Lipid-protein interactions in frog rod outer segment disc membranes. Characterization by spin labels.

Freely-diffusing phospholipid spin labels have been employed to study rhodopsin-lipid interactions in frog rod outer segment disc membranes. Examination of the ESR spectra leads us to the conclusion that there are two motionally distinguishable populations of lipid existing in frog rod outer segment membranes over a wide physiological temperature range. Each of the spin probes used shows a two-component electron spin resonance (ESR) spectrum, one component of which is motionally restricted on the ESR timescale, and represents between 33 and 40% of the total integrated spectral intensity. The second spectral component which accounts for the remainder of the spectral intensity possesses a lineshape characteristic of anisotropic motion in a lipid bilayer, very similar in shape to that observed from the same spin labels in dispersions of whole extracted frog rod outer segment lipid. The motionally restricted spectral component is attributed to those spin labels in contact with the surface of rhodospin, while the major component is believed to originate from spin labels in the fluid lipid bilayer region of the membranes. Calculations indicate that the motionally restricted lipid is sufficient to cover the protein surface. This population of lipids is shown here and elsewhere (Watts, A., Volotovski, I.D. and Marsh, D. (1979) Biochemistry 18, 5006-5013) to be by no means rigidly immobilized, having motion in the 20 ns time regime as opposed to motions in the one nanosecond time regime found in the fluid bilayer. Little selectivity for the motionally restricted population is observed between the different spin-labelled phospholipid classes nor with a spin-labelled fatty acid or sterol.

HCFA's health care quality improvement program: the medical informatics challenge.

The peer-review organizations (PROs) were created by Congress in 1984 to monitor the cost and quality of care received by Medicare beneficiaries. In order to do this, the Health Care Financing Administration (HCFA) contracted with the PROs through a series of contracts referred to as "Scopes of Work." Under the Fourth Scope of Work, the HCFA initiated the Health Care Quality Improvement Program (HCQIP) in 1990, as an application of the principles of continuous quality improvement. Since then, the PROs have participated with health care providers in cooperative projects to improve the quality of primarily inpatient care provided to Medicare beneficiaries. Through HCFA-supplied administrative data and clinical data abstracted from patient records, the PROs have been able to identify opportunities for improvements in patient care. In May 1995, the HCFA proposed a new Fifth Scope of Work, which will shift the focus of HCQIP from inpatient care projects to projects in outpatient and managed care settings. This article describes the HCQIP process, the types of data used by the PROs to conduct cooperative projects with health care providers, and the informatics challenges in improving the quality of care received by Medicare beneficiaries.

Case study: a data warehouse for an academic medical center.

The clinical data repository (CDR) is a frequently updated relational data warehouse that provides users with direct access to detailed, flexible, and rapid retrospective views of clinical, administrative, and financial patient data for the University of Virginia Health System. This article presents a case study of the CDR, detailing its five-year history and focusing on the unique role of data warehousing in an academic medical center. Specifically, the CDR must support multiple missions, including research and education, in addition to administration and management. Users include not only analysts and administrators but clinicians, researchers, and students.

Adding value to clinical data by linkage to a public death registry.

We describe the methodology and impact of merging detailed statewide mortality data into the master patient index tables of the clinical data repository (CDR) of the University of Virginia Health System (UVAHS). We employ three broadly inclusive linkage passes (designed to result in large numbers of false positives) to match the patients in the CDR to those in the statewide files using the following criteria: a) Social Security Number; b) Patient Last Name and Birth Date; c) Patient Last Name and Patient First Name. The results from these initial matches are refined by calculation and assignment of a total score comprised of partial scores depending on the quality of matching between the various identifiers. In order to validate our scoring algorithm, we used those patients known to have died at UVAHS over the eight year period as an internal control. We conclude that we are able to update our CDR with 97% of the deaths from the state source using this scheme. We illustrate the potential of the resulting system to assist caregivers in identification of at-risk patient groups by description of those patients in the CDR who were found to have committed suicide. We suggest that our approach represents an efficient and inexpensive way to enrich hospital data with important outcomes information.

Lipid mobility and order in bovine rod outer segment disk membranes. A spin-label study of lipid-protein interactions.

