Disulfide Bond Engineering of Soluble ACE2 for Thermal Stability Enhancement.

Although the primary pandemic of SARS-CoV-2 is over, there are concerns about the resurgence of the next wave of related viruses, including a wide range of variant viruses. The soluble ACE2 (sACE2) inhibits the SARS-CoV-2 spike protein ACE2 interaction and has potential as a variant-independent therapeutic against SARS-CoV-2. Here, we introduce novel disulfide bonds in the wild-type sACE2-Fc by structure-guided mutagenesis, aiming to improve its stability. The stability of each mutant was assessed by a thermal shift assay to screen mutants with increased thermal stability. As a result, we identified a mutant sACE2-Fc with a significantly increased melting temperature. X-ray crystal structure determination of the sACE2 mutant confirmed the correct formation of the designed disulfide bond, and there were no significant structural disturbances. We also proved that the thermostable sACE2-Fc preserved the spike protein binding affinity comparable to the wild-type sACE2-Fc in both molecular and cellular environments, suggesting its therapeutic potential.

Characterization of high Zn content Cd0.87Zn0.13Te0.98Se0.02 grown using Bridgman technique.

CdZnTe (CZT) is a promising commercial material used as a room-temperature operating semiconductor detector for gamma-ray detection. Recently, CdZnTeSe (CZTS) detectors improved upon the properties of CZT by improving homogeneity and reducing defect properties, thereby enabling higher production yield of high-quality crystals. However, addition of selenium to CZT will reduce the bandgap and increase the amount of thermally stimulated electrons, resulting in low resistivity of the crystal. In this study, the enhancement of zinc content was introduced to compensate the bandgap reduction owing to selenium addition, while maintaining the improved properties of selenium addition. The morphology and stoichiometry of CZTS were determined using scanning electron microscopy and electron probe micro-analyzer. Furthermore, the calculated bandgap with stoichiometry was compared with the measured bandgap using UV-Vis measurement and Tauc plot. The electrical, chemical, and other spectroscopic properties were characterized using an I-V curve, X-ray photoelectron spectroscopy, and gamma-spectroscopic techniques, respectively. Moreover, it was proven that the high zinc CZTS can exhibit superior properties owing to selenium addition without affecting the bandgap reduction.

Effectiveness of the triglyceride-glucose index and triglyceride-glucose-related indices in predicting cardiovascular disease in middle-aged and older adults: A prospective cohort study.

BACKGROUNDS: Cardiovascular disease (CVD) risk assessment is a crucial component of public health. We aimed to determine the predictive value of the triglyceride-glucose (TyG) index and TyG-related indices for new-onset CVD. METHODS: This prospective study included 7,808 participants aged 40-69 years from the Ansung-Ansan cohort database. Our analysis was stratified by diabetes status. The hazard ratio (HR) with a 95% confidence interval (CI) for incident CVD was computed using multiple Cox proportional-hazards regression models. To evaluate the predictive performance of these indices for new-onset CVD, we calculated the Harrell's C-index (95% CI). RESULTS: In this study, a total of 6,890 participants did not have diabetes at baseline, while 918 participants had diabetes. In participants without diabetes, compared to the lowest tertile, fully adjusted HR and 95% CI for new-onset CVD in the highest tertile were as follows: TyG (HR 1.42, 95% CI 1.06-1.90), TyG-body mass index (BMI) (HR 1.92, 95% CI 1.19-3.10), TyG-waist circumference (WC) (HR 2.37, 95% CI 1.61-3.49), and TyG-waist-to-height ratio (WHtR) (HR 2.20, 95% CI 1.47-3.28). However, no significant associations were observed between TyG, modified TyG indices, and new-onset CVD in participants with diabetes. Notably, the C-indice of TyG-WC and TyG-WHtR were significantly higher than those of TyG and TyG-BMI in participants without diabetes. CONCLUSIONS: TyG-BMI, TyG-WC, and TyG-WHtR were associated with an increased risk of new-onset CVD in participants without diabetes. Furthermore, TyG-WC and TyG-WHtR showed better predictive performances for new-onset CVD than TyG and TyG-BMI in participants without diabetes.

Nanoengineered Macrophages Armed with TLR7/8 Agonist Enhance Remodeling of Immunosuppressive Tumor Microenvironment.

