Increase In Polyamine Levels Research Articles

Polyamines in Ovarian Aging and Disease.

Ovarian aging and disease-related decline in fertility are challenging medical and economic issues with an increasing prevalence. Polyamines are a class of polycationic alkylamines widely distributed in mammals. They are small molecules essential for cell growth and development. Polyamines alleviate ovarian aging through various biological processes, including reproductive hormone synthesis, cell metabolism, programmed cell death, etc. However, an abnormal increase in polyamine levels can lead to ovarian damage and promote the development of ovarian disease. Therefore, polyamines have long been considered potential therapeutic targets for aging and disease, but their regulatory roles in the ovary deserve further investigation. This review discusses the mechanisms by which polyamines ameliorate human ovarian aging and disease through different biological processes, such as autophagy and oxidative stress, to develop safe and effective polyamine targeted therapy strategies for ovarian aging and the diseases.

Application of exogenous glutathione confers salinity stress tolerance in tomato seedlings by modulating ions homeostasis and polyamine metabolism

The objective of this study was to investigate the effects of exogenous glutathione (GSH) on the ion balance and micro-distribution, polyamine metabolism (PA) levels, activity of key enzymes, expression of PA synthesis and metabolism genes in tomato (Solanum lycopersicum L. cv. Zhongshu No. 4) seedlings under salt (NaCl) stress (100 mM). we found that NaCl stress caused damage to tomato, including seedling growth inhibition, imbalanced intracellular ion homeostasis caused by the accumulation of Na+ and Cl− in roots and leaves, and reduced transport capacity of K+, Ca2+, and Mg2+ from roots to leaves. Salt stress also led to a significant increase in polyamine levels in leaves. BSO (L-Buthionine-sulfoximine, an inhibitor of key GSH synthesis enzyme gamma- glutamylcysteine synthetase) application under salt stress exacerbated growth inhibition and ion imbalance in tomato seedlings and induced further accumulation of polyamine. However, the application of exogenous GSH reduced the Na+ and Cl- content of roots and leaves of plants under salt stress and NB (NaCl + BSO) treatments, regulated ion homeostasis and microdomain distribution, inhibited the selective transport of Na+, and promoted the selective transport of K+ and Ca2+ from root to leaf, thus alleviating the ion imbalance and poisoning caused by salt stress. In addition, exogenous GSH also down-regulated the activities and transcriptional levels of the PA synthesis- and degradation-related key enzymes ADC (arginine decarboxylase), SAMDC (S-adenosylmethionine decarboxylase), and DAO (diamine oxidase) under salt stress and NB treatments, and up-regulated the activities and the transcriptional levels of PAO (PA oxidase) and ODC (ornithine decarboxylase), thereby reducing the level of PAs and promoting the transformation of polyamines between different morphologies. These findings suggest that exogenous GSH applied to salt-stressed tomato confers salinity tolerance in tomato seedlings by modulating ion absorption, microdomain distribution, and the ion selective transport ratio and by regulating polyamine synthesis and metabolism to maintain cellular ions and polyamine homeostasis. This is the first study to provide evidence of the interaction between GSH and PAs in plant adaptive responses to salinity.

Abstract 4565: Antizyme inhibitor regulates the expression of proteins involved in mitosis and affects prostate cancer cell growth

Abstract Upregulation of polyamine biosynthesis is a requirement for cell growth and proliferation. Increases in polyamine levels are mediated by the enzyme ornithine decarboxylase (ODC), which is inhibited by antizyme (AZ). Rescue of ODC activity is accomplished by expression of antizyme inhibitor (AZI), which prevents binding of AZ to ODC. Increases in AZI gene copy number, mRNA transcripts, protein expression and AZI nuclear localization are all associated with prostate cancer. Furthermore, knockdown of AZI expression prevents prostate cancer cell growth in vitro and in vivo. To determine if AZI regulation affects prostate cancer cell growth via mechanisms that are independent of polyamide levels, we conducted a proteomic analysis of the AZI interactome by co-IP and MS/MS. This resulted in the identification of 29 high-confidence interacting proteins (HCIPs), 10 of which are associated with microtubules or with the mitotic spindle including TPX2 and KIFC1. Constitutive overexpression of AZI in PC3M-LN4 prostate cancer cells leads to a decrease in expression of the microtubule associated protein KIFC1, further supporting an interaction between AZI and KIFC1. Silencing of AZI gene expression using siRNA nanoparticles results in a decrease in prostate cancer cell proliferation and altered expression of proteins involved in mitosis. Taken together, this data suggests that AZI may influence prostate cancer cell proliferation via mechanisms that are independent of polyamine regulation. Citation Format: James M. Rice, Amanda Kusztos, Bruce R. Zetter. Antizyme inhibitor regulates the expression of proteins involved in mitosis and affects prostate cancer cell growth. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4565.

