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.     

Poisoning Pyridoxal 5-Phosphate-Dependent Enzymes: A New Strategy to Target the Malaria Parasite Plasmodium falciparum

The human malaria parasite Plasmodium falciparum is able to synthesize de novo pyridoxal 5-phosphate (PLP), a crucial cofactor, during erythrocytic schizogony. However, the parasite possesses additionally a pyridoxine/pyridoxal kinase (PdxK) to activate B6 vitamers salvaged from the host. We describe a strategy whereby synthetic pyridoxyl-amino acid adducts are channelled into the parasite. Trapped upon phosphorylation by the plasmodial PdxK, these compounds block PLP-dependent enzymes and thus impair the growth of P. falciparum. The novel compound PT3, a cyclic pyridoxyl-tryptophan methyl ester, inhibited the proliferation of Plasmodium very efficiently (IC₅₀-value of 14 µM) without harming human cells. The non-cyclic pyridoxyl-tryptophan methyl ester PT5 and the pyridoxyl-histidine methyl ester PHME were at least one order of magnitude less effective or completely ineffective in the case of the latter. Modeling in silico indicates that the phosphorylated forms of PT3 and PT5 fit well into the PLP-binding site of plasmodial ornithine decarboxylase (PfODC), the key enzyme of polyamine synthesis, consistent with the ability to abolish ODC activity in vitro. Furthermore, the antiplasmodial effect of PT3 is directly linked to the capability of Plasmodium to trap this pyridoxyl analog, as shown by an increased sensitivity of parasites overexpressing PfPdxK in their cytosol, as visualized by GFP fluorescence.     

Polyamine levels and the activity of their biosynthetic enzymes in human erythrocytes infected with the malarial parasite, Plasmodium falciparum.

Human erythrocytes contain only trace amounts of polyamines and lack active polyamine biosynthetic enzymes. A remarkable increase in polyamine content, and in the activity of ornithine and S-adenosyl-L-methionine decarboxylases, is noted in synchronous cultures of the malarial parasite, Plasmodium falciparum. Polyamine biosynthesis reached peak values during the early trophozoite stage, whereas nucleic acid and protein synthesis occurred later in mature trophozoites. DL-alpha-Difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, did not interfere with merozoite invasion and with ring-form development, but prevented the transformation of trophozoites to schizonts. Concomitantly, the synthesis of proteins and nucleic acids was significantly inhibited. These inhibitory effects could be readily reversed by the diamine putrescine. Macromolecular synthesis and schizogony were normal when 5-10 mM-DL-alpha-difluoromethylornithine and 0.1 mM-putrescine were added to the cultures simultaneously.     

Binding of the chymotrypsin substrate,tryptophan methyl ester,by rat α-fetoprotein

We studied how tryptophan methyl ester and related compounds inhibit binding of estrone to rat α-fetoprotein and find that: (a) like chymotrypsin, α-fetoprotein binds tryptophan esters with higher affinity than tryptophan or its amides; (b) the affinity of α-fetoprotein for tryptophan methyl ester is 3.7 · 10^?4 M, which is close to the affinity of chymotrypsin (10^?4 M); (c) α-fetoprotein binding of tryptophan methyl ester is stereoselective and pH dependent. All of these observations suggest that there is a specific interaction between α-fetoprotein and the chymotrypsin substrate, tryptophan methyl ester, and that rat α-fetoprotein contains a site with some structural similarities to the catalytic site in chymotrypsin. Since we also find that tryptophan methyl ester is a competitive inhibitor of estrone binding to α-fetoprotein, it is possible that the protease substrate binding site on α-fetoprotein is spatially close to the estrone binding site.     

Purification and some properties of carboxylesterase of rat adipose tissue

Carboxyl ester hydrolase was obtained from rat epididymal adipose tissue in an electrophoretically homogeneous form. Purification was achieved by acetone precipitation, followed by successive chromatographies on DEAE-cellulose and hydroxyapatite and then isoelectric focusing. The monomeric molecular weight of the enzyme was 65 000 and the enzyme associated to form trimers. The enzyme had an isoelectric point at pH 5.9 and contained 2.1% carbohydrate moiety per protein with a molecular weight of 65 000. The amino terminal residue of the enzyme was glycine. The enzyme catalyzed the hydrolysis of short chain triacylglycerols such as tributyrin and medium chain monoacylglycerols such as monocaprin, but not the hydrolysis of cholesterol ester. The optimum pH for the enzymatic function of this enzyme for methyl butylate was 8.0. An antibody against the highly purified enzyme preparation induced in rabbits strongly inhibited the esterase of rat adipose tissue, but did not inhibit the esterase of rat liver, intestinal mucosa and serum.     

