Aims: Apolipoprotein A-I (ApoA-I), the major apolipoprotein of the high density lipoprotein (HDL), plays key roles in the removal of cholesterol excess from peripheral cells, in a recognized anti-atherosclerotic process called “reverse cholesterol transport” (RTC)a. In detail, it stimulates cholesterol (C) efflux and ApoE secretion from macrophages, and enhances Lecithin-Cholesterol Acyl-Transferase (LCAT) activity. The acute phase protein Haptoglobin (Hpt) was found to inhibit RCT, as binding ApoA-I and preventing its stimulation on LCAT. This study aimed to find out whether Hpt influences essential ApoA-I stimulated mechanisms in RCT, such as cholesterol efflux, LCAT activity, and ApoE secretion from macrophages. Methods: Monocytes were isolated from human buffy coats, and kept for 6 days in culture for differentiation into macrophages. After treatment with ³H-C for 24 h, the cells were incubated with ApoA-I (0.04 mg/mL), or ApoA-I plus increasing Hpt amounts (0.1-0.75 mg/mL). After 16 h of incubation, homologous plasma was added as LCAT source. After further incubation for 16 h, supernatants were aliquoted from culture medium to measure their radioactivity content, representing the released C. Supernatant lipids were extracted and separated by TLC to measure the LCAT activity as conversion of unesterified ³H-C into C esters. Other macrophages, not treated with ³H-C, were incubated with ApoA-I (20 µg/mL), or ApoA-I plus Hpt (200 µg/mL). The supernatants of these cultures were collected after 16 h, and analyzed by western blotting to detect the amount of secreted ApoE. Results: Addition of Hpt to macrophages significantly (P<0.01) inhibited, with dose-dependent effect, the ApoA-I stimulation of C efflux (down to 27% of the control value, i.e. without Hpt), LCAT activity (down to 50% of the control value), and secretion of ApoE. Conclusions: Macrophages play a key role in atherosclerosis onset and progression, as they differentiate to foam cell triggering the formation of lipid streaks and ateromatose plaques, when RCT is defective. Increase in Hpt concentration, as occurring during inflammatory process, might impair the efficiency of both cholesterol efflux and LCAT activity. Moreover, our results also suggest that Hpt might impair macrophage secretion of the anti-atherosclerotic protein ApoE. Therefore high levels of Hpt might contribute to adverse cardiovascular events. a Fielding C et al., (1995) J. Lipid Res 36: 211-228.

Haptoglobin Influences ApoA-I Activities in Reverse Cholesterol Transport / C. R., Pugliese; Cigliano, Luisa; E., Santoro; A., Dalessio; E., Picardi; B., Maresca; A., Salvatore; A., Carlucci; Abrescia, Paolo. - STAMPA. - (2008), pp. 2.13-2.13. (Intervento presentato al convegno 53rd National Meeting of the Italian Society of Biochemistry and Molecular Biology tenutosi a Riccione, Italy nel 23-26 September 2008).

Haptoglobin Influences ApoA-I Activities in Reverse Cholesterol Transport.

CIGLIANO, LUISA;ABRESCIA, PAOLO
2008

Abstract

Aims: Apolipoprotein A-I (ApoA-I), the major apolipoprotein of the high density lipoprotein (HDL), plays key roles in the removal of cholesterol excess from peripheral cells, in a recognized anti-atherosclerotic process called “reverse cholesterol transport” (RTC)a. In detail, it stimulates cholesterol (C) efflux and ApoE secretion from macrophages, and enhances Lecithin-Cholesterol Acyl-Transferase (LCAT) activity. The acute phase protein Haptoglobin (Hpt) was found to inhibit RCT, as binding ApoA-I and preventing its stimulation on LCAT. This study aimed to find out whether Hpt influences essential ApoA-I stimulated mechanisms in RCT, such as cholesterol efflux, LCAT activity, and ApoE secretion from macrophages. Methods: Monocytes were isolated from human buffy coats, and kept for 6 days in culture for differentiation into macrophages. After treatment with ³H-C for 24 h, the cells were incubated with ApoA-I (0.04 mg/mL), or ApoA-I plus increasing Hpt amounts (0.1-0.75 mg/mL). After 16 h of incubation, homologous plasma was added as LCAT source. After further incubation for 16 h, supernatants were aliquoted from culture medium to measure their radioactivity content, representing the released C. Supernatant lipids were extracted and separated by TLC to measure the LCAT activity as conversion of unesterified ³H-C into C esters. Other macrophages, not treated with ³H-C, were incubated with ApoA-I (20 µg/mL), or ApoA-I plus Hpt (200 µg/mL). The supernatants of these cultures were collected after 16 h, and analyzed by western blotting to detect the amount of secreted ApoE. Results: Addition of Hpt to macrophages significantly (P<0.01) inhibited, with dose-dependent effect, the ApoA-I stimulation of C efflux (down to 27% of the control value, i.e. without Hpt), LCAT activity (down to 50% of the control value), and secretion of ApoE. Conclusions: Macrophages play a key role in atherosclerosis onset and progression, as they differentiate to foam cell triggering the formation of lipid streaks and ateromatose plaques, when RCT is defective. Increase in Hpt concentration, as occurring during inflammatory process, might impair the efficiency of both cholesterol efflux and LCAT activity. Moreover, our results also suggest that Hpt might impair macrophage secretion of the anti-atherosclerotic protein ApoE. Therefore high levels of Hpt might contribute to adverse cardiovascular events. a Fielding C et al., (1995) J. Lipid Res 36: 211-228.
2008
Haptoglobin Influences ApoA-I Activities in Reverse Cholesterol Transport / C. R., Pugliese; Cigliano, Luisa; E., Santoro; A., Dalessio; E., Picardi; B., Maresca; A., Salvatore; A., Carlucci; Abrescia, Paolo. - STAMPA. - (2008), pp. 2.13-2.13. (Intervento presentato al convegno 53rd National Meeting of the Italian Society of Biochemistry and Molecular Biology tenutosi a Riccione, Italy nel 23-26 September 2008).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/368169
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