AOP report: Development of an adverse outcome pathway for oxidative DNA damage leading to mutations and chromosomal aberrations

The Genetic Toxicology Technical Committee (GTTC) of the Health and Environmental Sciences Institute (HESI) is developing adverse outcome pathways (AOPs) that describe modes of action leading to potentially heritable genomic damage. The goal was to enhance the use of mechanistic information in genotoxicity assessment by building empirical support for the relationships between relevant molecular initiating events (MIEs) and regulatory endpoints in genetic toxicology. Herein, we present an AOP network that links oxidative DNA damage to two adverse outcomes (AOs): mutations and chromosomal aberrations. We collected empirical evidence from the literature to evaluate the key event relationships between the MIE and the AOs, and assessed the weight of evidence using the modified Bradford-Hill criteria for causality. Oxidative DNA damage is constantly induced and repaired in cells given the ubiquitous presence of reactive oxygen species and free radicals. However, xenobiotic exposures may increase damage above baseline levels through a variety of mechanisms and overwhelm DNA repair and endogenous antioxidant capacity. Unrepaired oxidative DNA base damage can lead to base substitutions during replication and, along with repair intermediates, can also cause DNA strand breaks that can lead to mutations and chromosomal aberrations if not repaired adequately. This AOP network identifies knowledge gaps that could be filled by targeted studies designed to better define the quantitative relationships between key events, which could be leveraged for quantitative chemical safety assessment. We anticipate that this AOP network will provide the building blocks for additional genotoxicity-associated AOPs and aid in designing novel integrated testing approaches for genotoxicity.

Biomarkers of DNA damage response improve in vitro micronucleus assays by revealing genotoxic mode of action and reducing the occurrence of irrelevant positive results

We have previously described two flow cytometry-based in vitro genotoxicity tests: micronucleus (MN) scoring (MicroFlow®) and a multiplexed DNA damage response biomarker assay (MultiFlow®). Here, we describe a strategy for combining the assays in order to efficiently supplement MN analyses with a panel of biomarkers that comment on cytotoxicity (i.e. relative nuclei count, relative increased nuclei count, cleaved PARP-positive chromatin and ethidium monoazide-positive chromatin) and genotoxic mode of action (MoA; i.e. γH2AX, phospho-histone H3, p53 activation and polyploidy). For these experiments, human TK6 cells were exposed to each of 32 well-studied reference chemicals in 96-well plates for 24 continuous hours. The test chemicals were evaluated over a range of concentrations in the presence and absence of a rat liver S9-based metabolic activation system. MultiFlow assay data were acquired at 4 and 24 h, and micronuclei were scored at 24 h. Testing 32 chemicals in two metabolic activation arms translated into 64 a priori calls: 42 genotoxicants and 22 non-genotoxicants. The MN assay showed high sensitivity and moderate specificity (90% and 68%, respectively). When a genotoxic call required significant MN and MultiFlow responses, specificity increased to 95% without adversely affecting sensitivity. The dose-response data were analysed with PROAST Benchmark Dose (BMD) software in order to calculate potency metrics for each endpoint, and ToxPi software was used to synthesise the resulting lower and upper bound 90% confidence intervals into visual profiles. The BMD/ToxPi combination was found to represent a powerful strategy for synthesising multiple BMD confidence intervals, as the software output provided MoA information as well as insights into genotoxic potency.

Analysis of historical negative control group data from the rat in vivo micronucleus assay

A database of micronuclei counts for historical negative control data from rat in vivo micronuclei tests performed in 10 different laboratories was established. Data were available from over 4000 negative control rats from 10 laboratories. The mean frequency of micronucleated cells (MN)/1000 cells ranged from 0.44 to 2.22, a 5-fold range. Overall there were no major sex or strain differences in frequency, although there were some small but statistically significant differences within laboratories. There was appreciable variability between experiments compared with variability within experiments in some laboratories. No specific factor was identified which could explain this variability although it was noted that many different vehicles were used in the experiments. It is hoped that these data will help laboratories beginning studies with the rat micronucleus assay and those involved in the assessment of micronucleus assay results.

Diagnostically challenging human papillomavirus-associated primary squamous cell carcinoma of the rectum with metastasis in both ovaries: a case report

Introduction

Squamous cell carcinomas of the rectum are extremely rare and their pathogenesis is still under debate. Their proper diagnosis and treatment may thus be challenging.

