TSC1 and TSC2 deletions differ in size, preference for recombinatorial sequences, and location within the gene.

Large TSC gene rearrangements are not rare findings in tuberous sclerosis. Interestingly, all deletions, duplications and inversions so far described involve TSC2, none being associated with TSC1. In order to shed light on the structural basis of the preferential DNA rearrangements in TSC2 over TSC1 and to assess, in an unselected patient population, the prevalence of large re-arrangements in both TSC loci, we screened 202 tuberous sclerosis patients consecutively referred at our center. Southern blot analysis on EcoRI+HindIII double-digested DNA identified 19 partial or full-length gene deletions: three involved TSC1 and sixteen TSC2. The breakpoint sequence of seven internal deletions, three in TSC1 and four in TSC2, allowed us to speculate on the mechanism favoring TSC2 unequal recombinations and to identify a deletion hot spot that lies in TSC1 and that may be relevant in the routine genetic testing of tuberous sclerosis. Briefly, three major features appear to distinguish TSC1 from TSC2 deletions: (1) deletion size: all TSC1 deletions are within the transcriptional unit, whereas 12 of the 16 TSC2 deletions have at least one external breakpoint; (2) location within the gene: all TSC1 deletions are confined to the 3'end of the gene (all three 5' breakpoints being located in intron 20) thus resulting in the same frameshift mutation following amino acid K875, whereas the TSC2 internal breakpoints appear to be scattered along the gene; (3) preference for recombinatorial sequences: six out of eight internal TSC2 breakpoints map within Alu repeats, whereas none of the three TSC1 deletions appear to be Alu-mediated. Indeed, in the latter gene, unique structural features (a purine-rich tract flanked by pyrimidine-rich segments) surrounding one of the two identified breakpoint cluster regions might play a role in promoting inappropriate recombinations.

Evaluation of resistance in Osteospermum ecklonis (DC.) Norl. plants transgenic for the N protein gene of tomato spotted wilt virus.

The nucleocapsid protein (N) gene of tomato spotted wilt virus (TSWV) was inserted into Osteospermum ecklonis via Agrobacterium tumefaciens leaf strips co-cultivation. Sixteen primary transformant clones of two O. ecklonis genotypes were analysed. Southern blots of restricted genomic DNA demonstrated integration of the transgene and indicated the number of integrated copies. Expression of the transgene was estimated by DAS-ELISA and Western and Northern blotting. Plants were challenged with TSWV inoculation, either mechanically or by the thrips Frankliniella occidentalis; they were then monitored for symptom appearance and tested by TAS-ELISA for infection. Inoculation of the transgenic clones via the natural TSWV vector was more efficient and led to the identification of 1 clone, characterised by multiple transgene integration and no transgene expression, with improved resistance to TSWV.

Induction of micronuclei and of enzyme-altered foci in the liver of female rats exposed to progesterone and three synthetic progestins.

Progesterone (PG) and three structurally similar synthetic progestins-norethisterone (NE), allylestrenol (AE), and dydrogesterone (DG)-have been compared for their ability to induce the formation of micronuclei and of enzyme-altered foci in the liver of female rats. In the micronucleus assay, carried out in rats given a single p.o. dose of 100 mg kg-1 3 days before partial hepatectomy and sacrificed for cell sampling 2 days later, the frequency of micronucleated hepatocytes was 3.5-fold higher than in controls with PG, 2.8-fold with DG, 2.2-fold with NE and 2.1-fold with AE, but the increase was statistically significant only for PG. In the liver foci assay, performed to evaluate the tumor initiating activity of p. o. dosing with 100 mg kg-1 once a week for 6 successive weeks, the values of the number and area of gamma-glutamyltranspeptidase-positive foci were, as compared to controls, 15.9- and 100-fold higher with NE, and 13.9- and 52-fold higher with AE, but only the increase of area produced by NE was statistically significant; PG and DG did not display in this test any activities. Considered together with previous findings, these results suggest that NE might be biotransformed in the liver into reactive species and thus behave as a weak genotoxic agent.

