7 α-hydroxy-3-oxo-4-cholestenoic acid in cerebrospinal fl uid refl ects the integrity of the blood-brain barrier

Article abstract of DOI:10.1194/jlr.P044982

Abstract There is a continuous fl ux of the oxysterol 27- hydroxycholesterol (27-OHC) from the circulation across the blood-brain barrier (BBB) into the brain. The major metabolite of 27-OHC in the brain is 7 α -hydroxy-3-oxo-4- cholestenoic acid (7-HOCA). We confirm a recent report describing the presence of this metabolite in cerebrospinal fl uid (CSF) at a relatively high concentration. A simple and accurate method was developed for assay of 7-HOCA in CSF based on isotope dilution-mass spectrometry and use of 2 H 4 -labeled internal standard. The concentration of this metabolite was found to be markedly increased in CSF from patients with a dysfunctional BBB. There was a high correlation between the levels of 7-HOCA in CSF and the CSF/serum albumin ratio. The concentration of 7-HOCA in CSF was not significantly affected by neurodegeneration. Our findings suggest that 7-HOCA could be used as a diagnostic marker for conditions with a dysfunctional BBB. -Saeed, A., F. Floris, U. Andersson, I. Pikuleva, A. LOevgren-Sandblom, M. Bjerke, M. Paucar, A. Wallin, P. Svenningsson, and I. BjOerkhem. 7 α -hydroxy-3-oxo-4-cholestenoic acid in cerebrospinal fl uid refl ects the integrity of the blood-brain barrier. Copyright

Full text of DOI:10.1194/jlr.P044982

patient-oriented and epidemiological research
7
␣-hydroxy-3-oxo-4-cholestenoic acid in cerebrospinal
fluid reflects the integrity of the blood-brain barrier
1
,
,†
1,
§
Ahmed Saeed, * Federico Floris, * Ulla Andersson,* Irina Pikuleva, Anita Lövgren-Sandblom,*
†
†
††
2,
Maria Bjerke,** Martin Paucar, Anders Wallin,** Per Svenningsson, and Ingemar Björkhem *
†
†
Division of Clinical Chemistry, Department of Laboratory Medicine,* and Department of Neuroscience,
†
Karolinska Institute, Stockholm, Sweden; Department of Biochemistry, Faculty of Medicine, University of
Khartoum, Khartoum, Sudan; Departments of Ophthalmology and Visual Sciences, Case Western Reserve
§
University, Cleveland, Ohio; and Sahlgrenska Academy,** University of Gothenburg, Gothenburg, Sweden
Abstract There is a continuous flux of the oxysterol 27-
fluid (CSF) under normal conditions. In patients with sub-
arachnoid hemorrhage, however, the concentration was
also increased in the CSF (6). The findings by Nagata et al.
hydroxycholesterol (27-OHC) from the circulation across
the blood-brain barrier (BBB) into the brain. The major me-
tabolite of 27-OHC in the brain is 7␣-hydroxy-3-oxo-4-
cholestenoic acid (7-HOCA). We confirm a recent report
describing the presence of this metabolite in cerebrospinal
fluid (CSF) at a relatively high concentration. A simple and
accurate method was developed for assay of 7-HOCA in
(
4) suggest that there is a local production of 7-HOCA in
the brain.
7-Hydroxycholesterol (27-OHC) is a precursor to
-HOCA, and it was shown by Heverin et al. (7) that there
4
2
7
is a continuous uptake of about 5 mg/24 h of 27-OHC
from the circulation by the human brain. In the brain there
is a very efficient metabolism of 27-OHC, and 7-HOCA was
shown to be the major end metabolite (2). This conversion
involves participation of the enzymes oxysterol 7␣-hydroxylase
CSF based on isotope dilution-mass spectrometry and use
2
of H -labeled internal standard. The concentration of this
4
metabolite was found to be markedly increased in CSF from
patients with a dysfunctional BBB. There was a high correla-
tion between the levels of 7-HOCA in CSF and the CSF/se-
rum albumin ratio. The concentration of 7-HOCA in CSF
was not significantly affected by neurodegeneration. Our
findings suggest that 7-HOCA could be used as a diagnostic
marker for conditions with a dysfunctional BBB.—Saeed,
A., F. Floris, U. Andersson, I. Pikuleva, A. Lövgren-Sandblom,
M. Bjerke, M. Paucar, A. Wallin, P. Svenningsson, and I.
Björkhem. 7␣-hydroxy-3-oxo-4-cholestenoic acid in cerebro-
spinal fluid reflects the integrity of the blood-brain barrier.
