Adriamycin affects plasma membrane redox functions

Decavanadate interacts with microsomal NADH oxidation system and enhances cytochrome c reduction

Oxidation of NADH with accompanying oxygen consumption (NADH:O(2) = 1:1) was observed in the combined presence of metavanadate (MV), decavanadate (DV) and microsomes. Oxygen consumption was negligible in the absence of MV, but NADH was oxidized and DV was reduced to a form of vanadyl-V(IV), colored blue like vanadyl sulfate but differed from it in having a 23-fold higher absorbance at 700 nm. DV can interact with the NADH oxidation system of microsomes as an electron acceptor, in addition to the known ferricyanide and cytochrome c. DV enhances rate of cytochrome c reduction significantly at microM concentrations. These studies indicate potential of DV as a redox intermediate.

Characterization of VDAC1 as a plasma membrane NADH-oxidoreductase

We have recently demonstrated that voltage dependent anion selective channel~1 (porin, isoform 1) can function as a transplasma membrane NADH:ferricyanide-reductase. However, both the specific redox characteristics and the mechanism of electron transport in this enzyme presently remain unclear. Here we demonstrate that the redox capability of porin 1 is specific for ferricyanide as this same enzyme cannot reduce DCIP or cytochrome c in vitro. Furthermore, NADH-dependent ferricyanide reduction associated with VDAC1 is not sensitive to the anion channel inhibitors DIDS and dextran sulfate. However, this activity can be inhibited by thiol chelators, suggesting that at least one of the two cysteine groups present in VDAC1 are critical for electron transfer. We propose a model on how electron transport may occur in VDAC1.

NADH-dependent decavanadate reductase, an alternative activity of NADP-specific isocitrate dehydrogenase protein

The well known NADP-specific isocitrate dehydrogenase (IDH) obtained from pig heart was found to oxidize NADH with accompanying consumption of oxygen (NADH:O(2)=1:1) in presence of polyvanadate. This activity of the soluble IDH-protein has the following features common with the previously described membrane-enzymes: heat-sensitive, active only with NADH but not NADPH, increased rates in acidic pH, dependence on concentrations of the enzyme, NADH, decavanadate and metavanadate (the two constituents of polyvanadate), and sensitivity to SOD and EDTA. Utilizing NADH as the electron source the IDH protein was able to reduce decavanadate but not metavanadate. This reduced form of vanadyl (V(IV)) was similar in its eight-band electron spin resonance spectrum to vanadyl sulfate but had a 20-fold higher absorbance at its 700 nm peak. This decavanadate reductase activity of the protein was sensitive to heat and was not inhibited by SOD and EDTA. The IDH protein has the additional enzymic activity of NADH-dependent decavanadate reductase and is an example of "one protein--many functions".

Rhein enhances the effect of adriamycin on mitochondrial respiration by increasing antibiotic-membrane interaction

The effect of the combination of Adriamycin (ADM) with rhein (RH), an anti-inflammatory drug, on the electron flow through site III and IV of the respiratory chain of rat liver mitochondria was investigated. RH, even at high concentrations, does not inhibit either duroquinol (DHQ) oxidation or cytochrome oxidase activity both of which are decreased by ADM in a dose-dependent manner. The analysis of interaction, performed with the isobolar method, shows a strong synergistic effect that cannot be ascribed to increased permeability of the mitochondrial membranes brought about by RH. The mechanism by which RH potentiates the effect of ADM on DHQ oxidation and cytochrome oxidase activity is most likely to be changes induced in the physical status of the inner mitochondrial membrane such as to permit low ADM concentrations to bind and segregate enough cardiolipin to inhibit electron transport through complex III and IV.

