Molecular characterization of two deletion events involving Alu-sequences, one novel base substitution and two tentative hotspot mutations in the hypoxanthine phosphoribosyltransferase (HPRT) gene in five patients with Lesch-Nyhan syndrome

Mutations identified in the hypoxanthine phosphoribosyltransferase (HPRT) gene of patients with Lesch-Nyhan (LN) syndrome are dominated by simple base substitutions. Few hotspot positions have been identified, and only three large genomic rearrangements have been characterized at the molecular level. We have identified one novel mutation, two tentative hot spot mutations, and two deletions by direct sequencing of HPRT cDNA or genomic DNA from fibroblasts or T-lymphocytes from LN patients in five unrelated families. One is a missense mutation caused by a 610C-->T transition of the first base of HPRT exon 9. This mutation has not been described previously in an LN patient. A nonsense mutation caused by a 508C-->T transition at a CpG site in HPRT exon 7 in the second patient and his younger brother is the fifth mutation of this kind among LN patients. Another tentative hotspot mutation in the third patient, a frame shift caused by a G nucleotide insertion in a monotonous repeat of six Gs in HPRT exon 3, has been reported previously in three other LN patients. The fourth patient had a tandem deletion: a 57-bp deletion in an internally repeated Alu-sequence of intron 1 was separated by 14 bp from a 627-bp deletion that included HPRT exon 2 and was flanked by a 4-bp repeat. This complex mutation is probably caused by a combination of homologous recombination and replication slippage. Another large genomic deletion of 2969 bp in the fifth patient extended from one Alu-sequence in the promoter region to another Alu-sequence of intron 1, deleting the whole of HPRT exon 1. The breakpoints were located within two 39-bp homologous sequences, one of which overlapped with a well-conserved 26-bp Alu-core sequence previously suggested as promoting recombination. These results contribute to the establishment of a molecular spectrum of LN mutations, support previous data indicating possible mutational hotspots, and provide evidence for the involvement of Alu-mediated recombination in HPRT deletion mutagenesis.

Spectrum of point mutations in the coding region of the hypoxanthine-guanine phosphoribosyltransferase (hprt) gene in human T-lymphocytes in vivo

The hypoxanthine-guanine phosphoribosyl transferase (hprt) locus in 6-thioguanine (TG) resistant T-lymphocytes is a useful target for the study of somatic in vivo mutagenesis, since it provides information about a broad spectrum of mutation. Mutations in the hprt coding region were studied in 124 TG-resistant T-cell clones from 38 healthy, non-smoking male donors from a previously studied population of bus maintenance workers, fine-mechanics and laboratory personnel. Their mean age was 43 years (range 23-64) and their hprt mutant frequency was 9.3 +/- 5.2 x 10(-6) (mean +/- SD, range 1.4-22.6 x 10(-6)). Sequence analysis of hprt cDNA identified 115 unique mutations; 76% were simple base substitutions, 10% were +/-1 bp frameshifts, and 10% were small deletions within exons (3-52 bp). In addition, two tandem base substitutions and one complex mutation were observed. Simple base substitutions were observed at 55 (20%) of 281 sites known to be mutable in the hprt coding sequence. The distribution of these mutations was significantly different than would be expected based upon a Poisson distribution (P < 0.0001), suggesting the existence of 'hotspots'. All of the 87 simple base substitutions occurred at known mutable sites, but eight were substitutions of a kind that have not previously been reported at these sites. The most frequently mutated sites were cDNA positions 197 and 146, with six and five independent mutations respectively. Four mutations were observed at position 131, and three each at positions 143, 208, 508 and 617. Transitions (52%) were slightly more frequent than tranversions (48%), and mutations at GC base pairs (56%) more common than mutations at AT base pairs (44%). GC > AT was the most common type of base pair substitution (37%). The majority of the mutations at GC base pairs (78%) occurred at sites with G in the non-transcribed strand. All but one of eight mutations at CpG-sites were of the kind expected from deamination of methylated cytosine. Deletion of a single base pair (-1 frameshift) was three times more frequent than insertion of a single bp (+1 frameshift). Almost half (6/13) of the small (3-52 bp) deletions within the coding sequence clustered in the 5' end of exon 2. Short repeats and other sequence motifs that have been associated with replication error were found in the flanking regions of most of the frameshifts and small deletions. However, several differences in the local sequence context between +/-1 frameshift and deletion mutations were also noticed. The present results identify positions 197, 146 and possibly 131 as hotspots for base substitution mutations, and confirm previously reported hotspots at positions 197, 508 and 617. In addition, the earlier notion of a deletion hotspot in the 5'end of exon 2 was confirmed. The observations of these mutational cluster regions in different human populations suggest that they are due to endogeneous mechanisms of mutagenesis, or to ubiquitous environmental influences. The emerging background spectrum of somatic in vivo mutation in the human hprt gene provides a useful basis for comparisons with radiation or chemically induced mutational spectra, as well as with gene mutations in human tumors.

