A HYPERALPHALIPOPROTEINEMIC FAMILY WITH NORMAL CHOLESTERYL ESTER TRANSFER EXCHANGE ACTIVITY

Reports of two independent studies suggest that familial hyperalphalipoproteinaemia (FHALP) may be caused by a deficiency of cholesteryl ester transfer/exchange activity (CETP). We also have studied CETP in the plasma of an Italian FHALP kindred. The study group was divided into blood relatives with > 1.70 mM high-density-lipoprotein cholesterol (HDL-C) (group I, n = 9), with < 1.70 mM-HDL-C (group II, n = 12) and in spouses (group III, n = 6). Two different assays were performed to measure CETP activity. In method A the interfering endogenous lipoproteins in the plasma samples were removed by poly(ethylene glycol) precipitation or by ultracentrifugation at a relative density (d) of 1.180. The CETP-activity of these samples was measured in a system consisting of fixed amounts HDL and cholesteryl [1-14C]oleate-labelled low-density lipoproteins (LDL). In method B, trace amounts of HDL (radiolabelled with cholesteryl [1-14C]oleate) were incubated with plasma for 3 h at 37.degree. C and the distribution of the label among lipoproteins was measured (CET activity). The results can be summarized as follows. The mean CETP activities measured by method A were 187, 213 and 243 nmol/h per ml in groups I, II and III respectively. The proband with the highest HDL-C (4.98 mM) had a CETP activity of 231 nmol/h per ml. The corresponding CET activities measured by method B and expressed as percentage transfer/h were 4.3, 8.0 and 11.2 in groups I-III. The proband with HDL-C = 4.98 mM had a value of only 1.7%/h. There was a strong negative correlation between percentage CE transfer and HDL-C concentration. Calculating these data in terms of CE exchange (nmol/h per ml), groups I, II and III exhibited mean activities of 86, 124 and 110 nmol/h per ml respectively; for the proband this value was 80 nmol/h per ml. Only a slight correlation was found between these values and the HDL-C value. Thus by both methods, (A), measuring the CETP activity per se and (B), measuring the activity in whole plasma (reflecting the activity of the protein and the concentration and composition of lipoproteins), no major differences could be found between the three groups. In our family, therefore, no connection between FHALP and CETP deficiency could be found. It is concluded that, for hyper- and dys-lipoproteinaemic samples, a careful selection of the assay procedure as well as the mode of calculating results is essential. Since this may not hold the previous studies, the supposed connection between FHALP and CETP deficiency is challenged.