Platelet factors are induced by longevity factor klotho and enhance cognition in young and aging mice

Platelet factors regulate wound healing and can signal from the blood to the brain1,2. However, whether platelet factors modulate cognition, a highly valued and central manifestation of brain function, is unknown. Here we show that systemic platelet factor 4 (PF4) permeates the brain and enhances cognition. We found that, in mice, peripheral administration of klotho, a longevity and cognition-enhancing protein3-7, increased the levels of multiple platelet factors in plasma, including PF4. A pharmacologic intervention that inhibits platelet activation blocked klotho-mediated cognitive enhancement, indicating that klotho may require platelets to enhance cognition. To directly test the effects of platelet factors on the brain, we treated mice with vehicle or systemic PF4. In young mice, PF4 enhanced synaptic plasticity and cognition. In old mice, PF4 decreased cognitive deficits and restored aging-induced increases of select factors associated with cognitive performance in the hippocampus. The effects of klotho on cognition were still present in mice lacking PF4, suggesting this platelet factor is sufficient to enhance cognition but not necessary for the effects of klotho-and that other unidentified factors probably contribute. Augmenting platelet factors, possible messengers of klotho, may enhance cognition in the young brain and decrease cognitive deficits in the aging brain.

Longevity factor klotho enhances cognition in aged nonhuman primates

Cognitive dysfunction in aging is a major biomedical challenge. Whether treatment with klotho, a longevity factor, could enhance cognition in human-relevant models such as in nonhuman primates is unknown and represents a major knowledge gap in the path to therapeutics. We validated the rhesus form of the klotho protein in mice showing it increased synaptic plasticity and cognition. We then found that a single administration of low-dose, but not high-dose, klotho enhanced memory in aged nonhuman primates. Systemic low-dose klotho treatment may prove therapeutic in aging humans.

KL1 Domain of Longevity Factor Klotho Mimics the Metabolome of Cognitive Stimulation and Enhances Cognition in Young and Aging Mice

Cognitive deficits are a major biomedical challenge-and engagement of the brain in stimulating tasks improves cognition in aged individuals (Wilson et al., 2002; Gates et al., 2011) and rodents (Aidil-Carvalho et al., 2017), through unknown mechanisms. Whether cognitive stimulation alters specific metabolic pathways in the brain is unknown. Understanding which metabolic processes are involved in cognitive stimulation is important because it could lead to pharmacologic intervention that promotes biological effects of a beneficial behavior, toward the goal of effective medical treatments for cognitive deficits. Here we show using male mice that cognitive stimulation induced metabolic remodeling of the mouse hippocampus, and that pharmacologic treatment with the longevity hormone α-klotho (KL), mediated by its KL1 domain, partially mimicked this alteration. The shared, metabolic signature shared between cognitive stimulation and treatment with KL or KL1 closely correlated with individual mouse cognitive performance, indicating a link between metabolite levels and learning and memory. Importantly, the treatment of mice with KL1, an endogenous circulating factor that more closely mimicked cognitive stimulation than KL, acutely increased synaptic plasticity, a substrate of cognition. KL1 also improved cognition, itself, in young mice and countered deficits in old mice. Our data show that treatments or interventions mimicking the hippocampal metabolome of cognitive stimulation can enhance brain functions. Further, we identify the specific domain by which klotho promotes brain functions, through KL1, a metabolic mimic of cognitive stimulation.SIGNIFICANCE STATEMENT Cognitive deficits are a major biomedical challenge without truly effective pharmacologic treatments. Engaging the brain through cognitive tasks benefits cognition. Mimicking the effects of such beneficial behaviors through pharmacological treatment represents a highly valuable medical approach to treating cognitive deficits. We demonstrate that brain engagement through cognitive stimulation induces metabolic remodeling of the hippocampus that was acutely recapitulated by the longevity factor klotho, mediated by its KL1 domain. Treatment with KL1, a close mimic of cognitive stimulation, enhanced cognition and countered cognitive aging. Our findings shed light on how cognition metabolically alters the brain and provide a plausible therapeutic intervention for mimicking these alterations that, in turn, improves cognition in the young and aging brain.

A second X chromosome contributes to resilience in a mouse model of Alzheimer's disease

A major sex difference in Alzheimer's disease (AD) is that men with the disease die earlier than do women. In aging and preclinical AD, men also show more cognitive deficits. Here, we show that the X chromosome affects AD-related vulnerability in mice expressing the human amyloid precursor protein (hAPP), a model of AD. XY-hAPP mice genetically modified to develop testicles or ovaries showed worse mortality and deficits than did XX-hAPP mice with either gonad, indicating a sex chromosome effect. To dissect whether the absence of a second X chromosome or the presence of a Y chromosome conferred a disadvantage on male mice, we varied sex chromosome dosage. With or without a Y chromosome, hAPP mice with one X chromosome showed worse mortality and deficits than did those with two X chromosomes. Thus, adding a second X chromosome conferred resilience to XY males and XO females. In addition, the Y chromosome, its sex-determining region Y gene (Sry), or testicular development modified mortality in hAPP mice with one X chromosome such that XY males with testicles survived longer than did XY or XO females with ovaries. Furthermore, a second X chromosome conferred resilience potentially through the candidate gene Kdm6a, which does not undergo X-linked inactivation. In humans, genetic variation in KDM6A was linked to higher brain expression and associated with less cognitive decline in aging and preclinical AD, suggesting its relevance to human brain health. Our study suggests a potential role for sex chromosomes in modulating disease vulnerability related to AD.

Peripheral Elevation of a Klotho Fragment Enhances Brain Function and Resilience in Young, Aging, and α-Synuclein Transgenic Mice

Cognitive dysfunction and decreased mobility from aging and neurodegenerative conditions, such as Parkinson and Alzheimer diseases, are major biomedical challenges in need of more effective therapies. Increasing brain resilience may represent a new treatment strategy. Klotho, a longevity factor, enhances cognition when genetically and broadly overexpressed in its full, wild-type form over the mouse lifespan. Whether acute klotho treatment can rapidly enhance cognitive and motor functions or induce resilience is a gap in our knowledge of its therapeutic potential. Here, we show that an α-klotho protein fragment (αKL-F), administered peripherally, surprisingly induced cognitive enhancement and neural resilience despite impermeability to the blood-brain barrier in young, aging, and transgenic α-synuclein mice. αKL-F treatment induced cleavage of the NMDAR subunit GluN2B and also enhanced NMDAR-dependent synaptic plasticity. GluN2B blockade abolished αKL-F-mediated effects. Peripheral αKL-F treatment is sufficient to induce neural enhancement and resilience in mice and may prove therapeutic in humans.

