[Research advances in the non-invasive diagnosis of metabolic dysfunction-associated fatty liver disease based on magnetic resonance technology]

Metabolic dysfunction-associated fatty liver disease is becoming the most common cause of chronic liver disease worldwide, with a disease spectrum including simple steatosis, steatohepatitis, hepatic fibrosis/cirrhosis, and liver cancer. Most metabolic dysfunction-associated fatty liver diseases progress slowly, but steatohepatitis, especially in patients accompanied by significant liver fibrosis, has a significantly increased risk of adverse liver disease outcomes and all-cause death. Therefore, early-stage identification of medium-and high-risk groups carried out by stratified management has important clinical significance. Pathological diagnosis is the gold standard for diagnosing steatohepatitis and liver fibrosis. However, its invasiveness, sampling errors, and unsuitability for dynamic monitoring limit its clinical application. In recent years, a large number of non-invasive diagnostic methods based on somatology, serology, and imaging have shown great development prospects in order to meet the clinical needs of assessing disease severity and risk stratification. This article reviews and summarizes the application and progress of magnetic resonance imaging technology in the non-invasive diagnosis of metabolic dysfunction-associated fatty liver disease.

[Metabolic study of iron deposition based on magnetic resonance in patients with nonalcoholic fatty liver disease]

Objective: To explore the relationship between liver iron deposition and steatosis in patients with non-alcoholic fatty liver disease (NAFLD) through MRI. Methods: 163 cases of liver biopsy underwent MRI examination. R2* was used to measure liver iron content. Dixon-based proton density fat fraction (PDFF) was used to measure liver fat content. One-way ANOVA, r-correlation, ROC curve, and others were used to assess the relationship between clinical case data, serological indices, and imaging results in accordance with the pathological results of the liver biopsy. Results: R2* gradually increased as the pathological steatosis grade rose. The R2* that corresponded to no steatosis (< 5%), mild steatosis (14.95%±8.55%), moderate steatosis (46.30%±9.32%), and severe steatosis (73.86%±6.35%) were 27.56±4.40, 31.06±5.95, 38.06±4.80, and 48.10±5.55 (P < 0.001), respectively. There was a positive correlation between R2* and liver steatosis content (r= 0.769, P < 0.05). The area under the ROC curve and cut-off value were 0.88 and 31.77, respectively, and there was no distinct relationship with liver inflammation or fibrosis. Conclusion: R2* can quantitatively and non-invasively evaluate liver iron deposition in patients with NAFLD. A distinct relationship exists between liver steatosis and iron deposition, and iron deposition tends to increase as the steatosis aggravates.

[Improvement situation on indexes of the zebrafish disease model of non-alcoholic fatty liver disease with FGF21 analogues]

Objective: To detect the therapeutic efficacy of FGF21 analogues on the zebrafish model of non-alcoholic fatty liver disease. Methods: A zebrafish model of non-alcoholic fatty liver disease was established by providing the normal diet fed to wild-type zebrafish three times daily. PF-05231023 was administered exogenously at a final concentration of 0.5 μmol/L. Body length, body weight, triglycerides, and other indexes were measured after 20 days. Pathological changes were evaluated in liver tissue sections by HE staining. Quantitative PCR was used to identify expressional changes in genes related to lipid metabolism, endoplasmic reticulum stress, and inflammation. Results: QPCR and immunofluorescence staining results showed that FGF21 was highly expressed in the zebrafish model group. The addition of the FGF21 analogue PF-05231023 significantly reduced the body length and body weight (P < 0.01), and the triglyceride content (P < 0.05) in the zebrafish model group. The liver HE staining results showed that PF-05231023 had alleviated the large and tiny bullae fat, lesions, and others in the zebrafish model group. The quantitative PCR results demonstrated that PF-05231023 reduced the expression of lipogenic factors (P < 0.01), inflammatory-related factors (P < 0.001), and genes related to endoplasmic reticulum stress (P < 0.05), but raised lipid-oxidation-related factors (P < 0.05) in the zebrafish model group. The addition of PF-05231023 reduced oleic acid-induced lipid and triglyceride levels in HepG2 cells. Conclusion: FGF21 analogue addition can improve indexes in the zebrafish disease model of non-alcoholic fatty liver disease.

[Status of HVPG clinical application in China in 2021]

Objective: The investigation and research on the application status of Hepatic Venous Pressure Gradient (HVPG) is very important to understand the real situation and future development of this technology in China. Methods: This study comprehensively investigated the basic situation of HVPG technology in China, including hospital distribution, hospital level, annual number of cases, catheters used, average cost, indications and existing problems. Results: According to the survey, there were 70 hospitals in China carrying out HVPG technology in 2021, distributed in 28 provinces (autonomous regions and municipalities directly under the central Government). A total of 4 398 cases of HVPG were performed in all the surveyed hospitals in 2021, of which 2 291 cases (52.1%) were tested by HVPG alone. The average cost of HVPG detection was (5 617.2±2 079.4) yuan. 96.3% of the teams completed HVPG detection with balloon method, and most of the teams used thrombectomy balloon catheter (80.3%). Conclusion: Through this investigation, the status of domestic clinical application of HVPG has been clarified, and it has been confirmed that many domestic medical institutions have mastered this technology, but it still needs to continue to promote and popularize HVPG technology in the future.

[Studying the correlation between ferritin and non-alcoholic fatty liver disease]

Objective: To analyze the correlation between serum ferritin and steatosis in non-alcoholic fatty liver disease. Methods: Data of 167 cases who underwent liver biopsy in the Affiliated Hospital of Hangzhou Normal University were collected. Hydrogen proton magnetic resonance spectroscopy were performed within one week. The pathological results of liver biopsy were used as the gold standard to analyze the case data, serological indicators, magnetic resonance spectroscopy-proton density fat fraction. Results: Pathological monitoring result showed that the serum ferritin in patients without steatosis, and with mild, moderate and severe steatosis were (206.20 ± 189.83), (286.65 ± 200.80), (326.55 ± 214.71), (391.50 ± 184.93) ng/ml, respectively, P < 0.005. Serum ferritin was correlated to body mass index, PDFF, alanine aminotransferase, gamma glutamyltransferase, low-density lipoprotein, high-density lipoprotein. The area under ​​the receiver operating characteristic curve with ferritin for the diagnosis of non-alcoholic fatty liver disease was 0.716, and the optimal diagnostic threshold was 214.56 ng/ml. The sensitivity and specificity were 80.1%, and 68.8%, respectively. There was no statistically significant difference between the intralobular inflammation, fibrosis, and ferritin. Prussian blue iron staining had no apparent deposition of iron particles. Conclusion: Ferritin has significant positive correlation with the results of pathological and magnetic resonance imaging for liver steatosis. Therefore, it can be used as a non-invasive diagnostic method for liver steatosis evaluation.

