Hemostatic variables in homozygous familial hypercholesterolemia. Effect of regular plasma cholesterol removal by low density lipoprotein apheresis

Treatment with PCSK9 Inhibitors in Patients with Familial Hypercholesterolemia Lowers Plasma Levels of Platelet-Activating Factor and Its Precursors: A Combined Metabolomic and Lipidomic Approach

INTRODUCTION

Familial hypercholesterolemia (FH) is characterized by extremely high levels of circulating low-density lipoprotein cholesterol (LDL-C) and is caused by mutations of genes involved in LDL-C metabolism, including LDL receptor (LDLR), apolipoprotein B (APOB), or proprotein convertase subtilisin/Kexin type 9 (PCSK9). Accordingly, PCSK9 inhibitors (PCSK9i) are effective in LDL-C reduction. However, no data are available on the pleiotropic effect of PCSK9i. To this end, we performed an untargeted metabolomics approach to gather a global view on changes in metabolic pathways in patients receiving treatment with PCSK9i.

METHODS

Twenty-five FH patients starting treatment with PCSK-9i were evaluated by an untargeted metabolomics approach at baseline (before PCSK9i treatment) and after 12 weeks of treatment.

RESULTS

All the 25 FH subjects enrolled were on maximal tolerated lipid-lowering therapy prior to study entry. After a 12 week treatment with PCSK9i, we observed an expected significant reduction in LDL-cholesterol levels (from 201.0 ± 69.5 mg/dL to 103.0 ± 58.0 mg/dL, p < 0.001). The LDL-C target was achieved in 36% of patients. After peak validation and correction, after 12 weeks of PCSK9i treatment as compared to baseline, we observed increments in creatine (p-value = 0.041), indole (p-value = 0.045), and indoleacrylic acid (p-value= 0.045) concentrations. Conversely, significant decreases in choline (p-value = 0.045) and phosphatidylcholine (p-value < 0.01) together with a reduction in platelet activating factor (p-value = 0.041) were observed.

CONCLUSIONS

Taking advantage of untargeted metabolomics, we first provided evidence of concomitant reductions in inflammation and platelet activation metabolites in FH patients receiving a 12 week treatment with PCSK9i.

Inflammatory and thrombotic processes are associated with vascular dysfunction in children with familial hypercholesterolemia

BACKGROUND

Evidence suggests that children with familial hypercholesterolemia (FH) have endothelial dysfunction. Inflammatory and haemostatic abnormalities are associated with advanced atherosclerosis and increased cardiovascular events. However, it is unknown whether these abnormalities present in FH children and contribute to their vascular dysfunction.

METHODS AND RESULTS

We studied 38 children with FH (19 males, 19 females aged 14.8+/-0.9 years mean+/-S.E.) and 41 healthy children (controls; 22 males, 19 females aged 15.4+/-0.7 years). Endothelium-dependent reactive hyperemia (RH%) and endothelium-independent nitrate hyperemia dilatation (NH%) were measured by strain gauge plethysmography. Inflammatory and haemostatic parameters were assessed by ELISA. RH% and NH% were significantly reduced in FH compared to controls (91.3+/-9.3% vs. 120.4+/-10.6% and 53.6+/-3.8% vs. 74.5+/-7.4%, p<0.05 for both). Total cholesterol and lipoprotein (a) were increased in FH children compared to controls (282.3+/-8.8 mg/dl vs. 163.8+/-4.6 mg/dl and 11.0[4.6, 30.7]mg/dl vs. 5.24[2.63, 11.0]mg/dl median [IQR] respectively; p<0.001 for both). Intercellular cell adhesion molecule (ICAM-1) and interleukin 1 beta (IL-1 beta) serum levels were increased in FH compared to controls (p<0.05 and <0.001, respectively). Plasminogen activator inhibitor 1 (PAI-1) levels were also higher in FH children (p<0.001). Multivariate analysis revealed that reactive hyperemia was independently associated with nitrate-dependent reactive hyperemia (beta=0.597(0.199), p<0.01), PAI-1(beta=-6.78(2.65), p<0.05), log IL-1 beta (beta=-102.8 (30.2), p<0.01), age (beta=-5.06 (2.35), p<0.05) and FH status (beta=-25.2(10.6), p<0.05) (R(2) for the model: 0.63, p=0.001).

CONCLUSIONS

Inflammatory and haemostatic abnormalities are present in FH children and contribute to the endothelial dysfunction observed in these children.

