A novel whole "Joint-in-Motion" device reveals a permissive effect of high glucose levels and mechanical stress on joint destruction

OBJECTIVE

Osteoarthritis (OA) has recently been suggested to be associated with diabetes. However, this association often disappears when accounting for body mass index (BMI), suggesting that mechanical stress may be a confounding factor. We investigated the combined influence of glucose level and loading stress on OA progression using a novel whole joint-in-motion (JM) culture system.

DESIGN

Whole mouse knee joints were placed in an enclosed chamber with culture media and actuated to recapitulate leg movement, with a dynamic stress regimen of 0.5 Hz, 8 h/day for 7 days. These joints were treated with varying levels of glucose and controlled for osmolarity and diffusion. Joint movement and joint space were examined by X-ray fluoroscopy and microCT. Cartilage matrix levels were quantified by blinded Mankin scoring and immunohistochemistry.

RESULTS

Culturing in the JM device facilitated proper leg extension and flexion movements, and adequate mass transport for analyzing the effect of glucose on cartilage. Treatment with higher levels of glucose either via media supplementation or intra-articular injection caused a significant decrease in levels of glycosaminoglycan (GAG) and an increase in aggrecan neoepitope in articular cartilage, but only under dynamic stress. Additionally, collagen II level was slightly reduced by high glucose levels.

CONCLUSIONS

High levels of glucose and dynamic stress have permissive effects on articular cartilage GAG loss and aggrecan degradation, implicating that mechanical stress confounds the association of diabetes with OA. The JM device supports novel investigation of mechanical stress on the integrity of an intact living mouse joint to provide insights into OA pathogenesis.

Suppressed phase segregation for triple-junction perovskite solar cells

The tunable band gaps and facile fabrication of perovskites make them attractive for multi-junction photovoltaics^1,2. However, light-induced phase segregation limits their efficiency and stability^3-5: this occurs in wide band gap (> 1.65 eV) I/Br mixed perovskite absorbers, and becomes even more acute in the top cells of triple-junction solar photovoltaics that requires a fully 2.0 eV band gap absorber^2,6. We report herein that lattice distortion in I/Br mixed perovskites is correlated with the suppression of phase segregation, generating an increased ion migration energy barrier arising from the decreased average interatomic distance between A-site cation and iodide. Using a ~2.0 eV Rb/Cs mixed-cation inorganic perovskite with large lattice distortion in the top subcell, we fabricated all-perovskite triple-junction solar cells and achieved an efficiency of 24.3% (23.3% certified quasi-steady-state efficiency) with an open-circuit voltage of 3.21 V. This is, to our knowledge, the first reported certified efficiency for perovskite-based triple-junction solar cells. The triple-junction devices retain 80% of their initial efficiency following 420 hours of operation at the maximum power point.

[Human bone marrow mesenchymal stem cell exosome-derived miR-335-5p promotes osteogenic differentiation of human periodontal ligament stem cells to alleviate periodontitis by downregulating DKK1]

OBJECTIVE

To observe the effect of miR-335-5p derived from human bone marrow mesenchymal stem cell (hBMMSCs) exosomes on osteogenic differentiation of human periodontal ligament stem cell (PDLSCs) model of periodontitis and explore its mechanism.

METHODS

The exosomes extracted from hBMMSCs were identified by transmission electron microscopy, Western blotting and PKH67 labeling. The human PDLSC model of TNF-α-induced periodontitis were co-cultured with the extracted exosomes, and qRT-PCR was performed to detect the changes in the expressions of miR-335-5p and the mRNA levels of pro-inflammatory cytokines (IL-1β, IL-6, and IL-8) and the osteogenic marker genes (RunX2, OCN and BMP-2). Alizarin red staining and ALP staining were used to detect the formation of calcium nodules in the treated cells, and the expression level of DKK1 protein was detected with Western blotting. Dual luciferase reporter gene assay was used to verify the targeting relationship between miR-335-5p and DKK1.

