Tomoaki Okuda

Oxidative stress is a key mechanism that contributes to the toxicity of atmospheric aerosol particles. We investigated the mass-normalized oxidative potential (OP) of fine particles collected at three sites in Japan: Yokohama (an urban background site in the Greater Tokyo Area), Fukuoka (an urban background site in western Japan), and Noto (a rural site on the Noto Peninsula facing the Sea of Japan). The OP was evaluated using two assays: a cell-free dithiothreitol (DTT) assay (OPmDTT) and a cell-based assay employing 5-(and-6)-chloromethyl-2 ^′ ,7 ^′ -dichlorodihydrofluorescein diacetate, acetyl ester (CM-H ₂ DCFDA) with alveolar epithelial cells (OPmDCFH). Both OP metrics exhibited significant spatial variation, with the highest values in Yokohama, followed by those in Fukuoka and Noto. This spatial pattern suggests that fine particles influenced by local urban emissions have higher intrinsic OP than those affected by long-range transport from continental Asia. Secondary particle formation during atmospheric transport likely alters the chemical composition of the particles, providing a plausible explanation for the lower intrinsic OP compared to locally emitted urban aerosol particles. OPmDCFH was correlated with carbonaceous components derived from fuel combustion and transition metals (Cu, Mn, and Fe) ( r =0.47–0.84), whereas OPmDTT was associated mainly with the transition metals ( r =0.67–0.82). These results indicate different pathways for reactive oxygen species (ROS) generation in the two assays. Despite these differences, OPmDTT and OPmDCFH were positively correlated ( r =0.81), indicating that DTT reactivity can reasonably predict the anthropogenic fine particle-induced increase in intracellular oxidative activity.

Oxidative stress is a key mechanism that contribute to the toxicity of atmospheric aerosol particles. This study investigated the mass-normalized oxidative potential (OP) of fine particles collected at three sites in Japan: Yokohama (an urban background site in the Greater Tokyo Area), Fukuoka (an urban background site in western Japan), and Noto (a rural site on the Noto Peninsula facing the Sea of Japan). The OP was evaluated using two assays: a cell-free dithiothreitol (DTT) assay (OP^DTT _m) and a cell-based assay employing 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H₂DCFDA) with alveolar epithelial cells (OP^DCFH _m). Both OP metrics exhibited significant spatial variation, with the highest values in Yokohama, followed by those in Fukuoka and Noto. This spatial pattern suggests that fine particles influenced by local urban emissions have higher intrinsic OP than those affected by long-range transport from continental Asia. Secondary particle formation during atmospheric transport likely alters the chemical composition of the particles, providing a plausible explanation for the lower intrinsic OP compared to those of locally emitted urban aerosol particles. OP^DCFH _m was correlated strongly with carbonaceous components derived from fuel combustion and transition metals (Cu, Mn, and Fe), whereas OP^DTT _m was associated mainly with the transition metals. These results indicate different pathways for reactive oxygen species (ROS) generation in the two assays. Despite these differences, OP^DTT _m and OP^DCFH _m were correlated strongly (r = 0.81), indicating that DTT reactivity can reasonably predict cellular ROS-generating capacity of anthropogenic fine particles.

Background: Postharvest losses of sweet potatoes remain substantial due to microbial spoilage and suboptimal storage conditions, with curing commonly used to enhance wound healing and reduce decay. Aims: This pilot study compared spoilage incidence of sweet potatoes (Ipomoea batatas cv. 'Beniharuka') stored under continuous low-level chlorine dioxide (ClO₂) gas exposure with and without curing treatment. Study Design: A two-by-two treatment arrangement in a single non-replicated pilot trial. ClO₂-exposed and non-exposed sweet potatoes were stored in separate warehouse compartments, with cured and non-cured lots placed within each compartment. Place and Duration of Study: Two agricultural warehouses in Ibaraki Prefecture, Japan, from 12 December 2024 to 24 January 2025. Methodology: A total of 507 tubers (80 kg) were allocated to four groups according to the presence or absence of ClO₂ exposure (mean concentration 0.039 ppm for the first 14 days; reduced thereafter due to equipment malfunction) and curing (40 °C, 100% RH, 90 h). Temperature, relative humidity, and ClO₂ concentration were monitored continuously. Spoilage was assessed weekly by visual inspection and palpation, and risk ratios (RR) with 95% confidence intervals were calculated using Fisher's exact test. Results: During weeks 3–6, spoilage incidence was lower in the ClO₂ exposure group than in the non-exposure group (12/236 vs 58/235; RR = 0.206, 95% CI 0.114–0.373, P < .001), whereas curing was associated with higher spoilage incidence (48/253 vs 22/218; RR = 1.88, 95% CI 1.17–3.01, P = .009). However, the ClO₂ compartment was operated at lower temperature (−1.9 °C) and relative humidity (−18.5 percentage points) than the control; therefore, the observed reduction cannot be attributed to ClO₂ exposure alone. Conclusion: In this single pilot warehouse trial, continuous low-level ClO₂ exposure at concentrations below the OSHA occupational exposure limit (TWA 0.10 ppm) was associated with reduced sweet potato spoilage. Because environmental conditions differed between compartments, further trials under controlled conditions are needed to isolate the effect of ClO₂ from that of temperature and humidity.

