Relationship between aneurysm volume and histologic healing after coil embolization in elastase-induced aneurysms: a retrospective study

BACKGROUND AND PURPOSE

There are, to our knowledge, no histologic data correlating aneurysm volume with histologic healing following coil embolization of aneurysms. We report a retrospective study comparing histologic outcome with aneurysm volume in elastase-induced aneurysms in rabbits.

MATERIALS AND METHODS

Aneurysm volume and histologic healing after coil embolization were retrospectively analyzed in 37 elastase-induced aneurysms in rabbits. Aneurysm dimensions (including neck, width, height, and volume) were measured and calculated. Packing density (PD) was calculated. Angiographic results were evaluated as recurrence, stable, and progressive occlusion. An ordinal grading system was used to evaluate the histologic healing after embolization. Correlations among aneurysm volume, PD, and histologic healing were analyzed by conducting linear regression analysis.

RESULTS

For all the aneurysms in this study, mean aneurysm volume was 80.8 +/- 48.6 mm(3) (from 22 to 192 mm(3)), mean PD was 30.4 +/- 8.3% (from 17% to 49%), and mean histologic score was 6.1 +/- 2.0 (from 0.5 to 9.5), respectively. Correlations between aneurysm volume and PD, aneurysm volume and histologic healing, and aneurysm packing and histologic healing were all significant (P < .01).

CONCLUSION

In this study, aneurysms with smaller volumes and higher PD were associated with the most complete histologic healing. The incomplete healing seen in the larger aneurysms is consistent with the higher incidence of recurrences after endovascular treatment that is seen in large human aneurysms.

Bone formation in elastase-induced rabbit aneurysms embolized with platinum coils: report of 2 cases

Histologic findings in 71 elastase-induced rabbit aneurysms embolized with platinum coils were retrospectively reviewed. Mature bone formation was found in 2 aneurysms, one with coils implanted for 3 months and the other with coils implanted for 1 year. We present the histologic findings and offer potential explanations for these observations. These findings may be relevant in understanding mechanisms of aneurysm healing after coil embolization.

Endovascular treatment of aneurysms: healing mechanisms in a Swine model are associated with increased expression of matrix metalloproteinases, vascular cell adhesion molecule-1, and vascular endothelial growth factor, and decreased expression of tissue inhibitors of matrix metalloproteinases

BACKGROUND AND PURPOSE

The mechanism of aneurysm healing after coiling remains poorly understood. The purpose of the study was to obtain a better understanding of the cellular and molecular events that are associated with aneurysm healing after endovascular coiling in a swine aneurysm model.

MATERIALS AND METHODS

Twenty sidewall aneurysms were created surgically in common carotid arteries in 10 swine. These aneurysms were embolized immediately after creation by using platinum coils by endovascular means. Two and 12 weeks after implantation, aneurysm samples were collected for histologic and biochemical analysis.

RESULTS

All aneurysms were completely or nearly completely occluded angiographically at the time of embolization and at follow-up. At 2 weeks, aneurysm cavities were filled with inflammatory cells and myofibroblasts. At 12 weeks, aneurysm cavities were filled with richly vascularized fibrous tissue and disorganized collagen bundles. The expression of matrix metalloproteinase (MMP)-2 and -9 was found to be elevated at 2 weeks. Expression remained greater than that in control tissue at 12 weeks but was significantly decreased compared with the earlier time point. Expression of tissue inhibitors of MMPs (TIMPs) was diminished at both time points. Expression of vascular cell adhesion molecule-1 (VCAM-1) and vascular endothelial growth factor (VEGF) was elevated at both 2 weeks and 12 weeks. Endothelial nitric oxide synthase expression was not different from that in controls. Transforming growth factor-beta expression was elevated at 2 weeks only.

CONCLUSION

The coil occlusion in this model that is prone to heal is associated with increased expression of MMP-2, MMP-9, VCAM-1, and VEGF, and decreased expression of TIMPs.

