Phosphocitrate inhibits mitochondrial and cytosolic accumulation of calcium in kidney cells in vivo

Lithium isotopes differentially modify mitochondrial amorphous calcium phosphate cluster size distribution and calcium capacity

Lithium is commonly prescribed as a mood stabilizer in a variety of mental health conditions, yet its molecular mode of action is incompletely understood. Many cellular events associated with lithium appear tied to mitochondrial function. Further, recent evidence suggests that lithium bioactivities are isotope specific. Here we focus on lithium effects related to mitochondrial calcium handling. Lithium protected against calcium-induced permeability transition and decreased the calcium capacity of liver mitochondria at a clinically relevant concentration. In contrast, brain mitochondrial calcium capacity was increased by lithium. Surprisingly, 7Li acted more potently than 6Li on calcium capacity, yet 6Li was more effective at delaying permeability transition. The size distribution of amorphous calcium phosphate colloids formed in vitro was differentially affected by lithium isotopes, providing a mechanistic basis for the observed isotope specific effects on mitochondrial calcium handling. This work highlights a need to better understand how mitochondrial calcium stores are structurally regulated and provides key considerations for future formulations of lithium-based therapeutics.

Molecular Crystallization Inhibitors for Salt Damage Control in Porous Materials: An Overview

The use of inhibition chemicals holds the prospect of an efficient strategy to control crystallization in porous materials, thereby potentially contributing to the prevention or mitigation of the salt decay phenomenon in modern as well as historical building materials in a more sustainable manner. In this review, we first provide an essential background on the mechanism of salt crystallization and on the factors influencing this phenomenon; next, we illustrate the mechanism at the basis of the action of crystal growth inhibitors, and critically discuss the major advances in the development of different families of inhibitors, particularly focusing on their influence on salt transport and crystallization within the structure of porous media. Specifically, correlations between the crystallization inhibition processes in porous materials and variables, such as porous substrate composition and properties, contaminant salt type and concentrations, microclimatic conditions, inhibiting solution concentration and properties, and application methods, will be highlighted. Environmental aspects, limitations, and problems associated with some inhibition chemicals are also taken into account. Finally, a survey and a discussion on the most representative experimental techniques and instrumentation available to assess qualitatively and quantitatively the inhibitor effectiveness, as well as recently developed modelling tools are given out.

Calcium-Containing Crystals and Osteoarthritis: an Unhealthy Alliance

PURPOSE OF REVIEW

Osteoarthritis (OA) is the most common form of joint disease globally and is associated with significant morbidity and disability. Increasing evidence points to an important inflammatory component in the development and progression of OA. The precise pathways involved in OA inflammatory processes remain to be clarified. Basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate (CPP) crystals can induce inflammation and arthritis and recent studies point to a potential pathogenic role in OA. In the light of this evidence, we explore the relationship and potential mechanistic pathways linking calcium-containing crystals and OA.

RECENT FINDINGS

CPP crystals induce inflammation through the NLRP3 inflammasome while BCP crystals mediate both NLRP3 dependent and independent effects. BCP crystals have been demonstrated to induce key mitogenic and inflammatory pathways and contribute to cartilage degradation. Calcium-containing crystals induce key inflammatory pathways and may represent an attractive novel target in OA, a condition devoid of effective treatments.

Brain mitochondrial calcium transport: Origins of the set-point concept and its application to physiology and pathology

The transport of calcium across the inner mitochondrial membrane plays a key role in neuronal physiology and pathology. The kinetic responses of the uniporter and efflux pathways are such that a cytosolic free calcium 'set-point' can be established - above which there is net calcium accumulation into the matrix that is reversed when plasma membrane transport lowers cytosolic calcium. Pathological activation of N-methyl-d-aspartate receptor mediated sodium and calcium entry into the neuron, as occurs in stroke and spreading depression, places severe demands on both the ATP-generating and calcium loading capacities of the neuronal mitochondria as the set-point is exceeded. Experiments that led to the concept of the set-point are reviewed.