Chromosomal instability in human lymphocytes after low dose rate gamma-irradiation and delayed mitogen stimulation

PURPOSE

To study the possibility that radiation induced chromosomal instability in human lymphocytes is promoted by a conflict between mitogen-induced growth stimulation and radiation-induced genotoxic stress.

MATERIALS AND METHODS

Peripheral blood lymphocytes were exposed to low LET-irradiation at: (1) low-dose rate (LDR, 1-3 Gy, 0.024 Gy h[-1]) in order to minimize genotoxic stress; (2) high dose rate (HDR, 1-3 Gy, 45 Gy h[-1]) followed by immediate mitogen stimulation; and (3) HDR followed by a recovery period of 5 days before mitogen stimulation. Subsequent analyses included cell viability and clonogenic cell survival, chromosome aberrations at the first post-irradiation mitosis, and karyotype analysis of long term cultured cells, 11-57 days after mitogen stimulation.

RESULTS

Dose (1-3 Gy) and dose rate (LDR and HDR) effects on the frequency of dicentric chromosomes at the first post-irradiation mitosis were in agreement with published data, with a pronounced dose rate effect of 2 and 3 Gy exposures. G-handed karyotypes after 11 days of growth in vitro showed increased frequencies of chromosome breaks and rearrangements in all irradiated cell cultures. Clones with complex karyotype abnormalities and increased frequencies of de novo aberrations developed in the irradiated cultures during extended growth for 22-57 days. These results show that: (1) LDR-irradiation induces chromosomal instability in primary human lymphocytes; (2) mitogen stimulation rescues HDR-irradiated cells from death at the expense of an increased level of chromosome aberrations; and (3) HDR-irradiated cells that are allowed 5 days of recovery before mitogen stimulation develop chromosomal instability during subsequent long-term proliferation.

CONCLUSIONS

Neither the acute genotoxic stress of HDR-irradiation compared with LDR-irradiation, nor the hypothesized conflict between mitogen-induced growth stimulation and irradiation-induced growth arrest, seem to be critical conditions for the development of chromosomal instability in primary human T lymphocytes. Post-irradiation incubation allowing apoptotic processes to remove damaged cells does not prevent the subsequent development of chromosomal instability during long-term cell proliferation.

Sodium saccharin inhibits adenylyl cyclase activity in non-taste cells

We have studied the in vitro effect of sodium saccharin (NaSacch) on the rat adipocyte adenylyl cyclase complex. NaSacch (2.5-50 mM) inhibited significantly in a dose-dependent manner basal and isoproterenol-stimulated cAMP accumulation on isolated rat adipocytes. Similarly, NaSacch (2.5-50 mM) inhibited forskolin-stimulated adenylyl cyclase activity measured in the presence of Mg(2+)-ATP on adipocyte, astrocyte and thyrocyte membrane fractions. In contrast, NaSacch did not inhibit but slightly increased the forskolin-stimulated adenylyl cyclase activity measured in the presence of Mn(2+)-ATP and GDP beta S, a stable GDP analogue. The effect of NaSacch was not mediated through either the A1-adenosine receptor (A1R) or the alpha 2-adrenergic receptor (alpha 2AR). The inhibitory effect of NaSacch was additive to that of A1R agonist and was not blocked by the addition of the alpha 2AR antagonist RX 821002. Pretreatment of adipocytes with pertussis toxin slightly attenuated but did not abolish the inhibitory effect of NaSacch on forskolin-stimulated adenylyl cyclase activity on membrane fractions. These data suggest that the inhibitory effect of NaSacch on forskolin stimulated-adenylyl cyclase in adipocytes does not imply only Gi protein but also other direct or indirect inhibitory pathway(s) which remain to be determined.

