Effect of convection enhanced delivery on the microstructure of brain extracellular space in aged rats / 北京大学学报(医学版)

OBJECTIVE@#To compare the changes of extracellular space (ECS) structure and local drug distribution in adult brain and aged brain at different drug delivery rates in minimally invasive treatment of encephalopathy by convection enhanced delivery (CED) via ECS pathway.@*METHODS@#Thirty-six SD male rats were divided into adult rats group (2-8 months, n=18) and aged rats group (18-24 months, n=18) according to the age of the month. According to the drug rates (0.1 μL/min, 0.2 μL/min, and 0.3 μL/min), they were randomly divided into 3 subgroups, 6 in each subgroup. Gadolinium-diethylene triamine pentaacetic acid (Gd-DTPA) with a concentration of 10 mmol/L were introduced into the caudate nucleus of each group of rats by stereotactic injection. Tracer-based magnetic resonance imaging (MRI) was used to dynamically monitor the diffusion and distribution images of the Gd-DTPA in the brain interstitial system (ISS). Using the self-developed MRI image measurement and analysis system software to process and analyze the obtained images, the diffusion coefficient, clearance rate, volume fraction, and half-life of each group of rats in the caudate nucleus ECS could be acquired. The effects and differences of drug clearance and ECS structural function in the brain of aged rats and adult rats were compared and analyzed at different drug delivery rates. Magnetic tracer DECS-mapping technique was used to observe the distribution and drainage of tracer in caudate nucleus.@*RESULTS@#At the injection rate of 0.1 μL/min, the volume fraction in the aged rats was increased compared with that in the adult rats (18.20%±0.04% vs. 17.20%±0.03%, t=3.752, P=0.004), and the degree of tortuosity was decreased (1.63±0.04 vs. 1.78±0.09, t=-3.680, P=0.004), the drug clearance rate was decreased [(1.94±0.68) mm2/s vs. (3.25±0.43) mm2/s, t=-3.971, P=0.003], and the molecular diffusion in ECS was increased [(3.99±0.21)×10-4 mm2/s vs. (3.36±0.37)×10-4 mm2/s, t=3.663, P=0.004]. When the rate of injection increased to 0.2 μL/min, the drug clearance in ECS of the aged rats was slowed down [(2.53±0.45) mmol/L vs. (3.37±0.72) mmol/L, t=-1.828, P=0.021]. However, there were no significant differences in volume fraction, molecular diffusion in ECS and macroscopic drug metabolism parameters. When the rate of injection increased to 0.3 μL/min, the volume fraction in the aged rats was decreased (17.20%±0.03% vs. 18.20%±0.05%, t=-0.869, P=0.045), and the drug clearance rate in ECS was significantly accelerated [(4.04±0.76) mmol/L vs. (3.26±0.55) mmol/L, t=1.786, P=0.014], and there was no significant difference in tortuosity and the rate of molecular diffusion in the ECS.@*CONCLUSION@#The drug clearance and ECS structural parameters of brain ECS in aged brain with CED administration were changed at different rates, and it has the least effect on ECS in the aged brain at the injection rate of 0.2 μL/min. For the application of CED for the treatment of encephalopathy, we should consider the influence of factors such as age and injection rate, and provide reference for the development of individualized clinical treatment plan for minimally invasive treatment of encephalopathy via ECS pathway.

Role of aquaporin-4 in the change of interstitial fluid drainage in Alzheimer's disease / 北京大学学报(医学版)

OBJECTIVE@#To observe the characteristics of the interstitial fluid (ISF) drainage in the Alzheimer's disease (AD) rats through magnetic resonance imaging (MRI) tracer gadolinium-diethylene triamine pentacetic acid (Gd-DTPA)spread in the brain extracellular space (ECS) and to discuss the role of aquaporin-4 (Aqp4) in the AD.@*METHODS@#Wild type SD rats (300-350 g) and Aqp4 gene knock out (Aqp4-/-) SD rats (300-350g) were divided into Sham group, AD group, Aqp4-/--Sham group and Aqp4-/--AD group. Sham group and Aqp4-/--Sham group were injected with saline by intraperitoneal each day for 6 weeks, and the AD group and Aqp4-/--AD group were injected with D-galactose by intraperitoneal each day for 6 weeks. MRI tracer Gd-DTPA (10 mmol/L, 2 μL) was injected into the hippocampus of the rats. MRI scan was performed at the end of 0.5 h, 1.5 h, 1 h, 2 h, and 3 h to observe the dynamic distribution of the Gd-DTPA in the hippocampus and the diffusion rate D*, clearance rate k' and half-life t1/2 measured.@*RESULTS@#The diffusion rate D* in Sham group was (2.66±0.36)×10-6 mm2/s, the diffusion rate D* in AD group was (2.72±0.62)×10-6 mm2/s, the diffusion rate D* in Aqp4-/--Sham group was (2.75±0.47)×10-6 mm2/s, the diffusion rate D* in Aqp4-/--AD group was (2.802±0.55)×10-6 mm2/s, and there was no statistically significant difference in the four groups (One-Way ANOVA, P>0.05).The clearance rate k' in Sham group was (4.57±0.14)×10-4/s, the clearance rate k' in AD group was (3.68±0.22)×10-4/s, the clearance rate k' in Aqp4-/--Sham group was (3.17±0.16)×10-4/s, the clearance rate k' in Aqp4-/--AD group was (2.59±0.19)×10-4/s, and there was significant difference in the four groups (One-Way ANOVA, P<0.05). The half-life t1/2 in Sham group was (0.67±0.12) h, the half-life t1/2 in AD group was (0.88±0.08) h, the half-life t1/2 in Aqp4-/--Sham group was (1.12±0.15) h, the half-life t1/2 in Aqp4-/--AD group was (1.58±0.11) h, and there was significance difference in the four groups(one-way ANOVA,P<0.05).@*CONCLUSION@#The ISF drainage is slow after AD and the loss of Aqp4 in the AD makes the ISF drainage obviously slow down, Aqp4 plays an important role in AD to remove the metabolism of waste out of the brain.