Catalytic Mechanism of Mammalian Adenylyl Cyclase: A Computational Investigation.

Adenylyl cyclase (AC) catalyzes the synthesis of cyclic AMP, an important intracellular regulatory molecule, from ATP. We propose a catalytic mechanism for class III mammalian AC based on density functional theory calculations. We employ a model of the AC active site derived from a crystal structure of mammalian AC activated by Gα·GTP and forskolin at separate allosteric sites. We compared the calculated activation free energies for 13 possible reaction sequences involving proton transfer, nucleophilic attack, and elimination of pyrophosphate. The proposed most probable mechanism is initiated by deprotonation of 3'OH and water-mediated transfer of the 3'H to the γ-phosphate. Proton transfer is followed by changes in coordination of the two magnesium ion cofactors and changes in the conformation of ATP to enhance the role of 3'O as a nucleophile and to bring 3'O close to Pα. The subsequent phosphoryl transfer step is concerted and rate-limiting. Comparison of the enzyme-catalyzed and nonenzymatic reactions reveals that the active site residues lower the free energy barrier for both phosphoryl transfer and proton transfer and significantly shift the proton transfer equilibrium. Calculations for mutants K1065A and R1029A demonstrate that K1065 plays a significant role in shifting the proton transfer equilibrium, whereas R1029 is important for making the transition state of concerted phosphoryl transfer tight rather than loose.

Computational tests of quantum chemical models for excited and ionized states of molecules with phosphorus and sulfur atoms.

Time-dependent density functional theory (TD-DFT) and electron propagator theory (EPT) are used to calculate the electronic transition energies and ionization energies, respectively, of species containing phosphorus or sulfur. The accuracy of TD-DFT and EPT, in conjunction with various basis sets, is assessed with data from gas-phase spectroscopy. TD-DFT is tested using 11 prominent exchange-correlation functionals on a set of 37 vertical and 19 adiabatic transitions. For vertical transitions, TD-CAM-B3LYP calculations performed with the MG3S basis set are lowest in overall error, having a mean absolute deviation from experiment of 0.22 eV, or 0.23 eV over valence transitions and 0.21 eV over Rydberg transitions. Using a larger basis set, aug-pc3, improves accuracy over the valence transitions via hybrid functionals, but improved accuracy over the Rydberg transitions is only obtained via the BMK functional. For adiabatic transitions, all hybrid functionals paired with the MG3S basis set perform well, and B98 is best, with a mean absolute deviation from experiment of 0.09 eV. The testing of EPT used the Outer Valence Green's Function (OVGF) approximation and the Partial Third Order (P3) approximation on 37 vertical first ionization energies. It is found that OVGF outperforms P3 when basis sets of at least triple-ζ quality in the polarization functions are used. The largest basis set used in this study, aug-pc3, obtained the best mean absolute error from both methods -0.08 eV for OVGF and 0.18 eV for P3. The OVGF/6-31+G(2df,p) level of theory is particularly cost-effective, yielding a mean absolute error of 0.11 eV.

Surface Anchoring of the Kingella kingae Galactan Is Dependent on the Lipopolysaccharide O-Antigen.

Kingella kingae is a leading cause of bone and joint infections and other invasive diseases in young children. A key K. kingae virulence determinant is a secreted exopolysaccharide that mediates resistance to serum complement and neutrophils and is required for full pathogenicity. The K. kingae exopolysaccharide is a galactofuranose homopolymer called galactan and is encoded by the pamABC genes in the pamABCDE locus. In this study, we sought to define the mechanism by which galactan is tethered on the bacterial surface, a prerequisite for mediating evasion of host immune mechanisms. We found that the pamD and pamE genes encode glycosyltransferases and are required for synthesis of an atypical lipopolysaccharide (LPS) O-antigen. The LPS O-antigen in turn is required for anchoring of galactan, a novel mechanism for association of an exopolysaccharide with the bacterial surface. IMPORTANCE Kingella kingae is an emerging pediatric pathogen and produces invasive disease by colonizing the oropharynx, invading the bloodstream, and disseminating to distant sites. This organism produces a uniquely multifunctional exopolysaccharide called galactan that is critical for virulence and promotes intravascular survival by mediating resistance to serum and neutrophils. In this study, we established that at least some galactan is anchored to the bacterial surface via a novel structural interaction with an atypical lipopolysaccharide O-antigen. Additionally, we demonstrated that the atypical O-antigen is synthesized by the products of the pamD and pamE genes, located downstream of the gene cluster responsible for galactan biosynthesis. This work addresses how the K. kingae exopolysaccharide can mediate innate immune resistance and advances understanding of bacterial exopolysaccharides and lipopolysaccharides.

