Usefulness of Silent MR Angiography for Intracranial Aneurysms Treated with a Flow-Diverter Device.

BACKGROUND AND PURPOSE: The flow-diverter device has been established as a treatment procedure for large unruptured intracranial aneurysms. The purpose of this study was to compare the usefulness of Silent MR angiography and time-of-flight MRA to assess the parent artery and the embolization state of the aneurysm after a flow-diverter placement. MATERIALS AND METHODS: Seventy-eight large, unruptured internal carotid aneurysms in 78 patients were the subjects of this study. After 6 months of treatment, they underwent follow-up digital subtraction angiography, Silent MRA, and TOF-MRA, performed simultaneously. All images were independently reviewed by 2 neurosurgeons and 1 radiologist and rated on a 4-point scale from 1 (not visible) to 4 (excellent) to evaluate the parent artery. The aneurysmal embolization status was assessed with 2 ratings: complete or incomplete occlusion. RESULTS: The mean scores of Silent MRA and TOF-MRA regarding the parent artery were 3.18 ± 0.72 and 2.31 ± 0.86, respectively, showing a significantly better score with Silent MRA (P < .01). In the assessment of the embolization of aneurysms on Silent MRA and TOF-MRA compared with DSA, the percentages of agreement were 91.0% and 80.8%, respectively. CONCLUSIONS: Silent MRA is superior for visualizing blood flow images inside flow-diverter devices compared with TOF-MRA. Furthermore, Silent MRA enables the assessment of aneurysmal embolization status. Silent MRA is useful for assessing the status of large and giant unruptured internal carotid aneurysms after flow-diverter placement.

Non-Contrast-Enhanced Silent Scan MR Angiography of Intracranial Anterior Circulation Aneurysms Treated with a Low-Profile Visualized Intraluminal Support Device.

BACKGROUND AND PURPOSE: The Low-Profile Visualized Intraluminal Support Device comprises a small-cell nitinol structure and a single-wire braided stent that provides greater metal coverage than previously reported intracranial stents, as well as assumed strong susceptibility artifacts. This study aimed to assess the benefits of non-contrast-enhanced MRA by using a Silent Scan (Silent MRA) for intracranial anterior circulation aneurysms treated with Low-Profile Visualized Intraluminal Support Device stents. MATERIALS AND METHODS: Thirty-one aneurysms treated with Low-Profile Visualized Intraluminal Support Device stents were assessed by using Silent MRA, 3D TOF-MRA, and x-ray DSA. The quality of MRA visualization of the reconstructed artery was graded on a 4-point scale from 1 (not visible) to 4 (excellent). Aneurysm occlusion status was evaluated by using a 2-grade scale (total occlusion/remnant [neck or aneurysm]). Weighted κ statistics were used to evaluate interobserver and intermodality agreement. RESULTS: The mean scores ± SDs for Silent MRA and 3D TOF-MRA were 3.16 ± 0.79 and 1.48 ± 0.67 (P < .05), respectively, with substantial interobserver agreement (κ = 0.66). The aneurysm occlusion rates of the 2-grade scale (total occlusion/remnant [neck or aneurysm]) were 69%/31% for DSA, 65%/35% for Silent MRA, and 92%/8% for 3D TOF-MRA, respectively. The intermodality agreements were 0.88 and 0.30 for DSA/Silent MRA and DSA/3D TOF-MRA, respectively. CONCLUSIONS: Silent MRA seems to be useful for visualizing intracranial anterior circulation aneurysms treated with Low-Profile Visualized Intraluminal Support Device stents.

Xenotransplantation--how far have we come?

The immunologic barriers to xenotransplantation are summarized and approaches to overcome them briefly reviewed. Intensive investigation is being directed to the problem of acute humoral xenograft rejection, which is the major current barrier. Although the induced antibody response appears to be prevented by combination therapy with an anti-CD154 monoclonal antibody and mycophenolate mofetil, deposition of natural anti-Gal antibody on the graft endothelial cells appears to be sufficient to lead to rejection or a state of consumptive coagulopathy. Approaches towards the induction of tolerance are described. The potential microbiologic risks and physiologic incompatibilities of pig-to-human organ transplantation are also briefly discussed.

Pig hematopoietic cell chimerism in baboons conditioned with a nonmyeloablative regimen and CD154 blockade.

