Uncoupling of oxidative phosphorylation

AOP Report: Uncoupling of Oxidative Phosphorylation Leading to Growth Inhibition via Decreased Cell Proliferation

This report describes a novel adverse outcome pathway (AOP) on uncoupling of oxidative phosphorylation (OXPHOS) leading to growth inhibition via decreased adenosine triphosphate (ATP) pool and cell proliferation (AOPWiki, AOP263). Oxidative phosphorylation is a major metabolic process that produces the primary form of energy (ATP) supporting various biological functions. Uncoupling of OXPHOS is a widely recognized mode of action of many chemicals and is known to affect growth via different biological processes. Capturing these events in an AOP can greatly facilitate mechanistic understanding and hazard assessment of OXPHOS uncouplers and growth regulators in eukaryotes. The four proposed key events in this AOP are intentionally generalized to cover a wide range of organisms and stressors. Three out of four events can be measured using in vitro high-throughput bioassays, whereas for most organisms, growth inhibition can also be measured in a high-throughput format using standard in vivo toxicity test protocols. The key events and key event relationships in this AOP are further assessed for weight of evidence using evolved Bradford-Hill considerations. The overall confidence levels range from moderate to high with only a few uncertainties and inconsistencies. The chemical applicability domain of the AOP mainly contains protonophores uncouplers, which can be predicated using the quantitative structure-activity relationship (QSAR) approach and validated using in vitro high-throughput bioassays. The biological domain of the AOP basically covers all eukaryotes. The AOP described in this report is part of a larger AOP network linking uncoupling of OXPHOS to growth inhibition, and is considered highly relevant and applicable to both human health and ecological risk assessments.

Bioenergetic Pathways in the Sperm of an Under-Ice Spawning Fish, Burbot (Lota lota): The Role of Mitochondrial Respiration in a Varying Thermal Environment

Regarding the sperm of cold-water fish, the contributions of different bioenergetic pathways, including mitochondrial respiration, to energy production at the spawning temperature and its adaptation at the maximum critical temperature (CTmax) are unclear. The roles of glycolysis, fatty acid oxidation, oxidative phosphorylation (OXPHOS) at 4 °C, and OXPHOS at 15 °C for energy production in burbot (Lota lota) spermatozoa were studied by motility and the oxygen consumption rate (OCR) (with and without pathway inhibitors and the OXPHOS uncoupler). At both temperatures, the effects of the inhibitors and the uncoupler on the motility duration, curvilinear velocity, and track linearity were insignificant; in addition, the OCRs in activation and non-activation media differed insignificantly and were not enhanced after uncoupler treatment. After inhibitor treatment in both media, OXPHOS was insignificantly different at the 2, 30, and 60 s time points at 4 °C but was reduced significantly at the 30 and 60 s time points after treatment with sodium azide at 15 °C. In conclusion, for burbot sperm at both the spawning temperature and the CTmax, the energy synthesized via OXPHOS during motility was insufficient. Therefore, the majority of the energy required to sustain motility was derived from pre-accumulated energy produced and stored during the quiescent state of the spermatozoa.

Predicting the toxicity of substituted phenols to aquatic species and its changes in the stream and effluent waters

The changes in the acute toxicity of 16 phenols toward Selenastrum capricornutum and Daphnia magna were examined as a function of their physical/chemical properties. The results demonstrated that phenols with a higher octanol-water partition coefficient (K(ow)) had a higher toxicity toward aquatic organisms. The toxicity of phenols was closely related to the log K(ow) values, with correlation coefficients of 0.93 (except for the nitrophenols) and 0.89 for S. capricornutum and D. magna, respectively. The changes in the phenols toxicities in the site waters (i.e., stream and effluent waters) were investigated by calculating the water effect ratios (WER) from the results of the toxicity tests in the site waters using D. magna. The results showed that the degree of ionization for each phenolic compound was altered by the differences in the dissociation constant (pK(a)), and the change in the toxicity could be predicted. Therefore, the WER should be considered when the toxicity of phenolic compounds is estimated in site waters. The quantitative structure-activity relationships (QSAR) study showed that the toxicity of the phenols to D. magna could be predicted by the hydrophobicity (log K(ow)) alone and by combining the log K(ow) with pK(a), while the toxicity to S. capricornutum was predicted by a combination of hydrophobicity (log K(ow)) and E(LUMO) (or pK(a)).

