1,25-Dihydroxyvitamin D3 exerts neuroprotective effects in an ex vivo model of mild hyperhomocysteinemia

Physical exercise improves memory in sedentary middle-aged adults: Are these exercise-induced benefits associated with S-Klotho and 1,25-dihydroxivitamin D? The FIT-AGEING randomized controlled trial

We aimed to investigate the effect of three types of exercise interventions on memory (i.e., immediate memory (IM), long-term memory (LTM), and recognition). We also investigated whether exercise-induced changes in circulating S-Klotho and 1,25-dihydroxivitamin D (1,25(OH)2 D) levels were related to those observed in memory in healthy middle-aged sedentary adults. A 12-week randomized controlled trial was performed with a parallel-group design. Seventy-four participants (45-65 years old: 53% women) were randomly assigned to (1) no exercise (control) group, (2) concurrent training based on the international physical activity recommendations (PAR) group, (3) high-intensity interval training (HIIT) group, or (4) HIIT plus whole-body electromyostimulation (HIIT-EMS) group. Memory outcomes were assessed using the Wechsler Memory Scale-third edition. S-Klotho plasma levels were determined according to a solid-phase sandwich enzyme-linked immunosorbent assay kit while 1,25(OH)2 D plasma levels were measured using a DiaSorin-Liaison immunochemiluminometric analyzer. IM-Verbal Paired Associates (IM-VPA) and IM-Logical Memory (IM-LM) were improved in both the HIIT and HIIT-EMS groups compared with the control group (all p ≤ 0.045). Exercise-induced changes in S-Klotho plasma levels were positively associated with those observed in IM, LTM, and recognition (all p ≤ 0.007), whereas exercise-induced changes in 1,25(OH)2 D plasma levels were directly related to changes in IM and LTM (all p ≤ 0.048). In conclusion, a 12-week HIIT intervention with or without WB-EMS seems to be the most effective exercise program to improve IM. The significant and positive associations between exercise-induced changes in S-Klotho and 1,25(OH)2 D levels with those observed in memory outcomes suggest that these factors may be potentially related to exercise-induced improvements of memory in middle-aged adults.

From the Bench to the Bedside: Branched Amino Acid and Micronutrient Strategies to Improve Mitochondrial Dysfunction Leading to Sarcopenia

With extended life expectancy, the older population is constantly increasing, and consequently, so too is the prevalence of age-related disorders. Sarcopenia, the pathological age-related loss of muscle mass and function; and malnutrition, the imbalance in nutrient intake and resultant energy production, are both commonly occurring conditions in old adults. Altered nutrition plays a crucial role in the onset of sarcopenia, and both these disorders are associated with detrimental consequences for patients (e.g., frailty, morbidity, and mortality) and society (e.g., healthcare costs). Importantly, sarcopenia and malnutrition also share critical molecular alterations, such as mitochondrial dysfunction, increased oxidative stress, and a chronic state of low grade and sterile inflammation, defined as inflammageing. Given the connection between malnutrition and sarcopenia, nutritional interventions capable of affecting mitochondrial health and correcting inflammageing are emerging as possible strategies to target sarcopenia. Here, we discuss mitochondrial dysfunction, oxidative stress, and inflammageing as key features leading to sarcopenia. Moreover, we examine the effects of some branched amino acids, omega-3 PUFA, and selected micronutrients on these pathways, and their potential role in modulating sarcopenia, warranting further clinical investigation.

Vitamin D levels and oxidative stress markers in patients hospitalized with COVID-19

Background

COVID-19 is characterized by the presence of oxidative stress. Vitamin D status has been reviewed as one of the factors that may affect disease severity. The aim of this study was to assess the relationship between serum vitamin D levels, oxidative stress markers and disease severity in hospitalized COVID-19 patients.

Methods

Vitamin D levels were measured in 33 patients with COVID-19. The total antioxidant power and plasma peroxides were determined in serum.

