Hybrid Molecules of Benzylguanidine and the Alkylating Group of Melphalan: Synthesis and Effects on Neuroblastoma Cells

The therapy of neuroblastoma relies, amongst other things, on administering chemotherapeutics and radioactive compounds, e.g., the (meta-iodobenzyl)guanidine [¹³¹I]mIBG. For special applications (conditioning before stem cell transplantation), busulfan and melphalan (M) proved to be effective. However, both drugs are not used for normal chemotherapy in neuroblastoma because of their side effects. The alkylating drug melphalan contains a (Cl-CH₂-CH₂-)₂N- group in the para-position of the phenyl moiety of the essential amino acid phenylalanine (Phe) and can, therefore, be taken up by virtually all kinds of cells by amino acid transporters. In contrast, mIBG isotopologs are taken up more selectively by neuroblastoma cells via the noradrenaline transporter (NAT). The present study aimed at synthesising and studying hybrid molecules of benzylguanidine (BG) and the alkylating motif of M. Such hybrids should combine the preferential uptake of BGs into neuroblastoma cells with the cytotoxicity of M. Besides the hybrid of BG with the dialkylating group (Cl-CH₂-CH₂-)₂N- bound in the para-position as in M (pMBG), we also synthesised mMBG, which is BG meta-substituted by a (Cl-CH₂-CH₂-)₂N- group. Furthermore, two monoalkylating hybrid molecules were synthesised: the BG para-substituted by a (Cl-CH₂-CH₂-)NH- group (pM*BG) and the BG meta-substituted by a (Cl-CH₂-CH₂-)NH- group (mM*BG). The effects of the four new compounds were studied with human neuroblastoma cell lines (SK-N-SH, Kelly, and LS) with regard to uptake, viability, and proliferation by standard test systems. The dialkylating hybrid molecules pMBG and mMBG were at least as effective as M, whereas the monoalkylating hybrid molecules pM*BG and mM*BG were more effective than M. Considering the preferred uptake via the noradrenaline transporter by neuroblastoma cells, we conclude that they might be well suited for therapy.

Proposal for the use of an inhalation drug containing 2-5 oligoadenylates for treatment of COVID-19

Interferons (IFN), first described 1957 by Isaacs and Lindemann, are antiviral proteins generated in cells after viral infections. One of several interferon-induced effector mechanisms is the so called 2-5A / RNaseL system: Interferon is produced in the virus-affected cells and released. After binding to cell membrane receptors of adjacent cells, 2-5 A synthetase (oligoadenylate synthetase, OAS) is generated, attaches to dsRNA section areas of the viral RNA and catalyses the production of 2-5 oligoadenylates from ATP. In 2-5 oligoadenylates, several adenosine residues (3–4 and more) are combined via phosphodiester binding in the unusual 2′-5′ positions of the riboses. 2-5 oligoadenylates activate a RNaseL which degrades the viral RNA. Recently, characteristic gene mutations and other disturbances concerning the interferon system were detected in patients with severe COVID-19, leading to problems of 2-5 oligoadenylate synthesis and the activation of RNAseL. In order to circumvent these problems, we hypothesize that a direct application of 2-5 oligoadenylates, included in an inhalation spray, may be effective in treatment of severe COVID-19 infections of the respiratory system. In contrast to some other anti-COVID-19 drugs, oligoadenylates act inside the cells (like e.g. Paxlovid) and are therefore independent of cell surface mutations of the virus. For confirmation of our hypothesis, proof of concept investigations in vitro are suggested, before a possible clinical application can be considered.

