Ruminal metabolism of plant toxins with emphasis on indolic compounds.
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Ruminal bacteria can perform biochemical transformations on plant constituents that may affect the health of ruminant animals. Reactions carried out by ruminal bacteria on oxalates and some pyrrolizidine alkaloids include decarboxylation, hydrolysis and reduction steps. Prior exposure of ruminal bacteria to these substances increases the rate of detoxification, indicating an adaptive response by the bacteria to these substrates. The formation of toxic substances by ruminal bacteria also occurs and may involve similar reactions. Hydrolysis of cyanogenic glycosides and miserotoxins , reduction of nitrate and S-methylcysteine sulfoxide to nitrite and dimethyl disulfide can result in toxicity in ruminants. Similarly, the deamination and decarboxylation reactions associated with the degradation of tryptophan and tryosine result in the formation of 3-methylindole and p-cresol, which are toxic. Formation of 3-methylindole results from fermentation of tryptophan to indoleacetic acid, with subsequent decarboxylation of indoleacetic acid to 3-methylindole by a Lactobacillus sp. The 3-methylindole causes acute pulmonary edema and emphysema in ruminants as a result of mixed function oxidase metabolism in tissues. The 3-methylindole is also the cause of naturally-occurring acute bovine pulmonary edema and emphysema after abrupt pasture change. Inhibition of ruminal 3-methylindole formation by monensin and other antibiotics lowers ruminal 3-methylindole concentrations and prevents acute lung injury in experimental animals. (+info)
Role of metabolism in the immediate effects and pneumotoxicity of 3-methylindole in goats.
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Rapid infusion of 3-methylindole (3-MI) dissolved in 10% Cremophor EL in water was immediately followed by pulmonary arterial hypertension, systemic arterial hypotension, decreased minute volume and periods of apnoea in goats. Rapid intravenous infusion of Cremophor EL/water alone caused similar immediate effects to those of Cremophor EL plus 3-MI in various dosages. Pretreatment of goats with piperonyl butoxide or phenobarbitone did not significantly alter these immediate cardiopulmonary responses. But pretreatment with piperonyl butoxide prevented clinical signs and pulmonary lesions of 3-MI toxicity, whereas phenobarbitone pretreatment shortened survival time and enhanced pulmonary pathology. Cremophor EL and 3-MI dissolved in Cremophor EL caused severe in vitro haemolysis of caprine and bovine erythrocytes. There was no relationship between the immediate effects of 3-MI and the subsequent development of 3-MI-induced pneumotoxicity and deaths in control goats or in goats pretreated with piperonyl butoxide or phenobarbitone. Induction or inhibition of mixed function oxidase activity had no influence on immediate responses to 3-MI but did change the severity of clinical and pathological responses. It is concluded that there is no apparent relationship between the immediate and the pneumotoxic effects of 3-MI. It is possible that the immediate effects are the result of intravascular haemolysis. (+info)
The primary structure of the cytotoxin restrictocin.
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The complete amino acid sequence of the single polypeptide chain of cytotoxin restrictocin has been determined. Its structure was established by automated Edman degradation of the intact molecule reduced and [14C]carboxymethylated and of fragments obtained by chemical cleavage of the protein with cyanogen bromide and BNPS-skatole and by enzymatic cleavage of the polypeptide chain with trypsin. The molecule consists of 149 amino acid residues with a calculated relative molecular mass of 16836. The protein presents two disulfide bridges, one between cysteine residues at positions 5 and 147 and the other one formed by cysteine residues at positions 75 and 131. The amino acid sequence of restrictocin shows a high degree of homology (86%) with that of the cytotoxin named alpha-sarcin. (+info)
Ultrastructural changes in intraacinar pulmonary veins. Relationship to 3-methylindole-induced acute pulmonary edema and pulmonary arterial changes in cattle.
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In 3-methylindole (3MI)-treated cattle electron-microscopic examination of intrapulmonary arteries showed changes of an arteritis which could be related to pulmonary hypertension. To further elaborate on this concept, the present study describes the ultrastructural pathology of intraacinar pulmonary veins in cattle 72 hours after oral administration of 3MI. The changes include significant thickening of the muscular pads of the media, massive glycogen accumulation in the venous smooth muscle cells, proliferation of the myointimal cells, focal protrusion of cytoplasmic portion of a smooth muscle cell into an adjacent cell body suggestive of vasoconstriction and emigration of lymphocytes and platelets through the vascular wall. The experimental data are discussed in relation to the ultrastructural pathology of intraacinar pulmonary arteries and acute pulmonary edema. The authors further present evidence that 3MI acute pneumotoxicosis is also associated with drastic vascular changes which may signify sudden elevation in arterial and venous pressures in the pulmonary system of cattle. (+info)
Pathologic changes in 3-methylindole-induced equine bronchiolitis.
