[Retrospective evaluation of treatment outcomes in immature teeth treated with regenerative endodontic procedures with an over-36-month review].

OBJECTIVE: To evaluate the clinical outcomes of immature teeth treated with regenerative endodontic procedures with an over-36-month review, to identify potential contributing factors of root deve-lopment, and to provide new reference for long-time prognosis of regenerative endodontic procedures. METHODS: We recruited teeth that had undergone regenerative endodontic procedures at the Department of Pediatric Dentistry in Peking University School and Hospital of Stomatology from January 2013 to June 2017 and had a follow-up period of more than 36 months.Clinical and radiographic records were collected.We evaluated the treatment outcomes and summarized different patterns of root development.Changes in root length, root canal wall thickness were compared between preoperative and recall radiographs.A statistical analysis was performed using software SPSS 22.0 to identify potential contributing factors of root development. RESULTS: In this study, 84 teeth were recruited and the mean follow-up period was (44.7±19.3) months.The longest follow-up period was 81 months.Sixty-eight teeth (81.0%) were clinical success with bony healing, and 55 teeth (80.9%) gained the continued root development.Forty teeth completed root development with apical closure.The rate of the apical closure reached 58.8%.Twenty-four teeth gained normal root morphology with the increasing of root length and canal wall thickness and apical closure.The rate of continued root development was 92.5% in teeth with broken central cusp and 58.3% in teeth with trauma, which was statistically significant (P < 0.05).There was a statistically significant difference (P < 0.05) between the root development rates of teeth with different induced bleeding heights (orifice/middle/tip of the root)(92.9%/81.0%/63.2%). CONCLUSION: Most of the teeth treated with regenerative endodontic procedures achieved continued root development with an over 36-month follow-up.However, the patterns of root development were different.The morphology of some teeth were close to the physiological state.Etiology and the height of induced bleeding are two factors significantly associated with the rate of the continued development root.

[Mechanism of pepsin promoting lingual tonsil hypertrophy by stimulating macrophage].

Objective: To investigate the possible pathophysiological mechanism of laryngopharyngeal reflux (LPR) in the development of lingual tonsil hypertrophy (LTH). Methods: The lingual tonsil tissues were collected from 73 patients [48 males and 25 females, aged from 24 to 76 (52.86±12.04) years] who underwent surgery for laryngopharyngeal diseases at the Department of Otolaryngology and Head and Neck Surgery, Southern Hospital of Southern Medical University from October 2019 to December 2020, and the lingual tonsil grade (LTG), reflux symptom index (RSI) and reflux finding score (RFS) were assessed. The expression of pepsin in LTH was detected by immunohistochemistry. The coexpression of pepsin and macrophages were detected by immunohistofluorescence. In vitro, cytological experiments and pathway assays were performed on macrophages stimulated by pepsin. Pathway alterations of macrophages in pepsin-positive high-grade LTH were detected by double-fluorescence immunohistochemistry. Data were analyzed by SPSS 20.0 software. Results: There were 44 clinically significant LPRD patients with LTG 3 and 4, and the pepsin positive rate was 88.6% (39/44). While, the pepsin positive rate of LTG 1 and 2 was 48.3% (14/29). LTG was significantly positively correlated with RFS/RSI positive rate(χ2=23.01/19.62, P<0.001/0.001; r=0.54/0.51, P<0.001/0.001) and pepsin tissue staining intensity (H=21.58, P<0.001; r=0.53, P<0.001), respectively. Pepsin and macrophages were clearly colocalized in high grade LTH. In vitro, pepsin promoted macrophage proliferation (P<0.05) and production of IL-6/IL-8 (P<0.05). Pepsin significantly up-regulated the p38/JNK MAPK pathway in macrophages (P<0.05). Pepsin up-regulated the expression of IL-6 and IL-8 of macrophages by activating the p38 MAPK pathway (P<0.05), and up-regulated the expression of IL-8 by activating the JNK pathway (P<0.05). The p38/JNK MAPK pathways were highly expressed in macrophages of pepsin-positive LTH (P<0.05). Conclusions: LPR is an important pathogenic factor in LTH. Macrophages may mediate pepsin-induced inflammation and the pathogenesis of LTH.

[Analysis of discordance between HbA1c and FPG criteria for dysglycemia screening in physical examination individuals].

