Development and assessment of an educational intervention to improve the recognition of frailty on an acute care respiratory ward.

BACKGROUND: Frailty is a robust predictor of poor outcomes among patients with chronic obstructive pulmonary disease yet is not measured in routine practice. We determined barriers and facilitators to measuring frailty in a hospital setting, designed and implemented a frailty-focused education intervention, and measured accuracy of frailty screening before and after education. METHODS: We conducted a pilot cross-sectional mixed-methods study on an inpatient respiratory ward over 6 months. We recruited registered nurses (RNs) with experience using the Clinical Frailty Scale (CFS). RNs evaluated 10 clinical vignettes and assigned a frailty score using the CFS. A structured frailty-focused education intervention was delivered to small groups. RNs reassigned frailty scores to vignettes 1 week after education. Outcomes included barriers and facilitators to assessing frailty in hospital, and percent agreement of CFS scores between RNs and a gold standard (determined by geriatricians) before and after education. RESULTS: Among 26 RNs, the median (IQR) duration of experience using the CFS was 1.5 (1-4) months. Barriers to assessing frailty included the lack of clinical directives to measure frailty and large acute workloads. Having collateral history from family members was the strongest perceived facilitator for frailty assessment. The median (IQR) percent agreement with the gold-standard frailty score across all cases was 55.8% (47.2%-60.6%) prior to the educational intervention, and 57.2% (44.1%-70.2%) afterwards. The largest increase in agreement occurred in the 'mildly frail' category, 65.4%-81% agreement. CONCLUSIONS: Barriers to assessing frailty in the hospital setting are external to the measurement tool itself. Accuracy of frailty assessment among acute care RNs was low, and frailty-focused rater training may improve accuracy. Subsequent work should focus on health system approaches to empower health providers to assess frailty, and on testing the effectiveness of frailty-focused education in large real-world settings.

A systematic review of interventions aiming to improve communication of prognosis to adult patients.

OBJECTIVE: Our objective was to describe interventions that aim to improve communication of prognosis to adult patients and to summarize the effect of interventions. METHODS: We included randomized controlled trials of interventions that included prognosis delivery. We excluded studies of decision aids. Our analysis was a narrative synthesis of interventions and outcomes. RESULTS: Our search identified 1151 unique records. After screening, and full text review we included 21 reports from 17 RCTs. Only 2 studies used a prediction model to generate prognostic estimates. Four studies used education, ten used patient mediated interventions, and 2 used coordination of care. In some studies education that includes prognosis improves patient reported outcomes, communication and treatment decisions, patient mediated interventions can increase the number of questions patients ask about prognosis. Coordination of care may improve satisfaction. CONCLUSIONS: Education for clinicians that includes teaching about how to communicate prognosis may improve patient reported outcomes. Patient mediated interventions can increase the number of prognosis related questions asked by patients. PRACTICE IMPLICATIONS: Communication skills training that includes training on delivering prognosis may improve communication and patient reported outcomes, but the evidence is uncertain. Giving patients question prompt lists can help them ask more prognosis related questions.

Predicting the need for supportive services after discharged from hospital: a systematic review.

BACKGROUND: Some patients admitted to acute care hospital require supportive services after discharge. The objective of our review was to identify models and variables that predict the need for supportive services after discharge from acute care hospital. METHODS: We performed a systematic review searching the MEDLINE, CINAHL, EMBASE, and COCHRANE databases from inception to May 1st 2017. We selected studies that derived and validated a prediction model for the need for supportive services after hospital discharge for patients admitted non-electively to a medical ward. We extracted cohort characteristics, model characteristics and variables screened and included in final predictive models. Risk of bias was assessed using the Quality in Prognostic Studies tool. RESULTS: Our search identified 3362 unique references. Full text review identified 6 models. Models had good discrimination in derivation (c-statistics > 0.75) and validation (c-statistics > 0.70) cohorts. There was high quality evidence that age, impaired physical function, disabilities in performing activities of daily living, absence of an informal care giver and frailty predict the need for supportive services after discharge. Stroke was the only unique diagnosis with at least moderate evidence of an independent effect on the outcome. No models were externally validated, and all were at moderate or higher risk of bias. CONCLUSIONS: Deficits in physical function and activities of daily living, age, absence of an informal care giver and frailty have the strongest evidence as determinants of the need for support services after hospital discharge. TRIAL REGISTRATION: This review was registered with PROSPERO #CRD42016037144.

