Mechanisms of Pathologic Calcification

Long noncoding RNA MALAT1 mediates fibrous topography-driven pathologic calcification through trans-differentiation of myoblasts

Prosthesis-induced pathological calcification is a significant challenge in biomaterial applications and is often associated with various reconstructive medical procedures. It is uncertain whether the fibrous extracellular matrix (ECM) adjacent to biomaterials directly triggers osteogenic trans-differentiation in nearby cells. To investigate this possibility, we engineered a heterogeneous polystyrene fibrous matrix (PSF) designed to mimic the ECM. Our findings revealed that the myoblasts grown on this PSF acquired osteogenic properties, resulting in mineralization both in vitro and in vivo. Transcriptomic analyses indicated a notable upregulation in the expression of the long noncoding RNA metastsis-associated lung adenocarcinoma transcript 1 (Malat1) in the C2C12 myoblasts cultured on PSF. Intriguingly, silencing Malat1 curtailed the PSF-induced mineralization and downregulated the expression of bone morphogenetic proteins (Bmps) and osteogenic markers. Further, we found that PSF prompted the activation of Yap1 signaling and epigenetic modifications in the Malat1 promoter, crucial for the expression of Malat1. These results indicate that the fibrous matrix adjacent to biomaterials can instigate Malat1 upregulation, subsequently driving osteogenic trans-differentiation in myoblasts and ectopic calcification through its transcriptional regulation of osteogenic genes, including Bmps. Our findings point to a novel therapeutic avenue for mitigating prosthesis-induced pathological calcification, heralding new possibilities in the field of biomaterial-based therapies.

Intracranial calcifications simulating Aicardi-Goutières syndrome in PARS2-related mitochondrial disease

PARS2 encodes an aminoacyl-tRNA synthetase that catalyzes the ligation of proline to mitochondrial prolyl-tRNA molecules. Diseases associated with PARS2 primarily affect the central nervous system, causing early infantile developmental epileptic encephalopathies (EIDEE; DEE75; MIM #618437) with infantile-onset neurodegeneration. Dilated cardiomyopathy has also been reported in the affected individuals. About 10 individuals to date have been described with pathogenic biallelic variants in PARS2. While many of the reported individuals succumbed to the disease in the first two decades of life, autopsy findings have not yet been reported. Here, we describe neuropathological findings in a deceased male with evidence of intracranial calcifications in the basal ganglia, thalamus, cerebellum, and white matter, similar to Aicardi-Goutières syndrome. This report describes detailed autopsy findings in a child with PARS2-related mitochondrial disease and provides plausible evidence that intracranial calcifications may be a previously unrecognized feature of this disorder.

The role of extracellular vesicles in vascular calcification in chronic kidney disease

Widespread vascular calcification (VC) in patients with chronic kidney disease (CKD) is the pathological basis for the development of cardiovascular disease, and VC has been identified as an independent risk factor for increased cardiovascular mortality in cases of CKD. While VC was earlier thought to be a passive deposition process following calcium and phosphorus supersaturation, recent studies have suggested that it is an active, modifiable, biological process similar to bone development. The involvement of extracellular vesicles (EVs) in the process of VC has been reported as an important transporter of material transport and intercellular communication. This paper reviews the mechanism of the role of EVs, especially exosomes, in VC and the regulation of VC by stem cell-derived EVs, and discusses the possible and promising application of related therapeutic targets in the clinical setting.

Pathophysiology of Atherosclerosis

Atherosclerosis is the main risk factor for cardiovascular disease (CVD), which is the leading cause of mortality worldwide. Atherosclerosis is initiated by endothelium activation and, followed by a cascade of events (accumulation of lipids, fibrous elements, and calcification), triggers the vessel narrowing and activation of inflammatory pathways. The resultant atheroma plaque, along with these processes, results in cardiovascular complications. This review focuses on the different stages of atherosclerosis development, ranging from endothelial dysfunction to plaque rupture. In addition, the post-transcriptional regulation and modulation of atheroma plaque by microRNAs and lncRNAs, the role of microbiota, and the importance of sex as a crucial risk factor in atherosclerosis are covered here in order to provide a global view of the disease.

Genetics of Subclinical Coronary Atherosclerosis

Purpose of Review

This review highlights recent findings regarding genetics of coronary artery calcification (CAC), a marker of subclinical atherosclerosis burden, that is a precursor of clinical coronary artery disease.

Recent findings

CAC quantity is heritable. Genome wide association studies of common single nucleotide polymorphisms have identified genomic regions explaining ~2.4% of CAC heritability. Low frequency and rare variants explain additional variation in CAC. Evidence suggests that there may be different genetic etiologies for variation in CAC progression than for cross-sectional measures of CAC. Studies integrating multiple -omics data are providing new insights into the pathobiology of subclinical coronary atherosclerosis.

Summary

The future is promising for innovative studies utilizing whole genome sequencing data as well as other -omics such as epigenomic modifications of genes and gene expression. These studies may provide multiple sources of data pointing to the same gene or pathway, thus providing greater confidence in findings.

A histological and radiographic study of pulpal calcification in periodontally involved teeth in a Taiwanese population

BACKGROUND/PURPOSE

The prevalence of pulpal calcifications was widely studied in the past. The purposes of this study were to investigate the incidence of pulpal calcifications of periodontally involved teeth in a Taiwan Chinese population using radiographic and histological examinations, and to find out any association of pulpal calcification with systemic disease and dental conditions.

MATERIALS AND METHODS

A total of 197 teeth freshly extracted because of severe periodontal destruction were collected and prepared for histological and radiographic studies of the incidence of pulpal tissue calcifications. The occurrences of calcifications were recorded based on the different types of classifications proposed by Seltzer (1972). The number of examined teeth with pulpal calcifications was calculated, and they were statistically analyzed with the Chi-square test.

RESULTS

The patient population ranged in age from 16 years to 85 years. Of them, 165 (84%) were male and 32 (17%) were female. The results show that the incidence of pulpal calcifications of periodontally involved teeth was 62% in histological and 30% in radiographic examinations. The occurrences were slightly higher than that reported in some previous studies and significantly different between the two examined methods. No significant association of pulpal calcification with age and systemic disease was found. Moreover, molars were observed to have more pulpal calcifications than bicuspids and incisors statistically (P < 0.001).

CONCLUSION

The true incidence of pulpal calcifications of periodontally involved teeth is likely to be higher in histological examination because pulpal calcifications with a small diameter may not be seen on radiographs. The prevalence of pulpal calcifications was found to increase significantly in molar teeth, and the results indicated that localized calcifications occur mostly in the radicular area of the pulp tissue.

