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Biomedical subjects

A Weston

Publications and source records attributed to A Weston.

At least 19 recordsLinked to original sources
PubMed1997

p53 haplotype determination in breast cancer.

Inheritance of certain germ line haplotypes consisting of three biallelic polymorphisms of p53 has been proposed as a risk factor for breast cancer and colorectal cancer [A. Själander et al., Carcinogenesis (Lond.), 17: 1313-1316, 1996, and Carcinogenesis (Lond.), 16: 1461-1464, 1995]. In their studies, pairwise haplotypes of these three polymorphisms were estimated. Extended haplotypes were further projected from the pairwise combinations. To overcome the necessity to estimate pairwise and extended haplotype frequencies, a PCR method has been developed to determine the absolute extended p53 haplotypes in diploid genomes. The method requires allele-specific PCR, confirmed by restriction analysis, and successive amplicon analysis. It has been applied to a nested case-control study of breast cancer (284 subjects; 99 cases and 185 controls; 182 Caucasians, 56 Hispanics, and 46 African-Americans). Evidence is presented that minor variants of the intron 3, codon 72, and intron 6 polymorphisms were moderately elevated in Caucasian breast cancer cases (intron 3, P = 0.03 for genotype and P = 0.01 for allelic frequency; codon 72, P = 0.07 for genotype and P = 0.054 for allelic frequency; and intron 6, P = 0.02 for genotype and P = 0.02 for allele frequency). Accordingly, analysis of haplotype distributions suggested an association of minor p53 haplotypes with breast cancer risk in Caucasians (P = 0.07). The relative allelic frequencies in breast cancer cases compared with controls also differed by age and menopausal status; the 1-2-1 haplotype was overrepresented in postmenopausal cases (P = 0.02) and cases older than 50 years (P = 0.02), whereas the other minor haplotypes (1-1-2 and rare variants) were overrepresented in premenopausal cases (P = 0.003) and cases 50 years of age and younger (P = 0.02). Genotype distributions at each locus and for all control groups were consistent with Hardy-Weinberg equilibria. Differences in haplotype distribution were associated with ethnicity (Caucasians versus African-Americans and Caucasians versus Hispanics, P < 0.001). The new haplotyping method may be useful in the study of gene-environment interactions.

Adult↗
PubMed1996

Enzymatic synthesis of UDP-galactofuranose and an assay for UDP-galactopyranose mutase based on high-performance liquid chromatography.

A method to prepare UDP-galactofuranose (UDP-Galf) free of UDP-galactopyranose (UDP-Galp) is described. The UDP-Galf is synthesized enzymatically from UDP-Galp using the enzyme UDP-galactopyranose mutase. Treatment of UDP-Galp with the enzyme yields an equilibrium mixture of UDP-Galp and UDP-Galf in which UDP-Galf is approximately 7%. In spite of its low yield, the UDP-Galf is readily purified from starting UDP-Galp using a Dionex PA-100 ion exchange HPLC column. The purified UDP-Galf was characterized by chemical degradations, by electrospray mass spectrometry, and by several nuclear magnetic resonance techniques. In addition, an HPLC assay for the enzyme UDP-galactopyranose mutase is presented that requires 0.5 microgram of UDP-Galf per assay and can be used for both qualitative and quantitative measurements of the enzyme activity. These procedures should thus aid in the characterization of the enzymes involved in galactofuranosyl biosynthesis for the cell walls of Mycobacteria, for the lipophosphoglycan of Leishmania, and for other microorganisms where galactofuranosyl residues are found.

Bacterial Proteins↗
PubMed1996

Galactofuranose biosynthesis in Escherichia coli K-12: identification and cloning of UDP-galactopyranose mutase.

