Mutagenicity of 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid treated with nitrite in the presence of alcohols

Pharmacogenomic Next-Generation DNA Sequencing: Lessons from the Identification and Functional Characterization of Variants of Unknown Significance in CYP2C9 and CYP2C19

CYP2C9 and CYP2C19 are highly polymorphic pharmacogenes; however, clinically actionable genetic variability in drug metabolism due to these genes has been limited to a few common alleles. The identification and functional characterization of less-common open reading frame sequence variation might help to individualize therapy with drugs that are substrates for the enzymes encoded by these genes. The present study identified seven uncharacterized variants each in CYP2C9 and CYP2C19 using next-generation sequence data for 1013 subjects, and functionally characterized the encoded proteins. Constructs were created and transiently expressed in COS-1 cells for the assay of protein concentration and enzyme activities using fluorometric substrates and liquid chromatography- tandem mass spectrometry with tolbutamide (CYP2C9) and (S)-mephenytoin (CYP2C19) as prototypic substrates. The results were compared with the SIFT, Polyphen, and Provean functional prediction software programs. Cytochrome P450 oxidoreductase (CPR) activities were also determined. Positive correlations were observed between protein content and fluorometric enzyme activity for variants of CYP2C9 (P < 0.05) and CYP2C19 (P < 0.0005). However, CYP2C9 709G>C and CYP2C19 65A>G activities were much lower than predicted based on protein content. Substrate intrinsic clearance values for CYP2C9 218C>T, 343A>C, and CYP2C19 337G>A, 518C>T, 556C>T, and 557G>A were less than 25% of wild-type allozymes. CPR activity levels were similar for all variants. In summary, sequencing of CYP2C9 and CYP2C19 in 1013 subjects identified low-frequency variants that had not previously been functionally characterized. In silico predictions were not always consistent with functional assay results. These observations emphasize the need for high-throughput methods for pharmacogene variant mutagenesis and functional characterization.

Micronuclei levels in peripheral blood lymphocytes as a potential biomarker for pancreatic cancer risk

To find biomarkers for risk prediction of pancreatic cancer (PC), we evaluated the frequency of micronuclei (MN) in peripheral lymphocytes of 346 patients with PC and 449 healthy controls. The levels of baseline MN (mean ± standard error of micronucleated cells per 1000 binucleated cells) were significantly higher in patients (15.3 ± 0.3) than those in controls [9.7 ± 0.5; adjusted for body mass index (BMI), P < 0.001]. Using the median levels found in controls as the cut point, 78.9% of patients and 43.7% of controls had a higher frequency of MN. Logistic regression analysis with adjustment for known risk factors for PC showed that having a higher level of MN was significantly associated with increased risk of PC [odds ratio (OR): 8.32, 95% confidence interval (CI): 5.06-13.67, P < 0.001]; and the risk was much higher in men than in women [OR (95% CI): 14.19 (7.09-28.40) versus 4.19 (1.90-9.27)]. The level of MN was not associated with disease stage or resection status but was related to smoking status in men and to BMI in women among patients. The level of MN was higher in smokers (14.5 ± 0.6) than in nonsmokers (12.1 ± 0.6; P = 0.023) and in obese (25.3 ± 2.8) versus normal weight individuals (17.7 ± 0.8; P = 0.024). These data showed that elevated level of MN in peripheral lymphocytes was associated with increased risk of PC.

Harmane and harmalan are bioactive components of classical clonidine-displacing substance

Elucidation of the structure of the endogenous ligand(s) for imidazoline binding sites, clonidine-displacing substance (CDS), has been a major goal for many years. Crude CDS from bovine lung was purified by reverse-phase high-pressure liquid chromatography. Electrospray mass spectrometry (ESMS) and nuclear magnetic resonance ((1)H NMR) analysis revealed the presence of L-tryptophan and 1-carboxy-1-methyltetrahydro-beta-carboline in the active CDS extract. Competition radioligand binding studies, however, failed to show displacement of specific [(3)H]clonidine binding to rat brain membranes for either compound. Further purification of the bovine lung extract allowed the isolation of the beta-carbolines harmane and harmalan as confirmed by ESMS, (1)H NMR, and comparison with synthetic standards. Both compounds exhibited a high (nanomolar) affinity for both type 1 and type 2 imidazoline binding sites, and the synthetic standards were shown to coelute with the active classical CDS extracts. We therefore propose that the beta-carbolines harmane and harmalan represent active components of classical CDS. The identification of these compounds will allow us to establish clear physiological roles for CDS.

