Inhibition Of Ornithine Decarboxylase Activity Research Articles

Role of nonmuscle myosin II in polyamine-dependent intestinal epithelial cell migration.

The current study determines whether nonmuscle myosin II is involved in the process requiring polyamines for the stimulation of cell migration in an in vitro model that mimics the early stages of epithelial restitution. Treatment with alpha-difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase (ODC), for 4 days totally inhibited ODC activity and depleted intracellular polyamines in the IEC-6 cells. Nonmuscle myosin II concentrations in DFMO-treated cells were decreased by 75%, and stress fibers were sparse or absent. The most striking feature of DFMO-treated cells was the appearance of many small punctate foci of myosin II in the cell interior. Migration of DFMO-treated cells was reduced by 80%. In the presence of DFMO, exogenous putrescine not only returned nonmuscle myosin II levels and distribution toward normal but also restored cell migration to control levels. The administration of wortmannin, an inhibitor of myosin light chain kinase, significantly inhibited cell migration over the denuded area in control cells and in those treated with DFMO + polyamines. These results indicate that 1) polyamine depletion by DFMO is associated with decreased concentration and reorganization of nonmuscle myosin II in IEC-6 cells and 2) exogenous spermidine reverses the inhibitory effects of DFMO.

The inhibition of ornithine decarboxylase activity in developing rat tissues by central nervous system β-endorphin is mediated by μ-opioid receptors, but not by δ- or ϵ-opioid receptors

Our laboratory has previously shown that intracerebroventricular (i.c.v.) administration of β-endorphin suppresses brain and liver ornithine decarboxylase activity (ODC; a growth regulatory enzyme) in preweanling rats. This investigation examined, in 6-day-old rats, the relative participation of brain μ-, δ- and ϵ-opioid receptors in β-endorphin's ODC effects, by comparing tissue ODC responses to β-endorphin given alone i.c.v. and in the presence of d-Phe-Cys-Tyr- d-Trp-Orn-Thr-Pen-Thr-NH 2 (CTOP; μ-opioid receptor antagonist), N,N-diallyl-Tyr-Aib-Aib-Phe-Leu-OH (ICI-174,864; δ-opioid receptor antagonist) or β-endorphin-(1–27) (ϵ-opioid receptor antagonist). Administration of 0.5 μg of β-endorphin alone significantly decreased brain and liver ODC activity 4 h after injection, and the effect was completely blocked by coinjection of CTOP (0.075 μg) but not by ICI-174,864 (0.75 or 3.75 μg) or β-endorphin-(1–27) (3.75 or 7.5 μg). The blockade of endogenous opioid:opioid receptor interactions by either CTOP (at doses > 0.075 μg) or ICI-174,864 alone was accompanied by increased levels of basal ODC activity. The results obtained demonstrate that i.c.v. β-endorphin downregulates ODC expression in central as well as in peripheral tissues by interacting with brain μ-opioid receptors, but not with δ- or ϵ-opioid receptors or μ/δ-opioid receptor complexes. Also, they indicate that endogenous opioid systems have a tonic inhibitory influence on ODC activity which is mediated, at least in part, by μ- and δ-opioid receptors.

Leishmania donovani: Cellular control of ornithine decarboxylase in promastigotes

Ornithine decarboxylase, a key enzyme in polyamine biosynthesis, is essential for normal cell growth and proliferation. Furthermore, the inhibition of this enzyme is a potential way of controlling such growth. In order to shed light on the role of ornithine decarboxylase in regulation of Leishmania growth we examined the activity of this enzyme during the life cycle of these organisms. Exponentially growing Leishmania promastigotes were resuspended at a density of 3 × 10 6 cells/ml. 2 × 10 7 cells were withdrawn 24 hr later at different time intervals for induction studies and ornithine decarboxylase activity was measured. Ornithine decarboxylase showed a growth related pattern in L. donovani promastigotes. Induction studies showed that ornithine decarboxylase activity rapidly increased in late log phase cells when resuspended in fresh medium. A biphasic induction curve was observed similar to that observed in mammalian cells. The first peak was observed at 6 hr and the second at 16 hr. Cycloheximide and Actinomycin D inhibited induction at 16 hr by 65–68%. Polyamines at a level not inhibitory to growth (10 μM) inhibited ornithine decarboxylase induction by 30–40% late in the induction period. Putrescine and spermidine both inhibited the first peak of induction. Putrescine suppressed ornithine decarboxylase activity by 39% at 16 hr whereas spermidine by only 29%. The half life of ornithine decarboxylase in promastigote forms grown in the presence of cycloheximide was > 6 hr. These studies indicate that although the Leishmanial ornithine decarboxylase follows a similar induction pattern to that previously reported in the mammalian cells, it is less susceptible to exogenous polyamines and is comparatively stable. This lack of ornithine decarboxylase regulation and turnover may be exploitable in the development of various therapeutic agents to inhibit Leishmanial growth.

