Dysfunction of endothelial protein C activation in severe meningococcal sepsis

BACKGROUND

Impairment of the protein C anticoagulation pathway is critical to the thrombosis associated with sepsis and to the development of purpura fulminans in meningococcemia. We studied the expression of thrombomodulin and the endothelial protein C receptor in the dermal microvasculature of children with severe meningococcemia and purpuric or petechial lesions.

METHODS

We assessed the integrity of the endothelium and the expression of thrombomodulin and the endothelial protein C receptor in biopsy specimens of purpuric lesions from 21 children with meningococcal sepsis (median age, 41 months), as compared with control skin-biopsy specimens.

RESULTS

The expression of endothelial thrombomodulin and of the endothelial protein C receptor was lower in the patients with meningococcal sepsis than in the controls, both in vessels with thrombosis and in vessels without thrombosis. On electron microscopical examination, the endothelial cells were generally intact in both thrombosed and nonthrombosed vessels. Plasma thrombomodulin levels in the children with meningococcal sepsis (median, 6.4 ng per liter) were higher than those in the controls (median, 3.6 ng per liter; P=0.002). Plasma levels, protein C antigen, protein S antigen, and antithrombin antigen were lower than those in the controls. In two patients treated with unactivated protein C concentrate, activated protein C was undetectable at the time of admission, and plasma levels remained low.

CONCLUSIONS

In severe meningococcal sepsis, protein C activation is impaired, a finding consistent with down-regulation of the endothelial thrombomodulin-endothelial protein C receptor pathway.

The structure of heparin oligosaccharide fragments with high anti-(factor Xa) activity containing the minimal antithrombin III-binding sequence. Chemical and 13C nuclear-magnetic-resonance studies

The chemical composition and the 13C n.m.r. spectra of heparin oligosaccharides (essentially octasaccharides), having high affinity for antithrombin III and high anti-(Factor Xa) activity, prepared by three independent approaches (extraction, partial deaminative cleavage with HNO2 and partial depolymerization with bacterial heparinase), leading to different terminal residues, have been studied and compared with those of the corresponding inactive species. Combined wit chemical data, the spectra of the active oligosaccharides and of their fragmentation products afforded information on composition and sequence. The three types of active oligosaccharides were shown to have the common hexasaccharide core I-Aa-G-As*-Is-As, where I and alpha-L-idopyranosyl-uronic acid, Aa = 2-acetamido-2-deoxy-alpha-D-glucopyranose, G = beta-D-glucopyranosyl-uronic acid, Is = alpha-L-idopyranosyluronic acid 2-O-sulphate, As = 2-deoxy-2-sulphamino-alpha-D-glucopyranose 6-O-sulphate. The fourth residue (As*) is an unusually substituted amino sugar resistant to mild deamination. The 13C spectra of the active species are characterized by signals from the above atypical amino sugar, the most evident of which is at 57.7 p.p.m. These signals, compared with those of appropriate synthetic model compounds, are compatible with the recently proposed 3-O-sulphation of the residue As* [Lindahl, Bäckström, Thunberg & Leder (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 6551-6555].

Evaluation of the profile of thrombin generation during the process of whole blood clotting as assessed by thrombelastography

The objective of this study was to evaluate the possibility of linking the tracing of whole blood clotting in a thrombelastograph (TEG) hemostasis system with the generation of thrombin assessed by thrombin/antithrombin complex (TAT). Citrated whole blood containing corn trypsin inhibitor from volunteers was clotted in the presence of CaCl2 and tissue factor. Clotting was monitored with the eight channels of a TEG system. At different time points, the whole blood TEG reaction cups were kept in a cold quenching solution, centrifuged, and the supernatants were kept at -80 degrees C until assayed for TAT by ELISA. The total thrombus generation (TTG) was calculated from the first derivative of the TEG waveform and was compared with thrombin generation measured by TAT. The two vector values--the TAT thrombin generation data and the corresponding TEG TTG--were analyzed using Pearson correlation coefficients (r) and linear, non-linear and natural log (ln) transformation of TAT values for least-squares goodness-of-fit curves. The best least-squares fit is an exponential curve. Linearizing using the ln of the TAT thrombin generation variable produces the same r (0.94) as of the exponential curve. The prediction equation is y = 8.0465 + 0.0005x (P < or = 0.0001), where y is the TAT thrombin generation variable in the ln transformation and x is the TEG TTG variable. The high magnitude of r and the high significance of the prediction equation demonstrate the high efficacy of the prediction of TAT thrombin generation by the use of TEG TTG.

