Railway noise annoyance modeling: Accounting for noise sensitivity and different acoustical features.

Noise annoyance due to railway traffic is a growing issue in today's society. This annoyance may be predicted using noise-exposure relationships with mean energy-based index. However, there is room for improvement of models as other acoustical and non-acoustical factors also influence noise annoyance responses. In this paper, it is proposed to highlight annoying auditory sensations evoked by the railway noise and determine acoustical and psychoacoustical indices combined in a predictive model. A laboratory experiment involving railway pass-by noise in urban areas was carried out. Annoyance ratings, noise sensitivity ratings, and free verbalization data were gathered. The analysis underlined annoying auditory sensations caused by railway pass-by noises. Two indices were proposed to account for irregular amplitude fluctuation and noise event duration-related sensations. A multilevel regression analysis was conducted, leading to two annoyance models considering noise indices and noise sensitivity. These models were finally compared to a similarly obtained multilevel regression model related to tramway noise annoyance. The comparison was carried out as a cross-validation considering the models and the respective datasets collected in laboratory conditions for model construction. Results showed that the railway noise annoyance model led to a good prediction of tramway noise annoyance and vice versa.

Short communication: Effect of freezer storage time and thawing method on the recovery of Mycoplasma bovis from bovine colostrum.

Mycoplasma bovis is an important cause of mastitis in dairy cattle, and pneumonia, arthritis, and otitis in calves. Milk and colostrum are considered important sources of infection for calves. knowledge on the effect of on-farm freezing (-18°C) and thawing methods on the recovery of M. bovis from colostrum samples is missing. In this study, 2 separate experiments were performed. The first experiment consisted of a longitudinal study examining the survival [as measured by log(10) reduction] of 2 M. bovis strains in frozen colostrum over 14 wk. The second experiment examined the effect of different thawing temperatures (45 and 20°C), thawing frequencies (once or twice), and initial colostrum titer (104 or 106 cfu/mL) on M. bovis survival. A single freeze-thaw cycle led to an approximate 1 log reduction of M. bovis titer, independent of the thawing temperature. Freezing for 14 wk did not significantly further reduce the titer of bacteria compared with freezing for 2 wk. A second freeze-thaw cycle further reduced the M. bovis count by approximately 0.5 log compared with a single freeze-thaw cycle. Thawing temperature and initial bacterial concentration did not significantly affect M. bovis reduction. In conclusion, storage of colostrum samples in the freezer at -18°C during epidemiological studies, herd monitoring, or test and cull programs will probably have little influence on qualitative bacteriological test results for M. bovis. The epidemiological or clinical relevance of an approximate 1 log reduction of M. bovis in colostrum is currently unclear.

A Deep Nasopharyngeal Swab Versus Nonendoscopic Bronchoalveolar Lavage for Isolation of Bacterial Pathogens from Preweaned Calves With Respiratory Disease.

BACKGROUND: Nonendoscopic bronchoalveolar lavage (BAL) is a practical alternative for a deep nasopharyngeal swab (DNS) to sample the airways of a large number of calves in a short period of time. The extent of commensal overgrowth and agreement of BAL with DNS culture results in preweaned calves are unknown. OBJECTIVES: To compare commensal overgrowth and bacterial culture results between DNS and BAL samples. ANIMALS: A total of 183 preweaned calves (144 with bovine respiratory disease and 39 healthy animals). METHODS: Cross-sectional study. Deep nasopharyngeal swab and BAL samples were taken from each calf and cultured to detect Pasteurellaceae and Mycoplasma bovis. Agreement and associations between culture results of DNS and BAL samples were determined by kappa statistics and logistic regression. RESULTS: Bronchoalveolar lavage samples were less often polymicrobial, more frequently negative and yielded more pure cultures compared to DNS, leading to a clinically interpretable culture result in 79.2% of the cases compared to only in 31.2% of the DNS samples. Isolation rates were lower in healthy animals, but not different between DNS and BAL samples. Only Histophilus somni was more likely to be isolated from BAL samples. In clinical cases, a polymicrobial DNS culture result did not increase the probability of a polymicrobial BAL result by ≥30%, nor did it influence the probability of a negative culture. A significant herd effect was noted for all observed relationships. CONCLUSIONS AND CLINICAL RELEVANCE: Nonendoscopic BAL samples are far less overgrown by bacteria compared to DNS samples under the conditions of this study, facilitating clinical interpretation and resulting in a higher return on investment in bacteriologic culturing.

