Radiolabeled metaiodobenzylguanidine (mibg) in diagnosis and therapy of neuroblastoma - results from basic research (review)

[I-131]mIBG, meta-iodobenzylguanidine, a catecholamine analogous compound, was synthesized by Wieland et al in 1979. It has been used for scintigraphic imaging of normal sympathetic tissue, of pheochromocytoma, and since 1983/84 also of neuroblastoma. Later, protocols for treatment of neuroblastoma stage IV using high dose [I-131]mIBG were established. In this review the basic mechanisms concerning uptake and storage of mIBG in neuroblastoma cells as well as the cytotoxic effects of unlabeled and radiolabeled mIBG are documented. Results of these investigations have promoted the development of new concepts for optimizing the application of mIBG in diagnosis and therapy of neuroblastoma.

Efficient in vitro generation of adult multipotent cells from mobilized peripheral blood CD133+ cells

OBJECTIVES

To generate non-haematopoietic tissues from mobilized haematopoietic CD133(+) stem cells.

MATERIALS AND METHODS

Mobilized peripheral blood CD133(+) cells from adult healthy donors were used. In vitro ability of highly enriched CD133(+) cells from mobilized peripheral blood to generate multipotent cells, and their potential to give rise to cells with characteristics of neuroectoderm, endoderm and mesoderm layers was investigated.

RESULTS

We found that a recently identified population of CD45(+) adherent cells generated in vitro after culture of highly purified CD133(+) cells for 3-5 weeks with Flt3/Flk2 ligand and interleukin-6 can, in presence of the appropriate microenvironmental cues, differentiate into neural progenitor-like cells (NPLCs), hepatocyte-like cells and skeletal muscle-like cells. We have termed them to be adult multipotent haematopoietic cells (AMHCs). AMHC-derived NPLCs expressed morphological, phenotypic and molecular markers associated with primary neural progenitor cells. They can differentiate into astrocyte-like cells, neuronal-like cells and oligodendrocyte-like cells. Moreover, AMHC-derived NPLCs produced 3,4-dihydrophenylalanine and dopamine and expressed voltage-activated ion channels, suggesting their functional maturation. In addition, AMHC-derived hepatocyte-like cells and skeletal muscle-like cells, showed typical morphological features and expressed primary tissue-associated proteins.

CONCLUSION

Our data demonstrate that AMHCs may therefore serve as a novel source of adult multipotent cells for autologous replacement cell therapies.

Niemann-Pick disease type A and B are clinically but also enzymatically heterogeneous: pitfall in the laboratory diagnosis of sphingomyelinase deficiency associated with the mutation Q292 K

This study describes a diagnostic pitfall in the laboratory diagnosis of patients with sphingomyelinase deficiency (SMD; Niemann-Pick disease types A and B; NPA and NPB), in cases where sphingomyelinase activity was not determined with sphingomyelin as the natural enzymic substrate. Four of 24 SMD patients studied had falsely normal or enhanced activity, when a so-called artificial sphingomyelinase substrate, 2-N-(hexadecanoyl)-amino-4-nitrophenyl phosphorylcholine (HNP), was used, whereas SMD was clear with the sphingomyelin substrate. Those four patients had the Q292 K mutation of the acid sphingomyelinase gene (SMPD1) on at least one allele. Three of the four patients (no data available from one) experienced only late-infantile or juvenile, though distinct, neurological involvement, where learning disabilities, hypo- or areflexia or mild ataxia were initial signs. The laboratory pitfall with HNP substrate, which is used in many laboratories, raises the risk that some SMD patients are overlooked, and it prevents the consideration of a late-manifesting neurological course in some patients as well as the planning of enzyme substitution therapy in non-neurological SMD (NPB) patients. Since classical NPB is very rare, it is suggested that SMD patients with late- or mild-manifesting neurological symptoms should better be assigned to additional SMD subgroups than grouped with NPB.

Reconstitution of bactericidal activity in chronic granulomatous disease cells by glucose-oxidase-containing liposomes

Chronic granulomatous disease (CGD) is an inherited primary immunodeficiency characterized by phagocytes devoid of a functioning nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. The failure of CGD phagocytes to produce reactive oxygen species (ROS) results in a marked increase in the susceptibility of affected patients to life-threatening bacterial and fungal infections. This study investigated whether loading of CGD phagocytes with glucose oxidase (GO)-containing liposomes (GOLs) could restore cellular production of bactericidal ROS (eg, H2O2 and HOCl) in vitro. Results indicate that GO encapsulated in liposomes enabled NADPH oxidase-deficient phagocytes to use H2O2 for the production of highly bactericidal HOCl. The intracellular colocalization of bacteria and liposomes (or liposome-derived ferritin) was demonstrated by confocal laser microscopy and electron microscopy. After uptake of GOLs (approximately 0.2 U/mL at 1 mM total lipid concentration, size approximately 180 nm), CGD granulocytes produced HOCl levels comparable to those of normal phagocytes. Remarkably, after treatment with GOLs, CGD phagocytes killed Staphylococcus aureus as efficiently as normal granulocytes. Moreover, treated cells retained sufficient motility toward chemotactic stimuli as measured by chemotaxis assay. Side effects were evaluated by measuring the H2O2 concentrations and the production of methemoglobin in whole blood. These studies revealed that H2O2 produced by GOLs was degraded immediately by the antioxidative capacity of whole blood. Elevated methemoglobin levels were observed only after application of extremely high amounts of GOLs (2 U/mL). In summary, the application of negatively charged GOLs might provide a novel effective approach in the treatment of patients with CGD at high risk for life-threatening infections.

Analysis of metabolites of glucose pathways in human erythrocytes by analytical isotachophoresis

The aim of this study was to establish an isotachophoretic (ITP) method for the determination of the main compounds of glycolysis in human erythrocytes in order to analyze the influence of different glucose concentrations (mimicking the situation in diabetes mellitus) on this pathway. Samples for ITP were prepared by isolation of erythrocytes, lysis of the cells by heating in double-distilled water and subsequent ultrafiltration (Mr cut-off: 5000). All the main compounds of glycolysis were characterized by ITP. The influence of different glucose concentrations on the main compounds of the energy metabolism (ATP, ADP, lactate, pyruvate) and 2,3-diphosphoglycerate were analyzed in short- and long-time incubations.

6-fluorodopamine selectively destroys neuroblastoma cells expressing the noradrenaline transporter

BACKGROUND

6-Hydroxydopamine (6-OHDA) was used for ex vivo purging of bone marrow from neuroblastoma cells before autologous transplantation. However, this concept failed because of the rapid autoxidation of 6-OHDA, which leads to the generation of cytotoxic reactive oxygen species (ROS), mainly in the incubation medium before 6-OHDA can be incorporated by neuroblastoma cells.

PROCEDURE

We based our experiments on the theory that, in contrast, 6-fluorodopamine (6-FDA), which is slowly converted to 6-OHDA at neutral pH, is able to enter neuroblastoma cells via the noradrenaline transporter (NA-T). Therefore, most ROS are generated inside the target cells.

