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Biomedical subjects

M Greaves

Publications and source records attributed to M Greaves.

At least 19 recordsLinked to original sources
PubMed2003

Platelet activation is increased in peripheral arterial disease.

OBJECTIVE: Platelet activation was assessed in patients with peripheral arterial disease compared with healthy control subjects. METHODS: This prospective comparative study included 100 subjects: 40 consecutive patients with intermittent claudication, 20 consecutive patients with critical ischemia and tissue loss, and 40 healthy control subjects. Whole blood flow cytometric analysis was performed to determine resting and stimulated platelet P-selectin expression and resting and stimulated platelet fibrinogen binding. Results are presented as platelet percentage and also as mean fluorescence intensity. RESULTS: P-selectin expression was significantly increased in patients with intermittent claudication (median, 0.85%; range, 0.31%-4.77%; P =.023) and critical ischemia (median, 1.11%; range, 0.2%-3.26%; P =.028) compared with control subjects (median, 0.59%; range, 0.16%-4.58%). The percentage of platelets binding fibrinogen was also significantly higher in patients with intermittent claudication (median, 2.89%; range, 1.08%-9.59%; P <.001) compared with control subjects (median, 1.57%; range, 0.17%-10.7%). There was no significant difference in percentage of platelet fibrinogen binding between control subjects and patients with critical ischemia. Fibrinogen binding by stimulated platelets was significantly diminished in patients with critical limb ischemia compared with control subjects (67.2% vs 77.9%; P =.006). CONCLUSIONS: Platelet activation is increased in patients with peripheral arterial disease, suggesting an underlying prothrombotic state. Platelets from patients with critical limb ischemia are less responsive to in vitro stimulation.

Aged↗
PubMed2002

Exposure to power frequency electric fields and the risk of childhood cancer in the UK.

The United Kingdom Childhood Cancer Study, a population-based case-control study covering the whole of Great Britain, incorporated a pilot study measuring electric fields. Measurements were made in the homes of 473 children who were diagnosed with a malignant neoplasm between 1992 and 1996 and who were aged 0-14 at diagnosis, together with 453 controls matched on age, sex and geographical location. Exposure assessments comprised resultant spot measurements in the child's bedroom and the family living-room. Temporal stability of bedroom fields was investigated through continuous logging of the 48-h vertical component at the child's bedside supported by repeat spot measurements. The principal exposure metric used was the mean of the pillow and bed centre measurements. For the 273 cases and 276 controls with fully validated measures, comparing those with a measured electric field exposure >/=20 V m(-1) to those in a reference category of exposure <10 V m(-1), odds ratios of 1.31 (95% confidence interval 0.68-2.54) for acute lymphoblastic leukaemia, 1.32 (95% confidence interval 0.73-2.39) for total leukaemia, 2.12 (95% confidence interval 0.78-5.78) for central nervous system cancers and 1.26 (95% confidence interval 0.77-2.07) for all malignancies were obtained. When considering the 426 cases and 419 controls with no invalid measures, the corresponding odds ratios were 0.86 (95% confidence interval 0.49-1.51) for acute lymphoblastic leukaemia, 0.93 (95% confidence interval 0.56-1.54) for total leukaemia, 1.43 (95% confidence interval 0.68-3.02) for central nervous system cancers and 0.90 (95% confidence interval 0.59-1.35) for all malignancies. With exposure modelled as a continuous variable, odds ratios for an increase in the principal metric of 10 V m(-1) were close to unity for all disease categories, never differing significantly from one.

Adolescent↗
PubMed2002

Aspirin dilemma. Remodelling the hypothesis from a fertility perspective.

Many clinical trials in obstetrics have failed to demonstrate improved outcomes with low-dose aspirin. This is not entirely surprising as prescribing aspirin for compromised tissue perfusion without insight into underlying pathology inevitably leads to suboptimal outcomes. We argue that a mismatch between the aspirin dose and the underlying pathology of altered tissue perfusion is the key factor to this failure. Based on this groundwork, we address the question of how best to optimize the dose of aspirin for use in fertility management, by providing examples from the assisted conception and recurrent miscarriage settings.

Abortion, Habitual↗
PubMed2002

Prothrombotic genotypes are not associated with pre-eclampsia and gestational hypertension: results from a large population-based study and systematic review.

