Search PubMed⌕ Search

Biomedical subjects

R A Miller

Publications and source records attributed to R A Miller.

At least 55 records · Page 3Linked to original sources
PubMed2001

Biomarkers of aging: prediction of longevity by using age-sensitive T-cell subset determinations in a middle-aged, genetically heterogeneous mouse population.

Seven T-cell subset values were measured in each of 559 mice at 8 months of age, and then again in the 494 animals that reached 18 months of age. The group included virgin males, virgin females, and mated females, and it was produced by using a four-way cross-breeding system that generates genetic heterogeneity equivalent to a very large sibship. An analysis of covariance showed that four T-cell subsets-CD4, CD4 memory, CD4 naïve, and CD4 cells expressing P:-glycoprotein-were significant predictors (p <.003) of longevity when measured at 18 months of age after adjustment for the possible effects of gender and mating. The subset marked by CD4 and P:-glycoprotein expression showed a significant interaction effect: this subset predicted longevity only in males. Among subsets measured when the mice were 8 months of age, only the levels of CD8 memory cells predicted longevity (p =.016); the prognostic value of this subset was largely limited to mated females. A cluster analysis that separated mice into two groups based upon similarity of T-cell subset patterns measured at 18 months showed that these two groups differed in life expectancy. Specifically, mice characterized by relatively low levels of CD4 and CD8 memory cells, high levels of CD4 naïve cells, and low levels of CD4 cells with P:-glycoprotein (64% of the total) lived significantly longer (50 days = 6%; p <.0007) than mice in the other cluster. The results are consistent with the hypothesis that patterns of T-cell subsets vary among mice in a manner than can predict longevity in middle age, and they suggest that these subsets may prove to be useful for further studies of the genetics of aging and age-sensitive traits.

Aging↗
PubMed2001

Unexpected effects of a heterozygous dnmt1 null mutation on age-dependent DNA hypomethylation and autoimmunity.

DNA methylation modifies gene expression. Methylation patterns are established during ontogeny, but they change with aging, usually with a net decrease in methylation. The significance of this change in T cells is unknown, but it could contribute to autoimmunity, senescence, or both. We examined the effects of a null mutation in DNA methyltransferase 1 (Dnmt1), a gene maintaining DNA methylation patterns, on immune aging. Whereas aged control mice developed hypomethylated DNA, autoimmunity, and signs of immune senescence as predicted, the knockout mice surprisingly increased DNA methylation and developed signs of autoimmunity and senescence more slowly. To identify potential mechanisms, we compared transcripts of DNA methyltransferase and methylcytosine binding protein family members in control and knockout mice. MeCP2, a methylcytosine binding protein involved in gene suppression and chromatin inactivation, was the only transcript differentially expressed between old knockout mice and controls, and thus it is a candidate for a gene product mediating these effects.

Aging↗
PubMed2001

Genetic variability in responses to caloric restriction in animals and in regulation of metabolism and obesity in humans.

Panel 5 focused on genetic factors that might mediate or moderate the effects of caloric restriction (CR) on longevity. Panel members stated that currently there is limited information directly addressing these issues. Therefore, they focused attention on what studies could be done. In addition, the panel believed that certain conceptual issues merited clarification and focused attention on this issue. Human studies and studies of nonhuman model organisms were discussed. The panel found at least three reasons why it would be valuable to find genes that influence the (putative) longevity-promoting effect of CR in humans. Such knowledge would offer: (a) the ability to predict individual responses to CR; (b) increased understanding of physiological mechanisms; and (c) the potential to develop mechanism-based interventions to promote longevity or healthy aging. In addition, the panel emphasized several macro-level recommendations regarding research strategies to avoid, research strategies to emphasize, and resources needing development.

Animals↗
PubMed2001

Antioxidant enzyme expression in clinical isolates of Pseudomonas aeruginosa: identification of an atypical form of manganese superoxide dismutase.

