Liver Tryptophan Oxygenase Activity Research Articles

ROUGH AND ROCKY ROAD TO THE RETINOID REVOLUTION

Some of us who were born in the middle of Europe between World Wars I and II had to face quite a few unusual challenges that we all met in different ways. I was born and raised in Prague, Czechoslovakia, a country at the time of my birth that was governed by a Western style of democracy, which was later destroyed by the occupation by Nazi Germany and subsequently by the takeover by the equally cruel Communists. Life required special means of adaptation to the changing living conditions and a great deal of luck to survive. After graduating from the School of Technology, I started working in the Department of Medicine at Charles University in Prague as a clinical chemist in endocrinology. This work was followed with training in basic biochemistry and the study of metabolic changes in stress. This rather diversified research, due to my changing of workplaces, led to the findings that diet can change enzymatic activity of liver tryptophan oxygenase. For a short time I worked on the metabolism of cyclic AMP in Escherichia coli, and at the age of 41, I made a risky move and succeeded in escaping with my family from the "paradise of communism." The reasons for this decision will become clear. After settling in the United States, I worked on the mechanism of activation of liver tryptophan oxygenase by cyclic AMP and eventually moved to the Vanderbilt University School of Medicine. There I initially worked on the mechanism of action of steroid hormones and finally on the molecular mechanism of action of retinoids, retinol, and retinoic acid. Also in cooperation with neonatologists, I initiated studies on prematurely born human neonates which led to successful supplementation of these patients with vitamin A. The work from my laboratory and my coworkers eventually became recognized.

Involvement of Protein Synthesis in the Action of Glucocorticoids on the Working Capacity of Adrenalectomized Rats

The administration of cortisol for 3 or 5 days increased the maximal duration of swimming under additional load, equal to 3% of body weight, in adrenalectomized but not in intact Wistar rats. The liver tryptophan oxygenase activity also increased. The blockade of RNA synthesis by actinomycin D excluded both results of cortisol administration. High doses of progesterone (25 or 75 mg/day) decreased the working capacity, rendering the action of cortisol on the working capacity of adrenalectomized rats insignificant. However, the antagonism between two hormones was not striking at the level of liver tryptophan oxygenase induction. The results suggest that the action of glucocorticoids on the working capacity is mediated by RNA and, further, by protein synthesis. The competition for glucocorticoid cytoplasmic receptors, to be found between glucocorticoids and a high level of progesterone, can disturb this mechanism. The synthesis of hepatic enzyme proteins is not responsible for the action of glucocorticoids on the working capacity.

Ethanol-induced increase in liver tryptophan oxygenase activity in the starved rat: Evidence against tryptophan mediation

A single oral dose of ethanol (4.0 g/kg) increased the activity of liver tryptophan oxygenase in starved male rats. The peak increase of 340% for the total activity and 400% for the holoenzyme activity occurred 6 hr after ethanol administration. At or after these peaks, the levels of tryptophan in plasma and brain but not in liver, decreased significantly. Plasma total tryptophan and brain tryptophan started to decrease significantly as early as 0.5–1.0 hr after the ethanol treatment, while the activity of liver tryptophan oxygenase was still at the control level. These findings suggest that not all the changes in tissue tryptophan concentrations seen after acute ethanol treatment are caused by increased liver tryptophan oxygenase activity. Prior to the increase in liver tryptophan oxygenase activity, an increase of 104 and 50% in plasma corticosterone and free tryptophan, respectively, were seen 15 min after ethanol treatment. However, the increase in liver tryptophan at this time appeared to be small (13%) and statistically insignificant. With tryptophan treatment, the initial peak levels of liver tryptophan and plasma free tryptophan required to stimulate an increase in tryptophan oxygenase activity were 170 times higher than those caused by ethanol. It was therefore concluded that increases in plasma and liver tryptophan after acute ethanol ingestion, probably mediated by the lipolytic action of ethanol, are too small to cause the increase in liver tryptophan oxygenase activity seen after ethanol administration. However, experiments with different corticosterone doses showed that ethanol-induced increases in plasma corticosterone concentrations are high enough to cause an increase in liver tryptophan oxygenase activity.

Effect of propranolol and cycloheximide on the ethanol-induced increase in liver tryptophan oxygenase activity in starved rats

Increased supply of trytophan to the liver, resulting from the lipolytic action of ethanol, is suggested to be responsible for the increased activity of liver tryptophan oxygenase after ingestion of a single large dose of ethanol. This hypothesis was tested using an antilipolytic drug, propranolol, prior to ethanol treatment. It was found that, while propronolol did inhibit the ethanol-induced increase in blood unesterified fatty acids and free tryptophan concentrations it did not prevent the activation of tryptophan oxygenase by ethanol. In another experiment, where cycloheximide was used to block protein synthesis, it was found that increased protein synthesis rather than decreased protein degradation is probably responsible for the accumulation of liver tryptophan oxygenase after ethanol ingestion.