RESULTS

Small amounts of ascorbate prevent the extracellular conversion of 6-FDA to 6-OHDA without affecting its cytotoxicity, leading to an even more selective effect of 6-FDA.

CONCLUSIONS

We conclude that 6-FDA is a promising substance for selective destruction of NA-T-positive neuroblastoma cells.

Effect of amifostine on neuroblastoma during high dose chemotherapy: in vivo and in vitro investigations

Amifostine (Ethyol, WR-2721) has been clinically used in combination with high dose therapy of neuroblastoma stage 4 with melphalan, carboplatin and VP-16 in 14 patients. The amifostine group was compared to a historical control group of 24 comparably-treated patients. There were no significant differences regarding the time of hematological recovery, the duration of hospitalization, the duration of antibiotic treatment and the extent of renal toxicity. However, in contrast to four patients of the control group, no patient in the amifostine group developed such severe mucositis that artificial ventilation became necessary. Pretreatment of neuroblastoma cell lines for 30 minutes with amifostine and the free thiol(WR-1065) did not reduce the cytotoxic effects of melphalan, carboplatin and VP-16. Evidence was obtained that the uptake of the activated thiol could be achieved by a polyamine transporter. Taken together, the data do not support the use of amifostine in high dose chemotherapy of neuroblastoma prior to autologous stem cell transplantation. However, amifostine may be more effective in conventional neuroblastoma therapy where protection of bone marrow stem cells is necessary.

Isotachophoretic analysis of the dihydrofolate reductase reaction in the presence of methotrexate and ascorbic acid

The antifolate methotrexate (MTX) is widely used in cancer chemotherapy. In this study, we show that MTX (MTX-Glu1) and MTX-polyglutamates (MTX-Glu2-5) strongly inhibited the growth of the leukemic cell line MOLT-4. This effect, however, was mitigated by ascorbic acid. We investigated whether ascorbic acid is able to reduce dihydrofolic acid (DHF) to tetrahydrofolic acid (THF) directly or by circumventing the MTX inhibition of dihydrofolate reductase (DHFR). The inhibition of this NADPH-dependent reduction of DHF by MTX-Glun in the absence or presence of ascorbate, was determined by analytical isotachophoresis. Using 0.01 M HCl/histidine, pH 6.0, as a leading electrolyte (L) and 0.005 M 2-(N-morpholino)ethanesulfonic acid (MES)/histidine, pH 6.0, as a terminating electrolyte (T), MTX-Glun derivatives including MTX-Glu1 could be easily separated, whereas the quantitative estimation of THF was not possible. A quantitative characterization of the DHFR reaction by measuring NADPH, NADP+ and ascorbate was achieved with another system (L: 0.01 M HCI/beta-alanine, pH 3.73; T: 0.01 M caproic acid, pH 3.27). Nanomolar concentrations of MTX-Glu1-5 inhibited consumption of NADPH and production of NADP+. Ascorbic acid was not able to reduce DHF, neither directly nor after inhibition of DHFR by MTX. However, ascorbic acid seemed to diminish the oxidation of THF and this may account for its capacity to reduce the inhibitory effect of MTX on MOLT-4 cells.

Neuroblastoma cells expressing the noradrenaline transporter are destroyed more selectively by 6-fluorodopamine than by 6-hydroxydopamine

6-Hydroxydopamine (6-OHDA) has been used for lesioning catecholaminergic neurons and attempted purging of neuroblastoma cells from hematopoietic stem cells in autologous bone marrow transplantation (ABMT). Neurotoxicity is mediated primarily by reactive oxygen species. In ABMT, 6-OHDA, as a purging agent, has been unsuccessful. At physiological pH it autooxidizes before targeted uptake, resulting in nonspecific cytotoxicity of nontarget cells. A catecholamine analogue, similar to 6-OHDA but with a lower rate of autooxidation enabling uptake by target cells, is thus required. Electron paramagnetic resonance spectra in this study show that 6-fluorodopamine (6-FDA) hydrolyzes slowly to 6-OHDA at physiological pH. Oxygen consumption, H(2)O(2), and quinone production are found to be intermediate between those of 6-OHDA and dopamine (DA). Relative neurotoxicity of these compounds was assessed by cell viability and DNA damage in the human neuroblastoma lines SH-SY5Y and SK-N-LO, which express and lack the noradrenaline transporter, respectively. Specific uptake of DA and 6-FDA by SH-SY5Y cells was demonstrated by competitive m-[(131)I]iodobenzylguanidine uptake inhibition. The competition by 6-OHDA was low owing to rapid autooxidation during incubation with equal toxicity toward both cell types. 6-FDA toxicity was preferential for SH-SY5Y cells and reduced in the presence of desipramine, a catecholamine uptake inhibitor. We demonstrate that 6-FDA cytotoxicity is more specific for cells expressing catecholamine reuptake systems than is 6-OHDA cytotoxicity.

Detection by ELISA of low transferrin levels in bronchoalveolar secretions of preterm infants

Transferrin levels in bronchoalveolar secretions (BAS) are very low compared to serum levels in humans. For the exact measurement of transferrin concentrations in BAS a very sensitive assay was developed as a double sandwich enzyme immunoassay using the combination of a polyclonal and a monoclonal antibody against human transferrin. The measurable range of the assay was 1.5 to 100 ng/ml of human transferrin. The lowest measurable value was 0.84 ng/ml and the sensitivity of the assay was 0.88 ng/ml. The coefficient of variation was 14.1% for 25 ng/ml (intra-assay) and 11-20% (inter-assay). The levels measured in 123 samples of BAS of preterm infants ranged between 0.03 and 8.93 (microgram/microgram secretory component (SC)). The determination of transferrin in BAS of preterm infants is helpful in determining oxidative damage, e.g. the availability of free iron, in the neonatal lung. The transferrin concentration in BAS of neonates who recovered from respiratory distress syndrome (RDS) in the first six days of life was 0.48 compared to 0.52 ((microgram/microgram SC), median range) for infants who developed chronic lung disease.

SiMa, a new neuroblastoma cell line combining poor prognostic cytogenetic markers with high adrenergic differentiation

We describe the establishment and characterization of a new neuroblastoma (Nb) cell line, SiMa, carrying the major recurrent chromosome changes associated with poor prognosis Nb, including amplification of N-MYC by formation of double minutes (dmin), der(1)t(1;17)(p35;q12) and der(22)t(17;22)(q22;p13), and loss of chromosome 11, documented at both initiation and late passage. In contrast to these cytogenetic stigmata of poor prognosis, analysis of catecholamine synthesis by high pressure liquid chromatography (HPLC) measurement revealed an advanced degree of adrenergic differentiation with high rates of 3,4-Dihydroxyphenylalanine (DOPA), noradrenaline, homovanillic acid (HVA), and vanillylmandelic acid (VMA) production. Contrastingly advanced differentiation and poor prognostic genetic markers combine to render SiMa a unique instrument for investigating the pathology and therapy of Nb.

