RESUMEN
Objective:To explore the possible mechanisms of remote ischemic preconditioning (RIPC) combined with melatonin (MT) against cerebral ischemia-reperfusion injury and to evaluate the value of multimodal MRI.Methods:From December 2021 to December 2022, fifty SPF-grade male SD rats were selected and divided into sham surgery group ( n=10), middle cerebral artery occlusion model group ( n=10), melatonin (MT) group ( n=10), remote ischemic preconditioning (RIPC) group ( n=10) and MT+RIPC group ( n=10). Neurological function scoring and multimodal MRI examinations, including T 2 fluid-attenuated inversion recovery (FLAIR) imaging, diffusion-weighted imaging (DWI), and arterial spin labeling (ASL) imaging, were performed on rats after surgery. After the scans, the rats were euthanized. The brain tissues of 3 rats in each group were randomly selected for HE staining and immunohistochemical staining to observe the pathological morphology of brain tissues and to validate the expression of nuclear factor-E2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1). The remaining 6 rats were used for enzyme-linked immunosorbent assay to detect levels of interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) in brain infarction tissues. ANOVA test or Kruskal-Wallis H test was performed to compare the differences between groups. Results:There were statistically significant differences in neurological function scores and brain infarct volumes among the five groups ( P<0.001). Compared with the sham surgery group, the rats′ neurological function scores and brain infarct volumes were increased in the model group, RIPC group, MT group, and MT+RIPC group ( P<0.05); While compared with the model group, the rats′ neurological function scores and brain infarct volumes were decreased in the RIPC group, MT group, and MT+RIPC group ( P<0.05). MRI showed that abnormal signals were observed on the lesion hemisphere on the right side in rats of the four groups except for the sham surgery group. The lesions showed high signal on T 2 FLAIR and DWI, low signal on apparent diffusion coefficient map, and low perfusion on cerebral blood flow map. Pathological examination showed neuronal nuclear shrinkage in the necrotic area of the brain tissue in the model group, with surrounding neurons exhibiting edema and degeneration. In the RIPC and MT groups, edema and degeneration of neural cells around the infarction area were reduced, while the MT+RIPC group showed primarily neuronal edema with overall structural preservation. The range of Nrf2 and HO-1 protein positivity was significantly increased in the MT+RIPC group compared with the model group. The overall differences in IL-1β, TNF-α and IL-6 levels of 5 groups were statistically significant ( P<0.05), in which IL-1β, TNF-α and IL-6 levels in the model group, RIPC group, MT group, and MT+RIPC group increased compared with the sham-operated group ( P<0.05), and IL-1β, TNF-α, and IL-6 levels decreased in the RIPC group, MT group, and MT+RIPC group compared with the model group ( P<0.05). Conclusion:RIPC+MT exerts antioxidant effects through Nrf2/HO-1 pathway and also exhibits anti-inflammatory properties by reducing levels of IL-1β, IL-6, and TNF-α, thereby alleviating brain edema and neuronal damage, reducing infarct volume and improving neurological deficits in rats with cerebral artery occlusion. The multimodal MRI evaluation demonstrates the value of RIPC+MT in protecting against cerebral ischemia-reperfusion injury.