A review of research related to blood transfusion in Canada, 2000-2002

The former National Blood Safety Council undertook a comprehensive review of blood transfusion research in Canada for the years 2000 through 2002. Data were acquired by direct contact with agencies which support such research and by searches of the relevant websites. Total grant support increased markedly over the 3-year period, from 4.1 million dollars to 18.5 million dollars. Publicly funded granting agencies, biopharmaceutical companies, the blood services and the province of Ontario were major supporters. Much smaller amounts were granted from charitable organizations. Clinical research attracted the majority of the funding, although a larger number of projects were basic science in nature. Most research was carried out in the provinces of Ontario, Québec and British Columbia. Although we have not assessed the productivity of blood-related research, it appears that substantial amounts of funding were allocated to these projects between 2000 and 2002. These data may provide a helpful perspective to investigators in transfusion medicine elsewhere, who may also be assessing the relative priority given to this field of research in their own countries.

Home management of haemophilia

The demonstrated benefits of home care for haemophilia include improved quality of life, less pain and disability, fewer hospitalizations, and less time lost from work or school. Although reduced mortality has not been demonstrated, the substantial increase in longevity since the early 1980s correlates with the introduction of home treatment and prophylaxis programmes. These programmes must be designed and monitored by haemophilia treatment centres (HTC), which are staffed with professionals with broad and complementary expertise in the disease and its complications. In return, patients and their families must be willing to accept the reciprocal responsibilities that come from administering blood products or their recombinant equivalents at home. Patients with inhibitors to factors VIII or IX pose special challenges, but these complications do not obviate participation in home care programmes. Home care was an essential prerequisite to the introduction of effective prophylactic factor replacement therapy. Prophylaxis offers significant improvements in quality of life, but requires a substantial commitment. The use of implantable venous access devices can eliminate some of the difficulty and discomfort of peripheral venous access in small children, but brings additional risks. The future holds the promise of factor concentrates for home use that have longer half-lives, or can be administered by alternate routes. Knowledge of patient genotypes may allow treatments tailored to avoid complications such as inhibitor development. Gene therapy trials, which are currently ongoing, will ultimately lead to gene-based treatments as a complement to traditional protein-based therapy.

Unexpected bleeding disorders

Patients with known coagulation deficiencies, either congenital or acquired, may bleed spontaneously with trauma or with surgical intervention. In contrast, however, are the unchallenged patients who bleed in a variety of clinical settings that demand rapid diagnosis so that appropriate therapy can be instituted. In the first section Dr. Louis M. Aledort demonstrates a series of vignettes of actual cases who presented with unexpected bleeding or a screening laboratory abnormality prior to a needed surgical intervention. Settings include dental, oral surgical, obstetrical, surgical and gynecological. The differential diagnoses of these cases are discussed. In the second section Dr. David Green also uses vignettes to demonstrate how the laboratory is used to differentiate the various clinical entities. The choice and priority of required tests indicated by the settings, history, site and type of bleeding, and the syllogisms used to define the abnormality are stressed. In the third section, Dr. Jerome Teitel reviews in detail the therapeutic armamentarium available to the clinician and presents algorithms for the management of these bleeding disorders.

Health-related quality-of-life treatments for severe haemophilia: utility measurements using the Standard Gamble technique

Prophylaxis for haemophilia improves outcomes, but at a substantial cost. Cost-utility analysis balances improvements seen in health-related quality of life (HRQoL) against costs, with the purpose of aiding healthcare decision-making. This analysis uses a measure of HRQoL known as utility. The objective of this study was to measure HRQoL (utility) values for states of health that result from on-demand therapy or prophylaxis. The HRQoL for different health states (including target joint bleeding, different intensities of prophylaxis, and indwelling intravenous catheters [ports]) was measured for healthy adults (n=30), parents of haemophilic children (n=30), and adults with haemophilia (n=28). Parents and patients rated health states similarly. Healthy adults gave the lowest ratings. The following rank, in order of HRQoL, was obtained: prophylaxis (low > medium > high) > on-demand therapy > prophylaxis with port> prophylaxis with infected port > on-demand therapy with development of a target joint. We conclude that: (1) haemophilia and its treatment reduce HRQoL; (2) prophylaxis is preferred to on-demand therapy; (3) intravenous ports substantially reduce HRQoL; (4) and an intravenous port to provide prophylaxis is preferable to on-demand therapy if a target joint develops.

