Nataša Škalko-Basnet - Academia.edu (original) (raw)

Papers by Nataša Škalko-Basnet

Nanophotonics, Jun 20, 2022

The article elucidates the physical mechanism behind the generation of superior-contrast and high... more The article elucidates the physical mechanism behind the generation of superior-contrast and highresolution label-free images using an optical waveguide. Imaging is realized by employing a high index contrast multi-moded waveguide as a partially coherent light source. The modes provide near-field illumination of unlabeled samples, thereby repositioning the higher spatial frequencies of the sample into the far-field. These modes coherently scatter off the sample with different phases and are engineered to have random spatial distributions within the integration time of the camera. This mitigates the coherent speckle noise and enhances the contrast (2-10) × as opposed to other imaging techniques. Besides, the coherent scattering of the different modes gives rise to fluctuations in intensity. The technique demonstrated here is named chip-based Evanescent Light Scattering (cELS). The concepts introduced through this work are described mathematically and the high-contrast image

European Journal of Pharmaceutical Sciences, Oct 1, 2022

Journal of Proteomics, Sep 1, 2018

Enterococcus faecium is a commensal but also a bacteremia causing pathogen, which is inherently r... more Enterococcus faecium is a commensal but also a bacteremia causing pathogen, which is inherently resistant to several antimicrobials and has a great ability to acquire new traits. Bacterial membrane vesicles (MVs) are increasingly recognized as a mode of cell-free communication and a way to deliver virulence factors and/or antimicrobial resistance determinants. These features make MVs interesting research targets in research on critical hospital pathogens. This study describes for the first time that E. faecium strains produce MVs. It presents a morphological as well as a proteomic analysis of MVs isolated from four different, clinically relevant E. faecium strains grown under two different conditions and identifies MV-associated proteins in all of them. Interestingly, 11 virulence factors are found among the MV-associated proteins, including biofilm-promoting proteins and extracellular matrix-binding proteins, which may aid in enterococcal colonization. Additionally, 11 antimicrobial resistance-related proteins were MV-associated. Among those, all proteins encoded by the vanA-cluster of a vancomycin resistant strain were found to be MV-associated. This implies that E. faecium MVs may be utilized by the bacterium to release proteins promoting virulence, pathogenicity and antimicrobial resistance. Significance: Enterococcal infections, especially bacteremia and endocarditis, are challenging to treat because E. faecium have acquired resistance to multiple classes of antimicrobials, including ampicillin, aminoglycosides, and glycopeptides. Thus, research on different modes of enterococcal pathogenicity is warranted. This study utilized a proteomic approach to identify MV-associated proteins of different nosocomial E. faecium strains representing four clinically relevant sequence types (STs), namely ST17, ST18, ST78, and ST192. The presented data suggest that E. faecium MVs are involved in virulence and antimicrobial resistance.

Neuroreport, Sep 1, 2000

pH-Sensitive liposomes composed of dioleoylphosphatidylethanolamine and cholesterol hemisuccinate... more pH-Sensitive liposomes composed of dioleoylphosphatidylethanolamine and cholesterol hemisuccinate (3:2 mol/mol) were applied in delivery of antisense oligodeoxynucleotides (asODN) into NG 108-15 neuroblastoma and glioma cells. Fluorescently labelled asODN were entrapped in liposomes by a modi®ed freeze-thawing method (20% encapsulation ef®ciency). The uptake of asODN (free or entrapped in liposomes) by NG 108-15 cells was monitored by¯uorescence-activated cell sorting and confocal microscopy. Delivery of asODN was signi®cantly improved when antisense were entrapped in liposomes as compared to free (nonliposomal) asODN. The uptake was dose-dependent and optimum was achieved after 2 h incubation. NeuroReport 11:3117±3121 & 2000 Lippincott

