[Hot issues in robotic-assisted thoracic day surgery]

The application of day surgery on thoracic surgery is just started, and the innovation of surgical robots and their application on thoracic surgery bring new opportunities to the development of thoracic day surgery. However, the clinical practice of robot-assisted thoracic day surgery (RTDS) in China still has challenges and disagreements. Based on the experience of domestic experts in the field of RTDS clinical practice, this review discussed several key points of RTDS, including the future direction of RTDS, adjusting the indications according to their own conditions for the institutions carrying out RTDS, the robot-assisted advantage of RTDS being brought into play during the operation, and the perfect post-discharge follow-up mechanism being an important guarantee for the safe development of RTDS, to promote the application progress of RTDS in China.

[Association between hyponatremia and hemodynamic and prognosis in patients with intermediate-risk acute pulmonary embolism]

Objective: To investigate the association between hyponatremia and hemodynamic and prognosis in patients with intermediate-risk acute pulmonary embolism. Methods: We retrospectively recruited 110 intermediate-risk acute pulmonary embolism patients (right ventricular dysfunction was confirmed by echocardiography and CT scan with or without the elevated levels of cardiac injury biomarkers) in the first and the second affiliated hospital of Harbin medical university from January 1,2011 to December 31, 2014. The patients were aged (58.4±14.9) years old.There were 49 males and 61 females.Patients were divided into 2 groups as non-hyponatremia group (plasma sodium>135 mmol/L, 93 cases) and hyponatremia group (plasma sodium≤135 mmol/L, 17 cases). Baseline clinical and hemodynamic parameters were obtained from these patients. All enrolled patients were followed up after discharge. Results: Heart rate ((106.7±21.9) beats per minute vs. (93.4±19.4) beats per minute, P=0.043),N-terminal pro B type natriuretic peptide (NT-proBNP, (5 561±1 593) ng/L vs. (1 738±589) ng/L, P=0.005), mean pulmonary arterial pressure((42.6±12.6)mmHg(1 mmHg=0.133 kPa) vs. (33.9±13.3)mmHg, P=0.046), mean right atria pressure ((20.6±8.1)mmHg vs. (10.2±5.4)mmHg, P=0.014), systolic right atria pressure ((27.3±9.0)mmHg vs. (15.6±6.1)mmHg,P=0.013) and diastolic right atria pressure(6.5(4.3,15.5)mmHg vs. 5.0(2.0,8.0)mmHg,P=0.016) were significantly higher in hyponatremia group than in non-hyponatremia group,and systolic blood pressure was significantly lower in hyponatremia group than in non-hyponatremia group ((113.5±21.9)mmHg vs.(129.5±28.9)mmHg, P=0.048). Pearson correlation analysis showed that hyponatremia was negatively correlated with heart rate (r=-0.262, P=0.043), NT-proBNP (r=-0.227, P=0.048), mean pulmonary arterial hypertension (r=-0.259, P=0.046), mean right ventricular pressure (r=-0.296, P=0.047), mean right atria pressure (r=-0.550, P=0.001), systolic right atria pressure (r=-0.552, P=0.001), and diastolic right atria pressure (r=-0.542, P=0.001). Kaplan-Meier survival analysis showed that the 1-year, 2-year and 3-year cumulative survival rates were 76.5%,70.6%,and 64.7% in the hyponatremia group, and 90.3%,86.0%,and 83.9% in the non-hyponatremia group(log-rank test, P=0.036).Multivariate Cox regression analysis showed that hyponatremia was an independent risk factor of death of intermediate-risk pulmonary embolism patient(HR=4.126, 95%CI 1.982-11.343, P=0.036). Conclusion: Hyponatremia is associated with adverse hemodynamic and reduced survival in patients with intermediate-risk pulmonary embolism.

[Analysis of dietary pattern and diabetes mellitus influencing factors identified by classification tree model in adults of Fujian]

Objective: To find out the dietary patterns and explore the relationship between environmental factors (especially dietary patterns) and diabetes mellitus in the adults of Fujian. Methods: Multi-stage sampling method were used to survey residents aged ≥18 years by questionnaire, physical examination and laboratory detection in 10 disease surveillance points in Fujian. Factor analysis was used to identify the dietary patterns, while logistic regression model was applied to analyze relationship between dietary patterns and diabetes mellitus, and classification tree model was adopted to identify the influencing factors for diabetes mellitus. Results: There were four dietary patterns in the population, including meat, plant, high-quality protein, and fried food and beverages patterns. The result of logistic analysis showed that plant pattern, which has higher factor loading of fresh fruit-vegetables and cereal-tubers, was a protective factor for non-diabetes mellitus. The risk of diabetes mellitus in the population at T2 and T3 levels of factor score were 0.727 (95%CI:0.561-0.943) times and 0.736 (95%CI: 0.573-0.944) times higher, respectively, than those whose factor score was in lowest quartile. Thirteen influencing factors and eleven group at high-risk for diabetes mellitus were identified by classification tree model. The influencing factors were dyslipidemia, age, family history of diabetes, hypertension, physical activity, career, sex, sedentary time, abdominal adiposity, BMI, marital status, sleep time and high-quality protein pattern. Conclusion: There is a close association between dietary patterns and diabetes mellitus. It is necessary to promote healthy and reasonable diet, strengthen the monitoring and control of blood lipids, blood pressure and body weight, and have good lifestyle for the prevention and control of diabetes mellitus.

Fluconazole induces rapid high-frequency MTL homozygosis with microbiological polymorphism in Candida albicans

BACKGROUND

Candida albicans, a common fungal pathogen that can cause opportunistic infections, is regarded as an apparently asexual, diploid fungus. A parasexual cycle was previously found between homozygotes with opposite mating type-like loci (MTLa/α). Fluconazole-resistant strains had a higher proportion of MTL homozygotes, whereas MTL homozygous C. albicans was found in only about 3.2% of clinical strains. MTL heterozygotes had a low frequency (1.4 × 10^-4) of white-opaque switching to MTL homozygotes in nature.

METHODS

Here, a reference C. albicans strain (SC5314) was used in a fluconazole-induced assay to obtain standard opaque MTL homozygous strains and first-generation daughter strains from the fluconazole inhibition zone. Further separation methods were employed to produce second- and third-generation daughter strains. Polymerase chain reaction analysis based on MTL genes was used to define MTL genotypes, and microscopic observations, a flow-cytometric assay, and an antifungal E-test were used to compare microbiological characteristics.

