Electrothermal atomic absorption spectrometric diagnosis of familial hypercholesterolemia

We have developed a new nonradioactive assay to identify human low-density lipoprotein receptor defects. It is based on the incubation of cultured cel ls with colloidal gold-LDL conjugates and quantitation of the gold associat ed with the cells by electrothermal atomic absorption spectrometry, After a n oxidative treatment with nitric and hydrochloric acids, the biological ma trix interferes neither with the gold recovery nor with the gold measuremen ts, which are linear, at least from 0.15 to 3 ng of gold. When cells expres sing a functional LDL receptor are incubated with increasing amounts of col loidal-gold LDL conjugates, the obtained saturation curve parallels that de scribed when [I-125]LDL is used as ligand, Moreover, this new assay allows us to clearly distinguish among fibroblasts from normal subjects or from he terozygous or homozygous patients of familial hypercholesterolemia, a very common autosomal disease. The assay is easy to perform, is sensitive, and a voids the use of radioactive compounds. Therefore, it could be successfully employed in the clinical diagnosis of this disease. Furthermore, since the methodology developed here can be applied to quantify the association of o ther gold-conjugated ligands to cells, it could have a widespread use in a variety of clinical and basic research studies.