Mitochondrial uptake of rhodamine 123 by rabbit articular chondrocytes

Hemolin triggers cell survival on fibroblasts in response to serum deprivation by inhibition of apoptosis

Fibroblasts are the main cellular component of connective tissues and play important roles in health and disease through the production of collagen, fibronectin and growth factors. Under certain conditions, such as wound healing, fibroblasts intensify their metabolic demand, while the restriction of nutrients affect matrix composition, cell metabolism and behavior. In lepidopterans, wound healing is regulated by ecdysteroid hormones, which upregulate multifunctional proteins such as hemolin. However, the role of hemolin in cell proliferation and wound healing is not clear. rLosac is a recombinant hemolin from the caterpillar Lonomia obliqua whose proliferative and cytoprotective effects on endothelial cells have been described. Here, we show that rLosac induces a marked cell survival effect on fibroblast submitted to serum deprivation, which is observable as early as 24h, as demonstrated through the MTT assay, as well as an increase in migration of human dermal fibroblasts (HDF). No effects on cell proliferation or cell cycle distribution of fibroblasts in normal conditions were observed, suggesting that rLosac induces an effect in stressful conditions such serum deprivation but not when nutrient are sufficient. By flow cytometry, rLosac caused an apparent dose-dependent increase in cells in the S phase of the cell cycle and a significant reduction of cells with fragmented DNA. Furthermore, treatment with rLosac results in a significant decrease in the production of reactive oxygen species and in the loss of mitochondrial membrane potential, indicating that a reduction in oxidative stress is involved in rLosac-mediated cytoprotection. Our results also show an up-regulation of Bcl-2 and a down-regulation of Bax protein levels, inhibition of cytochrome c release and a reduction in caspase-3 levels, all considered critical factors for apoptosis. Moreover, rLosac treatment reduces the morphological changes induced by prolonged serum deprivation including the emergence of apoptotic bodies, nucleus fragmentation, cytoplasmic vacuolization and loss of extracellular matrix organization. The wound scratch test assay revealed that rLosac could enhance wound healing in vitro. Altogether, these findings suggest that rLosac strongly induces cellular protection in conditions of stress by serum deprivation preventing damage and loss of mitochondrial function by inhibiting apoptosis. This finding opens a new perspective to further understand the role of hemolin proteins during cellular processes such as wound healing and development.

Amblyomin-X induces ER stress, mitochondrial dysfunction, and caspase activation in human melanoma and pancreatic tumor cell

During the last two decades, new insights into proteasome function and its role in several human diseases made it a potential therapeutic target. In this context, Amblyomin-X is a Kunitz-type FXa inhibitor similar to endogenous tissue factor pathway inhibitor (TFPI) and is a novel proteasome inhibitor. Herein, we have demonstrated Amblyomin-X cytotoxicity to different tumor cells lines such as pancreatic (Panc1, AsPC1BxPC3) and melanoma (SK-MEL-5 and SK-MEL-28). Of note, Amblyomin-X was not cytotoxic to normal human fibroblast cells. In addition, Amblyomin-X promoted accumulation of ER stress markers (GRP78 and GADD153) in sensitive (SK-MEL-28) and bortezomib-resistant (Mia-PaCa-2) tumor cells. The intracellular calcium concentration [Ca²⁺]_i was slightly modulated in human tumor cells (SK-MEL-28 and Mia-PaCa-2) after 24 h of Amblyomin-X treatment. Furthermore, Amblyomin-X induced mitochondrial dysfunction, cytochrome-c release, PARP cleavage, and activation of caspase cascade in both human tumor (SK-MEL-28 and Mia-PaCa-2) cells. These investigations might help in further understanding of the antitumor properties of Amblyomin-X.

