Haematolytic disease due to ABO incompatibility: incidence and value of screening in an Asian population

The population in Singapore is predominantly Asian, with Chinese forming the major ethnic group. The incidence of haemolytic disease of the newborn (HDN) due to Rh incompatibility is very low. The true incidence of HDN due to ABO incompatibility is unknown. Early discharge is practised in Singapore making it important to predict severe HDN due to ABO incompatibility as this would constitute the main cause of haemolysis next to G6PD deficiency. One thousand, six hundred and eight baby-maternal pairs were typed for ABO, Rh, and tested for direct Coombs' test, maternal titre, cord bilirubin and haptoglobin levels. Two hundred and fifty-one were found to be ABO incompatible, with 141 group A and 110 group B babies. The incidence of HDN due to ABO incompatibility was 3.7% of all group O mothers. Coombs' test, maternal antibody titre, cord bilirubin and haptoglobin levels were of low predictive value for severe HDN due to ABO incompatibility. The data further support the notion that it is not cost effective to screen for ABO incompatibility.

Enzyme enhancement for the measurement of protein C

Protein C measurement is now a necessary work-up of a patient with thrombosis. We described an enzyme enhancement of Laurell's immunoelectrophoresis for assay of protein C antigen. With this modification, the rockets are well defined and easily visualized and the sensitivity of the assay increased (2.5%). Samples with low protein C antigen are easily assayed.

Wilms' tumour with acquired von Willebrand's disease

A young infant with Wilms' tumour was found to have acquired von Willebrand's syndrome but no bleeding symptoms. Neither parent of the infant had evidence of von Willebrand's syndrome. Postoperatively, after removal of the tumour, factor VIII complex levels returned to normal. The mechanism of the acquired von Willebrand's syndrome was unclear. No evidence was found of an inhibitor of factor VIII complex or entrapment of factor VIII in the tumour.

The noncoding region of HPV-6vc contains two distinct transcriptional enhancing elements

HPV-6vc subgenomic fragments were inserted into an enhancer-dependent expression vector for chloramphenicol acetyltransferase (CAT) and assayed for the presence of transcriptional enhancing elements. A transcriptional enhancing element was detected in the noncoding region (NCR) of the HPV-6vc viral genome when the CAT assays were performed in viral transformed human kidney cell lines (293 and 324K), in human cervical carcinoma cell lines (HeLa and Siha), and in bovine papillomavirus type 1 (BPV-1) transformed mouse cells (C127-53). The NCR region of the HPV-6b genome was only capable of enhancing transcription of the CAT gene in the HeLa cell line at a level one-third that of the HPV-6vc NCR. The HPV-6vc NCR enhancing activity in C127-53 cells was further stimulated by the addition of sodium butyrate to the growth medium. Localization of the DNA sequences in the HPV-6vc NCR responsible for enhancing transcription revealed two distinct enhancer elements. One element (HPV-6vc position 7218-7544) was active in the 293, HeLa, Siha, and C127-53 cells. The second enhancer element (HPV-6vc position 7544-7971) was only capable of stimulating transcription in HeLa, C127-53, and Siha cells. When the HPV NCR-CAT expression vectors were cotransfected with a competitor plasmid (pNCR75) into C127-53 or HeLa cells then transcriptional enhancement decreased, indicating competition of cellular factors which affect both segments of the HPV-6vc NCR.

Activation of chicken liver fructose- 1,6-bisphosphatase by oxidized glutathione

Treatment of chicken liver fructose- 1,6-bisphosphatase with oxidized glutathione (GSSG) leads to an increase in activity. This activation is markedly enhanced if treatment is performed in the presence of AMP or Mn2+. The effects of AMP and Mn2+ appear to be synergistic. The maximal activation is over 13-fold and is accompanied by the disappearance of 4 sulfhydryl groups per molecule of enzyme. Both fructose 1,6-bisphosphate and fructose 2,6-bisphosphate can largely prevent this activation. Activation can be reversed by dithiothreitol or cysteine. It appears that GSSG activates this enzyme by thiol/disulfide exchanges with the enzyme's specific sulfhydryl groups.

