The spin-trapping of enzymatically and chemically catalyzed free radicals from indolic compounds

Effect of nitroethane and nitroethanol on the production of indole and 3-methylindole (skatole) from bacteria in swine feces by gas chromatography

Indole and 3-methylindole (skatole) are odor pollutants in livestock waste, and skatole is a major component of boar taint. Skatole causes pulmonary edema and emphysema in ruminants and causes damage to lung Clara cells in animals and humans. A gas chromatographic method that originally used a nitrogen-phosphorus detector to increase sensitivity was modified resulting in an improved flame ionization detection response for indole and skatole of 236% and 207%, respectively. The improved method eliminates the large amount of indole decomposition in the injector. A 10 micro g mL(-1) spike of indole and skatole in water and swine fecal slurries resulted in recovery of 78.5% and 96% in water and 76.1% and 85.8% in fecal slurries, respectively. The effect of the addition of nitroethane and nitroethanol at 21.8 mM in swine fecal slurries was studied on the microbial production of indole and skatole. Nitroethane and nitroethanol decreased the production of skatole in swine fecal slurries at 24 h. The nitroethane effect on l-tryptophan-supplemented fecal slurries after 6 and 24 h incubation resulted in a decrease of 69.0% (P = 0.02) and 23.5% skatole production, respectively, and a decrease of 14.9% indole at 6 h, but an increase in indole production of 81.1% at 24 h.

Effects of feeding aspirin and supplemental vitamin E on plasma concentrations of 3-methylindole, 3-methyleneindolenine-adduct concentrations in blood and pulmonary tissues, lung lesions, and growth performance in feedlot cattle

OBJECTIVE

To evaluate the effect of feeding aspirin and supplemental vitamin E on growth performance, lung lesions, plasma concentrations of 3-methylindole (3MI), and 3-methyleneindolenine (3MEIN)-adduct concentrations in blood and pulmonary tissues of feedlot cattle.

ANIMALS

256 crossbred steers; 64 cattle were used in experiment 1 and 192 cattle were used in experiment 2.

PROCEDURES

A 2 X 2 factorial design was used for each experiment. Treatment factors were aspirin (0 or 3 g daily) and vitamin E (200 or 1,500 IU daily). Steers were housed in pens (8 steers/pen). Steers were slaughtered on days 59 and 138 for experiments 1 and 2, respectively. Lungs were grossly evaluated. 3MEIN-adduct concentrations were determined, and blood and pulmonary tissues.

RESULTS

Treatment was not associated with improvement or adverse effects on weight gain, dry-matter intake, or feed efficiency in experiment 2. In experiment 1, 36 of 63 (57.1%) steers had lung lesions. Lesions were not associated with treatment or concentrations of 3MI and 3MEIN-adduct. Plasma 3MI concentration and concentrations of 3MEIN-adduct in blood and pulmonary tissues were 3.11 microg/mL, 0.51 U/microg of protein, and 0.49 U/microg of protein, respectively. Aspirin was associated with increased blood concentrations of 3MEIN-adduct for diets that did not contain supplemental vitamin E.

CONCLUSIONS AND CLINICAL RELEVANCE

Differences n performance of feedlot steers were not associated with treatment diet. It is possible that concurrent exposure of feedlot cattle to other factors typically associated with development of respiratory tract disease would affect these findings.

Sudden infant death syndrome: is it a transepithelial transport disorder?

The first limiting factor of dietary zinc deficiency has been described as a loss of the protective role of zinc against auto-oxidation of membrane sulfhydryl (SH) compounds. It has now been established that the prohormones (nutriuretic peptides) of the intestinal guanylin family are activated extracellularly by conversion of cysteines in the peptide to disulfide bridges. The induction of uroguanylin mRNA is elevated in intestinal zinc deficiency and nutriuretic peptides regulate epithelial transport of salt and water. Nitric oxide (NO) is also a modulator of salt and water transport. The constitutive forms of nitric oxide synthase (cNOS) in neurons and endothelial cells are calcium-dependent. The inducible form of nitric oxide synthase (iNOS) is activated by bacterial entero-toxins and damaged mucosa with NO penetrating the cell and acting directly on guanylate cyclase. The activated receptor-guanylate cyclases initiating the intracellular cycle 3'-5' guanasine monophosphate (cyclic GMP) cascade in target cells results in a flux of chloride and water into the intestinal lumen. Most of the actions of NO are mediated by activation of cyclic GMP. High-altitude pulmonary edema (HAPE) is associated with a defect in transepithelial water transport. It is suggested that dietary zinc, by modulating thiol oxidation to disulfides in guanylin prohormones to active hormones, is associated with salt and water secretion such that the overworked heart in hypoxemia increases the production and release of natriuretic peptides to activate guanylate cyclase receptors in target tissue in sudden infant death syndrome.