Case presentation

A 52-year-old Caucasian woman was transferred to our department with a history of pelvic pain. Colonoscopy revealed a small tumorous lesion of the upper rectum and an endoscopic biopsy showed infiltration of the rectal mucosa by a squamous cell carcinoma. Afterward, tumorous lesions were found on imaging in both her ovaries. A laparoscopy with adnexectomy and anal mapping was performed and revealed tumor masses of squamous cell carcinoma in both ovaries. Based on the large size of the ovarian tumors and the concurrence of extensive, partly ciliated, macrocystic epithelium in one of the ovaries, a diagnosis of ovarian squamous cell carcinoma arising from a mature teratoma was rendered. However, human papillomavirus genotyping analyses were positive for human papillomavirus-16 in both the rectal tumor and ovarian tumors leading to a final diagnosis of a human papillomavirus-associated rectal squamous cell carcinoma metastatic to both ovaries. Neoadjuvant chemoradiation therapy of her rectum, total mesorectal excision, and hysterectomy were performed followed by adjuvant chemotherapy.

Conclusion

Colorectal squamous cell carcinoma is a rare disease. In cases of colorectal squamous cell carcinoma, metastatic disease at any other location has to be excluded. Human papillomavirus genotyping is essential in this context. Discussion of the treatment strategies should be interdisciplinary and include chemoradiation therapy and radical surgery.

In vivo genotoxicity testing strategies: Report from the 7th International workshop on genotoxicity testing (IWGT)

The working group reached complete or majority agreement on many issues. Results from TGR and in vivo comet assays for 91 chemicals showed they have similar ability to detect in vivo genotoxicity per se with bacterial mutagens and Ames-positive carcinogens. TGR and comet assay results were not significantly different when compared with IARC Group 1, 2 A, and unclassified carcinogens. There were significantly more comet assay positive responses for Group 2B chemicals, and for IARC classified and unclassified carcinogens combined, which may be expected since mutation is a sub-set of genotoxicity. A liver comet assay combined with the bone marrow/blood micronucleus (MNviv) test would detect in vivo genotoxins that do not exhibit tissue-specific or site-of-contact effects, and is appropriate for routine in vivo genotoxicity testing. Generally for orally administered substances, a comet assay at only one site-of-contact GI tract tissue (stomach or duodenum/jejunum) is required. In MNviv tests, evidence of target tissue exposure can be obtained in a number of different ways, as recommended by ICH S2(R1) and EFSA (Hardy et al., 2017). Except for special cases the i.p. route is inappropriate for in vivo testing; for risk evaluations more weight should be given to data from a physiologically relevant administration route. The liver MN test is sufficiently validated for the development of an OECD guideline. However, the impact of dosing animals >6 weeks of age needs to be evaluated. The GI tract MN test shows promise but needs more validation for an OECD guideline. The Pig-a assay detects systemically available mutagens and is a valuable follow-up to in vitro positive results. A new freeze-thaw protocol provides more flexibility. Mutant reticulocyte and erythrocyte frequencies should both be determined. Preliminary data are available for the Pig-a assay in male rat germ cells which require validation including germ cell DNA mutation origin.

Differential micronucleus frequency in isogenic human cells deficient in DNA repair pathways is a valuable indicator for evaluating genotoxic agents and their genotoxic mechanisms

The micronucleus (MN) test has become an attractive tool both for evaluating the genotoxicity of test chemicals because of its ability to detect clastogenic and aneugenic events and for its convenience. As the MN assay has been mostly performed using only DNA repair-proficient mammalian cells, we believed that the comparison of the MN frequency between DNA repair-proficient and -deficient human cells may be an excellent indicator for detecting the genotoxic potential of test chemicals and for understanding their mode of action. To address this issue, the following five genes encoding DNA-damage-response (DDR) factors were disrupted in the TK6 B cell line, a human cell line widely used for the MN test: FANCD2, DNA polymerase ζ (REV3), XRCC1, RAD54, and/or LIG4. Using these isogenic TK6 cell lines, the MN test was conducted for four widely-used DNA-damaging agents: methyl methanesulfonate (MMS), hydrogen peroxide (H₂ O₂ ), γ-rays, and mitomycin C (MMC). The frequency of micronuclei in the double strand break repair-deficient RAD54^-/- /LIG4^-/- cells after exposure to γ-rays, H₂ O₂ , MMS and MMC was 6.2-7.5 times higher than that of parental wild-type TK6 cells. The percentages of cells exhibiting micronuclei in the base excision repair- and single strand break repair-deficient XRCC1^-/- cells after exposure to H₂ O₂ , MMC and MMS were all ∼5 times higher than those of wild-type cells. In summary, a supplementary MN assay using the combination of RAD54^-/- /LIG4^-/- , XRCC1^-/- and wild-type TK6 cells is a promising method for detecting the genotoxic potential of test chemicals and their mode of action. Environ. Mol. Mutagen., 2018. © 2018 Wiley Periodicals, Inc.