The validation of three human reliability quantification techniques--THERP, HEART and JHEDI: Part II--Results of validation exercise

This is the second of three papers dealing with the validation of three Human Reliability Assessment (HRA) techniques. The first paper introduced the need for validation, the techniques themselves and pertinent validation issues. This second paper details the results of the validation study carried out on the Human Reliability Quantification techniques THERP, HEART and JHEDI. The validation study used 30 real Human Error Probabilities (HEPs) and 30 active Human Reliability Assessment (HRA) assessors, 10 per technique. The results were that 23 of the assessors showed a significant correlation between their estimates and the real HEPs, supporting the predictive accuracy of the techniques. Overall precision showed 72% (60-87%) of all HEPs to be within a factor of 10 of the true HEPs, with 38% of all estimates being within a factor of three of the true values. Techniques also tended to be pessimistic rather than optimistic, when they were imprecise. These results lend support to the empirical validity of these three approaches.

Frequency and cell specificity of T-cell receptor interlocus recombination in human cells

Immunoglobulin and T-cell receptor (TCR) genes are assembled by a site-specific rearrangement known as V(D)J [variable-(diversity)-joining] recombination. These rearrangements occur normally in pre-B- and pre-T-cells using signal sequences adjacent to coding exons for immunoglobulin and TCR genes, respectively. However, aberrant recombination may result in the generation of hybrid TCR genes by joining of TCR-beta with TCR-gamma specific sequences. Such hybrid TCR genes occur at a low frequency in peripheral blood lymphocytes (PBL) of healthy individuals, and can be detected by PCR amplification. We have determined the in vivo frequency of hybrid V gamma-J beta 1 TCR (hybrid TCR) genes in lymphocyte DNA from 12 healthy individuals. The average frequency was found to be 5.83 in 0.75 x 10(6) PBL, with a threefold difference between the highest and lowest individual value. The presence of similar TCR gene rearrangements in individual samples suggests that T-cells with a hybrid TCR gene are capable of clonal expansion in vivo. The individual hybrid TCR gene frequency remained relatively constant during 72 hours of in vitro cultivation. In long-term culture, the frequency gradually decreased, and after 28 days no hybrid TCR genes were detectable in lymphocyte DNA. These results show that T-cells with a hybrid TCR gene are able to respond to mitogen stimulation in vitro, and may have a proliferative disadvantage or are selected against during prolonged in vitro cultivation. No hybrid TCR genes were detected in ten proliferating T-cell clones, indicating that the rate of hybrid TCR gene formation is < 2.0 x 10(-8) per cell per cell division. No hybrid TCR genes were detected in DNA from B-lymphocytes, sperm, granulocytes, fibroblasts, keratinocytes, and three B-lymphoblastoid ataxia telangiectasia cell lines. In agreement with previous reports, the frequency of hybrid TCR genes in peripheral blood DNA from two ataxia telangiectasia patients was found to be more than 15-fold higher than in lymphocytes from normal individuals. These data show that formation of hybrid TCR genes is restricted to T-cells in vivo, and occurs at a very low frequency, if at all, in proliferating T-cells in vitro, and with an increased frequency in patients with ataxia telangiectasia.

GSTM1 and NAT2 genotypes and urinary mutagens in coke oven workers

The influence of the metabolic genotypes GSTM1 and NAT2 on the urinary excretion of mutagens in 46 coke oven workers (27 of them smokers) was studied. Exposure to polycyclic aromatic hydrocarbons (PAH) was estimated from urinary 1-pyrenol levels, which varied from 0.23 to 5.59 micromol/mol creatinine. Fourteen urine samples (30.4%), all but one belonging to smokers, were positive for mutagenic activity (i.e. at least one of the assayed doses was able to double the number of spontaneous revertants). Nine of the urine-positive subjects were both GSTM1-null and NAT2-ss (64.3%), while the same combination of genotypes was found in nine out of 31 urine-negative subjects (29.0%) (P < 0.05). Significantly more smoking workers with the genotype combination GSTM1-null/NAT2-ss showed positive urine mutagenicity than the other subjects (75.0 versus 28.6%, P < 0.05). Smokers with the slow acetylator genotype showed a significantly higher frequency of positive urine samples than smoking fast acetylators (64.7 versus 22.2%, P < 0.05). Our results suggest that smoking coke oven workers with genotypes unfavourable for detoxification of aromatic amines (NAT2-ss) and PAH (GSTM1-null) may have an increased risk of developing bladder cancer.

