Comparison of the inhibitory effects of ApoB100 and tissue factor pathway inhibitor on tissue factor and the influence of lipoprotein oxidation

Alterations in the lipid profile associate with a dysregulated inflammatory, prothrombotic, anti-fibrinolytic state and development of severe acute kidney injury in coronavirus disease 2019 (COVID-19): A study from Cincinnati, USA

BACKGROUND AND AIMS

Reduction of atherogenic lipoproteins is often the ultimate goal of nutritional interventions, however this is complicated given that hypolipidemia is frequently observed in coronavirus disease 2019 (COVID-19) patients. We aimed to explore the association of hypolipidemia with patient outcomes in terms of immunothrombosis and multiorgan injury, focusing on specialized apolipoproteins apo A1 and apo B.

METHODS

Lipid profiles of 50 COVID-19 patients and 30 sick controls presenting to the Emergency Department (ED) were measured in this prospective observational study. The primary outcome was development of severe acute kidney injury (AKI). Need for hospitalization and ICU admission were secondary outcomes. Lipoproteins were analyzed for independent association with serum creatinine (SCr) increase ratio and correlated with a wide panel of biomarkers.

RESULTS

COVID-19 cohort had significantly lower apo A1 (p = 0.006), and higher apo B/apo A1 ratio (p = 0.041). Patients developing severe AKI had significantly lower LDL-C (p = 0.021). Apo B/apo A1 was associated with 2.25-fold decrease in serum SCr increase ratio, while LDL-C with a 1.5% decrease. Hypolipidemia correlated with low plasminogen, ADAMTS13 activity/VWF:Ag, and high inflammatory biomarkers (CRP, IL-6, IL-8, IL-10), plasminogen activator inhibitor-1 (PAI-1), ED creatinine, and SCr increase ratio.

CONCLUSION

Although favored in dietetics, findings of a low LDL-C in COVID-19 patients should be alarming in light of our observations. Low apo B/apo A1 ratio and LDL-C are predictive of renal deterioration in COVID-19 patients, and low LDL-C in particular may potentially serve to indicate COVID-19 related AKI driven by disrupted fibrinolysis and a secondary thrombotic microangiopathy-like process.

Identification of Receptor Ligands in Apo B100 Reveals Potential Functional Domains

LDL, VLDL and other members of the low-density lipoparticles (LLPs) enter cells through a large family of receptors. The actual receptor ligand(s) in apolipoprotein B100, one of the main proteins of LLP, remain(s) unknown. The objective of this study was to identify true receptor ligand(s) in apo B100, a molecule of 4563 residues. Apo B100 contains 33 analogues of Cardin-Weintraub arginine/lysine-based receptor ligand motifs and shares key lysine motifs and sequence similarity with the LDL receptor-associated protein, MESD, and heat shock proteins. Eleven FITC-labeled synthetic peptides of 21-42 residues, with at least one ligand, were tested for binding and internalization using HeLa cells. All peptides bind but display different binding capacities and patterns. Peptides B0013, B0582, B2366, and B2932 mediate endocytosis and appear in distinct sites in the cytoplasm. B0708 and B3181 bind and remain on the cell surface as aggregates/clusters. Peptides B3119 (Site A) and B3347 (Site B), the putative ligands, showed low binding and no cell entry capacity. Apo B100 regions in this study share similarities with related proteins of known function including chaperone proteins and Apo BEC stimulating protein, and not directly related proteins, e.g., the DNA-binding domain of interferon regulatory factors, MSX2-interacting protein, and snake venom Zinc metalloproteinase-disintegrin-like proteins.

