TestSmart-high production volume chemicals: an approach to implementing alternatives into regulatory toxicology.

This article examines the status and application of alternatives defined as replacements, refinements, and reduction for screening high production volume (HPV) chemicals. It specifically focuses on the Screening Information Data Set (SIDS), a series of toxicological tests recommended by the Organization for Economic Cooperation and Development to screen such chemicals. Alternative tests associated with acute, repeat-dose, genetic, and reproductive and developmental toxicity were examined at 2 meetings of academic, industry, and regulatory scientists and their status determined. Tests were placed in 1 of 3 categories: ready for immediate use, in need of or currently undergoing validation, or needing research/developmental work. With respect to traditional acute toxicity testing, the basal cytotoxicity approach was placed in the category of research with the up-and-down, fixed-dose, limit test, and the acute toxic class categorized as available for immediate use and the neutral red assay under validation. Cell culture methods that could provide information on acute target organ toxicity were all categorized in the research stage. Studies of the Ah receptor were placed under validation. All alternative tests for repeat-dose toxicity were placed in the category of research. With regard to genetic toxicity, the Ames, mouse lymphoma, and Chinese hamster ovary methods were considered ready for immediate use, while the in vitro micronucleus and Syrian hamster ovary assays were placed in the validation category. All alternatives for developmental toxicity, with the exception of gene chip technology, were placed in the category of validation. Gene chip technology is considered to be in the research stage. For reproductive toxicity, sperm motility and morphology were considered as ready for immediate use, with the other assays categorized as needing validation or in the research stage. Follow-up to these results is obvious. Work needs to be conducted to move those tests from the research stage to the validation and use stage. This is one approach to the development of alternatives to SIDS. Progress along these lines would apply not only to SIDS but also to toxicology in general.

The TestSmart-HPV Program--development of an integrated approach for testing high production volume chemicals.

The TestSmart program was developed in response to the High Production Volume Chemical Challenge, a voluntary initiative under which chemical producers provide basic toxicity data on chemicals produced in greater than one million pounds annually. Specifically, under the Challenge, chemical producers will generate data as needed to complete the Screening Information Data Set (SIDS), as defined by the Organization for Economic Cooperation and Development (OECD). The TestSmart program is a collaborative effort of the Johns Hopkins Center for Alternatives to Animal Testing, the Environmental Defense Fund, Carnegie-Mellon University, and the University of Pittsburgh. The goal of the TestSmart program is to provide a humane and efficient approach to collecting SIDS data. The program has two objectives, one immediate and the other more long term. The immediate objective has been to make recommendations to reduce the number of animals used in collecting SIDS data under the Challenge. This was accomplished, through a group process, by examining the current status of alternative methods for SIDS endpoints and by providing an assessment of the "state of readiness" of current and potential future alternatives. The long-term objective is to provide a model for other programs to follow the TestSmart concept of a more efficient and humane approach to obtain toxicological data of interest to regulators and the public.

Encephalocoele as a complication of intranasal sinus surgery: optimal evaluation with magnetic resonance imaging.

We report a case of post-operative frontal basal encephalocoele evaluated using a new magnetic resonance imaging (MRI) sequence, fast inversion recovery for myelin suppression (FIRMS). FIRMS was developed to enhance the differentiation between grey and white matter. In this case, the sequence was beneficial in distinguishing the encephalocoele from adjacent nasal mucosa and secretions.

Internal derangement of the knee after ipsilateral femoral shaft fracture: MR imaging findings.

