1.Predicting intraoperative blood transfusion risk in hip fracture patients using explainable machine learning models
Fengting LU ; Xiaoming LI ; Dekui LI ; Xianyuan XIE ; Jiazhong WANG ; Qing YU ; Gan HUANG ; Jun SHEN
Chinese Journal of Blood Transfusion 2026;39(2):196-202
Objective: To investigate the factors influencing intraoperative blood transfusion in patients with hip fractures and to develop a machine learning (ML) model for predicting this risk. Methods: A total of 424 patients with hip fractures who underwent surgical treatment between November 2022 and March 2025 in our hospital were selected. Key feature variables of intraoperative blood transfusion risk were identified using the Boruta algorithm. Four different ML algorithms—support vector machine (SVM), linear discriminant analysis (LDA), mixed discriminant analysis (MDA), and extreme gradient boosting (XGBoost)—were used to develop predictive models for intraoperative blood transfusion risk. The predictive performance of the four ML models were evaluated using accuracy, precision, receiver operating characteristic (ROC) curves, precision-recall curves (PRC), precision-recall gain curves (PRGC), and F1 scores. Shapley additive interpretation (SHAP) was used to interpret the final model. Results: Among the 424 patients, 77(18.2%) received intraoperative blood transfusion. The Boruta algorithm identified albumin (ALB), activated partial thromboplastin time (APTT), types of anesthesia, types of fracture, and hemoglobin (Hb) as key feature variables for predicting intraoperative blood transfusion risk. In model evaluation, the SVM model outperforms the other three models across multiple metrics, including the area under the receiver operating characteristic curve (AUC), recall, recall gain, accuracy, precision, F1 score, and the area under the precision-recall curve (PRC-AUC). The SVM model, interpreted and visualized based on SHAP values, effectively predicted intraoperative blood transfusion risk in patients with hip fracture. A visual online application was developed based on the SVM model (https://pbo-nomogram.shinyapps.io/blood/). Conclusion: Preoperative low ALB and Hb levels, prolonged APTT, general anesthesia, and intertrochanteric fractures are risk factors for intraoperative blood transfusion in hip fracture patients. The risk prediction model for intraoperative blood transfusion constructed based on the SVM algorithm has optimal performance, which provides new ideas and methods for the clinical early identification of hip fracture patients with high transfusion risk and the implementation of targeted interventions.
2.Innovative Development and Cutting-edge Applications of Split Intein Technology
Jin-Qiu GAN ; Xiang-Yu DENG ; Xin-Yan WANG ; Jia-Bin LI
Progress in Biochemistry and Biophysics 2026;53(6):1520-1540
Inteins are unique protein insertion sequences capable of self-excision, enabling the covalent ligation of flanking extein peptides via amide bond formation. This process proceeds spontaneously without requiring external enzymes, cofactors, or chemical reagents, granting inteins exceptional biocompatibility and traceless performance in protein engineering applications. Split inteins represent a specialized and versatile subclass whose splicing domains are encoded by two separate gene fragments rather than a single continuous open reading frame. These fragments, known as the N-terminal (IntN) and C-terminal (IntC) split inteins, associate through non-covalent interactions including hydrophobic forces, hydrogen bonds, and van der Waals forces to assemble into an active three-dimensional structure, which then drives efficient extein ligation and enables protein trans-splicing. Protein trans-splicing mediated by split inteins has become a cornerstone for traceless protein ligation owing to its high specificity and irreversibility, fundamentally reshaping strategies for protein modification, assembly, and functional regulation. Compared with traditional chemical ligation methods, split intein systems require no complex chemical derivatization of peptide fragments and can operate efficiently at micromolar concentrations under physiological conditions, thus avoiding structural and functional damage caused by organic reagents. In contrast to enzymatic ligation tools such as sortase, split inteins eliminate the need for additional enzymes or cofactors, simplifying reaction systems, reducing costs, and minimizing non-specific side products. These distinctive advantages render split inteins highly promising for applications in chemical biology, synthetic biology, and biopharmaceutical development. In recent years, deepened mechanistic understanding has established structure-guided rational design as the primary approach to overcoming key limitations of split inteins, including intrinsic aggregation propensity, strict extein sequence dependence, and limited splicing efficiency. Bioinformatic tools have been used to identify aggregation-prone