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

Development of a Redox-Sensitive Spermine Prodrug for the Potential Treatment of Snyder Robinson Syndrome

Snyder Robinson Syndrome (SRS) is a rare disease associated with a defective spermine synthase gene and low intracellular spermine levels. In this study, a spermine replacement therapy was developed using a spermine prodrug that enters cells via the polyamine transport system. The prodrug was comprised of three components: a redox-sensitive quinone "trigger", a "trimethyl lock (TML)" aryl "release mechanism", and spermine. The presence of spermine in the design facilitated uptake by the polyamine transport system. The quinone-TML motifs provided a redox-sensitive agent, which upon intracellular reduction generated a hydroquinone, which underwent intramolecular cyclization to release free spermine and a lactone byproduct. Rewardingly, most SRS fibroblasts treated with the prodrug revealed a significant increase in intracellular spermine. Administering the spermine prodrug through feeding in a Drosophila model of SRS showed significant beneficial effects. In summary, a spermine prodrug is developed and provides a lead compound for future spermine replacement therapy experiments.

Spermine with Sodium Taurocholate Enhances Pulmonary Absorption of Macromolecules in Rats

The improvement effect of the combined use of spermine (SPM), a polyamine, with sodium taurocholate (STC) on the pulmonary drug absorption was investigated utilizing poorly absorbable drugs with various molecular sizes in rats. The pulmonary absorption of rebamipide, a low molecular but poorly absorbable drug after oral administration, was significantly improved by the combined use of SPM with STC (SPM-STC formulation), while poly- L-lysine did not show a significant change in rebamipide absorption from the lungs. Furthermore, the safety of the SPM-STC formulation for the lungs was assessed in rats by the histopathological study and any local toxicity was not observed while poly-L-lysine, a typical chemical causing the toxicity for the epithelial cells, provided several histopathological changes. In addition, the SPM-STC formulation significantly improved the pulmonary absorption of fluorescein isothiocyanate dextran 4 (FD-4, Mw ca 4000) and interferon-α (IFN-α, Mw ca 25,000) as well. Our present results clearly indicated that the SPM-STC formulation significantly improved the pulmonary absorption of poorly absorbable small and large molecular drugs without any harmful effects on the lungs. Therefore, the SPM-STC formulation would be a useful one for the pulmonary absorption of drugs, specifically macromolecular ones, which are very difficult to be absorbed after oral administration.

Exercise training preserves ischemic preconditioning in aged rat hearts by restoring the myocardial polyamine pool

BACKGROUND

Ischemic preconditioning (IPC) strongly protects against myocardial ischemia reperfusion (IR) injury. However, IPC protection is ineffective in aged hearts. Exercise training reduces the incidence of age-related cardiovascular disease and upregulates the ornithine decarboxylase (ODC)/polyamine pathway. The aim of this study was to investigate whether exercise can reestablish IPC protection in aged hearts and whether IPC protection is linked to restoration of the cardiac polyamine pool.

METHODS

Rats aging 3 or 18 months perform treadmill exercises with or without gradient respectively for 6 weeks. Isolated hearts and isolated cardiomyocytes were exposed to an IR and IPC protocol.

RESULTS

IPC induced an increase in myocardial polyamines by regulating ODC and spermidine/spermine acetyltransferase (SSAT) in young rat hearts, but IPC did not affect polyamine metabolism in aged hearts. Exercise training inhibited the loss of preconditioning protection and restored the polyamine pool by activating ODC and inhibiting SSAT in aged hearts. An ODC inhibitor, α-difluoromethylornithine, abolished the recovery of preconditioning protection mediated by exercise. Moreover, polyamines improved age-associated mitochondrial dysfunction in vitro.

CONCLUSION

Exercise appears to restore preconditioning protection in aged rat hearts, possibly due to an increase in intracellular polyamines and an improvement in mitochondrial function in response to a preconditioning stimulus.

