Encapsulation of benznidazole in nanostructured lipid carriers and increased trypanocidal activity in a resistant Trypanosoma cruzi strain

Abstract Chagas disease is a neglected parasitic disease caused by Trypanosoma cruzi, whose treatment has remained unsatisfactory for over 50 years, given that it is limited to two drugs. Benznidazole (BZN) is an efficient antichagasic drug used as the first choice, although its poor water-solubility, irregular oral absorption, low efficacy in the chronic phase, and various associated adverse effects are limiting factors for treatment. Incorporating drugs with such characteristics into nanostructured lipid carriers (NLC) is a promising alternative to overcome these limiting obstacles, enhancing drug efficacy and bioavailability while reducing toxicity. Therefore, this study proposed NLC-BZN formulations in different compositions prepared by hot-melt homogenization followed by ultrasound, and the optimized formulation was characterized by FTIR, DRX, DSC, and thermogravimetry. Biological activities included in vitro membrane toxicity (red blood cells), fibroblast cell cytotoxicity, and trypanocidal activity against epimastigotes of the Colombian strain of T. cruzi. The optimized NLC-BZN had a small size (110 nm), negative zeta potential (-18.0 mV), and high encapsulation (1.64% of drug loading), as shown by infrared spectroscopy, X-ray diffraction, and thermal analysis. The NLC-BZN also promoted lower in vitro membrane toxicity (<3% hemolysis), and 50% cytotoxic concentration (CC50) for NLC-BZN in L929 fibroblast cells (110.7 µg/mL) was twice the value as the free BZN (51.3 µg/mL). Our findings showed that the NLC-BZN had higher trypanocidal activity than free BZN against the epimastigotes of the resistant Colombian strain, and this novel NLC-BZN formulation proved to be a promising tool in treating Chagas disease and considered suitable for oral and parenteral administration

Preformulation screening of lipids using solubility parameter concept in conjunction with experimental research to develop ceftriaxone loaded nanostructured lipid carriers

Abstract Development of ceftriaxone loaded nanostructured lipid carriers to increase permeability of ceftriaxone across uninflamed meninges after parenteral administration. Lipids were selected by theoretical and experimental techniques and optimization of NLCs done by response surface methodology using Box-Behnken design. The Δδt for glyceryl monostearate and Capryol90 were 4.39 and 2.92 respectively. The drug had maximum solubility of 0.175% (w/w) in glycerol monostearate and 2.56g of Capryol90 dissolved 10mg of drug. The binary mixture consisted of glyceryl monostearate and Capryol90 in a ratio of 70:30. The optimized NLCs particle size was 130.54nm, polydispersity index 0.28, % entrapment efficiency 44.32%, zeta potential -29.05mV, and % drug loading 8.10%. In vitro permeability of ceftriaxone loaded NLCs was 5.06x10-6 cm/s; evidently, the NLCs pervaded through uninflamed meninges, which, was further confirmed from in vivo biodistribution studies. The ratio of drug concentration between brain and plasma for ceftriaxone loaded NLCs was 0.29 and that for ceftriaxone solution was 0.02. With 44.32% entrapment of the drug in NLCs the biodistribution of ceftriaxone was enhanced 7.9 times compared with that of ceftriaxone solution. DSC and XRD studies revealed formation of imperfect crystalline NLCs. NLCs improved permeability of ceftriaxone through uninflamed meninges resulting in better management of CNS infections.

Curcumin solid dispersion based on three model acrylic polymers: formulation and release properties

Abstract To investigate structure-property relationship of polymer-based curcumin solid dispersion (SD), three acrylic polymers were used to formulate curcumin SD by solvent evaporation method. Curcumin Eudragit EPO SD (cur@EPO), curcumin Eudragit RS PO SD (cur@RSPO) and curcumin Eudragit RL PO SD (cur@RLPO) showed deep red, golden orange and reddish orange color, respectively. Cur@RSPO entrapped 15.42 wt% of curcumin followed by cur@RL PO and cur@EPO. FTIR spectra indicated that in cur@EPO, curcumin may transfer hydrogen to the dimethylaminoethyl methacrylate group and thus change its color to red. In contrast, curcumin may form hydrogen bonding with Eudragit RS PO and Eudragit RL. Curcumin exists in amorphous state in three SDs as proved by differential scanning calorimetry and X-Ray diffraction measurement. In vitro digestion presented that lower pH value in simulated gastric fluid (SGF) stimulates the curcumin release from cur@EPO while permeability influences the release profile in other two SDs. When in simulated intestinal fluid (SIF), first order release model governs the release behaviors of all three SDs which showed sustained release pattern. Our results are helpful to elucidate how structure of polymer may impact on the major properties of curcumin contained SD and will be promising to broaden its therapeutic applications.