Simulant molecules with trivalent or pentavalent phosphorus atoms: bond dissociation energies and other thermodynamic and structural properties from quantum chemical models.

The CBS-QB3 and G4 thermochemical models have been used to generate energetic, structural, and spectroscopic data on a set of molecules with trivalent or pentavalent phosphorus atoms that can serve as simulants of chemical warfare agents. Based on structural data, the conformational stabilities of these molecules are explained in terms of the anomeric interaction within the OPOC and OPSC fragments. For those cases where experimental data are available, comparisons have been made between calculated and previously reported vibrational frequencies. All varieties of bond dissociation energies have been examined except those for C-H and P═O bonds. In trivalent phosphorus molecules, the O-C and S-C bonds have the lowest dissociation energies. In the pentavalent phosphorus set, the S-C bonds, followed by P-S bonds, have the lowest dissociation energies. In the fluorinated simulant molecules, the P-F bond is strongest, and the P-C or O-C bonds are weakest.

Computational tests of models for kinetic parameters of unimolecular reactions of organophosphorus and organosulfur compounds.

A computational study of the kinetics of isomerization and elimination reactions of organophosphorus and organosulfur reactions is presented with a view to characterizing the predictive capabilities of widely applied techniques for processes that pertain to the destruction of chemical warfare agents. A set of 22 reactions has been studied, and the results have been compared to experimentally derived data. The BMK functional and the MG3S basis set have been used to compute minimum energy paths. Corrections have been added from CBS-QB3, CASSCF, and CASMP2 calculations. Thermal rate constants at experimental temperatures have been calculated with canonical variational transition state theory and small-curvature tunneling theory. The quality of these results may depend on recrossing of the variational transition state, the amount of radical or diradical character found in the minimum energy paths, or the accuracy of barrier heights.

Computational tests of quantum chemical models for structures, vibrational frequencies, and heats of formation of molecules with phosphorus and sulfur atoms.

The Gaussian-n, complete basis set, and Weizmann-1 quantum chemical models for heats of formation are applied to a set of molecules with relevance to the combustion or pyrolysis of chemical warfare materials. Most of these models generate standard deviations from experiment that are less than 2 kcal/mol. The structures and vibrational frequencies that are generated in the course of these calculations are in good agreement with experimental data. Detailed comparisons with respect to structural types indicate that the present computational models are likely to generate useful data for complex models of combustion and pyrolysis of chemical warfare materials.

Adjuvant embolization with N-butyl cyanoacrylate in the treatment of cerebral arteriovenous malformations: outcomes, complications, and predictors of neurologic deficits.

