Residues determining the binding specificity of uncompetitive inhibitors to tissue-nonspecific alkaline phosphatase

Inhibition of lactate dehydrogenase A by diclofenac sodium induces apoptosis in HeLa cells through activation of AMPK

Cancer cells exhibit a unique metabolic preference for the glycolytic pathway over oxidative phosphorylation for maintaining the tumor microenvironment. Lactate dehydrogenase A (LDHA) is a key enzyme that facilitates glycolysis by converting pyruvate to lactate and has been shown to be upregulated in multiple cancers due to the hypoxic tumor microenvironment. Diclofenac (DCF), a nonsteroidal anti-inflammatory drug, has been shown to exhibit anticancer effects by interfering with the glucose metabolism pathway. However, the specific targets of this drug remain unknown. Using in silico, biochemical, and biophysical studies, we show that DCF binds to LDHA adjacent to the substrate binding site and inhibits its activity in a dose-dependent and allosteric manner in HeLa cells. Thus, DCF inhibits the hypoxic microenvironment and induces apoptosis-mediated cell death. DCF failed to induce cytotoxicity in HeLa cells when LDHA was knocked down, confirming that DCF exerts its antimitotic effects via LDHA inhibition. DCF-induced LDHA inhibition alters pyruvate, lactate, NAD+, and ATP production in cells, and this could be a possible mechanism through which DCF inhibits glucose uptake in cancer cells. DCF-induced ATP deprivation leads to mitochondria-mediated oxidative stress, which results in DNA damage, lipid peroxidation, and apoptosis-mediated cell death. Reduction in intracellular ATP levels additionally activates the sensor kinase, adenosine monophosphate-activated protein kinase (AMPK), which further downregulates phosphorylated ribosomal S6 kinase (p-S6K), leading to apoptosis-mediated cell death. We find that in LDHA knocked down cells, intracellular ATP levels were depleted, resulting in the inhibition of p-S6K, suggesting the involvement of DCF-induced LDHA inhibition in the activation of the AMPK/S6K signaling pathway.

Synthesis of new class of indole acetic acid sulfonate derivatives as ectonucleotidases inhibitors

Ectonucleotidases inhibitors (ENPPs, e5'NT (CD73) and h-TNAP) are potential therapeutic candidates for the treatment of cancer. Adenosine, the cancer-developing, and growth moiety is the resultant product of these enzymes. The synthesis of small molecules that can increase the acidic and ionizable structure of adenosine 5-monophosphate (AMP) has been used in traditional attempts to inhibit ENPPs, ecto-5'-nucleotidase and h-TNAP. In this article, we present a short and interesting method for developing substituted indole acetic acid sulfonate derivatives (5a-5o), which are non-nucleotide based small molecules, and investigated their inhibitory potential against recombinant h-ENPP1, h-ENPP3, h-TNAP, h-e5'NT and r-e5'NT. Their overexpression in the tumor environment leads to high adenosine level that results in tumor development as well as immune evasion. Therefore, selective, and potent inhibitors of these enzymes would be expected to decrease adenosine levels and manage tumor development and progression. Our intended outcome led to the discovery of new potent inhibitors like' 5e (IC50 against h-ENPP1 = 0.32 ± 0.01 μM, 58 folds increased with respect to suramin), 5j (IC50 against h-ENPP3 = 0.62 ± 0.003 μM, 21 folds increase with respect to suramin), 5c (IC50 against h-e5'NT = 0.37 ± 0.03 μM, 115 folds increase with respect to sulfamic acid), 5i (IC50 against r-e5'NT = 0.81 ± 0.05 μM, 95 folds increase with respect to sulfamic acid), and 5g (IC50 against h-TNAP = 0.59 ± 0.08 μM, 36 folds increase with respect to Levamisole). Molecular docking studies revealed that inhibitors of these selected target enzymes induced favorable interactions with the key amino acids of the active site, including Lys255, Lys278, Asn277, Gly533, Lys528, Tyr451, Phe257, Tyr340, Gln465, Gln434, Lys437, Glu830, Cys818, Asn499, Arg40, Phe417, Phe500, Asn503, Asn599, Tyr281, Arg397, Asp526, Phe419 and Tyr502. Enzyme kinetic studies revealed that potent compounds such as 5j and 5e blocked these ectonucleotidases competitively while compounds 5e and 5c presented an un-competitive binding mode. 5g revealed a non-competitive mode of inhibition.

Shedding Light on the Role of Na,K-ATPase as a Phosphatase during Matrix-Vesicle-Mediated Mineralization

Matrix vesicles (MVs) contain the whole machinery necessary to initiate apatite formation in their lumen. We suspected that, in addition to tissue-nonspecific alkaline phosphatase (TNAP), Na,K,-ATPase (NKA) could be involved in supplying phopshate (P_i) in the early stages of MV-mediated mineralization. MVs were extracted from the growth plate cartilage of chicken embryos. Their average mean diameters were determined by Dynamic Light Scattering (DLS) (212 ± 19 nm) and by Atomic Force Microcopy (AFM) (180 ± 85 nm). The MVs had a specific activity for TNAP of 9.2 ± 4.6 U·mg^-1 confirming that the MVs were mineralization competent. The ability to hydrolyze ATP was assayed by a colorimetric method and by ³¹P NMR with and without Levamisole and SBI-425 (two TNAP inhibitors), ouabain (an NKA inhibitor), and ARL-67156 (an NTPDase1, NTPDase3 and Ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1) competitive inhibitor). The mineralization profile served to monitor the formation of precipitated calcium phosphate complexes, while IR spectroscopy allowed the identification of apatite. Proteoliposomes containing NKA with either dipalmitoylphosphatidylcholine (DPPC) or a mixture of 1:1 of DPPC and dipalmitoylphosphatidylethanolamine (DPPE) served to verify if the proteoliposomes were able to initiate mineral formation. Around 69-72% of the total ATP hydrolysis by MVs was inhibited by 5 mM Levamisole, which indicated that TNAP was the main enzyme hydrolyzing ATP. The addition of 0.1 mM of ARL-67156 inhibited 8-13.7% of the total ATP hydrolysis in MVs, suggesting that NTPDase1, NTPDase3, and/or NPP1 could also participate in ATP hydrolysis. Ouabain (3 mM) inhibited 3-8% of the total ATP hydrolysis by MVs, suggesting that NKA contributed only a small percentage of the total ATP hydrolysis. MVs induced mineralization via ATP hydrolysis that was significantly inhibited by Levamisole and also by cleaving TNAP from MVs, confirming that TNAP is the main enzyme hydrolyzing this substrate, while the addition of either ARL-6715 or ouabain had a lesser effect on mineralization. DPPC:DPPE (1:1)-NKA liposome in the presence of a nucleator (PS-CPLX) was more efficient in mineralizing compared with a DPPC-NKA liposome due to a better orientation of the NKA active site. Both types of proteoliposomes were able to induce apatite formation, as evidenced by the presence of the 1040 cm^-1 band. Taken together, the findings indicated that the hydrolysis of ATP was dominated by TNAP and other phosphatases present in MVs, while only 3-8% of the total hydrolysis of ATP could be attributed to NKA. It was hypothesized that the loss of Na/K asymmetry in MVs could be caused by a complete depletion of ATP inside MVs, impairing the maintenance of symmetry by NKA. Our study carried out on NKA-liposomes confirmed that NKA could contribute to mineral formation inside MVs, which might complement the known action of PHOSPHO1 in the MV lumen.

Anticalcification effects of DS-1211 in pseudoxanthoma elasticum mouse models and the role of tissue-nonspecific alkaline phosphatase in ABCC6-deficient ectopic calcification

Pseudoxanthoma elasticum (PXE) is a multisystem, genetic, ectopic mineralization disorder with no effective treatment. Inhibition of tissue-nonspecific alkaline phosphatase (TNAP) may prevent ectopic soft tissue calcification by increasing endogenous pyrophosphate (PPi). This study evaluated the anticalcification effects of DS-1211, an orally administered, potent, and highly selective small molecule TNAP inhibitor, in mouse models of PXE. Calcium content in vibrissae was measured in KK/HlJ and ABCC6^-/- mice after DS-1211 administration for 13-14 weeks. Pharmacokinetic and pharmacodynamic effects of DS-1211 were evaluated, including plasma alkaline phosphatase (ALP) activity and biomarker changes in PPi and pyridoxal-phosphate (PLP). Anticalcification effects of DS-1211 through TNAP inhibition were further evaluated in ABCC6^-/- mice with genetically reduced TNAP activity, ABCC6^-/-/TNAP^+/+ and ABCC6^-/-/TNAP^+/-. In KK/HlJ and ABCC6^-/- mouse models, DS-1211 inhibited plasma ALP activity in a dose-dependent manner and prevented progression of ectopic calcification compared with vehicle-treated mice. Plasma PPi and PLP increased dose-dependently with DS-1211 in ABCC6^-/- mice. Mice with ABCC6^-/-/TNAP^+/- phenotype had significantly less calcification and higher plasma PPi and PLP than ABCC6^-/-/TNAP^+/+ mice. TNAP plays an active role in pathomechanistic pathways of dysregulated calcification, demonstrated by reduced ectopic calcification in mice with lower TNAP activity. DS-1211 may be a potential therapeutic drug for PXE.

