S-adenosyl-L-methionine protects the hippocampal CA1 neurons from the ischemic neuronal death in rat

Neuroprotective Effect of Platinum Nanoparticles Is Not Associated with Their Accumulation in the Brain of Rats

Platinum nanoparticles (nPts) have neuroprotective/antioxidant properties, but the mechanisms of their action in cerebrovascular disease remain unclear. We investigated the brain bioavailability of nPts and their effects on brain damage, cerebral blood flow (CBF), and development of brain and systemic oxidative stress (OS) in a model of cerebral ischemia (hemorrhage + temporary bilateral common carotid artery occlusion, tBCAO) in rats. The nPts (0.04 g/L, 3 ± 1 nm diameter) were administered to rats (N = 19) intraperitoneally at the start of blood reperfusion. Measurement of CBF via laser Doppler flowmetry revealed that the nPts caused a rapid attenuation of postischemic hypoperfusion. The nPts attenuated the apoptosis of hippocampal neurons, the decrease in reduced aminothiols level in plasma, and the glutathione redox status in the brain, which were induced by tBCAO. The content of Pt in the brain was extremely low (≤1 ng/g). Thus, nPts, despite the extremely low brain bioavailability, can attenuate the development of brain OS, CBF dysregulation, and neuronal apoptosis. This may indicate that the neuroprotective effects of nPts are due to indirect mechanisms rather than direct activity in the brain tissue. Research on such mechanisms may offer a promising trend in the treatment of acute disorders of CBF.

H2S attenuates injury after ischemic stroke by diminishing the assembly of CaMKII with ASK1-MKK3-p38 signaling module

Cerebral ischemia/reperfusion (I/R) injury is a leading cause of learning and memory dysfunction. Hydrogen sulfide (H₂S) has been shown to confer neuroprotection in various neurodegenerative diseases, including cerebral I/R-induced hippocampal CA1 injury. However, the underlying mechanisms have not been completely understood. In the present study, rats were pretreated with SAM/NaHS (SAM, an H₂S agonist, and NaHS, an H₂S donor) only or SAM/NaHS combined with CaM (an activator of CaMKII) prior to cerebral ischemia. The Morris water maze test demonstrated that SAM/NaHS could alleviate learning and memory impairment induced by cerebral I/R injury. Cresyl violet staining was used to show the survival of hippocampal CA1 pyramidal neurons. SAM/NaHS significantly increased the number of surviving cells, whereas CaM weakened the protection induced by SAM/NaHS. The immunohistochemistry results indicated that the number of Iba1-positive microglia significantly increased after cerebral I/R. Compared with the I/R group, the number of Iba1-positive microglia in the SAM/NaHS groups significantly decreased. Co-Immunoprecipitation and immunoblotting were conducted to demonstrate that SAM/NaHS suppressed the assembly of CaMKII with the ASK1-MKK3-p38 signal module after cerebral I/R, which decreased the phosphorylation of p38. In contrast, CaM significantly inhibited the effects of SAM/NaHS. Taken together, the results suggested that SAM/NaHS could suppress cerebral I/R injury by downregulating p38 phosphorylation via decreasing the assembly of CaMKII with the ASK1-MKK3-p38 signal module.

Remote ischemic conditioning as a cytoprotective strategy in vasculopathies during hyperhomocysteinemia: An emerging research perspective