Oxygen and reactive oxygen species in articular cartilage: modulators of ionic homeostasis

Articular cartilage is an avascular tissue dependent on diffusion mainly from synovial fluid to service its metabolic requirements. Levels of oxygen (O(2)) in the tissue are low, with estimates of between 1 and 6%. Metabolism is largely, if not entirely, glycolytic, with little capacity for oxidative phosphorylation. Notwithstanding, the tissue requires O(2) and consumes it, albeit at low rates. Changes in O(2) tension also have profound effects on chondrocytes affecting phenotype, gene expression, and morphology, as well as response to, and production of, cytokines. Although chondrocytes can survive prolonged anoxia, low O(2) levels have significant metabolic effects, inhibiting glycolysis (the negative Pasteur effect), and also notably matrix production. Why this tissue should respond so markedly to reduction in O(2) tension remains a paradox. Ion homeostasis in articular chondrocytes is also markedly affected by the extracellular matrix in which the cells reside. Recent work has shown that ion homeostasis also responds to changes in O(2) tension, in such a way as to produce significant effects on cell function. For this purpose, O(2) probably acts via alteration in levels of reactive oxygen species. We discuss the possibility that O(2) consumption by this tissue is required to maintain levels of ROS, which are then used physiologically as an intracellular signalling device. This postulate may go some way towards explaining why the tissue is dependent on O(2) and why its removal has such marked effects. Understanding the role of oxygen has implications for disease states in which O(2) or ROS levels may be perturbed.

The mitochondrial consequences of uncoupling intact cells depend on the nature of the exogenous substrate

In isolated mitochondria the consequences of oxidative phosphorylation uncoupling are well defined, whereas in intact cells various effects have been described. Uncoupling liver cells with 2,4-dinitrophenol (DNP) in the presence of dihydroxyacetone (DHA) and ethanol results in a marked decrease in mitochondrial transmembrane electrical potential (DeltaPsi), ATP/ADP ratios and gluconeogenesis (as an ATP-utilizing process), whereas the increased oxidation rate is limited and transient. Conversely, when DHA is associated with octanoate or proline, DNP addition results in a very large and sustained increase in oxidation rate, whereas the decreases in DeltaPsi, ATP/ADP ratios and gluconeogenesis are significantly less when compared with DHA and ethanol. Hence significant energy wastage (high oxidation rate) by uncoupling is achieved only with substrates that are directly oxidized in the mitochondrial matrix. Conversely in the presence of substrates that are first oxidized in the cytosol, uncoupling results in a profound decrease in mitochondrial DeltaPsi and ATP synthesis, whereas energy wastage is very limited.

Recording of mitochondrial transmembrane potential and volume in cultured rat osteoclasts by confocal laser scanning microscopy

Osteoclasts are multinuclear bone-resorbing cells which contain abundant mitochondria. Morphological studies have suggested that a correlation may exist between mitochondrial concentration and bone resorption by osteoclasts. However, investigation of mitochondrial transmembrane potential (delta psi) and volume has been hampered by the difficulty in obtaining a sufficient number of osteoclasts for assessing these characteristics by flow cytometric analysis. In this study, we have used confocal laser scanning microscopy after loading the cells with Rhodamine 123 and 10-nonyl Acridine Orange to record mitochondrial delta psi and volume, respectively, in isolated rat osteoclasts cultured on bovine bone slices. Optimal staining conditions were found to be 10 micrograms ml-1 for 40 min for Rhodamine, and 1 microM for 10 min for the 10-nonyl Acridine Orange derivative. Two osteoclast populations, whose shape seemed to reflect bone resorption and migratory functions, were identified depending on their shape and on the distribution of the two dye probes. 'Round-shaped' osteoclasts had significantly higher mitochondrial delta psi and volume in the apical regions than in the basolateral portions (p < 0.00001). In contrast, mitochondrial delta psi and volume in 'irregular-shaped' osteoclasts were rather evenly distributed in both these regions (p > 0.05). Our results indicate that there is an apical polarization of mitochondria in osteoclasts corresponding to the energy demands associated with bone resorption.

Static cytofluorometry and fluorescence morphology of mitochondria and DNA in proliferating fibroblasts

The shape, distribution, and content of mitochondria in individual cells were examined during the cell cycle phases (G(0)/G(1), S, G(2) mitosis) in living human fibroblasts by static cytofluorometry and fluorescence microscopy. The morphocytochemical evaluations were performed in cell cultures submitted to double supravital fluorochrome staining with Hoechst 33342 and DiOC(6) to label DNA and mitochondria, respectively. The staining modalities were based on the stability of mitochondrial labeling. The G(1) to early S phases were characterized by the presence of filamentous mitochondria, except during the early postmitotic period. During late S, G(2), and mitotic phases, mitochondrial mass reached its highest value and mitochondria became short and numerous. During the last stage of mitosis, mitochondria were distributed among daughter cells through a cytoplasmic bridge.