A Molecular View of Pathological Microcalcification in Breast Cancer

Breast microcalcification is a potential diagnostic indicator for non-palpable breast cancers. Microcalcification type I (calcium oxalate) is restricted to benign tissue, whereas type II (calcium hydroxyapatite) occurs both in benign as well as in malignant lesions. Microcalcification is a pathological complication of the mammary gland. Over the past few decades, much attention has been paid to exploit this property, which forms the basis for advances in diagnostic procedures and imaging techniques. The mechanism of its formation is still poorly understood. Hence, in this paper, we have attempted to address the molecular mechanism of microcalcification in breast cancer. The central theme of this communication is "how a subpopulation of heterogeneous breast tumor cells attains an osteoblast-like phenotype, and what activities drive the process of pathophysiological microcalcification, especially at the invasive or infiltrating front of breast tumors". The role of bone morphogenetic proteins (BMPs) and tumor associated macrophages (TAMs) along with epithelial to mesenchymal transition (EMT) in manipulating this pathological process has been highlighted. Therefore, this review offers a novel insight into the mechanism underlying the development of microcalcification in breast carcinomas.

Vascular Calcification in Uremia: New-Age Concepts about an Old-Age Problem

A hallmark of aging, and major contributor to the increased prevalence of cardiovascular disease in patients with chronic kidney disease (CKD), is the progressive structural and functional deterioration of the arteries and concomitant accrual of mineral. Vascular calcification (VC) was long viewed as a degenerative age-related pathology that resulted from the passive deposition of mineral in the extracellular matrix; however, since the discovery of "bone-related" protein expression in calcified atherosclerotic plaques over 20 years ago, a plethora of studies have evoked the now widely accepted view that VC is a highly regulated and principally cell-mediated phenomenon that recapitulates many features of physiologic ossification. Central to this theory are changes in vascular smooth muscle cell (VSMC) phenotype and viability, thought to be driven by chronic exposure to a number of dystrophic stimuli characteristics of the uremic state. Here, dedifferentiated synthetic VSMCs are seen to spawn calcifying matrix vesicles that actively seed mineralization of the arterial matrix. This review provides an overview of the major epidemiological, histological, and molecular aspects of VC in the context of CKD, and a counterpoint to the prevailing paradigm that emphasizes the primacy of VSMC-mediated mechanisms. Particular focus is given to the import of protein and small molecule inhibitors in regulating physiologic and pathological mineralization and the emerging role of mineral nanoparticles and their interplay with proinflammatory processes.

Differential miRNA Expression in Cells and Matrix Vesicles in Vascular Smooth Muscle Cells from Rats with Kidney Disease

Vascular calcification is a complex process and has been associated with aging, diabetes, chronic kidney disease (CKD). Although there have been several studies that examine the role of miRNAs (miRs) in bone osteogenesis, little is known about the role of miRs in vascular calcification and their role in the pathogenesis of vascular abnormalities. Matrix vesicles (MV) are known to play in important role in initiating vascular smooth muscle cell (VSMC) calcification. In the present study, we performed miRNA microarray analysis to identify the dysregulated miRs between MV and VSMC derived from CKD rats to understand the role of post-transcriptional regulatory networks governed by these miRNAs in vascular calcification and to uncover the differential miRNA content of MV. The percentage of miRNA to total RNA was increased in MV compared to VSMC. Comparison of expression profiles of miRNA by microarray demonstrated 33 miRs to be differentially expressed with the majority (~ 57%) of them down-regulated. Target genes controlled by differentially expressed miRNAs were identified utilizing two different complementary computational approaches Miranda and Targetscan to understand the functions and pathways that may be affected due to the production of MV from calcifying VSMC thereby contributing to the regulation of genes by miRs. We found several processes including vascular smooth muscle contraction, response to hypoxia and regulation of muscle cell differentiation to be enriched. Signaling pathways identified included MAP-kinase and wnt signaling that have previously been shown to be important in vascular calcification. In conclusion, our results demonstrate that miRs are concentrated in MV from calcifying VSMC, and that important functions and pathways are affected by the miRs dysregulation between calcifying VSMC and the MV they produce. This suggests that miRs may play a very important regulatory role in vascular calcification in CKD by controlling an extensive network of post-transcriptional targets.

Nonhydrolyzable ATP analogues as selective inhibitors of human NPP1: a combined computational/experimental study

Elevated nucleotide pyrophosphatase/phosphodiesterase-1 (NPP1) activity is implicated in health disorders including pathological calcification. Specific NPP1 inhibitors would therefore be valuable for studying this enzyme and as potential therapeutic agents. Here we present a combined computational/experimental study characterizing 13 nonhydrolyzable ATP analogues as selective human NPP1 inhibitors. All analogues at 100 μM inhibited (66-99%) the hydrolysis of pnp-TMP by both recombinant NPP1 and cell surface NPP1 activity of osteocarcinoma (HTB-85) cells. These analogues only slightly altered the activity of other ectonucleotidases, NPP3 and NTPDases. The Ki,app values of the seven most potent and selective inhibitors were in the range of 0.5-56 μM, all with mixed type inhibition, predominantly competitive. Those molecules were docked into a newly developed homology model of human NPP1. All adopted ATP-like binding modes, suggesting competitive inhibition with the endogenous ligand. NPP1 selectivity versus NPP3 could be explained in terms of the electrostatic potential of the two proteins that of NPP1 favoring negatively charged ligands. Inhibitor 2 that had the lowest Ki,app (0.5 μM) was also inactive toward P2Y receptors. Overall, analogue 2 is the most potent and selective NPP1 inhibitor described so far.

Multimodal imaging of optic disc drusen

PURPOSE

To evaluate optic disc drusen, extracellular protein deposits known to contain numerous aggregates of mitochondria, using multimodal modalities featuring optical coherence tomography (OCT) and autofluorescence imaging.

DESIGN

Retrospective observational case series.

METHODS

Eyes with optic nerve drusen were examined with enhanced depth imaging (EDI)-OCT, swept source OCT, and fundus autofluorescence using a fundus camera.

RESULTS

Twenty-six eyes of 15 patients with optic disc drusen were evaluated. EDI-OCT and swept source OCT showed multiple optic disc drusen at different levels; most were located immediately anterior to the lamina cribrosa. The drusen were ovoid regions of lower reflectivity that were bordered by hyperreflective material, and in 12 eyes (46.2%) there were internal hyperreflective foci. The mean diameter of the optic disc drusen as measured in OCT images was 686.8 (standard deviation ± 395.2) μm. There was a significant negative correlation between the diameter of the optic disc drusen and the global retinal nerve fiber layer thickness (r = -0.61, P = .001). There was a significant negative correlation between proportion of the optic disc drusen area occupied by optic nerve drusen as detected by autofluorescence imaging and the global retinal nerve fiber layer thickness (r = -0.63, P = .001).

