(Stroke. 2000;31:1838.)
© 2000 American Heart Association, Inc.
Original Contributions |
From the Department of Neurology (J.-X.L., H.T., I.A., A.M., H.W., H.S.), Faculty of Medicine, Kyoto University, Kyoto, Japan; and Institute of Neurology (H.B.), University of Vienna, Wien, Austria.
Correspondence to Jin-Xi Lin, MD, Department of Neurology, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan.
| Abstract |
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MethodsA total of 20 brains were examined: 10 from patients with BD and 10 from age-matched nonneurological control patients. The alterations in the vascular cell components were examined with quantitative immunohistochemistry and immunoelectron microscopy for collagen and smooth muscle actin.
ResultsThe nonneurological control patients showed no white matter lesions. In contrast, the patients with BD invariably had marked white matter lesions, as well as fibrohyalinosis of the medullary arteries. The ratio of the area immunolabeled for collagen type I and type IV to the cross-sectional area was 2-fold higher in the BD patients than in the control patients, regardless of the vessel caliber (P<0.005). Although the ratio for smooth muscle actin in the BD brains was increased in arteries of <100 µm (P<0.0001), there was no corresponding increase in the arteries of >100 µm. However, in the ultrastructure of these vessels, the cell bodies immunolabeled for smooth muscle actin were hypertrophic and segregated from each other by proliferated fibrils. The basal lamina appeared multilayered, and the endothelial cells were swollen. Collagen type I and type IV immunoreactive fibrils also proliferated in the pericapillary space of the BD brains.
ConclusionsThe proliferation of collagen fibrils in the media and adventitia of the blood vessels in BD brains was not specific to small arteries and arterioles but also occurred in the pericapillary spaces. Pericapillary sclerosis, smooth muscle cell proliferation in the terminal arterioles, and their morphological transformation in the proximal arteries may alter the shear rates and thus cause profound microcirculatory disturbances in BD brains.
Key Words: Binswangers disease dementia leukoencephalopathy white matter
| Introduction |
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Although numerous studies have characterized the white matter lesions in BD, which consist of myelin degeneration, gliosis, edema, and necrotic foci,4 7 8 9 10 11 the vasculopathy associated with this syndrome has not been entirely clear in previous publications.1 12 13 14 15 16 Little information is available as to the extent of the adventitial fibrosis in BD with respect to the vessel sizes.17 In addition, there have been inconsistent reports on the medial changes of the medullary arteries, such as hypertrophy,18 degeneration, and lipohyalinosis,1 19 20 which might have resulted from caliber differences or from difficulties in defining the media-adventitia border on routine histological staining.
In the present study, we performed a quantitative estimation of the vascular cell components of medullary arteries of a defined caliber by using collagen and smooth muscle actin as immunohistochemical markers. The ultrastructural features were further characterized with immunoelectron microscopy. The results indicated that the vasculopathy observed in BD brains was accompanied by changes in the cellular constituents, which are dependent on the external diameter, and that these changes may profoundly impair the cerebral microcirculation.
| Materials and Methods |
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With regard to the demographic information, the control patients died of malignancy (n=3), cardiac failure (n=2), and pulmonary embolism, suppurative spondylitis, and renal failure (n=1). The BD patients died of pneumonia (n=7), malignancy (n=1), and cardiac failure (n=1). The direct cause of death was not specified in 2 control patients and 1 BD patients. All of the BD patients had either hypertension or a history of hypertension. The duration of illness ranged from 19 months to 5 years 10 months for the BD patients. The postmortem delay did not differ significantly between the control and BD patients: from 2 to 6 hours and from 3 to 10 hours, respectively.
The brains were fixed in formalin and then embedded in paraffin. Each paraffin section was cut coronally at the level of the anterior horn of the lateral ventricles and included the frontal cortex and the underlying white matter. Standard histological examinations were then performed with Klüver-Barrera and Masson trichrome stains.
