ObjectivePancreatic ductal adenocarcinoma (PDAC) exhibits a limited response to current treatments due to its dense fibrotic stroma and highly immunosuppressive tumor microenvironment. In recent years, advancements in cellular immunotherapy, particularly chimeric antigen receptor macrophage (CAR-M) therapy, have offered new hope for pancreatic cancer treatment. Although CAR-M therapy demonstrates dual potential in directly killing tumor cells and remodeling the immune microenvironment, it still faces challenges such as complex in vitro preparation processes and low in vivo targeting and delivery efficiency. Therefore, developing strategies for efficient and targeted in vivo delivery of CAR genes has become crucial for overcoming current therapeutic limitations. This study aims to develop an orally administrable nano-gene delivery system for the targeted delivery of CAR genes to pancreatic tumor sites. MethodsCore nano-gene particles (PNP/pCAR) were constructed by loading plasmid DNA encoding CAR (pCAR) with cationic polypeptides (PNP). Subsequently, PNP/pCAR was surface-modified with β-glucan to prepare the targeted nanoparticles (βGlus-PNP/pCAR). The loading efficiency of PNP for pCAR was quantitatively assessed by gel retardation assay. The particle size, Zeta potential, morphology, and storage stability of PNP/pCAR were characterized using a Malvern particle size analyzer and transmission electron microscopy. At the cellular level, RAW 264.7 macrophages were selected. The cytotoxicity of PNP/pCAR was evaluated using the CCK-8 assay. The cellular uptake efficiency and lysosomal escape ability of the nanoparticles were assessed via flow cytometry and confocal microscopy. Transfection efficiency was quantitatively evaluated by detecting the expression of the reporter gene GFP using flow cytometry. At the in vivo level, an orthotopic pancreatic cancer mouse model was established. Cy7-labeled βGlus-PNP/pCAR nanoparticles were administered orally, and the fluorescence distribution in mice was dynamically monitored at 1, 2, 4, 8, and 16 h post-administration using a small animal in vivo imaging system. Forty-eight hours after oral gavage, the mice were euthanized, and pancreatic tumor tissues were collected for further analysis of intratumoral fluorescence signals using the imaging system. Additionally, βGlus-PNP/pCAR-GFP nanoparticles loaded with the reporter gene (GFP) were administered orally. Forty-eight hours post-administration, pancreatic tumor tissues were harvested to prepare frozen sections, and GFP expression was observed and analyzed under a fluorescence microscope. ResultsThe PNP carrier exhibited a high loading capacity for pCAR. The successfully prepared PNP/pCAR nanoparticles were regular spheres with a hydrodynamic diameter of approximately (120±10) nm and a Zeta potential of about +(6±1) mV. They maintained good structural stability after incubation in PBS buffer for 7 d. Cell experiments demonstrated that PNP/pCAR exhibited no significant cytotoxicity in RAW 264.7 cells while being efficiently internalized and effectively escaping lysosomal degradation. The transfection positive rate of PNP/pCAR-GFP in RAW 264.7 cells reached (25±3)%, surpassing that of Lipofectamine 2000-loaded pCAR-GFP (Lipo/pCAR-GFP), which was (20±1)%.In vivo experiments revealed that, compared to unmodified PNP/pCAR, βGlus-PNP/pCAR exhibited strongerin situ pancreatic tumor targeting ability after oral administration. Furthermore, oral administration of βGlus-PNP/pCAR-GFP resulted in significant GFP protein expression detectable within pancreatic tumor tissues. ConclusionThis study successfully constructed and validated an orally administrable, pancreatic cancer-targeting polypeptide-based nano-gene delivery system. It provides an important technological foundation in delivery systems and experimental basis for the subsequent development of in situ CAR-M-based therapeutic strategies for pancreatic cancer.