CONCLUSIONS

Deeper-penetration OCT imaging demonstrated the internal characteristics of optic disc drusen and their relationship with the lamina cribrosa in vivo. This study also showed that both the larger the drusen and the more area of the optic canal occupied by drusen, the greater the associated retinal nerve fiber layer abnormalities.

Role of extracellular vesicles in de novo mineralization: an additional novel mechanism of cardiovascular calcification

Extracellular vesicles are membrane micro/nanovesicles secreted by many cell types into the circulation and the extracellular milieu in physiological and pathological conditions. Evidence suggests that extracellular vesicles, known as matrix vesicles, play a role in the mineralization of skeletal tissue, but emerging ultrastructural and in vitro studies have demonstrated their contribution to cardiovascular calcification as well. Cells involved in the progression of cardiovascular calcification release active vesicles capable of nucleating hydroxyapatite on their membranes. This review discusses the role of extracellular vesicles in cardiovascular calcification and elaborates on this additional mechanism of calcification as an alternative pathway to the currently accepted mechanism of biomineralization via osteogenic differentiation.

Bone formation controlled by biologically relevant inorganic ions: role and controlled delivery from phosphate-based glasses

The role of metal ions in the body and particularly in the formation, regulation and maintenance of bone is only just starting to be unravelled. The role of some ions, such as zinc, is more clearly understood due to its central importance in proteins. However, a whole spectrum of other ions is known to affect bone formation but the exact mechanism is unclear as the effects can be complex, multifactorial and also subtle. Furthermore, a significant number of studies utilise single doses in cell culture medium, whereas the continual, sustained release of an ion may initiate and mediate a completely different response. We have reviewed the role of the most significant ions that are known to play a role in bone formation, namely calcium, zinc, strontium, magnesium, boron, titanium and also phosphate anions as well as copper and its role in angiogenesis, an important process interlinked with osteogenesis. This review will also examine how delivery systems may offer an alternative way of providing sustained release of these ions which may effect and potentiate a more appropriate and rapid tissue response.

Composition and distribution of elements and ultrastructural topography of a human cardiac calculus

Trace elements (TEs) may contribute to the formation of calculi or stones or be involved in the aetiopathogenesis of stone diseases. The compositions and spatial distribution of elements from the inner nucleus to outer crust of the cardiac calculus were investigated by energy-dispersive X-ray fluorescence (EDXRF) spectrometer. The surface topograph, distribution map of elements, elemental and chemical compositions were also determined by environmental scanning electron microscope (ESEM)-energy-dispersive X-ray (EDX) analysis. Twenty-five elements were identifiable from 18 positions on the cardiac calculus by EDXRF spectrometer, in which the highest concentrations of toxic TEs (Ni, Pt, Hg, Sn, Pb, W, Au, Al, Si) and higher levels of essential TEs (Ca, Sr, Cr, P) were detected. A moderate positive Pearson's correlation between TEs concentrations of Mg, Ca or P and location differences from centre to periphery in the cardiac calculus was observed. A positive correlation was also found for Ca/Zn and Ca/Cu, indicating the gradual increase of calcium concentration from inner nucleus to outer crust of cardiac calculus. The drop-like nodules/crystals on the surface of petrous part of cardiac calculus were observed from ESEM analysis. ESEM-EDX analysis determined the calculus to be predominantly composed of calcium hydroxyapatite and cholesterol, as indicated by the petrous surface and drop-like nodules/crystals, respectively. This composition was confirmed using a portable Raman analyser. The spatial distribution analysis indicated a gradual increase in Mg, P and Ca concentrations from the inner nucleus to the outer crust of the cardiac calculus. The major chemical compositions of calcium hydroxyapatite and cholesterol were detected on this cardiac calculus.

Nummular dystrophic calcification of an Ahmed glaucoma valve in a child

We report the case of an otherwise-healthy 4.5-year-old girl with primary congenital glaucoma who had multiple nummular calcium deposits on the dorsal plate of a previously-implanted Ahmed glaucoma valve. The child had received the implant in the right eye at 6 months of age and developed increased intraocular pressure requiring surgical excision of surrounding fibrous encapsulation. Intraoperative inspection revealed that the dorsal plate surface was covered with multiple white nummular lesions; staining and X-ray microanalysis confirmed the lesions to be calcium deposits. Calcium deposits have been documented for various ophthalmic implants, including silicone scleral buckles and intraocular lenses, but to the best of our knowledge they have not previously been described in association with a glaucoma drainage device.

Mitochondrial Ca2+ sequestration and precipitation revisited

The ability of mitochondria to sequester and retain divalent cations in the form of precipitates consisting of organic and inorganic moieties has been known for decades. Of these cations, Ca(2+) has emerged as a major player in both signal transduction and cell death mechanisms, and, as a consequence, the importance of mitochondria in these processes was soon recognized. Early studies showed considerable effort in identifying the mechanisms of Ca(2+) sequestration, precipitation and release by uncouplers of oxidative phosphorylation; however, relatively little information was obtained, and these processes were eventually taken for granted. Here, we re-examine: (a) the thermodynamic aspects of mitochondrial Ca(2+) uptake and release, (b) the insufficiently explained effect of uncouplers in inducing mitochondrial Ca(2+) release, (c) the thermodynamic effects of exogenously added adenine nucleotides on mitochondrial Ca(2+) uptake capacity and precipitate formation, and (d) the elusive nature of the Ca(2+) -phosphate precipitates formed in the mitochondrial matrix.

Nanobacteria: a possible etiology for type III prostatitis

PURPOSE

Nanobacteria are thought to be a pathopoiesis bacterium in urological disease. We observed pathological changes in nanobacteria infected prostates in Sprague-Dawley(R) rats and investigated the possible etiological relationships of nanobacteria and type III prostatitis.

MATERIALS AND METHODS

We randomized 40 adult male Sprague-Dawley rats each to the control and model groups. Rat prostate infection models were reproduced by infusing nanobacteria suspension transurethrally. Rats were sacrificed 1, 2, 4 and 8 weeks later, respectively. Prostatic pathology, and the cytokines interleukin-1beta and tumor necrosis factor-alpha were assessed. Nanobacteria isolation, culture and characterization were also analyzed.

