NDP-MSH reduces oxidative damage induced by palmitic acid in primary astrocytes

Polysorbate 80 coated chitosan nanoparticles for delivery of α-melanocyte stimulating hormone analog (NDP-MSH) to the brain reverse cognitive impairment related to neuroinflammation produced by a high-fat diet (HFD)

This study aimed to develop polysorbate 80-coated chitosan nanoparticles (PS80/CS NPs) as a delivery system for improved brain targeting of α-Melanocyte Stimulating Hormone analog (NDP-MSH). Chitosan nanoparticles loaded with NDP-MSH were surface-modified with polysorbate 80 ([NDP-MSH]-PS80/CS NP), which formed a flattened layer on their surface. Nanoparticle preparation involved ionic gelation, followed by characterization using scanning electron microscopy (SEM) for morphology, dynamic light scattering (DLS) for colloidal properties, and ATR-FTIR spectroscopy for structure. Intraperitoneal injection of FITC-PS80/CS NPs and [NDP-MSH]-PS80/CS NP in rats demonstrated their ability to cross the blood-brain barrier, reach the brain, and accumulate in CA1 neurons of the dorsal hippocampus within 2 h. Two experimental models of neuroinflammation were employed with Male Wistar rats: a short-term model involving high-fat diet (HFD) consumption for 5 days followed by an immune stimulus with LPS, and a long-term model involving HFD consumption for 8 weeks. In both models, [NDP-MSH]-PS80/CS NPs could reverse the decreased expression of contextual fear memory induced by the diets. These findings suggest that [NDP-MSH]-PS80/CS NPs offer a promising strategy to overcome the limitations of NDP-MSH regarding pharmacokinetics and enzymatic stability. By facilitating NDP-MSH delivery to the hippocampus, these nanoparticles can potentially mitigate the cognitive impairments associated with HFD consumption and neuroinflammation.

Activation of the melanocortin-1 receptor attenuates neuronal apoptosis after traumatic brain injury by upregulating Merlin expression

Traumatic brain injury (TBI) is a common disease worldwide with high mortality and disability rates. Besides the primary mechanical injury, the secondary injury associated with TBI can also induce numerous pathological changes, such as brain edema, nerve apoptosis, and neuroinflammation, which further aggravates neurological dysfunction and even causes the death due to the primary injury. Among them, neuronal apoptosis is a key link in the injury. Melanocortin-1 receptor (MC1R) is a G protein coupled receptor, belonging to the melanocortin receptor family. Studies have shown that activation of MC1R inhibits oxidative stress and apoptosis, and confers neuroprotective effects against various neurological diseases. Merlin is a protein product of the NF2 gene, which is widely expressed in the central nervous system (CNS) of mice, rats, and humans. Studies have indicated that Merlin is associated with MC1R. In this study, we explored the anti-apoptotic effects and potential mechanisms of MC1R. A rat model of TBI was established through controlled cortical impact. The MC1R-specific agonist Nle4-D-Phe7-α-Melanocyte (NDP-MSH) and the inhibitor MSG-606 were employed to explore the effects of MC1R and Merlin following TBI and investigated the associated mechanisms. The results showed that the expression levels of MC1R and Merlin were upregulated after TBI, and activation of MC1R promoted Merlin expression. Further, we found that MC1R activation significantly improved neurological dysfunction and reduced brain edema and neuronal apoptosis induced by TBI in rats. Mechanistically, its neuroprotective function and anti-apoptotic were partly associated with MC1R activation. In conclusion, we demonstrated that MC1R activation after TBI may inhibit apoptosis and confer neuroprotection by upregulating the expression of Merlin.

Modulatory role of α-MSH in hippocampal-dependent memory impairment, synaptic plasticity changes, oxidative stress, and astrocyte reactivity induced by short-term high-fat diet intake

