Metabolomic transition trajectory and potential mechanisms of N-nitrosomethylbenzylamine induced esophageal squamous cell carcinoma in rats.

Esophageal squamous cell carcinoma (ESCC) is an environment-relevant malignancy with a high mortality. Nitrosamines, a class of nitrogen-containing environmental carcinogens, are widely suggested as a risk factor for ESCC. However, how nitrosamines affect metabolic regulation to promote ESCC tumorigenesis is largely unknown. In this study, the transition trajectory of serum metabolism in the course of ESCC induced by N-nitrosomethylbenzylamine (NMBA) in rats was depicted by an untargeted metabolomic analysis, and the potential molecular mechanisms were revealed. The results showed that the metabolic alteration in rats was slight at the basal cell hyperplasia (BCH) stage, while it became apparent when the esophageal lesion developed into dysplasia (DYS) or more serious conditions. Moreover, serum metabolism of severe dysplasia (S-DYS) showed more similar characteristics to that of carcinoma in situ (CIS) and invasive cancer (IC). Aberrant nicotinate (NA) and nicotinamide (NAM) metabolism, tryptophan (TRP) metabolism, and sphingolipid metabolism could be the key players favoring the malignant transformation of esophageal epithelium induced by NMBA. More particularly, NA and NAM metabolism in the precancerous stages and TRP metabolism in the cancerous stages were demonstrated to replenish NAD+ in different patterns. Furthermore, both the IDO1-KYN-AHR axis mediated by TRP metabolism and the SPHK1-S1P-S1PR1 axis by sphingolipid metabolism provided an impetus to create the pro-inflammatory yet immune-suppressive microenvironment to facilitate the esophageal tumorigenesis and progression. Together, these suggested that NMBA exerted its carcinogenicity via more than one pathway, which may act together to produce combination effects. Targeting these pathways may open up the possibility to attenuate NMBA-induced esophageal carcinogenesis. However, the interconnection between different metabolic pathways needs to be specified further. And the integrative and multi-level systematic research will be conducive to fully understanding the mechanisms of NMBA-induced ESCC.

Anti-Leukemic Properties of Aplysinopsin Derivative EE-84 Alone and Combined to BH3 Mimetic A-1210477.

Aplysinopsins are a class of marine indole alkaloids that exhibit a wide range of biological activities. Although both the indole and N-benzyl moieties of aplysinopsins are known to possess antiproliferative activity against cancer cells, their mechanism of action remains unclear. Through in vitro and in vivo proliferation and viability screening of newly synthesized aplysinopsin analogs on myelogenous leukemia cell lines and zebrafish toxicity tests, as well as analysis of differential toxicity in noncancerous RPMI 1788 cells and PBMCs, we identified EE-84 as a promising novel drug candidate against chronic myeloid leukemia. This indole derivative demonstrated drug-likeness in agreement with Lipinski's rule of five. Furthermore, EE-84 induced a senescent-like phenotype in K562 cells in line with its cytostatic effect. EE-84-treated K562 cells underwent morphological changes in line with mitochondrial dysfunction concomitant with autophagy and ER stress induction. Finally, we demonstrated the synergistic cytotoxic effect of EE-84 with a BH3 mimetic, the Mcl-1 inhibitor A-1210477, against imatinib-sensitive and resistant K562 cells, highlighting the inhibition of antiapoptotic Bcl-2 proteins as a promising novel senolytic approach against chronic myeloid leukemia.

Mitigation of Oxidation in Therapeutic Antibody Formulations: a Biochemical Efficacy and Safety Evaluation of N-Acetyl-Tryptophan and L-Methionine.

