EpilepsyHyaluronic acid inhibits the glial scar formation after brain damage with tissue loss in rats
Introduction
Traumatic brain injury is the most common acquired injury in both children and adults [7]. Brain tissue damage and defect sometimes occur after TBI or cerebral surgery. Posttraumatic epilepsy is a clinical syndrome in which a person suffers from repeated late posttraumatic seizures resulting from TBI or brain tissue damage by mechanical energy. The incidence of posttraumatic seizures has been reported to be around 4% to 53% [4], and the epilepsy may develop as a result of trauma to the brain with scarring due to factors such as bleeding or changes in the structure of brain. In multiple epileptogenesis of PTE, glial scarring is probably one of the most important factors related to the gliosis and inflammatory reaction of central nervous system (CNS)–repairing processes. However, the adult CNS has limited capacity for regeneration, and the poor neural regrowth is possibly caused by glial scarring around the margin of the brain damage, which inhibits the regeneration of axons across the damaged area.
The CNS damages after trauma are well known as primary mechanical damage and the secondary damage. The primary damage results from the impact force and energy at the time of accident, and the treatment goal is to prevent patients from the secondary damage. The long-term preservation of neuronal function is believed to be correlated directly with the severity of the secondary damage, and the severity of the secondary damage is determined by sequential processes inducing apoptotic neuronal cell death, and stimulating astrocyte and microglial proliferation. Glial scarring after brain tissue damage prevents axonal regeneration and extension, and generates abnormal neuronal electric activity. Therefore, reducing glial scar formation may improve the outcome after brain tissue injury. The purpose of this study was to investigate the effect of topical application of HA [8] on reducing glial scar formation after the mechanical brain injury with tissue loss in rats.
Hyaluronic acid is naturally occurring linear polysaccharide with repeating disaccharide units composed of glucuronic acid and N-acetylglucosamine. Discovered by Meyer and Palmer [8] in 1934, HA widely exists in the human body tissues, notably in synovial fluid and the vitreous body of the eye, and in loose connective tissues, such as rooster comb, umbilical cord, dermis [5], and the ground substance of the brain [2]. Hyaluronic acid is an agent known to reduce the extent of scar formation by inhibiting lymphocyte migration, proliferation and chemotaxis, granulocyte phagocytosis and degranulation, and macrophage motility. HA has been used for a variety of clinical application, such as ocular surgery, wound healing, and plastic surgery. Further application for the CNS seems to be possible. Hyaluronic acid has been shown to play a vital role in cell-matrix interactions in proliferating and migrating cells during a number of biological processes that involve the deposition and remodeling of an extracellular fibrin matrix [1], [10]. We injected the HA or normal saline into the injured cortex of SD rats and compared the glial scar formation among the HA groups and the NS groups at different time points after treatment.
Section snippets
Experimental design and surgical protocol
Forty-eight male Sprague-Dawley rats (∼70 days old) with weight of approximately 225 to 250 g were purchased from the National Laboratory Animal Center, Taipei, Taiwan. All animals were housed in a room with 12-hour light/dark cycle, and the temperature and humidity of the animal room were maintained at 19°C to 21°C and 50% to 60%. All the experimental procedures conformed to the Guide for the Care and Use of Laboratory Animals published by National Institutes of Health and were approved by the
Results
We performed the cortical defect with brain tissue block measuring 4 × 2 × 2 mm removed in 48 adult rats and coated the defect cutting surface with HA or NS for comparison. We measured the thickness of marginal glial scar under digital microscope for all animals from each group, including the 4-, 8-, and 12-week groups (Fig. 2). The results were shown in Fig. 3. Among the HA groups, the glial scar thickness was approximately 10 μm. There was no significant difference among these 3 HA groups. On
Discussion
Hyaluronic acid plays a role in promoting cell motility and proliferation by integrating the receptors on the cell surface [13], and matrix HA is shown associated with the perineuronal net surrounding neuronal cell bodies and proximal dendrites in the central nervous system through globular hyaluronian-binding domains [3], [11]. The proliferation may in part explain some of the spontaneous recovery that occurs in all of CNS insults, which include spinal cord injury, excitotoxic injury, ischemic
Acknowledgments
This research was supported by Taiwan National Science Council Grant NSC 96-2320-B-038-022 (LYY), Grant NSC 98-2314-B-038-009-MY2 (WTC), TMU Grant 94 TMU-WFH-220 (LYY), Department of Health Grant DOH-TD-B--111-002 and Center of Excellence for Clinical Trial and Research in Neurology and Neurosurgery.
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