Targeting polyamines and biogenic amines by green tea epigallocatechin-3-gallate.

Biogenic amines and polyamines are organic polycations derived from aromatic or cationic amino acids. They exert pleiotropic effects, more related to intercellular communication in the case of biogenic amines, and to intracellular signaling in the case of polyamines. The bioactive compound epigallocatechin-3-gallate (EGCG), a major component of green tea, has been shown to target key enzyme of biogenic amine and polyamine metabolic pathways. Herein, we review the specific effects of EGCG on concrete molecular targets of both biogenic amine and polyamine metabolic pathways, and discuss the relevance of these data to support the potential therapeutic interest of this compound.

Suppression of TNF-alpha production by S-adenosylmethionine in human mononuclear leukocytes is not mediated by polyamines.

Endotoxin-induced cytokine production is an important mechanism in the development of several types of liver damage. Methionine, some of its precursors and metabolites were reported to have protective effects against such injury. The aim of this study was to investigate whether methionine, its precursors or metabolites [phosphatidylcholine, choline, betaine, S-adenosylmethionine (SAM)] have a modulating effect on tumor necrosis factor alpha (TNF-alpha) production by endotoxin-stimulated human mononuclear leukocytes and whether SAM-dependent polyamines (spermidine, spermine) are mediators of SAM-induced inhibition of TNF-alpha synthesis. Methionine and betaine had a moderate stimulatory effect on TNF-alpha production, whereas phosphatidylcholine (ID(50) 5.4 mM), SAM (ID(50) 131 microM), spermidine (ID(50) 4.5 microM) and spermine (ID(50) 3.9 microM) had a predominantly inhibitory effect. Putrescine did not alter TNF-alpha release. Inhibitors of polyamine synthesis that blocked either putrescine (difluoromethylornithine) or spermine (CGP48664A) production did not affect TNF-alpha synthesis. Endotoxin stimulation of leukocytes did not alter the intracellular levels of polyamines. In addition, supplementation with SAM did not change the intracellular concentration of either polyamine measured. We conclude that phosphatidylcholine-induced immunosuppression is not caused by methionine and polyamines are not involved in SAM-induced inhibition of TNF-alpha production. The limitation of TNF-alpha release by spermidine is specific and is not due to its conversion into spermine.

Ornithine decarboxylase activity is inhibited by the polyamine precursor amino acids at the protein stability level in Caco-2 cells.

High concentrations of certain amino acids are known to affect hormonal secretion, immune function, electrolyte balance or metabolic functions. However, there is a lack of knowledge regarding the molecular mechanisms responsible for these effects. We showed that, as well as spermidine transport, the activity of ornithine decarboxylase (ODC), the first and rate-limiting enzyme in polyamine biosynthesis, is decreased in human colon adenocarcinoma cells, Caco-2, following a 4-h supplementation with one of the two polyamine precursor amino acids, L-arginine or L-methionine. Dose-response assays indicated that the inhibitory effect of supplemental L-methionine was stronger than that of supplemental L-arginine. However, it was transient, being even replaced by ODC induction after 8 h, whereas the inhibitory effect of L-arginine lasted for at least 8 h. Unlike L-cysteine, neither L-methionine nor L-arginine could inhibit ODC activity in a crude acellular preparation of the enzyme. The inhibition of ODC activity in cells exposed to L-methionine or L-arginine was due to a decreased abundance of ODC protein without change at the mRNA level and each of these amino acids could counteract ODC induction by a glycine supplement. Contrary to the latter, supplemental L-methionine or L-arginine induced a marked decrease in ODC half-life, concomitantly with an increase in the activity of antizyme, an ODC inhibitory protein. Thus, depending on their nature, amino acids can up- or downregulate ODC activity at the protein stability level.

Geraniol, a component of plant essential oils, inhibits growth and polyamine biosynthesis in human colon cancer cells.

Geraniol and other monoterpenes found in essential oils of fruits and herbs have been suggested to represent a new class of agents for cancer chemoprevention. As a first step in clarifying the mode of action of geraniol on colon carcinogenesis, we studied its effects on the growth of a human colon cancer cell line (Caco-2). Geraniol (400 microM) caused a 70% inhibition of cell growth, with cells accumulating in the S transition phase of the cell cycle, and concomitant inhibition of DNA synthesis. No signs of cytotoxicity or apoptosis were detected. Geraniol caused a 50% decrease of ornithine decarboxylase activity, a key enzyme of polyamine biosynthesis, which is enhanced in cancer growth. This led to a 40% reduction of the intracellular pool of putrescine. Geraniol also activated the intracellular catabolism of polyamines, indicated by enhanced polyamine acetylation. These observations indicate that polyamine metabolism is presumably a target in the antiproliferative properties of geraniol.

