Modern Advances in Magnetic Materials of Wireless Power Transfer Systems: A Review and New Perspectives.

The magnetic coupling resonant wireless power transfer (MCR-WPT) system is considered to be the most promising wireless power transfer (WPT) method because of its considerable transmission power, high transmission efficiency, and acceptable transmission distance. For achieving magnetic concentration, magnetic cores made of magnetic materials are usually added to MCR-WPT systems to enhance the coupling performance. However, with the rapid progress of WPT technology, the traditional magnetic materials gradually become the bottleneck that restricts the system power density enhancement. In order to meet the electromagnetic characteristics requirements of WPT systems, high-performance Mn-Zn and Ni-Zn ferrites, amorphous, nanocrystalline, and metamaterials have been developed rapidly in recent years. This paper introduces an extensive review of the magnetic materials of WPT systems, concluding with the state-of-the-art WPT technology and the development and application of high-performance magnetic materials. In addition, this study offers an exclusive reference to researchers and engineers who are interested in learning about the technology and highlights critical issues to be addressed. Finally, the potential challenges and opportunities of WPT magnetic materials are presented, and the future development directions of the technology are foreseen and discussed.

Geranylgeranyltransferase I inhibitors target RalB to inhibit anchorage-dependent growth and induce apoptosis and RalA to inhibit anchorage-independent growth.

Geranylgeranyltransferase I inhibitors (GGTIs) are presently undergoing advanced preclinical studies and have been shown to disrupt oncogenic and tumor survival pathways, to inhibit anchorage-dependent and -independent growth, and to induce apoptosis. However, the geranylgeranylated proteins that are targeted by GGTIs to induce these effects are not known. Here we provide evidence that the Ras-like small GTPases RalA and RalB are exclusively geranylgeranylated and that inhibition of their geranylgeranylation mediates, at least in part, the effects of GGTIs on anchorage-dependent and -independent growth and tumor apoptosis. To this end, we have created the corresponding carboxyl-terminal mutants that are exclusively farnesylated and verified that they retain the subcellular localization and signaling activities of the wild-type geranylgeranylated proteins and that Ral GTPases do not undergo alternative prenylation in response to GGTI treatment. By expressing farnesylated, GGTI-resistant RalA and RalB in Cos7 cells and human pancreatic MiaPaCa2 cancer cells followed by GGTI-2417 treatment, we demonstrated that farnesylated RalB, but not RalA, confers resistance to the proapoptotic and anti-anchorage-dependent growth effects of GGTI-2417. Conversely, farnesylated RalA but not RalB expression renders MiaPaCa2 cells less sensitive to inhibition of anchorage-independent growth. Furthermore, farnesylated RalB, but not RalA, inhibits the ability of GGTI-2417 to suppress survivin and induce p27(Kip1) protein levels. We conclude that RalA and RalB are important, functionally distinct targets for GGTI-mediated tumor apoptosis and growth inhibition.

Identification of the hydrophobic ligand binding pocket of the S1P1 receptor.

Sphingosine 1-phosphate (S1P), a naturally occurring sphingolipid mediator and also a second messenger with growth factor-like actions in almost every cell type, is an endogenous ligand of five G protein-coupled receptors (GPCRs) in the endothelial differentiation gene family. The lack of GPCR crystal structures sets serious limitations to rational drug design and in silico searches for subtype-selective ligands. Here we report on the experimental validation of a computational model of the ligand binding pocket of the S1P1 GPCR surrounding the aliphatic portion of S1P. The extensive mutagenesis-based validation confirmed 18 residues lining the hydrophobic ligand binding pocket, which, combined with the previously validated three head group-interacting residues, now complete the mapping of the S1P ligand recognition site. We identified six mutants (L3.43G/L3.44G, L3.43E/L3.44E, L5.52A, F5.48G, V6.40L, and F6.44G) that maintained wild type [32P]S1P binding with abolished ligand-dependent activation by S1P. These data suggest a role for these amino acids in the conformational transition of S1P1 to its activated state. Three aromatic mutations (F5.48Y, F6.44G, and W6.48A) result in differential activation, by S1P or SEW2871, indicating that structural differences between the two agonists can partially compensate for differences in the amino acid side chain. The now validated ligand binding pocket provided us with a pharmacophore model, which was used for in silico screening of the NCI, National Institutes of Health, Developmental Therapeutics chemical library, leading to the identification of two novel nonlipid agonists of S1P1.

Structure-activity studies on a library of potent calix[4]arene-based PDGF antagonists that inhibit PDGF-stimulated PDGFR tyrosine phosphorylation.