OBJECTIVE: This study uses magnetic resonance (MR) imaging to delineate the types and frequencies of injuries seen in the knee after ipsilateral femoral shaft fracture. We also compare the results of the orthopedic knee examination with the MR findings. DESIGN AND PATIENTS: MR imaging of the ipsilateral knee was performed on 34 patients with closed femoral shaft fractures. Indications for knee MR imaging included knee pain at the time of fracture, soft tissue swelling or an effusion of the knee, or a positive knee examination under anesthesia. The patients had a mean age of 27 years and all were stabilized with intramedullary nails. Imaging was performed a mean time of 2.5 days after surgery. All patients had knee examinations done under anesthesia, and the MR results were compiled and compared with the clinical examinations. RESULTS: Ninety-seven percent of patients demonstrated knee effusions. Twenty-seven percent of patients demonstrated meniscal tears, with the posterior horn of the medial meniscus most frequently torn. The medial collateral ligament was the most frequent site of ligamentous injury (38%) followed by the posterior cruciate ligament (21%). Fifty percent of patients had injuries of the extensor mechanism. Bone bruises were noted in 32% of patients. Articular cartilage injuries were confined to the patella in four cases. One occult tibial plateau fracture and one meniscocapsular separation were seen. CONCLUSIONS: There is a common incidence of both ligamentous and meniscal injury to the knee after ipsilateral femoral shaft fracture. MR imaging can be useful in assessing the extent of injury, and may reveal findings unsuspected after clinical examination of the knee.

Asbestos plaques in a typical Veteran's hospital population.

Previous authors have described several pleural abnormalities on chest radiology as being pathognomonic for asbestos exposure. We sought to determine the percentage of admissions and outpatients at a typical Veteran's Affairs hospital with these findings, and researched medical records to verify the frequency at which patients having positive radiographs were suspected either by clinical/occupational history or radiologically to have had prior significant exposure to asbestos. Radiographs of 1,212 consecutive patients were evaluated by a certified B reader, and the medical records as well as previous radiology reports of all positive patients were reviewed. Twenty-eight (2.3%t) of the radiographs had pleural abnormalities consistent with asbestos exposure, with the patients, all male, ranging in age from 50 to 98 years (mean 75.6). Radiology reports described pleural plaques in only 12 of the 21 (57%) cases with prior exams available; in only seven (33%) was an asbestos etiology considered by the interpreting radiologist. The plaques were misdiagnosed in four instances as being indicative of other, unrelated pathology. A history of known dust exposure was expressed by only five patients (18%). Eleven described working in occupations now known to have a high incidence of exposure, but neither patient nor examining physician expressed consideration of dust inhalation. In conclusion, we have found that a significant percentage of patients in certain subpopulations show radiographic evidence of asbestos exposure that may be a harbinger of related pathology. Unfortunately, because of a low index of suspicion, thorough environmental histories are often deferred, many radiographic changes are either not recognized or are misdiagnosed, and these patients are not followed with the stringent protocols they deserve.

Characterization of a primary hepatocyte culture system for toxicological studies.

An hepatocyte culture system was developed for potential use in toxicological studies in vitro. Rat hepatocytes were isolated by two-step collagenase perfusion and cultured on Vitrogen-coated Permanox dishes in a modified Chee's medium containing 1 microM dexamethasone and 1% dimethylsulfoxide. The cells remained highly viable for at least 10 d as determined by lactate dehydrogenase release and total protein levels. Albumin secretion into the medium, as a measure of differentiated function, was maintained at elevated levels over the course of 10 d in culture. A number of CYP activities were determined by the analysis of testosterone metabolism in freeze-thawed cells, diazepam metabolism in live cells, and specific assays for CYP 1A1/2, 2B1/2, 2E1, and 3A. Results of these assays indicated that a wide range of CYP isozymes were maintained, some activities were enhanced under the conditions of culture and some activities were inducible. Activities of the phase II enzymes, glutathione S-transferase and UDP-glucuronosyltransferase, and glutathione levels were also maintained in the cultured hepatocytes for at least 6 d. These results strongly support the use of this hepatocyte culture system for in vitro toxicological studies.

Questioning the clinical significance of upper gastrointestinal cytomegalovirus disease following heart transplantation.

