Pretreatment with vitamins E and C prevent the impairment of memory caused by homocysteine administration in rats

Hyperhomocysteinemia Induces Rat Memory Impairment Via Injuring Hippocampal CA3 Neurons and Downregulating cAMP Response Element-Binding Protein (CREB) Phosphorylation

Accumulated evidence demonstrated that an elevated plasma homocysteine level, hyperhomocysteinemia, induced cognitive impairment in animals, elderly and the patients with neurodegenerative diseases. To date, the underlying cellular and molecular mechanisms by which hyperhomocysteinemia induces cognitive impairment has not been clearly defined. The purpose of this study was to investigate the possible cellular and molecular mechanisms behind hyperhomocysteinemia signaling in rat memory impairment. The results from this study demonstrated that hyperhomocysteinemia induced neuronal damage and loss in hippocampal CA3 region and downregulated the cAMP response element-binding protein (CREB) phosphorylation. The findings of this study provide evidence that hyperhomocysteinemia induces rat memory impairment via injuring hippocampal CA3 neurons and downregulating CREB phosphorylation.

Homocysteine in Neurology: A Possible Contributing Factor to Small Vessel Disease

Homocysteine (Hcy) is a sulfur-containing amino acid generated during methionine metabolism, accumulation of which may be caused by genetic defects or the deficit of vitamin B12 and folate. A serum level greater than 15 micro-mols/L is defined as hyperhomocysteinemia (HHcy). Hcy has many roles, the most important being the active participation in the transmethylation reactions, fundamental for the brain. Many studies focused on the role of homocysteine accumulation in vascular or degenerative neurological diseases, but the results are still undefined. More is known in cardiovascular disease. HHcy is a determinant for the development and progression of inflammation, atherosclerotic plaque formation, endothelium, arteriolar damage, smooth muscle cell proliferation, and altered-oxidative stress response. Conversely, few studies focused on the relationship between HHcy and small vessel disease (SVD), despite the evidence that mice with HHcy showed a significant end-feet disruption of astrocytes with a diffuse SVD. A severe reduction of vascular aquaporin-4-water channels, lower levels of high-functioning potassium channels, and higher metalloproteinases are also observed. HHcy modulates the N-homocysteinylation process, promoting a pro-coagulative state and damage of the cellular protein integrity. This altered process could be directly involved in the altered endothelium activation, typical of SVD and protein quality, inhibiting the ubiquitin-proteasome system control. HHcy also promotes a constant enhancement of microglia activation, inducing the sustained pro-inflammatory status observed in SVD. This review article addresses the possible role of HHcy in small-vessel disease and understands its pathogenic impact.

The Controversial Role of Homocysteine in Neurology: From Labs to Clinical Practice

Homocysteine (Hcy) is a sulfur-containing amino acid that is generated during methionine metabolism. Physiologic Hcy levels are determined primarily by dietary intake and vitamin status. Elevated plasma levels of Hcy can be caused by deficiency of either vitamin B12 or folate. Hyperhomocysteinemia (HHcy) can be responsible of different systemic and neurological disease. Actually, HHcy has been considered as a risk factor for systemic atherosclerosis and cardiovascular disease (CVD) and HHcy has been reported in many neurologic disorders including cognitive impairment and stroke, independent of long-recognized factors such as hyperlipidemia, hypertension, diabetes mellitus, and smoking. HHcy is typically defined as levels >15 micromol/L. Treatment of hyperhomocysteinemia with folic acid and B vitamins seems to be effective in the prevention of the development of atherosclerosis, CVD, and strokes. However, data from literature show controversial results regarding the significance of homocysteine as a risk factor for CVD and stroke and whether patients should be routinely screened for homocysteine. HHcy-induced oxidative stress, endothelial dysfunction, inflammation, smooth muscle cell proliferation, and endoplasmic reticulum (ER) stress have been considered to play an important role in the pathogenesis of several diseases including atherosclerosis and stroke. The aim of our research is to review the possible role of HHcy in neurodegenerative disease and stroke and to understand its pathogenesis.

Exercise Mitigates Alcohol Induced Endoplasmic Reticulum Stress Mediated Cognitive Impairment through ATF6-Herp Signaling

Chronic ethanol/alcohol (AL) dosing causes an elevation in homocysteine (Hcy) levels, which leads to the condition known as Hyperhomocysteinemia (HHcy). HHcy enhances oxidative stress and blood-brain-barrier (BBB) disruption through modulation of endoplasmic reticulum (ER) stress; in part by epigenetic alternation, leading to cognitive impairment. Clinicians have recommended exercise as a therapy; however, its protective effect on cognitive functions has not been fully explored. The present study was designed to observe the protective effects of exercise (EX) against alcohol-induced epigenetic and molecular alterations leading to cerebrovascular dysfunction. Wild-type mice were subjected to AL administration (1.5 g/kg-bw) and subsequent treadmill EX for 12 weeks (5 day/week@7-11 m/min). AL affected mouse brain through increases in oxidative and ER stress markers, SAHH and DNMTs alternation, while decreases in CBS, CSE, MTHFR, tight-junction proteins and cellular H2S levels. Mechanistic study revealed that AL increased epigenetic DNA hypomethylation of Herp promoter. BBB dysfunction and cognitive impairment were observed in the AL treated mice. AL mediated transcriptional changes were abolished by administration of ER stress inhibitor DTT. In conclusion, exercise restored Hcy and H2S to basal levels while ameliorating AL-induced ER stress, diminishing BBB dysfunction and improving cognitive function via ATF6-Herp-signaling. EX showed its protective efficacy against AL-induced neurotoxicity.

Oxidative Stress in Homocystinuria Due to Cystathionine ß-Synthase Deficiency: Findings in Patients and in Animal Models

Homocystinuria is an inborn error of amino acid metabolism caused by deficiency of cystathionine ß-synthase (CBS) activity, biochemically characterized by homocysteine (Hcy) and methionine (Met) accumulation in biological fluids and high urinary excretion of homocystine. Clinical manifestations include thinning and lengthening of long bones, osteoporosis, dislocation of the ocular lens, thromboembolism, and mental retardation. Although the pathophysiology of this disease is poorly known, the present review summarizes the available experimental findings obtained from patients and animal models indicating that oxidative stress may contribute to the pathogenesis of homocystinuria. In this scenario, several studies have shown that enzymatic and non-enzymatic antioxidant defenses are decreased in individuals affected by this disease. Furthermore, markers of lipid, protein, and DNA oxidative damage have been reported to be increased in blood, brain, liver, and skeletal muscle in animal models studied and in homocystinuric patients, probably as a result of increased free radical generation. On the other hand, in vitro and in vivo studies have shown that Hcy induces reactive species formation in brain, so that this major accumulating metabolite may underlie the oxidative damage observed in the animal model and human condition. Taken together, it may be presumed that the disruption of redox homeostasis may contribute to the tissue damage found in homocystinuria. Therefore, it is proposed that the use of appropriate antioxidants may represent a novel adjuvant therapy for patients affected by this disease.

