Does the calcein-AM method assay the total cellular 'labile iron pool' or only a fraction of it?

The calcein-AM (calcein-acetoxymethyl ester) method is a widely used technique that is supposed to assay the intracellular 'labile iron pool' (LIP). When cells in culture are exposed to this ester, it passes the plasma membrane and reacts with cytosolic unspecific esterases. One of the reaction products, calcein, is a fluorochrome and a hydrophilic alcohol to which membranes are non-permeable and which, consequently, is retained within the cytosol of cells. Calcein fluorescence is quenched following chelation of low-mass labile iron, and the degree of quenching gives an estimate of the amounts of chelatable iron. However, a requirement for the assay to be able to demonstrate cellular LIP in total is that such iron be localized in the cytosol and not in a membrane-limited compartment. For some time it has been known that a major part of cellular, redox-active, labile, low-mass iron is temporarily localized in the lysosomal compartment as a result of the autophagic degradation of ferruginous materials, such as mitochondrial complexes and ferritin. Even if some calcein-AM may escape cytosolic esterases and enter lysosomes to be cleaved by lysosomal acidic esterases, the resulting calcein does not significantly chelate iron at Collapse

Key Words

• autophagy
• calcein
• iron
• labile iron pool
• lysosomes
• oxidative stress
• calcein-am, calcein-acetoxymethyl ester
• dmem, dulbecco's modified eagle's medium
• lip, labile iron pool
• sih, salicylaldehyde isonicotinoyl hydrazone
• ssm, sulfide-silver method

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MESH Headings

• Cell Membrane Permeability
• Cytosol/enzymology
• Esterases/metabolism
• Esters/analysis
• Esters/metabolism
• Fluoresceins/analysis
• Fluoresceins/metabolism
• HeLa Cells
• Humans
• Hydrogen-Ion Concentration
• Iron/analysis
• Iron/metabolism
• Iron Chelating Agents/analysis
• Iron Chelating Agents/metabolism
• Kinetics
• Lysosomes/metabolism
• Oxidative Stress
• Phagocytosis
• Substrate Specificity

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Grants Collapse

Acoustic cavitation, bubble dynamics and sonoluminescence

Basic facts on the dynamics of bubbles in water are presented. Measurements on the free and forced radial oscillations of single spherical bubbles and their acoustic (shock waves) and optic (luminescence) emissions are given in photographic series and diagrams. Bubble cloud patterns and their dynamics and light emission in standing acoustic fields are discussed.

Autophagy, ageing and apoptosis: the role of oxidative stress and lysosomal iron

As an outcome of normal autophagic degradation of ferruginous materials, such as ferritin and mitochondrial metalloproteins, the lysosomal compartment is rich in labile iron and, therefore, sensitive to the mild oxidative stress that cells naturally experience because of their constant production of hydrogen peroxide. Diffusion of hydrogen peroxide into the lysosomes results in Fenton-type reactions with the formation of hydroxyl radicals and ensuing peroxidation of lysosomal contents with formation of lipofuscin that amasses in long-lived postmitotic cells. Lipofuscin is a non-degradable polymeric substance that forms at a rate that is inversely related to the average lifespan across species and is built up of aldehyde-linked protein residues. The normal accumulation of lipofuscin in lysosomes seems to reduce autophagic capacity of senescent postmitotic cells--probably because lipofuscin-loaded lysosomes continue to receive newly formed lysosomal enzymes, which results in lack of such enzymes for autophagy. The result is an insufficient and declining rate of autophagic turnover of worn-out and damaged cellular components that consequently accumulate in a way that upsets normal metabolism. In the event of a more substantial oxidative stress, enhanced formation of hydroxyl radicals within lysosomes jeopardizes the membrane stability of particularly iron-rich lysosomes, specifically of autophagolysosomes that have recently participated in the degradation of iron-rich materials. For some time, the rupture of a limited number of lysosomes has been recognized as an early upstream event in many cases of apoptosis, particularly oxidative stress-induced apoptosis, while necrosis results from a major lysosomal break. Consequently, the regulation of the lysosomal content of redox-active iron seems to be essential for the survival of cells both in the short- and the long-term.