The functional role of threonine-205 in the mechanism-based inactivation of P450 2B1 by two ethynyl substrates: the importance of the F helix in catalysis

We have previously demonstrated that substituting Val for Thr-205 in P450 2B1 abolishes the 16beta-hydroxylation of testosterone and markedly decreases the ability of 2-ethnylnaphthalene (2EN) and 17alpha-ethynylestradiol (17EE) to inactivate P450 2B1. The role of Thr-205 has been further investigated by measuring the kinetics of the mechanism-based inactivation of the 7-ethoxy-(trifluoromethyl)coumarin deethylation activity of 2B1 by 2EN and 17EE in wild-type (WT) and mutant P450s. In general, the kinetics of the inactivation of the Ser and Ala mutants was not significantly altered compared with WT. In contrast, the efficiency of the inactivation of the Val mutant decreased by approximately 6- and approximately 30-fold for 2EN and 17EE, respectively. High-pressure liquid chromatography (HPLC) analysis and SDS gel electrophoresis demonstrated the covalent binding of radiolabeled 2EN- and 17EE-reactive intermediates to the WT apoprotein, but not the Val mutant. The Val mutant was able to metabolize 2EN to 2-naphthylacetic acid, except the initial rate was slower than the WT. HPLC analysis of the 17EE incubation mixtures revealed three major metabolites and showed a correlation between the efficiency of inactivation and the generation of one of the major metabolites (C). Metabolite C was generated by the WT, Ser mutant, and Ala mutant. Metabolite C may be formed by the oxidation of the ethynyl group, and this reactive intermediate contributes to the inactivation of P450 2B1 by 17EE. The site-specific mutation of one residue, Thr-205 to Val, is sufficient to alter the profile of products formed during 17EE metabolism, such that very low levels of metabolite C are formed and inactivation is essentially abolished.

Identification and occurrence of tryptamine- and tryptophan-derived tetrahydro-beta-carbolines in commercial sausages

The identification and occurrence of tetrahydro-beta-carbolines were studied in different kinds of commercial sausages including cooked, fresh, dry-fermented, and ripened sausages, such as salamis and Spanish chorizo, salchichon, fuet, and morcilla, both smoked and unsmoked. Four compounds were identified in several sausages by high-performance liquid chromatography-mass spectrometry (HPLC-MS): 1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (1), 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid diastereoisomers (2a,b), 1,2,3,4-tetrahydro-beta-carboline (3), and 1-methyl-1,2,3,4-tetrahydro-beta-carboline (4). The latter two (3 and 4) are now reported for the first time in meat products. The presence and occurrence of tetrahydro-beta-carbolines were highly variable depending on each particular sample of sausage, and it did not follow a single specific pattern. The concentration range taken as a sum of the four carbolines varied from undetectable levels to 33 microg/g, with the highest content found in ripened, dry-fermented, and smoked sausages (salami, chorizo, and morcilla) and the lowest in cooked sausages (Frankfurt). Formation of tetrahydro-beta-carbolines might occur during elaboration and the ripening process from a chemical condensation between tryptophan or tryptamine and aldehydes (formaldehyde and acetaldehyde). Smoked samples had higher concentrations of formaldehyde-derived 1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (1) and 1,2,3,4-tetrahydro-beta-carboline (tryptoline) (3) than those unsmoked. Also, 1 and 3 were more concentrated in the outer part of the sausage, likely to be in contact with smoke. It is concluded that some dry-fermented and/or smoked sausages may be significant dietary sources of tetrahydro-beta-carbolines.

Tetrahydro-beta-carboline alkaloids occur in fruits and fruit juices. Activity as antioxidants and radical scavengers

Tetrahydro-beta-carbolines are biologically active alkaloids that occur and accumulate in mammalian tissues, fluids, and brain, but their ultimate origin or biological role is still uncertain. Four tetrahydro-beta-carboline alkaloids: 1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid, 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid, 1-methyl-1,2,3,4-tetrahydro-beta-carboline, and 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline, are found as naturally occurring substances in some fruit and fruit juices. These compounds occur in the microg/g level in those products, and a characteristic and distinct profile appears to exist depending on the type of fruit and juice involved. Thus, 1-methyl-1,2,3,4-tetrahydro-beta-carboline may appear in tomato, tomato juice, and kiwi; 6-hydroxy-1-methyl-1,2,3,4-tetrahydro-beta-carboline in bananas, pineapple, tomato, and their corresponding juices; and 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid in oranges and grapefruits, although it also occurred in most juices. Fruit-occurring tetrahydro-beta-carboline alkaloids acted as antioxidants and free radical scavengers in the ABTS assay when compared with ascorbic acid and Trolox. This suggests that tetrahydro-beta-carboline alkaloids might act as antioxidants when absorbed and accumulated in the body, contributing to the antioxidant effect of fruit products containing these compounds.

