Metabolic remodeling of the human red blood cell membrane

Erythrocyte caspase-3 levels in children with chronic kidney disease

OBJECTIVES

In chronic kidney disease (CKD), a number of intra- and extracellular factors, e.g., uremic toxins, mechanic, oxidative or osmotic stress - induce changes (rearrangements) in the structure of cytoplasmatic membrane, while also simultaneously deregulating blood cell metabolism and, in consequence, contributing to preliminary ageing and suicidal death of red blood cells (RBCs).The aim of the reported study was an evaluation of caspase-3 and lactate dehydrogenase activities and of ATP concentrations in erythrocytes as cellular responses to CKD progress.

DESIGN AND METHODS

Conservatively treated sixty (60) CKD children were enrolled into the study and divided, according to CKD progression (stage I-IV). The control group consisted of twenty-five (25) healthy children. The activity of caspase-3 (Casp-3) and lactate dehydrogenase (LDH) were spectrophotometrically assayed in haemolysed erythrocytes. Adenosine triphosphate (ATP(e)) concentrations were measured by means of a luciferin-luciferase kit.

RESULTS

A gradual increase of LDH and ATP levels was observed in transition from CKD stage I to stage III. In Group IV, the levels of those parameters were statistically significantly lower than in the control group. The activity of Casp-3 in Group I was comparable to that in healthy children. The highest activity of Casp-3 was observed in Group III.

CONCLUSIONS

1. The activity of caspase-3 in RBCs of CKD children grows with progression of the disease. 2. The lower LDH activities and the ATP concentration drop below the values characteristic for the control group, as observed in stage IV of CKD, indicate a compromised energy balance.

Intrinsic reaction-cycle time scale of Na+,K+-ATPase manifests itself in the lipid-protein interactions of nonequilibrium membranes

Interaction between integral membrane proteins and the lipid-bilayer component of biological membranes is expected to mutually influence the proteins and the membrane. We present quantitative evidence of a manifestation of the lipid-protein interactions in liposomal membranes, reconstituted with actively pumping Na(+),K(+)-ATPase, in terms of nonequilibrium shape fluctuations that contain a relaxation time, τ, which is robust and independent of the specific fluctuation modes of the membrane. In the case of pumping Na(+)-ions, analysis of the flicker-noise temporal correlation spectrum of the liposomes leads to τ ~/= 0.5 s, comparing favorably with an intrinsic reaction-cycle time of about 0.4 s from enzymology.

Simple filter microchip for rapid separation of plasma and viruses from whole blood

Sample preparation is a significant challenge for detection and sensing technologies, since the presence of blood cells can interfere with the accuracy and reliability of virus detection at the nanoscale for point-of-care testing. To the best of our knowledge, there is not an existing on-chip virus isolation technology that does not use complex fluidic pumps. Here, we presented a lab-on-a-chip filter device to isolate plasma and viruses from unprocessed whole blood based on size exclusion without using a micropump. We demonstrated that viruses (eg, HIV) can be separated on a filter-based chip (2-μm pore size) from HIV-spiked whole blood at high recovery efficiencies of 89.9% ± 5.0%, 80.5% ± 4.3%, and 78.2% ± 3.8%, for viral loads of 1000, 10,000 and 100,000 copies/mL, respectively. Meanwhile, 81.7% ± 6.7% of red blood cells and 89.5% ± 2.4% of white blood cells were retained on 2 μm pore–sized filter microchips. We also tested these filter microchips with seven HIV-infected patient samples and observed recovery efficiencies ranging from 73.1% ± 8.3% to 82.5% ± 4.1%. These results are first steps towards developing disposable point-of-care diagnostics and monitoring devices for resource-constrained settings, as well as hospital and primary care settings.

Spectroscopic diffraction phase microscopy

We present spectroscopic diffraction phase microscopy (sDPM) as a method capable of measuring quantitative phase images at multiple wavelengths. sDPM uses a spatial light modulator at the Fourier plane of a lens to select desired wavelengths from the white light illumination of a grating. The quantitative phase information at different wavelengths allows us to decouple the refractive index and the thickness from the phase shift induced by biological cells. We demonstrate the capability of the setup by dispersion measurements of microsphere beads and RBCs.

