Suppression of mitochondrial ATPase inhibitor protein (IF1) in the liver of late septic rats

Peritoneal lavage with hydrogen-rich saline can be an effective and practical procedure for acute peritonitis

PURPOSE

Acute peritonitis has remained a fatal disease despite of recent advances in care and treatment, including antibiotic and anticoagulant treatments. The cause of death is mostly sepsis-induced multiple organ failure. Oxidative stress can play an important role in this situation, but antioxidant therapy to capture any excessive reactive oxygen species has not yet been fully established.

METHODS

Two experiments were performed. In the first experiment, we confirmed the effects of peritoneal lavage with hydrogen-rich saline (HRS) after a cecal ligation and puncture (CLP) operation in rats. In the second experiment, the changes in the hemodynamic state following this procedure were observed in a porcine model of abdominal sepsis to evaluate its safety and utility.

RESULTS

Peritoneal lavage with HRS significantly improved the survival after CLP in rats, and it ameliorated the levels of sepsis-induced organ failure. Moreover, it showed anti-inflammatory and anti-apoptosis as well as antioxidant effects. The second experiment demonstrated the potential safety and feasibility of this procedure in a large animal model.

CONCLUSION

This procedure can improve survival after sepsis through mitigating the sepsis-induced organ failure by inhibiting oxidative stress, apoptosis, and inflammatory pathways. Peritoneal lavage with HRS may therefore be an effective, safe, and practical therapy for patients with acute peritonitis.

The F1Fo-ATPase inhibitor, IF1, is a critical regulator of energy metabolism in cancer cells

In the last two decades, IF1, the endogenous inhibitor of the mitochondrial F1Fo-ATPase (ATP synthase) has assumed greater and ever greater interest since it has been found to be overexpressed in many cancers. At present, several findings indicate that IF1 is capable of playing a central role in cancer cells by promoting metabolic reprogramming, proliferation and resistance to cell death. However, the mechanism(s) at the basis of this pro-oncogenic action of IF1 remains elusive. Here, we recall the main features of the mechanism of the action of IF1 when the ATP synthase works in reverse, and discuss the experimental evidence that support its relevance in cancer cells. In particular, a clear pro-oncogenic action of IF1 is to avoid wasting of ATP when cancer cells are exposed to anoxia or near anoxia conditions, therefore favoring cell survival and tumor growth. However, more recently, various papers have described IF1 as an inhibitor of the ATP synthase when it is working physiologically (i.e. synthethizing ATP), and therefore reprogramming cell metabolism to aerobic glycolysis. In contrast, other studies excluded IF1 as an inhibitor of ATP synthase under normoxia, providing the basis for a hot debate. This review focuses on the role of IF1 as a modulator of the ATP synthase in normoxic cancer cells with the awareness that the knowledge of the molecular action of IF1 on the ATP synthase is crucial in unravelling the molecular mechanism(s) responsible for the pro-oncogenic role of IF1 in cancer and in developing related anticancer strategies.

Expression of genes belonging to the interacting TLR cascades, NADPH-oxidase and mitochondrial oxidative phosphorylation in septic patients

Background and objectives

Sepsis is a complex disease that is characterized by activation and inhibition of different cell signaling pathways according to the disease stage. Here, we evaluated genes involved in the TLR signaling pathway, oxidative phosphorylation and oxidative metabolism, aiming to assess their interactions and resulting cell functions and pathways that are disturbed in septic patients.

Materials and methods

Blood samples were obtained from 16 patients with sepsis secondary to community acquired pneumonia at admission (D0), and after 7 days (D7, N = 10) of therapy. Samples were also collected from 8 healthy volunteers who were matched according to age and gender. Gene expression of 84 genes was performed by real-time polymerase chain reactions. Their expression was considered up- or down-regulated when the fold change was greater than 1.5 compared to the healthy volunteers. A p-value of ≤ 0.05 was considered significant.