Expression of phosphocitrate-targeted genes in osteoarthritis menisci

Phosphocitrate (PC) inhibited calcium crystal-associated osteoarthritis (OA) in Hartley guinea pigs. However, the molecular mechanisms remain elusive. This study sought to determine PC targeted genes and the expression of select PC targeted genes in OA menisci to test hypothesis that PC exerts its disease modifying activity in part by reversing abnormal expressions of genes involved in OA. We found that PC downregulated the expression of numerous genes classified in immune response, inflammatory response, and angiogenesis, including chemokine (C-C motif) ligand 5, Fc fragment of IgG, low affinity IIIb receptor (FCGR3B), and leukocyte immunoglobulin-like receptor, subfamily B member 3 (LILRB3). In contrast, PC upregulated the expression of many genes classified in skeletal development, including collagen type II alpha1, fibroblast growth factor receptor 3 (FGFR3), and SRY- (sex determining region Y-) box 9 (SOX-9). Immunohistochemical examinations revealed higher levels of FCGR3B and LILRB3 and lower level of SOX-9 in OA menisci. These findings indicate that OA is a disease associated with immune system activation and decreased expression of SOX-9 gene in OA menisci. PC exerts its disease modifying activity on OA, at least in part, by targeting immune system activation and the production of extracellular matrix and selecting chondroprotective proteins.

Calcium in health and disease

Evolution has exploited the chemical properties of Ca(2+), which facilitate its reversible binding to the sites of irregular geometry offered by biological macromolecules, to select it as a carrier of cellular signals. A number of proteins bind Ca(2+) to specific sites: those intrinsic to membranes play the most important role in the spatial and temporal regulation of the concentration and movements of Ca(2+) inside cells. Those which are soluble, or organized in non-membranous structures, also decode the Ca(2+) message to be then transmitted to the targets of its regulation. Since Ca(2+) controls the most important processes in the life of cells, it must be very carefully controlled within the cytoplasm, where most of the targets of its signaling function reside. Membrane channels (in the plasma membrane and in the organelles) mediate the entrance of Ca(2+) into the cytoplasm, ATPases, exchangers, and the mitochondrial Ca(2+) uptake system remove Ca(2+) from it. The concentration of Ca(2+) in the external spaces, which is controlled essentially by its dynamic exchanges in the bone system, is much higher than inside cells, and can, under conditions of pathology, generate a situation of dangerous internal Ca(2+) overload. When massive and persistent, the Ca(2+) overload culminates in the death of the cell. Subtle conditions of cellular Ca(2+) dyshomeostasis that affect individual systems that control Ca(2+), generate cell disease phenotypes that are particularly severe in tissues in which the signaling function of Ca(2+) has special importance, e.g., the nervous system.

Biological activities of phosphocitrate: a potential meniscal protective agent

Phosphocitrate (PC) inhibited meniscal calcification and the development of calcium crystal-associated osteoarthritis (OA) in Hartley guinea pigs. However, the mechanisms remain elusive. This study sought to examine the biological activities of PC in the absence of calcium crystals and test the hypothesis that PC is potentially a meniscal protective agent. We found that PC downregulated the expression of many genes classified in cell proliferation, ossification, prostaglandin metabolic process, and wound healing, including bloom syndrome RecQ helicase-like, cell division cycle 7 homolog, cell division cycle 25 homolog C, ankylosis progressive homolog, prostaglandin-endoperoxide synthases-1/cyclooxygenase-1, and plasminogen activator urokinase receptor. In contrast, PC stimulated the expression of many genes classified in fibroblast growth factor receptor signaling pathway, collagen fibril organization, and extracellular structure organization, including fibroblast growth factor 7, collagen type I, alpha 1, and collagen type XI, alpha 1. Consistent with its effect on the expression of genes classified in cell proliferation, collagen fibril organization, and ossification, PC inhibited the proliferation of OA meniscal cells and meniscal cell-mediated calcification while stimulating the production of collagens. These findings indicate that PC is potentially a meniscal-protective agent and a disease-modifying drug for arthritis associated with severe meniscal degeneration.

