Inhibition of respiration and destruction of cytochrome A3 by light in mitochondria and cytochrome oxidase from beef heart

Light Stress in Yeasts: Signaling and Responses in Creatures of the Night

Living organisms on the surface biosphere are periodically yet consistently exposed to light. The adaptive or protective evolution caused by this source of energy has led to the biological systems present in a large variety of organisms, including fungi. Among fungi, yeasts have developed essential protective responses against the deleterious effects of light. Stress generated by light exposure is propagated through the synthesis of hydrogen peroxide and mediated by regulatory factors that are also involved in the response to other stressors. These have included Msn2/4, Crz1, Yap1, and Mga2, thus suggesting that light stress is a common factor in the yeast environmental response.

Protein kinase A controls yeast growth in visible light

Background

A wide variety of photosynthetic and non-photosynthetic species sense and respond to light, having developed protective mechanisms to adapt to damaging effects on DNA and proteins. While the biology of UV light-induced damage has been well studied, cellular responses to stress from visible light (400–700 nm) remain poorly understood despite being a regular part of the life cycle of many organisms. Here, we developed a high-throughput method for measuring growth under visible light stress and used it to screen for light sensitivity in the yeast gene deletion collection.

Results

We found genes involved in HOG pathway signaling, RNA polymerase II transcription, translation, diphthamide modifications of the translational elongation factor eEF2, and the oxidative stress response to be required for light resistance. Reduced nuclear localization of the transcription factor Msn2 and lower glycogen accumulation indicated higher protein kinase A (cAMP-dependent protein kinase, PKA) activity in many light-sensitive gene deletion strains. We therefore used an ectopic fluorescent PKA reporter and mutants with constitutively altered PKA activity to show that repression of PKA is essential for resistance to visible light.

Conclusion

We conclude that yeast photobiology is multifaceted and that protein kinase A plays a key role in the ability of cells to grow upon visible light exposure. We propose that visible light impacts on the biology and evolution of many non-photosynthetic organisms and have practical implications for how organisms are studied in the laboratory, with or without illumination.

Modulation of oxidative phosphorylation (OXPHOS) by radiation- induced biophotons

Radiation-induced biophotons are an electromagnetic form of bystander signalling. In human cells, biophoton signalling is capable of eliciting effects in non-irradiated bystander cells. However, the mechanisms by which the biophotons interact and act upon the bystander cells are not clearly understood. Mitochondrial energy production and ROS are known to be involved but the precise interactions are not known. To address this question, we have investigated the effect of biophoton emission upon the function of the complexes of oxidative phosphorylation (OXPHOS). The exposure of bystander HCT116 p53 +/+ cells to biophoton signals emitted from β-irradiated HCT116 p53 +/+ cells induced significant modifications in the activity of Complex I (NADH dehydrogenase or NADH:ubiquinone oxidoreductase) such that the activity was severely diminished compared to non-irradiated controls. The enzymatic assay showed that the efficiency of NADH oxidation to NAD+ was severely compromised. It is suspected that this impairment may be linked to the photoabsorption of biophotons in the blue wavelength range (492-455 nm). The photobiomodulation to Complex I was suspected to contribute greatly to the inefficiency of ATP synthase function since it resulted in a lower quantity of H⁺ ions to be available for use in the process of chemiosmosis. Other reactions of the ETC were not significantly impacted. Overall, these results provide evidence for a link between biophoton emission and biomodulation of the mitochondrial ATP synthesis process. However, there are many aspects of biological modulation by radiation-induced biophotons which will require further elucidation.

AcrySof Natural filter decreases blue light-induced apoptosis in human retinal pigment epithelium

PURPOSE

The effect of AcrySof filter (UV light-filtering chromophore; Alcon) and AcrySof Natural filter (UV- and blue light-filtering chromophores) on blue light-induced apoptosis in human retinal pigment epithelial (RPE) cells was evaluated.

