Changes in fertility intention among married Chinese couples with two children during COVID-19: a cross-sectional study

BACKGROUND

A three-child policy was implemented in China to stimulate a rise in fertility levels and coincided with the COVID-19 pandemic. Data suggested that COVID-19 has a negative impact on fertility intention.

AIM

To describe married couples' changes in intention to have a third child during the COVID-19 pandemic and determine factors associated with altered intentions.

METHODS

An online survey was conducted in October 2021, including sociodemographic characteristics, change of intention to have a third child after the COVID-19 pandemic outbreak, reasons for increased or decreased intention, and the Fertility Intention Scale (FIS). Bivariate and multivariable logistic regression were used to test the potential factors associated with changes in intention.

RESULTS

A total of 1308 participants provided responses. Following the COVID-19 outbreak, 35.8% of participants decreased their third-child intention, while 2.8% of participants increased their third-child intention. Males (aOR 1.90, 95% CI 1.42 to 2.54), youngsters (aOR 1.77, 95% CI 1.08 to 2.93) and those living in Estern China (aOR 2.12, 95% CI 1.13 to 3.98) were more likely to decrease their third-child intention. Perceived risk (aOR 1.07, 95% CI 1.03 to 1.10) and policy support (aOR 1.06, 95% CI 1.03 to 1.09) as measured on the FIS decreased couples' intention to have a third child. Social support (aOR 0.94, 95% CI 0.91 to 0.98) as measured on the scale protected participants from decreased intention.

CONCLUSIONS

During severe public health emergencies, strong prevention and control policies, together with enhancing support from partners and healthcare professionals for women, are necessary to improve intentions to give birth.

Increasing Understanding and Perceived Confidence of Nurses Working in an Emergency Department in Assessing Patients at Risk of Violent Behavior

PURPOSE

The aims of this quality improvement project were to improve understanding and perceived confidence in using a tool that assesses patients at risk of violence.

PROJECT DESCRIPTION

The Brøset Violence Checklist is valid at assessing patients at risk of violence. Participants were given access to an e-learning module that demonstrated how to use the tool. Improvement in understanding and perceived confidence in using the tool were assessed preintervention and postintervention via an investigator-developed survey. Analysis of the data was conducted using descriptive statistics, and open-ended survey responses were analyzed using content analysis.

OUTCOME

Participants did not demonstrate an increase in understanding and perceived confidence after introduction of the e-learning module. Nurses reported that the Brøset Violence Checklist was easy to use, clear, reliable, and accurate and could be used to standardize assessments of at-risk patients.

CONCLUSION

Emergency department nursing staff were educated in use of a risk assessment tool for identifying patients at risk of violence. This supported the implementation and integration of the tool into emergency department workflow.

Barriers and facilitators of psychological help-seeking behaviors for perinatal women with depressive symptoms: A qualitative systematic review based on the Consolidated Framework for Implementation Research

OBJECTIVE

To identify barriers and facilitators related to psychological help-seeking behaviors of perinatal depression from all related stakeholders (e.g., perinatal women, family members, mental health care providers, and policymakers).

DESIGN

A literature search of six English-language databases (PubMed, Web of Science, Embase, PsycINFO, the Cochrane Library, CINAHL) and three Chinese-language databases (China National Knowledge Infrastructure, Wan Fang, Chinese Biomedical Literature Databases). Studies published in English or Chinese using qualitative or mixed methods to explore the psychological help-seeking behaviors of women with perinatal depression were included. Data extraction was synthesized for common themes based on the Consolidated Framework for Implementation Research. The Joanna Briggs Institute Qualitative Assessment and Review Instrument was used to appraise methodologic quality.

PARTICIPANTS AND SETTINGS

Perinatal women with depression, mental health care providers (e.g., pediatricians/nurses, social workers, nurse-midwives, perinatal psychiatrists, community health workers, and administrators), partners and informal caregivers (e.g., community birth attendants, elderly mothers, and men of reproductive age) based in high, middle and low income countries.