The general data, blood routine, liver and kidney function, glucose metabolism and lipid metabolism of 11 922 participants who underwent physical examination at the Health Management Center of the Second Xiangya Hospital of Central South University from January 2019 to December 2019 were collected. Clinical characteristics and independent factors of patients with discordance between HbA1c and FPG were evaluated and analyzed. The prevalence of HbA1c-defined diabetes and prediabetes (respectively 8.13%, 34.79%) were significantly higher than that in FPG-defined diabetes and prediabetes (respectively 4.70%, 8.97%) (χ²=2 635.940;P<0.001). The prevalence of inconsistence between HbA1c and FPG was 35.65% and increased with increasing age. This inconsistence mainly occurred in population with HbA1c:5.7%-6.0% and FPG<5.6 mmol/L, followed by population with HbA1c:6.1%-6.4% and FPG<5.6 mmol/L. The risk factors of inconsistency included advanced age, overweight or obesity, hypoalbuminemia, dyslipidemia and hyperuricemia. Among these special participants, compared with participants under 45 years old, participants with over 45 years of age (OR=3.525, 95%CI: 3.216-3.863, P<0.001) were more likely to have inconsistence between HbA1c and FPG; and overweight participants (OR=1.474, 95%CI: 1.341-1.620, P<0.001) or obese participants (OR=1.856, 95%CI: 1.633-2.110, P<0.001) are prone to have the inconsistence than those with normal weight.

[Analysis of the relationship between the changes of lung function and serum proinflammatory cytokines in workers occupationally exposed to toluene diisocyanate].

Objective: To analyze the correlation between the changes of lung function and serum proinflammatory cytokines in workers occupationally exposed to toluene diisocyanate (TDI), and to explore the evaluation index of respiratory toxicity of TDI. Methods: In October 2014, 61 male workers engaged in TDI synthesis process, purification process, packaging process and the above production process in a TDI factory in western China were selected as TDI exposure group; 62 male enterprise managers who were not exposed to TDI and other known allergenic chemicals were selected as control group, which were matched at the age of workers in exposure group. The questionnaire survey obtained information such as gender, length of service, age, occupational history, exposed length of service and so on. The lung function indexes [forced expiratory volume in the first second (FEV1), forced vital capacity (FVC), FEV1/FVC] and serum levels of interleukin (IL)-1 ß, IL-6, IL-8, tumor necrosis factor (TNF)-α, macrophage inflammatory factor-1 ß, monocyte chemoattractant factor-1 and vascular endothelial growth factor were measured. The urine was collected after the weekend shift, and the concentration of (TDA), the metabolite of TDI, was determined as the index of internal exposure. Spearman rank correlation was used to analyze the correlation between cytokines and lung function indexes, and multivariate linear regression was used to analyze the changes of lung function indexes and cytokines with TDI exposure concentration and time. Results: The median age (P5-P95) of the exposed group and the control group was 36.5 (24.0-51.0) and 38.0 (24.0-50.0) years, respectively. In the exposed group, the median length of service (P5-P95) was 6.94 (0.97-26.33) years, and the median concentration of TDA in urine was 15.56 (2.28-112.16) ng/ml. The three indexes of lung function, FVC, FEV1, FEV1/FVC and the levels of serum IL-8 and TNF-α were significantly lower than those in the control group (P<0.01). With the increase of exposure concentration and exposure time, the level of serum TNF-α, FVC and FEV1 decreased, and showed a good dose-effect and time-effect relationship (all Ptrend values< 0.05). Serum IL-8 and TNF-α were positively correlated with FVC, FEV1 and FEV1/FVC (all P values<0.01). Conclusion: The levels of serum inflammatory factors IL-8 and TNF-α in worker exposed to TDI are related to lung function indexes, which can be used as early evaluation indexes of respiratory toxicity induced by TDI.

[Analysis of project results of preventive medicine from the National Natural Science Foundation of China in 2017].

We analyzed the project results of preventive medicine from the National Natural Science Foundation of China (NSFC) finished in 2017 based on the project-ending reports and data on science fund sharing service network. A total of 406 projects in this field were completed in 2017. A total of 3 122 published articles supported by these projects, including 1 789 articles in science citation index (SCI) journals and 525 articles in Chinese core journals. In addition, there were 224 patent application/software copyright and 589 trained postgraduates. The top three sub-disciplines of project were non-communicable disease epidemiology, human nutrition and hygienic toxicology, accounting for 45.32% of the total number of completed projects. There were 12 institutions which had more than 10 finished projects, accounting for 41.87%. During the recent 5 years, the number of SCI articles and patents/software copyrights per project showed a general uptrend. It should be noted that the number of articles in Chinese core journals and postgraduates decreased in recent two years. Our analyses demonstrated that the project results should be guided by the new era policy of science fund to promote sustainable development of scientific research.

