Fluorescein fluorescence hyperpolarization as an early kinetic measure of the apoptotic process

Role of mitochondrial raft-like microdomains in the regulation of cell apoptosis

Lipid rafts are envisaged as lateral assemblies of specific lipids and proteins that dissociate and associate rapidly and form functional clusters in cell membranes. These structural platforms are not confined to the plasma membrane; indeed lipid microdomains are similarly formed at subcellular organelles, which include endoplasmic reticulum, Golgi and mitochondria, named raft-like microdomains. In addition, some components of raft-like microdomains are present within ER-mitochondria associated membranes. This review is focused on the role of mitochondrial raft-like microdomains in the regulation of cell apoptosis, since these microdomains may represent preferential sites where key reactions take place, regulating mitochondria hyperpolarization, fission-associated changes, megapore formation and release of apoptogenic factors. These structural platforms appear to modulate cytoplasmic pathways switching cell fate towards cell survival or death. Main insights on this issue derive from some pathological conditions in which alterations of microdomains structure or function can lead to severe alterations of cell activity and life span. In the light of the role played by raft-like microdomains to integrate apoptotic signals and in regulating mitochondrial dynamics, it is conceivable that these membrane structures may play a role in the mitochondrial alterations observed in some of the most common human neurodegenerative diseases, such as Amyotrophic lateral sclerosis, Huntington's chorea and prion-related diseases. These findings introduce an additional task for identifying new molecular target(s) of pharmacological agents in these pathologies.

Photobleaching of fluorescein as a probe for oxidative stress in single cells

BACKGROUND

ROS are involved in the regulation of many physiological and pathological processes. Apoptosis and necrosis are processes that are induced by changes in concentrations of Reactive Oxygen Species (ROS). This study aims to detect and quantify the cellular response to changing ROS concentrations in the scope of apoptosis and necrosis.

METHODS

Photobleaching of the fluorescent substrate fluorescein is used as a probe to detect the response of individual Jurkat-T-lymphocytes and Prostate-Cancer-3(PC-3) cells to oxidative stress, induced by hydrogen peroxide (H₂O₂). A kinetic model is proposed to describe changes in intracellular dye quantities due to photobleaching, dye hydrolysis, influx and leakage, yielding a single time-dependent decaying exponent+constant.

RESULTS

Fluorescein photobleaching is controlled and used to detect intracellular ROS. An increase in the decay time of fluorescence of intracellular fluorescein (slow photobleaching) was measured from cells incubated with H₂O₂ at 50 μM. At higher H₂O₂ concentrations a decrease in the decay time was measured (fast photobleaching), in contrast to in vitro results with fluorescein and H₂O₂ in phosphate buffer saline (PBS), where the addition of H₂O₂ decreases the decay time, regardless of the irradiation dose used.

CONCLUSIONS

The anomalous, ROS-concentration dependent reduction of the photobleaching rate in cells, as opposed to solutions, might indicate on the regulation of the activity of intracellular oxidative-stress protective mechanisms, as seen earlier with other methods.

SIGNIFICANCE

Assessing photobleaching via the time decay of the fluorescence intensity of an ROS-sensitive fluorophore may be adapted to monitor oxidative stress or ROS-related processes in cells.

Context mediates antimicrobial efficacy of kinocidin congener peptide RP-1

Structure-mechanism relationships are key determinants of host defense peptide efficacy. These relationships are influenced by anatomic, physiologic and microbiologic contexts. Structure-mechanism correlates were assessed for the synthetic peptide RP-1, modeled on microbicidal domains of platelet kinocidins. Antimicrobial efficacies and mechanisms of action against susceptible ((S)) or resistant ((R)) Salmonella typhimurium (ST), Staphylococcus aureus (SA), and Candida albicans (CA) strain pairs were studied at pH 7.5 and 5.5. Although RP-1 was active against all study organisms, it exhibited greater efficacy against bacteria at pH 7.5, but greater efficacy against CA at pH 5.5. RP-1 de-energized SA and CA, but caused hyperpolarization of ST in both pH conditions. However, RP-1 permeabilized ST(S) and CA strains at both pH, whereas permeabilization was modest for ST(R) or SA strain at either pH. Biochemical analysis, molecular modeling, and FTIR spectroscopy data revealed that RP-1 has indistinguishable net charge and backbone trajectories at pH 5.5 and 7.5. Yet, concordant with organism-specific efficacy, surface plasmon resonance, and FTIR, molecular dynamics revealed modest helical order increases but greater RP-1 avidity and penetration of bacterial than eukaryotic lipid systems, particularly at pH 7.5. The present findings suggest that pH- and target-cell lipid contexts influence selective antimicrobial efficacy and mechanisms of RP-1 action. These findings offer new insights into selective antimicrobial efficacy and context-specificity of antimicrobial peptides in host defense, and support design strategies for potent anti-infective peptides with minimal concomitant cytotoxicity.

