NAMI-A inhibits the PMA-induced ODC gene expression in ECV304 cells: involvement of PKC/Raf/Mek/ERK signalling pathway

Imidazolium trans-imidazole dimethyl sulfoxide tetrachlororuthenate (NAMI-A) is a new compound active against lung metastasis of solid metastasizing tumours. While its in vivo effect has been studied, the molecular insights that underlie its action are largely unknown. Among the possible pathways responsible for malignant transformation, PKC arose as one of the most promising targets for new antineoplastic drugs. We demonstrated the capability of NAMI-A of inhibiting PMA induced-PKC activity in ECV304 in a dose-dependent fashion. Furthermore, NAMI-A through modulation of PKC activity has been proved capable of reducing the phorbol ester induced expression of ornithine decarboxilase (ODC) gene and to abrogate the activation of the Raf/MEK/ERK pathway. Taken together these results suggest that many of the in vivo outcomes of NAMI-A treatment may be the result of a direct action on PKC.

Resveratrol inhibition of lipid peroxidation

To define the molecular mechanism(s) of resveratrol inhibition of lipid peroxidation we have utilized model systems that allow us to study the different reactions involved in this complex process. Resveratrol proved (a) to inhibit more efficiently than either Trolox or ascorbate the Fe2+ catalyzed lipid hydroperoxide-dependent peroxidation of sonicated phosphatidylcholine liposomes; (b) to be less effective than Trolox in inhibiting lipid peroxidation initiated by the water soluble AAPH peroxyl radicals; (c) when exogenously added to liposomes, to be more potent than alpha-tocopherol and Trolox, in the inhibition of peroxidation initiated by the lipid soluble AMVN peroxyl radicals; (d) when incorporated within liposomes, to be a less potent chain-breaking antioxidant than alpha-tocopherol; (e) to be a weaker antiradical than alpha-tocopherol in the reduction of the stable radical DPPH*. Resveratrol reduced Fe3+ but its reduction rate was much slower than that observed in the presence of either ascorbate or Trolox. However, at the concentration inhibiting iron catalyzed lipid peroxidation, resveratrol did not significantly reduce Fe3+, contrary to ascorbate. In their complex, our data indicate that resveratrol inhibits lipid peroxidation mainly by scavenging lipid peroxyl radicals within the membrane, like alpha-tocopherol. Although it is less effective, its capacity of spontaneously entering the lipid environment confers on it great antioxidant potential.

Spectrophotometric measurement of hydroperoxides at increased sensitivity by oxidation of Fe2+ in the presence of xylenol orange

The method, developed by modifying the FOX methods described by Wolff (Methods Enzymol. 233, 182-189, 1994), involves the oxidation of Fe2- by peroxides at low pH in the presence of both the ferric-complexing dye xylenol orange and sucrose, the amplifier of the reaction. The method proved to be a convenient, simple and efficient assay for the direct measurement of both water and lipid soluble peroxides. In fact it improves by about 60% the sensitivity of the FOX1 method for water soluble peroxides, and by 7-8 times that of the FOX2 method for lipid soluble peroxides. It allows the detection of 0.1 microM peroxide in the test solution. The method is suitable to measure the lipid hydroperoxides present in phosphatidylcholine liposomes and in human LDL. The data obtained allowed us to define a mathematical expression to calculate the lipid hydroperoxide content of liposomes knowing their oxidation index.

Heparin down-regulates the phorbol ester-induced protein kinase C gene expression in human endothelial cells: enzyme-mediated autoregulation of protein kinase C-alpha and -delta genes

Overexpression of protein kinase C-alpha and protein kinase C-delta has been shown to modulate a number of biological effects, including the cell growth and differentiation. We hypothesized that heparin, a potent antimitogenic drug, could affect the cell proliferation by inhibiting the expression of specific protein kinase C genes. Heparin, markedly but not completely, inhibited the serum-stimulated protein kinase C-alpha and -delta mRNA expression. Protein kinase C inhibition or down-regulation significantly decreased the serum-induced protein kinase C isoenzyme gene expression. Heparin failed to inhibit the residual effect of serum that was resistant to the above-mentioned treatments. Phorbol 12-myristate 13-acetate elicited an increase of protein kinase C isoenzyme gene expression that was completely prevented by protein kinase C inhibition or down-regulation. Heparin dose-dependently counteracted and ultimately abolished the increase in the protein kinase C isoenzyme gene expression elicited by phorbol 12-myristate 13-acetate. These results suggest that the inhibition of an autoregulatory role wielded by protein kinase C on the protein kinase C-alpha and -delta gene expression might represent a possible mechanism by which glycosaminoglycans modulate the cell growth.

