Pathological correlates of brain arterial calcifications.

BACKGROUND: In clinical practice, calcifications seen on computed tomographic studies within the large brain arteries are often referred to as a surrogate marker for cholesterol-mediated atherosclerosis. However, limited data exist to support the association between calcification and atherosclerosis. In this study, we examined if intracranial arterial calcifications were associated with cholesterol-mediated intracranial large artery atherosclerosis (ILAA) within the arteries of the circle of Willis in an autopsy-based sample. METHODS: We carried out a cross-sectional analysis of histopathological characteristics of brain large arteries obtained from autopsy cases. Brain large arteries were examined for evidences of calcifications, which were rated as macroscopic (coalescent) and microscopic (scattered). In addition to calcification, we also obtained measurement of the arterial wall and the presence of ILAA and nonatherosclerotic arterial fibrosis. We built hierarchical models adjusted for demographic and vascular risk factors to assess the relationship between calcification and ILAA. RESULTS: In univariate analysis, the presence of any arterial calcifications was associated with cerebral infarcts (29% vs. 14%, P<.01). Multivariate analysis revealed that among all calcifications, coalescent calcifications were not associated with ILAA. In contrast, scattered calcifications were associated with ILAA (P<.001), decreased lumen diameter (-1.87 +/- 0.41 mm, P≤.001), and increased luminal stenosis (0.03% +/- 0.01%, P≤.006). These findings were independent of age, sex, or other vascular risk factors. CONCLUSIONS: This study demonstrates that coalescent calcifications in brain large arteries, although associated with morbidity, are not synonymous with cholesterol-driven ILAA. Understanding the precise pathological components of cerebrovascular disease, including nonatherosclerotic arterial calcifications, will help develop individualized therapies beyond amelioration of traditional risk factors such as hyperlipidemia.

Localization of the m5 muscarinic cholinergic receptor in rat circle of Willis and pial arteries.

The expression and microanatomical localization of the muscarinic cholinergic m5 receptor subtype was investigated in rat circle of Willis and pial arteries by in situ hybridization, immunoblotting and immunohistochemistry. In situ hybridization histochemistry revealed a strong signal in the endothelium of circle of Willis and pial arteries and a moderate signal in the tunica media of the same arteries, within smooth muscle. Exposure of membranes of arteries to anti-m5 receptor protein antibodies caused the development of a band of approximately 81 kDa. Immunohistochemistry revealed the accumulation of m5 receptor protein immunoreactivity primarily within endothelium of circle of Willis and cerebral arteries and to a lesser extent in the tunica media, within smooth muscle. Medium (external diameter 200-100 microm) and small-sized (external diameter smaller than 100 microm) pial arteries displayed a significantly higher immune staining than large-sized pial arteries or circle of Willis arteries. The above data that are consistent with recent functional studies reporting cholinergic dilation of cerebral blood vessels mediated via a m5 receptor, have shown that both endothelial and muscular components of cerebral arteries synthesize and express a muscarinic m5 receptor. In view of the peculiar localization in cerebral vessels, handling of the muscarinic m5 receptor may be considered as an approach in the treatment of cerebrovascular disease.

Collagen organization in the branching region of human brain arteries.

BACKGROUND AND PURPOSE: Unruptured saccular aneurysms are relatively common, occurring in 4% to 9% of autopsies. Their development at the apex region of brain artery bifurcations is attributed to a combination of structural factors and the effect of blood pressure. Collagen is a primary tension-bearing fabric of the vessel wall, and our purpose was to examine its 3-dimensional alignment at arterial branches. METHODS: Sixteen segments of arteries from the circle of Willis, including bifurcations, were pressure distended, fixed, and sectioned in 1 of 3 orthogonal planes. We measured the 3-dimensional organization of collagen at the flow divider by using the polarized light microscope. An electron microscopy study performed in tandem provided measurements on the collagen fibril diameters and packing density. RESULTS: Orientation data of the collagen fabric were obtained from sections from 3 different cutting planes. The tunica media of all bifurcations had an alignment that was primarily circumferential, and the medial gap (medial defect) was distinguishable at the apex of all bifurcations. The subendothelial layer was thin at the apex but thicker and more disorganized distally. Adventitial collagen showed little organization except for a high degree of alignment along the apex. Results from the electron microscopy study showed densely packed collagen fibrils of uniform diameter at the apex, compared with slightly smaller and less densely packed fibrils nearby. CONCLUSIONS: In the region of the medial gap, a narrow band of highly aligned tendonlike collagen running in the direction of the ridge of the flow divider was a consistent finding. This structure would provide strength and stability to the vessel and is inconsistent with the concept of an inherent defect in the structure of bifurcations.

Deficiency of total collagen content and of deoxypyridinoline in intracranial aneurysm walls.

The tissue contents of total collagen and of 3-hydroxypyridinium cross-links, pyridinoline (PYD) and deoxypyridinoline (DPD), were measured in 15 samples of human aneurysms of Willis' Circle obtained at surgery and in 25 autopsy control samples of intracranial arteries of Willis' Circle obtained from 6 subjects who died of other causes than cerebral hemorrhage. PYD and DPD were detected fluorimetrically after HPLC separation. Total collagen content was significantly lower (P < 0.001) in aneurysm samples (mean +/- S.E.M. 2.50 +/- 0.33 nmol of alpha 1(I) collagen chain per mg of delipidated and dried material) than in controls (mean +/- S.E.M. 3.86 +/- 0.14). DPD, but not PYD, content appears to be lower in aneurysm walls. In the aneurysms, the tissue contents of PYD ranged from 212 to 587 pmol/nmol of alpha 1(I) collagen chain (mean +/- S.E.M. 430 +/- 31) while in control samples the values observed ranged from 292 to 642 (mean +/- S.E.M. 471 +/- 21). The tissue content of DPD was measurable only in 6 aneurysm samples (60%), ranging from 12 to 60 pmol/nmol of alpha 1(I) collagen chain (mean +/- S.E.M. 33 +/- 9), while in control samples, DPD content ranged from 30 to 123 (mean +/- S.E.M. 75 +/- 5).