Results

Twenty-two genes were differently expressed in D0 samples; most of them were down-regulated. When gene expression was analyzed according to the outcomes, higher number of altered genes and a higher intensity in the disturbance was observed in non-survivor than in survivor patients. The canonical pathways altered in D0 samples included interferon and iNOS signaling; the role of JAK1, JAK2 and TYK2 in interferon signaling; mitochondrial dysfunction; and superoxide radical degradation pathways. When analyzed according to outcomes, different pathways were disturbed in surviving and non-surviving patients. Mitochondrial dysfunction, oxidative phosphorylation and superoxide radical degradation pathway were among the most altered in non-surviving patients.

Conclusion

Our data show changes in the expression of genes belonging to the interacting TLR cascades, NADPH-oxidase and oxidative phosphorylation. Importantly, distinct patterns are clearly observed in surviving and non-surviving patients. Interferon signaling, marked by changes in JAK-STAT modulation, had prominent changes in both survivors and non-survivors, whereas the redox imbalance (iNOS signaling, oxidative phosphorylation and superoxide radical degradation) affecting mitochondrial functions was prominent in non-surviving patients.

Oxidative stress in sepsis: Pathophysiological implications justifying antioxidant co-therapy

Sepsis is one of the main causes of death among critically ill patients. Sepsis pathogenesis includes infection by gram-negative and gram-positive bacteria, fungi, or both; exacerbated inflammatory response; hypotension, with potential to cause vasodilatory shock; and lesser delivery of oxygen to tissues due to impairment of oxygen utilization by cells. The participation of reactive species and/or free radicals such as nitric oxide (NO), peroxynitrite (ONOO^-), superoxide (O₂^-), hydrogen peroxide (H₂O₂), and hydroxyl radical (OH) has been reported to underlie these effects. Mitochondrial dysfunction is related to loss of inner membrane potential and inhibition of the mitochondrial electron transfer chain and FoF1-adenosine triphosphate-synthase, resulting in cellular energetic failure. In addition, overproduction of NO due to inducible nitric oxide synthase (iNOS) activity has been associated with harmful effects such as general vasodilatation and hypo-responsiveness to therapeutic vasoconstrictor agents. Considering that iNOS expression is regulated by nuclear factor-κB, which may be activated by ROS, antioxidants could inhibit the overexpression of iNOS in sepsis. In line with this, several antioxidants such as vitamins C and E, polyphenols, melatonin, β-glucan, N-acetylcysteine, mitochondrion-targeted antioxidants (MitoQ, MitoE, and peptides associated with dimethyltyrosine), selenium salts, and organoselenium compounds were effective in ameliorating oxidative stress in animal models of sepsis and in a number of clinical trials with septic patients.

Mitochondrial dysfunction in peripheral blood mononuclear cells in pediatric septic shock

OBJECTIVES

Mitochondrial dysfunction in peripheral blood mononuclear cells has been linked to immune dysregulation and organ failure in adult sepsis, but pediatric data are limited. We hypothesized that pediatric septic shock patients exhibit mitochondrial dysfunction within peripheral blood mononuclear cells which in turn correlates with global organ injury.

DESIGN

Prospective observational study.

SETTING

Academic PICU.

PATIENTS

Thirteen pediatric patients with septic shock and greater than or equal to two organ failures and 11 PICU controls without sepsis or organ failure.

INTERVENTIONS

Ex vivo measurements of mitochondrial oxygen consumption and membrane potential (ΔΨm) were performed in intact peripheral blood mononuclear cells on day 1-2 and day 5-7 of septic illness and in controls. The Pediatric Logistic Organ Dysfunction score, inotrope score, and organ failure-free days were determined from medical records.