RESULTS

High expressions of CD9 and CD81 were detected in the extracted hBMMSC exosomes (P < 0.05). In TNF-α-induced hPDLSCs, treatment with the extracted exosomes significantly reduced the mRNA expressions of IL-1β, IL-6 and IL-8, enhanced the mRNA expressions of RunX2, OCN, and BMP-2, and promoted the formation of calcium nodules. MiR-335-5p was highly expressed in hBMMSC-derived exosomes, and overexpression of miR-335-5p significantly downregulated DKK1 protein expression, inhibited the mRNA expressions of IL-1β, IL-6 and IL-8, and promoted the mRNA expressions of osteogenic markers and the formation of calcium nodules in hPDLSCs.

CONCLUSION

HBMMSC exosome-derived miR-335-5p promotes osteogenic differentiation of hPDLSCs and inhibits the development of periodontitis by downregulating DKK1.

A213 UNDERSTANDING PATIENT AND PHYSICIAN ATTITUDES AND EXPECTATIONS REGARDING IDENTIFYING AND MANAGING ANXIETY AND DEPRESSION IN IBD

Background

Patients living with Inflammatory Bowel Disease (IBD) commonly experience a number of mental health-related challenges, specifically anxiety and mood disorders (AMDs). Although there has been an awareness of the relationship between IBD and AMD within the GI research and clinical space; detection, treatment, and management amongst care providers is limited. Therefore, we are seeking to explore the overall experiences of patients living with Inflammatory Bowel Disease to identify and evaluate their experiences in interactions with GI clinicians around mental health in diverse care settings in order to determine how to best support mental health care amongst IBD patients.

Purpose

We aimed to explore perspectives, experiences and barriers to engaging with mental health-related challenges amongst IBD patients when interacting with gastroenterologists over the course of their health journey.

Method

We conducted 5 semi-structured online focus groups co-facilitated by patient researchers in early 2020 through Zoom which spanned for a total of 2.5 hours each. Participants were recruited through social media channels, GI clinics, the IMAGINE-SPOR unit, and Crohn’s and Colitis Canada. A semi-structured interview guide was developed for patient researchers to follow during the focus groups which provided guided questions that would allow patient participants to explore and reflect on: their experiences living with IBD, their expectations around mental health support, their perception of the engagement of GIs in mental health discussions, and their expectations for mental health support and services moving forward. Audio recordings from the semi-structured focus groups were then transcribed and thematic analysis was used to identify emerging themes and patient expectations.

Result(s)

We identified the following key themes: 1) experiences with IBD: difficulties related to reintegrating into social settings, feelings of loneliness; 2) expectations around mental health support: the need to develop their own resiliency strategies due to the lack of structural resources regarding mental health and IBD in the clinical space; 3) GI engagement: HCPs were dismissive of mental health symptoms, often gaslighting patients when mentioning mental health concerns during clinical encounters; and 4) expectations: a need to standardize mental health care across IBD care practice with a focus on potentially integrating healthcare providers of diverse care settings to help address the need for mental health support in such a vast patient population.

Conclusion(s)

Our study suggests that effective detection, management and awareness, along with the integration of feedback from patient lived experiences can help inform the development of mental health support and services which cater to the needs of people living with IBD. Results from this study will be interpreted in line with insight gathered from upcoming interviews of gastroenterologists and HCPs.

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CIHR, Other

Please indicate your source of funding;

IMAGINE SPOR INCUBATOR Grant

Disclosure of Interest

None Declared

Rational design of Lewis base molecules for stable and efficient inverted perovskite solar cells

Lewis base molecules that bind undercoordinated lead atoms at interfaces and grain boundaries (GBs) are known to enhance the durability of metal halide perovskite solar cells (PSCs). Using density functional theory calculations, we found that phosphine-containing molecules have the strongest binding energy among members of a library of Lewis base molecules studied herein. Experimentally, we found that the best inverted PSC treated with 1,3-bis(diphenylphosphino)propane (DPPP), a diphosphine Lewis base that passivates, binds, and bridges interfaces and GBs, retained a power conversion efficiency (PCE) slightly higher than its initial PCE of ~23% after continuous operation under simulated AM1.5 illumination at the maximum power point and at ~40°C for >3500 hours. DPPP-treated devices showed a similar increase in PCE after being kept under open-circuit conditions at 85°C for >1500 hours.