J. Lipid Res. 2014. 55: 313–318.
(CYP7B1), sterol 27-hydroxylase (CYP27A1), and 3␤-hydroxy-
delta-5-steroid dehydrogenase. Presence of CYP7B1 was
found to be restricted to neuronal cells only (2). Based on
measurements of arteriovenous concentration differences
in catheterization experiments, it was shown that there is a
continuous flux of 7-HOCA from the human brain into
the circulation (2). The magnitude of this flux is about
2
mg/24 h.
In the study by Nagata et al. (4), no significant levels of
-HOCA were detected in CSF under the conditions em-
ployed. The detection limit of their method was not defined,
however. Using combined liquid chromatography-mass
spectrometry, Ogundare et al. (8) recently reported the pres-
ence of 7-HOCA in the CSF.
Supplementary key words brain cholesterol homeostasis
7-hydroxycholesterol • CYP7B1
•
7
2
3
7
␣-Hydroxy-3-oxo-4-cholestenoic acid (7-HOCA) is a
metabolite of cholesterol that is formed extrahepatically
1, 2), present in the circulation (3–5), and taken up by
(
the liver (5). Thus there is a continuous flux of this steroid
to the liver where it is further oxidized into bile acids. In
Abbreviations: BBB, blood-brain barrier; CSF, cerebrospinal fluid;
CYP7B1, oxysterol 7␣-hydroxylase; CYP27A1, sterol 27-hydroxylase;
-HOCA, 7␣-hydroxy-3-oxo-4-cholestenoic acid; 27-OHC, 27-hydroxy-
1
992, Nagata et al. (4) reported an accumulation of this
7
compound in chronic subdural hematomas which con-
tained markedly higher levels than in the circulation. No
significant levels of 7-HOCA were detected in cerebrospinal
cholesterol.
1
A. Saeed and F. Floris contributed equally to this work.
To whom correspondence should be addressed.
e-mail: ingemar.bjorkhem@karolinska.se
2
3
According to the recommendation by The Lipid Map, the term
7
7
3
␣-hydroxy-3-oxocholest-4-en-26-oic acid should be used rather than
␣-hydroxy-3-oxo-4-cholestenoic acid. Here we prefer to use 7␣-hydroxy-
-oxo-4-cholestenoic acid in order to fit with our previous publi-
This work was supported by grants from the Swedish Science Council (I.B.,
A.W.), Swedish Brain Power (I.B., A.W.), National Institutes of Health Insti-
tute of General Medical Sciences Grant GM 062882 (I.P.), the Sahlgrenska
Hospital (A.W.), and the Swedish Dementia Foundation (A.W.).
cations.
4
According to a recent paper, the preferred nomenclature for 27-
Manuscript received 19 October 2013 and in revised form 26 November 2013.
hydroxylation and 27-hydroxycholesterol should be (25R)26-hydroxylation
and (25R)26-hydroxycholesterol, respectively (18). Here we prefer
to use 27-hydroxycholesterol to fit with our previous publications.
Published, JLR Papers in Press, December 8, 2013
DOI 10.1194/jlr.P044982
Copyright © 2014 by the American Society for Biochemistry and Molecular Biology, Inc.
This article is available online at http://www.jlr.org
Journal of Lipid Research Volume 55, 2014
313

In the present work, we have developed a simple accurate
method for assay of 7-HOCA based on isotope dilution
mass spectrometry and use of d4-labeled 7-HOCA as inter-
nal standard. We have confirmed the finding by Ogundare
et al. (8), that there are high levels of this steroid acid in
the CSF. We found that patients with a dysfunctional
blood-brain barrier (BBB) have markedly elevated levels
of this oxysterol in CSF and discuss the possibility that this
may be used diagnostically.