regions in the IntN fragment, and site-directed mutagenesis of hydrophobic residues, relocation of split sites, or removal of misfolding-prone sequences has substantially reduced in vitro aggregation and improved soluble expression and assembly activity. Rational engineering of catalytic residues and adjacent flexible loops has relaxed strict amino acid preferences at extein junctions, enhancing sequence tolerance and reducing the risk of functional impairment in target proteins. Consensus design based on multiple sequence alignments has yielded ultra-fast splicing variants such as Cfa DnaE and Cat-TerL, which exhibit significantly accelerated kinetics and improved tolerance to denaturing conditions. Meanwhile, advances in structural biology have further clarified the conformational dynamics and catalytic mechanisms of splicing, supporting the precise design of high-performance intein modules. On this basis, electrostatic interaction tuning and metagenomic screening have yielded multiple mutually orthogonal split intein pairs, enabling selective multi-fragment protein ligation and providing new routes for the efficient synthesis of large multi-domain functional proteins. With these engineered split inteins offering continuously improved performance and expanded applicability, protein trans-splicing has been widely applied in numerous cutting-edge areas of protein research and biomedicine. In gene delivery, split intein-based systems overcome the packaging limit of adeno-associated viral vectors, enabling the accurate reconstitution of large therapeutic proteins and base editors in target cells, thereby enhancing the efficacy and scope of gene therapy for genetic diseases. In internal protein sequence editing, split inteins mediate precise sequence replacement and modification in flexible regions or loops of target proteins, without the need for complex multi-step ligation and protein refolding involved in traditional protein semisynthesis. In protein-protein interaction studies, intein-mediated splicing covalently captures transient and weak intracellular complexes, enabling sensitive, high-throughput interaction detection and drug screening. In synthetic biology, conditionally controllable splicing systems support the construction of diverse intracellular and cell-surface biological logic gates for the precise regulation of cellular behavior. In mechanistic biochemical research, split inteins enable photocatalytic proximity labeling and site-specific tagging, allowing the preparation of homogeneous protein samples carrying precise post-translational modifications such as ubiquitination and polyglutamylation for chromatin interactome analysis and epigenetic studies. Moreover, covalent trapping strategies using split inteins stabilize transient enzymatic intermediates, providing unprecedented insights into molecular mechanisms such as nucleosome ubiquitination that are difficult to elucidate using conventional methods. This review systematically summarizes key technological advances in split inteins over the past decade, highlighting engineering strategies, mechanistic insights, and the development of orthogonal components. It comprehensively surveys emerging applications at the frontiers of protein research, analyzes current core challenges, and proposes future directions, particularly emphasizing artificial intelligence-driven de novo design and novel splicing pathways to break existing technical bottlenecks. By enabling traceless, efficient, and versatile protein manipulation, split inteins continue to serve as indispensable tools that drive innovation in protein engineering and fundamental life science research.
3.Efficacy and Safety of Qihuang Acupuncture Theory Combined with Opioid Analgesics in the Treatment of Moderate to Severe Cancer Pain in Lung Cancer Patients:a Randomize-Controlled Trial
Yingqi WANG ; Ruifang YU ; Jinpeng HUANG ; Guiya LIAO ; Ziyan GAN ; Zhenhu CHEN ; Xiaobing YANG ; Chunzhi TANG
Journal of Traditional Chinese Medicine 2025;66(4):358-366
ObjectiveTo observe the analgesic efficacy and safety of Qihuang acupuncture theory combined with opioid analgesics in patients with moderate to severe cancer pain due to lung cancer. MethodsPatients with moderate to severe cancer pain from lung cancer were randomly divided into Qihuang acupuncture group and control group, with 33 cases in each group. The control group was treated with long-acting opioid analgesics at maintenance doses and supplementary analgesic medications as needed. In case of breakthrough pain, short-acting opioids were used for rescue. The Qihuang acupuncture group received Qihuang acupuncture treatment in addition to the treatment used in the control group, administered once every other day, with 3 sessions constituting one treatment course. The treatment duration for both groups was 5 days. The primary outcome was the change in pain intensity, measured using the numerical rating scale (NRS) before and after treatment, and the