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Biomedical subjects

M A Khamashta

Publications and source records attributed to M A Khamashta.

At least 127 records · Page 7Linked to original sources
PubMed1998

Human beta 2-glycoprotein I binds to endothelial cells through a cluster of lysine residues that are critical for anionic phospholipid binding and offers epitopes for anti-beta 2-glycoprotein I antibodies.

Beta 2-Glycoprotein I (beta 2GPI) is a phospholipid-binding protein recognized by serum autoantibodies from the anti-phospholipid syndrome both in cardiolipin- and beta 2GPI-coated plates. We found that: 1) recombinant wild-type beta 2GPI bound to HUVEC and was recognized by both human monoclonal IgM and affinity-purified polyclonal IgG anti-beta 2GPI anti-phospholipid syndrome Abs; and 2) a single amino acid change from Lys286 to Glu significantly reduced endothelial adhesion. Double and triple mutants (from Lys284,287 to Glu284,287, from Lys286,287 to Glu286,287, and from Lys284,286,287 to Glu284,286,287) completely abolished endothelial binding. A synthetic peptide (P1) spanning the sequence Glu274-Cys288 of the beta 2GPI fifth domain still displayed endothelial adhesion. Another peptide (P8), identical with P1 except that Cys281 and Cys288 were substituted with serine residues, did not bind to HUVEC. Anti-beta 2GPI Abs, once bound to P1 adhered to HUVEC, induced E-selectin expression and up-regulated IL-6 secretion. Control experiments conducted with irrelevant Abs as well as with the P8 peptide did not show any endothelial Ab binding nor E-selectin and IL-6 modulation. Our results suggest that: 1) beta 2GPI binds to endothelial cells through its fifth domain; 2) the major phospholipid-binding site that mediates the binding to anionic phospholipids is also involved in endothelial binding; 3) HUVEC provide a suitable surface for beta 2GPI binding comparable to that displayed by anionic phospholipids dried on microtiter wells; and 4) the formation of the complex between beta 2GPI and the specific Abs leads to endothelial activation in vitro.

Amino Acid Sequence↗
PubMed1998

Arterial disease and thrombosis in the antiphospholipid syndrome: a pathogenic role for endothelin 1.

OBJECTIVE: To explore a possible correlation between endothelin 1 (ET-1), the most potent endothelium-derived contracting factor that modulates vascular smooth muscle tone, and arterial disease in patients with the antiphospholipid syndrome (APS). METHODS: Plasma levels of ET-1 were measured in APS patients with (n = 16) and without (n = 11) arterial thrombosis and in non-APS patients with arterial thrombosis (n = 9). In addition, steady-state prepro-ET-1 messenger RNA (mRNA) levels were determined in endothelial cells treated with a range of human monoclonal anticardiolipin antibodies (aCL) (as anti-beta2-glycoprotein I antibodies) by semiquantitative 32P-dCTP-labeled reverse transcription-polymerase chain reaction. RESULTS: Compared with healthy controls, markedly increased plasma levels of ET-1 were found in APS patients with arterial thrombosis (2.00 +/- 0.87 versus 0.96 +/- 0.37 pg/ml; P = 0.0001) but not in other groups. Three human monoclonal aCL induced prepro-ET-1 mRNA levels significantly more than did control monoclonal antibody lacking aCL activity. CONCLUSION: Plasma ET-1 levels correlated significantly with a history of arterial thrombosis in patients with APS. Prepro-ET-1 mRNA was induced by human monoclonal aCL in the in vitro experimental system. The induction of ET-1 by antiphospholipid antibodies might contribute to increased arterial tone, leading to vasospasm and, ultimately, to arterial occlusion.

Adult↗
PubMed1998

Effects of human monoclonal anticardiolipin antibodies on platelet function and on tissue factor expression on monocytes.

OBJECTIVE: To investigate the effect of human monoclonal anticardiolipin antibodies (aCL) on platelet interaction with the subendothelium under flow conditions and on tissue factor (TF) expression on normal monocytes. METHODS: Three monoclonal IgM aCL (TM1B3, GR1D5, and EY2C9) and 2 affinity-purified IgM aCL were studied. Immunoglobulins were added to normal blood and perfused through chambers containing denuded vascular segments. Platelet interactions were morphometrically evaluated by determining the percentage of total surface covered by platelets (PCS) or by large aggregates of thrombi platelets (TP). Expression of TF on monocytes was measured after immunoglobulin incubation with normal mononuclear cells. RESULTS: Significant increases in the total PCS and expression of TF were observed using all aCL. Increased levels of TP were induced by all aCL except EY2C9 (obtained from a patient without thrombosis). Previous incubations of these aCL with subendothelial surfaces did not increase platelet interaction. CONCLUSION: The effects of aCL on platelet function may help to explain the pathophysiology of thrombosis in the antiphospholipid syndrome.