Radiomics signature based on CECT for non-invasive prediction of response to anti-PD-1 therapy in patients with hepatocellular carcinoma

PURPOSE

This study aimed to develop a radiomics signature (RS) based on contrast-enhanced computed tomography (CECT) and evaluate its potential predictive value in hepatocellular carcinoma (HCC) patients receiving anti-PD-1 therapy.

METHOD

CECT scans of 76 HCC patients who received anti-PD-1 therapy were obtained in this study (training group = 53 and validation group = 23). The least absolute shrinkage and selection operator (LASSO) regression was applied to select radiomics features of primary and metastatic lesions and establish a RS to predict lesion-level response. Then, a nomogram combined the mean RS (MRS) and clinical variables with patient-level response as the end point.

RESULTS

In the lesion-level analysis, the area under the curves (AUCs) of RS in the training and validation groups were 0.751 (95% CI, 0.668-0.835) and 0.734 (95% CI, 0.604-0.864), respectively. In the patient-level analysis, the AUCs of the nomogram in the training and validation groups were 0.897 (95% CI, 0.798-0.996) and 0.889 (95% CI, 0.748-1.000), respectively. The nomogram stratified patients into low- and high-risk groups, which showed a significant difference in progression-free survival (PFS) (p<0.05).

CONCLUSIONS

The RS is a noninvasive biomarker for predicting anti-PD-1 therapy response in patients with HCC. The nomogram may be of clinical use for identifying high-risk patients and formulating individualised treatments.

Regulating surface potential maximizes voltage in all-perovskite tandems

The open-circuit voltage (V_OC) deficit in perovskite solar cells is greater in wide-bandgap (over 1.7 eV) cells than in perovskites of roughly 1.5 eV (refs. ^1,2). Quasi-Fermi-level-splitting measurements show V_OC-limiting recombination at the electron-transport-layer contact^3-5. This, we find, stems from inhomogeneous surface potential and poor perovskite-electron transport layer energetic alignment. Common monoammonium surface treatments fail to address this; as an alternative, we introduce diammonium molecules to modify perovskite surface states and achieve a more uniform spatial distribution of surface potential. Using 1,3-propane diammonium, quasi-Fermi-level splitting increases by 90 meV, enabling 1.79 eV perovskite solar cells with a certified 1.33 V V_OC and over 19% power conversion efficiency (PCE). Incorporating this layer into a monolithic all-perovskite tandem, we report a record V_OC of 2.19 V (89% of the detailed balance V_OC limit) and over 27% PCE (26.3% certified quasi-steady state). These tandems retained more than 86% of their initial PCE after 500 h of operation.

Engineering Electro-Optic BaTiO3 Nanocrystals via Efficient Doping

Electro-optic (EO) modulators provide electrical-to-optical signal conversion relevant to optical communications. Barium titanate (BaTiO₃ ) is a promising material system for EO modulation in light of its optical ultrafast nonlinearity, low optical loss, and high refractive index. To enhance further its spontaneous polarization, BaTiO₃ can be doped at the Ba and Ti sites; however, doping is often accompanied by ion migration, which diminishes EO performance. Here, donor-acceptor doping and its effect on EO efficiency are investigated, finding that La-doped BaTiO₃ achieves an EO coefficient of 42 pm V^-1 at 1 kHz, fully twice that of the pristine specimen; however, it is also observed that, with this single-element doping, the EO response falls off rapidly with frequency. From impedance spectroscopy, it is found that frequency-dependent EO is correlated with ion migration. Density functional theory calculations predict that the ion-migration barrier decreases with La³⁺ doping but can be recovered with further Mn²⁺ doping, a finding that prompts to prevent ion migration by incorporating Mn²⁺ into the Ti-site to compensate for the charge imbalance.

