Burden and trend of dietary risk-related colorectal cancer in China and its provinces: findings from the Global Burden of Disease Study 2019

OBJECTIVES

The objective of this experiment was to evaluate the spatial pattern and temporal trend of colorectal cancer (CRC) burden attributed to dietary risk factors in China from 1990 to 2019 using data from the Global Burden of Diseases, Injuries, and Risk Factors study (GBD) 2019.

METHODS

Numbers and age-standardised rates of deaths, disability-adjusted life years (DALYs) and corresponding average annual percentage change (AAPC) were determined. The joinpoint regression analysis was used to assess the temporal trends of CRC deaths and DALYs from 1990 to 2019.

RESULTS

In China, the number of diet-attributable CRC deaths and DALYs in 2019 were 90.41 (95% uncertainty interval: 65.69, 114.67) and 2234.06 (1609.96, 2831.24) per-1000 population, marking 2.05% and 1.68% annual increases since 1990, respectively. The region with the highest increase in age-standardised rates (ASRs) of diet-related CRC deaths and DALYs was in Taiwan with an AAPC of 2.00% (1.51, 2.48), whereas the highest decline in ASRs of CRC deaths and DALYs was observed in Hong Kong with an AAPC of -0.63% (-0.90, -0.35) (all P < 0.05). Nationally, men suffered higher CRC deaths and DALY burdens attributable to dietary risks than did women. Regarding the specific diet group, diets low in calcium, milk, and whole grains contributed to CRC deaths and DALYs the most.

CONCLUSIONS

Diet is an important contributor to increasing CRC burden in China. Necessary measures should be taken to kerb the growing burden attributed to dietary factors, particularly in males and in regions with middle Socio-demographic Index or lower.

[The 504th case: Multiple lymph node enlargement, renal insufficiency, blindness, and white matter lesions of the brain]

A 65-year-old male patient was admitted for recurrent lymph node enlargement for 5 years and elevated creatinine for 6 months. This patient was diagnosed with angioimmunoblastic T-cell lymphoma 5 years ago and underwent multiple lines of anti-tumor therapy, including cytotoxic chemotherapy; epigenetic modifying drugs such as chidamide and azacitidine; the immunomodulator lenalidomide; and targeted therapy such as rituximab, a CD20-targeting antibody, and brentuximab vedotin, which targets CD30. Although the tumor was considered stable, multiple virus activation (including BK virus, JC virus, and cytomegalovirus) accompanied by the corresponding organ damage (polyomavirus nephropathy, cytomegalovirus retinitis, and progressive multifocal leukoencephalopathy) occurred during anti-tumor treatment. Anti-tumor therapy was suspended and ganciclovir was used. The serum viral load decreased and organ functions were stabilized. The purpose of this report was to raise clinicians' awareness of opportunistic virus reactivation during anti-tumor treatment.

Tissue Distribution of mtDNA Copy Number And Expression Pattern of An mtDNA-Related Gene in Three Teleost Fish Species

Teleosts are the most speciose vertebrates and have diverse swimming performance. Based on swimming duration and speed, teleosts are broadly divided into sustained, prolonged, and burst swimming fish. Teleosts with different swimming performance have different energy requirements. In addition, energy requirement also varies among different tissues. As mitochondrial DNA (mtDNA) copy number is correlated with ATP production, we speculated that mtDNA copy number varies among fish with different swimming performance, as well as among different tissues. In other species, mtDNA copy number is regulated by tfam (mitochondrial transcription factor A) through mtDNA compaction and mito-genome replication initiation. In order to clarify the tissue distribution of mtDNA copy number and expression pattern of tfam in teleosts with disparate swimming performance, we selected representative fish with sustained swimming (Pseudocaranx dentex), prolonged swimming (Takifugu rubripes), and burst swimming (Paralichthys olivaceus). We measured mtDNA copy number and tfam gene expression in 10 tissues of these three fish. The results showed the mtDNA content pattern of various tissues was broadly consistent among three fish, and high-energy demanding tissues contain higher mtDNA copy number. Slow-twitch muscles with higher oxidative metabolism possess a greater content of mtDNA than fast-twitch muscles. In addition, relatively higher mtDNA content in fast-twitch muscle of P. olivaceus compared to the other two fish could be an adaptation to their frequent burst swimming demands. And the higher mtDNA copy number in heart of P. dentex could meet their oxygen transport demands of long-distance swimming. However, tfam expression was not significantly correlated with mtDNA copy number in these teleosts, suggesting tfam may be not the only factor regulating mtDNA content among various tissues. This study can lay a foundation for studying the role of mtDNA in the adaptive evolution of various swimming ability in teleost fish.

APP/PS1 Gene-Environmental Cadmium Interaction Aggravates the Progression of Alzheimer's Disease in Mice via the Blood-Brain Barrier, Amyloid-β, and Inflammation

BACKGROUND

There is limited information about gene-environment interaction on the occurrence and the progression of Alzheimer's disease.

OBJECTIVE

To explore the effect of environmental low-dose cadmium (Cd) exposure on the progress of Alzheimer's disease and the underlining mechanism.

METHODS

We administered 1 mg/L, 10 mg/L cadmium chloride (treated groups), and water (control group) to C57BL/6J and APP/PS1 mice through drinking water, from one week before mating, until the offspring were sacrificed at 6 months of age. The behaviors, Cd level, blood-brain barrier (BBB) leakage, Aβ1-42 deposition, and inflammation expression were evaluated in these mice.

RESULTS

Mice of both genotypes had similar blood Cd levels after exposure to the same dose of Cd. The toxic effects of Cd on the two genotypes differed little in terms of neuronal histomorphology and BBB permeability. Cd caused a series of pathological morphological changes in the mouse brains and more fluorescent dye leakage at higher doses. Furthermore, the APP/PS1 mice had more severe damage than the C57BL/6J mice, based on the following five criteria. They were increasing anxiety-like behavior and chaos movement, spatial reference memory damage, Aβ plaque deposition in mouse brains, increasing microglia expression in the brain, and IL-6 higher expression in the cortex and in the serum.

CONCLUSION

Low-dose Cd exposure for 6 months increases Aβ plaque deposition and BBB permeability, exacerbates inflammatory responses, and activates microglia, in APP/PS1 mice. APP/PS1 gene-environmental Cd interaction aggravates the progression of Alzheimer's disease in mice.

