Elsevier

Brain Research

Volume 1750, 1 January 2021, 147168
Brain Research

Research report
E2-BSA and G1 exert neuroprotective effects and improve behavioral abnormalities following traumatic brain injury: The role of classic and non-classic estrogen receptors

https://doi.org/10.1016/j.brainres.2020.147168Get rights and content

Highlights

  • The post-TBI administration of E2, E2-BSA, and G1 reduced brain edema and BBB disruption.

  • All forms of E2 and G1 reduced ICP and also increased CPP.

  • All forms of E2 and G1 improved memory and sensori-motor dysfunctions and also reduced anxiety.

  • Pretreatment with estrogen receptors antagonist, ICI 182780 and G15, reversed the effects of E2, E2-BSA.

  • Co-pretreatment of ICI and G15 was more effective than pretreatment with G15 alone.

Abstract

The role of classical and non-classical estrogen receptors (ERs) in mediating the neuroprotective effects of this hormone on brain edema and long-term behavioral disorders was evaluated after traumatic brain injury (TBI). Ovariectomized rats were divided as follows: E2 (17 β-estradiol), E2-BSA (E2 conjugated to bovine serum albumin), G1 [G-protein-coupled estrogen receptor agonist (GPER)] or their vehicle was injected following TBI, whereas ICI (classical estrogen receptor antagonist), G15 (GPER antagonist), ICI + G15, and their vehicle were injected before the induction of TBI and the injection of E2 and E2-BSA. Brain water (BWC) and Evans blue (EB) contents were measured 24 h and 5 h after TBI, respectively. Intracranial pressure (ICP) and cerebral perfusion pressure (CPP) were measured before and at different times after TBI. Locomotor activity, anxiety-like behavior, and spatial memory were assessed on days 3, 7, 14, and 21 after injury. E2, E2-BSA, and G1 prevented the increase of BWC and EB content after TBI, and these effects were inhibited by ICI and G15. ICI and G15 also inhibited the beneficial effects of E2, E2-BSA on ICP, as well as CPP, after trauma. E2, E2-BSA, and G1 prevented the cognitive deficiency and behavioral abnormalities induced by TBI. Similar to the above parameters, ICI and G15 also reversed this E2 and E2-BSA effects on days 3, 7, 14, and 21. Our findings indicated that the beneficial effects of E2-BSA and E2 were inhibited by both ICI and G15, suggesting that GPER and classic ERs were involved in mediating the long-term effects of E2.

Introduction

Permanent disability or death following traumatic brain injury (TBI) has become a public health concern over recent decades. TBI leads to pathophysiological changes that subsequently initiate diffuse secondary insults in the injured tissues (O’connor et al., 2011). Oxidative stress, increased inflammatory response, blood–brain barrier (BBB) damage, edema formation, increased intracranial pressure (ICP), and decreased cerebral perfusion pressure (CPP) are symptoms of secondary injury, which consequently reduce cerebral blood flow and induce brain ischemia (Unterberg et al., 2004, Gabrielian et al., 2011).

It is well known that the pathological changes caused by mechanical forces to the brain can lead to sensorimotor deficits (Soltani et al., 2015). In addition to locomotor dysfunctions, TBI survivors suffer from cognitive impairments and mood disorders (Hyder et al., 2007). Cognitive dysfunctions, including the impaired speed of information processing, poor memory, executive problems, and thought and reasoning difficulties are the most frequent detrimental neurobiological consequences of TBI (Fleminger, 2008). It has been shown that these disruptions in memory are associated with increased anxiety levels (Baykara et al., 2013).

It has been previously demonstrated that 17β-estradiol (E2) can reduce brain edema, ICP and BBB damage (Maghool et al., 2013), apoptosis (Soustiel et al., 2005), pro-inflammatory cytokines' levels (Sarkaki et al., 2011), and cortical contusion volumes (Bramlett and Dietrich, 2001). In addition, E2 can increase CPP and neurological scores (Hajmohammadi et al., 2019). These studies have also demonstrated that the neuroprotective effects of E2 are carried out via E2 interaction with classical receptors, including intracellular estrogen receptor-α (ERα) and estrogen receptor-β (ERβ), which trigger the genomic pathway (Dehghan et al., 2015). Blocking the genomic pathway using the estrogen classical receptors antagonist (ICI 182780) suggests that classical estrogen receptors are involved in the neuroprotective effects of E2 following brain injury (Sawada et al., 2000).

