Biomedical subjects

Heather Walker

Publications and source records attributed to Heather Walker.

8 recordsLinked to original sources

PubMed2026

Hypothesis-free evaluation of circulating metabolome provides cell-specific insights regarding the role of energy substrate availability in amyotrophic lateral sclerosis.

BACKGROUND: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with limited therapeutic options. The circulating metabolome comprises small molecules present in plasma/serum which are the intermediates and end-products of cellular metabolism, and is linked to ALS pathogenesis. METHODS: We conducted hypothesis-free two-sample Mendelian randomisation (MR) analysis of the concentration of 575 plasma/serum metabolites, to determine which are causally linked to risk of ALS. Significant metabolites were validated in an independent GWAS of plasma/serum metabolite concentrations and evaluated for sex-specific effects. Correlations between directly measured patient biofluid metabolite concentrations and ALS risk/severity were examined in 94 ALS patients and 40 controls. We experimentally assessed metabolic function in a murine neurons and human astrocytes carrying an ALS-associated G4C2-repeat expansion within C9orf72. RESULTS: MR causally associated five metabolites with ALS risk after multiple-testing correction. Higher serum concentration of glycoprotein acetyls (P = 9.7e - 9, β = 0.21) and the peptide DSGEGDFXAEGGGVR (P = 8.0e - 6, β = 0.22) was associated with increased ALS risk, whereas higher plasma concentration of phenylalanylserine, isobutyrylcarnitine, and acetylcarnitine was protective (P < 5e - 5, β = - 0.29 to - 0.72). DSGEGDFXAEGGGVR has been linked to glucose metabolism but we have used genetic fine-mapping to link DSGEGDFXAEGGGVR, neuronal glucose uptake through GLUT3, and ALS risk. Direct measurement of metabolite concentrations in patient biofluids revealed elevated acetylcarnitine levels in patients with ALS, which were associated with delayed symptom onset (Cox regression, P = 0.02, HR = 0.4). Similarly, lactate is elevated in ALS patient CSF (ANOVA, P = 1.3e - 3) and in patients with longer survival time (Cox regression, P = 0.03, HR = 0.3). Plasma fructose is elevated in ALS patients with shorter survival time (Cox regression, P = 0.02, HR = 1.1). In vitro, neurons and astrocytes carrying an ALS-associated G4C2-repeat expansion within C9orf72 demonstrated reduced metabolic flexibility. CONCLUSIONS: We provide evidence that impaired energy substrate availability contributes to ALS risk and severity. CNS cell types differ in their use of energy substrates and therefore we postulate the relative importance of different cell types for different stages of disease. Our findings support further investigation of metabolic interventions to treat or prevent ALS.

Amyotrophic Lateral Sclerosis↗

PubMed2004

Selective growth inhibition of tumor cells by a novel histone deacetylase inhibitor, NVP-LAQ824.

We have synthesized a histone deacetylase inhibitor, NVP-LAQ824, a cinnamic hydroxamic acid, that inhibited in vitro enzymatic activities and transcriptionally activated the p21 promoter in reporter gene assays. NVP-LAQ824 selectively inhibited growth of cancer cell lines at submicromolar levels after 48-72 h of exposure, whereas higher concentrations and longer exposure times were required to retard the growth of normal dermal human fibroblasts. Flow cytometry studies revealed that both tumor and normal cells arrested in the G(2)-M phase of the cell cycle after compound treatment. However, an increased sub-G(1) population at 48 h (reminiscent of apoptotic cells) was observed only in the cancer cell line. Annexin V staining data supported our hypothesis that NVP-LAQ824 induced apoptosis in tumor and transformed cells but not in normal cells. Western blotting experiments showed an increased histone H3 and H4 acetylation level in NVP-LAQ824-treated cancer cells, suggesting that the likely in vivo target of NVP-LAQ824 was histone deacetylase(s). Finally, NVP-LAQ824 exhibited antitumor effects in a xenograft animal model. Together, our data indicated that the activity of NVP-LAQ824 was consistent with its intended mechanism of action. This novel histone deacetylase inhibitor is currently in clinical trials as an anticancer agent.

Animals↗

PubMed2004

Combining clinical risk with D-dimer testing to rule out deep vein thrombosis.

We sought to determine whether the combination of low-intermediate clinical risk of acute lower extremity deep vein thrombosis (DVT) and negative ELISA D-dimer assay can eliminate the need for duplex ultrasonography. Three hundred thirty-six patients prospectively underwent clinical risk stratification (low, intermediate, and high), D-dimer testing, and duplex ultrasonography. Thirteen of 145 intermediate-risk patients had acute DVT; 11 (85%) had a positive D-dimer. Two of 118 low-risk patients had acute DVT; both had a positive D-dimer. Intermediate-high risk stratification alone had sensitivity of 93.9% (95% CI: 80.3-98.3%) and a NPV of 98.3% (95% CI: 94.0-99.5%) for acute DVT. For all patients, a positive D-dimer alone had a sensitivity of 93.9% (95% CI: 80.3-98.3%) and a NPV of 98.6% (95% CI: 95.1-99.6%). The combination of D-dimer and intermediate-high risk classification had a sensitivity of 100% (95% CI: 89.4-100%) and a NPV of 100% (95% CI: 98.9-100%). In suspected acute lower extremity DVT, the combination of intermediate-high clinical risk and positive D-dimer has a high sensitivity and NPV, possibly eliminating the need for duplex ultrasound in this group of patients.