A new predilection site of Mycoplasma bovis: Postsurgical seromas in beef cattle.

Mycoplasma bovis is a highly contagious bacterium, which predominantly causes chronic pneumonia, otitis and arthritis in calves and mastitis in adult cattle. In humans, Mycoplasma species have been associated with post-surgical infections. The present study aimed to identify the bacteria associated with three outbreaks of infected seromas after caesarian section in Belgian Blue beef cattle. A total of 10 cases occurred in three herds which were in close proximity of each other and shared the same veterinary practice. M. bovis could be cultured from seroma fluid in five of the six referred animals, mostly in pure culture and was isolated from multiple chronic sites of infection (arthritis and mastitis) as well. DNA fingerprinting of the isolates targeting two insertion sequence elements suggested spread of M. bovis from chronic sites of infection (udder and joints) to the postsurgical seromas. Identical genetic profiles were demonstrated in two animals from two separate farms, suggesting spread between farms. Mortality rate in the referred animals positive for M. bovis in a seroma was 80% (4/5), despite intensive treatment. A massive increase in antimicrobial use was observed in every affected farm. These observations demonstrate involvement of mycoplasmas in outbreaks of postsurgical seromas in cattle.

Antileishmanial activity of essential oil from Chenopodium ambrosioides and its main components against experimental cutaneous leishmaniasis in BALB/c mice.

UNLABELLED: Chenopodium ambrosioides have been used during centuries by native people to treat parasitic diseases. AIMS OF THE STUDY: To compare the in vivo anti-leishmanial activity of the essential oil (EO) from C. ambrosioides and its major components (ascaridole, carvacrol and caryophyllene oxide). MATERIALS AND METHODS: Anti-leishmanial effect was evaluated in BALB/c mice infected with Leishmania amazonensis and treated with the EO, main compounds and artificial mix of pure components by intralesional route at 30 mg/kg every 4 days during 14 days. Diseases progression and parasite burden in infected tissues were determined. RESULTS: EO prevented lesion development compared (p<0.05) with untreated animals and treated with vehicle. In addition, the efficacy of EO was also statistically superior (p<0.05) compared with the glucantime-treated animals. No potential effects were observed with pure components treatment. Mix of pure compounds cause death of animals after 3 days of treatment. CONCLUSIONS: Our results demonstrate the superiority of EO against experimental cutaneous leishmaniasis caused by L. amazonensis.

Genotoxic effects of deoxynivalenol in broiler chickens fed low-protein feeds.

Deoxynivalenol (DON) is one of the most abundant and important trichothecenes in food and feed, and it is a significant contaminant due to its frequent occurrence at toxicologically relevant concentrations worldwide. Deoxynivalenol has negative influences on the health and performance of chicks. However, there is little information available regarding the effect of DON on DNA fragmentation in blood lymphocytes. In addition, the effects of Mycofix select (Biomin GmbH, Herzogenburg, Austria) supplementation to DON-contaminated broiler diets on lymphocyte DNA have not yet been demonstrated. Therefore, the aim of the present study was to establish the effect of DON on lipid peroxidation and lymphocyte DNA fragmentation in broilers and to evaluate the potential of Mycofix select in the prevention of toxin-mediated changes. Thirty-two 1-d-old (Ross 308 male) broiler chicks were randomly divided into 4 groups. The control group was fed a noncontaminated diet, and a second group was fed the same diet but supplemented with Mycofix select (0.25%). A third group of broilers was fed a diet artificially contaminated with 10 mg of feed-grade DON/kg of diet, and a fourth group was fed a DON-contaminated diet supplemented with Mycofix select. At the end of the feeding trial, blood was collected and the degree of lymphocyte DNA damage was measured in the plasma by comet assay. Deoxynivalenol increased (P = 0.016) the amount of DNA damage in chicken lymphocytes by 46.8%. Mycofix select protected lymphocyte DNA from the DON effects. To our knowledge, these are the first data on genotoxic effects of a moderate dose of DON on chicken lymphocytes. However, the thiobarbituric acid reactive substances level in liver and liver enzyme activity did not differ among the groups. In conclusion, the present study demonstrated that the diets contaminated with the mycotoxin DON at moderate levels in combination with low-protein feed are able to induce lymphocyte DNA damage in chickens. Supplementation with Mycofix select protected lymphocyte DNA and it was beneficial for maintaining the lymphocyte DNA integrity.