NRS change rate was calculated. Secondary endpoints included the daily NRS change rate, the Eastern Cooperative Oncology Group (ECOG) Performance Status (PS) score, the European Organization for Research and Treatment of Cancer Quality of Life Core Questionnaire (EORTC QLQ-C30) score, and the 24-hour equivalent hydrocodone sustained-release tablet dose. Laboratory tests, including routine blood, urine, stool, liver function, and kidney function, were performed before and after treatment. Adverse events were recorded throughout the trial. ResultsAll patients completed the trial, and both groups showed a decrease in average NRS scores and PS scores after treatment, with the Qihuang acupuncture group showing lower average NRS scores and PS scores than the control group (P<0.05 or P<0.01). After treatment, the NRS change rate in the Qihuang acupuncture group was (0.42±0.17), significantly higher than that in the control group (0.14±0.27, P<0.01). The daily NRS change rate during treatment was also higher in the Qihuang acupuncture group compared to the control group (P<0.01). The Qihuang acupuncture group showed an increase in overall health status and functional scores in the EORTC QLQ-C30, and a decrease in symptom scores for fatigue, nausea and vomiting, pain, dyspnea, insomnia, appetite loss, constipation, and financial difficulties. In contrast, overall health status and constipation scores in the control group increased, while scores of fatigue, nausea and vomiting, pain, and appetite loss decreased (P<0.05 or P<0.01). After treatment, the 24-hour equivalent hydrocodone sustained-release tablet dose did not show significant difference in the Qihuang acupuncture group (P>0.05), while the control group showed a significant increase in the 24-hour dose (P<0.01). No significant abnormalities were observed in laboratory tests before and after treatment in either group. During the study, the incidence of nausea and vomiting as well as constipation in the Qihuang acupuncture group was both 3.03% (1/33), while the incidence in the control group was 27.27% (9/33) and 36.36% (12/33), respectively, with the Qihuang acupuncture group showing significantly lower incidence (P<0.01). No serious adverse reactions were observed in either group. ConclusionQihuang acupuncture therapy combined with opioid analgesics is more effective than using opioids alone in relieving pain in patients with moderate to severe cancer pain due to lung cancer. It can improve the patients' physical condition and quality of life, reduce the dose of opioid analgesics, and has good safety.
4.Outcomes of Mandibular Reconstruction Using Free Flap After Head and Neck Cancer Resection and Approaches for Improvement
Unubold E ; Denis S ; Odontungalag Ts ; Yanjinlkham M ; Amarsanaa G ; Tsetsegkhen N ; Gantsetseg G ; Battsengel B ; Gan-Erdene B ; Bat-Erdene M ; Bulganchimeg S ; Ganbaatar Yu ; Odkhuu J ; Enkh-Orchlon B
Mongolian Journal of Health Sciences 2025;87(3):82-89
Background:
Reconstruction of mandibular and maxillary defects resulting
from malignant tumors has remained a complex challenge in recent years. Defects
caused by tumors—as well as trauma, inflammatory diseases, and congenital
anomalies—lead to impaired essential functions such as mastication,
swallowing, and speech. Prior to the 1950s, reconstruction of maxillofacial
hard tissue was not commonly performed. Instead, metal plates were used to
reestablish bony continuity, and surrounding tissues were utilized to close soft
tissue defects, without effectively restoring function.
With modern advances in three-dimensional (3D) virtual planning, it is now possible
to accurately plan free bone flaps for reconstructing jaw defects. During
surgery, manually bending reconstruction plates to fit donor bone precisely is
often not feasible. Preoperative 3D planning allows for precise fabrication of
surgical guides and fixation plates, improving accuracy and significantly reducing
operative time. Additionally, incorporating dental implant planning into
the reconstruction process facilitates restoration of both structural and functional
outcomes.
Aim:
To evaluate the outcomes of mandibular defect reconstruction using
scapular free flaps in Mongolia and explore potential approaches to optimize
the technique.
Materials and Methods:
This was a case study series. Data from reconstructive
surgeries performed at the National Cancer Center of Mongolia, Central
Dental Hospital, and the Mongolia-Japan Hospital were collected. Variables
included patient age and sex, etiology of the mandibular defect, size of the
scapular bone segment, operative time, ischemia time of the free flap, number
of vascular anastomoses performed, and pedicle length.
For 3D planning, CT scans of the patient's head and lower limb (slice thickness
<1 cm) were used to generate 3D models via the 3D Slicer software. Cutting
guides for the mandible and scapula (ASIGA), as well as the reconstruction
models (AMS), were printed using a 3D printer.