Isotachophoretic determination of phosphate splitting from Amifostine and p-nitrophenyl phosphate in serum and neuroblastoma cells

Amifostine [WR-2721; H2N-(CH2)3-NH-(CH2)2-S-PO3H2] is used as a protecting agent in the chemotherapy of neuroblastoma. It is supposed that Amifostine will be transformed into its active form, the free thiol (WR-1065), easier by normal cells than by tumour cells. Analytical capillary isotachophoresis was used to determine the dephosphorylation of Amifostine in serum and on neuroblastoma cells and peripheral blood cells. Furthermore, the biological effects of Amifostine and its free thiol, on cell proliferation of neuroblastoma cells were measured in combination with Carboplatin. It was found that neuroblastoma cells did not split phosphate less efficiently than normal peripheral blood cells. Furthermore, neither Amifostine (as expected) nor the free thiol (not expected according to the theory) were able to inhibit the effects of Carboplatin. Therefore, the current hypothesis concerning the mode of action of Amifostine must be questioned.

Presence of bleomycin-detectable free iron in the alveolar system of preterm infants

Chronic lung disease (CLD) is a major cause of long term morbidity in preterm infants. Reactive oxygen species (ROS) play an important role in the pathogenesis of CLD. We show that a high percentage (63 to 83%) of the investigated bronchoalveolar secretions (BAS) of neonates contain bleomycin-detectable free iron concentrations (0. 04-0.124 nmol/micrograms SC, median range). Beside the presence of redox-active iron several iron-binding proteins like transferrin, ferritin and lactoferrin were determined in BAS. Comparison of protein distribution within the first three days of life showed slight differences between the group of preterm infants who developed CLD and the neonates who recovered from RDS. Because of the existence of free iron we suggest a higher risk of hydroxyl radical formation in the alveolar space. In an artificial system with addition of iron and hydrogen peroxide we were able to demonstrate OH-radical production in BAS by electron paramagnetic resonance (EPR). OH-radical formation by H2O2 and iron in buffer solution was slightly enhanced in the presence of BAS, indicating the absence of OH-radical-scavengers in BAS.

Growth inhibition of neuroblastoma cells by lovastatin and L-ascorbic acid is based on different mechanisms

Hydroxymethyl-glutaryl-CoA-reductase (HMG-CoA-reductase), the key enzyme for cholesterol synthesis and essential for the synthesis of the precursor for p21ras farnesylation, was inhibited in neuroblastoma cells by lovastatin or L-ascorbic acid. Both compounds inhibited clonogenic colony formation of neuroblastoma cells in soft agar. However, while the addition of mevalonate, the product of HMG-CoA-reductase, circumvented the inhibition by lovastatin it had no reversing effect on the inhibition by L-ascorbic acid. The role of reactive oxygen compounds generated by the degradation of catecholamines, and the pro-oxidative effects of L-ascorbic acid are discussed as mechanisms of action of L-ascorbic acid.

Kinetics of redox interaction between substituted 1,4-benzoquinones and ascorbate under aerobic conditions: critical phenomena

Redox cycling is believed to be the most general molecular mechanism of quinone (Q) cytotoxicity. Along with redox cycling induced by a reductase, a similar process is known to occur via electron transfer from ascorbate (AscH-) to Q with formation of a semiquinone radical (Q.-): (1) Q + AscH- (k1)--> Q.- + Asc.- + H+ (2) Q.- + O2 --> Q + O2.-. The net effect of reactions (1) and (2) provides for the catalytic oxidation of AscH-, with Q serving as a catalyst. In this work, the kinetics of oxygen consumption accompanying this process were studied with several substituted 1,4-benzoquinones (BQ) at 37 degrees C in phosphate buffer, pH 7.40, using the Clark electrode technique. The value of k1 determined from the initial rate of oxygen consumption was typically found to increase when the one-electron reduction potential E(Q/Q.-) shifted to more positive values. With Q, for which E(Q/Q.-) is less than -100 mV, the rate of oxygen uptake (R(OX)) was found to be directly correlated with the [Q][AscH-] value independent of the concentration of individual reagents, remaining constant for a long period. With mono- and dialkyl-substituted 1,4-BQs, for which E(Q/Q.-) is higher than -100 mV, significant deviations from the above simple kinetic regularities were observed. In particular, R(OX) decreased dramatically with time and critical phenomena (the existence of certain concentrations of Q and/or AscH- above or below which the catalytic oxidation of AscH- ceased completely after a non-stationary period of short duration) were observed. These abnormalities can be explained on the basis of the kinetic scheme which contains, in addition to reactions (1) and (2), several side reactions including that between Q.- and AscH-. Implications of critical phenomena discovered in this study for the problems of Q toxicity and vitamin C avitaminosis are discussed.

Ascorbic acid stimulates DOPA synthesis and tyrosine hydroxylase gene expression in the human neuroblastoma cell line SK-N-SH

Ascorbic acid is well known to induce noradrenaline synthesis in sympathetic nervous cells. In a series of experiments we found that incubation of the neuroblastoma cell line SK-N-SH with ascorbic acid (100-500 microM) for 2 h results in a significantly enhanced synthesis of 3,4-dihydroxyphenylalanine (DOPA) and dopamine. Additionally, cDNA-polymerase chain reaction (cDNA-PCR) analysis of relative mRNA levels corresponding to the enzymes involved in catecholamine synthesis revealed a 3-fold increase of tyrosine hydroxylase gene expression after 5 days of incubation with ascorbic acid (200 microM), whereas expression of dopamine-beta-hydroxylase was found to be unaltered. In summary the data give evidence that ascorbic acid leads to enhanced DOPA production in SK-N-SH cells by two different mechanisms: at the metabolic level after short-term incubation and by increasing the tyrosine hydroxylase gene expression after long-term incubation. Based on these data we suppose that enhancement of DOPA synthesis by ascorbic acid may be useful in the treatment of early Parkinson's disease.

Anthracycline-derived chemotherapeutics in apoptosis and free radical cytotoxicity (Review)

Anthracycline-derivatives are frequently used chemotherapeutics in treatment of numerous human malignancies. Anthracyclines are known for their complex cytotoxic mechanism involving i) inhibition of enzymes such as topoisomerase II, RNA polymerase, cytochrome c oxidase and others; ii) intercalation into DNA; iii) chelation of iron and generation of reactive oxygen species (ROS); iv) induction of apoptosis. Here, mechanistic aspects for successful cytostasis and for side effects, e.g. cardiomyopathy, are discussed. We emphasize recent developments in anthracycline-mediated apoptosis and focus on a well known representative, doxorubicin (adriamycin, adriblastin). We reflect on the role of oxidative stress and interactions with intracellular signaling pathways.

