Neither nitrite nor nitric oxide mediate toxic effects of nitroglycerin on mitochondria

Light-activated mitochondrial fission through optogenetic control of mitochondria-lysosome contacts

Mitochondria are highly dynamic organelles whose fragmentation by fission is critical to their functional integrity and cellular homeostasis. Here, we develop a method via optogenetic control of mitochondria–lysosome contacts (MLCs) to induce mitochondrial fission with spatiotemporal accuracy. MLCs can be achieved by blue-light-induced association of mitochondria and lysosomes through various photoactivatable dimerizers. Real-time optogenetic induction of mitochondrial fission is tracked in living cells to measure the fission rate. The optogenetic method partially restores the mitochondrial functions of SLC25A46^−/− cells, which display defects in mitochondrial fission and hyperfused mitochondria. The optogenetic MLCs system thus provides a platform for studying mitochondrial fission and treating mitochondrial diseases.

Existing methods can lack spatiotemporal accuracy to manipulate dynamic mitochondrial behaviour in live cells. Here the authors report an optogenetic method to control mitochondria-lysosome contacts and induce mitochondrial fission; they use photoactivatable dimerizers including CRY2/CIB and SspB/iLID.

Nitroglycerin as a radiosensitizer in non-small cell lung cancer: Results of a prospective imaging-based phase II trial

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Nitroglycerin didn’t improve overall survival of NSCLC patients.

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The toxicity of combining nitroglycerin with standard treatment was mild.

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Increased uptake of HX4 showed negative prognostic significance in NSCLC patients.

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Tumor perfusion after nitroglycerin treatment did not correlate with outcome.

Background

Nitroglycerin is proposed as an agent to reduce tumour hypoxia by improving tumour perfusion. We investigated the potential of nitroglycerin as a radio-sensitizer in non-small cell lung cancer (NSCLC) and the potential of functional imaging for patient selection.

Material and methods

Trial NCT01210378 is a single arm phase II trial, designed to detect 15% improvement in 2-year overall survival (primary endpoint) in stage IB-IV NSCLC patients treated with radical (chemo-) radiotherapy and a Transiderm-Nitro 5 patch during radiotherapy. Patients underwent dynamic contrast-enhanced CTs (DCE-CT) and HX4 (hypoxia) PET/CTs before and after nitroglycerin. Secondary endpoints were progression-free survival, toxicity and the prognostic value of tumour perfusion/hypoxia at baseline and after nitroglycerin.

Results

The trial stopped after a futility analysis after 42 patients. At median follow-up of 41 months, two-year and median OS were 58% (95% CI: 44–78%) and 38 months (95% CI: 22–54 months), respectively. Nitroglycerin could not reduce tumour hypoxia. DCE-CT parameters did not correlate with OS, whereas hypoxic tumours had a worse OS (p = 0.029). Changes in high-uptake fraction of HX4 and tumour blood flow were negatively correlated (r = -0.650, p = 0.022). The heterogeneity in treatment modalities and patient characteristics combined with a small sample size made further subgroup analysis of survival results impossible. Toxicity related to nitroglyerin was limited to headache (17%) and hypotension (2.4%).

Conclusion

Nitroglycerin did not improve OS of NSCLC patients treated with (chemo-)radiotherapy. A general ability of nitroglycerin to reduce hypoxia was not shown.

Nitroglycerin and Iloprost Improve Mitochondrial Function in Colon Homogenate Without Altering the Barrier Integrity of Caco-2 Monolayers

Locally applied nitroglycerin [nitric oxide (NO) donor] and iloprost (analog of prostacyclin PGI₂) improve regional gastric oxygenation and nitroglycerin preserves gastric mucosal barrier integrity. This suggests direct effects of these substances on oxygenation and barrier function. The aim of this study was to analyze the effect of iloprost and nitroglycerin on intestinal mitochondrial function and on mucosal barrier function in vitro. Mitochondrial oxygen consumption (respirometry) was determined in colon homogenates from 16 healthy rats before (baseline) and 15 min after incubation with nitroglycerin (25 and 250 μg/ml) and iloprost (0.1 and 1 μg/ml). State 2 (substrate-dependent oxygen consumption) and state 3 respiration (ADP-dependent oxygen consumption) were assessed and ADP/O ratio (ADP added/oxygen consumed) for complex I and II were calculated. For permeability measurement we used the Caco-2 monolayer. Fluorescein sulfonic acid (FS) (200 μg/ml) and the drugs were administered into the apical compartment of the transwell chamber. After 48 h, FS translocation was assessed as basolateral/apical FS. Both concentrations of nitroglycerin and iloprost reduced state 3 by stimulation via both complexes. Iloprost increased ADP/O ratio after stimulation via both complexes at both concentrations. Nitroglycerin increased ADP/O ratio at the higher concentration (250 μg/ml) after stimulation via complex I and at the lower concentration (25 μg/ml) via complex II. Neither nitroglycerin nor iloprost influenced FS translocation. Iloprost and nitroglycerin reduce the maximal mitochondrial respiration and improve the efficacy of oxidative phosphorylation in colon homogenates. Both drugs have no direct influence on mucosal barrier integrity of Caco-2 monolayers.

