Product Putrescine Research Articles

THU277 Deletion Or inhibition Of Ornithine Decarboxylase Protects Islet β-cell Health And Is Associated With Preserved Residual C-peptide In Persons With Recent Onset Type 1 Diabetes

Abstract Disclosure: B. Hammoud: None. L.A. DiMeglio: None. A. Kulkarni: None. A. Hull: None. S. Woerner: None. S. Cabrera: None. L.D. Mastrandrea: None. F. Ouyang: None. S.N. Perkins: None. C. Evans-Molina: None. T.L. Mastracci: None. S.A. Tersey: None. S. Sarkar: None. E. Nakayasu: None. B. Webb-Robertson: None. E. Gerner: None. R.G. Mirmira: None. E.K. Sims: None. Inhibition of polyamine biosynthesis using α-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase, reduces β cell stress and type 1 diabetes (T1D) incidence in preclinical animal models. However, the cellular and molecular mechanisms by which polyamines promote β-cell stress and the tolerability and effectiveness of their depletion by DFMO in humans with T1D remain unknown. We hypothesized that β-cell protection from stress occurs via cell-autonomous effects of polyamine depletion. To test this hypothesis, we generated β-cell specific knockout of ornithine decarboxylase in mice, performed comprehensive proteomics and transcriptomics on human islets treated with DFMO under inflammatory conditions in vitro, and performed a clinical study of DFMO tolerability, safety, and efficacy in persons with new-onset T1D. β-cell-specific deletion of the gene encoding ornithine decarboxylase in mice demonstrated protection of these animals against toxin (streptozotocin)-induced β-cell loss and hyperglycemia, implicating a cell-autonomous role for ornithine decarboxylase in β-cell stress. RNA sequencing and proteomics analyses of human islets exposed to a cytokine mix (1000 U/mL IFNγ + 50 U/mL IL-1β) +/- 5 mM DFMO identified 130 differentially regulated transcripts and 701 differentially regulated proteins. Pathway analysis implicated endosomal transport, vesicle organization and regulation of exocytosis, mRNA processing, and antigen cross presentation as mechanisms underlying DFMO effects on the islet response. To test DFMO in humans, we performed a 3-site randomized, placebo-controlled, double masked dose-ranging study of 3 months daily oral DFMO in persons with recent-onset T1D (<100 days). Dosing at 125, 250, 500, 750 or 1000 mg/m2/day was tested in 41 persons (12-34 y/o, 59% male, mean HbA1c 7.3%), with 6-10 participants/dosing group. Only mild and moderate adverse effects (AEs) were noted. Possible drug-related AEs included mild-moderate gastrointestinal symptoms, headache, upper respiratory infections, a pump site infection, and anemia. Urinary levels of the ODC product putrescine were decreased (p=0.05) in the 1000 mg/m2 dosing group. Compared to placebo, individuals receiving 750 and 1000 mg/m2 doses had significantly higher mixed-meal C-peptide area under the curve values at the 6-month post-randomization visit (p<0.05 vs. placebo). In conclusion, β-cell ODC inhibition protects β-cell health and function in the context of the proinflammatory T1D milieu. A 3-month course of oral DFMO was well tolerated with a favorable AE profile in persons with recent-onset T1D. Higher doses were associated with greater β-function compared to placebo. DFMO may have utility as a β-cell preservation therapy in recent-onset T1D. Presentation: Thursday, June 15, 2023

Arginine Decarboxylase Gene ADC2 Regulates Fiber Elongation in Cotton

Cotton is an important agro-industrial crop providing raw material for the textile industry. Fiber length is the key factor that directly affects fiber quality. ADC, arginine decarboxylase, is the key rate-limiting enzyme in the polyamine synthesis pathway; whereas, there is no experimental evidence that ADC is involved in fiber development in cotton yet. Our transcriptome analysis of the fiber initiation material of Gossypium arboreum L. showed that the expression profile of GaADC2 was induced significantly. Here, GhADC2, the allele of GaADC2 in tetraploid upland cotton Gossypium hirsutum L., exhibited up-regulated expression pattern during fiber elongation in cotton. Levels of polyamine are correlated with fiber elongation; especially, the amount of putrescine regulated by ADC was increased. Scanning electron microscopy showed that the fiber length was increased with exogenous addition of an ADC substrate or product putrescine; whereas, the fiber density was decreased with exogenous addition of an ADC specific inhibitor. Next, genome-wide transcriptome profiling of fiber elongation with exogenous putrescine addition was performed to determine the molecular basis in Gossypium hirsutum. A total of 3163 differentially expressed genes were detected, which mainly participated in phenylpropanoid biosynthesis, fatty acid elongation, and sesquiterpenoid and triterpenoid biosynthesis pathways. Genes encoding transcription factors MYB109, WRKY1, and TCP14 were enriched. Therefore, these results suggested the ADC2 and putrescine involvement in the development and fiber elongation of G. hirsutum, and provides a basis for cotton fiber development research in future.