Fully reversible redox cycling of 2,6-dimethoxy-1,4-benzoquinone induced by ascorbate

The kinetics of cyclic redox transformation of 2,6-dimethoxy-1, 4-benzoquinone (DMOBQ)--the well-known effective anticancer agent--induced by ascorbate (AscH-) were studied in phosphate buffer, pH 7.40, at 37 degreesC using the Clark electrode and ESR techniques. The process is due to the electron transfer from AscH- to quinone (Q): Q + AscH- --> Q*- + Asc.- + H+ (1), followed by semiquinone (Q.-) oxidation: Q.- + O2 --> Q + O2.- (2). DMOBQ, taken even at submicromolar concentrations, effectively catalyzed AscH- oxidation that manifested itself by intensive oxygen consumption and an increase in the steady-state concentration of the ascorbyl radical (Asc.-). The rate of oxygen consumption, ROX, was kept almost constant for a long time. ROX was found to be proportional to the [Q][AscH-] product and not dependent on the concentrations of the individual reagents. The rate constant for reaction (1) determined from ROX and [Asc.-] was as much as 380 +/- 40 and 280 +/- 30 M-1.sec-1, respectively. When DMOBQ was mixed with the corresponding hydroquinone, QH2, in oxygen-free buffer, the ESR signal of Q.- which formed due to the equilibrium Q + QH2 left and right arrow 2Q.- + 2H+ (3) was observed. The equilibrium constant K3 of (2.6 +/- 0.4).10-5 and the change in the reduction potential, DeltaE3 = E(Q/Q.-) - E(Q.-/QH2), of -280 mV were calculated from the steady-state concentration of Q.- at pH 7.4 and 37 degrees C. From combination of DeltaE3 determined in this study with E7(Q/Q.-) reported in the literature, a value of +190 mV was calculated for the standard second one-electron reduction potential E(Q*-/QH2). The latter is lower by 270-230 mV than that for all the studied 1, 4-hydroquinones. The very beneficial combination of E(Q/Q.-) and E(Q.-/QH2) was suggested to be the basic reason for the perfect work of DMOBQ as a redox cycling agent and its pronounced anticancer activity.

Ubiquinone-0 (2,3-dimethoxy-5-methyl-1,4-benzoquinone) as effective catalyzer of ascorbate and epinephrine oxidation and damager of neuroblastoma cells

The kinetics of ascorbate (AscH ) and epinephrine (EP) oxidation in the presence of 2,3-dimethoxy-5-methyl-1,4-benzoquinone (UQ) were studied in 0.05 M phosphate buffer, pH 7.4, at 37 degrees C by using a Clark electrode and ESR techniques. UQ at nanomolar concentrations displayed a pronounced catalytic effect on AscH oxidation which exceeded that of all reported organic catalysts tested in this system. The process was accompanied by the intensive oxygen consumption and increase in the steady-state concentration of the ascorbyl radical Asc.-. The rate of oxygen consumption (R[OX]) was maximal at the moment of reagent mixing ((R[OX]0) and then reduced over a few minutes until a steady-state level ((R[OX])SS) was achieved. (R[OX])0 was found to be proportional to [UQ][AscH-] without regard to the concentrations of the individual reagents; (R[OX])SS was directly related to [UQ] at a given concentration of AscH-. The difference between (R[OX])0 and (R[OX])SS decreased as [AscH-] decreased. The presence of a lipid phase (sodium dodecylsulphate micelles) only moderately decreased UQ activity as a catalyst of AscH- oxidation. Adding micromolar concentrations of UQ induced the acceleration of EP autoxidation. The capability of UQ to catalyze the oxidation of EP exceeded by approximately 25 times that of adrenochrome, a quinoid product of EP oxidation. These catalytic properties of UQ allowed us to predict its pronounced cytotoxicity, especially in the presence of AscH- and to cells of the sympathetic nervous system which are rich in catecholamines. This possibility was confirmed by experiments with human neuroblastoma cells in culture. The capability of UQ to injure neuroblastoma cell line SK-N-SH exceeded that of well-known neurotoxic agents 6-hydroxydopamine and menadione.

Toxic reactions of oxidized LDL on cells of acute myeloid leukemia

In AML patients LDL concentration of the serum is reduced due to the high LDL receptor activity of the AML cells. This phenomenon enables the use of LDL particles as vehicles for drug targeting. Toxic lipid peroxides and aldehydes were introduced into LDL particles by the simple but effective oxidation with 10 microM CuSO4. Up to 250 nmol peroxides and 6 nmol malondialdehyde were formed per mg LDL protein within 30 h of oxidation. This oxidized LDL is effectively taken up by AML cells of the FAB type M3 and M5 indicating the presence of scavenger receptors on these cells. Within 96 h 61-84% of the AML cells are killed by the oxidized LDL. Our results open a possibility to achieve specificity for targeting lipophilic antineoplastic drugs towards AML cells using oxidized LDL as vehicles. The use of oxidized LDL as drug carrier is recommended for purging of AML bone marrow because hematopoietic stem cells that don't possess scavenger receptors are protected from toxic action.

Cytotoxic effect of immunoconjugate composed of glucose-oxidase coupled to an anti-ganglioside (GD2) antibody on spheroids

As a new treatment protocol for neuroblastoma, the chimeric (human/mouse) antiganglioside GD2 antibody chl4.18 is being clinically tested. To improve the therapeutic effect of the antibody alone, we are currently investigating the cytotoxicity of glucose-oxidase coupled to the antibody chl4.18 on spheroids of the neuroblastoma cell line SK-N-LO. The cytotoxic effect of glucose-oxidase is achieved by the production of hydrogenperoxide (H2O2) and probably by the following reaction of H2O2 with iron to form hydrogen radicals (OH.). The cytotoxicity of glucose-oxidase was measured by two viability tests (MTT and WST 1). After a 4 hour treatment of the spheroids with the immunoconjugate, a reduction of viability to 50% (MTT-test) and 25% (WST 1-test), respectively, was obtained. The difference between the results of these two tests, might be explained by the different measurement protocols.

Iron bound to ferritin catalyzes ascorbate oxidation: effects of chelating agents

Ferritin is the main intracellular iron storage protein. Ferritin iron may be released by many reducing agents including ascorbate. In this work we report ferritin to catalyze the oxidation of ascorbate. The kinetics of this process were studied in detail in phosphate buffer (pH 7.40), at 37 degrees C by using the Clark electrode technique and ESR. The catalytic effect of ferritin manifested itself as the increase both in the rate of oxygen uptake and steady-state concentration of the ascorbate radical. The ferritin catalytic activity was found to be modified by iron chelators, EDTA. Desferal (DFO) as well as by ferrozine (FRZ) which is widely used in kinetic studies on ferritin iron release thanks to the formation of a coloured complex with Fe(II). While EDTA promotes the catalytic action of ferritin, DFO and FRZ diminished it. From the comparison of the kinetics of ascorbate oxidation obtained in the current work and data on the kinetics of ferritin iron release reported by Boyer and McCleary ((1987) Free Rad. Biol. Med. 3, 389-395), we conclude that iron bound to ferritin rather than the iron released is likely responsible for ferritin catalytic action. In addition, it has been concluded that the use of FRZ as an analytical reagent in kinetic studies of reductive ferritin iron release requires taking into account the competitive character of the formation of the Fe(II)-FRZ complex.