In vitro evaluation of the cytotoxic, hemolytic and clastogenic activities of Rhizostoma pulmo toxin(s).

Cytotoxic, hemolytic and clastogenic activities of Rhizostoma pulmo toxin(s) contained in the jelly tissue free of nematocysts were investigated in mammalian cells with in vitro procedures. At the concentration of 37.6 microg/ml the tissue protein produced the death of 50% V79 cells; a similar potency was observed in terms of hemolytic activity. The toxin(s) was not clastogenic for human lymphocytes in culture at the concentration of 5 microg/ml.

Induction of micronuclei and initiation of enzyme-altered foci in the liver of female rats treated with cyproterone acetate, chlormadinone acetate, or megestrol acetate.

The synthetic anti-androgen and progestin cyproterone acetate (CPA), recently found to be genotoxic for the liver, and two structurally similar progestins, chlormadinone acetate (CMA) and megestrol acetate (MGA), have been compared for clastogenic and tumor-initiating activities in female rats. In the micronucleus assay, carried out in rats given a single p.o. dose of 100 mg/kg, CPA induced the maximum increase in the frequency of micronucleated hepatocytes (6.6-fold as compared to controls) when treatment was performed 3 days before partial hepatectomy and cell sampling 2 days later. Under the same experimental conditions the clastogenic potencies of CMA and MGA were 69% and 36% of that of CPA respectively. In the liver foci assay, p.o. dosing with 100 mg/kg CPA once a week for 6 successive weeks induced, as compared to controls, a significant increase in the number and area of gamma-glutamyltranspeptidase-positive foci. At the same dosage schedule the tumor-initiating activity of CMA and MGA was 7- to 10-fold lower than that of CPA. These findings suggest that the 1,2 alpha-methylene group, present in CPA but absent in both CMA and MGA, favours the activation to a reactive species and/or hinders the biotransformation to non-toxic metabolites.

In vitro and in vivo testing of hydralazine genotoxicity.

Hydralazine (HDZ), a p.o. effective antihypertensive drug, was evaluated for its genotoxic effects in both rodent and human cultured cells and in the intact rat. Dose-dependent amounts of DNA fragmentation, as measured by the alkaline elution technique, and of DNA repair synthesis, as revealed by autoradiography, were produced in primary cultures of metabolically competent rat hepatocytes by subtoxic HDZ concentrations ranging from 0.32 to 1.0 mM. A similar potency in inducing DNA repair synthesis was displayed by HDZ in primary cultures of hepatocytes from four human donors. A modest reduction of both DNA fragmentation (-13%) and DNA repair (approximately -50%) was observed in hepatocytes obtained from rats pretreated with indomethacin in order to reduce prostaglandin synthetase activity. In contrast, neither in rat nor in human hepatocytes, differences in N-acetyltransferase activity resulted in meaningful changes of the same end points. V79 cells, which are essentially deficient of monooxygenases catalyzing the biotransformation of xenobiotics, were as sensitive as hepatocytes to the DNA-damaging activity of HDZ. Moreover, after exposure to 0.1 to 0.3 mM HDZ, a modest (2.1- to 2.8-fold), but significant, increase in the frequency of mutation to 6-thioguanine resistance was observed in V79 cells in the absence of a metabolic activation system. In rats, a single p.o. dose of 80 mg/kg produced a clastogenic effect in the liver, but not in the bone marrow, and the p.o. administration for 14 successive days of approximately 46 mg/kg/day increased the average diameter of liver basophilic foci initiated by diethylnitrosamine.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of DNA-damaging, clastogenic, and promoting activities of metoclopramide and procainamide in rats.

