Selective mitochondrial antioxidant MitoTEMPO reduces renal dysfunction and systemic inflammation in experimental sepsis in rats.

BACKGROUND: Excess mitochondrial reactive oxygen species (mROS) in sepsis is associated with organ failure, in part by generating inflammation through the NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasome. We determined the impact of a mitochondrial-targeted antioxidant (MitoTEMPO) on mitochondrial dysfunction in renal proximal tubular epithelial cells, peritoneal immune cell function ex vivo, and organ dysfunction in a rat model of sepsis. METHODS: The effects of MitoTEMPO were assessed ex vivo using adenosine triphosphate and lipopolysaccharide-stimulated rat peritoneal immune cells and fresh rat kidney slices exposed to serum from septic rats. We assessed mROS production and phagocytotic capacity (flow cytometry), mitochondrial functionality (multiphoton imaging, respirometry), and NLRP3 inflammasome activation in cell culture. The effect of MitoTEMPO on organ dysfunction was evaluated in a rat model of faecal peritonitis. RESULTS: MitoTEMPO decreased septic serum-induced mROS (P<0.001) and maintained normal reduced nicotinamide adenine dinucleotide redox state (P=0.02) and mitochondrial membrane potential (P<0.001) in renal proximal tubular epithelial cells ex vivo. In lipopolysaccharide-stimulated peritoneal immune cells, MitoTEMPO abrogated the increase in mROS (P=0.006) and interleukin-1ß (IL-1ß) (P=0.03) without affecting non-mitochondrial oxygen consumption or the phagocytotic-induced respiratory burst (P>0.05). In vivo, compared with untreated septic animals, MitoTEMPO reduced systemic IL-1ß (P=0.01), reduced renal oxidative stress as determined by urine isoprostane levels (P=0.04), and ameliorated renal dysfunction (reduced serum urea (P<0.001) and creatinine (P=0.05). CONCLUSIONS: Reduction of mROS by a mitochondria-targeted antioxidant reduced IL-1ß, and protected mitochondrial, cellular, and organ functionality after septic insults.

P2X7 receptor antagonism ameliorates renal dysfunction in a rat model of sepsis.

Sepsis is a major clinical problem associated with significant organ dysfunction and high mortality. The ATP-sensitive P2X7 receptor activates the NLRP3 inflammasome and is a key component of the innate immune system. We used a fluid-resuscitated rat model of fecal peritonitis and acute kidney injury (AKI) to investigate the contribution of this purinergic receptor to renal dysfunction in sepsis. Six and 24 h time-points were chosen to represent early and established sepsis, respectively. A selective P2X7 receptor antagonist (A-438079) dissolved in dimethyl sulfoxide (DMSO) was infused 2 h following induction of sepsis. Compared with sham-operated animals, septic animals had significant increases in heart rate (-1(-4 to 8)% vs. 21(12-26)%; P = 0.003), fever (37.4(37.2-37.6)°C vs. 38.6(38.2-39.0)°C; P = 0.0009), and falls in serum albumin (29(27-30)g/L vs. 26(24-28); P = 0.0242). Serum IL-1ß (0(0-10)(pg/mL) vs. 1671(1445-33778)(pg/mL); P < 0.001) and renal IL-1ß (86(50-102)pg/mg protein vs. 200 (147-248)pg/mg protein; P = 0.0031) were significantly elevated in septic compared with sham-operated animals at 6 h. Serum creatinine was elevated in septic animals compared with sham-operated animals at 24 h (23(22-25) µmol/L vs. 28 (25-30)µmol/L; P = 0.0321). Renal IL-1ß levels were significantly lower in A-438079-treated animals compared with untreated animals at 6 h (70(55-128)pg/mg protein vs. 200(147-248)pg/mg protein; P = 0.021). At 24 h, compared with untreated animals, A-438079-treated animals had more rapid resolution of tachycardia (22(13-36)% vs. -1(-6 to 7)%; P = 0.019) and fever (39.0(38.6-39.1)°C vs. 38.2(37.6-38.7)°C; P < 0.024), higher serum albumin (23(21-25)g/L vs. (27(25-28)g/L); P = 0.006), lower arterial lactate (3.2(2.5-4.3)mmol/L vs. 1.4(0.9-1.8)mmol/L; P = 0.037), and lower serum creatinine concentrations (28(25-30)µmol/L vs. 22(17-27)µmol/L; P = 0.019). P2X7 A treatment ameliorates the systemic inflammatory response and renal dysfunction in this clinically relevant model of sepsis-related AKI.