MEASUREMENTS AND MAIN RESULTS

Spare respiratory capacity, an index of bioenergetic reserve, was lower in septic peripheral blood mononuclear cells on day 1-2 (median, 1.81; interquartile range, 0.52-2.09 pmol O2/s/10 cells) compared with controls (5.55; 2.80-7.21; p = 0.03). Spare respiratory capacity normalized by day 5-7. Patients with sepsis on day 1-2 exhibited a higher ratio of LEAK to maximal respiration than controls (17% vs < 1%; p = 0.047) with normalization by day 5-7 (1%; p = 0.008), suggesting mitochondrial uncoupling early in sepsis. However, septic peripheral blood mononuclear cells exhibited no differences in basal or adenosine triphosphate-linked oxygen consumption or ΔΨm. Oxygen consumption did not correlate with Pediatric Logistic Organ Dysfunction score, inotrope score, or organ failure-free days (all p > 0.05). Although there was a weak overall association between ΔΨm on day 1-2 and organ failure-free days (Spearman ρ = 0.56, p = 0.06), patients with sepsis with normal organ function by day 7 exhibited higher ΔΨm on day 1-2 compared with patients with organ failure for more than 7 days (p = 0.04).

CONCLUSIONS

Mitochondrial dysfunction was present in peripheral blood mononuclear cells in pediatric sepsis, evidenced by decreased bioenergetic reserve and increased uncoupling. Mitochondrial membrane potential, but not respiration, was associated with duration of organ injury.

Mitochondrial function in sepsis

BACKGROUND

The relevance of mitochondrial dysfunction as to pathogenesis of multiple organ dysfunction and failure in sepsis is controversial. This focused review evaluates the evidence for impaired mitochondrial function in sepsis.

DESIGN

Review of original studies in experimental sepsis animal models and clinical studies on mitochondrial function in sepsis. In vitro studies solely on cells and tissues were excluded. PubMed was searched for articles published between 1964 and July 2012.

RESULTS

Data from animal experiments (rodents and pigs) and from clinical studies of septic critically ill patients and human volunteers were included. A clear pattern of sepsis-related changes in mitochondrial function is missing in all species. The wide range of sepsis models, length of experiments, presence or absence of fluid resuscitation and methods to measure mitochondrial function may contribute to the contradictory findings. A consistent finding was the high variability of mitochondrial function also in control conditions and between organs.

CONCLUSION

Mitochondrial function in sepsis is highly variable, organ specific and changes over the course of sepsis. Patients who will die from sepsis may be more affected than survivors. Nevertheless, the current data from mostly young and otherwise healthy animals does not support the view that mitochondrial dysfunction is the general denominator for multiple organ failure in severe sepsis and septic shock. Whether this is true if underlying comorbidities are present, especially in older patients, should be addressed in further studies.

Suppression of autophagy in rat liver at late stage of polymicrobial sepsis

Sepsis develops as a result of the host response to infection, and its mortality rate in ICU remains high. Severe inflammation usually causes overproductions of proinflammatory cytokines, i.e., TNF-α and reactive oxygen species, which lead to mitochondrial damage and energetic depletion. Autophagy is a survival mechanism for eukaryote to recycle intracellular nutrients and maintain energy homeostasis. We hypothesize that autophagy plays a beneficial role in the pathogenesis of organ failure during sepsis. A rat model of cecal ligation and puncture (CLP) that simulate peritonitis-induced sepsis was used, and indicators for liver dysfunction, serum glutamic oxaloacetic, serum glutamic pyruvic, alkaline phosphatase, and bilirubin were measured. Levels of LC3-II and LC3 aggregation were quantified by Western blot analysis and by immunohistochemistry, respectively. The tissue localization of autophagy was identified by immunohistochemistry and transmission electron microscopy. Our results showed that (a) increase in LC3-II level in liver tissue occurs at 3 h, peaks at 6 h, and then surprisingly declines quickly until 18 h after CLP (CLP18h); (b) significant hepatic dysfunction was observed at CLP18h; (c) ratio of LC3 aggregation is significantly higher in hepatocytes than in Kupffer cells, and (d) loss of Atg7, an essential gene for autophagosome formation, exaggerates the TNF-α-induced cell death, depletion of ATP, and decrease of albumin production in hepatocytes. These results indicate that autophagy occurs transiently in hepatocytes at early stage, and the decline in autophagy at late stage may contribute to the functional failure in liver during polymicrobial sepsis.