The influence of vitamins E and C and exercise on brain aging

Age-related declines in motor and cognitive function have been associated with increases in oxidative stress. Accordingly, interventions capable of reducing the oxidative burden would be capable of preventing or reducing functional declines occurring during aging. Popular interventions such as antioxidant intake and moderate exercise are often recommended to attain healthy aging and have the capacity to alter redox burden. This review is intended to summarize the outcomes of antioxidant supplementation (more specifically of vitamins C and E) and exercise training on motor and cognitive declines during aging, and on measures of oxidative stress. Additionally, we will address whether co-implementation of these two types of interventions can potentially further their individual benefits. Together, these studies highlight the importance of using translationally-relevant parameters for interventions and to study their combined outcomes on healthy brain aging.

Effect of intrahippocampal administration of vitamin C and progesterone on learning in a model of multiple sclerosis in rats

PURPOSE

The purpose of this study was to evaluate the effect of intrahippocampal injection of vitamin C and progesterone, alone or in combination, on passive avoidance learning (PAL) in multiple sclerosis.

METHODS

Sixty- three male wistar rats were divided into nine groups (n=7) as following: control (saline), lesion, vitamin C (0.2, 1, 5 mg/kg), progesterone (0.01, 0.1, 1 µg/µl) and combination therapy. Lesion was induced by intrahippocampal injection of ethidium bromide. In combination therapy, animals were treated with vitamin C (5 mg/kg) plus progesterone (0.01 mg/kg). Animals in experimental groups received different treatments for 7 days, and then all groups were tested for step through latency (STL).

RESULTS

Our results showed that intrahippocampal injection of ethidium bromide destroys PAL significantly (p<0.001). Treatment with vitamin C (5mg/kg) significantly (p<0.05) improved PAL. Lower doses of progesterone did not affect latency but dose of 1 µg/µl significantly (p<0.05) increased STL. In combination therapy group STL was significantly (p<0.05) more than in the lesion group, although it was not significantly different from the vitamin C group.

CONCLUSION

Based on our results, we concluded that intrahippocampal injection of vitamin C improves memory for PAL, but progesterone alone or in combination with vitamin C had no improving effects on memory.

Effect of vitamin B deprivation during pregnancy and lactation on homocysteine metabolism and related metabolites in brain and plasma of mice offspring

Epidemiological and experimental studies indicate that the altered fetal and neonatal environment influences physiological functions and may increase the risk of developing chronic diseases in adulthood. Because homocysteine (Hcy) metabolic imbalance is considered a risk factor for neurodegenerative diseases, we investigated whether maternal Vitamin B deficiency during early development alters the offspring's methionine-homocysteine metabolism in their brain. To this end, the dams were submitted to experimental diet one month before and during pregnancy or pregnancy/lactation. After birth, the offspring were organized into the following groups: control (CT), deficient diet during pregnancy and lactation (DPL) and deficient diet during pregnancy (DP). The mice were euthanized at various stages of development. Hcy, cysteine, glutathione (GSH), S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH), folate and cobalamin concentrations were measured in the plasma and/or brain. At postnatal day (PND) 0, total brain of female and male offspring exhibited decreased SAM/SAH ratios. Moreover, at PND 28, we observed decreased GSH/GSSG ratios in both females and males in the DPL group. Exposure to a Vitamin B-deficient diet during the ontogenic plasticity period had a negative impact on plasma folate and brain cortex SAM concentrations in aged DPL males. We also observed decreased plasma GSH concentrations in both DP and DPL males (PND 210). Additionally, this manipulation seemed to affect the female and male offspring differently. The decreased plasma GSH concentration may reflect redox changes in tissues and the decreased brain cortex SAM may be involved in changes of gene expression, which could contribute to neurodegenerative diseases over the long term.

Metformin Eased Cognitive Impairment Induced by Chronic L-methionine Administration: Potential Role of Oxidative Stress

Chronic administration of L-methionine leads to memory impairment, which is attributed to increase in the level of oxidative stress in the brain. On the other hand, metformin is a commonly used antidiabetic drug with strong antioxidant properties. In the current study, we tested if chronic metformin administration prevents memory impairment induced by administration of L-methionine. In addition, a number of molecules related to the action of metformin on cognitive functions were examined. Both metformin and L-methionine were administered to animals by oral gavage. Testing of spatial learning and memory was carried out using radial arm water maze (RAWM). Additionally, hippocampal levels or activities of catalase, thiobarbituric acid reactive substances (TBARs), glutathione peroxidase (GPx), glutathione (GSH), oxidized glutathione (GSSG) and GSH/GSSG ratio were determined. Results showed that chronic L-methionine administration resulted in both short- and long- term memory impairment, whereas metformin treatment prevented such effect. Additionally, L-methionine treatment induced significant elevation in GSSG and TBARs, along with reduction in GSH/GSSG ratio and activities of catalase, and GPx. These effects were shown to be restored by metformin treatment. In conclusion, L-methionine induced memory impairment, and treatment with metformin prevented this impairment probably by normalizing oxidative stress in the hippocampus.

Effect of tempol on the passive avoidance and novel object recognition task in diabetic rats

Diabetes mellitus (DM) has several effects, including cognitive impairment. Oxidative stress is associated with complications from diabetes. It seems that antioxidants can reduce some complications of the diabetes induced by oxidative stress. The objective of this study was to evaluate the effect of synthetic antioxidant, tempol on the passive avoidance (PA) memory and novel object recognition (NOR) tests in the diabetic rats. Forty male Wistar rats randomly divided into the control, diabetic, diabetic receiving tempol and healthy receiving tempol groups. Diabetes was induced by injection of streptozotocin (STZ) (60 mg/kg, i.p.). Then, the rats received saline or tempol (30 mg/kg) orally by gavages for 60 days. After that, they were assessed using the PA memory and NOR tests. The results of NOR test showed that the discrimination index (DI) in the healthy receiving tempol group and diabetic control group was significantly lower than control group. Also the amount of this index in diabetic receiving tempol group was significantly higher than diabetic group. The results of PA test indicated that the number of trials to acquisition in the diabetic rats is significantly more than control and diabetic tempol treated groups. Also, the time spent in the dark compartment (TDC) in the control and diabetic receiving tempol groups was less than diabetic group. TDC in the healthy receiving tempol group was more than control group. It can be concluded that although use of tempol is restricted as a cognitive enhancer in non-diabetic subjects but long-term administration of synthetic antioxidant, tempol, is able to dramatically improve diabetes-induced learning and memory deficit in both PA and NOR tests.