The interplay of mitochondria with calcium: an historical appraisal

Indirect findings in the 1950s had indicated that mitochondria could accumulate Ca(2+), but only in 1961 isolated mitochondria were directly shown to take it up in a process driven by the activity of the respiratory chain or by the hydrolysis of added ATP. The uptake of Ca(2+) could be accompanied by the simultaneous uptake of inorganic phosphate, leading to the precipitation of hydroxyapatite in the matrix and to the effective buffering of the free Ca(2+) concentration in it. The uptake of Ca(2+) occurred via an electrophoretic uniporter that has been molecularly identified only recently. Ca(2+) was then released through a Na(+)/Ca(2+) exchanger that has also been identified very recently (a H(+)/Ca(2+) antiporter has also been described in some mitochondrial types). In the matrix two TCA cycle dehydrogenases and pyruvate dehydrogenase phosphate phosphatase were found to be regulated by Ca(2+), providing a rationale for the Ca(2+) cycling process. The affinity of the uptake uniporter was found to be too low to efficiently regulate Ca(2+) in the low to mid nM concentration in the cytosol. However, a number of findings showed that energy linked transport of Ca(2+) did nevertheless occur in mitochondria in situ. The enigma was solved in the 1990s, when it was found that perimitochondrial Ca(2+) pools are created by the discharge of Ca(2+) from vicinal endoplasmic reticulum stores in which the concentration of Ca(2+) is high enough to satisfy the poor affinity of the uniporter. Thus, mitochondria have now regained a key role in the regulation of cytosolic Ca(2+) (not only of their own internal Ca(2+)).

Phosphate-dependent stimulation of MGP and OPN expression in osteoblasts via the ERK1/2 pathway is modulated by calcium

Inorganic phosphate (Pi) acts as a signaling molecule in bone-forming cells, affecting cell functions and gene expression. Particularly, Pi stimulates the expression of mineralization-associated genes such as matrix gla protein (MGP) and osteopontin (OPN) through the ERK1/2 pathway. With respect to the presence of elevated extracellular calcium and Pi levels during bone remodeling, we questioned whether calcium might play a role in the Pi-dependent effects in osteoblasts. We first showed by Western blot and real-time PCR that the concomitant presence of 10 mM Pi and 1.8 mM calcium is required to stimulate ERK1/2 phosphorylation and MGP/OPN genes expression. The mechanisms involved in the cellular effects of calcium in the presence of Pi were subsequently examined. Firstly, the use of the calcium-sensing receptor (CaSR) agonist gadolinium and the G-protein inhibitor pertussis toxin enabled us to determine that a CaSR mechanism is not involved in the Pi and calcium mediated cellular effects. By transmission electron microscopy, we next demonstrated that adding 10mM Pi to the culture medium containing 1.8mM calcium led to the formation calcium phosphate precipitates (CaPp). Moreover, treatment of osteoblasts with exogenous pre-synthesized CaPp stimulated ERK1/2 phosphorylation and MGP/OPN genes expression. In spite of high extracellular calcium and Pi concentrations, this stimulation was blunted in the presence of phosphocitrate, an inhibitor of crystal formation. Finally, we showed that despite that CaPp are not endocytosed, their effect on ERK1/2 phosphorylation and MGP/OPN genes expression were dependent on lipid rafts integrity. In summary, we showed that calcium is required for Pi-dependent ERK1/2 phosphorylation and regulation of mineralization-associated genes in osteoblasts and that its effect could originate from extracellular-related effects of CaPp that are dependent on the integrity of lipid rafts.

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.

The fateful encounter of mitochondria with calcium: how did it happen?