Non-Gaussian energy landscape of a simple model for strong network-forming liquids: Accurate evaluation of the configurational entropy

We present a numerical study of the statistical properties of the potential energy landscape of a simple model for strong network-forming liquids. The model is a system of spherical particles interacting through a square-well potential, with an additional constraint that limits the maximum number of bonds Nmax per particle. Extensive simulations have been carried out as a function of temperature, packing fraction, and Nmax. The dynamics of this model are characterized by Arrhenius temperature dependence of the transport coefficients and by nearly exponential relaxation of dynamic correlators, i.e., features defining strong glass-forming liquids. This model has two important features: (i) Landscape basins can be associated with bonding patterns. (ii) The configurational volume of the basin can be evaluated in a formally exact way, and numerically with an arbitrary precision. These features allow us to evaluate the number of different topologies the bonding pattern can adopt. We find that the number of fully bonded configurations, i.e., configurations in which all particles are bonded to Nmax neighbors, is extensive, suggesting that the configurational entropy of the low temperature fluid is finite. We also evaluate the energy dependence of the configurational entropy close to the fully bonded state and show that it follows a logarithmic functional form, different from the quadratic dependence characterizing fragile liquids. We suggest that the presence of a discrete energy scale, provided by the particle bonds, and the intrinsic degeneracy of fully bonded disordered networks differentiates strong from fragile behavior.

Gel to glass transition in simulation of a valence-limited colloidal system

We numerically study a simple model for thermoreversible colloidal gelation in which particles can form reversible bonds with a predefined maximum number of neighbors. We focus on three and four maximally coordinated particles, since in these two cases the low valency makes it possible to probe, in equilibrium, slow dynamics down to very low temperatures T. By studying a large region of T and packing fraction phi we are able to estimate both the location of the liquid-gas phase separation spinodal and the locus of dynamic arrest, where the system is trapped in a disordered nonergodic state. We find that there are two distinct arrest lines for the system: a glass line at high packing fraction, and a gel line at low phi and T. The former is rather vertical (phi controlled), while the latter is rather horizontal (T controlled) in the phi-T plane. Dynamics on approaching the glass line along isotherms exhibit a power-law dependence on phi, while dynamics along isochores follow an activated (Arrhenius) dependence. The gel has clearly distinct properties from those of both a repulsive and an attractive glass. A gel to glass crossover occurs in a fairly narrow range in phi along low-T isotherms, seen most strikingly in the behavior of the nonergodicity factor. Interestingly, we detect the presence of anomalous dynamics, such as subdiffusive behavior for the mean squared displacement and logarithmic decay for the density correlation functions in the region where the gel dynamics interferes with the glass dynamics.

Energy landscape of a simple model for strong liquids

We calculate the statistical properties of the energy landscape of a minimal model for strong network-forming liquids. Dynamic and thermodynamic properties of this model can be computed with arbitrary precision even at low temperatures. A degenerate disordered ground state and logarithmic statistics for the local minima energy distribution are the landscape signatures of strong liquid behavior. Differences from fragile liquid properties are attributed to the presence of a discrete energy scale, provided by the particle bonds, and to the intrinsic degeneracy of topologically disordered networks.

Model for reversible colloidal gelation

We report a numerical study, covering a wide range of packing fraction Phi and temperature T, for a system of particles interacting via a square well potential supplemented by an additional constraint on the maximum number n(max) of bonded interactions. We show that, when n(max)<6, the liquid-gas coexistence region shrinks, giving access to regions of low Phi where dynamics can be followed down to low T without an intervening phase separation. We characterize these arrested states at low densities (gel states) in terms of structure and dynamical slowing down, pointing out features which are very different from the standard glassy states observed at high Phi values.

Methyl group dynamics in a confined glass

We present a neutron scattering investigation on methyl group dynamics in glassy toluene confined in mesoporous silicates of different pore sizes. The experimental results have been analysed in terms of a barrier distribution model, such a distribution following from the structural disorder in the glassy state. Confinement results in a strong decreasing of the average rotational barrier in comparison to the bulk state. We have roughly separated the distribution for the confined state in a bulk-like and a surface-like contribution, corresponding to rotors at a distance from the pore wall respectively larger and smaller than the spatial range of the interactions which contribute to the rotational potential for the methyl groups. We have estimated a distance of 7 A as a lower limit of the interaction range, beyond the typical nearest-neighbour distance between centers-of-mass (4.7 A).

Cholestasis induced by chronic treatment with alpha-naphthyl-isothiocyanate (ANIT) affects rat renal mitochondrial bioenergetics

Chronic cholestasis is characteristic of many human liver diseases. Renal injury has been often associated with this type of disease. The aim of this study was to evaluate the effect of cholestasis on kidney mitochondrial bioenergetics following in vivo chronic administration of alpha-naphthyl-isothiocyanate (ANIT), a known cholestatic agent. Serum markers of renal injury, kidney morphology and endogenous adenine nucleotides were measured in ANIT-treated rats (80 mg/kg per week s.c. for 16 weeks). Changes in membrane potential and mitochondrial respiration as well as alterations in mitochondrial calcium homeostasis were monitored. Cholestatic animals shown no alterations in renal morphology when compared with control. Additionally, following chronic ANIT administration, no significant alterations in mitochondrial respiratory function have been shown. The phosphorylation capacity of cholestatic kidney mitochondria was enhanced. Associated with these parameters, mitochondria from treated animals exhibited a decreased susceptibility to disruption of mitochondrial calcium homeostasis, due to permeability transition induction. These data suggest that, despite being submitted to chronic treatment with ANIT, kidney mitochondria from cholestasis-induced rats present some defense mechanisms to circumvent this aggression. They show improved phosphorylative capacity and, moreover, a decreased susceptibility to mitochondrial permeability transition induction, probably due to adaptative mechanisms of calcium transport.

Carvedilol reduces mitochondrial damage induced by hypoxanthine/xanthine oxidase: relevance to hypoxia/reoxygenation injury

The cardioprotective properties of new pharmaceuticals such as carvedilol might be explained by enhanced mitochondrial protection. The aim of this work was to determine the role of carvedilol in the protection of heart mitochondria from oxidative damage induced by hypoxanthine/xanthine oxidase, a known source of oxidative stress in the vascular system. Carvedilol reduced oxidative-stress-induced mitochondrial injury, as seen by the delay in the loss of the mitochondrial transmembranar potential (Delta Psi), the decrease in mitochondrial swelling, and the increase in mitochondrial calcium uptake. Carvedilol improved the mitochondrial respiratory activity in state III and offered an overall protection in the respiratory control and in the P/O ratios in mitochondria under oxidative stress. The data indicated that carvedilol was able to partly protect heart mitochondria from oxidative stress-induced damage. Our results suggest that mitochondria can be important targets for some cardioprotective pharmaceuticals.

