Radiographic contrast media-induced tubular injury: evaluation of oxidant stress and plasma membrane integrity.
BACKGROUND
Experimental and clinical investigations suggest that oxidant stress is a critical determinant of radiocontrast nephropathy (RCN), and that N acetyl cysteine (NAC) can prevent this damage. This study addresses these issues directly at the tubular cell level. Potential alternative mechanisms for RCN have also been sought.


METHODS
Isolated mouse proximal tubule segments (PTS), or cultured proximal tubule (HK-2) cells, were subjected to radiocontrast media (RCM) (Ioversol, Optiray 320) exposure, followed by assessments of cellular viability [% lactate dehydrogenase (LDH) release, tetrazolium dye (MTT), uptake] and lipid peroxidation. These experiments were conducted in the absence or presence of a variety of antioxidants [NAC, glutathione (GSH), superoxide dismutase, catalase] or pro-oxidant (GSH depletion, heme oxygenase inhibition) strategies. RCM effects on mitochondrial and plasma membrane integrity were also assessed.


RESULTS
RCM exposure did not induce PTS lipid peroxidation. Neither antioxidant nor pro-oxidant interventions mitigated or exacerbated RCM-induced tubular cell injury, respectively. RCM impaired mitochondrial integrity, as assessed by ouabain-resistant ATP reductions, and by cytochrome c release (before cell death). RCM also induced plasma membrane damage, as indicated by loss of key resident proteins (NaK-ATPase, caveolin) and by increased susceptibility to phospholipase A2 (PLA2) attack (increase of >/=2 times in free fatty acid and NaK-ATPase release). Hyperosmolality could not account for RCM's toxic effects.


CONCLUSIONS
RCM toxicity can be dissociated from tubular cell oxidant stress. Alternative mechanisms may include mitochondrial injury/cytochrome c release and plasma membrane damage. The latter results in critical protein loss, as well as a marked increase in plasma membrane susceptibility to exogenous/endogenous PLA2 attack.
Zager
Richard A
RA
The Fred Hutchinson Cancer Research Center, Seattle, Washington, USA. dzager@fhcrc.org
Johnson
Ali C M
AC
Hanson
Sherry Y
SY
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D051242:Caveolin 1; D022461:Caveolins / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane; D003287:Contrast Media / Q000494:pharmacology; D045304:Cytochromes c / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007674:Kidney Diseases / Q000139:chemically induced* / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism*; D015227:Lipid Peroxidation / Q000187:drug effects; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D008928:Mitochondria / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D018384:Oxidative Stress; D010741:Phospholipases A / Q000494:pharmacology; D054467:Phospholipases A2; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D014283:Triiodobenzoic Acids / Q000494:pharmacology
C495540:CAV1 protein, human; C495541:Cav1 protein, mouse; D051242:Caveolin 1; D022461:Caveolins; D003287:Contrast Media; D014283:Triiodobenzoic Acids; D010042:Ouabain; D000255:Adenosine Triphosphate; D045304:Cytochromes c; D010741:Phospholipases A; D054467:Phospholipases A2; D000254:Sodium-Potassium-Exchanging ATPase; C054871:ioversol