Results:
A total of 400 free flap reconstructions were performed during the
study period. Of these, 29 cases involved reconstruction of mandibular defects
using scapular free flaps. The mean age of patients was 40.0 ± 18.3 years,
with 52% (15 patients) being female. The etiologies of the defects included
malignant tumors (13 cases, 45%), benign tumors (6 cases, 21%), and pre-existing
defects (10 cases, 34%).
In one case, tumor resection and mandibular reconstruction were performed
using 3D planning. The total operative time was 9 hours and 30 minutes, and
the ischemia time was 2 hours and 40 minutes.
Conclusion
Between 2012 and 2025, a total of 29 mandibular reconstructions
using scapular free flaps were performed in Mongolia. Traditional reconstruction
methods were associated with prolonged ischemia time. The use of
3D surgical planning has shown potential in significantly reducing ischemia
time and improving surgical outcomes.
5.Fusion of Dual-targeting Peptides with MAP30 Promotes the Apoptosis of MDA-MB-231 Breast Cancer Cells
Yi-Xuan YANG ; Xin-Yi WANG ; Wei-Wei CHEN ; Li GAN ; Yu SUN ; Tong LIN ; Wei-Chun ZHAO ; Zhen-Hong ZHU
Chinese Journal of Biochemistry and Molecular Biology 2025;41(2):260-272
Momordica antiviral protein 30 kD(MAP30)is a type Ⅰ ribosome-inactivating protein(RIP)with antibacterial,anti-HIV and antitumor activities but lacks the ability to target tumor cells.To in-crease its tumor-targeting ability,the arginine-glycine-aspartic(RGD)peptide and the epidermal growth factor receptor interference(EGFRi)peptide were fused with MAP30,which was named ELRL-MAP30.The efficiency of targeted therapy for triple-negative breast cancer(TNBC)MDA-MB-231 cells,which lack the expression of estrogen receptor(ER),Progesterone receptor(PgR)and human epidermal growth factor receptor-2(HER2),is limited.In this study,we focus on exploring the effect and mecha-nism of ELRL-MAP30 on TNBC MDA-MB-231 cells.First,we discovered that ELRL-MAP30 significant-ly inhibited the migration and invasion of MDA-MB-231 cells and induced MDA-MB-231 cell apoptosis.Moreover,ELRL-MAP30 treatment resulted in a significant increase in Bax expression and a decrease in Bcl-2 expression.Furthermore,ELRL-MAP30 triggered apoptosis via the Fak/EGFR/Erk and Ilk/Akt signaling pathways.In addition,recombinant ELRL-MAP30 can inhibit chicken embryonic angiogenesis,and also inhibit the tube formation ability of human umbilical vein endothelial cells(HUVECs),indica-ting its potential therapeutic effects on tumor angiogenesis.Collectively,these results indicate that ELRL-MAP30 has significant tumor-targeting properties in MDA-MB-231 cancer cells and reveals potential ther-apeutic effects on angiogenesis.These findings indicate the potential role of ELRL-MAP30 in the targeted treatment of the TNBC cell line MDA-MB-231.
