Lesion severity and treatment complexity are associated with outcome after percutaneous infra-inguinal intervention

OBJECTIVES

Percutaneous revascularization has become increasingly utilized for the treatment of lower extremity ischemia. Patients with limb-threat have been shown to be at increased risk of failure, although the reasons for this remain unclear. This study analyzed factors associated with percutaneous treatment failure, focusing specifically on lesion characteristics and treatment complexity.

METHODS

We retrospectively reviewed percutaneous infra-inguinal interventions performed for peripheral occlusive disease between 2002 and 2005 using a prospectively maintained database. Lesion characteristics were assessed by angiography, and lesions were graded according to the TransAtlantic InterSociety Consensus (TASC) criteria. Patency was expressed by Kaplan-Meier method and compared by log-rank analysis. Multivariate Cox-regression analysis was used to assess significant factors on univariate analysis. Mean follow-up was 11.8 months.

RESULTS

A total of 324 interventions for claudication (55.8%), rest pain (18.4%), or tissue loss (25.8%) were analyzed, including 284 primary interventions and 40 re-interventions in 258 patients (mean age 72.1 +/- 10 years, 51.0% male). TASC lesion grades included: A (4.9%), B (29.3%), C (37.7%), and D (28.1%). Isolated single-level interventions (femoral, popliteal, or tibial) were performed in 38.9%, while two-level interventions were performed in 46.2% and three-level interventions in 14.9%. Overall primary patency (+/- SD) at 6, 12, and 18 months was 87 +/- 2%, 66 +/- 2% and 59 +/- 4%, respectively. Secondary patency at 6, 12, and 18 months was 89 +/- 2%, 76 +/- 3%, and 69 +/- 5%. One-year limb salvage rate (limb-threat patients) was 85 +/- 3%. Limb-threatening ischemia as the indication for intervention was most highly associated with failure of both primary and secondary patency and was associated with four indicators of lesion severity and treatment complexity, including increasing TASC grade, multilevel intervention, tibial intervention, and reduced tibial outflow. One-year primary patency was inversely correlated with TASC severity (TASC A-C: 67 +/- 6%, D: 61 +/- 4%; P < .05), multilevel intervention (76 +/- 5% and 49 +/- 9% for single vs multilevel, P = .002), distal interventions (74 +/- 5% and 57 +/- 7% for femoral vs tibial, P < .05), and decreased tibial runoff (83 +/- 6% and 52 +/- 6% for three- vs < three-vessels, P < .02). No differences in secondary patency or limb-salvage rates existed for these lesion- and treatment-related variables. Multilevel intervention and tibial intervention remained significant independently associated with primary patency on multivariate analysis.

CONCLUSIONS

Patients with limb-threatening ischemia are at increased risk of initial failure compared with claudicants, likely as a result of the increased prevalence of advanced lesion severity and treatment complexity, which are associated with decreased primary patency. However, this finding did not extend to secondary patency or limb-salvage in the overall patient population. Although additional studies with longer follow-up are needed, these findings argue that percutaneous intervention may still be considered as a primary treatment modality with the understanding that these patients may have higher re-intervention rates and may ultimately require salvage open surgical bypass for persistent failures of percutaneous therapy.

The CTP:phosphocholine cytidylyltransferase encoded by the licC gene of Streptococcus pneumoniae: cloning, expression, purification, and characterization

Streptococcus pneumoniae is a member of a small group of bacteria that display phosphocholine on the cell surface, covalently attached to the sugar groups of teichoic acid and lipoteichoic acid. The putative pathway for this phosphocholine decoration is, in its first two enzymes, functionally similar to the CDP-choline pathway used for phosphatidylcholine biosynthesis in eukaryotes. We show that the licC gene encodes a functional CTP:phosphocholine cytidylyltransferase (CCT). The enzyme has been expressed and purified to homogeneity. Assay conditions were optimized, particularly with respect to linearity with time, pH, Mg(2+), and ammonium sulfate concentration. The pure enzyme has K(M) values of 890+/-240 microM for CTP, and 390+/-170 microM for phosphocholine. The k(cat) is 17.5+/-4.0 s(-1). S. pneumoniae CTP:phosphocholine cytidylyltransferase (SpCCT) is specific for CTP or dCTP as the nucleotide substrate. SpCCT is strongly inhibited by Ca(2+). The IC(50) values for recombinant and native SpCCT are 0.32+/-0.04 and 0.27+/-0.03 mM respectively. The enzyme is also inhibited by all other tested divalent cations, including Mg(2+) at high concentrations. The cloning and expression of this enzyme sets the stage for design of inhibitors as possible antipneumococcal drugs.