FINDINGS

Forty-three articles were included in this review and presented according to the Consolidated Framework for Implementation Research domains (in parentheses). The most common barriers to help seeking were stigma (individual characteristics), misconceptions (individual characteristics), cultural beliefs (inner setting), and lack of social support (outer setting). The most common facilitators were providing adequate support (outer setting) and perinatal health care professional training on how to detect, manage and discuss depression; establishing supportive relationships with mental health care providers; and eroding stigma (all three implementation processes).

KEY CONCLUSIONS AND IMPLICATIONS FOR PRACTICE

This systematic review could serve as a reference framework for health authorities to develop diverse strategies for improving the psychological help-seeking behaviors of women with perinatal depression. More high-quality studies focused on the Consolidated Framework for Implementation Research characteristics of available interventions, and implementation processes are needed in future research.

Prevalence and Correlates of Weight Stigma among Postpartum Women in China

Weight stigma is linked to a variety of psychological and health problems. In the postpartum period, women may be more likely to experience weight-based discrimination because of their changing social roles, weight, and the new functions their bodies fulfill. However, few studies have explored the issue of postpartum women's weight stigma. Thus, to investigate the prevalence and correlates of weight stigma for postpartum women in China, we conducted a cross-sectional study of 507 postpartum women. Results showed that almost one quarter (21.1%) of postpartum women claimed to have experienced perceived weight stigma (PWS). Two thirds (66.1%) scored at the mean and 14.8% at the highest levels of weight bias internalization (WBI). During the postnatal period, the conditions of those most likely to report experiences of weight-based discrimination included low income [b = -0.203, p = 0.004], occupation as a worker [b = 0.921, p = 0.017] or farmer [b = 0.826, p = 0.033], stress [b = 0.044, p = 0.035], depression [b = 0.057, p = 0.021], and higher WBIS [b = 0.018, p = 0.002]. In addition, postpartum women who lived alone [b = 7.511, p = 0.048], were overweight or obese [b = 5.443, p = 0.000], and had higher PWS [b = 0.897, p = 0.004] and anxiety symptoms [b = 0.219, p = 0.011] had higher levels of internalized weight stigma. Findings from this study provide a foundation to better understand characteristics of postpartum women in China who are at risk for weight stigma.

Prevalence, awareness, and associated factors of high blood pressure among female migrant workers in Central South China

BACKGROUND

Although many young Chinese women migrate to urban regions for better opportunities, little is known about the prevalence and awareness of having high blood pressure (HBP) in this population. This study investigated the prevalence, awareness, and factors associated with HBP among young female migrant workers in Central South China.

METHODS

We conducted a cross-sectional study to identify HBP (2017 ACC/AHA guidelines) among female migrant workers aged 18-45 years in Central South China. Demographics, anthropometric measurements, hypertension-related lifestyle, awareness of HBP, and blood pressure were recorded. Logistic regression analysis was used to identify the factors associated with HBP (blood pressure ≥ 130/80 mmHg).

RESULTS

Overall, 232 female migrants participated in the study (mean age 34.4; standard deviation: 6.4 years). The prevalence of HBP was 27.2% (95% CI [21.6-33.2]), and 88.9% of the participants were unaware of their HBP status. Having rural medical insurance (odds ratio [OR] = 20.7; 95% confidence interval 95% CI [2.1-204.8]), awareness of having HBP (OR = 5.1; 95% CI [1.4-18.5]), physical inactivity (OR = 2.9; 95% CI [1.1-7.9]), and being overweight/obese (OR = 2.7; 95% CI [1.3-6.1]) were independently associated with HBP.

CONCLUSIONS

This study revealed a high prevalence of HBP among young Chinese female migrant workers, as well as a high frequency of being unaware of their condition and some associated factors (rural medical insurance, awareness of having HBP, physical inactivity, and overweight/obesity). The uncontrolled HBP among young Chinese female migrant workers suggested that health education needs further promotion in such a population.

Nurses' knowledge, attitudes, and behaviours related to pressure injury prevention: A large-scale cross-sectional survey in mainland China

AIMS AND OBJECTIVES

To determine the level of and factors in nurses' knowledge, attitudes and behaviours towards pressure injury (PI) prevention.