Lipid levels and risk of venous thrombosis: results from the MEGA-study

The relationship between lipid levels and risk of venous thrombosis is not well established. We aimed to assess the association between several lipids and risk of venous thrombosis using data from a population-based case-control study, and to evaluate the underlying mechanism, considering confounding by common risk factors and mediation via hemostatic factors and C-reactive protein. From the Multiple Environmental and Genetic Assessment of risk factors for venous thrombosis (MEGA) study, 2234 patients with a first venous thrombosis and 2873 controls were included. Percentile categories of total/low-density lipoprotein/high-density lipoprotein cholesterol, triglycerides, and apolipoproteins B and A1 were established in controls (<10th, 10th-25th, 25th-75th [reference], 75th-90th, >90th percentile). In age- and sex-adjusted models, decreasing levels of apolipoproteins B and A1 were dose-dependently associated with increased thrombosis risk, with odds ratios of 1.35 (95% confidence interval 1.12-1.62) and 1.50 (95% confidence interval 1.25-1.79) for the lowest category versus the reference category, respectively. The dose-response relation remained with further adjustment for body mass index, estrogen use, statin use, and diabetes. Although apolipoproteins B and A1 were associated with several hemostatic factors and C-reactive protein, none explained the increased risk in mediation analyses. The other lipids were not associated with venous thrombosis risk. In conclusion, decreasing levels of apolipoproteins B and A1 were associated with increased risk of venous thrombosis. Our findings are consistent with experimental data on the anticoagulant properties of apolipoproteins B and A1. These findings need to be confirmed and the underlying mechanism further investigated.

The Influence of Exogenous Tissue Factor on the Regulators of Proliferation and Apoptosis in Endothelial Cells

BACKGROUND

The exposure of tissue factor (TF) at the site of injury or trauma is a rapid process that leads to the initiation of blood coagulation as well as homeostatic processes giving rise to vascular repair.

AIMS AND METHODS

By exposing human endothelial cells to combinations of exogenous TF and factor VIIa (FVIIa) in serum-free medium, the influence of TF concentrations on cellular proliferation and apoptosis was investigated.

RESULTS

Lower concentrations of TF resulted in increased cellular proliferation as well as upregulation of cyclin D1, downregulation of p21 and p27 and induction of tube formation in vitro. Conversely, incubation with higher concentrations of TF resulted in the activation of caspase-3, expression of p53 and Bax, translocation of p53 into the nucleus and induction of DNA fragmentation. Incubation of the cells with TF/FVIIa led to a lower proliferation rate with additional upregulation in p27.

CONCLUSIONS

TF seems to have a bifunctional role in determining the fate of endothelial cells, depending on the concentration and the interactions of this protein. The release of TF in the locality of the injured tissue makes this protein an ideal factor for ascertaining the level of injury and determining the fate of the cells.

The relationship of TFPI, Lp(a), and oxidized LDL antibody levels in patients with coronary artery disease

OBJECTIVES

The aim of the present study was to determine and correlate tissue factor pathway inhibitor (TFPI), lipoprotein (a) (Lp(a)), oxidized low-density lipoprotein (LDL) antibody (oLAB), and thiobarbituric acid reactive substances (TBARS; as a marker of lipid peroxidation) levels in patients with coronary artery disease (CAD) and in a control group.

DESIGN AND METHODS

Peripheral blood samples from patients with coronary heart disease were provided by the Department of Cardiology. Serum oLAB, Lp(a), plasma total TFPI, and plasma-free TFPI levels were determined by ELISA. Serum TBARS levels were determined by a spectrophotometric method using thiobarbituric acid.

RESULTS

The CAD and the control group were matched for age and sex. Serum Lp(a), oLAB, and plasma total TFPI levels in patients with coronary heart disease were found to be significantly higher than in the control group (P < 0.001). But there was no difference in plasma-free TFPI levels between patients with CAD and the control group (P > 0.05). In patients with single (P < 0.05), double, and triple vessel (P < 0.01) disease, the mean serum Lp(a) levels were significantly higher than in the control group. On the other hand, in patients with single vessel disease (P < 0.05), double vessel disease (P < 0.05), and triple vessel disease (P < 0.001), plasma total TFPI levels were found to be significantly higher than in the control group. We also found a significant positive correlation (r = 0.28, P < 0.05) between serum Lp(a) and plasma total TFPI levels in CAD. In the patient group, TBARS, total cholesterol, triglyceride (TRG), and LDL cholesterol levels were found to be significantly higher than those in the control group. In addition, high-density lipoprotein (HDL) cholesterol levels were found to be significantly lower than the control group.