Spatially-resolved eigenmode decomposition of red blood cells membrane fluctuations questions the role of ATP in flickering

Red blood cells (RBCs) present unique reversible shape deformability, essential for both function and survival, resulting notably in cell membrane fluctuations (CMF). These CMF have been subject of many studies in order to obtain a better understanding of these remarkable biomechanical membrane properties altered in some pathological states including blood diseases. In particular the discussion over the thermal or metabolic origin of the CMF has led in the past to a large number of investigations and modeling. However, the origin of the CMF is still debated. In this article, we present an analysis of the CMF of RBCs by combining digital holographic microscopy (DHM) with an orthogonal subspace decomposition of the imaging data. These subspace components can be reliably identified and quantified as the eigenmode basis of CMF that minimizes the deformation energy of the RBC structure. By fitting the observed fluctuation modes with a theoretical dynamic model, we find that the CMF are mainly governed by the bending elasticity of the membrane and that shear and tension elasticities have only a marginal influence on the membrane fluctations of the discocyte RBC. Further, our experiments show that the role of ATP as a driving force of CMF is questionable. ATP, however, seems to be required to maintain the unique biomechanical properties of the RBC membrane that lead to thermally excited CMF.

Analysis of nanostructure of red blood cells membranes by space Fourier transform of AFM images

Atomic force microscopy (AFM) allows a researcher to obtain images of red blood cells (RBC) and their membranes. Various effects on blood lead to surface alterations of cell membranes. Such alterations are estimated by a corrugation of membrane surface. This problem is complicated for statistical analysis because the membrane is the ensemble of structures with different sizes. In the present work we used the space Fourier transform to decompose the complex AFM image of the surface into three simpler ones. The parameters of spectral windows were selected according to the natural structures of RBC membranes. This method allowed us to obtain high resolution images for the corresponding spectral windows, to establish specificity of alterations from each effect, to estimate quantitatively the membrane nanostructures at different space scales and to compare their sizes statistically after actions of different agents. The blood intoxication was modeled by adding hemin, furosemide, chlorpromazine and zinc ions into blood, in vitro.

Dissecting eukaryotic cells by coherent phase microscopy: quantitative analysis of quiescent and activated T lymphocytes

We present a concept for quantitative characterization of a functional state of an individual eukaryotic cell based on interference imaging. The informative parameters of the phase images of quiescent and mitogen-activated T lymphocytes included the phase thickness, phase volume, the area, and the size of organelles. These parameters were obtained without a special hypothesis about cell structure. Combinations of these parameters generated a "phase portrait" of the cell. A simplified spherical multilayer optic model of a T lymphocyte was used to calculate the refractivity profile, to identify structural elements of the image with the organelles, and to interpret the parameters of the phase portrait. The values of phase image parameters underwent characteristic changes in the course of mitogenic stimulation of T cells; thereby, the functional state of individual cells can be described using these parameters. Because the values of the components of the phase portrait are measured in absolute units, it is possible to compare the parameters of images obtained with different interference microscopes. Thus, the analysis of phase portraits provides a new and perspective approach for quantitative, real-time analysis of subcellular structure and physiologic state of an individual cell.

Polarization holographic microscopy for extracting spatio-temporally resolved Jones matrix

We present a high-speed holographic microscopic technique for quantitative measurement of polarization light-field, referred to as polarization holographic microscopy (PHM). Employing the principle of common-path interferometry, PHM quantitatively measures the spatially resolved Jones matrix components of anisotropic samples with only two consecutive measurements of spatially modulated holograms. We demonstrate the features of PHM with imaging the dynamics of liquid crystal droplets at a video-rate.

Dynamic spectroscopic phase microscopy for quantifying hemoglobin concentration and dynamic membrane fluctuation in red blood cells

We report a technique for simultaneous label-free quantification of cytoplasmic hemoglobin Hb concentration and dynamic membrane fluctuation in individual red blood cells (RBCs). Spectroscopic phase microscopy equipped with three different coherent laser sources and a color detector records three wavelength-dependent quantitative phase images in a single shot of a color-coded hologram. Using molecular specific dispersion, we demonstrate the extraction of Hb concentration and the dynamic membrane fluctuation from individual RBCs.

