New Scholarship from UNCW Faculty
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Simple Clinical Factors Associated With Radiation-Induced Lung Toxicity After Stereotactic Body Radiation Therapy in Lung Cancer: A Pooled Analysis of 70 Studies
Publication date: 1 September 2014
Source:International Journal of Radiation Oncology*Biology*Physics, Volume 90, Issue 1, Supplement
Author(s): J. Zhao , L. Ling , E.D. Yorke , M.T. Milano , W. Liu , B. Kavanagh , A. Li , J. Andy , M. Lawrence , M. Miften , A. Rimner , S. Timothy , J. Xue , J. Grimm , F. Kong
Publication date: June 2014
Source:Deep Sea Research Part II: Topical Studies in Oceanography, Volume 104
Author(s): Sandra Brooke , Steve W. Ross
The structure-forming, cold-water coral Lophelia pertusa is widely distributed throughout the North Atlantic Ocean and also occurs in the South Atlantic, North Pacific and Indian oceans. This species has formed extensive reefs, chiefly in deep water, along the continental margins of Europe and the United States, particularly off the southeastern U.S. coastline and in the Gulf of Mexico. There were, however, no records of L. pertusa between the continental slope off Cape Lookout, North Carolina (NC) (∼34°N, 76°W), and the rocky Lydonia and Oceanographer canyons off Cape Cod, Massachusetts (MA) (∼40°N, 68°W). During a research cruise in September 2012, L. pertusa colonies were observed on steep walls in both Baltimore and Norfolk canyons. These colonies were all approximately 2m or less in diameter, usually hemispherical in shape and consisted entirely of live polyps. The colonies were found between 381m and 434m with environmental observations of: temperature 6.4–8.6°C; salinity 35.0–35.6; and dissolved oxygen 2.06–4.41mlL−1, all of which fall within the range of known L. pertusa distributions. All colonies were observed on vertical walls or underneath overhangs in areas of high current, which differs from observations further south, where L. pertusa colonizes rocky ledges and outcroppings, often forming large bioherms. We discuss observations from Baltimore and Norfolk canyons in the context of the known distribution of this species in the North Atlantic.
The valuation of marine ecosystem goods and services in the Caribbean: A literature review and framework for future valuation efforts
Publication date: Available online 8 September 2014
Author(s): Peter W. Schuhmann , Robin Mahon
This paper reviews economic valuation of marine ecosystem services in the Wider Caribbean Region (WCR) for the three major marine ecosystems addressed by the Caribbean Large Marine Ecosystem (CLME) Project: reef, pelagic and continental shelf. A review of over 200 value estimates suggests that marine economic valuations in the WCR have focused on a limited number of benefits derived from marine ecosystems, primarily those that are relatively easy to measure and convey, such as recreation opportunities in protected areas, and benefits that are ascribed to easily measured market indicators. Values associated with reefs have received far more attention than those associated with the pelagic or shelf ecosystems. The economic impacts of overfishing remain largely unexplored. Regulating and maintenance services provided by the marine ecosystems of the WCR have been recognized as important, but have not been linked to valuation. Finally, estimates of non-use values for WCR marine ecosystem goods and services are few. It is suggested that future work on valuation be coordinated among countries and agencies so that gaps can be prioritized and valuation studies can be directed toward a more comprehensive understanding of the full value of the goods and services provided by marine ecosystems in the WCR.