Regulation of polyamine homeostasis through an antizyme citrullination pathway

This study reveals an uncovered mechanism for the regulation of polyamine homeostasis through protein arginyl citrullination of antizyme (AZ), a natural inhibitor of ornithine decarboxylase (ODC). ODC is critical for the cellular production of polyamines. AZ binds to ODC dimers and promotes the degradation of ODC via the 26S proteasome. This study demonstrates the protein citrullination of AZ catalyzed by peptidylarginine deiminase type 4 (PAD4) both in vitro and in cells. Upon PAD4 activation, the AZ protein was citrullinated and accumulated, leading to higher levels of ODC proteins in the cell. In the PAD4-overexpressing and activating cells, the levels of ODC enzyme activity and the product putrescine increased with the level of citrullinated AZ proteins and PAD4 activity. Suppressing cellular PAD4 activity reduces the cellular levels of ODC and downregulates cellular polyamines. Furthermore, citrullination of AZ in the C-terminus attenuates AZ function in the inhibition, binding, and degradation of ODC. This paper provides evidence to illustrate that PAD4-mediated AZ citrullination upregulates cellular ODC and polyamines by retarding ODC degradation, thus interfering with the homeostasis of cellular polyamines, which may be an important pathway regulating AZ functions that is relevant to cancer biology.

THE EFFECT OF INCREASING DOSES OF FOLIAR APPLIED REGULATORS OF POLYAMINE BIOSYNTHESIS IN MIXTURE WITH TRIAZINE HERBICIDE ON FORMATION OF SPRING BARLEY BIOMASS

The use of herbicides has become a potential tool in modern agriculture to get rid of weeds menace, but unknowingly the indiscriminate application of herbicides has resulted in adverse effects on the morphological, physiological and biochemical characteristics of crop plants. Herbicide effect of triazine herbicide (solo applied, or in combinations with regulators of polyamine biosynthesis: γ-aminobutyric acid, propylenediamine and salicyl acid) and quantitative parameters of spring barley (variety Kompakt) was evaluated under simulative conditions of hydroponic experiments under light platform. The experiment was carried out in hydroponics under light platform with linear fluorescent lamp at Department of chemistry SUA Nitra, where 9 pots was used with 24 barley grains/per pot of variety Kompakt and 5.5 litres of mineral solution, which were prepared from stock solutions containing optimal content of macro-elements (K, P, N, Ca, Mg) and micro-elements (B, Mn, Cl, Zn, S, Cu, Mo, Fe) for plants. At hydroponic experiment short-time negative effect of triazine herbicide at formation of biomass and root system and more significant negative influence at the amount of formed fresh biomass and root system were observed. Our experiments after foliar treatment of barley plants with herbicide confirm minimal short-time negative effect of mentioned herbicide. It indicates lowering of the amount of retained water in roots. Regulators of polyamine biosynthesis in hydroponics reduced inhibitory effect of tested pesticide on formation of organic matter, while their influence was manifested on amount of produced fresh biomass and root matter than on amount of dry matter. The most suitable doses of 100 g.ha-1 degradation product putrescine - GABA (γ-amino-butyric acid) and 59.2 g.ha-1 degradation product spermidine and spermine - DAP (1,3- propylendiamine) were used on elimination of negative effects of triazine herbicide in barley.

Polyamine Homeostasis in Snyder-Robinson Syndrome.