Delineation of the allosteric mechanism of a cytidylyltransferase exhibiting negative cooperativity

The dimeric enzyme CTP:glycerol-3-phosphate cytidylyltransferase (GCT) displays strong negative cooperativity between the first and second binding of its substrate, CTP. Using NMR to study the allosteric mechanism of this enzyme, we observe widespread chemical shift changes for the individual CTP binding steps. Mapping these changes onto the molecular structure allowed the formulation of a detailed model of allosteric conformational change. Upon the second step of ligand binding, NMR experiments indicate an extensive loss of conformational exchange broadening of the backbone resonances of GCT. This suggests that a fraction of the free energy of negative cooperativity is entropic in origin.

Negative cooperativity of substrate binding but not enzyme activity in wild-type and mutant forms of CTP:glycerol-3-phosphate cytidylyltransferase

CTP:glycerol-3-phosphate cytidylyltransferase (GCT) catalyzes the synthesis of CDP-glycerol for teichoic acid biosynthesis in certain Gram-positive bacteria. This enzyme is a model for a cytidylyltransferase family that includes the enzymes that synthesize CDP-choline and CDP-ethanolamine for phosphatidylcholine and phosphatidylethanolamine biosynthesis. We have used quenching of intrinsic tryptophan fluorescence to measure binding affinities of substrates to the GCT from Bacillus subtilis. Binding of either CTP or glycerol-3-phosphate to GCT was biphasic, with two binding constants of about 0.1-0.3 and 20-40 microm for each substrate. The stoichiometry of binding was 2 molecules of substrate/enzyme dimer, so the two binding constants represented distinctly different affinities of the enzyme for the first and second molecule of each substrate. The biphasic nature of binding was observed with the wild-type GCT as well as with several mutants with altered Km or kcat values. This negative cooperativity of binding was also seen when a catalytically defective mutant was saturated with two molecules of CTP and then titrated with glycerol-3-phosphate. Despite the pronounced negative cooperativity of substrate binding, negative cooperativity of enzyme activity was not observed. These data support a mechanism in which catalysis occurs only when the enzyme is fully loaded with 2 molecules of each substrate/enzyme dimer.

A comparison of CAL with a conventional method of delivery of cell biology to undergraduate nursing students using an experimental design

This paper describes the development and evaluation of a series of computer assisted learning (CAL) packages on cell biology produced for an undergraduate nursing course. The CAL packages were based on the material originally delivered in Kindermann's slide practical classes. The decision to convert this teaching material into CAL packages was taken for a number of reasons, but mainly in response to student evaluations and lack of equipment and staff resources needed to adequately deliver the sessions. Student feedback showed that CAL was preferred to the slide classes. Two studies were carried out to compare the CAL method of delivery with the conventional method using an experimental design. Students taught using CAL felt more confident that they would be able to use the material they had learnt if required as a basis for future work. The distributions rating 'how necessary was the contribution of a teacher in the session' were skewed towards the 'essential' end of the scale for the slide group but towards the 'unnecessary' end for the CAL group. Learning effectiveness was not compromised by the introduction of CAL, even though this meant that no lecturer was on hand to deal with questions.

Cloning and characterization of a lipid-activated CTP:phosphocholine cytidylyltransferase from Caenorhabditis elegans: identification of a 21-residue segment critical for lipid activation

The genome of the nematode Caenorhabditis elegans contains several genes that appear to encode proteins similar to CTP:phosphocholine cytidylyltransferase (CCT). We have isolated a 1044-nucleotide cDNA clone from a C. elegans cDNA library that encodes the 347-amino acid version of CCT that is most similar to previously-identified CCTs. Native and His-tagged forms were expressed and purified using a baculovirus expression system. The enzyme was maximally activated by 5 microM phosphatidylcholine:oleate (50:50) vesicles with a k(cat) value in the presence of lipid 37-fold greater than the k(cat) value in the absence of lipid. To localize the region of C. elegans CCT critical for lipid activation, a series of C-terminal truncation mutants was analyzed. CCT truncated after amino acids 225 or 245 was quite active in the absence of lipids and not further activated in the presence of lipids, supporting the concept that the lipid-activation segment is inhibitory to catalysis in the absence of lipids. CCT truncated after amino acids 266, 281, or 319 was activated by lipid similar to wild-type enzyme. Kinetic analysis in the absence of lipid revealed the lipid-independent CCT truncated after amino acid 245 to have a k(cat) value 15-fold greater than either full-length CCT or CCT truncated after amino acid 266. We conclude that elements critical for activation of C. elegans CCT by lipids are contained within amino acids 246-266, that this region is inhibitory in the absence of lipids, and that the inhibition is relieved by the association of the enzyme with lipid.