BACKGROUND

Although there has been a declining trend in global PI prevalence and hospital-acquired rates in recent years, this has not been the case in China. Evidence in the literature indicates the importance of nurses' knowledge, attitudes and behaviours for promoting PI prevention.

DESIGN

Cross-sectional study.

METHODS

A total of 1,806 nurses from 10 tertiary general hospitals in Hunan Province, China, participated in this study. Nurses' knowledge and attitudes were assessed using Pieper's Pressure Ulcer Knowledge Test and Attitude towards Pressure Ulcer Prevention Instrument, respectively, and behaviours were measured using a researcher self-designed questionnaire. Multiple logistic regression analysis determined factors affecting the nurses' PI-prevention knowledge, attitudes and behaviours. A STROBE checklist was used to report findings.

RESULTS

Among all nurses involved in this study, 41.7% had insufficient PI-prevention knowledge, 46.6% had negative PI-prevention attitudes, and 21.8% had poor PI-prevention behaviour. Nurses with a bachelor's degree or above were more likely to have adequate PI-prevention knowledge. Increased PI-prevention training frequency increased the nurses' positive attitude scores for PI prevention; longer years of service and a higher number of PI-prevention trainings attended predicted better PI-prevention behaviours.

CONCLUSION

Chinese nurses' PI-prevention knowledge and attitudes in this study were unsatisfactory, while their PI-prevention behaviour was acceptable. Increasing PI-prevention training frequency can help improve Chinese nurses' PI-prevention attitudes and further behaviour. Having a minimum of a bachelor degree may be beneficial to Chinese nurses' PI-prevention knowledge, but more evidence is needed.

RELEVANCE TO CLINICAL PRACTICE

Chinese nurses have insufficient knowledge about PI-repositioning, inadequate practices in PI nutrition assessment, and low confidence in their personal competence regarding PI-prevention. The key solution for the above issues is to promote ongoing education and training based on strong clinical leadership.

Influencing factors for placenta accreta in recent 5 years: a systematic review and meta-analysis

Objective: Assess influencing factors for placenta accreta in pregnant women documented in recent literature.Methods: A systematic review and meta-analysis were conducted based on English- and Chinese-language articles published from January 2014 to June 2019. Articles were retrieved from the following Chinese databases, CNKI, Wanfang Data, China Science and Technology Journal Database, CBM and English databases, PubMed, Web of Science, the Cochrane Library and Embase.Results: Eleven studies with 2,152,014 cases were included in the meta-analysis. The odds ratios of influencing factors were as follows: hypertension 2.51 (95% CI, 1.50-4.20), multifetal gestations 1.90 (95% CI, 1.26-2.88), male fetus 0.79 (95% CI, 0.74-0.84), and low socioeconomic status 0.51 (95% CI, 0.37-0.71).Conclusion: Evidence from English- and Chinese-language literature indicates that hypertension and multifetal gestations are risk factors for placenta accreta, while male fetus and low socioeconomic status are protective factors.

Frequency of depressive symptoms among female migrant workers in China: associations with acculturation, discrimination, and reproductive health

OBJECTIVES

Depression has been associated with numerous adverse health conditions. This study sought to determine the frequency of significant depressive symptoms and whether or not acculturative stress, discrimination, and reproductive health conditions were risk factors for significant depressive symptoms in migrant working women in China.

STUDY DESIGN

The design of this study is cross-sectional.

METHODS

Data were derived from a survey of female migrant workers at three employment sites in Changsha, China. The associations between acculturative stress, discrimination, reproductive health, and risk for significant depressive symptoms were obtained using F-tests for mean differences, correlations, ordinary least squares regression, and logistic regression analysis.

