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R A Miller

Publications and source records attributed to R A Miller.

At least 37 records · Page 2Linked to original sources
PubMed2002

Field dependence of mobilities for gas-phase-protonated monomers and proton-bound dimers of ketones by planar field asymmetric waveform ion mobility spectrometer (PFAIMS).

The dependence of the mobilities of gas-phase ions on electric fields from 0 to 90 Td at ambient pressure was determined for protonated monomers [(MH+(H2O)n] and proton bound dimers [M2H+(H2O)n] for a homologous series of normal ketones, from acetone to decanone (M=C3H6O to C10H20O). This dependence was measured as the normalized function of mobility alpha (E/N) using a planar field asymmetric waveform ion mobility spectrometer (PFAIMS) and the ions were mass-identified using a PFAIMS drift tube coupled to a tandem mass spectrometer. Methods are described to obtain alpha (E/N) from the measurements of compensation voltage versus amplitude of an asymmetric waveform of any shape. Slopes of alpha for MH+ versus E/N were monotonic from 0 to 90 Td for acetone, butanone, and pentanone. Plots for ketones from hexanone to octanone exhibited plateaus at high fields. Nonanone and decanone showed plots with an inversion of slope above 70 Td. Proton bound dimers for ketones with carbon numbers greater than five exhibited slopes for alpha versus E/N, which decreased continuously with increasing E/N. These findings are the first alpha values for ions from a homologous series under atmosphere pressure and are preliminary to explanations of alpha (E/N) with ion structure.

Chromatography, Gas↗
PubMed2002

Micro-machined planar field asymmetric ion mobility spectrometer as a gas chromatographic detector.

A planar high field asymmetric waveform ion mobility spectrometer (PFAIMS) with a micro-machined drift tube was characterized as a detector for capillary gas chromatography. The performance of the PFAIMS was compared directly to that of a flame ionization detector (FID) for the separation of a ketone mixture from butanone to decanone. Effluent from the column was continuously sampled by the detector and mobility scans could be obtained throughout the chromatographic analysis providing chemical inforrmation in mobility scans orthogonal to retention time. Limits of detection were approximately I ng for measurement of positive ions and were comparable or slightly better than those for the FID. Direct comparison of calibration curves for the FAIMS and the FID was possible over four orders of magnitude with a semi-log plot. The concentration dependence of the PFAIMS mobility scans showed the dependence between ion intensity and ion clustering, evident in other mobility spectrometers and atmospheric pressure ionization technologies. Ions were identified using mass spectrometry as the protonated monomer and the proton bound dimer of the ketones. Residence time for column effluent in the PFAIMS was calculated as approximately 1 ms and a 36% increase in extra-column broadening versus the FID occurred with the PFAIMS.

Butanones↗
PubMed2002

Outpatient clinic: where is the delay?

In outpatient clinics, consultation times are often eroded by extraneous activities. We measured the components of each outpatient episode in 167 patients attending a general urology follow-up clinic. 41% of time in the clinic was spent away from the patient-administration 17%, disturbances 15%, finding results 9%. The inefficiencies had changed little since a study in the same setting thirteen years earlier. Since then, parallel nurse-practitioner-run clinics have been introduced in the hope of giving consultants longer with the patient; however, time with each patient is now 4.8 min compared with a previous 7.6 min. The most easily addressed inefficiencies are those relating to missing information, such as radiology reports.

Consultants↗
PubMed2001

Redox cycling by motexafin gadolinium enhances cellular response to ionizing radiation by forming reactive oxygen species.