BACKGROUND: In an attempt to induce mixed hematopoietic chimerism and transplantation tolerance in the pig-to-primate model, we have infused high-dose porcine peripheral blood progenitor cells (PBPC) into baboons pretreated with a nonmyeloablative regimen and anti-CD154 monoclonal antibody (mAb). METHODS: Group 1 baboons (n=2) received a nonmyeloablative regimen including whole body irradiation, pharmacological immunosuppression, porcine hematopoietic growth factors, and immunoadsorption of anti-Galalpha1,3Gal (Gal) antibody before infusion of high doses of PBPC (2.7-4.6x10(10) cells/kg). In group 2 (n=5), cyclosporine was replaced by anti-CD154 mAb. Group 3 (n=3) received the group 1 regimen plus anti-CD154 mAb. RESULTS: In group 1, pig chimerism was detected in the blood by flow cytometry (FACS) for 5 days (with a maximum of 14%), and continuously up to 13 days by polymerase chain reaction (PCR). In group 2, pig chimerism was detectable for 5 days by FACS (maximum 33%) and continuously up to 28 days by PCR. In group 3, initial pig chimerism was detectable for 5 days by FACS (maximum 73%). Two of three baboons showed reappearance of pig cells on days 11 and 16, respectively. In one, in which no anti-Gal IgG could be detected for 30 days, pig cells were documented in the blood by FACS on days 16-22 (maximum 6% on day 19) and pig colony-forming cells were present in the blood on days 19-33, which we interpreted as evidence of engraftment. Microchimerism was continuous by PCR up to 33 days. CONCLUSIONS: These results suggest that there is no absolute barrier to pig hematopoietic cell engraftment in primates, and that this may be facilitated if the return of anti-Gal IgG can be prevented.

Depletion of anti-gal antibodies in baboons by intravenous therapy with bovine serum albumin conjugated to gal oligosaccharides.

BACKGROUND: Anti-Galalpha 1-3Gal (Gal) antibodies (Ab) play a key role in the rejection of pig cells or organs transplanted into primates. A course of extracorporeal immunoadsorption (EIA) of anti-Gal Ab using an immunoaffinity column of a Gal type 6 oligosaccharide depletes Ab successfully, but Ab returns during the next few days. Although therapy with an anti-CD154 monoclonal antibody (mAb) prevents an induced Ab response to Gal or non-Gal epitopes, T cell-independent natural anti-Gal IgM and IgG return to baseline (pretransplant) levels. We have investigated the capacity of continuous i.v. infusion of bovine serum albumin conjugated to Gal type 6 oligosaccharide (BSA-Gal) to deplete or maintain depletion of circulating anti-Gal Ab. METHODS: Porcine peripheral blood mobilized progenitor cells (PBPC) obtained by leukapheresis from MHC-inbred miniature swine (n=6) were transplanted into baboons. Group 1 baboons (n=4) underwent whole body (300 cGy) and thymic (700 cGy) irradiation, T cell depletion with antithymocyte globulin, complement depletion with cobra venom factor, short courses of anti-CD154 mAb therapy (20 mg/kg i.v. on alternate days), cyclosporine (CyA) (in two baboons only), mycophenolate mofetil, and porcine hematopoietic growth factors. Anti-Gal Ab depletion by EIA was carried out before transplantation of high doses (2-4x 1010 cells/kg) of PBPC. Group 2 baboons (n=3) received the group 1 regimen (including CyA) plus a continuous i.v. infusion of BSA-Gal. To prevent sensitization to BSA, anti-CD154 mAb therapy was continued until BSA-Gal administration was discontinued. RESULTS: In group 1, Gal-reactive Ab returned to pre-PBPC transplant levels within 15-21 days, but no induced Ab to Gal or non-Gal determinants developed while anti-CD154 mAb therapy was being administered. In group 2, anti-Gal Ab was either not measurable or minimally measurable while BSA-Gal was being administered. After discontinuation of BSA-Gal, Ab did not return to pre-PBPC transplant level for more than 40-60 days, and no sensitization developed even when all therapy was discontinued. In one baboon, however, Ab to Gal type 2, but not type 6, returned during BSA-Gal therapy. CONCLUSIONS: Prevention of the induced humoral response to Gal and non-Gal epitopes by anti-CD154 mAb therapy has been reported previously by our group, but our studies are the first to demonstrate a therapy that resulted in an absence of natural anti-Gal Ab for a prolonged period. The combination of BSA-Gal and T cell costimulatory blockade may facilitate survival of pig cells and organs transplanted into primates. The return in one baboon of Ab reactive with the Gal type 2 oligosaccharide, but not type 6, indicates some polymorphism of anti-Gal Ab and suggests that, to be effective in all cases, the infusion of a combination of type 6 and type 2 BSA-Gal may be required.