DESIGN

Laboratory investigation

CLINICAL RELEVANCE

Acrysof Natural filter reduces the blue-light toxicity in RPE cells and may have a positive impact on age-related macular degeneration (AMD).

METHODS

RPE cells were exposed to blue light (430-450 nm) in the presence of either the AcrySof (UV only) filter or Acrysof Natural (UV and blue light) filter for 10 days. The rate of apoptosis was analyzed.

RESULTS

Blue light induced significant apoptosis in RPE cells. AcrySof Natural filter significantly reduced the blue light-induced apoptosis when compared to AcrySof filter. The amount of blue-light energy reaching the cells with the AcrySof filter was 4.25 mW/cm(2) and with the AcrySof Natural filter was 2.5 mW/cm(2).

CONCLUSIONS

AcrySof Natural filter significantly reduced blue light-induced apoptosis. This was most likely due to its filtering effect on blue wavelength light, which reduces the energy that reaches the cells. In patients with cataract who are at a high risk for AMD, the implantation of a blue light-filtering intraocular lens may be considered.

Mitochondria-derived reactive oxygen species mediate blue light-induced death of retinal pigment epithelial cells

Throughout the lifetime of an individual, light is focused onto the retina. The resulting photooxidative stress can cause acute or chronic retinal damage. The pathogenesis of age-related macular degeneration (AMD), the leading cause of legal blindness in the developed world, involves oxidative stress and death of the retinal pigment epithelium (RPE) followed by death of the overlying photoreceptors. Evidence suggests that damage due to exposure to light plays a role in AMD and other age-related eye diseases. In this work a system for light-induced damage and death of the RPE, based on the human ARPE-19 cell line, was used. Induction of mitochondria-derived reactive oxygen species (ROS) is shown to play a critical role in the death of cells exposed to short-wavelength blue light (425 +/- 20 nm). ROS and cell death are blocked either by inhibiting the mitochondrial electron transport chain or by mitochondria-specific antioxidants. These results show that mitochondria are an important source of toxic oxygen radicals in blue light-exposed RPE cells and may indicate new approaches for treating AMD using mitochondria-targeted antioxidants.

Blue light induced apoptosis in rat retina

PURPOSE

To explore cell death in blue light induced retinal damage.

METHODS

Sprague-Dawley rats reared under cyclic light were exposed continuously to diffuse blue light (400-480 nm) at 0.64 W/m2 for 3 or 6 h after 22 h of dark adaptation. The rats were kept in darkness and killed immediately, 8, 16 and 24 h following light exposure. The retinal damage by the blue light was examined with a transmission electron microscope. The cell death was characterised by in situ terminal dUTP nick end labelling (TUNEL) and gel electrophoresis.

RESULTS

During the 24 h following light exposure, photoreceptor cell death was characterised by progressive condensation and margination of the chromatin, shrinkage or convolution and fragmentation of the nucleus, condensation of the cytoplasm, and formation of apoptotic bodies along with rapid removal of dying cells from damaged areas in the absence of inflammatory response. The TUNEL-positive nuclei were scattered individually in the outer nuclear layer just after light exposure. A wave of massive TUNEL labelling of photoreceptor nuclei peaked at 8-16 h and dropped at 24 h following light exposure. The distribution of TUNEL-positive nuclei was located predominantly at the upper temporal region of the retina, which was the most sensitive area to the damage caused by blue light. Furthermore, the multiples of internucleosomal cleavage of 180-200 base pairs were demonstrated at corresponding time points.

CONCLUSION

Photoreceptor cell apoptosis is seen early after the retina is damaged by blue light.