Mechanisms of the deleterious effects of tamoxifen on mitochondrial respiration rate and phosphorylation efficiency

Tamoxifen (TAM), the widely prescribed drug in the prevention and therapy of breast cancer, is a well-known modulator of estrogen receptor (ER) that also inhibits the proliferation of different cell types that lack the ER. However, the ER-independent action mechanisms of TAM and its side effects have not been yet clarified. Mitochondria are essential in supporting the energy-dependent regulation of cell functions. Changes in mitochondria result in bioenergetic deficits leading to the loss of vital functions to cell survival. Therefore, this study describes the effects of TAM on mitochondrial bioenergetics, contributing to a better understanding of the biochemical mechanisms underlying the multiple antiproliferative and toxic effects of this drug. TAM at concentrations above 20 nmol/mg protein, preincubated with isolated rat liver mitochondria at 25 degrees C for 3 min, significantly depresses, in a dose-dependent manner, the phosphorylation efficiency of mitochondria as inferred from the decrease in the respiratory control and ADP/O ratios, the perturbations in mitochondrial transmembrane potential (DeltaPsi), the fluctuations associated with mitochondrial energization, and the phosphorylative cycle induced by ADP. Furthermore, TAM at up to 40 nmol/mg protein stimulates the rate of state 4 respiration and at higher concentrations it strongly inhibits state 3 and uncouples the mitochondrial respiration. The stimulation of state 4 respiration parallels the decrease of DeltaPsi as a consequence of proton permeability. The TAM-stimulatory action of ATPase is also observed in intact mitochondria, suggesting that TAM promotes extensive permeability to protons due to destructive effects in the structural integrity of the mitochondrial inner membrane. These multiple effects of TAM on mitochondrial bioenergetic functions, causing changes in the respiration, phosphorylation efficiency, and membrane structure, may explain the cell death induced by this drug in different cell types, its anticancer activity in ER-negative cells, and its side effects.

Enhanced mitochondrial testicular antioxidant capacity in Goto-Kakizaki diabetic rats: role of coenzyme Q

Because diabetes mellitus is associated with impairment of testicular function, ultimately leading to reduced fertility, this study was conducted to evaluate the existence of a cause-effect relationship between increased oxidative stress in diabetes and reduced mitochondrial antioxidant capacity. The susceptibility to oxidative stress and antioxidant capacity (in terms of glutathione, coenzyme Q, and vitamin E content) of testis mitochondrial preparations isolated from Goto-Kakizaki (GK) non-insulin-dependent diabetic rats and from Wistar control rats, 1 yr of age, was evaluated. It was found that GK mitochondrial preparations showed a lower susceptibility to lipid peroxidation induced by ADP/Fe(2+), as evaluated by oxygen consumption and reactive oxygen species generation. The decreased susceptibility to oxidative stress in diabetic rats was associated with an increase in mitochondrial glutathione and coenzyme Q9 contents, whereas vitamin E was not changed. These results demonstrate a higher antioxidant capacity in diabetic GK rats. We suggest this is an adaptive response of testis mitochondria to the increased oxidative damage in diabetes mellitus.

Protective effect of carvedilol on chenodeoxycholate induction of the permeability transition pore

Intracellular accumulation of toxic, hydrophobic bile acids has been proposed as one of the putative final common pathways leading to cholestatic liver injury. Furthermore, bile acids have been proposed as a causative factor for hepatic cardiomyopathy. Hepatic tissue concentrations of chenodeoxycholic acid (CDCA) during cholestasis are greater than those of other toxic bile acids. In the presence of calcium and phosphate, CDCA induced the permeability transition pore (PTP) in freshly isolated rat liver mitochondria. In this study, we evaluated the effects of carvedilol, a multirole cardioprotective compound, on CDCA-induced PTP. Mitochondrial membrane potential, osmotic swelling, and calcium fluxes were monitored. CDCA-induced PTP, characterized by membrane depolarization, release of matrix calcium, and osmotic swelling, was prevented by carvedilol. Under the same conditions, its hydroxylated analog BM-910228 did not reveal any protective effect. This finding reinforces carvedilol's therapeutic interest, because it may potentially prevent mitochondrial dysfunction associated with cardiomyopathy in the pathophysiology of cholestatic liver disease

Carvedilol in heart mitochondria: protonophore or opener of the mitochondrial K(ATP) channels?

Carvedilol ([1-[carbazolyl-(4)-oxy]-3-[2-methoxyphenoxyethyl) amino]-propanol-(2)]) has been shown to protect cardiac mitochondria from oxidative stress. In this work we examined the mechanisms responsible for an observed depressive effect in the mitochondrial transmembrane potential (delta psi). Two possible mechanisms were considered: a protonophoretic activity and the opening of mitochondrial ATP-sensitive potassium channels. We show that carvedilol increases mitochondrial inner membrane permeability to protons, but not to potassium, causing an increase in state IV respiration in the presence and absence of oligomycin. By contrast, a K(ATP)-channel inhibitor, 5-hydroxydecanoic acid, did not affect carvedilol-induced depolarizations. Hence, our results suggest that carvedilol depresses mitochondrial delta psi by a weak protonophoretic mechanism.

Brain and liver mitochondria isolated from diabetic Goto-Kakizaki rats show different susceptibility to induced oxidative stress

BACKGROUND

Increased oxidative stress and changes in antioxidant capacity observed in both clinical and experimental diabetes mellitus have been implicated in the etiology of chronic diabetic complications. Many authors have shown that hyperglycemia leads to an increase in lipid peroxidation in diabetic patients and animals reflecting a rise in reactive oxygen species production. The aim of the study was to compare the susceptibility of mitochondria from brain and liver of Goto-Kakizaki (12-month-old diabetic) rats (GK rats), a model of non-insulin dependent diabetes mellitus, to oxidative stress and antioxidant defenses.

METHODS

Brain and liver mitochondrial preparations were obtained by differential centrifugation. Oxidative damage injury was induced in vitro by the oxidant pair ADP/Fe(2+) and the extent of membrane oxidation was assessed by oxygen consumption, malondialdehyde (MDA) and thiobarbituric acid reactive substances (TBARS) formation. Coenzyme Q and alpha-tocopherol contents were measured by high-performance liquid chromatography (HPLC).