Physician Availability in Long-Term Care and Resident Hospital Transfer: A Retrospective Cohort Study.

OBJECTIVES: To investigate whether same-day physician access in long-term care homes reduces resident emergency department (ED) visits and hospitalizations. DESIGN: Retrospective cohort study. SETTING AND PARTICIPANTS: 161 long-term care homes in Ontario, Canada, and 20,624 residents living in those homes. METHODS: We administered a survey to Ontario long-term care homes from March to May 2017 to collect their typical wait time for a physician visit. We linked the survey to administrative databases to capture other long-term care home characteristics, resident characteristics, hospitalizations, and ED visits. We defined a cohort of residents living in survey-respondent homes between January and May 2017 and followed each resident for 6 months or until discharge or death. We estimated negative binomial regression models on counts of hospitalizations and ED visits with random intercepts for long-term care homes. We controlled for residents' sociodemographic and illness characteristics, long-term care home size, chain status, rurality, and nurse practitioner access. RESULTS: Fifty-two homes (32%) reported same-day physician access. Among residents of homes with same-day physician access, 9% had a hospitalization and 20% had an ED visit during follow-up. In contrast, among residents in homes without same-day access, 12% were hospitalized and 22% visited an ED. The adjusted hospitalization and ED rates among residents of homes with same-day physician access were 21% lower (rate ratio = 0.79, P = .02) and 14% lower (rate ratio = 0.86, P = .07), respectively, than residents of other homes. We estimate that nearly 1 in 6 resident hospitalizations could be prevented if all long-term care homes had same-day physician access. CONCLUSIONS AND IMPLICATIONS: Residents of long-term care homes with same-day physician access experience lower hospitalization and ED visit rates than residents in homes that wait longer for physicians, even after adjusting for important resident and home characteristics. Improved on-demand access to physicians has the potential to reduce hospital transfer rates.

Characterization of Serious Adverse Drug Reactions in Hospital to Determine Potential Implications of Mandatory Reporting.

BACKGROUND: The Protecting Canadians from Unsafe Drugs Act will eventually require institutions to report all serious adverse drug reactions (ADRs), although the proposed regulations do not yet define what will need to be reported and by whom. Knowledge about the occurrence of serious ADRs in the hospital setting is needed to optimize the effectiveness of reporting and to determine the potential implications of mandatory reporting. OBJECTIVES: To quantify and characterize suspected serious ADRs in patients admitted to a general medicine service, to assess the likelihood of causality, and to determine inter-rater agreement for identification of ADRs and assessment of their likelihood. METHODS: This prospective observational study involved 60 consecutive patients admitted to a general medicine service at a tertiary care teaching centre starting on March 28, 2016. The primary outcome was the number of serious ADRs, defined by Health Canada as ADRs that result in hospital admission, congenital malformation, persistent or significant disability or incapacity, or death; that are life-threatening; or that require significant intervention to prevent one of these outcomes. Medical records were reviewed independently by pairs of pharmacists for serious ADRs, and the likelihood of causality was assessed using the World Health Organization-Uppsala Monitoring Centre system. Inter-rater agreement was calculated using the kappa score, and disagreements were resolved by discussion and consensus. RESULTS: Twenty-three serious ADRs occurred in the sample of 60 patients. The proportion of patients experiencing a serious ADR that contributed to the original hospital admission was 19/60 (32%, 95% confidence interval [CI] 20%-43%), and 4 patients (7%, 95% CI 0%-13%) experienced a serious ADR during their hospital stay. Inter-rater agreement for occurrence of serious ADRs was moderate (kappa 0.58, 95% CI 0.35-0.76). CONCLUSION: Reportable serious ADRs were common among patients admitted to a general medicine service. Canadian hospitals would face difficulties reporting all serious ADRs because of the frequency of their occurrence and the subjectivity of their identification.