Rhodamine 123: a useful probe for monitoring T cell activation

The T cell activation pathway involves an increase in mitochondrial activity. This can be evaluated in individual cells using the fluorescent probe rhodamine 123 (Rh123) and flow cytometry. Peripheral blood mononuclear cells (PBMC) were stimulated with optimal concentrations of phytohaemagglutinin (PHA), superantigens (Sag) SEA and SEC2, and allogeneic cells. Activation kinetics were followed at days 1, 2, 4 and 7. In all activation conditions, Rh123 uptake was augmented with the CD25 expression, cell size, and DNA synthesis. Rh123 uptake reflected an increase in mitochondrial activity and mass, as assessed by experiments in which Rh123 was substituted for by the 10-nonyl acridine orange, which stains mitochondria in an energy-independent manner. The spectral characteristics of Rh123 allowed us to double stain cells with Rh123 and phycoerythrin-conjugated monoclonal antibodies. In PHA-activated cultures, CD4+ and CD8+ cells incorporated essentially the same amount of Rh123 at all time points, suggesting that the two subsets did not differ in their activation kinetics. Accordingly, after 1 week of culture, no significant modification in the CD4/CD8 ratio was observed. Sag-activated CD4+ cells incorporated a higher amount of Rh123 than did CD8+ cells and preferentially expanded after 1 week of culture as indicated by the increase in the CD4/CD8 ratio. The different behavior of the CD4 and CD8 subsets observed by dual color flow cytometry in the PHA and Sag models was confirmed using purified CD4+ and CD8+ cell preparations obtained by immunomagnetic sorting. CD4+ cells were also the preferential target in the allogeneic model, although the magnitude of the phenomenon was lower than in the Sag model. Present data indicate that Rh123 is a reliable marker for monitoring the mitochondrial compartment during T cell activation. The possibility of phenotyping Rh123-stained cells adds to the applicability of the probe.

Cytofluorometric analysis of chondrotoxicity of fluoroquinolone antimicrobial agents

To better understand quinolone-related arthropathy, we conceived an experimental ex vivo model using cell cultures of articular chondrocytes issued from pretreated New Zealand White rabbits (NZW). Juvenile (4- to 5-week-old) NZW were orally dosed with ofloxacin or pefloxacin (300 mg/kg of body weight for 1 day) or with pefloxacin (300 mg/kg for 7 days). Adult (5-month-old) NZW were treated with pefloxacin (300 mg/kg for 1 day). Chondrocytes were enzymatically recovered from cartilage and were analyzed by cytofluorometry using 2',7'-dichlorofluorescein diacetate (DCFH-DA) and dihydrorhodamine 123 (DHR), reflecting cellular respiratory-burst activity, and rhodamine 123 (Rh123) and 10-N-nonyl-acridine orange (NAO), specific for the mitochondrial activity and mass, respectively. A significant increase in the respiratory burst was detected by DCFH-DA and DHR in all treated groups of young animals, compared with untreated control groups. No significant increase of respiratory burst was noted in older treated rabbits. The 7-day treatment resulted in a decrease in mitochondrial uptake of Rh123 and an increase in NAO uptake. Fluoroquinolone arthrotoxicity seems to involve in its early phase the respiratory burst of immature articular chondrocytes.

Rhodamine 123 fluorescence of immortal hybridoma cell lines as a function of glucose concentration

The fluorescence of rhodamine 123 stained cells has been described to specifically reflect the activity of mitochondria. Changes in the intensity of fluorescence observed in stimulated lymphocytes were attributed to an increased glycolytic activity of cells due to increased growth rates. Previously reported changes in mitochondrial activity observed in batch cultures were likewise attributed to changed growth rates. In this study we report that the Rh123 fluorescence of hybridoma cell lines in batch culture more closely correlates to the glucose concentration in the culture supernatant than to growth rates. When cells are transferred into glutamine free medium with defined glucose concentrations ranging from 0 to 3,000 mg/L the mean Rh123 fluorescence adapts to the respective glucose concentration within 6 hours and gives a linear correlation. This can be explained by the previously described dependence of specific glucose consumption rates on glucose availability in the medium. The importance of controlling glucose availability, especially in large scale fermentations, is discussed.

