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Biomedical subjects

A J Bitonti

Publications and source records attributed to A J Bitonti.

At least 55 records · Page 3Linked to original sources
PubMed1988

DL-alpha-difluoromethyl[3,4-3H]arginine metabolism in tobacco and mammalian cells. Inhibition of ornithine decarboxylase activity after arginase-mediated hydrolysis of DL-alpha-difluoromethylarginine to DL-alpha-difluoromethylornithine.

DL-alpha-Difluoromethylarginine (DFMA) is an enzyme-activated irreversible inhibitor of arginine decarboxylase (ADC) in vitro. DFMA has also been shown to inhibit ADC activities in a variety of plants and bacteria in vivo. However, we questioned the specificity of this inhibitor for ADC in tobacco ovary tissues, since ornithine decarboxylase (ODC) activity was strongly inhibited as well. We now show that [3,4-3H]DFMA is metabolized to DL-alpha-difluoromethyl[3,4-3H]ornithine [( 3,4-3H]DFMO), the analogous mechanism-based inhibitor of ODC, by tobacco tissues in vivo. Both tobacco and mammalian (mouse, bovine) arginases (EC 3.5.3.1) hydrolyse DFMA to DFMO in vitro, suggesting a role for this enzyme in mediating the indirect inhibition of ODC by DFMA in tobacco. These results suggest that DFMA may have other effects, in addition to the inhibition of ADC, in tissues containing high arginase activities. The recent development of potent agmatine-based ADC inhibitors should permit selective inhibition of ADC, rather than ODC, in such tissues, since agmatine is not a substrate for arginase.

Animals↗
PubMed1988

Decreased interleukin-2 responsiveness in leukocytes from Trypanosoma brucei-infected mice.

Immunosuppression with respect to those inducible processes which regulate lymphocyte mitogenesis was examined in experimental trypanosomiasis. Splenic leukocytes from Trypanosoma brucei-infected mice showed a decreased proliferative response to the T-cell mitogen concanavalin A. Activated cells secreted normal levels of the endogenous T-cell proliferative signal interleukin-2 (IL-2) and expressed high-affinity IL-2 receptors. However, the ability of activated cells to proliferate in response to exogenous IL-2 was inhibited. These results indicate an impairment of processes which occur after IL-2-receptor binding during lymphocyte mitogenesis. Furthermore, these data indicate that expression of high-affinity IL-2 receptors does not necessarily correlate with an ability to respond to IL-2.

Animals↗
PubMed1988

Effects of alpha-difluoromethylornithine on protein synthesis and synthesis of the variant-specific glycoprotein (VSG) in Trypanosoma brucei brucei.

Protein synthesis in Trypanosoma brucei brucei was rapidly inhibited during polyamine depletion by DL-alpha-difluoromethylornithine (DFMO) in vitro and in vivo. [3H]Leucine incorporation was depressed 30-40% by 24 h and 80-90% by 48 h of DFMO treatment. Concomitantly there was an apparent decrease in the synthesis of the variant-specific glycoprotein (VSG) in DFMO-treated trypanosomes, as measured by decreased incorporation of [3H]myristic acid into VSG. The discovery of decreased protein synthesis in T. b. brucei during DFMO treatment is noteworthy, because it was reported previously that protein synthesis was paradoxically stimulated 2-4-fold during DFMO treatment in these organisms. Decreased protein synthesis probably relates to the biochemical mechanism of action of DFMO on trypanosomes.

Animals↗
PubMed1988

Ornithine decarboxylase, polyamines, and pyrrolizidine alkaloids in senecio and crotalaria.

When tested for ornithine and arginine decarboxylases, pyrrolizidine alkaloid-bearing Senecio riddellii, S. longilobus (Compositae), and Crotalaria retusa (Leguminosae) plants exhibited only ornithine decarboxylase activity. This contrasts with previous studies of four species of pyrrolizidine alkaloid-bearing Heliotropium (Boraginaceae) in which arginine decarboxylase activity was very high relative to that of ornithine decarboxylase. Unlike Heliotropium angiospermum and Heliotropium indicum, in which endogenous arginine was the only detectable precursor of putrescine channeled into pyrrolizidines, in the species studied here-using difluoromethylornithine and difluoromethylarginine as the enzyme inhibitors-endogenous ornithine was the main if not the only precursor of putrescine converted into the alkaloid aminoalcohol moiety. In S. riddellii and C. retusa at flowering, ornithine decarboxylase activity was present mainly in leaves, especially the young ones. However, other very young organs such as inflorescence and growing roots exhibited much lower or very low activities; the enzyme activity in stems was negligible. There was no correlation between the enzyme activity and polyamine or alkaloid content in either species. In both species only free polyamines were detected except for C. retusa roots and inflorescence-with relatively very high levels of these compounds-in which conjugated putrescine, spermidine, and spermine were also found; agmatine was not identified by HPLC in any plant organ except for C. retusa roots with rhizobial nodules. Organ- or age-dependent differences in the polyamine levels were small or insignificant. The highest alkaloid contents were found in young leaves and inflorescence.

