Cerebral venous thrombosis at high altitude: A systematic review.

BACKGROUND AND OBJECTIVE: High altitude may be a factor associated with cerebral venous thrombosis (CVT). As our knowledge of CVT at high altitude is limited, it was decided to pool such information from the available case studies to determine whether high altitude can predispose to CVT. METHODS: A systematic review of the literature was performed for cases reporting CVT at high altitude. Searches of the PubMed database (up to July 2016) were performed for publications, using 'cerebral venous thrombosis' and 'high altitude' as keywords. Cross-referencing was also done to complete the search. RESULTS: Ultimately, 13 articles were included in our systematic review. The population consisted of 17 patients, predominately male (14/17), with a mean age of 32 (range: 19-47) years. Altitude range was 3000-8200m. Nine patients stayed at high altitude for>2 weeks; the duration of high altitude stay was unknown for the remainder. A hypercoagulable state was found in nine patients: secondary polycythemia in five; protein C deficiency in one; protein S deficiency in one; and factor V Leiden mutations in two. No comorbidities were found in any of these patients. CONCLUSION: Long-term stays at high altitude in association with a hypercoagulable state - in particular, congenital or acquired thrombophilia - appears to predispose to CVT. The association of CVT with a single exposure to high altitude seems low, but the risk cannot as yet be specifically estimated.

Parkinson's patients cope with daylight saving time.

Disturbances of the circadian timing system following daylight saving time (DST) may influence the symptoms of Parkinson's disease (PD). To address this question, we compared the severity of motor fluctuations and non-motor symptoms both before and after the time change. Total daily "off-time" based on diaries, excessive daytime sleepiness (Epworth Sleepiness Scale), depressive symptoms (Beck Depression Inventory), and psychosis associated with PD were assessed both before and after the DST. Eighty-three PD patients (mean age, 67±7.7years; mean disease duration, 10.4±6.4years) were included. Thirty-six patients had motor fluctuations (mean daily "off-time", 4.8±2.4h/day). There was no significant variation of the total daily "off-time" (2.5±2.6h/day versus 2.5±2.7h/day), ESS (8.3±4.8 versus 8.1±4.9), BDI (10.4±6.2 versus 10.0±6.9), or PAPD (1.4±1.6 versus 1.1±1.6) scores (P>0.05) after DST. Our results suggest that PD patients cope relatively well with DST.

Endoscopic 3rd ventriculocisternostomy: procedural complications and long-term dysfunctions?

BACKGROUND AND PURPOSE: The endoscopic third ventriculostomy (ETV) has become the treatment of choice for managing non-communicating hydrocephalus. The aim of this study was to evaluate the efficacy and the morbi-mortality of this procedure and its long-term outcome. PATIENTS AND METHODS: This retrospective study involved 82 consecutive patients treated for non-communicating hydrocephalus by ETV, in a single centre, between June 1999 and November 2008. The main criterion of efficacy was clinical improvement with shunt independence. The secondary criteria were the ventricular size (third and lateral ventricles) outcome and the procedural morbidity and mortality. In order to determine the predictive factors of dysfunction, a uni- and multivariate analysis was conducted. RESULTS: Divided in two groups, the overall success rate was 65.4% in the paediatric group (n=26) and 83.9% in the adult group (n=56), after respectively a mean follow-up of 59.1±36.7 and 49.3±27.7 months. A procedural complication occurred in 5 patients (6.1%), with no procedure-related death. The predictive factors of ETV failure were an infectious aetiology and an age less than 16. Changes in ventricular size and success rate were independent. CONCLUSIONS: ETV is an effective procedure at long-term for the management of non-communicating hydrocephalus with low morbidity. Therefore, it should be considered as first-line treatment. Cerebrospinal meningitis infection and young age both expose patients to possible dysfunction.

Electric block current induced detachment from surgical stainless steel and decreased viability of Staphylococcus epidermidis.

In vitro studies investigating the influence of electric DC current on bacterial detachment have demonstrated that continuous currents of only 25-125 microA stimulated staphylococcal strains to detach from surgical stainless steel. However, DC currents produce more power that has to be dissipated by the skin as compared to alternating currents. Also, an excess of ions on the steel can cause negative osteogenesis and fixation results. Therefore, it is the aim of this paper to examine whether detachment of Staphylococcus epidermidis from stainless steel surfaces in a parallel plate flow chamber can also be stimulated using electric block currents. Block currents of 15, 60 and 100 microA with different frequencies (0.1-2 Hz) and duty cycles (5-50%) were applied to induce bacterial detachment. Block currents of 100 microA cause detachment of about 76% of adhering staphylococci from stainless steel, whereas in addition the remaining bacteria are less viable, as determined by culturing the remaining bacteria on agar plates. Therewith, block current-induced detachment of adhering bacteria from stainless steel appears to be an equally promising method to prevent infection of orthopaedic fixation pins and screws than application of DC currents.