Anisotropic light scattering of individual sickle red blood cells

We present the anisotropic light scattering of individual red blood cells (RBCs) from a patient with sickle cell disease (SCD). To measure light scattering spectra along two independent axes of elongated-shaped sickle RBCs with arbitrary orientation, we introduce the anisotropic Fourier transform light scattering (aFTLS) technique and measured both the static and dynamic anisotropic light scattering. We observed strong anisotropy in light scattering patterns of elongated-shaped sickle RBCs along its major axes using static aFTLS. Dynamic aFTLS analysis reveals the significantly altered biophysical properties in individual sickle RBCs. These results provide evidence that effective viscosity and elasticity of sickle RBCs are significantly different from those of the healthy RBCs.

Diffraction phase microscopy with white light

We present white light diffraction phase microscopy (wDPM) as a quantitative phase imaging method that combines the single shot measurement benefit associated with off-axis methods, high temporal phase stability associated with common path geometries, and high spatial phase sensitivity due to the white light illumination. We propose a spatiotemporal filtering method that pushes the limit of the pathlength sensitivity to the subangstrom level at practical spatial and temporal bandwidths. We illustrate the utility of wDPM with measurements on red blood cell morphology and HeLa cell growth over 18 hours.

Gradient field microscopy of unstained specimens

We present a phase derivative microscopy technique referred to as gradient field microscopy (GFM), which provides the first-order derivatives of the phase associated with an optical field passing through a transparent specimen. GFM utilizes spatial light modulation at the Fourier plane of a bright field microscope to optically obtain the derivatives of the phase and increase the contrast of the final image. The controllable spatial modulation pattern allows us to obtain both one component of the field gradient (derivative along one direction) and the gradient intensity, which offers some advantages over the regular differential interference contrast (DIC) microscopy. Most importantly, unlike DIC, GFM does not use polarizing optics and, thus, it is applicable to birefringent samples. We demonstrate these features of GFM with studies of static and dynamic biological cells (HeLa cells and red blood cells). We show that GFM is capable of qualitatively providing information about cell membrane fluctuations. Specifically, we captured the disappearance of the bending mode of fluctuations in osmotically swollen red blood cells.

The potential utility of methoxypoly(ethylene glycol)-mediated prevention of rhesus blood group antigen RhD recognition in transfusion medicine

Red blood cell (RBC) transfusions are an important clinical intervention. However, RBC express hundreds of non-ABO antigens making alloimmunization a significant risk. RhD expression is the most immunologically important non-ABO antigen. Availability of RhD(-) blood, often problematic in North America and Europe, is a significant issue in Asia and Africa where RhD(-) blood is uncommon (<0.5% of supply). The immunocamouflage of RhD is readily accomplished by the covalent grafting of methoxypoly(ethylene glycol) [mPEG] to the RBC membrane. To determine if RhD immunocamouflage would inhibit its immunologic recognition, an in vitro RhD-sensitized antigen presentation assay using PBMC and dendritic cells (DC) from RhD-sensitized women was used. The immunological effects of polymer grafting to an immunodominant RhD peptide, purified RhD protein and intact RhD(+) RBC were examined via T cell proliferation and cytokine release assays. At Day 11, PEGylation significantly attenuated T cell proliferation arising from RhD peptide (~80 → 5%), protein (36 → 0.2%) and intact RBC (33 → 1.4%). Cytokine secretion was similarly blunted following PEGylation of the purified protein or intact RBC. These data support the immunomodulatory effects of PEGylation and the potential utility of this technology in transfusion medicine - especially in situations where RhD(-) blood is rare or in short supply.