Loss-of-function mutations of the spermine synthase gene (SMS) result in Snyder-Robinson Syndrome (SRS), a recessive X-linked syndrome characterized by intellectual disability, osteoporosis, hypotonia, speech abnormalities, kyphoscoliosis, and seizures. As SMS catalyzes the biosynthesis of the polyamine spermine from its precursor spermidine, SMS deficiency causes a lack of spermine with an accumulation of spermidine. As polyamines, spermine, and spermidine play essential cellular roles that require tight homeostatic control to ensure normal cell growth, differentiation, and survival. Using patient-derived lymphoblast cell lines, we sought to comprehensively investigate the effects of SMS deficiency on polyamine homeostatic mechanisms including polyamine biosynthetic and catabolic enzymes, derivatives of the natural polyamines, and polyamine transport activity. In addition to decreased spermine and increased spermidine in SRS cells, ornithine decarboxylase activity and its product putrescine were significantly decreased. Treatment of SRS cells with exogenous spermine revealed that polyamine transport was active, as the cells accumulated spermine, decreased their spermidine level, and established a spermidine-to-spermine ratio within the range of wildtype cells. SRS cells also demonstrated elevated levels of tissue transglutaminase, a change associated with certain neurodegenerative diseases. These studies form a basis for further investigations into the leading biochemical changes and properties of SMS-mutant cells that potentially represent therapeutic targets for the treatment of Snyder-Robinson Syndrome.

A Label-Free Continuous Fluorescence-Based Assay for Monitoring Ornithine Decarboxylase Activity with a Synthetic Putrescine Receptor

Polyamines play an important role in cell growth, differentiation, and cancer development, and the biosynthetic pathway of polyamines is established as a drug target for the treatment of parasitic diseases, neoplasia, and cancer chemoprevention. The key enzyme in polyamine biosynthesis is ornithine decarboxylase (ODC). We report herein an analytical method for the continuous fluorescence monitoring of ODC activity based on the supramolecular receptor cucurbit[6]uril (CB6) and the fluorescent dye trans-4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide (DSMI). CB6 has a significantly higher binding constant to the ODC product putrescine (>107 M–1) than to the substrate L-ornithine (340 M–1). This enables real-time monitoring of the enzymatic reaction through a continuous fluorescence change caused by dye displacement from the macrocycle by the formed product, which allowed a straightforward determination of enzyme kinetic parameters (kcat = 0.12 s–1 and KM = 24 µM) and inhibition constants of the two ODC inhibitors α-difluoromethylornithine (DFMO) and epigallocatechin gallate (EGCG). The potential for high-throughput screening (HTS) was demonstrated by excellent Z′ factors (>0.9) in a microplate reader format, and the sensitivity of the assay is comparable to or better than most established complementary methods, which invariably have the disadvantage of not being compatible with direct implementation and upscaling to HTS format in the drug discovery process.

Protein RS1 (RSC1A1) Downregulates the Exocytotic Pathway of Glucose Transporter SGLT1 at Low Intracellular Glucose via Inhibition of Ornithine Decarboxylase.

Na+-d-glucose cotransporter 1 (SGLT1) is rate-limiting for glucose absorption in the small intestine. Shortly after intake of glucose-rich food, SGLT1 abundance in the luminal membrane of the small intestine is increased. This upregulation occurs via glucose-induced acceleration of the release of SGLT1-containing vesicles from the trans-Golgi network (TGN), which is regulated by a domain of protein RS1 (RSC1A1) named RS1-Reg. Dependent on phosphorylation, RS1-Reg blocks release of vesicles containing SGLT1 or concentrative nucleoside transporter 1. The hypothesis has been raised that RS1-Reg binds to different receptor proteins at the TGN, which trigger release of vesicles with different transporters. To identify the presumed receptor proteins, two-hybrid screening was performed. Interaction with ornithine decarboxylase 1 (ODC1), the rate-limiting enzyme of polyamine synthesis, was observed and verified by immunoprecipitation. Binding of RS1-Reg mutants to ODC1 was characterized using surface plasmon resonance. Inhibition of ODC1 activity by RS1-Reg mutants and the ODC1 inhibitor difluoromethylornithine (DFMO) was measured in the absence and presence of glucose. In addition, short-term effects of DFMO, RS1-Reg mutants, the ODC1 product putrescine, and/or glucose on SGLT1 expressed in oocytes of Xenopus laevis were investigated. High-affinity binding of RS1-Reg to ODC1 was demonstrated, and evidence for a glucose binding site in ODC1 was provided. Binding of RS1-Reg to ODC1 inhibits the enzymatic activity at low intracellular glucose, which is blunted at high intracellular glucose. The data suggest that generation of putrescine by ODC1 at the TGN stimulates release of SGLT1-containing vesicles. This indicates a biomedically important role of ODC1 in regulation of glucose homeostasis.

Putrescine supplementation during in vitro maturation of aged mouse oocytes improves the quality of blastocysts.

