Phosphate metabolism: its impact on disorders of mineral metabolism

Regulatory molecules typically work cooperatively to ensure the efficient functioning of hormonal systems. Examples include LH and FSH in reproductive biology, insulin and glucagon in glucose metabolism. Similarly, calcium and phosphorus are important regulators of skeletal homeostasis. In the circulation, these molecules are under the control of PTH, 1,25(OHD), and FGF23. In turn, these hormones depend upon a mutual and complex interplay among themselves. For example, alterations in calcium metabolism influence phosphorus homeostasis, as occurs in primary hyperparathyroidism (PHPT). Not as well recognized is the influence that abnormalities in phosphorus metabolism can have on calcium homeostasis. In this review, we call attention to the impact that abnormalities in phosphorus can have on calcium metabolism.

Short-term starvation activates AMPK and restores mitochondrial inorganic polyphosphate, but fails to reverse associated neuronal senescence

Neuronal senescence is a major risk factor for the development of many neurodegenerative disorders. The mechanisms that drive neurons to senescence remain largely elusive; however, dysregulated mitochondrial physiology seems to play a pivotal role in this process. Consequently, strategies aimed to preserve mitochondrial function may hold promise in mitigating neuronal senescence. For example, dietary restriction has shown to reduce senescence, via a mechanism that still remains far from being totally understood, but that could be at least partially mediated by mitochondria. Here, we address the role of mitochondrial inorganic polyphosphate (polyP) in the intersection between neuronal senescence and dietary restriction. PolyP is highly present in mammalian mitochondria; and its regulatory role in mammalian bioenergetics has already been described by us and others. Our data demonstrate that depletion of mitochondrial polyP exacerbates neuronal senescence, independently of whether dietary restriction is present. However, dietary restriction in polyP-depleted cells activates AMPK, and it restores some components of mitochondrial physiology, even if this is not sufficient to revert increased senescence. The effects of dietary restriction on polyP levels and AMPK activation are conserved in differentiated SH-SY5Y cells and brain tissue of male mice. Our results identify polyP as an important component in mitochondrial physiology at the intersection of dietary restriction and senescence, and they highlight the importance of the organelle in this intersection.

Activation of Nuclear Factor Erythroid 2-Related Factor 2 Transcriptionally Upregulates Ectonucleotide Pyrophosphatase/Phosphodiesterase 1 Expression and Inhibits Ectopic Calcification in Mice

Calcification plays a key role in biological processes, and breakdown of the regulatory mechanism results in a pathological state such as ectopic calcification. We hypothesized that ENPP1, the enzyme that produces the calcification inhibitor pyrophosphate, is transcriptionally regulated by Nrf2, and that Nrf2 activation augments ENPP1 expression to inhibit ectopic calcification. Cell culture experiments were performed using mouse osteoblastic cell line MC3T3-E1. Nrf2 was activated by 5-aminolevulinic acid and sodium ferrous citrate. Nrf2 overexpression was induced by the transient transfection of an Nrf2 expression plasmid. ENPP1 expression was monitored by real-time RT-PCR. Because the promoter region of ENPP1 contains several Nrf2-binding sites, chromatin immunoprecipitation using an anti-Nrf2 antibody followed by real-time PCR (ChIP-qPCR) was performed. The relationship between Nrf2 activation and osteoblastic differentiation was examined by alkaline phosphatase (ALP) and Alizarin red staining. We used mice with a hypomorphic mutation in ENPP1 (ttw mice) to analyze whether Nrf2 activation inhibits ectopic calcification. Nrf2 and Nrf2 overexpression augmented ENPP1 expression and inhibited osteoblastic differentiation, as indicated by ALP expression and calcium deposits. ChIP-qPCR showed that some putative Nrf2-binding sites in the ENPP1 promoter region were bound by Nrf2. Nrf2 activation inhibited ectopic calcification in mice. ENPP1 gene expression was transcriptionally regulated by Nrf2, and Nrf2 activation augmented ENPP1 expression, leading to the attenuation of osteoblastic differentiation and ectopic calcification in vitro and in vivo. Nrf2 activation has a therapeutic potential for preventing ectopic calcification.

Histidine-Rich Glycoprotein Modulates the Toxic Effects of High-Dose Polyphosphate in Mice

BACKGROUND

Polyphosphate (polyP), a procoagulant released from platelets, activates coagulation via the contact system and modulates cardiomyocyte viability. High-dose intravenous polyP is lethal in mice, presumably because of thrombosis. Previously, we showed that HRG (histidine-rich glycoprotein) binds polyP and attenuates its procoagulant effects. In this study, we investigated the mechanisms responsible for the lethality of intravenous polyP in mice and the impact of HRG on this process.

METHODS

The survival of wild-type or HRG-deficient mice given intravenous synthetic or platelet-derived polyP in doses up to 50 mg/kg or saline was compared. To determine the contribution of thrombosis, the effect of FXII (factor XII) knockdown or enoxaparin on polyP-induced fibrin deposition in the lungs was examined. To assess cardiotoxicity, the ECG was continuously monitored, the levels of troponin I and the myocardial band of creatine kinase were quantified, and the viability of a cultured murine cardiomyocyte cell line exposed to polyP in the absence or presence of HRG was determined.

RESULTS

In HRG-deficient mice, polyP was lethal at 30 mg/kg, whereas it was lethal in wild-type mice at 50 mg/kg. Although FXII knockdown or enoxaparin administration attenuated polyP-induced fibrin deposition in the lungs, neither affected mortality. PolyP induced dose-dependent ECG abnormalities, including heart block and ST-segment changes, and increased the levels of troponin and myocardial band of creatine kinase, effects that were more pronounced in HRG-deficient mice than in wild-type mice and were attenuated when HRG-deficient mice were given supplemental HRG. Consistent with its cardiotoxicity, polyP reduced the viability of cultured cardiomyocytes in a dose-dependent manner, an effect attenuated with supplemental HRG.

CONCLUSIONS

High-dose intravenous polyP is cardiotoxic in mice, and HRG modulates this effect.

Mitochondrial Permeability Transition, Cell Death and Neurodegeneration

Neurodegenerative diseases are chronic conditions occurring when neurons die in specific brain regions that lead to loss of movement or cognitive functions. Despite the progress in understanding the mechanisms of this pathology, currently no cure exists to treat these types of diseases: for some of them the only help is alleviating the associated symptoms. Mitochondrial dysfunction has been shown to be involved in the pathogenesis of most the neurodegenerative disorders. The fast and transient permeability of mitochondria (the mitochondrial permeability transition, mPT) has been shown to be an initial step in the mechanism of apoptotic and necrotic cell death, which acts as a regulator of tissue regeneration for postmitotic neurons as it leads to the irreparable loss of cells and cell function. In this study, we review the role of the mitochondrial permeability transition in neuronal death in major neurodegenerative diseases, covering the inductors of mPTP opening in neurons, including the major ones-free radicals and calcium-and we discuss perspectives and difficulties in the development of a neuroprotective strategy based on the inhibition of mPTP in neurodegenerative disorders.

