Emissions of Liquid Crystal Monomers from Obsolete Smartphone Screens in Indoor Settings: Characteristics and Human Exposure Risk.

Liquid crystal monomers (LCMs) have been found to accumulate in indoor environments, but the emission kinetics of LCMs from electronic devices are not well understood. Leakage from damaged liquid crystal displays may be an important mechanism for LCMs to enter the environment and become potential health hazards to humans. To address this issue, we conducted chamber experiments to characterize the emissions of LCMs from obsolete smartphone screens and estimated the doses of residential and occupational exposures to LCMs. The emission rates of the detected LCMs were in the ranges of 0.1-7 µg m-2 h-1 at 80 °C, 0.05-7 µg m-2 h-1 at 60 °C, and 0.002-0.2 µg m-2 h-1 at 25 °C. Liquid crystal monomers with large molecular weights and low volatilities tended to accumulate at screen surfaces and were re-emitted at elevated temperatures, leading to high emission rates of heavy LCMs upon thermal treatment. The estimated doses of residential and occupational exposures to individual LCMs were 0.0001-0.009 and 0.007-2 ng kg-1 d-1, respectively. As LCMs are potentially carcinogenic based on in silico assessments, LCMs emitted from obsolete smartphones in indoor settings may become human health hazards.

Astragaloside IV improved antioxidative stress capacity and related gene expression of the Keap1-Nrf2 pathway in grass carp (Ctenopharyngodon idella) hepatocytes under heat stress.

This study aims to investigate the protective effects of astragaloside IV (AS-IV) on the hepatocytes of grass carp (Ctenopharyngodon idella) on heat stress. Cultured cells were treated with AS-IV (0, 50, 100 and 200 µg/ml) at 28°C for 24 h and then exposed to heat stress by increasing the culturing temperature (32 ± 0.5°C) for 6 h. The increased temperatures significantly reduced cell viability and superoxide dismutase (SOD) activity, and increased malondialdehyde (MDA) levels in the 0 µg/ml AS-IV treatment group at 32°C, but the grass carp hepatocytes treated with 100 and 200 µg/ml AS-IV had significantly increased cell viability and SOD activity and decreased MDA levels. The mRNA levels of keap1a, keap1b, nrf2, gsh-px, cat, cu-zn sod, mgst1 and il-6 were significantly lower in the 0 µg/ml AS-IV treatment group at 32°C, while those of keap1a, nrf2, gsh-px, cat, cu-zn sod, gstp1, ho-1 and il-6 were significantly higher in cells treated with 100 or 200 µg/ml AS-IV. Our findings indicate that AS-IV could enhance the antioxidative stress capacity of grass carp hepatocytes under heat stress, and its mechanism may be associated with the activation of the Keap1-Nrf2 pathway. Thus, these results provide new insights into how to alleviate heat stress in grass carp.

Children with cow's milk allergy following an elimination diet had normal growth but relatively low plasma leptin at age two.

AIM: To assess nutrient intake, growth and nutritional status of infants with cow's milk allergy (CMA) who follow a therapeutic elimination diet since the first few months of life. METHODS: Sixty infants younger than four months of age with challenge-proven CMA and 60 healthy age-matched children were investigated. Anthropometric and body composition (BC) were assessed up to 24 months. Dietary intake was recorded by the parents for three consecutive days before visits at 6, 12, 18 and 24 months. Blood albumin, prealbumin, retinol binding protein and metabolic-related hormones were examined at 24 months. RESULTS: The average age at enrolment was 2.9 ± 1.0 months. At the end of the follow-up, there were no differences in daily milk consumption, nutrient intake, weight and height z scores or BC measures between the groups; however, the plasma leptin level was lower in infants with CMA (1.67 ± 1.03 vs 2.05 ± 1.48) (ng/mL) (p < 0.05) compared to healthy children. CONCLUSIONS: Children with CMA who followed an elimination diet could achieve a normal nutritional status, except for relatively lower plasma leptin levels, at the age of 2. Further studies with larger cohorts and research on the long-term consequences of these early differences are needed.