[Role of gut-liver-immune axis in the pathogenesis of nonalcoholic steatohepatitis]

Nonalcoholic fatty liver disease (NAFLD) has become the most common chronic liver disease in the world. Liver cirrhosis, liver cancer and a variety of extrahepatic chronic diseases are important risk factors for NAFLD. Currently, there is still a lack of effective therapeutic drugs. Liver inflammation is a key driving factor for the progression of NAFLD, so regulating liver inflammation may provide a potential means to delay and reverse the progression of nonalcoholic steatohepatitis (NASH). Studies have found that the gut-liver-immune axis plays an important role in the progression of NASH. Gut microbiota can use its metabolites to induce glycolipid toxicity, oxidative stress and intestinal barrier damage, while bacterial components such as lipopolysaccharides, peptidoglycans, bacterial DNA and extracellular vesicles can translocate into the liver through the damaged intestinal barrier, causing excessive activation of immune cells, thus aggravating liver inflammation and promoting the progress of NASH. This paper focuses on the gut-liver-immune axis to analyze the gut microbiota mediated liver immunity and its mechanism in the occurrence and development of NASH, so as to lay a theoretical foundation for the research and development of new therapeutic strategies for NASH.

[Metabolic-associated fatty liver disease-related liver cirrhosis and cryptogenic liver cirrhosis]

Metabolic-associated fatty liver disease (MAFLD) is currently the most common chronic liver disease in the world, which may eventually progress to cirrhosis, hepatocellular carcinoma and liver failure. Fatty liver disease was once considered to be the most common cause of cryptogenic cirrhosis. Recently, a new definition of MAFLD suggests that MAFLD-related liver cirrhosis is no longer a kind of cryptogenic cirrhosis, and it belong to two different concepts and may have different liver and extrahepatic adverse outcomes. In this paper, the definition, epidemiology, diagnosis, treatment and other aspects of MALFD-related liver cirrhosis and cryptogenic liver cirrhosis are described in order to facilitate clinical practice, improve the efficiency of clinical research, and benefit clinicians and patients.

[Application analysis of noninvasive prenatal testing for fetal chromosome copy number variations in Chinese laboratories]

Objective: To investigate the general situation, detection range, testing reagents, and clinical performance of non-invasive prenatal testing (NIPT) for fetal chromosomal copy number variations (CNVs) in Chinese laboratories. Methods: The National Center for Clinical Laboratories of the National Health Commission designed a questionnaire for the detection of CNVs by NIPT, which included the investigation of whether the laboratory has carried out NIPT to detect CNVs and its testing scope, reagents/platforms, intended uses, screening populations and clinical performance. The questionnaires were distributed to 355 laboratories in 31 provinces, autonomous regions, and municipalities across the country on October, 2020. Further, the feedbacks were statistical analyzed. Results: Two hundred and twenty-eight laboratories had performed NIPT to detect CNVs, including 116 types of CNVs, and more than 95% of laboratories chose to detect the CNVs of 5p15 deletion, 22q11.2 deletion, 1p36 deletion, and 15q11.2 deletion. All testing reagents used were laboratory-developed tests and were based on massive parallel sequencing, the minimum amount of sequencing data was 3-15 M reads, the detection limit of fetal fraction was 3%-5%, and the minimum size of variants that can be detected was 1-5 Mb. The proportion of laboratories that apply CNVs testing for daily project, voluntary requirements of patients, and scientific research were 58.8% (134/228), 57.5% (131/228), and 20.6% (47/228), respectively. One hundred and thirty-four laboratories were fully or partially aware of the clinical performance of NIPT to detect microdeletion/microduplication syndromes, and the laboratories' declared sensitivity of NIPT for Cri du Chat syndrome, 22q11.2 deletion syndrome, 1p36 deletion syndrome, and Angelman syndrome were 50.0%-100%, 60.0%-100%, 50.0%-100%, and 33.3%-100%, and the positive predictive values were 9.0%-50.0%, 18.0%-100%, 20.0%-30.0%, and 20.0%. Conclusion: The detection of CNVs by NIPT in Chinese laboratories need to be standardized. Laboratories should detect CNVs with clear clinical significance in accordance with the guidelines, conduct performance validation of the reagents, then perform NIPT test and provide adequate interpretation after mastering the clinical performance sufficiently.

[The effect of welding ultraviolet on the antioxidant function and DNA of workers]

Objective: To explore the skin damage, oxidative damage and DNA damage of welding workers caused by ultra violet. Methods: From 1 May to 30 June 2017, 125 welding workers were selected as the contact group, which was divided into 2, 4, 6, 8 and 10-year-working age groups with 25 workers in each group and 25 healthy volunteers as the control group. The workers in the contact group were investigated with questionnaires on the distribution and wearing of protective equipment; the subjects in the two groups were examined in dermatology, and the peripheral blood was collected to detect the total antioxidant capacity (T-AOC) and DNA damage of mononuclear cells, and the influence of ultraviolet on the above indexes was analyzed. Results: The distribution rates of welding mask, dust mask and goggles were 100.0% (125/125) , 96.0% (120/125) , 98.4% (123/125) , respectively, and the distribution rates of welding gloves were 64.8% (81/125) ; the wearing rates of welding mask and goggles were 100.0% (125/125) , 90.4% (113/125) , and the wearing rates of dust mask and welding gloves were 89.6% (112/125) and 64.0% (80/125) , respectively. The acute skin injuries such as hand and face peeling and skin pruritus were serious in the 2-year-working age group, and the chronic skin injuries such as insensitive and numbness and verrucous vegetations were the main manifestations in the 10-year-working age group. Compared with the control group, T-AOC in peripheral blood of workers exposed to 6, 8 and 10 years decreased significantly, and DNA content in comet tail of workers exposed to various working years increased significantly (P<0.05) , while DNA content in comet tail increased with working years (F=1501.130, P<0.05) . Conclusion: UV welding can cause skin damage, reduce the antioxidant capacity of the body, and increase DNA damage with the increase of working age.

The CLDN5 locus may be involved in the vulnerability to schizophrenia

The present study was designed to detect three single nucleotide polymorphisms (SNPs) located on 22q11 that was thought as being of particularly importance for genetic research into schizophrenia. We recruited a total of 176 Chinese family trios of Han descent, consisting of mothers, fathers and affected offspring with schizophrenia for the genetic analysis. The transmission disequilibrium test (TDT) showed that of three SNPs, rs10314 in the 3′-untranslated region of the CLDN5 locus was associated with schizophrenia (χ2= 4.75,P= 0.029). The other two SNPs, rs1548359 present in the CDC45L locus centromeric of rs10314 and rs739371 in the 5′-flanking region of the CLDN5 locus, did not show such an association. The global chi-square (χ2) test showed that the 3-SNP haplotype system was not associated with schizophrenia although the 1-df test for individual haplotypes showed that the rs1548359(C)-rs10314(G)-rs739371(C) haplotype was excessively non-transmitted (χ2= 5.32,P= 0.02). Because the claudin proteins are a major component for barrier-forming tight junctions that could play a crucial role in response to changing natural, physiological and pathological conditions, the CLDN5 association with schizophrenia may be an important clue leading to look into a meeting point of genetic and environmental factors.

