Neuroprotective Effects of VEGF-A Nanofiber Membrane and FAAH Inhibitor URB597 Against Oxygen-Glucose Deprivation-Induced Ischemic Neuronal Injury

INTRODUCTION

Brain ischemia is a common neurological disorder worldwide that activates a cascade of pathophysiological events involving decreases in oxygen and glucose levels. Despite substantial efforts to explore its pathogenesis, the management of ischemic neuronal injury remains an enormous challenge. Accumulating evidence suggests that VEGF modified nanofiber (NF) materials and the fatty-acid amide hydrolase (FAAH) inhibitor URB597 exert an influence on alleviating ischemic brain damage. We aimed to further investigate their effects on primary hippocampal neurons, as well as the underlying mechanisms following oxygen-glucose deprivation (OGD).

METHODS

Different layers of VEGF-A loaded polycaprolactone (PCL) nanofibrous membranes were first synthesized by using layer-by-layer (LBL) self-assembly of electrospinning methods. The physicochemical and biological properties of VEGF-A NF membranes, and their morphology, hydrophilicity, and controlled-release of VEGF-A were then estimated. Furthermore, the effects of VEGF-A NF and URB597 on OGD-induced mitochondrial oxidative stress, inflammatory responses, neuronal apoptosis, and endocannabinoid signaling components were assessed.

RESULTS

The VEGF-A NF membrane and URB597 can not only promote hippocampal neuron adhesion and viability following OGD but also exhibited antioxidant/anti-inflammatory and mitochondrial membrane potential protection. The VEGF-A NF membrane and URB597 also inhibited OGD-induced cellular apoptosis through activating CB1R signaling. These results indicate that VEGF-A could be controlled-released by LBL self-assembled NF membranes.

DISCUSSION

The VEGF-A NF membrane and URB597 displayed positive synergistic neuroprotective effects through the inhibition of mitochondrial oxidative stress and activation of CB1R/PI3K/AKT/BDNF signaling, suggesting that a VEGF-A loaded NF membrane and the FAAH inhibitor URB597 could be of therapeutic value in ischemic cerebrovascular diseases.

Kaempferol Facilitated Extinction Learning in Contextual Fear Conditioned Rats via Inhibition of Fatty-Acid Amide Hydrolase

Background: Fear, stress, and anxiety-like behaviors originate from traumatic events in life. Stress response is managed by endocannabinoids in the body by limiting the uncontrolled retrieval of aversive memories. Pharmacotherapy-modulating endocannabinoids, especially anandamide, presents a promising tool for treating anxiety disorders. Here, we investigated the effect of kaempferol, a flavonoid, in the extinction of fear related memories and associated anxiety-like behavior. Methods: The ability of kaempferol to inhibit fatty-acid amide hydrolase (FAAH, the enzyme that catabolizes anandamide) was assessed in vitro using an enzyme-linked immunosorbent assay (ELISA) kit. For animal studies (in vivo), the extinction learning was evaluated using contextual fear conditioning (CFC, a behavioral paradigm based on ability to learn and remember aversive stimuli). Furthermore, an elevated plus-maze (EPM) model was used for measuring anxiety-like behavior, while serum corticosterone served as a biochemical indicator of anxiety. Lastly, the interaction of kaempferol with FAAH enzyme was also assessed in silico (computational study). Results: Our data showed that kaempferol inhibited the FAAH enzyme with an IC₅₀ value of 1 µM. In CFC, it reduced freezing behavior in rats. EPM data demonstrated anxiolytic activity as exhibited by enhanced number of entries and time spent in the open arm. No change in blood corticosterone levels was noted. Our computational study showed that Kaempferol interacted with the catalytic amino acids (SER241, PHE192, PHE381, and THR377) of FAAH enzyme Conclusion: Our study demonstrate that kaempferol facilitated the extinction of aversive memories along with a reduction of anxiety. The effect is mediated through the augmentation of endocannabinoids via the inhibition of FAAH enzyme.

