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Biomedical subjects

D L Miller

Publications and source records attributed to D L Miller.

At least 199 records · Page 11Linked to original sources
PubMed1994

Fatigue in operational settings: examples from the aviation environment.

The need for 24-h operations creates nonstandard and altered work schedules that can lead to cumulative sleep loss and circadian disruption. These factors can lead to fatigue and sleepiness and affect performance and productivity on the job. The approach, research, and results of the NASA Ames Fatigue Countermeasures Program are described to illustrate one attempt to address these issues in the aviation environment. The scientific and operational relevance of these factors is discussed, and provocative issues for future research are presented.

Aerospace Medicine↗
PubMed1994

The use of goal setting and contingency contracting for improving children's homework performance.

We examined the effects of goal setting and contingency contracting on children's homework performance. Subjects were 4 parent-child dyads in which the child exhibited substantial homework problems. Using a combination of multiple baseline and reversal (ABAB) designs, goal setting and contingency contracting produced significant improvements in children's homework accuracy. Two of the 4 subjects showed substantial improvements in on-task behavior. Consumer satisfaction with the procedures was supported by parent ratings conducted posttreatment.

Attention↗
PubMed1994

Emergence of MCF-7 cells overexpressing a transfected epidermal growth factor receptor (EGFR) under estrogen-depleted conditions: evidence for a role of EGFR in breast cancer growth and progression.

Overexpression of epidermal growth factor receptor (EGFR) is correlated with loss of estrogen receptor and poor prognosis in breast cancer. To investigate this phenomenon, we transfected a cytomegalovirus expression vector directing the expression of EGFR into estrogen receptor-positive MCF-7 breast cancer cells and into a clone of MCF-7 cells previously transfected with transforming growth factor alpha. Cells arising from single clones or pooled polyclonal populations maintained in charcoal-stripped calf serum, a medium devoid of estrogen, overexpressed EGFR. Switching these cells to a medium containing fetal calf serum or charcoal-stripped calf serum plus 17 beta-estradiol resulted in the emergence of a population expressing low EGFR levels. Loss of expression was not a consequence of nonspecific repression of the cytomegalovirus promoter, because expression of the fibroblast growth factor (FGF)-4 complementary DNA in a similar vector was not lost in fetal calf serum. While loss of EGFR overexpression in fetal calf serum was seen at both the protein and mRNA levels, Southern blotting shows that this was not due to loss of the transfected gene. Subclones of a cell population with low EGFR expression were capable of increasing expression upon estrogen withdrawal, demonstrating that the changes in EGFR expression were reversible and suggesting a growth advantage conferred by EGFR overexpression under these restrictive growth conditions. Overexpression of EGFR did not result in loss of ER expression. These results suggest a role for overexpression of EGFR in the growth of estrogen receptor-positive breast cancer cells in the absence of estrogen.

Animals↗
PubMed1994

The expression and processing of human beta-amyloid peptide precursors in Saccharomyces cerevisiae: evidence for a novel endopeptidase in the yeast secretory system.

In mammalian cells, the transmembrane beta-amyloid peptide precursor (beta-APP) undergoes a complex series of alternative proteolytic processing steps that result in the secretion of varying proportions of its extra-cellular domain (protease nexin II) and beta-amyloid peptide. The protein is also reinternalized and degraded in the endosomal-lysosomal system. The relative efficiencies of these competing processes determine the yield of beta-amyloid peptide. Several proteases have been implicated in this complex processing pathway, although none has been identified to date. The yeast secretory system contains proteases homologous to mammalian pro-hormone convertases and is susceptible to genetic manipulation. We therefore investigated the expression and processing of the beta-amyloid peptide precursors (beta-APP-695 and beta-APP-751) in Saccharomyces cerevisiae transformed with human beta-APP cDNA's. beta-APP (695 or 751) cDNA either with its authentic signal sequence or the yeast-derived prepro-alpha-factor leader, was inserted into a glucose-regulated expression vector and transfected into a protease-deficient yeast strain. In all instances, expression of beta-APP was about 1% of total protein. Protease protection studies indicated that either the natural human signal sequence or the alpha-factor leader sequence targetted beta-APP to the endoplasmic reticulum and inserted it with the amino-terminal domain in the lumen. All of the beta-APP fused to the alpha-factor leader proceeded to the trans-Golgi, where Kex2 endopeptidase removed the leader and released the normal amino-terminus of beta-APP. About one-half of the beta-APP was also cleaved at the "alpha-secretase" site in the middle of the beta-peptide sequence, 12 residues before the membrane-spanning sequence. A fraction of the alpha-secretase-cleaved beta-APP appeared in the culture medium; however, most of it associated with the exterior of the cells. The carboxyl-terminal fragments formed by cleavage at the alpha-secretase site accumulated in the membranes. Other proteolytic processes generated membrane-associated carboxyl-terminal fragments that also resembled those found in mammalian cells. These results indicate that the secretory system of S. cerevisiae possesses proteases with specificities similar to the mammalian enzymes that process beta-APP.