A Bacillus thuringiensis insecticidal crystal protein with a high activity against members of the family Noctuidae

The full characterization of a novel insecticidal crystal protein, named Cry9Ca1 according to the revised nomenclature for Cry proteins, from Bacillus thuringiensis serovar tolworthi is reported. The crystal protein has 1,157 amino acids and a molecular mass of 129.8 kDa. It has the typical features of the Lepidoptera-active crystal proteins such as five conserved sequence blocks. Also, it is truncated upon trypsin digestion to a toxic fragment of 68.7 kDa by removal of 43 amino acids at the N terminus and the complete C-terminal half after conserved sequence block 5. The 68.7-kDa fragment is further degraded to a nontoxic 55-kDa fragment. The crystal protein has a fairly broad spectrum of activity against lepidopteran insects, including members of the families Pyralidae, Plutellidae, Sphingidae, and Noctuidae. A 50% lethal concentration of less than 100 ng/cm2 of diet agar was found for diamondback moth, European corn borer, cotton bollworm, and beet armyworm. It is the first insecticidal crystal protein with activity against cutworms. No activity was observed against some beetles, such as Colorado potato beetle. The protein recognizes a receptor different from that recognized by Cry1Ab5 in Ostrinia nubilalis and Plutella xylostella. In Spodoptera exigua and P. xylostella, it binds to a receptor which is also recognized by Cry1Cax but with a lower affinity. In these insects, Cry1Cax probably binds with a higher affinity to an additional receptor which is not recognized by Cry9Ca1. Elimination of a trypsin cleavage site which is responsible for the degradation to a nontoxic fragment did result in protease resistance but not in increased toxicity against O. nubilalis.

Effects of sodium saccharin diet on fat-cell lipolysis: evidence for increased function of the adenylyl cyclase catalyst

OBJECTIVE

To evaluate the effect of a 14 days' sodium saccharin (NaS) diet on lipolysis and cyclic-AMP accumulation in isolated rat white epididymal adipocytes.

ANIMALS

Male Wistar rats (3 weeks old) were fed, for 14-days, ad libitum with a regular diet supplemented with or without 1-5% NaS dissolved in drinking water.

MEASUREMENTS

Lipolysis and cAMP accumulation were assessed on isolated adipocytes. Adenylyl cyclase activities were measured on membrane fractions prepared from isolated adipocytes. The levels of Gs and Gi proteins were determined by Western blot analysis using specific antisera.

RESULTS

Only high dietary NaS (5%) affected significantly the body growth and food consumption. Feeding rats with 2.5% of NaS increased both basal and isoproterenol-stimulated lipolysis and cAMP production. A 14-days diet of rats with 2.5% aspartame did not reproduce the effects of NaS on lipolysis and cAMP production. In fat-cell membranes of 2.5% NaS-treated rats, basal and stimulated-adenylyl cyclase activities were increased by 200% whatever the agonists used: GTP, GTP[S], [AIF4]-, isoproterenol or forskolin in the presence of Mg2+ or Mn2+ with or without GDP[S]. These effects cannot be explained by modifications of the expression of Gs and Gi proteins. The level of Gs alpha subunits was not affected by NaS treatment while the level of Gi alpha 1/2 was slightly increased. The stimulatory effect of NaS on adenylyl cyclase activity appears to be specific to adipocyte when compared with thyroid, brain or heart membrane fractions.

CONCLUSION

Based on these data, and on the fact that cAMP regulates the lipolytic rate, we conclude that NaS diet increases lipolysis and cAMP formation in fat-cells by modifying the activity of the adenylyl cyclase catalyst(s).

