Biomarkers of Genotoxicity in Medical Workers Exposed to Low-Dose Ionizing Radiation: Systematic Review and Meta-Analyses

Medical staff represent the largest group of workers occupationally exposed to ionizing radiation (IR). Chronic exposure to low-dose IR may result in DNA damage and genotoxicity associated with increased risk of cancer. This review aims to identify the genotoxicity biomarkers that are the most elevated in IR-exposed vs. unexposed health workers. A systematic review of the literature was performed to retrieve relevant studies with various biomarkers of genotoxicity. Subsequent meta-analyses produced a pooled effect size for several endpoints. The search procedure yielded 65 studies. Chromosome aberrations (CA) and micronuclei (MN) frequencies were significantly different between IR-exposed and unexposed workers (θpooled = 3.19, 95% CI 1.46–4.93; and θpooled = 1.41, 95% CI 0.97–1.86, for total aberrant cells and MN frequencies, respectively), which was not the case for ring chromosomes and nucleoplasmic bridges. Although less frequently used, stable translocations, sister chromatid exchanges (SCE) and comet assay endpoints were also statistically different between IR-exposed and unexposed workers. This review confirms the relevance of CA and MN as genotoxicity biomarkers that are consistently elevated in IR-exposed vs. unexposed workers. Other endpoints are strong candidates but require further studies to validate their usefulness. The integration of the identified biomarkers in future prospective epidemiological studies is encouraged.

Position effects of 22q13 rearrangements on candidate genes in Phelan-McDermid syndrome

Phelan-McDermid syndrome (PMS) is a multi-system disorder characterized by significant variability in clinical presentation. The genetic etiology is also variable with differing sizes of deletions in the chromosome 22q13 region and types of genetic abnormalities (e.g., terminal or interstitial deletions, translocations, ring chromosomes, or SHANK3 variants). Position effects have been shown to affect gene expression and function and play a role in the clinical presentation of various genetic conditions. This study employed a topologically associating domain (TAD) analysis approach to investigate position effects of chromosomal rearrangements on selected candidate genes mapped to 22q13 in 81 individuals with PMS. Data collected were correlated with clinical information from these individuals and with expression and metabolic profiles of lymphoblastoid cells from selected cases. The data confirmed TAD predictions for genes encompassed in the deletions and the clinical and molecular data indicated clear differences among individuals with different 22q13 deletion sizes. The results of the study indicate a positive correlation between deletion size and phenotype severity in PMS and provide evidence of the contribution of other genes to the clinical variability in this developmental disorder by reduced gene expression and altered metabolomics.

Outcomes in the dedifferentiated liposarcoma cohort of SAR-096, a phase II trial of ribociclib in combination with everolimus in advanced dedifferentiated liposarcoma (DDL), and leiomyosarcoma (LMS).

11515 Background: Dedifferentiated liposarcoma (DDL) is characterized by ring chromosomes of chromosone12, which includes amplification of MDM2 and CDK4. Exposure to CDK4 inhibitors in Rb+ leiomyosarcoma (LMS) cell lines leads to decreased cell proliferation, and increased senescence, and G0/G1-phase arrest. When combined, ribociclib a CDK4 inhibitor and everolimus, an mTOR inhibitor show synergistic growth inhibition in multiple tumor models. We hypothesized that this combination could lead to increased disease control in patients with DDL. Methods: This study enrolled patients (pts) into one of two cohorts: DDL or Rb+ LMS. LMS pts were required to have 1 prior line of therapy; DDL pts required no prior therapy. There were no limits to prior therapies in either group. Measurable disease by RECIST 1.1 was also required. Ribociclib was given at 300 mg daily for 21/28 days and everolimus was given continuously at 2.5 mg daily in 28 day cycles. The primary endpoint was progression free rate at 16 weeks. A Simon two-stage design was utilized and if at least 8 out of 24 pts were progression free at 16 weeks, the treatment was declared promising for the cohort. Here in we present data on the DDL cohort. Results: To date, 21 DDS pts, median age of 63 (range 40-79), of which 43% (n = 9) female were treated. Median prior lines of therapy was 1 (range 0-6). Of 19 pts with complete data, 8 (42%) met the primary endpoint of non-progression at 16 weeks. Confirmed partial response was seen in 2 pts (10%). Median PFS was 16 weeks, and stable disease occurring as best response in 11 (55%) pts. Grade 3-4 toxicities were uncommon except for lymphopenia (24%) and neutropenia (33%); no episode of neutropenic fever were observed. There was one death on study secondary to myocardial infarction, considered possibly related to therapy. Results of optional tissue biopsies pre and on therapy obtained to assess pharmacodynamic changes in PTEN, pAKT, CDK4, Rb and pS6 will be presented. Conclusions: The combination of ribociclib and everolimus demonstrates activity in DDL with prolonged stable disease (>16 weeks) meeting the primary protocol endpoint. Notably partial responses were also observed. The combination was well tolerated with acceptable side effects. Updated outcomes will be presented. Clinical trial information: NCT03114527.

