The defect of T4rII replication in Escherichia coli K-12 (lambda) can be phenotypically reversed by various supplements to the growth medium. Arginine, lysine, spermidine, and a number of diamines allowed varying levels of rII replication. The best reversion was obtained with 0.4 m sucrose in 0.002 to 0.005 m Ca(++). Monovalent cations severely inhibited reversion. A cell surface site of polyamine action is consistent with the fact that spermidine inhibits phage ghost-induced cell lysis and with the finding that sufficient polyamine is available within the cells to allow normal patterns of neutralization of phage deoxyribonucleic acid, as detected by the polyamine content of progeny phage. In the absence of effective supplements, rII-infected cells swelled and lost refractility. The data indicate that a leaky cell envelop is involved. No difference in mucopeptides of uninfected K-12 (lambda) and K-12 was detected and, because the mucopeptide in r(+) infected cells was found to be at least partially hydrolyzed midway through the lytic cycle, it did not appear that the rII defect concerned mucopeptide synthesis. The pattern of cell phospholipid synthesis changes after phage infection, but no difference was detected between r(+) and rII with regard to biosynthesis of phosphatidylethanolamine and phosphatidylglycerol.

Nucleosome-nucleosome interaction plays a fundamental role in chromatin folding and self-association. The cation-induced condensation of nucleosome core particles (NCPs) displays properties similar to those of chromatin fibers, with important contributions from the N-terminal histone tails. We study the self-association induced by addition of cations [Mg(2+), Ca(2+), cobalt(III)hexammine(3+), spermidine(3+) and spermine(4)(+)] for NCPs reconstituted with wild-type unmodified histones and with globular tailless histones and for NCPs with the H4 histone tail having lysine (K) acetylations or lysine-to-glutamine mutations at positions K5, K8, K12 and K16. In addition, the histone construct with the single H4K16 acetylation was investigated. Acetylated histones were prepared by a semisynthetic native chemical ligation method. The aggregation behavior of NCPs shows a general cation-dependent behavior similar to that of the self-association of nucleosome arrays. Unlike nucleosome array self-association, NCP aggregation is sensitive to position and nature of the H4 tail modification. The tetra-acetylation in the H4 tail significantly weakens the nucleosome-nucleosome interaction, while the H4 K→Q tetra-mutation displays a more modest effect. The single H4K16 acetylation also weakens the self-association of NCPs, which reflects the specific role of H4K16 in the nucleosome-nucleosome stacking. Tailless NCPs can aggregate in the presence of oligocations, which indicates that attraction also occurs by tail-independent nucleosome-nucleosome stacking and DNA-DNA attraction in the presence of cations. The experimental data were compared with the results of coarse-grained computer modeling for NCP solutions with explicit presence of mobile ions.

The colorectal mucosa of pre-symptomatic individuals with familial adenomatous polyposis (FAP) contains elevated levels of the proliferation-associated polyamines. The Min mouse, like humans with FAP, expresses an abnormal genotype for the APC tumor suppressor gene. In order to determine how APC mutation influences intestinal tissue polyamine content, we measured steady-state RNA levels of ornithine decarboxylase (ODC), the first enzyme in polyamine synthesis, antizyme (AZ), a protein which negatively regulates ODC, and the spermidine/spermine N(1)-acetyltransferase (SSAT), the first enzyme in polyamine catabolism. RNA content was increased 6- to 8-fold in both the small intestine and colon for ODC, decreased significantly in the small intestine but not the colon for AZ and was not statistically different in either intestinal tissue for SSAT in Min mice compared with normal littermates. Consistent with the changes in ODC and AZ gene expression, small intestinal, but not colonic, polyamine content was elevated in Min mice compared with normal littermates. Treatment of Min mice with the specific ODC inhibitor difluoromethylornithine (DFMO) suppressed small intestinal, but not colonic, polyamine content and tumor number. These data indicate that small intestinal tissue polyamine content is elevated in Min mice by a mechanism involving APC-dependent changes in ODC and AZ RNA. Further, ODC enzyme activity, which is influenced by both ODC and AZ RNA levels and inhibited by DFMO, is consequential for small intestinal tumorigenesis in this model. In the FAP population, DFMO may be of value in the chemoprevention of small intestinal adenocarcinoma that remains a risk following colectomy.