Extremely low arylsulfatase A enzyme activity does not necessarily cause symptoms: A long‐term follow‐up and review of the literature

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disease caused by deficiency of arylsulfatase A (ARSA). Heterozygous carriers of disease‐causing variants and individuals harbouring pseudodeficiency alleles in the ARSA gene exhibit reduced ARSA activity. In the context of these genotypes, low ARSA activity has been suggested to lead to an atypical form of MLD or other neurological abnormalities, but data are limited. The aim of our study was to analyse the impact of low ARSA activity in two subjects who are heterozygous for the ARSA pseudodeficiency allele and a disease‐causing variant. Biochemical testing included ARSA activity measurements and urinary sulfatide analysis. Biochemical data of a large cohort of MLD patients, heterozygotes, pseudodeficient individuals and healthy controls were analysed. MRI was performed at 3T using T1‐ and T2‐weighted sequences and MR spectroscopy. We present two long‐term follow‐ups who are heterozygous for the ARSA pseudodeficiency allele and a disease‐causing variant in the ARSA gene in cis. The two related index cases exhibit markedly reduced ARSA activity compared to controls and heterozygous carriers. The neurological evaluation and MRI do not reveal any abnormalities. Our data underline that extremely low enzyme activity due to a pseudodeficiency allele and a disease‐causing variant in the ARSA gene even in cis does not lead to clinical symptoms or pre‐symptomatic MRI changes suspicious for MLD. The review of literature corroborates that any association of low ARSA activity with disease features remains questionable. It seems important to combine the measurement of ARSA activity with elevated sulfatide as well as genetic testing, as done in current newborn screening approaches. Heterozygosity for metachromatic leukodystrophy and an arylsulfatase A pseudodeficiency allele does not cause neurological or neuropsychiatric features.

Very High Dehydroepiandrosterone Sulfate (DHEAS) in Serum of an Overweight Female Adolescent Without a Tumor

Introduction: An increase of serum dehydroepiandrosterone (DHEA) sulfate (DHEAS) is observed in premature adrenarche and congenital adrenal hyperplasia. Very high DHEAS levels are typical for adrenal tumors. Approximately 74% of DHEAS is hydrolyzed to DHEA by the steroid sulfatase (STS). The reverse reaction is DHEA sulfation. Besides these two enzyme reactions, the DHEAS transported through the cell membrane is important for its distribution and excretion. Case Presentation: We present a female adolescent with overweight and a very high DHEAS. The presence of a DHEAS-producing tumor was rejected using ultrasonography, Magnetic Resonance Tomography (MRT), and dexamethasone suppression. STS deficiency was suspected. Sequence analysis revealed a heterozygous nonsense mutation which predicts a truncation of the carboxyl region of the STS that is implicated in substrate binding. No partial gene deletion outside exon 5 was detected by multiplex ligation-dependent probe amplification. The bioassay revealed normal enzyme activity in the patient's leukocytes. A defect of transporter proteins was suggested. Both efflux [multidrug-resistance protein (MRP)2 and breast cancer-resistance protein (BCRP)] and uptake [organic anion-transporting polypeptide (OATP) and organic anion transporter (OAT) carriers] transporters were studied. Sequence analysis of exons revealed a heterozygous Q141K variant for BCRP. Conclusions: A novel heterozygous nonsense mutation in the STS gene and a known heterozygous missense variant in the BCRP gene were found. The heterozygous nonsense mutation in the STS gene is not supposed to be responsible for STS deficiency. The BCRP variant is associated with reduced efflux transport activity only in its homozygous state. The combination of the two heterozygous mutations could possibly explain the observed high levels of DHEAS and other sulfated steroids.

Improved selectivity of mIBG uptake into neuroblastoma cells in vitro and in vivo by inhibition of organic cation transporter 3 uptake using clinically approved corticosteroids

INTRODUCTION

Radiolabeled meta-iodobenzylguanidine (mIBG) is used for imaging and therapy of neuroblastoma as well as pheochromocytoma. However, non-tumorous tissues also incorporate mIBG mainly by organic cation transporters (OCTs). In this study, we tested different clinically approved corticosteroids as potential inhibitors of the OCT3-mediated uptake in vitro and in vivo, to achieve a more selective mIBG tumor uptake.

METHODS

The in vitro incorporation of [(3)H]norepinephrine ([(3)H]NE), [(3)H]dopamine ([(3)H]DA) and [(123)I]mIBG in neuroblastoma cells (SK-N-SH, Kelly, IMR-32) and in HEK-293 cells transfected with human OCT3 was measured with and without supplemental corticosteroids (hydrocortisone, prednisolone, dexamethasone, corticosterone). The in vivo biodistribution of [(123)I]mIBG in absence and presence of corticosteroids was studied in non-tumor bearing NOD scid gamma mice. Retrospectively, we selected patients with and without corticosteroid treatment prior to [(123)I]mIBG scintigraphy.

