Protection of neurons in the retinal ganglion cell layer against excitotoxicity by the N-acylethanolamine, N-linoleoylethanolamine

Plasma Metabolomics of Intermediate and Neovascular Age-Related Macular Degeneration Patients

To characterize metabolites and metabolic pathways altered in intermediate and neovascular age-related macular degeneration (IAMD and NVAMD), high resolution untargeted metabolomics was performed via liquid chromatography-mass spectrometry on plasma samples obtained from 91 IAMD patients, 100 NVAMD patients, and 195 controls. Plasma metabolite levels were compared between: AMD patients and controls, IAMD patients and controls, and NVAMD and IAMD patients. Partial least-squares discriminant analysis and linear regression were used to identify discriminatory metabolites. Pathway analysis was performed to determine metabolic pathways altered in AMD. Among the comparisons, we identified 435 unique discriminatory metabolic features. Using computational methods and tandem mass spectrometry, we identified 11 metabolic features whose molecular identities had been previously verified and confirmed the molecular identities of three additional discriminatory features. Included among the discriminatory metabolites were acylcarnitines, phospholipids, amino acids, and steroid metabolites. Pathway analysis revealed that lipid, amino acid, and vitamin metabolism pathways were altered in NVAMD, IAMD, or AMD in general, including the carnitine shuttle pathway which was significantly altered in all comparisons. Finally, few discriminatory features were identified between IAMD patients and controls, suggesting that plasma metabolic profiles of IAMD patients are more similar to controls than to NVAMD patients.

Changes in Retinal N-Acylethanolamines and their Oxylipin Derivatives During the Development of Visual Impairment in a Mouse Model for Glaucoma

Neurons are especially susceptible to oxidative damage, which is increasingly implicated in neurodegenerative disease. Certain N-acylethanolamines (NAEs) have been shown to protect neurons from oxidative stress. Since glaucoma may be considered a neurodegenerative disorder and the survival of retinal neurons could also be influenced by N-acylethanolamines, our goal was to quantify changes in certain N-acylethanolamine species and their oxylipin derivatives in the retina of a mouse model for glaucoma. We also sought to identify relationships between these and parameters of glaucoma disease development, specifically intraocular pressure, visual acuity, and contrast sensitivity. Five N-acylethanolamine species and three NAE oxylipin derivatives were quantified in retina from young and aged DBA/2Crl mice. N-Acylethanolamines and NAE-oxylipins in retinal extracts were quantified against deuterated standards by isotope dilution gas chromatography-mass spectrometry. Levels (nmol/g dry weight) of N-arachidonoylethanolamine (anandamide; NAE 20:4) were significantly (p = 0.008) decreased in aged (2.875 ± 0.6702) compared to young animals (5.175 ± 0.971). Conversely, the anandamide oxylipin, 15(S)-HETE ethanolamide (15(S)-HETE EA), was significantly (p = 0.042) increased in aged (0.063 ± 0.009) compared to young animals (0.039 ± 0.011). Enzymatic depletion of the anandamide pool by 15-lipoxygenase and consequent accumulation of 15(S)-HETE ethanolamine may contribute to decreased visual function in glaucomatous mice. Since N-acylethanolamines effectively attenuate glaucoma pathogenesis and associated visual impairment, our data provides additional rationale and novel targets for glaucoma therapies.

N-Palmitoylethanolamine Prevents the Run-down of Amplitudes in Cortical Spreading Depression Possibly Implicating Proinflammatory Cytokine Release

Cortical spreading depression (CSD), a wave of neuronal depolarization in the cerebral cortex following traumatic brain injury or cerebral ischemia, significantly aggravates brain damage. Here, we tested whether N-palmitoylethanolamine (PEA), a substance that effectively reduces lesion volumes and neurological deficits after ischemic stroke, influences CSD. CSD was elicited chemically in adult rats and occurrence, amplitude, duration and propagation velocity of CSD was determined prior to and for 6 hours after intraperitoneal injection of PEA. The chosen systemic administration of PEA stabilized the amplitude of CSD for at least four hours and prevented the run-down of amplitudes that is typically observed and was also seen in untreated controls. The propagation velocity of the CSD waves was unaltered indicating stable neuronal excitability. The stabilization of CSD amplitudes by PEA indicates that inhibition or prevention of CSD does not underlie PEA's profound neuroprotective effect. Rather, PEA likely inhibits proinflammatory cytokine release thereby preventing the run-down of CSD amplitudes. This contribution of PEA to the maintenance of neuronal excitability in healthy tissue during CSD potentially adds to neuroprotection outside a damaged area, while other mechanisms control PEA-mediated neuroprotection in damaged tissue resulting from traumatic brain injury or cerebral ischemia.