[Effect of mitogen-activated protein kinase signaling pathway on apoptosis induced by chloroacetic acid in human normal bronchial epithelial 16HBE cells].

Objective: The aim of this study was to investigate the effect of mitogen-activated protein kinase (MAPK) signaling pathway on apoptosis induced by chloroacetic acid in human normal bronchial epithelial 16HBE cells. Methods: 16HBE cells were exposed to 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5 mmol/L chloroacetic acid for 24 h in vitro. The cytotoxicity induced by chloroacetic acid was assessed by CCK-8 and LDH assays. Cell apoptosis was detected by Annexin V-FITC and PI staining. The protein expression levels of phosphorylation of p38, ERK1/2 and JNK were determined by western blotting. 16HBE cells were pretreated with MAPK signaling pathway specific inhibitors including SB203580, U0126 and SP600125 for 1 h, and these cells were subsequently treated with 2.5 mmol/L chloroacetic acid for 24 h. The expressions of p-p38, p-ERK1/2 and p-JNK as well as the changes of cell viability and apoptosis were measured after pretreated with inhibitors for 1 h. Results: The cell viability by CCK-8 and LDH methods gradually reduced in a dose-dependent manner when chloroacetic acid concentrations elevated (P<0.05) , and their correlation coefficients were -0.902 and -0.825, respectively. The detection efficiency of CCK-8 assay significantly increased compared with LDH assay (P<0.05) . The cell apoptosis rates, which were (17.2±4.0) %, (24.6± 4.2) %, (39.3 ± 5.7) % in 1.5, 2.0, 2.5 mmol/L chloroacetic acid-treated groups, were higher than that of the control group[ (5.6 ± 3.0) %] (P<0.05) . There was a time-or dose-dependent change in the protein expressions of p-p38, p-ERK1/2 and p-JNK. Compared with the control, the levels of p-p38 had 2.1 and 2.6-fold increases in 16 and 24 h treated groups (P<0.01) , while the levels of p-ERK1/2 distinctly decreased by 37% and 52% (P<0.01) . In comparison with the control group, the expressions of p-p38 had 1.9 and 2.6-fold increases in 1.5 and 2.5 mmol/L treatment groups (P<0.01) , whereas the expressions of p-ERK1/2 significantly decreased by 40% and 50% (P<0.01) . No significant change was observed in p-JNK protein expression between the chloroacetic acid-treated and control groups. In comparison with the vehicle control and the exposed group, p-p38, p-ERK1/2, p-JNK protein expressions significantly declined in the inhibitor controls and inhibitor groups. Compared with the controls, the cell survival rates had significant reductions of 28%, 18%, 36% and 26% respectively in chloroacetic acid treated group, SB203580 group, U0126 group and SP600125 group, and the apoptosis rates in the abovementioned groups were 7, 4, 8 and 7 times. Compared with chloroacetic acid-treated group, the cell viability increased by 14% in SB203580 group and decreased by 11% in U0126 group, and the cell apoptosis rates decreased by 36% in SB203580 group and increased by 18% in U0126 group (P<0.05) . But no significant changes were observed in cell viability and apoptosis between SP600125 and chloroacetic acid-treated group. Conclusion: Chloroacetic acid might activate p38 MAPK signaling pathway and inhibit ERK1/2 MAPK signaling pathway. The signaling pathways of p38 and ERK1/2 MAPK are involved in 16HBE cell apoptosis induced by chloroacetic acid, but JNK is not involved in chloroacetic acid-induced 16HBE cell apoptosis.

[Association of etheno-DNA adduct and DNA methylation level among workers exposed to diesel engine exhaust].