Evidence for the activation of myeloperoxidase by f-Meth-Leu-Phe prior to its release from neutrophil granulocytes

Activity and release of myeloperoxidase (MPO) was measured in heparinized whole blood samples after activation of neutrophil granulocytes by the chemoattractant N-formyl-methionyl-leucyl-phenylalanine (fMLP) using two different methods: (i) by determination of the amount of MPO released into the blood plasma using a MPO enzyme-immunoassay, and (ii) simultaneously, by measuring the remaining activity within the neutrophils by flow cytometry using the Bayer Technicon H3. Although a part of MPO was released immediately after addition of fMLP, remaining MPO activity within the neutrophils surprisingly increased during the first minutes after incubation. Subsequently, MPO activity dropped due to a continuous release of MPO. In addition to fMLP, granulocyte-macrophage colony stimulating factor (GM-CSF) enhanced MPO activity in neutrophils. These results indicate that MPO is present in resting granulocytes in an inactive or only partially active form and is activated by fMLP and GM-CSF.

Effects of cyclophosphamide and ifosfamide on neuroblastoma cells before and after activation by microsomes

Cyclophosphamide (CP) and Ifosfamide (IF) are of great importance in the therapy of neuroblastoma (NB). They are prodrugs which have to be activated by microsomes in order to become active compounds. We established a test system which allowed the activation of CP and IF by liver microsomes in the presence of NB cells. The data from these experiments showed that neuroblastoma cells (SK-N-SH, SK-N-LO and IMR-5) were unable to activate CP and IF, but in the presence of rat liver microsomes considerable cytotoxicity was achieved, similar to those of the preactivated derivatives maphosphamide (MP) and 4-hydroxy-ifosfamide (4-OH-IF). Compared to other compounds the final metabolite acrolein contributes significantly to the cytotoxicity of CP and IF, obviously through significant lowering of the glutathione levels in the cells. The incubation system as described allows the rapid determination of the cytotoxicity of CP and IF in the simultaneous presence of microsomes. The results show great differences in the sensibility of NB cells toCP and IF.

Cholesterol based antineoplastic strategies

Manipulation of cholesterol metabolism open several possibilities of interfering with the growth of malignant cells. Deprivation of cholesterol decreases the velocity of growth and alters the composition of the cell membrane. The high requirement for LDL of malignant cells can be utilized for drug targeting. Proliferation assays were performed with neuroblastoma cells and cell lines of acute myeloid leukemia deprived of cholesterol by inhibition of HMG-CoA-reductase or culture in LDL-deficient medium. The cholesterol content of the cell membrane when reduced to 50% had no effect on the toxicity of LAK-cells but the toxicity of the fluorescent dye merocyanine MC 540 was enhanced two-fold. LDL-mediated drug targeting to AML cells was performed with oxidized LDL and showed toxic reactions. These results proved that cholesterol deprivation could be used to support some therapeutic approaches.

Effect of concentration on the cytotoxic mechanism of doxorubicin--apoptosis and oxidative DNA damage

Anthracycline derivatives such as doxorubicin are part of many chemotherapeutic regimens and reach peak plasma concentrations of 5 microM. We investigated the cytotoxic mechanisms of various doxorubicin concentrations in MOLT-4 ALL-cells. Concentrations of up to 100 microM doxorubicin achieved similar cytotoxic effects in cultures of MOLT-4 cells, but acted via different mechanisms. Doxorubicin induced apoptosis (maximum effect at 1 microM), which was dependent on RNA synthesis and involved oxidative stress. Concentrations higher than 3 microM did not induce apoptosis, but significantly inhibited RNA synthesis. DNA strand breaks in MOLT-4 cells occurred in the presence of 1 to 5 microM doxorubicin to a similar extent, but showed a dose-dependence at higher concentrations. There was no GC/MS-detectable oxidation of DNA bases in apoptotic cells and only 1 out of 13 DNA base oxidation products, 8-hydroxyguanine, increased significantly in the presence of as much as 100 microM doxorubicin. These results suggest that at pharmacologically relevant concentrations apoptosis and not oxidative DNA damage is the main killing mechanism of doxorubicin against ALL-cells.

Phagocytic activity and oxidative burst of granulocytes in persons with myeloperoxidase deficiency

In the present study, phagocytosis and the oxidative metabolism of neutrophil granulocytes from five clinically healthy persons with different degrees of myeloperoxidase deficiency were investigated and compared to those of normal persons. The identification of individuals with myeloperoxidase deficiency was performed with the Bayer/Technicon H3 blood cell counter, which differentiates the leukocytes by measuring the peroxidase activity. Neutrophils of three out of five investigated myeloperoxidase deficient persons showed extremely low peroxidase indices (-53 and lower), but only the neutrophils of one person totally lacked myeloperoxidase. This was demonstrated by comparing myeloperoxidase mass concentration measured with an enzyme immunoassay, lack of HOCl production, and was further confirmed by measuring luminol- and lucigenin-enhanced chemiluminescence. Characteristically, myeloperoxidase deficient granulocytes showed a strikingly decreased luminol-enhanced chemiluminescence while the lucigenin-enhanced chemiluminescence was significantly increased compared to normal granulocytes. Although there is a DNA sequence homology of about 70%, the activity of peroxidase in eosinophils was not affected in any myeloperoxidase deficient person investigated. Moreover, a person with a very rare defect of eosinophil peroxidase had completely normal myeloperoxidase activity. The lack of myeloperoxidase activity is compensated for by an increased phagocytic activity, an increased production of superoxide anion (lucigenin-chemiluminescence) and probably by an alternative metabolism of H2O2; since persons lacking myeloperoxidase activity do not normally suffer from severe infections, H2O2 is obviously metabolized to other reactive oxygen substrates than HOCl, e.g. to OH-radicals.

Control of neuroblastoma cell proliferation and differentiation by human bone marrow

BACKGROUND

Neuroblastoma (NB) is one of the few tumors known to undergo spontaneous regression. Its progression, however, often leads to bone marrow (BM) metastasis. Proliferation and differentiation of human NB cells may be regulated in vitro by a variety of biologic agents, some of which are released by low-density BM and peripheral blood (PB) cells. Little is known regarding BM cell-derived control of NB cell growth and differentiation.

METHODS

The proliferative and differentiative responses of NB cells, to BM cell-, and to PB cell-derived conditioned medium (CM) were evaluated in comparison to cytokine-induced responses.

RESULTS

CM from unstimulated cultures of low density BM and PB cells, from healthy donors, from newborn infants, and from NB patients, significantly and reproducibly stimulate NB cell growth in vitro. The intensity of CM-induced stimulation was not attained by recombinant human tumor necrosis factor (rhTNF), interferon (rhIFN), or granulocyte-monocyte colony stimulating factor (rhGM-CSF); and although epidermal growth factor (rhEGF) and transforming growth factor alpha (rhTGF alpha) were strongly stimulatory, neutralizing antibodies against each of these agents did not affect CM-derived activity. In contrast to growth stimulation, differentiation of CM-treated NB cells, was reproducibly suppressed, as reflected in abrogation of neuronal cell morphology as well as of neurofilament and neuron specific enolase expression.

