Biomedical subjects

H K Lau

Publications and source records attributed to H K Lau.

At least 37 records · Page 2Linked to original sources

PubMed1993

Anticoagulant function of a 24-Kd fragment isolated from human fibrinogen A alpha chains.

A fibrinogen fragment obtained by limited-plasmin proteolysis has been isolated and purified to apparent homogeneity by gel filtrations. This fragment, denoted as 24-Kd fragment, has an apparent M(r) approximately 24,000 and contains an N-terminal sequence of met-glu-leu-glu-arg-pro-gly-gly-asn-glu-ile. The fragment contains a large number of acidic amino acid residues, and its amino acid composition is similar to several fibrinogen A alpha chains degradation fragments isolated previously. It corresponds to a peptide of the fibrinogen A alpha chains, the N-terminal of which starts at alpha Met-240. This peptide delays thrombin plasma clotting time. It does not bind calcium ions and does not inhibit thrombin's amidolytic activity. It binds to immobilized fibrin but not fibrinogen. It also inhibits the polymerization of desAA and desAABB fibrin monomers by simultaneously decreasing the maximum rate and the maximum level of the polymerization reaction. However, the initial lag period of this reaction is not affected by the fragment.

Amino Acid Sequence↗

PubMed1993

Modulation of the plasminogen activation system in murine macrophages.

We have dissected the state of fibrinolytic balance in the C57/BL mouse macrophages, by means of immunotrap assays and zymography. We have monitored the individual changes of plasminogen activator (PA) and plasminogen activator inhibitor (PAI) activities of cellular lysates and secretions of these macrophages, after they were stimulated by various exogenous agents. The resident peritoneal macrophages were found to have very little PA but high level of PAI, and are therefore highly anti-fibrinolytic in nature. Upon stimulation by thioglycollate, PA activity increased and PAI activity decreased, thus raising the fibrinolytic balance in these macrophages. Upon incubation of resident or thioglycollate-activated macrophages by lipopolysaccharide (LPS), the PA level was depressed while the PAI level was increased, resulting in a large drop in the total fibrinolytic balance of the activated cells. When resident or thioglycollate-activated macrophages were incubated with the anti-inflammatory agent dexamethasone, the drug depressed both the expressions of PA and PAI, in the lysate and conditioned medium of both cell types. Thus cell-bound or secreted forms of macrophage PA and PAI activities were either increased or decreased in response to thioglycollate, LPS or dexamethasone challenge. The changes in PA and PAI resulted in different state of fibrinolytic balance in macrophages, and could be related to the different functions of these macrophages at different stages of their development.

Animals↗

PubMed1993

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.

Adult↗

PubMed1993

Characterization of immunotrap assays for urokinase plasminogen activator and its inhibitors and measurements of these molecules in human plasma and mouse macrophage in culture.

1. Immunotrap assays that can measure the activities of urokinase-type plasminogen activator (uPA) and its inhibitors (PAIs) were characterized. 2. Both human plasma and mouse macrophages in culture were found to contain much higher inhibitor activity than uPA-like activity. 3. The balance between pro- and anti-fibrinolytic activities was quantitatively changed in the murine macrophages after the injection of thioglycollate. uPA-like materials were synthesized by the macrophages and secreted to the conditioned medium continuously, while PAI activity was unchanged during the same time period.

Animals↗

PubMed1993

Characterization of radioimmunoassays for high- and low-molecular weight urokinases and estimation of different molecular forms of urokinase in urine and plasma.

Antibody populations against high- and low-molecular weight urokinases (HUK and LUK) were purified by passage of rabbit antiserum immunoglobulin fractions made against HUK and LUK through HUK- or LUK-bound Sepharose 4B (Pharmacia AB, Uppsala, Sweden) gels, respectively. Radioimmunoassays were then set up with these antibody populations. The characteristics of these radioimmunoassays were studied by competition of different antigens against radiolabeled HUK or LUK for these antibodies. We found that the anti-HUK antibody population recognizes epitopes on the light chain of HUK, most of which are situated outside of the urokinase-receptor binding sequence of amino acids. The anti-LUK antibody population probably recognizes a region on LUK distinct from its catalytic site. This region is also present in HUK but is altered in single-chain urokinase, suggesting that a conformation change takes place when single-chain urokinase is converted to HUK. The complexes of HUK and LUK with plasminogen activator inhibitor 1 or 2 could compete in either radioimmunoassay, with different and diminished efficiencies. Taking advantage of this result, we devised a procedure to measure the concentrations of various urokinase species in human urine. We found that freshly voided urine contained substantial amounts of free HUK, some HUK- and LUK-plasminogen activator inhibitor complexes, and a small amount of single-chain urokinase. By using a combination of radioimmunoassay and zymography, we found that human plasma contains mostly HUK-plasminogen activator inhibitor 1 complexes, a small amount of single-chain urokinase or HUK, and no LUK or LUK-inhibitor complexes.

