Cholesterol ester accumulation: An immediate consequence of acute in vivo ischemic renal injury

Background. Cholesterol is a major constituent of plasma membranes, and rec ent evidence indicates that it is up-regulated during the maintenance phase of acute renal failure (ARF). However, cholesterol's fate and that of the cholesterol ester (CE) cycle [shuttling between free cholesterol (FC) and C Es] during the induction phase of ARF have not been well defined. The prese nt studies sought to provide initial insights into these issues. Methods. FC and CE were measured in mouse renal cortex after in vivo ischem ia (15 and 45 minutes)/reperfusion (0 to 120 minutes and glycerol-induced m yoglobinuria (1 to 2 hours). FC/CE were also measured in (1) cultured human proximal tubule (HK-2) cells three hours after ATP depletion and in (2) is olated mouse proximal tubule segments (PTSs) subjected to plasma membrane d amage (with cholesterol oxidase, sphingomyelinase, phospholipase A(2), or c ytoskeletal disruption with cytochalasin B). The impact of cholesterol synt hesis inhibition (with mevastatin) and FC traffic blockade (with progestero ne) on injury-evoked FC/CE changes was also assessed. Results. In vivo ischemia caused approximately threefold to fourfold CE ele vations. but not FC elevations. that persisted for at least two hours of re perfusion. Conversely, myoglobinuria had no effect. Isolated CE increments were observed in ATP-depleted HK-2 cells. Neither mevastatin nor progestero ne blocked this CE accumulation. Plasma membrane injury induced with sphing omyelinase or cholesterol oxidase, but not with phospholipase A(2) or cytoc halasin B, increased tubule CE content. High CE levels, induced with choles terol oxidase, partially blocked hypoxic PTS attack. Conclusions. In vivo ischemia/reperfusion acutely increases renal cortical CE, but not FC, content, indicating perturbed CE/FC cycling. The available data suggest that this could stem from specific types of plasma membrane da mage, which then increase FC flux via aberrant pathways to the endoplasmic reticulum, where CE formation occurs. That CE levels are known to inversely correlate with both renal and nonrenal cell injury suggests the potential relevance of these observations to the induction phase of ischemic ARF.