Investigation of the tuber constituents of maca (Lepidium meyenii Walp.)

Lepidium meyenii, known in South America as maca, has received attention worldwide as a powerful energizer that improves physical and mental conditions and increases fertility. Because of these reports, we investigated the secondary metabolites of the tuber of maca. The methanol extract of the tuber of maca contained, in addition to free sugars and amino acids, the following: uridine, malic acid and its benzoyl derivative, and the glucosinolates, glucotropaeolin and m-methoxyglucotropaeolin. Because glucosinolates and their derived products have received increasing attention due to their biological activities, the occurrence of glucosinolate degradation products in the hexane extract was also investigated, and benzylisothiocyanate and its m-methoxy derivative were isolated. The two glucosinolates were semiquantified by HPLC, and benzylisothiocyanate was semiquantified by GC/MS. The methanol extract of maca tuber also contained (1R,3S)-1-methyltetrahydro-beta-carboline-3-carboxylic acid, a molecule which is reported to exert many activities on the central nervous system.

Degradation of tetrahydro-beta-carbolines in the presence of nitrite: HPLC-MS analysis of the reaction products

Motivated by the identification of numerous novel tetrahydro-beta-carboline-carboxylic acids in food samples, we studied the reactions of tetrahydro-beta-carbolines in the presence of nitrosating agents. The anticipated formation of nitroso derivatives from unsubstituted tetrahydro-beta-carbolines, and from tetrahydro-beta-carboline-3-carboxylic acids was indicated by HPLC-MS/MS analysis and validated by the characteristic product ion spectra of the respective nitroso compounds. In addition, oxidative decarboxylation resulted in formation of the corresponding dihydro-beta-carbolines, and in the generation of the beta-carbolines harman or norharman. Subsequently, we studied the reactivity of tetrahydro-beta-carboline-1-carboxylic acids derived from the Pictet-Spengler condensation of indole amines with alpha-oxo acids. Again, in the presence of nitrosating agents the rapid disappearance of the starting material was obvious, but no nitroso derivatives could be observed. Instead, further HPLC-MS/MS studies demonstrated that dihydro-beta-carbolines were the major products of tetrahydro-beta-carboline-1-carboxylic acids. Finally, we demonstrated that freshly isolated nitroso-precursors spontaneously decomposed to yield harman alkaloids. In conclusion, we revealed that nitroso-tetrahydro-beta-carbolines can represent intermediates involved in the generation of beta-carbolines, and we established a novel pathway for the formation of harman alkaloids from nutritional tetrahydro-beta-carbolines.

Identification and functional characterization of a new CYP2C9 variant (CYP2C9*5) expressed among African Americans

CYP2C9 is a polymorphic gene for which there are four known allelic variants; CYP2C9*1, CYP2C9*2, CYP2C9*3, and CYP2C9*4. In the present study, DNA from 140 European Americans and 120 African Americans was examined by single-strand conformational polymorphism and restriction fragment length polymorphism analyses, resulting in the identification of a new CYP2C9 variant, CYP2C9*5. This variant is derived from a C1080G transversion in exon 7 of CYP2C9 that leads to an Asp360Glu substitution in the encoded protein. The CYP2C9*5 variant was found to be expressed only in African Americans, such that approximately 3% of this population carries the CYP2C9*5 allele. The variant was expressed in, and purified from, insect cells infected with a recombinant baculovirus. Comparative kinetic studies using the purified wild-type protein CYP2C9*1; the Ile359Leu variant, CYP2C9*3; and the Asp360Glu variant, CYP2C9*5 were carried out using (S)-warfarin, diclofenac, and lauric acid as substrates. The major effect of the Asp360Glu mutation was to increase the K(m) value relative to that of CYP2C9*1 for all three substrates: 12-fold higher for (S)-warfarin 7-hydroxylation, 5-fold higher for the 4'-hydroxylation of diclofenac, and 3-fold higher for the omega-1 hydroxylation of lauric acid. V(max) values differed less than K(m) values between the CYP2C9*1 and CYP2C9*5 proteins. In vitro intrinsic clearances for CYP2C9*5, calculated as the ratio of V(max)/K(m), ranged from 8 to 18% of CYP2C9*1 values. The corresponding ratio for CYP2C9*3 was 4 to 13%. Accordingly, the in vitro data suggest that carriers of the CYP2C9*5 allele would eliminate CYP2C9 substrates at slower rates relative to persons expressing the wild-type protein.

