Quantifying mitochondrial and plasma membrane potentials in intact pulmonary arterial endothelial cells based on extracellular disposition of rhodamine dyes

Mitochondrial Diabetes Is Associated with the ND4 G11696A Mutation

Type 2 diabetes mellitus (T2DM) is a common endocrine disorder which remains a large challenge for clinicians. Previous studies have suggested that mitochondrial dysfunction plays an active role in T2DM progression, but a detailed mechanism is still elusive. In the current study, two Han Chinese families with maternally inherited T2DM were evaluated using clinical, genetic, molecular, and biochemical analyses. The mitochondrial genomes were PCR amplified and sequenced. Phylogenetic and bioinformatic analyses were used to assess the potential pathogenicity of mitochondrial DNA (mtDNA) mutations. Interestingly, the matrilineal relatives of these pedigrees exhibited variable severity of T2DM, in particular, the age at onset of T2DM varied from 26 to 65 years, with an average of 49 years. Sequence analysis revealed the presence of ND4 G11696A mutation, which resulted in the substitution of an isoleucine for valine at amino acid (AA) position 312. Indeed, this mutation was present in homoplasmy only in the maternal lineage, not in other members of these families, as well as 200 controls. Furthermore, the m.C5601T in the tRNA^Ala and novel m.T5813C in the tRNA^Cys, showing high evolutional conservation, may contribute to the phenotypic expression of ND4 G11696A mutation. In addition, biochemical analysis revealed that cells with ND4 G11696A mutation exhibited higher levels of reactive oxygen species (ROS) productions than the controls. In contrast, the levels of mitochondrial membrane potential (MMP), ATP, mtDNA copy number (mtDNA-CN), Complex I activity, and NAD⁺/NADH ratio significantly decreased in cell lines carrying the m.G11696A and tRNA mutations, suggesting that these mutations affected the respiratory chain function and led to mitochondrial dysfunction that was involved in T2DM. Thus, our study broadened the clinical phenotypes of m.G11696A mutation.

In vivo molecular imaging stratifies rats with different susceptibilities to hyperoxic acute lung injury

99mTc-hexamethylpropyleneamine oxime (HMPAO) and 99mTc-duramycin in vivo imaging detects pulmonary oxidative stress and cell death, respectively, in rats exposed to >95% O2 (hyperoxia) as a model of acute respiratory distress syndrome (ARDS). Preexposure to hyperoxia for 48 h followed by 24 h in room air (H-T) is protective against hyperoxia-induced lung injury. This study's objective was to determine the ability of 99mTc-HMPAO and 99mTc-duramycin to track this protection and to elucidate underlying mechanisms. Rats were exposed to normoxia, hyperoxia for 60 h, H-T, or H-T followed by 60 h of hyperoxia (H-T + 60). Imaging was performed 20 min after intravenous injection of either 99mTc-HMPAO or 99mTc-duramycin. 99mTc-HMPAO and 99mTc-duramycin lung uptake was 200% and 167% greater (P < 0.01) in hyperoxia compared with normoxia rats, respectively. On the other hand, uptake of 99mTc-HMPAO in H-T + 60 was 24% greater (P < 0.01) than in H-T rats, but 99mTc-duramycin uptake was not significantly different (P = 0.09). Lung wet-to-dry weight ratio, pleural effusion, endothelial filtration coefficient, and histological indices all showed evidence of protection and paralleled imaging results. Additional results indicate higher mitochondrial complex IV activity in H-T versus normoxia rats, suggesting that mitochondria of H-T lungs may be more tolerant of oxidative stress. A pattern of increasing lung uptake of 99mTc-HMPAO and 99mTc-duramycin correlates with advancing oxidative stress and cell death and worsening injury, whereas stable or decreasing 99mTc-HMPAO and stable 99mTc-duramycin reflects hyperoxia tolerance, suggesting the potential utility of molecular imaging for identifying at-risk hosts that are more or less susceptible to progressing to ARDS.