We have compared chicken erythrocyte linker histones H1 and H5 binding to a synthetic four-way DNA junction. Each histone binds to form a single complex, with an affinity which permits competition against a large excess of linear duplex DNA. The affinity of H5 is higher than that of H1. The globular domain from either protein will also bind strongly, but in this case multiple binding occurs. Binding of intact H1 is inhibited by cations: Mg2+ and spermidine are very effective, Na+ much less so. This inhibition is not likely to be a general ion-competition effect, for Mg2+ is much less effective in inhibiting the binding of H1 to linear DNA. Instead, the inhibition of binding may be due to ion-dependent changes in the conformation of the four-way junction, which are known to occur under similar conditions. These results strongly suggest that the angle formed between the arms of the DNA junction could be a major determinant in the interaction of H1 with DNA crossovers.

The antizyme family consists of closely homologous proteins believed to regulate cellular polyamine pools. Antizyme1, the first described, negatively regulates ornithine decarboxylase, the initial enzyme in the biosynthetic pathway for polyamines. Antizyme1 targets ornithine decarboxylase for degradation and inhibits polyamine transport into cells, thereby diminishing polyamine pools. A polyamine-stimulated ribosomal frameshift is required for decoding antizyme1 mRNA. Recently, additional novel conserved members of the antizyme family have been described. We report here the properties of one of these, antizyme2. Antizyme2, like antizyme1, binds to ornithine decarboxylase and inhibits polyamine transport. Using a baculovirus expression system in cultured Sf21 insect cells, both antizymes were found to accelerate ornithine decarboxylase degradation. Expression of either antizyme1 or 2 in Sf21 cells also diminished their uptake of the polyamine spermidine. Both forms of antizyme can therefore function as negative regulators of polyamine production and transport. However, in contrast to antizyme1, antizyme2 has negligible ability to stimulate degradation of ornithine decarboxylase in a rabbit reticulocyte lysate.

We have previously shown that the gene (speD) for S-adenosylmethionine decarboxylase is part of an operon that also contains the gene (speE) for spermidine synthase (Tabor, C. W., Tabor, H., and Xie, Q.-W. (1986) Proc. Natl. Acad. Sci. U. S. A. 83, 6040-6044). We have now determined the nucleotide sequence of this operon and have found that speD codes for a polypeptide of Mr = 30,400, which is considerably greater than the subunit size of the purified enzyme. Our studies show that S-adenosylmethionine decarboxylase is first formed as a Mr = 30,400 polypeptide and that this proenzyme is then cleaved at the Lys111-Ser112 peptide bond to form a Mr = 12,400 subunit and a Mr = 18,000 subunit. The latter subunit contains the pyruvoyl moiety that we previously showed is required for enzymatic activity. Both subunits are present in the purified enzyme. These conclusions are based on (i) pulse-chase experiments with a strain containing a speD+ plasmid which showed a precursor-product relationship between the proenzyme and the enzyme subunits, (ii) the amino acid sequence of the proenzyme form of S-adenosylmethionine decarboxylase (derived from the nucleotide sequence of the speD gene), and (iii) comparison of this sequence of the proenzyme with the N-terminal amino acid sequences of the two subunits of the purified enzyme reported by Anton and Kutny (Anton, D. L., and Kutny, R. (1987) J. Biol. Chem. 262, 2817-2822).

Acetylation of polyamines by spermidine/spermine N(1)-acetyltransferase (SSAT) has been implicated in their degradation and/or export out of the cell. The relationship of SSAT to polyamine pool dynamics and cell growth is not yet clearly understood. MCF-7 human breast carcinoma cells were transfected with tetracycline-regulated (Tet-off) SSAT human cDNA or murine gene. Doxycycline removal for >2 days caused a approximately 20-fold increase in SSAT RNA and a approximately 10-fold increase in enzyme activity. After 4 days, intracellular putrescine and spermidine pools were markedly lowered, and cell growth was inhibited. Growth inhibition could not be prevented with exogenous polyamines due to a previously unrecognized ability of SSAT to rapidly acetylate influxing polyamines and thereby prevent restoration of the endogenous pools. Instead, cells accumulated high levels of N(1)-acetylspermidine, N(1)-acetylspermine, and N(1), N(12)-diacetylspermine, a metabolite not previously reported in mammalian cells. Doxycycline deprivation before treatment with N(1), N(11)-diethylnorspermine markedly increased analog induction of SSAT mRNA and activity and enhanced growth sensitivity to the analog by approximately 100-fold. Overall, the findings demonstrate that conditional overexpression of SSAT lowers polyamine pools, inhibits cell growth, and markedly enhances growth sensitivity to certain analogs. The enzyme also plays a remarkably efficient role in maintaining polyamine pool homeostasis during challenges with exogenous polyamines.