Intracoronary enalaprilat during angioplasty for acute myocardial infarction: alleviation of postischaemic neurohumoral and inflammatory stress?

AIM

Reperfusion after myocardial ischaemia is associated with a distinct ischaemia/reperfusion injury. Since ACE-inhibition, beyond its influence on cardiac angiotensin II formation and kinin metabolism, has been shown to be cardioprotective by decreasing leucocyte adhesion and endothelin-1 (ET-1) release, we investigated the effects of intracoronary (i.c.) enalaprilat during primary angioplasty in acute myocardial infarction.

METHODS AND RESULTS

Twenty-two patients were randomized to receive i.c. enalaprilat (50 micro g) or placebo immediately after reopening of the infarct-related artery (IRA). Plasma concentrations of soluble L-selectin, P-selectin, intercellular adhesion molecule-1 (sICAM-1), vascular cell adhesion molecule-1 (sVCAM-1), ET-1 and nitric oxide metabolite concentrations (NOx) were measured in pulmonary arterial blood. Coronary blood flow was assessed using corrected thrombolysis in myocardial infarction (TIMI) frame counts (CTFC). During reperfusion, there was a significant increase in sL-selectin, sP-selectin and ET-1 in the placebo group, which was greatly diminished by enalaprilat. Levels of sVCAM-1 and sICAM-1 were not affected in either group. CTFC in the placebo group remained higher than normal in both the IRA and nonculprit vessels, whereas myocardial blood flow improved with enalaprilat.

CONCLUSION

Enalaprilat as adjunct to primary angioplasty might be a protective approach to prevent leucocyte adhesion and the release of ET-1, thereby improving coronary blood flow.

Lysosomal labilization

The lysosomal compartment is the place for cellular degradation of endocytosed and autophagocytosed material and a center for normal turnover of organelles as well as most long-lived proteins. Lysosomes were long considered stable structures that broke and released their many hydrolytic enzymes only following necrotic cell death. It is now realized that lysosomes instead are quite vulnerable, although in a heterogeneous way. Their exposure to a number of events, such as oxidative stress, lysosomotropic detergents and aldhydes, as well as overexpression of the p53 protein, causes time-and-dose-dependent lysosomal rupture that is followed by apoptosis or necrosis. Partial lysosomal rupture has often been found to be an early upstream event in apoptosis, while necrosis results from fulminant lysosomal rupture. Consequently, factors influencing the stability of lysosomes, for instance their content of labile and redox-active iron, seem to be essential for the survival of cells.

Tuning the magnetic properties of GaAs:Mn/MnAs hybrids via the MnAs cluster shape

We report a systematic study of ferromagnetic resonance in granular GaAs:Mn/MnAs hybrids grown on GaAs(001) substrates by metal-organic vapour-phase epitaxy. The ferromagnetic resonance of the MnAs clusters can be resolved at all temperatures below T(c). An additional broad absorption is observed below 60 K and is ascribed to localized charge carriers of the GaAs:Mn matrix. The anisotropy of the MnAs ferromagnetic resonance field originates from the magneto-crystalline field and demagnetization effects of the ferromagnetic MnAs clusters embedded in the GaAs:Mn matrix. Its temperature dependence basically scales with magnetization. Comparison of the observed angular dependence of the resonance field with model calculations yields the preferential orientation and shape of the clusters formed in hybrid layers of different thickness (150-1000 nm) grown otherwise at the same growth conditions. The hexagonal axes of the MnAs clusters are oriented along the four cubic GaAs space diagonals. Thin layers contain lens-shaped MnAs clusters close to the surface, whereas thick layers also contain spherical clusters in the bulk of the layer. The magnetic properties of the hexagonal MnAs clusters can be tuned by a controlled variation of the cluster shape.

