Ethidium bromide as an uncoupler of oxidative phosphorylation

Low micromolar concentrations of the superoxide probe MitoSOX uncouple neural mitochondria and inhibit complex IV

MitoSOX Red is a fluorescent probe used for the detection of mitochondrial reactive oxygen species by live cell imaging. The lipophilic, positively charged triphenylphosphonium moiety within MitoSOX concentrates the superoxide-sensitive dihydroethidium conjugate within the mitochondrial matrix. Here we investigated whether common MitoSOX imaging protocols influence mitochondrial bioenergetic function in primary rat cortical neurons and microglial cell lines. MitoSOX dose-dependently uncoupled neuronal respiration, whether present continuously in the assay medium or washed following a ten minute loading protocol. Concentrations of 5-10μM MitoSOX caused severe loss of ATP synthesis-linked respiration. Redistribution of MitoSOX to the cytoplasm and nucleus occurred concomitant to mitochondrial uncoupling. MitoSOX also dose-dependently decreased the maximal respiration rate and this impairment could not be rescued by delivery of a complex IV specific substrate, revealing complex IV inhibition. As in neurons, loading microglial cells with MitoSOX at low micromolar concentrations resulted in uncoupled mitochondria with reduced respiratory capacity whereas submicromolar MitoSOX had no adverse effects. The MitoSOX parent compound dihydroethidium also caused mitochondrial uncoupling and respiratory inhibition at low micromolar concentrations. However, these effects were abrogated by pre-incubating dihydroethidium with cation exchange beads to remove positively charged oxidation products, which would otherwise by sequestered by polarized mitochondria. Collectively, our results suggest that the matrix accumulation of MitoSOX or dihydroethidium oxidation products causes mitochondrial uncoupling and inhibition of complex IV. Because MitoSOX is inherently capable of causing severe mitochondrial dysfunction with the potential to alter superoxide production, its use therefore requires careful optimization in imaging protocols.

Intracellular oxidation of hydroethidine: compartmentalization and cytotoxicity of oxidation products

Hydroethidine (HE) is a blue fluorescent dye that is intracellularly converted into red-emitting products on two-electron oxidation. One of these products, namely 2-hydroxyethidium, is formed as the result of HE superoxide anion-specific oxidation, and so HE is widely used for the detection of superoxide in cells and tissues. In our experiments we exploited three cell lines of different origin: K562 (human leukemia cells), A431 (human epidermoid carcinoma cells), and SCE2304 (human mesenchymal stem cells derived from endometrium). Using fluorescent microscopy and flow cytometry analysis, we showed that HE intracellular oxidation products accumulate mostly in the cell mitochondria. This accumulation provokes gradual depolarization of mitochondrial membrane, affects oxygen consumption rate in HE-treated cells, and causes cellular apoptosis in the case of high HE concentrations and/or long cell incubations with HE, as well as a high rate of HE oxidation in cells exposed to some stimuli.

Chemical modifiers of unstable expanded simple sequence repeats: what goes up, could come down

A mounting number of inherited human disorders, including Huntington disease, myotonic dystrophy, fragile X syndrome, Friedreich ataxia and several spinocerebellar ataxias, have been associated with the expansion of unstable simple sequence DNA repeats. Despite a similar genetic basis, pathogenesis in these disorders is mediated by a variety of both loss and gain of function pathways. Thus, therapies targeted at downstream pathology are likely to be disease specific. Characteristically, disease-associated expanded alleles in these disorders are highly unstable in the germline and somatic cells, with a tendency towards further expansion. Whereas germline expansion accounts for the phenomenon of anticipation, tissue-specific, age-dependent somatic expansion may contribute towards the tissue-specificity and progressive nature of the symptoms. Thus, somatic expansion presents as a novel therapeutic target in these disorders. Suppression of somatic expansion should be therapeutically beneficial, whilst reductions in repeat length could be curative. It is well established that both cis- and trans-acting genetic modifiers play key roles in the control of repeat dynamics. Importantly, recent data have revealed that expanded CAG.CTG repeats are also sensitive to a variety of trans-acting chemical modifiers. These data provide an exciting proof of principle that drug induced suppression of somatic expansion might indeed be feasible. Moreover, as our understanding of the mechanism of expansion is refined more rational approaches to chemical intervention in the expansion pathway can be envisioned. For instance, the demonstration that expansion of CAG.CTG repeats is dependent on the Msh2, Msh3 and Pms2 genes, highlights components of the DNA mismatch repair pathway as therapeutic targets. In addition to potential therapeutic applications, the response of expanded simple repeats to genotoxic assault suggests such sequences could also have utility as bio-monitors of environmentally induced genetic damage in the soma.