Depolarized mitochondrial membrane potential and protection with duroquinone in isolated perfused lungs from rats exposed to hyperoxia

Dissipation of mitochondrial membrane potential (Δψ_m) is a hallmark of mitochondrial dysfunction. Our objective was to use a previously developed experimental-computational approach to estimate tissue Δψ_m in intact lungs of rats exposed to hyperoxia and to evaluate the ability of duroquinone (DQ) to reverse any hyperoxia-induced depolarization of lung Δψ_m. Rats were exposed to hyperoxia (>95% O₂) or normoxia (room air) for 48 h, after which lungs were excised and connected to a ventilation-perfusion system. The experimental protocol consisted of measuring the concentration of the fluorescent dye rhodamine 6 G (R6G) during three single-pass phases: loading, washing, and uncoupling, in which the lungs were perfused with and without R6G and with the mitochondrial uncoupler FCCP, respectively. For normoxic lungs, the protocol was repeated with 1) rotenone (complex I inhibitor), 2) rotenone and either DQ or its vehicle (DMSO), and 3) rotenone, glutathione (GSH), and either DQ or DMSO added to the perfusate. Hyperoxic lungs were studied with and without DQ and GSH added to the perfusate. Computational modeling was used to estimate lung Δψ_m from R6G data. Rat exposure to hyperoxia resulted in partial depolarization (-33 mV) of lung Δψ_m and complex I inhibition depolarized lung Δψ_m by -83 mV. Results also demonstrate the efficacy of DQ to fully reverse both rotenone- and hyperoxia-induced lung Δψ_m depolarization. This study demonstrates hyperoxia-induced Δψ_m depolarization in intact lungs and the utility of this approach for assessing the impact of potential therapies such as exogenous quinones that target mitochondria in intact lungs.NEW & NOTEWORTHY This study is the first to measure hyperoxia-induced Δψ_m depolarization in isolated perfused lungs. Hyperoxia resulted in a partial depolarization of Δψ_m, which was fully reversed with duroquinone, demonstrating the utility of this approach for assessing the impact of potential therapies that target mitochondria such as exogenous quinones.

Quantitative analysis of mitochondrial membrane potential heterogeneity in unsynchronized and synchronized cancer cells

Mitochondrial membrane potential (ΔΨm) is a global indicator of mitochondrial function. Previous reports on heterogeneity of ΔΨm were qualitative or semiquantitative. Here, we quantified intercellular differences in ΔΨm in unsynchronized human cancer cells, cells synchronized in G1, S, and G2, and human fibroblasts. We assessed ΔΨm using a two-pronged microscopy approach to measure relative fluorescence of tetramethylrhodamine methyl ester (TMRM) and absolute values of ΔΨm. We showed that ΔΨm is more heterogeneous in cancer cells compared to fibroblasts, and it is maintained throughout the cell cycle. The effect of chemical inhibition of the respiratory chain and ATP synthesis differed between basal, low and high ΔΨm cells. Overall, our results showed that intercellular heterogeneity of ΔΨm is mainly modulated by intramitochondrial factors, it is independent of the ΔΨm indicator and it is not correlated with intercellular heterogeneity of plasma membrane potential or the phases of the cell cycle.

Quantification of mitochondrial membrane potential in the isolated rat lung using rhodamine 6G

Mitochondrial membrane potential (Δψ_m) plays a key role in vital mitochondrial functions, and its dissipation is a hallmark of mitochondrial dysfunction. The objective of this study was to develop an experimental and computational approach for estimating Δψ_m in intact rat lungs using the lipophilic fluorescent cationic dye rhodamine 6G (R6G). Rat lungs were excised and connected to a ventilation-perfusion system. The experimental protocol consisted of three single-pass phases, loading, washing, and uncoupling, in which the lungs were perfused with R6G-containing perfusate, fresh R6G-free perfusate, or R6G-free perfusate containing the mitochondrial uncoupler FCCP, respectively. This protocol was carried out with lung perfusate containing verapamil vehicle or verapamil, an inhibitor of the multidrug efflux pump P-glycoprotein (Pgp). Results show that the addition of FCCP resulted in an increase in R6G venous effluent concentration and that this increase was larger in the presence of verapamil than in its absence. A physiologically based pharmacokinetic (PBPK) model for the pulmonary disposition of R6G was developed and used for quantitative interpretation of the kinetic data, including estimating Δψ_m. The estimated value of Δψ_m [-144 ± 24 (SD) mV] was not significantly altered by inhibiting Pgp with verapamil and is comparable with that estimated previously in cultured pulmonary endothelial cells. These results demonstrate the utility of the proposed approach for quantifying Δψ_m in intact functioning lungs. This approach has potential to provide quantitative assessment of the effect of injurious conditions on lung mitochondrial function and to evaluate the impact of therapies that target mitochondria.NEW & NOTEWORTHY A novel experimental and computational approach for estimating mitochondrial membrane potential (Δψ_m) in intact functioning lungs is presented. The isolated rat lung inlet-outlet concentrations of the fluorescent cationic dye rhodamine 6G were measured and analyzed by using a computational model of its pulmonary disposition to determine Δψ_m. The approach has the potential to provide quantitative assessment of the effect of injurious conditions and their therapies on lung mitochondrial function.