Abnormalities of collagen cross-linkage in posterior communicating artery aneurysms: a preliminary study.

The collagen of tissues submitted to mechanical load (i.e. arterial wall) is characterised by the presence of intermolecular covalent cross-links (hydroxylysyl pyridinoline or pyridinoline: PYD; and lysyl-pyridinoline or deoxypyridinoline: DPD) which stabilise the molecular structure. In this preliminary study we look for quantitative or qualitative alterations of collagen cross-linkage in intracranial aneurysms of posterior communicating artery (PCoA) which may be considered a site of elective weakening in the intracranial arterial circulation, being one of the most frequent locations of intracranial aneurysms and of so called "infundibular widening'. We analysed the collagen cross-linkage in 6 autopsy samples of intracranial arterial segments of the Circle of Willis which were removed from patients whose cause of death was other than cerebral hemorrhage, and in 6 samples of intracranial PCoA aneurysms obtained at surgery. The analysis of cross-links showed that there was no significant difference in collagen and cross-link content between autopic and aneurysmatic samples except for PCoA. In autoptic nonaneurysmatic samples of PCoA a lower content of PYD than in internal carotid artery (ICA) and a lower content of DPD than in all other arterial segments has been demonstrated; moreover a lower content of cross-links (DPD + PYD/ Collagen) was evident in nonaneurysmatic PCoA samples when compared to other segments (ICA and Anterior Communicating Artery). On the other hand, the mean content of DPD was significantly lower in PCoA aneurysms than in nonaneurysmatic samples of the artery and moreover, a significantly low content of cross-links (DPD + PYD/Collagen) is overemphasised in PCoA aneurysms, suggesting that the peculiar lower content of DPD in PCoA arteries may be considered the expression of minor resistance of the arterial wall at this site, and may be related to the higher incidence of aneurysms or infundibular widening of this arterial segment.

Distribution and effects of neuropeptide Y, vasoactive intestinal peptide, substance P, and calcitonin gene-related peptide in human middle meningeal arteries: comparison with cerebral and temporal arteries.

A sparse to moderate supply of nerve fibers containing neuropeptide Y-like immunoreactivity (NPY-LI), vasoactive intestinal polypeptide (VIP-LI), substance P (SP-LI), and calcitonin gene-related peptide (CGRP-LI) was demonstrated in the walls of human middle meningeal arteries. Comparison with similar studies on human cerebral and temporal arteries indicated a similar distribution and density. The immunoreactive material in all three arterial regions was characterized by reversed-phase high pressure liquid chromatography (HPLC) and radioimmunoassay (RIA). The major peak of NPY-LI, VIP-LI, SP-LI, and CGRP-LI in each extract eluted approximately with the same elution volume as that of the corresponding synthetic analogues. The concentration of NPY in the middle meningeal arteries was lower as compared to the temporal arteries. Low concentrations of SP-LI and CGRP-LI were found in the middle meningeal arteries as compared to the cerebral arteries. In isolated ring segments of human middle meningeal and cerebral arteries, NPY caused vasoconstriction but did not potentiate the contractile response of noradrenaline. In the temporal artery, NPY did not induce contraction but potentiated the vasoconstrictor response to noradrenaline. Vasoactive intestinal polypeptide, peptide histidine methionine-27, SP, neurokinin A, and CGRP relaxed all three types of cephalic arteries. The peptide effects were not antagonized by propranolol, atropine, or cimetidine. Comparison of the responses to VIP and SP of vessels from the different regions showed a similar pattern of reactivity. The response to SP was slightly (p less than 0.05) more potent, whereas the responses to CGRP were less potent in the middle meningeal as compared to that in cerebral (p less than 0.005) vessels.

Vasoactive intestinal polypeptide receptors in rat cerebral vessels: an autoradiographic study.

1. Localization and pharmacological properties of the vasoactive intestinal polypeptide (VIP) receptors in rat circle of Willis arteries and in the arteries of pial-arachnoid membrane were studied using light microscope autoradiography combined with radioreceptor binding techniques. 2. [125I]-VIP was specifically bound to sections of rat cerebral arteries with a dissociation constant value of 0.5 nM and a binding site density of 80 fmol mg protein-1. Radioreceptor binding experiments revealed that the binding characteristics of [125I]-VIP were consistent with the labelling of specific VIP receptors. The rank order of potency of various substances tested to inhibit [125I]-VIP binding was the following: VIP greater than peptide histidine methionine greater than secretin greater than glucagon. 3. Light microscope autoradiography revealed the localization of [125I]-VIP binding sites in the medial layer of circle of Willis and pial arteries. Quantitative determination of [125I]-VIP binding site density in the different circle of Willis arteries demonstrated a higher accumulation of silver grains in the anterior than in the posterior cerebral arteries. Pial arteries are richer in VIP receptor sites than circle of Willis arteries. 4. These results suggest that the physiological neurogenic vasodilation elicited by VIP on cerebral arteries is mediated by the interaction with specific receptor sites located primarily within cerebral vessels structures involved in the control of cerebrovascular resistances.