Spin label studies of the essential sulfhydryl group environment in chicken liver fructose-1,6-bisphosphatase

The local environment of the essential sulfhydryl groups in chicken liver fructose-1,6-bisphosphatase has been investigated by ESR techniques using a series of iodoacetamide spin labels, varying in chain length between the iodoacetate and nitroxide free radical group. The ESR spectrum of spin-labeled chicken liver fructose-1,6-bisphosphatase showed that the sites of labeling were highly immunobilized when the enzyme was chemically modified by spin label iodoacetate, suggesting that the sulfhydryl groups of the protein are in a small, confined environment. From the change in the ESR spectra of these nitroxides as a function of chain length, we conclude that the sulfhydryl group is located in a cleft approx. 10.5A in depth.

Haemostasis in children: anything new?

Our understanding of haemostatic mechanisms has increased in the last decades. This knowledge at the cellular and molecular levels has helped us to appreciate the complexity of haemostatic mechanisms and their disturbance in various disorders. The advance in techniques to measure early activation of coagulation and platelets opens hope of treating acquired bleeding disorders e.g., disseminated intravascular coagulation before the full blown picture. More study needs to be done to define what constitutes normal haemostasis in newborns. The better understanding of control mechanisms of haemostasis will help us in diagnosis and treatment.

Simple procedure for removal of AMP from NADP preparation

A simple and reliable procedure for removal of AMP from NADP preparation is described. In this procedure, a mixture of AMP and NADP solution is first incubated with 5'-nucleotidase to hydrolyze AMP to adenosine and inorganic phosphate (Pi). The reaction mixture is then applied to a Dowex 1 (formate) column. Adenosine and 5'-nucleotidase are removed by washing the column with 20 mM HCOOH. NADP is finally eluted with 3.5 M HCOOH followed by precipitation and washing with acetone. The yield of salt-free NADP is about 80%. Although Pi is coeluted with NADP in the acid form (H3PO4), it is removed during the precipitation and repeated washing with acetone. A slight modification of this procedure for simultaneous removal of AMP, ADP, and ATP from NADP preparation has also been discussed.

Normal standards of in vitro induced platelet aggregation

Measurement of in vitro induced platelet aggregation by turbidimetric method is a very important investigative tool when patients are evaluated for bleeding diasthesis due to possible underlying platelet functional disorders. As commercial controls are not available, it is important that each laboratory establishes its own normal pattern of platelet aggregation induced by standard aggregating agents. The aggregation curves in terms of maximal % aggregation, Vmax and lag time in 50 normal Chinese controls are reported. The final concentrations of the aggregating agents used, namely adenosine diphosphate, adrenaline, collagen and ristocetin, are 20 microM, 10 microM, 0.2 mg/ml and 1.0 mg/ml, respectively. 20% of the controls had either no aggregation or only primary aggregation with adrenaline. Lag time by collagen-induced aggregation is significantly longer, but other parameters of platelet aggregation by adenosine diphosphate, adrenaline and collagen in Chinese are comparable to one reported control study. The maximal % aggregation induced by ristocetin in Chinese does not differ significantly from the reported values in whites but is significantly higher than in Blacks at a concentration of 1.0 mg/ml. Interpretation of platelet aggregometry in patients with bleeding tendency should be based on the normal patterns established from a group of normal controls in each laboratory rather than by comparison with a single control alone.

Effect of the calcium-entry blocking agent nifedipine on activation of human platelets and comparison with verapamil

The effects of the calcium-entry blocking agent nifedipine on the activation of human platelets by various agonists has been studied and compared with verapamil. Like verapamil, nifedipine inhibited platelet aggregation and secretion caused by collagen, the second phase of ADP-induced aggregation, and aggregation caused by the ionophore A23187. Both agents inhibited the formation of TXB2 from endogenous arachidonate, whereas only nifedipine inhibited platelet aggregation and decreased TXB2 formation caused by exogenous arachidonate without inhibiting uptake. These results indicate that both calcium-blocking agents may be inhibiting the release of arachidonate in platelets by phospholipases, and that nifedipine also inhibits the formation and action of thromboxane A2 in platelets. Epinephrine-induced aggregation was inhibited by low concentrations of verapamil while nifedipine only inhibited aggregation by epinephrine at much higher concentrations. It is suggested that low concentrations of verapamil inhibit epinephrine-induced aggregation by interacting with platelet alpha-adrenergic receptors, and that higher concentrations of both calcium-blocking agents inhibit platelet responses to other aggregating agents by preventing intracellular calcium mobilization.