Control of aneurysm volume by adjusting the position of ligation during creation of elastase-induced aneurysms: a prospective study

BACKGROUND AND PURPOSE

Animal models with appropriate volume are crucial for preclinical assessment of aneurysm therapies. Our purpose was to control the aneurysm volume by adjusting the position of ligation during creation of elastase-induced aneurysms in rabbits.

MATERIALS AND METHODS

Sixty elastase-induced aneurysms in rabbits were created. Two different methods were used for creation, including group 1 (n=30) by using a lower ligation (from the origin of the right common carotid artery [RCCA] to the ligation point, 10 mm) and group 2 (n=30) by using a higher ligation (from the origin of the RCCA to the ligation point, 15 mm). Aneurysm sizes (neck diameter, width, and height) and volumes in the 2 groups were measured and calculated, and they were compared by using the Student t test.

RESULTS

The mean aneurysm neck diameter, width, and height for group 2 were significantly larger than those of group 1 (3.3 +/- 0.8 versus 2.7 +/- 0.6 mm, P<.001; 3.7 +/- 0.7 versus 2.5 +/- 0.7 mm, P<.001; 9.0 +/- 1.7 versus 7.3 +/- 1.9 mm, P<.001, respectively). The aneurysm volume in group 2 was significantly larger than that in group 1 (102.4 +/- 54.8 mm(3) versus 36.6 +/- 26.8 mm(3), P<.001).

CONCLUSION

The aneurysm volume of elastase-induced models in rabbits can be controlled by adjusting the position of the ligation. Using a higher ligation can create relatively more voluminous aneurysms, compared with using a lower ligation.

mRNA expression in rabbit experimental aneurysms: a study using gene chip microarrays

BACKGROUND AND PURPOSE

The molecular characteristics of intracranial aneurysms are still poorly documented. A rabbit elastase aneurysm model has been helpful in the evaluation of devices and strategies involved in endovascular treatment of aneurysms. The goal of this project was to document the molecular changes, assessed by gene chip microarrays, associated with the creation of aneurysms in this model compared with the contralateral carotid artery.

MATERIALS AND METHODS

A microarray of rabbit genes of interest was constructed using rabbit nucleotide sequences from GenBank. Elastase-induced saccular aneurysms were created at the origin of the right common carotid artery in 4 rabbits. Twelve weeks after aneurysm creation, RNA was isolated from the aneurysm as well as the contralateral common carotid artery and used for microarray experiments. Reverse transcription-polymerase chain reaction (RT-PCR) was performed on 1 animal as a confirmatory test.

RESULTS

Ninety-six (46%) of 209 genes in the microarray were differentially expressed in the rabbit aneurysm compared with the contralateral common carotid artery. In general, differential gene expression followed specific molecular pathways. Similarities were found between rabbit aneurysms and human intracranial aneurysms, including increased metalloproteinase activity and decreased production of the extracellular matrix. RT-PCR results confirmed the differential expression found by the gene chip microarray.

CONCLUSIONS

The molecular characteristics of the rabbit elastase-induced saccular aneurysm are described. The rabbit aneurysm model shares some molecular features with human intracranial aneurysms. Future studies can use the rabbit model and the new rabbit gene chip microarray to study the molecular aspects of saccular aneurysms.

Characterization of the Crystal and Magnetic Structures of the Mixed-Anion Coordination Polymer Cu(HCO2)(NO3)(pyz) {pyz = Pyrazine} by X-ray Diffraction, ac Magnetic Susceptibility, dc Magnetization, Muon-Spin Relaxation, and Spin Dimer Analysis