The Relationship of the Efficiency of Energy Conversion Into Growth as an Indicator for the Determination of the Optimal Dosage for Mutation Breeding With the Appearance of Chromosomal Bridges, Ring Chromosomes, Micronuclei and Incomplete Mitosis After Gamma Irradiation of Kernels of Triticum Turgidum Ssp. Durum L. Cultivar Orania

BackgroundA 50% growth reduction of seedling height (GR50) after acute gamma irradiation of dormant kernels is widely used as a measure of irradiation damage to obtain the ideal irradiation dosage for mutation breeding. It became clear in recent years that the GR50 is not sensitive enough to predict the ideal gamma irradiation dosage for mutation breeding and it predicts a value that is higher than ideal. The study aim was to determine whether root, shoot and seedling growth on the one side and the efficiency of energy conversion into growth on the other are measuring different growth retardation effects of gamma irradiation that are the result of DNA damage (bridges, ring chromosomes, micronuclei, incomplete mitosis) in Triticum turgidum ssp. durum. If the efficiency of energy conversion into growth is measuring different effects, the usefulness of efficiency of energy conversion into growth to predict the optimal dosage for mutation breeding will be investigated. ResultsThe kernels were gamma irradiated from 50 - 350 Gy using a 60Cobalt source. The kernels were left to germinate and grow for a period of 132 hours for the shoot and root growth and the efficiency of energy conversion into growth determination and for a period of 47.5 hours for the determination of the number of bridges, ring chromosomes, micronuclei and incomplete mitosis. The control differed highly significantly from 50 Gy and higher dosages and from 250 Gy and higher dosages for root and shoot growth respectively and from 250 Gy for the efficiency of energy conversion into growth. There was a highly significant increase in the number of bridges and micronuclei between 50 Gy and 150 Gy together with the higher irradiation dosages and only from 250 Gy for the ring chromosomes and interphase cells with incomplete mitosis. Root and seedling growth on the one hand and the efficiency of energy conversion into growth on the other were found to be measuring different effects of gamma irradiation on plant growth. ConclusionThe optimal dosage for mutation breeding was determined by making use of the efficiency of energy conversion into growth.

Complex biology of constitutional ring chromosomes structure and (in)stability revealed by somatic cell reprogramming

Human ring chromosomes are often unstable during mitosis, and daughter cells can be partially or completely aneuploid. We studied the mitotic stability of four ring chromosomes, 8, 13, 18, and 22, in long-term cultures of skin fibroblasts and induced pluripotent stem cells (iPSCs) by GTG karyotyping and aCGH. Ring chromosome loss and secondary aberrations were observed in all fibroblast cultures except for r(18). We found monosomy, fragmentation, and translocation of indexed chromosomes. In iPSCs, aCGH revealed striking differences in mitotic stability both between iPSC lines with different rings and, in some cases, between cell lines with the same ring chromosome. We registered the spontaneous rescue of karyotype 46,XY,r(8) to 46,XY in all six iPSC lines through ring chromosome loss and intact homologue duplication with isoUPD(8)pat occurrence, as proven by SNP genotype distribution analysis. In iPSCs with other ring chromosomes, karyotype correction was not observed. Our results suggest that spontaneous correction of the karyotype with ring chromosomes in iPSCs is not universal and that pluripotency is compatible with a wide range of derivative karyotypes. We conclude that marked variability in the frequency of secondary rearrangements exists in both fibroblast and iPSC cultures, expanding the clinical significance of the constitutional ring chromosome.

Turner’s syndrome mosaicism in girls with neurodevelopmental disorders: a cohort study and hypothesis

Background Turner’s syndrome is associated with either monosomy or a wide spectrum of structural rearrangements of chromosome X. Despite the interest in studying (somatic) chromosomal mosaicism, Turner’s syndrome mosaicism (TSM) remains to be fully described. This is especially true for the analysis of TSM in clinical cohorts (e.g. cohorts of individuals with neurodevelopmental disorders). Here, we present the results of studying TSM in a large cohort of girls with neurodevelopmental disorders and a hypothesis highlighting the diagnostic and prognostic value. Results Turner’s syndrome-associated karyotypes were revealed in 111 (2.8%) of 4021 girls. Regular Turner’s syndrome-associated karyotypes were detected in 35 girls (0.9%). TSM was uncovered in 76 girls (1.9%). TSM manifested as mosaic aneuploidy (45,X/46,XX; 45,X/47,XXX/46,XX; 45,X/47,XXX) affected 47 girls (1.2%). Supernumerary marker chromosomes derived from chromosome X have been identified in 11 girls with TSM (0.3%). Isochromosomes iX(q) was found in 12 cases (0.3%); one case was non-mosaic. TSM associated with ring chromosomes was revealed in 5 girls (0.1%). Conclusion The present cohort study provides data on the involvement of TSM in neurodevelopmental disorders among females. Thus, TSM may be an element of pathogenic cascades in brain diseases (i.e. neurodegenerative and psychiatric disorders). Our data allowed us to propose a hypothesis concerning ontogenetic variability of TSM levels. Accordingly, it appears that molecular cytogenetic monitoring of TSM, which is a likely risk factor/biomarker for adult-onset multifactorial diseases, is required.