The DNA-damaging and clastogenic activities of metoclopramide (MCA) and procainamide (PCA), two substituted benzamides not systematically tested for genotoxicity before clinical use, were investigated in rats given a single high oral dose (500 mg/kg) of these drugs. Neither MCA nor PCA induced DNA fragmentation in liver, kidney, gastric mucosa, spleen, and bone marrow, as detected by the alkaline elution technique. Moreover, neither drug increased the frequency of micronucleated hepatocytes and the frequency of micronucleated polychromatic erythrocytes in the bone marrow of partially hepatectomized rats. However, in rats initiated with N-nitrosodiethylamine and given water containing 0.125% MCA for 14 successive days a clear-cut and statistically significant increase in the number and size of liver gamma-glutamyltranspeptidase-positive foci and basophilic foci, which are consistent with potential promoting activity, was observed. Under the same experimental conditions the effect of PCA was markedly lower, only limited to a modest increase of the number and area of gamma-glutamyltranspeptidase-positive foci.

Resistance to tospoviruses in Nicotiana benthamiana transformed with the N gene of tomato spotted wilt virus: correlation between transgene expression and protection in primary transformants.

Nicotiana benthamiana was transformed with the nucleoprotein (N) gene of an Italian isolate of tomato spotted wilt virus (TSWV). Forty-five T1 primary transformant lines were analyzed for the expression of N protein and for resistance to TSWV and three other tospoviruses: impatiens necrotic spot virus (INSV), groundnut bud necrosis virus (GBNV), and groundnut ringspot virus (GRSV). Thirteen of these lines were further characterized. Resistance to all TSWV isolates tested was found in two lines. The expression of the transgene (N mRNA) was lower in these resistant lines than in any of the susceptible lines, and the transgene N protein was either absent or present below detectable levels. These lines were susceptible to the other tospoviruses tested, but they developed symptoms milder than controls when inoculated with GRSV. Some of the lines producing high levels of N protein showed delays (of 2-3 weeks) in symptom expression with at least one of the TSWV isolates tested and symptom delay or attenuation with INSV or GRSV (or both). From our results it appears that high expression of TSWV N protein retards, in some cases, disease development by TSWV and INSV. In contrast, the lack of detectable expression of the transgenic N protein, accompanied by limited production of N transcripts, conferred TSWV-specific resistance.

Low clastogenic activity in vivo of the N-nitroso derivatives of 5 beta-adrenergic-blocking drugs proved to be potent genotoxins in vitro.

The N-nitroso derivatives formed by the in vitro reaction of 5 beta-adrenergic-blocking drugs with sodium nitrite and previously found to induce DNA fragmentation and repair in primary cultures of both rat and human hepatocytes were tested for their ability to exert a clastogenic effect in vivo. In partially hepatectomized rats given by gavage a single dose of 1000 mg/kg, all 5 N-nitroso derivatives caused a statistically significant increase in the frequency of micronucleated hepatocytes, the clastogenic potencies of NO-propranolol, NO-metoprolol, and NO-nadolol being slightly greater than those of NO-atenolol and NO-sotalol. In contrast, none of them produced a significant increase in the frequency of micronucleated polychromatic erythrocytes in the bone marrow and the spleen. For all 5 N-nitroso derivatives the in vivo clastogenic potency, i.e. the ratio between the number of micronuclei observed in the liver and the dose administered, was markedly lower than the in vitro DNA-damaging potency calculated as the ratio between the amount of DNA fragmentation and the concentration tested. This suggests a preferential detoxification in vivo of the 5 N-nitroso derivatives.

Comparison in human and rat hepatocytes of the DNA-damaging activity of five chemicals probably carcinogenic to humans.

