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Biomedical subjects

R M Williams

Publications and source records attributed to R M Williams.

At least 73 records · Page 4Linked to original sources
PubMed1997

FR900482, a close cousin of mitomycin C that exploits mitosene-based DNA cross-linking.

BACKGROUND: The class of antitumor antibiotics that includes FR900482 has a very close structural analogy to the mitomycins, one of which, mitomycin C, has been in widespread clinical use for more than 20 years. Like mitomycin C, these antitumor antibiotics are reductively activated in vivo and covalently cross-link DNA as a result of activity of the mitosene moiety generated on reduction. Owing to differences in structure and the attendant mechanistic differences in bioreductive activation between the mitomycins and FR900482, FR900482 does not produce an adventitious superoxide radical anion during reductive activation and thus does not exhibit oxidative strand scission of DNA. It is postulated that the low clinical toxicity of FR900482 relative to mitomycin C is a direct manifestation of the mechanistic differences of bioreductive activation leading to the highly reactive DNA cross-linking mitosenes. RESULTS: Using Fe(II)-EDTA footprinting, we showed that the two natural products FR900482 (1) and dihydro, FR66979 (3), and the semi-synthetically derived triacetate FK973 (2), display remarkable selectivity for 5' deoxy-CG sequences of DNA, and that this selectivity is abolished upon deletion of the exocyclic N2 amine of either participating guanosine residue. In addition, we investigated the mono alkylation abilities of FR66979 with respect to a number of inosine-substituted oligonucleotides and observed that the FR900482 class of compounds were able to give rise to easily separable orientation isomers of their respective cross-links. CONCLUSIONS: The FR900482 class of antitumor antibiotics cross-link DNA in a fashion analogous to the mitomycins. The cross-linking reaction yields two orientation isomers which are of vastly different electrophoretic mobility and which also exhibit radically different DNA-protein recognition properties upon reaction with AluI restriction endonuclease. In addition, mono-alkylation of DNA by FR66979 shows little, if any, dependence upon pre-covalent interactions deemed necessary for the mitomycins. These insights support the proposal that the FR900482 class of compounds represents a compelling clinical replacement for mitomycin C, given its greatly reduced host toxicity and superior DNA interstrand cross-linking efficacy.

Alkylation↗
PubMed1997

Progress notes model.

The largest part of the medical record today consists of notes documenting the care delivered to patients and the clinical events relevant to diagnosis and treatment. These "progress notes" serve as the repository of medical facts and clinical thinking, and are intended as a concise vehicle of communication about a patient's condition to those who access the health record. They should be readable, easily understood, complete, accurate, and concise. They must also be flexible enough to logically convey to others what happened during an encounter, e.g., the chain of events during the visit, as well as guaranteeing full accountability for documented material, e.g., who recorded the information and when it was recorded. This paper describes a model for progress notes, which addresses the above needs, and outlines the rationale and principles which led to that model.

Documentation↗
PubMed1996

Secretion and serotonin release in the isolated rat lacrimal gland: the effects of substance P and calcitonin gene-related peptide.

A close anatomical relationship between nerves containing substance P and calcitonin gene-related peptide (CGRP) and mast cells containing serotonin has been demonstrated in the rat lacrimal gland. This study investigates the potential for peptidergic regulation of lacrimal mast cells by examining the actions of substance P, CGRP and serotonin on protein and peroxidase secretion from isolated lacrimal segments and on substance P and CGRP to release serotonin from the lacrimal mast cells. Substance P, CGRP and serotonin evoked marked increases in total protein and peroxidase from the lacrimal. Sodium cromoglycate, a mast cell stabilizer, significantly reduced or blocked the secretory responses elicited by these agonists. Chromatographic analysis using electrochemical detection revealed that substance P, but not CGRP, augmented the release of serotonin from the gland. The substance P evoked peroxidase secretion and serotonin release was blocked by CGRP and by sodium cromoglycate. These results support a role for mast cells in the regulation of lacrimal secretion and suggest a novel regulatory interaction between substance P and CGRP in the control of lacrimal function through a neuro-immune interaction.

Animals↗
PubMed1996

Multiphoton fluorescence excitation: new spectral windows for biological nonlinear microscopy.

Intrinsic, three-dimensionally resolved, microscopic imaging of dynamical structures and biochemical processes in living preparations has been realized by nonlinear laser scanning fluorescence microscopy. The search for useful two-photon and three-photon excitation spectra, motivated by the emergence of nonlinear microscopy as a powerful biophysical instrument, has now discovered a virtual artist's palette of chemical indicators, fluorescent markers, and native biological fluorophores, including NADH, flavins, and green fluorescent proteins, that are applicable to living biological preparations. More than 25 two-photon excitation spectra of ultraviolet and visible absorbing molecules reveal useful cross sections, some conveniently blue-shifted, for near-infrared absorption. Measurements of three-photon fluorophore excitation spectra now define alternative windows at relatively benign wavelengths to excite deeper ultraviolet fluorophores. The inherent optical sectioning capability of nonlinear excitation provides three-dimensional resolution for imaging and avoids out-of-focus background and photodamage. Here, the measured nonlinear excitation spectra and their photophysical characteristics that empower nonlinear laser microscopy for biological imaging are described.