[Clinical analysis of 8 cases with anti-GQ1b antibody syndrome]

Objective: To investigate the clinical characterization, treatment and prognosis of anti-GQ1b antibody syndrome. Methods: The clinical data of 8 patients with positive serum anti-GQ1b antibody from the Department of Neurology of Nanjing Brain Hospital between June 2016 and July 2018 were analyzed retrospectively. Their serums were tested by immunoblotting. Relevant literatures were reviewed to investigate possible pathogenesis. Results: Of the 8 cases, 4 cases were male, 4 cases were female; their age ranged from 16 to 76 (47±21) years old. Seven of them were with acute onset, the time course of the disease ranged from 2 to 15 (7±4) days. Six cases had a history of influenza prior to the onset of the presenting symptoms. In terms of the clinical manifestations of the eight patients, two were affected with Guillain-Barre syndrome (GBS), two with Cavernous sinus syndrome, one with Miller Fisher syndrome, one with both GBS and spinal cord demyelination, one with Bulbar paralysis, and one with chronic inflammatory demyelinating polyneuropathy (CIDP). The anti-GQ1b antibody IgG in serum was positive in 6 patients, two of whom were combined with positive IgG of anti-GD1b antibody in serum. The anti-GQ1b antibody IgM in serum was positive in 1 patient, and the anti-GQ1b antibody IgM and anti-GT1b antibody IgM in cerebrospinal fluid (CSF) were both positive in the other patient. In terms of the treatment, 3 patients (3/8) received vitamin B treatment only, 2 patients (2/8) received steroid plus vitamin B treatment, 2 patients (2/8) received intravenous immunoglobulin (IVIG) plus vitamin B treatment, and 1 patient (1/8) received steroid plus IVIG treatment. During the 8-33 months' follow-up after discharge, 6 patients were significantly improved in their symptoms, one with mild diplopia, one with limbs weakness, numbness and difficulty in walking. The symptoms of one patient (case 3) fluctuated twice and recovered again after treatment. Conclusions: The disease spectrum of anti-GQ1b antibodies syndrome is broad, and main symptom is ophtalmoplegia. Immunotherapy with IVIG and steroid would be beneficial to prognosis.

[Sivelestat alleviates nonalcoholic steatohepatitis in mice through inhibiting activation of Kupffer cells]

Objective: To investigate the role of neutrophil elastase inhibitor, sivelestat, in preventing and treating nonalcoholic steatohepatitis (NASH) and its underling mechanisms. Methods: A total of forty 4-week-old male C57BL/6J ApoE-/-mice were equally divided into the following four groups: standard chow (SC)+isotonic saline; SC+sivelestat; high-fat, high-cholesterol (HFHC) diet+isotonic saline; and HFHC+sivelestat. These mice were treated with above methods for 12 weeks. Blood and liver tissue samples were collected to measure biochemical parameters, hepatic steatosis and non-alcoholic fatty liver disease (NAFLD) activity score (inflammation) were evaluated by oil red O staining and HE staining, respectively. The mRNA and protein expression levels of hepatic inflammatory cytokines, CD68, and F4/80 were determined by quantitative RT-PCR and immunohistochemistry, respectively. Comparison of means between the four groups was made by one-way analysis of variance, and comparison between any two groups was made by the LSD or SNK method (for data with homogeneity of variance) or the Tamhane or Dunnett method (for data with heterogeneity of variance). Results: Mice fed with an HFHC diet for 12 weeks developed typical pathological features of NASH compared with those fed with SC. Compared with mice fed with HFHC diet without sivelestat, those treated with HFHC and sivelestat exhibited the following features: (1) significantly reduced fast blood glucose, blood cholesterol, and hepatic biochemical parameters, as well as increased insulin sensitivity; (2) significantly reduced NAFLD activity score (5.71±1.11 vs 3.16±1.16, P < 0.05); (3) reduced monocyte chemoattractant protein-1 and tumor necrosis factor -α; (4) significantly reduced mRNA levels of CD68 and F4/80; and (5) reduced expression of CD68 in the liver. Conclusion: Sivelestat alleviates the hepatic steatosis and inflammation of NASH in mice by inhibiting the activation of Kupffer cells.

Genetic vulnerability to DUSP22 promoter hypermethylation is involved in the relation between in utero famine exposure and schizophrenia

Epigenetic changes may account for the doubled risk to develop schizophrenia in individuals exposed to famine in utero. We therefore investigated DNA methylation in a unique sample of patients and healthy individuals conceived during the great famine in China. Subsequently, we examined two case-control samples without famine exposure in whole blood and brain tissue. To shed light on the causality of the relation between famine exposure and DNA methylation, we exposed human fibroblasts to nutritional deprivation. In the famine-exposed schizophrenia patients, we found significant hypermethylation of the dual specificity phosphatase 22 (DUSP22) gene promoter (Chr6:291687-293285) (N = 153, p = 0.01). In this sample, DUSP22 methylation was also significantly higher in patients independent of famine exposure (p = 0.025), suggesting that hypermethylation of DUSP22 is also more generally involved in schizophrenia risk. Similarly, DUSP22 methylation was also higher in two separate case-control samples not exposed to famine using DNA from whole blood (N = 64, p = 0.03) and postmortem brains (N = 214, p = 0.007). DUSP22 methylation showed strong genetic regulation across chromosomes by a region on chromosome 16 which was consistent with new 3D genome interaction data. The presence of a direct link between famine and DUSP22 transcription was supported by data from cultured human fibroblasts that showed increased methylation (p = 0.048) and expression (p = 0.019) in response to nutritional deprivation (N = 10). These results highlight an epigenetic locus that is genetically regulated across chromosomes and that is involved in the response to early-life exposure to famine and that is relevant for a major psychiatric disorder.

[Establishment of zebrafish model for non-alcoholic steatohepatitis]

Objective: To establish overfed zebrafish model for non-alcoholic steatohepatitis. Methods: The wild-type zebrafish was fed 3 times a day with normal diet. Body length, weight, and triglyceride levels were measured after 20 days of feeding. The changes in expression of genes associated with cholesterol metabolism, lipid metabolism, endoplasmic reticulum stress, and inflammation were detected by quantitative PCR. Liver tissue sections were stained with H&E. Statistical analyses between groups were compared using t-test. Results: The body length (0.71±0.014) cm and body weight (44.83±1.833) mg of model group were higher than that of control group (0.50±0.009) cm and body weight (19.33±2.753) mg (total (body length) = 12.36, total (body weight) = 7.71, P < 0.01). Triglyceride content in the model group was (59.15 ± 0.5612) μmol / L, higher than the control group (16.71 ± 0.3562) μmol / L (t = 63.84, P < 0.001). Quantitative PCR results showed that the expression of genes related to cholesterol synthesis in the model group was higher than that in the control group (P < 0.01). The expression levels of lipid production and lipid oxidation related factors in the model group were higher than the control group. The difference between the two groups was statistically significant (P < 0.05). The expression of inflammation-related factors in the model group was higher than that in the control group (P < 0.001), and the expression of genes related to endoplasmic reticulum stress in the model group was higher than that to control group (P<0.001). Liver H&E staining showed that the model group had pathological changes such as large bulla and vesicles compared to the control group. Conclusion: A continuous 3 times 20 days of normal diet can simulate the disease characteristics of human non-alcoholic steatohepatitis in a zebrafish.