Association of Obesity in Early Adulthood and Middle Age With Incipient Left Ventricular Dysfunction and Structural Remodeling The CARDIA Study (Coronary Artery Risk Development in Young Adults)
Publication date: Available online 3 September 2014
Source:JACC: Heart Failure
Author(s): Satoru Kishi , Anderson C. Armstrong , Samuel S. Gidding , Laura A. Colangelo , Bharath A. Venkatesh , David R. Jacobs Jr. , J. Jeffery Carr , James G. Terry , Kiang Liu , David C. Goff Jr. , João A.C. Lima
Objectives The goal of this study was to investigate the relationship of body mass index (BMI) and its 25-year change to left ventricular (LV) structure and function. Background Longstanding obesity may be associated with clinical cardiac dysfunction and heart failure. Whether obesity relates to cardiac dysfunction during young adulthood and middle age has not been investigated. Methods The CARDIA (Coronary Artery Risk Development in Young Adult) study enrolled white and black adults ages 18 to 30 years in 1985 to 1986 (Year-0). At Year-25, cardiac function was assessed by conventional echocardiography, tissue Doppler imaging (TDI), and speckle tracking echocardiography (STE). Twenty-five–year change in BMI (classified as low: <27 kg/m2 and high: ≥27 kg/m2) was categorized into 4 groups (Low-Low, High-Low, Low-High, and High-High). Multiple linear regression was used to quantify the association between categorical changes in BMI (Low-Low as reference) with LV structural and functional parameters obtained in middle age, adjusting for baseline and 25-year change in risk factors. Results The mean BMI was 24.4 kg/m2 in 3,265 participants included at Year-0. Change in BMI adjusted for risk factors was directly associated with incipient myocardial systolic dysfunction assessed by STE (High-High: β-coefficient = 0.67; Low-High: β-coefficient = 0.35 for longitudinal peak systolic strain) and diastolic dysfunction assessed by TDI (High-High: β-coefficient = −074; Low-High: β-coefficient = −0.45 for e′) and STE (High-High: β-coefficient = −0.06 for circumferential early diastolic strain rate). Greater BMI was also significantly associated with increased LV mass/height (High-High: β-coefficient = 26.11; Low-High: β-coefficient = 11.87). Conclusions Longstanding obesity from young adulthood to middle age is associated with impaired LV systolic and diastolic function assessed by conventional echocardiography, TDI, and STE in a large biracial cohort of adults age 43 to 55 years.
Publication date: Available online 29 August 2014
Author(s): Nick Galli , Trent Petrie , Christy Greenleaf , Justine Reel , Jennifer Carter
Despite a proliferation of research on disordered eating in female athletes, few studies have included male athletes. The purpose of this study was to determine which of five personality and psychological variables of interest (i.e., perfectionism, self-esteem, optimism, reasons for exercise, and appearance orientation) best predicted eating disorder status (i.e., symptomatic or asymptomatic) in male athletes. Two hundred three male athletes (M age =20.29, SD =1.64) from three National Collegiate Athletic Association (NCAA) Division I institutions participated. More athletes were asymptomatic (80.8%) than symptomatic (19.2%). None of the variables significantly predicted symptomatic status. These findings contrast the literature on predictors of disordered eating symptomatology among female athletes, and suggest the need for further research to identify other potential predictors of eating disturbance among male athletes.
Nile Delta exhibited a spatial reversal in the rates of shoreline retreat on the Rosetta promontory comparing pre- and post-beach protection
Publication date: 1 January 2015
Source:Geomorphology, Volume 228
Author(s): Eman Ghoneim , Jehan Mashaly , Douglas Gamble , Joanne Halls , Mostafa AbuBakr
The coastline of the Nile Delta experienced accelerated erosion since the construction of the Aswan High Dam in 1964 and, consequently, the entrapment of a large amount of river sediments behind it. The coastline of the Rosetta promontory showed the highest erosion in the Delta with an average retreat rate of 137.4m year−1. In 1991, in an effort to mitigate sediment loss, a 4.85km long seawall was built on the outer margin of the promontory. For additional beach protection, 15 groins were constructed along the eastern and western sides of the seawall in 2003 and 2005. To quantify erosion and accretion patterns along the Rosetta promontory, 11 Landsat images acquired at unequal intervals during a 40year time span (1972 and 2012) were analyzed. The positions of shorelines were automatically extracted from satellite imagery and compared with three very high resolution QuickBird and WorldView2 images for data validation. Analysis of the rates of shoreline change revealed that the construction of the seawall was largely successful in halting the recession along the tip of the promontory, which lost 10.8km2 prior to coastal protection. Conversely, the construction of the 15 groins has negatively affected the coastal morphology of the promontory and caused a reversal from accretion to fast erosion along the promontory leeside, where some segments of the shoreline have undergone as much as 30.8m year−1 of erosion. Without hard structures, the tip of the Rosetta promontory would have retreated 2.3km by 2013 and lost 7.2km2 of land. About 10% of this land is deltaic fertile cultivated farms. Moreover, without additional protection the sides of the promontory will lose about 1.3km2 of land and the coastline would recede at an average rate of 200m by 2020. Unless action is taken, coastal erosion, enhanced by rising sea level, will steadily eat away the Nile Delta at an alarming rate. The successful demonstration of the advocated procedures in this study could be adopted, with appropriate modifications, for other deltas worldwide.