Glutathione influences the proliferation as well as the extent of mitochondrial activation in rat splenocytes

The time-dependent changes of mitochondrial membrane potential and mass have been investigated on rat splenic lymphocytes stimulated with Con A in the presence and absence of reduced glutathione (GSH). Rhodamine-123 (Rh-123) and nonyl acridine orange (NAO) were used as specific dyes to monitor the membrane potential and mass of mitochondria, respectively. The percentage of cells showing blast transformation and the level of Rh-123 or NAO uptake were analyzed by flow cytometry. Present results demonstrate that a large number of cells showed activated mitochondria already at 24 hr after Con A stimulation and the activation of these organelles was not related to blast transformation. The addition of GSH into the culture medium increased the number of cells responding to mitogenic stimulation. In parallel it augmented the percentage of lymphocytes with activated mitochondria and also prevented their depolarization.

Cell cycle, cell size and mitochondrial activity of hybridoma cells during batch cultivation

Cell cycle, cell size and rhodamine 123 fluorescence in cell populations of two batch cultures were analysed and quantified with a fluorescence-activated cell sorter (FACS). Two cultures derived from either exponential or stationary phase innocula were investigated in order to demonstrate the dependency of the subsequent cell growth on innoculum condition. The results demonstrated that the level of activity of cells in the innoculum culture could have a significant effect on cellular activity during the initial phase of the inoculated culture, as it advances through its growth cycle. Positive correlation was found between the cell size and mitochondrial activity (as measured by rhodamine 123 uptake) with S and G2 fractions as the cell progressed through the cell cycle. The enumeration of the fractions of cell cycle phases has helped in prediction of the changes in cell numbers following perturbation of the culture condition.

Analysis of the membrane potential of rat- and mouse-liver mitochondria by flow cytometry and possible applications

Washed and purified rat- or mouse-liver mitochondria exhibiting high membrane integrity and metabolic activity were studied by flow cytometry. The electrophoretic accumulation/redistribution of cationic lipophilic probes, rhodamine 123, safranine O and a cyanine derivative, 3,3'-dihexyloxadicarbocyanine iodide, during the energization process was studied and was consistent with the generation of a negative internal membrane potential. An exception to this was nonylacridine orange which spontaneously bound to the mitochondrial membrane by hydrophobic interactions via its hydrocarbon chain. Energized purified mitochondria stained with potentiometric dyes exhibited both higher fluorescence and population homogeneity than the non-energized or deenergized (nigericin plus valinomycin) mitochondria. By contrast, under non-energized or deenergized conditions, the mitochondrial population exhibited fluorescence intensity heterogeneity related to the residual membrane potential; two subpopulations were evident, one of low fluorescence which may be related to the autofluorescence of the mitochondria (plus non-specific dye binding) and a second population which exhibited high fluorescence. Flow cytometry of the unpurified, simply washed, rat-liver mitochondria stained with rhodamine 123, a classically used dye, provided evidence of their heterogeneity in terms of light-scattering properties and membrane-potential-related fluorescence. One third of the washed mitochondria were found to be non-functional by such assays. The fluorescence of purified rat-liver mitochondria due to the membrane potential built up by endogenous substrates indicates heterogeneity of the mitochondrial population with respect to levels of endogenous substrates. The low-angle light scattering increases upon energization and provides some original information about the shape and modification of the inner mitochondrial conformation accompanying the energization. The heterogeneity of the rat liver mitochondrial population, from a structural, metabolic (existence of endogenous substrates) and functional (active and non-active mitochondrial population dispersion) point of view could thus be demonstrated by flow-cytometry analysis. Two animal models were examined with regard to the alteration of the mitochondrial membrane potential under the effects of drugs (rat-liver mitochondria), and the effects of ammonium toxicity (mouse-liver mitochondria). These results are promising and open new perspectives in the study of mitochondriopathies.