PURPOSE: To examine the mechanism of radiation enhancement by motexafin gadolinium (Gd-Tex) in vitro. METHODS AND MATERIALS: Oxidation of ascorbate and NADPH by Gd-Tex was evaluated in a neutral buffer. Growth inhibition of human uterine cancer cell line MES-SA was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) dye. Clonogenic assays were used to measure radiation response in MES-SA, A549 human lung carcinoma, E89, a CHO cell line variant deficient in glucose-6-phosphate dehydrogenase activity, and murine lymphoma cell lines LYAR and LYAS. RESULTS: Gd-Tex catalyzed the oxidation of NADPH and ascorbate under aerobic conditions, forming hydrogen peroxide. Decreased viability was observed in MES-SA cells incubated with Gd-Tex in media containing NADPH or ascorbate. Gd-Tex and ascorbate increased fluorescence in dichlorofluorescin acetate-treated cultures. Synergistic effects on the aerobic radiation response in MES-SA and A549 were seen using Gd-Tex in combination with L-buthionine-(S,R)-sulfoximine (BSO). Incubation with Gd-Tex in the presence of ascorbate increased the aerobic radiation response of E89 and the apoptosis-sensitive B-cell line (LYAS). CONCLUSIONS: Gd-Tex sensitizes cells to ionizing radiation by increasing oxidative stress as a consequence of futile redox cycling. Optimization of the concentration of ascorbate (or other reducing species) may be required when evaluating Gd-Tex activity in vitro.

Animals↗
PubMed2001

Biomarkers of aging.

As a subgenre of biogerontology, biomarker research has developed a thoroughly tarnished reputation, and those who believe that biomarker studies should be a major focus in experimental aging research must now try to prove to their doubting colleagues that under the tarnish lies true metal, rather than more layers of tarnish. In this Perspective, the author argues that the discovery of biomarkers of aging is possible.

Aging↗
PubMed2001

Lifespan extension and delayed immune and collagen aging in mutant mice with defects in growth hormone production.

Single-gene mutations that extend lifespan provide valuable tools for the exploration of the molecular basis for age-related changes in cell and tissue function and for the pathophysiology of age-dependent diseases. We show here that mice homozygous for loss-of-function mutations at the Pit1 (Snell dwarf) locus show a >40% increase in mean and maximal longevity on the relatively long-lived (C3H/HeJ x DW/J)F(1) background. Mutant dw(J)/dw animals show delays in age-dependent collagen cross-linking and in six age-sensitive indices of immune system status. These findings thus demonstrate that a single gene can control maximum lifespan and the timing of both cellular and extracellular senescence in a mammal. Pituitary transplantation into dwarf mice does not reverse the lifespan effect, suggesting that the effect is not due to lowered prolactin levels. In contrast, homozygosity for the Ghrhr(lit) mutation, which like the Pit1(dw) mutation lowers plasma growth hormone levels, does lead to a significant increase in longevity. Male Snell dwarf mice, unlike calorically restricted mice, become obese and exhibit proportionately high leptin levels in old age, showing that their exceptional longevity is not simply due to alterations in adiposity per se. Further studies of the Pit1(dw) mutant, and the closely related, long-lived Prop-1(df) (Ames dwarf) mutant, should provide new insights into the hormonal regulation of senescence, longevity, and late life disease.

Aging↗
PubMed2001

Miniature radio-frequency mobility analyzer as a gas chromatographic detector for oxygen-containing volatile organic compounds, pheromones and other insect attractants.

A high electric field, radio-frequency ion mobility spectrometry (RF-IMS) analyzer was used as a small detector in gas chromatographic separations of mixtures of volatile organic compounds including alcohols, aldehydes, esters, ethers, pheromones, and other chemical attractants for insects. The detector was equipped with a 2 mCi 63Ni ion source and the drift region for ion characterization was 5 mm wide, 15 mm long and 0.5 mm high. The rate of scanning for the compensation voltages was 60 V s(-1) and permitted four to six scans to be obtained across a capillary chromatographic elution profile for each component. The RF-IMS scans were characteristic of a compound and provided a second dimension of chemical identity to chromatographic retention adding specificity in instances of co-elution. Limits of detection were 1.6-55 x 10(-11) g with an average detection limit for all chemicals of 9.4 x 10(-11) g. Response to mass was linear from 2-50 x 10(-10) g with an average sensitivity of 4 pA ng(-1). Separations of pheromones and chemical attractants for insects illustrated the distinct patterns obtained from gas chromatography with RF-IMS scans in real time and suggest an analytical utility of the RF-IMS as a small, advanced detector for on-site gas chromatographs.