Carvedilol inhibition of lipid peroxidation. A new antioxidative mechanism

To define the molecular mechanism(s) of carvedilol inhibition of lipid peroxidation we have utilized model systems that allow us to study the different reactions involved in this complex process. Carvedilol inhibits the peroxidation of sonicated phosphatidylcholine liposomes triggered by FeCl2 addition whereas atenolol, pindolol and labetalol are ineffective. The inhibition proved not to be ascribable (a) to an effect on Fe2+ autoxidation and thus on the generation of oxygen derived radical initiators; (b) to the scavenging of the inorganic initiators O2*- and *OH; (c) to an effect on the reductive cleavage of organic hydroperoxides by FeCl2; (d) to the scavenging of organic initiators. The observations that (a) carvedilol effectiveness is inversely proportional to the concentration of FeCl2 and lipid hydroperoxides in the assay; (b) the drug prevents the onset of lipid peroxidation stimulated by FeCl3 addition and; (c) it can form a complex with Fe3+, suggest a molecular mechanism for carvedilol action. It may inhibit lipid peroxidation by binding the Fe3+ generated during the oxidation of Fe2+ by lipid hydroperoxides in the substrate. The lag time that carvedilol introduces in the peroxidative process would correspond to the time taken for carvedilol to be titrated by Fe3+; when the drug is consumed the Fe3+ accumulates to reach the critical parameter that stimulates peroxidation. According to this molecular mechanism the antioxidant potency of carvedilol can be ascribed to its ability to bind a species, Fe3+, that is a catalyst of the process and to its lipophilic nature that concentrates it in the membranes where Fe3+ is generated by a site specific mechanism.

Nuclear opioid receptors activate opioid peptide gene transcription in isolated myocardial nuclei

Opioid-binding sites were identified in highly purified nuclei isolated from hamster ventricular myocardial cells. A significant increase in the maximal binding capacity for a kappa opioid receptor ligand was observed in myocardial nuclei from BIO 14.6 cardiomyopathic hamsters, as compared with nuclei obtained from normal myocytes of the F1B strain. The exposure of isolated nuclei to dynorphin B, a natural agonist of kappa opioid receptors, markedly increased opioid peptide gene transcription. The transcriptional effect was mediated by nuclear protein kinase C activation and occurred at a higher rate in nuclei from cardiomyopathic myocytes than in nuclei isolated from normal cells. Thus, a nuclear endorphinergic system may play an intracrine role in the regulation of gene transcription under both normal and pathological conditions.

Heparin inhibits phorbol ester-induced ornithine decarboxylase gene expression in endothelial cells

Glycosaminoglycans regulate angiogenesis by affecting the availability of different growth factors for the endothelial cell (EC). However, little is known about the molecular and functional consequences resulting from direct interaction of these polyelectrolytes with the EC. Here we show that heparin markedly inhibited serum-stimulated DNA synthesis and ornithine decarboxylase (ODC) mRNA expression in human endothelial cells (HEC). About 50% of the serum effect on DNA synthesis and ODC gene expression was prevented by the selective protein kinase C (PKC) inhibitor chelerythrine or by PKC down-regulation. Heparin was ineffective in counteracting that part of the effect of serum that was resistant to PKC inhibition or down-regulation. In serum-free cultured HEC, heparin completely abolished the increase in DNA synthesis and ODC mRNA expression elicited by a number of PKC activators. Cell exposure to difluoromethylornithine, an irreversible inhibitor of ODC enzyme, dramatically antagonised both serum- and phorbol 12-myristate 13-acetate (PMA)-stimulated DNA synthesis. These results suggest that inhibition of PKC-mediated ODC gene expression by glycosaminoglycans may represent an important mechanism in the regulation of HEC proliferation.

Iron (III) stimulation of lipid hydroperoxide-dependent lipid peroxidation

In an experimental system where both Fe2+ autoxidation and generation of reactive oxygen species is negligible, the effect of FeCl2 and FeCl3 on the peroxidation of phosphatidylcholine (PC) liposomes containing different amounts of lipid hydroperoxides (LOOH) was studied; Fe2+ oxidation, oxygen consumption and oxidation index of the liposomes were measured. No peroxidation was observed at variable FeCl2/FeCl3 ratio when PC liposomes deprived of LOOH by triphenylphosphine treatment were utilized. By contrast, LOOH containing liposomes were peroxidized by FeCl2. The FeCl2 concentration at which Fe2+ oxidation was maximal, defined as critical Fe2+ concentration [Fe2+]*, depended on the LOOH concentration and not on the amount of PC liposomes in the assay. The LOOH-dependent lipid peroxidation was stimulated by FeCl3 addition; the oxidized form of the metal increased the average length of radical chains, shifted to higher values the [Fe2+]* and shortened the latent period. The iron chelator KSCN exerted effects opposite to those exerted by FeCl3 addition. The experimental data obtained indicate the kinetics of LOOH-dependent lipid peroxidation depends on the Fe2+/Fe3+ ratio at each moment during the time course of lipid peroxidation. The results confirm that exogenously added FeCl3 does not affect the LOOH-independent but the LOOH-dependent lipid peroxidation; and suggest that the Fe3+ endogenously generated exerts a major role in the control of the LOOH-dependent lipid peroxidation.

Opioid peptide gene expression in the primary hereditary cardiomyopathy of the Syrian hamster. II. Role of intracellular calcium loading

We have previously shown that prodynorphin gene expression was markedly increased in adult myocytes of BIO 14.6 cardiomyopathic hamsters and that nuclear protein kinase C (PKC) may be involved in the induction of this opioid gene. Here we report that the cytosolic Ca2+ concentration was significantly increased in resting and in KCl-depolarized cardiomyopathic myocytes compared with normal cells. In normal and in cardiomyopathic cells, KCl significantly increased prodynorphin mRNA levels and prodynorphin gene transcription. These effects were abolished by the Ca2+ channel blocker verapamil. In control myocytes, the KCl-induced increase in prodynorphin mRNA expression was in part attenuated by chelerythrine or calphostin C, two selective PKC inhibitors. In these cells, KCl induced the translocation of PKC-alpha into the nucleus, increasing nuclear PKC activity. In resting cardiomyopathic myocytes, the increase in prodynorphin mRNA levels and gene transcription were significantly attenuated by the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxy-methylester being completely abolished when the chelating agent was administered in the presence of PKC inhibitors. KCl and the PKC activator 1,2-dioctanoyl-sn-glycerol additively stimulated prodynorphin gene expression both in normal and in cardiomyopathic cells. Therefore, we conclude that PKC activation and intracellular Ca2+ overload may represent the two major signaling mechanisms involved in the induction of the prodynorphin gene in cardiomyopathic cells.