RESULTS

Between March and June 2017, 232 eligible female participants completed the survey among whom the median age was 34.36 years (standard error 0.43) and 25.58% reported significant depressive symptoms. Significant depressive symptoms were associated with higher education (F-test, P = .006), all four acculturative stress factors (r = 0.15 to r = 0.29), both institutional and interpersonal discrimination (r = 0.29, r = 0.35), age (r = - 0.13), and self-rated health (r = - 0.19). In multivariate regression analysis of depression scale scores, interpersonal discrimination was the strongest predictor (beta = 0.238, P = .002) among the nine factors identified in bivariate analysis. None of the other predictors (age, self-rated health, education, acculturative stress, and institutional discrimination) showed significant associations with the depression scale. Similar results were obtained for a multivariate logistic regression analysis of a clinically important threshold for depression (<10 versus ≥ 10 on the depression scale). Only interpersonal discrimination significantly distinguished between clinical depression categories (odds ratio = 2.607 per unit change in the index, P = .001).

CONCLUSIONS

Migrant women workers in China appear to be at risk for significant depressive symptoms, and interpersonal discrimination appears to be an important risk factor in this setting. Acculturative stress and institutional discrimination may also be relevant risk factors, as suggested in our bivariate analysis, but in our sample, the correlations between the stress and discrimination factors are high enough to compromise identification of unique associations between acculturation stress and depression. Government, community and workplace education, and psychosocial services for migrant women are recommended.

The risk, perceived and actual, of developing type 2 diabetes mellitus for mothers of preschool children in urban China

BACKGROUND

The perceived risk of developing type 2 diabetes mellitus (T2DM) can motivate individuals to adopt preventive health behaviors. Compared with fathers, mothers of young children often experience unique risk factors for developing T2DM: pregnancy-related weight gain, lifestyle changes related to child care, and the increased incidence of gestational diabetes mellitus. Understanding how actual risk factors affect the perceived risk of developing T2DM can foster effective diabetes prevention interventions for this population. The aims of this study were to describe the risk, perceived and actual, of developing T2DM and to explore the influencing factors of perceived risk for Chinese mothers of preschool children in China.

METHODS

A multisite, cross-sectional survey was conducted and included 176 mothers (mean age of 31.19 years old) of preschool children (aged 3-7 years old) from four preschools in Changsha, the capital city of Hunan Province, China. The overall perceived risk of developing T2DM was measured by one item "Your own personal health risk is at almost no risk, slight risk, moderate risk or high risk from diabetes" from the Risk Perception Survey for Developing Diabetes (RPS-DD). PRS-DD and the Chinese version of the Canadian Diabetes Risk Assessment Questionnaire (CHINARISK) were used to assess perceived risk related worry, personal control, optimistic bias, and diabetes risk knowledge and actual risk of T2DM. Mothers also reported their height, weight, and waist circumference followed by the NIH protocol. Pearson correlation and stepwise multivariate linear regression were used to explore how the actual risk factors affected the perceived risk of developing diabetes (RPS-DD)).

RESULTS

Nearly 90% of mothers perceived almost no/slight risk for developing diabetes. Nearly half of the mothers had parents or siblings with diabetes. Roughly 70% of the mothers did not eat five servings of fruits and vegetables per day, and more than 50% did not exercise at least 30 minutes a day. In the five stepwise multivariate linear regression models, young mothers (95% CI .400-1.311) and those with a family history of diabetes (95% CI -0.74- .000) were founded a higher overall perceived risk. Mothers who reported more sedentary time (95% CI -0.029- -0.008) and less physical activity had less personal control (95% CI -0.354- -0.046). Mothers with more sedentary time had more worries about developing T2DM(95% CI 0.008-0.035) . Mothers who were older (95% CI -0.440-0.055) or had more physical activities (95% CI 0.003-0.048) had more optimistic bias of not developing T2DM. Mothers who had a higher education level (95% CI .354-1.422) and a family history of diabetes (95% CI .029-2.231) had more diabetes risk knowledge of developing T2DM.

CONCLUSION

This study found that Chinese mothers of preschool children in urban areas reported low perceived risk of developing T2DM, although they have actual risk factors. These women did not associate anthropometric, health history, or health behavior factors with the risk of developing T2DM. Anthropometrics and risk factors associated with behavioral risk factors may be the focus of diabetes prevention programs.

