Sister chromatid exchanges in the peripheral lymphocytes of newborns with Down syndrome after in vitro exposure to blue or green light

Cytotoxicity and genotoxicity of blue LED light and protective effects of AA2G in mammalian cells and associated DNA repair deficient cell lines

Light emitting diode (LED) devices emit narrow bands of the blue, green, and red light spectrum rather than the continuous spectrum emitted from sunlight and fluorescent light bulbs. LED devices have become considerably common in society, and the fluence of blue light from LED devices is more intense than other light sources. Previous studies presented that the blue light spectrum may harness potentially inimical genotoxicity. Therefore, the aim of this study was to investigate this potential cytotoxicity and genotoxicity, as well as identify the mechanism of the cellular effects induced by blue LED light exposure in mammalian cell lines with their DNA repair deficient mutants. Our results demonstrated that blue LED light induced both oxidative stress to cells and cytotoxic and genotoxic effects including reduction of clonogenicity, cell cycle arrest, induction of sister chromatid exchanges, endoreduplicated chromosomes, and increased frequency of HPRT locus mutations. In DNA repair deficient cells, particularly those involving double strand break repair deficiency, cells presented hypersensitivity to blue LED light exposure. Blue LED light also induced chromosome aberrations more in DNA repair deficient cells than wild type cells. The cytotoxicity of blue LED light was reduced by an effective antioxidant, ascorbic acid 2-glucoside, which can suppress blue LED light induced oxidative stress. These results indicated that prolonged, high intensity exposure to blue LED light induces genotoxic stress to cells, and oxidative stress induced by blue LED light is targeting DNA to induce these biological effects.

Oxidative stress and endoreduplication induced by blue light exposure to CHO cells

Blue light is commonly used for the treatment of Neonatal Jaundice and as a photodynamic therapy for cancer. In comparison to ultraviolet light, blue light has a lower toxicity due to the differences in photon energies. However, blue light can still be mutagenic to cells. The proposed mechanism suggests blue light exposure induces reactive oxygen species inducing oxidative stress. In this study, we examined how blue light exposure caused genotoxic effects utilizing Chinese hamster ovary (CHO) cells and UV135 cells when exposed to fluorescent blue light. Cytotoxic effects of blue light exposure were quantified through cellular oxidative stress analysis, cell survival assay, and in cell cycle arrest experiments. Genotoxicity was studied in sister chromatid exchange (SCE) only, and endoreduplication formation. Following blue light exposure, an increase of cell cycle arrest, oxidative stress, and cytotoxicity was observed. Blue light treatment also produced an increased amount of SCE, and more importantly, induced endoreduplicated chromosomes. In conclusion, exposure to blue light resulted in significant genotoxicity of the treated cells.

Genotoxic effects of white fluorescent light on human lymphocytes in vitro

Sources of light beams such as white fluorescent light, are present in our daily life to meet the needs of life in the modern world. This study was conducted with the objective of determining the possible genotoxic, cytotoxic and aneugenic effects caused by this agent in different stages of the cell cycle (G0/early G1, S, and late G2), using different cytogenetic parameters (sister chromatid exchanges--SCE, chromosome aberrations--CA, and detection of aneugenic effects) in lymphocytes from temporary cultures of human peripheral blood. WFL showed a genotoxic effect in vitro, expressed by an increase in the frequency of SCE's, regardless of the cell cycle stage. However, no increase in the frequency of CAs was observed. In addition, disturbances in cell cycle kinetics and chromosomal segregation were also observed. Taken together, such data may contribute to a better understanding and a different management in the use of phototherapy for some pathological conditions.

Oxidative stress: A bridge between Down's syndrome and Alzheimer's disease

Besides the genetic, biochemical and neuropathological analogies between Down's syndrome (DS) and Alzheimer's disease (AD), there is ample evidence of the involvement of oxidative stress (OS) in the pathogenesis of both disorders. The present paper reviews the publications on DS and AD in the past 10 years in light of the "gene dosage" and "two-hit" hypotheses, with regard to the alterations caused by OS in both the central nervous system and the periphery, and the main pipeline of antioxidant therapeutic strategies. OS occurs decades prior to the signature pathology and manifests as lipid, protein and DNA oxidation, and mitochondrial abnormalities. In clinical settings, the assessment of OS has traditionally been hampered by the use of assays that suffer from inherent problems related to specificity and/or sensitivity, which explains some of the conflicting results presented in this work. For DS, no scientifically proven diet or drug is yet available, and AD trials have not provided a satisfactory approach for the prevention of and therapy against OS, although most of them still need evidence-based confirmation. In the future, a balanced up-regulation of endogenous antioxidants, together with multiple exogenous antioxidant supplementation, may be expected to be one of the most promising treatment methods.