RESULTS

MTL homozygotes were found at a high frequency (17 of 35; 48.6%) in fluconazole-induced first-generation daughter strains, as were morphological polymorphisms, decreased DNA content, and modified antifungal drug susceptibility. High-frequency MTL homozygosity was identified inside the fluconazole inhibition zone within 24 hours. The DNA content of fluconazole-induced daughter strains was reduced compared with their progenitor SC5314 and standard MTL homozygous strains.

CONCLUSION

Treatment with fluconazole, commonly used to treat invasive candidiasis, inhibited the growth of C. albicans and altered its microbiological characteristics. Our results suggest that fluconazole treatment induces the high frequency of loss of heterozygosity and microbiological polymorphism in C. albicans.

Complexity and diversity of F8 genetic variations in the 1000 genomes

BACKGROUND

Hemophilia A (HA) is an X-linked bleeding disorder caused by deleterious mutations in the coagulation factor VIII gene (F8). To date, F8 mutations have been documented predominantly in European subjects and in American subjects of European descent. Information on F8 variants in individuals of more diverse ethnic backgrounds is limited.

OBJECTIVES

To discover novel and rare F8 variants, and to characterize F8 variants in diverse population backgrounds.

PATIENTS/METHODS

We analyzed 2535 subjects, including 26 different ethnicities, whose data were available from the 1000 Genomes Project (1000G) phase 3 dataset, for F8 variants and their potential functional impact.

RESULTS

We identified 3030 single nucleotide variants, 31 short deletions and insertions (Indels) and a large, 497 kb, deletion. Among all variants, 86.4% were rare variants and 55.6% were novel. Eighteen variants previously associated with HA were found in our study. Most of these 'HA variants' were ethnic-specific with low allele frequency; however, one variant (p.M2257V) was present in 27% of African subjects. The p.E132D, p.T281A, p.A303V and p.D422H 'HA variants' were identified only in males. Twelve novel missense variants were predicted to be deleterious. The large deletion was discovered in eight female subjects without affecting F8 transcription and the transcription of genes on the X chromosome.

CONCLUSION

Characterizing F8 in the 1000G project highlighted the complexity of F8 variants and the importance of interrogating genetic variants on multiple ethnic backgrounds for associations with bleeding and thrombosis. The haplotype analysis and the orientation of duplicons that flank the large deletion suggested that the deletion was recurrent and originated by homologous recombination.

Cloning and sequence analysis of the Blumea balsamifera DC farnesyl diphosphate synthase gene

Blumea balsamifera DC is a member of the Compositae family and is frequently used as traditional Chinese medicine. Blumea balsamifera is rich in monoterpenes, which possess a variety of pharmacological activities, such as antioxidant, anti-bacteria, and anti-viral activities. Farnesyl diphosphate synthase (FPS) is a key enzyme in the biosynthetic pathway of terpenes, playing an important regulatory role in plant growth, such as resistance and secondary metabolism. Based on the conserved oligo amino acid residues of published FPS genes from other higher plant species, a cDNA sequence, designated BbFPS, was isolated from B. balsamifera DC using polymerase chain reaction. The clones were an average of 1.6 kb and contained an open reading frame that predicted a polypeptide of 342 amino acids with 89.07% identity to FPS from other plants. The deduced amino acid sequence was dominated by hydrophobic regions and contained 2 highly conserved DDxxD motifs that are essential for proper functioning of FPS. Phylogenetic analysis indicated that FPS grouped with other composite families. Prediction of secondary structure and subcellular localization suggested that alpha helices made up 70% of the amino acids of the sequence.

Characterizing polymorphisms and allelic diversity of von Willebrand factor gene in the 1000 Genomes

BACKGROUND

The von Willebrand factor (VWF) gene is highly polymorphic, with variants correlated with VWF antigen levels, adhesion activity, clearance and factor VIII binding. VWF mutations are detected in patients with von Willebrand disease (VWD), whereas polymorphic variants could be associated with thrombosis. However, information on the ethnic diversity of VWF variants and their association with diseases is limited.

OBJECTIVES

To characterize novel VWF variants from different ethnicities in the general population.

PATIENTS/METHODS

We analyzed samples from 1092 subjects of 14 ethnicities available in the 1000 Genomes database for VWF variants and their potential functional impacts.

RESULTS

We identified 2728 SNPs and 91 insertions and deletions that had a high level of ethnic diversity, with Africans having the highest number of variants. The highest level of diversity was found in the D' and D2 domains. Among 94 non-synonymous variants, 31 were predicted to be deleterious, including 19 that were previously associated with VWD. Most of these 'VWD variants' had allele frequencies consistent with disease incidence in European subjects, but some had a significantly higher frequency in other ethnicities. The mutations R2185Q, H817Q and M740I associated with type 1 and type 2N VWD were present in more than 13% of African subjects.

CONCLUSIONS

These results highlight the complexity of VWF variations in different ethnic groups and emphasize the importance of interrogating variations on multiple ethnic backgrounds for associations with bleeding and thrombosis.

Nephrotoxicity of vancomycin in patients with methicillin-resistant Staphylococcus aureus bacteraemia

AIM

Vancomycin and teicoplanin are the two most used glycopeptides for the treatment of methicillin-resistant Staphylococcus aureus (MRSA). Vancomycin is suspected to have more nephrotoxicity but this has not been clearly established. The aim of this study was to assess its nephrotoxicity by a consensus definition of acute kidney injury (AKI): the risk (R), injury (I), failure (F), loss and end-stage renal disease (RIFLE) classification.

METHODS

Patients with MRSA bacteraemia who were prescribed either vancomycin or teicoplanin between 2003 and 2008 were classified. Patients who developed AKI were classified by RIFLE criteria. Variables such as comorbidities, laboratory data and medical cost information were also obtained from the database. Outcomes determined were: (i) the rate of nephrotoxicity and mortality; and (ii) the association of nephrotoxicity with the length of hospital stay and costs.

