Elsevier

Brain Research Bulletin

Volume 143, October 2018, Pages 217-224
Brain Research Bulletin

Research report
Astaxanthin attenuates neuroinflammation contributed to the neuropathic pain and motor dysfunction following compression spinal cord injury

https://doi.org/10.1016/j.brainresbull.2018.09.011Get rights and content

Highlights

  • Astaxanthin (AST) improved sensory-motor performance after compression SCI.

  • AST inhibited glutamate-initiated signaling pathway following compression SCI.

  • AST decreased post- SCI tissue damage and preserved neurons after SCI.

  • AST treatment led to down-regulation of NR2B, p-p38MAPK and TNF-α in the spine.

Abstract

Spinal cord injury (SCI) is a debilitating condition in which inflammatory responses in the secondary phase of injury leads to long lasting sensory-motor dysfunction. The medicinal therapy of SCI complications is still a clinical challenge. Understanding the molecular pathways underlying the progress of damage will help to find new therapeutic candidates. Astaxanthin (AST) is a ketocarotenoid which has shown anti-inflammatory effects in models of traumatic brain injury. In the present study, we examined its potential in the elimination of SCI damage through glutamatergic-phospo p38 mitogen-activated protein kinase (p-p38MAPK) signaling pathway. Inflammatory response, histopathological changes and sensory-motor function were also investigated in a severe compression model of SCI in male rats.

The results of acetone drop and inclined plane tests indicated the promising role of AST in improving sensory and motor function of SCI rats. AST decreased the expression of n-methyl-d-aspartate receptor subunit 2B (NR2B) and p-p38MAPK as inflammatory signaling mediators as well as tumor necrosis factor-α (TNF-α) as an inflammatory cytokine, following compression SCI. The histopathological study culminated in preserved white mater and motor neurons beyond the injury level in rostral and caudal parts. The results show the potential of AST to inhibit glutamate-initiated signaling pathway and inflammatory reactions in the secondary phase of SCI, and suggest it as a promising candidate to enhance functional recovery after SCI.

Introduction

Spinal cord injury (SCI) is a debilitating disorder whose prevalence is progressively increasing and leads to sensory-motor and autonomic dysfunction as well as nerve tissue degeneration (Gruener et al., 2018; Kong and Gao, 2017; Luo et al., 2015; Sekhon and Fehlings, 2001). There are two phases after SCI. The first phase is related to the direct death of cells resulting from traumatic mechanical injury. It affects the local cells and disrupts axon tracts connecting the brain and spinal cord, causing neuronal damage to the spinal grey matter to a larger extent when compared to the white matter. Subsequent to the primary injury, a cascade of molecular and cellular processes including inflammation can exacerbate the injury resulted by the primary damage, which is called secondary phase (Beattie, 2004; David et al., 2013; Tator and Fehlings, 1991). The secondary phase starts with the inflammatory responses and is characterized by increased blood-brain barrier (BBB) permeability, glial and neuronal cell apoptosis, alongside complex neuroinflammatory responses (Donnelly and Popovich, 2008; Profyris et al., 2004).

The secondary phase lasts for months and years and causes sensory-motor dysfunction. Despite the progress in the preclinical and clinical studies, there is no effective treatment for improving sensory-motor dysfunction following SCI; therefore, developing new therapies via targeting the main mechanisms involved in the SCI is of special clinical importance. However, the mechanisms of secondary injury have remained poorly defined, and unlike the acute phase, it may be reversible (Koda et al., 2004; Lerch et al., 2014; Schwab and Bartholdi, 1996). Among the underlying mechanisms, inflammation is the most important (Faden et al., 2016). Subjects with SCI have a higher plasma level of cytokines (e.g. tumor necrosis factor-α (TNF-α)) and other inflammatory agents (Bank et al., 2015). So, trying to find a new strong anti-inflammatory agent can be a key therapeutic goal (Kidd, 2011; Shen et al., 2009).

Astaxanthin (AST) is a lipid-soluble keto-carotenoid (Baralic et al., 2015; Nakao et al., 2010), which is found in different microorganisms (Ambati et al., 2014), marine animals, seafood (Higuera-Ciapara et al., 2006), and phytoplanktons (Balietti et al., 2016), and acts as a strong anti-oxidant agent (Pan et al., 2017; Xue et al., 2017). It captures radicals in the membrane and scavenges them outside and inside the membrane because of the structure of its polyene chain and terminal rings, respectively (Augusti et al., 2012). This polar-nonpolar-polar structure of AST allows for making a precise fit into the same structural part of the cell membrane, permitting AST cross easily through the BBB and affecting different signaling pathways (Higuera-Ciapara et al., 2006; Kidd, 2011). The reactive oxygen species are a primary candidate stimulus for the induction of inflammation (Elmarakby and Sullivan, 2012). Therefore, owing to its antioxidant effects, AST is an anti-inflammatory agent and possesses promising effects in different acute and chronic neurodegenerative conditions (Speranza et al., 2012; Suzuki et al., 2006).