The dynamic relationship between inorganic polyphosphate and adenosine triphosphate in human non-small cell lung cancer H1299 cells

Inorganic polyphosphate (polyP) plays a vital role in cellular energy metabolism and signaling, owing to its structure and high-energy phosphate bonds. Intracellular ATP functions both as a cellular energy source and a key factor in cell death, and ATP dynamics in tumor cells are crucial for advancing cancer therapy. In this study, we explored the interplay between polyP and ATP in cellular energy metabolism. Treatment with polyP did not affect cell proliferation of human non-small cell lung cancer H1299 and human glioblastoma T98G cell lines as compared to their respective control cells until 72 h post-treatment. The mitochondrial membrane potential (MMP) in polyP-treated cells was low, contrasting with the time-dependent increase observed in control cells. While the ATP content increased over time in untreated and Na-phosphate-treated control cells, it remained unchanged in polyP-treated cells. Furthermore, the addition of cyclosporine A, a mitochondrial permeability transition pore (mPTP) inhibitor, failed to restore ATP levels in polyP-treated cells. We performed lactate assays and western blot analysis to evaluate the effect of polyP on glucose metabolism and found no significant differences in lactate secretion or glucose-6-phosphate dehydrogenase (G6PD) activity between polyP-treated and control cells. Additional pyruvate restored MMP but had no effect on the cellular ATP content in polyP-treated cells. We observed no correlation between the Warburg effect and glucose metabolism during ATP depletion in polyP-treated cells. Further investigation is warranted to explore the roles of polyP and ATP in cancer cell energy metabolism, which might offer potential avenues for therapeutic interventions.

Vitamin D and cancer

The role of vitamin D in the prevention of chronic diseases including cancer, has received a great deal of attention during the past few decades. The term "Cancer" represents multiple disease states with varying biological complexities. The strongest link between vitamin D and cancer is provided by ecological and studies like observational, in preclinical models. It is apparent that vitamin D exerts diverse biological responses in a tissue specific manner. Moreover, several human factors could affect bioactivity of vitamin D. The mechanism(s) underlying vitamin D initiated anti-carcinogenic effects are diverse and includes changes at the muti-system levels. The oncogenic environment could easily corrupt the traditional role of vitamin D or could ensure resistance to vitamin D mediated responses. Several researchers have identified gaps in our knowledge pertaining to the role of vitamin D in cancer. Further areas are identified to solidify the role of vitamin D in cancer control strategies.

Inorganic polyphosphate regulates functions of thymocytes via activation of P2X purinoreceptors

Inorganic polyphosphate (polyP) is an ancient polymer, which was proven to be a signalling molecule in the mammalian brain, mediating the communication between astrocytes via activation of P2Y1 purinoreceptors and modulating the activity of neurons. There is very limited information regarding the ability of polyP to transmit the information as an agonist of purinoreceptors in other cells and tissues. Here, we show that application of polyP to the suspension of primary thymocytes increases the concentration of intracellular calcium. PolyP evoked calcium signal was dependent on the presence of P2X inhibitors but not P2Y1 inhibitor. PolyP dependent increase in intracellular calcium concentration caused mild mitochondrial depolarization, which was dependent on inhibitors of purinoreceptors, extracellular calcium and inhibitor of mitochondrial calcium uniporter but wasn't dependent on cyclosporin A. Application of polyP modulated cell volume regulation machinery of thymocytes in calcium dependent manner. Molecular docking experiments revealed that polyP can potentially bind to several types of P2X receptors with binding energy similar to ATP - natural agonist of P2X purinoreceptors. Further molecular dynamics simulations with P2X4 showed that binding of one molecule of polyP dramatically increases permeability of this receptor-channel for water molecules. Thus, in this research we for the first time showed that polyP can interact with P2X receptors in thymocytes and modulate physiological processes.

The effect of Si species released from bioactive glasses on cell behaviour: A quantitative review

Despite over 50 years of silicate bioactive glass (SBG) research, commercial success, and 6000+ published articles, there remains a lack of understanding of how soluble silicate (Si) species released from SBGs influences cellular responses. Using a systematic approach, this article quantitatively compares the in vitro responses of cells to SBG dissolution products reported in the literature and determines if there is a Si concentration ([Si]) dependent effect on cell behaviour. Cell behavioural responses to SBGs [Si] in dissolution products included metabolic activity (reported in 52 % of articles), cell number (24 %), protein production (22 %), gene expression (22 %) and biomineralization (24 %). There was a difference in the [Si] reported to cause increased (desirable) cellular responses (median = 30.2 ppm) compared to the [Si] reported to cause decreased (undesirable) cellular responses (median = 52.0 ppm) (P ≤ 0.001). The frequency of undesirable outcomes increased with increasing [Si], with ∼3 times more negative outcomes reported above 52 ppm. We also investigated the effect of [Si] on specific cellular outcomes (e.g., metabolic activity, angiogenesis, osteogenesis), if cell type/species influenced these responses and the impact of other ions (Ca, P, Na) within the SBG dissolution media on cell behaviour. This review has, for the first time, quantitatively compared the cellular responses to SBGs from the literature, providing a quantitative overview of SBG in vitro practices and presents evidence of a range of [Si] where desirable cellular responses may be more likely (30-52 ppm). This review also demonstrates the need for greater standardisation of in vitro methodological approaches and recommends some minimum reporting standards. STATEMENT OF SIGNIFICANCE: This systematic review investigates the relationship between the concentration of Si released from Si-bioactive glasses (SBG) and in vitro cellular responses. Si releasing materials continue to be of considerable scientific, commercial, and medical interest (with 1500+ articles published in the last 3 years) but there is considerable variation in the reported biologically effective Si concentrations and on the importance of Si on cell behaviour. Despite the variation in methodological approaches, this article demonstrated statistical commonalities in the Si concentrations that cause desirable and undesirable cellular behaviours, suggesting a window where positive cellular outcomes are more likely. This review also provides a quantitative analysis of in vitro practices within the bioactive glass field and highlights the need for greater standardisation.

Sodium Hexametaphosphate Serves as an Inducer of Calcium Signaling

In bacteria, polymers of inorganic phosphates, particularly linear polyphosphate, are used as alternative phosphate donors for adenosine triphosphate production. A six-chain form of sodium metaphosphate, sodium hexametaphosphate (SHMP), is believed to have no physiological functions in mammalian cells. In this study, we explored the possible effects of SHMP on mammalian cells, using mouse oocytes, which are useful for observing various spatiotemporal intracellular changes. Fertilization-competent oocytes were isolated from the oviducts of superovulated mice and cultured in an SHMP-containing medium. In the absence of co-incubation with sperm, SHMP-treated oocytes frequently formed pronuclei and developed into two-cell embryos owing to the increase in calcium concentration in the cytoplasm. We discovered an intriguing role for SHMP as an initiator of calcium rise in mouse oocytes, presumably in a wide variety of mammalian cells.

FGF23 Actions in CKD-MBD and other Organs During CKD

Fibroblast growth factor 23 (FGF23) is a new endocrine product discovered in the past decade. In addition to being related to bone diseases, it has also been found to be related to kidney metabolism and parathyroid metabolism, especially as a biomarker and a key factor to be used in kidney diseases. FGF23 is upregulated as early as the second and third stages of chronic kidney disease (CKD) in response to relative phosphorus overload. The early rise of FGF23 has a protective effect on the body and is essential for maintaining phosphate balance. However, with the decline in renal function, eGFR (estimated glomerular filtration rate) declines, and the phosphorus excretion effect caused by FGF23 is weakened. It eventually leads to a variety of complications, such as bone disease (Chronic Kidney Disease-Mineral and Bone Metabolism Disorder), vascular calcification (VC), and more. Monoclonal antibodies against FGF23 are currently used to treat genetic diseases with increased FGF23. CKD is also a state of increased FGF23. This article reviews the current role of FGF23 in CKD and discusses the crosstalk between various organs under CKD conditions and FGF23. Studying the effect of hyperphosphatemia on different organs of CKD is important. The prospect of FGF23 for therapy is also discussed.