Species profiles, in-situ photochemistry and health risk of volatile organic compounds in the gasoline service station in China

Accompanying with increases in vehicle population and gasoline consumption, gasoline evaporation accounted for an enlarged portion of total volatile organic compound (VOC) emissions in China, raising increasing environmental concerns especially in megacities. In this study, an intensive sampling campaign was performed in a gasoline service station, to reveal emission characteristics, environmental and health impacts of VOCs. It was strikingly found that 24 % of air samples exceeded the national standard of 4 mg/m³ for non-methane hydrocarbons (NMHCs) on the boundary of the station, with the equipment of Stage I and II controls. VOC groups and species profiles showed that alkanes dominated total VOCs. As typical markers of evaporative loss of gasoline, C4-5 species (i-pentane, n-pentane and n-butane) as well as methyl tert-butyl ether (MTBE) accounted for 49.6 % of VOCs. Species profile and diagnostic ratios indicated the prominent contribution of gasoline evaporative losses from refueling or breathing processes, as well as the interference of vehicle exhaust in the ambient air at the site. Intensive O₃ production was reproduced by the photochemical box model, demonstrating that O₃ formation was co-limited by both VOCs (especially trans-2-butene) and NO_x. Inhalation health risk assessment proved that exposure to hazardous VOCs caused non-cancer risk (HQ = 3.08) and definitely posed cancer risks at a probability of 1.3 × 10^-4 to workers. Remarkable health risks were mainly imposed by halocarbons, aromatics and alkenes, in which 1,2-dichloropropane caused the highest non-cancer risk (HQ = 1.3) and acted as the primary carcinogen (ICR = 5.1 × 10^-5). This study elucidated the high unqualified rate in gasoline service stations after the implementation of latest standards in China, where new regulations targeted halocarbons and updates in existing vapor recovery systems were suggested for VOC mitigation.

Impact of NOx reduction on long-term surface ozone pollution in roadside and suburban Hong Kong: Field measurements and model simulations

Continuous measurements of ozone (O₃) and nitrogen oxides (NO_x = NO + NO₂) were conducted from 2007 to 2019 in Hong Kong in order to evaluate the effectiveness of control strategies for NO_x emission from diesel commercial vehicles (DCV). DCV control programs were periodically applied in three phases starting from 2007, 2010 and 2014. It was found that NO and NO₂ levels decreased during the study period but more dramatically after the implementation of DCV Phase III than pre-DCV Phase III. Source apportionment analysis confirmed that the ambient NO and NO₂ in Hong Kong attributed to the regulated DCV emissions in Phase III reduced at rates of 5.1-14.4 ppbv/yr in roadside environment and 1.6-3.1 ppbv/yr in suburban area. Despite overall NO_x reduction, increased NO₂/NO_x ratios were recorded during the study period possibly due to the application of diesel particulate filter (DPF) in DCVs. However, after introducing DCV Phase III, observed O₃ values experienced more dramatic increasing trends in most areas of Hong Kong than pre-DCV Phase III. Model simulations revealed that O₃ production rate kept increasing and turned to be less sensitive to NO_x from 2014 to 2019. On the roadside, net O₃ production rate was more than doubled during 2014-2019 owing to NO_x reduction. Moreover, the levels of oxidants (OH, HO₂ and RO₂) were 1.5-5 times those before 2014. In suburban environment, NO_x reduction also facilitated O₃ production and radical cycling, but made smaller contributions than those on the roadside during 2014-2019. This study unraveled that NO_x reductions benefited from DCV regulations caused increase in surface O₃ and fueled O₃ photochemistry in various environments. More stringent control measures on emissions of VOCs, especially those with high OH reactivity, might help to better mitigate O₃ pollution.