Verapamil and collagen-induced platelet reactions--evidence for a role for intracellular calcium in platelet activation

Calcium is considered to have an essential role in various platelet reactions. Using platelets preincubated with chlortetracycline, a fluorescent divalent cation indicator, and suspended in a calcium free medium, it was shown that collagen-induced intracellular calcium redistribution occurred before the platelet shape change, the release reaction and thromboxane B2 formation. Verapamil, at concentrations which affect intracellular calcium movements, inhibited intracellular calcium redistribution in platelets and the subsequent collagen-induced platelet reactions. Low concentrations of the ionophore A23187 overcame the inhibitory effect of verapamil. These experiments provide evidence that intracellular calcium mobilization is involved in the activation of platelets by collagen. Furthermore, calcium may be released from different cellular pools since platelet secretion, aggregation and thromboxane B2 formation were inhibited at lower concentrations of verapamil than was the platelet shape change.

Platelet tests and antiplatelet drugs in coronary artery disease

This study was designed to clarify discrepancies in the literature concerning platelet survival time and beta-thromboglobulin (beta TG) levels in patients with coronary artery disease (CAD) and the effect of platelet-suppressant drugs on these tests. Platelet survival time and plasma beta TG levels were determined in 48 patients with angiographically documented CAD. The effect of sulfinpyrazone or aspirin/dipyridamole on these measurements was investigated in a double-blind, crossover trial that included a placebo phase. In patients with CAD, the mean plasma beta TG concentration was significantly elevated, but the mean platelet survival time was not significantly different from that in controls. Treatment with sulfinpyrazone or aspirin/dipyridamole did not produce changes in platelet survival time or plasma beta TG concentration that were significantly different from the values during the placebo phase. This study demonstrates that compared with the spontaneous variation in platelet survival time or beta TG concentration, there was no measureable effect of sulfinpyrazone or aspirin/dipyridamole on the results of the tests.

Inhibition of platelet function of antiarrhythmic drugs, verapamil and disopyramide

Various cardiovascular drugs such as nitrates and propranolol, used in the treatment of coronary artery disease have been shown to have an antiplatelet effect. We have studied the in vitro effects of two antiarrhythmic drugs, verapamil and disopyramide, and have shown their inhibitory effect on platelet function. Verapamil, a calcium channel blocker, inhibited the second phase of platelet aggregation induced by adenosine diphosphate (*ADP) and inhibited aggregation induced by collagen. Disopyramide similarly inhibited the second phase of platelet aggregation caused by ADP and aggregation induced by collagen. Either drug in synergism with propranolol inhibited ADP or collagen-induced platelet aggregation. Disopyramide at high concentrations inhibited arachidonic acid whereas verapamil was without effect. Verapamil, but not disopyramide, inhibited aggregated induced by the ionophore A23187.

Plasma and urine beta-thromboglobulin concentration in patients with deep vein thrombosis

Plasma and urine beta-thromboglobulin (BTG) were measured in 52 patients with established deep vein thrombosis (DVT) and in 100 patients with clinically suspected DVT but with a negative venogram. Both plasma BTG (geometric mean 54: 95% range 12--239 ng/ml) and urine BTG (0.25; 0.03--3.1 ng/ml) were significantly elevated (p less than 0.005) in patients with DVT compared to symptomatic patients with a negative venogram (plasma BTG 32, 9--112 ng/ml; urine BTG 0.12, 0.02--0.58 ng/ml). Sensitivity (35%) and specificity (80%) of the plasma BTG assay for the diagnosis of DVT were low. The urine BTG assay had a sensitivity of 37% but a specificity of 100%. There was a significant correlation between plasma and urine BTG (r = 0.68, p less than 0.005). Serial BTG measurements were made in urine (40 patients) and plasma (20 patients) from high-risk neurosurgical cases who were screened with 125I-fibrinogen leg scanning and impedance plethysmography. BTG was elevated postoperatively and returned to normal within 2 or 3 days, but rose again in 10 patients in association with the development of DVT. The rise of BTG preceded the uptake of 125I-fibrinogen and lasted for only a few days. The return to normal of BTG was not related to treatment with anticoagulants. While measurement of BTG in plasma and urine is of limited value in the clinical diagnosis of venous thrombosis, the data indicate platelet activation occurs in venous thrombosis, but is maximal or perhaps limited to the initial phase of thrombus development.