Cruising on the Internet highway

This study evaluated differences in sexual behavior and risk for sexually transmitted diseases (STDs) among men who have sex with men (MSM) who met their partners on-line and those who did not. A self-administered questionnaire on sexual behavior was offered to a convenience sample of patients seeking public STD services. Thirty-two percent of MSM patients reported meeting a sexual partner over the Internet in the past year. MSM with on-line partners were younger, more likely to report sex with an HIV-positive person in the last year, and more likely to report casual partners in the last year compared with MSM with only off-line partners. HIV-negative MSM with on-line partners were more likely than HIV-negative MSM with only off-line partners to have received money or drugs for sex in the past year and to report sex with an HIV-positive partner in the past year. Although meeting partners on the Internet was common and associated with increased risk for STDs in MSM, it also presents new untapped opportunities for on-line health promotion and disease prevention.

Fleeting foreskins: the misclassification of male circumcision status

BACKGROUND

Errors in the classification of male circumcision status could bias studies linking infection to lack of circumcision.

GOAL

To determine the frequency and factors associated with the reproducibility of reporting circumcision status.

STUDY DESIGN

Secondary analysis of data using logistic regression modeling from a multicenter randomized controlled trial was performed.

RESULTS

At follow-up assessment, 15.6% of clinician reports on circumcision status disagreed with baseline reports. Disagreement was more common if both clinicians were women than if both were men (odds ratio [OR], 2.8; 95% CI, 1.9-4.1). As compared with whites reported as circumcised (4%, 19/532 visits), the highest disagreement involved uncircumcised Hispanic (OR, 3.3; 95% CI, 1.7-6.3), white (OR, 12.2; 95% CI, 5.8-25.6), or black (OR, 17.1; 95% CI, 10.4-27.9) men.

CONCLUSIONS

This is one study among a small number of studies examining the reproducibility of clinician-reported circumcision status by comparing multiple clinical examinations of the same patient. The magnitude of the misclassification discovered could bias results and indicates the need for greater accuracy in reporting circumcision status in future studies.

Determinants of persistent and recurrent Chlamydia trachomatis infection in young women: results of a multicenter cohort study

BACKGROUND

Sequelae of genital Chlamydia trachomatis infection in women are more strongly linked to repeat infections than to initial ones, and persistent or subsequent infections foster continued transmission.

OBJECTIVE

To identify factors associated with persistent and recurrent chlamydial infection in young women that might influence prevention strategies.

METHODS

Teenage and young adult women with uncomplicated C trachomatis infection attending reproductive health, sexually transmitted disease, and adolescent medicine clinics in five US cities were recruited to a cohort study. Persistent or recurrent chlamydial infection was detected by ligase chain reaction (LCR) testing of urine 1 month and 4 months after treatment.

RESULTS

Among 1,194 women treated for chlamydial infection, 792 (66.4%) returned for the first follow-up visit, 50 (6.3 %) of whom had positive LCR results. At that visit, women who resumed sex since treatment were more likely to have chlamydial infection (relative risk [RR], 2.0; 95% CI, 1.03-3.9), as were those who did not complete treatment (RR, 3.4; 95% CI, 1.6-7.3). Among women who tested negative for C trachomatis at the first follow-up visit, 36 (7.1%) of 505 had positive results by LCR at the second follow-up visit. Reinfection at this visit was not clearly associated with having a new sex partner or other sexual behavior risks; new infection was likely due to resumption of sex with untreated partners. Overall, 13.4% of women had persistent infection or became reinfected after a median of 4.3 months, a rate of 33 infections per 1,000 person months.

CONCLUSIONS

Persistent or recurrent infection is very common in young women with chlamydial infection. Improved strategies are needed to assure treatment of women's male sex partners. Rescreening, or retesting of women for chlamydial infection a few months after treatment, also is recommended as a routine chlamydia prevention strategy.