Sequential hydrolysis of FAD by ecto-5' nucleotidase CD73 and alkaline phosphatase is required for uptake of vitamin B2 into cells

Extracellular hydrolysis of flavin-adenine dinucleotide (FAD) and flavin mononucleotide (FMN) to riboflavin is thought to be important for cellular uptake of vitamin B₂ because FAD and FMN are hydrophilic and do not pass the plasma membrane. However, it is not clear whether FAD and FMN are hydrolyzed by cell surface enzymes for vitamin B₂ uptake. Here, we show that in human cells, FAD, a major form of vitamin B₂ in plasma, is hydrolyzed by CD73 (also called ecto-5' nucleotidase) to FMN. Then, FMN is hydrolyzed by alkaline phosphatase to riboflavin, which is efficiently imported into cells. We determined that this two-step hydrolysis process is impaired on the surface of glycosylphosphatidylinositol (GPI)-deficient cells due to the lack of these GPI-anchored enzymes. During culture of GPI-deficient cells with FAD or FMN, we found that hydrolysis of these forms of vitamin B₂ was impaired, and intracellular levels of vitamin B₂ were significantly decreased compared with those in GPI-restored cells, leading to decreased formation of vitamin B₂-dependent pyridoxal 5'-phosphate and mitochondrial dysfunction. Collectively, these results suggest that inefficient uptake of vitamin B₂ might account for mitochondrial dysfunction seen in some cases of inherited GPI deficiency.

In Vitro and In Vivo Pharmacological Profiles of DS-1211, a Novel Potent, Selective, and Orally Bioavailable Tissue-Nonspecific Alkaline Phosphatase Inhibitor

Inhibition of tissue-nonspecific alkaline phosphatase (TNAP) may prevent ectopic soft tissue calcification by increasing endogenous pyrophosphate (PPi). DS-1211 is a potent and selective novel small molecule TNAP inhibitor with well-characterized pharmacokinetics (PKs) in rodent and monkey. Herein, we report a comprehensive summary of studies establishing the pharmaceutical profile of DS-1211. In vitro studies characterized the mode of inhibition and inhibitory effects of DS-1211 on three human alkaline phosphatase (ALP) isozymes-TNAP, human intestinal ALP, human placental ALP-and on ALP activity across species in mouse, monkey, and human plasma. In vivo PK and pharmacodynamic (PD) effects of a single oral dose of DS-1211 in mice and monkeys were evaluated, including biomarker changes in PPi and pyridoxal 5'-phosphate (PLP). Oral bioavailability (BA) was determined through administration of DS-1211 at a 0.3-mg/kg dose in monkeys. In vitro experiments demonstrated DS-1211 inhibited ALP activity through an uncompetitive mode of action. DS-1211 exhibited TNAP selectivity and potent inhibition of TNAP across species. In vivo studies in mice and monkeys after single oral administration of DS-1211 showed linear PKs, with dose-dependent inhibition of ALP activity and increases in plasma PPi and PLP. Inhibitory effects of DS-1211 were consistent in both mouse and monkey. Mean absolute oral BA was 73.9%. Overall, in vitro and in vivo studies showed DS-1211 is a potent and selective TNAP inhibitor across species. Further in vivo pharmacology studies in ectopic calcification animal models and clinical investigations of DS-1211 in patient populations are warranted. © 2022 Daiichi Sankyo, Inc. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Evaluation of the predictive values of elevated serum L-homoarginine and dimethylarginines in preeclampsia

L-homoarginine (hARG) is involved in nitric oxide biosynthesis, but its role and concentration in preeclampsia (PE) have not been fully revealed. The purpose of this study was to develop and validate a feasible clinical assay to quantify serum hARG, arginine (ARG), asymmetric (ADMA) and symmetric dimethylarginines (SDMA) levels by LC-MS/MS and investigate their differences at different stages of pregnancy with or without preeclampsia. Serum samples were collected from 84 pregnant women without complications (controls), 84 with mild preeclampsia (MPE), and 81 with severe preeclampsia (SPE) at various gestation stages (before the 20th week, during the 20th-28th week or after the 28th week of gestation). No significant difference in ARG levels was observed between PE and controls at any stage (P > 0.05). The serum hARG levels and hARG/ADMA ratios of MPE before the 20th week were higher than those of controls (P < 0.001). ADMA levels of MPE were higher than those of controls during the 20th-28th week (P < 0.01). SDMA levels of SPE were higher than those of MPE (P < 0.01) and controls (P < 0.05) after the 28th week. Elevated serum hARG before the 20th week was identified as an independent predictor for PE (OR = 1.478, 95% CI 1.120-1.950). ROC curve analysis showed serum hARG before the 20th week had a good potential to predict MPE (AUC = 0.875, 95% CI 0.759-0.948). In conclusion, our study indicated that elevated serum hARG and dimethylarginine levels detected by LC-MS/MS might serve as potential biomarkers for the early prediction of PE.

Phase I studies of the safety, tolerability, pharmacokinetics, and pharmacodynamics of DS-1211, a tissue-nonspecific alkaline phosphatase inhibitor

Tissue-nonspecific alkaline phosphatase (TNAP) hydrolyzes and inactivates inorganic pyrophosphate (PPi), a potent inhibitor of calcification; therefore, TNAP inhibition is a potential target to treat ectopic calcification. These two first-in-human studies evaluated safety, tolerability, pharmacokinetics (PKs), and pharmacodynamics (PDs) of single (SAD) and multiple-ascending doses (MAD) of DS-1211, a TNAP inhibitor. Healthy adults were randomized 6:2 to DS-1211 or placebo, eight subjects per dose cohort. SAD study subjects received one dose of DS-1211 (range, 3-3000 mg) or placebo, whereas MAD study subjects received DS-1211 (range, 10-300 mg) once daily, 150 mg twice daily (b.i.d.), or placebo for 10 days. Primary end points were safety and tolerability. PK and PD assessments included plasma concentrations of DS-1211, alkaline phosphatase (ALP) activity, and TNAP substrates (PPi, pyridoxal 5'-phosphate [PLP], and phosphoethanolamine [PEA]). A total of 56 (DS-1211: n = 42; placebo: n = 14) and 40 (DS-1211: n = 30; placebo: n = 10) subjects enrolled in the SAD and MAD studies, respectively. In both studies, adverse events were mild or moderate and did not increase with dose. PKs of DS-1211 were linear up to 100 mg administered as a single dose and 150 mg b.i.d. administered as a multiple-dose regimen. In multiple dosing, there was minimal accumulation of DS-1211. Increased DS-1211 exposure correlated with dose-dependent ALP inhibition and concomitant increases in PPi, PLP, and PEA. In two phase I studies, DS-1211 appeared safe and well-tolerated. Post-treatment PD assessments were consistent with exposure-dependent TNAP inhibition. These data support further evaluation of DS-1211 for ectopic calcification diseases.

Tissue-Nonspecific Alkaline Phosphatase in Central Nervous System Health and Disease: A Focus on Brain Microvascular Endothelial Cells

Tissue-nonspecific alkaline phosphatase (TNAP) is an ectoenzyme bound to the plasma membranes of numerous cells via a glycosylphosphatidylinositol (GPI) moiety. TNAP's function is well-recognized from earlier studies establishing its important role in bone mineralization. TNAP is also highly expressed in cerebral microvessels; however, its function in brain cerebral microvessels is poorly understood. In recent years, few studies have begun to delineate a role for TNAP in brain microvascular endothelial cells (BMECs)-a key component of cerebral microvessels. This review summarizes important information on the role of BMEC TNAP, and its implication in health and disease. Furthermore, we discuss current models and tools that may assist researchers in elucidating the function of TNAP in BMECs.