Inorganic Polyphosphate: Coacervate Formation and Functional Significance in Nanomedical Applications

Inorganic polyphosphates (polyP) are long-chain polymers of orthophosphate residues, which, depending on the external conditions, can be present both physiologically and synthetically in either soluble, nanoparticulate or coacervate form. In recent years, these polymers have received increasing attention due to their unprecedented ability to exhibit both morphogenetic and metabolic energy delivering properties. There are no other physiological molecules that contain as many metabolically utilizable, high-energy bonds as polyP, making these polymers of particular medical interest as components of advanced hydrogel scaffold materials for potential applications in ATP-dependent tissue regeneration and repair. However, these polymers show physiological activity only in soluble form and in the coacervate phase, but not as stable metal-polyP nanoparticles. Therefore, understanding the mechanisms of formation of polyP coacervates and nanoparticles as well as their transformations is important for the design of novel materials for tissue implants, wound healing, and drug delivery and is discussed here.

Inorganic Polyphosphate-Regulator of Cellular Metabolism in Homeostasis and Disease

Inorganic polyphosphate (polyP), a simple anionic polymer consisting of even hundreds of orthophosphate units, is a universal molecule present in both simple and complex organisms. PolyP controls homeostatic processes in animals, such as blood coagulation, tissue regeneration, and energy metabolism. Furthermore, this polymer is a potent regulator of inflammation and influences host immune response in bacterial and viral infections. Disturbed polyP systems have been related to several pathological conditions, including neurodegeneration, cardiovascular disorders, and cancer, but we lack a full understanding of polyP biogenesis and mechanistic insights into the pathways through which polyP may act. This review summarizes recent studies that describe the role of polyP in cell homeostasis and show how disturbances in polyP levels may lead to disease. Based on the collected findings, we highlight the possible usage of this polymer as a promising therapeutic tool in multiple pathologies.

Inorganic Polymeric Materials for Injured Tissue Repair: Biocatalytic Formation and Exploitation

Two biocatalytically produced inorganic biomaterials show great potential for use in regenerative medicine but also other medical applications: bio-silica and bio-polyphosphate (bio-polyP or polyP). Biosilica is synthesized by a group of enzymes called silicateins, which mediate the formation of amorphous hydrated silica from monomeric precursors. The polymeric silicic acid formed by these enzymes, which have been cloned from various siliceous sponge species, then undergoes a maturation process to form a solid biosilica material. The second biomaterial, polyP, has the extraordinary property that it not only has morphogenetic activity similar to biosilica, i.e., can induce cell differentiation through specific gene expression, but also provides metabolic energy through enzymatic cleavage of its high-energy phosphoanhydride bonds. This reaction is catalyzed by alkaline phosphatase, a ubiquitous enzyme that, in combination with adenylate kinase, forms adenosine triphosphate (ATP) from polyP. This article attempts to highlight the biomedical importance of the inorganic polymeric materials biosilica and polyP as well as the enzymes silicatein and alkaline phosphatase, which are involved in their metabolism or mediate their biological activity.

Biomimetic Polyphosphate Materials: Toward Application in Regenerative Medicine

In recent years, inorganic polyphosphate (polyP) has attracted increasing attention as a biomedical polymer or biomaterial with a great potential for application in regenerative medicine, in particular in the fields of tissue engineering and repair. The interest in polyP is based on two properties of this physiological polymer that make polyP stand out from other polymers: polyP has morphogenetic activity by inducing cell differentiation through specific gene expression, and it functions as an energy store and donor of metabolic energy, especially in the extracellular matrix or in the extracellular space. No other biopolymer applicable in tissue regeneration/repair is known that is endowed with this combination of properties. In addition, polyP can be fabricated both in the form of a biologically active coacervate and as biomimetic amorphous polyP nano/microparticles, which are stable and are activated by transformation into the coacervate phase after contact with protein/body fluids. PolyP can be used in the form of various metal salts and in combination with various hydrogel-forming polymers, whereby (even printable) hybrid materials with defined porosities and mechanical and biological properties can be produced, which can even be loaded with cells for 3D cell printing or with drugs and support the growth and differentiation of (stem) cells as well as cell migration/microvascularization. Potential applications in therapy of bone, cartilage and eye disorders/injuries and wound healing are summarized and possible mechanisms are discussed.

Triple-target stimuli-responsive anti-COVID-19 face mask with physiological virus-inactivating agents

Conventional face masks to prevent SARS-CoV-2 transmission are mostly based on a passive filtration principle. Ideally, anti-COVID-19 masks should protect the carrier not only by size exclusion of virus aerosol particles, but also be able to capture and destroy or inactivate the virus. Here we present the proof-of-concept of a filter mat for such a mask, which actively attracts aerosol droplets and kills the virus. The electrospun mats are made of polycaprolactone (PCL) a hydrophilic, functionalizable and biodegradable polyester, into which inorganic polyphosphate (polyP) a physiological biocompatible, biodegradable and antivirally active polymer (chain length, ∼40 Pi units) has been integrated. A soluble Na-polyP as well as amorphous calcium polyP nanoparticles (Ca-polyP-NP) have been used. In this composition, the polyP component of the polyP-PCL mats is stable in aqueous protein-free environment, but capable of transforming into a gel-like coacervate upon contact with divalent cations and protein like mucin present in (virus containing) aerosol droplets. In addition, the Ca-polyP-NP are used as a carrier of tretinoin (all-trans retinoic acid) which blocks the function of the SARS-CoV-2 envelope (E) protein, an ion channel forming viroporin. The properties of this novel mask filter mats are as follows: First, to attract and to trap virus-like particles during the polyP coacervate formation induced in situ by aerosol droplets on the spun PCL fibers, as shown here by using SARS-CoV-2 mimicking fluorescent nanoparticles. Second, after disintegration the NP by the aerosol-mucus constituents, to release polyP that binds to and abolishes the function of the receptor binding domain of the viral spike protein. Third, to destroy the virus by releasing tretinoin, as shown by the disruption of virus-mimicking liposomes with the integrated recombinant viral viroporin. It is proposed that these properties, which are inducible (stimuli responsive), will allow the design of antiviral masks that are smart.

The promises of lysine polyphosphorylation as a regulatory modification in mammals are tempered by conceptual and technical challenges

Polyphosphate (polyP) is a ubiquitous biomolecule thought to be present in all cells on Earth. PolyP is deceivingly simple, consisting of repeated units of inorganic phosphates polymerized in long energy-rich chains. PolyP is involved in diverse functions in mammalian systems-from cell signaling to blood clotting. One exciting avenue of research is a new nonenzymatic post-translational modification, termed lysine polyphosphorylation, wherein polyP chains are covalently attached to lysine residues of target proteins. While the modification was first characterized in budding yeast, recent work has now identified the first human targets. There is significant promise in this area of biomedical research, but a number of technical issues and knowledge gaps present challenges to rapid progress. In this review, the current state of the field is summarized and existing roadblocks related to the study of lysine polyphosphorylation in higher eukaryotes are introduced. It is discussed how limited methods to identify targets of polyphosphorylation are further impacted by low concentration, unknown regulatory enzymes, and sequestration of polyP into compartments in mammalian systems. Furthermore, suggestions on how these obstacles could be addressed or what their physiological relevance may be within mammalian cells are presented.