Evaluation of mitochondrial content and activity with nonyl-acridine orange and rhodamine 123: flow cytometric analysis and comparison with quantitative morphometry

Mouse fibroblasts 3T3.4E and two cells lines obtained by fusion (3T3.4E cells x normal human keratinocytes), (3T3 x NHK), and (3T3.4E cells x hand wart keratinocytes), (3T3 x HWK), were compared for mitochondrial activity and content between 5 and 20 days of culture, from the 16th to 20th passage, by using Rh 123 and NAO respectively. In 3T3.4E cells both Rh 123 and NAO fluorescence were similar after 5 and 7 days of culture, indicating no modification of mitochondrial activity and content at that time. However, in cells derived from fusion of 3T3 x NHK or 3T3 x HWK, Rh 123 increased from 5 to 20 days whereas NAO fluorescence was maximal at 7 days of culture and then decreased, indicating that their mitochondrial activity differed from that of 3T3.4E cells. No difference was observed between the 16th and 20th passage. Quantitative morphometry and flow cytometry gave good correlations at 7 days of culture for the cell size, estimated either by the cell area or the cell diameter, and for mitochondria content, evaluated either by the number of mitochondria per cell or NAO fluorescence intensity.

Use of nonyl acridine orange and rhodamine 123 to follow biosynthesis and functional assembly of mitochondrial membrane during L1210 cell cycle

Specific mitochondrial incorporation of 10 N-nonyl acridine orange (NAO) is demonstrated by subcellular fractionation of rat hepatocytes. Moreover, comparative studies with NAO and rhodamine 123 (Rh 123) prove that acridine orange-derivative uptake is independent of transmembrane mitochondrial potential, a property allowing its utilization for the assessment of mitochondrial membrane mass modifications under various physiological states. Using NAO and Rh 123, we have respectively followed the biosynthesis of mitochondrial membrane and its assembly under a functional state during the L1210 cell cycle. Their evolution occurs in two stages according to a well-defined sequential order. Mitochondrial biogenesis, as revealed by NAO incorporation, occurs essentially in the G1 phase (probably mitochondrion enlargement) but also starts in late S phase (probably mitochondrion division). The increased amount of functional mitochondrial membrane, monitored by Rh 123 uptake, is emphasized in late G1 (prerequisite to DNA synthesis) and during G2M phases (prerequisite to mitosis). This alternative succession of phases displays the existence of a time-lag between the biosynthesis of mitochondrial membrane and its functional organization. Such an analysis confirms the potential of the NAO probe to evaluate mitochondrial membrane mass changes in various biological fields.

Simultaneous analysis of mitochondrial activity and DNA content in Ehrlich ascites tumor cells by dual parameter flow cytometry

Ehrlich ascites tumor cells were permeabilized using low concentrations of digitonin, 8 micrograms/10(6) cells. Permeabilization was monitored by the assay of lactate dehydrogenase released into the incubation medium and of hexokinase partially bound to mitochondria. Integrity of the cellular organelles was unaffected as determined by assay of the mitochondrial enzyme glutamate dehydrogenase. Cells were stained with rhodamine 123 as a mitochondrial specific dye and propidium iodide/mithramycin as DNA specific dyes. The green fluorescence of bound rhodamine 123 versus red fluorescence of DNA in individual cells was analysed by dual parameter flow cytometry. Incubation of cells with inhibitors of mitochondrial energy metabolism, such as, potassium cyanide and carbonyl cyanide m-chlorophenylhydrazone abolished binding of rhodamine 123. Flow cytometric data allowed a correlation between cell position in the mitotic cycle with total mitochondrial activity. In addition, comparison of the characteristics of propidium iodide and ethidium bromide staining further elucidated the molecular basis of the staining with the positively-charged fluorescent dye rhodamine 123.