(1 mg) was oxidized with cholesterol oxidase (Cellulomonas
species, Sigma C-5421) under the conditions recommended
by Sigma. The reaction mixture was extracted with Folch solution
(
chloroform/methanol, 2:1, v/v). The yield of d7-7␣-hydroxy-4-
cholesten-3-one was about 800 ␮g as quantitated by GC-MS. This
material was used directly without purification (remaining d7-7␣-
hydroxycholesterol will not interfere with later quantitation). d7-
7␣-Hydroxy-4-cholesten-3-one (16 ␮g) was further oxidized by a
reconstituted human CYP27A1 system consisting of CYP27A1, ad-
renodoxin, and adrenodoxin reductase (2). The material was ex-
tracted from the acidified reaction mixture with diethyl ether
and the ether phase was washed with water until neutral. The
yield in this reaction was about 12 ␮g of d4-7-HOCA (75%). It
should be noted that the oxidation of the steroid side-chain will
remove three atoms of deuterium from one of the two methyl
groups. The material had a mass spectrum as trimethylsilyl (TMS)
ether that differed from the mass spectrum of the unlabeled ref-
erence compound (3, 4) with 4 mass units.
MATERIALS AND METHODS
Patients
Headache controls. This group consisted of eight subjects
four women and four men, age range 30–49 years, median age
(
4
4 years) referred to the neurological clinic because of headache,
Synthesis and quantitation of unlabeled 7-HOCA
Unlabeled 7-HOCA was synthesized as above from unlabeled
who were investigated with a CT-scan of the brain, plasma analy-
sis, and a lumbar puncture. All these patients had a normal CSF/
serum albumin ratio (<10) (9), and therefore were used as a con-
trol group.
7␣-hydroxy-4-cholesten-3-one. The material was quantitated by
two methods: spectrophotometry utilizing the strong absorp-
tion band at 241 m␮ with 4-cholesten-3-one as calibrator and
combined gas chromatography-mass spectrometry (GC-MS) (as
methyl ester TMS ether) using total ion current and comparison
with 4-cholesten-3-one as calibrator. The material had a mass
spectrum as TMS derivative identical to that published previ-
ously (3, 4).
Alzheimer’s disease group. This group consisted of 11 subjects
(4 females and 7 males, age range 52–72 years, median age 64 years).
The patients were diagnosed as having Alzheimer’s disease based on
the National Institute of Neurological and Communicative Disor-
ders and Stroke and the Alzheimer´s Disease and Related Disorders
Association (NINCDS-ADRDA) criteria (10). With one exception,
all these patients had a normal CSF/serum albumin ratio.
Assay of 7-HOCA
d4-7-HOCA (60 ng) dissolved in 10 ␮l ethanol, 1 ml CSF, and
5
2
ml ether were added to a separation funnel. After addition of
0 ␮l of 0.1 M HCl, extraction was performed and the water
Patients with vascular dementia. This group consisted of 13
subjects (5 females and 8 males, age range 59–79 years, median age
6
phase was removed and saved for the subsequent extraction. The
extraction was repeated, and the ether phases were pooled and
washed with water until neutral. The ether was evaporated under
nitrogen. Then the material was converted into methyl ester with
TMS -diazomethane (Aldrich) by adding 100 ␮l of methanol, 400 ␮l
of toluene, and 40 ␮l of hexane solution containing 2 M of TMS-
diazomethane directly to a glass tube. The mixture was vortexed
for 10 s and agitated for 5 min. The solvent and reagents were
removed under a stream of nitrogen.
After methylation, the material was converted into TMS
ether. TMS reagent (pyridine/hexamethyldisilazane/chlorot-
rimethylsilane, 3:2:1, v/v/v) was added to the dried extracts
and the sealed tube was treated at 60°C for 30 min. The sol-
vent and reagents were removed under a stream of nitrogen
until complete dryness. The residue was then dissolved in 20 ␮l
of hexane and transferred to a glass vial, suitable for GC/MS
injection.
8 years). The diagnostic criteria used were those of Erkinjuntti
et al. (11). Three of the patients had a slightly increased CSF/
serum albumin ratio (11–13, normally <10).
Patients with BBB dysfunction. This group consisted of 22
subjects (12 females and 10 males, age range 23–77 years, median
age 55 years) who had a defective BBB function defined as an
increased CSF/serum albumin ratio (14–160, normally <10) . Di-
agnoses in this group included Guillain-Barré’s disease (n = 5),
meningitis (n = 9), encephalitis (n = 2), polyneuropathy (n = 1),
pareses (n = 2), and miscellaneous (n = 3).
Synthesis of d4-7-HOCA
The synthetic procedure is depicted in Fig. 1. The starting ma-
terial was 25,26,26,26,27,27,27-d7-labeled 7␣-hydroxycholesterol
obtained from Avanti Polar Lipids. d -7␣-Hydroxycholesterol
7
Fig. 1. Synthesis of d4-labeled 7-HOCA.