Red blood cell extrudes nucleus and mitochondria against oxidative stress

Mammal red blood cells (erythrocytes) contain neither nucleus nor mitochondria. Traditional theory suggests that the presence of a nucleus would prevent big nucleated erythrocytes to squeeze through these small capillaries. However, nucleus is too small to hinder erythrocyte deformation. And, there is no sound reason to abandon mitochondria for the living cells. Here, we found that mammal erythrocyte reactive oxygen species (ROS) levels kept stable under diabetes, ischemia reperfusion, and malaria conditions or in vitro sugar/heme treatments, whereas bird erythrocyte ROS levels increased dramatically in these circumstances. Nuclear and mitochondrial extrusion may help mammal erythrocytes to better adapt to high-sugar and high-heme conditions by limiting ROS generation.

Two-component coarse-grained molecular-dynamics model for the human erythrocyte membrane

We present a two-component coarse-grained molecular-dynamics model for simulating the erythrocyte membrane. The proposed model possesses the key feature of combing the lipid bilayer and the erythrocyte cytoskeleton, thus showing both the fluidic behavior of the lipid bilayer and the elastic properties of the erythrocyte cytoskeleton. In this model, three types of coarse-grained particles are introduced to represent clusters of lipid molecules, actin junctions, and band-3 complexes, respectively. The proposed model facilitates simulations that span large length scales (approximately micrometers) and timescales (approximately milliseconds). By tuning the interaction potential parameters, we were able to control the diffusivity and bending rigidity of the membrane model. We studied the membrane under shearing and found that at a low shear strain rate, the developed shear stress was due mainly to the spectrin network, whereas the viscosity of the lipid bilayer contributed to the resulting shear stress at higher strain rates. In addition, we investigated the effects of a reduced spectrin network connectivity on the shear modulus of the membrane.

Real-time quantitative phase imaging with a spatial phase-shifting algorithm

This Letter reports on the use of a spatial phase-shifting algorithm in a fast, straightforward method of real-time quantitative phase imaging. The computation time for phase extraction is five times faster than a Fourier transform and twice as fast as a Hilbert transform. The fact that the phase extraction from an interferogram of 512 × 512 pixels takes less than 8.93 ms with a typical desktop computer suggests the proposed method can be readily applied to high-speed dynamic quantitative phase imaging. The proposed method of quantitative phase imaging is effective and sufficiently general for application to the dynamic phenomena of biological samples.

Multiscale modeling of red blood cell mechanics and blood flow in malaria

Red blood cells (RBCs) infected by a Plasmodium parasite in malaria may lose their membrane deformability with a relative membrane stiffening more than ten-fold in comparison with healthy RBCs leading to potential capillary occlusions. Moreover, infected RBCs are able to adhere to other healthy and parasitized cells and to the vascular endothelium resulting in a substantial disruption of normal blood circulation. In the present work, we simulate infected RBCs in malaria using a multiscale RBC model based on the dissipative particle dynamics method, coupling scales at the sub-cellular level with scales at the vessel size. Our objective is to conduct a full validation of the RBC model with a diverse set of experimental data, including temperature dependence, and to identify the limitations of this purely mechanistic model. The simulated elastic deformations of parasitized RBCs match those obtained in optical-tweezers experiments for different stages of intra-erythrocytic parasite development. The rheological properties of RBCs in malaria are compared with those obtained by optical magnetic twisting cytometry and by monitoring membrane fluctuations at room, physiological, and febrile temperatures. We also study the dynamics of infected RBCs in Poiseuille flow in comparison with healthy cells and present validated bulk viscosity predictions of malaria-infected blood for a wide range of parasitemia levels (percentage of infected RBCs with respect to the total number of cells in a unit volume).

One of the most severe forms of cerebral malaria is caused by the parasite Plasmodium falciparum. During its development inside the host red blood cell it causes major mechanical and biochemical changes to the cell and can even alter its biconcave shape. The two main mechanical modifications are significant stiffening of the cell and increased cytoadherence to the arterial wall and other cells. These two effects can lead to dramatic flow modifications of infected blood, especially in the smallest vessels where occlusions are possible. In this work we combine a first-principles mathematical approach together with single-cell measurements to model seamlessly the infected and healthy red blood cells as well as the plasma flow, and predict their collective behavior in blood flow. Through systematic parallel simulations we quantify the mechanical and rheological properties of infected blood in malaria for a wide range of parasitemia levels, investigating in particular the effect of temperature.

