Spermine toxicity and glutathione depletion in BHK-21/C13 cells

Expression of Polyamine Oxidase in Fibroblasts Induces MMP-1 and Decreases the Integrity of Extracellular Matrix

Polyamine oxidase (PAOX) (N¹-acetylpolyamine oxidase) is a major enzyme in the polyamine catabolism pathway that generates hydrogen peroxide. Hydrogen peroxide plays a crucial role in skin aging via extracellular matrix (ECM) degradation by increasing the matrix metalloproteinase-1 (MMP-1) levels. We analyzed the integrity of the ECM in foreskin fibroblasts using PAOX expression. PAOX increased the MMP-1 secretion and type Ι collagen degradation in 2D and 3D cultures of fibroblasts, respectively. Similarly, PAOX overexpression increased the messenger ribonucleic acid (mRNA) level of MMP-1. PAOX expression induced polyamine catabolism, decreased the spermine levels, and increased the putrescine levels. However, the exogenous polyamine treatment did not change the MMP-1 and type I collagen levels as much as PAOX expression. PAOX expression increased the reactive oxygen species (ROS) production in fibroblasts, and exogenous hydrogen peroxide increased both the ROS production and MMP-1 secretion. Furthermore, N-acetylcysteine, an antioxidant, reversed the PAOX-induced ROS production and MMP-1 secretion. PAOX induced the signaling pathways that activate activator protein-1 (AP-1) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), which are important transcription factors for MMP-1 transactivation. We concluded that PAOX increased the ROS levels in fibroblasts, leading to an increase in MMP-1 expression. Therefore, we propose that PAOX is a potential target molecule in protecting the ECM integrity.

Response of Osteosarcoma Cell Metabolism to Platinum and Palladium Chelates as Potential New Drugs

This paper reports the first metabolomics study of the impact of new chelates Pt2Spm and Pd2Spm (Spm = Spermine) on human osteosarcoma cellular metabolism, compared to the conventional platinum drugs cisplatin and oxaliplatin, in order to investigate the effects of different metal centers and ligands. Nuclear Magnetic Resonance metabolomics was used to identify meaningful metabolite variations in polar cell extracts collected during exposure to each of the four chelates. Cisplatin and oxaliplatin induced similar metabolic fingerprints of changing metabolite levels (affecting many amino acids, organic acids, nucleotides, choline compounds and other compounds), thus suggesting similar mechanisms of action. For these platinum drugs, a consistent uptake of amino acids is noted, along with an increase in nucleotides and derivatives, namely involved in glycosylation pathways. The Spm chelates elicit a markedly distinct metabolic signature, where inverse features are observed particularly for amino acids and nucleotides. Furthermore, Pd2Spm prompts a weaker response from osteosarcoma cells as compared to its platinum analogue, which is interesting as the palladium chelate exhibits higher cytotoxicity. Putative suggestions are discussed as to the affected cellular pathways and the origins of the distinct responses. This work demonstrates the value of untargeted metabolomics in measuring the response of cancer cells to either conventional or potential new drugs, seeking further understanding (or possible markers) of drug performance at the molecular level.

A preliminary study procedure for detection of polyamines in plasma samples as a potential diagnostic tool in prostate cancer

BACKGROUND

Many scientific contributions recognize polyamines as important biomarkers for the diagnosis and treatment of cancer. Several authors have suggested the use of LC/MS instruments as an elective method for their measurement, providing good detection limits and specificity; however, many of these procedures suffer from long chromatographic run times, high detection limits and lengthy and expensive sample pre-treatment steps.

METHODS

UHPLC coupled with high-resolution Orbitrap mass spectrometry (UHPLC/Orbitrap) was set up for the identification and separation ofpolyamines, together with some of their metabolites and catabolites, in the plasma of healthy and prostate cancer human patients. Thirteen metabolites were measured in deproteinized plasma samples through a new analytical approach known as the parallel reaction monitoring (PRM) for targeted quantitative analysis.

RESULTS

The calibration curves were linear and R2 ranged from 0.9913 to 0.9995 for all analytes. LOQ values are between 0.382 and 25 ng mL^-1 and LOD values are between 0.109 and 7.421 ng mL^-1. The method shows an accuracy and precision for intra-day and inter-day < 15% RSD and R.E.% for all the QC samples. The matrix effect calculated at different concentration levels did not exceed 15%.

CONCLUSIONS

The method developed provides rapid, easy and robust identification and measurement of a wide range of polyamines, and some of their metabolites that can be evaluated as biomarkers to predict the clinical features of prostate cancer patients, avoiding invasive diagnostic procedures.

