The correlation between certain tryptophan metabolites and the N-nitrosamine content in the urine of bilharzial bladder cancer patients.

The present work is an up-to-date approach to study the correlation between the excretion pattern of tryptophan metabolites along the kynurenine pathway (after loading with 2 gm. L-tryptophan), and the N-nitrosamine content in urine of bilharzial bladder cancer patients. The control group was composed of healthy subjects who had no reported history of S. haematobium infection and no current bacterial cystitis. The N-nitrosamine content was determined by the colorimetric method of Eisebrand and Preussmann (1970). It was demonstrated that 64 per cent of the patients metabolized the tryptophan load abnormally and the others metabolized it almost normally. Moreover, the N-nitrosamines were present in 43 per cent of controls and 93 per cent of patients have these derivatives in higher values. The presence of an inverse correlation between certain tryptophan metabolites, shown previously to be bladder carcinogens, and the N-nitrosamine content, especially after loading, was interpreted in view of the possible conversion of some tryptophan metabolites into N-nitrosamines either under endovesical conditions or during the execution of the colorimetric determination of these compounds. Therefore, thorough investigation is urgently needed to study the origin of these urinary N-nitrosamines. Moreover, improved method(s) for their colorimetric determination are also urgently needed.

Effect of some xenobiotics on kynurenine hydrolase and kynurenine aminotransferase of mouse liver.

The effects of some xenobiotics on the activity of the B6-dependent kynurenine hydrolase (KH) and kynurenine aminotransferase (KATE) in mouse liver, were investigated. Polychlorinated biphenyl (Aroclor 1254) (400mg/kg/day x4) markedly decreased the activity of both enzymes. Benzo(a)pyrene (BP) and 3-methylcholanthrene (3-MC) (40mg/Kg/day x1) as well as phenobarbital (PB) (75mg/kg/day x3) did not alter the activity of KH, while that of KATE was mildy reduced. The response of the two enzymes to treatment with chlorpromazine (CPZ) (5mg/Kg/day x5) were opposite with marked elevation of KH and inhibition of KATE activities. Treatment with B-naphthoflavone (B-NF) (80mg/Kg/day x2), Pyrazole (200mg/Kg/day x1) or indole (400mg/kg/day x1) produce no change in the activity of either enzyme. It, seems therefore, that Aroclor (1254) and chlorpromazine may cause disordered kynurenine metabolism through alterations in the activities of its metabolizing enzymes. This, in turn, might affect nicotinamide adenine dinucleotide biosynthesis and/or the accumulation of some tryptophan metabolites suspected of being carcinogenic or co-carcinogenic.

Studies on the effectiveness of liver and bacterial beta-glucuronidase enzymes in the hydrolysis of urinary beta-glucosiduronides of some tryptophan metabolites.

The effectiveness of Escherichia coli and bovine liver beta-glucuronidases in the hydrolysis of the urinary beta-glucosiduronides of tryptophan metabolites was studied. Moreover, the effect of the prolonged contact of these conjugates to the urinary enzyme was investigated in the first and second voiding urine samples. It is found that both enzymes have no important role in releasing the free carcinogens from their glucosiduronides. The presence of free carcinogens could be attributed to the spontaneous hydrolysis of some labile conjugates. However, the prolonged contact of the freely active substances during the sleeping hours with the epithelium of the bladder may enhance the process of bladder carcinogenicity. The increased accumulation of these metabolites in the first voiding urine could be interpreted in terms of their rate of excretion rather than by the enzymatic hydrolysis of their conjugates.

Functional capacity of the tryptophan-niacin pathway in the premenarchial phase and in the menopausal age.

Studies on the interrelationship between female hormones associated with reproduction and the vitamin B6-dependent enzymes along the kynurenin pathway of trytophan metabolism were carried out in girls with an age less, and more than 10 years (just before the onset of the first menstrual cycle), and in postmenapausal women with and without relative (excess) production of estradioll from the adrenal cortex. It is found that most of the determined metabolites are retained by the girls with age less than 10 years after tryptophan loading without and with vitamin B6 supplementation. Estradiol from either the ovaries (in girls just before menarch), or the adrenal cortex-in postmenopausal women with relative (excess) production of this hormone-interferes with the further degradation of 3-hydroxyanthranilic acid. However, this interference could be completely restored by vitamin B6 supplementation. The extra presence of a partial impairment in the kynureninase enzyme is also suggested in these postmenopausal women. In the latter case, this enzymatic activity could be partially resored by vitamin B6 supplementation. On the contrary, the enzymes: kynureninases and adrenocortical estradio. Pyridoxine supplementation partially corrected the inhibition especially that of 3-hydroxykynurenine transaminase enzyme.

Studies on the effectiveness of mammalian and bacterial beta-glucuronidase enzymes in the hydrolysis of urinary beta-glucosiduronides of some tryptophan metabolites excreted in urine.

The effectiveness of E. coli and bovine liver beta-glucuronidases in the hydrolysis of the urinary beta-glucosiduronides of tryptophan metabolites was studied. Some of these metabolites demonstrate carcinogenic activity in the mouse bladder. Moreover, the effect of the prolonged contact of these conjugates to the urinary enzyme was investigated in the first and second voiding urine samples. The former urine was that retained in the bladder during sleep (about 8 hours) and the latter was collected 3 hours after the first. It is found that both enzymes have no important role in releasing the free carcinogens from their glucosiduronides. The presence of free carcinogens could be attributed to the spontaneous hydrolysis of some labile conjugates. However, the prolonged contact of the freely active substances during the sleeping hours with the epithelium of the bladder may enhance the process of bladder carcinogenicity. The increased accumulation of these metabolites in the first voiding urine could be interpreted in terms of their rate of excretion rather than by the enzymatic hydrolysis of their conjugates.

The influence of sex, age, synthetic oestrogens, progestogens and oral contraceptives on the excretion of urinary tryptophan metabolites.

PIP: The excretion of urinary tryptophan metabolites was studied in normal and postmenopausal women and in women taking norethindrone and ethinyl estradiol, singly and in combination. The results showed that the altered tryptophan metabolism found in the preovulatory phase of the cycle and in postmenopausal women was the result of an interaction between Vitamin-B6 and endogenous sex hormones. During the preovulatory phase, endogenous estradiol disrupted the normal activity of the Vitamin-B6-dependent quinolinic acid decarboxylase, which resulted in the accumulation of bladder carcinogens in urine. During the postovulatory phase, endogenous progesterone and the production of metabolites antagonized this effect. Administration of naturally occurring progesterone and of ethinyl estradiol, alone and in combination with norethindrone, was able to counter the interaction between Vitamin-B6 and endogenous estradiol. It is suggested that the cyclic excretion pattern of endogenous bladder carcinogens in young, nonpregnant women may contribute, in part, to the low incidence of bladder cancer in women.^ieng

Studies with tryptophan metabolites in vitro. Kynurenine metabolism in kidneys of mice infested with Schistosoma mansoni.

The conversion in vitro of kynurenine into kynurenic acid and anthranilic acid in both normal kidneys and those obtained from mice infested with Schistosoma mansoni was investigated. Normal mouse kidneys seem to possess an excess of functional pyridoxal phosphate over those obtained from infested mice. Kynureninase and kynurenine transaminase in the latter kidneys are more easily inhibited by deoxypyridoxal phosphate and tartar emetic, indicating low stores of active pyridoxal phosphate. The possible implication of these findings in relation to the role of the kidneys in producing abnormal patterns of tryptophan metabolism and possibly contributing to the production of bladder tumours in bilharzial patients is discussed.