Pharmacological TNAP inhibition efficiently inhibits arterial media calcification in a warfarin rat model but deserves careful consideration of potential physiological bone formation/mineralization impairment

Arterial media calcification is frequently seen in elderly and patients with chronic kidney disease (CKD), diabetes and osteoporosis. Pyrophosphate is a well-known calcification inhibitor that binds to nascent hydroxyapatite crystals and prevents further incorporation of inorganic phosphate into these crystals. However, the enzyme tissue-nonspecific alkaline phosphatase (TNAP), which is expressed in calcified arteries, degrades extracellular pyrophosphate into phosphate ions, by which pyrophosphate loses its ability to block vascular calcification. Here, we aimed to evaluate whether pharmacological TNAP inhibition is able to prevent the development of arterial calcification in a rat model of warfarin-induced vascular calcification. To investigate the effect of the pharmacological TNAP inhibitor SBI-425 on vascular calcification and bone metabolism, a 0.30% warfarin rat model was used. Warfarin exposure resulted in distinct calcification in the aorta and peripheral arteries. Daily administration of the TNAP inhibitor SBI-425 (10 mg/kg/day) for 7 weeks significantly reduced vascular calcification as indicated by a significant decrease in calcium content in the aorta (vehicle 3.84 ± 0.64 mg calcium/g wet tissue vs TNAP inhibitor 0.70 ± 0.23 mg calcium/g wet tissue) and peripheral arteries and a distinct reduction in area % calcification on Von Kossa stained aortic sections as compared to vehicle. Administration of SBI-425 resulted in decreased bone formation rate and mineral apposition rate, and increased osteoid maturation time and this without significant changes in osteoclast- and eroded perimeter. Administration of TNAP inhibitor SBI-425 significantly reduced the calcification in the aorta and peripheral arteries of a rat model of warfarin-induced vascular calcification. However, suppression of TNAP activity should be limited in order to maintain adequate physiological bone mineralization.

Bisthioureas of pimelic acid and 4-methylsalicylic acid derivatives as selective inhibitors of tissue-nonspecific alkaline phosphatase (TNAP) and intestinal alkaline phosphatase (IAP): Synthesis and molecular docking studies

Alkaline phosphatases (ALPs) are membrane bound metalloenzymes, distributed all over the body. Recent studies have revealed that by targeting ALPs can lead towards the treatment of many deadliest diseases including cardiac, cancerous and brain diseases. Thioureas and their derivatives are of considerable significance and are privileged scaffolds in medicinal chemistry. They show a wide range of pharmacological activities such as antibacterial, antiparasitic, anti-inflammatory and antioxidants etc. On the other hand, salicylic acid and its derivatives are known for its broad spectrum of activities. The work presented comprises of synthesis of N-acyl-N'-aryl substituted bisthioureas of pimelic acid (1-7) and 3,5-dimethyl pyrazole (11), 1-aroyl-3-aryl thiourea (12) and 1,3,4-oxadiazole (13) derivatives of 4-methyl salicylic acid. Structures of all the synthesized compounds were characterized by FT-IR and ¹H NMR spectroscopic analysis. Synthesized compounds were evaluated for their alkaline phosphatases inhibition potential and exhibited high potency as well as selectivity towards h-TNAP and h-IAP. Compound 7 and 12 which were the bisthiourea derivative of pimmelic acid and thiourea derivative of 4-methyl salicylic acid, respectively, showed excellent selectivity against h-TNAP and h-IAP, respectively.

Synthesis and computational studies of highly selective inhibitors of human recombinant tissue non-specific alkaline phosphatase (h-TNAP): A therapeutic target against vascular calcification

In this study, we have discovered small druglike molecules as selective inhibitors of human tissue-nonspecific alkaline phosphatase (h-TNAP), an enzyme critical for the regulation of extracellular matrix calcification. The upregulation of h-TNAP is associated with various pathologies particularly the vascular calcification (VC). Selective inhibition of h-TNAP over h-NPP1 may serve as a useful therapeutic strategy against vascular calcification. A series of novel triazolyl pyrazole derivatives (10a-y) in which thiol bearing triazole moiety as the zinc binding functional group was introduced to a pyrazole based pharmacophore was synthesized and evaluated as potent and selective inhibitors of h-TNAP over h-NPP1. The biological screening against h-TNAP, h-IAP, h-NPP1 and h-NPP3 showed that many of the synthesized compounds are selective inhibitors of TNAP. Particularly, the compounds 10a-h, 10j, 10m-q, 10u, 10w and 10x displayed high potency and complete selectivity towards h-TNAP over h-NPP1. Compound 10q emerged as a highly potent inhibitor (IC₅₀ = 0.16 µM or 160 nM) against h-TNAP with 127-fold increased inhibition compared to levamisole. On the other hand, compound 10e was found to be most selective inhibitor against the tested APs and NPPs (IC₅₀ = 1.59 ± 0.36 µM). Binding sites architecture analysis, molecular-docking and molecular dynamics simulations (MDS), revealed the basis for h-TNAP and h-IAP ligand selectivity as well as selectivity towards h-TNAP over h-NPP1. These newly discovered inhibitors are believed to represent valuable lead structures to further streamline the generation of candidate compounds to target VC.

Is Homoarginine a Protective Cardiovascular Risk Factor?

A series of recent epidemiological studies have implicated the endogenous nonproteinogenic amino acid l-homoarginine as a novel candidate cardiovascular risk factor. The association between homoarginine levels and the risk of adverse cardiovascular outcomes is inverse (ie, high cardiovascular risk is predicted by low rather than high homoarginine levels), which makes it plausible to normalize systemic homoarginine levels via oral supplementation. The emergence of homoarginine as a potentially treatable protective cardiovascular risk factor has generated a wave of hope in the field of cardiovascular prevention. Herein, we review the biochemistry, physiology, and metabolism of homoarginine, summarize the strengths and weaknesses of the epidemiological evidence linking homoarginine to cardiovascular disease and its potential protective cardiovascular effects, and identify priorities for future research needed to define the clinical utility of homoarginine as a prognostic factor and therapeutic target in cardiovascular disease.

HLA-B27-mediated activation of TNAP phosphatase promotes pathogenic syndesmophyte formation in ankylosing spondylitis

Ankylosing spondylitis (AS) is a type of axial inflammation. Over time, some patients develop spinal ankylosis and permanent disability; however, current treatment strategies cannot arrest syndesmophyte formation completely. Here, we used mesenchymal stem cells (MSCs) from AS patients (AS MSCs) within the enthesis involved in spinal ankylosis to delineate that the HLA-B27-mediated spliced X-box-binding protein 1 (sXBP1)/retinoic acid receptor-β (RARB)/tissue-nonspecific alkaline phosphatase (TNAP) axis accelerated the mineralization of AS MSCs, which was independent of Runt-related transcription factor 2 (Runx2). An animal model mimicking AS pathological bony appositions was established by implantation of AS MSCs into the lumbar spine of NOD-SCID mice. We found that TNAP inhibitors, including levamisole and pamidronate, inhibited AS MSC mineralization in vitro and blocked bony appositions in vivo. Furthermore, we demonstrated that the serum bone-specific TNAP (BAP) level was a potential prognostic biomarker to predict AS patients with a high risk for radiographic progression. Our study highlights the importance of the HLA-B27-mediated activation of the sXBP1/RARB/TNAP axis in AS syndesmophyte pathogenesis and provides a new strategy for the diagnosis and prevention of radiographic progression of AS.

Salivary extracellular vesicles can modulate purinergic signalling in oral tissues by combined ectonucleoside triphosphate diphosphohydrolases and ecto-5'-nucleotidase activities

We reported previously that the rat submandibular gland is able to release nanovesicles capable to hydrolyse millimolar concentrations of ATP, ADP and AMP in vitro. Here, we show that rat saliva also contains nanovesicles with the ability to hydrolyse ATP. Our aim was to identify and characterize vesicular nucleotidases by using kinetic, immunological and in silico approaches. Nucleotidase activity in the absence or presence of specific inhibitors allowed us to assume the participation of NTPDase1, -2 and -3, together with ecto-5'-nucleotidase, confirmed using specific antibodies. At neutral pH, initial ATPase activity would be mostly due to NTPDase2, which was thereafter inactivated, leaving NTPDase1 and NTPDase3 to hydrolyse ATP and ADP with an efficacy ATPase/ADPase around 2. Ecto-5'nucleotidase would be mainly responsible for AMP hydrolysis and adenosine accumulation. We proposed a kinetic model for NTPDase2 as a tool to isolate and analyse the turnover of this enzyme in the presence of different ATP concentrations, including those expected in extracellular media. Our study characterizes the ectonucleotidases carried by extracellular vesicles which contribute to modulate ATP and adenosine concentrations in the oral cavity, essential players in purinergic signalling.