PURPOSE: Biotherapeutics can be susceptible to oxidation during manufacturing and storage. Free L-methionine is known to protect methionine residues in proteins from oxidation. Similarly, free tryptophan and other indole derivatives have been shown to protect tryptophan residues from oxidation. N-acetyl-DL-tryptophan was previously identified as a potentially superior antioxidant to tryptophan as it has a lower oxidation potential and produces less peroxide upon light exposure. This study sought to confirm the antioxidant efficacy and safety of N-acetyl-DL-tryptophan and L-methionine as formulation components for biotherapeutic drugs. METHODS: Antibodies were subjected to AAPH and light exposure in the presence of N-acetyl-DL-tryptophan and L-methionine. Oxidation in relevant CDR and Fc residues was quantified by peptide map. In silico, in vitro, and in vivo studies were performed to evaluate the safety of N-acetyl-DL-tryptophan and L-methionine. RESULTS: Peptide mapping demonstrated that N-acetyl-DL-tryptophan was effective at protecting tryptophans from AAPH stress, and that the combination of N-acetyl-DL-tryptophan and L-methionine protected both tryptophan and methionine from AAPH stress. The safety assessment suggested an acceptable safety profile for both excipients. CONCLUSIONS: N-acetyl-tryptophan and L-methionine effectively reduce the oxidation of susceptible tryptophan and methionine residues in antibodies and are safe for use in parenteral biotherapeutic formulations.

Toxicity and cardiac effects of acute exposure to tryptophan metabolites on the kynurenine pathway in early developing zebrafish (Danio rerio) embryos.

Defects in tryptophan metabolism on the l-kynurenine pathway (KP) are implicated in a number of human diseases, including chronic kidney disease, brain edema or injury, tuberculosis and malaria - as well as cancer, neurodegenerative and autoimmune disorders. However, it is unclear to what extent detrimental effects of exposure to tryptophan metabolites might impact the early development of organism. Thus, this study examined the effects of KP exposure in zebrafish embryos starting at the blastula period (4hpf) and the segmentation stage (24hpf). 24-hour EC50 and LC50 values were determined in 4hpf embryos as: 26.74 and 331.6µM for anthranilic acid (AA), 62.88 and 616.4µM for quinolinic acid (QUIN), and EC50 - 96.10µM for picolinic acid (PA) and LC50 - 400µM in kynurenic acid (KYNA). In addition, treatment with nanomolar concentrations of KYNA (50nM, 48 and 72hpf embryos) caused a dose-dependent increase in heartbeat. The increase was also seen with l-kyn treatment (50µM, 72hpf), which was the opposite of other applied l-kyn metabolites. A significant drop in heartbeat was observed after a 20-min acute exposure to 626µM PA, 594µM XA and 499µM QUIN, and complete recovery was seen only when PA had been removed. Concentrations of KP metabolites reached in people with different pathological conditions did not exert toxicity to zebrafish embryos and seems to be safe for developing embryos and therefore, the risk of developing impairments in pregnancy of women carrying KP-associated pathologies is initially low.

Inhibition studies of DNA methyltransferases by maleimide derivatives of RG108 as non-nucleoside inhibitors.

AIM: DNA methyltransferases (DNMTs) are important drug targets for epigenetic therapy of cancer. Nowadays, non-nucleoside DNMT inhibitors are in development to address high toxicity of nucleoside analogs. However, these compounds still have low activity in cancer cells and mode of action of these compounds remains unclear. MATERIALS & METHODS: In this work, we studied maleimide derivatives of RG108 by biochemical, structural and computational approaches to highlight their inhibition mechanism on DNMTs. RESULTS: Findings demonstrated a correlation between cytotoxicity on mesothelioma cells of these compounds and their inhibitory potency against DNMTs. Noncovalent and covalent docking studies, supported by crystallographic (apo structure of M.HhaI) and differential scanning fluorimetry assays, provided detailed insights into their mode of action and revealed essential residues for the stabilization of such compounds inside DNMTs. [Formula: see text].

Tryptophan administration induces oxidative stress in brain cortex of rats.