Results

Severe COVID-19 patients have lower vitamin D levels (18.39 ± 2.29 ng/mL vs. 28.47 ± 3.05 ng/mL, p < .05) and higher oxidative stress compared to the moderate group. When divided according to serum vitamin D levels, significantly higher values of LDH (604.8 ± 76.98 IU/mL vs. 261.57 ± 47.33 IU/mL) and D-dimer (5978 ± 2028ng/mL vs. 977.7 ± 172 ng/mL) were obtained in the group with vitamin D below 30 ng/mL, followed with significantly higher levels of plasma peroxides (d-ROMs: 414.9 ± 15.82 U.Carr vs. 352.4 ± 18.77 U.Carr; p < .05) and oxidative stress index (OSI: 92.25 ± 6.60 vs. 51.89 ± 6.45; p < .001).

Conclusion

The presented data provide a justification to consider vitamin D as an important factor that could ameliorate disease severity through its anti-inflammatory and antioxidant effects.

Organic zinc and manganese and 25-hydroxycholecalciferol improves eggshell thickness in late-phase laying hens

The aim of this study was to evaluate the effects of organic micromineral zinc (Zn) and manganese (Mn) and 25-hydroxycholecalciferol supplementation in late-phase laying hens' diets on performance, egg quality, lipid stability of fresh and stored eggs, and bone quality. The treatments were a basal diet and diets supplemented with 32 mg Zn-Met/kg diet; 26 mg Mn-Met/kg diet; 32 mg Zn-Met/kg diet and 26 mg Mn-Met/kg diet; 1500 IU 25-hydroxycholecalciferol/kg diet; 32 mg Zn-Met/kg diet; 26 mg Mn-Met/kg diet; and 1500 IU 25-hydroxycholecalciferol/kg diet. On performance, the birds supplemented with organic manganese had the lowest feed intake. Regarding egg quality, the birds supplemented with Zn-Met and Mn-Met, with 25-hydroxycholecalciferol alone, and with Zn-Met, Mn-Met and 25-hydroxycholecalciferol presented a greater eggshell thickness than those receiving the basal diet. Lipid stability of the yolk varied only according to storage time. No effect of supplementation was observed on bone quality. Supplementation with Zn-Met and Mn-Met, or associated with 25-hydroxycholecalciferol, or 25-hydroxycholecalciferol alone, improved eggshell thickness in aged white layers. However, the associated or isolated supplementation with these nutrients did not influence performance, lipid stability of fresh and stored egg yolk or bone quality.

Potential Effects of Melatonin and Micronutrients on Mitochondrial Dysfunction during a Cytokine Storm Typical of Oxidative/Inflammatory Diseases

Exaggerated oxidative stress and hyper-inflammation are essential features of oxidative/inflammatory diseases. Simultaneously, both processes may be the cause or consequence of mitochondrial dysfunction, thus establishing a vicious cycle among these three factors. However, several natural substances, including melatonin and micronutrients, may prevent or attenuate mitochondrial damage and may preserve an optimal state of health by managing the general oxidative and inflammatory status. This review aims to describe the crucial role of mitochondria in the development and progression of multiple diseases as well as the close relationship among mitochondrial dysfunction, oxidative stress, and cytokine storm. Likewise, it attempts to summarize the main findings related to the powerful effects of melatonin and some micronutrients (vitamins and minerals), which may be useful (alone or in combination) as therapeutic agents in the treatment of several examples of oxidative/inflammatory pathologies, including sepsis, as well as cardiovascular, renal, neurodegenerative, and metabolic disorders.

Vitamin D Deficiency and Risk of Metabolic Syndrome in Aging Men

The elderly population is rapidly increasing; hence, the disability due to age-related diseases has become an important socioeconomic burden. Amongst age-related diseases cardiovascular ones (CVD) have a huge impact on morbidity and mortality and are associated with metabolic syndrome (MetS). Several studies investigated the role of hypovitaminosis D in the pathogenesis of MetS and of CVD, this review unravels the relationship between aging/senescence, vitamin D, gender, and pathogenesis of MetS.