RESULTS

A concentration-dependent inhibitory effect of different corticosteroids on the [(3)H]NE and [(3)H]DA uptake via OCT3 was illustrated in vitro. The highest OCT3 inhibition was observed for corticosterone, but clinically used corticosteroids, showed also promising inhibitory effects. In contrast, the uptake in neuroblastoma cells was reduced only moderately. Hydrocortisone or prednisolone had only minor effects on [(123)I]mIBG uptake of both neuroblastoma cells, but reduced uptake in OCT3 expressing cells significantly. In mice tissues, [(123)I]mIBG uptake was inhibited by corticosteroids especially in the small intestine and kidney. Finally, in one patient with hydrocortisone treatment performed prior to [(123)I]mIBG scan, heart and liver uptake was reduced compared to untreated patients.

CONCLUSIONS

The OCT3 is widely spread in many organs and responsible for non-targeted uptake of radiolabeled mIBG. In our study, clinically approved corticosteroids inhibited mIBG uptake in OCT3 expressing cells effectively, whereas tracer accumulation in NT (norepinephrine transporter) expressing neuroblastoma cells showed consistency. We conclude, that a single dose of hydrocortisone or prednisolone prior to [(123)I]mIBG scintigraphy may improve specificity and reduce radiation dose to non-target organs.

Nifurtimox reduces N-Myc expression and aerobic glycolysis in neuroblastoma

Neuroblastoma is one of the most common solid tumors in childhood and usually accompanied with poor prognosis and rapid tumor progression when diagnosed with amplification of the proto-oncogene N-Myc. The amplification of N-Myc has major influence on the maintenance of aerobic glycolysis, also known as the Warburg effect. This specific switch in the conversion of pyruvate to lactate instead of the conversion of pyruvate to acetyl-coenzyme A even in the presence of oxygen has important benefits for the tumor, e.g. increased production of enzymes and enzyme substrates that are involved in tumor progression, angiogenesis and inhibition of apoptosis. The antiprotozoal drug nifurtimox, which is generally used for the treatment of infections with the parasitic protozoan Trypanosoma cruzi, has been reported to have cytotoxic properties in the therapy of neuroblastoma. However, its action of mechanism has not been described in detail yet. The presented in vitro study on the neuroblastoma cell lines LA-N-1, IMR-32, LS and SK-N-SH shows an increased production of oxidative stress, a reduced lactate dehydrogenase enzyme activity and reduced lactate production after nifurtimox treatment. Furthermore, nifurtimox leads to reduced mRNA and protein levels of the proto-oncogene protein N-Myc. Thus, the current work gives new insights into the effect of nifurtimox on tumor metabolism revealing a shifted glucose metabolism from production of lactate to oxidative phosphorylation and a reduced expression of the major molecular prognostic factor in neuroblastoma N-Myc, presenting nifurtimox as a possible adjuvant therapeutic agent against (high risk) neuroblastoma.

DCA promotes progression of neuroblastoma tumors in nude mice

Even in the presence of oxygen most cancer cells convert glucose to lactate via pyruvate instead of performing oxidative phosphorylation (aerobic glycolysis-Warburg effect). Thus, it has been considered to shift pyruvate - the metabolite of aerobic glycolysis - to acetylCoA by activation of pyruvate dehydrogenase (PDH). AcetylCoA will then be metabolized by oxidative phosphorylation. Therefore, the purpose of this study was to shift tumor cells from aerobic glycolysis to oxidative phosphorylation using dichloroacetate (DCA), an inhibitor of PDH-kinase. The effects of DCA were assayed in vitro in Neuro-2a (murine neuroblastoma), Kelly and SK-N-SH (human neuroblastoma) as well as SkBr3 (human breast carcinoma) cell lines. The effects of DCA on tumor development were investigated in vivo using NMRI nu/nu mice bearing subcutaneous Neuro-2a xenografts. For that purpose animals were treated continuously with DCA in the drinking water. Tumor volumes were monitored using caliper measurements and via [18F]-FDG-positron emission tomography. DCA treatment increased viability/proliferation in Neuro-2a and SkBr3 cells, but did not cause significant alterations of PDH activity. However, no significant effects of DCA could be observed in Kelly and SK-N-SH cells. Accordingly, in mice bearing Neuro-2a xenografts, DCA significantly increased tumor proliferation compared to mock-treated mice. Thus, we could demonstrate that DCA - an indicated inhibitor of tumor growth - efficiently promotes tumor growth in Neuro-2a cells in vitro and in vivo.