Growth inhibition of the androgen responsive DDT1MF-2 cell line by glucocorticoids: the role of ornithine decarboxylase

While testosterone (T) stimulates the growth of DDT(1)MF-2 cells, glucocorticoids arrest the growth of these cells in the G(0)/G(1) stage of the cycle. Ornithine decarboxylase (ODC), the first and rate-limiting enzyme in the polyamine biosynthetic pathway, is highly sensitive both to growth and inhibitory stimuli. To assess the mechanism of glucocorticoid inhibition of cell growth, the effect of triamcinolone acetonide (TA) on growth and ODC was studied. DDT(1)-MF-2 cell growth was inhibited by TA and difluoromethyl ornithine (DFMO), an irreversible inhibitor of ODC. TA (10NM: ) inhibited the ODC activity to 10% of the control levels by 12 h and inhibition was maintained at all later intervals studied. Ten μM: DFMO inhibited ODC activity to a maximum of 50% of control. The concentration of ODC mRNA was maximally decreased at 15 h after TA administration.Though TA and DFMO inhibited cell growth and ODC activity in DDT(1)-MF2 cells, growth inhibition by DFMO, but not by TA, was overcome by the addition of putrescine, the product of ODC reaction. Thus, inhibition of ODC is one pathway through which glucocorticoids inhibit DDT(1)MF-2 cell growth. ODC inhibition, however, is not the only pathway through which glucocorticoids act.

Combined action of inhibitors of polyamine biosynthetic pathway with a known antimalarial drug chloroquine on plasmodium falciparum

Difluoromethylornithine (α-DFMO), a specific enzyme activated inhibitor of ornithine decarboxylase activity, a bis (benzyl) polyamine analogue (MDL 27695) and chloroquine resulted in a dose-dependent inhibition of the parasite. The IC 50 value of α-DFMO, MDL 27695 and chloroquine was 1.85 m m, 2.0μm and 23 ng ml −1 respectively. The combined action of MDL 27695 (3μ m) and chloroquine (5 ng ml −1 on P. falciparum growth showed near additive effect, whereas the combination of α-DFMO (1.0 m m) and chloroquine (5 ng ml −1 was more than the effect of each drug individually but not additive. Similarly the combined effect of MDL 27695 (3 μ m and α-DFMO (1.0 m m) on P. falciparum growth was not additive. The effect of these inhibitors alone and in combination on polyamine biosynthesis is also reported.

The inhibition of DMBA-induced carcinogenesis by neoxanthin in hamster buccal pouch.

Neoxanthin, a major carotenoid pigment of spinach, is found in the Chloroplast membrane and has an unknown function in plants. Neoxanthin inhibited the production of superoxide anions in an artificial xanthine and xanthine oxidase system and depressed DNA synthesis in methylcholanthrene (MCA)-initiated C3H10T1/2 fibroblasts. in two-stage carcinogenesis experiments, neoxanthin at 0.2 micrograms/0.2 ml inhibited the formation of tumors that were induced sequentially by 7,12-dimethylbenz[a]anthracene (DMBA) and 12-O-tetradecanoylphorbol-13-acetate (TPA) in the buccal pouch of Syrian Golden hamsters. To assess the ongoing process of carcinogenesis, the activity of ornithine decarboxylase (ODC), required for cell proliferation, was analyzed. Neoxanthin inhibited the activity of ODC when animals were treated with neoxanthin one hour before the application of TPA in two-stage carcinogenesis. However, neoxanthin did not inhibit ODC activity when animals were treated with neoxanthin one hour before the application of DMBA in two-stage carcinogenesis, and there was no subsequent tumor formation. In a short-term anti-initiation experiment, neoxanthin inhibited the covalent binding of isotope-labeled DMBA to DNA by 53%. These results indicate that neoxanthin inhibits the initiation stage and the promotion stage in two-stage carcinogenesis. This suggests that neoxanthin may act as a potential chemopreventive agent.