High-fat diet (HFD) consumption is associated with cognitive deficits and neurodegenerative diseases. Since the hippocampus is extremely sensitive to pathophysiological changes, neuroinflammation and the concomitant oxidative stress induced by HFD can significantly interfere with hippocampal-dependent functions related to learning and memory. The neuropeptide alpha-melanocyte stimulating hormone (α-MSH) mediates neuroprotective actions in the central nervous system and can reverse the effects of neuroinflammation in cognitive functions that depend on the hippocampus. In this study, we used male Wistar rats to evaluate the effect of short-term HFD intake (5 days) plus a mild immune challenge, Lipopolysaccharide (LPS 10 μg/kg) on contextual fear, changes in structural plasticity, oxidative stress, and astrocyte reactivation in the hippocampus. We also determined the possible modulatory role of α-MSH. HFD consumption was associated with an increase in markers of oxidative stress (Advanced oxidation protein products and Malondialdehyde) in the dorsal hippocampus (DH). We also found changes in hippocampal structural synaptic plasticity, observing a decrease in total spine in the DH after HFD plus LPS. We observed astrocyte proliferation and a significant increase in the percentage of the area occupied by GFAP. Treatment with α-MSH (0.1 μg/0.25 μl) in the DH reversed the effect of short-term HFD plus LPS on contextual fear memory, oxidative stress, and spine density. α-MSH also reduced astrocyte proliferation. Our present results indicate that HFD consumption for a short period sensitizes the central nervous system (CNS) to a subsequent immune challenge and impairs contextual fear memory and that α-MSH could have a modulatory protective effect.

Elucidating glial responses to products of diabetes-associated systemic dyshomeostasis

Diabetic retinopathy (DR) is a leading cause of blindness in working age adults. DR has non-proliferative stages, characterized in part by retinal neuroinflammation and ischemia, and proliferative stages, characterized by retinal angiogenesis. Several systemic factors, including poor glycemic control, hypertension, and hyperlipidemia, increase the risk of DR progression to vision-threatening stages. Identification of cellular or molecular targets in early DR events could allow more prompt interventions pre-empting DR progression to vision-threatening stages. Glia mediate homeostasis and repair. They contribute to immune surveillance and defense, cytokine and growth factor production and secretion, ion and neurotransmitter balance, neuroprotection, and, potentially, regeneration. Therefore, it is likely that glia orchestrate events throughout the development and progression of retinopathy. Understanding glial responses to products of diabetes-associated systemic dyshomeostasis may reveal novel insights into the pathophysiology of DR and guide the development of novel therapies for this potentially blinding condition. In this article, first, we review normal glial functions and their putative roles in the development of DR. We then describe glial transcriptome alterations in response to systemic circulating factors that are upregulated in patients with diabetes and diabetes-related comorbidities; namely glucose in hyperglycemia, angiotensin II in hypertension, and the free fatty acid palmitic acid in hyperlipidemia. Finally, we discuss potential benefits and challenges associated with studying glia as targets of DR therapeutic interventions. In vitro stimulation of glia with glucose, angiotensin II and palmitic acid suggests that: 1) astrocytes may be more responsive than other glia to these products of systemic dyshomeostasis; 2) the effects of hyperglycemia on glia are likely to be largely osmotic; 3) fatty acid accumulation may compound DR pathophysiology by promoting predominantly proinflammatory and proangiogenic transcriptional alterations of macro and microglia; and 4) cell-targeted therapies may offer safer and more effective avenues for DR treatment as they may circumvent the complication of pleiotropism in retinal cell responses. Although several molecules previously implicated in DR pathophysiology are validated in this review, some less explored molecules emerge as potential therapeutic targets. Whereas much is known regarding glial cell activation, future studies characterizing the role of glia in DR and how their activation is regulated and sustained (independently or as part of retinal cell networks) may help elucidate mechanisms of DR pathogenesis and identify novel drug targets for this blinding disease.

Fatty Acids: An Insight into the Pathogenesis of Neurodegenerative Diseases and Therapeutic Potential

One of the most common lipids in the human body is palmitic acid (PA), a saturated fatty acid with essential functions in brain cells. PA is used by cells as an energy source, besides being a precursor of signaling molecules and protein tilting across the membrane. Although PA plays physiological functions in the brain, its excessive accumulation leads to detrimental effects on brain cells, causing lipotoxicity. This mechanism involves the activation of toll-like receptors (TLR) and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathways, with the consequent release of pro-inflammatory cytokines, increased production of reactive oxygen species (ROS), endoplasmic reticulum (ER) stress, and autophagy impairment. Importantly, some of the cellular changes induced by PA lead to an augmented susceptibility to the development of Alzheimer's and Parkinson´s diseases. Considering the complexity of the response to PA and the intrinsic differences of the brain, in this review, we provide an overview of the molecular and cellular effects of PA on different brain cells and their possible relationships with neurodegenerative diseases (NDs). Furthermore, we propose the use of other fatty acids, such as oleic acid or linoleic acid, as potential therapeutic approaches against NDs, as these fatty acids can counteract PA's negative effects on cells.