Chemically induced increases and decreases in the rate of expansion of a CAG*CTG triplet repeat

Somatic mosaicism of repeat length is prominent in repeat expansion disorders such as Huntington disease and myotonic dystrophy. Somatic mosaicism is age-dependent, tissue-specific and expansion-biased, and likely contributes toward the tissue-specificity and progressive nature of the symptoms. We propose that therapies targeted at somatic repeat expansion may have general utility in these disorders. Specifically, suppression of somatic expansion would be expected to be therapeutic, whilst reversion of the expanded mutant repeat to within the normal range would be predicted to be curative. However, the effects of genotoxic agents on the mutational properties of specific nuclear genes are notoriously difficult to define. Nonetheless, we have determined that chronic exposure over a three month period to a number of genotoxic agents can alter the rate of triplet repeat expansion in whole populations of mammalian cells. Interestingly, high doses of caffeine increased the rate of expansion by approximately 60%. More importantly, cytosine arabinoside, ethidium bromide, 5-azacytidine and aspirin all significantly reduced the rate of expansion by from 35 to 75%. These data establish that drug induced suppression of somatic expansion is possible. These data also suggest that highly unstable expanded simple sequence repeats may act as sensitive reporters of genotoxic assault in the soma.

Effects of 4-alkylmorpholine N-oxides on ATP-producing processes in Ehrlich ascites and L1210 leukaemia cells

The main purpose of the present investigation was to study the effect of the homologous series of 4-alkylmorpholine N-oxides on ATP-producing processes in Ehrlich ascites and L1210 murine leukaemia cells. The effects on aerobic glucose consumption, lactic acid formation, content of total (T-SH) and non-protein thiol groups (NP-SH), endogenous and exogenous respiration and the level of ATP in tumour cells incubated in vitro were investigated. 4-Dodecylmorpholine N-oxide (DMNO), one of the most active compounds, decreased the level of ATP immediately after addition to the suspension of Ehrlich cells in an ice bath. After 2 h incubation at 37 degrees C the drop in the ATP level was much lower. A possible explanation for the decrease in the ATP level might be interaction of the amine oxide with the cell membrane.

Cytoxicity of 1-alkylperhydroazepine N-oxides and quantitative structure-activity relationships

A new class of nonaromatic amine oxides was tested for cytotoxic activity. The main aim of the present investigation was to screen a series of 1-alkylperhydroazepine N-oxides for in vitro cytotoxicity and to find out whether there is a quantitative structure-activity correlation (QSAR) between cytotoxic effect and structure (as a structural parameter the number of carbon atoms m in the alkyl chain was used). Cytotoxicity was determined here by inhibition of incorporation of [14C]adenine into nucleic acid or [14C]valine into proteins in Ehrlich ascites carcinoma (EAC) cells. On the basis of primary screening, one of the most active compounds, namely 1-tetradecylperhydroazepine N-oxide (TPNO), was chosen for further biochemical study. The drug inhibited the incorporation rate of [14C] labeled precursors (adenine, thymidine, uridine, valine) into appropriate macromolecules of Ehrlich cells. The extent of inhibition was dependent on both time and drug concentration. The lengthening of the alkyl chain in 1-alkylperhydroazepine N-oxides positively affected their cytotoxic activity in EAC cells. For these compounds the optimal m value is 12-14.