Isolation and characterization of cell lines with reduced urokinase binding

Six cell lines have been generated from the human fibrosarcoma HT-1080 by mutagenesis. They were selected on the basis of reduced urokinase (uPA) binding on replicate polyester filters. Single cell clones were then isolated by limited dilution cloning. All cloned cells showed less uPA binding on filters, and as cell monolayers. These cell lines were able to bind only 10 to 65% as much uPA as the wild-type HT-1080 cells. Surface-bound uPA proteolytic activity and surface activation of plasminogen from these cells were also reduced relative to the wild-type. uPA could activate MAP kinases in the wild-type and two of the cell lines with the least uPA-binding, but the amount of the activated forms of the signalling molecules were reduced. Immunoblotting using two different anti-uPA receptor antibodies showed two cross-reacting protein species of approximately 53 kDa and approximately 38 kDa. The proportion of the lower Mr band to the higher Mr band was found to be reduced in all the cell lines relative to the wild-type. Chemical cross-linking with single-chain urokinase (scuPA) showed only one high-molecular-weight adduct, with Mr approximately 90 kDa, in all the cell lines tested. Similarly, cross-linking with the amino terminal fragment of uPA yielded a single approximately 70 kDa adduct. These would indicate that only the approximately 53 kDa band was responsible for cross-linking reactions. Equilibrium binding experiments showed that only one set of high-affinity binding sites for the wild-type cells. However, the binding of scuPA to two of these cell lines was best fitted to a two-site model, one of which was similar to the high-affinity binding sites of the wild-type, although the number of sites was reduced, while the other was of much lower affinity but was large in number. These results are discussed in relation to changes in the structure of ligand binding machinery in these cells, which affect other cellular functions.

Clinical approach to the patient with unexpected bleeding

Bleeding can be considered unexpected if it is disproportionate to the intensity of the haemostatic stress in a patient with no known haemorrhagic disorder or if it occurs in a patient in whom a bleeding disorder has been characterized but is adequately treated. A thorough history usually allows the clinician to predict reasonably accurately whether the patient is likely to have a systemic haemostatic defect (and if so whether it is congenital or acquired), or whether the bleeding likely has a purely anatomical basis. The nature of bleeding is instructive with respect to preliminary categorization. Thus, mucocutaneous bleeding suggests defects of primary haemostasis (disordered platelet-vascular interactions). Bleeding into deeper structures is more suggestive of coagulation defects leading to impaired fibrin clot formation, and delayed bleeding after primary haemostasis is characteristic of hyperfibrinolysis. Localized bleeding suggests an anatomical cause, although an underlying haemostatic defect may coexist. Where bleeding is so acutely threatening as to require urgent intervention, diagnosis and treatment must proceed simultaneously. In the case of minor haemorrhage (not threatening to life or limb) it may be preferable to defer therapy while the nature of the bleeding disorder is methodically investigated. Initial laboratory evaluation is guided by the preliminary clinical impression. The amount of blood loss can be inferred from the haematocrit or haemoglobin concentration, and the platelet count will quickly identify cases in which thrombocytopenia is the likely cause of bleeding. In the latter instance, examination of the red cell morphology, leucocyte differential, and mean platelet volume may allow the aetiological mechanism to be presumptively identified as hypoproliferative or consumptive. With regard to coagulation testing, the activated PTT, prothrombin time, and thrombin time usually constitute an adequate battery of screening tests, unless the clinical picture is sufficiently distinctive to indicate the immediate need for more focused testing. In any event, sufficient blood should be taken to allow more detailed studies to be done based on the results of these screening tests. These results will direct the need for further assays, such as specific clotting factor activity levels, von Willebrand factor assays, tests for coagulation inhibitors, platelet function assays, and markers of primary or secondary fibrinolytic activity.

Unexpected bleeding disorders: Algorithm for approach to therapy

The management of unexpected bleeding must be directed at the specific abnormality identified, as there is no universally effective and safe procoagulant product. Where practical, a purely pharmaceutical approach obviates the residual risks of exposure to plasma-derived products. Desmopressin is often effective in bleeding due to mild haemophilia A, Type I von Willebrand's disease and some platelet function disorders. Where replacement therapy is necessary, it should be as specific as possible, preferably using purified components singly or in combination. Recombinant proteins provide the greatest margin of safety, but it must be borne in mind that these are biologicals, and that they may contain human and animal plasma-derived proteins. Where specific replacement is unavailable or impractical, plasma or crudely fractionated plasma derivatives may be used. In the case of inhibitor antibodies to factor VIII, high dose human factor VIII or porcine factor VIII may be used. Where replacement therapy is impossible due to a high inhibitory titre, it may be necessary to bypass the specific haemostatic defect using activated prothrombin complex concentrates or recombinant activated factor VIIa. The latter product is being studied in patients with various disorders of platelet function, and in the more global haemostatic failure that accompanies end-stage liver disease. Ancillary methods are often of great value in securing haemostasis. These may be derived from pharmacological or biological sources, and their sites of action may be systemic or topical. Examples include antifibrinolytic lysine analogues, corticosteroids where inflammation accompanies bleeding, and the topical application of fibrin sealants or thrombin. Simple physical measures such as pressure, ice, or splinting are also valuable adjunctive measures. Finally, it must be emphasized that the ultimate control of bleeding often depends upon effective management of the inciting cause, such as eliminating the trigger for DIC, or suppressing the causative antibody of ITP. These principles will be presented using a practical algorithmic approach. The initial question when considering treatment should be whether or not the patient is acutely unstable. Instability may be due to one of two causes: the volume of blood loss leading to a compromised cardio-vascular status, or the site of the bleed. The relevance of the site of the bleed is independent of the volume of blood loss, so for example, a closed bleed into CNS will cause critical functional compromise even though the volume of bleeding may be minimal. Similarly bleeding into a compartment, such as into a forearm or a calf will cause critical functional compromise irrespective of the volume of bleeding.