[Treatment and prognosis of immunoglobulin G4-related hepatobiliary disease]

Currently, there is no randomized controlled clinical trial of immunoglobulin (Ig) G4-related diseases in the world. Therefore, the best-known evidence-based medical treatment plan for this disorder is unavailable. The goal of IgG4-related hepatobiliary diseases treatment is to alleviate symptoms, prevent disease-related complications and fibrosis progression. A definite diagnosis is warranted before treatment. Hormonal therapy has become the basis of induction of remission in IgG4-related hepatobiliary disease. An initial prednisone dose is 30 ~ 40mg/d or 0.6 mg.kg-1.d-1 for 2 to 4 weeks, thereafter, gradually the dose is reduced within 2-3 months. Maintenance therapy with low-dose glucocorticoids hormone (prednisone 2.5 to 5.0 mg/d) is recommended for 1 to 3 years to prevent disease recurrence. In addition, immunosuppressive agents are equally effective, and in most cases, hormone combined immunosuppressive therapy may respond. Rituximab, a monoclonal antibody is a promising drug for treatment of this kind of diseases.

[Realization of design regarding experimental research in the clinical real-world research]

Real world study (RWS), a further verification and supplement for explanatory randomized controlled trial to evaluate the effectiveness of intervention measures in real clinical environment, has increasingly become the focus in the field of research on medical and health care services. However, some people mistakenly equate real world study with observational research, and argue that intervention and randomization cannot be carried out in real world study. In fact, both observational and experimental design are the basic designs in real world study, while the latter usually refers to pragmatic randomized controlled trial and registry-based randomized controlled trial. Other nonrandomized controlled and adaptive designs can also be adopted in the RWS.

Hepatic Steatosis as a Predictive Factor of Antiviral Effect of Pegylated Interferon Therapy in Patients With Hepatitis B

BACKGROUND AND AIMS

This study sought to evaluate the impact of hepatic steatosis, a common hepatocyte change in nonalcoholic fatty liver disease, upon response to pegylated interferon (PEG-IFN) therapy in patients with chronic hepatitis B (CHB).

METHODS

Eighty-nine consecutive CHB patients from the Affiliated Hospital of Hangzhou Normal University receiving 48 weeks of PEG-IFN therapy were enrolled in this study, and 56 patients were followed up for 48 weeks among subjects with completed therapy. Baseline characteristics, end-of-treatment response (ETR), and sustained viral response (SVR) to PEG-IFN therapy were evaluated. Univariate analysis and multivariate logistic regression were applied to find independent factors of hepatic steatosis and PEG-IFN treatment failure.

RESULTS

Steatosis was present in 34.5% (31 of 89) of liver biopsy samples. ETR to PEG-IFN therapy was 56.17% (50 of 89) at 48 weeks, and SVR to PEG-IFN therapy was 57.6% (32 of 56) at 96 weeks. There was no significant difference in ETR between the patients with hepatic steatosis and those without hepatic steatosis at 48 weeks (P > .05), whereas SVR was higher in patients without hepatic steatosis than in those with hepatic steatosis at 96 weeks (P < .05). Multivariate analysis showed that the sustained response rate was independently associated with steatosis, fibrosis, aspartate aminotransferase, C-reactive protein, and ferritin. Hepatic steatosis was a prediction factor with the sustained response.

CONCLUSIONS

Hepatic steatosis may be a predictive factor of response to PEG-IFN therapy in patients with CHB.

[Establishment and evaluation of a mouse model of nonalcoholic steatohepatitis-related hepatocellular carcinoma]

OBJECTIVE

To establish an apolipoprotein E (ApoE) and low-density lipoprotein receptor (LDLR) double-knockout (ApoE(-/-)/LDLR(-/-)) mouse model of nonalcoholic steatohepatitis (NASH)-related hepatocellular carcinoma (HCC) induced by high-fat and high-cholesterol (HFHC) diet.

METHODS

ApoE(-/-) knockout mice were crossed with LDLR(-/-) knockout mice to obtain ApoE(-/-)/LDLR(-/-) mice. The ApoE(-/-)/LDLR(-/-) mice mated with each other, and the offspring were injected with low-dose streptozotocin (STZ) at 2-3 days after birth. Some mice were fed with HFHC diet after weaning as the model group (n = 15), and some mice were fed with normal diet as the control group (n = 15). Mice were sacrificed at the end of weeks 10, 16, and 20 (5 mice at each time point). The body weight was measured. Liver tissue and blood were collected to measure biochemical parameters, evaluate the pathological changes in the liver tissue by HE staining, oil red O staining, and Masson staining, and detect the expression of glypican-3 (a marker of HCC) by immunohistochemical staining.

RESULTS

The model group had significantly higher levels of fasting blood glucose and total cholesterol than the control group (P < 0.01). Serum levels of alanine aminotransferase, aspartate aminotransferase, and total triglyceride gradually increased with time in the model group; at week 20, there were significant differences in above three indices between the two groups (P < 0.05). HE staining showed that compared with the control group at the corresponding time point, the model group developed sequential histological changes: NASH at week 10, dysplastic nodules at week 16, and early HCC at week 20. Oil red O staining showed that in the model group, the degree of liver steatosis increased within 10 weeks and gradually decreased later. Masson staining demonstrated that the model group developed pathological changes: mild perisinusoidal fibrosis at week 16 and bridging fibrosis around tumors at week 20. HE staining, oil red O staining, and Masson staining showed that no histological or pathological changes were found in the control group. Glypican-3 was detected in the nodules at week 16 and in the cytoplasm of HCC cells at week 20 in the model group.

CONCLUSION

The mouse model of NASH-related HCC can be developed by giving STZ injection to neonatal ApoE(-/-)/LDLR(-/-) mice and feeding them with HFHC diet after weaning for 20 weeks. Early HCC may develop directly from NASH.

[Value of a two-step approach with cytokeratin-18 and controlled attenuation parameter in noninvasive differential diagnosis of nonalcoholic steatohepatitis]

OBJECTIVE

To investigate the value of a two-step approach with cytokeratin-18 (CK-18) and controlled attenuation parameter (CAP) in the noninvasive diagnosis of nonalcoholic steatohepatitis (NASH).

METHODS

A total of 65 patients with biopsy-proven nonalcoholic fatty liver disease were enrolled, including 30 patients with NASH. The M30 and M65 enzyme-linked immunosorbent assay kits were used to measure serum CK-18, and FibroScan was used to measure CAP. The receiver operating characteristic (ROC) curve was plotted, and the area under the ROC curve (AUROC) was used to determine the value of noninvasive diagnosis. The binary logistic regression model was used to calculate the predicted probability of combined diagnosis. The maximum Youden index, a sensitivity of >90%, and a specificity of > 90% were used to determine the optimal cut-off value, the low value, and the high value, respectively.