Post-Transcriptional Suppression of Human Ornithine Decarboxylase Gene Expression by Phorbol Esters in Human Keratinocytes

The induction of ornithine decarboxylase levels by the phorbol ester 12-0-tetradecanoyl-phorbol-13-acetate (TPA) in mouse skin has been shown to be integral to tumor promotion by TPA, and changes in ornithine decarboxylase activity indicate the proliferative state of many different cell types. However, in cultured human epidermal cells, TPA has been reported to be antiproliferative. Therefore, to elucidate pathways that TPA activates in cultured human skin cells, we have examined the levels at which TPA regulates ornithine decarboxylase gene expression in two immortalized human epidermal keratinocyte cell lines, and in normal neonatal keratinocytes. We have found that in cultured human keratinocytes, TPA cases a marked decrease in ornithine decarboxylase enzyme activity (50-90%), with no detectable effect on ornithine decarboxylase mRNA levels. TPA decreased steady-state levels of ornithine decarboxylase immunoreactive protein (approximately 50-67%), accounting for the 50-90% suppression of ornithine decarboxylase activity levels, as well as decreasing new synthesis of ornithine decarboxylase protein (48-50%). However, measurement of ornithine decarboxylase protein half-life showed no significant effect of TPA. Also, prolonged treatment of keratinocytes with phorbol esters abolished the suppression of ornithine decarboxylase activity by TPA. Our data, therefore, suggest that phorbol esters suppress ornithine decarboxylase gene expression predominantly by decreasing ornithine decarboxylase mRNA translatability.

Polyamine metabolism and in vitro cell multiplication and differentiation in leaf explants of Chrysanthemum morifolium Ramat

Arginine decarboxylase (ADC), ornithine decarboxylase (ODC), diamine oxydase (DAO) free amine and conjugated amine titers were estimated in leaf explants of Chrysanthemum morifolium Ramat. var. Spinder cultivated in vitro in relation to hormone treatment. Addition of benzyladenine (BA) to a basal medium caused the formation of buds on the explants. BA plus 2,4 dichlorophenoxyacetic acid (2,4 D) caused callus formation and proliferation. Formation of roots was obtained by addition of indolylacetic acid (IAA). Arginine decarboxylase (ADC) ornithine decarboxylase (ODC) and diamine oxidase (DAO) activities increased during the first days of culture when cell multiplication was rapid, followed by a sharp decline as the rate of cell division decreased and differentiation took place. DAO activities increased rapidly in proliferating and growing organs and decreased during maturity. This increase was concomitant with ADC and ODC activities and polyamine content (free and conjugated polyamines). The biosynthesis and oxidation of polyamines which occurred simultaneously in physiological states of intense metabolism such as cell division or organ formation were directly correlated. In callus cultures DAO activity was blocked throughout development and regulated neither the cellular levels of polyamines nor polyamine conjugates. Levels of polyamine conjugates were high in callus cultures throughout development. In foliar explants cultivated on a medium promoting callus, inhibition of ODC activity by DFMO (α-DL-difluoromethylornithine, a specific enzyme-activated ODC inhibitor) resulting in an amide deficiency facilated the expression of differentiated cell function; substantial activation of DAO was observed until the emergence of the buds. On a medium promoting bud formation, β-OH ethylhydrazine (DAO inhibitor) promoted callus formation without differentiation. In this system DAO activity was blocked and there were high levels of polyamines, especially polyamine conjugates, throughout the culture period. The relationship among free and conjugated polyamines related biosynthetic enzyme activities, DAO activities, cell division and organ formation is discussed.