Sequence homology between human alpha 1-antichymotrypsin, alpha 1-antitrypsin, and antithrombin III

alpha 1-Antichymotrypsin mRNA was isolated by specific polysome immunoprecipitation from turpentine-treated baboon liver. The highly enriched mRNA was used for synthesis and cloning of the corresponding cDNA. Baboon alpha 1-antichymotrypsin cDNA clones were identified by hybrid-selected translation, and the insert DNA fragment from one of the putative clones was used as a probe to screen a human liver cDNA library comprised of 40 000 independent transformants. One of the human cDNA clones was unambiguously identified to contain alpha 1-antichymotrypsin DNA sequences by comparison of its 5'-terminal nucleotide sequence with the N-terminal amino acid sequence of the protein. This cDNA clone, designated phACT235, contains 1524 base pairs of human DNA, which was sequenced in its entirety. The inserted DNA codes for a 25 amino acid signal peptide sequence and the entire mature alpha 1-antichymotrypsin of 408 amino acid residues. Comparison of the amino acid sequence of alpha 1-antichymotrypsin with that of the human alpha 1-antitrypsin has revealed a homology level similar to that between chymotrypsin and trypsin.

P-selectin- and CD63-exposing platelet microparticles reflect platelet activation in peripheral arterial disease and myocardial infarction

BACKGROUND

Platelet-derived microparticles (PMPs) are generally considered a marker of platelet activation in cardiovascular disease. We studied the extent to which PMP subpopulations parallel platelet activation in vitro and in vivo.

METHODS

Using flow cytometry, we analyzed PMP subpopulations from resting and activated platelets in vitro (n = 6) as well as from plasma samples of patients with stable angina, peripheral arterial disease, or myocardial infarction [non-ST-elevation (NSTEMI) and ST-elevation (STEMI)] and from older, age- and sex-matched and young healthy individuals [n = 10 for all groups except NSTEMI (n = 11)]. Coagulation markers prothrombin fragment F(1 + 2) and thrombin-antithrombin complexes were determined by ELISA. The PMP-associated fraction of soluble (s)P-selectin was estimated by ELISA.

RESULTS

In vitro, stimulation of platelets with thrombin receptor-activating peptide (15 micromol/L) or the calcium ionophore A23187 (2.5 micromol/L) increased fractions of both platelets and PMPs exposing P-selectin or CD63 (P <0.001 for all). Whereas the number of PMPs released by A23187-stimulated platelets increased significantly (P <0.001), the number of PMPs released from thrombin receptor-activating peptide-stimulated platelets remained constant (P >0.05). Ex vivo, numbers of circulating PMPs were comparable in all groups. Compared with young persons, P-selectin-exposing PMPs were increased in older persons (P = 0.02) and were further increased in patients with NSTEMI (P = 0.007) and STEMI (P = 0.045). CD63-exposing PMPs were increased in patients with peripheral arterial disease (P = 0.041), NSTEMI (P = 0.001), and STEMI (P = 0.049). Subpopulations exposing P-selectin or CD63 correlated with each other (r = 0.581; P <0.001), but neither correlated with the plasma concentrations of F(1 + 2) or thrombin-antithrombin complexes. The PMP-associated fraction of sP-selectin constituted only 2.2 (4.7)% [mean (SD)] of total sP-selectin.

CONCLUSIONS

PMP subpopulations reflect platelet activation status better than the total number of PMPs. Increased concentrations of circulating PMP subpopulations are found in aging, and further increases are encountered in peripheral arterial disease and myocardial infarction.

Breast cancer chemotherapy induces the release of cell-free DNA, a novel procoagulant stimulus

BACKGROUND

Thrombosis is a common complication for breast cancer patients receiving chemotherapy. However, the mechanisms by which breast cancer chemotherapeutic agents increase this risk are largely uncharacterized. Nucleic acids released by injured cells may enhance coagulation via the activation of the contact pathway.