Journal Article↗
PubMed1987

Catalytic irreversible inhibition of bacterial and plant arginine decarboxylase activities by novel substrate and product analogues.

Arginine decarboxylase (ADC) activity from Escherichia coli and two plant species (oats and barley) was inhibited by five new substrate (arginine) and product (agmatine) analogues. The five compounds, (E)-alpha-monofluoromethyldehydroarginine (delta-MFMA), alpha-monofluoromethylarginine (MFMA), alpha-monofluoromethylagatine (FMA), alpha-ethynylagmatine (EA) and alpha-allenylagmatine (AA), were all more potent inhibitors of ADC activity than was alpha-difluoromethylarginine (DFMA), the only irreversible inhibitor of this enzyme described previously. The inhibition caused by the five compounds was apparently enzyme-activated and irreversible, since the loss of enzyme activity followed pseudo-first-order kinetics, was time-dependent, the natural substrate of ADC (arginine) blocked the effects of the inhibitors, and the inhibition remained after chromatography of inhibited ADC on Sephadex G-25 or on overnight dialysis of the enzyme. DFMA, FMA, delta-MFMA and MFMA were effective at very low concentrations (10 nM-10 microM) at inhibiting ADC activity in growing E. coli. FMA was also shown to deplete putrescine effectively in E. coli, particularly when combined with an inhibitor of ornithine decarboxylase, alpha-monofluoromethyl-putrescine. The potential uses of the compounds for the study of the role of polyamine biosynthesis in bacteria and plants is discussed.

Agmatine↗
PubMed1987

Plasmodium falciparum and Plasmodium berghei: effects of ornithine decarboxylase inhibitors on erythrocytic schizogony.

Five ornithine decarboxylase inhibitors: alpha-difluoromethylornithine (DFMO) (eflornithine); alpha-monofluoromethyl-3,4-dehydroornithine; alpha-monofluoromethyl-3,4-dehydroornithine methyl ester; alpha-monofluoromethyl-3,4-dehydroornithine ethyl ester; and (2R,5R)-delta-methyl-alpha-acetylenic putrescine were shown to inhibit erythrocytic schizogony of Plasmodium falciparum in vitro and reduced spermidine levels in infected erthrocytes. Only DFMO was effective at limiting erythrocytic schizogony of P. berghei in vivo. Administration of DFMO as a 2% solution in the drinking water for 4 days reduced parasitemia in mice by 50% in a 4-day suppression test but did not increase survival time of infected mice. This is the first demonstration of an effect of DFMO on plasmodial erythrocytic schizogony in vivo and suggests that interference with polyamine biosynthesis may, in fact, be a viable chemotherapeutic target in erythrocytic malaria.

Animals↗
PubMed1987

Polyamine metabolism in Acanthamoeba: polyamine content and synthesis of ornithine, putrescine, and diaminopropane.

Five polyamines which could be separated by high performance liquid chromatography were found in Acanthamoeba castellanii (strain Neff). These included in order of decreasing abundance: 1,3-diaminopropane, spermidine, spermine, norspermidine, and putrescine. Only diaminopropane and norspermidine had been found previously. Spermine was present in cultures grown in broth, but not in defined medium. Radioactive substrates were used to establish that putrescine was synthesized by decarboxylation of ornithine, ornithine was synthesized from arginine or citrulline, and diaminopropane was synthesized from spermidine. The presence of ornithine decarboxylase (EC 4.1.1.17), arginase (EC 3.5.3.1), and urease (EC 3.5.1.5) and the absence of arginine decarboxylase (EC 4.1.1.19) were established. A scheme for polyamine biosynthesis in A. castellanii is proposed.

