Serial measurement of plasma cholesterol and lecithin:cholesterol acyl transferase activity in adults receiving total parenteral nutrition.

The effect of total parenteral nutrition (TPN) containing approximately 800 ml Nutralipid daily on plasma cholesterol and lecithin:cholesterol acyl transferase (LCAT) activity was studied in 11 adult hospital patients. LCAT was assayed using an endogenous (S/N) and an artificial (ASA) substrate to differentiate between altered plasma substrate composition (which would influence the S/N method) and enzyme quantity (measured by the exogenous ASA method). Total cholesterol levels increased significantly during TPN, but generally remained within normal range. In comparison to laboratory reference values, free cholesterol was elevated and high-density lipoprotein cholesterol and ASA LCAT activity was reduced in patients before the start of TPN and remained unaltered by the TPN regime. S/N LCAT activity was normal and not altered by TPN. Since changes in plasma high-density lipoprotein and free cholesterol and ASA LCAT were present in patients before TPN, it must be concluded that they resulted from the underlying disease rather than the TPN per se. Longitudinal analyses showed that during the first 21 days of TPN nine patients showed a further fall in ASA LCAT and a rise in free cholesterol, thereafter ASA LCAT activity rose and free cholesterol fell despite continuation of TPN. It is suggested that ASA is a more reliable indicator of cholesterol esterification than S/N and that change in LCAT activity, although not caused by TPN, was related to the altered plasma lipid profile in the patients studied.