The Oxidation of Catecholamines and 6-Hydroxydopamine by Molecular Oxygen: Effect of Ascorbate

Comparative kinetic studies on the oxidation of catecholamines (CA) (dopamine (DA), epinephrine (EP). norepinephrine (NEP)) serving as a neuromediator in the sympathetic nervous system, 3,4-dihydroxyphenylalanine (DOPA) and 6-hydroxydopamine (6-OHDA), a wellknown neurotoxic agent, were performed in the presence of ascorbate (AscH- ) in 50 mᴍ phosphate buffer, pH 7.40, at 37 °C by using a Clark electrode, EPR and the absorption spectroscopy. The oxidation of CA and DOPA alone was found to be a self-accelerating process, with quinone products (Q) acting as autocatalysts. The rate of oxygen consumption (Rox) increased with time and reached a steady-state level. A starting value of Rox increased in the order: EP < DOPA ≈ NEP ≪ DA ≪ 6-OHDA, whereas a steady-state value of Rox changed in the order: DOPA < DA < NEP ≪ EP ≪ 6-OHDA. The changes in Rox with time were found to correlate with the resistance of primary Q to the intramolecular cyclization.

The effect of AscH- on CA oxidation depended dramatically on whether AscH- was added to non-oxidized or preoxidized CA. Added to non-oxidized CA and DOPA, AscH- inhibited their oxidation (but not that of 6-OHDA). For the case of DA, a pronounced lag period was observed by both a Clark electrode and spectrophotometrically. The addition of AscH- to preoxidized CA, DOPA and 6-OHDA induced an increase in Rox a steadystate concentration of the ascorbyl radical. The kinetic behaviour of the systems was determined by two major factors: 1) AscH- suppressed the formation of Q, a catalyst for CA oxidation, most likely due to the reaction of AscH- with the semiquinone formed from CA; 2) Q derived both from CA and 6-OHDA catalyzed AscH- oxidation. The elevated cytotoxicity of 6-OHDA was found to be in part caused by the condition that 6-OHDA oxidation was not inhibited by AscH- and by the high efficiency of 6-OHDA as a redox cycling agent in combination with A scH−. These observations explain the very pronounced and prolonged cytotoxicity of 6-OHDA even at low concentrations that increases at elevated concentrations of AscH- .

Synthesis and biological effects of new hybrid compounds composed of benzylguanidines and the alkylating group of busulfan on neuroblastoma cells

(131)Iodine-labelled (meta-iodobenzyl)guanidine ([(131)I]-mIBG) and busulfan [butane-1,4-diylbis(methanesulfonate)] are well-established pharmaceuticals in neuroblastoma therapy. We report the design, synthesis, and testing of hybrid molecules-mBBG and pBBG-which combine key structural features of (meta-iodobenzyl)guanidine and busulfan: they contain a benzylguanidine moiety for accumulating in neuroblastoma cells via the noradrenaline transporter and, in the meta- or para-position, respectively, one of the two identical alkylating motives of busulfan for killing cells. Uptake and toxicity of hybrids mBBG and pBBG in human neuroblastoma cells compared favorably to their ancestors [(131)I]-mIBG and busulfan.

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.