RESULTS

In model rats we observed prostatic acute inflammatory changes 1 to 2 weeks after nanobacteria infusion and chronic inflammatory changes after 4 weeks. At 8 weeks we noted microcalculous formation in the prostatic glandular cavity in 7 of the 10 model rats, which was not seen in controls. Interleukin-1beta and tumor necrosis factor-alpha in prostatic tissues were higher in model rats than in controls at different time points (p <0.01). In model rats interleukin-1beta and tumor necrosis factor-alpha were higher 2 weeks after infusion than at 1, 4 and 8 weeks (p <0.05). Prostatic tissue was nanobacteria positive in 35 model rats and in 0 controls.

CONCLUSIONS

Nanobacteria may be an important etiological factor for type III prostatitis.

Verapamil inhibits calcification and matrix vesicle activity of bovine vascular smooth muscle cells

Calcium channel activity in vascular smooth muscle cells is a critical component during vascular calcification and formation of matrix vesicles. Here, we examined whether the blockade of L-type calcium channels inhibits these functions. Bovine vascular smooth muscle cells or rat aorta organ cultures were incubated in media known to promote calcification and treated with the L-type calcium channel inhibitors verapamil, nifedipine, or nimodipine. The phenylalkylamine, verapamil, significantly decreased calcification of the vascular smooth muscle cells and rat aorta, in a dose-dependent manner, whereas the dihydropyridines, nifedipine and nimodipine, had no effect. Furthermore, verapamil, but not nifedipine, significantly decreased the alkaline phosphatase activity of bovine vascular smooth muscle cells. Verapamil pretreatment of the cells also inhibited matrix vesicle alkaline phosphatase activity and reduced the ability of these matrix vesicles to subsequently calcify on a type I collagen extracellular matrix scaffold. As L-type channels are blocked by verapamil and dihydropyridines, we suggest that verapamil inhibits vascular smooth muscle mineralization and matrix vesicle activity by mechanisms other than the simple blockade of this calcium channel activity.

Information storing by biomagnetites

Since the discovery of the presence of biogenic magnetites in living organisms, there have been speculations on the role that these biomagnetites play in cellular processes. It seems that the formation of biomagnetite crystals is a universal phenomenon and not an exception in living cells. Many experimental facts show that features of organic and inorganic processes could be indistinguishable at nanoscale levels. Living cells are quantum "devices" rather than simple electronic devices utilizing only the charge of conduction electrons. In our opinion, due to their unusual biophysical properties, special biomagnetites must have a biological function in living cells in general and in the brain in particular. In this paper, we advance a hypothesis that while biomagnetites are developed jointly with organic molecules and cellular electromagnetic fields in cells, they can record information about the Earth's magnetic vector potential of the entire flight in migratory birds.

Inorganic pyrophosphate as a regulator of hydroxyapatite or calcium pyrophosphate dihydrate mineral deposition by matrix vesicles

OBJECTIVE

Pathological mineralization is induced by unbalance between pro- and anti-mineralization factors. In calcifying osteoarthritic joints, articular chondrocytes undergo terminal differentiation similar to that in growth plate cartilage and release matrix vesicles (MVs) responsible for hydroxyapatite (HA) or calcium pyrophosphate dihydrate (CPPD) deposition. Inorganic pyrophosphate (PP(i)) is a likely source of inorganic phosphate (P(i)) to sustain HA formation when hydrolyzed but also a potent inhibitor preventing apatite mineral deposition and growth. Moreover, an excess of PP(i) can lead to CPPD formation, a marker of pathological calcification in osteoarthritic joints. It was suggested that the P(i)/PP(i) ratio during biomineralization is a turning point between physiological and pathological mineralization. The aim of this work was to determine the conditions favoring either HA or CPPD formation initiated by MVs.

METHODS

MVs were isolated from 17-day-old chicken embryo growth plate cartilages and subjected to mineralization in the presence of various P(i)/PP(i) ratios. The mineralization kinetics and the chemical composition of minerals were determined, respectively, by light scattering and infrared spectroscopy.

RESULTS

The formation of HA is optimal when the P(i)/PP(i) molar ratio is above 140, but is completely inhibited when the ratio decreases below 70. The retardation of any mineral formation is maximal at P(i)/PP(i) ratio around 30. CPPD is exclusively produced by MVs when the ratio is below 6, but it is inhibited for the ratio exceeding 25.

CONCLUSIONS

Our findings are consistent with the P(i)/PP(i) ratio being a determinant factor leading to pathological mineralization or its inhibition.

Myringosclerosis in patients with chronic renal failure: comparative analysis with a control group

Myringosclerosis is a scar of the tympanic membrane lamina propria, resulting from trauma or inflammation, characterized by proliferation of collagen, hyalinization, calcium and phosphate deposits and cartilaginous or osseous metaplasia of the middle ear mucosa, a sequence that is similar to that taking place in other types of pathologic calcification, common in chronic renal failure (CRF).

AIM

To verify the influence of chronic renal failure on the prevalence of myringosclerosis.

METHOD

The otoscopic examination was done in 341 chronic renal failure patients and in 356 normal control individuals. The frequency of positive otoscopies was compared between the two groups, based on individual variables and those pertaining to CRF.

RESULTS

11.7% of the patients had a positive otoscopy in the CRF group, compared to 5.1% in the control group. There was no statistical difference in the frequency of myringosclerosis according to gender, ethnic group, time of dialysis or serum minerals. The groups had a wide age range.

CONCLUSION

Although the findings of this study suggest a higher occurrence of myringosclerosis in patients with renal disease, they do not provide a basis for stating that there is any relation between renal failure and tympanic alterations.

Mineralization of annexin-5-containing lipid-calcium-phosphate complexes: modulation by varying lipid composition and incubation with cartilage collagens

Matrix vesicles (MVs) in the growth plate bind to cartilage collagens and initiate mineralization of the extracellular matrix. Native MVs have been shown to contain a nucleational core responsible for mineral formation that is comprised of Mg(2+)-containing amorphous calcium phosphate and lipid-calcium-phosphate complexes (CPLXs) and the lipid-dependent Ca(2+)-binding proteins, especially annexin-5 (Anx-5), which greatly enhances mineral formation. Incorporation of non-Ca(2+)-binding MV lipids impedes mineral formation by phosphatidylserine (PS)-CPLX. In this study, nucleators based on amorphous calcium phosphate (with or without Anx-5) were prepared with PS alone, PS + phosphatidylethanolamine (PE), or PS + PE and other MV lipids. These were incubated in synthetic cartilage lymph containing no collagen or containing type II or type X collagen. Dilution of PS with PE and other MV lipids progressively retarded nucleation. Incorporation of Anx-5 restored nucleational activity to the PS:PE CPLX; thus PS and Anx-5 proved to be critical for nucleation of mineral. Without Anx-5, induction of mineral formation was slow unless high levels of Ca(2+) were used. The presence of type II collagen in synthetic cartilage lymph improved both the rate and amount of mineral formation but did not enhance nucleation. This stimulatory effect required the presence of the nonhelical telopeptides. Although type X collagen slowed induction, it also increased the rate and amount of mineral formation. Both type II and X collagens markedly increased mineral formation by the MV-like CPLX, requiring Anx-5 to do so. Thus, Anx-5 enhances nucleation by the CPLXs and couples this to propagation of mineral formation by the cartilage collagens.

