Peter Schönfeld - Academia.edu (original) (raw)

Papers by Peter Schönfeld

Neurochemistry International, Sep 1, 2021

Neurons spurn hydrogen-rich fatty acids for energizing oxidative ATP synthesis, contrary to other... more Neurons spurn hydrogen-rich fatty acids for energizing oxidative ATP synthesis, contrary to other cells. This feature has been mainly attributed to a lower yield of ATP per reduced oxygen, as compared to glucose, and the use of fatty acids as hydrogen donor is accompanied by severe β-oxidation-associated ROS generation. Neurons are especially susceptible to detrimental activities of ROS due to their poor antioxidative equipment. It is also important to note that free fatty acids (FFA) initiate multiple harmful activities inside the cells, particularly on phosphorylating mitochondria. Several processes enhance FFA-linked lipotoxicity in the cerebral tissue. Thus, an uptake of FFA from the circulation into the brain tissue takes place during an imbalance between energy intake and energy expenditure in the body, a situation similar to that during metabolic syndrome and fat-rich diet. Traumatic or hypoxic brain injuries increase hydrolytic degradation of membrane phospholipids and, thereby elevate the level of FFA in neural cells. Accumulation of FFA in brain tissue is markedly associated with some inherited neurological disorders, such as Refsum disease or X-linked adrenoleukodystrophy (X-ALD). What are strategies protecting neurons against FFA-linked lipotoxicity? Firstly, spurning the β-oxidation pathway in mitochondria of neurons. Secondly, based on a tight metabolic communication between neurons and astrocytes, astrocytes donate metabolites to neurons for synthesis of antioxidants. Further, neuronal autophagy of ROS-emitting mitochondria combined with the transfer of degradation-committed FFA for their disposal in astrocytes, is a potent protective strategy against ROS and harmful activities of FFA. Finally, estrogens and neurosteroids are protective as triggers of ERK and PKB signaling pathways, consequently initiating the expression of various neuronal survival genes via the formation of cAMP response element-binding protein (CREB).

Biochimica Et Biophysica Acta - Bioenergetics, Nov 1, 1995

The perinatal development of the adenine nucleotide translocation in isolated rat brain mitochond... more The perinatal development of the adenine nucleotide translocation in isolated rat brain mitochondria was studied. For that purpose the content of the adenine nucleotide translocase (ANT), the activity of adenine nucleotide translocation and the control of the ANT protein over State 3 respiration were estimated. From the newborn to the adult state there was a 4-fold increase in State 3 respiration which was paralleled by a 3-fold increase in the respiratory control ratio. The capacity of uncoupled respiration exceeded that of State 3 respiration in all developmental stages indicating that the activity of oxidative phosphorylation is influenced by that of ANT and/or ATP synthase. The content of the ANT protein, measured as bound pmoles of [3H]atractyloside per mg mitochondrial protein, increased more than 2-fold from birth to adultness in the first three postnatal weeks. The size of the exchangeable matrix (ATP + ADP)-pool was only sligthly expanded during the same period. The translocation activity increased 2-fold from the newborn to the adult state and was a linear function of the ANT protein. Control of the ANT protein over State 3 respiration (quantified as flux control coefficient, CJA%T), was remarkable in brain mitochondria from newborn rats (CJ°NT = 0.45 __+ 0.15), but declined during further development (C~T = 0. I 1 + 0.03, at the 20th day). The obtained results suggest that the postnatal enrichment of the ANT protein in rat brain mitochondria is an essential factor for the development of oxidative phosphorylation capacity in the early postnatal period.

PubMed, 1989

In the early phase of iron/ascorbate induced peroxidation in rat liver mitochondria a progressive... more In the early phase of iron/ascorbate induced peroxidation in rat liver mitochondria a progressively diminished active and uncoupled respiration, likely caused by an attack at the level of the respiratory chain was established, whereas the transmembrane potential (delta psi) under phosphorylating conditions did, however, not reflect this inhibition. A tentative explanation for this behaviour was suggested on the basis of an impairment of both membrane potential generating and consuming processes. By measurements of the velocity of mitochondrial 32Pi-uptake during the time course of peroxidation an inhibition of the Pi-carrier was detected. The calculated flux control coefficients for the Pi- and ATP/ADP-translocator indicate that the last one exerts a large control independent on the respiration rate during the initial phase of peroxidation. The data show that the predominant step in the control of oxidative phosphorylation at the site of the consumers must be attributed to the ATP/ADP-exchanger.