Effects of pyrazole on rat liver tryptophan oxygenase

The effects of pyrazole administration on rat liver tryptophan oxygenase have been studied both under basal conditions and after induction by cortisol or activation by tryptophan. Pyrazole administration is followed by a decrease of the basal holoenzyme and total enzyme activities. It induces furthermore a considerable inhibition of the cortisol mediated tryptophan oxygenase induction. These effects are not mediated by a modification of a tryptophan oxygenase effector, as shown by mixed homogenate experiments. The tryptophan enhancement of total tryptophan oxygenase activity is not affected by pyrazole administration contrary to the holoenzyme activity. Pyrazole added in vitro inhibits liver tryptophan oxygenase activity only when used at concentrations which are considerably higher that those occuring in vivo after pyrazole administration.

Experimental biharzial bladder cancer: tryptophan metabolism in nonhuman primates experimentally infected with Schistosoma haematobium.

A nonhuman primate species infected with Schistosoma haematobium provided a model system for controlled studies on biharzial bladder cancer. Urinary excretion of tryptophan metabolites by capuchin monkeys (Cebus apella) was similar to that of humans when expressed per g creatinine. Liver tryptophan oxygenase activity of the capuchin monkeys was comparable to that of humans. Excretion of 3-hydroxykynurenine and 3-hydroxyanthranilic acid was elevated above control levels in capuchin monkeys infected experimentally with S. haematobium. The capuchin-S. haematobium system closely resembles the human biharziasis system and offers a reproducible laboratory model system for the controlled study of the parasitology, pathogenesis, and biochemistry of biharzial bladder cancer.

The effect of ethyl alcohol on rat liver tryptophan oxygenase

The activity of liver tryptophan oxygenase was determined in rats administered intoxicating dose of ethanol. Following intraperitoneal injection of ethanol there was a rise in the enzyme activity reaching levels considerably above those of the control animals. Maximum enzyme activity was reached 5 hours after ethanol administration and then returned to within control levels in about 9 hours. It is suggested that the observed increase in tryptophan oxygenase in the liver may be the result of increased plasma adrenocortical hormone level following ethanol intoxication, or may be secondary to the induction of ALA (delta-aminolevulinic acid) synthetase and consequent enhanced heme production.

The induction of host tryptophan oxygenase by staphylococcal infection. 1.

SummaryInfection of mice with Staphylococcus aureus leads to increased activity of liver tryptophan oxygenase, probably in an increased corticosteroid response associated with the infection. Nicotinamide was found to be effective in prolonging the survival of infected mice if given between 3 hr prior to and 1 hr after infection. None of the other tryptophan metabolites were effective against the challenge with staphylococci. Nicotinamide, as well as other chemicals which prolong the survival of infected mice can induce tryptophan oxygenase in the presence or absence of infection, but the studies reported here would seem to indicate that the mechanisms of protection do not involve changes in the activity of the enzyme.

Expression of total enzyme activity by means of thermal activation of hepatic tryptophan oxygenase

Procedures for the activation and determination of rat liver tryptophan oxygenase activity are described. The assay procedure combines simplicity and reproducibility, contains no lag phase, is linear with time and amount of enzyme, and permits the expression of the total amount of tryptophan oxygenase present in the hepatic cytosol.

Relationship between urinary excretion of kynurenine and liver tryptophan oxygenase activity

Relationship between urinary excretion of kynurenine and liver tryptophan oxygenase activity

Chlorpromazine inhibition of tryptophan oxygenase

The effect of chlorpromazine on the activity of liver tryptophan oxygenase was examined in rat liver homogenates and in perfused rat livers. Chlorpromazine was found to inhibit the enzyme in the assay system (50 per cent inhibition at 3 · 10 −4M). The tryptophan oxygenase activity in perfused livers, however, was not decreased by perfusing with 10 −4M chlorpromazine for 3 hr. A slight decrease was found in livers perfused with 4·10 −4M for 3 hr. Chlorpromazine did not interfere with the steroid induction of the enzyme. This indicates that the effect of dexamethasone on protein synthesis in the liver does not depend on any of the membrane functions which are influenced by the membrane stabilizing effect of chlorpromazine.

Role of liver tryptophan oxygenase activity in mice on outcome of endotoxin poisoning

Injection of cortisone into mice simultaneously with typhoid endotoxin prevents the decrease in tryptophan oxygenase activity in the liver and prevents death of the animals. Tryptophan also maintained a normal level of activity of the enzyme but did not prevent death of the animals poisoned with endotoxin. The role of the level of tryptophan oxygenase activity in the pathogenesis of poisoning produced by endotoxin is discussed.

Inhibition of tryptophan oxygenase in rat liver by steroid hormones.

Pregnant women and normal humans treated with estrogens show evidence of increased conversion of L-tryptophan into nicotinic acid ribonucleotide. Increased activity of liver tryptophan oxygenase caused by the action of estrogens or elevated corticosteroid concentration is thought to be the cause. Progesterone caused a decrease in tryptophan oxygenase activity when given alone or in combination with estradiol. In vitro in supernatant fractions prepared from rat livers progesterone and deoxycortiscosterone produced inhibition of enzyme activity. The synthetic estrogen ethinyl estradiol also produced this inhibition but mestranol did not. The 11beta-hydroxylated steroids cortisol corticosterone and fluoxymesterone did not inhibit tryptophan oxygenase despite their structural similarity to progesterone. Other steroids with different structures were considered unimportant with respect to inhibition of tryptophan oxygenase. Increased concentration of hematin in the assay system reversed the enzyme inhibition by progesterone. The inhibitory mechanism may involve the heme cofactor of the enzyme.