Beta-thromboglobulin radioimmunoassay. A laboratory characterization and evaluation

Platelets release beta-thromboglobulin from alpha-granules when they are activated by various stimuli. An evaluation and optimization of a radioimmunoassay for beta-thromboglobulin is described. The optimum conditions for the reaction have been characterized, and the use of second antibody and polyethylene glycol allows completion of the assay within 24 hours. Similar BTG concentrations were obtained using a 1-hour non-equilibration assay but the 1-hour assay was inefficient for processing large volumes of specimens and has the potential for cross reactivity. BTG standards were unstable but the shelf-life was prolonged with aprotinin or by storage at -70 degrees C. Plasma BTG concentration in 80 normal individuals was 28 +/- 18 ng/ml. (mean +/- 2 S.D.).

Plasma beta-thromboglobulin: differentiation between intravascular and extravascular platelet destruction

To elucidate the usefulness of beta-thromboglobulin (beta TG) in the differentiation of the mechanism of thrombocytopenia, plasma beta TG concentration was measured in one patient with amegakaryocytic thrombocytopenia, four patients with autoimmune thrombocytopenia (ATP), two patients with thrombotic thrombocytopenia (TTP), and one patient with thrombocytopenia secondary to disseminated intravascular coagulation (DIC). Plasma beta TG was not measurable in amegakaryocytic thrombocytopenia, was normal in ATP, and was increased in TTP and DIC. These data indicate that in thrombocytopenic patients, increased plasma beta TG concentration may result from intravascular platelet consumption with release of platelet constituents in contrast to extravascular platelet destruction by the macrophage-monocyte system.

Thrombotic Thrombocytopenic Purpura: Mechanism for Effectiveness of Plasmapheresis

Thrombotic thrombocytopenic purpura (TTP) is a rare but serious illness of unknown etiology. Treatment by plasmapheresis has been reported to be effective but the mechanism for benefit is unknown. We have investigated the effect of plasmapheresis in 2 patients with TTP by quantitating platelet associated IgG (PAIgG) levels prior to and following plasmapheresis. Both patients had very high levels of PAIgG at presentation (90 and A8 fg IgG/platelet respectively, normal 0-5). in both, the PAIgG levels progressively fell to within the normal range and the platelet count rose following plasmapheresis. One patient remained in remission with normal platelet counts and PAIgG levels. The other relapsed after plasmapheresis and the PAIgG level rose prior to the fall in platelet count. Plasmapheresis was repeated and resulted in normalization of both the platelet count and PAIgG level. It is suggested that plasmapheresis removes antiplatelet antibody or immune complexes which may be of etiological importance in this illness.

The Effect of Contrast Media, 125Iodine-Labelled Fibrinogen, Heparin and Aspirin on Plasma BTG Concentration

Betathromboglobulin, a platelet-specific protein, released on activation of platelets is being evaluated as a marker of active thrombosis. Theoretically, several diagnostic and therapeutic procedures used in the thrombotic disorders might affect BTG by inducing platelet release or by interfering with the radioimmunoassay (RIA) method. This study determined the effect on plasma BTG concentration of contrast media used in venography, I125-labelled fibrinogen for leg scanning and heparin or aspirin used in the management of venous thrombosis. Mean plasma BTG in normals was 28 ± 8 ng/ml. (n = 70), and do not fluctuate. Plasma BTG, in 10 patients with normal venogram measured before and 30 minutes post-venorrraphiv was 23 ± 10 ng/ml, and 26 ± 15 ng/ml, respectively (p > 0.1). 125I fibrinogen in plasma by, conrecinitating in the BTG/antibody complex, elevates bound radioactivity in the RIA and results in spuriously low levels of BTG and may proclude its use as a diagnostic test in patients having leg scanning. In-vitro, henarin (> 50 units/ml.) or aspirin (> 40 mg/100 ml.) affect the 1 hour incubation assay and give falsely high BTG levels but do not affect an optimized assay with 24 hours incubation. This study indicates that diagnostic and therapeutic measures in venous thrombosis patients may influence BTG, measurement and caution is necessary to avoid confusing the results.