DNA samples collected as part of a large population-based case-control study were genotyped to examine the associations of five prothrombotic gene polymorphisms with pre-eclampsia (PE) and gestational hypertension (GH). The polymorphisms studied were: G1691A in Factor V (Factor V Leiden; FVL), prothrombin G20210A, methylenetetrahydrofolate reductase (MTHFR) C677T, plasminogen activator inhibitor-1 4G/5G and the platelet collagen receptor alpha2beta1 C807T. A group of 404 women who developed PE were retrospectively compared with 303 women with GH and 164 control women. The frequency of genotypes did not differ significantly between cases of PE or GH and controls for any of the five polymorphisms studied. We conclude that these prothrombotic genotypes are not associated with the development of PE or GH in our population. The systematic review supports our conclusion, for all but cases of severe disease. which appear to be associated with FVL and, to a lesser extent, MTHFR C677T. There is little value in antenatal screening for prothrombotic polymorphisms to predict the development of pre-eclampsia or gestational hypertension.

3' Untranslated Regions↗
PubMed2001

Thrombin-induced activation of RhoA in platelet shape change.

Thrombin-induced activation of RhoA and its involvement in the regulation of myosin II light chain(20) phosphorylation (MLC-P) in alpha-toxin permeabilized platelets was investigated. Permeabilized platelets, expressing normal levels of P-selectin, displayed a Ca(2+)-dependent increase in shape change and MLC-P. Thrombin activated RhoA as measured by a rhotekin-binding assay within 30 s of stimulation under conditions of constant [Ca(2+)](i). Under the same conditions and timecourse, thrombin or GTPgammaS induced an increase in MLC-P and platelet shape change which was not dependent on an increase in [Ca(2+)](i). The thrombin- and GTPgammaS-induced MLC-P in constant [Ca(2+)](i) was inhibited by the addition of Y27632, a Rho-kinase inhibitor. This study directly demonstrates that thrombin can activate RhoA in platelets in a timecourse compatible with a role in increasing MLC-P and shape change (not involving an increase in [Ca(2+)](i)). This is also Rho-kinase-dependent.

Amides↗
PubMed2001

Characterization of germline TP53 splicing mutations and their genetic and functional analysis.

Germline TP53 splicing mutations have been described infrequently (>2%) in the literature, however in a series of 40 patients and families identified by our group in which there are germline TP53 mutations, seven affect splicing (18%). The low figure reported in the literature might reflect the method of mutation detection, which in many studies does not include all splice junctions. These data indicate that a significant proportion of TP53 germline mutations are currently unrecognized. We have carried out detailed studies of the effects of the different mutations on splicing, and see distinct variations in the effects of the same mutation in different patients. Furthermore we have identified the usage of a non-consensus splice donor site in four families with an intron 4 splice donor mutation.

Alternative Splicing↗
PubMed2001

GPHN, a novel partner gene fused to MLL in a leukemia with t(11;14)(q23;q24).

We report a novel MLL-associated chromosome translocation t(11;14)(q23;q24) in a child who showed signs of acute undifferentiated leukemia 3 years after intensive chemotherapy that included the topoisomerase-II inhibitor VP 16. Screening of a cDNA library of the patient's leukemic cells showed a novel fusion transcript between MLL and the Gephyrin (GPHN) gene on 14q24. The resulting MLL-GPHN fusion gene encodes MLL AT hook motifs and a DNA methyltransferase homology domain fused to the C-terminal half of Gephyrin, including a presumed tubulin binding site and a domain homologous to the Escherichia coli molybdenum cofactor biosynthesis protein MoeA. Genomic breakpoint analysis showed potential in vitro topoisomerase-II DNA-binding sites spanning the breakpoints in both MLL and GPHN but no flanking sequences that might mediate homologous recombination. This suggests that MLL-GPHN may have been generated by VP 16/topoisomerase-II-induced DNA double-strand breaks, followed by error-prone DNA repair via non-homologous end joining. Gephyrin was originally identified as a submembraneous scaffold protein that anchors and immobilizes postsynaptic membrane neurotransmitter receptors to underlying cytoskeletal elements. It also is reported to bind to phosphatidylinositol 3,4,5-triphosphate binding proteins involved in actin dynamics and downstream signaling and interacts with ATM-related family member RAFT1. Gephyrin domains in the chimeric protein therefore could contribute novel signal sequences or might modify MLL activity by oligomerization or intracellular redistribution.

Amino Acid Sequence↗
PubMed2001

In vivo platelet activation in atherothrombotic stroke is not determined by polymorphisms of human platelet glycoprotein IIIa or Ib.