The emerging role of phosphorus in human health

Phosphorus, an essential nutrient, performs vital functions in skeletal and non-skeletal tissues and is pivotal for energy production. The last two decades of research on the physiological importance of phosphorus have provided several novel insights about its dynamic nature as a nutrient performing functions as a phosphate ion. Phosphorous also acts as a signaling molecule and induces complex physiological responses. It is recognized that phosphorus homeostasis is critical for health. The intake of phosphorus by the general population world-wide is almost double the amount required to maintain health. This increase is attributed to the incorporation of phosphate containing food additives in processed foods purchased by consumers. Research findings assessed the impact of excessive phosphorus intake on cells' and organs' responses, and highlighted the potential pathogenic consequences. Research also identified a new class of bioactive phosphates composed of polymers of phosphate molecules varying in chain length. These polymers are involved in metabolic responses including hemostasis, brain and bone health, via complex mechanism(s) with positive or negative health effects, depending on their chain length. It is amazing, that phosphorus, a simple element, is capable of exerting multiple and powerful effects. The role of phosphorus and its polymers in the renal and cardiovascular system as well as on brain health appear to be important and promising future research directions.

Hyperphosphatemia and Cardiovascular Disease

Hyperphosphatemia or even serum phosphate levels within the “normal laboratory range” are highly associated with increased cardiovascular disease risk and mortality in the general population and patients suffering from chronic kidney disease (CKD). As the kidney function declines, serum phosphate levels rise and subsequently induce the development of hypertension, vascular calcification, cardiac valvular calcification, atherosclerosis, left ventricular hypertrophy and myocardial fibrosis by distinct mechanisms. Therefore, phosphate is considered as a promising therapeutic target to improve the cardiovascular outcome in CKD patients. The current therapeutic strategies are based on dietary and pharmacological reduction of serum phosphate levels to prevent hyperphosphatemia in CKD patients. Large randomized clinical trials with hard endpoints are urgently needed to establish a causal relationship between phosphate excess and cardiovascular disease (CVD) and to determine if lowering serum phosphate constitutes an effective intervention for the prevention and treatment of CVD.

Model systems for studying polyphosphate biology: a focus on microorganisms

Polyphosphates (polyP) are polymers of inorganic phosphates joined by high-energy bonds to form long chains. These chains are present in all forms of life but were once disregarded as 'molecular fossils'. PolyP has gained attention in recent years following new links to diverse biological roles ranging from energy storage to cell signaling. PolyP research in humans and other higher eukaryotes is limited by a lack of suitable tools and awaits the identification of enzymatic players that would enable more comprehensive studies. Therefore, many of the most important insights have come from single-cell model systems. Here, we review determinants of polyP metabolism, regulation, and function in major microbial systems, including bacteria, fungi, protozoa, and algae. We highlight key similarities and differences that may aid in our understanding of how polyP impacts cell physiology at a molecular level.

Is there a link between inorganic polyphosphate (polyP), mitochondria, and neurodegeneration?

Mitochondrial dysfunction - including increased apoptosis, calcium and protein dyshomeostasis within the organelle, and dysfunctional bioenergetics and oxidative status - is a common, early feature in all the major neurodegenerative diseases, including Alzheimer's Disease (AD) and Parkinson's Disease (PD). However, the exact molecular mechanisms that drive the organelle to dysfunction and ultimately to failure in these conditions are still not well described. Different authors have shown that inorganic polyphosphate (polyP), an ancient and well-conserved molecule, plays a key role in the regulation of mitochondrial physiology under basal conditions. PolyP, which is present in all studied organisms, is composed of chains of orthophosphates linked together by highly energetic phosphoanhydride bonds, similar to those found in ATP. This polymer shows a ubiquitous distribution, even if a high co-localization with mitochondria has been reported. It has been proposed that polyP might be an alternative to ATP for cellular energy storage in different organisms, as well as the implication of polyP in the regulation of many of the mitochondrial processes affected in AD and PD, including protein and calcium homeostasis. Here, we conduct a comprehensive review and discussion of the bibliography available regarding the role of polyP in the mitochondrial dysfunction present in AD and PD. Taking into account the data presented in this review, we postulate that polyP could be a valid, innovative and, plausible pharmacological target against mitochondrial dysfunction in AD and PD. However, further research should be conducted to better understand the exact role of polyP in neurodegeneration, as well as the metabolism of the polymer, and the effect of different lengths of polyP on cellular and mitochondrial physiology.

Phosphate as a Signaling Molecule

Phosphorus plays a vital role in diverse biological processes including intracellular signaling, membrane integrity, and skeletal biomineralization; therefore, the regulation of phosphorus homeostasis is essential to the well-being of the organism. Cells and whole organisms respond to changes in inorganic phosphorus (Pi) concentrations in their environment by adjusting Pi uptake and altering biochemical processes in cells (local effects) and distant organs (endocrine effects). Unicellular organisms, such as bacteria and yeast, express specific Pi-binding proteins on the plasma membrane that respond to changes in ambient Pi availability and transduce intracellular signals that regulate the expression of genes involved in cellular Pi uptake. Multicellular organisms, including humans, respond at a cellular level to adapt to changes in extracellular Pi concentrations and also have endocrine pathways which integrate signals from various organs (e.g., intestine, kidneys, parathyroid glands, bone) to regulate serum Pi concentrations and whole-body phosphorus balance. In mammals, alterations in the concentrations of extracellular Pi modulate type III sodium-phosphate cotransporter activity on the plasma membrane, and trigger changes in cellular function. In addition, elevated extracellular Pi induces activation of fibroblast growth factor receptor, Raf/mitogen-activated protein kinase/ERK kinase (MEK)/extracellular signal-regulated kinase (ERK) and Akt pathways, which modulate gene expression in various mammalian cell types. Excessive Pi exposure, especially in patients with chronic kidney disease, leads to endothelial dysfunction, accelerated vascular calcification, and impaired insulin secretion.

Inorganic polyphosphate is produced and hydrolyzed in F0F1-ATP synthase of mammalian mitochondria

Inorganic polyphosphate (polyP) is a polymer present in all living organisms. Although polyP is found to be involved in a variety of functions in cells of higher organisms, the enzyme responsible for polyP production and consumption has not yet been identified. Here, we studied the effect of polyP on mitochondrial respiration, oxidative phosphorylation and activity of F₀F₁-ATPsynthase. We have found that polyP activates mitochondrial respiration which does not coupled with ATP production (V₂) but inhibits ADP-dependent respiration (V₃). Moreover, PolyP can stimulate F₀F₁-ATPase activity in the presence of ATP and, importantly, can be hydrolyzed in this enzyme instead of ATP. Furthermore, PolyP can be produced in mitochondria in the presence of substrates for respiration and phosphate by the F₀F₁-ATPsynthase. Thus, polyP is an energy molecule in mammalian cells which can be produced and hydrolyzed in the mitochondrial F₀F₁-ATPsynthase.

Importance of Dietary Phosphorus for Bone Metabolism and Healthy Aging

Inorganic phosphate (Pi) plays a critical function in many tissues of the body: for example, as part of the hydroxyapatite in the skeleton and as a substrate for ATP synthesis. Pi is the main source of dietary phosphorus. Reduced bioavailability of Pi or excessive losses in the urine causes rickets and osteomalacia. While critical for health in normal amounts, dietary phosphorus is plentiful in the Western diet and is often added to foods as a preservative. This abundance of phosphorus may reduce longevity due to metabolic changes and tissue calcifications. In this review, we examine how dietary phosphorus is absorbed in the gut, current knowledge about Pi sensing, and endocrine regulation of Pi levels. Moreover, we also examine the roles of Pi in different tissues, the consequences of low and high dietary phosphorus in these tissues, and the implications for healthy aging.