We performed a retrospective review of patients who underwent esophagogastroduodenoscopy after heart transplantation to determine the clinical setting in which upper gastrointestinal cytomegalovirus disease is identified. No gastrointestinal cytomegalovirus disease was found prior to transplant 51 and this period (from transplant 1 to 50) correspond to a time when significantly fewer esophagogastroduodenoscopies included biopsy. Patients in whom cytomegalovirus was identified were more likely to have been CMV seronegative and to have received a heart from a seropositive donor (60% vs 20%, P = 0.029). In addition, patients with cytomegalovirus used aspirin more commonly (90% vs 31%, P = 0.001), and underwent esophagogastroduodenoscopy earlier after transplantation (123d vs 652d, P = 0.029). We conclude that factors that increase the use of esophagogastroduodenoscopy and biopsy in the early transplant period increase the likelihood of identifying cytomegalovirus in gastrointestinal tissue. However, the clinical course and significance of cytomegalovirus identified in the upper gastrointestinal tract in heart transplant patients may be difficult to discern.

Growth stimulation followed by growth inhibition in livers of female rats treated with ethinyl estradiol.

Ethinyl estradiol (EE) is a strong promoter of hepatocarcinogenesis in female rats. A common effect shared by many non-genotoxic hepatic promoters is the stimulation of hyperplastic growth. However, studies by others with several hepatic promoters have shown that following an initial, transient increase in liver growth, continued exposure causes an inhibition in basal and/or induced growth. We have shown that EE also causes an initial, transient increase in hepatocyte proliferation (Carcinogenesis, 7, 2007-20014, 1986). The objective of the investigation reported here was to determine whether chronic EE treatment also becomes inhibitory to basal and/or induced liver growth. Female Lewis rats were treated with EE at 2.5 and 5.0 micrograms/rat/day using time-release tablets. Seven days prior to sacrifice, the rats were implanted with osmotic minipumps containing bromodeoxyuridine (BrdU) to allow the cumulative labeling of replicating hepatocytes. At sacrifice, liver tissue was fixed, sectioned and the percent labeled hepatocyte nuclei determined by immunohistochemistry. The results of these experiments revealed that, as expected, during the first 7 days of treatment, EE increased hepatocyte proliferation. However, after 28 and 42 days of EE treatment, the basal level of liver growth was dramatically inhibited. Thus, hepatocyte nuclear labeling indices, compared to controls, were reduced by 72 and 88% after 28 and 42 days of treatment respectively. An analysis of 125I-labeled EGF binding to isolated liver membranes revealed that EGF receptor levels decreased during the initial period of growth, but had returned to control levels by day 21 when replication had ceased. In another experiment, rats were treated with EE at 5.0 micrograms/rat/day for 21 days; control rats received placebo time-release tablets. At the end of that time, the rats were surgically partially hepatectomized and the level of subsequent regenerative DNA synthesis was determined using [3H]thymidine administered 2 h prior to sacrifice 24, 48, 72 and 96 h later. The results showed that EE caused an inhibition of regenerative growth. While at each time point the level of DNA synthesis in EE-treated rats was not significantly less than in corresponding controls, statistical analysis indicated that overall, EE caused a significant reduction in liver growth. The results of these studies demonstrate that chronic EE treatment leads to the appearance of a mitosuppressed state in the liver which is characterized by reduced cell turnover and decreased growth responsiveness.(ABSTRACT TRUNCATED AT 400 WORDS)

Sex hormones and tumor promotion in liver.