BACKGROUND AND PURPOSE: The purpose of this study was to assess the frequency, severity, and predictors of neurological deficits after adjuvant embolization for cerebral arteriovenous malformations. METHODS: From 1997 to 2006, 202 of 275 patients with arteriovenous malformation received embolization before microsurgery (n=176) or radiosurgery (n=26). Patients were examined before and after endovascular embolization and at clinical follow-up (mean, 43.4+/-34.6 months). Outcome was classified according to the modified Rankin Scale. New neurological deficits after embolization were defined as minimal (no change in overall modified Rankin Scale), moderate (modified Rankin Scale < or =2), or significant (modified Rankin Scale >2). RESULTS: Two hundred two patients were treated in 377 embolization procedures. There were a total of 29 new clinical deficits after embolization (8% of procedures; 14% of patients), of which 19 were moderate or significant. Postembolization deficits resolved in a significant number of patients over time (P<0.0001). Five patients had persistent neurological deficits due to embolization (1.3% of procedures; 2.5% of patients). In multivariate analysis, the following variables significantly predicted new neurological deficit after embolization: complex arteriovenous malformation with treatment plan specifying more than one embolization procedure (OR, 2.7; 95% CI, 1.4 to 8.6), diameter <3 cm (OR, 3.2; 95% CI, 1.2 to 9.1), diameter >6 cm (OR, 6.2; 95% CI, 1.0 to 57.0), deep venous drainage (OR, 2.7; 95% CI, 1.1 to 6.9), or eloquent location (OR, 2.4; 95% CI, 1.0 to 5.7). These variables were weighted and used to compute an arteriovenous malformation Embolization Prognostic Risk Score for each patient. A score of 0 predicted no new deficits, a score of 1 predicted a new deficit rate of 6%, a score of 2 predicted a new deficit rate of 15%, a score of 3 predicted a new deficit rate of 21%, and a score of 4 predicted a new deficit rate of 50% (P<0.0001). CONCLUSIONS: Small and large size, eloquent location, deep venous drainage, and complex vascular anatomy requiring multiple embolization procedures are risk factors for the development of immediate postembolization neurological deficits. Nevertheless, a significant number of patients with treatment-related neurological deficits improve over time. The low incidence of permanent neurological deficits underscores the usefulness of this technique in carefully selected patients.

Stagnation of flow in protein cavities by boundary element microhydrodynamics.

In this work, we apply the boundary element method to describe the fluid velocity profiles in pockets in protein surfaces that are crucial to their function as enzymes. First, we study a simplified model, that of a dimpled sphere, in order to properly interpret the behavior in more complex surfaces such as proteins. In that case, we are able to observe the difference between an unphysical sharp edge for the dimple and a smooth edge. The sharp edge produces extra dissipation in the fluid, accounting for much more friction for all types of body motions. We were able to observe the direct correlation of the stagnation depth with the depth of the dimple in this simple case, allowing us to interpret this feature in a similar fashion for proteins. We have found that the fluid in the protein pockets translates with the body, irrespective of the direction body motion, for a distance comparable to the size of the pocket, and that such stagnation volumes are larger for motions parallel to the pocket axis. Outside of these pockets, the fluid velocity profile decays to that of the surrounding fluid far away from the protein (taken to be zero in our case, for convenience), as the Oseen tensor requires. We have also found that there is weak local motion of fluid inside of the pockets, with velocities about 1% of those of the body. This study suggests that there may be a role for the hydrodynamics of solvent inside of pockets for the transport of substrates to protein active sites. If solvent is effectively stagnant inside of a pocket, then transport must occur by diffusion near the pocket surface even if the fluid around the protein is stirred. The weak local motions inside of the pocket may also be relevant in this transport process, but these may be easily overwhelmed by any electrostatic interactions that are likely present at active sites.

Efficacy of lamina terminalis fenestration in reducing shunt-dependent hydrocephalus following aneurysmal subarachnoid hemorrhage: a systematic review. Clinical article.

