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Native and modified low-density-lipoprotein interaction with human platelets in normal and homozygous familial-hypercholesterolaemic subjects.

ABSTRACT: The binding of low-density lipoproteins (LDL) as well as LDL modified by cyclohexanedione (CHD-LDL) to gel-filtered platelets (GFP) and its effect on platelet function were studied in normal and in homozygous familial hypercholesterolaemic (HFH) subjects. Only normal-derived LDL could significantly compete with normal 125I-labelled LDL for binding to normal platelets. When GFP from normal subjects were incubated with normal LDL at concentrations of 25-200 micrograms of protein/ml, platelet aggregation in the presence of thrombin (0.5 i.u./ml) was increased by 65-186%. CHD-LDL, at similar concentrations, caused the opposite effect and decreased platelet aggregation by 26-47%. Both LDL and CHD-LDL (100 micrograms/ml) from HFH patients, when incubated with normal GFP, caused a significant reduction in platelet aggregation (33 and 50% respectively). When HFH-derived platelets were used, both patient LDL and CHD-LDL (but not the normal lipoprotein) could markedly compete with the patient 125I-labelled LDL for binding to the platelets. LDL and CHD-LDL (100 micrograms/ml) from normal subjects decreased aggregation of HFH-platelets by 52 and 85% respectively, while corresponding concentrations of LDL derived from HFH subjects (HFH-LDL) and CHD-LDL derived from HFH subjects (CHD-HFH-LDL) increased platelet aggregation by 165 and 65% respectively. The present results support the following conclusions: platelet activation by LDL in normal subjects is through the arginine-rich apoprotein-binding site; more than one binding site for LDL exists on platelets; under certain circumstances, LDL binding can cause a reduction in platelet activity; specificity for LDL binding to the platelets resides in different regions of the lipoprotein in HFH and in normal subjects. We have thus suggested a model for LDL-platelet interaction in normal and in HFH subjects.

SUBMITTER: Shmulewitz A

PROVIDER: S-EPMC1144392 | biostudies-other | 1984 Nov

REPOSITORIES: biostudies-other

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Project description:OBJECTIVE:Evolocumab, a PCSK9 (proprotein convertase subtilisin kexin type 9)-neutralizing antibody, lowers low-density lipoprotein cholesterol (LDL-C) in homozygous familial hypercholesterolemic (HoFH) patients with reduced LDLR (low-density lipoprotein receptor) function. However, their individual responses are highly variable, even among carriers of identical LDLR genetic defects. We aimed to elucidate why HoFH patients variably respond to PCSK9 inhibition. APPROACH AND RESULTS:Lymphocytes were isolated from 22 HoFH patients enrolled in the TAUSSIG trial (Trial Assessing Long Term Use of PCSK9 Inhibition in Subjects With Genetic LDL Disorders). Ten patients were true homozygotes (FH1/FH1) and 5 identical compound heterozygotes (FH1/FH2). Lymphocytes were plated with or without mevastatin, recombinant PCSK9 (rPCSK9), or a PCSK9-neutralizing antibody. Cell surface LDLR expression was analyzed by flow cytometry. All HoFH lymphocytes had reduced cell surface LDLR expression compared with non-FH lymphocytes, for each treatment modality. Lymphocytes from FH1/FH2 patients (LDLR defective/negative) displayed the lowest LDLR expression levels followed by lymphocytes from FH1/FH1 patients (defective/defective). Mevastatin increased, whereas rPCSK9 reduced LDLR expression. The PCSK9-neutralizing antibody restored LDLR expression. Lymphocytes displaying higher LDLR expression levels were those isolated from patients presenting with lowest levels of LDL-C and apolipoprotein B, before and after 24 weeks of evolocumab treatment. These negative correlations remained significant in FH1/FH1 patients and appeared more pronounced when patients with apolipoprotein E3/E3 genotypes were analyzed separately. Significant positive correlations were found between the levels of LDLR expression and the percentage reduction in LDL-C on evolocumab treatment. CONCLUSIONS:Residual LDLR expression in HoFH is a major determinant of LDL-C levels and seems to drive their individual response to evolocumab.

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Native and modified low-density-lipoprotein interaction with human platelets in normal and homozygous familial-hypercholesterolaemic subjects.

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