Tryptophan metabolism during infectious illness in man

Reprogramming of Amino Acid Metabolism Differs between Community-Acquired Pneumonia and Infection-Associated Exacerbation of Chronic Obstructive Pulmonary Disease

Amino acids and their metabolites are key regulators of immune responses, and plasma levels may change profoundly during acute disease states. Using targeted metabolomics, we evaluated concentration changes in plasma amino acids and related metabolites in community-acquired pneumonia (CAP, n = 29; compared against healthy controls, n = 33) from presentation to hospital through convalescence. We further aimed to identify biomarkers for acute CAP vs. the clinically potentially similar infection-triggered COPD exacerbation (n = 13). Amino acid metabolism was globally dysregulated in both CAP and COPD. Levels of most amino acids were markedly depressed in acute CAP, and total amino acid concentrations on admission were an accurate biomarker for the differentiation from COPD (AUC = 0.93), as were reduced asparagine and threonine levels (both AUC = 0.92). Reduced tryptophan and histidine levels constituted the most accurate biomarkers for acute CAP vs. controls (AUC = 0.96, 0.94). Only kynurenine, symmetric dimethyl arginine, and phenylalanine levels were increased in acute CAP, and the kynurenine/tryptophan ratio correlated best with clinical recovery and resolution of inflammation. Several amino acids did not reach normal levels by the 6-week follow-up. Glutamate levels were reduced on admission but rose during convalescence to 1.7-fold above levels measured in healthy control. Our data suggest that dysregulated amino acid metabolism in CAP partially persists through clinical recovery and that amino acid metabolism constitutes a source of promising biomarkers for CAP. In particular, total amino acids, asparagine, and threonine may constitute plasma biomarker candidates for the differentiation between CAP and infection-triggered COPD exacerbation and, perhaps, the detection of pneumonia in COPD.

Aflatoxin B1 alters central and systemic tryptophan and tyrosine metabolism: influence of immunomodulatory drugs

Semi-chronic exposure of ICR male Mice to Aflatoxin B1 (AFB1) in non-toxic doses results in elevated lung tryptophan (TRP) levels without change in serotonin (5-HT) or 5-hydroxyindole-3-acetic acid (5-HIAA) levels. This change is organ specific in that TRP levels are not altered in spleen, duodenum, heart or central nervous system (CNS). Acute (48 hour) flunixin treatment decreases lung TRP levels and reverses the AFB1 mediated increase in lung TRP levels. On the other hand, flunixin treatment decreases CNS TRP levels in control mice but not in AFB1 treated mice. Aflatoxin B1 treated mice have an increase in splenic serotonin (5-HT) content. Acute (48 hour) treatment of mice with E. coli lipopolysaccharide (LPS) also increases splenic 5-HT, and AFB1 treatment followed by LPS have a slightly additive effect on spleen 5-HT content. Treatment of mice with LPS increases heart 5-HT, an effect which is not altered in AFB1 pretreated mice. Both LPS and AFB1 per se increases lung TYR levels although the combination of treatments is not significantly different from the control value. Flunixin treatment increases lung tyrosine (TYR) levels, an effect which is not altered by AFB1 pretreatment. Acute treatment with either LPS or flunixin decreases the CNS TRP/TYR ratio; pretreatment with AFB1 prevents those changes in the CNS TRP/TYR ratio. Central nervous system catecholamines are reduced in AFB1 pretreated mice. However, CNS catecholamine changes in AFB1 treated mice are normalized by vitamin E supplementation during the treatment period.

Systemic endotoxin increases L-tryptophan, 5-hydroxyindoleacetic acid, 3-hydroxykynurenine and quinolinic acid content of mouse cerebral cortex

Systemic infections and injection of endotoxin are known to increase L-tryptophan release from skeletal muscle and increase systemic L-tryptophan catabolism through the kynurenine pathway. To investigate the effects of systemically administered endotoxin on brain L-tryptophan metabolites. C57BL6/6NCR mice were given an intraperitoneal injection of 10 micrograms of lipopolysaccharide from Salmonella abortus equii and samples of serum and cerebral cortex collected. After 9 h, serum L-tryptophan concentration was decreased by 51%. At 9 h and 24 h, increases in L-tryptophan metabolites in cerebral cortex were: L-tryptophan, 42% and 39%; 5-hydroxyindoleacetic acid, 38% and 67%; 3-hydroxykynurenine, 235% and 381%; and quinolinic acid, 76% and 306%. Cortical quinolinic acid concentration was still elevated at 48 h (88%) and 72 h (79%) after lipopolysaccharide. No significant changes in cortical serotonin concentrations were found at the time points examined. When L-tryptophan (0.37 mmol/kg) was administered systemically to either normal or lipopolysaccharide-treated mice, increases in cortical L-tryptophan, serotonin, 5-hydroxyindoleacetic acid and 3-hydroxykynurenine concentrations were largest in mice treated with both lipopolysaccharide and L-tryptophan. These results suggest that disturbances in L-tryptophan metabolism that follow systemic endotoxin administration extend to the central nervous system. The consequences of these changes in L-tryptophan metabolites remain to be determined.