CONTEXTE: La Loi visant à protéger les Canadiens contre les drogues dangereuses obligera éventuellement les établissements à déclarer tout cas de réactions indésirables graves aux médicaments (RIM), quoique les règlements proposés n'indiquent pas encore ce qui devra être déclaré et par qui. Des données sur la survenue de RIM graves en milieu hospitalier sont nécessaires pour optimiser l'efficacité de la déclaration et pour déterminer les implications potentielles d'une déclaration obligatoire. OBJECTIFS: Quantifier les RIM graves soupçonnées chez les patients admis à un service de médecine générale et en offrir un portrait, évaluer la probabilité d'une relation de causalité et déterminer l'accord interévaluateurs pour le repérage des RIM et l'évaluation de leur probabilité. MÉTHODES: La présente étude observationnelle prospective comptait 60 patients admis consécutivement à partir du 28 mars 2016 à un service de médecine générale d'un centre hospitalier universitaire de soins tertiaires. Le principal paramètre d'évaluation était le nombre de RIM graves, définies par Santé Canada comme des RIM qui mènent à une hospitalisation, à une malformation congénitale, à une invalidité ou à une incapacité persistante ou importante; qui mettent la vie en danger ou entraînent la mort; ou qui nécessitent une intervention significative pour prévenir l'un de ces résultats. Les dossiers médicaux ont été examinés indépendamment par des paires de pharmaciens à la recherche de RIM graves et la probabilité d'une causalité a été évaluée à l'aide du système du Centre de pharmacovigilance d'Uppsala de l'Organisation mondiale de la Santé. L'accord interévaluateurs a été mesuré à l'aide du coefficient kappa et les désaccords ont été résolus par la discussion et l'atteinte d'un consensus. RÉSULTATS: Vingt-trois RIM graves sont survenues dans l'échantillon composé de 60 patients. La proportion de patients ayant subi une RIM grave qui a contribué à l'hospitalisation initiale était 19/60 (32 %, intervalle de confiance [IC] de 95 % de 20 %­43 %); de plus, 4 patients (7 %, IC de 95 % de 0 %­13 %) avaient subi une RIM grave au cours de leur séjour à l'hôpital. L'accord interévaluateurs sur la survenue de RIM graves était modéré (kappa = 0,58, IC de 95 % de 0,35­0,76). CONCLUSION: Les RIM graves à déclaration obligatoire étaient courantes chez les patients admis à un service de médecine générale. Les hôpitaux canadiens auraient de la difficulté à déclarer tous les cas de RIM graves à cause de leur fréquence et de la subjectivité de leur repérage.

Clinical factors contributing to high cost hospitalizations in a Canadian tertiary care centre.

BACKGROUND: Like much of the developed world, healthcare costs in Canada are rising. A small proportion of patients account for a large proportion of healthcare spending and much of this spending occurs in acute care settings. The purpose of our study was to determine potentially modifiable factors related to care processes that contribute to high-cost admissions. METHODS: Using a mixed-methods study design, factors contributing to high-cost admissions were identified from literature and case review. We defined pre- and post-admission factors contributing to high-cost admissions. Pre-admission factors included reason for admission (e.g. complex medical, elective surgery, trauma, etc.). Post-admission factors included medical complications, disposition delays, clinical services delays, and inefficient clinical decision-making. We selected a random sample of admissions in the top decile of inpatient cost from the Ottawa Hospital between January 1 and December 31, 2010. A single reviewer classified cases based on the pre- and post-admission factors. We combined this information with data derived from the Ottawa Hospital Data Warehouse to describe patient-level clinical and demographic characteristics and costs incurred. RESULTS: We reviewed 200 charts which represents ~5% of all high cost admissions within the Ottawa Hospital in 2010. Post-admission factors contributing to high-cost admissions were: complications (60%), disposition delays (53%), clinical service delays (39%), and inefficient clinical decision-making (13%). Further, these factors varied substantially across service delivery lines. The mean (standard deviation (SD)) cost per admission was $49,923 CDN ($45,773). The most common reason for admission was "complex medical" (49%) and the overall median (IQR) length of stay was 27 (18-48) days. Approximately 1 in 3 high cost admissions (29%) included time in the intensive care unit (ICU). CONCLUSIONS: While high cost admissions often include time in ICU and have long lengths of stay, a substantial proportion of costs were attributable to complications and potentially preventable delays in care processes. These findings suggest opportunities exist to improve outcomes and reduce costs for this diverse patient population.