OBJECTIVES

In this study, we examined the effects of breast cancer chemotherapy agents on the release of cell-free DNA (CFDNA) and its relationship to thrombin generation using in vitro and in vivo methods.

METHODS

CFDNA release and thrombin-antithrombin (TAT) levels were measured in plasma of breast cancer patients and healthy mice receiving chemotherapy. Venous whole blood and cultured cells were exposed to chemotherapy and CFDNA release and levels of DNA-histone complexes were measured. The procoagulant activity of isolated CFDNA was measured with calibrated, automated thrombin generation.

RESULTS

Breast cancer patients receiving chemotherapy had elevated levels of CFDNA 24 h post-chemotherapy, a time-point at which elevated thrombin-antithrombin levels have been previously reported. Treatment of healthy mice with doxorubicin, epirubicin and 5-fluorouracil increased CFDNA release, with a corresponding elevation in TAT complex formation. Venous whole blood and neutrophils incubated with chemotherapeutic agents had elevated CFDNA in plasma or cell supernatants. In addition, incubation of venous whole blood with chemotherapy decreased histone-DNA complex levels. CFDNA released from epirubicin-treated whole blood significantly elevated thrombin generation in a dose-dependent manner, and involved activation of the contact pathway.

CONCLUSIONS

Release of CFDNA from chemotherapy-injured cells may represent a novel mechanism by which thrombosis is triggered in cancer patients.

Safety, Tolerability, Pharmacodynamics, and Pharmacokinetics of Rivaroxaban-an Oral, Direct Factor Xa Inhibitor-Are Not Affected by Aspirin

Rivaroxaban (BAY 59-7939) is an oral, direct Factor Xa inhibitor in advanced clinical development for the prevention and treatment of thromboembolic disorders. This was a randomized, 2-way crossover study in healthy male subjects, with an aspirin run-in period, to examine whether aspirin influences the safety, tolerability, pharmacodynamics, and pharmacokinetics of rivaroxaban. All treatments were well tolerated; drug-related adverse events were mild and transient. Aspirin did not alter the effects of rivaroxaban on Factor Xa activity or clotting tests. Platelet aggregation and bleeding time were not affected by rivaroxaban, and rivaroxaban did not influence the effects of aspirin on these parameters to a clinically relevant extent. Aspirin did not affect the pharmacokinetics of rivaroxaban, including the fraction unbound. This study suggests that there is no clinically relevant interaction between rivaroxaban and aspirin and that the 2 drugs could be administered concomitantly at the doses used in this study.

Thrombophilia in sickle cell disease: the red cell connection

Complex pertubations of hemostasis occur in sickle cell disease (SCD). Although the procoagulant property of sickle erythrocytes in vitro is tied to exposure of phosphatidylserine (PS), no study has directly linked this PS positivity to in vivo thrombin generation. This study was designed to determine if thrombin generation in SCD correlates with erythrocyte PS, or whether platelets play a significant role. PS was quantified on erythrocytes and platelets from 40 patients with SCD (SS genotype = 25; SC genotype = 15) and 11 controls. Markers of thrombin generation (prothrombin fragment F1.2; thrombin-antithrombin or TAT complexes) and fibrin dissolution (D-dimer; plasmin-antiplasmin or PAP complexes) were also evaluated. Thrombin generation and activation of fibrinolysis occurred with elevations in F1.2, TAT, and D-dimer. Although numbers of both PS-positive erythrocytes and platelets were elevated, there was no correlation between PS-positive platelets and any hemostatic markers. In contrast, correlations were noted between PS-positive erythrocytes and F1.2 (P <.0002), D-dimer (P <.000002), and PAP (P <.01). Correlations between F1.2 and D-dimer (P <.0001) demonstrated that fibrinolysis was secondary to thrombin generation. In patients with the SC genotype, abnormalities in coagulation, although present, were of a lesser magnitude than in SS disease. This study suggests that the sickle erythrocyte is the cell responsible for the thrombophilic state in SCD because associations between erythrocyte PS and thrombin generation were observed. No such relationship with platelet PS was noted. The use of erythrocyte PS as a surrogate marker in trials testing new therapeutic modalities may provide insights into the vascular complications of SCD.