Expression of superoxide dismutases (FeSOD and MnSOD) and catalases by laboratory strains of Pseudomonas aeruginosa is modulated by exogenous factors. Whether clinical isolates behave similarly and whether antioxidant enzyme expression influences P. aeruginosa virulence remain unclear. Fifty-seven P. aeruginosa blood culture isolates, plus seven pairs of blood and local-site isolates, were examined for FeSOD, MnSOD, and catalase production in vitro. Under iron-replete growth conditions FeSOD and catalase activities were maximized. MnSOD was not detected. FeSOD and catalase activity decreased under iron-limited growth conditions, whereas MnSOD activity appeared. SOD and catalase activity did not change with site of isolation or by patient. MnSOD could not be expressed by one isolate due to a missense mutation in sodA that produced a premature stop codon. Eleven percent of the isolates expressed a novel, rapidly migrating MnSOD that was associated with missense mutations in the normal stop codon of sodA. We conclude that clinical P. aeruginosa isolates vary little in FeSOD and catalase expression. Some strains produce a newly described MnSOD variant, whereas one is deficient in MnSOD production. The absence of MnSOD expression in a P. aeruginosa strain causing invasive human disease indicates that MnSOD is probably not essential for P. aeruginosa virulence.

Antioxidants↗
PubMed2001

Motexafin gadolinium: a redox active drug that enhances the efficacy of bleomycin and doxorubicin.

The effect of motexafin gadolinium (MGd), a redox mediator, on tumor response to doxorubicin (Dox) and bleomycin (Bleo) was investigated in vitro and in vivo. MES-SA human uterine sarcoma cells were studied in vitro using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide viability assay. Rif-1, a murine fibrosarcoma cell line, was studied using a clonogenic survival assay. Tumor growth delay assays were performed using the EMT-6 murine mammary sarcoma cell line in BALB/c mice. MGd (25-100 microM) produced dose-dependent enhancement of Bleo cytotoxicity to MES-SA cells. The IC(50) for Bleo was reduced by approximately 10-fold using 100 microM MGd. In clonogenic assays using Rif-1 cells, MGd enhanced the activity of Bleo approximately 1000-fold. This effect was shown to be mediated, in part, by MGd inhibition of potentially lethal damage repair. MGd enhanced the tumor response to bleomycin and Dox in vivo. MGd had no significant effect on the systemic exposure to Dox (expressed in terms of the plasma area under the curve, 0-24 h) and did not increase Dox myelosuppression. MGd enhanced the effectiveness of the redox active drugs, Bleo and Dox.

Animals↗
PubMed2001

A computer based intervention on the appropriate use of arterial blood gas.

OBJECTIVE: To evaluate impact of a computer-based intervention on arterial blood gas (ABG) usage in an intensive care setting. DESIGN: Retrospectively examined, via mixed group analysis, the effects of the intervention on ABG usage in the intensive care unit (ICU). SUBJECTS: Included all clinicians who placed ABG orders in an ICU using the computerized physician order-entry system, as well as controls in non-order entry units. METHODS: Computer-based intervention presenting ordering clinician with patient s previous ABG values and limiting forward duration of tests ordered. Study spanned 12 weeks, 5 weeks pre-intervention and 7-weeks post-intervention. Of 8 ICUs, intervention implemented in 6, not implemented in 2. Data analyzed using the repeated measure ANOVA. RESULTS: Physicians entered <40% ABG orders. 376 ABGs per week processed pre-intervention, 387 per week post. Results nonsignificant with a p= 0.09. Orders placed declined from 1039 per week, Jan 2000 to 662 per week, April 2001. DISCUSSION: Study did not demonstrate significant change; limited power. Need longer study periods. Impact improved in the future by targeting physician users and tailoring intervention to specific work flow pattern of high utilization units.

Analysis of Variance↗
PubMed2001

The effects on clinician ordering patterns of a computerized decision support system for neuroradiology imaging studies.