Factors contributing to high-cost hospital care for patients with COPD.

Chronic obstructive pulmonary disease (COPD) is a leading cause of hospital admission, the fifth leading cause of death in North America, and is estimated to cost $49 billion annually in North America by 2020. The majority of COPD care costs are attributed to hospitalizations; yet, there are limited data to understand the drivers of high costs among hospitalized patients with COPD. In this study, we aimed to determine the patient and hospital-level factors associated with high-cost hospital care, in order to identify potential targets for the reorganization and planning of health services. We conducted a retrospective cohort study at a Canadian academic hospital between September 2010 and 2014, including adult patients with a first-time admission for COPD exacerbation. We calculated total costs, ranked patients by cost quintiles, and collected data on patient characteristics and health service utilization. We used multivariable regression to determine factors associated with highest hospital costs. Among 1,894 patients included in the study, the mean age was 73±12.6 years, median length of stay was 5 (interquartile range 3-9) days, mortality rate was 7.8% (n=147), and 9% (n=170) required intensive care. Hospital spending totaled $19.8 million, with 63% ($12.5 million) spent on 20% of patients. Factors associated with highest costs for COPD care included intensive care unit admission (odds ratio [OR] 32.4; 95% confidence interval [CI] 20.3, 51.7), death in hospital (OR 2.6; 95% CI 1.3, 5.2), discharge to long-term care facility (OR 5.7; 95% CI 3.5, 9.2), and use of the alternate level of care designation during hospitalization (OR 23.5; 95% CI 14.1, 39.2). High hospital costs are driven by two distinct groups: patients who require acute medical treatment for severe illness and patients with functional limitation who require assisted living facilities upon discharge. Improving quality of care and reducing cost in this high-needs population require a strong focus on early recognition and management of functional impairment for patients living with chronic disease.

The prevalence of potentially preventable deaths in an acute care hospital: A retrospective cohort.

Studies estimate that 6% to 27% of deaths in hospitals might be prevented with higher quality care. These estimates may be inaccurate because they fail to account for the uncertainty associated with classifying preventability. The purpose of this study was to measure the prevalence of preventable deaths, accounting for the uncertainty in preventability ratings.We created standardized structured case abstracts for all deaths at a multisite academic teaching hospital over a 3-month period. Each case abstract was evaluated independently by 4 reviewers who rated death preventability on a 100-point scale ranging from 0 ("Definitely not preventable") to 100 ("Definitely preventable"). Ratings were categorized into a 4-level ordinal scale and latent class analysis was used to measure the prevalence of each preventability class and estimate the probability that deaths in each class were preventable.There were 480 deaths (3.4% of all admissions) during the study period. The latent class model (LCM) found that 91.6% (95% CI: 88.4-94.8%) of deaths were "nonpreventable" and 8.4% (5.2-11.6%) were "possibly preventable." "Possibly preventable" deaths could be identified with 90% certainty, but due to error in reviewer ratings, a "possibly preventable" death had a 50% probability of being receiving a rating of less than 25/100 by any single reviewer. Only 5 of 31 deaths classified as a "possibly preventable" (1.0% of all deaths) were judged to likely be alive in 3 months with perfect care.After accounting for uncertainty associated with rating the preventability of hospital deaths, we found that 8.4% of deaths were deemed possibly preventable. There was only moderate probability that these deaths were truly preventable.

Risk assessment tools to predict location of discharge and need for supportive services for medical patients after discharge from hospital: a systematic review protocol.

BACKGROUND: Patients who are discharged from hospital after an acute medical illness often have impaired function that prevents them from returning to their previous place of residence. Assessing each patient's post-discharge needs takes time and resources but is important in order to reduce unplanned readmissions and adverse events post-discharge. METHODS/DESIGN: We will conduct a systematic review to synthesize the evidence on prognostic models and their reported accuracy in predicting the location of discharge after a medical admission to an acute care hospital. We will perform searches in MEDLINE, EMBASE, CINAHL, and COCHRANE databases. Pre-defined study, population, and model characteristics will be reported. We will write a narrative summary of included studies. Methodological quality of the studies will be assessed using the QUIPS tool, and the quality of evidence will be evaluated using the GRADE tool. DISCUSSION: Early and accurate assessment of patient needs for supportive services after discharge has the potential to improve patient outcomes and health system efficiency. This systematic review will identify factors that can accurately predict location of discharge using existing tools and identify priority knowledge gaps to inform future research. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42016037144.