Intralysosomal iron chelation protects against oxidative stress-induced cellular damage

Oxidant-induced cell damage may be initiated by peroxidative injury to lysosomal membranes, catalyzed by intralysosomal low mass iron that appears to comprise a major part of cellular redox-active iron. Resulting relocation of lytic enzymes and low mass iron would result in secondary harm to various cellular constituents. In an effort to further clarify this still controversial issue, we tested the protective effects of two potent iron chelators--the hydrophilic desferrioxamine (dfo) and the lipophilic salicylaldehyde isonicotinoyl hydrazone (sih), using cultured lysosome-rich macrophage-like J774 cells as targets. dfo slowly enters cells via endocytosis, while the lipophilic sih rapidly distributes throughout the cell. Following dfo treatment, long-term survival of cells cannot be investigated because dfo by itself, by remaining inside the lysosomal compartment, induces apoptosis that probably is due to iron starvation, while sih has no lasting toxic effects if the exposure time is limited. Following preincubation with 1 mM dfo for 3 h or 10 microM sih for a few minutes, both agents provided strong protection against an ensuing approximately LD50 oxidant challenge by preventing lysosomal rupture, ensuing loss of mitochondrial membrane potential, and apoptotic/necrotic cell death. It appears that once significant lysosomal rupture has occurred, the cell is irreversibly committed to death. The results lend strength to the concept that lysosomal membranes, normally exposed to redox-active iron in high concentrations, are initial targets of oxidant damage and support the idea that chelators selectively targeted to the lysosomal compartment may have therapeutic utility in diminishing oxidant-mediated cell injury.

Metallothionein protects against oxidative stress-induced lysosomal destabilization

The introduction of apo-ferritin or the iron chelator DFO (desferrioxamine) conjugated to starch into the lysosomal compartment protects cells against oxidative stress, lysosomal rupture and ensuing apoptosis/necrosis by binding intralysosomal redox-active iron, thus preventing Fenton-type reactions and ensuing peroxidation of lysosomal membranes. Because up-regulation of MTs (metallothioneins) also generates enhanced cellular resistance to oxidative stress, including X-irradiation, and MTs were found to be capable of iron binding in an acidic and reducing lysosomal-like environment, we propose that these proteins might similarly stabilize lysosomes following autophagocytotic delivery to the lysosomal compartment. Here, we report that Zn-mediated MT up-regulation, assayed by Western blotting and immunocytochemistry, results in lysosomal stabilization and decreased apoptosis following oxidative stress, similar to the protection afforded by fluid-phase endocytosis of apo-ferritin or DFO. In contrast, the endocytotic uptake of an iron phosphate complex destabilized lysosomes against oxidative stress, but this was suppressed in cells with up-regulated MT. It is suggested that the resistance against oxidative stress, known to occur in MT-rich cells, may be a consequence of autophagic turnover of MT, resulting in reduced iron-catalysed intralysosomal peroxidative reactions.

Comparison of carvedilol and metoprolol in patients with acute myocardial infarction undergoing primary coronary intervention

BACKGROUND

The value of early therapy with beta-blocking agents in acute myocardial infarction (AMI) undergoing reperfusion is not yet well established. Newer beta-blocking agents such as carvedilol offer potential advantages in the setting of ischemia and reperfusion injury.

METHODS

We randomized 100 patients with acute ST-elevation myocardial infarction (STEMI) to receive either 12.5 mg carvedilol or 50 mg metoprolol tartrate orally already before percutaneous coronary intervention (PCI) of the infarct-related artery, uptitrating to a daily target dose of 50 mg carvedilol or 150 mg metoprolol during the first week. Pts. were subjected to left ventricular (LV) angiography just before reperfusion and after 14 days to compare ejection fraction (EF) and regional wall motion abnormalities by quantitative LV analysis. Furthermore, kinetics of cardiac troponin T (cTnT), NT-proANP, NT-proBNP, endothelin, argenine vasopressin, epinephrine and norepinephrine were assessed during the first 12 hours and again at 2 weeks. In addition, reperfusion-induced rhythm abnormalities like VT, triplets, couplets, and bradycardic events were assessed continuously during the first 12 hours starting at reperfusion by Holter analysis.

RESULTS

Both groups did not differ with respect to onset of pain, target vessel, extent of coronary heart disease, age, gender, rate of stenting or use of a GP IIb/IIIa inhibitor, pre- and postinterventional TIMI flow grade, time course of heart rate or blood pressure. There were neither significant differences in the cardiac and neurohumoral markers nor in the occurrence of arrhythmias between both treatment groups. Within 14 days, EF improved by 5.8+/-2.0% (mean+/-SEM) in the metoprolol group and by 5.2+/-2.1% in the carvedilol group (n.s.). Area of infarction was reduced by 6.1+/-2.9% in the metoprolol group and by 12.8+/-3.6% of total LV outline in the carvedilol group (n.s.). Maximum hypokinesia in the central infarcted region was diminished by 0.40+/-0.11 standard deviation (SD) in the metoprolol group and by 0.34+/-0.13 SD in the carvedilol group (n.s.).

