(Hypertension. 1998;32:324-330.)
© 1998 American Heart Association, Inc.
Erythrocyte Disaggregation Shear Stress, Sialic Acid, and Cell Aging in Humans
Alexandra L. Hadengue;
Muriel Del-Pino;
Alain Simon;
; Jaime Levenson
From the Centre de Médecine Préventive Cardio-Vasculaire
and Institut National de la Santé et de la Recherche Médicale
(CRI-INSERM), Hôpital Broussais, Paris, France.
Correspondence to Dr Jaime Levenson, Centre de Médecine Préventive Cardio-Vasculaire, Hôpital Broussais, 96 rue Didot, 75674 Paris, Cedex 14, France. E-mail levenso{at}worldnet.sec.fr
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Abstract
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Abstract—Erythrocyte aggregation,
which plays an important role in the physiological
behavior of blood fluidity, was found to be enhanced in hypertension
and hypercholesterolemia. While the role of
macromolecule bridging force has been widely described, cellular
factors related to membrane sialic acid content, which might contribute
to the negative charge of cell surface causing the repulsion of
erythrocytes, have been less studied. Cell age–dependent changes in
membrane sialic acid content (in micromoles per gram of integral
membrane protein) were investigated in 24 normotensive and 24
hypertensive matched subjects, each divided into 2 identical subgroups
according to a cutoff of 6.2 mmol/L serum cholesterol.
A progressive and significant (P<0.001) decrease in
membrane sialic acid content associated with an increase
(P<0.001) of disaggregation shear rate threshold (laser
reflectometry in the presence of dextran) were observed with increased
erythrocyte density (erythrocytes fractionated by density using
ultracentrifugation) in both normotensive and
hypertensive groups regardless of the cholesterol level.
However, disaggregation shear rate threshold was significantly higher
and sialic acid content was lower (P<0.001) in both
hypertensive and normotensive subjects with
hypercholesterolemia compared with either
normotensive or hypertensive subjects with low cholesterol,
respectively. A high membrane sialic acid content variance, beginning
in the younger erythrocytes, was due mainly to triglyceride
and LDL cholesterol levels
(R2=0.49 for low,
R2=0.43 for middle, and
R2=0.54 for high densities, ie, young, mean,
and senescent erythrocytes, respectively). We conclude that an early
decrease in erythrocyte sialic acid content may influence the
rheological properties of blood by increasing the adhesive energy of
erythrocyte aggregates.
Key Words: erythrocyte aggregation • rheology • sialic acid • hypertension, essential • hypercholesterolemia
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Introduction
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Erythrocyte
aggregation is one of the main determinants influencing blood
circulation at low shear rates by increasing blood viscosity and
inducing "sludging" in the capillary.1
Aggregation of red blood cells is a reversible process that occurs when
the bridging force due to the adsorption of macromolecules onto
adjacent cell surfaces exceeds the disaggregation forces caused by
electrostatic repulsion, membrane strain, and mechanical
shearing.1 2 3
An increase in erythrocyte aggregation was found to be associated with
cardiovascular risk factors such as
hypertension,4
hyperlipoproteinemia,5 6
and smoking7 and in clinical situations such as
myocardial ischemia,8 thromboembolic
states,9 and retinal venous
occlusion.10 In general, most studies have
focused on the ability of plasma proteins and various polymers to
induce erythrocyte aggregation. We showed that in hypertension and
hypercholesterolemia the increase in
erythrocyte aggregation could be attributed to an increase in the
concentration of plasma fibrinogen.4 6 In
addition, in hypercholesterolemia,
concentrations of LDL cholesterol, apolipoprotein B, and
lipoprotein AI:AII correlated positively with aggregation
parameters.6 11 Cellular factors and
erythrocyte aging have been less well studied. Membrane-bound sialic
acid with carboxyl groups contributes to the majority of the negative
surface charge of the erythrocyte.12 13 It has
been shown that neuraminidase-treated erythrocytes show a
decrease in surface-charge density and an increase in aggregation
induced by dextran.2 14 15 There have been few
studies on the role of cell age in erythrocyte aggregation. Greater
aggregation for aged versus young erythrocytes has been reported in
healthy subjects.16 17 Furthermore, in a recent
study we observed a diminished erythrocyte sialic acid content
modulated by triglycerides and fibrinogen in
hypercholesterolemic subjects, which might intensify
the effect of fibrinogen on aggregation and disaggregation of
erythrocytes and therefore contribute to the development of
atherothrombotic complications.18
To our knowledge, the relation between cell age–dependent changes in
sialic acid content and erythrocyte aggregation has not been
extensively studied in subjects with cardiovascular
risk factors. The purpose of this investigation was to examine the
impact of sialic acid content of erythrocytes related to in vivo aging
on the aggregation process in essential hypertension with or without
primary hypercholesterolemia. We therefore
measured the membrane sialic acid content of density-fractionated
erythrocytes as well as their aggregation induced by an exogenous
neutral polymer, dextran.