Higher levels of nonprotein amino acid homocysteine (Hcy), that is, hyperhomocysteinemia (HHcy) (~5% of general population) has been associated with severe vasculopathies in different organs; however, precise molecular mechanism(s) as to how HHcy plays havoc with body's vascular networks are largely unknown. Interventional modalities have not proven beneficial to counter multifactorial HHcy's effects on the vascular system. An ancient Indian form of exercise called 'yoga' causes transient ischemia as a result of various body postures however the cellular mechanisms are not clear. We discuss a novel perspective wherein we argue that application of remote ischemic conditioning (RIC) could, in fact, deliver anticipated results to patients who are suffering from chronic vascular dysfunction due to HHcy. RIC is the mechanistic phenomenon whereby brief episodes of ischemia-reperfusion events are applied to distant tissues/organs; that could potentially offer a powerful tool in mitigating chronic lethal ischemia in target organs during HHcy condition via simultaneous reduction of inflammation, oxidative and endoplasmic reticulum stress, extracellular matrix remodeling, fibrosis, and angiogenesis. We opine that during ischemic conditioning our organs cross talk by releasing cellular messengers in the form of exosomes containing messenger RNAs, circular RNAs, anti-pyroptotic factors, protective cytokines like musclin, transcription factors, small molecules, anti-inflammatory, antiapoptotic factors, antioxidants, and vasoactive gases. All these could help mobilize the bone marrow-derived stem cells (having tissue healing properties) to target organs. In that context, we argue that RIC could certainly play a savior's role in an unfortunate ischemic or adverse event in people who have higher levels of the circulating Hcy in their systems.

Metabolomic changes in the mouse retina after optic nerve injury

In glaucoma, although axonal injury drives retinal ganglion cell (RGC) death, little is known about the underlying pathomechanisms. To provide new mechanistic insights and identify new biomarkers, we combined latest non-targeting metabolomics analyses to profile altered metabolites in the mouse whole retina 2, 4, and 7 days after optic nerve crush (NC). Ultra-high-performance liquid chromatography quadrupole time-of-flight mass spectrometry and liquid chromatography Fourier transform mass spectrometry covering wide spectrum of metabolites in combination highlighted 30 metabolites that changed its concentration after NC. The analysis displayed similar changes for purine nucleotide and glutathione as reported previously in another animal model of axonal injury and detected multiple metabolites that increased after the injury. After studying the specificity of the identified metabolites to RGCs in histological sections using imaging mass spectrometry, two metabolites, i.e., L-acetylcarnitine and phosphatidylcholine were increased not only preceding the peak of RGC death in the whole retina but also at the RGC layer (2.3-fold and 1.2-fold, respectively). These phospholipids propose novel mechanisms of RGC death and may serve as early biomarkers of axonal injury. The combinatory metabolomics analyses promise to illuminate pathomechanisms, reveal biomarkers, and allow the discovery of new therapeutic targets of glaucoma.

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.

Mechanisms involved in the ischemic tolerance in brain: effect of the homocysteine

Hyperhomocysteinemia (hHCy) is recognized as a co-morbid risk factor of human stroke. It also aggravates the ischemia-induced injury by increased production of reactive oxygen species, and by the homocysteinylation and thiolation of functional proteins. Ischemic preconditioning represents adaptation of the CNS to sub-lethal ischemia, resulting in increased brain tolerance to subsequent ischemia. We present here an overview of recent data on the homocysteine (Hcy) metabolism and on the genetic and metabolic causes of hHCy-related neuropathologies in humans. In this context, the review documents for an increased oxidative stress and for the functional modifications of enzymes involved in the redox balance in experimentally induced hHCy. Hcy metabolism leads also to the redox imbalance and increased oxidative stress resulting in elevated lipoperoxidation and protein oxidation, the products known to be included in the neuronal degeneration. Additionally, we examine the effect of the experimental hHCy in combination with ischemic insult, and/or with the preischemic challenge on the extent of neuronal degeneration as well as the intracellular signaling and the regulation of DNA methylation. The review also highlights that identification of the effects of co-morbid factors in the mechanisms of ischemic tolerance mechanisms would lead to improved therapeutics, especially the brain tissue.