We have cloned two open reading frames (orf6 and orf8) from the Escherichia coli K-12 rfb region. The genes were expressed in E. coli under control of the T7lac promoter, producing large quantities of recombinant protein, most of which accumulated in insoluble inclusion bodies. Sufficient soluble protein was obtained, however, for use in a radiometric assay designed to detect UDP-galactopyranose mutase activity (the conversion of UDP-galactopyranose to UDP-galactofuranose). The assay is based upon high-pressure liquid chromatography separation of sugar phosphates released from both forms of UDP-galactose by phosphodiesterase treatment. The crude orf6 gene product converted UDP-[alpha-D-U-14C]-galactopyranose to a product which upon phosphodiesterase treatment gave a compound with a retention time identical to that of synthetic alpha-galactofuranose-1-phosphate. No mutase activity was detected in extracts from cells lacking the orf6 expression plasmid or from orf8-expressing cells. The orf6 gene product was purified by anion-exchange chromatography and hydrophobic interaction chromatography. Both the crude extract and the purified protein converted 6 to 9% of the UDP-galactopyranose to the furanose form. The enzyme was also shown to catalyze the reverse reaction; in this case an approximately 86% furanose-to-pyranose conversion was observed. These observations strongly suggest that orf6 encodes UDP-galactopyranose mutase (EC 5.4.99.9), and we propose that the gene be designated glf accordingly. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified UDP-galactopyranose mutase revealed one major band, and analysis by electrospray mass spectrometry indicated a single major species with a molecular weight of 42,960 +/- 8, in accordance with that calculated for the Glf protein. N-terminal sequencing revealed that the first 15 amino acids of the recombinant protein corresponded to those expected from the published sequence. UV-visible spectra of purified recombinant enzyme indicated that the protein contains a flavin cofactor, which we have identified as flavin adenine dinucleotide.

Amino Acid Sequence↗
PubMed1996

Human DNA adduct measurements: state of the art.

Human DNA adduct formation (covalent modification of DNA with chemical carcinogens) is a promising biomarker for elucidating the molecular epidemiology of cancer. Classes of compounds for which human DNA adducts have been observed include polycyclic aromatic hydrocarbons (PAHs), nitrosamines, mycotoxins, aromatic amines, heterocyclic amines, ultraviolet light, and alkylating cancer chemotherapeutic agents. Most human DNA adduct exposure monitoring has been performed with either 32P-postlabeling or immunoassays, neither of which is able to chemically characterize specific DNA adducts. Recently developed combinations of methods with chemical and physical end points have allowed identification of specific adducts in human tissues. Studies are presented that demonstrate that high ambient levels of benzo[a]pyrene are associated with high levels of DNA adducts in human blood cell DNA and that the same DNA adduct levels drop when the ambient PAH levels decrease significantly. DNA adduct dosimetry, which has been achieved with some dietary carcinogens and cancer chemotherapeutic agents, is described, as well as studies correlating DNA adducts with other biomarkers. It is likely that some toxic, noncarcinogenic compounds may have genotoxic effects, including oxidative damage, and that adverse health outcomes other than cancer may be correlated with DNA adduct formation. The studies presented here may serve as useful prototypes for exploration of other toxicological end points.

Biomarkers↗
PubMed1996

A prospective audit of cholecystectomy in a single health district.

Laparoscopic cholecystectomy is becoming the treatment of choice for patients presenting with gallstones. A prospective audit of all patients undergoing cholecystectomy in a single health district over a six-month period was carried out. The aim was to define those patients not having laparoscopic cholecystectomy and determine the morbidity and mortality associated with open and laparoscopic procedures. Cholecystectomy was performed on 173 patients; 149 operations were attempted laparoscopically, of which 134 were successful, giving a conversion rate of 10%. Elective open cholecystectomy was performed on 24 patients. Twenty of these patients were under the care of a consultant who only performs open cholecystectomy and the others were not offered a laparoscopic procedure because of previous abdominal operations. The median time taken for open cholecystectomy was significantly shorter (P < 0.05) than for laparoscopic cholecystectomy or for converted procedures. Laparoscopic cholecystectomy resulted in bile duct injury in one patient (0.7%). This study shows that the majority of patients with gallstones are being offered laparoscopic cholecystectomy, although some patients will undergo open cholecystectomy. The latter include patients under the care of surgeons not performing laparoscopic cholecystectomy, those presenting as an emergency where laparotomy is performed and those where laparoscopy is contra-indicated. The findings of this study are probably representative of other health districts where a similar mix of surgical practice exists.

Adult↗
PubMed1995

Biracial differences in physical activity and body composition among women.