ObjectivePancreatic ductal adenocarcinoma (PDAC) exhibits a limited response to current treatments due to its dense fibrotic stroma and highly immunosuppressive tumor microenvironment. In recent years, advancements in cellular immunotherapy, particularly chimeric antigen receptor macrophage (CAR-M) therapy, have offered new hope for pancreatic cancer treatment. Although CAR-M therapy demonstrates dual potential in directly killing tumor cells and remodeling the immune microenvironment, it still faces challenges such as complex in vitro preparation processes and low in vivo targeting and delivery efficiency. Therefore, developing strategies for efficient and targeted in vivo delivery of CAR genes has become crucial for overcoming current therapeutic limitations. This study aims to develop an orally administrable nano-gene delivery system for the targeted delivery of CAR genes to pancreatic tumor sites. MethodsCore nano-gene particles (PNP/pCAR) were constructed by loading plasmid DNA encoding CAR (pCAR) with cationic polypeptides (PNP). Subsequently, PNP/pCAR was surface-modified with β-glucan to prepare the targeted nanoparticles (βGlus-PNP/pCAR). The loading efficiency of PNP for pCAR was quantitatively assessed by gel retardation assay. The particle size, Zeta potential, morphology, and storage stability of PNP/pCAR were characterized using a Malvern particle size analyzer and transmission electron microscopy. At the cellular level, RAW 264.7 macrophages were selected. The cytotoxicity of PNP/pCAR was evaluated using the CCK-8 assay. The cellular uptake efficiency and lysosomal escape ability of the nanoparticles were assessed via flow cytometry and confocal microscopy. Transfection efficiency was quantitatively evaluated by detecting the expression of the reporter gene GFP using flow cytometry. At the in vivo level, an orthotopic pancreatic cancer mouse model was established. Cy7-labeled βGlus-PNP/pCAR nanoparticles were administered orally, and the fluorescence distribution in mice was dynamically monitored at 1, 2, 4, 8, and 16 h post-administration using a small animal in vivo imaging system. Forty-eight hours after oral gavage, the mice were euthanized, and pancreatic tumor tissues were collected for further analysis of intratumoral fluorescence signals using the imaging system. Additionally, βGlus-PNP/pCAR-GFP nanoparticles loaded with the reporter gene (GFP) were administered orally. Forty-eight hours post-administration, pancreatic tumor tissues were harvested to prepare frozen sections, and GFP expression was observed and analyzed under a fluorescence microscope. ResultsThe PNP carrier exhibited a high loading capacity for pCAR. The successfully prepared PNP/pCAR nanoparticles were regular spheres with a hydrodynamic diameter of approximately (120±10) nm and a Zeta potential of about +(6±1) mV. They maintained good structural stability after incubation in PBS buffer for 7 d. Cell experiments demonstrated that PNP/pCAR exhibited no significant cytotoxicity in RAW 264.7 cells while being efficiently internalized and effectively escaping lysosomal degradation. The transfection positive rate of PNP/pCAR-GFP in RAW 264.7 cells reached (25±3)%, surpassing that of Lipofectamine 2000-loaded pCAR-GFP (Lipo/pCAR-GFP), which was (20±1)%.In vivo experiments revealed that, compared to unmodified PNP/pCAR, βGlus-PNP/pCAR exhibited strongerin situ pancreatic tumor targeting ability after oral administration. Furthermore, oral administration of βGlus-PNP/pCAR-GFP resulted in significant GFP protein expression detectable within pancreatic tumor tissues. ConclusionThis study successfully constructed and validated an orally administrable, pancreatic cancer-targeting polypeptide-based nano-gene delivery system. It provides an important technological foundation in delivery systems and experimental basis for the subsequent development of in situ CAR-M-based therapeutic strategies for pancreatic cancer.

Health economics evidence plays an important role in linking clinical value evidence with health resource allocation decisions in the development of clinical practice guidelines. It can not only effectively balance clinical effectiveness and economic feasibility but also avoid forming "idealized" recommendations that are detached from the affordability of the healthcare system or the burden-bearing capacity of patients. To promote guideline developers to use health economics evidence more standardizedly and fully, this paper conducts an in-depth analysis of the current application status, existing challenges, access channels, and application processes of health economics evidence in current guidelines, and on this basis, puts forward considerations and suggestions for strengthening and standardizing the application of health economics evidence in China's clinical practice guidelines.

