Physiological variation in plasma total homocysteine concentrations in rats

Melatonin as a Reducer of Neuro- and Vasculotoxic Oxidative Stress Induced by Homocysteine

The antioxidant properties of melatonin can be successfully used to reduce the effects of oxidative stress caused by homocysteine. The beneficial actions of melatonin are mainly due to its ability to inhibit the generation of the hydroxyl radical during the oxidation of homocysteine. Melatonin protects endothelial cells, neurons, and glia against the action of oxygen radicals generated by homocysteine and prevents the structural changes in cells that lead to impaired contractility of blood vessels and neuronal degeneration. It can be, therefore, assumed that the results obtained in experiments performed mainly in the in vitro models and occasionally in animal models may clear the way to clinical applications of melatonin in patients with hyperhomocysteinemia, who exhibit a higher risk of developing neurodegenerative diseases (e.g., Parkinson’s disease or Alzheimer’s disease) and cardiovascular diseases of atherothrombotic etiology. However, the results that have been obtained so far are scarce and have seldom been performed on advanced in vivo models. All findings predominately originate from the use of in vitro models and the scarcity of clinical evidence is huge. Thus, this mini-review should be considered as a summary of the outcomes of the initial research in the field concerning the use of melatonin as a possibly efficient attenuator of oxidative stress induced by homocysteine.

Effects of Hyperhomocysteinemia on the Platelet-Driven Contraction of Blood Clots

Hyperhomocysteinemia (HHcy) is associated with thrombosis, but the mechanistic links between them are not understood. We studied effects of homocysteine (Hcy) on clot contraction in vitro and in a rat model of HHcy. Incubation of blood with exogenous Hcy for 1 min enhanced clot contraction, while 15-min incubation led to a dose-dependent suppression of contraction. These effects were likely due to direct Hcy-induced platelet activation followed by exhaustion, as revealed by an increase in fibrinogen-binding capacity and P-selectin expression determined by flow cytometry. In the blood of rats with HHcy, clot contraction was enhanced at moderately elevated Hcy levels (10–50 μM), while at higher Hcy levels (>50 μM), the onset of clot contraction was delayed. HHcy was associated with thrombocytosis combined with a reduced erythrocyte count and hypofibrinogenemia. These data suggest that in HHcy, platelets get activated directly and indirectly, leading to enhanced clot contraction that is facilitated by the reduced content and resilience of fibrin and erythrocytes in the clot. The excessive platelet activation can lead to exhaustion and impaired contractility, which makes clots larger and more obstructive. In conclusion, HHcy modulates blood clot contraction, which may comprise an underappreciated pro- or antithrombotic mechanism.

Histone Hyperacetylation as a Response to Global Brain Ischemia Associated with Hyperhomocysteinemia in Rats

Epigenetic regulations play an important role in both normal and pathological conditions of an organism, and are influenced by various exogenous and endogenous factors. Hyperhomocysteinemia (hHcy), as a risk factor for several pathological conditions affecting the central nervous system, is supposed to alter the epigenetic signature of the given tissue, which therefore worsens the subsequent damage. To investigate the effect of hHcy in combination with ischemia-reperfusion injury (IRI) and histone acetylation, we used the hHcy animal model of global forebrain ischemia in rats. Cresyl violet staining showed massive neural disintegration in the M1 (primary motor cortex) region as well as in the CA1 (cornu ammonis 1) area of the hippocampus induced by IRI. Neural loss was significantly higher in the group with induced hHcy. Moreover, immunohistochemistry and Western blot analysis of the brain cortex showed prominent changes in the acetylation of histones H3 and H4, at lysine 9 and 12, respectively, as a result of IRI and induced hHcy. It seems that the differences in histone acetylation patterns in the cortical region have a preferred role in pathological processes induced by IRI associated with hHcy and could be considered in therapeutic strategies.