Endogenous toxic metabolites and implications in cancer therapy

It is well recognized that many metabolic enzymes play essential roles in cancer cells in producing building blocks such as nucleotides, which are required in greater amounts due to their increased proliferation. On the other hand, the significance of enzymes in preventing the accumulation of their substrates is less recognized. Here, we outline the evidence and underlying mechanisms for how many metabolites normally produced in cells are highly toxic, such as metabolites containing reactive groups (e.g., methylglyoxal, 4-hydroxynonenal, and glutaconyl-CoA), or metabolites that act as competitive analogs against other metabolites (e.g., deoxyuridine triphosphate and l-2-hydroxyglutarate). Thus, if a metabolic pathway contains a toxic intermediate, then we may be able to induce accumulation and poison a cancer cell by targeting the downstream enzyme. Furthermore, this poisoning may be cancer cell selective if this pathway is overactive in a cancer cell relative to a nontransformed cell. We describe this concept as illustrated in selenocysteine metabolism and other pathways and discuss future directions in exploiting toxic metabolites to kill cancer cells.

Cytotoxic Mechanism of Excess Polyamines Functions through Translational Repression of Specific Proteins Encoded by Polyamine Modulon

Excessive accumulation of polyamines causes cytotoxicity, including inhibition of cell growth and a decrease in viability. We investigated the mechanism of cytotoxicity caused by spermidine accumulation under various conditions using an Escherichia coli strain deficient in spermidine acetyltransferase (SAT), a key catabolic enzyme in controlling polyamine levels. Due to the excessive accumulation of polyamines by the addition of exogenous spermidine to the growth medium, cell growth and viability were markedly decreased through translational repression of specific proteins [RMF (ribosome modulation factor) and Fis (rRNA transcription factor) etc.] encoded by members of polyamine modulon, which are essential for cell growth and viability. In particular, synthesis of proteins that have unusual locations of the Shine–Dalgarno (SD) sequence in their mRNAs was inhibited. In order to elucidate the molecular mechanism of cytotoxicity by the excessive accumulation of spermidine, the spermidine-dependent structural change of the bulged-out region in the mRNA at the initiation site of the rmf mRNA was examined using NMR analysis. It was suggested that the structure of the mRNA bulged-out region is affected by excess spermidine, so the SD sequence of the rmf mRNA cannot approach initiation codon AUG.

Supplementation with spermine during in vitro maturation of porcine oocytes improves early embryonic development after parthenogenetic activation and somatic cell nuclear transfer

Spermine plays an important role in protection from reactive oxygen species (ROS) in bacteria, yeast, and mammalian cells, but there are few studies on the effects of spermine on porcine oocyte maturation and subsequent embryo development. The aim of this study was to determine the effects of spermine on in vitro maturation (IVM) of porcine oocytes and their developmental competence after parthenogenetic activation (PA) and somatic cell nuclear transfer (SCNT). We evaluated nuclear maturation, intracellular glutathione (GSH), and ROS levels in oocytes, and their subsequent embryonic development, as well as gene expression in mature oocytes, cumulus cells, and PA blastocysts. After treatment with various concentrations of spermine in IVM culture medium, there was no significant difference in nuclear maturation rate. However, spermine treatment groups (10- 500 µM) showed significantly increased intracellular GSH levels and decreased ROS levels compared to the control ( < 0.05). Furthermore, 10 µM spermine supported significantly higher blastocyst formation rates after PA than the control group ( < 0.05). According to the optimal condition from the PA results, we investigated the effects of 10 µM spermine on SCNT, and it also significantly improved blastocyst formation rates compared with the control group ( < 0.05). In evaluating the effects of 10 µM spermine on gene expression, there was significantly lower expression of a proapoptotic gene () and higher expression of an antiapoptotic gene () in cumulus cells ( < 0.05). was increased in spermine-treated oocytes. Levels of transcription for and were significantly increased in PA blastocysts. In conclusion, 10 µM spermine supplementation during IVM improved the development of porcine PA and SCNT embryos by increasing intracellular GSH, scavenging ROS levels, and regulating gene expression.

Cardiac responses to β-adrenoceptor stimulation is partly dependent on mitochondrial calcium uniporter activity

BACKGROUND AND PURPOSE

Despite the importance of mitochondrial Ca(2+) to metabolic regulation and cell physiology, little is known about the mechanisms that regulate Ca(2+) entry into the mitochondria. Accordingly, we established a system to determine the role of the mitochondrial Ca(2+) uniporter in an isolated heart model, at baseline and during increased workload following β-adrenoceptor stimulation.

EXPERIMENTAL APPROACH

Cardiac contractility, oxygen consumption and intracellular Ca(2+) transients were measured in ex vivo perfused murine hearts. Ru360 and spermine were used to modify mitochondrial Ca(2+) uniporter activity. Changes in mitochondrial Ca(2+) content and energetic phosphate metabolite levels were determined.