The Immunosuppressive Effect of Methotrexate in Active Rheumatoid Arthritis Patients vs. its Stimulatory Effect in Nonactive Patients, as Indicated by Cytometric Measurements of CD4 + T Cell Subpopulations

This cytometric study assesses the effects of methotrexate (MTX) on the expanded CD4+ lymphocyte population in active and nonactive rheumatoid arthritis (RA) patients. In the active patients, MTX was found to reduce the predominant CD4+ CD28+ subpopulation (by 30%), and the minor subpopulation of CD4+ CD28- (by 34%). The incidence of CD25 phenotype was downregulated by 15%. These reductions can be attributed to immunosuppression through apoptosis, which was demonstrated by MTX-induced fluorescein diacetate (FDA) hyperpolarization (an established indicator of early apoptosis). In contrast, in nonactive RA patients, the major CD4+ CD28+ subpopulation of small lymphocytes appeared to be activated by MTX, subsequently transforming into a major hyperblast population, whereas the minor CD4+ CD28- subpopulation was not affected by MTX treatment. The activation by MTX in this group of patients is evidenced by MTX-induced FDA depolarization (an indicator of early activation). Thus, MTX immunosuppressive effect on CD4+ subsets was found in active patients, whereas immunostimulation by MTX was shown in nonactive patients. The found discriminative effect of MTX may suggest a higher effectiveness of low-dose MTX therapy in active RA patients.

Raft component GD3 associates with tubulin following CD95/Fas ligation

In a previous investigation, we demonstrated that after CD95/Fas triggering, raft-associated GD3 ganglioside, normally localized at the plasma membrane of T cells, can be detected in mitochondria, where they contribute to apoptogenic events. Here, we show the association of the glycosphingolipid GD3 with microtubular cytoskeleton at very early time points following Fas ligation. This was assessed by different methodological approaches, including fluorescence resonance energy transfer, immunoelectron microscopy, and coimmunoprecipitation. Furthermore, docking analysis also showed that GD3 has a high affinity for the pore formed by 4 tubulin heterodimers (type I pore), thus suggesting a possible direct interaction between tubulin and GD3. Finally, time-course analyses indicated that the relocalization of GD3 to the mitochondria was time related with the alterations of the mitochondrial membrane potential. Hence, microtubules could act as tracks for ganglioside redistribution following apoptotic stimulation, possibly contributing to the mitochondrial alterations leading to cell death.

EGFP fluorescence as an indicator of cancer cells response to methotrexate

Methotrexate action in viable cells was monitored by registering changes in EGFP (Enhanced Green Fluorescent Protein) fluorescence intensity. Treatment with 1 microM methotrexate for 48 h of human colorectal adenocarcinoma C85 cells, stably transfected to express EGFP, caused 5-fold increase in EGFP fluorescence assayed by flow cytometry with no distinct increase in EGFP protein level. This was correlated with morphological changes, including an increase of cell granularity and cell shape flattening, as well as cell cycle G1 phase arrest revealed by DNA content analysis. Methotrexate removal allowed the morphology of the cells in culture to revert in 10 days to normal. The cells that survived methotrexate exposure were propagated as C85r cell subline and displayed kinetics of methotrexate sensitivity parallel to that of the parental C85 line. As the increase in EGFP fluorescence could also be visualized by fluorescence microscopy, this reporter system may be employed to image methotrexate action in cancer cells in living models.

