Closing the Gap between Experiment and Simulation─A Holistic Study on the Complexation of Small Interfering RNAs with Polyethylenimine.

Rational design is pivotal in the modern development of nucleic acid nanocarrier systems. With the rising prominence of polymeric materials as alternatives to lipid-based carriers, understanding their structure-function relationships becomes paramount. Here, we introduce a newly developed coarse-grained model of polyethylenimine (PEI) based on the Martini 3 force field. This model facilitates molecular dynamics simulations of true-sized PEI molecules, exemplified by molecules with molecular weights of 1.3, 5, 10, and 25 kDa, with degrees of branching between 50.0 and 61.5%. We employed this model to investigate the thermodynamics of small interfering RNA (siRNA) complexation with PEI. Our simulations underscore the pivotal role of electrostatic interactions in the complexation process. Thermodynamic analyses revealed a stronger binding affinity with increased protonation, notably in acidic (endosomal) pH, compared to neutral conditions. Furthermore, the molecular weight of PEI was found to be a critical determinant of binding dynamics: smaller PEI molecules closely enveloped the siRNA, whereas larger ones extended outward, facilitating the formation of complexes with multiple RNA molecules. Experimental validations, encompassing isothermal titration calorimetry and single-molecule fluorescence spectroscopy, aligned well with our computational predictions. Our findings not only validate the fidelity of our PEI model but also accentuate the importance of in silico data in the rational design of polymeric drug carriers. The synergy between computational predictions and experimental validations, as showcased here, signals a refined and precise approach to drug carrier design.

Efficient and Targeted siRNA Delivery to M2 Macrophages by Smart Polymer Blends for M1 Macrophage Repolarization as a Promising Strategy for Future Cancer Treatment.

Cancer remains an issue on a global scale. It is estimated that nearly 10 million people succumbed to cancer worldwide in 2020. New treatment options are urgently needed. A promising approach is a conversion of tumor-promoting M2 tumor-associated macrophages (TAMs) as part of the tumor microenvironment to tumor-suppressive M1 TAMs by small interfering RNA (siRNA). In this work, we present a well-characterized polymeric nanocarrier system capable of targeting M2 TAMs by a ligand-receptor interaction. Therefore, we developed a blended PEI-based polymeric nanoparticle system conjugated with mannose, which is internalized after interaction with macrophage mannose receptors (MMRs), showing low cytotoxicity and negligible IL-6 activation. The PEI-PCL-PEI (5 kDa-5 kDa-5 kDa) and Man-PEG-PCL (2 kDa-2 kDa) blended siRNA delivery system was optimized for maximum targeting capability and efficient endosomal escape by evaluation of different polymer and N/P ratios. The nanoparticles were formulated by surface acoustic wave-assisted microfluidics, achieving a size of ∼80 nm and a zeta potential of approximately +10 mV. Special attention was given to the endosomal escape as the so-called bottleneck of RNA drug delivery. To estimate the endosomal escape capability of the nanocarrier system, we developed a prediction method by evaluating the particle stability via the inflection temperature. Our predictions were then verified in an in vitro setting by applying confocal microscopy. For cellular experiments, however, human THP-1 cells were polarized to M2 macrophages by cytokine treatment and validated through MMR expression. To show the efficiency of the nanoparticle system, GAPDH and IκBα knockdown was performed in the presence or absence of an MMR blocking excess of mannan. Cellular uptake, GAPDH knockdown, and NF-κB western blot confirmed efficient mannose targeting. Herein, we presented a well-characterized nanoparticle delivery system and a promising approach for targeting M2 macrophages by a mannose-MMR interaction.

First-Line Pembrolizumab Mono- or Combination Therapy of Non-Small Cell Lung Cancer: Baseline Metabolic Biomarkers Predict Outcomes.