Matrix vesicles in the fibrous cap of atherosclerotic plaque: possible contribution to plaque rupture

Plaque rupture is the most common type of plaque complication and leads to acute ischaemic events such as myocardial infarction and stroke. Calcification has been suggested as a possible indicator of plaque instability. Although the role of matrix vesicles in the initial stages of arterial calcification has been recognized, no studies have yet been carried out to examine a possible role of matrix vesicles in plaque destabilization. Tissue specimens selected for the present study represented carotid specimens obtained from patients undergoing carotid endarterectomy. Serial frozen cross-sections of the tissue specimens were cut and mounted on glass slides. The thickness of the fibrous cap (FCT) in each advanced atherosclerotic lesion, containing a well developed lipid/necrotic core, was measured at its narrowest sites in sets of serial sections. According to established criteria, atherosclerotic plaque specimens were histologically subdivided into two groups: vulnerable plaques with thin fibrous caps (FCT <100 μm) and presumably stable plaques, in which fibrous caps were thicker than 100 μm. Twenty-four carotid plaques (12 vulnerable and 12 presumably stable plaques) were collected for the present analysis of matrix vesicles in fibrous caps. In order to provide a sufficient number of representative areas from each plaque, laser capture microdissection (LCM) was carried out. The quantification of matrix vesicles in ultrathin sections of vulnerable and stable plaques revealed that the numbers of matrix vesicles were significantly higher in fibrous caps of vulnerable plaques than those in stable plaques (8.908±0.544 versus 6.208±0.467 matrix vesicles per 1.92 μm² standard area; P= 0.0002). Electron microscopy combined with X-ray elemental microanalysis showed that some matrix vesicles in atherosclerotic plaques were undergoing calcification and were characterized by a high content of calcium and phosphorus. The percentage of calcified matrix vesicles/microcalcifications was significantly higher in fibrous caps in vulnerable plaques compared with that in stable plaques (6.705±0.436 versus 5.322±0A94; P= 0.0474). The findings reinforce a view that the texture of the extracellular matrix in the thinning fibrous cap of atherosclerotic plaque is altered and this might contribute to plaque destabilization.

A New Classification of Calcification of Intraocular Lenses

OBJECTIVE

To define and classify the major types of intraocular lens (IOL) calcification.

DESIGN

Retrospective observational case series with clinicopathologic correlation.

PARTICIPANTS

More than 400 IOLs explanted because of opacification.

METHODS

The authors reviewed the clinical information and histologic findings of all IOLs that had been explanted because of opacification or calcification of the IOLs accessioned in their laboratory between January 1999 and December 2004.

MAIN OUTCOME MEASURE

The proposed mechanism that led to calcification of each IOL design.

RESULTS

Three major types of calcification were identified: (1) primary calcification, (2) secondary calcification, and (3) false-positive calcification or pseudocalcification. The primary form refers to calcification that is inherent in the IOL, that is, is based on possible inadequate formulation of the polymer, fabrication of the IOL, or issues with its packaging process. The calcification presumably occurs in otherwise normal eyes and generally is not associated with preexisting diseases. The secondary form refers to deposition of calcium onto the surface of the IOL most likely the result of environmental circumstances (e.g., changes in the aqueous milieu surrounding the implanted IOL associated with preexisting or concurrent diseases or indeed any condition that has disrupted the blood-aqueous barrier). By definition, it is not related to any problem with the IOL itself. The false-positive or pseudocalcification refers to those cases in which other pathology is mistaken for calcification or false-positive staining for calcium occurs.

CONCLUSIONS

When evaluating the pathogenesis and nature of IOL calcification in or on any given design, one should categorize it according to these types. Primary calcification is IOL related and the IOL should be withdrawn or modified to correct the problem. After the cause is identified and the lens is implanted again, patients should be followed up for up to 2 years to be sure the problem is alleviated. Secondary calcification is by definition not IOL related; it may occur with virtually all IOL designs implanted under various adverse circumstances. No IOL, hydrophilic or hydrophobic, is immune to secondary calcification. The false-positive form is recognized readily in the laboratory and this erroneous diagnosis is avoided.

In vitro modeling of matrix vesicle nucleation: synergistic stimulation of mineral formation by annexin A5 and phosphatidylserine

Annexins A5, A2, and A6 (Anx-A5, -A2, and -A6) are quantitatively major proteins of the matrix vesicle nucleational core that is responsible for mineral formation. Anx-A5 significantly activated the induction and propagation of mineral formation when incorporated into synthetic nucleation complexes made of amorphous calcium phosphate (ACP) and Anx-A5 or of phosphatidylserine (PS) plus ACP (PS-CPLX) and Anx-A5. Incorporation of Anx-A5 markedly shortened the induction time, greatly increasing the rate and overall amount of mineral formed when incubated in synthetic cartilage lymph. Constructed by the addition of Ca(2+) to PS, emulsions prepared in an intracellular phosphate buffer matched in ionic composition to the intracellular fluid of growth plate chondrocytes, these biomimetic PS-CPLX nucleators had little nucleational activity. However, incorporation of Anx-A5 transformed them into potent nucleators, with significantly greater activity than those made from ACP without PS. The ability of Anx-A5 to enhance the nucleation and growth of mineral appears to stem from its ability to form two-dimensional crystalline arrays on PS-containing monolayers. However, some stimulatory effect also may result from its ability to exclude Mg(2+) and HCO(-)(3) from nucleation sites. Comparing the various annexins for their ability to activate PS-CPLX nucleation yields the following: avian cartilage Anx-A5 > human placental Anx-A5 > avian liver Anx-A5 > or = avian cartilage Anx-A6 >> cartilage Anx-A2. The stimulatory effect of human placental Anx-A5 and avian cartilage Anx-A6 depended on the presence of PS, since in its absence they either had no effect or actually inhibited the nucleation activity of ACP. Anx-A2 did not significantly enhance mineralization.