A large-scale genome-wide association analysis reveals QTL and candidate genes for intramuscular fat content in Duroc pigs

This study aimed at identifying genomic regions and genes associated with intramuscular fat content (IMF) in Duroc pigs using a weighted single-step GWAS. Data from 3912 pigs, of which 3770 animals were genotyped with GeneSeek Porcine 50K Bead chip, were used for the association analysis. We identified 19 genomic regions that each explained >1% of the additive genetic variance associated with IMF. Notably, a consistent QTL on SSC7 (117.42-117.92 Mb) was confirmed, explaining 3.70% of the additive genetic variance, and two genes, BDKRB2 and ATG2B, were highlighted as promising candidates for IMF. Two QTL (SSC7, 94.19-94.64 Mb; SSC14, 123.25-123.75 Mb), which harbored MED6 and MAP3K9 genes and TCF7L2 gene respectively, were newly identified as associated with IMF. In conclusion, we identified a consistent QTL and additional genomic regions and genes that contributed to the genetic variance of IMF using a large-scale sample size of genotyped pigs and genealogical information.

Translating Fecobionics Into a Technique That Addresses Clinical Needs for Objective Perineal Descent Measurements

INTRODUCTION

Perineal descent is a phenomenon associated with anorectal dysfunction. It is diagnosed by defecography but subjected to manual measurements on the images/videos and interobserver bias. Fecobionics is a simulated feces for assessing important physiological parameters during defecation. Here, we translate Fecobionics into a new method for estimation of perineal descent based on electronic signals from the embedded inertial measurement units (IMUs).

METHODS

A displacement measurement method by a combined zero-velocity update and gravity compensation algorithm from IMUs was developed. The method was verified in a robot model, which mimicked perineal descent motion.

RESULTS

The method correlated well with the reference (R = 0.9789) and had a deviation from the peak displacement (range 0.25-2.5 cm) of -0.04 ± 0.498 cm. The method was further validated in 5 human experiments with comparison to the benchmark defecography technology (R = 0.79).

DISCUSSION

The proposed technology is objective, i.e., electronic measurements rather than by fluoroscopy or MRI. The development may impact clinical practice by providing a resource-saving and objective technology for diagnosing perineal descent in the many patients suffering from anorectal disorders. The technology may also be used in colon experiments with Fecobionics and for other gastrointestinal devices containing IMUs such as ingestible capsules like the Smartpill.

An analysis of the variations and clinical applications of the lateral circumflex femoral artery

BACKGROUND

Identifying the arterial variation of the lateral circumflex femoral artery (LCFA) is a vital step in planning surgical and radiological approach. The aim of the study was to evaluate the variations and discuss the clinical correlates of the LCFA.

MATERIALS AND METHODS

Fifty eight adult cadavers (male 45, female 13) with 115 usable sides were used to assess and classify the origin and branches of the LCFA. Also its external diameter, distance from mid-inguinal ligament to sites of origin from the profunda femoris artery or femoral arteries.

RESULTS

There were seven types of LCFA variations in this sample. We classified them as types A to G, of which type A was normal, that is, the one showing a single LCFA arising from the profunda femoris artery. Nearly 50.43% of the sample had type B-G variations, each having 13, 10, 23, 4, 4, and 3 cases, accounting for 11.30%, 8.70%, 20.00%, 3.48%, 3.48%, and 2.61%, respectively.

CONCLUSIONS

There are many variant types in the LCFA. To avoid iatrogenic injuries, clinicians must have a sound understanding of the variation types of this important blood vessel.

Effect of trichloroacetaldehyde on the activation of CD4+T cells in occupational medicamentosa-like dermatitis: An in vivo and in vitro study

Occupational medicamentosa-like dermatitis induced by trichloroethylene (OMLDT) is a hypersensitivity disease with autoimmune liver injury, which has increasingly become a serious occupational health problem in China. However, the pathogenesis of OMLDT remained undefined. In this study, 30 TCE-induced OMLDT patients, 58 exposure controls, and 40 non-exposure controls were recruited. We showed that the ratio of activated CD4⁺ T cells (downregulation of CD62 L) was dramatically increased in OMLDT patients compared to exposure and non-exposure control, suggesting that CD4⁺ T cells activation was a key cellular event in the development of OMLDT. In parallel, the expression of cytokine including IL-2, IFN-γ, TNF-α and IL-17A were increased obviously and IL-4 decreased in CD4⁺ T cells from OMLDT patients. in vitro assay, we found that trichloroethylene metabolites trichloroacetaldehyde (TCAH), not trichloroacetic acid (TCA) or Trichloroethanol (TCOH) could activate the naïve CD4⁺ T cells characterized by a rise in intracellular calcium, down-regulated CD62 L and subsequently trigger the secretion of IL-2, IFN-γ and TNF-α. Notably, the phosphorylation status of NF-κB and p38MAPK were elevated in OMLDT patients. Moreover, TCAH also could activate the p38MAPK and NF-κB, suggesting the role of p38MAPK and NF-κB pathways in the activation of CD4⁺ T cells. In addition, we found that the inhibition of Schiff base formation decreased the ability of TCAH to induce the activation of naïve CD4⁺ T cells and p38MAPK and NF-κB pathway. In conclusion, we revealed that the CD4⁺ T activation and increased the cytokines including IL-2, IFN-γ and TNF-α but decreased IL-4 in CD4⁺ T cells were associated with OMLDT. TCAH could activate naïve CD4⁺ T cells through NF-κB and p38MAPK activation induced by Schiff base formation, which might contribute to the development of OMLDT. These findings provide a new insight into the pathogenesis of OMLDT.

The applied anatomy and clinical significance of the proximal, V1 segment of vertebral artery

BACKGROUND

The aim of the study was to probe the morphological features of the proximal segment (V1) of vertebral artery (VA) in a sample of Chinese cadavers.

MATERIALS AND METHODS

The origin, course and outer diameter at origin of the pre-vertebral part of the VAs were evaluated in 119 adult cadavers.