OBJECT: Chronic hydrocephalus requiring shunt placement is a common complication following aneurysmal subarachnoid hemorrhage (SAH). Controversy exists over whether microsurgical fenestration of the lamina terminalis during aneurysm surgery affords a reduction in the development of shunt-dependent hydrocephalus. To resolve this debate, the authors performed a systematic review and quantitative analysis of the literature to determine the efficacy of lamina terminalis fenestration in reducing aneurysmal SAH-associated shunt-dependent hydrocephalus. METHODS: A MEDLINE (1950-2007) database search was performed using the following keywords, singly and in combination: "ventriculoperitoneal shunt," "hydrocephalus," "subarachnoid hemorrhage," "aneurysm," "fenestration," and "lamina terminalis." Additional studies were manually singled out by scrutinizing references from identified manuscripts, major neurosurgical journals and texts, and personal files. A recent study from the authors' institution was also incorporated into the review. Data from included studies were analyzed using the chi-square analysis and Student t-test. The Cochran-Mantel-Haenszel test was used to compare overall incidence of shunt-dependent hydrocephalus. RESULTS: The literature search revealed 19 studies, but only 11 were included in this review, involving 1973 patients. The fenestrated and nonfenestrated cohorts (combined from the various studies) differed significantly with regard to patient sex, age, and clinical grade as well as aneurysm location (p=0.0065, 0.0028, 0.0003, and 0.017, respectively). The overall incidence of shunt-dependent hydrocephalus in the fenestrated cohort was 10%, as compared with 14% in the nonfenestrated cohort (p=0.089). The relative risk of shunt-dependent hydrocephalus in the fenestrated cohort was 0.88 (95% CI 0.62-1.24). CONCLUSIONS: This systematic review revealed no significant association between lamina terminalis fenestration and a reduced incidence of shunt-dependent hydrocephalus. The interpretation of these results, however, is restricted by unmatched cohort differences as well as other inherent study limitations. Although the overall literature supports lamina terminalis fenestration, a number of authors have questioned the technique's benefits, thus rendering its efficacy in reducing shunt-dependent hydrocephalus unclear. A well-designed, multicenter, randomized controlled trial is needed to definitively address the efficacy of this microsurgical technique.

The incidence of heparin-induced thrombocytopenia Type II in patients with subarachnoid hemorrhage treated with heparin versus enoxaparin.

OBJECT: Heparin-induced thrombocytopenia Type II (HIT II) is a serious complication that occurs in 0.2-3% of patients treated with heparin and is associated with a high risk of thrombotic events. One center recently reported an incidence of HIT II of 15% in a population of patients with aneurysmal subarachnoid hemorrhage (aSAH). Because these patients are typically exposed to heparin during angiography, controversy exists regarding whether prophylaxis with enoxaparin rather than heparin affords any reduction in the risk of developing HIT II. In this study, the authors investigated the effect of heparin compared with enoxaparin on the incidence of HIT II in patients with aSAH. METHODS: The authors reviewed the medical records of 300 patients treated for aSAH who received thromboprophylaxis with either heparin or enoxaparin, and identified patients who developed HIT II. The incidences of HIT II in the 2 treatment groups were then compared. RESULTS: One hundred sixty-six patients with aSAH were treated with heparin, and 134 patients were treated with enoxaparin. Sixteen (5.3%) of 300 patients met the diagnostic criteria for HIT II. Of those treated with heparin, 8 (4.8%) of 166 developed HIT II, compared with 8 (6%) of 134 treated with enoxaparin (difference not significant). CONCLUSIONS: The authors report a lower incidence of HIT II in patients with aSAH than has previously been reported. The data also suggest that patients with aSAH who receive heparin are at no greater risk of developing HIT II than those who receive enoxaparin. This finding challenges the merit of choosing enoxaparin rather than heparin for thromboprophylaxis in patients with a SAH.

Evaluation of a revised Glasgow Coma Score scale in predicting long-term outcome of poor grade aneurysmal subarachnoid hemorrhage patients.

