Hyperhomocysteinaemia Induced By Dietary Folate Restriction Causes Behavior Changing In Rats

Background and Objection:Folate, an essential water-soluble vitamin which mediated one-carbon metabolism is a network of interconnected metabolic pathways necessary for the synthesis of purine nucleotides,thymidylate and the remethylation of homocysteine to methionine.Homocysteine is a non-essential sulfur-containing amino acid that is metabolized by remethylation to methionine or by transsulfuration to cysteine via cystathionine. Homocysteine catabolism depends on folate,vitamin B12, vitamin B6. and superoxide dismutase.An elevated plasma level of Homocysteine (more than15μmol/L) is termed hyperhomocysteinemia, which is most commonly caused by diets poor in homocysteine-lowering vitamins, i.e. folate,or disruptions in one-carbon metabolism pathway.Hyperhomocysteinemia is associated with neuropsychiatric disease. Some studies showed that older people with higher level homocystein had the higher possibility of encephalatrophy result from neurotoxic effects of homocystein. Hyperhomocysteinemia was found in some patients with Alzheimer disease and homocystein was higher in50%depression patients whose scores of Hamilton Depression Rating Scale were higher.Hyperhomocysteinemia is a mojor risk factor for CVD,epidemiological investigation suggests that folate deficiency and hyperhomocysteinemia may be causatively linked to depression,but specific mechanisms is not clear.There were many epidemiological investigations about the relationship between folate,homocysteine and depression,but the results are not consistent,someone regarded folate as a risk factor for depression,but others thought homocysteine was related to depression,the risk of which increased2%-5%when homocysteine raised every1μmol/L.The etiological factors of depression are complicated and the mechanism is not clear,neural circuit, monoamine neurotransmitter, neurotrophic factors,the hypothesis of cytokine are research hotspots,but the mechanism of folate and homocysteine in depression is less known,neurotoxic effects of homocysteine, oxidative stress, folate deficiency affects one-carbon metabolism pathway and neurotransmitter synthesis may be its possible mechanisms.The mechanism of neurotoxic effects of homocysteine is main related to over-stimulation of N-methyl--aspartate receptors and oxidative stress.Homocysteine is an endogenous glutamate receptor agonist that is prone to act on N-methyl-D-aspartate receptor.Over-stimulation of NMDA receptors leads to increases in the Lvels of cytoplasmic Ca2+and Ca2+influx induced by gutamate can cause mitochondrial apoptosis, stimulate nucleicacidase,phosphoesterase,nitric oxide synthetase through calcineurin dephosphorylation of Bad in hippocampal neurons.Oxidative stress appeared to possess an important role in neurodegenerative diseases.This condition can be defined as a serious imbalance between production of reactive species and antioxidant defenses, and could result from diminished levels of antioxidants and/or increased production of reactive species. It has been showed that oxidative stress was one of important mechanisms for homocysteine toxicity in neuronal cells. Homocysteine itself can undergo autooxidation, generating superoxide anion, hydrogen peroxide, thus causing the disruption of redox homeostasis and affecting the redox signaling pathways in vascular and neuronal cells. It is well known that superoxide dismutase own sequential functions in reactive oxygen species removing.The activity of superoxide dismutase reflects body ability of oxygen radicals elimination.Homocystein can inhibit the activies of antioxidase superoxide dismutase,reduce reactive species elimination, which lead to reactive species accumulation in intra-cellulars and mitochondrions, promote lipid peroxidation reaction in blood,cell membrane,mitochondria membrane and finely result in cells damage.Folate is a effective antioxidant which can scavenge such free radicals as H2O2and O-2,maintain stability of central nervous system, inhibit over apoptosis of cells and DNA damage.Folate deficiency leads to an imbalance in cellular antioxidant defense systems, increased oxidative stress, and apoptosis. Any of these events may compromise normal central nervous system function and contribute to the development of various neurological, behavioral, and neurocognitive dysfunctions. It is shown that Flote supplementation helped in improving antioxidant ability of rats’ brain tissue by increasing the activity of superoxide dismutase and catalase enzymes, the glutathione content to reduce oxidative stress.folate plays an impotent role in one-carbon metabolism pathway,folate deficiency interrupts that way and results in homocystein accumulation which may increase neurotoxic effects of homocysteine.Brain derived neurotrophic factor,a member of the neurotrophin family,promotes neuronal survival and reguates the proliferation and differentiation of nerve cells in the peripheral and central nervous systems. Brain derived neurotrophic factor is synthesized and released from neurons as well as from innervated non-neuronal tissues.Neurotrophins are well-known for their supporting action in regulating neuronal development, repair and protection. Brain derived neurotrophic factor is the neurotrophin targeted most efficiently to the regulated pathway of secretion and expressed at high levels in rats hippocampus immunohistochemisty.It is suggested that single homocysteine administration decreased brain derived neurotrophic factor in the hippocampus of rats, impaired memory consolidation and ethology changing,but the relevant studies were less and the mechanism is less known.Folate can not be synthesized by human and other mammals,occur naturally in select foods as well as in the synth eticform (folic acid) used in supplements and in food fortification programs.folate deficiency is one of most common reasons for hyperhomocysteinemia.In the present study our main objective was to establish experimental hyperhomocysteinemia animal model by folate deficiency diet in adult rats,explore the impact of behavior difference,changes of neurons in the Hippocampi CA3region of rats, influence of brain derived neurotrophic factor and oxidation state, investigate possible mechanism of hyperhomocysteinemia affect behavioristics and nervous system.Methods and materialsA total of Twenty-eight male SD rats were assigned to receive either folic acid deficiency diet (folate deficiency group) or ordinary diet (control group,folate in diet was1.6mg/kg) for six weeks and the model of folate deficiency,hyperhomocysteinemia was established. Before and after the experiment,serum concentrations of folate,homocysteine and superoxide dismutase were tested and behavior’s changes were monitored through an opening field test. After six weeks, the rats were killed and neurons in hippocampus were stained by hematoxylin and eosin stain to observe the changes and hippocampus brain-derived neurotrophic factor (BDNF) level was tested. Statistical analysis:Data were expressed as mean±S.E.M.Statistical Package for the Social Sciences (SPSS16.0) software.The significance of inter-group differences was evaluated by Student’s t-test.Repeated measures data were evaluated by repeated measures analysis of variance. Differences were considered statistically significant if P<0.05.ResultAs times went by,the fur of control group rats were clean and tidy but folate deficiency group were confused and had less movement.The body weight of folate deficiency group were significantly lower (P<0.05) than control group at the end of experiment.Open field test showed that the number of crossing scores and fecal boli in folate deficiency group were significantly higher than control group (P<0.05),the number of rearings were not altered by different treatments.Folate levels in serum of two group rats were no differences at the beginning,but at the end of the6weeks experimental period, folate deficiency group rats had a significantly lower folate(P<0.01) than control group while homocysteine were higher(P<0.01) and superoxide dismutase activities were increase in folate deficiency group.The hippocampus brain derived neurotrophic factor levels in the folate deciency group was lower than control group (P<0.05).Neurons of CA1and CA3hippocampus were integrated and regular in control group,but in folate deciency group were scattered and some neurons lost and signs of apoptosis appeared especially in CA3.ConclusionThe body weight of rats were decreased with folate deficiency diet and appearanced a depressive state. Hyperhomocysteinaemia was induced by folate deficiency diet and serum superoxide dismutase was increased.Hyperhomocysteinaemia was induced by folate deficiency diet maybe caused neurons in the Hippocampi CA3region changing in rats and decreased the expression of brain derived neurotrophic factor in hippocampus.