Lipopolysaccharide is transferred from high-density to low-density lipoproteins by lipopolysaccharide-binding protein and phospholipid transfer protein.

Lipopolysaccharide (LPS), the major outer membrane component of gram-negative bacteria, is a potent endotoxin that triggers cytokine-mediated systemic inflammatory responses in the host. Plasma lipoproteins are capable of LPS sequestration, thereby attenuating the host response to infection, but ensuing dyslipidemia severely compromises this host defense mechanism. We have recently reported that Escherichia coli J5 and Re595 LPS chemotypes that contain relatively short O-antigen polysaccharide side chains are efficiently redistributed from high-density lipoproteins (HDL) to other lipoprotein subclasses in normal human whole blood (ex vivo). In this study, we examined the role of the acute-phase proteins LPS-binding protein (LBP) and phospholipid transfer protein (PLTP) in this process. By the use of isolated HDL containing fluorescent J5 LPS, the redistribution of endotoxin among the major lipoprotein subclasses in a model system was determined by gel permeation chromatography. The kinetics of LPS and lipid particle interactions were determined by using Biacore analysis. LBP and PLTP were found to transfer LPS from HDL predominantly to low-density lipoproteins (LDL), in a time- and dose-dependent manner, to induce remodeling of HDL into two subpopulations as a consequence of the LPS transfer and to enhance the steady-state association of LDL with HDL in a dose-dependent fashion. The presence of LPS on HDL further enhanced LBP-dependent interactions of LDL with HDL and increased the stability of the HDL-LDL complexes. We postulate that HDL remodeling induced by LBP- and PLTP-mediated LPS transfer may contribute to the plasma lipoprotein dyslipidemia characteristic of the acute-phase response to infection.

Effects on coagulation of levonorgestrel- and desogestrel-containing low dose oral contraceptives: a cross-over study.

Combined oral contraceptives (OC) are known to increase the risk of venous thromboembolism. The aim of this randomized, cycle-controlled, cross-over study in 28 healthy volunteers was to assess potential differences between the effects of an OC containing 150 microg levonorgestrel (as representative of the so-called second generation OC) and an OC containing 150 microg desogestrel (as representative of the third generation OC) in combination with 30 microg ethinylestradiol on several coagulation factors and markers of thrombin formation. All participants used each OC for two cycles, and were switched to the other OC after a washout period of two menstrual cycles. The plasma concentrations of factors II, VII, X, and fibrinogen significantly increased during use of both the levonorgestrel- and desogestrel-containing OC's. The plasma concentrations of factor VIII increased, and of factor V decreased, changes which only reached statistical significance during the use of the desogestrel-containing OC. During exposure to the desogestrel-containing OC, as compared with the levonorgestrel-containing OC, both factor VII and factor II showed a greater increase (FVII: 32% and 12% respectively; p <0.0001; FII: 16% and 12% respectively; p = 0.048), whereas factor V showed a greater decrease (-11% and -3% respectively; p = 0.010). Only one of the markers for ongoing coagulation (prothrombin fragment 1+2) showed a significant increase during OC use, whereas concentrations of thrombin-antithrombin complexes and soluble fibrin remained unchanged. For these markers, there was no difference between the tested OC's. We conclude that there are differences between the effects of levonorgestrel and desogestrel-containing OC's on some coagulation factors. Whether these changes provide a biological explanation for the reported differences in venous thromboembolic risk is as yet unclear. The real challenge now becomes to define a pattern of changes in the various systems which, if affected simultaneously, may tip the hemostatic balance towards a prethrombotic state and may lead to overt clinical venous thromboembolism.

Increased fibrinolytic activity during use of oral contraceptives is counteracted by an enhanced factor XI-independent down regulation of fibrinolysis: a randomized cross-over study of two low-dose oral contraceptives.