Polyamine transport in parasites: a potential target for new antiparasitic drug development

The metabolism of the naturally occurring polyamines-putrescine, spermidine and spermine-is a highly integrated system involving biosynthesis, uptake, degradation and interconversion. Metabolic differences in polyamine metabolism have long been considered to be a potential target to arrest proliferative processes ranging from cancer to microbial and parasitic diseases. Despite the early success of polyamine inhibitors such as alpha-difluoromethylornithine (DFMO) in treating the latter stages of African sleeping sickness, in which the central nervous system is affected, they proved to be ineffective in checking other major diseases caused by parasitic protozoa, such as Chagas' disease, leishmaniasis or malaria. In the use and design of new polyamine-based inhibitors, account must be taken of the presence of up-regulated polyamine transporters in the plasma membrane of the infectious agent that are able to circumvent the effect of the drug by providing the parasite with polyamines from the host. This review contains information on the polyamine requirements and molecular, biochemical and genetic characterization of different transport mechanisms in the parasitic agents responsible for a number of the deadly diseases that afflict underdeveloped and developing countries.     

Selective inhibition of the insulin-stimulated phosphorylation of the 95,000 dalton subunit of the insulin receptor by TAME or BAEE

Added N alpha-p-tosyl-l-arginine methyl ester or N alpha-benzoyl-l-arginine ethyl ester inhibited the stimulation by insulin of phosphorylation of the 95,000 dalton subunit of the insulin receptor both in a partially purified insulin receptor fraction from rat adipocytes and in a highly purified insulin receptor preparation from human placenta. N-alpha-p-tosyl-l-lysine chloromethyl ketone, N alpha-p-tosyl-l-lysine methyl ester, or N-acetyl-l-phenylalanine ethyl ester were much less potent, while N-benzoyl-1-alanine methyl ester was without effect. Inhibition of the phosphorylation by the arginine analogues did not require preincubation of the insulin receptor with inhibitors in the presence of insulin prior to phosphorylation. Inhibition by N alpha-p-tosyl-l-arginine methyl ester was decreased by preincubation of the receptor fraction with cold ATP and MnCl2. These results suggest that N alpha-p-tosyl-l-arginine methyl ester inhibits an initial ATP and Mn2+ dependent reaction in insulin-stimulated phosphorylation process.     

Fibronectin-induced protein carboxy-O-methylation in aortic endothelial cells

In a previous report (Bowersox, J.C. and Sorgente, N. (1982) Cancer Res. 42, 2547–2551) we demonstrated that the glycoprotein fibronectin is a chemoattractant for vascular endothelial cells. In probing the mechanisms by which fibronectin induces endothelial cell chemotaxis, we have discovered that the carboxy-O-methylation of cellular proteins is stimulated by fibronectin. By measuring the incorporation of l-[methyl-³H]methionine into alkali-labile, [³H]methyl ester linkages, we determined that fibronectin stimulated protein carboxy-O-methylation in aortic endothelial cells in a time- and concentration-dependent manner; the greatest stimulation occurred at 100 μg/ml fibronectin (approx. 35% above controls). When inhibitors of carboxymethylation were added, fibronectin-induced stimulation of protein methylation did not occur. Furthermore, inhibitors of methylation prevented the chemotaxis of endothelial cells in response to fibronectin. These data support our hypothesis that fibronectin mediates endothelial cell chemotaxis, such as that occurring during neovascularization. As carboxy-O-methylation of cell proteins is also effected by fibronectin, transmethylation reactions may be an important component of endothelial cell chemotaxis.     