Overweight among black females is almost two times as frequent as among white females. Genetics, caloric intake, and physical activity have been identified as possible explanatory factors. This study assessed the differences in physical activity and body composition in 76 white and 66 black adult females. Black women had significantly higher (p = .0001) percent body fat (32.2 +/- 7.1) than white women (27.7 +/- 6.5) with a similar difference in weight (4.4 kg) approaching significance (p = .055). Physical activity was assessed using a structured 24-hour recall instrument. A purposive sampling design was implemented to control for age, education and occupation. A summary physical activity value unit for the 24-hour period revealed a significantly greater mean value for white females (41.93 +/- 4.7) than for black females (40.01 +/- 3.9) suggesting white females were more physically active (p = .02) although this was not a function of biracial differences in play/recreation and exercise/sport type of activities. Although both black and white females were found to be sedentary (MET value < or = 2) over 90 percent of the time, black women are significantly more sedentary (p = .03). Biracial differences in discretionary non-exercise oriented activities may contribute to different rates of overweight observed between black and white women.

Adult↗
PubMed1995

Solid matrix, room temperature phosphorescence identification and quantitation of the tetrahydrotetrols derived from the acid hydrolysis of benzo[a]pyrene-DNA adducts from human lung.

A new method, suitable for human biomonitoring, that uses room temperature phosphorescence for the detection of DNA damage by carcinogenic metabolites of polycyclic aromatic hydrocarbons is described. Samples of human lung DNA (1 mg) that had been subjected to immunoaffinity chromatography (anti-benzo[a]pyrene-diol-epoxide deoxyguanosine monoclonal antibodies) were acid hydrolyzed (0.1 N HCl, 90 degrees C, 3 h) and the resulting DNA lung hydrolyzates separated by high performance liquid chromatography. Relevant fractions were combined with a solid matrix support which consisted of a mixture of alpha-cyclodextrin (alpha-CD):NaCl (1:9) or alpha-CD:TINO3: aNO3 (1:1:8). The dried and powdered sample-matrix material was analyzed by phosphorescence spectroscopy at room temperature. Certain fractions of human lung samples were found to contain materials that yielded phosphorescence spectra that were indistinguishable from those produced when an authentic r-7, t-8, t-9, c-10-tetrahydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene reference standard was analyzed. The data confirm previous studies that have reported the presence of r-7, t-8 dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene-DNA adducts in human tissues at levels of 1 adduct/10(7)-10(8) nucleotides. The alpha-cyclodextrin solid matrix, room temperature phosphorescence technique was performed with a commercially available instrument, but is 50 times more sensitive than the synchronous fluorescence spectroscopic technique previously used.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1995

Interindividual differences in the concentration of 1-hydroxypyrene-glucuronide in urine and polycyclic aromatic hydrocarbon-DNA adducts in peripheral white blood cells after charbroiled beef consumption.

Biological markers of internal dose and macromolecular dose from PAHs provide a potential means of assessing environmental exposure to PAHs through inhalation, ingestion and percutaneous absorption. In this study we examined the time course and interindividual variation of 1-hydroxypyrene-glucuronide (1-OHP-gluc) excretion in urine and PAH-DNA adduct formation in peripheral white blood cells (WBCs) after charbroiled (CB) beef consumption. As a marker of internal dose, 1-OHP-gluc was measured in human urine using immunoaffinity chromatography and synchronous fluorescence spectroscopy. PAH-DNA adducts were measured in WBCs by enzyme-linked immunosorbent assay (ELISA) in order to assess macromolecular dose. Ten healthy non-smoking males consumed identical amounts of CB beef on five consecutive days. Multiple blood and urine samples were collected before, during, and after the feeding period. The morning after the first day of CB beef consumption, individual urinary concentrations of 1-OHP-gluc increased 10- to 80-fold (range: 2.0-16.6 pmol/ml urine) above pre-feed baseline concentrations (0.23 +/- 0.11 pmol/ml) in the 10 subjects. 1-OHP-gluc concentration decreased to near baseline levels by 24-72 h after CB beef consumption ended. In contrast, PAH-DNA adducts in WBCs increased markedly in only four of 10 subjects during or after CB beef consumption. Significant interindividual variation was observed for both urinary 1-OHP-gluc concentration (P < 0.001 by Kruskal-Wallis) and PAH-DNA adduct levels (P < 0.005) during the feeding period. The mean urinary 1-OHP-gluc concentration for each subject during and immediately after (days 2-8) the feeding period was significantly correlated with their mean PAH-DNA adduct level in WBCs during the same time period (Spearman r = 0.79, P < 0.01). Evidence of segregation of the subjects into separate response groups based on level of urinary 1-OHP-gluc was observed, suggesting that discrete determinants may regulate the absorption, metabolism and/or excretion of ingested pyrene.