Identification in vitro of an endothelial cell surface cofactor for antithrombin III. Parallel studies with isolated perfused rat hearts and microcarrier cultures of bovine endothelium

Two in vitro systems were used to identify an antithrombin III cofactor activity on vascular endothelium. Langendorff rat heart preparations or columns packed with endothelium cultured on microcarrier beads were perfused with mixtures of purified thrombin and antithrombin III. With each preparation, accelerated inhibition of thrombin by antithrombin III occurred during passage over endothelium. Platelet factor 4, protamine sulfate and diisopropylphosphoryl thrombin, all antagonists of the antithrombin III cofactor activity of heparin, significantly reduced the capacity of the preparation to inhibit thrombin. It is concluded that a substance with the functional properties of a stationary phase cofactor for antithrombin III is present on the microvascular endothelium and there catalyzes the inactivation of circulating free thrombin.

Lepirudin for prophylaxis of thrombosis in patients with acute isolated heparin-induced thrombocytopenia: an analysis of 3 prospective studies

This analysis of 3 prospective multicenter trials in patients with laboratory-confirmed acute heparin-induced thrombocytopenia (HIT) without clinically evident thromboembolic complications (TECs), isolated HIT, assessed the combined individual end points of death, new TECs, and limb amputation. Patients with the same inclusion criteria who did not receive lepirudin or danaparoid served as a contemporaneous control group. Ninety-one patients were treated with lepirudin (intravenous infusion 0.10 mg/kg/h, no bolus, activated partial thromboplastin time [aPTT]-adjusted to 1.5-2.5 times baseline) for a median of 11.0 days (range, 1-68 days). During the observation period (median 24 days), 13 (14.3%) deaths, 4 (4.4%) new TECs, 3 (3.3%) limb amputations (combined 18 [19.8%]), and 13 (14.3%) major bleeding events occurred. In comparison to the control group (N = 47), the combined end point (P = .0281) and new TECs (P = .02) were reduced, and major bleeding was not significantly different between groups (P = .5419). In renal impairment, lepirudin did not reach its steady state within 4 hours, and additional monitoring every 4 hours after start of lepirudin until steady state is reached is recommended. Lepirudin seems to be effective in patients with isolated HIT. Dose reductions in renal impairment are important. Keeping the aPTT in the range corresponding to 600 to 700 microg/L lepirudin during treatment may minimize bleeding complications.

The role of thrombin in preterm parturition

OBJECTIVE

Previous reports from our laboratory have shown that thrombin is a potent uterotonic agonist; those studies have suggested a role for thrombin during parturition, especially with regard to intrauterine bleeding. Thrombin activation can be quantified in peripheral blood by measurement of thrombin-antithrombin III (TAT) complex levels. This study sought to determine whether thrombin activation, as measured by thrombin-antithrombin III levels, is associated with premature labor.

STUDY DESIGN

Thrombin-antithrombin III levels were measured in patients and control subjects with preterm labor. Quantitative TAT levels were determined by use of an enzyme-linked immunoassay with a working range from 0 to 60 ng/mL. All patients were monitored for pregnancy outcome. Receiver operating curve analysis was performed to determine the optimal TAT cutoff values. Further statistical analyses with one-way ANOVA, the chi2 test, or the Fisher exact test were performed to determine statistical significance (P <.05).

RESULTS

Patients admitted with preterm labor who were subsequently delivered within 3 weeks had significantly higher mean TAT levels (7.80 +/- 2.86 ng/mL; P <.05) than control subjects (5.77 +/- 1.43 mL) or patients with preterm labor who were not delivered within 3 weeks of presentation with preterm labor (5.57 +/- 1.69 ng/mL; P <.05). Given a diagnosis of preterm labor, a TAT level of 8.0 ng/mL had a positive predictive value of 80% for delivery within 3 weeks of enrollment.