RESULTS

The results of the multivariate analysis showed that M65 (OR = 1.004, 95% CI 1.002-1.007, P = 0.003) and CAP (OR = 1.017, 95% CI 1.001-1.033, P = 0.036) were independent predictors of NASH. The AUROC of M65+CAP was 0.851 (95% CI 0.761-0.942), higher than 0.808 (95% CI 0.702-0.913) of M65 and 0.677 (95% CI 0.545-0.808) of CAP alone. A two-step approach with high (820.8 U/L) and low (527.7 U/L) values for M65 and the optimal cut-off value (293.5 dB/m) for CAP was used for the differential diagnosis of NASH, with a positive predictive value of 85.7%, a negative predictive value of 100%, and a coincidence rate of 92.0%.

CONCLUSION

A two-step approach with M65 and CAP can improve the value of noninvasive diagnosis of NASH, and a high negative predictive value can avoid unnecessary liver biopsy.

AIMS baby movement scale application in high-risk infants early intervention analysis

OBJECTIVE

We investigated the application of Alberta Infant Motor Scale (AIMS) in screening motor development delay in the follow-up of high-risk infants who were discharged from NICU, to explain the state of infants' motor development and propose early individualized intervention.

PATIENTS AND METHODS

The study design was a randomized, single-blind trial by selecting patients between April 2015 and November 2015 in our hospital, children nerve recovery branch clinics and 77 cases of high-risk infants. We randomly divided the patients into observation group (39 cases) and control group (38 cases). To evaluate the application with AIMS, observation group was based on evaluation results for the first time to give rehabilitation training plan making, early intervention, control group according to the growth and development milestone in order to guide parents to take family training interval of 3 months.

RESULTS

While comparing the two groups of high-risk infants before the intervention, the months of age, gender, risk factors, it was found that the AIMS scores, each position AIMS scores did not show a significant difference in percentile (p>0.05). There was also no significant difference between two groups in the seat and stand AIMS scores before and after intervention (p>0.05). However, the comparison of two groups of high-risk infants after intervention in comparison showed that the observation group supine AIMS scores and AIMS scores were significantly higher than the control group (p<0.05). Prone position AIMS scores observation group was also significantly higher than that of the control group (p<0.01). The corresponding percentile for two groups after the intervention of AIMS scores was less than 10% of cases, which was significantly lower in the observation group (p<0.01).

CONCLUSIONS

AIMS can predict the development delay in high-risk infants, for improving the early hypernymic diagnosis and intervention.

Investigation of single nucleotide polymorphisms in phosphodiesterase 4D gene in Mongol and Han patients with ischemic stroke in Inner Mongolia

We investigated single nucleotide polymorphisms (SNP) at 87 sites of the phosphodiesterase 4D (PDE4D) gene in Mongol and Han patients with ischemic stroke in Inner Mongolia. SNPs in 226 patients with ischemic stroke (case group, 110 Mongol patients, 116 Han patients) and 220 patients without neurological disease (control group, 102 Mongol patients, 118 Han patients) were detected by polymerase chain reaction-restriction fragment length polymorphism and gene sequencing. The genotype and allele frequencies of all groups were compared. There were no statistically significant differences in genotypes in the PDE4D gene at 87 sites between the case and control groups (P > 0.05). The C allele frequency in the case group was significantly higher than that in the control group (P < 0.05). The CC genotype and C allele frequencies in the Mongol case subgroup were higher than those in the Mongol control subgroup (P < 0.05). The CC genotype and C allele frequencies in the Han case subgroup were higher than those in the Han control subgroup (P < 0.05). In the case group, there were no significant differences at 87 sites for genotypes and allele frequencies between the Mongol and Han subgroups. In the control group, there were no significant differences at 87 site genotypes and allele frequencies between the Mongol and Han subgroups. The increase in the C allele frequency at 87 SNP sites in PDE4D may increase ischemic stroke risk. We found no differences in the risk between Mongol and Han populations in Inner Mongolia.

Meta-analysis of differentially expressed genes in autism based on gene expression data

The purpose of this study was to identify differentially expressed (DE) genes and biological processes associated with changes in gene expression in autism. We performed a meta-analysis using new publicly available Gene Expression Omnibus (GEO) datasets of autism. We performed Gene Ontology (GO) enrichment analyses and pathway analysis using the Kyoto Encyclopedia of Genes and Genomes (KEGG). Ten GEO datasets, including 364 cases and 248 controls, were available for the meta-analysis. We identified 3105 genes that were consistently DE in autism (1425 upregulated and 1680 downregulated genes). We also found that 7 genes were associated with phospholipase A2 (PLA2), including LYPLA2P1, PLA2G4D, PNPLA2, LYPLA2, PLA2G6, PLA2G7, and PLA2G5. We found GO terms for molecular functions significantly enriched in structural constituent of ribosome (GO: 0003735, P = 1.87-E06) and transcription regulator activity (GO: 0030528, P = 8.86E-04), while for biological processes, the enriched GO terms were involved in translational elongation (GO: 0006414, P = 1.74E-12) and the response to cytokine stimuli (GO: 0034097, P = 2.76E-05). The most significant pathway in our KEGG analysis was the ribosome pathway (P = 7.90E-12). Our meta-analysis identified genes that were consistently DE and biological pathways associated with gene expression changes in autism.

Long-term effects of salt substitution on blood pressure in a rural north Chinese population

Dietary sodium and potassium intake can influence blood pressure. The effects of salt substitution on patients with hypertension and normotensive family member controls, however, have not been evaluated in a rural Chinese population. The objective of this study, accordingly, was to assess the long-term effects of salt substitution on blood pressure. We conducted a double-blind, randomized controlled trial among 200 families in rural China to establish the 2-year effects of a reduced-sodium, high-potassium salt substitute (65% sodium chloride, 25% potassium chloride, 10% magnesium sulfate) compared with normal salt (100% sodium chloride) on blood pressure. Of the 462 individuals in the trial, 372 completed the study (81%). For normotensive subjects, the mean overall difference in systolic and diastolic blood pressure between the two groups at the 24-month follow-up was 2 mm Hg (95% confidence interval (CI) 0-4 mm Hg, P<0.05) and 2 mm Hg (95% CI 1-3 mm Hg, P<0.05), respectively. For subjects with hypertension, the mean overall decrease in systolic blood pressure showed a 4-mm Hg (95% CI 2-6 mm Hg, P<0.05) decrease between the two groups. Diastolic blood pressure was not affected by salt use in the hypertensive group. Salt substitution lowers systolic blood pressure in hypertensive patients and lowers both systolic and diastolic blood pressure in normotensive controls. Salt substitution, therefore, may be an effective adjuvant therapy for hypertensive patients and the potential efficacy in preventing hypertension in normotensive individuals.

No association between the PTGS2/PLA2G4A locus and schizophrenia in a Chinese population

The present study was undertaken to replicate an association between the PTGS2/PLA2G4A locus and schizophrenia among a Chinese population. We recruited 168 Chinese parent-offspring trios of Han descent, consisting of fathers, mothers and affected offspring with schizophrenia. Of 3 informative SNPs genotyped, no one showed allelic association with schizophrenia; the haplotype analysis also failed to capture a haplotypic association with the illness. Because the frequencies of alleles and genotypes of SNPs analyzed differ in the Chinese population as compared with a British population that initially showed the genetic association between the PTGS2/PLA2G4A locus and schizophrenia, the ethnic background may be a major reason for poor replication of the initial finding.