Although many scales attempt to predict outcome following aneurysmal subarachnoid hemorrhage (aSAH), none have achieved universal acceptance, and most scales in common use are not statistically derived. We propose a statistically validated scale for poor grade aSAH patients that combines the Hunt and Hess grades and the Glasgow Coma Scale (GCS) scores; we refer to this as the Poor Grade GCS (PGS). The GCS scores of 160 poor grade aSAH patients (Hunt and Hess Grades 4 and 5) were recorded throughout their hospital stay. Outcomes were assessed by the modified Rankin scale (mRS). Analysis of variance and the Chi-square test were used to guide an analysis of GCS breakpoints according to outcomes. Multivariable logistic regression analysis was used to assess the ability of the Hunt and Hess, GCS, World Federation of Neurological Surgeons Grading Scale, and the PGS to predict long-term outcome. Outcome analysis revealed significant breakpoints in admission GCS scores: PGS-A (GCS 10-12); PGS-B (GCS 8-9); PGS-C (GCS 5-7); PGS-D (GCS 3-4) (p<0.001). In surgical patients, 95.2% of PGS-A, 58.1% of PGS-B, 35.4% of PGS-C, and 28.6% of PGS-D had a favorable one-year outcome. When controlling for age, sex, and operation status, PGS was the only scale predictive of long-term outcome. The odds ratios (OR) for unfavorable outcome according to PGS admission scores (with PGS-A as the reference) were: PGS-B, OR=14.2 (95% CI 1.5-140.5); PGS-C, OR=38.5 (95% CI 4.2-340.0); and PGS-D, OR=63.4 (95% CI 5.6-707.1). In addition to PGS admission scores, an age of 70 or greater was a significant predictor of poor outcome with an OR of 7.5 (95% CI 1.8-30.7). No patients with a PGS-C or PGS-D over the age of 70 had a favorable long-term outcome. Therefore, elements of the Hunt and Hess and GCS can be combined into the PGS to predict long-term outcome in poor grade aSAH patients. However, patients with PGS-C and PGS-D over the age of 70 should be assessed carefully prior to definitive treatment.

Plasma levels of vascular endothelial growth factor after treatment for cerebral arteriovenous malformations.

BACKGROUND AND PURPOSE: The role of abnormal angiogenesis in the formation and progression of cerebral arteriovenous malformations (AVMs) is unclear. Previous studies have demonstrated increased local expression of vascular endothelial growth factor (VEGF) in AVM tissue and increased circulating levels of VEGF in AVM patients. We sought to further investigate the role of VEGF in AVM pathophysiology by examining changes in plasma VEGF levels in patients undergoing treatment for AVMs. METHODS: Three serial blood samples were obtained from 13 AVM patients undergoing treatment: (1) before any treatment, (2) 24 hours postresection, and (3) 30 days postresection. Plasma VEGF concentrations were measured via commercially available enzyme-linked immunosorbent assay (ELISA). For controls, blood samples were obtained from 29 lumbar laminectomy patients. RESULTS: The mean plasma VEGF level in AVM patients at baseline was 36.08+/-13.02 pg/mL, significantly lower than that of the control group (80.52+/-14.02 pg/mL, P=0.028). Twenty-four hours postresection, plasma VEGF levels dropped to 20.09+/-4.54 pg/mL, then increased to 66.81+/-26.45 pg/mL 30 days later (P=0.048). The mean plasma VEGF concentration 30 days after resection was no longer significantly different from the control group (P=0.33). CONCLUSIONS: Plasma VEGF levels in 13 AVM patients were unexpectedly lower than controls, dropped early after AVM resection, then significantly increased 30 days later. These results support the key role of abnormal angiogenesis in AVM pathophysiology and suggest that a disruption in systemic VEGF expression may contribute to the natural history of these lesions.

Impact of a protocol for acute antifibrinolytic therapy on aneurysm rebleeding after subarachnoid hemorrhage.

BACKGROUND AND PURPOSE: epsilon-Aminocaproic acid (EACA) is an antifibrinolytic agent used to prevent rebleeding in aneurysmal subarachnoid hemorrhage. Although studies have found that a decrease in rebleeding with long-term antifibrinolytic therapy is offset by an increase in ischemic deficits, more recent studies have indicated that early, short-term therapy may be beneficial. METHODS: We instituted a protocol for acute EACA administration starting at diagnosis and continued for a maximum duration of 72 hours after subarachnoid hemorrhage onset. We compared 73 patients treated with EACA with 175 non-EACA-treated patients. We sought to identify differences in the occurrence of rebleeding, side effects, and outcome. RESULTS: Baseline characteristics were similar in the 2 groups. There was a significant decrease in rebleeding in EACA-treated patients (2.7%) versus non-EACA patients (11.4%). There was no difference in ischemic complications between cohorts. There was a significant 8-fold increase in deep venous thrombosis in the EACA group but no increase in pulmonary embolism. There was a nonsignificant 76% reduction in mortality attributable to rebleeding, a 13.3% increase in favorable outcome in good-grade EACA-treated patients, and a 6.8% increase in poor-grade patients. CONCLUSIONS: When used acutely, short-term EACA treatment resulted in decreased rebleeding without an increase in serious side effects in our selected group of patients. Randomized placebo-controlled trials are needed to determine whether acute antifibrinolytic therapy should be accepted as the standard of care in all patients.

