Novel, bedside, tissue factor-dependent clotting assay permits improved assessment of combination antithrombotic and antiplatelet therapy.

BACKGROUND: Because optimal use of combinations of antiplatelet and antithrombotic drugs requires improved methods for assessment of therapeutic efficacy, we developed an assay designed to increase sensitivity that is based on initiation of clotting by tissue factor in minimally altered whole blood. METHODS AND RESULTS: Blood samples were obtained from healthy subjects, and the contact pathway of coagulation was inhibited with corn trypsin inhibitor (a specific factor XIIa inhibitor without effect on other coagulation factors). Clotting was initiated with relipidated tissue factor and detected with a Hemochron ACT instrument. Results were reproducible with samples from 25 healthy volunteers (mean time to clot, 125+/-17 seconds). Blood was also exposed to pharmacological concentrations of antithrombotic and antiplatelet agents in vitro. Heparin (0.25 anti-IIa/Xa U/mL) prolonged the time to clot by 2.4-fold (172 seconds, P:<0.05); hirudin (1.0 anti-IIa U/mL), by 3-fold (250 seconds P:<0.05); and enoxaparin (0.6 anti-Xa U/mL), by 2 -fold (123 seconds, P:<0.05). Additive effects of antiplatelet agents were readily detectable with both heparin and hirudin. Thus, addition of 3 microg/mL abciximab to 1.0 anti-IIa/Xa U/mL heparin and to 1.0 anti-IIa U/mL hirudin further prolonged the times to clot by 140 and 67 seconds, respectively (P:<0.05 for each). Addition of abciximab to enoxaparin did not further prolong the time to clot (increment, 13 seconds; P:=NS). CONCLUSIONS: The assay developed should facilitate improved dose selection, titration, and monitoring of combination antithrombotic and antiplatelet treatment regimens.

Bone formation rate in older normal women: concurrent assessment with bone histomorphometry, calcium kinetics, and biochemical markers.

In 12 younger (age, 30-41 yr) and 11 older (age, 55-73 yr) normal women we assessed bone formation rate using multiple methods. Bone formation (mean +/- SE) was higher in the older women than in the younger women, based on measurements of serum bone Gla-protein (1.67 +/- 0.07 vs. 1.14 +/- 0.10 nmol/L; P less than 0.01), serum bone-specific alkaline phosphatase activity (388 +/- 42 vs. 223 +/- 22 nanokatal/L, P less than 0.01), and bone formation rate by histomorphometry of iliac biopsy (31.1 +/- 4.9% vs. 15.1 +/- 2.7%/yr; P less than 0.01), but was similar in the two groups when accretion rates were assessed by calcium kinetics (5.9 +/- 1.0 vs. 7.5 +/- 1.2; P = NS). This latter discrepancy may have been caused by several age-related factors, especially reduced mineralization of completed osteons, and by not correcting for the decrease in total skeletal calcium in the older group. Our data call into question the traditional belief that bone turnover decreases in older women.

Assessment of bone turnover in postmenopausal osteoporosis by measurement of serum bone Gla-protein.

Controversy persists regarding the abnormality of bone turnover responsible for bone loss in women with postmenopausal osteoporosis. To evaluate this, we measured serum bone Gla-protein (BGP), a specific marker for bone turnover, in 62 untreated patients with postmenopausal osteoporosis. Results were compared with those in 142 normal women and were expressed as standard deviations from the age-adjusted predicted mean (Z score). Serum BGP was increased (+0.48 S.D., p = 0.002) in the osteoporotic patients; 9.7% of patients were greater than 2 S.D. above but none were greater than 2 S.D. below the normal mean. Moreover, when data from normal postmenopausal women (ages 51 to 75 years) and the osteoporotic patients were merged, significant negative correlation existed (r = -0.36, p less than 0.001) between serum BGP and bone density of the lumbar spine assessed by dual photon absorptiometry. Serum alkaline phosphatase, a less specific marker for bone formation, was also increased (+0.96 S.D., p less than 0.001) in the osteoporotic patients. The data suggest that overall bone turnover is increased in patients with postmenopausal osteoporosis and do not support the concept that an absolute decrease in bone formation is the major cause of the bone loss.