Systemic lipopolysaccharide and pokeweed mitogen increase quinolinic acid content of mouse cerebral cortex

The effects of lipopolysaccharide and pokeweed mitogen on brain L-tryptophan and quinolinic acid (QUIN) concentrations were investigated in C57BL/6NCR mice. Twenty-four hours after an intraperitoneal injection of lipopolysaccharide (5 micrograms from Salmonella abortus equii) or pokeweed mitogen (500 micrograms), cortical QUIN concentrations were increased by 81 +/- 6% and 182 +/- 15%, respectively. Plasma QUIN was increased 175 +/- 7% of control in pokeweed-mitogen treated mice only. Brain L-tryptophan concentrations were increased, whereas plasma L-tryptophan concentrations were decreased. The consequences of increased QUIN concentrations during endotoxin and mitogen exposure remain to be determined.

Distribution and metabolism of 14C-tryptophan in normal and endotoxin-poisoned mice

dl-Tryptophan (benzene ring-(14)C) and its metabolites persist longer and in greater quantity in tissues of endotoxin-poisoned mice than in tissues of normal mice. Correspondingly less label is excreted in urine and feces and expired as (14)CO(2) in the poisoned animals. The distribution of label (1.1 x 10(6) dpm per microgram of tryptophan) was relatively constant whether it was administered alone or in combination with 20 mg of unlabeled l-tryptophan. Tryptophan must be metabolized through the tryptophan oxygenase pathway to be converted to carbon dioxide, but attempts to quantitatively correlate depressed tryptophan oxygenase activity with depressed carbon dioxide production were unsuccessful. It appears that neither tryptophan oxygenase nor substrate availability exclusively determine the quantity of tryptophan converted to (14)CO(2) except under highly selected conditions. The validity of an earlier suggestion that expired (14)CO(2) could be used to monitor in vivo tryptophan oxygenase activity is not supported by our data.

Nitrogen metabolism and protein synthesis during pneumococcal sepsis in rats

Markedly increased synthesis of alpha(2) and beta globulins and alpha(1), alpha(2), and beta glycoglobulins occurs during pneumococcal sepsis in the rat simultaneously with decreased albumin formation, diminished tritiated leucine incorporation into muscle protein, and enhanced excretion of nitrogen. This augmented synthesis of specific serum proteins does not become evident until fever and bacteremia develop, and it appears to be a fundamental aspect of host response to a proliferating bacterial infection in that it occurs even in rats fed a protein-deficient (6% protein) diet after weaning and before exposure to Diplococcus pneumoniae. Although amino acid catabolism, in general, appears to be increased during infection, tryptophan degradation via the kynurenine pathway, as assessed by measuring diazotizable urinary metabolites, changes little or is, at times, significantly less than in control animals. Coincidentally, functional tryptophan oxygenase activity decreases at 16 hr after exposure. Total tryptophan oxygenase activity, however, is unchanged.

Effect of Newcastle disease on serum copper, zinc, cholesterol, and carotenoid values in the chick

Experimentally induced Newcastle disease virus infection of chicks, with a mortality index of 48%, was accompanied by increased concentrations in serum of copper and cholesterol and decreased concentrations of zinc and total carotenoids. These changes distorted, or were superimposed upon, the rhythmic variability in the normal serum concentrations of each of these moieties. Changing values for copper, zinc, and cholesterol became apparent before any overt signs of disease.

Enzyme activities of the livers of mice infected with Salmonella typhimurium

The activities of the mouse liver enzymes tryptophan oxygenase, tyrosine aminotransferase, and pyruvate kinase were measured after infection with three dose levels of Salmonella typhimurium strain SR-11. Infection occurred in all groups as evidenced by an increase in bacterial numbers and by death of the animals. The activities of the enzymes increased in all groups during the course of the infection. The results obtained during infection are compared with those obtained after endotoxin injection.