4-Aminopyridine based amide derivatives as dual inhibitors of tissue non-specific alkaline phosphatase and ecto-5'-nucleotidase with potential anticancer activity

Ecto-nucleotidase members i.e., ecto-5'-nucleotidase and alkaline phosphatase, hydrolyze extracellular nucleotides and play an important role in purinergic signaling. Their overexpression are implicated in a variety of pathological states, including immunological diseases, bone mineralization, vascular calcification and cancer, and thus they represent an emerging drug targets. In order to design potent and selective inhibitors, new derivatives of 4-aminopyridine have been synthesized (10a-10m) and their structures were established on the basis of spectral data. The effect of nature and position of substituent was interestingly observed and justified on the basis of their detailed structure activity relationships (SARs) against both families of ecto-nucleotidase. Compound 10a displayed significant inhibition (IC₅₀ ± SEM = 0.25 ± 0.05 µM) that was found ≈168 fold more potent as compared to previously reported inhibitor suramin (IC₅₀ ± SEM = 42.1 ± 7.8 µM). This compound exhibited 6 times more selectivity towards h-TNAP over h-e5'NT. The anticancer potential and mechanism were also established using cell viability assay, flow cytometric analysis and nuclear staining. Molecular docking studies were also carried out to gain insight into the binding interaction of potent compounds within the respective enzyme pockets and herring-sperm DNA.

Discovery of 5-((5-chloro-2-methoxyphenyl)sulfonamido)nicotinamide (SBI-425), a potent and orally bioavailable tissue-nonspecific alkaline phosphatase (TNAP) inhibitor

Tissue-nonspecific alkaline phosphatase (TNAP) is an ectoenzyme crucial for bone matrix mineralization via its ability to hydrolyze extracellular inorganic pyrophosphate (ePP_i), a potent mineralization inhibitor, to phosphate (P_i). By the controlled hydrolysis of ePP_i, TNAP maintains the correct ratio of P_i to ePP_i and therefore enables normal skeletal and dental calcification. In other areas of the body low ePP_i levels lead to the development of pathological soft-tissue calcification, which can progress to a number of disorders. TNAP inhibitors have been shown to prevent these processes via an increase of ePP_i. Herein we describe the use of a whole blood assay to optimize a previously described series of TNAP inhibitors resulting in 5-((5-chloro-2-methoxyphenyl)sulfonamido)nicotinamide (SBI-425), a potent, selective and oral bioavailable compound that robustly inhibits TNAP in vivo.

Alkaline phosphatase: a novel treatment target for cardiovascular disease in CKD

Cardiovascular disease is the main cause of early death in the settings of chronic kidney disease (CKD), type 2 diabetes mellitus (T2DM), and ageing. Cardiovascular events can be caused by an imbalance between promoters and inhibitors of mineralization, which leads to vascular calcification. This process is akin to skeletal mineralization, which is carefully regulated and in which isozymes of alkaline phosphatase (ALP) have a crucial role. Four genes encode ALP isozymes in humans. Intestinal, placental and germ cell ALPs are tissue-specific, whereas the tissue-nonspecific isozyme of ALP (TNALP) is present in several tissues, including bone, liver and kidney. TNALP has a pivotal role in bone calcification. Experimental overexpression of TNALP in the vasculature is sufficient to induce vascular calcification, cardiac hypertrophy and premature death, mimicking the cardiovascular phenotype often found in CKD and T2DM. Intestinal ALP contributes to the gut mucosal defence and intestinal and liver ALPs might contribute to the acute inflammatory response to endogenous or pathogenic stimuli. Here we review novel mechanisms that link ALP to vascular calcification, inflammation, and endothelial dysfunction in kidney and cardiovascular diseases. We also discuss new drugs that target ALP, which have the potential to improve cardiovascular outcomes without inhibiting skeletal mineralization.

New frontiers in the treatment of colorectal cancer: Autophagy and the unfolded protein response as promising targets

Colorectal cancer (CRC), despite numerous therapeutic and screening attempts, still remains a major life-threatening malignancy. CRC etiology entails both genetic and environmental factors. Macroautophagy/autophagy and the unfolded protein response (UPR) are fundamental mechanisms involved in the regulation of cellular responses to environmental and genetic stresses. Both pathways are interconnected and regulate cellular responses to apoptotic stimuli. In this review, we address the epidemiology and risk factors of CRC, including genetic mutations leading to the occurrence of the disease. Next, we discuss mutations of genes related to autophagy and the UPR in CRC. Then, we discuss how autophagy and the UPR are involved in the regulation of CRC and how they associate with obesity and inflammatory responses in CRC. Finally, we provide perspectives for the modulation of autophagy and the UPR as new therapeutic options for CRC treatment.

Minimal C-terminal modification boosts peptide self-assembling ability for necroptosis of cancer cells

Here we reported the first case in which enhancing self-assembling ability boosts anti-cancer efficacy through a simple and minimal modification of the C-terminus of a d-tripeptide. By only a 2% change of the molecular weight, this facile approach increases the inhibitory activity by over an order of magnitude (IC50 from 431 to 23 μM) towards an osteosarcoma cell line.

Molecular Genetics of Hypophosphatasia and Phenotype-Genotype Correlations

Hypophosphatasia (HPP) is due to deficient activity of the tissue-nonspecific isoenzyme of alkaline phosphatase (TNAP). This enzyme cleaves extracellular substrates inorganic pyrophosphates (PPi), pyridoxal-5'-phosphate (PLP), phosphoethanolamine (PEA) and nucleotides, and probably other substrates not yet identified. During the last 15 years the role of TNAP in mineralization, and to a less degree in brain, has been investigated, providing hypotheses and explanations for both bone and neuronal HPP phenotypes. ALPL, the gene encoding TNAP, is subject to many mutations, mostly missense mutations. A few number of mutations are recurrently found and may be quite frequent in particular populations. This reflects founder effects. The great variety of mutations results in a great number of compound heterozygous genotypes and in highly variable clinical expressivity. A good correlation was observed between the severity of the disease and in vitro enzymatic activity of the mutant protein measured after site-directed mutagenesis. Many missense mutations found in severe hypophosphatasia produced a mutant protein that failed to reach the cell membrane , was accumulated in the cis-Golgi and was subsequently degraded in the proteasome. Missense mutations located in the catalytic site or in the homodimer interface were often shown by site-directed mutagenesis to have a dominant negative effect. Currently molecular diagnosis of HPP is based on the sequencing of the coding sequence of ALPL that allows detection of approximately 95 % of mutations in severe cases. In addition, other genes, especially genes encoding proteins involved in the regulation of extracellular PPi concentration, could modify the phenotype (modifier genes).

Tissue Non-specific Alkaline Phosphatase (TNAP) in Vessels of the Brain

The microvessels of the brain represent around 3-4 % of the brain compartment but constitute the most important length (400 miles) and surface of exchange (20 m(2)) between the blood and the parenchyma of brain. Under influence of surrounding tissues, the brain microvessel endothelium expresses a specific phenotype that regulates and restricts the entry of compounds and cells from blood to brain, and defined the so-called blood-brain barrier (BBB). Evidences that alkaline phosphatase (AP) is a characteristic feature of the BBB phenotype that allows differentiating capillary endothelial cells from brain to those of the periphery have rapidly emerge. Thenceforth, AP has been rapidly used as a biomarker of the blood-brain barrier phenotype. In fact, brain capillary endothelial cells (BCECs) express exclusively tissue non-specific alkaline phosphatase (TNAP). There are several lines of evidence in favour of an important role for TNAP in brain function. TNAP is thought to be responsible for the control of transport of some compounds across the plasma membrane of the BCECs. Here, we report that levamisole-mediated inhibition of TNAP provokes an increase of the permeability to Lucifer Yellow of the endothelial monolayer. Moreover, we illustrate the disruption of the cytoskeleton organization. Interestingly, all observed effects were reversible 24 h after levamisole removal and correlated with the return of a full activity of the TNAP. This reversible effect remains to be studied in details to evaluate the potentiality of a levamisole treatment to enhance the entry of drugs in the brain parenchyma.