The mechanism of iron (III) stimulation of lipid peroxidation

A study conducted on Fe2+ autoxidation showed that its rate was extremely slow at acidic pH values and increased by increasing the pH; it was stimulated by Fe3+ addition but the stimulation did not present a maximum at a Fe2+/Fe3+ ratio approaching 1:1. The species generated during Fe(3+)-catalyzed Fe2+ autoxidation was able to oxidize deoxyribose; the increased Fe2+ oxidation observed at higher pHs was paralleled by increased deoxyribose degradation. The species generated during Fe(3+)-catalyzed Fe2+ autoxidation could not initiate lipid peroxidation in phosphatidylcholine liposomes from which lipid hydroperoxides (LOOH) had been removed by treatment with triphenylphosphine. Neither Fe2+ oxidation nor changes in the oxidation index of the liposomes due to lipid peroxidation were observed at pHs where the Fe3+ effect on Fe2+ autoxidation and on deoxyribose degradation was evident. In our experimental system, a Fe2+/Fe3+ ratio ranging from 1:3 to 2:1 was unable to initiate lipid peroxidation in LOOH-free phosphatidylcholine liposomes. By contrast Fe3+ stimulated the peroxidation of liposomes where increasing amounts of cumene hydroperoxide were incorporated. These results argue against the participation of Fe3+ in the initiation of LOOH-independent lipid peroxidation and suggest its possible involvement in LOOH-dependent lipid peroxidation.

Phorbol ester regulation of opioid peptide gene expression in myocardial cells. Role of nuclear protein kinase

Opioid peptide gene expression was characterized in adult rat ventricular cardiac myocytes that had been cultured in the absence or the presence of phorbol 12-myristate 13-acetate. The phorbol ester induced a concentration- and time-dependent increase of prodynorphin mRNA, the maximal effect being reached after 4 h of treatment. The increase in mRNA expression was suppressed by incubation of cardiomyocytes with staurosporine, a putative protein kinase C inhibitor, and was not observed when the cells were cultured in the presence of the inactive phorbol ester 4 alpha-phorbol 12,13-didecanoate. Incubation of cardiac myocytes with phorbol 12-myristate 13-acetate also elicited a specific and staurosporine-sensitive increase in immunoreactive dynorphin B, a biologically active end product of the precursor, both in the myocardial cells and in the culture medium. In vitro run-off transcription assays indicated that transcription of the prodynorphin gene was increased both in nuclei isolated from phorbol ester-treated myocytes and in nuclei isolated from control cells and then exposed to phorbol 12-myristate 13-acetate. No transcriptional effect was observed when cardiac myocytes or isolated nuclei where exposed to 4 alpha-phorbol 12,13-didecanoate. The phorbol ester-induced increase in prodynorphin gene transcription was prevented by pretreatment of myocytes or isolated nuclei with staurosporine, suggesting that myocardial opioid gene expression may be regulated by nuclear protein kinase C. In this regard, cardiac myocytes expressed protein kinase C-alpha, -delta, -epsilon, and -zeta, as shown by immunoblotting. Only protein kinase C-delta and protein kinase C-epsilon were expressed in nuclei that have been isolated from control myocytes, suggesting that these two isotypes of the enzyme may be part of the signal transduction pathway involved in the effect elicited by the phorbol ester on opioid gene transcription in isolated nuclei. The incubation of myocardial nuclei isolated from control cells in the presence of a protein kinase C activator induced the phosphorylation of the myristoylated alanine-rich protein kinase C substrate peptide, a specific fluorescent substrate of the enzyme. The possibility that prodynorphin gene expression may control the heart function through autocrine or paracrine mechanisms is discussed.

Effects of taurine and hypotaurine on lipid peroxidation

It has been suggested that hypotaurine might inhibit lipid peroxidation in vivo by scavenging the initiator OH. The results presented demonstrate that hypotaurine affects other reactions relevant to the initiation, propagation and termination phases of lipid peroxidation. Hypotaurine a) decreases Fe2+ autoxidation, either spontaneous or catalyzed by Fe3+, that may generate perferryl iron; b) decreases Fe2+ oxidation, by cumene hydroperoxide, that forms the alkoxy radical; c) inhibits the lipid hydroperoxide dependent lipid peroxidation, favoring the onset of the termination phase. Hypotaurine does not affect the autoxidation of Fe2+ bound to phosphatidic acid containing liposomes. Taurine is ineffective in all the experimental systems tested.