Endothelial nitric oxide synthase gene single-nucleotide polymorphism predicts cerebral vasospasm after aneurysmal subarachnoid hemorrhage.

Vasospasm is a major cause of morbidity and mortality after aneurysmal subarachnoid hemorrhage (aSAH). Studies have shown a link between single-nucleotide polymorphisms (SNPs) in the endothelial nitric oxide synthase (eNOS) gene and the incidence of coronary spasm and aneurysms. Alterations in the eNOS T-786 SNP may lead to an increased risk of post-aSAH cerebral vasospasm. In this prospective clinical study, 77 aSAH patients provided genetic material and were followed for the occurrence of vasospasm. In multivariate logistic regression analysis, genotype was the only factor predictive of vasospasm. The odds ratio (OR) for symptomatic vasospasm in patients with one T allele was 3.3 (95% confidence interval (CI): 1.1 to 10.0, P=0.034) and 10.9 for TT. Patients with angiographic spasm were 3.6 times more likely to have a T allele (95% CI: 1.3 to 9.6, P=0.013; for TT: OR 12.6). Patients with severe vasospasm requiring endovascular therapy were more likely to have a T allele (OR 3.5, 95% CI: 1.3 to 9.5, P=0.016; for TT: OR 12.0). Patients with the T allele of the eNOS gene are more likely to have severe vasospasm. Presence of this genotype may allow the identification of individuals at high risk for post-aSAH vasospasm and lead to early treatment and improved outcome.

Monocyte chemoattractant protein-1 predicts outcome and vasospasm following aneurysmal subarachnoid hemorrhage.

OBJECT: Despite efforts to elucidate both the molecular mechanism and the clinical predictors of vasospasm after aneurysmal subarachnoid hemorrhage (ASAH), its pathogenesis remains unclear. Monocyte chemoattractant protein-1 (MCP-1) is a chemokine that has been firmly implicated in the pathophysiology of vasospasm and in neural tissue injury following focal ischemia in both animal models and human studies. The authors hypothesized that MCP-1 would be found in increased concentrations in the blood and cerebrospinal fluid (CSF) of patients with ASAH and would correlate with both outcome and the occurrence of vasospasm. METHODS: Seventy-seven patients who presented with ASAH were prospectively enrolled in this study between July 2001 and May 2002. Using an enzyme-linked immunosorbent assay, MCP-1 levels were measured in serum daily and in CSF when available. The mean serum and CSF MCP-1 concentrations were calculated for each patient throughout the entire hospital stay. Neurological outcome was evaluated at discharge or 14 days posthemorrhage using the modified Rankin Scale. Vasospasm was evaluated on angiography. RESULTS: The serum MCP-1 concentrations correlated with negative outcome such that a 10% increase in concentration predicted a 25% increase in the probability of a poor outcome, whereas the serum MCP-1 levels did not correlate with vasospasm. Concentrations of MCP-1 in the CSF, however, proved to be significantly higher in patients with angiographically demonstrated vasospasm. CONCLUSIONS: These findings suggest a role for MCP-1 in neurological injury and imply that it may act as a biomarker of poor outcome in the serum and of vasospasm in the CSF.

Post-carotid endarterectomy neurocognitive decline is associated with cerebral blood flow asymmetry on post-operative magnetic resonance perfusion brain scans.

