maleic-acid and Ischemia

Maleate injection causes dose-dependent injury in proximal tubular cells. This study sought to better define underlying pathogenic mechanisms and to test whether maleate toxicity recapitulates critical components of the hypoxic/ischemic renal injury cascade. CD-1 mice were injected with maleate or used as a source for proximal tubule segments (PTS) for in vitro studies. Maleate induced dose-dependent PTS injury [lactate deydrogenase (LDH) release, ATP reductions, nonesterified fatty acid (NEFA) accumulation]. These changes were partially dependent on maleate metabolism (protection conferred by metabolic inhibitors: succinate, acetoacetate). Maleate toxicity reproduced critical characteristics of the hypoxia/ATP depletion-induced injury cascade: 1) glutathione (GSH) conferred protection, but due to its glycine, not cysteine (antioxidant), content; 2) ATP reductions reflected decreased production, not Na-K-ATPase-driven increased consumption; 3) cell death was completely blocked by extracellular acidosis (pH 6.6); 4) intracellular Ca(2+) chelation (BAPTA) mitigated cell death; 5) maleate and hypoxia each caused plasma membrane cholesterol shedding and in both instances, this was completely glycine suppressible; 6) maleate + hypoxia caused neither additive NEFA accumulation nor LDH release, implying shared pathogenic pathways; and 7) maleate, like ischemia, induced renal cortical cholesterol loading; increased HMG CoA reductase (HMGCR) activity (statin inhibitable), increased HMGCR mRNA levels, and increased RNA polymerase II recruitment to the HMGCR locus (chromatin immunoprecipitation, ChIP, assay) were involved. These results further define critical determinants of maleate nephrotoxicity and suggest that it can serve as a useful adjunct for studies of ischemia/ATP depletion-induced, proximal tubule-specific, cell death.

Topics: Acute Kidney Injury; Adenine Nucleotides; Adenosine Triphosphate; Animals; Apoptosis; Cell Hypoxia; Cholesterol; Disease Models, Animal; Dose-Response Relationship, Drug; Fatty Acids; Fatty Acids, Nonesterified; Hydroxymethylglutaryl CoA Reductases; Ischemia; Kidney Tubules, Proximal; L-Lactate Dehydrogenase; Male; Maleates; Mice; Mice, Inbred Strains; Succinates

The actin cytoskeleton of proximal tubule cells is important for both the maintenance of membrane domains and attachment to neighboring cells and underlying substrata. Adenosine triphosphate (ATP) depletion during ischemic injury causes early alterations in the actin cytoskeleton, resulting in loss of membrane domains and cellular attachment. We examined the actin cytoskeleton during recovery from ischemic injury. As shown previously in cell culture studies, ATP depletion to 14% of control values from in vivo ischemia resulted in decreases in G-actin consistent with net polymerization of the cytoskeleton. After 20 minutes of recovery restored ATP levels to 24% of control values, percent G-actin increased back to control values, yet cytoplasmic actin polymerized with little evidence of apical recovery. After 120 minutes of recovery, ATP levels had increased to 48% of control values with little qualitative or quantitative change in actin polymerization from 20 minutes of recovery. When ATP levels recovered to 65% of control values at 360 minutes after ischemia, movement of F-actin back toward the apical surface was observed. These data, along with prior data using maleic acid, suggest that thresholds of cellular ATP may cause differing effects on distinct cellular actin pools. We conclude that actin cytoskeletal recovery occurs very early and may be necessary for reestablishment of polarity essential for normal reabsorptive functions.

Topics: Absorption; Actins; Adenosine Monophosphate; Adenosine Triphosphate; Animals; Cell Adhesion; Cell Membrane; Cytoplasm; Cytoskeleton; Ischemia; Kidney; Kidney Tubules, Proximal; Male; Maleates; Rats; Rats, Sprague-Dawley; Reperfusion; Time Factors