High concentration of vitamin E decreases thermosensation and thermotaxis learning and the underlying mechanisms in the nematode Caenorhabditis elegans

α-tocopherol is a powerful liposoluble antioxidant and the most abundant isoform of vitamin E in the body. Under normal physiological conditions, adverse effects of relatively high concentration of vitamin E on organisms and the underlying mechanisms are still largely unclear. In the present study, we used the nematode Caenorhabditis elegans as an in vivo assay system to investigate the possible adverse effects of high concentration of vitamin E on thermosensation and thermotaxis learning and the underlying mechanisms. Our data show that treatment with 100-200 µg/mL of vitamin E did not noticeably influence both thermosensation and thermotaxis learning; however, treatment with 400 µg/mL of vitamin E altered both thermosensation and thermotaxis learning. The observed decrease in thermotaxis learning in 400 µg/mL of vitamin E treated nematodes might be partially due to the moderate but significant deficits in thermosensation, but not due to deficits in locomotion behavior or perception to food and starvation. Treatment with 400 µg/mL of vitamin E did not noticeably influence the morphology of GABAergic neurons, but significantly decreased fluorescent intensities of the cell bodies in AFD sensory neurons and AIY interneurons, required for thermosensation and thermotaxis learning control. Treatment with 400 µg/mL of vitamin E affected presynaptic function of neurons, but had no remarkable effects on postsynaptic function. Moreover, promotion of synaptic transmission by activating PKC-1 effectively retrieved deficits in both thermosensation and thermotaxis learning induced by 400 µg/mL of vitamin E. Therefore, relatively high concentrations of vitamin E administration may cause adverse effects on thermosensation and thermotaxis learning by inducing damage on the development of specific neurons and presynaptic function under normal physiological conditions in C. elegans.

Acetyl-L-carnitine attenuates homocysteine-induced Alzheimer-like histopathological and behavioral abnormalities

Hyperhomocystinemia could induce tau protein hyperphosphorylation, β-amyloid (Aβ) accumulation, and memory deficits as seen in Alzheimer disease (AD), the most common cause of senile dementia with no effective cure currently. To search for possible treatment for AD, we produced a hyperhomocysteinemia model by vena caudalis injection of homocystine (Hcy) for 2 weeks and studied the effects of acetyl-L-carnitine (ALC) in rats. We found that simultaneous supplement of ALC could improve the Hcy-induced memory deficits remarkably, with attenuation of tau hyperphosphorylation and Aβ accumulation. Supplement of ALC almost abolished the Hcy-induced tau hyperphosphorylation at multiple AD-related sites. Supplementation of ALC also suppressed the phosphorylation of β-amyloid precursor proteins (APP), which may underlie the reduction of Aβ. Our data suggest that ALC could be a promising candidate for arresting Hcy-induced AD-like pathological and behavioral impairments.

Behavioral and neurochemical effects of proline

Proline is an amino acid with an essential role for primary metabolism and physiologic functions. Hyperprolinemia results from the deficiency of specific enzymes for proline catabolism, leading to tissue accumulation of this amino acid. Hyperprolinemic patients can present neurological symptoms and brain abnormalities, whose aetiopathogenesis is poorly understood. This review addresses some of the findings obtained, mainly from animal studies, indicating that high proline levels may be associated to neuropathophysiology of some disorders. In this context, it has been suggested that energy metabolism deficit, Na(+),K(+)-ATPase, kinase creatine, oxidative stress, excitotoxicity, lipid content, as well as purinergic and cholinergic systems are involved in the effect of proline on brain damage and spatial memory deficit. The discussion focuses on the relatively low antioxidant defenses of the brain and the vulnerability of neural tissue to reactive species. This offers new perspectives for potential therapeutic strategies for this condition, which may include the early use of appropriate antioxidants as a novel adjuvant therapy, besides the usual treatment based on special diets poor in proline.

Antioxidants prevent memory deficits provoked by chronic variable stress in rats

Learning and memory deficits occur in depression and other stress related disorders. Although the pathogenesis of cognitive impairment after stress has not been fully elucidated, factors such as oxidative stress and neurotrophins are thought to play possible roles. Here we investigated the effect of treatment with vitamin E (40 mg/kg) and vitamin C (100 mg/kg) on the effects elicited by chronic variable stress on rat performance in Morris water maze. Brain-derived neurotrophic factor (BDNF) immunocontent was also evaluated in hippocampus of rats. Sixty-day old Wistar rats were submitted to different stressors for 40 days (stressed group). Half of stressed group received administration of vitamins once a day, during the period of stress. Chronically stressed rats presented a marked decrease in reference memory in the water maze task as well as a reduced efficiency to find the platform in the working memory task. Rats treated with vitamins E and C had part of the above effects prevented, suggesting the participation of oxidative stress in such effects. The BDNF levels were not altered in hippocampus of stressed group when compared to controls. Our findings lend support to a novel therapeutic strategy, associated with these vitamins, to the cognitive dysfunction observed in depression and other stress related diseases.

Reactive oxygen species in the regulation of synaptic plasticity and memory

The brain is a metabolically active organ exhibiting high oxygen consumption and robust production of reactive oxygen species (ROS). The large amounts of ROS are kept in check by an elaborate network of antioxidants, which sometimes fail and lead to neuronal oxidative stress. Thus, ROS are typically categorized as neurotoxic molecules and typically exert their detrimental effects via oxidation of essential macromolecules such as enzymes and cytoskeletal proteins. Most importantly, excessive ROS are associated with decreased performance in cognitive function. However, at physiological concentrations, ROS are involved in functional changes necessary for synaptic plasticity and hence, for normal cognitive function. The fine line of role reversal of ROS from good molecules to bad molecules is far from being fully understood. This review focuses on identifying the multiple sources of ROS in the mammalian nervous system and on presenting evidence for the critical and essential role of ROS in synaptic plasticity and memory. The review also shows that the inability to restrain either age- or pathology-related increases in ROS levels leads to opposite, detrimental effects that are involved in impairments in synaptic plasticity and memory function.

Short-term influence of elevation of plasma homocysteine levels on cognitive function in young healthy adults

BACKGROUND

Acute homocysteine elevation has been shown to have a significant impact on cognitive function in animal models.

OBJECTIVES

Investigation of the short-term impact of elevation of plasma homocysteine levels through a dietary intervention on cognitive abilities of young healthy adults.

PARTICIPANTS

100 healthy medical students of both genders were enrolled in the study.

DESIGN AND MEASUREMENTS

Homocysteine levels and cognitive abilities were measured at 08:30 (before breakfast) and at 15:00 (two hours after lunch and six hours after breakfast). Food intake was restricted to specified comestibles. The cognitive assessment comprised a version of the Short Test for General Intelligence, three subtests of the Syndrome Short Test and the Stroop test.

RESULTS

At 15:00 plasma homocysteine was significantly elevated in 56 participants (P < 0.00001), whilst in 44 it was decreased (P < 0.00001) in comparison to baseline (08:30). The decrease was however of limited clinical significance. The differences in the changes in cognitive performance between the two groups did not attain statistical significance (P > 0.05) and the direction of the changes did not differ between them. Accordingly, the multiple linear regression analysis did not reveal an important influence of homocysteine elevation on cognitive performance variations.