RESULTS

It was found that 94.12% of the VAs originated from the subclavian arteries, bilaterally. The variant origins were present in 5.88% of the cadavers and all originated directly from the arch of the aorta. All the variations were observed on the left side of male cadavers. The average outer diameters at origin of the normal and variation groups were 4.35 ± 1.00 mm and 4.82 ± ± 1.42 mm, respectively, p = 0.035. In the normal group, but not in the variation group, the average diameter in the males was significantly larger than that in the females (4.50 ± 0.99 mm, 3.92 ± 0.92 mm, respectively, p = 0.000). In addition, only 5 cadavers in the normal group had hypoplastic VAs (4.20%, 4 males, 3 right-sided). Vertebral artery dominance (VAD) was present in 91 (69 males) out of 112 cadavers and more common on the left (n = 48). In addition, 3 cadavers satisfied conditions for coexistence of VAD and vertebral artery hypoplasia. All 7 cadavers in the variation group exhibited VAD, which was more common on the right side (n = 5).

CONCLUSIONS

The morphologic variations and frequencies described above have implications for the early prevention, abnormal anatomy detection, accurate diagnosis, safe surgery and endovascular treatment of cardiovascular and neurological disease.

Induction of M2 Macrophages Prevents Bone Loss in Murine Periodontitis Models

Periodontitis is characterized by the progressive destruction of tooth-supporting alveolar bone, which is mainly caused by chronic inflammation in response to persistent bacterial insult. It has recently become clear that the pathogenesis of periodontitis is associated with a high ratio of proinflammatory M1 (classically activated) macrophages to anti-inflammatory M2 (alternatively activated). To decrease the inflammatory activity, we locally delivered the C-C motif chemokine ligand 2 (CCL2) using controlled-release microparticles (MPs). CCL2 is known to promote chemotaxis of M0 or M2 phenotype macrophages to the inflamed site and induce M2 phenotype polarization locally. Our in vitro data showed that CCL2 increased the number of M2 phenotype macrophages, decreased TNF-α secretion, and enhanced chemotaxis of RAW264.7 cells toward CCL2 MPs. Moreover, we induced periodontal disease in 2 animal models through inoculation of Porphyromonas gingivalis and ligature around the murine molar. Micro-computed tomography analysis showed significant reduction of alveolar bone loss in the CCL2 MP treatment group when compared with a blank MP group and a no-treatment periodontitis group in both models. Immunohistologic analysis showed a significant increase in the M2 phenotype subset and a decrease in the M1 phenotype subset in the CCL2 MP group of the P. gingivalis-induced model. Also, in both models, tartrate-resistant acidic phosphatase staining showed significantly fewer numbers of osteoclasts in the CCL2 MP group in alveolar bone area. Moreover, quantitative polymerase chain reaction results showed a significant increase in IL-1RA (interleukin 1 receptor antagonist) mRNA expression and a decrease in RANKL (receptor activator of nuclear factor kappa-Β ligand) mRNA expression in the CCL2 MP group in the ligature model. In summary, manipulation of endogenous M2 phenotype macrophages with CCL2 MPs decreased the M1 phenotype:M2 phenotype ratio and prevented alveolar bone loss in mouse periodontitis models. The delivery of CCL2 MPs provides a novel approach to treat periodontal disease.

Apparent diffusion coefficient measurement in luminal breast cancer: will tumour shrinkage patterns affect its efficacy of evaluating the pathological response?

AIM

To determine which region of interest (ROI) placement method of apparent diffusion coefficient (ADC) measurement has the best performance for predicting pathological complete response (PCR) at two cycles of neoadjuvant chemotherapy (NAC) according to different tumour shrinkage patterns of luminal breast cancer and to assess the evaluative accuracy of ADC value combined with other clinicopathological indicators.

MATERIALS AND METHODS

Sixty-one patients who underwent NAC for histopathologically confirmed breast cancer were enrolled in this retrospective study. The ADC values of different shrinkage patterns (concentric shrinkage, nest or dendritic shrinkage, and mixed shrinkage) for tumours shown by diffusion-weighted imaging (DWI) were measured independently using three ROI placement methods (single-round, three-round, and freehand). Intraclass correlation coefficients (ICCs) were used to assess the interobserver variability in the ADC values. Multivariate logistic regression analysis was performed to identify the independent predictors of PCR.

RESULTS

The best placement method found was single-round ROI in all the patients (AUC=0.863). When analysed separately, the effectiveness results differed: the single-round method was optimal for concentrically shrinking tumours (AUC=0.970); the freehand method was optimal for nest or dendritically shrinking tumours (AUC=0.714); and the three-round method was optimal for mixed shrinking tumours (AUC=0.975). Multivariate logistic analysis showed that oestrogen receptor (ER), ΔADC% and tumour diameter reduction (ΔD%) were independent factors in evaluating the PCR.

CONCLUSION

The methods for measuring ADC values vary across different shrinkage patterns of luminal tumours. ΔADC%, ER and ΔD% were independent factors for evaluating the PCR.

Arsenic exposure assists ccm3 genetic polymorphism in elevating blood pressure

Epidemiologic study has suggested that arsenic exposure is positively related to increased blood pressure. However, the underlying mechanism concerning interaction between genetic polymorphisms and arsenic exposure remains unclear. In present study, within 395 Chinese, the effects of interaction between arsenic exposure and CCM3 gene polymorphisms on elevation of blood pressure were probed by multiple Logistic regression models after adjusting for confounding factors. Firstly, we found that serum arsenic was positively associated with blood pressure, cholesterol, glucose and C-reactive protein. Then, adjusted for confounding factors of age, gender, smoking, alcohol consumption, BMI and degree of education, arsenic exposure incurred the hazard of increased systolic pressure and diastolic pressure, with odds ratios (ORs) being 1.725 and 1.425, respectively. Distinctly, we found that interactions between rs3804610^* rs9818496, rs6784267^*rs9818496, and rs3804610^* rs6784267 variant genotype can increase significantly risks of SBP. Additionally, interactions between rs9818496, rs3804610 and rs6784267 genotypic variantions and arsenic exposure boosted the hazard of increased systolic pressure, with ORs being 1.496, 1.496 and 1.312. In conclusion, our fingdings suggest that As exposure of population can assist CCM3 polymorphism in elevating SBP.

Utility of apparent diffusion coefficient as an imaging biomarker for assessing the proliferative potential of invasive ductal breast cancer

AIM

To determine the clinical utility of apparent diffusion coefficient (ADC) metrics for the non-invasive assessment of tumour proliferation indicated by Ki-67 labelling index (LI) in invasive ductal breast cancer.