Fabrication of coated bovine serum albumin (BSA)-epigallocatechin gallate (EGCG) nanoparticles and their transport across monolayers of human intestinal epithelial Caco-2 cells

The bovine serum albumin (BSA)-epigallocatechin gallate (EGCG) nanoparticles were fabricated using a desolvation method, and coated with poly-ε-lysine or chitosan. BSA-EGCG nanoparticles (BEN), poly-ε-lysine coated BSA-EGCG nanoparticles (PBEN), and chitosan coated BSA-EGCG nanoparticles (CBEN) had a spherical morphology and a size of 186, 259, and 300 nm, respectively. The loading efficiency of EGCG in these nanoparticles was 32.3%, 35.4%, and 32.7%, whereas the loading capacity was 18.9%, 17.0%, and 16.0% (w/w), respectively. Poly-ε-lysine or chitosan coating prevented the aggregation of nanoparticles at pH 4.5-5.0. However, they caused particle aggregation at pH 6.5-7.0. BEN had negative zeta-potentials between pH 4.5 and 6.0. Poly-ε-lysine or chitosan coating changed the zeta-potentials to positive. The release study of EGCG from the nanoparticles in the simulated gastric or intestinal fluid with or without digestive enzymes showed that poly-ε-lysine and chitosan coatings delayed EGCG release from the nanoparticles. Poly-ε-lysine or chitosan coating improved the stability of EGCG during storage at 60 °C compared with EGCG in the uncoated particles. EGCG in BEN, PBEN, and CBEN had a decreasing apparent permeability coefficient (Papp) on Caco-2 monolayers, whereas pure EGCG showed relatively stable Papp during the incubation over time. EGCG in CBEN showed significantly higher Papp, suggesting that chitosan coated BSA-EGCG nanoparticles may improve the absorption of EGCG.

Interaction of poly(ethylenimine)-DNA polyplexes with mitochondria: implications for a mechanism of cytotoxicity

Poly(ethylenimine) (PEI) and PEI-based systems have been widely studied for use as nucleic acid delivery vehicles. However, many of these vehicles display high cytotoxicity, rendering them unfit for therapeutic use. By exploring the mechanisms that cause cytotoxicity, and through understanding structure-function relationships between polymers and intracellular interactions, nucleic acid delivery vehicles with precise intracellular properties can be tailored for specific function. Previous research has shown that PEI is able to depolarize mitochondria, but the exact mechanism as to how depolarization is induced remains elusive and therefore is the focus of the current study. Potential mechanisms for mitochondrial depolarization include direct mitochondrial membrane permeabilization by PEI or PEI polyplexes, activation of the mitochondrial permeability transition pore, and interference with mitochondrial membrane proton pumps, specifically Complex I of the electron transport chain and F(0)F(1)-ATPase. Herein, confocal microscopy and live cell imaging showed that PEI polyplexes do colocalize to some degree with mitochondria early in transfection, and the degree of colocalization increases over time. Cyclosporin a was used to prevent activation of the mitochondrial membrane permeability transition pore, and it was found that early in transfection cyclosporin a was unable to prevent the loss of mitochondrial membrane potential. Further studies done using rotenone and oligomycin to inhibit Complex I of the electron transport chain and F(0)F(1)-ATPase, respectively, indicate that both of these mitochondrial proton pumps are functioning during PEI transfection. Overall, we conclude that direct interaction between polyplexes and mitochondria may be the reason why mitochondrial function is impaired during PEI transfection.

Improvement of pulmonary absorption of insulin and other water-soluble compounds by polyamines in rats

The absorption enhancing effects of polyamines, spermine (SPM), spermidine (SPD) and putrescine (PUT) on the pulmonary absorption of poorly absorbable drugs were studied in rats. Insulin, 5(6)-carboxyfluorescein (CF), and fluorescein isothiocyanate-labeled dextrans (FDs) were chosen as models of poorly absorbable drugs. The absorption of insulin from the lung was enhanced in the presence of SPM and SPD, while PUT had almost no absorption enhancing effect for improving the pulmonary absorption of insulin in rats. SPM also improved the pulmonary absorption of FDs with various molecular weights, although we found almost no significant difference in the pulmonary absorption of CF with or without SPM. As for the pulmonary membrane toxicity of SPM, there was no significant difference in the release of protein and lactate dehydrogenase (LDH) with or without SPM in bronchoalveolar lavage fluid (BALF), indicating that SPM did not cause any membrane damage to the lung tissues. Furthermore, SPM did not affect the stability of insulin in BALF, suggesting that SPM might increase the permeability of insulin across the alveolar epithelium. In conclusion, polyamines, especially SPM can effectively improve the pulmonary absorption of insulin and other macromolecules without any membrane damage to the lung tissues.