Purification and kinetic characterization of CTP:phosphocholine cytidylyltransferase from Saccharomyces cerevisiae

CTP:phosphocholine cytidylyltransferase (CCT) regulates the biosynthesis of phosphatidylcholine in mammalian cells. In order to understand the mechanism by which this enzyme controls phosphatidylcholine synthesis, we have initiated studies of CCT from the model genetic system, the yeast Saccharomyces cerevisiae. The yeast CCT gene was isolated from genomic DNA using the polymerase chain reaction and was found to encode tyrosine at position 192 instead of histidine, as originally reported. Levels of expression of yeast CCT activity in Escherichia coli or in the yeast, Pichia pastoris, were somewhat low. Expression of yeast CCT in a baculovirus system as a 6x-His-tag fusion protein was higher and was used to purify yeast CCT by a procedure that included delipidation. Kinetic characterization revealed that yeast CCT was activated approximately 20-fold by 20 microM phosphatidylcholine:oleate vesicles, a level 5-fold lower than that necessary for maximal activation of rat CCT. The k(cat) value was 31.3 s(-1) in the presence of lipid and 1.5 s(-1) in the absence of lipid. The K(m) values for the substrates CTP and phosphocholine did not change significantly upon activation by lipids; K(m) values in the presence of lipid were 0.80 mM for phosphocholine and 1.4 mM for CTP while K(m) values in the absence of lipid were 1.2 mM for phosphocholine and 0.8 mM for CTP. Activation of yeast CCT, therefore, appears to be due to an increase in the k(cat) value upon lipid binding.

Circumcision and STD in the United States: cross sectional and cohort analyses

BACKGROUND

Male circumcision status has been shown to be associated with sexually transmitted disease (STD) acquisition in some, but not all, studies. Most studies have been cross sectional.

OBJECTIVES

We examined the association between circumcision status and the prevalence and incidence of gonorrhoea, chlamydia, and syphilis.

METHODS

We analysed cross sectional and cohort study data from a multicentre controlled trial in the United States. Between July 1993 and September 1996, 2021 men visiting public inner city STD clinics in the United States were examined by a clinician at enrolment and 1456 were examined at follow up visits 6 and 12 months later. At each visit, men had laboratory tests for gonorrhoea, chlamydia, and syphilis and were examined for circumcision status. We used multiple logistic regression to compare STD risk among circumcised and uncircumcised men adjusted for potentially confounding factors.

RESULTS

Uncircumcised men were significantly more likely than circumcised men to have gonorrhoea in the multivariate analyses, adjusted for age, race, and site, in both the cross sectional (odds ratio (OR), 1.3; 95% confidence interval (CI), 0.9 to 1.7) and in the cohort analysis (OR, 1.6; 95% CI, 1.0 to 2.6). There was no association between lack of circumcision and chlamydia in either the cross sectional (OR, 1.0; 95% CI 0.7-1.4) or the cohort analysis (OR, 0.9; 95% CI 0.5-1.5). The magnitude of association between lack of circumcision and syphilis was similar in the cross sectional (OR, 1.4; 95% CI 0.6 to 3.3) and cohort analysis (OR, 1.5; 95% CI 0.4 to 6.1).

CONCLUSION

Uncircumcised men in the United States may be at increased risk for gonorrhoea and syphilis, but chlamydia risk appears similar in circumcised and uncircumcised men. Our results suggest that risk estimates from cross sectional studies would be similar to cohort findings.

A prototypical cytidylyltransferase: CTP:glycerol-3-phosphate cytidylyltransferase from bacillus subtilis

BACKGROUND

The formation of critical intermediates in the biosynthesis of lipids and complex carbohydrates is carried out by cytidylyltransferases, which utilize CTP to form activated CDP-alcohols or CMP-acid sugars plus inorganic pyrophosphate. Several cytidylyltransferases are related and constitute a conserved family of enzymes. The eukaryotic members of the family are complex enzymes with multiple regulatory regions or repeated catalytic domains, whereas the bacterial enzyme, CTP:glycerol-3-phosphate cytidylyltransferase (GCT), contains only the catalytic domain. Thus, GCT provides an excellent model for the study of catalysis by the eukaryotic cytidylyltransferases.

RESULTS

The crystal structure of GCT from Bacillus subtilis has been determined by multiwavelength anomalous diffraction using a mercury derivative and refined to 2.0 A resolution (R(factor) 0.196; R(free) 0.255). GCT is a homodimer; each monomer comprises an alpha/beta fold with a central 3-2-1-4-5 parallel beta sheet. Additional helices and loops extending from the alpha/beta core form a bowl that binds substrates. CTP, bound at each active site of the homodimer, interacts with the conserved (14)HXGH and (113)RTXGISTT motifs. The dimer interface incorporates part of a third motif, (63)RYVDEVI, and includes hydrophobic residues adjoining the HXGH sequence.