OBJECTIVE: To evaluate the impact of computerized ordering guidelines on clinician ordering patterns for neuroradiology imaging studies of the head. DESIGN: A retrospective analysis was performed using a pre-post design. A 9-week control period was followed by an 8-week intervention period. SUBJECTS: All clinicians who placed an order for either an MRI of the brain or a CT of the head on inpatients using a computerized order entry system. METHODS: We designed, implemented, and evaluated a decision support system for the implementation of test ordering guidelines. Changes in ordering patterns were evaluated with a Chi-square analysis. RESULTS: 742 tests were ordered in the pre-intervention period, while 704 studies were ordered after the intervention. A significant change in the distribution of tests ordered resulted from the intervention (p=0.048). Changes trended toward the guideline recommendations for all tests considered. 60% of users receiving a recommendation ordered the suggested study. DISCUSSION: Our intervention successfully influenced clinician ordering patterns. Examination of detailed usage patterns may aid in further quality improvement of both the guidelines and the decision support tool used to implement them.

Brain↗
PubMed2000

Age-dependent alterations in the assembly of signal transduction complexes at the site of T cell/APC interaction.

TCR interaction with peptide-MHC complexes triggers migration of protein kinases, actin-binding proteins, and other accessory molecules to the T cell/APC synapse. We used confocal immunofluorescence methods to show that the adapter protein LAT (linker for activation of T cells) and the guanine nucleotide exchange factor Vav also move to the APC interface in mouse CD4 T cells conjugated to anti-CD3 hybridoma cells, and in TCR-transgenic CD4 cells conjugated to APC bearing agonist (but not closely related nonagonist) peptides. The proportion of CD4+ T cells able to relocalize LAT or Vav, or to relocate cytoplasmic NT-AT (NF-ATc) from cytoplasm to nucleus, declines about 2-fold in aged mice. The decline in LAT relocalization is accompanied by a similar decline in tyrosine phosphorylation of LAT in CD4 cells stimulated by CD3/CD4 cross-linking. Two-color experiments show that LAT redistribution is strongly associated with relocalization of both NF-ATc and protein kinase C-theta among individual cells. LAT migration to the immunological synapse depends on actin polymerization as well as on activity of Src family kinases, but aging leads to only a small change in the percentage of CD4 cells that redistribute F-actin to the site of APC contact. These results suggest that defects in the ability of T cells from aged donors to move kinase substrates and coupling factors, including LAT and Vav, into the T cell/APC contact region may contribute to the decline with age in NF-ATc-dependent gene expression, and thus to defects in T cell clonal expansion.

Actins↗
PubMed2000

Program for testing biological interventions to promote healthy aging.

The National Institute on Aging (NIA) sponsored a workshop on September, 1999 to discuss the feasibility of establishing a program to evaluate potential intervention strategies to decelerate the rate of aging in mammals. The ultimate goal is to identify promising interventions in animals that might lead to clinical trials in humans. The participants discussed various animal models, biological endpoints and possible structure of such a program. The ability to implement such a program will require a decision by NIA staff about whether the anticipated benefits to be derived from identification of effective interventions under well controlled conditions in an animal model, in this case the mouse, would justify the anticipated cost of the testing program.

Aging↗
PubMed2000

Altered composition of the immunological synapse in an anergic, age-dependent memory T cell subset.