Abnormal Pupil Finding After an Orbital Floor Fracture in a Child.

PURPOSE: Trauma to the pupillary fibers can occur during repair of orbital floor fracture resulting in a fixed and dilated pupil. The authors report, discuss, and propose an etiology of an abnormal pupil in a child with an orbital floor fracture before surgical repair. METHODS: A case report is described. RESULTS: Although the orbital fracture was repaired, anisocoria persisted 18 months after the initial trauma. CONCLUSIONS: Pupillary function must be assessed before surgical repair of an orbital floor fracture as damage of the pupillary fibers can occur secondary to the orbital floor fracture.

Label-Free Fluorescent Detection of Trypsin Activity Based on DNA-Stabilized Silver Nanocluster-Peptide Conjugates.

Trypsin is important during the regulation of pancreatic exocrine function. The detection of trypsin activity is currently limited because of the need for the substrate to be labeled with a fluorescent tag. A label-free fluorescent method has been developed to monitor trypsin activity. The designed peptide probe consists of six arginine molecules and a cysteine terminus and can be conjugated to DNA-stabilized silver nanoclusters (DNA-AgNCs) by Ag-S bonding to enhance fluorescence. The peptide probe can also be adsorbed to the surface of graphene oxide (GO), thus resulting in the fluorescence quenching of DNA-AgNCs-peptide conjugate because of Förster resonance energy transfer. Once trypsin had degraded the peptide probe into amino acid residues, the DNA-AgNCs were released from the surface of GO, and the enhanced fluorescence of DNA-AgNCs was restored. Trypsin can be determined with a linear range of 0.0-50.0 ng/mL with a concentration as low as 1 ng/mL. This label-free method is simple and sensitive and has been successfully used for the determination of trypsin in serum. The method can also be modified to detect other proteases.

Factors associated with prehospital delay in patients with ST-segment elevation acute myocardial infarction in China.

BACKGROUND: Prehospital delay is the most critical factor to prognosis of ST-elevation myocardial infarction (STEMI). Few study had examined a series of predictors of prehospital delay by multivariate analysis of sociodemographic and clinical characteristics, onset features, and symptom condition of STEMI in China. METHODS: A total of 1088 hospitalized STEMI participants were screened to collect sociodemographic data, medical history information, and symptom onset status from clinical medical records. Factors associated with prehospital delay were examined using bivariate and multivariate analysis method. RESULTS: The median prehospital delay time (PDT) was 130 minutes in STEMI participants. Multivariate regression models examining 8 predictors were associated with prehospital delay, including senior high school or above educational level, myocardial infarction (MI) history, vertigo onset symptom, ambulance transportation, onset in daytime (6:00-18:00), onset at home, anterior wall MI, and posterior wall MI. Mortality in PDT more than 120 minutes group was 5.5%, whereas it was 4.3% in PDT 120 minutes of less group without significant statistically difference (P > .05). CONCLUSIONS: Multivariate analysis results found that symptom onset-related variables strongly influenced PDT. Onset-related status of STEMI needed to be combined into interventions of participants, and more emergency education should be recommended to both participants and their relatives. Most importantly, more efforts should be taken to educate the public about the symptoms and signs to increase the recognition of STEMI.

Characteristic structures of liquid crystal monomers in EI-MS analysis and the potential application in suspect screening.