Although adoptive cell-based therapy is illuminated as one of the promising approaches in cancer immunotherapy, it shows low antitumor efficacy because transferred cells adapt and alter toward a pro-tumoral phenotype in response to the tumor's immunosuppressive milieu. Herein, nanoengineered macrophages anchored with functional liposome armed with cholesterol-conjugated Toll-like receptor 7/8 agonist (masked TLR7/8a, m7/8a) are generated to overcome the shortcomings of current macrophage-based therapies and enhance the remodeling of the immunosuppressive tumor microenvironment (TME). The liposome-anchored macrophages (LAMΦ-m7/8a), are fabricated by anchoring dibenzocyclooctyne-modified liposome(m7/8a) onto azido-expressing macrophages via a bio-orthogonal click reaction, are continuously invigorated due to the slow internalization of liposome(m7/8a) and sustained activation. LAMΦ-m7/8a secreted ≈3 and 33-fold more IL-6 and TNF-α than conventional M1-MΦ, maintained the M1 phenotype, and phagocytosed tumor cells for up to 48 h in vitro. Both intratumoral and intravenous injections of LAMΦ-m7/8a induced effective antitumor efficacy when treated in combination with doxorubicin-loaded liposomes in 4T1-tumor bearing mice. It not only increases the infiltration of antigen-specific CD8+ T cells secreting granzyme B, IFN-γ, and TNF-α within the TME, but also reduces myeloid-derived suppressor cells. These results suggest that LAMΦ-m7/8a may provide a suitable alternative to next-generation cell-based therapy platform.

Assessment of the viability of integrating virtual reality programs in practical tests for the Korean Radiological Technologists Licensing Examination: a survey study

PURPOSE: The objective of this study was to assess the feasibility of incorporating virtual reality/augmented reality (VR/AR) programs into practical tests administered as part of the Korean Radiological Technologists Licensing Examination (KRTLE). This evaluation is grounded in a comprehensive survey that targeted enrolled students in departments of radiology across the nation. METHODS: In total, 682 students from radiology departments across the nation were participants in the survey. An online survey platform was used, and the questionnaire was structured into 5 distinct sections and 27 questions. A frequency analysis for each section of the survey was conducted using IBM SPSS ver. 27.0. RESULTS: Direct or indirect exposure to VR/AR content was reported by 67.7% of all respondents. Furthermore, 55.4% of the respondents expressed that VR/AR could be integrated into their classes, which signified a widespread acknowledgment of VR among the students. With regards to the integration of a VR/AR or mixed reality program into the practical tests for purposes of the KRTLE, a substantial amount of the respondents (57.3%) exhibited a positive inclination and recommended its introduction. CONCLUSION: The application of VR/AR programs within practical tests of the KRTLE will be used as an alternative for evaluating clinical examination procedures and validating job skills.

Oxidative balance score inversely associated with the prevalence and incidence of metabolic syndrome: analysis of two studies of the Korean population.

Background: Pro-oxidant/antioxidant imbalances leading to chronic inflammation and insulin resistance can contribute to the development of metabolic syndrome (MetS). Oxidative Balance Score (OBS), a comprehensive measure of exposure to pro- and anti-oxidants, represents an individual's total oxidative balance. This study aimed to evaluate the association between OBS and MetS using two large datasets. Methods: We analyzed data from 2,735 adults older than 19 years from the 2021 Korean National Health and Nutritional Examination Survey (KNHANES) and 5,807 adults aged 40-69 years from the Korean Genome and Epidemiology Study (KoGES). In each dataset, OBS was categorized into sex-specific tertiles (T). Results: In KNHANES, the odds ratios and 95% confidence intervals for prevalent MetS in T3, compared to T1, were 0.44 (0.29-0.65) in men and 0.34 (0.23-0.50) in women after adjusting for confounders. In KoGES, the hazard ratios and 95% confidence intervals for incident MetS in T3, compared to T1, were 0.56 (0.48-0.65) in men and 0.63 (0.55-0.73) in women after adjusting for confounders. Conclusion: OBS appears to be inversely related to MetS, which suggests that adopting lifestyle behaviors that decrease oxidative stress could be an important preventive strategy for MetS.

Inverse Association between Oxidative Balance Score and Incident Type 2 Diabetes Mellitus.