A number of findings in the 1950s had offered indirect indications that mitochondria could accumulate Ca2+. In 1961, the phenomenon was directly demonstrated using isolated mitochondria: the uptake process was driven by respiratory chain activity or by the hydrolysis of added ATP. It could be accompanied by the simultaneous uptake of inorganic phosphate, in which case precipitates of hydroxyapatite were formed in the matrix, buffering its free Ca2+ concentration. The properties of the uptake process were established in the 1960s and 1970s: the uptake of Ca2+ occurred electrophoretically on a carrier that has not yet been molecularly identified, and was released from mitochondria via a Na+/Ca2+ antiporter. A H+/Ca2+ release exchanger was also found to operate in some mitochondrial types. The permeability transition pore was later also found to mediate the efflux of Ca2+ from mitochondria. In the mitochondrial matrix two TCA cycle dehydrogenases and pyruvate dehydrogenase phosphate phosphatase were found to be regulated in the matrix by the cycling of Ca2+ across the inner membrane. In conditions of cytoplasmic Ca2+ overload mitochondria could store for a time large amounts of precipitated Ca2+-phosphate, thus permitting cells to survive situations of Ca2+ emergency. The uptake process was found to have very low affinity for Ca2+: since the bulk concentration of Ca2+ in the cytoplasm is in the low to mid-nM range, it became increasingly difficult to postulate a role of mitochondria in the regulation of cytoplsmic Ca2+. A number of findings had nevertheless shown that energy linked Ca2+ transport occurred efficiently in mitochondria of various tissues in situ. The paradox was only solved in the 1990s, when it was found that the concentration of Ca2+ in the cytoplasm is not uniform: perimitochondrial micropools are created by the agonist-promoted discharge of Ca2+ from vicinal stores in which the concentration of Ca2+ is high enough to activate the low affinity mitochondrial uniporter. Mitochondria thus regained center stage as important regulators of cytoplasmic Ca2+ (not only of their own internal Ca2+). Their Ca2+ uptake systems was found to react very rapidly to cytoplasmic Ca2+ demands, even in the 150-200 msec time scale of processes like the contraction and relaxation of heart. An important recent development in the area of mitochondrial Ca2+ transport is its involvement in the disease process. Ca2+ signaling defects are now gaining increasing importance in the pathogenesis of diseases, e.g., neurodegenerative diseases. Since mitochondria have now regained a central role in the regulation of cytoplasmic Ca2+, dysfunctions of their Ca2+ controlling systems have expectedly been found to be involved in the pathogenesis of numerous disease processes.

A Novel Strategy for the Preparation of Naturally Occurring Phosphocitrate and Its Partially Esterified Derivatives

A novel method for the synthesis of phosphocitrate (1, PC) starting from triethyl ester of citric acid and MeOPCl2 is described. The method is based on selective stepwise hydrolysis of ester moieties from the intermediate Me-O-P(O)(Cl)(Z) (Z = triethylcitrate), 4a, which also allows one to prepare partially esterified derivatives of PC with good yield and purity without chromatographic purifications.

Phosphocitrate blocks calcification-induced articular joint degeneration in a guinea pig model

OBJECTIVE

Calcium deposition occurs frequently in osteoarthritic (OA) joints. However, evidence for a causal role of calcification in cartilage degeneration is inferential. The present study was undertaken to examine the role of calcification in OA disease progression and to evaluate a formulation of phosphocitrate (PC) as a potential therapeutic agent.

METHODS

We have identified a guinea pig OA model in which meniscal calcification appears to correlate with aging and disease progression. We synthesized a new formulation of PC, [CaNa(PC)2(H2O)](n) (CaNaPC), which is a potent antimineralization agent and a specific inhibitor of crystal-induced biologic effects. After weekly treatment of guinea pigs with experimental OA with CaNaPC for 3 months, we examined calcification in menisci and cartilage degeneration. As a control, we examined whether similar CaNaPC treatment had any therapeutic effect in a hemi-meniscectomy model in which there is no known crystal involvement.

RESULTS

Meniscal calcification correlated with cartilage degeneration in this animal model. PC treatment led to significant reduction of calcium deposits and arrested OA disease progression. Similar treatment had no effect in the hemi-meniscectomy model.

CONCLUSION

CaNaPC diminishes mineralization in a cutaneous calcergy model and a model of OA in which intraarticular mineralization is a prominent feature. In the OA guinea pig model, inhibition of calcification is accompanied by diminished cartilage degeneration. CaNaPC has no therapeutic effect in the hemi-meniscectomy model. We conclude that pathologic calcification may initiate or amplify processes leading to cartilage degeneration and that CaNaPC may interrupt such a pathway.