Reduced proliferation rate of hypoxanthine-phosphoribosyl transferase mutant human T-lymphocytes in vitro

The clonal hprt mutation assay in human T-cell is based on the assumption that wild-type cells and hypoxanthine-phosphoribosyl transferase (hprt) mutant cells survive and proliferate at the same rate during the expression phase which is required for the expression of in vitro-induced mutants. We have tested this assumption in a study of mutant frequency (MF) and proliferation rate at different time points during in vitro expansion of human T-cells in non-selective medium. Peripheral blood lymphocytes from 11 individuals were studied using standard cloning procedures to determine the cloning efficiency (CE) and the hprt MF by 6-thioguanine (TG) selection. Another cell portion from each individual was allowed to proliferate in bulk culture for 8 days in vitro, before measuring CE and MF as above. In the directly plated cell population the CE was 45% and the MF 18.7 +/- 15.3 x 10(-6) (mean +/- S.D.), whereas the in vitro expanded cell population showed a CE of 38% and a significantly reduced MF of 8.3 +/- 6.9 x 10(-6) (P = 0.0033). Thus, the mean MF was 56% lower in the in vitro expanded than in the directly plated cell population. The experiment was repeated in another group of ten individuals with essentially the same result. In a third experiment, freshly prepared cells from two donors were allowed to grow for up to 15 days in bulk culture in vitro. Cell growth, CE, and MF were determined every third day. The MF decreased gradually, and at day 12-15 it was only 25% of the initial value. The total number of clonable cells increased 13-fold during the 15 days of in vitro expansion, while the mutant, TG-resistant cell population increased only 3-fold. These results suggest that human hprt mutant T-lymphocytes have a reduced proliferation rate compared to wild-type cells during in vitro proliferation. Thus, measurements of chemical and radiation induced MF with the T-cell clonal assay may underestimate the true MF by a factor of 2 or more.

Analysis of mutation at the hprt locus in human T lymphocytes

Studies of mutation at the hypoxanthine phosphoribosyl transferase (hrpt) locus in human T-cells have the potential to elucidate the molecular basis of in vivo mutagenesis, reveal exposure dependent changes in ther background frequency of mutation, and provide knowledge on individual sensitivity. Styrene exposed lamination workers in Bohemia showed a significantly higher frequency of hprt mutant cells than Swedish control populations studied simultaneously. In a study of 47 healthy, non-smoking male bus maintenance workers exposed to diesel exhausts, soot and oil, and 22 unexposed controls, a significant correlation (P = 0.008) was obtained between the levels of aromatic DNA adducts and frequencies of hprt-mutant T-cells. In the group of workers with the highest exposure, subjects with glutathione S-transferase (GSTM1) deficiency showed significantly higher (P < 0.05) frequency of hprt mutant T-cells than GSTM1-positive subjects. The highest adduct levels were found in subjects with the combined genotype of GSTM1 and NAT2 deficiency (GSTM1-negative slow acetylators). These results indicate that GSTM1 and NAT2 genotypes may play a role in determining the individual levels of hprt mutation and DNA adducts. Using PCR-based screening methods, hprt mutations have been classified in 462 T-cell clones from 43 subjects in this study population. Deletions were found in 3% of the mutants, coding errors in 81% and splice mutations in 17%. Transitions and transversions were equally common, and all types of base substitutions were detected.

Spontaneous length variation in microsatellite DNA from human T-cell clones

Recently, much interest has been focused on instability of microsatellite DNA sequences such as di- and tri-nucleotide repeats in human cancers. Certain tumors show an increased frequency of mutation leading to repeat length variation at microsatellite loci, and it is thought that such instability may be a marker for the transformed phenotype. However, the spontaneous frequency by which repetitive DNA such as CA-repeats undergoes size changes in normal human somatic cells is not known. Therefore, it is not possible to decide if there is an increase in the frequency of microsatellite mutation in specific tumors or if the change observed simply reflects the frequency of microsatellite mutation in the cell population from which the tumor originates. To investigate this we have established panels of T-lymphocyte clones from 28 healthy males and determined the spontaneous length variations at three CA-repeat markers that are often used to investigate satellite instability: D2S123, D9S180, and D10S197. We found 3 T-cell clones with altered microsatellite size in a total of 178. This corresponds to a background frequency of 3 somatic microsatellite mutations in 1,028 alleles studied, i.e., 2.9 x 10(-3). This frequency is comparable to that found in many tumors of the breast, brain, ovary, and skin but is considerably lower than the frequency of microsatellite mutation in tumors related to hereditary non-polyposis colorectal cancer.