Publication date: Available online 27 August 2014
Author(s): Nicholas S. Thaler , Griffin P. Sutton , Daniel N. Allen
Social cognition is a functionally relevant predictor of capacity in schizophrenia (SZ), though research concerning its value for bipolar disorder (BD) is limited. The current investigation examined the relationship between two social cognitive factors and functional capacity in bipolar disorder. This study included 48 individuals with bipolar disorder (24 with psychotic features) and 30 patients with schizophrenia. Multiple regression controlling for estimated IQ scores was used to assess the predictive value of social cognitive factors on the UCSD Performance-Based Functional Skills Assessment (UPSA). Results found that for the bipolar with psychosis and schizophrenia groups, the social/emotion processing factor predicted the UPSA. The theory of mind factor only predicted the UPSA for the schizophrenia group.. Findings support the clinical utility of evaluating emotion processing in individuals with a history of psychosis. For BD, theory of mind may be better explained by a generalized cognitive deficit. In contrast, social/emotion processing may be linked to distinct neurobiological processes associated with psychosis.
Publication date: Available online 26 August 2014
Author(s): S.D. Emslie , M.J. Polito , R. Brasso , W.P. Patterson , L. Sun
Ornithogenic or bird-formed soils have accumulated in many coastal regions around Antarctica as a result of breeding activities by pygoscelid penguins, especially the Adélie penguin (Pygoscelis adeliae). These soils are often deep, range from hundreds to thousands of years old, and contain a natural archive of penguin tissues and those of their prey. In some regions, these tissues are extremely well preserved by the dry, cold environment and include complete and partial penguin mummies, feathers, bone, and eggshell. Hard parts of prey (fish bones, otoliths, and squid beaks) also commonly occur in these deposits from the penguin guano as it accumulates during soil development. Here, we review how research on these soils and the tissues they contain has progressed since they were first identified and described. These studies have provided not only valuable information on penguin occupation history with climate change since the Pleistocene, but also whole ecosystem responses to perturbations such as the ‘krill surplus’ that is hypothesized to have occurred following historic depletion of seals and whales in the 18th–20th centuries. New findings in the Ross Sea indicate how penguin occupation and abandonment cycles have progressed over millennia in relation to climate change. In addition, stable isotope analysis of δ15N and δ13C in ancient and modern Adélie penguin tissues (feathers, bone, eggshell and membrane) and guano support the ‘krill surplus’ hypothesis in showing a dietary shift from fish to krill over the past ∼200 years. Other recent studies have focused on stable isotope analyses of penguin prey remains, as well as ancient DNA and mercury analyses of penguin tissues recovered from ornithogenic soils. An analysis of fish otoliths recovered from ancient guano provide a means to investigate values of otolith carbonate δ18O, which correlates with other paleoclimatic records, and can be used as a proxy for changing ocean temperatures through time. In addition, measurements of total mercury (Hg) in penguin egg membrane from abandoned colonies up to 800 years old indicate significantly higher mercury levels in the past compared to modern penguins, likely due to a greater reliance on higher trophic prey prior to the proposed ‘krill surplus’. All of these studies indicate that ornithogenic soils and the natural archive of tissues they contain provide a unique means to integrate both terrestrial and marine records with ecosystem studies and climate change, past and present, in Antarctica.