Basic calcium phosphate crystal-induced prostaglandin E2 production in human fibroblasts: Role of cyclooxygenase 1, cyclooxygenase 2, and interleukin-1?

OBJECTIVE

To elucidate the mechanism of basic calcium phosphate (BCP) crystal-induced prostaglandin E(2) (PGE(2)) production in human foreskin fibroblasts (HFFs), to identify the signaling pathway involved in the induction of cyclooxygenase 2 (COX-2) messenger RNA (mRNA) by BCP crystals, to examine the effect of BCP crystals on interleukin-1beta (IL-1beta) mRNA expression, and to investigate the potential of phosphocitrate to abrogate the BCP crystal-induced effects.

METHODS

PGE(2) levels were quantified using a commercial enzyme immunoassay kit. COX-2 and COX-1 transcript levels were quantified using real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Induction of IL-1beta and COX-2 mRNA was examined by end-point RT-PCR. COX-2 protein expression was assessed by Western blotting.

RESULTS

PGE(2) production measured 4 and 30 hours after BCP crystal treatment was higher in BCP crystal-treated (mean +/- SEM 1,891 +/- 273 pg/microg and 1,792 +/- 233 pg/microg, respectively) than in untreated (88 +/- 5 pg/microg and 205 +/- 93 pg/microg, respectively) HFFs. The PGE(2) produced after 4 hours was sensitive to inhibition with NS398, a selective COX-2 inhibitor, implying that it was COX-2 mediated, whereas the PGE(2) produced at 30 hours could not be completely inhibited by NS398. Real-time RT-PCR demonstrated a 23-fold increase in COX-2 mRNA that was maximal at 4 hours, whereas analysis of mRNA for COX-1 showed up-regulation of transcript peaking at 24 hours poststimulation (1.75-fold increase). The protein kinase C and phosphatidylinositol 3-kinase signal-transduction inhibitors bisindolylmaleimide I and LY294002, respectively, blocked BCP crystal-induced COX-2 mRNA in HFFs. In addition, BCP crystals were found to up-regulate the proinflammatory cytokine IL-1beta (maximal at 8 hours). The induction of both COX-2 and IL-1beta by BCP crystals was attenuated when the cells were treated with phosphocitrate.

CONCLUSION

These findings indicate that BCP crystals may be an important amplifier of PGE(2) production through induction of the COX enzymes and the proinflammatory cytokine IL-1beta.

Phosphocitrate inhibits calcium hydroxyapatite induced mitogenesis and upregulation of matrix metalloproteinase-1, interleukin-1beta and cyclooxygenase-2 mRNA in human breast cancer cell lines

Microcalcifications containing calcium hydroxyapatite (HA) are often associated with malignant human breast lesions. Frequently, they are the only mammographic features that indicate the presence of a tumoural lesion. We previously reported the induction of both mitogenesis and prostaglandin E2 (PGE2) production and the increased activities of matrix metalloproteinases (MMPs) MMP-2 and MMP-9 in normal human mammary epithelial cells and breast cancer cell lines, treated with HA. In the present study we attempted to elucidate the mechanism of these biological effects. Firstly, we found that direct cell-crystal contact was required for induction of mitogenesis as the effect was not merely a result of isotopic exchange of calcium into the culture medium. Treatment with bafilomycin A1, a proton pump inhibitor, abrogated HA-induced mitogenesis to control cell levels. These results suggest that phagocytosis and intracellular crystal dissolution is required for HA-induced mitogenesis. We also demonstrated that the increase in prostaglandin E2, previously reported, is due, at least in part, to HA-induced upregulation of cyclooxygenase-2 (COX-2) in Hs578T cells. An accumulation of MMP-1 mRNA was also shown in response to HA stimulation in Hs578T cells. Furthermore, a HA-induced increase in interleukin-1beta (IL-1beta), a potent inducer of MMP-1 gene expression, was demonstrated in Hs578T cells at 2 and 4 h. Treatment with phosphocitrate (PC) (a naturally occurring inhibitor of calcium phosphate crystallisation, which is known to block a number of HA-induced biological effects in other cell types) blocked HA-mediated mitogenesis, as well as, COX-2, MMP-1 and IL-1beta induction, at the transcriptional level. These results show that calcium HA crystals are capable of exerting significant biological effects on surrounding cells which can be abrogated by PC and emphasise the role of calcium HA in amplifying the pathological process involved in breast cancer.