Effect of age and extent of dietary restriction on hepatic microsomal lipid peroxidation potential in mice

Lipid peroxidation potential in hepatic microsomes from young and old mice following two different caloric restriction regimens was measured by a colorimetric thiobarbituric acid method under conditions where Fe2+ autoxidation and free oxygen radical production were undetectable. Peroxidation was highest in the young (3.5-month-old) slightly restricted group (caloric intake 75% of ad libitum mice) but very low in young severely restricted (caloric intake 50% of ad libitum mice) and in both old (27-month-old) slightly and severely restricted groups. Very old (45-month-old) severely restricted animals had intermediate lipid peroxidation potentials. Fatty acid composition of liver homogenates was also determined. Significant differences between groups were found for only three fatty acids. Linoleic acid (18:2(n-6)) decreased in aged slightly restricted animals while it remained stable in severely restricted animals during aging. Dihomo-gamma-linolenic acid (20:3(n-6)) was higher in very old restricted animals than in old slightly restricted animals. Docosahexaenoic acid (22:6(n-3)) decreased in old slightly restricted animals. These results indicated that the effect of diets on hepatic fatty acid composition and the potential for microsomal lipid peroxidation in mice was dependent on the degree of caloric restriction and age.

Fe3+ binding to liposomes of different phospholipid composition

The possibility that phospholipid polar heads may influence lipid peroxidation by affecting the binding and location of the metal catalyst was investigated. The multilamellar liposomes containing dimyristoyl phosphatidylcholine (DMPC) and an equal amount of either dipalmitoyl phosphatidylcholine (DPPC) or dipalmitoyl phosphatidic acid (DPPA) were utilized to study Fe3+ location. Two simple colorimetric methods were utilized, which were developed to evaluate: a) Fe3+ both sequestered within and bound in a non reducible form on the surface of the liposomes; Fe3+ chelated to strong complexing agents present both on the surface and in the inner compartment of the liposomes. The results obtained clearly show that the two types of polar heads differently bind the metal. Whereas DMPC/DPPC liposomes do not affect Fe3+ detection by both methods, suggesting that the metal is not internalized and strongly bound, DMPC/DPPA liposomes greatly interfere with Fe3+ detection. Analysis of the binding data indicates that a large amount of the metal is sequestered by the liposomes both in a complexed and free form.

Phospholipid polar heads affect the generation of oxygen active species by Fe2+ autoxidation

The possibility that phospholipid polar heads may influence Fe2+ reaction with molecular oxygen and, thus, the generation of oxygen active species was investigated. Dipalmitoyl phosphatidylcholine (DPPC) and DPPC/dipalmitoyl phosphatidic acid (DPPA) were utilized as model liposomes. Fe2+ oxidation, oxygen consumption, nitro blue tetrazolium reduction and 2-deoxyribose degradation were the parameters evaluated. Comparison of the results obtained clearly shows that the two types of polar heads differently affect iron chemistry. DPPC liposomes are ineffective. By contrast, Fe2+ oxidation by oxygen occurs in the presence of DPPC/DPPA liposomes. During this reaction, species able to reduce nitro blue tetrazolium and to degrade 2-deoxyribose are generated. The results obtained indicate that the polar heads of phospholipids, by influencing Fe2+ autoxidation, generate dangerous oxygen species which may exert an active role in the oxidation of the associated hydrophobic components of the phospholipids.

The influence of phospholipid polar head on the lipid hydroperoxide dependent initiation of lipid peroxidation

In a buffer (Mes) and at a pH (6.5) where Fe2+ is very stable, we have studied the peroxidation of liposomes catalyzed by FeCl2. The liposomes studied, prepared by sonolysis, contained either phosphatidylcholine or 1:1 molar ratio of phosphatidylcholine and phosphatidic acid. The presence of the negatively charged phospholipid causes: 1) rapid Fe2+ oxidation and oxygen consumption; 2) increased generation of lipid hydroperoxides; 3) decreased generation of thiobarbituric acid-reactive materials; 4) very low inhibition of Fe2+ oxidation and lipid hydroperoxide generation by BHT; 5) inhibition of the termination phase of lipid peroxidation at high FeCl2 concentrations. A hypothesis is proposed to explain the results obtained.

The influence of pH on OH. scavenger inhibition of damage to deoxyribose by Fenton reaction

Hydroxyl radicals (OH.) can be formed in aqueous solution by direct reaction of hydrogen peroxide (H2O2) with ferrous salt (Fenton reaction). OH. damage to deoxyribose, measured as formation of thiobarbituric acid-reactive material, was evaluated at different pHs to study the mechanism of action of classical OH. scavengers. OH. scavenger effect on Fe2+ oxidation was also evaluated in the same experimental conditions. In the absence of OH. scavengers, OH. damage to deoxyribose is higher at acidic compared to neutral and moderately basic pH. At acidic pH deoxiribose is per se able to inhibit Fe2+ oxidation by H2O2. Most of OH. scavengers tested inhibit deoxyribose damage and Fe2+ oxidation in a similar manner: both inhibitions are most relevant at acidic pH and decrease by increasing the pH. These results are not due to OH. scavenger inhibition of Fenton reaction. The influence of pH on the parameters studied appears to be due to the competition of deoxyribose and OH. scavengers for iron. These results suggest the prominent role of iron binding in the degradation of deoxyribose and in the OH. scavenging ability of different compounds. Results obtained with triethylenetetramine, a iron chelator with a low rate constant with OH., confirm that both deoxyribose and the OH. scavengers interact with iron bringing about a site specific Fenton reaction; that the OH. formed at these sites oxidize these molecules to their radical forms which in turn reduce the Fe3+ produced by Fenton reaction. The results presented indicate that most of classical OH. scavengers exert their effect predominantly by preventing the site specific reaction between Fe2+ and H2O2 on the deoxyribose molecule.