Oxidative stress is a key mechanism that contribute to the toxicity of atmospheric aerosol particles. This study investigated the mass-normalized oxidative potential (OP) of fine particles collected at three sites in Japan: Yokohama (an urban background site in the Greater Tokyo Area), Fukuoka (an urban background site in western Japan), and Noto (a rural site on the Noto Peninsula facing the Sea of Japan). The OP was evaluated using two assays: a cell-free dithiothreitol (DTT) assay (OP^DTT _m) and a cell-based assay employing 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H₂DCFDA) with alveolar epithelial cells (OP^DCFH _m). Both OP metrics exhibited significant spatial variation, with the highest values in Yokohama, followed by those in Fukuoka and Noto. This spatial pattern suggests that fine particles influenced by local urban emissions have higher intrinsic OP than those affected by long-range transport from continental Asia. Secondary particle formation during atmospheric transport likely alters the chemical composition of the particles, providing a plausible explanation for the lower intrinsic OP compared to those of locally emitted urban aerosol particles. OP^DCFH _m was correlated strongly with carbonaceous components derived from fuel combustion and transition metals (Cu, Mn, and Fe), whereas OP^DTT _m was associated mainly with the transition metals. These results indicate different pathways for reactive oxygen species (ROS) generation in the two assays. Despite these differences, OP^DTT _m and OP^DCFH _m were correlated strongly (r = 0.81), indicating that DTT reactivity can reasonably predict cellular ROS-generating capacity of anthropogenic fine particles.

Oxidative stress is a key mechanism that contribute to the toxicity of atmospheric aerosol particles. This study investigated the mass-normalized oxidative potential (OP) of fine particles collected at three sites in Japan: Yokohama (an urban background site in the Greater Tokyo Area), Fukuoka (an urban background site in western Japan), and Noto (a rural site on the Noto Peninsula facing the Sea of Japan). The OP was evaluated using two assays: a cell-free dithiothreitol (DTT) assay (OP^DTT _m) and a cell-based assay employing 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H₂DCFDA) with alveolar epithelial cells (OP^DCFH _m). Both OP metrics exhibited significant spatial variation, with the highest values in Yokohama, followed by those in Fukuoka and Noto. This spatial pattern suggests that fine particles influenced by local urban emissions have higher intrinsic OP than those affected by long-range transport from continental Asia. Secondary particle formation during atmospheric transport likely alters the chemical composition of the particles, providing a plausible explanation for the lower intrinsic OP compared to those of locally emitted urban aerosol particles. OP^DCFH _m was correlated strongly with carbonaceous components derived from fuel combustion and transition metals (Cu, Mn, and Fe), whereas OP^DTT _m was associated mainly with the transition metals. These results indicate different pathways for reactive oxygen species (ROS) generation in the two assays. Despite these differences, OP^DTT _m and OP^DCFH _m were correlated strongly (r = 0.81), indicating that DTT reactivity can reasonably predict cellular ROS-generating capacity of anthropogenic fine particles.

Oxidative stress is a key mechanism that contribute to the toxicity of atmospheric aerosol particles. This study investigated the mass-normalized oxidative potential (OP) of fine particles collected at three sites in Japan: Yokohama (an urban background site in the Greater Tokyo Area), Fukuoka (an urban background site in western Japan), and Noto (a rural site on the Noto Peninsula facing the Sea of Japan). The OP was evaluated using two assays: a cell-free dithiothreitol (DTT) assay (OP^DTT _m) and a cell-based assay employing 5-(and-6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate, acetyl ester (CM-H₂DCFDA) with alveolar epithelial cells (OP^DCFH _m). Both OP metrics exhibited significant spatial variation, with the highest values in Yokohama, followed by those in Fukuoka and Noto. This spatial pattern suggests that fine particles influenced by local urban emissions have higher intrinsic OP than those affected by long-range transport from continental Asia. Secondary particle formation during atmospheric transport likely alters the chemical composition of the particles, providing a plausible explanation for the lower intrinsic OP compared to those of locally emitted urban aerosol particles. OP^DCFH _m was correlated strongly with carbonaceous components derived from fuel combustion and transition metals (Cu, Mn, and Fe), whereas OP^DTT _m was associated mainly with the transition metals. These results indicate different pathways for reactive oxygen species (ROS) generation in the two assays. Despite these differences, OP^DTT _m and OP^DCFH _m were correlated strongly (r = 0.81), indicating that DTT reactivity can reasonably predict cellular ROS-generating capacity of anthropogenic fine particles.