Despite the significant brain abnormalities, the neurotoxic mechanisms of brain injury in hypertryptophanemia are virtually unknown. In this work, we determined the thiobarbituric acid-reactive substances, 2',7'-dihydrodichlorofluorescein oxidation, reduced glutathione and the activities of catalase, superoxide dismutase and glutathione peroxidase in cerebral cortex from rats loaded with L-tryptophan. High L-tryptophan concentrations, similar to those found in hypertryptophanemic patients were induced by three subcutaneous injections of saline-buffered tryptophan (2 micromol/g body weight) to 30-day-old Wistar rats. The parameters were assessed 1 h after the last injection. It was observed that tryptophan significantly increased thiobarbituric acid-reactive substances, 2',7'-dihydrodichlorofluorescein oxidation and reduced glutathione, whereas it reduced catalase activity. Pre-treatment with taurine (1.6 micromol/g of body weight), or alpha-tocopherol plus ascorbic acid (40 and 100 microg/g body weight, respectively) prevented those effects of tryptophan, reinforcing the hypothesis that tryptophan induces oxidative stress in brain cortex of the rats. Therefore, these findings also occur in human hypertryptophanemia or in other neurodegenerative diseases in which tryptophan accumulates, then oxidative stress may be involved in the mechanisms leading to the brain injury observed in patients affected by these disorders.

Misincorporation of amino acid analogues into proteins by biosynthesis.

Despite astounding diversity in their structure and function, proteins are constructed from 22 protein or 'canonical' amino acids. Hundreds of amino acid analogues exist; many occur naturally in plants, some are synthetically produced or can be produced in vivo by oxidation of amino acid side-chains. Certain structural analogues of the protein amino acids can escape detection by the cellular machinery for protein synthesis and become misincorporated into the growing polypeptide chain of proteins to generate non-native proteins. In this review we seek to provide a comprehensive overview of the current knowledge on the biosynthetic incorporation of amino acid analogues into proteins by mammalian cells. We highlight factors influencing their incorporation and how the non-native proteins generated can alter cell function. We examine the ability of amino acid analogues, representing those commonly found in damaged proteins in pathological tissues, to be misincorporated into proteins by cells in vitro, providing us with a useful tool in the laboratory to generate modified proteins representing those present in a wide-range of pathologies. We also discuss the evidence for amino acid analogue incorporation in vivo and its association with autoimmune symptoms. We confine the review to studies in which the synthetic machinery of cell has not been modified to accept non-protein amino acids.

Generation of quinoneimine intermediates in the bioactivation of 3-(N-phenylamino)alanine (PAA) by human liver microsomes: a potential link between eosinophilia-myalgia syndrome and toxic oil syndrome.

Eosinophilia-myalgia syndrome (EMS) was an intoxication episode that occurred in the US in 1989 and affected 1,500 people. EMS was associated with the ingestion of manufactured L-tryptophan, and 3-(N-phenylamino)alanine (PAA) was identified as one of the contaminants present in the L-tryptophan batches responsible for intoxication. In previous studies (Martínez-Cabot et al., Chem Res. Toxicol., in press), we have shown that the incubation of 3-(N-phenylamino)propane-1,2-diol (PAP), a toxic biomarker of the oil batches that caused Toxic Oil Syndrome in Spain, with human liver microsomes generates a reactive quinoneimine intermediate. The structural similarity between PAA and PAP led Mayeno and co-workers (Mayeno et al. (1995) Chem. Res. Toxicol. 8, 911-916) to hypothesize that both xenobiotics could be linked to a common etiologic agent. We thus set about to study the bioactivation of PAA by human liver microsomes. Under these conditions, PAA is converted to its 4'-hydroxy derivative, an unstable intermediate that is rapidly transformed into the final metabolites 4-aminophenol and formylglycine, which were identified in the incubations by GC/MS using the H2(18)O-labeled medium. We also provide evidence that 4-aminophenol and formylglycine are formed from a quinoneimine intermediate via a pathway similar to that demonstrated for PAP bioactivation. This quinoneimine, in the absence of nucleophiles in the incubation medium, could isomerize to give the corresponding imine, which could undergo hydrolysis to yield the aforementioned final products. These findings establish that EMS and TOS are linked by a common toxic metabolite (4-aminophenol) and that they may be further linked by the concomitant release of potentially hazardous carbonyl species.