OBJECTIVE: Up to 25% of patients experience subtle declines in post-operative neurocognitive function following, otherwise uncomplicated, carotid endarterectomy (CEA). We sought to determine if post-CEA neurocognitive deficits are associated with cerebral blood flow (CBF) abnormalities on post-operative MR perfusion brain scans. METHODS: We enrolled 22 CEA patients to undergo a battery of neuropsychometric tests pre-operatively and on post-operative day 1 (POD 1). Neurocognitive dysfunction was defined as a two standard deviation decline in performance in comparison to a similarly aged control group of lumbar laminectomy patients. All patients received MR perfusion brain scans on POD 1 that were analysed for asymmetries in CBF distribution. One patient experienced a transient ischemic attack within 24 hours before the procedure and was excluded from our analysis. RESULTS: Twenty-nine percent of CEA patients demonstrated neurocognitive dysfunction on POD 1. One hundred percent of those patients with cognitive deficits demonstrated CBF asymmetry, in contrast to only 27% of those patients without cognitive impairment. Post-CEA cognitive dysfunction was significantly associated with CBF abnormalities (RR=3.75, 95% CI: 1.62-8.67, p=0.004). CONCLUSION: Post-CEA neurocognitive dysfunction is significantly associated with post-operative CBF asymmetry. These results support the hypothesis that post-CEA cognitive impairment is caused by cerebral hemodynamic changes. Further work exploring the relationship between CBF and post-CEA cognitive dysfunction is needed.

Polarizability and Kerr constant of proteins by boundary element methods.

A precise implementation of the boundary element method has been applied to the computation of the polarizability and the Kerr constant of eight soluble proteins. The method is demonstrated to be accurate and precise by comparison with analytical values for spheroids. Two different integral equations have been solved: (1) an exact equation with explicit dielectric constant dependence, and (2) an exact equation for a metallic body. The dielectric dependence for the metallic body case is built in with a generalization of the ellipsoid formula. Both methods agree quantitatively with each other for low relative dielectric constants. A full tensor expression for the Kerr constant yields perfect agreement with experiment for some proteins and badly under reports for the rest. The protein structure is obtained from a crystallographic database and is assumed rigid throughout the TEB measurement. Electrolyte effects are neglected. The Kerr constant is dominated by the protein dipole moment and is quite sensitive to the orientation of the dipole moment relative to the principal axes of the polarizability tensor. Several possible reasons for the large discrepancy between some computed and measured values are discussed.

Quality of evidence in studies evaluating neuroimaging for neurologic prognostication in adult patients resuscitated from cardiac arrest.

AIM: Neuroimaging has been proposed as a predictor of neurologic outcome in comatose survivors of cardiac arrest. We reviewed the quality and level of evidence of the current neuroimaging literature for predicting neurologic outcome in cardiac arrest patients treated with or without therapeutic hypothermia (TH). DATA SOURCES: Medline, EMBASE, and Cochrane Databases were searched using the terms "cardiac arrest," "cardiopulmonary resuscitation," "brain hypoxia," "brain anoxia," "brain hypoxia-ischaemia," "neuroimaging," and "prognosis." Eligible studies were reviewed and classified by level of evidence and methodological quality as defined by the International Liaison Committee on Resuscitation (ILCOR). RESULTS: 928 studies were identified, 84 of which met inclusion criteria: 74 were supportive of neuroimaging to predict outcome, eight unsupportive, and two equivocal. Several studies investigated more than one imaging modality: 27 investigated computed tomography (CT), 46 magnetic resonance imaging (MRI), and 18 alternate imaging modalities, including positron emission tomography and single photon emission computed tomography. No randomized controlled trials were identified. Seven cohort and case control studies were identified, only one of which was graded "good" quality, two were "fair" and four were "poor." CONCLUSION: Neuroimaging is an evolving modality as a prognostic parameter in cardiac arrest survivors. However, the quality of the available literature is not robust, highlighting the need for higher quality studies before neuroimaging can be supported as a standard tool for prognostication in the patient population.

Systemic expression of matrix metalloproteinase-9 in patients with cerebral arteriovenous malformations.