Styrene oxide-induced HPRT mutations, DNA adducts and DNA strand breaks in cultured human lymphocytes

Styrene-7,8-oxide (SO) is the major in vivo metabolite of styrene, a widely used plastic monomer. SO has been classified as probably carcinogenic to humans. We studied the genotoxic effects of SO in human peripheral blood lymphocytes (PBL) in vitro. SO-treatment in the range of 0.05-0.6 mM for 24 h resulted in a dose-dependent decrease of cell survival and increase of HPRT mutation, O6-guanine DNA adducts and DNA strand breaks, whereas higher concentrations caused pronounced cell death. SO was a weak mutagen, inducing at most 10-20 mutants per 10(6) clonable cells (approximately 4-fold over the background) after treatment with 0.2-0.4 mM for 24 h or 6 days. The levels of DNA adducts in treated cells correlated with SO-concentrations, but only four adducts per 10(8) nucleotides were detected at the highest treatment concentrations. Yet, adducts were still detectable in cells that had been cultured for 6-8 days after treatment. SO-induced DNA strand breaks, measured with the Comet assay, were detectable after 1 h exposure to 0.05-0.1 mM. Post-treatment incubation for 24 h decreased the level of DNA strand breaks to the control level. There was no correlation between the levels of DNA adducts and frequency of HPRT mutation. The present results indicate that SO is relatively inefficient in inducing HPRT mutation and O6-guanine DNA adducts in human lymphocytes in vitro, which may be related to its pronounced cytotoxicity at concentrations above 0.4 mM. A comparison with previous in vivo data obtained by the same assays in T-lymphocytes of styrene-exposed workers suggests that chronic, low dose exposure to styrene in the work environment may be more efficient in inducing persistent DNA adducts and HPRT mutation than acute, short-term exposure.

Binding of the Escherichia coli UvrAB proteins to the DNA mono- and diadducts of cis-[N-2-amino-N-2-methylamino-2,2,1-bicycloheptane]dichloroplatinum(II ) and cisplatin. Analysis of the factors controlling recognition and proof of monoadduct-mediated UvrB-DNA cross-linking

The interactions of the Escherichia coli endonuclease UvrAB proteins with the DNA mono- and diadducts of both the cis-racemic exo-[N-2-amino-N-2-methylamino-2,2,1-bicycloheptane]dichloroplatin um(II) (complex 1) and cisplatin (cis-diamminedichloroplatinum(II) (cis-DDP)), have been studied. Complex 1 reacts faster with DNA than cis-DDP and gives monoadducts with a longer lifetime (8 h 20 min chelation t 1/2 compared with 2 h 40 min for cis-DDP). Using pSP65 plasmid [3H]DNA, the filter binding assay was associated with the analysis of the nucleoprotein complexes to characterize the UvrAB recognition of the platinum adducts and to demonstrate the occurrence of platinum-mediated DNA-protein cross-linking. First, it is shown that the UvrAB proteins recognize the complex 1 mono- and diadducts with a higher affinity than those of cis-DDP. Fifteen times more cis-DDP adducts per plasmid are required than complex 1 adducts, to lead to similar UvrAB binding. However, the UvrAB proteins recognize monoadducts and diadducts of each complex with a similar affinity. Second, it is shown that UvrB is the protein involved in the nucleo-protein complexes formed from mono- and diadducts of complex 1 and cis-DDP. This protein is also partly cross-linked to DNA with a similar efficiency by monoadducts derived from complex 1 and cis-DDP. However, as UvrB has a greater affinity for the DNA adducts of complex 1 than for those of cis-DDP, more UvrB-platinum-DNA cross-links are formed with complex 1 than with cis-DDP. This study, using a bacterial repair system as a model, points to a possible strategy for making new cytotoxic platinum complexes for mammalian cells.

