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Biomedical subjects

D R Phillips

Publications and source records attributed to D R Phillips.

At least 19 recordsLinked to original sources
PubMed2006

How low-energy weak reactions can constrain three-nucleon forces and the neutron-neutron scattering length.

We show that chiral symmetry and gauge invariance enforce relations between the short-distance physics that occurs in a number of electroweak and pionic reactions on light nuclei. Within chiral perturbation theory, this is manifested via the appearance of the same axial isovector two-body contact term in pi(-)d --> nngamma, p-wave pion production in NN collisions, tritium beta decay, pp fusion, nud scattering, and the hep reaction. Using a Gamow-Teller matrix element obtained from calculations of pp fusion as input, we compute the neutron spectrum obtained in pi(-)d --> nngamma. With the short-distance physics in this process controlled from pp --> de(=)nu(e), the theoretical uncertainty in the nn scattering length extracted from pi(-)d --> nngamma is reduced by a factor larger than 3, to approximately < or = 0.05 fm.

Journal Article↗
PubMed2005

Dynamic instability in intergranular fracture.

A molecular-dynamics model for crack propagation under steady-state conditions is used to study dynamic instabilities along a grain boundary in aluminum that occur when the crack speed approaches 1/3 of the material's Rayleigh wave speed. Instead of crack branching, as is characteristic for a crack propagating in a homogeneous environment, the instability of an intergranular crack results in a periodic series of dislocation bursts. These bursts limit the crack speed and produce velocity oscillations with a large increase in energy dissipation that increases the grain boundary toughness.

Journal Article↗
PubMed2005

Therapeutic approaches in arterial thrombosis.

The current standard of care for the treatment of arterial thrombosis includes anticoagulants and three classes of antiplatelet agents--aspirin, thienopyridines and glycoprotein IIb-IIIa antagonists. Although these drugs have had a significant impact on morbidity and mortality in several patient populations, up to 15% of the high risk patients with acute coronary syndrome continue to suffer from ischemic events. This problem may occur, in part, because the platelets in many patients are non-responsive to aspirin and clopidogrel. Murine models now indicate that platelets are not only responsible for arterial occlusion, they are also involved in the progression of atherosclerotic disease. New opportunities have emerged identifying potential targets and strategies for drug discovery suited to address these deficiencies by more effectively modulating platelet adhesion, thrombus growth, thrombus stability and the pro-inflammatory activity of platelets. In addition, a growing need has emerged for the development of bedside devices capable of bringing personalized medicine to patients being treated with antithrombotic drugs in order to measure the pharmacodynamic activities of new therapies, to assess the activities achieved by combined antithrombotic therapy, and to identify patients that fail to respond.

Animals↗
PubMed2005

Recent advances in understanding and exploiting the activation of anthracyclines by formaldehyde.

The anthracycline group of compounds are amongst the most effective chemotherapy agents currently in use for cancer treatment. They are generally classified as topoisomerase II inhibitors but also have a variety of other targets in cells. It has been known for some years that the anthracyclines are capable of forming DNA adducts, but the relevance and extent of these DNA adducts in cells and their role in causing cell death has remained obscure. When the adduct structure was solved, it became clear that formaldehyde was an absolute requirement for adduct formation. This led to a renewed interest in the capacity of anthracyclines to form DNA adducts, and there are now several ways in which adduct formation can be facilitated in cells. These involve strategies to provide the requisite formaldehyde in the form of anthracycline-formaldehyde conjugates, and the use of formaldehyde-releasing drugs in combination with anthracyclines. Of particular interest is the new therapeutic compound AN-9 that releases both butyric acid and formaldehyde, leading to efficient anthracycline-DNA adduct formation, and synergy between the two compounds. Targeted formation of adducts using anthracycline-formaldehyde conjugates tethered to cell surface targeted molecules is now also possible. Some of the cellular consequences of these adducts have now been studied, and it appears that their formation can overcome anthracycline-resistance mechanisms, and that they are more efficient at inducing apoptosis than when functioning primarily through impairment of topoisomerase II. The clinical application of the use of anthracyclines as DNA adduct forming agents is now being explored.

Animals↗
PubMed2002

Effectiveness of manipulative physiotherapy for the treatment of a neurogenic cervicobrachial pain syndrome: a single case study -- experimental design.