Implications of Oxidative Stress and Potential Role of Mitochondrial Dysfunction in COVID-19: Therapeutic Effects of Vitamin D

Due to its high degree of contagiousness and like almost no other virus, SARS-CoV-2 has put the health of the world population on alert. COVID-19 can provoke an acute inflammatory process and uncontrolled oxidative stress, which predisposes one to respiratory syndrome, and in the worst case, death. Recent evidence suggests the mechanistic role of mitochondria and vitamin D in the development of COVID-19. Indeed, mitochondrial dynamics contribute to the maintenance of cellular homeostasis, and its uncoupling involves pathological situations. SARS-CoV-2 infection is associated with altered mitochondrial dynamics with consequent oxidative stress, pro-inflammatory state, cytokine production, and cell death. Furthermore, vitamin D deficiency seems to be associated with increased COVID-19 risk. In contrast, vitamin D can normalize mitochondrial dynamics, which would improve oxidative stress, pro-inflammatory state, and cytokine production. Furthermore, vitamin D reduces renin–angiotensin–aldosterone system activation and, consequently, decreases ROS generation and improves the prognosis of SARS-CoV-2 infection. Thus, the purpose of this review is to deepen the knowledge about the role of mitochondria and vitamin D directly involved in the regulation of oxidative stress and the inflammatory state in SARS-CoV-2 infection. As future prospects, evidence suggests enhancing the vitamin D levels of the world population, especially of those individuals with additional risk factors that predispose to the lethal consequences of SARS-CoV-2 infection.

Cholecalciferol abolishes depressive-like behavior and hippocampal glucocorticoid receptor impairment induced by chronic corticosterone administration in mice

Several attempts have been made to understand the role of cholecalciferol (vitamin D₃) in the modulation of neuropsychiatric disorders. Notably, the deficiency of vitamin D₃ is considered a pandemic and has been postulated to enhance the risk of major depressive disorder (MDD). Therefore, this study aims to investigate the antidepressant-like effect of cholecalciferol in a mouse model of depression induced by corticosterone, and the possible role of glucocorticoid receptors (GR), NLRP3 and autophagic pathways in this effect. Corticosterone administration (20 mg/kg, p.o., for 21 days) significantly increased the immobility time and grooming latency, as well as reduced the total time spent grooming in mice subjected to the tail suspension test (TST) and splash test (ST), respectively. Importantly, these behavioral alterations were associated with reduced GR immunocontent in the hippocampus of mice. Conversely, the repeated administration of cholecalciferol (2.5 μg/kg, p.o.) in the last 7 days of corticosterone administration was effective to prevent the increased immobility time in the TST and the reduced time spent grooming in the ST, and partially abolished the increase in the grooming latency induced by corticosterone, suggesting its antidepressant-like effect. These behavioral effects were similar to those exerted by fluoxetine (10 mg/kg, p.o.). Moreover, the corticosterone-induced reduction on hippocampal GR immunocontent was not observed in mice treated with cholecalciferol. Additionally, cholecalciferol treatment per se reduced the immunocontent of NLRP3 inflammasome-related proteins ASC, caspase-1, and TXNIP in the hippocampus of mice. No alterations on hippocampal immunocontent of the autophagic-related proteins phospho-mTORC1, beclin-1, and LC3A/B were observed following cholecalciferol treatment and/or corticosterone administration. Collectively, our results provide insights into the effects of cholecalciferol in depression-related behaviors that seem to be related, at least in part, to GR modulation.