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The pathologic features of bronchiolitis were studied in horses and ponies from 30 minutes to 27 days after an oral dose of 3-methylindole (3MI). From 30 minutes to 3 hours, lesions were limited to nonciliated bronchiolar epithelial (Clara) cells, which lost apical caps and cytoplasmic granules and had dilated smooth endoplasmic reticulum (SER). At 12 hours, necrotic Clara cells were exfoliated; degeneration and necrosis were evident, in bronchiolar ciliated cells. Rare epithelial cells with hyperplastic SER appeared on the denuded basal lamina at 24 hours. Inflammatory cells, epithelia, fibroblastlike cells, collagen, and debris occluded many bronchiolar lumens from 3 to 6 days. Reorganization resulted in a simple columnar bronchiolar epithelium with relatively normal ciliated cells and fewer fibroblastlike cells. However, mature Clara cells were rare at 27 days, and collagenous bands still divided bronchiolar lumens. Thus, 3MI toxicosis is a persistent model of equine bronchiolitis with many morphologic features of the spontaneous disease. (+info)
The effect of dietary and sulfur compounds in alleviating 3-methylindole-induced pulmonary toxicity in goats.
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The present experiment was designed to determine the effect of tissue concentrations of glutathione (GSH) and GSH-S-transferase activity on 3-methylindole (3MI)-induced pulmonary toxicity in vivo. Forty goats were given high protein, normal protein, high cysteine, high sulfate or diethyl maleate (DEM) to vary tissue concentrations of GSH before i.v. infusion of 3MI. The severity of lung lesion was scored. Tissue GSH concentration, GSH-S-transferase activity and cytochrome P-450 content were measured. Compared to goats fed normal protein diet, high cysteine or high sulfate increased the tissue GSH levels and reduced the severity of the lung lesion induced by 3MI. Pretreatment with DEM, by which the tissue GSH was depleted, increased the severity of 3MI-induced lung lesion. Tissue GSH-S-transferase activity was not changed. These results indicate that the tissue concentration of conjugating agents play an important role in 3MI-induced lung disease. (+info)
Some effects of indole on the interaction of amino acids with tryptophanase.
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Although indole is a potent inhibitor (KI = 0.01 mM) of pyruvate formation from substrates of tryptophanase (EC 4.1.99.1, from Escherichia coli), we could not detect binding of indole to free tryptophanase (KD greater than 1.0 mM). However, indole, skatole, and toluene increased the affinity of tryptophanase for certain inhibitory amino acids. Binding of amino acids with small side chains (e.g. Ala, Gly) was increased, but there was little or no effect on the binding of amino acids with bulky side chains (e.g. norvaline, ethionine). These effects were quantitated by using changes in the absorption spectra of the enzyme . amino acid complexes. Indole decreases the absorbance obtainable at 500 nm for amino acids with small hydrophobic side chains (L-Ala, Gly), increases this absorbance for amino acids with small polar side chains (beta-cyano-L-alanine), and does not change the spectra of tryptophanase complexes with amino acids with bulky side chains, i.e. amino acids whose binding affinities are unaffected by indole. These spectral differences are interpreted in terms of an effect of bound indole (or side chain binding) on the partitioning of the bound amino acid between catalytic forms of the enzyme. The data indicate that substrate-induced conformational changes occur at the enzyme active site that generate a high affinity indole-binding site during catalytic turnover of tryptophanase and are important in the catalytic functioning of the enzyme. These changes also explain reproducible differences in KI values observed previously for amino acids in different assay systems used for steady state kinetic inhibition studies. The optimal conditions for the growth of E. coli for tryptophanase production are outlined, together with a procedure for purification of holotryptophanase. (+info)
The role of nitro groups in the binding of nitroaromatics to protein MOPC 315.
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Two series of dinitrophenyl haptens, in which chlorine replaces one or both nitro groups, were used to investigate, by a combination of high-resolution 1H n.m.r. and fluorescence quenching, the presence of groups in the combining site of protein MOPC 315, which form hydrogen bonds to the aromatic-ring substituents of the hapten. The large differences in binding constants on successive replacement of nitro groups were shown to be due to specific hapten-substituent-protein interactions by (a) showing that there was little difference in the interaction between these haptens and 3-methylindole (a model for the residue tryptophan-93L with which the hapten stacks in protein MOPC 315), (b) proving by 1H n.m.r. that the mode of hapten binding is constant and (c) showing that the differences in Kd were consistent with the relative hydrogen-bonding capacities of chlorine and the nitro moiety. In this way it was established that each nitro group forms a hydrogen bond. Furthermore, from consideration of the 1H n.m.r. chemical shifts of several dinitrophenyl haptens and their trinitrophenyl analogues, it was shown that there is no distortion of the o-nitro group on binding to the variable fragment of protein MOPC 315. (+info)