Effect of serotonergic blockade on calf pulmonary function after the intravenous administration of 3-methylindole

This study was designed to investigate whether 3-methylindole (3-Mi), a tryptamine analogue, could cause pulmonary injury in calves other than by cytotoxicity. Injection of 3-Mi resulted in a marked increase of respiratory rate, decrease of tidal volume and increase in minute ventilation. Pulmonary mechanics values were also profoundly affected, lung dynamic compliance being reduced to approximately one-third of its baseline value and total pulmonary resistance being increased two-fold. Arterial oxygen partial pressure was dramatically reduced. Successive challenges with 3-Mi after physiological saline pretreatment resulted in quantitatively identical alterations of pulmonary function values. Conversely, all these ventilatory, mechanical and gas exchange changes were abolished by pretreatment with serotonergic antagonists. It was concluded that intravenous administration of 3-Mi to healthy calves induced immediate and reversible bronchoconstriction which affected both central and peripheral airways. Because the effect was abolished by pretreatment with antiserotonin drugs, it is suggested that 3-Mi acts either directly by stimulating serotonergic receptors or indirectly through the release of serotonin from platelets. Current concepts of the physiopathological cascade underlying the toxicity of 3-Mi should, therefore, be re-evaluated in the light of this pharmacological mechanism.

Sudden infant death syndrome and superoxide/nitric oxide

In a sudden infant death syndrome review Valdès-Dapena describes Naeye's report of increased medial muscle mass in walls of small pulmonary arteries and increased weight of cardiac right ventricles. These findings point to cardiorespiratory insufficiency, a problem in fast growing chicks raised at high altitudes. The vascular epithelium lining all blood vessels synthesises nitric oxide which induces relaxation of smooth muscle in vessel walls, and is possibly an important neurotransmitter. Others demonstrate that nitric oxide is involved in regulating vessel calibre, blood pressure and blood flow, as well as falls in ventricular outputs. Superoxide interacts with nitric oxide and removes it from the circulation. Superoxide is thus a vasoconstrictor. Superoxide is produced by activated phagocytes and possibly lymphocytes and other cell types in the immune response. Elevated immunoglobulins in mucus secretions are a hallmark in sudden infant death syndrome and hypoxic chicks. Our approach therefore is that cardiorespiratory insufficiency may be induced by superoxide in small pulmonary arteries preventing nitric oxide from acting as a muscle relaxant in vascular walls.

The metabolic basis of 3-methylindole-induced pneumotoxicity

3-Methylindole (3MI), an abnormal metabolite of tryptophan, causes acute pulmonary edema and emphysema. 3MI toxicity is species-, tissue- and cell-specific and is an excellent model for understanding the processes of chemically-induced lung injury. Experimental evidence showed that 3MI is metabolically activated by both microsomal cytochrome P-450-dependent mixed function oxidase (MFO) and prostaglandin H synthase (PHS) systems in the lung. Formation of a free radical intermediate during 3MI metabolism is the initial chemical event which is responsible for the pneumotoxicity. 3MI free radicals bind covalently to microsomal protein and induce lipid peroxidation. Microsomal enzymes which regulate the glycogen and phospholipid biosynthesis in the lung are altered during the cellular repair processes after 3MI-induced lung injury. Inhibition of cellular differentiation from Type II to Type I cells and impaired surfactant function may be crucial to the disease process.

Spin trapping of lipid-derived radicals in liposomes

Electron-spin resonance-spin trapping has been used to detect lipid-derived radicals in liposomes. Using the lipid-soluble spin trap 2-methyl-nitrosopropane (MNP), we have detected both the lipid and hydrogen-atom spin adducts in liposomes composed of a fully saturated phospholipid (dimyristoylphosphatidylcholine, DMPC) with various mol fractions of unsaturated phospholipid (1-palmitoyl-2-arachidonoylphosphatidylcholine, PAPC) or fatty acid (arachidonic acid, AA). The lipid-derived spin adduct formed during autoxidation of liposomes was separated by thin-layer chromatography and found to co-migrate with the product(s) formed by direct addition of MNP to the corresponding unsaturated lipid or fatty acid. Both the MNP-PAPC and MNP-AA spin adducts showed some restriction of rotational motion when in the liposome bilayer (rotational correlation times 0.72 and 0.69.10(-9) s, respectively), and nitrogen hyperfine coupling constants (14.94-14.96 G) consistent with a hydrophobic localization. Radical versus non-radical mechanisms of spin adduct formation during liposome autoxidation were separated using alpha-tocopherol as a radical scavenger. The utility of nitroso spin traps in trapping of radicals in liposomes is discussed.

3-Methylindole-induced nasal mucosal damage in mice

3-Methylindole (3MI) damages nasal olfactory epithelium in mice. Lesions were studied histologically from 30 minutes to 28 days after intraperitoneal injection of 400 mg 3MI/kg. Cellular swelling was apparent in olfactory epithelium by 6 hours after injection of 3MI, while respiratory epithelium was normal. Necrosis of olfactory epithelium and subepithelial glands was diffuse by 48 hours. Subsequent ulceration resulted in epithelial hyperplasia, squamous metaplasia, fibroplasia, and ossification. Partially occlusive intranasal fibrous and osseous tissue persisted through 28 days after 3MI injection.