PubMed, Sep 1, 2008

Present study was carried out to find out the prevalence of methicillin resistant Staphylococcus ... more Present study was carried out to find out the prevalence of methicillin resistant Staphylococcus aureus (MRSA) in school children of Pokhara city in western, Nepal. A total of 184 randomly selected children younger than 15 years were included in the study. Nasal swabs collected were subjected to standard bacteriological culture. S. aureus isolates were identified by mannitol fermentation, coagulase positivity and DNase positivity. Antimicrobial susceptibility test was performed on muller-hinton agar (MHA) by modified Kirby-Bauer disc diffusion method. Out of total 184 nasal swabs, S. aureus was isolated in 31.0% (n=57). Among the isolates, 35.1% (n=20) were from male children whereas 64.9% (n=37) were from female. There was no significant sex difference in colonization of S. aureus. Out of 57 isolates, 56.1% (n=32) were MRSA. MRSA isolates indicated relatively high rate of resistance to antibiotic cloxacillin (68.7%) followed by ofloxacin (40.6%), tetracycline (15.6%), erythromycin (9.4%), ciprofloxacin (6.2%) and vancomycin (3.1%).This study showed a high prevalence of MRSA carriage in school children indicating the spread of MRSA in the community.

European Journal of Pharmaceutical Sciences, Oct 1, 2019

The aim of this work was to clarify the dynamics behind the influence of ionic strength on the ch... more The aim of this work was to clarify the dynamics behind the influence of ionic strength on the changes in drug release from large unilamellar vesicles (LUVs). For this purpose, we have investigated the transport of two different model drugs (caffeine and hydrocortisone) formulated into liposomes through different types of barriers with different retention properties (regenerated cellulose and the newly introduced biomimetic barrier, Permeapad ®). Drug release from liposomes was studied utilizing the standard Franz diffusion cells. LUV dispersions were exposed to the isotonic, hypotonic and hypertonic environment (difference of 300 mOsm/kg between the initial LUVs and the environment) and experimental data treated with both linear and nonlinear (Korsmeyer-Peppas) regression models. To alter the rigidity of the liposomal membranes, cholesterol was introduced in the liposomal barriers (up to 25% w/w). Korsmeyer-Peppas model was proven to be suited to analyse experimental data throughout the experimental time frame, providing important additive information in comparison to standard linear approximation. The obtained results are highly relevant as they improve the interpretation of drug release kinetics from LUVs under osmotic stress. Moreover, the findings can be utilized in the development of liposomal formulations intended for nose-to-brain targeted drug delivery.

European Journal of Pharmaceutical Sciences, 2020

From a patient-centric perspective, oromucosal drug delivery is highly attractive due to the ease... more From a patient-centric perspective, oromucosal drug delivery is highly attractive due to the ease of administration without the need of swallowing, and improved patient safety. The aim of the presented work was to prepare a buccal film using a self-forming micellar drug solubiliser as the film matrix, combining it with a mucoadhesive polymer for an enhanced retention on the buccal mucosa. Specifically, we propose the use of a graft co-polymer (Soluplus®), as a solubiliser and film former, supplemented with polymers with more hydrophilic properties and known mucoadhesive properties; hydroxypropyl methylcellulose (HPMC) or modified hydroxypropyl pea starch (Lycoat®). The film was manufactured by the solvent casting method. The resulting dual polymer film containing HPMC exhibited resistance to erosion and mucoadhesive properties superior to the control films of single polymers. In an in vitro oral cavity model, these properties were shown to correlate with increased residence time on simulated oral mucosa. Furthermore, all films containing the graft co-polymer showed similar permeability characteristics of furosemide towards buccal TR146 epithelial cells. This work illustrated that it is possible to manufacture dry, solid, dual polymer films containing an advanced drug delivery system with a cheap and simple method. The combination of a graft co-polymer with a mucoadhesive polymer transform into drug solubilising micelles in a mucin-retentive hydrogel scaffold with longer retention time on buccal mucosa for safe and enhanced advanced formulation.