[Identification of thiamine monophosphate hydrolyzing enzymes in chicken liver]

In animals, thiamine monophosphate (TMP) is an intermediate on the path of thiamine diphosphate, the coenzyme form of vitamin B1, degradation. The enzymes involved in TMP metabolism in animal tissues are not identified hitherto. The aim of this work was to study TMP hydrolysis in chicken liver. Two phosphatases have been found to contribute to TMP hydrolysis in liver homogenate. The first one, possessing a maximal activity at pH 6.0, is soluble, whereas the second one represents a membrane-bound enzyme with a pH optimum of 9.0. Membrane-bound TMPase activity was enhanced 1.7-fold by 5 mM Mg2+ ions and strongly inhibited by levamisole in uncompetitive manner with K1 of 53 μM, indicating the involvement of alkaline phosphatase. An apparent Km of alkaline phosphatase for TMP was calculated from the Hanes plot to be 0.6 mM. The soluble TMPase has an apparent Km of 0.7 mM; this enzyme is Mg2+ independent and insensitive to levamisole. As estimated by gel filtration on a Toyopearl HW-55 column, the soluble enzyme has a molecular mass of 17.8 kDa, TMPase activity being eluted simultaneously with peaks of flavinmononucleotide and p-nitrophenyl phosphatase activity. Thus, TMP appears to be a physiological substrate for a low-molecular weight acid phosphatase, also known as low-molecular-weight protein phosphotyrosine phosphatase.

Simultaneous retention of thermostability and specific activity in chimeric human alkaline phosphatases

Alkaline phosphatases (APs) are a family of dimeric metalloenzymes that has been utilized in many areas due to its ability to hydrolyze a variety of phosphomonoesters. While mammalian APs have higher specific activity than prokaryotic APs, they are generally less thermostable. To cultivate the possibility to confer mammalian APs with higher thermostability as well as high activity, we focused on human AP isozymes. Among the four isozymes of human APs, placental AP (PLAP) retains the highest thermostability, while intestinal AP (IAP) has the highest specific activity. Since the two APs display high homology, a series of chimeric enzymes were made in a secreted form to analyze their properties. Surprisingly, chimeric APs with IAP residues at the N-terminal and PLAP residues at the C-terminal regions showed higher specific activity than PLAP, while keeping thermostability as high as PLAP. Especially, one showed similar specific activity to IAP, while showing slower inactivation than PLAP after incubation at 75°C. Interestingly, the mutant also showed higher resistance to uncompetitive inhibitors Phe and Leu than their parent enzymes, possibly due to increased hydrophilicity of the active site entrance residues. The obtained chimera will be useful as a novel reporter in various assays including gene hybridization.

Alkaline phosphatase protects lipopolysaccharide-induced early pregnancy defects in mice

Excessive cytokine inflammatory response due to chronic or superphysiological level of microbial infection during pregnancy leads to pregnancy complications such as early pregnancy defects/loss and preterm birth. Bacterial toxin lipopolysaccharide (LPS), long recognized as a potent proinflammatory mediator, has been identified as a risk factor for pregnancy complications. Alkaline phosphatase (AP) isozymes have been shown to detoxify LPS by dephosphorylation. In this study, we examined the role of alkaline phosphatase (AP) in mitigating LPS-induced early pregnancy complications in mice. We found that 1) the uterus prior to implantation and implantation sites following embryo implantation produce LPS recognition and dephosphorylation molecules TLR4 and tissue non-specific AP (TNAP) isozyme, respectively; 2) uterine TNAP isozyme dephosphorylates LPS at its sites of production; 3) while LPS administration following embryo implantation elicits proinflammatory cytokine mRNA levels at the embryo implantation sites (EISs) and causes early pregnancy loss, dephosphorylated LPS neither triggers proinflammatory cytokine mRNA levels at the EISs nor induces pregnancy complications; 4) AP isozyme supplementation to accelerate LPS detoxification attenuates LPS-induced pregnancy complications following embryo implantation. These findings suggest that a LPS dephosphorylation strategy using AP isozyme may have a unique therapeutic potential to mitigate LPS- or Gram-negative bacteria-induced pregnancy complications in at-risk women.

Investigation of quinoline-4-carboxylic acid as a highly potent scaffold for the development of alkaline phosphatase inhibitors: synthesis, SAR analysis and molecular modelling studies

The present study is directed towards the development of quinoline-4-carboxylic acid derivatives as potential alkaline phosphatase inhibitors.

Polyoxometalates--potent and selective ecto-nucleotidase inhibitors

Polyoxometalates (POMs) are inorganic cluster metal complexes that possess versatile biological activities, including antibacterial, anticancer, antidiabetic, and antiviral effects. Their mechanisms of action at the molecular level are largely unknown. However, it has been suggested that the inhibition of several enzyme families (e.g., phosphatases, protein kinases or ecto-nucleotidases) by POMs may contribute to their pharmacological properties. Ecto-nucleotidases are cell membrane-bound or secreted glycoproteins involved in the hydrolysis of extracellular nucleotides thereby regulating purinergic (and pyrimidinergic) signaling. They comprise four distinct families: ecto-nucleoside triphosphate diphosphohydrolases (NTPDases), ecto-nucleotide pyrophosphatases/phosphodiesterases (NPPs), alkaline phosphatases (APs) and ecto-5'-nucleotidase (eN). In the present study, we evaluated the inhibitory potency of a series of polyoxometalates as well as chalcogenide hexarhenium cluster complexes at a broad range of ecto-nucleotidases. [Co4(H2O)2(PW9O34)2](10-) (5, PSB-POM142) was discovered to be the most potent inhibitor of human NTPDase1 described so far (Ki: 3.88 nM). Other investigated POMs selectively inhibited human NPP1, [TiW11CoO40](8-) (4, PSB-POM141, Ki: 1.46 nM) and [NaSb9W21O86](18-) (6, PSB-POM143, Ki: 4.98 nM) representing the most potent and selective human NPP1 inhibitors described to date. [NaP5W30O110](14-) (8, PSB-POM144) strongly inhibited NTPDase1-3 and NPP1 and may therefore be used as a pan-inhibitor to block ATP hydrolysis. The polyoxoanionic compounds displayed a non-competitive mechanism of inhibition of NPPs and eN, but appeared to be competitive inhibitors of TNAP. Future in vivo studies with selected inhibitors identified in the current study are warranted.

Ovarian cancer stem-like cells show induced translineage-differentiation capacity and are suppressed by alkaline phosphatase inhibitor

Spheroid formation is one property of stem cells—such as embryo-derived or neural stem cells—that has been used for the enrichment of cancer stem-like cells (CSLCs). However, it is unclear whether CSLC-derived spheroids are heterogeneous or whether they share common embryonic stemness properties. Understanding these features might lead to novel therapeutic approaches. Ovarian carcinoma is a deadly disease of women. We identified two types of spheroids (SR1 and SR2) from ovarian cancer cell lines and patients' specimens according to their morphology. Both types expressed stemness markers and could self-renew and initiate tumors when a low number of cells were used. Only SR1 could differentiate into multiple-lineage cell types under specific induction conditions. SR1 spheroids could differentiate to SR2 spheroids through epithelial–mesenchymal transition. Alkaline phosphatase (ALP) was highly expressed in SR1 spheroids, decreased in SR2 spheroids, and was absent in differentiated progenies in accordance with the loss of stemness properties. We verified that ALP can be a marker for ovarian CSLCs, and patients with greater ALP expression is related to advanced clinical stages and have a higher risk of recurrence and lower survival rate. The ALP inhibitor, levamisole, disrupted the self-renewal of ovarian CSLCs in vitro and tumor growth in vivo. In summary, this research provides a plastic ovarian cancer stem cell model and a new understanding of the cross-link between stem cells and cancers. This results show that ovarian CSLCs can be suppressed by levamisole. Our findings demonstrated that some ovarian CSLCs may restore ALP activity, and this suggests that inhibition of ALP activity may present a new opportunity for treatment of ovarian cancer.

Sex-dependent, zinc-induced dephosphorylation of phospholamban by tissue-nonspecific alkaline phosphatase in the cardiac sarcomere

We have previously reported that Zn(2+) infused into the coronary arteries of isolated rat hearts leads to the potent dephosphorylation of phospholamban (PLB) as well as a noticeable but less potent dephosphorylation of the ryanodine receptor 2. We hypothesized in the present study that a Zn(2+)-activated phosphatase is located in the vicinity of the sarcoplasmic reticulum (SR) where PLB and ryanodine receptor 2 reside. We report here the novel finding of tissue-nonspecific alkaline phosphatase (TNAP), a zinc-dependent enzyme, localized to the SR in the cardiac sarcomere of mouse myocardium. TNAP activity was enhanced by injection of Zn acetate into a tail vein before harvesting the heart and imaged using electron microscopy of electron dense deposits indicative of the hydrolysis of exogenous β-glycerophosphate. TNAP activity was observed localized to the ends of the Z-line corresponding to SR and was qualitatively more visible in myocardium of males compared with females. Correspondingly, PLB phosphorylation status was potently reduced in myocardium of males injected with Zn acetate, whereas there was no apparent effect of Zn acetate injection on PLB phosphorylation in females. Surprisingly, Western blot analysis of TNAP content suggested a significantly lower TNAP content in males compared with females. These data suggest that TNAP plays a role in governing the phosphorylation status of calcium handling proteins in the SR. Furthermore, the content and activity of TNAP are differentially regulated between the sexes and thus may account for some sex differences in cardiopathologies associated with calcium handling.