MATERIALS AND METHODS

Eighty patients with 80 histopathologically proven invasive ductal breast cancers underwent diffusion-weighted imaging with b-values of 0 and 800 s/mm² at a 3-T system. ADC metrics including ADC_mean, ADC_median, ADC_min, ADC_max, and ΔADC (ADC_max-ADC_min) were recorded from the entire tumour volume on ADC maps, and correlated with the Ki-67 LI. Ki-67 staining of ≥14% was considered to indicate high proliferation and <14% was considered to indicate low proliferation.

RESULTS

ADC_min, ADC_max, and ΔADC showed significant correlations with the Ki-67 LI (for all tumours, r=-0.311, 0.436, and 0.551, respectively; for luminal/human epidermal growth factor receptor 2 (HER2)-negative group, r=-0.437, 0.512, and 0.639, respectively; all p<0.01), whereas ADC_mean and ADC_median showed no significant correlation (both p>0.05). Receiver operating characteristic (ROC) curve analysis for the differentiation of high- from low-proliferation groups showed that ΔADC yielded the highest area under the ROC curve for the whole tumour population (0.825; 95% confidence interval [CI]: 0.724, 0.901), as well as for the luminal/HER2-negative group (0.844; 95% CI: 0.692, 0.940).

CONCLUSION

ΔADC may serve as a promising imaging biomarker for the prediction of Ki-67 proliferation status in invasive ductal breast cancer.

DNA damage levels in electronics workers in Southern China: A micro-whole blood comet assay

We evaluated DNA damage levels of different categories of workers exposed to hazards inside electronics factories in Southern China. To find out the most dangerous risk factor, a cross-sectional study was conducted on a total of 584 exposed subjects and 138 controls in an electronics factory in Southern China, where the electronics industry is prevalent. The exposed hazards included isopropanol (IPO), lead, noise, video display terminals (VDT), lead in a high-temperature (high-temp) environment, and IPO in a high-temp environment. DNA damage detection was performed by the micro-whole blood comet assay using peripheral blood. DNA damage levels were estimated by percent tail DNA (%T). Linear regression models were used to test DNA damage differences between exposed groups and control group with adjustments for potential confounding factors. The level of DNA damage was more significant in both lead in a high-temp and IPO in a high-temp environment groups than in that of the controls (p<0.05). The differences remained significant after stratifying by smoking status (p<0.05). There were no significant differences between groups exposed to IPO, lead, noise, VDT environment and controls. In conclusion, we identified potential risk factors for DNA damage to electronics workers. Special attention should be paid to workers exposed to IPO and lead in a high-temp environment.

Melatonin ameliorates anxiety and depression-like behaviors and modulates proteomic changes in triple transgenic mice of Alzheimer's disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease accompanied by neuropsychiatric symptoms, such as anxiety and depression. The levels of melatonin decrease in brains of AD patients. The potential effect of melatonin on anxiety and depression behaviors in AD and the underlying mechanisms remain unclear. In this study, we treated 10-month-old triple transgenic mice of AD (3xTg-AD) with melatonin (10 mg/kg body weight/day) for 1 month and explored the effects of melatonin on anxiety and depression-like behaviors in 3xTg-AD mice and the protein expression of hippocampal tissues. The behavioral test showed that melatonin ameliorated anxiety and depression-like behaviors of 3xTg-AD mice as measured by open field test, elevated plus maze test, forced swimming test, and tail suspension test. By carrying out two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) coupled with mass spectrometry, we revealed a total of 46 differentially expressed proteins in hippocampus between the wild-type (WT) mice and non-treated 3xTg-AD mice. A total of 21 differentially expressed proteins were revealed in hippocampus between melatonin-treated and non-treated 3xTg-AD mice. Among these differentially expressed proteins, glutathione S-transferase P 1 (GSTP1) (an anxiety-associated protein) and complexin-1 (CPLX1) (a depression-associated protein) were significantly down-regulated in hippocampus of 3xTg-AD mice compared with the WT mice. The expression of these two proteins was modulated by melatonin treatment. Our study suggested that melatonin could be used as a potential candidate drug to improve the neuropsychiatric behaviors in AD via modulating the expression of the proteins (i.e. GSTP1 and CPLX1) involved in anxiety and depression behaviors. © 2017 BioFactors, 43(4):593-611, 2017.

Exploring the regulatory role of isocitrate dehydrogenase mutant protein on glioma stem cell proliferation

OBJECTIVE

Glioma is the most lethal form of cancer that originates mostly from the brain and less frequently from the spine. Glioma is characterized by abnormal regulation of glial cell differentiation. The severity of the glioma was found to be relaxed in isocitrate dehydrogenase 1 (IDH1) mutant. The present study focused on histological discrimination and regulation of cancer stem cell between IDH1 mutant and in non-IDH1 mutant glioma tissue.

PATIENTS AND METHODS

Histology, immunohistochemistry and Western blotting techniques are used to analyze the glioma nature and variation in glioma stem cells that differ between IDH1 mutant and in non-IDH1 mutant glioma tissue.

RESULTS

The aggressive form of non-IDH1 mutant glioma shows abnormal cellular histological variation with prominent larger nucleus along with abnormal clustering of cells. The longer survival form of IDH1 mutant glioma has a control over glioma stem cell proliferation. Immunohistochemistry with stem cell markers, CD133 and EGFRvIII are used to demonstrate that the IDH1 mutant glioma shows limited dependence on cancer stem cells and it shows marked apoptotic signals in TUNEL assay to regulate abnormal cells. The non-IDH1 mutant glioma failed to regulate misbehaving cells and it promotes cancer stem cell proliferation.

CONCLUSIONS

Our finding supports that the IDH1 mutant glioma has a regulatory role in glioma stem cells and their survival.