CONCLUSIONS

Spontaneous regression of NB tumors, on one hand and BM metastasis on the other may be associated with the extent and nature of the NB cell response to regulatory activity released by BM and PB cells.

Mobilization of iron from cellular ferritin by ascorbic acid in neuroblastoma SK-N-SH cells: an EPR study

The mobilization of iron from intracellular ferritin by ascorbic acid has been analysed in situ by electron paramagnetic resonance (EPR) spectroscopy. EPR enables a distinction between ferritins and other Fe(3+)-binding cellular components. The ordered iron core of ferritin gives rise to a resonance signal which can be observed only at temperatures above 50 K. In the present study we clearly demonstrate that ascorbic acid is capable of mobilizing iron from ferritin in the cellular system by reduction of the ferric ion core in neuroblastoma SK-N-SH cells. This mechanism may open new ways in the therapy of this hardly curable tumor in stage IV, especially in combination with some cytostatic drugs.

[Clinical significance of reactive oxygen species]

There is increasing evidence that reactive oxygen substances are involved in the pathogenesis and/or progression of differ diseases. A short introduction to the biochemistry of reactive oxygen substances will be given in this review. Subsequently, the role of reactive oxygen substances will be discussed exemplarily on pathophysiological aspects of neutrophil granulocytes and of neurodegenerative diseases.

Presence of iron catalytic for free radical reactions in patients undergoing chemotherapy: implications for therapeutic management

We investigated the kinetics of generation of iron 'catalytic' for free radical reactions in children with diagnosed acute lymphoblastic leukaemia (ALL) who received high-dose methotrexate infusions. In 76% of the chemotherapy courses studied, 'catalytic' iron appeared in plasma in the concentration range from 0.1 to 3 mumol/l. Positive correlations between maximum levels of 'catalytic' iron and plasma hepatic enzymes could be established in the majority of cases and in one subset of patients (low and medium risk ALL) mean 'catalytic' iron levels correlated well to clinically observable toxicities. The damaging potential of 'catalytic' iron was also demonstrated experimentally: oxidative damage to proteins was significantly (P < 0.05) higher in plasma samples showing the presence of 'catalytic' iron and in addition a strong correlation (r = 0.95, P < 0.02) was seen between plasma concentration of 'catalytic' iron and the ability of the plasma to stimulate lipid peroxidation. Our data show that chemotherapy releases 'catalytic' iron which may relate to toxic side effects. Hence binding this 'catalytic' iron by judicious co-administration of iron chelating agents could be beneficial in minimizing the iatrogenic adverse effects of chemotherapy of acute leukaemia.

Cytotoxicity of ether phospholipid BM 41.440 on neuroblastoma cells

The thioether lysophospholipid BM 41.440 proved to be toxic against cells of two neuroblastoma cell lines in a dose- and time-dependent manner. The ID50 estimated in three different in vitro test systems declined from about 10 micrograms/ml after 24 h to 1 microgram/ml after a 1-week treatment of the neuroblastoma cells. These values are comparable to the ID50 found for neoplastic cells derived from other tissues. In comparison, hematopoietic progenitor cells (granulocyte/monocyte-colony-forming units) proved to be less sensitive to short-term treatment with BM 41.440. After long exposure to this drug the selectivity towards neuroblastoma cells decreased. This observation makes it unlikely that BM 41.440 can be used for treatment of neoplasia such as neuroblastoma, because only short-term treatment is acceptable considering the high bone marrow toxicity.

Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of monoamine transporters in neuroblastoma cell lines: correlations to meta-iodobenzylguanidine (MIBG) uptake and tyrosine hydroxylase gene expression

Radiolabelled meta-iodobenzylguanidine (MIBG) has been widely used in scintigraphy and targeted radiotherapy in patients with neuroblastoma. Recently, it has been demonstrated that MIBG is incorporated into neuroblastoma cells by the noradrenaline transporter. In vitro experiments on SK-N-SH human neuroblastoma cells performed in the present study showed that uptake of MIBG is inhibited by noradrenaline, more so by dopamine and to a lesser extent, by serotonin, indicating that the respective transporters may also contribute to MIBG uptake. However, neither dopamine nor serotonin transporter gene expression was detected. Noradrenaline transporter gene expression was found in 4 of 6 investigated cell lines, which correlated with specific MIBG uptake. Furthermore, an inverse correlation of noradrenaline transporter and tyrosine hydroxylase gene expression, the key regulatory enzyme of catecholamine synthesis, was observed. These data show that MIBG is specifically incorporated only in neuroblastoma cells in which there is noradrenaline transporter gene expression. Furthermore, the catecholamine status in neuroblastoma cells is regulated by a coordinate expression of the key elements of catecholamine synthesis and reuptake systems.

Ascorbic acid induces lipid peroxidation on neuroectodermal SK-N-LO cells with high endogenous ferritin content and loaded with MAb-ferritin immunoconjugates

Neuroblasma-and other malignant cells often contain elevated amounts of iron-rich ferritin and H2O2 and may therefore be a potential target for pro-oxidative effects of ascorbic acid (AA), generating cytotoxic products e.g. by lipid peroxidation (LPO). The influence of H2O2 and iron, either in its free form or bound to ferritin, on AA induced LPO was first investigated using erythrocyte ghosts as a model system. Results of these experiments showed that AA induced LPO not only in the presence of free available iron but also in the presence of ferritin. Similarly, AA induced significant LPO in neuroectodermal SK-N-LO cells with elevated intracellular ferritin levels. These LPO promoting effects of ferritin in the presence of AA on SK-N-LO cells could also be observed using ferritin-immunoconjugates: for this purpose, ferritin was bound to human monoclonal antibodies (MAb-ferritin) recognizing ganglioside GD2 which is present in large quantities on cell surfaces of SK-N-LO and many neuroblastoma cells. We conclude that the pro-oxidative effects of AA could be exploited in the treatment of ferritin rich neuroblastoma in combination with chemotherapy or with MAb-ferritin immunoconjugates.

Ascorbic-acid-mediated iron release from cellular ferritin and its relation to the formation of DNA strand breaks in neuroblastoma cells

Ascorbic acid at pharmacologically attainable concentrations effectively inhibited the growth of the catecholamine-positive neuroblastoma cell line SK-N-SH; it inhibited LS cells to a smaller extent and catecholamine-negative SK-N-LO cell growth least effectively. In all three cell lines high concentrations of H2O2 were found. Since ascorbic acid was shown to release iron from ferritin in vitro and to keep it in the reduced state, we suggested that it acted as a pro-oxidant in ferritin-rich neuroblastoma cells in the presence of H2O2 and Fe2+ (Fenton reaction), implying iron release from cellular ferritin. We show here that iron could be mobilized from cellular ferritin by 1 mM ascorbic acid in iron-59-preloaded SK-N-SH and LS cells, but not in SK-N-LO cells. In agreement with these results, DNA strand break formation by ascorbate was only observed in SK-N-SH and LS cells. In SK-N-LO cells, DNA strand breaks could be induced by a combination of 1 mM ascorbic acid and 100 microM H2O2. Since cell-damaging effects caused by chemotherapy further facilitate iron release from ferritin, we conclude that ascorbate could be a powerful enhancer of some cytostatic drugs in neuroblastoma therapy.