Characterization of Kcnk3-Mutated Rat, a Novel Model of Pulmonary Hypertension

RATIONALE

Pulmonary arterial hypertension is a severe lethal cardiopulmonary disease. Loss of function mutations in KCNK3 (potassium channel subfamily K member 3) gene, which encodes an outward rectifier K⁺ channel, have been identified in pulmonary arterial hypertension patients.

OBJECTIVE

We have demonstrated that KCNK3 dysfunction is common to heritable and nonheritable pulmonary arterial hypertension and to experimental pulmonary hypertension (PH). Finally, KCNK3 is not functional in mouse pulmonary vasculature.

METHODS AND RESULTS

Using CRISPR/Cas9 technology, we generated a 94 bp out of frame deletion in exon 1 of Kcnk3 gene and characterized these rats at the electrophysiological, echocardiographic, hemodynamic, morphological, cellular, and molecular levels to decipher the cellular mechanisms associated with loss of KCNK3. Using patch-clamp technique, we validated our transgenic strategy by demonstrating the absence of KCNK3 current in freshly isolated pulmonary arterial smooth muscle cells from Kcnk3-mutated rats. At 4 months of age, echocardiographic parameters revealed shortening of the pulmonary artery acceleration time associated with elevation of the right ventricular systolic pressure. Kcnk3-mutated rats developed more severe PH than wild-type rats after monocrotaline exposure or chronic hypoxia exposure. Kcnk3-mutation induced a lung distal neomuscularization and perivascular extracellular matrix activation. Lungs of Kcnk3-mutated rats were characterized by overactivation of ERK1/2 (extracellular signal-regulated kinase1-/2), AKT (protein kinase B), SRC, and overexpression of HIF1-α (hypoxia-inducible factor-1 α), survivin, and VWF (Von Willebrand factor). Linked with plasma membrane depolarization, reduced endothelial-NOS expression and desensitization of endothelial-derived hyperpolarizing factor, Kcnk3-mutated rats presented predisposition to vasoconstriction of pulmonary arteries and a severe loss of sildenafil-induced pulmonary arteries relaxation. Moreover, we showed strong alteration of right ventricular cardiomyocyte excitability. Finally, Kcnk3-mutated rats developed age-dependent PH associated with low serum-albumin concentration.

CONCLUSIONS

We established the first Kcnk3-mutated rat model of PH. Our results confirm that KCNK3 loss of function is a key event in pulmonary arterial hypertension pathogenesis. This model presents new opportunities for understanding the initiating mechanisms of PH and testing biologically relevant therapeutic molecules in the context of PH.

Integrated Computational Model of Lung Tissue Bioenergetics

Altered lung tissue bioenergetics plays a key role in the pathogenesis of lung diseases. A wealth of information exists regarding the bioenergetic processes in mitochondria isolated from rat lungs, cultured pulmonary endothelial cells, and intact rat lungs under physiological and pathophysiological conditions. However, the interdependence of those processes makes it difficult to quantify the impact of a change in a single or multiple process(es) on overall lung tissue bioenergetics. Integrated computational modeling provides a mechanistic and quantitative framework for the bioenergetic data at different levels of biological organization. The objective of this study was to develop and validate an integrated computational model of lung bioenergetics using existing experimental data from isolated perfused rat lungs. The model expands our recently developed computational model of the bioenergetics of mitochondria isolated from rat lungs by accounting for glucose uptake and phosphorylation, glycolysis, and the pentose phosphate pathway. For the mitochondrial region of the model, values of kinetic parameters were fixed at those estimated in our recent model of the bioenergetics of mitochondria isolated from rat lungs. For the cytosolic region of the model, intrinsic parameters such as apparent Michaelis constants were determined based on previously published enzyme kinetics data, whereas extrinsic parameters such as maximal reaction and transport velocities were estimated by fitting the model solution to published data from isolated rat lungs. The model was then validated by assessing its ability to predict existing experimental data not used for parameter estimation, including relationships between lung nucleotides content, lung lactate production rate, and lung energy charge under different experimental conditions. In addition, the model was used to gain novel insights on how lung tissue glycolytic rate is regulated by exogenous substrates such as glucose and lactate, and assess differences in the bioenergetics of mitochondria isolated from lung tissue and those of mitochondria in intact lungs. To the best of our knowledge, this is the first model of lung tissue bioenergetics. The model provides a mechanistic and quantitative framework for integrating available lung tissue bioenergetics data, and for testing novel hypotheses regarding the role of different cytosolic and mitochondrial processes in lung tissue bioenergetics.

