Enzyme activities and metabolites along the kynurenine pathway in mice with Harding-Passey melanoma.

Tryptophan metabolism has been studied in mice with Harding-Passey melanoma and in controls, after a load of 1.0 g/kg b.w. of L-tryptophan by determining ten urinary metabolites of the kynurenine pathway and some enzyme activities involved in the degradation of this aminoacid. Kynurenine was the only tryptophan derivative excreted in significantly higher quantities in mice with melanoma with respect to the controls. This result is in agreement with a significantly higher activity of hepatic tryptophan pyrrolase in mice with melanoma. Liver kynureninase and liver and kidney kynurenine aminotransferase activities were similar in the two groups of mice. These findings point to a possible role of tryptophan in the biogenesis of melanins in pathological conditions such as in melanoma.

Strain differences in the tryptophan metabolite excretion and enzyme activities along the kynurenine pathway in rats.

The strain differences of the urinary excretion of the tryptophan metabolites along the kynurenine pathway and the variations of enzyme activities metabolizing the tryptophan have been studied in different strains of rats. There is a good correlation between urinary excretory values of the metabolites and enzyme activities in the same strain of rats. However, some differences appear when the data are compared among different strains. Wistar, heterozygous Gunn and Sprague-Dawley rats show similar total urinary excretion of tryptophan metabolites, while the Long Evans rats have significantly lower values, in accordance with the lower activity of tryptophan pyrrolase. Kynureninase activity is slightly but not significantly higher in Sprague-Dawley rats, in agreement with the high levels of anthranilic acid excreted. As regards kynurenine aminotransferase, Sprague-Dawley rats show lower activity in the liver, but higher activity in the kidneys in comparison to other strains of Wistar, Long Evans and heterozygous Gunn rats. The importance of considering strain differences is emphasized when making comparisons of measurements carried out in different laboratories.

Metabolism and serum levels of tryptophan in senile cataract patients.

In order to clarify the role of tryptophan in the patogenesis of senile cataract, we have studied the serum total and free levels of tryptophan in cataract patients as compared with age and sex-matched controls, and the urinary excretion of 10 metabolites after oral load of the amino acid. This excretion increases in the cataract group both as total per cent and as kynurenine. No difference has been found in the free and total serum tryptophan between normal subjects and cataract patients. A possible role of the kynurenines in the pathogenesis of senile cataract is suggested.

Alterations of the tryptophan--nicotinic acid metabolism in vitiligo.

Tryptophan metabolism "via kynurenine" is altered in vitiligo: after a load of the amino acid the urinary excretion of 3-hydroxykynurenine and 3-hydroxyanthranilic acid is decreased, whereas that of xanthurenic acid and its 8-methyl ether is increased. The excretory values of the metabolites suggest a deficiency of the activity of kynurenine hydroxylase and kynunerinase, the enzymes involved in the metabolism of 3-hydroxykynurenine and 3-hydroxyanthranilic acid. The reduced excretion of 3-hydroxykynurenine, a tryptophan metabolite involved in melanin biosynthesis, may indicate a smaller utilization of tryptophan in the biogenesis of the melanins.

[Tryptophan metabolism in patients with vitiligo]. / Studi sul metabolismo del triptofano in pazienti con vitiligine.

Our previous research showed that tryptophan is an important precursor in the biogenesis of melanins. Therefore, with the purpose of observing whether a relationship exists between tryptophan metabolism and diseases characterized by an altered process of skin pigmentation in man, we studied the metabolism of this aminoacid along the kynurenine pathway in 29 vitiliginous patients (11 males and 18 females) and in 21 control subjects (11 males and 10 females) by determining 10 urinary metabolites after an oral loading of 50 mg/kg body weight L-tryptophan. The mean total excretion of the metabolites in patients resulted similar to that of the controls. However, considering the individual metabolites one can observe a decreased excretion of 3-hydroxykynurenine, o-aminohippuric acid and 3-hydroxyanthranilic acid and an increased excretion of xanthurenic acid and of its 8-methyl ether in the group of vitiliginous patients in respect to the controls. These results seem to indicate a decreased formation of nicotinic acid from tryptophan. Moreover, in relation to the fact that 3-hydroxykynurenine could be the metabolite through which tryptophan is involved in melanin biosynthesis, this study supports the hypothesis of a connection of tryptophan metabolism with the lack of pigmentation in vitiligo.

Effect of blue light on the urinary excretion of tryptophan metabolites in adult heterozygous and homozygous Gunn rats.

Tryptophan metabolism along the kynurenine pathway has been studied in male and female heterozygous and homozygous adult Gunn rats after load of amino acid before and after exposure to blue light. The percentage of tryptophan metabolites in each group of rats was slightly higher in females than in males. Before irradiation the excretion of metabolites was larger in male and female heterozygous groups than the corresponding groups of the homozygotes. After irradiation only the groups of male and female heterozygous Gunn rats showed a decrease in the total excretion of the metabolites. Therefore blue light exposure dose not seem to influence the metabolism of tryptophan in homozygous Gunn rats.