Objective: To investigate the association between etheno-DNA adduct and the promoter of DNA methylation levels of cyclin dependent kinase inhibitor 2A (P16), Ras association domain family 1 (RASSF1A) and O-6-methylguanine-DNA methyltransferase (MGMT) in workers with occupational exposure to diesel engine exhaust (DEE). Methods: We recruited 124 diesel engine testing workers as DEE exposure group and 112 water pump operator in the same area as control group in Henan province in 2012 using cluster sampling. The demographic data were obtained by questionnaire survey; urine after work and venous blood samples were collected from each subject. The urinary etheno-DNA adducts were detected using UPLC-MS/MS, including 1,N6-etheno-2'-deoxyadenosine (εdA) and 3,N4-etheno-2'-deoxycytidine(εdC). The DNA methylation levels of P16, RASSF1A, and MGMT were evaluated using bisulfite-pyrosequencing assay. The percentage of methylation was expressed as the 5-methylcytosine (5mC) over the sum of cytosines (%5mC). Spearman correlation and multiple linear regression were applied to analyze the association between etheno-DNA adducts and DNA methylation of P16, RASSF1A, and MGMT. Results: The median (P(25)-P(75)) of urinary εdA level was 230.00 (98.04-470.91) pmol/g creatinine in DEE exposure group, and 102.10 (49.95-194.48) creatinine in control group. The level of εdA was higher in DEE exposure group than control group (P<0.001). DNA methylation levels of P16, RASSF1A and MGMT were 2.04±0.41, 2.19 (1.94-2.51), 2.22 (1.94-2.46)%5mC in exposure group, and 2.19±0.40, 2.41 (2.11-2.67), 2.44 (2.15-2.91)%5mC in control group. DNA methylation levels were lower in exposure group (P values were 0.005, 0.002 and 0.001, respectively). Spearman correlation analysis showed that DNA methylation levels of P16, RASSF1A, and MGMT were negative associated with urinary εdA level (r values were -0.155, -0.137, and -0.198, respectively, P<0.05). No significant correlation was observed between the εdC level and any measured DNA methylation levels (P>0.05) . Multiple linear regression confirmed the negative correlation between εdA and DNA methylation levels of P16, RASSF1A, and MGMT in non-smoking group (ß (95%CI) was -0.068 (-0.132--0.003), -0.082 (-0.159--0.004) and -0.048 (-0.090--0.007), P values were 0.039, 0.039 and 0.024, respectively). Moreover, εdC was negative associated with DNA methylation level of MGMT in non-smoking group (ß (95%CI) was -0.094 (-0.179--0.008), P=0.032). Conclusion: DEE exposure could induce the increased of εdA and decreased of DNA methylation levels of P16, RASSF1A and MGMT.

[Effects of chronic exposure to monochloroacetic acid on the lung function and lymphocyte subsets in occupational exposed workers].

Objective: To investigate the effects of chronic exposure to monochloroacetic acid on the lung function and whole blood counts in occupational exposed workers, and provide new markers for occupational health surveillance. Methods: We conducted a cross-sectional molecular epidemiology study of 121 workers who were occupationally exposed to monochloroacetic acid and 69 unexposed workers frequency-matched by age and smoking status from the same geographic region. The lung function was measured by portable lung function instrument, and the lymphocyte subsets were measured by flow cytometry. Linear regression was used to test for differences in the levels of each marker between exposed and control workers. Results: FEV1.0/FVC was significantly decreased in both male and female workers exposed to monochloroacetic acid compared to unexposed workers (P<0.01) after adjusting for potential confounders, which were highly consistent when stratified by smoking status. Among male workers, monochloroacetic acid exposure was associated with significant decrease in the levels of CD8+ T cells (P<0.05) and monocytes (P<0.05) , and these statistically significant differences were observed between exposure and control workers only among smokers, not among non-smokers. However, there were no significant differences in the levels of whole blood cells and lymphocyte subsets between two groups among female workers. Conclusion: The chronic monochloroacetic acid exposure was associated with pulmonary dysfunction and immunosuppression, which mainly occurred among male workers and smokers.

[Analysis of correlation between pulmonary function and expression levels of matrix metalloproteinases-9 and tissue inhibitor of metalloproteinase-1 among toluene diisocyanate exposed workers].