Platelet membrane glycoprotein polymorphisms are candidate risk factors for thrombosis, but epidemiological data are conflicting. Thus, demonstration of a genotype-dependent alteration in function is desirable to resolve these inconsistencies. We investigated in vivo platelet activation in acute thrombosis and related this to platelet genotype. Frequencies of the 1b and 2b alleles of the HPA 1a/1b and HPA 2a/2b platelet glycoprotein polymorphisms were determined in 150 (52 men/98 women, mean age 58.3 years) patients with atherothrombotic stroke, and the influence of genotype on markers of platelet activation was assessed. Platelet P-selectin (CD62P) expression and fibrinogen binding was measured using whole blood flow cytometry within 24 h of stroke and 3 months later in 77 patients who provided a repeat blood sample. Results were compared with matched controls. Neither the 1b allele [allele frequency 0.11 vs. 0.13, odds ratio (OR) confidence interval (CI) 0.8 (0.5-1.3)] nor the 2b allele [0.09 vs. 0.07, OR (CI) 1.4 (0.8-2.4)] was significantly over-represented in patients. Increased numbers of activated platelets were found following stroke (acute mean P-selectin expression 0.64% vs. control 0.35%, P < 0.001; acute mean fibrinogen binding 1.6% vs. control 0.9%, P < 0.001). Activation persisted in the convalescent phase (P < 0.001 and P = 0.005 vs. controls for P-selectin and fibrinogen respectively). Expression of P-selectin and fibrinogen was not influenced by either the HPA 1a/1b genotype (P > 0.95 for each marker, Scheffe's test) or the 2a/2b genotype (P > 0.95 for each). Although persisting platelet activation is seen in atherothrombotic stroke, it is independent of HPA 1a/1b and 2a/2b genotypes. These data suggest an underlying prothrombotic state, but do not support the polymorphisms studied as risk factors for thrombotic stroke in this population.

Case-Control Studies↗
PubMed2001

Rare acquired bleeding disorders.

Accurate diagnosis of the cause of bleeding is a prerequisite for determination of the optimal therapeutic response. Clinicians are generally aware of the more prevalent hemorrhagic syndromes but some rare acquired conditions are also of importance. In many of these, inhibitors of coagulation factors or of platelet adhesion/aggregation cause bleeding. These inhibitors are generally, but not always, immunoglobulins. In this review, the less common inhibitors of coagulation and hemostasis, as well as some important but rare nutritional, iatrogenic and disease associated hemorrhagic disorders, are described.

Autoantibodies↗
PubMed2001

The effects of treatment with alpha-lipoic acid or evening primrose oil on vascular hemostatic and lipid risk factors, blood flow, and peripheral nerve conduction in the streptozotocin-diabetic rat.

Oxidative stress and defective fatty acid metabolism in diabetes may lead to impaired nerve perfusion and contribute to the development of peripheral neuropathy. We studied the effects of 2-week treatments with evening primrose oil (EPO; n = 16) or the antioxidant alpha-lipoic acid (ALA; n = 16) on endoneurial blood flow, nerve conduction parameters, lipids, coagulation, and endothelial factors, in rats with streptozotocin-induced diabetes. Compared with their nondiabetic littermates, untreated diabetic rats had impaired sciatic motor and saphenous sensory nerve-conduction velocity (NCV; P <.001), reduced endoneurial blood flow (P <.001), and increased serum triglycerides (P <.01), cholesterol (P < 0.01), plasma factor VII (P <.0001), and von Willebrand factor (vWF; P <.0001). Plasma fibrinogen and serum high-density lipoprotein concentrations were not significantly different. Treatment with either ALA or EPO effectively corrected the deficits in NCV and endoneurial blood flow. ALA was associated with marked and statistically significant decreases in fibrinogen, factor VII, vWF, and triglycerides (P <.01, paired t tests before v after treatment). In contrast, EPO was associated with significant (P <.05) increases in fibrinogen, factor VII, vWF, triglycerides, and cholesterol and a significant decrease in high-density lipoprotein. Changes in levels of coagulation factors and lipids, qualitatively similar to those found with EPO, were obtained with a diet containing sunflower oil (to control for calorific and lipid content) or with a normal diet alone. Blood glucose and hematocrit levels were not significantly altered by treatments. These data suggest that although both ALA and EPO improve blood flow and nerve function, their actions on vascular factors differ. The marked effects of ALA in lowering lipid and hemostatic risk factors for cardiovascular disease indicate potential antithrombotic and antiatherosclerotic actions that could be of benefit in human diabetes and merit further study.