Tetrahydro-beta-carboline-3-carboxylic acid compounds in fish and meat: possible precursors of co-mutagenic beta-carbolines norharman and harman in cooked foods

The presence of tetrahydro-beta-carbolines and beta-carbolines was studied in raw, cooked and smoked fish and meat. 1,2,3,4-Tetrahydro-beta-carboline-3-carboxylic acid (THCA) usually was the major beta-carboline found, whereas 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (MTCA) appeared in smoked and 'well done' cooked samples. THCA was detected in raw fish (nd-2.52 micrograms/g), cooked fish (nd-6.43 micrograms/g), cooked meats (nd-0.036 microgram/g), smoked fish (0.19-0.67 microgram/g) and smoked meats (0.02-1.1 micrograms/g). Smoked and cooked samples contained higher amounts of THCA and MTCA than raw products. Deep cooking of fish and meat increased both THCA and MTCA, and this was accompanied by the formation of more beta-carbolines, norharman and harman. The tetrahydro-beta-carbolines THCA and MTCA were chemical precursors of the co-mutagens norharman and harman during cooking. These and previous results confirm that foods are an important source of beta-carbolines in humans.

Analyses of TCRB rearrangements substantiate a profound deficit in recombination signal sequence joining in SCID foals: implications for the role of DNA-dependent protein kinase in V(D)J recombination

We reported previously that the genetic SCID disease observed in Arabian foals is explained by a defect in V(D)J recombination that profoundly affects both coding and signal end joining. As in C.B-17 SCID mice, the molecular defect in SCID foals is in the catalytic subunit of the DNA-dependent protein kinase (DNA-PKCS); however, in SCID mice, signal end resolution remains relatively intact. Moreover, recent reports indicate that mice that completely lack DNA-PKCS also generate signal joints at levels that are indistinguishable from those observed in C.B-17 SCID mice, eliminating the possibility that a partially active version of DNA-PKCS facilitates signal end resolution in SCID mice. We have analyzed TCRB rearrangements and find that signal joints are reduced by approximately 4 logs in equine SCID thymocytes as compared with normal horse thymocytes. A potential explanation for the differences between SCID mice and foals is that the mutant DNA-PKCS allele in SCID foals inhibits signal end resolution. We tested this hypothesis using DNA-PKCS expression vectors; in sum, we find no evidence of a dominant-negative effect by the mutant protein. These and other recent data are consistent with an emerging consensus: that in normal cells, DNA-PKCS participates in both coding and signal end resolution, but in the absence of DNA-PKCS an undefined end joining pathway (which is variably expressed in different species and cell types) can facilitate imperfect signal and coding end joining.

Inhibitory effects of tea extracts on the mutagenicity of 1-methyl-1, 2,3,4-tetrahydro-beta-carboline-3-carboxylic acid on treatment with nitrite in the presence of ethanol

It has been shown that the mutagenicity of 1-methyl-1,2,3, 4-tetrahydro-beta-carboline-3-carboxylic acid (MTCCA), a major mutagen precursor in soy sauce on treatment with nitrite and ethanol, was strongly decreased by the addition of hot water extracts of green, black and oolong teas in the reaction mixture when it was treated with 50mM nitrite at pH3.0, 37 degrees C for 60min in the presence of 7.5% ethanol. The mutagenicity-decreasing activity of the teas was scarcely decreased by washing the teas with chloroform and benzene and was partly decreased by butanol and ethyl acetate. Typical polyphenols such as catechins were shown to have the antimutagenicity dose dependently. The antimutagenicity and the reducing power of tea extracts gave a positive good correlation. The results suggest that the mutagenicity of MTCCA on treatment with nitrite in the presence of ethanol may be decreased by the mixed fractions of lyophilic components such as polyphenols, which have high reducing power such as catechins and the other compounds which have little reducing power including the derivatives of the catechins and so on. Although the antimutagenicity of teas and catechins was also considerably effective when they were added after the nitrosation, that of black tea and some catechins was less effective.