OBJECTIVE: To investigate the effect of occupational toluene diisocyanate(TDI) exposure on matrix metalloproteinases-9 (MMP-9) and tissue inhibitor of metalloproteinase-1(TIMP-1), and analysis of the correlation of MMP-9,TIMP-1,MMP-9/TIMP-1 and lung function. METHODS: In October 2014, based on cluster sampling, we conducted a cross-sectional study in a TDI production factory located in China's western region. 61 exposed workers were recruited from workers engaged in packing, operating and checking. Based on different levels of the external exposure, the packers were classified as high exposed group, while operators and checkers as low exposed group. 58 factory managers, matching age and agent, were selected as controls, having same work intense and not contacting the TDI or other allergens. The questionnaire surveys were used to obtain the agent, age, work age, smoking and drinking, personal and family allergic history, occupational history, and the recent health conditions. The levels of MMP-9 and TIMP-1 in serum of subjects were determind by ELISA. The time weighted average concentrations (8h-TWA) were used to describe the levels of TDI air exposure in working environment. Spearman correlation assay was used to investigate the correlation of MMP-9, TIMP-1, MMP-9/TIMP-1 and lung function, exposure time. RESULTS: 8-hour TWA means of TDI air levels in exposed group, packers, operators and checkers were 0.39, 0.76, 0.25 mg/m(3), respectively . According to the external exposure concentration, the packers were classified as high exposed group, and the operators and checkers were classified as low exposed group. In controls, low exposed group and high exposed group, the levels of MMP-9, respectively, were (807.21±347.70),(586.91±317.50),(388.94±312.01) ng/ml (χ(2)=16.69, P<0.001), respectively, and the P50(P25-P75) of MMP-9/TIMP-1 were 4.67(2.87-6.68), 2.3(1.44-3.48), 1.11(0.59-1.48) (χ(2)=39.42, P<0.001), respectively, and the concentrations of TIMP-1, were (173.44±72.67), (236.12±51.98), (302.81±44.39) ng/ml (F=20.09, P< 0.001), respectively. The levels P50(P25-P75) of FVC, FEV1.0 and FEV1.0/FVC in exposed group were, 92.8% (86.0%-101.8%), 85.5%(76.7%-92.8%), 112.5(108.2-118.5), respectively, which were lower than that in control group (124.3%(107.9%-144.2%), 142.7%(119.1%-155.7%), 129.2(123.5-134))(Z values were 7.70, 8.97, 8.62, and all P<0.001). Spearman rank correlation analysis showed that levels of MMP-9 were positively associated with FEV1.0, and FEV1.0/FVC (r values were 0.27, 0.25, respectively, all P<0.05), and The levels of TIMP-1 were negatively associated with FVC, FEV1.0, and FEV1.0/FVC (r valuse were -0.33, -0.39, -0.39, all P<0.05).The levels of MMP-9 were negatively correlated with exposure time(r=-0.26, P=0.040). The positive correlations of MMP-9/TIMP-1 with FVC, FEV1.0, and FEV1.0/FVC were also found (r valuse were 0.34, 0.44, 0.40, all P<0.05). CONCLUSION: TDI exposure could induce the downs of MMP-9 and MMP-9/TIMP-1 associated with lung functions. The MMP-9 and MMP-9/TIMP-1,in a way, could reflect the respiratory inflammatory injury caused by TDI exposure.

Critical role of arachidonic acid-activated mTOR signaling in breast carcinogenesis and angiogenesis.

The mammalian target of rapamycin (mTOR) signaling pathway is upregulated in the pathogenesis of many cancers. Arachidonic acid (AA) and its metabolites play critical role in the development of breast cancer, but the mechanisms through which AA promotes mammary tumorigenesis and progression are poorly understood. We found that the levels of AA and cytosolic phospholipase A2 (cPLA2) strongly correlated with the signaling activity of mTORC1 and mTORC2 as well as the expression levels of vascular epithelial growth factor (VEGF) in human breast tumor tissues. In cultured breast cancer cells, AA effectively activated both mTOR complex 1 (mTORC1) and mTORC2. Interestingly, AA-stimulated mTORC1 activation was independent of amino acids, phosphatidylinositol 3-kinase (PI3-K) and tuberous sclerosis complex 2 (TSC2), which suggests a novel mechanism for mTORC1 activation. Further studies revealed that AA stimulated mTORC1 activity through destabilization of mTOR-raptor association in ras homolog enriched in brain (Rheb)-dependent mechanism. Moreover, we showed that AA-stimulated cell proliferation and angiogenesis required mTOR activity and that the effect of AA was mediated by lipoxygenase (LOX) but not cyclooxygenase-2 (COX-2). In animal models, AA-enhanced incidences of rat mammary tumorigenesis, tumor weights and angiogenesis were inhibited by rapamycin. Our findings suggest that AA is an effective intracellular stimulus of mTOR and that AA-activated mTOR plays critical roles in angiogenesis and tumorigenesis of breast cancer.

Quantum criticality and nodal superconductivity in the FeAs-based superconductor KFe2As2.

