The polyamine oxidase inactivator MDL 72527

Polyamine oxidase is a FAD-dependent amine oxidase, which is constitutively expressed in nearly all tissues of the vertebrate organism. In 1985, N1,N4-bis(2,3-butadienyl)-1,4-butanediamine (MDL 72527) was designed as a selective enzyme-activated irreversible inhibitor of polyamine oxidase (EC 1.5.3.11). It inactivates, at micromolar concentration and time-dependently, the enzyme in cells, as well as in all organs of experimental animals, without inhibiting other enzymes of polyamine metabolism. MDL 72527 served during nearly two decades as a unique tool in the elucidation of the physiological roles of polyamine oxidase. The compound has anticancer and contragestational effects, and it improves the anticancer effect of the ornithine decarboxylase inactivator (D,L)-2-(difluoromethyl)ornithine (DFMO). Profound depletion of the polyamine pools of tumour cells and effects on different components of the immune defence system are responsible for the anticancer effects of MDL 72527/DFMO combinations. Recently a direct cytotoxic effect of MDL 72527 at concentrations above those required for polyamine oxidase inactivation was observed. The induction of apoptosis by MDL 72527 was ascribed to its lysosomotropic properties. Therapeutic potentials of the apoptotic effect of MDL 72527 need to be explored. Polyamine oxidase is the last enzyme of the polyamine interconversion pathway that awaits the detailed elucidation of its structure and regulation. MDL 72527 should be useful as a lead in the development of inactivators which are selective for the isoforms of polyamine oxidase. Isozyme-selective inhibitors will give more profound insights into and reveal a diversity of specific functions of polyamine oxidase.

Role of polyamine metabolism in kainic acid excitotoxicity in organotypic hippocampal slice cultures

Polyamines are ubiquitous cations that are essential for cell growth, regeneration and differentiation. Increases in polyamine metabolism have been implicated in several neuropathological conditions, including excitotoxicity. However, the precise role of polyamines in neuronal degeneration is still unclear. To investigate mechanisms by which polyamines could contribute to excitotoxic neuronal death, the present study examined the role of the polyamine interconversion pathway in kainic acid (KA) neurotoxicity using organotypic hippocampal slice cultures. Treatment of cultures with N1,N(2)-bis(2,3-butadienyl)-1,4-butanediamine (MDL 72527), an irreversible inhibitor of polyamine oxidase, resulted in a partial but significant neuronal protection, especially in CA1 region. In addition, this pre-treatment also attenuated KA-induced increase in levels of lipid peroxidation, cytosolic cytochrome C release and glial cell activation. Furthermore, pre-treatment with a combination of cyclosporin A (an inhibitor of the mitochondrial permeability transition pore) and MDL 72527 resulted in an additive and almost total neuronal protection against KA toxicity, while the combination of MDL 72527 and EUK-134 (a synthetic catalase/superoxide dismutase mimetic) did not provide additive protection. These data strongly suggest that the polyamine interconversion pathway partially contributes to KA-induced neurodegeneration via the production of reactive oxygen species.

Effect of drugs inhibiting spermidine biosynthesis and metabolism on the in vitro development of Plasmodium falciparum

Treatment of Plasmodium falciparum with the potent inhibitor dicyclohexylamine completely arrests in vitro cell proliferation of the chloroquine-susceptible P. falciparum strain NF54 and the R strain, which shows less sensivity to chloroquine. The average inhibitory concentration (IC50) values determined for both strains revealed different inhibition profiles. The IC50 value for the chloroquine-sensitive NF54 strain was 97 microM and 501 microM for the R strain. Monitoring polyamine pools after treatment with dicyclohexylamine leads to a significant decrease in the intracellular spermidine content, which was nearly reversed by supplementation with spermidine. Since spermidine is an important precursor for the biosynthesis of hypusine and homospermidine in eukaryotes, we studied the developmental effect on both P. falciparum strains of 1,7-diaminoheptane as an inhibitor of deoxyhypusine synthase (EC 1.1.1.249) in mammalian cells, and agmatine as a moderate inhibitor of homospermidine synthase (EC 2.5.1.44). Inhibition profiles with 1,7-diaminoheptane resulted in an IC50 value of 466 microM for the NF54 strain and 319 microM for the R strain. Spermidine pools changed significantly. Inhibition with agmatine caused a strong decrease in parasitemia for the chloroquine-susceptible NF54 strain, with a determined IC50 value of 431 microM and an IC50 value of 340 microM for the less chloroquine-susceptible R strain. Spermidine was not detectable after inhibition. The uncommon triamine homospermidine occurred in both P. falciparum strains. To our knowledge this is the first evidence of homospermidine in P. falciparum. The use of specific inhibitors of spermidine metabolism might be a novel strategy for the design of new antimalarials, and suggests the occurrence of both enzymes in the parasite.