Antibodies↗

PubMed1990

Cell mutants defective in synthesizing a heparan sulfate proteoglycan with regions of defined monosaccharide sequence.

We have demonstrated that mouse LTA cells synthesize cell-surface heparan sulfate proteoglycans (HSPGs) with regions of defined monosaccharide sequence that specifically interact with antithrombin (HSPGact). It remains unclear how HSPGact can be generated by a biosynthetic pathway with no simple template for directing the ordered assembly of monosaccharide units. To examine this issue, we treated LTA cells with ethyl methanesulfonate and then isolated seven stable mutants that synthesize only 8-27% of the wild-type HSPGact but produce normal amounts of other HSPGs. These mutants are recessive in nature and fall into at least two different complementation groups. The delineation of the molecular basis of these defects should help to elucidate the manner by which cells synthesize HSPGs with regions of defined monosaccharide sequence.

Animals↗

PubMed1990

A study of tissue plasminogen activator forms from human small intestine.

At least two forms of plasminogen activators which crossreacted with antiserum against tissue plasminogen activator (tPA) have been found in human small intestine homogenates. One of these activities has very slow mobility on Sephadex G-200 and is presumably a degraded form of tPA. The other moved very fast and was dispersed on gel filtration matrices, and probably represents aggregates of tPA with some other materials. Whereas 1 M NaCl, 1% Triton X-100 or 1 M potassium thiocyanate was unable to break up these aggregates, the high molecular weight components co-migrating with tPA could be separated from tPA by 4 M guanidine-HCl.

Chromatography, Ion Exchange↗

PubMed1989

Conformational changes in human prothrombin as detected by antibody populations.

The amino-terminal peptides of human prothrombin corresponding to residues 1-51 and 52-156 have been isolated from a thrombin digest of prothrombin fragment 1. The products of digestion were purified by means of barium citrate and ammonium sulfate precipitations, followed by gel filtration and hydroxyapatite chromatographies. They were identified by their molecular sizes as well as their amino acid compositions. Peptides 1-51 (F1A) and 52-156 (F1B) were used as affinity ligands for the isolation of antibody populations from antisera that were elicited against human prothrombin or prothrombin fragment 1. These antibody populations displayed restricted specificity for the respective ligands as shown by competitive radioimmunoassays. They were used to study the conformational changes in prothrombin and fragment 1. The F1A-specific antibody populations detected a conformational change which is stabilized by calcium ions and which has a transition midpoint at approximately 0.2 mM calcium ion concentration. The F1B-specific antibody populations identified a different conformational change which is destabilized by calcium ions and which has a transition midpoint at approximately 0.5 mM calcium.

Antibody Affinity↗

PubMed1988

Cervical myelopathy due to ossification of the posterior longitudinal ligament. A clinical, radiological and evoked potentials study in six Chinese patients.

Six consecutive Chinese patients with cervical myelopathy due to ossification of the posterior longitudinal ligament (OPLL) who presented in a 4 yr period were studied. There were 5 males and 1 female whose mean age at presentation was 67 yrs. The common clinical features were spastic tetraparesis more marked in the lower limbs, spinothalamic and posterior column sensory deficits of varying degree and sphincter disturbance in advanced cases. OPLL was diagnosed on plain radiographs and cord compression ascertained by conventional and computer-assisted myelography. Somatosensory evoked potentials correlated with posterior column signs and appeared to reflect the clinical course following treatment. While the cord pathology in OPLL is similar to that of cervical spondylotic myelopathy (CSM), the pathogenetic mechanism probably differs in one aspect. Compression by OPLL is the determining factor in most cases whereas the combined presence of a congenitally narrow canal and spondylosis is essential for the development of CSM. Other contributory factors include coexisting spondylosis, a congenitally narrow canal, friction between cord and OPLL during neck movement and acute trauma. Cord damage is probably mediated by ischaemia which is due to disturbances of the microcirculation caused by the mechanical factors.

Aged↗

PubMed1987

Physicochemical characterization of human intestinal lactase.