Hypoxia-inducible factor 1α regulates the expression of the mitochondrial ATPase inhibitor protein (IF1) in rat liver

A growing number of reports indicate that bioenergetic failure plays a crucial role in the development of multiple organ failure during sepsis. Our previous results showed that the suppression of IF1 (mitochondrial ATPase inhibitor protein) expression and subsequent elevated mitochondrial F(o)F₁-ATPase activity might contribute to the bioenergetic failure in the liver during sepsis, and the influence of the decreased transcriptional level of IF1 might be an important factor. In this study, we investigated the interaction of IF1 protein expression and hypoxia-inducible factor 1 (HIF-1), a transcription factor that is correlated with the inflammatory status in sepsis. The results showed that nuclear HIF-1α protein, a subunit of HIF-1, and IF1 mRNA expression were coincidently reduced in late septic liver of rats. Furthermore, in vitro, overexpression of HIF-1α by hypoxia or CoCl₂ (HIF-1α activator) treatment augmented IF1 protein levels. On the contrary, HIF-1α antisense oligonucleotide and siRNA were used to specifically downregulate HIF-1α expression, and then IF1 protein levels were significantly decreased in clone 9 cells. Meanwhile, downregulation of HIF-1α expression led to elevate the mitochondrial F(o)F₁-ATPase activity in the presence of Bis-Tris buffer (pH 6.5). In conclusion, these results suggested for the first time that the HIF-1 might play a crucial role in regulating IF1 protein expression in late septic liver.

The ectopic F(O)F(1) ATP synthase of rat liver is modulated in acute cholestasis by the inhibitor protein IF1

Rat liver plasma membranes contain F(O)F(1) complexes (ecto-F(O)F(1)) displaying a similar molecular weight to the mitochondrial F(O)F(1) ATP synthase, as evidenced by Blue Native PAGE. Their ATPase activity was stably reduced in short-term extra-hepatic cholestasis. Immunoblotting and immunoprecipitation analyses demonstrated that the reduction in activity was not due to a decreased expression of ecto-F(O)F(1) complexes, but to an increased level of an inhibitory protein, ecto-IF(1), bound to ecto-F(O)F(1). Since cholestasis down regulates the hepatic uptake of HDL-cholesterol, and ecto-F(O)F(1) has been shown to mediate SR-BI-independent hepatic uptake of HDL-cholesterol, these findings provide support to the hypothesis that ecto-F(O)F(1) contributes to the fine control of reverse cholesterol transport, in parallel with SR-BI. No activity change of the mitochondrial F(O)F(1) ATP synthase (m-F(O)F(1)), or any variation of its association with m-IF(1) was observed in cholestasis, indicating that ecto-IF(1) expression level is modulated independently from that of ecto-F(O)F(1), m-IF(1) and m-F(O)F(1).

IF(1): setting the pace of the F(1)F(o)-ATP synthase

When mitochondrial function is compromised and the mitochondrial membrane potential (Deltapsi(m)) falls below a threshold, the F(1)F(o)-ATP synthase can reverse, hydrolysing ATP to pump protons out of the mitochondrial matrix. Although this activity can deplete ATP and precipitate cell death, it is limited by the mitochondrial protein IF(1), an endogenous F(1)F(o)-ATPase inhibitor. IF(1), therefore, preserves ATP at the expense of Deltapsi(m). Despite a wealth of detailed knowledge on the biochemistry of the interaction of IF(1) and the F(1)F(o)-ATPase, little is known about its physiological activity. Emerging research suggests that IF(1) has a wider ranging impact on mitochondrial structure and function than previously thought.