Maternal Hyperhomocysteinemia Induces Neuroinflammation and Neuronal Death in the Rat Offspring Cortex

Maternal hyperhomocysteinemia is one of the common complications of pregnancy that causes offspring cognitive deficits during postnatal development. In the present work, we evaluated the effect of prenatal hyperhomocysteinemia on structural and ultrastructural organization, neuronal and glial cell number, apoptosis (caspase-3 content and activity), inflammatory markers (tumor necrosis factor-α, interleukin-6, and interleukin-1β), and p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation in the offspring brain cortex in early ontogenesis. Wistar female rats received methionine (0.6 g/kg body weight) by oral administration during pregnancy. Histological and biochemical analyses of 5- and 20-day-old pups' cortical tissue were performed. Lysosome accumulation and other neurodegenerative changes in neurons of animals with impaired embryonic development were investigated by electron microscopy. Neuronal staining (anti-NeuN) revealed a reduction in neuronal number, accompanied by increasing of caspase-3 active form protein level and activity. Maternal hyperhomocysteinemia also elevated the number of astroglial and microglial cells and increased expression of interleukin-1β and p38 MAPK phosphorylation, which indicates the development of neuroinflammatory processes.

Homocysteine and age-associated disorders

There are numerous theories of aging, a process which still seems inevitable. Aging leads to cancer and multi-systemic disorders as well as chronic diseases. Decline in age- associated cellular functions leads to neurodegeneration and cognitive decline that affect the quality of life. Accumulation of damage, mutations, metabolic changes, failure in cellular energy production and clearance of altered proteins over the lifetime, and hyperhomocysteinemia, ultimately result in tissue degeneration. The decline in renal functions, nutritional deficiencies, deregulation of methionine cycle and deficiencies of homocysteine remethylation and transsulfuration cofactors cause elevation of homocysteine with advancing age. Abnormal accumulation of homocysteine is a risk factor of cardiovascular, neurodegenerative and chronic kidney disease. Moreover, approximately 50% of people, aged 65 years and older develop hypertension and are at a high risk of developing cardiovascular insufficiency and incurable neurodegenerative disorders. Increasing evidence suggests inverse relation between cognitive impairment, cerebrovascular and cardiovascular events and renal function. Oxidative stress, inactivation of nitric oxide synthase pathway and mitochondria dysfunction associated with impaired homocysteine metabolism lead to aging tissue degeneration. In this review, we examine impact of high homocysteine levels on changes observed with aging that contribute to development and progression of age associated diseases.

Neuroprotective role of vitamin D in primary neuronal cortical culture

Background

A role of Vitamin D in brain development and function has been gaining support over the last decade. There are compelling pieces of evidence that suggest vitamin D may have a neuroprotective role. The administration of vitamin D or its metabolites has been shown to reduce neurological injury and/or neurotoxicity in a variety of animal systems. The detail biochemical mechanism mediating neurons, to its ability to withstand greater oxidative stress in the presence of Vitamin D is unclear. This study was undertaken to study the biochemical effect of treatments of primary cortical neuronal cultures, with the active form of vitamin D(1,25(OH)₂D3), against the induced oxidative stress.

Methods

Primary neuronal cultures from cerebral cortex were set up from neonatal (from 6 to 7 days old) Wister Rat's brain. Different doses of [1,25(OH)₂D₃], ranges from 0 to 1 μg/ml, was added to the culture medium and the cells were cultured in its presence for 24 h to 120 h. The effect of induced extracellular oxidative stress was measured by subjecting these cultured cells with 0.5 mM H₂O₂ for 2 h, prior to collection of condition medium and the cell pellet for biochemical assay. The control and H₂O₂ treated cultures were maintained in similar culture conditions, for similar periods of time without any [1,25(OH)₂D₃] treatments.