arXiv (Cornell University), Aug 24, 2021

Chip-based Evanescent Light Scattering (cELS) utilizes the multiple modes of a high-index contras... more Chip-based Evanescent Light Scattering (cELS) utilizes the multiple modes of a high-index contrast optical waveguide to provide a near-field illumination for unlabeled samples. The scattered light off the sample is engineered to have random phase differences within the integration time of the camera to mitigate the coherent speckle noise, thus enabling label-free superior-contrast imaging of weakly scattering nanosized specimens such as extracellular vesicles (EVs) and liposomes, dynamics of living HeLa cells etc. The article explains and validates experimentally the physics behind cELS, by demonstrating a wide highly multimoded straight waveguide as a partially coherent light source. Next, to circumvent the diffraction-limit in cELS, intensity-fluctuation based algorithms are employed with spatially incoherent light engineered via multiple-arms waveguide chip. The proof-of-concept results are demonstrated on 100 nm polystyrene beads. We believe cELS will further propel the nascent field of label-free super-resolution microscopy finding applications in cell biology.

Methods in Enzymology, 2004

The aim of our study was to develop a liposomal drug carrier system, able to provide sustained an... more The aim of our study was to develop a liposomal drug carrier system, able to provide sustained and controlled release of appropriate drug for local vaginal therapy. To optimise the preparation of liposomes with regards to size and entrapment efficiency, liposomes containing calcein were prepared by five different methods. Two optimal liposomal preparations (proliposomes and polyol dilution liposomes) were tested for their in vitro stability in media that simulate human vaginal conditions (buffer, pH 4.5). To be closer to in vivo application of liposomes and to achieve further improvement of their stability, liposomes were incorporated in vehicles suitable for vaginal self-administration. Gels of polyacrylate were chosen as vehicles for liposomal preparations. Due to their hydrophilic nature and bioadhesive properties, it was possible to achieve an adequate pH value corresponding to physiological conditions as well as desirable viscosity. In vitro release studies of liposomes incorporated in these gels (Carbopol 974P NF or Carbopol 980 NF) confirmed their applicability as a novel drug carrier system in vaginal delivery. Regardless of the gel used, even 24 h after the incubation of liposomal gel in the buffer pH 4.5 more than 80% of the originally entrapped substance was still retained.

Drug Development and Industrial Pharmacy, 2000

The one-step spray-drying method was applied in the preparation of liposomes containing drug and ... more The one-step spray-drying method was applied in the preparation of liposomes containing drug and cyclodextrin (CD). Spray-dried lecithin liposomes, entrapping metronidazole or verapamil alone or together with hydroxypropyl-beta-cyclodextrin (HP beta CD), were characterized for morphology, size distribution, and drug entrapment efficiency. The main factor influencing the liposomal size was the volume of aqueous medium used for hydration of the spray-dried product. No differences in size or entrapment between liposomes prepared by immediate hydration of dried powder or by hydration after 1 year of powder storage at 4 degrees C were observed. All liposomes were tested for their serum stability. The most stable liposomes (still retaining about 10% of the originally entrapped drug even after 24 hr incubation with serum) were liposomes prepared by the direct spray-drying of the mixture of lipid, drug, and HP beta CD.