Mouse ovaries exhibit a peri-ovulatory rise of ornithine decarboxylase and its product putrescine concurrent with oocyte maturation. Older mice exhibit a deficiency of both the enzyme and putrescine. Peri-ovulatory putrescine supplementation in drinking water increases ovarian putrescine levels, reduces embryo resorption and increases live pups in older mice. However, it is unknown if putrescine acts in the ovaries to improve oocyte maturation. This study examined the impact of putrescine supplementation during oocyte in vitro maturation (IVM) on the developmental potential of aged oocytes. Cumulus-oocyte complexes from 9-12-month-old C57BL/6 mice were subjected to IVM with or without 0.5mM putrescine, followed by in vitro fertilisation and culture to the blastocyst stage. Putrescine supplementation during IVM did not influence the proportion of oocyte maturation, fertilisation or blastocyst formation, but significantly increased blastocyst cell numbers (44.5±1.9, compared with 36.5±1.9 for control; P=0.003). The putrescine group also had a significantly higher proportion of blastocysts with top-grade morphology (42.9%, compared with 26.1% for control; P=0.041) and a greater proportion with octamer-binding transcription factor 4 (OCT4)-positive inner cell mass (38.3%, compared with 19.8% for control; P=0.005). Therefore, putrescine supplementation during IVM improves egg quality of aged mice, providing proof of principle for possible application in human IVM procedures for older infertile women.

Deficiency of ovarian ornithine decarboxylase contributes to aging‐related egg aneuploidy in mice

It has been known for more than four decades that during mammalian estrous cycles, luteinizing hormone stimulates a transitory rise in the ovaries of ornithine decarboxylase (ODC) activity and its enzymatic product putrescine, concurrent with oocyte maturation in vivo. Inhibition of this transitory ODC/putrescine rise, however, does not appear to affect oocyte maturation or ovulation. Using several mouse models and combining in vitro and in vivo approaches, we demonstrated that deficiency of ODC during oocyte maturation is correlated with increased levels of egg aneuploidies. These results suggest that the transitory ovarian ODC rise in late proestrus is important for ensuring proper chromosome segregation during oocyte maturation. Older mice (8 months of age) exhibited about 1/3 that of young mice in LH-stimulated ovarian ODC activity and a corresponding increase in egg aneuploidies. Moreover, a combination of putrescine supplementation in mouse drinking water leading up to oocyte retrieval and in oocyte maturation medium reduced egg aneuploidies of the older mice from 12.7% to 5.3%. Therefore, ovarian ODC deficiency might be an important etiology of maternal aging-related aneuploidies, and peri-ovulatory putrescine supplementation might reduce the risk of aneuploid conceptions in older women.