Publication date: Available online 21 August 2014
Source:The Journal of Social Studies Research
Author(s): Jeremy Hilburn , Brad M. Maguth
This qualitative case study draws on interview and focus group data from six Civics teachers. As global education scholars assert, local, national, and global “levels of citizenship” do not occur in a vacuum, instead, each level is invariably connected to one another. Teachers in this study, however, placed different priorities on the levels – prioritizing the national, minimizing the local, and marginalizing the global. Participants also used different teaching strategies in order to teach the different levels: emphasizing knowledge acquisition and values transmission at the national level and more active civic behaviors at the local level.
Evidence-Based Knowledge, Skills, and Attitudes for Scholarly Writing Development Across all Levels of Nursing Education
Publication date: July–August 2014
Source:Journal of Professional Nursing, Volume 30, Issue 4
Author(s): Diane F. Hunker , Elizabeth A. Gazza , Teresa Shellenbarger
Because nursing care in health care settings becomes more complex, nurses are called upon to work effectively with other health care providers to deliver high-quality evidence-based care. To do so in a cost effective and efficient manner requires the development of effective oral and written communication skills in nurses. One form of written communication is scholarly writing. Scholarly writing is defined by the authors as writing that is specialized in nursing, communicates original thought, includes support from a body of literature, contains formal language consistent with the discipline of nursing, and is formatted in a manner consistent with peer-review publications. Faculty who facilitate the development of these skills face inconsistencies in students' writing ability and development across programs and levels of education. Nurse educators need to understand how to develop these communication skills for students enrolled at various educational levels and to teach students how to share information in a scholarly way.
Validation of taxon-specific sampling by novice collectors for studying drilling predation in fossil bivalves
Publication date: 15 October 2014
Source:Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 412
Author(s): Kelly E. Hattori , Patricia H. Kelley , Gregory P. Dietl , Nicholas O. Moore , Sarah L. Simpson , Anna M. Zappulla , Kristina J. Ottens , Christy C. Visaggi
Although bulk sampling has been considered to provide more robust information on predation in the fossil record than taxon-specific (targeted) sampling, previous work suggested that targeted sampling, even by a trained novice, can yield results comparable to bulk sampling. The present study further investigates potential bias introduced by collectors with different experience levels by comparing drilling predation metrics for samples made by five novice and three veteran collectors. We demonstrate that trained novices produce results comparable to those of experienced collectors, and that results of targeted sampling are comparable to bulk sampling. Targeted sampling was performed in the lower Waccamaw Formation (lower Pleistocene) at Register Quarry near Old Dock, NC. Five replicate taxon-specific samples were obtained by each collector for the bivalves Astarte concentrica, Cyclocardia granulata, and Lirophora latilirata. Shell length and thickness were measured and position and size of drillholes were determined. Frequency of left valves, drilling frequency, prey effectiveness, and size selectivity were determined for each taxon replicate. For each variable, the results for the novice collectors were compared to those from bulk samples and all veteran collectors. Nearly all significant differences in the unstandardized data occurred in the size-related variables length and thickness. When data were size standardized, as in many other drilling predation studies, only 3.3% of 174 tests for statistical differences in collection methods were significant, and none of the 157 tests for differences in novice and veteran sampling was significant. Previous results were not anomalous; use of targeted sampling in studying drilling predation is again validated and collector expertise is shown to have minimal impact.