Enhancement of drug delivery to bone: characterization of human tissue-nonspecific alkaline phosphatase tagged with an acidic oligopeptide

Hypophosphatasia is caused by deficiency of activity of the tissue-nonspecific alkaline phosphatase (TNSALP), resulting in a defect of bone mineralization. Enzyme replacement therapy (ERT) with partially purified plasma enzyme was attempted but with little clinical improvement. Attaining clinical effectiveness with ERT for hypophosphatasia may require delivering functional TNSALP enzyme to bone. We tagged the C-terminal-anchorless TNSALP enzyme with an acidic oligopeptide (a six or eight residue stretch of L-Asp), and compared the biochemical properties of the purified tagged and untagged enzymes derived from Chinese hamster ovary cell lines. The specific activities of the purified enzymes tagged with the acidic oligopeptide were the same as the untagged enzyme. In vitro affinity experiments showed the tagged enzymes had 30-fold higher affinity for hydroxyapatite than the untagged enzyme. Lectin affinity chromatography for carbohydrate structure showed little difference among the three enzymes. Biodistribution pattern from single infusion of the fluorescence-labeled enzymes into mice showed delayed clearance from the plasma up to 18 h post infusion and the amount of tagged enzyme retained in bone was 4-fold greater than that of the untagged enzyme. In vitro mineralization assays with the bone marrow from a hypophosphatasia patient using each of the three enzymes in the presence of high concentrations of pyrophosphate provided evidence of bone mineralization. These results show the anchorless enzymes tagged with an acidic oligopeptide are delivered efficiently to bone and function bioactively in bone mineralization, at least in vitro. They suggest potential advantages for use of these tagged enzymes in ERT for hypophosphatasia, which should be explored.

Micro-Raman spectroscopy used to identify and grade human skin pilomatrixoma

Raman microspectroscopy was applied to analyze the changes in structural conformation and chemical composition of the mass of human skin pilomatrixoma (PMX). The normal skin dermis, collagen type I, and hydroxyapatite (HA) were used as control. The excised specimens from two patients diagnosed as a typical PMX were detected, in which one specimen was a soft mass, but the other was a hard mass with somewhat calcified deposits via histopathological examination. The Raman spectrum of normal skin dermis was found to be similar to the Raman spectrum of collagen type I, confirming that the collagen type I was a predominant component in normal skin dermis. The differences of Raman peak intensity between normal skin dermis and soft or hard PMX mass were obvious at 1,622-1,558, 1,400-1,230, 1,128, 1,000-850, 749, and 509 cm(-1). In particular, the peak at 1,665 cm(-1) assigned to amide I band shifted to 1,655 cm(-1) and the peak at 1,246 cm(-1) corresponding to amide III band was reduced in its intensity in hard PMX mass. The significant changes in collagen content and its structural conformation, the higher content of tryptophan, and disulfide formation in PMX masses were markedly evidenced. In addition, the shoulder and weak peak at 960 cm(-1) assigned to the stretching vibration of PO(4) (3-) of HA also appeared respectively in the Raman spectra of soft and hard PMX masses, suggesting the occurrence of calcification of HA in the PMX tissue, particularly in the hard PMX mass. The result indicates that the micro-Raman spectroscopy may provide a highly sensitive and specific method for identifying normal skin dermis and how it differs in chemical composition from different PMX tissues.

Calcification of senile cataractous lens determined by Fourier transform infrared (FTIR) and Raman microspectroscopies

A calcified plaque on the surface of a senile cataractous lens (CL) isolated from a 79-year-old male patient was identified and its chemical composition quantified using Fourier transform infrared (FTIR) and confocal Raman microspectroscopies. The noncalcified area of the same CL and hydroxyapatite (HA) were selected as a control. Several unique absorption bands, at 960, 1034 and 1090 cm(-1) assigned to the nu(1) and nu(3) stretching modes of phosphate and at 875 cm(-1) attributed to carbonate, were clearly displayed in the infrared (IR) spectra of calcified plaque and HA. A peak at 961 cm(-1) due to the nu(1) stretching mode of phosphate was also evidenced in the Raman spectra of calcified plaque and HA. The calcified plaque formed within the lens protein was found to mainly consist of a mature HA, in which type-A carbonate apatites (11.4%), type-B carbonate apatites (55.6%) and liable surface carbonate ions (33.0%) were presented. A higher content of the liable carbonate implies that the calcification or mineralization in this calcified lens was incomplete and still in progress. Moreover, calcification seems not to influence the secondary structure of lens protein because both IR and Raman spectra for the lens protein in the noncalcified area and calcified plaque were similar. The result suggests that both microscopic FTIR and Raman spectroscopies were easy to perform and capable of determination of the chemical composition of a calcified CL.

Cartilage formation in growth plate and arteries: from physiology to pathology

Vascular calcifications are the consequence of several pathological conditions such as atherosclerosis, diabetes, hypercholesterolemia and chronic renal insufficiency. They are associated with risks of amputation, ischemic heart disease, stroke and increased mortality. A growing body of evidence indicates that vascular smooth muscle cells (VSMCs) undergo chondrogenic commitment eventually leading to vascular calcification, by mechanisms similar to those governing ossification in the cartilage growth plate. Our knowledge of the formation of cartilage growth plate can therefore help us to understand why and how arteries calcify and, consequently, develop new therapeutic strategies. Reciprocally, thorough consideration of the events leading to ectopic chondrocyte differentiation appears crucial to further increase our understanding of growth plate formation. In this context, we will review the effects of known or suspected factors that promote chondrogenic differentiation in growth plate and arteries.

Inhibition of nanobacteria by antimicrobial drugs as measured by a modified microdilution method

Compounds from 16 classes of antimicrobial drugs were tested for their abilities to inhibit the in vitro multiplication of nanobacteria (NB), a newly discovered infectious agent found in human kidney stones and kidney cyst fluids from patients with polycystic kidney disease (PKD). Because NB form surface calcifications at physiologic levels of calcium and phosphate, they have been hypothesized to mediate the formation of tissue calcifications. We describe a modified microdilution inhibitory test that accommodates the unique growth conditions and long multiplication times of NB. This modified microdilution method included inoculation of 96-well plates and determination of inhibition by periodic measurement of the absorbance for 14 days in cell culture medium under cell culture conditions. Bactericidal or bacteriostatic drug effects were distinguished by subsequent subculture in drug-free media and monitoring for increasing absorbance. NB isolated from fetal bovine serum (FBS) were inhibited by tetracycline HCl, nitrofurantoin, trimethoprim, trimethoprim-sulfamethoxazole, and ampicillin at levels achievable in serum and urine; all drugs except ampicillin were cidal. Tetracycline also inhibited multiplication of isolates of NB from human kidney stones and kidney cyst fluids from patients with PKD. The other antibiotics tested against FBS-derived NB either had no effect or exhibited an inhibitory concentration above clinically achievable levels; the aminoglycosides and vancomycin were bacteriostatic. Antibiotic-induced morphological changes to NB were observed by electron microscopy. Bisphosphonates, aminocaproic acid, potassium citrate-citric acid solutions, and 5-fluorouracil also inhibited the multiplication of NB in a cidal manner. Insights into the nature of NB, the action(s) of these drugs, and the role of NB in calcifying diseases may be gained by exploiting this in vitro inhibition test system.