Five chemicals-acrylonitrile, adriamycin, bischloroethyl nitrosourea, phenacetin and procarbazine-classified by the International Agency for Research on Cancer as probably carcinogenic to humans were assayed for DNA-damaging activity in primary cultures of human and rat hepatocytes in order to assess possible interspecies differences that might cast doubt on the extrapolation to humans of results obtained in rodents. DNA damage was measured by the alkaline elution technique. In the range of subtoxic concentrations indicated, dose-related increases in the frequencies of DNA single-strand breaks were induced in cells of both species by acrylonitrile (1.0-5.6 mm) and procarbazine (5.6-18 mm), whereas phenacetin was inactive up to the maximal soluble dose (3.2 mm). Adriamycin (1.8-5.6 mum) and bischloroethyl nitrosourea (18-56 mum) produced in cells of both species dose-dependent increases in the frequencies of both DNA breaks and cross-links. The responses of human hepatocytes were qualitatively similar to those of rat hepatocytes, but modest statistically significant differences between the two species in the average frequencies of DNA lesions were observed with the four active agents: the amount of DNA damage was greater in rat than in human hepatocytes with acrylonitrile (1.7-fold), adriamycin (1.4-fold), and BCNU (1.3-fold), whereas procarbazine was more genotoxic (1.4-fold) for human hepatocytes. However, as the interindividual variability of the response was greater than that occurring between the two species, the results should be interpreted as indicating that rat hepatocytes are good predictors of metabolic activation/detoxification and DNA-damaging activity in humans for the five chemicals studied.

Cytotoxic and genotoxic activity of 1,3-dichloropropene in cultured mammalian cells.

1,3-Dichloropropene (DCP), a widely used soil fumigant previously found to be carcinogenic in both mice and rats, was evaluated for its cytotoxic and genotoxic effects in cultured rodent and human cells. A reduction of cell viability that was dependent on the dose and the length of treatment was observed with the trypan blue and the neutral red assay in both V79 cells and rat hepatocytes exposed to DCP concentrations ranging from 0.18 to 5.6 mM. In the absence of a metabolic activation system, a dose-dependent frequency of DNA single-strand breaks, that were only partially repaired within 24 hr, was revealed by the alkaline elution technique in V79 cells exposed to subtoxic DCP concentrations. The genotoxicity of DCP was confirmed by the results obtained in metabolically competent primary cultures of both rat and human hepatocytes which displayed similar dose-related amounts of DNA fragmentation and DNA repair synthesis, and showed, in comparison to metabolically deficient V79 cells, a somewhat greater sensitivity to the cytotoxic and DNA-damaging effects of DCP. The increase in the frequency of DNA breaks observed in rat hepatocytes after GSH depletion confirms the role of this tripeptide in DCP detoxification; its reduction in hepatocytes simultaneously exposed to metyrapone is consistent with a cytochrome P450-dependent biotransformation of DCP to more toxic metabolites.

Genotoxic activity of 1,3-dichloropropene in a battery of in vivo short-term tests.

The genotoxic activity of 1,3-dichloropropene, which has been classified as possibly carcinogenic to humans, was investigated in rats given high single doses of this chloroolefin. A dose-related amount of DNA fragmentation was observed at doses ranging from 62.5 to 250 mg/kg in liver and gastric mucosa, both of which are targets of DCP carcinogenic activity, as well as in the kidney. The frequency of DNA breaks, that were to a large extent repaired within 24 hr, was higher after po than after ip administration in the liver, while the converse occurred in the kidney. Any evidence of DNA fragmentation was, in contrast, absent in lung, bone marrow, and brain which are not sites of DCP-induced tumor development. A role of cytochrome P450 in the activation of DCP is suggested by the lower degree of liver DNA fragmentation observed in rats pretreated with methoxsalen. DCP produced a dose-dependent reduction of the liver GSH level, an effect that presumably hinders its detoxification and thus favors its DNA-damaging activity. In contrast with the satisfactory prediction of DCP carcinogenic activity provided by the results of the in vivo DNA damage/alkaline elution assay, neither the in vivo rat hepatocyte DNA repair assay nor the micronucleus assay, carried out on bone marrow, spleen, and liver cells of partially hepatectomized rats, supplied any evidence of DCP genotoxicity.

Effects of ethinyl estradiol and epidermal growth-factor on DNA-synthesis in human cultured-hepatocytes.