Effect of spermine on association of protein kinase C with phospholipid vesicles

The in vitro mechanism by which polyamines affect protein kinase C (PK C) activation process was investigated in a reconstituted system consisting of purified enzyme and phospholipid vesicles of various phosphatidylserine content. It was found that the addition of spermine greatly interferes with the association of PK C to liposomes. This tetramine, at micromolar concentrations, was most potently effective while other polyamines such as spermidine and putrescine were almost ineffective; therefore the modulatory action appeared to be structure specific. The spermine effect is dramatically influenced by the density of the phosphatidylserine present on the liposome, suggesting the complex formation with the acidic component on phospholipid vesicles to be the mechanism by which this polyamine exerts its modulatory action.

The influence of polyunsaturated fatty acids on spermine inhibition of lipoperoxidation. Studies on liposomes prepared with microsomal and mitochondrial phospholipids of sea bass (Dicentrarchus labrax L.) and rat liver

1. Composition of phospholipids extracted from different organelles of European sea bass liver was determined and compared with that of phospholipids extracted from the same organelles of rat liver. 2. Spermine binding to the vesicles prepared from microsomal and mitochondrial phospholipids and their aggregation was studied: these parameters indicate that only the presence of acidic phospholipids and not their unsaturation was essential for polyamine action. 3. No correlation exists between polyunsaturated fatty acid and spermine inhibition of lipid peroxidation. In fact microsomal phospholipids, which have a low content of acidic phospholipids, and a prevalent presence of phosphatidylinositol, are not protected by spermine. 4. Mitochondrial phospholipids, which have high content of cardiolipin, elicit the capability of spermine to inhibit lipid peroxidation.

Lipid peroxidation. Definition of experimental conditions for selective study of the propagation and termination phases

To find experimental conditions to selectively study the propagation phase of lipoperoxidation we studied the lipoperoxidation, catalyzed by FeCl2, of liposomes in a buffering condition where Fe2+ autoxidation and oxygen active species generation does not occur. Liposomes from egg yolk phosphatidylcholine, prepared by vortex mixing, do not oxidize Fe2+; on the contrary they oxidize Fe2+ when prepared by ultrasonic irradiation. Dimyristoyl phosphatidylcholine liposomes prepared by ultrasonic irradiation do not oxidize Fe2+. During sonication polyunsaturated fatty acid residues autoxidize and lipid hydroperoxides (LOOH) are generated. Only when LOOH are present in the liposomes Fe2+ oxidizes and its rate of oxidation depends on the amount of LOOH in the assay. The reaction results in the generation of both LOOH and thiobarbituric acid reactive material (TBAR); it is inhibited by butylated hydroxytoluene and has a acidic pH optimum; it is not inhibited by catalase and OH scavengers. The reaction studied, thus, appears to be the chain branching and propagation phase of lipoperoxidation. When we studied the dependence of Fe2+ oxidation, LOOH and TBAR generation on FeCl2 concentration, we observed that at high FeCl2 concentrations the termination phase of lipoperoxidation was prevalent. Thus, by selecting the appropriate FeCl2 concentration the proposed experimental system allows study of either the propagation or the termination phase of lipoperoxidation.

Oxygen toxicity. The influence of adenine-nucleotides and phosphate on Fe2+ autoxidation

FeCl2 in Na phosphate buffer autoxidizes forming active oxygen species which damage deoxyribose. Di- and triphosphate adenine-nucleotides inhibit both Fe2+ autoxidation and deoxyribose damage in Na phosphate buffer pH 7.4. The inhibition is related to the number of charges of the adenine-nucleotide molecule: ATP at pH 7.4 is a better inhibitor than ADP; at a pH (6.5) close to the pK's of the third and fourth charge of ADP and ATP, ADP inhibition is greatly decreased whereas ATP inhibition is slightly affected. The extent of ATP inhibition of Fe2+ autoxidation depends both on ATP/Mg2+ and ATP/Fe2+ ratios in the reaction mixture. Formation of a Fe2+-nucleotide complex appears to be the mechanism through which ATP and ADP inhibit autoxidation and thus the generation of active oxygen species. These findings are discussed in relation to physiological and pathological fluctuations of nucleotide concentrations.

The influence of polyamine-nucleic acid complexes on Fe2+ autoxidation

Polyamines are able to affect Fe2+ autoxidation in the presence of suitable low molecular weight phosphorus-containing compounds; the inhibitory effect exerted by polyamines is directly related to their ability to bind phosphorus-containing compounds. It is well known that polyamines, as polycations at physiological pH, bind strongly to nucleic acids. In this paper it is shown that polyamines, also in the presence of nucleic acids, inhibit Fe2+ autoxidation and thus depress the generation of free oxygen radicals. Most of the nucleic acids tested inhibited Fe2+ autoxidation although the concentration which causes half maximal effect differs. Polyamine effect on Fe2+ autoxidation varies greatly depending on the single or double stranded nature of the nucleic acid. In the present of single stranded nucleic acids, spermine and spermidine potentiate the inhibition of Fe2+ autoxidation by these nucleic acids. A relationship exists between the ability of spermine to interact with single stranded nucleic acids and to inhibit Fe2+ autoxidation in their presence. When double stranded nucleic acids are present, polyamines reverse the inhibition of Fe2+ autoxidation exerted by these nucleic acids. Molecular mechanisms are proposed to explain these experimental results. The hypothesis that polyamines may inhibit oxidative damage caused to nucleic acids by Fe2+ autoxidation, is also discussed.