Peri-ovulatory putrescine to reduce aneuploid conceptions

Women experience diminished fertility, increased risk of miscarriages and congenital birth defects in their late 30s and early 40s, 10-15 years before reaching menopause. Egg aneuploidy (having an incorrect number of chromosomes) is the most important etiology for these reproductive problems in older women. Science correspondent Jon Cohen wrote a News piece in 2002 [1] on the quest to understand the mechanisms of maternal aging-related aneuploidies in humans, which is still applicable today. Although we have made impressive progress in understanding how aneuploidies arise, we know little about providing medical interventions to reduce them. “My Holy Grail is to deliver some sort of aneuploidy-reduction pill, …”, Dr. Terry Hassold, a leading geneticist in the field, is quoted as saying. Our recent study [2] may be a step towards developing such a pill. Aneuploid eggs result in aneuploid conceptions, most of which are lost either prior to clinical recognition of pregnancies or by miscarriages. The small proportion that survive inevitably carry major birth defects. Accurate egg aneuploidy rates in the general population are not known, but numerous analyses of IVF samples have revealed staggeringly high rates. Notably, a recent study of more than 20,000 IVF eggs revealed significant age-related aneuploidies, reaching >40% in the 40 year old age group [3]. Furthermore, this study [3] employs fluorescence in situ hybridization of polar bodies and is therefore limited in the number of chromosomes (five) that can be analyzed simultaneously. The true aneuploidy rates in older women, considering all 23 chromosomes, would be expected to be much higher. This unusually high egg aneuploidy rate in humans is likely due to a combination of our longevity and the peculiar oogenesis (the process of generating eggs) in all vertebrates including humans. Unlike vertebrate males that continuously generate mature sperm from germ line stem cells through adulthood, in vertebrates oogenesis begins during the embryonic stage when germ line stem cells initiate meiosis and develop into primary oocytes. By birth, the females have developed a finite number of primary oocytes arrested in meiotic prophase that comprises their lifetime egg supply. The prophase oocytes contain chromosome bivalents each having four chromatids linked together by a combination of sister chromotid cohesion and non-sister cross-over (Figure ​(Figure1),1), with this linkage persisting for decades in women. During ovulation the two sister chromatids are segregated to the same cell (egg or 1st polar body) in a process called oocyte maturation; in the subsequent fertilization, the sisters are segregated between the 2nd polar body and the haploid egg. As females age, chromosome cohesion becomes progressively weakened [4], predisposing the oocytes to greater risk of premature separation of sister chromatids (PSSC) during oocyte maturation [2-5] (Figure ​(Figure11). Figure 1 Premature separation of sister chromatids (PSSC) during oocyte maturation Given the great time lapse, it seems daunting that any measure can be found to keep these primary oocytes “fresh” while women age. Our study however suggests that a metabolic deficiency during ovulation in older females, which can be easily corrected, is an important compounding factor in age-related egg aneuploidies. It has been known for more than four decades [6] that during mammalian ovulation, the ovaries exhibit a transitory (i.e. a few hours) rise in the enzyme ornithine decarboxylase (ODC) and its product putrescine and yet its physiological function remains enigmatic. We found that inhibition of ODC during ovulation results in significant increase of incidence of PSSC in eggs of young mice. Interestingly, older mice exhibit a diminished ODC rise in the ovaries, and a corresponding increase of PSSC in eggs. Most remarkably, a combination of putrescine supplementation in mouse drinking water leading up to oocyte retrieval and in oocyte maturation medium reduced the incidence of PSSC in eggs by more than 50% [2]. Putrescine is a naturally occurring, small metabolite easily absorbed and distributed throughout the organism. A high dose of putrescine supplementation similar to that used in our study has been given safely to neonatal calves and pigs as an ingredient of soybean-based milk replacement [7]. However, post-conception putrescine supplementation in mouse drinking water compromises fetal development, likely due to excess reactive oxygen species produced by placental diamine oxidase oxidizing the exogenous putrescine [8]. In contrast, periovulatory putrescine supplementation is safe for gestation, because exogenous putrescine administered around ovulation is cleared long before placental development (Tao and Liu, in preparation). Nonetheless, further studies, including that employing primates, are required to formulate effective and safe putrescine supplementation protocols to reduce egg aneuploidies, both in IVF clinics and in natural conception.

Ornithine decarboxylase activity, a clinical biomarker for evaluating cancer chemopreventive efficacy of phytomolecules

AbstractBiomarkers of cancer have made a strong traipse in predicting the disease pattern and contributed significantly to the understanding of tumour state, progression, characteristics and response to therapies. Polyamines such as putrescine, spermine and spermidine are cationic biomolecules essential for the cell cycle function and serve as excellent biomarkers of tumour progression. The polyamine biosynthesis is tightly regulated by ornithine decarboxylase, a highly inducible enzyme specific to pH, temperature, time and substrate concentration. The expression of this enzyme is very high during cell transformation and tumour progression leading to elevated level of polyamines. To measure the activity of ornithine decarboxylase an improved, easy, simple, reliable and cost-effective method has been developed utilizing small quantity of chemicals. The methodology is based on the cognizance that enzyme transforms L-ornithine hydrochloride substrate to a yellow coloured product putrescine soluble in pentanol, the absorbance of which was measured spectrophotometrically. The procedure is being utilized for evaluating cancer chemopreventive efficacy of phytomolecules. We have analyzed hundreds of molecules belonging to flavonoid, terpenes and alkaloid groups and very few were found to inhibit enzyme activity in a concentration dependent manner (0.4-50µg/mL). In addition, the molecules were also tested for their radical scavenging properties. Our results depict that molecules having phenolic groups and lactone rings in their structure are better inhibitors than their counterparts. The comparative analysis of the groups reassures flavonoids as better scavengers of radical formation and a positive correlation was observed among the nitric oxide and 2, 2-diphenyl-1-picrylhydrazyl inhibition (p<0.01). Further evaluation and augmentation may reveal novel ornthine decarboxylase inhibitors and cancer chemopreventive agents from plants.

Androgen interaction with the polyamine system of the rat prostate.

