Coupling and pathway control of coenzyme Q redox state and respiration in isolated mitochondria

Redox states of the mitochondrial coenzyme Q pool, which reacts with the electron transfer system, reflect the balance between (1) reducing capacities of electron flow from fuel substrates converging at the Q-junction, (2) oxidative capacities downstream of Q to O2, and (3) the load on the OXPHOS system utilizing or dissipating the protonmotive force. A three-electrode sensor (Rich 1988; Moore et al 1988) was implemented into the NextGen-O2k to monitor continuously the redox state of CoQ2 added as a Q-mimetic simultaneously with O2 consumption. The Q-Module was optimized for high signal-to-noise ratio, minimum drift, and minimum oxygen diffusion. CoQ2 equilibrates in the same manner as Q at Complexes CI, CII and CIII. The CoQ2 redox state is monitored amperometrically with the working electrode, which is poised at CoQ2 redox peak potentials determined by cyclic voltammetry. The voltammogram also provides quality control of the Q-sensor and reveals chemical interferences. The CoQ2 redox state and O2 consumption were measured simultaneously in isolated mouse cardiac and brain mitochondria. CoQ2 ― and by implication mitochondrial Q ― was more oxidized when O2 flux was stimulated by coupling control: when energy demand increased from LEAK to OXPHOS and electron transfer capacities in the succinate pathway. In contrast, CoQ2 was more reduced when O2 flux was stimulated by pathway-control of electron input capacities, increasing from the NADH (N)- to succinate (S)-linked pathway which converge at the Q-junction, with CI-Q-CIII and CII-Q-CIII segments, respectively. N- and S- respiratory pathway capacities were not completely additive, compatible with partitioning of Q intermediary between the solid-state and liquid-state models of supercomplex organization. The direct proportionality of CoQ2 reduction and electron input capacities through the CI-Q-CIII and CII-Q-CIII segments suggests that CoQ2 is accurately mimicking mitochondrial Q-redox changes

Melatonin protects rats from radiotherapy-induced small intestine toxicity

Radiotherapy-induced gut toxicity is among the most prevalent dose-limiting toxicities following radiotherapy. Prevention of radiation enteropathy requires protection of the small intestine. However, despite the prevalence and burden of this pathology, there are currently no effective treatments for radiotherapy-induced gut toxicity, and this pathology remains unclear. The present study aimed to investigate the changes induced in the rat small intestine after external irradiation of the tongue, and to explore the potential radio-protective effects of melatonin gel. Male Wistar rats were subjected to irradiation of their tongues with an X-Ray YXLON Y.Tu 320-D03 irradiator, receiving a dose of 7.5 Gy/day for 5 days. For 21 days post-irradiation, rats were treated with 45 mg/day melatonin gel or vehicle, by local application into their mouths. Our results showed that mitochondrial oxidative stress, bioenergetic impairment, and subsequent NLRP3 inflammasome activation were involved in the development of radiotherapy-induced gut toxicity. Oral treatment with melatonin gel had a protective effect in the small intestine, which was associated with mitochondrial protection and, consequently, with a reduced inflammatory response, blunting the NF-κB/NLRP3 inflammasome signaling activation. Thus, rats treated with melatonin gel showed reduced intestinal apoptosis, relieving mucosal dysfunction and facilitating intestinal mucosa recovery. Our findings suggest that oral treatment with melatonin gel may be a potential preventive therapy for radiotherapy-induced gut toxicity in cancer patients.This study was partially supported by grant no. SAF2009-14037 from the Spanish Ministry of Economy and Competitivity (MINECO), GREIB.PT_2010_04 from the CEIBiotic Program of the University of Granada, Spain, and CTS-101 from the Consejería de Innovación, Ciencia y Empresa, Junta de Andalucía, Spain

The Endoplasmic Reticulum Stress Response in Neuroprogressive Diseases: Emerging Pathophysiological Role and Translational Implications

The endoplasmic reticulum (ER) is the main cellular organelle involved in protein synthesis, assembly and secretion. Accumulating evidence shows that across several neurodegenerative and neuroprogressive diseases, ER stress ensues, which is accompanied by over-activation of the unfolded protein response (UPR). Although the UPR could initially serve adaptive purposes in conditions associated with higher cellular demands and after exposure to a range of pathophysiological insults, over time the UPR may become detrimental, thus contributing to neuroprogression. Herein, we propose that immune-inflammatory, neuro-oxidative, neuro-nitrosative, as well as mitochondrial pathways may reciprocally interact with aberrations in UPR pathways. Furthermore, ER stress may contribute to a deregulation in calcium homoeostasis. The common denominator of these pathways is a decrease in neuronal resilience, synaptic dysfunction and even cell death. This review also discusses how mechanisms related to ER stress could be explored as a source for novel therapeutic targets for neurodegenerative and neuroprogressive diseases. The design of randomised controlled trials testing compounds that target aberrant UPR-related pathways within the emerging framework of precision psychiatry is warranted