[Therapeutic mechanism of emodin for treatment of rheumatoid arthritis: a network pharmacology-based analysis]

OBJECTIVE

To investigate the therapeutic mechanism of emodin in the treatment of rheumatoid arthritis (RA) using a network pharmacology-based method and validate this mechanism in a fibroblast-like synovial cell line.

METHODS

The PubChem, Targetnet, SwissTargetPrediction, Genecards, OMIM, and DisGeNET databases were searched to obtain emodin targets and RA-related genes. A protein-protein interaction (PPI) network was constructed, and GO and KEGG pathway enrichment analyses were carried out to analyze the intersection genes. AutoDock4.2.6 software was used to simulate molecular docking between emodin and its candidate targets. In a cultured fibroblast-like synovial cell line (MH7A), the effects of different concentrations of emodin on proliferation of tumor necrosis factor-α (TNF-α)-induced cells were investigated using CCK-8 assay, cell scratch experiment and flow cytometry; the changes in the expressions of nuclear factor-κB (NF-κB) pathway proteins were detected using Western blotting, and the mRNA expressions of the hub genes were examined with RT-qPCR.

RESULTS

We identified 32 intersection genes of emodin and RA, and the key targets including CAPS3, ESR1, and MAPK14 involved mainly the NF-κB signaling pathway. Cell scratch experiment and flow cytometry demonstrated a strong inhibitory effect of emodin on MH7A cell proliferation. Treatment with TNF-α significantly increased the cellular expressions of the NF-κB pathway proteins, which were obviously lowered by treatment with 80 μmol/L emodin. The results of RT-qPCR showed that TNF-α treatment obviously up-regulated the expressions of the hub genes COX2 and P38MAPK, and emodin treatment significantly down-regulated the expressions of MAPK and PTGS2 and up-regulated the expression of CASP3.

CONCLUSION

The therapeutic effect of emodin on RA is mediated mainly through regulation of cell proliferation, apoptosis, and the NF-κB pathway.

[Correlation between professional quality of life and social support of Chinese nurses: a meta-analysis]

Objective: To systematically evaluate the correlation between professional quality of life and social support of Chinese nurses based on Pearson and Spearman correlation coefficients. Methods: In databases including PubMed, Cochrane Library, CINAHL, Medline, CBM, CNKI、Wanfang, and other databases were searched by computer for the literatures on correlation between Chinese nurses' professional quality of life and social support from January 2005 to July 2020. The Chinese and English search terms are "nurse" "professional quality of life" "empathy satisfaction" "empathy fatigue" "professional quality of life" "ProQOL" "comparison satisfaction" "comparison fatigue" "social support" "competent social support" "SSRS" "PSSS", etc. Literatures were screened according to the inclusion and exclusion criteria. After evaluating quality and extracting data, meta-analysis was conducted using RevMan 5.3 software. Results: A total of 12 studies were included. The meta analysis showed that nurses' compassion satisfaction, burnout, secondary traumatic stress were related to social support, summary r were 0.35, -0.26 and -0.23 respectively. The correlation between compassion satisfaction and social support were increased with sample, the south was higher than the north, and comprehensive departments were higher than other departments (P<0.05) . The correlation between burnout and social support were increased with time and sample, and the south was higher than the north, oncology was higher than others, non-random sampling was higher than random sampling, using ProQOL and Perceived Social Support Scale (PSSS) was higher than Professional Quality of Life Scale (ProQOL) and Social Support Racting Scale (SSRS) (P<0.05) . The correlation coefficient between secondary traumatic stress and social support in oncology was higher than others, random sampling was higher than non-random sampling, using ProQOL and PSSS was higher than ProQOL and SSRS (P<0.05) . Conclusion: There is a positive and weak correlation between compassion satisfaction and social support, and a negative and weak correlation between burnout and secondary traumatic stress and social support. There are differences in different time, research design, region and department.