S-adenosyl-L-methionine restores photoreceptor function following acute retinal ischemia

The survival and function of retinal neurons is dependent on mitochondrial energy generation and its intracellular distribution by creatine kinase. Post ischemic disruption of retinal creatine synthesis, creatine kinase activity, or transport of creatine into neurons may impair retinal function. S-adenosyl-L-methionine (SAMe) is required for creatine synthesis, phosphatidylcholine and glutathione synthesis, and transducin methylation. These reactions are essential for photoreceptor function but may be downregulated after ischemia due to a reduction in SAMe. Our aim was to determine whether administration of SAMe after ischemia could improve retinal function. Unilateral retinal ischemia was induced in adult rats by increasing the intraocular pressure to 110 mm Hg for 60 min. Immediately after the ischemic insult, SAMe was injected into the vitreous (100 microM), followed by oral administration (69 mg/kg/day) for 5 or 10 days. Retinal function (electroretinography), histology, and creatine transporter (CRT-1) expression were analyzed. Photoreceptoral responses (R(mP3), S), rod and cone bipolar cell responses (PII), and oscillatory potentials were reduced by the ischemia/reperfusion insult. Although SAMe treatment ameliorated the ischemia-induced histological damage by day 5, there was no improvement in retinal function and the intensity of CRT-1 labeling in ischemic retinas was markedly reduced. However, 10 days after ischemia, a recovery in CRT-1 immunolabeling was evident and SAMe supplementation significantly restored photoreceptor function and rod PII responses. In conclusion, these data suggest that creatine transport and methylation reactions, such as creatine synthesis, may be compromised by an ischemic insult contributing to retinal dysfunction and injury. Oral SAMe supplementation after retinal ischemia may provide an effective, safe, and accessible neuroprotective strategy.

Cytidine-5-diphosphocholine supplement in early life induces stable increase in dendritic complexity of neurons in the somatosensory cortex of adult rats

Cytidine-5-diphosphocholine (CDP-choline or citicholine) is an essential molecule that is required for biosynthesis of cell membranes. In adult humans it is used as a memory-enhancing drug for treatment of age-related dementia and cerebrovascular conditions. However the effect of CDP-choline on perinatal brain is not known. We administered CDP-choline to Long Evans rats each day from conception (maternal ingestion) to postnatal day 60 (P60). Pyramidal neurons from supragranular layers 2/3, granular layer 4 and infragranular layer 5 of somatosensory cortex were examined with Golgi–Cox staining at P240. CDP-choline treatment significantly increased length and branch points of apical and basal dendrites. Sholl analysis shows that the complexity of apical and basal dendrites of neurons is maximal in layers 2/3 and layer 5. In layer 4 significant increases were seen in basilar dendritic arborization. CDP-choline did not increase the number of primary basal dendrites on neurons in the somatosensory cortex. Primary cultures from somatosensory cortex were treated with CDP-choline to test its effect on neuronal survival. CDP-choline treatment neither enhanced the survival of neurons in culture nor increased the number of neurites. However significant increases in neurite length, branch points and total area occupied by the neurons were observed. We conclude that exogenous supplementation of CDP-choline during development causes stable changes in neuronal morphology. Significant increase in dendritic growth and branching of pyramidal neurons from the somatosensory cortex resulted in enlarging the surface area occupied by the neurons which we speculate will augment processing of sensory information.

Folate and methylation status in relation to phosphorylated tau protein(181P) and beta-amyloid(1-42) in cerebrospinal fluid

BACKGROUND

Increased plasma total homocysteine (tHcy) is a risk factor for neurological diseases, but the underlying pathophysiology has not been adequately explained.

METHODS

We evaluated concentrations of tHcy, S-adenosyl homocysteine (SAH), S-adenosyl methionine (SAM), folate, and vitamin B(12) in cerebrospinal fluid (CSF) and plasma or serum from 182 patients with different neurological disorders. We measured concentrations of phosphorylated tau protein (P-tau)((181P)) and beta-amyloid(1-42) in the CSF.

RESULTS

Aging was associated with higher concentrations of tHcy and SAH in the CSF, in addition to lower concentrations of CSF folate and lower SAM:SAH ratio. Concentrations of CSF SAH and CSF folate correlated significantly with those of P-tau (r = 0.46 and r = -0.28, respectively). Moreover, P-tau correlated negatively with SAM:SAH ratio (r = -0.40, P <0.001). The association between SAH and higher P-tau was observed in 3 age groups (<41, 41-60, and >60 years). CSF tHcy was predicted by concentrations of CSF cystathionine (beta = 0.478), folate (beta = -0.403), albumin (beta = 0.349), and age (beta = 0.298).