Anti-arthritic effect of methotrexate: is it really mediated by adenosine?

The mechanism of action for the anti-arthritic effect of methotrexate (MTX) was investigated in rats with antigen-induced arthritis (AIA). Arthritis intensity was quantified as area under the curve (AUC) for the joint swelling. The response to MTX was in several respects similar to what is seen in the clinic. The drug reduced the AUC in a dose-dependent manner after oral weekly (2-4 mg/kg/week) or daily (0.3 mg/kg/day) dosing. This effect was not affected by supplementation with an equal dose of folate. The model thus seemed suitable for this type of study. Supplementation with folate in excess abolished the effect of MTX. A structurally similar antifolate, aminopterin, also reduced the arthritis. The effect thus seemed to be due to folate antagonism although a complete inhibition of dihydrofolate reductase (DHFR) might not be essential. Hence, it could be that the main target is a process downstream of DHFR. It has been proposed that inhibition of AICAR-transformylase induce the release of adenosine with anti-inflammatory properties. Here the adenosine antagonist R-PIA reduced the arthritis but when MTX was combined with adenosine antagonists no attenuation of the anti-arthritic effect was seen. On the contrary, three adenosine agonists (8-p-sulphophenyltheophyllamine 30 mg/kg i.p. twice daily; 3,7-dimethyl-1-propargylxanthine, p.o. 3 mg/kg/day and 8-cyclopentyl-1,3-dipropylxanthine, 1.5 mg/kg/day p.o.) potentiated MTX. The specific thymidylate synthase inhibitor 5-fluourouracil (0. 3-3.0 mg/kg/day) had no anti-arthritic effect. Neither did our data support the hypotheses that syntheses of polyamines or cytokines were primary targets. It is thus possible that the mechanism of action is inhibition of a process downstream of DHFR but the release of adenosine seems not to be important.

Gene structure and chromosomal localization of mouse S-adenosylmethionine decarboxylase.

The structure of the mouse S-adenosylmethionine decarboxylase (AdoMetDC) gene has been determined. The mouse gene (AMD1) consisted of eight exons and seven introns, similar to the rat AdoMetDC gene, and was mapped to chromosome 10. The characteristics of AMD1 gene were as follows: (1) The region of the promoter necessary for maximal transcriptional activity was located about 400 nucleotides upstream of the transcriptional initiation point, and contained a TATA box and two GC boxes. The transcriptional activity of the promoter was nearly equal to that of the SV40 promoter. (2) Two polyadenylation signals for transcription were observed, and the larger AdoMetDC mRNA, which is the dominant form of mRNA, corresponded to mRNA that is generated using the second polyadenylation signal. (3) Using stable transfectants, we confirmed that the upstream open reading frame (uORF) in the 5'-untranslated region (5'-UTR) of AdoMetDC mRNA functioned as a negative regulatory element. Lower concentrations of polyamines affect both stimulation and inhibition of AdoMetDC synthesis, through the uORF in the mRNA, than affect general protein synthesis.

Effect of one hyperbaric oxygen-induced convulsion on cortical polyamine content in two strains of mice.

In rat striatum, after one hyperbaric oxygen (HBO)-induced convulsion, polyamine changes are found that could promote N-methyl-D-aspartate (NMDA) activation. In the HBO-sensitive CD1 mouse, unlike in the common C57 strain, there is some support for NMDA activation after the HBO seizure. We measured PA cortical content before and after the first HBO-induced convulsion (about 608 kPa O2) in CD1 and C57 strains. Putrescine, spermidine and spermine were dansyl derived and analysed by HPLC. Exposure to HBO significantly increased putrescine content only in CD1 though a similar trend was observed in C57. No further increase was observed after convulsion whatever the strain. There were no significant changes in spermidine or spermine to support NMDA activation. Therefore, putrescine increase in CD1 cortex could reflect the free radical formation that is known to be greater in CD1 than in C57 mouse. Attempts to increase putrescine levels before HBO exposure hastened HBO-induced convulsion, less than spermidine or spermine. Because of physiological polyamine interconversion, additional experiments with indirect manipulation of putrescine levels and study of their time-course would precise these preliminary reports on putrescine and HBO.