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Methods
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Selection of Subjects
This study was conducted in 48 subjects: 24 hypertensive
patients with mild to moderate essential hypertension and 24
normotensive subjects. Cholesterol measurement enabled us
to classify both populations into 2 subgroups: LC
(cholesterol <240 mg/dL; 6.2 mmol/L) and HC
(cholesterol 
240 mg/dL; 6.2
mmol/L).19 Systemic blood pressure was measured
with a sphygmomanometer 3 times for each subject after at least 10
minutes of rest in the supine position; hypertension was diagnosed if
systolic blood pressure was 160 mm Hg (Korotkoff phase
V) and/or diastolic blood pressure was 95 mm Hg
(Korotkoff phase V).20 None of the normotensive
patients were taking any medication. Fifty percent of the hypertensive
patients had never taken any medication. The remaining 50% of
hypertensive patients had been withdrawn from treatment at least 4
weeks before the study. None had cardiac, neurological, or renal
complications or peripheral vascular disease. Primary
hypercholesterolemia was confirmed by exclusion
of diseases or factors causing secondary
hypercholesterolemia.
Sample Preparation
Venous blood was collected after an overnight fast onto
EDTA-anticoagulant and used within 4 hours. PBS was prepared as
follows:
Na2HPO4,7H2O
8 mmol/L, KH2PO4
1.5 mmol/L, KCl 2.7 mmol/L, and NaCl 137 mmol/L, pH
adjusted to 7.4.
Cell Fractionation
Erythrocytes were density (ie, age)–fractionated by the method
of Murphy.21 We used high-speed centrifugal
density separation of least and most dense fractions from the remainder
of the cell population (middle fraction); as previously
reported,22 the least dense fraction
represents relatively young cells and the most dense
represents relatively old cells. Blood was centrifuged
at 2000g for 10 minutes at 37°C. After the plasma and
buffy coat were removed, erythrocytes were washed 3 times in PBS. The
cells were resuspended at a level of 0.8 hematocrit in
autologous plasma. The blood suspension was centrifuged at
36 000g for 1 hour at 37°C (ultracentrifuge XL
90, 52.Ti rotor, Beckman) in long tubes with a small diameter. The top
10% of the packed cell column (relatively rich in younger cells), the
intermediate fraction (80%), and the bottom fraction (10%, relatively
older cells) were separately harvested and washed once in PBS.
Erythrocytes separated by this method had characteristics of aged cells
as demonstrated by measurement of mean corpuscular hemoglobin
concentration (MCHC) and mean corpuscular hemoglobin (MCH) from 5
healthy subjects, using the cyanmethemoglobin method (Sigma Chemical
Co). We observed a significant (P<0.05) and progressive
increase in MCHC from the top to the bottom of the cell column (top,
33.8±0.4%; intermediate, 36.2±0.4%; bottom, 39.2±0.7%),
contrasting with a similar MCH (top, 30.8±2.1 pg; intermediate,
31.2±1.7 pg; bottom, 31.4±1.6 pg).