Effect of the novel radical scavenger AD0261 on lymphocyte activation

A recent investigation has indicated that reactive oxygen species (ROS) may play an important role in the activation of lymphocytes. The main aim of the present study is to find out what effect on lymphocyte activation is attributable to radical scavengers (RSs). AD0261 (AD) is a novel RS which displays strong inhibitory action on the generation of lipid peroxides and superoxide anions. This compound has been shown to be effective in inhibiting tritiated thymidine ([3H]TdR) incorporation into, IL-2 release from and IL-2 receptor (Rc) expression on Con A-stimulated mouse spleen cells and PHA-P-stimulated lymphocytes of human peripheral blood, IC50 values being in the range 1–10 μM. It also inhibited erythema formation elicited by transferring PHA-P-stimulated lymphocytes into guinea pigs (30–40% inhibition at 10 μM,p<0.05). Further study showed that the activity of ornithine decarboxylase (ODC), which is a critical enzyme for cell proliferation, was inhibited by AD in a dose-dependent manner (IC50=1.0 μM). In summary, AD would seem to affect the lymphocyte activation by inhibiting ODC activity, probably through the action of ROS trapping.

Perturbing cell surface beta-(1,4)-galactosyltransferase on F9 embryonal carcinoma cells arrests cell growth and induces laminin synthesis.

Cell growth and differentiation are influenced by intercellular contact, suggesting that cell adhesion molecules may be instrumental in triggering these events. F9 embryonal carcinoma cells are an ideal system in which to examine the function of cell adhesion molecules in growth and differentiation, since the relevant cell adhesion molecules and differentiation markers are well defined. Intercellular adhesion in F9 cells is mediated by uvomorulin, or E-cadherin, and cell surface beta-(1,4)-galactosyltransferase. Since previous studies suggested that neither F9 cell growth nor differentiation is directly dependent on uvomorulin function, in this study we examined whether cell surface galactosyltransferase plays any role in F9 cell growth or differentiation. A variety of galactosyltransferase perturbants, including anti-galactosyltransferase antibodies, UDPgalactose, and the substrate modifier protein alpha-lactalbumin, inhibited the growth of F9 cells, whereas control reagents did not. To examine this in more detail, we analyzed the effects of perturbing surface galactosyltransferase on progression through the F9 cell cycle. Anti-galactosyltransferase IgG treatment inhibited ornithine decarboxylase activity and lengthened the F9 cell cycle during G1 and G2, the latter mimicking the effects of retinoic acid, a reagent known to prolong the F9 cell cycle and induce differentiation. In contrast, anti-uvomorulin antibodies had no effect on F9 cell growth, ornithine decarboxylase activity, or progression through the cell cycle. Furthermore, perturbation of surface galactosyltransferase adhesions in F9 cell aggregates induced precocious F9 cell differentiation, as assayed by increased laminin synthesis, whereas control reagents had no effect. Thus, perturbing surface galactosyltransferase adhesions in F9 cells both decreases growth and stimulates synthesis of laminin. These results imply that interactions between surface galactosyltransferase and its oligosaccharide ligand during cell adhesion may affect the normal growth-regulatory and differentiation-inducing signals, as is seen, in part, during treatment with retinoic acid.

Tumor‐derived components were responsible for suppression of ornithine decarboxylase activity in the rat wounded skin

To elucidate the principal cause of delayed wound healing in a tumor-bearing host, the effect of Yoshida sarcoma-derived components on dermal wound healing was investigated in rats with the aid of ornithine decarboxylase (ODC) activity and in vivo bromodeoxyuridine (BrdU) labeling index. The ODC activity in the wounded skin decreased 3 and 7 days after intraperitoneal inoculation of Yoshida sarcoma cells (378.0 +/- 37.3 on Day 3, 280.0 +/- 140.0 on Day 7 vs. 809.3 +/- 109.5 pmol/mg protein/hour on Day 0). When administered 24 hours before and immediately after wounding, the crude nuclear component of the tumor cells significantly decreased the ODC activity in the wounded skin as compared with the control (185.9 +/- 159.8 vs. 534.0 +/- 59.1), but the non-nuclear component was not effective. When nuclear extracts of Yoshida sarcoma cells were intraperitoneally administered immediately after wounding, the 0.15 M or 0.35 M NaCl extract significantly suppressed ODC activity in the wounded skin (233.5 +/- 14.5 and 352.3 +/- 63.2 pmol/mg protein/hour, respectively) in comparison to the control (445.9 +/- 73.6). The BrdU labeling index of epidermal basal cells adjacent to the edge of the wound decreased up to 52% of the control by injection of the 0.15 M extract. It seems that tumor-derived nuclear components may be responsible for delayed wound healing which is commonly observed in cancer cachexia.