The ventral and dorsal lobes of the rat prostate contain larger quantities of the aliphatic amines putrescine, spermidine and spermine and higher activities of the enzyme ornithine decarboxylase (ODC; EC 4.1.1.17) than other accessory sex glands. In contrast, the coagulating glands and the seminal vesicles contain only small quantities of the amines but the highest activities of the arginase (ARG; EC 3.5.3.1). Lineweaver-Burk plots indicated that the Km-values for ARG in the coagulating gland and ODC in the ventral prostate lobe were 20 mM and 0.2 mM, respectively. Castration decreased ODC and ARG activities to 3 and 50% of control levels, respectively, after 3 days, whilst the Km-values were unaffected. Daily administration of 3 mg dihydrotestosterone (DHT) prevented these castrational changes. Oestrogen treatment alone had no effect on the activities of the enzymes, but appeared to exert a synergistic effect with androgen on the ODC. Administration of androgen to intact rats for 7 days caused a dose-related alteration in the ratios of the various amines, particularly the spermine: putrescine ratio. A minor but significant decrease was also recorded in the activity of the ODC, which was mirrored by an increase in the levels of putrescine in the tissue. The data suggest that androgen control of the polyamine pathway is biphasic, first stimulatory and later inhibitory with lesions occurring at the ODC, possibly via short loop feedback of its product putrescine, but also at subsequent enzymic steps in spermidine and spermine biosynthesis.

Phylogenetic Diversity and the Structural Basis of Substrate Specificity in the β/α-Barrel Fold Basic Amino Acid Decarboxylases

The beta/alpha-barrel fold type basic amino acid decarboxylases include eukaryotic ornithine decarboxylases (ODC) and bacterial and plant enzymes with activity on L-arginine and meso-diaminopimelate. These enzymes catalyze essential steps in polyamine and lysine biosynthesis. Phylogenetic analysis suggests that diverse bacterial species also contain ODC-like enzymes from this fold type. However, in comparison with the eukaryotic ODCs, amino acid differences were identified in the sequence of the 3(10)-helix that forms a key specificity element in the active site, suggesting they might function on novel substrates. Putative decarboxylases from a phylogenetically diverse range of bacteria were characterized to determine their substrate preference. Enzymes from species within Methanosarcina, Pseudomonas, Bartonella, Nitrosomonas, Thermotoga, and Aquifex showed a strong preference for L-ornithine, whereas the enzyme from Vibrio vulnificus (VvL/ODC) had dual specificity functioning well on both L-ornithine and L-lysine. The x-ray structure of VvL/ODC was solved in the presence of the reaction products putrescine and cadaverine to 1.7 and 2.15A, respectively. The overall structure is similar to eukaryotic ODC; however, reorientation of the 3(10)-helix enlarging the substrate binding pocket allows L-lysine to be accommodated. The structure of the putrescine-bound enzyme suggests that a bridging water molecule between the shorter L-ornithine and key active site residues provides the structural basis for VvL/ODC to also function on this substrate. Our data demonstrate that there is greater structural and functional diversity in bacterial polyamine biosynthetic decarboxylases than previously suspected.

Cloning and functional expression of a rodent brain cDNA encoding a novel protein with agmatinase activity, but not belonging to the arginase family

A rat brain cDNA encoding for a novel protein with agmatinase activity was cloned and functionally expressed. The protein was expressed as a histidine-tagged fusion product with a molecular weight of about 63 kDa. Agmatine hydrolysis was strictly dependent on Mn 2+; K m and k cat values were 2.5 ± 0.2 mM and 0.8 ± 0.2 s −1, respectively. The product putrescine was a linear competitive inhibitor ( K i = 5 ± 0.5 mM). The substrate specificity, metal ion requirement and pH optimum (9.5) coincide with those reported for Escherichia coli agmatinase, the best characterized of the agmatinases. However, as indicated by the k cat/ K m (320 M −1 s −1), the recombinant protein was about 290-fold less efficient than the bacterial enzyme. The deduced amino sequence revealed great differences with all known agmatinases, thus excluding the protein from the arginase family. It was, however, highly identical (>85%) to the predicted sequences for fragments of hypothetical or unnamed LIM domain-containing proteins. As a suggestion, the agmatinase activity is adscribed to a protein with an active site that promiscuously catalyze a reaction other than the one it evolved to catalyze.

Altering the reaction specificity of eukaryotic ornithine decarboxylase.

