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(Circulation. 2000;102:2867.)
© 2000 American Heart Association, Inc.
Basic Science Reports |
,25-Dihydroxyvitamin D3 and Its Potent Synthetic Analogs Downregulate Tissue Factor and Upregulate Thrombomodulin Expression in Monocytic Cells, Counteracting the Effects of Tumor Necrosis Factor and Oxidized LDL
From the School of Allied Health Sciences (M.O., T.K., S.K., R.K.), Institute for Biomaterials and Bioengineering (K.Y.), and First Department of Internal Medicine (S.H.), Tokyo Medical and Dental University, Tokyo, Japan.
Correspondence to Takatoshi Koyama, MD, School of Allied Health Sciences, Faculty of Medicine, Tokyo Medical and Dental University 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8519, Japan. E-mail int1koya.mtec{at}med.tmd.ac.jp
| Abstract |
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|
|
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,25-dihydroxyvitamin
D3 [1,25(OH)2D3], exerts
anticoagulant effects by upregulating the expression of an
anticoagulant glycoprotein, thrombomodulin (TM), and
downregulating the expression of a critical coagulation factor, tissue
factor (TF), in monocytic cells including human peripheral
monocytes. In this study, we investigated the counteracting effects of
1,25(OH)2D3 and its potent analogs on TF
induction and TM downregulation by tumor necrosis factor and oxidized
LDL in monocytic cells and the modulatory effects of potent analogs on
TF and TM expression. Methods and ResultsEffects of 1,25(OH)2D3 and its potent synthetic analogs (22R)-22-methyl-20-epi-1,25(OH)2D3 (KY3) and 22-oxacalcitriol on TF and TM antigen levels, cell surface activities, and mRNA levels in monocytic cells were examined. 1,25(OH)2D3 and its potent analogs showed anticoagulant effects in monocytic cells by downregulating TF and upregulating TM expression, counteracting the effects of tumor necrosis factor and oxidized LDL. KY3 was most potent in its regulatory effect on TF and TM expression.
ConclusionsBecause KY3 has the highest affinity for vitamin D receptor, our findings suggest that TF and TM regulation by 1,25(OH)2D3 analogs is also mediated by vitamin D receptor. The 1,25(OH)2D3 analogs KY3 and 22-oxacalcitriol may have the potential to serve as an agent for preventing and treating atherosclerotic and other cytokine-mediated thrombotic diseases and as a tool for studying the molecular mechanisms of TF and TM regulation.
Key Words: anticoagulants coagulation thrombosis
| Introduction |
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We have recently found that a hormonally active form of vitamin
D, 1
,25-dihydroxyvitamin D3
[1,25(OH)2D3],2
as well as vitamin A derivatives, retinoic acids,3 4
exerts anticoagulant effects by upregulating the expression of an
anticoagulant glycoprotein, thrombomodulin (TM), and
downregulating the expression of a critical coagulation factor, tissue
factor (TF), in monocytic cells including human peripheral
monocytes. Because
1,25(OH)2D3 derivatives are
expected to be adjunctive antithrombotic agents, its analogs are
promising as useful therapeutic agents without adverse effects.
22-Oxa-1,25(OH)2D3
(22-oxacalcitriol, maxacalcitol; OCT) (Figure 1
) is a so-called "noncalcemic"
vitamin D analog with accentuated
differentiation-inducing/antiproliferative properties and reduced
ability to cause hypercalcemia.5 Its affinity to vitamin
Dbinding protein is 500 times lower than that of
1,25(OH)2D3, which means
that OCT can achieve higher cellular levels for a much shorter
duration.1
|
(22R)-22-Methyl-20-epi-1,25(OH)2D3
(KY3) (Figure 1
) was recently synthesized and found to have the
highest VDR binding affinity so far known.6 KY3 has
20
times higher affinity for VDR than
1,25(OH)2D3 and does not
bind to the transport protein vitamin Dbinding
protein.6
In cultured endothelial cells, expression of TF procoagulant activity and/or mRNA is induced and expression of TM anticoagulant activity and/or mRNA is suppressed by tumor necrosis factor (TNF), lipopolysaccharides (LPS), and oxidized LDL (ox-LDL).7 8 9 Similar results have been found in monocytic cells, in which expression of TF procoagulant activity and/or mRNA is stimulated by LPS and ox-LDL.7 10 On the other hand, all-trans retinoic acid (ATRA) downregulates the induction of TF by TNF or LPS in vascular endothelial cells11 or monocytes.12
In this study, we investigated the counteracting effects of 1,25(OH)2D3 and its potent analogs on TF induction and TM downregulation by TNF and ox-LDL in monocytic cells and the modulatory effects of potent analogs on TF and TM expression.
| Methods |
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All other chemicals were reagent-grade products and were purchased from Wako Pure Chemicals unless otherwise indicated.