Quantitative biomarkers derived from positron-emission tomography/computed tomography (PET/CT) have been suggested as prognostic variables in immune-checkpoint inhibitor (ICI) treated non-small cell lung cancer (NSCLC). As such, data for first-line ICI therapy and especially for chemotherapy-ICI combinations are still scarce, we retrospectively evaluated baseline 18F-FDG-PET/CT of 85 consecutive patients receiving first-line pembrolizumab with chemotherapy (n = 70) or as monotherapy (n = 15). Maximum and mean standardized uptake value, total metabolic tumor volume (MTV), total lesion glycolysis, bone marrow-/and spleen to liver ratio (BLR/SLR) were calculated. Kaplan-Meier analyses and Cox regression models were used to assess progression-free/overall survival (PFS/OS) and their determinant variables. Median follow-up was 12 months (M; 95% confidence interval 10-14). Multivariate selection for PFS/OS revealed MTV as most relevant PET/CT biomarker (p < 0.001). Median PFS/OS were significantly longer in patients with MTV ≤ 70 mL vs. >70 mL (PFS: 10 M (4-16) vs. 4 M (3-5), p = 0.001; OS: not reached vs. 10 M (5-15), p = 0.004). Disease control rate was 81% vs. 53% for MTV ≤/> 70 mL (p = 0.007). BLR ≤ 1.06 vs. >1.06 was associated with better outcomes (PFS: 8 M (4-13) vs. 4 M (3-6), p = 0.034; OS: 19 M (12-/) vs. 6 M (4-12), p = 0.005). In patients with MTV > 70 mL, concomitant BLR ≤ 1.06 indicated a better prognosis. Higher MTV is associated with inferior PFS/OS in first-line ICI-treated NSCLC, with BLR allowing additional risk stratification.

Sex-Based Clinical Outcome in Advanced NSCLC Patients Undergoing PD-1/PD-L1 Inhibitor Therapy-A Retrospective Bi-Centric Cohort Study.

Men with non-small cell lung cancer (NSCLC) have a more favorable response to immune-checkpoint inhibitor (ICI) monotherapy, while women especially benefit from ICI-chemotherapy (CHT) combinations. To elucidate such sex differences in clinical practice, we retrospectively analyzed two cohorts treated with either ICI monotherapy (n = 228) or ICI-CHT combination treatment (n = 80) for advanced NSCLC. Kaplan-Meier analyses were used to calculate progression-free (PFS) and overall survival (OS), influencing variables were evaluated using Cox-regression analyses. No significant sex differences for PFS/OS could be detected in either cohort. Men receiving ICI monotherapy had a statistically significant independent impact on PFS by Eastern Cooperative Oncology Group performance status (ECOG) ≥2 (hazard ratio (HR) 1.90, 95% confidence interval (CI): 1.10-3.29, p = 0.021), higher C-reactive protein (CRP; HR 1.06, 95%CI: 1.00-1.11, p = 0.037) and negative programmed death-ligand 1 (PD-L1) status (HR 2.04, 95%CI: 1.32-3.15, p = 0.001), and on OS by CRP (HR 1.09, 95%CI: 1.03-1.14, p = 0.002). In men on ICI-CHT combinations, multivariate analyses (MVA) revealed squamous histology (HR 4.00, 95%CI: 1.41-11.2, p = 0.009) significant for PFS; and ECOG ≥ 2 (HR 5.58, 95%CI: 1.88-16.5, p = 0.002) and CRP (HR 1.19, 95%CI: 1.06-1.32, p = 0.002) for OS. Among women undergoing ICI monotherapy, no variable proved significant for PFS, while ECOG ≥ 2 had a significant interaction with OS (HR 1.90, 95%CI 1.04-3.46, p = 0.037). Women treated with ICI-CHT had significant MVA findings for CRP with both PFS (HR 1.09, 95%CI: 1.02-1.16, p = 0.007) and OS (HR 1.11, 95%CI: 1.03-1.19, p = 0.004). Although men and women responded similarly to both ICI mono- and ICI-CHT treatment, predictors of response differed by sex.

Serum Tumor Marker Dynamics as Predictive Biomarkers in NSCLC Chemo-Immunotherapy and Mono-Immunotherapy Maintenance: A Registry-Based Descriptive Study.