Promotion of oxidative stress by L-tryptophan in cerebral cortex of rats.

Despite the significant brain abnormalities, the neurotoxic mechanisms of brain injury in hypertryptophanemia are virtually unknown. In this work, it was investigated the in vitro effect of l-tryptophan on various parameters of oxidative stress, namely spontaneous chemiluminescence, thiobarbituric acid-reactive substances (TBA-RS), total radical-trapping antioxidant potential (TRAP), total antioxidant reactivity (TAR) and glutathione (GSH) levels in cerebral cortex from 30-day-old rats. Tryptophan significantly increased chemiluminescence and TBA-RS measurements indicating that this amino acid induced lipid peroxidation in vitro. We also observed that tryptophan significantly decreased the brain antioxidant defenses by reducing the values of TRAP, TAR and GSH, reflecting that the overall content of antioxidants was reduced by tryptophan. Furthermore, the tryptophan-induced increase of TBA-RS was fully prevented by GSH and by combination of catalase plus superoxide dismutase, but not by the inhibitor of nitric oxide synthase N(omega)-nitro-L-arginine methyl ester (L-NAME). In case these findings also occur in human hypertryptophanemia or in other neurodegenerative diseases in which tryptophan accumulates, it is feasible that oxidative stress may be involved in the mechanism leading to the brain injury observed in patients affected by these disorders.

L-tryptophan contaminant 'peak E' induces the release of IL-5 and IL-10 by peripheral blood mononuclear cells from patients with functional somatic syndromes.

In 1989, the development of eosinophilia myalgia syndrome (EMS) was observed in some patients after the intake of l-tryptophan containing several contaminants, including 1,1'-ethylidenebis[l-tryptophan] ('peak E'). Since l-tryptophan has been taken particularly by individuals suffering from functional somatic syndromes (FSS), such as fibromyalgia syndrome (FMS), we put forward the hypothesis that EMS may have developed preferentially in patients with FSS as an allergic reaction towards the contaminant peak E. We therefore studied the immunological reactivity towards l-tryptophan and peak E in these individuals (n = 12) and compared these data with those obtained in 12 healthy controls and 12 patients with other chronic disorders. Peripheral blood mononuclear cells (PBMC) were cultured for 7 days with pure l-tryptophan and peak E. Supernatant fluids were collected at day 7. The type 2 cytokines IL-4, IL-5 and IL-10, and the type 1 cytokines IL-2 and IFN-gamma, were determined by a double sandwich ELISA. PBMC from seven of the 12 FSS patients, but only three of the 24 controls, produced cytokines after incubation with peak E (P < 0.05). Interestingly, six of the seven FSS patients reacting with peak E produced IL-5 and/or IL-10. In contrast, PBMC from only one patient with other chronic disorders and one healthy control secreted type 2 cytokines in response to peak E. The observed heightened type 2 reactivity towards the more immunogenic contaminant 1,1'-ethylidenebis[l-tryptophan] in FSS patients may therefore be taken as an additional argument for our concept that EMS may have developed as a kind of drug-induced allergic disease.

Tryptophan toxicity--time and dose response in rats.