CONCLUSIONS

This study showed that TAT levels are elevated in patients with preterm labor who are destined to deliver before term. These results suggest that preterm labor resulting in premature delivery is associated with the activation of thrombin. Future studies will further elucidate the role of thrombin in preterm parturition and confirm whether tests for thrombin activation can accurately identify those patients destined for preterm delivery.

Relationship between hypercoagulable state and erythrocyte phosphatidylserine exposure in splenectomized haemoglobin E/beta-thalassaemic patients

Small pulmonary arterial thromboses can occur following splenectomy of patients with haemoglobin E/beta-thalassaemia (Hb E/beta-thal). We compared plasma markers of coagulation activation in vivo and red blood cell (RBC) markers of procoagulant activity in 15 Hb E/beta-thal patients who were not splenectomized (NS), 15 who had been splenectomized (S), and 15 normal controls (NC). Levels of plasma thrombin-antithrombin III complex (TAT) were significantly higher in the S group than in either the NS or the NC groups, and levels of prothrombin fragment 1.2 (F 1.2) were significantly higher in the S than in the NC group. Diluted Russell's viper venom clotting times were significantly shorter when RBCs from group S patients were added to the assay compared with RBCs from the NC group. Phosphatidylserine (PS) expression (% of annexin V-positive RBCs) on the outer leaflet of RBC membrane of both 'larger'- and 'smaller'-sized RBCs was significantly higher for the S than the NC group. The RBC PS expression of the S and the NS groups, respectively, accounted for 25 x 3% (P = 0 x 174) and 6.3% (P = 0 x 675) of the variation in plasma TAT levels. Our findings indicated that, when compared with NC, splenectomized patients with Hb E/beta-thal were in a chronic low-grade hypercoagulable state associated with increased numbers of circulating PS exposed RBCs. This condition may have a role in the risk of these patients for pulmonary arterial thromboses.

Hemostatic changes in dogs with naturally occurring sepsis

Sepsis is a frequent source of morbidity and mortality in critically ill patients. The goal of this case control study was to measure hemostatic changes in dogs with naturally occurring sepsis. Blood was collected within 24 hours of admission from 20 dogs that fulfilled the criteria for sepsis. Sepsis was defined as histologic or microbiological confirmation of infection and 2 or more of the following criteria: hypo- or hyperthermia, tachycardia, tachypnea, or leukopenia, leukocytosis, or > 3% bands. Culture and sensitivities were performed on appropriate samples from all septic dogs. Twenty-eight control dogs were enrolled on the basis of normal results of physical examination, CBC, serum biochemistry, and coagulation profile. Plasma samples were analyzed for prothrombin time (PT), partial thromboplastin time (PTT), fibrin(ogen) degradation products (FDP), D-dimer (DD) concentrations, antithrombin (AT) activity, and protein C (PC) activity. Data were compared between groups by chi-square or independent t-tests. PC (P < .001) and AT (P < .001) activities were significantly lower in dogs with sepsis compared to controls. Dogs with sepsis had significantly higher PT (P = .007), PTT (P = .005), D-dimer (P = .005), and FDP (P = .001) compared to controls. Platelet counts were not significantly different between groups. Ten of the 20 septic dogs (50%) died, but no association was identified between any of the measured variables and outcome. These findings are consistent with previous studies in animals with experimentally induced disease and in clinical studies of humans. On the basis of these results, further investigation of the role of AT and PC in canine sepsis is warranted.

Anticoagulant and signaling functions of antithrombin

Antithrombin (AT) is a major plasma glycoprotein of the serpin superfamily that regulates the proteolytic activity of the procoagulant proteases of both intrinsic and extrinsic pathways. Two important structural features that participate in the regulatory function of AT include a mobile reactive center loop that binds to active site of coagulation proteases, trapping them in the form of inactive covalent complexes, and a basic D-helix that binds to therapeutic heparins and heparan sulfate proteoglycans (HSPGs) on vascular endothelial cells. The binding of D-helix of AT by therapeutic heparins promotes the reactivity of the serpin with coagulation proteases by several orders of magnitude by both a conformational activation of the serpin and a template (bridging) mechanism. In addition to its essential anticoagulant function, AT elicits a potent anti-inflammatory signaling response when it binds to distinct vascular endothelial cell HSPGs, thereby inducing prostacyclin synthesis. Syndecans-4 has been found as a specific membrane-bound HSPG receptor on endothelial cells that relays the signaling effect of AT to the relevant second messenger molecules in the signal transduction pathways inside the cell. However, following cleavage by coagulation proteases and/or by spontaneous conversion to a latent form, AT loses both its anti-inflammatory activity and high-affinity interaction with heparin and HSPGs. Interestingly, these low-affinity heparin conformers of AT elicit potent proapoptotic and antiangiogenic activities by also binding to specific HSPGs by unknown mechanisms. This review article will summarize current knowledge about mechanisms through which different conformers of AT exert their serine protease inhibitory and intracellular signaling functions in these biological pathways.