Early mucosal restitution is a rapid process by which differentiated intestinal epithelial cells migrate to reseal superficial wounds. However, most of the in vitro studies for restitution employ undifferentiated intestinal crypt cells as a model. The transcription factor, Cdx2, plays an important role in the regulation of intestinal epithelial differentiation. Forced expression of the Cdx2 gene in undifferentiated intestinal crypt cells induces the development of a differentiated phenotype. The current study was designed to determine changes in differentiated intestinal epithelial cell migration after wounding in the stable Cdx2-transfected IEC-6 cells and then to examine involvement of polyamines and nonmuscle myosin II in the process of cell motility. Cdx2-transfected IEC-6 cells were associated with a highly differentiated phenotype and exhibited increased cell migration after wounding. Migration of Cdx2-transfected IEC-6 cells were approximately four times that of nontransfected IEC-6 cells. Migration after wounding was associated with significant increases in polyamine synthesis. Depletion of cellular polyamines by 5 mM alpha-difluoromethylornithine (DFMO), a specific inhibitor of polyamine biosynthesis, inhibited cell migration without affecting the differentiated phenotype. DFMO also decreased levels of nonmuscle myosin II mRNA and protein and resulted in reorganization of myosin II, along with a marked reduction in stress fibers. Exogenous spermidine given together with DFMO not only returned nonmuscle myosin II levels and cellular distribution toward normal but also restored cell migration to control levels. These results indicate that 1) Cdx2-transfected IEC-6 cells exhibit increased cell migration after wounding and 2) cellular polyamines are absolutely required for stimulation of cell migration in association with their ability to modulate the structural organization of nonmuscle myosin II.

The lysosomal endoprotease cathepsin D (CatD) is an essential player in general protein turnover and specific peptide processing. CatD-deficiency is associated with neurodegenerative diseases, whereas elevated CatD levels correlate with tumor malignancy and cancer cell survival. Here, we show that the CatD ortholog of the budding yeast Saccharomyces cerevisiae (Pep4p) harbors a dual cytoprotective function, composed of an anti-apoptotic part, conferred by its proteolytic capacity, and an anti-necrotic part, which resides in the protein's proteolytically inactive propeptide. Thus, deletion of PEP4 resulted in both apoptotic and necrotic cell death during chronological aging. Conversely, prolonged overexpression of Pep4p extended chronological lifespan specifically through the protein's anti-necrotic function. This function, which triggered histone hypoacetylation, was dependent on polyamine biosynthesis and was exerted via enhanced intracellular levels of putrescine, spermidine and its precursor S-adenosyl-methionine. Altogether, these data discriminate two pro-survival functions of yeast CatD and provide first insight into the physiological regulation of programmed necrosis in yeast.

1. A higher concentration of polyamines (spermine, spermidine, putrescine and cadaverine) during development of the chick embryo was observed between the fifth and tenth day of incubation; the concentrations of nucleic acids showed a parallel increase. 2. When spermine (5mumoles) was injected into the yolk sac of embryos at the tenth day of incubation, a high amine-oxidase activity was noted and the spermine and spermidine concentrations were decreased; also, there was a remarkable decrease in RNA and DNA concentrations and a parallel increase in that of total free nucleotides. 3. On the other hand, when iproniazid (16mumoles) was injected there was an inhibition of amine-oxidase activity and a similar increase in the concentrations of spermine and spermidine and of nucleic acids, whereas that of total free nucleotides decreased. 4. Another group of embryos injected with spermine and iproniazid together showed a remarkable increase in spermine and spermidine concentrations and a parallel increase in those of RNA and DNA, and a decrease in that of total free nucleotides.