Human lactase was isolated from solubilized small-intestinal brush-border membranes by a combination of chromatography on concanavalin A-Sepharose, Bio-Gel 1.5m and chromatofocusing, with a yield of approx. 1% and a 750-fold purification. The enzyme appeared to be homogeneous on SDS/polyacrylamide-gel electrophoresis under both reduced and non-reduced conditions, with an apparent Mr of approx. 170,000. On gel filtration, however, it displayed an apparent Mr of approx. 380,000. The protein had a pI of 4.8, as judged by the chromatofocusing experiment, and had a lactase activity whose optimum is at pH 6.0. In addition to the beta-galactosidase activity, the protein also hydrolysed to various extents cellobiose, phlorizin, p-nitrophenyl beta-D-galactoside, p-nitrophenyl beta-D-glucoside, o-nitrophenyl beta-D-galactoside and o-nitrophenyl beta-D-fucoside. Antisera had been raised against the purified enzyme in two rabbits. One of the antibody populations could inhibit the enzyme in a concentration-dependent manner. This antibody population was used to set up an antibody-bound Sepharose column for the use in an immunoaffinity purification of lactase from crude intestinal homogenate. A partially purified preparation of lactase could thus be obtained. The antibody population was also used to set up a radioimmunoassay for quantifying the enzyme. The competition assay could detect about 0.5 micrograms of lactase protein/ml.

Chromatography, Affinity↗

PubMed1987

Treatment of unstable trochanteric fractures with Dimon-Hughston osteotomy displacement fixation and acrylic cement.

For the management of unstable trochanteric fractures, a new method consisting of Dimon-Hughston medial displacement osteotomy, fixation with a sliding screw sleeve-plate device, with augmentation of the posterior and medial upper femoral cortical defect with acrylic cement, was performed in 84 patients. All patients were allowed full weight bearing on the affected extremity within 1 week of operation. Sixty-five patients were available for follow-up more than 12 months after operation. Complication rates were low and 77 per cent of the patients achieved excellent and good functional results.

Aged↗

PubMed1987

Isolation and characterization of a specific antibody population against human fibrinogen.

A specific antibody population against human fibrinogen was isolated from a rabbit antiserum by affinity chromatography on fibrinogen-bound Sepharose gel. Using a sensitive competitive radioimmunoassay, the antibody population was found to recognize epitopes on native fibrinogen but crossreacted minimally with fibrinogen fragment D and an early plasmin-degraded fibrinogen A alpha-chain product, but not at all with fragment E or fibrinopeptides A and B. Fibrin monomers shared part of these epitopes. The antibody population crossreacted to a small extent with bovine, horse and baboon fibrinogens and not at all with fibrinogens from sheep, rat, pig, goat, guinea pig, dog and rabbit.

Animals↗

PubMed1987

Development of a radioimmunoassay for quantitating prethrombin 2 in human plasma.

We have developed a radioimmunoassay (RIA) for prethrombin 2 (Pr2), a potential intermediate in the transformation of prothrombin to thrombin. Antisera against human Pr2 were raised in rabbits and the respective immunoglobulin G fractions were chromatographed on prothrombin-Sepharose. The specific antibody population obtained was used to construct a double-antibody RIA capable of measuring as little as 0.05 nmol/L of this component. The immunoreactivity of prothrombin was approximately 40,000 times less than that of Pr2 on a molar basis. Because of nonspecific contributions of plasma constituents to the immunoreactive signal, the measurement of Pr2 in this milieu required the use of a titration curve in which Pr2 was added back to Pr2-depleted plasma. This assay was then used to determine the levels of this species in two patient populations with increased prothrombin activation as determined by the prothrombin fragment F1 + 2 RIA, a measure of the in vivo cleavage of prothrombin by factor Xa. The mean Pr2 concentrations in eight patients with disseminated intravascular coagulation and six asymptomatic individuals with congenital antithrombin deficiency not receiving antithrombotic therapy were not significantly elevated as compared with those of normal controls (0.244 nmmol/L and 0.242 nmol/L vs. 0.184 nmol/L, respectively). Our studies show that Pr2 is cleared from the plasma of dogs with a t1/2 of approximately 25 minutes. Given that the t1/2 of F1 + 2 is estimated to be approximately 90 minutes, the low plasma levels of Pr2 observed in patients with thrombophilia cannot result from rapid clearance of this component.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1986

Isolation and partial characterization of a proteinase inhibitor from human colorectal adenocarcinoma.