Polyamine inhibition of lipoperoxidation. The influence of polyamines on iron oxidation in the presence of compounds mimicking phospholipid polar heads

Polyamines appear to inhibit peroxidation of vesicles containing acidic phospholipids. A correlation exists between polyamine binding to phospholipid vesicles and its protective effect. However, phosphatidylinositol-containing vesicles which bind spermine are not protected by the polyamine [Tadolini, Cabrini, Landi, Varani & Pasquali (1985) Biogenic Amines 3, 97-106]. In the present paper I tested the hypothesis that polyamines, in particular spermine, by forming a ternary complex with iron and the phospholipid polar head may change the susceptibility of Fe2+ to autoxidation and thus its ability to generate free oxygen radicals. Different compounds mimicking phospholipid polar heads were studied, namely AMP, mimicking phosphatidic acid, CDP-choline, mimicking phosphatidylcholine, and glycerophosphoinositol, mimicking phosphatidylinositol. The results support the proposed hypothesis. In the presence of CDP-choline or of glycerophosphoinositol, spermine poorly affects Fe2+ autoxidation, whereas a considerable inhibition is observed in the presence of AMP. The ability of other phosphorus-containing compounds (ATP, ADP, cyclic AMP, sodium phosphate) to affect Fe2+ autoxidation in the presence of polyamines was also evaluated to understand the molecular mechanism of this phenomenon. It is proposed that polyamines may be part of the passive cellular defence mechanism against the oxidative damage caused by Fe2+.

Inhibitory action of polyamines on protein kinase C association to membranes

Physiological activation of protein kinase C requires the interaction of this enzyme with cellular membranes [Nishizuka (1986) Science 233, 305-312]. In the present work a reconstituted system of protein kinase C and human inside-out erythrocyte vesicles was utilized to study the effect in vitro of naturally occurring polyamines on the activation process of protein kinase C. The active membrane-associated complex was conveniently determined by its ability to bind radioactive phorbol ester with an exact 1:1 stoichiometry. The association reaction of the enzyme to membrane was rapid, being complete within 1 min at 25 degrees C. The addition of polyamines, particularly spermine, greatly decreased in a dose-dependent manner the amount of protein kinase C bound to membranes (i.e. in the activated form). The effect observed was quite specific, since it was dependent on the chemical structure of the polyamine and it was manifest at micromolar concentrations of the polycation; the order of potency was spermine greater than spermidine greater than putrescine. A characterization of this effect is presented and possible physiological implications are discussed.

Iron autoxidation in Mops and Hepes buffers

Iron autoxidation in Mops and Hepes buffers is characterized by a lag phase that becomes shorter with increasing FeCl2 concentration and pH. During iron oxidation in these buffers a yellow colour develops in the solution. When the reaction is conducted in the presence of nitro blue tetrazolium (NBT), blue formazan is formed. Of the many OH scavengers tested, mannitol and sorbitol are most effective in inhibiting Fe2+ oxidation, yellow colour development and NBT reduction. Some inhibition was also noted with catalase. The iron product of the oxidative reaction differs from Fe3+ in its absorption spectrum and its low reactivity with thiocyanate. Similar results are obtained when iron autoxidation is studied in unbuffered solutions brought to alkaline pH with NaOH. In phosphate buffer, no lag phase is evident and the absorption spectrum of the final solution is identical to that of Fe3+ in this buffer. The iron product reacts immediately with thiocyanate. When iron oxidation is conducted in the presence of NBT the formation of formazan is almost undetectable. Of the many compounds tested only catalase inhibits iron autoxidation in this buffer. The sequence of reactions leading to iron autoxidation in Good-type buffers thus resembles that occurring in unbuffered solutions brought to alkaline pH with NaOH and greatly differs from that occurring in phosphate buffer. These results are in agreement with the observation that these buffers have very low affinity for iron. The data presented define experimental conditions where Fe2+ is substantially stable for a considerable length of time in Mops buffer.

Iron oxidation in Mops buffer. Effect of phosphorus containing compounds

Fe2+ autoxidation in Mops buffer both in absence and presence of substoichiometric concentrations of EDTA, H2O2 and of Fe3+ is greatly affected by phosphorus containing compounds. They increase the lag phase, characteristic of Fe2+ oxidation in this buffer, and decrease the rate of the reaction. This effect is due to the phosphates of the molecule. The ability of the different compounds tested to affect Fe2+ oxidation, however, appears to be influenced also by the rest of the molecule. The concentration of the different phosphorus containing compounds that inhibits 50% of Fe2+ oxidation is rather different. The effect exerted appears to be the result of an equilibrium between an inhibitory effect on the pathway of Fe2+ oxidation that occurs in Mops buffer and the onset of a different oxidation pathway of Fe2+ similar to that occurring in Na phosphate buffer. A hypothesis is proposed that the phosphorus containing compounds inhibit Fe2+ oxidation by binding Fe3+ and decreasing its ability to accelerate Fe2+ autoxidation. It is suggested that the presence in vitro and in vivo of phosphorus containing compounds may modify Fe2+ autoxidation and thus the production of oxygen active species.