Liquid crystal monomers (LCMs) are of emerging concern due to their ubiquitous presence in indoor and outdoor environments and their potential negative impacts on human health and ecosystems. Suspect screening approaches have been developed to monitor thousands of LCMs that could enter the environment, but an updated suspect list of LCMs is difficult to maintain given the rapid development of material innovations. To facilitate suspect screening for LCMs, in-silico mass fragmentation model and quantitative structure-activity relationship (QSPR) models were applied to predict electron ionization (EI) mass spectra of LCMs. The in-silico model showed limited predictive power for EI mass spectra, while the QSPR models trained with 437 published mass spectra of LCMs achieved an acceptable absolute error of 12 percentage points in predicting the relative intensity of the molecular ion, but failed to predict the mass-to-charge ratio of the base peak. A total of 41 characteristic structures were identified from an updated suspect list of 1606 LCMs. Multi-phenyl groups form the rigid cores of 85% of LCMs and produce 154 characteristic peaks in EI mass spectra. Monitoring the characteristic structures and fragments of LCMs may help identify new LCMs with the same rigid cores as those in the suspect list.

Efficacy and safety of carrimycin in ten patients with severe pneumonia following solid organ transplantation.

BACKGROUND: The number of patients undergoing solid organ transplantation has increased annually. However, infections in solid organ transplant recipients can have a severe effect on patient survival owing to the continued use of immunosuppressants. Carrimycin is a novel macrolide antibiotic produced by genetically engineered streptomyces spiramyceticus harboring a 4''-O-isovaleryltransferase gene (ist) from streptomyces thermotoleran. Carrimycin has good antibacterial and antiviral effects. However, no relevant studies have been conducted on the efficacy and safety of carrimycin in patients with severe pneumonia (SP) after solid organ transplantation. AIM: To explore the efficacy and safety of carrimycin in patients with SP after solid organ transplantation to provide a medication reference for clinical treatment. METHODS: In March 2022, ten patients with SP following solid-organ transplantation were treated at our hospital between January 2021 and March 2022. When the condition was critical and difficult to control with other drugs, carrimycin was administered. These ten patients' clinical features and treatment protocols were retrospectively analyzed, and the efficacy and safety of carrimycin for treating SP following solid organ transplantation were evaluated. RESULTS: All ten patients were included in the analysis. Regarding etiological agent detection, there were three cases of fungal pneumonia, two cases of bacterial pneumonia, two cases of Pneumocystis pneumonia, and three cases of mixed infections. After treatment with carrimycin, the disease in seven patients significantly improved, the course of the disease was significantly shortened, fever was quickly controlled, chest computed tomography was significantly improved, and oxygenation was significantly improved. Finally, the patients were discharged after curing. One patient died of acute respiratory distress syndrome, and two patients discontinued treatment. CONCLUSION: Carrimycin is a safe and effective treatment modality for SP following solid organ transplantation. Carrimycin may have antibacterial and antiviral effects in patients with SP following solid organ transplantation.

Per- and polyfluoroalkyl substances (PFAS) exposure in plasma and their blood-brain barrier transmission efficiency-A pilot study.

Per- and polyfluoroalkyl substances (PFAS) have been shown to penetrate the blood-brain barrier (BBB) and accumulate in human brain. The BBB transmission and accumulation efficiency of PFAS, as well as the potential health risks from human co-exposure to legacy and emerging PFAS due to differences in transport efficiency, need to be further elucidated. In the present pilot study, 23 plasma samples from glioma patients were analyzed for 17 PFAS. The concentrations of PFAS in six paired brain tissue and plasma samples were used to calculate the BBB transmission efficiency of PFAS (RPFAS). This RPFAS analysis was conducted with utmost care and consideration amid the limited availability of valuable paired samples. The results indicated that low molecular weight PFAS, including short-chain and emerging PFAS, may have a greater potential for accumulation in brain tissue than long-chain PFAS. As an alternative to perfluorooctane sulfonic acid (PFOS), 6:2 chlorinated polyfluorinated ether sulfonate (6:2 Cl-PFESA) exhibited brain accumulation potential similar to that of PFOS, suggesting it may not be a suitable substitute concerning health risk in brain. The BBB transmission efficiencies of perfluorooctanoic acid, PFOS, and 6:2 Cl-PFESA showed similar trends with age, which may be an important factor influencing the entry of exogenous compounds into the brain. A favorable link between perfluorooctane sulfonamide (FOSA) and the development and/or progression of glioma may be implicated by a strong positive correlation (r2 = 0.94; p < 0.01) between RFOSA and Ki-67 (a molecular marker of glioma). However, a causal relationship between RFOSA and glioma incidence were not established in the present study. The present pilot study conducted the first examination of BBB transmission efficiency of PFAS from plasma to brain tissue and highlighted the importance of reducing and/or controlling exposure to PFAS.

