Sometimes less is more: inhibitory infrared light during early reperfusion calms hyperactive mitochondria and suppresses reperfusion injury.

Ischemic stroke affects over 77 million people annually around the globe. Due to the blockage of a blood vessel caused by a stroke, brain tissue becomes ischemic. While prompt restoration of blood flow is necessary to save brain tissue, it also causes reperfusion injury. Mitochondria play a crucial role in early ischemia-reperfusion injury due to the generation of reactive oxygen species (ROS). During ischemia, mitochondria sense energy depletion and futilely attempt to up-regulate energy production. When reperfusion occurs, mitochondria become hyperactive and produce large amounts of ROS which damages neuronal tissue. This ROS burst damages mitochondria and the cell, which results in an eventual decrease in mitochondrial activity and pushes the fate of the cell toward death. This review covers the relationship between the mitochondrial membrane potential (ΔΨm) and ROS production. We also discuss physiological mechanisms that couple mitochondrial energy production to cellular energy demand, focusing on serine 47 dephosphorylation of cytochrome c (Cytc) in the brain during ischemia, which contributes to ischemia-reperfusion injury. Finally, we discuss the use of near infrared light (IRL) to treat stroke. IRL can both stimulate or inhibit mitochondrial activity depending on the wavelength. We emphasize that the use of the correct wavelength is crucial for outcome: inhibitory IRL, applied early during reperfusion, can prevent the ROS burst from occurring, thus preserving neurological tissue.

Cytochrome c oxidase-modulatory near-infrared light penetration into the human brain: Implications for the noninvasive treatment of ischemia/reperfusion injury.

Near-infrared light (IRL) has been evaluated as a therapeutic for a variety of pathological conditions, including ischemia/reperfusion injury of the brain, which can be caused by an ischemic stroke or cardiac arrest. Strategies have focused on modulating the activity of mitochondrial electron transport chain (ETC) enzyme cytochrome c oxidase (COX), which has copper centers that broadly absorb IRL between 700 and 1,000 nm. We have recently identified specific COX-inhibitory IRL wavelengths that are profoundly neuroprotective in rodent models of brain ischemia/reperfusion through the following mechanism: COX inhibition by IRL limits mitochondrial membrane potential hyperpolarization during reperfusion, which otherwise causes reactive oxygen species (ROS) production and cell death. Prior to clinical application of IRL on humans, IRL penetration must be tested, which may be wavelength dependent. In the present study, four fresh (unfixed) cadavers and isolated cadaver tissues were used to examine the transmission of infrared light through human biological tissues. We conclude that the transmission of 750 and 940 nm IRL through 4 cm of cadaver head supports the viability of IRL to treat human brain ischemia/reperfusion injury and is similar for skin with different skin pigmentation. We discuss experimental difficulties of working with fresh cadavers and strategies to overcome them as a guide for future studies.

Efficient synthesis of CN2097 using in situ activation of sulfhydryl group.

CN2097 (R7Cs-sCYK[KTE(ß-Ala)]V) is a rationally designed peptidomimetic that shows effectiveness in preclinical models for the treatment of neurological disorders, such as Angelman syndrome, traumatic brain injury (TBI) and stroke. Because of its therapeutic activity for the treatment of human CNS disorders, there was an urgent need to develop an efficient strategy for large-scale synthesis of CN2097. The synthesis of CN2097 was accomplished using Fmoc/tBu solid phase chemistry in multiple steps. Two different peptide fragments (activated polyarginine peptide Npys-sCR7 and CYK[KTE(ß-Ala)]V) were synthesized, followed by solution phase coupling in water. Activation of the polyarginine (CR7) was achieved in situ during cleavage of protected peptide (C(Trt)R(Pbf)7) from the Rink amide resin using 5 equiv. of 2,2-dithopyridine in TFA:TIS:H2O (95:2.5:2.5, v/v/v) for 4 h. The disulfide coupling was efficient which provided a 60% yield.

Inhibition of N-Methyl-D-aspartate-induced Retinal Neuronal Death by Polyarginine Peptides Is Linked to the Attenuation of Stress-induced Hyperpolarization of the Inner Mitochondrial Membrane Potential.