Cell Culture
Because anticoagulant effects have been detected in human
peripheral monocytes as well as in monocytic leukemia cell
lines,2 we mainly used U937 cells in this study as a model
of monocytic cells. Monoblastic leukemia cell lines U937 and THP-1 were
provided by Health Science Research Resources Bank, Osaka, Japan.
U937 and THP-1 cells were cultured for the indicated periods in RPMI
medium supplemented with 10% FCS, sodium carbonate, glutamine,
penicillin, and streptomycin with vitamin D derivatives at the
indicated concentrations. Vitamin D derivatives were dissolved in
absolute ethanol and then added to the growth media at the desired
final concentration. The final concentration of ethanol in the culture
media was <0.1%. At this concentration, the cells exhibited no signs
of damage. The culture media without vitamin D derivatives, used for
the control cells, contained the same concentration of ethanol as the
culture media used for the treated cells. All of the procedures
involving vitamin D derivatives were performed under subdued light.
Whole blood was collected from healthy donors and treated with heparin (10 U/mL blood) to prevent coagulation. The mononuclear cell fraction was freshly isolated from 4 different healthy donors as previously described.4 The percentage of monocytes was between 15% and 25% before adhesion. The isolated cells were cultured as U937 cells.
Measurement of Levels of TF and TM Antigens
Leukemic cells were incubated with vitamin D derivatives for 24
hours and then washed with PBS 3 times. Cell numbers were determined
and adjusted. To prepare cell lysates, the cells were then treated with
0.5% Triton X-100 in PBS for 30 minutes at 4°C. Cellular debris was
removed by centrifugation at 12 000g for 20
minutes. The cell lysates were stored at -80°C until assay. Total
levels of TF and TM antigens in cell lysates were measured by ELISA,
with the IMUBIND Tissue Factor ELISA Kit, American
Diagnostica Inc, and the EIA TM kit Teijin, Teijin Inc,
according to the manufacturers instructions.
Cell Surface TF Cofactor Activity: Analysis of Procoagulant
Activity in Clotting Assays
Suspensions of U937, THP-1, and freshly isolated mononuclear
cells were prepared in PBS. The U937 cell suspension was adjusted to
1x107 cells/mL in PBS. A portion of the cell
suspension (106 cells) was added to 0.1 mL of
pooled human normal plasma. After incubation at 37°C for 3 minutes,
0.1 mL of 25 mmol/L calcium chloride was added and the plasma
recalcification time was determined with a CA-100 semiautomatic
coagulator (Sysmex). Our previous study showed that the procoagulant
activity associated with the surface of U937 cells determined as
described above was attributable to the occurrence of TF
expression2 and thus the prolongation of the
recalcification time is mainly due to downregulation of TF expression
by vitamin D3 derivatives. TF cofactor activity
was quantitatively measured by reference to standard curves (log-log
plot) constructed with human placental TF, and the amount of TF
activity that yielded a 50-second recalcification time was defined as 1
U/mL.
Measurement of Cell Surface TM Cofactor Activity
Cell surface TM cofactor activity was measured as previously
described.2 In this assay, exogenous protein C (0.16
µmol/L) was activated by intact cells in the presence of
thrombin (0.83 NIHU/mL, 6.5 nmol/L) and Ca2+
(1.3 mmol/L). After completely inactivating the thrombin activity
by treatment with hirudin, cleavage of the small molecular weight
substrate S2266 by activated protein C was measured with a
spectrophotometer. The results were expressed as the changes in optical
density at 405 nm per minute or as the percentage of the initial
velocity of activated protein C formation (with 100% taken to
be the rate in the case of cell surface TM under basal conditions).
Controls with cells in the absence of thrombin and protein C were
treated similarly, and no activation of protein C was observed.