An appraisal of the developmental importance of polyamine changes in early Xenopus embryos.

The biological importance of the various changes in polyamine metabolism that occur during early Xenopus development have been investigated. Incubation of embryos in high salt medium was observed to cause a precocious fall in ornithine decarboxylase activity without affecting development. Similarly, inhibiting ornithine decarboxylase activity with specific inhibitors did not affect development. Injecting spermidine, within physiologically relevant limits, caused a dose-dependent inhibition of mitotic divisions in the injected blastomere. Increasing the intracellular putrescine did not affect cell division or development. Co-injection of both spermidine and putrescine, so that the original molar ratio of these two polyamines was conserved, abrogated the inhibition of cell division observed when spermidine was injected alone. Therefore, in Xenopus embryos the intracellular spermidine concentration must be retained within certain limits relative to that of putrescine to allow normal development.

Inhibition of Ornithine Decarboxylase Activity and Cell Proliferation by Ultraviolet B Radiation in EGF-Stimulated Cultured Human Epidermal Keratinocytes

Irradiation of EGF-stimulated human keratinocytes in vitro with ultraviolet B (UVB) radiation inhibited both ornithine decarboxylase (ODC) activity and cellular proliferation. A dose-dependent reduction in ODC activity occurred in primary cultures of adult facial keratinocytes and neonatal foreskin keratinocytes, and in an SV40-transformed keratinocyte cell line derived from neonatal foreskin. When SV40-transformed keratinocytes were treated with epidermal growth factor (EGF), ODC activity was induced up to 21 times in the absence of ultraviolet radiation. However, pre-treatment with UVB significantly reduced the EGF induction of ODC. For example, 85% less ODC activity was observed in cultures treated with EGF (10 ng/ml) plus 2.5 mJ/cm2 of UVB than cultures treated with EGF alone. To assess the effect of UVB on cell proliferation, normal human epidermal keratinocytes grown in medium containing EGF were irradiated with 5 and 10 mJ/cm2 UVB. At days 3 and 5 post-irradiation a significant (up to 78%) decrease in proliferation was observed. Nevertheless, the mean proportion of viable to dead cells remained similar in both UVB-treated and non-irradiated cell cultures. Northern blot analysis of total RNA isolated from irradiated and sham-irradiated cultures showed that UVB caused approximately a one third reduction in steady-state ODC mRNA levels in EGF-stimulated keratinocyte cultures. Because ODC is an enzyme required for cell proliferation, we propose that the UVB-induced decrease in cell proliferation may result at least in part from UVB inhibition of ODC mRNA accumulation and reduced enzyme activity.

Inhibition of ornithine decarboxylase activity decreases polyamines and suppresses DNA synthesis in human colonic lamina propria lymphocytes

Ornithine decarboxylase (ODC) and the polyamines are essential for cell proliferation in a variety of cells including lymphocytes. In this study, we investigated the potential role of ODC and polyamines in human colonic lamina propria lymphocytes (LPL) compared to peripheral blood lymphocytes (PBL). Our results show that con A stimulation of LPL and PBL was associated with marked increases in ODC and polyamines. The specific inhibitor of ODC, alpha-difluoromethylornithine (DFMO), resulted in a complete inhibition of ODC activity and depletion of putrescine, spermidine and spermine levels. DFMO also suppressed DNA synthesis of LPL and PBL by up to 48% and 62% respectively. This antiproliferative effect was reversed by adding back the polyamines putrescine (1 mM), spermidine (10 μM) or spermine (10 μM) to the culture medium. We conclude that ODC and the polyamines are important for human LPL proliferation, and hence may play a role in human mucosal immune function.