The mixed-anion coordination polymer Cu(HCO2)(NO3)(pyz) was synthesized, its crystal structure was determined by X-ray diffraction, and its magnetic structure was characterized by ac susceptibility, dc magnetization, muon-spin relaxation, and spin dimer analysis. The crystal structure consists of five-coordinate Cu2+ ions that are connected through syn-anti bridging mu-HCO2- and mu-pyz ligands to form a highly corrugated two-dimensional layered network. Bulk magnetic measurements show a broad maximum in chi(T) at 6.6 K. The HCO2- and pyz ligands mediate ferromagnetic and antiferromagnetic spin exchange interactions between adjacent Cu2+ ions with the spin exchange parameters J/kB = 8.17 and -5.4 K, respectively (H = -JSigmaSi x Sj). The muon-spin relaxation data show a transition to a long-range magnetic ordering below TN = 3.66(3) K. For T < TN, the M(H) and chi'ac measurements provide evidence for a field-induced spin-flop transition at 15.2 kOe. That Cu(HCO2)(NO3)(pyz) undergoes a long-range magnetic ordering is an unexpected result because the one-dimensional Cu(NO3)2(pyz) and three-dimensional Cu(HCO2)2(pyz) compounds display linear chain antiferromagnetism with no long-range magnetic ordering down to 2 K.

Can neck size in elastase-induced aneurysms be controlled? A retrospective study

BACKGROUND AND PURPOSE

Reproducible animal models with appropriate neck size are crucial for preclinical assessment of aneurysm therapies. Our purpose was to determine whether the neck size of elastase-induced aneurysms could be controlled by adjusting the position of the temporary occlusion balloon.

METHODS

Seventy-two elastase-induced aneurysms in rabbits were retrospectively analyzed. Three groups (group 1, n = 35; group 2, n = 32; group 3, n = 5) were defined according to different balloon position (lowest, intermediate, and highest, respectively) related to the origin of right common carotid artery (CCA). Aneurysm sizes in different groups were measured and compared; parent artery dilation was assessed as present or absent. The Wilcoxon rank sum test, the Fisher exact test, and the chi(2) test were used for statistics process.

RESULTS

The mean aneurysm neck diameter in group 1 was significantly wider than that in group 2 (P = .0001). The proportion of wide-necked (diameter of neck >4 mm) aneurysms in group 1 was significantly higher than that in group 2 (P = .0011). The mean dome/neck ratio in group 1 was smaller than that of group 2 (P = .0031). Aneurysm width and height and the frequency of parent artery dilation were not different in groups 1 and 2 (P = .43, P = .10, and P = .25). No aneurysms formed in group 3.

CONCLUSION

The neck size of elastase-induced aneurysms can be controlled by adjusting the position of the inflated balloon, with balloon positioning that bridges from the CCA to the subclavian/brachiocephalic arteries yielding narrow-necked aneurysms.

Intra-arterial digital subtraction angiography through the ear artery for experimental aneurysm imaging

Digital subtraction angiography through the central artery of the ear was performed to show elastase-induced aneurysms in 34 rabbits. Twenty-eight (82%) aneurysms in which common origins of the bilateral common carotid artery (CCA) were found were well shown. All 6 other aneurysms not well shown had separate origins of the CCAs from the aortic arch (P < .001). This method can be used for angiographic follow-up when there is a common origin of the CCAs.

Femtosecond ground state recovery: Measuring the intersystem crossing yield of polyspirobifluorene

Measurement of the quantum yield of triplet formation has been made for the prototypical conjugated polymer polyspirobifluorene in solution and solid state. An updated method has been described based on femtosecond time resolved ground state recovery following photoexcitation of the polymer. The two components to the recovery of the ground state due to the decay of the singlet and triplet excited states are clearly visible and from these it is possible to calculate Phi(T)=0.05+/-0.01 in solution, this gives k(isc)=5.4 x 10(7) s(-1) which compares favorably with other conjugated polymers. In polymer films an increased triplet yield of Phi(T)=0.12+/-0.02 is found to be independent of temperature, the increased yield is attributed to triplet recombination from charged states.