Basic calcium phosphate crystals up-regulate metalloproteinases but down-regulate tissue inhibitor of metalloproteinase-1 and -2 in human fibroblasts

OBJECTIVE

To examine the effect of basic calcium phosphate (BCP) crystals on expression of tissue inhibitors of metalloproteinases (TIMP)-1 and -2 in human fibroblasts.

METHOD

Using a semi-quantitative reverse transcription-polymerase chain reaction method and phosphocitrate (PC), a specific inhibitor of the biological effects of BCP crystals, we examined the effects of BCP on the steady state transcript levels of metalloproteinase (MMP)-1, -3, -9 and -13 and TIMP-1 and -2 in human fibroblasts. DNA primers against elongation factor were used as internal controls. RNAs isolated from human fibroblasts treated with BCP crystals (50 microg/ml) in the presence or absence of PC (10(-3) M) were used as templates, and RNA from untreated control cultures and cultures treated with Interleukin-1-beta (IL-1beta) were used as negative and positive controls, respectively.

RESULTS

We observed increases in MMP-1, -3, -9 and -13 transcripts by BCP crystals. BCP crystal down-regulated TIMP-1 and -2 over untreated controls. Western blot analysis confirmed that BCP crystals down-regulate the synthesis of TIMP-1 and -2. While IL-1beta up-regulated MMP-1, -3, -9 and -13, it had no significant effect on expression of either TIMP. In all cases, PC specifically reversed the differential regulation of MMPs and TIMPs by BCP crystals but had no effect on IL-1beta induction of MMP expression.

CONCLUSION

The ability of BCP to induce the synthesis of degradative MMPs while down-regulating the synthesis of the naturally occurring counterpart TIMPs may explain the changes consistent with a role of BCP crystal in the pathogenesis of degenerative changes in osteoarthritis. The ability of PC to reverse both degradative effects of BCP crystal suggests that PC can be a potential therapeutic agent for BCP crystal deposition diseases.

Phosphocitrate as a potential therapeutic strategy for crystal deposition disease

The deposition of basic calcium phosphate and calcium pyrophosphate dihydrate crystals in articular tissues is probably an under-recognized event. Clinical observations indicate that exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Measurements of putative markers of cartilage breakdown suggest that these crystals magnify the degenerative process. In vitro studies reveal two potential mechanisms by which crystals cause degeneration. These involve the stimulation of mitogenesis in synovial fibroblasts and the secretion of metalloproteinases by cells that phagocytose these crystals. Approaches that may ameliorate the degenerative process may ensue from new information about how crystals form and how they exert their biologic effects.

Calcium crystal effects on the cells of the joint: implications for pathogenesis of disease

In the past three years, there has been considerable progress in delineating the mechanism of calcium-containing crystal-induced cell activation: (1) the identification of Ca2+ influx and p42/44 mitogen-activated protein kinase activation as the signal transduction pathways; (2) induction of nuclear transcription factors of cyclic adenosine monophosphate (cAMP) response element binding protein, activator protein-1, and nuclear factor kappaB; (3) the differential role of crystal endocytosis and dissolution in crystal-induced metalloproteinase synthesis and mitogenesis; (4) crystal upregulation of matrix metalloproteinases, including MMP-13 but downregulation of tissue inhibitor of metalloproteinase-1 and -2, thus magnifying the degenerative effect of crystals. Phosphocitrate, a specific inhibitor of biologic effect of calcium crystals, reverses the degenerative effects of crystals.