Rat lens glycolysis after in vivo exposure to narrow band UV or blue light radiation

UV radiation and short wavelength visible light are known to damage various tissues in the eye. This paper investigates the effect on rat lens glycolysis after in vivo exposure with 90 kJ m-2 narrow band UV radiation (UVB, 300 nm) and 90 kJ m-2 blue light (435 nm) radiation. After exposure, all lenses were incubated in Medium 199. Samples of culture medium were withdrawn after 2, 4, 6 h and 5, 10, 20 h in two UVB studies and after 5, 10 and 20 h in a blue light study. Lactate is the major end product of lens glycolysis. Lactate was determined with a modified enzymatic-photometric method. Intralenticular lactate was determined in one UVB experiment. In the UVB experiments we found a lower lactate production in the exposed lenses 2-6 h after exposure. There was an accumulation of lactate inside UVB-exposed lenses after 6 h incubation compared with their contralateral lenses. No significant effect on lactate production was observed in the blue light experiment. CONCLUSIONS. UVB induced a reversible inhibition of glycolysis. UVB also induced an accumulation of lactate inside the lens. Blue light tended to increase glycolysis.

Free radicals and ocular disease

Ames, Shigenaga, and Hagen recently published a thorough review of the relationship between oxidants, antioxidants, and degenerative diseases of ageing. They point out that only 9% of Americans daily consume the two fruits and three vegetables recommended by the National Cancer Institute and the National Research Council/National Academy of Science. In addition to antioxidants, these foodstuffs contain many essential micronutrients. To date, specific recommendations for antioxidant supplementation have not been made by any governmental agency or professional association. A number of clinical, basic, and epidemiological studies have implicated free radical induced lipid peroxidation in various ocular disorders. It would seem prudent that those persons at greatest risk for these disorders take some precautions, which could include sunglasses that filter ultraviolet light; hats that shield the eyes from direct sunlight; and the ingestion of fruits, vegetables, and antioxidants.

Spectral sensitivity of the blood-retinal barrier at the pigment epithelium for blue light in the 400-500 nm range

To specify the spectral sensitivity of the retinal pigment epithelium (RPE) for blue light damage, pigmented rabbits were exposed to light of 408, 418, 439, 455, 485, and 500 nm (half-peak bandwidth approximately 12 nm). The range of radiant exposure was 15-275 J cm-2 (1.7-19 mW cm-2 for 0.5-5 h). Vitreous fluorophotometry was used to functionally evaluate the blood-retinal barrier at the RPE in vivo, and electron microscopy to visualize RPE ultrastructure in vitro. A significant increase in permeability of the blood-retinal barrier was seen only after exposure to light of 418 nm. Radiant exposure at threshold for permeability increase was 18 J cm-2. Electron microscopy of the RPE demonstrated dispersion and clumping of melanin granules. The results suggest that the RPE is most sensitive to light in the range 412-425 nm, possibly due to damage-mediating chromophores such as cytochrome c oxidase and lipofuscin.

Inhibition of cytochrome oxidase and blue-light damage in rat retina

The activity of cytochrome oxidase, outer nuclear layer thickness, and edema were quantitatively evaluated in the blue-light exposed rat retina. Dark-adapted or cyclic-light reared rats were exposed to blue light with a retinal dose of 380 kJ/m2. Immediately, 1, 2, and 3 day(s) after exposure, the retinas of six rats from each adaptation group were examined. There was no difference between the dark-adapted and cyclic-light reared rats. Immediately after light exposure, cytochrome oxidase activity decreased. The activity in the inner segments remained low at day 1, while severe edema was observed in the inner and outer segments. The outer nuclear layer thickness decreased 1-3 days after exposure. The blue-light exposure inhibited cytochrome oxidase activity and caused retinal injury. Similarity of the injury process in the dark-adapted and cyclic-light reared retinas suggests that rhodopsin was not involved. The inhibition of cytochrome oxidase could be a cause of retinal damage.