Viral safety of haemophilia treatment products

The epidemics of HIV and hepatitis C in treated haemophiliacs spurred rapid technological advances in the viral safety of clotting factor concentrates produced from large donor pools. Sequential steps are now employed to minimize infectious risks. The initial viral burden is reduced by screening donors and by testing individual donations and plasma pools for antivirus antibodies, viral antigens, and nucleic acid. These techniques are supplemented by nonspecific viral reduction steps based on physical partitioning and inactivation of pathogens by physical (eg, heat) or chemical (eg, solvent-detergent) means. Although these processes have virtually eliminated the transmission of HIV and hepatitis B and C, there is still evidence that concentrates can transmit small nonenveloped viruses, such as parvovirus B19 and hepatitis A virus. Furthermore, new agents which may not be susceptible to current viral inactivation procedures continue to be identified. Concerns such as these have also given impetus to the development of recombinant clotting factor proteins. Recombinant factor IX concentrate is now produced without the use of human plasma proteins at any step in the manufacturing or formulation process. In practice, the risk of viral transmission by clotting factor concentrates is now so remote that any manipulations to further reduce this risk may be counter-productive, by enhancing cost (hence compromising availability) and potentially promoting other adverse effects such as immunogenicity.

Homocysteine, lipoprotein(a), and restenosis after percutaneous transluminal coronary angioplasty: a prospective study

BACKGROUND

Restenosis complicates 30% to 40% of angioplasty procedures and may be unrelated to traditional coronary risk factors. Homocysteine, lipoprotein(a), and methylenetetrahydrofolate reductase (MTHFR 677T) (a genetic determinant of plasma homocysteine concentrations) are novel risk factors for coronary artery disease. Their roles in restenosis are unclear, and the potential synergism between homocysteine and lipoprotein(a) has not previously been studied. The objective of this study was to determine the relations among homocysteine, lipoprotein (a), MTHFR 677T, and restenosis after percutaneous transluminal coronary angioplasty.

METHODS

This prospective study enrolled patients with successful elective percutaneous transluminal coronary angioplasty or stenting of a single, de novo, native coronary lesion. Fasting blood was drawn the morning of the procedure for homocysteine, lipoprotein(a), and MTHFR 677T. Follow-up angiography was performed 6 months after the procedure or earlier if clinically indicated. All cineangiograms were analyzed quantitatively.

RESULTS

A total of 144 (92%) of 156 eligible patients underwent follow-up coronary angiography. The overall angiographic restenosis rate (residual stenosis >50%) was 31%. Mean homocysteine concentration was 10.1 +/- 3.7 micromol/L. Plasma homocysteine concentrations were not significantly different in patients with or without angiographic restenosis (9.6 +/- 3.3 vs 10.3 +/- 3.8 micromol/L; P =.31). Mean lipoprotein(a) concentration was 21.2 +/- 20.1 mg/dL. Plasma lipoprotein(a) concentrations were not significantly different in patients with or without restenosis (21.9 +/- 21.8 vs 20.9 +/- 19.5 mg/dL). Homozygosity for MTHFR 677T was present in 6.5% and was not associated with increased restenosis. No interaction between homocysteine and lipoprotein(a) was detected.

CONCLUSIONS

Homocysteine, lipoprotein(a), and MTHFR 677T are not associated with restenosis after percutaneous transluminal coronary angioplasty.

Plasma urokinase antigen and plasminogen activator inhibitor-1 antigen levels predict angiographic coronary restenosis

BACKGROUND

The fibrinolytic system is intimately involved in several processes that contribute to restenosis, including clot dissolution, cell migration, and tissue remodeling. However, the role of the individual activators (urokinase [uPA] and tissue plasminogen [tPA] activators) and inhibitors (plasminogen activator inhibitor [PAI-1]) of the fibrinolytic system in maintaining patency after coronary artery angioplasty and stenting is unclear.