Proteomic analysis of hippocampus in mice following long-term exposure to low levels of copper

Recent studies suggest that copper exposure, even at very low levels, can produce significant toxic effects on the brains of mice. This study is aimed to explore the effects of low levels of copper on the hippocampal proteome of mice. Two-dimensional fluorescence difference gel electrophoresis was performed on hippocampal homogenate obtained from mice, which were given either drinking water only (control) or water supplemented with 0.13 ppm copper (copper-treated) for a period of 8 months beginning at an age of 3 months. A total of 9 differentially expressed proteins between copper-treated mice and control mice were identified. Protein functional analysis revealed that the altered proteins mainly involved energy metabolism-related proteins, synaptic proteins, molecular chaperones and cellular structural components. Among these differentially expressed proteins, serine racemase (SRR) and glial fibrillary acidic protein (GFAP) were significantly down-regulated and up-regulated, respectively, in the hippocampus of copper-treated mice compared with the control mice. SRR was shown to be involved in memory formation. The increased expression of GFAP, an astrocyte marker, indicated that long-term low levels of copper exposure caused activation of the inflammatory response, a process linked to spatial memory impairment. In agreement with the data from proteomic analysis, memory impairment was observed in copper-treated mice as measured by the Morris water maze test. In summary, this study has identified a number of abnormally expressed proteins in the hippocampus of copper-treated mice, and the identified protein, such as SRR, together with inflammatory responses, as evidenced by the increased expression of GFAP, could contribute to memory impairment resulting from copper exposure. Our findings provide insights for a better understanding of copper neurotoxicity at the protein level in response to low levels of copper exposure.

Pretreated baseline neutrophil count and chemotherapy-induced neutropenia may be conveniently available as prognostic biomarkers in advanced gastric cancer

BACKGROUND

Increasing evidence suggests that neutrophils play a critical role in tumorigenesis, tumour cell proliferation and metastasis. The prognostic significance of such inflammation-associated markers has been explored in different cancers.

AIM

To evaluate the prognostic effect of baseline neutrophil counts and nadir neutrophils on advanced gastric cancer (AGC) patients who were treated with two different chemotherapy regimens in our institution.

METHODS

Data were collected retrospectively for 260 AGC patients treated between 1 February 2009 and 31 December 2011. The prognostic effect of baseline neutrophil counts and nadir neutrophils on AGC patients was evaluated.

RESULTS

Approximately 79% of the patients experienced neutropenia during chemotherapy. The median survival was 369 days for patients with neutrophil counts ≤7.5 × 10(9) /L and 326 days for patients with neutrophil counts >7.5 × 10(9) /L (P < 0.001).The median survival was 340 days for patients with no neutropenia (grade 0), 422 days for patients with mild neutropenia (grade 1-2) and 339 days for patients with severe neutropenia (grade 3-4) (P < 0.001).The adjusted hazard ratios (HR) for mild and severe neutropenia compared with absent neutropenia were 0.572 (P = 0.002) and 1.246 (P = 0.219) respectively. Furthermore, it was suggested that pretreatment baseline neutrophil counts ≤7.5 × 10(9) /L may be an independent predictor (HR = 0.683; P = 0.005). We also observed that other factors were independently associated with worse survival, such as higher performance status, stage IV and the presence of ascites.

CONCLUSION

Our findings suggest that baseline neutrophil count and chemotherapy-induced neutropenia can be conveniently available as clinical biomarkers in AGC. Mild myelosuppression in patients with AGC most likely leads to better overall survival, whereas a high baseline neutrophil count may be associated with a worse prognosis.

Poly(ADP-Ribose) Glycohydrolase (PARG) Silencing Suppresses Benzo(a)pyrene Induced Cell Transformation

Benzo(a)pyrene (BaP) is a ubiquitously distributed environmental pollutant and known carcinogen, which can induce malignant transformation in rodent and human cells. Poly(ADP-ribose) glycohydrolase (PARG), the primary enzyme that catalyzes the degradation of poly(ADP-ribose) (PAR), has been known to play an important role in regulating DNA damage repair and maintaining genomic stability. Although PARG has been shown to be a downstream effector of BaP, the role of PARG in BaP induced carcinogenesis remains unclear. In this study, we used the PARG-deficient human bronchial epithelial cell line (shPARG) as a model to examine how PARG contributed to the carcinogenesis induced by chronic BaP exposure under various concentrations (0, 10, 20 and 40 μM). Our results showed that PARG silencing dramatically reduced DNA damages, chromosome abnormalities, and micronuclei formations in the PARG-deficient human bronchial epithelial cells compared to the control cells (16HBE cells). Meanwhile, the wound healing assay showed that PARG silencing significantly inhibited BaP-induced cell migration. Furthermore, silencing of PARG significantly reduced the volume and weight of tumors in Balb/c nude mice injected with BaP induced transformed human bronchial epithelial cells. This was the first study that reported evidences to support an oncogenic role of PARG in BaP induced carcinogenesis, which provided a new perspective for our understanding in BaP exposure induced cancer.

Mitochondrial DNA hypomethylation in chrome plating workers

A matched case-control study was conducted to examine the relationship between chromium (Cr) exposure and variation in mitochondrial (mt) DNA methylation. We enrolled 29 pairs of subjects in this study; Cr exposure was confirmed in the cases by detecting blood Cr and other metal ion concentrations. DNA damage caused by Cr exposure was determined in terms of binucleated micronucleus frequency (BNMN) and mtDNA copy number. Finally, a Sequenom MassARRAY platform was applied to inspect the DNA methylation levels of mitochondrially encoded tRNA phenylalanine (MT-TF), mitochondrially encoded 12S RNA (MT-RNR1), and long interspersed nucleotide element-1 (LINE-1) genes. The blood Cr ion concentration and micronucleus frequency of the Cr-exposed group were higher than those of the control group, whereas the mtDNA copy number remained unchanged. The methylation levels of MT-TF and MT-RNR1 but not LINE-1 were significantly lower in Cr-exposed workers. Pearson correlation analysis showed that workers with higher blood Cr ion concentrations exhibited lower MT-TF and MT-RNR1 gene methylation, and multiple linear regression analysis indicated that CpG sites 1 and 2 in MT-TF and CpG site 6 in MT-RNR1 were affected. These results suggested that methylation level of mtDNA has the possibility of acting as an alternative effect biomarker for Cr exposure.