It is widely accepted that overactivation of NMDA receptors, resulting in calcium overload and consequent mitochondrial dysfunction in retinal ganglion neurons, plays a significant role in promoting neurodegenerative disorders such as glaucoma. Calcium has been shown to initiate a transient hyperpolarization of the mitochondrial membrane potential triggering a burst of reactive oxygen species leading to apoptosis. Strategies that enhance cell survival signaling pathways aimed at preventing this adverse hyperpolarization of the mitochondrial membrane potential may provide a novel therapeutic intervention in retinal disease. In the retina, brain-derived neurotrophic factor has been shown to be neuroprotective, and our group previously reported a PSD-95/PDZ-binding cyclic peptide (CN2097) that augments brain-derived neurotrophic factor-induced pro-survival signaling. Here, we examined the neuroprotective properties of CN2097 using an established retinal in vivo NMDA toxicity model. CN2097 completely attenuated NMDA-induced caspase 3-dependent and -independent cell death and PARP-1 activation pathways, blocked necrosis, and fully prevented the loss of long term ganglion cell viability. Although neuroprotection was partially dependent upon CN2097 binding to the PDZ domain of PSD-95, our results show that the polyarginine-rich transport moiety C-R(7), linked to the PDZ-PSD-95-binding cyclic peptide, was sufficient to mediate short and long term protection via a mitochondrial targeting mechanism. C-R(7) localized to mitochondria and was found to reduce mitochondrial respiration, mitochondrial membrane hyperpolarization, and the generation of reactive oxygen species, promoting survival of retinal neurons.

Impairment of TrkB-PSD-95 signaling in Angelman syndrome.

Angelman syndrome (AS) is a neurodevelopment disorder characterized by severe cognitive impairment and a high rate of autism. AS is caused by disrupted neuronal expression of the maternally inherited Ube3A ubiquitin protein ligase, required for the proteasomal degradation of proteins implicated in synaptic plasticity, such as the activity-regulated cytoskeletal-associated protein (Arc/Arg3.1). Mice deficient in maternal Ube3A express elevated levels of Arc in response to synaptic activity, which coincides with severely impaired long-term potentiation (LTP) in the hippocampus and deficits in learning behaviors. In this study, we sought to test whether elevated levels of Arc interfere with brain-derived neurotrophic factor (BDNF) TrkB receptor signaling, which is known to be essential for both the induction and maintenance of LTP. We report that TrkB signaling in the AS mouse is defective, and show that reduction of Arc expression to control levels rescues the signaling deficits. Moreover, the association of the postsynaptic density protein PSD-95 with TrkB is critical for intact BDNF signaling, and elevated levels of Arc were found to impede PSD-95/TrkB association. In Ube3A deficient mice, the BDNF-induced recruitment of PSD-95, as well as PLCγ and Grb2-associated binder 1 (Gab1) with TrkB receptors was attenuated, resulting in reduced activation of PLCγ-α-calcium/calmodulin-dependent protein kinase II (CaMKII) and PI3K-Akt, but leaving the extracellular signal-regulated kinase (Erk) pathway intact. A bridged cyclic peptide (CN2097), shown by nuclear magnetic resonance (NMR) studies to uniquely bind the PDZ1 domain of PSD-95 with high affinity, decreased the interaction of Arc with PSD-95 to restore BDNF-induced TrkB/PSD-95 complex formation, signaling, and facilitate the induction of LTP in AS mice. We propose that the failure of TrkB receptor signaling at synapses in AS is directly linked to elevated levels of Arc associated with PSD-95 and PSD-95 PDZ-ligands may represent a promising approach to reverse cognitive dysfunction.

Non-invasive treatment of ischemia/reperfusion injury: Effective transmission of therapeutic near-infrared light into the human brain through soft skin-conforming silicone waveguides.

Noninvasive delivery of near-infrared light (IRL) to human tissues has been researched as a treatment for several acute and chronic disease conditions. We recently showed that use of specific IRL wavelengths, which inhibit the mitochondrial enzyme cytochrome c oxidase (COX), leads to robust neuroprotection in animal models of focal and global brain ischemia/reperfusion injury. These life-threatening conditions can be caused by an ischemic stroke or cardiac arrest, respectively, two leading causes of death. To translate IRL therapy into the clinic an effective technology must be developed that allows efficient delivery of IRL to the brain while addressing potential safety concerns. Here, we introduce IRL delivery waveguides (IDWs) which meet these demands. We employ a low-durometer silicone that comfortably conforms to the shape of the head, avoiding pressure points. Furthermore, instead of using focal IRL delivery points via fiberoptic cables, lasers, or light-emitting diodes, the distribution of the IRL across the entire area of the IDW allows uniform IRL delivery through the skin and into the brain, preventing "hot spots" and thus skin burns. The IRL delivery waveguides have unique design features, including optimized IRL extraction step numbers and angles and a protective housing. The design can be scaled to fit various treatment areas, providing a novel IRL delivery interface platform. Using fresh (unfixed) human cadavers and isolated cadaver tissues, we tested transmission of IRL via IDWs in comparison to laser beam application with fiberoptic cables. Using the same IRL output energies IDWs performed superior in comparison to the fiberoptic delivery, leading to an up to 95% and 81% increased IRL transmission for 750 and 940 nm IRL, respectively, analyzed at a depth of 4 cm into the human head. We discuss the unique safety features and potential further improvements of the IDWs for future clinical implementation.