THE ROLE OF POLYAMINES IN ANTI-PROLIFERATIVE EFFECT OF SELECTED MALAYSIAN HERBS IN HUMAN LUNG ADENOCARCINOMA CELL LINE

Polyamine is a group of aliphatic amine that is necessary for cell growth and development. However, potential of developing cancer is enhanced with the increase of polyamine levels in the body. Since polyamines can be obtained through diet intake, it is essential for cancer patients to consume foods that have low level of polyamines. Therefore, this study aims to determine the polyamine level of selected plants; Sabah Snake Grass (Clinacanthus nutans), Daun Kadok (Piper sarmentosum) and Fig (Ficus auriculata). The antiproliferative effects of C. nutans, P. sarmentosum and F. auriculata were investigated using MTT assay and the polyamines content in these plants and intracellular content were quantified using High Performance Liquid Chromatography (HPLC). The results showed that polyamines content in C. nutans (41.49 nmol/g), P. sarmentosum (55.01 nmol/g) anf F. auriculata (39.28 nmol/g) were classified under low level. The IC50 values for these plants were in the range of 20-30 mg/ml. This study demonstrated that these plants inhibit the A549 cell’s growth after 24 hours to 96 hours of exposure. Depletion of intracellular polyamine after 48 hours to 96 hours of exposure was also identified. In conclusion, the study showed that C. nutans, P. sarmentosum and F.auriculata contain low level of polyamine and have anti-proliferative effect against A549 cells. Therefore these plants are recommended to reduce or delayed the occurrence of malignancy and prevention of cancer recurrence after successful treatment.

Hessian fly larval feeding triggers enhanced polyamine levels in susceptible but not resistant wheat.

BackgroundHessian fly (Mayetiola destructor), a member of the gall midge family, is one of the most destructive pests of wheat (Triticum aestivum) worldwide. Probing of wheat plants by the larvae results in either an incompatible (avirulent larvae, resistant plant) or a compatible (virulent larvae, susceptible plant) interaction. Virulent larvae induce the formation of a nutritive tissue, resembling the inside surface of a gall, in susceptible wheat. These nutritive cells are a rich source of proteins and sugars that sustain the developing virulent Hessian fly larvae. In addition, on susceptible wheat, larvae trigger a significant increase in levels of amino acids including proline and glutamic acid, which are precursors for the biosynthesis of ornithine and arginine that in turn enter the pathway for polyamine biosynthesis.ResultsFollowing Hessian fly larval attack, transcript abundance in susceptible wheat increased for several genes involved in polyamine biosynthesis, leading to higher levels of the free polyamines, putrescine, spermidine and spermine. A concurrent increase in polyamine levels occurred in the virulent larvae despite a decrease in abundance of Mdes-odc (ornithine decarboxylase) transcript encoding a key enzyme in insect putrescine biosynthesis. In contrast, resistant wheat and avirulent Hessian fly larvae did not exhibit significant changes in transcript abundance of genes involved in polyamine biosynthesis or in free polyamine levels.ConclusionsThe major findings from this study are: (i) although polyamines contribute to defense in some plant-pathogen interactions, their production is induced in susceptible wheat during interactions with Hessian fly larvae without contributing to defense, and (ii) due to low abundance of transcripts encoding the rate-limiting ornithine decarboxylase enzyme in the larval polyamine pathway the source of polyamines found in virulent larvae is plausibly wheat-derived. The activation of the host polyamine biosynthesis pathway during compatible wheat-Hessian fly interactions is consistent with a model wherein the virulent larvae usurp the polyamine biosynthesis machinery of the susceptible plant to acquire nutrients required for their own growth and development.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-014-0396-y) contains supplementary material, which is available to authorized users.