Child and maternal household chemical exposure and the risk of acute leukemia in children with Down's syndrome: a report from the Children's Oncology Group

Compared with the general pediatric population, children with Down's syndrome have a much higher risk of acute leukemia. This case-control study was designed to explore potential risk factors for acute lymphoblastic leukemia and acute myeloid leukemia in children with Down's syndrome living in the United States or Canada. Mothers of 158 children with Down's syndrome and acute leukemia (97 acute lymphoblastic leukemia, 61 acute myeloid leukemia) diagnosed between January 1997 and October 2002 and mothers of 173 children with Down's syndrome but without leukemia were interviewed by telephone. Positive associations were found between acute lymphoblastic leukemia and maternal exposure to professional pest exterminations (odds ratio = 2.25, 95% confidence interval: 1.13, 4.49), to any pesticide (odds ratio = 2.18, 95% confidence interval: 1.08, 4.39), and to any chemical (odds ratio = 2.72, 95% confidence interval: 1.17, 6.35). Most of the associations with acute myeloid leukemia were nonsignificant, and odds ratios were generally near or below 1.0. This exploratory study suggests that household chemical exposure may play a role in the development of acute lymphoblastic leukemia in children with Down's syndrome.

Formation of photoproducts and cytotoxicity of bilirubin irradiated with turquoise and blue phototherapy light

AIM

To compare a new turquoise ("green") fluorescent phototherapy lamp (490 nm) with a conventional blue phototherapy lamp (450 nm) with respect to cytotoxicity and photochemical effects of bilirubin.

METHODS

Mouse lymphoma cells (L5178Y-R) in the presence of bilirubin solutions were exposed to phototherapy light. Occurrence of necrosis and apoptosis, reduction of mitotic index and inhibited cell growth was assayed by appropriate methods. The presence of bilirubin and its photoisomers was measured by high-pressure liquid chromatography analysis and absorption spectroscopy.

RESULTS

At constant and equal light irradiances, the cytotoxic effects in the presence of bilirubin bound to human serum albumin showed that the green lamp caused significantly less necrosis (n = 4, p < 0.05) and less inhibition of cell multiplication (n = 3, p < 0.05) than the blue lamp. A slightly lower apoptotic fraction, although not statistically significant, was observed in cells exposed to the blue lamp. Photo-oxidation of bilirubin was more prominent with blue light irradiation. The photoequilibria between geometric isomers of bilirubin were different for the two lamps; more geometric photoisomers were formed by blue irradiation (n = 6, p < 0.05). The amounts of the most water-soluble isomers (presumably mainly lumirubin) were rather similar for the two lamps.

CONCLUSION

The two lamps were similar in the formation of therapeutically relevant photoproducts, but the blue lamp showed potential in forming more photo-oxidation products and in causing more severe cellular damage in the presence of bilirubin.

Cytogenetic study of workers exposed to chromium compounds

The frequency of sister chromatid exchanges (SCEs), high SCE frequency cells (HFCs), and genetic polymorphism of genotypes glutathione S-transferase (GST) M1 and T1 were analyzed in peripheral lymphocytes of 35 workers occupationally exposed to chromium (Cr) and 35 matched control group. Results showed that workers exposed to Cr showed 6.07 SCE/cell, as compared to 4.76 SCE/cell for the control group (p<0.01). Smokers showed a statistically significant higher frequency of SCE than non-smokers in both groups. The work duration of Cr workers was an important factor. Workers exposed for more than 5 years showed a significantly higher level of SCEs (p<0.05). Workers exposed to Cr for 5 or more years had higher HFC rates (51.4%) than those exposed for less than 5 years (22.9%), with an odds ratio of 4.5 times than those exposed for less than 5 years. In HFC analysis, Cr workers who smoked showed a higher level of HFC (60%) than the control group (5.7%) and also had a higher odds ratio (60.4) compared with the control group. Among non-smokers, the odds ratio was 9.0. Another objective of this study is to investigate the relationship between SCE and genetic polymorphisms of GST M1 and T1 in Cr workers. The results showed that the incidence of GSTM1 null genotype was 60% in the control group and 77.1% in Cr workers, and percentages of GSTT1 deletion were 42.9% and 62.9% in control and exposed individuals, respectively. There was a slightly increased frequency of SCE among Cr workers with GSTM1 null genotype as opposed to non-null genotype individuals. A similar result was seen among the control group; however, there were no statistically significant differences. In conclusion, the current study found the positive induction of SCE in workers who smoked or/and were exposed to Cr. However, different GST genotypes did not influence the level of cytogenetic damage between groups. Despite slight variation in numbers, they all appear to be not different.