On the Origin of the Metallic and Anisotropic Magnetic Properties of NaxCoO2 (x ≈ 0.75)

Nonstoichiometric Na(x)CoO2 (0.5 < x < 1) consists of CoO2 layers made up of edge-sharing CoO6 octahedra and exhibits strongly anisotropic magnetic susceptibilities as well as metallic properties. A modified Curie-Weiss law was proposed for systems containing anisotropic magnetic ions to analyze the magnetic susceptibilities of Na(x)CoO2 (x approximately 0.75), and implications of this analysis were explored. Our study shows that the low-spin Co4+ (S = 1/2) ions of Na(x)CoO2 generated by the Na vacancies cause the anisotropic magnetic properties of Na(x)CoO2 and suggests that the six nearest-neighbor Co3+ ions of each Co4+ ion adopt the intermediate-spin electron configuration, thereby behaving magnetically like low-spin Co4+ ions. The Weiss temperature of Na(x)CoO2 is more negative along the direction of the lower g factor (i.e., theta|| < theta(perpendicular) < 0 and g|| < g(perpendicular)). The occurrence of intermediate-spin Co3+ ions surrounding each Co4+ ion accounts for the apparently puzzling magnetic properties of Na(x)CoO2 (x approximately 0.75), i.e., the large negative Weiss temperature, the three-dimensional antiferromagnetic ordering below approximately 22 K, and the metallic properties. The picture of the magnetic structure derived from neutron scattering studies below approximately 22 K is in apparent conflict with that deduced from magnetic susceptibility measurements between approximately 50 and 300 K. These conflicting pictures are resolved by noting that the spin exchange between Co3+ ions is more strongly antiferromagnetic than that between Co4+ and Co3+ ions.

A longitudinal immunohistochemical study of the healing of experimental aneurysms after embolization with platinum coils

BACKGROUND AND PURPOSE

The purpose of this study was to probe the cellular mechanism of healing in aneurysms after platinum coil embolization, by using multiple special stains and immunolabels.

METHODS

Elastase-induced aneurysms were created and embolized in 28 rabbits. Aneurysms were excised between 2 and 24 weeks after embolization. Specimens were embedded in paraffin, sectioned, and stained with hematoxylin-eosin, Masson trichrome, and multiple immunostains.

RESULTS

At 2 weeks, peripheral sparse spindle-nucleated cells were positive for alpha-smooth muscle actin (SMA), myosin, and vimentin, indicating myofibroblastic differentiation. At 4 weeks, all spindle-nucleated cells in the aneurysm were positive for SMA, myosin, desmin, and vimentin. Ten weeks after embolization, positive immunohistochemical staining in the cells populating the aneurysm significantly decreased. Mean positive SMA cells, per high-powered field were 5 +/- 3, 45 +/- 9, 10 +/- 5, 0 +/- 0, and 0 +/- 0 at 2, 4, 10, 16, and 24 weeks, respectively. Findings of a Kruskal-Wallis test showed these data to be significantly different (P =.0001). Post hoc tests revealed significantly greater amounts of SMA-positive staining in the cells at 4 weeks compared with those at 2, 10, 16, and 24 weeks (P < .05). In addition, the 10-week group had significantly more positive cells than the 16- and 24-week groups (P < .05). There was a 78% decrease in apoptotic cells between 4 (37 +/- 11) and 10 weeks (8 +/- 4) after implantation. Apoptotic cells were completely absent beyond 10 weeks.

CONCLUSION

Aneurysm healing, in response to platinum coil embolization, appeared to progress through the stages of thrombus formation, granulated tissue organization, and loose connective tissue formation. Myofibroblasts, the key cellular component involved in healing, appeared within the aneurysm early. They progressively reduced in number with time and finally disappeared through the mechanism of apoptosis.

A proposed ordinal scale for grading histology in elastase-induced, saccular aneurysms

BACKGROUND AND PURPOSE

The elastase-induced aneurysm model in rabbits, though widely applied, still offers no quantitative or qualitative metric for histologic outcome. This study is aimed at producing such a scale to evaluate outcome and facilitate meaningful, preclinical comparison among devices proposed for aneurysm treatment.