RESULTS

Brain mitochondria isolated from 12-month-old control rats displayed a higher susceptibility to lipid peroxidation, as assessed by oxygen consumption and formation of MDA and TBARS, compared to liver mitochondria. In GK rats, mitochondria isolated from brain were more susceptible to in vitro oxidative damage than brain mitochondria from normal rats. In contrast, liver mitochondria from diabetic rats were less susceptible to oxidative damage than mitochondria from normal rats. This decreased susceptibility was inversely related to their alpha-tocopherol and coenzyme Q (CoQ) content.

CONCLUSIONS

The present results indicate that the diabetic state can result in an elevation of both alpha-tocopherol and CoQ content in liver, which may be involved in the elimination of mitochondrially generated reactive oxygen species. The difference in the antioxidant defense mechanisms in the brain and liver mitochondrial preparations of moderately hyperglycemic diabetic GK rats may correspond to a different adaptive response of the cells to the increased oxidative damage in diabetes.

Inhibitory effect of carvedilol in the high-conductance state of the mitochondrial permeability transition pore

The mitochondrial permeability transition is a widely studied, but poorly understood, phenomenon in mitochondrial bioenergetics. It has been recognised that this phenomenon is related to the opening of a protein pore in the inner mitochondrial membrane, and that opening of this pore is the cause of some forms of mitochondrial dysfunction. In this work, we propose that carvedilol, a multi-role cardioprotective compound, may act as an inhibitor of the high-conductance state of the mitochondrial permeability transition pore, a conclusion supported by the finding that carvedilol provides differential protection against mitochondrial swelling in sucrose and KCl-based media, and that it is unable to protect against calcium-induced depolarisation of the mitochondrial membrane. We also show that carvedilol inhibits the oxidation of mitochondrial thiol groups and that, beyond causing a slight depression of the membrane potential, it has no inhibitory effect on mitochondrial calcium uptake.A decrease in the number of oxidised protein thiol groups may be the main mechanism responsible for this selective inhibition of the permeability transition pore in heart mitochondria. These effects may be important for the role of carvedilol in some cardiac pathologies.

Chenodeoxycholate is a potent inducer of the permeability transition pore in rat liver mitochondria

Several reports support the concept that bile acids may be cytotoxic during cholestatic disease process by causing mitochondrial dysfunction. Here we report additional data and findings aimed at a better understanding of the involvement of the permeability transition pore (PTP) opening in bile acids toxicity. The mitochondrial PTP is implicated as a mediator of cell injury and death in many situations. In the presence of calcium and phosphate, chenodeoxycholic acid (CDCA) induced a permeability transition in freshly isolated rat liver mitochondria, characterized by membrane depolarization, release of matrix calcium, and osmotic swelling. All these events were blocked by cyclosporine A (CyA) and the calcium uniporter inhibitor ruthenium red (RR). The results suggest that CDCA increases the sensitivity of isolated mitochondria in vitro to the calcium-dependent induction of the PTP.

Decreased susceptibility of heart mitochondria from diabetic GK rats to mitochondrial permeability transition induced by calcium phosphate

Type 2 diabetes (or non-insulin dependent diabetes mellitus, NIDDM) is a common metabolic disease in man. The Goto-Kakizaki (GK) rat has been designed as a NIDDM model. Previous studies with this strain have shown differences at the mitochondrial level. The mitochondrial permeability transition (MPT) is a widely studied phenomenon but yet poorly understood, that leads to mitochondrial dysfunction and cell death. The aim of this work was to compare the differences in susceptibility of induction of the MPT with calcium phosphate in GK and Wistar rats. Our results show that heart mitochondria from GK rats are less susceptible to the induction of MPT, and show a larger calcium accumulation before the overall loss of mitochondrial impermeability.

Inhibition of heart mitochondrial lipid peroxidation by non-toxic concentrations of carvedilol and its analog BM-910228

Carvedilol, a non-selective beta-adrenoreceptor blocker, has been shown to possess a high degree of cardioprotection in experimental models of myocardial damage. Reactive oxygen species have been proposed to be implicated in such situations, and antioxidants have been demonstrated to provide partial protection to the reported damage. The purpose of our study was to investigate the antioxidant effect of carvedilol and its metabolite BM-910228 by measuring the extent of lipid peroxidation in a model of severe oxidative damage induced by ADP/FeSO(4) in isolated rat heart mitochondria. Carvedilol and BM-910228 inhibited the thiobarbituric acid-reactive substance formation and oxygen consumption associated with lipid peroxidation with IC(50) values of 6 and 0.22 microM, respectively. Under the same conditions, the IC(50) values of alpha-tocopheryl succinate and Trolox were 125 and 31 microM, respectively. As expected, the presence of carvedilol and BM-910228 preserved the structural and functional integrity of mitochondria under oxidative stress conditions for the same concentration range shown to inhibit lipid peroxidation, since they prevented the collapse of the mitochondrial membrane potential (DeltaPsi) induced by ADP/FeSO(4) in respiring mitochondria. It should be stressed that neither carvedilol nor BM-910228 induced any toxic effect on mitochondrial function in the concentration range of the compounds that inhibits the peroxidation of mitochondrial membranes. In conclusion, the antioxidant properties of carvedilol may contribute to the cardioprotective effects of the compound, namely through the preservation of mitochondrial functions whose importance in myocardial dysfunction is clearly documented. Additionally, its hydroxylated analog BM-910220, with its notably superior antioxidant activity, may significantly contribute to the therapeutic effects of carvedilol.

ihfA gene of the bacterium Myxococcus xanthus and its role in activation of carotenoid genes by blue light

Myxococcus xanthus responds to blue light by producing carotenoids. Several regulatory genes are known that participate in the light action mechanism, which leads to the transcriptional activation of the carotenoid genes. We had already reported the isolation of a carotenoid-less, Tn5-induced strain (MR508), whose mutant site was unlinked to the indicated regulatory genes. Here, we show that OmegaMR508::Tn5 affects all known light-inducible promoters in different ways. It blocks the activation of two of them by light but makes the activity of a third one light independent. The OmegaMR508 locus has been cloned and sequenced. The mutation had occurred at the promoter of a gene we propose is the M. xanthus ortholog of ihfA. This encodes the alpha subunit of the histone-like integration host factor protein. An in-frame deletion within ihfA causes the same effects as the OmegaMR508::Tn5 insertion. Like other IhfA proteins, the deduced amino acid sequence of M. xanthus IhfA shows much similarity to HU, another histone-like protein. Sequence comparison data, however, and the finding that the M. xanthus gene is preceded by gene pheT, as happens in other gram-negative bacteria, strongly argue for the proposed orthology relationship. The M. xanthus ihfA gene shows some unusual features, both from structural and physiological points of view. In particular, the protein is predicted to have a unique, long acidic extension at the carboxyl terminus, and it appears to be necessary for normal cell growth and even vital for a certain wild-type strain of M. xanthus.