Development and optimization of metoclopramide containing polymeric patches: impact of permeation enhancers

Abstract The study is aimed to develop a monolithic controlled matrix transdermal patches containing Metoclopramide as a model drug by solvent casting method. Eudragit L100, Polyvinylpyrrolidone K-30, and Methylcellulose were used in different ratios and Polyethylene glycol 400 added as a plasticizer. Resulting patches were evaluated for their physicochemical characters like organoleptic characters, weight variation, folding endurance, thickness, swelling index, flatness, drug content, swelling index, percentage erosion, moisture content, water vapor transmission rate and moisture uptake. Formed patches were also evaluated through Fourier transform spectroscopy (FT-IR), X-ray diffraction (XRD), Differential Scanning calorimetry (DSC) and Scanning Electron Microscopy (SEM). Results of SEM unveiled smooth surface of drug-loaded patches. In-vitro dissolution studies were conducted by using dissolution medium phosphate buffer saline pH 7.4. Effect of natural permeation enhancers was elucidated on two optimized formulations (Z4 and Z9). Different concentrations (5%-10 %) of permeation enhancers i.e. Olive oil, Castor oil and Eucalyptus oil were evaluated on Franz diffusion cell using excised abdominal rat skin. Z4-O2 (Olive oil 10%) had enhanced sustain effect and flux value (310.72) close to the desired flux value. Z4-O2 followed Higuchi release model (R2= 0.9833) with non-fickian diffusion release mechanism (n=0.612)

Synthesis and characterization of Sophora alopecuroides L. green synthesized of Ag nanoparticles for the antioxidant, antimicrobial and DNA damage prevention activity

Abstract In this study, it was aimed to investigate the amount of antioxidant, protective properties against DNA damage and antibacterial properties against various pathogens after the interaction of Ag metal (Ag NPs/Sa) of Sophora alopecuroides L. (S. alopecuroides L) plant seed, which is grown in Igdir and used in the treatment of many diseases. The DPPH radical quenching activity of Ag NPs/Sa was performed by using Blois method, DNA damage prevention activity by gel electrophoresis and antibacterial property by disk diffusion method. With the green synthesis method, AgNPs obtained as a result of the reaction of the plant and Ag metal are UV visible spectrophotometer (UV-vis), fourier-transformed infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscope (SEM). DPPH radical quenching activity of Ag NPs/Sa was investigated in the concentration range of 25-250 µg/ml. The radical quenching activity at a concentration of 250 µg/ml was 85,215 ± 0,101%, while this value was 93,018% for the positive control BHA. It has been observed that the protective property of pBR322 plasmid DNA damage against OH radicals originating from H2O2 increases with concentration. It has been observed that Ag NPs/Sa has significant antimicrobial properties against some pathogens (B. subtilis ATCC 6633 E. coli ATCC 25952, B. cereus ATCC 10876, P. aeruginosa ATCC 27853, E. faecalis ATCC 29212, S. aureus ATTC 29213 and C. albicans ATTC 90028) that cause disease and even some pathogens are more effective than antibiotics

Effects of radiation damage and inelastic scattering on single-particle imaging of hydrated proteins with an X-ray Free-Electron Laser.

We present a computational case study of X-ray single-particle imaging of hydrated proteins on an example of 2-Nitrogenase-Iron protein covered with water layers of various thickness, using a start-to-end simulation platform and experimental parameters of the SPB/SFX instrument at the European X-ray Free-Electron Laser facility. The simulations identify an optimal thickness of the water layer at which the effective resolution for imaging the hydrated sample becomes significantly higher than for the non-hydrated sample. This effect is lost when the water layer becomes too thick. Even though the detailed results presented pertain to the specific sample studied, the trends which we identify should also hold in a general case. We expect these findings will guide future single-particle imaging experiments using hydrated proteins.

Tools for supporting solution scattering during the COVID-19 pandemic.