In addition to genomic responses, E2 has rapid non-genomic actions via the interaction of E2 with novel G-protein-coupled estrogen receptor (GPER, formerly known as GPR30) and membrane-associated ERα and ERβ (Alexander et al., 2017). Recent studies have demonstrated that GPER activation enhances the protection against brain injuries (Lu et al., 2016), while GPER selective antagonist reduces the neuroprotective effects of E2 (Gingerich et al., 2010, Roque et al., 2019). Elimination of E2 membrane permeability by using E2-BSA (E2 conjugated to bovine serum albumin) illustrated that non-genomic signaling pathways are activated by membrane receptors (Stevis et al., 1999).

It has been reported that E2 can inhibit the detrimental outcomes of TBI on cognition and anxiety levels in mice (Lu et al., 2018). Additionally, several studies have provided evidence that classic ERα and ERβ improve learning and memory and reduce anxiety-like behaviors (Raval et al., 2013, Handa et al., 2012). Furthermore, non-genomic signaling of E2 can enhance memory performance and improve mood disorders such as anxiety (Hadjimarkou and Vasudevan, 2018).

Previously, we have shown that E2 plays a neuroprotective role, in the short term after TBI (Dehghan et al., 2015). Therefore, the present study evaluated the effects of E2 on cognitive, locomotor activity, and anxiety-like behavior in the long-term. Besides, we used E2-BSA, G1 (GPER selective agonist), ICI, and G15 (GPER selective antagonist) to determine the role of classical and non-classic E2 receptors in mediating the effects of this hormone following TBI.

Section snippets

The effect of E2, E2-BSA, G1, and estrogen receptors antagonists on brain edema

Changes in brain water content (BWC) showed a significant difference between the groups (F15, 80 = 23.42, P < 0.001).Fig. 2 As shown in Fig. 3A, BWC was increased in the TBI, oil, DMSO, and PBS groups compared to the sham group (P < 0.001). BWC was decreased in the E2 (P < 0.001), E2-BSA (P < 0.001), and G1 (P < 0.05) groups compared to their vehicle groups. Moreover, BWC in the group receiving E2 was lower than in the G1 (P < 0.05) (Fig. 3B).

Fig. 3C illustrates the effects of E2, E2-BSA

Discussion

In the present study, the effects of different forms of E2 on post-traumatic behaviors such as sensorimotor, cognitive, and mood disorders, as well as the role of classic and non-classic estrogen receptors on the E2 neuroprotective effect were examined in OVX rats. The main findings are as follows: 1) The post-TBI administration of E2, E2-BSA, and G1 reduced brain edema and BBB disruption; 2) G1 and all forms of E2 reduced ICP and increased CPP after TBI; 3) they improved memory and

Animals

Adult female Wistar rats were caged in a photoperiod-controlled room (12-h light/dark cycle) with a temperature of 22 ± 2 °C. Food and water were available ad libitum. All the experimental procedures were carried out under the approval of the Animal Research Ethics Committee of Kerman University of Medical Sciences (Ethical code: IR.KMU.REC.1396.1540).

Bilateral ovariectomy

After two-week acclimation, bilateral ovariectomy was performed under general anesthesia with an intraperitoneal injection of ketamine (80 mg/kg)

CRediT authorship contribution statement

Ladan Amirkhosravi: Formal analysis, Investigation, Software, Writing - original draft. Mohammad Khaksari: Conceptualization, Data curation, Project administration, Writing - review & editing, Supervision. Zahra Soltani: Methodology, Formal analysis. Saeed Esmaeili-Mahani: Methodology, Data curation, Visualization. Gholamreza Asadi Karam: Methodology, Project administration. Mojtaba Hoseini: Investigation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

The present study was financially supported by the Physiology Research Center of Kerman University of Medical Sciences (Kerman, Iran).

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