PubMed, 1986

The transmembrane potential delta psi of isolated rat liver mitochondria was determined by means ... more The transmembrane potential delta psi of isolated rat liver mitochondria was determined by means of a dibenzyl dimethyl ammonium (DDA+)-sensitive electrode and the 86Rb+ distribution after separation by a centrifugation technique under identical incubation conditions. The delta psi determined with the electrode were higher throughout. There was no indication that the lower delta psi measured by means of 86Rb+ distribution were the result of anaerobic events connected with separation of rat liver mitochondria from the medium. The higher delta psi found by using the DDA+-sensitive electrode were due to anion-dependent changes in the activity of DDA+ ions, which were probably caused by complexing between DDA+ and different anions. A procedure was developed to correct the delta psi for this effect. The corrected values were in relatively good agreement with the delta psi obtained from the 86Rb+ distribution.

PubMed, 1984

The regulation of oxidative phosphorylation by the extramitochondrial ATP/ADP ratio was investiga... more The regulation of oxidative phosphorylation by the extramitochondrial ATP/ADP ratio was investigated with pyruvate (malate) or pyruvate (malate) plus octanoate as substrates in experiments with isolated rat liver mitochondria. Steady states in the supply of non-saturating substrate concentrations and the activity of oxidative phosphorylation were adjusted by means of a perifusion technique which is based on immobilisation of mitochondria on glass filters. Michaelis-Menten parameters of the pyruvate oxidation in active state respiration were determined both in the absence and presence of octanoate. Octanoate yielded only slight Km value increase, whereas the maximal rate of pyruvate oxidation was diminished to one half. Therefore, it is concluded that the inhibitory action of octanoate on pyruvate oxidation comes close to a non-competitive mechanism. The inhibitory effect of octanoate is completely reversible. When a change in substrate supply was accomplished by substituting pyruvate (malate) plus octanoate for pyruvate (malate) under conditions of a simulated extramitochondrial energy demand, respiration was stimulated and ATP/ADP ratios generated outside mitochondria were shifted to a higher value. Two different responses of the mitochondrial respiration to the extramitochondrial ATP/ADP ratios were found as a function of the presence or absence of octanoate.

PubMed, 1982

1. The influence of a diminished hydrogen supply on the regulation of oxidative phosphorylation o... more 1. The influence of a diminished hydrogen supply on the regulation of oxidative phosphorylation of isolated rat liver mitochondria in dependence on the extramitochondrial (ATP)/(ADP) ratio was investigated. 2. The hydrogen supply was diminished by using various (beta-hydroxybutyrate)/(acetoacetate) ratios as a redox buffer and the results were compared with those of experiments using perifusion of immobilized mitochondria with non-saturating substrate concentrations. 3. In both experimental approaches the influence of a diminished hydrogen pressure on the maximum (ATP)/(ADP) ratio at minimum flux was low. An extreme decrease in the (beta-hydroxybutyrate)/(acetoacetate) ratio by more than two orders of magnetitude causes the (APT)/(ADP) ratio to decrease by about 50%. 4. The load capacity of oxidative phosphorylation (maximum flux) is considerably decreased by diminished hydrogen pressure. 5. The borderline cases of purely kinetic and thermodynamic limitations of hydrogen supply were calculated by computer simulation with respect to the regulating behaviour of oxidative phosphorylation and changes in the control strength of adenine nucleotide translocator and hydrogen supply in the overall reaction. 6. A prevalent thermodynamic influence of hydrogen supply on oxidative energy transformation in the cell is discussed in the light of experimental data.