Integrated computational model of the bioenergetics of isolated lung mitochondria

Integrated computational modeling provides a mechanistic and quantitative framework for describing lung mitochondrial bioenergetics. Thus, the objective of this study was to develop and validate a thermodynamically-constrained integrated computational model of the bioenergetics of isolated lung mitochondria. The model incorporates the major biochemical reactions and transport processes in lung mitochondria. A general framework was developed to model those biochemical reactions and transport processes. Intrinsic model parameters such as binding constants were estimated using previously published isolated enzymes and transporters kinetic data. Extrinsic model parameters such as maximal reaction and transport velocities were estimated by fitting the integrated bioenergetics model to published and new tricarboxylic acid cycle and respirometry data measured in isolated rat lung mitochondria. The integrated model was then validated by assessing its ability to predict experimental data not used for the estimation of the extrinsic model parameters. For example, the model was able to predict reasonably well the substrate and temperature dependency of mitochondrial oxygen consumption, kinetics of NADH redox status, and the kinetics of mitochondrial accumulation of the cationic dye rhodamine 123, driven by mitochondrial membrane potential, under different respiratory states. The latter required the coupling of the integrated bioenergetics model to a pharmacokinetic model for the mitochondrial uptake of rhodamine 123 from buffer. The integrated bioenergetics model provides a mechanistic and quantitative framework for 1) integrating experimental data from isolated lung mitochondria under diverse experimental conditions, and 2) assessing the impact of a change in one or more mitochondrial processes on overall lung mitochondrial bioenergetics. In addition, the model provides important insights into the bioenergetics and respiration of lung mitochondria and how they differ from those of mitochondria from other organs. To the best of our knowledge, this model is the first for the bioenergetics of isolated lung mitochondria.

Protection by Inhaled Hydrogen Therapy in a Rat Model of Acute Lung Injury can be Tracked in vivo Using Molecular Imaging

Inhaled hydrogen gas (H2) provides protection in rat models of human acute lung injury (ALI). We previously reported that biomarker imaging can detect oxidative stress and endothelial cell death in vivo in a rat model of ALI. Our objective was to evaluate the ability of Tc-hexamethylpropyleneamineoxime (HMPAO) and Tc-duramycin to track the effectiveness of H2 therapy in vivo in the hyperoxia rat model of ALI. Rats were exposed to room air (normoxia), 98% O2 + 2% N2 (hyperoxia) or 98% O2 + 2% H2 (hyperoxia+H2) for up to 60 h. In vivo scintigraphy images were acquired following injection of Tc-HMPAO or Tc-duramycin. For hyperoxia rats, Tc-HMPAO and Tc-duramycin lung uptake increased in a time-dependent manner, reaching a maximum increase of 270% and 150% at 60 h, respectively. These increases were reduced to 120% and 70%, respectively, in hyperoxia+H2 rats. Hyperoxia exposure increased glutathione content in lung homogenate (36%) more than hyperoxia+H2 (21%), consistent with increases measured in Tc-HMPAO lung uptake. In 60-h hyperoxia rats, pleural effusion, which was undetectable in normoxia rats, averaged 9.3 gram/rat, and lung tissue 3-nitrotyrosine expression increased by 790%. Increases were reduced by 69% and 59%, respectively, in 60-h hyperoxia+H2 rats. This study detects and tracks the anti-oxidant and anti-apoptotic properties of H2 therapy in vivo after as early as 24 h of hyperoxia exposure. The results suggest the potential utility of these SPECT biomarkers for in vivo assessment of key cellular pathways in the pathogenesis of ALI and for monitoring responses to therapies.