Response to adriamycin of transplasma membrane electron transport in adriamycin-resistant and nonresistant HL-60 cells

Adriamycin, 10(-8) - 10(-5) M, inhibited transplasma membrane electron transport of uninduced HL-60 cells susceptible to adriamycin and not in uninduced HL-60 cells resistant to adriamycin as measured by reduction of external ascorbate free radical. Electron flow across the plasma membrane was measured with the intact living cells by means of a simple assay procedure whereby the transported electrons were captured by ascorbate free radical to slow the rate of chemical oxidation of ascorbate. The response to adriamycin was rapid with maximum inhibition in less than 1 min. Preincubation was not required and the inhibition presumably was not mediated through effects on DNA replication or transcription. Except at the highest concentration tested of 10 microM, both transplasma membrane electron transport and growth were unaffected by adriamycin with a line of HeLa cells resistant to the drug. The findings provide evidence, using a physiological acceptor, ascorbate free radical, for a direct inhibition of transmembrane electron transport of HL-60 cells by adriamycin that correlates closely with adriamycin inhibition of cell growth. The lack of response with resistant cells suggests an alternative mechanism for adriamycin resistance not necessarily based on transport control.

Polyvanadate-stimulated NADH oxidation by plasma membranes--the need for a mixture of deca and meta forms of vanadate

Polyvanadate solutions obtained by extracting vanadium pentoxide with dilute alkali over a period of several hours contained increasing amounts of decavanadate as characterized by NMR and ir spectra. Those solutions having a metavanadate:decavanadate ratio in the range of 1-5 showed maximum stimulation of NADH oxidation by rat liver plasma membranes. Reduction of decavanadate, but not metavanadate, was obtained only in the presence of the plasma membrane enzyme system. High simulation of activity of NADH oxidation was obtained with a mixture of the two forms of vanadate and this further increased on lowering the pH. Addition of increasing concentrations of decavanadate to metavanadate and vice versa increased the stimulatory activity, reaching a maximum when the metavanadate:decavanadate ratio was in the range of 1-5. Increased stimulatory activity can also be obtained by reaching these ratios by conversion of decavanadate to metavanadate by alkaline phosphate degradation, and of metavanadate to decavanadate by acidification. These studies show for the first time that both deca and meta forms of vanadate present in polyvanadate solutions are needed for maximum activity of NADH oxidation.

Characterization of oxygen free radicals generated during vanadate-stimulated NADH oxidation

The oxidation of NADH and accompanying reduction of oxygen to H2O2 stimulated by polyvanadate was markedly inhibited by SOD and cytochrome c. The presence of decavanadate, the polymeric form, is necessary for obtaining the microsomal enzyme-catalyzed activity. The accompanying activity of reduction of cytochrome c was found to be SOD-insensitive and therefore does not represent superoxide formation. The reduction of cytochrome c by vanadyl sulfate was also SOD-insensitive. In the presence of H2O2, all the forms of vanadate were able to oxidize reduced cytochrome c, which was sensitive to mannitol, tris and also catalase, indicating H2O2-dependent generation of hydroxyl radicals. Using ESR and spin trapping technique only hydroxyl radicals, but not superoxide anion radicals, were detected during polyvanadate-dependent NADH oxidation.

Flavoenzymes reduce vanadium(V) and molecular oxygen and generate hydroxyl radical

ESR spectroscopic evidence is presented for the formation of vanadium(IV) in the reduction of vanadium(V) by three typical, NADPH-dependent, flavoenzymes: glutathione reductase, lipoyl dehydrogenase, and ferredoxin-NADP+ oxidoreductase. The vanadium(V)-reduction mechanism appears to be an enzymatic one-electron reduction process. Addition of superoxide dismutase (SOD) showed that the generation of vanadium(IV) does not involve the superoxide (O2-) radical significantly. Measurements under anaerobic atmosphere showed, however, that the enzymes-vanadium-NADPH mixture can cause the reduction of molecular oxygen to generate H2O2. The H2O2 and vanadium(IV) thus formed react to generate hydroxyl (.OH) radical. The .OH formation is inhibited strongly by catalase and to a lesser degree by SOD, but it is enhanced by exogenous H2O2, suggesting the occurrence of a Fenton-like reaction. The inhibition of vanadium(IV) formation by N-ethylmaleimide indicates that the SH group on the flavoenzyme's cystine residue plays an important role in the enzyme's vanadium(V) reductase function. These results thus reveal a new property of the above-mentioned, NADPH-dependent flavoenzymes--their function as vanadium(V) reductases, as well as that as generators of .OH radical in the vanadium(V) reduction mechanism.

