New therapeutic and diagnostic approaches with which to influence mitochondrial dysfunctions

Tuboly Eszter
New therapeutic and diagnostic approaches with which to influence mitochondrial dysfunctions.
Doctoral thesis (PhD), University of Szeged.
(2014) (Unpublished)

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Abstract in foreign language

Methane (CH4) was earlier thought to be produced in the gastrointestinal (GI) tract by methanogenic bacterial fermentation, under strictly anaerobic conditions. Humans can be CH4 producers or CH4 nonproducers, depending on the presence of methanogenic strains, age, race and lifestyle. The producer status, or a higher CH4 level in the exhaled breath, is considered to be associated with various GI disorders, such as chronic constipation or lactose malabsorption. Nevertheless, the exclusivity of bacterial CH4 formation was challenged recently when in vitro and in vivo studies revealed the possibility of non-microbial CH4 formation in mitochondria and eukaryote cells, in both plants and animals. The classical CH4 detection method is based on gas chromatography, which has many limitations, and real-time measurement is not possible. We set out to develop a photoacoustic spectroscopy (PAS)-based on-line method with appropriate specificity and sensitivity to describe the process of CH4 emission in rodents and also in human volunteers. Our next objective was to investigate nonbacterial biotic methanogenesis and to shed light on the mechanistic details of the reaction. The initial in vitro studies led to the proposal that a continuous lack of the electron acceptor oxygen will maintain an elevated mitochondrial NADH/NAD+ ratio, causing reductive stress. Electrophilic methyl groups bound to positively-charged nitrogen moieties, such as in phosphatidylcholine molecules, may potentially act as substitute electron acceptors, and in consequence CH4 may be liberated. Thus, priming during hypoxia occurs as a progressive process involving depressed electron transport, the loss of cytochrome c and antioxidants, and the triggering of methane release during the abnormal formation of reactive oxygen species induced by reoxygenation or reperfusion. We therefore hypothesized that the formation and emission of CH4 in mammals may be connected with hypoxic events leading to, or associated with a mitochondrial dysfunction. A further aim was to influence the consequences of mitochondrial dysfunction by the administration of a water-soluble, deacylated derivative of phosphatidylcholine, L-alpha-glycerylphosphorylcholine (GPC). Here, we took into account the earlier in vivo findings that GPC is a centrally-acting cholinergic precursor which increases the tolerance to ischemic tissue damage and is clinically effective in various neurodegenerative diseases. We assumed that GPC treatment could moderate the CH4 generation and also the inflammatory consequences of experimental oxidoreductive stress. In three parallel studies, we determined data on the applicability of a novel PAS-based instrument. As compared with gas chromatography, this allows real-time and dynamic measurements, while the gas-sampling procedure does not demand the use of disposable bags or syringes and operates without chemicals. The use of the instrument is noninvasive, allows the detection of the whole-body gas emission of rodents and is appropriate for human exhaled breath analysis too. Moreover, it is relatively cost-effective due to the application of near-infrared diode lasers. After the development of an appropriately specific and sensitive detection system for CH4, we investigated the functional role of mitochondrial electron transport in biogenesis. We demonstrated that the extent of CH4 generation is significantly increased in rodents exposed to chronic sodium azide challenge or endotoxemia. The phenomenon proved to be independent of the methanogenic flora, since the CH4 emission was also elevated in antibiotic-treated groups. As endotoxemia and specific inhibition of mitochondrial complex IV with sodium azide led to an increased CH4 output, we assumed that mitochondrial distress and the subsequent inflammatory reaction might be common denominators of CH4 biogenesis. The results pointed to a possible role of CH4 as an alarm signal for the development of mitochondrial responses under hypoxic conditions, and accordingly it may be a biomarker of such events. In our studies, the stress-induced CH4 generation, the hepatic microcirculatory reduction and the increased pro-oxidant and inflammatory responses were markedly attenuated by GPC treatment. When the consequence of mesenteric ischemia/reperfusion, or gamma-irradiation of the hippocampus were investigated, it emerged that GPC maintained the decreased ATP content of the liver. In conclusion, the results suggest that PAS-based spectroscopy is an excellent approach for CH4 detection, not only in animal experiments, but also in human investigations. CH4 production in mammals is connected with hypoxic events and is associated with a mitochondrial dysfunction. GPC is protective against the inflammatory consequences of a hypoxic reaction that might involve cellular or mitochondrial CH4 generation.

Item Type: Thesis (Doctoral thesis (PhD))
Creators: Tuboly Eszter
Hungarian title: Új diagnosztikai és terápiás lehetőségek mitokondriális funkciózavarral járó kórképekben
Position, academic title, institution
MTMT author ID
Boros Mihály
egyetemi tanár, SZTE ÁOK Sebészeti Műtéttani Intézet
Subjects: 03. Medical and health sciences > 03.01. Basic medicine
Divisions: Doctoral School of Multidisciplinary Medical Sciences
Discipline: Medicine > Theoretical Medicine
Language: English
Date: 2014. November 27.
Item ID: 2493
MTMT identifier of the thesis: 2834129
Date Deposited: 2014. Nov. 20. 15:26
Last Modified: 2020. Apr. 17. 13:47
Depository no.: B 5814
Defence/Citable status: Defended.

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