Occurrence of the same peroxidative compounds in low density lipoprotein and in atherosclerotic lesions from a homozygous familial hypercholesterolemic patient: a case report

Oxidative modification of low density lipoprotein (LDL) and its byproducts may play a fundamental role in atherosclerosis. We report an in vitro analysis of LDL peroxidative compounds in an homozygous familial hypercholesterolemic (HFH) patient who subsequently died. During the autopsy, we analyzed lipids extracted directly from different atherosclerotic plaques, and we also provided an immunocytochemical analysis using the specific monoclonal antibody MDA2 (directed against malondialdeyde-lysine epitopes of oxidized LDL). The results showed that the same species of peroxidative compounds were present both in LDL in vitro and in lipids extracted directly from atherosclerotic lesions. Moreover, the immunocytochemistry analysis revealed a positive staining of atherosclerotic plaques, confirming the presence of LDL oxidation-specific epitopes. Although observation of a single case is necessarily limited, our findings are consistent with the hypothesis that oxidative modification of LDL is involved in human atherogenesis.

Decreased low-density lipoprotein oxidation after repeated selective apheresis in homozygous familial hypercholesterolemia

Familial hypercholesterolemia was the first genetic disorder recognized to cause myocardial infarction. Patients with homozygous familial hypercholesterolemia have rapidly progressive coronary atherosclerosis with angina pectoris, myocardial infarction, or sudden death at a young age. Selective apheresis on dextran sulfate cellulose columns reduces mortality and may induce regression of coronary lesions. These patients have both increased levels and prolonged circulation residence time of low-density lipoprotein (LDL), which is not removed by cellular receptor. LDL oxidation may play a pivotal role in atherogenesis. LDL undergoes oxidation before being taken up by macrophages and then transformed into arterial wall foam cells. The aim of this study was to investigate LDL oxidation in eight homozygous patients with familial hypercholesterolemia during repeated LDL apheresis. LDL lipid peroxidation, estimated by conjugated-diene absorbance at 234 nm, lipid peroxides, and malondialdehyde showed an increased resistance against oxidation after repeated LDL apheresis. This phenomenon was also observed in the oxidative indexes of protein moiety of LDL (apolipoprotein-B100 fragmentation, trinitrobenzenesulfonic acid reactivity, and electrophoresis agarose mobility). Similarly, cholesteryl esterification was decreased after LDL apheresis. Thus selective LDL apheresis not only decreases the pool of LDL, but it also induces changes that render LDL less susceptible to oxidation. This phenomenon might contribute to reduce coronary atherosclerosis and thus mortality of these particular patients.

Platelet Activation in Hypercholesterolemic Patients Submitted to Therapeutic Plasmapheresis. An Ultrastructural Study

Therapeutic plasmapheresis has been recommended as the choice therapy in patients with familial hypercholesterolemia. Little is known about the effect of plasmapheresis on platelet behavior. By means of electron microscopy we have studied the platelet plasma membrane of 4 patients with familial hypercholesterolemia who were submitted to repeated plasmaphereses. After each procedure of plasmapheresis, at the 15th day, morphometrical studies revealed a statistically significant increase in the surface density of the Open Canalicular System, which is considered a marker of platelet activation. However, during 12 months of plasmapheresis, a significant mean decrease in the morphometric parameters was observed. On one hand, these results indicate the necessity to consider the blood hemocoagulatory state in the patient who has been submitted to the above mentioned treatment, since the variation of these parameters after the therapeutic procedure, in a short time, could be potentially harmful to the patient; on the other hand, these results indicate, for the first time, the ability of the procedure to improve platelet behavior after repeated treatments on long term basis.

Abnormally high circulation levels of tissue plasminogen activator and plasminogen activator inhibitor-1 in patients with a history of ischemic stroke

We evaluated 106 subjects with and 109 subjects without a history of ischemic stroke. All were attending a metabolic ward. The two groups were compared for major risk factors for ischemic events. A positive family history for ischemic complications of atherosclerosis was more common in subjects with a history of stroke than in those without; moreover, plasma levels of plasminogen activator inhibitor-1 (PAI-1) and tissue-type plasminogen activator (TPA) were higher in patients with documented previous events. A strong positive significant correlation was found between TPA and PAI-1 levels, and an interaction between age and TPA was observed when the sample was stratified according to ages being above or below 70 years. When the patient population was analyzed according to the number of ischemic events, it was found that 62 of the 106 subjects with a history of stroke had experienced more than one ischemic event. Under these conditions, the levels of TPA and PAI-1 still correlated with the occurrence of previous ischemic episodes. As in the whole patient sample, TPA was the strongest discriminator. We conclude that in subjects attending a metabolic ward, TPA and PAI-1 levels consistently help identify subjects with a history of cerebral ischemic episodes and that TPA is the strongest discriminator.

