A - Organic ARF
Renal Cortical Pyruvate Depletion during AKI
Richard A. Zager, Ali C.M. Johnson and Kirsten Becker
JASN May 2014 vol. 25 no. 5 : 998-1012
+ Author Affiliations
Fred Hutchinson Cancer Research Center, University of Washington, Seattle, Washington
Correspondence:
Dr. Richard A. Zager, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue N,
Room D2-190, Seattle, WA 98109. Email: dzager@fhcrc.org
ABSTRACT
Pyruvate is a key intermediary in energy metabolism and can exert antioxidant and antiinflammatory effects. However, the fate of pyruvate during AKI remains unknown. Here, we
assessed renal cortical pyruvate and its major determinants (glycolysis, gluconeogenesis,
pyruvate dehydrogenase [PDH], and H2O2 levels) in mice subjected to unilateral ischemia (15–
60 minutes; 0–18 hours of vascular reflow) or glycerol-induced ARF. The fate of postischemic
lactate, which can be converted back to pyruvate by lactate dehydrogenase, was also
addressed. Ischemia and glycerol each induced persistent pyruvate depletion. During ischemia,
decreasing pyruvate levels correlated with increasing lactate levels. During early reperfusion,
pyruvate levels remained depressed, but lactate levels fell below control levels, likely as a result
of rapid renal lactate efflux. During late reperfusion and glycerol-induced AKI, pyruvate
depletion corresponded with increased gluconeogenesis (pyruvate consumption). This finding
was underscored by observations that pyruvate injection increased renal cortical glucose
content in AKI but not normal kidneys. AKI decreased PDH levels, potentially limiting pyruvate
to acetyl CoA conversion. Notably, pyruvate therapy mitigated the severity of AKI. This
renoprotection corresponded with increases in cytoprotective heme oxygenase 1 and IL-10
mRNAs, selective reductions in proinflammatory mRNAs (e.g., MCP-1 and TNF-α), and
improved tissue ATP levels. Paradoxically, pyruvate increased cortical H2O2 levels. We
conclude that AKI induces a profound and persistent depletion of renal cortical pyruvate, which
may induce additional injury.
COMMENTS
A key point in the pathophysiology of Acute Kidney Insufficiency, demonstrated using ischemic
protocols, glycerol-induced protocol and using Pyruvate therapy in mice. Increasing evidence
indicates the diverse role that pyruvate can play as a potential modulator of tissue injury.
Pyruvate is classically viewed as a key determinant of cellular energy metabolism. Under
aerobic conditions, pyruvate, generated from glucose by glycolysis, undergoes decarboxylation
by the enzyme complex pyruvate dehydrogenase (PDH), forming acetyl CoA. Alternatively,
pyruvate can be carboxylated by pyruvate carboxylase, yielding oxaloacetate, with subsequent
acetyl CoA/oxaloacetate metabolism through the Krebs cycle and increased aerobic ATP
production results. Conversely, under anaerobic conditions, pyruvate is metabolized by lactate
dehydrogenase (LDH) to lactate, and in the process, NAD is generated, which is required for
additional glycolytic ATP production. In addition to its central role in supporting both aerobic and
anaerobic energy production, pyruvate may exert a variety of cytoprotective effects. Pyruvate is
a potent H2O2 scavenger, which was assessed in an in vitro system. Furthermore, pyruvate
administration decreased renal injury after intrarenal H2O2 injection and during the course of
the glycerol model of rhabdomyolysis-induced ARF. In addition to its antioxidant properties,
pyruvate may also exert anti-inflammatory and cytoprotective effects against experimental
ischemic-reperfusion injury and shock. The goals of this study were threefold: first, document
the influence of evolving ischemic and toxic AKI on pyruvate levels within renal cortex; second,
ascertain the metabolic pathways that ultimately alter pyruvate expression; third, further
elucidate the potential effects of pyruvate on the course and selected potential mediators of
experimental models of ARF. Finally, given that pyruvate administration can attenuate AKI, it
seems reasonable to postulate that pyruvate depletion as defined by this study is not merely a
benign consequence of ischemic or toxic renal injury; rather, it likely plays a significant
pathophysiologic role in their development.