Adult↗
PubMed1995

Biosynthetic origin of mycobacterial cell wall arabinosyl residues.

Designing new drugs that inhibit the biosynthesis of the D-arabinan moiety of the mycobacterial cell wall arabinogalactan is one important basic approach for treatment of mycobacterial diseases. However, the biosynthetic origin of the D-arabinosyl monosaccharide residues themselves is not known. To obtain information on this issue, mycobacteria growing in culture were fed glucose labeled with 14C or 3H in specific positions. The resulting radiolabeled cell walls were isolated and hydrolyzed, the arabinose and galactose were separated by high-pressure liquid chromatography, and the radioactivity in each sugar was determined. [U-14C]glucose, [6-3H]glucose, [6-14C]glucose, and [1-14C]glucose were all converted to cell wall arabinosyl residues with equal retention of radioactivity. The positions of the labeled atoms in the arabinose made from [1-14C]glucose and [6-3H]glucose were shown to be C-1 and H-5, respectively. These results demonstrated that the arabinose carbon skeleton is formed via the nonoxidative pentose shunt and not via hexose decarboxylation or via triose condensations. Since the pentose shunt product, ribulose-5-phosphate, is converted to arabinose-5-phosphate as the first step in 3-keto-D-manno-octulosonic acid biosynthesis by gram-negative bacteria, such a conversion was then searched for in mycobacteria. However, cell-free enzymatic analysis using both phosphorous nuclear magnetic resonance spectrometry and colorimetric methods failed to detect the conversion. Thus, the conversion of the pentose shunt intermediates to the D-arabino stereochemistry is not via the expected isomerase but rather must occur via novel metabolic transformations.

Arabinose↗
PubMed1994

Possible link between anaphylactoid reactions to anaesthetics and chemicals in cosmetics and biocides.

Binding-inhibition studies involving human IgE antibody to suxamethonium, SUX (from a patient with a near-fatal reaction), were performed with five different quaternary ammonium compounds (QAC): three common ingredients of cosmetics and two commonly used disinfectants, cetrimide and benzalkonium. All the five QAC showed immunological cross-reaction with SUX. In addition, at high concentrations, they released histamine from basophils of normal subjects. Thus, QAC may be both sensitizers and histamine releasers.

Anaphylaxis↗
PubMed1994

Identification of 1-hydroxypyrene glucuronide as a major pyrene metabolite in human urine by synchronous fluorescence spectroscopy and gas chromatography-mass spectrometry.

Humans are exposed to polycyclic aromatic hydrocarbons (PAHs) from various occupational, environmental, medicinal and dietary sources. The measurement of specific PAH metabolites, particularly 1-hydroxypyrene, in human urine treated with deconjugating enzymes (e.g. beta-glucuronidase) has been extensively used as a means of assessing recent exposure to PAHs. We have examined pyrene metabolites in human urine prior to enzymatic deconjugation in order to determine the relative proportions of conjugated and unconjugated pyrene metabolites. The analytical method utilized immunoaffinity chromatography, high performance liquid chromatography (HPLC) and the complementary techniques of synchronous fluorescence spectroscopy (SFS) and gas chromatography-mass spectrometry (GC-MS) to measure pyrene-containing metabolites. SFS analysis of immunoaffinity-purified urine samples showed fluorescence spectra characteristic of the pyrene moiety (using wavelength differences of 34 nm, 54 nm and 102 nm). These spectra are produced by several PAHs containing the pyrene moiety. HPLC analysis with fluorescence detection indicated that the major fluorescent metabolite in immunoaffinity-purified urine was much more polar than simple hydroxylated metabolites of pyrene (1-hydroxypyrene) or benzo[a]pyrene (benzo[a]pyrene-diols or -tetrols). Following digestion with beta-glucuronidase, this metabolite co-chromatographed with authentic 1-hydroxypyrene and exhibited fluorescence spectra characteristic of 1-hydroxypyrene, suggesting that the major metabolite was a glucuronide conjugate of 1-hydroxypyrene. This was subsequently confirmed by GC-MS analysis of trimethylsilyl derivatives of the major metabolite; both 1-hydroxypyrene and glucuronic acid were detected independently as derivatized products. Since 1-hydroxypyrene glucuronide is approximately 5-fold more fluorescent than 1-hydroxypyrene, it may provide a more sensitive biomarker for assessing exposure to pyrene in mixtures of PAHs.