CONCLUSION

In the setting of direct PCI in acute STEMI, administration of carvedilol before reperfusion appears not to be superior to metoprolol with respect to myocardial injury and improvement of global and regional LV function. The study documents equivalent improvement of LV function and similar kinetics of cardiac and neurohumoral markers in pts. with acute STEMI undergoing direct PCI if the pts. were immediately treated with either carvedilol or metoprolol. Thus, superiority of carvedilol in experimental studies did not translate into a clinical benefit.

Radiation-induced cell death: importance of lysosomal destabilization

The mechanisms involved in radiation-induced cellular injury and death remain incompletely understood. In addition to the direct formation of highly reactive hydroxyl radicals (HO*) by radiolysis of water, oxidative stress events in the cytoplasm due to formation of H2O2 may also be important. Since the major pool of low-mass redox-active intracellular iron seems to reside within lysosomes, arising from the continuous intralysosomal autophagocytotic degradation of ferruginous materials, formation of H2O2 inside and outside these organelles may cause lysosomal labilization with release to the cytosol of lytic enzymes and low-mass iron. If of limited magnitude, such release may induce 'reparative autophagocytosis', causing additional accumulation of redox-active iron within the lysosomal compartment. We have used radio-resistant histiocytic lymphoma (J774) cells to assess the importance of intralysosomal iron and lysosomal rupture in radiation-induced cellular injury. We found that a 40 Gy radiation dose increased the 'loose' iron content of the (still viable) cells approx. 5-fold when assayed 24 h later. Cytochemical staining revealed that most redox-active iron was within the lysosomes. The increase of intralysosomal iron was associated with 'reparative autophagocytosis', and sensitized cells to lysosomal rupture and consequent apoptotic/necrotic death following a second, much lower dose of radiation (20 Gy) 24 h after the first one. A high-molecular-mass derivative of desferrioxamine, which specifically localizes intralysosomally following endocytic uptake, added to the culture medium before either the first or the second dose of radiation, stabilized lysosomes and largely prevented cell death. These observations may provide a biological rationale for fractionated radiation.

A genome-wide screen on the genetics of atopy in a multiethnic European population reveals a major atopy locus on chromosome 3q21.3

BACKGROUND

Dissecting complex diseases in underlying distinct traits and studying these for their genetic basis might enhance the power as well as the specificity, of detection of disease genes. These phenotypes are known as intermediate phenotypes.

OBJECTIVE

We were interested in the atopic basis of asthma, and used the sensitization to mite (Dermatophagoides pteronyssinus) allergens as a pathophysiologically important intermediate phenotype.

METHODS

This time we performed a genome-wide scan based on the same already used multiethnic European population consisting of 82 nuclear families with at least two affected siblings. We carried out nonparametric as well as parametric MOD-score analyses based on the genotypes of 603 microsatellite markers.

RESULTS

In comparison with our first genome-wide candidate region search three novel regions additionally appeared to be significant. We obtained significant results for the region 2p12 with a MOD score of 3.35 and for the region 16q21 with a MOD score of 4.18. The most significant result was found for the region 3q21.3 with the same microsatellite marker, which showed significant linkage to atopic dermatitis (AD) in another study with a MOD score of 4.51 and an nonparametric linkage analysis (NPL) of 4.00.

CONCLUSION

Our findings indicate that atopy, allergic asthma, allergic rhinitis and AD on the one hand are distinct traits on both the clinical and genetic basis, but on the other hand, our results also underline that these traits are closely related diseases concerning the atopic basis of the traits.