The role of crystals in articular tissue degeneration

The deposition of calcium-containing crystals in articular tissues is probably an underrecognized event. Clinical observations indicate that exaggerated and uniquely distributed cartilage degeneration is associated with these deposits. Perhaps the most compelling argument favoring a role for crystals in causing osteoarthritis stems from their in vitro effects on articular tissues. In this short review, we will discuss the fact that crystals can cause the degeneration of articular tissues in 2 separate pathways. In the "Direct" pathway, crystals directly induce fibroblast-like synoviocytes to proliferate and produce metalloproteinases and prostaglandins. The other "Paracrine pathway" involves the interaction between crystals and macrophages/monocytes, which leads to synthesis and release of cytokines that can reinforce the action of crystals on synoviocytes and induce chondrocytes to secrete enzymes, eventually causing the degeneration of articular tissues.

Phosphocitrate inhibits a basic calcium phosphate and calcium pyrophosphate dihydrate crystal-induced mitogen-activated protein kinase cascade signal transduction pathway

Calcium deposition diseases caused by calcium pyrophosphate dihydrate (CPPD) and basic calcium phosphate (BCP) crystals are a significant source of morbidity in the elderly. We have shown previously that both types of crystals can induce mitogenesis, as well as metalloproteinase synthesis and secretion by fibroblasts and chondrocytes. These responses may promote degradation of articular tissues. We have also shown previously that both CPPD and BCP crystals activate expression of the c-fos and c-jun proto-oncogenes. Phosphocitrate (PC) can specifically block mitogenesis and proto-oncogene expression induced by either BCP or CPPD crystals in 3T3 cells and human fibroblasts, suggesting that PC may be an effective therapy for calcium deposition diseases. To understand how PC inhibits BCP and CPPD-mediated cellular effects, we have investigated the mechanism by which BCP and CPPD transduce signals to the nucleus. Here we demonstrate that BCP and CPPD crystals activate a protein kinase signal transduction pathway involving p42 and p44 mitogen-activated protein (MAP) kinases (ERK 2 and ERK 1). BCP and CPPD also cause phosphorylation of a nuclear transcription factor, cyclic AMP response element-binding protein (CREB), on serine 133, a residue essential for CREB's ability to transactivate. Treatment of cells with PC at concentrations of 10(-3) to 10(-5) M blocked both the activation of p42/p44 MAP kinases, and CREB serine 133 phosphorylation, in a dose-dependent fashion. At 10(-3) M, a PC analogue, n-sulfo-2-aminotricarballylate and citrate also modulate this signal transduction pathway. Inhibition by PC is specific for BCP- and CPPD-mediated signaling, since all three compounds had no effect on serum-induced p42/P44 or interleukin-1beta induced p38 MAP kinase activities. Treatment of cells with an inhibitor of MEK1, an upstream activator of MAPKs, significantly inhibited crystal-induced cell proliferation, suggesting that the MAPK pathway is a significant mediator of crystal-induced signals.

Inhibition of calcium pyrophosphate dihydrate crystal formation in articular cartilage vesicles and cartilage by phosphocitrate

Articular cartilage vesicles (ACV), isolated by differential centrifugation of adult hyaline articular cartilage collagenase digests, mineralized in the presence of calcium and ATP. Mineral analysis by microscopy, chemical analysis, energy-dispersive analysis, and infrared spectroscopy revealed crystals resembling calcium pyrophosphate dihydrate (CPPD). Adult articular cartilage also underwent ATP-dependent mineralization, supporting the contention that vesicles in situ fostered adult articular cartilage mineralization. Phosphocitrate (PC) is a recognized in vitro inhibitor of hydroxyapatite and calcium oxalate monohydrate crystal formation, but it is not known whether PC can similarly restrict CPPD crystal development. In the present study we examine the effect of PC, citrate, and n-sulfo-2-amino-tricarballylate (SAT, a PC analogue) on the ATP-induced CPPD crystal formation in both ACV and articular cartilage models. Only PC (10-1000 microM) blocked both the ATP-dependent and -independent mineralization in ACV in a dose-dependent fashion. At 1 mM, SAT and citrate blocked the ATP-independent mineralization. Similarly, only PC blocked both the ATP- and non-ATP-dependent mineralization in native articular cartilage slices. PC, SAT, and citrate had no effect on ACV nucleoside triphosphate pyrophosphohydrolase activity, suggesting that none of these agents blocked mineralization through the inhibition of nucleoside triphosphate pyrophosphohydrolase activity, which generates inorganic pyrophosphate from ATP.