Inflammation, carcinogenesis and neurodegeneration studies in transgenic animal models for polyamine research

Natural polyamines (PA) are cationic molecules affecting cell growth and proliferation. An association between increased polyamine biosynthesis and inflammation-induced carcinogenesis has been recognised. On the other hand, there are indications that inflammatory stimuli can up-regulate polyamine catabolism and that altered polyamine metabolism could affect pro- and anti-inflammatory cytokines. Since the polyamine content is strictly related to cell growth, a consistent number of evidences relate polyamine metabolism dysfunction with cancer. The increase of polyamine levels in malignant and proliferating cells attracted the interest of scientists during last decades, addressing polyamine depletion as a new strategy to inhibit carcinogenesis. Several studies suggest that PA also play an important role in neurodegeneration, but the mechanisms by which they participate in neuronal death are still unclear. Furthermore, the role of endogenous PA in normal brain functioning is yet to be elucidated. The consequences of an alteration of polyamine metabolism have also been approached in vivo with the use of transgenic animals overexpressing or devoid of some enzymes involved in polyamine metabolism. In the present work we review the experimental investigation carried out on inflammation, cancerogenesis and neurodegeneration using transgenic animals engineered as models for polyamine research.

Synergistic effect of heat treatment and salicylic acid on alleviating internal browning in cold-stored peach fruit

The effect of heat treatment (38 °C, 12 h in air) and salicylic acid (SA, 1 mM) either separately or combined, on internal browning (IB) in cold-stored peach fruit ( Prunus persica Batsch) was investigated. The results showed that heat combined with SA treatment was the most effective method of alleviating IB in peach fruit during cold storage at 0 °C. The activities of antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase were significantly induced, while lipoxygenase activity was decreased by heat combined with an SA treatment. In addition, the combined treatment increased the levels of polyamines including putrescine, spermidine and spermine. These results suggest that the combination of heat and SA treatment may be a useful technique to alleviate IB in cold-stored peach fruit and the reduction in IB by the combined treatment may be due to the induction of antioxidant enzymes and increase in polyamine levels.

Difluoromethylornithine (DFMO) reduces deficits in isolation-induced ultrasonic vocalizations and balance following neonatal ethanol exposure in rats

Neonatal ethanol (EtOH) exposure is associated with central nervous system dysfunction and neurotoxicity in rats. Increases in polyamine levels have been implicated as one underlying mechanism for some of EtOH’s effects on the developing brain. In this study we addressed whether the inhibition of polyamine biosynthesis by α-difluoromethylornithine (DFMO) could reduce behavioral deficits induced by early EtOH exposure. Male and female rat pups received ethanol (6 g/kg/day EtOH i.g.), or isocaloric maltose (control) from postnatal days (PND) 1–8. On PND 8, animals were injected with either saline or DFMO (500 mg/kg, s.c.) immediately following the final neonatal treatment. Subjects were tested for isolation-induced ultrasonic vocalizations (USV) on PND 16; spontaneous activity in an open field apparatus on PND 20 and 21; and balance on PND 31. Animals exposed to EtOH neonatally displayed an increased latency to the first USV and reduced frequencies of USV, hyperactivity and preference for the center of the open field and poorer balance relative to controls. DFMO minimized these deficits in latency to the first USV and balance. These data provide further support that polyamines play a role in some of the functional deficits associated with EtOH exposure during early development and that reducing polyamine activity can improve outcome.

Polyamines enhance Agrobacterium tumefaciens vir gene induction and T-DNA transfer

We report here the enhancement of acetosyringone-mediated virulence gene induction in Agrobacterium tumefaciens by polyamines. The diamine putrescine and triamine spermidine enhanced vir gene induction when agrobacterial cells were treated prior to acetosyringone addition. An increase in polyamine levels was observed in Agroacterium following the polyamine treatments, which was positively correlated with the magnitude of vir gene induction. Plant transformation experiments have shown that modulation of polyamine levels in Agrobacterium results in the enhanced T-DNA transfer. These results suggest the involvement of polyamines in the processes that lead to vir gene induction and T-DNA transfer. And these findings may be useful in achieving a high transformation frequency in those plant species, which show minimal vir gene induction.