Effect of conformation on the chemiluminescence efficiency of light-producing 2-methyl-6-(4-methoxyphenyl)imidazo[1,2-alpha]pyrazin-3(7H)-ones.

Analogues of the light-producing substrate 2-methyl-6-(4-methoxyphenyl)imidazo[1,2-alpha]pyrazin-3(7H)-one, with restrictions on the dihedral angles between the pyrazine and the 4-methoxyphenyl rings, were synthesized. These compounds were used to investigate the effects of the conformation between the pyrazine and 4-methoxyphenyl rings on their chemiluminescence efficiencies in aqueous solutions. The effects of the conformation on the chemiluminescence efficiencies were clearly observed; the decrease of the dihedral angle caused a light-enhancing effect and, conversely, the increase of the angle dramatically decreased the chemiluminescence efficiency. These effects on the chemiluminescence efficiencies are attributed to the influence of the conformation on the fluorescence efficiency of the emitter.

Assessment of methotrexate as a potential immunosuppressive agent in baboons.

Methotrexate is an anti-proliferative agent that affects both T-cell and B-cell immunity, and therefore might be expected to suppress antibody (Ab) production. Although it has been used in xenotransplantation studies to suppress anti-pig Ab production, it has always been used in combination with other immunosuppressants. The purpose of this study was to measure its effect as a single immunosuppressant on anti-Gal Ab production in baboons (n=4). Pharmacokinetic studies showed that methotrexate was not detected in the blood when administered per os. Prolonged daily IV or IM administration (i) reduced T-cell and B-cell numbers by 50% to 70% and modestly reduced responsiveness on mixed lymphocyte reaction (but only at toxic doses) and (ii) did not result in lowered anti-Gal Ab levels, only marginally reducing the rate of return of Ab after extracorporeal immunoadsorption. Our observations would suggest that methotrexate will not contribute significantly to immunosuppressive regimens in the baboon at non-toxic doses.

The crystal structure of the photoprotein aequorin at 2.3 A resolution.

Aequorin is a calcium-sensitive photoprotein originally obtained from the jellyfish Aequorea aequorea. Because it has a high sensitivity to calcium ions and is biologically harmless, aequorin is widely used as a probe to monitor intracellular levels of free calcium. The aequorin molecule contains four helix-loop-helix 'EF-hand' domains, of which three can bind calcium. The molecule also contains coelenterazine as its chromophoric ligand. When calcium is added, the protein complex decomposes into apoaequorin, coelenteramide and CO2, accompanied by the emission of light. Apoaequorin can be regenerated into active aequorin in the absence of calcium by incubation with coelenterazine, oxygen and a thiol agent. Cloning and expression of the complementary DNA for aequorin were first reported in 1985 (refs 2, 6), and growth of crystals of the recombinant protein has been described; however, techniques have only recently been developed to prepare recombinant aequorin of the highest purity, permitting a full crystallographic study. Here we report the structure of recombinant aequorin determined by X-ray crystallography. Aequorin is found to be a globular molecule containing a hydrophobic core cavity that accommodates the ligand coelenterazine-2-hydroperoxide. The structure shows protein components stabilizing the peroxide and suggests a mechanism by which calcium activation may occur.

Light-emitters involved in the luminescence of coelenterazine.

Coelenterazine emits light by chemi-and bioluminescence reactions, decomposing into coelenteramide and CO(2). To ascertain the light emitters involved, the fluorescence of coelenteramide and five analogues were studies in four kinds of solvent. The results showed that coelenteramides can form five kinds of light emitters, ie unionized (lambda(max) 386-423 nm), phenolate anion (lambda(max) 480-490 nm), phenolate anion temporarily formed from the ion-pair state (lambda(max) 465-479 nm), amide anion (lambda(max) 435-458 nm) and pyrazine-N(4) anion (lambda(max) 530-565 nm). The chemiluminescence light emitter of coelenterazine in the presence of alkali (lambda(max) 530-550 nm) was found to be the pyrazine-N(4) anion and not the dianion (ie phenolate anion/amide anion), as previously believed. In chemiluminescence, the normal light emitter is the amide anion, and the pyrazine-N(4) anion emission may occur in the presence of alkali, but light emission from any other emitters has not been observed. In the bioluminescence reaction, the normal light emitter is the amide anion, but no other light emitter was observed except the unionized form found in the Ca-triggered luminescence of semisynthetic aequorins prepared with an e-type coelenterazine instead of coelenterazine.

Investigation of cyclomaltooligosaccharide-bound 6-(4-methoxyphenyl)imidazo[1,2-a]pyrazin-3(7H)-one for enhanced chemiluminescence.