Cell surface actions of adriamycin

Adriamycin has a vast range of reported actions on the structural and functional properties of cells. This review summarizes the literature on the ability of the drug to modulate the cell surface membrane and attempts to address the question of how such actions could be linked to cytotoxicity. In addition, we consider the use of polymer immobilization of adriamycin to separate intracellular from plasma membrane effects of the drug, and show how this approach has been helpful in interpreting the pharmacology of adriamycin. Finally, a range of biophysical and spectroscopic approaches to defining the molecular details of adriamycin-bilayer interactions is surveyed, and the results used to discuss a model for how this antineoplastic agent binds to membranes.

Hydroxyl radicals is not a significant intermediate in the vanadate-stimulated oxidation of NAD(P)H by O2

The vanadate-stimulated oxidation of NADH by an enzymatic flux of O2- is inhibited by superoxide dismutase, but not by catalase. Keller et al. (1989, Free Radical Biol. Med. 6, 15-22) observed inhibition by catalase presumably because they used a commercial preparation contaminated with superoxide dismutase. Their proposal, that H2O2 and hydroxyl radical play significant roles in vanadate-stimulation of NAD(P)H oxidation, may be discounted on the basis of these and of previously reported results.

Daunorubicin and vincristine binding to plasma membrane vesicles from daunorubicin-resistant and wild type Ehrlich ascites tumor cells

Tumor cell resistance to anthracyclines, epipodophyllotoxins and vinca alkaloids, called multi-drug resistance (MDR) is intimately linked to changes in the plasma membrane which facilitate an increased energy dependent drug extrusion in the resistant cell compared to the wild type cell. Isolated plasma membrane vesicles from wild type Ehrlich ascites tumor cells (EHR2) and the daunorubicin (DNR) resistant subline EHR2/DNR+ were utilised to study binding and possible transport of DNR and vincristine (VCR). A significant ATP enhanced increase in VCR binding to vesicles from EHR2/DNR+ compared to EHR2 was demonstrated. Furthermore, an increase in ATP enhanced VCR binding in proportion to content of the MDR associated P-glycoprotein was seen in plasma membrane vesicles prepared from various benign human endocrine tumors. VCR binding to EHR2/DNR+ vesicles was inhibited by other vinca alkaloids greater than actinomycin D greater than colchicine greater than anthracyclines, with 35-75 microM concentrations of anthracyclines needed for 50% inhibition. VCR binding to EHR2/DNR+ vesicles was pH and temperature dependent with an activation energy of -30 kJ/mol and was decreased by replacement of Na+ with K+ and by addition of Ca2+. Preincubation of vesicles with monoclonal antibody against the C terminal of P-glycoprotein had no effect on VCR binding and osmolality tests failed to show genuine transmembranal transport of VCR. DNR binding was similar in plasma membrane vesicles from both cell lines, and showed none of the characteristics mentioned for VCR. Furthermore, a radiolabeled N-hydroxysuccinimide ester derivative of doxorubicin, which inhibited VCR binding to EHR2/DNR+ membranes to an even greater extent than doxorubicin, labeled plasma membrane proteins from EHR2 and EHR2/DNR+ identically and did not demonstrate any binding to P-glycoprotein. Therefore, even though the study confirms the close link between vinca alkaloid binding and P-glycoprotein, it could not detect a similar association between anthracyclines and P-glycoprotein thus attesting to the complexity of the MDR phenotype.

Methotrexate: studies on cellular metabolism. III.--Effect on the transplasma-membrane redox activity and on ferricyanide-induced proton extrusion by HeLa cells

The effect of methotrexate (MTX) on transplasma-membrane electron transport and ferricyanide-induced proton extrusion by HeLa cells was studied. Both systems were inhibited by MTX. It is suggested that inhibition of electron transport and proton extrusion caused by MTX could be associated with other metabolic alterations such as response to the increase in NADH levels and decrease in intracellular pH.