Identification of the key molecules involved in chronic copper exposure-aggravated memory impairment in transgenic mice of Alzheimer's disease using proteomic analysis

Alzheimer's disease (AD) is the most common neurodegenerative disease characterized by a progressive impairment of cognitive functions including spatial learning and memory. Excess copper exposure accelerates the development of AD; however, the potential mechanisms by which copper exacerbates the symptoms of AD remain unknown. In this study, we explored the effects of chronic copper exposure on cognitive function by treating 6 month-old triple AD transgenic (3xTg-AD) mice with 250 ppm copper sulfate in drinking water for 6 months, and identified several potential key molecules involved in the effects of chronic copper exposure on memory by proteomic analysis. The behavioral test showed that chronic copper exposure aggravated memory impairment of 3xTg-AD mice. Two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) coupled with mass spectrometry revealed a total of 44 differentially expressed proteins (18 upregulated and 26 down-regulated) in hippocampus between the wild-type (WT) mice and non-exposed 3xTg-AD mice. A total of 40 differentially expressed proteins were revealed (20 upregulated and 20 down-regulated) in hippocampus between copper exposed and non-exposed 3xTg-AD mice. Among these differentially expressed proteins, complexin-1 and complexin-2, two memory associated proteins, were significantly decreased in hippocampus of 3xTg-AD mice compared with the WT mice. Furthermore, the expression of these two proteins was further down-regulated in 3xTg-AD mice when exposed to copper. The abnormal expression of complexin-1 and complexin-2 identified by proteomic analysis was verified by western blot analysis. Taken together, our data showed that chronic copper exposure accelerated memory impairment and altered the expression of proteins in hippocampus in 3xTg-AD mice. The functional analysis on the differentially expressed proteins suggested that complexin-1 and complexin-2 may be the key molecules involved in chronic copper exposure-aggravated memory impairment in AD.

Comparison of Simulated Workplace Protection Factors Offered by N95 and P100 Filtering Facepiece and Elastomeric Half-Mask Respirators against Particles of 10 to 400 nm

This study compared the simulated workplace protection factors (SWPFs) between NIOSH-approved N95 respirators and P100 respirators, including two models of filtering facepiece respirator (FFR) and two models of elastomeric half-mask respirator (EHR), against sodium chloride particles (NaCl) in a range of 10 to 400 nm. Twenty-five human test subjects performed modified OSHA fit test exercises in a controlled laboratory environment with the N95 respirators (two FFR models and two EHR models) and the P100 respirators (two FFRs and two EHRs). Two Scanning Mobility Particle Sizers (SMPS) were used to measure aerosol concentrations (in the 10-400 nm size range) inside (Cin) and outside (Cout) of the respirator, simultaneously. SWPF was calculated as the ratio of Cout to Cin. The SWPF values obtained from the N95 respirators were then compared to those of the P100 respirators. SWPFs were found to be significantly different (P<0.05) between N95 and P100 class respirators. The 10th, 25th, 50th, 75th and 90th percentiles of the SWPFs for the N95 respirators were much lower than those for the P100 models. The N95 respirators had 5th percentiles of the SWPFs > 10. In contrast, the P100 class was able to generate 5th percentiles SWPFs > 100. No significant difference was found in the SWPFs when tested against nano-size (10 to 100 nm) and large-size (100 to 400 nm) particles. Overall, the findings suggest that the two FFRs and two EHRs with P100 class filters provide better performance than those with N95 filters against particles from 10 to 400 nm, supporting current OSHA and NIOSH recommendations.

[Proteomic study on HaCaT cell membrane proteins after exposed to silica nanomaterials]

OBJECTIVE

To identify the differential expression of membrane proteins after HaCaT cell was treated with 15 nm silica nanomaterials (SiO2).

METHODS

The HaCaT cells were cultured for 24 h under 15 nm SiO2 in various concentrations (2. 5, 5. 0, 10. 0 mg/L), and ddH2O were used as control. The cell viability were measured with CCK-8 assay. The membrane proteins of SiO2-treated group (10. 0 mg/L) and controls were extracted by ProteoExtract subcellular proteome extraction kit. The differentially expressed membrane proteins were analyzed by a two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) and matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry (MALDI-TOF-MS). Bioinformatics analysis was used to reveal the biological functions and predict transmembrane domains of differential expressed proteins. The expression of differential membrane proteins were measured by Western blot analysis.

RESULTS

The cell viability was significantly decreased with the increases of 15 nm SiO2 exposure levels. After treatment with 2. 5, 5. 0, 10. 0 mg/L of 15nm SiO2, the cell viability was assessed to (91. 3% ± 6. 1%), (81. 7% ± 7. 0%) and (74. 0% ± 2. 6%) of control level (P < 0. 05), respectively. In the proteomic analysis, a total of 10 proteins were identified as differential expression in the SiO2-treated simples compared with controls. Among these, 7 of these proteins were predicted as membrane proteins with at least one significant transmembrane domain. The most dominant function that the identified proteins involved in was binding and structural molecule activity. The differential expression of G protein-coupled receptor 179 (GPR 179) and L-plastin (LCP1) were verified by Western-blot analysis under 15nm SiO2 exposure in various concentrations.

CONCLUSION

The exposure of 15 nm SiO2 can significantly reduce the cell proliferation and induce a down-regulation of membrane protein expression in HaCaT cells.

[Effect of silicon dioxide nanoparticles on expression and DNA methylation of PARP-1 gene in HaCaT cells]

OBJECTIVE

To study the effect of silicon dioxide nanoparticles on the expression and promoter region CpG islands methylation of (Poly [ADP-ribose] polymerase 1, PARP-1) gene in human HaCaT Cell.

METHODS

HaCaT Cells were treated with nm-SiO₂at 0, 2.5, 5 and 10 µg/mL and micro-SiO₂at 10 µg/ml for 24 h and DAC treatment was given at 10 µg/ml group for 48 h. Real-time PCR and western blot assay was used to detect the expression of PARP-1 mRNA and protein. BSP (Bisulfite Pyrosequence, BSP) assay was used to detect the promoter region CpG islands methylation status of PARP-1 gene.

RESULTS

After exposure to nano-SiO₂particles, compared to CTRL group, the mRNA and protein expression of PARP-1 in micro-SiO₂and 2.5 µg/ml group unchanged, but he mRNA and protein expression of PARP-1 in 5, 10 µg/ml as well as DAC group was down-regulated and there are statistical significance between CTRL group and 5, 10 µg/ml as well as DAC group and the PARP-1 promoter region CpG islands showed methylation.

CONCLUSION

nano-SiO₂can down-regulate PARP-1 expression in HaCaT Cell and this is associated with the change in the methylation of PARP-1 gene promoter region CpG islands induced by nano-SiO₂particles.

Gestational Weight Gain and Overweight in Children Aged 3-6 Years

Objective

To determine whether gestational weight gain (GWG) was associated with increased odds of childhood overweight after accounting for pre-pregnancy BMI.