Chemical mapping of tumor progression by FT-IR imaging: towards molecular histopathology

Fourier-transform infrared (FT-IR) spectro-imaging enables global analysis of samples, with resolution close to the cellular level. Recent studies have shown that FT-IR imaging enables determination of the biodistribution of several molecules of interest (carbohydrates, lipids, proteins) for tissue analysis without pre-analytical modification of the sample such as staining. Molecular structure information is also available from the same analysis, notably for protein secondary structure and fatty acyl chain peroxidation level. Thus, several cancer markers can be identified from FT-IR tissue images, enabling accurate discrimination between healthy and tumor areas. FT-IR imaging applications are now able to provide unique chemical and morphological information about tissue status. With the fast image acquisition provided by modern mid-infrared imaging systems, it is now envisaged to analyze cerebral tumor exereses in delays compatible with neurosurgery. Accordingly, we propose to take FT-IR imaging into consideration for the development of new molecular histopathology tools.

Application of a static fluorescence-based cytometer: the CellScan in clinical immunology

The CellScan system is a laser scanning cytometer which enables repetitive fluorescence intensity (FI) and polarization (FP) measurements in living cells, as a means of monitoring lymphocyte activation. By monitoring FP changes in peripheral blood lymphocytes (PBL) following exposure to antigenic stimuli, the CellScan may have a role in the diagnosis of autoimmune diseases. Monitoring changes in FI and FP in PBLs from patients with atherosclerosis following exposure to various stimuli, has illustrated the role of the immune system in the atherosclerotic process. The CellScan has also been evaluated as a diagnostic tool for drug-induced allergy, based on FP reduction in PBLs following incubation with the suspected drugs. FI and FP changes in cancer cells have been found to correlate with the cytotoxic effect of different anti-neoplastic drugs, illustrating the potential role of the CellScan system in clinical oncology. In conclusion, the CellScan is a promising new tool with a variety of applications in cell biology, immunology, cancer research and clinical pharmacology.

Application of a static fluorescence-based cytometer (the CellScan) in basic cytometric studies, clinical pharmacology, oncology and clinical immunology

The CellScan apparatus is a laser scanning cytometer enabling repetitive fluorescence intensity (FI) and polarization (FP) measurements in living cells, as a means of monitoring lymphocyte activation. The CellScan may serve as a tool for diagnosis of rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) as well as other autoimmune diseases by monitoring FP changes in peripheral blood lymphocytes (PBLs) following exposure to autoantigenic stimuli. Changes in FI and FP in atherosclerotic patients' PBLs following exposure to various stimuli have established the role of the immune system in atherosclerotic disease. The CellScan has been evaluated as a diagnostic tool for drug-allergy, based on FP reduction in PBLs following incubation with allergenic drugs. FI and FP changes in cancer cells have been found to be well correlated with the cytotoxic effect of anti-neoplastic drugs. In conclusion, the CellScan has a variety of applications in cell biology, immunology, cancer research and clinical pharmacology.

Erythrocyte Adaptation to Oxidative Stress in Endurance Training

BACKGROUND

We tested the hypothesis that endurance training may reduce exercise oxidative stress damage on erythrocytes.

METHODS

Fifteen subjects performed a standardized endurance exercise at 75% of maximal oxygen consumption weekly during a 19-week training period. Blood samples taken before and after exercise were analyzed by Fourier transform-infrared (FT-IR) spectrometry to determine exercise-induced change in plasma concentrations and erythrocyte IR absorptions.

RESULTS

Training first induced a stabilization of plasma concentration changes during exercise (unchanged for glucose, increased for lactate, triglycerides, glycerol, and fatty acids), whereas erythrocyte phospholipid alterations remained elevated (p <0.05). Further, training reduced the exercise-induced erythrocyte lactate content increase (nuC-O; p <0.05) and phospholipid alterations (nuC-H(n) and nuP=O; p <0.05) during exercise. These changes paralleled the decrease of exercise-induced hemoconcentration (p <0.05) and plasma lactate increase (p <0.05).

CONCLUSIONS

These correlated changes between plasma and erythrocyte parameters suggest that endurance training reduces erythrocyte susceptibility to oxidative stress.