During the COVID-19 pandemic, synchrotron beamlines were forced to limit user access. Performing routine measurements became a challenge. At the Life Science X-ray Scattering (LiX) beamline, new instrumentation and mail-in protocols have been developed to remove the access barrier to solution scattering measurements. Our efforts took advantage of existing instrumentation and coincided with the larger effort at NSLS-II to support remote measurements. Given the limited staff-user interaction for mail-in measurements, additional software tools have been developed to ensure data quality, to automate the adjustments in data processing, as users would otherwise rely on the experience of the beamline staff, and produce a summary of the initial assessments of the data. This report describes the details of these developments.

Dynamic Structural Biology Experiments at XFEL or Synchrotron Sources.

Macromolecular crystallography (MX) leverages the methods of physics and the language of chemistry to reveal fundamental insights into biology. Often beautifully artistic images present MX results to support profound functional hypotheses that are vital to entire life science research community. Over the past several decades, synchrotrons around the world have been the workhorses for X-ray diffraction data collection at many highly automated beamlines. The newest tools include X-ray-free electron lasers (XFELs) located at facilities in the USA, Japan, Korea, Switzerland, and Germany that deliver about nine orders of magnitude higher brightness in discrete femtosecond long pulses. At each of these facilities, new serial femtosecond crystallography (SFX) strategies exploit slurries of micron-size crystals by rapidly delivering individual crystals into the XFEL X-ray interaction region, from which one diffraction pattern is collected per crystal before it is destroyed by the intense X-ray pulse. Relatively simple adaptions to SFX methods produce time-resolved data collection strategies wherein reactions are triggered by visible light illumination or by chemical diffusion/mixing. Thus, XFELs provide new opportunities for high temporal and spatial resolution studies of systems engaged in function at physiological temperature. In this chapter, we summarize various issues related to microcrystal slurry preparation, sample delivery into the X-ray interaction region, and some emerging strategies for time-resolved SFX data collection.

Enantioselective recognition of amino acid based on electrochemical deposition and X-ray diffraction technology.

Addition of D-Asp in the electrochemical deposition process of Bismuth film resulted the generation of a new diffraction peak in X-ray diffraction (XRD) spectrum. This phenomenon was not observed in the situation of L-Asp. The new diffraction peak might suggest D-Asp could result in the generation of a specific Bismuth structure. Enantioselective recognition of D- and L-Asp can be realized based on this new XRD peak. The limit of detection was determined to be 3.5 × 10-8 and 1.7 × 10-8 mol L-1 for D- and L-Asp, respectively. The XRD spectra of electrodeposited Copper films fabricated in the presence of D- or L-Asp showed different lattice plane diffraction peak intensity ratios. The reason was believed to be chirality induced different binding capabilities of Asp enantiomers that influenced Copper film growth. Therefore, the combination of electrochemical deposition using Copper as metal source and XRD technology can be used to achieve enantioselective recognition of Asp. The limit of detection for D- and L-Asp were determined to be 1.5 × 10-10 and 1.2 × 10-11 mol L-1, respectively.

Simulation based evaluation of a fan beam coded aperture x-ray diffraction imaging system for biospecimen analysis.

X-ray diffraction (XRD) imaging yields spatially resolved, material-specific information, which can aid medical diagnosis and inform treatment. In this work we used simulations to analyze the utility of fan beam coded aperture XRD imaging for fast, high-resolution scatter imaging of biospecimens for tissue assessment. To evaluate the proposed system's utility in a specific task, we employed a deterministic model to produce simulated data from biologically realistic breast tissue phantoms and model-based reconstruction to recover a spatial map of the XRD signatures throughout the phantoms. We found an XRD spatial resolution of ≈1 mm with a mean reconstructed spectral accuracy of 0.98 ± 0.01 for a simulated 1 × 150 mm2 fan beam operating at 160 kVp, 10 mA, and 4.5 s exposures. A classifier for cancer detection was developed utilizing cross-correlation of XRD spectra against a spectral library, with a receiver operating characteristic curve with an area under the curve value of 0.972. Our results indicated a potential diagnostic modality that could aid in tasks ranging from analysis of ex-vivo pathology biospecimens to intraoperative cancer margin assessment, motivating future work to develop an experimental system while enabling the development of improved algorithms for imaging and tissue analysis-based classification performance.