KEY RESULTS

The addition of Ru360 , a selective inhibitor of the mitochondrial Ca(2+) uniporter, induced progressively and sustained negative inotropic effects that were dose-dependent with an EC50 of 7 μM. Treatment with spermine, a uniporter agonist, showed a positive inotropic effect that was blocked by Ru360 . Inotropic stimulation with isoprenaline elevated oxygen consumption (2.7-fold), Ca(2+) -dependent activation of pyruvate dehydrogenase (5-fold) and mitochondrial Ca(2+) content (2.5-fold). However, in Ru360 -treated hearts, this parameter was attenuated. In addition, β-adrenoceptor stimulation in the presence of Ru360 did not affect intracellular Ca(2+) handling, PKA or Ca(2+) /calmodulin-dependent PK signalling.

CONCLUSIONS AND IMPLICATIONS

Inhibition of the mitochondrial Ca(2+) uniporter decreases β-adrenoceptor response, uncoupling between workload and production of energetic metabolites. Our results support the hypothesis that the coupling of workload and energy supply is partly dependent on mitochondrial Ca(2+) uniporter activity.

Polyamines in biological samples: rapid and robust quantification by solid-phase extraction online-coupled to liquid chromatography-tandem mass spectrometry

Polyamines are ubiquitous active biogenic amines which contribute to basic cellular functions. Hence, their quantification in samples of diverse biological origins is essential for understanding how they function, especially in disease-relevant conditions. We present here a robust, high-throughput solid-phase extraction online coupled to a liquid chromatography-tandem mass spectrometry (SPE-LC/MS/MS) approach for the simultaneous quantification of eight polyamines in various biological samples. The polyamines include 1,3-diaminopropane, putrescine, cadaverin, N-acetyl-putrescine, spermidine, spermine, N(1)-acetyl-spermine, and l-ornithine. The novelty of the work is the use of two SPE columns online coupled to LC/MS/MS, which minimizes the sample pretreatment to a single derivatization step. The analysis is complete within 4min, making the method highly suitable for routine clinical analysis and high throughput screenings. The method was fully validated with serum samples. Dynamic ranges were 0.03 to 15μg/ml for ornithine and 1 to 500ng/ml for other polyamines, which cover physiological concentrations in serum samples. Lower limits of quantification (LLoQ) were found to be between 0.1 and 5ng/ml. As a proof of concept, we investigated gender differences in polyamine levels by analyzing the serum levels of 102 subjects.

Cloning and molecular characterization of an ornithine decarboxylase gene and its expression during embryonic development of the housefly, Musca domestica

We are interested in identifying targets that may be used to develop new control products for the common housefly, Musca domestica, a vector of disease for many vertebrates. One such target, ornithine decarboxylase (ODC), is an embryonic enzyme involved in the regulation of polyamines and is a critical enzyme during M. domestica development. In this study, the cDNA for ODC from M. domestica was cloned, sequenced, and characterized. The full-length cDNA was 1,337-bp, consistent with a single band of approximately 1.35 kb obtained by northern analysis. The open-reading frame contains 1,191 bp, yielding a deduced polypeptide of 396 amino acid residues with a predicted mass of 44,618 Da. The deduced M. domestica ODC protein was homologous to other ODC proteins. mRNA expression profiles analyzed by real-time PCR indicated that the ODC transcript is temporally regulated throughout embryogenesis. Sequence data and Southern blot analysis suggests that there were likely only one or two closely linked copies of the M. domestica ODC gene.

Estrogen regulates amiloride-binding protein 1 through CCAAT/enhancer-binding protein-beta in mouse uterus during embryo implantation and decidualization

Embryo implantation is an intricate interaction between receptive uterus and active blastocyst. The mechanism underlying embryo implantation is still unknown. Although histamine and putrescine are important for embryo implantation and decidualization, excess amount of histamine and putrescine is harmful. Amiloride binding protein 1 (Abp1) is a membrane-associated amine oxidase and mainly metabolizes histamine and putrescine. In this study, we first showed that Abp1 is strongly expressed in the decidua on d 5-8 of pregnancy. Abp1 expression is not detected during pseudopregnancy and under delayed implantation but is detected after estrogen activation. Because Abp1 is mainly localized in the decidua and also strongly expressed during in vitro decidualization, Abp1 might play a role during mouse decidualization. The regulation of estrogen on Abp1 is mediated by transcription factor CCAAT/enhancer-binding protein-β. Abp1 expression is also regulated by cAMP, bone morphogenetic protein 2, and ERK1/2. Abp1 may be essential for mouse embryo implantation and decidualization.