Quantification of rapid,transient increases in jasmonic acid in wounded plants using a monoclonal antibody

A monoclonal antibody (MAB JAH1-8-B4) for the analysis of 3R, 7R-jasmonic acid and its methyl ester is described. An IgG₁(kappa) immunoglobulin, MAB JAH1-8-B4, was used to set up a competitive enzymelinked immunoassay employing 3R, 7R-jasmonate coupled to alkaline phosphatase as tracer. The assay has a linearity range (logit/log) between 50 fmol and 50 pmol (approx. 10 pg-10 ng) of 3R, 7R-methyljasmonate, the assay standard. A procedure combining prepurification of plant extracts by solid-phase extraction, followed by high-performance liquid chromatography and quantitation has been worked out, which uses 4 g of fresh plant material and has a detection limit between 0.2 and 0.4 g of 3R, 7R-jasmonic acid (determined as its methyl ester) per kg of tissue, depending on the tissue. Internal standards of 3R, 7R-methyljasmonate, added to split samples during extraction as well as a second internal standard, 3R, 7R-methyljasmonate-[O-C³H₃], added to all samples prior to methylation, served to correct for workup losses and for the monitoring of Chromatographie separations. Using this assay, it was found that levels of jasmonic acid rise immediately and transiently in the tissues analyzed as a consequence of wounding. These data provide further and direct evidence for the hypothesis that wound-induction of the plant defense reactions is mediated by endogenous jasmonates.Abbreviations DHJA 9,10-dihydrojasmonic acid - ELISA enzyme-linked immunosorbent assay - GC-MS gas chromatography-mass spectrometry - HCy hemocyanin - HPLC high-performance liquid chromatography - JA jasmonic acid - MAB monoclonal antibody - ME methyl ester - PDA 12-oxo-phytodienoic acid This work was supported by the Deutsche Forschungsgemeinschaft, Bonn, FRG, by the Fonds der Chemischen Industrie, Frankfurt, FRG (literature provision), and by the Ministerium fü Wissenschaft und Forschung des Landes Sachsen-Anhalt, Magdeburg, FRG. We thank Drs. M. H. Zenk and Z.-Q. Xia, Pharmazeutische Biologie, Universität München, FRG, for gifts of reference compounds. We are especially grateful to Dr. M. J. Müller from the same institute for GC-MS analyses.     

Phorbol ester stimulation of pancreatic beta-cell replication, polyamine content and insulin secretion.

Long-term effects of the protein kinase C activating phorbol ester, TPA, on pancreatic beta-cell proliferation and insulin production were investigated. It was found that beta-cell replication and long-term insulin secretion were enhanced in TPA-treated islets. This was not accompanied by a corresponding increase in (pro)insulin biosynthesis, presumably contributing to the lowered islet insulin content. TPA also increased islet polyamine content but when this increase was prevented by blocking polyamine synthesis, DNA replication and insulin secretion remained elevated. These findings indicate that TPA stimulates beta-cell replication and insulin secretion and suggest a stimulatory role for protein kinase C, but not for polyamines, in these processes.     

Methylation of TMV RNA

Several plant and animal viral RNAs contain a tRNA like structure at their 3′ ends. In this communication we show that tobacco mosaic virus (TMV) RNA is an acceptable substrate for a specific tRNA methyltransferase. Using a crude preparation of $\text{E. coli}$ ribothymidine (rT) forming uracil methylase and (methyl ³H) S-adenosyl-L-methionine (SAM) as a methyl donor, 0.7 moles of methyl group is incorporated per mole of TMV RNA in 10 hours at 30°C. Upon T₂ RNAse digestion of the labeled RNA, all of the radioactivity was found to be in TMP. T₁ RNAse digestion of ³H methylated TMV RNA showed that all of the label was located in a tetranucleotide which co-migrated with authentic TpψpCpGp, an oligonucleotide characteristically found in normal cellular tRNA.The use of this specific methyl transferase reaction may provide a simple assay for the detection of tRNA like structures in large RNAs.     

