Showing papers on "Mimosine published in 1982"

Effect of mimosine on RNA synthesis in Ehrlich ascites-tumour cells

Abstract: Mimosine {leucenol; fiIN-(3-hydroxypyrid-4-one)l-a-aminopropionic acid; 3-I3-hydroxy-4-oxo- 1 (4H)-pyridinyl lalanine} is a non-protein amino acid found in the foliage and seeds of plants of the two legume genera Leucaena and Mimosa (see Thompson et al., 1969). Its toxicity has been studied in animals (Owen, 1958; Hylin & Lichton, 1965; Dewreede & Wayman, 1970) and in cells in culture (Tsai & Ling, 1971, 1972; Hegarty et al., 1978; Reisner & Bucholtz, 1979). In particular, mimosine has an inhibitory effect on hair growth (Montagna & Yun, 1963), which may be related to the reported inhibition of DNA synthesis in hair-follicular cells (Ishibashi & Seiji, 1976; Ward & Harris, 1976). It has been suggested that the biological effects of mimosine may be due to its action as a tyrosine antagonist (Crounse et al., 1962; Lin et al., 1964; Prabhakaran et al., 1973), but the exact mechanism of its action has not been elucidated. The purpose of this study is to investigate the action of mimosine on macromolecular synthesis in a single cell type. We here describe the effect of mimosine on RNA synthesis in Ehrlich ascites-tumour cells. These cells were grown in mice (Itzhaki, 1972), harvested, washed with 0.9% NaCl and suspended in phosphate-buffered saline. RNA synthesis was measured as the rate of [5-'H]uridine incorporation into RNA of cells incubated at 37°C with the labelled precursor for predetermined periods (Harwood & Itzhaki, 1973). The results show that in the presence of 1-5 mwmimosine the rate of RNA synthesis is inhibited by about 25% and slows down greatly after 1&15min, reaching almost a plateau after 20-30 min depending on the concentration of mimosine. There is also an indication that longer periods of incabation of the cells with mimosine slow down RNA synthesis to even greater extents. Therefore we investigated the effect of longer periods of contact of cells with mimosine. This was done by preincubating cells with mimosine for 1 h, followed by the addition of [ .'H]uridine and further incubation for 20min. The results from this series of experiments were compared with those where the effect of mimosine was tested directly without a period of preincubation. Investigations in the concentration range of 0.05-1 mwmimosine show that in the preincubation series the inhibition of RNA synthesis by mimosine is concentrationdependent, reaching an inhibition of up to 75%, whereas in the tests where mimosine and [ 'Hluridine were added together maximum inhibition of only 20% was observed. Further experiments showed that even shorter periods of preincubation with mimosine of 30min or less enhanced the inhibitory action of mimosine, but the effect was not as pronounced as in the 1-lfh period of preincubation. The interpretation of these results is that mimosine is converted in the cell into a metabolite which may be the actual inhibitor; therefore a minimum period of exposure of the cells to mimosine is required before the pronounced inhibitory effect of mimosine on RNA synthesis is observed. Indeed, mimosine is known to be metabolized, though its metabolism has been studied mainly in plants; however, in animal tissues as well, several metabolites have been detected (Tang & Ling, 1977). Crounse, R. G., Maxwell, J. D. & Blank, H. (1962) Nature (London)

Comparative investigations of the action of mimosine on nucleic acid synthesis in Ehrlich ascites-tumour cells

