Hepatocarcinogenesis (Z#2)/mutagenesis during initiation stage.

Previously, we developed a model for high incidence, endogenously generated hepatocellular carcinoma (HCC), the human alpha-1-antitrypsin (alpha1AT) Z gene transgenic mouse (Z#2). We now examine the potential utility of a model for endogenous carcinogenesis utilizing the Z#2 mouse also transgenic for the lacI gene, a convenient target for in vivo mutagenesis studies. We crossed the Z#2 line and mice transgenic for lambda/lacI shuttle vector (Big Blue), for determination of lacI mutant frequency during initiation of endogenous carcinogenesis. Five month old double transgenic mice (Z#2+/lacI+) successfully displayed: (1) the expected post-inflammatory stage of Z#2 carcinogenesis; and (2) hepatic lacI mutants measured at frequencies (10(-5)-10(-4)) useful to mutagenesis studies. In this study, hepatic lacI mutation frequencies in Z#2 transgenic mice appeared to be only slightly increased (< 2x) when compared to age matched negative controls. In the future, it may be important to reconcile possibly limited lacI mutagenesis at the time of initiation and demonstrated high incidence of hepatocarcinogenesis.

Evaluation of the transgenic Lambda/LacI mouse model as a short-term predictor of heritable risk.

Transgenic male C57BL/6 lambda/lacI mice were used to assess the mutagenic response in seminiferous tubules and epididymal spermatozoa 3 days after exposure to ethylnitrosourea (ENU), iso-propyl methanesulfonate (iPMS) and methyl methanesulfonate (MMS). No significant mutagenic response was observed in epididymal spermatozoa for all three compounds, as expected 3 days after treatment. However, ENU and iPMS treated samples demonstrated significant mutagenic inductions relative to controls in seminiferous tubules while MMS treated samples did not. The failure of MMS to induce a mutagenic response in lambda/lacI transgenic mice is likely due to a combination of the low dose used, the short expression time after exposure and the reduced sensitivity to large deletion events in transgenic lambda/lacI shuttle vectors. In addition, ex vivo mutations were measured in control samples and iPMS treated samples, where 33% of mutants from control samples and 35% of mutants from iPMS treated samples were mosaic.

Databases and software for the analysis of mutations in the human p53 gene, the human hprt gene and both the lacI and lacZ gene in transgenic rodents.

We have created databases and software applications for the analysis of DNA mutations at the humanp53gene, the humanhprtgene and both the rodent transgeniclacIandlacZlocus. The databases themselves are stand-alone dBASE files and the software for analysis of the databases runs on IBM-compatible computers. Each database has a separate software analysis program. The software created for these databases permit the filtering, ordering, report generation and display of information in the database. In addition, a significant number of routines have been developed for the analysis of single base substitutions. One method of obtaining the databases and software is via the World Wide Web (WWW). Open the following home page with a Web Browser: http://sunsite.unc.edu/dnam/mainpage.ht ml . Alternatively, the databases and programs are available via public FTP from: anonymous@sunsite.unc.edu . There is no password required to enter the system. The databases and software are found beneath the subdirectory: pub/academic/biology/dna-mutations. Two other programs are available at the site-a program for comparison of mutational spectra and a program for entry of mutational data into a relational database.

Species-specific differences in hepatic mutant frequency and mutational spectrum among lambda/lacI transgenic rats and mice following exposure to aflatoxin B1.

In vivo mutations were studied in lambda/lacI (Big Blue) transgenic C57BL/6 mice and F344 rats following exposure to either AFB1 (aflatoxin B1) or DMSO vehicle. Fourteen days after exposure, livers were removed for DNA extraction and subsequent mutational analysis of the lacI gene. Mice injected with a single i.p. dose of AFB1 at 2.5 mg/kg did not show a significant increase in liver mutant frequency relative to vehicle-treated controls. DNA sequence analysis of lacI mutations collected from the AFB1-treated mice showed a pattern of mutation similar to that of the previously observed spontaneous mouse liver mutational spectrum. In contrast, rats subjected to one-tenth the mouse AFB1 dosage responded with an approximate 20-fold induction in liver mutant frequency over background. Sequencing of lacI mutations also revealed spectral differences between vehicle- and AFB1-treated rats. A large increase in G:C-->T:A transversions was observed among lacI mutations isolated from the AFB1-treated rats. This work is among the first multi-species in vivo mutagenicity studies using transgenic rodents harboring the same shuttle vector. Such multi-species in vivo assays may prove to be valuable in the areas of mechanistic analysis and risk assessment.

The use of shuttle vectors for mutation analysis in transgenic mice and rats.