Flash visual evoked potentials in preterm infants.

OBJECTIVE: To describe the development of flash visual evoked potentials (FVEPs) in preterm infants from 1 to 18 months and to determine if the maturation of FVEPs is similar to that of term infants. DESIGN: Longitudinal follow-up study. PARTICIPANTS: Twenty very low birth weight (VLBW) preterm infants, 42 low birth weight (LBW) preterm infants, and 41 term infants underwent FVEP recordings and neurodevelopmental examinations at 1, 3, 6, 9, 12, and 18 months of corrected and chronological ages. METHODS: The FVEP recordings were carried out with the VikingQuest-IV neuroelectrophysiological device (VikingQuest, Nicolet, WI), and neurodevelopmental assessments were made by the Development Screen Test and Bayley Scales of Infant Development, Second Edition. MAIN OUTCOME MEASURES: At 1, 3, 6, and 9 months of age, neurodevelopment was measured with the Mental Index and Developmental Quotient. At 12 and 18 months, neurodevelopment was assessed using the Mental Developmental Index and Psychomotor Developmental Index. Two FVEP values were analyzed: the P2 amplitude (peak to peak from the preceding N2 wave) and the latency of the P2 wave. RESULTS: There was no significant difference for age-dependent decreased pattern of FVEP P2 latency between preterm infants and the control group. This pattern consisted of a rapid decrease in the first 6 months of life, a gradual decline from 6 to 12 months of age, and a steady reduction from 12 to 18 months of age. The P2 latencies were prolonged significantly at all 6 recorded times in the VLBW group compared with the controls and showed a delay in the LBW group at 1 and 3 months of corrected age. The maturation of P2 latency in LBW infants is similar to that of the controls at 3 months of corrected age, but the maturation of P2 latency in VLBW children remained delayed when compared with the controls until 18 months of corrected age. CONCLUSIONS: Although the FVEP development pattern of preterm infants was similar to that of healthy full-term infants, the former had deficits in visual electrophysiologic maturation, especially for VLBW children.

Predicted health and environmental hazards of liquid crystal materials via quantitative structure-property relationship modeling.

Liquid crystal materials (LCMs) are considered as emerging contaminants with high persistent and bioaccumulative potentials, but their toxicological effects are not well understood. To address this issue, a list of 1431 LCMs commercially available in the market was established through literature reviews and surveys of LCM suppliers. Toxicological properties of 221 target LCMs were derived from the Classification and Labeling Inventory by the European Chemicals Agency. More than 80 % of target LCMs likely pose adverse effects on human health or aquatic ecosystems. Two quantitative structure-property relationship (QSPR) models developed from the toxicological properties of LCMs achieved approximately 90 % accuracy in external data sets. The probability-based approach was more efficient in defining the applicability domain for the QSPR models than a range- or distance-based approach. The highest accuracy was achieved for chemicals within the probability-based applicability domain. The QSPR models were applied to predict health and environmental hazards of 1210 LCMs that had not been notified to the Classification and Labeling Inventory, and 301 and 94 LCMs were recognized as posing potential hazards to human health and the environment, respectively. The present study highlights the potential detrimental effects of LCMs and offers a specific in silico technique for screening hazardous LCMs.

Effect of muscle activation on dynamic responses of neck of pilot during emergency ejection: a finite element study.

