Michele M. Henry

Therapeutic photobiomodulation for methanol-induced retinal toxicity

Methanol intoxication produces toxic injury to the retina and optic nerve, resulting in blindness. The toxic metabolite in methanol intoxication is formic acid, a mitochondrial toxin known to inhibit the essential mitochondrial enzyme, cytochrome oxidase. Photobiomodulation by red to near-IR radiation has been demonstrated to enhance mitochondrial activity and promote cell survival in vitro by stimulation of cytochrome oxidase activity. The present studies were undertaken to test the hypothesis that exposure to monochromatic red radiation from light-emitting diode (LED) arrays would protect the retina against the toxic actions of methanol-derived formic acid in a rodent model of methanol toxicity. Using the electroretinogram as a sensitive indicator of retinal function, we demonstrated that three brief (2 min, 24 s) 670-nm LED treatments (4 J/cm2), delivered at 5, 25, and 50 h of methanol intoxication, attenuated the retinotoxic effects of methanol-derived formate. Our studies document a significant recovery of rod- and cone-mediated function in LED-treated, methanol-intoxicated rats. We further show that LED treatment protected the retina from the histopathologic changes induced by methanol-derived formate. These findings provide a link between the actions of monochromatic red to near-IR light on mitochondrial oxidative metabolism in vitro and retinoprotection in vivo. They also suggest that photobiomodulation may enhance recovery from retinal injury and other ocular diseases in which mitochondrial dysfunction is postulated to play a role.

Anesthetic preconditioning improves adenosine triphosphate synthesis and reduces reactive oxygen species formation in mitochondria after ischemia by a redox dependent mechanism.

Background Mitochondrial changes that characterize the heart after anesthetic preconditioning (APC) or the mechanisms by which mitochondrial triggering factors lead to protection are unknown. This study hypothesized that generation of reactive oxygen species (ROS) during APC is required to initiate the mitochondrial protective effects, and that APC leads to improved mitochondrial electron transport chain function and cardiac function during reperfusion. Methods Isolated guinea pig hearts were subject to 30 min ischemia and 120 min reperfusion. Prior to ischemia hearts were either untreated (I/R), or treated with sevoflurane (APC), in the presence or absence of the ROS scavenger tiron (TIR), or the superoxide dismutase mimetic MnTBAP (TBAP). Intracellular ROS were measured by spectrofluorometry using the fluorescent probe dihydroethidium (DHE). In another series of experiments, using the same protocol, hearts were reperfused for only 5 min and removed for measurement of adenosine triphosphate (ATP) synthesis by luciferin–luciferase luminometry and ROS generation by dichlorohydro-fluorescein (DCF) fluorescence in isolated mitochondria. Results The APC improved cardiac function and reduced infarction. Tiron or MnTBAP abrogated the protection afforded by APC. Mitochondrial ATP synthesis was decreased by 70 ± 3% after IR alone, by only 7 ± 3% after APC, by 69 ± 2% after APC+TIR, and by 71 ± 3% after APC + TBAP. Mitochondrial ROS formation (DCF) increased by 48 ± 3% after IR alone, by 0 ± 2% after APC, by 43 ± 4% after APC + TIR, and by 46 ± 3% after APC + TBAP. ROS generation (DHE) was increased in I/R group at 5 and 120 min reperfusion. This was attenuated by APC but this protective effect was abrogated in APC + TIR and APC + TBAP groups. Conclusions The results indicate that ROS are central both in triggering and mediating APC, and that the mitochondrion is the target for these changes.

Increased mitochondrial K(ATP) channel activity during chronic myocardial hypoxia: is cardioprotection mediated by improved bioenergetics?