Classification of mutations at the human hprt-locus in T-lymphocytes of bus maintenance workers by multiplex-PCR and reverse transcriptase-PCR analysis

Polymerase chain reaction (PCR)-based screening methods were used to classify mutations arising in vivo at the hypoxanthine guanine phosphoribosyl-transferase (hprt) locus in small samples of human T-lymphocyte clones (< 5 x 10(4) cells) from 29 bus maintenance workers exposed to diesel exhaust, and 14 control individuals. All subjects were healthy, non-smoking males. Among 462 T-cell mutants studied by multiplex-PCR of genomic DNA, only 12 (2.6%) deletions were found: three total deletions, five partial exon deletions and four mutants with one or two exons deleted. Point mutations were classified in 323 mutants using reverse transcriptase-PCR amplification: 74 (22.9%) of these had splice site mutations and 241 (74.6%) had coding errors. Splice mutation was more frequent among the garage workers (24.8%) as compared to the controls (19.5%), possibly reflecting a polycyclic aromatic hydrocarbon-specific mutation induction in these workers. Our results also show that both gene deletion and splice mutation at the hprt-locus in T-cells of healthy non-smokers could be less frequent than previously reported.

Relationship between hprt mutant frequency, aromatic DNA adducts and genotypes for GSTM1 and NAT2 in bus maintenance workers

We have studied the mutant frequency in the human gene for hypoxanthine-guanine phosphoribosyl transferase (hprt) using the T-cell cloning assay, the aromatic DNA adduct level using the 32P-postlabelling assay, and related the levels of these biomarkers to the genotypes for glutathione transferase (GST mu) and N-acetyltransferase (NAT2) in non-smoking bus maintenance workers exposed to diesel exhaust. No difference in mutant frequency was observed between the 47 exposed (8.6 x 10(-6), age range 27-65) and the 22 control individuals (8.4 x 10(-6), age range 23-61), while the difference in adduct level (3.2 versus 2.3 x 10(-8)) was highly significant (P = 0.0009). Both mutant frequency and adduct level were highest in the 16 most heavily exposed workers. Overall, a significant increase of mutant frequency was observed with adduct level (P = 0.008) as well as with age (P < 0.0001). The age dependence was higher in the GSTM1-negative slow acetylators (3.1%/year) as compared to the three other genotype combinations (2.4-2.5%/year). There was no significant difference in mutant frequency or in adduct level between the GSTM1-negative (49.3% of the population) and positive individuals, or between the slow (60.9% of the population) and rapid acetylators. Among the slow acetylators, however, a significantly higher adduct level (P = 0.03) was obtained for the GSTM1-negative individuals as compared to the GSTM1-positive individuals. These results suggest a possible role of both GST mu and NAT2 for individual susceptibility to carcinogen exposure.

Biomarkers of styrene exposure in lamination workers: levels of O6-guanine DNA adducts, DNA strand breaks and mutant frequencies in the hypoxanthine guanine phosphoribosyltransferase gene in T-lymphocytes

Occupational exposure to styrene was studied in nine workers of a hand lamination plant in Bohemia. Personal dosimeters were used to monitor the styrene workplace exposure, and the levels of styrene in blood and mandelic acid in urine were measured. Blood samples were taken at four occasions during a 7 month period to determine styrene-specific O6-guanine DNA adducts in lymphocytes and granulocytes, DNA strand breaks and hypoxanthine guanine phosphoribosyltransferase (HPRT) mutant frequency in T-lymphocytes. Seven administrative employees in the same factory (factory controls) and eight persons in a research laboratory (laboratory controls) were used as referents. DNA adduct levels determined by the 32P-postlabelling method in lymphocytes of laminators were remarkably constant and significantly higher (P < 0.0001) than in factory controls at all four sampling times. HPRT mutant frequencies (MF) measured by the T-cell cloning assay were higher in the laminators (17.5 x 10(-6), group mean) than in the factory controls (15.7 x 10(-6), group mean) at three of the four sampling times, but the differences were not statistically significant. However, a statistically significant (P = 0.021) difference between MF in the laminators (18.0 x 10(-6), group mean) and laboratory controls (11.8 x 10(-6), group mean) was observed at sampling time 4 (the only sampling time when this latter group was studied). This result indicates that styrene exposure may induce gene mutation in T-cells in vivo. DNA strand breaks were studied by the 'Comet assay' at the fourth sampling time. The laminators were found to have significantly higher levels of DNA strand breaks than the factory controls (P = 0.032 for tail length, TL; P = 0.007 for percentage of DNA in tail, T%; and P = 0.020 for tail moment, TM). A statistically significant correlation was also found between the levels of lymphocyte DNA adducts and all three DNA strand break parameters (TL P = 0.046; T% P = 0.026 and TM P = 0.034). On the contrary, no significant correlations were found between DNA adduct levels and the HPRT mutant frequencies or between the mutant frequencies and DNA strand breaks. Taken together, these results add further support to the genotoxic and possibly mutagenic effects of styrene exposure in vivo. However, no simple quantitative relationship seems to exist between the levels of styrene-induced DNA damage and frequency of HPRT mutation in T-lymphocytes.