The establishment in recent years of transgenic shuttle vector-based mutagenicity assays has provided improved systems for analysis of mutagenic and carcinogenic processes. Results in the mouse have stimulated the development of an alternate species suitable for mutation analysis and have increased our understanding of the existing models. A previously described shuttle vector (lambda LIZ), based on a lacI target gene, was constructed in this laboratory for the study of mutagenesis in transgenic mice and in cultured cell lines. The shuttle vector allows for several options in its recovery from the host genome and in mutant identification. Of the 9 transgenic lineages that were generated with the lambda LIZ vector, one was chosen for use in a standardized mutagenicity assay (Big Blue, mouse lineage A1). Characterization of this lineage included copy-number determination, chromosomal localization of transgene integration and analysis of copy-number stability. As part of the validation process, the standardized color-screening assay has been tested in the mouse, both for spontaneous mutant frequencies and with a variety of model mutagenic compounds, and has been shown to identify most major classes of mutations as evidenced by mutant spectra data. A discussion of the relative sensitivity of the shuttle vector to each of these classes of mutations is included. These studies have now been extended to the generation of transgenic rats containing the same shuttle vector for cross-species analysis. Spontaneous mutant frequencies in two transgenic rat lineages were measured in liver and in germ cells. Preliminary data suggest that spontaneous mutant frequencies in somatic tissue are lower in rats than in mice, a result consistent with historical observations of DNA damage and repair in these two species. Also under evaluation are alternative selectable systems for mutant identification, and hybrid animals obtained from mating lambda LIZ transgenics with genetically engineered mice possessing an inactivated tumor suppressor gene. It is expected that each of these widely varying endeavors will contribute, not only in furthering our understanding of the role transgenic systems should play in human risk assessment, but in illuminating the mechanisms of mutation in general.

Hepatocarcinogenesis is the sequel to hepatitis in Z#2 alpha 1-antitrypsin transgenic mice: histopathological and DNA ploidy studies.

Z mutant-associated alpha 1-antitrypsin deficiency in human beings leads to hepatitis and, in some cases, hepatocellular carcinoma. To begin to delineate the molecular basis for the development of hepatocellular carcinoma in alpha 1-antitrypsin deficiency, we previously developed transgenic mice using human alpha 1-antitrypsin M and Z genomic clones. High-copy Z lineage mice (12 gene copies/haploid mouse genome; "Z#2") had hepatocytes distended with human alpha 1-antitrypsin deficiency globules. Hepatitis was present, and the morphological changes mimicked those observed in human alpha 1-antitrypsin deficiency-related liver disease. The numbers of hepatocytes containing alpha 1-antitrypsin globules decreased with age, and alpha 1-antitrypsin-negative nodular aggregates of hepatocytes increased in number and size. Hepatocytic dysplasia occurred as early as 6 wk and was almost universally present at 1 yr. Nodules of dysplastic cells demonstrating aneuploidy were seen as early as 10 wks. These became persistent, proliferative lesions. Dysplasia and aneuploidy distinctly increased with time and advancing microscopic stage as lesions progressed to malignancy. Tumors were seen after 1 yr as adenomas, which are aneuploid and most likely well-differentiated hepatocellular carcinoma, and borderline malignant lesions; and, in 82% of Z#2 mice 16 to 20 mo old, as invasive hepatocellular carcinoma. These observations suggest but do not conclusively prove that hepatocellular carcinoma in alpha 1-antitrypsin deficiency and other hepatic disorders arises as a result of a common, endogenously stimulated pathway for hepatocellular carcinogenesis.

Transgenic systems for in vivo mutation analysis.

Transgenic mice carrying shuttle vectors containing the lacI gene as the target permit the in vivo measurement of mutations in multiple tissues and have been used to test the mutagenic effects of several compounds. Tissue-specific and time-dependent responses have been observed, and the spectrum of mutations determined by sequencing allows analysis of the role of expression time in mutagenesis. The results obtained from sequencing analysis have demonstrated spectra paralleling those observed in alternative in vivo assays. In addition to color screening, modifications to this system have permitted direct selection for mutations in the lacI target by a variety of methods. Transgenic rats containing the same lambda/lacI shuttle vector have been developed for inter-species comparison of mutagenesis testing results, which may offer a better understanding of the specific mechanisms involved in mutagenesis at the molecular level in vivo.

Histopathology of alpha 1-antitrypsin liver disease in a transgenic mouse model.