RESULTS

The study included 190 patients (vancomycin 33, teicoplanin 157). Fifteen patients on vancomycin and 27 patients on teicoplanin developed AKI (P = 0.0004). In the vancomycin group, four, eight and three patients were classified to RIFLE criteria R, I and F, respectively. In the teicoplanin group, 17, nine and one patient were classified to RIFLE criteria R, I and F, respectively. Kaplan-Meier analysis showed significant difference in time to nephrotoxicity for the vancomycin group compared to the teicoplanin group. No significant differences were found between the groups in terms of total mortality, length of hospital stay and costs.

CONCLUSION

The study data suggest that vancomycin is associated with a higher likelihood of nephrotoxicity using the RIFLE classification.

The effect of 17beta-estradiol-DNA adducts on the replication of exon # 5 of the human suppressor gene p53

Using a PCR technique, exon # 5 of the human tumor suppressor gene p53 was amplified and ligated into the pCRII vector and transformed into Escherichia coli INV alphaF' competent cells. The cloned exon # 5 was 184 bp long. Evidence is presented to show that after dimethyldioxirane epoxidation, 17beta-estradiol was able to form 17beta-estradiol-DNA adducts and to strongly inhibit the replication of the cloned exon # 5 producing smaller sizes of DNA fragments and introducing errors of incorporation at the 3'-end of the terminating DNAs. The errors occurred mainly at the clusters of the complementary 'G' and 'A' bases on the template strand DNA, presumably, the major sites where the 17beta-estradiol-DNA adducts were formed.

The transcriptional effects and DNA-binding specificities of 17beta-estradiol after dimethyldioxirane activation

It was found recently that 17beta-estradiol (E2) could be activated by the epoxide-forming oxidant dimethyldioxirane (DMDO) resulting in the inhibition of rat liver nuclear and nucleolar RNA synthesis in vitro (Carcinogenesis, 17, 1957-1961, 1996). To further study the mechanism of this inhibition, several synthetic DNAs with different base content and sequence were used to study the transcriptional effects and binding specificities of E2 after DMDO activation in vitro. The results show: (1) E2 after activation had a strong inhibitory effect on the template function of both A-T and G-C containing double-stranded DNAs, e.g. poly[d(A-T)], polydG x polydC and poly[d(I-C)], and only a weak inhibition on the single-stranded DNA template, polydC. The inhibition was dose-dependent, and only after DMDO activation. (2) 3H-labeled E2, after DMDO activation, was able to bind DNAs containing both A-T and G-C bases. The order of the binding preference was: calf thymus DNA > poly[d(A-T)] > poly[d(G-C)]. (3) The covalent binding nature of E2 to DNA after activation was further confirmed by 32P-post-labeling analysis using calf thymus DNA. (4) The absorption spectrum of E2 changed, after DMDO treatment, from a peak around 280-290 nm to 260-270 nm with a shoulder appearing around 300-320 nm. These studies have not only confirmed our earlier observation that E2, after DMDO activation, can inhibit DNA-dependent RNA synthesis, but also provided new insights into the DNA-binding properties after activation. Additionally, since epoxidation is often required for the activation of chemical carcinogens to bind DNA, these studies lend further support to our proposed hypothesis that E2 epoxidation may play an initiation role in estrogen carcinogenesis.

Evidence for the DNA binding and adduct formation of estrone and 17beta-estradiol after dimethyldioxirane activation

Estrogens, used widely from hormone replacement therapy to cancer treatment, are themselves carcinogenic, causing uterine and breast cancers. However, the mechanism of their carcinogenic action is still not known. Recently, we found that estrone (E1) and 17beta-estradiol (E2) could be activated by the versatile epoxide-forming oxidant dimethyldioxirane (DMDO), resulting in the inhibition of rat liver nuclear and nucleolar RNA synthesis in a dose-dependent manner in vitro. Since epoxidation is often required for the activation of chemical carcinogens, we proposed that estrogen epoxidation is the underlying mechanism for the initiation of estrogen carcinogenesis (Carcinogenesis 17 (1996) 1957-1961). It is known that initiation requires the binding of a carcinogen to DNA with the formation of DNA adducts. One of the critical tests of our hypothesis is therefore to determine whether E1 and E2 after activation are able to bind DNA. This paper reports that after DMDO activation, [3H]E1 and [3H]E2 were able to bind to both A-T and G-C containing DNAs. Furthermore. the formation of E1-DNA and E2-DNA adducts was detected by 32P-postlabeling analysis.

Effect of aflatoxin B1-8,9-epoxide-DNA adducts on transcription of a supF gene fragment

A linearized template, obtained from the vector pGEM-3Zf(+) containing a supF gene fragment, was treated with aflatoxin B1-8,9-epoxide (AFB1 epoxide) and transcription in vitro was then studied. The template functions of both strands of the supF gene were similarly inhibited as shown by transcription with both T7 and SP6 RNA polymerases. This inhibition was dose-dependent and affected the elongation step more extensively than the initiation step. Gel electrophoretic analysis of RNA formed by T7 RNA polymerase indicated that template treated with different AFB1 epoxide doses yielded the same three major truncated RNA fragments. Sequence analysis showed that these major sites of RNA truncation occurred in the vicinity of adjacent guanine residues in the template.

Activation of 17beta-estradiol and estrone by dimethyldioxirane and inhibition of rat liver nuclear and nucleolar RNA synthesis in vitro

17beta-estradiol (E2), estrone and diethylstilbestrol (DES) had no effect on nuclear and nucleolar RNA synthesis in vitro. However, after reacting with dimethyldioxirane (DMDO), a versatile epoxide-forming oxidant, these estrogens were able to inhibit and in a dose-dependent manner nuclear and nucleolar RNA synthesis in vitro. It was also found that the time required for the maximal activation of these chemicals by DMDO varied: estrone, 10 min; E2, 30 min; DES, 60 min. Tamoxifen (TAM) was also able to inhibit nuclear and nucleolar RNA synthesis in a dose-dependent manner, but the mechanism of this inhibition was more complex. Control experiments clearly indicated, unlike E2, estrone and DES, TAM per se was able to directly inhibit RNA synthesis in vitro. TAM after activation by DMDO was able to further inhibit RNA synthesis contributing part of the total observed inhibition. These data show for the first time that E2, estrone, DES and TAM can be activated by DMDO and possibly to epoxides. We propose that epoxidation of E2 and estrone may be the underlying mechanism of carcinogenesis for these estrogens in vivo.