It has been demonstrated that the liver tumor promoter ethinyl estradiol (EE) potentiates the DNA synthetic response of cultured rat hepatocytes to epidermal growth factor (EGF), probably acting as a comitogen with a growth factor of the EGF/TGF family. The present study investigated the effects of EE and EGF on DNA synthesis in cultures of rat and human hepatocytes obtained from 5 female donors. The cultures were given the following treatments: a. 15 muM EE for 30 h; b. 25 ng/ml of EGF for 12 h; c. combination of treatments a and b. The results obtained in rat hepatocytes confirm that EE potentiates the.DNA synthetic response to EGF, as evaluated by the labelling index. As to human hepatocytes, in only one case the response to EGF produced a significant increase of DNA synthesis and the EE pretreatment did not potentiate this effect. The results of this study indicate that, in contrast to the response observed in rat hepatocytes, EE does not seem to affect the DNA synthesis in primary cultures of human hepatocytes, and the association EE+EGF does not produce any synergic effect.

In vitro and in vivo evaluation of the genotoxicity of N-nitrosooxprenolol.

N-nitrosooxprenolol (NO-oxprenolol) might be formed in the stomach of patients taking the beta-adrenergic blocking drug, oxprenolol. This nitroso derivative has previously been shown to induce DNA damage and repair in both rat and human cultured hepatocytes. The results of the present study show that in the presence of co-cultured rat hepatocytes, 0.03 mM NO-oxprenolol produced a significant increase in the frequency of 6-thioguanine-resistant but not of ouabain-resistant mutants. No mutagenic activity was detected in the absence of metabolic activation. In mice, NO-oxprenolol (1 g/kg) increased the incidence of micronucleated cells in the liver but not in the bone marrow and the spleen. These results suggest that NO-oxprenolol, consistent with its chemical nature of nitrosamine, is biotransformed into short-lived reactive species.

Evaluation in a battery of in vivo assays of four in vitro genotoxins proved to be noncarcinogens in rodents.

2-Chlorethanol, 8-hydroxyquinoline, 2,6-toluenediamine, and eugenol, previously found to behave as genotoxins in in vitro systems and as noncarcinogens in rodents, were evaluated for their ability to induce genotoxic effects in vivo. Rats were given by gavage a single or two successive doses equal to one-half the corresponding LD50, killed at different times after treatment, and examined for the following end points: the frequency of both micronucleated polychromatic erythrocytes in the bone marrow and micronucleated hepatocytes (after partial hepatectomy); the in vivo-in vitro induction of DNA fragmentation, as measured by the alkaline elution technique, and of unscheduled DNA synthesis, as measured by autoradiography, in hepatocyte primary cultures. The two latter end points were also evaluated after in vitro exposure of hepatocytes to log-spaced subtoxic concentrations. 2-Chloroethanol, 8-hydroxyquinoline, and eugenol never produced effects indicative of genotoxic activity. The same happened with 2,6-toluenediamine, with the exception of a significant increase over controls in the amounts of DNA damage and repair displayed by hepatocyte cultures obtained from rats given two 1/2 LD50 separated by a 24 h interval. Our results, which, apart the above mentioned exception, are in concordance with the rodent carcinogenicity results, contribute to underline the role of in vivo short-term tests for the detection of potential genotoxic carcinogens.

Genotoxicity testing of chloramphenicol in rodent and human cells.

The results of this work, carried out to extend the limited information at present available on the genotoxic potential of chloramphenicol (CAP), indicate that in millimolar concentrations this antibacterial agent produced a minimal amount of DNA fragmentation in both V79 cells and metabolically competent rat hepatocytes. Moreover, a level of DNA-repair synthesis indicative of a weak but positive response was detected in primary cultures of liver cells obtained from 2 of 3 human donors, and a borderline degree of repair was present in those prepared from rats. The promutagenic character of CAP-induced DNA lesions was confirmed by a low but significant increase in the frequency of 6-thioguanine-resistant clones of V79 cells, which, however, was absent when the exposure was done in the presence of co-cultured rat hepatocytes. Finally, oral administration to rats of 1/2 LD50 CAP did not increase the incidence of either micronucleated polychromatic erythrocytes or micronucleated hepatocytes. Taken as a whole these findings suggest that CAP should be considered a compound intrinsically capable of producing a very weak genotoxic effect, but only at concentrations about 25 times higher than those occurring in patients treated with maximal therapeutic dosages.