The subcellular localization of the polyamine transporter TPO1 of Saccharomyces cerevisiae was determined by sucrose gradient centrifugation and indirect immunofluorescence microscopy. When expressed from a multi-copy vector, TPO1 was located mainly on the plasma membrane, but with some localization on the vacuolar membrane. Polyamine transport by TPO1 was dependent on pH. Uptake of spermidine and spermine occurred at alkaline pH (pH 8.0), whereas inhibition of spermidine uptake, but not spermine uptake, was observed at acidic pH (pH 5.0). This suggests that TPO1 catalyzes polyamine excretion at acidic pH, similar to the PotE transporter in Escherichia coli. Paraquat, a polyamine analogue, was excreted by TPO1 at a rate comparable with the excretion of spermidine (deduced from the inhibition of spermidine uptake) at pH 5.0. However, excretion of preloaded radiolabeled spermidine and spermine was not observed in intact cells, suggesting that preloaded spermidine (or spermine) exists mainly as spermidine (or spermine)-ribosome complex in cells. The transport activity of TPO1 was enhanced through phosphorylation at Ser19 by protein kinase C and at Thr52 by casein kinase 1. Sorting of TPO1 from the endoplasmic reticulum to the plasma membrane was enhanced through phosphorylation at Ser342 by cAMP-dependent protein kinases 1 and 2.

1. Injections of sublethal doses of methylglyoxal bis(guanylhydrazone), a potent inhibitor of putrescine-activated S-adenosylmethionine decarboxylase in vitro, resulted after a few days in an immense increase in the activity of S-adenosylmethionine decarboxylase in normal and regenerating rat liver and in rat thymus. The increase in the activity of S-adenosylmethionine decarboxylase was at least partly due to a marked lengthening of the half-life of the enzyme. 2. In regenerating liver and thymus there was also a moderate stimulation of the activity of ornithine decarboxylase (EC 4.1.1.17) and a marked accumulation of tissue putrescine. 3. Injection of methylglyoxal bis(guanylhydrazone) into the rat also markedly decreased the activity of diamine oxidase (EC 1.4.3.6) in thymus. 4. In no cases where doses of methylglyoxal bis(guanylhydrazone) close to the LD(50) dose for the rat were used was it possible to lower tissue spermidine content to any significant extent. 5. Methylglyoxal bis(guanylhydrazone) seemed to act as a competitive inhibitor for the substrate S-adenosylmethionine and as an uncompetitive inhibitor for the activator putrescine in the decarboxylation of S-adenosylmethionine in vitro. 6. In the diamine oxidase reaction, with putrescine as the substrate, methylglyoxal bis(guanylhydrazone) was a non-competitive inhibitor for putrescine.

The polyamines are ubiquitous polycationic compounds. Over the past 40 yr, investigation has shown that some of these, namely spermine, spermidine, and putrescine, are essential to male and female reproductive processes and to embryo/fetal development. Indeed, their absence is characterized by infertility and arrest in embryogenesis. Mammals synthesize polyamines de novo from amino acids or import these compounds from the diet. Information collected recently has shown that polyamines are essential regulators of cell growth and gene expression, and they have been implicated in both mitosis and meiosis. In male reproduction, polyamine expression correlates with stages of spermatogenesis, and polyamines appear to function in promoting sperm motility. There is evidence for polyamine involvement in ovarian follicle development and ovulation in female mammals, and polyamine synthesis is required for steroidogenesis in the ovary. Studies of the embryo indicate a polyamine requirement that can be met from maternal sources before implantation, whereas elimination of polyamine synthesis abrogates embryo development at gastrulation. Polyamines play roles in embryo implantation, in decidualization, and in placental formation and function, and polyamine privation during gestation results in intrauterine growth retardation. Emerging information implicates dietary arginine and dietary polyamines as nutritional regulators of fertility. The mechanisms by which polyamines regulate these multiple and diverse processes are not yet well explored; thus, there is fertile ground for further productive investigation.

We report that voltage-gated Na+ channels (Na(V)) from rat muscle (mu1) expressed in HEK293 cells exhibit anomalous rectification of whole-cell outward current under conditions of symmetrical Na+. This behavior gradually fades with time after membrane break-in, as if a diffusible blocking substance in the cytoplasm is slowly diluted by the pipette solution. The degree of such block and rectification is markedly altered by various mutations of the conserved Lys(III) residue in Domain III of the Na(V) channel selectivity filter (DEKA locus), a principal determinant of inorganic ion selectivity and organic cation permeation. Using whole-cell and macropatch recording techniques, we show that two ubiquitous polyamines, spermine and spermidine, are potent voltage-dependent cytoplasmic blockers of mu1 Na(V) current that exhibit relief of block at high positive voltage, a phenomenon that is also enhanced by certain mutations of the Lys(III) residue. In addition, we find that polyamines alter the apparent rate of macroscopic inactivation and exhibit a use-dependent blocking phenomenon reminiscent of the action of local anesthetics. In the presence of a physiological Na+/K+ gradient, spermine also inhibits inward Na(V) current and shifts the voltage dependence of activation and inactivation. Similarities between the endogenous blocking phenomenon observed in whole cells and polyamine block characterized in excised patches suggest that polyamines or related metabolites may function as endogenous modulators of Na(V) channel activity.