OBJECTIVE: To evaluate serum tumor markers (STM) as predictive biomarkers in advanced non-small cell lung cancer (NSCLC) treated with chemo-immunotherapy. METHODS: Patients having received platinum-based chemo-(CHT) and PD-1/PD-L1-directed immune checkpoint inhibitor (ICI) combination therapy were retrospectively followed. Carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA19-9), cytokeratin-19 fragments (CYFRA 21-1) and neuron specific enolase (NSE) were routinely measured at NSCLC diagnosis. The marker with the highest relative elevation was defined "leading STM", its change was assessed between CHT-ICI as well as mono-ICI maintenance initiation and the respective subsequent restaging. Corresponding computed tomography evaluations were analyzed using response evaluation criteria in solid tumors (RECIST). For CHT-ICI combination and subsequent mono-ICI-maintenance therapy, leading STM and RECIST response were evaluated regarding progression-free (PFS) and overall survival (OS) in Kaplan-Meier analyses. RESULTS: Among 80 CHT-ICI patients (41% women, mean age 63 years), median PFS was 5 months (M;4,9), median OS was 15M (10,/). PFS was significantly (p=0.042) longer, when the leading STM had decreased at first restaging under CHT-ICI combination therapy (9M (5,12; n=41) vs 5M (3,6; n=16)). In the 54 (67.5%) patients who received subsequent mono-ICI maintenance therapy, STM decrease was similarly associated with significantly (p<0.001) longer PFS (16M (7,/; n=16) vs 3.5M (2,6; n=22)). Patients with radiologically stable or progressive disease and concomitant leading STM decrease had similar PFS in the CHT-ICI combination phase (4M (3,7; n=16) vs 4.5M (2,6; n=14)), but longer PFS in the mono-ICI maintenance setting (13M (7,16; n=10) vs 3M (2,4; n=17)). Median OS was not reached in most subgroups. CONCLUSION: Leading STM dynamics provide predictive biomarker information additional to radiological response evaluation patients receiving CHT-ICI combination therapy, especially in the mono-ICI maintenance setting.

Quality of Life and Limitations in Daily Life of Stable COPD Outpatients in a Real-World Setting in Austria - Results from the CLARA Project.

Background: COPD patients suffer from respiratory symptoms and limitations in daily life. We aimed to characterize the impact of disease on overall health, daily life, and perceived well-being in COPD outpatients. Methods: We conducted a national, cross-sectional study among pulmonologists and general practitioners (GPs). The St. George's Respiratory Questionnaire for COPD patients (SGRQ-C) was used. Inclusion criteria were a physician's diagnosis of COPD and age ≥40 years. Subjects with a history of lung surgery, lung cancer or COPD exacerbation within the last four weeks were excluded. Results: Sixty-seven pulmonologists and 6 GPs enrolled 1175 COPD patients. Two hundred forty-eight of those did not fulfill GOLD criteria for COPD (FEV1/FVC <0.7) and 77 were excluded due to missing data. Finally, 850 patients (62.8% men; mean age 66.2 ± 0.3 (SE) years; mean FEV1%pred. 51.5 ± 0.6 (SE)) were analyzed. Last year, 55.4% reported at least one exacerbation, and 12.7% were hospitalized for COPD exacerbation. Mean SGRQ-C total score was 43.1 ± 0.83 (SE) and mean component scores for symptoms, activity and impacts were 55.6, 55.4 and 30.5, respectively. Half of the patients (50.3%) reported not being able to do any sports and 78.7% stated that their respiratory symptoms did not allow them doing anything they would like to do. In patients with less severe COPD (FEV1pred ≥50% and non-frequent exacerbations), global health status was overrated, ie, estimated as better by the physician than by the patient, while it was underrated in more severe COPD. Conclusion: In Austria, the burden of disease in COPD outpatients tends to be underestimated in patients with milder airway obstruction and less exacerbations and overestimated in patients with more severe airway obstruction and frequent exacerbations. Our finding suggests that validated assessment of global health status might decrease these differences of perception.

Drug repositioning is an alternative for the treatment of coronavirus COVID-19.

Given the extreme importance of the current pandemic caused by COVID-19, and as scientists agree there is no identified pharmacological treatment, where possible, therapeutic alternatives are raised through drug repositioning. This paper presents a selection of studies involving drugs from different pharmaceutical classes with activity against SARS-CoV-2 and SARS-CoV, with the potential for use in the treatment of COVID-19 disease.

Therapy Line and Associated Predictors of Response to PD-1/PD-L1-Inhibitor Monotherapy in Advanced Non-small-Cell Lung Cancer: A Retrospective Bi-centric Cohort Study.