Thrombotic Thrombocytopenic Purpura: Mechanism for Effectiveness of Plasmapheresis

Thrombotic thrombocytopenic purpura (TTP) is a rare but serious illness of unknown etiology. Treatment by plasmapheresis has been reported to be effective but the mechanism for benefit is unknown. We have investigated the effect of plasmapheresis in 2 patients with TTP by guantitating platelet associated IgG (PAIgG) levels prior to and following plasmapheresis. Both patients had very high levels of PAIgG at presentation (90 and 48 fg IgG/platelet respectively, normal 0-5). In both, the PAIgG levels progressively fellto within the normal range and the platelet count rose following plasmapheresis. One patient remained in remission with normal platelet counts and PAIgG levels. The other relapsed after plasmapheresis and the PAIgG levelrose prior to the fall in platelet count. Plasmapheresis was repeated and resulted in normalization of both the platelet count and PAIgG level. It is suggested that plasmapheres is removes antiplatelet antibody or immune complexes which may be of etiologicalimportance in this illness.

Plasma Betathromboglobulin Measurement to Differentiate Types of Thrombocytopenia

It is important to differentiate betwteen extravascular (autoimmune thrombocytopenia, ATP) and intravascular (thrombotic thrombocytopenia, TTP) platelet destruction in thrombocytopenia. Betathromboglobulin (BTG), a platelet-specific protein with a plasma half life of 20 minutes is released in-vivo from platelets by various stimuli and may reflect platelet activation or destruction. BTG concentration can be measured in plasma usin a radioimmunoassay to a sensitivity of 1 ng/ml., (nomal 28.0 ± 8.0 ng/ml., n = 70). Plasma BTG was measured in 3 patients with ATP (platelet counts: 17, 20, 16 x 109/L) and 2 patients with TTP (platelet counts: 20, 40 x 109/L). In ATP, BTG was normal (22, 11, 17 ng/ml.) and in TTP, BTG was elevated (80, 72 ng/ml.). Plasma BTG remained normal in ATP after treatment. BTG remained elevated in TTP (120 ng/ml.) even when the platelet count became normal (220 x 109/L) but while fragmented RBC were still present and became normal (21 ng/ml.) on complete recovery. These data suggest that plasma BTG may be useful in differenfiating extravascu1ar from intravascular platelet destruction by detecting increased concentrations of BTG in plasma.

The Effect of Antiplatelet Drugs on Piasma Retatiromboglobulin in Coronary Artery Disease

Platelets play a role in the development and complications of coronary artery disease (CAD) and a number of abnormalities of Platelet function which can be corrected by antiplatelet drugs have been described. Betathromboglobulin (BTG), a platelet-specific protein which is released from α-granules during platelet activation is significantly elevated in patients with angiographically demonstrated CAD (51.0 ± 31.0 ng/ml., n = 50) compared to normal (28.0 ± 8.0 ng/ml., n = 70) p < 0.001 . The effect of sulphinpyra-zone (800 mg.) or aspirin (1200 mg.)/dipyridamole (200 mg.) on plasma BTG in CAD was studied in a blind prospective crossover trial in 25 patients, Mean BTG concentration pre-treatment was 52.3 ng/ml. and after 1 month’s treatment with placebo, sulphinpyra-zone or aspirin/dipyridamole mean plasma BTG concentrations were 53.5, 49.6 and 56.7 ng/ml. respectively. Analysis of variance showed no significant difference between the means (p > 0.1). This study confirms increased plasma BTG concentrations in patients with CAD and indicates that therapeutic doses of these antiplatelet drugs do not significantly effect the BTG level and thus appear not to prevent α-granule release in CAD.