Phase I clinical and pharmacogenetic trial of irinotecan and raltitrexed administered every 21 days to patients with cancer

PURPOSE

Irinotecan and raltitrexed display schedule-dependent synergy in vitro, which supports the clinical investigation of the combination. Functional polymorphisms of the methylenetetrahydrofolate reductase (MTHFR) gene result in intracellular redistribution of folate derivatives, which may affect raltitrexed-associated cytotoxicity.

PATIENTS AND METHODS

Patients with a range of solid cancers and good performance status received irinotecan as a 90-minute infusion on day 1 and raltitrexed as a 15-minute infusion on day 2, repeated every 21 days. Samples were collected for MTHFR C677T genotyping and fasting plasma homocysteine during the first cycle.

RESULTS

Thirty-nine assessable patients received 127 cycles of therapy. Irinotecan doses ranged from 100 to 350 mg/m(2), and raltitrexed, 1.0 to 4.0 mg/m(2). Raltitrexed doses of more than 3.0 mg/m(2) were not tolerated and were associated with dose-limiting asthenia, diarrhea, and AST/ALT elevation. Irinotecan/raltitrexed doses of 350/3.0 mg/m(2) were well-tolerated; principal toxicities included neutropenia, diarrhea, and fatigue. Two partial responses were observed in patients with pretreated gastroesophageal cancers. Homozygotes with the MTHFR 677 TT polymorphism incurred significantly less raltitrexed-associated toxicity than those with either wild-type or heterozygous genotypes (P = .05). No significant differences were noted in plasma homocysteine values between the genotypic subtypes, and plasma homocysteine levels did not predict the risk of toxicity.

CONCLUSION

Irinotecan and raltitrexed doses of 350 and 3.0 mg/m(2) are recommended for further study on a day 1, 2 schedule every 21 days. Efficacy results suggest that trials in upper and lower gastrointestinal malignancies are warranted. MTHFR C677T genotypes may be predictive of clinical raltitrexed toxicity.

Folate activation and catalysis in methylenetetrahydrofolate reductase from Escherichia coli: roles for aspartate 120 and glutamate 28

The flavoprotein Escherichia coli methylenetetrahydrofolate reductase (MTHFR) catalyzes the reduction of 5,10-methylenetetrahydrofolate (CH(2)-H(4)folate) to 5-methyltetrahydrofolate (CH(3)-H(4)folate). The X-ray crystal structure of the enzyme has revealed the amino acids at the flavin active site that are likely to be relevant to catalysis. Here, we have focused on two conserved residues, Asp 120 and Glu 28. The presence of an acidic residue (Asp 120) near the N1-C2=O position of the flavin distinguishes MTHFR from all other known flavin oxidoreductases and suggests an important function for this residue in modulating the flavin reactivity. Modeling of the CH(3)-H(4)folate product into the enzyme active site also suggests roles for Asp 120 in binding of folate and in electrostatic stabilization of the putative 5-iminium cation intermediate during catalysis. In the NADH-menadione oxidoreductase assay and in the isolated reductive half-reaction, the Asp120Asn mutant enzyme is reduced by NADH 30% more rapidly than the wild-type enzyme, which is consistent with a measured increase in the flavin midpoint potential. Compared to the wild-type enzyme, the mutant showed 150-fold decreased activity in the physiological NADH-CH(2)-H(4)folate oxidoreductase reaction and in the oxidative half-reaction involving CH(2)-H(4)folate, but the apparent K(d) for CH(2)-H(4)folate was relatively unchanged. Our results support a role for Asp 120 in catalysis of folate reduction and perhaps in stabilization of the 5-iminium cation. By analogy to thymidylate synthase, which also uses CH(2)-H(4)folate as a substrate, Glu 28 may serve directly or via water as a general acid catalyst to aid in 5-iminium cation formation. Consistent with this role, the Glu28Gln mutant was unable to catalyze the reduction of CH(2)-H(4)folate and was inactive in the physiological oxidoreductase reaction. The mutant enzyme was able to bind CH(3)-H(4)folate, but reduction of the FAD cofactor was not observed. In the NADH-menadione oxidoreductase assay, the mutant demonstrated a 240-fold decrease in activity.

Antisense modulation of 5,10-methylenetetrahydrofolate reductase expression produces neural tube defects in mouse embryos

The role of folate metabolism in producing neural tube defects (NTDs) in humans is unknown. In the current study, antisense oligodeoxyribonucleotide technology was utilized to disrupt normal expression of the gene for 5,10-methylenetetrahydrofolate reductase (MTHFR) in organogenesis-stage mouse embryos. Two different antisense probes were microinjected into the amniotic sac of gestation day (GD) 8 mouse embryos with PBS or scrambled sense oligodeoxyribonucleotides injected into control embryos. Concentration-dependent increases in the frequencies of embryos with NTDs were observed for both antisense sequences. The level of mRNA for MTHFR was decreased in embryos treated with the higher concentration of one antisense sequence, indicating that the sequence is able to decrease gene expression. 5-methyltetrahydrofolate, the product of the MTHFR reaction, was able to decrease the incidence of antisense-induced NTDs, but co-injection with L-methionine did not. These results suggest that reduced expression of MTHFR may play a role in producing NTDs.