Modification of sialic acid carboxyl group of ganglioside

A simple and quantitative method for the modification of sialic acid carboxyl group in ganglioside is described. Methyl iodide was added to the ganglioside in dimethylsulfoxide. The reaction was completed quickly at room temperature, giving the methyl ester with practically no by-products. Reduction of the methyl ester was achieved by sodium borohydride. These modified gangliosides were chemically characterized. Reduced GM1 has a strong antigenicity compared with the original GM1, and it raised high titer antisera which did not crossreact with the original GM1 nor with its methyl ester. Peanut agglutinin, which binds strongly to asialo GM1 but weakly to GM1, bound to the methyl ester of GM1 and reduced GM1. Cholera toxin, which is specific for GM1, also reacted with the methyl ester of GM1 and reduced GM1 to a certain extent.     

Fatty acid composition of seeds of Satureja thymbra and S. cuneifolia

The chemical composition of fatty acid methyl esters (FAMEs) from seeds of S. thymbra and S. cuneifolia were analyzed by GC/MS. 7 FAMEs were identified from the seeds of S. thymbra mainly as 9-octadecenoic acid methyl ester (43.9%), hexadecanoic acid methyl ester (11.4%), 9,12,15-octadecatrienoic acid methyl ester (Z,Z,Z) (30.2%), and octadecanoic acid methyl ester (14.1%), while from the seed of S. cuneifolia 10 FAMEs were obtained with the main components, similar to S. thymbra. These were identified as 9-octadecenoic acid methyl ester (10.1%), hexadecanoic acid methyl ester (methyl palmitate, 34.6%), 9,12,15-octadecatrienoic acid methyl ester (Z,Z,Z) (6.3%) and octadecanoic acid methyl ester (1.8%).     

Feeding stimulants eliciting the probing behavior for Peregrinator blannulipes Montrouzier et Signore (Hemiptera: Ruduviidae) from Tribolium confusum (Jacquelin du Val)

Four fatty acid methyl esters identified in the solvent extract of Tribolium confusum (Jacquelin du Val) larvae as kairomones were individually and collectively tested for probing behavior of Peregrinator biannulipes Montrouzier et Signoret. All identified fatty acid methyl eaters, methyl palmitate, methyl linolate, methyl oleate and methyl stearate, exhibited characterisitic kairomonal probing behavior of P. biannulipe toward the lure. These fatty acid methyl ester were active at 0.2 microg/lure but a synergistic effect was not observed among them. Commercially available C8-C14 even-numbered fatty acid methyl esters that were not detected in the extract of T. confusum larvae also elicited a probing behavior but their activities were weaker than those of four fatty acid methyl ester (C16:0, C18:0, C18:1 and C18:2) identified in the extract. On the other hand, C17 and C19 odd-numbered fatty acid methyl esters did not show any activity at all.     

Methylated amino acids and lysosomal function in cultured heart cells

Methylated amino acids inhibit lysosomal function in cultured rat heart myocytes more effectively than the classically employed lysosomotropic weak bases. Moreover, L-leucine methyl ester (L-Leu-OMe) or L-methionine methyl ester (L-Meth-OMe) do not alter lysosomal pH or inactivate lysosomal cysteine proteinases, but do inhibit protein degradation more efficiently than either chloroquine or NH4Cl. These observations suggest that amino acid methyl esters are more effective probes to investigate lysosomal function in cultured myocytes than chloroquine or NH4Cl.     

Glucuronoyl esterase--novel carbohydrate esterase produced by Schizophyllum commune

The cellulolytic system of the wood-rotting fungus Schizophyllum commune contains an esterase that hydrolyzes methyl ester of 4-O-methyl-d-glucuronic acid. The enzyme, called glucuronoyl esterase, was purified to electrophoretic homogeneity from a cellulose-spent culture fluid. Its substrate specificity was examined on a number of substrates of other carbohydrate esterases such as acetylxylan esterase, feruloyl esterase and pectin methylesterase. The glucuronoyl esterase attacks exclusively the esters of MeGlcA. The methyl ester of free or glycosidically linked MeGlcA was not hydrolysed by other carbohydrate esterases. The results suggest that we have discovered a new type of carbohydrate esterase that might be involved in disruption of ester linkages connecting hemicellulose and lignin in plant cell walls.     