Colorectal cancer (CRC) is characterized by persistently high incidence and mortality. Current therapies are limited by drug resistance and modest patient benefit, underscoring the urgent need for new perspectives rooted in tumor biology. The unique metabolic landscape of CRC makes it an ideal model in which to dissect the pathological roles of lactylation regulatory networks: microsatellite-stable (MSS) CRC, which accounts for approximately 85% of cases, concurrently upregulates glycolysis and oxidative phosphorylation, engaging in intense metabolic competition with immune cells; the intratumoral lactate pool exhibits a distinctive “dual-source supply” feature—in addition to tumor-intrinsic glycolysis, substantial exogenous lactate is provided by gut microbiota dysbiosis and by colonizing bacteria within liver metastases; high-frequency oncogenic mutations and lactylation modifications establish a feed-forward circuit of “oncogene-driven lactate accumulation-lactylation-facilitated tumor progression”. Moreover, MSS CRC displays near-complete unresponsiveness to immune checkpoint inhibitors, a phenomenon underpinned by multiple immune evasion mechanisms mediated by lactate and lactylation. Lactate metabolism is a hallmark of metabolic reprogramming in cancer. Lactate homeostasis provides tumor cells with metabolic substrates, modulates redox status, and regulates fatty acid metabolism to promote malignant progression. Notably, lactate can drive lactylation—an emerging post-translational modification (PTM) in which lactyl groups are attached to lysine residues, dynamically governing gene transcription and protein function and thereby establishing a bridge between metabolism and epigenetics. Lactate and lactylation form a multidimensional, coordinated network: lactylation of key metabolic enzymes such as LDHA reinforces a positive feedback loop that sustains lactate production; lactylation of upstream transcription factors such as HIF-1α drives metabolic reprogramming; furthermore, lactylation engages in crosstalk with m6A and m5C RNA modifications as well as with other PTMs such as acetylation, profoundly reshaping cellular behavior. In CRC, histone lactylation drives malignant phenotypes by activating immunosuppressive programs, inhibiting ferroptosis, and promoting invasion and migration; non-histone lactylation accelerates translation elongation, stabilizes β‑catenin, maintains redox homeostasis, and prevents PD-L1 degradation, thereby facilitating tumor progression. Lactylation-related gene signatures have demonstrated potential for prognostic stratification. Therapeutic strategies targeting the lactylation network range from upstream metabolic intervention to modulation of the modifying enzymes and direct blockade of lactylation modifications, forming a hierarchical interventional framework. However, current evidence derives predominantly from cell lines and xenograft models, and a causal relationship between lactylation and malignant progression in CRC has yet to be rigorously established. Whether inhibition of lactylation can alter CRC phenotypes independently of metabolic alterations and acetylation fluctuations remains a central unanswered question in the field. This review systematically examines the research progress and translational challenges surrounding lactylation regulatory networks, aiming to provide a circumspect assessment to inform the development of novel therapeutic strategies for CRC.

Body weight abnormalities, including overweight, obesity, and underweight, have become a dual public health challenge in Chinese adults: overweight and obesity lead to a variety of chronic complications, while underweight increases the risks of malnutrition, sarcopenia, and organ dysfunction. To systematically address these issues, multidisciplinary experts in endocrinology, sports science, nutrition, and psychiatry from various regions have held multiple weight management seminars. Based on the latest epidemiological data and clinical evidence, they expanded the guideline to include assessment and intervention strategies for underweight, in addition to the core content of obesity management. This guideline outlines the etiological mechanisms, evaluation methods, and multidimensional management strategies for overweight and obesity, covering key areas such as diagnosis and assessment, medical nutrition therapy, exercise prescription, pharmacological intervention, and psychological support. It is intended to provide a scientific and standardized approach to weight management across the adult population, aiming to curb the rising prevalence of obesity, mitigate complications associated with abnormal body weight, and improve nutritional status and overall quality of life.