PubMed, 1979

It was observed that borosilicate glass prefilters have a high absorptive capacity for isolated r... more It was observed that borosilicate glass prefilters have a high absorptive capacity for isolated rat-liver mitochondria and that this binding does not need any kind of chemical procedure. This observation has led to the development of a perifusion technique for isolated rat-liver mitochondria. During perifusion the mitochondria are immobilized on a prefilter. Their morphological and functional intactness is conserved. During the course of the perifusion no loss of marker enzymes (adenylate kinase and malate dehydrogenase) can be detected. The respiration rates in the controlled and the active state are similar to those observed in a conventional closed polarographic vessel. The respiratory control is maintained for more than 30 min. With the perifusion technique it is possible to adjust respiration rates to stationary steady states between the controlled and the active state. It was shown that the control of respiration by the extramitochondrial ATP/ADP ratio is independent of the succinate concentration in the range of 1 to 10 mM.

PubMed, 1987

The electrochemical proton gradient (delta/uH+) and the rate of respiration were determined as fu... more The electrochemical proton gradient (delta/uH+) and the rate of respiration were determined as function of the work load at conditions where isolated rat heart mitochondria utilize pyruvate and/or l-palmitoyl-carnitine as hydrogen donors. Delta/uH+ was calculated from the distribution of 86Rb+ (delta psi marker) and [14C]-dimethyloxazolidine-2,4-dione (delta pH marker) between the mitochondrial matrix space and the medium. A transition from l-palmitoylcarnitine to pyruvate utilization did not change the rate of hydrogen supply or the mitochondrial energy state.

PubMed, 1983

The effect of changes in hydrogen supply on the rate of energy transformation (measured as respir... more The effect of changes in hydrogen supply on the rate of energy transformation (measured as respiration rate), on the redox state of the NAD(P) and cytochrome c couples and on the extramitochondrial ATP/ADP was investigated with isolated rat liver mitochondria. Hydrogen supply was changed by variation of the beta-hydroxybutyrate/acetoacetate ratio in the incubation medium. In the active state respiration rate was strongly diminished by lowering the beta-hydroxybutyrate/acetoacetate ratio, whereas in the resting state a minor effect was observed. This resulted in a decrease in the respiratory control index (RCI). Even under a metabolic situation of strongly diminished hydrogen supply corresponding to a beta-hydroxybutyrate/acetoacetate ratio equal to 0.5 added ADP was phosphorylated. However, the ATP/ADP ratio generated extramitochondrially amounted to half that obtained at a beta-hydroxybutyrate/acetoacetate ratio of more than 100. Nevertheless at a beta-hydroxybutyrate/acetoacetate ratio of 0.5 the generated extramitochondrial ATP/ADP ratio is near to 100. A comparison of the changes in the available free redox energy with those in the extramitochondrial phosphorylation potential points to a disequilibrium between them in the resting state, too. The experimental results are discussed in the light of the metabolic conditions in vivo.

British Journal of Ophthalmology, Aug 1, 1999

Background/aims-To investigate the in vitro eVect of a short time exposure to the anthracycline i... more Background/aims-To investigate the in vitro eVect of a short time exposure to the anthracycline idarubicin on proliferation, protein synthesis, and motility of human Tenon's capsule fibroblasts in comparison with the antitumour antibiotic mitomycin C. Methods-After determination of eVective concentrations of idarubicin, fibroblasts of the human Tenon's capsule were exposed to idarubicin or mitomycin C at concentrations ranging from 0.1 µg/ml to 1 µg/ml or from 2.5 µg/ml to 250 µg/ml, respectively, for 0.5, 2, or 5 minutes and cultured for 60 days. Cell death by apoptosis caused by idarubicin treatment was confirmed by Hoechst 33258 staining. Further proliferation was explored by cell counting and by 3 H-thymidine uptake. Protein synthesis was measured by 3 Hproline uptake and motility was assessed by agarose droplet motility assay. Results-Idarubicin is able to exert toxicity and to induce apoptosis during a short time exposure of 0.5 minutes at concentrations of 0.3-1 µg/ml resulting in a significant reduction in cell number compared with the control after 60 days. For mitomycin C, higher concentrations and longer expositions were necessary. Even after treatment with 1 µg/ml idarubicin or 250 µg/ml mitomycin C a few cells were able to incorporate 3 H-thymidine. 3 Hproline uptake up to 10 days after exposure to 0.3 µg/ml idarubicin was found not to be decreased. Cell motility was reduced after treatment with 1 µg/ml idarubicin for 5 minutes or with 250 µg/ml mitomycin C for 2 or 5 minutes. For low mitomycin C concentrations, an increase in motility was found during the first 10 days. Conclusion-Idarubicin reduces proliferation of human Tenons's capsule fibroblasts after incubation for 0.5 minutes at concentrations as low as 0.3-1 µg/ml. In comparison, mitomycin C requires longer exposure times and higher doses for equal results. Therefore, idarubicin may be useful in the prevention of glaucoma filtering surgery failure.