Aggregation Measurements
Dextran-induced aggregation was used to evaluate the influence
of erythrocyte properties on cell age–dependent aggregation. Washed
erythrocytes were resuspended in an artificial medium composed of 40
g/L dextran 70 (dextran with mean molecular weight of 70 kDa;
Fluka). The aggregation parameters were measured
with a laser technique (erythroaggregameter SEFAM) that has been
previously described and validated.4 6 This
technique measures the intensity of laser backscattered light with a
blood suspension situated in a narrow gap between 2 coaxial cylinders.
The inner cylinder is fixed, and the outer cylinder is transparent and
rotatable. The outer cylinder can be adjusted to provide shear rates
from 7 to 600 s-1. The intensity of
backscattered light by blood suspension is recorded as a function
of time and shear rate. The variation of intensity of backscattered
light as a function of time and shear rate allows the determination of
the aggregation time, which represents the time of formation of
aggregates and the DSRT (
t), which is related to the shear rate
needed to break up the aggregates. After 10 minutes of incubation at
37°C, aggregation parameters were measured twice. To
avoid the effect of cell concentration on erythrocyte aggregation, the
samples were adjusted to a hematocrit level of 0.40±0.01 by
addition of PBS, after duplicate determination by use of an Hermle
centrifuge (Roucaire) at 12 000g for 3
minutes.
Total Sialic Acid and Integral Membrane Proteins
To determine the total content of sialic acid (NANA) in
erythrocytes, ghosts were prepared by hypotonic hemolysis with a buffer
(5P8; composition
Na2HPO4,
2H2O 5 mmol/L, adjusted to pH 8) and
centrifugation at 12 000g for 20 minutes to
obtain a white pellet of ghosts. Then ghosts were washed and stored as
a suspension in PBS. Erythrocyte sialic acid content was measured by a
colorimetric assay for an enzymatic determination
(Boehringer)23 as follows: bound sialic
acid was hydrolyzed from sialoglycoconjugates by neuraminidase. In the
presence of NANA aldolase, NANA is cleaved into N-acetyl
mannosamine and pyruvate. The pyruvate formed was oxidized by pyruvate
oxidase to H2O2, and the
amount of formed H2O2
equivalent to the free NANA was converted by peroxidase to a red dye
(absorbance, 550 nm). Erythrocyte sialic acid concentrations were
determined from a calibration curve using N-acetylneuraminic
acid (2.4 mmol/L; from a kit, ref 784192, Boehringer) as a
standard. Results are expressed in micromoles per gram of integral
lipid bilayer spanning protein. The quantity of integral membrane
protein was determined by the method of
Bradford24 (Bio-Rad), which assays only soluble
proteins obtained after a detergent treatment with Triton X-100
(Merck). The only integral proteins determined were the anion channel
protein and a group of glycophorins; peripheral or
submembrane proteins (spectrin, actin, and proteins 4.1 and 4.9), which
are insoluble in nonionic detergents such as Triton X-100, were not
measured. Concentrations of proteins were measured from a calibration
curve using an animal serum as the standard (Biotrol 33 plus, Biotrol).
Results were expressed in micrograms per microliter suspension.
Serum sialic acid was determined by the same
colorimetric assay as described above. Results were
expressed in micromoles per liter.
Lipids and Apolipoproteins
Levels of serum total cholesterol (TC), HDL
cholesterol (HDL-C) after precipitation of LDL
cholesterol and VLDL, and triglycerides (TG)
were measured using phosphotungstic acid/magnesium chloride
reagent.4 LDL cholesterol (LDL-C) was
calculated according to Friedewald's formula (which is accurate for
triglyceride levels <4.5 mmol/L) as follows:
LDL-C=TC-HDL-C-(TG/2.2).