CONCLUSIONS

tHcy concentration in the brain is related to age, B vitamins, and CSF albumin. Increase of CSF SAH is related to increased CSF P-tau; decreased degradation of P-tau might be a plausible explanation. Disturbed methyl group metabolism may be the link between hyperhomocysteinemia and neurodegeneration. Lowering tHcy and SAH might protect the brain by preventing P-tau accumulation.

Ademetionine (S-adenosylmethionine) neuropharmacology: implications for drug therapies in psychiatric and neurological disorders

Ademetionine (S-adenosylmethionine; SAMe) is a ubiquitous metabolite present in all cells and biological fluids, and serves as a methyl donor in a multitude of different methylation reactions involving proteins, phospholipids, catecholamines and DNA. Pharmaceutical preparations of some stable salts of SAMe are available for parenteral and oral use in humans, and have been shown to increase plasma and cerebrospinal fluid SAMe concentrations. In experimental studies administration of SAMe is associated with increases in brain monoamine neurotransmitters and b-adrenergic and muscarinic receptor functions. These neuropharmacological effects are postulated to be involved in the antidepressant activity of SAMe which has been confirmed in numerous controlled studies. Preliminary studies indicate that SAMe has therapeutic potential in the treatment of other CNS disorders including dementia, acquired immune deficiency syndrome (AIDS)-associated myelopathy, and brain ischaemia. This review will focus on recent experimental and clinical aspects of SAMe in the central nervous system, and the therapeutic use in psychiatric and neurological disorders.

Possible neuroprotective effects of lecithin and alpha-tocopherol alone or in combination against ischemia/reperfusion insult in rat brain

A close correlation exists between ischemia/reperfusion (I/R)-induced insult and the release of free radicals. Lecithin is a polyunsaturated phosphatidylcholine that corresponds to the phosphatidylcholine molecule. Phosphatidylcholines are high-energy functional and structural elements of all biologic membranes. alpha-Tocopherol is the major lipid-soluble chain-breaking antioxidant in the body tissues and effectively protects against neuronal damage. Therefore, we studied the effect of lecithin (300 mg/kg, p.o., 14 days) and alpha-tocopherol (200 mg/kg, p.o., 14 days), alone or in combination, on the brain redox state during I/R. Adult male Wistar rats were subjected to global ischemia by the occlusion of the two carotid arteries 24 h after the last dose of drug administration. Reperfusion was carried out 1 h after induction of ischemia and lasted for another hour. Brain lipid peroxides (MDA) and glutathione (GSH) contents, as well as superoxide dismutase (SOD) and catalase (CAT) activities were assessed. The results showed that I/R elevated brain lipid peroxides content which was accompanied by a reduction in both antioxidant enzyme activities, however, brain GSH level remained unaltered. Lecithin, alpha-tocopherol and their combination restored MDA content, as well as CAT activity with a slight tendency to normalize SOD activity. We conclude that lecithin has a possible neuroprotective effect partly through its antioxidant action which is comparable to that of alpha-tocopherol.

Citicoline decreases phospholipase A2 stimulation and hydroxyl radical generation in transient cerebral ischemia