The chemiluminescence compound 2-methyl-6-(4-methoxyphenyl)imidazo[1, 2-a]pyrazin-3(7H)-one (MCLA) was attached to cyclomaltooligosaccharides (cyclodextrins) through a single spacer by the formation of an amide bond. The properties of oxygen-induced chemiluminescence of the synthesized cyclodextrin-bound MCLA were investigated in an aqueous phosphate buffer, pH 8.0. The light-emitting efficiency was remarkably dependent on the kind of bound cyclodextrin, spacer length between the MCLA and cyclodextrin, and the binding site in cyclodextrin. The light-emitting efficiencies of cyclomaltooctaose (gamma-cyclodextrin)-bound compounds were higher than those of cyclomaltohexaose- or cyclomaltoheptaose-bound compounds. Especially, compounds in which MCLA attached to the secondary side of gamma-cyclodextrin through a short chain showed an up to 44-fold enhancement over that of a non-cyclodextrin compound. In the current case, the efficiency of single excited-state formation was 23 times greater than that of the non-cyclodextrin compound and significantly responsible for greater light-emitting efficiency. The chemiluminescence spectra indicated the wide entrance of the secondary side of gamma-cyclodextrin, and the short spacer allowed suitable intramolecular affinity between the singlet excited-state chromophore moiety and the cyclodextrin.

Chemiluminescence of 2-methyl-6-arylimidazo-[1,2-a]pyrazin-3(7H)-one in protic solvents: electron-donating substituent effect on the formation of the neutral singlet excited-state molecule.

2-Methyl-6-arylimidazo[1,2-a]pyrazin-3(7H)-ones with a substituent such as phenyl, 4-methoxyphenyl or 4-trifluoromethoxyphenyl at the 6-position of the imidazo[1,2-a]pyrazin-3(7H)-one ring system, produced chemiluminescence emission in mixtures of water and DMF and in several mixtures of MeOH and DMF under neutral conditions. Under these protic luminescence conditions, the respective light emissions were generated from neutral singlet excited-state molecules. The electron-donating effect of the 4-methoxy substituent on the phenyl group increased the efficiency of the neutral singlet excited state formation, whereas non-substitution and a 4-trifluoromethoxy group having no electron donating ability decreased the efficiency. The compound having the electron-donating methoxy group substituent showed two chemiluminescence emitters, which generated light at lambda(max) 410-420 nm and 460 nm. It was determined that the neutral molecules in the excited state generating light emission at the shorter wavelengths are neutral singlet excited-state molecules suitable for highly efficient singlet excited-state formation. A role of the electron-donating effect of the methoxy group is postulated to be generation of the special neutral singlet excited-state molecules.

Partial maze procedure is effective treatment for chronic atrial fibrillation associated with valve disease.

The maze procedure may be performed in combination with valve operations to treat chronic atrial fibrillation associated with valve dysfunction. Although we initially used the modified Cox maze III procedure, a more limited partial maze procedure is now preferred because the left atrium might be considered as the electrical impetues for atrial fibrillation. In this study we compared the results of 30 patients (group I) who underwent the full biatrial modified Cox maze III and 20 (group II) patients the partial maze procedure. While the rates of restored sinus rhythm were the same in both groups at 6-month follow-up (I: 83.3%, vs II: 80%), the following advantages were noted in the patients undergoing the partial maze procedure: shorter operative times, lesser elevations of creatine phosphokinase, lower rate of blood transfusion, lower rate of junctional rhythm soon after the operation, and a higher P wave in those patients with restored sinus rhythm. The effectiveness of the partial maze procedure seems equal to that of the biatrial modified Cox maze III procedure for atrial fibrillation associated with valve disease. The partial maze procedure is simple and less invasive, and thus might be applied more frequently as an additional procedure to valve operations without additional risk.

Adhesion of polysaccharides to intact cells and protoplasts of Nicotiana tabacum BY-2 and its stimulative effects on protoplast growth.

The adhesion of water-soluble beta-d-glycans, including cellulose-adhesive schizophyllan, xyloglucan, and locust bean gum to intact cells and protoplasts of Nicotiana tabacum BY-2 was examined using their fluorescent derivatives. Fluorescence microscopy showed that schizophyllan, xyloglucan, locust bean gum, and xanthan gum bound to the intact cells, and that schizophyllan, xanthan gum, and succinoglycan bound to the protoplasts. These adhesive beta-d-glycans raised considerably the number of the cells regenerated from protoplasts. The results suggest that some water soluble beta-d-glycans showing affinity for intact cells and/or protoplasts will be suitable for use as stabilizers of protoplast division.