Electric-current-induced detachment of Staphylococcus epidermidis strains from surgical stainless steel.

Infection of percutaneous biomaterials implants, such as fixation frames used for the repair of complicated fractures in orthopedics, is a major complication that almost inevitably leads to replacement of the implant. As antibiotic therapy usually has little impact on biomaterial-associated infections, it is the aim of this article to examine whether implant-associated Staphylococcus epidermidis and Staphylococcus aureus strains could be stimulated to detach from a surgical stainless steel anode during application of an electric current. First, bacteria were allowed to adhere from a flowing suspension of physiological ionic strength in a parallel plate flow chamber to a stainless-steel surface, after which the suspension was replaced by a bacterium-free solution with a specified ionic strength (0.5-150-mM potassium phosphate). DC currents ranging from 15 to 125 microA were applied to induce bacterial detachment. Initial detachment decreased with increasing ionic strength at 100 microA. The percentage detachment achieved by application of an electric current after 2.5 h was highest (95%) in 1-mM potassium phosphate and decreased to 15% when the ionic strength exceeded 40 mM. The electric current did not significantly affect the percentage detachment, but initial detachment rates increased with increasing current from 1000 cm(-2) s(-1) at 15 microA to 7000 cm(-2) s(-1) at 125 microA. Although different isolates of S. epidermidis and S. aureus showed different patterns of current-induced detachment, all strains could be stimulated to detach. The results of this study define ionic-strength conditions and electric currents yielding staphylococcal detachment from surgical stainless steel and therewith point to a pathway for the treatment and prevention of percutaneous metal-implant infection.

Intrinsic polymerase activities of UmuD'(2)C and MucA'(2)B are responsible for their different mutagenic properties during bypass of a T-T cis-syn cyclobutane dimer.

In wild-type Escherichia coli, translesion replication is largely dependent upon the UmuD'(2)C complex (DNA polymerase V [polV]) or its plasmid-encoded homologs, such as MucA'(2)B. Interestingly, both the efficiency of translesion replication of a T-T cis-syn dimer and the spectra of mutations observed are different in Umu- and Muc-expressing strains. We have investigated whether the polIII core is responsible for these differences by measuring the frequency of dimer bypass, the error rate of bypass, and the resulting mutation spectrum in mutants carrying a deletion of dnaQ (epsilon subunit) or holE (theta subunit) or carrying the dnaQ allele mutD5, which is deficient in proofreading but is competent in the structural function of epsilon, or the dnaE antimutator allele spq-2. The chromosomal copy of the umuDC operon was deleted in each strain, and the UmuDC, UmuD'C, MucAB, or MucA'B proteins were expressed from a low-copy-number plasmid. With only few exceptions, we found that the characteristically different mutation spectra resulting from Umu- and Muc-mediated bypass are maintained in all of the strains investigated, indicating that differences in the activity or structure of the polIII core are not responsible for the observed phenotype. We also demonstrate that the MucA'(2)B complex is more efficient in promoting translesion replication than the UmuD'(2)C proteins and show that, contrary to expectation, the T-T dimer is bypassed more accurately by MucA'(2)B than by UmuD'(2)C. These results are consistent with the view that in a wild-type cell, the polV-like enzymes are responsible for the spectra of mutations generated during translesion replication and that polIII may simply be required to fix the misincorporations as mutations by completing chromosomal replication. Our observations also show that the mutagenic properties of a lesion can depend strongly on the particular enzyme employed in bypass.

Efficient translesion replication in the absence of Escherichia coli Umu proteins and 3'-5' exonuclease proofreading function.