Lipid-protein interactions in bovine rod outer segment disk membranes have been studied by using a series of eight stearic acid spin-label probes which were labeled at different carbon atom positions in the chain. In randomly oriented membrane dispersions, the electron spin resonance (ESR) spectra of the C-8, C-9, C-10, C-11, C-12, C-13, and C-14 atom positional isomers all apparently consist of two components. One of the components corresponds closely to the spectra obtained from dispersions of the extracted membrane lipids, and the other, which is characterized by a considerably greater degree of motional restriction of the lipid chains, is induced by the presence of the protein. Digital subtraction has been used to separate the two components. The proportion of the motionally restricted lipid component is approximately constant, independent of the position of the spin-label group, and corresponds to 30-40% of the total spin-label spectral intensity. The hyperfine splitting of the outer maxima in the difference spectra of the motionally restricted component decreases, and concomitantly, the line widths increase with increasing temperature but change relatively little with increasing distance of the spin-label group from the polar head-group region. This indicates that the corresponding chain motions of the protein-interacting lipids lie in the slow-motion regime of spin-label ESR spectroscopy (tau R approximately 10(-8) S) and that the mobility of these lipids increases with increasing temperature but does not vary greatly along the length of the chain. The data from the hyperfine splittings also suggest the existence of a polarity gradient immediately adjacent to the protein surface, as observed in the fluid lipid regions of the membrane. The more fluid lipid component is only slightly perturbed relative to the lipids alone (for label positions 5-14, inclusive), indicating the presence of chain motions on the nanosecond time scale, and the spectra also reveal a similar polarity profile in both lipid and membrane environments. ESR spectra have also been obtained as a function of magnetic field orientation with oriented membrane samples. For the C-14 atom positional isomer, the motionally restricted component is observed to have a large hyperfine splitting, with the magnetic field oriented both parallel and perpendicular to the membrane normal. This indicates that the motionally restricted lipid chains have a broad distribution of orientations at this label position.(ABSTRACT TRUNCATED AT 400 WORDS)

31P NMR spectra of rod outer segment and sarcoplasmic reticulum membranes show no evidence of immobilized components due to lipid-protein interactions.

31P NMR studies of rod outer segment (ROS) and sarcoplasmic reticulum (SR) membranes have been performed under conditions where broad and narrow spectral components can be clearly resolved. Control studies of an anhydrous, solid powder of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), as well as aqueous binary mixtures of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), demonstrate clearly that broad spectral components can be detected. For the codispersions of DSPC and DOPC in the mixed-phase region at 22 degrees C, the 31P NMR spectra consist of a superposition of a broad component and a narrow, axially symmetric component, due to coexisting solid and liquid-crystalline domains, which are in slow exchange on the 31P NMR time scale. The 31P NMR spectra of the native ROS and SR membranes, however, consist of only a narrow component, to within experimental error, indicating that most or all of the phospholipids are in the liquid-crystalline (L alpha) phase at 22 degrees C. The above conclusions are in agreement with many, but not all, previous studies [see, e.g., Yeagle, P.L. (1982) Biophys. J. 37, 227-239]. It is estimated that at most 10% of the phospholipids in the ROS and SR membranes could give rise to broad 31P NMR spectral components, similar to those seen for anhydrous or solid-phase lipids, corresponding to approximately 7 phospholipids/rhodopsin molecule and approximately 11 phospholipids/Ca2+-ATPase molecule, respectively.

Lipid-protein interactions mediate the photochemical function of rhodopsin.

We have investigated the molecular features of recombinant membranes that are necessary for the photochemical function of rhodopsin. The magnitude of the metarhodopsin I to metarhodopsin II phototransient following a 25% +/- 3% bleaching flash was used as a criterion of photochemical activity at 28 degrees C and pH 7.0. Nativelike activity of rhodopsin can be reconstituted with an extract of total lipids from rod outer segment membranes, demonstrating that the protein is minimally perturbed by the reconstitution protocol. Rhodopsin photochemical activity is enhanced by phosphatidylethanolamine head groups and docosahexaenoyl (22:6 omega 3) acyl chains. An equimolar mixture of phosphatidylethanolamine and phosphatidylcholine containing 50 mol% docosahexaenoyl chains results in optimal photochemical function. These results suggest the importance of both the head-group and acyl chain composition of the rod outer segment lipids in the visual process. The extracted rod lipids and those lipid mixtures favoring the conformational change from metarhodopsin I to II can undergo lamellar (L alpha) to inverted hexagonal (HII) phase transitions near physiological temperature. Interaction of rhodopsin with membrane lipids close to a L alpha to HII (or cubic) phase boundary may thus lead to properties which influence the energetics of conformational states of the protein linked to visual function.

ESR spin-label studies of lipid-protein interactions in membranes.