A single case study ABC design was used to evaluate the effectiveness of manipulative physiotherapy in a 44-year-old woman with an 8-month history of neurogenic cervicobrachial pain. Clinical examination demonstrated significant signs of upper quadrant neural tissue mechanosensitivity indicating that neural tissue was the dominant tissue of origin for the subject's complaint of pain. Magnetic resonance imaging revealed correlating discal pathology at the C5/6 intersegmental level. The study involved a 4-week pre-assessment phase, a 4-week treatment phase and a 2-week home exercise phase. Functional disability was measured using the Northwick Park Neck Pain Questionnaire and pain was assessed using the McGill Short Form Pain Questionnaire. Cervical motion was measured by a cervical range of motion device (CROM) and the range of shoulder abduction with a mediclino inclinometer. Manipulative physiotherapy treatment involved a cervical lateral glide mobilization technique. Following treatment, visual analysis revealed beneficial effects on pain, functional disability as well as cervical and shoulder mobility. These improvements were maintained over the home exercise phase and at 1-month follow-up. The single case limits generalization of the findings, but the results support previous studies in this area and gives further impetus to controlled clinical trials.

Adult↗
PubMed2001

Barminomycin functions as a potent pre-activated analogue of Adriamycin.

The anthracycline Adriamycin is known to form adducts with DNA, but requires prior activation by formaldehyde. In contrast, the anthracycline barminomycin is also able to form adducts with DNA, but does not require activation by formaldehyde. Barminomycin, therefore, appears to function as a pre-activated form of Adriamycin. The DNA adducts formed by both anthracyclines are bound covalently to only one strand of DNA, but both also stabilise duplex DNA sufficiently that they can be detected as virtual interstrand crosslinks in heat denaturation electrophoretic crosslinking assays. The barminomycin-DNA adducts form extremely rapidly with DNA, and at exceedingly low concentrations (approximately 50-fold lower than with Adriamycin in the presence of excess formaldehyde), both characteristics consistent with barminomycin being in a pre-activated state, hence, undergoing a bimolecular reaction with DNA compared with the trimolecular reaction (drug, formaldehyde and DNA) required with Adriamycin. Surprisingly, barminomycin-DNA adducts are substantially more stable (essentially irreversible) than Adriamycin-DNA adducts (half life of approximately 25 h at 37 degrees C). Due to this understanding of the reactivity of barminomycin and its exceptional cytotoxicity (1000-fold more cytotoxic than Adriamycin), detailed structural studies of barminomycin-DNA adducts are now warranted, both in vitro and in tumour cells.

Animals↗
PubMed2001

Molecular basis for the synergistic interaction of adriamycin with the formaldehyde-releasing prodrug pivaloyloxymethyl butyrate (AN-9).

The interaction of Adriamycin and pivaloyloxymethyl butyrate (AN-9) was investigated in IMR-32 neuroblastoma and MCF-7 breast adenocarcinoma cells. Adriamycin is a widely used anticancer drug, whereas AN-9 is an anticancer agent presently undergoing Phase II clinical trials. The anticancer activity of AN-9 has been attributed to its ability to act as a butyric acid prodrug, although it also releases formaldehyde and pivalic acid. Adriamycin and AN-9 in combination display synergy when exposed simultaneously to cells or when AN-9 treatment is up to 18 h after Adriamycin administration. However, the reverse order of addition results in antagonism. These interactions have been established using cell viability assays and classical isobologram analysis. To understand the molecular basis of this synergy, the relative levels of Adriamycin-DNA adducts were determined using various treatment combinations. Levels of Adriamycin-DNA adducts were enhanced when treatment combinations known to be synergistic were used and were diminished using those treatments known to be antagonistic. The relative timing of the addition of Adriamycin and AN-9 was critical, with a 20-fold enhancement of Adriamycin-DNA adducts occurring when AN-9 was administered 2 h after the exposure of cells to Adriamycin. The enhanced levels of these adducts and the accompanying decreased cell viability were directly related to the esterase-dependent release of formaldehyde from AN-9, providing evidence for the formaldehyde-mediated activation of Adriamycin.

Adenocarcinoma↗
PubMed2001

Increased thrombogenesis and embolus formation in mice lacking glycoprotein V.