Translesion replication (TR) past a cyclobutane pyrimidine dimer in Escherichia coli normally requires the UmuD'2C complex, RecA protein, and DNA polymerase III holoenzyme (pol III). However, we find that efficient TR can occur in the absence of the Umu proteins if the 3'-5' exonuclease proofreading activity of the pol III epsilon-subunit also is disabled. TR was measured in isogenic uvrA6 DeltaumuDC strains carrying the dominant negative dnaQ allele, mutD5, or DeltadnaQ spq-2 mutations by transfecting them with single-stranded M13-based vectors containing a specifically located cis-syn T-T dimer. As expected, little TR was observed in the DeltaumuDC dnaQ+ strain. Surprisingly, 26% TR occurred in UV-irradiated DeltaumuDC mutD5 cells, one-half the frequency found in a uvrA6 umuDC+mutD5 strain. lexA3 (Ind-) derivatives of the strains showed that this TR was contingent on two inducible functions, one LexA-dependent, responsible for approximately 70% of the TR, and another LexA-independent, responsible for the remaining approximately 30%. Curiously, the DeltaumuDC DeltadnaQ spq-2 strain exhibited only the LexA-independent level of TR. The cause of this result appears to be the spq-2 allele, a dnaE mutation required for viability in DeltadnaQ strains, since introduction of spq-2 into the DeltaumuDC mutD5 strain also reduces the frequency of TR to the LexA-independent level. The molecular mechanism responsible for the LexA-independent TR is unknown but may be related to the UVM phenomenon [Palejwala, V. A., Wang, G. E., Murphy, H. S. & Humayun, M. Z. (1995) J. Bacteriol. 177, 6041-6048]. LexA-dependent TR does not result from the induction of pol II, since TR in the DeltaumuDC mutD5 strain is unchanged by introduction of a DeltapolB mutation.

Mutagenic properties of the T-C cyclobutane dimer.

G x C-->A x T transitions within T-C or C-C bipyrimidine sequences are by far the most frequent class of mutation induced by 254-nm UV irradiation in most genes and species investigated, but the reason for the high degree of mutability and specificity at these sites is uncertain. Some data implicate the deamination of cytosine to uracil as a possible cause, but other results appear to indicate that the rate of deamination is too low for this to be significant in Escherichia coli. If deamination is not the cause, the high degree of mutability must presumably reflect the inherent properties of T-C and C-C dimers. We investigated this question by transfecting excision-deficient and excision-proficient strains of E. coli with single-stranded vectors that carried a site-specific cis-syn T-C cyclobutane dimer and by analyzing the nucleotide sequences of replicated vector products. We found that replication past the T-C dimer, like replication past its T-T and U-U counterparts, is in fact >95% accurate and that the frequencies of bypass are also very similar for these photoproducts. Since the T-C dimer appears to be only weakly mutagenic, the high frequency of UV-induced mutations at T-C sites presumably depends on some other process, such as deamination, although the mechanism remains to be established.

Non-mutagenic repair of (6-4)photoproducts by (6-4)photolyase purified from Drosophila melanogaster.

The (6-4)photoproduct DNA photolyase ((6-4)photolyase) repairs UV-induced pyrimidine (6-4) pyrimidone photoproduct ((6-4)photoproduct, pyr[6,4]pyr) in a light dependent manner. Drosophila (6-4)photolyase was purified to near homogeneity from Drosophila embryonic cells and is shown to be a 62 kDa protein as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified (6-4)photolyase repairs (6-4)photoproducts induced at 5'-CC-3' site (C[6,4]C) as well as T[6,4]T and T[6,4]C. Photoreactivation of (6-4)photoproduct constructed in M13 phage eliminates the replication block and abolishes induced mutagenesis in E. coli cells, suggesting that the (6-4)photolyase repairs the photoproduct to the unmodified form.

Analysis of the mutagenic properties of the UmuDC, MucAB and RumAB proteins, using a site-specific abasic lesion.

The mucAB and rumAB loci have been shown to promote mutagenesis to a greater extent than the structurally and functionally homologous Escherichia coli umuDC operon. We have analyzed the basis of this enhanced mutagenesis by comparing the influence of these operons, relative to umuDC, on the mutagenic properties of each of two abasic sites, specifically located in a single-stranded vector. Experiments with these vectors are useful analytical tools because they provide independent estimates of the efficiency of translesion synthesis and of the relative frequencies of each type of nucleotide insertion or other kind of mutagenic event. The umuDC, mucAB, and rumAB genes were expressed from their natural LexA-regulated promoter on low-copy-number plasmids in isogenic strains carrying a umuDC deletion. In addition, plasmids expressing the UmuD'C, MucA'B, or RumA'B proteins were also used. Compared to umuDC, the chief effect of mucAB was to increase the efficiency of translesion synthesis past the abasic site. The enhanced capacity of mucAB for translesion synthesis depended about equally on an inherently greater capacity to promote this process and on a greater susceptibility of the MucA protein to proteolytic processing. The RumA protein also appeared to be more susceptible to proteolytic processing, but the inherent capacity of the Rum products for translesion synthesis was no greater than that of UmuDC. dAMP was inserted opposite one of the two abasic sites studied at a somewhat greater frequency in strains expressing rum (82%) compared to those expressing umu (72%), which might result in higher mutation frequencies in rumAB than in umuDC strains.