Effects of vanadate on the oxidation of NADH by xanthine oxidase

Vanadate (V(V)) stimulates the oxidation of NADH by xanthine oxidase and superoxide dismutase eliminates the effect of V(V). Paraquat stimulates both the oxidation of NADH by xanthine oxidase and the V(V) enhancement of that oxidation. Xanthine, which is a better substrate for xanthine oxidase than is NADH, causes a V(V)-dependent co-oxidation of NADH which is transient and eliminated by SOD. Urate inhibits the V(V)-stimulated oxidation of NADH by xanthine oxidase or by Rose Bengal plus light. Measurement of rates of both O2- production and V(V)-stimulated NADH oxidation showed that many molecules of NADH were oxidized per O2-. These chain lengths were an inverse function of overall reaction rate. Minimum chain lengths, calculated on the basis of 100% univalent reduction of O2 to O2-, were smaller than measured average chain lengths by a factor of five. All of these results are in accord with the view that V(V) does not directly affect the activity of the enzyme, but rather catalyzes the free radical chain oxidation of NADH by O2-. It was further shown that phosphate was not involved and that the active form of V(V) was orthovanadate, rather than decavanadate.

Free radical formation by antitumor quinones

Quinones are among the most frequently used drugs to treat human cancer. All of the antitumor quinones can undergo reversible enzymatic reduction and oxidation, and form semiquinone and oxygen radicals. For several antitumor quinones enzymatic reduction also leads to formation of alkylating species but whether this involves reduction to the semiquinone or the hydroquinone is not always clear. The antitumor activity of quinones is frequently linked to DNA damage caused by alkylating species or oxygen radicals. Some other effects of the antitumor quinones, such as cardiotoxicity and skin toxicity, may also be related to oxygen radical formation. The evidence for a relationship between radical formation and the biological activity of the antitumor quinones is evaluated.

Vanadate-stimulated oxidation of NAD(P)H

Vanadate stimulates the oxidation of NAD(P)H by biological membranes because such membranes contain NAD(P)H oxidases which are capable of reducing dioxygen to O2- and because vanadate catalyzes the oxidation of NAD(P)H by O2-, by a free radical chain mechanism. Dihydropyridines, such as reduced nicotinamide mononucleotide (NMNH), which are not substrates for membrane-associated NAD(P)H oxidases, are not oxidized by membranes plus vanadate unless NAD(P)H is present to serve as a source of O2-. When [NMNH] greatly exceeds [NAD(P)H], in such reaction mixtures, one can observe the oxidation of many molecules of NMNH per NAD(P)H consumed. This reflects the chain length of the free radical chain mechanism. We have discussed the mechanism and significance of this process and have tried to clarify the pertinent but confusing literature.

A study on the mechanism of the vanadate-dependent NADH oxidation

The mechanism of the vanadate (V(V]-dependent oxidation of NADH was different in phosphate buffers and in phosphate-free media. In phosphate-free media (aqueous medium or HEPES buffer) the vanadyl (V(IV] generated by the direct V(V)-dependent oxidation of NADH formed a complex with V(V). In phosphate buffers V(IV) autoxidized instead of forming a complex with V(V). The generated superoxide radical (O2-) initiated, in turn, a high-rate free radical chain oxidation of NADH. Phosphate did not stimulate the V(V)-dependent NADH oxidation catalyzed by O2--generating systems. Monovanadate proved to be a stronger catalyzer of NADH oxidation as compared to polyvanadate.

Vanadate-stimulated NADH oxidation requires polymeric vanadate, phosphate and superoxide

NADH oxidation, catalyzed by the microsomal enzyme system is stimulated on addition of polymeric vanadate. Maximum stimulation by polymeric vanadate was obtained in the presence of phosphate buffer. The small stimulation obtained by metavanadate (500 microM) increased on acidification followed by neutralization, or on adding a trace amount of polymeric vanadate (1 microM).