BACKGROUND: Evidence on PD-1/PD-L1-directed immune checkpoint inhibitor (ICI) therapy for advanced non-small-cell lung cancer (NSCLC) is mainly based on clinical trials in first- or second-line settings. OBJECTIVE: We aimed to investigate response and prognostic factors with special regard to third- or later-line therapy. PATIENTS AND METHODS: We retrospectively analyzed all patients who had received ICI monotherapy with nivolumab, pembrolizumab, or atezolizumab for advanced NSCLC. Computed tomography evaluations were analyzed using response evaluation criteria in solid tumors (RECIST, version 1.1). Kaplan-Meier analyses were conducted to calculate progression-free (PFS) and overall (OS) survival; the impact of influencing variables was evaluated using uni- and multivariate Cox-regression analyses. RESULTS: Among 153 patients (59% men, mean age 66 years), median PFS was 4 months [mo; 95% confidence interval (95% CI) 3-5], OS was 13 mo (10-17), and objective response rate (ORR) was 22%. Therapy line ≥ 3 was associated with significantly inferior PFS (p = 0.003) and OS (p = 0.001). In first-line therapy PFS, OS, and ORR were 7 mo (3-11), 17 mo [9-not evaluable (n.e.)], and 36%; in second-line 4 mo (3-7), 18 mo (13-n.e.) and 19%, and in ≥ third-line 2 mo (1-3), 9 mo (4-12), and 13%. PFS was significantly influenced by PD-L1 expression in first-line therapy (p = 0.006). In ≥ third-line patients, Eastern Cooperative Oncology Group (ECOG) performance status significantly affected PFS and OS (both p < 0.001). CONCLUSIONS: Third- or later-line single-agent anti-PD-1/PD-L1 therapy is less efficacious as compared to first- and second-line treatment. In that setting, ECOG performance status predominates known predictors like PD-L1 expression or presence of an alteration in EGFR or ALK.

Early serum tumor marker dynamics predict progression-free and overall survival in single PD-1/PD-L1 inhibitor treated advanced NSCLC-A retrospective cohort study.

OBJECTIVES: To evaluate serum tumor markers (STM) as biomarkers for treatment monitoring and prognosis in advanced non-small cell lung cancer (NSCLC) treated with single-agent PD-1/PD-L1-directed immune checkpoint inhibitor (ICI) therapy. MATERIALS AND METHODS: Carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA19-9), cytokeratin-19 fragments (CYFRA 21-1) and neuron specific enolase (NSE) were routinely measured at NSCLC diagnosis, initially elevated markers were used for follow-up. Leading STM change between ICI initiation and first subsequent restaging as well as corresponding computed tomography evaluations according to response evaluation criteria in solid tumors (RECIST) were retrospectively analyzed regarding progression-free (PFS) and overall survival (OS). In uni- and multivariate stepwise Cox-regression analyses, STM and RECIST response were analyzed for their impact on PFS and OS together with other known prognostic patient and tumor characteristics. RESULTS: Among 84 patients (61% men, mean age 68 years), median PFS was significantly (p < 0.001) longer, when STM decreased (11 M (7,19) N = 37) than in case of increases (<2-fold: 6 M (3,8) N = 31; ≥2-fold: 2 M (1,2) N = 16). Patients with initial STM decrease had longer (p < 0.001) median OS (not reached) than with STM increase (<2-fold: 14 M (12,26); ≥2-fold: 4 M (3,7)). Patients with stable or progressive disease by RECIST and concomitant STM decrease had longer (p < 0.001) PFS and OS (8 M (4,14) and 18 M (10,n.e.) N = 24) than upon STM increase (PFS: 2 M (2,4); OS: 10 M (6,13) N = 42). Significant impact on PFS was shown for STM response (p < 0.001), RECIST response (p = 0.003) and PD-L1 status (p = 0.003). For OS, STM response (p < 0.001), presence of cerebral metastases (p = 0.036) and therapy line ≥3 (p = 0.001) were identified. CONCLUSION: Decreasing leading STM at first restaging predict longer PFS and OS and identify patients with favorable outcomes among initial radiological non-responders in ICI treated NSCLC patients.

Overdiagnosis of COPD in Subjects With Unobstructed Spirometry: A BOLD Analysis.