To determine the effect of muscle activation on the dynamic responses of the neck of a pilot during simulated emergency ejections. A complete finite element model of the pilot's head and neck was developed and dynamically validated. Three muscle activation curves were designed to simulate different activation times and levels of muscles during pilot ejection: A is the unconscious activation curve of the neck muscles, B is the pre-activation curve, and C is the continuous activation curve. The acceleration-time curves obtained during ejection were applied to the model, and the influence of the muscles on the dynamic responses of the neck was investigated by analyzing both angles of rotation of the neck segments and disc stresses. Muscle pre-activation reduced fluctuations in the angle of rotation in each phase of the neck. Continuous muscle activation caused a 20% increase in the angle of rotation compared to pre-activation. Moreover, it resulted in a 35% increase in the load on the intervertebral disc. The maximum stress on the disc occurred in the C4-C5 phase. Continuous muscle activation increased both the axial load on the neck and the posterior extension angle of rotation of the neck. Muscle pre-activation during emergency ejection has a protective effect on the neck. However, continuous muscle activation increases the axial load and rotation angle of the neck. A complete finite element model of the pilot's head and neck was established and three neck muscle activation curves were designed to investigate the effects of muscle activation time and level on the dynamic response of the pilot's neck during ejection. This increased insights into the protection mechanism of neck muscles on the axial impact injury of the pilot's head and neck.

Enrichment of Circulating Tumor Cells of Lung Cancer and Correlation With Serum Leukomonocyte and Tumor Biomarkers: A Retrospective Study.

STUDY DESIGN: Circulating tumor cells is important in the clinical diagnosis of cancer and there are a number of circulating tumor cell detection systems associated with different isolation strategies being validated. There is a novel platform, the CytoBot 2000, which utilizes a combination of physical and immunological technologies to isolate and capture circulating tumor cells. METHODS: In this retrospective study, 39 lung cancer patients and 11 normal healthy individuals were enrolled and performed circulating tumor cell tests and immunofluorescence staining with CytoBot 2000. The performance of this device was assessed by receiver operating characteristic curve. The clinical relevance of circulating tumor cells was assessed by Chi-square. The correlations between circulating tumor cell number and blood lymphocytes and tumor biomarkers were analyzed by Pearson correlation coefficient. RESULTS: The number of circulating tumor cell is significantly increased in lung cancer patients (3.74 > 0.45, P < .0001). The CytoBot 2000 presented a 100% (39/39) circulating tumor cell detection rate in lung cancer patients and 36% (4/11) in healthy individual blood samples, the sensitivity and specificity were 89.7% and 90.9%, respectively, and with the area under curve of 0.966. Further, there was a positive correlation between circulating tumor cell count and carcinoembryonic antigen 211 (R2 = 0.125, P = .027), but not blood lymphocytes (P = .089). CONCLUSIONS: This automatic platform showed excellent performance of circulating tumor cell detection by clinical sample. The tumor biomarkers increased with the number of circulating tumor cell in the lung cancer patients.

Adjuvant activity of Sargassum pallidum polysaccharides against combined Newcastle disease, infectious bronchitis and avian influenza inactivated vaccines.

This study evaluates the effects of Sargassum pallidum polysaccharides (SPP) on the immune responses in a chicken model. The adjuvanticity of Sargassum pallidum polysaccharides in Newcastle disease (ND), infectious bronchitis (IB) and avian influenza (AI) was investigated by examining the antibody titers and lymphocyte proliferation following immunization in chickens. The chickens were administrated combined ND, IB and AI inactivated vaccines containing SPP at 10, 30 and 50 mg/mL, using an oil adjuvant vaccine as a control. The ND, IB and AI antibody titers and the lymphocyte proliferation were enhanced at 30 mg/mL SPP. In conclusion, an appropriate dose of SPP may be a safe and efficacious immune stimulator candidate that is suitable for vaccines to produce early and persistent prophylaxis.

[Clinicopathological analysis of aggressive angiomyxoma].