Ancillary Study: Removal of Sialic Acid From Erythrocytes
Washed erythrocytes from 5 healthy subjects, kept at a constant
adjusted hematocrit level (0.4), were incubated several times at 37°C
with 10 mIU/mL neuraminidase (from Clostridium
perfringens; activity, 0.5 IU/mg protein using
N-acetylneuraminyl-lactose; Sigma) in PBS during gentle
shaking. After incubation, the suspension was cooled and the
erythrocytes were washed with cold PBS twice. In each sample,
aggregation measurements were performed with dextran 70 (40 g/L), and
membrane sialic acid content was measured as described above.
Statistical Analysis
Variables are expressed as mean±SD. Comparisons among the 4
groups were performed with ANOVA. Comparisons between erythrocytes
before and after treatment with neuraminidase were performed with
paired Student's t test. The linear correlations between
parameters were performed with the least-squares method.
The statistical analysis was carried out using an Apple
Macintosh computer with Statview II (Abacus Concepts Inc) software.
Statistical significance was considered to be
P
0.05.
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Results
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Table 1
shows the clinical
characteristics of normotensive and hypertensive subjects, with each
group separated according to cholesterol level into LC and
HC subgroups. Age, body mass index, gender ratio, and percentage of
current smokers were similar in the normotensive and hypertensive
groups. By definition, hypertensives had higher blood pressure than
normotensive subjects, and patients with high cholesterol
had higher serum total cholesterol, LDL
cholesterol, and triglyceride levels than
subjects with low cholesterol.
Normotensive Subjects
In both LC and HC subgroups, there was a marked effect of cell
density on the DSRT and aggregation time. Table 2 shows the progressive and significant
(P<0.001) increase of DSRT with enhancing erythrocyte
density. Compared with LC, erythrocytes of the HC subgroup were
characterized at each density by an increased DSRT
(P<0.001). The aggregation time decreased progressively
with erythrocyte density (P<0.05) but was similar at each
density in both LC and HC subgroups (Table 2).
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Table 2. DSRT and Aggregation Time for Density-Separated
Erythrocytes Suspended in Dextran 70 in Normotensive and Hypertensive
Subjects
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The erythrocyte sialic acid content decreased progressively with
increasing erythrocyte density in both LC and HC subgroups (Table 3). Furthermore, when compared with LC,
erythrocytes of the HC subgroup were characterized at each density by a
reduced sialic acid content (P<0.001). We observed a
significant decrease (P<0.001) in integral membrane protein
content when the erythrocyte density increased in both LC and HC
subgroups (Table 3). However, no significant difference was shown in
integral membrane protein content between LC and HC subgroups, whatever
the density of erythrocytes. An enhanced total serum sialic acid
(P<0.001) was observed in the HC compared with the
LC subgroup (2093.9±76.2 versus 1980.7±69.0 µmol/L).
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Table 3. Membrane Sialic Acid and Integral Protein Content
for Density-Separated Erythrocytes Suspended in Dextran 70 in
Normotensive and Hypertensive Subjects
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Hypertensive Subjects
Results observed in hypertensive patients were similar to those
obtained in normotensive subjects. Table 2
shows that in both LC and HC
subgroups, DSRT increased with erythrocyte density. In addition,
erythrocytes of the HC subgroup had a higher DSRT than those of the LC
subjects. The aggregation time decreased with erythrocyte density
(P<0.05) but was similar when the LC subgroup was
compared with the HC subgroup.
The erythrocyte sialic acid content decreased with erythrocyte density
regardless of the cholesterol level (Table 3). Moreover,
membrane sialic acid content was lower in the HC than in the LC
subgroup at each erythrocyte density. The concentration of integral
membrane proteins decreased progressively (P<0.001), but
regardless of the density, erythrocytes had a similar integral membrane
protein content in both LC and HC subgroups. There was no difference
between LC and HC groups for total serum sialic acid (2045.1±81.9
versus 2105.7±64.3 µmol/L).