Epidemiological and experimental data strongly support a causal relationship between exposure to excessive levels of estrogens and the development of cancer in various tissues. In this paper, we have presented background information that shows a correlation between the prolonged use of oral contraceptives and the development of liver cancer. The clinical data supported the hypothesis that the estrogenic components of oral contraceptives were promoters of hepatocarcinogenesis, and the experimental evidence in support of this hypothesis and bearing on the mechanisms involved are also reviewed. The effects of estrogens on liver neoplasia and growth are: (i) synthetic steroidal estrogens are potent promoters of hepatocarcinogenesis in female rats; (ii) these estrogens stimulate liver growth at doses that are not hepatotoxic; (iii) the mechanisms by which the estrogens stimulate liver growth are indirect and include the enhancement of a serum/plasma growth factor, co-mitogenic effects which result in enhanced responsiveness of cultured hepatocytes to epidermal growth factor and decreased sensitivity of hepatocytes to growth inhibition by transforming growth factor-beta; (iv) the co-mitogenic effects of synthetic estrogens extend to endogenous estrogens and natural product estrogens; and (v) the co-mitogenic effects of estrogens for epidermal growth factor are associated with increased epidermal growth factor receptor protein levels caused by an increase in the half-life of the receptor protein. The synthetic estrogens also have weak "complete" carcinogenic activity in rat liver and strong complete carcinogenic activity in Syrian hamster kidney and Armenian hamster liver. Evidence from the literature is presented in support of a hypothesis that this process may involve indirect genotoxicity mediated through redox cycling and the formation of hydroxylated DNA bases. This process, together with the potent promoting activity of these estrogenic chemicals, may account for their complete carcinogenicity.

A phase I/II trial of zidovudine, interferon-alpha, and granulocyte-macrophage colony-stimulating factor in the treatment of human immunodeficiency virus type 1 infection.

Twenty-four patients infected with human immunodeficiency virus type 1 (HIV-1) who had CD4+ counts of 0.2-0.5 x 10(9) cells/l received granulocyte-macrophage colony-stimulating factor (GM-CSF) in combination with zidovudine plus escalating doses of daily subcutaneous interferon-alpha. Mean neutropenia-inducing doses of interferon-alpha were 9.4 x 10(6) and 10.6 x 10(6) IU/day for groups receiving 100 or 200 mg zidovudine every 4 h, respectively. Mean GM-CSF doses used to reverse neutropenia were 0.64 and 0.63 microgram/kg/day for these two groups, respectively, although the mean minimum effective GM-CSF dose for both was only 0.30 microgram/kg/day. Serum p24 antigen declined greater than 70% in all 5 antigenemic patients. Toxicities included a dose-dependent increase in lymphokine-like side effects (100%), anorexia and weight loss (42%), fatigue (42%), and anemia (50%). While toxicities of the combination can be significant, low-dose GM-CSF readily ameliorated neutropenia associated with zidovudine and interferon-alpha therapy without adversely affecting the antiviral properties of the combination.

Characterization of preneoplastic and neoplastic lesions in the rat pancreas.

Nodules of acinar cells with increased proliferative potential develop in the pancreas of carcinogen-treated rats and in untreated aged rats. Large nodules are classed as adenomas. Phenotypic and genotypic characteristics of nodule cells were compared with normal pancreas and transplantable acinar cell carcinomas by several methods. Nuclei of acinar cells from normal pancreas, adenomas, and three carcinomas in situ had normal diploid DNA content as determined by flow cytometry. One of two primary carcinomas had a hypodiploid DNA content. Two of three transplantable carcinomas were aneuploid with a DNA content in the tetraploid range. Explants from nodules and adenomas failed to grow in soft agar, whereas several carcinomas were positive in this assay. A primary carcinoma was serially transplanted, but transplantation of nodules or adenomas failed. Transfection of DNA from carcinomas in situ yielded a higher frequency of NIH 3T3 transformants than DNA from adenomas. DNAs from the transformants did not contain ras sequences. These studies indicate that cells from nodules and adenomas have low growth potential and lack critical phenotypic and genotypic characteristics of transformed malignant cells that were present in some primary and transplanted carcinomas.

Regulation of the steady state level of Fc gamma RI mRNA by IFN-gamma and dexamethasone in human monocytes, neutrophils, and U-937 cells.