Amino Acid Sequence↗
PubMed1993

Factors influencing physicians in recommending in-hospital cardiopulmonary resuscitation.

BACKGROUND: Cardiopulmonary resuscitation (CPR) is a dramatic, costly, and often futile intervention whose appropriate use is under scrutiny. Physicians often ask patients and families to make decisions about resuscitation for themselves or loved ones. Clinical variables and personal beliefs may influence physician recommendations about CPR. METHODS: Physicians (N = 451) at a tertiary care hospital were surveyed to determine the following: (1) the factors they consider when recommending in-hospital CPR, (2) the conditions under which they discuss CPR with patients, (3) their recent participation in CPR attempts, (4) their perceptions of its effectiveness, (5) their personal wishes regarding their own resuscitation, and (6) their personal and professional characteristics. RESULTS: The patient's self-reported wishes about resuscitation and physician judgment of medical utility were the most important influences on physician recommendations. Most physicians believe that patients with metastatic cancer or late Alzheimer's disease should not be resuscitated. Age alone was not viewed as an important clinical consideration. Guidance from hospital policies and ethics committees had the least influence on physicians. Physicians overestimated the likelihood of survival to hospital discharge after in-hospital CPR by as much as 300% for some clinical situations and predicted an overall success rate of 30%. CONCLUSION: These findings suggest that most physicians are thoughtful and discriminating in their recommendations to patients about CPR. Patient's wishes are of paramount importance, followed by physician judgment of medical utility. However, physicians do overestimate the efficacy of CPR and may thus misrepresent the potential utility of this therapy to patients and their families.

Adult↗
PubMed1993

Prostitution and risk of HIV: female prostitutes in London.

OBJECTIVE: To measure the prevalence of HIV and to describe established risk factors in female prostitutes. DESIGN: A cross sectional survey. SETTING: A genitourinary medicine clinic, streets, and magistrates' courts in London. SUBJECTS: 280 female prostitutes recruited between April 1989 and August 1991. MAIN OUTCOME MEASURES: Infection with HIV-1, reported risk behaviours, and prevalence of sexually transmitted infections. RESULTS: 228 of the women had HIV tests, and two (0.9% (95% confidence interval 0% to 2.1%)) were infected with HIV-1. Reported use of condoms was high for commercial clients and low for non-paying partners: 98% (251/255) of women used condoms with all clients and 12% (25/207) with non-paying partners for vaginal intercourse. Twenty two women were current or past injecting drug users. Of the 193 women examined for sexually transmitted infections, 27 had an acute infection (gonorrhoea, chlamydia, trichomonas, or primary genital herpes) at the time of interview. Infection was associated with younger age and increasing numbers of non-paying sexual partners, but not with duration of prostitution, numbers of clients, or reports of condom failures. When age and numbers of non-paying partners were analysed by logistic regression they remained significantly associated with sexually transmitted infections. CONCLUSIONS: A large and diverse sample of prostitutes had a low prevalence of infection with HIV and high levels of use of condoms in commercial sex. There was a significant risk of other sexually transmitted infections associated with prostitutes' non-commercial sexual relationships, in which unprotected sex is common. Interventions to reduce the risk of sexually transmitted infections in prostitutes should address both commercial and non-commercial sexual partnerships.

Acquired Immunodeficiency Syndrome↗
PubMed1993

Interaction between the beta-amyloid peptide precursor and histones.

