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Biomedical subjects

G E Davis

Publications and source records attributed to G E Davis.

At least 37 records · Page 2Linked to original sources
PubMed1999

Induction and alternative splicing of the Bax gene mediated by p53 in a transformed endothelial cell line.

Overexpression of the normal p53 protein in tumor cell lines is known to induce apoptosis and a potential mediator of this response is the apoptotic inducer, Bax. The expression of Bax mRNA products were investigated in the ECV-304 endothelial cell tumor line and primary human umbilical vein endothelial cells (HUVEC) that were induced to overexpress the p53 protein. Induction of p53 in ECV-304 and HUVEC cells was mediated by infection with a p53 recombinant adenovirus (AdCMV-p53). The expression of Bax transcripts in p53-induced cells was investigated by reverse-transcription polymerase chain reaction (RT-PCR). The Bax alpha mRNA species was detected in both ECV-304 and HUVEC cells. Surprisingly, Bax alpha expression was reduced several-fold in ECV-304 endothelial cells overproducing p53 and no change in Bax alpha was detected in HUVEC cells after induction of p53. However, the Bax delta spliced transcript was observed to be induced by p53 in the ECV-304 tumor cell line. Bax alpha was the predominant species expressed in normal human endothelial cells but, in contrast to the immortalized ECV-304 endothelial cell line, induction of p53 failed to alter the expression of Bax alpha or to induce any other Bax transcripts. HUVEC cells were more resistant to p53, since at least 80% of the HUVEC cell population survived the overexpression of p53 after 24 h of infection with AdCMV-p53. An ECV-304-derived cell line (DECV) resistant to p53-mediated apoptosis did not show any changes in expression of Bax mRNA products, even in the presence of high levels of p53. ECV-304 endothelial cells that expressed the Bax delta species underwent apoptosis much more rapidly and more extensively after induction of p53, suggesting that the Bax delta species enhances p53-mediated apoptosis.

Journal Article↗
PubMed1998

Modulation of calcium current in arteriolar smooth muscle by alphav beta3 and alpha5 beta1 integrin ligands.

Vasoactive effects of soluble matrix proteins and integrin-binding peptides on arterioles are mediated by alphav beta3 and alpha5 beta1 integrins. To examine the underlying mechanisms, we measured L-type Ca2+ channel current in arteriolar smooth muscle cells in response to integrin ligands. Whole-cell, inward Ba2+ currents were inhibited after application of soluble cyclic RGD peptide, vitronectin (VN), fibronectin (FN), either of two anti-beta3 integrin antibodies, or monovalent beta3 antibody. With VN or beta3 antibody coated onto microbeads and presented as an insoluble ligand, current was also inhibited. In contrast, beads coated with FN or alpha5 antibody produced significant enhancement of current after bead attachment. Soluble alpha5 antibody had no effect on current but blocked the increase in current evoked by FN-coated beads and enhanced current when applied in combination with an appropriate IgG. The data suggest that alphavbeta3 and alpha5 beta1 integrins are differentially linked through intracellular signaling pathways to the L-type Ca2+ channel and thereby alter control of Ca2+ influx in vascular smooth muscle. This would account for the vasoactive effects of integrin ligands on arterioles and provide a potential mechanism for wound recognition during tissue injury.

Animals↗
PubMed1998

Determining the number of state psychiatric hospital beds by measuring quality of care with artificial neural networks.

This study uses a new paradigm to calculate the minimum and the optimum number of involuntary psychiatric beds at a state hospital in Maine with 5538 admissions over a 7-year period. The method measures quality of care (Q) based upon the accuracy of prediction of length-of-stay for the hospital, and of community length-of-stay for the community, each corrected for the severity of illness of the average patient. When Q in the hospital equals Q in the community, there is no net movement of patients from one phase of care to the other, analogous to a zero electromotive force, and the census at that point is the minimum number of beds (22 beds/100,000 population). When patients in the community were least ill, relative to the hospital then hospital bed census is at its optimum (31 beds/100,000) given current resources and technology. In studying specific diagnosis groups with the same methodology the authors found that patients with schizophrenia having the benefit of clozapine for most of the study period had a Q averaged over 7 years that was nearly equal in both hospital and community settings. This explains the perception that tertiary psychiatric hospitals comprised mostly of patients with schizophrenia can downsize significantly. However, affective disorders and "borderline" personality disorders clearly benefit from structured hospital care with specialized experienced staff. We make arguments for the role of the state hospital as a homeostat for the mental health care delivery system.