Mutagenicity of a unique thymine-thymine dimer or thymine-thymine pyrimidine pyrimidone (6-4) photoproduct in mammalian cells.

The mutagenic properties of UV-induced photoproducts, both the cis-syn thymine-thymine dimer (TT) and the thymine-thymine pyrimidine pyrimidone (6-4) photoproduct [T(6-4)T] were studied in mammalian cells using shuttle vectors. A shuttle vector able to replicate in both mammalian cells and bacteria was produced in its single-stranded DNA form. A unique photoproduct was inserted at a single restriction site and after recircularization of the single-stranded DNA vector, this latter was transfected into simian COS7 cells. After DNA replication the vector was extracted from cells and used to transform bacteria. Amplified DNA was finally analyzed without any selective screening, DNA from randomly picked bacterial colonies being directly sequenced. Our results show clearly that both lesions are mutagenic, but at different levels. Mutation frequencies of 2 and 60% respectively were observed with the TT dimer and the T(6-4)T. With the TT dimer the mutations were targeted on the 3'-T. With the T(6-4)T a large variety of mutations were observed. A majority of G-->T transversions were semi-targeted to the base before the 5'-T of the photoproduct. These kinds of mutations were not observed when the same plasmid was transfected directly into SOS-induced JM105 bacteria or when the T(6-4)T oligonucleotide inserted in a different plasmid was replicated in SOS-induced SMH10 Escherichia coil bacteria. These semi-targeted mutations are therefore the specific result of bypass of the T(6-4)T lesion in COS7 cells by one of the eukaryotic DNA polymerases.

The T-T pyrimidine (6-4) pyrimidinone UV photoproduct is much less mutagenic in yeast than in Escherichia coli.

We have examined the mutagenic properties of the T-T pyrimidine (6-4) pyrimidinone UV photoproduct in Saccharomyces cerevisiae, transforming the yeast cells either with single-stranded vectors that carried this adduct at a unique site or with gapped duplex vectors in which the adduct was located within a 28 nt single-stranded region. In an earlier study with SOS-induced Escherichia coli, we found that this photoproduct is highly mutagenic, specifically generating 3' T-->C substitutions in >85% of replicated molecules, and ascribed this specificity to the formation of a stable guanine-pyrimidinone mispair via hydrogen bonds at N-3 and O-2. In contrast, this adduct is very much less mutagenic in yeast, with 60-70% of molecules being replicated accurately and only 12-20% of them exhibiting 3' T-->C substitutions. The enhanced accuracy may reflect the ability of a yeast DNA polymerase, but not E.coli DNA polymerase III, to trap the adduct in a configuration favorable for the formation of an adenine-pyrimidinone base pair.

Mutagenesis induced by single UV photoproducts in E. coli and yeast.

Data from experiments with single-stranded vectors that carry a site-specific cyclobutane dimer, pyrimidine (6-4) pyrimidone adduct, or abasic lesion, replicated in either E. coli or, in some cases, bakers' yeast, Saccharomyces cerevisiae, are used to examine two questions: (i) what factors are responsible for the lesion's mutagenicity? and (ii) what are the relative contributions of different photoproducts to the spectrum of UV-induced mutations? With respect to the first question, we suggest that the structure of the mutagen-modified template itself largely determines the kinds of mutations induced, but the relative frequencies of these mutations, the error frequency, and the bypass frequency are strongly dependent on the particular organism studied. With respect to the second question, we suggest that cyclobutane dimers may be responsible for most of the mutations in slowly replicating genomes because of the deamination of cytosine, and that the T-T, and to a lesser extent the T-C, (6-4) adducts play a greater role in the UV mutagenesis of quickly replicating viruses, such as M13 and lambda phage.

The thymine-thymine pyrimidine-pyrimidone(6-4) ultraviolet light photoproduct is highly mutagenic and specifically induces 3' thymine-to-cytosine transitions in Escherichia coli.