Methods

In a prospective cohort study based on a premarital and perinatal health care system in China, data of 100 612 mother-child pairs were obtained. The main exposure was GWG as both a continuous and categorical variable. The outcome measure was overweight, defined by age- and sex-specific cutoff values for body mass index (BMI) in children aged 3–6 years.

Results

A 1-kg increase in maternal GWG was associated with an increase of 0.009 (95% confidence interval [CI]: 0.007–0.010, P < 0.001) in children’s mean BMI; in the subgroup of pre-pregnancy overweight/obese mothers, the increase in children’s BMI was 0.028 (95% CI, 0.017–0.039, P < 0.001). Excessive GWG played an important role in childhood overweight when adequate GWG was used as the reference, with an odds ratio (OR) of 1.21 (95% CI, 1.12–1.29). The risk was highest (OR 2.22; 95% CI, 1.79–2.76) in the children of mothers who were overweight/obese before pregnancy and gained excessive weight during pregnancy.

Conclusions

Greater maternal GWG was associated with greater offspring BMI, and the risk of overweight was doubled in children whose mothers were overweight/obese before pregnancy and gained excessive weight during pregnancy. As a result, maintenance of appropriate weight gain during pregnancy and prophylaxis of maternal overweight/obesity before pregnancy should be a strategy for preventing childhood overweight/obesity.

[Establishment a method for identification of the poly(ADP-ribose) binding proteins induced by benzo(a)pyrene]

OBJECTIVE

To establish a method for identification of the poly(ADP-ribose) binding proteins induced by benzo (a) pyrene.

METHODS

Poly (ADP-ribose) binding protein were screened by immunoprecipitation assay and further separated by high performance liquid chromatography (HPLC) and two dimensional electrophoresis, then identified by MALDI-TOF-MS/MS. The proteins sequence were identified by two methods and compared the common binding motif with literature reports.

RESULTS

Three poly (ADP-ribose) binding proteins were identified by MALDI-TOF-MS/MS combined with immunoprecipitation assay and HPLC, and twelve poly (ADP-ribose) binding proteins were identified by MALDI-TOF-MS/MS combined with immunoprecipitation assay and two dimensional electrophoresis. Most of them have a common binding motif which was consistent with the reported.

CONCLUSION

Combined the immunoprecipitation assay and two dimensional electrophoresis with MALDI-TOF-MS/MS could be used to analyze the poly(ADP-ribose) binding proteins, and these proteins have a common conserved binding motif.

[Investigation of trichloroethylene-induced effects on subcellular proteomes in L-02 hepatic cells]

OBJECTIVE

To put the insight into the trichloroethylene (TCE)-induced effect on the differential expression of subcellular proteins in human normal liver cell line (L-02).

METHODS

The membrane proteins and nuclear proteins of TCE-treated (8.0 mmol/L) group and controls were extracted by subcellular proteome extraction kit, respectively. The TCE-induced differentially expressions were analyzed by a two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) and matrix-assisted laser desorption/ionization tandem time-of-flight spectrometry (MALDI-TOF-MS). Bioinformatics analysis was used to reveal the biological processes and predict transmembrane domains of differential expressed proteins. The expression of ATP synthase subunit beta (ATP5B), heterogeneous nuclear ribonucleoprotein H2 (hnRNP H2) and far up steam element-binding protein 1 (FUBP1) were measured under TCE treatment by Western blot.

RESULTS

After TCE treatment for 24 h in L-02 cells, 14 membrane proteins and 18 nuclear proteins were identified as differential expression. After treated with TCE in concentrations of 0, 2.0, 4.0 and 8.0 mmol/L for 24 h, the relative levels of ATP5B expression were 1.00±0.03, 1.21±0.14, 1.25±0.12 and 1.48±0.17 (F = 8.51, P = 0.007), the relative levels of hnRNP H2 expression were 1.00±0.09, 1.22±0.15, 1.43±0.21, 1.53±0.17 (F = 6.57, P = 0.015), respectively; the relative levels of FUBP1 expression were 1.00±0.11, 0.91±0.07, 0.73±0.04 and 0.67±0.03 (F = 15.81, P = 0.001), respectively, which were consistent with the results in proteomics. The bioinformatics analysis showed that the most dominant biological process were involved in RNA processing (10 proteins, P = 2.46×10(-6)), especially in RNA splicing (9 proteins, P = 1.77×10(-7)).

CONCLUSION

The exposure of TCE could alter the expression of membrane proteins and nuclear proteins in L-02 cells. These abnormal expressed proteins involved in RNA splicing would provide novel clues for further understanding of TCE-induced hepatotoxicity.

1,2-Dichloroethane induced nephrotoxicity through ROS mediated apoptosis in vitro and in vivo

1,2-Dichloroethane (DCE) decreased kidney cell proliferation, even induced cell apoptosisviaincreasing the generation of ROS in the presence of an extra-metabolic system.

Poly(ADP-ribose) glycohydrolase silencing down-regulates TCTP and Cofilin-1 associated with metastasis in benzo(a)pyrene carcinogenesis

Benzo(a)pyrene (BaP) is a ubiquitously distributed environmental pollutant. BaP is a known carcinogen and can induce malignant transformation of rodent and human cells. Many evidences suggest that inhibitor of poly(ADP-ribose) glycohydrolase (PARG) is potent anticancer drug candidate. However, the effect of PARG on BaP carcinogenesis remains unclear. We explored this question in a PARG-deficient human bronchial epithelial cell line (shPARG cells) treated with various concentration of BaP for 15 weeks. Soft agar assay was used to examine BaP-induced cell malignancy of human bronchial epithelial cells and shPARG cells. Mechanistic investigations were used by 2D-DIGE and mass spectrometry. Western blot analysis and Double immunofluorescence detection were used to confirm some of the results obtained from DIGE experiments. We found that PARG silencing could dramatically inhibit BaP-induced cell malignancy of human bronchial epithelial cells in soft agar assay. Altered levels of expression induced by BaP were observed within shPARG cells for numerous proteins, including proteins required for cell mobility, stress response, DNA repair and cell proliferation pathways. Among these proteins, TCTP and Cofilin-1 involved in malignancy, were validated by western blot analysis and immunofluorescence assay. PARG inhibition contributed to down-regulation of TCTP and Cofilin-1. This is the first experimental demonstration of a link between PARG silencing and reduced cell migration after BaP exposure. We propose that PARG silencing might down-regulate TCTP and Cofilin-1 associated with metastasis in BaP carcinogenesis.