Polyamine transport by mammalian cells and mitochondria: role of antizyme and glycosaminoglycans

The role of antizyme (AZ) and glycosaminoglycans in polyamine uptake by mammalian cells and mitochondria was examined using NIH3T3 and FM3A cells and rat liver mitochondria. AZ is synthesized as two isoforms (29 and 24.5 kDa) due to the existence of two initiation codon AUGs in the AZ mRNA. Most AZ existed as the 24.5-kDa form translatable from the second AUG, but a portion of the 29-kDa AZ from the first AUG was associated with mitochondria because of the presence of a mitochondrial targeting signal between the first and the second methionine. The predominance of the 24.5-kDa isoform was mainly due to the presence of spermidine and a favorable sequence context (Kozak sequence) at the second initiation codon AUG. Spermine uptake by NIH3T3 cells was inhibited by both 29- and 24.5-kDa AZs, but uptake by rat liver mitochondria was not influenced by either form of AZ. Because spermine uptake by mitochondria caused a release of cytochrome c, an enhancer of apoptosis, we looked for inhibitors of mitochondrial spermine uptake other than AZ. Cations such as Na+, K+, and Mg2+ were inhibitors of the mitochondrial uptake. It has been reported that heparan sulfate on glypican-1 plays important roles in spermine uptake by human embryonic lung fibroblasts. Heparin, but not heparan sulfate, slightly inhibited spermine uptake by FM3A cells in the absence of Mg2+ and Ca2+ but had no effect under physiological conditions in the presence of Mg2+ and Ca2+.

Effects of polyamines on mitochondrial Ca2+ transport

Mammalian mitochondria are able to enhance Ca(2+) accumulation in the presence of polyamines by activating the saturable systems of Ca(2+) inward transport and buffering extramitochondrial Ca(2+) concentrations to levels similar to those in the cytosol of resting cells. This effect renders them responsive to regulate free Ca(2+) concentrations in the physioloical range. The mechanism involved is due to a rise in the affinity of the Ca(2+) transport system, induced by polyamines, most probably exhibiting allosteric behaviour. The regulatory site of this mechanism is the so-called S(1) binding site of polyamines, which operates in physiological conditions and is located in the energy well between the two peaks present in the energy profile of mitochondrial spermine transport. Spermine is bidirectionally transported across teh inner membrane by cycling, in which influx and efflux are driven by electrical and pH gradients, respectively. Most probably, polyamine affects the Ca(2+) transport system when it acts from the outside-that is, in the direction of its uniporter channel, in order to reach the S(1) site. Important physiological functions are related to activation of Ca(2+) transport systems by polyamines and their interactions with the S(1) site. These functions include a rise in the metabolic rate for energy supply and modulation of mitochondrial permeability transition induction, with consequent effects on the triggering of the apoptotic pathway.

Polyamines reverse non-steroidal anti-inflammatory drug-induced toxicity in human colorectal cancer cells

Naproxen, sulindac and salicylate, three NSAIDs (non-steroidal anti-inflammatory drugs), were cytotoxic to human colorectal cancer cells in culture. Toxicity was accompanied by significant depletion of intracellular polyamine content. Inhibition of ornithine decarboxylase (the first enzyme of the polyamine biosynthetic pathway), induction of polyamine oxidase and spermidine/spermine N(1)-acetyltransferase (the enzymes responsible for polyamine catabolism) and induction of polyamine export all contributed to the decreased intracellular polyamine content. Morphological examination of the cells showed typical signs of apoptosis, and this was confirmed by DNA fragmentation and measurement of caspase-3-like activity. Re-addition of spermidine to the cells partially prevented apoptosis and recovered the cell number. Thus polyamines appear to be an integral part of the signalling pathway mediating NSAID toxicity in human colorectal cancer cells, and may therefore also be important in cancer chemoprevention in humans.