Objective:To analyze the dynamic changes of serum exosome miR-552 and miR-653 levels in pa-tients with gastric cancer before and after chemotherapy and their relationship with clinical benefit.Methods:IA total of 128 patients with gastric cancer received chemotherapy from January 2022 to January 2024.According to the chemo-therapy effect,the two groups were divided into disease progression group and disease remission group.The levels of serum exosome miR-552 and miR-653 before and after chemotherapy were detected in the two groups,the risk fac-tors affecting the chemotherapy effect of gastric cancer patients were screened,the risk nomogram model was con-structed,and the efficacy was evaluated.Results:The proportion of TNM stage(Ⅲ+Ⅳ),lymph node metastasis,dis-tant metastasis,tumor size(>5 cm),invasion depth(T3/T4)and tumor growth pattern(invasive type)in disease progres-sion group was higher than that in disease remission group(P<0.05).The levels of serum exosomes miR-552 and miR-653 in disease progression group were higher than those in remission group before and after chemotherapy(P<0.05).Compared with before chemotherapy,miR-552 and miR-653 levels in both groups decreased(P<0.05).Logistic regres-sion analysis showed that TNM stage,lymph node metastasis,distant metastasis,tumor size,invasion depth,miR-552 and miR-653 were all risk factors affecting the chemotherapy efficacy of gastric cancer(P<0.05).ROC curve results showed that the AUC,95%CI,sensitivity and specificity of risk nomogram model to predict chemotherapy efficacy of gastric cancer were 0.867,0.672～0.991,92.80%and 80.40%,respectively(P<0.001).Calibration curve results showed that both predicted and actual predicted values were near the ideal curve,and the Hosmer-Lemeshow goodness of fit curve test χ2=1.869,P=0.782.Conclusion:The levels of serum exosomes miR-552 and miR-653 are closely related to the chemotherapy efficacy of gastric cancer,and dynamic monitoring of the above indexes is helpful for the evaluation of the disease and prognosis of gastric cancer.In this study,the risk nomogram model constructed based on the above indexes and other risk factors has high predictive value and clinical practicability for chemotherapy efficacy in patients with gastric cancer.

Objective:To explore the association between the use of tetracyclines during pregnancy and congenital malformations, with the aim of providing evidence-based guidance for the rational use of antibiotics during pregnancy.Methods:Data from the U.S. Food and Drug Administration Adverse Event Reporting System (FAERS) and the Canada Vigilance Adverse Reaction (CVAR) database from January 2015 to September 2024 were collected. Five methods including Tree-based scan statistic (TreeScan), proportional reporting ratio (PRR), reporting odds ratio (ROR), the UK Medicines and Healthcare Products Regulatory Agency (MHRA) comprehensive standard, and the Bayesian confidence propagation neural network (BCPNN) were used to detect signals of risk for congenital malformations in offspring following maternal use of tetracyclines during pregnancy. A signal that met the threshold criteria of all above 5 methods was considered as a risk signal. Based on population-based cohort of the drug exposures and adverse pregnancy outcomes (DEEP) data from January 2013 to December 2021 in Xiamen City, propensity score matching (PSM)-based Poisson regression was applied to evaluate the association between the first-trimester tetracyclines exposure and congenital malformations in offspring. Adjusted relative risk (a RR) and its 95% confidence interval ( CI) were calculated. Sensitivity analysis was conducted to validate the reliability of the results. Results:A total of 304 098 reports of adverse events during pregnancy were obtained from the FAERS and CVAR databases. Among them, 5 028 reports were related to tetracyclines, including 1 026 reports of congenital malformations in offspring, involving congenital malformations of musculoskeletal system, other digestive system, and other congenital malformations. Signal detection results suggested that tetracyclines may be a risk signal for above congenital malformations in offspring. The DEEP data included 411 936 pregnant women. After PSM, 240 pregnant women exposed to tetracyclines were included. The results showed no significant association between the first-trimester tetracyclines exposure and congenital malformations in offspring (a RR=0.75, 95% CI: 0.26-2.17), sensitivity analysis also showed no correlation. Conclusions:Data mining from the FAERS and CVAR databases suggests a potential association between tetracyclines use during pregnancy and congenital malformations in offspring. However, the DEEP data study shows no significant correlation.

