Hepatic resection as a safe and effective treatment for hepatocellular carcinoma involving a single large tumor, multiple tumors, or macrovascular invasion.

This systematic review examined whether the available evidence justifies using hepatic resection (HR) during later stages of hepatocellular carcinoma (HCC), which contravenes treatment guidelines but is current practice at many medical centers.Official guidelines and retrospective studies recommend different roles for HR for patients with large/multinodular HCC or with HCC involving macrovascular invasion (MVI).Several databases were systematically searched for studies examining the safety and efficacy of HR for treating HCC involving a single large tumor (>5 cm) or multiple tumors, or for treating HCC involving MVI.We identified 50 studies involving 14, 808 patients that investigated the use of HR to treat large/multinodular HCC, and 24 studies with 4389 patients that investigated HR to treat HCC with MVI. Median in-hospital mortality for patients with either type of HCC was significantly lower in Asian studies (2.7%) than in non-Asian studies (7.3%, P < 0.001). Median overall survival (OS) was significantly higher for all Asian patients with large/multinodular HCC than for all non-Asian patients at both 1 year (81% vs 65%, P < 0.001) and 5 years (42% vs 32%, P < 0.001). Similar results were obtained for median disease-free survival at 1 year (61% vs 50%, P < 0.001) and 5 years (26% vs 24%, P < 0.001). However, median OS was similar for Asian and non-Asian patients with HCC involving MVI at 1 year (50% vs 52%, P = 0.45) and 5 years (18% vs 14%, P = 0.94). There was an upward trend in 5-year OS in patients with either type of HCC.HR is reasonably safe and effective at treating large/multinodular HCC and HCC with MVI. The available evidence argues for expanding the indications for HR in official treatment guidelines.

Methylenetetrahydrofolate reductase gene polymorphism and risk of type 2 diabetes mellitus.

OBJECTIVE: This review aimed to comprehensively assess the literature examining a possible link between the rs1801133 polymorphism (677C → T) in the gene encoding the methylenetetrahydrofolate reductase (MTHFR) gene and risk of type 2 diabetes mellitus (DM). RESEARCH DESIGN AND METHODS: Several research databases were systematically searched for studies examining the genotype at the rs1801133 polymorphism in healthy control individuals and individuals with type 2 DM. Genotype frequency data were examined across all studies and across subsets of studies according to ethnicity and presence of serious DM-related complications. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. RESULTS: A total of 4855 individuals with type 2 DM and 5242 healthy controls from 15 countries comprising Asian, Caucasian and African ethnicities were found to satisfy the inclusion criteria and included in the review. Genotype at the rs1801133 polymorphism was not consistently associated with either increased or reduced risk of type 2 DM; the OR across all studies was 0.91 (95%CI 0.82 to 1.00) for the C- vs. T-allele, 0.88 (0.75 to 1.03) for CC vs. CT+TT, 0.82 (0.71 to 0.95) for CC vs. TT, and 1.15 (1.03 to 1.29) for TT vs. CC+CT. Similar results were found when the meta-analysis was repeated separately for each ethnic subgroup, and for subgroups with or without serious DM-related complications. CONCLUSIONS: There does not appear to be compelling evidence of an association between the genotype at the rs1801133 polymorphism of the MTHFR gene and risk of type 2 DM.

Challenges to implementation of medical residency programs in China: a five-year study of attrition from West China hospital.

PURPOSE: To increase opportunities for advanced clinical training, a few medical schools in China have created U.S.-style, temporary-contract residency programs for medical graduates, but nearly nothing is known about what proportion of residents successfully complete these programs or what factors affect attrition. METHOD: By directly surveying and interviewing residents who withdrew voluntarily, the authors examined attrition from 16 medical specialties in the residency program of West China Hospital, Sichuan University, from the start of the program in 2003 through 2008. RESULTS: During the study period, 562 trainees matriculated into the program, and 127 (22.6%) withdrew before completing it; 106 (18.9%) withdrew voluntarily. Those who left voluntarily most frequently cited three reasons: (1) permanent employment in other hospitals, (2) pursuit of a higher academic degree, and (3) personal reasons. Nearly 90% (n = 92) of the residents who left voluntarily did so within two years of obtaining their medical license. Women were 1.82-fold more likely than men to leave (95% CI 1.20-2.76, P = .005). Attrition by specialty ranged from 3.7% to 42.9% over the study period. Surgery had one of the lowest attrition rates. CONCLUSIONS: Attrition is a challenge for the West China residency program just as it is for U.S. residency programs, but the factors behind attrition in each country differ significantly. To reduce attrition from temporary-contract residency programs in China, the programs themselves and government policies may need to change so that completing such residencies is as competitive an option as taking permanent hospital positions immediately after graduation.