The defect in transcription-coupled repair displayed by a Saccharomyces cerevisiae rad26 mutant is dependent on carbon source and is not associated with a lack of transcription

Nucleotide excision repair (NER) is an evolutionarily conserved pathway that removes DNA damage induced by ultraviolet irradiation and various chemical agents that cause bulky adducts. Two subpathways within NER remove damage from the genome overall or the transcribed strands of transcribing genes (TCR). TCR is a faster repair process than overall genomic repair and has been thought to require the RAD26 gene in Saccharomyces cerevisiae. Rad26 is a member of the SWI/SNF family of proteins that either disrupt chromatin or facilitate interactions between the RNA Pol II and transcription activators. SWI/SNF proteins are required for the expression or repression of a diverse set of genes, many of which are differentially transcribed in response to particular carbon sources. The remodeling of chromatin by Rad26 could affect transcription and/or TCR following formation of DNA damage and other stress-inducing conditions. We speculate that another factor(s) can substitute for Rad26 under particular growth conditions. We therefore measured the level of repair and transcription in two different carbon sources and found that the defect in the rad26 mutant for TCR was dependent on the type of carbon source. Furthermore, TCR did not correlate with transcription rate, suggesting that disruption of RAD26 leads to a specific defect in DNA repair and not transcription.

The 26S proteasome negatively regulates the level of overall genomic nucleotide excision repair

Regulation of protein expression can be achieved through destruction of proteins by the 26S: proteasome. Cellular processes that are regulated by proteolysis include cell cycle progression, stress responses and differentiation. Several nucleotide excision repair proteins in yeast and humans, such as Rad23, Rad4 and XPB, have been shown to co-purify with Cim3 and Cim5, AAA ATPases of the 19S: proteasome regulatory subunit. However, it has not been determined if nucleotide excision repair is regulated through protein destruction. We measured nucleotide excision repair in yeast mutants that are defective in proteasome function and found that the repair of the transcribed and non-transcribed strands of an RNA polymerase II-transcribed reporter gene was increased in the absence of proteasome function. Additionally, overexpression of the Rad4 repair protein, which is bound to the repair/proteolytic factor Rad23, conferred higher rates of nucleotide excision repair. Based on our data we suggest that a protein (or proteins) involved in nucleotide excision repair or in regulation of repair is degraded by the 26S proteasome. We propose that decreased proteasome function enables increased DNA repair, due to the transient accumulation of a specific repair factor, perhaps Rad4.

Transcription-coupled repair in yeast is independent from ubiquitylation of RNA pol II: implications for Cockayne's syndrome

Cockayne's syndrome cells lack transcription-coupled nucleotide excision repair (TCR) and ubiquitylation of RNA polymerase II large subunit (RNA pol II LS), suggesting that ubiquitylation of RNA pol II LS may be necessary for TCR in eukaryotes. Rsp5 is the sole yeast ubiquitin-protein ligase that ubiquitylates RNA pol II LS in cells exposed to DNA-damaging agents. In yeast lacking functional Rsp5, there is no ubiquitylation of RNA pol II LS. We show here that removal, repression, or over-expression of Rsp5 has no effect on TCR, demonstrating that ubiquitylation of the RNA pol II LS is not required for TCR. We infer that the lack of ubiquitylation of RNA pol II LS in Cockayne's syndrome cells does not cause their defect in TCR.

Transcription-coupled DNA repair in yeast transcription factor IIE (TFIIE) mutants

We examined the role of yeast transcription initiation factor IIE (TFIIE) in eukaryotic transcription-coupled repair (TCR), the preferential removal of DNA damage from the transcribed strands of genes over non-transcribed sequences. TFIIE can recruit the transcription initiation/repair factor TFIIH to the RNA polymerase II (RNA pol II) initiation complex to facilitate promoter clearance. Following exposure to UV radiation, the RNA pol II elongation complex is blocked at sites of UV-induced DNA damage, and may be recognized by nucleotide excision repair proteins, thus enabling TCR. The TFA1 gene encodes the large subunit of TFIIE. We determined how DNA repair is affected by TFA1 conditional mutations. In particular, we find proficient TCR in a heat-sensitive tfa1 mutant at the non-permissive temperature during which growth is inhibited and overall RNA pol II transcription is reported to be inhibited. We demonstrate that transcription of the RPB2 gene was reduced, but readily detectable, in the heat-sensitive tfa1 mutant at the non-permissive temperature and thereby prove that TCR does occur in an expressed gene in the absence of TFIIE in vivo. We demonstrate that TCR occurs even at low levels of transcription.