Quantitative Reverse Transcription Polymerase Chain Reaction and
Densitometric Analysis
TF and TM mRNA levels in U937 cells were measured by performing
quantitative reverse transcription polymerase chain reaction (RT-PCR)
assays with the Super-Script Preamplification System, Life
Technologies, Inc, as described previously.2 Relative
signal intensity was determined on Scion Image Software and
standardized by use of the relative density of
glyceraldehydes-3-dehydrogenase (GAPDH) signal. TM mRNA
half-life was calculated with actinomycin D. Briefly, U937 cells were
exposed to 0.1 µmol/L
1,25(OH)2D3 for 1 hour; 10
µg/mL actinomycin D was then added, and total RNA was extracted at 0,
2.5, and 5 hours later. RT-PCR and the determination of signal
intensity were performed as well.
| Results |
|---|
|
|
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|
RT-PCR Analysis of TF and TM mRNA Levels in U937
Cells
To examine the changes in TF and TM mRNA levels, U937 cells were
treated with 0.1 nmol/L
1,25(OH)2D3, KY3, or OCT.
The pharmacological concentration of
1,25(OH)2D3 is 0.1 nmol/L
in serum. Both KY3 and OCT markedly decreased the expression of TF mRNA
and increased the expression of TM mRNA, as observed in the case of
1,25(OH)2D3 (Figure 3
). These effects were in parallel with
the changes in TF and TM antigen levels. TM mRNA half-life was not
different in the absence and presence of
1,25(OH)2D3 (3.0±0.42 and
2.75±0.75 hours, n=3), which indicates that TM gene is
regulated at the level of transcription.
|
Counteracting Effects of 1,25(OH)2D3 and
Its Potent Analogs on Upregulation of TF and Downregulation of TM by
TNF or Ox-LDL in Monocytic Cells
We next examined whether 1 nmol/L
1,25(OH)2D3 or its analogs
could suppress the induction of TF activity in U937 cells treated with
1 nmol/L TNF or 50 µg/mL ox-LDL (Figure 4A
) and the decrease in TM activity
caused by TNF (Figure 4B
). TF activity on the surface of U937
cells was upregulated by both ox-LDL and TNF (Figure 4A
, lanes 5
and 9), whereas TM activity was downregulated by TNF (Figure 4B
, lane 9). Induction of TF activity was more marked when the cells were
treated with TNF. Ox-LDL mildly upregulated TM activity as reported in
the case of THP-1 cells, another monocytic cell line (Figure 4B
, lane 5). Preincubation with
1,25(OH)2D3, KY3, or OCT
for 1 hour counteracted the upregulation of TF activity by ox-LDL
(Figure 4A
, lanes 6 to 8) and TNF (Figure 4A
, lanes 10 to
12) and the downregulation of TM activity by TNF (Figure 4B
, lane 10 to 12). TF activity induced by TNF was suppressed to 11% by
KY3. Although somewhat weaker, similar effects were observed when U937
cells were treated with
1,25(OH)2D3 1 hour after
the start of incubation with TNF or ox-LDL (data not shown). Similar
results were obtained in experiments using THP-1 cells (data not shown)
or peripheral mononuclear cells (Figure 4C and D
)
rather than U937 cells. KY3 suppressed TF activity induced by TNF in
mononuclear cells weaker than in U937 cells.
|
Levels of TF and TM mRNA in U937 cells treated with ox-LDL, TNF, and/or
1,25(OH)2D3 were measured
by the RT-PCR method (Figure 5
). The
increase in TF mRNA levels induced by ox-LDL (Figure 5A
, lane 2)
or TNF (Figure 5B
, lane 5) as determined after 5 hours of
incubation was antagonized by
1,25(OH)2D3 (Figure 5A
, lane 3 and Figure 5B
, lane 6) in cells preincubated
with 1,25(OH)2D3 for 1
hour. TM mRNA levels were markedly increased when the cells were
preincubated with
1,25(OH)2D3 (Figure 5C
, lane 3) as compared with incubation with ox-LDL alone
(Figure 5C
, lane 2). The decrease in TM mRNA levels induced by
TNF as determined after 5 hours of incubation (Figure 5D
, lane
5) was markedly counteracted by
1,25(OH)2D3 (Figure 5D
, lane 6) in cells preincubated with
1,25(OH)2D3 for 1 hour.
|
| Discussion |
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Monocyte TF activity is induced by a variety of agents, such as LPS in bacterial infection, cytokines TNF and interleukin-1, antigen-antibody complexes and complement fragments in inflammatory diseases, and ox-LDL in atherosclerotic diseases. Furthermore, LPS and TNF downregulate TM expression in monocytes. In patients with infections or inflammatory diseases, upregulation of TF and downregulation of TM expression in endothelial cells and monocytes/macrophages are major mechanisms involved in triggering thrombosis.