[The effectiveness of psychological intervention on nursing staff' compassion fatigue: a meta-analysis]

Objective: To systematically evaluate the impact of psychological intervention on nursing staff' compassion fatigue. Methods: From March to May 2020, PubMed, Cochrane Library, EMbase, Web of Science, CNKI, VIP, Wanfang and other databases were electronically searched to collect randomized controlled trials (RCTs) on the influence of psychological intervention on nursing staff' compassion fatigue with the main search terms including compassion fatigue, nurs*, psychological intervention, mental intervention, RCT and so on from inception to March 31, 2020. Screened literature, extracted data and assessed the risk of bias of included studies. The Stata 16.0 software was used to calculate the pooled effectiveness of psychological intervention on nursing staff' compassion fatigue. Results: All 13 RCTs were enrolled, including 940 nursing staff. Meta-analysis results demonstrated that the psychological intervention group was superior to the control group in the improvement of the compassion fatigue score (SMD=-0.96, 95%CI: -1.17-0.74, P=0.001) , compassion satisfaction score (SMD=0.61, 95%CI: 0.45-0.77, P=0.002) , burnout score (SMD=-0.46, 95%CI: -0.62-0.29, P=0.006) , secondary trauma score (SMD=-0.40, 95%CI: -0.68-0.12, P=0.020) , and the difference was statistically significant. Subgroup analysis found that the psychological intervention group was more effective than the control group in improving compassion satisfaction score, reducing burnout score and secondary trauma score, and the differences were statistically significant (P<0.05) in different intervention time (<8 weeks and ≥8 weeks) and intervention methods. Conclusion: The psychological intervention can improve the level of compassion satisfaction, and reduce the compassion fatigue among nursing staff, and have a certain preventive effect on compassion fatigue.

Ambient volatile organic compounds at a receptor site in the Pearl River Delta region: Variations, source apportionment and effects on ozone formation

We present the continuously measurements of volatile organic compounds (VOCs) at a receptor site (Wan Qing Sha, WQS) in the Pearl River Delta (PRD) region from September to November of 2017. The average mixing ratios of total VOCs (TVOCs) was 36.3 ± 27.9 ppbv with the dominant contribution from alkanes (55.5%), followed by aromatics (33.3%). The diurnal variation of TVOCs showed a strong photochemical consumption during daytime, resulting in the formation of ozone (O₃). Five VOC sources were resolved by the positive matrix factorization (PMF) model, including solvent usage (28.6%), liquid petroleum gas (LPG) usage (24.4%), vehicle exhaust (21.0%), industrial emissions (13.2%) and gasoline evaporation (12.9%). The regional transport air masses from the upwind cities of south China can result in the elevated concentrations of TVOCs. Low ratios of TVOCs/NO_x (1.53 ± 0.88) suggested that the O₃ formation regime at WQS site was VOC-limited, which also confirmed by a photochemical box model with the master chemical mechanism (PBM-MCM). Furthermore, the observation on high-O₃ episode days revealed that frequent O₃ outbreaks at WQS were mainly caused by the regional transport of anthropogenic VOCs especially for aromatics and the subsequent photochemical reactions. This study provides valuable information for policymakers to propose the effective control strategies on photochemical pollution in a regional perspective.

Molecular characterization and clinical outcomes in EGFR-mutant de novo MET-overexpressed advanced non-small-cell lung cancer

Background

Approximately 2%-8% of non-small-cell lung cancer (NSCLC) harbors concurrent epidermal growth factor receptor (EGFR) sensitizing mutation and mesenchymal–epithelial transition factor (MET) amplification prior to EGFR-tyrosine kinase inhibitor (EGFR-TKI) therapy. This study aimed to investigate the optimal first-line therapeutic options for patients with concurrent EGFR-mutant, MET-overexpressed/amplified advanced NSCLC.