Regulation of light-harvesting chlorophyll-binding protein mRNA accumulation in Chlamydomonas reinhardi. Possible involvement of chlorophyll synthesis precursors

Light induction of light-harvesting chlorophyll a/b-binding protein (LHCP) mRNA accumulation was studied in light-dark synchronized cultures of Chlamydomonas reinhardi. LHCP mRNA accumulation was prevented by the chlorophyll-synthesis inhibitor alpha,alpha-dipyridyl which blocks late steps in the chlorophyll biosynthetic pathway and leads to the accumulation of the porphyrin intermediate magnesium protoporphyrin methyl ester. LHCP mRNA accumulated normally, however, when chlorophyll synthesis was blocked by inhibitors such as hemin and levulinic acid which interfere with early steps in the chlorophyll biosynthesis pathway prior to the formation of magnesium protoporphyrin methyl ester. Similar effects were observed in the light induction of LHCP mRNA levels in protoporphyrin IX-accumulating mutants, brc-1 and brs-1. These mutants have low levels of LHCP mRNA when grown under heterotrophic conditions in the dark where they accumulate protoporphyrin IX. However, LHCP mRNA is light-induced in brc-1 which synthesizes chlorophyll in the light and presumably consumes porphyrin intermediates in doing so. These results suggest that the chlorophyll-synthesis intermediates, magnesium protoporphyrin methyl ester and its immediate precursors, inhibit by a feedback mechanism the light induction of LHCP mRNA accumulation. Low magnesium protoporphyrin methyl ester levels permit the light-induced accumulation of LHCP mRNA, whereas high magnesium protoporphyrin methyl ester levels destabilize LHCP mRNA regardless of the illumination conditions. Preliminary experiments show that LHCP mRNA accumulation in C. reinhardi is stimulated by blue light, and not by red light which stimulates LHCP mRNA accumulation in higher plants.     

Biosynthetic relations between protoberberine-, benzo(C)phenanthridine- and B-secoprotoberberine type alkaloids in Corydalis incisa

The biosynthetic relations between protoberberine-, benzo[C]phenanthridine- and B-secoprotoberberine type alkaloids were demonstrated by use of (±)-tetrahydrocoptisine-[8,14-³H HCl, (±)-tetrahydrocorysamine-[8,14-³H]HCl and corynoline-[6-³H]HCl in Corydalis incisa, and the following results were presented. (±)-Tetrahydrocoptisine was converted to corynoline, corydalic acid methyl ester and corydamine hydrochloride. (±)-Tetrahydrocorysamine was converted to corynoline and corydalic acid methyl ester. Evidence that N-methyl-3-[6′-(3′,4′-methylenedioxyphenethylalcohol)]-4-methyl-7,8-methylenedioxy-1,2,3,4-tetrahydroisoquinoline-[α-³H] HCl was incorporated into corynoline-[11-³H] indicates the occurrence of the ring fission at C₆-N followed by linking ofthe C₆ and C₁₃ positions in (±)-tetrahydrocoptisine and (±)-tetrahydrocorysamine, and suggests the participation of one of two possible intermediates in the biosynthesis of these alkaloids.     

Influence of Methyl Bromide Fumigation on Microbe-induced Resistance in Cucumber

Field experiments were conducted to evaluate growth promotion and induced systemic disease resistance (ISR) in cucumber mediated by plant growth-promoting rhizobacteria (PGPR) with and without methyl bromide soil fumigation. In both fumigated and nonfumigated plots, numbers of cucumber beetles, Acalymma vittata (F.), and the incidence of bacterial wilt disease, caused by the beetle-transmitted pathogen Erwinia tracheiphila , were significantly lower with PGPR treatment compared with the nonbacterized control. However, in PGPR-treated plots, the incidence of bacterial wilt was more than 2-fold lower in the nonfumigated treatments compared with fumigated treatments, indicating that the level of PGPR-mediated ISR was greater without methyl bromide fumigation than with methyl bromide. Cucumber plant growth at 21 days after planting was greater in fumigated plots than in nonfumigated plots; however, plant height values in the nonfumigated, PGPR treatments and the fumigated, PGPR treatments were equivalent. This suggests that PGPR treatment compensated for delayed plant growth that often occurs in nonfumigated soil. These results indicate that, in cucumber production systems, withdrawal of methyl bromide will not negatively impact PGPRmediated ISR, and also that PGPR may have potential as an alternative to methyl bromide fumigation.