Effects of selective LDL-apheresis and pravastatin therapy on platelet function in familial hypercholesterolaemia

Platelet function was studied in 10 patients with familial hypercholesterolaemia, following lipid-lowering treatment with selective LDL-apheresis and with the HMG-CoA reductase inhibitor pravastatin. Platelet function was assessed before, and 2, 5 and 14 days after LDL-apheresis, and before and after 4 weeks of pravastatin therapy. Both treatments significantly reduced total- and LDL-cholesterol, whereas LDL-apheresis also reduced VLDL-cholesterol. Lp(a)-levels were reduced by LDL-apheresis and elevated by pravastatin treatment. Pravastatin therapy significantly enhanced platelet aggregability in vivo, as measured by ex vivo filtragometry. Plasma serotonin levels also increased. Other markers of in vivo activation of platelets, i.e. beta-thromboglobulin in plasma and urine, and 11-dehydro-thromboxane B2 in urine were unaltered. Adenosine diphosphate-induced platelet aggregation in vitro remained unchanged during pravastatin therapy, and the platelet volume distribution was not affected. LDL-apheresis reduced the mean platelet volume, as well as the percentage of large platelets, whereas the percentage of small platelets increased. Other measures of platelet function in vivo or in vitro were, however, unaltered following LDL-apheresis. Thus, pravastatin therapy enhances certain aspects of platelet aggregability in vivo, whereas a single treatment with selective LDL-apheresis does not consistently affect platelet aggregability during resting conditions. These results do not support the concept that reduction of LDL-cholesterol improves platelet function in hypercholesterolaemic patients, at least not in the short-term. However, the reduction of platelet volume after LDL-apheresis may be beneficial for patients receiving this therapy regularly.

Effects of LDL-apheresis on serum lipoprotein (a), C4b binding protein, protein C, protein S, and complement components

The short-term effects of low-density lipoprotein (LDL) apheresis using a dextran sulfate-cellulose (DSC) column equipped with a plasma separator using a polysulfone (PS) membrane filter on the serum total cholesterol, lipoprotein(a) (Lp(a)), C4b binding protein (C4bp), protein C and protein S and complement components levels were examined in a patient with familial hypercholesterolemia (heterozygote, type IIa). PS/DSC-LDL apheresis markedly lowered the total cholesterol by 69.9 +/- 2.9%, serum Lp(a) level by 80.2 +/- 3.4%, and C4bp by 81.1 +/- 2.5% after 8 apheresis sessions. All the above parameters gradually returned to the baseline levels within 10 days. The free protein S level was not significantly changed, while the C4bp/protein S complex level was markedly decreased relative to the decrease in C4bp. The protein C level was moderately reduced by 29%. Almost all serum complements and complement co-factors as well as C4bp were moderately to markedly decreased after LDL apheresis, but returned to the initial levels within a few days. PS/DSC-LDL apheresis effectively eliminated both serum LDL and Lp(a), and did not have an adverse effect on fibrinolysis or complement cascade in the blood.

The actions of lovastatin on platelet function and platelet eicosanoid receptors in type II hypercholesterolaemia. A double-blind, placebo-controlled, prospective study

We have studied the effects of 12 weeks of lovastatin (20 mg per day) on platelet function and thromboxane formation in 18 patients with type II hypercholesterolaemia in a double-blind, placebo-controlled, prospective study. Lovastatin significantly reduced total serum and LDL-cholesterol by 20% and 25% respectively. Washed platelets of lovastatin-treated patients had significantly reduced collagen-induced aggregation and thromboxane formation ex vivo. There was no change in ADP-induced platelet aggregation, but a significant increase in prostacyclin (iloprost)-stimulated platelet cyclic AMP concentrations in lovastatin-treated patients. This was associated with a significant increase in the number of prostacyclin receptors in platelet membranes prepared from lovastatin-treated patients. There was also an increase in platelet thromboxane receptors. There were no such changes in the placebo group. These data confirm our original observation of normalization of platelet function in hypercholesterolaemia by HMGCoA reductase inhibitors and suggest changes in platelet membrane composition at the megakaryocyte level as a possible site of action.

Different effects of two methods of low-density lipoprotein apheresis on the coagulation and fibrinolytic systems

OBJECTIVE

Immunoadsorption (IMA) and dextran sulfate adsorption (DSA) are two methods for selective extracorporeal elimination of low-density lipoproteins which are known as LDL apheresis. Their influence on haemostasis until now is widely unknown.