BACKGROUND: There are several reports on underdiagnosis of COPD, while little is known about COPD overdiagnosis and overtreatment. We describe the overdiagnosis and the prevalence of spirometrically defined false positive COPD, as well as their relationship with overtreatment across 23 population samples in 20 countries participating in the BOLD Study between 2003 and 2012. METHODS: A false positive diagnosis of COPD was considered when participants reported a doctor's diagnosis of COPD, but postbronchodilator spirometry was unobstructed (FEV1/FVC > LLN). Additional analyses were performed using the fixed ratio criterion (FEV1/FVC < 0.7). RESULTS: Among 16,177 participants, 919 (5.7%) reported a previous medical diagnosis of COPD. Postbronchodilator spirometry was unobstructed in 569 subjects (61.9%): false positive COPD. A similar rate of overdiagnosis was seen when using the fixed ratio criterion (55.3%). In a subgroup analysis excluding participants who reported a diagnosis of "chronic bronchitis" or "emphysema" (n = 220), 37.7% had no airflow limitation. The site-specific prevalence of false positive COPD varied greatly, from 1.9% in low- to middle-income countries to 4.9% in high-income countries. In multivariate analysis, overdiagnosis was more common among women, and was associated with higher education; former and current smoking; the presence of wheeze, cough, and phlegm; and concomitant medical diagnosis of asthma or heart disease. Among the subjects with false positive COPD, 45.7% reported current use of respiratory medication. Excluding patients with reported asthma, 34.4% of those with normal spirometry still used a respiratory medication. CONCLUSIONS: False positive COPD is frequent. This might expose nonobstructed subjects to possible adverse effects of respiratory medication.

Complications of CT-guided transthoracic lung biopsy : A short report on current literature and a case of systemic air embolism.

Percutaneous computed tomography (CT)-guided transthoracic needle biopsy (PCNB) is a common diagnostic procedure and is especially indispensable in thoracic oncology. Complications, such as pulmonary hemorrhage and pneumothorax are frequent, but usually easy to manage. Systemic air embolism is a rare but relevant adverse event and its true incidence is probably underestimated, as not all cases may become clinically apparent. We present a case of systemic air embolism following a core-needle biopsy of a left upper lobe lesion, where immediately after the procedure CT scans documented air in the thoracic aorta and in the left ventricle. In this context, we review the current literature on technical aspects as well as on frequent and infrequent major complications of PCNB, together with risk factors, emergency treatment and prevention strategies.

Stable Europium(III) Complexes with Short Linkers for Site-Specific Labeling of Biomolecules.

In this study, two new terpyridine-based EuIII complexes were synthesized, the structures of which were optimized for luminescence resonance energy-transfer (LRET) experiments. The complexes showed high quantum yields (32 %); a single long lifetime (1.25 ms), which was not influenced by coupling to protein; very high stability in the presence of chelators such as ethylenediamine-N,N,N',N'-tetraacetate and ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid; and no interaction with cofactors such as adenosine triphosphate and guanosine triphosphate. A special feature is the short length of the linker between the EuIII ion and the maleimide or hydrazide function, which allows for site-specific coupling of cysteine mutants or unnatural keto amino acids. As a consequence, the new complexes appear particularly suited for accurate distance measurements in biomolecules by LRET.

Pneumonia caused by Bordetella bronchiseptica in two HIV-positive patients / Pneumonia causada por Bordetella bronchiseptica em dois pacientes HIV-positivos

ABSTRACT: CONTEXT AND OBJECTIVE: Bordetella bronchiseptica (BB) is a Gram-negative coccobacillus responsible for respiratory diseases in dogs, cats and rabbits. Reports on its development in humans are rare. However, in immunosuppressed patients, especially in those with the immunodeficiency virus (HIV), BB can cause severe pulmonary infections. We report on two cases of pneumonia caused by BB in HIV-positive male patients in a university hospital. CASE REPORT: The first case comprised a 43-year-old patient who was admitted presenting chronic leg pain and coughing, with suspected pneumonia. BB was isolated from sputum culture and was successfully treated with trimethoprim/sulfamethoxazole in association with levofloxacin. The second case comprised a 49-year-old patient who was admitted presenting fever, nausea, sweating and a dry cough, also with suspected pneumonia. BB was isolated from sputum culture, tracheal secretions and bronchoalveolar lavage. The disease was treated with ciprofloxacin but the patient died. CONCLUSION: BB should be included in the etiology of pneumonia in immunodeficient HIV patients. As far as we know, these two were the first cases of pneumonia due to BB to occur in this university hospital.