Physiopathological roles of vesicular nucleotide transporter (VNUT), an essential component for vesicular ATP release

Vesicular nucleotide transporter (VNUT) is the last identified member of the SLC17 organic anion transporter family, which plays a central role in vesicular storage in ATP-secreting cells. The discovery of VNUT demonstrated that, despite having been neglected for a long time, vesicular ATP release represents a major pathway for purinergic chemical transmission, which had been mainly attributed to ATP permeation channels. This article summarizes recent advances in our understanding of the mechanism of VNUT and its physiopathological roles as well as the development of inhibitors. Regulating the activity and/or the expression of VNUT represents a new and promising therapeutic strategy for the treatment of multiple diseases.

Inorganic Polyphosphates As Storage for and Generator of Metabolic Energy in the Extracellular Matrix

Inorganic polyphosphates (polyP) consist of linear chains of orthophosphate residues, linked by high-energy phosphoanhydride bonds. They are evolutionarily old biopolymers that are present from bacteria to man. No other molecule concentrates as much (bio)chemically usable energy as polyP. However, the function and metabolism of this long-neglected polymer are scarcely known, especially in higher eukaryotes. In recent years, interest in polyP experienced a renaissance, beginning with the discovery of polyP as phosphate source in bone mineralization. Later, two discoveries placed polyP into the focus of regenerative medicine applications. First, polyP shows morphogenetic activity, i.e., induces cell differentiation via gene induction, and, second, acts as an energy storage and donor in the extracellular space. Studies on acidocalcisomes and mitochondria provided first insights into the enzymatic basis of eukaryotic polyP formation. In addition, a concerted action of alkaline phosphatase and adenylate kinase proved crucial for ADP/ATP generation from polyP. PolyP added extracellularly to mammalian cells resulted in a 3-fold increase of ATP. The importance and mechanism of this phosphotransfer reaction for energy-consuming processes in the extracellular matrix are discussed. This review aims to give a critical overview about the formation and function of this unique polymer that is capable of storing (bio)chemically useful energy.

Deorphanizing NUDIX hydrolases from Trypanosoma: tantalizing links with metabolic regulation and stress tolerance

An explosion of sequence information in the genomics era has thrown up thousands of protein sequences without functional assignment. Though our ability to predict function based on sequence alone is improving steadily, we still have a long way to go. Proteins with common evolutionary origins carry telling sequence signatures, which ought to reveal their biological roles. These sequence signatures have allowed us to classify proteins into families with similar structures, and possibly, functions. Yet, evolution is a perpetual tinkerer, and hence, sequence signatures alone have proved inadequate in understanding the physiological activities of proteins. One such enigmatic family of enzymes is the NUDIX ( nu cleoside di phosphate linked to a moiety X ) hydrolase family that has over 80000 members from all branches of the tree of life. Though MutT, the founding member of this family, was identified in 1954, we are only now beginning to understand the diversity of substrates and biological roles that these enzymes demonstrate. In a recent article by Cordeiro et al. in Bioscience Reports [Biosci. Rep. (2019)], two members of this protein family from the human pathogen Trypanosoma brucei were deorphanized as being polyphosphate hydrolases. The authors show that of the five NUDIX hydrolases coded by the T. brucei genomes, TbNH2 and TbNH4, show in vitro hydrolytic activity against inorganic polyphosphate. Through classical biochemistry and immunostaining microscopy, differences in their substrate specificities and sub-cellular localization were revealed. These new data provide a compelling direction to the study of Trypanosome stress biology as well as our understanding of the NUDIX enzyme family.

Inorganic Polyphosphate Regulates AMPA and NMDA Receptors and Protects Against Glutamate Excitotoxicity via Activation of P2Y Receptors

Glutamate is one of the most important neurotransmitters in the process of signal transduction in the CNS. Excessive amounts of this neurotransmitter lead to glutamate excitotoxicity, which is accountable for neuronal death in acute neurological disorders, including stroke and trauma, and in neurodegenerative diseases. Inorganic polyphosphate (PolyP) plays multiple roles in the mammalian brain, including function as a calcium-dependent gliotransmitter mediating communication between astrocytes, while its role in the regulation of neuronal activity is unknown. Here we studied the effect of PolyP on glutamate-induced calcium signal in primary rat neurons in both physiological and pathological conditions. We found that preincubation of primary neurons with PolyP reduced glutamate-induced and AMPA-induced but not the NMDA-induced calcium signal. However, in rat hippocampal acute slices, PolyP reduced ion flux through NMDA and AMPA receptors in native neurons. The effect of PolyP on glutamate and specifically on the AMPA receptors was dependent on the presence of P2Y1 but not of P2X receptor inhibitors and also could be mimicked by P2Y1 agonist 2MeSADP. Preincubation of cortical neurons with PolyP significantly reduced the initial calcium peak as well as the number of neurons with delayed calcium deregulation in response to high concentrations of glutamate and resulted in protection of neurons against glutamate-induced cell death. As a result, activation of P2Y1 receptors by PolyP reduced calcium signal acting through AMPA receptors, thus protecting neurons against glutamate excitotoxicity by reduction of the calcium overload and restoration of mitochondrial function.SIGNIFICANCE STATEMENT One of the oldest polymers in the evolution of living matter is the inorganic polyphosphate (PolyP). It is shown to play a role of gliotransmitter in the brain; however, the role of polyphosphate in neuronal signaling is not clear. Here we demonstrate that inorganic polyphosphate is able to reduce calcium signaling induced by physiological or high concentrations of glutamate. The effect of polyphosphate on glutamate-induced calcium signal in neurons is due to the effect of this polymer on the AMPA receptors. The effect of PolyP on glutamate-induced and AMPA-induced calcium signal is dependent on P2Y receptor antagonist. The ability of PolyP to restrict the glutamate-induced calcium signal lies in the basis of its protection of neurons against glutamate excitotoxicity.

Role of Polyphosphate in Amyloidogenic Processes

Polyphosphate (polyP), an extremely simple polyanion, has long been known to be involved in a variety of different cellular processes, ranging from stress resistance, biofilm formation, and virulence in bacteria to bone mineralization, blood clotting, and mammalian target of rapamycin (mTOR) signaling in mammalian organisms. Our laboratory recently discovered a completely unexpected role of polyP as a stabilizing scaffold for β-sheet-containing protein-folding intermediates. This realization led us to investigate the effects of polyP on amyloidogenic processes and the novel concept that polyP might play a role in neurodegenerative diseases. In this review, we will summarize recent results that show that polyP is a physiological modifier that accelerates amyloid fiber formation, alters fiber morphology, and protects cells against amyloid toxicity. We will review the current knowledge on the distribution, levels, and roles of polyP in the mammalian brain, and discuss potential mechanisms by which polyP might ameliorate amyloid toxicity.

[A fluorometric method for direct detection of inorganic polyphosphate in enterohemorrhagic Escherichia coli O157:H7]

OBJECTIVE

To establish a quantitative fluorescent detection method using DAPI for detecting inorganic polyphosphate (polyP) in enterohemorrhagic Escherichia coli (EHEC) O157:H7.