Neuroprotection by citicoline (CDP-choline) in transient cerebral ischemia has been demonstrated previously. Citicoline has undergone several Phase III clinical trials for stroke, and is being evaluated for treatment of Alzheimer's and Parkinson's diseases. Phospholipid degradation and generation of reactive oxygen species (ROS) are major factors causing neuronal injury in CNS trauma and neurodegenerative diseases. Oxidative metabolism of arachidonic acid (released by the action of phospholipases) contributes to ROS generation. We examined the effect of citicoline on phospholipase A(2) (PLA(2)) activity in relation to the attenuation of hydroxyl radical (OH.) generation after transient forebrain ischemia of gerbil. PLA(2) activity (requires mM Ca(2+)) increased significantly (P < 0.05) in both membrane (50.2 +/- 2.2 pmol/min/mg protein compared to sham 35.9 +/- 3.2) and mitochondrial fractions (77.0 +/- 1.2 pmol/min/mg protein compared to sham 33.9 +/- 1.2) after cerebral ischemia and 2 hr reperfusion in gerbil, which was significantly attenuated (P < 0.01) by citicoline (membrane, 39.9. +/- 2.2 and mitochondria, 41.9 +/- 3.2 pmol/min/mg protein). In vitro, citicoline and its components cytidine and choline had no effect on PLA(2) activity, and thus citicoline as such is not a PLA(2) inhibitor. Ischemia/reperfusion resulted in significant OH. generation (P < 0.01) and citicoline significantly (P < 0.01) attenuated their formation (expressed as 2,3-dihydroxybenzoic acid/salicylate ratio; ischemia/24 hr reperfusion, 6.30 +/- 0.23; sham, 2.56 +/- 0.27; ischemia/24 hr reperfusion + citicoline, 4.85 +/- 0.35). These results suggest that citicoline affects PLA(2) stimulation and decreases OH. generation after transient cerebral ischemia.

Citicoline mechanisms and clinical efficacy in cerebral ischemia

Citicoline, an intermediate in the biosynthesis of phosphatidylcholine (PtdCho), has shown beneficial effects in various CNS injury models and neurodegenerative diseases. PtdCho hydrolysis by phospholipase A(2) (PLA(2)) after cerebral ischemia and reperfusion yields arachidonic acid (ArAc) and lyso-PtdCho. ArAc oxidative metabolism results in formation of reactive oxygen species and lipid peroxides. Lyso-PtdCho could inhibit activity of cytidine triphosphate-phosphocholine cytidylyltransferase (the rate-limiting enzyme in PtdCho biosynthesis), resulting in impaired PtdCho synthesis. Citicoline significantly increased glutathione levels and attenuated release of ArAc and the loss of PtdCho, cardiolipin, and sphingomyelin following transient cerebral ischemia. These effects could be explained by an effect of citicoline on PLA(2). Based on these observations, a mechanism has been hypothesized. This Mini-Review summarizes recent experimental data on the effects of citicoline in cerebral ischemia and evaluates several factors that might have hindered efficacy of citicoline in stroke clinical trials in the United States. Clinical stroke trials of citicoline in Europe and Japan have demonstrated beneficial effects. U.S. trials shown only marginal effects, which might be due to the 24 hr time window, the dose and route of administration, and the stringency of the primary outcome parameters. Recent evaluation of U.S. clinical data suggests that reduction of infarct growth may be a more sensitive measure of the citicoline effect than improvement on the NIH Stroke Scale (NIHSS) by > or =7 points. The citicoline neuroprotective mechanism has not been clearly identified, and its potential in stroke treatment might still be fully recognized in the United States. The clinical efficacy of citicoline should be examined further in light of the recent phase III stroke clinical trials and experimental data for cerebral ischemia.

DNA methyltransferase contributes to delayed ischemic brain injury

DNA methylation is important for controlling the profile of gene expression and is catalyzed by DNA methyltransferase (MTase), an enzyme that is abundant in brain. Because significant DNA damage and alterations in gene expression develop as a consequence of cerebral ischemia, we measured MTase activity in vitro and DNA methylation in vivo after mild focal brain ischemia. After 30 min middle cerebral artery occlusion (MCAo) and reperfusion, MTase catalytic activity and the 190 kDa band on immunoblot did not change over time. However, [(3)H]methyl-group incorporation into DNA increased significantly in wild-type mice after reperfusion, but not in mutant mice heterozygous for a DNA methyltransferase gene deletion (Dnmt(S/+)). Dnmt(S/+) mice were resistant to mild ischemic damage, suggesting that increased DNA methylation is associated with augmented brain injury after MCA occlusion. Consistent with this formulation, treatment with the MTase inhibitor 5-aza-2'-deoxycytidine and the deacetylation inhibitor trichostatin A conferred stroke protection in wild-type mice. In contrast to mild stroke, however, DNA methylation was not enhanced, and reduced dnmt gene expression was not protective in an ischemia model of excitotoxic/necrotic cell death. In conclusion, our results demonstrate that MTase activity contributes to poor tissue outcome after mild ischemic brain injury.