Mitigating the risk of type 2 diabetes mellitus (T2DM) can be achieved through the maintenance of a healthy weight, the adoption of a healthy diet, and engaging in regular physical activity. The oxidative balance score (OBS), an integrated measure of pro- and antioxidant exposure conditions, represents an individual's overall oxidative balance status. This study aimed to evaluate the association between OBS and T2DM incidence using data from a large, community-based, prospective cohort study. Data from 7369 participants aged 40-69 years who engaged in the Korean Genome and Epidemiology Study (KoGES) were analyzed. The hazard ratio (HR) and 95% confidence interval (CI) for T2DM incidence of sex-specific OBS tertile groups were calculated using univariable and multivariable Cox proportional hazard regression analyses. During the mean 13.6-year follow-up period, 908 men and 880 women developed T2DM. The fully-adjusted HR (95% CI) for incident T2DM of the middle and highest tertile groups, compared with the referent lowest tertile group, were 0.86 (0.77-1.02) and 0.83 (0.70-0.99) in men and were 0.94 (0.80-1.11) and 0.78 (0.65-0.94) in women, respectively. Individuals with a high OBS are at lower risk for the development of T2DM. This implies that lifestyle modification with more antioxidant properties could be a preventive strategy for T2DM.

Adaptive Beam Divergence Control to Mitigate Scintillation Effect Caused by Pointing Error in Vertical FSO Transmissions.

Free-space optical (FSO) communication has been studied for next-generation network systems. Because an FSO system establishes point-to-point communication links, maintaining alignment among the transceivers is a critical challenge. In addition, atmospheric turbulence causes significant signal loss in FSO vertical links. Even in clear weather conditions, transmitted optical signals suffer significant scintillation losses due to random variations. Thus, the effect of atmospheric turbulence should be considered in vertical links. In this paper, we analyze the relationship between pointing error and scintillation from the aspect of beam divergence angle. Furthermore, we propose an adaptive beam that optimizes its divergence angle according to the pointing error between the communicating optical transceivers to mitigate the effect of scintillation due to pointing error. We performed a beam divergence angle optimization and compared it with adaptive beamwidth. The proposed technique was demonstrated using simulations, which revealed an enhanced signal-to-noise ratio and the mitigation of the scintillation effect. The proposed technique would be useful in minimizing the scintillation effect in vertical FSO links.

Pure copper nanoparticles prepared by coating-assisted vapor phase synthesis without agglomeration.

Modern electronic devices, such as smartphones and electric vehicles, require multilayer ceramic capacitors (MLCCs), which comprise highly pure Cu terminations and Ni electrodes. Vapor-phase synthesis (VPS) is a promising method for synthesizing nanoparticles (NPs) with high purity and crystallinity. However, the agglomeration of the NPs occurs during their synthesis, which degrades the performance of the MLCC electrodes owing to several factors, including electrical shorts and low packing density. This paper proposes a coating-assisted VPS to inhibit agglomeration using potassium chloride (KCl) as the coating agent. The agglomeration ratio of the Cu NPs synthesized by in-flight coating with KCl at 950 °C significantly decreased from 48.20% to 3.80%, compared to without KCl coating. Furthermore, X-ray fluorescence and X-ray diffraction analyses confirmed that the KCl coating agent and residual copper chloride were removed by washing with ammonium hydroxide.

New markers in metabolic syndrome.

Metabolic syndrome (MetS) is increasing globally and is clinically significant due to its association with cardiovascular disease, type 2 diabetes and cancer. Although the pathogenesis of MetS has not been clearly elucidated, insulin resistance and chronic low-grade inflammation derived from central obesity are the most widely accepted as underlying pathophysiology. Accordingly, insulin resistance indices, adipokines and various inflammatory markers have been suggested as reliable biomarkers for MetS. Others, such as uric acid, alkaline phosphatase, γ-glutamyl transferase, are also known to positively correlate with MetS and could be diagnostically useful. In this review, we provide a comprehensive overview of MetS biomarkers and the development of a systematic approach to laboratory analysis.

Effects of Induction Culture on Osteogenesis of Scaffold-Free Engineered Tissue for Bone Regeneration Applications.