Inhibition of pig liver and Zea mays L. polyamine oxidase: a comparative study

Polyamine oxidase (PAO) is involved in polyamine metabolism and production of hydrogen peroxide in animal and plants, thus representing a key system in development and programmed cell death. In the present study, the inhibitory effect of amiloride, p-aminobenzamidine, clonidine, 4',6-diamidino-2-phenyl-indole (DAPI), gabexate mesylate, guazatine, and N,N'-bis(2,3-butadienyl)-1,4-butane-diamine (MDL72527) on the catalytic activity of pig liver and Zea mays L. PAO, Lens culinaris L. and Pisum sativum L. and swine kidney copper amine oxidase, bovine trypsin, as well as neuronal constitutive nitric oxide synthase (NOS-I) was investigated. Moreover, agmatine and N(3) -prenylagmatine (G3) were observed to inhibit pig liver and Zea mays L. PAO, bovine trypsin, and NOS-I action, but were substrates for Lens culinaris L., Pisum sativum L. and swine kidney copper amine oxidase. Guazatine and G3 inhibited selectively Zea mays L. PAO with K(i) values of 7.5 x 10(-9) M and 1.5 x 10(-8) M, respectively (at pH 6.5 and 25.0 degrees C). As a whole, the data reported here represent examples of enzyme cross-inhibition, and appear to be relevant in view of the use of cationic L-arginine-and imidazole-based compounds as drugs.

Aminohexanoic hydroxamate is a potent inducer of the differentiation of mouse neuroblastoma cells

Deoxyhypusine synthase is the key enzyme for modifying a lysine residue to hypusine in the cellular protein eukaryotic initiation factor 5A (eIF-5A). Deletion of the deoxyhypusine synthase or the eIF-5A gene in yeast produces lethal phenotype. Inhibition of deoxyhypusine synthase by 1-guanidino-7-aminoheptane (GC7) suppresses tumor cell growth. Hypusine formation represents one of the most specific polyamine-dependent biochemical reactions. In view of the importance of polyamines in growth regulation and cancer biology, deoxyhypusine synthase has been considered to be a good target for chemotherapeutic drug design. Using GC7 as a prototype we have synthesized and tested three classes of diamine analogs, namely, guanidino-, pyrimidino-, and hydroxamate derivatives, as potential inhibitors for deoxyhypusine synthase. Our study shows that (i) among all the compounds tested, GC7 remained to be the most potent inhibitor for deoxyhypusine synthase; (ii) N,N'-bispyrimidino-1, 9-diaminononane, although a poor inhibitor of deoxyhypusine synthase, was a potent growth inhibitor; and (iii) one of the hydroxamate derivatives, 6-aminohexanoic hydroxamate (HC6), prominently induced the differentiation of mouse neuroblastoma cells at sub-millimolar concentrations. Interestingly, other hydroxamates with different chain length were not nearly as effective as HC6 in inducing neuroblastoma cell differentiation. The effect of HC6 was also unique in that it could induce neurite outgrowth and the expression of neuron-specific genes such as synapsin I and MAP-2 in neuroblastoma cells in the absence of other promoting agents such as cAMP. The effect of HC6 on neuroblastoma cell differentiation was comparable with, or better than that of N(6),O(2)'-dibutyryl cAMP (Bt(2)cAMP), a standard reagent commonly used for inducing the differentiation of mouse and human neuroblastoma cells in culture.

Effect of the polyamine oxidase inactivator MDL 72527 on N(1)-(n-octanesulfonyl)spermine toxicity

N(1)-(n-octanesulfonyl)spermine (N(1)OSSpm) is a potent calmodulin antagonist. In the present work, its toxicity to DHD/K12/TRb and CaCo-2 cells, two colon carcinoma-derived cell lines, was studied with the aim to identify those properties of the cells, which determine their sensitivity to N(1)OSSpm and related structures. Exposure of the cells to MDL 72527, a compound considered to be a selective inactivator of polyamine oxidase (PAO) increased the cytotoxicity of N(1)OSSpm to both cell lines. In contrast, toxicity of trifluoperazine, a calmodulin antagonist with a polyamine-unrelated structure, was not enhanced by MDL 72527. Combined exposure of cells to 2-(difluoromethyl)ornithine (DFMO) (a selective inactivator of ornithine decarboxylase), MDL 72527 and N(1)OSSpm produced a synergistic cytotoxic effect. Neither the intrinsic PAO activity of the cells (as determined with N(1), N(12)-diacetylspermine as substrate), nor their ability to accumulate the drug was a determinant of the cytotoxic effect of N(1)OSSpm. These data suggest that MDL 72527 has a target unrelated to PAO, which is responsible for the enhancement of N(1)OSSpm (and spermine) toxicity. Identification of this target may be of use if the therapeutic potentials of MDL 72527 are to be exploited.