Implicit alcohol cognitions in risky drinking nicotine users with and without co-morbid major depressive disorder
Publication date: April 2014
Source:Addictive Behaviors, Volume 39, Issue 4
Author(s): Amy M. Cohn , Caroline Cobb , Brett T. Hagman , Amy Cameron , Sarah Ehlke , Jessica N. Mitchell
Objective Alcohol consumption, nicotine use, and major depressive disorder (MDD) are highly co-morbid. The negative reinforcement model of addiction would suggest that smokers may consume alcohol to relieve negative affective symptoms, such as those associated with MDD and withdrawal from nicotine. Over time, these behaviors may become so strongly paired together that they automatically activate a desire to use alcohol, even in the absence of conscious or deliberate intention. This study examined implicit alcohol cognitions in 146 risky drinking nicotine users (n=83) and non-users (n=63), to help uncover cognitive mechanisms that link drinking, nicotine use, and depression together. We proposed that nicotine users with a history of MDD would have stronger implicit motivations to drink than non-nicotine users without MDD. Method Participants were assessed on lifetime MDD (n=84) or no MDD (n=62), and then completed an Implicit Association Task designed to test the strength of associations between alcohol pictures and “approach” words. Results Regression analyses showed that implicit alcohol–approach attitudes were stronger among risky drinking nicotine users than non-users. Alcohol–approach motivations were also stronger among risky drinking nicotine users compared to non-users with a history of MDD; nicotine use was unrelated to implicit alcohol cognitions for risky drinkers without MDD. Conclusions Implicit cognitive processes may be targeted in behavioral and pharmacological treatments in risky drinking nicotine users, particularly those with depression comorbidity.
Goal specificity: A proxy measure for improvements in environmental outcomes in collaborative governance
Publication date: 1 December 2014
Source:Journal of Environmental Management, Volume 145
Author(s): Jennifer C. Biddle , Tomas M. Koontz
Collaborative governance critics continually call for evidence to support its prevalent use. As is often the case in environmental policy, environmental outcomes occur at a rate incompatible with political agendas. In addition, a multitude of possibly confounding variables makes it difficult to correlate collaborative governance processes with environmental outcomes. The findings of this study offer empirical evidence that collaborative processes have a measurable, beneficial effect on environmental outcomes. Through the use of a unique paired-waterbody design, our dataset reduced the potential for confounding variables to impact our environmental outcome measurements. The results of a path analysis indicate that the output of setting specific pollutant reduction goals is significantly related to watershed partnerships' level of attainment of their environmental improvement goals. The action of setting specific goals (e.g. percentage of load reductions in pollutant levels) is fostered by sustained participation from partnership members throughout the lifecycle of the collaborative. In addition, this study demonstrates the utility of logic modeling for environmental planning and management, and suggests that the process of setting specific pollutant reduction goals is a useful proxy measure for reporting progress towards improvements in environmental outcomes when long-term environmental data are not available.
Isolated salt marsh colonization by a resident species, mummichog (Fundulus heteroclitus), and a transient species, pinfish (Lagodon rhomboides)
Publication date: November 2014
Source:Journal of Experimental Marine Biology and Ecology, Volume 460
Author(s): David L. Meyer , Martin H. Posey
The potential for species to populate habitat patches is directly influenced by dispersal and colonization abilities. To test the dispersal and colonization capabilities of a resident, mummichog (Fundulus heteroclitus), and a transient, pinfish (Lagodon rhomboides), marsh species, isolated-island marsh sites were used for removal and colonization assessments, while a nearby non-removal site was used to concurrently monitor temporal catch variability. F. heteroclitus and L. rhomboides were removed from island marshes using baited minnow traps during mid-fall 2004 (after F. heteroclitus spring/summer spawn, and prior to L. rhomboides winter recruitment), then monitored for colonization through the peak F. heteroclitus spawning season the following year (July 2005). Significant abundance reductions occurred for F. heteroclitus and L. rhomboides due to removal efforts, and for L. rhomboides due to temperature-dependent offshore migration. F. heteroclitus and L. rhomboides were capable of seasonally colonizing marsh sites separated by >800m of open water, which was twice the previously documented distance for F. heteroclitus movement within marsh habitats. Results from size-class analysis indicated that F. heteroclitus populated sites via adult colonization from nearby marshes within weeks to months of removal. L. rhomboides site colonization occurred by young-of-year (YOY) recruitment and was documented within months of removal efforts, when YOY attained sufficient size for gear collection. Low population contribution by F. heteroclitus YOY to island compared to mainland type marsh indicated that island marshes were primarily sustained by immigrants, which colonized during late fall and winter, while YOY production sustained the population at the mainland marsh. Island marshes acted as sinks for estuarine F. heteroclitus populations. F. heteroclitus population characteristics were determined during: (1) the spring/summer spawn and recruitment, and (2) the late fall/winter dispersal–colonization by adult F. heteroclitus. Further, the F. heteroclitus dispersal–colonization phase maintains the species' large-scale (geographic) distribution, while the spawn–recruitment phase maintains the small-scale (local) populations. L. rhomboides recruitment and dispersal–colonization occur simultaneously during late fall/winter when pulsed dispersal–colonization by recruits maintains geographic and local populations.