Lipoic acid inhibits cell proliferation of tumor cells in vitro and in vivo

Cancer cells convert glucose preferentially to lactate even in the presence of oxygen (aerobic glycolysis-Warburg effect). New concepts in cancer treatment aim at inhibition of aerobic glycolysis. Pyruvate dehydrogenase converts pyruvate to acetylCoA thus preventing lactate formation. Therefore, the aim of this study was to evaluate compounds that could activate pyruvate dehydrogenase in cancer cells. We investigated the effects of (R)-(+)-α-lipoic acid (LPA) and dichloroacetate (DCA), possible activators of pyruvate dehydrogenase, on suppression of aerobic glycolysis and induction of cell death. The neuroblastoma cell lines Kelly, SK-N-SH, Neuro-2a and the breast cancer cell line SkBr3 were incubated with different concentrations (0.1-30 mM) of LPA and DCA. The effects of both compounds on cell viability/proliferation (WST-1 assay), [18F]-FDG uptake, lactate production and induction of apoptosis (flow cytometric detection of caspase-3) were evaluated. Furthermore, NMRI nu/nu mice that had been inoculated s.c. with SkBr3 cells were treated daily for four weeks with LPA (i.p, 18.5 mg/kg) starting at day 7 p.i.. Tumor development was measured with a sliding caliper and monitored via [18F]-FDG-PET. Residual tumors after therapy were examined histopathologically. These data suggests that LPA can reduce (1) cell viability/proliferation, (2) uptake of [18F]-FDG and (3) lactate production and increase apoptosis in all investigated cell lines. In contrast, DCA was almost ineffective. In the mouse xenograft model with s.c. SkBr3 cells, daily treatment with LPA retarded tumor progression. Therefore, LPA seems to be a promising compound for cancer treatment.

Influence of dichloroacetate (DCA) on lactate production and oxygen consumption in neuroblastoma cells: is DCA a suitable drug for neuroblastoma therapy?

Many cancer cells metabolize glucose preferentially via pyruvate to lactate instead to CO(2) and H(2)O (oxidative phosphorylation) even in the presence of oxygen (Warburg effect). Dichloroacetate (DCA) is a drug which is able to shift pyruvate metabolism from lactate to acetyl-CoA (tricarboxylic acid cycle) by indirect activation of pyruvate dehydrogenase (PDH). This can subsequently lead to an increased flow of oxygen in the respiratory chain, associated with enhanced generation of reactive oxygen species (ROS) which may cause apoptosis. In order to investigate if DCA may be suitable for neuroblastoma therapy, it was investigated on three human neuroblastoma cell lines whether DCA can reduce lactate production and enhance oxygen consumption. The data show, that DCA (in the low millimolar range) is able to reduce lactate production, but there was only a slight shift to increased oxygen consumption and almost no effect on cell vitality, proliferation and apoptosis of the three cell lines investigated. Therefore, DCA at low millimolar concentrations seems to be only of minor efficacy for neuroblastoma treatment.

H(2)O(2)-mediated cytotoxicity of pharmacologic ascorbate concentrations to neuroblastoma cells: potential role of lactate and ferritin

By intravenous (but not oral) application of ascorbate, millimolar serum concentrations can be reached, which are preferentially cytotoxic to cancer cells. Cytotoxicity is mediated by transition metal-dependent generation of H(2)O(2) in the interstitial space. In this study, the sensitivity of neuroblastoma cells (Kelly, SK-N-SH) to ascorbate and H(2)O(2) and their defense mechanisms against H(2)O(2) were investigated. Since aerobic glycolysis (the Warburg effect) is a feature of many tumour cells, their glucose consumption and lactate production were monitored. Furthermore, synthesis and release of ferritin by neuroblastoma cells were analysed in order to examine whether ferritin is possibly an iron source for H(2)O(2) generation. Ascorbate (0.6-5.0 mM) and H(2)O(2) (25-100 muM) were found to be similarly cytotoxic to Kelly and SK-N-SH cells. In each case, cytotoxicity increased if cell concentrations decreased, in accordance with low cell concentrations having lower capacities to detoxify H(2)O(2). Kelly and SK-N-SH cells produced and released remarkable amounts of lactate and ferritin. We propose the selective cytotoxicity of high dose ascorbate to tumour cells to be due to the preferential generation of H(2)O(2) in the acidic and ferritin-rich tumour microenvironment, combined with reduced defense systems against H(2)O(2) as a consequence of aerobic glycolysis.