Polyamines are essential in embryo implantation: expression and function of polyamine-related genes in mouse uterus during peri-implantation period

Polyamines are key regulators in cell growth and differentiation. It has been shown that ornithine decarboxylase (Odc) was essential for post-implantation embryo development, and overexpression of spermidine/spermine N1-acetyltransferase will lead to ovarian hypofunction and hypoplastic uteri. However, the expression and function of polyamine-related genes in mouse uterus during early pregnancy are still unknown. In this study we investigated the expression, regulation, and function of polyamine-related genes in mouse uterus during the peri-implantation period. Odc expression was strongly detected at implantation sites and stimulated by estrogen treatment. The expression of Odc antizyme 1 and spermidine/spermine N1-acetyltransferase was also highly shown at implantation sites and regulated by Odc or polyamine level in uterine cells. Embryo implantation was significantly inhibited by alpha-difluoromethylornithine, an Odc inhibitor. Moreover, the reduction of Odc activity caused by alpha-difluoromethylornithine treatment was compensated by the up-regulation of S-adenosylmethionine decarboxylase gene expression. Collectively, our results indicated that the coordinated expression of uterine polyamine-related genes may be important for embryo implantation.

Polyamines inhibit apoptosis in porcine parthenotes developing in vitro

Polyamines, namely putrescine, spermidine, and spermine, are biogenic low-molecular-weight aliphatic amines which play essential roles in cell growth and proliferation. The aim of this study was to determine the effects of polyamines on the viability and development of porcine diploid parthenotes developing in vitro. The addition of 0.1 or 1.0 microM of putrescine, spermidine, or spermine, individually, to the culture medium did not enhance the development of 2-cell parthenotes to the blastocyst stage and did not change the total number of nuclei in the blastocysts. However, combined addition of these three compounds increased developmental rate to blastocyst and total cell numbers. Apoptosis in blastocyst stage parthenotes was decreased in the presence of exogenous polyamines. Real time PCR revealed that addition of polyamines to the culture media decreased the ratio of mRNA expression of Bak/Bcl-xL, Fas/Bcl-xL, and caspase 3, and enhanced mRNA expression of ornithine decarboxylase (ODC) and spermidine synthase, enzymes of polyamine biosynthesis. In the presence of L-alpha-difluoromethyl ornithine (an inhibitor of ODC) or cyclohexylamine (an inhibitor of spermidine synthase) development of porcine parthenotes decreased, apoptosis increased, and mRNA expression of the ratio of Bak/Bcl-xL and Fas/Bcl-xL, and caspase 3 increased. These results suggest that exogenous polyamines in the culture medium prevent apoptosis of porcine parthenotes and results in the net enhancement of porcine embryo viability.

A perspective of polyamine metabolism

Polyamines are essential for the growth and function of normal cells. They interact with various macromolecules, both electrostatically and covalently and, as a consequence, have a variety of cellular effects. The complexity of polyamine metabolism and the multitude of compensatory mechanisms that are invoked to maintain polyamine homoeostasis argue that these amines are critical to cell survival. The regulation of polyamine content within cells occurs at several levels, including transcription and translation. In addition, novel features such as the +1 frameshift required for antizyme production and the rapid turnover of several of the enzymes involved in the pathway make the regulation of polyamine metabolism a fascinating subject. The link between polyamine content and human disease is unequivocal, and significant success has been obtained in the treatment of a number of parasitic infections. Targeting the polyamine pathway as a means of treating cancer has met with limited success, although the development of drugs such as DFMO (alpha-difluoromethylornithine), a rationally designed anticancer agent, has revolutionized our understanding of polyamine function in cell growth and provided 'proof of concept' that influencing polyamine metabolism and content within tumour cells will prevent tumour growth. The more recent development of the polyamine analogues has been pivotal in advancing our understanding of the necessity to deplete all three polyamines to induce apoptosis in tumour cells. The current thinking is that the polyamine inhibitors/analogues may also be useful agents in the chemoprevention of cancer and, in this area, we may yet see a revival of DFMO. The future will be in adopting a functional genomics approach to identifying polyamine-regulated genes linked to either carcinogenesis or apoptosis.

Growth-inhibitory effects of the chemopreventive agent indole-3-carbinol are increased in combination with the polyamine putrescine in the SW480 colon tumour cell line

BACKGROUND

Many tumours undergo disregulation of polyamine homeostasis and upregulation of ornithine decarboxylase (ODC) activity, which can promote carcinogenesis. In animal models of colon carcinogenesis, inhibition of ODC activity by difluoromethylornithine (DFMO) has been shown to reduce the number and size of colon adenomas and carcinomas. Indole-3-carbinol (I3C) has shown promising chemopreventive activity against a range of human tumour cell types, but little is known about the effect of this agent on colon cell lines. Here, we investigated whether inhibition of ODC by I3C could contribute to a chemopreventive effect in colon cell lines.