Health Services Research↗
PubMed1998

A comparative study of the psychiatric care between locum tenens and staff physicians in a state hospital.

Artificial neural networks (ANNs) were used to measure the quality of care (Q) at two admission units in a state psychiatric hospital, each unit having two treatment teams, one led by a permanent (PM) staff physician, and one led by various locum tenens (LT) physicians. An LT physician's tour of duty (TOD) averaged approximately 30 days. Over nearly a 2 1/2-year period the four treatment teams received 744 admissions. Our previous research has reported measuring Q using percent accurate prediction of hospital length-of-stay (LOS), divided by a measure of severity of patient illness. We calculated Q for each treatment team's test set of patients using a trained ANN for each team. All the teams' test sets were run through each of the trained ANNs resulting in a set of four Q values for each ANN. We defined the standard deviation of Qs resulting from a single team's test set run through it own as well as the other three teams' ANNs as representative of the "diversity" of the patients in that test set. We defined the reciprocal of the standard deviation of the Qs resulting from each of the teams' test sets run through a single team's ANN as that team's "robustness." The product of "robustness" times "diversity" was defined as the value (V) of the treatment team. The V of the PM physician-led teams was 1.9 times that of the LT physician-led teams. We normalized V for patient entropy (uncertainty) with a metric called the "risk ratio" (RR), derived from Boltzmann's law. This resulted in the V/RR of one PM physician-led team as superior, despite treating patients with the highest risk. The LT physician-led teams, despite having fewer patients afflicted with the more problematic diagnosis of schizophrenia, were handicapped by not having preexisting therapeutic relationships with their patients, giving both LT teams low robustness. There was no statistically significant difference in patient LOS between the teams. Because the greatest change in team composition was due to LT physicians, we assumed that the differences in V/RR were due to the short (30-day) TOD and not to any skill deficits in the LT physicians. This article explores a new paradigm which compares the value of patient care in separate delivery systems despite differences in severity of illness, case-mix, and uncertainty associated with an imperfect therapeutic environment.

Adult↗
PubMed1998

Comparing the value of service between a state hospital and a private, for-profit psychiatric hospital: a clarified role for tertiary care.

We apply pattern-recognizing artificial neural networks (ANNs) to the patients of two psychiatric hospitals, a private, for-profit hospital (PH) and a state hospital (SH), both serving the southern tier of Maine (approximately two-thirds of the state's population, i.e., 800,000 persons) over a 19-month period. In our data from the PH, N = 837 admissions, and at the SH, N = 834. Unique patient identifiers were assigned to patients so that their individual patterns of care could be incorporated into our ANNs. We used a previously reported methodology to measure quality of care (Q), and developed a measure of value of service (V) from the patients' perspective for both facilities. A random portion of the demographic and outcome data of patients from each hospital was sequestered as a test set, whereas the remainder was used to train ANNs with length-of-stay (LOS) as an outcome measure. Q, and V normalized for risk (RR), i.e., V/RR, were calculated for each test set, which included multiple admissions of individual patients to each hospital. The methodology for V accounts for the severity of illness with the calculation of a metric called U/G, for the differences in case-mix by exchanging "virtual patients" between ANNs, and for entropy in the health care system by using a metric called the risk ratio (RR). Results showed that V/RR was 2.4 times greater at the SH than at the PH. This advantage is likely due to prior knowledge of individual patient patterns of treatment by the SH's staff. Data sets from each hospital using only single admissions for each patient in the study period (thereby eliminating unique patient patterns of LOS), yielded a V/RR that was only 21% greater at the SH. We hypothesize that this difference is due to the SH's ability to use treatment and discharge based upon patient strengths and level of clinical improvement, unfettered by insurance deadlines. Approximately 5% of the admissions to our studied PH went on to our SH, namely, the most severely impaired and indigent patients. The SH not only had twice the value, but also had half the cost of the PH, despite the greater number of treatment non-responders and non-compliants at the SH. The reasons for this are skilled staff and specialized ancillary services, staff knowledge of patients' responses to previous therapy, and individualized LOSs. These are features that create a caring environment and better compliance with treatment. This study emphasizes the value of tertiary care psychiatric facilities in a comprehensive mental health care delivery system. There are few studies of the effects of excessive downsizing of SHs on the community, but reports from Massachusetts (in 1995) suggest a 79% increase in suicides when the closing of SH beds exceeded 98% of maximum historical census. Routine use of pattern-recognizing tools such as ANNs would serve to inform the public about the value of mental health services so that the most vulnerable in our society are not neglected.