PubMed, 1980

The influence of the fungicidic compound beta-thujaplicin (beta-isopropyl-tropolone) on the energ... more The influence of the fungicidic compound beta-thujaplicin (beta-isopropyl-tropolone) on the energy transformation processes of oxidative phosphorylation was investigated in isolated rat liver mitochondria with succinate (plus rotenone) as substrate. To elucidate the observed strong inhibition of active respiration by beta-thujaplicin three possibilities were assayed: the inhibition of 1) transport processes across the inner mitochondrial membrane for inorganic phosphate, adenine nucleotides, or succinate, 2) electron flux along the respiratory chain, and 3) mitochondrial ATPase. In this respect a remarkable inhibition of both Pi transport and the translocation of adenine nucleotides could not be observed. However, the effective suppression of the DNP-induced ATPase by beta-thujaplicin explains the pronounced inhibition of active respiration. An impairment of succinate transport and the measured partial inhibition of the terminal respiratory chain at the level of cytochrome oxidase contribute to the less marked inhibition of the uncoupled respiration. The ability of beta-thujaplicin to extract mitochondrial Mg++ and the prevention of the effects of beta-thujaplicin by an excess of Mg++ in the medium suggest a common mode of action of beta-thujaplicin as a lipophilic chelator of Mg++ and other divalent cations.

Biochimica Et Biophysica Acta - Bioenergetics, Dec 1, 1988

Octanoate applied to rat liver mitochondria respiring with glutamate plus malate or succinate (pl... more Octanoate applied to rat liver mitochondria respiring with glutamate plus malate or succinate (plus rotenone) under resting-state (State 4) conditions stimulates oxygen uptake and decreases the membrane potential, both effects being sensitive to oligomycin but not to carboxyatractyloside. Octanoate also decreases the rate of pyruvate carboxylation under the same conditions, this effect being correlated with the decrease of intramitochondrial content of ATP and increase of AMP. The decrease of pyruvate carboxylation and the change of mitochondrial adenine nucleotides are both reversed by 2-oxoglutarate. Fatty acids of shorter chain length have similar effects, though at higher concentrations. Addition of octanoate in the presence of fluoride (inhibitor of pyrophosphatase) produces intramitochondrial accumulation of pyropbosphate, even under conditions when oxidation of octanoate is prevented by rotenone. In isolated hepatocytes incubated with lactate plus pyruvate, octanoate also increases oxygen uptake and produces a shift in the profile of adenine nucleotides similar to that observed in isolated mitochondria. It decreases the 'efficiency' of gluconeogenesis, as expressed by the ratio between an increase of glucose production and an increase of oxygen uptake upon addition of gluconeogenic suhstrates (lactate plus pyruvate), and increases the reduction state of mitochondrial NAD. These effects taken together are not compatible with uncoupling, but point to intramitochondrial hydrolysis of octanoyl-CoA and probably also shorter chain-length acyI-CoAs. This mechanism probably functions as a 'safety valve' preventing a drastic decrease of intramitochondrial free CoA under a large supply of medium-and short-chain fatty acids.

FEBS Letters, Jun 1, 1992

The action of such membranepermeant cations as tetraphenyl phosphonium and dibenzyldimethyl ammon... more The action of such membranepermeant cations as tetraphenyl phosphonium and dibenzyldimethyl ammonium upon fatty acid-uncoupled respiration has been studied with oligomycin-inhibited rat liver mitochondria. Both cations enhance fatty acid-stimulated respiration, This synergistic effect is explained by a facilitated permeation of the fatty acid anion across the inner membrane due to an ion-pair complex. It is concluded that fatty acid uncoupling in rat liver mitochondria is limited by fatty acid anion permeation.

