Succinate Ameliorates Energy Deficits and Prevents Dysfunction of Complex I in Injured Renal Proximal Tubular Cells

Abstract

We previously reported that mitochondrial function, intracellular ATP levels, and complex I activity are decreased in renal proximal tubular cells (RPTC) after oxidant (tert-butyl hydroperoxide; TBHP)-induced injury. This study examined the hypothesis that succinate supplementation decreases mitochondrial dysfunction, ameliorates energy deficits, and increases viability in TBHP-injured RPTC. Basal and uncoupled respirations in injured RPTC decreased 33 and 35%, respectively, but remained unchanged in injured RPTC supplemented with 10 mM succinate (electron donor to respiratory complex II). State 3 respiration supported by electron donors to complex I decreased 40% in injured RPTC but improved significantly by succinate supplements. The activity of mitochondrial complex I in TBHPinjured RPTC decreased 48%, whereas complex II activity remained unchanged. Succinate supplementation prevented decreases in complex I activity. ATP levels decreased 43% in injured RPTC but were maintained in injured cells supplemented with succinate. Lipid peroxidation increased 19-fold in injured RPTC but only 9-fold in injured cells supplemented with succinate. Exposure of primary cultures of RPTC to TBHP produced 24% cell injury and lysis but no apoptosis. In contrast, no cell lysis was found in RPTC supplemented with succinate. We conclude that mitochondrial dysfunction and energy deficits in oxidant-injured RPTC are ameliorated by succinate, and we propose that succinate supplementation may prove therapeutically valuable. Succinate 1) uses an alternate pathway of mitochondrial energy metabolism, 2) improves activity of complex I and oxidation of substrates through complex I, and 3) decreases oxidative stress and cell lysis in oxidant-injured RPTC.The major source of energy for metabolic processes and active transport in renal proximal tubular cells (RPTC) is oxidative metabolism, and ATP levels in RPTC are maintained almost entirely by oxidative phosphorylation. Therefore, decreases in ATP levels are the initiating factor in the development of both lethal and sublethal RPTC injury, and the degree of ATP decline determines the severity of injury (Bonventre and Weinberg, 2003). RPTC are the major target of ischemic and nephrotoxic injury within the kidney due to their dependence on oxidative phosphorylation and their limited capacity for generating ATP in glycolysis (Bagnasco et al., 1985;Bonventre and Weinberg, 2003). Ischemia and toxicants impair oxidative phosphorylation in RPTC both in vivo and in vitro and result in ATP depletion, leading to the loss of ion homeostasis, opening of the glycine-sensitive plasma membrane death channels/pores, and necrotic cell death (Miller et al., 1994;Dong et al., 1998;Chen et al., 2001;Bonventre and Weinberg, 2003).Structural and functional alterations of mitochondria are important pathogenic factors underlying injury induced by ischemia, hypoxia, and toxicants in many cell types, including RPTC

Cell-permeable succinate prodrugs rescue mitochondrial respiration in cellular models of acute acetaminophen overdose

“…Supplementation of an alternative energy source that liver cells can utilize despite the inhibitory effect of APAP on CI-linked metabolism could potentially allow them to maintain the required level of energy production and thus, rescue already injured liver cells. Succinate treatment has previously demonstrated by others to improve bioenergetics and reduce cell death in vitro in models of traumatic brain injury, metformin-induced and oxidant-induced mitochondrial dysfunction [24][25][26], thus, further supporting this hypothesis. The cell-permeable succinate prodrug presented in this study is the lead candidate of the first generation of an extensive rational drug design program focused around Krebs cycle intermediates for treatment of mitochondrial dysfunction and related disorders.…”

Protein kinase Cε targets respiratory chain and mitochondrial membrane potential but not F0F1‐ATPase in renal cells injured by oxidant

“…LDH activity was determined spectrophotometrically at 340 nm by measuring nicotinamide adenine dinucleotide hydride (NADH) (0.3 mM) oxidation in the presence of 1.8 mM pyruvate as a substrate as described previously. 26,32…”

Mitochondrial Signaling in Hypoxia

“…This process is associated with activation of MtC II (SDH) and increased contribution of succinate oxidation to cell respiration; this contribution may reach 70% -80% [4,[6][7][8][9][10][11][16][17][18][19]21,22,[24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41].…”