Peroxide(s) of vanadium: a novel and potent insulin-mimetic agent which activates the insulin receptor kinase

The actions of insulin, vanadate (V) and hydrogen peroxide (H2O2) on IGF-II binding and insulin receptor tyrosine kinase activity were studied in rat adipocytes. Incubating adipocytes with a combination of V plus H2O2 resulted in a potent synergistic effect on both the increase in IGF-II binding and the activation of the insulin receptor kinase. Catalase, which removes H2O2, abolished this synergism if added at the time of mixing of V plus H2O2 but not if added 10 min. later, suggesting that the formation of peroxide(s) of vanadate generated a potent insulin mimicker. The data support a critical role for the insulin receptor kinase in insulin action. The novel insulin-mimetic compound, a presumed peroxide of vanadate, could prove useful for investigating insulin action and may be valuable for treating insulin resistance.

Alteration of EGF-receptor binding in human breast cancer cells by antineoplastic agents

Polypeptide growth factors bind to membrane receptors on human breast cancer cells and stimulate cell proliferation, suggesting that they may be important in growth regulation. Inhibition of the stimulatory effects of these factors might result in antineoplastic activity. Since cytotoxic drugs have been shown to alter cell membrane characteristics, we have examined the effects of a variety of antitumor drugs on the binding of epidermal growth factor (EGF) to the membrane receptor of human breast cancer cells. Twenty-four standard or investigational cytotoxic drugs were screened at a concentration of one-tenth the achievable peak plasma level for their ability to inhibit binding of 125I-EGF to its receptor in MCF-7 human breast cancer cells. Although at this concentration statistically significant inhibition of binding was observed with 11 drugs, the maximum inhibition observed was only 27%. Five agents, representing classes of drugs with different modes of action, were then studied in more detail. Of these, preincubation with 5-fluorouracil, 4-hydroperoxy-cylophosphamide and doxorubicin inhibited MCF-7 colony formation in a dose-dependent manner, but these drugs had no effect on EGF-binding even at a concentration of 10 times the peak plasma level. Preincubation of cells with vinblastine and cisplatin, however, resulted in both reduced colony survival and a parallel reduction in EGF receptor binding. Membrane integrity, as measured by trypan blue exclusion, was not altered. Scatchard analysis of EGF binding demonstrated that the major effect of cisplatin was a reduction in binding affinity. We conclude that cisplatin and vinblastine at high concentrations can inhibit the binding of EGF to human breast cancer cells offering an additional possible mechanism for their antiproliferative activity.

The vanadate-stimulated oxidation of NAD(P)H by biomembranes is a superoxide-initiated free radical chain reaction

Rat liver microsomes catalyze a vanadate-stimulated oxidation of NAD(P)H, which is augmented by paraquat and suppressed by superoxide dismutase, but not by catalase. NADPH oxidation was a linear function of the concentration of microsomes in the absence of vanadate, but was a saturating function in the presence of vanadate. Microsomes did not catalyze a vanadate-stimulated oxidation of reduced nicotinamide mononucleotide (NMNH), but gained this ability when NADPH was also present. When the concentration of NMNH was much greater than that of NADPH a minimal average chain length could be calculated from 1/2 the ratio of NMNH oxidized per NADPH added. The term chain length, as used here, signifies the number of molecules of NMNH oxidized per initiating event. Chain length could be increased by increasing [vanadate] and [NMNH] and by decreasing pH. Chain lengths in excess of 30 could easily be achieved. The Km for NADPH, arrived at from saturation of its ability to trigger NMNH oxidation by microsomes in the presence of vanadate, was 1.5 microM. Microsomes or the outer mitochondrial membrane was able to catalyze the vanadate-stimulated oxidation of NADH or NADPH but only the oxidation of NADPH was accelerated by paraquat. The inner mitochondrial membrane was able to cause the vanadate-stimulated oxidation of NAD(P)H and in this case paraquat stimulated the oxidation of both pyridine coenzymes. Our results indicate that vanadate stimulation of NAD(P)H oxidation by biomembranes is a consequence of vanadate stimulation of NAD(P)H or NMNH oxidation by O-2, rather than being due to the existence of vanadate-stimulated NAD(P)H oxidases or dehydrogenases.