Abstract: Mimosine (leucenol; 3 [ 3 -hydroxy-rl-oxo1 (4H)-pyridinyllalanine } is a non-protein amino acid of plant origin (see Fowden et al., 1967). Several studies .have shown that mimosinecontaining plants and mimosine itself are toxic to animals (Matsumoto et al., 1951; Owen, 1958; Hegarty et al., 1964). The toxicity of mimosine has also been studied in cell culture (Tsai & Ling, 1971; Prabhakaran et al., 1973). Exposure of cells in culture for relatively long periods causes inhibition of DNA synthesis (Tsai & Ling, 1971, 1972; Hegarty et al., 1978). In a previous report we showed that mimosine had an inhibitory effect on RNA synthesis in Ehrlich ascites-tumour cells. The inhibition was concentration-dependent in the range of 0.05-1 mwmimosine. It was found also that the inhibition was much more pronounced when the cells were preincubated with mimosine before their capacity for RNA synthesis was determined (Itzhaki & Abdulla, 1982). The work was extended to study the action of mimosine in a wider range of concentration on the synthesis of both RNA and DNA. Ehrlich ascites-tumour cells were grown in mice (Itzhaki, 1972), harvested, washed with 0.9% NaCl and suspended in the incubation medium. RNA synthesis was measured as the rate of [5-3H]uridine incorporation into RNA of cells incubated at 37OC with the labelled precursor for 20min (Harwood & Itzhaki, 1973). In a similar set of determinations DNA synthesis was measured as the rate of incorporation of Irneth~l-~Hlthymidine into DNA. Comparison was made in all cases between cells which were incubated with mimosine for 1 h before the determination of RNA or DNA synthesis and those where the effect of mimosine was tested directly without a period of preincubation. The results show that for RNA synthesis, mimosine has a biphasic action in the preincubated series of experiments. A gradual increase in inhibition of RNA synthesis is observed when the concentration of mimosine is increased from 0 . 0 2 m ~ to about 0.5 mM, reaching a maximum inhibition of 75%. When the concentration of mimosine is raised from 1 to 6 m ~ , the inhibition of RNA synthesis gradually decreased, such that the rate of RNA synthesis returned to almost 80% of the control value. However, when RNA synthesis was measured directly in a 20min period of incubation without a period of preincubation, a slight inhibitory effect was observed at the higher range of mimosine concentrations. The results also confirm the earlier observations (Itzhaki & Abdulla, 1982) that a preincubation period is required to detect the action of mimosine. The effect of mimosine on DNA synthesis was quite different. Here, no noticeable effect was obtained with 0.02-0.2 m ~ mimosine. As the concentration was raised there was a gradual stimulation of DNA synthesis, with a broad peak around 3-4m~-mimosine, when the rate of DNA synthesis reached a value of 40-50% above that of control. Moreover, the pattern of thymidine incorporation into DNA is similar in both the preincubated and the non-preincubated series. The results indicate clearly that the requirement for a period of contact of the cells with mimosine for the latter to act on RNA synthesis may be related to its metabolism inside the cell during the duration of preincubation. The metabolism of mimosine in animal tissues has been studied, and among the products found to be formed are mimosinic acid and mimosinamine (Tang & Ling, 1977). It is possible that the action of mimosine on RNA synthesis observed here is due to a metabolite, or it may be brought about by a combination of effects of more than one metabolite of mimosine. In contrast. mimosine may itself exert the stimulatory action on DNA synthesis observed here; however, we have no indication as to its mechanism of action.

Growth performance of, and mimosine excretion by,

Abstract: D'Mello, J.P.F. and Acamovic, T., 1982. Growth performance of, and mimosine excretion by, young chicks fed on Leucaena leucocephala. Anim. Feed Sci. Technol., 7 : 247--255. Growth performance and mimosine output in excreta have been measured in young chicks fed on diets containing three forms of Leueaena leaf meal (LLM) imported from Malawi. In one of the experiments, the effects of supplementation of LLM with selected metal ions and enzymes were also measured. Growth and efficiency of food utilisation were similar in groups fed on a control soya bean meal diet or a basal diet containing 150 g kg -~ of the whole leaf (WL) form of LLM. Supplementation of this basal LLM diet with FeSO 4 or AI~(SO4) 3 had little effect on growth or efficiency of food utilisation, but the ratio of mimosine output to mimosine ingested (MO/MI) increased from 0.781 to 0.881 and 1.003 on addition of FeSO 4 and AI~(SO4)3, respectively. Growth performance was unaffected by the addition of an enzyme mixture (containing cellulase, acid and neutral proteases and alpha amylase) to the basal LLM diet. In the second experiment, two other forms of LLM were also tested: a ground leaf (GL) form, and a powder produced by grinding pellets of Leucaena leaf (GP). The WL and GP forms were each added at 50 and 100 g kg -~ diet, and the GL form at 100 g kg -~ diet. These diets permitted daily intakes of mimosine ranging from 80 to 350 mg per replicate of 4 chicks. In comparison with control groups, growth performance was not impaired significantly in any of the LLM-fed groups. Mimosine excretion was high in all LLM-fed groups, the GP form inducing a maximum MO]MI ratio of 0.924.