Animals↗
PubMed2001

Plasma homocysteine concentrations in the acute and convalescent periods of atherothrombotic stroke.

BACKGROUND AND PURPOSE: Homocysteine is a proposed causal risk factor for atherosclerosis, but this remains controversial. We measured fasting plasma homocysteine concentrations immediately after atherothrombotic stroke and in the convalescent period to investigate this controversy. METHODS: One hundred six patients (59 men and 47 women, mean age 57.2 [25 to 70] and 56.5 [26 to 69] years, respectively) were recruited within 24 hours of admission, and 82 patients were resampled at least 3 months later. Fasting total plasma homocysteine (tHcy) concentrations were measured by high-performance liquid chromatography. RESULTS: Median tHcy in the acute phase of stroke was not significantly higher than in matched control subjects (men 9.2 [range 4.4 to 22.8] versus 8.7 [4.9 to 20] micromol/L, P:=0.09, Mann-Whitney U: test; women 8.1 [4.8 to 32.3] versus 7.6 [3.3 to 14.4] micromol/L, P:=0.58). Median plasma concentrations increased significantly in the convalescent period (from 8.5 [4.8 to 19.2] to 10.1 [4.3 to 31.5] micromol/L, P:<0.001, Wilcoxon signed rank test) and were then significantly higher than in control subjects in both men and women (P:=0.03 and 0.05, respectively, Mann-Whitney U: test). This did not appear to be explained by alteration in the known covariates red-cell folate, serum B(12), or creatinine concentrations. CONCLUSIONS: Homocysteine concentrations are not elevated after recent atherothrombotic stroke but rise in the convalescent period. These data do not support the hypothesis that raised plasma homocysteine concentrations predate atherothrombotic stroke. Instead, they offer an explanation for the discrepancies between prospective and retrospective studies and suggest that elevated tHcy levels may be caused by the disease process itself.

Acute Disease↗
PubMed2000

Recruitment of the nuclear receptor corepressor N-CoR by the TEL moiety of the childhood leukemia-associated TEL-AML1 oncoprotein.

The t(12;21)(p13;q22) chromosomal translocation is the most frequent illegitimate gene recombination in a pediatric cancer and occurs in approximately 25% of common acute lymphoblastic leukemia (cALL) cases. This rearrangement results in the in frame fusion of the 5'-region of the ETS-related gene, TEL (ETV6), to almost the entire acute myeloid leukemia 1 (AML1) (also called CBFA2 or PEBP2AB1) locus and expression of the TEL-AML1 chimeric protein. Although AML1 stimulates transcription, TEL-AML1 functions as a repressor of some AML1 target genes. In contrast to the wild type AML1 protein, both TEL and TEL-AML1 interact with N-CoR, a component of the nuclear receptor corepressor complex with histone deacetylase activity. The interaction between TEL and N-CoR requires the central region of TEL, which is retained in TEL-AML1, and TEL lacking this domain is impaired in transcriptional repression. Taken together, our results suggest that TEL-AML1 may contribute to leukemogenesis by recruiting N-CoR to AML1 target genes and thus imposing an altered pattern of their expression.

Core Binding Factor Alpha 2 Subunit↗
PubMed2000

Microclustering of TEL-AML1 translocation breakpoints in childhood acute lymphoblastic leukemia.

TEL-AML1 fusions are the most common chromosome translocations in childhood leukemia and often, if not always, occur in utero. We previously reported the genomic sequencing of nine TEL-AML1 translocations and showed unique structural features of a breakpoint cluster region in TEL intron 5. We now report data on sequencing and mapping of TEL-AML1 from an additional 11 patients and, using Monte Carlo statistical methods, have analyzed the intronic distribution of the 24 TEL-AML1 fusion junctions sequenced to date. Compared to a null hypothesis of random breakpoint allocation within TEL intron 5 and AML1 introns 1 and 2, significant microclustering was evident on both TEL and AML1. In contrast to previous reports, the two strongest microclusters on TEL were 3' to an unstable repeat region. AML1 demonstrated four highly significant microclusters, two of which were proximal to exons. We note the necessity of sequencing multiple breakpoints before the description of putative microcluster regions. TEL-AML1 breakpoints may be distributed into microclusters because of specific DNA sequence or chromatin features in susceptible cells. We also report on additional features of breakpoints, including a complex t(12;3;21) in one patient and an inverted sequence in another.

Base Sequence↗