Adolescent↗
PubMed1998

Osteopontin is a ligand for the alpha4beta1 integrin.

Recent work has shown that osteopontin expression is upregulated at sites of cardiovascular injury. It has been hypothesized that osteopontin provides an adhesive matrix for endothelial and smooth muscle cells during remodeling of the vascular wall following injury. Osteopontin has also been found to be synthesized by monocytes and macrophages within injury sites. Here, we present data showing that osteopontin can promote leukocyte adhesion through the alpha4beta1 integrin. In the presence of physiologic concentrations of Mg2+ and Ca2+, osteopontin purified from bovine milk promoted cell-substrate adhesion of HL-60 and Ramos cells, two model leukocyte cell lines. As with other adhesive ligands, adhesion to osteopontin required leukocyte activation. Under these conditions, no adhesion to control substrates such as bovine serum albumin was observed. Leukocyte adhesion was inhibited by anti-integrin antibodies directed at either the alpha4 or beta1 integrin subunits but not by control antibodies directed to other integrins. Further adhesion experiments revealed that leukocyte binding to osteopontin was completely inhibited by an alpha4beta1-binding peptide containing the leucine-aspartate-valine (LDV) sequence, while a control, non-binding peptide containing leucine-glutamate-valine (LEV) had minimal effects. Affinity chromatography using either surface labeled HL-60 or Ramos cell extracts revealed that the alpha4beta1 integrin specifically bound to osteopontin. Immunoprecipitation of eluted fractions from these columns positively identified the alpha4beta1 integrin. In order to localize potential alpha4beta1-binding sites within osteopontin, the protein was proteolytically cleaved with thrombin. A 30 kDa N-terminal osteopontin fragment purified using fast protein liquid chromatography promoted alpha4beta1 dependent leukocyte adhesion in a manner similar to that of the intact protein. These data collectively demonstrate that the alpha4beta1 integrin is a new adhesion receptor for osteopontin and that an alpha4beta1 binding site exists in the NH2-terminal thrombin fragment of osteopontin.

Animals↗
PubMed1997

RGDN peptide interaction with endothelial alpha5beta1 integrin causes sustained endothelin-dependent vasoconstriction of rat skeletal muscle arterioles.

The ability of an integrin-binding Arg-Gly-Asp-Asn (RGDN)- containing peptide to influence vascular tone by interacting with the alpha5beta1 integrin was studied using rat skeletal muscle arterioles. After blockade of beta3 integrin function, isolated arterioles with spontaneous tone showed concentration-dependent vasoconstrictions to topical application of GRGDNP, a peptide that shows a greater ability to interact with alpha5beta1 than with alphavbeta3. The constriction to GRGDNP (2.1 mM) was inhibited by blocking alpha5 integrin function, and was intensified by blocking beta3 integrin function. In contrast, GRGDSP, a peptide that interacts better with alphavbeta3, was unable to induce sustained constrictions. Removal of the endothelium abolished the vasoconstriction in response to GRGDNP, suggesting that the response was due to release of an endothelium-dependent factor. Indeed, blockade of ETA endothelin receptors with BQ-610 (1 microM), similar to removal of the endothelium and alpha5 integrin blockade, inhibited the vasoconstriction. These data indicate that interaction of RGD peptides, and in particular the RGDN sequence with endothelial cell alpha5beta1, causes endothelin-mediated arteriolar vasoconstriction. These results indicate that integrins are novel signaling receptors within the vascular wall that affect vasomotor tone, and may play an important role in vascular control.

