Toxic Non-protein Amino Acid Research Articles

Mimosine Blocks Cell Cycle Progression by Chelating Iron in Asynchronous Human Breast Cancer Cells

Mimosine is a toxic nonprotein amino acid that is a major constituent of the tropical legumesLeucaenaandMimosa.Mimosine has been shown to cause acute and chronic toxicosis in livestock fed from forage containing these plants. Recently, mimosine has been demonstrated to reversibly block cell cycle progression in mammalian cells in culture. In this study, we compared the effects of mimosine to desferrioxamine (DFO), a well-characterized iron chelator, and found that both chemicals similarly altered cell cycle progression in MDA-MB-453 human breast cancer cells. Mimosine (400 μm) and DFO (150 μm) both reduced DNA synthesis by greater than 90% of control within 4 hr of treatment, and suppressed total proline-directed protein kinase activity to less than 10% of control after 16 hr treatment. These effects were antagonized by the addition of iron as ferrous sulfate (250 μm), which is bound to transferrin and imported into the cell via transferrin receptor endocytosis, or as hemin (100 μm), which passes through the cell membrane and releases iron into the cytosol. After 24 hr treatment with the chelators, a large portion of the available transferrin receptors moved to the cell surface, indicating that the cells were iron-starved. Our data demonstrate that mimosine, through iron chelation, blocks cell cycle progression in MDA-MB-453 human breast cancer cells.

Cytotoxicity in MA-104 cells and rumen protozoa of some phytotoxins and their effect on fermentation by faunated and defaunated rumen inocula

Toxic compounds present in plants are an important factor limiting the nutritional use of tropical legumes. This work deals particularly with the toxic nonprotein amino acid analogues mimosine, DOPA, and canavanine and structurally related compounds such as nicotinic acid, 3-hydroxypyridine, and catechol. The effect of these toxins was measured on the viability of eukaryote cultured cells (MA-104) and rumen protozoa and on the fermentation activity (production of VFAs, ammonia, and gas) by inocula from faunated and defaunated sheep in vitro. Toxins did not increase cell death of protozoa, wile catechol and nicotinic acid increased cell death of MA-104 cells

Characterization of nitrogenous solutes in tissues and xylem sap of Leucaena leucocephala.

Amino acid profiles of leaf, stem, and root tissues from nodulated and nonnodulated Leucaena leucocephala (Lam.) de Wit plants were determined by gas chromatography-mass spectrometry. High concentrations of mimosine and several other potentially toxic nonprotein amino acids, including pipecolic acid and two isomers of hydroxypipecolic acid, were identified in the tissues. Five metabolites remain unidentified. Of the foliar free amino acid nitrogen, 57-66% was associated with the potentially toxic amino acids. Major constituents in the leaf tissues of nonnodulated plants were mimosine and hydroxypipecolic acid (isomer 1). Mimosine was recovered in both the neutral plus basic and acidic amino acid fractions. Major differences between amino acid profiles of nodulated and nonnodulated roots were the low percentages of asparagine + aspartate (3.6% of the total pool compared to 33% in nodulated plants) and pipecolic acid in nonnodulated roots (1% of the total compared to 12.5% in nodulated plants). A novel plant betaine (dihydroxypipecolic acid betaine) was identified by fast-atom-bombardment mass spectrometry in leaf tissues, albeit at relatively low concentrations (< 1 micro mol per gram fresh weight). Analyses of the xylem sap collected from nodulated plants confirmed that Leucaena is an asparagine transporter, as suggested by the high concentrations of asparagine and the low concentrations of ureides in its root nodules. Amino acid profiles of xylem sap from nonnodulated plants showed extremely low concentrations of asparagine + aspartate (0.12 micro mol ml(-1)), whereas asparagine + aspartate was the major constituent (4.38 micro mol ml(-1)) in the xylem sap of nodulated plants. Two nonprotein amino acids, pipecolic acid and hydroxypipecolic acid, were major constituents of the xylem sap of nodulated and nonnodulated plants, respectively. Three unidentified compounds detected in xylem sap samples from both nodulated and nonnodulated plants did not correspond with any of the peaks characterized from tissue samples.