Embryonic growth inhibition induced by cocaine is associated with the suppression of ornithine decarboxylase activity.

Cocaine use during pregnancy results in significant increases in fetal morbidity and mortality. Multiple maternal and environmental variables influence the fetal response to cocaine, and growth suppression of the developing child is frequently associated with in utero cocaine exposure. Using intact chick embryos as well as cultured embryonic tissue as a model, we report that the growth suppression induced by cocaine exposure is correlated with molecular changes occurring directly in the embryonic cells and that these molecular changes appear to be distinct from other maternal, placental, or environmental effects of the drug, including anoxia. Specifically, embryonic cocaine exposure suppresses the normal developmental increase in ornithine decarboxylase (ODC) enzymatic activity. The loss of ODC activity during the early stages of development is dose dependent and is correlated with the degree of growth suppression. The cocaine-induced loss of decarboxylase activity is specific to ODC, but cocaine, per se, has no effect on ODC activity in vitro. Moreover, a single dose of exogenous putrescine given at 120 hr of incubation blocks the cocaine-induced growth suppression. In cultured embryonic tissue, cocaine exposure inhibits the ability of a known trophic factor (insulin) to induce growth and also blocks the associated increase in ODC activity. Preliminary data suggest that cocaine hinders the binding of insulin to embryonic cells. Because ODC is a focal enzyme for the regulation of growth, the data suggest that cocaine-induced changes in the mitogenic induction of embryonic/fetal ODC activity may be a part of the biochemical mechanism by which cocaine-induced growth inhibition occurs.

Effects of gastrin and difluoromethylornithine on growth of human colon cancer.

The effect of difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase activity, was evaluated in vivo and in vitro on the growth of a gastrin-sensitive human colon carcinoma (WiDr). In vivo, mice bearing the tumor treated with pentagastrin had larger tumors with higher ornithine decarboxylase activity and polyamine content (P < 0.05) than mice not treated with pentagastrin. Difluoromethylornithine treatment significantly decreased ornithine decarboxylase in both the pentagastrin-treated and the untreated animals; however, DFMO had no effect on tumor volume, weight, protein, or DNA content. In cell culture, gastrin treatment increased WiDr cell number and [3H]thymidine incorporation in the presence or absence of serum. In serum-free conditions, however, gastrin stimulated cell growth without concomitantly increasing ODC activity. DFMO, on the other hand, decreased both ODC activity and growth. These studies suggest that the trophic effect of gastrin on WiDr human colon cancer is independent of ODC activity. Since gastrin treatment increased ODC activity in vivo, gastrin may interact in vitro with other factors present in serum that can alter ODC activity.

Polyamines and Intestinal Epithelial Hyperplasia in Streptozotocin-Diabetic Rats

We measured specific activity of ornithine decarboxylase (ODC) and contents of putrescine and of the polyamines (spermidine and spermine) in isolated villus and crypt enterocytes from the jejunum of adolescent streptozotocin-diabetic and weight-matched control rats and diabetic and control rats treated with difluoromethyl ornithine (DFMO) 10 days after induction of diabetes. Consistent with previous observations by others of elevated ODC activity and contents of putrescine and of the polyamines in the intestinal epithelium undergoing hyperplasia, our studies showed elevated ODC activity and contents of putrescine and spermidine, but not of spermine, in the hyperplastic intestinal epithelium of diabetic rats. As in previous studies, suppression of ODC activity by DFMO prevented not only the jejunal epithelial hyperplasia in the diabetic rats, but also retarded jejunal epithelial growth in the control rats. DFMO administration lowered ODC activity by over 80% in both diabetic and control rat enterocytes and prevented the rise in enterocyte contents of putrescine and spermidine in the diabetic rat. The observation that, in both diabetic and control rats, treatment with DFMO lowered spermidine content in the crypt enterocytes but had no similar consistent effect on contents of putrescine or spermine suggested that spermidine could have been responsible for the intestinal epithelial hyperplasia in the diabetic rats and for the normal growth of the intestinal epithelium in control rats.