BACKGROUND: Restoration of the bone defects caused by infection or disease remains a challenge in orthopedic surgery. In recent studies, scaffold-free engineered tissue with a self-secreted extracellular matrix has been proposed as an alternative strategy for tissue regeneration and reconstruction. Our study aimed to engineer and fabricate self-assembled osteogenic and scaffold-free tissue for bone regeneration. METHODS: Osteogenic scaffold-free tissue was engineered and fabricated using fetal cartilage-derived progenitor cells, which are capable of osteogenic differentiation. They were cultured in osteogenic induction environments or using demineralized bone powder for differentiation. The fabricated tissue was subjected to real-time qPCR, biochemical, and histological analyses to estimate the degree of in vitro osteogenic differentiation. To demonstrate bone formation in an in vivo environment, scaffold-free tissue was transplanted into the dorsal subcutaneous site of nude mice. Bone development was monitored postoperatively over 8 weeks by the observation of calcium deposition in the matrix. RESULTS: In the in vitro experiments, engineered osteogenically induced scaffold-free tissue demonstrated three-dimensional morphological characteristics, and sufficient osteogenic differentiation was confirmed through the quantification of specific osteogenic gene markers expressed and calcium accumulation within the matrix. Following the evaluation of differentiation efficacy, in vivo experiments revealed distinct bone formation, and that blood vessels had penetrated the fabricated tissue. CONCLUSION: The novel engineering of scaffold-free tissue with osteogenic potential can be used as an optimal bone graft substitute for bone regeneration.

Inhibition of GP130/STAT3 and EMT by combined bazedoxifene and paclitaxel treatment in ovarian cancer.

The interleukin 6 (IL­6)/glycoprotein 130 (GP130)/signal transducer and activator of transcription 3 (STAT3) signalling pathway, with GP130 as an intermediate membrane receptor, is involved in the survival, metastasis, and resistance of ovarian cancer. Bazedoxifene, an FDA­approved drug, is an inhibitor of GP130 and a selective estrogen modulator (SERM). We studied the mechanism of the combination therapy of bazedoxifene and paclitaxel in inhibiting the IL­6­mediated GP130/STAT3 signaling pathway in ovarian cancer. Surface plasmon resonance (SPR) was used to assess the binding of bazedoxifene to GP130. Migration, invasion, and apoptosis of ovarian cancer cells were assessed using bazedoxifene and paclitaxel. In addition, we determined the effects of bazedoxifene and paclitaxel alone or in combination on the GP130/STAT3 pathway and epithelial­mesenchymal transition (EMT). The results revealed that the combination of bazedoxifene and paclitaxel suppressed cell viability, migration, and invasion in the ovarian cancer cells. In addition, the combination treatment increased apoptosis. Furthermore, bazedoxifene combined with paclitaxel inhibited the growth of ovarian cancer cells in a xenograft tumour model. This combination reduced STAT3 phosphorylation and suppressed gene expression and EMT. In conclusion, inhibition of GP130/STAT3 signalling and EMT via a combination of bazedoxifene and paclitaxel could be used as a therapeutic strategy by which to overcome ovarian cancer.

Association Between the Severity of Periodontitis and Osteoarthritis in Middle-Aged and Older Patients With Type 2 Diabetes Mellitus: A Nationwide Population-Based Study.

OBJECTIVE: Periodontitis and osteoarthritis are major public health concerns that result in decreased quality of life among middle-aged and older adults. We sought to examine whether the severity of periodontitis is related to osteoarthritis according to the presence of type 2 diabetes mellitus. METHODS: This study included 3,527 participants age ≥50 years from the Korean National Health and Nutrition Examination Survey. Periodontitis was assessed using the Community Periodontal Index; severe periodontitis was defined as periodontal tissue forming deep periodontal pockets ≥6-mm depth. Osteoarthritis was defined as Kellgren/Lawrence grade ≥2 on radiographic images of the knee or hip area with joint pain. The odds ratios (ORs) and 95% confidence intervals (95% CIs) for osteoarthritis according to the severity of periodontitis, stratified by type 2 diabetes mellitus, were calculated using multiple logistic regression analyses. RESULTS: Participants with type 2 diabetes mellitus were more likely to have osteoarthritis as the severity of periodontitis increased (nonsevere periodontitis OR 1.23 [95% CI 0.67-2.32]; severe periodontitis OR 3.01 [95% CI 1.51-5.84]) after adjusting for age, sex, body mass index, smoking status, alcohol consumption, regular exercise, education level, household income, hypertension, and frequent tooth-brushing. However, this positive association was not found in individuals without type 2 diabetes mellitus after adjusting for the same covariables. CONCLUSION: Severe periodontitis was positively and significantly associated with osteoarthritis in middle-aged and older individuals with type 2 diabetes mellitus. Our findings suggest that the oral inflammation manifesting in periodontitis may be at least partly involved in the pathogenesis of osteoarthritis, particularly in patients with type 2 diabetes mellitus.

Tinnitus and Its Association With Mental Health and Health-Related Quality of Life in an Older Population: A Nationwide Cross-Sectional Study.