The glycoprotein (GP) Ib-V-IX complex plays a critical role in initiating platelet adhesion to von Willebrand factor (vWF) at the site of vascular injury. The complex also forms a high-affinity binding site for thrombin. Using an intravital microscopy mouse model, it was previously established that vWF plays a critical role in mediating platelet adhesion and thrombus formation following mesenteric arteriolar injury induced by ferric chloride. Further characterization of this model showed that these thrombotic events were also thrombin dependent. Using this vWF- and thrombin-dependent model, this study shows that GP V gene deficiency significantly accelerates both platelet adhesion and thrombus formation in mice following arteriolar injury. The time required for vessel occlusion in GP V-deficient (GP V(-/-)) mice was significantly shorter than that in wild-type mice. Interestingly, large emboli were also produced in GP V(-/-) mice, but not in wild-type mice, causing frequent downstream occlusion. However, when the 2 genotypes were compared in the in vitro perfusion chamber where thrombin was inhibited by heparin, no significant differences were found in either initial single-platelet adhesion or thrombus volume. These results demonstrate that GP V(-/-) mice have accelerated thrombus growth in response to vascular injury and suggest that this is caused by enhanced thrombin-induced platelet activation rather than enhanced binding of GPIb-V-IX to vWF. Absence of GP V also compromises thrombus stability.

Animals↗
PubMed2001

A thrombin receptor function for platelet glycoprotein Ib-IX unmasked by cleavage of glycoprotein V.

Glycoprotein (GP) V is a major substrate cleaved by the protease thrombin during thrombin-induced platelet activation. Previous analysis of platelets from GP V-null mice suggested a role for GP V as a negative modulator of platelet activation by thrombin. We now report the mechanism by which thrombin activates GP V -/- platelets. We show that proteolytically inactive forms of thrombin induce robust stimulatory responses in GP V null mouse platelets, via the platelet GP Ib--IX--V complex. Because proteolytically inactive thrombin can activate wild-type mouse and human platelets after treatment with thrombin to cleave GP V, this mechanism is involved in thrombin-induced platelet aggregation. Platelet activation through GP Ib-IX depends on ADP secretion, and specific inhibitors demonstrate that the recently cloned P2Y(12) ADP receptor (G(i)-coupled ADP receptor) is involved in this pathway, and that the P2Y(1) receptor (G(q)-coupled ADP receptor) may play a less significant role. Thrombosis was generated in GP V null mice only in response to catalytically inactive thrombin, whereas thrombosis occurred in both genotypes (wild type and GP V null) in response to active thrombin. These data support a thrombin receptor function for the platelet membrane GP Ib--IX--V complex, and describe a novel thrombin signaling mechanism involving an initiating proteolytic event followed by stimulation of the GP Ib--IX via thrombin acting as a ligand, resulting in platelet activation.

Animals↗
PubMed2001

Cytosine methylation enhances mitoxantrone-DNA adduct formation at CpG dinucleotides.

Recently, we have shown that mitoxantrone can be activated by formaldehyde in vitro to form DNA adducts that are specific for CpG and CpA sites in DNA. The CpG specificity of adduct formation prompted investigations into the effect of cytosine methylation (CpG) on adduct formation, since the majority of CpG dinucleotides in the mammalian genome are methylated and hypermethylation in subsets of genes is associated with various neoplasms. Upon methylation of a 512-base pair DNA fragment (containing the lac UV5 promoter) using HpaII methylase, three CCGG sites downstream of the promoter were methylated at C5 of the internal cytosine residue. In vitro transcription studies of mitoxantrone-reacted DNA revealed a 3-fold enhancement in transcriptional blockage (and hence adduct formation) exclusively at these methylated sites. In vitro cross-linking assays also revealed that methylation enhanced mitoxantrone adduct formation by 2-3-fold, and methylation of cytosine at a single potential drug binding site on a duplex oligonucleotide also enhanced adduct levels by 3-fold. Collectively, these results indicate preferential adduct formation at methylated CpG sites. However, adducts at these methylated sites exhibited the same stability as nonmethylated sites, suggesting that cytosine methylation increases drug accessibility to DNA rather than being involved in kinetic stabilization of the adduct.

Base Pairing↗
PubMed2001

The binding of [(en)Pt(mu-dpzm)2Pt(en)]4+ to G/C-rich regions of DNA.