Biochimica Et Biophysica Acta: Molecular Basis Of Disease, May 1, 2015

Astrocyte Mitochondrion Peroxisomal disorder Reactive oxygen species Very long chain fatty acids ... more Astrocyte Mitochondrion Peroxisomal disorder Reactive oxygen species Very long chain fatty acids (VLCFA) X-linked adrenoleukodystrophy (X-ALD) is a severe neurodegenerative disorder resulting from defective ABCD1 transport protein. ABCD1 mediates peroxisomal uptake of free very-long-chain fatty acids (VLCFA) as well as their CoA-esters. Consequently, VLCFA accumulate in patients' plasma and tissues, which is considered as pathogenic X-ALD triggering factor. Clinical symptoms are mostly manifested in neural tissues and adrenal gland. Here, we investigate astrocytes from wild-type control and a genetic X-ALD mouse model (Abcd1-knockout), exposed to supraphysiological VLCFA (C22:0, C24:0 and C26:0) concentrations. They exhibit multiple impairments of energy metabolism. Furthermore, brain mitochondria from Abcd1 −/− mice and wild-type control respond similarly to VLCFA with increased ROS generation, impaired oxidative ATP synthesis and diminished Ca 2+ uptake capacity, suggesting that a defective ABCD1 exerts no adaptive pressure on mitochondria. In contrast, astrocytes from Abcd1 −/− mice respond more sensitively to VLCFA than wild-type control astrocytes. Moreover, longterm application of VLCFA induces high ROS generation, and strong in situ depolarization of mitochondria, and, in Abcd1 −/− astrocytes, severely diminishes the capability to revert oxidized pyridine nucleotides to NAD(P)H. In addition, observed differences in responses of mitochondria and astrocytes to the hydrocarbon chain length of VLCFA suggest that detrimental VLCFA activities in astrocytes involve defective cellular functions other than mitochondria. In summary, we clearly demonstrate that VLCFA increase the vulnerability of Abcd1 −/− astrocytes.

FEBS Letters, Aug 27, 1999

Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid), a branched chain fatty acid accumulating ... more Phytanic acid (3,7,11,15-tetramethylhexadecanoic acid), a branched chain fatty acid accumulating in Refsum disease to high levels throughout the body, induces uncoupling of rat liver mitochondria similar to non-branched fatty acids (e.g. palmitic acid), but the contribution of the ADP/ATP carrier or the aspartate/glutamate carrier in phytanic acid-induced uncoupling is of minor importance. Possible deleterious effects of phytanic acid on membrane-linked energy coupling processes were studied by ESR spectroscopy using rat liver mitochondria and a membrane preparation labeled with the lipid-specific spin probe 5-doxylstearic acid (5-DSA) or the protein-specific spin probe MAL-TEMPO (4-maleimido-2,2,6,6-tetramethyl-piperidine-1-oxyl). The effects of phytanic acid on phospholipid molecular dynamics and on the physical state of membrane proteins were quantified by estimation of the order parameter or the ratio of the amplitudes of the weakly to strongly immobilized MAL-TEMPO binding sites (W/S ratio), respectively. It was found, that phytanic acid (1) increased the mobility of phospholipid molecules (indicated by a decrease in the order parameter) and (2) altered the conformational state and/or the segmental mobility of membrane proteins (indicated by a drastic decrease in the W/S ratio). Unsaturated fatty acids with multiple cis-double bonds (e.g. linolenic or arachidonic acid), but not nonbranched FFA (ranging from chain length C10:0 to C18:0), also decrease the W/S ratio. It is hypothesized that the interaction of phytanic acid with transmembrane proteins might stimulate the proton permeability through the mitochondrial inner membrane according to a mechanism, different to a protein-supported fatty acid cycling.