Regulation of methionine adenosyltransferase activity by the glutathione level in rat liver during ischemia-reperfusion

Hepatic ischemia was induced by clamping the hepatic artery, portal vein, and bile duct. After 15 min of ischemia, the hepatic glutathione (GSH) content rapidly decreased. On the other hand, after the start of reperfusion, the hepatic GSH levels promptly increased and reached a peak at about 1 h, and thereafter decreased to a minimum level by 2 h. Under such conditions, we examined the changes in the methionine adenosyltransferase (MAT) activity in the liver. Though the time course of MAT activity was somewhat delayed compared with that of the hepatic GSH levels, both patterns were substantially similar during ischemia-reperfusion. In contrast to the changes in the MAT activity during ischemia-reperfusion, the levels of MAT protein were unchanged during these periods. When endogenous antioxidant coenzyme Q(10) (CoQ(10)) was administered to rats prior to ischemia, both the reduction in the MAT activity and hepatic GSH levels induced by ischemia-reperfusion were protected. Our findings suggest that CoQ(10) may posttranslationally regulate the MAT activity via the changes in the GSH level in the liver.

Ornithine decarboxylase activity in cerebral post-ischemic reperfusion damage: effect of methionine sulfoximine

Excessive activation of glutamate receptors via the N-methyl-D-aspartate (NMDA) subtype appears to play a role in the sequence of cellular events which lead to irreversible ischemic damage to neurons. Furthermore, NMDA receptor activation induces a stimulation of ornithine decarboxylase (ODC), the rate-limiting enzyme for polyamine (PA) biosynthesis. In order to better understand the role of PA we have measured ODC activity and the effect of methionine sulfoximine (MSO), a molecule able to stimulate ODC, on a model of transient cerebral ischemia. There was a significant increase in ODC activity in the rat cerebral cortex during post-ischemic reperfusion. The treatment with MSO induced a significant decrease in cerebral glutamine synthetase activity accompanied by a marked increase in ODC activity. In MSO-pretreated rats there was a significant decrease in the survival rate when compared to untreated ischemic rats.

Beneficial effects of S-adenosyl-L-methionine on blood-brain barrier breakdown and neuronal survival after transient cerebral ischemia in gerbils

We have studied the beneficial effects of S-adenosyl-L-methionine (SAM) tosylate on blood-brain barrier (BBB) breakdown and neuronal survival after transient cerebral ischemia in gerbils. BBB breakdown experiments were performed in pentobarbital anesthetized gerbils subjected to 10 min of bilateral carotid artery occlusion and 6 h of reperfusion. For BBB breakdown measurements, SAM (120 mg/kg, i.p.) was administered to gerbils just after occlusion and thereafter every hour up to 5 h. Fluorometric measurements quantified the blood-brain permeability tracer, Evans blue (EB). SAM treatment significantly reduced the BBB breakdown as indicated by reduced levels of EB fluorescence. Neuronal count experiments were conducted in gerbils subjected to transient ischemia and 7 days of reperfusion. For neuronal count experiments SAM (15-120 mg/kg) was administered at 6 and 12 h after reperfusion, and twice each day thereafter for 7 days. SAM dose dependently protected the hippocampal CA1 neurons assessed by histopathological methods. SAM has a beneficial effect on the outcome of ischemic injury by reducing the BBB breakdown and neuronal death.

