Evidence that spermine, spermidine, and putrescine are transported electrophoretically in mitochondria by a specific polyamine uniporter

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.

Spermine causes caspase activation in leukaemia cells

Exposure of several leukaemia cell types to the polyamine spermine triggered caspase activation. In HL60 cells, the onset of caspase activity correlated with the accumulation of spermine, and was accompanied by the processing of the caspase-3 precursor and the digestion of the substrate proteins PARP and gelsolin. Spermine also induced the accumulation of cytochrome c in the cytosol. Caspase activation triggered by spermine was not blocked by antioxidants or inhibition of polyamine oxidase. The deregulation of polyamine uptake strongly sensitised the cells to spermine-induced caspase activation. These data show that an excessive intracellular level of spermine triggers caspase activation that is not mediated by oxidative mechanisms, and suggest a model where elevated free cytosolic polyamines may act as transducers of a death message.

Polyamine modulation of mitochondrial calcium transport. II. Inhibition of mitochondrial permeability transition by aliphatic polyamines but not by aminoglucosides

In this study, the effects of polyamines and analogous compounds on mitochondrial permeability transition were characterized to distinguish between these effects and those on mitochondrial Ca2+ uptake, which are described in an accompanying report (Rustenbeck et al., Biochem Pharmacol 8: 977-985, 1998). When a transitional Ca2+ release from Ca2+-loaded mitochondria was induced by an acute increase in Ca2+ concentration in a cytosol-adapted incubation medium (Ca2+ pulse), this process was inhibited, but not abolished by spermine in the concentration range of 0.4 to 20 mM. The aminoglucoside, gentamicin, and the basic polypeptide, poly-L-lysine, which like spermine are able to enhance mitochondrial Ca2+ accumulation (preceding paper), had no or only a minimal inhibitory effect, while the aliphatic polyamine, bis(hexamethylene)triamine, which is unable to enhance mitochondrial Ca2+ accumulation, achieved a complete inhibition at 4 mM. The conclusion that the Ca2+ efflux was due to opening of the permeability transition pore was supported by measurements of mitochondrial membrane potential, ATP production, and oxygen consumption. Mg2+, a known inhibitor of mitochondrial membrane permeability transition, did not mimic the effects of spermine on mitochondrial Ca2+ accumulation, while ADP, the main endogenous inhibitor, showed both effects. However, a combination of spermine and ADP was significantly more effective than ADP alone in restoring low Ca2+ concentrations after a Ca2+ pulse. Two different groups of spermine binding sites were found at intact liver mitochondria, characterized by dissociation constants of 0.5 or 4.7 mM and maximal binding capacities of 4.6 or 19.7 nmol/mg of protein, respectively. In contrast to aminoglucosides, the aliphatic polyamine bis(hexamethylene)triamine did not displace spermine from mitochondrial binding sites. The total intracellular concentration of spermine in hepatocytes was measured to be ca. 450 microM and the free cytoplasmic concentration was estimated to be in the range of 10-100 microM. In conclusion, the enhancement of mitochondrial Ca2+ uptake by spermine is not an epiphenomenon of the inhibition of permeability transition. The physiological role of spermine appears to be that of an enhancer of mitochondrial Ca2+ accumulation rather than an inhibitor of permeability transition.

A possible involvement of endogenous polyamines in the TNF-alpha cellular sensitivity

A critical step in the cytotoxic action mechanism of tumor necrosis factor-alpha (TNF-alpha) involves, among mitochondrial dysfunctions, an early change of the inner membrane permeability displaying the characteristics of permeability transition. Cytosolic polyamines, especially spermine, are known to inhibit it. Our results show that spermine is only detectable in the TNF-alpha resistant C6 cells while N1-acetylspermidine is present in the TNF-alpha sensitive WEHI-164 cells, and putrescine and spermidine are found in both. TNF-alpha treatment does not change this distribution but only induces a quantitative alteration in TNF-alpha sensitive cells. Omission of glutamine (energetic substrate) from the culture media alters neither the TNF-alpha responsiveness of both cell lines nor their polyamine distributions, only their quantitative polyamine contents.

Spermine binding to liver mitochondria deenergized by ruthenium red plus either FCCP or antimycin A

Thermodynamic analysis of spermine binding to mitochondria treated with ruthenium red and deenergized with either FCCP or antimycin A confirms the presence of two polyamine binding sites, S1 and S2, both with monocoordination, as previously observed in energized mitochondria [Dalla Via et al., Biochim. Biophys. Acta 1284 (1996) 247-252]. Both sites undergo a marked change in binding capacity and binding affinity upon mitochondrial deenergization. This change is most likely responsible for the incomplete or delayed spermine-mediated inhibition of the permeability transition induced in deenergized mitochondria.

Spermine binding to liver mitochondria

Non-equilibrium binding of spermine to mitochondrial membranes is studied in rat liver mitochondria by applying a new thermodynamic treatment of ligand-receptor interactions (Di Noto, V., Dalla Via, L., Toninello, A. and Vidali, M. (1996) Macromol. Theory Simul. 5, 165-181). The presence on mitochondrial membranes of two spermine binding sites, both with monocoordination, is demonstrated. The calculated binding energy is characteristic for weak interactions. The treatment allows also to evaluate the variations of the molar fraction ratio of spermine bound to sites 1 and 2 as function of total bound spermine. The possible role of the two sites is discussed.

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.