Association of Induced Hyperhomocysteinemia with Alzheimer's Disease-Like Neurodegeneration in Rat Cortical Neurons After Global Ischemia-Reperfusion Injury

Alzheimer's disease (AD) is a progressive and irreversible neurodegenerative disorder that results in massive hippocampal and neocortical neuronal loss leading to dementia and eventual death. The exact cause of Alzheimer's disease is not fully explored, although a number of risk factors have been recognized, including high plasma concentration of homocysteine (Hcy). Hyperhomocysteinemia (hHcy) is considered a strong, independent risk factor for stroke and dementia. However, the molecular background underlying these mechanisms linked with hHcy and ischemic stroke is not fully understood. Paper describes rat model of global forebrain ischemia combined with the experimentally induced hHcy. Global ischemia-reperfusion injury (IRI) was developed by 4-vessels occlusion lasting for 15 min followed by reperfusion period of 72 h. hHcy was induced by subcutaneous injection of 0.45 µmol/g of Hcy in duration of 14 days. The results showed remarkable neural cell death induced by hHcy in the brain cortex and neurodegeneration is further aggravated by global IRI. We demonstrated degeneration of cortical neurons, alterations in number and morphology of tissue astrocytes and dysregulation of oxidative balance with increased membrane protein oxidation. Complementary to, an immunohistochemical analysis of tau protein and β-amyloid peptide showed that combination of hHcy with the IRI might lead to the progression of AD-like pathological features. Conclusively, these findings suggest that combination of risk factor hHcy with IRI aggravates neurodegeneration processes and leads to development of AD-like pathology in cerebral cortex.

Age-Related Changes in Sulfur Amino Acid Metabolism in Male C57BL/6 Mice

Alterations in sulfur amino acid metabolism are associated with an increased risk of a number of common late-life diseases, which raises the possibility that metabolism of sulfur amino acids may change with age. The present study was conducted to understand the age-related changes in hepatic metabolism of sulfur amino acids in 2-, 6-, 18- and 30-month-old male C57BL/6 mice. For this purpose, metabolite profiling of sulfur amino acids from methionine to taurine or glutathione (GSH) was performed. The levels of sulfur amino acids and their metabolites were not significantly different among 2-, 6- and 18-month-old mice, except for plasma GSH and hepatic homocysteine. Plasma total GSH and hepatic total homocysteine levels were significantly higher in 2-month-old mice than those in the other age groups. In contrast, 30-month-old mice exhibited increased hepatic methionine and cysteine, compared with all other groups, but decreased hepatic S-adenosylmethionine (SAM), S-adenosylhomocysteine and homocysteine, relative to 2-month-old mice. No differences in hepatic reduced GSH, GSH disulfide, or taurine were observed. The hepatic changes in homocysteine and cysteine may be attributed to upregulation of cystathionine β-synthase and down-regulation of γ-glutamylcysteine ligase in the aged mice. The elevation of hepatic cysteine levels may be involved in the maintenance of hepatic GSH levels. The opposite changes of methionine and SAM suggest that the regulatory role of SAM in hepatic sulfur amino acid metabolism may be impaired in 30-month-old mice.

Anxiety-related behavior in hyperhomocysteinemia induced by methionine nutritional overload in rats: role of the brain oxidative stress

The aim of this study was to examine the effects of a methionine-enriched diet on anxiety-related behavior in rats and to determine the role of the brain oxidative status in these alterations. Adult male Wistar rats were fed from the 30th to 60th postnatal day with standard or methionine-enriched diet (double content comparing with standard diet: 7.7 g/kg). Rats were tested in open field and light-dark tests and afterwards oxidative status in the different brain regions were determined. Hyperhomocysteinemia induced by methionine-enriched diet in this study decreased the number of rearings, as well as the time that these animals spent in the center of the open field, but increased index of thigmotaxy. Oxidative status was selectively altered in the examined regions. Lipid peroxidation was significantly increased in the cortex and nc. caudatus of rats developing hyperhomocysteinemia, but unaltered in the hippocampus and thalamus. Based on the results of this research, it could be concluded that hyperhomocysteinemia induced by methionine nutritional overload increased anxiety-related behavior in rats. These proanxiogenic effects could be, at least in part, a consequence of oxidative stress in the rat brain.