Result

The optimum concentration of [1,25(OH)₂D₃] for treatment of primary cortical neuronal cultures was found to be 0.25 μg/ml by Trypan exclusion assay and MTT assay. Pre-treatments of cultured neuronal cells with 0.25 μg/ml of [1,25(OH)₂D₃] caused significantly increased levels of reduced glutathione, accompanied by a similar increase in the enzyme levels of GST, to neutralize the induced oxidative stress by H₂O₂. The level of Lipid peroxidation was significantly higher in the cells treated with H₂O₂ alone, but it was completely reversed in the neuronal cultures pre-treated with [1,25(OH)₂D₃]. The levels of Catalase enzyme also significantly reduced (≥0.05) in the [1,25(OH)₂D₃] pre-treated neuronal cultures.

Conclusion

We concluded that the systemic treatment of primary neuronal cultures with [1,25(OH)₂D₃] gave better protection to neurons against the induced oxidative stress, as shown by quantitative measurements of various biomarkers of oxidative stress. This study also suggested that Vitamin D is vital for the growth, survival, and proliferation of the neurons and hence it has a potential therapeutic role against various neurodegenerative diseases.

Cholecalciferol counteracts depressive-like behavior and oxidative stress induced by repeated corticosterone treatment in mice

Depression is one of the most frequent neuropsychiatric diseases in the western world and its physiological causes are not yet fully understood. Since the available antidepressants failed to provide a complete illness remission, the diversification of the therapy in the management of depression could be a useful contribution. The present study aimed to investigate the cholecalciferol capability to revert depressive-like behavior induced by chronic corticosterone (CORT) treatment in mice and its implication on the oxidative stress modulation. Sixty minutes after having orally received different doses of cholecalciferol, adult male mice were evaluated in the forced swimming and tail suspension tests, whereas in the seven-day treatment they were only tested in tail suspension. Additionally, for 21 days, the animals received CORT (20 mg/kg, p.o.) and cholecalciferol or fluoxetine, once a day for the last 7-days of the CORT treatment. Moreover, the markers of oxidative stress, lipid peroxidation, protein carbonyl and nitrite levels were assessed in the plasma and brain's mice after the splash and tail suspension tests. It was observed that corticosterone treatment resulted in depressive-like behavior with established oxidative stress in mice, while cholecalciferol ameliorated both, behavioral (immobility time and grooming latency) and biochemical (protein carbonyl and nitrite levels) changes induced by CORT model, suggesting that cholecalciferol has antidepressant-like effect with the involvement of the oxidative stress modulation.

Vitamin D3 attenuates cognitive deficits and neuroinflammatory responses in ICV-STZ induced sporadic Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by intracellular neurofibrillary tangles and extracellular Aβ deposition. Growing experimental evidence indicate diverse biological effects of vitamin D₃ including antioxidant, neuroprotective, anti-inflammatory and cardiovascular benefits. However, the underlying neuroprotective mechanism of vitamin D₃ is still largely elusive. Therefore, the present study was aimed to investigate the neuroprotective effects of vitamin D₃ on ICV-STZ induced sporadic AD. Our study demonstrated that vitamin D3 pretreatment significantly improved spatial learning and memory functions and effectively mitigated ICV-STZ mediated neuronal oxidative stress, mitochondrial aberrations and improved cholinergic functions. Moreover, vitamin D₃ attenuated hippocampal neuroinflammatory response and reduced neuronal death in cortex and hippocampus. Our findings indicated that prophylactic vitamin D₃ supplementation ameliorated ICV-STZ mediated neurobehavioral alterations, oxidative stress and neuroinflammation thereby improving cholinergic functions and reversed degenerative changes in brain. Thus, our study further provides evidence for its therapeutic supplementation for various neurodegenerative disorders including AD.