Blood testing at the single cell level using quantitative phase and amplitude microscopy

It has recently been shown that quantitative phase imaging methods can provide clinically relevant parameters for red blood cell analysis with unprecedented detail and sensitivity. Since the quantitative phase information is dependent on both the thickness and refractive index, a major limitation to clinical translation has been a simple and practical approach to measure both simultaneously. Here we demonstrate both theoretically and experimentally that, by combining quantitative phase with a single absorption measurement, it is possible to measure both quantities at the single cell level. We validate this approach by comparing our results to those acquired using a clinical blood analyzer. This approach to decouple the thickness and refractive index for red blood cells may be used with any quantitative phase imaging method that can operate in tandem with bright field microscopy at the Soret-band wavelength.

Dispersion-relation phase spectroscopy of intracellular transport

We used quantitative phase imaging to measure the dispersion relation, i.e. decay rate vs. spatial mode, associated with mass transport in live cells. This approach applies equally well to both discrete and continuous mass distributions without the need for particle tracking. From the quadratic experimental curve specific to diffusion, we extracted the diffusion coefficient as the only fitting parameter. The linear portion of the dispersion relation reveals the deterministic component of the intracellular transport. Our data show a universal behavior where the intracellular transport is diffusive at small scales and deterministic at large scales. Measurements by our method and particle tracking show that, on average, the mass transport in the nucleus is slower than in the cytoplasm.

One-dimensional deterministic transport in neurons measured by dispersion-relation phase spectroscopy

We studied the active transport of intracellular components along neuron processes using a new method developed in our laboratory: dispersion-relation phase spectroscopy. This method is able to quantitatively map spatially the heterogeneous dynamics of the concentration field of the cargos at submicron resolution without the need for tracking individual components. The results in terms of density correlation function reveal that the decay rate is linear in wavenumber, which is consistent with a narrow Lorentzian distribution of cargo velocity.

Optical imaging techniques for the study of malaria

Malarial infection needs to be imaged to reveal the mechanisms behind malaria pathophysiology and to provide insights to aid in the diagnosis of the disease. Recent advances in optical imaging methods are now being transferred from physics laboratories to the biological field, revolutionizing how we study malaria. To provide insight into how these imaging techniques can improve the study and treatment of malaria, we summarize recent progress on optical imaging techniques, ranging from in vitro visualization of the disease progression of malaria infected red blood cells (iRBCs) to in vivo imaging of malaria parasites in the liver.

Combined confocal Raman and quantitative phase microscopy system for biomedical diagnosis

We have developed a novel multimodal microscopy system that incorporates confocal Raman, confocal reflectance, and quantitative phase microscopy (QPM) into a single imaging entity. Confocal Raman microscopy provides detailed chemical information from the sample, while confocal reflectance and quantitative phase microscopy show detailed morphology. Combining these intrinsic contrast imaging modalities makes it possible to obtain quantitative morphological and chemical information without exogenous staining. For validation and characterization, we have used this multi-modal system to investigate healthy and diseased blood samples. We first show that the thickness of a healthy red blood cell (RBC) shows good correlation with its hemoglobin distribution. Further, in malaria infected RBCs, we successfully image the distribution of hemozoin (malaria pigment) inside the cell. Our observations lead us to propose morphological screening by QPM and subsequent chemical imaging by Raman for investigating blood disorders. This new approach allows monitoring cell development and cell-drug interactions with minimal perturbation of the biological system of interest.