bioRxiv (Cold Spring Harbor Laboratory), May 22, 2023

Nanoscale carriers such as liposomes and extracellular vesicles (EVs) are readily being explored ... more Nanoscale carriers such as liposomes and extracellular vesicles (EVs) are readily being explored for personalized medicine or disease prediction and diagnostics, respectively. Owing to their small size, such nanocarriers can undergo endocytosis or exocytosis, providing means to either transport cargo to the cells (liposomes) or to serve as a biomarker (EVs). When looking at current analysis methods, there is a growing need for detailed characterization of the content and composition of such nanocarriers in their natural state in aqueous media. This can be achieved through surface-enhanced Raman spectroscopy (SERS), which provides a molecular fingerprint of the analytes while reducing the detection limit. In this paper, we utilize a nano-structured SERS substrate to study different bio-nanoparticles such as liposomes, EVs and DNA nanogel in suspension. A silver-coated polydimethylsiloxane (PDMS) film-based honeycomb shaped nano-bowl surface passively traps and reduces the mobility of the nanosized bio-particles, improving the intensity and the reproducibility of the SERS signal. FDTD simulations are used for substrate geometry optimization, and a detection limit of 10−15M is demonstrated for Rhodamine 6G (R6G). The potential of the proposed SERS nano-bowl is shown through distinct spectral features following surface-(polyethylene glycol) and bilayer-(cholesterol) modification of empty liposomes. For DNA nanogels, the characterization of highly crosslinked DNA specimens exhibits enhanced peaks for nitrogenous bases, sugar, and phosphate groups. EVs isolated from various cells provided spectral signatures of specific protein content, lipid components, and nucleic acids. Concluding, the findings of the spectral signatures of a wide range of molecular complexes and chemical morphology of bio-membranes in their natural state highlight the possibilities of using SERS as a sensitive and instantaneous characterization alternative.

arXiv (Cornell University), Aug 20, 2020

Fluorescence fluctuations-based super-resolution microscopy (FF-SRM) is an emerging field promisi... more Fluorescence fluctuations-based super-resolution microscopy (FF-SRM) is an emerging field promising low-cost and live-cell compatible imaging beyond the resolution of conventional optical microscopy. A comprehensive overview on how the nature of fluctuations, label density, out-of-focus light, subcellular dynamics, and the sample itself influence the reconstruction in FF-SRM is crucial to design appropriate biological experiments. We have experimentally compared several of the recently developed FF-SRM techniques (namely ESI, bSOFI, SRRF, SACD, MUSICAL and HAWK) on widefield fluorescence image sequences of a diverse set of samples (namely liposomes, tissues, fixed and living cells), and on three-dimensional simulated data where the ground truth is available. The simulated microscopy data showed that the different techniques have different requirements for signal fluctuation to achieve their optimal performance. While different levels of signal fluctuations had little effect on the SRRF, ESI and SACD images, image reconstructions from both bSOFI and MUSICAL displayed a substantial improvement in their noise rejection, z-sectioning, and overall super-resolution capabilities.

Journal of Controlled Release, Feb 1, 2023

Nanophotonics, Sep 5, 2022

After the publication of this article, the authors found that the yellow boxes (nucleus of the ce... more After the publication of this article, the authors found that the yellow boxes (nucleus of the cell) in Figure 6 of the Figure 6: Comparison between cELS and TIRF images of Hela cells, scale bar 25 μm. Three different regions of interest enclosed by red, yellow, and green boxes are blown-up and provided alongside. The yellow box shows the nucleus region of the cell whereas the red and green boxes are the filaments, scale bar 8 μm. The color bars given alongside the magnified regions indicate the pixel values.

Up to now, a new drug development has been divided into two parallel fields ; one which focused o... more Up to now, a new drug development has been divided into two parallel fields ; one which focused on newly discovered synthetic materials encapsulated in either novel drug delivery systems (NDDS) or traditional (conventional) drug dosage forms and the second one which focused on the traditional medicinal ingredients, mostly of plant origin, but with almost no interest in developing more sophisticated formulations or systems, which could improve the final effect of the remedy. Why is it so? Is not the 21st century time to combine all efforts for the improvement of therapy? Can we have NDDS with active ingredient of plant origin? The answer is very simple. Yes. The newest trend in drug development is providing just those liposomes with curcumin. Turmeric has been used in therapy for thousands of years, hundreds of papers are published on its beneficial therapeutic activities, but how do we deliver it to the cell? We know that our targets are receptors, cell organelles, specific sites. Why not use NDDS known to be able to target and to deliver entrapped material at desired sites to deliver active ingredient of plant origin. Our laboratory, together with several others in the world, started to focus on NDDS, especially liposomes, with active ingredients of plant origin. Our targets are liposomes with capsaicin for improved local action on the skin, liposomes with curcumin, and liposomes with other newly discovered constituents of Himalayan plants. To optimise therapy we can combine the knowledge on delivery systems, superior in many ways to the conventional treatment, with the knowledge on traditionally used ingredient of natural origin, up to now administered in rather primitive formulations. Based on our preliminary data, we are optimistic that those combinations will result in improved therapeutic outcome