DESIGN

The effects of both LDL apheresis procedures on the coagulation and fibrinolytic systems were compared amongst five patients treated with IMA and four patients who received a DSA therapy.

SUBJECTS

All patients with severe heterozygous familial hypercholesterolaemia were participants in a long-term LDL apheresis programme with treatments every 1-2 weeks.

INTERVENTION

Combined anticoagulation with heparin and citrate in IMA, and also heparin exclusively in DSA were used for the extracorporeal circulation.

MEASURES

Blood samples were taken immediately before and after a single LDL apheresis and five times during the weekly interval until the next therapy.

RESULTS

DSA had a significantly greater effect on standard clotting tests than IMA at the end of plasma therapy despite identical dosages of heparin. DSA caused a considerable reduction of the coagulation factors V, VIII:C, vWF:Ag, XI, XII, and prekallikrein by 48-99% at the end of apheresis treatment whereas only factor VIII:C showed a marked decrease of 72% after IMA. All abnormalities of the global coagulation tests and of most clotting factors were restored 1 day after treatment in both procedures followed by a moderate rebound phenomenon of single coagulation factors during the next few days in IMA-treated patients.

CONCLUSION

DSA exerts a more profound effect on the coagulation system than IMA by a substantial co-elimination of various clotting factors in addition to the desired removal of atherogenic lipoproteins.

Abnormally high thromboxane biosynthesis in homozygous homocystinuria. Evidence for platelet involvement and probucol-sensitive mechanism

Homocystinuria due to homozygous cystathionine beta-synthase deficiency is an inborn error of metabolism characterized by a high incidence of thrombosis and premature atherosclerosis. We evaluated TXA2 biosynthesis in vivo and several in vitro tests of platelet function in 11 homocystinuric patients and 12 healthy controls. In vitro, patients' platelet aggregation was within control values as were TXB2 formation, fibrinogen binding, and ATP secretion in response to thrombin. In contrast, the urinary excretion of 11-dehydro-TXB2, a major enzymatic derivative of TXA2, was > 2 SD of controls in all patients (1,724 +/- 828 pg/mg creatinine, mean +/- SD, in patients vs. 345 +/- 136 in controls, P < 0.001). The administration to four patients of low-dose aspirin (50 mg/d for 1 wk) reduced metabolite excretion by > 80%. The recovery of 11-dehydro-TXB2 excretion over the 10 d that followed aspirin cessation occurred with a pattern consistent with the entry into the circulation of platelets with intact cyclooxygenase activity. Prolonged partial reduction in the abnormally high excretion of both 11-dehydro-TXB2 and 2,3-dinor-TXB2, was also observed in seven patients who ingested 500 mg daily for 3 wk of the antioxidant drug probucol. These results provide evidence for enhanced thromboxane biosynthesis in homocystinuria and for its partial dependence on probucol-sensitive mechanisms. Furthermore, the elevated TXA2 formation in homocystinuria is likely to reflect, at least in part, in vivo platelet activation.

Functionally abnormal monocytes in hypercholesterolemia

We investigated some functions of monocytes from 20 type IIa hypercholesterolemic (HC) and five homozygous familial hypercholesterolemic (FH) patients. Monocytes from the HC patients contained as much cholesterol and formed as much thromboxane B2 in response to N-formyl-methionyl-leucyl-phenylalanine (fMLP) or calcium ionophore A23187 as those from normal individuals. In contrast, the generation of prostaglandin E2 and 6-ketoprostaglandin F1 alpha in response to these agonists was 1.5-3 times normal, and that of leukotriene B4 was 40-60% of the normal value (p < 0.05 for all). Studies in which the combination of fMLP or A23187 with sodium arachidonate were employed suggested that these abnormalities were independent of the availability of the endogenous substrate for the lipoxygenase or cyclooxygenase enzymes. Quantitatively and qualitatively comparable abnormalities were found in monocytes from the five FH patients, and these were little affected when the patients' plasma cholesterol levels were almost normalized by low density lipoprotein apheresis. In keeping with the abnormalities in the eicosanoid metabolism, monocytes from HC patients exhibited a defective ability (p < 0.05) to generate O2-, the extent of which was correlated with the impaired formation of leukotriene B4. On the other hand, adhesion studies indicated that patients' cells exhibited an abnormally high ability to adhere to glass (p < 0.01). These data indicate the presence of functionally abnormal monocytes in hypercholesterolemia and suggest a direction to be followed to understand the importance of such cells in the premature atherosclerosis that occurs in these patients.