Optical measurement of cycle-dependent cell growth

Determining the growth patterns of single cells offers answers to some of the most elusive questions in contemporary cell biology: how cell growth is regulated and how cell size distributions are maintained. For example, a linear growth in time implies that there is no regulation required to maintain homeostasis; an exponential pattern indicates the opposite. Recently, there has been great effort to measure single cells using microelectromechanical systems technology, and several important questions have been explored. However, a unified, easy-to-use methodology to measure the growth rate of individual adherent cells of various sizes has been lacking. Here we demonstrate that a newly developed optical interferometric technique, known as spatial light interference microscopy, can measure the cell dry mass of many individual adherent cells in various conditions, over spatial scales from micrometers to millimeters, temporal scales ranging from seconds to days, and cell types ranging from bacteria to mammalian cells. We found evidence of exponential growth in Escherichia coli, which agrees very well with other recent reports. Perhaps most importantly, combining spatial light interference microscopy with fluorescence imaging provides a unique method for studying cell cycle-dependent growth. Thus, by using a fluorescent reporter for the S phase, we measured single cell growth over each phase of the cell cycle in human osteosarcoma U2OS cells and found that the G2 phase exhibits the highest growth rate, which is mass-dependent and can be approximated by an exponential.

Detrended fluctuation analysis of membrane flickering in discocyte and spherocyte red blood cells using quantitative phase microscopy

Dynamic analyses of vibrational motion in cell membranes provide a lot of information on the complex dynamic motilities of a red blood cell (RBC). Here, we present the correlation properties of membrane fluctuation in discocyte and spherocyte RBCs by using quantitative phase microscopy (QPM). Since QPM can provide nanometer sensitivity in thickness measurement within a millisecond time scale, we were able to observe the membrane flicking of an RBC in nanometer resolution up to the bandwidth of 50 Hz. The correlation properties of the vibrational motion were analyzed with the detrended fluctuation analysis (DFA) method. Fractal scaling exponent α in the DFA method was calculated for the vibrational motion of a cell surface at various surface points for normal discocyte and abnormal spherocyte RBCs. Measured α values for normal RBCs are distributed between 0.7 and 1.0, whereas those for abnormal spherocyte RBCs are within a range from 0.85 to 1.2. We have also verified that the vibrational motion of background fluid outside of a cell has an α value close to 0.5, which is a typical property of an uncorrelated white noise.

Biophysics of malarial parasite exit from infected erythrocytes

Upon infection and development within human erythrocytes, P. falciparum induces alterations to the infected RBC morphology and bio-mechanical properties to eventually rupture the host cells through parasitic and host derived proteases of cysteine and serine families. We used previously reported broad-spectrum inhibitors (E64d, EGTA-AM and chymostatin) to inhibit these proteases and impede rupture to analyze mechanical signatures associated with parasite escape. Treatment of late-stage iRBCs with E64d and EGTA-AM prevented rupture, resulted in no major RBC cytoskeletal reconfiguration but altered schizont morphology followed by dramatic re-distribution of three-dimensional refractive index (3D-RI) within the iRBC. These phenotypes demonstrated several-fold increased iRBC membrane flickering. In contrast, chymostatin treatment showed no 3D-RI changes and caused elevated fluctuations solely within the parasitophorous vacuole. We show that E64d and EGTA-AM supported PV breakdown and the resulting elevated fluctuations followed non-Gaussian pattern that resulted from direct merozoite impingement against the iRBC membrane. Optical trapping experiments highlighted reduced deformability of the iRBC membranes upon rupture-arrest, more specifically in the treatments that facilitated PV breakdown. Taken together, our experiments provide novel mechanistic interpretations on the role of parasitophorous vacuole in maintaining the spherical schizont morphology, the impact of PV breakdown on iRBC membrane fluctuations leading to eventual parasite escape and the evolution of membrane stiffness properties of host cells in which merozoites were irreversibly trapped, recourse to protease inhibitors. These findings provide a comprehensive, previously unavailable, body of information on the combined effects of biochemical and biophysical factors on parasite egress from iRBCs.

Effective temperature of red-blood-cell membrane fluctuations

Biologically driven nonequilibrium fluctuations are often characterized by their non-Gaussianity or by an "effective temperature", which is frequency dependent and higher than the ambient temperature. We address these two measures theoretically by examining a randomly kicked particle, with a variable number of kicking motors, and show how these two indicators of nonequilibrium behavior can contradict. Our results are compared with new experiments on shape fluctuations of red-blood cell membranes, and demonstrate how the physical nature of the motors in this system can be revealed using these global measures of nonequilibrium.