Vas deferens neuro-effector junction: from kymographic tracings to structural biology principles

The vas deferens is a simple bioassay widely used to study the physiology of sympathetic neurotransmission and the pharmacodynamics of adrenergic drugs. The role of ATP as a sympathetic co-transmitter has gained increasing attention and furthered our understanding of its role in sympathetic reflexes. In addition, new information has emerged on the mechanisms underlying the storage and release of ATP. Both noradrenaline and ATP concur to elicit the tissue smooth muscle contractions following sympathetic reflexes or electrical field stimulation of the sympathetic nerve terminals. ATP and adenosine (its metabolic byproduct) are powerful presynaptic regulators of co-transmitter actions. In addition, neuropeptide Y, the third member of the sympathetic triad, is an endogenous modulator. The peptide plus ATP and/or adenosine play a significant role as sympathetic modulators of transmitter's release. This review focuses on the physiological principles that govern sympathetic co-transmitter activity, with special interest in defining the motor role of ATP. In addition, we intended to review the recent structural biology findings related to the topology of the P2X1R based on the crystallized P2X4 receptor from Danio rerio, or the crystallized adenosine A2A receptor as a member of the G protein coupled family of receptors as prototype neuro modulators. This review also covers structural elements of ectonucleotidases, since some members are found in the vas deferens neuro-effector junction. The allosteric principles that apply to purinoceptors are also reviewed highlighting concepts derived from receptor theory at the light of the current available structural elements. Finally, we discuss clinical applications of these concepts.

Multisystemic functions of alkaline phosphatases

Human and mouse alkaline phosphatases (AP) are encoded by a multigene family expressed ubiquitously in multiple tissues. Gene knockout (KO) findings have helped define some of the precise exocytic functions of individual isozymes in bone, teeth, the central nervous system, and in the gut. For instance, deficiency in tissue-nonspecific alkaline phosphatase (TNAP) in mice (Alpl (-/-) mice) and humans leads to hypophosphatasia (HPP), an inborn error of metabolism characterized by epileptic seizures in the most severe cases, caused by abnormal metabolism of pyridoxal-5'-phosphate (the predominant form of vitamin B6) and by hypomineralization of the skeleton and teeth featuring rickets and early loss of teeth in children or osteomalacia and dental problems in adults caused by accumulation of inorganic pyrophosphate (PPi). Enzyme replacement therapy with mineral-targeting TNAP prevented all the manifestations of HPP in mice, and clinical trials with this protein therapeutic are showing promising results in rescuing life-threatening HPP in infants. Conversely, TNAP induction in the vasculature during generalized arterial calcification of infancy (GACI), type II diabetes, obesity, and aging can cause medial vascular calcification. TNAP inhibitors, discussed extensively in this book, are in development to prevent pathological arterial calcification. The brush border enzyme intestinal alkaline phosphatase (IAP) plays an important role in fatty acid (FA) absorption, in protecting gut barrier function, and in determining the composition of the gut microbiota via its ability to dephosphorylate lipopolysaccharide (LPS). Knockout mice (Akp3 (-/-)) deficient in duodenal-specific IAP (dIAP) become obese, and develop hyperlipidemia and hepatic steatosis when fed a high-fat diet (HFD). These changes are accompanied by upregulation in the jejunal-ileal expression of the Akp6 IAP isozyme (global IAP, or gIAP) and concomitant upregulation of FAT/CD36, a phosphorylated fatty acid translocase thought to play a role in facilitating the transport of long-chain fatty acids into cells. gIAP, but not dIAP, is able to modulate the phosphorylation status of FAT/CD36. dIAP, even though it is expressed in the duodenum, is shed into the gut lumen and is active in LPS dephosphorylation throughout the gut lumen and in the feces. Akp3 (-/-) mice display gut dysbiosis and are more prone to dextran sodium sulfate-induced colitis than wild-type mice. Of relevance, oral administration of recombinant calf IAP prevents the dysbiosis and protects the gut from chronic colitis. Analogous to the role of IAP in the gut, TNAP expression in the liver may have a proactive role from bacterial endotoxin insult. Finally, more recent studies suggest that neuronal death in Alzheimer's disease may also be associated with TNAP function on certain brain-specific phosphoproteins. This review recounts the established roles of TNAP and IAP and briefly discusses new areas of investigation related to multisystemic functions of these isozymes.

Catalytic signature of a heat-stable, chimeric human alkaline phosphatase with therapeutic potential

Recombinant alkaline phosphatases are becoming promising protein therapeutics to prevent skeletal mineralization defects, inflammatory bowel diseases, and treat acute kidney injury. By substituting the flexible crown domain of human intestinal alkaline phosphatase (IAP) with that of the human placental isozyme (PLAP) we generated a chimeric enzyme (ChimAP) that retains the structural folding of IAP, but displays greatly increased stability, active site Zn²⁺ binding, increased transphosphorylation, a higher turnover number and narrower substrate specificity, with comparable selectivity for bacterial lipopolysaccharide (LPS), than the parent IAP isozyme. ChimAP shows promise as a protein therapeutic for indications such as inflammatory bowel diseases, gut dysbioses and acute kidney injury.

Identification of a selective inhibitor of murine intestinal alkaline phosphatase (ML260) by concurrent ultra-high throughput screening against human and mouse isozymes

Alkaline phosphatase (AP) isozymes are present in a wide range of species from bacteria to man and are capable of dephosphorylation and transphosphorylation of a wide spectrum of substrates in vitro. In humans, four AP isozymes have been identified-one tissue-nonspecific (TNAP) and three tissue-specific-named according to the tissue of their predominant expression: intestinal (IAP), placental (PLAP) and germ cell (GCAP) APs. Modulation of activity of the different AP isozymes may have therapeutic implications in distinct diseases and cellular processes. For instance, changes in the level of IAP activity can affect gut mucosa tolerance to microbial invasion due to the ability of IAP to detoxify bacterial endotoxins, alter the absorption of fatty acids and affect ectopurinergic regulation of duodenal bicarbonate secretion. To identify isozyme selective modulators of the human and mouse IAPs, we developed a series of murine duodenal IAP (Akp3-encoded dIAP isozyme), human IAP (hIAP), PLAP, and TNAP assays. High throughput screening and subsequent SAR efforts generated a potent inhibitor of dIAP, ML260, with specificity for the Akp3-, compared to the Akp5- and Akp6-encoded mouse isozymes.

Alkaline phosphatases contribute to uterine receptivity, implantation, decidualization, and defense against bacterial endotoxin in hamsters

Alkaline phosphatase (AP) activity has been demonstrated in the uterus of several species, but its importance in the uterus, in general and during pregnancy, is yet to be revealed. In this study, we focused on identifying AP isozyme types and their hormonal regulation, cell type, and event-specific expression and possible functions in the hamster uterus during the cycle and early pregnancy. Our RT-PCR and in situ hybridization studies demonstrated that among the known Akp2, Akp3, Akp5, and Akp6 murine AP isozyme genes, hamster uteri express only Akp2 and Akp6; both genes are co-expressed in luminal epithelial cells. Studies in cyclic and ovariectomized hamsters established that while progesterone (P₄) is the major uterine Akp2 inducer, both P₄ and estrogen are strong Akp6 regulators. Studies in preimplantation uteri showed induction of both genes and the activity of their encoded isozymes in luminal epithelial cells during uterine receptivity. However, at the beginning of implantation, Akp2 showed reduced expression in luminal epithelial cells surrounding the implanted embryo. By contrast, expression of Akp6 and its isozyme was maintained in luminal epithelial cells adjacent to, but not away from, the implanted embryo. Following implantation, stromal transformation to decidua was associated with induced expressions of only Akp2 and its isozyme. We next demonstrated that uterine APs dephosphorylate and detoxify endotoxin lipopolysaccharide at their sites of production and activity. Taken together, our findings suggest that uterine APs contribute to uterine receptivity, implantation, and decidualization in addition to their role in protection of the uterus and pregnancy against bacterial infection.