The effect of oral contraceptives (OC) on fibrinolytic parameters was investigated in a cycle-controlled cross-over study in which 28 non-OC using women were randomly prescribed either a representative of the so-called second (30 microg ethinylestradiol, 150 microg levonorgestrel) or third generation OC (30 microg ethinylestradiol, 150 microg desogestrel) and who switched OC after a two month wash out period. During the use of OC, the levels of tissue-type plasminogen activator (tPA) activity, plasminogen, plasmin-alpha2-antiplasmin complexes and D-dimer significantly increased (by 30 to 80%), while the levels of plasminogen activator inhibitor- (PAI-1) antigen, PAI-1 activity and tPA antigen significantly decreased (25 to 50%), suggesting an increase in endogenous fibrinolytic activity. These OC-induced changes were not different between the two contraceptive pills. TAFI (thrombin-activatable fibrinolysis inhibitor) levels increased on levonorgestrel, and even further increased on desogestrel. A clot lysis assay that probes both fibrinolytic activity and the efficacy of the coagulation system to generate thrombin necessary to down regulate fibrinolysis via TAFI showed no change of the clot lysis time during OC use. This finding suggests that the OC-induced increase in endogenous fibrinolytic activity is counteracted by an increased capacity of the coagulation system to down regulate fibrinolysis via TAFI. Indeed we observed that during OC use there was a significant increase of F1+2 generation during clot formation. When these assays were performed in the presence of an antibody against factor XI, we observed that the clot lysis time was significantly increased during OC use and that the increase in F1+2 generation during OC therapy was due to a factor XI-independent process, which was significantly higher on desogestrel than on levonorgestrel. These data indicate that the OC-induced inhibition of endogenous fibrinolysis takes place in a factor XI-independent way and is more pronounced on desogestrel than on levonorgestrel-containing OC.

Lipoprotein[a] is not present in the plasma of patients with some peroxisomal disorders.

Peroxisomal disorders arise either from defects in the biogenesis of peroxisomes or from the defective synthesis of one or more peroxisomal enzymes. These defects result in metabolic disturbances in peroxisomal beta-oxidation of various fatty acids and derivatives and/or in the biosynthesis of ether lipids. In the current study, lipoprotein levels were determined in plasma samples from patients diagnosed with one of four different peroxisomal disorders. While low density lipoprotein (LDL) levels were found to be within the normal range, lipoprotein[a] (Lp[a]) could not be detected by enzyme-linked immunosorbent assay (ELISA) in plasma from patients with cerebro-hepato-renal (Zellweger) syndrome (ZS) and rhizomelic chondrodysplasia punctata (RCDP). Conversely, Lp[a] was clearly present in control plasma obtained from healthy newborns and from patients affected with one of two other peroxisomal disorders, X-linked adrenoleukodystrophy (X-ALD) and Refsum disease (RD) as determined by ELISA. The lack of Lp[a] in plasma of patients with ZS may result from defective secretion of apolipoprotein[a] (apo[a]) (the distinguishing protein component of Lp[a]), as apo[a] mRNA transcripts were clearly present in ZS livers as assessed by PCR, and intracellular apo[a] protein was detected in total liver homogenates from ZS patients as determined by Western blot analysis. Furthermore, LDL present in the plasma of ZS patients was able to associate with recombinant apo[a] in an in vitro Lp[a] assembly assay.

A compound heterozygote for lipoprotein lipase deficiency, Val69-->Leu and Gly188-->Glu: correlation between in vitro LPL activity and clinical expression.

We analyzed the molecular defects in the lipoprotein lipase gene of a patient with type I hyperlipidemia suffering from recurrent pancreatitis, indicative for lipoprotein lipase deficiency. Postheparin lipoprotein lipase activity in the patient was decreased by 70%. Direct genomic sequencing revealed compound heterozygosity for two mutation: the well-known Gly188-->Glu and a new Val69-->Leu substitution. Val69 is situated in a conserved hydrophobic region of the lipoprotein lipase protein, and the substitution with leucine gives rise to a 80% decrease in specific catalytic activity, as supported by site-directed mutagenesis experiments, followed by expression in COS-cells. The combination of both defects in the lipoprotein lipase gene was incidentally associated with severe clinical expression of disease, and triglyceride levels of more than 30 mmol/l were measured. In our patient, triglyceride levels wer usually below 10 mmol/l. We, therefore, postulate that the residual LPL activity in our patient is usually sufficient to keep the triglyceride level within bounds and expression of disease occurred only when conditions such as alcohol abuse or poor compliance to diet were present.