Photo-induced cytomorphologic changes in an advanced cancer phase I clinical trial

BACKGROUND AND OBJECTIVES

The aim of this study was to investigate whether the application of an Infrared Pulsed Laser Device (IPLD) photo-induced significant cytomorphologic changes during the monitoring of advanced cancer patients participating in a phase I clinical trial.

MATERIALS AND METHODS

Patients were irradiated with an IPLD (904 nm pulsed at 3 MHz) under a one-dose, one-schedule, and one-procedure design. Total daily dose consisted of a Radiant Exposure of 4.5x10(5) J/m(2). Thirty-one tissue samples from eleven patients with progressive solid neoplastic diseases (TNM IV, UICC) were obtained at three intervals: Time 0 (15-90 days pre-treatment, n=11); Time I (2-5 months post-treatment; n=11); Time II (6-12 months post-treatment, n=09). Three blinded pathologists evaluated samples; scores were determined by consensus. Data were evaluated by using the Wilcoxon matched-pairs signed-rank test and Spearman rank correlation coefficient. The level of statistical significance was alpha=0.05.

RESULTS

Increased apoptosis (Time I, P<0.003; Time II, P<0.007), necrosis (Time I, NS; Time II, P<0.01), cytoplasmic vacuoles (Time I, P<0.03; Time II, P<0.02), and nuclear vacuoles (Time I, NS; Time II, P<0.01), reduced cell size (Time I, P<0.007; Time II, P<0.01) and intercellular adhesion (Time I, P<0.01; Time II, P<0.02) were present in neoplastic cells after IPLD treatment. No apparent changes were noted in non-neoplastic cells. The Spearman rank correlation coefficient between apoptosis, necrosis, nuclear vacuoles, cytoplasmatic vacuoles, intercellular adhesion, and cell size was positive and highly significant (P<0.006).

CONCLUSIONS

Although further research is necessary, our preliminary results support the novel possibility that the IPLD photo-induces chaotic dynamics that modulate complex physiologically reparative bioeffects.

Uncoupling effect of anacardic acids from cashew nut shell oil on oxidative phosphorylation of rat liver mitochondria

Anacardic acids are one of natural products found in not only the cashew nut shell oil but also the nut and fruit juice. The present study was conducted to investigate the uncoupling effect of anacardic acids on oxidative phosphorylation of rat liver mitochondria using succinate (plus rotenone) as a substrate. Four anacardic acids with C15:0, C15:1, C15:2 or C15:3 as an alkyl side chain exhibited uncoupling effects similar to the classical uncoupler, 2,4-dinitrophenol on ADP/O ratio, state 4 and respiratory control ratio (RCR). Anacardic acid with C15:1 side chain was most effective for uncoupling of these compounds. Salicylic acid, which has no alkyl side chain, exhibited a very weak uncoupling effect on oxidative phosphorylation. When the carboxyl group in anacardic acids was lost converting them to the corresponding cardanols, uncoupling activity dramatically decreased regardless of the number of double bonds in the long alkyl chain. These results suggest that the C15 alkyl side chain as well as the carboxyl group may play an important role in assisting the uncoupling activity of anacardic acids in liver mitochondria of animals. This study provides the first evidence of an uncoupling effect of anacardic acids on liver mitochondria