Normotensive and Hypertensive Subjects
The comparison of DSRT, aggregation time, and erythrocyte sialic
acid content values between normotensive and hypertensive subjects
showed no significant difference whether subjects belonged to the LC or
HC subgroups. However, among both the normotensive and the hypertensive
subjects, we observed a significant increase in DSRT
(P<0.001) and a significant decrease in erythrocyte
sialic acid content (P<0.001) in the HC subgroups compared
with the LC subgroups. Thus, both DSRT and erythrocyte sialic acid
content were significantly different in
hypercholesterolemic subjects only. Total serum sialic
acid was increased (P<0.05) in hypertensive patients,
whatever the cholesterol level, compared with the
normotensive LC subgroup. There was no difference in integral membrane
protein content between normotensive and hypertensive subjects.
Table 4 shows that in the overall
population, sialic acid content at each erythrocyte density correlated
negatively with levels of total and LDL cholesterol,
triglycerides, and DSRT. In addition, total serum sialic
acid was inversely related with membrane sialic acid content only for
erythrocytes with low and middle densities. Because total and LDL
cholesterol levels are highly related (r=0.95;
P<0.0001), only LDL cholesterol was included in
the multiple regression analysis (Table 5), together with
triglycerides, age, and blood pressure, to determine the
main risk factors influencing erythrocyte sialic acid content. This
analysis showed that 49%, 43%, and 54% of the variance of
sialic acid content of erythrocytes of low, middle, and high density,
respectively, could be explained by LDL cholesterol and
triglyceride levels.
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Table 4. Correlation Coefficients Between Erythrocyte Sialic
Acid Content of Density-Separated Erythrocytes and Clinical, Blood, and
Rheological Variables in Overall Population
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Table 5. Multiple Regression Modeling of Sialic Acid Content
of Density-Separated Erythrocytes and Age, LDL Cholesterol,
Triglycerides, Body Mass Index, and Blood Pressure in
Overall Population
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Ancillary Study: Removal of Sialic Acid From Erythrocytes
The Figure shows the behavior of
DSRT as a function of membrane sialic acid content reduction. The
membrane sialic acid content decreases progressively as a function of
increased time of incubation with neuraminidase (6.1% at 5 mn, 14.9%
at 7 mn, 17.35% at 10 mn, 26.3% at 15 mn, and 33.5% at 20 mn). A
significant linear increase of DSRT was observed with membrane sialic
acid content reduction. The DSRT increase was observed as early as the
6.1% decrease in membrane sialic acid content
(P<0.05).
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Discussion
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In the present study, we investigated dextran-induced
aggregation behavior of erythrocytes and its relation with membrane
sialic acid content in essential hypertension with or without primary
hypercholesterolemia. The use of dextran and
not fibrinogen, which is a physiological bridging
molecule, enabled us to study the specific influence of erythrocyte
parameters independently of plasma environment. In
addition, this study also examined the influence of the aging process
of erythrocytes on both aggregation and membrane sialic acid
content.