METHODS

The DNA of wild-type strain of EHEC O157:H7 was extracted and purified. DAPI was combined with the extracted DNA and polyP45 standards for measurement of the emission spectra at 360 nm and 415 nm fluorescence spectrophotometry. The fluorescence of DAPI-DNA and DAPI-polyP complexes was detected by fluorescence confocal microscopy to verify the feasibility of DAPI for detecting polyP. To determine the optimal pretreatment protocol for improving the cell membrane permeability, the effects of 6 pretreatments of the cells (namely snap-freezing in liquid nitrogen, freezing at -80 ℃, and freezing at -20 ℃, all followed by thawing at room temperature; heating at 60 ℃ for 10 min; treatment with Triton x-100; and placement at room temperature) were tested on the survival of EHEC O157:H7. The fluorescence values of the treated bacteria were then measured after DAPI staining. A standard calibration curve of polyP standard was established for calculation of the content of polyP in the live cells of wildtype EHEC strain and two ppk1 mutant strains.

RESULTS

At the excitation wavelength of 360 nm, the maximum emission wavelength of DAPI-DNA was 460 nm, and the maximum emission wavelength of DAPI-polyP was 550 nm at the excitation wavelength of 415 nm. The results of confocal microscopy showed that 405 nm excitation elicited blue fluorescence from DAPIDNA complex with the emission wavelength of 425-475 nm; excitation at 488 nm elicited green fluorescence from the DAPIpolyP complex with the emission wavelength of 500-560 nm of. Snap-freezing of cells at -80 ℃ followed by thawing at room temperature was the optimal pretreatment to promote DAPI penetration into the live cells. The standard calibration curve was Y=1849X+127.5 (R²=0.991) was used for determining polyP content in the EHEC strains. The experimental results showed that wild-type strain had significantly higher polyP content than the mutant strains with ppk1 deletion.

CONCLUSIONS

We established a convenient quantitative method for direct and reliable detection polyP content to facilitate further study of polyP and its catalytic enzymes in EHEC O157:H7.

Dual role of inorganic polyphosphate in cardiac myocytes: The importance of polyP chain length for energy metabolism and mPTP activation

We have previously demonstrated that inorganic polyphosphate (polyP) is a potent activator of the mitochondrial permeability transition pore (mPTP) in cardiac myocytes. PolyP depletion protected against Ca²⁺-induced mPTP opening, however it did not prevent and even exacerbated cell death during ischemia-reperfusion (I/R). The central goal of this study was to investigate potential molecular mechanisms underlying these dichotomous effects of polyP on mitochondrial function. We utilized a Langendorff-perfused heart model of I/R to monitor changes in polyP size and chain length at baseline, 20 min no-flow ischemia, and 15 min reperfusion. Freshly isolated cardiac myocytes and mitochondria from C57BL/6J (WT) and cyclophilin D knock-out (CypD KO) mice were used to measure polyP uptake, mPTP activity, mitochondrial membrane potential, respiration and ATP generation. We found that I/R induced a significant decrease in polyP chain length. We, therefore, tested, the ability of synthetic polyPs with different chain length to accumulate in mitochondria and induce mPTP. Both short and long chain polyPs accumulated in mitochondria in oligomycin-sensitive manner implicating potential involvement of mitochondrial ATP synthase in polyP transport. Notably, only short-chain polyP activated mPTP in WT myocytes, and this effect was prevented by mPTP inhibitor cyclosprorin A and absent in CypD KO myocytes. To the contrary, long-chain polyP suppressed mPTP activation, and enhanced ADP-linked respiration and ATP production. Our data indicate that 1) effect of polyP on cardiac function strongly depends on polymer chain length; and 2) short-chain polyPs (as increased in ischemia-reperfusion) induce mPTP and mitochondrial uncoupling, while long-chain polyPs contribute to energy generation and cell metabolism.

Bisphosphonic acids and related compounds as inhibitors of nucleotide- and polyphosphate-processing enzymes: A PPK1 and PPK2 case study

Bisphosphonic acids, which are structural analogs of pyrophosphate, constitute a class of compounds with very high potential for the construction of effective inhibitors of enzymes operating on oligo- and polyphosphates. The bisphosphonate-based methodology was applied for the discovery of inhibitors of two families of polyphosphate kinases (PPK1 and PPK2). Screening of thirty-two structurally diverse bisphosphonic acids and related compounds revealed several micromolar inhibitors of both enzymes. Importantly, selectivity of bisphosphonates could be achieved by application of the appropriate side chain.

Role of phosphate sensing in bone and mineral metabolism

Inorganic phosphate (P_i) is essential for signal transduction and cell metabolism, and is also an essential structural component of the extracellular matrix of the skeleton. P_i is sensed in bacteria and yeast at the plasma membrane, which activates intracellular signal transduction to control the expression of P_i transporters and other genes that control intracellular P_i levels. In multicellular organisms, P_i homeostasis must be maintained in the organism and at the cellular level, requiring an endocrine and metabolic P_i-sensing mechanism, about which little is currently known. This Review will discuss the metabolic effects of P_i, which are mediated by P_i transporters, inositol pyrophosphates and SYG1-Pho81-XPR1 (SPX)-domain proteins to maintain cellular phosphate homeostasis in the musculoskeletal system. In addition, we will discuss how P_i is sensed by the human body to regulate the production of fibroblast growth factor 23 (FGF23), parathyroid hormone and calcitriol to maintain serum levels of P_i in a narrow range. New findings on the crosstalk between iron and P_i homeostasis in the regulation of FGF23 expression will also be outlined. Mutations in components of these metabolic and endocrine phosphate sensors result in genetic disorders of phosphate homeostasis, cardiomyopathy and familial basal ganglial calcifications, highlighting the importance of this newly emerging area of research.

Role of ATP during the initiation of microvascularization: acceleration of an autocrine sensing mechanism facilitating chemotaxis by inorganic polyphosphate

The in vitro tube formation assay with human umbilical vein endothelial cells (HUVEC) was applied to identify the extra- and intracellular sources of metabolic energy/ATP required for cell migration during the initial stage of microvascularization. Extracellularly, the physiological energy-rich polymer, inorganic polyphosphate (polyP), applied as biomimetic amorphous calcium polyP microparticles (Ca-polyP-MP), is functioning as a substrate for ATP generation most likely via the combined action of the alkaline phosphatase (ALP) and the adenylate kinase (AK). The linear Ca-polyP-MP with a size of 40 phosphate units, close to the polyP in the acidocalcisomes in the blood platelets, were found to increase endothelial cell tube formation, as well as the intracellular ATP levels. Depletion of extracellular ATP with apyrase suppressed tube formation during the initial incubation period. Inhibition experiments revealed that inhibitors (levamisole and Ap5A) of the enzymes involved in extracellular ATP generation strongly reduce the Ca-polyP-MP-induced tube formation. The stimulatory effect of Ca-polyP-MP was also diminished by the glycolysis inhibitor oxamate and trifluoperazine which blocks endocytosis, as well as by MRS2211, an antagonist of the P2Y₁₃ receptor. Oligomycin, an inhibitor of the mitochondrial F₀F₁-ATP synthase, displayed no effect at lower concentrations on tube formation. Electron microscopic data revealed that after cellular uptake, the Ca-polyP-MP accumulate close to the cell membrane. We conclude that in HUVEC exposed to polyP, ATP is formed extracellularly via the coupled ALP-AK reaction, and intracellularly during glycolysis. The results suggest an autocrine signaling pathway of ATP with polyP as an extracellular store of metabolic energy for endothelial cell migration during the initial vascularization process.