T-type voltage gated calcium channels are involved in endothelium-dependent relaxation of mice pulmonary artery

In pulmonary arterial endothelial cells, Ca²⁺ channels and intracellular Ca²⁺ concentration ([Ca²⁺]_i) control the release of vasorelaxant factors such as nitric oxide and are involved in the regulation of pulmonary arterial blood pressure. The present study was undertaken to investigate the implication of T-type voltage-gated Ca²⁺ channels (T-VGCCs, Ca_v3.1 channel) in the endothelium-dependent relaxation of intrapulmonary arteries. Relaxation was quantified by means of a myograph in wild type and Ca_v3.1^-/- mice. Endothelial [Ca²⁺]_i and NO production were measured, on whole vessels, with the fluo-4 and DAF-fm probes. Acetylcholine (ACh) induced a nitric oxide- and endothelium-dependent relaxation that was significantly reduced in pulmonary arteries from Ca_v3.1^-/- compared to wild type mice as well as in the presence of T-VGCC inhibitors (NNC 55-0396 or mibefradil). ACh also increased endothelial [Ca²⁺]_i and NO production that were both reduced in Ca_v3.1^-/- compared to wild type mice or in the presence of T-VGCC inhibitors. Immunofluorescence labeling revealed the presence of Ca_v3.1 channels in endothelial cells that co-localized with endothelial nitric oxide synthase in arteries from wild type mice. TRPV4-, beta2 adrenergic- and nitric oxide donors (SNP)-mediated relaxation were not altered in Ca_v3.1^-/- compared to wild type mice. Finally, in chronically hypoxic mice, a model of pulmonary hypertension, ACh relaxation was reduced but still depended on Ca_v3.1 channels activity. The present study thus demonstrates that T-VGCCs, mainly Ca_v3.1 channel, contribute to intrapulmonary vascular reactivity in mice by controlling endothelial [Ca²⁺]_i and ACh-mediated relaxation.

Carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) pre-exposure ensures follicle integrity during in vitro culture of ovarian tissue but not during cryopreservation in the domestic cat model

PURPOSE

Temporary and reversible downregulation of metabolism may improve the survival of tissues exposed to non-physiological conditions during transport, in vitro culture, and cryopreservation. The objectives of the study were to (1) optimize the concentration and duration of carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP-a mitochondrial uncoupling agent) exposures for biopsies of domestic cat ovarian tissue and (2) examine the effects of FCCP pre-exposures on follicle integrity after tissue culture and/or cryopreservation.

METHODS

Biopsies of cat ovarian tissue were first treated with various concentrations of FCCP (0, 10, 40, or 200 nM) for 10 or 120 min to determine the most suitable pre-exposure conditions. Based on these results, tissues were pre-exposed to 200 nM FCCP for 120 min for the subsequent studies on culture and cryopreservation. In all experiments and for each treatment group, tissue activity and integrity were measured by mitochondrial membrane potential (relative optical density of rhodamine 123 fluorescence), follicular viability (calcein assay), follicular morphology (histology), granulosa cell proliferation (Ki-67 immunostaining), and follicular density.

RESULTS

Ovarian tissues incubated with 200 nM FCCP for 120 min led to the lowest mitochondrial activity (1.17 ± 0.09; P < 0.05) compared to control group (0 nM; 1.30 ± 0.12) while maintaining a constant percentage of viable follicles (75.3 ± 7.8 %) similar to the control group (71.8 ± 11.7 %; P > 0.05). After 2 days of in vitro culture, percentage of viable follicles (78.8 ± 8.9 %) in similar pre-exposure conditions was higher (P < 0.05) than in the absence of FCCP (61.2 ± 12.0 %) with percentages of morphologically normal follicles (57.6 ± 17.3 %) not different from the fresh tissue (70.2 ± 7.1 %; P > 0.05). Interestingly, percentages of cellular proliferation and follicular density were unaltered by the FCCP exposures. Based on the indicators mentioned above, the FCCP-treated tissue fragments did not have a better follicle integrity after freezing and thawing.

CONCLUSIONS

Pre-exposure to 200 nM FCCP during 120 min protects and enhances the follicle integrity in cat ovarian tissue during short-term in vitro culture. However, FCCP does not appear to exert a beneficial or detrimental effect during ovarian tissue cryopreservation.