Chromatography, Gas↗
PubMed2001

Multicenter phase Ib/II trial of the radiation enhancer motexafin gadolinium in patients with brain metastases.

PURPOSE: Motexafin gadolinium is a magnetic resonance imaging (MRI)--detectable redox active drug that localizes selectively in tumor cells and enhances the effect of radiation therapy. This phase Ib/II trial of motexafin gadolinium, administered concurrently with 30 Gy in 10 fractions whole-brain radiation therapy (WBRT), was conducted to determine maximum-tolerated dose (MTD), dose-limiting toxicity, pharmacokinetics, and biolocalization in patients with brain metastases. Additional endpoints were radiologic response rate and survival. PATIENTS AND METHODS: Motexafin gadolinium was administered before each radiation treatment in this open-label, multicenter, international trial. In phase Ib, drug dose was escalated until the MTD was exceeded. In phase II, drug was evaluated in a narrow dose range. RESULTS: In phase Ib, the motexafin gadolinium dose was escalated in 39 patients (0.3 mg/kg to 8.4 mg/kg). In phase II, 22 patients received 5 mg/kg to 6.3 mg/kg motexafin gadolinium. Ten once-daily treatments were well tolerated. The MTD was 6.3 mg/kg, with dose-limiting reversible liver toxicity. Motexafin gadolinium's tumor selectivity was established using MRI. The radiologic response rate was 72% in phase II. Median survival was 4.7 months for all patients, 5.4 months for recursive partitioning analysis (RPA) class 2 patients, and 3.8 months for RPA class 3 patients. One-year actuarial survival for all patients was 25%. CONCLUSION: Motexafin gadolinium was well tolerated at doses up to 6.3 mg/kg, was selectively accumulated in tumors, and, when combined with WBRT of 30 Gy in 10 fractions, was associated with a high radiologic response rate.

Adult↗
PubMed2001

Single-cell analyses reveal two defects in peptide-specific activation of naive T cells from aged mice.

Confocal fluorescent microscopy was used to study redistribution of membrane-associated proteins in naive T cells from young and old mice from a transgenic stock whose T cells express a TCR specific for a peptide derived from pigeon cytochrome C. About 50% of the T cells from young mice that formed conjugates with peptide-pulsed APC were found to form complexes, at the site of binding to the APC, containing CD3epsilon, linker for activation of T cells (LAT), and Zap-70 in a central area and c-Cbl, p95(vav), Grb-2, PLC gamma, Fyn, and Lck distributed more uniformly across the interface area. Two-color staining showed that those cells that were able to relocalize c-Cbl, LAT, CD3epsilon, or PLC gamma typically relocalized all four of these components of the activation complex. About 75% of conjugates that rearranged LAT, c-Cbl, or PLC gamma also exhibited cytoplasmic NF-AT migration to the T cell nucleus. Aging had two effects. First, it led to a diminution of approximately 2-fold in the proportion of T cell/APC conjugates that could relocalize any of the nine tested proteins to the immune synapse. Second, aging diminished by approximately 2-fold the frequency of cytoplasmic NF-AT migration among cells that could generate immune synapses containing LAT, c-Cbl, or PLC gamma. Thus naive CD4 T cells from old mice exhibit at least two separable defects in the earliest stages of activation induced by peptide/MHC complexes.

Active Transport, Cell Nucleus↗
PubMed2001

Photoangioplasty with local motexafin lutetium delivery reduces macrophages in a rabbit post-balloon injury model.