A method for measuring particle number emissions from vehicles driving on the road

Earlier research has demonstrated that the conditions of dilution of engine exhaust gases profoundly influence the size distribution and total number of particles emitted. Since real world dilution conditions are variable and therefore difficult to simulate, this research has sought to develop and validate a method for measuring particle number emissions from vehicles driving past on a road. This has been achieved successfully using carbon dioxide as a tracer of exhaust gas dilution. By subsequent adjustment of data to a constant dilution factor, it is possible to compare emissions from different vehicles using different technologies and fuels based upon real world emission data. Whilst further optimisation of the technique, especially in terms of matching the instrument response times is desirable, the measurements offer useful insights into emissions from gasoline and diesel vehicles, and the substantial proportion of particles emitted in the 3-7 nanometre size range.

Melatonin treatment for age-related insomnia

Older people typically exhibit poor sleep efficiency and reduced nocturnal plasma melatonin levels. The daytime administration of oral melatonin to younger people, in doses that raise their plasma melatonin levels to the nocturnal range, can accelerate sleep onset. We examined the ability of similar, physiological doses to restore nighttime melatonin levels and sleep efficiency in insomniac subjects over 50 yr old. In a double-blind, placebo-controlled study, subjects who slept normally (n = 15) or exhibited actigraphically confirmed decreases in sleep efficiency (n = 15) received, in randomized order, a placebo and three melatonin doses (0.1, 0.3, and 3.0 mg) orally 30 min before bedtime for a week. Treatments were separated by 1-wk washout periods. Sleep data were obtained by polysomnography on the last three nights of each treatment period. The physiologic melatonin dose (0.3 mg) restored sleep efficiency (P < 0.0001), acting principally in the midthird of the night; it also elevated plasma melatonin levels (P < 0.0008) to normal. The pharmacologic dose (3.0 mg), like the lowest dose (0.1 mg), also improved sleep; however, it induced hypothermia and caused plasma melatonin to remain elevated into the daylight hours. Although control subjects, like insomniacs, had low melatonin levels, their sleep was unaffected by any melatonin dose.

Identification of a potential physiological substrate for oncogenic Ras-activated protein kinases in activated Xenopus egg extracts: correlation with oncogenic Ras-induced cell cycle arrest

Activated Xenopus egg extracts are capable of undergoing cell-free cell cycling. Using these activated extracts, we previously showed that purified, bacterially expressed oncogenic human RasH protein arrests cell cycle progression. Because oncogenic Ras activates many serine/threonine protein kinases in Xenopus oocytes and egg extracts, it is possible that induction of cell cycle arrest involves the action of oncogenic Ras-activated kinases. Thus, the identification of the physiological substrates for oncogenic Ras-activated kinases is important for elucidating the molecular mechanism underlying oncogenic Ras-induced cell cycle arrest. We used 32P-orthophosphate as a label to identify the potential substrates. Our results demonstrated that the 32P-labeling of both a 32 and a 33 kDa protein were greatly enhanced by oncogenic Ras during the incubation of activated Xenopus egg extracts. The enhanced labeling correlated with the induced cell cycle arrest and was contributed by serine phosphorylation. Moreover, the 33 kDa protein was detected only in the presence of oncogenic Ras and was a serine-hyperphosphorylated form of the 32 kDa protein. Furthermore, new protein synthesis was not required for the enhanced labeling, consistent with the concept that the enhanced serine phosphorylation of the 32 kDa protein is by oncogenic Ras-activated protein kinases. In addition to serine phosphorylation, our results also suggested that an as yet unidentified modification of the 32 kDa protein might also be induced by oncogenic Ras. Our results suggest that the 32 kDa protein is a potential physiological substrate for oncogenic Ras-activated protein kinases.

Lung cancer in nonsmoking Chinese women: a case-control study

The risk factors for lung cancer in lifetime nonsmoking women were investigated in a hospital-based case-control study in the urban area of Shenyang, China, between April 1992 and May 1994. One-hundred thirty-five newly-diagnosed lung cancer cases and an equal number of controls, matched for age and sex, were enrolled and interviewed by trained personnel who administered a standardized questionnaire. The histopathological cell type was predominantly adenocarcinoma (54.5%), followed by small cell carcinoma (20%), squamous cell carcinoma (16.4%), and others (9.1%). The data were analyzed using the Mantel-Haenszel method and by multivariate logistic regression analysis. The odds ratio (OR) and confidence interval (CI) associated with cooking oil vapors and with family history of cancer were 3.79 (95% CI, 2.29-6.27) and 2.29 (95% CI, 1.01-5.17), respectively. No association was found between exposure to environmental tobacco smoke (ETS), presence of previous lung diseases, and "kang" use. Cooking practices, exposure to cooking fumes, and a family history of cancer were found to significantly increase the risk of lung cancer.

Evidence that specificity of microhelix charging by a class I tRNA synthetase occurs in the transition state of catalysis

Determinants for the identities of tRNAs are located in the acceptor stem and, commonly, in the anticodon as well. Although the anticodon is an important determinant for the identity of methionine tRNA, RNA microhelices whose sequences are based on the acceptor stem alone can be aminoacylated by the class I methionyl-tRNA synthetase. We show here that specific nucleotide substitutions in a microhelix significantly reduced its rate of aminoacylation. In contrast, affinity coelectrophoresis analysis showed that microhelix binding to the enzyme was not significantly affected by the same substitutions. These and additional experiments and considerations imply that specific determinants for microhelix aminoacylation are needed for orientation of the acceptor stem in the transition state of catalysis rather than for enhanced binding interactions. The effect of linking together acceptor stem interactions with those in the anticodon, as occurs in the whole tRNA molecule, was also evaluated. This analysis showed that linkage results in some of the favorable acceptor stem and anticodon interactions being used to offset the free energy cost of straining the structure of the enzyme-tRNA complex.

Region of a conserved sequence motif in a class II tRNA synthetase needed for transfer of an activated amino acid to an RNA substrate

The class II Escherichia coli alanine tRNA synthetase aminoacylates RNA miniduplexes, which reconstruct the acceptor end of alanine tRNA with the critical G3:U70 base pair. A benzophenone photoaffinity label attached adjacent to G3:U70 in a miniduplex substrate was previously cross-linked to a long enzyme peptide that begins at Gly161 between the class-defining motifs 2 and 3 [Musier-Forsyth, K., & Schimmel, P. (1994) Biochemistry 33, 773-779]. To identify side chains in this peptide that potentially contribute hydrogen bonding or catalytic determinants for the RNA-dependent step of the aminoacylation reaction, peptide functional side chains that are conserved among sequenced alanine enzymes (Asp, Asn, Arg, Glu, Gln, and Tyr) were individually replaced. Of the 21 mutant proteins so generated, one was identified that was not viable even though it accumulated in vivo. This Asp235-->Ala mutant enzyme is defective in the rate of transfer of the activated amino acid to the 3'-end of the RNA substrate. The conserved Asp235 is at the beginning of motif 3. By comparison with the crystal structure of the related class II yeast aspartate tRNA synthetase complexed with tRNA(Asp) (Cavarelli et al., 1993), we suggest that D235 is not in direct contact with acceptor helix base pairs such as G3:U70. Instead, we propose that D235 contributes to transfer-step interactions at the 3'-end of alanine tRNA. Because D235 in alanine tRNA synthetase is at the beginning of one of the conserved motifs that define class II tRNA synthetases, this region of the structure may in general be important for the transfer step.