METHODS

Cell cycle progression and induction of apoptosis were assessed by flow cytometry. Ornithine decarboxylase activity was determined by liberation of CO2 from 14C-labelled substrate, and polyamine levels were measured by HPLC.

RESULTS

I3C inhibited proliferation of the human colon tumour cell lines HT29 and SW480, and of the normal tissue-derived HCEC line, and at higher concentrations induced apoptosis in SW480 cells. The agent also caused a decrease in ODC activity in a dose-dependent manner. While administration of exogenous putrescine reversed the growth-inhibitory effect of DFMO, it did not reverse the growth-inhibition following an I3C treatment, and in the case of the SW480 cell line, the effect was actually enhanced. In this cell line, combination treatment caused a slight increase in the proportion of cells in the G2/M phase of the cell cycle, and increased the proportion of cells undergoing necrosis, but did not predispose cells to apoptosis. Indole-3-carbinol also caused an increase in intracellular spermine levels, which was not modulated by putrescine co-administration.

CONCLUSION

While indole-3-carbinol decreased ornithine decarboxylase activity in the colon cell lines, it appears unlikely that this constitutes a major mechanism by which the agent exerts its antiproliferative effect, although accumulation of spermine may cause cytotoxicity and contribute to cell death. The precise mechanism by which putrescine enhances the growth inhibitory effect of the agent remains to be elucidated, but does result in cells undergoing necrosis, possibly following accumulation in the G2/M phase of the cell cycle.

Analysis of polyamines as markers of (patho)physiological conditions

The aliphatic polyamines, putrescine, spermidine and spermine, are normal cell constituents that play important roles in cell proliferation and differentiation. The equilibrium between cellular uptake and release and the balanced activities of biosynthetic and catabolic enzymes of polyamines are essential for normal homeostasis in the proliferation and functions of cells and tissues. However, the intracellular polyamine content increases in hyperplastic or neoplastic growth. Although the involvement of polyamines in physiological and pathological cell proliferation and differentiation has been well established, the role they play is quite different in relation to cell systems and animal models and is dependent on inducer agents and stimuli. Also, the experimental procedures used to deplete polyamines have been shown to influence the cell responses. In this paper, the assay methods currently in use for polyamines are reviewed and compared with respect to sensitivity, reproducibility and applicability to routine analysis. The relevance of polyamine metabolism and the uptake/release process in many physiological and pathological processes is highlighted, and the cellular polyamine pathways are discussed in relation to the possible diagnostic and therapeutic significance of these mediators.

Thiols and polyamines in the potentiation of malathion toxicity in larval stages of the toad Bufo arenarum

Treatment with exogenous spermidine enhanced acute malathion toxicity during larval development of the toad Bufo arenarum Hensel. The polyamine was rapidly incorporated in the larvae with a subsequent metabolization to putrescine and spermine, which were excreted to the media. Endogenous polyamine levels were not changed by either spermidine or malathion treatments. However, 0.5-mM spermidine modified malathion uptake and bioavailability increasing the concentration of the xenobiotic in the larvae. The amount of reduced thiols was decreased by both compounds, but the depletion was insufficient to induce cytotoxicity. The oxidative degradation of polyamines competes for the pool of reduced glutathione used in the conjugation of malathion in the larvae, thus leading to the reported potentiation of toxicity. Our results suggest that exposure to thiols-depleting agents may induce alteration of organophosphate degradation in amphibian larvae.

Polyamines in the lung: polyamine uptake and polyamine-linked pathological or toxicological conditions

The natural polyamines putrescine, cadaverine, spermidine, and spermine are found in all cells. These (poly)cations exert interactions with anions, e.g., DNA and RNA. This feature represents their best-known direct physiological role in cellular functions: cell growth, division, and differentiation. The lung and, more specifically, alveolar epithelial cells appear to be endowed with a much higher polyamine uptake system than any other major organ. In the lung, the active accumulation of natural polyamines in the epithelium has been studied in various mammalian species including rat, hamster, rabbit, and human. The kinetic parameters (Michaelis-Menten constant and maximal uptake) of the uptake system are the same order of magnitude regardless of the polyamine or species studied and the in vitro system used. Also, other pulmonary cells accumulate polyamines but never to the same extent as the epithelium. Although different uptake systems exist for putrescine, spermidine, and spermine in the lung, neither the nature of the carrier protein nor the reason for its existence is known. Some pulmonary toxicological and/or pathological conditions have been related to polyamine metabolism and/or polyamine content in the lung. Polyamines possess an important intrinsic toxicity. From in vitro studies with nonpulmonary cells, it has been shown that spermidine and spermine can be metabolized to hydrogen peroxide, ammonium, and acrolein, which can all cause cellular toxicity. In hyperoxia or after ozone exposure, the increased polyamine synthesis and polyamine content of the rat lung is correlated with survival of the animals. Pulmonary hypertension induced by monocrotaline or hypoxia has also been linked to the increased polyamine metabolism and polyamine content of the lung. In a small number of studies, it has been shown that polyamines can contribute to the suppression of immunologic reactions in the lung.