Optical Cryoimaging Reveals a Heterogeneous Distribution of Mitochondrial Redox State in ex vivo Guinea Pig Hearts and Its Alteration During Ischemia and Reperfusion

Oxidation of substrates to generate ATP in mitochondria is mediated by redox reactions of NADH and FADH2. Cardiac ischemia and reperfusion (IR) injury compromises mitochondrial oxidative phosphorylation. We hypothesize that IR alters the metabolic heterogeneity of mitochondrial redox state of the heart that is only evident in the 3-D optical cryoimaging of the perfused heart before, during, and after IR. The study involved four groups of hearts: time control (TC: heart perfusion without IR), global ischemia (Isch), global ischemia followed by reperfusion (IR) and TC with PCP (a mitochondrial uncoupler) perfusion. Mitochondrial NADH and FAD autofluorescence signals were recorded spectrofluorometrically online in guinea pig ex vivo-perfused hearts in the Langendorff mode. At the end of each specified protocol, hearts were rapidly removed and snap frozen in liquid N2 for later 3-D optical cryoimaging of the mitochondrial NADH, FAD, and NADH/FAD redox ratio (RR). The TC hearts revealed a heterogeneous spatial distribution of NADH, FAD, and RR. Ischemia and IR altered the spatial distribution and caused an overall increase and decrease in the RR by 55% and 64%, respectively. Uncoupling with PCP resulted in the lowest level of the RR (73% oxidation) compared with TC. The 3-D optical cryoimaging of the heart provides novel insights into the heterogeneous distribution of mitochondrial NADH, FAD, RR, and metabolism from the base to the apex during ischemia and IR. This 3-D information of the mitochondrial redox state in the normal and ischemic heart was not apparent in the dynamic spectrofluorometric data.

Inhibition of Mitochondrial Voltage-Dependent Anion Channels Increases Radiosensitivity of K562 Leukemic Cells

We studied the effect of inhibition of mitochondrial voltage-dependent anion channels with DIDS on radiosensitivity and mitochondrial status of K562 leukemic cells. The number of apoptotic and necrotic cells, mitochondrial transmembrane potential, and mitochondrial mass were evaluated after irradiation of cells in doses of 4 and 12 Gy in the presence and absence of the inhibitor. Inhibition of mitochondrial voltage-dependent anion channels increased radiosensitivity of K562 cells by 50-70% and decreased both mitochondrial transmembrane potential and mitochondrial mass. Inhibitors of voltage-dependent anion channels are promising agents capable of improving the effectiveness of cancer radiotherapy.

Mitochondrial dependent oxidative stress in cell culture induced by laser radiation at 1265 nm

Photodynamic therapy is the main technique applied for surface carcinoma treatment. This technique employs singlet oxygen generated via a laser excited photosensitizer as a main damaging agent. However, prolonged sensitivity to intensive light, relatively low tissue penetration by activating light the cost of photosensitizer (PS) administration can limit photodynamic therapy applications. Early was reported singlet oxygen generation without photosensitizer induced by a laser irradiation at the wavelength of 1250-1270 nm. Here, we study the dynamics of oxidative stress, DNA damage, changes of mitochondrial potential, and mitochondrial mass induced by a laser at 1265 nm have been studied in HCT-116 and CHO-K cells. Laser irradiation of HCT-116 and CHO-K cells has induced a dose-dependent cell death via increasing intracellular reactive oxygen species (ROS) concentration, increase of DNA damage, decrease of mitochondrial potential, and reduced glutathione. It has been shown that, along with singlet oxygen generation, the increase of the intracellular ROS concentration induced by mitochondrial damage contributes to the damaging effect of the laser irradiation at 1265 nm.

The effects of mitochondrial complex I blockade on ATP and permeability in rat pulmonary microvascular endothelial cells in culture (PMVEC) are overcome by coenzyme Q1 (CoQ1)

In isolated rat lung perfused with a physiological saline solution (5.5mM glucose), complex I inhibitors decrease lung tissue ATP and increase endothelial permeability (Kf), effects that are overcome using an amphipathic quinone (CoQ1) [Free Radic. Biol. Med.65:1455-1463; 2013]. To address the microvascular endothelial contribution to these intact lung responses, rat pulmonary microvascular endothelial cells in culture (PMVEC) were treated with the complex I inhibitor rotenone and ATP levels and cell monolayer permeability (PS) were measured. There were no detectable effects on ATP or permeability in experimental medium that, like the lung perfusate, contained 5.5mM glucose. To unmask a potential mitochondrial contribution, the glucose concentration was lowered to 0.2mM. Under these conditions, rotenone decreased ATP from 18.4±1.6 (mean±SEM) to 4.6±0.8nmol/mg protein, depolarized the mitochondrial membrane potential (Δψm) from -129.0±3.7 (mean±SEM) to -92.8±5.5mV, and decreased O2 consumption from 2.0±0.1 (mean±SEM) to 0.3±0.1nmol/min/mg protein. Rotenone also increased PMVEC monolayer permeability (reported as PS in nl/min) to FITC-dextran (~40kDa) continually over a 6 h time course. When CoQ1 was present with rotenone, normal ATP (17.4±1.4nmol/mg protein), O2 consumption (1.5±0.1nmol/min/mg protein), Δψm (-125.2±3.3mV), and permeability (PS) were maintained. Protective effects of CoQ1 on rotenone-induced changes in ATP, O2 consumption rate, Δψm, and permeability were blocked by dicumarol or antimycin A, inhibitors of the quinone-mediated cytosol-mitochondria electron shuttle [Free Radic. Biol. Med.65:1455-1463; 2013]. Key rotenone effects without and with CoQ1 were qualitatively reproduced using the alternative complex I inhibitor, piericidin A. We conclude that, as in the intact lung, PMVEC ATP supply is linked to the permeability response to complex I inhibitors. In contrast to the intact lung, the association in PMVEC was revealed only after decreasing the glucose concentration in the experimental medium from 5.5 to 0.2mM.