Polyamines increase in sympathetic neurons and non-neuronal cells after axotomy and enhance neurite outgrowth in nerve growth factor-primed PC12 cells

Following axonal damage, sympathetic neurons are capable of regenerating and reinnervating their target tissues. Some years ago exogenous administration of polyamines was shown to enhance this regeneration. Recently, it was found that axonal injury leads to a dramatic up-regulation of the expression of arginase I in sympathetic neurons. This enzyme catalyzes the conversion of arginine to ornithine, which can subsequently be converted to the diamine putrescine and, ultimately, to the polyamines spermidine and spermine. In the present study, using an antiserum that reacts with both spermidine and spermine, we have found an increase in polyamine levels in both neurons and non-neuronal cells in the superior cervical ganglion 2 and 5 days following transection of the ganglion's postganglionic trunks. Using PC12 cells primed with nerve growth factor and then stripped off the culture dish and replated as a model system for axotomized sympathetic neurons, we found that spermidine treatment, with or without nerve growth factor, resulted in an increased percentage of cells with a neurite whose length was at least twice the diameter of the neuron's cell body. These increases could be seen within 48 h and were still evident after 8 days. Together, these data support the possibility that endogenous polyamines are involved in the normal regeneration which occurs following sympathetic axonal damage.

Early alterations of polyamine metabolism induced after acute administration of clenbuterol in mouse heart

An acute treatment of mice with clenbuterol, a β-adrenergic agonist, produced a marked increase of polyamines levels in heart, particularly during the early phase of administration of the drug. A single dose of 1.5 mg/kg caused as much as a 10 fold induction in activity of ornithine decarboxylase (ODC) and 3 to 4 fold increase in levels of putrescine, spermidine and spermine in mouse heart. Maximum changes were observed 3 to 4 hours post-administration of clenbuterol. This treatment did not produce any change in S-adenosylmethionine decarboxylase activity. The induction of cardiac ODC by clenbuterol was also dose dependent with a peak at about 5 μmol/kg. Co-administration of difluoromethylornithine, an irreversible inhibitor of ODC, or propranolol, a nonspecific β-antagonist, with clenbuterol completely prevented the induction of ODC activity as well as the increase in polyamine levels in heart. However, pretreatment with alprenolol or metoprolol, the specific β 1 and β 2-antagonists, respectively, produced only partial prevention. The cardiac ODC from controls as well as clenbuterol treated mice exhibited similar affinity (Km) for its substrate, ornithine, while maximum enzyme activity (Vmax) was about 14 fold higher in clenbuterol treated mouse heart than in the control. Clenbuterol produced no change in the level of specific ODC mRNA or the protein, but the enzyme from the drug-treated mouse heart was considerably more stable than the control. Pretreatment of mice with either cycloheximide or actinomycin D followed by administration of clenbuterol could not prevent the induction in ODC activity suggesting that de novo biosynthesis of the enzyme protein or ODC mRNA was not responsible for induction of ODC activity. Post-translational changes in ODC may be responsible for an early increase of ODC activity due to clenbuterol treatment.

Anti-tumor activity of antizyme which targets the ornithine decarboxylase (ODC) required for cell growth and transformation.

Anti-tumor activity of antizyme which targets the ornithine decarboxylase (ODC) required for cell growth and transformation Cell proliferation and transformation induced by growth factor stimulation or by carcinogens, viruses, or oncogenes are characterized by an associated increase in polyamine levels, which is mediated by increased polyamine biosynthesis and enhanced uptake of polyamines. Polyamine biosynthesis is catalyzed particularly, in the level of ornithine decarboxylase (ODC). The elevation of cellular polyamine levels on the other hand accelerates the induction of ornithine decarboxylase antizyme (antizyme), which is involved not only in ODC-degradation, but in the negative regulation of polyamine transport. Taking advantage of these characteristics of antizyme, the potential of antizyme as a factor having anti-cell growth and anti-tumor activity was investigated. We show that antizyme can induce cell death associated with a rapid decline of intracellular polyamine contents. The possible anti-tumor activities of ectopically expressed antizyme were tested in p21H-ras (Val 12)-transformed NIH3T3 cells and several human malignant cell lines including a line with loss of p53 expression, and they were shown to be as sensitive as nontransformed NIH3T3 cells in vitro. The in vivo anti-tumor activity was also tested using nude mice inoculated with H-ras transformed NIH3T3 cells that had been transfected with inducible antizyme expression vector and the results showed that antizyme expression in vivo blocks tumor formation in these mice. These results suggest that ectopic antizyme expression is of possible therapeutic benefit in the treatment of cancer, which is mediated by ODC inactivation and intracellular polyamine depletion.