1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid and 1,2, 3,4-tetrahydro-beta-carboline-3-carboxylic acid in fruits

1,2,3,4-Tetrahydro-beta-carboline-3-carboxylic acid (THCA) and 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (MTCA), as two diastereoisomers (1S,3S and 1R,3S), occurred in commercial fruits. Citrus fruits exhibited the highest content; other fruits contained very low levels or none at all. The content of MTCA was as follows: orange, 0.35-2.47 microg/g; lemon, 0.15-2.05 microg/g; grapefruit, 1.12-8.37 microg/g; mandarin, 0.57-2.5 microg/g; banana, nd-0.74 microg/g; pear, nd-0.017 microg/g; grape, 0.01-0.22 microg/g, tomato, 0.05-0.25 microg/g; and apple, nd-0.012 microg/g). THCA, if present, usually occurred at <0.05 microg/g. Fruit ripening and softening during storage were accompanied with a significant increase of MTCA, in both pears and bananas. Those and previous results confirm that foods are an important source of tetrahydro-beta-carbolines in humans.

Inhibitory effects of citrus fruits on the mutagenicity of 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid treated with nitrite in the presence of ethanol

It has been shown that the mutagenicity of 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (MTCCA), a mutagen precursor in soy sauce treated with nitrite, was strongly increased when it was treated with nitrite in the presence of alcohols. We found that the mutagenicity of MTCCA treated with 50 mM nitrite at pH 3, 37 degrees C for 60 min in the presence of 7.5% ethanol was reduced by the addition of citrus fruits sudachi (Citrus sudachi), lemon (C. limon) and yuzu (C. junos), to the reaction mixture. The mutagenicity-reducing activity per weight of flavedos (outer colored portions of peel) of the citrus fruits was considerably higher than that of the juices. The juices of the other citrus fruits commercially available in Japan also had mutagenicity-reducing activity against the nitrite-treated MTCCA. Among the many components of citrus fruits, dietary fibers lignin and pectin showed strong antimutagenic activity in the reaction mixture, suggesting that the mixed fractions of these components including lignin, pectin, D-limonene, naringin, hesperidin, ascorbic acid and citric acid reduce the mutagenicity of MTCCA in the reaction mixture containing nitrite and ethanol.

Interaction of Ku protein and DNA-dependent protein kinase catalytic subunit with nucleic acids

The Ku protein-DNA-dependent protein kinase system is one of the major pathways by which cells of higher eukaryotes respond to double-strand DNA breaks. The components of the system are evolutionarily conserved and homologs are known from a number of organisms. The Ku protein component binds directly to DNA ends and may help align them for ligation. Binding of Ku protein to DNA also nucleates formation of an active enzyme complex containing the DNA-dependent protein kinase catalytic subunit (DNA-PKcs). The interaction between Ku protein, DNA-PKcs and nucleic acids has been extensively investigated. This review summarizes the results of these biochemical investigations and relates them to recent molecular genetic studies that reveal highly characteristic repair and recombination defects in mutant cells lacking Ku protein or DNA-PKcs.

Presence of tetrahydro-beta-carboline-3-carboxylic acids in foods by gas chromatography-mass spectrometry as their N-methoxycarbonyl methyl ester derivatives

Various tetrahydro-beta-carboline-3-carboxylic acids (TH beta C-3-COOH) are identified in commercial foods and drinks by GC-MS. Positive identification of 1-methyl-1,2,3,4-tetrahydro-beta-carboline-3-carboxylic acid (MTCA) is demonstrated in soy and tabasco sauces, wine, beer, wine vinegar, cider, orange juice, toasted bread, blue cheese and yoghurt. 1,2,3,4-Tetrahydro-beta-carboline-3-carboxylic acid (THCA) occurs in toasted bread, beer, cider, wine vinegar, soy and tabasco sauce, orange juice and blue cheese. MTCA and THCA are reported for the first time in several of these products. MTCA appears as a mixture of two diastereoisomers with the same mass spectra. MTCA is the major TH beta C-3-COOH in foodstuffs except for toasted bread that contains more THCA. GC-MS analysis of N-methoxycarbonyl methyl ester derivatives of TH beta C-3-COOHs was used for chemical identification. Those derivatives were synthesized in a qualitatively using methyl chloroformate or methyl chloroformate and diazomethane reagents. Electron impact mass spectra of N-methoxycarbonyl-TH beta C-3-COOH methyl esters are reported and fragmentation assigned and discussed. These results prove the presence of TH beta C-3-COOHs in commercial foodstuffs suggesting their uptake during the daily consumption of foods.