Seasonal fluctuations in the chemical composition of fine particulate matter (PM_2.5) are known to influence its toxicological properties; however, their integrated biological effects remain incompletely understood. In this study, PM_2.5 was continuously collected over two consecutive years at a single urban site in Japan and classified by season. The samples were comprehensively characterized for ionic species, metals, carbonaceous fractions, and polycyclic aromatic hydrocarbons (PAHs), and their pulmonary effects were evaluated in vivo following intratracheal administration in mice. Seasonal PM_2.5 exhibited pronounced compositional differences, with higher levels of secondary inorganic aerosol components in summer and enrichment of PAHs and mineral-associated components in winter. These seasonal differences translated into distinct biological responses. Reactive oxygen species (ROS) production (1.6–2.7-fold increase) and bronchoalveolar lavage (BAL) neutrophil infiltration were strongly associated with PAH-rich PM_2.5, whereas interleukin-1α (IL-1α) showed robust positive correlations with mineral components, including K⁺, Ca²⁺, and Mg²⁺, which were predominantly enriched in winter PM_2.5. In contrast, secondary inorganic aerosol species displayed a limited capacity to induce IL-1α. Compared with summer samples, winter PM_2.5 induced significantly higher levels of ROS production and IL-1α (approximately 1.5–2.6-fold increase). Using TLR2- and TLR4-deficient mice, we further demonstrated that PM_2.5-induced increases in BAL cell counts, ROS, IL-6, and TNF-α were partially attenuated in TLR4 knockout mice, indicating a contributory but not exclusive role for TLR4 signaling in PM_2.5-driven pulmonary inflammation. Collectively, these findings demonstrate that seasonal variations in PM_2.5 composition, not particle mass alone, critically shape oxidative stress and innate immune responses in the lungs. In particular, winter PM_2.5 enriched in mineral-associated components preferentially activates IL-1α-mediated alarmin pathways, underscoring the importance of the particle composition in determining seasonal air pollution toxicity.

Assessment of the toxicity of insoluble particulate matter (PM) in the atmosphere is crucially important. However, because of challenges associated with extracting insoluble PM from filters, the toxicity of insoluble PM remains largely uncharacterized. For this study, the water-soluble filter made of poly (vinyl alcohol) (PVA) was developed with high particle collection efficiency, durability, and weather resistance, which are necessary for ambient PM sampling. The PVA filter is water-soluble under certain conditions, allowing for the recovery of insoluble PM, which can be exposed directly to cells or animals for toxicological studies. The PVA filter was made from PVA nanofibers using the electrospinning (ES) method. Its durability and weather resistance were comparable to those of polytetrafluoroethylene (PTFE) and quartz fiber (QF) filters, and were superior to those of commercially available gelatin filters. The PVA filter particle collection efficiency was evaluated by comparing concentrations of inorganic elements (Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu and Zn) and water-soluble ionic components (Na ⁺ , NH ₄ ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , Cl ⁻ , NO ₃ ⁻ , and SO ₄ ²⁻ ) in the PVA filter-collected ambient PM with those in the PTFE filter-collected PM. The concentrations of almost all measured components in the PVA filter-collected PM were comparable to those in the PTFE filter-collected PM. When the PVA filter dissolved in cell culture medium was exposed to cells, no significant difference was found in cell viability compared to a blank solution containing only culture medium, suggesting that the PVA filter has potential use for cell exposure experiments. Graphical Abstract

Polycyclic aromatic sulfur heterocycles (PASHs) sulfur-containing analogues of polycyclic aromatic hydrocarbons (PAHs) are emerging atmospheric pollutants of concern due to their potential toxicity and environmental persistence. This study presents the first comparative analysis of PASHs in PM _2.5 between two representative East Asian cities: Xi’an, China, and Yokohama, Japan. Ambient PM _2.5 samples were collected from July 2022 to July 2023, and four PASHs compounds were quantified using gas chromatography tandem mass spectrometry (GC–MS/MS). Concentrations, seasonal variations, and emission sources were systematically analyzed. The results showed that the annual mean PASHs concentration in Xi’an (156.6 pg/mg) was significantly higher than that in Yokohama (102.6 pg/mg). Source apportionment using the Positive Matrix Factorization (PMF) model identified four major pollution sources in each city, revealing notable differences in source composition between the two countries. This study advances the understanding of the atmospheric behavior and origins of PASHs in East Asian urban environments and highlights cross-regional differences in their pollution profiles. Graphical Abstract