Antifungal protein PAF severely affects the integrity of the plasma membrane of Aspergillus nidulans and induces an apoptosis-like phenotype

The small, basic, and cysteine-rich antifungal protein PAF is abundantly secreted into the supernatant by the beta-lactam producer Penicillium chrysogenum. PAF inhibits the growth of various important plant and zoopathogenic filamentous fungi. Previous studies revealed the active internalization of the antifungal protein and the induction of multifactorial detrimental effects, which finally resulted in morphological changes and growth inhibition in target fungi. In the present study, we offer detailed insights into the mechanism of action of PAF and give evidence for the induction of a programmed cell death-like phenotype. We proved the hyperpolarization of the plasma membrane in PAF-treated Aspergillus nidulans hyphae by using the aminonaphtylethenylpyridinium dye di-8-ANEPPS. The exposure of phosphatidylserine on the surface of A. nidulans protoplasts by Annexin V staining and the detection of DNA strand breaks by TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) gave evidence for a PAF-induced apoptotic-like mechanism in A. nidulans. The localization of reactive oxygen species (ROS) by dichlorodihydrofluorescein diacetate and the abnormal cellular ultrastructure analyzed by transmission electron microscopy suggested that ROS-elicited membrane damage and the disintegration of mitochondria played a major role in the cytotoxicity of PAF. Finally, the reduced PAF sensitivity of A. nidulans strain FGSC1053, which carries a dominant-interfering mutation in fadA, supported our assumption that G-protein signaling was involved in PAF-mediated toxicity.

Tracing apoptosis and stimulation in individual cells by fluorescence intensity and anisotropy decay

Presented is the use of fluorescence lifetime (FLT), anisotropy decay, and associated parameters as differential indicators of cellular activity. A specially designed combination of a frequency mode based time resolved microscope and a picoliter well-per-cell array have been used to perform temporal measurements in individual cells under various biological conditions. Two biological models have been examined: mitogenic activation of peripheral blood mononuclear cells (PBMC) and induction of programmed cell death (apoptosis) in Jurkat T cells (JTC). The FLT of fluorescein stained PBMC was found to increase from 4+/-0.02 to 4.5+/-0.025 ns due to mitogenic activation, whereas during apoptosis in fluorescein stained JTC, the FLT remained constant. Notably, the rotational correlation times changed in both models: decreased in PBMC from 2.5+/-0.08 to 2+/-0.1 ns, and increased in JTC from 2.1+/-0.07 to 3.3+/-0.09 ns. FLT and rotational correlation time were used to calculate the steady state fluorescence anisotropy (FA) which was compared to directly measured FA values. The present study suggests that in addition to bioindication, the said parameters can provide valuable information about cellular mechanisms that may involve complex molecular diffusion dynamics, as well as information about structural changes that a cellular fluorophore undergoes in the course of cell activation.

A novel approach for on line monitoring of apoptotic cell shrinkage in individual live lymphocytes

The apoptotic process occurs asynchronically in most cell populations and its duration is variable. Therefore, the ability to continuously monitor the death process occurring in individual blood cells before, during and following apoptosis induction is crucial in the evaluation of the efficiency of pro- or anti-apoptotic drugs. We applied a kinetic approach by performing real time measurements of individual living cells. This approach is based on an easy and unique method for monitoring intracellular staining reaction, which accompanied early apoptotic cell shrinkage. The intracellular enzymatic reaction rates were determined by taking repeated, sequential measurements of fluorescence intensity of the same individual cells. These rates were found to correlate with the respective radii of the cells under different conditions, and to decrease following apoptosis induction. The ability to remeasure the same cell before and after apoptosis induction enabled the detection of specific individual lymphocytes, which were more susceptible or resistant to pro-apoptotic stimulus.