Activation of polyamine catabolism in transgenic rats induces acute pancreatitis

Polyamines are required for optimal growth and function of cells. Regulation of their cellular homeostasis is therefore tightly controlled. The key regulatory enzyme for polyamine catabolism is the spermidine/spermine N(1)-acetyltransferase (SSAT). Depletion of cellular polyamines has been associated with inhibition of growth and programmed cell death. To investigate the physiological function SSAT, we generated a transgenic rat line overexpressing the SSAT gene under the control of the inducible mouse metallothionein I promoter. Administration of zinc resulted in a marked induction of pancreatic SSAT, overaccumulation of putrescine, and appearance of N(1)-acetylspermidine with extensive depletion of spermidine and spermine in transgenic animals. The activation of pancreatic polyamine catabolism resulted in acute pancreatitis. In nontransgenic animals, an equal dose of zinc did not affect pancreatic polyamine pools, nor did it induce pancreatitis. Acetylated polyamines, products of the SSAT-catalyzed reaction, are metabolized further by the polyamine oxidase (PAO) generating hydrogen peroxide, which might cause or contribute to the pancreatic inflammatory process. Administration of specific PAO inhibitor, MDL72527 [N(1),N(2)-bis(2,3-butadienyl)-1,4-butanediamine], however, did not affect the histological score of the pancreatitis. Induction of SSAT by the polyamine analogue N(1),N(11)-diethylnorspermine reduced pancreatic polyamines levels only moderately and without signs of organ inflammation. In contrast, the combination of N(1), N(11)-diethylnorspermine with MDL72527 dramatically activated SSAT, causing profound depletion of pancreatic polyamines and acute pancreatitis. These results demonstrate that acute induction of SSAT leads to pancreatic inflammation, suggesting that sufficient pools of higher polyamine levels are essential to maintain pancreatic integrity. This inflammatory process is independent of the production of hydrogen peroxide by PAO.

Inhibition of polyamine oxidase enhances the cytotoxicity of polyamine oxidase substrates. A model study with N1-(n-octanesulfonyl)spermine and human colon cancer cells

N(1)-(n-octanesulfonyl)spermine (N(1) OSSpm) is a substrate of polyamine oxidase. It shares several properties with spermine, such as antagonism of NMDA-type glutamate receptors, calmodulin antagonism, and cytotoxicity, but it is more potent by orders of magnitude in these regards than spermine. The human colon carcinoma-derived cell line CaCo-2 was used as a model to study the toxicity of N(1) OSSpm as a function of polyamine oxidase (PAO) activity and differentiation. If the formation of hydrogen peroxide and aminoaldehyde by the PAO-catalysed reactions was prevented by selective inactivation of the enzyme with MDL 72527, cytotoxicity of N(1)OSSpm was not diminished, but on the contrary, enhanced. Exponentially growing CaCo-2 cells were considerably more sensitive to N(1)OSSpm than differentiating cells. The results suggest that cytotoxic substrates of PAO exhibit enhanced cytotoxicity in cells, if PAO activity is inhibited. Since tumour cells are known to have lower polyamine oxidase activities than their normal counterparts, it will be interesting to explore whether cytotoxic substrates of polyamine oxidase, for which N(1)OSSpm is an example, are suited to preferentially kill tumour cells.

Oxidation of polyamines and brain injury

Several amine oxidases are involved in the metabolism of the natural polyamines putrescine, spermidine, and spermine, and play a role in the regulation of intracellular concentrations, and the elimination of these amines. Since the products of the amine oxidase-catalyzed reactions -- hydrogen peroxide and aminoaldehydes -- are cytotoxic, oxidative degradations of the polyamines have been considered as a cause of apoptotic cell death, among other things in brain injury. Since a generally accepted, unambiguous nomenclature for amine oxidases is missing, considerable confusion exists with regard to the polyamine oxidizing enzymes. Consequently the role of the different amine oxidases in physiological and pathological processes is frequently misunderstood. In the present overview the reactions, which are catalyzed by the different polyamine-oxidizing enzymes are summarized, and their potential role in brain damage is discussed.