Monocytes/macrophages in atheromatous plaques display TF activity, and it is well established that these cells have thrombogenic activity.14 Monocytes in patients with coronary ischemic syndrome bear TF antigen.15 Ox-LDL has been shown to be present in human atherosclerotic lesions, and it enhances the progression of these lesions. Ox-LDL induces macrophage foam cell generation, smooth muscle cell proliferation, platelet adhesion, and aggregation as well as triggering thrombosis by inducing TF expression.
In this context, upregulation of TM and downregulation of TF expression in monocytic cells by 1,25(OH)2D3 analogs may be an intriguing novel strategy to prevent thrombosis in inflammatory and atherosclerotic diseases.
Enhancement of TM mRNA by
1,25(OH)2D3 analogs is not
due to higher stability of mRNA but due to an increase in the
transcription of the TM gene. The more potent effect of KY3
on TM mRNA expression may be due to its higher affinity to VDR.
1,25(OH)2D3 analogs may
mediate upregulation of TM expression at least in part by the retinoic
acid-responsive element (RARE) of the TM
gene.2 The TM RARE is in a manner a vitamin
Dresponsive element, which suggests a cross-talk between the cellular
RAR and VDR pathways. Whereas ATRA upregulates TM expression in both
monocytic and vascular endothelial cells,
1,25(OH)2D3 does not in the
latter.2 Such a cell-specific response in terms of TM
regulation may be associated with cell- or tissue-specific expression
and regulation of VDR. On the other hand, the mechanism of
TF gene repression is not yet clear. The TF promoter
contains 2 activator protein-1 (AP-1)-binding sites and a
nuclear factor-
B (NF-
B) site, which serve as binding sites for
c-Fos/c-Jun and c-Rel/p65
heterodimers, respectively. Functional interactions between these
transcription factors are required for maximal induction of
TF gene transcription by TNF in vascular
endothelial cells.7 Similar
interactions are necessary for induction of TF gene
transcription by LPS in monocytic cells such as THP-1
cells.7 It has been reported that
1,25(OH)2D3 inhibits
interleukin-12 production by activated THP-1 cells
through downregulation of NF-
B activation.16 On the
other hand, ATRA selectively inhibits LPS induction of TF
gene expression in THP-1 cells by a mechanism that does not involve
repression of AP-1 and NF-
B-mediated
transcription.17 Effects of
1,25(OH)2D3 analogs on AP-1
and NF-
B activation are now under investigation.
In contrast with downregulation of TM expression in endothelial cells,9 ox-LDL induces mild upregulation of TM expression in human monocytic leukemia cell line, U937 and THP-1 cells,18 by a mechanism that is not yet known.
It has been shown also that increased expression of TF in human malignant cells such as melanoma cells promotes metastasis by enhancing angiogenesis or by other mechanisms.19 On the other hand, diminished expression of TM appears to play an important role in the metastatic process of esophageal20 and hepatic cancers.21 Upregulation of TM and downregulation of TF expression by 1,25(OH)2D3 or ATRA have also been observed in several cancer cell lines (our unpublished observations). Thus, 1,25(OH)2D3 analogs may be novel agents capable of preventing cancer cell metastasis through induction of TM expression and suppression of TF expression.
In summary, 1,25(OH)2D3 analogs, with a potent capacity to suppress TF expression and to induce TM expression, are expected to serve as adjunctive antithrombotic agents in treatment of inflammatory and atherosclerotic diseases. 1,25(OH)2D3 analogs such as OCT, already in use in clinical trials as agents for treatment of secondary hyperparathyroidism and psoriasis, and KY3 should be examined further in in vivo models of thrombotic disease. OCT and KY3 are expected to avoid an adverse effect of hypercalcemia. Although KY3 is twice as hypercalcemic in vivo than 1,25(OH)2D3, its binding affinity to VDR or biological activities are far stronger (20-fold or >100-fold) than 1,25(OH)2D3.13 The 1,25(OH)2D3 analogs examined in this study may have the potential to serve as an agent for preventing and treating atherosclerotic and other cytokine-mediated thrombotic diseases and as a tool for studying the molecular mechanisms of TF and TM regulation.
| Acknowledgments |
|---|
Received April 18, 2000; revision received June 28, 2000; accepted June 30, 2000.
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