UNLABELLED: During the past decade L-tryptophan (Trp) ingestion have been associated with a multisystemic syndrome, known as eosinophilia myalgia syndrome (EMS). Even though an epidemic studies indicated that a contaminant, 1,1'-ethylidene-bis-L-tryptophan was involved in EMS, abnormalities in metabolism of Trp have been reported in other similar clinical syndromes such as carcinoid syndrome, scleroderma or eosinophilic fasciitis. The purpose of the study was to investigate the role of Trp or its metabolite, given in different dosing regimens in induction of tissue damage. METHOD: 3 months old female rats (Charles River CD-1) were fed for 3, 6, 12 weeks on a diet containing 20% protein diet derived from casein and supplemented with 1%, 2%, or 5% Trp. On the last week of feeding, half of the animals fed on a control diet and half of the animals fed on the Trp diet were injected with 2 injections of para-chlorophenyl alanine (p-CPA), a Trp hydroxylase inhibitor, 300 mg/kg i.p. followed by 3 injection of 100 mg/kg every alternate day. RESULTS: Body weight of rats fed higher levels of Trp increased slowly and injection of p-CPA induced loss in body weight. 2/6 of the animals treated with 1% Trp and 1/6 treated with 5% Trp for 3 weeks and 2/4 animals treated with 1% Trp and 1/4 treated with 5% Trp for 12 weeks died after injection of p-CPA. No mortality was detected in 1-5% Trp treated animals. Alopecia and skin changes were seen after p-CPA in 1-5% Trp treated animals. Increased amounts of connective tissue and induction of inflammatory cell proliferation were observed in lung, spleen and in gastrocnemia muscle of rats treated with higher dose of Trp for longer period. Induction of kynurenine pathway by injection of p-CPA caused more tissue damage. It is concluded that excessive Trp or elevation of its metabolites could play a role in amplifying some of pathological features of EMS. This pathological damage is further augmented by metabolites of the kynurenine pathway.

1,1'-Ethylidenebis[tryptophan] induces pathologic alterations in muscle similar to those observed in the eosinophilia-myalgia syndrome.

1,1'-Ethylidenebis[tryptophan] (EBT), a derivative of L-tryptophan (LT), is a trace contaminant in batches of LT implicated by epidemiologic evidence in the pathogenesis of the eosinophilia-myalgia syndrome (EMS). We treated female Lewis rats with EBT or unimplicated LT (4 mg per 100 grams daily) by intraperitoneal injection. No rash or weakness occurred in either group. All three EBT rats had a few necrotic muscle fibers. In two rats, perimysium and fascia were abnormally thickened and infiltrated with lymphocytes, macrophages, and sparse eosinophils; two rats had sparse perineurial inflammatory cells. Rats treated with unimplicated LT showed no abnormality. These findings replicate an important feature of human EMS and support the epidemiologic evidence linking EBT to the pathogenesis of the human disease.

Synergistic action of near-UV and phenylalanine, tyrosine or tryptophan on the inactivation of phage T7: role of superoxide radicals and hydrogen peroxide.

Near ultraviolet (NUV) light can cause a variety of damage to biological systems. The effects of NUV are significantly enhanced in the presence of sensitizers. One of the most important targets of such synergistic effects is DNA. Cellular DNA exposed to NUV plus sensitizers is damaged in a variety of ways, DNA strand breaks and interstrand cross-links being the most common effects. In this study, phenylalanine, tyrosine and tryptophan are shown to act as sensitizers for NUV action of phage T7; superoxide anions are produced. The reactive species probably interacts with phage DNA causing damage responsible for phage inactivation. Superoxide dismutase reverses the synergistic activities of phenylalanine and tyrosine on NUV-induced phage inactivation, but catalase is additionally required to reverse the effect of tryptophan. Therefore, it is probable that NUV photolysis of tryptophan causes the production of superoxide ions and hydrogen peroxide, both of which contribute to phage inactivation. The ubiquitous nature of NUV in our environment and the presence of amino acids in skin cells suggests that an important mechanism for the induction of skin cancer in humans by solar exposure is amino acid photolysis by NUV.

Pathological and immunological effects of ingesting L-tryptophan and 1,1'-ethylidenebis (L-tryptophan) in Lewis rats.