Signal transduction in astrocytes: Localization and release of inorganic polyphosphate

Inorganic polyphosphate (polyP) is present in every cell and is highly conserved from primeval times. In the mammalian cells, polyP plays multiple roles including control of cell bioenergetics and signal transduction. In the brain, polyP mediates signaling between astrocytes via activation of purinergic receptors, however, the mechanisms of polyP release remain unknown. Here we report identification of polyP-containing vesicles in cortical astrocytes and the main triggers that evoke vesicular polyP release. In cultured astrocytes, polyP was localized predominantly within the intracellular vesicular compartments which express vesicular nucleotide transporter VNUT (putative ATP-containing vesicles), but not within the compartments expressing vesicular glutamate transporter 2 (VGLUT2). The number of lysosomes which contain polyP was dependent on the conditions of astrocytes. Release of polyP from a proportion of lysosomes could be induced by calcium ionophores. In contrast, polyP release from the VNUT-containing vesicles could be triggered by various physiological stimuli, such as pH changes, polyP induced polyP release and other stimuli which increase [Ca2+ ] i . These data suggest that astrocytes release polyP predominantly via exocytosis from the VNUT-containing vesicles. © 2018 Wiley Periodicals, Inc.

Degradation of phosphate polymer polyP enhances lactic fermentation in mice

In bacteria, a polymer of inorganic phosphate (Pi) (inorganic polyphosphate; polyP) is enzymatically produced and consumed as an alternative phosphate donor for adenosine triphosphate (ATP) production to protect against nutrient starvation. In vertebrates, polyP has been dismissed as a "molecular fossil" due to the lack of any known physiological function. Here, we have explored its possible role by producing transgenic (TG) mice widely expressing Saccharomyces cerevisiae exopolyphosphatase 1 (ScPPX1), which catalyzes hydrolytic polyP degradation. TG mice were produced and displayed reduced mitochondrial respiration in muscles. In female TG mice, the blood concentration of lactic acid was enhanced, whereas ATP storage in liver and brain tissues was reduced significantly. Thus, we suggested that the elongation of polyP reduces the intracellular Pi concentration, suppresses anaerobic lactic acid production, and sustains mitochondrial respiration. Our results provide an insight into the physiological role of polyP in mammals, particularly in females.

Amorphous, Smart, and Bioinspired Polyphosphate Nano/Microparticles: A Biomaterial for Regeneration and Repair of Osteo-Articular Impairments In-Situ

Using femur explants from mice as an in vitro model, we investigated the effect of the physiological polymer, inorganic polyphosphate (polyP), on differentiation of the cells of the bone marrow in their natural microenvironment into the osteogenic and chondrogenic lineages. In the form of amorphous Ca-polyP nano/microparticles, polyP retains its function to act as both an intra- and extracellular metabolic fuel and a stimulus eliciting morphogenetic signals. The method for synthesis of the nano/microparticles with the polyanionic polyP also allowed the fabrication of hybrid particles with the bisphosphonate zoledronic acid, a drug used in therapy of bone metastases in cancer patients. The results revealed that the amorphous Ca-polyP particles promote the growth/viability of mesenchymal stem cells, as well as the osteogenic and chondrogenic differentiation of the bone marrow cells in rat femur explants, as revealed by an upregulation of the expression of the transcription factors SOX9 (differentiation towards osteoblasts) and RUNX2 (chondrocyte differentiation). In parallel to this bone anabolic effect, incubation of the femur explants with these particles significantly reduced the expression of the gene encoding the osteoclast bone-catabolic enzyme, cathepsin-K, while the expression of the tartrate-resistant acid phosphatase remained unaffected. The gene expression data were supported by the finding of an increased mineralization of the cells in the femur explants in response to the Ca-polyP particles. Finally, we show that the hybrid particles of polyP complexed with zoledronic acid exhibit both the cytotoxic effect of the bisphosphonate and the morphogenetic and mineralization inducing activity of polyP. Our results suggest that the Ca-polyP nano/microparticles are not only a promising scaffold material for repairing long bone osteo-articular damages but can also be applied, as a hybrid with zoledronic acid, as a drug delivery system for treatment of bone metastases. The polyP particles are highlighted as genuine, smart, bioinspired nano/micro biomaterials.

Amorphous polyphosphate, a smart bioinspired nano-/bio-material for bone and cartilage regeneration: towards a new paradigm in tissue engineering

Physiological amorphous polyphosphate nano/micro-particles, injectable and implantable, attract and stimulate MSCs into implants for tissue regeneration.

Uptake of polyphosphate microparticles in vitro (SaOS-2 and HUVEC cells) followed by an increase of the intracellular ATP pool size

Recently two approaches were reported that addressed a vitally important problem in regenerative medicine, i. e. the successful treatment of wounds even under diabetic conditions. Accordingly, these studies with diabetic rabbits [Sarojini et al. PLoS One 2017, 12(4):e0174899] and diabetic mice [Müller et al. Polymers 2017, 9, 300] identified a novel (potential) target for the acceleration of wound healing in diabetes. Both studies propose a raise of the intracellular metabolic energy status via exogenous administration either of ATP, encapsulated into lipid vesicles, or of polyphosphate (polyP) micro-/nanoparticles. Recently this physiological polymer, polyP, was found to release metabolic energy in form of ATP into both the extra- and also intra-cellular space. In the present work the uptake mechanism of the amorphous polyP microparticles "Ca-polyP-MP" has been described and found to be a clathrin-dependent endocytosis import, based on inhibition studies with the inhibitor trifluoperazine, which blocks the clathrin-dependent endocytosis import. The experiments had been performed with SaOS-2 cells, by studying the uptake and distribution of the electron-dense particles into the cells, and with HUVEC cells, for analysis of the intracellular accumulation of polyP, visualized by fluorescent staining of polyP. Concurrently with the uptake of particular polyP the intracellular ATP level increased as well. In contrast to "Ca-polyP-MP" the soluble polyP, administered as "Na-polyP[Ca2+]", did not cause an increase in the intracellular Ca2+ level, suggesting a different mode of action of these two forms of polyP. Based on existing data on the effect of polyP and ATP on the induction of vascularization during wound repair, both groups (Sarojini et al. and Müller et al.) propose that the acceleration of wound repair is based on an increased metabolic energy supply directly to the regenerating wound area.

Restoration of Impaired Metabolic Energy Balance (ATP Pool) and Tube Formation Potential of Endothelial Cells under "high glucose", Diabetic Conditions by the Bioinorganic Polymer Polyphosphate

Micro-vascularization is a fast, energy-dependent process that is compromised by elevated glucose concentrations such as in diabetes mellitus disease. Here, we studied the effect of the physiological bioinorganic polymer, polyphosphate (polyP), on the reduced ATP content and impaired function of endothelial cells cultivated under "high glucose" (35 mM diabetes mellitus conditions) concentrations. This high-energy biopolymer has been shown to provide a source of metabolic energy, stored in its phosphoanhydride bonds. We show that exposure of human umbilical vein endothelial cells (HUVEC cells) to "high glucose" levels results in reduced cell viability, increased apoptotic cell death, and a decline in intracellular ATP level. As a consequence, the ability of HUVEC cells to form tube-like structures in the in vitro cell tube formation assay was almost completely abolished under "high glucose" conditions. Those cells were grown onto a physiological collagen scaffold (collagen/basement membrane extract). We demonstrate that these adverse effects of increased glucose levels can be reversed by administration of polyP to almost normal values. Using Na-polyP, complexed in a stoichiometric (molar) ratio to Ca2+ ions and in the physiological concentration range between 30 and 300 µM, an almost complete restoration of the reduced ATP pool of cells exposed to "high glucose" was found, as well as a normalization of the number of apoptotic cells and energy-dependent tube formation. It is concluded that the adverse effects on endothelial cells caused by the metabolic energy imbalance at elevated glucose concentrations can be counterbalanced by polyP, potentially opening new strategies for treatment of the micro-vascular complications in diabetic patients.