Role of endocannabinoid signalling in the dorsolateral periaqueductal grey in the modulation of distinct panic-like responses

Panic attacks, a major feature of panic disorder, can be modelled in rats by exposing animals to stimuli that induce escape reactions, such as the elevated T-maze or the activation of the dorsolateral periaqueductal grey. Since the cannabinoid CB1 receptor modulates various types of aversive responses, this study tested the hypothesis that enhancement of endocannabinoid signalling in the dorsolateral periaqueductal grey inhibits panic-like reactions in rats. Local injection of the CB1 agonist, arachidonoyl 2-Chloroethylamide (0.005-0.5 pmol), attenuated the escape response from the open arm of the elevated T-maze, a panicolytic effect. The anandamide hydrolysis inhibitor, URB597 (0.3-3 nmol), did not induce consistent results. In the test of dorsolateral periaqueductal grey stimulation with d,l-homocysteic acid, arachidonoyl 2-Chloroethylamide, at the lowest dose, attenuated the escape reaction. The highest dose of URB597 also inhibited this response, contrary to the result obtained in the elevated T-maze. This effect was reversed by the CB1 antagonist, AM251 (100 pmol). The present results confirm the anti-aversive property of direct CB1 receptor activation in the dorsolateral periaqueductal grey. The effect of the anandamide hydrolysis inhibitor, however, could be detected only in a model employing direct stimulation of this structure. Altogether, these results suggest that anandamide signalling is recruited only under certain types of aversive stimuli.

Increased angiotensin II contraction of the uterine artery at early gestation in a transgenic model of hypertensive pregnancy is reduced by inhibition of endocannabinoid hydrolysis

Increased vascular sensitivity to angiotensin II (Ang II) is a marker of a hypertensive human pregnancy. Recent evidence of interactions between the renin-angiotensin system and the endocannabinoid system suggests that anandamide and 2-arachidonoylglycerol may modulate Ang II contraction. We hypothesized that these interactions may contribute to the enhanced vascular responses in hypertensive pregnancy. We studied Ang II contraction in isolated uterine artery (UA) at early gestation in a rat model that mimics many features of preeclampsia, the transgenic human angiotensinogen×human renin (TgA), and control Sprague-Dawley rats. We determined the role of the cannabinoid receptor 1 by blockade with SR171416A, and the contribution of anandamide and 2-arachidonoylglycerol degradation to Ang II contraction by inhibiting their hydrolyzing enzyme fatty acid amide hydrolase (with URB597) or monoacylglycerol lipase (with JZL184), respectively. TgA UA showed increased maximal contraction and sensitivity to Ang II that was inhibited by indomethacin. Fatty acid amide hydrolase blockade decreased Ang IIMAX in Sprague-Dawley UA, and decreased both Ang IIMAX and sensitivity in TgA UA. Monoacylglycerol lipase blockade had no effect on Sprague-Dawley UA and decreased Ang IIMAX and sensitivity in TgA UA. Blockade of the cannabinoid receptor 1 in TgA UA had no effect. Immunolocalization of fatty acid amide hydrolase and monoacylglycerol lipase showed a similar pattern between groups; fatty acid amide hydrolase predominantly localized in endothelium and monoacylglycerol lipase in smooth muscle cells. We demonstrated an increased Ang II contraction in TgA UA before initiation of the hypertensive phenotype. Anandamide and 2-arachidonoylglycerol reduced Ang II contraction in a cannabinoid receptor 1-independent manner. These renin-angiotensin system-endocannabinoid system interactions may contribute to the enhanced vascular reactivity in early stages of hypertensive pregnancy.

