AIMS: Haptoglobin (Hpt) is a plasma acute phase glycoprotein produced mainly in the liver, but also synthesized in extrahepatic tissues including skin. The main function of circulating Hpt is to bind free haemoglobin (Hb) for scavenging iron, and Apolipoprotein A1 (ApoA1) for regulating the cholesterol reverse transport. The function of extrahepatic Hpt is not yet understood. Information on disease-associated isoforms of tissue-specific Hpt is available though poor. The aim of this work was to asses whether Hpt, in psoriasis, displays activity alteration which might be related to structure modification. METHODS: Two affinity chromatography steps, using resin-coupled Hb or anti-Hpt antibodies, were carried out to purify Hpt from human plasma. ELISA with Hb-coated wells was used to assay Hpt binding. After incubation of 0.05, 0.1, 0.2 or 0.3 μM Hpt, bound Hpt was detected by anti-Hpt antibodies. Assays of Lecithin-Cholesterol Acyl Transferase (LCAT) 1, the enzyme which esterifies cholesterol under ApoA1 stimulation, were carried out with Hpt purified from psoriatic patients or healthy subjects. RESULTS: Hpt from patients was found less efficient than control Hpt in Hb binding (30 to 60%). In particular, significant differences were found with 0.1, 0.2 or 0.3 μM Hpt (P<0.001). Hpt inhibited LCAT, as displacing ApoA1 from the enzyme. The LCAT inhibition was significantly lower when Hpt from patients was used (0.5 μM: 0 vs 20% for control Hpt, P<0.01; 2 μM: 40% vs 67% for control Hpt, P<0.01). This difference in the enzyme inhibition by Hpt suggests that this protein does not display the same structure in patients and controls. Hpt from patients might bind ApoA1 less efficiently than normal Hpt, thus allowing higher stimulation of LCAT activity. DISCUSSION: Here we provide evidence that plasma, in psoriasis, contains Hpt forms which are different from those circulating in normal condition. The disease-associated forms might have oxidative damage or carbohydrate modification, which might affect the peptide domain or the glycan code involved in the interaction with Hb and Apo1. 1.Chen CH et al., (1982) J Lipid Res. 23, 680-691.

Activity of haptoglobin from psoriatic patients.

CIGLIANO, LUISA;MONFRECOLA, GIUSEPPE;AYALA, FABIO;ABRESCIA, PAOLO
2007

Abstract

AIMS: Haptoglobin (Hpt) is a plasma acute phase glycoprotein produced mainly in the liver, but also synthesized in extrahepatic tissues including skin. The main function of circulating Hpt is to bind free haemoglobin (Hb) for scavenging iron, and Apolipoprotein A1 (ApoA1) for regulating the cholesterol reverse transport. The function of extrahepatic Hpt is not yet understood. Information on disease-associated isoforms of tissue-specific Hpt is available though poor. The aim of this work was to asses whether Hpt, in psoriasis, displays activity alteration which might be related to structure modification. METHODS: Two affinity chromatography steps, using resin-coupled Hb or anti-Hpt antibodies, were carried out to purify Hpt from human plasma. ELISA with Hb-coated wells was used to assay Hpt binding. After incubation of 0.05, 0.1, 0.2 or 0.3 μM Hpt, bound Hpt was detected by anti-Hpt antibodies. Assays of Lecithin-Cholesterol Acyl Transferase (LCAT) 1, the enzyme which esterifies cholesterol under ApoA1 stimulation, were carried out with Hpt purified from psoriatic patients or healthy subjects. RESULTS: Hpt from patients was found less efficient than control Hpt in Hb binding (30 to 60%). In particular, significant differences were found with 0.1, 0.2 or 0.3 μM Hpt (P<0.001). Hpt inhibited LCAT, as displacing ApoA1 from the enzyme. The LCAT inhibition was significantly lower when Hpt from patients was used (0.5 μM: 0 vs 20% for control Hpt, P<0.01; 2 μM: 40% vs 67% for control Hpt, P<0.01). This difference in the enzyme inhibition by Hpt suggests that this protein does not display the same structure in patients and controls. Hpt from patients might bind ApoA1 less efficiently than normal Hpt, thus allowing higher stimulation of LCAT activity. DISCUSSION: Here we provide evidence that plasma, in psoriasis, contains Hpt forms which are different from those circulating in normal condition. The disease-associated forms might have oxidative damage or carbohydrate modification, which might affect the peptide domain or the glycan code involved in the interaction with Hb and Apo1. 1.Chen CH et al., (1982) J Lipid Res. 23, 680-691.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/368164
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