Involvement of polyamines in apoptosis. Facts and controversies: effectors or protectors?

The natural polyamines (putrescine, spermidine and spermine) are ubiquitous low-molecular aliphatic amines that play multifunctional roles in cell growth and differentiation. Recently, evidence has merging that polyamines are actively involved in cell death. Changes in polyamine homeostasis have been reported during cell death of nerve cells, in programmed cell death of embryonic cells and in various in vitro models of apoptosis. Polyamines and many of their structural analogs exert cytotoxic effects in vitro as well in vivo. Furthermore, polyamine analogs and inhibitors of the polyamine anabolic/catabolic pathways modulate processes of cell death in a cell-type specific way. Much ambiguity exists in the working mechanisms by which polyamines mediate apoptosis since they have been shown to act as promoting, modulating or protective agents in apoptosis. Nevertheless, from the studies reviewed here it can be concluded that polyamines are critically involved in cellular survival which makes them suitable targets for therapeutic intervention that is specifically directed to cell death pathways.

N8-acetyl spermidine protects rat cerebellar granule cells from low K+-induced apoptosis

The endogenous polyamines have been extensively studied with respect to their role in cellular death mechanisms, although the results are contradictory. In contrast, their primary metabolites, the N-acetyl polyamines, have not been much studied. It has been hypothesized that the N-acetyl metabolites may play a role in cellular death mechanisms, and some of the variability between different reports may be due to altered polyamine metabolic capacities. Using primary cultures of rat cerebellar granule cells, the effects of N-acetyl metabolites have been examined on basal, cytosine beta-D-arabinofuranoside (Ara-C)-induced and low K+-induced apoptosis. None of the compounds affected either basal or Ara-C-induced apoptosis at low doses. At higher doses, all compounds were toxic. Two compounds, N8-acetyl spermidine and N1-acetyl spermine, were found to protect cells from low K+-induced apoptosis, which has been shown to be p53-independent. In contrast, the parent polyamines were devoid of protective activity at subtoxic doses. This represents the first time that an antiapoptotic effect of N-acetyl polyamines has been demonstrated. These results raise the possibility that these compounds may act as endogenous neuroprotectants. The lack of effect on basal apoptosis provides evidence of at least two forms of p53-independent apoptosis that can be regulated independently.

Modulation of cis-diamminedichloroplatinum (II) accumulation and cytotoxicity by spermine in sensitive and resistant human ovarian carcinoma cells

The effect of spermine (Sp), a natural polycationic amine, on cisplatin (CDDP) sensitivity and accumulation of a human ovarian CDDP-sensitive cell line (2008) and its resistant variant (C13*) was investigated. Survival was also studied. The C13* cells were approximately 20-fold resistant to CDDP, yet were found to be just as sensitive to Sp as 2008 cells. When Sp was concurrently added with CDDP to the colony-forming assay, the IC50 dose was approximately 3-fold lower than that of CDDP alone. This decrease was the result of a synergistic interaction, as assessed by median effect analysis. The incubation of cells with the approximate IC50 dose of Sp for 1-8 h indicated that this synergism could be due to stimulation of CDDP accumulation, showing maximal uptake after 4 h of Sp exposure. This stimulation may be the result of a modulation of cellular membrane permeability by Sp, as assessed by the accumulation of [3H]mannitol. Exposure to Sp concentrations active on CDDP uptake also significantly increased [3H]mannitol accumulation in both cell lines. The triamine spermidine (Spd) did not significantly affect either the sensitivity of the two cell lines or CDDP and [3H]mannitol accumulation. These results suggest that Sp is a positive modulator of CDDP uptake, and thus of its cytotoxicity, even in resistant cells, where the phenotype is partly due to a CDDP accumulation defect.