Adult↗

PubMed2003

N-hydroxy-3-phenyl-2-propenamides as novel inhibitors of human histone deacetylase with in vivo antitumor activity: discovery of (2E)-N-hydroxy-3-[4-[[(2-hydroxyethyl)[2-(1H-indol-3-yl)ethyl]amino]methyl]phenyl]-2-propenamide (NVP-LAQ824).

A series of N-hydroxy-3-phenyl-2-propenamides were prepared as novel inhibitors of human histone deacetylase (HDAC). These compounds were potent enzyme inhibitors, having IC(50)s < 400 nM in a partially purified enzyme assay. However, potency in cell growth inhibition assays ranged over 2 orders of magnitude in two human carcinoma cell lines. Selected compounds having cellular IC(50) < 750 nM were tested for maximum tolerated dose (MTD) and for efficacy in the HCT116 human colon tumor xenograft assay. Four compounds having an MTD > or = 100 mg/kg were selected for dose-response studies in the HCT116 xenograft model. One compound, 9 (NVP-LAQ824), had significant dose-related activity in the HCT116 colon and A549 lung tumor models, high MTD, and low gross toxicity. On the basis, in part, of these properties, 9 has entered human clinical trials in 2002.

Acetyltransferases↗

PubMed2003

Regulating intensity using perceived exertion during extended exercise periods.

The present study was undertaken to examine the validity of using the OMNI scale of perceived exertion to regulate intensity during extended exercise periods. Forty-eight subjects (24 male, 24 female) were recruited and each subject completed a maximal graded exercise test (GXT) and two 20-min submaximal exercises. During the GXT, ratings of perceived exertion (RPE) as well as oxygen uptake (VO(2)) and heart rate (HR) equivalent to 50 and 70% of maximum VO(2) (VO(2max)) were estimated. During each submaximal exercise, subjects were instructed to produce and maintain a workload equivalent to the RPE estimated at 50 or 70% VO(2max), and VO(2) and HR were measured every 5 min throughout the exercise. Of the 48 subjects, 12 (6 male and 6 female) performed both the estimation and production trials on a treadmill (TM/TM), 12 (6 male and 6 female) performed both the estimation and production trials on a cycle ergometer (C/C), 12 (6 male and 6 female) performed the estimation trial on a treadmill and the production trial on a cycle ergometer (TM/C), and 12 (6 male and 6 female) performed the estimation trial on a cycle ergometer and the production trial on a treadmill (C/TM). No differences in VO(2) between the estimation and any 5 min of the production trial were observed at either intensity in TM/TM and C/C. No differences in HR between the estimation and any 5 min of the production trial were also observed at 50% VO(2max) in TM/TM and at both 50 and 70% VO(2max) in C/C. However, HR was higher at 20th min of the production trial at 70% VO(2max) in TM/TM. Both the VO(2) and HR were generally lower in TM/C and higher in C/TM. However, these differences diminished when values were normalized using VO(2max) of the same mode that other groups had attained. These data suggest that under both intra- and intermodal conditions, using the OMNI perceived exertion scale is effective not only in establishing the target intensity at the onset of exercise, but also in maintaining the intensity throughout a 20-min exercise session.

Adaptation, Physiological↗

PubMed2003

High-performance liquid chromatography/inductively coupled plasma mass spectrometry with iodine-specific detection for profiling the metabolites produced in the earthworm Eisenia veneta by exposure to 2-fluoro-4-iodoaniline.

High-performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC/ICPMS) provided a rapid and specific means for profiling the iodine-containing metabolites produced by the earthworm Eisenia veneta following exposure to 2-fluoro-4-iodoaniline. Profiles were obtained, using gradient reversed-phase HPLC, from extracts of whole earthworms and from coleomic fluid with as little as 25 ng/peak of iodine detected. The use of ICPMS in this way provides a convenient means of determining the metabolic fate of iodinated compounds without the need for radiolabelled compounds.

Aniline Compounds↗

PubMed2002

Inhibitors of human histone deacetylase: synthesis and enzyme and cellular activity of straight chain hydroxamates.

Inhibitors of histone deacetylase (HDAC) have been shown to induce terminal differentiation of human tumor cell lines and to have antitumor effects in vivo. We have prepared analogues of suberoylanilide hydroxamic acid (SAHA) and trichostatin A and have evaluated them in a human HDAC enzyme inhibition assay, a p21(waf1) (p21) promoter assay, and in monolayer growth inhibition assays. One compound, 4-(dimethylamino)-N-[7-(hydroxyamino)-7-oxoheptyl]-benzamide, was found to affect the growth of a panel of eight human tumor cell lines differentially.

Antineoplastic Agents↗

PubMed2002

Quantitation in gradient high performance liquid chromatography/inductively coupled mass spectrometry investigated using diclofenac and chlorpromazine.

The use of directly coupled high performance liquid chromatography/inductively coupled plasma mass spectroscopy (HPLC/ICPMS) employing chlorine ((35)Cl/(37)Cl) detection has been investigated with respect to the detection and quantitation of the drugs diclofenac and chlorpromazine. By integration of peak areas in the 'chloratogram' (the chlorine specific HPLC chromatogram), a calibration curve was constructed, from which the concentrations could be determined. Chlorine detected HPLC/ICPMS is quantitative over a wide range of concentrations of pharmaceutical relevance for metabolite detection and the results reproducible (standard deviation +/- 0.43%) over multiple injections. Application of gradient chromatography and variation in the bulk mobile phase physicochemical properties has little effect on the ICPMS detection response for these compounds. This work indicates that the use of HPLC/ICPMS is likely to be quantitatively reliable for metabolism studies for a range of chlorinated xenobiotics.

Anti-Inflammatory Agents, Non-Steroidal↗