Abstract
Domestic egg-laying hens have a high incidence of spontaneous ovarian cancer as they become older. Between the ages of four and six, 11–35% of these hens will develop ovarian adenocarcinoma or oviductal adenocarcinoma. The high rate of ovarian cancer can be explained by the “incessant ovulation” hypothesis, where it is believed that repeated cycles of epithelial damage and repair during ovulation lead to DNA damage and neoplastic transformation. In both the laying hen and in women, the risk of ovarian cancer increases with the number of ovulations. Thus, Hakim et al. are investigating the utility of the laying hen as a model of human ovarian cancer for preclinical chemoprevention studies. As part of their work in validating this model, they analyzed ovarian tumors from hens to determine if genetic alterations in this species were similar to known mutations in humans. Specifically, they screened for mutations in the p53 tumor suppressor gene and H-ras and K-ras oncogenes by direct sequencing, and examined HER-2/neu overexpression by immunohistochemistry. Samples (n = 172) were obtained from two flocks. Hens in Flock A had normal ovulation until the age of 2 when they underwent caloric restriction to inhibit ovulation until age 4. Hens in Flock B had normal ovulation until age 4. Some hens in both groups received chemopreventive strategies. Mutatons in p53 were present in only 14% of tumors from Flock A (fewer lifetime ovulations) but 96% of tumors from Flock B (prolonged ovulation). Ras mutations were rare in both flocks. HER-2/neu was overexpression in the majority of ovarian adenocarcinomas but rarely in oviductal adenocarcinomas. Overall, these results—high rates of p53 mutations, rare ras mutations, and overexpression of HER-2/neu—parallel what is seen in human ovarian carcinoma. Interestingly, the staining pattern of HER-2/neu in tumor cells was somewhat different in the hens than in humans; the significance of this is unclear. This study supports the use of the egg-laying hen as a model for human ovarian cancer and may be useful for future preventive and therapeutic trials.
Hakim AA, Barry CP, Barnes HJ, et al. Ovarian adenocarcinomas in the laying hen and women share similar alterations in p53, ras, and HER-2/neu. Cancer Prev Res
Canine degenerative myelopathy (DM) typically presents in dogs 8 years of age or older. It is a fatal neurodegenerative disease with increased incidence in the Pembroke Welsh corgi, Boxer, Rhodesian ridgeback, German shepherd and Chesapeake Bay retriever. Awano and colleagues performed a genome-wide association study using samples from affected and unaffected Pembroke Welsh corgis to identify candidate genes for DM. The strongest candidate was the superoxide dismutase 1 (SOD1) gene on canine chromosome 31. Mutations in SOD1 are associated with amyotrophic lateral sclerosis (ALS), which is a fatal neurodegenerative disease of humans. Sequencing of genomic DNA uncovered a G to A transition in exon 2 that predicts an E40K missense mutation in the protein. Affected dogs from all 5 predisposed breeds had a high rate of homozygosity for the A/A genotype, while dogs from breeds in which DM is rare had a much lower rate of the A allele. Histologic examination of the spinal cord from a subset of affected dogs showed white matter degeneration in the dorsal and lateral columns. Neurons contained cytoplasmic inclusions that stained positive with anti-SOD1 antibodies. Skeletal muscle lesions were consistent with denervation atrophy, and peripheral nerves showed loss of myelinated fibers and endoneurial fibrosis. This study demonstrates that dogs with DM have both upper and lower motor neuron disease, and identifies the dogs as the first spontaneously occurring animal model of ALS.
Awano T, Johnson GS, Wade CM, et al. Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis. Proc Natl Acad Sci USA
Granulomas, the hallmark of mycobacterial infection, have long been considered a protective mechanism by which the host can wall off and contain the infection. Recent work by Davis and Ramakrishnan, however, shows that granulomas may actually facilitate the spread of the microorganism early in the infectious process. Transparent zebrafish embryos were infected with Mycobacterium marinum and quantitative intravital microscopy was used to follow granuloma formation during the course of infection. The mycobacteria recruit macrophages to the nascent granuloma, where they quickly phagocytose bacteria-containing macrophages undergoing apoptosis. This occurs at a rate of 2.3 newly recruited macrophages per infected cell, and leads to rapid expansion of bacterial numbers. Mycobacteria lacking RD1, a component of the ESX-1/RD1 virulence locus, had greatly reduced capacity to recruit uninfected cells to the site of infection. Some of the newly infected macrophages migrate to other locations and become secondary granulomas. The adaptive immune response eventually recruits T lymphocytes and enhances formation of mature granulomas. This work suggests that the adaptive immune response does not restrain mycobacterial expansion by granuloma formation, as previously thought, but instead plays a role in transforming the granuloma to a more mature form that allows equilibrium between the host and pathogen.
Davis JM, Ramakrishnan L. The role of the granuloma in expansion and dissemination of early tuberculous infection. Cell
Drug-induced liver injury (DILI) is frequently responsible for drug failure during development and also for a drug to be withdrawn from the market after regulatory approval. Therefore, the negative impact of DILI cannot be underestimated. In order to restructure how potential DILI can be detected in preclinical studies the Liver Toxicity Biomarker Study (LTBS) was formed to determine if biomarkers predictive of DILI could be discovered, validated, and incorporated into the drug development process. The LTBS is a collaborative undertaking between the FDA's National Center for Toxicological Research and BG Medicine, Inc, with support from seven pharmaceutical companies and three technology partners. This article reports on Phase I of the LTBS in which two compounds, entacapone and tolcapone, were studied in rats. These drugs were chosen for comparison because entacapone is not associated with hepatotoxicity, whereas tolcapone is associated with dose-related increases in transaminases and was withdrawn from the market following reports of fatal hepatotoxicity. Preliminary results from 3-day and 28-day dosing studies in rats identified several promising biomarkers derived from a thorough molecular systems analysis of liver tissue, plasma and urine on an impressive array of platforms. These biomarkers will be the basis for testing in Phase II. Work arising from the LTBS could result in substantial economic and health benefits in the future.
McBurney RN, Hines WM, Von Tungeln LS, et al. The Liver Toxicity Biomarker Study: Phase I design and preliminary results. Toxicol Pathol