Ratiometric fluorescence polarization as a cytometric functional parameter: theory and practice

The use of ratiometric fluorescence polarization (RFP) as a functional parameter in monitoring cellular activation is suggested, based on the physical phenomenon of fluorescence polarization dependency on emission wavelengths in multiple (at least binary) solutions. The theoretical basis of this dependency is thoroughly discussed and examined via simulation. For simulation, aimed to imitate a fluorophore-stained cell, real values of the fluorescence spectrum and polarization of different single fluorophore solutions were used. The simulation as well as the experimentally obtained values of RFP indicated the high sensitivity of this measure. Finally, the RFP parameter was utilized as a cytometric measure in three exemplary cellular bioassays. In the first, the apoptotic effect of oxLDL in a human Jurkat FDA-stained T cell line was monitored by RFP. In the second, the interaction between cell surface membrane receptors of human T lymphocyte cells was monitored by RFP measurements as a complementary means to the fluorescence resonance energy transfer (FRET) technique. In the third bioassay, cellular thiol level of FDA- and CMFDA-labelled Jurkat T cells was monitored via RFP.

The induction of apoptosis by methotrexate in activated lymphocytes as indicated by fluorescence hyperpolarization: a possible model for predicting methotrexate therapy for rheumatoid arthritis patients

The objectives of this study were to test the in vitro response of healthy non-activated, activated, and rheumatoid arthritis (RA) lymphocytes to methotrexate (MTX), and design an in vitro model for predicting the efficiency of MTX treatment for RA patients. Considering the RA profile of clonal-expanded CD4(+) T cells, phytohemagglutinin-activated mononuclear cells taken from healthy donors were incubated with different concentrations of MTX. The MTX-immunosuppressive effect was tested by fluorescence intensity measurements, including PI assay and annexin V assay. For simple detection, we used the Individual Cell Scanner (IC-S), which enables the measurement of early events in individual cells. Healthy mononuclear cells (MNC), and MNC derived from RA patients, were tested by the IC-S while utilizing fluorescence polarization (FP) measurements of fluorescein diacetate (FDA) as an established marker of activation or suppression. In healthy activated MNC, we found that MTX, through its early incubation period, interferes with the activation signal obtained by PHA and exerts an apoptotic signal, which is noted by increases in the FP. Comparing our model to six long-standing RA patients and five newly-diagnosed patients revealed significant differences in the FP measurements, including fluorescence depolarization as an early established measurement of lymphocyte activation, and hyperpolarization as a measurement of an early immunosuppressive effect. We conclude that MTX, an effective therapy for RA patients, could easily be tested by fluorescence polarization measurements of FDA before (or during) clinical use in order to predict its efficiency on a specific RA patient. Moreover, the FP measurements can be used for the diagnosis, and making timing and dosage decisions.

Analysis of early apoptotic events in individual cells by fluorescence intensity and polarization measurements

Apoptosis is a dynamic process of variable duration. The ability to continuously detect the death process occurring in single or subgroups of cells is therefore very important in identifying apoptotic cells within a complex population. The Individual Cell Scanner (ICS), a multiparametric, multilaser-based scanning static cytometer, was used in the present report for the continuous monitoring of the apoptosis process. Fluorescence intensity (FI), polarization (FP), kinetic measurements, and cluster analysis of subpopulations were carried out utilizing various fluorescent probes. Hydrogen peroxide-induced apoptosis was monitored online in intact live lymphocytes by continuous sequential measurements of intracellular hyperpolarization. Plasma membrane asymmetry, mitochondrial membrane potential, and lysosomal rupture were monitored in individual cells. Cytoplasmic condensations, due to cell shrinkage and early lysosomal rupture, were found to be very early events of apoptosis. The new analytical capabilities suggested here may provide simple and convenient methods for detecting apoptosis from its earlier stages.

Determination of individual cell Michaelis-Menten constants

BACKGROUND

A novel methodology for the measurement and analysis of apparent K(M) (Michaelis-Menten constant) and V(MAX) values of individual cells is suggested. It is based on a mathematical model that considers substrate influx into the cell, its intracellular enzymatic hydrolysis, and the product efflux. The mathematical formulation was approximated linearly in order to analyze intracellular substrate conversion characteristics via Michaelis-Menten theory.

METHODS

Utilizing static cytometry, the time dependence of the fluorescence intensity [FI(t)] emitted from prelocalized and defined FDA stained cells was recorded. This required frequent periodical measurements of the same cells, which are sequentially exposed to various fluorogenic substrate concentrations.