Protective effect of spermine on DNA exposed to oxidative stress

Pathological conditions that cause oxidative stress can affect DNA integrity. The aim of this research was to study the protective effect of spermine against DNA damage induced by an oxygen-radical generating system. Deoxyguanosine and DNA were separately dissolved in phosphate buffer and incubated for 1 h at 40 degrees C in the presence of 50 mM H2O2/10 mM ascorbic acid. Single nucleosides and their products of oxidation were then obtained by enzymatic digestion of DNA. The compounds were separated by micellar electrokinetic capillary chromatography (MECC) with SDS-modified mobile phase and detected at 254 nm. Two major products of DNA oxidation have been identified as derivatives of deoxyguanosine with electrophoretic properties different from 8-hydroxy-2'-deoxyguanosine. When the oxidation of DNA was carried out in the presence of 0.1 mM spermine, the formation of the two by-products of deoxyguanosine was markedly reduced. On the contrary, spermine did not prevent the oxidation of deoxyguanosine alone, suggesting that the polyamine should be bound to the DNA strands to exert its antioxidative effect.

Inorganic cation dependence of putrescine and spermidine transport in human breast cancer cells

The mechanism of polyamine uptake in mammalian cells is still poorly understood. The role of inorganic cations in polyamine transport was investigated in ZR-75-1 human breast cancer cells. Although strongly temperature dependent, neither putrescine nor spermidine uptake was mediated by a Na+ cotransport mechanism. In fact, Na+ and cholinium competitively inhibited putrescine uptake relative to that measured in a sucrose-based medium. On the other hand, ouabain, H+, Na+, and Ca2+ ionophores, as well as dissipation of the K+ diffusion potential, strongly inhibited polyamine uptake in keeping with a major role of membrane potential in that process. Polyamine transport was inversely dependent on ambient osmolality at near physiological values. Putrescine transport was inhibited by 70% by decreasing extracellular pH from 7.2 to 6.2, whereas spermidine uptake had a more acidic optimum. Deletion of extracellular Ca2+ inhibited putrescine uptake more strongly than chelation of intracellular Ca2+. In fact, bound divalent cations were absolutely required for polyamine transport, as shown after brief chelation of the cell monolayers with EDTA. Either Mn2+, Ca2+, or Mg2+ sustained putrescine uptake activity with high potency (Km = 50-300 microM). Mn2+ was a much stronger activator of spermidine than putrescine uptake, suggesting a specific role for this metal in polyamine transport. Other transition metals (Co2+, Ni2+, Cu2+, and Zn2+) were mixed activators/antagonists of carrier activity, while Sr2+ and Ba2+ were very weak agonists, while not interfering with Ca2+/Mg(2+)-dependent transport. Thus, polyamine uptake in human breast tumor cells is negatively affected by ionic strength and osmolality, and is driven, at least in part, by the membrane potential, but not by the Na+ electrochemical gradient. Moreover, the polyamine carrier, or a tightly coupled accessory component, appears to have a high-affinity binding site for divalent cations, which is essential for the uptake mechanism.

The effect of respiration on the permeability of the mitochondrial membrane to ions

1. The rates of cation uptake, for either organic cations such as tetrapropylammonium, TPA+, at variable tetraphenylboron concentrations, TPB-, or inorganic cations such as Mn2+, or K+ plus valinomycin, have been measured in mitochondria either respiring, under uncoupler titrations, or non-respiring, under variable K+ diffusion potentials. 2. The flow-force relationship for the respiration-coupled ion fluxes during titrations with uncouplers is almost identical to that obtained for the K(+)-diffusion driven fluxes. Similar results are obtained when TPA+ is replaced with inorganic cations, either monovalent such as K+ (+valinomycin), or divalent such as Mn2+. 3. By applying the Eyring analysis, as developed by Garlid et al. (Garlid, K.D., Beavis, A.D. and Ratkje, S.K. (1989) Biochim. Biophys. Acta 976, 109-121), from the flux-voltage relationships the values for the permeability coefficients and for the energy barriers have been obtained for the transport of the ion pair TPA(+)-TPB-, of Mn2+ and of K+ plus valinomycin, in non-respiring and in respiring, coupled and uncoupled, mitochondria. 4. The findings that the rates of respiration-coupled ion fluxes, at all values of membrane potential, are similar to the rates of the K+ diffusion potential-coupled ion fluxes and the similar pattern of the flux-voltage relationships during the titrations with uncouplers and artificial gradients indicate that the membrane permeability for ions is not modified by respiration.

Spermine-mediated casein kinase II-uptake by rat liver mitochondria

Spermine, ubiquitous intracellular polyamine, is able to promote the transmembrane translocation of casein kinase CKII through the outer membrane of rat liver mitochondria and its binding to more internal mitochondrial structures. These findings suggest that spermine may play a critical role in regulating the subcellular distribution of casein kinase CKII.

The Ca(2+)-induced permeability transition pore is involved in Ca(2+)-induced mitochondrial oscillations. A study on permeabilised Ehrlich ascites tumour cells

The Ca(2+)-induced permeability transition of the mitochondrial inner membrane was studied in digitonin-permeabilized Ehrlich ascites tumour cells respiring on succinate in an isotonic medium. Addition of a sufficient amount of Ca2+ to induce an efflux of accumulated Ca2+ from mitochondria produced an oscillatory state with periodically changing rates of respiration, transmembrane potential, delta pH and direction of Ca2+ fluxes. This contrasts with liver mitochondria in which only a Ca2+ efflux is induced under these conditions. Addition of traces of cyclosporin A (approximately 0.1 nM) damped the oscillations by inhibiting the phase in which Ca2+ efflux occurs and promoting the reestablishment of a higher transmembrane potential. Efflux was also prevented by addition of ATP or ADP, ATP being more potent. Efflux was also inhibited by low concentrations of spermine. It is concluded that Ca(2+)-induced oscillations involve the cyclosporin A-sensitive pore and that the Ehrlich ascites tumour cell mitochondria differ from liver mitochondria in being far more sensitive to cyclosporin A and ATP. The possible physiological role of the oscillatory state is discussed.