Association study of polymorphisms within interleukin-18 in juvenile idiopathic arthritis and bronchial asthma

BACKGROUND

Interleukin-18 (IL-18) plays an important role in the regulation of TH1 as well as TH2 immunologic responses and thus in the development of chronic inflammatory diseases. Positive association studies of polymorphisms in IL-18 with different diseases have underlined the involvement of IL-18 in the pathogenetics processes. Our interest was to test polymorphisms of IL-18 for association with a typical TH1-mediated disease--juvenile idiopathic arthritis--and the TH2-mediated disease bronchial asthma in Caucasian children.

METHODS

We genotyped five polymorphisms that were in association with chronic inflammatory diseases (-607C, -137C, 113G, 127T, and -133G). This was performed by restriction fragment length polymorphism in populations of asthmatic children, control individuals, and children with antinuclear antibodies (ANA)-positive juvenile idiopathic arthritis. Statistical analysis was performed by the Armitage trend test; haplotypes were calculated by the Arlequine program.

RESULTS

No significant association was found between any single nucleotide polymorphism or any haplotype and bronchial asthma or ANA-positive juvenile idiopathic arthritis.

CONCLUSION

We conclude that the effect of IL-18 in the immunologic context of diseases like bronchial asthma or juvenile arthritis might be too complex to be reflected in a simple one-way association study. Furthermore, the polymorphisms under investigation might be nonfunctional.

Promoter polymorphisms of the CD14 gene are not associated with bronchial asthma in Caucasian children

Several studies have investigated the association of a promoter polymorphism in CD14 with atopic phenotypes. We screened this and another polymorphism in 182 asthmatic children and found no association with asthma. Furthermore, there was substantial linkage disequilibrium of the polymorphisms. Thus CD14 does not play a major role in the development of asthma in our population of Caucasian children.

Relocalized redox-active lysosomal iron is an important mediator of oxidative-stress-induced DNA damage

Oxidative damage to nuclear DNA is known to involve site-specific Fenton-type chemistry catalysed by redox-active iron or copper in the immediate vicinity of DNA. However, the presence of transition metals in the nucleus has not been shown convincingly. Recently, it was proposed that a major part of the cellular pool of loose iron is confined within the acidic vacuolar compartment [Yu, Persson, Eaton and Brunk (2003) Free Radical Biol. Med. 34, 1243-1252; Persson, Yu, Tirosh, Eaton and Brunk (2003) Free Radical Biol. Med. 34, 1295-1305]. Consequently, rupture of secondary lysosomes, as well as subsequent relocation of labile iron to the nucleus, could be an important intermediary step in the generation of oxidative damage to DNA. To test this concept we employed the potent iron chelator DFO (desferrioxamine) conjugated with starch to form an HMM-DFO (high-molecular-mass DFO complex). The HMM-DFO complex will enter cells only via fluid-phase endocytosis and remain within the acidic vacuolar compartment, thereby chelating redox-active iron exclusively inside the endosomal/lysosomal compartment. Both free DFO and HMM-DFO equally protected lysosomal-membrane integrity against H2O2-induced oxidative disruption. More importantly, both forms of DFO prevented H2O2-induced strand breaks in nuclear DNA, including telomeres. To exclude the possibility that lysosomal hydrolases, rather than iron, caused the observed DNA damage, limited lysosomal rupture was induced using the lysosomotropic detergent O-methyl-serine dodecylamine hydrochloride; subsequently, hardly any DNA damage was found. These observations suggest that rapid oxidative damage to cellular DNA is minimal in the absence of redox-active iron and that oxidant-mediated DNA damage, observed in normal cells, is mainly derived from intralysosomal iron translocated to the nucleus after lysosomal rupture.

Lysosomal Redox-Active Iron Is Important for Oxidative Stress-Induced DNA Damage

Data show that specifically chelating lysosomal redox-active iron can prevent most H(2)O(2)-induced DNA damage. Lysosomes seem to contain the major pool of redox-active labile iron within the cell. Under oxidative stress conditions, this iron may then relocate to the nucleus and play an important role for DNA damage by taking part in Fenton reactions.

Norepinephrine release is reduced in cardiac tissue of Type 2 diabetic patients

AIMS/HYPOTHESIS

The aim of this study was to assess whether cardiac catecholamine release is affected in patients with Type 2 diabetes mellitus.