Vanadate-stimulated NADH oxidation by xanthine oxidase: an intrinsic property

Vanadate-dependent oxidation of NADH by xanthine oxidase does not require the presence of xanthine and therefore is not due to cooxidation. Addition of NADH or xanthine had no effect on the oxidation of the other substrate. Oxidation of NADH was high at acid pH and oxidation of xanthine was high at alkaline pH. The specific activity was relatively very high with NADH. Concentration-dependent oxidation of NADH Concentration-dependent oxidation of NADH was obtained in the presence of the polymeric form of vanadate, but not orthovanadate or metavanadate. Both NADH and NADPH were oxidized, as in the nonenzymatic system. Oxidation of NADH, but not xanthine, was inhibited by KCN, ascorbate, MnCl2, cytochrome c, mannitol, Tris, epinephrine, norepinephrine, and triiodothyronine. Oxidation of NADH was accompanied by uptake of oxygen and generation of H2O2 with a stoichiometry of 1:1:1 for NADH:O2:H2O2. A 240-nm-absorbing species was formed during the reaction which was different from H2O2 or superoxide. A mechanism of NADH oxidation is suggested wherein Vv and O2 receive one electron each successively from NADH followed by VIV giving the second electron to superoxide and reducing it to H2O2.

Effect of adriamycin on experimental proliferative vitreoretinopathy in the rabbit

The cell injection model of proliferative vitreoretinopathy (PVR) in the rabbit was used to study the therapeutic value of intravitreal adriamycin (doxorubicin). Adriamycin in a dose of 10 nmol per eye, if injected at the same time as the cells, controls PVR. At the cell doses used, PVR is not affected if there is a time interval between cell and drug injection. Because of retinal toxicity, as evidenced by electroretinographic and histopathologic changes, the beneficial effects of adriamycin on membrane formation cannot be exploited at this time.

Superoxide radical reactions with anthracycline antibiotics

The reaction of superoxide with daunorubicin or its aglycones in the aprotic solvents dimethyl sulfoxide and dimethylformamide was studied. This interaction generated the blue anthracycline phenolate anion as monitored by u.v.-visible spectrometry and molecular oxygen as determined by a modified Clark-type oxygen electrode. The visible spectrum of the phenolate anion (gamma max 604, 652 nm) was subject to considerable shifts dependent on the size of the cation present. The phenolate anion could be further oxidized by molecular oxygen to generate the C-6, C-11 (B-ring) semiquinone as detected by a weak electron paramagnetic resonance spectrometry signal. These results raise the possibility that similar reactions of superoxide with anthracyclines in vivo may play a role in the antitumor activity and/or the etiology of the toxic side effects of this class of drugs.

Further studies of the mechanism of the enhancement of NADH oxidation by vanadate

O2-., whether generated photochemically, or introduced as a solution of KO2 in a nonprotic solvent, caused rapid oxidation of NADH in the presence, but not in the absence of vanadate. Superoxide dismutase inhibited this vanadate-stimulated oxidation of NADH, while catalase had no effect. This NADH oxidation appears to be a free-radical chain reaction whose average chain length was estimated to be 15 in the photochemical system. Vanadate stimulation of NADH oxidation by biological membranes can now be viewed as a sensitive indicator of O2-. production by those membranes.

Hyperpolarization of mouse skeletal muscle plasma membrane induced by extracellular NADH

Extracellularly applied NADH, but not NAD or NADPH, increases the resting membrane potential from -74.1 to -76.6 mV in freshly isolated muscles in the presence of K+ in the incubation medium and from -64.6 to -72.9 mV in muscles equilibrated for 4-6 h in a K+-free solution. The NADH-induced hyperpolarization is blocked by pretreatment of muscles with ouabain, and the inhibitors of plasma membrane NADH dehydrogenase (adriamycin, azide, PCMB, atebrine, DIDS and bleomycin). The effect of NADH is accompanied by the disappearance of NADH from the incubation medium and by decreased membrane resistance. We conclude that NADH hyperpolarization is due to the enhancement of passive membrane permeability, apparently for K+, which might result from the conformational changes in the plasma membrane during the NADH dehydrogenase reaction. The possibility is discussed that NADH dehydrogenase mediates transport of K+ out from the cell using a pathway connected with the transmembrane Na+/K+ pump.