Light and Electron Microscopic Immunohistochemistry
The sections were incubated overnight with the following primary
antibodies: a mouse monoclonal antibody directed against human smooth
muscle actin (diluted 1:100; DAKO) and rabbit polyclonal antisera
raised against human collagen type I (diluted 1:100; Chemicon) and
collagen type IV (diluted 1:100; Chemicon). These sections were
subsequently incubated with the appropriate secondary antibody (diluted
1:200) for 1 hour and then an avidin-biotin peroxidase complex solution
(diluted 1:200) for 1 hour. After each incubation, the sections were
rinsed for 15 minutes in 0.1 mol/L PBS (pH 7.4). Finally, the
immunoreaction products were visualized in a mixed solution of
0.02% 3,3'-diaminobenzidine tetrahydrochloride and 0.005%
H2O2 in 0.05 mol/L Tris
buffer (pH 7.6).
For immunoelectron microscopy, the brains were initially perfused with 0.01 mol/L PBS (pH 7.4) and then with 4% paraformaldehyde, 0.2% picric acid, and 0.1% glutaraldehyde in 0.1 mol/L phosphate buffer (pH 7.4). These brains were postfixed overnight at 4°C in 4% paraformaldehyde in 0.1 mol/L phosphate buffer (pH 7.4) and then sectioned on a vibratome into 50-µm-thick slices. The sections were immunostained as described for the light microscopic immunohistochemistry. They were osmicated, stained en block with 1% uranyl acetate, and then flat embedded in Spurrs embedding medium. Ultrathin sections were finally examined under a transmission electron microscope.
Morphometry
The immunoreactive areas from monochromatic photo images were
digitized with an Apple personal computer (PC7500) with a LS-1000 film
scanner (Nikon) at a resolution of 1350 dots per inch and were saved as
8-bit gray scale TIFF files (256 shades of gray). The image files were
converted to PICT files and analyzed with NIH Image
analyzer software. The medullary arteries were classified into
3 groups according to their external diameters (<50 µm, 50 to
100 µm, and >100 µm). In all patients, 10 arteries from
each diameter group were examined in the deep white matter regions
2 mm distant from the gray and white matter border at the level
of the anterior horn. The ratio of the immunoreactive area to the
cross-sectional area of each artery was assessed in the sections
immunostained for smooth muscle actin, collagen type I, or
collagen type IV. Differences between the control and BD patients were
determined by a Mann-Whitney U test with StatView II
software (Abacus Concepts, Inc) for the Macintosh computer.
| Results |
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Immunoelectron microscopy of the BD brains confirmed that the fibrils
immunoreactive for collagen type I proliferated in the pericapillary
space (Figure 4A
) and in the media and
adventitia of the medullary arteries of the BD brains (Figures 4B
and 4C
). The fibrils immunoreactive for collagen type IV were
localized adjacent to the endothelial cells in the
control brains (not shown), but in the BD brains they extended into the
adventitia (Figure 4D
). Electron-dense immunoreaction
products for smooth muscle actin were observed in a few layers of
the hypertrophic cytoplasm in the BD brains (Figure 4F
) compared with
the spindle-shaped ones in the control brains (Figure 4E
). In the BD
brains, the basal lamina was thickened beneath the
endothelial cells and in the surroundings of the smooth
muscle cells, resulting in a multilayered appearance. The
endothelial cells appeared swollen occasionally.
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The morphometric analysis indicated that in vessels with a
diameter of <50 µm, the ratio of the area immunoreactive for
collagen type I to the cross-sectional area was 67.1±14.5% in the BD
patients, which was significantly higher than the ratio of 36.9±13.4%
(mean±SD) observed in the control subjects (Figure 5a
). There also was a significant
increase in the ratio for collagen type I in the BD brains:
48.8±15.8% and 25.0±10.6% in the BD and control patients,
respectively, for vessels with a diameter of 50 to 100 µm and
31.8±13.6% and 23.5±11.8% in the BD and control patients,
respectively, for vessels with a diameter of >100 µm. A similar
increase was observed in the ratio for collagen type IV in the BD
brains: 51.8±14.8% versus 26.3±10.4% for vessels with a diameter of
<50 µm, 36.8±13.0% versus 19.4±6.7% for vessels with a
diameter of 50 to 100 µm, and 23.9±11.0% versus 11.7±5.2%
for vessels with a diameter of >100 µm (Figure 5b
),
respectively.