Synthetic chromanol derivatives and their interaction with complex III in mitochondria from bovine, yeast, and Leishmania.

Synthetic chromanol derivatives (TMC4O, 6-hydroxy-2,2,7,8-tetramethyl-chroman-4-one; TMC2O, 6-hydroxy-4,4,7,8-tetramethyl-chroman-2-one; and Twin, 1,3,4,8,9,11-hexamethyl-6,12-methano-12H-dibenzo[d,g][1,3]dioxocin-2,10-diol) share structural elements with the potent inhibitor of the mitochondrial cytochrome (cyt) bc(1) complex stigmatellin. Studies with isolated bovine cyt bc(1) complex demonstrated that these compounds partially inhibit the mammalian enzyme. The aim of this work was to comparatively investigate these toxicological aspects of synthetic vitamin E derivatives in mitochondria of different species. The chromanols and atovaquone as reference compound were evaluated for their inhibition of the cyt bc(1) activity in mitochondrial fractions from bovine hearts, yeast, and Leishmania. In addition, compounds were evaluated in vitro for their inhibitory activity against whole-cell Leishmania and mouse peritoneal macrophages. In these organisms, the chromanols showed a species-selective inhibition of the cyt bc(1) activity different from that of atovaquone. While in atovaquone the side chain mediates species-selectivity, the marked differences for TMC2O and TMC4O in cyt bc(1) inhibition suggests that direct substitution of the chromanol headgroup will control selectivity in these compounds. Low micromolar concentrations of TMC2O (IC(50) = 9.5 ± 0.5 µM) inhibited the growth of Leishmania, and an esterified TMC2CO derivative inhibited the cyt bc(1) activity with an IC(50) of 4.9 ± 0.9 µM. These findings suggest that certain chromanols also exhibit beyond their antioxidative properties antileishmanial activities and that TMC2O derivatives could be useful toward the development of highly active antiprotozoal compounds.

Ubiquinone and tocopherol: dissimilar siblings.

Research on antioxidants and their potential health benefits expanded over the last decades from basic science to the medical and nutritional fields. This included supplementation studies of both vitamin E compounds and the endogenous antioxidant ubiquinone, to prevent or alleviate cardiovascular diseases and their pathophysiological consequences. In many of these studies, only one antioxidant or one group of antioxidants was considered, disregarding the pharmacological and toxicological properties of their metabolites as well as possible cooperative and competitive effects on the overall physiological response. There are many--often indirect--effects, especially in gene regulation, observed on administration of both compound groups in cells, which have been assigned to these molecules without identifying the cellular targets. Therefore, this article focuses on direct chemical and biochemical effects of ubiquinone- and alpha-tocopherol-related compounds, which are evident from direct binding studies or direct interaction leading to chemical modification of the compounds. These groups include para-benzoquinones (ubiquinone and alpha-tocopheryl quinone) and chroma(e)nols (alpha-tocopherol and bicyclic ubiquinone derivatives). Their effects as antioxidants, co-antioxidants, and pro-oxidants as well as direct interactions with proteins are considered, pointing out similarities and dissimilarities of the two compound groups in a wider context. The review of the isolated findings about one or a few of these compounds in the literature, disregarding structurally related compounds, suggests that comprehensive structure/activity relationship studies including related compounds would promote the understanding of biological functions and pharmacological effects of ubiquinone- and alpha-tocopherol-related compounds.