A gentamicin-resistant mutant of Pseudomonas aeruginosa PAO503 was selected after ethyl methane sulfonate mutagenesis. The strain, P. aeruginosa PAO2401 had increased resistance to all aminoglycosides tested but exhibited no change for other antibiotics. The mutation designated aglA (aminoglycoside resistance) was 50% cotransducible with the 8-min ilvB,C marker on the P. aeruginosa chromosome. It showed a marked reduction in cytochrome c(552) and nitrate reductase (Nar) and a change in terminal oxidase activity. Cytochrome c(552) is a component of the P. aeruginosa Nar. No changes in succinate and reduced nicotinamide adenine dinucleotide dehydrogenases, ubiquinone content, Mg(2+)/Ca(2+) membrane adenosine triphosphatase, and energy coupling of electron transport to adenosine 5'-triphosphate synthesis were detected. Transport of gentamicin and dihydrostreptomycin was impaired in PAO2401, but transport of proline, arginine, glutamine, glucose or the polyamine spermidine was not reduced. Ribosomes of PAO2401, and PAO503 bound dihydrostreptomycin equally well, and cell extracts did not inactivate gentamicin or dihydrostreptomycin. Strain PAO2401 is resistant to gentamicin and dihydrostreptomycin because of impaired transport of these compounds. The transport studies indicate a selective coupling of dihydrostreptomycin and gentamicin transport with terminal electron transport. This conclusion was supported by results from another mutant (PAO417-T2) with increased Nar activity, enhanced dihydrostreptomycin and gentamicin transport and a reduction in resistance to these drugs. These results are discussed in relation to a refined model for aminoglycoside transport and briefly relative to plasmid-mediated aminoglycoside resistance.

Nucleoids isolated from Escherichia coli at low salt concentrations in the presence of spermidine (Kornberg et al., Proc. Natl. Acad. Sci. USA, 71, 3189-3193 (1974)) retain large amounts of protein and RNA and are, thus, potentially useful in structural and other studies. However, these preparations have neither been visualized nor extensively characterized with regard to their protein and other components. We have investigated this type of nucleoid preparation and here supply both light and electron microscope appearances and a description of the DNA-associated proteins. Light microscopy is used to follow the stages of nucleoid release and to demonstrate characteristically rounded nucleoids after chloramphenicol treatment of the cells from which the nucleoids were isolated. The nucleoids are "envelope-associated" particles. Electron microscopy shows an irregular central core that is partially covered with small, membranous vesicles. A significant fraction of the nucleoids have a characteristic doublet/dumbbell-shaped appearance by light microscopy. The nucleoids contain large amounts of protein and RNA in addition to DNA. The DNA and RNA are rendered acid-soluble by very low levels of nucleases, indicating an open structure. A small group of proteins, including H-NS, FIS, HU, and RNA polymerase, is released from the particles upon enzymatic digestion of the DNA.

Cadmium (Cd) contamination is a serious agricultural and environmental hazard. The study investigates cross-protection roles of putrescine (Put, 0.2 mM) and nitric oxide (sodium nitroprusside; SNP, 1 mM) in conferring Cd (CdCl2, 1.5 mM) tolerance in mung bean (Vigna radiata L. cv. BARI Mung-2) seedlings. Cadmium stress increased root and shoot Cd content, reduced growth, destroyed chlorophyll (chl), modulated proline (Pro) and reduced leaf relative water content (RWC), increased oxidative damage [lipid peroxidation, H2O2 content, O2(∙-) generation rate, lipoxygenase (LOX) activity], methylglyoxal (MG) toxicity. Put and/or SNP reduced Cd uptake, increasd phytochelatin (PC) content, reduced oxidative damage enhancing non-enzymatic antioxidants (AsA and GSH) and activities of enzymes [superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione S-transferase (GST), and glutathione peroxidase (GPX)]. Exogenous Put and/or SNP modulated endogenous polyamines, PAs (putrescine, Put; spermidine, Spd; spermine, Spm), and NO; improved glyoxalase system in detoxifying MG and improved physiology and growth where combined application showed better effects which designates possible crosstalk between NO and PAs to confer Cd-toxicity tolerance.