Therapeutic potentials of ecto-nucleoside triphosphate diphosphohydrolase, ecto-nucleotide pyrophosphatase/phosphodiesterase, ecto-5'-nucleotidase, and alkaline phosphatase inhibitors

The modulatory role of extracellular nucleotides and adenosine in relevance to purinergic cell signaling mechanisms has long been known and is an object of much research worldwide. These extracellular nucleotides are released by a variety of cell types either innately or as a response to patho-physiological stress or injury. A variety of surface-located ecto-nucleotidases (of four major types; nucleoside triphosphate diphosphohydrolases or NTPDases, nucleotide pyrophosphatase/phosphodiesterases or NPPs, alkaline phosphatases APs or ALPs, and ecto-5'-nucleotidase or e5NT) are responsible for meticulously controlling the availability of these important signaling molecules (at their respective receptors) in extracellular environment and are therefore crucial for maintaining the integrity of normal cell functioning. Overexpression of many of these ubiquitous ecto-enzymes has been implicated in a variety of disorders including cell adhesion, activation, proliferation, apoptosis, and degenerative neurological and immunological responses. Selective inhibition of these ecto-enzymes is an area that is currently being explored with great interest and hopes remain high that development of selective ecto-nucleotidase inhibitors will prove to have many beneficial therapeutic implications. The aim of this review is to emphasize and focus on recent developments made in the field of inhibitors of ecto-nucleotidases and to highlight their structure activity relationships wherever possible. Most recent and significant advances in field of NTPDase, NPP, AP, and e5NT inhibitors is being discussed in detail in anticipation of providing prolific leads and relevant background for research groups interested in synthesis of selective ecto-nucleotidase inhibitors.

Homoarginine and progression of chronic kidney disease: results from the Mild to Moderate Kidney Disease Study

Background

Homoarginine is an amino acid derivative mainly synthesized in the kidney. It is suggested to increase nitric oxide availability, enhance endothelial function and to protect against cardiovascular diseases. We aimed to investigate the relation between homoarginine, kidney function and progression of chronic kidney disease (CKD).

Methods

We measured plasma homoarginine concentrations in baseline samples of the Mild to Moderate Kidney Disease (MMKD) Study, a prospective cohort study of 227 patients with CKD in Europe. Homoarginine concentrations were available in 182 of the baseline samples and in 139 of the prospectively-followed patients. We correlated homoarginine concentrations to parameters of kidney function. The association between homoarginine and progression of CKD was assessed during a follow-up of up to seven years (median 4.45 years, interquartile range 2.54–5.19) using Cox regression analysis. Progression of CKD was defined as doubling of baseline serum creatinine and/or end-stage renal disease.

Results

Study participants were at baseline on average 47±13 years old and 65% were male. Mean±standard deviation of homoarginine concentrations were 2.5±1.1 µmol/L and concentrations were incrementally lower at lower levels of GFR with mean concentrations of 2.90±1.02 µmol/L (GFR>90 ml/min), 2.64±1.06 µmol/L (GFR 60–90 ml/min), 2.52±1.24 µmol/L (GFR 30–60 ml/min) and 2.05±0.78 µmol/L (GFR<30 ml/min), respectively (p = 0.002). The age- and sex-adjusted risk to reach the renal endpoint was significantly higher by 62% with each decrease by one standard deviation (1.1 µmol/L) of homoarginine (HR 1.62, 95% CI 1.16–2.27, p = 0.005). This association was independent of proteinuria (HR 1.56, 95% CI 1.11–2.20, p = 0.01), and was slightly attenuated when adjusting for GFR (HR 1.40 (95% CI 0.98–1.98, p = 0.06).

Conclusions

Homoarginine concentrations are directly correlated with kidney function and are significantly associated with the progression of CKD. Low homoarginine concentrations might be an early indicator of kidney failure and a potential target for the prevention of disease progression which needs further investigations.

Identification of a metabolizing enzyme in human kidney by proteomic correlation profiling

Molecular identification of endogenous enzymes and biologically active substances from complex biological sources remains a challenging task, and although traditional biochemical purification is sometimes regarded as outdated, it remains one of the most powerful methodologies for this purpose. While biochemical purification usually requires large amounts of starting material and many separation steps, we developed an advanced method named "proteomic correlation profiling" in our previous study. In proteomic correlation profiling, we first fractionated biological material by column chromatography, and then calculated each protein's correlation coefficient between the enzyme activity profile and protein abundance profile determined by proteomics technology toward fractions. Thereafter, we could choose possible candidates for the enzyme among proteins with a high correlation value by domain predictions using informatics tools. Ultimately, this streamlined procedure requires fewer purification steps and reduces starting materials dramatically due to low required purity compared with conventional approaches. To demonstrate the generality of this approach, we have now applied an improved workflow of proteomic correlation profiling to a drug metabolizing enzyme and successfully identified alkaline phosphatase, tissue-nonspecific isozyme (ALPL) as a phosphatase of CS-0777 phosphate (CS-0777-P), a selective sphingosine 1-phosphate receptor 1 modulator with potential benefits in the treatment of autoimmune diseases including multiple sclerosis, from human kidney extract. We identified ALPL as a candidate protein only by the 200-fold purification and only from 1 g of human kidney. The identification of ALPL as CS-0777-P phosphatase was strongly supported by a recombinant protein, and contribution of the enzyme in human kidney extract was validated by immunodepletion and a specific inhibitor. This approach can be applied to any kind of enzyme class and biologically active substance; therefore, we believe that we have provided a fast and practical option by combination of traditional biochemistry and state-of-the-art proteomic technology.

Polyoxometalates as potent and selective inhibitors of alkaline phosphatases with profound anticancer and amoebicidal activities

The biological significance of polyoxometalates is well renowned owing to their anticancer, antiviral and antibiotic properties. Here another therapeutic aspect of polyoxometalates has been explored as alkaline phosphatase inhibitors along with the remarked anticancer and amoebicidal properties. Synthesis and inhibitory studies of a set of seven polyoxotungstates against two major isozymes of alkaline phosphatase i.e. tissue specific and tissue non-specific alkaline phosphatase revealed their promising activity as alkaline phosphatase inhibitors. All compounds exhibited alkaline phosphatase inhibitory potency in nanomolar ranges. For tissue specific alkaline phosphatase, Na(10)[H(2)W(12)O(42)]·27H(2)O (A6) was found to be the most potent inhibitor (K(i) value 313 ± 7 nM), while for tissue non-specific alkaline phosphatase Na(33)[H(7)P(8)W(48)O(184)]·92H(2)O (A3) showed the highest inhibition potency (K(i) values 135 ± 10 nM). Moreover cytotoxicity evaluation of these compounds against lung carcinoma cells and immortalized human corneal epithelial cells demonstrated their anticancer potential with no cytotoxic effects on normal human cell lines. All anticancer drugs result in an impaired immune system and such immunocompromised persons become vulnerable to opportunistic infections specially Acanthamoeba which causes granulomatous amoebic encephalitis (GAE) which almost always results in death. The exclusive property of our tested polyoxotungstates is their strong amoebicidal activity against Acanthamoeba. Hence the study reveals a new window towards cancer therapy with the combined control of elevated levels of alkaline phosphatase and granulomatous amoebic encephalitis in cancer patients.