Quality gaps identified through mortality review.

BACKGROUND: Hospital mortality rate is a common measure of healthcare quality. Morbidity and mortality meetings are common but there are few reports of hospital-wide mortality-review processes to provide understanding of quality-of-care problems associated with patient deaths. OBJECTIVE: To describe the implementation and results from an institution-wide mortality-review process. DESIGN: A nurse and a physician independently reviewed every death that occurred at our multisite teaching institution over a 3-month period. Deaths judged by either reviewer to be unanticipated or to have any opportunity for improvement were reviewed by a multidisciplinary committee. We report characteristics of patients with unanticipated death or opportunity for improved care and summarise the opportunities for improved care. RESULTS: Over a 3-month period, we reviewed all 427 deaths in our hospital in detail; 33 deaths (7.7%) were deemed unanticipated and 100 (23.4%) were deemed to be associated with an opportunity for improvement. We identified 97 opportunities to improve care. The most common gap in care was: 'goals of care not discussed or the discussion was inadequate' (n=25 (25.8%)) and 'delay or failure to achieve a timely diagnosis' (n=8 (8.3%)). Patients who had opportunities for improvement had longer length of stay and a lower baseline predicted risk of death in hospital. Nurse and physician reviewers spent approximately 142 h reviewing cases outside of committee meetings. CONCLUSIONS: Our institution-wide mortality review found many quality gaps among decedents, in particular inadequate discussion of goals of care.

Clinical characteristics and preventable acute care spending among a high cost inpatient population.

BACKGROUND: A small proportion of patients account for the majority of health care spending. The objectives of this study were to explore the clinical characteristics, patterns of health care use, and the proportion of acute care spending deemed potentially preventable among high cost inpatients within a Canadian acute-care hospital. METHODS: We identified all individuals within the Ottawa Hospital with one or more inpatient hospitalization between April 1, 2010 and March 31, 2011. Clinical characteristics and frequency of hospital encounters were captured in the information systems of the Ottawa Hospital Data Warehouse. Direct inpatient costs for each encounter were summed using case costing information and those in the upper first and fifth percentiles of the cumulative direct cost distribution were defined as extremely high cost and high cost respectively. We quantified preventable acute care spending as hospitalizations for ambulatory care sensitive conditions (ACSC) and spending attributable to difficulty discharging patients as measured by alternate level of care (ALC) status. RESULTS: During the study period, 36,892 patients had 44,066 hospitalizations. High cost patients (n = 1,844) accounted for 38 % of total inpatient spending ($122 million) and were older, more likely to be male, and had higher levels of co-morbidity compared to non-high cost patients. In over half of the high cost cohort (54 %), costs were accumulated from a single hospitalization. The majority of costs were related to nursing care and intensive care unit spending. High cost patients were more likely to have an encounter deemed to be ambulatory care sensitive compared to non-high cost inpatients (6.0 versus 2.8 %, p < 0.001). A greater proportion of inpatient spending was attributable to ALC days for high cost versus non-high cost patients (9.1 versus 4.9 %, p < 0.001). CONCLUSIONS: Within a population of high cost inpatients, the majority of costs are attributed to a single, non-preventable, acute care episode. However, there are likely opportunities to improve hospital efficiency by focusing on different approaches to community based care directed towards specific populations.

Variations in Resource Intensity and Cost Among High Users of the Emergency Department.