Interactions between Endoplasmic Reticulum Stress and Autophagy: Implications for Apoptosis and Neuroplasticity-Related Proteins in Palmitic Acid-Treated Prefrontal Cells

Lipotoxicity of palmitic acid (PA) or high-fat diets has been reported to increase endoplasmic reticulum (ER) stress and autophagy in peripheral tissue as well as apoptotic cell death. It also can lead to an AD-like pathological pattern. However, it has been unknown that PA-induced ER stress and autophagy are involved in the regulation of neuroplastic abnormalities. Here, we investigated the roles of ER stress and autophagy in apoptosis and neuroplasticity-related protein expression in PA-treated prefrontal cells. Prefrontal cells dissected from newborn Sprague-Dawley rats were treated with PA compound with ER stress inhibitor 4-phenylbutyric acid (4-PBA) and autophagy inhibitor 3-methyladenine (3-MA) or PA alone. PA promoted ER stress and autophagy and also cause apoptosis as well as a decline in the expression of neuroplasticity-related proteins. Inhibition of ER stress decreased the expressions of neuroplasticity-related proteins and reduced autophagy activation and apoptosis in PA-treated prefrontal cells. Inhibition of autophagy exacerbated apoptosis and enhanced ER stress in PA-treated prefrontal cells. The present study illustrated that both ER stress and autophagy could be involved in apoptosis and decreased neuroplasticity-related proteins, and the interaction between ER stress and autophagy may play a critical role in apoptosis in PA-treated prefrontal cells. Our results provide new insights into the molecular mechanisms in vitro of lipotoxicity in obesity-related cognitive dysfunction.

Antifibrotic and Anti-Inflammatory Actions of α-Melanocytic Hormone: New Roles for an Old Player

The melanocortin system encompasses melanocortin peptides, five receptors, and two endogenous antagonists. Besides pigmentary effects generated by α-Melanocytic Hormone (α-MSH), new physiologic roles in sexual activity, exocrine secretion, energy homeostasis, as well as immunomodulatory actions, exerted by melanocortins, have been described recently. Among the most common and burdensome consequences of chronic inflammation is the development of fibrosis. Depending on the regenerative capacity of the affected tissue and the quality of the inflammatory response, the outcome is not always perfect, with the development of some fibrosis. Despite the heterogeneous etiology and clinical presentations, fibrosis in many pathological states follows the same path of activation or migration of fibroblasts, and the differentiation of fibroblasts to myofibroblasts, which produce collagen and α-SMA in fibrosing tissue. The melanocortin agonists might have favorable effects on the trajectories leading from tissue injury to inflammation, from inflammation to fibrosis, and from fibrosis to organ dysfunction. In this review we briefly summarized the data on structure, receptor signaling, and anti-inflammatory and anti-fibrotic properties of α-MSH and proposed that α-MSH analogues might be promising future therapeutic candidates for inflammatory and fibrotic diseases, regarding their favorable safety profile.

Maternal hypercaloric diet affects factors involved in lipid metabolism and the endogenous cannabinoid systems in the hypothalamus of adult offspring: sex-specific response of astrocytes to palmitic acid and anandamide

Aim: We aimed to investigate whether maternal malnutrition during gestation/lactation induces long-lasting changes on inflammation, lipid metabolism and endocannabinoid signaling in the adult offspring hypothalamus and the role of hypothalamic astrocytes in these changes.Methods: We analyzed the effects of a free-choice hypercaloric palatable diet (P) during (pre)gestation, lactation and/or post-weaning on inflammation, lipid metabolism and endogenous cannabinoid signaling in the adult offspring hypothalamus. We also evaluated the response of primary hypothalamic astrocytes to palmitic acid and anandamide.Results: Postnatal exposure to a P diet induced factors involved in hypothalamic inflammation (Tnfa and Il6) and gliosis (Gfap, vimentin and Iba1) in adult offspring, being more significant in females. In contrast, maternal P diet reduced factors involved in astrogliosis (vimentin), fatty acid oxidation (Cpt1a) and monounsaturated fatty acid synthesis (Scd1). These changes were accompanied by an increase in the expression of the genes for the cannabinoid receptor (Cnr1) and Nape-pld, an enzyme involved in endocannabinoid synthesis, in females and a decrease in the endocannabinoid degradation enzyme Faah in males. These changes suggest that the maternal P diet results in sex-specific alterations in hypothalamic endocannabinoid signaling and lipid metabolism. This hypothesis was tested in hypothalamic astrocyte cultures, where palmitic acid (PA) and the polyunsaturated fatty acid N-arachidonoylethanolamine (anandamide or AEA) were found to induce similar changes in the endocannabinoid system (ECS) and lipid metabolism.Conclusion: These results stress the importance of both maternal diet and sex in long term metabolic programming and suggest a possible role of hypothalamic astrocytes in this process.