This study investigated the relationship of tinnitus with mental health and health-related quality of life (QoL) in older people. Data source included 5,129 community-dwelling men and women ≥60 years old from the Korean National Health and Nutrition Examination Survey. Tinnitus was categorized into three groups: normal, tolerable tinnitus, and annoying tinnitus. Mental health and health-related QoL were assessed according to three dimensions (depressive mood, psychological distress, and suicidal ideation) and five domains (impaired mobility, impaired self-care, impaired usual activities, pain/discomfort, and anxiety/depression). The odds ratios (ORs) and 95% confidence intervals (CIs) of mental health and health-related QoL were calculated using multiple logistic regression analyses. Annoying tinnitus was positively and independently associated with deteriorated mental health and health-related QoL, suggesting comprehensive care is needed in older people with annoying tinnitus.

Chemical Vapor Synthesis of Nonagglomerated Nickel Nanoparticles by In-Flight Coating.

Nickel (Ni) nanoparticles (NPs) prepared through vapor-phase synthesis (VPS) are preferred for multilayer ceramic capacitor electrodes due to their high purity and crystallinity advantages. Agglomerated Ni NPs are usually generated using VPS but are undesirable because they cause various problems such as low packing density and electrical shorts. This study proposes the use of coating-assisted chemical vapor synthesis (CVS) for agglomerate inhibition using NaCl or KCl as a coating agent. We have found that the agglomeration ratio, 34.40%, for conventional CVS, can be reduced to 4.80% in the proposed method by in-flight coating with KCl at 900 °C by image analysis using field-emission scanning electron microscopy. Furthermore, the X-ray diffraction and X-ray fluorescence analyses confirm that the NaCl and KCl coating agent can be removed by washing with distilled water. We believe that this coating process can be used to inhibit the formation of agglomerates during the CVS of Ni NPs.

Using Dietary Macronutrient Patterns to Predict Sarcopenic Obesity in Older Adults: A Representative Korean Nationwide Population-Based Study.

Older adults with sarcopenic obesity (SO) are at increased risk of adverse health outcomes. It has not been identified which pattern of macronutrient intake is appropriate in relation to SO. We aimed to compare the patterns of macronutrient intake for predicting SO in older adults. Data from a total of 3828 older adults who participated in the 2008-2011 Korea National Health and Nutrition Examination Survey were analyzed. The one-day 24 h dietary recall method was used to assess macronutrient intake. SO was defined by a combination of body mass index (BMI) ≥ 25 kg/m2 and BMI adjusted-appendicular skeletal muscle mass <0.789 for men and <0.512 for women. Weighted logistic regression analysis revealed the odds ratio (95% confidence interval) for SO of total calorie intake per 100 increments and carbohydrate (CHO) intake (g/kg/day) per 1 increment to be 0.95 (0.91-0.99) and 0.83 (0.74-0.94), respectively, after adjusting for confounding variables in women. The predictive power for SO of CHO intake (g/kg/day) was higher compared with the other patterns of macronutrient intake both in men and women. In conclusion, total calorie intake and CHO intake (g/kg/day) are inversely related to SO in women. CHO intake (g/kg/day) could be the best index for determining SO.

The complete mitochondrial genome of Japanese sea lion, Zalophus japonicus (Carnivora: Otariidae) analyzed using the excavated skeletal remains from Ulleungdo, South Korea.

The Japanese sea lion, Zalophus japonicus, is an extinct pinniped species, which had inhabited along the coast of the Japanese archipelago and Korean peninsula. Its mitochondrial genome was determined by the assembly of PCR amplicons from the skeletal remains excavated from the Ulleungdo, South Korea. The whole mitogenome was 16,698 bp in length, which encoded 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNA), 2 ribosomal RNAs (rRNA), an origin of light-strand replication (OL), and a control region (D-loop). Unusual start codons were identified in ND2 (ATA), ND3 (ATA), and ND5 (ATC), while COIII, ND3, and ND4 were terminated with an incomplete stop codon (T-/TA-). Phylogenetic analysis showed that Z. japonicus was a sister species to Z. californianus with 98.61% nucleotide sequence identity among 11 pinniped species in the infraorder Pinnipedia, which supported the previous results. The complete mitochondrial genome sequence of Z. japonicus would be valuable information for its restoration and the evolutional understandings of pinniped species in the Pacific Ocean.