Blockade of ornithine decarboxylase enzyme protects against ischemic brain damage.

Polyamines are derived from ornithine by the actions of ornithine decarboxylase (ODC), which is the rate-limiting step in this pathway. Polyamines play a role in cell growth, neoplasia, differentiation, and response to injury. We have shown that transient cerebral ischemia gives rise to increased ODC mRNA and enzyme activity in the gerbil brain. ODC and polyamines are thought to be important in the generation of edema and the neuronal cell loss associated with cerebral ischemia. To test this theory, we examined the ODC activity, putrescine levels, and neuronal density in the CA1 region of the hippocampus following ischemia and reperfusion injury in the absence and presence of an inhibitor of ODC activity, alpha-difluoromethylornithine (DFMO). Pretreatment of animals with DFMO resulted in attenuation of the ODC activity following 5 min of ischemia and 4 h of reperfusion. In addition, DFMO prevented the increase in polyamine levels, as determined by measurement of putrescine in the ischemic brain. These alterations were not due to changes in ODC mRNA level. Further analysis revealed that DFMO treatment blocked the delayed neuronal cell death in the CA1 region of the hippocampus that accompanies ischemia and reperfusion injury. Administration of DFMO resulted in a dose-dependent beneficial effect upon neuronal cell survival. These results suggest that ODC enzyme activity and the production of polyamines play a significant role in the response of the brain to ischemic injury.

Polyamines and their biosynthetic enzymes in dormant embryos of the spindle tree ( Euonymus europaeus L.) and in dormancy break obtained after treatment with gibberellic acid

Dormancy break of spindle tree embryos after gibberellic acid treatment was followed by an increase in polyamine levels and the activities of their biosynthetic enzymes, especially arginine decarboxylase (ADC). Increasing levels of putrescine, spermidine and ADC activity occurred during the first hours of culture (before the emergence of the radicle). Dormancy break was also correlated with a decrease of tyramine. Treatment with α- dl-difluoromethylarginine (DFMA), a specific and irreversible inhibitor of the putrescine-synthesizing enzyme, arginine decarboxylase (ADC), led to the maintenance of embryo dormancy in a GA 3-medium. Application of agmatine or putrescine to the inhibited system resulted in a reversal of inhibition. With α- dl-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of putrescine biosynthesis by ornithine decarboxylase (ODC), embryo dormancy in a GA 3-medium was completely broken and germination was complete within 36 h. Our results suggest that polyamines (via ADC pathway) mediate hormone-induced growth responses in spindle tree embryos.

Effect of dibutyltin dilaurate on regional brain polyamines in rats

Administration of dibutyltin dilaurate (DBTL; 0, 20 or 40 mg/kg body wt.) by gavage to rats for 3 consecutive days produced a significant increase in polyamine levels in selected brain areas. At the higher dose of DBTL (40 mg/kg) Spermidine levels were raised in pons-medulla, hypothalamus and frontal cortex while spermine levels increased in pons-medulla, hippocampus and frontal cortex regions. At the lower dose (20 mg/kg) only a slight increase in polyamine levels occurred. The observed induction in regional brain polyamines in DBTL-treated rats may lead to disturbances in synaptic function and further enhance its neurotoxic potential.

Triadimefon stimulates rooting in bean hypocotyl

Triadimefon, a broad spectrum fungicide and an inhibitor of gibberellic biosynthesis, whitened, thickened, and shortened the roots of bean (Phaseolus vulgaris L. cv. Spring Green) seedlings and stimulated the development of root primordia along the hypocotyl. In a comparative study, triadimefon, IAA, spermidine, putrescine and spermine all stimulated adventitious root growth, but triadimefon was more effective than the other 4 compounds. Equimolar concentrations of gibberellic acid (GA3) completely eliminated the stimulatory effect of triadimefon. Stimulation of root development by triadimefon was accompanied by inhibition of ethylene biosynthesis followed by removal of basal dominance and an increase in polyamine levels, both of which occurred after rooting had begun. Although triadimefon was effective in stimulating rooting, its mechanism of action is apparently not mediated via the control of ethylene and polyamine biosynthesis.