Novel Flurometric Tool to Assess Mitochondrial Redox State of Isolated Perfused Rat Lungs after Exposure to Hyperoxia

Recently we demonstrated the utility of optical fluorometry to detect a change in the redox status of mitochondrial autofluorescent coenzymes NADH (Nicotinamide Adenine Dinucleotide) and FAD (oxidized form of Flavin Adenine Dinucleotide (FADH2,)) as a measure of mitochondrial function in isolated perfused rat lungs (IPL). The objective of this study was to utilize optical fluorometry to evaluate the effect of rat exposure to hyperoxia (>95% O2 for 48 hours) on lung tissue mitochondrial redox status of NADH and FAD in a nondestructive manner in IPL. Surface NADH and FAD signals were measured before and after lung perfusion with perfusate containing rotenone (ROT, complex I inhibitor), potassium cyanide (KCN, complex IV inhibitor), and/or pentachlorophenol (PCP, uncoupler). ROT- or KCN-induced increase in NADH signal is considered a measure of complex I activity, and KCN-induced decrease in FAD signal is considered a measure of complex II activity. The results show that hyperoxia decreased complex I and II activities by 63% and 55%, respectively, as compared to lungs of rats exposed to room air (normoxic rats). Mitochondrial complex I and II activities in lung homogenates were also lower (77% and 63%, respectively) for hyperoxic than for normoxic lungs. These results suggest that the mitochondrial matrix is more reduced in hyperoxic lungs than in normoxic lungs, and demonstrate the ability of optical fluorometry to detect a change in mitochondrial redox state of hyperoxic lungs prior to histological changes characteristic of hyperoxia.

The role of mitochondria in the development of radiation-induced oxidative stress in K562 leukemia cells

Radiation-induced accumulation of active oxygen species and the role of the mitochondria in this process were studied on cultured K562 leukemia cells. Intracellular concentrations of active oxygen species in the presence of rotenone and without it and the mitochondrial potential were analyzed 15, 30 min, 1, 4, 8, 12, 24, and 48 h after X-ray exposure in doses of 4 and 12 Gy. Radiation-induced generation of active oxygen species had two time peaks: 30 min and 24 h after the exposure. Addition of rotenone reduced the levels of active oxygen species 24 and 48 h after the exposure. Increase of active oxygen species concentrations was paralleled by an increase of the mitochondrial potential. The mitochondria were responsible for the increase in the concentrations of active oxygen species 12-48 h after irradiation.

Imaging of reactive oxygen species burst from mitochondria using laser scanning confocal microscopy

OBJECTIVE

Although several methods have been used to detect the intracellular reactive oxygen species (ROS) generation, it is still difficult to determine where ROS generate from. This study aimed to demonstrate whether ROS generate from mitochondria during oxidative stress induced mitochondria damage in cardiac H9c2 cells by laser scanning confocal microscopy (LSCM).

METHODS

Cardiac H9c2 cells were exposed to H2 O2 (1200μM) to induce mitochondrial oxidant damage. Mitochondrial membrane potential (ΔΨm) was measured by staining cells with tetramethylrhodamine ethyl ester (TMRE); ROS generation was measured by staining cells with dichlorodihydrofluorescein diacetate (H2 DCFDA).