Adult↗
PubMed1998

Antiphospholipid syndrome in SLE.

The antiphospholipid syndrome, initially described in systemic lupus erythematosus (SLE), occurs in 20-35% of patients with this condition. Its clinical manifestations may precede, be concurrent with, or follow clinical features of SLE. There are no major differences between the primary antiphospholipid syndrome and the secondary form that associates with SLE. Several studies suggest that the presence of an antiphospholipid syndrome in patients with SLE conveys a worse prognosis. To prevent recurrence of thrombotic events (particularly arterial events), oral anticoagulation with an international normalized ratio (INR) close to 3 is recommended. Treatment of recurrent fetal loss is with aspirin, or with aspirin plus heparin. Controlled studies are underway to determine optimal treatment in patients with cerebral ischaemia as well as the optimal treatment in women with recurrent pregnancy loss.

Abortion, Spontaneous↗
PubMed1998

Binding of anticardiolipin antibodies to protein C via beta2-glycoprotein I (beta2-GPI): a possible mechanism in the inhibitory effect of antiphospholipid antibodies on the protein C system.

It is known that antiphospholipid antibodies (aPL) hamper the anticoagulant activity of the protein C system, but the mechanism is still obscure. In this study, we demonstrate that anticardiolipin antibodies (not anti-protein C autoantibodies) can bind protein C via beta2-GPI, which bears their binding epitope, in a fashion dependent on negatively charged phospholipids. We studied the binding of IgG from aPL to protein C in the presence of beta2-GPI by ELISA (anti-'protein C' antibody ELISA), and compared their binding with those obtained in the absence of beta2-GPI. In the anti-'protein C' antibody ELISA system, 47% of 78 aPL+ patients had a positive titre in the presence of cardiolipin (CL) and beta2-GPI, but binding was not found in the absence of beta2-GPI. Highly significant correlations were found between the titre of anti-'protein C' antibody in the presence of beta2-GPI and that of anti-beta2-GPI antibody (r = 0.802, P = 0.0001). We further analysed the interaction between protein C, phospholipids, beta2-GPI and human aCL MoAbs established from patients with antiphospholipid syndrome. In a first set of experiments, the binding of beta2-GPI to protein C and its phospholipid dependency were investigated. Beta2-GPI bound to protein C in the presence of CL or phosphatidylserine, but not in the presence of phosphatidylcholine or phosphatidylethanolamine. In a second group of experiments, the binding of three human monoclonal aCL recognizing the cryptic epitope of beta2-GPI (virtually anti-beta2-GPI antibodies) was evaluated in the presence of cardiolipin and beta2-GPI. All three human monoclonal aCL bound to protein C in the presence of CL and beta2-GPI, whereas they did not in the absence of either beta2-GPI or CL. These data suggest that protein C could be a target of aCL by making a complex with CL and beta2-GPI, leading to protein C dysfunction.

Adolescent↗
PubMed1998

Antiphospholipid, anti-beta 2-glycoprotein-I and anti-oxidized-low-density-lipoprotein antibodies in antiphospholipid syndrome.

Antiphospholipid antibodies (aPL), anti-beta 2-glycoprotein I (anti-beta 2-GPI) and anti-oxidized-low-density lipoprotein (LDL) antibodies are all implicated in the pathogenesis of antiphospholipid syndrome. To investigate whether different autoantibodies or combinations thereof produced distinct effects related to their antigenic specificities, we examined the frequencies of antiphospholipid syndrome (APS)-related features in the presence of different antibodies [aPL, beta 2-GPI, anti-oxidized low density lipoprotein (LDL)] in 125 patients with APS. Median follow-up was 72 months: 58 patients were diagnosed as primary APS and 67 as APS plus systemic lupus erythematosus (SLE). Anticardiolipin antibodies (aCL), anti-beta 2-GPI and anti-oxidized LDL antibodies were determined by ELISA; lupus anticoagulant (LA) by standard coagulometric methods. Univariate analysis showed that patients positive for anti-beta 2-GPI had a higher risk of recurrent thrombotic events (OR = 3.64, 95% CI, p = 0.01) and pregnancy loss (OR = 2.99, 95% CI, p = 0.004). Patients positive for anti-oxidized LDL antibodies had a 2.24-fold increase in the risk of arterial thrombosis (2.24, 95% CI, p = 0.03) and lower risk of thrombocytopenia (OR = 0.41 95% CI, p = 0.04). Patients positive for aCL antibodies had a higher risk of pregnancy loss (OR = 4.62 95% CI, p = 0.001). When these data were tested by multivariate logistic regression, the association between anti-beta 2-GPI and pregnancy loss and the negative association between anti-oxidized LDL antibodies and thrombocytopenia disappeared.