[Effects of AF64A on neurons containing both nitric oxide synthase and choline acetyltransferase in the rat septal complex]

Ethylcholine mustard aziridinium ion (AF64A), a neurotoxic choline analog, was injected (ICV) bilaterally (1.5 nmol/ventricle, n = 10) into male adult rats to induce a model of Alzheimer's disease (AD). One month later, using NADPH-diaphorase (NADPH-d) histochemistry followed by choline acetyltransferase (ChAT) immunocytochemistry (PAP) on the coronal sections of the septal complex, double-staining experiments were performed to assay the alterations of septal cholinergic neurons coexisted with nitric oxide synthase (NOS). Compared to controls, AF64A can significantly reduce the numbers of ChAT single labelled neurons and NADPH-d + ChAT double labelled neurons in the dorsal subgroup (29.5% and 26.7%, respectively, P < 0.01). Moreover, the dendrites of these neurons were damaged. While administration of AF64A resulted in a significant decrease in the number of ChAT single labelled neurons (35.2%, P < 0.01) in the intermediate subgroup (rostral extension of the nucleus/substantia innominata) NADPH-d + ChAT double labelled neurons were unchanged (P > 0.05). In the midline and the ventral subgroups, both of these two kinds of cholinergic neurons were not affected significantly by AF64A (P > 0.05). Furthermore, AF64A had no effect on NADPH-diaphorase single labelled neurons in all subgroups of septal complex. These results indicate that: (1) the administration of AF64A has different effects on the cholinergic neurons with or without NOS in different subgroups of the septal complex, and the NADPH-d + ChAT double labelled neurons resist the neurotoxicity of AF64A; (2) in the intermediate subgroup, the cholinergic neurons containing NOS may have projections different from those without NOS.

Studies on the isolated transcriptionally active and inactive chromatin fractions from rat liver nuclei

Using mild sonication, nucleoplasmic, nucleolar, and subnucleolar P-3 and S-3 chromatin fractions are isolated from rat liver nuclei. These fractions differ widely (over 80-fold) from each other in transcriptional activity as measured by the chromatin bound engaged RNA polymerases. Chemical analyses indicate that the active chromatin, e.g. P-3 and nucleolar fractions, are rich in RNA and protein as compared to the inactive chromatin, e.g. nucleoplasmic, and S-3 fractions. However, the DNA base content are all the same, showing 40% GC and 60% AT, including P-3 which is enriched in rDNA. Polyacrylamide gel electrophoresis of the 0.25 N HCl extracted proteins shows that all five histones are present in active chromatin. Additionally, the gel reveals two protein bands, one ahead of histone H2B and another ahead of histone H4, that are diminished or missing from the inactive chromatin. On the other hand, there is a fast moving protein band ahead of H4 in the inactive chromatin that is almost absent in the active chromatin. Transcriptional tests using E. coli RNA polymerase and several synthetic DNA templates of known base content and sequence indicate that the 0.25 N HCl soluble protein extracts from active chromatin contain activator proteins which are capable of countering the histone suppressors present in the extracts in a DNA base and sequence specific manner. The data show that although the histone suppressors are able to strongly inhibit the template function of poly[d(A-T)], the protein activators are able to overcome the suppressor activity and stimulate RNA synthesis several-fold when poly(dA).poly(dT) or poly(dT) is used.

Studies on the binding and transcriptional properties of aflatoxin B1-8,9-epoxide

[3H]Aflatoxin B1-8,9-epoxide ([3H]AFB1-8,9-epoxide), the putative ultimate carcinogen of AFB1, was synthesized and tested for its binding specificity to and transcriptional effect on several single- and double-stranded DNAs containing cytosine. The test was carried out over a 200-fold concentration range (i.e. 0.1-20 microgram [3H]AFB1-8,9-epoxide per 0.025 A260 units of DNA). The results show: (i) [3H]AFB1-8,9-epoxide bound preferentially to the double-stranded alternating co-polymer poly[d(G-C)] over the double-stranded poly(dG).poly(dC) and single-stranded poly(dG) or poly(dC) homopolymers. (ii) The binding affinity of [3H]AFB1-8,9-epoxide to poly(dC) was essentially the same as the poly(dG). (iii) Under identical conditions, [3H]AFB1-8,9-epoxide bound to poly(dG).poly(dC) 2.5-3 times more than to poly[d(I-C)]; however, poly[d(I-C)]-directed RNA synthesis was clearly more sensitive to [3H]AFB1-8,9-epoxide inhibition than poly(dG).poly(dC). Conversely, the binding affinity of [3H]AFB1-8,9-epoxide to poly(dC) and to poly[d(I-C)] was quite similar, yet poly(dC)-directed RNA synthesis was much more resistant to [3H]AFB1-8,9-epoxide inhibition than poly[d(I-C)]. (iv) After [3H]AFB1-8,9-epoxide was hydrolyzed to [3H]AFB1-8,9-dihydrodiol (0.01 N NaOH, 10 min 23 degrees C), it was no longer able to bind poly[d(G-C)] or to inhibit poly[d(G-C)]-directed RNA synthesis. These results confirm our earlier studies using microsome-activated AFB1 and AFB1-Cl2 that AFB1 after activation is able to bind cytosine in DNA, and the binding is not via AFB1-8,9-dihydrodiol. Furthermore, the results also suggest that AFB1 adducts may not have the same biological effect depending on the base, sequence as well as the conformation of the DNA where the adducts are formed.

Transcriptional specificities of adriamycin

The transcriptional effect of adriamycin using E. coli RNA polymerase on several single- and double-stranded DNAs of known base content and sequence is studied in vitro. The results show that adriamycin inhibits strongly and with little difference toward both poly[d(A-T)] and poly[d(G-C)] templates, and that it inhibits both single- and double-stranded DNA directed RNA synthesis, albeit the inhibition is clearly preferential to the double-stranded alternating copolymers over the double- and single-stranded homopolymers. Since adriamycin inhibition of RNA synthesis can be totally abolished when assayed in excess amount of DNA, the possibility that adriamycin may also directly inhibit the enzyme RNA polymerase per se is ruled out.