CONCLUSIONS

Significant increase of plasma homocysteine is not associated with a straightforward inhibitory or facilitatory short-term effect on physiological cognitive parameters in young healthy adults.

Genetic and cellular studies of oxidative stress in methylmalonic aciduria (MMA) cobalamin deficiency type C (cblC) with homocystinuria (MMACHC)

Methylmalonic aciduria (MMA) cobalamin deficiency type C (cblC) with homocystinuria (MMACHC) is the most frequent genetic disorder of vitamin B(12) metabolism. The aim of this work was to identify the mutational spectrum in a cohort of cblC-affected patients and the analysis of the cellular oxidative stress and apoptosis processes, in the presence or absence of vitamin B(12). The mutational spectrum includes nine previously described mutations: c.3G>A (p.M1L), c.217C>T (p.R73X), c.271dupA (p.R91KfsX14), c.331C>T (p.R111X), c.394C>T (p.R132X), c.457C>T (p.R153X), c.481C>T (p.R161X), c.565C>A (p.R189S), and c.615C>G (p.Y205X), and two novel changes, c.90G>A (p.W30X) and c.81+2T>G (IVS1+2T>G). The most frequent change was the known c.271dupA mutation, which accounts for 85% of the mutant alleles characterized in this cohort of patients. Owing to its high frequency, a real-time PCR and subsequent high-resolution melting (HRM) analysis for this mutation has been established for diagnostic purposes. All cell lines studied presented a significant increase of intracellular reactive oxygen species (ROS) content, and also a high rate of apoptosis, suggesting that elevated ROS levels might induce apoptosis in cblC patients. In addition, ROS levels decreased in hydroxocobalamin-incubated cells, indicating that cobalamin might either directly or indirectly act as a scavenger of ROS. ROS production might be considered as a phenotypic modifier in cblC patients, and cobalamin supplementation or additional antioxidant drugs might suppress apoptosis and prevent cellular damage in these patients.

Effects of combined treatment with vitamins C and E on passive avoidance learning and memory in diabetic rats

Learning and memory deficits occur in diabetes mellitus. Although the pathogenesis of cognitive impairment in diabetes has not been fully elucidated, factors such as metabolic impairments, vascular complications and oxidative stress are thought to play possible roles. Here we investigated the effect of chronic treatment with vitamin C (50mg/kg, p.o), vitamin E (100mg/kg, p.o) and both together on passive avoidance learning (PAL) and memory in male Wistar control and diabetic rats. Treatments were begun at the onset of hyperglycemia. Passive avoidance learning was assessed 30 days later. Retention was tested 24h after training. At the end, animals were weighed and blood samples were drawn for plasma glucose measurement. Diabetes caused impairment in acquisition and retrieval processes of PAL and memory. The combination of vitamin C and E improved learning and memory in controls and reversed learning and memory deficits in diabetic rats. Combined treatment also affected the body weight and plasma glucose level of diabetic treated animals compared to untreated diabetic animals. Hypoglycemic effects and antioxidant properties of the vitamins may be involved in the nootropic effect of such treatment. These results show that combined treatment with vitamins C and E improved PAL and memory of control rats. In addition, combined vitamins administration to rats for 30 days from onset of diabetes alleviated the negative influence of diabetes on learning and memory. Therefore, combined vitamins treatment may provide a new potential alternative for prevention of impaired cognitive functions associated with diabetes and may warrant further clinical study.

Acute homocysteine administration impairs memory consolidation on inhibitory avoidance task and decreases hippocampal brain-derived neurotrophic factor immunocontent: prevention by folic acid treatment

In the present study, we first investigated the effect of single homocysteine administration on consolidation of short- and long-term memories of inhibitory avoidance task in Wistar rats. We also measured brain-derived neurotrophic factor levels in the hippocampus and parietal cortex of rats. The influence of pretreatment with folic acid on behavioral and biochemical effects elicited by homocysteine was also studied. Wistar rats were subjected to a folic acid or saline pretreatment from their 22(nd) to 28(th) day of life; 12 h later they were submitted to a single administration of homocysteine or saline. For motor activity and memory evaluation we performed open-field and inhibitory avoidance tasks. Hippocampus and parietal cortex were obtained for brain-derived neurotrophic factor immunocontent determination. Results showed that homocysteine impaired short- and long-term memories and reduced brain-derived neurotrophic factor levels in the hippocampus. Pretreatment with folic acid prevented both the memory deficit and the reduction in the brain-derived neurotrophic factor immunocontent induced by homocysteine injection. Further studies are required to determine the entire mechanism by which folic acid acts and its potential therapeutic use for memory impairment prevention in homocystinuric patients.

Two types of seizures in homocysteine thiolactone-treated adult rats, behavioral and electroencephalographic study

D,L-homocysteine thiolactone (H), a reactive homocysteine metabolite, contributes to total homocysteine pool. The aim of the present study was to determine the effects of H after acute application in increasing doses to rats. Adult Wistar rat were intraperitoneally administered saline or H in increasing doses (5.5, 8.0, or 11.0 mmol/kg). For electroencephalographic (EEG) recordings, three gold-plated screws were implanted into the skull and animals were supervised. We observed H-induced two types of seizures, the coexistence of convulsive and nonconvulsive epilepsy. Dose-related increase in the number and severity (0-4) of displaying convulsions was recorded. In H(5.5) group, the majority of seizure episodes were grade 1 (62.5 and 0% lethality), in H(8) 40% grade 2, and in H(11) grade 4 in 42.11% (100% lethal outcome). EEGs recordings in convulsive animals showed a high-voltage spike-wave and polyspikes complexes. The second, absence-like, nonconvulsive seizures were accompanied by the EEGs mostly with 6-8 Hz spikes-and-wave discharges (SWD). Latency time to the generalized clonic-tonic seizures overlapped with the time of the maximal median number and median duration of the SWD per 15 min during 90-min observing period. The results show that acute H administration significantly changes neurons, EEG tracings, and behavioral responses and suggests a possible model for studying petit mal epilepsy.