METHODS AND RESULTS

We prospectively studied 159 patients with stable angina who underwent successful elective angioplasty (n=110) or stenting (n=49) of de novo native coronary artery lesions. Plasma samples were drawn at baseline (before angioplasty) and serially after angioplasty (immediately afterward and 6 hours, 24 hours, 3 days, 7 days, 1 month, 3 months, and 6 months afterward). Antigen and activity assays were performed for uPA, tPA, and PAI-1. Follow-up quantitative coronary angiography was performed in 92% of eligible patients. The overall angiographic restenosis rate (diameter stenosis >50%) was 31% (37% in PTCA patients, 17% in stented patients). At all time periods, including baseline, uPA antigen levels were significantly higher and PAI-1 antigen levels were significantly lower in patients with restenosis. Restenosis rates for patients in the upper tertile of baseline uPA antigen levels were 2-fold higher than for those in the lower 2 tertiles (46% versus 24% and 22%, respectively; P<0.004). In a stepwise regression multivariate analysis, obstruction diameter after the procedure and uPA antigen were significant predictors of follow-up diameter stenosis.

CONCLUSIONS

Plasma uPA antigen levels and PAI-1 antigen levels identify patients at increased risk for restenosis after percutaneous coronary revascularization.

The impact of inhibitors on the cost of clotting factor replacement therapy in Haemophilia A in Canada

A retrospective case controlled study was performed to determine the comparative costs of clotting factor concentrate therapy for haemophilia A patients with and without inhibitors. We examined treatment records for a 3.5-year period for nine patients with factor VIII inhibitors and nine noninhibitor control patients matched for age and severity of disease. Inhibitor patients used FEIBA, porcine factor VIII, recombinant factor VIIa, and recombinant factor VIII over the study period. Controls used recombinant factor VIII and small amounts of monoclonal antibody purified plasma-derived factor VIII and DDAVP. The total and mean cost for treating the nine inhibitor patients was 2.25-fold greater than the cost for treating the controls. However, in six of the nine pairs the replacement product costs were actually less for the control patient than for the inhibitor patient, and the median cost of concentrates was comparable in the two groups (CDN$150 686 and $133 342 for inhibitor and control patients, respectively). This discrepancy was largely accounted for by a single inhibitor patient who required frequent hospitalizations for severe bleeding episodes. This individual, who did not receive an immune tolerance protocol, accounted for 62% of the total costs for the entire inhibitor group. In summary, over the study period the cost of haemostatic therapy for most inhibitor patients did not exceed that of control patients. However, due to the high per-unit cost of the products used to treat inhibitor patients, the effect of individual outliers greatly magnifies the overall costs of treating patients with this complication.

Laboratory and clinical markers of HIV infection in a national haemophilia cohort treated with recombinant factor VIII concentrate. The Association of Hemophilia Clinic Directors of Canada

Over an interval of approximately six months beginning in October 1993, most haemophilia A patients in Canada were switched from a plasma-derived intermediate-purity factor VIII concentrate (i.p. VIII) to a recombinant factor VIII (rVIII). In order to determine the consequence of this change in therapy on progression of HIV infection, we gathered surveillance data on clinical status and CD4 and CD8 cell counts in those patients who were HIV seropositive at the time of switching concentrates. Data were recorded at the time of switchover, annually for 2 years thereafter, and retrospectively at a point 1 year prior to the switch. CD4 cells fell significantly over the study period. Multiple direct comparisons revealed that this decline was restricted to the time intervals which included the final year in which patients received intermediate-purity factor VIII concentrate (i.p. VIII). In the 2 year interval in which rVIII was used exclusively, there was a nonsignificant fall in CD4 cells. Changes in CD4 cells did not correlate with the intensity of exposure to either i.p.VIII or rVIII. CD8 cells did not fall significantly over the study period. There was no obvious reduction in the incidence of death or clinical progression over the 2 years in which rVIII was used. However, we are hopeful that the stabilizing trend in CD4 cell counts which followed the introduction of rVIII will be predictive of corresponding clinical stabilization over the coming years.

Safety of coagulation factor concentrates

Many of the adverse effects of the early crude plasma-derived concentrates were ameliorated by increasing their purity. Ironically, this strategy may have increased the risks of inhibitor formation and pathogen transmission due to the addition of processing steps which can alter the immunogenicity of clotting factors and the use of very large plasma pools, as dictated by economic considerations. In the absence of extremely sensitive donor screening, these large pools have a high probability of contamination with pathogens, which may be only partially offset by their removal during protein purification. One approach to minimize the risk of viral transmission is to use recombinant clotting factors produced without the use of human or animal plasma proteins at any step in the manufacturing or formulation process. However, as these proteins are synthesized in mammalian cells, even they pose a theoretical risk of pathogen transmission. For plasma-derived concentrates, the initial viral burden is minimized by screening individual donations and plasma pools with tests which detect virus-specific antibodies, protein antigens, or nucleic acid. These techniques are supplemented by non-specific viral reduction steps based on physical partitioning and/or inactivation of pathogens which share chemical or physical characteristics. Prion proteins, the putative causative agents of transmissible spongiform encephalopathies, do not share these characteristics with viruses, and it remains to be determined whether they partition into clotting factor concentrates and whether the current strategies can efficiently remove or inactivate them. For all blood-borne pathogens, active immunization (currently available only for hepatitis B and A) and continued surveillance of susceptible recipients are critical approaches to achieving optimal safety of coagulation factor concentrates.