Measurement of the nonlinear elasticity of red blood cell membranes

The membranes of human red blood cells (RBCs) are a composite of a fluid lipid bilayer and a triangular network of semiflexible filaments (spectrin). We perform cellular microrheology using the dynamic membrane fluctuations of the RBCs to extract the elastic moduli of this composite membrane. By applying known osmotic stresses, we measure the changes in the elastic constants under imposed strain and thereby determine the nonlinear elastic properties of the membrane. We find that the elastic nonlinearities of the shear modulus in tensed RBC membranes can be well understood in terms of a simple wormlike chain model. Our results show that the elasticity of the spectrin network can mostly account for the area compression modulus at physiological osmolality, suggesting that the lipid bilayer has significant excess area. As the cell swells, the elastic contribution from the now tensed lipid membrane becomes dominant.

Low level of lead can induce phosphatidylserine exposure and erythrophagocytosis: a new mechanism underlying lead-associated anemia

Anemia is probably one of the most well-known toxic effects of lead. Previously, lead-induced anemia was considered to be from the inhibition of δ-aminolevulinic acid dehydratase participating in the heme biosynthesis. However, little is known whether lead could affect the destruction of erythrocyte, another important factor for anemia. In the present study, we demonstrated that lead could accelerate the splenic sequestration of erythrocytes through phosphatidylserine (PS) exposure and subsequently increased erythrophagocytosis. In freshly isolated human erythrocytes, Pb(2+)- induced PS exposure at relatively low concentrations (∼0.1 μM) by inhibiting flippase, a key aminophospholipid translocase for the maintenance of PS asymmetry and adenosine triphosphate depletion appeared to underlie this phenomenon. Abnormal shape changes of erythrocytes and microvesicle generation and other triggers for the erythrophagocytosis were also observed in the Pb(2+)-exposed erythrocytes. In vitro data showed that human macrophage indeed recognized and phagocytosis PS-exposed erythrocytes. In good accordance with these in vitro results, the oral administration of Pb(2+) increased PS exposure on erythrocytes in rat in vivo. In addition, reduction of hematocrit and hemoglobin and increased spleen weight were observed along with enhanced splenic sequestration of erythrocytes in the rats exposed to Pb(2+) subchronically for 4 weeks through drinking water. In conclusion, these results suggest that Pb(2+)-induced anemia may be explained at least in part by increased PS exposure on erythrocytes, erythrophagocytosis, and splenic sequestration.

Quantitative microscopy and nanoscopy of sickle red blood cells performed by wide field digital interferometry

We have applied wide-field digital interferometry (WFDI) to examine the morphology and dynamics of live red blood cells (RBCs) from individuals who suffer from sickle cell anemia (SCA), a genetic disorder that affects the structure and mechanical properties of RBCs. WFDI is a noncontact, label-free optical microscopy approach that can yield quantitative thickness profiles of RBCs and measurements of their membrane fluctuations at the nanometer scale reflecting their stiffness. We find that RBCs from individuals with SCA are significantly stiffer than those from a healthy control. Moreover, we show that the technique is sensitive enough to distinguish classes of RBCs in SCA, including sickle RBCs with apparently normal morphology, compared to the stiffer crescent-shaped sickle RBCs. We expect that this approach will be useful for diagnosis of SCA and for determining efficacy of therapeutic agents.

Effective 3D viscoelasticity of red blood cells measured by diffraction phase microscopy

We present optical measurements of nanoscale red blood cell fluctuations obtained by highly sensitive quantitative phase imaging. These spatio-temporal fluctuations are modeled in terms of the bulk viscoelastic response of the cell. Relating the displacement distribution to the storage and loss moduli of the bulk has the advantage of incorporating all geometric and cortical effects into a single effective medium behavior. The results on normal cells indicate that the viscous modulus is much larger than the elastic one throughout the entire frequency range covered by the measurement, indicating fluid behavior.

Label-free intracellular transport measured by spatial light interference microscopy

We show that applying the Laplace operator to a speckle-free quantitative phase image reveals an unprecedented level of detail in cell structure, without the gradient artifacts associated with differential interference contrast microscopy, or photobleaching and phototoxicity limitations common in fluorescence microscopy. This method, referred to as Laplace phase microscopy, is an efficient tool for tracking vesicles and organelles in living cells. The principle is demonstrated by tracking organelles in cardiomyocytes and vesicles in neurites of hippocampal neurons, which to our knowledge are the first label-free diffusion measurements of the organelles in such cells.