Melatonin prevents gestational hyperhomocysteinemia-associated alterations in neurobehavioral developments in rats

Chronic hyperhomocysteinemia is a risk factor in cardiovascular diseases and neurodegeneration. Among the putative mechanisms of homocysteine-induced neurotoxicity, an increased production of reactive oxygen species has been suggested. However, elevated homocysteine levels might disturb neurogenesis during brain development and lead to persistent congenital malformations in the fetus. In this study, we examined whether administration of melatonin inhibits maternal hyperhomocysteinemia-induced cognitive deficits in offspring. Hyperhomocysteinemia was induced in female rats by administration of methionine during pregnancy at a dose of 1 g/kg body weight dissolved in drinking water. Some animals received methionine plus 10 mg/kg/day melatonin subcutaneously throughout pregnancy. The levels of glial fibrillary acidic protein, S100B protein, and neural cell adhesion molecules were determined in the brain tissue from the pups. Learning and memory performances of the young-adult offspring were tested using the Morris water maze test. There were significant reductions in the expression of glial fibrillary acidic protein and S100 B protein in the brains of pups from hyperhomocysteinemic rat dams. Furthermore, maternal hyperhomocysteinemia altered the expression pattern of neural cell adhesion molecules in the fetal brain. In addition, maternal hyperhomocysteinemia significantly reduced learning abilities in offspring. Treatment with melatonin during pregnancy improved learning deficits and prevented the reduction of glial and neuronal markers induced by hyperhomocysteinemia. In conclusion, administration of melatonin throughout pregnancy reduces the effects of hyperhomocysteinemia on the development of fetal brain; therefore, it might be beneficial in preventing persistent congenital malformations.

Supplementation with vitamins E plus C or soy isoflavones in ovariectomized rats: effect on the activities of Na(+), K (+)-ATPase and cholinesterases

Since a previous study demonstrated that ovariectomized rats present an activation of Na(+), K(+)-ATPase and acetylcholinesterase (AChE) activities, in the present study we investigated the influence of vitamins E plus C or soy isoflavones on the effects elicited by ovariectomy on the activities of these enzyme in hippocampus of ovariectomized rats. We also determined the effect of the same compounds on the reduction of serum butyrylcholinesterase (BuChE) activity caused by ovariectomy. Female adult Wistar rats were assigned to one of the following groups: sham (submitted to surgery without removal of the ovaries) and ovariectomized. Seven days after surgery, animals were treated for 30 days with a single daily intraperitoneous injection of vitamins E (40 mg/kg) plus C (100 mg/kg) or saline (control). In another set of experiments, the rats were fed for 30 days on a special diet with soy protein or a standard diet with casein (control). Rats were sacrificed after treatments and the hippocampus was dissected and serum was separated. Data demonstrate that vitamins E plus C reversed the activation of Na(+), K(+)-ATPase and AChE in hippocampus of ovariectomized rats. Conversely, soy protein supplementation reversed the increase of AChE activity, but not of Na(+), K(+)-ATPase activity, caused by ovariectomized group. Neither treatment was able to reverse the reduction of serum BuChE activity. Furthermore, treatments with vitamins E plus C or soy were unable to reverse the decrease in estradiol levels caused by ovariectomy. Our findings show that the treatment with vitamins E plus C significantly reversed the effect of ovariectomy on hippocampal Na(+), K(+)-ATPase and AChE activities. However, a soy diet that was rich in isoflavones was able to reverse just the increase of AChE. Neither treatment altered the reduction in serum BuChE activity. Taken together, these vitamins and soy may have a protective role against the possible brain dysfunction observed in some menopause women. Vitamins E plus C and soy isoflavones may be a good alternative as a novel therapeutic strategy.

Effects of maternal hyperhomocysteinemia induced by high methionine diet on the learning and memory performance in offspring

In this study, we suggest that chronic maternal hyperhomocysteinemia results in learning deficits in the offspring due to delayed brain maturation and altered expression pattern of neural cell adhesion molecule. Although the deleterious effects of hyperhomocysteinemia were extensively investigated in the adults, there is no clear evidence suggesting its action on the developing fetal rat brain and cognitive functions of the offspring. Therefore, in the present work we aimed to investigate effects of maternal hyperhomocysteinemia on the fetal brain development and on the behavior of the offspring. A group of pregnant rats received daily methionine (1 g/kg body weight) dissolved in drinking water to induce maternal hyperhomocysteinemia, starting in the beginning of gestational day 0. The levels of glial fibrillary acidic protein, S100B protein, and neural cell adhesion molecule were determined in the tissue samples from the pups. Learning and memory performances of the young-adult offsprings were tested using Morris water maze test. There were significant reductions in the expressions of glial fibrillary acidic protein and S100B protein in the brains of maternally hyperhomocysteinemic pups on postnatal day 1, suggesting that hyperhomocysteinemia delays brain maturation. In conclusion, maternal hyperhomocysteinemia changes the expression pattern of neural cell adhesion molecule and therefore leads to an impairment in the learning performance of the offspring.

Homocysteine thiolactone and human cholinesterases

1. The cholinergic system is important in cognition and behavior as well as in the function of the cerebral vasculature. 2. Hyperhomocysteinemia is a risk factor for development of both dementia and cerebrovascular disease. 3. Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) are serine hydrolase enzymes that catalyze the hydrolysis of the neurotransmitter acetylcholine, a key process in the regulation of the cholinergic system. 4. It has been hypothesized that the deleterious effects of elevated homocysteine may, in part, be due to its actions on cholinesterases. 5. To further test this hypothesis, homocysteine and a number of its metabolites and analogues were examined for effects on the activity of human cholinesterases. 6. Homocysteine itself did not have any measurable effect on the activity of these enzymes. 7. Homocysteine thiolactone, the cyclic metabolite of homocysteine, slowly and irreversibly inhibited the activity of human AChE. 8. Conversely, this metabolite and some of its analogues significantly enhanced the activity of human BuChE. 9. Structure-activity studies indicated that the unprotonated amino group of homocysteine thiolactone and related compounds represents the essential feature for activation of BuChE, whereas the thioester linkage appears to be responsible for the slow AChE inactivation. 10. It is concluded that hyperhomocysteinemia may exert its adverse effects, in part, through the metabolite of homocysteine, homocysteine thiolactone, which is capable of altering the activity of human cholinesterases, the most pronounced effect being BuChE activation.

Mechanisms of homocysteine neurotoxicity in neurodegenerative diseases with special reference to dementia

Mild to moderate hyperhomocysteinemia is a risk factor for neurodegenerative diseases. Human studies suggest that homocysteine (Hcy) plays a role in brain damage, cognitive and memory decline. Numerous studies in recent years investigated the role of Hcy as a cause of brain damage. Hcy itself or folate and vitamin B12 deficiency can cause disturbed methylation and/or redox potentials, thus promoting calcium influx, amyloid and tau protein accumulation, apoptosis, and neuronal death. The Hcy effect may also be mediated by activating the N-methyl-D-aspartate receptor subtype. Numerous neurotoxic effects of Hcy can be blocked by folate, glutamate receptor antagonists, or various antioxidants. This review describes the most important mechanisms of Hcy neurotoxicity and pharmacological agents known to reverse Hcy effects.