Levonorgestrel levels in serum and uterine flushings in women bearing LNG-Cu-IUD

Radioimmunoassay was employed to measure levonorgestrel levels in serum and uterine flushings in women using intrauterine device releasing both copper ions and levonorgestrel (LNG-Cu-IUD) after one-year insertion. In the meanwhile physical characteristics of cervical mucus have been observed in women using LNG-Cu-IUD and compared with those using Tcu-220c-IUD. The mean concentrations of levonorgestrel in serum and uterine flushings (5 ml) were 84.53 pg/ml and 266.93 pg/ml respectively. In LNG-Cu-IUD group, the cervical mucus lacking in ferny crystals had a viscosity significantly higher than that in Tcu-220c-IUD group, suggesting that the local high concentration of levonorgestrel changed the environment of the uterine cavity and the cervical mucus status.

RNA tetraloops as minimalist substrates for aminoacylation

Previous work established that seven-base-pair hairpin microhelices with sequences based on the acceptor stems of alanine, glycine, methionine, and histidine tRNAs can be aminoacylated specifically with their cognate amino acids. To obtain "minimalist" substrates with fewer base pairs, we took advantage of the high thermodynamic stability of RNA tetraloop motifs that are found in ribosomal RNAs. We show here that rationally designed RNA tetraloops with as few as four base pairs are substrates for aminoacylation. Major nucleotide determinants for recognition by the class II synthetases were incorporated into each of the respective tetraloop substrates, resulting in specific aminoacylation by the alanine, glycine, and histidine tRNA synthetases. An analysis of the kinetics of aminoacylation shows that, for the alanine system, the majority of the transition-state stabilization provided by the synthetase-tRNA interaction is reproduced by the interaction of the synthetase with nucleotides in its minimalist tetraloop substrate. In an extension of this work, we also observed specific aminoacylation with the class I methionine tRNA synthetase of RNA tetraloops based on sequences in the acceptor stem of methionine tRNA. Thus, the results demonstrate four different examples where specific aminoacylation is directed by sequences/structures contained in less than half of a turn of an RNA helix.

Overlapping nucleotide determinants for specific aminoacylation of RNA microhelices

A seven-base pair microhelix that recapitulates a glycine transfer RNA (tRNA) acceptor helix can be specifically aminoacylated with glycine. A single base pair and the single-stranded discriminator base near the attachment site are essential for aminoacylation. These nucleotide sequence elements, and those in microhelices that can be charged with histidine and alanine, occur in the same positions and therefore overlap. Studies on a systematic set of sequence variants showed that no microhelix could be charged with more than one amino acid. Also, none of the three cognate aminoacyl-tRNA synthetases (aaRSs) gave a detectable amount of aminoacylation of the CCA trinucleotide that is common to the 3' ends of all tRNAs, showing that the specific acceptor stem nucleotide bases confer aminoacylation. An analysis of the relative contributions of these microhelices to overall tRNA recognition indicated that their interaction with aaRSs constitutes a substantial part of the recognition of the whole tRNAs.

Studies on the antifertility components from Marsdenia koi

By random screening test, Marsdenia koi was found to have antifertility activity on SD rat. From MeOH extracts of this plant two steroidal glycosides, marsdekoiside A and B, were isolated, and their structures were elucidated on the basis of spectral evidence and by comparison of the hydrolysis products with the authentic samples. Both are newly identified compounds, and marsdekoiside A has good antifertility activity.

Arginyl-tRNA synthetase from Escherichia coli affinity labeling with 3'-oxidized tRNA(Arg)

The covalent modification of E. coli arginyl-tRNA synthetase by the 2',3'-dialdehyde derivative of tRNA(Arg) (tRNA(oxArg)) resulted in the complete inactivation of the ATP-PPi exchange and aminoacylation activities of the enzyme. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of the ArgRS-tRNA(oxArg) covalent complexes indicated that two bands simultaneously appeared on the gel parallel with inactivation corresponding to different higher molecular weights. This result was different from that of the other aminoacyl-tRNA synthetase labeling systems as previously reported. Upon the ribonuclease treatment of the modified ArgRS, less than 15% of both the initial ATP-PPi exchange and aminocylation activities were recovered. During the whole process of labeling and RNase treatment, the two activities of the enzyme were closely associated.

Aminoacylation of alanine minihelices. "Discriminator" base modulates transition state of single turnover reaction

RNA hairpin minihelices that recreate the acceptor-T psi C stem of Escherichia coli alanine tRNA are charged specifically with alanine, provided that they encode the critical G3:U70 base pair that is the major determinant for the identity of an alanine tRNA. These model substrates were used to investigate the role in charging of N73, the unpaired nucleotide that is just three positions removed from the amino acid attachment site and which is sometimes referred to as the "discriminator" base. Previous work showed that, while substrates which encode G3:U70 are all charged by alanine tRNA synthetase regardless of the base at position 73, catalytic efficiency is substantially higher with substrates that have the wild-type A73. To identify a specific step in aminoacylation that is affected by substitutions of A73, we studied the single turnover charging of A73, U73, C73, and G73 minihelices, using preformed, enzyme-bound alanyl adenylate and saturating concentrations of the respective minihelices. Compared to the A73 substrate, the transfer of activated amino acid to bound RNA is sharply reduced for the substituted N73 minihelices. The low efficiency of transfer is not due to an abortive reaction in which the adenylate or a transiently charged RNA is hydrolyzed. Instead, under the conditions used, the active adenylate remains on the enzyme for extended periods and simply reacts slowly with bound N73 RNA. The results suggest that the nature of the discriminator base is a critical determinant of the transition state for the reaction of bound alanyl adenylate with RNA on the surface of the enzyme.

A nucleotide that enhances the charging of RNA minihelix sequence variants with alanine

We showed earlier that a single G3.U70 base pair within the amino acid acceptor helix is a major determinant of the identity of tRNA(Ala). In addition, we demonstrated that an RNA hairpin minihelix that recreates the 12 base pair acceptor-T psi C stem of tRNA(Ala) is also aminoacylated in a G3.U70-dependent manner. Determinants for efficient aminoacylation at pH 7.5 have been further investigated with minihelix substrates that have sequence variations at 3.70 and other locations. Although a U,U mismatch and other 3.70 nucleotide alternatives to G.U were recently proposed by others as also important for alanine acceptance, neither that mismatch nor any of four other 3.70 nucleotide combinations confer aminoacylation in vitro with alanine, even with substrate levels of enzyme. In contrast, permutations of the so-called discriminator nucleotide N73 (at position 73) strongly modulate, but do not block, aminoacylation of those substrates that encode G3.U70. In particular, the efficiency of G3.U70-dependent aminoacylation with alanine is strongly enhanced by having the wild-type A73. The effect of N73 alone can explain most of the difference in aminoacylation efficiency of a G3.U70-containing tRNA and a minihelix substrate whose sequences vary significantly from their tRNA(Ala) counterparts. Comparison with earlier work suggests that the substantial modulating effect of N73 is partly or completely obscured when N73 tRNA variants are expressed as amber suppressors in vivo.