In young mice, memory CD4 T lymphocytes with high P-glycoprotein activity (P-gp(high)) are unresponsive to TCR stimulation in vitro but can be activated by PMA plus ionomycin. The proportion of these hyporesponsive cells increases considerably with age. The earliest events in T cell activation were studied in P-gp(high) and P-gp(low) CD4 memory cells at the single-cell level using confocal immunofluorescence methods. Recruitment of both linker for activation of T cells (LAT) and protein kinase C-theta to the immunological synapse, i.e., the site of T cell interaction with stimulator cells, was greatly impaired in P-gp(high) cells from both young and old mice. Translocation of NF-AT to the nucleus, CD69 expression, and proliferative capacity were also diminished to a similar extent in P-gp(high) cells under the same activation conditions. In contrast, movement of c-Cbl to the synapse region occurred in a high proportion of CD4 memory T cells regardless of P-gp subset or age. Moreover, although P-gp(low) cells frequently recruited both c-Cbl and LAT to the APC synapse, cells in the less responsive P-gp(high) subset frequently relocated c-Cbl, but not LAT, to the interface region. In some systems, c-Cbl can act as a negative regulator of receptor-dependent tyrosine kinases, and alterations of c-Cbl to LAT ratios in the P-gp(high) subset may thus contribute to the hyporesponsiveness of this age-dependent, anergic memory cell population.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Texaphyrins: new drugs with diverse clinical applications in radiation and photodynamic therapy.

The texaphyrins are quintessential metal-coordinating expanded porphyrins. They constitute a new series of synthetic porphyrin analogues that show promise as drugs for use in a range of medical therapies. Currently, two different water-solubilized lanthanide(III) texaphyrin complexes, namely the gadolinium(III) and lutetium(III) derivatives 1 and 2 (Gd-Tex and Lu-Tex, respectively), are being tested clinically. The first of these, XCYTRIN, is in a pivotal Phase III clinical trial as a potential enhancer of radiation therapy for patients with metastatic cancers to the brain receiving whole brain radiation therapy. The second, in various formulations, is being tested as a photosensitizer for use in: (i) the photodynamic treatment of recurrent breast cancer (LUTRIN; Phase II clinical trials complete), (ii) photoangioplastic reduction of atherosclerosis involving peripheral arteries (ANTRIN; now in Phase II testing), and (iii) light-based treatment of age-related macular degeneration (OPTRIN; currently in Phase I clinical trials), a vision-threatening disease of the retina. Taken in concert, these two metallotexaphyrins provide a powerful new class of experimental drugs whose diverse potential utility is abetted by a combination of well-optimized physical features, favorable tissue biolocalization characteristics, and novel mechanisms of action. Interestingly, these mechanisms may alter conventional wisdom regarding mechanisms of radiation therapy and the pathophysiology of atherosclerosis.

Arteriosclerosis↗
PubMed2000

A practical and efficient preparation of the releasable naphthosultam side chain of a novel anti-MRSA carbapenem.

A practical large-scale synthesis of the naphthosultam-based side chain of the anti-MRSA antibiotic 1 has been achieved in 29% overall yield over seven steps from 1-methylnaphthalene. The synthesis was completed without the use of protecting groups, featuring a novel naphthosultam annelation, a chemoselective acid-catalyzed triflation, and the use of a novel naphthosultam dianion to effect functionalization through benzylic metalation.

Bridged Bicyclo Compounds, Heterocyclic↗
PubMed2000

Effect of aging on T lymphocyte activation.

Studies of the early stages of T-cell activation reveal that T cells from aged mice show multiple abnormalities within the first few minutes after stimulation, including decline in the activation of the Raf-1/MEK/ERK kinases and in JNK protein kinase. Zap-70 kinase associated with the CD3zeta chain shows a 2-fold increase with age in resting CD4 T cells, despite a three-fold decline with age in the levels of tyrosine phosphorylation of CD3zeta; nonetheless, there is no effect of aging on Zap-70 kinase function in activated T cells as measured by in vitro kinase methods. Age-related impairment of the translocation of PKC&theta; from cytoplasm to the site of T-cell interaction with antigen-presenting cells may underlie downstream defects in the activation cascade.

Aging↗
PubMed2000

Altered development of intestinal intraepithelial lymphocytes in P-glycoprotein-deficient mice.