Polyphosphates inhibit extracellular matrix mineralization in MC3T3-E1 osteoblast cultures

Studies on various compounds of inorganic phosphate, as well as on organic phosphate added by post-translational phosphorylation of proteins, all demonstrate a central role for phosphate in biomineralization processes. Inorganic polyphosphates are chains of orthophosphates linked by phosphoanhydride bonds that can be up to hundreds of orthophosphates in length. The role of polyphosphates in mammalian systems, where they are ubiquitous in cells, tissues and bodily fluids, and are at particularly high levels in osteoblasts, is not well understood. In cell-free systems, polyphosphates inhibit hydroxyapatite nucleation, crystal formation and growth, and solubility. In animal studies, polyphosphate injections inhibit induced ectopic calcification. While recent work has proposed an integrated view of polyphosphate function in bone, little experimental data for bone are available. Here we demonstrate in osteoblast cultures producing an abundant collagenous matrix that normally show robust mineralization, that two polyphosphates (PolyP5 and PolyP65, polyphosphates of 5 and 65 phosphate residues in length) are potent mineralization inhibitors. Twelve-day MC3T3-E1 osteoblast cultures with added ascorbic acid (for collagen matrix assembly) and β-glycerophosphate (a source of phosphate for mineralization) were treated with either PolyP5 or PolyP65. Von Kossa staining and calcium quantification revealed that mineralization was inhibited in a dose-dependent manner by both polyphosphates, with complete mineralization inhibition at 10μM. Cell proliferation and collagen assembly were unaffected by polyphosphate treatment, indicating that polyphosphate inhibition of mineralization results not from cell and matrix effects but from direct inhibition of mineralization. This was confirmed by showing that PolyP5 and PolyP65 bound to synthetic hydroxyapatite in a concentration-dependent manner. Tissue-nonspecific alkaline phosphatase (TNAP, ALPL) efficiently hydrolyzed the two PolyPs as measured by Pi release. Importantly, at the concentrations of polyphosphates used in this study which inhibited bone cell culture mineralization, the polyphosphates competitively saturated TNAP, thus potentially interfering with its ability to hydrolyze mineralization-inhibiting pyrophosphate (PPi) and mineralizing-promoting β-glycerophosphate (in cell culture). In the biological setting, polyphosphates may regulate mineralization by shielding the essential inhibitory substrate pyrophosphate from TNAP degradation, and in the same process, delay the release of phosphate from this source. In conclusion, the inhibition of mineralization by polyphosphates is shown to occur via direct binding to apatitic mineral and by mixed inhibition of TNAP.

Calcifying human aortic smooth muscle cells express different bone alkaline phosphatase isoforms, including the novel B1x isoform

BACKGROUND

Vascular calcification, causing cardiovascular morbidity and mortality, is associated with hyperphosphatemia in chronic kidney disease (CKD). In vitro, phosphate induces transdifferentiation of vascular smooth muscle cells to osteoblast-like cells that express alkaline phosphatase (ALP). In vivo, raised serum ALP activities are associated with increased mortality. A new bone ALP isoform (B1x) has been identified in serum from CKD patients. The present study investigated the different ALP isoforms in calcifying human aortic smooth muscle cells (HAoSMCs).

METHODS

HAoSMCs were cultured for 30 days in medium containing 5 or 10 mmol/l β-glycerophosphate in the presence or absence of the ALP-specific inhibitor tetramisole.

RESULTS

All known bone-specific ALP (BALP) isoforms (B/I, B1x, B1 and B2) were identified in HAoSMCs. β-Glycerophosphate stimulated calcification of HAoSMCs, which was associated with increased BALP isoforms B/I, B1x and B2. Tetramisole inhibited the β-glycerophosphate-induced HAoSMC calcification, which was paralleled by the inhibition of the B1x and B/I, but not the other isoforms.

CONCLUSIONS

HAoSMCs express the four known BALP isoforms. B/I, B1x and B2 could be essential for soft tissue calcification. B/I and B1x were more affected by tetramisole than the other isoforms, which suggests different biological functions during calcification of HAoSMCs.

Inhibitors of tissue-nonspecific alkaline phosphatase (TNAP): from hits to leads

The optimization of active hits, commonly derived from high-throughput screening campaigns (see Chapters 2 and 4), into promising small-molecule lead compounds is one of the fundamental steps in early drug discovery. Directions taken during this stage can have important consequences reaching through lead optimization into preclinical development and beyond. Considering the ever-increasing costs of preclinical as well as clinical development phases (DiMasi et al., J Health Econ 22:151-185, 2003) the choices made at the early stages of drug discovery can have a real impact on the likelihood of the best lead becoming a viable candidate (Bleicher et al., Nat Rev Drug Discov 2:369-378, 2003). Thus it is important to utilize proven and robust methodologies to turn promising hits into suitable lead series with propitious characteristics. Here, we describe such an approach using the example of a tissue-nonspecific alkaline phosphatase (see Chapter 3) inhibitor developed in our group (Sidique et al., Bioorg Med Chem Lett 19:222-225, 2009).

Pharmacological inhibition of PHOSPHO1 suppresses vascular smooth muscle cell calcification

Medial vascular calcification (MVC) is common in patients with chronic kidney disease, obesity, and aging. MVC is an actively regulated process that resembles skeletal mineralization, resulting from chondro-osteogenic transformation of vascular smooth muscle cells (VSMCs). Here, we used mineralizing murine VSMCs to study the expression of PHOSPHO1, a phosphatase that participates in the first step of matrix vesicles-mediated initiation of mineralization during endochondral ossification. Wild-type (WT) VSMCs cultured under calcifying conditions exhibited increased Phospho1 gene expression and Phospho1(-/-) VSMCs failed to mineralize in vitro. Using natural PHOSPHO1 substrates, potent and specific inhibitors of PHOSPHO1 were identified via high-throughput screening and mechanistic analysis and two of these inhibitors, designated MLS-0390838 and MLS-0263839, were selected for further analysis. Their effectiveness in preventing VSMC calcification by targeting PHOSPHO1 function was assessed, alone and in combination with a potent tissue-nonspecific alkaline phosphatase (TNAP) inhibitor MLS-0038949. PHOSPHO1 inhibition by MLS-0263839 in mineralizing WT cells (cultured with added inorganic phosphate) reduced calcification in culture to 41.8% ± 2.0% of control. Combined inhibition of PHOSPHO1 by MLS-0263839 and TNAP by MLS-0038949 significantly reduced calcification to 20.9% ± 0.74% of control. Furthermore, the dual inhibition strategy affected the expression of several mineralization-related enzymes while increasing expression of the smooth muscle cell marker Acta2. We conclude that PHOSPHO1 plays a critical role in VSMC mineralization and that "phosphatase inhibition" may be a useful therapeutic strategy to reduce MVC.

Associations of homoarginine with bone metabolism and density, muscle strength and mortality: cross-sectional and prospective data from 506 female nursing home patients

In female nursing home patients, homoarginine was associated with lower bone turnover, higher bone density, lower mortality and, by trend, with muscle strength.

INTRODUCTION

Homoarginine, a cationic amino acid, may be relevant for muscusloskeletal health because it inhibits alkaline phosphatases (AP) and is involved in nitric oxide and energy metabolism. We aimed to evaluate whether homoarginine serum concentrations are associated with bone density and metabolism, muscle strength, fractures and mortality.

METHODS

We examined a cohort of female nursing home patients that underwent quantitative bone ultrasound (QUS) measurements and assessments of knee extensor strength. Measurements of serum homoarginine, C-terminal telopeptide cross-links (β-CTxs) and osteocalcin were also performed at baseline. Thereafter, patients were followed-up with respect to fractures and mortality.

RESULTS

Serum homoarginine concentrations were determined in 506 female study participants (mean age: 83.9 ± 6.0 years). Homoarginine was inversely correlated with β-CTxs (r = -0.26; p < 0.001) and osteocalcin (r = -0.21; p < 0.001), and these associations remained significant in multiple regression analyses. Multivariate regression analyses showed that homoarginine is significantly associated with calcaneus stiffness (beta coefficient = 0.11; p = 0.020) and by trend with knee extensor strength (beta coefficient = 0.09; p = 0.065). During a mean follow-up time of 27 ± 8 months, we recorded 119 deaths (23.5%) and 63 fractures (12.5%). In multivariate analyses, homoarginine was associated with significantly reduced risk of mortality and the combined endpoint of fractures and mortality.

CONCLUSIONS

Whether homoarginine metabolism is critically involved into the pathogenesis of musculoskeletal diseases and fatal events warrants further studies.

Cellular function and molecular structure of ecto-nucleotidases

Ecto-nucleotidases play a pivotal role in purinergic signal transmission. They hydrolyze extracellular nucleotides and thus can control their availability at purinergic P2 receptors. They generate extracellular nucleosides for cellular reuptake and salvage via nucleoside transporters of the plasma membrane. The extracellular adenosine formed acts as an agonist of purinergic P1 receptors. They also can produce and hydrolyze extracellular inorganic pyrophosphate that is of major relevance in the control of bone mineralization. This review discusses and compares four major groups of ecto-nucleotidases: the ecto-nucleoside triphosphate diphosphohydrolases, ecto-5'-nucleotidase, ecto-nucleotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Only recently and based on crystal structures, detailed information regarding the spatial structures and catalytic mechanisms has become available for members of these four ecto-nucleotidase families. This permits detailed predictions of their catalytic mechanisms and a comparison between the individual enzyme groups. The review focuses on the principal biochemical, cell biological, catalytic, and structural properties of the enzymes and provides brief reference to tissue distribution, and physiological and pathophysiological functions.