Removal of feedback inhibition of delta(1)-pyrroline-5-carboxylate synthetase results in increased proline accumulation and protection of plants from osmotic stress

The Delta(1)-pyrroline-5-carboxylate synthetase (P5CS; EC not assigned) is the rate-limiting enzyme in proline (Pro) biosynthesis in plants and is subject to feedback inhibition by Pro. It has been suggested that the feedback regulation of P5CS is lost in plants under stress conditions. We compared Pro levels in transgenic tobacco (Nicotiana tabacum) plants expressing a wild-type form of Vigna aconitifolia P5CS and a mutated form of the enzyme (P5CSF129A) whose feedback inhibition by Pro was removed by site-directed mutagenesis. Transgenic plants expressing P5CSF129A accumulated about 2-fold more Pro than the plants expressing V. aconitifolia wild-type P5CS. This difference was further increased in plants treated with 200 mM NaCl. These results demonstrated that the feedback regulation of P5CS plays a role in controlling the level of Pro in plants under both normal and stress conditions. The elevated Pro also reduced free radical levels in response to osmotic stress, as measured by malondialdehyde production, and significantly improved the ability of the transgenic seedlings to grow in medium containing up to 200 mM NaCl. These findings shed new light on the regulation of Pro biosynthesis in plants and the role of Pro in reducing oxidative stress induced by osmotic stress, in addition to its accepted role as an osmolyte.

Spermine cytotoxicity to human colon carcinoma-derived cells (CaCo-2)

Spermine is a constituent of all vertebrate cells. Nevertheless, it exerts toxic effects if it accumulates in cells. Spermine is a natural substrate of the FAD-dependent polyamine oxidase, a constitutive enzyme of many cell types. It has been reported that the toxicity of spermine was enhanced if polyamine oxidase was inhibited. We were interested to examine spermine toxicity to human colon carcinoma-derived CaCo-2 cells because, in contrast to most tumor cell lines, CaCo-2 cells undergo differentiation, which is paralleled by changes in polyamine metabolism. CaCo-2 cells were remarkably resistant to spermine accumulation, presumably because spermine is degraded by polyamine oxidase at a rate sufficient to provide spermidine for the maintenance of growth. Inactivation of polyamine oxidase increased the sensitivity to spermine. A major reason for the enhanced spermine cytotoxicity at low polyamine oxidase activity is presumably the profound depletion of spermidine, and the consequent occupation of spermidine binding sites by spermine. Hydrogen peroxide and the aldehydes 3-aminopropanal and 3-acetamidopropanal, the products of polyamine oxidase-catalyzed splitting of spermine and N1-acetylspermine, contribute little to spermine cytotoxicity. Activation of caspase by spermine was insignificant, and the formation of DNA ladders, another indicator of apoptotic cell death, could not be observed. Thus it appears that cell death due to excessive accumulation of spermine in CaCo-2 cells was mainly nonapoptotic. The content of brush border membranes did not change between days 6 and 8 after seeding, and it was not affected by exposure of the cells to spermine. However, the activities of alkaline phosphatase, sucrase, and aminopeptidase in nontreated cells were considerably enhanced during this period, but remained low if cells were exposed to spermine. These changes appear to indicate that differentiation is prevented by intoxication with spermine, although other explanations cannot be excluded.

Some properties of the H2O2/O2- generating system from the lignifying xylem of Zinnia elegans

The properties of the enzymatic system responsible for generating H2O2/O2- in the lignifying xylem of Zinnia elegans were studied using the starch/KI method for monitoring H2O2 production and the nitroblue tetrazolium method for monitoring superoxide anion production. The results showed that H2O2/O2- production by lignifying xylem tissues was insensitive to inhibitors of peroxidase and poly(di)amine oxidases. However, H2O2/O2 production in the xylem of Z. elegans was sensitive to the inhibitors of phagocytic plasma membrane NADPH oxidase, pyridine, imidazole, quinacrine and diphenylene iodonium. The sensitivity of H2O2/O2- production to the respective inhibitors of calmodulin (R-24571), phospholipase C (neomycin sulfate), and protein kinase (staurosporine), and its reversion by an inhibitor of protein phosphatases (cantharidin); pointed to the analogies existing between the mechanism of H2O2/O2- production in the lignifying xylem of Z. elegans and the oxidative burst observed during the hypersensitive plant cell response. These results suggest the existence of a metabolic cascade involving calmodulin, IP3 and protein phosphorylation in the activation of the enzymatic system responsible for H2O2/O2- production in the lignifying xylem of Z. elegans.

The polyamine oxidase inhibitor MDL-72,527 selectively induces apoptosis of transformed hematopoietic cells through lysosomotropic effects