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.

Regulation of Ca2+ channel and phosphatase activities by polyamines in intestinal and vascular smooth muscle--implications for cellular growth and contractility

Polyamines added extracellularly to intestinal and vascular smooth muscle cells cause relaxation through inhibition of Ca2+ channel activity. Intracellularly applied polyamines also affect Ca2+ channel properties. Polyamines do not readily pass over the plasma membrane because of their positive charges but in permeabilized smooth muscle preparations they have free access to the cytoplasm. In this system they increase sensitivity of the contractile machinery to Ca2+ through inhibition of myosin phosphatase activity. The magnitude of Ca2+ channel and phosphatase inhibition depends on the number of positive charges on the polyamine molecule. Polyamines have an obligatory, but yet undefined, role in regulation of cell growth and proliferation. Several groups of protein kinases, such as tyrosine and mitogen activated protein (MAP)-kinases transmit the growth signal from the plasma membrane to the cell nucleus where mitosis and protein synthesis are initiated. The data reviewed here show that polyamines may affect such signal transmission via inhibition of phosphatase activity.

Polycations induce the release of soluble intermembrane mitochondrial proteins

The release of proapoptotic proteins from the intermembrane space of mitochondria is an early critical step in many pathways to apoptosis. Induction of the mitochondrial permeability transition pore (PTP) was suggested to be the mechanism of the release of soluble mitochondrial intermembrane proteins (SIMP) in apoptosis. However, several studies suggested that proapoptotic proteins (e.g. Bax and Bid) can induce the release of SIMP (e.g. cytochrome c (cyt c) and adenylate kinase 2 (AK2)) in vivo and in vitro independent of PTP. We have found that a number of structurally diverse polycations, such as aliphatic polyamines (e.g. spermine and to a lesser extent spermidine), aminoglycosides (e.g. streptomycin, gentamicin and neomycin), and cytotoxic peptides (e.g. melittin), induce the release of SIMP from liver mitochondria, in vitro. All the polycations released AK2 together with cyt c, suggesting that rupture of the outer membrane is a common mechanism of cyt c release by these polycations. Several polycations (e.g. spermine, spermidine and neomycin) induced SIMP release without inducing significant swelling, and this release was not inhibited significantly by the PTP inhibitor cyclosporin. In contrast, under the same conditions, streptomycin and melittin induced swelling and SIMP release that was inhibited strongly by cyclosporin. Gentamicin-induced swelling and release of SIMP were partially inhibited by cyclosporin. The affinity of polyamines to the anionic phospholipids of the mitochondrial membranes (spermine=neomycin>gentamicin>streptomycin=spermidine) correlated roughly with their ability to induce PTP-independent release of SIMP, which suggests that the binding of polycations to the anionic phospholipids of the outer mitochondrial membrane facilitates the rupture of this membrane. However, some polycations facilitated the induction of PTP, possibly by binding to cardiolipin on the inner membrane. This dual mechanism may be relevant to the induction of SIMP release in apoptosis.

Inactivation of mitochondrial permeability transition pore by octylguanidine and octylamine

Mitochondrial permeability transition occurs through a Ca2+-dependent opening of a transmembrane pore, whose identity has been attributed to that of the adenine nucleotide translocase (ANT). In this work, we induced permeability transition by adding 0.5 microM carboxyatractyloside. The process was evaluated analyzing Ca2+ efflux, a drop in transmembrane electric gradient, and swelling. We found that the amphiphyllic cations octylguanidine and octylamine, at the concentration of 100 microM, inhibited, almost completely, nonspecific membrane permeability. Hexylguanidine, hexylamine, as well as guanidine chloride and hydroxylamine failed to do so. The inhibition was reversed after the addition of 40 mM Li+, Na+ K+, Rb+, or Cs+; K+ was the most effective. We propose that the positive charge of the amines interact with negative charges of membrane proteins, more likely the ADP/ATP carrier, while the alkyl chain penetrates into the hydrophobic milieu of the inner membrane, fixing the reagent.