Decreased pneumotoxicity of deuterated 3-methylindole: bioactivation requires methyl C-H bond breakage

The bioactivation of the pulmonary toxin 3-methylindole has been postulated to proceed via the formation of an imine methide. To test this hypothesis, the toxicity in mice of 3-methylindole has been compared to the toxicity of its perdeuteromethyl analog. Deuteration of the methyl group should slow the rate of production of the corresponding imine methide and diminish the toxicity of deutero-3-methylindole, if C-H bond breakage occurs prior to or during the rate-determining step. In agreement with this hypothesis, deutero-3-methylindole was synthesized and was shown to be significantly less toxic (LD50 735 mg/kg) than 3-methylindole (LD50 578 mg/kg). Both compounds produced the same lesion at the LD50 dose, bronchiolar damage and mild alveolar edema, indicating that deuteration of 3-methylindole did not change the pathologic process. However, at a much lower dose (25 mg/kg), 3-methylindole produced a mild bronchiolar lesion whereas deutero-3-methylindole did not damage lung tissue. Additionally, administration of deutero-3-methylindole caused less pulmonary edema compared to 3-methylindole, as assessed by increased wet lung weights. Finally, the depletion of pulmonary glutathione by deutero-3-methylindole was considerably slower than depletion by 3-methylindole. The electrophilic imine methide has been postulated to be the intermediate which binds with and depletes glutathione. Therefore, the evidence presented here supports the involvement of an imine methide as the primary reactive intermediate in 3-methylindole-mediated pneumotoxicity.

Application of ESR spectroscopy in toxicology

Spin trapping in vivo was first achieved in the author's laboratory and is shown to be a feasible method for demonstrating that highly reactive free radical intermediates are generated in the tissues of intact animals as a result of the exposure to certain toxic compounds and to ionizing radiation. The method is based on the property of spin trapping agents (nitrones) to react readily with reactive free radicals to produce stable radical adducts at the site of their origin in target organs. The radical adducts can then be detected by electron spin resonance spectroscopy to determine the intensity of radical production (i.e., number of radicals which were trapped), and, in most cases, identify the nature of the radical that was produced. The type of spin trapping agent employed determines the type of radicals which can be trapped and, at this stage of development of the technique, the number of useful in vivo trapping agents is rather limited.

Spin trapping: ESR parameters of spin adducts

Spin trapping has become a valuable tool for the study of free radicals in biology and medicine. The electron spin resonance hyperfine splitting constants of spin adducts of interest in this area are tabulated. The entries also contain a brief comment on the source of the radical trapped.

Chemical modulation of 3-methylindole toxicosis in mice: effect on bronchiolar and olfactory mucosal injury

C57BL/6N mice were treated to induce tolerance, to modulate the mixed function oxidase system or to deplete glutathione (GSH) before injection with 400 mg 3-methylindole (3MI)/kg. Effect of pretreatment was determined by histologic comparison of pulmonary and nasal lesions 24 hours after 3MI. beta-Naphthoflavone and 3MI pretreatment significantly decreased 3MI-induced bronchiolar epithelial damage in male and female mice, while phenobarbital protection was significant only in female mice. Only beta-naphthoflavone decreased nasal olfactory epithelial damage. Pretreatment with piperonyl butoxide, SKF 525-A, or alpha-naphthoflavone had no significant effect on development of lesions. Diethylmaleate pretreatment significantly increased mortality and bronchiolar damage in both sexes. Significant differences between male and female mice were not detected in any group. The results suggest that pretreatment with low doses of 3MI or induction of cytochrome P-448 or P-450 protects against 3MI toxicosis while GSH depletion increases mortality and pulmonary lesions.

Transient radicals in heterogeneous systems: detection by spin trapping

The application of spin trapping to the detection of transient radicals generated in heterogeneous systems is discussed. The major part of this review focuses on the interaction of light with particles in dispersion and the resultant radicals which are produced. This includes photoactive pigments such as CdS, TiO2, ZnO and phthalocyanine in a variety of solvents as well as micelles, vesicles and microemulsions containing molecules such as phthalocyanine or chlorophyll. The utility of spin trapping in heterogeneous systems which are not a function of illumination (i.e. electrochemical reactions, catalysis and biological systems) is also discussed. It is demonstrated that reaction mechanisms can be better understood by the indirect detection of the radical intermediates which are involved in the various processes. This impacts studies in solar energy utilization, electrophotography, catalysis, electrochemistry, photosynthesis and the disease process.

Electrophilic metabolites of 3-methylindole as toxic intermediates in pulmonary oedema

[methyl-14C]-3-Methylindole (3MI) was incubated with goat-lung microsomes, an NADPH-generating system and glutathione. An adduct between an oxidative metabolite of 3MI and glutathione was formed only when the complete system was employed. The adduct, which was detected by u.v. absorbance and scintillation counting of h.p.l.c. fractions, was purified to homogeneity by reverse-phase h.p.l.c. The ability of 3MI to bind to microsomal protein was reduced to 52% and 46% of controls when 2 mM and 4 mM glutathione, respectively, were included in the incubations. These results suggest the involvement of an electrophilic metabolite as the toxic intermediate in 3MI-mediated pulmonary oedema.