Effects of mild hyperhomocysteinemia on electron transport chain complexes, oxidative stress, and protein expression in rat cardiac mitochondria

Hyperhomocysteinemia (HHcy) is an independent risk factor of cardiovascular disease, but the mechanisms of tissue injury are poorly understood. In the present study, we investigated the effect of HHcy on rat heart function, activities electron transport chain (ETC) complexes, mitochondrial protein expression, and protein oxidative damage. HHcy was induced by subcutaneous injection of Hcy (0.45 μmol/g of body weight) twice a day for a period of 2 weeks. Performance of hearts excised after the Hcy treatment was examined according to the Langendorff method at a constant pressure. Left ventricular developed pressure, as well as maximal rates of contraction (+dP/dt) and relaxation (-dP/dt), was significantly depressed in HHcy rats. HHcy was accompanied by significant inhibition of ETC complexes II-IV, whereas activity of the complex I was unchanged. The decline in ETC activities was not associated with elevated protein oxidative damage, as indicated by unchanged protein carbonyl, thiol, and dityrosine contents. Moreover, the level of protein adducts with 4-hydroxynonenal was decreased in HHcy rats. Additionally, 2D-gel electrophoresis with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry did not show alterations in contents of inhibited ETC complexes. However, mass spectrometry analyses identified 8 proteins whose expression was significantly increased by HHcy. These proteins are known to play important roles in the cellular stress response, bioenergetics, and redox balance. Altogether, the results suggest that oxidative damage and altered protein expression are not possible causes of ETC dysfunction in HHcy rats. Increased expression of the other mitochondrial proteins indicates a protective response to Hcy-induced myocardial injury.

Central and systemic responses to methionine-induced hyperhomocysteinemia in mice

Hyperhomocysteinemia has been considered a risk factor for neuropsychiatric disorders, but the mechanisms involved in this process have not been completely elucidated. The aim of this study was to analyze the influence of hyperhomocysteinemia induction by methionine supplementation considering different levels and periods of exposure in mice. For this purpose, methionine supplementation at concentrations of 0.5 and 1% were administered in water to increase homocysteinemia in male C57BL/6 mice, and was maintained for 3 time periods (2, 4 and 6 months of treatment). The results from one-carbon metabolism parameters, brain-derived neurotrophic factor (BDNF) concentrations and behavioral evaluation were compared. The 0.5% supplementation was efficient in increasing plasma homocysteine levels after 2 and 6 months. The 1% supplementation, increased plasma homocysteine after 2, 4 and 6 months. Little influence was observed in cysteine and glutathione concentrations. Frontal cortex BDNF levels showed a lack of treatment influence in all periods; only the expected decrease due to increasing age was observed. Moreover, the only behavioral alteration observed using a novel object recognition task was that which was expected with increasing age. We found that responses to hyperhomocysteinemia varied based on how it was reached, and the length of toxicity. Moreover, hyperhomocysteinemia can affect the normal pattern of one carbon metabolism during age increase in mice. These findings allow the establishment of a reliable animal model for studies in this field.

Fluoxetine, 17-β estradiol or folic acid combined with intra-lateral septal infusions of neuropeptide Y produced antidepressant-like actions in ovariectomized rats forced to swim

Folic acid is antidepressant, either alone or combined with several antidepressant drugs. However, the antidepressant-like actions of folic acid combined with intra-lateral septal (LSN) infusions of neuropeptide Y (NPY) in the forced swimming test (FST) have not been tested before. Thus, systemic injections of fluoxetine (20.0mg/kg, P<0.05; s.c.) or 17-β estradiol (10.0 μg/rat, P<0.05; s.c.) or oral administrations of folic acid (50.0 mg/kg, P<0.05; 75.0 mg/kg, P<0.05) or NPY intra-LSN (3.0 μg, P<0.05; 3.5 μg, P<0.05) reduced immobility of ovariectomized Wistar rats. Subthreshold doses of: folic acid (25.0 mg/kg) or 17-β estradiol (5.0 μg/rat, P<0.05) or fluoxetine (15.0 mg/kg, P<0.05; s.c.) combined with subthreshold doses of NPY (2.5 μg/rat, P<0.05; intra-LSN) and these combinations produced antidepressant-like actions; which were canceled by BIBP 3226 (a NPY-Y1 receptor antagonist). It is concluded that folic acid produced antidepressant-like effects probably through the participation of the NPY Y1 receptors found in the lateral septal nuclei.