Adult stem cells as an alternative source of multipotential (pluripotential) cells in regenerative medicine

Embryonic stem cells are by definition the master cells capable of differentiating into every type of cells either in vitro or in vivo. Several lines of evidence suggest, however, that adult stem cells and even terminally differentiated somatic cells under appropriate microenvironmental cues are able to be reprogrammed and contribute to a much wider spectrum of differentiated progeny than previously anticipated. This has been demonstrated by using tissue- specific stem cells, which like embryonic stem cells do not express CD45 as an exclusive hematopoietic marker (skin, adipose, cord blood and bone marrow- derived stem cells). On the other side, there is a great number of reports which demonstrate that hematopoietic cells (CD45+) from different sources (peripheral blood, cord blood, bone marrow) are also able to cross the tissue boundaries and give rise to the cells of the other germ layers. Herein we discuss the differentiation and reprogramming potential of both hematopoietic and non- hematopoietic stem cells along endodermal, mesodermal and neuroectodermal lineage and their importance for regenerative medicine.

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.

In vitro analysis of multipotent mesenchymal stromal cells as potential cellular therapeutics in neurometabolic diseases in pediatric patients

Multipotent mesenchymal stromal cells (MSCs) play an important role in stromal support for hematopoietic stem cells, immune modulation, and tissue regeneration. We investigated their potential as cellular therapeutic tools in neurometabolic diseases as a growing number of affected children undergo to bone marrow transplantation. MSCs were isolated from bone marrow aspirates and expanded ex vivo under various culture conditions. MSCs under optimal good medical practice (GMP)-conform culture conditions showed the typical morphology, immunophenotype, and plasticity. Biochemically, the activities of beta-hexosaminidase A, total beta-hexosaminidase, arylsulfatase A (ASA), and beta-galactosidase measured in MSCs were comparable to those in fibroblasts of healthy donors. These four enzymes were interesting for their expression in MSCs, as each of them is defective, respectively, in well-known neurometabolic diseases. We found that MSCs released significant amounts of ASA into the media. In coculture experiments, fibroblasts from patients with metachromatic leukodystrophy, who are deficient for ASA, took up a substantial amount of ASA that was released into the media from MSCs. Mannose-6-phosphate (M6P) inhibited this uptake, which was in accordance with the M6P receptor-mediated uptake of lysosomal enzymes. Taken together, we show that MSCs produce appreciable amounts of lysosomal enzyme activities, making these cells first-choice candidates for providing metabolic correction when given to enzyme-deficient patients. With the example of ASA, it was also shown that an enzyme secreted from MSCs is taken up by enzyme-deficient patient fibroblasts. Given the plasticity of MSCs, these cells represent an interesting add-on option for cellular therapy in children undergoing bone marrow transplantation for lysosomal storage diseases and other neurometabolic diseases.

Pitfalls in detection of contaminating neuroblastoma cells by tyrosine hydroxylase RT-PCR due to catecholamine-producing hematopoietic cells

BACKGROUND

RT-PCR analysis of compounds of catecholamine metabolism (in particular tyrosine hydroxylase, TH) is widely used for the detection of contaminating neuroblastoma cells in hematopoietic stem cell preparations. Due to reports in the literature showing that hematopoietic cells are also able to produce catecholamines, we investigated whether TH-RT-PCR is really suitable for this purpose.

MATERIALS AND METHODS

Besides neuroblastoma cells, mononuclear blood cells, apheresis preparations and hematopoietic stem cells were used for single and nested RT-PCR. In addition to TH, the expressions of dopamine-beta-hydroxylase and noradrenaline transporter were analyzed.

RESULTS

Using single RT-PCR, a clear discrimination between neuroblastoma and hematopoietic cells was possible. However, by using nested RT-PCR, the "neuroblastoma markers" were also detected in a significant percentage of non-mobilized mononuclear blood cells, in mononuclear blood cells of healthy donors mobilized with G-CSF, and in highly purified CD34+ and CD133+ stem cells from healthy mobilized donors.