Animals↗
PubMed1997

The alpha4beta1 integrin can mediate leukocyte adhesion to casein and denatured protein substrates.

An understanding of the binding specificity of leukocyte integrins is important to determine the range of ligands that interact with these receptors during inflammatory processes. In this study we show that the alpha4beta1 integrin can interact with casein and denatured albumin and promote leukocyte adhesion through these interactions. This was demonstrated with the use of blocking antibodies directed to alpha4beta1 and peptide adhesion competitors containing the alpha4beta1 binding tripeptide, Leu-Asp-Val (LDV). Consistent with this data, the adhesion is completely divalent cation-dependent and is stimulated by known activators of leukocyte integrin function, namely phorbol ester and the beta1 integrin activating antibody, 8A2. It is interesting to note that neither bovine alpha-casein or human albumin contain an LDV site (present in the CS-1 site of alternatively spliced fibronectin) or an IDS site (present in VCAM-1) yet they promote adhesion through this integrin. Furthermore, alpha4beta1 directly binds to Sepharose columns containing casein, casein fragments, or denatured albumin but does not bind columns containing native albumin. These data suggest that the binding specificity for the alpha4beta1 integrin is considerably broader than previously realized. This work has implications for how subsets of leukocytes may interact with damaged proteins during tissue injury and inflammation.

Amino Acid Sequence↗
PubMed1997

Isolation and biological properties of osteopontin from bovine milk.

A procedure for the isolation of osteopontin (OPN) from bovine milk using ion-exchange and hydrophobic chromatography is described. A DEAE-Sephacel column followed by dual phenyl-Sepharose columns yielded approximately 8 mg of purified protein per liter of milk. SDS-PAGE analysis revealed that the protein migrated at M(r) 60,000. NH2-terminal sequence analysis of the first seven amino acids revealed the protein to be identical to that previously reported for bovine OPN. Also, our preparation demonstrated expected biological properties of OPN including adhesion of both endothelial and vascular smooth muscle cells to OPN in a dose- and Arg-Gly-Asp-dependent manner. Furthermore, OPN coupled to Sepharose was capable of binding the alpha v beta 3 integrin from a detergent extract of endothelial cells. Thus, our procedure yielded biologically active OPN from an abundant and natural source.

Amino Acid Sequence↗
PubMed1997

Expression of Bax, Bcl-2, Waf-1, and PCNA gene products in an immortalized human endothelial cell line undergoing p53-mediated apoptosis.

Transfection of the wild-type p53 gene into an immortalized human endothelial cell line (ECV-304) by recombinant adenoviral delivery resulted in high level expression of the wild-type p53 protein and induction of apoptosis. Increases in the number of apoptotic cells were observed within 12 h after infection of ECV-304 cells with recombinant p53 adenovirus, as deter-mined by the appearance of internucleosomal DNA fragmentation ladders and by TUNEL and electron microscopic analyses. Control cells infected with a beta-galactosidase recombinant adenovirus exhibited little or no increase in apoptosis over uninfected cells. The expression of Waf-1 and Bax gene products were in-creased substantially in apoptotic ECV-304 cells as determined by Northern blot, reverse transcription-PCR and immunoblotting analyses. Lesser increases in the expression of the PCNA gene were detected in ECV-304 cells undergoing apoptosis. Both control and apoptotic ECV-304 cells did not express detectable levels of Bcl-2 mRNA or protein in Northern blotting and immunoblotting analyses, respectively. The data suggest a role for the Bax gene product in p53-mediated apoptosis of endothelial cells.

Journal Article↗
PubMed1997

Integrin-mediated reduction in vascular smooth muscle [Ca2+]i induced by RGD-containing peptide.