The high affinity IgG FcR Fc gamma RI, CD64, plays important roles in the immune response. Fc gamma RI is predominantly expressed on monocytes and macrophages, and barely detectable on neutrophils. rIFN-gamma markedly increases the expression of Fc gamma RI on neutrophils, monocytes, macrophages and myeloid cell lines such as U-937, HL-60, and THP-1. Glucocorticoids inhibit the augmentation of Fc gamma RI expression by rIFN-gamma on neutrophils and myeloid cell lines, but enhance the augmentation of Fc gamma RI expression by rIFN-gamma on monocytes. In this study, we examined the effect of rIFN-gamma and dexamethasone (Dex) on the steady state level of Fc gamma RI mRNA in U-937 cells, neutrophils, and monocytes by hybridizing total RNA with the Fc gamma RI cDNA probe, p135. We found that the amount of Fc gamma RI mRNA increased within 1 h of treatment with rIFN-gamma in all three cell types. This initial induction of Fc gamma RI mRNA by rIFN-gamma was completely blocked by an inhibitor of RNA synthesis, actinomycin D, suggesting that the rIFN-gamma-mediated induction of Fc gamma RI mRNA is dependent on gene transcription. Dex, used in combination with rIFN-gamma, partially blocked the induction of Fc gamma RI mRNA by rIFN-gamma in U-937 cells and neutrophils, but caused a synergistic increase in Fc gamma RI mRNA levels in monocytes. The inhibitory effect of Dex on the steady state level of Fc gamma RI mRNA in U-937 cells was blocked by an inhibitor of protein synthesis, cycloheximide, suggesting that Dex-induced proteins were involved in the regulation of Fc gamma RI expression. This study indicates that the regulation of Fc gamma RI expression on U-937 cells, neutrophils, and monocytes by rIFN-gamma and Dex occurs, at least in part, at the mRNA level. rIFN-gamma increases the steady state level of Fc gamma RI mRNA through a common pathway among U-937 cells, neutrophils, and monocytes, whereas the effect of Dex on rIFN-gamma-induced Fc gamma RI mRNA is cell-type specific.

Activation of c-Ki-ras not detectable in adenomas or adenocarcinomas arising in rat pancreas.

The objective of this study was to determine whether activation of c-Ki-ras occurs in carcinogen-induced rat pancreatic tumors. DNAs from 27 samples, which included adenomas, carcinomas in situ, and adenocarcinomas arising in azaserine-treated rats and corn oil-gavaged rats along with a nafenopin-induced rat pancreatic adenocarcinoma were examined for mutation of c-Ki-ras at codons 12, 13, and 61 by using the polymerase chain reaction. Our results indicate that activation of c-Ki-ras is not a common event during pancreatic carcinogenesis in the rat.

Expression of c-myc, c-raf-1, and c-Ki-ras in azaserine-induced pancreatic carcinomas and growing pancreas in rats.

We examined the pattern of expression of several proto-oncogenes during nonneoplastic growth and in acinar cell neoplasms in the rat pancreas. The levels of c-myc, c-raf-1, and c-Ki-ras mRNAs were increased in regenerating pancreata following surgical partial pancreatectomy and following administration of camostat. We also investigated proto-oncogene expression associated with the progression of pancreatic cancers in azaserine-treated rats. Injection of a single dose (30 mg/kg) of azaserine (O-diazoacetyl-L-serine) to 14-d-old rats leads to a variety of neoplastic lesions in the rat pancreas. Total RNA was isolated from lesions in various stages of tumor progression, including adenomas, carcinomas in situ, and invasive carcinomas. We observed increased expression of c-myc, c-raf-1, and c-Ki-ras in azaserine-induced adenomas and carcinomas. Actin expression was also increased in these tissues, whereas amylase expression was variable. However, when compared to the normal growing pancreas, the level of proto-oncogene expression in the adenomas and carcinomas was disproportionate to the degree of cellular division in those tissues. Thus, the alterations induced by azaserine apparently caused a deregulated increase in expression of cellular oncogenes associated with growth regulation.

Complement abnormalities in multiple myeloma.