Inhibition of plasma membrane NADH dehydrogenase by adriamycin and related anthracycline antibiotics

Doxorubicin (adriamycin) is cytotoxic to cells, but the biochemical basis for this effect is unknown, although intercalation with DNA has been proposed This study suggests that the cytotoxicity of this drug may be due to inhibition of the plasma membrane redox system, which is involved in the control of cellular growth. Concentrations between 10(-6) - 10(-7) M adriamycin inhibit plasma membrane redox reactions greater than 50%. AD32, a form of adriamycin which does not intercalate with DNA, but is cytotoxic, also inhibits the plasma membrane redox system. Thus, the cytotoxic effects of adriamycin, which limit its use as a drug, may be based on the inhibition of a transplasma membrane dehydrogenase involved in a plasma membrane redox system.

Lipid peroxidation and possible hydroxyl radical formation stimulated by the self-reduction of a doxorubicin-iron (III) complex

In the presence of ferric ions, doxorubicin forms a complex which self-reduces the iron moiety to form a ferrous complex. This ferrous complex can generate active radicals able to degrade deoxyribose as well as form a species greatly stimulatory towards lipid peroxidation. Both reactions may explain the damage to different sites within the body associated with doxorubicin therapy.

A link between transport and plasma membrane redox system(s) in carrot cells

Carrot (Daucus carota L.) cells grown in suspension culture oxidized exogeneous NADH. The NADH oxidation was able to stimulate K+ (86Rb+) transport into cells, but it did not affect sucrose transport. N,N'-Dicyclohexyl-carbodiimide, diethylstilbestrol, and oligomycin, which only partially inhibited NADH oxidation, almost completely collapsed the K+ (86Rb+) transport. Vanadate, which is less effective as an ion transport inhibitor, was less effective in inhibiting the NADH-driven transport of K+ (86Rb+). p-Fluormethoxycarbonylcyanide phenylhydrazone inhibits the K+ transport over 90% including that induced by NADH. The results are interpreted as evidence that a plasma membrane redox system in root cells is closely associated with the ATPase which can drive K+ transport. Because of the inhibitor effects, it appears that membrane components common to the redox system and ATPase function in the transport of K+.

DNA damage by superoxide-generating systems in relation to the mechanism of action of the anti-tumour antibiotic adriamycin

A mixture of NADPH and ferredoxin reductase is a convenient way of reducing adriamycin in vitro. Under aerobic conditions the adriamycin semiquinone reacts rapidly with O2 and superoxide radical is produced. Superoxide generated either by adriamycin:ferredoxin reductase or by hypoxanthine:xanthine oxidase can promote the formation of hydroxyl radicals in the presence of soluble iron chelates. Hydroxyl radicals produced by a hypoxanthine:xanthine oxidase system in the presence of an iron chelate cause extensive fragmentation in double-stranded DNA. Protection is offered by catalase, superoxide dismutase or desferrioxamine. Addition of double-stranded DNA to a mixture of adriamycin, ferredoxin reductase, NADPH and iron chelate inhibits formation of both superoxide and hydroxyl radicals. This is not due to direct inhibition of ferredoxin reductase and single-stranded DNA has a much weaker inhibitory effect. It is concluded that adriamycin intercalated into DNA cannot be reduced.

Transformed liver cells have modified transplasma membrane redox activity which is sensitive to adriamycin

Electron transport across the plasma membrane is found in all cells which have been tested. This activity has been implicated in control of cellular growth, transport and hormone response. In virus transformed cells and tumor cells we find the activity is decreased and becomes sensitive to the antitumor drug adriamycin. Inhibition of transmembrane redox by adriamycin parallels cytoxicity to transformed cells.