Experimental data suggesting that inflammation mediated rat liver mitochondrial dysfunction results from secondary hypoxia rather than from direct effects of inflammatory mediators

Systemic inflammatory response (SIR) comprises both direct effects of inflammatory mediators (IM) and indirect effects, such as secondary circulatory failure which results in tissue hypoxia (HOX). These two key components, SIR and HOX, cause multiple organ failure (MOF). Since HOX and IM occur and interact simultaneously in vivo, it is difficult to clarify their individual pathological impact. To eliminate this interaction, precision cut liver slices (PCLS) were used in this study aiming to dissect the effects of HOX and IM on mitochondrial function, integrity of cellular membrane, and the expression of genes associated with inflammation. HOX was induced by incubating PCLS or rat liver mitochondria at pO2 < 1% followed by reoxygenation (HOX/ROX model). Inflammatory injury was stimulated by incubating PCLS with IM (IM model). We found upregulation of inducible nitric oxide synthase (iNOS) expression only in the IM model, while heme oxygenase 1 (HO-1) expression was upregulated only in the HOX/ROX model. Elevated expression of interleukin 6 (IL-6) was found in both models reflecting converging pathways regulating the expression of this gene. Both models caused damage to hepatocytes resulting in the release of alanine aminotransferase (ALT). The leakage of aspartate aminotransferase (AST) was observed only during the hypoxic phase in the HOX/ROX model. The ROX phase of HOX, but not IM, drastically impaired mitochondrial electron supply via complex I and II. Additional experiments performed with isolated mitochondria showed that free iron, released during HOX, is likely a key prerequisite of mitochondrial dysfunction induced during the ROX phase. Our data suggests that mitochondrial dysfunction, previously observed in in vivo SIR-models, is the result of secondary circulatory failure inducing HOX rather than the result of a direct interaction of IM with liver cells.

Effect of remifentanil on mitochondrial oxygen consumption of cultured human hepatocytes

During sepsis, liver dysfunction is common, and failure of mitochondria to effectively couple oxygen consumption with energy production has been described. In addition to sepsis, pharmacological agents used to treat septic patients may contribute to mitochondrial dysfunction. This study addressed the hypothesis that remifentanil interacts with hepatic mitochondrial oxygen consumption. The human hepatoma cell line HepG2 and their isolated mitochondria were exposed to remifentanil, with or without further exposure to tumor necrosis factor-α (TNF-α). Mitochondrial oxygen consumption was measured by high-resolution respirometry, Caspase-3 protein levels by Western blotting, and cytokine levels by ELISA. Inhibitory κBα (IκBα) phosphorylation, measurement of the cellular ATP content and mitochondrial membrane potential in intact cells were analysed using commercial ELISA kits. Maximal cellular respiration increased after one hour of incubation with remifentanil, and phosphorylation of IκBα occurred, denoting stimulation of nuclear factor κB (NF-κB). The effect on cellular respiration was not present at 2, 4, 8 or 16 hours of incubation. Remifentanil increased the isolated mitochondrial respiratory control ratio of complex-I-dependent respiration without interfering with maximal respiration. Preincubation with the opioid receptor antagonist naloxone prevented a remifentanil-induced increase in cellular respiration. Remifentanil at 10× higher concentrations than therapeutic reduced mitochondrial membrane potential and ATP content without uncoupling oxygen consumption and basal respiration levels. TNF-α exposure reduced respiration of complex-I, -II and -IV, an effect which was prevented by prior remifentanil incubation. Furthermore, prior remifentanil incubation prevented TNF-α-induced IL-6 release of HepG2 cells, and attenuated fragmentation of pro-caspase-3 into cleaved active caspase 3 (an early marker of apoptosis). Our data suggest that remifentanil increases cellular respiration of human hepatocytes and prevents TNF-α-induced mitochondrial dysfunction. The results were not explained by uncoupling of mitochondrial respiration.

Vascular bioactivation of nitroglycerin is catalyzed by cytosolic aldehyde dehydrogenase-2

RATIONALE

According to general view, aldehyde dehydrogenase-2 (ALDH2) catalyzes the high-affinity pathway of vascular nitroglycerin (GTN) bioactivation in smooth muscle mitochondria. Despite having wide implications to GTN pharmacology and raising many questions that are still unresolved, mitochondrial bioactivation of GTN in blood vessels is still lacking experimental support.

OBJECTIVE

In the present study, we investigated whether bioactivation of GTN is affected by the subcellular localization of ALDH2 using immortalized ALDH2-deficient aortic smooth muscle cells and mouse aortas with selective overexpression of the enzyme in either cytosol or mitochondria.

METHODS AND RESULTS

Quantitative Western blotting revealed that ALDH2 is mainly cytosolic in mouse aorta and human coronary arteries, with only approximately 15% (mouse) and approximately 5% (human) of the enzyme being localized in mitochondria. Infection of ALDH2-deficient aortic smooth muscle cells or isolated aortas with adenovirus containing ALDH2 cDNA with or without the mitochondrial signal peptide sequence led to selective expression of the protein in mitochondria and cytosol, respectively. Cytosolic overexpression of ALDH2 restored GTN-induced relaxation and GTN denitration to wild-type levels, whereas overexpression in mitochondria (6-fold vs wild-type) had no effect on relaxation. Overexpression of ALDH2 in the cytosol of ALDH2-deficient aortic smooth muscle cells led to a significant increase in GTN denitration and cyclic GMP accumulation, whereas mitochondrial overexpression had no effect.

CONCLUSIONS

The data indicate that vascular bioactivation of GTN is catalyzed by cytosolic ALDH2. Mitochondrial GTN metabolism may contribute to oxidative stress-related adverse effects of nitrate therapy and the development of nitrate tolerance.