METHODS

A trial tissue was obtained from 19 diabetic (Type 2) and 43 non-diabetic patients undergoing coronary surgery. Endogenous norepinephrine release was examined under baseline conditions as well as during electrical field stimulation (effective voltage 5 V, stimulation frequency 4 Hz, pulse width 2 msec) by high performance liquid chromatography and electrochemical detection. Cardiac function and arterial blood pressure was assessed from coronary angiography.

RESULTS

In atrial tissue from diabetic patients, stimulation-induced norepinephrine release was reduced by 25% compared with non-diabetic patients, while baseline norepinephrine release did not differ between both groups. Preoperative plasma glucose and haemoglobin A(1C) concentrations were increased in patients with diabetes, however, no relation was found to catecholamine release. Diabetic and non-diabetic patients did not differ regarding left ventricular ejection fraction and arterial blood pressure.

CONCLUSION/INTERPRETATION

Cardiac norepinephrine release is suppressed in patients with Type 2 diabetes which could contribute to sympathetic neuropathy. The difference of norepinephrine release in diabetic and non-diabetic patients was independent of cardiac function and arterial blood pressure.

Plasma catecholamines and N-terminal proBNP in patients with acute myocardial infarction undergoing primary angioplasty. Relation to left ventricular function and clinical outcome

BACKGROUND

Neither profiles nor prognostic values of neurohormonal markers have been prospectively evaluated in patients with acute myocardial infarction (AMI) undergoing primary angioplasty.

METHODS AND RESULTS

In 118 consecutive patients with AMI undergoing successful reperfusion (TIMI 2 and 3) by primary angioplasty, plasma concentrations of norepinephrine, epinephrine and N-terminal proBNP (NT-proBNP) were measured before, 60 min and 10 days after angioplasty. Catecholamine concentrations (mean+/-SEM) rose to a maximum in the first hour after angioplasty (norepinephrine: 602+/-44 ng/L, epinephrine: 213+/-24 ng/L) and returned to normal at day 10. Conversely, NT-proBNP levels maintained a further increase from 799+/-44 pmol/L at baseline to 924+/-54 pmol/L at day 10. A NT-proBNP concentration above median at 60 min post-angioplasty predicted major adverse cardiac events (n=27) during the 18-36 month follow-up with an odds ratio of 5.9 (1.7-20.3) and was superior to catecholamines, to left ventricular ejection fraction and to other established postinfarction risk markers.

CONCLUSIONS

In a low-risk cohort of patients with AMI undergoing successful reperfusion therapy, plasma NT-proBNP concentrations are elevated for at least ten days. The prognostic value of early plasma NT-proBNP should be further evaluated concerning its ability to facilitate risk stratification of infarct patients.

Partial loss of dopaminergic neurons in the substantia nigra, ventrotegmental area and the retrorubral area -- model of the early beginning of Parkinson's symptomatology?

To test substances which might have protective effects on the dopaminergic system it is necessary to use models with a pathological symptomatology of the early beginning, i.e. models in which the chance exists to arrest the otherwise progressive pathological processes (see Heim et al., 2001). 6-hydroxydopamine (6-OHDA) injected unilaterally into the ventrolateral striatum of rats (6 microg dissolved in 2 microl 0.2% ascorbic acid) leads to specific stereotyped movements after subcutaneous injection of apomorphine both 3 and 13 weeks after surgery. Ten weeks after surgery decreased spontaneous motor activity could be observed. Twelve weeks after 6-hydroxydopamine injection, the animals had difficulties in performing a spatial navigation task when the submerged escape platform was moved to another position. The switching of motor programs was less pronounced. The application of tyrosine-hydroxylase-staining showed a loss of ipsilateral neurones of the substantia nigra compacta as well as of dendrites in the pars reticulata, neurones in the ventral tegmental area and in the retrorubral area ipsilaterally as well as a loss of dopaminergic fibres both ipsilaterally and contralaterally in the striatum which should belong to the contralateral acting substantia nigra afferents. The loss of the neurones and the afferents was induced by the retrograde denervation following the 6-OHDA injection within the ventrolateral striatum. The question arises whether the model used here with the partially loss of dopaminergic neurons and fibres reflects some of pathological symptoms of Parkinson's disease in the early states.