Dystrophic calcinosis in a child with a thumb sucking habit: case report

We present an uncommon case of a 3-year-old boy with a finger sucking habit who developed dystrophic calcification in his left thumb. Two years after excision, there was no recurrence, and the thumb retained full range of motion. We also discuss its probable pathogenesis and present a brief review of the literature about orthopedic complications in the hand due to this habit.

Coronary calcium: the good, the bad, and the uncertain

BACKGROUND

Coronary calcium deposits have been widely regarded to result from a passive process of encrustation or adsorption of mineral onto advanced, complex atherosclerotic lesions. Increasing interest has focused on noninvasive radiologic detection of these calcium deposits as a diagnostic and prognostic adjunct to clinical evaluation of coronary artery disease, particularly with the use of newer, high-resolution imaging techniques such as electron beam computed tomography.

METHODS AND RESULTS

We reviewed the literature on coronary calcium and its relation to pathologic atherosclerosis, angiographic stenoses,and clinical events. Clinical calcium detection studies have demonstrated an association between coronary calcium and both extent of coronary artery disease and risk of adverse events. These studies have in the past tended to reinforce the perception that calcific deposits result from a passive mineralization process, signify advanced coronary artery disease, and foreshadow future coronary events.

CONCLUSIONS

Recent pathologic, genetic, clinical, and biochemical evidence reviewed in this article suggests that coronary calcium deposits are a manifestation of a complex, organized, and regulated process similar in many respects to new bone formation and may not be a reliable indicator of either the extent of coronary disease or the risk of a future event. These studies also suggest that atherosclerosis and calcific deposits may be distinct pathologic entities that frequently occur together and are related to each other in ways that are poorly understood.

Parathyroid hormone-related proteins is abundant in osteoarthritic cartilage, and the parathyroid hormone-related protein 1-173 isoform is selectively induced by transforming growth factor beta in articular chondrocytes and suppresses generation of extracellular inorganic pyrophosphate

OBJECTIVE

Parathyroid hormone-related protein (PTHrP) is a major, locally expressed regulator of growth cartilage chondrocyte proliferation, differentiation, synthetic function, and mineralization. Because mechanisms that limit cartilage chondrocytes from maturing and mineralizing are diminished in osteoarthritis (OA), we studied PTHrP expression by articular chondrocytes.

METHODS

PTHrP was studied in normal knee cartilage samples and cultured articular chondrocytes, and in cartilage specimens from knees with advanced OA, obtained at the time of joint replacement.

RESULTS

PTHrP was more abundant in OA than in normal human knee articular cartilage. Both demonstrated PTH/PTHrP receptor expression. PTHrP 1-173, one of three alternatively spliced PTHrP isoforms, was exclusively expressed and induced by transforming growth factor beta in cultured chondrocytes. Chondrocytes mainly used the GC-rich P2 alternative promoter to express PTHrP messenger RNA. Inhibition by PTHrP 1-173, but not by PTHrP 1-146 or PTHrP 1-87, of inorganic pyrophosphate (PPi) elaboration suggested selective functional properties of the 1-173 isoform. Exposure to a neutralizing antibody to PTHrP increased PPi elaboration by articular chondrocytes.

CONCLUSION

Increased expression of PTHrP, including the 1-173 isoform, has the potential to contribute to the pathologic differentiated functions of chondrocytes, including mineralization, in OA.

Bone morphogenetic proteins and bFGF exert opposing regulatory effects on PTHrP expression and inorganic pyrophosphate elaboration in immortalized murine endochondral hypertrophic chondrocytes (MCT cells)

A fundamental question in endochondral development is why the expression of parathyroid hormone-related protein (PTHrP), which inhibits chondrocyte maturation and mineralization, becomes attenuated at the stage of chondrocyte hypertrophy. To address this question, we used clonal, phenotypically stable SV40-immortalized murine endochondral chondrocytes that express a growth-arrested hypertrophic phenotype in culture (MCT cells). Addition of individual cytokines to the medium of MCT cells revealed that bone morphogenetic protein (BMP)-6, which commits chondrocytes to hypertrophy, markedly inhibited PTHrP production. This activity was shared by three other osteogenic bone morphogenetic proteins (BMP-2, BMP-4, and BMP-7) and by transforming growth factor beta (TGF-beta), which all inhibited the level of PTHrP mRNA. In contrast, basic fibroblast growth factor (bFGF), an inhibitor of chondrocyte maturation to hypertrophy, induced PTHrP in MCT cells and antagonized the effects of BMP-2, BMP-4, BMP-6, and BMP-7 and TGF-beta on PTHrP expression. Opposing effects of bFGF and BMPs also were exerted on the elaboration of inorganic pyrophosphatase (PPi), which regulates the ability of hypertrophic chondrocytes to mineralize the matrix. Specifically, BMP-2 and BMP-4, but not BMP-6 and BMP-7, shared the ability of TGF-beta to induce PPi release, and this activity was inhibited by bFGF in MCT cells. Our results suggest that effects on PTHrP expression could contribute to the ability of BMP-6 to promote chondrocyte maturation. BMPs and bFGF exert opposing effects on more than one function in immortalized hypertrophic chondrocytes. Thus, the normal decrease in bFGF responsiveness that accompanies chondrocyte hypertrophy may function in part by removing the potential for bFGF to induce PTHrP expression and to oppose the effects of BMPs. MCT cells may be useful in further understanding the mechanisms regulating the differentiation and function of hypertrophic chondrocytes.