In both hypertensive and normotensive populations, our results show an
increase of DSRT during in vivo aging of human red blood cells,
suggesting marked direct effects of cellular factors on the aggregation
of age-separated cells. This observation is in line with data in the
literature reporting an increased dextran- or autologous
plasma–induced aggregation of senescent
erythrocytes.16 17 An original finding of our
study was that the increased DSRT was linked to the
cholesterol level, independently of blood pressure,
regardless of the age-related changes of cells. The fact that the force
needed to break the aggregates was related to
hypercholesterolemia and not to hypertension is
not in contradiction with a previously observed elevation of DSRT in
the whole blood of hypertensive subjects, in which the enhanced level
of plasma proteins such as fibrinogen or globulins may strongly
influence the bridging aggregation force between red cell
membranes.4
The results of the present work also show that a
hypercholesterolemia-associated increase in
DSRT was observed even in the younger red blood cells, suggesting an
intrinsic cellular abnormality. It is known that geometric as well as
mechanical properties and internal viscosity are altered with aging of
erythrocytes. Smaller cell volume, surface area, or deformability
during aging have been reported, whereas hemoglobin content remained
constant, so the cytoplasmic hemoglobin concentration increased as did
cell density.25 26 The decrease in surface area
might be explained by a reduction in the concentration of phospholipids
or a loss of membrane fragments, including proteins. In the present
study, the important difference in membrane sialic acid content between
young and old erythrocytes (30%) contrasts with the small difference
in membrane protein content (8%). This may be explained by the fact
that only proteins related to the anion channel protein and
glycophorins, and not the total protein content, were determined. In
addition, Greenwalt et al27 have reported that
the area loss is most likely accompanied by some thickening or increase
in density of the membrane underlying the protein network. Moreover,
these authors have observed the presence of a new
glycoprotein on the surface of older cells, which was
probably generated by modification of preexisting proteins. These
observations are in agreement with the small decreased integral
membrane protein content observed during erythrocyte aging in both
normotensive and hypertensive subjects. However, Seaman et
al28 have stated that the loss of sialic acid can
be explained on the basis of the loss of membrane area during in vivo
aging.
A limitation of our study was the lack of erythrocyte mean corpuscular
volume measurements in subpopulations of erythrocytes, which did not
allow the surface area calculation during cell aging. Nevertheless, in
young erythrocytes from hypercholesterolemic subjects,
where the membrane surface area would not yet be reduced by in vivo
aging, the membrane sialic acid content was significantly decreased and
associated with an increased DSRT when compared with young erythrocytes
from subjects with low cholesterol.
The reduced membrane sialic acid content of old versus young
erythrocytes in both hypertensive and normotensive subjects could
partially explain the increase of DSRT with erythrocyte in vivo aging.
Indeed, a negative relation between sialic acid and DSRT was
demonstrated in the present study with age-related changes.
However, the relevance of this finding to erythrocyte aggregation is
complicated by the results of earlier studies of cell electrophoresis
in saline or buffer that reported no differences of density-surface
charge between old and young erythrocytes despite a loss of membrane
sialic acid content.17 28 29 However, an
increased electrophoretic mobility with cell age has been observed in
erythrocytes suspended in dextran or plasma.16 29
The differences detected in polymer solutions are most likely a
consequence of cell- and polymer-specific
interactions.29 The decreased membrane sialic
acid content may be due to a possible alteration of glycophorin A, a
major sialoglycoprotein of human erythrocyte membrane that
may contribute to the rouleaux formation. Removal of sialic acid
residues of the saccharide chains of glycophorin A during red
cell aging results in exposure of a new antigen recognized by
immunoglobulin G, leading to the normal process of elimination of aged
cells by macrophage.30 It has been shown
that the sialosaccharide chains of glycophorin A are also
recognized by macrophage scavenger receptors, which selectively
bind and take up chemically modified LDL such as oxidized
LDL.31 The cell age–dependent loss of sialic
acid may be also related to an alteration of membrane permeability to
calcium. Indeed, sialic acid of membrane glycoprotein is
the main calcium-binding component of the outer surface of the
membrane.32 Furthermore, it has been reported
that an accumulation of calcium inside the erythrocyte may lead to
changes in cytoskeletal conformation and viscoelasticity of the
membrane, so the cells would become less
deformable.33 34
Another original finding of our study was the lack of difference in
erythrocyte sialic acid content between normotensive and hypertensive
subjects, whereas hypercholesterolemia was
associated with decreased erythrocyte sialic acid content in both
normotensive and hypertensive groups compared with subjects with low
cholesterol. The observation of similar levels of membrane
sialic acid content in both hypertensive and normotensive groups was in
good agreement with the literature data reporting that total sialic
acid content in erythrocyte membrane did not differ between
normotensive patients and those with essential or renal
hypertension.35 To determine whether the decrease
in membrane sialic acid content in
hypercholesterolemia could play a direct role
in erythrocyte aggregation, we carried out an additional study using
neuraminidase to reduce membrane sialic acid content by the amount
of the difference seen between subjects with low and high
cholesterol. We observed an increase of DSRT associated
with the decrease of membrane sialic acid content, suggesting a
specific effect of sialic acid. This result was in good agreement with
previous studies2 14 and further suggested a
specific effect on the increased DSRT in
hypercholesterolemic subjects.