Light scattering of human red blood cells during metabolic remodeling of the membrane

We present the light scattering properties of individual human red blood cells (RBCs). We show that both the RBC static and dynamic scattering signals are altered by adenosine 5'-triphosphate (ATP)-driven membrane metabolic remodeling. To measure the light scattering signal from individual RBCs, we use diffraction phase microscopy together with a Fourier transform light scattering technique. RBC cytosolic ATPs are both chemically and metabolically depleted, and the corresponding scattering signals are compared with the light scattering signal of normal RBCs having physiologic levels of ATP.

A low-dimensional model for the red blood cell

The red blood cell (RBC) is an important determinant of the rheological properties of blood because of its predominant number density, special mechanical properties and dynamics. Here, we develop a new low-dimensional RBC model based on dissipative particle dynamics (DPD). The model is constructed as a closed-torus-like ring of 10 colloidal particles connected by wormlike chain springs combined with bending resistance. Each colloidal particle is represented by a single DPD particle with a repulsive core. The model is able to capture the essential mechanical properties of RBCs, and allows for economical exploration of the rheology of RBC suspensions. Specifically, we find that the linear and non-linear elastic deformations of healthy and malaria-infected cells match those obtained in optical tweezers experiments. Through simulations of some key features of blood flow in vessels, i.e., the cell-free layer (CFL), the Fahraeus effect and the Fahraeus-Lindqvist effect, we verify that the new model captures the essential shear flow properties of real blood, except for capillaries of sizes comparable to the cell diameter. Finally, we investigate the influence of a geometrical constriction in the flow on the enhancement of the downstream CFL. Our results are in agreement with recent experiments.

One-particle-thick, solvent-free, coarse-grained model for biological and biomimetic fluid membranes

Biological membranes are involved in numerous intriguing biophysical and biological cellular phenomena of different length scales, ranging from nanoscale raft formation, vesiculation, to microscale shape transformations. With extended length and time scales as compared to atomistic simulations, solvent-free coarse-grained membrane models have been exploited in mesoscopic membrane simulations. In this study, we present a one-particle-thick fluid membrane model, where each particle represents a cluster of lipid molecules. The model features an anisotropic interparticle pair potential with the interaction strength weighed by the relative particle orientations. With the anisotropic pair potential, particles can robustly self-assemble into fluid membranes with experimentally relevant bending rigidity. Despite its simple mathematical form, the model is highly tunable. Three potential parameters separately and effectively control diffusivity, bending rigidity, and spontaneous curvature of the model membrane. As demonstrated by selected examples, our model can naturally simulate dynamics of phase separation in multicomponent membranes and the topological change of fluid vesicles.

Shape and Biomechanical Characteristics of Human Red Blood Cells in Health and Disease

The biconcave shape and corresponding deformability of the human red blood cell (RBC) is an essential feature of its biological function. This feature of RBCs can be critically affected by genetic or acquired pathological conditions. In this review, we highlight new dynamic in vitro assays that explore various hereditary blood disorders and parasitic infectious diseases that cause disruption of RBC morphology and mechanics. In particular, recent advances in high-throughput microfluidic devices make it possible to sort/identify healthy and pathological human RBCs with different mechanobiological characteristics.

Static and dynamic light scattering of healthy and malaria-parasite invaded red blood cells

We present the light scattering of individual Plasmodium falciparum-parasitized human red blood cells (Pf-RBCs), and demonstrate progressive alterations to the scattering signal arising from the development of malaria-inducing parasites. By selectively imaging the electric fields using quantitative phase microscopy and a Fourier transform light scattering technique, we calculate the light scattering maps of individual Pf-RBCs. We show that the onset and progression of pathological states of the Pf-RBCs can be clearly identified by the static scattering maps. Progressive changes to the biophysical properties of the Pf-RBC membrane are captured from dynamic light scattering.