The in-plane resistivity rho and thermal conductivity kappa of the FeAs-based superconductor KFe2As2 single crystal were measured down to 50 mK. We observe non-Fermi-liquid behavior rho(T) approximately T{1.5} at H{c{2}}=5 T, and the development of a Fermi liquid state with rho(T) approximately T{2} when further increasing the field. This suggests a field-induced quantum critical point, occurring at the superconducting upper critical field H{c{2}}. In zero field, there is a large residual linear term kappa{0}/T, and the field dependence of kappa_{0}/T mimics that in d-wave cuprate superconductors. This indicates that the superconducting gaps in KFe2As2 have nodes, likely d-wave symmetry. Such a nodal superconductivity is attributed to the antiferromagnetic spin fluctuations near the quantum critical point.

Expression of human factor IX cDNA in mice by implants of genetically modified skin fibroblasts from a hemophilia B patient.

Double-copy retroviral vector containing human factor IX cDNA driven by human cytomegalovirus enhancer-promoter was constructed. The vector was introduced into the amphotropic packaging cell line PA317. The recombinant virus produced in PA317 was used to transduce skin fibroblasts from a hemophilia B patient. The infected cells produced high levels of biologically active human factor IX at a rate of 3420 ng/10(6) cells/24 h. These cells were embedded in a collagen matrix and implanted into the peritoneal cavity or subcutaneous space of mice. It was demonstrated that human factor IX was produced by the implants for at least 12 days in vivo, reaching a peak of 105 ng/ml plasma. Over 90% of the protein was functionally active. This technique has the potential to be developed into a new approach for gene therapy for hemophilia B.

High efficient transfer and expression of human clotting factor IX cDNA in cultured human primary skin fibroblasts from hemophilia B patient by retroviral vectors.

To study the possibility of somatic gene therapy for hemophilia B via gene transfer to primary factor IX-deficient skin fibroblasts, we constructed four retroviral vectors containing factor IX cDNA driven by retroviral LTR promoter, SV40 early promoter and mouse MT-I promoter, respectively. These retroviral vectors were transfected into an amphotropic packaging cell line, PA317 cells, by electroporation, and a human fibrosarcoma cell line, HT1080 cells, was used to assay the factor IX-virus titers of these four virus-producing PA317 cells, which ranged from 2 x 10(4) to 5 x 10(5) cfu/ml. The factor IX proteins produced by bulk population of four virus-producing PA317 cells were determined by ELISA. Results showed that LTR promoter directed the highest production of factor IX at the rate of 584 ng/10(6) cells/24 h, while SV40 early promoter and MT promoter directed about 10 and 20 times less production of factor IX than LTR promoter. The highest expressed retroviral vector XL-IX was used to infect a line of factor IX-deficient human primary skin fibroblasts, FDIX cells. The factor IX secretion rate of the infected FDIX cells was about 549 ng/10(6) cells/24 h and over 75% of secreted factor IX was biologically active. We are convinced that this factor IX-deficient human primary skin fibroblast had been cured, or genetically corrected, by retroviral-mediated gene therapy in vitro.

On the relationship between adenosine diphosphoribosyl transferase and S phase DNA synthesis in cultured mammalian cells.

The cell cycle dependent fluctuation of adenosine diphosphoribosyl transferase (ADPRT) activity was demonstrated by both nicotinamide adenine dinucleotide (3H-NAD+) incorporation into the acid insoluble fraction of permeabilized cells and changes in the cellular content of NAD, the only substrate of ADPRT, in intact FL cells. The ADPRT activity was lowest in the G1 phase and highest in the S/G2-G2 phase. Aphidicolin, a specific inhibitor of DNA polymerase a, abolished the fluctuation of ADPRT activity. Meanwhile, in 5-fluorodeoxy-uridine (FUdR) exposed cells whose DNA synthesis was interfered with by the inhibition of thymidylate synthetase and the rate of ligation of short replicative intermediates, the ADPRT activity remained at a higher level than in controls. However, 3-aminobenzamide (3AB), a potent ADPRT inhibitor, showed down DNA synthesis in the S phase and also extended the S phase. These results indicate that ADP-ribosylation may be involved in DNA replication and cell cycle progression, and suggest that ADPRT activity may be stimulated by transient short fragments of newly replicated DNA, exerting its effects at the later stages of DNA replication, most probably at the ligation step of DNA synthesis.