RESULTS

A rapid/transient ROS burst from mitochondria was induced in cardiac cells treated with H2 O2 compared with the control group, suggesting that mitochondria are the main source of ROS induced by oxidative stress in H9c2 cells. Meanwhile, the TMRE fluorescence intensity of mitochondria which had produced a great deal of ROS decreased significantly, indicating that the burst of ROS induces the loss of ΔΨm. In addition, the structure of mitochondria was damaged seriously after ROS burst. However, we also demonstrated that the TMRE fluorescence intensity might be affected by H2 DCFDA.

CONCLUSIONS

Mitochondria are the main source of ROS induced by oxidative stress in H9c2 cells and these findings provide a new method to observe whether ROS generate from mitochondria by LSCM. However, these observations also suggested that it is inaccurate to test the fluorescence intensities of cells stained with two or more different fluorescent dyes which should be paid more attention to.

Surface fluorescence studies of tissue mitochondrial redox state in isolated perfused rat lungs

We designed a fiber-optic-based optoelectronic fluorometer to measure emitted fluorescence from the auto-fluorescent electron carriers NADH and FAD of the mitochondrial electron transport chain (ETC). The ratio of NADH to FAD is called the redox ratio (RR = NADH/FAD) and is an indicator of the oxidoreductive state of tissue. We evaluated the fluorometer by measuring the fluorescence intensities of NADH and FAD at the surface of isolated, perfused rat lungs. Alterations of lung mitochondrial metabolic state were achieved by the addition of rotenone (complex I inhibitor), potassium cyanide (KCN, complex IV inhibitor) and/or pentachlorophenol (PCP, uncoupler) into the perfusate recirculating through the lung. Rotenone- or KCN-containing perfusate increased RR by 21 and 30%, respectively. In contrast, PCP-containing perfusate decreased RR by 27%. These changes are consistent with the established effects of rotenone, KCN, and PCP on the redox status of the ETC. Addition of blood to perfusate quenched NADH and FAD signal, but had no effect on RR. This study demonstrates the capacity of fluorometry to detect a change in mitochondrial redox state in isolated perfused lungs, and suggests the potential of fluorometry for use in in vivo experiments to extract a sensitive measure of lung tissue health in real-time.

Coenzyme Q(1) as a probe for mitochondrial complex I activity in the intact perfused hyperoxia-exposed wild-type and Nqo1-null mouse lung

Previous studies showed that coenzyme Q(1) (CoQ(1)) reduction on passage through the rat pulmonary circulation was catalyzed by NAD(P)H:quinone oxidoreductase 1 (NQO1) and mitochondrial complex I, but that NQO1 genotype was not a factor in CoQ(1) reduction on passage through the mouse lung. The aim of the present study was to evaluate the complex I contribution to CoQ(1) reduction in the isolated perfused wild-type (NQO1(+/+)) and Nqo1-null (NQO1(-)/(-)) mouse lung. CoQ(1) reduction was measured as the steady-state pulmonary venous CoQ(1) hydroquinone (CoQ(1)H(2)) efflux rate during infusion of CoQ(1) into the pulmonary arterial inflow. CoQ(1)H(2) efflux rates during infusion of 50 μM CoQ(1) were not significantly different for NQO1(+/+) and NQO1(-/-) lungs (0.80 ± 0.03 and 0.68 ± 0.07 μmol·min(-1)·g lung dry wt(-1), respectively, P > 0.05). The mitochondrial complex I inhibitor rotenone depressed CoQ(1)H(2) efflux rates for both genotypes (0.19 ± 0.08 and 0.08 ± 0.04 μmol·min(-1)·g lung dry wt(-1) for NQO1(+/+) and NQO1(-/-), respectively, P < 0.05). Exposure of mice to 100% O(2) for 48 h also depressed CoQ(1)H(2) efflux rates in NQO1(+/+) and NQO1(-/-) lungs (0.43 ± 0.03 and 0.11 ± 0.04 μmol·min(-1)·g lung dry wt(-1), respectively, P < 0.05 by ANOVA). The impact of rotenone or hyperoxia on CoQ(1) redox metabolism could not be attributed to effects on lung wet-to-dry weight ratios, perfusion pressures, perfused surface areas, or total venous effluent CoQ(1) recoveries, the latter measured by spectrophotometry or mass spectrometry. Complex I activity in mitochondria-enriched lung fractions was depressed in hyperoxia-exposed lungs for both genotypes. This study provides new evidence for the potential utility of CoQ(1) as a nondestructive indicator of the impact of pharmacological or pathological exposures on complex I activity in the intact perfused mouse lung.