Increased resistance to myocardial ischemia in chronically hypoxic immature rabbit hearts is associated with activation of ATP-sensitive K+ (KATP) channels. We determined whether chronic hypoxia from birth alters the function of the mitochondrial KATP channel. The KATP channel opener bimakalim (1 &mgr;mol/L) increased postischemic recovery of left ventricular developed pressure in isolated normoxic (Fio2=0.21) hearts to values (42±4% to 67±5% ) not different from those of hypoxic controls but did not alter postischemic recovery of developed pressure in isolated chronically hypoxic (Fio2=0.12) hearts (69±5% to 72±5%). Conversely, the KATP channel blockers glibenclamide (1 &mgr;mol/L) and 5-hydroxydecanoate (5-HD, 300 &mgr;mol/L) attenuated the cardioprotective effect of hypoxia but had no effect on postischemic recovery of function in normoxic hearts. ATP synthesis rates in hypoxic heart mitochondria (3.92±0.23 &mgr;mol ATP · min−1 · mg mitochondrial protein−1) were significantly greater than rates in normoxic hearts (2.95±0.08 &mgr;mol ATP · min−1 · mg mitochondrial protein−1). Bimakalim (1 &mgr;mol/L) decreased the rate of ATP synthesis in normoxic heart mitochondria consistent with mitochondrial KATP channel activation and mitochondrial depolarization. The effect of bimakalim on ATP synthesis was antagonized by the KATP channel blockers glibenclamide (1 &mgr;mol/L) and 5-HD (300 &mgr;mol/L) in normoxic heart mitochondria, whereas glibenclamide and 5-HD alone had no effect. In hypoxic heart mitochondria, the rate of ATP synthesis was not affected by bimakalim but was attenuated by glibenclamide and 5-HD. We conclude that mitochondrial KATP channels are activated in chronically hypoxic rabbit hearts and implicate activation of this channel in the improved mitochondrial bioenergetics and cardioprotection observed.

Attenuation of Mitochondrial Respiration by Sevoflurane in Isolated Cardiac Mitochondria Is Mediated in Part by Reactive Oxygen Species

BackgroundAnesthetic preconditioning protects against cardiac ischemia/reperfusion injury. Increases in reduced nicotinamide adenine dinucleotide and reactive oxygen species during sevoflurane exposure suggest attenuated mitochondrial electron transport as a trigger of anesthetic preconditioning. The authors investigated the effects of sevoflurane on respiration in isolated cardiac mitochondria. MethodsMitochondria were isolated from fresh guinea pig hearts, and mitochondrial oxygen consumption was measured in the presence of complex I (pyruvate) or complex II (succinate) substrates. The mitochondria were exposed to 0, 0.13, 0.39, 1.3, or 3.9 mm sevoflurane. State 3 respiration was determined after adenosine diphosphate addition. The reactive oxygen species scavengers manganese(III) tetrakis (4-benzoic acid) porphyrin chloride and N-tert-Butyl-a-(2-sulfophenyl)nitrone sodium (10 &mgr;m each), or the KATP channel blockers glibenclamide (2 &mgr;m) or 5-hydroxydecanoate (300 &mgr;m), were given alone or before 1.3 mm sevoflurane. ResultsSevoflurane attenuated respiration for both complex I and complex II substrates, depending on the dose. Glibenclamide and 5-hydroxydecanoate had no effect on this attenuation. Both scavengers, however, abolished the sevoflurane-induced attenuation for complex I substrates, but not for complex II substrates. ConclusionThe findings suggest that sevoflurane-induced attenuation of complex I is mediated by reactive oxygen species, whereas attenuation of other respiratory complexes is mediated by a different mechanism. The opening of mitochondrial KATP channels by sevoflurane does not seem to be involved in this effect. Thus, reactive oxygen species formation may not only result from attenuated electron transport by sevoflurane, but it may also contribute to complex I attenuation, possibly leading to a positive feedback and amplification of sevoflurane-induced reactive oxygen species formation in triggering anesthetic preconditioning.

Effects of photodegradation on the physical and antioxidant properties of melanosomes isolated from retinal pigment epithelium

