Phenotype of haptoglobin and presence of subclinical vascular disease: Population study

Haptoglobin is a protein involved in the protection against oxidative damage caused by iron in haemoglobin. This protein is polymorphic, with 3 isomorphs prevalent in the population. The carriers of the Hp2-2 isoform have a lower antioxidant capacity and, in the population with diabetes, an increased risk of subclinical vascular disease and cardiovascular complications. The objective of this study was to evaluate whether this isomorphy is associated with an increased risk of carotid arteriosclerosis in subjects with and without diabetes, and free of cardiovascular disease.

A study was conducted in a population between 45 and 74years of age, randomly selected from the northwest area of Madrid. The participants were characterised in terms of their glycaemic status by oral glucose overload and the determination of the concentration of Hb1Ac. The haptoglobin phenotypes in all of them were determined by means of an immunoenzymatic assay, and the presence of carotid arteriosclerosis by ultrasound.

Of the 1,256 participants included in the present analysis (mean age 61.6±6years, 41.8% males), the distribution of the isoforms of haptoglobin was as follows: Hp1-1: 13.3%, Hp1-2: 48.5%, and Hp2-2: 38.2%. In comparison with subjects Hp1-1 and Hp1-2, those with the Hp2-2 phenotype had a higher prevalence of dyslipidaemia (53.3% vs 43%; P<.0001) and arterial hypertension (39.2% vs. 32.2%, P=.012), and they more frequently received treatment with statins (31.5% vs 21.6%, P<.0001), and with antihypertensive agents (38.4% vs 30.8%, P=.006). The carriers of the Hp2-2 isoform had a higher prevalence of carotid plaques (OR: 1.35, 95%CI: 1.07-1.69, P=.011), with no differences in that prevalence as regards the glycaemic status. There were no differences in the intima-media thickness between the different phenotypes. The relationship of the Hp2-2 phenotype with the presence of plaques in the carotid was independent of age, gender, presence of risk factors (dyslipidaemia, hypertension and diabetes), the concentration of LDL-cholesterol, C-reactive protein and uric acid, blood pressure, and treatment with statins, and hypertensive drugs (OR: 1.31, 95%CI 1.01-1.70, P=.044).

Subjects with the Hp2-2 phenotype of haptoglobin have a higher prevalence of carotid arteriosclerosis, which is independent of the presence of other cardiovascular risk factors and their glycaemic status.