Methods

A total of 104 treatment-naïve patients with EGFR-mutant de novo MET-overexpressed advanced NSCLC were identified using immunohistochemistry and stratified to four groups according to treatment regimen: EGFR-TKI monotherapy (n = 48), EGFR-TKI combined with either crizotinib (n = 9) or chemotherapy (n = 12), and chemotherapy (n = 35). A subpopulation of 28 patients was also tested with next-generation sequencing (NGS). Objective response rate (ORR) and progression-free survival (PFS) outcomes were analyzed according to treatment strategies and molecular features.

Results

All the patients (n = 104) achieved ORR of 36.5% and median PFS (mPFS) of 7.0 months. Baseline clinicopathologic characteristics were similar among the four treatment groups. Compared with chemotherapy, EGFR-TKI monotherapy or EGFR-TKI combination therapy achieved significantly higher ORR (P < 0.001) and longer mPFS (P = 0.003). No ORR or PFS difference was observed between EGFR-TKI monotherapy and combination therapy. In the NGS-identified population (n = 28), patients who received EGFR-TKI plus crizotinib (n = 9) achieved similar ORR (88.9% versus 57.9%, P = 0.195) and mPFS (9.0 versus 8.5 months, hazard ratio 1.10, 95% confidence interval 0.43-2.55, P = 0.45) than those who received EGFR-TKI monotherapy (n = 19), regardless of MET copy number status. Grade 3/4 rashes were significantly more among patients who received EGFR-TKI plus crizotinib (P = 0.026).

Conclusions

Our findings provided clinical evidence that patients with concurrent EGFR sensitizing mutation and de novo MET amplification/overexpression could benefit from first-line EGFR-TKI monotherapy.

•

Concomitant EGFR sensitizing mutation and MET overexpression/amplification were detected in 2.6% of lung cancer patients.

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EGFR-TKI monotherapy elicited a higher response rate and longer PFS than chemotherapy.

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EGFR-TKI with or without crizotinib elicited comparable PFS regardless of MET copy number.

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EGFR-TKI monotherapy achieved lower number of grade 3/4 adverse events than EGFR-TKI plus crizotinib.

Photochemical ozone pollution in five Chinese megacities in summer 2018

To investigate photochemical ozone (O₃) pollution in urban areas in China, O₃ and its precursors and meteorological parameters were simultaneously measured in five megacities in China in summer 2018. Moderate wind speeds, strong solar radiation and high temperature were observed in all cities, indicating favorable meteorological conditions for local O₃ formation. However, the unusually frequent precipitation caused by typhoons reaching the eastern coastline resulted in the least severe air pollution in Shanghai. The highest O₃ level was found in Beijing, followed by Lanzhou and Wuhan, while relatively lower O₃ value was recorded in Chengdu and Shanghai. Photochemical box model simulations revealed that net O₃ production rate in Lanzhou was the largest, followed by Beijing, Wuhan and Chengdu, while it was the lowest in Shanghai. Besides, the O₃ formation was mainly controlled by volatile organic compounds (VOCs) in most cities, but co-limited by VOCs and nitrogen oxides in Lanzhou. Moreover, the dominant VOC groups contributing to O₃ formation were oxygenated VOCs (OVOCs) in Beijing and Wuhan, alkenes in Lanzhou, and aromatics and OVOCs in Shanghai and Chengdu. Source apportionment analysis identified six sources of O₃ precursors in these cities, including liquefied petroleum gas usage, diesel exhaust, gasoline exhaust, industrial emissions, solvent usage, and biogenic emissions. Gasoline exhaust dominated the O₃ formation in Beijing, and LPG usage and industrial emissions made comparable contributions in Lanzhou, while LPG usage and solvent usage played a leading role in Wuhan and Chengdu, respectively. The findings are helpful to mitigate O₃ pollution in China.