A hypothesis for chemical carcinogen induced chromatin condensation

A hypothesis for chemical carcinogen induced condensation of nuclear and nucleolar chromatin is proposed. Chromatin condensation is believed to be a result of cascade effects initiated by the inhibition of messenger RNA synthesis after exposure to chemical carcinogen in vivo. Inhibition of messenger RNA synthesis leads to the loss of protein production, which in turn causes the dephosphorylation of histone H1 and triggers the condensation of chromatin in vivo.

Evidence for the covalent binding of aflatoxin B1-dichloride to cytosine in DNA

In vitro studies of the effect of aflatoxin B1-dichloride (AFB1-Cl2) on the template function for RNA synthesis of several single- and double-stranded synthetic DNAs containing cytosine and/or hypoxanthine bases are reported. The results indicate: (i) AFB1-Cl2 strongly inhibits the template function of the single-stranded homopolymer polydC and has no effect on polydI, (ii) the inhibition is stronger when cytosine is in the double-stranded alternating copolymer poly[d(I-C)], and (iii) polydI directed RNA synthesis can be inhibited if it is in the double-stranded homopolymer polydI.polydC, although the template function of the polydC strand is still inhibited to a greater extent. The evidence that the selective inhibition of the DNA template function is a direct reflection of the binding specificities of AFB1-Cl2 is provided by the binding studies of [3H]AFB1-Cl2 to these DNAs. The binding of AFB1-Cl2 to polydC is substantiated by the dose-response template inhibition and by the dose-response template binding studies. Additionally, these results show that AFB1 per se has neither inhibitory nor binding activity. Auto radiography of [alpha-32P]GTP labeled RNAs suggests that the mechanism of inhibition of polydC template function by AFB1-Cl2 is mainly due to the inhibition of the elongation of RNA synthesis. Spectrum measurement of the products of enzyme digestion of the AFB1-Cl2 modified polydC reveals that the deoxycytidine fraction gives a typical cytosine absorption peak at 275 nm followed by a broad peak between 300 and 400 nm with a maximum at 390 nm. High performance liquid chromatography confirms the existence of a cytosine-AFB1 adduct which absorbs strongly in the regions between 250 and 400 nm with peaks identifiable at 260, 350 and 390 nm. These results strongly suggest that AFB1 in the activated form of AFB1-Cl2 is able to covalently bind to cytosine in DNA.

Transcriptional effect of aflatoxin B1 on cytosine and/or hypoxanthine containing DNAs

The effect of aflatoxin B1 (AFB1) on the template function for RNA synthesis of several single and double-stranded synthetic DNAs containing cytosine (C) and/or hypoxanthine (H) bases is studied in vitro. The results indicate that AFB1, after liver microsome activation, strongly inhibits the template function of poly[d(I-C)] and has little, if any, effect on polydI.polydC, polydI, or polydC. This conclusion is reached whether rat liver nuclear free RNA polymerase or E. coli RNA polymerase is used for the transcription. The mechanism of this inhibition is believed mainly due to the inhibition of elongation of RNA synthesis, because autoradiography of the [alpha-32 P]GTP labeled RNAs after polyacrylamide gel electrophoresis clearly shows that the size of the RNA from AFB1 treated group is dramatically reduced. The evidence that the selective inhibition of poly[d(I-C)] template function is a direct reflection of the binding of AFB1 to poly[d(I-C)] is provided by the use of radioactive [3H]AFB1 for the binding and by spectrum analysis of the appearance of a broad AFB1-DNA adduct peak between 300 nm and 400 nm right after the typical DNA peak at 260 nm. These data, which are in direct support to our recent report (F.L. Yu, et al., Carcinogenesis, 11, 475-478, 1990), suggest that the binding of AFB1 prefers alternating, double-stranded DNA, and the binding affinity of AFB1 to DNA is greatly reduced when the bases are in either single- or double-stranded homopolymer forms.(ABSTRACT TRUNCATED AT 250 WORDS)

Base and sequence specificities of aflatoxin B1 binding to single- and double-stranded DNAs

The inhibitory effect of alfatoxin B1 (AFB1) on the template function for RNA synthesis of several single- and double-stranded DNAs with known base content and sequence was studied in vitro. The results showed that AFB1 strongly inhibits the template function of poly[d(G-C)] and has little, if any, effect on poly[d(A-T)]. Using [3H]AFB1 for the binding, and by spectrum analysis of the appearance of a broad AFB1-DNA adduct peak between 300 and 400 nm right after the typical DNA peak at 260 nm, it is possible to conclude that the binding preference of AFB1 to DNA is: poly[d(G-C)] greater than polydG.polydC greater than polydG greater than polydC, with no detectable binding to poly[d(A-T)]. These studies have therefore provided evidence that the selective inhibition of DNA template function is a direct reflection of the binding specificities of AFB1 to DNA. Furthermore, since there is a 3-fold binding preference of AFB1 for poly[d(G-C)] over polydG.polydC on an equal weight basis, and with very low binding affinity toward either G or C when it is in single-stranded form, these data also suggest: (i) AFB1 binds preferentially to DNA with an alternating G-C sequence compared to DNA with a sequence of contiguous Gs or Cs; and (ii) intercalation may be part of the mechanism for the binding of AFB1 to DNA.

Template specificities of aclacinomycin B on the inhibition of DNA-dependent RNA synthesis in vitro

The effect of Aclacinomycin B (ACM-B), an anthracycline antitumor antibiotic, on the DNA-dependent RNA synthesis using single- and double-stranded DNAs of known base content and sequence is studied. The data show that ACM-B effectively inhibits the double-stranded DNA-directed RNA synthesis with a preference of poly[d(A-T)] greater than poly[d(G-C)] greater than poly[d(I-C)]. In contrast, it has no inhibitory effect on the template function of single-stranded DNA (e.g. poly dA, poly dT, and poly dC). These results suggest that the mechanism of ACM-B inhibition, like other anthracycline antibiotics, is by intercalation. In addition to the base specificity, there are also dramatic differences in inhibition depending on the base sequence in the DNA template. Thus, ACM-B preferentially inhibits the alternating double-stranded copolymers over the double-stranded homopolymers; e.g. poly[d(A-T)] is inhibited to a greater extent than poly dA.poly dT and poly [d(G-C)] is inhibited more than poly dG.poly dC. Since the inhibition by ACM-B can be totally abolished when assayed in excess amount of DNA, this result suggests that ACM-B inhibition of RNA synthesis is solely on the DNA template (which is in support of the intercalation model), and has ruled out the possibility that ACM-B may also exert an inhibitory effect on the activity of RNA polymerase per se.

