Dihydroxvpyridone : a Review

Subabul (leucaena leucocephala) is considered as a miracle tree due to its protein rich foliage (20-30% CP), fast growing and drought tolerant habits. Use of its foliage as animal feed is being limited by presence of a toxic amino acid-mlmosine and its metabolites 3,4 DHP and 2, 3 DHP. Inclusion of subabul leaves on ration of farm animals results in varied response to severe advt:<rse effects. Treatment of subabulleaf meal with mimosine binding agents reduce mimosine toxicity significantly and this seems to be the most effective detoxification method for nonruminants. But for ruminants a new hope has arisen from the discovery of presence of DHP degrading rumen microbes. in some rE:gions of the world including Karnal area of India. Such microbes were identified as Clostridium strain 162 in Venezuela; Synergistes jonsii in USA and a strain of Streptococcus bOllis in India. This paper reviews the topic and provides an update information about detoxification of mimosine and DHP. Subabul (Leucaena leucocephala) is considered as a miracle tree for its ever-green protein rich foliage (20-30% CP), fast growing habit, drought tolerance, good high energy fuel, organic nitrogen fertilizer and its charcoal, gum etc. (NAS,1977). It also prevents soil erosion and fixes large amount of nitrogen in the soil. Its pest resistance and durability under grazing, cutting, fire and drought have become legendary. Its leaves are also rich in j3-carotene and minerals (Akbar and Gupta, 1985). It produces more than 3tlha crude protein with amino acid composition similar to lucerne (Jones .. 1979; NAS, 1981). It is also considered suitable for alley cropping. Despite so many good qualities, its use as livestock feed is being limited by presence of a toxic amino acidmimosine and its metabolites 3, 4 DHP and 2, 3 DHP. Through researchers have been trying to detoxify mimosine for more than 50 years, some major break-through have been achieved only very recently. This paper reviews upto date progress on detoxification of mimosine and DHP. NUTRIENT COMPOSITION OF SUBABUL LEAF MEAL AND SEED : The range of various nutrients in leucaena leaf meal reported by several workers is CP 15.22 to 31.43;EE 2.50 to 7.10 ; NEE 38.62 to 57; NDF 27.3 to 46.30; ADF 14.4 to 29.79; cellulose 7.10 to 16.7; Ugnin 4.4 to 12.81; total ash 6.8 to 12.5; Ca 1.80 to 2.70; P 0.17 to 0.23 per cent, GE 19.0 to 20.1 MJ/kg, j3-carotene 227 to 546.66 .ppm. Upadhyay et aI., 1974: NAS, 1977; Kharat et al. 1980; Pal et al., 1979: D'Mello and Fraser, 1981; Jones and Megarrity, 1989; Kurar et aI., 1984; Akbar and Gupta, 1985; Gupta et al., 1986: Sunaria and Vidyasagar, 1989: Samanta et aI., 1994 : Onwudike, 1995; Gupta, 1995). The range of various nutrients in subabul seed is CP 21 to 30.4; CF 6 to 11; EE 4.9 to 8; )\;EE 41.1 to 55.98; total ash 4.3 to 10.8 and P 0.3 to 0.38 per cent (Shukla et al., 1987; Gupta et at., 1986; Bhaskar et aI., 1987 ; Chakraborty and Chhabra, 1988 ; Dharamsare et aI., 1991). INCRIMINATING FACTORS IN SUBABUL : The use of subabul as livestock feed is being prevented by the presence of mimosine and its degradation products 3,4 DHP (Ross and Springhall 1963) and 2,3 DHP (D'Mello, 1992). The mimosine content is different in different parts of the plant. In leaf meal and hay it varies from 1 to 4.40 per cent of DM (Hegarty et aI., 1964; Sobale et aI., 1978; D'Mello and Taplin, 1978; Meuline et aI., 1984; Gupta et aI., 1988; Sunaria and Vidyasagar, 1889; Samanta 1991; Ram 1992; Gupta 1995). The concentration in seed varies from 3.6 to 5.0 per cent of DM (Jones, 1979;Gupta and Raheja, 1988; Chakraborty and Chhabra, 1988). D'Mello and Acamovic (1982) observed upto 14.5 per cent mimosine in subabul seed. Mimosi~e is degraded to 3,4 DHP and further to 2,3 DHP by endogenous enzymes of leucaena plant. 