We have constructed single-stranded, M13-based vectors that contain a specifically located thymine-thymine pyrimidine-pyrimidone(6-4) UV photoproduct and have used these to estimate the frequency and accuracy of DNA replication past this adduct in uvrA6 cells of Escherichia coli. Both the normal and the Dewar valence photoisomer of the (6-4) adduct were studied. In the absence of SOS induction, vectors carrying the photoproducts were rarely replicated; relative to the lesion-free control, 1.9% of vectors carrying the normal (6-4) isomer produced plaques, and with the Dewar valence isomer the proportion was 0.4%. In SOS-induced cells, these frequencies rose to 22.1% and 12.3%, respectively. The error frequency of replication past the normal isomer in SOS-induced cells was high; in a random sample of 185 progeny phage analyzed, 169 (91%) contained mutations, all of which were targeted. Equally striking, a high proportion of the mutations (158/169; 93%) were of only one type, namely 3' T----C transitions. Both the error frequency and the specificity were much reduced with the Dewar valence isomer; overall, 74/140 (53%) of the phage analyzed were mutant, and of these only 34 (46%) entailed the 3' T----C transition. We speculate that the high error frequency and specificity arise from the formation of a stable T-G base pair, involving hydrogen bonds at O-2 and N-3 in the pyrimidone ring. Potential hydrogen bonds at these sites are coplanar in the normal but not in the Dewar isomer, perhaps explaining the reduced specificity of mutagenesis with the latter adduct.

T-T cyclobutane dimers are misinstructive, rather than non-instructive, mutagenic lesions.

The lesions produced by SOS-dependent mutagens in Escherichia coli are commonly referred to as nonpairing or non-instructive. Although these terms are likely to be appropriate for some lesions, particularly the abasic site, for others, such as the cyclobutane dimer, their suitability is open to question. To address this question, we have compared the error frequencies and spectra that result when a uniquely located T-T sequence, carried in a single-stranded vector, contains either a cis-syn or a trans-syn cyclobutane dimer, or when either the 5'T or 3'T is converted to an abasic site. The data suggest that the high accuracy with which the dimer-containing templates are replicated is unlikely to be the consequence of polymerase preference for the non-instructive insertion of dAMP. Similarly, mispairing, rather than non-pairing, is likely to cause mutations. Cyclobutane dimers seem therefore to be misinstructive rather than non-instructive lesions, and the common feature shared by SOS-inducing lesions is more their ability to block replication than inability to form correct base pairs.

SOS-dependent replication past a single trans-syn T-T cyclobutane dimer gives a different mutation spectrum and increased error rate compared with replication past this lesion in uninduced cells.

We have transfected SOS-induced and uninduced cells of a uvrA6 strain of Escherichia coli with single-stranded M13mp7-based vectors that carried a single trans-syn T-T cyclobutane dimer at a unique site. Unlike constructs carrying the cis-syn isomer of this lesion, these vectors could be replicated with modest efficiency (14%) in the absence of SOS induction and therefore provided an opportunity to measure directly the influence of such induction on error rate and mutation spectrum. We found that translesion synthesis in the absence of SOS induction was remarkably accurate; only 4% of the replicated bacteriophage contained mutations, which were exclusively targeted single T deletions. In SOS-induced cells, error frequency increased to 11% and the resulting mutations included targeted substitutions and near-targeted single base additions, as well as the T deletions. Replication efficiency was 29% in these conditions. SOS induction therefore leads not only to an enhanced capacity to replicate damaged DNA but also to a marked change in mutation frequency and spectrum.

Mutation frequency and spectrum resulting from a single abasic site in a single-stranded vector.

We have investigated the mutagenic properties of an abasic site in DNA by transfecting SOS-induced and uninduced cells of E. coli with a single-stranded M13mp7-based vector that carries a single example of this lesion at one or other of two unique and adjacent sites. Random samples of progeny phage were sequenced to determine the nature of the replication events that occurred at and around these locations. 5% to 7% of the vectors could be replicated in SOS-induced cells, but only 0.1% to 0.7% of them gave plaques in the absence of SOS induction. In SOS-induced cells, 93% and 96% of the phage replicated resulted from the insertion of a nucleotide opposite the abasic site, while the remainder resulted from a targeted omission of a single nucleotide. At one of the sites, nucleotide insertions were 54% dAMP, 25% dTMP, 20% dGMP and 1% dCMP. At the other site they were 80% dAMP, 4% dTMP, 15% dGMP and 1% dCMP. The sequence variation in all but two of the 204 sequences analyzed was restricted to the abasic site itself. In the remaining two, a change at the abasic site was accompanied by a mutation at an immediately flanking nucleotide.