Limited tryptic digestion of leucyl-tRNA synthetase and characterization of its active fragment

Leucyl-tRNA synthetase (LeuRS, EC 6.1.1.4) from E. coli underwent limited proteolysis by trypsin which cut off 6K peptide and converted the intact LeuRS into a 96K fragment. The truncated enzyme retained the PPi exchange activity with the same kinetic parameters as those of native LeuRS but lost the tRNALeu charging, binding and other tRNALeu-related activities. N-terminus analysis showed that the 6K peptide was located at the C-terminus of Leu-RS. This small part played a crucial role in tRNALeu binding. Our results suggest that the two activities, PPi exchange and tRNA charging are independent of each other and correspond to different structural regions of LeuRS. The C-terminal region might be the tRNALeu binding site of LeuRS.

Arginyl-tRNA synthetase from Escherichia coli, purification by affinity chromatography, properties, and steady-state kinetics

A Blue Sephadex G-150 affinity column adsorbs the arginyl-tRNA synthetase of Escherichia coli K12 and purifies it with high efficiency. The relatively low enzyme content was conveniently purified by DEAE-cellulose chromatography, affinity chromatography, and fast protein liquid chromatography to a preparation with high activity capable of catalyzing the esterification of about 23,000 nmol of arginine to the cognate tRNA per milligram of enzyme within 1 min, at 37 degrees C, pH 7.4. The turnover number is about 27 s-1. The purification was about 1200-fold, and the overall yield was more than 30%. The enzyme has a single polypeptide chain of about Mr 70,000 and binds arginine and tRNA with 1:1 stoichiometry. For the aminoacylation reaction, the Km values at pH 7.4, 37 degrees C, for various substrates were determined: 12 microM, 0.9 mM, and 2.5 microM for arginine, ATP, and tRNA, respectively. The Km value for cognate tRNA is higher than those of most of the aminoacyl-tRNA synthetase systems so far reported. The ATP-PPi exchange reaction proceeds only in the presence of arginine-specific tRNA. The Km values of the exchange at pH 7.2, 37 degrees C, are 0.11 mM, 2.9 mM, and 0.5 mM for arginine, ATP, and PPi, respectively, with a turnover number of 40 s-1. The pH dependence shows that the reaction is favored toward slightly acidic conditions where the aminoacylation is relatively depressed.

Affinity labelling of E. coli leucyl-tRNA synthetase with 3'-oxidized tRNA(Leu)

The E. coli leucyl-tRNA synthetase (E.C. 6.1.1.4) was specifically labelled with 3'-oxidized tRNA(Leu) (tRNA(oxLeu)). The procedure involves a Schiff's base formation and its subsequent reduction by sodium cyanoborohydride. Stoichiometric inactivation of aminoacylation was achieved with the incorporation of 1 mol of tRNA(oxLeu) per mol LeuRS. On the other hand, the amino acid activation activity of LeuRS-tRNA(ox) complex was partially inhibited. After extensive digestion of the complex by pancreatic ribonuclease, the amino acid activation activity was fully recovered, while the aminoacylation activity was not restored at all.

Hydrogen bonding and biological specificity analysed by protein engineering

The role of complementary hydrogen bonding as a determinant of biological specificity has been examined by protein engineering of the tyrosyl-tRNA synthetase. Deletion of a side chain between enzyme and substrate to leave an unpaired, uncharged hydrogen-bond donor or acceptor weakens binding energy by only 0.5-1.5 kcal mol-1. But the presence of an unpaired and charged donor or acceptor weakens binding by a further approximately 3 kcal mol-1.

Fidelity of DNA replication under conditions used for oligodeoxynucleotide-directed mutagenesis

The fidelity of DNA replication in vitro by DNA polymerase I (large subfragment) of Escherichia coli has been measured by the standard bioassay: single-stranded phi X174 DNA (plus strand) containing an amber codon was primed with a synthetic oligodeoxynucleotide, replicated and the frequency of point mutations formed in the synthetic minus strand of the resultant double-stranded DNA determined from the number of revertant phage produced in a spheroplast assay. Since the assay depends crucially on the frequency of expression of the mutations in the heteroduplex, and this can vary for a variety of reasons, parallel control experiments were performed using a primer that covered the amber codon but contained the same mismatch that occurred during replication. The frequency of expression of these mutations was found to vary from 40 to 100% in fully ligated heteroduplexes, depending upon the age and batch of spheroplasts used. The variation probably reflects the viability of the post-replicative mismatch repair enzymes in the spheroplasts used for transfection. Far lower frequencies of expression were found under conditions of poor replication. Accurate data and rate laws for fidelity are obtained only when the bioassay is normalized for the variation in the expression frequency. There is active proofreading by the 3'-5'-exonuclease activity of the polymerase of a misincorporation resulting from a dGTP:T mismatch. The contribution of proofreading to fidelity is low: accuracy is enhanced by a factor of less than 7 at the concentrations of dNTPs in vivo. The lower accuracy of Pol I than Pol III is due mainly to poorer proofreading, which is manifested in a lower "cost" of replication: only 0.7 to 1.7% of the dNTPs are turned over to dNMPs during replication compared with 6 to 13% for Pol III. The error rates measured for Pol I under conditions used for oligodeoxynucleotide-directed mutagenesis are sufficiently low that extraneous errors should not be induced when the concentrations of dNTPs are balanced. However, even higher fidelity will be obtained using the lowest concentrations of dNTPs consistent with efficient replication (approximately 20 microM). Highly unbalanced concentrations as used in pulsed labelling should be avoided.

Kinetics of base misinsertion by DNA polymerase I of Escherichia coli

A simple kinetic analysis of the values of kcat and KM for base insertion and misinsertion during DNA replication is presented and applied to the problem of base misinsertion by DNA polymerase I of Escherichia coli. The role of minor tautomeric forms of deoxynucleoside triphosphates (dNTPs) in purine x pyrimidine mismatching has been examined and it has been shown that the misinsertion frequency via this route should be close to the tautomerization constant in solution and is independent of any effect of the polymerase on the tautomerization of a dNTP when bound. Kinetic data on purine x pyrimidine mismatching indicate that the dNTP in a polymerase-DNA-mismatched-dNTP complex is predominantly in the major tautomeric form. The mutagenic effect of Mn2+ in DNA replication is shown to be mediated by decreasing the values of kcat/KM for the insertion of correct dNTPs, whilst the values of this rate constant for misinsertion are relatively unaffected or increased.