Antihyperhomocysteinemic and antihyperlipidemic effect of Trichilia connaroides in methionine-induced hyperhomocysteinemic animals

The current study investigates the antihyperhomocysteinemic and antihyperlipidemic effect of chloroform and methanol extracts of the leaves of Trichilia connaroides in methionine-induced hyperhomocysteinemic rats. Hyperhomocysteinemia was induced in albino Wistar rats by oral administration of L-Methionine (1 gm / kg) and they were treated simultaneously with chloroform and methanol extracts (100 mg / kg) from the leaves of Trichilia connaroides. Serum homocysteine, lipid profile, and products of lipid peroxidation (MDA) in the heart homogenate were recorded and treated for statistical significance. Hyperhomocysteinemic animals recorded significantly elevated serum homocysteine changes in lipid profile (P < 0.01) and Thibarbituric acid reactive substances (P < 0.01), compared to the vehicle control animals. Animals treated with chloroform and methanol extracts recorded significantly (P < 0.01) lower serum homocysteine, entire lipid profile, LPO (P < 0.01), except a significant increase in HDL-cholesterol (P < 0.01) compared to hyperhomocysteinemic animals. Thus, we conclude that chloroform and methanol extracts of Trichilia connaroides have significant antihyperhomocysteinemic and antihyperlipidemic effects on methionine–induced hyperhomocysteinemic animals. Trichilia connaroides, therefore, holds promise as a cardioprotective herb.

The folic acid combined with 17-β estradiol produces antidepressant-like actions in ovariectomized rats forced to swim

Folic acid or 17-β estradiol produces antidepressant effects, either alone or combined with several antidepressants. However, the antidepressant-like actions of folic acid combined with 17-β estradiol in the forced swimming test (FST) have not been tested before. Thus, in the present study, ovariectomized female rats received folic acid (5.0 nmol/i.c.v., P<0.05; 10.0 nmol/ i.c.v., P<0.05; or 50mg/kg, P<0.05, p.o.; 75.0; mg/kg, P<0.05, p.o.), or fluoxetine (20.0mg/kg, P<0.05; 25.0mg/kg, P<0.05) or 17-β estradiol (10.0 μg/rat, P<0.05; 20.0 μg/rat, P<0.05) and they displayed reduced immobility by increasing swimming behavior when they were tested in the FST. Combination of subthreshold doses of folic acid (2.5 nmol/i.c.v.; or 25.0mg/kg, p.o.) with subthreshold doses of 17-β estradiol (5.0 μg/rat, P<0.05) or with subthreshold doses of fluoxetine (15.0mg/kg, P<0.05) produced antidepressant-like actions. Ketanserin was used to evaluate the participation of the drugs used in the serotonergic pathway; ketanserin cancelled the antidepressant-like actions of the several combinations used. In conclusion, folic acid alone or combined with estradiol or fluoxetine in the FST reduced immobility in the FST. These antidepressant-like actions probably were due to modifications of the serotonergic system since swimming behavior was increased and these effects were cancelled by ketanserin.