Lipids and Oxidative Stress Associated with Ethanol-Induced Neurological Damage

The excessive intake of alcohol is a serious public health problem, especially given the severe damage provoked by chronic or prenatal exposure to alcohol that affects many physiological processes, such as memory, motor function, and cognitive abilities. This damage is related to the ethanol oxidation in the brain. The metabolism of ethanol to acetaldehyde and then to acetate is associated with the production of reactive oxygen species that accentuate the oxidative state of cells. This metabolism of ethanol can induce the oxidation of the fatty acids in phospholipids, and the bioactive aldehydes produced are known to be associated with neurotoxicity and neurodegeneration. As such, here we will review the role of lipids in the neuronal damage induced by ethanol-related oxidative stress and the role that lipids play in the related compensatory or defense mechanisms.

Synthesis of phenoxyacyl-ethanolamides and their effects on fatty acid amide hydrolase activity

N-Acylethanolamines (NAEs) are involved in numerous biological activities in plant and animal systems. The metabolism of these lipids by fatty acid amide hydrolase (FAAH) is a key regulatory point in NAE signaling activity. Several active site-directed inhibitors of FAAH have been identified, but few compounds have been described that enhance FAAH activity. Here we synthesized two sets of phenoxyacyl-ethanolamides from natural products, 3-n-pentadecylphenolethanolamide and cardanolethanolamide, with structural similarity to NAEs and characterized their effects on the hydrolytic activity of FAAH. Both compounds increased the apparent Vmax of recombinant FAAH proteins from both plant (Arabidopsis) and mammalian (Rattus) sources. These NAE-like compounds appeared to act by reducing the negative feedback regulation of FAAH activity by free ethanolamine. Both compounds added to seedlings relieved, in part, the negative growth effects of exogenous NAE12:0. Cardanolethanolamide reduced neuronal viability and exacerbated oxidative stress-mediated cell death in primary cultured neurons at nanomolar concentrations. This was reversed by FAAH inhibitors or exogenous NAE substrate. Collectively, our data suggest that these phenoxyacyl-ethanolamides act to enhance the activity of FAAH and may stimulate the turnover of NAEs in vivo. Hence, these compounds might be useful pharmacological tools for manipulating FAAH-mediated regulation of NAE signaling in plants or animals.

Antioxidant drug therapy approaches for neuroprotection in chronic diseases of the retina

The molecular pathways contributing to visual signal transduction in the retina generate a high energy demand that has functional and structural consequences such as vascularization and high metabolic rates contributing to oxidative stress. Multiple signaling cascades are involved to actively regulate the redox state of the retina. Age-related processes increase the oxidative load, resulting in chronically elevated levels of oxidative stress and reactive oxygen species, which in the retina ultimately result in pathologies such as glaucoma or age-related macular degeneration, as well as the neuropathic complications of diabetes in the eye. Specifically, oxidative stress results in deleterious changes to the retina through dysregulation of its intracellular physiology, ultimately leading to neurodegenerative and potentially also vascular dysfunction. Herein we will review the evidence for oxidative stress-induced contributions to each of the three major ocular pathologies, glaucoma, age-related macular degeneration, and diabetic retinopathy. The premise for neuroprotective strategies for these ocular disorders will be discussed in the context of recent clinical and preclinical research pursuing novel therapy development approaches.