46,XY,r(8)/45,XY,−8 Mosaicism as a Possible Mechanism of the Imprinted Birk-Barel Syndrome: A Case Study

Ring chromosome 8 (r(8)) is one of the least frequent ring chromosomes. Usually, maternal chromosome 8 forms a ring, which can be lost from cells due to mitotic instability. The 8q24 region contains the imprinted KCNK9 gene, which is expressed from the maternal allele. Heterozygous KCNK9 mutations are associated with the imprinting disorder Birk-Barel syndrome. Here, we report a 2.5-year-old boy with developmental delay, microcephaly, dysmorphic features, diffuse muscle hypotonia, feeding problems, motor alalia and noncoarse neurogenic type of disturbance of muscle electrogenesis, partially overlapping with Birk-Barel syndrome phenotype. Cytogenetic analysis of lymphocytes revealed his karyotype to be 46,XY,r(8)(p23q24.3)[27]/45,XY,−8[3]. A de novo 7.9 Mb terminal 8p23.3p23.1 deletion, a 27.1 Mb 8p23.1p11.22 duplication, and a 4.4 Mb intact segment with a normal copy number located between them, as well as a 154-kb maternal LINGO2 gene deletion (9p21.2) with unknown clinical significance were identified by aCGH + SNP array. These aberrations were confirmed by real-time PCR. According to FISH analysis, the 8p23.1-p11.22 duplication was inverted. The ring chromosome originated from maternal chromosome 8. Targeted massive parallel sequencing did not reveal the KCNK9 mutations associated with Birk-Barel syndrome. Our data allow to assume that autosomal monosomy with inactive allele of imprinted gene arising from the loss of a ring chromosome in some somatic cells may be an etiological mechanism of mosaic imprinting disorders, presumably with less severe phenotype.

Cytogenetic Study on the Biostimulation Potential of the Aqueous Fruit Extract of Hippophae rhamnoides for a Sustainable Agricultural Ecosystem

This cytogenetic study evaluates the biostimulation potential of the aqueous extract of seabuckthorn fruits (AESF) in plant cells, using the Allium cepa species as a test plant. The effects were monitored both at the macroscopic and microscopically level. The onion bulbs were exposed to the action of different concentrations of AESF (0.5, 1, 1.5, 2, and 2.5%) for 72 h. The obtained results showed the positive effect induced by the aqueous extract on the growth of the meristematic roots, but only at concentrations ranging between 0.5–1.5%, when the average length of the roots had values between 2.51–3.40 cm, which means an increase compared to the untreated control with 3.71–40.49%. Within the same concentration range of the AESF, an effect of intensifying the mitotic activity was recorded. On the other hand, at the 2–2.5% concentration of the AESF, there was an inhibitory effect on the growth of meristematic roots. Additionally, concentrations ≥2% of AESF induced a cytotoxic and genotoxic effect through the occurrence of some chromosomal and nuclear abnormalities in A. cepa cells (sticky, laggards, ring chromosomes, and micronucleus). The obtained results suggest the biostimulation potential of the AESF for plant cells and the possibility of using it as an eco-friendly fertilizer.

Modeling of dynamic mosaicism on ring chromosomes in human fibroblasts and IPSCS

Митотическая нестабильность кольцевых хромосом может приводить к появлению клеточных клонов с различной генетической структурой. В качестве модели нестабильности кольцевых хромосом в митозе мы использовали фибробласты от пациентов с r(8), r(13), r(18) и r(22) и полученные из них индуцированные плюрипотентные стволовые клетки (ИПСК). Линии ИПСК с r(22) имели относительно стабильный кариотип на протяжении десятков (до 60) пассажей и сохраняли неизменную структуру кольцевой хромосомы. Кариотип линий ИПСК с r(8) и r(18) на ранних пассажах стабильный, планируется его изучение на поздних пассажах. Наибольшее разнообразие кариотипа выявлено в линиях ИПСК с r(13), в которых наблюдали различные перестройки и выраженную клеточную гетерогенность. Определение факторов, влияющих на митотическую стабильность кольцевых хромосом, может иметь значение для консультирования пациентов. Mitotic instability of ring chromosomes can lead to the appearance of cell clones with different genetic structure. IPSCs from fibroblasts of patients with r(8), r(13), r(18), and r(22) were used as a model of ring chromosomes mitotic behavior. Karyotypes of iPSC lines with r(8) and r(18) have so far been evaluated only in the early passages, lines with r(22) have maintained a relatively stable karyotype up to 60 passages. The occurrence of rearrangements and cellular heterogeneity was found characteristic for r(13) iPSCs. The determination of factors affecting the ring chromosomes mitotic stability would be beneficial for the patient’s prognosis.