CONCLUSIONS

Structure superpositions relate GCT to the catalytic domains from class I aminoacyl-tRNA synthetases, and thus expand the tRNA synthetase family of folds to include the catalytic domains of the family of cytidylyltransferases. GCT and aminoacyl-tRNA synthetases catalyze analogous reactions, bind nucleotides in similar U-shaped conformations, and depend on histidines from analogous HXGH motifs for activity. The structural and other similarities support proposals that GCT, like the synthetases, catalyzes nucleotidyl transfer by stabilizing a pentavalent transition state at the alpha-phosphate of CTP.

Resection and permanent I-125 brachytherapy without whole brain irradiation for solitary brain metastasis from non-small cell lung carcinoma

We assessed a treatment plan of local therapy (resection and placement of permanent low dose-rate I-125 seeds) without whole brain irradiation in 15 patients with solitary brain metastasis (SBM) from primary non-small cell lung cancer between January, 1991 and May, 1996. Thirteen lesions were confirmed as solitary by MRI scan, and 2 patients had CT scan only. With median follow up of 14 months, 3 patients remain alive at 6, 33, and 62 months post-resection. Median survival is 14 months for all patients and 26 months for patients with SBM as the only site of disease. Five tumors failed in the brain: 2 solitary recurrences adjacent to the site of SBM, 2 multiple metastases outside the primary site, and 1 multiple recurrence including the primary site. No failures were seen with SBM <2.5 cm. Only 2 of 13 patients with SBM confirmed with MRI experienced relapses elsewhere in the brain. Recurrence rates both adjacent and outside the area of the initial brain lesion are similar to studies employing resection plus whole brain irradiation (WBI), and the patient is spared the acute and potential late toxicity of WBI. This approach may be considered for selected patients with solitary brain metastases (SBMs), although further experience with larger patient numbers is needed.

Enzymatic and cellular characterization of a catalytic fragment of CTP:phosphocholine cytidylyltransferase alpha

To probe the mechanism of lipid activation of CTP:phosphocholine cytidylyltransferase (CCTalpha), we have characterized a catalytic fragment of the enzyme that lacks the membrane-binding segment. The kinetic properties of the purified fragment, CCTalpha236, were characterized, as well as the effects of expressing the fragment in cultured cells. CCTalpha236 was truncated after residue 236, which corresponds to the end of the highly conserved catalytic domain. The activity of purified CCTalpha236 was independent of lipids and about 50-fold higher than the activity of wild-type CCTalpha assayed in the absence of lipids, supporting a model in which the membrane-binding segment functions as an inhibitor of the catalytic domain. The kcat/Km values for CCTalpha236 were only slightly lower than those for lipid-activated CCTalpha. The importance of the membrane-binding segment in vivo was tested by expression of CCTalpha236 in CHO58 cells, a cell line that is temperature-sensitive for growth and CCTalpha activity. Expression of wild-type CCTalpha in these cells complemented the defective growth phenotype when the cells were cultured in complete or delipidated fetal bovine serum. Expression of CCTalpha236, however, did not complement the growth phenotype in the absence of serum lipids. These cells were capable of making phosphatidylcholine in the delipidated medium, so the inability of the cells to grow was not due to defective phosphatidylcholine synthesis. Supplementation of the delipidated medium with an unsaturated fatty acid allowed growth of CHO58 cells expressing CCTalpha236. These results indicate that the membrane-binding segment of CCTalpha has an important role in cellular lipid metabolism.

CTP:phosphocholine cytidylyltransferase: insights into regulatory mechanisms and novel functions

A key regulatory enzyme in phosphatidylcholine biosynthesis, CTP:cholinephosphate cytidylyltransferase (CCT), catalyzes the formation of CDP-choline. This review discusses the essential features of CCT and addresses intriguing new insights into the catalytic and regulatory properties of this complex enzyme. Characterization of a lipid-binding segment in rat CCT is described and the role of lipids in CCT activation is discussed. An analysis of the phosphorylation domain is presented and possible physiological rationales for reversible phosphorylation of CCT are discussed. The nuclear localization of CCT is examined in the context of multiple CCT isoforms, as is recent evidence establishing a potential link between CCT activity and vesicular transport.

Interactions among pathways for phosphatidylcholine metabolism, CTP synthesis and secretion through the Golgi apparatus

Phosphatidylcholine is the major phospholipid in eukaryotic cells. It serves as a structural component of cell membranes and a reservoir of several lipid messengers. Recent studies in yeast and mammalian systems have revealed interrelationships between the two pathways of phosphatidylcholine metabolism, and between these pathways and those for CTP synthesis and secretion via the Golgi. These processes involve the regulation of the CDP-choline and phosphatidylethanolamine-methylation pathways of phosphatidylcholine synthesis, CTP synthetase, phospholipase D and the phospholipid-transfer protein Sec14p.