Publication date: October 2014
Source:Neurobiology of Learning and Memory, Volume 114
Author(s): Andrew Hawkey , L. Brooke April , Mark Galizio
The effects of acute and sub-chronic MDMA were assessed using a procedure designed to test rodent working memory capacity: the odor span task (OST). Rats were trained to select an odor that they had not previously encountered within the current session, and the number of odors to remember was incremented up to 24 during the course of each session. In order to separate drug effects on the OST from more general performance impairment, a simple olfactory discrimination was also assessed in each session. In Experiment 1, acute doses of MDMA were administered prior to select sessions. MDMA impaired memory span in a dose-dependent fashion, but impairment was seen only at doses (1.8 and 3.0mg/kg) that also increased response omissions on both the simple discrimination and the OST. In Experiment 2, a sub-chronic regimen of MDMA (10.0mg/kg, twice daily over four days) was administered after OST training. There was no evidence of reduced memory span following sub-chronic MDMA, but a temporary increase in omission errors on the OST was observed. In addition, rats exposed to sub-chronic MDMA showed delayed learning when the simple discrimination was reversed. Overall, the disruptive effects of both acute and sub-chronic MDMA appeared to be due to non-mnemonic processes, rather than effects on specific memory functions.
Assessing source contributions to particulate organic matter in a subtropical estuary: A biomarker approach
Publication date: October 2014
Source:Organic Geochemistry, Volume 75
Author(s): Ding He , Ralph N. Mead , Laura Belicka , Oliva Pisani , Rudolf Jaffé
Assessing the sources and quantifying the contributions of particulate organic matter (POM) in estuaries is a challenge. Here we apply source-specific biomarkers to assess POM sources in an estuary receiving suspended material from freshwater wetlands, fringe mangroves and coastal environments. A three end-member mixing model, including terrestrial, estuarine and marine end-member contributions was developed and successfully validated to assess general OM dynamics and hydrologic processes that control POM distributions within the Shark River estuary in South Florida. Low tide and wet season conditions coincided with an enhanced signal of the freshwater end-member biomarker abundance, while high tide and dry season conditions resulted in enhanced POM input of marine origin. Incoming tide was observed to be an important factor in the re-suspension and tidal pumping of mangrove-derived POM, which seems to be the dominant source of particulate organic carbon (POC) in the estuary. The three end-member conceptual model was tested to obtain a rough estimate of POC source strength, with the ultimate goal of constraining carbon budgets in this sub-tropical estuary. Mangrove-derived POC flux of ca. 5.3×105 to 1.0×106 kg/yr POC from the Shark River to the Gulf of Mexico were estimated, but end-member values used in the assessment need to be better constrained to reduce the degree of variability.