Methods for Crystallization and Structural Determination of M-T7 Protein from Myxoma Virus.

The myxoma virus has become of interest in human medicine in the last two decades as it has the ability to infect many types of human cancer cells and is being used as a platform to develop viro-therapeutic agents that suppress aggressive and damaging immune responses and inflammation. Furthermore, the myxoma virus encodes proteins that have strong immunosuppressive effects, and several of the myxoma virus-encoded immunomodulators are being developed to treat systemic inflammatory syndromes such as cardiovascular disease and transplant rejection. Myxoma virus encodes the M-T7 protein, the most abundantly secreted protein expressed in myxoma virus-infected cells, originally identified as a rabbit species-specific interferon-gamma (IFN-γ) receptor homolog and as a chemokine-modulating protein binding a wide range of mammalian chemokines. M-T7 is a critical virulence factor for viral pathogenesis that increases virus lethality when expressed. Although M-T7 has been extensively studied using biochemical and biophysical techniques and its interactome map is well known, its three-dimensional (3D) structure remains elusive. Obtaining the 3D structure of M-T7 would be greatly beneficial and is a crucial step toward advancing M-T7 research through understanding the molecular function and activity of M-T7 as a novel therapeutic reagent and to rationally develop this protein as a drug. This chapter provides an overview of the structural determination techniques, especially X-ray crystallography, that can be applied toward the goal of achieving the first high-resolution structure of M-T7. In addition, details of up-and-coming methods are discussed, including X-ray diffraction at X-ray free electron lasers (XFELs), nuclear magnetic resonance (NMR), cryo-electron microscopy (cryo-EM), Micro-electron diffraction (Micro-ED), and small-angle X-ray scattering (SAXS), and their potential applications to M-T7 structural biology.

Structural Characterization of Biomaterials by Means of Small Angle X-rays and Neutron Scattering (SAXS and SANS), and Light Scattering Experiments.

Scattering techniques represent non-invasive experimental approaches and powerful tools for the investigation of structure and conformation of biomaterial systems in a wide range of distances, ranging from the nanometric to micrometric scale. More specifically, small-angle X-rays and neutron scattering and light scattering techniques represent well-established experimental techniques for the investigation of the structural properties of biomaterials and, through the use of suitable models, they allow to study and mimic various biological systems under physiologically relevant conditions. They provide the ensemble averaged (and then statistically relevant) information under in situ and operando conditions, and represent useful tools complementary to the various traditional imaging techniques that, on the contrary, reveal more local structural information. Together with the classical structure characterization approaches, we introduce the basic concepts that make it possible to examine inter-particles interactions, and to study the growth processes and conformational changes in nanostructures, which have become increasingly relevant for an accurate understanding and prediction of various mechanisms in the fields of biotechnology and nanotechnology. The upgrade of the various scattering techniques, such as the contrast variation or time resolved experiments, offers unique opportunities to study the nano- and mesoscopic structure and their evolution with time in a way not accessible by other techniques. For this reason, highly performant instruments are installed at most of the facility research centers worldwide. These new insights allow to largely ameliorate the control of (chemico-physical and biologic) processes of complex (bio-)materials at the molecular length scales, and open a full potential for the development and engineering of a variety of nano-scale biomaterials for advanced applications.

X-ray-based living-cell motion analysis of individual serotonin receptors.

G protein-coupled receptors (GPCRs) are seven-transmembrane proteins, which transmit extracellular signals inside cells via activating G proteins. GPCRs are involved in a wide variety of physiological functions, such as signal sensing, immune system processes, and neurotransmission. Although the structures and functions of GPCRs have been well studied, little has been known about their real-time dynamics on live cells. In this study, we used Diffracted X-ray Tracking (DXT) and Diffracted X-ray Blinking (DXB) techniques for analysis. These methods are very precise single-molecular analytical techniques that elucidate protein dynamics by analyzing the diffraction spots from the gold nanocrystals labeled on the protein surface. DXT tracks diffraction spot movements, whereas DXB analyzes continuation of signals by calculating the autocorrelation function of each pixel from the recorded data. Serotonin receptor subtype 2A (5-HT2A receptors) were transiently expressed on HEK 293 cells, and the gold nanocrystals were attached to the N-terminally introduced FLAG-tag via anti-FLAG antibodies. Fast- and mid-range motions were recorded by DXT with 100µs and 1.25 ms/frame rate, respectively. Slow-range motion was obtained using the DXB method with 100 ms/frame rate. An agonist interestingly suppressed the fluctuations of 5-HT2A receptors at the microsecond-ranged fast measurement. On the contrary, the motion was enhanced by the agonist in the hundred-millisecond-ranged slow time scale. These dual-natured data may suggest that we succeeded in extracting different modes of receptor's motion on live cells; microsecond ranged fluctuation on the cell membrane, and millisecond-ranged dynamic movement comprising interactions with intracellular signaling molecules.