α-Tocopherol and ascorbic acid prevent memory deficits provoked by chronic hyperprolinemia in rats

In the present study we investigated the action of alpha-tocopherol and ascorbic acid on the effects elicited by chronic hyperprolinemia on rat performance in the Morris water maze. Rats received subcutaneous injections of proline (experimental group) twice a day, with 10 h-interval, from the 6 to 28th days of age or an equivalent volume of 0.9% saline solution (controls). Half of the proline-treated group also received intraperitoneal administration of alpha-tocopherol (40 mg/kg) and of ascorbic acid (100 mg/kg) from the 6 to 28th days of life. On the 60th day of life, rats were subjected to testing in the water maze. Results show that chronic proline administration provokes impairment on spatial learning in reference memory task, as revealed by the increase of latency in acquisition, in the probe trial and in crossing over the platform location, as well as by the number of crossings, when compared to saline-treated animals. Proline-treated rats also demonstrated a reduced efficiency to find the platform position in the working memory task. Rats chronically treated with proline plus alpha-tocopherol and ascorbic acid had above effects prevented, suggesting the participation of oxidative stress in such effects. Our findings lend support to a novel therapeutic strategy, based on these vitamins, to the cognitive dysfunction associated with hyperprolinemia type II.

Hyperhomocysteinemia increases damage on brain slices exposed to in vitro model of oxygen and glucose deprivation: prevention by folic acid

In the present study we evaluate the effects of homocysteine on cellular damage using hippocampal slices from Wistar rats exposed to oxygen and glucose deprivation (OGD, followed by reoxygenation), an in vitro model of hypoxic-ischemic events. For chronic treatment, we induced elevated levels of homocysteine in blood (500 microM), comparable to those of human homocystinuria, and in brain (60 nmol/g wet tissue) of young rats by subcutaneous injections of homocysteine (0.3-0.6 micromol/g of body weight), twice a day with 8 h intervals, from the 6 th to the 28 th postpartum day and controls received saline. Rats were sacrificed 1, 3 or 12 h after the last injection. For acute treatment, 29-day-old rats received one single injection of homocysteine (0.6 micromol homocysteine/g body weight) or saline and were sacrificed 1h later. In another set of experiments rats were pretreated with Vitamins E (40 mg/kg) and C (100 mg/kg) or folic acid (5 mg/kg) during 1 week; 12 h after the last administration they received a single injection of homocysteine or saline and were sacrificed 1 h later. Results showed that both chronic (1 h after homocysteine administration) and acute hyperhomocysteinemia increased the cellular damage measured by LDH released to de incubation medium, suggesting an increase of tissue damage caused by OGD. Pretreatment with folic acid completely prevented the damage caused by acute hyperhomocysteinemia, whereas Vitamin E just partially prevented such effect. These findings may be relevant to explain, at least in part, the higher susceptibility of hyperhomocysteinemic patients to be susceptible to ischemic events and point to a possible preventive treatment.

Folic acid pretreatment prevents the reduction of Na+,K+‐ATPase and butyrylcholinesterase activities in rats subjected to acute hyperhomocysteinemia

The main objective of the present study was to evaluate the effect of folic acid pretreatment on parietal cortex Na(+),K(+)-ATPase and serum butyrylcholinesterase activities in rats subjected to acute hyperhomocysteinemia. Animals were pretreated daily with an intraperitoneal injection of folic acid (5 mg/kg) or saline from the 22th to the 28th day of age. Twelve hours after the last injection of folic acid or saline, the rats received a single subcutaneous injection of homocysteine (0.6 micromol/g of weight body) or saline and were killed 1h later. Serum was collected and the brain was quickly removed and parietal cortex dissected. Results showed that acute homocysteine administration significantly decreased the activities of Na(+),K(+)-ATPase and butyrylcholinesterase on parietal cortex and serum, respectively. Furthermore, folic acid pretreatment totally prevented these inhibitory effects. We also evaluated the effect of acute homocysteine administration on some parameters of oxidative stress, namely thiobarbituric acid-reactive substances and total thiol content in parietal cortex of rats. No alteration of these parameters were observed in parietal cortex of homocysteinemic animals, indicating that these oxidative stress parameters were probably not responsible for the reduction of Na(+),K(+)-ATPase and butyrylcholinesterase activities. The presented results confirm previous findings that acute hyperhomocysteinemia produces an inhibition of Na(+),K(+)-ATPase and butyrylcholinesterase activities and that pretreatment with folic acid prevents such effects. Assuming that homocysteine might also reduce the activities of these enzymes in human beings, our results support a new potential therapeutic strategy based on folic acid supplementation to prevent the neurological damage found in hyperhomocysteinemia.

Vitamins E and C pretreatment prevents ovariectomy-induced memory deficits in water maze

We investigated whether the pretreatment with vitamins E (alpha-tocopherol) and C (ascorbic acid) would act on ovariectomy-induced memory deficits in Morris water maze tasks. Adult female Wistar rats were divided into three groups: (1) naive (control), (2) sham (submitted to surgery without removal of ovaries) and (3) ovariectomized. Thirty days after surgery, they were trained in the Morris water maze in order to verify ovariectomy effects both on reference and working memory tasks. Results show that ovariectomized rats presented impairment in spatial navigation in the acquisition phase, as well as in the time spent in target quadrant and in the latency to cross over the location of the platform in test session, when compared to naive and sham groups (controls), in the reference memory task. Ovariectomy did not affect performance in the working memory task. Confirming our hypothesis, ovariectomized rats pretreated for 30 days with vitamins E and C had those impairments prevented. We conclude that ovariectomy significantly impairs spatial reference learning/memory and that pretreatment with vitamins E and C prevents such effect. Assuming this experimental memory impairment might mimic, at least in part, the cognitive deficit sometimes present in the human condition of lack of reproductive hormones, our findings lend support to a novel therapeutic strategy, based on vitamins E and C, to cognitive impairments in post-menopausal women.

Methionine alters Na+,K+‐ATPase activity, lipid peroxidation and nonenzymatic antioxidant defenses in rat hippocampus

In the present study we investigated the effect of methionine exposure of hippocampus homogenates on Na+,K+-ATPase activity from synaptic plasma membrane of rats. Results showed that methionine significantly decreased this enzyme activity. We also evaluated the effect of incubating glutathione (GSH) and trolox (alpha-tocopherol) alone or combined with methionine on Na+,K+-ATPase activity. The tested antioxidants per se did not alter the enzymatic activity, but prevented the inhibitory action of methionine on Na+,K+-ATPase activity, indicating that Met inhibitory effect was probably mediated by free radical formation. Besides, we tested the in vitro effect of methionine on some parameters of oxidative stress, namely chemiluminescence, thiobarbituric acid reactive substances (TBARS), total radical-trapping antioxidant potential (TRAP), as well as on the antioxidant enzyme activities catalase, glutathione peroxidase and superoxide dismutase in rat hippocampus. We observed that methionine significantly increased chemiluminescence and TBARS, decreased TRAP, but did not change the activity of the antioxidant enzymes. These findings suggest that reduction of Na+,K+-ATPase activity and induction of oxidative stress may be involved in the brain damage observed in human hypermethioninemia.