Molluscan live–dead agreement in anthropogenically stressed seagrass habitats: Siliciclastic versus carbonate environments
Publication date: 15 September 2014
Source:Palaeogeography, Palaeoclimatology, Palaeoecology, Volume 410
Author(s): Chelsea A. Korpanty , Patricia H. Kelley
Molluscan live–dead fidelity studies investigate the influences of anthropogenic activities on marine ecosystems by comparing the taxonomic composition of a living community to its corresponding death assemblage. Environments subjected to intense anthropogenic stresses tend to yield low fidelity (high discordance) in rank-order abundance and taxonomic similarity between living and dead assemblages. This project assesses the sensitivity of the live–dead approach by applying various fidelity metrics – community richness (Delta-S), evenness (Delta-PIE), rank-order correlation (Spearman rho), and taxonomic similarity (Jaccard–Chao) – to molluscan assemblages in seagrass habitats exposed to anthropogenic stresses in different sedimentary environments. Our study sites include siliciclastic sites in North Carolina, carbonate sites in Florida Bay, and a siliciclastic–carbonate transition locality along the coast of southern Florida. The dominant forms of human stresses at these seagrass sites consist of increased freshwater runoff, increased nutrient runoff, and physical substrate disturbance by dredging (North Carolina) and propeller scarring (Florida Bay). As a result of such anthropogenic stresses, we expected to find low live–dead fidelity results at all of our study sites. We also anticipated variations in the results between sedimentary environments, reflecting intrinsic differences in how molluscan material accumulates and is preserved in siliciclastic versus carbonate settings. Using bulk sediment samples, fidelity analyses consistently yield greater live–dead disagreement at the siliciclastic sites. Despite well-documented historical human stresses to Florida Bay and sediment cores indicating multiple ecological shifts in response to human impacts over time, results from carbonate localities yield higher fidelity and provide little evidence for ecological change. We argue that greater time averaging allows for the death assemblages at the siliciclastic sites to retain a longer memory of the local communities, thus preserving evidence of local ecological changes. In contrast, less time averaging and more rapid live–dead equilibration in carbonate sediments reduces the signal of community changes. Thus we propose that the live–dead fidelity approach is more sensitive at detecting recent ecological changes in siliciclastic versus carbonate environments, confirming the conservative nature of the approach and demonstrating the role of taphonomic bias in live–dead methodology.
Lysylated phospholipids stabilize models of bacterial lipid bilayers and protect against antimicrobial peptides
Publication date: September 2014
Source:Biochimica et Biophysica Acta (BBA) - Biomembranes, Volume 1838, Issue 9
Author(s): Elizabeth Cox , Austen Michalak , Sarah Pagentine , Pamela Seaton , Antje Pokorny
Aminoacylated phosphatidylglycerols are common lipids in bacterial cytoplasmic membranes. Their presence in Staphylococcus aureus has been linked to increased resistance to a number of antibacterial agents, including antimicrobial peptides. Most commonly, the phosphatidylglycerol headgroup is esterified to lysine, which converts anionic phosphatidylglycerol into a cationic lipid with a considerably increased headgroup size. In the present work, we investigated the interactions of two well-studied antimicrobial peptides, cecropin A and mastoparan X, with lipid vesicles composed of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG), containing varying fractions of an aminoacylated phosphatidylethanolamine, a stable analog of the corresponding phosphatidylglycerol-derivative. To differentiate between the effects of headgroup size and charge on peptide–lipid interactions, we synthesized two different derivatives. In one, the headgroup was modified by the addition of lysine, and in the other, by glutamine. The modification by glutamine results in a phospholipid with a headgroup size comparable to that of the lysylated version. However, whereas lysyl-phosphatidylethanolamine (Lys-PE) is cationic, glutaminyl-phosphatidylethanolamine (Gln-PE) is zwitterionic. We found that binding of mastoparan X and cecropin A was not significantly altered if the content of aminoacylated phosphatidylethanolamines did not exceed 20mol.%, which is the concentration found in bacterial membranes. However, a lysyl-phosphatidylethanolamine content of 20mol% significantly inhibits dye release from lipid vesicles, to a degree that depends on the peptide. In the case of mastoparan X, dye release is essentially abolished at 20mol.% lysyl-phosphatidylethanolamine, whereas cecropin A is less sensitive to the presence of lysyl-phosphatidylethanolamine. These observations are understood through the complex interplay between peptide binding and membrane stabilization as a function of the aminoacylated lipid content. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.