3,4 DHP and 2,3 DHP are equally toxic and Vol. 21. No.2, 2000 105 hoth are potent goitrogen (D'Mello, 1992). Other less important toxic constituents of subabul are tannin, protease inhibitor and galactomannan (D'Mello, 1992; D'Mello and Acamovic, 1982). METABOLIC AND TOXIC EFFECT OF MIMOSINE AND ITS METABOLITES : Mimosine heing structurally very similar to tyrosine may inhibit tyrosine decarboxylase or tyrosinase by acting as tyrosine analogue (Crounse et aJ., 1962). It may complex with pyridoxal phosphate and various meta lions such as zinc, copper etc. (Hegarty, 1978; Stunzi et a1., 1979). Jones et al., (1978) have reported that mineral supplement containing Zinc reduce the toxicity of Leucaena in cattle and suggested that some of the toxic signs (e.g .. skin lesions) resembles zinc deficiency. In mice study it was observed that gross damage in hair follicle and alopecia may be due to inhibitory action of mimosine on the proliferative phase of hair growth i.e. mitotic phase rather than on keratinization phase (Montagna and Yun,1963 Hegarty et al., 1964). Mimosine is an inhibitor of cystathionine synsthetase and cystathionase enzyme involved in the conversion of methionine to cystine. This inhibition could also be an important factor in mimosine induced alopecia (Cheek and Shull, 1995). The metabolic product of mimosine MlMOSINE 3, 4 DHP prevents iodinisation of tyrosine-an amino acid responsible for synthesis of thyroxine. 3,4 DHP reduces level of peroxidase which is necessary for conversion of iodine molecule to iodite radical or nascent iodine, which is important for its incorporation into tyrosine, hence affecting thyroxine synthesis (Hegarty et al., 1976) which results in compensatory enlargement of thyroid gland (goitre). Mimosine and DHP has hepatotoxic effect and increase plasma SGOT and SGPT in rabbit (Gupta, 1995). 3, 4 DHP is comparatively less toxic than mimosine (Lowry, 1982).3,4 DHP and 2, 3 DHP are equally toxic and both are potent goitrogen (D'Mello, 1992). Mimosine, 3, 4DHP and 2, 3 DHP produce a variety of toxic effects in Uvestock such as alopecia, depressed growth, excessive salivation, ulcer in mouth (Owen, 1958; NAS, 1981; Ram, 1994). METABOLISM OF MIMOSINE : Hegarty et al., (1964) observed that mimosine was extensively degraded to 3,4 DHP and other unidentified products in sheep rumen but there was no degradation of mimosine during or after absorption in the body. There is no evidence of detoxification of mimosine or DHP on the animal body. Mimosine gets converted to 3, 4 DHP by RUMEN MICROBES, ENDOGENOUS ENNMES CHEMICAL (pH & TEMPERATURE 3,4 DHP (Hegarty et a1., 1964; Shiroma & Akashl, 1976; Atreja et a1.,1990; Allison et a1.,1992 RUMEN MICROBES, Paul et a1., 1997) ENDOGENOUS PLANT ENNMES PYRWATE AND AMMONIA (Smith and Fowden, 1966) 2,3 DHP (0' Mello, 1992; Gupta and Atreja, 1994; Paul et al., 1999) \ RUMEN MICROBES e.g.Synergistes jonsll Streptococcus etc. RUMEN MICROBES UNIDENnFJED NONTOXIC RESIDUES (Allison et al., 1992; Hammond, 1995; Gupta and Atreja, 1994; Paul et a1., 1999) FIG. 1 : PATHWAYS OF MIMOSINE DEGRADATION. 106 AGRICULTURAL REVIEWS endogenous enzymes of Subabul plant (Lowry,1982; Tangendjaja et aI., 1984) by rumen microbes (Hegarty et aI., 1997), by chemical reaction of mimosine under appropriate pH and temperature (Wills and Tangendjaja ,1981). 