1 The ability of ruthenium red (RuR) to inhibit tissue factor (TF)-initiate
d blood coagulation was demonstrated at the protein and cellular levels as
well as in human plasma.
2 In a single-stage clotting assay, RuR concentration-dependently inhibited
rabbit brain thromboplastin (rbTF)-induced coagulation and offset bacteria
l endotoxin (LPS)-induced monocytic TF (mTF) hypercoagulation; the IC(50)s
were estimated at 7.5 and 12.3 muM, respectively.
3 A 15-min preincubation of RuR with rbTF or monocyte suspension resulted i
n the pronounced inhibition with a significantly lowered IC50 at 1.8 or 7.7
muM for rbTF or mTF procoagulation, respectively. The differences in IC(50
)s between rbTF and mTF without or with the preincubation indicated that TF
was a primary target for RuR action.
4 The effect of RuR on the physiological function of TF in FVII activation
was demonstrated by the proteolytic cleavage of FVII zymogen to its active
forms of serine protease on Western blotting analyses. RuR readily blocked
TF-catalyzed FVII activation (diminished FVIIa formation), thus down regula
ting the initiation of blood coagulation.
5 Inclusion of RuR into human plasma samples in vitro significantly prolong
ed prothrombin time, indicating the depressed coagulation. FVII activity wa
s inhibited by 30-60% depending on the dose; as a result, FX activity also
decreased. However, RuR showed no effect on thrombin time. Thus, RuR inhibi
ted FVII activation to block the initiation of coagulation.