6.Established cell model and mechanism of visceral hypersensitivity and nerve hyperplasia in IBS using P815 and N2a co-culture
Hongbin LI ; Chunli GAN ; Xiangyu XIE ; Shan LIU ; Qin LU ; Wei KE ; Shi-yu QI ; Yusheng HUANG ; Hongmei TANG
Chinese Journal of Pathophysiology 2025;41(4):825-832
AIM:To establish a cell model of visceral hypersensitivity and nerve hyperplasia in irritable bowel syndrome(IBS)by conducting an in vitro co-culture of mouse P815 mast cells and N2a nerve cells and explore its possible mechanism.METHODS:Enzyme-linked immunosorbent assay(ELISA)with three replicates was used to confirm the C48/80-induced P815 degranulation.The length of neurites was observed under bright field microscopy to determine the number of differentiated neurons,thereby selecting the concentration of retinoic acid(RA)for stimulating the differentia-tion of N2a cells,with four replicates.A co-culture system of P815 and N2a cells was established using Transwell cham-bers with four replicates.The following groups were established:N2a cells cultured alone,N2a cells co-cultured with P815 cells,N2a cells co-cultured with P815 cells plus C48/80,and N2a cells plus RA group.After co-culturing,the num-ber of differentiated N2a cells was observed under bright field.The expression of nerve growth factor(NGF),tyrosine ki-nase receptor A(TRKA),growth-associated protein-43(GAP43),neuron-specific enolase(NSE),synapsin(SYN),and postsynaptic density protein-95(PSD-95)at both protein and gene levels in N2a cells was detected using Western blot and polymerase chain reaction(PCR),with four replicates.RESULTS:The best condition for N2a differentiation was stimulation with 10 μmol/L RA for 24 hours,whereas the best condition for degranulation was stimulation of P815 cells with 20 mg/L C48/80 for 24 hours.Compared with N2a cells cultured alone,the differentiation ratio of the N2a+P815+C48/80 and N2a+RA groups was significantly increased(P<0.01),and the protein and mRNA expressions of NGF,TRKA,GAP43,NSE,SYN,and PSD-95 were significantly increased(P<0.05).CONCLUSION:Our results revealed that mast cell degranulation enhances the level of nerve hyperplasia in enteric nerve cells and promotes changes in nerve structure and function.Synaptic remodeling regulated by abnormal expression of key proteins such as NGF,TRKA,and GAP43 is involved in the nerve hyperplasia induced by mast cell degranulation.
7.Research progress on experimental models of Diamond-Blackfan anemia
Weiwei CAI ; Jiaying GAN ; Jingbin YU ; Huiling LI ; Jiahui WU ; Xue WANG ; Donghua XIONG ; Xuegeng WANG ; Fang LIANG
Acta Laboratorium Animalis Scientia Sinica 2025;33(6):905-913
Diamond-Blackfan anemia(DBA),also known as congenital pure red cell aplasia,is a rare genetic disorder characterized by bone marrow failure,congenital anomalies,and severe red blood cell abnormalities.The rarity of the condition,and consequently limited patient pool and scarcity of research models,means that the pathogenic mechanisms associated with genetic mutations in DBA remain uncertain,and the clinical treatment options are limited.This review synthesizes the findings from zebrafish,mouse,and human cellular models of DBA mutations.We clarify the pathogenic mechanisms and monitor the progression of drugs into clinical trials,thereby aiding further in-depth explorations into the etiology and therapeutic advancements for DBA.
8.Effect of mindfulness-based cognitive therapy in the sense of personal control and illness perception of young and middle-aged patients after PCI
Weiling HAO ; Xiaoxiang YU ; Yanfang ZHAO ; Jiayu HAN ; Jing YU ; Shunna GAN ; Minrou XU ; Ying XU ; Meng YUAN ; Mingxing XU
Chinese Journal of Practical Nursing 2025;41(22):1681-1687
Objective:To investigate the effect of mindfulness-based cognitive therapy on the sense of personal control and illness perception of young and middle-aged patients after percutaneous coronary intervention (PCI), so as to provide theoretical and practical guidance for the psychological care of patients after PCI.Methods:A randomized controlled trial was conducted. From January 2022 to December 2023, young and middle-aged patients after PCI admitted to the Department of Cardiology, Qinhuai Medical District, Eastern Theater Command General Hospital of the Chinese People′s Liberation Army were selected as the research subjects by convenient sampling method, patients were divided into the experimental group and the control group by the random number table method. The control group was given routine nursing, and the experimental group was given mindfulness-based cognitive therapy on the basis of routine nursing. The Personal Mastery Scale (PMS), Cardiac Self-Efficacy Questionnaire (CSEQ), and Brief Illness Perception Questionnaire (BIPQ) were used to evaluate personal sense of control, self-efficacy, and illness perception before and after the intervention respectively.Results:A total of 80 young and middle-aged patients after PCI were included. There were 40 cases in the control group, including 25 males and 15 females, aged (49.43 ± 5.55) years old. There were 40 cases in the experimental group, including 19 males and 21 females, aged (49.03 ± 4.19) years old. Before the intervention, there was no statistically significant difference in the PMS, CSEQ and BIPQ scores between the two groups of patients (all P>0.05). After the intervention, the PMS, CSEQ scores of the patients in the experimental group were (23.03 ± 2.54), (45.85 ± 8.16) points respectively, which were higher than (21.95 ± 2.28), (39.05 ± 8.78) points in the control group, the BIPQ score of the patients in the experimental group was(39.63 ± 8.12) points, which was lower the (45.45 ± 8.64) points in the control group, the differences were statistically significant ( t=-2.00, -3.59, 3.11, all P<0.05). Conclusions:Mindfulness-based cognitive therapy can effectively improve the sense of personal control and self-efficacy of young and middle-aged patients after PCI, reduce the sense of threat to the disease.