Platelet-derived growth factor (PDGF) and its receptor PDGFR are required for tumor growth and angiogenesis, so disruption of the PDGF-PDGFR interaction should lead to starvation of tumors and reduction of tumor growth. Potent PDGF antagonists have been discovered through the synthesis of a series of calix[4]arene-based compounds that are designed to bind to the three-loop region of PDGF. The effect of lower-rim alkylation, linker and number of interacting head groups on the calix[4]arene scaffold on PDGF affinity and cellular activity has been investigated.

Inhibiting angiogenesis and tumorigenesis by a synthetic molecule that blocks binding of both VEGF and PDGF to their receptors.

Angiogenesis depends on vascular endothelial growth factor (VEGF) for initiation and platelet-derived growth factor (PDGF) for maintenance of blood vessels. We have designed a targeted library of compounds from which we identified a novel molecule, GFB-204, that binds PDGF and VEGF, blocks binding of PDGF and VEGF to their receptors (200-500 nM) and subsequently inhibits PDGFR and Flk-1 tyrosine phosphorylation and stimulation of the protein kinases Erk1, Erk2 and Akt and the signal transducer and activator of transcription STAT3. GFB-204 is selective for PDGF and VEGF and does not inhibit EGF, IGF-1 and FGF stimulation of Erk1/2, Akt and STAT3. GFB-204 inhibits endothelial cell migration and capillary network formation in vitro. Finally, treatment of mice with GFB-204 suppresses human tumor growth and angiogenesis. Thus, inhibition of VEGF and PDGF receptor binding with a synthetic molecule results in potent inhibition of angiogenesis and tumorigenesis.

Palmitoylated cysteine 192 is required for RhoB tumor-suppressive and apoptotic activities.

RhoA and RhoB share 86% amino acid sequence identity, yet RhoA promotes whereas RhoB suppresses malignant transformation. Amino acids 29, 100, 116, 123, 129, 140-143, 141, 146, 152, 154, 155, 173, 181, 183-187, 189, 190, 191, 192, and 193 in RhoB were mutated to the corresponding RhoA residues to determine those critical for RhoB tumor-suppressive activity. Of all the mutants made, only the cysteine 192 (one of two palmitoylation sites) and cysteine 193 (the prenylation site) point mutations abolish RhoB functions. In contrast, mutation of the other palmitoylation site, cysteine 189, did not affect RhoB functions. Moving cysteine 192 to position 190 did not affect RhoB function either. Mutation of cysteine 192 to glycine, alanine, or serine blocks the ability of RhoB to suppress transforming growth factor beta type II receptor, p2lwaf, and AP-1 promoter transcriptional activities. Furthermore, mutations of cysteines 192 and 193, but not 189, mislocalize RhoB and prevent RhoB from inhibiting anchorage-dependent and anchorage-independent tumor growth and colony formation as well as prevent it from inducing apoptosis. The cysteine 192 RhoB mutant is farnesylated and geranylgeranylated as efficiently as wild type RhoB. A RhoA-(1-180)/RhoB-(181-196) chimera inhibited tumor cell proliferation and induced apoptosis as efficiently as RhoB. These results demonstrate that the presence of neither cysteine 193 nor cysteine 192 alone is sufficient and that both palmitoylated cysteine 192 and prenylated cysteine 193, but not palmitoylated cysteine 189, are required for RhoB tumor-suppressive and proapoptotic activities.

Optimal lysophosphatidic acid-induced DNA synthesis and cell migration but not survival require intact autophosphorylation sites of the epidermal growth factor receptor.

Lysophosphatidic acid (LPA)-elicited transphosphorylation of receptor tyrosine kinases has been implicated in mediating extracellular signal-regulated kinase (ERK) 1/2 activation, which is necessary for LPA-induced cell proliferation, migration, and survival. B82L cells lack epidermal growth factor receptor (EGFR) but express LPA(1-3), platelet-derived growth factor (PDGF), ErbB2, and insulin-like growth factor receptor transcripts, yet LPA caused no detectable transphosphorylation of these receptor tyrosine kinases. LPA equally protected B82L cells, or transfectants expressing EGFR, the kinase dead EGFR(K721A), EGFR(Y5F) receptor mutant, which lacks five autophosphorylation sites, or EGFR(Y845F), which lacks the Src phosphorylation site from tumor necrosis factor-alpha-induced apoptosis. In contrast, LPA-elicited DNA synthesis and migration were augmented in cells expressing EGFR, EGFR(K721A), or EGFR(Y845F), but not EGFR(Y5F), although the PDGF responses were indistinguishable. LPA-induced transphosphorylation of the EGFR, ErbB2, or PDGF receptor was not required for its antiapoptotic effect. EGFR with or without intrinsic kinase activity or without the Src-phosphorylation site augmented, but was not required for, LPA-elicited cell proliferation or migration. In B82L cells, augmentation of these two LPA responses required intact autophosphorylation sites because among the four EGFR mutants, only cells expressing the EGFR(Y5F) mutant showed no enhancement. In EGFR(Y5F)-expressing cells, LPA failed to elicit tyrosine phosphorylation of Src homologous and collagen protein (SHC) and caused only a modest increase in ERK1/2 phosphorylation similar to that in wild-type B82L cells. The present data pinpoint the lack of importance of the intrinsic kinase activity in contrast to the importance of autophosphorylation sites of the EGFR for SHC phosphorylation in the enhancement of select ERK1/2-dependent LPA responses.