Adult↗
PubMed1998

Multiple antiphospholipid tests do not increase the diagnostic yield in antiphospholipid syndrome.

The family of antiphospholipid antibodies (aPL) includes a heterogeneous population of autoantibodies whose specificity is directed against not only phospholipids, but their complex with plasma proteins. Anticardiolipin antibodies (aCL) and lupus anticoagulant (LA) tests are widely performed to screen the aPL family which is associated with thrombotic complications in patients with systemic lupus erythematosus (SLE) or antiphospholipid syndrome (APS). The clinical significance of other aPL tests, including antibodies against phosphatidylserine (aPS), phosphatidylinositol (aPI), phosphatidic acid (aPA), phosphatidylcholine (aPC) and phosphatidylethanolamine (aPE), has not been established. The purpose of this study was to evaluate whether multiple aPL tests have enhanced diagnostic value for APS. We tested IgG/M/A aPS, aPI, aPA, aPC and aPE by ELISA using 10% bovine serum as blocking and sample diluent in 26 SLE patients with clinical manifestations of APS, but negative for both aCL and LA (Group 1). The results were compared with 32 SLE patients without any features of APS (Group 2) and 24 SLE patients with APS (aCL and/or LA positive) (Group 3). In Group 1, 1/26 (4%) was positive for IgA aPE, less frequent than in other groups, and none of the patients had any other aPL. In Group 2, 1/32 (3%) was positive for aPS, two (6%) for aPI, one (3%) for aPA and four (12.5%) for aPE. None was positive for aPC. In the third group, 13/24 (54%) were positive for aPS, 11 (46%) for aPI, 15 (63%) for aPA, four (17%) for aPC and seven (29%) for aPE. Since aPE was found in some patients, we extended the study, including 207 SLE patients, and tested aPE. IgG/M/A aPE was found in six (3%), 10(5%) and 21 (10%), respectively, but no association was found between aPE and any clinical features of APS. This study suggests that screening by multiple aPL tests does not increase the diagnostic yield in APS.

Adolescent↗
PubMed1998

Lack of cross-reaction between antibodies to beta2-glycoprotein-I and oxidized low-density lipoprotein in patients with antiphospholipid syndrome.

Previous studies have shown a cross-reaction between anticardiolipin and anti-oxidized low-density lipoprotein (LDL) antibodies in patients with the antiphospholipid syndrome (APS). The aim was to investigate the existence of a cross-reaction between anti-beta2-glycoprotein-I (beta2-GP-I) and anti-oxidized LDL antibodies in a group of APS patients. Ninety-three patients with APS were included in the study; 47 of these patients were diagnosed as primary APS, while the rest (46 patients) fulfilled criteria for the classification of systemic lupus erythematosus (SLE). All patients were positive for the IgG isotype of anticardiolipin antibodies (aCL). Twelve (26%) SLE-associated APS and 14 (29.7%) primary APS patients had raised concentrations of IgG antibodies to oxidized LDL. There was no correlation between anti-beta2-GP-I and anti-oxidized LDL antibodies. Inhibition experiments showed no cross-reaction either between anti-beta2-GP-I and anti-oxidized LDL antibodies, or between anti-beta2-GP-I and anti-native LDL antibodies. Our study suggests that the presence of both anti-beta2-GP-I and anti-oxidized LDL antibodies in patients with APS is not due to the structural similarity and consequent cross-reaction, and that they are two different populations of antibodies directed against different antigens.

Adolescent↗
PubMed1998

Arterial disease in lupus and secondary antiphospholipid syndrome: association with anti-beta2-glycoprotein I antibodies but not with antibodies against oxidized low-density lipoprotein.

The prevalence and clinical significance of antibodies against beta2-glycoprotein I (anti-beta2GPI) and antibodies against oxidized low-density lipoprotein (anti-ox-LDL) were evaluated as potential indicators of arterial disease in patients with systemic lupus erythematosus (SLE) and SLE with secondary antiphospholipid syndrome (APS). IgG anti-beta2GPI and IgG anti-ox-LDL were measured by enzyme-linked immunosorbent assay (ELISA) in serum samples from 118 patients with SLE, including 40 with secondary APS. IgG anti-beta2GPI were positive in 17% (20/118) of SLE patients. The presence and titres of IgG anti-beta2GPI were strongly associated with a history of arterial thrombosis. Haemolytic anaemia was also significantly associated with the presence of IgG anti-beta2GPI. The prevalence of IgG anti-ox-LDL was 53% (63/118), but there was no association with arterial thrombosis. No correlation between the values of anti-ox-LDL and those of anti-beta2GPI was found. These results suggest that IgG anti-beta2GPI could be a marker for arterial thrombosis in SLE patients, while IgG anti-ox-LDL were not associated with arterial disease in this group of lupus patients.

Adolescent↗
PubMed1998

Therapeutic advances in systemic lupus erythematosus.