High-quality reconstruction of coherent modulation imaging using weak cascade modulators.

Coherent modulation imaging (CMI) has been shown to be an effective lensless diffraction approach to imaging general extended samples with fast algorithmic convergence and high robustness to data imperfection. Being a single-shot technique, CMI holds a high potential for imaging dynamics with ultrafast pulses like the ones from free-electron lasers. In the reported work, strong modulators have been suggested for CMI to have the optimal performance, which may be an obstacle for the wide adoption of the method. Here we show that with our improved reconstruction algorithm the requirements on the modulation depth and feature size of a modulator can be relaxed. Furthermore, we demonstrate that when cascade configuration is used, the modulators can be even weaker while providing lower image errors in reconstruction than the case of a single modulator. Detailed numerical studies in both far-field and near-field experiment geometry are given via simulation. A relaxed requirement on modulators in CMI could pave the way for its wide use in biology and materials science.

Myosin filament-based regulation of the dynamics of contraction in heart muscle.

Myosin-based mechanisms are increasingly recognized as supplementing their better-known actin-based counterparts to control the strength and time course of contraction in both skeletal and heart muscle. Here we use synchrotron small-angle X-ray diffraction to determine the structural dynamics of local domains of the myosin filament during contraction of heart muscle. We show that, although myosin motors throughout the filament contribute to force development, only about 10% of the motors in each filament bear the peak force, and these are confined to the filament domain containing myosin binding protein-C, the "C-zone." Myosin motors in domains further from the filament midpoint are likely to be activated and inactivated first in each contraction. Inactivated myosin motors are folded against the filament core, and a subset of folded motors lie on the helical tracks described previously. These helically ordered motors are also likely to be confined to the C-zone, and the associated motor conformation reforms only slowly during relaxation. Myosin filament stress-sensing determines the strength and time course of contraction in conjunction with actin-based regulation. These results establish the fundamental roles of myosin filament domains and the associated motor conformations in controlling the strength and dynamics of contraction in heart muscle, enabling those structures to be targeted to develop new therapies for heart disease.

In Meso In Situ Serial X-Ray Crystallography (IMISX): A Protocol for Membrane Protein Structure Determination at the Swiss Light Source.

The lipid cubic phases (LCP) have enabled the determination of many important high-resolution structures of membrane proteins such as G-protein-coupled receptors, photosensitive proteins, enzymes, channels, and transporters. However, harvesting the crystals from the glass or plastic plates in which crystals grow is challenging. The in meso in situ serial X-ray crystallography (IMISX) method uses thin plastic windowed plates that minimize LCP crystal manipulation. The method, which is compatible with high-throughput in situ measurements, allows systematic diffraction screening and rapid data collection from hundreds of microcrystals in in meso crystallization wells without direct crystal harvesting. In this chapter, we describe an IMISX protocol for in situ serial X-ray data collection of LCP-grown crystals at both cryogenic and room temperatures which includes the crystallization setup, sample delivery, automated serial diffraction data collection, and experimental phasing. We also detail how the IMISX method was applied successfully for the structure determination of two novel targets-the undecaprenyl-pyrophosphate phosphatase BacA and the chemokine G-protein-coupled receptor CCR2A.

Structural Analysis of RNA by Small-Angle X-ray Scattering.

Over the past two decades small-angle X-ray scattering (SAXS) has become a popular method to characterize solutions of biomolecules including ribonucleic acid (RNA). In an integrative structural approach, SAXS is complementary to crystallography, NMR, and electron microscopy and provides information about RNA architecture and dynamics. This chapter highlights the practical advantages of combining size-exclusion chromatography and SAXS at synchrotron facilities. It is illustrated by practical case studies of samples ranging from single hairpins and tRNA to a large IRES. The emphasis is also put on sample preparation which is a critical step of SAXS analysis and on optimized protocols for in vitro RNA synthesis ensuring the production of mg amount of pure and homogeneous molecules.

