Effect Of Dietary Nε-carboxymethyl-lysine On Learning And Memory Of The Rats

Advanced glycation end products(AGEs)are a series of compounds with complex structures formed via the Maillard reaction pathway between the reducing sugars and free amino groups of proteins, peptides and amino acids. As one of the typical compounds N?-(carboxymethyl) lysine(CML) is widely studied. CML can be synthesized in the body, or through food intake. Numerous studies show that, accumulation of CML in the body are closely related to occurrence of Alzheimer’s disease. Decline of the ability of learning and memory is one of the main symptoms of Alzheimer’s disease, it has been proved to have important links with CML accumulation in vivo. However, studies on effects of exogenous especially dietary sources of CML on the ability of learning and memory are few. So the purpose of this paper is to investigate the effects of dietary CML on brain tissue of rats. In this paper, healthy Sprague-Dawley rats were used as the experimental object, effects of different dietary conditions during long-term oral administration of CML on the accumulation of protein- bound CML in the brain and the influence of different doses of CML intake on learning and memory of rats from three aspects, behavioul, cell and molecular( CML accumulation and neurotransmitter release)were studied.Firstly, adult male SD rats were randomly divided into 4 groups(n=7 in each group):normal diet group, normal diet + CML(60 mg/kg·d)group, high fat diet group and high fat+ CML(60 mg/kg·d)group, after 12 weeks the rats were killed and the brain protein bound CML content were detected. The results showed that in the concentration range of 82.43~2637.50 ng/m Lng/m L it exhibited a good linear relationship, the correlation coefficient was greater than 0.9996.The detection limit was 13.10 ng/m L(LOD, S/N = 3), quantification limit was 44.93 ng/m L(LOD, S/N = 10).The average recovery at three spiked levels ranged from92.0% to 115.4%, the relative standard deviation ranged from 4.39% to 11.91%.The content of protein-bound CML in the brain of rats gastric group were higher than those in the non-gastric group for each diet condition( P<0.05) and high fat diet can accelerate the formation of protein-bound CML in the rat brain.To study intakes of different doses of CML on learning and memory of the rats, the young male SD rats were randomly divided into 4 groups(n = 8 in each group): control group,low dose group(1.5 g CML/kg feed), middle dose group(4.5 g CML/kg feed), high dose group(13.5 g CML/kg feed). 5 weeks later the water maze test was held, then the rats were killed, HE staining of the hippocampus was held to observe the pathological morphology, the protein-bound CML content of the brain and the neurotransmitter content in hippocampus,striatum and prefrontal cortex were both detected.In the navigation test of water maze, the escape latency of rats in high dose group were significantly lower than the control group, low dose group and middle dose group(P<0.05); In the water maze probe trial, the number of crossing platform and percentage of distances in the platform quadrant of rats in high dose group were significantly less than the other three groups(P<0.05); In the hippocampal slices,in the dentate gyrus low dose group showed nuclear swelling, a small part karyopyknosis;middle dose group showed a deeper level of karyopyknosis; high dose group showed karyopyknosis and obvious perinuclear halo; Protein-bound CML content in the rat brain increased as CML doses increased and each of the two groups showed significant differences;In hippocampus, the intake of CML can reduce the releases of excitatory amino acid,inhibitory amino acid neurotransmitters, D-serine, norepinephrine, histamine, acetylcholine and increase the releases of tyrosine, did not affect the releases of tryptophan; In striatum,CML intake may reduce the releases of norepinephrine, histamine, acetylcholine and increase the tryptophan release, but had no effects on the inhibitory and excitatory amino acids,D-serine and tyrosine; In prefrontal cortex, CML intake will increase the releases of inhibitory amino acid, norepinephrine and histamine, reduce the releases of excitatory amino acids and acetylcholine, had no effects on D-serine, tyrosine and tryptophan releases. These results show that dietary intake of a certain dose of CML on rats can cause a certain degree of damage on learning and memory ability, at the same time it will lead to the disorders of neurotransmitter release.