The eosinophilia-myalgia syndrome (EMS) has been associated with ingestion of L-tryptophan (L-TRP) produced by a single manufacturer. Epidemiological data implicated 1,1'-ethylidenebis (L-tryptophan) (EBT) (peak 97 or peak E) as a possible etiologic agent. We showed previously that Lewis rats treated with the L-TRP implicated in EMS develop fasciitis and perimyositis similar to those seen in human EMS. We now report the pathology associated with the treatment of Lewis rats with synthetic EBT and/or L-TRP. All animals treated for 6 wk with case-associated L-TRP or EBT developed significant myofascial thickening, compared with animals in the vehicle control and control L-TRP groups. However, even those animals receiving the control L-TRP showed a mild but significant increase in the thickness of the myofascia, compared with vehicle-treated control animals. All animals except vehicle controls also exhibited significant pancreatic pathology, including fibrosis and acinar changes. Only animals treated with case-associated L-TRP for 6 wk showed evidence of immune activation with increased frequency of CD8, Ia, and IL-2 receptor-positive cells in the peripheral blood. Animals receiving L-TRP or EBT for < 6 wk did not show significant differences in myofascial thickness, although these animals did show pancreatic acinar changes. Although these results demonstrate for the first time the pathological effects of EBT, they do not rule out the possibility that other impurities in the EMS-case-associated L-TRP may also contribute to some of the features of EMS.

Effect of synthesized constituents in the L-tryptophan product on the differentiation of eosinophils and the induction of IL-6: a possible cause of eosinophilia-myalgia syndrome.

While the pathogenesis of eosinophilia-myalgia syndrome (EMS) remains obscure, the ingestion of L-trypophan (LT) and possibly certain constituents in the LT product might be associated. We investigated the effect of chemically synthesized substances, 1,1'-ethylidene bis[tryptophan] (EBT) and its decomposition product, 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (MTCA) recently identified in the implicated LT, on the eosinophil differentiation and the induction of IL-1 and IL-6. EBT and MTCA alone did not support colony formation. However, EBT or MTCA in conjunction with IL-2 induced colony-forming activity containing a small number of eosinophils. In addition, these LT constituents induced a significant level of IL-6 but not IL-1 beta in the mononuclear cells from normal volunteers and a patient with hypereosinophilic syndrome. These results suggest that certain constituents of LT product are associated with the pathogenesis of EMS through the induction of colony-stimulating factors and IL-6, hence giving rise to eosinophilia and inflammation.

Carcinogenic tryptophan pyrolysis products in the environment.

The purpose of this study is to evaluate the risk of carcinogenic tryptophan pyrolysis products to human health. During the last decade, a new series of heterocyclic amines has been isolated as potent mutagens and later shown to be potent carcinogens in experimental animals. Among them, 3-amino-1, 4-dimethyl-5H-pyrido [4, 3-b]indole (Trp-P-1) and 3-amino-1-methyl-5H-pyrido [4, 3-b]indole (Trp-P-2), carcinogenic tryptophan pyrolysis products, have been investigated from various points of view and useful pieces of information about them have been collected. These carcinogens are widely distributed in the environment such as airborne particles, rain water, cigarette smoke and cooked foods, and they possess various pharmacotoxicological activities such as convulsant activities and potent inhibitory effects on platelet function and dopamine metabolism. Recent investigations revealed that these compounds are present in human samples such as plasma, urine and bile, indicating that humans are actually exposed to these compound. It is a matter of urgency to establish a suitable method for monitoring the exposure levels of these compounds to humans.

Toxic effect of a photo-induced tryptophan-riboflavin adduct on F9 teratocarcinoma cells and preimplantation mouse embryos.

Solutions containing L-tryptophan and riboflavin exposed to visible light, under N2 atmosphere, yield a tryptophan-riboflavin adduct, able to inhibit the growth of cultured F9 teratocarcinoma cells. This same effect was found in the presence of a mixture of the tryptophan photooxidation products and the adduct, when using solutions previously irradiated with visible light in an O2 atmosphere. A cytotoxic effect was also observed with embryos incubated in the presence of a tryptophan-riboflavin adduct, in the latter case necrosis and embryo development arrest occurred.

Effect of L-tryptophan excess and vitamin B6 deficiency on rat urinary bladder cancer promotion.