Metabolism and actions of CDP-choline as an endogenous compound and administered exogenously as citicoline

CDP-choline, supplied exogenously as citicoline, has beneficial physiological actions on cellular function that have been extensively studied and characterized in numerous model systems. As the product of the rate-limiting step in the synthesis of phosphatidylcholine from choline, CDP-choline and its hydrolysis products (cytidine and choline) play important roles in generation of phospholipids involved in membrane formation and repair. They also contribute to such critical metabolic functions as formation of nucleic acids, proteins, and acetylcholine. Orally-administered citicoline is hydrolyzed in the intestine, absorbed rapidly as choline and cytidine, resynthesized in liver and other tissues, and subsequently mobilized in CDP-choline synthetic pathways. Citicoline is efficiently utilized in brain cells for membrane lipid synthesis where it not only increases phospholipid synthesis but also inhibits phospholipid degradation. Exogenously administered citicoline prevents, reduces, or reverses effects of ischemia and/or hypoxia in most animal and cellular models studied, and acts in head trauma models to decrease and limit nerve cell membrane damage, restore intracellular regulatory enzyme sensitivity and function, and limit edema. Thus, considerable accumulated evidence supports use of citicoline to enhance membrane maintenance, membrane repair, and neuronal function in conditions such as ischemic and traumatic injuries. Beneficial effects of exogenous citicoline also have been postulated and/or reported in experimental models for dyskinesia, Parkinson's disease, cardiovascular disease, aging, Alzheimer's disease, learning and memory, and cholinergic stimulation.

Polyamines in neurotrauma. Ubiquitous molecules in search of a function

In spite of their abundance, the function of PAs in the adult nervous system remains enigmatic. It is postulated that after trauma, the induction of polyamine metabolism (i.e. the polyamine response), which is inherently transient, is an integral part of a protective biochemical program that is essential for neuronal survival. Several functions ascribed to PAs may assume importance in cellular defense. Thus, regulation of the ionic environment, modulation of signal pathways, control of cellular Ca2+ homeostasis, inhibition of lipid peroxidation, and interaction with nucleic acids are all putative sites for PA action. During maturation, the CNS, unlike the peripheral nervous system, undergoes changes which result in the expression of an incomplete polyamine response after trauma. This may be due to an altered pattern of gene expression, and/or restrictive compartmentalization of the PAs and their metabolizing enzymes. Induction of this partial polyamine response after injury results in a sustained accumulation of putrescine, which by itself may be harmful, without the concomitant increase in spermidine and spermine. Administration of exogenous PAs after trauma exerts a neuroprotective effect. Exogenous PAs are postulated to gain access into cells via an induced uptake system after trauma, and function similarly to newly synthesized PAs. Besides the injured neurons themselves, tissues which are connected or associated with these neurons may be potential targets where PAs could act to stimulate neurotrophic factor production. Based on the neuroprotective effects of PAs in laboratory animals and on their proposed role in mechanisms of neuronal survival, the development of PA-based compounds as therapeutic neuroprotective agents should be pursued.

Polyamines can protect against ischemia-induced nerve cell death in gerbil forebrain

We have previously demonstrated that administration of the polyamines putrescine, spermidine, or spermine can prevent neuronal degeneration in rats during naturally occurring cell death or after injurious treatments such as nerve injury or monosodium glutamate neurotoxicity. The present study demonstrates that also in adult gerbils polyamine treatment can protect forebrain neurons from degeneration after ischemia. Neurons in the hippocampus and striatum were rescued from delayed cell death after brief (5 min) global ischemia in gerbils which were treated with daily injections (10 mg/kg) of polyamines. The evidence accrued, so far, indicates that systemic polyamines can protect a wide variety of central and peripheral neurons from natural or induced degeneration.