Pregnancy Hypertension, Jul 1, 2017

Introduction: Untreated vaginal inflammation can cause miscarriage, preterm labour, placental dys... more Introduction: Untreated vaginal inflammation can cause miscarriage, preterm labour, placental dysfunction and perinatal complications. Trichomonas vaginalis infection and inflammation are of serious concerns due to lipophosphoglycan (LPG) which triggers selective up regulation of cytokines, especially IL-8, in the female reproductive tract [1]. There are several anti-inflammatory and anti-microbial drugs currently available on the market, however, there is no general consensus regarding safe formulation especially for use in early pregnancy and considering microbial resistance. Resveratrol, a natural polyphenol, showed promising results comparing to clinically used drug metronidazole [2]. However, due to poor solubility and low bioavailability of resveratrol, its clinical application remains challenging. Our aim was to develop a non-teratogenic and nontoxic formulation which can be used in early pregnancy for the treatment of Trichomonas infection and inflammation. Methods: Liposomes carrying resveratrol were characterized for their stability, size and entrapment efficiency. Antioxidant activities were evaluated by DPPH/ABTS+ and SOD activities. Antioxidant and anti-inflammatory activities of resveratrol and their corresponding vesicle-based formulation were compared. Anti-inflammatory activities were evaluated by measuring LPS-induced NO and proinflammatory cytokines such as IL-1b, TNF-a, IL-8 in macrophages (J774.1) and LPG-induced cytokines IL-8 in human vaginal cells lines (VK2/E6E7). Results: Phospholipid-based vesicles, liposomes, of average size around 100 nm were found to be stable with a high resveratrol load (77%). Liposomal resveratrol was found to be 3 folds more potent than resveratrol in inhibiting NO production and up to 30% proinflammatory cytokines in macrophages were inhibited. IL-8 was inhibited up to 36% by the liposomal resveratrol in human vaginal cell lines VK2/E6E7 as compared to resveratrol. Conclusion: Standardized liposomal resveratrol might be an appropriate, effective and safe topical formulation for the treatment of vaginal infection and inflammation against trichomoniasis in early pregnancy. P 26 Cesarean delivery in preeclamptic patients-clinical assessment focusing on coagulation.

Journal of Medicinal Food, Aug 1, 2009

A simple method has been described for simultaneous determination of phenolic acid, flavonoid, an... more A simple method has been described for simultaneous determination of phenolic acid, flavonoid, and other phenol contents in various natural honey samples collected from various regions of Yemen. Multi-walled carbon nanotubes were used as a solid-phase adsorbent for extraction of the polyphenols from honey samples. The total contents of phenolic acids, flavonoids, and phenolic components of the 12 different samples were found in the range of 363−2658, 261−1646, and 224−1355 μg/100 g of honey samples, respectively. The major phenolic acid, flavonoid, and phenolic compound in these samples were found to be 4-hydroxybenzoic acid (1410 μg/100 g), chrysin (850 μg/100 g), and cinnamic acid (1336 μg/100 g), respectively. A total of 25 compounds (10 phenolic acids, 9 flavonoids, and 6 phenols) were analyzed, and a total of 24 were detected, while only 23 compounds were determined quantitatively in the honey samples. The developed method showed potential usefulness for the analysis of honey and was used for the determination of polyphenols in honey extracts.

The 18th Pharmaceutical Technology Conference Book, vol. 1, 1999