RESUMO CONTEXTO E OBJETIVO: Bordetella bronchiseptica (BB) é um cocobacilo Gram-negativo responsável por causar doenças no trato respiratório de cães, gatos e coelhos. São raros os relatos do desenvolvimento desse microrganismo em seres humanos. Porém, em pacientes imunodeprimidos, especialmente nos portadores do vírus da imunodeficiência humana (HIV), a BB pode causar infecções pulmonares graves. Nós relatamos dois casos de pneumonia por BB em pacientes do sexo masculino, HIV-positivos em um hospital universitário. RELATO DE CASO: No primeiro caso, o paciente de 43 anos foi internado apresentando dor crônica nos membros inferiores e tosse com suspeita de pneumonia. Na cultura de escarro, foi isolado BB, e a infecção foi tratada com sucesso com a associação de sulfametoxazol/trimetroprima e levofloxacino. No segundo caso, o paciente de 49 anos foi internado apresentando febre, náuseas, sudorese e tosse seca, também com suspeita de pneumonia. Das culturas de escarro, secreção traqueal e lavado bronco-alveolar, foi isolado BB, infecção tratada com ciprofloxacino: porém, o paciente foi a óbito. CONCLUSÃO: BB deve ser incluído na etiologia de pneumonia em pacientes imunocomprometidos com HIV. Pelo que é de nosso conhecimento, estes dois relatos foram os primeiros casos de pneumonia por BB que ocorreram neste hospital universitário.

Staphylococcal scalded skin syndrome in a premature newborn caused by methicillin-resistant Staphylococcus aureus: case report / Síndrome da pele escaldada estafilocócica em um recém-nascido prematuro causada por Staphylococcus aureus meticilina-resistente: relato de caso

CONTEXT: Staphylococcal scalded skin syndrome is an exfoliative skin disease. Reports of this syndrome in newborns caused by methicillin-resistant Staphylococcus aureus are rare but, when present, rapid diagnosis and treatment is required in order to decrease morbidity and mortality. CASE REPORT: A premature newly born girl weighing 1,520 g, born with a gestational age of 29 weeks and 4 days, developed staphylococcal scalded skin syndrome on the fifth day of life. Cultures on blood samples collected on the first and fourth days were negative, but Pseudomonas aeruginosa and Enterococcus sp. (vancomycin-sensitive) developed in blood cultures performed on the day of death (seventh day), and Pseudomonas aeruginosa and Serratia marcescens were identified in cultures on nasopharyngeal, buttock and abdominal secretions. In addition to these two Gram-negative bacilli, methicillin-resistant Staphylococcus aureus was isolated in a culture on the umbilical stump (seventh day). The diagnosis of staphylococcal scalded skin syndrome was based on clinical criteria.

CONTEXTO: A síndrome da pele escaldada estafilocócica é uma doença esfoliativa de pele. São raros os relatos desta síndrome causada por Staphylococcus aureusresistente à meticilina em neonatos, mas, quando presentes, exigem diagnóstico e tratamento rápidos para diminuir a morbidade e mortalidade. RELATO DE CASO: Uma menina recém-nascida prematura, pesando 1.520 g ao nascimento, com idade gestacional de 29 semanas e 4 dias, desenvolveu síndrome da pele escaldada estafilocócica no quinto dia de vida. As culturas de sangue coletadas no primeiro e quarto dias foram negativas, mas houve desenvolvimento de Pseudomonas aeruginosa e Enterococcus sp. (vancomicina sensível) na hemocultura realizada no dia do óbito (sétimo dia) e Pseudomonas aeruginosa e Serratia marcescens foram identificadas nas culturas de secreção da nasofaringe, nádega e da secreção abdominal. Na cultura do coto umbilical (sétimo dia), além desses dois bacilos Gram-negativos, foi isolado o Staphylococcus aureus resistente à meticilina. O diagnóstico da síndrome da pele escaldada estafilocócica foi baseado em critério clínico.

Electrostatically induced recruitment of membrane peptides into clusters requires ligand binding at both interfaces.

Protein recruitment to specific membrane locations may be governed or facilitated by electrostatic attraction, which originates from a multivalent ligand. Here we explored the energetics of a model system in which this simple electrostatic recruitment mechanism failed. That is, basic poly-L-lysine binding to one leaflet of a planar lipid bilayer did not recruit the triply-charged peptide (O-Pyromellitylgramicidin). Clustering was only observed in cases where PLL was bound to both channel ends. Clustering was indicated (i) by the decreased diffusional PLL mobility D(PLL) and (ii) by an increased lifetime τ(PLL) of the clustered channels. In contrast, if PLL was bound to only one leaflet, neither D(PLL) nor τ(P) changed. Simple calculations suggest that electrostatic repulsion of the unbound ends prevented neighboring OPg dimers from approaching each other. We believe that a similar mechanism may also operate in cell signaling and that it may e.g. contribute to the controversial results obtained for the ligand driven dimerization of G protein-coupled receptors.