3, 4 DHP can be further converted to 2,3 DHP by endogenous plant enzymes or rumen microbes (D'Mello, 1992; Ram et aJ.; 1994; Gupta 1995; Paul et a1., 1995). The pathway of biodegradation of mimosine and its metabolites are presented in Fig. 1. The products of ruminal mimosine degradation are DHP, pyruvic acid and ammonia (Smith and Fowden, 1966). There is considerable variation on ruminal metabolism of DHP in different part of the world. Rumen microflora from certain geographical regions can degrade 3,4 DHP or 2,3 DHP to unidentified nontoxic compounds (Allison et a1., 1992; Hammond, 1995; Gupta and Atreja, 1994; Paul et aI., 1999) whereas rumen microflora from certain region fail to do so (Kudo et aI., 1989; Wang,1992). Though the end products of DHP degradation are not clearly defined, probably pyridone ring is broken down. DETOXIFICATION OF MIMOSINE AND DHP : In the follOWing text, a review of the research finciings on detoxification of mimosine and DHP is being made under two subheads. (i) Physicochemical methods : Ross and Springhall (1963) obsetved that application of ferrous sulphate to leucaena leaf meal (LLM) reduces its toxicity in poultry by increasing faecal mimosine excretion. They speculated that mineral form chelate with mimosine which prevent absorption of mimosine from Gl tract. Un et aI., (1964) showed that L-phenylalanine and L-tyrosine supplementation could partially reduce rnimosine toxicity in rats. But Labadan (1960) found tyrosine to be completely ineffective. Tsai and Ung (1973) -';showed that aluminium formed stronger complexes with rrumosine than ferrous sulphate for inducing faecal excretion of mimosine. D'Mello and Acamovic (1982) obsetved.that ferrous 'sulphate at 0.5% level and aluminium at 1.17% level were effective in increasing mimosine excretion through faeces. They suggested that ferric sulphate is rriore effective than ferrous sulphate. They obtained best result when bath PEG and ferrous sulphate were used. Lowry (1982) reported that maceration helps in converting v,\ry toxic mimosine to less toxic 3, 4 DHP. Akbar and Gupta (1985) obsetved that spraying 6.7 per cent ferrous sulphate reduced mimosine content from 3.5 to 2.37 per cent. Sunaria and Vidyasagar (1989) reported 1.26 per cent ferrous sulphate to be optimum for detoxifying 4.04 per cent mimosine in LLM. Mali et aI., 1994; reported 17 to 19 per cent reduction on dry heating at 100°C and 19 to 23 per cent reduction in mimosine content of seed in auto-claving but Atreja et aI., (1990) did not obsetve any beneficial effect of dry heat treatment. Akbar and Gupta (1985) obsetved that moist heat at 70 to 1000C caused 50% reduction in mimosine content. But it is not clear whether mimosine was converted to DHP by moist heat treatment in these studies hence reduction in mimosine level might have resulted in increased DHP level which may be of no practical benefit. Supplementation of molasses to the leucaena diet increased excretion of mimosine and 3,4 DHP via faeces and thus prevented lowering of thyroxine level (Elliot et aI., 1985). Probably high level of minerals especially zinc, ferrous and copper present in molasses binds with mimosine and DHP and increase their excretion via faeces. Tawata et aI., (1986) reported that leaching of leucaena leaves with 0.05 N sodium acetate removed 95 per cent mimosine without loss of any important nutrients. Shyam etal., (1990) observed 42.65% reduction in mimosine content of LLM when it was ensiled along with other roughages. Sharma et a1., (1990) found that leucaena leaf meal heated with 0.2 per cent calcium sulphate or ferrous sulphate gave similar performance in rams while rams fed untreated leucaena shed wooi. Samanta et aI., (1994) observed that when sole LLM diet was supplemented with copper sulphate (10ppm Cu) mimoslne excretion In faeces increased. But they 'also obsetved that iron supplementation ata level of 4g/kg or above level and copper supplementation at level of 10mg!kg and above reduced in vitro rumen microbial degradation of mimosine. This effect might possible be due to binding effect of copper and iron on mimosine which inhibited its conversion to 3,4 DHP by rumen microbes. Ram et aJ., (1994) reported improved gain when calves were given sole diet of LLM treated with Cu(10ppm). Through, at present, the nature of cOfnplex of mimosine with metalions is not known, Ii is clear that these metal ions are