Effect of psyllium in hypercholesterolemia at two monounsaturated fatty acid intakes

We performed two studies to determine whether the lipid-lowering effect of viscous soluble fiber was modified by monounsaturated fatty acid (MUFA). First, psyllium (1.4 g/MJ) was compared with wheat bran (control) in 1-mo metabolic diets by using a randomized crossover design (n = 32 hyperlipidemic subjects). The background diet contained approximately 6% of energy as MUFA (20% of total fat). The second study (n = 27 hyperlipidemic subjects) was similar to the first but the background diet contained approximately 12% MUFA (29% of total fat) because of the addition of canola oil. At both fat intakes, psyllium resulted in significant reductions in total, low-density-lipoprotein (LDL), and high-density-lipoprotein (HDL) cholesterol compared with the wheat bran control. For the psyllium diet at 6% compared with 12% MUFA, the decreases in LDL cholesterol were 12.3 +/- 1.5% (P < 0.001) and 15.3 +/- 2.4% (P < 0.001), respectively. With the higher-MUFA diet triacylglycerol fell significantly over the control phase (16.6 +/- 5.5%, P = 0.006) and the ratio of LDL to HDL cholesterol fell significantly over the psyllium phase (7.3 +/- 2.8%, P = 0.015). Psyllium and MUFA intakes were negatively related to the percentage change in the ratio of LDL to HDL cholesterol (r = -0.34, P = 0.019 and r = -0.44, P = 0.002, respectively). Chenodeoxycholate synthesis rate increased (30 +/- 13%, P = 0.038) with the psyllium diet in the 12 subjects in whom this was assessed. We conclude that psyllium lowered LDL- and HDL-cholesterol concentrations similarly at both MUFA intakes. However, there may be some advantage in combining soluble fiber and MUFA to reduce the ratio of LDL to HDL cholesterol.

Hypofibrinolysis in patients with hypercoagulability: the roles of urokinase and of plasminogen activator inhibitor

The prevalence of abnormalities of fibrinolysis in patients with venous thromboembolism is as yet unknown. Defined abnormalities include congenital dysfunction and deficiency of plasminogen, and probably impaired plasminogen activation secondary to elevated levels of plasminogen activator inhibitor type 1 (PAI-1) or to impaired release of tissue plasminogen activator (tPA). In this preliminary study, we analyzed plasma samples from 21 patients for whom an investigation for possible thrombophilia was requested. Twenty of the patients had venous thromboembolism, and one had arterial thrombosis at an early age. Two patients had deficiency of protein C or protein S, but no other recognized biochemical disturbances related to thrombophilia were identified. Patient samples and plasma from 25 normal controls were assayed for tPA activity, PAI-1 activity, and urokinase (uPA) activity and antigen. tPA activity and antigen were not significantly different in patients than in controls. PAI-1 activity was significantly greater in patients (P < 0.0001). uPA activity was not different in the two groups. However, uPA antigen was significantly reduced in patients compared to controls (P = 0.001). These data suggest that hypofibrinolysis leading to a risk of thrombosis may be caused not only by elevated PAI-1 activity but also by reduced total uPA concentration.

Use of porcine factor VIII for surgical procedures in hemophilia A patients with inhibitors

We have described the use of polyelectrolyte fractionated porcine factor VIII (HYATE:C, Porton Speywood Ltd, Wrexham, UK) to provide hemostasis in 45 patients with hemophilia A complicated by inhibitor antibodies. The cases were collected from hemophilia care providers in seven nations and represent some of the experience with porcine factor VIII generated over the past 12 years. A wide variety of procedures was performed with varying degrees of associated hemostatic challenge in a difficult treatment group. The patients were representative of the hemophilia population in general and ranged in age from 1 to 67 years. The results of our survey should encourage clinicians to consider use of porcine factor VIII to provide hemostatic coverage in hemophilia patients with inhibitors who require surgical procedures. Hemostatic coverage was satisfactory in the vast majority of episodes; there have been only a small number of easily controlled, well-tolerated adverse reactions, which were usually self-limited in nature. No life-threatening reactions to porcine factor VIII were seen during coverage for surgical procedures in our survey, although serious reactions can occur as noted above. This is remarkable, since surgical patients usually are treated with higher doses of porcine factor VIII for greater periods of time than most other hemophilic patients treated for hemarthroses or soft-tissue bleeding, for example. Thrombocytopenia in association with porcine factor VIII therapy has been a major concern since the first crude preparations were used in the 1950s. Modern series, however, note the incidence of thrombocytopenia in only a minority of patients treated with the current polyelectrolyte fractionated preparations of porcine factor VIII. In our series, thrombocytopenia with platelet counts of less than 150 x 10(9)/L occurred in 11 of 54 treatment episodes (20%). The mechanism for thrombocytopenia demonstrated in a previous study involves porcine von Willebrand factor, which may copurify with porcine factor VIII and cause platelet aggregation and/or clearance from the circulation. The phenomenon of thrombocytopenia appears to be related to the administration of high doses of porcine factor VIII in some cases; however, in other patients, it may develop inconsistently at modest doses. It may be that there are idiosyncratic differences between patients that determine the dose of porcine factor VIII likely to cause thrombocytopenia. As yet, there is no way to predict which patient will develop thrombocytopenia while being treated with porcine factor VIII.(ABSTRACT TRUNCATED AT 400 WORDS)