Effects of the novel antidepressant S-adenosyl-methionine on alpha 1- and beta-adrenoceptors in rat brain

alpha 1- and beta-adrenoceptors were studied ex vivo in the brains of rats receiving repeated daily treatment with the standard antidepressant imipramine or the atypical antidepressant S-adenosyl-L-methionine (SAM), which has minimal effects on monoamine reuptake or turnover. Consistent with past studies, a decrease in the density of beta receptors at three weeks and an increase in the affinity of alpha 1 receptors for the agonist phenylephrine at one week of treatment was observed with imipramine. By comparison, an increase in the density of beta receptors and a decrease in the affinity of alpha 1 receptors for phenylephrine was observed at one week of treatment with SAM. These changes were no longer apparent at three weeks of treatment. The results suggest that treatment with SAM does lead to changes in adrenergic neurotransmission, but that down regulation of beta receptors or increased agonist affinity of alpha 1 receptors may not be necessary for the production of antidepressant effects.

S-adenosyl-L-methionine. A review of its pharmacological properties and therapeutic potential in liver dysfunction and affective disorders in relation to its physiological role in cell metabolism

S-Adenosyl-L-methionine (SAMe) is a naturally occurring molecule distributed to virtually all body tissues and fluids. It is of fundamental importance in a number of biochemical reactions involving enzymatic transmethylation, contributing to the synthesis, activation and/or metabolism of such compounds as hormones, neurotransmitters, nucleic acids, proteins, phospholipids and certain drugs. The administration of a stable salt of SAMe, either orally or parenterally, has been shown to restore normal hepatic function in the presence of various chronic liver diseases (including alcoholic and non-alcoholic cirrhosis, oestrogen-induced and other forms of cholestasis), to prevent or reverse hepatotoxicity due to several drugs and chemicals such as alcohol, paracetamol (acetaminophen), steroids and lead, and to have antidepressant properties. In all of these studies SAMe has been very well tolerated, a finding of great potential benefit given the well-known adverse effects of tricyclic antidepressants with which it has been compared in a few trials. Thus, with its novel mechanisms of action and good tolerability, SAMe is an interesting new therapeutic agent in several diverse disease conditions, but its relative value remains to be determined in appropriate comparisons with other treatment modalities in current use.

Affective disorders and S-adenosylmethionine: a new hypothesis

S-Adenosyl-L-methionine (AdoMet) is a safe and probably effective antidepressant agent in certain forms of clinical depression. This article presents a new hypothesis to account for the mechanism of action of S-adenosylmethionine in such illnesses, based upon the known biochemistry of this compound, and upon current knowledge of clinical and genetic aspects of affective disorders. Giulio Cantoni, S. Harvey Mudd and V. Andreoli postulate that at least some major mood disorders are due to abnormalities affecting the AdoMet-dependent methylation of a substance in the CNS. For convenience and without prejudging the chemical structure of this substance, they call it 'barinine'. The model requires that barinine be subject to AdoMet-dependent methylation and that methylbarinine be subject to metabolic demethylation to regenerate the original barinine. Methylbarinine should be mood elevating, whereas barinine itself should not be. Depression is a result of abnormalities lowering the normal steady-state concentration of methylbarinine, whereas mania results from an abnormal elevation of methylbarinine.

A physico-chemical approach to the study of the binding interaction between S-adenosyl-L-methionine and polyanions: binding constants and nature of the interaction with sodium poly(styrene sulfonate)

The interaction between S-adenosyl-L-methionine (AdoMet) and sodium poly(styrene sulfonate) NaPSS) was studied by means of ultrafiltration and ultraviolet absorption spectroscopy at several pH values and sodium sulfate concentrations. The results obtained are interpreted mainly in terms of electrostatic interactions and permit the evaluation of the binding constants under different experimental conditions. Furthermore, ultraviolet absorption spectroscopy data show a specific short-range interaction between the aromatic electronic system of AdoMet and the NaPSS aromatic ring. The results indicate that the binding strength is greatly affected by the AdoMet positive charge on the adenine ring. The other positive charges on both the sulfonic pole and the amino acidic group of AdoMet contribute only weakly to the binding to the polyanionic matrix, thus assuring some stability of AdoMet even at physiological pH.