Chemical constraints to the use of tropical legumes in animal nutrition

Browse and grain legumes offer considerable potential for enhancing animal productivity in the tropics. However, a major factor limiting the wider use of these plants is the ubiquitous distribution of a diverse array of natural compounds which are capable of precipitating adverse effects in animals. Manifestations of toxicity range from a marked reduction in animal performance and nutrient utilisation to profound neurological effects and increased mortality. This review identifies the primary anti-nutritional factors in tropical legumes and evaluates the prospects for their detoxification. Although protease inhibitors are widely distributed in legume forage and grains, their role appears to be secondary to that of other toxic compounds. Recent studies highlight the dominant impact of lectins in determining the nutritional value of seeds of Psophocarpus tetragonolobus (winged bean) and Canavalia ensiformis (jack bean). The presence of condensed tannins is a characteristic feature of many browse legumes, including Gliricidia sepium, Acacia species, Leucaena leucocephala and Albizia falcataria. These polyphenolic compounds are sometimes accorded with beneficial attributes in ruminant nutrition by virtue of their capacity to suppress bloat and to prevent excessive degradation of high-quality leaf protein in the rumen. However, with respect to the condensed tannins of tropical forage legumes, there is increasing evidence of toxicity in all classes of livestock, including ruminants. The occurrence of toxic non-protein amino acids is a distinguishing feature of many forage and grain legumes. These amino acids contribute significantly to the toxicity of Leucaena leucocephala, Canavalia ensiformis and Lathyrus species. The distribution of several anti-nutritional factors in a single legume species causes difficulties with detoxification, particularly if the deleterious compounds are heat stable. Significant experimental procedures have recently been described for the detoxification of the winged bean and the jack bean, and these methods now await economic appraisal. The treatment of harvested leaves or the spraying of leguminous shrubs with polyethylene glycol (PEG) to alleviate the deleterious effects of condensed tannins is a comparatively recent innovation worthy of further investigation, particularly in view of striking improvements in the performance of sheep fed Acacia aneura. The most no'able advance in detoxification relates to biotechnological manipulation of rumen function, enabling cattle grazing Leucaena forage to degrade the deleterious amino acid, mimosine, to innocuous residues. The prospects for exploiting this technique in the detoxification of other tropical legumes and forage plants hould now be considered. However, the scope for any significant role of leguminous leaf meals in the utrition of non-ruminant animals now appears to be limited, despite recent advances in detoxificaion. In the case of these feedingstuffs, the major constraints are the intrinsic low digestibility of the protein fraction and the inferior metabolisable energy content relative to that of the legume grains.

Tobacco budworm, Heliothis virescens [Noctuidae] resistance to l-canavanine, a protective allelochemical

l-Canavanine, the toxic guanidinooxy structural analog of l-arginine found in many leguminous plants was fed to fifth instar larvae of the tobacco budworm, Heliothis virescens [Noctuidae] in agar-based artificial diet. These feeding studies revealed H. virescens to be resistant to the potentially insecticidal effects of this allelochemical in larval stages and established its LC 50 in the terminal instar larvae at 300 m M. The canavanine-treated larvae did not show any of the pupal developmental aberrations exhibited by a canavanine-sensitive insect such as the tobacco horworm, Manduca sexta. Parenterally injected canavanine evaluations complemented the dietary toxicity data and established the LD 50 in the terminal instar larvae at 10.7 g kg −1. H. virescens stressed by exposure to 150 m M-canavanine-containing diet for 48 hr, excreted only 0.6% of the canavanine consumed during a subsequent 24-hr exposure to this diet. Parenterally injected canavanine cleared from the hemolymph with a t 1 2 of 135 min. It was evident that canavanine was not merely excreted or sequestered but rather was metabolized effectively by this insect. Feeding studies employing other nonprotein amino acids revealed that this destructive generalist feeder could not cope with all potentially toxic nonprotein amino acids.