OBJECTIVES: High users of emergency department (ED) services are often identified by number of visits per year, with little exploration of the distribution/pattern of visits over time. The purpose of this study was to examine patient- and encounter-level factors and costs related to periods of short-term resource intensity among high users of the ED within a tertiary care teaching facility. METHODS: We identified all adults with at least three visits to the Ottawa Hospital ED within a 1-year period from April 1, 2012, to March 31, 2013. Within this high-user cohort, we then measured intensity of use by calculating average daily visit rates to identify individuals with a cluster of ED visits. Those with at least three ED visits/7 days at any point during follow-up were considered patients with clustered ED use (i.e., a period of short-term resource intensity). Detailed clinical and administrative data were used to compare patient- and encounter-level characteristics and cost profiles between the clustered and nonclustered groups. Analyses were repeated using varying cut points to define high users (at least five and at least eight visits per year). RESULTS: Of the 16,153 patients identified as high ED users during the study period, 13.5% had their visits clustered within a short period of time. These clustered users were more likely to be homeless, to require psychiatric services, and to leave without being seen by a physician and less likely to be admitted to the hospital. Approximately one in three (31.2%) high ED users with clustered visits returned for the same medical problem (namely pain-related disorders, shortness of breath, and cellulitis) within a 1-week period. Similar trends were observed when the high-user cohort was restricted to those with at least five and at least eight ED visits/year. Finally, patients with short-term intensity periods had lower direct and indirect costs per encounter than those without. CONCLUSIONS: Using a novel methodology that accounts for both number and intensity of ED encounters over time, we were able to identify specific subpopulations of high ED users. Further work is required to determine if this methodology has utility for targeting care pathways within this heterogeneous and high-risk patient group.

Patterns of health care use in a high-cost inpatient population in Ottawa, Ontario: a retrospective observational study.

BACKGROUND: A small proportion of patients account for the majority of health care spending. We used detailed clinical and administrative data to explore clinical characteristics, patterns of health care use and changes in cost profiles over time among high-cost inpatients in an acute tertiary care hospital in Ottawa, Ontario. METHODS: We identified all people who had 1 or more inpatient admissions to The Ottawa Hospital between Apr. 1, 2009, and Mar. 31, 2012. We calculated the direct inpatient costs using case-costing information to categorize patients into persistently high-cost, episodic high-cost and non-high-cost groups. Within each group, we used discharge abstracts to measure encounter-level characteristics and patterns of inpatient health care use over time. We also developed transition matrices to explore how inpatient costing states changed over time. RESULTS: During the study period, 100 178 patients had 132 996 hospital admissions. Hospital spending was often limited to a single year for most of the patients (90.2%), with only a small proportion (7.4%) of patients remaining in the high-cost group in the subsequent year. Patients in the persistently (n = 236) and episodic (n = 5062) high-cost groups were often older, had medically complex conditions and generated most of the costs from nursing care and intensive care. Compared with patients in the other cost groups, those in the persistently high-cost group were more likely to have multiple readmissions (43.4%) and multiple placements in an alternate level of care (19.0%) and were high users of health care services outside of the hospital setting. INTERPRETATION: Hospital spending was often limited to a single year for most patients, and only a small proportion of patients remained in the high-cost group in the subsequent year. These persistently high-cost patients had medically complex conditions and often required expensive care. A greater understanding of the circumstances that result in persistent hospital spending remains an area for future work, including an exploration of the potential barriers impeding efficient transition out of acute care for high-risk patients.

Influence of educational, audit and feedback, system based, and incentive and penalty interventions to reduce laboratory test utilization: a systematic review.

Laboratory and radiographic tests are often ordered unnecessarily. This excess testing has financial costs and is a burden on patients. We performed a systematic review to determine the effectiveness interventions to reduce test utilization by physicians. The MEDLINE and EMBASE databases were searched for the years 1946 through to September 2013 for English articles that had themes of test utilization and cost containment or optimization. Bibliographies of included papers were scanned to identify other potentially relevant studies. Our search resulted in 3236 articles of which 109 met the inclusion criteria of having an intervention aimed at reducing test utilization with results that could be expressed as a percent reduction in test use relative to the comparator. Each intervention was categorized into one or more non-exclusive category of education, audit and feedback, system based, or incentive or penalty. A rating of study quality was also performed. The percent reductions in test use ranged from a 99.7% reduction to a 27.7% increase in test use. Each category of intervention was effective in reducing test utilization. Heterogeneity between interventions, poor study quality, and limited time horizons makes generalizations difficult and calls into question the validity of results. Very few studies measure any patient safety or quality of care outcomes affected by reduced test use. There are numerous studies that use low investment strategies to reduce test utilization with one time changes in the ordering system. These low investment strategies are the most promising for achievable and durable reductions in inappropriate test use.