S100B and homocysteine in the acute alcohol withdrawal syndrome

Elevations of serum homocysteine levels are a consistent finding in alcohol addiction. Serum S100B levels are altered in different neuropsychiatric disorders but not well investigated in alcohol withdrawal syndromes. Because of the close connection of S100B to ACTH and glutamate secretion that both are involved in neurodegeneration and symptoms of alcoholism the relationship of S100B and homocysteine to acute withdrawal variables has been examined. A total of 22 male and 9 female inpatients (mean age 46.9 ± 9.7 years) with an ICD-10 diagnosis of alcohol addiction without relevant affective comorbidity were examined on admission and after 24, 48, and 120 h during withdrawal. S100B and homocysteine levels in serum were collected, and severity of withdrawal symptoms (AWS-scale), applied withdrawal medication, initial serum ethanol levels and duration of addiction were recorded. Serum S100B and homocysteine levels declined significantly (P < .05) over time. Both levels declined with withdrawal syndrome severity. Females showed a trend to a more intense decline in serum S100B levels compared to males at day 5 (P = .06). Homocysteine levels displayed a negative relationship to applied amount of clomethiazole (P < .05) and correlated with age of onset of addiction. No withdrawal seizures were recorded during the trial. As it is known for homocysteine, S100B revealed to decline rapidly over withdrawal treatment in alcoholism. This effect is more pronounced in female patients. S100B could be of relevance in the neurobiology of alcohol withdrawal syndromes. It may be indirectly related to the level of stress level or glutamatergic activity during alcohol withdrawal.

Daily variations of homocysteine concentration may influence methylation of DNA in normal healthy individuals

The regulation of genetic expression is tightly controlled and well balanced in the organism by different epigenetic mechanisms such as DNA methylation and histone modifications. DNA methylation occurring after embryogenesis is seen mainly as an irreversible event. Even small changes in genomic DNA methylation might be of biological relevance, and several factors influencing DNA methylation have been identified so far, one being homocysteine. In this study, genomic DNA methylation was analyzed and homocysteine plasma levels were measured over a 24 h period in 30 healthy students (15 males and 15 females) exposed to a standard 24 h regime of daytime activity alternating with nighttime sleep. Plasma homocysteine concentrations were measured using HPLC detection. DNA was extracted from whole EDTA blood, and genomic DNA methylation was assessed by fluorescently labeled cytosine extension assay. Both homocysteine and DNA methylation showed 24 h variation. Homocysteine showed a significant daily rhythm with an evening peak and nocturnal nadir in all subjects (p<0.001). Males showed higher overall homocysteine levels compared to females (p=0.002). Genomic DNA methylation showed a significant rhythm with increased levels at night (p=0.021), which was inverse to plasma homocysteine levels.

A diet rich in phosphatidylethanolamine increases plasma homocysteine in mink: a comparison with a soyabean oil diet

The effects of high dietary levels of phosphatidylethanolamine (PE) on plasma concentrations of homocysteine (tHcy) have not previously been studied. Eighteen mink (Mustela vison) studied were fed one of three diets during a 25d period in a parallel-group design. The compared diets had 0, 17 and 67% extracted lipids from natural gas-utilising bacteria (LNGB), which were rich in PE. The group with 0% LNGB was fed a diet of 100% soyabean oil (SB diet). Phospholipids are the main lipid components in LNGB andMethylococcus capsulatusis the main bacteria (90%). The fasting plasma concentration of tHcy was significantly higher when the mink consumed the diet with 67% LNGB than when they consumed the SB diet (P=0·039). A significantly lower glutathione peroxidase activity was observed in mink consuming the 17% LNGB diet or the 67% LNGB diet than was observed in mink fed the SB diet. The lack of significant differences in the level of plasma PE due to the diets indicates that most of the PE from the 67% LNGB diet was converted to phosphatidylcholine (PC) in the liver. It has previously been hypothesised that phosphatidylethanolamine N-methyltransferase is an important source of tHcy. The present results indicate that plasma tHcy is at least partly regulated by phospholipid methylation from PE to PC. This methylation reaction is a regulator of physiological importance.

The Influence of Exercise on the Daily Rhythm of Serum Homocysteine in Horses

The aim of this study was to determine the daily rhythms in the blood serum of homocysteine in horses. Ten thoroughbred horses, five athletic (trained for 1 h, 6 days a week) and five sedentary, were used. Blood samples were collected on each subject every 4 h for two days by means of the jugular vein. On each individual sample, the serum concentration of homocysteine was assessed. The results obtained during the experimental period indicated the existence of a daily rhythm of serum homocysteine in sedentary and athletic horses. They also demonstrated that in horses, physical exercise influences the daily rhythm of serum homocysteine.