In vivo interference of paromomycin with mitochondrial activity of Leishmania

Paromomycin is an aminocyclitol aminoglycoside antibiotic used for the treatment of leishmaniasis. In view of the central role of mitochondria in cellular energetics and metabolism, its effect on in vivo mitochondrial activities of Leishmania donovani promastigotes-the parasite flagellate form-was investigated. The approach used flow cytometry, amperometric measure of O2 consumption, and, as a global estimate of mitochondrial dehydrogenases, thiazolyl blue reduction (MTT test); some in vitro controls were also made. When added to promastigote cultures for 24-72 h at 150-200 microM (= LC50), paromomycin doubled the generation time, inhibited respiration, and lowered its associated electric potential difference across mitochondrial membranes, as measured by rhodamine 123 fluorescence. The chemical analogue neomycin was ineffective. Furthermore, the in vivo mitochondrial dehydrogenase activities were lower, seemingly because of the shortage of respiratory substrates. Indeed, succinate addition to paromomycin-treated cultures partly restored mitochondrial membrane potential. However, no immediate effect of paromomycin on respiration was observed, neither inhibition of redox chain nor increase of membrane permeability (uncoupling). It is proposed that paromomycin acts at a metabolic level upstream of the respiratory chain itself. This would have the observed delayed consequence because the cell energy supply would progressively decline since it depends upon the proton gradient-viz., membrane potential-generated by respiration. In conclusion, paromomycin is an antibiotic affecting the cell's energetic metabolism; the respiratory dysfunction it induces may be a crucial aspect of its action against Leishmania and possibly other cells.

Ca2+ transport by digitonin-permeabilized Leishmania donovani. Effects of Ca2+, pentamidine and WR-6026 on mitochondrial membrane potential in situ

The use of low concentrations of digitonin allowed the quantitative determination of the mitochondrial membrane potential of Leishmania donovani promastigotes in situ using safranine O. L. donovani mitochondria were able to build up and retain a membrane potential of a value comparable with that of mammalian mitochondria. The response of promastigotes mitochondrial membrane potential to phosphate, carbonyl cyanide p-(trifluoromethoxy)phenylhydrazone (FCCP), valinomycin and Ca2+ indicates that these mitochondria behave similarly to vertebrate mitochondria with regard to the properties of their electrochemical proton gradient. When L. donovani promastigotes were permeabilized with digitonin in a reaction medium containing MgATP, succinate and 3.5 microM free Ca2+, they lowered the medium Ca2+ concentration to the submicromolar level (0.05-0.1 microM). The presence of 1 microM-FCCP decreased by about 75% the initial rate of Ca2+ sequestration by these permeabilized cells. This FCCP-insensitive Ca2+ uptake, probably by the endoplasmic reticulum, was completely inhibited by 500 microM-vanadate. On the other hand, when vanadate instead of FCCP was present, the initial rate of Ca2+ accumulation was decreased by about 25% and the Ca2+ set point was increased to 0.7 microM. The succinate-dependence and FCCP-and Ruthenium Red-sensitivity of the Ca2+ uptake detected in the presence of vanadate indicate that this uptake is probably by the mitochondria. This interpretation was further supported by the Ruthenium Red-sensitive decrease in the mitochondrial membrane potential caused by Ca2+ addition. The anti-leishmanial cationic drugs pentamidine and WR-6026 also induced a rapid collapse of the mitochondrial inner membrane potential of L. donovani promastigotes.

Cloturin: effect on energy-producing processes in Ehrlich ascites and P388 murine leukaemia cells

The main purpose of the present investigation was to study the effect of cloturin on aerobic glycolysis, endogenous and exogenous respiration and the level of ATP in both Ehrlich ascites carcinoma (EAC) and P388 murine leukaemia cells incubated in vitro. Also its effect on the level of total (T-SH) and non-protein (NP-SH) thiol groups was investigated. A significant inhibition of aerobic glycolysis was found only in P388 cells after 60 min of cloturin action. Cloturin inhibited both endogenous and exogenous respiration of EAC with succinate as substrate. Cloturin decreased the level of ATP after 2 h incubation in both types of tumour cell. The level of NP-SH was decreased more than that of T-SH in both types of cell.