Liposome and multiple emulsion formulations augment the anticalcifying efficacy of phosphocitrate in a cutaneous calcergy model

The anticalcifying agent phosphocitrate was incorporated into phosphatidylcholine/cholesterol liposomes by reverse-phase evaporation. The compound was entrapped to the extent of 11.6% (mol mol-1 of lipid) and the liposomes exhibited prolonged retention of the compound when incubated with rat plasma. Phosphocitrate's ionic contribution in solution adversely influenced the encapsulation efficiency but improvements were made through ion-pairing with the quaternary ammonium detergent centrimide, or with the inclusion of stearylamine in the lipid phase. The liposomal dose that could be practically administered in-vivo was restricted to 2.5 mg phosphocitrate kg-1 day-1. The formulation of a multiple emulsion preparation of phosphocitrate, however, offered an alternative delivery mode permitting infrequent dosing to be successfully investigated. In a rat calcergy model, both vehicles effectively reduced the formation of induced subcutaneous calcified plaques at doses for which the phosphocitrate salt alone was inactive. The current formulations demonstrate that the therapeutic efficacy of phosphocitrate can be markedly improved through an appropriately designed drug delivery system, signalling a new approach for the future therapeutic application of this compound.

Phosphocitrate prevents disease progression in murine progressive ankylosis

OBJECTIVE

Mice with progressive ankylosis, a spontaneous arthropathy, were treated with phosphocitrate (PC) in vivo to determine the effect of PC on disease progression.

METHODS

Two groups of mice with progressive ankylosis (matched for age, weight, and sex) were treated parenterally for 6 weeks with either PC or saline vehicle.

RESULTS

Clinically, histologically, and microradiographically, there were significant differences in disease progression and severity in the PC-treated and the saline-treated mice.

CONCLUSION

PC appears to inhibit disease progression in murine progressive ankylosis.

High-performance liquid chromatographic and mass spectrometric identification of phosphocitrate synthesized by human kidney homogenate

Two high-performance liquid chromatographic techniques for the analysis of phosphocitrate, a metabolite synthesized by the cell that is thought to play a role in a number of physiological as well as pathological events, have been developed. The mass spectra of the isolated compound obtained under fast-atom bombardment and collisionally activated decomposition mass-analysed ion kinetic energy conditions are also reported.

Ultrastruct pathology of phalloidin-intoxicated hepatocytes in the presence and absence of extracellular calcium

The killing of cultured hepatocytes by phalloidin can be dissociated into two phases by manipulation of the Ca2+ concentration of the medium. In the absence of extracellular Ca2+, hepatocytes are injured but not killed by phalloidin. Addition of 1.8 mM Ca2+ to the culture medium kills 60-70% of the cells by three hours. As an initial attempt to identify the mechanisms whereby Ca2+ ions irreversibly injure phalloidin-damaged hepatocytes, we have examined the ultrastructural pathology of phalloidin-intoxicated liver cells in the presence or absence of extracellular Ca2+. In the absence of extracellular Ca2+ ions, the morphologic manifestations of phalloidin intoxication reflect entirely the interaction between phalloidin, microfilaments, and the plasma membrane. In the presence of Ca2+ ions, the morphologic manifestations of the lethal effects of Ca2+ are described: the swelling of mitochondria accompanied by the accumulation of dense, amorphous precipitates; a supercontracture of microfilaments, and a loss of volume control with intracellular edema and a change in cell shape. These alterations can be attributed to the known biologic actions of Ca2+ ions on cellular structure and function. The present study allows, therefore, a preliminary identification of mechanisms by which extracellular Ca2+ ions may mediate cell death in this as well as in other similar situations.