2,2'-Dithiobis(N-ethyl-spermine-5-carboxamide) is a high affinity, membrane-impermeant antagonist of the mammalian polyamine transport system

We have synthesized 2,2'-dithiobis(N-ethyl-spermine-5-carboxamide) (DESC), its thiol monomer (MESC), and the mixed MESC-cysteamine disulfide (DEASC) as potential inhibitors of polyamine transport in mammalian cells. DESC was the most potent antagonist of spermine transport in ZR-75-1 human breast cancer cells, with Ki values of 5. 0 +/- 0.7, 80 +/- 31, and 16 +/- 3 microM for DESC, MESC, and DEASC, respectively. DESC also strongly blocked putrescine and spermidine uptake in ZR-75-1 cells (Ki = 1.6 +/- 0.5 and 2.7 +/- 1.1 microM, respectively). While DESC and MESC were purely competitive inhibitors of putrescine transport, DEASC was a mixed competitive/noncompetitive antagonist. Remarkably, DESC was virtually impermeant in ZR-75-1 cells despite its low Ki toward polyamine transport. The marked difference in affinity between DESC and MESC was essentially due to the tail-to-tail juxtaposition of two spermine-like structures, suggesting that dimeric ligands of the polyamine transporter might simultaneously interact with more than one binding site. While DESC strongly decreased the initial rate of [3H]spermidine transport, even a 40-fold molar excess of antagonist could not completely abolish intracellular spermidine accumulation. Moreover, as little as 0.3 microM spermidine fully restored growth in ZR-75-1 cells treated with an inhibitor of polyamine biosynthesis in the presence of 50 microM DESC, thus emphasizing the importance of uptake of trace amounts of exogenous polyamines. Thus, reducing the exogenous supply of polyamines with a potent competitive inhibitor may be kinetically inadequate to block replenishment of the polyamine pool in polyamine-depleted tumor cells that display high transport capacity. These results demonstrate that polyamine analogues cross-linked into a dimeric structure such as DESC interact with high affinity with the mammalian polyamine carrier without being used as substrates. These novel properties provide a framework for the design of specific irreversible inhibitors of the polyamine transporter, which should present advantages over competitive antagonists for an efficient blockade of polyamine transport in tumor cells.

Inhibition of cell growth by accumulated spermine is associated with a transient alteration of cell cycle progression

Exposure of HL-60 cells to millimolar levels of spermine resulted in the inhibition of cell growth. Flow cytometry revealed that the addition of exogenous spermine prevented the accumulation of cells in the S and G2/M phases of the cell cycle as observed in the control cells. High intracellular levels of spermine completely suppressed the early onset of ornithine decarboxylase activity and, consequently, the intracellular increase in spermidine and putrescine. On the other hand, the addition of exogenous spermidine or putrescine also abolished ornithine decarboxylase activity, but in this case neither the growth of spermidine- or putrescine-treated cells nor the cell cycle phase distribution was affected. In the latter cells, intracellular levels of spermidine were not significantly different from control ones. These results suggest that the addition of exogenous spermine inhibits cell proliferation by hindering the increase in cellular spermidine needed to accelerate the G1 to S phase transition.

Use of aminopropyltransferase inhibitors and of non-metabolizable analogs to study polyamine regulation and function

The polyamines spermidine and spermine are essential for the growth of mammalian cells. This review describes the properties of the two aminopropyltransferases that are responsible for their biosynthesis, the synthesis and use of specific aminopropyltransferase inhibitors, and the use of analogs of the polyamines to investigate polyamine transport and function. Highly specific and potent multisubstrate adduct inhibitors of these enzymes have been synthesized while less potent inhibitors have been obtained by the synthesis of amines that bind at the active site. Studies with these inhibitors indicate that polyamines are needed for a normal rate of growth and that, although some of the functions of polyamines may be interchangeable, other functions may have a specific requirement for spermidine or spermine. Two groups of growth-promoting polyamine analogs can be distinguished: the many that are effective in short-term experiments compared to the few that can act over a prolonged period. The more stringent structural requirements for long-term growth are probably due to a need for spermidine, or a closely related analog, as a precursor of hypusine in the protein eIF-5A. Metabolically resistant polyamine analogs can be used as model substrates for studies of the polyamine transport system, which plays a critical role in maintaining normal cellular polyamine levels. The feedback regulation by high levels of polyamines that downregulates transport is essential to prevent the accumulation of polyamines at toxic levels. Such accumulation may be associated with apoptosis and, therefore, polyamine analogs are useful tools for investigating the mechanism(s) of polyamine-mediated toxicity.

Culture of a differentiated liver cell line, Hep G2, in serum with application to a bioartificial liver: effect of supplementation of serum with amino acids

Much effort has been directed toward the development of serum-free, hormonally defined culture conditions for the maintenance of differentiated functions in many cell types, including hepatocytes. However, in the development of a hepatocyte bioreactor for artificial liver support, many designs propose the maintenance of cells in plasma as opposed to defined culture medium. There is very little reported literature on the growth and function of cells cultured in plasma or serum; therefore, the effect of increasing serum concentrations was investigated using the human hepatoma, Hep G2, as a model cell line. It was found that Hep G2 can survive and grow in 100% serum if the serum is supplemented with L-glutamic acid, glycine, and L-cysteine.