Preferential repair of the transcribed DNA strand in the dihydrofolate reductase gene throughout the cell cycle in UV-irradiated human cells

We examined repair of UV-induced cyclobutane pyrimidine dimers (CPD) in each strand of the expressed dihydrofolate reductase gene in human cells in different phases of the cell cycle: G1, early S, middle S, late S, and G2/M. After 4 h of incubation, repair of the transcribed strand was substantially more efficient than repair of the non-transcribed strand in all phases. Furthermore, we observed no remarkable cell cycle-dependent differences in either the initial lesion frequency or the efficiency of repair of the transcribed strand. We conclude that transcription coupled repair operates generally and with high efficiency throughout the cell cycle.

Preferential repair of ultraviolet light-induced DNA damage in the transcribed strand of the human p53 gene

Mutations in the p53 tumor suppressor gene have been found in most human tumors. Analyses of the spectrum of p53 mutations in certain tumor types have shown a bias for mutations originating from lesions presumed to be in the untranscribed strand of the gene. This implies strand specificity for the formation or repair of DNA damage. We measured the induction and repair of ultraviolet light-induced cyclobutane pyrimidine dimers (CPD) in each strand of the human p53 gene in a normal human lung fibroblast cell line using quantitative Southern hybridization. We found that the removal of CPD from the transcribed strand was more rapid than that from the untranscribed strand of this gene, although the frequency of CPD induction was similar in both strands. Preferential repair of the transcribed strand of the p53 gene may account for the mutational spectra of this gene in human tumors.

Increased UV resistance of a xeroderma pigmentosum revertant cell line is correlated with selective repair of the transcribed strand of an expressed gene

A UV-resistant revertant (XP129) of a xeroderma pigmentosum group A cell line has been reported to be totally deficient in repair of cyclobutane pyrimidine dimers (CPDs) but proficient in repair of 6-4 photoproducts. This finding has been interpreted to mean that CPDs play no role in cell killing by UV. We have analyzed the fine structure of repair of CPDs in the dihydrofolate reductase gene in the revertant. In this essential, active gene, we observe that repair of the transcribed strand is as efficient as that in normal, repair-proficient human cells, but repair of the nontranscribed strand is not. Within 4 h after UV at 7.5 J/m2, over 50% of the CPDs were removed, and by 8 h, 80% of the CPDs were removed. In contrast, there was essentially no removal from the nontranscribed strand even by 24 h. Our results demonstrate that overall repair measurements can be misleading, and they support the hypothesis that removal of CPDs from the transcribed strands of expressed genes is essential for UV resistance.

The genetic defect in the Chinese hamster ovary cell mutant UV61 permits moderate selective repair of cyclobutane pyrimidine dimers in an expressed gene

We examined removal of cyclobutane pyrimidine dimers (CPDs) from the dihydrofolate reductase (DHFR) gene in ultraviolet-irradiated Chinese hamster ovary (CHO) UV61 and UV5 cells. The sensitivity of UV61 cells to UV-irradiation is intermediate between that of the parental CHO cells and that of mutants such as UV5 that are highly defective in excision repair. UV61 cells have been characterized as having normal repair of pyrimidine(6-4)pyrimidone photoproducts (6-4 PPs) but no detectable removal of CPDs from the genome overall. We find that the extent of removal of CPDs from the DHFR gene in UV61 cells is intermediate between that of the parental CHO cells and that of the UV5 mutant, and the observed repair appears to be confined to the transcribed strand. We detected no removal of CPDs from the DHFR gene in UV5 cells. Our findings in UV61 cells demonstrate a correlation between survival after UV-irradiation and CPD repair in an expressed gene in a cell line with moderate UV-sensitivity and yet no apparent removal of CPDs from the genome as a whole. We have thus demonstrated that overall repair measurements can be misleading. Our results have implications for the determination of the relative biological importance of the CPD and the 6-4 PP, and they further support the hypothesis that removal of CPDs from transcriptionally active DNA is crucial for UV-resistance.