Ornithine decarboxylase (ODC) catalyzes the first committed step in the biosynthesis of polyamines, and it has been identified as a drug target for the treatment of African sleeping sickness, caused by Trypanosoma brucei. ODC is a pyridoxal 5'-phosphate (PLP) dependent enzyme and an obligate homodimer. X-ray structural analysis of the complex of the T. brucei wild-type enzyme with the product putrescine reveals two structural changes that occur upon ligand binding: Lys-69 is displaced by putrescine and forms new interactions with Glu-94 and Asp-88, and the side chain of Cys-360 rotates into the active site to within 3.4 A of the imine bond. Mutation of Cys-360 to Ala or Ser reduces the k(cat) of the decarboxylation reaction by 50- and 1000-fold, respectively. However, HPLC analysis of the products demonstrates that the mutant enzymes almost exclusively catalyze a decarboxylation-dependent transamination reaction to form pyridoxamine 5-phosphate (PMP) and gamma-aminobutyraldehyde, instead of PLP and putrescine. This side reaction arises when the decarboxylated substrate intermediate is protonated at C4' of PLP instead of at the C(alpha) of substrate. For the reaction catalyzed by the wild-type enzyme, this side reaction occurs infrequently (<0.01% of the turnovers). Single turnover analysis and multiwavelength stopped-flow spectroscopic studies suggest that for the mutant ODCs protonation at C4' occurs either very rapidly or in a concerted reaction with decarboxylation and that the rate-limiting step in the steady-state reaction is Schiff base hydrolysis/product release. These studies demonstrate a role for Cys-360 in the control of the C(alpha) protonation step that catalyzes the formation of the physiological product putrescine. The results further provide insight into the mechanism by which this class of PLP-dependent enzymes controls reaction specificity.

INTERLEUKIN-1β INDUCES ORNITHINE DECARBOXYLASE ACTIVITY IN INSULIN-PRODUCING CELLS

Cytokines might play a role in the development of insulin-dependent diabetes. Interleukin 1β (IL-1β) has been shown to alter the functional state of insulin-producing β cells. This effect appears mediated through induction of certain proteins and suppression of others. The present study demonstrates that the ornithine decarboxylase (ODC) activity of rat β cells and insulin-producing rat insulinoma (RIN) cells increases more than three-fold within 2h of IL-1β exposure. Both basal and IL-1β induced ODC activities completely disappear following a 2h block of protein translation. In Western blot analysis, a 51-kDa protein varies in parallel with the ODC-activity. Exposure to IL-1β increases the 51-kDa band through an effect at the transcriptional level. The higher cellular ODC activity in IL-1β treated RIN cells is associated with an increased cellular content of its enzymatic product putrescine, but not of putrescine-derived products such as polyamines and GABA. The 30-fold lower ODC activity in rat β cells forms a technical obstacle to studies on the regulation and functional significance of this enzyme in normal cells. The present findings list ODC-activity as an early response to the effect of interleukin 1β on the transcriptional activity in insulin-producing cells. Further work is needed to identify whether ODC activation contributes to the previously described functional changes in pancreatic β cells.

Evidence That Histidine-163 Is Critical for Catalytic Activity, but Not for Substrate Binding to Escherichia coli Agmatinase

Agmatinase (agmatine ureohydrolase, EC 3.5.3.11) from Escherichia coli was inactivated by diethyl pyrocarbonate (DEPC) and illumination in the presence of Rose bengal. Protection against photoinactivation was afforded by the product putrescine, and the dissociation constant of the enzyme–protector complex (12 mM) was essentially equal to the Ki value for this compound acting as a competitive inhibitor of agmatine hydrolysis. Upon mutation of His163 by phenylalanine, the agmatinase activity was reduced to 3–5% of wild-type activity, without any change in Km for agmatine or Ki for putrescine inhibition. The mutant was insensitive to DEPC and dye-sensitized inactivations. We conclude that His163 plays an important role in the catalytic function of agmatinase, but it is not directly involved in substrate binding.