3
14
Journal of Lipid Research Volume 55, 2014

GC-MS was performed on a Hewlett Packard 6890 Plus series
gas chromatograph equipped with an HP-5MS capillary column
The standard curve obtained in the analyses of standard
mixtures of unlabeled and d4-labeled 7-HOCA was linear
with the equation Y (relative response) = 1.03 × 7-HOCA
(30 m × 0.25 mm, 0.25 ␮m phase thickness). The chromatograph
was connected to an HP 5963 mass selective detector and to CTC
Analytics Pal system automatic injector. The oven temperature
program was as follows: 180°C for 1 min, 20°C/min to 250°C, and
then 4°C/min to 300°C where the temperature was kept for
2
level + 0.01 and r = 0.999.
Figure 2 shows a typical ion chromatogram obtained in
the analysis of a sample of CSF to which d4-7-HOCA had
been added. It should be mentioned that in addition to
the selected ion monitoring, full scan chromatograms of
the methylated and trimethylsilylated serum extract were
also generated. Such analyses did not reveal any heteroge-
neity of the chromatographic peaks.
Replicate analysis of the same pool of CSF (a pool ob-
tained by mixing CSF from about 10 anonymized patient
samples) gave a coefficient of variation of 5%. The level of
the steroid acid in this pool was 13.9 ± 0.7 ng/ml. Analyses
of four replicates of this pool after addition of 20 ng/ml of
the steroid acid increased the measured level to 34.6 ± 2.0 ng.
The recovery of the added 7-HOCA was thus 104%. The
difference between the expected and found levels after
the addition was 2%.
8
min. Helium was used as a carrier gas. The gas chromatograph
was operated in the constant flow mode, with the flow rate set to
.8 ml He/min. The injector was operated in the splitless mode
and was kept at 270°C, and the detector transfer line was kept at
80°C. The samples were analyzed with GC-MS using single ion
monitoring, following the ion m/z 426 (for the derivative of
0
2
7-HOCA) and the ion m/z 430 (for d4-7-HOCA).
Replicas of samples (n = 5) were analyzed by GC-MS. For the
recovery experiment, four replicas of the same sample, with the
addition of 20 ng of 7-HOCA, were also analyzed by GC-MS.
Ethical aspects
All patients gave their informed consent to this study. All the
investigations of the patients and the analyses of their serum and
CSF were approved by the ethic committees of the respective
institutions.
Analyses of CSF from controls and patients
Figure 3 shows the results of analyses of CSF from the
control group (subjects affected by headache with normal
findings on CT-scan of the brain and serum and CSF anal-
ysis). The levels of 7-HOCA were 15 ± 3 ng/ml (mean ±
SD). The upper normal level (mean + 2 SD) was 21 ng/ml.
We also analyzed CSF from two populations of patients
with neurodegeneration: 1) patients with established Al-
zheimer’s disease according to the diagnostic criteria de-
scribed in (10); and 2) patients with vascular dementia
according to the criteria described in (11). The levels of
7-HOCA in these two populations were both similar to
those of the controls, indicating that neurodegeneration
does not significantly affect the level of 7-HOCA in CSF.
The levels of 7-HOCA in patients with Alzheimer’s disease
were found to be 13 ± 4 ng/ml, whereas the correspond-
ing levels in patients with vascular dementia were found to
be 14 ± 7 ng/ml.
Figure 3 also shows the results of analyses of CSF from
22 patients with a BBB defect, defined as increased CSF/
serum albumin ratio. All but three of these patients had
increased levels of 7-HOCA in CSF (range 7–392 ng/ml).
There were no trends in the levels of 7-HOCA between the
different diagnoses. Thus the levels of 7-HOCA in patients
with encephalitis and meningitis varied from 33 to 392 ng/ml
RESULTS
Assay
Different conditions were tested for extraction of
-HOCA by diethyl ether. Increased acidification of the
CSF increased the recovery of the steroid up to a certain
level. At a high degree of acidification, there was an in-
creased decomposition of 7-HOCA into 3-oxo-cholesta-4,
-dienoic acid. Addition of 20 ␮l of 0.1 M HCl to 1 ml of
CSF was found to give the best recovery of intact 7-HOCA
under the conditions employed.