Objective To propose a brain electrical phase prediction method based on long short-term memory network(LSTM)to improve the accuracy and robustness of phase synchronization prediction in transcranial magnetic stimulation(TMS).Methods First,an LSTM consisting of an input layer,an LSTM layer,an ReLU activation layer,a fully connected layer and a regression layer was constructed to capture the EEG signal features through the synergistic action of input gates,forgetting gates and output gates.Second,eye-open resting-state EEG data from 30 healthy subjects were trained using the LSTM to obtain a predictive model for EEG signal and EEG phase prediction.Finally,the LSTM method and the traditional autoregressive(AR)method were compared in terms of the phase prediction errors at the overall and individual levels and the prediction performance for peaks and troughs.A regression model was used to explore the relationships between instantaneous EEG amplitude,signal-to-noise ratio and phase prediction error with the LSTM method.Results The LSTM method achieved a total phase prediction error of 0.04°±5.69°,which was lower than that of the traditional AR method(-3.36°±51.13°).For each subject,the LSTM method demonstrated superior phase prediction accuracy compared to the traditional AR method(P＜0.001).The accuracy for predicting peaks(troughs)by the LSTM method(about 89％)was higher than that by the traditional AR method(about 10％).Unlike the traditional AR method,the LSTM method didnot result in linear relationships between instantaneous EEG amplitude,signal-to-noise ratio and phase prediction error,with Pvalues being 0.58 and 0.18,respectively.Conclusion The LSTM-based brain electrical phase prediction method shows high accuracy and robustness when used for EEG phase-synchronized TMS.[Chinese Medical Equipment Journal,2025,46(3):1-8]

Objective To explore the association between cardiorespiratory fitness and total atherosclerotic burden of brain-and heart-arteries in patients with ischemic stroke.Methods This study retrospectively enrolled consecutive patients with ischemic stroke of the large-artery atherosclerosis or small-artery occlusion subtypes accompanied by cervicocephalic atherosclerosis,who were admitted to the Department of Neurology,Xuanwu Hospital,Capital Medical University,between May 2023 and December 2024.General and clinical data,including age(＜60years,≥60years),sex,admission blood pressure,body mass index,history of hypertension,diabetes mellitus,hyperlipidemia,ischemic stroke,symptomatic coronary artery disease,smoking,alcohol consumption,and medication use(including antiplatelet drugs,anticoagulants,lipid-lowering drugs,antidiabetic drugs,antihypertensive drugs,and β-blockers),characteristics of ischemic stroke(including the duration of onset,ischemic side[left,right,bilateral],and ischemic location[anterior circulation,posterior circulation,bilateral circulation])were collected from all patients enrolled.On the morning after admission,fasting venous blood samples were collected to measure the levels of triglycerides,total cholesterol,low-density lipoprotein cholesterol,high-density lipoprotein cholesterol,fasting blood glucose,glycated hemoglobin,homocysteine,fibrinogen,D-dimer,C-reactive protein,high-sensitivity C-reactive protein,N-terminal pro-B-type natriuretic peptide,creatine kinase-MB,cardiac troponin T,and myoglobin.Transthoracic echocardiography was performed within 7 days after admission to evaluate cardiac function.Left ventricular ejection fraction and cardiac output were recorded,and cardiac index were calculated.Upon admission,neurological impairment,disability,motor function,and balance ability were assessed using the National Institutes of Health stroke scale(NIHSS),modified Rankin scale(mRS),Fugl-Meyer assessment(FMA),and Berg balance scale,respectively.The Saltin-Grimby physical activity level scale was used to evaluate the intensity of habitual physical activity prior to stroke onset.Cardiopulmonary exercise testing was performed within 7 days after admission to assess cardiopulmonary fitness.During the test,peak oxygen uptake(VO2peak),percentage of predicted VO2peak(VO2peak%pred),and metabolic equivalent of task(MET)were recorded.Based on the minimum oxygen uptake required for independent living(15 ml/[kg·min]),VO2peak was classified into low VO2peak(＜15 ml/[kg·min])and high VO2peak(≥15 ml/[kg·min]).With VO2peak%pred＜0.60 as the cutoff,VO2peak%pred was divided into low VO2peak%pred(＜0.60)and high VO2peak%pred(≥0.60).MET were categorized into low MET(＜mean MET)and high MET(≥mean MET)according to the mean value of MET in this study population.Imaging data of cardio-cerebral arteries were obtained by simultaneous CT arteriography within 7 days after admission.Total atherosclerotic burden of brain-and heart-supplying arteries(TAB-BHAs)was used to quantitatively evaluate