A case for neuroprotection in ophthalmology: developments in translational research

Cellular aging occurs by the lifelong accumulation of oxidative damage leading to neuronal apoptosis, termed 'neurodegeneration', and the functional deficits of aging. Loss of visual function is one of the most important quality of life measures for older adults. We discuss recent clinical and laboratory advances in the neuroprotective treatment of the aging eye with particular emphasis on the three major ocular neurodegenerative conditions: glaucoma, age-related macular degeneration (AMD), and diabetic retinopathy (DR).

N-Palmitoylethanolamine depot injection increased its tissue levels and those of other acylethanolamide lipids

N-Palmitoylethanolamine (NAE 16:0) is an endogenous lipid signaling molecule that has limited water solubility, and its action is short-lived due to its rapid metabolism. This poses a problem for use in vivo as oral administration requires a high concentration for significant levels to reach target tissues, and injection of the compound in a dimethyl sulfoxide- or ethanol-based vehicle is usually not desirable during long-term treatment. A depot injection of NAE 16:0 was successfully emulsified in sterile corn oil (10 mg/kg) and administered in young DBA/2 mice in order to elevate baseline levels of NAE 16:0 in target tissues. NAE 16:0 levels were increased in various tissues, particularly in the retina, 24 and 48 hours following injections. Increases ranged between 22% and 215% (above basal levels) in blood serum, heart, brain, and retina and induced an entourage effect by increasing levels of other 18 carbon N-Acylethanolamines (NAEs), which ranged between 31% and 117% above baseline. These results indicate that NAE 16:0 can be used as a depot preparation, avoiding the use of inadequate vehicles, and can provide the basis for designing tissue-specific dosing regimens for therapies involving NAEs and related compounds.

Protective effects of 7,8-dihydroxyflavone on retinal ganglion and RGC-5 cells against excitotoxic and oxidative stress

A preferential loss of retinal ganglion cells (RGCs) is observed in glaucoma and optic neuritis. Loss of tropomyosin-related kinase receptor B (TrkB)-mediated signaling has been implicated in this degeneration. Our study indicates that 7,8-dihydroxyflavone (7,8 DHF) robustly upregulates the TrkB signaling in the primary rat RGCs and the retinal neuronal precursor RGC-5 cell line by promoting phosphorylation of TrkB receptor, leading to enhanced TrkB receptor tyrosine kinase activity. The flavonoid derivative 7,8 DHF acts a potent TrkB agonist and upregulates the downstream AKT and MAPK/ERK survival signaling pathways in a TrkB-dependent manner in both primary rat RGCs as well as the RGC-5 cell line. Excitotoxicity and oxidative injury have been alleged in the specific RGC degeneration in various forms of glaucoma. A novel finding of this study is that treatment with 7,8 DHF protects these cells significantly from excitotoxic and oxidative stress-induced apoptosis and cell death. 7,8 DHF also promotes neuritogenesis by stimulating neurite outgrowth, suggesting a possible therapeutic strategy for protection of RGCs in various optic neuropathies.

YC-1 targeting of hypoxia-inducible factor-1α reduces RGC-5 cell viability and inhibits cell proliferation

PURPOSE

The survival of retinal ganglion cells (RGCs) is a hallmark of many optic neurodegenerative diseases such as glaucoma. YC-1, a potential anticancer drug, is known to be able to decrease the stability and protein expression of hypoxia-inducible factor (HIF)-1α that is triggered by hypoxia and related to RGC survival. We hypothesized that YC-1 may alter RGC cell viability through the down-regulation of HIF-1α.

METHODS

Cell viability of the RGC-5 cell line was measured with a 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Flow cytometry, a LIVE/DEAD viability assay, and high-content screening (HCS) with MKI67 (K(i)-67) monoclonal antibodies were used to detect cell death and cellular proliferation.

RESULTS

We found that cells treated with 20 µM YC-1 for 24 h decreased the HIF-1α level in an RGC-5 cell line using immunoblotting and reduced the live cell number in an MTT assay. Results of flow cytometry and HCS demonstrated that reducing the cell proliferation of RGC-5 cells, not cell death, led to the decreased level in the MTT assay.

CONCLUSIONS

Our findings demonstrate that YC-1-induced down-regulation of HIF-1α might reduce RGC cell proliferation and viability under normoxia, which implies a role of YC-1 in the neuroprotective effect for further clinical applications.