Activation markers of coagulation and fibrinolysis in twins: heritability of the prethrombotic state

BACKGROUND

Activation markers of coagulation and fibrinolysis are increased in individuals at risk of coronary-artery disease and other thrombotic disorders--a condition defined as the prethrombotic state. We aimed to find out the extent to which the prethrombotic state is determined by genetic factors.

METHODS

We analysed concentrations of prothrombin, prothrombin fragment 1+2, thrombin-antithrombin complex, crosslinked fibrin degradation product D-dimer, and thrombin-activatable fibrinolysis inhibitor by ELISA in 118 monozygotic and 112 dizygotic unselected female twins aged 21-73 years from the St Thomas' UK Adult Twin Registry. We used quantitative genetic-model fitting to estimate heritability.

FINDINGS

We found significant heritabilities in concentrations of the activation markers in plasma. Genetic factors contributed 45, 40, and 65% of the variation in concentrations of fragment 1+2, thrombin-antithrombin complex, and D-dimer, respectively. Age was important only in fragment 1+2 concentrations, in which it accounted for 12% of the variation. The remaining variation could be attributed to unique environmental factors. Variation in concentrations of precursor prothrombin in plasma was determined by 57% heritability, and that of zymogen thrombin-activatable fibrinolysis inhibitor showed a very strong genetic component (82%).

INTERPRETATION

The activation mechanisms of the coagulation and fibrinolytic systems, and therefore the prethrombotic state, are controlled to a substantial degree by genetic factors. Genes influencing activation of haemostasis are likely to be an important component of the overall thrombotic tendency in the general population.

Prevention of bone loss in postmenopausal women treated with lasofoxifene compared with raloxifene

OBJECTIVE

Osteoporosis is a significant health problem in postmenopausal women. Consequently, new and effective therapies are being sought to preserve bone mass and prevent osteoporosis in this population of women. The objective of this study was to compare the effects of lasofoxifene with raloxifene and placebo on indices of bone health in postmenopausal women.

DESIGN

A randomized, double-blind, placebo- and active treatment-controlled study of 2 years duration was conducted. Women included 410 postmenopausal women aged 47 to 74 years. The four treatment groups were: lasofoxifene 0.25 mg/day, or 1.0 mg/day, raloxifene 60 mg/day, or placebo daily. All women received daily calcium and vitamin D supplements. The primary endpoint was percent change from baseline to 2 years in lumbar spine bone mineral density (BMD) in all women having baseline and at least one follow-up bone density measurement. Total hip BMD, biochemical markers of bone turnover, low-density lipoprotein cholesterol, and safety were also evaluated in all women.

RESULTS

Both doses of lasofoxifene significantly increased lumbar spine BMD compared with raloxifene (P < or = 0.05) and with placebo treatment (P < or = 0.05). Least squares mean increases (95% CI) from baseline in lumbar spine BMD, compared with placebo, were 3.6% (1.9, 5.2) for lasofoxifene 0.25 mg/day, 3.9% (2.4, 5.5) for lasofoxifene 1.0 mg/day, and 1.7% (0.3, 3.0) for raloxifene. The two doses of lasofoxifene and raloxifene were equally effective at increasing total hip BMD. Lasofoxifene and raloxifene significantly reduced the levels of biochemical markers of bone turnover compared with placebo. In general, the effects of lasofoxifene were greater than the responses to raloxifene. At 2 years, lasofoxifene significantly (P < or = 0.05) reduced low-density lipoprotein cholesterol levels by 20.6% and 19.7% with 0.25 mg/day and 1 mg/day, respectively, compared with raloxifene (12.1%) and placebo (3.2%). Lasofoxifene and raloxifene had a similar adverse event profile with low rate of discontinuations due to adverse events.