The binding of aflatoxin B1 to rat liver nuclear proteins and its effect on DNA-dependent RNA synthesis

This paper reports studies on the binding of aflatoxin B1 (AFB1) to rat liver nuclear proteins in vivo and in vitro, and its effect on RNA synthesis. Two hours after rats (200 g) were given a single i.p. injection of 300 micrograms AFB1 containing 50 microCi [3H]AFB1/100 g body wt, AFB1 was found bound to the free nuclear proteins (29.7 pmol/mg protein), histones (20.3 pmol/mg protein) and chromatin-bound non-histone proteins (13.8 pmol/mg protein). The binding of AFB1 to histones was further studied in vitro. We found that for a given type of histone, the binding level varied greatly depending on the conditions used. Under both in vivo and in vitro conditions, however, H3 was always the most efficient substrate, and H4/H2B always the least efficient substrates for AFB1 binding. These results suggest that the binding preference was mainly related to the intrinsic properties of the histone type, and was little affected by the geometric arrangement of the histones in chromatin. Using nuclear proteins added to the RNA synthesizing system in vitro, we found that only the histone fraction had a strong inhibitory effect. Further studies, however, indicated that this inhibition was not due to histones per se, but rather to poly-ADP-ribosylated histones present in the histone preparations. No detectable difference in effect was found between control and AFB1-bound nuclear proteins on RNA synthesis. Moreover, higher levels of AFB1 binding to histones did not potentiate the inhibitory effect. We therefore conclude, and in direct support to our previous correlation studies (see the preceding paper), that the binding of AFB1 to nuclear proteins has no inhibitory effect on RNA synthesis.

Correlation studies between the binding of aflatoxin B1 to chromatin components and the inhibition of RNA synthesis

Aflatoxin B1 (AFB1) is a potent inhibitor of rat liver nuclear and nucleolar RNA synthesis. However, since after activation AFB1 binds to both DNA and chromosomal proteins, the question is which form of binding is responsible for the inhibition of RNA synthesis. Male Sprague-Dawley rats (200 g) were given i.p. injections of 10, 50, 100, 300 and 500 micrograms AFB1 per 100 g body wt containing 50 microCi [3H]AFB1 (sp. act. 25 Ci/mmol), and the animals sacrificed 2 h later. Liver nuclei, nucleoli and P-3 (a transcriptionally active subnucleolar fraction that is 3.4-fold enriched in active rDNA) were isolated and the binding of AFB1 to DNA and protein of each fraction was determined by DNase I digestion and 5% trichloracetic acid (TCA) hydrolysis. We found that the binding of AFB1 to both nuclear and nucleolar DNA plateaus at 300 micrograms AFB1 per 100 g body wt with values around 100 and 400 pmol AFB1 per mg nuclear and nucleolar DNA, respectively. On the other hand, the binding to protein is linear, although with different slopes, for both nuclear and nucleolar fractions even at 500 micrograms AFB1 per 100 g body wt, the highest dose used. Since AFB1 inhibition of nuclear and nucleolar RNA synthesis plateaus respectively at 60% and 90% inhibition levels at the dose of 300 micrograms AFB1 per 100 g body wt, these results suggest the binding of AFB1 to DNA, but not to protein, is responsible for the inhibition of RNA synthesis. Further support for this contention is obtained by comparing the binding and the inhibition data between P-3 and nucleoli. P-3 is three times more transcriptionally active than nucleoli and, as a result, is more sensitive to AFB1 inhibition. This greater sensitivity is reflected by the specific binding activity of AFB1 to P-3 DNA, which is greater than 50% higher than to nucleolar DNA. In contrast, this effect is not reflected by the specific binding activity of AFB1 to protein which is exactly the same for both fractions.

Errors from using 3H-labeled ribonucleoside triphosphates to monitor nuclear RNA synthesis in vitro

The [3H]XTPs are used widely to monitor RNA synthesis in vitro. Recently, we discovered that they reflected only 40-45% of the true rate of nuclear RNA synthesis. Thus, when [8-14C]GTP was used, 1466 pmol [8-14C]GMP was incorporated per mg DNA/10 min. On the other hand, when [8-3H]GTP was used, only 564 pmol [8-3H]GMP was incorporated per mg DNA/10 min. There are three obvious factors that could have contributed to this greater than 2-fold difference in the apparent incorporation rate: commercial [8-3H]GTP sample was contaminated with substances causing the assay medium to be less efficient in RNA synthesis; 3H exchange occurred during acid washing of the [3H]RNA; and there was a greater quenching effect on [3H]RNA. Experiments were designed to test each of these alternatives. We are able to conclude that none of the above three are contributing factors. Our data also show that the 3H label was removed after it was incorporated into RNA. Similar differences were observed when 3H and 14C labeled pairs of ATP, UTP and CTP were compared. Furthermore, when nuclei were fractionated into nucleolar and nucleoplasmic fractions and carried out RNA synthesis, the loss of 3H label was observed mainly from the nucleoplasmic fraction.

Evidence for an indirect mechanism of aflatoxin B1 inhibition of rat liver nuclear RNA polymerase II activity in vivo

Previous studies suggested multiple sites of action of aflatoxin B1 (AFB1) in vivo to inhibit rat liver nuclear RNA synthesis--it impairs nucleolar DNA template function and inhibits RNA polymerase II activity. We have previously shown that AFB1 activated in vitro inhibits nucleolar RNA synthesis. The question is whether AFB1 can inhibit RNA polymerase II under these in vitro conditions. Male Sprague-Dawley rats, 200 g, were injected i.p. with 0.6 mg AFB1 and liver nuclei were isolated 2 h later. When the total nuclear free RNA polymerases were extracted and assayed in the absence and presence of alpha-amanitin (3.2 micrograms/ml), we found that only alpha-amanitin-sensitive (i.e., RNA polymerase II) activity was inhibited (97%). DEAE-Sephadex chromatography confirmed this result. When total nuclear free RNA polymerases were incubated with AFB1 activated in vitro under conditions producing 70% inhibition of nucleolar RNA synthesis, no inhibition was observed for either alpha-amanitin-sensitive or -resistant activities. Similar results were obtained with low and high (28 and 167 micrograms/ml) concentrations of AFB1. This was further confirmed using highly purified RNA polymerase II. We conclude that AFB1 inhibition of RNA polymerase II activity in vivo is not a result of direct interaction of AFB1 to the enzyme.