Cell-cycle radiation response: role of intracellular factors

We have been studying variations of radiosensitivity and endogenous cellular factors during the course of progression through the human and hamster cell cycle. After exposure to low-LET radiations, the most radiosensitive cell stages are mitosis and the G1/S interface. The increased activity of a specific antioxidant enzyme such as superoxide dismutase in G1-phase, and the variations of endogenous thiols during cell division are thought to be intracellular factors of importance to the radiation survival response. These factors may contribute to modifying the age-dependent yield of lesions or more likely, to the efficiency of the repair processes. These molecular factors have been implicated in our cellular measurements of the larger values for the radiobiological oxygen effect late in the cycle compared to earlier cell ages. Low-LET radiation also delays progression through S phase which may allow more time for repair and hence contribute to radioresistance in late-S-phase. The cytoplasmic and intranuclear milieu of the cell appears to have less significant effects on lesions produced by high-LET radiation compared to those made by low-LET radiation. High-LET radiation fails to slow progression through S phase, and there is much less repair of lesions evident at all cell ages; however, high-LET particles cause a more profound block in G2 phase than that observed after low-LET radiation. Hazards posed by the interaction of damage from sequential doses of radiations of different qualities have been evaluated and are shown to lead to a cell-cycle-dependent enhancement of radiobiological effects. A summary comparison of various cell-cycle-dependent endpoints measured with low- or high-LET radiations is given and includes a discussion of the possible additional effects introduced by microgravity.

Sequential exposures of mammalian cells to low- and high-LET radiations. II. As a function of cell-cycle stages

The synergistic effects of low- and high-LET radiations were further studied with partially synchronized Chinese hamster V79 cells. Principally, nearly monoenergetic 425 MeV/u neon ions and 570 MeV/u argon ions produced near the Bragg peak were employed as the high-LET radiations and 225 kVp X rays as the low-LET counterpart. It was found that the killing effect due to damage interaction after sequential irradiations with the particle beam and X rays varies throughout the cell cycle. The greatest effect was observed in late-S phase which was most resistant to either of the radiations. The effect was quantitatively less in the G1/S border and in G2. Effects on pure mitotic cells have not been investigated in this study. For all cell stages studied, a dose of high-LET particles modified the shape of the X-ray survival curve in a way similar to the modification predicted by an appropriately selected X-ray dose. This finding suggests that the mechanism for the synergistic effects is similar to that operating for sequential treatments with X rays alone. Experiments with an S population, either incubated at 37 degrees C or room temperature between fractionation of high- and low-LET radiation treatments further verified that the damage involved is a repairable type. At a certain fractionation interval (6 to 8 h) following a dose of high-LET treatment, initially asynchronous cells were found to be very sensitive to X-irradiation. It is noteworthy that the net killing measured at this "radiosensitive window" was as effective as the killing observed by "immediately" sequential treatments with the same doses of high- and low-LET radiations. Such a time window also existed when the order of the treatment sequence was reversed except that the time of occurrence was earlier and the window was broader. This sensitization effect may be explained by radiation-induced G2 arrest together with an increase of radiosensitivity as the previously irradiated cells progress into S phase. Radiotherapy strategies using combined high-LET and low-LET radiations for rapidly proliferative tumors are presented.