Retinal thickness and subnormal retinal oxygenation response in experimental diabetic retinopathy.

PURPOSE: To test the hypothesis that subnormal retinal oxygenation response (DeltaPo2) found at 3 months of experimental diabetes is associated with cellular swelling and increased retinal thickness. METHODS: Two groups of animals were studied: control rats injected intraperitoneally with either 15% body weight of saline or distilled water (cellular swelling model) or with intravitreal N-methyl-D-aspartate (NMDA) and 3-month-old diabetic and age-matched control rats. Intraocular pressure and retinal thickness was assessed using an applanation tonometer or high-resolution MRI (23.4 microm2 in-plane). In separate studies, functional MRI was used to measure blood-retinal barrier (BRB) integrity after Gd-DTPA injection intravenously and retinal DeltaPo2 during carbogen provocation. RESULTS: Inner and total retinal thickness were lower (P < 0.05) after NMDA injection, not different (P > 0.05) between control, before and after saline injection and before distilled water injection, and supernormal (P < 0.05) after distilled water injection. In diabetic rats, thickness was normal (P > 0.05) at most distances from the optic nerve but was subnormal (P < 0.05) in superior retina (0.5 mm from the optic nerve). Intraocular pressure was not different (P > 0.05) between groups. BRB was intact (P > 0.05) after saline and distilled water injection. DeltaPo2 was normal (P > 0.05) after saline injection and over inferior hemiretina of the diabetic group but was subnormal (P < 0.05) after distilled water injection and over superior hemiretina of diabetic rats. CONCLUSIONS: The lack of increased thickness in 3-month-old diabetic rats in vivo raises the possibility that intracellular swelling is unlikely to underlie subnormal DeltaPo2 in experimental diabetes. In diabetic rats, the spatial disconnect between subnormal DeltaPo2 pansuperiorly and retinal thinning only superiorly to the optic nerve suggests that neurovascular coupling is perturbed.

Noninvasive and simultaneous imaging of layer-specific retinal functional adaptation by manganese-enhanced MRI.

PURPOSE: To test the hypothesis that high-resolution (23.4 microm intraretinal resolution) manganese-enhanced magnetic resonance imaging (MEMRI) can be used to noninvasively and simultaneously record from distinct layers of the rat retina cellular demand for ions associated with functional adaptation. METHODS: In control rats, high-resolution images were collected with or without systemic injection of MnCl2 during light or dark adaptation; inner and outer retinal signal intensities were compared. In separate experiments, 1 month after systemic administration of MnCl2 to awake dark-adapted control rats, possible toxic effects of Mn2+ on ocular health were assessed with the use of the following metrics: retinal layer thickness, intraocular pressure, and blood retinal barrier integrity. RESULT: In nonmanganese-injected rats, the signal intensity difference between light and dark states for inner and outer retina was not significantly different (P>0.05). In contrast, after manganese administration, the change in outer retinal signal intensity under light/dark conditions was significantly greater than that of inner retina. At 1 month after MnCl2 injection, comparisons with controls revealed no evidence for deleterious ocular health effects as assessed by whole and inner retinal thickness, intraocular pressure, and blood retinal barrier integrity. CONCLUSIONS: The present MEMRI examination was a safe (i.e., nontoxic) and relatively straightforward procedure that appeared to robustly reflect layer-specific retinal ion demand that correlates with normal retinal physiology responses associated with light and dark visual processing. Comprehensive MEMRI measures of retinal ion demand may be envisioned in a range of animal models for the study of normal development and aging.

Agonist-stimulated cobalt uptake provides selective visualization of neurons expressing AMPA- or kainate-type glutamate receptors in the retina.

Fast-acting excitatory neurotransmission in the retina is mediated primarily by glutamate, acting at alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) -selective and kainate-selective receptors. To localize these sites of action, cat retinas were stimulated with either AMPA or kainate and processed for histochemical visualization of cobalt uptake through calcium-permeable channels. Treatment with both agonists resulted in staining of A- and B-type horizontal cells and several types of OFF cone bipolar cells; there was no evidence for staining of ON cone bipolar cells or rod bipolar cells. The subpopulations of OFF cone bipolar cells differed in their responses with two distinct types that stained heavily with cobalt after exposure to AMPA and three different types that were preferentially labeled after exposure to kainate. Although many amacrine and ganglion cells appeared to respond to both agonists, AII amacrine cells were stained after stimulation by AMPA but not by kainate. The OFF cone bipolar cells that exhibit AMPA-stimulated cobalt uptake were found to have a high level of correspondence with cells that show immunocytochemical staining for the AMPA-selective glutamate receptor subunits GluR1 and GluR2/3. Similarly, the cone bipolar cells exhibiting kainate-stimulated cobalt uptake resemble those that are immunoreactive for the kainate subunit GluR5. The results indicate that, whereas many retinal neurons express both AMPA and kainate receptors, AII amacrine cells and subpopulations of OFF cone bipolar cells are limited to the expression of either AMPA or kainate receptors. This differential expression may contribute to the unique character of transmission by these cell types.