Acanthamoeba↗
PubMed1987

Effects of the ornithine decarboxylase inhibitors DL-alpha-difluoromethylornithine and alpha-monofluoromethyldehydroornithine methyl ester alone and in combination with suramin against Trypanosoma brucei brucei central nervous system models.

Two ornithine decarboxylase inhibitors, DL-alpha-difluoromethylornithine (eflornithine; DFMO) and a-monofluoromethyldehydroornithine methyl ester (delta MFMO X CH3) were compared in their ability to cure two distinct Trypanosoma brucei brucei central nervous system murine model infections. Both inhibitors cured the TREU 667 and LUMP 1001 isolates if used in combination with a single (20 mg/kg) injection of suramin, a trypanocide in current clinical use. The curative dose of delta MFMO X CH3 in combination with suramin was 1.09 g/kg/day, administered in the drinking water for 14 days; used with suramin, the curative dose of DFMO was 5.3 g/kg/day for 14 days (5 times the delta MFMO X CH3 dose required). In host animals, delta MFMO X CH3 was not toxic and was accumulated by trypanosomes 6-8 times faster than DFMO. Since DFMO by itself has been highly effective against T. b. gambiense infections in humans (12-15 g/day for 6 weeks) the present data suggest that delta MFMO X CH3 might be effective in a shorter regimen and at lower doses.

Animals↗
PubMed1986

Characterization of Trypanosoma brucei brucei S-adenosyl-L-methionine decarboxylase and its inhibition by Berenil, pentamidine and methylglyoxal bis(guanylhydrazone).

Trypanosoma brucei brucei S-adenosyl-L-methionine (AdoMet) decarboxylase was found to be relatively insensitive to activation by putrescine as compared with the mammalian enzyme, being stimulated by only 50% over a 10,000-fold range of putrescine concentrations. The enzyme was not stimulated by up to 10 mM-Mg2+. The Km for AdoMet was 30 microM, similar to that of other eukaryotic AdoMet decarboxylases. T.b. brucei AdoMet decarboxylase activity was apparently irreversibly inhibited in vitro by Berenil and reversibly by pentamidine and methylglyoxal bis(guanylhydrazone). Berenil also inhibited trypanosomal AdoMet decarboxylase by 70% within 4 h after administration to infected rats and markedly increased the concentration of putrescine in trypanosomes that were exposed to the drug in vivo. Spermidine and spermine blocked the curative effect of Berenil on model mouse T.b. brucei infections. This effect of the polyamines was probably not due to reversal of Berenil's inhibitory effects on the AdoMet decarboxylase.

Adenosylmethionine Decarboxylase↗
PubMed1986

Necessity of antibody response in the treatment of African trypanosomiasis with alpha-difluoromethylornithine.

The role of the immune system in the clearance of Trypanosoma brucei brucei from the bloodstream during alpha-difluoromethylornithine (DFMO) treatment was studied by determining the effects of dexamethasone on immune and therapeutic responses in rats infected with T.b. brucei. Normal DFMO-treated animals exhibited strong antibody responses to trypanosomes and were cured of T. b. brucei infection by a 7-day regimen of 2% DFMO in drinking water. Animals pretreated with dexamethasone were not cured by the same level of DFMO treatment. Nonetheless, in rats pretreated with dexamethasone, trypanosomes were cleared from blood during treatment with DFMO, but all immunocompromised animals eventually succumbed to relapses of the infection. Athymic (nude) mice were cured of T. b. brucei infection by a 72-hr course of treatment with 2% DFMO in their drinking water. These findings suggest that relatively low levels of T-cell-independent, antitrypanosomal antibodies are adequate to clear the bloodstream of parasites during DFMO therapy but that an intact immune response is necessary for cures of the disease to be obtained.

Animals↗
PubMed1986

Polyamine depletion following exposure to DL-alpha-difluoromethylornithine both in vivo and in vitro initiates morphological alterations and mitochondrial activation in a monomorphic strain of Trypanosoma brucei brucei.