Inhibition of the membrane localization of p21 ras proteins by lovastatin in tumor cells possessing a mutated N-ras gene

Mutated ras genes are found in a variety of human tumors. For biological activity the gene product p21 ras needs to be bound to the cell membrane by a farnesyl residue. Treatment of tumor cells with lovastatin reduces the availability of farnesyl pyrophosphate for the modification of the ras proteins. The membrane localization of p21 ras has been reduced by 30-36% after the tumor cells have grown in the presence of 10 microM lovastatin for 7 days. The extent of the inhibition depends on the growth kinetics of the cell lines.

Measurement of endogenous and TNF alpha-mediated H2O2 production in supernatants of SK-N-SH neuroblastoma cells with an enhanced chemiluminescence assay

A sensitive peroxidase-dependent luminol-enhanced chemiluminescence (ECL) assay for determination of hydrogen peroxide (H2O2) generation by tumour cells was established. This test system allows determination of H2O2 in concentrations as low as 25 pmol (50 nmol/L) and yields results which are comparable to those obtained using a less sensitive photometric method and a previously described scopoletin fluorescence assay. After 3 h incubation time 10(4) SK-N-SH neuroblastoma cells released 60 +/- 5 pmol H2O2 in the supernatant and this level was significantly (p < 0.025) increased by about 70% in the presence of 5 pmol (100 ng/mL) recombinant tumour necrosis factor alpha (TNF alpha). In contrast, H2O2 production was slightly reduced by TNF alpha at a very low concentration of 0.5 fmol (0.01 ng/mL).

Chemotactic activity of substances derived from antibody-loaded tumor cells on granulocytes

Chemotactic activity of granulocytes attracted by tumor cells loaded either with anti-ganglioside monoclonal antibodies (mAb) or with antibody-glucose oxidase conjugates (mAb-GO) was investigated. The melanoma cell line SK-Mel-28 which expresses the ganglioside GD3 at high density as well as the neuroectodermal cell line SK-N-LO which expresses GD2 were used for the experiments. In the presence of 50% human AB-serum, antibody-loaded tumor cells induced chemotactic activity on granulocytes, probably due to the generation of C3a/C5a which could be detected in serum incubated with anti-GD3 loaded SK-Mel-28 cells. Both compounds could also be detected in vivo in the plasma of patients suffering from neuroblastoma during therapy with anti-GD2 antibodies. In another set of experiments mAb-GO conjugates generating high amounts of H2O2 in the presence of glucose were bound to these tumor cells. A significant lipid peroxidation could be observed in the simultaneous presence of iron and ascorbate. The lipid peroxidation products were measured as thiobarbituric acid-reactive substances (TBARS) and were also shown to induce chemotactic effects on granulocytes.

Activation of cellular cytotoxicity and complement-mediated lysis of melanoma and neuroblastoma cells in vitro by murine antiganglioside antibodies MB 3.6 and 14.G2a

Mouse monoclonal antibodies against tumour-associated gangliosides GD2 (14.G2a) and GD3 (MB 3.6) were tested to mediate antibody-dependent cellular cytotoxicity (ADCC) with various effector cells or complement-dependent cytolysis (CDC). We also evaluated the immunomodulating potential of interferons in combination with cellular cytotoxicity. Using effector:target (E/T) ratios of 40:1, ADCC with effector cells such as granulocytes or mononuclear blood cells was not detectable against melanoma cell lines GR, SK-MEL-28 and G-361 which preferentially express GD3 and bind antibody MB 3.6. Neuroblastoma cell line SK-N-LO, which was used for comparative purposes, mainly expressed GD2 and the tumour cells were killed effectively after labelling with antibody 14.G2a. Granulocytes did not show significant killing of melanoma cells by ADCC, but neuroblastoma cells were killed very efficiently. Peripheral blood mononuclear cells (PBMC) also failed to kill melanoma cells. Interferon-beta slightly stimulated PBMC and increased killing of neuroblastoma cells, but no additive effects with ADCC were detectable. Incubation of target cells with interferons produced no significant differences in susceptibility of the target cells to interferon-activated PBMC cytotoxicity. Despite the lack of effectiveness in mediating cellular cytotoxicity, GD3 antibody MB 3.6 showed strong complement-dependent cytolysis in the presence of human plasma. There were remarkable differences in individual activity and different susceptibility of the melanoma cell lines. We assume that CDC may have more activity against melanoma cells than cytotoxicity associated with various effector cells.

Uptake and cytotoxicity of ascorbic acid and dehydroascorbic acid in neuroblastoma (SK-N-SH) and neuroectodermal (SK-N-LO) cells

Ascorbic acid (AA) was found to be cytotoxic to neuroblastoma cells in vitro and in vivo. In the present, study we investigated whether the reduced--(AA) or oxidized form (dehydroascorbic acid, DhAA) and its rapidly formed metabolites were the main cytotoxic agents. In neuroblastoma SK-N-SH cells, AA was found to be more cytotoxic than DhAA, although considerably higher amounts of [14C]DhAA than of [14C]AA were incorporated. In contrast, SK-N-LO cells derived from neuroectodermal tissue in fact showed a similar uptake but were much less injured by both substances. We observed that uptake of [14C]AA and [14C]DhAA was impaired in the presence of dithiothreitol and glutathione. Once inside the cell, [14C]DhAA was partially reduced to [14C]AA. From these data we conclude first that at least part of AA is oxidized prior to its uptake, and second that the reduced form of AA and perhaps ascorbyl radicals but not DhAA or its metabolites are the most important forms in mediating cytotoxic reactions in neuroblastoma cells. Furthermore, the results strengthen the previous assumption that AA acts as a pro-oxidant in neuroblastoma cells and supports its use in the treatment of neuroblastoma, especially in combination with existing chemotherapeutics.