The factor VIII bypassing activity of prothrombin complex concentrates: the roles of factor VIIa and of endothelial cell tissue factor

An experimental model incorporating cultured endothelial cells (EC) was used to study the "factor VIII bypassing" activity of prothrombin complex concentrates (PCC), a property exploited in the treatment of hemophiliacs with alloantibodies to factor VIII. Two PCC preparations were ineffective as stimuli of tissue factor expression by EC. However, incubation with a combination of PCC plus endotoxin (lipopolysaccharide, LPS) or tumor necrosis factor (TNF) induced much greater tissue factor expression than was seen in response to either substance alone. PCC expressed an additional direct procoagulant activity at the EC surface, which could not be attributed to either thrombin or factor Xa, and which was diminished by an anti-tissue factor antibody. Therefore factor VIIa, which was detectable in both PCC preparations, likely provided this additional direct procoagulant activity at the EC surface. We also excluded the possibility that coagulation proteases contained in or generated in the presence of PCC are protected from inactivation by AT III. Therefore, PCC can indirectly bypass factor VIII by enhancing induced endothelial tissue factor expression, and also possess direct procoagulant activity, probably mediated by factor VIIa.

Endothelial cells modulate both T-cell-dependent and T-cell-independent plaque-forming cell generation in vitro

The effects of live endothelial cells (EC), paraformaldehyde fixed EC, and EC supernatant were measured on pokeweed mitogen (PWM)-induced T-cell-dependent plaque-forming cell (PFC) generation by peripheral blood mononuclear cell (PBM). At low doses (less than or equal to 2 x 10(4) cells/culture) live EC helped PFC generation. At higher doses (greater than or equal to 10 x 10(4) cells/culture) the effect of live EC was always marked suppression (less than 10% of baseline PFC). In contrast both fixed EC and EC supernatant provided help exclusively over a wide dose range. The EC-helper effect enhanced the sensitivity of PBM to suboptimal PWM doses and also accelerated the rate of PFC generation during culture. EC influences on PFC could not be modified by gamma-interferon induction of surface DR which is known to modify EC accessory cell ability. There was also only minimal helper activity of live EC and fixed EC on the PFC generation by Epstein-Barr virus-induced cultures of purified B cells (which had been depleted of both T cells and monocytes). In contrast, suppression (greater than 97%) of PFC in isolated B-cell cultures was found even when EC constituted less than 1% of cultured cells. These results imply EC have the potential of providing multiple regulatory signals which modulate in vitro antibody production. EC-derived mechanisms are independent of their accessory cell function and require interaction with non-B cells for help, but suppression may occur directly at the B-cell level.(ABSTRACT TRUNCATED AT 250 WORDS)

Two-year evaluation of clinical and laboratory variables of immune function in 117 hemophiliacs seropositive or seronegative for HIV-1

Fifty-nine HIV-1 antibody positive and 58 antibody negative hemophiliacs were evaluated over a 2 year study period to gain insight into the natural history and prognosis of HIV-1 disease in members of this risk group. Mean CD4 (Leu 3+) cell counts calculated at 6 month intervals decreased gradually in seropositive patients (from 403 to 311/microliters) whereas CD8 (Leu 2+) counts remained stable but above the normal range. CD4 cell counts correlated closely with advancing CDC clinical stage; CD8 numbers showed no such association, but were markedly lower in the six patients with overt AIDS. Serum P24 antigenemia was associated with low CD4 cell counts and with advanced clinical stage (58% of antigenemic and 14% of non-antigenemic seropositive patients were in stage IV). In addition to CD4 cell counts, significant reductions in Leu 11+ natural killer cell (NK) subsets and in Leu 3 + 8 - cells occurred in seropositive patients over the study period; Leu 2 + DR + cells increased significantly. When expressed as a percentage of lymphocytes, the reduction in Leu 19 + NK cells was also significant, as were the increases in Leu 4 + DR + cells and Leu 12 + 8 + B cells. In summary, declining CD4 cell numbers and percentages are valuable markers of progressive HIV-1 disease in hemophiliacs, but may not always accurately reflect the degree of disease activity. Progressive changes in additional variables such as serum P24 antigen, and numbers and percentages of NK cell subsets and (as AIDS supervenes) CD8 cell numbers, may allow more precise monitoring of HIV-1 disease. This will, in turn, facilitate the design of optimal individualized strategies for therapeutic intervention.