DL-alpha-difluoromethylornithine (DFMO), a specific irreversible inhibitor of ornithine decarboxylase (ODC), rapidly depletes cells of intracellular putrescine. When administered to animals and humans, DFMO cures acute infections of trypanosomiasis. In order to determine if the mechanism of drug action is related to initiation of transformation and biochemical alterations subsequent to polyamine depletion, trypanosome morphology and mitochondrial activation were studied in a monomorphic strain of Trypanosoma brucei brucei. Exposure of trypanosomes to DFMO in vivo in infected rodents or in vitro in culture resulted in a depletion of intracellular putrescine and a cessation of cell division without specific cytotoxicity. These events were followed by a transformation of the long slender bloodstream form to a short stumpy form via an intermediate morphology. Putrescine, the product of the ODC reaction, abrogates this effect. When introduced into SDM-79 medium, the intermediate form is capable of further transformation to an "insect" procyclic trypomastigote whereas the long slender form and short stumpy form are not. Short stumpy forms are incapable of binary fission and have lost their infectivity for the vertebrate host. In addition, the mitochondrial marker enzyme, NAD diaphorase, was found only in the short stumpy and intermediate forms. We hypothesize that the short stumpy phenotype may not be a viable stage in the natural transformation of the trypanosome from its mammalian host to the insect vector.

Animals↗
PubMed1985

Inhibition of Trypanosoma brucei brucei peptidyl transferase activity by sparsomycin analogs and effects on trypanosome protein synthesis and proliferation.

Peptidyl transferase activity of Trypanosoma brucei brucei polyribosomes was competitively inhibited by analogs of sparsomycin (Ki = 1-100 microM). The analogs were also potent inhibitors of [3H]-leucine and [3H]mannose incorporation into the proteins of intact trypanosomes with little or no effect on overall respiratory rate, suggesting a specific site of action for these analogs on protein synthesis. The peptidyl transferase inhibitors were effective at low concentrations at limiting the proliferation of trypanosomes both in vitro and in vivo. The potency of the compounds as inhibitors of cell proliferation was positively correlated with their efficacy as inhibitors of peptidyl transferase activity. One compound, MDL 20828 (1 mg/kg), increased the survival time of T. b. brucei-infected mice 4-fold in the absence of any overt drug toxicity to the hosts.

Acyltransferases↗
PubMed1985

Catalytic irreversible inhibition of Trypanosoma brucei brucei ornithine decarboxylase by substrate and product analogs and their effects on murine trypanosomiasis.

Ornithine decarboxylase from Trypanosoma brucei brucei was inhibited by several substrate (ornithine) and product (putrescine) analogs both in vitro and in vivo. Since alpha-difluoromethylornithine is effective for the treatment of experimental and clinical African trypanosomiasis, it was possible that the more potent ornithine and putrescine analogs might be more active in treating the disease. However, only alpha-monofluoromethyldehydroornithine methyl ester was more potent than alpha-difluromethylornithine against mouse trypanosomiasis and warrants further study in model infections.

Animals↗
PubMed1985

Activation and stabilization of the catalytic unit of adenylate cyclase.

The requirements for stability and activity of the catalytic unit (C) of adenylate cyclase were investigated. After solubilization of bovine brain membranes in the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]propane-1-sulphonate (Chaps), the catalytic unit was separated from the stimulatory guanine-nucleotide-binding protein (Gs) by gel filtration on Ultrogel AcA-34. The partially purified C unit was rapidly inactivated at 30 degrees C; 0.25 mM-ATP stabilized activity. Although C-unit activity was dependent on Mg2+ or Mn2+, stabilization by ATP did not require bivalent cations. Activity of the Ultrogel-AcA-34-purified C unit was increased by Ca2+ plus calmodulin and by phosphatidylcholine plus lysophosphatidylcholine; activity in the presence of both activators was significantly greater than with each alone. Calmodulin plus Ca2+ and phospholipids also stabilized C unit. The column-purified C unit was activated by forskolin; the effect of forskolin was additive to those of calmodulin plus Ca2+ and phospholipids. p[NH]ppG-stimulated adenylate cyclase activity was reconstituted by mixing samples from the gel-filtration column containing Gs with C unit. Activation by Ca2+ plus calmodulin and Gs plus p[NH]ppG was additive; Ca2+ plus calmodulin did not alter the concentration of p[NH]ppG required for half-maximal activation. Results were similar with forskolin and Gs plus p[NH]ppG; the presence of one activator did not alter the effect of the other. These studies define conditions for separation of C unit and Gs from brain adenylate cyclase and demonstrate that ATP (in the absence of bivalent cations), phospholipids, calmodulin plus Ca2+, and forskolin all interact with C unit in a manner that is independent of functional Gs.

Adenosine Triphosphate↗