Combined effects of magnesium deficiency and an atherogenic level of low density lipoprotein on uptake and metabolism of low density lipoprotein by cultured human endothelial cells. I. Biochemical data.

The effects of magnesium deficiency on uptake and metabolism of low density lipoprotein (LDL) were investigated using human arterial endothelial cells cultured in media containing various concentrations of magnesium (100-1000 microM) and a high concentration of LDL (2 mg LDL cholesterol/ml) labelled with [3H]cholesteryl linoleate. The LDL uptake was time-dependent and increased for up to 8 h in both the magnesium-deficient and magnesium-sufficient treatments. The extent of LDL uptake progressively increased with the decrease in magnesium concentration of the medium. Surface-bound LDL also increased in a similar manner during the incubation but less extensively than the LDL uptake. The majority of radioactivity from internalized LDL was detected in unesterified cholesterol at all time points in both the magnesium deficiency and sufficiency groups. Only small amounts of radioactivity were found in cholesteryl esters. These findings indicate that most LDL taken up by the cells was rapidly hydrolysed but not readily re-esterified. The lack of re-esterification may be due to a relative deficiency of acyl-CoA:cholesterol acyltransferase (ACAT) and the presence of large amounts of unesterified cholesterol.