Iron oxidation in Mops buffer. Effect of EDTA, hydrogen peroxide and FeCl3

The effect of EDTA and H2O2 on iron autoxidation in Mops buffer depends on the pH of the solution. At acidic pH, EDTA caused the oxidation of a stoichiometric amount of iron. At neutral and alkaline pH, EDTA and H2O2 not only oxidizes a stoichiometric amount of iron but also causes the oxidation of the Fe2+ exceeding the concentration of these compounds. In the presence of EDTA, oxidation of Fe2+ in exceeding the concentration of these compounds has a shorter lag phase and an increased rate compared with that in the absence. The solution develops a yellow colour whose intensity is proportional to the amount of Fe2+ exceeding the concentration of these compounds in solution. When the reaction is conducted in the presence of NBT, formazan formation is greatly reduced compared to the control without EDTA and H2O2. The Fe3+-EDTA complex and Fe3+ affected iron oxidation, development of the yellow colour and NBT reduction in a similar fashion. In all these experimental conditions, iron oxidation is greatly reduced in the presence of mannitol, sorbitol and catalase. In phosphate buffer, EDTA oxidized a stoichiometric amount of iron without affecting free Fe2+ oxidation. Fe3+ has no effect on iron oxidation in this buffer.

The influence of poly(ethylene glycol) 6000 on spermine-induced aggregation of liposomes

Poly(ethylene glycol) 6000 affected the aggregation of mixed liposomes induced by spermine. It lowered the concentration of spermine causing 50% maximal aggregation, accelerated the rate and increased the extent of aggregation. The effect was inversely proportional to the density of the acidic phospholipid in the vesicles. These effects were not due either to poly(ethylene glycol) 6000-induced permanent structural modification of the liposome or increased binding of spermine to the vesicles. These findings are discussed in relation to a decreased hydration force caused by the ability of poly(ethylene glycol) 6000 to alter the water of hydration of the phospholipid polar groups in the liposome.

Interaction of spermine with polyphosphoinositides containing liposomes and myo-inositol 1,4,5 triphosphate

The interaction of spermine with liposomes containing 2% phosphatidylinositol, phosphatidylinositol 4 phosphate and phosphatidylinositol 4,5 biphosphate was inferred from the ability of these liposomes to interfere with spermine binding to the resin heparin-Sepharose. The inositol phospholipids tested showed different affinities for spermine: the order of binding strength appear to be phosphatidylinositol phosphatidylinositol 4 phosphate phosphatidylinositol 4,5 biphosphate. The ability of vesicles containing 2% polyphosphoinositides to interact with spermine is comparable to that of either single stranded RNAs or highly negatively charged liposomes. Myo-inositol 1,4,5 triphosphate has a much lower ability to bind spermine.

Intracellular location of polyamines associated to red blood cells

The polyamines associated to human erythrocytes from healthy donors are mainly localized intracellularly. In fact chromatography of the erythrocytes on a resin which has a high affinity and capacity for polyamines does not affect the amount of polyamines associated to the erythrocytes. The low ability of spermine to adsorb to the external surface of erythrocytes at physiological ionic strength is suggested also by studies conducted with sealed ghosts. Also erythrocytes from patients with hematological and dermatological diseases which contain increased levels of polyamines show an intracellular location of these amines.

Antioxidant behaviour of ubiquinone and beta-carotene incorporated in model membranes

Experiments with model membranes, in which ubiquinone was incorporated, were performed in order to clarify the mechanism by which ubiquinone can prevent or control chain lipid peroxidation in biomembranes. Comparing the behavior of ubiquinone-containing vesicles with beta-carotene containing vesicles we suggest that a possible explanation of the ubiquinone antioxidant effect could be to scavenge singlet oxygen and to affect structurally the lipid bilayer inhibiting hydroperoxide decomposition.

Incorporation of ubiquinones into lipid vesicles and inhibition of lipid peroxidation

Ubiquinone incorporation into vesicles to evaluate its antioxidative effect on lipid peroxidation has been studied. Only sonication and not vortication allows comparable incorporation patterns of the various ubiquinone homologues into lipid vesicles. The measure of malondialdehyde, a convenient index for determining the extent of autoxidation, shows that both the naturally occurring homologues and synthetic shorter-chain ones, also in the oxidized form, possess similar antioxidant efficiency.

Determination of the polyamine content of rat heart mitochondria by the use of heparin-sepharose

Heparin-sepharose has been utilized to remove polyamines adsorbed to the cytoplasmic surface of rat heart mitochondria. The results obtained can be summarized as follows: Heparin-sepharose removes 90% of the spermine, 98% of the spermidine, and 98% of the putrescine adsorbed. Polyamine contents of chromatographed mitochondria amount to 2.66 and 0.36 nmol spermine and spermidine, respectively, per mg of mitochondrial protein.