The function of the beta-amyloid peptide precursors (beta-APPs) remains undefined. In a search for ligands of beta-APP we found that the most prominent beta-APP-binding proteins were histones. To measure the specificity of binding the secreted or extracellular form of beta-APP(751), beta-APP-S, was purified from recombinant baculovirus-infected Sf-9 cells and was labeled with iodine-125. The labeled beta-APP-S bound to each of the histones, which had previously been adsorbed to nitrocellulose membranes. Differences in their apparent affinities were small. beta-APP-S did not bind to histones incorporated into chromatin. beta-APP-S bound relatively weakly to fibronectin, laminin, collagen type I, or collagen type IV. It did not bind to other basic proteins tested, myelin basic protein, or cytochrome c. The beta-APP-S-histone complex adhered to most filters and gel media, which precluded a direct determination of its stability. The apparent dissociation constant of beta-APP-S bound to histone-4-Sepharose was about 30 nM. Although beta-APP normally does not contact histones, it may bind those that are released from damaged cells. A function of beta-APP may be to bind and recycle substances such as histones, proteases, and matrix proteins from the extracellular medium.

Amyloid beta-Protein Precursor↗
PubMed1993

A system for studying the effect(s) of familial Alzheimer disease mutations on the processing of the beta-amyloid peptide precursor.

Three different point mutations have been observed in some familial Alzheimer's disease pedigrees at a unique valine, Val717, near the carboxyl end of the beta Amyloid Peptide Precursor (beta APP). The effects of these mutations on the processing and cellular functions of beta APP can best be determined in the absence of the normal form(s) of the protein. We have used targeted mRNA degradation by a trans-acting hammerhead ribozyme to cleave and inactivate beta APP expression in vitro. The consensus ribozyme cleavage site, 5'GUC decreases X3, matches the Val717 nucleotide sequence in beta APP mRNA. Introduction of FAD point mutations which change Val717 decrease the rate of ribozyme cleavage by more than three orders of magnitude. Thus, ribozyme targeting of this site should allow the study of protein processing in vivo. Furthermore, a ribozyme targeted to mutant beta APP mRNA (Val717-->Ile) cleaved the mutant sequence 300-fold faster than the normal sequence. This suggests that ribozymes might lower mutant beta APP mRNA levels in FAD cells.

Alzheimer Disease↗
PubMed1993

Peptide compositions of the cerebrovascular and senile plaque core amyloid deposits of Alzheimer's disease.

The pathological findings of Alzheimer's disease include amyloid deposition in cerebral blood vessels and in senile plaques. Both deposits are known to include peptides that contain a common sequence. Both forms of amyloid were isolated and their peptide compositions were determined. The peptides were resolved by size-exclusion chromatography in 70% formic acid, and reverse-phase chromatography in 60% formic acid, 0-40% acetonitrile. Senile plaque amyloid cores contain about 25% protein, about 70% of which is composed of peptides containing the beta-amyloid sequence. Amino-terminal sequencing of the core amyloid peptides (CAPs) revealed extensive amino-terminal heterogeneity, with variable amounts of blocked amino termini. Matrix-assisted, laser-desorption-time-of-flight mass spectrometry of the CAP mixture revealed an array of peptides the molecular weights of which corresponded to peptides beginning with each of the first 11 amino acids of the beta-peptide sequence and ending with Ala-42 of that sequence. The carboxyl-terminal residues were identified by tandem mass spectrometry of chymotrypsin digests. CAP possessed a minor degree of carboxyl-terminal heterogeneity. Cerebrovascular amyloid peptides (CVAPs) possessed minor degrees of both amino- and carboxyl-terminal heterogeneity. The major CVAP commenced at Asp-1 and ended at Val-40. Minor components of CAP possessed masses of 8000-9000 Da and the same amino-terminal residues as the major components of CAP. They may be precursors to the smaller CAPs. The differences in amino termini and carboxyl termini of CAPs and CVAPs suggest that the two types of amyloid form by different pathways, on which they encounter different proteases.

Alzheimer Disease↗
PubMed1993

Biological, physical, and electrical parameters for in vitro studies with ELF magnetic and electric fields: a primer.

This paper presents material which is intended to assist researchers in identifying and controlling a range of biological, electrical, and other physical parameters that can affect the outcome of in vitro studies with extremely low frequency (ELF) magnetic and electric fields. Brief descriptions of power line magnetic and electric fields are provided and methods for the generation of 60 Hz as well as other ELF fields in the laboratory are surveyed. Methods for calculating and measuring exposure parameters in culture medium are also described. Relating in vitro and internal in vivo exposure conditions across different animal species is discussed to aid researchers in selecting levels of field exposure. The text is purposely elementary, and sometimes brief, with references provided to aid the interested reader in obtaining a fuller understanding of the many topics. Because the range of experimental parameters that can influence the outcome of in vitro studies with ELF fields is so broad, a multidisciplinary approach is normally required to carry out the research.

