Long-term maintenance of synaptic plasticity by Fullerenol Ameliorates lead-induced-impaired learning and memory in vivo

Abstract

Fullerenol, a functional and water-soluble fullerene derivative, plays an important role in antioxidant, antitumor and antivirus, implying its enormous potential in biomedical applications. However, the in vivo performance of fullerenol remains largely unclear. We aimed to investigate the effect of fullerenol (i.p., 5 mg/kg) on the impaired hippocampus in a rat model of lead exposure. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is a kind of newly developed soft-ionization mass spectrometry technology. In the present study, an innovative strategy for biological distribution analysis using MALDI-TOF-MS confirmed that fullerenol could across the blood-brain barrier and accumulate in the brain. Results from behavioral tests showed that a low dose of fullerenol could improve the impaired learning and memory induced by lead. Furthermore, electrophysiology examinations indicated that this potential repair effect of fullerenol was mainly due to the long-term changes in hippocampal synaptic plasticity, with enhancement lasting for more than 2-3 h. In addition, morphological observations and biochemistry analyses manifested that the long-term change in synaptic efficacy was accompanied by some structural alteration in synaptic connection. Our study demonstrates the therapeutic feature of fullerenol will be beneficial to the discovery and development as a new drug and lays a solid foundation for further biomedical applications of nanomedicines.

Keywords: Fullerenol; In vivo; Lead-induced impairment; Learning and memory; Synaptic plasticity.

Fig. 1

Schematics of the experimental procedures and characterization of fullerenol. A Experimental timeline, B Transmission electron microscope image, C Size distribution and zeta potential of fullerenol (1 μM, dissolved in water)

Fig. 2

Fullerenol may across the blood–brain barrier and lead can accumulate in the body. A Mass spectrometry of water-suspended fullerenol, B–E Distribution of exogenous fullerenol in brain, Liver, Kidney and spleen were detected by MALDI-TOF–MS. F Lead contents in blood and hippocampus of experiment rats were analyzed by ICP-MS. MALDI-TOF–MS: Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry; ICP-MS: Inductively Coupled Plasma Mass Spectrometry. One-way ANOVA analysis with Tukey-test post hoc analysis. *** p < 0.001 compared with the control group

Fig. 3

Fullerenol improved hippocampus-dependent spatial learning and memory. A, B The number of crossing squares and rearing in open field test indicated that exploratory activity of rats were normal. C–F The performances of rats in Morris water maze, including latency to the correct platform during training period, time-spent in the correct area, latency to the correct area and velocity, indicated that fullerenol improved the learning and memory. Two-way ANOVA with Tukey-test post hoc analysis was used in the training period of the Morris Water Maze. One-way ANOVA with Tukey-test post hoc analysis was for all other studies. ** p < 0.01, *** p < 0.001 compared with the control group. ^## p < 0.01, ^### p < 0.001 compared with the lead-exposed group. N.S. not significant

Fig. 4

Fullerenol enhanced long-term synaptic plasticity in hippocampal PP-DG pathway. A, B The I/O curve shown as fEPSP slope and PS amplitude, C, D The PPF ratio shown as fEPSP2/fEPSP1 and PS2/PS1, E, F The LTP induction shown as fEPSP slope in percent and PS amplitude in percent indicated that long-term maintenance of synaptic plasticity by fullerenol was found in hippocampal DG area. One-way ANOVA with Tukey-test post hoc analysis was used in the peak analysis of the PPF ratio curve. Two-way ANOVA with Tukey-test post hoc analysis was for all other studies. * p < 0.05, ** p < 0.01, *** p < 0.001 compared with the control group. ^# p < 0.05, ^### p < 0.001 compared with the lead-exposed group

Fig. 5

Fullerenol enhanced long-term synaptic plasticity in hippocampal Sch-CA1 pathway. A The I/O curve shown as fEPSP slope, B The PPF ratio shown as fEPSP2/fEPSP1, C The LTP induction shown as fEPSP slope in percent indicated that long-term maintenance of synaptic plasticity by fullerenol was found in hippocampal CA1 area. One-way ANOVA with Tukey-test post hoc analysis was used in the peak analysis of the PPF ratio curve. Two-way ANOVA with Tukey-test post hoc analysis was for all other studies. ** P < 0.01, *** P < 0.001 compared with the control group. ^## P < 0.01, ^### P < 0.001 compared with the lead-exposed group

Fig. 6

The PSD-dependent structural alteration by fullerenol at the synapse in hippocampus. A, B Representative image and statistical analysis of the number of spines, C, D The number of PSD, E, F Western blot and statistical analysis of PSD95 protein, p-CaMKIIα/total CaMKII showed that fullerenol up-regulated the PSD-dependent structures. One-way ANOVA with Tukey-test post hoc analysis. The estimation of mixed effect model used in statistical analysis of the number of spines eliminated the type I error from the random effect. Date were represented as mean ± SEM. * p < 0.05, ** p < 0.01, *** p < 0.001 compared with the control group. ^# p < 0.05, ^### p < 0.001 compared with the lead-exposed group

Fig. 7

The protective effect of fullerenol was not dependent on the reduction–oxidation pathway. A The H₂O₂ level. B The total SOD activity. C The total antioxidant capacity. D The total GSH concentration. One-way ANOVA with Tukey-test post hoc analysis. * p < 0.05, ** p < 0.01, *** p < 0.001 compared with the control group