Effects of ac-sdkp (n-acetyl-seryl-aspartyl-lysyl-proline) administration on the NLRP3 inflammasome complex and blood-spinal cord barrier in experimental spinal cord injury

Objective: This study aims to investigate the effects of Ac-SDKP (N-acetyl-seryl-aspartyl-lysyl-proline) treatment on the NLRP3 inflammasome complex and blood-spinal cord barrier (BSCB) permeability in an experimental spinal cord injury model. The study specifically targets the potential regulatory effects of Ac-SDKP on the inflammatory response and BSCB integrity. Introduction: Spinal cord injuries weaken the protective barriers in the central nervous system, triggering inflammatory processes and increasing the permeability of the blood-spinal cord barrier (BSCB). This increase in permeability facilitates the migration of inflammatory cells into the damaged tissue but also leads to barrier disruption and a reduction in neuroprotective efficacy. The NLRP3 inflammasome stands out as an inflammatory complex activated during spinal cord injury. Activation of the NLRP3 inflammasome contributes to the severity of the injury by intensifying the inflammatory process. The immunomodulatory peptide AC-SDKP (N-acetyl-seryl-aspartyl-lysyl-proline) is thought to have the potential to regulate inflammation and preserve BSCB integrity. The hypothesis underpinning this study is that AC-SDKP may suppress NLRP3 inflammasome activity, thereby controlling the inflammatory response and aiding in the preservation of BSCB in spinal cord injuries. This research aims to examine in detail the effects of AC-SDKP on the NLRP3 inflammasome and BSCB in a spinal cord injury model. Materials and Methods: This study was conducted with the approval of the Çukurova University Local Ethics Committee for Animal Experiments. A total of 78 male Wistar rats, aged 3–6 months and weighing 300–350 grams, were used in the experiments. The rats were divided into three main groups: a control group with no intervention and only sampling (n=10), a sham group that underwent only laminectomy (n=20), and an experimental group with induced spinal cord injury (SCI) (n=48). The experimental group was further divided into two subgroups following SCI: an experimental control group that received only saline (n=24) and a treatment group that received AC-SDKP (n=24). Tissue samples were analyzed using light and electron microscopic methods along with biochemical and molecular biological techniques. Levels of IL-1β, IL-18, NLRP3, caspase-1, NeuN, MMP-9, NF-κB, occludin, claudin-5, and VE-cadherin were investigated in all groups. IL-1β and IL-18 levels were determined by biochemical analysis (ELISA). NeuN, MMP-9, occludin, claudin-5, and VE-cadherin levels were identified by immunohistochemical methods. NF-κB, NLRP3, caspase-1, IL-1β, and IL-18 expression levels were determined by qRT-PCR. Findings: In the treatment group, NF-ΚB and NLRP3 inflammasome activity were suppressed. Levels of inflammatory cytokines IL-1β and IL-18 were observed to decrease, indicating AC-SDKP's effect in controlling inflammation. Additionally, post-treatment expression levels of proteins that maintain barrier integrity, such as occludin, claudin, and VE-cadherin, were found to increase. However, contrary to expectations, an increase in BSCB permeability was noted, which is interpreted as possibly due to the activation of inflammatory cells like microglia and macrophages during the treatment. Microscopic examination also revealed that AC-SDKP reduced the number of inflammatory cells and alleviated edema. Conclusion: The findings of this study indicate that AC-SDKP exhibits inflammation-regulating and tissue-healing properties in the context of spinal cord injury. AC-SDKP treatment suppressed NF-κB and NLRP3 inflammasome activity, reducing cytokine levels such as IL-1β and IL-18 by mitigating the inflammatory response. This suppression of NLRP3 inflammasome activity contributed to controlling the inflammatory process and reduced the accumulation of inflammatory cells in damaged tissue. Additionally, AC-SDKP treatment was observed to increase the expression of proteins such as occludin, claudin, and VE-cadherin, which support BSCB integrity. However, the observed increase in BSCB permeability is considered a factor that may limit AC-SDKP's neuroprotective efficacy, potentially due to the activation of inflammatory cells.While AC-SDKP shows promise as an agent for inflammation control and recovery in spinal cord injuries, further research is required to better understand its effects on NLRP3 inflammasome activity and BSCB permeability. This includes studies that detail the appropriate dosage, treatment duration, and long-term impacts on the inflammatory response. AC-SDKP offers potential in terms of inflammation control and tissue healing, but additional research is necessary to evaluate its effects on BSCB permeability and its safety profile.