Abstract Melanosomes of the retinal pigment epithelium (RPE) are relatively long-lived organelles that are theoretically susceptible to changes induced by exposure to visible light. Here melanosomes were isolated from porcine RPE cells and subjected to high intensity visible light to determine the effects of illumination on melanosome structure and on the content and antioxidant properties of melanin. As compared to untreated melanosomes, illuminated granules showed morphologic changes consistent with photodegradation, which included variable reductions in electron density demonstrated by transmission electron microscopy (TEM), and particle fragmentation and surface disruption revealed by scanning electron microscopy (SEM) and atomic force microscopy. Illuminated melanosomes had lower melanin content, indicated by measures of absorbance and electron spin resonance (ESR) signal intensity, and reduced ability to bind iron, shown by chemical and ESR analyses. Compared to untreated melanosomes, ESR–spin trapping analyses further indicated that illuminated melanosomes show increased photogeneration of superoxide anion and reduced ability to inhibit the iron ion–catalyzed free radical decomposition of hydrogen peroxide. It appears therefore that visible light irradiation can disrupt the structure of RPE melanosomes and reduce the amount and antioxidant properties of melanin. Some of these changes occur in human RPE melanosomes with aging and the results obtained here suggest that visible light irradiation is at least partly responsible. The consequence of light-induced changes in RPE melanosomes may be a diminished capacity of melanin to help protect aged cells from oxidative damage, perhaps increasing the risk of diseases with an oxidative stress component such as age-related macular degeneration.

KATP Channel Openers Have Opposite Effects on Mitochondrial Respiration Under Different Energetic Conditions

Mitochondrial (m) KATP channel opening has been implicated in triggering cardiac preconditioning. Its consequence on mitochondrial respiration, however, remains unclear. We investigated the effects of two different KATP channel openers and antagonists on mitochondrial respiration under two different energetic conditions. Oxygen consumption was measured for complex I (pyruvate/malate) or complex II (succinate with rotenone) substrates in mitochondria from fresh guinea pig hearts. One of two mKATP channel openers, pinacidil or diazoxide, was given before adenosine diphosphate in the absence or presence of an mKATP channel antagonist, glibenclamide or 5-hydroxydecanoate. Without ATP synthase inhibition, both mKATP channel openers differentially attenuated mitochondrial respiration. Neither mKATP channel antagonist abolished these effects. When ATP synthase was inhibited by oligomycin to decrease [ATP], both mKATP channel openers accelerated respiration for both substrate groups. This was abolished by mKATP channel blockade. Thus, under energetically more physiological conditions, the main effect of mKATP channel openers on mitochondrial respiration is differential inhibition independent of mKATP channel opening. In contrast, under energetically less physiological conditions, mKATP channel opening can be evidenced by accelerated respiration and blockade by antagonists. Therefore, the effects of mKATP channel openers on mitochondrial function likely depend on the experimental conditions and the cells underlying energetic state.

Formate, the toxic metabolite of methanol, in cultured ocular cells

Methanol has neurotoxic actions on the human retina due to its metabolite, formic acid, which is a mitochondrial toxin. In methanol poisoned animals, morphologic changes were seen both in retinal photoreceptors and in cells of the underlying retinal pigment epithelium (RPE). Here the effects of formate exposure on the two retinal cell types were analyzed in more detail in vitro using photoreceptor (661W) and RPE (ARPE-19) cell lines. Cells were exposed for time courses from minutes to days to sodium formate at pH 7.4 or to formic acid at pH 6.8, to simulate the metabolic acidosis that accompanies methanol poisoning. Formate accumulation, cellular ATP, cytotoxicity (lactate dehydrogenase (LDH) release) and cell phenotype were analyzed. Formate accumulated with a similar biphasic pattern in both cell types, and to similar levels whether delivered as sodium formate or as formic acid. ATP changes with sodium formate treatment differed between cell types with only 661W cells showing a rapid (within minutes), transient ATP increase. The subsequent ATP decrease was earlier in 661W cells (6 h) than the ATP decrease in ARPE-19 cells (24 h), and although both cell types showed evidence of cytotoxicity, the effects were greater for 661W cells. Both cell types showed enhanced morphologic and biochemical changes with formic acid treatment including earlier and/or greater effects on ATP depletion and cytotoxicity; again effects were more pronounced in 661W cells. Formate therefore is toxic for both cell lines, with 661W cells exhibiting greater sensitivity. Medium pH also appears to play a significant role in formate toxicity in vitro.