MATERIAL AND METHOD

Elastase-induced aneurysms were created and embolized in 30 rabbits. Aneurysms were harvested between 2 and 24 weeks. Specimens were embedded in paraffin, sectioned, and stained with hematoxylin and eosin. The scale comprised 3 subcategories: extent and degree of recanalization/coil compaction; neck healing, based on thickness and type of tissue across the neck; and dome healing. Neck healing was assessed by both gross and microscopic inspections. Compaction was assessed by using both the angiographic and histologic images. Dome healing was assessed by using the microscopic images only. Data were analyzed with either analysis of variance for the quantitative data or Kruskal-Wallis tests when analyzing the nonparametric data.

RESULTS

We noted a significant main effect for healing over time (P = .0016). Post hoc tests showed that, at 2 weeks, the mean score was 1.4 +/- 0.8, as compared with a mean score of 7.2 +/- 1.6 for the 24-week time point (P < or = .05). Further, significant differences in healing between narrow-necked (6.0 +/- 1.3) and wide-necked aneurysms (3.5 +/- 1.1) were seen at 4 weeks (P = .0433). The dynamic range of the scale also appears to be appropriate, because there was adequate range at the upper portion of the scale to reflect improved healing that might be achieved with future devices.

CONCLUSIONS

This scale is a potentially relevant outcome measurement tool for elastase-induced aneurysms after endovascular therapy. Future studies are still required to confirm its practical relevance.

Long-term patency of elastase-induced aneurysm model in rabbits

BACKGROUND AND PURPOSE

Long-term patency in untreated experimental aneurysms represents a critical attribute of any system proposed for the testing of aneurysm occlusion devices. Our purpose was to evaluate the long-term patency in elastase-induced saccular aneurysm models in rabbits.

METHODS

Serial intravenous digital subtractive angiography (IVDSA) was performed in 20 elastase-induced saccular aneurysm models in rabbits 1, 3, 6, 9, 12, and 24 months after creation. Aneurysm dimensions, including neck diameter, width, and height, were measured and calculated from IVDSA images. Comparisons of the aneurysm sizes across time were performed by using the paired Wilcoxon signed rank test and the Friedman test.

RESULTS

None of the 20 aneurysms showed spontaneous thrombosis at any time point. Mean dimensions did not change over time for any parameter. Mean aneurysm neck, width, and height were not significantly changed at interval evaluations of 1, 3, 6, 9, 12, and 24 months (P = .210; P = .413, and P = .405, respectively).

CONCLUSION

Long-term patency in elastase-induced saccular aneurysm models in rabbits is excellent. Aneurysm dimensions remain stable for as long as 2 years following creation.

Importance of Supersuperexchange Interactions in Determining the Dimensionality of Magnetic Properties. Determination of Strongly Interacting Spin Exchange Paths in A2Cu(PO4)2 (A = Ba, Sr), ACuP2O7 (Ba, Ca, Sr, Pb), CaCuGe2O6, and Cu2UO2(PO4)2 on the Basis of Qualitative Spin Dimer Analysis

The patterns of the Cu(2+) ion arrangements in the magnetic oxides A(2)Cu(PO(4))(2) (A = Ba, Sr), ACuP(2)O(7) (Ba, Ca, Sr, Pb), CaCuGe(2)O(6), and Cu(2)UO(2)(PO(4))(2) are quite different from the patterns of the strongly interacting spin exchange paths deduced from their magnetic properties. This apparently puzzling observation was explained by evaluating the strengths of the Cu-O-Cu superexchange and Cu-O...O-Cu supersuperexchange interactions of these oxides on the basis of qualitative spin dimer analysis. Supersuperexchange interactions are found to be crucial in determining the dimensionality of magnetic properties of these magnetic oxides.