Long-term homocysteine exposure induces alterations in spatial learning, hippocampal signalling and synaptic plasticity

Abnormally high levels of homocysteine (HCY) have been linked to neurodegenerative diseases, but it remains unclear whether this is the cause or effect of degenerative processes. Here, we investigated the effects of prolonged HCY exposure on cognitive abilities and physiological parameters by injecting rats daily with either 20 or 200 mg/kg HCY over a period of up to 14 weeks. Notwithstanding a significant weight reduction in the 200 mg HCY group, HCY-exposed animals did not show a behavioural deficit when tested repeatedly (in weeks 1, 3, 5, 7 and 13) in a reference memory version of the water maze. Unexpectedly, some improvement in repeated reversal learning was observed in HCY exposed animals compared to controls. Pre-treatment with HCY for 3 weeks before water maze training did not uncover any cognitive alterations. Increased plasma concentrations of HCY were revealed only for the 200 mg HCY group after 14 weeks of injections, but no evidence for DNA damage was obtained. Immunocytochemically, HCY was detected in the brain after 14 weeks of treatment (both 20 and 200 mg/kg), but not after 5 weeks. Bidirectional changes in basic synaptic transmission and long-term potentiation of hippocampal CA1 pyramidal cells were observed at 5, 7 and 14 weeks in both HCY groups, indicative of complex, multifactorial time- and concentration-dependent changes. Overall, it is concluded that healthy adult rats are able to cope with continuous exposure to HCY. While HCY affects growth and neuronal excitability, this does not precipitate into an immediate impairment of cognitive function.

Reduction of butyrylcholinesterase activity in rat serum subjected to hyperhomocysteinemia

In the present study we investigate the effect of homocysteine (Hcy) administration, the main metabolite accumulating in homocystinuria, on butyrylcholinesterase (BuChE) activity in serum of rats. For the acute treatment, 29-day-old Wistar rats received one subcutaneous injection of Hcy (0.6 micromol/g) or saline (control) and were killed 1 h later. For the chronic treatment, Hcy was administered subcutaneously to rats from the 6th to the 28th day of life. Control rats received saline. The rats were killed 12 h after the last injection. In another set of experiments, rats were pretreated for one week with vitamins E and C or saline and 12 h after the last injection received one single injection of Hcy or saline, being killed 1 h later. Serum was used to determine BuChE activity. Our results showed that acute and chronic administration of Hcy significantly decreased BuChE activity. Furthermore, vitamins E and C per se did not alter BuChE activity, but prevented the reduction of this enzyme activity caused by acute administration of Hcy. The data suggest that the inhibitory effect of Hcy on BuChE activity is probably mediated by free radicals, since vitamins E and C administration prevented such effect.

Homocysteine in relation to cognitive performance in pathological and non-pathological conditions

Elevated serum homocysteine has been associated with increased risk of Alzheimer's disease. Furthermore, elevated homocysteine levels are related to cognitive dysfunction in the elderly. The aim of the present study was to explore the disease specificity of the relation between serum total homocysteine levels and cognitive function. For this, we summarize data from several studies on homocysteine levels in both normal and pathological conditions performed in our laboratories and evaluate possible mechanisms of effects of elevated homocysteine levels in the central nervous system. Total homocysteine levels were measured in serum of: 1) healthy aging individuals; 2) patients with Alzheimer's and Parkinson's disease and patients with other cognitive disorders; and 3) patients with multiple sclerosis. Increased serum homocysteine concentration was related to worse cognitive performance over a 6-year period in the normal aging population (r=−0.36 to −0.14, p<0.01 for the Word learning tests; r=0.76, p<0.05 for the Stroop Colored Word test). Homocysteine was only increased in patients with Parkinson's disease on L-Dopa therapy (18.9 vs. 16.5μmol/L in healthy controls), and not in dementia patients. Homocysteine was elevated in patients with progressive multiple sclerosis (15.0μmol/L, n=39, compared to 12.0 μmol/L in 45 controls) and correlated to both cognitive and motor function (r=−0.33 and −0.33, p<0.05, respectively). The relationship between homocysteine and cognitive function in non-pathological and pathological situations indicates that changes in its levels may play a role in cognitive functioning in a broad spectrum of conditions.

Enhanced hippocampal long-term potentiation in rats after chronic exposure to homocysteine

Homocysteine (HCY) is a sulphur-containing amino acid, which has been linked to neurodegenerative diseases such as Alzheimer's disease, and is widely reported to enhance vulnerability of neurons to oxidative, excitotoxic and apoptotic injury via perturbed calcium homeostasis, activation of N-methyl-D-aspartate (NMDA) and metabotropic glutamate (mGlu) receptors. The present study was undertaken to investigate the effects of HCY on long-term potentiation (LTP) and synaptic transmission after chronic 4-week systemic exposure to HCY in adult rats, and possible longer-term effects of HCY 4 weeks after exposure had ended. Contrary to expectation, LTP was enhanced, not retarded after chronic HCY exposure relative to controls. Basic synaptic transmission was not affected at this time point. However, after the 4-week wash out period, a decrease in speed of basic synaptic transmission emerged, and LTP was still partially enhanced, particularly for time points >30 min post-tetanus. In summary, we provide first evidence for sustained HCY-induced changes in hippocampal plasticity and a slow-onset disruption in synaptic transmission. These changes may reflect the suggested (excito-)toxicity of HCY and its putative contribution to neurodegenerative disease.

Chronic hyperhomocysteinemia provokes a memory deficit in rats in the Morris water maze task

Homocystinuria is an inherited metabolic disease biochemically characterized by tissue accumulation of homocysteine. Affected patients present mental retardation and other neurological symptoms whose mechanisms are still obscure. In the present study, we investigated the effect of chronic hyperhomocysteinemia on rat performance in the Morris water maze task. Chronic treatment was administered from the 6th to the 28th day of life by s.c. injection of homocysteine, twice a day at 8-h intervals; control rats received the same volume of saline solution. Animals were left to recover until the 60th day of life. Morris water maze tasks were then performed, in order to verify any effect of early homocysteine administration on reference and working memory of rats. Results showed that chronic treatment with homocysteine impaired memory of the platform location and that homocysteine treated animals presented fewer crossings to the place where the platform was located in training trials when compared to saline-treated animals (controls). In the working memory task, homocysteine treated animals also needed more time to find the platform. Our findings suggest that chronic experimental hyperhomocysteinemia causes cognitive dysfunction and that might be related to the neurological complications characteristic of homocystinuric patients.