Enhanced T-cell-activation due to combined stimulation by both endothelial cells and monocytes

Mitogen-induced interleukin 2 (IL-2) secretion by T cells was greatly enhanced by the combined presence of endothelial cells (EC) and monocytes (AC). EC also altered the time course of IL-2 secretion by peripheral blood mononuclear cells (PBM) in response to mitogens. The response to EC did not require expression of HLA-DR antigen and occurred equally well in response to autologous EC. At least one live accessory cell was required to induce T cells to secrete IL-2. When added to T cells plus live AC, both fixed EC and EC supernatant partially reproduced the enhancing effect of EC. Surface membrane IL-1 was present on both live and fixed EC. However, active EC supernatant contained no detectable IL-1 activity. Anti-IL-1 abolished the enhancement of T-cell responses by fixed but not live EC.

Carrier detection in hemophilia A: ABO blood group, multiple measurements, and application of logistic discrimination

In healthy 20- to 50-year-old women, the ABO blood group has a significant effect on levels of von Willebrand factor (VWF:Ag, formerly VIIIR:Ag) and on factor VIII activity (F.VIII:C). However, there is no significant effect of ABO group or subject age on the ratio log e(F.VIII:C/VWF:Ag). Multiple measurements of the "ratio" on possible carriers of hemophilia A may be combined with pedigree information using logistic discrimination to yield final risk assessment. To reduce misclassification of carriers as normal women, a lower limit, specified by the logistic model, is set on the logistic carrier probabilities. In this study, the proportion of blood group A for a population of obligate carriers was significantly higher than that expected for the general population (60% vs. 42%); for a population of control women it was lower than expected (22.5 vs. 42%). The effect for the carriers came primarily from daughters of affected fathers, as 81.3% were of blood group A. These observations indicate that a "universal" discriminant should be applied with caution.

The endothelial cell and the factor VIII bypassing activity of prothrombin complex concentrate

Some classical hemophiliacs have a paradoxical hemostatic response to prothrombin complex concentrate (PCC). We hypothesized that vascular endothelial cells (EC) may contribute to this "factor VIII bypassing activity". When PCC were incubated with suspensions or monolayer cultures of EC, they acquired the ability to partially bypass the defect of factor VIII deficient plasma. This factor VIII bypassing activity distributed with EC and not with the supernatant PCC, and was not a general property of intravascular cells. The effect of PCC was even more dramatic on fixed EC monolayers, which became procoagulant after incubation with PCC. The time courses of association and dissociation of the PCC-derived factor VIII bypassing activity of fixed and viable EC monolayers were both rapid. We conclude that EC may provide a privileged site for sequestration of constituents of PCC which express coagulant activity and which bypass the abnormality of factor VIII deficient plasma.

Specific inhibition of endothelial cell proliferation by isolated endothelial plasma membranes

Cultures of human vascular endothelial cells were used to study the phenomenon of density-dependent inhibition of cell growth. Endothelial cells were disrupted by nitrogen cavitation, and a plasma membrane-enriched fraction was prepared by differential centrifugation followed in some cases by sucrose density gradient fractionation. Membrane suspension was added to low-density early-passage endothelial cultures grown in microwells. Hemocytometer cell counts and 6 hr 3H-thymidine pulses were performed in triplicate wells at varying intervals. Plasma membranes suppressed cell proliferation in a reversible, dose-dependent fashion. Increasing the ambient concentration of endothelial cell growth factor did not alter the inhibitory effect. The antiproliferative effect was sensitive to heat and trypsin and to incubation with 0.1 M sodium carbonate, pH 11.5. Membrane vesicles selectively derived from the apical cell surface also suppressed proliferation. This phenomenon showed at least some specificity for cell type and species in both human and bovine models. Therefore, cell-cell contact is capable of regulating endothelial cell proliferation in vitro despite the presence of available growth surfaces and of optimally supportive culture medium.