RESULTS

Model simulations correlated with experimental results. Differences in distributions of individual K(M) and V(MAX) values of cells incubated with and without PHA were evident. Average K(M) and V(MAX) values of PHA-stimulated cells increased by 99% and 540%, respectively.

CONCLUSIONS

This study may provide a tool for assessing intracellular enzymatic activity in individual intact cells under defined physiologic conditions. This may open new vistas in various areas, giving answers to critical questions arising in the field of cell and developmental biology, immunology, oncology, and pharmacology.

Generation of heterohybridomas secreting human immunoglobulins; pokeweed mitogen prestimulation is highly effective but phytohemagglutinin drives most B cells into apoptosis

Human monoclonal antibodies have commonly been generated by forming hybridomas of stable lymphoblastoid cell lines and Epstein-Barr virus (EBV)-transformed human B cells that have been exposed to phytohaemagglutin (PHA)-stimulated T cells. However, this technique has predominantly given rise to IgM- but very rarely IgG- or IgA-producing clones. We now report that, regardless of prior EBV infection, pokeweed mitogen (PWM) stimulation of human peripheral blood mononuclear cells (PBMCs) generated much higher numbers of IgM-, IgA- and IgG-producing B cells than did stimulation with PHA. Fusion of PWM-stimulated PBMCs with a mouse myeloma cell line also gave rise to 7- to 12-fold higher numbers of IgG- and IgA-producing heterohybridomas than PBMCs that were prestimulated with PHA. Judged by Annexin V staining, stimulation with PHA induced a very high rate of B cell apoptosis within 24 h, whereas, even after 7 days, PWM stimulation only induced marginal B cell apoptosis. This should explain why PHA is much inferior to PWM in stimulating immunoglobulin (Ig) production in vitro and in generating immunoglobulin-producing human B cell hybridomas. It is concluded that PWM stimulation may greatly facilitate the generation of human monoclonal antibodies of all isotypes.

Analysis of laser scattering pattern as an early measure of apoptosis

Light scattering pattern analysis (LSPA) was applied in the current study for accurate and sensitive detection of subtle changes in cell size, which occur in mouse thymocytes undergoing apoptosis. The decrease in cell diameter as measured by LSPA was found to be an early signal of apoptosis preceding the externalization of phosphatidylserine on the outer membrane. When apoptosis was induced by dexamethasone, the change in cell size was dose and time dependent, and could be blocked by pretreatment of the thymocytes with N-acetylcysteine (NAC). This implies that the scattering pattern, when combined with fluorescent markers such as annexine-V, may be a powerful tool for early detection of apoptosis. Another advantage gained by the use of this method is the ability to repeatedly trace the same cells and to monitor the kinetics of their size changes.

Inhibition of apoptosis: a potential mechanism for syndromic craniosynostosis

The biologic pathogenesis of syndromic craniosynostosis remains unknown. The purpose of this investigation was to determine whether specific biologic differences exist between normal calvarial osteoblasts and osteoblasts derived from patients with syndromic craniosynostosis. This study (1) examined the apoptotic rate and cell cycle of osteoblasts derived from patients with syndromic craniosynostosis, and (2) investigated for the presence of soluble factors released from syndrome-derived osteoblasts. Osteoblast cell lines were established from calvarial specimens of patients with clinically diagnosed syndromic synostosis and from normal controls. A co-culture technique was used to investigate for the presence of elaborated soluble factors. Apoptotic rate and cell cycle analyses were performed by using flow cytometry after staining with annexin V-fluorescein isothiocyanate and propidiumiodide, respectively. The apoptotic rate was significantly reduced in syndrome-derived osteoblasts as compared with control osteoblasts. Control osteoblasts co-cultured with syndromic osteoblasts demonstrated a dramatic reduction in their apoptotic rate as compared with those co-cultured with control osteoblasts. These results indicate that osteoblasts derived from patients with syndromic craniosynostosis display a lower apoptotic rate, a normal DNA synthetic rate, and the capability to reduce the apoptotic rate in normal calvarial osteoblasts through the elaboration of soluble factors.