Effect of vitamins C and E on cognitive function in mouse

The aim of this study was to verify the role of Vitamins C and E on the cognitive function of young and aged mice. First and second groups of young animals (aged 3 months) received either Vitamin E (250mg/kg per day) or Vitamin C (300mg/kg per day) for 60 days. Third group was treated with the combination of Vitamin E (250mg/kg per day) and Vitamin C (300mg/kg per day) for 60 days. The control group received only vehicle. The aged animal group (aged 15 months) were treated as the young group. Passive avoidance method was used for the assessment of cognitive function in both young and aged animals. The results indicated a significant improvement in the cognitive function of aged mice while there were no significant changes in young animals.

NTPDase and 5'-nucleotidase activities in synaptosomes of hippocampus and serum of rats subjected to homocysteine administration

Patients with homocystinuria, an inborn error of metabolism, present neurological dysfunction and commonly experience frequent thromboembolic complications. The nucleoside triphosphate diphosphohydrolase (NTPDase) and 5'-nucleotidase enzymes regulate the nucleotide/nucleoside ratio in the central nervous system and in the circulation and are thought to be involved in these events. Thus, the current study investigated the effect of homocysteine administration on NTPDase and 5'-nucleotidase activities, in the synaptosomal fraction of rat hippocampus, and on nucleotidase activities in rat serum. Twenty-nine-day-old Wistar rats were divided in two groups: group I (control), animals received 0.9% saline; group II (homocysteine-treated), animals received one single subcutaneous injection of homocysteine (0.6 micromol/g). Rats were killed 1 h after the injection. NTPDase and 5'-nucleotidase activities from brain and serum were significantly increased in the homocysteine-treated group. Results show that, in hippocampus, ATP and ADP hydrolysis increased by 20.5% and 20%, respectively, and AMP hydrolysis increased by 48%, when compared to controls. In serum, ATP and ADP hydrolysis increased 136% and 107%, respectively, and AMP hydrolysis increased 95%, in comparison to controls. The current data strongly indicate that in vivo homocysteine administration alters the activities of the enzymes involved in nucleotide hydrolysis, both in the central nervous system and in the serum of adult rats.

In vivo and in vitro effects of homocysteine on Na+,K+‐ATPase activity in parietal, prefrontal and cingulate cortex of young rats

In the present study we determined the effect of chronic administration of homocysteine on Na+,K+-ATPase activity in synaptic membranes from parietal, prefrontal and cingulate cortex of young rats. We also studied the in vitro effect of homocysteine on this enzyme activity and on some oxidative stress parameters, namely thiobarbituric acid-reactive substances (TBA-RS) and total radical-trapping antioxidant potential (TRAP) in the same cerebral structures. For the in vivo studies, we induced elevated levels of homocysteine in blood (500 microM), comparable to those of human homocystinuria, and in brain (60 nmol/g wet tissue) of young rats by injecting subcutaneously homocysteine (0.3-0.6 micromol/g of body weight) twice a day at 8 h intervals from the 6th to the 28th postpartum day. Controls received saline in the same volumes. Rats were killed 12 h after the last injection. Chronic administration of homocysteine significantly decreased (50%) Na+,K+-ATPase activity in parietal, increased (36%) in prefrontal and did not alter in cingulate cortex of young rats. In vitro homocysteine decreased Na+,K+-ATPase activity and TRAP and increased TBA-RS in all cerebral structures studied. It is proposed that the alteration of Na+,K+-ATPase and induction of oxidative stress by homocysteine in cerebral cortex may be one of the mechanisms related to the neuronal dysfunction observed in human homocystinuria.

Role of hippocampal oxidative stress in memory deficits induced by sleep deprivation in mice

Numerous animal and clinical studies have described memory deficits following sleep deprivation. There is also evidence that the absence of sleep increases brain oxidative stress. The present study investigates the role of hippocampal oxidative stress in memory deficits induced by sleep deprivation in mice. Mice were sleep deprived for 72 h by the multiple platform method-groups of 4-6 animals were placed in water tanks, containing 12 platforms (3 cm in diameter) surrounded by water up to 1 cm beneath the surface. Mice kept in their home cage or placed onto larger platforms were used as control groups. The results showed that hippocampal oxidized/reduced glutathione ratio as well as lipid peroxidation of sleep-deprived mice was significantly increased compared to control groups. The same procedure of sleep deprivation led to a passive avoidance retention deficit. Both passive avoidance retention deficit and increased hippocampal lipid peroxidation were prevented by repeated treatment (15 consecutive days, i.p.) with the antioxidant agents melatonin (5 mg/kg), N-tert-butyl-alpha-phenylnitrone (200 mg/kg) or vitamin E (40 mg/kg). The results indicate an important role of hippocampal oxidative stress in passive avoidance memory deficits induced by sleep deprivation in mice.

Homocysteine inhibits butyrylcholinesterase activity in rat serum

In the present work we investigated the in vitro effects of homocysteine (Hcy) and methionine (Met), metabolites accumulated in homocystinuria, on butyrylcholinesterase (BuChE) activity in rat serum. We also studied the kinetics of the inhibition of BuChE activity caused by Hcy. For determination of BuChE we used serum of 60-day-old Wistar rats, which was incubated in the absence (control) or presence of Hcy (0.01-0.5 mM) or Met (0.2-2.0 mM). The kinetics of the interaction of Hcy and BuChE was determined using the Lineweaver-Burk double reciprocal plot. Results showed that serum BuChE activity was not altered by Met, but it was significantly inhibited (37%) by 500 microM Hcy, a concentration similar to those found in blood of homocystinuric patients. The apparent Km values, in the absence and presence of 500 microM of Hcy, were 0.034 and 0.142 mM, respectively, and V(max) of BuChE for acetylcholine (ACh) as substrate was 1.25 micromol ACSCh/h/mg of protein. The Ki value obtained was 120 microM, and the inhibition was of the competitive type, suggesting a common binding site for Hcy and ACh. It is proposed that inhibition of cholinesterase activity may be one of the mechanisms involved in the neurological dysfunction observed in homocystinuria.

Impairment of energy metabolism in hippocampus of rats subjected to chemically-induced hyperhomocysteinemia

Homocystinuria is an inherited metabolic disease biochemically characterized by tissue accumulation of homocysteine (Hcy). Mental retardation, ischemia and other neurological features, whose mechanisms are still obscure are common symptoms in homocystinuric patients. In this work, we investigated the effect of Hcy administration in Wistar rats on some parameters of energy metabolism in the hippocampus, a cerebral structure directly involved with cognition. The parameters utilized were 14CO2 production, glucose uptake, lactate release and the activities of succinate dehydrogenase and cytochrome c oxidase (COX). Chronic hyperhomocysteinemia was induced by subcutaneous administration of Hcy twice a day from the 6th to the 28th day of life in doses previously determined in our laboratory. Control rats received saline in the same volumes. Rats were killed 12 h after the last injection. Results showed that Hcy administration significantly diminished 14CO2 production and glucose uptake, as well as succinate dehydrogenase and COX activities. It is suggested that impairment of brain energy metabolism may be related to the neurological symptoms present in homocystinuric patients.