Intraepithelial lymphocytes (IEL) that reside in the intestinal epithelium are known to exhibit phenotypic and functional characteristics that are distinct from other T cells. We have recently shown that peripheral T cells exclusively express an isoform of P-glycoprotein (P-gp) encoded by the mdr1a gene, but do not require mdr1a expression for normal proliferative, cytokine, or cytotoxic responses. In the present study, we have used mdr1-type knockout (KO) mice to demonstrate that IEL also utilize mdr1a, but only preferentially, in that the mdr1b isoform can be expressed in the absence of mdr1a expression. We also report that a high level of P-gp activity appears to be necessary for the normal development of certain IEL subpopulations. In specific, while the total number of IEL was relatively unaffected by the absence of mdr1a expression, the proportions of CD8 alpha beta and TCR alpha beta+ IEL increased significantly in mdr1a and mdr1a/b KO mice at the expense of CD8 alpha alpha and TCR gamma delta+ IEL, respectively. Moreover, these subset alterations also appeared to have functional consequences, in that proliferative, IL-2, and IFN-gamma responses of IEL from KO mice were distinct from those of normal IEL. In summary, our data suggest that mdr1a expression is required for the development of certain IEL subpopulations, most notably TCR gamma delta+ cells, and thereby indirectly influences the balance of T cell subsets in the intestinal epithelium.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2000

Pigmented squamous cell carcinoma of the skin: morphologic and immunohistochemical study of five cases.

Invasive pigmented squamous cell carcinoma (PSCC) of the skin is reportedly rare. Herein, we evaluate an additional five cases and compare their relative frequency with non-pigmented squamous cell carcinoma (SCC). Of 46,791 archived cases of SCC, a total of five cases of PSCC were discovered for a relative frequency of approximately 0.01%. Grossly, each tumor presented as a rapidly growing crusted papule on actinic damaged skin of the face. Microscopically, all were composed of a mixture of keratininized squamous cells and melanin-producing dendritic melanocytes. The squamous cells stained for epithelial membrane antigen, and both low and high molecular keratins. The melanocytes stained for S-100 and HMB-45. A matched series of 31 SCCs were subjected to an identical immunohistochemical battery of stains to determine if a histologically subtle and unsuspected number of intratumoral melanocytes existed in SCC. Each of the cases failed to show intratumoral melanocytes. The differential diagnosis and possible histogenesis of PSCC is discussed and the importance of extensive pathologic examination to prevent misdiagnosis is emphasized. Despite the histologic dissimilarity, the long-term prognosis of the reported cases was similar to conventional SCC.

Aged↗
PubMed2000

Telomere diminution as a cause of immune failure in old age: an unfashionable demurral.

The hypothesis that cellular proliferation leads to telomere shortening, which in turn leads to replicative failure, which in turn leads to a failure of immune function in aged individuals, is here evaluated against the published evidence about the nature and pace of immune decline in animals and humans. Although the evidence is strong that telomere shortening in late-passage human lymphocyte and non-lymphocytic cell lines induces a state in which the cells can no longer divide, there is no compelling evidence to suggest that replicative senescence of this kind is an important contributor to immune deficiency in old age. On the contrary, the accelerated pace of immune decline in mice and rats, whose telomeres are much longer than those of humans, argues strongly that the factors that pace age-dependent immune decline do not include telomere shortening. In addition, three subsidiary arguments - (a) the decline with age in naive T cell proliferation despite their relatively long telomeres; (b) the preservation of T cell proliferation in Werner's syndrome patients despite their cell lines' proclivity to replicative senescence in vitro; and (c) the ability of PMA and ionomycin to stimulate proliferation in T cells from old donors, but not in late-passage T celt lines - all support the conclusion that aging of the immune system in living animals is not a consequence of the kind of replicative senescence typically caused by short telomeres in vitro.

Aging↗
PubMed2000

Principles of animal use for gerontological research.

This essay presents some practical advice and suggestions for those who wish to use mice and rats in experiments on the biology of aging. Ten principles set forth guidance on choice of ages, choice of stocks, the importance of specific pathogen-free status, the uses of necropsy data, the dangers of pooling samples from different individuals, planning ahead for loss of aged mice to death and disease, the use of cost-adjusted power calculations, and the dangers of inferring causal associations from correlated age effects.

Aging↗