[Chronic, refractory ulcer on the ring finger : Manifestation of distal epithelioid sarcoma]

The epithelioid sarcoma classic, "distal" type was first published in 1970. It is a very rare, malignant, aggressive subcutaneous soft tissue sarcoma that shows characteristic positivity for both epithelial and mesenchymal immunohistochemical markers. It grows very slowly and mostly presents in young men. Clinically the tumor is characterized as a coarse cutaneous or subcutaneous nodular induration that often ulcerates in the course of the disease. An association with trauma is often described and can lengthen time to diagnosis. Most frequently it is found on the flexural side of fingers, the back of the hands, soles of the feet, and extensor sides of arms and legs. Specific for this type of sarcoma is the progression along nerves, tendons, and fasciae. Treatment of choice should be wide excision of the tumor, sentinel node biopsy, and possibly even localized postoperative radiation therapy. Unfortunately the epithelioid sarcoma is very likely to recur and is then associated with metastases in the lung and lymph nodes.

Measurement of cytogenetic damage in rodent blood with a single-laser flow cytometer

The in vivo rodent micronucleus test is widely utilized to screen chemicals for genotoxic activity. Double-strand chromosome breaks or dysfunction of the mitotic spindle apparatus can lead to micronuclei formation in dividing cells. Erythrocytes have become the target population of choice, as precursor cells are continuously dividing and micronuclei are readily observable after extrusion of nuclei. The traditional method has been to stain peripheral blood or bone marrow smears and microscopically determine the frequency of micronucleated erythrocytes. Because these events are rare, the process is tedious and time consuming. This unit describes a procedure for fixing and staining rodent peripheral blood for flow cytometric enumeration. The combination of reagents provides for differential labeling and enumeration of four subpopulations: mature erythrocytes, micronucleus-containing mature erythrocytes, young erythrocytes (reticulocytes), and micronucleus-containing young erythrocytes. Malaria-infected rodent erythrocytes, which closely mimic micronucleus-containing erythrocytes, serve as a biological standard to facilitate rational and consistent equipment calibration.

Performance of flow cytometric analysis for the micronucleus assay--a reconstruction model using serial dilutions of malaria-infected cells with normal mouse peripheral blood

To confirm the performance and statistical power of a flow cytometric method for scoring micronucleated erythrocytes, reconstruction experiments were performed. For these investigations, peripheral blood erythrocytes from untreated mice, with a micronucleated erythrocyte frequency of approximately 0.1% were combined with known quantities of Plasmodium berghei (malaria) infected mouse erythrocytes. These cells had an infected erythrocyte frequency of approximately 0.7%, and mimic the DNA content of micronuclei (MN). For an initial experiment, samples with a range of MN/malaria (Mal) content were constructed and analysed in triplicate by flow cytometry until 2000, 20,000 and 200,000 total erythrocytes were acquired. In a second experiment, each specimen was analysed in triplicate until 2000, 20,000, 200,000 and 1,000,000 erythrocytes were acquired. As expected, the sensitivity of the assay to detect small changes in rare erythrocyte sub-population frequencies was directly related to the number of cells analysed. For example, when 2000 cells were scored, increases in MN/Mal frequencies of 3.9- or 2.7-fold were detected as statistically significant. When 200,000 cells were analysed, a 1.2-fold increase was detected. These data have implications for the experimental design and interpretation of micronucleus assays that are based on automated scoring procedures, since previously unattainable numbers of cells can now be readily scored.

[Hyperparathyroidism -- a differential diagnosis of cystic bone tumors]

Clinical manifestations of primary hyperparathyroidism include neuromuscular, intestinal, and osseous symptoms with osteolytic lesions of the bone and pathological fractures. In most cases a primary adenoma of the parathyroid gland leads to an increased production of the parathormone with subsequent osteoclastic bone catabolism. Surgical treatment entails removal of the parathyroid adenoma. We present a female patient and the possible diagnostic and differential diagnostic difficulties encountered in interdisciplinary management.