Enzyme activities of tryptophan metabolism in heterozygous and homozygous Gunn rats before and after blue light exposure.

The effect of light exposure in the enzyme activities, involved in the tryptophan metabolism along the kynurenine pathway, has been studied in male and female adult hetero-and homozygous Gunn rats. Light exposure did not seem to influence these enzyme activities. The groups of non-icteric heterozygotes however showed a higher activity of liver tryptophan pyrrolase than in the groups of icteric homozygotes. Kynureninase activity was similar in all the groups of rats, whereas liver kynurenine aminotransferase activity appeared slightly higher in the groups of male rats with respect to female rats, but no difference existed before and after irradiation. In addition the male heterozygotes showed a higher kynurenine aminotransferase activity in kidneys than the other groups of rats.

Effect of psoralen-induced photodermatitis on tryptophan metabolism in guinea pigs.

Tryptophan metabolism after load test, along the kynurenine pathway was studied in guinea pigs, before and during the psoralen-induced photodermatitis. This skin injury, during the acute phase, causes a large increase in urinary excretion of total metabolites and a significant increase of liver tryptophan pyrrolase.

Effect of psoralen-induced photodermatitis on tryptophan metabolism in rats.

Tryptophan metabolism 'via kynurenine' has been studied in rats before and after induction of experimental light-conditioned dermatitis with psoralen. Tryptophan load in animals during the acute phase of dermatitis (one day after induction) causes a markedly increased urinary excretion of total metabolites in comparison with that obtained before dermatitis. During this phase of the skin disease tryptophan pyrrolase activity is significantly increased and kynureninase activity significantly decreased in liver in respect to the control animals. Kynurenine aminotransferase activity shows no significant variations in both liver and kidneys. After 6 days of dermatitis, when the skin damage is in repair, both the excretory values of the urinary metabolites after L-tryptophan load and the enzymic activities are similar to those before dermatitis.

Total and free tryptophan levels in serum of newborn infants. Relationships with the Serotonin and nicotinic acid pathways.

The levels of total and free serum tryptophan have been determined in a group of newborn babies at birth, one day later and five days after birth. Total and free tryptophan levels are very high in the umbilical cord at birth, decrease quickly and significantly 24 hours after birth and show a slight, but not significant increase five days after birth. The high tryptophan levels at birth and their decrease in the first day after birth recall previous data on tryptophan metabolism "via" serotonin and "via" nicotinic acid. Since the synthesis of cerebral serotonin depends on the availability of tryptophan, and is thus linked to the level of free tryptophan in blood, these data suggest that synthesis of serotonin as well may be elevated at birth and may reach the values of adult soon afterwards. With respect to the nicotinic acid pathway the high levels of tryptophan in blood may be related to the synthesis of tryptophan pyrrolase, which is present in the liver of newborn babies.

Tryptophan metabolism in animals with dermatitis. I) In Rats.

Tryptophan metabolism "via kynurenine" after load of amino-acid has been studied in urine of rats before and after induction of experimental light-conditioned dermatitis with psoralen. Tryptophan load in animals during the acute phase of dermatitis (one day after induction) causes a markedly increased urinary excretion of total metabolites in comparison with that obtained before dermatitis. After six days of dermatitis, when the skin damage was in repair, the excretory values after tryptophan load in rats are only slightly increased indicating that the metabolic disturbance is correlated with the skin damage.

Tryptophan metabolism in animals with dermatitis. II) In guinea pigs.

Tryptophan load in guinea pigs after induction of a photodermatitis from psoralen caused marked increase of urinary excretion of total metabolites "via kynurenine" in comparison with that obtained before dermatitis. Xanthurenic acid is the metabolite which showed the most increased levels in urine during dermatitis. This dermatitis from furocoumarin caused an alteration of tryptophan metabolism in guinea pigs as well as rats, but species differences in the excretion of metabolites after amino acid load are observed.

Studies on the tryptophan load test in man.

Studies on the tryptophan load test were carried out by measuring the urinary excretion of 10 tryptophan metabolites via the kynurenine pathway in 25 healthy men and 20 women after oral L-tryptophan loading with dosages of 2 g. 50 mg/kg or 75 mg/kg body weight. With increasing doses of the amino acid, a difference was found between the male and female groups in the pattern of excretion of the tryptophan metabolites. In both groups, kynurenine and kynurenic acid were the metabolites excreted in the greatest amounts. The results indicate that the most useful loading dose of L-tryptophan for both men and women is 50 mg/kg body weight, as with 2 g L-tryptophan the excretion of the metabolites is too low and varies too much between the two groups of male and female subjects. On the other hand, the load with 75 mg/kg body weight can cause an overloading, particularly in women. No significant variations in the levels of the metabolites were found in the urine of two female subjects at different stages of the menstrual cycle after loading doses of 2 g and 50 mg/kg body weight. On the basis of the determination of the serum tryptophan levels, the period of urine collection was established as 10 h.