It has previously been shown that synthetic peptides containing the sequence arginine-glycine-aspartic acid (RGD) cause vasodilation by activation of alpha(v)beta3-integrin present on vascular smooth muscle (VSM) cells. The purpose of this study was to determine whether this dilatory effect is mediated by a reduction in VSM cytosolic Ca2+ concentration ([Ca2+]i). First-order arterioles from the rat cremaster were isolated, cannulated, and pressurized. [Ca2+]i was quantitated from the ratio of emitted fluorescence intensity during alternate excitation of fura 2-loaded vessels at 340 and 380 nm. Cyclo(-Arg-Gly-Asp-D-Phe-Val) (cycloRGD; 0.21-210 microM) produced a concentration-dependent dilation of arterioles that had developed basal myogenic tone. Over the entire concentration range tested, [Ca2+]i decreased from 91 +/- 6 to 27 +/- 4 nM (69.7 +/- 5.0% reduction). In association with the decrease in [Ca2+]i, arteriolar lumen diameter increased from 89 +/- 8 to 184 +/- 8 pm (89.8 +/- 1.8% dilation). At intermediate concentrations, cycloRGD induced rhythmic spiking of Ca2+ superimposed on the concentration-dependent lowering of basal [Ca2+]i. These data directly link integrin activation with alterations in Ca2+ regulation, the net effect of which is a reduction in [Ca2+]i. These data further suggest that integrins, through their role in mediating cellular attachment to the extracellular matrix and in cellular signaling involving Ca2+, could provide a logical link to mechanotransduction and myogenic phenomena.

Acetylcholine↗
PubMed1997

Measuring quality of care in a psychiatric hospital using artificial neural networks.

This study investigates a new method of measuring quality of care. Taking place at a tertiary psychiatric hospital with 5,128 admissions from January 1989 through December 1995, this study uses artificial neural networks (ANNs) to predict hospital length-of-stay (LOS) and uses the standard deviation of LOS in a formula to measure quality of care, Q. ANNs are trained with data using unique patient identifiers and are compared with identical ANNs trained without these identifiers. These two types of ANNs make a LOS prediction, P, with a slightly different accuracies, and this fact is exploited in measuring Q. The authors defined U as the standard deviation of the difference between the actual and the predicted LOS of the ANNs with unique patient identifiers, and defined G as the standard deviation of the difference between the actual and the predicted LOS of the ANNs without using these unique identifiers. Dividing U, the variation of individual LOS patterns intertwined with systemic LOS patterns, by G, the variation of predominately systemic LOS patterns, yields the ratio U/G, in which systemic effects are factored out leaving a measure of the average severity of patient illness. Ratios that exceed unity are seen in the patients who are more severely ill. The formula for quality of care, Q, divides the best LOS prediction accuracy, P, which is inversely proportional to overall variation in the delivery system, by U/G, which is inversely proportional to quality of care, written as: Q = P/(U/G). Q reflects the patients' perspective because LOS is concrete and tangible to patients. The study took place during hospital downsizing (political change), a consent decree (policy change), new administrative and medical personnel (staffing change), and the introduction of clozapine and risperidone for schizophrenia (therapeutic change). These events had a predominantly positive impact on Q. The value of Q correlated well with the Joint Commission on Accreditation of Health Care Organizations (JCAHO) triennial evaluations. Some conclusions that emerged from this study: 1) System variation, reflected in the standard deviation of LOS, increased with frequent changes in top management. 2) There was a clear-cut beneficial effect of clozapine, and to a lesser extent of risperidone in schizophrenia, allowing more community placement. 3) With a dedicated professional staff quality of care can prevail despite increasing variation in LOS (systemic problems). 4) The number of hospital employees per Q unit halved when the overall hospital Q ranged from low to high values as a result of policy and staffing improvements, suggesting an increased efficiency of operation. 5) Q can be an objective outcome measure of quality care from the patients' perspective.

Efficiency, Organizational↗
PubMed1996

An alpha 2 beta 1 integrin-dependent pinocytic mechanism involving intracellular vacuole formation and coalescence regulates capillary lumen and tube formation in three-dimensional collagen matrix.

Human endothelial cells, when suspended within three-dimensional collagen matrices, develop intracellular vacuoles that coalesce to form capillary lumens and tubes. Vacuole and lumen formation are completely dependent on the collagen-binding integrin alpha 2 beta 1, while other endothelial cell integrins had no apparent influence. Vacuole formation occurs by a pinocytic process with internalization of plasma membrane and molecules from the extracellular space, such as fluorescent tracers. By immunofluorescence, vacuole membranes were found to contain associated cell surface proteins, proteins involved in endosomal trafficking (i.e., caveolin and annexin II), and F-actin. Furthermore, some vacuole compartments contained von Willebrand factor. Integrin-regulated vacuole formation and coalescence are major mechanisms controlling capillary lumen and tube formation within a three-dimensional extracellular matrix.