Ecto-phosphodiesterase/pyrophosphatase of lymphocytes and non-lymphoid cells: structure and function of the PC-1 family

Many developmentally regulated membrane proteins of lymphocytes are ecto-enzymes, with their active sites on the external surface of the cell. These enzymes commonly have peptidase, phosphodiesterase or nucleotidase activity. Their biological roles are just beginning to be discovered. Although their expression is usually associated with particular stages of lymphoid differentiation, the same gene products are often expressed on the surface of certain non-lymphoid cell types outside the immune system, indicating that their functions cannot be unique to lymphocytes, nor can they be ubiquitous. The plasma cell membrane protein PC-1 (phosphodiesterase I; EC 3.1.4.1/nucleotide pyrophosphatase; EC 3.6.1.9), which was one of the first serological markers for lymphocyte subsets to be discovered, is a typical example. Within the immune system, PC-1 is confined to plasma cells, which represent about 0.1% of lymphocytes. However, PC-1 is also expressed on cells of the distal convoluted tubule of the kidney, chondrocytes, osteoblasts, epididymis and hepatocytes. Recent work has shown that PC-1 is a member of a multigene family of ecto-phosphodiesterases that currently has two other members, PD-1 alpha (autotaxin) and PD-1 beta (B10). Within this family, the extracellular domains are highly conserved, especially around the active site. In contrast, the transmembrane and cytoplasmic domains are highly divergent. Individual members of the eco-phosphodiesterase family have distinct patterns of distribution in different cell types, and even within the same cell. For example, PC-1 is present only on the basolateral surface of hepatocytes, while B10 (PD-1 beta) is confined to the apical surface. Analysis of conservation and differences in the sequence of their cytoplasmic tails may illuminate intracellular targetting signals. Ecto-phosphodiesterases may play a part in diverse activities in different tissues, including recycling of nucleotides. They may also regulate the concentration of pharmacologically active extracellular compounds such as adenosine or its derivatives and cell motility. Some members may modulate local concentrations of pyrophosphate, and hence influence calcification in bone and cartilage.

Pathology of explanted cryopreserved allograft heart valves: comparison with aortic valves from orthotopic heart transplants

OBJECTIVE

We sought to determine the morphology, mechanisms of deterioration, cellular viability, extracellular matrix integrity, and the role of immune responses in the dysfunction of cryopreserved aortic and pulmonic valve allografts.

METHODS

We studied 33 explanted left-sided (n = 20) or right-sided (n = 13) cryopreserved human allograft heart valves explanted several hours to 9 years after operation, 14 nonimplanted allografts, and 16 aortic valves removed from transplanted allograft hearts 2 days to 4 years after operation. Analysis included gross inspection, radiography, light microscopy, electron microscopy, and immunohistochemical studies.

RESULTS

Allografts implanted for more than 1 day had progressive collagen hyalinization and loss of normal structural complexity and cellularity, including endothelium and deep connective tissue cells. Inflammatory cells were generally minimal or absent in the allografts. Transmission electron microscopy of long-term cryopreserved allograft valves revealed no viable cells, focal calcification centered around dead cell remnants, and distorted but preserved collagen. In contrast, aortic valves from transplanted hearts showed remarkable structural preservation, including endothelium and abundant deep connective tissue cells; inflammatory infiltrates were generally mild and of no apparent deleterious consequence, including valves from patients who died of fatal rejection.

CONCLUSIONS

Cryopreserved allografts are morphologically nonviable; their collagen is flattened but largely preserved. They are unlikely to grow, remodel, or exhibit active metabolic functions, and their usual degeneration cannot be attributed to immunologic responses. In contrast, aortic valves of transplanted hearts maintain near-normal overall architecture and cellularity and do not show apparent immunologic injury, even in the setting of fatal myocardial parenchymal rejection or graft arteriosclerosis.

Differential effects of aging on human chondrocyte responses to transforming growth factor beta: increased pyrophosphate production and decreased cell proliferation

OBJECTIVE

To address the influence of age on inorganic pyrophosphate (PPi) accumulation in human articular chondrocytes.

METHODS

Articular cartilage was obtained from men and women in 2 different age groups: ages 15-55 and 56-91. The effects of transforming growth factor beta1 (TGFbeta1) on PPi levels in the media and cell lysates of chondrocytes were investigated. In addition, the effects of TGFbeta on PPi accumulation were compared with chondrocyte proliferation.

RESULTS

TGFbeta1 increased PPi levels to a greater extent in chondrocytes from subjects in the older age group compared with those obtained from younger subjects. Treatment of chondrocytes with TGFbeta1 led to a similar increase in total intracellular protein in both age groups. Although TGFbeta increased nucleoside triphosphate pyrophosphohydrolase activity and decreased alkaline phosphatase activity, these effects did not differ between the 2 age groups. Analysis of the same cell preparations showed an age-related decrease in TGFbeta-induced chondrocyte proliferation, whereas these same cells showed an increased response with respect to PPi elaboration.

CONCLUSION

These results show that aging differentially affected TGFbeta-induced PPi accumulation versus proliferation in human articular chondrocytes. These differences in TGFbeta response are likely to contribute to the development of age-associated cartilage diseases such as osteoarthritis.

Expression of the nucleoside triphosphate pyrophosphohydrolase PC-1 is induced by basic fibroblast growth factor (bFGF) and modulated by activation of the protein kinase A and C pathways in osteoblast-like osteosarcoma cells

The closely related cytokines bFGF and aFGF regulate the function of bone cells and mineralization. Osteoblasts express PPi-generating nucleoside triphosphate pyrophosphohydrolase (NTPPPH)/nucleotide phosphodiesterase I activity. bFGF and aFGF (10 ng/ml) up-regulated NTPPPH in human SaOS-2 and U2OS osteosarcoma cells, which express osteoblast-like features in culture. The induction was selective as alkaline phosphatase activity was down-regulated and specific as insulin-like growth factor-1 (IGF-1) and interleukin-1 beta (IL-1 beta) were not active. Furthermore, IL-1 beta but not IGF-1 inhibited bFGF-induced up-regulation of NTPPPH. The induced NTPPPH remained predominantly associated with cells. bFGF can induce signaling through pathways including protein kinase A (PKA) and protein kinase C (PKC)-mediated transduction. An activator of the PKA pathway (8-bromo cyclic adenosine monophosphate [cAMP]) induced NTPPPH. Furthermore, pretreatment with the PKC activator phorbol myristate acetate (PMA) (80 nM) markedly increased subsequent NTPPPH induction by both bFGF and cAMP. The PMA effect was associated with morphologic changes characterized by long, thin intercellular extensions. PKC desensitization also potentially contributed to this effect because the PKC inhibitors staurosporine and H-7 enhanced bFGF-induced and cAMP-induced NTPPPH expression in the absence of morphologic changes. We observed that bFGF induced expression of PC-1, a member of the NTPPPH gene family. The majority of NTPPPH activity was depleted by immunoadsorption using a monoclonal antibody to native human PC-1. bFGF- and aFGF-induced production of PC-1/NTPPPH in osteoblastoid cells may contribute to the effects of FGFs on bone metabolism.