Human sperm mitochondrial function related to motility: a flow and image cytometric assessment

Current evaluation of male fertility, routinely estimated by sperm count, motility, and morphology, provides only crude information about the fertility state of individuals. Both flow and image cytometry were applied to mitochondrial activity and sperm motility respectively. Sperm samples from fertile donors were concomitantly measured for Rhodamine 123 (Rh123) uptake (an estimation of mitochondrial activity), percentage of dead cells, and motility characteristics, such as percentage of motility, curvilinear velocity, and amplitude of lateral head displacement. These measurements were done under experimental conditions known to modulate sperm motility (temperature and time course survival in a capacitating medium). Bimodal distributions were found for Rh123 uptake. Flow cytometry-derived parameters were essentially time-dependent whereas motility characteristics were primarily temperature-dependent. Correlations were found between various flow cytometry-derived parameters and motility characteristics. Most of the correlations were obtained after a 24 h incubation in a capacitating medium. The most significant correlation in every experimental condition concerned the percentage of motile spermatozoa and the Rh123 uptakes. The drop in motility observed after a 24 h incubation was paralleled by a markedly lower drop in mitochondrial activity. The data suggest that these two complementary techniques represent an improvement in basic and/or clinical assessment of the functional spermatozoa status.

Dynamic aspects of rhodamine dye photosensitization in vitro with an argon-ion laser

Phototoxicity in cultured human bladder carcinoma cells treated by 514.5-nm argon-ion laser irradiation plus rhodamine-123 (R123) or tetrabromo-R123 (TBR) was assessed counting total cell number and percent viability at 1, 24, 48, 72, and 96 h after irradiation. TBR was markedly more efficient than R123 at causing both reversible and persistent phototoxic cytostasis. Furthermore, TBR photosensitization caused net cytocidal effects at 0.5 J/cm2, which were not seen with R123 photosensitization at up to 40 J/cm2. The reduced phototoxic efficiency of R123 as compared to TBR appears, in part, to reflect the presence of a fraction of cells refractory to R123 photosensitization.

In situ flow cytometric analysis of nonyl acridine orange-stained mitochondria from splenocytes

Due to its spectral characteristics, the fluorochrome nonyl acridine orange (NAO) (lambda abs:489 nm, lambda em:525 nm), which is spontaneously incorporated by mitochondria with a high relative specificity, provides a new probe for the in situ study of these organelles by flow cytometry. In 15 min at 20 degrees C, the dye at 4.75 X 10(-6) M saturates the mitochondrial binding sites present in 1.5 X 10(6) cells. Unlike Rh 123, the fixation of the probe is not affected by the action of uncouplers and ionophores. Unlike acridine orange, its binding is not sensitive to nucleases. By studying the mitochondrial incorporation of the fluorochrome during the cell cycle of murine splenocytes, it was possible to show that the biogenesis of NAO-stained mitochondrial constituents mainly occurs during the G1 phase.

Rabbit articular chondrocytes: an in vitro model for studying the effect of sodium aurothiopropanol sulfonate on proliferation kinetics, type II collagen phenotype and mitochondrial activity

Despite the benefits of chrysotherapy the responsible mechanism of action of gold compounds remains unclear. At a concentration of 5 x 10(-4) M, sodium aurothiopropanol sulfonate (SAS) modified the in vitro proliferation kinetics of articular chondrocytes by reducing growth, viability and plating efficiency. Flow cytometry analysis, using propidium iodide DNA staining, revealed slight but significant cell arrest in G2+M which, in fact, represents an increase in the proportion of binucleate cells. SAS did not induce any variations in chondrocyte phenotype stability as far as the biosynthesis of type II collagen was concerned, and no appreciable changes in overall mitochondrial activity reflected by rhodamine 123 incorporation.

Rhodamine 123 uptake and mitochondrial DNA content in rabbit articular chondrocytes evolve differently upon transfer from cartilage to culture conditions

Mitochondrial DNA (mtDNA) represents 0.15% of the total cell DNA (at least an order of magnitude less than in liver or heart) of rabbit articular chondrocytes. Besides the already well-documented low respiratory activity, chondrocyte differentiation thus involves a specific control of mitochondrial biogenesis. When transferred to in vitro conditions, chondrocytes increase their stock of mtDNA at the same time they resume growth, even more efficiently (8 times) than they do for cell volume (4.4 times). On the contrary, overall mitochondrial activity, estimated as the uptake of rhodamine 123, does not follow the same trend (2.5 times increase). Chondrocytes apparently keep these functional characteristics for some generations in culture.