Lipid spin labels have been used to study lipid-protein interactions in bovine and frog rod outer segment disc membranes, in (Na+, K+)-ATPase membranes from shark rectal gland, and in yeast cytochrome oxidase-dimyristoyl phosphatidylcholine complexes. These systems all display a two component ESR spectrum from 14-doxyl lipid spin-labels. One component corresponds to the normal fluid bilayer lipids. The second component has a greater degree of motional restriction and arises from lipids interacting with the protein. For the phosphatidylcholine spin label there are effectively 55 +/- 5 lipids/200,000-dalton cytochrome oxidase, 58 +/- 4 mol lipid/265,000 dalton (Na+, K+)-ATPase, and 24 +/- 3 and 22 +/- 2 mol lipid/37,000 dalton rhodopsin for the bovine and frog preparations, respectively. These values correlate roughly with the intramembrane protein perimeter and scale with the square root of the molecular weight of the protein. For cytochrome oxidase the motionally restricted component bears a fixed stoichiometry to the protein at high lipid:protein ratios, and is reduced at low lipid:protein ratios to an extent which can be quantitatively accounted for by random protein-protein contacts. Experiments with spin labels of different headgroups indicate a marked selectivity of cytochrome oxidase and the (Na+, K+)-ATPase for stearic acid and for cardiolipin, relative to phosphatidylcholine. The motionally restricted component from the cardiolipin spin label is 80% greater than from the phosphatidylcholine spin label for cytochrome oxidase (at lipid:protein = 90.1), and 160% greater for the (Na+, K+)-ATPase. The corresponding increases for the stearic acid label are 20% for cytochrome oxidase and 40% for (Na+, K+)-ATPase. The effective association constant for cardiolipin is approximately 4.5 times greater than for phosphatidylcholine, and that for stearic acid is 1.5 times greater, in both systems. Almost no specificity is found in the interaction of spin-labeled lipids (including cardiolipin) with rhodopsin in the rod outer segment disc membrane. The linewidths of the fluid spin-label component in bovine rod outer segment membranes are consistently higher than those in bilayers of the extracted membrane lipids and provide valuable information on the rate of exchange between the two lipid components, which is suggested to be in the range of 10(6)-10(7) s-1.

Ownership and utilization of MR imagers in the Commonwealth of Virginia.

PURPOSE: To assess distribution, operation, and ownership of magnetic resonance (MR) imagers in Virginia in 1991. MATERIALS AND METHODS: Questionnaires regarding ownership, location, hours of operation, annual throughput, sources and amounts of revenue, and expenses were mailed to identified providers. Data, specifically regarding ownership and location, were analyzed. RESULTS: Staff from 95% of MR facilities responded. Most facilities were located in and around major metropolitan areas. Population density per imager ranged from one per 76,000 to one per 222,000 persons. Imagers in larger metropolitan areas were operated for longer hours with higher revenues and greater expenses than were those in lower-population-density areas. Imagers owned by physicians in a position to self-refer had the highest patient throughput, the most revenue, and a much lower percentage of revenues from Medicare and Medicaid than did other ownership types. CONCLUSION: Patient access to MR services in Virginia is inhomogeneous. Important aspects of utilization are location and ownership. Ownership by physicians who can self-refer is associated with higher use, greater overall revenues, and less service to the poor and elderly.

Creation of state-level Medicare database for healthcare evaluation applications.

The Health Care Quality Improvement Initiative (HCQII) of the Health Care Financing Administration (HCFA) calls for Professional Review Organizations (PROs) to undertake pattern analysis of large administrative datasets for the purposes of quality of care assessment. The limitations of such administrative databases (primarily the MEDPAR file and derivatives thereof) include impoverished information regarding clinical attributes of Medicare enrollees and the process and outcome of their healthcare. This paper describes preliminary efforts to address this problem by the creation of a database, the PRO Concatenated Database (PCD), from the pooled implicit judgment review data of four Peer Review Organizations (PROs). The data elements comprising the PCD were carefully selected to provide important information regarding quality and appropriateness of care. Preliminary inter-state comparative studies employing the PCD are discussed. A method is also described by which the analytical power of state-level databases may be enhanced by linkage to state-level Modeled MEDPAR data which are issued by HCFA and contain patient-level risk-adjusted mortality data. This approach to the acquisition of data whose clinical content is enriched may prove to be particularly useful to the PRO community during the pattern analysis phase of the HCQII. Such analyses will evolve into more detailed studies involving primary data collection followed by dissemination of the results to local healthcare providers. In this manner, the PCD may facilitate rapid feedback regarding the effectiveness of healthcare delivery to the local community.

Development of an enterprise-wide clinical data repository: merging multiple legacy databases.

We describe the development of a clinical data repository whose core consists of four years of inpatient administrative and billing data from the mainframe legacy systems of the University of Virginia Health System (UVAHS). To these data we have linked a cardiac surgery clinical database and our physician billing data (inpatient and outpatient). Other databases will be merged in the future. A relational database management system (Sybase) running on a dedicated IBM RS/6000 minicomputer was employed to assemble 2.5 Gigabytes of core data describing approximately 100,000 hospital admissions over the four year period. To enable convenient data queries, the system has been equipped with a custom-built WWW user interface, which generates Structured Query Language (SQL) automatically. We illustrate the rapid reporting capabilities of the resulting system with reference to patients undergoing coronary artery bypass graft surgery (CABG). We conclude that this information system: a) constitutes a convenient and low-cost method to increase data availability across the UVAHS; b) provides clinicians with a tool for surveillance of patient care and outcomes; c) forms the core of a comprehensive database from which clinical research may proceed; d) provides a flexible interface empowering a wide variety of clinical departments to share and enrich their own clinical data.