CONCLUSIONS

These results suggest that elevated plasma levels of total TFPI, Lp(a), and oLAB may be useful diagnostic and monitoring markers in patients with CAD.

Inhibition of Plasma Coagulation through Interaction between Oxidized Low-Density Lipoprotein and Blood Coagulation Factor VIII

Oxidatively modified low-density lipoprotein (OxLDL) is present in atherosclerotic lesions and has been proposed to play an important role in atherogenesis. Thrombosis is the major mechanism underlying acute complications of atherosclerosis. In the present study, we analyzed the interaction between OxLDL and blood coagulation factors, which are involved in the blood coagulation pathway. We investigated the effect of OxLDL on plasma coagulation by measuring prothrombin time (PT) as a parameter of the extrinsic pathway of blood coagulation and activated partial thromboplastin time (APTT) as a parameter of the intrinsic pathway of blood coagulation following the addition of OxLDL to plasma. OxLDL, but not native LDL, caused prolongation of APTT in a dose- and oxidation time-dependent manner. In addition, the oxidatively modified product of acetylated LDL (AcLDL), but not AcLDL, also caused prolongation of APTT. The inhibition of lysophosphatidylcholine production in OxLDL by phenylmethylsulfonyl fluoride or Pefabloc pretreatment of LDL resulted in a prolongation of APTT, which was equivalent to the effect of OxLDL. Moreover, OxLDL significantly inhibited blood coagulation factor VIII, IX, and XI activity. Furthermore, we demonstrated that recombinant factor VIII binds to OxLDL and that factor VIII associated with OxLDL is detected in the incubation mixture of OxLDL and plasma. These results indicate that the binding of factor VIII to OxLDL affects the intrinsic pathway of the blood coagulation cascade. The present study suggests that the interaction between OxLDL and factor VIII may provide important information on the initiation and progression of atherosclerosis.

The state of macrophage differentiation determines the TNF alpha response to nitrated lipoprotein uptake

Inflammatory cytokine synthesis by monocyte-macrophages in the developing plaque represents an important amplification point in atherosclerotic disease progression. Here we have investigated whether the state of monocyte-macrophage differentiation can influence TNF alpha synthesis in response to scavenged modified low-density lipoprotein (LDL). We show that LDL modified by nitration induces TNF alpha synthesis when added to undifferentiated human monocytes or a mouse cell line (RAW264.7) bearing an incompletely differentiated phenotype. However, significantly reduced levels of TNF alpha were released from in vitro differentiated human macrophages (P=0.006) or a mouse cell line (IC-21) bearing a well-differentiated macrophage phenotype (P<0.001). A possible scavenging insufficiency in macrophagic cell types was ruled out by lipoprotein-uptake studies and competency to synthesise TNF alpha was confirmed using lipopolysaccharide (LPS) as a stimulus. However, LPS-induced TNF alpha secretion in IC-21 cells was partially suppressed by pre-treatment with nitrated LDL (46%, P=0.0076), with no equivalent effect seen in RAW264.7 cells. Based on these data, we hypothesise that the state of differentiation of intimal monocyte-macrophages may play an important role in their inflammatory response to scavenged modified lipoproteins and that the fully differentiated macrophage end-point may be associated with a non-inflammatory and therefore, atheroprotective, phenotype.