R116C mutation of cationic trypsinogen in a Turkish family with recurrent pancreatitis illustrates genetic microheterogeneity of hereditary pancreatitis

Hereditary pancreatitis is due to heterozygosity for gain-of-function mutations in the cationic trypsinogen gene which result in increased levels of active trypsin within pancreatic acinar cells and autodigestion of the pancreas. The number of disease-causing defects is generally considered to be low. To gain further insight into the molecular basis of this disorder, DNA sequence analysis of all five exons was performed in 109 unrelated patients with idiopathic chronic pancreatitis in order to determine the variability of the underlying mutations. Two German females and one German male were carriers of the most common N29I and R122H mutations (trypsinogen numbering system). In a Turkish proband, an arginine (CGT) to cysteine (TGT) substitution at amino acid position 116 was identified. Family screening demonstrated that the patient had inherited the mutation from his asymptomatic father and that he had transmitted it to both of his children, his daughter being symptomatic since the age of 3 years. In addition, a German male was found to be a heterozygote for a D100H (GAC-->CAC) amino acid replacement. Our data provide evidence for genetic heterogeneity of hereditary pancreatitis. The growing number of cationic trypsinogen mutations is expected to change current mutation screening practices for this disease.

Actinomyces neuii and neonatal sepsis

Actinomyces neuii belongs to the coryneform bacteria. In the case presented here this gram-positive rod had to be considered the pathogen causing not only the chorioam nionitis but also the neonatal sepsis. Conventional therapeutic regimes are effective due to the high sensitivity of A. neuii to beta-lactam antibiotics.

De-differentiated chondrosarcoma is not a 'de-differentiated' chondrosarcoma

AIMS

De-differentiated chondrosarcoma is characterized by the presence of two distinct chondroid and nonchondroid tumour portions. The aim of our study was to investigate the distribution of extracellular matrix components in this tumour entity and thus to shed light on its histogenetic origin.

METHODS AND RESULTS

Histochemical and immunohistochemical analyses were performed for collagen subtypes I, II, III and VI and cartilage proteoglycans in three samples of de-differentiated as well as conventional chondrosarcomas (various grades). In the chondroid tumour areas of de-differentiated chondrosarcoma, typical cartilage matrix components could be detected similar to chondroid areas of grade 1 and 2 conventional chondrosarcomas. In contrast, the tumour matrix of the nonchondroid portions of de-differentiated chondrosarcomas contained matrix molecules which are typical for fibroblastic tissue. This matrix composition was not identical with less differentiated (nonchondroid) areas of grades 2 and 3 conventional chondrosarcomas.

CONCLUSIONS

Our results confirm the chondroid nature of the differentiated portion of de-differentiated chondrosarcoma and indicate a nonchondrocytic nature of the nonchondroid portion. De-differentiated chondrosarcoma should not be considered as a 'de'-differentiated chondrosarcoma (grade 4 neoplasm), but as a tumour entity showing two types of mesenchymal differentiation.

[Changes in regional CNS perfusion in obstructive sleep apnea syndrome: initial SPECT studies with injected nocturnal 99mTc-HMPAO]

Some of the clinical features of obstructive sleep apnoea syndrome (OSA) are suggestive of impaired cerebral blood flow. Cerebral blood flow alterations might, for example, be responsible for headaches, which are frequent complaints in patients with OSA. Even the high frequency of ischaemic cerebral complications in patients with OSA might be caused in part by sleep apnoea-associated impairment of cerebral perfusion. Previous studies have demonstrated reduced total cerebral blood flow in patients with OSA, but regional changes of cerebral perfusion have not been studied up to now. We performed SPECT studies using 99mTc-(d,l)-hexamethyl-propylenaminoxim (HMPAO) as a tracer in 14 adult patients with moderate to severe OSA (AHI > 30/h; mean AHI 59.2 +/- 4.3). The injection of the tracer took place between 2:00 and 4:00 a.m. while repeated episodes of obstructive apnoea were detected by polysomnography during stage II sleep. Data acquisition took place at 7:30 a.m. All measurements were repeated some nights later under effective treatment with nCPAP. Visual analysis showed marked frontal hyperperfusion in 5 patients. When regional perfusion indices were calculated for 32 regions of interest statistical analysis showed reduced perfusion of the left parietal region. These changes were completely reversed by effective nCPAP therapy. These data suggest that OSA is associated with reversible changes of regional cerebral perfusion. The underlying pathophysiologic mechanisms are matter of speculation so far. There might be an apnoea-associated effect of local vascular autoregulation mechanisms acting to compensate systemic blood flow alterations or blood gas changes in OSA. The observed frontal hyperperfusion might be caused by activation of the frontal lobe by repetitive cortical arousals.