OBJECTIVE: To explore the clinicopathological characteristics of aggressive angiomyxoma (AAM) so as to boost the level of diagnosis and treatment. METHODS: Seven cases of aggressive angiomyxoma were studied with light microscope and immunohistochemistry. Antibody of Vimentin, Desmin, CD34, smooth muscle actin (SMA), estrogen receptor (ER), progesterone receptor (PR), androgen receptor (AR), S-100, p53 and Ki67 were used. RESULTS: There were 3 males and 4 females with an average age of 43.1 years. Three patients had urinary compressive complaints while others were symptom-free. All underwent surgical resection. Three patients were recurrent after operation. The tumor was generally nodular and its cut surface appeared jelly-like. Histologically, on myxoid stroma background, it was composed of a mixture of spindle and stellar cells without atypical cell and mitosis. There were various-sized vessels with thin to thick walls. The scattered muscle-like cells had a perivascular distribution. Immunohistochemistry showed that tumor cells were positive for Vimentin(+)7/7, Desmin(+)7/7, CD34(+)3/7, SMA(+)2/7, ER(+)6/7, p53(+)4/7, Ki67(+) 1% - 8% and negative for PR, AR and S-100. CONCLUSIONS: As a rare soft tissue tumor, AAM extremely rare in males. Owing to its local invasion and high recurrence, extensive resection and long-term follow-up are necessary.

[The effects of SV40 PolyA sequence and its AATAAA signal on upstream GFP gene expression and transcription termination].

SV40 PolyA (Simian virus 40 PolyA, also called PolyA) sequence is DNA sequence (240 bp) that possesses the activity of transcription termination and can add PolyA tail to mRNA. PolyA contains AATAAA hexanucleotide polyadenylation signal. Fourteen copies of Alu in sense orientation (Alu14) were inserted downstream of GFP in pEGFP-C1 to construct pAlu14 plasmid, and then HeLa cells were transiently transfected with pAlu14. Northern blot and fluorescence microscope were used to observe GFP RNA and protein expressions. Our results found that Alu tandem sequence inhibited remarkably GFP gene expression, but produced higher-molecular-mass GFP fusion RNA. PolyA and its sequence that was deleted AATAAA signal in sense or antisense orientation were inserted between GFP and Alu tandem sequence in pAlu14. The results showed that all the inserted PolyA sequences partly eliminated the inhibition induced by Alu14. PolyA sequences without AATAAA signal in sense or antisense orientation still induced transcription termination. Antisense PolyA (PolyAas) was divided into four fragments that all are 60 bp long and the middle two fragments were named 2F2R and 3F3R. 2F2R or 3F3R was inserted upstream of Alu tandem sequence in pAlu14. The molecular mass of GFP fusion RNA increased when the copy number of 2F2R increased. 2F2R can support transcription elongation when 2F2R is located upstream of other 2F2R. Nevertheless, 2F2R located upstream of Alu tandem sequence can induce transcription termination. Inserting one copy or 64 copies of 3F3R in upstream of Alu tandem sequence caused the production of lower-molecular-mass GFP RNA.

Measurement of octanol-air partition coefficients for liquid crystals based on gas chromatography-retention time and its implication in predicting long-range transport potential.

Liquid crystals (LCs) are widely used in the modern society, but their environmental fate and related human health effects remain inadequately recognized. To assist in better understanding the environmental fate of LCs, the octanol-air partition coefficients (KOA) of 21 target LCs were determined with a gas chromatography-retention time (GC-RT) approach. Four classes of traditional organic pollutants, including polycyclic aromatic hydrocarbons, organochlorides, polybrominated diphenyl ethers, and polychlorinated biphenyls were employed as reference or calibration compounds. Cluster analysis indicated that the reference and calibration compounds somewhat influenced the relative and absolute magnitudes of GC-RT results. A quantitative structure-property relationship (QSPR) model was constructed from the experimental results and outperformed a widely-used model, KOAWIN, in estimating log KOA of LCs. This model was used to predict log KOAs for 116 LCs with the same element compositions and similar structures as the target LCs. Overall persistence and long-range transport potential were predicted based on the measured and estimated log KOA values, yielding consistent results. Several LCs were shown to have comparable characteristic travel distances and transport efficiencies as the traditional organic pollutants, suggesting they are potential environmental pollutants and the QSPR model is applicable in predicting the environmental fate of LCs.