Polyamine oxidase functions in the polyamine catabolic pathway, converting N1-acetyl-spermidine and -spermine into putrescine (Put) and spermidine (Spd), respectively, thereby facilitating homeostasis of intracellular polyamine pools. Inhibition of polyamine oxidase in hematopoietic cells by a specific inhibitor, N,N'-bis(2,3-butadienyl)-1,4-butanediamine (MDL-72,527), reduces the levels of Put and Spd and induces the accumulation of N1-acetylated Spd. Although previously thought to be relatively nontoxic, we now report that this inhibitor overrides survival factors to induce cell death of several immortal and malignant murine and human hematopoietic cells, but not of primary myeloid progenitors. Cells treated with MDL-72,527 displayed biochemical changes typical of apoptosis, and cell death was associated with the down-regulation of the antiapoptotic protein Bcl-X(L). However, enforced overexpression of Bcl-X(L), or treatment with the universal caspase inhibitor zVAD-fmk, failed to block MDL-72,527-induced apoptosis in these hematopoietic cells. Despite decreases in Put and Spd pools, MDL-72,527-induced apoptosis was not blocked by cotreatment with exogenous Put or Spd, nor was it influenced by overexpression or inhibition of the polyamine biosynthetic enzyme ornithine decarboxylase. Significantly, MDL-72,527-induced apoptosis was associated with the rapid formation of numerous lysosomally derived vacuoles. Malignant leukemia cells were variably sensitive to the lysosomotropic effects of MDL-72,527, yet pretreatment with the ornithine decarboxylase inhibitor L-alpha-difluoromethylornithine sensitized all of these leukemia cells to the deleterious effects of the inhibitor by stimulating its intracellular accumulation. The lysosomotropic nature of select polyamine analogues may, thus, provide a novel chemotherapeutic strategy to selectively induce apoptosis of malignant hematopoietic cells.

Contribution of polyamine oxidase to brain injury after trauma

OBJECT

The possible role of the polyamine interconversion pathway on edema formation, traumatic injury volume, and tissue polyamine levels after traumatic brain injury (TBI) was studied using an inhibitor of the interconversion pathway enzyme, polyamine oxidase.

METHODS

Experimental TBI was induced in Sprague-Dawley rats by using a controlled cortical impact device at a velocity of 3 m/second, resulting in a 2-mm deformation. Immediately after TBI was induced, 100 mg/kg of N1,N4-bis(2,3-butadienyl)-1,4-butanediamine 2HCl (MDL 72527) or saline was injected intraperitoneally. Brain water content and tissue polyamine levels were measured at 24 hours after TBI. Traumatic injury volume was evaluated using 2% cresyl violet solution 7 days after TBI occurred. The MDL 72527 treatment significantly reduced brain edema (80.4+/-0.8% compared with 81.2+/-1.2%, p < 0.05) and injury volume (30.1+/-6.6 mm3 compared with 42.7+/-13.3 mm3, p < 0.05) compared with the saline treatment. The TBI caused a significant increase in tissue putrescine levels at the traumatized site (65.5+/-26.5 nmol/g [corrected] in the cortex and 70.9+/-22.4 nmol/g [corrected] in the hippocampus) compared with the nontraumatized site (7+/-2.4 nmol/g [corrected] in the cortex and 11.4+/-6.4 nmol/g [corrected] in the hippocampus). The increase in putrescine levels in both the traumatized and nontraumatized cortex and hippocampus was reduced by a mean of 60% with MDL 72527 treatment.

CONCLUSIONS

These results demonstrate, for the first time, that the polyamine interconversion pathway has an important role in the increase of putrescine levels after TBI and that the polyamine oxidase inhibitors, blockers of the interconversion pathway, can be neuroprotective against edema formation and necrotic cavitation after TBI.

Biochemical and electrochemical characterization of quinohemoprotein amine dehydrogenase from Paracoccus denitrificans

A new quinohemoprotein amine dehydrogenase from Paracoccus denitrificans IFO 12442 was isolated and characterized in views of biochemistry and electrochemistry. This enzyme exists in periplasm and catalyzes the oxidative deamination of primary aliphatic and aromatic amines. n-Butylamine or benzylamine as a carbon and energy source strongly induces the expression of the enzyme. Carbonyl reagents inhibit the enzyme activity irreversibly. This enzyme is a heterodimer constituted of alpha and beta subunits with the molecular mass of 59.5 and 36.5 kDa, respectively. UV-vis and EPR spectroscopy, and the quinone-dependent redox cycling and heme-dependent peroxidative stains of SDS-PAGE bands revealed that the alpha subunit contains one quinonoid cofactor and one heme c per molecule, while the beta subunit has no prosthetic group. The redox potential of the heme c moiety was determined to be 0.192 V vs NHE at pH 7.0 by a mediator-assisted continuous-flow column electrolytic spectroelectrochemical technique. The analysis of the substrate titration curve allowed the evaluation of the redox potential of the quinone/semiquinone and semiquinone/quinol redox couples as 0.19 and 0.11 V, respectively.