Animals↗
PubMed1996

Orientation of functional activating regions in the Escherichia coli CRP protein during transcription activation at class II promoters.

At class II CRP-dependent promoters the DNA site for CRP overlaps the DNA site for RNA polymerase, covering the -35 region. Transcription activation at class II CRP- dependent promoters requires a contact between an activating region in the upstream subunit of the bound CRP dimer and a contact site in the C-terminal domain of the alpha-subunit of RNA polymerase. Transcription activation is suppressed by amino acid substitutions in the activating region, but activation can be restored by second site substitutions at K52 or E96. These substitutions identify two separate regions on the surface of CRP that appear to be able to interact with RNA polymerase specifically at class II promoters. Using the method of 'oriented heterodimers' we show that these alternative activating regions are functional in the downstream subunit of the bound CRP dimer.

Bacterial Proteins↗
PubMed1996

The costs of visits to emergency departments.

BACKGROUND: Many visits to emergency departments are for minor medical problems, and these visits are criticized as being expensive and economically inefficient. This study examines the marginal costs (the extra costs for an additional visit) of emergency department visits. METHODS: Monthly data on the costs of hospital and physicians' services from 1991 through 1993 were obtained from a sample of six community hospitals in Michigan. The data were analyzed with ordinary least-squares regression techniques to determine the ratio of marginal to average costs. Average and marginal costs were then determined for 24,010 visits during 12 randomly selected weeks in 1993. A visit by an individual patient was the unit analysis, and visits were classified as nonurgent, semiurgent, or urgent according to explicit criteria. Costs and charges were determined for all visits and were classified according to the degree of urgency. RESULTS: For all emergency department visits, the average charge was $383, the average cost was $209, and the marginal cost was $88 (42 percent of the average cost). Thirty-two percent of the visits were classified as nonurgent, 26 percent as semiurgent, and 42 percent as urgent. For nonurgent visits, the average charge was $124, the average cost was $62, and the marginal cost was only $24. For semiurgent visits, the average charge was $312, the average cost was $159, and the marginal cost was $67. For urgent visits, the average charge was $621, the average cost was $351, and the marginal cost was $148. CONCLUSIONS: The true costs of nonurgent care in the emergency department are relatively low. The potential savings from a diversion of nonurgent visits to private physicians' offices may therefore be much less than is widely believed.

Adolescent↗
PubMed1996

Real time measurements of elongation by a reverse transcriptase using surface plasmon resonance.

A rapid direct assay for polymerase-induced elongation along a given template is an obligate requirement for understanding the processivity of polymerization and the mode of action of drugs and inhibitors on this process. Surface plasmon resonance can be used to follow the association and the dissociation rates of a given reverse transcriptase on DNA.RNA and DNA.DNA hybrids immobilized on a biotin-streptavidin surface. The addition of nucleotides complementary to the template strand produces an increase in the local mass, as deduced from an increase in the measured signal, due to elongation of the primer strand that allows an estimation of both the extent and rate of the polymerization process. The terminator drug 3'-deoxy-3'-azidothymidine triphosphate completely abolishes the increase in signal as would be expected from an inhibition of elongation. This technique provides a sensitive assay for the affinities of different polymerases for specific templates and for the effects of terminators of the elongation process.

Bacterial Proteins↗
PubMed1996

Distribution of emergency department costs.

STUDY OBJECTIVE: To report the distribution of emergency department costs by category of expense and level of patient urgency. METHODS: Cost-to-charge and relative-value methods were used to determine direct and indirect physician, facility, supply, pharmacy, laboratory, radiology, and miscellaneous costs for 24,010 ED patients. Explicit criteria were used to classify patient visits as nonurgent, semiurgent, or urgent. RESULTS: For all patients, the average costs were physician, $64; facility, $84; laboratory, $21; radiology, $24, and total, $209. Laboratory and radiology costs accounted for 5% of the total costs for nonurgent visits and 23% of the total costs for urgent visits. CONCLUSION: The distribution of ED costs varies significantly according to the urgency of the medical condition. For nonurgent patient visits, most costs are represented by the hospital facility and ED physicians' costs. Ancillary services represent a much greater proportion of costs for patients with urgent conditions. Although reduced test-ordering might result in some savings among patients with urgent conditions, overall improved cost efficiency can be achieved only through reductions in the fixed costs of operation of hospital EDs.

Ancillary Services, Hospital↗
PubMed1996

Cytochrome P450-catalyzed hydroxylation of taxa-4(5),11(12)-diene to taxa-4(20),11(12)-dien-5alpha-ol: the first oxygenation step in taxol biosynthesis.