Intracellular calcium buffering declines in aging adrenergic nerves

Stimulation-evoked norepinephrine release from rat tail artery adrenergic nerves increased with advancing age in the Fischer-344 rat when function of norepinephrine uptake mechanisms and prejunctional alpha-2 adrenoceptors were blocked. When calcium channels were bypassed with the ionophore, ionomycin (4 microM), norepinephrine release from aged nerves (20 months) was still elevated as compared to 6-month-old nerves. Norepinephrine release stimulated by high K+ was also higher in 20-month nerves. The intracellular calcium chelator, 1,2 bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetomethylester (BAPTA/AM), was used to determine whether age-related increases in norepinephrine release could be reversed with the addition of an artificial intracellular calcium buffer. Exposure to BAPTA/AM decreased stimulation-evoked norepinephrine release in both old and young tail arteries; however, the effect was significantly greater in older arteries. When mitochondrial calcium uptake was compromised using the uncoupler of mitochondrial oxidative phosphorylation, dinitrophenol, BAPTA caused a further decrease in stimulation-evoked norepinephrine release in 20-month tail arteries with much less effect in 6-month-old nerves. These results suggest that intracellular calcium buffering is less efficient in older nerves.

pH-dependent effects of 2,4-dinitrophenol (DNP) on proliferation, endocytosis, fine structure and DNP resistance in Tetrahymena

In view of the importance of external pH on cytotoxic effects of ionizable agents, the pH-dependent effects of 2,4-dinitrophenol (DNP) were investigated. As uncoupler of oxidative phosphorylation, DNP interferes with the proton gradient across the inner mitochondrial membrane. DNP was added to proliferating Tetrahymena pyriformis in media of different initial pH. Effects studied were rates of cell proliferation and endocytosis, and fine structure. Findings correlated with the calculated concentration of undissociated DNP, taking into account that pH changes with time and cell density in Tetrahymena cultures. A linear relationship thus emerged between initial concentrations of undissociated DNP and lengths of the lag preceding cell proliferation. Once resumed, the rate of proliferation corresponded to that of control cells, even in different concentrations of undissociated DNP, presumably indicating an adaptation mechanism. Endocytosis was elevated throughout a wide range of undissociated DNP concentrations with a sharp transition towards inhibition at high DNP concentrations causing lethality with time. Changes in fine structure of DNP-treated cells (mitochondria, peroxisomes, nucleoli) also depended on the concentration of undissociated DNP.

Mechanism of anoxic conduction block in mammalian nerve

The mechanism by which anoxia blocks impulse conduction was studied in isolated sciatic nerves from the rat. The desheathed nerve was mounted in a recording chamber, and the compound action potential (CAP) was measured at controlled temperature (23 and 37 degrees C). When the nerve was irrigated with nitrogenated Ringer's solution compound action potential decreased to 50% in 10 min at 37 degrees C and in 35 min at 23 degrees C, whereas in oxygenated solution compound action potential decreased less than 5% in 60 min. A Na-free nitrogenated solution similarly caused anoxic block, that is the effect was independent of impulse activity. Ouabain (1 mM) decreased compound action potential by only ca. 4% in 30 min, and the effect of anoxia was delayed in presence of ouabain. Dinitrophenol (0.05 mM) reduced compound action potential to 50% in 5 min. These findings indicated that the anoxic block was not related to changes in axonal concentration of Na or K following impulse activity or inhibition of Na-K-ATPase. Instead the findings imply that the anoxic block is due to inactivation of Na-channels as a consequence of inhibition of another ATP-dependent process in the axon.