Extracellular DNA (eDNA) is in the environment, bodily fluids, in the matrix of biofilms, and accumulates at infection sites. eDNA can function as a nutrient source, a universal biofilm matrix component, and an innate immune effector in eDNA traps. In biofilms, eDNA is required for attachment, aggregation, and stabilization of microcolonies. We have recently shown that eDNA can sequester divalent metal cations, which has interesting implications on antibiotic resistance. eDNA binds metal cations and thus activates the Mg(2+)-responsive PhoPQ and PmrAB two-component systems. In Pseudomonas aeruginosa and many other Gram-negative bacteria, the PhoPQ/PmrAB systems control various genes required for virulence and resisting killing by antimicrobial peptides (APs), including the pmr genes (PA3552-PA3559) that are responsible for the addition of aminoarabinose to lipid A. The PA4773-PA4775 genes are a second DNA-induced cluster and are required for the production of spermidine on the outer surface, which protects the outer membrane from AP treatment. Both modifications mask the negative surface charges and limit membrane damage by APs. DNA-enriched biofilms or planktonic cultures have increased antibiotic resistance phenotypes to APs and aminoglycosides. These dual antibiotic resistance and immune evasion strategies may be expressed in DNA-rich environments and contribute to long-term survival.

Polyamines (PAs) are ubiquitous, polycationic biogenic amines that are implicated in many biological processes, including plant growth and development, but their precise roles remain to be determined. Most of the previous studies have involved three biogenic amines: putrescine (Put), spermidine (Spd) and spermine (Spm), and their derivatives. We have expressed a yeast spermidine synthase (ySpdSyn) gene under constitutive (CaMV35S) and fruit-ripening specific (E8) promoters in Solanum lycopersicum (tomato), and determined alterations in tomato vegetative and fruit physiology in transformed lines compared with the control. Constitutive expression of ySpdSyn enhanced intracellular levels of Spd in the leaf, and transiently during fruit development, whereas E8-ySpdSyn expression led to Spd accumulation early and transiently during fruit ripening. The ySpdSyn transgenic fruits had a longer shelf life, reduced shriveling and delayed decay symptom development in comparison with the wild-type (WT) fruits. An increase in shelf life of ySpdSyn transgenic fruits was not facilitated by changes in the rate of water loss or ethylene evolution. Additionally, the expression of several cell wall and membrane degradation-related genes in ySpdSyn transgenic fruits was not correlated with an extension of shelf life, indicating that the Spd-mediated increase in fruit shelf life is independent of the above factors. Crop maturity, indicated by the percentage of ripening fruits on the vine, was delayed in a CaMV35S-ySpdSyn genotype, with fruits accumulating higher levels of the antioxidant lycopene. Notably, whole-plant senescence in the transgenic plants was also delayed compared with WT plants. Together, these results provide evidence for a role of PAs, particularly Spd, in increasing fruit shelf life, probably by reducing post-harvest senescence and decay.

This review surveys the literature about changes in polyamine contents and levels of activity of the enzymes involved in the polyamine biosynthetic pathway in organs of ageing mammals. The literature about changes in the polyamine levels in physiological fluids in healthy ageing humans is also reviewed. Generally speaking, decreases in the levels of the main polyamines (noticeably putrescine and spermidine) are observed in different mammalian organs with ageing. The polyamine levels in serum and in urine of healthy human beings are also age-related, declining progressively with increasing age. Some major enzymes (i.e., ornithine decarboxylase (EC 4.1.1.17) and S-adenosyl-L-methionine decarboxylase (EC 4.1.1.50) involved in the polyamine biosynthetic pathway show similar trends. Hormonal induction of ornithine decarboxylase activity is strongly reduced in organs of aged animals, as it is in neoplastic organs. There is also some evidence for an age-related decrease in the level of ornithine decarboxylase and its inducibility in mammalian cells cultured in vitro. Some in vitro effects of spermidine and spermine on aged structures or systems are briefly summarized. There is no evidence yet that this generally reduced capacity of mammalian aged organs for polyamine biosynthesis is one of the factors responsible for the well known high incidence of some neoplasias in elderly humans. In view of the typical stimulatory effects of the tumour promoters on polyamine biosynthesis in target tissues and the effects of senescence on the same metabolic pathway, it can be excluded that the ageing process has a tumour promoting effect by itself. However, although the exact mechanism responsible for the increased occurrence of some tumors during mammalian senescence is still obscure, there are enough experimental data (both in humans and in animals) to indicate that the reduced polyamine biosynthetic capacity of aged mammals can account for the slower course of some tumors in elderly patients.