Characterization of hydroxyl radical-induced damage after sparsely and densely ionizing irradiation

The extent of hydroxyl radical mediated cell inactivation was measured for a variety of particle beams ranging from 8.5 Me V/u neon ions to 570 Me V/u argon ions. In general, the fraction of the total radiosensitivity caused by OH decreases from close to 60 per cent at low ionization density or low linear energy transfer (low LET) to close to 25 per cent at high LET for aerobically irradiated mammalian cells. The extent of OH induced cell lethality can be explained in terms of LET infinity only for low energy or low atomic number particles where fragmentations and complicated track structures do not contaminate the characteristic particle LET. For example, at a calculated LET infinity of 100 ke V/micron, the OH mediated fraction of the total radiation damage is about 25 per cent for low energy carbon but close to 40 per cent for high energy carbon ions. For low energy charged nuclei of approximately the same energy, as the 5.4-13.4 MeV/u He, Li, C and Ne ions in this report, there is a predictable diminution of the OH mediated effect with increasing LET infinity; however, the biological effect cannot be predicted accurately from calculated LET infinity values for high energy particle irradiation, nor indeed from a variety of low energy charged particles of quite different energies (incident velocities). This illustrates the unsuitability of using LET as a unifying parameter, except under specific circumstances. As more is learned about the energy deposition for energized charged particles in terms of track structure (core and penumbra), it may be possible to characterize the radiobiological data with a better physical parameter than LET infinity.

Response of sensitive human ataxia and resistant T-1 cell lines to accelerated heavy ions

We have studied the radiation dose responses of two human fibroblast lines: cells from a patient with Ataxia telangiectasia (AT-2SF) and an established line of human T-1 cells. Aerobic and hypoxic 225 kVp X-ray survival curves were used as controls to the heavy ion exposures. Nearly monoenergetic accelerated neon and argon ions were used at the Berkeley Bevalac with various residual range values. The LET of the particles varied from 30 keV microns-1 to over 1,000 keV microns-1. All Ataxia survival curves were exponential functions of the dose. Their radiosensitivity reached peak values at 100-200 keV microns-1. Human T-1 cells have effective sublethal damage repair as has been evidenced by split dose experiments, and they are much more resistant to low LET than to high LET radiation. At high LET their radiosensitivity approached that of the Ataxia cells. The repair-misrepair model has been used to interpret these results. According to this model, the molecular repair processes culminate either in eurepair or in misrepair. We have obtained mathematical expressions that describe the cross sections and inactivation coefficients for both human cell lines as a function of the LET and the type of particle used. We assume that the lesions induced in T-1 and Ataxia cells are qualitatively similar and that each cell line attempts to repair these lesions. The result in most irradiated Ataxia cells, however, is either lethal misrepair or incomplete repair leading to cell death. T-1 cells have efficient repair mechanisms at low LET, and the repair-misrepair model suggests that at high LET the T-1 cells can still efficiently repair individual lesions, but that as the lesions become closely spaced along the tracks, the probability of misrepair increases.

A comparison of the DNA binding, cytotoxicity and repair synthesis induced in human fibroblasts by reactive derivatives of aromatic amide carcinogens

The cytotoxicity of three structurally-related direct-acting carcinogens, N-acetoxy-2-acetylaminofluorene, N-acetoxy-2-acetylaminophenanthrene and N-acetoxy-4-acetylaminobiphenyl, was compared in normal cells and in excision repair deficient xeroderma pigmentosum cells (XP12BE). All three proved significantly more cytotoxic to the XP cells than to the normal cells. At equicytoxic levels, substantially more residues were initially bound to the DNA of the normal cells than to the XP cells, suggesting that the former are able to remove a large percentage of the DNA bound residues before these can result in cell death. The ability of these cell strains to remove bound residues from DNA, to incorporate thymidine into parental strands of DNA during repair replication, and to recover from potentially lethal damage if held in the non-replicating, density-inhibited G0 state was compared as a function of dose and time. The XP12BE cells proved virtually incapable of excision repair of DNA damage induced by these carcinogens and of recovery. In contrast, normal cells recovered from the potentially lethal effects of these three compounds and did so at a rate comparable to their rate of removal of bound residues and of repair synthesis. In the excision-deficient XP12BE cells, DNA adducts induced by N-acetoxy-2-acetylaminophenanthrene proved 3- to 6-fold more cytotoxic than adducts induced by the other two carcinogens.