Biochemical basis of cytotoxic activity of some new N'-oxides of N',N'-dimethylaminoalkylamides of dodecanoic acid

The objective of the present investigation was to screen a series of new N'-oxides of N',N'-dimethylaminoalkylamides of dodecanoic acid for activity in vitro and to investigate the biochemical mode of action. On the basis of primary screening, one of the most active compounds, namely the N'-oxide of 10-(N',N'-dimethylaminodecyl)amide of dodecanoic acid (n = 10) was chosen for detailed biochemical study. This compound inhibited the incorporation of 14C-precursors (adenine, valine, thymidine, uridine) into appropriate macromolecules of P388 murine leukemia and Ehrlich ascites carcinoma cells. The amine oxide also interfered with energy-yielding processes (aerobic glycolysis, endogenous respiration). Cytotoxicity is a consequence of the cytolytic activity of the compounds mentioned above. Membranous effects were demonstrated by the measuring of the release of cytoplasmic materials absorbing at 260 and 280 nm, marker enzyme activities (LDH, MDH), release of protein from the cells into the culture medium, as well as by morphological examination. It is evident that the site of action of the amine oxides investigated was the biological membrane which, after interaction with the amine oxides, showed changes in molecular organization and osmotic and permeability characteristics.

Effects of benfluron and its two metabolites on respiratory processes in P388 murine leukemia and Ehrlich ascites cells

This paper presents data on the effects of benfluron and its two metabolites DBF and NOBF on both endogenous and exogenous, respiration in the presence of succinate as substrate, of both P388 murine leukemia and Ehrlich ascites carcinoma cells. The most efficient inhibitors of endogenous and exogenous respiration were benfluron and DBF. NOBF did not interfere with respiratory processes in Ehrlich cells, even at quite high concentration. BF and DBF exert an almost identical inhibitory effect on exogenous respiration, the least effective being NOBF (Ehrlich cells). The decrease in the respiratory rates in cancer cells might be due to the effects of benfluron and its metabolites on the cell membrane. P388 murine leukemia cells are less "sensitive" than Ehrlich ascites cells.

Primary screening and inhibition of macromolecular biosynthesis in Ehrlich ascites cells by benzo(C)fluorene derivatives

The main objective of the present investigation was to screen a series of new benzo(c)fluorene compounds for in vitro activity. It can be stated that each of the 9 newly synthesized benzo(c)fluorene derivatives was about 10 times as active as tilorone. To elucidate the biochemical mode of action, the effects of 2 new compounds (13468 and 14200) on biosynthesis of macromolecules indicated by the incorporation rate of [14C]adenine (DNA, RNA), [14C]-thymidine (DNA), [14C]uridine (RNA) and [14C]valine (protein) were studied in concentration and time dependence. Both compounds inhibited the incorporation of the 4 precursors into the TCA-insoluble fraction of Ehrlich ascites carcinoma cells.

Relationships between the chemical structure and cytotoxicity of 4-alkylmorpholine N-oxides

The main objective of the present investigation was to screen a series of 4-alkylmorpholine N-oxides for in vitro cytotoxicity and to find out whether there is a quantitative structure-activity correlation (QSAR) between cytotoxic effect represented here by inhibition of incorporation of [14C]adenine into nucleic acid or [14C]valine into proteins in Ehrlich ascites carcinoma (EAC) cells and structure (as a structural parameter the number of carbon atoms m in the alkyl chain was used). On the basis of primary screening, one of the most active compounds, namely 4-dodecylmorpholine N-oxide, was chosen for further biochemical study. The drug inhibited the incorporation rate of [14C] precursors (adenine, thymidine, uridine, valine) into appropriate macromolecules of Ehrlich cells, the extent of inhibition being dependent on both time and concentration of the compound in the incubation medium. The lengthening of the alkyl chain in 4-alkyl-morpholine N-oxides positively affected their cytotoxic activity in Ehrlich cells. For these compounds the optimal m-value is 15-16.

Pseudomonas aeruginosa toxins: effect on Ehrlich carcinoma and Vero cells in vitro

The main objective of the present investigation was to screen P. aeruginosa toxins for in vitro activity and investigate biochemical mode of action. Toxins were isolated after concentration of the culture filtrate and separation of the filtrate on Sephadex G-100 column in four fractions. On the basis of primary screening results the dialysate and fractions 3 and 4 effectively inhibited incorporation of [14C]adenine (DNA, RNA) and [14C]valine (protein) into the TCA-insoluble fraction of both Ehrlich ascites carcinoma (EAC) and Vero cells. The toxins also interfered with energy-yielding processes (endogenous respiration). The dialysate decreased the level of ATP in EAC cells after two hours incubation in vitro.