Two catabolic pathways exist for spermidine and spermine. One is responsible for the interconversion of the polyamines, a physiological intracellular event. The first and probably rate limiting step of the polyamine interconversion pathway is acetylation in the N1-position by a cytosolic enzyme. The reaction products N1-acetylspermine and N1-acetylspermidine are substrates of the cytoplasmic polyamine oxidase. This enzyme transforms the N1-acetylpolyamines into spermidine and putrescine respectively. N1-Acetylspermidine is at the same time a major urinary excretion product. The factors which control the rates of N1-acetylspermidine degradation by polyamine oxidase versus its elimination via transport are not known. The second catabolic pathway forms putreanine from spermidine and N8-(2-carboxyethyl)-spermidine and spermic acid from spermine. It is catalyzed by the well known serum spermine oxidase. The second step in this reaction sequence, the dehydrogenation of the aldehydes formed by the serum spermine oxidase occurs intracellularly and is catalyzed either by specific or non-specific aldehyde dehydrogenases. The function of this "two compartment reaction sequence" is most probably to protect tissues from extracellular or exogenous (alimentary) polyamines. Its end-products appear to be physiologically indifferent urinary excretion products. Both catabolic pathways may have marked effects on the urinary polyamine pattern. Drugs as well as a variety of physiological and pathological states may influence polyamine catabolism and elimination at various levels, and may cause characteristic alterations in the urinary excretion of free and conjugated polyamines and of the amino acids deriving from the polyamines.

BACKGROUND

Spermidine, a naturally occurring polyamine, has recently emerged as exhibiting anti-aging properties. Its supplementation increases lifespan and resistance to stress, and decreases the occurrence of age-related pathology and loss of locomotor ability. Its mechanisms of action are just beginning to be understood.

OBJECTIVE

An up-to-date overview of the so far identified mechanisms of action of spermidine and other polyamines on aging is presented.

METHODS

Studies of aging and of the molecular effects of polyamines in general and spermidine in particular are used to synthesize our knowledge on what molecular mechanisms spermidine and other polyamines trigger to positively affect aging.

RESULTS

Autophagy is the main mechanism of action of spermidine at the molecular level. However, recent research shows that spermidine can act via other mechanisms, namely inflammation reduction, lipid metabolism and regulation of cell growth, proliferation and death. It is suggested that the main pathway used by spermidine to trigger its effects is the MAPK pathway.

CONCLUSIONS

Given that polyamines can interact with many molecules, it is not surprising that they affect aging via several mechanisms. Many of these mechanisms discovered so far have already been linked with aging and by acting on all of these mechanisms, polyamines may be strong regulators of aging.

Biogenic amines putrescine, spermidine and spermine are ubiquitous in nature and have interested researchers because they are essential for cell division and viability, and due to a large body of their pharmacological effects on growth and development in most living cells. The genes and enzymes involved in their biosynthetic pathways are now established and characterized. In recent years, molecular aspects of polyamine action have also begun to emerge. Our model is the ripening tomato fruit in which processes of cell division, cell expansion and cell growth have ceased, and yet the cells are responsive at biochemical and molecular levels to genetically manipulated concentrations of putrescine (Put), spermidine (Spd) and spermine (Spm). Thus, transcriptome, limited protein profiling, and metabolome studies of transgenic tomato fruit have yielded significant new information on cellular processes impacted by polyamine manipulation. We have used these datasets to determine the linear correlation coefficients between the endogenous levels of Put, Spd and Spm with several parameters. Results of our analysis presented here show that effects of the diamine Put generally contrast those with polyamines Spd and Spm, emphasizing that individual biogenic amines should be considered to have defined action in plant biology and that they differentially affect growth and development. A multiple function model of polyamine action is discussed to explain the role of polyamines in most organisms, in general, and ripening fruit, in particular.