Poly-ADP-ribosylated histones: potent DNA suppressors

When rat liver nuclear chromatin was sonicated in buffer containing 0.35 M (NH4)2SO4 to release the engaged RNA polymerases, a potent inhibitor was also released. This inhibitor elicited dramatic inhibition of RNA synthesis regardless of whether the free or engaged RNA polymerase was used. On further analysis, it became apparent that the site of inhibition was on the DNA template, not on the enzyme. This inhibitor could be extracted into 0.25 N HCl by the standard procedure for the isolation of histones. This acid-soluble inhibitor, showing typical histone band on gel, was RNase A and DNase I resistant, but was sensitive to both pronase and snake venom phosphodiesterase digestion, as well as to 0.1 N KOH hydrolysis. Furthermore, when [14C]adenine labeled poly-ADP-ribosylated histones were digested by snake venom phosphodiesterase, the release of radioactivity was in parallel to the loss of inhibitor activity. We conclude that the inhibitor substances are poly-ADP-ribosylated histones and propose that the poly-ADP-ribosylated histones rather than the histones are the natural suppressors of the gene.

Actinomycin D-binding in vivo: active chromatin preferred

Escherichia coli RNA polymerase and the endogenous engaged RNA polymerase I were used as specific probes to monitor the physiologically inactive and active nucleolar chromatin template function, respectively. Actinomycin D bound preferentially to the physiologically active regions of rat liver nucleolar chromatin in vivo.

Effect of methylazoxymethanol acetate on rat liver nuclear and nucleolar RNA synthesis

The effect of methylazoxymethanol acetate on rat liver nuclear and nucleolar RNA synthesis is investigated at various doses (5 to 50 mg/100 g body weight) and for various lengths of time (1 to 24 hr). The results show that this carcinogen is a potent inhibitor of both nuclear and nucleolar RNA synthesis. Like other carcinogens studied previously in this laboratory, e.g., N-hydroxy-2-acetylaminofluorene, aflatoxin B1, and actinomycin D, methylazoxymethanol acetate inhibits RNA synthesis at multiple sites. It impairs chromatin template function and selectively inhibits the activity of RNA polymerase II. Experimental evidence suggests the mechanism of inhibition of RNA polymerase II activity is due to a decrease in catalytic efficiency rather than in the total number of the enzyme. In addition, it is found that methylazoxymethanol acetate induces a dramatic condensation of nucleoplasmic chromatin.

Preferential binding of aflatoxin B1 to the transcriptionally active regions of rat liver nucleolar chromatin in vivo and in vitro

The literature on various isolated carcinogen-DNA adducts indicates clearly that the binding of chemical carcinogens to DNA is highly specific. Since DNA in eukaryotic cells is complexed with chromosomal proteins and organized into transcriptionally active and inactive chromatin, chemical carcinogens also might show binding specificities at the chromatin level. Using Escherichia coli RNA polymerase and the endogenous engaged RNA polymerase I as specific probes to monitor respectively the physiologically inactive and active nucleolar chromatin template function, this paper reports that aflatoxin B1, after metabolic activation either in vivo or in vitro, binds preferentially to the physiologically active regions of rat liver nucleolar chromatin, and that this binding specificity is largely lost after the removal of chromosomal proteins from the nucleoli.

Evidence for the transcription os physiologically inactive rat-liver nucleolar chromatin by Escherichia coli RNA polymerase

Rat-liver nucleoli (10-15 micrograms DNA) were digested with either 0.6 or 3 units of DNase I for various times (up to 1 h). RNA synthesis was then measured in the absence or presence of 3 units of Escherichia coli RNA polymerase. It was found that the nucleolar chromatin supporting the endogenous engaged RNA polymerase I transcription was completely destroyed in 3 min with either concentration of DNase I. The nucleolar chromatin template transcribed by E. coli RNA polymerase retained 50% of its original capacity even 60 min after 3 units of DNase I digestion. When hybridization experiments were conducted, it was found that the DNAs derived from both levels of DNase-I-digested nucleoli were incapable of forming hybrids with the labelled nucleolar RNA synthesized by the engaged RNA polymerase I from the untreated nucleoli. Since the engaged RNA polymerase I transcribes only the physiologically active genes of the nucleolar chromatin, and the RNA transcripts represent active gene product, these data suggest that DNase I digestion has completely destroyed the active genes of the nucleolar chromatin, and E. coli RNA polymerase is able to transcribe the inactive nucleolar chromatin template.

Tissue, sex, and animal species specificity of aflatoxin B1 inhibition of nuclear RNA polymerase II activity

Recent studies from this laboratory have shown that several chemical carcinogens, i.e., aflatoxin B1, N-OH-2-acetyl-aminofluorene, actinomycin D, and methylazoxymethanol acetate, when administered in vivo, have all produced a selective and dramatic inhibition of rat liver nuclear RNA polymerase II activity. To determine whether this inhibition is related to carcinogenesis, aflatoxin B1 is used as a model system to test tissue, sex, and animal species specificity that is known to be characteristic of carcinogenesis. The results show that aflatoxin B1 (3 mg/kg body weight, i.p., 2h) inhibits RNA polymerase II activity only in the target tissue, liver, and not in the non-target tissues, e.g., lung and brain. It inhibits liver RNA polymerase II activity preferentially in male over female rats, and has no effect on mouse liver RNA polymerase II activity. These results are in good agreement with the specificities of aflatoxin B1 carcinogenesis in the whole animal systems. Furthermore, with the four principal aflatoxins tested, the order of inhibitor effect on RNA polymerase II is: B1 greater than G1 greater than B2, G2. It is concluded, therefore, that the inhibition of RNA polymerase II activity and carcinogenesis are likely to be related and that it is theoretically sound to use this inhibition as a diagnostic tool to screen potential carcinogens.