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The ratio for immunoreactive smooth muscle actin was higher in the BD
patients than in the control subjects: 56.1±16.2% and 39.9±14.4%
(BD and controls, respectively) for vessels with a diameter of
<50 µm and 32.1±13.1% and 24.6±12.2% for vessels with a
diameter of 50 to 100 µm. However, there were no statistically
significant differences between the ratio of BD and control patients in
vessels with a diameter of >100 µm (16.7±11.3% versus
15.4±9.0%) (Figure 5c
).
| Discussion |
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Zhang and Olsson22 also reported reduced immunostaining for smooth muscle actin in the larger medullary arteries of BD patients. In hypertension and aging, the number of smooth muscle cell nuclei decreases in the larger medullary arteries.23 However, in the present investigation, there were no quantitative differences in the smooth muscle actin immunoreactive areas in the larger vessels. This might have been due to the hypertrophic changes in cell size compensating for the decrease in the number of cell bodies. The stippled pattern of immunostaining may be attributable to a proliferation of interstitial tissues, which segregate the cell bodies from each other. However, it still remains unclear whether these morphological changes reflect a degenerative process or a morphological transformation of the smooth muscle cells in response to chronic hypertension.
Fibrohyalinosis is a diffuse change in the medullary arteries that is likely to differ from fibrinoid necrosis, a focal or segmental microangiopathy that mainly involves the penetrating arteries in the deep gray matter and cerebral cortex.4 In experimental animals, fibrohyaline thickening occurs in association with a breakdown of the blood-brain barrier,24 which has been demonstrated in the white matter in BD.25 26 Although previous studies failed to detect any morphological abnormalities in the intima of the vessels from BD brains,22 the endothelial cell swelling and basal lamina thickening observed in the present investigation suggest the presence of blood-brain barrier dysfunction in BD.
The proliferation of collagen fibrils may have been triggered by chronic hypertension and high flow rates, because endothelial cells are known to be one of the major sources of collagen production in response to shear stress, as well as the fibroblasts and smooth muscle cells.27 There are at least 14 distinct subtypes of collagen that are different gene products and have specific localizations and functions.28 Although there is little information available for BD, the composition of collagen has been shown to change in hypertensives; for example, collagen type IV, a constituent of the basal lamina, is ubiquitously increased.29 As demonstrated here, adventitial fibrosis was accompanied by an alteration of the matrix components; an increase in collagen type I, and an emergence of collagen type IV in the adventitia.
White matter lesions due to chronic cerebral hypoperfusion can be induced experimentally in the rat brain by bilateral clipping of the carotid arteries.30 A progressive reduction of the arterial pressure has been shown to produce a cessation of blood flow in the centrum semiovale while the cortical gray matter is perfused.31 Therefore, adventitial fibrosis that occurs in all 3 size categories of medullary arteries may impair the regulation of microvascular blood flow. These arteries may in turn be susceptible to a reduction in perfusion pressure and thus cause white matter lesions. It is also likely that these microcirculation disturbances may further reduce the blood flow in the larger vessels. Degeneration of the smooth muscle cells, which has been demonstrated in the larger medullary arteries of BD brains, may be compensated for by the thickened media of the terminal arterioles. These alterations in the vascular cytoarchitecture may cause a profound shear rate change and thus result in damage to the microvascular endothelium due to a higher shear stress and permeability changes in the blood-brain barrier.
| Acknowledgments |
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Received January 31, 2000; revision received April 25, 2000; accepted May 16, 2000.
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