Human topoisomerase IIalpha rapidly relaxes positively supercoiled DNA: implications for enzyme action ahead of replication forks.

Movement of the DNA replication machinery through the double helix induces acute positive supercoiling ahead of the fork and precatenanes behind it. Because topoisomerase I and II create transient single- and double-stranded DNA breaks, respectively, it has been assumed that type I enzymes relax the positive supercoils that precede the replication fork. Conversely, type II enzymes primarily resolve the precatenanes and untangle catenated daughter chromosomes. However, studies on yeast and bacteria suggest that type II topoisomerases may also function ahead of the replication machinery. If this is the case, then positive DNA supercoils should be the preferred relaxation substrate for topoisomerase IIalpha, the enzyme isoform involved in replicative processes in humans. Results indicate that human topoisomerase IIalpha relaxes positively supercoiled plasmids >10-fold faster than negatively supercoiled molecules. In contrast, topoisomerase IIbeta, which is not required for DNA replication, displays no such preference. In addition to its high rates of relaxation, topoisomerase IIalpha maintains lower levels of DNA cleavage complexes with positively supercoiled molecules. These properties suggest that human topoisomerase IIalpha has the potential to alleviate torsional stress ahead of replication forks in an efficient and safe manner.

Investigating the role of the latch in the positive supercoiling mechanism of reverse gyrase.

Reverse gyrase is the only topoisomerase known to positively supercoil DNA and the only protein unique to hyperthermophiles. The enzyme comprises an N-terminal ATPase domain and a C-terminal topoisomerase I domain, which interact to couple the hydrolysis of ATP to the overwinding of DNA. The part of the ATPase domain termed the "latch" represses topoisomerase activity in the absence of nucleotide. Here I provide evidence that the latch, in addition to its regulatory role, participates in the supercoiling mechanism during the DNA cleavage and religation steps. The latch also contributes to the coordination of ATP hydrolysis and positive supercoiling by inhibiting ATPase activity in the absence of supercoiling. The latch therefore plays an important role in the communication between the two domains of reverse gyrase.

Studies of a positive supercoiling machine. Nucleotide hydrolysis and a multifunctional "latch" in the mechanism of reverse gyrase.

Reverse gyrase, the only topoisomerase known to positively supercoil DNA, has an N-terminal ATPase domain that drives the activity of a topoisomerase domain. This study shows that the N-terminal domain represses topoisomerase activity in the absence of nucleotide, and nucleotide binding is sufficient to relieve the repression. A "latch" region in the N-terminal part was observed to close over the topoisomerase domain in the reverse gyrase crystal structure. Mutants lacking all or part of the latch relax DNA in the absence of nucleotide, indicating that this region mediates topoisomerase repression. The mutants also show altered DNA-dependent ATPase activity, suggesting that the latch may be involved in coupling nucleotide hydrolysis to supercoiling. It is not required for this process, however, because the mutants can still positively supercoil DNA. Nucleotide hydrolysis is essential to the specificity of reverse gyrase for increasing the linking number of DNA. Although with ATP the enzyme performs strand passage always toward increasing linking number, it can increase or decrease the linking number in the presence of a nonhydrolyzable ATP analog. This suggests that the mechanism of reverse gyrase is best described by a combination of recently proposed models.

Crystal structure of reverse gyrase: insights into the positive supercoiling of DNA.

Reverse gyrase is the only topoisomerase known to positively supercoil DNA. The protein appears to be unique to hyperthermophiles, where its activity is believed to protect the genome from denaturation. The 120 kDa enzyme is the only member of the type I topoisomerase family that requires ATP, which is bound and hydrolysed by a helicase-like domain. We have determined the crystal structure of reverse gyrase from Archaeoglobus fulgidus in the presence and absence of nucleotide cofactor. The structure provides the first view of an intact supercoiling enzyme, explains mechanistic differences from other type I topoisomerases and suggests a model for how the two domains of the protein cooperate to positively supercoil DNA. Coordinates have been deposited in the Protein Data Bank under accession codes 1GKU and 1GL9.