Increased steady state mRNA levels of DNA-repair genes XRCC1, ERCC2 and ERCC3 in brain of patients with Down syndrome

Although deficient DNA-repair was proposed for neurodegenerative disorders including Down Syndrome (DS), repair genes for nucleotide excision repair or X-ray repair have not been studied in brain yet. As one of the hypotheses for the pathogenesis of brain damage in DS is oxidative stress and cells of patients with DS are more susceptible to ionizing irradiation, we decided to study ERCC2, ERCC3 and XRCC1, representatives of repair genes known to be involved in the repair of oxidative DNA-damage. mRNA steady state levels of ERCC2, ERCC3, XRCC1, a transcription activator (TAF-DBP) and an elongation factor (EF1A) were determined and normalized versus the housekeeping gene beta-actin in five individual brain regions of nine controls and nine DS patients. Although different in the individual regions, DNA-repair genes were consistently higher in temporal, parietal and occipital lobes of patients with DS accompanied by comparable changes of TFA-DBP and EF1A. Our results are the first to describe DNA-repair gene patterns in human brain regions providing the basis for further studies in this area. We showed that DNA-repair genes ERCC2 and ERCC3 (excision-repair-cross-complementing-) for nucleotide excision repair and XRCC1 (X-ray-repair-cross-complementing-) for X-ray-repair, were increased at the transcriptional level with the possible biological meaning that this increase may be compatible with permanent (oxidative?) DNA damage.

Effect of vitamin E on chromosomal aberrations in lymphocytes from patients with Down's syndrome

A possible protective effect of vitamin E (DL-alpha-tocopherol) on chromosomal damage was evaluated in lymphocytes from patients with Down's syndrome (DS) and from controls. This included the analysis of the basal and G2 chromosomal aberration frequencies in lymphocytes cultured with and without 100 microM vitamin E. The chromosomal damage in G2 was determined by scoring the number of chromosomal aberrations in lymphocyte cultures treated with 5 mM caffeine, 2 h before harvesting. Vitamin E treatment decreased the basal and G2 chromosomal aberrations both in control and DS lymphocytes. In DS cells, this protective effect, expressed as a decrease in the chromosomal damage, was greater (50%) than in controls (30%). These results suggest that the increment in basal and G2 aberrations yield in DS lymphocytes may be related to the increase in oxidative damage reported in these patients.

Expression of DNA excision-repair-cross-complementing proteins p80 and p89 in brain of patients with Down Syndrome and Alzheimer's disease

Although deficient DNA repair was proposed for neurodegenerative disorders including Down syndrome (DS), repair proteins for nucleotide excision repair have not been studied in brain yet. As one of the hypotheses for the pathogenesis of brain damage in DS and Alzheimer's disease (AD), is oxidative stress, and cells of patients with DS were shown to be more susceptible to ionizing irradiation. We decided to study expression of excision repair-cross-complementing (ERCC) gene products, proteins 80 and 89, representatives of repair genes known to be involved in the repair of different types of DNA damage. ERCC2-protein 80 kDa and ERCC3-protein p89 were determined in five individual brain regions of controls, aged DS and AD patients. Although different in the individual regions, DNA repair proteins were consistently higher in temporal and frontal lobes of patients with DS and higher in all brain regions of patients with AD. Our results are the first to describe DNA repair gene protein patterns in human brain regions providing the basis for further studies in this area. We showed that DNA repair genes ERCC2 and ERCC3 (excision-repair-cross-complementing) for nucleotide excision repair were increased at the protein level with the possible biological meaning that this increase may be compatible with and indicate ongoing (oxidative?) DNA damage.