The non-covalent binding of [(en)Pt(mu-dpzm)2Pt(en)]4+ to segments of DNA containing only G and C bases has been studied to gain an understanding of the pre-covalent binding association of cationic polynuclear platinum(II) anti-cancer drugs at G/C sites. 1H-NMR and CD spectroscopy were used to study the binding of the metal complex to the oligonucleotide d(GC)5 and the polynucleotide poly(dG-dC).poly(dG-dC), respectively. NOE contacts between the metal complex protons and the oligonucleotide sugar H1' protons observed in NOESY spectra indicated that the metal complex bound in the minor groove at the central C4 to G7 region of the oligonucleotide. This result indicates that even though cationic polynuclear platinum(II) complexes bind covalently in the major groove at G/C sites, the pre-covalent binding association is favoured in the minor groove. CD spectra indicated that the addition of the metal complex to poly(dG-dC)-poly(dG-dC) induced some conformational changes, but it was not possible to conclude that [(en)Pt(mu-dpzm)2Pt(en)]4+ induced a B- to Z-type DNA transition. In addition, in vitro transcription assays using the lac UV5 promoter showed that the non-covalent binding of [(en)Pt(mu-dpzm)2Pt(en)]4+ was sufficiently stable to inhibit transcription, and at particular sites.

Antineoplastic Agents↗
PubMed2001

Integrin tyrosine phosphorylation in platelet signaling.

The beta 3 integrin cytoplasmic tyrosine (ICY) motif of alpha IIb beta 3 becomes tyrosine phosphorylated during platelet aggregation, causing Shc and myosin to interact with the beta-integrin cytoplasmic domain. Platelets from mice lacking beta 3 ICY motif tyrosines formed defective aggregates and poorly retracted clots, establishing integrin tyrosine phosphorylation as a key mediator of beta 3-integrin signals.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Differential effects of citrate versus PPACK anticoagulation on measured platelet inhibition by abciximab, eptifibatide and tirofiban.

BACKGROUND: High levels of glycoprotein (GP) IIb/IIIa receptor inhibition are required to prevent arterial thrombosis following percutaneous coronary intervention. Ex-vivo turbidometric platelet aggregation in citrate anticoagulated blood samples has been the primary method previously utilized to derive dose regimens for administering platelet GP IIb/IIIa inhibitors. Enhanced GP IIb/IIIa binding and inhibition of platelet aggregation for eptifibatide secondary to citrate induced reduction of ionized plasma calcium concentrations has been reported. METHODS/RESULTS: We evaluated the differential effects of citrate versus PPACK anticoagulation on turbidometric platelet inhibition in normal volunteers by eptifibatide, tirofiban or abciximab. The decrease in ionized calcium afforded by citrate was associated with enhanced in vitro platelet inhibition for all three GP IIb/IIIa inhibitors, including abciximab. The magnitude of citrate effect was greatest for eptifibatide. Both tirofiban and abciximab have similar citrate calcium chelation associated enhancement of measured platelet inhibition. CONCLUSION: Accurate assessment and comparison of platelet inhibition by GP IIb/IIIa inhibitors may require avoidance of calcium chelating anticoagulants.

Abciximab↗
PubMed2001

Atopic eczema and the home environment.

BACKGROUND: There is strong evidence to suggest that the prevalence of atopic eczema is increasing in developed countries. Environmental factors have been implicated in the disease. OBJECTIVES: This descriptive case-control study sheds light on the possible association between atopic eczema in school children and various home environmental factors, and generates hypotheses for further studies. METHODS: The study uses data on reported atopic eczema symptoms collected via a cross-sectional parental postal survey (n = 1350) in Nottingham, U.K. Estimates of the risk of reported eczema associated with various home environmental factors were calculated by means of odds ratios (OR), along with population attributable risk percentages. RESULTS: The study showed statistically significant associations between atopic eczema symptoms and dampness in the home [OR 1.40; 95% confidence interval (CI) 1.00-1.97], the use of a radiator to heat the child's bedroom (OR 1.50; 95% CI 1.05-2.16) and the use of synthetic pillows (OR 1.51; 95% CI 1.01-2.28). Frequent vacuuming in the home was associated with a decreased prevalence of atopic eczema (OR 0.74; 95% CI 0.58-0.94). The associations with dampness in the home, synthetic pillows and frequency of vacuuming were not altered significantly after adjustment for age, sex and socio-economic status. Population attributable risk percentages for the use of a radiator and synthetic pillows indicate that although the relative risk estimates for these factors may be small, the population impact of these factors is considerable (26% and 28%, respectively), owing to the high prevalence of exposure to these factors among this group of school children. CONCLUSIONS: Further research is needed to confirm these associations and additional research is needed to see whether they might be causative. Practical public health advice about the importance of controlling the home environment may then be targeted at families with atopic eczema.

