Haptoglobin from psoriatic patients exhibits decreased activity in binding haemoglobin and inhibiting lecithin‐cholesterol acyltransferase activity

Objective  The aim of this work was to assess whether psoriasis is associated with phenotype prevalence and altered activity of haptoglobin (Hpt). Background  Hpt is a plasma acute‐phase glycoprotein, displaying in humans three phenotypes. Phenotype prevalence or structure modification of Hpt was associated with several diseases. The Hpt main function is to bind and carry to the liver free haemoglobin for degradation and iron recycling. Hpt was recently found able to bind the apolipoprotein A‐I (ApoA‐I), thus impairing its stimulation on the activity of the enzyme lecithin‐cholesterol acyl‐transferase (LCAT). Study design  Hpt was isolated from patients with psoriasis vulgaris, and its activity in haemoglobin or ApoA‐I binding and LCAT inhibition was compared with that of normal protein. Methods  Two affinity chromatography steps, the first using resin‐coupled haemoglobin and the second anti‐Hpt antibodies, were used to purify Hpt. The protein phenotype was assessed by electrophoresis. Binding experiments were performed by Enzyme‐linked immunosorbent assay with stationary haemoglobin or ApoA‐I, Hpt in solution and anti‐Hpt antibodies for detection of bound Hpt. Standard LCAT assays were carried out in the presence of Hpt purified from patients or healthy subjects. Results  Phenotype prevalence of Hpt in psoriasis was not found. After affinity chromatography by haemoglobin, albumin and ApoA‐I were routinely found heavily contaminating only Hpt from normal subjects. Isolated Hpt from patients had lower activity than normal protein in both haemoglobin binding and LCAT inhibition. Conclusions  In psoriasis, Hpt displays some structure modification(s), which might be associated with the protein function in the disease.