A free-radical hypothesis for the instability and evolution of genotype and phenotype in vitro

It has been known for several decades that cultured murine cells undergo a defined series of changes, i.e., an in vitro evolution, which includes crisis, spontaneous transformation ('immortalization'), aneuploidy, and spontaneous neoplastic transformation. These changes have been shown to be caused by the in vitro environment rather than an inherent instability of the murine phenotype or genotype. Serum amine oxidases were recently identified as a predominant cause of crisis. These enzymes generate hydrogen peroxide from polyamine substrates that enter the extracellular milieu. This finding implicates free-radical toxicity as the underlying cause of in vitro evolution. We propose an oxyradical hypothesis to explain each of the stages of in vitro evolution and discuss its significance for cytotechnology and long-term cultivation of mammalian cell types.

Abnormal accumulation and toxicity of polyamines in a difluoromethylornithine-resistant HTC cell variant

Mammalian cells possess an inducible, active polyamine transport system that is stringently regulated by feedback controls. This study provides evidence that DH23b cells, which were initially selected from the rat hepatoma HTC line for overproduction of ornithine decarboxylase, demonstrate an abnormality in the regulation of polyamine transport. Exposure of these cells to micromolar levels of spermidine or spermine resulted in inhibition of protein synthesis and eventual cell lysis. These effects were not due to by-products of polyamine oxidation by serum oxidases as neither inhibition of protein synthesis nor cell lysis was mitigated by aminoguanidine, reduced glutathione, dithiothreitol, or catalase. Although the polyamine transport system in the DH23b cells has the same Km and Vmax as that in the parental HTC line, the variant cells accumulated abnormally high levels of both spermidine (8-times normal) and spermine (4-times normal). In the HTC line, however, transport of both polyamines as well as putrescine was feedback inhibited within approx. 3 h, while in the variant cells uptake was not diminished by 12 h and terminated only with cell lysis. The DH23b cells appear to lack the normal mechanism responsible for feedback control of active polyamine incorporation. This defect provided the opportunity to manipulate intracellular levels of spermidine from 30 to approx. 800% of normal, allowing the demonstration that cellular protein synthesis is as sensitive to spermidine levels as previous in-vitro studies had suggested.

Sequestered end products and enzyme regulation: the case of ornithine decarboxylase

The polyamines (putrescine, spermidine, and spermine) are synthesized by almost all organisms and are universally required for normal growth. Ornithine decarboxylase (ODC), an initial enzyme of polyamine synthesis, is one of the most highly regulated enzymes of eucaryotic organisms. Unusual mechanisms have evolved to control ODC, including rapid, polyamine-mediated turnover of the enzyme and control of the synthetic rate of the protein without change of its mRNA level. The high amplitude of regulation and the rapid variation in the level of the protein led biochemists to infer that polyamines had special cellular roles and that cells maintained polyamine concentrations within narrow limits. This view was sustained in part because of our continuing uncertainty about the actual biochemical roles of polyamines. In this article, we challenge the view that ODC regulation is related to precise adjustment of polyamine levels. In no organism does ODC display allosteric feedback inhibition, and in three types of organism, bacteria, fungi, and mammals, the size of polyamine pools may vary radically without having a profound effect on growth. We suggest that the apparent stability of polyamine pools in unstressed cells is due to their being largely bound to cellular polyanions. We further speculate that allosteric feedback inhibition, if it existed, would be inappropriately responsive to changes in the small, freely diffusible polyamine pool. Instead, mechanisms that control the amount of the ODC protein have appeared in most organisms, and even these are triggered inappropriately by variation of the binding of polyamines to ionic binding sites. In fact, feedback inhibition of ODC might be maladaptive during hypoosmotic stress or at the onset of growth, when organisms appear to require rapid increases in the size of their cellular polyamine pools.

Mechanisms of spermine toxicity in baby-hamster kidney (BHK) cells. The role of amine oxidases and oxidative stress

Spermine was toxic to BHK-21/C13 cells in the absence of any extracellular metabolism of the amine. Inhibition of copper-containing amine oxidases with aminoguanidine partially prevented the response, whereas inhibition of polyamine oxidase with MDL-72,527 exacerbated the effect. Oxidation by an intracellular copper-containing amine oxidase may be involved in the toxicity of spermine, whereas the polyamine-interconversion pathway appears to play a cytoprotective role. There was no evidence for spermine imposing a state of oxidative stress within the cells. Inhibition of catalase and glutathione reductase did not alter the cytotoxicity of spermine, and there was no excretion of oxidized glutathione into the extracellular medium. The results suggest that spermine itself can exert a toxic effect directly on the cells.