9.Expert consensus on infection prevention and control of Creutzfeldt-Jakob disease in medical institutions
Tianxiang GE ; Yangyang JIA ; Chunhui LI ; Jianrong HUANG ; Xiujuan MENG ; Xiaodong GAO ; Jingping ZHANG ; Fu QIAO ; Lijuan XIONG ; Hui LIANG ; Wei LI ; Haiyan LOU ; Wenjuan WU ; Tianxin XIANG ; Jiansen CHEN ; Biao ZHU ; Kaijin XU ; Zhihui ZHOU ; Hongliu CAI ; Meihong YU ; Yan ZHANG ; Yanwan SHANGGUAN ; Haiting FENG ; Hangping YAO ; Lei GUO ; Tieer GAN ; Weihong ZHANG ; Jimin SUN ; Ye LU ; Qun LU ; Meng CAI ; Jin SHEN ; Yunsong YU ; Anhua WU ; Liu-yi LI ; Tingting QU
Chinese Journal of Infection Control 2025;24(4):437-450
Creutzfeldt-Jakob disease(CJD)is a rapidly progressive and fatal neurodegenerative disorder caused by prions,with certain infectivity and iatrogenic transmission risks.With the rapid progress and application of new dia-gnostic biomarkers and detection methods,as well as the construction and improvement of surveillance and reporting systems,the detection of CJD in patients domestically and internationally has shown an increasing trend year by year.Due to its long incubation period and heterogeneity of early symptoms,early identification and diagnosis of the disease is difficult,increasing the risk of transmission within medical institutions.Currently,there is a lack of con-sensus on the infection prevention and control of CJD.In order to timely identify and diagnose CJD as well as effec-tively block its transmission in medical institutions,this consensus summarizes 15 clinical concerns and formulates 24 specific recommendations based on the latest domestic and international research findings and clinical evidence,as well as combines with clinical practice,aiming to standardize healthcare-associated infection prevention and control measures for CJD and reduce its transmission risk in medical institutions.
10.Teaching Practice and Exploration of"Tutorial System"Based on The Cultivation of Scientific Research and Innovation Ability of Medical Students
Qiao ZHANG ; Yin-Feng YANG ; Yue-Li NI ; Zhuo-Ran TENG ; Wen-Jing LIU ; Jing WU ; Yan-Rui WU ; Yu DOU ; Ming HE ; Shu-De LI ; Ping GAN ; Fang YUAN ; Zhe YANG ; Xin-Wang YANG
Chinese Journal of Biochemistry and Molecular Biology 2025;41(3):470-480
The scientific research and innovation capabilities of medical students are intrinsically linked to the sustained and high-quality development of national healthcare initiatives.Cultivating outstanding medi-cal students with independent scientific capabilities and innovative consciousness is a critical component in the education and training of high-level medical professionals.Our investigation revealed that within the imperfections of the cultivating model,some faculty and students at medical schools have an insufficient understanding of scientific research and innovation and lack motivation for engaging in such activities,which hinder the progression of scientific research activities.Consequently,we initiated a teaching practice and exploratory study on the"tutorial system"aimed at fostering medical students'scientific research and innovation abilities.Based on the principle of"research informing teaching,teaching and research advan-cing together,"this study implements a"tutorial system"coordinated by tutors,supplemented by graduate and undergraduate student mentors,to cultivate innovative thinking,stimulate interest in scientific re-search,and enhance practical and research skills among medical students.Through collaborative efforts within"scientific research innovation teams,"various educational methods—including preliminary re-search,in-class and extracurricular activities,intra-group and inter-group interactions,and theoretical and practical applications—are employed to improve and strengthen the cultivation of medical students'scientif-ic research and innovation abilities.This study aims to provide valuable references for optimizing medical education management systems and enhancing the quality of medical student training.

Result Analysis
Print
Save
E-mail