Under the standard conditions employed, the limit of
detection was about 0.5 ng/ml and the limit of quantita-
tion about 1 ng/ml. It was possible, however, to reduce the
limit of detection by increasing the volume of CSF in rela-
tion to the internal standard.
The mass spectrum of the methyl ester TMS derivative
of unlabeled and d4-labeled 7-HOCA were in accordance
with previously published spectra of the unlabeled com-
pound (3, 4) and showed prominent peaks at m/z 426 and
m/z 430, respectively, corresponding to loss of a trimethyl-
silanol group from the molecular ion.
7
6
Fig. 2. Selected ion monitoring of the ions m/z 426
and m/z 430 in an analysis of an extract of a CSF sam-
ple to which the internal standard d4-7-HOCA had
been added (see Materials and Methods).
7-HOCA in the CSF reflects the integrity of the BBB
315

2
The internal standard used was H -24-hydroxycholesterol.
6
This procedure is considerably more laborious then the
present method. From an accuracy point of view, the most
obvious advantage of the present method in relation to
the method used by Ogundare et al. (8) is the use of an
ideal internal standard. It should be emphasized that
7
7
-HOCA is very labile, in particular to alkaline. Thus the
␣-hydroxyl group is easily lost by transaxial elimination
together with the 6␤-hydrogen to form 3-oxo-cholesta-4,6-
dienoic acid. The methyl ester of the latter compound has
a mass spectrum containing the ion at m/z 426, and in
most analyses we could see at least traces of this compound.
In some analyses the amount of 3-oxo-cholesta-4,6-dienoic
acid was up to 30% that of 7-HOCA. The ratio between the
2
unlabeled and the H -labeled compound was, however,
4
always about the same in 7-HOCA as in 3-oxo-cholesta-4,6-
dienoic acid. Thus it was evident that most of the 3-oxo-
cholesta-4,6-dienoic acid appearing in the chromatogram
had been formed from 7-HOCA during extraction and/or
work up with the same degree of dehydration of the ana-
lyte as of the internal standard. In the absence of the pres-
ent ideal internal standard with the same chemical identity
as the authentic compound, falsely low levels of 7-HOCA
can be expected in the assay.
Fig. 3. Levels of 7-HOCA in patients with headache (controls)
n = 8), Alzheimer’s disease (n = 11), vascular dementia (n = 13),
and BBB defects (n = 22). For details, see Materials and Methods.
(
In the present work, we have utilized combined GC-MS.
It is likely that combined liquid chromatography-mass
spectrometry can be used as well with the same extraction
procedure as here.
Similarly to Ogundare et al. (8), we found relatively
high levels of 7-HOCA in the CSF. The levels obtained
with the present assay, about 15 ng/ml, are however
about twice those reported by Ogundare et al. (8) (about
and in patients with Guillain-Barré’s disease from 24 to
4
7 ng/ml.
Figure 4 shows a highly significant correlation between
the CSF/serum albumin ratio and the level of 7-HOCA in
CSF (P < 0.001). In this figure the patient with the highest
level of 7-HOCA has been excluded.
We measured 27-OHC in a few (n = 5) of the CSF sam-
2
7
ng/ml). Part of the explanation for this could be our
ples analyzed for 7-HOCA (r = 0.94, P < 0.01). In the pa-
use of an ideal internal standard that compensates for
degradation of the compound during extraction and
workup.
It should be emphasized that the level of 7-HOCA found in
CSF in the present work and in the work by Ogundare et al.
tients with Alzheimer’s disease (n = 11), there was also a
2
significant correlation between these two oxysterols (r =
0
.50, P < 0.05) (results not shown).
(
8) is higher than that of any other oxysterol hitherto quanti-
tated in this fluid. The levels of 24S-hydroxycholesterol and
7-OHC are present at considerably lower concentrations
DISCUSSION
2
In the previous assay of 7-HOCA in plasma or serum
1–5), two chromatographic steps had to be included in
(12–14). The upper normal limits for 24S-hydroxycholesterol
and 27-OHC in CSF have been reported to be 3.0 and 1.5
ng/ml, respectively (13).