Aging and Disease, 2016

It is increasingly understood that in the aging brain, especially in the case of patients sufferi... more It is increasingly understood that in the aging brain, especially in the case of patients suffering from neurodegenerative diseases, some fatty acids at pathologically high concentrations exert detrimental activities. To study such activities, we here analyze genetic diseases, which are due to compromised metabolism of specific fatty acids, either the branched-chain phytanic acid or very long-chain fatty acids (VLCFAs). Micromolar concentrations of phytanic acid or of VLCFAs disturb the integrity of neural cells by impairing Ca 2+ homeostasis, enhancing oxidative stress or de-energizing mitochondria. Finally, these combined harmful activities accelerate cell death. Mitochondria are more severely targeted by phytanic acid than by VLCFAs. The insertion of VLCFAs into the inner membrane distorts the arrangement of membrane constituents and their functional interactions. Phytanic acid exerts specific protonophoric activity, induces reactive oxygen species (ROS) generation, and reduces ATP generation. A clear inhibition of the Na + , K +-ATPase activity by phytanic acid has also been reported. In addition to the instantaneous effects, a chronic exposure of brain cells to low micromolar concentrations of phytanic acid may produce neuronal damage in Refsum disease by altering epigenetic transcriptional regulation. Myelin-producing oligodendrocytes respond with particular sensitivity to VLCFAs. Deleterious activity of VLCFAs on energy-dependent mitochondrial functions declines with increasing the hydrocarbon chain length (C22:0 > C24:0 > C26:0). In contrast, the reverse sequence holds true for cell death induction by VLCFAs (C22:0 < C24:0 < C26:0). In adrenoleukodystrophy, the uptake of VLCFAs by peroxisomes is impaired by defects of the ABCD1 transporter. Studying mitochondria from ABCD1deficient and wild-type mice proves that the energy-dependent functions are not altered in the disease model. Thus, a defective ABCD1 apparently exerts no obvious adaptive pressure on mitochondria. Further research has to elucidate the detailed mechanistic basis for the failures causing fatty acid-mediated neurodegeneration and should help to provide possible therapeutic interventions.

Neurochemistry International, Oct 1, 2017

Brain energy metabolism spurns fatty acids as fuel due to their inherent mitotoxicity and potenti... more Brain energy metabolism spurns fatty acids as fuel due to their inherent mitotoxicity and potential capacity to unleash neurodegeneration

FEBS Letters, Apr 5, 2000

Swelling of non-respiring rat liver mitochondria suspended in isotonic potassium acetate at pH 6.... more Swelling of non-respiring rat liver mitochondria suspended in isotonic potassium acetate at pH 6.5^7.4 in the presence of valinomycin was promoted by long-chain fatty acids, such as myristate, indicating a protonophoric mechanism. This swelling was partly inhibited by inhibitors or substrates of mitochondrial anion carriers. The results show that the fatty acid cycling mechanism responsible for uncoupling of oxidative phosphorylation can also operate in the direction opposite to that originally proposed [Skulachev, V.P. (1991) FEBS Lett. 294, 158^162], i.e. the inwardly directed transfer of the fatty acid anion accompanied by outwardly directed free passage of undissociated fatty acid. They also extend the list of mitochondrial anion carriers, that are involved in this process, over the mono-and tricarboxylate transporters. At pH 8, myristate, but not the synthetic protonophore, p-trifluoromethoxycarbonylcyanide phenylhydrazone, induced mitochondrial swelling in both potassium acetate and KCl media, that did not require the presence of valinomycin. This indicates that, at alkaline pH, myristate facilitates permeation of the inner mitochondrial membrane to monovalent cations and, possibly, activates the inner membrane anion channel.

PubMed, 1991

In incubations with isolated rat liver mitochondria we studied the fuel properties of octanoate a... more In incubations with isolated rat liver mitochondria we studied the fuel properties of octanoate as medium-chain fatty acid and respiratory substrate and the extent of control exerted by adenine nucleotide translocase on mitochondrial respiration. While, compared with pyruvate, octanoate improved the hydrogen supply in the active state to be seen from a high reduction of the mitochondrial NAD(P) system and an increased delta psi, it also decreased the efficiency of energy transduction indicated by a low ADP/O ratio. Based on measurements of the dependence of respiration on the extramitochondrial ATP/ADP ratio, we conclude that a switch-over from pyruvate to fatty acid oxidation does not change the kinetic parameters which make respiration respond to the ATP/ADP ratio. It is shown that the decrease of the exchangeable intramitochondrial adenine nucleotide pool due to the activation of octanoate results in a decrease of the activity of the adenine nucleotide translocase and an increase of its flux control coefficient.