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.