(
the assay prior to quantitation by combined GC-MS of the
1
4
methyl ester TMS derivative. C-labeled 3-oxocholanoic
acid was used as a recovery marker in the method de-
scribed by Axelson and Sjövall (3). It should be empha-
sized that CSF contains fewer lipids than plasma. Thus, it
is not possible to use the present simple method for analy-
sis of 7-HOCA in plasma without including a least one pu-
rification step prior to combined GC-MS. The levels of
The increased level of 7-HOCA in CSF of patients with a
BBB defect is in accord with our previous observation that
the flux of the precursor, 27-OHC, into CSF is increased
under such conditions (14). As expected, there was a sig-
nificant correlation between 7-HOCA and 27-OHC in CSF
from the few patients in which both these steroids could
be measured.
7
-HOCA in plasma have been reported to be about 130
The CSF/serum albumin ratio reflects the blood-CSF
barrier, but is generally used as a marker for the integrity
of the BBB. The possibility must be considered that the
high levels of 7-HOCA in CSF in patients with an increased
CSF/serum albumin ratio is due to a direct flux of this acid
from the circulation into the CSF. Given the net uptake of
27-OHC by the brain from the circulation (7), the very high
capacity to convert this steroid into 7-HOCA (2), and the net
ng/ml (4), about 9-fold higher than the normal levels in
CSF found in the present work.
In the method reported by Ogundare et al. (8), the ox-
ysterols in CSF are first isolated by reversed phase C18
chromatography, converted into a hydrazine derivative,
and subjected to one additional C18 column chromatog-
raphy before liquid chromatography-mass spectrometry.
3
16
Journal of Lipid Research Volume 55, 2014

Fig. 4. Correlation between CSF/serum albumin
ratio and level of 7-HOCA in CSF in control patients
and 21 patients with a BBB defect. The patient with
the highest level of 7-HOCA and CSF/serum albu-
min ratio was excluded and the upper normal levels
for the CSF/serum albumin ratio (normal 10) and
7
-HOCA (normal 21) are indicated.
flux of this acid from the brain into the circulation (2), most
of the acid present in CSF is likely to originate from the
brain rather than from the circulation. While the flux of
Due to the low number of patients, it is not possible to
calculate diagnostic sensitivity and specificity from the
present study. Three of the patients with BBB defects, ac-
cording to the CSF/serum albumin ratio, had levels of
7-HOCA within normal limits. 7-HOCA may thus have a
lower sensitivity for detection of BBB defects than the
CSF/albumin ratio. One of the control subjects had a level
7
-HOCA across the BBB is about 2 mg/24 h (2), the flux
of this steroid from CSF into the circulation can be calcu-
lated to be less than 10 ␮g/24 h. The different fluxes are
summarized in Fig. 5.
Fig. 5. Fluxes of 27-OHC from the circulation into
the brain and from the brain into CSF and fluxes of
7
-HOCA from the brain into the circulation and CSF.
The figure is a modification of Fig. 12 in the publica-
tion by Björkhem (17).
7-HOCA in the CSF reflects the integrity of the BBB
317

of 7-HOCA in CSF slightly above the upper normal level in
spite of a normal CSF/albumin ratio. There is, however,
no golden standard, and further work is needed to evalu-
ate whether assay of 7-HOCA has merits in relation to the
CSF/albumin ratio.
Neurodegenerative conditions like Alzheimer’s disease
are associated with loss of neuronal cells. Because CYP7B1 is
located in these cells (2), and because this enzyme activity is
critical for the formation of 7-HOCA, neurodegenerative
diseases would be expected to be associated with reduced
levels of this steroid in CSF. The patients with neurodegen-
eration studied here, however, had normal levels of 7-HOCA
in CSF. Neurodegeneration is sometimes associated with a
BBB defect (15), and a long-standing BBB defect may lead
to neurodegeneration (16). This may be part of the expla-
nation for the relatively low degree of correlation between
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of a novel oxidative mechanism for elimination of intracellular cho-
lesterol in humans. Arterioscler. Thromb. Vasc. Biol. 16: 208–212.
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. Heverin, M., S. Meaney, D. Lütjohann, U. Diczfalusy, J. Wahren,
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-HOCA in CSF and the CSF/serum albumin ratio in a mi-
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and E. M. Stadlan. 1984. Clinical diagnosis of Alzheimer’s disease:
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nority of the patients studied here. There is a marked differ-
ence in molecular weight and polarity between 7-HOCA
and albumin, and it seems likely that different types of dam-
age to the BBB may have somewhat different effects on the
permeability toward different compounds.
To summarize, the levels of 7-HOCA in CSF seem to re-
flect the integrity of the BBB and may be used diagnosti-
cally as an alternative to the CSF/serum albumin ratio.
1
1
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