Effects of carvedilol and its analog BM-910228 on mitochondrial function and oxidative stress

The antioxidant effects of carvedilol and its analog BM-910228 (also known as SB 211475) were studied in rat liver mitochondria as well as their action on mitochondrial bioenergetics. Carvedilol and BM-910228 inhibited ADP/Fe(2+)-initiated lipid peroxidation (measured in mitochondrial membranes as thiobarbituric acid reactive substances and oxygen consumption) with IC(50) values of 10.9 and 0. 33 microM, respectively. Under the same conditions, the IC(50) value for Trolox C was 18.8 microM. At the same concentration range showing antioxidant activity both compounds prevent the collapse of transmembranar electric potential induced by ADP/Fe(2+) on respiring mitochondria. Furthermore, both carvedilol and BM-910228 do not display toxic effects on mitochondria up to the concentration showing maximal antioxidant effects ( approximately 40 microM for carvedilol and approximately 1 microM for BM-910228). At higher concentrations of carvedilol (>40 microM), however, the phosphorylation efficiency of mitochondria is depressed as deduced from a decrease in respiratory control and in the ADP/oxygen ratio. The Brand approach was used to assess the effects of carvedilol on oxidative phosphorylation. We found that carvedilol stimulated membrane proton leak and inhibited substrate oxidation, but had no measurable effect on phosphorylation reactions. Because carvedilol exerts its antioxidant properties for nontoxic concentrations, its therapeutic interest is reinforced because it may potentially prevent mitochondrial dysfunctions associated to cell death in several pathophysiological states where excessive production of reactive oxygen species by mitochondria is well documented (e.g., ischemia/reperfusion). Additionally, its hydroxylated analog BM-910228 with notable superior antioxidant activity may significantly contribute to the known therapeutic effects of carvedilol.

Effects of carvedilol on isolated heart mitochondria: evidence for a protonophoretic mechanism

Carvedilol (¿1-[carbazolyl-(4)-oxy]-3-[2-methoxyphenoxyethyl)amino]-pro panol-(2) ¿) is a novel compound used in clinical practice for the treatment of congestive heart failure, mild to moderate hypertension, and myocardial infarction. Carvedilol was also shown to protect cardiac mitochondria from oxidative stress events. Because mitochondria are the main suppliers of ATP for cardiac muscle work, a study of the effects of carvedilol in mitochondrial bioenergetics is necessary to fully understand the basis of its protective role in myocardial energetics. In this work we show that carvedilol acts as an uncoupler of oxidative phosphorylation, decreasing mitochondrial electric potential (DeltaPsi) by a weak protonophoretic mechanism. Theoretical studies were carried out to determine the relevance of conformation and proton affinity of the protonable amino side-chain group in the proton-shuttling activity across the inner mitochondrial membrane. BM910228, a hydroxylated metabolite of carvedilol, was also studied for comparison with the parent compound. Implications for the protective role of carvedilol in heart mitochondrial bioenergetics are discussed.

Bile acids affect liver mitochondrial bioenergetics: possible relevance for cholestasis therapy

It has been pointed out that intracellular accumulation of bile acids cause hepatocyte injury in cholestatic disease process. This study was aimed to test if cytotoxicity of these compounds is mediated through mitochondria dysfunction. Bile acids effects on isolated rat liver mitochondrial were analyzed by monitoring changes in membrane potential and mitochondrial respiration, as well as alterations in H(+) membrane permeability and mitochondrial permeability transition pore induction. Increasing concentrations of the bile acids litocholic (LCA), deoxycholic (DCA), ursodeoxycholic (UDCA), chenodeoxycholic (CDCA), glycochenodeoxycholic (GCDC), or taurochenodeoxycholic (TCDC) decrease transmembrane potential (delta psi) developed upon succinate energization. These compounds also decreased state 3 respiration and enhanced state 4. We have also demonstrated that the observed concentration-dependent stimulation of state 4 by LCA, DCA, CDCA, TCDC, and GCDC, is associated with an enhanced permeability of mitochondria to H(+). Addition of LCA, DCA, CDCA, TCDC, GCDC, and UDCA to mitochondria energized with succinate resulted in a dose-dependent membrane depolarization and stimulation of mitochondrial permeability transition. Tauroursodeoxycholate (TUDC) elicited no significant effect on succinate-supported mitochondrial bioenergetics. In contrast, in the presence of glycoursodeoxycholic (GUDC), delta psi increases as a function of bile salt concentration. The results of this investigation demonstrate that at toxicologically relevant concentrations, most but not all bile acids alter mitochondrial bioenergetics, so impairment of mitochondrial function can be clinically relevant for patients with cholestasis.

Carvedilol inhibits the exogenous NADH dehydrogenase in rat heart mitochondria

There are several reports on the oxidation of external NADH by an exogenous NADH dehydrogenase in the outer leaflet of the inner membrane of rat heart mitochondria. Until now, however, little was known about its physiological role in cellular metabolism. The present work shows that carvedilol (¿1-[carbazolyl-(4)-oxy]-3-[2-methoxyphenoxyethyl)amino]-pro - panol-(2)¿) is a specific inhibitor of an exogenous NADH dehydrogenase in rat heart mitochondria. Carvedilol does not affect oxygen consumption linked to the oxidation of succinate and internal NADH. It is also demonstrated that the inhibition of exogenous NADH dehydrogenase by carvedilol is accompanied by the inhibition of alkalinization of the external medium. In contrast to the addition of glutamate/malate or succinate, exogenous NADH does not generate a membrane potential in rat heart mitochondria, as observed with a TPP(+) electrode. It is also demonstrated that the oxygen consumption linked to NADH oxidation is not due to permeabilized mitochondria, but to actual oxidase activity in the inner membrane. The enzyme has a K(m) for NADH of 13 microM. Carvedilol is a noncompetitive inhibitor of this external NADH dehydrogenase with a K(i) of 15 microM. Carvedilol is the first inhibitor described to this organospecific enzyme. Since this enzyme was demonstrated to play a key role in the cardiotoxicity of anticancer drugs of the anthracycline family (e.g., adriamycin), we may suggest that the administration of carvedilol to tumor patients treated with adriamycin might be of great help in the prevention of the cardioselective toxicity of this antibiotic.