In treating systemic lupus erythematosus, clinicians need to consider not only the organ involvement and the complications of therapy, but also associated conditions such as premature atherosclerosis and thrombosis. A variety of agents are now available to treat cutaneous disease, including the antimalarials and thalidomide. Controversy exists about the most appropriate immunosuppressive regimen in severe disease. Experience with using cyclosporine, mycophenolate mofetil, dehydroepiandrosterone, and intravenous immunoglobulin is increasing, but plasmapheresis has not been shown to be of benefit. Autologous bone marrow transplantation has been performed. The advent of the biological era, particularly with monoclonal antibodies, gives promise of more targeted therapy.

Arteriosclerosis↗
PubMed1998

Beta2-glycoprotein I as a 'cofactor' for anti-phospholipid reactivity with endothelial cells.

Beta2-glycoprotein I (beta2GPI) is a cofactor for anti-phospholipid (aPL) binding to cardiolipin (CL)-coated plates. Beta2GPI is also able to bind to endothelial cell (EC) membranes as supported by in-vivo as well as by in-vitro studies. The PL-binding site in the fifth domain of the molecule is involved in the adhesion to endothelium. Actually, specific mutations in this molecular portion abolish endothelium binding and a synthetic peptide spanning the sequence Glu274-Cys288 of the CL-binding site displays comparable adhesion to EC monolayers. Heparan sulphate appears to be one of the anionic EC membrane structures with which cationic beta2GPI interacts, as supported by studies with heparitinase-treated EC. Beta2GPI binding to EC might be related to its activity as endothelial growth factor or as a lipid-carrying glycoprotein. Adhesion of beta2GPI to endothelial membranes offers suitable epitopes for circulating aPL that, once bound, can induce cell activation

Amino Acid Substitution↗
PubMed1998

Management of thrombosis and pregnancy loss in the antiphospholipid syndrome.

More than a decade has gone by since the detailed clinical description of the Antiphospholipid (Hughes) Syndrome. Because of the wide spectrum of manifestations, virtually any physician may encounter patients with this potentially treatable condition. Because of limited controlled, prospective data, current therapy remains empirical and directed at coagulation mechanisms, immune mechanisms, or both. There is now good evidence that patients with antiphospholipid-associated thrombosis will be subject to recurrences and require prophylactic therapy. Although most authorities agree about the efficacy of warfarin alone or warfarin plus low-dose aspirin in preventing recurrences of venous and arterial thrombosis, there is still doubt regarding the intensity and duration of warfarin therapy. Steroids and immunosuppressive drugs have not provided long-term benefit. Controlled clinical trials of the treatment of pregnant women with antiphospholipid antibody demonstrated that prednisolone is ineffective, and possibly detrimental, in treatment of recurrent pregnancy loss and that heparin plus low-dose aspirin is beneficial.

Abortion, Habitual↗
PubMed1998

Outcome of patients with anticardiolipin antibodies: a 10 year follow-up of 52 patients.

We report a 10-year follow-up on 52 patients with raised levels of anticardiolipin antibodies (aCL) who were first seen at our tertiary referral centre in 1986. The clinical and serological features of these 52 patients are described. Thirty-one patients had the antiphospholipid syndrome (APS) in 1986. Nine of these patients (29%) had further thrombotic events during the follow-up period. Of the other 21 aCL positive patients without clinical manifestations of APS, 11 (52%) developed the syndrome over this period. Five patients (10%) died during the follow-up. Close monitoring of patients with connective tissue diseases and aCL is essential as the likelihood of developing antiphospholipid syndrome is high.

Adolescent↗
PubMed1998

Elevated plasma lipoprotein(a) level and its association with impaired fibrinolysis in patients with antiphospholipid syndrome.

OBJECTIVE: To assess the significance of lipoprotein(a) [Lp(a)], a risk factor for atherothrombosis, and its relationship with fibrinolysis in a cohort of patients with antiphospholipid syndrome (APS). METHODS: Plasma levels of Lp(a) were measured in 68 patients with APS (42 primary, 26 secondary to systemic lupus erythematosus). RESULTS: Elevated plasma levels of Lp(a) were found in patients with APS compared to 22 healthy controls (p = 0.0001). The significance persisted after comparing Lp(a) levels in 3 APS subgroups (arterial thrombosis, n = 37; venous thrombosis, n = 31; recurrent miscarriages, n = 24) with those of controls (p < 0.0001). Patients with APS with maximal elevation of Lp(a) showed a lower fibrinolytic activity (lower D-dimer and higher plasminogen activator inhibitor) than patients whose Lp(a) was within a normal range. CONCLUSION: These findings suggest that Lp(a) may represent a marker of APS and that Lp(a) has a negative effect on the fibrinolytic system that might contribute to the thrombotic tendency of APS.

Adult↗