CONCLUSION

Our results raise the question of whether the RT-PCR analysis of compounds of catecholamine metabolism is suitable and selective enough to detect the contamination of hematopoietic stem cells by a low number of neuroblastoma cells.

Determination of glucose metabolites in stored erythrocytes and in erythrocytes from patients with thalassemia by analytical isotachophoresis

Glycolysis is for some cells, such as erythrocytes, neutrophil granulocytes and many cancer cells, the only or most important source of energy (ATP) production. Based on previous studies we developed an isotachophoretic (ITP) method which allows, in principle, the simultaneous determination of all metabolites of glycolysis. Since glucose metabolites are small anions, mobility of some of them may overlap in isotachophoresis and, therefore, partial mixed zones are generated. By variation of the leading/terminating system, however, it is possible to separate the compounds of interest. In this communication, we describe a method for analysis of glucose metabolites in erythrocytes from healthy donors during storage in blood bags, and from patients with thalassemia, with special respect to intracellular 2,3 bisphosphoglycerate, lactate and ATP/ADP. The well known characteristic changes of glycolysis in erythrocytes during blood storage and in erythrocytes from thalassemia patients, which are often analysed by separate enzymatic assays, could be confirmed with this isotachophoretic procedure. The method is currently adapted for analysis of glycolysis in neutrophil granulocytes and cancer cells which requires some modifications of sample preparation and performance of the isotachophoretic analysis.

Potential pitfalls of comparative measurements of reticulocytes with flow cytometry and microscopy in prematures and infants

Reticulocyte counting by flow cytometry (Bayer H*3, ADVIA 120) in blood of prematures, infants and children > 1 year of age was compared with microscopic counting under research conditions (9000 counted red blood cells per slide). While in children > 1 year a good concordance of both methods was observed, 2.3–2.4-fold higher values were obtained in neonates by microscopy (Brilliant Cresyl Blue stain, 0.5%). However, another laboratory found good agreement between H*3-counting and microscopy in samples also obtained from neonates using the same methods. Despite very similar results for all age groups in comparative flow cytometry measurements in both laboratories, counting of smears from neonates differed, showing an approximately 2.3-fold larger amount of reticulocytes in our laboratory. The reason for these observations was a greater enlargement (1250-fold) used routinely in our laboratory compared with 800-fold in the other one. Thus very mature reticulocytes frequently found in neonates could only be detected using a 1250-fold enlargement. Similarly, the low concentration of the colouring matter used in the H*3 (0.0005% oxazin or 0.001% ADVIA 120) is obviously not sufficient for detection of mature reticulocytes. Therefore, it is important to consider this phenomenon and to standardise microscopic enlargement, especially for comparisons in multicentre studies.

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.

Receptor activator of nuclear factor kappaB ligand plays a nonredundant role in doxorubicin-induced apoptosis

Doxorubicin induces apoptosis in a variety of cells. We investigated the expression and function of various tumor necrosis factor (TNF)alpha-homologues and their receptors. CEM cells did not differentially express any one of the TNFalpha-homologous receptors investigated nor TNF-related apoptosis-inducing ligand or TNF-related weakly apoptosis-inducing ligand (TWEAK) in the presence of doxorubicin. In addition to CD95 ligand, however, receptor activator of nuclear factor kappaB ligand (RANKL) was strongly up-regulated. Doxorubicin-induced apoptosis was greatly suppressed in the presence of either neutralizing antibody or RANK-Fc fusion protein. Moreover, neutralizing RANKL also prevented cytochrome c release from mitochondria. RANKL alone was unable to induce significant levels of apoptosis in CEM cells. However, doxorubicin-induced apoptosis was increased >2-fold when exogenous RANKL was added. Therefore, RANKL is necessary but not sufficient to account for early doxorubicin-induced apoptosis in CEM cells. This finding suggests improved chemotherapeutic efficiency of the anthracyclin against susceptible malignant cells in the presence with RANKL.