Modified phosphatidylethanolamine as the active component of oxidized low density lipoprotein promoting platelet prothrombinase activity

We analyzed the influence of the atherogenic oxidized low density lipoproteins (LDL) on the activity of the platelet prothrombinase complex, a major contributor to overall thrombin formation in vivo. Platelet dependent thrombin generation was found to be strongly stimulated by in vitro oxidized LDL. The enhancement was additive to that observed with the platelet agonist thrombin. Oxidized LDL increased the platelet binding of annexin-V, suggesting that the augmented surface exposure of aminophospholipids promoted the prothrombinase activity. All of the stimulatory activity of the oxidized LDL could be recovered in the microemulsions prepared from the lipid portion of the modified particles. Phospholipid vesicles were prepared containing the total lipids of the oxidized LDL but lacking specifically in one lipid component. Following the selective removal of the ethanolamine phospholipids (PE) from the LDL lipids, the platelet-dependent thrombin formation was markedly reduced. Vesicles enriched with the isolated PE fraction alone enhanced the thrombin generation. Analyses with autoxidized phospholipids indicated that oxidation products of unsaturated diacyl-PE were mainly responsible for the increased prothrombinase activity. Oxidized LDL and its PE fraction lost their stimulatory activity after treatment with NaCNBH(3), a chemical reductant of Schiff base adducts. Phospholipid vesicles supplemented with synthetic aldehyde-PE adducts largely reproduced the stimulation of the thrombin generation. We conclude that the oxidized LDL particles elicit a pronounced prothrombotic response by increasing the activity of the platelet prothrombinase complex. Specific oxidative modifications of the LDL-associated ethanolamine phospholipids are mainly responsible for this stimulation.

III. Instantaneous inhibition by compound 48/80 of tissue factor-initiated extrinsic coagulation is mediated by the downregulation of factor VII activation

Our previous study has demonstrated a unique biological function of compound 48/80 (48/80) in the downregulation of monocytic tissue factor (TF)-initiated hypercoagulation in response to bacterial endotoxin (lipopolysaccharide, LPS) [A. J. Chu et al. (1999) Biochim. Biophys. Acta 1472, 386-395]. The inhibition was not due to the blockade of LPS cell signaling as evidenced by the unaffected LPS-induced TF synthesis. In the present study, we investigate the direct inhibitory action of 48/80 on the extrinsic coagulation cascade. TF-initiated coagulation was assayed by a single-stage clotting assay. Chromogenic assays dissected the extrinsic pathway to measure the activities of FVII, FX, and prothrombin by monitoring the hydrolyses of nitroaniline-conjugated substrates, identifying the inhibitory site(s). We report that 48/80 in vitro instantaneously inhibited rabbit brain thromboplastin (rbTF)-initiated coagulation in a dose-dependent manner. 48/80 preferentially inhibited FVII activation without any detectable effect on FVIIa, FXa, and thrombin activities. Neither FX activation nor prothrombin activation was affected. The significant inhibition on FVII activation was found to be noncompetitive with a fourfold reduction in the apparent Vmax of FVIIa formation from 7.1 to 1.7 nM/min, while the apparent Km (approximately 365 nM) remained unaffected. Western blotting analysis further confirmed that FVIIa formation derived from FVII was significantly diminished by 48/80, which was accompanied by blocked FVII binding to rbTF. In conclusion, 48/80 readily blocked FVII binding to rbTF, leading to diminished FVII activation and FVIIa formation. As a result, TF-initiated extrinsic coagulation was downregulated.

The role of the C-terminal domain in the inhibitory functions of tissue factor pathway inhibitor

Tissue factor pathway inhibitor (TFPI) inhibits the activity of coagulation factors VIIa and Xa through Kunitz domains, thereby inhibiting the activity of tissue factor. However, it has been shown that the C-terminal of this inhibitor is essential for the maximal anticoagulant activity of TFPI. We have investigated the endogenous ability of the C-terminal of TFPI to influence coagulation. A synthetic peptide corresponding to residues 254-265 within the C-terminal of TFPI was prepared and shown to be capable of inhibiting tissue factor pathway by preventing the activation of factor VII. Mutational analysis of the peptide revealed the identity of the key lysine residues.