PURPOSE: Patients with multiple myeloma have been shown to have defective opsonization and C3 deposition. Previous studies have suggested that defective C3 deposition may be related to a failure of C3 activation in myeloma serum, the mechanism of which is unknown. We therefore decided to investigate the underlying mechanism responsible for the failure in C3 activation and deposition. PATIENTS AND METHODS: The study consisted of 10 patients from whom a total of 12 serum specimens were obtained. Normal serum was prepared from a pool of serum specimens in four healthy male donors. We evaluated, in vitro, the kinetics of C3 deposition onto zymosan using radiolabeled C3 under various conditions. We also measured the serum levels of a variety of complement components using standard methods. RESULTS: Five of 10 patients' sera demonstrated poor C3 deposition onto zymosan at all time points, whereas an additional two showed poor C3 deposition at early time points but a rebound to normal by 30 minutes. Multiple components of the classical and alternative complement pathways were decreased in many patients, with the most striking abnormalities occurring in those with the poorest C3 deposition. No single complement component abnormality was found to be common to the group. Elevations in Bb fragment concentration strongly suggest in vivo activation as the likely mechanism for depletion of alternative pathway components; the mechanism for classical pathway abnormalities is less clear. There was an inverse correlation between paraprotein concentration and abnormal C3 deposition (p less than 0.0001) and C3 (p less than 0.0005) and C4 (p less than 0.0001) concentrations. However, no consistent evidence of fluid-phase complement consumption was present. CONCLUSION: The defect in C3 activation and deposition in multiple myeloma cannot be explained on the basis of a single complement component abnormality but rather is due to a heterogeneous group of complement abnormalities. Although no correlation between in vitro abnormalities and clinical status was identified in this small group of patients, it is likely that the described complement defects play an important role in defective host defense in multiple myeloma.

Correlation between the induction of heat shock protein 70 and enhanced viral reactivation in mammalian cells treated with ultraviolet light and heat shock.

Enhanced viral reactivation (EVR) is considered to be one manifestation of an inducible response to DNA damage in mammalian cells analogous to the SOS response in Escherichia coli. EVR is characterized by the increased survival of ultraviolet (UV)-irradiated virus in cells which have been pretreated with DNA-damaging agents or by another type of cellular stress, heat shock (HS). In this study, we have analyzed the induction of nuclear proteins from Vero cells treated with either UV or HS, with the goal of identifying the protein(s) which mediate the EVR response. Results of 2-dimensional protein gel electrophoresis and fluorographic analysis of [35S]methionine-labeled nuclear proteins showed that UV-irradiation caused the increased synthesis of five proteins at 4-9 h after treatment. At 19-24 h, one of these proteins was still being synthesized at a higher level in UV-irradiated cells, and there were nine additional proteins whose syntheses were enhanced over control levels. In contrast, HS induced only one Mr 72,000 nuclear protein whose synthesis was maximal during the 4-9-h labeling period and corresponded to one of the proteins induced by UV at 19-24 h. Subsequent Western and Northern blot analyses have confirmed that this protein is a member of the heat shock protein (hsp) 70 family. Elevated nuclear levels of this protein correlated temporally with the maximum EVR response induced by each treatment (4 h after HS and 24 h after UV). Since the kinetics of EVR is different following UV and HS and parallels the difference in the induction of nuclear levels of hsp70 following each treatment, the results suggest that hsp70 may be involved in mediating the EVR response. In addition, this protein may also play a role in the recovery of DNA synthesis in UV-irradiated cells.

Expression of c-raf-1 and A-raf-1 during regeneration of rat liver following surgical partial hepatectomy.