Ischemic heart disease: the role of mitochondria--carvedilol prevents lipid peroxidation of mitochondrial membranes

Depriving heart tissue of their blood supply leads to a decrease in high-energy compounds and many metabolic disturbances. Following short periods of ischemia, heart can recover their physiological functions after reperfusion, but prolonged ischemia injures heart irreversibly. Mitochondrial disfunction is one of the most critical events associated to injury irreversibility because regeneration of a high ATP level is indispensable for recovery of cellular functions. Reperfusion injury is also implicated in the irreversible damage of the ischemic heart. Even after a period of ischemia that is too short to injure the heart, reperfusion can cause further irreversible damage. The formation of oxygen radicals caused by reintroduction of O2 is probably the most important factor of this phenomenon. The mitochondrial redox chain is one of the main sources of O2 radicals responsible for causing damage to mitochondria, and thus mitochondria can be damaged during reperfusion. Most probably the opening of the mitochondrial permeability transition pore due to increased production of oxygen radicals is associated with the irreversible disruption of mitochondria for oxidative phosphorylation. Carvedilol, a potent antioxidant, prevents the lipoperoxidation of mitochondrial membranes what suggest a strong contribution to the known cardioprotective activity of this compound through protection of mitochondrial functions.

Tamoxifen inhibits induction of the mitochondrial permeability transition by Ca2+ and inorganic phosphate

Tamoxifen (TAM) is a synthetic, nonsteroidal antiestrogenic agent that is widely prescribed in the treatment of estrogen-dependent neoplasias, including breast cancer. The mechanism of action has yet to be defined, but likely is independent of estrogen receptor binding. In light of its high lipophilicity and peroxyl radical scavenging activities, we hypothesized that TAM might be an effective inhibitor of the mitochondrial permeability transition (MPT), which is widely implicated in the mechanisms of chemical-induced tissue injury and apoptosis. The MPT was induced in vitro by incubating freshly isolated rat liver mitochondria in 1 mM Pi with increasing concentrations of calcium. Induction of the MPT was characterized by the calcium-dependent depolarization of mitochondrial membrane potential, release of matrix calcium, and large amplitude swelling. Membrane potential and calcium release were measured with ion-selective electrodes; mitochondrial swelling was monitored spectrophotometrically. Preincubation with either cyclosporine A or TAM prevented, in a dose-dependent manner, the calcium-induced MPT. TAM also inhibited the calcium-induced release of matrix glutathione. TAM caused a time-dependent reversal of both the calcium-induced membrane depolarization and calcium release, suggesting that the effect was on the permeability transition pore and not due to inhibition of the mitochondrial calcium uniport. The results suggest that TAM mimics cyclosporine A to inhibit induction of the MPT and that this activity is not related to the antioxidant properties of TAM.

Acrylic acid induces the glutathione-independent mitochondrial permeability transition in vitro

Acrylic acid (AA) is used widely in the synthesis of esters essential in the production of paints, adhesives, plastics, and coatings. The minimal systemic toxicity of AA is attributed to its rapid oxidation to acetyl-CoA and CO2 via the vitamin B12-independent beta-oxidation pathway. This oxidation is localized to the mitochondria and preliminary evidence suggests a possible inhibition of mitochondrial metabolism by acrylic acid. The purpose of this investigation was to evaluate whether AA interferes with mitochondrial bioenergetics in vitro. Incubation of isolated rat liver mitochondrial with AA resulted in a dose-dependent induction of the mitochondrial permeability transition (MPT). This was evidenced by an increased sensitivity to calcium-induced stimulation of state 4 oxygen consumption, depolarization of membrane potential, and swelling, all of which were prevented by preincubating the mitochondrial with cyclosporine A, a potent and specific inhibitor of the mitochondrial permeability transition pore. Both N-ethylmaleimide (NEM) and dithiothreitol (DTT) showed only partial protection against induction of the MPT by AA. Associated with the induction of the MPT by AA was the loss of mitochondrial glutathione (GSH), which was due to efflux from the matrix rather than oxidation to GSSG. Cyclosporine A, by inhibiting the permeability transition, prevented the AA-induced loss of mitochondrial GSH. In conclusion, AA increases the sensitivity of isolated mitochondria in vitro to the calcium-dependent induction of the MPT. Although the molecular mechanism has yet to be defined, it does not appear to be related to the oxidation of critical thiols.

The use of the mitochondrial transmembrane electric potential as an effective biosensor in ecotoxicological research

In this work, the mitochondrial transmembrane electric potential (delta psi) of isolated mitochondria was used to evaluate the toxicity of some chemicals (endosulfan, 3,4-dichloroaniline, parathion, tributyltin and cadmium) and wastewater. Mitochondria were isolated from rat liver, and the delta psi measured in a suitable assay medium, using a sensitive tetraphenylphosphonium (TPP+) electrode. The test substance was pre-incubated in a rotenone-containing medium during 3 min with 1.0 mg of mitochondrial protein. Mitochondria were energised with succinate and after the establishment of a constant maximal potential ADP was added to induce the phosphorylative cycle. Chosen endpoints were the membrane potential from mitochondria oxidising succinate and the depolarisation induced by ADP. After the appropriate transformations the EC50 (effective concentration) was calculated for each toxicant. Even very low concentrations of a toxicant were able to affect the delta psi, thus showing its suitability as a biosensor in ecotoxicology and results were reproducible between tests. The utilisation of delta psi in screening tests of pure substances and wastewater seems to be very effective and can be carried out routinely.