To further evaluate the role of tryptophan and vitamin B6 in bladder carcinogenesis, male Fischer 344 rats were fed 0.2% N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) in semipurified diet or were given semipurified diet alone for 4 weeks. One week later, rats from each group were assigned for the remainder of the experiment to one of four experimental diets, labeled as follows: group 1, control semipurified; group 2, L-tryptophan excess (2%); group 3, vitamin B6-deficient (1.0 mg/kg diet); or group 4, L-tryptophan excess, plus vitamin B6-deficient diet. All surviving rats were killed at 80 weeks of the experiment. Throughout the study, body weights were reduced in the groups fed FANFT and, at 70 and 80 weeks, body weights were reduced in the groups given tryptophan excess. The incidence of urinary bladder carcinoma was highest in the group treated with FANFT, followed by diet with control tryptophan and vitamin B6 levels (40%). The disease incidence was reduced in the vitamin B6-deficient group (13%) and of an intermediate range in the groups fed a tryptophan excess with or without vitamin B6 deficiency (28-29%). Tumors at other sites were greatest in number in FANFT-treated rats fed vitamin B6-deficient diet with excess tryptophan and were significantly fewer in FANFT-treated rats fed vitamin B6-deficient diet alone. Animals given diet deficient in vitamin B6 consistently had depressed levels of alanine aminotransferase activity and plasma pyridoxyl phosphate. FANFT pretreatment decreased alanine aminotransferase activities in rats in some groups and the feeding of tryptophan had variable effects on alanine aminotransferase and plasma pyridoxyl phosphate levels. Urinary tryptophan metabolites were influenced by all treatments, but the results did not correlate with tumor yields. Urinary bladder ornithine decarboxylase activity was not altered in vitamin B6-deficient female rats. These results do not support the hypothesis that increased dietary L-tryptophan promotes bladder carcinogenesis in rats, but other dietary factors might modify the process following FANFT initiation.

Induction of DNA repair in HeLa S3 carcinoma cells by the N-nitroso derivatives of 1-(N-L-tryptophan)-1-deoxy-D-fructose and 1-(5-hydroxytryptamino)-1-deoxy-D-fructose.

HeLa S3 cells, when incubated at 37 degrees C with the N-nitroso derivative of the Amadori compounds 1-(N-L-tryptophan)-1-deoxy-D-fructose (FRU-TRP) or 1-(5-hydroxytryptamino)-1-deoxy-D-fructose (FRU-SEROT) in the presence of a six-fold molar excess of sodium nitrite, exhibit increased intracellular DNA synthesis. Sodium nitrite alone, at identical levels, elicits a similar response, albeit to a much lesser degree. No response whatsoever is produced when the cells are incubated with the parent Amadori compounds. The observed stimulation of DNA replication is DNA repair. Two major routes are suggested by which nitrosated FRU-TRP (NO-FRU-TRP) and nitrosated FRU-SEROT (NO-FRU-SEROT) could damage intracellular DNA.

Role of tryptophan in carcinogenesis.

This paper reviews some of the earlier experimental studies concerning the role that tryptophan plays in enhancing tumorigenesis induced by selected chemical carcinogens. For many years, tryptophan has been implicated in carcinogenesis of the bladder. The evidence regarding tryptophan's effect on hepatic tumorigenesis is conflicting; an enhancing effect has been reported by some investigators, but a reduction in tumorigenesis has been reported by other workers. Some of the unique effects that tryptophan exerts upon the liver are reviewed. Also, experimental studies from our laboratory are reported in which we observed a potentiating effect of increased dietary tryptophan on the induction of gamma-glutamyltranspeptidase-positive foci in liver when rats were fed a choline-supplemented diet but no potentiation was found when rats were fed a choline-deficient diet for 10 weeks. The results suggest that increased dietary tryptophan has a promoting effect on liver carcinogenesis as measured by the induction of gamma-glutamyltranspeptidase-positive foci in the livers of rats exposed to diethylnitrosamine. The possible significance of these findings is reviewed.