CONCLUSIONS

Lasofoxifene may be an effective and well-tolerated treatment option for the prevention of bone loss in postmenopausal women.

Stronger host response per parasitized erythrocyte in Plasmodium vivax or ovale than in Plasmodium falciparum malaria

OBJECTIVE AND METHODS

Fever tends to start at a lower level of parasitemia in Plasmodium vivax or ovale than in P. falciparum malaria, but hyperparasitemia and complications are more likely to occur in P. falciparum malaria. Therefore, we compared the relationship between parasitemia and host response parameters before therapy in 97 patients with P. faciparum malaria (18 with complications), and 28 with P. vivax or ovale malaria.

RESULTS

In both types of malaria, parasitemia correlated with blood levels of tumour necrosis factor alpha (TNF-alpha), lactate dehydrogenase (LDH), Thrombin-antithrombin III (TAT) and elastase, and these parameters were higher in P. falciparum malaria than in P. vivax or ovale malaria. In contrast, the ratios of TNF-alpha, TAT, elastase, and LDH per parasitized erythrocyte were higher in P. vivax or ovale malaria than in uncomplicated P. falciparum malaria. They were lowest in complicated disease. Multivariate regression analysis confirmed that parasitemia did not affect these differences.

CONCLUSION

The host response may reach full strength at lower parasitemia in Plasmodium vivax or ovale, than in P. falciparum malaria. With hyperparasitemia in P. falciparum malaria, the host response seems to be unable to control parasite multiplication.

Studies on the Antithrombin and Heparin Co-factor Activities of a Fraction Adsorbed from Plasma by Aluminum Hydroxide

A chemical method has been devised for the quantitative determination of plasma antithrombin. A concentrate of antithrombin has been prepared from plasma. It also contains heparin cofactor activity. The two distinct activities could not be separated and may quite possibly be the properties of a single substance. When the concentrate is combined with heparin the capacity of the concentrate to destroy thrombin is not increased but there is interference with the thrombin fibrinogen interaction. In a mixture of the concentrate and thrombin there is simultaneous destruction of antithrombin, and thrombin activities. Small amounts of the concentrate significantly prolong the clotting time of blood.

Biochemical basis for the hypercoagulable state seen in Cushing syndrome; discussion 1006-7

HYPOTHESIS

Cushing syndrome (CS) is associated with a hypercoagulable state that results in a 4-fold increase in the incidence of pulmonary embolism, deep venous thrombosis, and a 4-fold mortality rate compared with the general population. The incidence of CS in humans is approximately 2 to 5 per million per year, whereas in dogs it is much higher. The clinical complications of CS in humans are also manifested in dogs. We used a dog model of CS to better define the biochemical basis for the hypercoagulable state seen in the disease.

DESIGN

A consecutive sample of dogs with CS and a cohort of healthy control dogs identified at a "well-dog check" were enrolled. All dogs underwent blood assays to identify the levels of procoagulant factors, natural antithrombotics, and the degree of ongoing activation of the coagulation cascade.

SETTING

University veterinary medical teaching hospital.

RESULTS

A total of 86 dogs were enrolled, 56 with CS and 30 control dogs. Levels of procoagulation factors II, V, VII, IX, X, XII, and fibrinogen were significantly increased in dogs with CS (P<.05). The natural antithrombotic antithrombin was significantly decreased in dogs with CS (P<.02). Thrombin-antithrombin complexes, a marker of subclinical thrombosis, were significantly increased in dogs with CS (P<.05).

CONCLUSIONS

The hypercoagulable state of CS is demonstrated by an increase in thrombin-antithrombin complexes. This hypercoagulable state may be caused in part by (1) an elevation of procoagulant factors, and (2) a decrease in antithrombin. Because of the similar clinical and biochemical changes between dogs with CS and humans, this canine model may be a useful tool for the future study of the hypercoagulable state in CS.