PKC-δ inhibition does not block preconditioning-induced preservation in mitochondrial ATP synthesis and infarct size reduction in rats

Abstract We have previously demonstrated that cardioprotection induced by the infusion of a selective δ1-opioid agonist is mediated by the specific translocation of PKC-δ to the mitochondria in in vivo rat hearts and via opening of the mitochondrial KATP channel. Ischemic preconditioning (IPC) is also thought to involve the translocation of specific isoforms of PKC and KATP channel activation. Therefore, we utilized the PKC-δ selective antagonist, rottlerin, to assess the effect of inhibition of this isozyme on cardioprotection induced by one-cycle of IPC prior to 30 minutes of ischemia and 2 hours of reperfusion. Infarct size (IS) was determined by tetrazolium chloride staining and expressed as a percent of the area at risk (AAR). Non-preconditioned control animals had an IS/AAR of 59.7 ± 1.6. IPC significantly reduced the extent of myocardial infarction (6.3 ± 1.4). Rottlerin, 0.3 mg/kg, did not alter IS/AAR in control animals (55.0 ± 5.6), and had no significant effect on IS/AAR in preconditioned animals (14.4 ± 3.8). Additionally, we demonstrated, using a luciferase-based assay to determine the rate of ATP synthesis and state of mitochondrial bioenergetics, that IPC preserves ATP synthesis in the ischemic myocardium and that this preservation is attenuated by the isoform non-selective PKC inhibitor, chelerythrine, but not by the δ-selective antagonist, rottlerin. These data suggest that PKC-δ does not play an important role in IPC and that differences in isoform importance are evident during pharmacological versus ischemia-induced preconditioning.

Therapeutic effect of near infrared (NIR) light on Parkinson's disease models.

Parkinsons disease (PD) is a neurodegenerative disorder that affects large numbers of people, particularly those of a more advanced age. Mitochondrial dysfunction plays a central role in PD, especially in the electron transport chain. This mitochondrial role allows the use of inhibitors of complex I and IV in PD models, and enhancers of complex IV activity, such as NIR light, to be used as possible therapy. PD models fall into two main categories; cell cultures and animal models. In cell cultures, primary neurons, mutant neuroblastoma cells, and cell cybrids have been studied in conjunction with NIR light. Primary neurons show protection or recovery of function and morphology by NIR light after toxic insult. Neuroblastoma cells, with a gene for mutant alpha-synuclein, show similar results. Cell cybrids, containing mtDNA from PD patients, show restoration of mitochondrial transport and complex I and IV assembly. Animal models include toxin-insulted mice, and alpha-synuclein transgenic mice. Functional recovery of the animals, chemical and histological evidence, and delayed disease progression show the potential of NIR light in treating Parkinsons disease.

Photobleaching of melanosomes from retinal pigment epithelium: I. Effects on protein oxidation.

Melanin in the long‐lived melanosomes of the retinal pigment epithelium (RPE) may undergo photobleaching with aging, which appears to diminish the antioxidant function of melanin and could make photobleached melanosomes less efficient in protecting biomolecules from oxidative modification. Here we analyzed whether photobleaching of melanosomes affects their ability to modify the oxidation state of nearby protein. As conventional methods developed to study soluble antioxidants are not well suited for analysis of granules such as melanosomes, we developed a new analytic method to focus on particle surfaces that involves experimentally coating granules with the cytoskeletal protein β‐actin to serve as a reporter for local protein oxidation. Isolated porcine RPE melanosomes were photobleached with visible light to simulate aging, then photobleached melanosomes, untreated melanosomes and control particles (black latex beads) were actin coated and illuminated in a photosensitized cell free system. Protein was re‐stripped from particles and analyzed for carbonylation by Western blotting. Quantitative densitometry showed no reproducible differences for protein associated with untreated melanosomes when compared with control particles. Melanin has both anti‐ and pro‐oxidant functions when light irradiated, but neither of these functions predominated in the protein oxidation assay when untreated melanosomes were used. However, protein extracted from photobleached melanosomes showed markedly increased carbonylation, both of associated actin and of endogenous melanosomal protein(s), and the effect increased with extent of granule photobleaching. Photobleaching of RPE melanosomes therefore changes the oxidation state of protein endogenous to the organelle and reduces the ability of the granule to modify the oxidation of exogenous protein near the particle surface. The results support the growing body of evidence that photobleaching of RPE melanosomes, which is believed to occur with aging, changes the physicochemical properties of the organelle and reduces the likelihood that the granules perform an antioxidant function.