Rebalancing β-Amyloid-Induced Decrease of ATP Level by Amorphous Nano/Micro Polyphosphate: Suppression of the Neurotoxic Effect of Amyloid β-Protein Fragment 25-35

Morbus Alzheimer neuropathology is characterized by an impaired energy homeostasis of brain tissue. We present an approach towards a potential therapy of Alzheimer disease based on the high-energy polymer inorganic polyphosphate (polyP), which physiologically occurs both in the extracellular and in the intracellular space. Rat pheochromocytoma (PC) 12 cells, as well as rat primary cortical neurons were exposed to the Alzheimer peptide Aβ25-35. They were incubated in vitro with polyphosphate (polyP); ortho-phosphate was used as a control. The polymer remained as Na⁺ salt; or complexed in a stoichiometric ratio to Ca²⁺ (Na-polyP[Ca²⁺]); or was processed as amorphous Ca-polyP microparticles (Ca-polyP-MP). Ortho-phosphate was fabricated as crystalline Ca-phosphate nanoparticles (Ca-phosphate-NP). We show that the pre-incubation of PC12 cells and primary cortical neurons with polyP protects the cells against the neurotoxic effect of the Alzheimer peptide Aβ25-35. The strongest effect was observed with amorphous polyP microparticles (Ca-polyP-MP). The effect of the soluble sodium salt; Na-polyP (Na-polyP[Ca²⁺]) was lower; while crystalline orthophosphate nanoparticles (Ca-phosphate-NP) were ineffective. Ca-polyP-MP microparticles and Na-polyP[Ca²⁺] were found to markedly enhance the intracellular ATP level. Pre-incubation of Aβ25-35 during aggregate formation, with the polyP preparation before exposure of the cells, had a small effect on neurotoxicity. We conclude that recovery of the compromised energy status in neuronal cells by administration of nontoxic biodegradable Ca-salts of polyP reverse the β-amyloid-induced decrease of adenosine triphosphate (ATP) level. This study contributes to a new routes for a potential therapeutic intervention in Alzheimer’s disease pathophysiology.

Enhancement of Wound Healing in Normal and Diabetic Mice by Topical Application of Amorphous Polyphosphate. Superior Effect of a Host⁻Guest Composite Material Composed of Collagen (Host) and Polyphosphate (Guest)

The effect of polyphosphate (polyP) microparticles on wound healing was tested both in vitro and in a mice model in vivo. Two approaches were used: pure salts of polyphosphate, fabricated as amorphous microparticles (MPs, consisting of calcium and magnesium salts of polyP, "Ca⁻polyp-MPs" and "Mg⁻polyp-MPs"), and host⁻guest composite particles, prepared from amorphous collagen (host) and polyphosphate (guest), termed "col/polyp-MPs". Animal experiments with polyP on healing of excisional wounds were performed using both normal mice and diabetic mice. After a healing period of 7 days "Ca⁻polyp-MP" significantly improved re-epithelialization in normal mice from 31% (control) to 72% (polyP microparticle-treated). Importantly, in diabetic mice, particularly the host⁻guest particles "col/polyp-MP", increased the rate of re-epithelialization to ≈40% (control, 23%). In addition, those particles increased the expression of COL-I and COL-III as well as the expression the α-smooth muscle actin and the plasminogen activator inhibitor-1. We propose that "Ca⁻polyp-MPs", and particularly the host⁻guest "col/polyp-MPs" are useful for topical treatment of wounds.

Interaction of misfolded proteins and mitochondria in neurodegenerative disorders

The number of the people affected by neurodegenerative disorders is growing dramatically due to the ageing of population. The major neurodegenerative diseases share some common pathological features including the involvement of mitochondria in the mechanism of pathology and misfolding and the accumulation of abnormally aggregated proteins. Neurotoxicity of aggregated β-amyloid, tau, α-synuclein and huntingtin is linked to the effects of these proteins on mitochondria. All these misfolded aggregates affect mitochondrial energy metabolism by inhibiting diverse mitochondrial complexes and limit ATP availability in neurones. β-Amyloid, tau, α-synuclein and huntingtin are shown to be involved in increased production of reactive oxygen species, which can be generated in mitochondria or can target this organelle. Most of these aggregated proteins are capable of deregulating mitochondrial calcium handling that, in combination with oxidative stress, lead to opening of the mitochondrial permeability transition pore. Despite some of the common features, aggregated β-amyloid, tau, α-synuclein and huntingtin have diverse targets in mitochondria that can partially explain neurotoxic effect of these proteins in different brain regions.

Inorganic polyphosphate enhances radio-sensitivity in a human non-small cell lung cancer cell line, H1299

Inorganic polyphosphate is a linear polymer containing tens to hundreds of orthophosphate residues linked by high-energy phosphoanhydride bonds. Polyphosphate has been recognized as a potent anti-metastasis reagent. However, the molecular mechanism underlying polyphosphate action on cancer cells is poorly understood. In this study, we investigated the involvement of polyphosphate in radio-sensitivity using a human non-small cell lung cancer cell line, H1299. We found that polyphosphate treatment decreases cellular adenosine triphosphate levels, suggesting a disruption of energy metabolism. We also found that the induction of DNA double-strand breaks was enhanced in polyphosphate-treated cells after X-ray irradiation and colony formation assay revealed that cell survival decreased compared with that of the control groups. These findings suggest that polyphosphate is a promising radio-sensitizer for cancer cells. Therefore, we hypothesized that polyphosphate treatment disrupts adenosine triphosphate-mediated energy transfer for cellular survival and DNA repair, thereby reducing the cellular capability to resist X-ray irradiation.

Fabrication of a new physiological macroporous hybrid biomaterial/bioscaffold material based on polyphosphate and collagen by freeze-extraction

A macroporous hybrid biomaterial/bioscaffold material, eliciting morphogenetic activity, was fabricated with polyphosphate, chondroitin sulfate and collagen by the freeze-extraction technology.

Improvement of biochemical methods of polyP quantification

Polyphosphate (polyP) is an abundant and physiologically important biomolecule for virtually any living cell. Therefore, determination of changes in cellular content of polyP is crucial for its functional characterization. Determination of cellular polyP has been performed by many different methods, and the lack of a standardized procedure is possibly responsible for the large dispersion of results found in the relevant literature. For a relatively simple organism, such as the yeast Saccharomyces cerevisiae, this variation can be up to 12-fold. polyP extraction and determination of free phosphate released by enzymatic degradation of the polymer is a method quite common and relatively straightforward for polyP determination. By using the yeast S. cerevisiae as model, we have experimentally evaluated the different steps in this procedure in order to identify critical issues that might explain the disparate reported results. As the main output of this evaluation we propose a straightforward and robust procedure that can be used as gold standard protocol for cellular polyP purification and determination from unicellular organisms, thus providing consistency to measurements and facilitating inter-laboratory comparisons and biological interpretation of the results.