The finding that levels of triglyceride, LDL
cholesterol, and membrane sialic acid are negatively
related confirms results of our previous study.18
Moreover, in the present work, we observed that the high variance
of membrane sialic acid content, beginning even in young erythrocytes,
was mainly explained by the levels of triglycerides and LDL
cholesterol. Triglycerides may be involved in
the decrease of membrane sialic acid content by an inhibition of
sialyltransferase activity, the enzyme responsible for the transfer of
NANA residues on the glycoproteins. Another mechanism that
may also participate in the decreased erythrocyte sialic acid content
is the activation by triglycerides of sialidase linked to
the membrane by a glycosylphosphatidyl anchor, able to remove sialic
acid of intact erythrocytes.36 Regarding LDL, an
interaction with membrane erythrocyte that is not altered by sialic
acid removal has been observed.37 A biological
function proposed for this binding may be an exchange of
cholesterol between the cell membrane and lipoproteins.
Nevertheless, it has not been demonstrated whether an exchange of
sialic acid with LDL, which is a sialolipoprotein, exists. Contrasting
with the decrease in membrane sialic acid content, an enhanced serum
sialic acid was observed in hypertensive and/or
hypercholesterolemic subjects. Furthermore, serum
sialic acid correlated negatively with membrane sialic acid content of
young and middle-age erythrocytes. The elevation of serum sialic acid
could result from a release of sialic acid bound from membrane
glycophorin A, but the mechanism is unclear. An increased fibrinogen
level, as observed in hypertension and
hypercholesterolemia, may induce an enhanced
serum sialic acid content.4 38 It was also
observed that serum sialic acid level was affected by
triglycerides and LDL
cholesterol39 40 and was increased in
atherosclerotic patients or after myocardial
infarction.41 42 The inverse relationship between
increased serum sialic acid and decreased membrane sialic acid and DSRT
may be one of the mechanisms that links blood rheological modifications
to cardiovascular risk factors, as suggested by
long-term follow-up indicating that serum sialic acid is a predictor of
cardiovascular mortality.43
In conclusion, the aging process of erythrocytes was accompanied by a
progressive increase of DSRT related to a decrease of membrane sialic
acid. In addition, an increased DSRT and an altered red blood cell
membrane sialic acid content were observed only in patients with
hypercholesterolemia regardless of the age of
cells, suggesting that in hypertension, enhanced erythrocyte
aggregation is influenced mainly by increased macromolecule bridging
force.
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Selected Abbreviations and Acronyms
|
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| DSRT |
= |
disaggregation shear rate threshold |
| HC |
= |
high cholesterol |
| LC |
= |
low cholesterol |
| NANA |
= |
N-acetyl neuraminic acid |
|
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Acknowledgments
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This work was supported by a grant from the Institut National de
la Santé et de la Recherche Médicale (Contrat Recherche
INSERM No. 4U010B). The authors express their gratitude to Dr
Véronique Atger for constructive discussion of this article. We
wish to thank Nelly Poulain for her excellent technical assistance and
Isabelle d'Argentré for her secretarial assistance.
Received January 27, 1998;
first decision February 11, 1998;
accepted April 7, 1998.
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Top
Abstract
Introduction
P<0.01;
P<0.001 compared with DSRT before neuraminidase
treatment.