Low-density lipoprotein modification by normal, myeloperoxidase-deficient and NADPH oxidase-deficient granulocytes and the impact of redox active transition metal ions

The modification of low-density lipoprotein (LDL) by normal, myeloperoxidase (MPO)-deficient and NADPH oxidase-deficient granulocytes was investigated using the monoclonal antibody (mAb) OB/04, which was originally generated against copper-oxidized LDL. Incubation of LDL with normal granulocytes increased the reactivity of LDL with mAb OB/04. These effects were even more pronounced using MPO-deficient granulocytes. Inhibitors of oxidative reactions (the NADPH oxidase inhibitor diphenyleneiodonium chloride [DPI], catalase, superoxide dismutase [SOD]) did not significantly reduce LDL oxidation by normal granulocytes. Furthermore, granulocytes of a patient with NADPH oxidase deficiency were almost equally effective as normal granulocytes, indicating that oxidative burst-derived reactive oxygen species are of only minor importance in the generation of mAb OB/04-detectable new epitopes on LDL in vitro. In contrast, incubation of LDL with iron and copper prior to and during incubation with normal granulocytes markedly enhanced the generation of OB/04-detectable epitopes. It is supposed that, besides superoxide (in normal and MPO-deficient granulocytes) or instead of superoxide (in NADPH oxidase-deficient granulocytes), lytic enzymes released by activated granulocytes may enhance the availability of transition metals for oxidation of LDL. Our results support the concept that transition-metal-dependent pathways of LDL oxidation in combination with degranulation products of granulocytes are important.

Bone marrow-derived factors support growth of N-type, but not of melanocytic neuroblastoma cells

BACKGROUND

Neuroblastoma and melanoma cells have a common embryonal origin. In contrast to melanoma, most neuroblastoma tumours preferentially metastasize into bone marrow. Previously, we described that bone marrow-conditioned medium (BM-CM) supports the proliferation of catecholamine-producing (N-type) neuroblastoma (SK-N-SH, IMR-32, Kelly)-, but not of melanoma cells. Both neuroblastoma and melanoma produce DOPA (3,4 dihydroxyphenylalanine); while melanoma cells use tyrosinase for DOPA synthesis, neuroblastoma cells usually utilize tyrosine hydroxylase.

RESULTS

Certain neuroblastoma cells (in our study: SK-N-LO, LS, SH-EP) express tyrosinase instead of tyrosine hydroxylase for synthesis of DOPA, and do not synthesize catecholamines, as shown by HPLC and RT-PCR analysis. Strikingly and in contrast to catecholamine-producing N-type cells, the proliferation of these melanocytic neuroblastoma cells is not supported by BM-CM.

CONCLUSION

With respect to proliferation in the presence of BM-CM, melanocytic neuroblastoma cells behave more like melanoma cells and may represent the subfraction of neuroblastoma cells with a minor tendency to metastasize into bone marrow.

Differences in the accumulation of ascorbic acid in normal, myeloperoxidase deficient and NADPH-oxidase deficient granulocytes

Granulocytes contain large quantities of ascorbic acid (AA). The uptake mechanism is mainly restricted to the accumulation of the oxidized form, dehydroascorbate (DHA). We investigated the uptake of ascorbic acid and dehydroascorbate of normal, myeloperoxidase (MPO)-deficient, and NADPH-oxidase-deficient granulocytes. The accumulation of ascorbic acid was increased in all types of granulocytes after stimulation with phorbol-myristate-acetate, whereas the NADPH-oxidase-deficient cells showed a decreased uptake compared to normal and MPO-deficient cells. The intracellular concentration of ascorbic acid was further enhanced after incubation of granulocytes with DHA, most prominently in NADPH-oxidase-deficient granulocytes. MPO-deficient granulocytes are not able to produce HOCl after activation. The granulocytes of one individual with total MPO deficiency accumulated ascorbate in higher concentrations than did cells with partial MPO deficiency, indicating that HOCl is of minor importance for the oxidation of ascorbate. Since the ability of MPO-deficient cells to kill microorganisms is pronounced in contrast to NADPH-oxidase-deficient cells, effective mechanisms of compensating for the absence of HOCl must exist. We hypothesize that the enhanced uptake of ascorbic acid combined with an enhanced superoxide anion production may favor the generation of OH radicals via the Fenton reaction.

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.