The triglyceride-glucose index is a more powerful surrogate marker for predicting the prevalence and incidence of type 2 diabetes mellitus than the homeostatic model assessment of insulin resistance.

AIMS: Insulin resistance is an independent risk factor for developing type 2 diabetes. Therefore, this study compared the predictability of the triglyceride-glucose (TyG) index and the homeostatic model assessment of insulin resistance (HOMA-IR) for the prevalence and incidence of type 2 diabetes. METHODS: We analyzed data from 9730 adults aged 40-69 years at baseline and 7783 participants without diabetes who were followed up in the Korean Genome and Epidemiology Study survey. From 2001 to 2002 (baseline survey) to 2013-2014, this survey was conducted biennially (six follow-ups). The average follow-up period was 9.0 years. RESULTS: The TyG index showed better predictability for the prevalence of type 2 diabetes than HOMA-IR (TyG index: 0.784, HOMA-IR: 0.728, p < 0.001). The area under the time-dependent receiver operating characteristic curve of the TyG index for incident type 2 diabetes was 0.640 (0.628-0.652), which was significantly higher than that of HOMA-IR [0.531 (0.521-0.541)] (p < 0.001). CONCLUSIONS: The TyG index is superior to HOMA-IR for predicting type 2 diabetes. The TyG index could, therefore, be more useful for the early detection and prevention of type 2 diabetes.

Antioxidant activity and short-chain fatty acid production of lactic acid bacteria isolated from Korean individuals and fermented foods.

Compounds of the cell walls of heat-killed lactic acid bacteria show immunomodulatory properties which boost immunological systems, and are used ad postbiotics (paraprobiotics). In this study, we used 17 different heat-killed isolates as postbiotics and evaluated their anti-inflammatory potential on the expression of proinflammatory mediators and cellular signaling pathways of murine macrophage, RAW 264.7 cells. Bifidobacterium bifidum MG731 showed the high 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity (90.6%), followed by Bifidobacterium lactis MG741 (59.6%). The Bi. lactis MG741 showed the high ABTS free radical scavenging activity (99.5%), followed by Lactobacillus plantarum MG989 (98.9%), Lactobacillus salivarius MG242 (97.1%), and Bi. bifidum MG731 (96.1%). In addition, Bi. bifidum MG731 showed the lowest nitric oxide production (4.28 µM), followed by B. lactis MG741 (10.80 µM), L. salivarius MG242 (14.60 µM), and L. plantarum MG989 (19.60 µM). The selected strains showed a decreased nitric oxide production via downregulation of inducible nitric oxide synthase and cyclooxygenase 2, which were upregulated via LPS-stimulated RAW 264.7 macrophages. Short-chain fatty acids (SCFA) including acetic, propionic, and butyric acid were produced by four strains. The Bi. bifidum MG731 showed total SCFAs production (4998.6 µg/g), Bi. lactis MG741 (2613.9 µg/g), L. salivarius MG242 (1456.1 µg/g), and L. plantarum MG989 (630.2 µg/g). These results indicated that the various selected strains may possess an anti-inflammatory potential and provide a molecular basis for the development of functional probiotics.

Inverse association between serum bilirubin level and testosterone deficiency in middle-aged and older men.

Low serum bilirubin levels have been associated with increased risk of cardiovascular disease (CVD) and metabolic syndrome. Testosterone deficiency could also contribute to increased risk of CVD and metabolic syndrome. Therefore, this study aimed to examine the relationship between serum bilirubin level and testosterone deficiency in 1284 Korean men aged 45 to 70 years. Serum bilirubin level was categorized into quartiles: Q1 ≤ 0.7, Q2 0.8-0.9, Q3 1.0-1.1, and Q4 ≥ 1.2 mg/dL. Testosterone deficiency was defined as level less than 8.0 nmol/L, as suggested by the position statement of International Society of Andrology. The overall prevalence of testosterone deficiency was 5.8% and significantly decreased with the quartiles from Q1 to Q4. Compared with the referent fourth quartile (serum bilirubin ≥ 1.2 mg/dL), the ORs (95% CIs) for testosterone deficiency was 2.29 (1.04-4.94) for the first quartile after adjusting for age, fasting glucose, triglyceride, HDL-cholesterol, leukocyte count, hemoglobin, smoking status, and alcohol intake. We found inversely graded associations of serum bilirubin level with testosterone deficiency. These findings suggest that low bilirubin level may be interpreted as a state of testosterone deficiency in middle-aged and older men.