光生物调节加速脑组织间液引流及其机制

Epidural photobiomodulation accelerates the drainage of brain interstitial fluid and its mechanism

目的:探讨光生物调节(photobiomodulation,PBM)对脑组织间液(interstitial fluid,ISF)引流的影响,为PBM治疗阿尔兹海默病(Alzheimer’s disease)提供新的解释。方法:24只SD雄性大鼠随机分为PBM组(n=12)、假PBM组(n=6)及空白对照组(n=6),其中PBM组根据磁示踪分子探针注射部位的不同又分为PBM同侧示踪组(n=6)和PBM对侧示踪组(n=6)。PBM组和假PBM组大鼠在脑尾状核区ISF引流到达的额叶皮层区对应的颅骨上微创暴露硬膜;PBM组使用630 nm光纤(5~6 mW/cm 2)按照每次光照5 min,暂停2 min的方式,总共照射5次;假PBM组于相同位置使用光纤但不打开电源,保持相同时间;空白对照组不进行任何操作。PBM结束后,将示踪分子探针注射到每组大鼠的尾状核区,之后利用磁示踪技术根据探针分子的扩散和分布,观察大鼠尾状核区ISF引流的变化规律,并使用细胞外间隙(extracellular space,ECS)扩散参数图像(diffusion rate in ECS-mapping,D_(ECS)-mapping)技术分析脑ECS结构的变化,最后得到反映脑ECS结构和ISF引流情况的参数:容积占比(α)、迂曲度(λ)、半衰期(T_(1/2))和扩散参数(D_(ECS))。比较各组间参数差异从而分析PBM对脑ECS及ISF的影响。结果:参数T_(1/2)、D_(ECS)和λ在PBM同侧示踪组、PBM对侧示踪组和假PBM组间差异有统计学意义(F=79.286,P<0.001;F=13.458,P<0.001;F=10.948,P=0.001),而参数α在三组间差异无统计学意义(F=1.217,P=0.324)。与假PBM组和PBM对侧示踪组相比,PBM同侧示踪组的T_(1/2)显著减小[(45.45±6.76)min vs.(76.01±3.44)min,P<0.001;(45.45±6.76)min vs.(78.07±4.27)min,P<0.001],说明脑ISF引流速度明显加快;D_(ECS)显著增大[(4.51±0.77)×10^(-4)mm^(2)/s vs.(3.15±0.44)×10^(-4)mm^(2)/s,P<0.001;(4.51±0.77)×10^(-4)mm^(2)/s vs.(3.01±0.38)×10^(-4)mm^(2)/s,P<0.001],说明脑ECS内分子扩散速率明显增快;λ显著减小(1.51±0.21 vs.1.85±0.12,P=0.001;1.51±0.21 vs.1.89±0.11,P=0.001),说明脑ECS结构的迂曲程度下降。结论:PBM可以调控脑ISF引流,这可能是PBM治疗阿尔兹海默病的潜在作用机制之一,也为经脑ECS途径提升脑功能的主动调控策略提供了全新方案。

Objective:To evaluate the effect of photobiomodulation(PBM)on the drainage of brain interstitial fluid(ISF)and to investigate the possible mechanism of the positive effect of PBM on Alzheimer’s disease(AD).Methods:Twenty-four SD male rats were randomly divided into PBM group(n=12),sham PBM group(n=6),and negative control group(n=6).According to the injection site of tracer,the PBM group was further divided into PBM-ipsilateral traced group(n=6)and PBM-contralateral traced group(n=6).Rats in the PBM group and the sham PBM group were exposed to the dura minimally invasively on the skull corresponding to the frontal cortical area reached by ISF drainage from caudate nucleus region.The PBM group was irradiated by using 630 nm red light(5-6 mW/cm 2),following an irradiation of 5 min with a 2 min pause,and a total of 5 times;the sham PBM group was kept in the same position for the same time using the light without power.The negative control group was kept without any measure.After PBM,tracer was injected into caudate nucleus of each group.The changes of ISF drainage in caudate nucleus were observed according to the diffusion and distribution of tracer molecule by tracer-based magnetic resonance imaging,and the structural changes of brain extracellular space(ECS)were analyzed by diffusion rate in ECS-mapping(D_(ECS)-mapping)technique.Finally,parameters reflecting the structure of brain ECS and the drainage of ISF were obtained:volume fraction(α),tortuo-sity(λ),half-life(T_(1/2)),and D_(ECS).The differences of parameters among different groups were compared to analyze the effect of PBM on brain ECS and ISF.One-Way ANOVA post hoc tests and independent sample t test were used for statistical analysis.Results:The parameters including T_(1/2),D_(ECS),andλwere significantly different among the PBM-ipsilateral traced group,the PBM-contralateral traced group,and the sham PBM group(F=79.286,P<0.001;F=13.458,P<0.001;F=10.948,P=0.001),while there was no difference in the parameterαof brain ECS among the three groups(F=1.217,P=0.324).Compared with the sham PBM group and the PBM-contralateral traced group,the PBM-ipsilateral traced group had a significant decrease in the parameter T_(1/2)[(45.45±6.76)min vs.(76.01±3.44)min,P<0.001;(45.45±6.76)min vs.(78.07±4.27)min,P<0.001],representing a significant acceleration of ISF drainage;the PBM-ipsilateral traced group had a significant increase in the parameter D_(ECS)[(4.51±0.77)×10^(-4)mm^(2)/s vs.(3.15±0.44)×10^(-4)mm^(2)/s,P<0.001;(4.51±0.77)×10^(-4)mm^(2)/s vs.(3.01±0.38)×10^(-4)mm^(2)/s,P<0.001],representing a significantly increased molecular diffusion rate of in the brain ECS;the PBM-ipsilateral traced group had a significant decrease in the parameterλ(1.51±0.21 vs.1.85±0.12,P=0.001;1.51±0.21 vs.1.89±0.11,P=0.001),representing a significant decrease in the degree of tortuosity in the brain ECS.Conclusion:PBM can regulate the brain ISF drainage actively,which may be one of the potential mechanisms of the effect of PBM therapy on AD.This study provides a new method for enhancing the brain function via ECS pathway.