Formation of the N-nitroso derivatives of six beta-adrenergic-blocking agents and their genotoxic effects in rat and human hepatocytes.

Six beta-adrenergic-blocking drugs, atenolol, metoprolol, nadolol, oxprenolol, propranolol and sotalol, were found to react with sodium nitrite in HCl solution, yielding the corresponding N-nitrosamines. The genotoxic activity of the six nitrosamines was evaluated in primary cultures of both rat and human hepatocytes; DNA fragmentation was measured by the alkaline elution technique, and DNA repair synthesis by quantitative autoradiography. Positive dose-related responses were produced in cells of both species after 20 h of exposure to the following subtoxic concentrations: NO-propranolol, 0.01-0.1 mM; NO-oxprenolol, 0.03-1 mM; NO-atenolol and NO-metoprolol, 0.1-1 mM; and NO-nadolol and NO-sotalol, 0.3-3 mM. Modest but statistically significant differences between the DNA-damaging potencies for the two species were observed with NO-atenolol and NO-oxprenolol, which were both more active against rat hepatocytes, and with NO-propranolol, which was more active against human hepatocytes. At equal or higher concentrations, the six N-nitrosamines did not produce DNA fragmentation in Chinese hamster lung V79 cells; this indicates that they behave as indirectly acting compounds, which need to be transformed into reactive metabolites in order to exert a genotoxic effect.

Comparison of the sensitivity of human and rat hepatocytes to the genotoxic effects of metronidazole.

Metronidazole (MNZ), an antiprotozoan and antibacterial agent, has been shown to yield DNA-damaging reactive species after nitroreductive biotransformation. The genotoxic effect of MNZ was studied in primary cultures of both rat and human hepatocytes. In millimolar concentrations MNZ produced DNA fragmentation, as measured by the alkaline elution technique, and unscheduled DNA synthesis, as evaluated by quantitative autoradiography, in rat hepatocytes. The amount of DNA damage was directly related to the dose and the length of exposure, was increased by hypoxia and GSH depletion, and was markedly reduced by inhibition of cytochrome P-450 activity. In the same experimental conditions human hepatocytes resulted constantly more resistant than rat hepatocytes to the genotoxic activity of MNZ. These findings suggest that the rat hepatocyte model might be an inappropriate predictor of nitroimidazoles genotoxicity.

Genotoxicity of N-nitrosochlordiazepoxide in cultured mammalian cells.

Chlordiazepoxide, a benzodiazepine derivative commonly used for the treatment of anxiety, was found to react with sodium nitrite in HCl aqueous solution yielding, at pH ranging from 0.5 to 5,N-nitrosochlordiazepoxide (NO-CDE). In the absence of a metabolic activation system, a dose-dependent frequency of DNA single-strand breaks was revealed by the alkaline elution technique in V79 cells exposed to subtoxic NO-CDE concentrations ranging from 33 to 330 microM. DNA lesions were only partially repaired within 48 hr, and their promutagenic character was demonstrated by the induction of 6-thioguanine resistance in the same cells. The genotoxicity of NO-CDE was confirmed by results obtained in metabolically competent primary cultures of both rat and human hepatocytes, which displayed similar dose-related amounts of DNA fragmentation and of DNA repair synthesis after treatment with concentrations ranging from 33 to 1000 microM. In conclusions similar to those which might occur in the stomach of a patient taking chlordiazepoxide the concentration of NO-CDE in the reaction mixture (50 microM) was of the same order as the concentrations found to induce a genotoxic effect in cultured mammalian cells.