Polyamine binding to phospholipid vesicles and inhibition of lipid peroxidation

A study of the possible mechanism of inhibition by polyamines of lipid peroxidation was made utilizing vesicles prepared with mixed soy bean phospholipids. The results obtained can be summarized as follows: 1) Polyamines inhibit lipid peroxidation only when bound to the negative charges on vesicle surface. 2) Polyamines inhibit lipid peroxidation at concentrations lower than those required to cause precipitation of the vesicles and similar to those required for formation of the polyamine/phospholipid vesicle complex. 3) Spermine bound to vesicles, in contrast to free spermine, highly decreases the reactivity of both Fe2+ and Fe3+ versus superoxide.

Representative applications of heparin-sepharose in the removal of polyamines from biological materials

Many experimental systems would greatly benefit from the availability of a simple and effective technique to remove polyamines from biological materials. We have examined the possibility of utilizing heparin-sepharose in the removal of polyamines from rat heart mitochondria, DNA-spermine complex, and fetal calf serum. Heparin-sepharose removes 90% of spermine adsorbed to the cytoplasmic surface of rat heart mitochondria. Heparin-sepharose almost totally removes spermine from DNA-spermine complex, leaving less than 0.003 mol spermine/mol DNA phosphorus. Heparin-sepharose is highly effective in removing spermine and spermidine (99.5 and 95% adsorbed, respectively) from fetal calf serum. Under the same experimental conditions only 50% of putrescine is adsorbed. A higher amount of resin corresponding to an increased capacity for putrescine must be used to achieve a satisfactory removal of putrescine.

Spermine binding to submitochondrial particles and activation of adenosine triphosphatase

Studies on the effects of polyamines on oligomycin-sensitive ATPase activity of ox heart submitochondrial particles showed that, of the polyamines tested, only spermine affected the enzyme activity. Spermine within the physiological concentration range increased the Vmax. of the enzyme, but the Km for ATP was virtually unaffected. Binding studies of [14C]spermine to submitochondrial particles, under the same conditions as used for the ATPase assay, showed that the spermine binds to submitochondrial particles in a co-operative way; Hill plots of the data gave a Hill coefficient of 2 and a Kd of 8 microM. When submitochondrial particles were treated with trypsin, ATPase was not stimulated by spermine and the amount of spermine bound concomitantly was drastically decreased. The ATPase activity of isolated F1-ATPase was not affected by spermine. Removal of the natural protein ATPase inhibitor did not suppress either the stimulation of the ATPase activity by spermine or the spermine binding to the particles. The results obtained suggested that the polyamine binds and acts at the level of the liaison between the coupling factor F1 and the membrane sector F0 of the ATPase complex.

Heparin-sepharose as a tool in the subcellular fractionation of a polyamine-rich organ (rat ventral prostate)

Heparin-sepharose forms complexes with putrescine, spermidine, and spermine and indirect measurements of its affinity for polyamines gives values similar to those obtained with free heparin. A direct measurement of the binding of heparin-sepharose to spermine gives an apparent dissociation constant (Kd) of 1.5 X 10(-6)M spermine. Unlike free heparin, heparin-sepharose does not cause either disruption of the nuclei or more sutble modifications able to modify their sedimentation behavior. The heparin-sepharose polyamine complex formed by the addition of heparin-sepharose to the homogenate can easily be removed and the homogenate can be processed according to normal schedules. Heparin-sepharose is able to sequester 85% of the exchangeable spermine present in the homogenate of rat ventral prostate. The distribution of the marker enzyme galactosyltransferase (Golgi apparatus) on a sucrose density gradient was followed to assess the usefulness of heparin-sepharose in minimizing the aggregation of cellular organelles brought about by polyamines.

Isolation of a Golgi rich fraction from rat ventral prostate

Unmodified procedures for isolation of fractions rich in Golgi elements from other tissues have not proved applicable to the rat ventral prostate because of the tendency of membranous material to aggregate. We have devised a new procedure whereby: 1) a Golgi rich fraction from rat ventral prostate was released by a gentle two-step homogenization and isolated by centrifugation through discontinuous sucrose density gradients; 2) the specific activity of UDP-galactose: glycoprotein galactosyltransferase increased 69-fold in this fraction; 3) the isolated Golgi fraction was reasonably free from mitochondria, lysosomes, endoplasmic reticulum and plasma membranes as shown by the relatively low activities of marker enzymes; 4) the specific activities of acid phosphatase and 5'-nucleotidase in the Golgi rich fraction was 4 times greater than that in prostate homogenate. Both enzymes are secretory products and their presence in Golgi elements is probably associated with their packaging in secretory granules.

Glycoprotein glycosyltransferases in male reproductive organs and their hormonal regulation

The prostate glands of rats, mice, guinea pigs and hamsters were found to be a rich source of enzymes catalyzing the Mn2+-dependent transfer of galactose from UDP-galactose to glycoprotein acceptors such as ovomucoid and ovalbumin. The ventral prostate was also very active in promoting transfer of fucose from GDP-fucose to ovomucoid. The prostatic enzymes promoting both galactosyl and fucosyl transfers to glycoproteins were very largely membrane-bound, and were markedly activated by the non-ionic detergent Triton X-100. Castration of adult male resulted in a many-fold and roughly parallel decline in both glycosyltransferase activities over a period of two weeks, which was reversed by subsequent daily treatment with testosterone for 8 days. The very low galactosyltransferase of the ventral prostate of hypophysectomized rats was markedly enhanced by testosterone administration, whereas prolactin alone or in combination with androgen had no significant effect.