Entrenchment-Based Horn Contraction

The AGM framework is the benchmark approach in belief change. Since the framework assumes an underlying logic containing classical Propositional Logic, it can not be applied to systems with a logic weaker than Propositional Logic. To remedy this limitation, several researchers have studied AGM-style contraction and revision under the Horn fragment of Propositional Logic (i.e., Horn logic). In this paper, we contribute to this line of research by investigating the Horn version of the AGM entrenchment-based contraction. The study is challenging as the construction of entrenchment-based contraction refers to arbitrary disjunctions which are not expressible under Horn logic. In order to adapt the construction to Horn logic, we make use of a Horn approximation technique called Horn strengthening. We provide a representation theorem for the newly constructed contraction which we refer to as entrenchment-based Horn contraction. Ideally, contractions defined under Horn logic (i.e., Horn contractions) should be as rational as AGM contraction. We propose the notion of Horn equivalence which intuitively captures the equivalence between Horn contraction and AGM contraction. We show that, under this notion, entrenchment-based Horn contraction is equivalent to a restricted form of entrenchment-based contraction.

Role of poly(ADP-ribose) glycohydrolase silencing in DNA hypomethylation induced by benzo(a)pyrene

Benzo(a)pyrene (BaP) is a known carcinogen cytotoxic which can trigger extensive cellular responses. Many evidences suggest that inhibitors of poly(ADP-ribose) glycohydrolase (PARG) are potent anticancer drug candidates. However, the role of PARG in BaP carcinogenesis is less understood. Here we used PARG-deficient human bronchial epithelial cell line (shPARG cell) as an in vitro model, and investigated the role of PARG silencing in DNA methylation pattern changed by BaP. Our study shows, BaP treatment decreased global DNA methylation levels in 16HBE cells in a dose-dependent manner, but no dramatic changes were observed in shPARG cells. Further investigation revealed PARG silencing protected DNA methyltransferases (DNMTs) activity from change by BaP exposure. Interestingly, Dnmt1 is PARylated in PARG-null cells after BaP exposure. The results show a role for PARG silencing in DNA hypomethylation induced by BaP that may provide new clue for cancer therapy.

Heavy metal-induced metallothionein expression is regulated by specific protein phosphatase 2A complexes

Induction of metallothionein (MT) expression is involved in metal homeostasis and detoxification. To identify the key pathways that regulate metal-induced cytotoxicity, we investigate how phosphorylated metal-responsive transcription factor-1 (MTF-1) contributed to induction of MT expression. Immortal human embryonic kidney cells (HEK cells) were treated with seven kinds of metals including cadmium chloride (CdCl2), zinc sulfate (ZnSO4), copper sulfate(CuSO4), lead acetate (PbAc), nickel sulfate (NiSO4), sodium arsenite (NaAsO2), and potassium bichromate (K2Cr2O7). The MT expression was induced in a dose-response and time-dependent manner upon various metal treatments. A cycle of phosphorylation and dephosphorylation was required for translocation of MTF-1 from cytoplasm to nucleus, leading to the up-regulation of MTs expression. Protein phosphatase 2A (PP2A) participated in regulating MT expression through dephosphorylation of MTF-1. A loss-of-function screen revealed that the specific PP2A complexes containing PR110 were involved in metal-induced MT expression. Suppression of PP2A PR110 in HEK cells resulted in the persistent MTF-1 phosphorylation and the disturbance of MTF-1 nuclear translocation, which was concomitant with a significant decrease of MT expression and enhanced cytotoxicity in HEK cells. Notably, MTF-1 was found in complex with specific PP2A complexes containing the PR110 subunit upon metal exposure. Furthermore, we identify that the dephosphorylation of MTF-1 at residue Thr-254 is directly regulated by PP2A PR110 complexes and responsible for MTF-1 activation. Taken together, these findings delineate a novel pathway that determines cytotoxicity in response to metal treatments and provide new insight into the role of PP2A in cellular stress response.

[Investigation of the action mechanisms of poly-ADP-ribosylation in hexavalent chromium induced cell damage]

OBJECTIVE

To investigate the effect of poly-ADP-ribosylation in hexavalent chromium Cr(VI) induced cell damage.

METHODS

The study object, poly (ADP-ribose) glycohydrolase (PARG) deficient human bronchial epithelial cells (16HBE cells), was constructed previously by our research group. Normal 16HBE cells and PARG-deficient cells were treated with different doses of Cr (VI) for 24 h to compare the differences to Cr (VI) toxicity, meanwhile set up the solvent control group. On this basis, 5.0 µmol/L of Cr (VI) was selected as the exposure dose, after the exposure treatment, total proteins of both cells were extracted for two dimension fluorescence difference gel electrophoresis (2D-DIGE) separation, statistically significant differential protein spots were screened and identified by matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS/MS), and further validated by Western blot.

RESULTS

After Cr (VI) treatment, the survival rate of PARG-deficient cells was higher than normal 16HBE cells. When the doses reached up to 5.0 µmol/L, the survival rate of 16HBE cells and PARG-deficient cells were respectively (59.67 ± 6.43)% and (82.00 ± 6.25)%, the difference between which was significant (t = -4.32, P < 0.05). 18 protein spots were selected and successfully identified after 2D-DIGE comparison of differential proteins between normal 16HBE cells and PARG-deficient cells before and after exposure. The function of those proteins was involved in the maintenance of cell shape, energy metabolism, DNA damage repair and regulation of gene expression. The differential expression of cofilin-1 was successfully validated by Western blot. The expression level of cofilin-1 in the 16HBE cells increased after Cr (VI) exposure with the relative expression quantity of 1.41 ± 0.04 in treated group and 1.00 ± 0.01 in control group, the difference of which was statistically significant (t = -18.00, P < 0.05), while the expression level in PARG-deficient cells had no statistically significant difference (t = -8.61, P > 0.05).

CONCLUSION

Most of the identified differential proteins are closely related to tumorigenesis, suggesting that poly-ADP-ribosylation reaction may resist the cytotoxicity of Cr(VI) by inhibiting Cr (VI) induced tumorigenesis, which provides important reference data to clarify the mechanisms of poly-ADP-ribosylation in Cr (VI) induced cell damage.