Bedding and Linens↗
PubMed2001

Beta3 tyrosine phosphorylation in alphaIIbbeta3 (platelet membrane GP IIb-IIIa) outside-in integrin signaling.

The platelet integrin alphaIIbbeta3 not only binds fibrinogen and von Willebrand factor to mediate platelet aggregation and adhesion, it also serves as a signaling receptor. Platelet agonists such as ADP, thrombin and collagen induce "inside-out" signaling which activates the receptor function of alphaIIbbeta3 for soluble fibrinogen. Subsequent platelet aggregation leads to "outside-in" signaling, inducing platelet aggregate stabilization and triggering a variety of functions important to platelet physiology. This review focuses on the role of beta3 tyrosine phosphorylation in alphaIIbbeta3 outside-in signaling. Tyrosine phosphorylation of beta3 in platelets is a dynamic process which is initiated upon platelet aggregation and also by adhesion of platelets to immobilized fibrinogen. Tyrosine phosphorylation occurs on the beta3 integrin cytoplasmic tyrosine (ICY) domain, a conserved motif found in the beta subunits of several integrins. Beta3 ICY domain tyrosine phosphorylation induces the recruitment of two proteins to the cytoplasmic domains of alphaIIbbeta3: the cytoskeletal protein myosin, important to clot retraction; and the signaling adapter protein Shc, important to platelet stimulation, The critical role of beta3 tyrosine phosphorylation to platelet function was established by the diYF mouse, a novel strain which expresses an alphaIIbbeta3 in which the two beta3 ICY domain tyrosines have been mutated to phenylalanine. These mice are selectively impaired in outside-in alphaIIbbeta3 signaling, with defective aggregation and clot-retraction responses in vitro, and an in vivo bleeding defect which is characterized by a pronounced tendency to rebleed. Taken together, the data suggest that the beta3 tyrosine phosphorylation signaling mechanism is important to alphaIIbbeta3 function and might be applicable to a wide variety of integrin-mediated events.

Amino Acid Motifs↗
PubMed2000

Identification of shc as the primary protein binding to the tyrosine-phosphorylated beta 3 subunit of alpha IIbbeta 3 during outside-in integrin platelet signaling.

Outside-in signaling mediated by the integrin alpha(IIb)beta(3) (GPIIbIIIa) is critical to platelet function and has been shown to involve the phosphorylation of tyrosine residues on the cytoplasmic tail of beta(3). To identify proteins that bind directly to phosphorylated beta(3), we utilized an affinity column consisting of a peptide modeled on the tyrosine-phosphorylated cytoplasmic domain of beta(3). Tandem mass spectrometric sequencing and immunoblotting demonstrated that Shc was the primary protein binding to phosphorylated beta(3). To determine the involvement of Shc in outside-in alpha(IIb)beta(3) signaling, the phosphorylation of Shc during platelet aggregation was examined; transient Shc phosphorylation was observed when thrombin-stimulated platelets were allowed to aggregate or when aggregation was induced by an LIBS (ligand-induced binding site) antibody, D3. Moreover, Shc was co-immunoprecipitated with tyrosine-phosphorylated beta(3) in detergent lysates of aggregated platelets. Using purified, recombinant protein, it was found that the binding of Shc to monophosphorylated (C-terminal tyrosine) and diphosphorylated beta(3) peptides was direct, demonstrating Shc recognition motifs on phospho-beta(3). Aggregation-induced Shc phosphorylation was also observed to be robust in platelets from wild-type mice, but not in those from mice expressing (Y747F,Y759F) beta(3), which are defective in outside-in alpha(IIb)beta(3) signaling. Thus, Shc is the primary downstream signaling partner of beta(3) in its tyrosine phosphorylation outside-in signaling pathway.

Adaptor Proteins, Signal Transducing↗