BACKGROUND: The structural complexity of taxol dictates continued reliance on biological production methods, which may be improved by a detailed understanding of taxol biosynthesis, especially the rate-limiting steps. The biosynthesis of taxol involves the cyclization of the common isoprenoid intermediate geranylgeranyl diphosphate to taxa-4(5), 11(2)-diene followed by extensive, largely oxidative, modification of this diterpene olefin. We set out to define the first oxygenation step in taxol biosynthesis. RESULTS: Microsomal enzymes from Taxus stem and cultured cells were used to define the first hydroxylation of taxadiene. We confirmed the structure of the reaction product (taxa-4(20), 11(12)-dien-5alpha-ol) by synthesizing this compound. The responsible biological catalyst was characterized as a cytochrome P450 (heme thiolate protein). In vivo studies confirmed that taxadienol is a biosynthetic intermediate and indicated that the hydroxylation step that produces this product is slow relative to subsequent metabolic transformations. CONCLUSIONS: The structure of the first oxygenated intermediate on the taxol pathway establishes that the hydroxylation reaction proceeds with an unusual double bond migration that limits the mechanistic possibilities for subsequent elaboration of the oxetane moiety of taxol. The reaction is catalyzed by a cytochrome P450, suggesting that the seven remaining oxygenation steps in taxol biosynthesis may involve similar catalysts. Because the first oxygenation step is slow relative to subsequent metabolic transformations, it may be possible to speed taxol biosynthesis by isolating and manipulating the gene for the taxadiene-5-hydroxylase that catalyzes this reaction.

Alkenes↗
PubMed1996

Probing the structure, function, and interactions of the Escherichia coli H-NS and StpA proteins by using dominant negative derivatives.

Twelve different dominant negative mutants of the Escherichia coli nucleoid-associated protein, H-NS, have been selected and characterized in vivo. The mutants are all severely defective in promoter repression activity in a strain lacking H-NS, and they all disrupt the repression normally exerted by H-NS at two of its target promoters. From the locations of the alterations in these mutants, which result in both large truncations and amino acid substitutions, we propose that H-NAS contains at least two distinct domains. The in vitro protein-protein cross-linking data presented in this report indicate that the proposed N-terminal domain of H-NS has a role in H-NS multimerization. StpA is a protein with known structural and functional homologies to H-NS. We have analyzed the extent of these homologies by constructing and studying StpA mutants predicted to be dominant negative. Our data indicate that the substitutions and deletions found in dominant negative H-NS have similar effects in the context of StpA. We conclude that the domain organizations and functions in StpA and H-NS are closely related. Furthermore, dominant negative H-NS can disrupt the activity of native StpA, and reciprocally, dominant negative StpA can disrupt the activity of native H-NS. We demonstrate that the N-terminal domain of H-NS can be chemically cross-linked to both full-length H-NS and StpA. We account for these observations by proposing that H-NS and StpA have the ability to form hybrid species.

Bacterial Outer Membrane Proteins↗
PubMed1995

Netropsin and spermine conjugates of a water-soluble quinocarcin analog: analysis of sequence-specific DNA interactions.

BACKGROUND: Quinocarcin is the simplest of the bioxalmycin/naphthyridinomycin/tetrazomine/saframycin class of anti-tumor antibiotics, which damage DNA in a process that is inhibited by superoxide dismutase (SOD). The oxazolidine moiety of this class of anti-tumor antibiotics undergoes a redox self-disproportionation reaction of the Cannizzaro type. The reaction is proposed to proceed via an intermediate carbon-centered radical, which then reduces molecular oxygen to give superoxide. We set out to determine whether the DNA-cleavage properties of these anti-tumor antibiotics could be retained in less complex analogs of quinocarcin. RESULTS: A totally synthetic, water-soluble analog of quinocarcin has been prepared. This analog produced superoxide, but had considerably reduced ability to cleave supercoiled circular DNA compared to quinocarcin or tetrazomine. When conjugated to the DNA-binding molecule spermine, however, it cleaved DNA as effectively as quinocarcin at less than 1/10 the concentration. A conjugate with netropsin displayed selective cleavage around the sequence 5'-d(ATTT)-3'. Molecular modeling of the interaction between the conjugate and DNA, together with the pattern of cleavage, indicates that a non-diffusable oxidant is involved in sequence-selective DNA cleavage. The spermine conjugate displayed weak antimicrobial activity. CONCLUSIONS: Knowledge of the stereoelectronic requirements for superoxide production by quinocarcin has allowed us to design a structurally less complex analog which has many of the same physical properties, including water solubility, the ability to produce superoxide and the ability to cleave DNA. Covalently attaching known DNA-binding molecules to this analog gave a compound that produced sequence-specific DNA damage. Our results suggest that a mechanism other than superoxide production can mediate DNA damage by the netropsin conjugate.

Aerobiosis↗
PubMed1995

The future of wellness care.

The current restructuring of the US healthcare system will result in a new emphasis on wellness services. Hospitals are challenged to define the wellness role they will play within managed care. This article reports on interviews with wellness experts and hospital CEOs, who reflect on these challenges and define strategic priorities. The interviews highlight the need to understand that this challenge requires a powerful paradigm shift from illness to preventive services, and a major rethinking of how hospitals operate to offer cost-effective preventive services. The interviewees see great opportunity, but also great need for thorough planning, careful design, and implementation. Hospital leaders must understand clearly what wellness means, and how best to position their hospital for strategic advantage. In the final analysis, wellness emerges as an integral strategy in the overall process of managing change.

Canada↗