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Mitochondrial physiology

As the knowledge base and importance of mitochondrial physiology to evolution, health and disease expands, the necessity for harmonizing the terminology concerning mitochondrial respiratory states and rates has become increasingly apparent. The chemiosmotic theory establishes the mechanism of energy transformation and coupling in oxidative phosphorylation. The unifying concept of the protonmotive force provides the framework for developing a consistent theoretical foundation of mitochondrial physiology and bioenergetics. We follow the latest SI guidelines and those of the International Union of Pure and Applied Chemistry (IUPAC) on terminology in physical chemistry, extended by considerations of open systems and thermodynamics of irreversible processes. The concept-driven constructive terminology incorporates the meaning of each quantity and aligns concepts and symbols with the nomenclature of classical bioenergetics. We endeavour to provide a balanced view of mitochondrial respiratory control and a critical discussion on reporting data of mitochondrial respiration in terms of metabolic flows and fluxes. Uniform standards for evaluation of respiratory states and rates will ultimately contribute to reproducibility between laboratories and thus support the development of data repositories of mitochondrial respiratory function in species, tissues, and cells. Clarity of concept and consistency of nomenclature facilitate effective transdisciplinary communication, education, and ultimately further discovery

Protective effects of synthetic kynurenines on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced parkinsonism in mice

Producción CientíficaMitochondrial complex I inhibition is thought to underlie the neurodegenerative process in Parkinson's disease (PD). Moreover, an overproduction of nitric oxide due to both cytosolic (iNOS) and mitochondrial (i-mtNOS) inducible nitric oxide synthases causes free radicals generation and oxidative/nitrosative stress, contributing to mitochondrial dysfunction and neuronal cell death. Looking for active molecules against mitochondrial dysfunction and inflammatory response in PD, we show here the effects of four synthetic kynurenines in the MPTP model of PD in mice. After MPTP administration, mitochondria from substantia nigra and, in a lesser extent, from striatum showed a significant increase in i-mtNOS activity, nitric oxide production, oxidative stress, and complex I inhibition. The four kynurenines assayed counteracted the effects of MPTP, reducing iNOS/i-mtNOS activity, and restoring the activity of the complex I. Consequently, the cytosolic and mitochondrial oxidative/nitrosative stress returned to control values. The results suggest that the kynurenines here reported represent a family of synthetic compounds with neuroprotective properties against PD, and that they can serve as templates for the design of new drugs able to target the mitochondria

Mitochondrial impairment and melatonin protection in parkinsonian mice do not depend of inducible or neuronal nitric oxide synthases

<div><p>MPTP-mouse model constitutes a well-known model of neuroinflammation and mitochondrial failure occurring in Parkinson’s disease (PD). Although it has been extensively reported that nitric oxide (NO^●) plays a key role in the pathogenesis of PD, the relative roles of nitric oxide synthase isoforms iNOS and nNOS in the nigrostriatal pathway remains, however, unclear. Here, the participation of iNOS/nNOS isoforms in the mitochondrial dysfunction was analyzed in iNOS and nNOS deficient mice. Our results showed that MPTP increased iNOS activity in substantia nigra and striatum, whereas it sharply reduced complex I activity and mitochondrial bioenergetics in all strains. In the presence of MPTP, mice lacking iNOS showed similar restricted mitochondrial function than wild type or mice lacking nNOS. These results suggest that iNOS-dependent elevated nitric oxide, a major pathological hallmark of neuroinflammation in PD, does not contribute to mitochondrial impairment. Therefore, neuroinflammation and mitochondrial dysregulation seem to act in parallel in the MPTP model of PD. Melatonin administration, with well-reported neuroprotective properties, counteracted these effects, preventing from the drastic changes in mitochondrial oxygen consumption, increased NOS activity and prevented reduced locomotor activity induced by MPTP. The protective effects of melatonin on mitochondria are also independent of its anti-inflammatory properties, but both effects are required for an effective anti-parkinsonian activity of the indoleamine as reported in this study.</p></div

Control respiratory index (RCR) in ST and SN mitochondria.

<p>Control respiratory index (RCR) in ST and SN mitochondria.</p

Values of the ADP:O ratio in ST and SN mitochondria.

<p>Values of the ADP:O ratio in ST and SN mitochondria.</p