Mutations induced in the hypoxanthine phosphoribosyl transferase gene by three urban air pollutants: acetaldehyde, benzo[a]pyrene diolepoxide, and ethylene oxide

Provisional mutational spectra at the hypoxanthine phosphoribosyl transferase (HPRT) locus in vitro have been worked out for acetaldehyde (AA) and benzo[a]pyrene diolepoxide (BPDE) in human (T)-lymphocytes and for ethylene oxide (EtO) in human diploid fibroblasts using Southern blotting and polymerase chain reaction (PCR)-based DNA sequencing techniques. The results indicate that large genomic deletions are the predominating hprt mutations caused by AA and EO, whereas BPDE induces point mutations that are mainly GC > TA transversions. The mutational spectra induced by the three agents are clearly different from the background spectrum in human T-cells. Thus, the hprt locus is a useful target for the study of chemical-specific mutational events that may help identify causes of background mutation in human cells in vivo.

Complex hyperplasia of the endometrium. Predictive value of curettage vs. hysterectomy specimens

We reviewed 94 cases of complex endometrial hyperplasia (CH) with and without atypia to assess some of the clinical and pathologic changes observed on curettage and in hysterectomy specimens. Age, parity, height, weight and nomograms did not differ between CH with or without atypia, and CH associated with endometrial carcinoma. CH without atypia, however, predicted lesser degrees of malignancy as compared to CH with atypia. Progesterone or progestinlike treatment is indicated for CH without atypia along with endometrial monitoring, but CH with atypia necessitates diagnostic and therapeutic hysterectomy whenever fertility is not a priority.

Cancer risk in humans predicted by increased levels of chromosomal aberrations in lymphocytes: Nordic study group on the health risk of chromosome damage

Cytogenetic assays in peripheral blood lymphocytes (PBL) have been used extensively to survey the exposure of humans to genotoxic agents. The conceptual basis for this has been the hypothesis that the extent of genetic damage in PBL reflects critical events for carcinogenic processes in target tissues. Until now, no follow-up studies have been performed to assess the predictive value of these methods for subsequent cancer risk. In an ongoing Nordic cohort study of cancer incidence, 3182 subjects were examined between 1970 and 1988 for chromosomal aberrations (CA), sister chromatid exchange or micronuclei in PBL. In order to standardize for the interlaboratory variation, the results were trichotomized for each laboratory into three strata: low (1-33 percentile), medium (34-66 percentile), or high (67-100 percentile). In this second follow-up, a total of 85 cancers were diagnosed during the observation period (1970-1991). There was no significant trend in the standardized incidence ratio with the frequencies of sister chromatid exchange or micronuclei, but the data for these parameters are still too limited to allow firm conclusions. There was a statistically significant linear trend (P = 0.0009) in CA strata with regard to subsequent cancer risk. The point estimates of the standardized incidence ratio in the three CA strata were 0.9, 0.7, and 2.1, respectively. Thus, an increased level of chromosome breakage appears to be a relevant biomarker of future cancer risk.

A missense mutation in the hypoxanthine phosphoribosyltransferase gene in a pediatric patient with hyperuricemia

We have identified a mutation in the gene coding for the enzyme hypoxanthine phosphoribosyltransferase in a pediatric patient with hyperuricemia and nephrolithiasis. The mutation is a nucleotide substitution causing an amino acid substitution in the hypoxanthine phosphoribosyltransferase protein. In this patient, fibroblasts but not lymphocytes showed resistance to 6-thioguanine, and reduced enzyme activity was detected in lymphocytes. These results are consistent with the intermediary phenotype associated with partial hypoxanthine phosphoribosyltransferase enzyme deficiency. Altogether, six males in this family suffered from hyperuricemic symptoms, and small differences in phenotype were seen.