Analysis of the Spin Exchange Interactions and the Ordered Magnetic Structures of Lithium Transition Metal Phosphates LiMPO4 (M = Mn, Fe, Co, Ni) with the Olivine Structure

The olivine-type compounds LiMPO4 (M = Mn, Fe, Co, Ni) consist of MO4 layers made up of corner-sharing MO6 octahedra of high-spin M2+ ions. To gain insight into the magnetic properties of these phosphates, their spin exchange interactions were estimated by spin dimer analysis using tight binding calculations and by electronic band structure analysis using first principles density functional theory calculations. Three spin exchange interactions were found to be important for LiMPO4, namely, the intralayer superexchange J1, the intralayer super-superexchange Jb along the b-direction, and the interlayer super-superexchange J2 along the b-direction. The magnetic ground state of LiMPO4 was determined in terms of these spin exchange interactions by calculating the total spin exchange interaction energy under the classical spin approximation. In the spin lattice of LiMPO4, the two-dimensional antiferromagnetic planes defined by the spin exchange J1 are antiferromagnetically coupled by the spin exchange J2, in agreement with available experimental data.

Dramatic Variation of Magnetic Exchange through Double End-on Azide Bridges in a Series of Ladder-Like Copper(II) Coordination Polymers

Three ladder-like coordination polymers, [Cu2(phprpy)2-mu-(N3)2(N3)2], 1; [Cu2(terpy)2-mu-(N3)4Cu2-mu-(N3)2(N3)2], 2; and[Cu2(terpy)2-mu-(N3)2(N3)2Cu3-mu-(N3)4(N3)2], 3, consisting of Cu2+ ions with double end-on azide bridges were synthesized, their crystal structures and magnetic properties were determined, and spin dimer analysis was performed to explain the signs and strengths of their strong spin exchange interactions [phprpy is 4-(3-phenylpropyl)pyridine and terpy is 2,2':6,2''-terpyridine]. Although these compounds have ladder-like arrangements of Cu2+ ions, their magnetic structures are described as isolated dimers for 1 and 2 and as isolated trimers for 3. The predominant spin exchange paths in 1-3 have double end-on azide bridges linking adjacent Cu2+ ions, and the geometrical parameters of these bridging structures are similar. However, the spin dimer of 1 exhibits a strong ferromagnetic coupling; that of 2, a strong antiferromagnetic coupling; and that of 3, a weak ferromagnetic coupling. These findings are well explained by the present spin dimer analysis and show that the nature and geometry of the nonbridging ligands can have a strong influence on the sign and strength of the spin exchange interaction between Cu2+ ions connected by double end-on azide bridges.

Investigation of the incommensurate and commensurate magnetic superstructures of LiCuVO4 and CuO on the basis of the isotropic spin exchange and classical spin approximations

The spin lattices of magnetic oxides LiCuVO(4) and CuO are made up of CuO(2) ribbon chains. The incommensurate and commensurate magnetic superstructures of these oxides were examined by calculating the total spin exchange interaction energies of their long-range order spin arrangements on the basis of the isotropic spin exchange and classical spin approximations. The incommensurate superstructure (0, 0.532, 0) of LiCuVO(4) was analyzed to find that the next-nearest-neighbor spin exchange interaction J(nnn) is more strongly antiferromagnetic than the nearest-neighbor spin exchange interaction J(nn) in the CuO(2) chains. With this finding, we reassessed the relative strengths of the spin exchange interactions of LiCuVO(4) and CuO and then analyzed the relative energies of their long-range order spin arrangements. The incommensurate superstructure (0, 0.532, 0) of LiCuVO(4) is explained when the J(nn)/J(nnn) ratio is -0.40. Both the incommensurate superstructure (0.506, 0, -0.483) and the commensurate superstructure (0.5, 0, -0.5) of CuO, which occur at 231 and 212.5 K, respectively, are well explained in terms of the calculated total spin exchange interaction energies. The incommensurate superstructure of CuO becomes commensurate by a slight change in one interchain spin exchange interaction, which is due probably to a slight structure change brought about by the temperature lowering.