Endocannabinoid regulation in human endometrium across the menstrual cycle

Humans produce endogenous cannabinoids (endocannabinoids), a group of molecules that activate the same receptors as tetrahydrocannabinol. Endocannabinoids play important roles in reproduction in multiple species, but data in human endometrium are limited. Because endocannabinoids such as anandamide (AEA) and 2-arachidonoyl glycerol (2-AG) often act within tissues as paracrine factors, their effects can be modulated by changes in expression of locally produced synthetic and degradative/oxidative enzymes. The objective of this study was to localize and quantify expression of these key synthetic and degradative/oxidative enzymes for AEA and 2-AG in human endometrium throughout the menstrual cycle. Key synthetic enzymes include N-arachidonyl-phosphatidylethanolamine phospholipase-D (NAPE-PLD), diacylglycerol-lipase a (DAGL-α, and DAGL-β. Key degradative enzymes include fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL); cyclooxygenase 2 (COX2) is an oxidative enzyme. Endometrial samples were collected in 49 regularly cycling, normal women. Protein localization and expression were achieved by immunohistochemistry and messenger RNA (mRNA) expression by real-time reverse transcriptase polymerase chain reaction. No significant cycle-dependent mRNA expression was observed except that of COX2 (P = .002), which demonstrated maximum expression in the proliferative phase. During the secretory phase, NAPE-PLD protein had increased expression in luminal (P = .001), stromal (P = .007), and glandular (P = .04) epithelia, while FAAH had increased glandular (P = .009) and luminal (P = .01) expression. Increased expression in glandular epithelia was identified for MAGL (P = .03). The COX2 had increased luminal expression during the early secretory phase (P < .0001). In conclusion, maximal expression of degradatory/oxidative enzymes in the secretory phase may foster decreased endocannabinoid tone during implantation.

Endocannabinoids decrease neuropathic pain-related behavior in mice through the activation of one or both peripheral CB₁ and CB₂ receptors

The two most studied endocannabinoids are anandamide (AEA), principally catalyzed by fatty-acid amide hydrolase (FAAH), and 2-arachidonoyl glycerol (2-AG), mainly hydrolyzed by monoacylglycerol lipase (MGL). Inhibitors targeting these two enzymes have been described, including URB597 and URB602, respectively. Several recent studies examining the contribution of CB₁ and/or CB₂ receptors on the peripheral antinociceptive effects of AEA, 2-AG, URB597 and URB602 in neuropathic pain conditions using either pharmacological tools or transgenic mice separately have been reported, but the exact mechanism is still uncertain. Mechanical allodynia and thermal hyperalgesia were evaluated in 436 male C57BL/6, cnr1KO and cnr2KO mice in the presence or absence of cannabinoid CB₁ (AM251) or CB₂ (AM630) receptor antagonists in a mouse model of neuropathic pain. Peripheral subcutaneous injections of AEA, 2-AG, WIN55,212-2 (WIN; a CB₁/CB₂ synthetic agonist), URB597 and URB602 significantly decreased mechanical allodynia and thermal hyperalgesia. These effects were inhibited by both cannabinoid antagonists AM251 and AM630 for treatments with 2-AG, WIN and URB602 but only by AM251 for treatments with AEA and URB597 in C57BL/6 mice. Furthermore, the antinociceptive effects for AEA and URB597 were observed in cnr2KO mice but absent in cnr1KO mice, whereas the effects of 2-AG, WIN and URB602 were altered in both of these transgenic mice. Complementary genetic and pharmacological approaches revealed that the anti-hyperalgesic effects of 2-AG and URB602 required both CB₁ and CB₂ receptors, but only CB₂ receptors mediated its anti-allodynic actions. The antinociceptive properties of AEA and URB597 were mediated only by CB₁ receptors.

Antidepressant-like activity and modulation of brain monoaminergic transmission by blockade of anandamide hydrolysis

Although anecdotal reports suggest that cannabis may be used to alleviate symptoms of depression, the psychotropic effects and abuse liability of this drug prevent its therapeutic application. The active constituent of cannabis, delta9-tetrahydrocannabinol, acts by binding to brain CB1 cannabinoid receptors, but an alternative approach might be to develop agents that amplify the actions of endogenous cannabinoids by blocking their deactivation. Here, we show that URB597, a selective inhibitor of the enzyme fatty-acid amide hydrolase, which catalyzes the intracellular hydrolysis of the endocannabinoid anandamide, exerts potent antidepressant-like effects in the mouse tail-suspension test and the rat forced-swim test. Moreover, URB597 increases firing activity of serotonergic neurons in the dorsal raphe nucleus and noradrenergic neurons in the nucleus locus ceruleus. These actions are prevented by the CB1 antagonist rimonabant, are accompanied by increased brain anandamide levels, and are maintained upon repeated URB597 administration. Unlike direct CB1 agonists, URB597 does not exert rewarding effects in the conditioned place preference test or produce generalization to the discriminative effects of delta9-tetrahydrocannabinol in rats. The findings support a role for anandamide in mood regulation and point to fatty-acid amide hydrolase as a previously uncharacterized target for antidepressant drugs.