascular cells (CVCs), a subpopulation of osteoblast-like cells derived from the artery wall, were cocultured with human peripheral blood monocytes for 5 days. Results showed that alkaline phosphatase (ALP) activity, a marker of osteoblastic differentiation, was significantly greater in cocultures than in cultures of CVCs or monocytes alone. Both ALP activity and matrix mineralization increased in proportion to the number of monocytes added. Activation of monocyte/macrophages (M/Ms) by oxidized LDL further increased ALP activity in cocultures. However, neither conditioned medium from oxidized-LDL-activated M/Ms or transwell coculture had this effect on CVCs, which suggests a need for cell-to-cell contact. In contrast, conditioned medium from lipopolysaccharide-activated M/Ms increased ALP activity of CVCs. ELISA showed that lipopolysaccharide-activated M/Ms secreted tumor necrosis factor-alpha, and neutralizing antibody to tumor necrosis factor-alpha attenuated the induction of ALP activity by the conditioned media.

CONCLUSIONS

These results suggest that M/Ms enhance in vitro vascular calcification via 2 independent mechanisms: cell-cell interaction and production of soluble factors such as tumor necrosis factor-alpha.