Influence of cryopreservation on mitochondrial functions in equine spermatozoa.

Cryopreservation of spermatozoa is of essential importance for artificial insemination and breeding programs in horses. Besides other factors, spermatozoal motility depends on mitochondrial energy metabolism. Based on changes of single mitochondrial functions it has been suggested that mitochondrial damage during cryopreservation could be a major reason for diminished post thaw semen quality. However, it is still unclear to which extent this influences the whole bioenergetic performance of mitochondria and whether this plays a role during routine cryopreservation procedures. Therefore, it was the aim of this study to compare changes in mitochondrial bioenergetics in spermatozoa during shock freezing and routine cryopreservation. Mitochondrial integrity in spermatozoa was studied by determination of oxygen consumption, mitochondrial membrane potential, and the oxidation of externally added cytochrome c(2+). Shock freezing of spermatozoa resulted in an irreversible loss of mitochondrial functions. However, respiration difference of uncoupled minus resting state and routine respiration also decreased by 48+/-14 and 58+/-6% (p<0.05), respectively, after routine cryopreservation. This was accompanied by a decline in the mitochondrial membrane potential to 83+/-4% (p<0.05) and spermatozoal motility to 56+/-11% (p<0.05) of pre-freezing values. In contrast, the oxidation rates of externally added cytochrome c(2+) by cytochrome c oxidase slightly increased by 26+/-14% (p<0.1) suggesting a partial rupture of cellular and outer mitochondrial membranes. Our data indicate that also widely used cryopreservation protocols for equine spermatozoa need adjustment to optimize post thaw mitochondrial functions.

Cell respiration and formation of reactive oxygen species: facts and artefacts.

It is generally taken as an established fact that mitochondrial respiration is associated with the generation of small amounts of ROS (reactive oxygen species). There are many arguments supporting this side activity. A major argument is the particular physico-chemical configuration of dioxygen, which prevents the transfer of a pair of electrons. Instead, oxygen is reduced by the successive transfer of single electrons, necessarily leading to intermediates with odd electrons. The high rate of turnover of oxygen in the respiratory chain in combination with the existence of single-electron carriers supports the concept of mitochondria as the major cellular ROS generator. Experimental evidence on the ability of mitochondria to generate ROS was, however, based essentially on in vitro experiments with isolated mitochondria. A variety of structural and functional alterations associated with the removal of mitochondria from the cell, as well as the routinely applied ROS detection methods, may lead to artefactual deviation of odd electrons to dioxygen. We therefore checked these correlations in view of ROS formation, including the often reported effect of the membrane potential on the establishment of a redox couple with oxygen out of sequence. For this purpose we developed novel methods to prove the authenticity of mitochondria for ROS generation in the living cell. Based on our experiments, we can exclude spontaneous release of ROS from mitochondria. However, we describe conditions under which mitochondria can be transformed to mild ROS generators. The site of single-electron deviation to dioxygen was found to be ubiquinol interacting with the Rieske iron-sulphur protein and low-potential cytochrome b of the bc (1) complex.

The existence and significance of redox-cycling ubiquinone in lysosomes.

Ubiquinone is inhomogeneously distributed in subcellular biomembranes. Apart from mitochondria, where ubiquinone was demonstrated to exert bioenergetic and pathophysiological functions, unusually high levels of ubiquinone were also reported to exist in Golgi vesicles and lysosomes. In lysosomes the interior differs from other organelles by the low pH value which is important not only to arrest proteins but also to ensure optimal activity of proteases. Since redox cycling of ubiquinone is associated with the acceptance and release of protons, we assumed that ubiquinone is a part of a redox chain contributing to unilateral proton distribution. A similar function of ubiquinone was earlier reported to exist in Golgi vesicles. Support for the involvement of ubiquinone in a presumed couple of redox carriers came from our observation that almost 70% of total lysosomal ubiquinone was in the divalently reduced state. Further reduction was seen in the presence of external NADH. Analysis of the components involved in the transfer of reducing equivalents from cytosolic NADH to ubiquinone revealed the existence of a flavin adenine dinucleotide-containing NADH dehydrogenase. The latter was found to reduce ubiquinone by means of a b-type cytochrome. Proton translocation into the interior was linked to the activity of the novel lysosomal redox chain. Oxygen was found to be the terminal electron acceptor thereby also regulating acidification of the lysosomal matrix. The role of the proton-pumping redox chain has to be elucidated.