Renal Tubular Cell Mitochondrial Dysfunction Occurs Despite Preserved Renal Oxygen Delivery in Experimental Septic Acute Kidney Injury.

OBJECTIVE: To explain the paradigm of significant renal functional impairment despite preserved hemodynamics and histology in sepsis-induced acute kidney injury. DESIGN: Prospective observational animal study. SETTING: University research laboratory. SUBJECTS: Male Wistar rats. INTERVENTION: Using a fluid-resuscitated sublethal rat model of fecal peritonitis, changes in renal function were characterized in relation to global and renal hemodynamics, and histology at 6 and 24 hours (n = 6-10). Sham-operated animals were used as comparison (n = 8). Tubular cell mitochondrial function was assessed using multiphoton confocal imaging of live kidney slices incubated in septic serum. MEASUREMENTS AND MAIN RESULTS: By 24 hours, serum creatinine was significantly elevated with a concurrent decrease in renal lactate clearance in septic animals compared with sham-operated and 6-hour septic animals. Renal uncoupling protein-2 was elevated in septic animals at 24 hours although tubular cell injury was minimal and mitochondrial ultrastructure in renal proximal tubular cells preserved. There was no significant change in global or renal hemodynamics and oxygen delivery/consumption between sham-operated and septic animals at both 6- and 24-hour timepoints. In the live kidney slice model, mitochondrial dysfunction was seen in proximal tubular epithelial cells incubated with septic serum with increased production of reactive oxygen species, and decreases in nicotinamide adenine dinucleotide and mitochondrial membrane potential. These effects were prevented by coincubation with the reactive oxygen species scavenger, 4-hydroxy-2,2,6,6-tetramethyl-piperidin-1-oxyl. CONCLUSIONS: Renal dysfunction in sepsis occurs independently of hemodynamic instability or structural damage. Mitochondrial dysfunction mediated by circulating mediators that induce local oxidative stress may represent an important pathophysiologic mechanism.

Host factors that interact with the pestivirus N-terminal protease, Npro, are components of the ribonucleoprotein complex.

UNLABELLED: The viral N-terminal protease N(pro) of pestiviruses counteracts cellular antiviral defenses through inhibition of IRF3. Here we used mass spectrometry to identify a new role for N(pro) through its interaction with over 55 associated proteins, mainly ribosomal proteins and ribonucleoproteins, including RNA helicase A (DHX9), Y-box binding protein (YBX1), DDX3, DDX5, eIF3, IGF2BP1, multiple myeloma tumor protein 2, interleukin enhancer binding factor 3 (IEBP3), guanine nucleotide binding protein 3, and polyadenylate-binding protein 1 (PABP-1). These are components of the translation machinery, ribonucleoprotein particles (RNPs), and stress granules. Significantly, we found that stress granule formation was inhibited in MDBK cells infected with a noncytopathic bovine viral diarrhea virus (BVDV) strain, Kyle. However, ribonucleoproteins binding to N(pro) did not inhibit these proteins from aggregating into stress granules. N(pro) interacted with YBX1 though its TRASH domain, since the mutant C112R protein with an inactive TRASH domain no longer redistributed to stress granules. Interestingly, RNA helicase A and La autoantigen relocated from a nuclear location to form cytoplasmic granules with N(pro). To address a proviral role for N(pro) in RNP granules, we investigated whether N(pro) affected RNA interference (RNAi), since interacting proteins are involved in RISC function during RNA silencing. Using glyceraldehyde-3-phosphate dehydrogenase (GAPDH) silencing with small interfering RNAs (siRNAs) followed by Northern blotting of GAPDH, expression of N(pro) had no effect on RNAi silencing activity, contrasting with other viral suppressors of interferon. We propose that N(pro) is involved with virus RNA translation in the cytoplasm for virus particle production, and when translation is inhibited following stress, it redistributes to the replication complex. IMPORTANCE: Although the pestivirus N-terminal protease, N(pro), has been shown to have an important role in degrading IRF3 to prevent apoptosis and interferon production during infection, the function of this unique viral protease in the pestivirus life cycle remains to be elucidated. We used proteomic mass spectrometry to identify novel interacting proteins and have shown that N(pro) is present in ribosomal and ribonucleoprotein particles (RNPs), indicating a translational role in virus particle production. The virus itself can prevent stress granule assembly from these complexes, but this inhibition is not due to N(pro). A proviral role to subvert RNA silencing through binding of these host RNP proteins was not identified for this viral suppressor of interferon.