Type X collagen expression and hypertrophic differentiation in chondrogenic neoplasias

Little is known about matrix biochemistry and cell differentiation patterns in chondrogenic neoplasms. This is the first description of the focal expression of collagen type X by neoplastic chondrocytes in situ and its incorporation into the extracellular matrix of cartilaginous tumors. This shows that neoplastic chondrocytes have the potential to undergo the full program of cell differentiation, including hypertrophy, comparable to their physiological counterparts in the growth plate. However, only in benign osteochondromas was a zonal expression of type X collagen found similar to that observed in the growth plate, where the cells immediately above the ossification frontier are selectively positive for type X collagen. In enchondromas and chondrosarcomas, the expression was randomly distributed within the tumors. Surprisingly, in less differentiated chondrosarcomas with spindle-shaped cells and non-cartilaginous extracellular matrix, exceptional expression of collagen type X was observed, which indicates potential uncoupling of collagen type X expression from the differentiated chondrocytic phenotype in neoplastic chondrocytes in vivo.

Phenotypic diversity of neoplastic chondrocytes and extracellular matrix gene expression in cartilaginous neoplasms

Chondrocyte differentiation is characterized by distinct cellular phenotypes, which can be identified by specific extracellular matrix gene expression profiles. By applying in situ analysis on the mRNA and protein level in a series of benign and malignant human chondrogenic neoplasms, we were able to identify for the first time different phenotypes of neoplastic chondrocytes in vivo: 1) mature chondrocytes, which synthesized the characteristic cartilaginous extracellular tumor matrix, 2) cells resembling hypertrophic chondrocytes of the fetal growth plate, 3) cells resembling so-called dedifferentiated chondrocytes, and 4) well differentiated chondrocytic cells, which expressed type I collagen, indicating the presence of post-hypertrophic differentiated neoplastic chondrocytes. Chondrocytes exhibiting a range of phenotypes were found to be present in the same neoplasm. The different observed phenotypes, including the dedifferentiated phenotype, were in contrast to the anaplastic cells of high-grade chondrosarcomas. Comparison of expression data with tumor morphology revealed a relationship between the cellular phenotypes, the tumor matrix composition, and the matrix and cell morphology within the neoplasms. The distinctly different phenotypes of neoplastic chondrocytes are the basis of the characteristic high biochemical and morphological heterogeneity of chondroid neoplasms and shed light on their biological and clinical behavior.

Chondrocytic cell differentiation in clear cell chondrosarcoma

Clear cell chondrosarcoma is a rare mesenchymal neoplasm of unclear differentiation. Besides having a chondrogenic nature, an osteogenic differentiation was also proposed. In this study, expression analysis of extracellular matrix genes, which are specific for different mesenchymal cell differentiation pathways, were used to get a better understanding of origin and differentiation pattern of the clear cell chondrosarcoma tumor cells. Our in situ analysis of two cases shows that (1) chondrocytic cell differentiation as marked by the expression of cartilage collagen type II and proteoglycans is a characteristic feature within the development of the neoplasm, (2) multifocal chondrocyte hypertrophy as shown by the expression of type X collagen does occur, and (3) no significant expression of collagen type I, the main gene product of osteoblastic cells, is found by the neoplastic cells. Thus, our study indicates that clear cell chondrosarcoma shows a chondrogenic, but not osteogenic, differentiation and represents a true chondrosarcoma. The unusual scarcity of its extracellular and the multifocal expression of type X collagen marks clear cell chondrosarcoma as a chondrosarcoma tumor entity of a particular cell differentiation pattern. The expression of cartilage type collagens represents a distinct marker from bone metastases of clear cell neoplasms of other origins.

[Presacral phlegmons and meningitis as the complications of a foreign body in the rectosigmoid]

A 24-year-old patient presented with severe back pain in the lumbar and sacral regions and septic temperatures up to 40 degrees C. Lasègue's sign was bilaterally positive. An enhanced cell count was seen in the CSF (1877 cells/microliters, erythrocytes 1024/microliters). Total protein concentration was 4440 mg/dl. The patient also suffered from granulocytic pleocytosis. X-ray as well as scintigrams revealed inflammation of the presacral soft parts involving the os sacrum and bone marrow. Treatment with doxycycline (200 mg/d), fosfomycin (5 g/d), netilmicin (400 mg/d) and ofloxacin (200 mg/d) succeeded in curing the meningitis, whereas the presacral phlegmon persisted. Endoscopic examination showed a rod-shaped foreign body in the rectum that had penetrated deeply into the mucosa and required deformation and removal by laser. The plastic rod of 10 cm length was probably a liquorice stick. The patient denied introducing it per anum; he suspected having swallowed it while drunk. The inflammation subsided rapidly after removal of the foreign body.