A decade of large scale experience in dissolved air flotation.

In April 1990 Antwerpse Waterwerken brought a new DAF-plant into operation at the production centre Notmeir-Walem. The flotation unit, which has a capacity of 200,000 m3/d, was integrated in one of the two existing treatment lines. Its main objective was to eliminate the important raw water quality fluctuations caused by increasing algal growths. During the past ten years several optimisation studies were carried out which resulted in a further simplification of operation and mechanical design. This paper will focus mainly on the integration of dissolved air flotation in the entire treatment line, the consequences on the dual layer filtration and the operational experience and information gathered during the past decade.

The ubiquinol/bc1 redox couple regulates mitochondrial oxygen radical formation.

The generation of oxygen radicals in biological systems and their sites of intracellular release were subject of numerous studies in the last decades. Based on these studies mitochondria were considered as the major source of intracellular oxygen radicals. Although this finding is more or less accepted the mechanism of univalent oxygen reduction in mitochondria is still obscure. One of the most critical electron transfer steps of the respiratory chain is the electron bifurcation at the bc1 complex. From recent studies with genetically mutated mitochondria it became clear that electron bifurcation from ubiquinol to the bc1 complex requires an underanged mobility of the head domain of the Rieske iron sulfur protein. On the other hand it is long known that inhibition of electron bifurcation by antimycin A causes the leakage of single electrons to dioxygen, which results in the release of O2*- radicals. These findings made us to prove whether the impediment of the interaction of ubiquinol with the bc1 complex is the regulator of single electron diversion to oxygen. Impediment of electron bifurcation was observed following alterations of the physical state of membrane phospholipids in which the bc1 complex is inserted. Irrespectively, whether the fluidity of membrane lipids was elevated or decreased electron flow rates to the Rieske iron sulfur protein and to low potential cytochrome b were drastically reduced. Concomitantly O2*- radicals were released from these mitochondria, suggesting an effect on the mobility of the head domain of the Rieske iron sulfur protein. These results including the well known effect of antimycin A revealed the involvement of the ubiquinol bc1 redox couple in mitochondrial O2*- formation. The regulator which controls leakage of electrons to oxygen appears to be the electron branching activity of the bc1 complex.

The multiple functions of coenzyme Q.

The coenzyme function of ubiquinone was subject of extensive studies in mitochondria since more than 40 years. The catalytic activity of ubiquinone (UQ) in electron transfer and proton translocation in cooperation with mitochondrial dehydrogenases and cytochromes contributes essentially to the bioenergetic activity of ATP synthesis. In the past two decades UQ was recognized to exert activities which differ from coenzyme functions in mitochondria. From extraction/reincorporation experiments B. Chance has drawn the conclusion that redox-cycling of mitochondrial ubiquinone supplies electrons for univalent reduction of dioxygen. The likelihood of O2(.-) release as normal byproduct of respiration was based on the existence of mitochondrial SOD and the fact that mitochondrial oxygen turnover accounts for more than 90% of total cellular oxygen consumption. Arguments disproving this concept are based on results obtained from a novel noninvasive, more sensitive detection method of activated oxygen species and novel experimental approaches, which threw light into the underlying mechanism of UQ-mediated oxygen activation. Single electrons for O2(.-) formation are exclusively provided by deprotonated ubisemiquinones. Impediment of redox-interaction with the bc1 complex in mitochondria or the lack of stabilizing interactions with redox-partners are promotors of autoxidation. The latter accounts for autoxidation of antioxidant-derived ubisemiquinones in biomembranes, which do not recycle oxidized ubiquinols. Also O2(.-)-derived H2O2 was found to interact with ubisemiquinones both in mitochondria and nonrecycling biomembranes when ubiquinol was active as antioxidant. The catalysis of reductive homolytic cleavage of H2O2, which contributes to HO. formation in biological systems was confirmed under defined chemical conditions in a homogenous reduction system. Apart from dioxygen and hydrogen peroxide we will provide evidence that also nitrite may chemically interact with the ubiquinol/bc1 redox couple in mitochondria. The reaction product NO was reported elsewhere to be a significant bioregulator of the mitochondrial respiration and O2 activation. Another novel finding documents the bioenergetic role of UQ in lysosomal proton intransport. A lysosomal chain of redox couples will be presented, which includes UQ and which requires oxygen as the terminal electron acceptor.