Studies on the mechanism of aflatoxin B1 inhibition of rat liver nucleolar RNA synthesis

In an earlier report, it was shown that aflatoxin B1 treatment strongly inhibits rat liver nucleolar RNA synthesis (Yu, F. L. (1977) J. Biol. Chem. 252, 3245-3251). The present paper is an attempt to elucidate the mechanism of this inhibition. Two h after aflatoxin B1 injection (0.3 mg/100 g body weight), rat liver nucleolar RNA synthesis, in vitro, was inhibited by an average of 90%. This inhibition could result from (a) inhibited RNA polymerase I activity per se, (b) impaired nucleolar DNA template, or (c) impaired nucleolar chromatin. Earlier studies found that the total RNA polymerase I activity was not affected by aflatoxin B1 treatment. In the present work the total nucleolar DNAs from control and from aflatoxin B1-treated groups were isolated and compared for template efficiencies in directing RNA synthesis with solubilized RNA polymerase I from the control group. No difference was found. However, when nucleolar chromatin function was analyzed, it was found that aflatoxin B1 treatment resulted in a dramatic reduction in the RNA chain elongation rate to only 13% of the control. The chain number, which is a measure of the number of engaged enzymes transcribing the nucleolar chromatin initiated in vivo, was only slightly reduced (33%). Furthermore since it was found that aflatoxin B1 treatment did not increase RNase activity in the treated nucleoli, the dramatic decrease in RNA chain elongation is therefore believed to be the major mechanism of aflatoxin B1 inhibition of rat liver nucleolar RNA synthesis. DNase I digestion of the nucleolar chromatin suggests that aflatoxin B1 treatment may have altered the conformation of the transcriptionally active regions of the nucleolar chromatin.

Selective inhibition of rat liver nuclear RNA polymerase II by actinomycin D in vivo

It is well known that actinomycin D, a carcinogen, inhibits DNA-dependent RNA synthesis. The interpretation of this inhibition has been that this carcinogen binds specifically to the deoxyguanosine moiety of a DNA molecule, and thus blocks the template function. This paper presents evidence which suggests that this single mechanistic interpretation of actinomycin D action may not be adequate in eukaryotic cells. Thirty minutes after actinomycin D injection (250 microg/100 g body weight), rat liver nuclear RNA synthesis was inhibited by 81% and nucleolar RNA synthesis was inhibited by 98%. In order to determine whether this inhibition is due to an inhibition of DNA template function or of the RNA polymerase activity, the total nuclear free and engaged RNA polymerases were solubilized and the individual RNA polymerase species were partially purified by DEAE-Sephadex column chromatography. It was found that while the overall enzyme activities of RNA polymerase I and III were not affected, there was a selective inhibition of RNA polymerase II activity (42%). This result suggests that actinomycin D, like aflatoxin B1 and N-hydroxy-2-acetylaminofluorene, inhibits nuclear RNA synthesis at multiple sites; it inhibits nucleolar RNA synthesis by blocking the nucleolar DNA template function, and it inhibits messenger RNA synthesis by inhibiting at least partially the enzyme RNA polymerase II activity per se.

High concentration of RNA polymerase I is responsible for the high rate of nucleolar transcription

When isolated rat liver nuclei and nucleoli are compared for RNA synthesis in vitro, the rate of nucleolar RNA synthesis is found to be more than 10 times higher. In order to understand this high rate of nucleolar transcription, DNA from both nuclear and nucleolar fractions was isolated and compared for the ability to direct RNA synthesis with homologous RNA polymerases. No difference between these two templates is evident. On the other hand, when the total nuclear and nucleolar RNA polymerases are isolated and compared on a per-unit-weight-of-DNA basis, it becomes clear that the nucleolus has a 10-fold higher RNA polymerase concentration than the nucleus. This result suggests that RNA polymerase I concentration rather than the nucleolar DNA template efficiency is responsible for the observed high rate of nucleolar transcription under the normal steady-state condition.

Mechanism of aflatoxin B1 inhibition of rat hepatic nuclear RNA synthesis

This paper reports the evidence for the existence of multiple sites of action of aflatoxin B1 in relation to its inhibition of rat hepatic nuclear RNA synthesis. Two hours after aflatoxin B1 injection (0.3 mg/100 g body weight), rat hepatic nuclear and nucleolar RNA synthesis, in vitro, were inhibited 70 and 90% respectively. When total nuclear free and engaged RNA polymerases were solubilized and assayed in the presence of alpha-amanitin (3.2 micrograms/ml), only alpha-amanitin-sensitive activity was reduced (50 to 70%) by aflatoxin B1. DEAE-Sephadex column chromatography confirmed this finding and further demonstrated that RNA polymerase II was the activity selectively inhibited. Since aflatoxin B1 dramatically inhibited nucleolar RNA synthesis, but had little effect on RNA polymerase I activity per se, it is concluded, therefore, that, in addition to its direct inhibitory effect on the enzymic function of RNA polymerase II, aflatoxin B1 must also cause impairment of the nucleolar DNA template function.

Multiple sites of action of N-hydroxy-2-acetylaminofluorene rat hepatic nuclear transcription

This study attempts to identify the site(s) of action of N-hydroxy-2-acetylaminofluorene (N-OH-AAF) in relation to its inhibition of rat hepatic nuclear RNA synthesis. Two hr after N-OH-AAF injection (3 mg/100 g body weight), rat hepatic nuclear synthesis and nucleolar RNA synthesis in vitro were inhibited by 60 and 80%, respectively. When total nuclear RNA polymerases were solubilized and assayed in the presence of alpha-amanitin (3.2 mug/ml), only alpha-amanitin-sensitive activity was reduced (50%) by N-OH-AAF. Diethylamino-ethyl-Sephadex column chromatography confirmed this finding and further demonstrated that RNA polymerase II was the activity selectively inhibited. Since N-OH-AAF dramatically inhibited nucleolar RNA synthesis but had little effect on RNA polymerase I activity, per se, we therefore concluded that, in addition to its direct inhibitory effect on the enzymic function of RNA polymerase II, N-OH-AAF must also cause impairment of the nucleolar DNA template function.