Selective blockade of CaMKII-alpha inhibits NMDA-induced caspase-3-dependent cell death but does not arrest PARP-1 activation or loss of plasma membrane selectivity in rat retinal neurons.

Calcium/calmodulin-dependent protein kinase II-alpha (CaMKII-alpha) has been implicated in a number of receptor mediated events in neurons. Pharmacological blockade of CaMKII-alpha has been shown to prevent phosphorylation of NMDA-R2A and R2B receptor subunits, suggesting that this enzyme may be linked to receptor trafficking of glutamate receptors and serve as a regulatory protein for neuronal cell death. In the retina, inhibition of CaMKII-alpha has been reported to be neuroprotective against NMDA-induced cell death by preventing the activation of the caspase-3 dependent pathway. However, the effects of CaMKII-alpha blockade on the caspase-3 independent, PARP-1 dependent and the non-programmed cell death pathways have not previously been investigated. In the present study, blockade of CaMKII-alpha with the highly specific antagonist myristoylated autocamtide-2-related inhibitory peptide (AIP) was used in a rat in vivo model of retinal toxicity to compare the effects of on NMDA-induced caspase-3-dependent, PARP-1 dependent and the non-programmed (necrosis) cell death pathways. Results confirmed that AIP fully attenuates caspase-3 activation for at least 8 h following NMDA insult and also significantly improves retinal ganglion cell survival. However, this blockade had little effect on reducing the loss of plasma membrane selectivity (LPMS, e.g. necrosis) in cells located in the ganglion cell and inner nuclear layers and did not alter NMDA-induced PARP-1 hyperactivation, or prevent TUNEL labeling following a moderate NMDA-insult. These findings support a specific role for CaMKII-alpha in mediating the caspase-3 dependent cell death pathway and provide evidence that it is not directly linked to the signaling of either the PARP-1 dependent or the non-programmed cell death pathways.

Blockade of PARP activity attenuates poly(ADP-ribosyl)ation but offers only partial neuroprotection against NMDA-induced cell death in the rat retina.

Recent reports have linked neuronal cell death by necrosis to poly(ADP-ribose) polymerase-1 (PARP-1) hyperactivation. It is believed that under stress, the activity of this enzyme is up-regulated, resulting in extensive poly(ADP-ribosyl)ation of nuclear proteins, using NAD(+) as its substrate, which, in turn, leads to the depletion of NAD(+). In efforts to restore the level of NAD(+), depletion of ATP occurs, resulting in the shutdown of ATP-dependent ionic pumps. This results in cell swelling and eventual loss of membrane selectivity, hallmarks of necrosis. Reports from in vitro and in vivo studies in the brain have shown that NMDA receptor activation stimulates PARP activity and that blockade of the enzyme provides substantial neuroprotection. The present study was undertaken to determine whether PARP activity is regulated by NMDA in the rat retina, and whether blockade of PARP activity provides protection against toxic effects of NMDA. Rat retinas exposed to intravitreal injections containing NMDA, with or without the PARP inhibitor N-(6-oxo-5, 6-dihydrophenanthridin-2-yl)-(N,-dimethylamino) acetamide hydrochloride (PJ-34), were assessed for changes in PARP-1 activity as evidenced by poly(ADP-ribosyl)ation (PAR), loss of membrane integrity, morphological indicators of apoptosis and necrosis, and ganglion cell loss. Results showed that: NMDA increased PAR formation in a concentration-dependent manner and caused a decline in retinal ATP levels; PJ-34 blockade attenuated the NMDA-induced formation of PAR and decline in ATP; NMDA induced the loss of membrane selectivity to ethidium bromide (EtBr) in inner retinal neurons, but loss of membrane selectivity was not prevented by blocking PARP activity; cells stained with EtBr, or reacted for TUNEL-labeling, displayed features characteristic of both apoptosis and necrosis. In the presence of PJ-34, greater numbers of cells exhibited apoptotic features; PJ-34 provided partial neuroprotection against NMDA-induced ganglion cell loss. These findings suggest that although blockade of PARP activity fully attenuates NMDA-induced PAR formation and loss of retinal ATP content, and improves the survival of select populations of ganglion cells, this approach does not provide full neuroprotection. In contrast, blockade of PARP activity promotes apoptotic-like cell death in the majority of cells undergoing cell death. Furthermore, these studies show that the loss of membrane selectivity is not dependent upon PAR formation or the resulting decline of ATP, and suggests that an alternative pathway, other than PARP activation, exists to mediate this event.