Animals↗
PubMed1993

Novel cleavage of a hammerhead ribozyme targeted to beta-amyloid peptide precursor mRNA.

A trans-acting hammerhead ribozyme (D0) was designed to cleave at the first GUC decreases X target sequence in Alzheimer amyloid precursor (beta APP) mRNA. A synthetic 26-base substrate analog of beta APP mRNA, labeled with either [alpha-32P]CTP or [alpha-35S]CTP underwent Mg(+2)-dependent, site-specific cleavage in vitro. Cleavage was found to occur at two sites. The major product of the reaction, a 13-base oligonucleotide, resulted from cleavage at the consensus cut site of hammerhead ribozymes. A minor 12-base product was formed by cleavage one base 5' to this site. When the beta APP substrate analog was labeled with [alpha-35S]ATP (Rp isomer) another cleavage site, amounting to 25-30% of the total product formed, was also activated. A series of ribozyme deletion mutants delimited the new cleavage site to the phosphate linkage 5' to the G residue of the hammerhead consensus cut site, GUC decreases X. We conclude that small changes in RNA conformation can dramatically alter ribozyme specificity in vitro. This may have implications for targeting hammerhead ribozymes in vivo.

Amyloid beta-Protein Precursor↗
PubMed1993

A metabolic view of receptor activation in cultured cells following cryopreservation.

The effect of cryopreservation on agonist-induced receptor activation in mammalian cells was investigated with the Cytosensor microphysiometer, a biosensor that monitors cellular metabolic activity by measuring changes in extracellular pH. In this study, two different cell types--nonadherent TF-1 cells (from a human erythroleukemia patient) and adherent WT3 cells (CHO-K1 cells transfected with the m1 muscarinic acetylcholine receptor)--were cryopreserved by freezing in a disposable cell capsule used in the microphysiometer. The recovery of metabolic activity by TF-1 cells was observed over approximately 1 h following thawing. Responses of the TF-1 cells to granulocyte-macrophage colony-stimulating factor (GM-CSF) and platelet activating factor (PAF) were measured before cryopreservation and 90 min after thawing. The GM-CSF and PAF responses retained 71 +/- 14% and 73 +/- 10% of maximum stimulation, respectively. Post-thaw cholinergic stimulation of WT3 cells was 73 +/- 9% of its level in similarly treated but unfrozen cells. Cryopreservation caused no detectable difference in desensitization of the response due to repeated application of carbachol. These results demonstrate the feasibility of pharmacological studies with cryopreserved cells in the microphysiometer and further suggest that the microphysiometer may be useful in exploring the biological consequences of cryopreservation in the early post-thaw period.

Animals↗
PubMed1993

A comparison of hemolytic and sonochemical activity of ultrasonic cavitation in a rotating tube.

Biological effects of in vitro ultrasonic exposure may result from mechanical and from sonochemical mechanisms related to ultrasonic cavitation. Mechanical cell lysis by 1.61 MHz ultrasonic cavitation was assessed in a rotating tube exposure system by hemolysis measurements. Free radical generation was assessed by the terephthalic acid dosimeter, calibrated by gamma-ray dosage. Sonochemical production was assessed by measuring residual hydrogen peroxide using the sensitive isoluminol method. Exposure conditions were similar for all tests, except longer durations were needed for the free radical and hydrogen peroxide tests. The sonochemical mechanisms were relatively more important for increasing intensity, and increasing temperature. Increasing rotation speed or bubbling with argon before exposure enhanced all cavitation activity. Stopping the rotation reduced all cavitation activity. Burst-mode ultrasound (10.5 microseconds bursts, 1:1 or 1:3 duty cycle) reduced cavitation activity, but gave relatively greater sonochemical activity under some conditions. These results indicate that the mechanical and sonochemical mechanisms can be separately favored to some extent by varying exposure conditions. The observed trends should be helpful for selecting exposure conditions favorable for studying bioeffects of the sonochemical mechanism.

Erythrocytes↗