Chromatography, High Pressure Liquid↗
PubMed1994

Determination of the allelic frequencies of an L-myc and a p53 polymorphism in human lung cancer.

The L-myc and p53 genes have been implicated in lung cancer. Both of these genes have restriction fragment length polymorphisms (RFLPs) that could account for differential expression or activity of variant forms. An EcoRI restriction site in the L-myc gene was previously reported to be a predictor of poor prognosis in Japanese lung cancer patients. There are several RFLPs in the p53 gene. In exon 4 there is a polymorphism that codes for either an arginine or proline residue at codon 72. We previously reported the frequency of DNA-RFLPs at these gene loci revealed by EcoRI and AccII respectively. Here we report results from a study comparing lung cancer cases (n = 31) with chronic obstructive pulmonary disease controls (n = 49). No association was found between these RFLPs and disease status. Previous observations that the frequencies of these RFLPs varied by race were confirmed. The p53 arginine allele was found to be more common in Caucasians (0.71) than African-Americans (0.50). The EcoRI restriction site present allele in L-myc was more frequent in African-Americans (0.71) than Caucasians (0.49). Thus, the allelic frequency for L-myc was similar in African-Americans to that reported for Japanese, and the allelic frequency for p53 was similar in Caucasians to that reported for Japanese.

Base Sequence↗
PubMed1994

Analysis of cytochrome P450 2E1 genetic polymorphisms in relation to human lung cancer.

Human cancer risk assessment using molecular genetic techniques is a rapidly emerging field. Many studies suggest that both inherited and acquired genetic predispositions play an important role in carcinogenesis. Cytochrome P450 (CYP) 2E1 is involved in the metabolic activation of N-nitrosamines and other low molecular weight compounds. A recently described genetic polymorphism of CYP2E1 [DraI restriction fragment length polymorphism (RFLP)] has been associated with an increased risk of lung cancer in Japanese. We have assessed the allelic frequency of three RFLPs (PstI, RsaI, and DraI) in African-Americans (n = 109), Caucasian Americans (n = 153), and octogenarian Japanese (n = 42), and also in a United States case-control study of lung cancer (histologically confirmed lung cancer, n = 58; controls, n = 56; total, n = 114). The relationship of the CYP2E1 DraI polymorphism to other CYP2E1 polymorphisms (PstI and RsaI RFLP) was examined. The allelic frequency of the DraI C minor allele for all subjects was 0.09 in Caucasians, 0.09 in African-Americans, and 0.31 in Japanese. In the case-control study of lung cancer, no association of the CYP2E1 DraI genotype with lung cancer was found (odds ratio, 1.57; 95% confidence interval, 0.59-4.18). Comparison after discordant CYP2E1 genotypes suggests the presence of different haplotypes in Americans and Japanese. These results indicate that the CYP2E1 DraI RFLP is probably not a cancer risk factor in United States Caucasian or African-Americans, although statistical power is limited given the low frequency of the CYP2E1 DraI C minor alleles.

Aged↗
PubMed1993

Protein O-mannosylation in Candida albicans. Determination of the amino acid sequences of peptide acceptors for protein O-mannosyltransferase.