the overall degree of cardio-cerebral atherosclerosis.And patients were stratified into high TAB-BHAs(≥4 points)and low TAB-BHAs(＜4 points)groups.The differences in general and clinical characteristics,as well as cardiopulmonary fitness indices,were assessed among different groups of TAB-BHAs.Spearman' s correlation was used in the preliminary analysis of the relationship between cardiorespiratory fitness indicators and TAB-BHAs.Multivariate Logistic regression was conducted with VO2peak,low VO2peak%pred,and low METs as independent variables,and high TAB-BHAs as the dependent variable to assess the association between cardiopulmonary fitness and TAB-BHAs.Covariates were selected through regressions stratified by age≥60 years,male,the least absolute shrinkage and selection operator(LASSO),and the variables exhibit statistically significant differences between the low and high TAB-BHAs groups,respectively.Results A total of 104 patients with ischemic stroke were enrolled.Among all patients enrolled,60patients(with ages ranging from 30 to 72years and a mean age of[54±11]years)met the inclusion and exclusion criteria,and were ultimately included.Amid the 60 patients,52 were male and 8 were female.There were 20 patients(33.3%)with low VO2peak,28 patients(46.7%)with low VO2peak%pred,and 31 patients(51.7%)with low MET(MET＜5.0).45 patients were classified into the low TAB-BHAs group and 15 into the high TAB-BHAs group.(1)Compared with the low TAB-BHAs group,patients in the high TAB-BHAs group were significantly older and had a higher proportion of patients aged≥60 years,they also showed significantly higher fibrinogen levels and a history of antihypertensive drug use(all P＜0.05).No significant differences were observed in other general or clinical characteristics between the two groups(all P＞0.05).Regarding cardiopulmonary fitness parameters,patients in the high TAB-BHAs group had lower VO2peak and MET levels,and higher proportions of patients with low VO2peak,low VO2peak%pred,and low MET compared with those in the low TAB-BHAs group(all P＜0.05).(2)Based on the Spearman's correlation analysis,VO2peak(r=-0.298,P=0.021),VO2peak%pred(r=-0.305,P=0.018),MET(r=-0.303,P=0.018)all exhibited negative correlations between and TAB-BHAs.(3)LASSO regression was used to identify the most pertinent variables for high TAB-BHAs,including low VO2peak,low VO2peak%pred,and fibrinogen.Multivariate Logistic regression analysis was then performed with low VO2peak,low VO2peak%pred,and low MET as independent variables and high TAB-BHAs as the dependent variable.The results showed that after adjusting for age≥60 years,male,and fibrinogen,both low VO2peak(adjusted OR,4.420,95%CI 1.052-18.573,P=0.042)and low VO2peak%pred(adjusted OR,7.423,95%CI 1.411-39.046,P=0.018)were independently associated with high TAB-BHAs in ischemic stroke patients.After further adjusting for variables that differed among high and low TAB-BHAs groups(including age≥60 years,male,fibrinogen,and history of using antihypertensive drugs),multivariate Logistic regression showed that low VO2peak%pred remained independently associated with high TAB-BHAs in ischemic stroke patients(adjusted OR,6.347,95%CI 1.170-34.418,P=0.032).Conclusion Poor cardiopulmonary fitness might be associated with high degree of overall cardio-cerebral atherosclerosis,suggesting cardiorespiratory fitness as a potential correlated indicator that could provide clues for improving early screening of patients with heavy cardio-cerebral atherosclerotic burden and for exploring the underlying mechanisms.

Aim To explore the effect of astragalosideⅣ(AS-Ⅳ)on lipopolysaccharide(LPS)-induced po-larization and migration of RAW 264.7 macrophages and the underlying mechanism.Methods 1 mg·L-1 LPS was used to construct cell migration model.Scratch assay was utilized to determine cell migration rate.Immunofluorescence staining was utilized to de-tect the expression and location of F4/80,iNOS and Arg-1.CCK-8 assay was used to determine the viabili-ty of RAW 264.7 cells.Griess assay was used to measure NO content.Molecular docking was used to analyze the interaction between AS-Ⅳ and the core tar-gets such as cGAS and STING protein.Western blot was employed to detect the expression of iNOS,Arg-1,cGAS,STING,NF-κB p65 and p-NF-κB p65 protein.Results AS-Ⅳ significantly inhibited the migration and M1 polarization of RAW 264.7 cells induced by LPS.Moreover,AS-Ⅳ could interact with cGAS and STING protein,especially cGAS.Further Western blot assay showed that AS-Ⅳ significantly downregulated the expression of iNOS,cGAS,STING and p-NF-κB p65 protein.Conclusions AS-Ⅳ could promote mac-rophage M1 to M2 polarization,thereby inhibited mac-rophage migration through restraining the cGAS/STING/NF-κB signaling pathway,which provides a new therapeutic target for AS-Ⅳ to improve the early inflammatory response of AS.