Cationic amphipathic peptides accumulate sialylated proteins and lipids in the plasma membrane of eukaryotic host cells.

Cationic antimicrobial peptides (CAMPs) selectively target bacterial membranes by electrostatic interactions with negatively charged lipids. It turned out that for inhibition of microbial growth a high CAMP membrane concentration is required, which can be realized by the incorporation of hydrophobic groups within the peptide. Increasing hydrophobicity, however, reduces the CAMP selectivity for bacterial over eukaryotic host membranes, thereby causing the risk of detrimental side-effects. In this study we addressed how cationic amphipathic peptides-in particular a CAMP with Lysine-Leucine-Lysine repeats (termed KLK)-affect the localization and dynamics of molecules in eukaryotic membranes. We found KLK to selectively inhibit the endocytosis of a subgroup of membrane proteins and lipids by electrostatically interacting with negatively charged sialic acid moieties. Ultrastructural characterization revealed the formation of membrane invaginations representing fission or fusion intermediates, in which the sialylated proteins and lipids were immobilized. Experiments on structurally different cationic amphipathic peptides (KLK, 6-MO-LF11-322 and NK14-2) indicated a cooperation of electrostatic and hydrophobic forces that selectively arrest sialylated membrane constituents.

Routes of epithelial water flow: aquaporins versus cotransporters.

The routes water takes through membrane barriers is still a matter of debate. Although aquaporins only allow transmembrane water movement along an osmotic gradient, cotransporters are believed to be capable of water transport against the osmotic gradient. Here we show that the renal potassium-chloride-cotransporter (KCC1) does not pump a fixed amount of water molecules per movement of one K(+) and one Cl(-), as was reported for the analogous transporter in the choroid plexus. We monitored water and potassium fluxes through monolayers of primary cultured renal epithelial cells by detecting tiny solute concentration changes in the immediate vicinity of the monolayer. KCC1 extruded K(+) ions in the presence of a transepithelial K(+) gradient, but did not transport water. KCC1 inhibition reduced epithelial osmotic water permeability P(f) by roughly one-third, i.e., the effect of inhibitors was small in resting cells and substantial in hormonal stimulated cells that contained high concentrations of aquaporin-2 in their apical membranes. The furosemide or DIOA (dihydroindenyl-oxy-alkanoic acid)-sensitive water flux was much larger than expected when water passively followed the KCC1-mediated ion flow. The inhibitory effect of these drugs on water flux was reversed by the K(+)-H(+) exchanger nigericin, indicating that KCC1 affects water transport solely by K(+) extrusion. Intracellular K(+) retention conceivably leads to cell swelling, followed by an increased rate of endocytic AQP2 retrieval from the apical membrane.

Coupled diffusion of peripherally bound peptides along the outer and inner membrane leaflets.

Transmembrane signaling implies that peripheral protein binding to one leaflet be detected by the opposite leaflet. Therefore, protein recruitment into preexisting cholesterol and sphingolipid rich platforms may be required. However, no clear molecular picture has evolved about how these rafts in both leaflets are connected. By using planar lipid bilayers, we show that the peripheral binding of a charged molecule (poly-lysine, PLL) is detected at the other side of the bilayer without involvement of raft lipids. The diffusion coefficient, D(P), of PLL differed by a factor of radical2 when PLL absorbed to one or to both leaflets of planar membranes. Fluorescence correlation spectroscopy showed that the changes of the lipid diffusion coefficient, D(M), were even more pronounced. Although D(M) remained larger than D(P) on PLL binding to the first membrane leaflet, D(M) dropped to D(P) on PLL binding to both leaflets, which indicated that the lipids sandwiched between two PLL molecules had formed a nanodomain. Due to its small area of approximately 20 nm(2) membrane electrostriction or leaflet interaction at bilayer midplane can only make a small contribution to interleaflet coupling. The tendency of the system to maximize the area where the membrane is free to undulate seems to be more important. As a spot with increased bending stiffness, the PLL bound patch in one leaflet attracts a stiffening additive on the other leaflet. That is to say, instead of suppressing undulations in two spots, two opposing PLL molecules migrate along a membrane at matching positions and suppress these undulations in a single spot. The gain in undulation energy is larger than the energy required for the alignment of two small PLL domains in opposite leafs and their coordinated diffusion. We propose that this type of mechanical interaction between two membrane separated ligands generally contributes to transmembrane signaling.