Complex formation between deoxyhypusine synthase and its protein substrate, the eukaryotic translation initiation factor 5A (eIF5A) precursor

Deoxyhypusine synthase catalyses the first step in the post-translational synthesis of hypusine [Nepsilon-(4-amino-2-hydroxybutyl) lysine] in a single cellular protein, the precursor of eukaryotic initiation factor 5A (eIF5A). Deoxyhypusine synthase exists as a tetramer with four potential active sites. The formation of a stable complex between human deoxyhypusine synthase and its protein substrate, human recombinant eIF5A precursor (ec-eIF5A), was examined by affinity chromatography using polyhistidine-tagged (His.Tag) ec-eIF5A, by a gel mobility-shift method, and by analytical ultracentrifugation. Deoxyhypusine synthase was selectively retained by His.Tag-ec-eIF5A immobilized on a resin. The complex of deoxyhypusine synthase and ec-eIF5A was separated from the free enzyme and protein substrate by electrophoresis under non-denaturing conditions. The stoichiometry of the two components in the complex was estimated to be 1 deoxyhypusine synthase tetramer to 1 ec-eIF5A monomer by N-terminal amino acid sequencing of the complex. Equilibrium ultracentrifugation data further supported this 1:1 ratio and indicated a very strong interaction of the enzyme with ec-eIF5A (Kd Collapse

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MESH Headings

• Cell Extracts
• Chromatography, Affinity
• Dose-Response Relationship, Drug
• Electrophoresis, Polyacrylamide Gel
• Escherichia coli/genetics
• Guanine/analogs & derivatives
• Guanine/pharmacology
• Humans
• Hydrogen-Ion Concentration
• Molecular Weight
• NAD/pharmacology
• Oxidoreductases Acting on CH-NH Group Donors/antagonists & inhibitors
• Oxidoreductases Acting on CH-NH Group Donors/metabolism
• Peptide Initiation Factors/metabolism
• Protein Binding/drug effects
• Protein Precursors/metabolism
• Protons
• RNA-Binding Proteins
• Recombinant Fusion Proteins/metabolism
• Sequence Analysis
• Spermidine/pharmacology
• Temperature
• Thermodynamics
• Ultracentrifugation
• Eukaryotic Translation Initiation Factor 5A

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Pentylenetetrazol-induced kindling stimulates the polyamine interconversion pathway in rat brain

The levels of polyamines, N-acetylpolyamines, and GABA in the cerebral cortex and brainstem of rat brain after completion of pentylenetetrazol (PTZ)-induced kindling were investigated. Pretreatment with the polyamine oxidase inhibitor MDL72527 caused an accumulation of N1-acetylspermidine and N1-acetylspermine in normal rats. After a kindling seizure, the levels of N-acetylpolyamines were elevated, particularly in the cerebral cortex, indicating activation of polyamine interconversion. The levels of putrescine and GABA were lower in kindled rats pretreated with MDL72527. In addition, pretreatment with MDL72527 enhanced the seizure susceptibility to PTZ in normal rats. These results suggest that the polyamine interconversion pathway is involved in brain excitability, probably through the regulation of putrescine and GABA levels.

Enhanced uptake of [3H] spermidine by 9L rat brain tumors after direct intratumoral infusion of inhibitors of enzymes of the polyamine biosynthetic pathway

We have been exploring the feasibility of delivering ionizing radiation to brain tumor cells by using tritium labeled polyamines. Polyamines are taken up preferentially by dividing cells and form noncovalent bonds with DNA. Their uptake can be enhanced by drugs which deplete endogenous polyamines. To test this in vivo, 9L cells were implanted in the striatal region of the brain in male Fisher 344 rats. Osmotic pumps containing trace amounts of [3H] spermidine or [3H] putrescine with either difluoromethylornithine or combinations of 3 inhibitors of enzymes of the polyamine biosynthetic pathway were implanted subcutaneously and were connected to intratumoral cannulas. After 14-16 days the brains were removed and sliced in the coronal plane. The diameters of the tumors were measured and tumor tissue was dissected from each slice, weighed and lysed for scintillation counting. It was found that difluoromethylornithine enhanced the uptake of [3H] putrescine while a combination of inhibitors of enzymes of the polyamine biosynthetic pathway enhanced the uptake of [3H] putrescine and [3H] spermidine producing a localized region of radioactivity in the 9L tumor. It is estimated that if the [3H] polyamines were at higher specific activity (commercially available), instead of the trace dose given here, the [3H] polyamine uptake would be sufficient to kill 9L tumor cells within a 2 to 3 week period.

A 30-angstrom-long U-shaped catalytic tunnel in the crystal structure of polyamine oxidase

BACKGROUND

Polyamines are essential for cell growth and differentiation; compounds interfering with their metabolism are potential anticancer agents. Polyamine oxidase (PAO) plays a central role in polyamine homeostasis. The enzyme utilises an FAD cofactor to catalyse the oxidation of the secondary amino groups of spermine and spermidine.

RESULTS

The first crystal structure of a polyamine oxidase has been determined to a resolution of 1.9 Angstroms. PAO from Zea mays contains two domains, which define a remarkable 30 Angstrom long U-shaped catalytic tunnel at their interface. The structure of PAO in complex with the inhibitor MDL72527 reveals the residues forming the catalytic machinery and unusual enzyme-inhibitor CH.O H bonds. A ring of glutamate and aspartate residues surrounding one of the two tunnel openings contributes to the steering of the substrate towards the inside of the tunnel.

