Slawomir Pikula

Phosphodiesterase Activity of Alkaline Phosphatase in ATP-initiated Ca2+ and Phosphate Deposition in Isolated Chicken Matrix Vesicles

Inorganic pyrophosphate is a potent inhibitor of bone mineralization by preventing the seeding of calcium-phosphate complexes. Plasma cell membrane glycoprotein-1 and tissue nonspecific alkaline phosphatase were reported to be antagonistic regulators of mineralization toward inorganic pyrophosphate formation (by plasma cell membrane glycoprotein-1) and degradation (by tissue nonspecific alkaline phosphatase) under physiological conditions. In addition, they possess broad overlapping enzymatic functions. Therefore, we examined the roles of tissue nonspecific alkaline phosphatase within matrix vesicles isolated from femurs of 17-day-old chick embryos, under conditions where these both antagonistic and overlapping functions could be evidenced. Addition of 25 μm ATP significantly increased duration of mineralization process mediated by matrix vesicles, while supplementation of mineralization medium with levamisole, an alkaline phosphatase inhibitor, reduces the ATP-induced retardation of mineral formation. Phosphodiesterase activity of tissue nonspecific alkaline phosphatase for bis-p-nitrophenyl phosphate was confirmed, the rate of this phosphodiesterase activity is in the same range as that of phosphomonoesterase activity for p-nitrophenyl phosphate under physiological pH. In addition, tissue nonspecific alkaline phosphatase at pH 7.4 can hydrolyze ADPR. On the basis of these observations, it can be concluded that tissue nonspecific alkaline phosphatase, acting as a phosphomonoesterase, could hydrolyze free phosphate esters such as pyrophosphate and ATP, while as phosphodiesterase could contribute, together with plasma cell membrane glycoprotein-1, in the production of pyrophosphate from ATP.

Phospholipases of Mineralization Competent Cells and Matrix Vesicles: Roles in Physiological and Pathological Mineralizations

The present review aims to systematically and critically analyze the current knowledge on phospholipases and their role in physiological and pathological mineralization undertaken by mineralization competent cells. Cellular lipid metabolism plays an important role in biological mineralization. The physiological mechanisms of mineralization are likely to take place in tissues other than in bones and teeth under specific pathological conditions. For instance, vascular calcification in arteries of patients with renal failure, diabetes mellitus or atherosclerosis recapitulates the mechanisms of bone formation. Osteoporosis—a bone resorbing disease—and rheumatoid arthritis originating from the inflammation in the synovium are also affected by cellular lipid metabolism. The focus is on the lipid metabolism due to the effects of dietary lipids on bone health. These and other phenomena indicate that phospholipases may participate in bone remodelling as evidenced by their expression in smooth muscle cells, in bone forming osteoblasts, chondrocytes and in bone resorbing osteoclasts. Among various enzymes involved, phospholipases A1 or A2, phospholipase C, phospholipase D, autotaxin and sphingomyelinase are engaged in membrane lipid remodelling during early stages of mineralization and cell maturation in mineralization-competent cells. Numerous experimental evidences suggested that phospholipases exert their action at various stages of mineralization by affecting intracellular signaling and cell differentiation. The lipid metabolites—such as arachidonic acid, lysophospholipids, and sphingosine-1-phosphate are involved in cell signaling and inflammation reactions. Phospholipases are also important members of the cellular machinery engaged in matrix vesicle (MV) biogenesis and exocytosis. They may favour mineral formation inside MVs, may catalyse MV membrane breakdown necessary for the release of mineral deposits into extracellular matrix (ECM), or participate in hydrolysis of ECM. The biological functions of phospholipases are discussed from the perspective of animal and cellular knockout models, as well as disease implications, development of potent inhibitors and therapeutic interventions.

Chapter 9:NMR of lipids

This chapter reviews articles on NMR and lipids published between June 2012 and May 2013. The number of papers devoted to NMR utilization to investigate lipids, their structures, behavior in native and artificial membranes, interactions with proteins and peptides, as well as with low molecular weight molecules, biomedical applications and new methods is growing (over 1300 articles in Pub-Med) although we included here only a selection of those papers that were accessible and peer-reviewed. The reviewed material has been arranged in chapters devoted to the structure and function of lipids in membranes, their roles in membrane-related processes including lipid-mediated signal transduction, interactions of lipids with membrane and soluble proteins, peptides and various low molecular weight compounds, lipid metabolomics, visualization of lipid related processes in biomedicine, lipid-based diagnosis, and methodological approaches.

NMR of lipids

This chapter reviews articles on NMR and lipids published between June 2011 and May 2012. The number of papers devoted to NMR utilization to investigate lipids, their structures, behavior in native and artificial membranes, interactions with proteins and peptides, as well as with low molecular weight compounds, and biomedical applications is quite large (over 1100 articles in Pub‐Med) although we included here only a selection of those papers that were accessible and peer‐reviewed. The reviewed material has been arranged in sections devoted to the structure and function of lipids in membranes, their roles in membrane‐related processes including membrane fusion and lipid‐mediated signal transduction, interactions of lipids with membrane and soluble proteins, peptides and antibiotics, lipid metabolomics, visualization of lipid related processes in biomedicine, diagnosis and therapy, as well as methodological approaches.