A proteinase inhibitor has been isolated from human colorectal adenocarcinomas by extraction with a low-ionic-strength buffer and a combination of Con A-Sepharose, Sephadex G-200, DEAE-cellulose and chromatofocusing steps. The preparation appeared to be homogeneous upon gel exclusion chromatography and SDS-polyacrylamide gel electrophoresis and had an estimated molecular weight of 66,000. The inhibitor was able to bind and inhibit urokinase, plasmin, trypsin, tissue plasminogen activator and thrombin. The binding appeared to be stoichiometric and relatively fast. The isoelectric point of the protein was 4.6-4.7. The inhibitor did not crossreact with antisera elicited against alpha 2-macroglobulin, alpha 2-antiplasmin, antithrombin III or C1-inhibitor, but it did crossreact with an antiserum against alpha 1-antitrypsin in double immunodiffusion. The antiserum only partially attenuated the activity of the inhibitor. Whereas alpha 1-antitrypsin completely inhibited the amidolytic activity of elastase, the tumor inhibitor had no effect on elastase under the same conditions.

Adenocarcinoma↗

PubMed1986

A plasminogen activator from benign ovarian cystadenoma: partial purification and characterization.

A plasminogen activator has been partially purified from benign serous cystadenomas by a combination of Sephadex G-200 gel filtration, CM-Sephadex ion exchange, Concanavalin A-Sepharose and arginine-Sepharose affinity chromatographies. Its apparent size was very large and could not penetrate Sepharose 6B or 5% SDS polyacrylamide gel. It hydrolyzed plasminogen in a manner similar to that of urokinase in terms of their apparent Michaelis constants, although a one-minute lag period had to be allowed for this activation before the hydrolysis of plasminogen. It was very sensitive to reducing agent such that 5 mM dithiothreitol could completely destroy its activity. The activator crossreacted with anti-uterine plasminogen activator IgG, but did not react with anti-urokinase at all. It also bound fibrin well. In the absence of plasminogen, the activator was devoid of amidolytic activity towards S-2251, S-2302 and S-2288 but had a small but measurable activity against S-2444.

Chromatography, Affinity↗

PubMed1986

Identification of plasmin as the major contaminant in immunoglobulin preparations.

A proteolytic enzyme could be isolated from rabbit serum by means of DEAE cellulose, Protein A-bound Sepharose and lysine-bound Sepharose chromatographies. This enzyme was found to be the major protease contaminating IgG preparations of rabbit serum. This enzyme was identified as plasmin because it displayed an apparent Mr of 90,000 on nonreduced SDS polyacrylamide gel electrophoresis, was able to directly lyse fibrin and the chromogenic substrate H-D-Val-Leu-Lys-p-nitroanilide, and was stable after heating at 56 degrees for 30 min but broke down at 80 degrees. Its Km toward the chromogenic substrate was 0.35 mM, which agreed well with the published value for plasmin.

Animals↗

PubMed1984

Demonstration of the presence of plasminogen activator in human small intestine.

A cytosolic fraction of human small intestine was prepared. It contained esterase activity toward N-alpha-acetyl-lysine-methyl ester and amidolytic activities toward substrates S-2238, S-2288 and S-2251. In addition there was present a plasminogen activator activity which could cleave plasminogen to produce plasmin and the plasmin hydrolysed the same chromogenic substrates. Plasmin generation was also followed by a time-dependent hydrolysis of 125-I labeled plasminogen or monitored by fibrin-agar plate. The plasminogen activator was related to urinary urokinase immunologically. Anti-urokinase IgG cross-reacted with cytosolic fraction in double immunodiffusion. When the cytosolic fraction was electrophoresed in discontinuous polyacrylamide gel, two regions of hydrolytic activity toward the urokinase-specific substrate S-2444 were found. The activity of one of these regions could be completely inhibited by anti-urokinase while the other was not. The plasminogen activator was partially purified by ammonium sulfate precipitation and Concanavalin A-bound Sepharose chromatography.

Amides↗

PubMed1983

Treatment of comminuted trochanteric femoral fractures with Dimon Hughston displacement fixation and acrylic cement--a preliminary report of sixteen cases.

A new method for the treatment of unstable intertrochanteric fracture of the femur is proposed. This consists of stabilizing the fracture with a Dimon and Hughston medial displacement osteotomy and then restoring the cortical defect at the fracture site with methylmethacrylate cement (Dimon and Hughston, 1967). A preliminary trial on sixteen patients showed the excellent stability of the fracture achievable by this method. No mechanical failure was encountered, even though patients were all starting to walk and bearing full weight within the first week. No infection or non-union occurred. Early walking by the elderly patient suffering from a comminuted trochanteric fracture is important to counter the ill effects of decubitus associated with this fracture.

Aged↗