CONCLUSIONS

PAO specifically oxidizes substrates that have both primary and secondary amino groups. The complex with MDL72527 shows that the primary amino groups are essential for the proper alignment of the substrate with respect to the flavin. Conservation of an N-terminal sequence motif indicates that PAO is member of a novel family of flavoenzymes. Among these, monoamine oxidase displays significant sequence homology with PAO, suggesting a similar overall folding topology.

Effects of MDL 72527, a specific inhibitor of polyamine oxidase, on brain edema, ischemic injury volume, and tissue polyamine levels in rats after temporary middle cerebral artery occlusion

The possible effects of the polyamine interconversion pathway on tissue polyamine levels, brain edema formation, and ischemic injury volume were studied by using a selective irreversible inhibitor, MDL 72527, of the interconversion pathway enzyme, polyamine oxidase. In an intraluminal suture occlusion model of middle cerebral artery in spontaneously hypertensive rats, 100 mg/kg MDL 72527 changed the brain edema formation from 85.7 +/- 0.3 to 84.5 +/- 0.9% in cortex (p < 0.05) and from 79.9 +/- 1.7 to 78.4 +/- 2.0% in subcortex (difference not significant). Ischemic injury volume was reduced by 22% in the cortex (p < 0.05) and 17% in the subcortex (p < 0.05) after inhibition of polyamine oxidase by MDL 72527. There was an increase in tissue putrescine levels together with a decrease in spermine and spermidine levels at the ischemic site compared with the nonischemic site after ischemia-reperfusion injury. The increase in putrescine levels at the ischemic cortical and subcortical region was reduced by a mean of 45% with MDL 72527 treatment. These results suggest that the polyamine interconversion pathway has an important role in the postischemic increase in putrescine levels and that blocking of this pathway can be neuroprotective against neuronal cell damage after temporary focal cerebral ischemia.

Ability of bisbenzylputrescine and propanediamine analogs to modulate the intracellular polyamine pool of P388D1 cells

The effects of a series of bisbenzyldiamine analogs have been tested on P388D1 cell line in vitro. Their effects on cell growth, polyamine oxidase (PAO) activity and intracellular polyamine content were determined. The cytotoxicity tests were performed in culture medium supplemented with 100 micromol/L aminoguanidine (I), 100 micromol/L aminoguanidine and 100 micromol/L N,N'-bis(2,3-butadienyl)-1,4-butanediamine (MDL 72,527) (II), and finally 100 micromol/L aminoguanidine and 200 micromol/L D,L-difluoromethylornithine (DFMO) (III). The IC50 values under conditions I and III were similar, suggesting that inhibition of ornithine decarboxylase by DFMO did not affect the biological effect of our derivatives. Spermine and spermidine remained nontoxic in conditions I and III. However in the condition II, the toxicity of all tested compounds (excepted spermidine) was increased, suggesting that the inhibition of cellular PAO increased their toxicity. The enzymatic test of PAO showed that at high doses inhibition of this enzyme by putrescine analogs occurred, while the N-methylated propanediamine derivative increased the enzyme activity; however, these results do not correlate with cytotoxicity tests. When these derivatives were incubated for 48 h with the cells, all of them increased the cell content in putrescine (approximately 160%) and spermine (approximately 145%) and decreased the spermidine content (approximately 75%) without any modification of the total amount of polyamine. The correlation between the cytotoxic results and the intracellular polyamine determination shows that the increase in spermine content along with the inhibition of retroconverting PAO enzyme increases the toxic effect of tested compounds (including spermine), suggesting that spermine toxicity is more important in the absence of intracellular oxidation processes.

Iron loading into ferritin by an intracellular ferroxidase

An intracellular, membrane-bound enzyme exhibiting both p-phenylenediamine oxidase activity and ferrous iron oxidase activity was isolated with the plasma membrane fraction of horse heart and studied for its ability to load iron into ferritin. The ferroxidase activity of the tissue oxidase was stimulated approximately twofold by horse spleen apoferritin, and the iron was loaded into ferritin. The loading of iron into ferritin by the tissue oxidase was inhibited by anti-horse serum ceruloplasmin antibody. The stoichiometry of iron oxidation and oxygen consumption during iron loading into ferritin by the tissue-derived oxidase and serum ceruloplasmin were 3.6 +/- 0.2 and 3.9 +/- 0.2, respectively. These data provide evidence that an enzyme analogous to ceruloplasmin is present on the plasma membrane of horse heart and that this ferroxidase is capable of catalyzing the loading of iron into ferritin. The implications of these data on the present models for the uptake and storage of iron by cells are discussed.