Role of polyamine biosynthesis during gut mucosal adaptation after burn injury

The induction of ornithine decarboxylase (ODC) mRNA and of ODC enzyme activity are important events in gut repair after cutaneous burn injury. ODC catalyzes the rate-limiting step in the biosynthesis of polyamines that are necessary for normal cell growth; alpha-difluoromethylornithine (DFMO) specifically inhibits ODC activity. The purpose of this study was to examine the role of polyamines in the adaptive response of gut mucosa after burn injury. In experiment 1, male Sprague-Dawley rats (250 to 300 g; n = 6/group) were randomized into sham, 60% burn, or 60% burn plus DFMO. In experiment 2, rats with either a 60% burn or 60% burn plus DFMO treatment received spermidine by gavage. We measured ODC activity, polyamine levels, and DNA content at 0, 12, 24, and 48 hours postburn in the mucosa of both the proximal and distal small intestine. Burn injury produced early atrophy (by 12 hours postburn) of the gut mucosa characterized by decreased mucosal weight and DNA content. Increased ODC activity and polyamine content in both the proximal and distal gut mucosa of burned rats preceded restoration of mucosal weight and DNA content that occurred at 48 hours postburn; these responses were prevented by DFMO treatment. Spermidine administration failed to accelerate gut mucosal recovery after burn injury alone, but oral administration of spermidine reversed the inhibitory action of DFMO on gut mucosal repair. These data suggest that the early increases of gut ODC activity and polyamine levels after burn injury are crucial cellular events for the repair of subsequent gut mucosa.

Effects of adriamycin and daunomycin on ornithine decarboxylase activity and DNA synthesis in mouse epidermal cells

Ornithine decarboxylase (ODC) activity is induced when epidermal cells are incubated for 5–12 hr in the presence of 10 μ m-adriamycin (ADR). The magnitude and duration of ODC induction by 5 μ m-daunomycin (DAU) are much smaller. At 10 μ m, ADR does not alter DNA synthesis but DAU inhibits ODC activity and DNA synthesis by 40 and 60%, respectively. ADR (10 μ m) and, to a lesser degree, DAU (5 μ m) also enhance 12- O-tetradecanoylphorbol-13-acetate (TPA)-induced ODC activity, but, in contrast to ADR, 10–50 μ m-DAU inhibit the ODC response to TPA by 50% or more. The induction and superinduction of ODC activities by ADR and/or TPA are all inhibited by the Ca 2+-channel blocker verapamil. The ODC-inducing activity of ADR, therefore, may have a role in the mechanism by which mouse epidermal cells escape from the cytotoxic activity of this anthracycline antibiotic.

DL-α-Difluoromethylarginine Inhibits Intracellular Trypanosoma cruzi Multiplication by Affecting Cell Division but Not Trypomastigote-Amastigote Transformation

DL-alpha-difluoromethylarginine (DFMA), a specific, irreversible inhibitor of arginine decarboxylase (ADC), decreases the capacity of Trypanosoma cruzi to invade and multiply within different types of mammalian host cells in vitro. In this work we found that inhibition of intracellular growth results from selective impairment of amastigote division without appreciable alteration of the capacity of the invading trypomastigotes to transform into the replicative amastigote form. Addition of agmatine, the product of arginine decarboxylation, reversed the inhibitory effect of DFMA. Inhibition of ornithine decarboxylase activity by DL-alpha-difluoromethylornithine present in the medium prior to and during infection did not affect trypomastigote transformation or amastigote replication and did not change the magnitude of the inhibitory effect of DFMA on parasite multiplication. Hence, neither polyamine synthesis via the ornithine decarboxylase pathway nor salvage of host cell polyamines by T. cruzi appeared to be a likely explanation for the normal rate of parasite transformation that was seen in the presence of DFMA. Two clones of T. cruzi, TMSU-1 and TMSU-2, were tested for their degrees of sensitivity to the inhibitory effects of DFMA. Both trypomastigote association with (i.e., binding to and penetration of) myoblasts, and intracellular amastigote multiplication by either clone were found to be significantly (P less than 0.05) but not completely inhibited by DFMA. Therefore, the partial inhibition of T. cruzi infectivity and replication caused by DFMA is unlikely to represent a composite of effects of the drug on DFMA-sensitive and insensitive clones.(ABSTRACT TRUNCATED AT 250 WORDS)