Interactions of 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene with mitochondrial oxidative phosphorylation

The effects of DDE (2,2-bis(p-chlorophenyl)-1,1-dichloroethylene), the major metabolite of DDT (2,2-bis(p-chlorophenyl)-1,1,1-trichloroethane), on rat liver mitochondrial bioenergetic activities were examined. The approach developed by M. D. Brand (Biochim Biophys Acta 1018: 128-133, 1990) was used to assess the effects of DDE because it is possible to discriminate the sites of action of compounds having pleiotypic effects on oxidative phosphorylation. Data were further confirmed using a "classical" approach, including measurements of transmembrane potential, respiratory indexes, enzymatic activities and membrane permeability to protons. DDE up to 40 nmol/mg protein affected the proton motive force generating system. In fact, DDE interacted with succinate dehydrogenase (complex II), decreasing respiration and membrane potential. In this concentration range, the permeability of the inner membrane to protons remained intact. Only higher concentrations (> or = 80 nmol/mg) increased permeability to protons, uncoupling oxidation from phosphorylation. The phosphorylative system was not affected because the rate of ATP synthesis was unchanged. In addition, data from carbonyl cyanide m-chlorophenylhydrazone-uncoupled rotenone-inhibited preparations or submitochondrial particles indicated that F0F1 ATPase activity is not affected by DDE. Therefore, DDE inhibition of complex II and putative inhibition of succinate translocation explain the depression of mitochondrial respiration. The use of appropriate substrates and assay conditions indicates that complexes I, III and IV were not affected by DDE. The uncoupling of oxidative phosphorylation at high concentrations (> 80 nmol DDE/mg protein) was probably related to deleterious effects on the integrity of the mitochondrial membrane. We confirmed that the technique originally proposed by Brand is useful for characterizing the effects of xenobiotics on oxidative phosphorylation. In addition, data provided by this technique closely agree with data from classical studies.

Renal oncocytoma: preoperative diagnosis using technetium 99m sestamibi imaging

OBJECTIVES

To determine if 99mTc-sestamibi (technetium 99m-methoxyisobutylisonitrile) can be used preoperatively to differentiate renal oncocytomas from other renal masses.

METHODS

We performed 99mTc-sestamibi scans on 6 patients with various renal masses, using a standard technique. The diagnosis in each patient was determined either by radiologic methods.

RESULTS

There was significantly increased uptake in the patient with the renal oncocytoma, whereas the other lesions had decreased uptake in comparison to normal kidney. This was determined visually and by mean pixel analysis.

CONCLUSIONS

Technetium 99m sestamibi scanning appears to have a potential role in the nonoperative diagnosis of renal oncocytomas, in combination with pathologic fine-needle biopsy confirmation. More definitive pathologic experience is required before recommending standard use.

A Soldier's Neck and Shoulder Pain

A 38-year-old male soldier presented to an acute care clinic complaining of 24 hours of persistent, bilateral shoulder and neck pain after a 12-mile road march. He denied any history of prior trauma to either area. On physical examination, there was diffuse tenderness in both supraclavicular areas as well as over the posterior neck.

Relationships between ATP depletion, membrane potential, and the release of neurotransmitters in rat nerve terminals. An in vitro study under conditions that mimic anoxia, hypoglycemia, and ischemia

BACKGROUND AND PURPOSE

It is known that the extracellular accumulation of glutamate during anoxia/ischemia is responsible for initiating neuronal injury. However, little information is available on the release of monoamines and whether the mechanism of its release resembles that of glutamate, which may itself influence the release of monoamines by activating presynaptic receptors. This study was designed to characterize the release of both amino acids and monoamines under chemical conditions that mimic anoxia, hypoglycemia, and ischemia.

METHODS

The contents of synaptosomes in adenine nucleotides (ATP, ADP, and AMP), amino acids (aspartate, glutamate, taurine, and gamma-aminobutyric acid), and monoamines (dopamine, noradrenaline, and 5-hydroxytryptamine) were measured by high-performance liquid chromatography, after the synaptosomes were subjected to anoxia (KCN + oligomycin), hypoglycemia (2 mmol/L 2-deoxyglucose in glucose-free medium), and ischemia (anoxia plus hypoglycemia).

RESULTS

The anoxia- and ischemia-induced release or noradrenaline, dopamine, 5-hydroxytryptamine, and glutamate correlated well with ATP depletion. The correlation observed between glutamate levels and the release of dopamine and 5-hydroxytryptamine in ischemic conditions suggests a functional linkage between the two transmitter systems. However, the antagonists of presynaptic glutamate receptors failed to alter the amount of monoamines released. The inhibition of Na+,K+-ATPase by ouabain had an effect similar to that produced by ischemia.

CONCLUSIONS

The decrease in Na+ and K+ gradients resulting from the energy depletion of the synaptosomes under ischemic conditions or resulting from the inhibition of Na+, K+-ATPase by ouabain promotes the reversal of the neurotransmitter transporters. The decrease in uptake of neurotransmitters may also contribute to the rise in the extracellular concentration of different transmitters observed during brain ischemia.

Continuous monitoring of mitochondrial membrane potential in hepatocyte cell suspensions

We report a simple fluorometric method for the continuous monitoring of mitochondrial membrane potential and cell viability in suspensions of hepatocytes exposed in vitro to cytotoxic agents. Suspensions of freshly isolated hepatocytes (10(6) cells/mL) preloaded with rhodamine 123 (Rh 123, 100 mumol/L) are transferred to a thermostatically controlled mixed cuvette to which the desired cytotoxic agent is added. Rh 123 is a cationic fluorophore that is actively accumulated by cells in direct proportion to the mitochondrial membrane potential. Cell viability was estimated by monitoring propidium iodide (PI) fluorescence. Exposure of cell suspensions to the mitochondrial uncoupling agent FCCP caused an immediate and titratable increase in Rh 123 fluorescence. Subsequent treatment with digitonin did not change Rh 123 fluorescence, suggeseting that Rh 123 equilibrates rapidly across the intact cell membrane. Likewise, treatment of hepatocyte suspensions with inhibitors of mitochondrial respiration (rotenone, cyanide, or menadione) caused an immediate increase in Rh 123 fluorescence. This was accompanied by a progressive increase in PI fluorescence, suggesting a causal relationship between mitochondrial depolarization and cell injury. In contrast, 1,4-benzoquinone caused a time-dependent and linear increase in PI fluorescence that paralleled changes in Rh 123 fluorescence. Comparing the time courses for changes in PI and Rh 123 fluorescence suggests that for benzoquinone, the depolarization of the mitochondria is a consequence rather than a cause of the cell injury. This modified procedure provides a simple and specific technique for continuously monitoring mitochondrial membrane potential and cell viability in suspensions of freshly isolated hepatocytes. The advantage is that there is no need to separate cells from the incubation medium, making it possible to record real-time changes in mitochondrial membrane potential and cell viability throughout the in vitro exposure period.

