P glycoprotein-mediated cholesterol cycling determines proximal tubular cell viability.
BACKGROUND
MDR P glycoproteins may help transport plasma membrane free cholesterol (FC) to the endoplasmic reticulum (ER), where it undergoes acylation, forming cholesterol esters (CE). This study assessed whether P glycoprotein inhibitors alter renal tubular FC/CE expression, thereby altering cell integrity.


METHODS
Mouse proximal tubule segments (PTS) were exposed to chemically dissimilar P glycoprotein inhibitors [progesterone (prog), trifluoperazine (TFP), or cyclosporine A (CsA)]. Their effects on FC/CE and adenosine 5'-triphosphate (ATP) levels, phospholipid expression, lipid peroxidation, and cell viability (lactate dehydrogenase release; LDH) were assessed. P glycoprotein inhibitor effects on cultured proximal tubular (HK-2) cell viability and susceptibility to Fe-induced oxidant stress were also addressed.


RESULTS
When applied to PTS, prog, TFP, and, to lesser extent, CsA induced dose-dependent ATP reductions (< or =90%), CE decrements (approximately 40%), and LDH release (< or =60%). No concomitant changes in lipid peroxidation or phospholipid profiles were observed. Ouabain did not preserve tubular ATP, suggesting that decreased ATP production, rather than increased consumption, was operative. Mechanisms leading to cell lysis were not identical, as glycine and arachidonic acid blocked prog- but not TFP-mediated cell death. When prog-driven CE reductions were attenuated in PTS with a procycling agent (cholesterol oxidase), decreased cell death resulted. P glycoprotein inhibitors also caused dose-dependent HK-2 cell death. Blocking Fe-mediated CE formation ( approximately x10) with sublethal CsA doses led to a marked increase in Fe-mediated cell death.


CONCLUSIONS
P glycoproteins may be critical to tubule cholesterol transport. If blocked with pharmacologic agents, decreased ATP production, overt cell lysis, and/or a marked propensity to superimposed tubular cell injury can result.
Zager
R A
RA
Department of Medicine, University of Washington, Seattle, Washington, USA. dzager@fhcrc.org
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002784:Cholesterol / Q000032:analysis / Q000378:metabolism*; D002788:Cholesterol Esters / Q000032:analysis; D016572:Cyclosporine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000502:physiology*; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D051379:Mice; D011374:Progesterone / Q000494:pharmacology; D014268:Trifluoperazine / Q000494:pharmacology
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D002788:Cholesterol Esters; D014268:Trifluoperazine; D011374:Progesterone; D016572:Cyclosporine; D000255:Adenosine Triphosphate; D002784:Cholesterol; D007770:L-Lactate Dehydrogenase