The major objective of this study was to investigate the expression of members of the raf family of proto-oncogenes during rat liver regeneration. The steady-state level of expression of both c-raf-1 and A-raf-1 increased three- to fivefold 18-24 h following partial hepatectomy, and it returned to basal levels by 72 h. Expression of c-myc and Ha-ras mRNA was increased at 3 and 18-24 h, respectively, confirming previous reports. Increased steady-state levels of c-raf-1, A-raf-1, and Ha-ras mRNA were also detected in hepatocytes isolated from rat liver 24 h after partial hepatectomy. Thus, elevated expression of the raf genes closely correlated with that of Ha-ras, beginning at 12 h and reaching maximal levels during the first peak of DNA synthesis following partial hepatectomy.

Effects of carcinogen treatment on rat liver DNA synthesis in vivo and on nascent DNA synthesis and elongation in cultured hepatocytes.

One objective of this study was to determine the effects of N-hydroxy-2-acetylaminofluorene (N-OH-AAF) treatment on DNA synthesis in regenerating rat liver. Rats were subjected to a two-thirds hepatectomy followed 20 h later by i.p. injection of N-OH-AAF. 4 h after carcinogen injection, it was found that N-OH-AAF caused a dose-dependent inhibition of [3H]thymidine incorporation into liver DNA. This inhibition was followed by a gradual, but incomplete recovery beginning 28 h after carcinogen treatment. Radioimmunoassay of deoxyguanine-C8 adducts remaining in liver DNA indicated that the recovery began prior to detection of adduct removal. The second objective of the study was to determine the effects of DNA damage on the size distribution and elongation of nascent hepatocyte DNA. Hepatocytes, which have been shown to demonstrate a pattern of inhibition and subsequent recovery of DNA synthesis following UV irradiation similar to that seen in vivo upon treatment with N-OH-AAF (Zurlo and Yager, 1984), were cultured under conditions that promote replicative DNA synthesis. The size distribution of nascent DNA after UV irradiation was determined by pH step gradient alkaline elution analysis. [3H]Thymidine pulse times and subsequent chase times were adjusted to equalize amounts of DNA synthesis in control and UV-irradiated cells. The results show that UV irradiation caused a dose-dependent decrease in the size distribution of nascent DNA suggesting an inhibition of elongation. Pulse-chase studies revealed that subsequent joining of nascent chains in UV-irradiated hepatocytes occurred at a rate comparable to or faster than controls and that this could be inhibited by caffeine. The results obtained from both the in vivo and in vitro studies show that resumption of DNA synthesis and nascent strand elongation occur on damaged templates. These observations along with our previous studies demonstrating the ability of UV-irradiated hepatocytes to carry out enhanced reactivation of UV-irradiated herpes virus lend support to the idea that DNA damage leading to inhibition of DNA synthesis may induce SOS-type processes which if mutagenic may play a role in the initiation of carcinogenesis.

Effect of pyridoxal deficiency on pancreatic DNA damage and nodule induction by azaserine.

The effects of pyridoxal deficiency on the genotoxicity and nodule inducing ability of azaserine in rat pancreas were examined. Azaserine at a dose of 10 mg/kg body weight which causes substantial DNA damage in normal rat pancreas, failed to induce DNA damage detectable by alkaline elution in the pancreas of pyridoxal-deficient rats. Studies of the distribution of [14C]azaserine in rat tissues revealed that uptake of azaserine in pancreas of pyridoxal deficient rats was not significantly different from that of normal rats. The ability of a structurally unrelated amino acid carcinogen N delta-(N-methyl-N- nitrosocarbamoyl )-L-ornithine to damage rat pancreatic DNA was not affected by pyridoxal deficiency. In another study, the pyridoxal antagonist 4'-deoxypyridoxine was administered i.p. to rats prior to and during azaserine treatment. Four months later, quantitative sterological analysis of atypical acinar cell nodules revealed that there was a significant reduction in the number but not size of nodules in the pancreases of 4'-deoxypyridoxine-treated rats. These results confirm the relationship of the induction of DNA damage by azaserine to its ability to induce pancreatic tumors, and support previous studies of azaserine metabolism, strongly suggesting that the in vivo activation of this carcinogen is pyridoxal dependent.