A protein-O-D-mannosyltransferase (PMT) assay was optimised using a microsomal membrane preparation from Candida albicans and a peptide acceptor, YNPTSV. [14C]Mannose was transferred from dolichyl phosphate [14C]mannose to the threonine or serine residues of the peptide. During the assay, the peptide was highly susceptible to proteolysis. A blocked peptide Ac-YNPTSV-NH2 was resistant to proteolysis and was apparently a better acceptor for O-mannosylation. This peptide had a Km value of 4.3 mM in the assay. A number of other peptides were tested with altered sequences. Maximum incorporation of [14C]mannose was obtained with a pentapeptide YATAV (Km 2.2 mM) which was further improved by blocking both ends: Ac-YATAV-NH2 (Km 0.25 mM). Finally, and unexpectedly, an improvement was noted if the acetyl group on the N terminus was replaced by a biotin residue. Biotin-YATAV-NH2 had a Km of 0.075 mM. The biotin residue may be important in increasing the lipophilicity of the peptide and thus aid its adhesion to the Candida membranes. The simplest peptide that could act as an efficient mannose acceptor was Ac-ATA-NH2, whilst no incorporation was observed with Ac-GTG-NH2.

Amino Acid Sequence↗
PubMed1993

Polycyclic aromatic hydrocarbon-DNA adducts in human lung and cancer susceptibility genes.

Molecular dosimetry for polycyclic aromatic hydrocarbon-DNA adducts, genetic predisposition to cancer, and their interrelationships are under study in numerous laboratories. This report describes a modified 32P-postlabeling assay for the detection of polycyclic aromatic hydrocarbon-DNA adducts that uses immunoaffinity chromatography to enhance chemical specificity and quantitative reliability. The assay incorporates internal standards to determine direct molar ratios of adducts to unmodified nucleotides and to assess T4 polynucleotide kinase labeling efficiency. High performance liquid chromatography is used to assure adequacy of DNA enzymatic digestion. The assay was validated using radiolabeled benzo(a)pyrene-diol-epoxide modified DNA (r = 0.76, P < 0.05) thereby assessing all variables from enzymatic digestion to detection. Thirty-eight human lung samples were examined and adducts were detected in seven. A subset of samples also was examined for benzo(a)pyrene-diol-epoxide-DNA adducts by immunoaffinity chromatography, high performance liquid chromatography, and synchronous fluorescence spectroscopy. A high correlation between the two assays was found (P = 0.006). The lung samples were then analyzed by the polymerase chain reaction for the presence of mutations in the cytochrome P-450 (CYP) 1A1 and glutathione S-transferase mu (GST mu) genes. A positive association was identified for adduct levels and GST mu null genotypes (P = 0.038). No correlation was found between polycyclic aromatic hydrocarbon-adduct levels and CYP1A1 exon 7 mutations. Age, race, and serum cotinine were not related to adduct levels. Multivariate analysis indicated that only the GST mu genotype was associated with polycyclic aromatic hydrocarbon-DNA adduct levels. This work demonstrates that the 32P-postlabeling assay can be modified for chemically specific adduct detection and that it can be used in the assessment of potentially important genetic factors for cancer risk. The absence of a functional GST mu gene in humans is likely one such factor.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1993

Simian virus 40 large tumor antigen-immortalized normal human liver epithelial cells express hepatocyte characteristics and metabolize chemical carcinogens.

Normal human liver tissue and cultured human hepatocytes are valuable models to study xenobiotic metabolism and toxicity, but they only have a limited in vitro life-span and are not readily available. This report describes the establishment of replicative cultures of human adult liver epithelial cells in serum-free medium. The longevity of three of these cultures, derived from different donors, was extended by introduction of the simian virus 40 large T antigen gene. Two cell lines, THLE-2 and -3, established with a recombinant simian virus 40 large T antigen virus have undergone > 100 population doublings, are nontumorigenic when injected into athymic nude mice, have near-diploid karyotypes, and do not express alpha-fetoprotein. The cells express cytokeratin 18 and albumin in early passage, whereas higher-passage cells in logarithmic-phase growth also express cytokeratin 19. THLE-2 and -3 cells metabolize benzo[a]pyrene, N-nitrosodimethylamine, and aflatoxin B1 to their ultimate carcinogenic metabolites that adduct DNA, which indicates functional cytochrome P450 pathways. Other enzymes involved in metabolism of chemical carcinogens, such as epoxide hydrolase, NADPH cytochrome P450 reductase, superoxide dismutase, catalase, glutathione S-transferases, and glutathione peroxidase are also retained by THLE cells. Thus, these immortalized human liver cells constitute an in vitro model for pharmacotoxicological studies and for the investigation of etiology and pathogenesis of human hepatocellular carcinoma.

Adult↗