Inhibition of Ca(2+) signalling by the sphingosine 1-phosphate receptor S1P(1).

The lysophospholipid, sphingosine 1-phosphate (S1P), regulates a multitude of cellular functions by activating specific G protein-coupled receptors (GPCRs) (S1P(1-5), plus three newly identified S1P receptors). The G(i)-coupled S1P(1) receptor inhibits adenylyl cyclase, stimulates mitogen-activated protein kinases (MAP kinases) and cell migration, and is required for blood vessel maturation. Here, we report that S1P(1) inhibits Ca(2+) signalling in a number of cell types. In HEK-293 cells, which endogenously express S1P(1-3), overexpression of S1P(1) reduced intracellular free Ca(2+) concentration ([Ca(2+)](i)) increases induced by various receptor agonists as well as thapsigargin. The inhibitory Ca(2+) signalling of S1P(1) was blocked by pertussis toxin (PTX) and the protein kinase C (PKC) inhibitor, Gö6976, and imitated by phorbol ester and overexpression of classical PKC isoforms. Activation of S1P(1) stably expressed in RH7777 cells, which endogenously do not express S1P receptors, also inhibited Ca(2+) signalling, without mediating Ca(2+) mobilization on its own. It is concluded that the widely expressed S1P receptor S1P(1) inhibits Ca(2+) signalling, most likely via G(i) proteins and classical PKC isoforms. Co-expression of S1P(1) with S1P(3), but not S1P(2), reversed the inhibitory effect of S1P(1), furthermore suggesting a specific interplay of S1P receptor subtypes usually found within a single cell type.

LPA protects intestinal epithelial cells from apoptosis by inhibiting the mitochondrial pathway.

We previously showed (Gastroenterology 123: 206-216, 2002) that lysophosphatidic acid (LPA) protects and rescues rat intestinal epithelial cells (IEC-6) from apoptosis. Here, we provide evidence for the LPA-elicited inhibition of the mitochondrial apoptotic pathway leading to attenuation of caspase-3 activation. Pretreatment of IEC-6 cells with LPA inhibited campothecin-induced caspase-9 and caspase-3 activation and DNA fragmentation. A caspase-9 inhibitor peptide mimicked the LPA-elicited antiapoptotic activity. LPA elicited ERK1/ERK2 and PKB/Akt phosphorylation. The LPA-elicited antiapoptotic activity and inhibition of caspase-9 activity were abrogated by pertussis toxin, PD 98059, wortmannin, and LY 294002. LPA reduced cytochrome c release from mitochondria and prevented activation of caspase-9. LPA prevented translocation of Bax from cytosol to mitochondria and increased the expression of the antiapoptotic Bcl-2 mRNA and protein. LPA had no effect on Bcl-xl, Bad, and Bak mRNA or protein expression. These data indicate that LPA protects IEC-6 cells from camptothecin-induced apoptosis through G(i)-coupled inhibition of caspase-3 activation mediated by the attenuation of caspase-9 activation due to diminished cytochrome c release, involving upregulation of Bcl-2 protein expression and prevention of Bax translocation.

Activation of human monocytic cells by lysophosphatidic acid and sphingosine-1-phosphate.

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are serum-borne lipid mediators with potential proinflammatory and atherogenic properties. We studied the effects of LPA and S1P on [Ca(2+)](i), a second messenger of cellular activation, in human monocytic Mono Mac 6 (MM6) cells. LPA and S1P induced [Ca(2+)](i) transients with EC(50) values of 47 and 340 nM, respectively. Ca(2+) signals evoked by LPA and S1P originated mainly from the stimulation of Ca(2+) entry, were blocked by the phospholipase C inhibitor U73122, and were inhibited by pertussis toxin. The LPA(1) and LPA(3) receptor antagonist dioctylglycerol pyrophosphate inhibited the LPA-induced Ca(2+) signal. Notably, serum and minimally modified LDL (mm-LDL) evoked [Ca(2+)](i) increases that were mediated entirely through activation of LPA receptors. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis showed the presence of the LPA and S1P receptor subtypes LPA(1), LPA(2,) S1P(1), S1P(2), S1P(4) in MM6 cells, human monocytes and macrophages. Together these results indicate that LPA, mm-LDL and serum induce via activation of the LPA(1) receptor a G(i)/phospholipase C/Ca(2+) signalling pathway in monocytes. Our study is the first report showing the receptor-mediated activation of human monocytic cells by low nanomolar concentrations of LPA and S1P, and suggests a role of these lipid mediators in inflammation and atherogenesis.