Effects of tocopheryl quinone on the heart: model experiments with xanthine oxidase, heart mitochondria, and isolated perfused rat hearts.

It is generally accepted that the protection effect of biological tissues by vitamin E is due to its radical scavenging potency in membranes, thereby being transformed to a vitamin E radical. A deficiency of appropriate reductants, which recycle vitamin E radicals back to its antioxidative active form, causes an irreversible degradation of vitamin E leading to tocopheryl quinone (TQ). TQ-like compounds were shown to result from both vitamin E and corresponding hydrophilic analogues of this antioxidant in vitro. In vivo elevated concentrations of tocopheryl quinones were detected after oxidative stress and TQ supplementation as well. Quinones in general are known to be efficient one-electron donors and acceptors. Therefore the question arises whether TQ-like compounds can undergo redox-cycling in conjunction with redox-active enzymes in the heart, thereby producing harmful oxygen radicals, or whether these compounds exhibit antioxidant properties. In order to elucidate this question we focused our interest on the interaction of TQ and a corresponding short-chain homologue (TQ(0)) with xanthine oxidase and heart mitochondria. Furthermore, we tested the influence of TQ on the recovery of isolated perfused rat hearts after ischemia/reperfusion. Our experiments revealed that hydrophilic TQ(0) was univalently reduced by xanthine oxidase (XOD) yielding semiquinone radicals in the absence of oxygen. However, under aerobic conditions TQ(0) enhanced the O(2)(*)(-) radical output of XOD. In the mitochondrial respiratory chain TQ was shown to interact with high potential cytochrome b in the bc(1) complex specifically. In contrast to the system XOD/TQ(0), lipophilic TQ in submitochondrial particles decreased the O(2)(*)(-) radical release during regular respiration possibly due to its interaction with b-cytochromes in the mitochondrial respiratory chain. In isolated rat hearts perfused with liposomes containing lipophilic TQ, it was efficiently accumulated in the heart tissue. When hearts were subjected to conditions of ischemia/reperfusion, infusion of TQ prior to ischemia significantly improved the recovery of hemodynamic parameters. Our results demonstrate that TQ derivatives may induce pro-oxidative and antioxidative effects depending on the distribution of TQ derivatives in the heart tissue and the interacting redox system.

Kynurenic acid influences the respiratory parameters of rat heart mitochondria.

In the present study the effect of L-kynurenine, kynurenic acid and quinolinic acid on the heart mitochondrial function were investigated. Mitochondria were incubated with saturating concentrations of respiratory substrates glutamate/malate (5 mmol/l), succinate (10 mmol/l) or NADH (1 mmol/l), with and without kynurenines. The concentration of kynurenines varied between 1.25 micromol/l and 10 mmol/l. From all investigated kynurenines, only kynurenic acid affected dose-dependently the respiratory parameters of heart mitochondria. Respiratory control and P/O values were reduced significantly with glutamate/malate and moderately with succinate as substrates in the presence of 125 micromol/l to 10 mmol/l kynurenic acid. A known elevation of L-kynurenine in the blood of patients with ischemic heart disease or essential hypertension may suggest the involvement of L-kynurenine metabolites in the impairment of heart mitochondrial function, for example in cardiomyopathy.

The existence of a lysosomal redox chain and the role of ubiquinone.