Potentiation of mitochondrial Ca2+ sequestration by taurine

The effects of taurine (2-aminoethanesulphonic acid) and its analogues, 2-aminoethylarsonic acid, 2-hydroxyethanesulphonic (isethionic) acid, 3-aminopropanesulphonic acid, 2-aminoethylphosphonic acid, and N,N-dimethyltaurine, were studied on the transport of Ca2+ by mitochondria isolated from rat liver. Taurine enhanced Ca2+ uptake in an apparently saturable process, with a Km value of about 2.63 mM. Taurine behaved as an uncompetitive activator of Ca2+ uptake, increasing both the apparent Km and Vmax values of the process. This effect was not modified in the presence of cyclosporin A (CsA). N,N-Dimethyltaurine also stimulated Ca2+ uptake at higher concentrations, but there was no evidence that the process was saturable over the concentration range used (1-10 mM). Aminoethylarsonate was a weak inhibitor of basal Ca2+ uptake, but inhibited that stimulated by taurine in an apparently competitive fashion (Ki = 0.05 mM). The other analogues had no significant effects on this process. Taurine either in the presence or the absence of CsA had no effect on Ca2+ release induced by 200 nM ruthenium red. Thus, the mechanism of taurine-enhanced Ca2+ accumulation appears to involve stimulation of Ca2+ uptake via the uniport system rather than inhibition of Ca2+ release via the ion (Na+/Ca2+ and/or H+/Ca2+) exchangers or by taurine modulating the permeability transition of the mitochondrial inner membrane. Overall, these findings indicate an interaction of taurine with an as yet unidentified mitochondrial site which might regulate the activity of the uniporter. The unique role of taurine in modulating mitochondrial Ca2+ homeostasis might be of particular importance under pathological conditions that are characterised by cell Ca2+ overload, such as ischaemia and oxidative stress.

Polyamine modulation of mitochondrial calcium transport. I. Stimulatory and inhibitory effects of aliphatic polyamines, aminoglucosides and other polyamine analogues on mitochondrial calcium uptake

In this study, the regulation of mitochondrial Ca2+ transport by polyamines structurally related to spermine and by analogous polycationic compounds was characterized. Similar to spermine, a number of amino groups containing cationic compounds exerted a dual effect on Ca2+ transport of isolated rat liver mitochondria: a decrease in Ca2+ uptake velocity and an enhancement of Ca2+ accumulation. In contrast to the effects of spermine and other aliphatic polyamines, however, the accumulation-enhancing effect of aminoglucosides, basic polypeptides, and metal-amine complexes turned into an inhibition of Ca2+ accumulation at higher concentrations. Within groups of structurally related compounds, the potency to decrease Ca2+ uptake velocity and to enhance Ca2+ accumulation correlated with the number of cationic charges. The presence of multiple, distributed cationic charges was a necessary, but not sufficient criterion for effects on mitochondrial Ca2+ transport, because cationic polyamines and basic oligopeptides which did not enhance mitochondrial Ca2+ accumulation could be identified. Spermine was not able to antagonize the blocking of Ca2+ uptake by ruthenium red, but rather showed an apparent synergism, which can be explained as a displacement of membrane-bound Ca2+ by spermine. The aminoglucosides, gentamicin and neomycin, but not the inactive polyamine bis(hexamethylene)-triamine, inhibited the binding of spermine to intact mitochondria. Apparently, the binding of spermine, gentamicin, and a number of polyamine analogues to low-affinity binding sites at mitochondria, which have low, but distinct structural requirements and which may correspond to phospholipid headgroups, indirectly influences the activity state of the mitochondrial Ca2+ uniporter. The ability of aminoglucosides to displace spermine from the mitochondria and to inhibit mitochondrial Ca2+ accumulation may contribute to the mitochondrial lesions, which are known to occur early in the course of aminoglucoside-induced nephrotoxicity.