Antioxidant and neuroprotective effects of mGlu3 receptor activation on astrocytes aged in vitro

Astrocytes play a key role by providing antioxidant support to nearby neurons under oxidative stress. We have previously demonstrated that in vitro astroglial subtype 3 metabotropic glutamate receptor (mGlu3R) is neuroprotective. However, its role during aging has been poorly explored. Our study aimed to determine whether LY379268, an mGlu3R agonist, exerts an antioxidant effect on aged cultured rat astrocytes. Aged cultured astrocytes obtained after 9-weeks (9w) in vitro were positive for β-galactosidase stain, showed decreased mGlu3R and glutathione (GSH) levels and superoxide dismutase (SOD) activity, while nuclear erythroid factor 2 (Nrf2) protein levels, reactive oxygen species (ROS) production and apoptosis were increased. Treatment of 9w astrocytes with LY379268 resulted in an increase in mGlu3R and Nrf2 protein levels and SOD activity, and decreased mitochondrial ROS levels and apoptosis. mGlu3R activation in aged astrocytes also prevented hippocampal neuronal death induced by Aβ_1-42 in co-culture assays. We conclude that activation of mGlu3R in aged astrocytes had an anti-oxidant effect and protected hippocampal neurons against Aβ-induced neurotoxicity. The present study suggests mGlu3R activation in aging astrocytes as a therapeutic strategy to slow down age-associated neurodegeneration.

NDP-MSH binding melanocortin-1 receptor ameliorates neuroinflammation and BBB disruption through CREB/Nr4a1/NF-κB pathway after intracerebral hemorrhage in mice

Background

Neuroinflammation and blood-brain barrier (BBB) disruption are two vital mechanisms of secondary brain injury following intracerebral hemorrhage (ICH). Recently, melanocortin-1 receptor (Mc1r) activation by Nle4-D-Phe7-α-MSH (NDP-MSH) was shown to play a neuroprotective role in an experimental autoimmune encephalomyelitis (EAE) mouse model. This study aimed to investigate whether NDP-MSH could alleviate neuroinflammation and BBB disruption after experimental ICH, as well as the potential mechanisms of its neuroprotective roles.

Methods

Two hundred and eighteen male C57BL/6 mice were subjected to autologous blood-injection ICH model. NDP-MSH, an agonist of Mc1r, was administered intraperitoneally injected at 1 h after ICH insult. To further explore the related protective mechanisms, Mc1r small interfering RNA (Mc1r siRNA) and nuclear receptor subfamily 4 group A member 1 (Nr4a1) siRNA were administered via intracerebroventricular (i.c.v) injection before ICH induction. Neurological test, BBB permeability, brain water content, immunofluorescence staining, and Western blot analysis were implemented.

Results

The Expression of Mc1r was significantly increased after ICH. Mc1r was mainly expressed in microglia, astrocytes, and endothelial cells following ICH. Treatment with NDP-MSH remarkably improved neurological function and reduced BBB disruption, brain water content, and the number of microglia in the peri-hematoma tissue after ICH. Meanwhile, the administration of NDP-MSH significantly reduced the expression of p-NF-κB p65, IL-1β, TNF-α, and MMP-9 and increased the expression of p-CREB, Nr4a1, ZO-1, occludin, and Lama5. Inversely, the knockdown of Mc1r or Nr4a1 abolished the neuroprotective effects of NDP-MSH.

Conclusions

Taken together, NDP-MSH binding Mc1r attenuated neuroinflammation and BBB disruption and improved neurological deficits, at least in part through CREB/Nr4a1/NF-κB pathway after ICH.