OBJECTIVE: Increased expression angiogenic factors, such as matrix metalloproteinases (MMPs), are associated with the formation of cerebral arteriovenous malformations (AVMs). The objective of this study was to determine plasma levels of MMP-9 of patients with AVMs. METHODS: Blood samples were drawn from 15 patients with AVMs before treatment, 24 hours postembolization, 24 hours postresection, and 30 days postresection. Blood samples were also obtained from 30 healthy controls. Plasma MMP-9 concentrations were measured via enzyme-linked immunosorbent assay. RESULTS: The mean plasma MMP-9 level in AVM patients at baseline was significantly higher than in control patients: 108.04 +/- 16.11 versus 41.44 +/- 2.44 ng/mL, respectively. The mean plasma MMP-9 level 1 day after embolization increased to 172.35 +/- 53.76 ng/mL, which was not significantly elevated over pretreatment levels. One day after resection, plasma MMP-9 levels increased significantly over pretreatment levels to 230.97 +/- 51.00 ng/mL. Mean plasma MMP-9 concentrations 30 days after resection decreased to 92.8 +/- 18.7 ng/mL, which was not different from pretreatment levels but was still significantly elevated over control levels. MMP-9 levels did not correlate with patient sex, age, presentation, or AVM size. CONCLUSION: Plasma MMP-9 levels are significantly elevated over controls at baseline, increase significantly immediately after surgery, and decrease to pretreatment levels during follow-up.

The impact of microsurgical fenestration of the lamina terminalis on shunt-dependent hydrocephalus and vasospasm after aneurysmal subarachnoid hemorrhage.

OBJECTIVE: Chronic hydrocephalus requiring shunt placement and cerebral vasospasm are common complications after aneurysmal subarachnoid hemorrhage. Recent publications have investigated the possibility that microsurgical fenestration of the lamina terminalis during aneurysm surgery may reduce the incidence of shunt-dependent hydrocephalus and cerebral vasospasm. We reviewed a single-surgeon series to compare postsurgical outcomes of patients who underwent fenestration of the lamina terminalis against those who did not. METHODS: This study is a retrospective review of the medical records of 369 consecutive patients with aneurysmal subarachnoid hemorrhage admitted to Columbia University Medical Center between January 2000 and July 2006. All patients underwent craniotomy and clipping of at least one ruptured cerebral aneurysm by a single neurosurgeon (ESC). The incidences of shunt-dependent hydrocephalus, conversion from acute hydrocephalus on admission to chronic hydrocephalus, and clinical cerebral vasospasm were compared in patients who underwent fenestration of the lamina terminalis with those who did not. The patient cohort was thus divided into three subgroups: 1) patients whose operative records clearly indicated that they underwent fenestration of the lamina terminalis, 2) patients whose operative records clearly indicated that they did not undergo fenestration of the lamina terminalis, and 3) patients whose operative records did not indicate one way or another whether they received fenestration of the lamina terminalis. We performed two separate analyses by comparing the postsurgical outcomes in those patients who were fenestrated versus those who were definitively not fenestrated and comparing the postsurgical outcomes in those patients who were fenestrated versus those who were not plus those whose records did not document fenestration. To further control for any cohort differences, we performed a comparison between patients who were fenestrated and those who were not after matching 1:1 for presenting radiographic and clinical characteristics predictive of hydrocephalus and vasospasm. Outcomes were compared using logistic regression and multivariable analysis. RESULTS: In the first model, fenestrated patients had a shunt rate, conversion rate, and rate of clinical vasospasm of 25, 50, and 23%, respectively, versus 20, 27, and 27% in nonfenestrated patients, respectively (P = 0.28, 0.21, and 0.32, respectively). In the second model, the nonfenestrated patients plus nondocumented patients had a shunt rate, conversion rate, and rate of clinical vasospasm of 16, 40, and 20%, respectively (P = 0.19, 0.33, and 0.60, respectively). In the matched cohort, fenestrated patients had a shunt rate, conversion rate, and rate of clinical vasospasm of 29, 67, and 20%, respectively, versus 20, 25, and 25% in nonfenestrated patients, respectively (P = 0.30, 0.24, and 0.20, respectively). CONCLUSION: In contrast to other retrospective multisurgeon series, our retrospective single-surgeon series suggests that microsurgical fenestration of the lamina terminalis may not reduce the incidence of shunt-dependent hydrocephalus or cerebral vasospasm after aneurysmal subarachnoid hemorrhage. A prospective multicenter trial is needed to definitively address the use of this maneuver.