Identification of amyloid plaques in the brain using an x-ray photon-counting strip detector.

Brain aggregates of ß amyloid (ßA) protein plaques have been widely recognized as associated with many neurodegenerative diseases, and their identification can assist in the early diagnosis of Alzheimer's disease. We investigate the feasibility of using a spectral x-ray coherent scatter system with a silicon strip photon-counting detector for identifying brain ßA protein plaques. This approach is based on differences in the structure of amyloid, white and grey matter in the brain. We simulated an energy- and angular-dispersive X-ray diffraction system with an x-ray pencil beam and Silicon strip sensor, energy-resolving detectors. The polychromatic beam is geometrically focused toward a region of interest in the brain. First, the open-source MC-GPU code for Monte Carlo transport was modified to accommodate the detector model. Second, brain phantoms with and without ßA were simulated to assess the method and determine the radiation dose required to obtain acceptable statistical power. For ßA targets of 3, 4 and 5 mm sizes in a 15-cm brain model, the required incident exposure was about 0.44 mR from a 60 kVp tungsten spectrum and 3.5 mm of added aluminum filtration. The results suggest that the proposed x-ray coherent scatter technique enables the use of high energy x-ray spectra and therefore has the potential to be used for accurate in vivo detection and quantification of ßA in the brain within acceptable radiation dose levels.

Structural Studies of Epithelial Mesenchymal Transition Breast Tissues.

At the supramolecular level, the proliferation of invasive ductal carcinoma through breast tissue is beyond the range of standard histopathology identification. Using synchrotron small angle x-ray scattering (SAXS) techniques, determining nanometer scale structural changes in breast tissue has been demonstrated to allow discrimination between different tissue types. From a total of 22 patients undergoing symptomatic investigations, different category breast tissue samples were obtained in use of surgically removed tissue, including non-lesional, benign and malignant tumour. Structural components of the tissues were examined at momentum transfer values between q = 0.2 nm-1 and 1.5 nm-1. From the SAXS patterns, axial d-spacing and diffuse scattering intensity were observed to provide the greatest discrimination between the various tissue types, specifically in regard to the epithelial mesenchymal transition (EMT) structural component in malignant tissue. In non-lesional tissue the axial period of collagen is within the range 63.6-63.7 nm (formalin fixed paraffin embedded (FFPE) dewaxed) and 63.4 (formalin fixed), being 0.9 nm smaller than in EMT cancer-invaded regions. The overall intensity of scattering from cancerous regions is a degree of magnitude greater in cancer-invaded regions. Present work has found that the d-spacing of the EMT positive breast cancer tissue (FFPE (dewaxed)) is within the range 64.5-64.7 nm corresponding to the 9th and 10th order peaks. Of particular note in regard to formalin fixation of samples is that no alteration is observed to occur in the relative differences in collagen d-spacing between non-lesional and malignant tissues. This is a matter of great importance given that preserved-sample and also retrospective study of samples is greatly facilitated by formalin fixation. Present results indicate that as aids in tissue diagnosis SAXS is capable of distinguishing areas of invasion by disease as well as delivering further information at the supramolecular level.

Graphene-based sensing of oxygen transport through pulmonary membranes.

Lipid-protein complexes are the basis of pulmonary surfactants covering the respiratory surface and mediating gas exchange in lungs. Cardiolipin is a mitochondrial lipid overexpressed in mammalian lungs infected by bacterial pneumonia. In addition, increased oxygen supply (hyperoxia) is a pathological factor also critical in bacterial pneumonia. In this paper we fabricate a micrometer-size graphene-based sensor to measure oxygen permeation through pulmonary membranes. Combining oxygen sensing, X-ray scattering, and Atomic Force Microscopy, we show that mammalian pulmonary membranes suffer a structural transformation induced by cardiolipin. We observe that cardiolipin promotes the formation of periodic protein-free inter-membrane contacts with rhombohedral symmetry. Membrane contacts, or stalks, promote a significant increase in oxygen gas permeation which may bear significance for alveoli gas exchange imbalance in pneumonia.