Several studies concerning the distribution of ubiquinone (UQ) in the cell report a preferential accumulation of this biogenic quinone in mitochondria, plasma membranes, Golgi vesicles, and lysosomes. Except for mitochondria, no recent comprehensive experimental evidence exists on the particular function of UQ in these subcellular organelles. The aim of a recent study was to elucidate whether UQ is an active part of an electron-transfer system in lysosomes. In the present work, a lysosomal fraction was prepared from a light mitochondrial fraction of rat liver by isopycnic centrifugation. The purity of our preparation was verified by estimation of the respective marker enzymes. Analysis of lysosomes for putative redox carriers and redox processes in lysosomes was carried out by optical spectroscopy, HPLC, oxymetry, and ESR techniques. UQ was detected in an amount of 2.2 nmol/mg of protein in lysosomes. Furthermore, a b-type cytochrome and a flavin-adenine dinucleotide (FAD) were identified as other potential electron carriers. Since NADH was reported to serve as a substrate of UQ redox chains in plasma membranes, we also tested this reductant in lysosomes. Our experiments demonstrate a NADH-dependent reduction of UQ by two subsequent one-electron-transfer steps giving rise to the presence of ubisemiquinone and an increase of the ubiquinol pool in lysosomes. Lysosomal NADH oxidation was accompanied by an approximately equimolar oxygen consumption, suggesting that O(2) acts as a terminal acceptor of this redox chain. DMPO/(*)OH spin adducts were detected by ESR in NADH-supplemented lysosomes, suggesting a univalent reduction of oxygen. The kinetic analysis of redox changes in lysosomes revealed that electron carriers operate in the sequence NADH > FAD > cytochrome b > ubiquinone > oxygen. By using the basic spin label TEMPAMINE, we showed that the NADH-related redox chain in lysosomes supports proton accumulation in lysosomes. In contrast to the hypothesis that UQ in lysosomes is simply a waste product of autophagy in the cell, we demonstrated that this lipophilic electron carrier is a native constituent of a lysosomal electron transport chain, which promotes proton translocation across the lysosomal membrane.

Critical aspects of the antioxidant function of coenzyme Q in biomembranes.

Coenzyme Q (ubiquinone, UQ) is increasingly considered as a significant natural antioxidant, which protects biomembranes in concert with alpha-tocopherol. In vitro experiments demonstrated that reduced UQ (ubiquinol) can improve the chain-breaking activities of alpha-tocopherol by recycling the antioxidant-derived reaction product, the chromanoxyl radical, to the native antioxidant. Less attention, however, was devoted to the antioxidant-derived reaction products of reduced UQ. Although both alpha-tocopherol and ubiquinol were found to be equally effective in scavenging chain-propagating lipid radicals. alpha-tocopherol protected lipid membranes from lipid peroxidation more efficiently than ubiquinol. The present study not only provides data which document this discrepancy but also contributes experimental data on the existence of ubiquinol derived pro-oxidants, which give an explanation of this phenomenon.

Dihydrolipoic acid maintains ubiquinone in the antioxidant active form by two-electron reduction of ubiquinone and one-electron reduction of ubisemiquinone.

Dihydrolipoic acid (DHLA) is a constituent of cellular energy metabolism, where it cycles between the oxidized and reduced form. The two thiol residues of DHLA make this biomolecule susceptible to most radical species and prevent Fenton-type reactions by chelating free iron. In this study we present a novel mode of action by which DHLA exerts antioxidant function in combination with coenzyme Q (ubiquinone). DHLA was found to reduce ubiquinone to ubiquinol by the transfer of a pair of electrons, thereby increasing the antioxidant capacity of coenzyme Q in biomembranes. In addition, ubisemiquinone, which was earlier shown to be an active oxygen radical source when existing in the anionic form, is removed from equilibrium by the addition of a single electron from DHLA. The high reactivity of DHLA with this potentially deleterious ubisemiquinone species not only prevents the formation of prooxidants, it also keeps ubiquinone in its antioxidant active form. Experimental data of this study demonstrate a superadditive effect of ubiquinone in combination with DHLA in preventing peroxidation of biomembranes.