Cytochrome oxidase activity in rat retina after exposure to 404 nm blue light

Cytochrome oxidase (CYO), a key enzyme in the respiratory chain, was observed as an indicator of retinal metabolism after an in vivo blue light exposure. Thirty Sprague-Dawley rats were exposed to optic radiation of 404 nm with a retinal dose of 110kJ/m2. Immediately after exposure, the CYO activity in the pigment epithelium, in the outer and inner segments of photoreceptors, and in the outer plexiform layer of the exposed retina, was reduced to one-third-to-half of the control level. However, there was an increase in CYO activity in the exposed retina one day after exposure. One week after exposure, the CYO activity in the inner segment and the outer plexiform layer was higher, while the activity in the other two layers was lower, than that at one day, although still higher than in the control. Two weeks after exposure, the CYO activity in the four retinal layers returned to the level of the control retina, as did the activity four weeks after. After exposure, no ophthalmoscopically visible retinal change and no light-microscopically evident morphological alterations were found. There was no retinal edema or loss of photoreceptor cells. The observed alteration in CYO activity after blue light exposure may represent an inhibition of retinal metabolism. The inhibition was reversible. If this compensation mechanism is overwhelmed, retinal damage may occur.

The potentiating effects of ethanol on the blue light depolarization of the retinal pigment epithelium

The retinal pigment epithelium (RPE) is the site of two major effects of ethanol. In humans, ethanol produces a slow damped oscillation in the steady electrical potential of the eye, which is generated primarily by the RPE. It has also been shown that ethanol potentiates the reversible, depolarizing effect of blue light on the transepithelial potential (TEP) of the isolated RPE. The present study demonstrates that in addition to the depolarizing effect of blue light on the TEP, a secondary, compensatory potential arises, which functions to maintain the TEP. The magnitude of the secondary response varies somewhat among preparations. It appears that ethanol eliminates or reduces the secondary, compensatory potential change which results in a large depolarization of the TEP when the RPE is irradiated with blue light. Microelectrode studies reveal that ethanol hyperpolarizes both the apical and basal membranes of the RPE with a greater effect noted in the apical membrane. This would account for the corneal positive potential elicited by ethanol in the human eye. Brief exposures (2-3 min) of blue light, after administration of 0.5% ethanol, results in a large (25-30 mV) depolarization of both membrane potentials as compared with 3 to 5 mV in untreated tissue. On the basis of our observations, it is hypothesized that some of the potentiating effects of ethanol in combination with other agents may result from an interference with a cellular adaptive response to impaired respiration rather than an additive effect on a common mechanism.

Hemoprotein(s) mediate blue light damage in the retinal pigment epithelium

In order to elucidate the mechanisms of blue light damage on ocular tissues, the transepithelial transport, electrical characteristics and ultrastructural properties of irradiated isolated bovine retinal pigment epithelium (RPE) were investigated. Blue light (430 nm) irradiation at 20 mW/cm2 significantly reduced the transepithelial potential and short circuit current of RPE. During blue light exposure, a decrease in chloride transport was observed, and this decrease appeared to be closely coupled to changes in the electrical properties of the pigment epithelium. A decrease in leucine transport was also noted, but the effect required 10-30 min of exposure to be manifested on some occasions. Utilizing the observed depolarizing effect of blue light, an action spectrum was determined which encompasses the absorption spectrum of the oxidized and reduced forms of cytochrome c oxidase. O2 uptake studies on isolated pigment epithelial cells verified the reduction of respiration by exposure to blue light, which is observed in other cells. Ultrastructural studies revealed that the major cytopathology observed up to 60 min after blue light exposure was a blistering of the mitochondria which progressed to a swollen, disrupted state within the post irradiation period of 1 h. Comparison of these results with those of other studies suggests that the mechanism of UV-A damage differs substantially from that of blue light.