Comparison of accessory cell functions of endothelial cells and monocytes: IL-2 production by T cells and PFC generation

It has been previously shown that endothelial cells (EC) can modulate T-cell responsiveness by mimicking monocyte (AC) function in several different in vitro systems. We now report that EC and AC differ quantitatively in their ability to provide help for IL-2 generation and T-cell induced B-cell differentiation into immunoglobulin secreting cells (ISC). Equal numbers of EC were deficient when compared to AC for promoting ISC generation, but exceeded AC for IL-2 production. Adding optimal numbers of EC drive non-adherent cell cultures to produce more than twice as much IL-2 as adding any number of AC. Furthermore, small numbers of EC were capable of modulating ongoing immune responses when added to cultures containing AC. IL-2 production by PBM was doubled by the addition of enough EC to comprise only 3% of the total culture. EC do not just mimic monocytes in immune responses, but modulate these responses in unique ways.

Anticoagulant therapy

Venous thromboembolic diseases are among the most important causes of morbidity and mortality in Canada. Agents which interfere with the coagulation mechanism are highly effective in treating these disorders, but at the potentially high cost of serious hemorrhagic complications. The optimal prevention of both serious outcomes and complications of therapy can be achieved by prophylactic treatment of high risk patients. Heparin and vitamin K antagonists remain the mainstays of antithrombotic therapy. The pharmacology of these agents is reviewed, and a rational approach to their clinical use is presented.

Protection of factor Xa from neutralization by the heparin-antithrombin complex

We have studied the accessibility of Factor Xa to neutralization by the heparin-antithrombin complex within plasma and whole blood. This serine protease was detected by measuring the concentrations of activation fragments (F2/F1+2) cleaved from prothrombin. The levels of F2/F1+2) were quantitated by means of a sensitive and specific radioimmunoassay. Our findings indicate that the binding of Factor Xa to "activated" platelets but not to phospholipid micelles results in the protection of the above enzyme from inactivation by the heparin-antithrombin complex. This sequestration of Factor Xa is not affected by the liberation of platelet release proteins or the molecular heterogeneity of the mucopolysaccharide preparations used. The magnitude of enzyme protection is strongly correlated with the extent of prothrombin activation at the time of heparin addition. On this basis, we suggest that high in vivo rates of thrombin generation may lead to the sequestration of Factor Xa on the platelet surface and hence allow this serine protease to resist the action of heparin until the complex is cleared from the circulation.

L-asparaginase induced antithrombin III deficiency: evidence against the production of a hypercoagulable state

L-asparaginase, a chemotherapeutic agent employed in the treatment of acute lymphocytic leukemia (ALL), is known to depress the synthesis of numerous plasma proteins. The plasma concentration of the major protease inhibitor of the coagulation mechanism, antithrombin III, is substantially decreased in patients receiving this drug. This observation has generated speculation that L-asparaginase may induce a hypercoagulable state in humans. To examine this hypothesis, we studied ten patients with ALL in remission who were being treated with the above chemotherapeutic agent. Our data revealed that infusion of this enzyme leads to a marked decrease in the plasma concentrations of prothrombin as well as antithrombin III. However, we have also observed a constant level of thrombin generation during the same period of time as monitored by plasma levels of prothrombin activation fragment (F1 + 2) and thrombin-antithrombin complex (TAT). Based upon these findings we suggest that administration of L-asparaginase does not usually lead to the induction of a hypercoagulable state.

Studies of the prothrombin activation pathway utilizing radioimmunoassays for the F2/F1 + 2 fragment and thrombin--antithrombin complex

We have evaluated the efficacy of utilizing radioimmunoassays (RIAs) for prothrombin activation fragments (F2/F1 + 2) and for thrombin--antithrombin complex (TAT) in purified systems and in whole blood. During venipuncture, appropriate anticoagulants were employed in order to prevent the generation of thrombin and factor Xa. The RIAs were shown to be specific for F2/F1 + 2 as well as TAT and did not interact with other plasma components. Initially, thrombin generation was studied in a purified human system of prothrombin, antithrombin, factor Xa, and factor V as well as phospholipid and Ca++. Under these conditions, the kinetics of F2/F1 + 2 and TAT generation were virtually superimposable. However, when factor V was omitted from the reaction mixture, a significantly greater amount of F2/F1 + 2 as compared to TAT was observable. Subsequently, prothrombin activation was monitored during the spontaneous coagulation of freshly drawn blood. Throughout the entire course of thrombin generation, the observable rate of formation of F2/F1 + 2 was considerably greater than that of TAT. We have examined the levels of F2/F1 + 2 and TAT in normal individuals. Our studies indicate that the concentrations of F1 + 2 and TAT average 1.97 nM and 2.32 nM, respectively. We have also quantitated the concentrations of F2/F1 + 2 and TAT in patients with disseminated intravascular coagulation. In these individuals, the levels of both components are elevated. However, the ratio of F1 + 2 to TAT ranges from 2.37 to 5.55. Thus, we conclude that under in vivo conditions, prothrombin activation is characterized by the accumulation of a stable precursor, such as prethrombin-2, and that this phenomenon may be related to an alteration of factor V function.