Homocysteine Induces Glial Reactivity in Adult Rat Astrocyte Cultures

Astrocytes are dynamic glial cells associated to neurotransmitter systems, metabolic functions, antioxidant defense, and inflammatory response, maintaining the brain homeostasis. Elevated concentrations of homocysteine (Hcy) are involved in the pathogenesis of age-related neurodegenerative disorders, such as Parkinson and Alzheimer diseases. In line with this, our hypothesis was that Hcy could promote glial reactivity in a model of cortical primary astrocyte cultures from adult Wistar rats. Thus, cortical astrocytes were incubated with different concentrations of Hcy (10, 30, and 100 μM) during 24 h. After the treatment, we analyzed cell viability, morphological parameters, antioxidant defenses, and inflammatory response. Hcy did not induce any alteration in cell viability; however, it was able to induce cytoskeleton rearrangement. The treatment with Hcy also promoted a significant decrease in the activities of Na⁺, K⁺ ATPase, superoxide dismutase (SOD), and glutathione peroxidase (GPx), as well as in the glutathione (GSH) content. Additionally, Hcy induced an increase in the pro-inflammatory cytokine release. In an attempt to elucidate the putative mechanisms involved in the Hcy-induced glial reactivity, we measured the nuclear factor kappa B (NFκB) transcriptional activity and heme oxygenase 1 (HO-1) expression, which were activated and inhibited by Hcy, respectively. In summary, our findings provide important evidences that Hcy modulates critical astrocyte parameters from adult rats, which might be associated to the aging process.

Crosstalk between sphingolipids and vitamin D3: potential role in the nervous system

Sphingolipids are both structural and bioactive compounds. In particular, ceramide and sphingosine 1-phosphate regulate cell fate, inflammation and excitability. 1-α,25-dihydroxyvitamin D3 (1,25(OH)₂ D₃ ) is known to play an important physiological role in growth and differentiation in a variety of cell types, including neural cells, through genomic actions mediated by its specific receptor, and non-genomic effects that result in the activation of specific signalling pathways. 1,25(OH)₂ D₃ and sphingolipids, in particular sphingosine 1-phosphate, share many common effectors, including calcium regulation, growth factors and inflammatory cytokines, but it is still not known whether they can act synergistically. Alterations in the signalling and concentrations of sphingolipids and 1,25(OH)₂ D₃ have been found in neurodegenerative diseases and fingolimod, a structural analogue of sphingosine, has been approved for the treatment of multiple sclerosis. This review, after a brief description of the role of sphingolipids and 1,25(OH)₂ D₃ , will focus on the potential crosstalk between sphingolipids and 1,25(OH)₂ D₃ in neural cells.

Effect of Hyperhomocysteinemia on Redox Balance and Redox Defence Enzymes in Ischemia-Reperfusion Injury and/or After Ischemic Preconditioning in Rats

Increased level of homocysteine (hHcy) in plasma is an accompanying phenomenon of many diseases, including a brain stroke. This study determines whether hyperhomocysteinemia (which is a risk factor of brain ischemia) itself or in combination with ischemic preconditioning affects the ischemia-induced neurodegenerative changes, generation of reactive oxygen species (ROS), lipoperoxidation, protein oxidation, and activity of antioxidant enzymes in the rat brain cortex. The hHcy was induced by subcutaneous administration of homocysteine (0.45 μmol/g body weight) twice a day in 8 h intervals for 14 days. Rats were preconditioned by 5 min ischemia. Two days later, 15 min of global forebrain ischemia was induced by four vessel's occlusion. The study demonstrates that in the cerebral cortex, hHcy alone induces progressive neuronal cell death and morphological changes. Neuronal damage was associated with the pro-oxidative effect of hHcy, which leads to increased ROS formation, peroxidation of lipids and oxidative alterations of cortical proteins. Ischemic reperfusion injury activates degeneration processes and de-regulates redox balance which is aggravated under hHcy conditions and leads to the augmented lipoperoxidation and protein oxidation. If combined with hHcy, ischemic preconditioning could preserve the neuronal tissue from lethal ischemic effect and initiates suppression of lipoperoxidation, protein oxidation, and alterations of redox enzymes with the most significant effect observed after prolonged reperfusion. Increased prevalence of hyperhomocysteinemia in the Western population and crucial role of elevated Hcy level in the pathogenesis of neuronal disorders makes this amino acid as an interesting target for future research. Understanding the multiple etiological mechanisms and recognition of the co-morbid risk factors that lead to the ischemic/reperfusion injury and ischemic tolerance is therefore important for developing therapeutic strategies in human brain stroke associated with the elevated level of Hcy.