Calcium-insensitive miniature endplate potentials at the neuromuscular junction

Several different types of acetylcholine secretion have been shown to coexist at the neuromuscular junction along with the Ca2+-dependent quantal release producing miniature endplate potentials (mepps) and endplate potentials. One of these, the Ca2+-insensitive, slow-rising mepps (slow mepps), is present in normal untreated muscles but is most prominent in many conditions where the Ca2+-dependent quantal release mechanism is not functioning properly. Slow mepps occur at a frequency of less than 0.1 Hz in normal muscles, with large variability between fibres and muscles, and can reach frequencies of 1-2 Hz in several pathological conditions. The potentials are also highly variable in size and shape, being generally of high amplitude (0.1-15 mV) and prolonged time course (1-15 ms rise time). Most importantly, slow mepps are not affected by procedures which increase the intraterminal Ca2+ concentration, including nerve stimulation, thus being unable to contribute to the function of synaptic transmission. The cellular source of the Ca2+-insensitive mepps has been determined to be the nerve terminal and not the Schwann cells or nerve sprouts. The release process producing slow mepps is generally insensitive to many drugs, ions, and procedures, stimulation being observed with vinblastine, cytochalasin B, and caffeine. Depression of this secretion is effected by uncouplers of oxidative phosphorylation and by a drug (AH5183) which inhibits the vesicular active acetylcholine transport system. It is concluded that the slow mepps are due to an exocytic fusion of unique synaptic vesicles with the plasma membrane near the active zones, in a process insensitive to many intracellular ions and regulators. Since slow mepps are prominent in many pathological conditions of nerve and muscle, it is speculated that they play some role in the recovery or development of synaptic function.

Inhibition of an oligomycin-sensitive ATPase by cationic dyes, some of which are atypical uncouplers of intact mitochondria

The inhibition of an oligomycin sensitive ATPase prepared from bovine heart submitochondrial particles (J.A. Berden and M.M. Voorn-Brouwer, 1978, Biochim. Biophys. Acta 501, 424-439) by a number of cationic dyes has been compared in order to develop a structure-function relationship. Two generalizations emerge from this comparison. First, the most effective dyes have net positive charge at neutral pH; and second, those dyes containing alkyl substituted secondary and tertiary amino groups are more effective than analogs with primary aromatic amino groups. Some of the cationic dyes exhibit uncoupling activity when added to intact rat liver mitochondria, stimulating both State 4 respiration and the latent ATPase activity. The order of effectiveness and concentrations for maximal stimulation of respiration are: coriphosphine (0.3 microM), Nile blue A (0.5 microM), pyronin Y (0.8 microM), and acridine orange (10 microM). Atypically, oligomycin inhibits the stimulation of respiration by these cationic acid uncouplers. The order of effectiveness and concentrations for maximal stimulation of the latent ATPase are: Nile blue A (2 microM), pyronin Y (8 microM), acridine orange (25 microM), and coriphosphine (75 microM). At concentrations greater than those shown for maximal stimulation, the uncoupling dyes inhibited respiration and the latent ATPase. The cationic dyes tested that were not uncouplers are inhibitors of respiration and the latent ATPase of intact mitochondria at all concentrations tested.

Energy utilization in the uptake of catecholamines by synaptic vesicles and adrenal chromaffin granules

Several inhibitors of energy metabolism decreased the ATP-stimulated uptake of catecholamines by isolated synaptic vesicles from rat brain and by chromaffin granules from bovine adrenal medulla. Catecholamine uptake was inhibited by dinitrophenol, S-13 and oleic acid, which are known to block active transport by dissipating trans-membrane proton gradients. Thus a proton gradient appears to be involved in catecholamine transport. Both catecholamine uptake and vesicle-associated Ca2+/Mg2+-ATPase were inhibited by dicyclohexylcarbodiimide and tributyltin, which had previously been shown to inhibit the Ca2+/Mg2+-ATPase of mitochondria. However, mitochondrial ATPase was not involved in catecholamine uptake as oligomycin and aurovertin, more specific inhibitors of mitochondrial ATPase, did not affect catecholamine uptake. It is suggested that ATP stimulates catecholamine uptake by serving as a substrate for the ATPase. Activity of this enzyme causes translocation of protons across the vesicle membrane establishing a trans-membrane proton gradient. The proton gradient drives the transport of catecholamines.

Reye's syndrome: patient serum alters mitochondrial function and morphology in vitro

A direct relationship between a putative Reye's syndrome "serum factor" and generalized mitochondrial damage has been demonstrated in vitro. The clinical features of Reye's syndrome may be secondary to disrupted mitochondrial structure and a consequent impairment of energy-linked functions involving many organs.