Thiols metabolism is altered by the herbicides paraquat, dinoseb and 2,4-D: a study in isolated hepatocytes

This report is an extension and complement of a previous study reporting the effect of three herbicides (paraquat, dinoseb and 2,4-D) on cell viability, GSH oxidation, NADH and ATP depletion (Arch. Toxicol. 68:24-31, 1994). Here we report additional data and findings aimed at a better understanding of the toxicity mechanisms induced by these herbicides. Biochemical mechanisms of cytotoxicity induced by the herbicides paraquat (1,1'-dimethyl-4,4'-bipyridylium dichloride), dinoseb (2-sec-butyl-4,6-dinitrophenol) and 2,4-D (2,4-dichlorophenoxyacetic acid) were investigated in freshly isolated rat hepatocytes. Herbicide metabolism, especially paraquat and 2,4-D, rapidly depletes GSH and protein thiols. Paraquat and 2,4-D (1-10 mM) decrease the GSH/GSSG ratio, promote loss of protein thiol contents and induce lipid peroxidation. Dinoseb, the most effective cytotoxic compound under study (used in concentrations 1000-fold lower than paraquat and 2,4-D), had moderate effects upon the GSH/GSSG ratio and lipid peroxidation, causing a depletion of protein thiols of about 20%. The results indicate that the herbicides paraquat and 2,4-D are hepatotoxic and may induce cell death by decreasing cellular GSH/GSSG ratio and protein thiols, and by inducing lipid peroxidation. The cytotoxic action of dinoseb is likely to be related with the uncoupling of oxidative phosphorylation in mitochondria. Therefore, it is likely that liver damage observed during the first phase of herbicide-intoxication is related to these metabolic processes.

Fortuitous imaging of a primary adrenocortical carcinoma with Tc-99m HDP

The importance of evaluating nonfunctional adrenal masses in the right clinical setting is discussed. A 60-year-old man was initially diagnosed of having a localized lung carcinoma. Metastatic work-up showed an adrenal mass that was not deemed to be related to the lung primary. Although biochemical testing revealed that the adrenal mass was nonfunctional, adrenal scintigraphy was not performed. On resection, the lung neoplasm was shown to be a poorly differentiated adenocarcinoma. Radiologic follow-up of the adrenal finding was recommended. A year later, the patient presented with an abdominal mass that was visualized by bone scintigraphy and, on resection, proved to be adrenocortical carcinoma. In retrospect, the lung mass was a metastasis of an adrenocortical carcinoma.

Effects of paraquat, dinoseb and 2,4-D on intracellular calcium and on vasopressin-induced calcium mobilization in isolated hepatocytes

The effects of the herbicides paraquat, dinoseb and 2,4-D on intracellular Ca2+ levels and on vasopressin-induced Ca2+ mobilization were investigated in intact isolated hepatocytes. Incubation of rat hepatocytes with paraquat (5 mM for 60 min) and dinoseb (10 microM) resulted in a time-dependent loss of viability by approximately 25%. Viability of cells treated with 2,4-D decreased significantly, dropping to about 20% at 10 mM and 60 min incubation. Exposure of hepatocytes to paraquat (1-10 mM) for 60 min had no effect on the basal level of [Ca2+]i. Additionally, exposure to paraquat had no effect on the magnitude and on the duration of the [Ca2+]i response to vasopressin. In the presence of 2,4-D (1-10 mM), basal [Ca2+]i increases as a function of herbicide concentration. The magnitude of the delta[Ca2+]i response decreases from 256 +/- 8 nM in control to 220 +/- 5 nM, at 10 mM 2,4-D. Exposure of hepatocytes to dinoseb (1-10 microM) had no effect on the basal level of [Ca2+]i. However, a strong concentration-dependent decrease in the magnitude of delta[Ca2+]i in response to vasopressin was noticed at 60 min incubation. Dinoseb markedly inhibited the stimulation of the production of inositol phosphates by vasopressin stimulus. The present study demonstrates that paraquat, 2,4-D and dinoseb cause cell death in hepatocytes by mechanisms not related to an early increase in [Ca2+]i. Additionally, it has been shown for the first time that dinoseb disturbs the transduction mechanism promoted by vasopressin by inhibiting the formation of IP3.

Mitochondrial bioenergetics is affected by the herbicide paraquat

The potential toxicity of the herbicide paraquat (1,1-dimethyl-4,4'-bipyridylium dichloride) was tested in bioenergetic functions of isolated rat liver mitochondria. Paraquat increases the rate of State 4 respiration, doubling at 10 mM, indicating uncoupling effects. Additionally, State 3 respiration is depressed by about 15%, at 10 mM paraquat, whereas uncoupled respiration in the presence of CCCP is depressed by about 30%. Furthermore, paraquat partially inhibits the ATPase activity through a direct effect on this enzyme complex. However, at high concentrations (5-10 mM), the ATPase activity is stimulated, probably as consequence of the described uncoupling effect. Depression of respiratory activity is mediated through partial inhibitions of mitochondrial complexes III and IV. Paraquat depresses delta psi as a function of herbicide concentration. In addition, the depolarization induced by ADP is decreased and repolarization is biphasic suggesting a double effect. Repolarization resumes at a level consistently higher than the initial level before ADP addition, for paraquat concentrations up to 10 mM. This particular effect is clear at 1 mM paraquat and tends to fade out with increasing concentrations of the herbicide.

Diagnosis of Menètrier's disease with Tc-99m human serum albumin scintigraphy

Technetium-99m labeled human serum albumin has been shown to detect protein leakage into the bowel. A case of a young adult is presented with endoscopic and pathological correlation of scintigraphic findings supporting Menètrier's disease.

Interactions of herbicides 2,4-D and dinoseb with liver mitochondrial bioenergetics

The herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) and dinoseb (2-sec-butyl-4,6-dinitrophenol), were tested in mitochondria because they are putative toxins to the organisms. To understand the toxic mechanisms involved, we have determined if mitochondrial bioenergetic functions are affected. Dinoseb partially inhibits uncoupled respiration, reflecting its limited interaction with the mitochondrial redox chain at the level of succinate dehydrogenase and cytochrome c reductase (complex III). Additionally, it increased the rate of state 4 oxygen consumption, stimulated ATPase activity, induced permeabilization of membrane mitochondria to H+, and depressed delta psi. These data characterize dinoseb as a classical proton uncoupler. The herbicide 2,4-D decreased delta psi as a function of concentration and the rate of repolarization was also progressively decreased. State 3 and uncoupled respiration were depressed by approximately the same extent (60%), ruling out interactions on phosphorylation assembly independent of the redox chain. The herbicide strongly inhibited succinate dehydrogenase and cytochrome c reductase (complex III), whereas cytochrome c oxidase was not affected. Additionally, 2,4-D also uncoupled mitochondria at concentrations 1000-fold higher than those required for a similar dinoseb effect. This study therefore suggests that dinoseb- and 2,4-D-induced cellular damage, as we have reported before, is putatively preceded by injury upon bioenergetic functions of mitochondria.