Effect of Growth Retardants on Root Formation and Polyamine Content in Apple Seedlings

Abstract Growth retardants [ancymidol (0.1-1.0 mg·liter−1), chlormequat (0.5-500 mg·liter−1), and paclobutrazol (0.1-1.0 mg·liter−1)] reduced shoot extension, promoted root initiation, and increased root weight in apple seedlings (Malus domestica Borkh ‘York Imperial’). The induction of root formation and increase in root weight were accompanied by a considerable increase in polyamine levels. Daminozide (0.1-250.0 mg·liter−1) and dikegulac (0.25-500 mg·liter−1) also inhibited apple seedling growth; however, these compounds did not promote rooting. Chemical names used: α-cyclopropyl-α-(4-methoxyphenyl)-5-pyrimidinemethanol (ancymidol); 2-chloro-N,N,N-trimethylethanaminium chloride (chlormequat chloride); butanedioic acid mono(2,2-dimethylhydrazide) (daminozide); 2,3:4,6-bis-O-(l-methylethylidene)-α-L-xylo-2-hexulofuranosonic acid (dikegulac); β-(4-chlorophenyl)methyl]-α-(l,l-dimethylethyl)-lH-1,2,4-triazole-l-ethanol (paclobutrazol).

Polyamine Titre in Relation to Chill-Sensitivity inPhaseolus sp.

Guye, M. G., Vigh, L. and Wilson, J. M. 1986. Polyamine titre in relation to chill-sensitivity in Phaseolus sp.—J. exp. Bot. 37: 1036-1043. Endogenous levels of the polyamines putrescine, spermidine and spermine were quantified in the primary leaves of five cultivars of bean (Phaseolus sp.) differing in their 'wilting response' to a chilling exposure of 5 °C for 24 h. Levels of polyamines prior to chilling treatment did not appear to be correlated with chill-tolerance as levels in the non-chilled controls were highest in cultivars of medium chill-sensitivity. Plants grown under a vapour saturation deficit (PSD) of 8-4 g m ~ 3 day/6-1 g m ~ 3 night exhibited a mild hardening as compared to plants grown under a VSD of 5-7 g m3 day/4-1 g m ~3 night, as the former showed less wilting on chilling. Hardening at high VSD had the effect of slightly lowering the putrescine content of non-chilled tissue but total polyamine content remained unchanged. However, on chilling, the largest relative increase in polyamine levels, in particular that of putrescine, occurred in hardened plants. There was also a significant relative increase in putrescine titre in response to chilling in non-hardened genotypes of high chill-tolerance, whereas more chill-sensitive genotypes remained unchanged or slightly declined in putrescine content on chilling. Relative changes in putrescine content rather than absolute levels appears to be correlated with chill-tolerance. These results are discussed in view of present knowledge on the adaptive significance of stress-induced changes in polyamines, especially with regard to membrane stability.

Association of increased polyamine levels with isoproterenol-stimulated mucin secretion in the rat submandibular gland

Incubation of rat submandibular gland slices with 50 μM isoproterenol for 10–40 min stimulated mucin secretion and induced a 3- to 4-fold increase in tissue concentrations of the polyamines putrescine, spermidine and spermine. α-Difluoromethylornithine, a specific inhibitor of ornithine decarboxylase, suppressed the isoproterenol-induced increase in submandibular polyamines and inhibited mucin secretion. Exogenous putrescine restored tissue polyamine levels and partially reversed the inhibitory effect of α-difluoromethylornithine on mucin secretion. Rapid increases in polyamine levels appear to mediate isoproterenol-stimulated mucin secretion in the rat submandibular gland.

Consequences of ornithine decarboxylase inactivation by alpha-difluoromethylornithine and 5-fluorouracil on the growth of rabbit fibroblasts.

The role of ornithine decarboxylase and polyamines in proliferative vitreoretinopathy (PVR) is ill-defined. An increase in the activity of this enzyme concurrent with an increase in polyamine levels may be essential in the process of intraocular cellular proliferation. Therefore, in this study, cultured rabbit fibroblasts were exposed to DL-alpha-difluoromethylornithine (alpha-DFMO), a mechanism-based irreversible inactivator of ornithine decarboxylase, alone and in combination with 5-fluorouracil (5-FU). Concentrations of 0.1mM alpha-DFMO and 0.125mM 5-FU decreased rabbit fibroblast cell number by 60% and 65%, respectively, after three days, while with either 5.0mM alpha-DFMO or 0.25mM 5-FU, cell number is decreased by 95%. The effectiveness of inhibitory concentrations of 5-FU and alpha-DFMO together in reducing cell number is additive.