Transgenic mice were constructed using human alpha 1-antitrypsin M and Z genomic clones. Livers of the M lineage mice showed slight cellular pleomorphism and immunohistochemically demonstrable finely granular alpha 1-antitrypsin material in hepatocytes. Z lineage mice with five gene copies per haploid mouse genome (Z#1) demonstrated fine granular alpha 1-antitrypsin material and a few large globules. In contrast, Z lineage mice with 12 gene copies per haploid mouse genome (Z#2) demonstrated hepatocytes filled with homogeneous, eosinophilic globules that were strongly reactive with diastase and periodic acid-Schiff and antibody to alpha 1-antitrypsin. Scattered microscopic polymorphonuclear leukocyte accumulations were seen that contained extracellular alpha 1-antitrypsin material, but there was neither histological nor serological evidence of mouse infectious hepatitis. In young animals, small clusters of hepatocytes lacking alpha 1-antitrypsin material were seen. These cells were the dominant population in older animals and formed nodular arrangements. Fibrosis was not demonstrable in neonatal and young animals or in any of the controls, but perisinusoidal fibrosis was seen in older Z#2 mice. Groups of hepatocytes without alpha 1-antitrypsin material showed dysplastic changes. We conclude that the transgenic mouse is a reliable and useful model in which to study the effects of alpha 1-antitrypsin in the liver because it demonstrates changes similar to those in the human disease.

Development of a short-term, in vivo mutagenesis assay: the effects of methylation on the recovery of a lambda phage shuttle vector from transgenic mice.

Transgenic mice suitable for the in vivo assay of suspected mutagens at the chromosome level have been constructed by stable integration of a lambda phage shuttle vector. The shuttle vector, which contains a beta-galactosidase (beta-gal) target gene, can be rescued from genomic DNA with in vitro packaging extracts. Mutations in the target gene are detected by a change in lambda phage plaque color on indicator agar plates. Initial rescue efficiencies of less than 1 plaque forming unit (pfu)/100 micrograms of genomic DNA were too low for mutation analysis. We determined the cause of the low rescue efficiencies by examining primary fibroblast cultures prepared from fetuses of lambda transgenic animals. The rescue efficiency of 5-azacytidine-treated cells increased 50-fold over non-treated controls indicating that methylation was inhibiting rescue. The inhibitory role of methylation was supported by the observation that mcr deficient E. coli plating strains and mcr deficient lambda packaging extracts further improved lambda rescue efficiency. Present rescue efficiencies of greater than 2000 pfu/copy/micrograms of genomic DNA represent a 100,000-fold improvement over initial rescue efficiencies, permitting quantitative mutational analysis. The background mutagenesis rate was estimated at 1 x 10(-5) in two separate lineages. Following treatment with the mutagen N-ethyl-N-nitrosourea (EtNU), a dose dependent increase in the mutation rate was observed in DNA isolated from mouse spleen, with significant induction also observed in mouse testes DNA.

Neonatal growth delay in alpha-1-antitrypsin disease. Influence of genetic background.

We have developed a transgenic mouse strain, Z#2, which represents a model for alpha 1-protease inhibitor (alpha 1-antitrypsin: alpha 1-Pi)-associated liver disease (Dycaico et al., 1988). Fifteen percent of human infants with alpha 1-Pi disease develop non-viral hepatitis which is sometimes associated with growth retardation. Such hepatitis and growth retardation tend to occur in a subset of families with other alpha 1-Pi affected members who have had non-viral hepatitis. The Z#2 mouse strain exhibits non-viral hepatitis and growth retardation. This phenotype is more pronounced in transgenic offspring of crosses between Z#2 mice and DBA/2J inbred mice, and less pronounced in transgenic offspring of crosses between Z#2 and CBA/J inbred mice. Such phenotypic differences resemble the phenotypic differences seen in human families with alpha 1-Pi-associated liver disease.

Neonatal hepatitis induced by alpha 1-antitrypsin: a transgenic mouse model.

Transgenic mouse lineages were established that carry the normal (M) or mutant (Z) alleles of the human alpha 1-antitrypsin (alpha 1-Pi) gene. All of the alpha 1-Pi transgenic mice expressed the human protein in the liver, cartilage, gut, kidneys, lymphoid macrophages, and thymus. The human M-allele protein was secreted normally into the serum. However, the human Z-allele protein accumulated in several cell types, but particularly in hepatocytes, and was found in serum in tenfold lower concentrations than the M-allele protein. Mice in one lineage carrying the mutant Z allele expressed high levels of human alpha 1-Pi RNA and displayed significant runting (50% of normal weight) in the neonatal period. This lineage was found to have alpha 1-Pi-induced liver pathology in the neonatal period, concomitant with the accumulation of human Z protein in diastase-resistant cytoplasmic globules that could be revealed in the Periodic acid-Schiff reaction (PAS). The phenotype of mice in the strain expressing high levels of the Z allele is remarkably similar to human neonatal hepatitis, and this strain may prove to be a useful animal model for studying this disease.