Induction of Ornithine Decarboxylase in Cerebral Cortex by Excitotoxin Lesion of Nucleus Basalis: Association with Postsynaptic Responsiveness and N‐Methyl‐d‐Aspartate Receptor Activation

The major cholinergic innervation of the rat cerebral cortex arises from the nucleus basalis in the basal forebrain. Introduction of the excitotoxins kainate or ibotenate into the nucleus basalis by stereotaxic injection results in degeneration of the cholinergic cells. We have investigated the effect of this excitotoxic action on ornithine decarboxylase (ODC) activity and cholinergic responsiveness in the cerebral cortex. A massive and rapid induction of ODC activity was seen in ipsilateral cortex after injection of excitotoxin. A maximal increase in ODC activity of 268 times the control value was seen in ipsilateral cerebral cortex 8 h after lesioning. Thereafter, ODC activity declined but remained significantly greater than control levels for 32 h. Pretreatment of animals with the irreversible ODC inhibitor difluoromethylornithine prevented the induction of ODC by kainate. Tissue content of the ODC product putrescine showed a marked increase in cerebral cortex ipsilateral to the lesion, increasing sevenfold at 24 h, the maximal concentration reached. After 24 h, the level of putrescine decreased but remained significantly elevated above control values for 5 days. Levels of the polyamines spermidine and spermine were unaffected by lesioning. Increases on ODC activity of much smaller magnitude were also seen in brain regions not directly innervated from the ipsilateral nucleus basalis. However, the response in ipsilateral cortex was found to be dependent on an intact projection from nucleus basalis to cortex. The induction of ODC was shown to be prevented by treatment of rats with MK-801, a result indicating the involvement of N-methyl-D-aspartate (NMDA) receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Starvation and Difluoromethylornithine (DFMO) on Diamine Oxidase Activity in Rat Ileum

Starvation and difluoromethylornithine (DFMO) administration have profound affects on intestinal proliferation, ornithine decarboxylase activity, and tissue polyamine levels. Diamine oxidase activity may play a role in the regulation of proliferation, and the activity of this enzyme may be influenced by ornithine decarboxylase activity. To determine if diamine oxidase is influenced by starvation and DFM administration, ileal diamine oxidase activities were determined on mucosal homogenates from five groups of rats: fed control, starved for 48 h, fed group receiving DFMO, a starved/refed group, and a starved/refed group receiving DMFO. The homogenates from starved rats were found to have decreased ornithine decarboxylase activity and increased diamine oxidase activity when compared to control values. The homogenates from the DFMO group also were found to have decreased ODC activity however, mucosal diamine oxidase activity was also decreased. Refeeding produced a dramatic increase in ornithine decarboxylase activity and a minimal change in diamine oxidase activity. The preservation of diamine oxidase activity during starvation implies a need for the enzyme not related to mucosal proliferation or digestion. However, in the fed state, diamine oxidase activity may be more dependent on ornithine decarboxylase activity or its reaction product putrescine.

Downregulation of T cell growth factor production by ornithine decarboxylase and its product putrescine: d,l-α-Difluoromethylornithine suppresses general protein synthesis but augments simultaneously the production of interleukin-2

Treatment of EL-4 lymphoma cells with tetradecanoylphorbol-acetate (TPA), a well-known activator of protein kinase C, induces the production of the T cell growth factor interleukin-2 (IL-2) and the expression of IL-2-specific mRNA within 4–8 h. This system is an ideal model for studies on the induction of a differentiated function in a homogeneous lymphoid cell population by a defined signal. TPA induces also an increase of ornithine decarboxylase (ODC) activity and elevates the intracellular concentrations of putrescine and polyamines within 4–8 h. A similar increase of intracellular putrescine and polyamine concentrations can be achieved by administration of 2 m M putrescine to the culture medium. However, putrescine cannot induce the production of IL-2 in the absence of TPA and cannot reconstitute the IL-2 production in cultures with PGE 2 or cyclosporine A, i.e., two well-known immunosuppressive substances which inhibit ODC activity. Putrescine has rather a counter-regulatory effect as concluded from the observation that the TPA-induced TCGF production and IL-2-specific mRNA expression are augmented (superinduced) by the ODC inhibitor d,l-α-difluoromethylornithine (DFMO) and again suppressed after the administration of putrescine or polyamines to DFMO-treated cultures. The glycolytic activity, general protein synthesis ([ 3H]leucine incorporation), and the cell cycle progression from G 2/M to G 1, in contrast, are inhibited by DFMO and reconstituted by putrescine. This demonstrates that the cells are able to sacrifice to a large extent several vital functions including their general protein synthesis and to devote themselves at the same time to a fulminant production of their functionally most relevant protein IL-2. This process is downregulated by ODC and its product putrescine. A correlation between increased IL-2 production and accumulation of cells in the G 2/M phase was also observed in cultures treated with hydroxyurea or with a combination of amethopterin and adenosine.