Adriamycin causes up regulation of epidermal growth factor receptors in actively growing cells

We have demonstrated a drug-dependent increase in the capacity of HeLa and 3T3 cells, grown in the presence of lethal and sublethal concentrations of adriamycin, to bind epidermal growth factor (EGF). Scatchard analysis ascribes this effect to an increase in the number of binding sites, with little change in affinity. The time course of binding of 125I-EGF is unchanged by adriamycin treatment, in both 3T3 and HeLa cells, at both 0 and 37 degrees C. This increase appears gradually over 3 or 4 days' exposure to the drug and is reversible over a similar period. Although in HeLa cells the increase reaches a maximum of about 4-fold, regardless of cell density, the maximum observed in 3T3 cells, over 100-fold, is seen only at low cell densities. This could be related to the density-dependent growth regulation seen in 3T3 cells, but not in HeLa cells. We suggest that the ability of the anticancer agent adriamycin to alter the cellular response to a growth-regulatory substance may be related to the mechanism of its cytotoxic action.

Iron and copper in plasma membranes

Nonheme iron has been found in pig erythrocyte and mouse liver plasma membranes. The amount found, 8.2 nmol/mg protein in erythrocyte membranes and 7.4 nmol/mg protein in liver plasma membrane, is slightly lower than values reported for endoplasmic reticulum and Golgi apparatus. Less than one-third of the erythrocyte membrane iron can be released by acid treatment, which indicates that most of it is not in the typical iron-sulfur structure. Copper has been found in pig erythrocyte plasma membrane at a concentration of 0.45 nmol/mg protein. These metals may be associated with the redox enzymes of plasma membranes.

Differential effects of metal ligands on synaptic membrane glutamate binding and uptake systems

The high affinity, Na+-independent L-[3H]glutamate binding process in synaptic membranes and in the purified binding protein was shown to be inhibited to an almost equal extent by the metal ligands NaN3, KCN, and o-phenanthroline, and by 2,4,5-trihydroxyphenylalanine (6-OH DOPA). The high affinity, Na+-dependent glutamate transport activity in these membranes was almost totally insensitive to NaN3, o-phenanthroline, KCN, and 6-OH DOPA. These agents, especially 6-OH DOPA, may be useful tools in achieving a discrimination between putative physiologic receptors and uptake carrier sites for L-glutamate in synaptic membranes. The sensitivity of the glutamate binding sites to the effects of the metal ligands may be correlated to the presence of an iron-sulfur center in the purified glutamate binding protein. some of the characteristics of this metallic center were explored by optical and paramagnetic resonance spectroscopic techniques and are described in this study.

Adriamycin-induced decrease of myocardial contraction reserve in rats treated with dobutamine

Muscle-mechanical and hemodynamic properties were measured in adriamycin-treated rats and in untreated controls. The respective parameters in both animal groups could not be distinguished at rest. Using a pharmacological stress test with dobutamine a differentiation of both groups was possible: the concentration-response curve of papillary muscles from ADM-rats was lower and shifted towards higher concentrations when compared with the respective curve of untreated animals. The maximum hemodynamic response following an i.v. bolus injection of dobutamine was considerably decreased in ADM-rats as compared to untreated rats. It is concluded that the estimation of impaired myocardial function due to adriamycin might be more accurate when the contraction reserve is evaluated.

Generation of hydrogen peroxide on oxidation of NADH by hepatic plasma membranes

The oxidation of NADH by mouse liver plasma membranes was shown to be accompanied by the formation of H2O2. The rate of H2O2 formation was less than one-tenth the rate of oxygen uptake and much slower than the rate of reduction of artificial electron acceptors. The optimum pH for this reaction was 7.0 and the Km value for NADH was found to be 3 X 10(-6) M. The H2O2-generating system of plasma membranes was inhibited by quinacrine and azide, thus distinguishing it from similar activities in endoplasmic reticulum and mitochondria. Both NADH and NADPH served as substrates for plasma membrane H2O2 generation. Superoxide dismutase and adriamycin inhibited the reaction. Vanadate, known to stimulate the oxidation of NADH by plasma membranes, did not increase the formation of H2O2. In view of the growing evidence that H2O2 can be involved in metabolic control, the formation of H2O2 by a plasma membrane NAD(P)H oxidase system may be pertinent to control sites at the plasma membrane.