Metabolic effects of fatty acid-bearing albumin on a proximal tubule cell line

In glomerular disease, fatty acids carried on albumin are taken up by the proximal tubule with filtered albumin. We postulate that the fatty acids carried on filtered albumin could contribute to the deleterious effects of proteinuria. The effects of fatty acid-albumin complexes on lipid metabolism have been studied in opossum kidney (OK) cells, a proximal tubule cell line. OK cells transported two-thirds of [¹⁴C]palmitate-albumin (5 mg/ ml) intracellularly within 16 h. [¹⁴C]palmitate-albumin was distributed into phosphatidylcholines, phosphatidylinositols, and tri- and diglycerides. ¹⁴C-labeled unsaturated fatty acid albumins (oleate, linoleate, and arachidonate) showed preferential incorporation into triglycerides, with lesser incorporation into phospholipids. Studies of total lipid pools showed that fatty acid-albumin uptake produced a particularly marked increase in total triglyceride levels (∼ 10-fold). Oil red O staining of OK cells cultured with oleate-albumin showed a marked increase in intracellular lipid droplets, compared with cells cultured with delipidated albumin, consistent with triglyceride accumulation. Less than 1% of [¹⁴C]palmitate taken up was isolated as intracellular free fatty acid. Less than 5% of [¹⁴C]palmitate internalized was oxidized to ¹⁴CO₂. Different fatty acids, when taken up by the OK cell, have distinct metabolic fates. Each fatty acid is incorporated in a characteristic fashion into certain complex lipids, possibly dependent on the presence or absence of double bonds. We propose that this may have functional consequences for the proximal tubule in the human nephrotic syndrome.