Determination of 2-5A synthetase and 2-5A phosphodiesterase in neuroblastoma cells by analytical capillary isotachophoresis: effects of cytokines and comparison with radioenzymatic methods

2-5A Synthetase and 2-5A phosphodiesterase were determined by analytical capillary isotachophoresis in comparison to radioenzymatic methods. By means of isotachophoretic analysis, a frequently used radioenzymatic 2-5A synthetase assay was optimized and the results of both assays were compared. Using the isotachophoretic assay the influence of interferon-related cytokines (tumor necrosis factor-alpha and interleukin-2) on 2-5A synthetase induction in neuroblastoma cells was estimated. In contrast to mononuclear blood cells, the tumor necrosis factor induced 2-5A synthetase in these cells. 2-5A Phosphodiesterase was determined using an isotachophoretic assay and a radioenzymatic method. Degradation of A2'p5'A2'p5'A (trimeric form of 2-5A core) was measured by isotachophoresis whereas degradation of a mixture of phosphorus-32 labeled 2-5A cores was registered by radioenzymatic assay. Activity of 2-5A phosphodiesterase was only insignificantly enhanced by interferon in mononuclear blood and neuroblastoma cells. In contrast to the radioenzymatic assays, an accurate determination of 2-5A synthetase as well as of 2-5A phosphodiesterase is possible using the isotachophoretic method because the reactions are followed by measuring the substrates ATP and A2'p5'A2'p5'A, respectively.

Isotachophoresis of nucleic acid constituents

Determination methods for purine and pyrimidine bases, nucleosides, nucleotides and related compounds using analytical capillary isotachophoresis are reviewed. First, the isotachophoretic characterization of these compounds, as well as methods for sample preparation prior to analysis, and the different ways of detecting unknown substances in complex biological systems are described. Then applications of isotachophoretic analysis in medical diagnosis and biomedical research are reviewed. In particular, the analysis of purines, pyrimidines, nucleosides and related compounds in blood and serum for the diagnosis and treatment of inherited diseases and cancer is described. Selected applications of nucleotide analysis in biomedical research using different tissue extracts are also reviewed, and some examples of nucleotide-dependent enzymic reactions, which were performed by means of analytical isotachophoresis, are presented.

Determination of ascorbic acid by isotachophoresis with regard to its potential in neuroblastoma therapy

Analytical capillary isotachophoresis was used to determine ascorbic acid (AA) in different matrices (cell-free system, neuroblastoma cell extracts and urine). The system for purging bone marrow of neuroblastoma cells, including 6-hydroxydopamine (6-OHDA) and AA, was analysed with regard to the interaction of AA with 6-OHDA and its autoxidation product, hydrogen peroxide. Furthermore, analyses concerning the uptake of AA into neuroblastoma cells as well as its excretion in urine after uptake of large amounts were carried out.

Determination of 2'-5'-oligoadenylate synthetase in serum and peripheral blood mononuclear cells before and after subcutaneous application of recombinant interferon beta and gamma

The interferon-inducible enzyme, 2'-5'-oligoadenylate synthetase, was estimated in healthy donors and in patients before and after subcutaneous application of recombinant interferon beta and gamma. Tests were carried out with lysates of peripheral blood mononuclear cells, using an established radioenzymatic assay, and in serum samples, using a new radioimmunoassay. Both test systems substantially yielded the same results: after a single injection of interferon beta (1-5 x 10(6) IU), 2'-5'-oligoadenylate synthetase increased in a dose-dependent manner reaching maximal catalytic concentrations in most patients after 24-48 hours (leukocytes) and 48-72 hours (serum). In contrast, interferon gamma (2-4 x 10(6) IU) caused only a small induction of 2'-5'-oligoadenylate synthetase. However, daily application of interferon gamma for 7 days led to a distinct time-dependent increase of 2'-5'-oligoadenylate synthetase activity concentration during this observation period. Characteristically, even during daily application, the 2'-5'-oligoadenylate synthetase activity concentration dropped just 48-72 hours after the first injection of interferon beta. The determination of 2'-5'-oligoadenylate synthetase proved to be useful for optimizing and monitoring subcutaneous therapy with interferon. The new radioimmunoassay which allows the determination of this enzyme in serum is superior to other methods used in the past.

Effect of constituents of burned skin and in vivo skin burning on the respiratory activity of rat liver mitochondria

The formation of toxic substances in the skin, due to the influence of thermal energy, is supposed to be one possible mechanism responsible for the high mortality rate after severe burns covering large areas of the body surface. The effects of low-molecular-weight volatile substances (dry distillates) generated after burning mouse skin were investigated. They led to reductions of the respiratory activity of rat liver mitochondria. Among other substances carbon disulphide, methylethylketone and pyrrole were isolated and characterized using gas chromatography. All of them had strong uncoupling effects on mitochondrial respiration. In a second study respiratory measurements were made on mitochondria from rats with 20-30 per cent TBSA full skin thickness burns. A decreased respiratory control ratio and thus uncoupling of mitochondrial respiration was found on days 1, 2 and 5 postburn. The basal mitochondrial respiration was significantly decreased on day 5, which could be important for the mortality mentioned above. Finally after cross-transplantations rats having burned skin grafted showed a reduction of the RCR when compared with rats with the unburned graft. Thus it can be concluded that toxic substances must have been present in burned skin.

A simple assay for determination of iron release from ferritin in neuroblastoma cells

A commercially available enzyme immunoassay was used to determine ferritin content and subsequently the loading and release of iron from ferritin in neuroblastoma cells. LS cells were incubated with 59Fe for 24 h, lysed, and the cytoplasmic ferritin was bound to monoclonal antibodies coupled to globules. After determination of the ferritin content the same globules with bound radioactive ferritin were measured in a gamma-counter. To illustrate the applicability of this test system, increased iron loading of cellular ferritin could be demonstrated in cycloheximide-treated cells; furthermore, release of iron was documented after incubation of LS cells with a combination of 6-hydroxydopamine and ascorbate. The assay turned out to be a simple method for determination of changes in 59Fe content of ferritin in neuroblastoma cells.

Ascorbic acid enhances the effects of 6-hydroxydopamine and H2O2 on iron-dependent DNA strand breaks and related processes in the neuroblastoma cell line SK-N-SH

Neuroblastoma cells accumulate ascorbic acid and iron. It was hypothesized that these features could be exploited for sensitizing neuroblastoma cells for therapy in combination with reactive oxygen intermediates. In the present study the effects of 6-hydroxydopamine (6-OHDA) and H2O2 on metabolic parameters critical for cell survival were investigated in cells with low and high ferritin content in the presence and absence of ascorbate. Human neuroblastoma SK-N-SH cells were pretreated with 100 microM FeSO4 and 10 microM desferrioxamine, respectively, for 24 h yielding cells with different ferritin contents. The effects of 6-OHDA and H2O2 (25 microM-250 microM) in the absence and presence of 1 mM ascorbic acid on DNA strand break formation, activation of poly(ADP-ribose) polymerase, and finally decrease in NAD+ and ATP concentration were investigated. All these parameters were influenced by 6-OHDA and H2O2 in a concentration-dependent manner in a similar way. The effects were most pronounced in ferritin-rich cells and in the presence of ascorbic acid. Using isolated CCC PM2 DNA, 6-OHDA and ascorbic acid caused strand breaks that were prevented in the presence of mannitol or desferrithiocine. H2O2-mediated strand breaks were observed only in the presence of ascorbic acid. Based on these data and data published by others a model explaining the deleterious effects of ascorbic acid on neuroblastoma cells is presented. It is suggested that continuous application of a high dosage of ascorbic acid might be a useful approach in neuroblastoma therapy.