Cosinor-rhythmometry for 24-h urinary sodium, potassium, creatinine excretion in the Chinese adult population.

BACKGROUND: The low accuracy of equations predicting 24-h urinary sodium excretion using a single spot urine sample contributed to the misclassification of individual sodium intake levels. The application of single spot urine sample is limited by a lack of representativity of urinary sodium excretion, possibly due to the circadian rhythm in urinary excretion. This study aimed to explore the circadian rhythm, characteristics, and parameters in a healthy young adult Chinese population as a theoretical foundation for developing new approaches. METHODS: Eighty-five participants (mean age 32.4 years) completed the 24-h urine collection by successively collecting each of the single-voided specimens within 24 h. The concentrations of the urinary sodium, potassium, and creatinine for each voided specimen were measured. Cosinor analysis was applied to explore the circadian rhythm of the urinary sodium, potassium, and creatinine excretion. The excretion per hour was computed for analyzing the change over time with repeated-measures analysis of variance and a cubic spline model. RESULTS: The metabolism of urinary sodium, potassium, and creatinine showed different patterns of circadian rhythm, although the urinary sodium excretion showed non-significant parameters in the cosinor model. A significant circadian rhythm of urinary creatinine excretion was observed, while the circadian rhythm of sodium was less significant than that of potassium. The circadian rhythm of urinary sodium and creatinine excretion showed synchronization to some extent, which had a nocturnal peak and fell to the lowest around noon to afternoon. In contrast, the peak of potassium was observed in the morning and dropped to the lowest point in the evening. The hourly urinary excretion followed a similar circadian rhythm. CONCLUSION: It is necessary to consider the circadian rhythm of urinary sodium, potassium, and creatinine excretion in adults while exploring the estimation model for 24-h urinary sodium excretion using spot urine.

Identification of six important amino acid residues of MenA from Bacillus subtilis natto for enzyme activity and formation of menaquinone.

The enzyme 1, 4-dihydroxy-2-naphthoic acid (DHNA) prenyltransferase (MenA) is a critical player in determining the efficiency of the menaquinone (MK) synthesis pathway and is an attractive target for the development of novel chemotherapeutics against pathogenic Gram-positive bacteria. However, there has been no report on structural properties or active region of MenA. To solve this challenge, we predicted the three-dimensiona structure and critical amino acid sites of MenA by bioinformatics analysis. Six amino acid sites were chosen by alligning the amino acid sequence of MenA from Bacillus subtilis natto with 4-hydroxybenzoate octaprenyl transferase (UbiA) from Escherichia coli, Aeropyrum pernix and Archaeoglobus fulgidus. Among them, four Asp sites located in two Asp-rich motifs (D78XXXXXD84 and D208XXXD212) were found to be indispensable amino acid residues in maintaining MenA activity. Site-directed mutagenesis of two other sites (Q67th, N74th) positively affected the catalytic activity of MenA and the MK titer. Q67R resulted in more than a 5-fold increase in specific 2-demethylmenaquinone (DMK) content (YP1/x) compared to wild-type, and the hydrophobic interaction between Cys63 and Arg67 could be the main reason according to the three-dimensional structure analysis. Moreover, a dramatic increase in specific MK content (YP2/x) was realized by co-expressing menG in EcMenA (Q67R). The results obtained could be useful not only in developing novel chemotherapeutics to combat potentially pathogenic Gram-positive bacteria, but also in regulating and optimizating E. coli mutant cultures for the efficient production of MK metabolites.