Injury-elicited differential transcriptional regulation of phospholipid growth factor receptors in the cornea.

The phospholipid growth factors (PLGFs), including lysophosphatidic acid (LPA), have been implicated in corneal wound healing. PLGF concentrations and activities are elevated after corneal injury. Using real-time PCR, we quantified receptor mRNA levels in the healing rabbit cornea. In intact corneas, transcripts for S1P(1), LPA(1), and LPA(3) receptor subtypes were detected, as was lipid phosphate phosphatase 1 (LPP1). After wounding, the trend for endothelium and keratocytes was for significant decreases in transcript numbers for the three receptor subtypes, whereas epithelial cells showed increased transcript numbers, except for an S1P(1) decrease in healing cells. LPP1 transcript numbers were decreased in keratocytes and endothelium, although LPP-specific activity was unchanged. LPA-elicited Ca(2+) transients were significantly reduced in the healing endothelium. Consistent with reduced LPA(3) receptor numbers, dioctylglycerol pyrophosphate, a selective antagonist, reduced LPA-induced Ca(2+) transients 2.7-fold in nonwounded epithelium but only 1.5-fold in wound-healing endothelium. These data for the first time establish physiologically relevant differential changes in the expression of PLGF receptor subtypes and provide evidence for the changing role of LPA(3) receptors in endothelial cells.

Lysophosphatidic acid protects and rescues intestinal epithelial cells from radiation- and chemotherapy-induced apoptosis.

BACKGROUND & AIMS: We have investigated whether the phospholipid growth factor lysophosphatidic acid (LPA) could prevent intestinal epithelial cells-6 (IEC-6) from apoptosis elicited by 4 different mechanisms. The antiapoptotic effect of LPA was also tested in a mouse model of radiation-induced apoptosis. METHODS: Apoptosis was elicited by serum withdrawal, exposure to camptothecin, gamma-irradiation, or rat tumor necrosis factor alpha and evaluated by DNA fragmentation enzyme-linked immunosorbent assay (ELISA) and annexin V staining. Caspase-3/CPP32 activity and activation was measured by ELISA and Western blotting, respectively. Reverse-transcription polymerase chain reaction (RT-PCR) was applied to examine the expression of LPA-receptor transcripts. Mice were treated with 250 microL of 1 mmol/L LPA and exposed to whole-body gamma-irradiation with a dose of 12 or 15 Gy and the number and localization of apoptotic bodies along the crypt were recorded. RESULTS: LPA pretreatment reduced DNA fragmentation induced in all models of apoptosis. LPA rescued cells from apoptosis when applied up to 1 hour after camptothecin treatment or 2 hours after irradiation. LPA inhibited the activation of caspase-3/CPP32 and attenuated its activity. Blocking LPA1 receptors by pertussis toxin and the inhibition of epithelial growth factor receptor tyrosine kinase significantly attenuated the protective effect. In irradiated mice, oral LPA significantly reduced the number of apoptotic bodies in the crypt. CONCLUSIONS: (1) LPA prevents and rescues IEC-6 from apoptosis elicited by 4 different mechanisms. (2) This antiapoptotic activity is mediated through LPA1 and LPA2 receptors through the inhibition of caspase-3/CPP32 activation. (3) LPA protects enterocytes against radiation-induced apoptosis. This study suggests that in patients undergoing cancer therapy, dietary LPA might have therapeutically useful antiapoptotic capacity in the intestinal epithelium.

Molecular basis for lysophosphatidic acid receptor antagonist selectivity.

Recent characterization of lysophosphatidic acid (LPA) receptors has made possible studies elucidating the structure-activity relationships (SAR) for agonist activity at individual receptors. Additionally, the availability of these receptors has allowed the identification of antagonists of LPA-induced effects. Two receptor-subtype selective LPA receptor antagonists, one selective for the LPA1/EDG2 receptor (a benzyl-4-oxybenzyl N-acyl ethanolamide phosphate, NAEPA, derivative) and the other selective for the LPA3/EDG7 receptor (diacylglycerol pyrophosphate, DGPP, 8:0), have recently been reported. The receptor SAR for both agonists and antagonists are reviewed, and the molecular basis for the difference between agonism and antagonism as well as for receptor-subtype antagonist selectivity identified by molecular modeling is described. The implications of the newly available receptor-subtype selective antagonists are also discussed.