1,25-Dihydroxyvitamin D3 prevents deleterious effects of homocysteine on mitochondrial function and redox status in heart slices

Because homocysteine (Hcy) is a risk factor for cardiovascular disease, and vitamin D deficiency can contribute to cardiovascular pathologies. In the present study, we tested the hypothesis that Hcy could impair energy metabolism, mitochondrial function, and redox status in heart slices of Wistar rats and that 1,25-dihydroxivitamin D₃ (calcitriol) treatment could prevent such effects. Heart slices were first pretreated with 3 different concentrations of calcitriol (50, 100, and 250nmol/L) for 30minutes at 37°C, after which Hcy was added to promote deleterious effects on metabolism. After 1 hour of incubation, the samples were washed, homogenized, and stored at -80°C before analysis. The results showed that Hcy caused changes in energy metabolism (respiratory chain enzymes), mitochondrial function, and cell viability. Homocysteine also induced oxidative stress, increasing lipid peroxidation, reactive oxygen species generation, and protein damage. An imbalance in antioxidant enzymes was also observed. Calcitriol (50nmol/L) reverted the effect of Hcy on the parameters tested, except for the immunocontent of catalase. Both treatments (calcitriol and Hcy) did not alter the vitamin D receptor immunocontent, which combined with the fact that our ex vivo model is acute, suggesting that the beneficial effect of calcitriol occurs directly through antioxidative mechanisms and not via gene expression. In this study, we show that Hcy impairs mitochondrial function and induces changes in the redox status in heart slices, which were reverted by calcitriol. These findings suggest that calcitriol may be a preventive/therapeutic strategy for complications caused by Hcy.

Role of Homocysteine in the Ischemic Stroke and Development of Ischemic Tolerance

Homocysteine (Hcy) is a toxic, sulfur-containing intermediate of methionine metabolism. Hyperhomocysteinemia (hHcy), as a consequence of impaired Hcy metabolism or defects in crucial co-factors that participate in its recycling, is assumed as an independent human stroke risk factor. Neural cells are sensitive to prolonged hHcy treatment, because Hcy cannot be metabolized either by the transsulfuration pathway or by the folate/vitamin B12 independent remethylation pathway. Its detrimental effect after ischemia-induced damage includes accumulation of reactive oxygen species (ROS) and posttranslational modifications of proteins via homocysteinylation and thiolation. Ischemic preconditioning (IPC) is an adaptive response of the CNS to sub-lethal ischemia, which elevates tissues tolerance to subsequent ischemia. The main focus of this review is on the recent data on homocysteine metabolism and mechanisms of its neurotoxicity. In this context, the review documents an increased oxidative stress and functional modification of enzymes involved in redox balance in experimentally induced hyperhomocysteinemia. It also gives an interpretation whether hyperhomocysteinemia alone or in combination with IPC affects the ischemia-induced neurodegenerative changes as well as intracellular signaling. Studies document that hHcy alone significantly increased Fluoro-Jade C- and TUNEL-positive cell neurodegeneration in the rat hippocampus as well as in the cortex. IPC, even if combined with hHcy, could still preserve the neuronal tissue from the lethal ischemic effects. This review also describes the changes in the mitogen-activated protein kinase (MAPK) protein pathways following ischemic injury and IPC. These studies provide evidence for the interplay and tight integration between ERK and p38 MAPK signaling mechanisms in response to the hHcy and also in association of hHcy with ischemia/IPC challenge in the rat brain. Further investigations of the protective factors leading to ischemic tolerance and recognition of the co-morbid risk factors would result in development of new avenues for exploration of novel therapeutics against ischemia and stroke.