OBJECTIVE: Motexafin lutetium (Lu-Tex, Antrin Injection) is a photosensitizer that selectively accumulates in atheromatous plaque where it can be activated by far-red light. The localization and retention of intra-arterially administered Lu-Tex and its efficacy following activation by endovascularly delivered light (photoangioplasty) was evaluated. METHODS: Bilateral iliac artery lesions were induced in 17 rabbits by balloon denudation, followed by a high cholesterol diet. Lu-Tex distribution within the atheroma was examined (n=8) following local injection. Fluorescence spectral imaging and chemical extraction techniques were used to measure Lu-Tex levels within the atheroma and adjacent normal tissue. Photoactivation was performed 15 min following Lu-Tex administration (180 J/cm fiber at 200 mW/cm fiber). Two weeks post photoangioplasty, vessels were harvested and hematoxylin and eosin (H&E) and RAM11 (macrophages) staining was performed. RESULTS: Local delivery of Lu-Tex achieved immediate high concentrations within plaque (mean 40x control iliac atheroma). Mean percent plaque area in the treated segments was significantly lower than in the non-treated contralateral lesions (73 vs. 82%, P<0.01). No medial damage was observed. Quantitative analysis using RAM11 positive cells revealed significant reduction of macrophages in treated lesions in both the intima (5 vs. 22%, P<0.01) and in media (8 vs. 23%, P<0.01) compared to untreated contralateral segments. CONCLUSIONS: Local delivery provides high levels of Lu-Tex selectively within atheroma. Photoactivation results in a significant decrease in macrophage and a small decrease in atheroma burden without damage to the normal vessel wall.

Angioplasty, Balloon↗
PubMed2001

Interpretation, design, and analysis of gene array expression experiments.

Experiments using arrays of cDNA targets to compare patterns of gene expression are beginning to play a prominent role in biogerontology, but drawing reliable conclusions from the resulting data sets requires careful application of statistical methods that discriminate chance events from those likely to reflect real differences among the samples under study. This essay discusses flaws in the logic of studies that base their conclusions on ratio calculations alone, reviews the multiple comparison traps inherent in high throughput systems that test a very large number of mRNAs simultaneously, and advocates a two-stage design in which significance testing applied to exploratory data is used to guide a second round of hypothesis-testing experiments conducted in a separate set of experimental samples.

Aging↗
PubMed2001

Array-based expression analysis of mouse liver genes: effect of age and of the longevity mutant Prop1df.

Ames dwarf mice, homozygous for the df allele at the Prop1 locus, live 40% to 70% longer than nonmutant siblings and represent the first single-gene mutant that extends life span in a mammal. To gain insight into the basis for the longevity of the Ames dwarf mouse, we measured liver mRNA levels for 265 genes in a group of 11 df/df mice, (three to four mice per age group), at ages 5, 13, and 22 months, and in 13 age- and sex-matched control mice. The analysis showed seven genes where the effects of age reach p < .01 in normal mice and six others with possible age effects in dwarf mice, but none of these met Bonferroni-adjusted significance thresholds. Thirteen genes showed possible effects of the df/df genotype at p < .01. One of these, insulin-like growth factor 1 (IGF-1), was statistically significant even after adjustment for multiple comparisons; and genes for two IGF-binding proteins, a cyclin, a heat shock protein, p38 mitogen-activated protein kinase, and an inducible cytochrome P450 were among those implicated by the survey. In young control mice, half of the expressed genes showed SDs that were more than 58% of the mean, and a simulation study showed that genes with this degree of interanimal variation would often produce false-positive findings when conclusions were based on ratio calculations alone (i.e., without formal significance testing). Many genes in our data set showed apparent young-to-old or normal-to-dwarf ratios above 2, but the large majority of these proved to be genes where high interanimal variation could create high ratios by chance alone, and only a few of the genes with large ratios achieved p < .05. The proportion of genes showing relatively large changes between 5 and 13 months, or from 13 to 22 months of age, was not diminished by the df/df genotype, providing no support for the idea that the dwarf mutation leads to global delay or deceleration of the pace of age-dependent changes in gene expression. These survey data provide the foundation for replication studies that should provide convincing proof for age- and genotype-specific effects on gene expression and thus reveal key similarities among the growing number of mouse models of decelerated aging.

Aging↗