Effect of ultraviolet radiation on the energy metabolism of the corneal epithelium of the rabbit

The present research was directed at quantifying possible alterations in corneal epithelial metabolic activity secondary to in vivo exposure to ultraviolet radiation (UVR). Microfluorometric energy metabolite assays on microgram (microgram) sized, freeze-dried tissue samples were used as an in vitro means of assessing overall metabolic activity in the epithelium of control rabbit corneas and in the epithelium of UVR-exposed rabbit corneas 2 min after discontinuation of exposure. The specific assays were for glucose, glycogen, adenosine triphosphate (ATP), and phosphocreatine (PCr). The radiant exposures were kept constant at 0.05 J cm-2 for all UVR wavelengths utilized (290, 300, 310 and 360 nm). Experimental UVR exposure conditions served to increase epithelial glucose and glycogen concentrations. Although the epithelial ATP concentrations were unchanged, the epithelial PCr concentrations (a high energy phosphate bond reservoir) decreased as a result of UVR exposure. Overall, the data demonstrate a decrease in corneal epithelial metabolic activity, which may be wavelength-dependent, as a result of UVR exposure. It is suggested that immediate metabolic stress can be responsible for the pattern of epithelial cell loss seen in photokeratitis.

Evidence for a photoactivation of CO rebinding to fully reduced cytochrome c oxidase after low-temperature flash photolysis

Carbon monoxide rebinding to isolated fully reduced cytochrome c oxidase has been investigated by low-temperature, flash photolysis, dual-wavelength spectrometry. By using separately different wavelength pairs to monitor the liganding of CO to Fe a3 and by keeping all other experimental conditions identical, there has been singled out a photoactivation effect on CO rebinding. For instance, at 187 K, the rate constant of CO rebinding observed at 425-475 nm was twice that derived from the kinetic at 444-475 nm despite a rate constant of photodissociation about 10 times larger at 425-475 nm than at 444-475 nm. This new finding is discussed with respect to previous investigations under similar conditions.

Damage to mitochondrial electron transport and energy coupling by visible light

The effect of treating mitochondria with visible light above 400 nm on electron transport and coupled reactions was examined. The temporal sequence of changes was: stimulation of respiration coupled to ATP synthesis, a decline in ATP synthesis, inactivation of respiration, increased ATPase activity and, later, loss of the membrane potential. Loss of respiration was principally due to inactivation of dehydrogenases. Of the components of dehydrogenase systems, flavins and quinones were most susceptible to illumination, the iron-sulfur centers were remarkably resistant to being damaged. Succinate dehydrogenase was inactivated before choline and NADH dehydrogenase. Redox reactions of cytochromes and cytochrome c oxidase activity were unaffected. Inactivation was O2-dependent and prevented by anaerobiosis or the presence of substrates for the dehydrogenases. Light in the range 400-500 nm was most effective and the presence of free flavins greatly enhanced inactivation of all of the above mitochondrial activities. This suggests that visible light mediates a flavin-photosensitized reaction that initiates damage involving participation of an activated species of oxygen in the damage propagation.

[Inhibition of the yeast respiratory system by Zn-protoporphyrin and effect of photolysis of this substance]

We have shown earlier that yeast cells grown in synthetic mediums supplemented with Zn++ accumulate large amounts of Zn-protoporphyrin within their mitochondria. This accumulation is accompanied by an inhibition of respiration (3). This study deals with the effect of light on the respiratory inhibition and the release of respiratory control which are observed if Zn-protoporphyrin is added to isolated mitochondria which are initially devoid of this pigment. In addition, we have studied the effect of light on the respiratory inhibition exerted by Zn-protoporphyrin accumulated in vivo. The following results were obtained: 1) The light-induced destruction of Zn-protoporphrin which had been added in vitro to Zn-protoporphyrin-free mitochondria significantly inhibits respiration and phosphorylation. Under these conditions, the extent of the inhibitions increases with the concentration of the added Zn-protoporphyrin and the duration of illumination. 2) Accumulation of Zn-protoporphyrin within the cells causes an inhibition of the respiratory activities and the activities of succinate-cytochrome c reductase and NADH-cytochrome c reductase of the mitochondria. Illumination of the isolated mitochondria from Zn-protoporphyrin-containing cells enhances the inhibition of these activities. No light-induced inhibition of these activities is observed with mitochondria from cells devoid of Zn-protoporphyrin.