Uncoupling of mitochondrial oxidative phosphorylation by hexetidine

To gain further insight into the biochemical properties of the antibacterial hexetidine, isolated rat liver mitochondria were added with this drug and investigation made of certain features related to mitochondrial bioenergetics. Hexetidine was found to cause oxidation of intramitochondrial pyridine nucleotides and stimulate the rate of oxygen uptake caused by respiratory substrates involving three, two and one site(s) of phosphorylation. Reversal of oxygen uptake inhibition by oligomycin was also determined. By investigating hexetidine effect on oxidative phosphorylation, hexetidine was found both to inhibit the rate of ATP synthesis and to cause ATP hydrolysis. Likewise, hexetidine capability to produce acidification of extramitochondrial medium and to collapse delta psi was also observed. The reported findings show that hexetidine exhibits uncoupling properties.

Inhibition of an oligomycin-sensitive ATPase by cationic dyes, some of which are atypical uncouplers of intact mitochondria

The inhibition of an oligomycin sensitive ATPase prepared from bovine heart submitochondrial particles (J.A. Berden and M.M. Voorn-Brouwer, 1978, Biochim. Biophys. Acta 501, 424-439) by a number of cationic dyes has been compared in order to develop a structure-function relationship. Two generalizations emerge from this comparison. First, the most effective dyes have net positive charge at neutral pH; and second, those dyes containing alkyl substituted secondary and tertiary amino groups are more effective than analogs with primary aromatic amino groups. Some of the cationic dyes exhibit uncoupling activity when added to intact rat liver mitochondria, stimulating both State 4 respiration and the latent ATPase activity. The order of effectiveness and concentrations for maximal stimulation of respiration are: coriphosphine (0.3 microM), Nile blue A (0.5 microM), pyronin Y (0.8 microM), and acridine orange (10 microM). Atypically, oligomycin inhibits the stimulation of respiration by these cationic acid uncouplers. The order of effectiveness and concentrations for maximal stimulation of the latent ATPase are: Nile blue A (2 microM), pyronin Y (8 microM), acridine orange (25 microM), and coriphosphine (75 microM). At concentrations greater than those shown for maximal stimulation, the uncoupling dyes inhibited respiration and the latent ATPase. The cationic dyes tested that were not uncouplers are inhibitors of respiration and the latent ATPase of intact mitochondria at all concentrations tested.

Inhibition of photo-induced Trichoderma viride conidiation by inhibitors of RNA synthesis

The photo-induced conidiation of Trichoderma viride is suppressed by ethidium bromide, acriflavin, lomofungin and 8-quinolinol at concentrations which do not inhibit the colony growth of this deuteromycete.

Inhibition of yeast sporulation by ethidium bromide

Ethidium bromide blocks ascus formation in the yeast Saccharomyces cerevisiae. This may mean that the presence of the mitochondrial genome is required for sporulation in this organism.

Sidedness of inhibition of energy transduction in oxidative phosphorylation in rat liver mitochondria by ethidium bromide

Ethidium bromide, a new type of inhibitor of energy transduction in oxidative phosphorylation, inhibited ATP synthesis in intact mitochondria but not in submitochondrial particles, the latter being inside-out relative to the membranes of intact mitochondria. Ethidium bromide incorporated inside the submitochondrial particles inhibited ATP synthesis in the particles. The decrease of the membrane potential by valinomycin (plus KCl) inhibited only slightly the energy-dependent binding of ethidium bromide to the mitochondria. The present results show clearly that ethidium bromide inhibited energy transduction in oxidative phosphorylation by acting on the outer side (C-side) of the inner mitochondrial membrane, perhaps by neutralizing negative charges created on the surface of the C-side, and that it had no inhibitory activity on the inner side (M-side) of the membrane. Th present results show also that the energy-dependent binding of ethidium is not due to electrophoretic transport down the membrane potential; ethidium may bind to negative charges on the surface of the C-side. The present study suggest that an anisotropic distribution of electric charge in the inner mitochondrial membrane is an intermediary high energy state of oxidatvie phosphorylation.