In mechanistic point of view, there are several in-vivo and in-vitro reports clarifying the anti-inflammatory effects of AST. In an in-vitro study, AST is shown to reduce the gene expression of inflammatory mediators like interleukin-6 (IL-6), interleukin-1β (IL-1β), and TNF-α in response to H2O2 induced cytotoxicity in U937 cell line (Suzuki et al., 2006). AST also inhibits cyclooxygenase-1 enzyme (COX-1) and nitric oxide (NO), demonstrating its anti-inflammatory actions (Choi et al., 2008; Nakano et al., 2008; Ohgami et al., 2003). AST has also proven to block the nuclear factor kappa B (NF-κB)-dependent signaling pathway in endotoxin-induced uveitis in rats (Speranza et al., 2012). It has been also shown that AST increases the anti-oxidant enzymes catalase (CAT), superoxide dismutase (SOD) (Heidari Khoei et al., 2018), along with peroxidase and thiobarbituric acid reactive substances in rat plasma and liver (Ranga Rao et al., 2010; Wu et al., 2015). In other studies, it is shown that AST modulates p38/mitogen-activated protein kinase (p38MAPK), activates phosphoinositide 3-kinase (PI3K)/AKT survival pathway, enhances Bad phosphorylation, and decreases the activation of cytochrome c and caspase 3 and 9 (Dong et al., 2013; Guo et al., 2015; Wu et al., 2015; Zhang et al., 2014). Elsewhere, it is also shown that AST affects the n-methyl-d-aspartate (NMDA) receptor subunit 1 (NR1) signaling pathway to prevent NMDA-triggered retinal damage, reduces the apoptotic death of retinal ganglion cells, decreases lipid peroxidation and oxidative DNA damage, and antagonizes methyl phenylpyridinium-induced oxidative stress (Dong et al., 2013; Nakajima et al., 2008; Ye et al., 2013). In our previous study we also reported the anti-apoptotic and protective effects of AST in a contusion SCI model of rats (Masoudi et al., 2017).

In the present study, we aimed to investigate the potential effects of AST to modulate sensory-motor and histopathological dysfunctions, through modifying the NR2B and phospho-p38MAPK (p-p38MAPK) signaling elements as well as an inflammatory cytokine (TNF-α), in a severe compression model of SCI in rats.

Section snippets

Experimental animals

Totally, 75 adult male Wistar rats (230–270 g, breeding colony of Neuroscience Research Center, Shahid Beheshti University of Medical Sciences) were kept in a room under standard laboratory conditions (temperature 24 ± 2 °C, 12-h light/dark cycle, with fresh food and water ad libitum, 10 days prior to the study). All the experiments were conducted in line with the guidelines and policies of the National Institutes of Health Guidelines for the Care and Use of Laboratory Animal and approved by

AST treatment improves sensory-motor dysfunction following SCI

The inclined plane test was used to assess the locomotor recovery after SCI. As demonstrated in Fig. 1, the rats in the laminectomy sham group continued their normal angle stay on inclined plane apparatus, suggesting that the surgery per se did not cause any functional impairments. SCI caused a significant reduction in the angle stays. In other words, the spinal cord injured rats indicated a decrease in the mean angle of stay on the inclined-plane apparatus as compared to the sham.

Discussion

Our results suggest that AST treatment produces a remarkable effect against post-SCI sensory-motor dysfunction. The downregulation of NR2B, p-p38MAPK, and TNF-α, as cytotoxic and inflammatory signaling elements, can be introduced as the underlying mechanism through which AST limits SCI-induced demyelination and tissue damage, pain-like behavior and motor dysfunction.

Complex pathophysiological mechanisms (Kwon et al., 2011a), high morbidity, and serious complications of SCI have raised the needs

Conflicts of interest

The authors state that there are no conflicts of interest.

Acknowledgments

The current research was performed as part of a Ph.D. thesis project of Sajad Fakhri and was supported by the Neuroscience Research Center (Grant No. S-N-56-1397) of Shahid Beheshti University of Medical Sciences, IRAN.

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