Capillaries↗
PubMed1996

Vascular smooth muscle alpha v beta 3 integrin mediates arteriolar vasodilation in response to RGD peptides.

Arteriolar vasodilation and the resultant increase in blood flow are characteristic vascular responses to tissue injury. The dilatory mediators signaling these responses are incompletely understood. We show that integrin-binding peptides containing the Arg-Gly-Asp (RGD) tripeptide sequence cause immediate and, in some instances, sustained vasodilation when applied to isolated rat cremaster arterioles. The vasodilation is dependent on interaction of the soluble RGD sequence with the alpha v beta 3 integrin expressed by smooth muscle cells in the arteriolar wall. Possible in vivo sources of soluble RGD sequences are fragments of extracellular matrix proteins that are generated after tissue injury. Indeed, protease-generated fragments of denatured collagen type I (a major source of RGD sequences) also cause cremaster arteriolar vasodilation through the alpha v beta 3 integrin. Thus, extracellular matrix protein fragments containing the RGD sequence may act as vascular wound recognition signals to regulate blood flow to injured tissue.

Animals↗
PubMed1996

Scientific application of sports medicine principles for acute low back problems. The Agency for Health Care Policy and Research Low Back Guideline Panel (AHCPR, Guideline #14)

The Agency for Health Care Policy and Research Low Back Guideline Panel (AHCPR, Guideline #14) truly brought to life sports medicine principles in the care of the most common and expensive musculoskeletal problem by focusing on the basic activity paradigm of musculoskeletal limitations. Twenty-three experts and seven international consultants led a review of over 10,000 abstracts and evaluation of over 4,600 articles. This effort was to establish scientifically how any clinician can: 1) safely be sure that the patient only has a back problem, 2) offer safe options for comfort, and 3) concentrate on the real treatment for an activity intolerance with sports medicine principles: activity, not rest, begets activity tolerance. Evidence tables and their subsequent derivation as "Finding and Recommendation Statements" provide an understanding of what medical science can and cannot presently support as predictable.

Clinical Trials as Topic↗
PubMed1995

Regulation of endothelial cell morphogenesis by integrins, mechanical forces, and matrix guidance pathways.

Basement membrane matrix is known to induce human endothelial cells to form cord-like structures that mimic those observed during early angiogenesis in vivo. Using this model, blocking antibody studies revealed a major role for the alpha 6 beta 1 integrin in cord formation. During this process, two alterations in the Matrigel structure were observed which suggested a mechanism for the precision of cord formation. First, Matrigel contracted and lifted off an agarose support and second, linear distortions became visible in the Matrigel that correspond to the migration pathways of endothelial cell processes. These pathways, which we have termed "matrix guidance pathways," appear to result from the generation of mechanical tension between endothelial cells. The above data support the concept that endothelial cell guidance during morphogenetic events could be controlled by the ability of these cells to exert mechanical forces on the surrounding extracellular matrix to create pathways for migration.

Cell Communication↗
PubMed1994

Blood pressure changes in head-injury patients during pre-hospital anaesthesia with propofol.

Intubation at the site of accident is often necessary for patients who have sustained significant head injuries. Propofol can attenuate the hypertensive response to intubation, and cause hypotension in anaesthetic doses which can be greatly exaggerated in hypovolaemic patients. We studied nine patients with isolated head injuries and 11 multiply injured patients with associated head injuries. Patients were resuscitated and then intubated with a small dose of propofol, titrated to ensure unconciousness, and then suxamethonium. In neither group was there a statistically significant fall in blood pressure afterwards although the multiply injured patients tended have greater falls. We conclude that propofol used thus does not cause clinically important hypotension in these potentially unstable patients, but only doctors with suitable anaesthetic and pre-hospital experience should attempt it.

Blood Pressure↗