Interactions of the Australian tree frog antimicrobial peptides aurein 1.2, citropin 1.1 and maculatin 1.1 with lipid model membranes: differential scanning calorimetric and Fourier transform infrared spectroscopic studies.

The interactions of the antimicrobial peptides aurein 1.2, citropin 1.1 and maculatin 1.1 with dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidylglycerol (DMPG) and dimyristoylphosphatidylethanolamine (DMPE) were studied by differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectroscopy. The effects of these peptides on the thermotropic phase behavior of DMPC and DMPG are qualitatively similar and manifested by the suppression of the pretransition, and by peptide concentration-dependent decreases in the temperature, cooperativity and enthalpy of the gel/liquid-crystalline phase transition. However, at all peptide concentrations, anionic DMPG bilayers are more strongly perturbed than zwitterionic DMPC bilayers, consistent with membrane surface charge being an important aspect of the interactions of these peptides with phospholipids. However, at all peptide concentrations, the perturbation of the thermotropic phase behavior of zwitterionic DMPE bilayers is weak and discernable only when samples are exposed to high temperatures. FTIR spectroscopy indicates that these peptides are unstructured in aqueous solution and that they fold into alpha-helices when incorporated into lipid membranes. All three peptides undergo rapid and extensive H-D exchange when incorporated into D(2)O-hydrated phospholipid bilayers, suggesting that they are located in solvent-accessible environments, most probably in the polar/apolar interfacial regions of phospholipid bilayers. The perturbation of model lipid membranes by these peptides decreases in magnitude in the order maculatin 1.1>aurein 1.2>citropin 1.1, whereas the capacity to inhibit Acholeplasma laidlawii B growth decreases in the order maculatin 1.1>aurein 1.2 congruent with citropin 1.1. The higher efficacy of maculatin 1.1 in disrupting model and biological membranes can be rationalized by its larger size and higher net charge. However, despite its smaller size and lower net charge, aurein 1.2 is more disruptive of model lipid membranes than citropin 1.1 and exhibits comparable antimicrobial activity, probably because aurein 1.2 has a higher propensity for partitioning into phospholipid membranes.

The relationship between the binding to and permeabilization of phospholipid bilayer membranes by GS14dK4, a designed analog of the antimicrobial peptide gramicidin S.

The cationic beta-sheet cyclic tetradecapeptide cyclo[VKLdKVdYPLKVKLdYP] (GS14dK(4)) is a diastereomeric lysine ring-size analog of the potent naturally occurring antimicrobial peptide gramicidin S (GS) which exhibits enhanced antimicrobial but markedly reduced hemolytic activity compared to GS itself. We have previously studied the binding of GS14dK(4) to various phospholipid bilayer model membranes using isothermal titration calorimetry [Abraham, T. et al. (2005) Biochemistry 44, 2103-2112]. In the present study, we compare the ability of GS14dK(4) to bind to and disrupt these same phospholipid model membranes by employing a fluorescent dye leakage assay to determine the ability of this peptide to permeabilize large unilamellar vesicles. We find that in general, the ability of GS14dK(4) to bind to and to permeabilize phospholipid bilayers of different compositions are not well correlated. In particular, the binding affinity of GS14dK(4) varies markedly with the charge and to some extent with the polar headgroup structure of the phospholipid and with the cholesterol content of the model membrane. Specifically, this peptide binds much more tightly to anionic than to zwitterionic phospholipids and much less tightly to cholesterol-containing than to cholesterol-free model membranes. In addition, the maximum extent of binding of GS14dK(4) can also vary considerably with phospholipid composition in a parallel fashion. In contrast, the ability of this peptide to permeabilize phospholipid vesicles is only weakly dependent on phospholipid charge, polar headgroup structure or cholesterol content. We provide tentative explanations for the observed lack of a correlation between the affinity and extent of GS14dK(4) binding to, and degree of disruption of the structure and integrity of, phospholipid bilayers membranes. We also present evidence that the lack of correlation between these two parameters may be a general phenomenon among antimicrobial peptides. Finally, we demonstrate that the affinity of binding of GS14dK4 to various phospholipid bilayer membranes is much more strongly correlated with the antimicrobial and hemolytic activities of this peptide than with its effect on the rate and extent of dye leakage in these model membrane systems.